Patent Publication Number: US-2022221013-A1

Title: Clutch Temperature Management In A Slip Control Method And Arrangement For A Drivetrain Including A Continuously Variable Transmission

Description:
FIELD 
     The present disclosure generally relates to drivetrains including a continuously variable transmission (CVT). More specifically, the present disclosure is concerned with the management of a clutch temperature in a slip control method and arrangement for such a drivetrain. 
     BACKGROUND 
     CVTs are very interesting in many 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. 
     There is therefore a need to provide a method and arrangement preventing the prime mover from stalling and multiplying the torque when the wheels are partially or totally prevented from rotating while managing the temperature of a clutch present in the arrangement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the appended drawings: 
         FIG. 1  is a block diagram of a drivetrain including a CVT and a slip control arrangement according to an illustrative embodiment; 
         FIG. 2  is a block diagram of a method to control the slip of a 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 
     An object is generally to provide an improved drivetrain including a CVT. More specifically, an object is to provide a clutch temperature management in a slip control method and arrangement used in a drivetrain including a CVT to reduce the risks of the prime mover stalling. 
     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 clutch having an input connected to the output of the transmission and an output; the clutch having a controllable slippage level between its input and output, means to obtain clutch temperature data; the slippage control method including: determining the usable torque of the prime mover using the clutch temperature data; 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 transmission having an input associated with the output shaft of the prime mover and an output; a clutch having an input associated with the output of the CVT and an output; means to determine the temperature of the clutch; 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, the clutch temperature determining means and the clutch slip controller; the main controller being so configured as to determine a usable torque of the prime mover using clutch temperature data 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. 
     The term “about” is used to indicate that a value includes an inherent variation of error for the device or the method being employed to determine the value. 
     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 is to be noted that the expression “overdrive” when used in the context of a CVT, is to be construed herein and in the appended claims as a condition where the CVT ratio is such that the CVT output speed is higher than the CVT input speed. The CVT ratio (of output speed to input speed) is therefore higher that one to one (1:1). 
     It is to be noted that the expression “underdrive” when used in the context of a CVT, is to be construed herein and in the appended claims as a condition where the CVT ratio is such that the CVT output speed is lower than the CVT input speed. The CVT ratio (of output speed to input speed) is therefore lower that one to one (1:1). 
     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 clutch temperature management in a slip control method and arrangement for a drivetrain 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 illustrate a drivetrain  10  comprising a prime mover in the form of an ICE  12 , a CVT  14 , a clutch  16 , including a temperature sensor  16 ′, and an optional synchro  18 . The output of the optional synchro  18  is connected to a load  20 , for example wheels of an off-highway vehicle. Of course, should the optional synchro  18  be absent from the design, the output of the clutch  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 second shaft  26  interconnects the output of the CVT  14  and the input of the clutch  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 clutch  16  and the input of the optional synchro  18 ; the speed of the third shaft  30  is measured via a third speed sensor  32 . Finally, a fourth shaft  34  interconnects the output of the optional synchro  18  and the load  20 . 
     Of course, as mentioned hereinabove, one skilled in the art will understand that should the synchro  18  be absent, the shaft  34  would not be present and the shaft  30  would interconnect the output of the clutch  16  and the load  20 . 
     Conventionally, the ICE  12  is associated with a user throttle control  36 , for example an acceleration pedal (not shown). 
     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 clutch controller  44  is so configured as to take a usable torque value from the main controller  42  and to control the clutch  16  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  16  is greater than the usable torque, the clutch  16  is so controlled as to slip. 
     It is believed that one skilled in the art will have no problem building such a clutch controller adapted to the technology used in the clutch  16 . 
     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 ratio of the CVT in real time. Furthermore, the speed data of the second and third speed sensors  28  and  32  is supplied to a slip quantifier  46  that may determine if slippage of the clutch  16  occurs and the slippage level, in real time, and supply this data to the main controller  42 . 
     The temperature sensor  16 ′ supplies clutch temperature data to the main controller  42 . 
     As shown in the appended drawings, the synchro  18  and its connection to the main controller  42  are optional and shown schematically. This synchro  18  is there to represent a conventional multi speed arrangement that allows different gear ratios to be interposed between the clutch  16  and the load. Since the configurations and the operation of such a synchro are believed known to those skilled in the art, they will not be further described herein. 
     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. One skilled in the art will understand that different ICEs have different available torque with respect to the RPM. 
     From the instantaneous available torque, the controller  42  determines a usable torque in step  104 . The usable torque is generally lower than the available torque and provides a safety margin to prevent the ICE  12  from stalling. The usable torque may vary depending on the clutch temperature data supplied by the temperature sensor  16 ′ to the controller  42 . 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  16 . Accordingly, should the temperature of the clutch reach a predetermined threshold, the controller  42  may be so configured as 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; completely disengage the clutch; modify the gear ratio of the CVT; change the rotational speed of the ICE  12 ; or change the cooling fluid flow rate in the clutch. 
     As a non-limiting example, the controller  42  could be so configured that when the clutch reaches a first temperature threshold, the pressure in the clutch is decreased to thereby reduce friction and therefore temperature increase and, should a second higher threshold be reached, the clutch is completely disengaged. Of course, one skilled in the art can configure the controller  42  according to the specific requirements of a particular drivetrain. 
     Again,  FIG. 3  illustrates a non-limiting example of a usable torque vs. RPM. 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 from 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 clutch  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 . 
     Furthermore, the double arrow  208  of  FIG. 3  illustrates that the controller may modulate the usable torque allowed to pass through the clutch  16  depending on the clutch temperature data. One skilled in the art will understand that the user throttle control and the CVT ratio also modulates the usable torque. 
     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 . 
     Returning to  FIG. 2 , the controller  42 , in step  106 , supplies the instantaneous usable torque to the clutch controller  44  that controls the clutch  16  so that slippage of the clutch  16  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  16  increases drastically and quickly exceeds the usable torque. When this occurs, the clutch  16  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  16  above a usable 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  16 , 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  16 . This is done by the slip quantifier  46  and the slippage level 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 controller  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  16 . Indeed, since the usable torque increases as the CVT ratio decreases, the slippage setpoint of the clutch  16  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, if the CVT ratio was controlled by the controller  42  as discussed hereinabove with respect to step  112 , 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 non-limiting example of 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  16  will be more pronounced at these speeds. 
     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 mainly to prevent the ICE from stalling. 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 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 and the torque supplied to the wheels would be increased by the control of the CVT ratio. All that without special intervention of the operator other than actuating the throttle control according to the desired speed of the vehicle. 
     Of course, a clutch pedal or other user control could be used to disengage the clutch  16  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 . 
     One skilled in the art will understand that while a temperature sensor  16 ′ has been integrated with the clutch  16  to supply temperature data to the main controller  42 , other techniques could be used to obtain or approximate the temperature of the clutch  16 . As a non-limiting example, the temperature of the oil used in the clutch could be measured. Alternatively, since we know that the clutch temperature increases when the clutch  16  slips and that we know when the clutch is slipping and the level of this slipping, thanks to the clutch slip quantifier  46  supplying data to the controller  42 , thanks to the slip quantifier  46 , the controller  42  may approximate the clutch temperature using the clutch slipping data. 
     Of course, one skilled in the art understands that limiting the temperature in the clutch  16  increases the useful life of the clutch and provides a more robust drivetrain. 
     It is to be understood that the clutch temperature management in a slip control method and arrangement for a drivetrain 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 clutch temperature management in a slip control method and arrangement for a drivetrain 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 clutch temperature management in a slip control method and arrangement for a drivetrain 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.