Abstract:
An auxiliary transmission module has an auxiliary transmission having an input shaft, an output shaft, and a mechanical synchronizer, and a controller. The controller is configured to command a downshift for the auxiliary transmission, control the input shaft to a generally synchronous speed with the output shaft for engagement, and increment the speed of the input shaft by a predetermined speed differential above the speed of the output shaft or engagement if the auxiliary transmission is unengaged after controlling to the generally synchronous speed. A method of downshifting includes commanding a downshift for the auxiliary transmission, controlling an input shaft to a generally synchronous speed with an output shaft for engagement, comparing a rotational speed upstream with a rotational speed downstream to verify engagement, and controlling the input shaft to an asynchronous speed with the output shaft for engagement during a recycle event when it is unverified.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional Application No. 61/577,619 filed Dec. 19, 2011, the disclosure of which is incorporated in its entirety by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The technical field is generally control systems for automated shifting of compound transmissions having both a main section and a range section, and particularly, coordinating shifting of the main section of the transmission with the shifting of the range section of the transmission. 
       BACKGROUND 
       [0003]    Compound transmissions of the range type are well known in the prior art. Such transmissions typically comprise a multiple speed main transmission section connected in series with a range type auxiliary section wherein the range step is commonly greater than the total ratio coverage of the main transmission section. 
         [0004]    In automated compound transmissions, the main section is typically shifted by means of an automated actuator responsive to an electronic control unit. The electronic control unit may be integrated into a control unit which operates a plurality of vehicle systems, such as the vehicle engine and the vehicle transmission, or may be a discrete and purpose-specific transmission electronic control unit (“TECU”). The control unit will be generically identified herein as a TECU. The automatic actuator of the main section may be an electric X-Y shifter of the type well known in the art, and described in U.S. Pat. No. 4,873,881, which is hereby incorporated by reference. The automatic main section actuator may alternatively be a pneumatically operated mechanism that is also well known in the art. An automatic range section actuator is responsive to control signals from the TECU. An exemplary range section actuator is shown in U.S. Pat. No. 7,861,612 which is hereby incorporated by reference. The actuator described therein is a pneumatic actuator responsive to electrical signals. Although the source of electrical signals described in U.S. Pat. No. 7,861,612 is an operator controlled switch, the range section actuator could alternatively be responsive to an electrical signal from the TECU. Yet alternatively, the range section actuator could be responsive to a switch controlled by the TECU. The precise mechanisms and configurations thereof used to shift the main transmission section and the range transmission section is not intended to be limiting to scope of application of the present invention. 
         [0005]    A common arrangement for a transmission has a plurality of gear ratios available for selection in the main section perhaps five for example, and two gear ratios, characterized as “High” and “Low” provided by the range section. The High range is commonly characterized as “direct” in which the output member of the range section rotates as a unit with the input member. With the range section in the Low range, the output member rotates at a lower speed than the input member, and provides a torque-multiplying effect. 
         [0006]    The particular concern addressed by this invention relates to coordinating shifting of the main section and the range section and ensuring engagement of the range section. More specifically, it is intended to facilitate shifting the range section from High to Low in an off-throttle condition, as might be desirable to achieve engine braking when operating a vehicle on a downhill grade. A number of factors relating to the interplay of the mechanical components can contribute to making it difficult to complete such a shift. 
         [0007]    It is desired to provide a control system which facilitates the completion of off-throttle range shifts from High into Low. 
       SUMMARY 
       [0008]    In an embodiment, a method of downshifting an auxiliary transmission having a mechanical synchronizer is provided. A downshift is commanded for the auxiliary transmission. An input shaft of the auxiliary transmission is controlled to a generally synchronous speed with an output shaft of the auxiliary transmission to engage the auxiliary transmission. A rotational speed upstream of the auxiliary transmission is compared with a rotational speed downstream of the transmission to verify engagement. The input shaft of the auxiliary transmission is controlled to an asynchronous speed with the output shaft of the auxiliary transmission to engage the auxiliary transmission during a recycle event when engagement is unverified. 
         [0009]    In another embodiment, an auxiliary transmission module is provided with an auxiliary transmission and a controller in communication with the auxiliary transmission. The auxiliary transmission has an input shaft, an output shaft, and a mechanical synchronizer. The controller is configured to (i) command a downshift for the auxiliary transmission, (ii) control the input shaft to a generally synchronous speed with the output shaft to engage the auxiliary transmission, and (iii) increment the speed of the input shaft by a predetermined speed differential above the speed of the output shaft to engage the auxiliary transmission if the auxiliary transmission is unengaged after controlling the input shaft to the generally synchronous speed. 
         [0010]    In yet another embodiment, a transmission is provided with a main transmission section, an auxiliary range transmission section downstream of the main transmission and connected to the main transmission section by a mainshaft, and a controller. The controller is configured to (i) command a downshift for the auxiliary transmission, (ii) control the mainshaft to a generally synchronous speed with the output shaft of the auxiliary transmission section to engage the auxiliary transmission, (iii) verify engagement of the auxiliary transmission, and (iv) increase the speed of the mainshaft by a predetermined speed differential above the speed of the output shaft to engage the auxiliary transmission if engagement is unverified. 
         [0011]    Various embodiments of the present disclosure have associated advantages. For example, a range selection control system for a multispeed compound transmission facilitates the completion of shifts from High to Low. In the case of a range downshift, the speed of a mainshaft of the main section is increased to provide a pre-determined speed difference between the mainshaft and the output shaft for the new range gear ratio and a generally synchronous speed within the range synchronizer section. The speed differential between the mainshaft and output shaft may be incremented by raising the mainshaft speed to cause an asynchronous speed across the range synchronizer section, until full engagement is achieved within the range section. For a transmission with a mechanical synchronizer in the range section, causing an asynchronized speed across the range synchronizer section pulls the range section off blocker pins or other mechanical engagement members and causes the range section to slide into engagement in the desired range gear after a shift, such as a downshift. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic illustration, not to scale, of a compound transmission having a range type auxiliary section. 
           [0013]      FIG. 2  is a sectional view of an exemplary range section and a range section actuator as might be used as part of the transmission of  FIG. 1 . 
           [0014]      FIG. 3  is a schematic of the control element elements associated with the transmission of  FIG. 1 . 
           [0015]      FIG. 4  is an exemplary flow chart of one form of the logic employed in the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    A detailed description of the illustrated embodiments of the present invention is provided below. The disclosed embodiments are examples of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale. Some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed in this application are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art how to practice the invention. 
         [0017]    Referring to  FIG. 1 , a range type compound transmission  10  is illustrated. Compound transmission  10  comprises a multiple speed main transmission section  12 , or more concisely, main section  12 , connected in series with a range type auxiliary section  14 , or more concisely range section  14 . Transmission  10  is housed within a housing H and includes an input shaft  16  driven by a prime mover such as diesel engine E through a selectively disengaged, normally engaged friction master clutch C having an input or driving portion  18  drivingly connected to the engine crankshaft  20  and a driven portion  22  rotatably fixed to the transmission input shaft  16 . 
         [0018]    In main section  12 , input shaft  16  carries an input gear  24  for simultaneously driving a pair of countershaft assemblies  26  at substantially identical rotational speeds. The two countershaft assemblies  26 , which may be substantially identical, are illustrated on diametrically opposite sides of a mainshaft  28  which is generally coaxially aligned with input shaft  16 . Each of countershaft assemblies  26  comprises a countershaft  30  supported by bearings  32  and  34  in the housing. Each of countershaft assemblies  26  is provided with a grouping of countershaft gears  38 ,  40 ,  42 ,  44 ,  46  and  48 , fixed for rotation therewith. A plurality of mainshaft gears  50 ,  52 ,  54 ,  56  and  58  surround mainshaft  28  and are selectively clutchable, one at a time, to mainshaft  28  for rotation therewith by sliding clutch collars  60 ,  62  and  64 , as is well known in the prior art. Clutch collar  60  may also be utilized to clutch input gear  24  to mainshaft  28  to provide a direct drive relationship between input shaft  16  and mainshaft  28 . 
         [0019]    Mainshaft gear  58  is the reverse gear and is in continuous meshing engagement with countershaft gears  48  by means of conventional intermediate idler gears (not shown). It should also be noted that while main section  12  does provide five selectable forward speed ratios, the lowest forward speed ratio, namely that provided by drivingly connecting mainshaft drive gear  56  to mainshaft  28 , is often of such a high gear reduction it has to be considered a low or “creeper” gear which is utilized only for starting of a vehicle under severe conditions, and is not usually utilized in the high transmission range. Accordingly, while main section  12  does provide five forward speeds, it is usually referred to as a “four plus one” main section as only four of the forward speeds are compounded by the range section  14  utilized therewith. It is appreciated that the configuration of main section  12  described above is exemplary and is not critical to the present invention. 
         [0020]    With continued reference to  FIG. 1 , range section  14  includes two substantially identical range countershaft assemblies  74  each comprising a range countershaft  76  supported by bearings  78  and  80  in housing H and carrying two range countershaft gears  82  and  84  for rotation therewith. Range countershaft gears  82  are constantly meshed with and support a range input/main section output gear  86  that is fixed to mainshaft  28 . Range section countershaft gears  84  are constantly meshed with a range section output gear  88  that surrounds transmission output shaft  90 . 
         [0021]    With reference to  FIGS. 1 and 2 , range section  14  further includes a synchronized two-position range jaw clutch assembly  92 . Jaw clutch assembly  92  is axially positioned by means of a range shift fork  94  (illustrated in  FIG. 2 ). Jaw clutch assembly  92  is rotatably fixed to output shaft  90  for rotation therewith. A range section shifting actuator assembly  96 , or more concisely, a range actuator  96 , is provided for clutching either gear  88  to output shaft  90  for low range operation, or gear  86  and mainshaft  28  to output shaft  90  for direct or high range operation of the compound transmission  10 . 
         [0022]    Although range section  14  is illustrated as a two-speed section which may utilize spur or helical type gearing, it is understood that the embodiments presented herein are also applicable to range type transmissions utilizing combined splitter/range type auxiliary sections, having three or more selectable range ratios and/or utilizing planetary type gearing. Also, as indicated above, any one or more of clutch collars  60 ,  62  or  64  may be of the synchronized jaw clutch type and transmission sections  12  and/or  14  may be of the single countershaft type. 
         [0023]    With reference to this disclosure, when two rotating members of the transmission  14  are at a synchronous speed with one another, it includes any speed difference between them caused by a gear ratio. For example, if there is a 4:1 gear ratio between a first and second shaft and the first shaft is rotating at 1000 rpm, the second shaft would be rotating at 250 rpm and be synchronous with the first shaft. 
         [0024]    With reference to  FIG. 1 , the shifting of gears in the main section  12  will be described in greater detail. Typically, clutch collars  60 ,  62  and  64  are axially positioned by means of shift forks or other collar displacement means (not shown). Clutch collars  60 ,  62  and  64  may be of the well known synchronized or nonsynchronized double acting jaw clutch type. 
         [0025]    Clutch collars  60 ,  62 , and  64  are three-position clutches in that they may be positioned, as illustrated in  FIG. 1 , in the centered nonengaged position, in a fore engaged position or in an aft engaged position by means of the collar displacement means. The collar displacement means are actuated by an automated selector mechanism (not shown) fixed relative to or incorporated into housing H and responsive to control signals from the TECU. Only one of the clutch collars  60 ,  62  and  64  is engageable at a given time, and a main section interlock means (not shown) may be provided to lock the other clutches in the neutral condition. The TECU provides signals to the automated selector mechanism to shift main section  12 . The TECU manipulates a switch  98  to shift range section  14 . Switch  98  may be mounted anywhere it is convenient for packaging purposes, including locations remote from transmission  10 . Initiation of range shifting is generally permitted only when main section  12  is in neutral. 
         [0026]    The overall transmission ratio between the speed of rotation of input shaft  16  and output shaft  90  is determined by a combination of the gear selected in main section  12  and the gear selected in range section  14 . 
         [0027]      FIG. 2  illustrates an embodiment of the synchronized two-position range jaw clutch assembly  92 . The two-position range jaw clutch assembly  92  is a sliding clutch rotatably fixed to output shaft  90  using splines and configured to slide longitudinally along the shaft  90  as controlled using the shift fork  94 . When the range section  14  is in the high range position, a high synchronization assembly  93  is engaged with clutch assembly  92 . Synchronization assembly  93  is connected for rotation with the mainshaft  28 . The synchronization assembly  93  has blocking pins  91  that engage with apertures in the clutch assembly  92 , thereby selectively connecting mainshaft  28  to the output shaft  90 . 
         [0028]    When the range section  14  is in the low range position, a low synchronization assembly  97  is engaged with clutch assembly  92 , as shown in  FIG. 2  with the larger diameter portion of pin  95  engaged with assembly  92 . Synchronization assembly  97  is connected for rotation with the range section output gear  88 . The synchronization assembly  97  has blocking pins  95  that engage with apertures in the clutch assembly  92 , thereby connecting mainshaft  28  to the output shaft  90  via the range section  14  gearing. Traditionally, during a downshift in the range section  14 , synchronizing frictional material in the assembly  97  transfers energy between rotating members to cause the jaw clutch and mainshaft to rotate at a generally synchronous speed with the output shaft. As the speed becomes synchronous, the force created between the angled portion  95   a  of the blocking pins  95  and the assembly  92  decreases and enables the assembly  92  to slide onto the larger diameter portion of the blocker pins, engage the clutch and complete the shift. 
         [0029]      FIG. 3  is a schematic representation of a powertrain system  100  incorporating transmission  10  and a powertrain control system  102 . Control system  100  includes several rotary speed sensors which may be mounted in a manner suited to determining the rotational speed of predetermined rotating members of the powertrain system. Exemplary rotary speed sensors include an engine speed sensor  104 , a transmission input shaft speed sensor  106 , a mainshaft speed sensor  108 , an output shaft speed sensor  110 , and a wheel speed sensor  112  associated which a wheel  114 . Any combination of sensors that will provide an indication of the ratio across range section  14  will be sufficient. It may be possible to use signals indicative of rotational speed that are already available in the system. Control system  102  also includes a vehicle operator transmission control interface commonly characterized as a shifter  116 . Shifter  116  enables the vehicle operator to establish the mode of operation of the transmission. Commonly available modes include Reverse, Neutral, and Drive. The form of the shifter is not important to the present invention.  FIG. 3  includes dotted lines representing control signal paths electrically, by wire or wirelessly, connecting TECU with sensors, a clutch actuator  118 , shifter  116 , transmission main section  12 , transmission range section  14  and switch  98  and engine E. 
         [0030]    An exemplary compound downshift is now described. With a compound downshift, ratio changes are being made in both the main section  12  and in the range section  14 . The exemplary target gear combination of main section and range section yields a drive ratio resulting in a greater engine speed at a given vehicle speed compare to that associated with the gear being shifted from. Assuming a constant vehicle speed, engine speed will be greater after the downshift than before. Main section  12  is initially in what is characterized herein as Sixth Gear, with collar  64 , given the orientation of  FIG. 1 , in a fore-most position and fixing gear  56  to mainshaft  28  for unitary rotation therewith. Alternatively, what is characterized as Sixth Gear could have collar  64  in a neutral position, and collar  62  in the aft-most position, fixing gear  54  to mainshaft  28 . The distinction is not critical to the invention. Range section  14  is in High, with jaw clutch assembly  92 , in the orientation of  FIG. 1 , in a fore-most position and fixing output shaft  90  to mainshaft  28  for unitary rotation therewith. 
         [0031]    The target gear is characterized as Fifth Gear for purposes of this example. For this exemplary Fifth Gear, collar  60  is displaced in the fore direction to connect mainshaft  28  to input shaft  16  for unitary rotation therewith. The range section has jaw clutch  93  in an aft-most position, wherein torque is transferred from mainshaft  28  to output shaft  90  through gears  86  and  82  and gears  84  and  88 . 
         [0032]    The invention is directed to a means of achieving a downshift, such as a shift from Sixth Gear to Fifth Gear. 
         [0033]    In an automated transmission, downshifts can be induced by control software installed in the TECU, or by input from the vehicle operator. The invention is intended to aid in downshifts, independent of the source of the command to downshift. In one example, a vehicle operator may wish to downshift on a grade to enable slowing of the vehicle through engine braking Downshifting will result in an increase in engine speed, which, when combined with zero throttle or little or no demand for engine torque results in increased engine resistance to vehicle movement, or engine braking. 
         [0034]      FIG. 4  illustrates an exemplary flow chart for one implementation of the invention. In the example described below with reference to  FIG. 4 , the offset is 15 rpm with the Target speed being establish by the TECU as a function of the target gear ratio and the vehicle speed. Of course, the offset may be set to other rpm values with the same effect. It should also be appreciated that, in accord with the disclosure, the limit on the number of cycles could be set to more or fewer than four. The described approach to downshifting is particularly effective for use with closed-clutch shifts in which clutch C remains engaged throughout the shift. 
         [0035]    The TECU receives a command to downshift at  120  and sets a cycle counter to zero at  122 . 
         [0036]    As a first step at  124 , the main section is disengaged with collar  64  moved to a neutral position where it engages neither gear  56  nor  58 . As a second step at  126 , range jaw clutch  92  is moved to an aft position in an effort to achieve full engagement with gear  88 , or the range section is commanded to shift. 
         [0037]    As a third step at  128 , the TECU commands engine E to rotate at a synchronous speed with the expected speed of mainshaft  28 , given the vehicle speed and presuming the engagement of clutch  92  and gear  88  has been successful. The main section is shifted into another gear at  130 , such as by moving collar  60  to a fore position to rotatably fix input shaft  16  and mainshaft  28 . As the speed of the mainshaft  28  increases such that the speed within the range synchronizer becomes synchronized, the clutch assembly  92  may engage and complete its shift as discussed above with respect to  FIG. 2 . The TECU compares the ratio of signals from sensors  110  and  108  to determine if the ratio of the rotational speeds is consistent with the gear ratio of range section  14  in the Low condition at  132 . If it is, then the downshift was successful, the process proceeds to  134 , and there is no need for any attempted recycling of the transmission. 
         [0038]    However, if the downshift was not successful, then the clutch assembly  92  could not complete the shift to engagement. For the clutch assembly  92  as shown in  FIG. 2 , the blocker pins are preventing engagement of the jaw clutch based on forces on the angles faces of the blocker pins. For an incomplete downshift, another attempt must be made to engage the clutch assembly  92  and the process proceeds to  136 . 
         [0039]    At  136 , the TECU increments the cycle counter, and then determines if more than a specified number of cycles have been run by the TECU at  138 . If more than the specified number of cycles have been run, such as four cycles, the TECU proceeds to  140  and exits the algorithm. The TECU may set a fault code or set a flag as an input into another transmission operating algorithm. 
         [0040]    If less than the specified number of cycles have been run, the TECU proceeds to  142  and increments the target speed by an offset value to set a new target speed value. For example, the offset may be 15 rpm, such that the new target speed is 15 rpm higher than the previous rpm speed. 
         [0041]    The TECU then returns to  124  for recycling the system. The first step in recycling the system is to place the main section in neutral again at  124 , and the put the range section back in the High condition with the jaw clutch in the fully fore position. The range section is then cycled back toward the Low condition with the jaw clutch in the aft position at  126 . The main section  12  is shifted back into its target gear at  130 , and engagement confirmed or not confirmed by the values from the speed sensors. In the prior art, the attempt to complete the shift would be made by setting the engine speed to the same speed as was used on the first cycle. Instead, in the inventive approach, the speed of the engine is set to rotate at  15  revolutions per minute (rpm) faster, causing the target gear in the main section to rotate faster than the precise synchronous speed at  128  using the new target speed from  142 . It is critical that the newly targeted speed is greater than synchronous. It has been found that engaging the target gear in the main section at a slightly elevated asynchronous speed has the beneficial effect of encouraging the jaw clutch  92  in the range section to complete its engagement on a downshift because the asynchronous speed allows the synchronizer to “pull off” from the angled portion of the blocker pins and engage with the wider diameter portion of the blocker pins. It is appreciated that the value of 15 rpm can be varied without departing from the scope of the present invention. The primary upper limit is established by the presence of excessive gear tooth chatter during engagement in the main section  12 . 
         [0042]    In a variation of this invention, in the event that the first recycle event is does not result in a successful engagement, engine speed is adjusted in a second recycle event to a higher speed. In this exemplary embodiment, the engine speed is set to provide a 30 rpm difference in speed, and a new recycle attempt made. 
         [0043]    In another variation of this invention, in the event that the second recycle event is does not result in a successful engagement, engine speed is adjusted in a second recycle event to a higher speed. In this exemplary embodiment, the engine speed is set to provide a 45 rpm difference in speed, and a new recycle attempt made. 
         [0044]    It is apparent that number of steps or the size of the steps is not critical to the present invention. The steps also need not be uniform in size. The size and number of steps will depend on the characteristics of the transmission itself. 
         [0045]    A surprising result is that increasing the engine speed would promote slowing of the vehicle. It is counterintuitive to increase engine speed in a circumstance where the vehicle operator is likely trying to slow the vehicle. Increasing engine speed has the effect of increasing vehicle speed momentarily when the desired effect of downshifting in a zero throttle condition is typically to slow the vehicle. However, it has been determined that a very brief surge in torque on gear engagement is more acceptable than an extended period of gear disengagement with the associated period of having no engine braking at all. The offset may be limited as too high of an offset may cause an undesirable torque surge for the vehicle during engagement, which may decrease shift quality for a vehicle in a low or no acceleration downshift. 
         [0046]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.