Patent Publication Number: US-2022227370-A1

Title: Slip control method and arrangement for a drivetrain architecture including a continuously variable transmission

Description:
FIELD 
     The present disclosure generally relates to drivetrains architectures including a continuously variable transmission (CVT). More specifically, the present disclosure is concerned with the architecture of such a drivetrain allowing slip control. 
     BACKGROUND 
     CVTs are very interesting in all kinds of vehicles for their ability to continuously vary the speed ratio between the output of a prime mover and the wheels or other rotating parts of a vehicle. 
     However, some vehicular applications conventionally require a so-called torque converter between the prime mover and the wheels to a) prevent the prime mover from stalling when the wheels are prevented from rotating while powered and b) increase the torque when the torque converter is slipping. These applications are generally not ideal candidates for continually variable transmissions since the advantages of the CVT are mitigated from the use of a torque converter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the appended drawings: 
         FIG. 1  is a block diagram of a drivetrain architecture including a CVT, a forward-reverse slip control clutch arrangement and an optional multi-speed gearbox according to an illustrative embodiment; 
         FIG. 2  is a block diagram of a method to control the slip of a forward-reverse clutch; and 
         FIG. 3  is a graph illustrating the torque vs. RPM of a prime mover and the torque allowed to pass through a clutch vs. RPM. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to a drivetrain including a CVT. More specifically, the present disclosure relates to a slip control method and an arrangement for a drivetrain architecture including a continuously variable transmission. 
     According to an illustrative embodiment, there is provided a method to control the slippage of a drivetrain including a prime mover having an output shaft, a transmission having an input connected to the output shaft of the prime mover and an output, a forward-reverse clutch arrangement having an input connected to the output of the transmission and an output, the forward-reverse clutch arrangement including a clutch having a controllable slippage level between its input and output, the slippage control method including: determining the usable torque of the prime mover; and controlling the clutch so as to allow the usable torque to pass therethrough and to cause the clutch to slip should a torque between the input and output of the clutch be greater than the usable torque. 
     According to another aspect, there is provided a drivetrain including: a prime mover having an output shaft; a prime mover speed sensor measuring the rotational speed of the output shaft; a transmission having an input associated with the output shaft of the prime mover and an output; a forward-reverse clutch arrangement having an input associated with the output of the transmission and an output; the forward-reverse clutch arrangement including a clutch having a controllable slippage level between its input and output; a clutch slip controller controlling the level of torque allowed to pass through the clutch before slippage occurs therein; and a main controller associated with the prime mover speed sensor, and with the clutch slip controller; the main controller being so configured as to determine a usable torque of the prime mover and to set the clutch slip controller so that the clutch slips when a torque higher than the usable torque attempts to pass through the clutch. 
     The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one”, but it is also consistent with the meaning of “one or more”, “at least one”, and “one or more than one”. Similarly, the word “another” may mean at least a second or more. 
     As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “include” and “includes”) or “containing” (and any form of containing, such as “contain” and “contains”), are inclusive or open-ended and do not exclude additional, unrecited elements or process steps. 
     The expressions “connected” and “coupled” should be construed herein and in the appended claims broadly so as to include any cooperative or passive association between mechanical parts or components. For example, such parts may be assembled together by direct connection, or indirectly connected using further parts therebetween. The connection can also be remote, using for example a magnetic field or else. 
     It is to be noted that the expression “prime mover” is to be construed herein and in the appended claims as an internal combustion engine (ICE) a turbine engine, or any other mechanical power production element or assembly. 
     It is to be noted that the term “CVT”, standing for Continuously Variable Transmission, is used herein to describe any type of CVT including, amongst others, a toroidal CVT, a dual-cavity full toroidal CVT, a half-toroidal CVT, a single cavity toroidal CVT, a hydrostatic CVT, a Variable diameter pulley CVT, a magnetic CVT, a ratcheting CVT and a cone CVT. 
     It will also be noted that the expressions “fixed disk”, when used herein and in the appended claims in the context of clutch technology, may be viewed as any element or group of elements constituting a clutch driving member. Similarly, the expressions “movable disk”, when used herein and in the appended claims in the context of clutch technology, may be viewed as any element or group of elements constituting a clutch driven member. 
     It is to be noted that the expression “off-highway vehicle” is to be construed herein and in the appended claims as any type of vehicle that is designed specifically for use off-road, including, amongst others, construction vehicles and agricultural vehicles. 
     Other objects, advantages and features of the slip control method and arrangement for a drivetrain architecture including a continuously variable transmission will become more apparent upon reading of the following non-restrictive description of illustrative embodiments thereof, given by way of example only with reference to the accompanying drawings. 
       FIG. 1  of the appended drawings illustrates a drivetrain  10  comprising a prime mover in the form of an ICE  12 , a CVT  14 , a forward-reverse clutch arrangement  16 , and an optional three-speed gearbox  18  including a creeping speed range. The output of the optional gearbox  18  is connected to a load  20 , for example the wheels of an off-highway vehicle (not shown). Of course, as will be apparent to one skilled in the art, should the gearbox  18  be absent from the drivetrain  10 , the output of the forward-reverse clutch arrangement  16  would be directly connected to the load  20 . 
     A first shaft  22  interconnects the output of the ICE  12  and the input of the CVT  14 ; the speed of the first shaft  22  is measured via a first speed sensor  24 . A gear train  25  is mounted to the output of the CVT  14 . A second shaft  26  interconnects the gear train  25  to the input of the forward-reverse clutch arrangement  16 ; the speed of the second shaft  26  is measured via a second speed sensor  28 . A third shaft  30  interconnects the output of the forward-reverse clutch arrangement  16  and the input of the optional gearbox  18 . Finally, a fourth shaft  34  interconnects the output of the gearbox  18  and the load  20 . 
     Conventionally, the ICE  12  is associated with a user throttle control  36 , for example an acceleration pedal (not shown). 
     The forward-reverse clutch arrangement  16  includes a three-position clutch C 4  having a central fixed disk  50  defining its input and two movable disks  52 ,  54  respectively defining the reverse and forward outputs of the clutch C 4 . The clutch arrangement  16  includes third and fourth speed sensors  32  and  33  that monitor the speed of a respective output of the clutch C 4 . 
     One skilled in the art will understand that the third and fourth sensors  32  and  33  could be replaced by a single sensor (not shown) that would be positioned at the output of the clutch arrangement  16 . In other words, this single sensor would monitor the speed of the third shaft  30 . 
     The forward-reverse clutch arrangement  16  also includes a reverse gear train  56  connected between the reverse output of the clutch C 4  and the third shaft  30  and a forward gear train  58  connected between the forward output of the clutch C 4  and the third shaft  30 . 
     As will be understood, the clutch C 4  is a three-position clutch that is so selected that the slipping between the fixed disk  50  and the movable disks  52  and  54  may be prolonged without adversely affecting the operation or the lifespan of the clutch C 4 . It is believed to be within the skills of one skilled in the art to select an appropriate three-position clutch C 4 . 
     The drivetrain  10  includes a ratio controller  38  so configured as to set the ratio of the CVT  14  according to either a ratio provided by the user via a user ratio control  40  or according to a ratio provided by a main controller  42  as will be described hereinbelow. It will be understood from the foregoing description that the ratio supplied by the main controller  42  has precedence over the user ratio control  40 . Accordingly, the main controller  42  may take over and dictate the ratio of the CVT  14 . 
     Alternatively, the user ratio control  40  could be omitted from the drivetrain  10  and the controller  42  would then control the ratio of the CVT according to the various data supplied thereto such as the speed of the output shaft of the ICE  12 . 
     A forward-reverse clutch controller  44  is so configured as to take a usable torque value from the main controller  42  and to control the clutch C 4  so as to slip when the torque attempting to pass through is greater than this usable torque. In other words, when the torque between the input and output of the clutch C 4  is greater than the usable torque, the clutch C 4  slips. 
     One skilled in the art will have no problem building such a clutch controller adapted to the technology used in the clutch C 4 . 
     Of course, the forward-reverse clutch controller  44  also controls the forward and reverse selection from a user direction control (not shown). 
     The speed data from the first and second speed sensors  24  and  28  is supplied to the main controller  42  so that the controller  42  may determine the actual instantaneous ratio of the CVT in real time. Furthermore, the speed data of the second, third and fourth speed sensors  28 ,  32  and  33  is supplied to a slip quantifier  46  that may determine if slippage of the clutch C 4  occurs, in real time, whether the clutch C 4  is in forward or reverse configuration, and supply this data to the main controller  42 . 
     The optional three-speed gearbox  18  includes a first planetary gear train  60  and a second planetary gear train  62 . The sun gear of the first planetary gear train  60  defines the input of the three-speed gearbox  18  while the carrier of the second planetary gear train  62  defines the output thereof. 
     A first clutch C 1  selectively interconnects the carrier and the ring gears of the first planetary gear train  60 ; a second clutch C 2  selectively interconnects the ring gears of the planetary gear trains and a third clutch C 3  selectively interconnects the ring gear of the second planetary gear train  62  to the casing (not shown) of the gearbox  18 . One will also note that the carrier of the first planetary gear train  60  is connected to the sun gear of the second planetary gear train  62 . 
     The three-speed gearbox  18  is in a creeping range configuration when the clutch C 2  and C 3  are engaged. When in this configuration, both ring gears are connected to the casing of the gearbox and are therefore prevented from rotating. In this configuration, both planetary gear trains are in a speed-reducing mode and are cascading. One skilled in the art will understand that this configuration decreases the power required of the ICE  12  since the very high resulting gear ratio increases the output power. 
     The three-speed gearbox  18  is in a medium speed range configuration when the clutch C 1  and C 3  are engaged. When in this configuration, the carrier and the ring of the first planetary gear train  60  are connected and the ring gear of the second planetary gear train  62  is connected to the casing and therefore prevented from rotating. 
     The three-speed gearbox  18  is in a high speed range configuration when the clutch C 1  and C 2  are engaged. When in this configuration, the carrier and the ring of the first planetary gear train  60  are connected and both are connected to the ring gear of the second planetary gear train  62 . 
     Of course, the selection of the creeping, medium or high speed ranges is made by the user using an input (not shown). Alternatively, the main controller  42  could determine the gear selection of the optional three-speed gearbox  18 . 
     Turning now to  FIG. 2  of the appended drawings, a slip control method  100  for a drivetrain including a continuously variable transmission will be described. 
     The first step  102  of the method  100  consists of determining the available torque from the prime mover. With reference to  FIG. 1 , the prime mover, in the form of the ICE  12 , has a map of available torque depending on the RPM of its output shaft. This table is either built in the ICE and can be supplied to the controller  42 , known and stored in the controller  42  or has been built by the drivetrain manufacturer and stored in the controller  42 . Since the controller  42  has the speed data from the first speed sensor  24 , it can look up the available torque in real time. 
       FIG. 3  of the appended drawings illustrates the available torque vs. RPM for a particular ICE. 
     From the instantaneous available torque, the controller  42  determines a usable torque in step  104 . The usable torque is lower than the available torque and provides a safety margin to prevent the ICE  12  from stalling. Indeed, the increase in clutch temperature is mainly caused by a partial slipping of the clutch, for example when a torque larger than the usable torque attempts to pass though the clutch C 4 . Accordingly, should the temperature of the clutch reach a predetermined threshold, the controller  42  may decide to either increase the pressure in the clutch to prevent slipping, decrease the pressure in the clutch to reduce friction and therefore reduce the temperature increase or completely disengage the clutch. 
     Again,  FIG. 3  illustrates the usable torque vs. RPM for a particular ICE. It is to be noted that the usable torque does not follow the available torque at low RPMs. The reason therefor will be explained hereinbelow. 
     It is to be noted that the usable torque illustrated in  FIG. 3  is the usable torque at the output of the ICE  12 . The use of a CVT  14  downstream of the ICE allows this usable torque to be modified by the CVT  14 . Indeed, the torque is multiplied as a function of the ratio of the CVT. The controller therefore uses its knowledge of the instantaneous ratio of the CVT  14  to determine a usable torque at the input of the forward-reverse clutch arrangement  16  and this value is used in the next steps. In other words, the usable torque graph of  FIG. 3  is modulated as a function of the CVT ratio by the controller  42 . 
     It is to be noted that the usable torque values can be stored in a look-up table provided in the main controller  42 , for example. Accordingly, the controller  42  may quickly determine the usable torque from the speed of the output of the ICE  12 . 
     The controller  42 , in step  106 , supplies the instantaneous usable torque to the clutch controller  44  that controls the forward-reverse clutch arrangement  16  so that slippage of the clutch C 4  occurs if a torque greater than the usable torque attempts to pass therethrough. Accordingly, should a block load be applied, for example by preventing wheels of the off-highway vehicle from turning, the torque requested by the wheels and therefore attempting to pass through the clutch C 4  increases drastically and quickly exceeds the usable torque. When this occurs, the clutch C 4  slips, preventing the ICE from stalling and protecting the various components of the drivetrain, including the CVT  14 . Indeed, as is well known to those skilled in the art, should the output shaft of the ICE be prevented from rotating while the ICE is operating, the ICE would stall. Slippage of the clutch C 4  above a torque level therefore ensures that the output shaft of the ICE is not prevented from rotating. 
     The method  100  could stop there. It would therefore loop back to step  102  and repeat the above-described steps. 
     However, since the drivetrain  10  includes a CVT that can inherently modify the speed ratio and therefore the available torque at the input of the clutch C 4 , supplemental steps may be added to the method  100  to improve the usability of the drivetrain  10 . 
     Step  108  involves the determination of the slippage level of the clutch C 4 . This is done by the slip quantifier  46  and the slippage data is supplied to the main controller  42 . 
     The controller  42 , in step  110 , branches to step  112  if the clutch slippage is non-null. In other words, if there is slippage, step  112  is performed. 
     In step  112 , the controller  42  takes over the ratio control  38  and dictates the ratio of the CVT  14 . The controller  42  is so configured that the ratio of the CVT is decreased in proportion of the slippage of the clutch C 4 . Indeed, since the usable torque increases as the CVT ratio decreases, the slippage setpoint of the clutch C 4  is automatically modified by the controller  42  and slippage may stabilize, decrease and/or stop. 
     One possible way of controlling the drivetrain  10  is to control the clutch slippage so as to stabilize it. This is done by gradually changing the CVT ratio until the clutch slippage remains substantially constant. 
     Step  112  loops back to step  102 . 
     Should no slippage be detected in step  110 , the step  114  is performed. In this step, the control of the CVT ratio is gradually returned back to the user since the usable torque is sufficient to drive the load  20 . This is done gradually so as to prevent sudden change in driving behavior, which is detrimental to the user driving sensations. 
     The performance of the drivetrain may be controlled by the user in those circumstances. This step returns to step  102  to loop the method  100 . 
     Returning to  FIG. 3 , the usable torque graph may be separated in three zones. A low RPM zone  202 , a medium RPM zone  204  and a high RPM zone  206 . 
     In the low RPM zone  202 , the usable torque is set significantly lower than the available torque. Accordingly, the slippage of the clutch C 4  will be more pronounced at these speeds. In this zone, the usable torque is set low enough as to either prevent rotation of the output or allow “creeping” of the output given a small load depending on the desired driving sensation. 
     In the medium RPM zone  204 , the usable torque linearly increases with the RPM but is still significantly lower than the available torque from the prime mover. The clutch slippage set-point will therefore increase with increasing RPM. Accordingly, should a small block load prevent rotation of the wheels, an increase in RPM (while in the zone  204 ) may cause the wheels to rotate. This has been found to give better driving sensations to the operator. Of course, the linearity of the medium RPM zone is not required, and other functions could be used. 
     Finally, in the high RPM zone  206 , the usable torque follows the available torque with a safety margin. 
     As an example of application of the drivetrain  10 , the operation of a wheel-loader tractor will be briefly described. Such a tractor often has to push against obstacles, for example when its bucket is being filled. When this is the case, the ICE must be prevented from stalling. By providing a drivetrain as proposed herein, the ICE stalling would be prevented by the selective slipping of the clutch C 4  and the torque supplied to the wheels would be increased both by the control of the CVT ratio and by placing the three-speed gearbox  18  is its creeping configuration. All that without special intervention of the operator other than actuating the throttle and speed-range controls according to the desired speed of the vehicle. 
     Of course, a clutch pedal or other user control could be used to disengage the clutch C 4  manually by the operator. 
     As will be easily understood by one skilled in the art, the main controller  42  could integrate the ratio controller  38 , the clutch controller  44  and/or the slip quantifier  46 . 
     It is to be understood that the slip control method and arrangement for a drivetrain architecture including a continuously variable transmission is not limited in its application to the details of construction and parts illustrated in the accompanying drawings and described hereinabove. The slip control method and arrangement for a drivetrain architecture including a continuously variable transmission is capable of other embodiments and of being practiced in various ways. It is also to be understood that the phraseology or terminology used herein is for the purpose of description and not limitation. Hence, although the slip control method and arrangement for a drivetrain architecture including a continuously variable transmission has been described hereinabove by way of illustrative embodiments thereof, it can be modified, without departing from the spirit, scope and nature thereof.