Patent Publication Number: US-11378167-B2

Title: Control of a limited slip differential based on an accelerator control position

Description:
CROSS-REFERENCE 
     The present application claims priority from U.S. Provisional Patent Application No. 62/560,591, filed on Sep. 19, 2017 and from United States Provisional Patent Application No. 62/585,913, filed on Nov. 14, 2017, the entirety of which being incorporated herein by reference. 
    
    
     FIELD OF TECHNOLOGY 
     The present technology relates to a control of a limited slip differential based on an accelerator control position, to a method of controlling a limited slip differential, and to a vehicle including the limited slip differential. 
     BACKGROUND 
     There exist various types of vehicles used mainly in off-road conditions. One such type is the side-by-side off-road vehicle. The name “side-by-side” refers to the seating arrangement of the vehicle in which the driver and a passenger are seated side-by-side. Some side-by-side off-road vehicles also have a second row of seats to accommodate one or more additional passengers. These vehicles typically have an open cockpit, a roll cage and a steering wheel. 
     To be able to operate in off-road conditions, a side-by-side off-road vehicle needs to be able to handle bumpy terrain and to operate on various surfaces including, but not limited to, sand, dirt and mud. These conditions represent unique challenges not typically encountered when designing on-road vehicles such as cars. One such challenge lies in the provision of torque to each driving wheel under various conditions such as amount of steering, vehicle orientation when climbing a hill, rate of acceleration, slippery or rocky terrain, and the like. 
     A differential is commonly used to receive torque from a driving shaft and to redirect the torque via half-shafts toward two driving wheels of the vehicle. The differential allows the half-shafts and corresponding wheels to rotate at distinct rates, as it is desirable to allow the inside wheel to rotate at a somewhat lower rate than the outside wheel when the vehicle is in a turn. However, when one of the wheels is on slippery terrain, the differential may direct all torque on that one wheel, which may spin unnecessarily without allowing the vehicle to move, no torque being delivered on the other wheel. A limited slip differential (LSD) is conventionally used to limit the rotational speed difference between left and right driven wheels of a wheel set. In a vehicle equipped with a LSD, should the left wheel (for example) be on a patch of low friction terrain, it will only spin to a small extent before the LSD starts transmitting torque on the opposite right wheel. As the right wheel may be on terrain providing better traction, this allows the vehicle to move until both wheels are on terrain providing better traction. 
     Conventional LSDs suffer from a number of operational limitations. 
     A conventional LSD may lock both wheels of the wheel set as soon as there is some rotational speed difference between the two wheels. This may cause the LSD to lock both wheels when the vehicle is in a curve even though both wheels may have good traction at the time. While locking the LSD may prevent wheel spin, steering of the vehicle becomes difficult when the LSD is locked because a locked LSD acts counter to natural speed differences between the slower wheel on the inside of a curve and the faster wheel on the outside of the curve. 
     To prevent locking of the LSD during every turn of the vehicle, the LSD may be configured to allow a fairly large rotational speed difference between the two wheels of the axis. While this design may prevent unnecessary locking of the LSD at every turn, it may delay the transfer of torque to the wheel having better traction when the opposite wheel is on slippery terrain. Such delays in the locking of the LSD may render the vehicle difficult to control on slippery terrain and lead to a negative driver experience. This lack of proactivity of the conventional LSD may even cause the vehicle to remain stuck on low friction terrain, such as when on mud or ice, or lose momentum when climbing on rocky terrain. Moreover, delays in the locking of the LSD may cause important spinning of the driven wheels upon heavy acceleration from a standing start. 
     When a vehicle is travelling in deep mud or in similar slippery driving conditions, the torque being applied to the wheels may change frequently and may change by a large amount. This could cause the LSD to constantly lock and unlock again. This behavior of the LSD is not only inefficient, but may be detrimental to the driving experience while potentially causing premature damage to the LSD. Some LSDs have a manual locking mode that may be used to overcome this constant locking and unlocking problem. The user of the vehicle may manually lock the LSD, for example when the user predicts that the vehicle is about to encounter a mud patch. The LSD remains locked until unlocked by the user. While this may help preventing that the vehicle becomes stuck in the mud patch, it may render the vehicle difficult to drive if the LSD is still manually locked when better surface conditions are met again, steering becoming difficult for example. In some off-road paths, the user might need to frequently lock and unlock again the LSD. The vehicle may remain stuck in a mud patch if the user does not react in good time to manually lock the LSD when slippery driving conditions are met. 
     There is therefore a desire for a control of limited slip differentials that addresses the above issues. 
     SUMMARY 
     It is an object of the present technology to ameliorate at least some of the inconveniences present in the prior art. 
     The present technology provides a limited slip differential (LSD) controlled according to a position of an accelerator control of a vehicle. The accelerator control position is determined. A speed of the vehicle is optionally determined. In order to prevent wheel spin, a high load is selectively applied to the LSD when the accelerator control position meets or exceeds a predetermined position threshold or, optionally, when the accelerator control position meets or exceeds the predetermined position threshold while the speed of the vehicle being less than a predetermined speed threshold. In order to enhance directional stability of the vehicle, a stabilization load is optionally applied when the speed of the vehicle meets or exceeds the predetermined speed threshold. 
     According to one aspect of the present technology, there is provided a method of controlling a limited slip differential (LSD) of a vehicle, the vehicle having an engine, an accelerator control, the LSD, and left and right driven wheels operably connected to the LSD. The method comprises: determining an accelerator control position; and selectively applying a high load to the LSD when the accelerator control position meets or exceeds a predetermined position threshold. 
     In some implementations of the present technology, the method further comprises locking the LSD. 
     In some implementations of the present technology, the method further comprises: detecting a full or partial release of the accelerator control; and releasing the high load to the LSD. 
     In some implementations of the present technology, the method further comprises determining a speed of the vehicle, selectively applying the high load being conditional to the speed of the vehicle being less than a predetermined speed threshold. 
     In some implementations of the present technology, determining the speed of the vehicle comprises: determining rotational speeds of the left and right wheels; and determining the speed of the vehicle based on an average of the rotational speeds of the left and right wheels and based on a dimension of the left and right wheels. 
     In some implementations of the present technology, the method further comprises releasing the high load when the speed of the vehicle meets or exceeds the predetermined speed threshold. 
     In some implementations of the present technology, the method further comprises applying a stabilization load to the LSD when the speed of the vehicle meets or exceeds the predetermined speed threshold, the stabilization load being less than the high load. 
     In some implementations of the present technology, the method further comprises: determining an engine output torque; applying the engine output torque and the speed of the vehicle to a trail active mapping table to read a value of a partial load for application to the LSD; and while the accelerator control position is less than the predetermined position threshold, applying the partial load to the LSD. 
     According to another aspect of the present technology, there is provided a method of controlling a limited slip differential (LSD) of a vehicle, the vehicle having an engine, an accelerator control, the LSD, and left and right driven wheels operably connected to the LSD. The method comprises: determining a speed of the vehicle; and selectively applying a stabilization load to the LSD when the speed of the vehicle is greater than a predetermined speed threshold. 
     In some implementations of the present technology, applying a load to the LSD comprises compressing a clutch of the LSD to reduce a rotational speed difference of the left and right wheels. 
     In some implementations of the present technology, compressing the clutch of the LSD comprises using an electric motor to drive a gear set and a ball ramp to apply a torque on the clutch. 
     In some implementations of the present technology, compressing the clutch of the LSD further comprises using a solenoid to lock the gear set. 
     According to a further aspect of the present technology, there is provided a differential assembly for use in a vehicle having an engine, an accelerator control, and left and right driven wheels. The differential assembly comprises: a limited slip differential (LSD) operatively connectable to a driveshaft and to the left and right driven wheels, the LSD being adapted for transferring torque from the driveshaft to the left and right driven wheels; an accelerator control sensor; and a control unit operatively connected to the LSD and to the accelerator control sensor, the control unit being adapted for controlling a selective application of a high load to the LSD when an accelerator control position indicated by the accelerator control sensor meets or exceeds a predetermined position threshold. 
     In some implementations of the present technology, the differential assembly further comprises an electric motor, wherein controlling the selective application of the high load to the LSD comprises controlling a load applied by the electric motor to the LSD. 
     In some implementations of the present technology, the LSD further comprises a compressible clutch and wherein controlling the load applied by the electric motor to the LSD comprises compressing the clutch. 
     In some implementations of the present technology, the LSD further comprises a gear set and a ball ramp, the gear set being adapted for applying the load from the electric motor to the ball ramp for compressing the clutch. 
     In some implementations of the present technology, the differential assembly further comprises a solenoid having a tooth adapted for engaging the gear set when the solenoid is energized, wherein the control unit is further adapted for controlling the solenoid for locking the LSD. 
     In some implementations of the present technology, the control unit is further adapted for controlling locking of the LSD. 
     In some implementations of the present technology, the control unit comprises: an input port adapted for receiving measurements from the accelerator control sensor; an output port adapted for forwarding control commands to the LSD; and a processor operatively connected to the input port and to the output port, the processor being adapted for causing the output port to forward the control commands for controlling the selective application of the high load to the LSD. 
     In some implementations of the present technology, the differential assembly further comprises a sensor of a speed of the vehicle, wherein: the input port is further adapted for receiving measurements from the sensor of the speed of the vehicle; and the processor is further adapted for controlling the selective application of the high load to the LSD when the speed of the vehicle is less than a predetermined speed threshold. 
     In some implementations of the present technology, the sensor of the speed of the vehicle comprises wheel speed sensors operatively connected to the left and right wheels, the wheel speed sensors determining rotational speeds of the left and right wheels; and 
     the processor is further adapted for determining the speed of the vehicle based on an average of the rotational speeds of the left and right wheels and based on a dimension of the left and right wheels 
     In some implementations of the present technology, the control unit further comprises a memory storing configuration information for controlling the LSD; the processor is operatively connected to the memory; and the configuration information comprises one or more of the predetermined position threshold, the predetermined speed threshold, and a trail active mapping table. 
     In some implementations of the present technology, the processor is further adapted for causing the output port to forward control commands for controlling a selective application of a stabilization load to the LSD when the speed of the vehicle is greater than the predetermined speed threshold, the stabilization load being less than the high load. 
     In some implementations of the present technology, the differential assembly further comprises an engine torque monitor, wherein: the input port is further adapted for receiving an engine output torque value from the engine torque monitor; and the processor is further adapted for: applying the engine output torque value and the speed of the vehicle to the trail active mapping table to read a value of a partial load for application to the LSD; and while the accelerator control position is less than the predetermined position threshold, causing the output port to forward a control command for controlling an application of the partial load to the LSD. 
     According to yet another aspect of the present technology, there is provided a vehicle, comprising: a frame; a front suspension assembly connected to the frame; a rear suspension assembly connected to the frame; a left driven wheel and a right driven wheel connected to one of the front and rear suspension assemblies; at least one other wheel connected to an other one of the front and rear suspension assemblies; a steering device operatively connected to one of both driven wheels and the at least one other wheel; an engine connected to the frame; a transmission operatively connected to the engine for receiving torque from the engine; a driveshaft operatively connected to the transmission for transferring torque from the transmission to the left and right driven wheels; and a differential assembly. The differential assembly comprises: a limited slip differential (LSD) operatively connected to the driveshaft and to the left and right driven wheels, the LSD being adapted for transferring torque from the driveshaft to the left and right driven wheels; an accelerator control sensor; and a control unit operatively connected to the LSD and to the accelerator control sensor, the control unit being adapted for controlling a selective application of a high load to the LSD when an accelerator control position indicated by the accelerator control sensor meets or exceeds a predetermined position threshold. 
     In some implementations of the present technology, the vehicle further comprises: a transaxle for transferring torque from the transmission to the at least one other wheel; and a selector adapted for selectively operatively connecting the LSD to the driveshaft. 
     Implementations of the present technology each have at least one of the above-mentioned object and/or aspects, but do not necessarily have all of them. It should be understood that some aspects of the present technology that have resulted from attempting to attain the above-mentioned object may not satisfy this object and/or may satisfy other objects not specifically recited herein. 
     Additional and/or alternative features, aspects and advantages of implementations of the present technology will become apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present technology, as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where: 
         FIG. 1  is a perspective view of an off-road vehicle taken from a front, left side; 
         FIG. 2  is a left side elevation view of the vehicle of  FIG. 1 ; 
         FIG. 3  is a rear elevation view of an instrument panel of the vehicle of  FIG. 1 ; 
         FIG. 4  is a left side elevation view of a powertrain of the vehicle of  FIG. 1 ; 
         FIG. 5  is a left side cutaway view of the powertrain of  FIG. 4 ; 
         FIG. 6  is a bottom plan view of the powertrain  FIG. 4 ; 
         FIG. 7  is a perspective view, taken from a rear, left side, of a front differential assembly of the powertrain of  FIG. 4 ; 
         FIG. 8  is a schematic cross-sectional view of the differential assembly of  FIG. 7 ; 
         FIG. 9  is a cross-sectional view of an example construction of the differential assembly of  FIG. 7 ; 
         FIG. 10  provides timing diagrams showing variations of a steering angle (top diagram), wheel slip variations and a range between maximum and minimum allowed wheel slips calculated by the engine control unit (middle diagram), and control commands for loading and/or locking the LSD (bottom diagram); 
         FIG. 11  is a graphical representation of a slip margin (top diagram) varying as a function of rotational speed of the front wheels of the vehicle of  FIG. 1  (bottom diagram); 
         FIGS. 12 a  and 12 b    are a logic diagram showing operations of a method for controlling a limited slip differential based on a steering angle of a vehicle; 
         FIG. 13  is a logic diagram showing details of a method of applying a load on the limited slip differential; 
         FIG. 14  is a block diagram of a control unit for the limited slip differential; 
         FIG. 15  is a block diagram showing internal operations of the control unit for determining the predicted engine torque, according to an implementation; 
         FIG. 16  is a logic diagram showing operations of a method for controlling a limited slip differential based on an engine torque; 
         FIG. 17  is a block diagram showing internal operations of the control unit for controlling the LSD in mud mode, according to an implementation; 
         FIG. 18  is a graph of an engine load line; 
         FIGS. 19 a  to 19 e    provide logic diagrams showing operations of a method for controlling a limited slip differential based on driving conditions; 
         FIG. 20  is a block diagram showing internal operations of the control unit for controlling the LSD in trail active mode, according to an implementation; 
         FIG. 21  is a logic diagram showing operations of a method for controlling a limited slip differential based on an accelerator control position; 
         FIG. 22  is a logic diagram showing operations of a method for controlling a limited slip to stabilize the steering of a vehicle; and 
         FIG. 23  is a block diagram showing internal operations of the control unit for determining the maximum and minimum allowed wheel according to an implementation. 
     
    
    
     DETAILED DESCRIPTION 
     Generally stated, the present technology provides control of a limited slip differential (LSD) mounted on an axle of a vehicle, this control being based at least in part on measurements provided by various sensors to a control unit operatively connected to the LSD. 
     The present technology will be described with respect to a four-wheel, off-road vehicle having two side-by-side seats and a steering wheel. However, it is contemplated that at least some aspects of the present technology may apply to other types of vehicles such as, but not limited to, off-road vehicles having a handlebar and a straddle seat (i.e. an all-terrain vehicle (ATV)), off-road vehicles having more or less than four wheels, and on-road vehicles having three or more wheels and having one or more seats. 
     Description of the Vehicle 
     The general features of the off-road vehicle  40  will be described with respect to  FIGS. 1, 2 and 3 . The vehicle  40  has a frame  42 , two front wheels  44  connected to a front of the frame  42  by a front suspension assembly  46  and two rear wheels  48  connected to the frame  42  by a rear suspension assembly  50 . Each one of the front and rear wheels  44 ,  48  has a rim  45  and a tire  47 . The rims  45  and tires  47  of the front wheels  44  may differ in size from the rims and tires of the rear wheels  48 . In addition, although four wheels  44 ,  48  are illustrated in the Figures, the vehicle  40  could include more or less than four wheels  44 ,  48 . 
     The frame  42  defines a central cockpit area  52  inside which are disposed a driver seat  54  and a passenger seat  56 . In the present implementation, the driver seat  54  is disposed on the left side of the vehicle  40  and the passenger seat  56  is disposed on the right side of the vehicle  40 . However, it is contemplated that the driver seat  54  could be disposed on the right side of the vehicle  40  and that the passenger seat  56  could be disposed on the left side of the vehicle  40 . It is also contemplated that the vehicle  40  could include a single seat for the driver, or a larger number of seats, or a bench accommodating the driver and at least one passenger. The driver operates the steering wheel  58  from the driver seat  54  to control an angle of the front wheels  44 . 
     As can be seen in  FIG. 2 , an engine  62  is connected to the frame  42  in a rear portion of the vehicle  40 . The engine  62  is connected to a continuously variable transmission (CVT)  64  disposed on a left side of the engine  62 . The CVT  64  is operatively connected to a transaxle  66  to transmit torque from the engine  62  to the transaxle  66 . The transaxle  66  is disposed behind the engine  62 . The transaxle  66  is operatively connected to the front and rear wheels  44 ,  48  to propel the vehicle  40 . The engine  62 , the CVT  64  and the transaxle  66  are supported by the frame  42 . A variant of the vehicle  40  having another transmission type is also contemplated. 
     The transaxle  66  is mechanically connected to a shifter  60  disposed laterally between the two seats  54 ,  56 . The shifter  60  allows the driver to select from a plurality of combinations of engagement of gears of the transaxle  66 , commonly referred to as gears. In the present implementation, the shifter  60  allows the driver to select between a reverse gear, two forward gears (high and low) and a neutral position in which the transaxle  66  does not transmit torque to the wheels  44 ,  48 . It is contemplated that other types of connections between the shifter  60  and the transaxle  66  could be used. 
     In an implementation, operative connection of the transaxle  66  to the front wheels  44  is selectable, the selection being made using a drive mode selector provided in the vicinity of the driver. The drive mode selector may comprise a toggle switch  59  ( FIG. 3 ) mounted on an instrument panel  61  of the vehicle  40 . The toggle switch  59  has two (2) positions for selecting a two-wheel mode or an all-wheel mode for the vehicle  40 . The drive mode selector may also comprise a toggle switch  63  having two (2) positions for manually locking and unlocking a limited slip differential (shown on later Figures). The drive mode selector may further comprise a toggle switch  65  having four (4) positions for selecting one of a normal mode, a trail active mode, a mud mode and a rock crawling mode. It is contemplated that the toggle switch  65  may only permit selection of one or two of the trail active mode, the mud mode and the rock crawling mode in a vehicle that only has one or two of these modes available. Use of a rotary knob for selecting one of the various modes and use of distinct switches for turning on and off each of the trail active mode, mud mode and rock crawling mode are also contemplated. It is also contemplated to the rotary knob or additional toggle switches may be used to select other modes, for example a sand mode, a snow mode, and the like. 
     Referring to  FIGS. 4 to 6 , the CVT  64  has a driving pulley  68  connected to and driven by the engine  62  as well as a driven pulley  72  mounted to the transaxle  66 . A belt  76  transmits a torque imparted on the driving pulley  64  by the engine  62  to the driven pulley  72  that in turn transmits the torque to the transaxle  66 . The driving pulley  68  and the driven pulley  72  permit a continuously variable transmission ratio by virtue of the opening or closing of opposed conical side faces of one or more of the pulleys. It should be understood that alternative transmission configurations may be used. 
     In the vehicle  40 , the transaxle  66  transmits the torque applied thereon by the driven pulley  72  to drive the rear wheels  48 , when the drive mode selector is in a two-wheel mode, or to drive the front and rear wheels  44 ,  48 , when the drive mode selector in an all-wheel mode. The transaxle applies a torque to the rear wheels  48  via corresponding half-shafts  78 . To this end, the transaxle  66  includes a differential  80  operatively connected to the half shafts  78 . Instead of the differential  80 , use of a spool gear is also contemplated. When the drive mode selector is in the all-wheel mode, the transaxle  66  applies a portion of the torque on the half shafts  78 , and also applies another portion of the torque on a front driveshaft  82 . A front end of the front driveshaft  82  is connected to another driveshaft  84  via a universal joint  86 . A front end of the driveshaft  84  drives an input shaft  90  of a limited slip differential (LSD)  302  via another universal joint  92 . 
     The LSD  302  is operatively connected to and drives left and right front half-shafts  98 . Laterally outward ends of the front half-shafts  98  are operatively connected to and drive the front wheels  44 . 
     Description of an Example of the Limited Slip Differential Assembly 
       FIGS. 7 and 8  show a limited slip differential assembly  300  including the LSD  302  connected to driven wheels of the vehicle  40 . In an implementation, the differential assembly  300  drives the front wheels  44  of the vehicle  40 . It should be understood that the differential assembly  300  could alternatively be used with the rear wheels  48  of the vehicle  40 , or to any pair of wheels of any other type of vehicle. The differential assembly  300  includes the LSD  302 , a control unit  370 , an actuator  372 , a solenoid  382 , and one or more sensors. The actuator  372 , the solenoid  382  and the sensors are electrically connected to the control unit  370 . Sensors may include one or more wheel speed sensors  376 ,  378 , a vehicle speed sensor  380 , a steering angle sensor  390 , an accelerator control sensor  392 , an engine torque monitor  394 , a shifter position indicator  396 , and a user command sensor  398 . The user command sensor  398  informs the control unit  370  of the state of the various toggle switches  59 ,  63  and  65 . Some of these sensors may be present in some implementations and not present in some other implementations. All of these sensors, when present, are communicatively coupled with the control unit  370 , to which they provide measurements and sensed information elements. 
       FIG. 8  illustrates a particular, non-limiting implementation of the LSD  302 . In the LSD  302  as shown on  FIG. 8 , the input shaft  90  is connected to a first bevel gear acting as an input gear  304 . Rotation of the input shaft  90  causes a rotation of the input gear  304  that, in turn, causes a rotation of a second bevel gear, or ring gear  306 . Rotation of the ring gear  306  causes a rotation of first clutch plates  308  and of a carrier  310 . A shaft  312  connects the carrier  310  to a gear set that includes at least two (2) planet gears  314 ,  316  and sun gears  318 ,  320 . An output shaft  322  is mounted to the sun gear  318 , the shaft  322  and the sun gear  318  rotating together. Likewise, an output shaft  324  is mounted to the sun gear  320 , the shaft  324  and the sun gear  320  rotating together. The output shafts  322  and  324  are operatively connected to the half shafts  98  via universal joints or joints of other types (not shown) contained in boot covers  326  and  328  (shown on  FIG. 7 ). 
     The LSD  302  has second clutch plates  330 . When the clutch plates  308  and  330  are not compressed, the LSD  302  is not loaded. The output shafts  322  and  324  may rotate at the same speed or at distinct speeds. When both output shafts  322  and  324  rotate at a same speed, they also both rotate at the same rate as the ring gear  306 , the carrier  310  and the sun gears  318 ,  320 . At that time, the planet gears  314  and  316  do not rotate about the axis of the shaft  312  (they only rotate about the axis of the ring gear  306 , following the movement of the carrier  310 ). When the two output shafts  322  and  324  rotate at distinct speeds, a rotational difference of the sun gears  318  and  316  causes a rotation of the planet gears  314  and  316  about the axis of the shaft  312 . In that case, torque from the input shaft  90  is unequally transferred to the output shafts  322  and  324  and, ultimately, to the left and right wheels  44 . 
     The actuator  372  may compress the clutch plates  308  and  330 . This compression reduces, and eventually eliminates, a rotational speed difference between the ring gear  306  and the output shaft  324 . If the clutch plates  308  and  330  are compressed to the point of eliminating any rotational speed difference between the ring gear  306  and the output shaft  324 , the carrier  310  also rotates at the same speed as the output shaft  324 . The planetary gears  314  and  316  cannot turn about the axis of the shaft  312  so the sun gear  318  and the output shaft  322  also rotate at the same speed as the output shaft  324 . The LSD  302  is then effectively locked. In case of partial loading of the LSD  302 , a moderate compression of the clutch plates  308  and  330  causes a reduction of a rotational speed difference between the ring gear  306  and the output shaft  324 , without totally eliminating this difference. The LSD  302  is at that time allowing a limited slip of the wheels  44 . 
     The LSD  302  is a conventional clutch-type limited slip differential and is controllable to allow a predetermined maximum difference in rotational speeds between the left and right front wheels  44 . It is contemplated that any other suitable type of LSD  302  may alternatively be used. 
     The LSD  302  is mechanically coupled to an actuator  372 , for example an electrical, hydraulic or magnetic actuator, that is electronically controlled by a control unit  370 . To regulate the difference in rotational speeds between the left and right front wheels  44 , the actuator  372  can vary the compression on the clutch plates  308  and  330  to vary the degree of engagement, or load, of the LSD  302 . The LSD  302  may be engaged, i.e. loaded, when the control unit  370  detects that one of the wheels  44  is slipping. 
     In at least one implementation, in order to prevent eventual slipping of the wheels  44 , the control unit  370  may control the LSD  302  to be loaded before the actual detection of a wheel slip. It can be said in such case that the LSD  302  is preloaded. In the context of the present disclosure, differences between the terms “load” and “preload” primarily relate to the circumstances under which the control unit  370  initiates the loading of the LSD  302 . The LSD  302  operates essentially in the same manner whether it is loaded or preloaded. Application of a preload to the LSD  302  does not preclude further or increased loading of the LSD  302  in the event of a wheel slip. 
     The control unit  370  may cause the LSD  302  to act as an open differential (fully disengaged), a locked differential (fully engaged), or at any intermediate degree of engagement. The control unit  370  is electrically connected to wheel speed sensors  376 ,  378  that, on  FIG. 8 , are connected to the output shafts  324  and  322 . The wheel speed sensors  376 ,  378  may alternatively be connected to the front wheels  44 , to the front half-shafts  98 , or to any other suitable component from which the control unit  370  receives signals indicative of the rotational speeds of the left and right front wheels  44 . 
       FIG. 9  is a cross-sectional view of an example construction of the differential assembly of  FIG. 7 . The actuator  372  comprises an electric motor  288  that drives a gear set  276 . A rotational motion of the gear set  276  is translated into an axial motion by a ball ramp  278 . This axial motion is used to apply a pressure generated by the electric motor  288  to compress the clutch plates  308  and  330  of a clutch  374 . This compression of the clutch  374  loads the LSD  302  to reduce the relative slip between the left and right half shafts  98 . Sufficient compression of the clutch  374  may effectively lock the LSD  302 . However, even under maximum compression, the clutch  374  may slip in some implementations, under severe conditions. Consequently, depending on the torque from the input shaft  90  being applied to the LSD  302  and depending on characteristics of the clutch  374 , the LSD  302  may not lock to an absolute degree. In the context of the present disclosure, the LSD  302  is considered locked when maximum torque is applied on the clutch  374  although at the time a modest relative slip may still be present between the left and right half shafts  98 . Consequently, the “locking of the LSD  302 ” should not be understood in the absolute. 
     In order to prevent overheating of the electric motor  288 , a solenoid  382  having a tooth  384  at its end may be energized so that the tooth  384  meshes with a largest gear  386  of the gear set  276 , thereby locking the gear set  276 , the ball ramp  278  and the clutch  374  in a selected load position. As a result, the electric motor  288  no longer needs to be energized to maintain the load to the LSD  302 . In an implementation, the solenoid  382  may be energized to lock the LSD  302  when the control unit  370  determines that loading has been applied for at least a predetermined time period duration. It should be observed that energizing the solenoid  382  requires much less current than energizing the electric motor  288 . De-energizing the solenoid  382  causes it to retract, releasing the tooth  384  from the largest gear  386  of the gear set  276  and releasing the load to the LSD  302 . In a variant, the solenoid  382  may be configured so that its tooth  384  meshes with the largest gear  386  of the gear set  276  when the solenoid  382  is not energized, energizing the solenoid  382  thus causing a release of the gear set  276  and unlocking of the clutch  374 . 
     In an implementation, maximum compression of the clutch  374  may be applied by the electric motor  288 , the gear set  276  and the ball ramp  278  prior to energizing the solenoid  382 . In the same or another implementation, the solenoid  382  may also be energized to lock the LSD  302  when a user manually activates the toggle switch  63  to select to lock the LSD  302 , as indicated by the user command sensor  398  that informs the control unit  370  of a user request to lock the LSD  302 . In such case, the user request to lock the LSD  302  may optionally cause a maximum load of the LSD  302  by maximum compression of the clutch  374  by the electric motor  288 , the gear set  276  and the ball ramp  278  prior to energizing the solenoid  382 . 
     Other implementations of the differential assembly  300  and of the LSD  302  are also contemplated. The present technology is not limited to the particular implementation illustrated on  FIGS. 7 to 9 . In particular, a differential assembly that does not contain a ball ramp or clutch plates is also contemplated. 
     Control of the LSD  302  Based on a Steering Angle of the Vehicle  40   
     One aspect of the present technology provides control of the LSD  302  connected to the driven wheels  44  of the vehicle  40  based at least in part on rotational speeds of both left and right driven wheels  44  of the vehicle  40  and at least in part on a steering angle. In the context of the present disclosure, the steering angle may represent the angle of a steering wheel  58  or the angle of a handlebar, depending on the type of steering control mounted on the vehicle. In vehicles having so-called drive-by-wire steering systems, the ratio of a steering wheel input to the angle of steered wheels may vary according to the speed of the vehicle and, in some cases, according to some other factors. 
     Considering that it is natural for the inside wheels  44  and  48  to rotate at a slower rate than the outside wheels  44  and  48  when the vehicle  40  is in a curve, in an implementation, the control unit  370  determines an allowable slipping range between the left and right front wheels  44 , the allowable slipping range being based at least in part on the steering angle and on the speed of the vehicle  40 . This allows the control unit  370  to control loading of the LSD  302  using a narrower slipping range instead of conventional, broad slipping range. 
       FIG. 10  provides timing diagrams showing variations of a steering angle (top diagram  400 ), wheel slip variations and a range between maximum and minimum allowed wheel slips calculated by the engine control unit  370  (middle diagram  404 ), and control commands for loading and/or locking the LSD  302  (bottom diagram  430 ). For ease of illustration and without limiting the generality of the present disclosure, the diagrams of  FIG. 10  are made in view of a constant speed of the vehicle  40 , with its front wheels  44  rotating at an average speed of 100 RPM. 
     The top diagram  400  illustrates a steering angle  402  showing rotations of the steering wheel  58  between −360 and +360 degrees, over a 32-second period of time. An equivalent diagram showing angular variations of the front wheels  44 , which are steered by action of the steering wheel  58  is also contemplated, in which case lesser angular ranges would be shown. The user initially maintains the steering wheel  58  in a straight (0 degree) position from an initial zero time to about 4.5 seconds. From that point in time, the user turns the steering wheel to cause the vehicle  40  to make a left turn, followed by a right turn, another left turn, and so on. A dashed line  424  highlights a starting point in time of the effect of this action from the user on other diagrams of  FIG. 10 . For illustration purposes, the user fully rotates the steering wheel  58 , between −360 in left turns and +360 degrees in right turns. 
     A middle diagram  404  illustrates wheel slip variations between the left and right front wheels  44  over time. For illustration purposes, the diagram  404  shows a wheel slip  406  illustrated from the standpoint of the left front wheel. In the context of the present disclosure, the “wheel slip” is defined as a difference in the rotational speeds of the two (2) front wheels  44  of the vehicle  40 . For illustration purposes, the wheel slip is calculated with the left wheel  44  as a reference. As such, a positive wheel slip value indicates that the left wheel rotates faster than the right wheel while a negative wheel slip value indicates that the left wheel rotates slower than the right wheel. When the vehicle  40  is taking a left turn for example, the left wheel naturally rotates slower than the right wheel, assuming no actual slip between the wheel and the ground. The curve of the wheel slip  406  therefore represents the speed of the left wheel minus the speed of the right wheel for different steering angles. 
     The vertical axis of the diagram  404  shows wheel slip values between −60 and +60 RPM. Assuming there is no slipping between the wheels and the terrain, the inside left wheel rotates at a slower rate than the outside right wheel when turning left and thus the wheel slip is negative for all steering angles between 0 and −360. When the steering wheel is turned in the opposite direction, between 0 and +360 steering angles, the left wheel rotates faster than the right wheel and thus the wheel slip is positive. Without any slipping between the wheels and the terrain, the curve for the wheel slip  406  follows an expected wheel slip that naturally results at a turning radius of the vehicle  40 , the turning radius being in turn a function of the steering angle. A large steering angle causes the vehicle  40  to take a small turning radius, in turn causing an important wheel slip. 
     As illustrated, the curve for the wheel slip  406  is jagged, primarily because of noise in the measurements from the wheel speed sensors  376 ,  378 , which may be caused for example by the wheels  44  hitting bumps and holes on the road. 
     The curve for the wheel slip  406  is for a particular implementation of the vehicle  40  with its front wheels  44  rotating at an average of 100 RPM without slipping with respect to the ground. For this implementation, the expected wheel slip at the maximum steering angle of +/−360 degrees is 30 RPM, with the inside front wheel  44  rotating at 85 RPM while the outside front wheel  44  rotates at 115 RPM, an average of the speeds of the front wheels  44  being 100 RPM. Otherwise stated, in this particular implementation, the vehicle  40  has a slip ratio of 30%, which is a fixed value defined as a ratio between the wheel slip value at the maximum steering angle over the average wheel speed. For the same vehicle  40 , with an average wheel speed of 200 RPM, the expected wheel slip at the maximum steering angle is thus 60 RPM. For another vehicle, the slip ratio may be different depending on the steering ratio within the steering system of that vehicle. Also, in an embodiment, another vehicle may have a steering that can rotate by more or less than +/−360 degrees. For example, a steering wheel could be turned by more than one full turn to steer the wheels. 
     The diagram  404  also shows a maximum allowed wheel slip  408  and a minimum allowed wheel slip  410 . Generally speaking, the maximum allowed wheel slip  408  has a peak value when the left wheel is on the outside of a curve (right turn) while the minimum allowed wheel slip  410  has a peak (negative) value when the left wheel is on the inside of a curve (left turn). Together, the maximum and minimum allowed wheel slips  408  and  410  define, for a given steering angle, a permissible slipping range for the front wheels  44 . The wheel slip  406  may vary between these values before intervention from the control unit  370  to start loading the LSD  302 . 
     The control unit  370  uses steering angle information from the steering angle sensor  390  to control the limited slip differential assembly  300 . The control unit  370  determines the expected wheel slip that naturally results at a turning radius of the vehicle  40 , the turning radius being in turn a function of the steering angle. The control unit  370  adds and subtracts a slip margin to and from the expected wheel slip, respectively, in order to expand the permissible range of relative slip between the front wheels  44 . The slip margin may be fixed. The wheel slip may alternatively vary according to the rotational speed of the front wheels  44 . The use of a slip margin prevents excessive reaction of the limited slip differential assembly  300  when a rotational speed difference of the front wheels  44  is within the permissible slipping range. The wheel slip margin is determined by the control unit  370 . In an implementation, the slip margin may be selected at least in part so that noise from the measurements by the wheel speed sensors  376 ,  378  does not cause accidental interaction of the LSD  302 . In the illustration of  FIG. 10 , the same slip margin is used for determining the maximum and minimum allowed wheel slips  408  and  410 . Using different slip margins for any given steering angle and/or for determining ranges of allowable wheel slips for inside and outside wheels  44  is also contemplated. To calculate the maximum allowed wheel slip  408 , the slip margin is added to the expected wheel slip at the current steering angle, for a given rotational speed of the front wheels  44 . To calculate the minimum allowed wheel slip  410 , the slip margin is subtracted from the expected wheel slip at the current steering angle, for a given rotational speed of the front wheels  44 . 
       FIG. 11  is a graphical representation of a slip margin (top diagram  418 ) varying as a function of the rotational speed for the front wheels  44  of the vehicle  40  (bottom diagram  414 ). A bottom diagram  414  shows a speed  416  of the front wheels  44  of the vehicle  40 , in RPM. A top diagram  418  shows a slip margin  420  for the wheels  44  and a noise level  422  from the measurements of the wheel speed sensors  376 ,  378 . As the speed  416  of the vehicle increases, the noise level  422  increases as well. For that reason, the slip margin  420  used in the determination of the maximum and minimum allowed wheel slips  408  and  410  depends at least in part on the speed  416  of the vehicle so that the slip margin  420  remains greater than the noise level  422  in most circumstances. A relationship between the slip margin  420  and the speed  416  of the front wheels  44  may be linear or non-linear. In an implementation, a slip margin  420  of 25 RPM corresponds to an average speed of the front wheels  44  equal to 100 RPM. In an implementation, the control unit  370  stores a slip mapping table (sometimes called a look up table) of the relations between values of the slip margin  420  and speed  416  of the front wheels  44 . A relationship between the steering angle and the angle of the steered wheels may be linear or non-linear. The ratio of the steering wheel input to the angle of the steered wheels is however known at all times by a controller of the drive-by-wire steering system. 
     Returning now to  FIG. 10 , the control unit  370  determines the speed of the front wheels  44  by averaging measurements of the wheel speed sensors  376 ,  378 . A measurement of the steering angle is provided to the control unit  370  by the steering angle sensor  390 . Before about 4.5 seconds (dashed line  424 ), the steering wheel  58  is held in a straight position and the expected wheel slip is zero RPM. The maximum and minimum allowed wheel slips  408 ,  410  are at the time respectively equal to the 25 RPM slip margin above and below the expected wheel slip value, this slip margin being for the front wheels  44  rotating at 100 RPM on average. At 4.5 seconds, the user starts turning the steering wheel  58 , at first to the left and then to the right, and so on. The control unit  370  uses measurements from the steering wheel angle sensor  390  to modify the maximum and minimum allowed wheel slips  408  and  410  that may be allowed before applying a load to the LSD  302 . In the illustrated example, at about 11.5 seconds (dashed line  426 ), the steering wheel  58  is turned to the right by 360 degrees, which causes a 30 RPM difference between the speeds of the front wheels  44 , given the current wheel speed of 100 RPM and the 30% slip ratio of the vehicle  40 . The left wheel  44  on the outside of the curve rotates at a higher speed while the right wheel  44  on the inside of the curve rotates at a lower speed (generally at point  428  on the wheel slip  406  curve). At that time, the minimum allowed wheel slip  410  is +5 RPM (30-25 RPM) while the maximum allowed wheel slip  408  is +55 RPM (30+25 RPM). Otherwise stated, the left wheel  44  being at the time the outside wheel would naturally rotate faster than the inside right wheel  44  by 30 RPM if on non-slippery terrain. Given the permissible slipping range, the left wheel  44  is allowed to rotate even faster, up to 55 RPM faster than the inside right wheel  44 , before the control unit  370  starts applying a load to the LSD  302 . At the same time, the positive value of the minimum allowed wheel slip  410  implies that the control unit  370  will apply a load to the LSD  302  if the outside left wheel  44  rotates less than 5 RPM faster than the inside right wheel  44 . The 5 RPM value is calculated as the expected wheel slip at the current angle of the steering device (30 RPM) minus the slip margin, which has a value of 25 RPM. The difference between the maximum allowed wheel slip  408  and the minimum allowed wheel slip  410  is maintained constant at 50 RPM, this value reflecting the slip margin of 25 RPM being applied on both sides of the expected wheel slip, for the 100 RPM wheel speed. 
     A lower diagram  430  of  FIG. 10  shows commands from the control unit  370  to load and then unload the LSD  302 . These commands are generated by the control unit  360  when the wheel slip  406  moves out of the bounds defined by the maximum and minimum allowed wheel slips  408  and  410 . The LSD  302  is initially unloaded (command is OFF). In the present example, the wheel slip  406  exceeds the minimum allowed wheel slip  410  at about 15.5 seconds and, in response, the control unit  370  sends a control command to the LSD  302  at a 16-second mark (dashed line  432 ; command is ON). The control unit  370  initially causes a load to be applied to the LSD  302  by energizing the electric motor  288 . The control unit  370  may further energize the solenoid  382  to lock the LSD  302 . In an implementation, the control unit  370  may determine a level of the load to be applied to the LSD  302  based on one or more of a plurality of parameters, including without limitation a torque provided by the engine  62 , a position of the shifter  60  selecting a gear ratio of the transaxle  66 , a magnitude of the wheel slip  406 , and a magnitude of an excess of the wheel slip  406  in relation to the maximum or minimum allowed wheel slips  408 ,  410 . The control unit  370  may also determine whether or not to lock the LSD  302  based on a combination of these parameters. 
     As illustrated, starting at the 16-second mark, the LSD  302  is sufficiently loaded, possibly being locked, to cause the wheel slip  406  to reduce substantially to zero RPM. At the same time, the control unit  370  adapts its calculation of the maximum and minimum allowed wheel slips  408  and  410 . Before detecting that the wheel slip  406  is moving out of the bounds defined by the maximum and minimum allowed wheel slips  408  and  410 , the maximum allowed wheel slip  408  calculated according to the steering angle is at −5 RPM (point  429 ) and the minimum allowed wheel slip  410  calculated according to the steering angle is at −55 RPM. The LSD  302  is loaded, and possibly locked, by the control unit  370 . The actual wheel slip is thus reduced substantially to zero RPM. 
     Assuming that the control unit  370  would still determine the maximum allowed wheel slip  408  based on the steering angle, in the manner as described earlier, the maximum allowed wheel slip  408  would be equal to −5 RPM at that time and the control unit  370  would control the application of a load to the LSD  302  because of the zero RPM wheel slip being greater than −5 RPM. The LSD  302  being already loaded, this action of the control unit  370  would be superfluous. Consequently, the control unit  370  modifies its calculation of the maximum allowed wheel slip  408  in the manner expressed hereinbelow. At the same time, the control unit  370  would not act upon the minimum allowed wheel slip  410  calculated in view of the steering angle because, at −55 RPM, this minimum allowed wheel slip would not be exceeded. There is no need to modify the calculation of the minimum allowed wheel slip  410  at that time. 
     When the LSD  302  is loaded, the control unit  370  updates the maximum allowed wheel slip  408  by selecting the greater of: (a) a sum of the expected wheel slip and the slip margin for the current wheel speed; and (b) the slip margin for the current wheel speed. In the present example, as shown on the diagram  404 , the maximum allowed wheel slip  408  becomes equal to the slip margin starting at the 16-second mark. The control unit also updates the minimum allowed wheel slip  410  by selecting the lower (most negative) of: (a) the expected wheel slip minus the slip margin for the current wheel speed; and (b) the slip margin for the current wheel speed expressed in the negative (i.e. zero minus the slip margin). In the present example, in that case, the minimum allowed wheel slip  410  remains unchanged because it is lower than the slip margin expressed in the negative. As a result, the maximum allowed wheel slip  408  is changed by the control unit  370  to 25 RPM (0+25 RPM), this value of the maximum allowed wheel slip  408  being the same as when the steering wheel  58  is held in a straight position (zero steering angle). Without this calculation change, the curve of the maximum allowed wheel slip  408  could intersect the actual wheel slip  406 , which is substantially zero RPM at the time. In the example as illustrated on  FIG. 10 , the minimum allowed wheel slip  410  continues being calculated based on the actual angle of the steering wheel  58  and no intersection takes place between the wheel slip  406  and the minimum allowed wheel slip  410 . 
     From the 16-second mark (dashed line  432 ), the control unit  370  tracks the wheel slip  406  and may gradually increase or decrease the load to the LSD  302  depending on a synchronization of the front wheels  44  and possibly depending on some of the above mentioned parameters used by the control unit  370  to determine the level of the load to be applied to the LSD  302 . At 18 seconds (dashed line  434 ), the wheel slip  406  is within the maximum and minimum allowed wheel slips  408  and  410 , and the level of load determined by the control unit  370  is at or near zero. The control unit  370  removes the loading command applied to the LSD  302  and recalculates the maximum allowed wheel slip  408  using the calculation method used before the 16-second mark, in which the maximum and minimum allowed wheel slips  408  and  410  are calculated according to the steering angle and to the slip margin, the latter optionally depending on the rotation speed of the wheels  44 . 
       FIG. 23  is a block diagram  1200  showing internal operations of the control unit  370  for determining the maximum and minimum allowed wheel slips  408  and  410  according to an implementation. The block diagram  1200  shows three (3) inputs that may be used by the control unit  370  to determine the maximum and minimum allowed wheel slips  420  and  410 . It is contemplated that, in an implementation, this determination may be based on additional inputs. One such input is an average rotational wheel speed  1202  of the front wheels  44 , expressed in RPM. Another input is a steering angle  1204  provided by the steering angle sensor  390 , expressed in degrees. The steering angle  1204  may represent the angle of a steering wheel  58  or the angle of a handlebar. A further input is a binary status  1206  of the LSD  302 . The binary status  1206  is set if the LSD  302  is loaded and/or locked. The binary status  1206  is reset otherwise. 
     The average rotational wheel speed  1202  is applied to the slip mapping table, which is illustrated as a block  1208  on  FIG. 28 . The slip mapping table outputs a slip margin  1210 . In the example of  FIG. 23 , the slip margin  1210  has a positive value applied to a first adder  1212  and to a multiplier  1214  that has a gain of −1 to produce a negative version  1216  of the slip margin  1210 , this negative version  1216  being applied to a second adder  1218 . 
     The steering angle  1204  is applied to a block  1220  that is illustrated as a graphical representation of a steering angle mapping table that provides a correction factor  1222  as a function of the steering angle  1204 . Table I is a non-limiting example of the steering angle mapping table. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 Steering angle 1204 (degrees) 
                 Correction factor 1222 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 −450 
                 0.32 
               
               
                   
                 −360 
                 0.23 
               
               
                   
                 −180 
                 0.1 
               
               
                   
                 −110 
                 0.078 
               
               
                   
                 −40 
                 0.015 
               
               
                   
                 40 
                 −0.015 
               
               
                   
                 110 
                 −0.078 
               
               
                   
                 180 
                 −0.1 
               
               
                   
                 360 
                 −0.23 
               
               
                   
                 450 
                 −0.32 
               
               
                   
                   
               
            
           
         
       
     
     The block  1220  outputs the correction factor  1222 . Because the steering angle  1204  may have a positive or a negative value, the correction factor  1222  may also have a positive or a negative value. A multiplier  1224  multiplies the average rotational wheel speed  1202  by the correction factor  1222  to provide an expected wheel slip  1226 . The expected wheel slip  1226  is applied to inputs of a first switch  1228  and of a second switch  1230 . It may be observed that the expected wheel slip  1226  may also have a positive or a negative value. 
     The steering angle  1204  is also applied to first and second comparators  1232  and  1234 . The first comparator  1232  outputs a logical value  1236 , for example a logical 1, when the steering angle is less than or equal to zero degrees. The second comparator  1234  outputs a logical value  1238 , for example a logical 1, when the steering angle is greater than or equal to zero degrees. The binary status  1206  of the LSD  302  is applied to first and second AND boxes  1240  and  1242 , along with, respectively, the logical values  1236  and  1238 . 
     If the binary status  1206  of the LSD  302  is not set, the outputs of both AND boxes are reset, for instance producing logical 0&#39;s applied to the switches  1228  and  1230 . In that case, outputs  1244  and  1246  of the switches  1228  and  1230  are both set to the expected wheel slip  1226 . The adder  1212  sums the expected wheel slip  1226  and the slip margin  1210  to yield the maximum allowed wheel slip  408 . The adder  1218  sums the expected wheel slip  1226  and the negative version  1216  of the slip margin  1210  to yield the minimum allowed wheel slip  410 . 
     If the binary status  1206  of the LSD  302  is set, the LSD  302  being loaded or locked at the time, provided that the steering angle is not equal to zero degree, one of the AND boxes  1240  or  1242  issues a logical 1. If the steering angle  1204  is negative, the logical value  1236  is set and the AND box  1240  issues a logical 1 applied to the switch  1228 . The output  1244  of the switch  1228  is set to a fixed value  1248 , for example equal to 0 RPM. This value is added to the slip margin  1210  and the maximum allowed wheel slip  408  becomes equal to the slip margin  1210 . This situation is exemplified on  FIG. 10 , between dashed lines  432  and  434 , when the steering angle  1204  is negative and the LSD  302  is locked. At the same time, the logical value  1238  from the comparator  1234  is reset because the steering angle  1204  is not greater than or equal to zero. The AND box  1242  issues a logical 0 applied to the switch  1230 . The output  1246  of the switch  1230  is not changed and the minimum wheel slip  410  remains equal to the sum of the expected wheel slip  1226  and the negative version  1216  of the slip margin  1210 . 
     If the binary status  1206  of the LSD  302  is set and if the steering angle  1204  is positive, the logical value  1238  is set and the AND box  1242  issues a logical 1 applied to the switch  1230 . The output  1246  of the switch  1230  is set to a fixed value  1250 , for example equal to 0 RPM. This value is added to the negative version  1216  of the slip margin  1210  and the minimum allowed wheel slip  410  becomes equal to the negative version  1216  of the slip margin  1210 . This situation is exemplified on  FIG. 10 , between dashed lines  436  and  438 , when the steering angle  1204  is positive and the LSD  302  is locked. At the same time, the logical value  1236  from the comparator  1232  is reset because the steering angle  1204  is not less than or equal to zero. The AND box  1240  issues a logical 0 applied to the switch  1228 . The output  1244  of the switch  1228  is not changed and the maximum wheel slip  408  remains equal to the sum of the expected wheel slip  1226  and the slip margin  1210 . 
     If the binary status  1206  of the LSD  302  is set and the steering angle is equal to zero degrees, the AND boxes  1240  and  1242  each issue a logical 1. Because the expected wheel slip  1226  is at or near 0 RPM at that times, all the selectable inputs of the switches  1228  and  1230  are equivalently set to 0 RPM and thus the outputs of the AND boxes  1240  and  1242  have no impact on the calculations of the maximum and minimum allowed wheel slips  408  and  410 . 
     Returning to  FIG. 10 , the control unit  370  may determine the proper time to remove the load to the LSD  302  according to a plurality of parameters. In a variant, the control unit  370  may remove the loading when the wheel slip  406  has remained within a permissible range defined by the maximum and minimum allowed wheel slips  420  and  410  for a predetermined time duration. In the same or another variant, a level of the loading may be gradually reduced by the control unit  370 , the level being based at least in part on the magnitude of the excess of the current wheel slip in relation to the range between the maximum and minimum allowed wheel slips  408  and  410 . 
     For example,  FIG. 13  is a logic diagram showing details of a method of applying a load on the limited slip differential. In a sequence  450 , operation  452  comprises monitoring signals and measurements from the wheel speed sensors  376 ,  378  for eventually detecting that the wheel slip  406  exceeds the permissible slipping range defined by the maximum and minimum allowed wheel slips  408  and  410 . Following such detection, the control unit  370  controls a loading of the LSD  302  at operation  454 . Referring again to  FIG. 9 , the control of the LSD  302  to reduce the current wheel slip  406  is effected by loading the LSD  302 . To this end, the clutch  374  of the LSD  302  is compressed to reduce a rotational speed difference of the output shafts  322  and  324 , which are operatively connected to the half shafts  98  and further to the left and right driven wheels  44 . Compression of the clutch  374  of the LSD  302  is made by the electric motor  288 , which rotates the gear set  276  that in turn translates its rotational movement into an axial motion of the ball ramp  278  to apply a torque TqDiff on the clutch  374 . 
     An initial torque value Tq is applied on the clutch  374 . The initial torque value Tq may, for example, be proportional to the torque provided by the engine  62 . If excessive wheel slip remains, the torque TqDiff is raised by an increment Δ_up1 at operation  456 . Operation  456  may be repeated until the current wheel slip  406  returns within the permissible slipping range. Once the current wheel slip  406  has returned within the permissible slipping range, operation  458  gradually decreases the torque TqDiff applied on the clutch  374  by Δ_down steps. If the wheel slip  406  increases and falls again outside the permissible slipping range, the torque TqDiff is raised an increment Δ_up2 at operation  460 , following which the sequence returns to operation  456 . The increments Δ_up1 and Δ_up2 may either have equal or unequal values. When the torque TqDiff falls to zero, the wheel slip  406  being within the permissible slipping range, slip monitoring resumes at operations  452 . 
     Other manners of calculating the torque TqDiff applied on the clutch  374  are contemplated. The torque may for example be calculated proportional to a difference between the current wheel slip  406  and the maximum and minimum allowed wheel slips  408  and  410 . 
     Returning to  FIG. 10 , the wheel slip  406  is once again out of bounds at 20 seconds (dashed line  436 ), with the steering wheel  58  now turned to the right. The control unit  370  sends a control command to load the LSD  302 . As a result, the LSD  302  becomes sufficiently loaded, and possibly locked, to reduce the wheel slip  406  substantially to zero RPM. At the same time, the control unit  370  adapts its calculation of the maximum and minimum allowed wheel slips  408  and  410 . Before detecting that the wheel slip  406  is moving out of the bounds defined by the maximum and minimum allowed wheel slips  408  and  410 , the maximum allowed wheel slip  408  calculated according to the steering angle is at about +55 RPM and the minimum allowed wheel slip  410  calculated according to the steering angle is at about +5 RPM (point  437 ). At the 20-second mark, the control unit  370  updates the maximum allowed wheel slip  408  by selecting the greater of: (a) a sum of the expected wheel slip and the slip margin for the current wheel speed; and (b) the slip margin for the current wheel speed. In the present example, as shown on the diagram  404 , the maximum allowed wheel slip  408  remains unchanged as it is greater than the slip margin. The control unit also updates the minimum allowed wheel slip  410  by selecting the lower (most negative) of: (a) the expected wheel slip minus the slip margin for the current wheel speed (b) zero minus the slip margin for the current wheel speed. In the present example, the minimum allowed wheel slip  410  becomes equal to the slip margin expressed in the negative starting at the 20-second mark. As a result, the minimum allowed wheel slip  410  is changed by the control unit  370  to −25 RPM (0-25 RPM), as when the steering wheel  58  is held in a straight position (zero steering angle). Without this calculation change, the curve of the minimum allowed wheel slip  410  could intersect the actual wheel slip  406 , which is substantially zero RPM at the time. In the example of  FIG. 10 , the maximum allowed wheel slip  408  continues being calculated based on the actual angle of the steering wheel  58  and no intersection takes place between the wheel slip  406  and the maximum allowed wheel slip  408 . 
     From the 20-second mark (dashed line  436 ), the control unit tracks the wheel slip  406  and may gradually release the load to the LSD  302 . At 22.5 seconds (dashed line  438 ), the wheel slip  406  is within the maximum and minimum allowed wheel slips  408  and  410  and the level of load determined by the control unit  370  is at or near zero. The control unit  370  removes the loading command applied to the LSD  302  and recalculates the minimum allowed wheel slip  410  according to the steering angle. 
     The wheel slip  406  exceeds the maximum allowed wheel slip  408  again at 24.5 seconds (dashed line  440 ), the steering wheel  58  being turned to the left at that time. The control unit  370  sends again a control command to load the LSD  302 , optionally further locking the LSD  302 . As a result, the LSD  302  becomes sufficiently loaded to substantially reduce the wheel slip  406  to zero RPM. At the same time, the control unit  370  adapts its calculation of the maximum and minimum allowed wheel slips  408  and  410 . Before detecting that the wheel slip  406  is moving out of the bounds defined by the maximum and minimum allowed wheel slips  408  and  410 , the maximum allowed wheel slip  408  calculated according to the steering angle is at about −5 RPM and the minimum allowed wheel slip  410  calculated according to the steering angle is at about −55 RPM. The control unit  370  updates the maximum allowed wheel slip  408  by selecting the greater of: (a) a sum of the expected wheel slip and the slip margin for the current wheel speed; and (b) the slip margin for the current wheel speed. In the present example, the maximum allowed wheel slip  408  becomes equal to the slip margin starting at the 24.5-second mark. The control unit also updates the minimum allowed wheel slip  410  by selecting the lower (most negative) of: (a) the expected wheel slip minus the slip margin for the current wheel speed; and (b) zero minus the slip margin for the current wheel speed. In the present example, the minimum allowed wheel slip  410  remains unchanged at the 24.5-second mark as it is lower than the slip margin expressed in the negative. As a result, the maximum allowed wheel slip  408  is changed by the control unit  370  to 25 RPM (0+25 RPM), as when the steering wheel  58  is held in a straight position (zero steering angle). The minimum allowed wheel slip  410  continues being calculated based on the actual angle of the steering wheel  58 . 
     The user continues turning the steering wheel  58 . At about 27 seconds (dashed line  442 ), the steering wheel  58  is turned to the right and the left wheel becomes the outside wheel. The control unit  370  continues selecting the maximum allowed wheel slip  408  as the greater of the maximum allowed wheel slip calculated according to the current steering angle and the slip margin. At the 27-second mark, the maximum allowed wheel slip  408  starts becoming greater than the slip margin. The control unit  370  also continues selecting the minimum allowed wheel slip  410  as the lesser (most negative) of: (a) the minimum allowed wheel slip calculated according to the current steering angle; and (b) the slip margin expressed in the negative. In that case, the minimum allowed wheel slip  410  becomes equal to the slip margin expressed in the negative starting at the 27-second mark. 
     The control unit  370  may issue a command to load the LSD  302  in response to other situations or driving conditions of the vehicle, for instance in response to a user command to lock the LSD  302 . The LSD  302  may thus be loaded even though at the time the wheel slip  406  may be within the range between the maximum and minimum allowed wheel slips  408  and  410 . Notwithstanding the reason for loading the LSD  302 , in an implementation, the control unit  370  may select the maximum allowed wheel slip  408  as the greater of: (a) a sum of the expected wheel slip and the slip margin for the current wheel speed; and (b) the slip margin, also selecting the minimum allowed wheel slip  410  as the lesser (most negative) of: (a) the expected wheel slip minus the slip margin for the current wheel speed; and (b) zero minus the slip margin for the current wheel speed, whenever the LSD  302  is loaded. 
     Considering the middle diagram  404 , it may be observed that a conventional limited slip differential not configured to react to the steering angle of the vehicle  40  and configured to allow a fixed wheel slip margin between +55 RPM and −55 RPM values (dotted lines  444  and  446 , respectively) would operate in the following manner at points  429  and  437 , at the 16-second mark and at the 20-second mark, respectively. In the event of a wheel slip exceeding +/−55 RPM bounds at those times, the conventional limited slip differential could be loaded and/or locked to bring back the wheel slip to about zero RPM. However, the conventional limited slip differential would not react as does the LSD  302  at the 24.5-second mark (dashed line  440 ) because the wheel slip would still be within the +/−55 RPM bounds. Otherwise stated, the conventional limited slip differential would be much slower to react to the onset of wheel slip than the present LSD  302 . 
     It will be understood that  FIG. 10  and its description relate to the wheel slip as a difference between the speed of the left wheel minus the speed of the right wheel, leading to obtaining negative wheel slip values when the left wheel rotates slower than the right wheel. The present technology can also be described in terms of wheel slip values for the right wheel, in which case a positive wheel slip value would be obtained when the left wheel rotates slower than the right wheel. In such a case, the present illustration would be modified in that the middle diagram  404  would be flipped so that the curve for the wheel slip  406  moves toward positive wheel slip values when the steering angle  402  moves towards negative values. The present LSD  302  and control unit  370  in fact react to differences between the speeds of the left and right driven wheels without prioritizing any of these wheels. 
       FIGS. 12 a  and 12 b    are a logic diagram showing operations of a method for controlling the LSD  302  based on a steering angle of the vehicle  40 . A sequence  500  is best understood by consideration of  FIGS. 12 a  and 12 b    along with  FIG. 23 . The sequence  500  comprises a plurality of operations that may be executed in variable order, some of the operations possibly being executed concurrently, some of the operations being optional. The sequence  500  may be implemented in a vehicle, for example the vehicle  40 . The vehicle  40  has a steering device, for example the steering wheel  58 . The vehicle may alternatively implement a handlebar as a steering device. A limited slip differential (LSD), for example the LSD  302 , is connected to the half-shafts  98  of the vehicle  40 . Left and right driven wheels such as the front wheels  44  are operably connected to the LSD  302  via the half-shafts  98 . 
     In the sequence  500 , operation  510  comprises determining rotational speeds of the left and right driven wheels  44 . A current wheel slip  406  is calculated at operation  515  as a difference between the rotational speeds of the left and right driven wheels  44 . The wheel slip  406  may either be calculated as the speed of the left wheel minus the speed of the right wheel or as the speed of the right wheel minus the speed of the left wheel. Operation  520  comprises determining the average rotational speed  1202  of the left and right driven wheels  44 . The steering angle  1204  is determined at operation  525 . Operation  530  comprises applying the current steering angle  1204  to the steering angle mapping table (Table I) to obtain the correction factor  1222  and multiplying the correction factor  1222  by the average rotational speed  1202  to determine the expected wheel slip  1226 . The slip margin  1210  is selected at operation  535  by applying the average rotational wheel speed  1202  to the slip mapping table, which is a representation of diagrams  414  and  418  in the control unit  370 . 
     At operation  540 , the control unit  370  determines whether or not the LSD  302  is currently loaded, and sets or resets the binary status  1206  of the LSD  302  accordingly. If the binary status  1206  is not set, the switch  1228  allows the maximum allowed wheel slip  408  to be calculated at operation  545  by adding the slip margin  1210  to the expected wheel slip  1210  in the adder  1212 . Also if the binary status  1206  is not set, the switch  1230  allows the minimum allowed wheel slip  410  to be calculated at operation  550  by subtracting the slip margin  1210  from the expected wheel slip  1226 , the adder  1218  effectively adding the expected wheel slip  1226  to the negative version  1216  of the slip margin  1210 . 
     If, at operation  540 , the LSD  302  is loaded, the binary status  1206  is set, and one of the AND boxes  1240  and  1242  outputs a logical 1, depending on the steering angle  1204 . As expressed in the foregoing description of  FIG. 23 , outputs of the AND boxes  1240  and  1242  are respectively applied to the switches  1228  and  1230 , causing the outputs  1244  and  1246  of the switches  1228  and  1230  to be equal either to the expected wheel slip  1226  or to the fixed values  1248  and  1250 , which are both equal to 0 RPM. If for example the steering angle  1204  is negative (the logical value  1236  is set) and LSD  302  is loaded, causing the binary status  1206  to be set, the AND box  1240  issues a logical 1, causing the output  1244  of the switch  1228  to be set to 0 RPM. At that time, because the steering angle  1204  is negative, the expected wheel slip  1226  is also negative. Consequently, when the binary status  1206  is set, the output  1244  of the switch  1228  is the greater of the expected wheel slip  1226  or 0 RPM. This output  1244  is added to the slip margin  1210  by the adder  1212 . As a result, the maximum allowed wheel slip  408  is calculated at operation  555  as the greater of: (a) the slip margin  1210 ; and (b) a sum of the expected wheel slip  1226  and the slip margin  1210 . In an equivalent manner, if the binary status  1206  is set, the minimum allowed wheel slip  410  is calculated at operation  560  as the lesser of: (a) the slip margin  1210  expressed in the negative  1216 ; and (b) the expected wheel slip  1226  minus the slip margin  1210 . 
     Operation  565  comprises detecting that the current wheel slip  406  is outside the range between the maximum and minimum allowed wheel slips  408  and  410 . This detection made at operation  565  causes the setting of the binary status  1206 , if not previously set. If not previously loaded, the LSD  302  is loaded at operation  570 . Increasing the loading of the LSD  302  following the detection made at operation  565 , if the LSD  302  was previously loaded, is also contemplated. 
     Returning to  FIGS. 10 and 13 , operation  570  may end, for example, at the 18-second mark (dashed line  434 ) and at the 22.5-second mark (dashed line  438 ), when the torque TqDiff falls to zero, at which time the binary status  1206  of the LSD  302  may be reset by the control unit  370 . 
     Each of the operations of the sequences  500  and  450  may be configured to be processed by one or more processors, the one or more processors being coupled to a memory. In more details,  FIG. 14  is a block diagram of an exemplary control unit  370 . The control unit  370  comprises a processor  602  operatively connected to a memory  604 , an input port  606  and an output port  608 . The processor  602  may include a plurality of co-processors. The memory  604  may include one or more memory modules. The input port  606  may include a plurality of input modules. Likewise, the output port  608  may include one or more output modules. The input port  606  and the output port  608  may be integrated as an input/output module. 
     In an implementation, the input port  606  receives signals and measurements from the wheel speed sensors  376 ,  378  and the steering angle sensor  390 , and may further receive measurements form the vehicle speed sensor  380 . The output port  608  provides control commands to the actuator  372  of the LSD  302  and to the solenoid  382  for loading and/or locking the LSD  302 . The memory  604  stores configuration information for the control of the LSD  302 , including the maximum steering angle or the vehicle  40 , for example +/−360 degrees, the slip ratio for the vehicle  40 , for example 30%, and the slip mapping table of the relations between values of the slip margin  420  and speed  416  of the front wheels  44 . 
     In operation, the processor  602  analyses speed measurements for both wheels driven by the LSD  302  as well as the current steering angle. The processor  602  averages the speed measurements of the driven wheels  44  provided by the wheel speed sensors  376 ,  378 . Use of measurements from the vehicle speed sensor  380  is also contemplated. Based on the current steering angle, on the average rotational speed of the wheels  44  and based on the slip ratio stored in the memory  604 , the processor  602  calculates an expected wheel slip for the wheels  44 . The processor  602  also reads the slip margin for the average rotational speed of the wheels  44  from the memory  604  and calculates the maximum and minimum allowed wheel slips by respectively adding and subtracting the slip margin to and from the expected wheel slip. 
     The processor  602  also calculates a current wheel slip as a difference between the rotational speeds of the left and right driven wheels  44 . The processor  602  may calculate a loading level that should be applied to the LSD  302 . If the wheel speed measurements show that the current wheel slip is within the range defined by the maximum and minimum allowed wheel slips  420  and  410 , the processor  602  may determine that no load is needed; however, the processor  602  may still determine that some load is to be applied to the LSD  302  for other reasons. If the processor  602  determines that the wheel slip is beyond the range defined by the maximum and minimum allowed wheel slips  408  and  410 , it may cause the output port  608  to provide a control command to the actuator  372 , in turn causing the actuator  372  to start applying load to the LSD  302 . The loading level for controlling the LSD  302  may for example be calculated as a function of a magnitude of the wheel slip or as a function of a difference between the actual wheel slip and the range defined by the maximum and minimum allowed wheel slips  408  and  410 . The calculated loading level may be part of the control command provided to the actuator  372 , for example in the form of a voltage or a current applied to the electric motor  288 , this voltage or current being calculated to provide the calculated TqDiff value to be applied on the clutch  374 . The processor  602  being continuously informed of the wheel speed measurements, the processor  602  may thus continuously recalculate the amount of load. Under some conditions, for example at maximum loading of the LSD  302  or when the loading is maintained for an extended period of time, the processor  602  may cause the output port  608  to provide another command to the solenoid  382  to lock the LSD  302 . The processor  602  may then remove the application of loading and/or locking to the LSD  302  when the conditions that caused the loading of the LSD  302  are no longer present. 
     As the average rotational speed of the wheels  44  may constantly change, the processor  602  continuously reevaluates the expected wheel slip for the wheels  44  and the maximum and minimum allowed wheel slips  408  and  410  in view of the changing expected wheel slip. The processor may obtain a new value of the slip margin from the memory  604  as the average rotational speed of the wheels  44  changes. 
     In an implementation, while any load is applied to the LSD  302  for any reason, the processor  602  continuously recalculates the maximum and minimum allowed wheel slips  408  and  410  so that the maximum allowed wheel slip  408  remains equal or greater than the slip margin and so that the minimum allowed wheel slip  410  remains equal or lower than the slip margin expressed in the negative. 
     Control of the LSD  302  Based on an Engine Torque (Rock Crawling Mode) 
     Another aspect of the present technology provides control of the LSD  302  connected to the driven wheels  44  of the vehicle  40 , this control being based at least in part on a current output torque of the engine  62 , on a position of an accelerator control, and on an average speed of the wheels  44 . The LSD  302  is preloaded in the sense that it is placed in condition for limiting an eventual slip between the two wheels  44  before an actual slip occurrence. 
     In an implementation, the user of the vehicle  40  can activate this feature, for example by setting the toggle switch  65  ( FIG. 3 ) to the rock crawling mode. In the rock crawling mode, the control unit  370  determines whether or not to apply a preload to the LSD  302 , this determination being based on the current output torque of the engine  62 , on a current speed of the vehicle  40 , and on a user demand placed on the engine  62  via the accelerator control. The user demand is detected by considering the position of the accelerator control, for example an accelerator pedal  91  ( FIG. 2 ). It is contemplated that a twist accelerator (not shown) or a pushbutton (not shown) mounted on a handlebar (not shown) could be used as an accelerator control. Considering for example a relatively low speed of the vehicle  40  concurrent with a high output torque of the engine  62  and/or with a sudden heavy actuation of the accelerator control, the user may be leading to vehicle  40  into a steep incline, for example readying the vehicle  40  for climbing on a rocky surface. Preloading the LSD  302  at that time, in view of an engine torque that can be predicted based on the position of the accelerator control, enhances the control of the vehicle  40  provided to the user by preventing wheel slip before it actually happens. 
     Table II is a non-limiting example of a loading mapping table that may be used by the control unit  370  to control a preload of the LSD  302 . The table shows torque values for application on the clutch  374  of the LSD  302 , in Newton-meters (Nm), as a function of a predicted engine torque, also in Nm, and as a function of a speed of the vehicle  40 , the speed being expressed both in kilometers per hour (KMH) and as an average of the rotational speeds of the left and right wheels  44  in revolutions per minute (RPM). 
     
       
         
           
               
               
             
               
                   
                 TABLE II 
               
             
            
               
                   
                   
               
               
                   
                 Average Wheel Speed (RPM) 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 0 
                 50 
                 100 
                 150 
                 200 
                 250 
                 300 
                 400 
               
            
           
           
               
               
            
               
                   
                 Vehicle Speed (KMH) 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 0.0 
                 6.7 
                 13.3 
                 20.0 
                 26.7 
                 33.3 
                 40.0 
                 53.3 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Pre- 
                 −20 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
               
               
                 dicted 
                 10 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
               
               
                 Engine 
                 20 
                  0 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
               
               
                 Torque 
                 30 
                 100 
                 100 
                  0 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
               
               
                 (Nm) 
                 40 
                 200 
                 200 
                 150 
                 100 
                  0 
                 Null 
                 Null 
                 Null 
               
               
                   
                 50 
                 300 
                 300 
                 250 
                 200 
                 100 
                 Null 
                 Null 
                 Null 
               
               
                   
                 70 
                 400 
                 400 
                 400 
                 300 
                 200 
                 Null 
                 Null 
                 Null 
               
               
                   
                 90 
                 500 
                 500 
                 500 
                 500 
                 500 
                 Null 
                 Null 
                 Null 
               
               
                   
               
            
           
         
       
     
     For illustration purposes, assuming an overall wheel diameter of about 71 centimeters, Table II provides torque values applied on the clutch  374  of the LSD  302  for speeds of the vehicle  40  up to about 53.3 KMH, corresponding to a wheel speed of 400 RPM, and for various predicted engine torque values. 
     Also in Table II, Null values reflect that the control unit  370  does not cause the application of any preload to the LSD  302  for corresponding combinations of predicted engine torque and of vehicle speed values. Though not shown in the particular example of Table II, the loading mapping table may also use Null values to represent situations where the electric motor  288  does not apply pressure to the clutch  374  while, at the same time, the clutch  274  and the LSD  304  are locked by energizing the solenoid  382  to lock the gear set  276 . Examples of Null values reflecting locking the LSD  304  by use of the solenoid are introduced hereinbelow. 
     The control unit  370  may determine the speed of the vehicle  40  either based on the measurements from the vehicle speed sensor  380  or by averaging the measurements from the wheel speed sensors  376 ,  378 . The control unit  370  also receives an engine torque measurement from the engine torque monitor  394 . In an implementation, the engine torque monitor  394  determines the engine output torque based on admitted air and fuel measurements and based on an ignition timing advance. Use of a torque sensor operatively connected to the engine  62  is also contemplated. 
     The control unit  370  controls a torque to be applied on the clutch  374  of the LSD  302  in view of the predicted engine torque, as determined from the loading mapping table of Table II. The torque value to be applied on the clutch  374  is converted by the control unit  370  into a level of current that should be provided to the electric motor  288  to provide the desired preload level. This conversion is dependent on characteristics of the electric motor  288 , of the gear set  276  and of the clutch  374 . In a particular implementation in which the electric motor  288  is a 12-volt DC motor, a 500 Nm torque value applied to the clutch  374  is obtained by applying a 10 amperes current to the electric motor  288 . The electric motor  288  may alternatively be a step motor, in which case the control unit  370  determines a number of steps sufficient to cause the electric motor  288  to apply the desired preload level to the LSD  302 . It is also contemplated that the control unit  370  may use pulse width modulation to control the electric motor  288 . 
     In a variant of the present technology, multiple tables similar to Table II may be defined in the control unit  370 . Use of distinct loading mapping tables defined for different available gear ratios of the transaxle  66 , as reported to the control unit  370  by the shifter position indicator  396  may be contemplated as well. 
     Without limitation, the above described shifter  60  for the transaxle  66  allows the driver to select between a reverse gear, high and low forward gears and a neutral position. For illustration purposes, the loading mapping table of Table II may apply to the reverse gear and to the low forward gear. When the high forward gear of the transaxle  66  is selected by the shifter  60 , a distinct loading mapping table is applied by the control unit  370 . Table III provides a non-limiting example of a loading mapping table applicable when the transaxle  66  is in high gear: 
     
       
         
           
               
               
             
               
                   
                 TABLE III 
               
             
            
               
                   
                   
               
               
                   
                 Average Wheel Speed (RPM) 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 0 
                 50 
                 100 
                 150 
                 200 
                 250 
                 300 
                 400 
               
            
           
           
               
               
            
               
                   
                 Vehicle Speed (KMH) 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 0.0 
                 6.7 
                 13.3 
                 20.0 
                 26.7 
                 33.3 
                 40.0 
                 53.3 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Pre- 
                 −20 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
               
               
                 dicted 
                 10 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
               
               
                 Engine 
                 20 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
               
               
                 Torque 
                 30 
                  0 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
               
               
                 (Nm) 
                 40 
                 100 
                 100 
                  0 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
               
               
                   
                 50 
                 200 
                 200 
                 150 
                 100 
                  0 
                 Null 
                 Null 
                 Null 
               
               
                   
                 70 
                 300 
                 300 
                 250 
                 200 
                 100 
                 Null 
                 Null 
                 Null 
               
               
                   
                 90 
                 400 
                 400 
                 400 
                 300 
                 200 
                 Null 
                 Null 
                 Null 
               
               
                   
               
            
           
         
       
     
     When the transmission is in high gear, for a given predicted engine torque and a given vehicle speed, the torque applied on the clutch  374  of the LSD  302  is lower than when the transmission is in low gear, with the predicted engine torque and the same vehicle speed. In the non-limitative example of Table III, when the transaxle  66  is in high gear, torque values applied on the clutch  374  of the LSD  302  as a function of the predicted engine torque and as a function of a speed of the vehicle  40  are shifted toward the bottom of the loading mapping table so that, for example, when in high gear, preloading is applied for a predicted engine torque of 90 Nm at the same level as for a predicted engine torque of 70 Nm when in low gear. 
     In the same or another variant of the present technology, an estimation of the desired acceleration by the user of the vehicle  40  may be made by the control unit  370 . To this end, the control unit  370  uses real-time information from the accelerator control sensor  392 . The accelerator control sensor  392  provides signals indicative of a current position of the accelerator control actuated by the user of the vehicle  40 , for example the accelerator pedal  91  ( FIG. 2 ). It is contemplated that the accelerator control sensor  392  may alternatively provide a position of a butterfly valve in a throttle of the engine  62 . The control unit  370  determines an acceleration of the accelerator control position based on the real-time information provided by the accelerator control sensor  392 . A large, positive acceleration of the accelerator control position indicates that the user wishes the vehicle  40  to accelerate rapidly. A large, negative acceleration (i.e. deceleration) of the accelerator control position indicates that the user intends the vehicle  40  to slow down rapidly. It may be noted that the accelerator control sensor  392  is expected to react more rapidly than the driveline of the vehicle  40 , including the engine  62 , the CVT  64 , the transaxle  66 , and the like. As such, the control  370  is able to modify the preload to the LSD  302  before the actual increase or decrease of torque from the engine  62  becomes present at the input shaft  90 . 
     The preload may thus be based on a predicted engine torque calculated according to equation (1): 
     
       
         
           
             
               
                 
                   
                     predicted_engine 
                     ⁢ 
                     _torque 
                   
                   = 
                   
                     sensed_torque 
                     + 
                     
                       
                         
                           ∂ 
                           
                             taccelerator 
                             ⁢ 
                             _ 
                             ⁢ 
                             position 
                           
                         
                         
                           ∂ 
                           t 
                         
                       
                       · 
                       constant 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     Wherein:
         predicted_engine_torque is a prediction of the engine output torque;   sensed_torque is a measurement of the engine output torque;   accelerator_position is a measurement of the accelerator control position;       

               ∂     taccelerator   ⁢   _   ⁢   position         ∂   t           
is a rate of change of the accelerator control position over time; and
         constant is a constant whose value is predetermined based on characteristics of the driveline of the vehicle  40 .       

     Per equation (1), the predicted engine torque is therefore calculated by adding a torque adjustment, which is proportional to the rate of change of the accelerator control position over time, to the actual engine output torque as measured. 
     In an implementation, the control unit  370  implements equation (1) to calculate the predicted engine torque. In an alternative implementation, the control unit  370  uses a torque mapping table to store relations between the predicted engine torque, the accelerator control position and the rate of change of the accelerator control position. 
       FIG. 15  illustrates a block diagram showing internal operations of the control unit  370  for determining the predicted engine torque, according to an implementation. The block diagram  610  shows that up to three (3) inputs may be used by the control unit  370  to determine the predicted engine torque. It is contemplated that, in an implementation, the control unit  370  may use additional inputs to determine the predicted engine torque. One such input is a current engine output torque  612 , expressed in Nm, this value being provided to the control unit  370  by the engine torque monitor  394 . Another input is a current accelerator control position  614 , expressed in percentage, for example the position of the accelerator pedal  91 , this value being provided to the control unit  370  by the accelerator control sensor  392 . Yet another input is a rate of change  616  of the accelerator, expressed in a percent variation of the accelerator position per second. In the implementation of  FIG. 15 , the rate of change  616  of the accelerator is determined by the control unit  370  based on a signal by the accelerator control sensor  392 . In a variant, the control unit  370  may internally track changes to the accelerator control position  614  to calculate the rate of change  616  of the accelerator. 
     The rate of change  616  of the accelerator is multiplied by a predetermined time-limiting interval  618  by a multiplier  620  to provide an accelerator control gain  622 . In the non-limiting example of  FIG. 15 , the time-limiting interval  618  is equal to 0.75 second. This value implies the rate of change  616  of the accelerator is considered over a 0.75-second period. The accelerator control gain  622  and the accelerator control position  614  are applied to an adder  624 . The adder  624  outputs an equivalent accelerator control position  626  that may be greater than 100% and thus exceed a realistic complete opening. This equivalent accelerator control position  626  is applied to a block  628 . The block  628  is illustrated as a graphical representation of a torque mapping table that provides an engine torque estimate  630  as a function of the equivalent accelerator control position  626 . Table IV provides a non-limiting example of a content of the torque mapping table that may be used by the control unit  370 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE IV 
               
               
                   
                   
               
               
                   
                 Equivalent accelerator  
                 Engine Torque  
               
               
                   
                 control position 626 (%) 
                 Estimate 630 (Nm) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 0 
                 0 
               
               
                   
                 9 
                 8.5 
               
               
                   
                 20 
                 17.2 
               
               
                   
                 30 
                 27.9 
               
               
                   
                 40 
                 41.7 
               
               
                   
                 50 
                 56.4 
               
               
                   
                 60 
                 70.4 
               
               
                   
                 70 
                 83.6 
               
               
                   
                 80 
                 118.6 
               
               
                   
                 100 
                 175 
               
               
                   
                 120 
                 175 
               
               
                   
                   
               
            
           
         
       
     
     The accelerator control position  614  and the accelerator control gain  622  are also applied to a selection box  632  that selects the lower of these two (2) inputs. The selection box  632  then outputs a minimum accelerator control position  634 , which is the lower of the accelerator control position  614  and the accelerator control gain  622 . A divider  636  divides the minimum accelerator control position  634  by the accelerator control position  614  to provide an accelerator control correction factor  638  to be applied to the engine torque estimate  630 . The accelerator control correction factor  638  is in a range between zero (0) and one (1), and is dimensionless. If both the minimum accelerator control position  634  and the accelerator control position  614  are equal to zero, the accelerator control correction factor  638  is set to one (1). A multiplier  640  multiplies the engine torque estimate  630  by the accelerator control correction factor  638  to provide a projected torque  642 . Because the accelerator control correction factor  638  is defined in a range between zero and one, the projected torque  642  is less than or equal to the engine torque estimate  630 . Otherwise stated, the accelerator control correction factor  638  limits the engine torque estimate  630  in view of a realistic accelerator control position prediction. A subtractor  644  subtracts the accelerator control correction factor  638  from unity  646  (i.e. from one (1)) to produce a torque correction factor  648 . A multiplier multiplies the engine output torque  612  by the torque correction factor  648  to produce a torque correction  652 . The torque correction  652  is added to the projected torque  642  in an adder  654  to produce the desired value, which is a predicted engine torque  656 . 
     Whether an implementation determines the predicted engine torque according to equation (1) or using the operations described in relation to  FIG. 15 , the effect of determining the predicted engine torque is similar. For illustration purposes, though the engine output torque may at a given time be equal to 20 Nm for example, as reported by the engine torque monitor  394 , a detection that the user is heavily acting upon the accelerator control may lead to the calculation of a predicted engine torque of 90 Nm for example. Assuming that, at that time, the speed of the vehicle  40  is 20 KMH, the torque to be applied on the clutch  374  would change from Null to 500 Nm. To control the preload, the control unit  370  inputs the predicted engine torque in the loading mapping tables of Table II and III, one of these loading mapping tables being selected according to the position of the shifter  60 . In the above example, LSD  302  would rapidly move from a no preload condition to a maximum preload condition, this result being reached much faster than when the LSD  302  is loaded following the detection that the front wheels  44  are slipping. Depending on characteristics of the engine  32 , the CVT  64 , the driveshafts  82 ,  84  and the LSD  302  itself, the LSD  302  will reach the maximum preload condition before any actual change of a torque at the input shaft  90  of the LSD  302 . It may be noted that the rate of change of the accelerator control position over time may be negative if the user releases the acceleration control. The predicted engine torque may therefore be lower than the engine output torque as measured, potentially causing a reduction or a release of the preload. 
       FIG. 16  is a sequence diagram showing operations of a method for controlling the LSD  302  based on an engine torque, an accelerator control position and a rate of change of the accelerator control position. A sequence  700  comprises a plurality of operations that may be executed in variable order, some of the operations possibly being executed concurrently, some of the operations being optional. The sequence  700  may be implemented in a vehicle, for example the vehicle  40 . The vehicle  40  has an engine and may have a transmission, for example the engine  62  and the CVT  64  coupled to the transaxle  66 . A limited slip differential (LSD), for example the LSD  302 , is operatively connected via the half-shafts  98  to wheels  44  driven by the engine  62 . Torque from the engine  62  is applied to the LSD  302  via the input shaft  90 . 
     In the sequence  700 , operation  712  comprises determining a current output torque of the engine  62 , this engine torque measurement being provided to the control unit  370  by the engine torque monitor  394 . The control unit  370  determines a position of the accelerator control at operation  714  based on a measurement from the accelerator control sensor  392 . A rate of change over time of the position of the accelerator control is determined at operation  716 . The rate of change over time of the position of the accelerator control may be provided to the control unit  370  by the accelerator control sensor  392 . Alternatively, the control unit  370  may calculate this rate of change based on successive measurements provided by the accelerator control sensor  392 . The control unit  370  determines a predicted engine torque at operation  718 , the predicted engine torque being based on the current output torque of the engine and on the rate of change over time of the position of the accelerator control. In operation  718 , the control unit  370  may add the torque adjustment to the current output torque of the engine, according to equation (1). Alternatively, in operation  718 , the control unit  370  may implement the operations of the block diagram  610  of  FIG. 15 . Another alternative in which the control unit  370  applies the current output torque of the engine, the position of an accelerator control and the rate of change over time of the position of the accelerator control to a three-dimensional look-up table to obtain the value of the predicted engine torque is also contemplated. 
     Then, a speed of the vehicle  40  is determined at operation  720 . The speed of the vehicle  40  may be provided to the control unit  370  by the vehicle speed sensor  380 . Alternatively, the operation  720  may include sub-operation  722  comprising measuring, by the wheel speed sensors  376 ,  378 , rotational speeds of the left and right wheels  44 . This measurement is provided to the control unit  370  that determines an average of the rotational speeds of the left and right wheels  44  to determine the speed of the vehicle  40 , based on this average and further based on a dimension of the left and right wheels  44 . 
     Operation  730  then comprises determining a value of a preload for eventual application to the LSD  302 , the value of the preload being based on the predicted engine torque and on the speed of the vehicle  40 . In an implementation, the operation  730  may comprise sub-operation  732  in which the predicted engine torque and the speed of the vehicle  40  are applied by the control unit  370  to a loading mapping table to read therefrom a value of a torque to be applied on the clutch  374  of the LSD  302 . In a variant, the control unit may select the loading mapping table among a plurality of loading mapping tables, for example those illustrated in Tables II and III, according to a position of the shifter  60 , this position being provided to the control unit  370  by the shifter position indicator  396 . 
     Considering the loading mapping tables illustrated in Tables II and III, the value of the preload for application to the LSD  302 , expressed in the form of a torque to be applied on the clutch  374  in the present example, may be zero (or Null) or may be greater than or equal to zero. At operation  740 , the control unit  370  conditionally causes the application of a preload to the LSD  302 , this application being conditional to the value of the preload being greater than zero (i.e. not Null or negative). Operation  740  may comprise sub-operation  742 , in which the control unit  370  controls the electric motor  288  to drive the gear set  276  and the ball ramp  278  to compress the clutch  374  according to the torque value obtained from the loading mapping table. This operation loads the LSD  302 , thereby preventing or reducing a rotational speed difference of the left and right wheels  44 . 
     Optionally, the gear set  276  may be locked at operation  750 . To this end, the control unit  370  may use the solenoid  382  to lock the gear set  276 . 
     Each of the operations of the sequence  700  may be configured to be processed by one or more processors, the one or more processors being coupled to a memory, for example the processor  602  and the memory  604  of the control unit illustrated in  FIG. 14 . 
     In an implementation, the input port  606  receives signals and measurements from the wheel speed sensors  376 ,  378 , the vehicle speed sensor  380 , the accelerator control sensor  392 , the engine torque monitor  394  and the shifter position indicator  396 . The output port  608  provides commands to the actuator  372  of the LSD  302  and to the solenoid  382  for preloading and/or locking the LSD  302 . The memory  604  stores configuration information for the control of the LSD  302 , including for example a loading mapping table or a plurality of such loading mapping tables for a plurality of positions of the shifter  60 , a torque mapping table of an engine torque estimate as a function of an accelerator control position, and dimensions of the wheels  44  expressed as a radius, a diameter or as a circumference. 
     In operation, the processor  602  analyses measurements obtained from the vehicle speed sensor  380  and/or measurements from the wheel speed sensors  376 ,  378  to determine a speed of the vehicle  40 . In an implementation using the measurements from the wheel speed sensors  376 ,  378 , the control unit determines the speed of the vehicle  40  based on an average of the rotational speeds of the left and right wheels  44 . The processor  602  also analyses measurements from the engine torque monitor  394 . The processor  602  determines, based on the measurements from the engine torque monitor  394 , a value of an output torque of the engine  62 . Based on the value of the output torque of the engine  62  and on the speed of the vehicle  40 , the processor  602  determines a value of a preload, if any, to be applied to the LSD  302 . The processor  602  causes the output port  608  to provide a command to the actuator  372 , in turn causing the actuator  372  to apply the preload to the LSD  302  by compressing the clutch  374 . 
     The configuration information stored in the memory  604  may include the loading mapping table of Table II. In an implementation, the memory  604  may optionally store a plurality of loading mapping tables for each of a plurality of positions of the shifter  60 , as shown for example in Tables II and III. The processor  602  may use an indication received at the input port  606  from the shifter position indicator  396  to select one of these loading mapping tables in the memory  604 . In any case, the processor  602  may apply the value of the output torque of the engine  62  and the speed of the vehicle  40  to the loading mapping table to determine a torque value to be applied on the clutch  374  of the LSD  302 . The configuration information stored in the memory  604  may also include the torque mapping table of Table IV. 
     The processor  602  is optionally informed, via the input port  606 , of a current position of the accelerator control provided by the accelerator control sensor  392 . The accelerator control sensor  392  may also provide a rate of change of the accelerator control position, or the processor  602  may continuously determine a rate of change of the accelerator control position based on successive signals from the accelerator control sensor  392 . If the processor  602  determines that the user has rapidly increased or decreased the accelerator control demand, the processor  602  may, in an implementation, apply the correction factor of equation (1) to obtain a prediction of the engine output torque of the engine  62 . In another implementation, the processor  602  may implement the elements of the block diagram  610  and execute its various operations to determine the prediction of the engine output torque of the engine  62 . In any case, this predicted output torque is used as the value of the output torque of the engine  62  for reading torque value to be applied on the clutch  374  of the LSD  302  from the loading mapping table, in view of preloading for the LSD  302 . 
     The processor  602  may cause the output port  608  to provide a command to energize the solenoid  382 , thereby causing the tooth  384  of the solenoid  382  to engage the gear set  276 , effectively locking the LSD  302 . This command to lock the LSD  302  may follow the application of a preload, for example a maximum compression of the clutch  374 . 
     Control of the LSD  302  Optimized for Slippery Driving Conditions (Mud Mode) 
     A further aspect of the present technology provides control of the LSD  302  connected to the driven wheels  44  of the vehicle  40 , this control being based at least in part on a detection of slippery driving conditions such as, for example, when the vehicle  40  is in deep mud or on other poorly tractable terrain. In the context of the present disclosure, the term “slippery driving conditions” is used for convenience purposes to refer to conditions such as driving on deep mud or on other very slippery surfaces, including without limitation loose gravel, icy roads, deep snow, shallow rivers, and the like. The present technology is applicable, in particular but not exclusively, to off-road vehicles. 
     In an implementation, the user of the vehicle  40  can activate this feature, for example by setting the toggle switch  65  ( FIG. 3 ) to the mud mode. The control unit  370  can detect or infer that the vehicle  40  is rolling in deep mud or in other slippery driving condition using any one or a combination of three (3) situations. A first situation is when a predetermined number of wheel slip occurrences is detected. A second situation is when a wheel is slipping despite the application of a preload to the LSD  302 . A third situation is when the torque output of the engine is above an engine load line. 
     These three (3) situations are exemplified in  FIG. 17 , which is a block diagram  800  showing internal operations of the control unit  370  for controlling the LSD  302  in mud mode, according to an implementation. The block diagram  800  shows that, in the present implementation, up to four (4) inputs may be used by the control unit  370  to control the LSD  302  in the mud mode. It is contemplated that, in an implementation, the control unit  370  may use additional inputs. 
     One such input is a wheel slip detection  802 . The wheel slip detection  802  may be internally generated by the control unit  370  when a difference between measurements of the rotational speeds of the left and right front wheels  44  from the wheel speed sensors  376 ,  378  indicates that one of the front wheels  44  is slipping by more than a predetermined threshold. Before detecting a wheel slip, the control unit  370  may allow a rotational speed difference exceeding a predetermined maximum difference in rotational speeds in order to account for the natural speed difference of the wheels  44  when the vehicle  40  is in a curve. For example in an implementation where the control of the LSD  302  based on a steering angle of the vehicle  40  and the control of the LSD  302  optimized for slippery driving conditions (Mud Mode) are both supported by the control unit  370 , the wheel slip detection  802  may be generated when the wheel slip  406  is out of the permissible slipping range defined by the maximum and minimum allowed wheel slips  408  and  410 . 
     A second input is an activity indication  804  for the LSD  302 , this activity indication  804  being set when a load is being applied to the LSD  302  through the electric motor  288 . A third input is a vehicle speed  806  that may be provided to the control unit  370  by the vehicle speed sensor  380 . Alternatively, the vehicle speed  666  may equivalently be based on measurements, by the wheel speed sensors  376 ,  378  of rotational speeds of the left and right wheels  44 , the vehicle speed  666  being deduced by the control unit  370  based on these measurements and on dimensions of the front wheels  44 . A fourth input is a current engine output torque  808 , expressed in Nm, this value being provided to the control unit  370  by the engine torque monitor  394 . 
     An example will now be described with reference to  FIG. 17 . The block diagram  800  includes a number of logical components that implement logical AND, OR and NOT functions. The present description is made with mentions of logical 1&#39;s and 0&#39;s at the output of some of the components. This manner of describing the block diagram  800  is for simplification purposes and does not limit the present disclosure. Other implementations using opposite 0&#39;s and 1&#39;s or using other logical values, such as True or False, and implementations of the logic events of the block diagram  800  using software code, are also contemplated. 
     Considering the first situation, the wheel slip detection  802  is set to 1 if a wheel slip is detected, or to 0 in the absence of a wheel slip. This output is applied at an input of a change determination box  810  that briefly outputs a change indication  812  set to 1 when the input changes from 0 to 1, that is, when a wheel slip is first detected. The change indication  812  returns to 0 after a short delay and remains at 0 if the wheel slip detection  802  is changed to 0. The change indication  812  is applied to a counter  814  that counts a number of occurrences of the change indications  812  being set to 1. In effect, the counter  814  counts a number of occurrences of distinct wheel slip events. When the counter  814  exceeds a predetermined number of wheel slip occurrences, for example three (3) wheel slip occurrences, it applies a logical 1 to an input of a first OR box  816  having two (2) inputs. Then, regardless of a value applied at the other input of the first OR box  816 , the first OR box  816  applies a logical 1 to an input of a second OR box  818  having two (2) inputs. Then, regardless of a value applied at the other input of the second OR box  818 , the second OR box  816  issues a locking request  820  for the LSD  302 . The locking request  820  may cause the application of a load to the LSD  302 , for example the application of a maximum torque on the clutch  374 , and may further cause to energize the solenoid  382  to effectively lock the LSD  302 . The first situation is realized by repetitive wheel slips causing the locking of the LSD  302 . 
     A reset box  846 , which is described in details hereinbelow, may cause resetting of the counter  814  when the torque of the engine output torque  808  falls to a low torque set-point  842 . The counter  814  is therefore expected to be reset at various times during normal operation of the vehicle  40 . Use of a timer to reset the counter  814  when no wheel slip detection  802  is applied to the change determination box  810  after a predetermined time threshold is also contemplated. 
     Considering now the second situation, the activity indication  804  for the LSD  302 , which is set when a load is applied to the LSD  302 , and the change indication  812  are both applied to inputs of an AND box  822 . The AND box  822  outputs a 1 when both of its inputs are set to 1, which is the case when the change indication  812  indicates that a wheel slip is detected while the activity indication  804  indicates that a load is already applied to the LSD  302 . The 1 that is output from the AND box  822  propagates through the first and second OR boxes  816 ,  818 , the latter issuing a locking request  820  for the LSD  302 . The second situation is realized by the occurrence of a wheel slip while the LSD  302  is loaded causing the locking of the LSD  302 . 
     Considering now the third situation, the vehicle speed  806  is applied to a load line mapping table  824 .  FIG. 18  is a graph  830  of an engine load line  832 . On the graph  830  shown in  FIG. 18 , the load line  832  is an idealized representation of an expected engine output torque  834  required to move the vehicle as a function of the vehicle speed  806  when the vehicle  40  travels along a flat level surface, with minimal external resistance. On the graph  830 , a point  836  represents a situation where the vehicle  40  is rolling in deep mud or under another slippery driving condition. In that situation, an actual engine torque  836 , is greater than the expected engine output torque  834  for a given speed  836 , of the vehicle  40 . 
     Table V is a non-limiting example of a load line mapping table  824  that may be used by the control unit  370  to determine when the torque requested by the user of the vehicle  40  is above the engine load line. The table shows the vehicle speed  806 , expressed as an average of the rotational speeds of the left and right wheels  44  in revolutions per minute (RPM), as a function of the engine output torque  808 , in Newton-meters (Nm). 
     
       
         
           
               
               
               
             
               
                   
                 TABLE V 
               
               
                   
                   
               
               
                   
                 Vehicle Speed 806 (front  
                 Expected Engine  
               
               
                   
                 wheels 44 (RPM)) 
                 Output Torque 834 (Nm) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 0 
                 20 
               
               
                   
                 20 
                 20 
               
               
                   
                 50 
                 20 
               
               
                   
                 100 
                 20 
               
               
                   
                 150 
                 25 
               
               
                   
                 200 
                 30 
               
               
                   
                 300 
                 40 
               
               
                   
                 400 
                 120 
               
               
                   
                 500 
                 200 
               
               
                   
                 800 
                 200 
               
               
                   
                   
               
            
           
         
       
     
     The load line mapping table  824  outputs the expected engine output torque  834  as a function of the vehicle speed  806 . Returning to  FIG. 17 , the engine output torque  808  is compared with the expected engine output torque  834  by a first comparator  838 . If the engine output torque  808  is greater than the expected engine output torque  834 , the torque demand by the user is above the engine load line and the first comparator  838  outputs a 1 that is applied to the second OR box  818 . The second OR box  818  issues a locking request  820  for the LSD  302 . The third situation is realized by the excess engine torque causing the locking of the LSD  302 . 
     When none of the inputs applied to the first and second OR boxes  816  and  818  is set to 1, their outputs are set to 0 and the locking request  820  is not issued. 
     Other components of the block diagram  800  are used to remove the effect of the locking request  820 , if it has already been issued. 
     The engine output torque  808  is compared by a second comparator  840  to a low torque set-point  842 , which is set to 5 Nm in the non-limiting example of  FIG. 17 . The second comparator  840  issues low torque indication  844  set to 1 if the engine output torque  808  is less than the low torque set-point  842 . The low torque indication  844 , if set to 1, causes a reset box  846  to reset the counter  814  to zero wheel slip occurrences. As a result, the counter  814  applies a logical 0 to the first OR box  816 . If no logical 1 is applied to other inputs of the OR boxes  816  and  818  at that time, this may lead to the removal of the locking request  820 . It may be noted that the removal of the locking request  820  is not sufficient to cause the unlocking of the LSD  302  as other operating conditions of the vehicle  40  may require that the LSD  302  remain locked. 
     The low torque indication  844  is also applied to a reset (R) input of a flip-flop box  848 . The low torque indication  844  in fact applies a logical 1 to the R input of the flip-flop box  848  when the engine output torque  808  is lower than the low torque set-point  842 . 
     The output of the first OR box  816  is also applied to a set (S) input of the flip-flop box  848 . A logical 1 is therefore applied to the S input of the flip-flop box  848  when either of the first and second situations applies, that is when either the predetermined number of wheel slip occurrences is detected or when a wheel  44  is slipping despite the application of a preload to the LSD  302 . The logical 1 is also applied to the S input of the flip-flop box  848  when both of these situations apply concurrently. The flip-flop box  848  has an output (Q)  850  that is set to 1 when the S input is set to 1. After being set to 1, the Q output  850  remains set if the S input is set to 0, until the R input of the flip-flop box  848  is set to 1, following which the Q output  850  is set to 0. Both S and R inputs are not expected to be set to 1 at the same time, as this condition would require slipping of the front wheels  44  while the engine torque  808  is very low. Regardless, the Q output  850  is set to 0 if this circumstance occurs. Summarily, the Q output  850  is set to 1 when conditions defined in the first and second situations for locking the LSD  302  are present. 
     The output of the first comparator  838  is negated by a NOT box  852 . Its output is a load line indication  854  set to 0 when the torque demand by the user is above the engine load line and to 1 otherwise. A switch  856  has three (3) inputs to which the Q output  850  of the flip-flop switch  848 , the load line indication  854  and the low torque indication  844  are applied. The switch  856  operates as follows. 
     If the Q output  850  is set to 1 (one of the first and second situations causing the issuance of the loading request  820 ), the switch  856  outputs the value of the low torque indication  844 . At the time, the value of the low torque indication  844  is expected be set to 0 because wheel slip events causing the setting of the S input of the flip flop box  848  are generally not expected to occur at very low engine torque values. If the Q output  850  is set to 1 and the low torque indication is set to 0, the switch  856  does not issue the unlocking request  858 . 
     If the Q output  850  is set to 0 (none of the first and second uses causing the issuance of the loading request  820 ) and if the load line indication  854  is set to 1, the switch  856  outputs the unlocking request  858 , the torque demand by the user not exceeding the engine load line at that time (the third situation not causing the issuance of the loading request  820 ). If the Q output  850  is set to 0 and the load line indication  854  is set to 0, the switch  856  does not issue the unlocking request  858 . 
       FIGS. 19 a  to 19 e    provide logic diagrams showing operations of a method for controlling the LSD  302  based on driving conditions. A sequence  900  comprises a plurality of operations that may be executed in variable order, some of the operations possibly being executed concurrently, some of the operations being optional. The sequence  900  may be implemented in a vehicle, for example the vehicle  40 . In the sequence  900 , operation  910  comprises determining at least one parameter indicative of a riding condition of the vehicle  40 . Based on the at least one parameter, a slippery driving condition is detected at operation  920 . In response to the detection made at operation  930 , the LSD  302  is selectively locked at operation  930 . The LSD  302  may be selectively unlocked at operation  940  when the slippery driving condition is no longer detected. 
     Operations  910  and  920  may optionally comprise sub-sequences  950  or  960 ,  970  or  980  ( FIGS. 19 b  to 19 e   ) or a combination of these sub-sequences. 
     In sub-sequence  950 , sub-operations  952  and  954  respectively comprise determining a speed of the vehicle  40  and a torque of the engine  62 . The slippery driving condition is detected at sub-operation  956  by determining that the torque of the engine is above a load line of the engine  62  for the speed of the vehicle  40 . 
     In sub-sequence  960 , a rotational speed of the left wheel  44  and a rotational speed of the right wheel  44  are determined at sub-operation  962 , following which the rotational speeds of the left and right wheels  44  are compared at sub-operation  964 . A wheel slip occurrence is detected at sub-operation  966  if a difference between the rotational speeds of the left and right wheels  44  exceeds a predetermined maximum difference in rotational speeds. The predetermined maximum difference in rotational speeds may be set to zero (0) RPM or to a larger value. 
     Sub-sequence  970  comprises the sub-sequence  960  for detecting wheel slip occurrences. The sub-sequence  960  is repeated multiple times and a count of the number of wheel slip occurrences is taken at sub-operation  972  The slippery driving condition is detected at sub-operation  974  when the number of wheel slip occurrences exceeds a predetermined number of wheel slip occurrences, for example three (3) wheel slip occurrences. Operation  976  may eventually detect that the torque of the engine is lower than a low threshold value, in which case operation  978  resets the counter of the number of wheel slip occurrences. Optionally, the counter of the number of wheel slip occurrences may also be reset when no such occurrence has been detected over a predetermined period of time. 
     In sub-sequence  980 , a preload is applied to the LSD  302  at sub-operation  982 . A wheel slip occurrence is detected at sub-sequence  960 . The slippery driving condition is detected at sub-operation  984  because the wheel slip is detected while the LSD  302  is preloaded. 
     Each of the operations of the sequence  900  may be configured to be processed by one or more processors, the one or more processors being coupled to a memory, for example the processor  602  and the memory  604  of the control unit illustrated in  FIG. 14 . 
     In an implementation, the input port  606  receives signals and measurements from the wheel speed sensors  376 ,  378 , from the vehicle speed sensor  380 , and from the engine torque monitor  394 . The output port  608  provides commands to the actuator  372  of the LSD  302  and to the solenoid  382  for loading and/or locking the LSD  302 . The memory  604  stores configuration information for the control of the LSD  302 , including for example a predetermined maximum difference in rotational speeds of the wheels  44  for wheel slip detection, a predetermined number of wheel slip occurrences for the detection of successive wheel slips, the load line mapping table  824 , a wheel dimension and/or the low torque set-point  842 . 
     In operation, the processor  602  analyses measurements and signals from one or more of the wheel speed sensors  376 ,  378 , the vehicle speed sensor  380 , and the engine torque monitor  394 . The processor  602  detects a slippery driving condition based on at least one parameter indicative of a riding condition of the vehicle  40 , the at least one parameter being received at the input port  606 . The processor  602  controls, via the output port  608 , locking of the LSD  302  in response to the detection of the slippery driving condition. In various implementations the processor  602  may detect the slippery driving condition using one or more of the following techniques. 
     For example, the processor  602  may compare the rotational speeds of the left and right wheels  44  reported by the wheel speed sensors  376 ,  378  and detect a wheel slip occurrence if a difference between the rotational speeds of the left and right wheels  44  exceeds the predetermined maximum difference in rotational speeds stored in the memory  604 . The processor may detect the slippery driving condition when a number of wheel slip occurrences exceeds the predetermined number of wheel slip occurrences stored in the memory  604 . As mentioned hereinabove, the counter for the number of wheel slip occurrences may be reset when the engine output torque  808  falls below a low torque set-point  842  or, optionally, after a predetermined period of time without any wheel slip occurrence. 
     In another example, the processor  602  causes the output port  608  to forward a command for applying a preload to the LSD  302 , for example in response to the detection of a first wheel slip occurrence or for other reasons. The processor  602  detects a slippery driving condition when a wheel slip occurrence is detected while the preload is applied to the LSD  302 . 
     In yet another example, the processor  602  may determine a vehicle speed based on the speed measurement received at the input port  606  from the vehicle speed sensor  380 , or based on an average of the rotational speeds of the left and right front wheels  44  as measured by the wheel speed sensors  376 ,  378 , factoring the dimension of the front wheels  44  to determine of the vehicle speed. The processor  602  then reads, from load line mapping table  824  stored in the memory  604 , an expected engine torque value corresponding to the vehicle speed. The processor  602  detects the slippery driving condition when the engine output torque measurement exceeds the expected engine torque value. 
     When the processor  602  has caused the LSD  302  to lock in response to the detection of a slippery driving condition, the processor  602  may eventually control unlocking of the LSD  302 . To this end, the processor  602  may detect, based on one or more readings from the various sensors, that none of the conditions for the detection of the slippery driving condition remains. The processor  602  may then control, via the output port  608 , the unlocking of the LSD  302 . In particular, the processor  602  may implement the various blocks of the block diagram  800 . 
     Control of the LSD  302  Based on an Accelerator Control Position (Trail Active Mode) 
     A still further aspect of the present technology provides control of the LSD  302  connected to the driven wheels  44  of the vehicle  40 , this control being based at least in part on the accelerator control position. Heavy actuation of the accelerator control, in what is colloquially called a “holeshot start” may, under some conditions, cause the application of a high load to the LSD  302  in order to prevent wheel spin. In view of enhancing directional stability, a stabilization load may also be applied to the LSD  302  when a speed of the vehicle  40  meets or exceeds a predetermined threshold. In at least one implementation, the high load applied to the LSD  302  upon heavy actuation of the accelerator control may be a maximum possible load that can be provided by the electric motor  288 . 
     In an implementation, the user of the vehicle  40  can activate this feature, for example by setting the toggle switch  65  ( FIG. 3 ) to the trail active mode. Upon heavy actuation of the accelerator control by the user at very low vehicle speed, for example upon a standing start, the control unit  370  may cause the application of a high load to the LSD  302 . This is expected to prevent wheel spin before it actually occurs, or at least significantly reduce the amount of wheel spin occurring as a result of high initial acceleration. A stabilization load is also selectively applied to the LSD  302  when the vehicle speed exceeds a predetermined speed threshold. This stabilization load reduces potential slipping of the front wheels  44  at high vehicle speeds, and thus improves the directional stability of the vehicle  40 . 
       FIG. 20  is a block diagram showing internal operations of the control unit  370  for controlling the LSD  302  in trail active mode, according to an implementation. A block diagram  660  shows that up to three (3) inputs may be used by the control unit  370  to load the LSD in trail active mode. It is contemplated that, in an implementation, the control unit  370  may use additional inputs to determine in the trail active mode. One such input is a current accelerator position  662 , expressed in percentage, this value being provided to the control unit  370  by the accelerator control sensor  392 . A minimum actuation of the accelerator control, for example a complete release of the accelerator pedal  91 , may be expressed as a 0% value. A maximum actuation of the accelerator control, for example a complete depression of the accelerator pedal  91  may be expressed as a 100% value. Another input is a current engine output torque  664 , expressed in Nm, this value being provided to the control unit  370  by the engine torque monitor  394 . Yet another input is a vehicle speed  666  that may be provided to the control unit  370  by the vehicle speed sensor  380 . Alternatively, the vehicle speed  666  may equivalently be based on measurements, by the wheel speed sensors  376 ,  378  of rotational speeds of the left and right wheels  44 , the vehicle speed  666  being deduced by the control unit  370  based on these measurements and on dimensions of the front wheels  44 . These inputs are applied to various blocks within the block diagram  660 . 
     The accelerator position  662  is applied to an accelerator position threshold block  668  that defines a predetermined accelerator position threshold that may generally be considered as indicative of a full actuation of the accelerator control. This threshold is for example at a 90% depression of the accelerator pedal  91  in the non-limiting example of  FIG. 20 . Other threshold values up to 100% as well as lower values are also contemplated. When the accelerator position  662  meets or exceeds the predetermined accelerator position threshold, the accelerator position threshold block  668  issues a loading command  670  applied as a first input to a switch  672 . 
     The vehicle speed  666  is applied to a steering stabilization threshold block  674  that defines a predetermined speed threshold. That threshold is at 40 KMH in the non-limiting example of  FIG. 20 . Higher and lower threshold values are also contemplated. When the vehicle speed  666  meets or exceeds the predetermined speed threshold, the steering stabilization threshold block  674  issues a torque assignment  676  defining a fixed torque value, for example 350 Nm, this value being selected so that a stabilization load is applied to the LSD  302 , the stabilization load being less than the high load. In order to prevent overheating of the electric motor  288 , application of the stabilization load to the LSD  302  be followed by a command to lock the LSD  302  by activation of the solenoid  382 , following which the electric motor  288  can be de-energized. 
     The engine output torque  664  and vehicle speed  666  are both applied to a trail active mapping table. The trail active mapping table is illustrated as a block  678  on  FIG. 20 . The block  678  provides a graphical representation of the trail active mapping table. Table VI provides a non-limiting example of a content of a trail active mapping table that may be used by the control unit  370  to control the application of a load to the LSD  302 . As in the case of Tables II and III, Table VI shows torque values for application on the clutch  374  of the LSD  302 , in Newton-meters (Nm), as a function of the output torque of the engine  62 , also in Nm, and as a function of a speed of the vehicle  40 , the speed being expressed both in kilometers per hour (KMH) and as an average of the rotational speeds of the left and right wheels  44  in revolutions per minute (RPM). 
     
       
         
           
               
               
             
               
                   
                 TABLE VI 
               
             
            
               
                   
                   
               
               
                   
                 Average Wheel Speed (RPM) 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 0 
                 50 
                 100 
                 150 
                 200 
                 250 
                 300 
                 400 
               
            
           
           
               
               
            
               
                   
                 Vehicle Speed (KMH) 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 0.0 
                 6.7 
                 13.3 
                 20.0 
                 26.7 
                 33.3 
                 40.0 
                 53.3 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Engine 
                 −20 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
               
               
                 Output 
                 10 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
               
               
                 Torque 
                 20 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
                 Null 
               
               
                 (Nm) 
                 30 
                 Null 
                 Null 
                 Null 
                  0 
                 50 
                 200 
                 350 
                 Null 
               
               
                   
                 40 
                 Null 
                 Null 
                 Null 
                  0 
                 100 
                 250 
                 350 
                 Null 
               
               
                   
                 50 
                 Null 
                 Null 
                 Null 
                  0 
                 150 
                 250 
                 350 
                 Null 
               
               
                   
                 70 
                 Null 
                 Null 
                  0 
                 100 
                 250 
                 300 
                 350 
                 Null 
               
               
                   
                 90 
                 Null 
                 Null 
                 100 
                 250 
                 350 
                 350 
                 350 
                 Null 
               
               
                   
               
            
           
         
       
     
     Application of engine output torque  664  and of the vehicle speed  666  to the trail active mapping table yields a torque value  680 , which may be a Null value, the torque value  680  being output by the block  678 . The torque value  680  is a second input to the switch  672 . A third input to the switch  672  is a predetermined, high loading torque parameter  682 , having a value of 750 Nm in the present implementation. 
     The switch  672  operates as follows. If the loading command  670  is present at its first input, the switch  672  issues a distinct torque assignment  684  having a value equal to the predetermined, high loading torque parameter  682 . If the loading command  670  is not present at the first input of the switch  672 , the torque assignment  684  is set to the torque value  680 , which may have a Null value. 
     It may be noted that, in the implementation of  FIG. 20 , the accelerator position threshold block  668  may issue the loading command  670  at any vehicle speed, provided that the current accelerator position  662  meets or exceeds the predetermined position threshold. For that reason, the torque assignment  684  may be set to the 750 Nm torque value of the high loading torque parameter  682  whenever the accelerator control is fully engaged. The effect of the loading command  670  may be ignored by the control unit  370  when the control unit  370  selects the torque assignment  676  due to it being a nonzero value, as is the case when the vehicle speed  666  is at least 40 KMH, effectively negating the effect of the torque assignment  684  and of the loading command  670 . When the torque assignment  676  is at zero because the vehicle speed is less than 40 KMH, the control unit  370  selects the torque assignment  684 , which may either have a zero or a nonzero value and may be equal to the 750 Nm torque value when the loading command  670  is present. The control unit  370  causes the application on the clutch  374  of the LSD  302  of the selected one of the torque assignments  676  or  684 , if one of the torque assignments  676  and  684  is greater than zero. 
       FIG. 21  is a logic diagram showing operations of a method for controlling the LSD  302  based on an accelerator control position. A sequence  1000  comprises a plurality of operations that may be executed in variable order, some of the operations possibly being executed concurrently, some of the operations being optional. The sequence  1000  may be implemented in a vehicle, for example the vehicle  40 . The vehicle  40  has an engine, for example the engine  62 , the engine having a throttle operatively connected to the accelerator control, for example, the accelerator pedal  91 , and a limited slip differential (LSD), for example the LSD  302 . 
     In the sequence  1000 , operation  1010  comprises determining an accelerator control position by the accelerator control sensor  392 . Optionally, a speed of the vehicle  40  may be determined at operation  1020 . In an implementation, operation  1020  may comprise reading the speed of the vehicle  40  from the vehicle speed sensor  380 . In another implementation, operation  1020  may comprise sub-operations  1022  and  1024 . In sub-operation  1022 , rotational speeds of the left and right wheels  44  are determined by the wheel speed sensors  376 ,  378 . The speed of the vehicle  40  is then determined at sub-operation  1024  based on an average of the rotational speeds of the left and right wheels  44  and based on a dimension of the left and right wheels  44 . 
     Regardless, a high load is selectively applied to the LSD  302  at operation  1030 , provided that the accelerator control position meets or exceeds a predetermined position threshold. The predetermined position threshold may generally be considered as indicative of a heavy actuation of the accelerator control, for example 90%. Optionally, selectively applying the high load may be conditional to the speed of the vehicle  40  being less than the predetermined speed threshold, for example the 40 KMH value defined by the steering stabilization threshold block  674  of  FIG. 20 . 
     The application of the high load to the LSD  302  may optionally be followed by the energizing of the solenoid  382  to lock the LSD  302 , using the technique described in the foregoing description of  FIG. 9 . 
     In an implementation where the speed of the vehicle  40  is determined, operation  1040  may comprise releasing the high load when the speed of the vehicle  40  meets or exceeds the predetermined speed threshold. In the same or another implementation, operation  1050  may comprise applying a stabilization load when the speed of the vehicle  40  meets or exceeds the predetermined speed threshold. In the example of  FIG. 20 , the steering stabilization threshold block  674  defines the predetermined speed threshold. 
     Regardless, when a full or partial release of the accelerator control is detected at operation  1060 , the high load is released at operation  1070 . A partial release of the accelerator control may for example be detected as soon as the accelerator control sensor  392  reports an accelerator control position that no longer meets or exceeds the predetermined position threshold. 
     While the high load is not applied to the LSD  302 , the accelerator control position being less than the predetermined position threshold, the control unit  370  may, at operation  1090 , apply the engine output torque and the speed of the vehicle to the trail active mapping table to read a value of a partial load for application to the LSD. The control unit  370  controls the application of the partial load to the LSD at operation  1095 . The partial load applied to the LSD is in most circumstances lower than the high load. 
     The values of the predetermined position threshold and of the predetermined speed threshold are illustrative only and do not limit the present disclosure. 
       FIG. 22  is a logic diagram showing operations of a method for controlling the LSD  302  to stabilize the steering of a vehicle. A sequence  1100  also comprises a plurality of operations that may be executed in variable order, some of the operations possibly being executed concurrently, some of the operations being optional. The sequence  1100  may also be implemented in vehicle  40 . 
     A speed of the vehicle  40  is determined at operation  1110 . As in the case of sequence  1100 , the speed of the vehicle  40  may be determined based on measurements provided by the vehicle speed sensor  380  or by the wheel speed sensors  376 ,  378 . A stabilization load is selectively applied to the LSD  302  at operation  1120  when the speed of the vehicle  40  is greater than the predetermined speed threshold. In this manner, directional stability of the vehicle  40  is enhanced. 
     In an implementation, the vehicle  40  may implement the sequence  1000  described hereinabove with reference to  FIG. 21 . In another implementation, the vehicle  40  may implement the sequence  1100  described hereinabove with reference to  FIG. 22 . In yet another implementation, the vehicle  40  may implement both sequences  1000  and  1100 . These sequences may therefore be implemented independently or jointly. 
     Each of the operations of the sequences  1000  and  1100  may be configured to be processed by one or more processors, the one or more processors being coupled to a memory, for example the processor  602  and the memory  604  of the control unit illustrated in  FIG. 14 . 
     In an implementation, the input port  606  receives signals and measurements from the accelerator control sensor  392  and, optionally, from the wheel speed sensors  376 ,  378  and/or the vehicle speed sensor  380 . The output port  608  provides control commands to the actuator  372  of the LSD  302  and to the solenoid  382  for loading and/or locking the LSD  302 . The memory  604  stores configuration information for the control of the LSD  302 , including for example a dimension of the left and right wheels  44 , the predetermined position threshold and, optionally, the predetermined speed threshold, and/or the trail active mapping table. 
     In operation, the processor  602  determines the control commands for controlling a selective application of a high load to the LSD  302  when the accelerator control position indicated by the accelerator control sensor  392  meets or exceeds the predetermined position threshold stored in the memory  604 . The processor  602  may receive a measurement of the speed of the vehicle  40  from the vehicle speed sensor  380  or determine the speed of the vehicle  40  based on an average of the rotational speeds of the left and right wheels  44  provided by the wheel speed sensors  376 ,  378  and based on a dimension of the left and right wheels  44 . Regardless, if the speed of the vehicle  40  is available, the processor  602  may control the selective application of the high load to the LSD  302  when the accelerator control position indicated by the accelerator control sensor  392  meets or exceeds the predetermined position threshold on the condition that the speed of the vehicle  40  is less than the predetermined speed threshold stored in the memory  604 . The processor  602  may cause the output port  608  to stop the control command for the application of the high load to the LSD  302  when informed by the accelerator control sensor  392  that the accelerator control position falls below the predetermined position threshold or when the vehicle speed meets of exceeds the predetermined speed threshold. 
     In an implementation, the control command forwarded by the output port  608  causes the actuator  372  to apply the high load may be followed by another control command for locking of the LSD  302  by the solenoid  382 . 
     Independently from the accelerator control position, if the speed of the vehicle  40  is known, the processor  602  may determine that the speed of the vehicle  40  is greater than the predetermined speed threshold stored in the memory  604 . In that case, the processor  602  may cause the output port  608  to forward a control command to the LSD  302  for the application of a stabilization load. The stabilization load limits, without preventing, a rotational speed difference between the left and right wheels  44  of the vehicle  40  to enhance directional stability. 
     The processor  602  may receive, via the input port  606 , an engine output torque value provided by the engine torque monitor  394 . The processor applies the speed of the vehicle and the engine output torque value to the trail active mapping table stored in the memory  604  to read a value of a partial load for application to the LSD  302 . This partial load is expressed in terms of a torque for application on the clutch  374 . If the accelerator control position is less than the predetermined position threshold, the processor  602  may cause the output port  608  to forward a control command for controlling an application of the partial load to the LSD  302 . Referring again to  FIG. 20 , it may be observed that if the loading command  670  is present at the input of the switch  672 , any partial load value from the trail active mapping table is ignored by the switch  672 . It may further be observed that if the torque assignment  676  has a nonzero value, any partial load value from the trail active mapping table is also ignored by the control unit  370 . 
     The present disclosure introduces various techniques for controlling the LSD  302 , these techniques being exemplified in the diagrams of  FIGS. 12 a , 12 b   ,  13 ,  15 ,  16 ,  17 ,  19   a - e ,  20 ,  21  and  22 . A particular implementation of limited slip differential assembly  300  mounted in a particular vehicle  40  may integrate any one of these techniques. Another implementation may integrate all of these techniques. Yet another implementation may integrate any combination of these techniques. 
     The method, differential assembly and vehicle implemented in accordance with some non-limiting implementations of the present technology can be represented as follows, presented in numbered clauses. 
     Clauses 
     [Clause 1] A method of controlling a limited slip differential (LSD) of a vehicle, the vehicle having an engine, an accelerator control, the LSD, and left and right driven wheels operably connected to the LSD, the method comprising: 
     determining an accelerator control position; and 
     selectively applying a high load to the LSD when the accelerator control position meets or exceeds a predetermined position threshold. 
     [Clause 2] The method of clause 1, further comprising locking the LSD. 
     [Clause 3] The method of clause 1 or 2, further comprising: 
     detecting a full or partial release of the accelerator control; and 
     releasing the high load to the LSD. 
     [Clause 4] The method of any one of clauses 1 to 3, further comprising determining a speed of the vehicle, selectively applying the high load being conditional to the speed of the vehicle being less than a predetermined speed threshold. 
     [Clause 5] The method of clause 4, wherein determining the speed of the vehicle comprises: 
     determining rotational speeds of the left and right wheels; and 
     determining the speed of the vehicle based on an average of the rotational speeds of the left and right wheels and based on a dimension of the left and right wheels. 
     [Clause 6] The method of clause 4 or 5, further comprising releasing the high load when the speed of the vehicle meets or exceeds the predetermined speed threshold. 
     [Clause 7] The method of any one of clauses 4 to 6, further comprising applying a stabilization load to the LSD when the speed of the vehicle meets or exceeds the predetermined speed threshold, the stabilization load being less than the high load. 
     [Clause 8] The method of any one of clauses 4 to 7, further comprising: 
     determining an engine output torque; 
     applying the engine output torque and the speed of the vehicle to a trail active mapping table to read a value of a partial load for application to the LSD; and 
     while the accelerator control position is less than the predetermined position threshold, applying the partial load to the LSD. 
     [Clause 9] A method of controlling a limited slip differential (LSD) of a vehicle, the vehicle having an engine, an accelerator control, the LSD, and left and right driven wheels operably connected to the LSD, the method comprising: 
     determining a speed of the vehicle; and 
     selectively applying a stabilization load to the LSD when the speed of the vehicle is greater than a predetermined speed threshold. 
     [Clause 10] The method of any one of clauses 1 to 9, wherein applying a load to the LSD comprises compressing a clutch of the LSD to reduce a rotational speed difference of the left and right wheels. 
     [Clause 11] The method of clause 10, wherein compressing the clutch of the LSD comprises using an electric motor to drive a gear set and a ball ramp to apply a torque on the clutch. 
     [Clause 12] The method of clause 11, wherein compressing the clutch of the LSD further comprises using a solenoid to lock the gear set. 
     [Clause 13] A differential assembly for use in a vehicle having an engine, an accelerator control, and left and right driven wheels, the differential assembly comprising: 
     a limited slip differential (LSD) connectable to a driveshaft and to the left and right driven wheels, the LSD being adapted for transferring torque from the driveshaft to the left and right driven wheels; 
     an accelerator control sensor; and 
     a control unit operatively connected to the LSD and to the accelerator control sensor, the control unit being adapted for controlling a selective application of a high load to the LSD when an accelerator control position indicated by the accelerator control sensor meets or exceeds a predetermined position threshold. 
     [Clause 14] The differential assembly of clause 13, further comprising an electric motor, wherein controlling the selective application of the high load to the LSD comprises controlling a load applied by the electric motor to the LSD. 
     [Clause 15] The differential assembly of clause 14, wherein the LSD further comprises a compressible clutch and wherein controlling the load applied by the electric motor to the LSD comprises compressing the clutch. 
     [Clause 16] The differential assembly of clause 15, wherein the LSD further comprises a gear set and a ball ramp, the gear set being adapted for applying the load from the electric motor to the ball ramp for compressing the clutch. 
     [Clause 17] The differential assembly of clause 16, further comprising a solenoid having a tooth adapted for engaging the gear set when the solenoid is energized, wherein the control unit is further adapted for controlling the solenoid for locking the LSD. 
     [Clause 18] The differential assembly of clause 17, wherein the control unit is further adapted for controlling locking of the LSD. 
     [Clause 19] The differential assembly of any one of clauses 13 to 17, wherein the control unit comprises: 
     an input port adapted for receiving measurements from the accelerator control sensor; 
     an output port adapted for forwarding control commands to the LSD; and 
     a processor operatively connected to the input port and to the output port, the processor being adapted for causing the output port to forward the control commands for controlling the selective application of the high load to the LSD. 
     [Clause 20] The differential assembly of clause 19, further comprising a sensor of a speed of the vehicle, wherein: 
     the input port is further adapted for receiving measurements from the sensor of the speed of the vehicle; and 
     the processor is further adapted for controlling the selective application of the high load to the LSD when the speed of the vehicle is less than a predetermined speed threshold. 
     [Clause 21] The differential assembly of clause 20, wherein: 
     the sensor of the speed of the vehicle comprises wheel speed sensors operatively connected to the left and right wheels, the wheel speed sensors determining rotational speeds of the left and right wheels; and 
     the processor is further adapted for determining the speed of the vehicle based on an average of the rotational speeds of the left and right wheels and based on a dimension of the left and right wheels 
     [Clause 22] The differential assembly of clause 20 or 21, wherein: 
     the control unit further comprises a memory storing configuration information for controlling the LSD; 
     the processor is operatively connected to the memory; and 
     the configuration information comprises one or more of the predetermined position threshold, the predetermined speed threshold, and a trail active mapping table. 
     [Clause 23] The differential assembly of clause 22, wherein the processor is further adapted for causing the output port to forward control commands for controlling a selective application of a stabilization load to the LSD when the speed of the vehicle is greater than the predetermined speed threshold, the stabilization load being less than the high load.
 
[Clause 24] The differential assembly of clause 22 or 23, further comprising an engine torque monitor, wherein:
 
     the input port is further adapted for receiving an engine output torque value from the engine torque monitor; and 
     the processor is further adapted for:
         applying the engine output torque value and the speed of the vehicle to the trail active mapping table to read a value of a partial load for application to the LSD; and   while the accelerator control position is less than the predetermined position threshold, causing the output port to forward a control command for controlling an application of the partial load to the LSD.
 
[Clause 25] A vehicle, comprising:
       

     a frame; 
     a front suspension assembly connected to the frame; 
     a rear suspension assembly connected to the frame; 
     a left driven wheel and a right driven wheel connected to one of the front and rear suspension assemblies; 
     at least one other wheel connected to an other one of the front and rear suspension assemblies; 
     a steering device operatively connected to one of both driven wheels and the at least one other wheel; 
     an engine connected to the frame; 
     a transmission operatively connected to the engine for receiving torque from the engine; 
     a driveshaft operatively connected to the transmission for transferring torque from the transmission to the left and right driven wheels; and 
     the differential assembly of any one of clauses 13 to 24, the LSD being operatively connected to the driveshaft and operatively connected to the left and right driven wheels. 
     [Clause 26] The vehicle of clause 25, further comprising: 
     a transaxle for transferring torque from the transmission to the at least one other wheel; and 
     a selector adapted for selectively operatively connecting the LSD to the driveshaft. 
     Modifications and improvements to the above-described implementations of the present technology may become apparent to those skilled in the art. For example, it is contemplated that the LSD  302  may be mounted at the rear of the vehicle  40  and operatively connected to the rear wheels  48 , whether the vehicle  40  has a two-wheel drive or an all-wheel drive configuration. The foregoing description is intended to be exemplary rather than limiting. The scope of the present technology is therefore intended to be limited solely by the scope of the appended claims.