METHOD AND APPARATUS FOR OPERATING A CLUTCH IN AN AUTOMATED MECHANICAL TRANSMISSION

Abstract: An apparatus and method for controlling the engagement rate of a clutch in a partially or fully automated mechanical transmission are responsive to certain calculations derived from the rotational speeds of the input member and the output member of the clutch. The apparatus includes an electronic controller which initially sets a desired speed for the vehicle engine during the shifting process, determines a rate of engagement movement of a release bearing of the clutch, and actuates appropriate valves to initiate the gradual engagement of the clutch. In a first embodiment, the electronic controller compares the rotational speeds of the input and output shafts of the clutch in order to determine if the difference therebetween is less than a first constant value. If so, it can be inferred that the clutch is sufficiently close to full engagement as to warrant the interruption of the gradual engagement process and immediately move the release bearing from its current position to the fully engaged position. To avoid a false inference of full engagement, the clutch input or output shaft speed signal is compared with the desired engine speed signal. When the magnitude of the difference between the clutch input shaft speed signal and the desired engine speed signal is less than a second constant value, then the inference that the clutch is sufficiently close to full engagement is confirmed. Thus, the release bearing can be immediately moved from its current position to the fully engaged position. In a second embodiment, an updated difference signal (calculated as the difference between an updated clutch input shaft speed signal and an updated clutch output shaft speed signal) is compared with a previous difference signal. An error signal is calculated as the difference between the updated difference signal and the previous difference signal. The electronic controller controls the movement of the release bearing such that the error signal closely follows a selected clutch engagement profile so as to consistently engage the clutch.

Description: TITLE METHOD AND APPARATUS FOR OPERATING A CLUTCH IN AN AUTOMATED MECHANICAL TRANSMISSION BACKGROUND OF THE INVENTION This invention relates in general to vehicle transmissions and in particular to a method and apparatus for automatically controlling the operation of a clutch for use with an automated mechanical transmission in a vehicle drive train assembly. In virtually all land vehicles in use today, a transmission is provided in a drive train between a source of rotational power, such as an internal combustion or diesel engine, and the driven axle and wheels of the vehicle. A typical transmission includes a case containing an input shaft, an output shaft, and a plurality of meshing gears. Means are provided for connecting selected ones of the meshing gears between the input shaft and the output shaft to provide a desired speed reduction gear ratio therebetween. The meshing gears contained within the transmission case are of varying size so as to provide a plurality of such gear ratios. By appropriately shifting among these various gear ratios, acceleration and deceleration of the vehicle can be accomplished in a smooth and efficient manner. To facilitate the operation of the transmission, it is well known to provide a clutch between the vehicle engine and the transmission. When the clutch is engaged, the transmission is driven by the vehicle engine to operate the vehicle at a selected gear ratio. To shift the transmission from a first gear ratio to a second gear ratio, the clutch is initially disengaged such that power is not transmitted from the vehicle engine to the transmission. This allows the gear shifting operation to occur within the transmission under a non-torque loading condition to prevent undesirable clashing of the meshing gear teeth. Thereafter, the clutch is re-engaged such that power is transmitted from the vehicle engine to the transmission to operate the vehicle at the second gear ratio. A typical structure for a vehicle clutch includes a cover which is connected to a flywheel secured to the end of the output shaft of the vehicle engine for rotation therewith. A pressure plate is disposed within the clutch between the cover and the flywheel. The pressure plate is connected for rotation with the flywheel and the cover, but is permitted to move axially relative thereto. Thus, the flywheel, the cover, and the pressure plate are all constantly rotatably driven by the vehicle engine. Between the flywheel and the pressure plate, a driven disc assembly is disposed. The driven disc assembly is supported on the input shaft of the transmission for rotation therewith, but is permitted to move axially relative thereto. To engage the clutch, the pressure plate is moved axially toward the flywheel to an engaged position, wherein the driven disc assembly is frictionally engaged between the flywheel and the pressure plate. As a result, the driven disc assembly (and the input shaft of the transmission upon which it is supported) are driven to rotate with the flywheel, the cover, and the pressure plate. To disengage the clutch, the pressure plate is moved axially away from the flywheel to a disengaged position. When the pressure plate is moved axially to this disengaged position, the driven disc assembly is not frictionally engaged between the flywheel and the pressure plate. As a result, the driven disc assembly (and the input shaft of the transmission upon which it is supported) are not driven to rotate with the flywheel, the cover, and the pressure plate. To effect such axial movement of the pressure plate between the engaged and disengaged positions, most vehicle clutches are provided with a release assembly including a generally hollow cylindrical release sleeve which is disposed about the output shaft of the clutch. The forward end of the release sleeve extends within the clutch and is connected through a plurality of levers or other mechanical mechanism to the pressure plate. In this manner, axial movement of the release sleeve causes corresponding axial movement of the pressure plate between the engaged and disengaged positions. Usually, one or more engagement springs are provided within the clutch to urge the pressure plate toward the engaged position. The engagement springs typically react between the release sleeve and the cover to normally maintain the clutch in the engaged condition. The rearward end of the release sleeve extends outwardly from the clutch through a central opening formed through the cover. Because the release sleeve is connected to the cover and the pressure plate of the clutch, it is also constantly driven to rotate whenever the vehicle engine is operating. Thus, an annular release bearing is usually mounted on the rearward end of the release sleeve. The release bearing is axially fixed on the release sleeve and includes an inner race which rotates with release sleeve, an outer race which is restrained from rotation, and a plurality of bearings disposed between the inner race and the outer race to accommodate such relative rotation. The non-rotating outer race of the release bearing is typically engaged by an actuating mechanism for moving the release sleeve (and, therefore, the pressure plate) between the engaged and disengaged positions to operate the clutch. In a conventional mechanical transmission, both the operation of the clutch and the gear shifting operation in the transmission are performed manually by an operator of the vehicle. For example, the clutch can be disengaged by depressing a clutch pedal located in the driver compartment of the vehicle. The clutch pedal is connected through a mechanical linkage to the outer race of the release bearing of the clutch such that when the clutch pedal is depressed, the pressure plate of the clutch is moved from the engaged position to the disengaged position. When the clutch pedal is released, the engagement springs provided within the clutch return the pressure plate from the disengaged position to the engaged position. Similarly, the gear shifting operation in the transmission can be performed when the clutch is disengaged by manually moving a shift lever which extends from the transmission into the driver compartment of the vehicle. Manually operated clutch/transmission assemblies of this general type are well known in the art and are relatively simple, inexpensive, and lightweight in structure and operation. Because of this, the majority of medium and heavy duty truck clutch/transmission assemblies in common use today are manually operated. More recently, however, in order to improve the convenience of use of manually operated clutch/transmission assemblies, various structures have been proposed for partially or fully automating the shifting of an otherwise manually operated transmission. In a partially or fully automated manual transmission, the driver-manipulated clutch pedal may be replaced by an automatic clutch actuator, such as a hydraulic or pneumatic actuator. The operation of the automatic clutch actuator can be controlled by an electronic controller or other control mechanism to selectively engage and disengage the clutch without manual effort by the driver. Similarly, the driver-manipulated shift lever may also be replaced by an automatic transmission actuator, such as a hydraulic or pneumatic actuator which is controlled by an electronic controller or other control mechanism to select and engage desired gear ratios for use. In both manually operated transmissions and in partially or fully automated manual transmissions, one of the most difficult operations to perform is to initially launch the vehicle from at or near a stand-still. This is because the force required to overcome the inertia of the vehicle is the greatest when attempting to initially accelerate the vehicle from at or near zero velocity. This relatively large amount of inertial force results in a relatively large load being placed on the vehicle engine when the clutch is engaged during a vehicle launch. Thus, the movement of the release bearing from the disengaged position to the engaged position must be carefully controlled during the initial launch of the vehicle to prevent the engine from stalling and to avoid undesirable sudden jerking movement of the vehicle. Although the same considerations are generally applicable when re-engaging the clutch during subsequent shifting operations in the higher gear ratios of the transmissions, the control of the movement of the release bearing from the disengaged position to the engaged position has been found to be less critical when shifting among such higher gear ratios because a much lesser force is required to overcome the inertia of the vehicle when the vehicle is already moving. To address these considerations, the total movement of the release bearing from the disengaged position to the engaged position can be divided into three ranges of movement. The first range of movement is from the disengaged position to a first intermediate position (referred to as the transition point). The transition point is selected to be relatively near, but spaced apart from, the position of the release bearing at which the driven disc assembly of the clutch is initially engaged by the flywheel and the pressure plate. Thus, during this first range of movement (referred to as the transition movement), the clutch is completely disengaged, and no torque is transmitted through the clutch to the transmission. The second range of movement is from the transition point to a second intermediate position (referred to as the kiss point). The kiss point is the position of the release bearing at which the driven disc assembly is initially engaged by the flywheel and the pressure plate. Thus, during this second range of movement (referred to as the approach movement) from the transition point to the kiss point, the clutch is disengaged until the release bearing reaches the kiss point, at which point the first measurable amount of torque is transmitted through the clutch to the transmission. The third range of movement of the release bearing is from the kiss point to the engaged position. The engaged position is the position of the release bearing at which the driven disc assembly is completely engaged by the flywheel and the pressure plate. Thus, during this third range of movement (referred to as the engagement movement), the clutch is gradually engaged so as to increase the amount of torque which is transmitted through the clutch to the transmission from the first measurable amount at the kiss point to the full capacity of the clutch at the engaged position. As mentioned above, during the engagement movement of the release bearing from the kiss point to the engaged position, the clutch is gradually engaged so as to increase the amount of torque which is transmitted through the clutch to the transmission from the first measurable amount at the kiss point to the full capacity of the clutch at the engaged position. Thus, although it is desirable that this engagement movement of the release bearing be accomplished as quickly as possible, it is still important to engage the clutch smoothly to prevent the engine from stalling and to avoid undesirable sudden jerking movement of the vehicle. In the past, the rate of engagement movement of the release bearing (referred to as the engagement rate) has been determined as a function of the difference between the rotational speeds of the input member and the output member of the clutch. However, it has been found that such a comparison of input and output member rotational speeds may not be well suited for all of the varying conditions under which the vehicle may be operated. Thus, it would be desirable to provide an apparatus and method for controlling the engagement rate of a clutch in a partially or fully automated mechanical transmission which is better suited for all of the varying conditions under which the vehicle may be operated. SUMMARY OF THE INVENTION This invention relates to an apparatus and method for controlling the engagement rate of a clutch in a partially or fully automated mechanical transmission in response to certain calculations derived from the rotational speeds of the input member and the output member of the clutch. The apparatus includes an electronic controller which initially sets a desired speed for the vehicle engine during the shifting process, determines a rate of engagement movement of a release bearing of the clutch, and actuates appropriate valves to initiate the gradual engagement of the clutch. In a first embodiment, the electronic controller compares the rotational speeds of the input and output shafts of the clutch in order to determine if the difference therebetween is less than a first constant value. If so, it can be inferred that the clutch is sufficiently close to full engagement as to warrant the interruption the gradual engagement process and immediately move the release bearing from its current position to the fully engaged position. To avoid a false inference of full engagement, however, the clutch input (or output) shaft speed signal is compared with the desired engine speed signal. When the magnitude of the difference between the clutch input shaft speed signal and the desired engine speed signal is less than a second constant value, then the inference that the clutch is sufficiently close to full engagement is confirmed. Thus, the release bearing can be immediately moved from its current position to the fully engaged position. In a second embodiment, an updated difference signal (calculated as the difference between an updated clutch input shaft speed signal and an updated clutch output shaft speed signal) is compared with a previous difference signal. An error signal is calculated as the difference between the updated difference signal and the previous difference signal. The electronic controller controls the movement of the release bearing of the clutch such that the error signal clo-r ly follows a selected clutch engagement profile so as to consistently engage the clutch. Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a vehicle drive train assembly including an electronic controller in accordance with this invention. Fig. 2 is sectional elevational view of the clutch actuator and portions of the clutch and transmission illustrated in Fig. 1 showing the clutch actuator and the clutch in a disengaged position, together with a block diagram of the valves and related control circuitry for operating the clutch actuator and the clutch. Fig. 3 is a flow chart of a first embodiment of an algorithm for controlling the movement of the release bearing of the clutch in its engagement movement from the kiss point to the engaged position. Fig. 4 is a flow chart of a second embodiment of an algorithm for controlling the movement of the release bearing of the clutch in its engagement movement from the kiss point to the engaged position. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, there is illustrated in Fig. 1 a block diagram of a vehicle drive train assembly, indicated generally at 10. The drive train assembly 10 includes a conventional engine 11 or other source of rotational power. The engine 11 is connected through an output shaft 11a, such as a crankshaft of the engine 11, to a clutch 12. The clutch 12 is also conventional in the art and functions to selectively connect the output shaft 11a of the engine 11 to an input shaft 13a of a transmission 13. The transmission 13 contains a plurality of meshing gears (not shown) which are selectively connected between the input shaft 13a and an output shaft 13b. The meshing gears contained within the transmission 13 are of varying size so as to - 1 - provide a plurality of such gear ratios. By appropriately shifting among these various gear ratios, a desired speed reduction gear ratio can be provided between the input shaft 13a and the output shaft 13b. Consequently, acceleration and deceleration of the vehicle can be accomplished in a smooth and efficient manner. The output shaft 13b is connected to a conventional axle assembly 14. The axle assembly 14 includes one or more wheels which are rotatably driven by the engine 11 whenever the clutch 12 and the transmission 13 are engaged. This general structure for the drive train assembly 10 is well known in the art. The illustrated transmission 13 may be either a partially or fully automated mechanical transmission. In a typical partially automated manual transmission, a driver-manipulated shift lever (not shown) engages and moves certain ones of a plurality of shift rails contained within the transmission to engage a first set of gear ratios for use. However, an automatically shifting transmission actuator 15 is provided on the transmission 13 to engage and move the remaining shift rails to engage a second set of gear ratios for use. For example, it is known to provide a partially automated manual transmission wherein the lower gear ratios are manually selected and engaged by the vehicle driver using the shift lever, while the higher gear ratios are automatically selected and engaged by the transmission actuator 15. One example of a typical partially automated manual transmission of this general structure is disclosed in detail in U.S. Patent No. 5,450,767, owned by the assigned of this application. The disclosure of that patent is incorporated herein by reference. In a fully automated manual transmission, the driver-operated shift lever is usually replaced by the transmission actuator 15. The transmission actuator 15 functions to shift all of the shift rails contained within the transmission so as to select and engage all of the available gear ratios. The above-referenced patent discusses the adaptability of the disclosed partially automated transmission actuator 15 to fully automate the shifting of the transmission disclosed therein. To facilitate the automatic shifting of the transmission 15, the clutch 12 is provided with a clutch actuator 16. The structure and operation of the clutch actuator 16 will be discussed further below. Briefly, however, the clutch actuator 16 is provided to replace a driver-manipulated clutch pedal so as to partially or fully automate the operation of the clutch 12. The clutch actuator 16 is effective to operate the clutch 12 in either an engaged or disengaged mode. When the clutch 12 is engaged, the transmission 13 is driven by the vehicle engine 11 to operate the vehicle at a selected gear ratio. To shift the transmission 13 from a first gear ratio to a second gear ratio, the clutch 12 is initially disengaged such that power is not transmitted from the vehicle engine 11 to the transmission 13. This allows the transmission actuator 15 to effect a gear shifting operation within the transmission 13 under a non-torque loading condition to prevent undesirable clashing of the meshing gear teeth. Thereafter, the clutch 12 is re-engaged such that power is transmitted from the vehicle engine 11 to the transmission 13 to operate the vehicle at the second gear ratio. The operation of the clutch actuator 16 and the transmission actuator 15 are controlled by an electronic controller 20. The electronic controller 20 can be embodied as any conventional microprocessor or similar computing apparatus which can be programmed to operate the clutch actuator 16 (to effect automatic disengagement and engagement of the clutch 12) and the transmission actuator 15 (to effect automatic shifting of the transmission 13 when the clutch 12 is disengaged) as described above. The operation of the electronic controller 20 will be described in detail below. A transmission output shaft speed sensor 21 provides an input signal to the electronic controller 20. The transmission output shaft speed sensor 21 is conventional in the art and is adapted to generate an electrical signal which is representative of the actual rotational speed of the output shaft 13b of the transmission 13. A clutch position sensor 22 also provides an input signal to the electronic controller 20. The structure and operation of the clutch position sensor 22 will be described below. An engine controller 23 is provided to control the operation of the vehicle engine 11. The engine controller 23 can also be embodied as any conventional microprocessor or similar computing apparatus which can be programmed to operate the engine 11 in a desired manner. Primarily, the engine controller 23 controls the operation of the engine 11 in response to an input signal generated by an accelerator pedal position sensor 24. The accelerator pedal position sensor 24 is conventional in the art and is adapted to generate an electrical signal which is representative of the actual position of the accelerator pedal (not shown) of the vehicle. As is well known, the accelerator pedal is physically manipulated by the foot of the driver of the vehicle to control the operation thereof. The accelerator pedal is depressed by the driver when it is desired to increase the speed of the engine 11 and move the vehicle. Conversely, the accelerator pedal is released when it is desired to decrease the speed of the engine 11 to slow or stop such movement of the vehicle. Thus, the engine controller 23 controls the speed of the engine 11 in response to the signal from the accelerator pedal position sensor 24 so as to operate the vehicle as desired by the driver. The accelerator pedal position sensor 24 may, if desired, be replaced by a throttle position sensor (not shown) or other driver-responsive sensor which generates a signal which is representative of the desired speed or mode of operation of the vehicle. A second input to the engine controller 23 is an engine output shaft speed sensor 25. The engine output shaft speed sensor 25 is conventional in the art and is adapted to generate an electrical signal which is representative of the actual rotational speed of the output shaft 1 la of the engine 11. The electronic controller 20 and the engine controller 23 communicate with one another over a data bus line 26 extending therebetween. In a manner which is generally conventional in the art, the electronic controller 20 and the engine controller 23 are programmed to communicate and cooperate with one another to so as to control the operation of the vehicle in a manner desired by the driver of the vehicle. Specifically, the electronic controller 20 and the engine controller 23 are effective to control the operation of the engine 11, the clutch 12, and the transmission 13 in such a manner that the vehicle can be started and stopped solely by physical mampulation of the accelerator and brake pedals, similar to a conventional automatic transmission in a passenger car. To accomplish this, the signals from the accelerator pedal position sensor 24 and the engine output shaft speed sensor 25 are available to the electronic controller 20 over the data bus line 26. Alternatively, the signals from the accelerator pedal position sensor 24 and the engine output shaft speed sensor 25 can be fed directly to the electronic controller 20. Referring now to Fig. 2, the clutch actuator 16 and portions of the clutch 12 and the transmission 13 are illustrated in detail. The structure and operation of the clutch actuator 16 are disclosed and illustrated in detail in co-pending application Serial No. 08/775,460, filed December 30, 1996 (owned by the assigned of this invention), the disclosure of which is incorporated herein by reference. Briefly, however, the clutch actuator 16 includes an outer cylinder housing 30, a hollow cylindrical piston 31, and an inner cylinder housing 32. The piston 31 has at least one, and preferably a plurality, of axially forwardly projecting protrusions 3 la, each of which has a circumferentially extending groove 3 lb formed therein. To assemble the clutch actuator 16, the piston 31 is initially disposed concentrically within the outer cylinder housing 30, and the inner cylinder housing 32 is disposed concentrically within the piston 31. Then, the outer cylinder housing 30 is secured to a forwardly facing surface of a case of the transmission 13 by threaded fasteners (not illustrated) or other means. When this is done, a forwardly facing surface 32a of the inner cylinder housing 32 abuts a complementary shaped, rearwardly facing annular surface 30a formed within the outer cylinder housing 30. At the same time, a rearwardly facing surface 30b of the outer cylinder housing 30 abuts portions of the case of the transmission 13. Thus, the inner cylinder housing 32 is captured between the case of the transmission 13 and the outer cylinder housing 30 so as to be fixed in position relative thereto. At the same time, a circumferential rim portion 31c of the piston 31 is received in an undercut 30c formed in the interior of the outer cylinder housing 30. Thus, the piston 31 is capable of limited axial movement relative to the outer cylinder housing 30 and the inner cylinder housing 32. The clutch 12 is a conventional pull-to-release type clutch and includes a cover 12a which is connected to a flywheel (not illustrated) which, in turn, is connected to the output shaft 11a of the engine 11. The flywheel and the cover 12a are thus rotatably driven by the engine 11 of the vehicle for rotation about an axis. The cover 12a has a central opening formed therethrough which receives a hollow, generally cylindrical release sleeve 12b. The release sleeve 12b is disposed concentrically about the transmission input shaft 13a. A driven disc assembly (not shown) is mounted within the clutch 12 on the forward end of the transmission input shaft 13a for rotation therewith and for axial movement relative thereto. When the clutch 12 is engaged, torque is transmitted from the driven disc assembly to the transmission input shaft 13a in a known manner. When the clutch 12 is disengaged, no torque is transmitted from the driven disc assembly to the transmission input shaft 13a. A forward end of the release sleeve 12b has an annular groove formed thereabout which receives the radially innermost ends of a plurality of clutch operating levers 12c therein. Thus, axial movement of the release sleeve 12b causes pivoting movement of the clutch operating levers 12c which, in turn, causes engagement and disengagement of the clutch 12 in a known manner. A plurality of clutch engagement springs 12d (only one of which is illustrated) reacts between the cover 12a and the forward end of the release sleeve 12b. The ends of the clutch engagement springs 12d are preferably supported on respective seats provided on the release sleeve 12b and the cover 12a. The springs 12d urge the release sleeve 12b axially forwardly (toward the left when viewing Fig. 2) toward an engaged position, wherein the components of the clutch 12 are frictionally engaged so as to cause the transmission input shaft 13a to be rotatably driven by the engine 11. When the release sleeve 12b is moved axially rearwardly (toward the right when viewing Fig. 2) against the urging of the engagement springs 12d toward a disengaged position, the components of the clutch 12 are frictionally disengaged so as to prevent the transmission input shaft 13a from being rotatably driven by the engine 11. The rearward end of the release sleeve 12b extends axially rearwardly through the central opening in the cover 12a. An annular release bearing 33 is disposed about the rearward end of the release sleeve 12b and is retained on one side by a snap ring 34 disposed within an annular groove. A retaining ring 35 is also disposed about the rearward end of the release sleeve 12b adjacent to the forward side of the release bearing 33. A snap ring 36 is disposed in an annular groove in the release sleeve 12b to retain the retaining ring 35 on the release sleeve 12b. Thus, the release bearing 33 and the retaining ring 35 are secured to the release sleeve 12b for axial movement therewith. A snap ring 37 is disposed within the groove formed in the outer surface of the retaining ring 35. The snap ring 37 connects the piston 31 with the retaining ring 35 such that axial movement of the piston 31 causes corresponding axial movement of the retaining ring 35, the release bearing 33, and the release sleeve 12b. An annular chamber 38 is defined between the outer surface of the body of the piston 31, the enlarged rim portion 31c formed at the rearward end of the piston 31, and the undercut 30c formed in the inner surface of the outer cylinder housing 30. The chamber 38 is sealed to form a fluid-tight chamber by sealing elements, such as O-rings. A radially extending port 39 is formed through the outer cylinder housing 30. As will be explained in detail below, pressurized fluid (hydraulic or pneumatic, as desired) is supplied through the port 39 used to effect axial movement of the piston 31 in one direction relative to the outer cylinder housing 30 and the inner cylinder housing 31. The clutch position sensor 22 is mounted on the outer cylinder housing 30 for generating an electrical signal which is representative of the axial position of the piston 31 relative to the outer and inner cylinder housings 30 and 32. Such an electrical position signal is used by an electronic controller 20 for automatically operating the clutch actuator 16 in a manner described in detail below. The clutch position sensor 22 is conventional in the art. The port 39 communicates through a conduit 40 with an engage valve 41 and a disengage valve 42. The engage valve 41 communicates with a reservoir (in hydraulic systems) or the atmosphere (in pneumatic systems), while the disengage valve 42 communicates with a source of pressurized fluid 43, either hydraulic or pneumatic as desired. The operation of the engage valve 41 is controlled by an engage solenoid 44, while the operation of the disengage valve 42 is controlled by a disengage solenoid 45. The engage solenoid 44 and the disengage solenoid 45 are, in turn, connected to the electronic controller 23 so as to be selectively operated thereby. The clutch 12 is normally maintained in the engaged position under the influence of the engagement springs 12d. When it is desired to disengage the clutch 12, the engage solenoid 44 is actuated by the electronic controller 20 to close the engage valve 41, and the disengage solenoid 45 is actuated by the electronic controller 20 to open the disengage valve 42. As a result, pressurized fluid from the source 43 is supplied to the chamber 38, causing the piston 31 to move rearwardly (toward the right when viewing Fig. 2) against the urging of the engagement springs 12d. As discussed above, such rearward movement of the piston 31 causes the clutch 12 to be disengaged. For several reasons which are well known in the art, the disengage valve 42 is operated by the electronic controller 20 in an on-off manner, i.e., either wide open or completely closed. When it is desired to subsequently re-engage the clutch 12, the engage solenoid 44 is actuated by the electronic controller 20 to open the engage valve 41, and the disengage solenoid 45 is actuated by the electronic controller 20 to close the disengage valve 42. As a result, the chamber 38 is vented to the reservoir, causing the piston 31 to move forwardly (toward the left when viewing Fig. 2) under the influence of the engagement springs 12d. As discussed above, such forward movement of the piston 31 causes the clutch 12 to be engaged. For several reasons which are well known in the art, the engage valve 44 is operated using pulse width modulation techniques to control the engagement of the clutch 12. The electronic controller 20 varies the duty cycle of the pulse width modulation of the engage valve 41 so as to adjust the rate at which the pressurized fluid in the chamber 38 is vented to the reservoir. By adjusting the rate of venting of the chamber 38 in this manner, the speed at which the release bearing 33 is moved from the disengaged position to the engaged position can be precisely controlled. Precise control of the speed of movement of the release bearing from the disengaged position to the engaged position is important to engage the clutch 12 smoothly and avoid undesirable sudden jerking movement of the vehicle. As discussed above, the total movement of the release bearing 33 from the disengaged position to the engaged position can be divided into three ranges of movement. The first range of movement of the release bearing 33 is from the disengaged position to a first intermediate position (referred to as the transition point). The transition point is selected to be relatively near, but spaced apart from, the position of the release bearing 33 at which the driven disc assembly of the clutch 12 is initially engaged by the flywheel and the pressure plate. Thus, during this first range of movement (referred to as the transition movement), the clutch 12 is completely disengaged, and no torque is transmitted through the clutch 12 to the transmission 13. The second range of movement of the release bearing 33 is from the transition point to a second intermediate position (referred to as the kiss point). The kiss point is the position of the release bearing 33 at which the driven disc assembly is initially engaged by the flywheel and the pressure plate. Thus, during this second range of movement (referred to as the approach movement) from the transition point to the kiss point, the clutch 12 is disengaged until the release bearing 33 reaches the kiss point, at which point the first measurable amount of torque is transmitted through the clutch 12 to the transmission 13. The third range of movement of the release bearing 33 is from the kiss point to the engaged position. The engaged position is the position of the release bearing 33 at which the driven disc assembly is completely engaged by the flywheel and the pressure plate. Thus, during this third range of movement (referred to as the engagement movement), the clutch 12 is gradually engaged so as to increase the amount of torque which is transmitted through the clutch 12 to the transmission 13 from the first measurable amount at the kiss point to the full capacity of the clutch 12 at the engaged position. Movement of the release bearing 33 through the first and second ranges of movement can be accomplished in any known manner. As suggested above, the initial movement of the release bearing 33 from the disengaged position to the transition point can be accomplished by pulse width modulating the engage valve 41 at a predetermined duty cycle so as to cause rapid movement of the release bearing 33 from the disengaged position to the transition point. To accomplish this, the engage valve 41 may be pulse width modulated at a constant rate throughout the transition movement of the release bearing 33. Alternatively, the engage valve 41 may be pulse width modulated at a rate which varies with the current position of the release bearing 33 relative to the transition point so as to decelerate the release bearing 33 somewhat as it approaches the transition point. The electronic controller 20 can be programmed to monitor the clutch position signal from the clutch position sensor 22 to determine when the release bearing 33 has reached the transition point. Regardless of the specific transition rate which is used, it is desirable that the initial transition movement of the release bearing 33 be performed as rapidly as possible because the clutch 12 is completely disengaged throughout. Therefore, no sudden and undesirable engagement of the clutch 12 will occur during this initial transition movement of the release bearing 33. Similarly, the approach movement of the release bearing 33 from the transition point to the kiss point can be accomplished by pulse width modulation of the engage valve 41 at a duty cycle which is initially relatively long (to initially maintain the rapid movement of the release bearing 33), but subsequently is shortened to decelerate the release bearing 33 as it approaches the kiss point. By slowing the movement of the release bearing 33 as it approaches the kiss point, the clutch 12 will be engaged smoothly so as to prevent the engine from stalling and avoid undesirable sudden jerking movement of the vehicle. The electronic controller 20 can be programmed to automatically alter the duty cycle of the engage valve during this approach movement of the release bearing 33 in response to sensed operating conditions. For example, the electronic controller 20 can be responsive to the amount of depression of the accelerator pedal from the pedal position sensor 24 for adjusting the duty cycle of the engage valve. However, any known algorithms may be used to control the movement of the release bearing 33 in its initial transition movement from the disengaged position to the transition point, and in its subsequent approach movement from the transition point to the kiss point. The algorithm of this invention relates to the control of the movement of the release bearing 33 in its engagement movement from the kiss point to the engaged position. As discussed above, during the engagement movement of the release bearing 33 from the kiss point to the engaged position, the clutch 12 is gradually engaged so as to increase the amount of torque which is transmitted through the clutch 12 to the transmission 13 from the first measurable amount at the kiss point to the full capacity of the clutch 12 at the engaged position. Thus, although it is desirable that this engagement movement of the release bearing 33 be accomplished as quickly as possible, it is still important to engage the clutch 12 smoothly to prevent the engine from stalling and avoid undesirable sudden jerking movement of the vehicle. Referring now to Fig. 3, there is illustrated a flow chart of a first embodiment of an algorithm, indicated generally at 50, for controlling the movement of the release bearing 33 in its engagement movement from the kiss point to the engaged position. In the first step 51 of the algorithm 50, the electronic controller 20 issues a command to the engine controller 23 setting a desired engine speed signal V ENG - The desired engine speed signal V ENG s selected to be sufficiently high such that the engine 11 is capable of overcoming the inertia of the vehicle as the clutch 12 is engaged and thereby avoid stalling during the engagement process. The desired engine speed signal V ENG can, therefore, vary with the specific structure of the engine 11, the transmission 13 used in conjunction with the engine 11, and other factors. The second step 52 of the algorithm 50 is to determine the engagement rate of the release bearing 33 of the clutch 12. For the purposes of this invention, the engagement rate can be determined in any conventional manner in response to a number of operating conditions of the vehicle. For example, the engagement rate can be selected to be a constant rate or may vary with the movement of the release bearing 33 from the kiss point to the engaged position in the manner discussed above. As will become apparent below, the algorithm 50 of this invention monitors the status of clutch engagement and alters the predetermined engagement rate under certain circumstances. Then, as shown in the third step 53 of the algorithm 50, the engage valve 41 and the disengage valve 42 are actuated (by means of the respective solenoids 44 and 45) to effect movement of the release bearing 33 of the clutch 12 according to the selected engagement rate. Thus, the clutch engagement process is initiated. Next, the fourth step 54 of the algorithm 50 causes the electronic controller 20 to read the clutch input shaft speed signal V^ from the engine controller 23. As discussed above, the engine output shaft speed sensor 25 generates the clutch input shaft speed signal V IN to the engine controller 23 which is representative of the actual rotational speed of the output shaft 1 la of the engine 11. That information is available to the electronic controller 20 from the engine controller 23 over the data bus line 26. In the fifth step 55 of the algorithm 50, the electronic controller 20 reads the transmission output shaft speed signal directly from the speed sensor 21. The sixth step 56 in the algorithm 50 is to calculate the clutch output shaft speed signal V 0 uτ- The clutch output shaft speed signal V 0 uτ can be calculated by multiplying the transmission output shaft speed with the gear ratio of the transmission 13 selected by the electronic controller 20 and implemented by the transmission actuator 15. The algorithm 50 next enters a decision point 57, wherein the clutch input shaft speed signal V IN is compared with the clutch output shaft speed signal V 0 uτ- In this step, the magnitude of the difference between the clutch input shaft speed signal V IN and the clutch output shaft speed signal V 0 uτ is compared against a first constant value Kl. The first constant value Kl is selected to be relatively small, typically about fifty revolutions per minute. If the magnitude of the difference between the clutch input shaft speed signal V IN and the clutch output shaft speed signal V OUT s greater than the first constant value Kl, then the clutch 12 is not close to full engagement. Thus, the algorithm 50 branches back to the second step 52, wherein the electronic controller 20 again determines the engagement rate of the clutch 12 in response to the operating conditions of the vehicle. This loop of the algorithm 50 is repeated until the magnitude of the difference between the clutch input shaft speed signal V M and the clutch output shaft speed signal V 0 uτ is less than or equal to the first constant value Kl. If the magnitude of the difference between the clutch input shaft speed signal V IN and the clutch output shaft speed signal V 0 uτ is less than or equal to the first constant value Kl, it can be inferred that the clutch 12 is sufficiently close to full engagement as to warrant the interruption the gradual engagement process and immediately move the release bearing 33 from its current position to the fully engaged position. This interruption is desirable because it decreases the overall time required to complete the engagement process, while preventing the engine from stalling and avoiding undesirable sudden jerking movement of the vehicle. In practice, however, it has been found that during the engagement of the clutch 12, the driven disc assembly is not always frictionally engaged between the flywheel and the pressure plate in a smooth manner. Rather, in some instances, the driven disc assembly is frictionally engaged in a somewhat stuttering or hesitating manner. If the samplings of the clutch input shaft speed signal V I and the clutch output shaft speed signal V 0 uτ are made during this stuttering engagement of the clutch 12, a false inference of full engagement of the clutch 12 may be generated when, in fact, the clutch 12 is not yet sufficiently close to full engagement as to warrant the interruption of the gradual engagement process. To address this, the algorithm 50 includes a second decision point 58, wherein the clutch input shaft speed signal V IN is compared with the desired engine speed signal V ENG - Specifically, the magnitude of the difference between the clutch input shaft speed signal V IN and the desired engine speed signal V E NG is compared against a second constant value K2. Alternatively, the magnitude of the difference between the clutch output shaft speed signal V 0 uτ and the desired engine speed signal V ENG could be compared against the second constant value K2. In either event, the second constant value K2 is selected to be relatively small, typically about twenty revolutions per minute. When the magnitude of the difference between the clutch input shaft speed signal V IN and the desired engine speed signal V ENG is greater than the second constant value K2, then it can be inferred that the clutch 12 is not close to full engagement. Thus, the gradual engagement process is continued, and the algorithm 50 branches back to the second step 52 as described above. This loop of the algorithm 50 is repeated until the magnitude of the difference between the clutch input shaft speed signal V and the desired engine speed signal V EN G is less than or equal to the second constant value K2. When the magnitude of the difference between the clutch input shaft speed signal V IN and the desired engine speed signal V E NG is less than or equal to the second constant value K2, then the inference that the clutch 12 is sufficiently close to full engagement is confirmed. Thus, the algorithm 50 enters the ninth step 59 wherein the engage valve 41 is actuated to interrupt the gradual engagement process and immediately move the release bearing 33 from its current position to the fully engaged position. Referring now to Fig. 4, there is illustrated a flow chart of a second embodiment of an algorithm, indicated generally at 60, for controlling the movement of the release bearing 33 in its engagement movement from the kiss point to the engaged position. In the first step 61 of the algorithm 60, the electronic controller 20 issues a command to the engine controller 23 setting a desired engine speed signal V ENG - AS discussed above, the desired engine speed signal V ENG is selected to be sufficiently high such that the engine 11 is capable of overcoming the inertia of the vehicle as the clutch 12 is engaged and thereby avoid stalling during the engagement process. The second step 62 of the algorithm 60 is to determine the engagement rate of the release bearing 33 of the clutch 12 and to determine a clutch engagement profile. As discussed above, the engagement rate can be determined in any conventional manner. The clutch engagement profile represents a preferred rate at which the clutch input shaft speed signal V I and the clutch output shaft speed signal V OUT approach synchronization. The clutch engagement profile may, for example, be a curve which is stored within the electronic controller 20 and is used to control the engagement rate of the release bearing 33 in a manner described below. If desired, a plurality of clutch engagement profiles may be stored within the electronic controller 20, and a desired one of such curves may be selected for use in response to certain operating conditions of the vehicle. As shown in the third step 63 of the algorithm 60, the engage valve 41 and the disengage valve 42 are actuated (by means of the respective solenoids 44 and 45) to effect movement of the release bearing 33 of the clutch 12 according to the selected engagement rate. Thus, the clutch engagement process is initiated. Next, the fourth step 64 of the algorithm 60 causes the electronic controller 20 to read the clutch input shaft speed signal V m from the engine controller 23. In the fifth step 65 of the algorithm 60, the electronic controller 20 reads the transmission output shaft speed signal directly from the speed sensor 21. The sixth step 66 in the algorithm 60 is to calculate the clutch output shaft speed signal V 0 uτ- The clutch output shaft speed signal V 0 uτ can be calculated by multiplying the transmission output shaft speed with the selected gear ratio of the transmission 13. In the seventh step 67 of the algorithm 60, a difference signal V DIFF is calculated as the difference between the clutch input shaft speed signal V IN and the clutch output shaft speed signal V 0 uτ- The difference signal V D ι FF is stored in the electronic controller 20 for later use. In the next three steps 68, 69, and 70 of the algorithm 60, the electronic controller 20 reads an updated clutch input shaft speed signal V IN + 1 from the engine controller 23, reads an updated transmission output shaft speed signal from the speed sensor 21, and calculates an updated clutch output shaft speed signal V 0 uτ + ι- Then, in step 71 of the algorithm 60, an updated difference signal V DIFF + I is calculated as the difference between the updated clutch input shaft speed signal V IN + I and the updated clutch output shaft speed signal V OUT - I • In the next step 72, the algorithm 60 compares the updated difference signal V DIFF -<- I with a constant value K. When the magnitude of the updated difference signal VDIFF - I is less than or equal to the constant value K, it can be inferred that the clutch 12 is sufficiently close to full engagement as to warrant the interruption the gradual engagement process and immediately move the release bearing 33 from its current position to the fully engaged position. Thus, the algorithm 60 enters the step 73 wherein the engage valve 41 is actuated to interrupt the gradual engagement process and immediately move the release bearing 33 from its current position to the fully engaged position. If desired, the above-discussed secondary step of comparing the magnitude of the difference between the clutch input shaft speed signal V IN (or clutch output shaft speed signal V 0 uτ) and the desired engine speed signal V ENG against the second constant value K2 may be performed as well. When the magnitude of the updated difference signal VDIFF + I is greater than the constant value K, it can be inferred that the clutch 12 is not yet sufficiently close to full engagement as to warrant the interruption the gradual engagement process and immediately move the release bearing 33 from its current position to the fully engaged position. Thus, the algorithm 60 next enters a step 74 wherein an error signal V ERR is calculated as the difference between the updated difference signal V DIFF + I and the prior difference signal VDIFF - This error signal V ERR is next compared in step 75 with the previously determined clutch engaged profile. If the error signal V ER corresponds closely to the clutch engagement profile, then the engagement process continues. However, if the error signal V ERR deviates from the clutch engagement profile by more than a predetermined amount, then the modulation of the engage valve 41 is adjusted such that the movement of the release bearing 33 of the clutch 12 more closely follows the clutch engagement profile, as shown in step 76. Thus, the electronic controller 20 controls the movement of the release bearing 33 of the clutch 12 to closely follow the selected clutch engagement profile so as to consistently engage the clutch 12. The last step in the algorithm 60 is, as shown in step 77, to re-define the prior difference signal V DIFF as the updated difference signal V DIFF I- I • Then the algorithm 60 loops back to step 68 wherein the updated clutch input shaft speed signal V I + I is read, the updated clutch output shaft speed V 0 uτ - I is calculated, and the updated difference signal V DIFF + I is calculated. Thus, the algorithm 60 continuously monitors the updated clutch input shaft speed signal V I + I with the constant K to determine when to complete the shifting process and, when that does not occur, continuously controls the movement of the release bearing 33 of the clutch 12 to closely follow the selected clutch engagement profile so as to consistently engage the clutch 12. In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.

Claims: What is claimed is: 1. An apparatus for controlling an engagement rate of a clutch having an input member and an output member for selectively connecting an engine to a transmission, the apparatus comprising: a first sensor for generating a signal which is representative of the rotational speed of the input member of the clutch; a second sensor for generating a signal which is representative of the rotational speed of the output member of the clutch; a controller for generating a desired engine speed signal and a control signal which is representative of an engagement rate of the clutch, said controller being responsive to said first sensor signal, said second sensor signal, and said desired engine speed signal for modifying said control signal when the rotational speeds of the input member of the clutch, the output member of the clutch, and the desired engine speed are approximately equal; and a clutch actuator for controlling the engagement rate of the clutch in response to said control signal.

Inventors: WHEELER JAMES A, WHEELER, JAMES, A.
Applicants: TRANSMISSION TECHNOLOGIES CORP, TRANSMISSION TECHNOLOGIES CORPORATION
Application year: 1998
Main classification: F16H
IPC codes: B60W10, B60W30, F16D48