FR2745533A1 - METHOD AND DEVICE FOR EVALUATING A TORQUE FROM THE CLUTCH TORQUE OF A CLUTCH THAT STARTS TO SKATE - Google Patents

Abstract

The device is used to evaluate the transmission torque transmitted by a clutch which is arranged in a power transmission system to allow the selective connection and disconnection of this power transmission system. The device is applied to a clutch (12) which is interposed between the engine (10) of a vehicle and an automatic transmission (14) for the driving wheels (18) of the vehicle and it comprises control means (36) clutch force (valve 34 and pressure P), speed measuring means (40, 42) for measuring the input speed and the output speed of the clutch (12), control means for controlling said clutch force control means in order to obtain the reduction of this clutch force to determine the clutch slip start torque.

Description

METHOD AND DEVICE FOR EVALUATING A COUPLE

  FROM THE CLUTCH TORQUE OF A CLUTCH

WHO'S STARTING TO PATINATE

  The present invention relates to a method for evaluating a torque, to a method for compensating data for calculating a torque. and a device for evaluating a torque. and more particularly to techniques for evaluating with very high precision a torque to be transmitted by a transmission system.

  power without using a relatively expensive torque sensor.

  Recently, a method has been proposed for reducing the engine torque of a motor vehicle by controlling the ignition timing of the engine, at the moment of switching an automatic transmission. in order to reduce the switching or shifting shock of the automatic transmission. Also known is a method of reducing the engine torque by controlling the amount of fuel injected by the traction control of the engine to control the driving force of the driving wheels of the vehicle. To control the output torque of the motor, as described above. it is necessary to measure the actual engine torque at the driving wheels (to the tires of the driving wheels). However. the known torque sensors are relatively expensive, and they have the defect of insufficient reliability in service. and that is why they are not used in commercially available motor vehicles that would be able to implement such a method. In this situation. the actual driving torque to the drive wheels is generally evaluated based on a predetermined engine torque database map and a compensation value based on engine acceleration and inertia, or it is estimated or evaluated from the torque ratio or transmission ratio of a torque converter provided on the vehicle. The SAE 950900 specification shows how to use not only the torque ratio but also the capacity coefficient of the torque converter, to improve the

  accuracy of estimation or evaluation of the couple.

  However. the data cards used to get the motor torque to

  the amount of air drawn or the throttle opening and the engine speed. or from the torque ratio or the capacitance coefficient of the torque converter. are predetermined without taking into account the variations in the engine torque that may occur due to unavoidable variations in

  during the manufacture of individual motor vehicles and under the influence of

  external interference. If the engine torque is compensated on the basis of the

  due to a predetermined inertia of the engine and the instantaneous acceleration of the engine.

  this engine acceleration is obtained by differentiating the measured engine speed. To differentiate the engine speed to get the engine acceleration. we

  usually uses a filter to suppress unwanted background noise.

  However, the engine acceleration obtained does not accurately represent the actual engine acceleration. because of fluctuation factors or variations that occur during the achievement of the engine acceleration. such as

  measurement errors on the motor speed and the instability of the filter operation.

  To deal with such variations, various methods have been proposed to increase the accuracy of the engine torque estimate, by compensating for the estimated values of these variations. or compensation using an I 0 () learning control technique. These methods are not satisfactory for

  guarantee the evaluation of the torque with high precision.

  Thus, the known techniques can not determine the desired or desired value of the engine torque, when the engine torque is reduced to reduce the switching shock of the automatic transmission. or when the couple

  The engine is controlled by the traction control to prevent excessive skating.

  sif driving wheels under the effect of an exaggerated driving force. Consequently. the known techniques do not allow feedback control or feedback of the engine torque with a sufficiently high precision to reduce the shock of

  switching or to perform the traction control.

  An object of the present invention is precisely to determine with a relatively high accuracy the torque transmitted by a transmission system.

  power, without having to use a relatively expensive torque sensor.

  For this purpose. according to a first aspect of the invention. a method is provided for evaluating the transmission torque transmitted by a clutch member which is disposed in a power transmission system. and whose clutch force is controllable. said transmission torque being the torque transmitted by the clutch member when the latter is engaged. the method comprising the steps of - reducing said clutch force of said clutch member to cause said clutch member to move into an intermediate clutch state between fully engaged state and fully disengaged state - to obtain a critical clutch torque of said clutch member when the latter is placed in said intermediate state, and - to evaluate said transmission torque transmitted by the clutch member

  based on the critical clutch torque.

  In the method for evaluating the torque according to the present invention, the force

  of the clutch member provided in the transmission system of

  is reduced until the clutch member is placed in its internal state.

  mediate, and we obtain the critical clutch torque of the clutch member placed in the intermediate state. The transmission torque transmitted by the clutch member is determined on the basis of the critical clutch torque obtained. The transmission torque transmitted by the clutch member is the torque transmitted through the clutch member, when the latter is substantially in fully engaged position. The clutch engagement torque of the clutch member can be obtained with high accuracy based on the clutch force, diameter values and other parameters of the clutch member and as a function of the clutch member. an equation well known in the prior art. The clutch in the intermediate state is about to be disengaged or engaged. This means that when the clutch is placed in the intermediate state,

  the clutch is about to start skating. or the amount of slippage

  or skating the clutch that skates is about to become zero. The critical clutch torque of the intermediate clutch member I5 represents the torque that is actually transmitted by the clutch member when the clutch member is substantially fully engaged. As a result, the transmission torque of the clutch member can be determined accurately on the basis of

  critical clutch torque, without having to use a relative torque sensor.

  expensive. Thus, the transmission torque transmitted by the clutch member, when the latter is substantially fully engaged. can be evaluated simply by detecting the intermediate state of the clutch member between the fully engaged state and the fully disengaged state (partial slip state). In this regard. the reduction of the engagement force of the clutch member to cause the clutch member to come into the intermediate state has no influence

  significant on the actual torque transmitted by the clutch member.

  If the clutch member is a clutch. the critical clutch torque of this clutch represents the transmission torque transmitted when the clutch is in substantially fully engaged position. If the clutch member is a brake used in a transmission in the power transmission system, the transmission torque transmitted by the brake when the brake is substantially fully engaged (tight) is calculated on the basis of the ratio of gear of the

  transmission and critical clutch torque.

  The principle of the present invention can be practically implemented

  required to evaluate the transmission torque transmitted by the clutch member disposed in the power transmission system of a motor vehicle, when

  the clutch member is substantially fully engaged. The couple of trans-

  estimated mission of the coupling member can be used appropriately to compensate for a torque data card which is in relation to the torque of a

* I:. ,, '. 1 7 - _ '

  vehicle engine and a predetermined operating parameter of the vehicle. If the clutch member is a clutch. for example. the present invention may be implemented to evaluate the torque transmitted by a power transmission system other than that used in a motor vehicle. If the invention is applied to a power transmission system of a motor vehicle, the clutch member is preferably an automatic vehicle start clutch disposed between the engine and a transmission. However, the clutch member may be a clutch or a switching brake used for switching an automatic transmission. The clutch member. whose clutch force must be controllable or variable, is preferably a clutch member to fi-iction. which is engaged by a friction force acting on friction members. or else Luni clutch member electromagnetically actuated, and which is engaged by a single electromagnetic force. The friction clutch member is preferably a hydraulically actuated member whose clutch force is controllable by hydraulic pressure applied thereto. However, the organ

  friction clutch may use resilient means such as a diagonal spring.

  diaphragm that solicits a frictional organ. In this type of friction clutch member

  tion. the amount of elastic deformation of the elastic means is modified to control the friction clutch force. The transmission provided in the power transmission system indicated above may be an automatic transmission having several transmission ratios, a transmission continuously

  variable or a manual transmission.

  The torque evaluation method according to the first aspect of the invention may further comprise a step of increasing the clutch force of the clutch member. until the complete engagement of the clutch member is achieved. immediately after the transmission torque of the clutch member has been evaluated. In that case. the reduction of the clutch force of the clutch member is only temporary, the reduction has practically no influence on the actual transmission torque which is transmitted through

the clutch member.

  The object indicated above can also be realized according to a second aspect of the invention, which proposes a method for evaluating a transmission torque transmitted via a clutch which is arranged in a power transmission system for the selective connection and disconnection of the power transmission system. the transmission torque being a torque transmitted by

  through the clutch when the clutch is engaged. the process comprises

the steps

'- 4'

  (a) reducing the clutch force of the clutch which is initially in a fully engaged position; (b) determining whether the clutch begins to spin as a result of the reduction of the clutch force (c) to be calculated the clutching torque of the start of the clutch slippage at the start of the clutch slippage. on the basis of the clutch Iforce when the clutch begins to slip: and (d) to evaluate the clutch transmission torque so that the torque

  of rated transmission is equal to the starting clutch torque of slip.

  The method of evaluating torque according to the second aspect of the invention has substantially the same advantages as the method according to the first aspect of the invention. In the present process. clutch torque of start of clutch slip. at the beginning of the clutch slip. is determined as the transmission torque transmitted by the clutch. This arrangement allows easier and more efficient determination or estimation of the transmission torque.

  of the clutch. as the arrangement in which the clutch torque of the clutch.

  when the clutch slips, as a result of the initial reduction of the clutch force.

  is about to be fully engaged. as a result of the subsequent increase in the clutch force. and is determined to be the couple of

transmission.

  The above method may further include a step of increasing the clutch force of the clutch. to cause the clutch to be fully engaged, immediately after the transmission torque transmitted by the clutch has been determined. In that case. also, the temporary reduction of the clutch force of the clutch member has substantially no influence on the

  actual transmission torque that is transmitted by the clutch member.

  The above method according to the second aspect of the invention is suitably implemented by means of a device constructed according to a third aspect of the present invention and which is able to evaluate the transmission torque of a clutch which is arranged in a power transmission system to make the selective connection and disconnection of the power transmission system, the

  transmission torque being a torque transmitted through the clutch.

  when the latter is engaged. the device comprising: (a) clutch force control means for controlling the clutch engagement force (b) speed measuring means for measuring the input speed and the output speed of the clutch force (c) control means for controlling the clutch force control means to reduce the clutch clutch force; (d) means for evaluating the start of slippage. to determine, based on the input and output speeds measured by the velocity measuring means. if the embravage begins to skate as a result of the reduction of the clutch force by the clutch force control molyens; and (e) torque evaluation means for calculating a starting clutch torque of slip (Tslip) of the clutch when starting the clutch slippage. based on the clutch force of the clutch at start 1 of the slip. and to determine the starting clutch torque of skating

  as the transmission torque of the clutch.

  The above device according to a third aspect of the invention presents

  the same advantages as described above with regard to the process

  according to the second aspect of the invention.

  The object indicated above can also be realized according to a fourth aspect.

  of the invention which proposes a method of compensating the torque

  sensing of a torque at a predetermined point in a power transmission system comprising a clutch for selective connection or disconnection of the power transmission system and a predetermined physical parameter of the power transmission system. the method comprising the steps of: (a) evaluating the transmission torque of the clutch when the clutch is

  engaged, according to the method corresponding to the second aspect of the invention described above.

  above: and (b) to compensate for a torque data card based on the torque of

  transmission evaluates the clutch.

  In this process. the couple at the predetermined point in the transmission system.

  power can be determined with high accuracy. on the basis of

  born of compensated couple. independently of the various differences in the power transmission system of individual motor vehicles that are due to

  variations during the manufacture of vehicles. as well as external disturbances

  EXTERIOR. and chronological changes in the transmission system of

  ciency. The torque thus obtained from the updated torque data can be used

  for different purposes to control the power transmission system.

  In one form of the method according to the fourth aspect of the invention. the para-

  Physical meter consists of a load of a motor whose output torque is transmitted by the power transmission system. and at a speed of rotation of the motor. and the method further comprises the step of calculating the engine torque based on at least the rated transmission torque of the clutch and the inertia of the engine. In that case. the torque data is provided by a motor torque data card. representative of the engine torque. and load and engine speed, and the engine torque data card is compensated for on the

base of the calculated torque of the motor.

  According to another aspect of the invention there is provided a method for evaluating transmission torque transmitted by a clutch which is disposed in a power transmission system for selective connection and disconnection of the power transmission system. the transmission torque being a torque transmitted by the clutch when the latter is ignited. the method comprising the steps of: (a) reducing the clutch clutch force to cause the clutch to come to an intermediate state between the fully engaged state and the fully disengaged state; ) to achieve a critical clutch engagement torque when the clutch is placed in an intermediate state; and (c) to evaluate the clutch transmission torque based on the torque

  critical clutch clutch.

  The critical clutch torque may be the slip start clutch torque, as used in the method of the second aspect of the invention described above. or an end-of-slip (clutch) clutch force obtained when the partially engaged clutch is about to be fully engaged, or when the amount of slippage of the clutch is about to become zero. The critical clutch torque may be the average of a plurality of clutch torque values that are obtained during

  reductions and repeated increases in clutch clutch force.

  when the latter is placed in its intermediate state. The clutch can be replaced by a chip provided in the power transmission system. by

  example in an automatic transmission.

  According to yet another aspect of the invention, there is provided a device for determining a transmission torque of a clutch such as a hydraulically actuated friction clutch. which is disposed between an engine and a transmission of a motor vehicle. and whose clutch force is controllable. comprising (a) clutch force control means for controlling the clutch clutch force, for example a hydraulic pressure applied to the hydraulically actuated friction clutch: (b) speed measuring means for measuring an input speed and a clutch output speed; (c) control means for controlling the clutch force control means to reduce the clutch engagement force (d) of the clutch force; skating start evaluation means for determining. based on the input and output speeds measured by the speed measuring means. if the clutch begins to skate as a result of the reduction of the clutch force by the clutch force control means; and (e) torque evaluation means for calculating the starting clutch torque of the clutch force; clutch slip at the beginning of the clutch slip. based on the clutch engagement force at the beginning of the clutch slip, and to consider the slip start clutch torque as the transmission torque that is transmitted by the clutch.

  1) through the clutch. when the latter is engaged.

  According to yet another aspect of the present invention. a device is proposed for reducing the torque to be transmitted to an automatic transmission of a motor vehicle. the automatic transmission having a plurality of transmission ratios. the device comprising (a) a device as described in the paragraph above. to evaluate the couple

  transmission of the clutch between the engine and the automatic transmission.

  matic; (b) setpoint transmission torque evaluation means for

  determining a set transmission torque to be transmitted to the transmission

  automatic transmission, based on the transmission torque of the clutch deter-

  undermined by the torque estimation means. such that the determined target transmission torque is reduced to reduce shocks at the time of the automatic transmission switching operation; and (c) torque reduction means for feedback control of the force control means. clutch. such that the clutch torque of the clutch coincides with the determined target transmission torque. and

  that the torque actually transmitted to the automatic transmission is reduced.

  The clutch torque of the clutch. when the latter begins to

  ner, represents the torque actually transmitted by the clutch to the transmission) automatic. As soon as this clutch engagement torque is controlled to coincide with the setpoint transmission torque. the torque actually transmitted to the automatic transmission is suitably reduced so as to reduce the switching shock of the automatic transmission. Thus, the torque transmitted to the automatic transmission is controlled by controlling the clutch torque (torque

  transmission) of the clutch by the clutch force control means.

  The arrangement described above allows a more efficient and accurate control of the torque transmitted to the automatic transmission, than the arrangement in which the torque transmitted to the transmission is controlled by controlling the output torque of the engine. The present device utilizes the torque evaluation means of the torque evaluation device described above. which is able to accurately determine the transmission torque that is transmitted by the clutch immediately before the transmission switching operation. in such a way that the automatic transmission is effectively protected against switching shocks. In a general way. the automatic transmission can suffer a switching shock when it is automatically switched according to the speed of

driving the vehicle.

  According to yet another aspect of the invention. a device is proposed for reducing the torque to be transmitted to a driving wheel of a motor vehicle. the device comprising: (a) a device as described in the paragraph above. for determining the translational torque of the clutch between the motor and the transmission (b) sliding detection (or measurement) means for measuring the

  slip of the drive wheel. as provided in an anti-lock device

  blocking or anti-skid device or in a traction control device; and (c) torque reduction means for controlling the clutch force control means to reduce the clutch force of the clutch force. clutch and cause slippage of the clutch, when the slippage of the driving wheel is detected by the slip detection means. in such a way that

  torque transmitted to the drive wheel is reduced to reduce the amount of

swimming the driving wheel.

  The torque reduction means can be actuated alone to reduce the slippage of the driving wheel. without the anti-lock braking device or the

  Traction control device only work.

  In a variant. the torque reduction means can cooperate with the disc

  positive anti-lock braking. or with the traction control device to reduce the slippage of the drive wheel. The torque reduction means may be adapted to control feedback of the clutch force control means. in such a way that the clutch torque of the clutch coincides with

  a predetermined set transmission torque to be transmitted to the driving wheel.

  The present device may reduce the engine torque of the driving wheel by controlling the transmission torque of the clutch. allows a more effective and precise control of the motor torque than the device adapted to reduce the torque

  motor by reducing the output torque of the motor.

  In the device for reducing the torque to be transmitted to the automatic transmission or to the driving wheel of the motor vehicle. as described above, the clutch may be a wet-type friction clutch provided with friction members whose friction coefficient g is kept substantially constant,

  regardless of any change in the slip speed AN of the clutch.

  In this case, the clutch torque (transmission torque or transmitted torque) of the clutch is obtained by assuming that the coefficient of friction of the clutch is constant. In this case, the clutch torque or transmission torque of the clutch can be calculated quickly and efficiently, based only on the load (clutch force) applied to the clutch. such as hydraulic pressure applied to the wet-type friction clutch. if the clutch is a

  I (clutch operated hydraulically.

  In the torque reduction device described above. the clutch may be a friction clutch of the dry type having a friction member whose coefficient of friction [t varies in case of variation of the sliding speed AN of the clutch. In that case. the clutch torque or the transmission torque of the clutch is obtained by using a coefficient of friction which varies with the speed of clutch slip. The coefficient of friction is determined on the basis of the slip speed, and as a function of a predetermined relationship between the coefficient of friction and the slip speed. This arrangement allows the precise determination of the desired clutch torque or the transmission torque of

the clutch, inde-

  while changing the coefficient of friction p. with the speed of

swim AN.

  In the torque reduction device described above. the clutch can be a hydraulically operated friction clutch. In that case. the torque evaluation means may comprise a pressure sensor for measuring a hydraulic pressure applied to the friction clutch via a hydraulic circuit, when the clutch begins to slip, to calculate the force

  clutch clutch from the measured hydraulic pressure. and to

  Cull the clutch torque from the calculated clutch force. This agency

  using the actual measured hydraulic pressure allows a more

  precise transmission torque of the clutch when the latter is engaged.

  that the arrangement in which a hydraulic pressure as represented by a

  pressure control signal, is used to calculate the clutch force.

  According to yet another aspect of the present invention there is provided a device for reducing the torque to be transmitted to a driving wheel of a motor vehicle, via a power transmission system. comprising an engine, a continuously variable transmission and a friction clutch operated

  hydraulically and arranged between the engine and the transmission. the device comprises

  (a) hydraulic pressure control means for controlling the hydraulic pressure to be applied to the friction clutch so as to control the clutch clutch force; (b) velocity measuring means for measuring the input speed and the output speed S of the clutch (c) control means for controlling the hydraulic pressure control means to reduce the clutch force clutch; (d) means for determining the start of slippage. to determine. from the input and output speeds measured by the speed measuring means, I0 if the clutch begins to spin. as a result of the reduction of the clutch force by the clutch force control means (e) of the torque estimation means for calculating a clutch torque of

  start of slippage of the clutch. at the beginning of the clutch slip. at

  firing clutch clutch force at the start of clutch slip. and to be able to consider the clutch torque of start of slippage. as the transmission torque that is transmitted by the clutch when the clutch is engaged (t) slip detection means for detecting or measuring the slippage of the driving wheel. as provided in an anti-lock braking device or in a traction control device; and (g) torque reduction means for controlling the clutch force control means. in order to reduce the clutch engagement force to cause the clutch to slip, when the slip of the drive wheel is detected by the slip detection means. in such a way that the torque transmitted to the driving wheel is reduced to reduce the amplitude of the slippage of the driving wheel. The torque reduction means can be actuated alone to reduce the

  slip of the drive wheel. without operating the anti-lock device

  blocking or a traction control device. In a variant. the torque reduction means can cooperate with the anti-lock braking device or

  with the traction control device to reduce the slippage of the driving wheel.

  The torque reduction means may be adapted to perform a feedback control of hydraulic pressure control means such that the clutch torque of the clutch coincides with a setpoint transmission torque to be transmitted to the drive wheel. The setpoint transmission torque can be determined on the basis of the transmission torque of the clutch evaluated by the

means for estimating torque.

  According to yet another aspect of the invention there is provided a device for reducing the torque to be transmitted to a driving wheel of a motor vehicle through a motor vehicle. automatic transmission having a plurality of transmission ratios and a switching clutch for switching the automatic transmission; the device comprising: (a) clutch force control means for controlling the clutch force of the clutch. switching (b) speed measuring means for measuring the input speed and the output speed of the switching clutch: (c) control means for controlling the force control means

  clutch to reduce the clutch force of the shift clutch.

  (d) Slip start evaluation means for determining, based on the input and output speeds measured by the velocity measuring means. if the switching clutch begins to slip due to the reduction of the clutch force by the clutch force control means (e) of the torque evaluation means to calculate a clutch torque of

  start of clutch slip when starting the clutch slip.

  based on the clutch engagement force at the beginning of the clutch slip. and to be able to consider the slip start clutch torque as the transmission torque that is transmitted through the clutch when the clutch is engaged (f) slip detection means for detecting or measuring skating of the driving wheel. as provided in an anti-lock braking device or in a traction control device; and (g) torque reduction means for controlling the clutch force control means to reduce the clutch force of the clutch. clutch to cause clutch slippage, when drive wheel slip is detected by slip detection means. in such a way that the torque transmitted to the driving wheel is reduced to reduce the amount of

slip of the drive wheel.

  Other goals. advantages and features will appear on reading the

  description of various embodiments of the invention. made in a non-limitative

  with reference to the appended drawing, in which

  FIG. 1 is a schematic representation illustrating a transmission system

  power mission of a motor vehicle equipped with a transmission

  automatic mission. this system comprising a torque evaluation device capable of practicing a torque evaluation method according to one embodiment of the present invention: FIG. 2 is a flowchart illustrating a subroutine for reducing the driving torque of the drive wheels of the motor vehicle by adjusting an automatic vehicle start clutch in the embodiment of Figure 1

  FIG. 3 is a view in elevation and in axial cross-section in half

  view of the automatic vehicle start clutch as used in the embodiment of FIG.

  - Figure 4 is a timing diagram showing. for example, the variations

  various parameters concerning the torque transmitted by the clutch.

  when the engine torque is reduced according to the subroutine of FIG. 2 - FIG. 5 is a diagram showing the relationship between the slip speed AN and the coefficient of friction / t of a wet-type clutch and a dry type clutch: FIG. 6 is an axial cross-sectional elevational view showing another type of automatic vehicle start clutch which is used in the power transmission system of FIG. 1; FIG. flow chart showing another embodiment of the present invention; and - Figure 8 is a flow chart showing another embodiment of the

present invention.

  Referring firstly to the schematic representation of FIG. 1, there is shown a power transmission system of a motor vehicle equipped with an automatic transmission. The power transmission system comprises an automatic vehicle start clutch 12 through which the output torque of a motor 10 is transmitted to an automatic transmission 14 having a plurality of transmission ratios, and further comprises a gear train. final reduction gear 16 through which the output torque of the automatic transmission

  14 is transmitted to the drive wheels of right and left 18 of the motor vehicle.

  The power transmission system includes a torque evaluation device for evaluating the torque of the vehicle start-up automatic clutch 12. The automatic vehicle start clutch 12 is capable of

  automatic connection and disconnection of a transmission link

  power transmission between the engine 10 and the automatic transmission 14, depending, for example, on the actuation of a switching lever or shift by the driver of the vehicle. The clutch 12 thus serves as a coupling member which is arranged in a power transmission system and whose

  Clutch force (i.e., friction applying force) is controllable.

  The automatic vehicle start clutch is for example a hydraulically actuated clutch. of the wet type and with multiple disks. as shown in Figure 3. The friction clutch 12 comprises: a housing 20 fixed to a crankshaft 11 of the engine 10 (Figure 1): a disc 24 connected to an input shaft 22 of the automatic transmission 14. of such that the disk 24 is rotated with the input shaft 22: a plurality of friction members 26 attached to the housing 20 to rotate therewith: a plurality of friction members 1 O28 attached to the disk 24 to rotate with the latter: and a piston 32 which is arranged sliding fluid-tight in a bore of the housing 20 and which is actuated by the hydraulic pressure provided by a passage of the oil 30, to obtain the clutch or the contact The hydraulic pressure applied to the piston 32 will be indicated as being "the clutch pressure P." The clutch or contact force of the friction members 26, 28 varies with the "clutch pressure P "applied to the piston 32. Because the clutch 12 is symmetrical about its axis (center line), it has

  shown in FIG 3 only the upper half of the clutch 12.

  The "clutch pressure P" is provided by a pressure regulating valve

  sion 34 which receives a circuit pressure PL and which is controlled as a function of a pressure adjustment signal SP * which is received from a control or control member 36 sometimes referred to as a "controller". A pressure sensor 38 is provided for measuring the clutch pressure P which is supplied by the pressure control valve 34 and which is applied to the piston 32 of the clutch 12. The control member 36 receives from the pressure sensor 38 a clutch pressure signal SP indicative of the clutch pressure P. The control member 36 also receives an input speed signal SNin from a speed sensor 40 provided for measuring the speed Nin of the crankshaft 11, and a signal SPEED OUTPUT SNout from a speed sensor 42 provided for measuring the speed Nout of an input shaft 22 of the automatic transmission 14. The automatic vehicle start clutch 12 is interposed between the crankshaft 11 and the input shaft 22 of the automatic transmission 14. The INPUT SPEED signal SNin represents the speed Nin of the crankshaft 11. While the signal SPEED OF

  OUTPUT SNout represents the speed Nout of the input shaft 22.

  The control member 36 comprises a microcomputer provided with a central processing unit (CPU), a random access memory (RAM) and a

  ROM (ROM). The CPU operates to perform processing operations

  signal based on control programs stored in the ROM, while using a temporary function of storing data from the RAM. The control programs include a program for performing a TORQUE REDUCTION CONTROL routine shown in the flow chart of Fig. 2. The TORQUE REDUCTION routine is adapted to control the vehicle start auto clutch 12. . to reduce the driving torque of the drive wheels 18 during a switching action or shift ratio transmission of the automatic transmission 14. especially during a downshift action of the automatic transmission 14 with the POWER switch in the cutoff position. to prevent a shock

  1 () switching due to the switching action of the automatic transmission 14.

  The switch of Pl ISSANCE is intended to establish a mode of TRANS-

  MISSION OF POWER. in which the automatic transmission 14 is

  switched to drive the vehicle with a relatively high degree of

  driving behavior. When the power switch is in the closed position. the

  The driver of the vehicle usually wishes to carry out a flexible driving of the vehicle.

  cule. Consequently. the switching shock during the switching operation

  Transmission 14 when the power switch is in the OFF position is not desirable. If the TORQUE REDUCTION CONTROL routine of FIG. 2 is performed during a switching operation of the automatic transmission 14, a TORQUE REDUCTION START control command adapted to control the clutch 12 to reduce the engine torque on the driving wheels 18. is received from a transmission controller (no

  shown) for controlling the transmission 14.

  In a variant. the TORQUE REDUCTION CONTROL routine of FIG. 2 may be adapted to control the automatic vehicle start clutch 12 to reduce the driving torque of the driving wheels 18 during a traction control operation. wherein the engine torque is reduced to prevent excessive slippage of the driving wheels 18. In this case, the TORQUE REDUCTION START control command to control the clutch 12 to reduce the engine torque. is received from a controller from

  traction control (not shown).

  The TORQUE REDUCTION COMMAND subroutine of the

  FIG. 2 is initialized in step S1 in which the PRESET ADJUSTMENT signal

  SION SP * is sent from the controller 36 to the pressure regulating valve 34 so that the clutch pressure P generated by the valve 34 and applied to the automatic vehicle start clutch 12 is reduced by one. predetermined decrement AP. such that the clutch force (friction-causing force between the friction members 26. 28) of the clutch 12 is reduced accordingly. The decrement AP may be a predetermined fixed value, or it may vary depending on the state of slippage or non slip of the clutch 12, the ordered switching action of the transmission 14. or any other running condition of the vehicle. and based on a predetermined card or data equation and stored. The control pulse then proceeds to step S2 in which a slip speed of the clutch is calculated. makes a difference AN = (Nin - Nout)? based on the INPUT SPEED and OUTPUT SPEED signals of the SNin and SNout signals. Step S2 is followed by step S3 to determine whether the

  calculated slip speed AN of the clutch 12 is greater than a predetermined threshold

  finished g (which is a positive value close to zero). If a negative decision (NO) is obtained at step S3. that is, if the slip speed AN is not greater than the threshold u. the control signal returns to step SI. and the steps S 1 to S 3 are carried out repeatedly until the sliding speed AN 1 5 becomes greater than the threshold s. that is, until the clutch begins to slip (the clutch is about to be disengaged). Thus, the CLUTCH PRESSURE P is reduced to a rate corresponding to the decrement AN. If an affirmative decision (YES) is obtained in step S3. that is, if the slip speed AN exceeds the threshold value s. the control pulse goes to step

S4 and the following steps.

  The timing diagram of FIG. 4 shows an example of the variations of the torque values of the automatic vehicle start clutch 12. speeds Nin and Nout of the crankshaft 11 and the input shaft 12. and the clutch pressure P of the clutch 12, when the torque transmitted through the clutch 12 is temporarily reduced. in a traction control mode. to reduce the driving torque of the drive wheels 18 to prevent excessive wheel spinning of the drive wheels 18. In the graph of Fig. 4, "tl" indicates a time point for which the torque control command routine of the Figure 2 is triggered, and "t2" indicates a time instant o the affirmative decision (YES) is obtained in step S3 of the routine. The single-dot dash line on the torque graph indicates the full clutch torque T of the clutch 12. while the solid line on this graph indicates the torque actually transmitted by the clutch 12 to the automatic transmission 14 The full clutch torque T represents the torque transmission capacity of the clutch 12, in fact the maximum torque that can be transmitted by the clutch to the transmission 14. The torque actually transmitted by the clutch 12 will be indicated.

  as being the "actual transmission torque" of the clutch 12.

  At step S4. the clutch pressure P at the instant when the affirmative decision (YES) was obtained in step S3. is determined as a start pressure of Pslip SKATING CLUTCH. Step S4 is followed by step S5 to calculate a start torque CLUTCH Tslip of the clutch 12 which is the full clutch torque T at the instant the clutch starts to skate or is on the point of being disengaged. This means that the TRIP START CLUTCH TORQUE Tslip is the maximum torque that can be transmitted through the clutch 12 to the transmission 14. as the clutch 12 begins to spin. The pair of PSlip START CLUTCH is calculated as a function of the Tslip CLUTCH START CLUTCH pressure. more specifically according to the following equation (1) which comprises the PACKING START CLUTCH pressure Pslip: Tslip = f (Pslip) = 1/3. iPslip.A.n. (Df3 df3) / (Df2 - dtf2) ... (1) in which

  p1 is the coefficient of friction of the friction surfaces of the friction members 26.

  28: n is the number of friction surfaces Df is the outside diameter of the friction surfaces df is the inside diameter of the friction surfaces A is the active surface area of the piston 32 = 7- / 4 (Dp- - 1) Dp is the outside diameter of the piston 32: and

  dp is the inside diameter of the piston 32.

  The CLUTCH PRESSURE P which is determined to be the PACKING START CLUTCH PRESSURE Pslip is preferably represented

  by the CLUTCH PRESSURE SP signal. but maybe the pressure

  PRESSURE ADJUSTMENT SP * which is sent from

  nance of the control member 36 to the pressure regulating valve 34. In the latter case. the relatively inexpensive pressure sensor 38 can be eliminated, and the torque evaluation device incorporated in the transmission system of

  Power is available at reduced cost.

  As can be seen from the graph of FIG. 4, the CLUTCH START CLUTCH pair Tslip of the clutch 12 at the beginning of the skating.

  the clutch 12 is equal to the actual transmission torque of the clutch 12 (i.e.

  the torque actually transmitted by the clutch 12) when the clutch 12 is initially fully engaged, that is to say to the transmission torque of

  the clutch 12 before the clutch 12 begins to skate.

  It will be understood that the steps S1 to S5 establish an embodiment of the torque evaluation method according to the invention and that the step S1 constitutes a form of a step of reducing the clutch force of the clutch. It will also be understood that steps S2 and S3 constitute a form of a step of determining whether the clutch 12 begins to skate, and that steps S3 and S4 constitute a form of a step of evaluating a torque. Clutch clutch 12. It will further be appreciated that control member 36 is a very important part of a torque evaluation device. for evaluating the clutch torque of the clutch 12. and a part of the control member 36 assigned to implement the step S1 constitutes control means for controlling the clutch force control means . to reduce the clutch force of the clutch 12. It will also be understood that a part of the control member 36 assigned to implement the steps S2 and S3 constitutes skate start evaluation means for determining whether the clutch begins to skid. and that a part of the control member 36 assigned to the implementation of the steps S4 and S5 constitutes clutch torque evaluation means for evaluating the clutch torque 12, when the clutch is substantially completely engaged. It will be further understood that the pressure regulating valve 34 serves as a clutch force control means indicated above, for controlling the hydraulic pressure P to be applied to the clutch 12. as a function of a signal of output of the control means indicated above. of

  to control the clutch force of the clutch 12.

  In equation (1) above. the value (pt.Pslip.A.n) represents the strength

  clutch 12 at the beginning of the slipping of this clutch. If the pressure

  CLUTCH P REPLACEMENT P replaces with the PACKING START CLUTCH pressure Pslip in Equation (1I). the full clutch torque T indicated by the single-dot dotted line in FIG. 4 is obtained. The clutch torque

  T includes the actual transmission torque of the clutch 12 at the beginning of its patient.

  swimming. The control pulse then proceeds to step S6 to determine the SETPOINT CLUTCH TRANSMISSION torque Tref. according to the CLUTCH BEGINNING CLUTCH torque Tslip. who is the couple of

  actual transmission of the clutch 12. when the clutch is fully engaged.

  That is, the SET CLUTCH TRANSMISSION torque Tref is calculated based on a predetermined functional equation including the Tslip slip start clutch torque. Step S6 is followed by step S7 in which the clutch pressure P is feedback-controlled so that the actual transmission torque (FULL CLUTCH TORQUE T) of the clutch 12 is equal to establish the torque. of CLUTCH CLUTCH TRANSMISSION Tref. The feedback control of the CLUTCH P pressure is performed while the full clutch torque T is calculated according to the equation shown (1) above. In the present embodiment. the automatic vehicle start clutch 12 is a wet-type friction clutch using the firearm 26. 28. whose coefficient of friction it varies with the slip speed AN of the clutch 12. as indicated by a line in full line on the graph of Figure 5. Because the amount of variation of the coefficient of friction p. of the clutch 12 of wet type. according to the slip speed AN. is more fainter than that of a dry type friction clutch, the full clutch torque T can be easily obtained with high accuracy according to equation (1). even if equation (1) uses the same coefficient of friction gp. that is, the nominal coefficient of friction Ft of the clutch 12. If it is desired to obtain the FULL CLUTCH TORQUE T with a higher accuracy. or if the clutch 12 is a clutch of the dry friction type. whose coefficient of friction varies considerably with the slip speed AN. as indicated by a single dot dotted line in Figure 5. It is preferable that the coefficient of friction it used in

  equation (1) is modified so that it varies according to the slip speed AN.

  The processing in step S7 is completed when the controller 36 receives a TORQUE REDUCTION control command command from the traction controller or the transmission controller. In the timing diagram of FIG. 4, "t3" represents a time instant for which the control command END OF TORQUE REDUCTION is received by the controller 36. After the TORQUE REDUCTION CONTROL routine of FIG. 2 is completed, the CLUTCH P pressure is increased to increase the actual transmission torque of the clutch 12 and bring it to a level corresponding to the

  torque output instant engine 10.

  In the present power transmission system of the motor vehicle. the clutch force of the clutch 12 is reduced by reducing the CLUTCH pressure P until the clutch 12 begins to skate, and the CLUTCH START CLUTCH torque Tslip at the beginning of the spinning of the clutch 12. The clutch 12 is obtained as the actual transmission torque of the clutch 12, so that the torque of the TARGET CLUTCH TRANSMISSION Tref is determined on the basis of the start torque CLUTCH Tslip. The Tslip BEGINNING CLUTCH torque is calculated accurately on the basis of the PSlip START CLUTCH PRESSURE and according to the equation given above. In addition. the start torque CLUTCH Tslip represents the actual torque that is transmitted through the clutch 12 when the latter begins to skate. that is, when the clutch is about to skate but is substantially fully engaged. So. the actual transmission torque of the clutch 12. when the latter is fully engaged. can be evaluated with

  great precision. without using an expensive torque sensor.

  In the embodiment of FIG. 2, the CLUTCH torque

  START OF SLIP Tslip is obtained when the clutch begins to

  while the clutch pressure P is reduced. However, the END OF SKATING CLUTCH torque can be obtained when clutch 12 slippage is about to end while the CLUTCH P pressure is increased after the initial reduction. Described in detail, the CLUTCH PI pressure is initially reduced to cause clutch slippage. and it is then increased until the slip speed AN I 5 of the clutch is equal to zero. in fact. until the clutch is fully engaged again. The CLUTCH END CLUTCH torque is the CLUTCH 12 CLUTCH TRIMMING torque when the partially slipped clutch slip speed is about zero or the clutch that Partially slips off is about to be fully engaged as a result of an increase in CLUTCH P pressure. The ZIP TRIGGER CLUTCH pair and the END TRACK CLUTCH pair are collectively referred to as "torque". of the clutch 12. obtained when the clutch 12 is placed in an intermediate state between the state completely

engaged and the state disengaged.

  In the present embodiment of FIG. 2, the TRACK BEGINNING CLUTCH torque Tslip at the beginning of the slowing of the vehicle start automatic clutch 12 is obtained to determine the actual transmission torque of the clutch 12. This arrangement permits easier and more efficient determination or estimation of the clutch transmission torque than the arrangement in which the end slip clutch torque indicated above is obtained to determine the transmission torque. In addition, the use for the clutch 12 of a friction clutch of the wet type allows easy adjustment. effective and accurate clutch force of the clutch 12 (in fact maximum and actual transmission torque values of the clutch 12), by

  adjusting the clutch pressure P to be applied to the piston 32.

  The present power transmission system is adapted such that the torque transmitted to the automatic transmission 14 or the driving torque of the driving wheels of the vehicle is reduced by reducing the clutch pressure P to reduce the actual transmission torque (the maximum transmission torque or full clutch torque T) of the clutch 12, rather than reducing the output torque of the engine 10. In addition. Clutch TRANSMISSION torque Tref can be accurately determined from the Tslip TRAP DEPUFF CLUTCH torque. which accurately represents the actual transmission torque of the clutch 12 when the latter is substantially fully engaged. This arrangement allows an efficient and precise adjustment of the

  motor torque during a switching action of the transmission to-

  tomatic 14 or traction control of the driving wheels. so as to

* see actually avoid a switching shock on the transmission 14 and a pati-

excessive swimming of the drive wheels.

  Referring now to FIG. 6, there is shown an automatic clutch

  vehicle starting system 50 which is used in another embodiment of the invention.

  of the invention. in place of the clutch 12. The clutch 50 is a friction clutch of the dry type comprising: a flywheel 52 connected to the crankshaft 11 of the engine 10;

  a clutch disk 54 which is connected to the input shaft 22 of the automatic transmission.

  14 to be rotated with the input shaft 22. and which has a friction member disposed at its outer peripheral portion. a pressure plate 56 which is disposed on one side of the friction member of the clutch disc 54, away from the steering wheel, and which is rotated with the flywheel 52; and a diaphragm spring 58 which urges the pressure plate 56 towards the flywheel 52 to tighten the clutch disk 54. The clutch 50 is actuated by an organ

  actuator 60 such as an electric motor. The actuating member 60 functions

  Like the clutch control means for controlling the clutch force of the clutch 50. When the inner peripheral portion of the diaphragm spring 58 is moved in the direction of the right (as can be seen in FIG. ) by the actuating member 60 by means of a release fork 62. the load or the force acting on the pressure plate 56 is reduced, and

  the clutch force of the clutch 50 due to friction is reduced accordingly.

  There is a predetermined relationship between the operating stroke of the actuating member 60 (declutching fork 62) and the load applied to the platen.

  pressure 56 by the diaphragm spring. According to this relationship. we can determine

  to reduce the load acting on the pressure plate 56 and. therefore, the clutch force of the clutch 50 from the actuating stroke of the actuating member 60 or the declutching fork 62. Alternatively. strength

  clutch 50 can be obtained according to a predefined relationship

  terminated between the driving force generated by the actuating member 60 and the load

  applied to the pressure plate 56 by the diaphragm spring 58.

  In the power transmission system using the automatic clutch

  Fig. 50 of dry type vehicle starting according to the present second embodiment. the CLUTCH START CLUTCH couple T of the clutch 50 can be obtained in the same manner as in the first embodiment. Since the coefficient of friction Ad of the dry-type clutch 50 varies in a comparatively large manner as a function of the variation of the slip speed AN. it is desirable that the coefficient of friction I_ used in

  equation (1) above. be modified according to the slip speed AN.

  In the first and second embodiments. the clutch torque T.sub.CLIP of the clutch 12.50 is calculated from the start-up pressure CLUTCH PRESSURE Pslip when the clutch 12.50 begins to spin. However. the torque control command routine of FIG. 2 can be modified as shown in the flowchart of FIG. 7. In this third embodiment shown in FIG. 7, the clutch pressure P is reduced by the decrement

  predetermined AP in step R I. and the full clutch torque T of the clutch 12.

  is calculated in step R2. depending on the clutch pressure P. according to a predetermined equation which is identical to equation (1) above. with the exception that the clutch pressure P is used in place of the slip start clutch pressure Pslip. Step R2 is followed by step R3 to calculate the slip speed AN of the clutch 12. 50. and by the step R4 to determine if the calculated slip speed AN exceeds the predetermined threshold s. that is, to determine if the clutch 12.50 begins to spin. The steps R1 to R4 are put

  repeatedly until the clutch 12. 50 begins to spin.

  When an affirmative decision (YES) is obtained in step R4, the flow chart proceeds to step R5 in which the full clutch torque T of the clutch 12. 50. when the clutch begins to skate. is determined to be the full start torque Tslip slip (actual transmission torque) of the clutch 12. 50. In this third embodiment, a portion of the control member 36 assigned to the achievement of the Step T1 is a control means for controlling the clutch force control means to reduce the clutch engagement force. and a portion of the control member 36 assigned to performing steps R3 and R4 is slippage start evaluation means for determining whether the clutch begins to spin. In addition. a part of the control member 36 assigned to the realization of the step R2 constitutes clutch torque evaluation means

274 553; 3

  to evaluate the torque of the clutch when the latter is substantially

completely engaged.

  While the reduction of the torque transmitted through the clutch has been described above, the principle of the present invention is applicable to a teaching control of the engine 10 torque. - engine torque data card teaching thinking to control the

  motor torque 10. is illustrated in the flow chart of FIG.

  third embodiment of the invention.

  The routine of FIG. 8 is triggered in step QI to determine whether the vehicle is in a steady speed taxiing state, in which the angle

  opening of the throttle valve and the driving speed V of the vehicle are sensi-

  consistently. If an affirmative decision (YES) is obtained in step Q1, the computer program proceeds. step Q2 for executing a torque evaluation routine element in which the clutch start clutch torque Tslip of the clutch 12 is obtained as the actual transmission torque when the clutch is substantially completely engaged. The clutch torque of

  Tslip is calculated in the same way as in steps S I to S5 of

  program in Figure 5 or only in the subprogram of Figure 7.

  The flow chart then proceeds to step Q3 to determine whether a predetermined teaching condition is satisfied. For example, step Q3 is formulated to determine whether the opening angle of the throttle valve Oth or whether the running speed of the vehicle during the realization of the torque evaluation routine element step Q2 'is less than a predetermined threshold. If an affirmative decision (YES) is obtained in step Q3. that is, if the predetermined teaching condition is satisfied. step Q3 is followed by step Q4 to read the measured instantaneous speed Ne of the engine 10, the opening angle of the throttle valve Oth. and the angular acceleration dNe / dt of the motor 12. The flow chart then proceeds to step Q5 to evaluate the torque Te of the motor 10 according to the following equation (2) which includes the inertia of the motor 10 and the elements related thereto Te = Tslip-le. (dNe / dt) ... (2) Step Q5 is followed by step Q6 to update a motor torque data map which establishes a relationship between the motor torque Te and the opening angle of the throttle valve Oth and the engine speed Ne. More specifically, the engine torque determined by the measured instantaneous opening angle of the throttle valve Oth and the engine speed Ne. and according to this engine torque data card. is compared to the engine torque rated Te. If the difference between the engine torque determined according to the present engine torque data card and the rated engine torque Te is greater than a predetermined threshold, the current engine torque map is updated. in such a way that the engine torque evaluated Te

  obtained from the updated engine torque data card.

  The present fourth embodiment of the invention proposes a method for updating or compensating torque data. more specifically updating motor torque data maps, such that the torque Te of the motor 10 is obtained with great accuracy from the updated engine torque data card. irrespective of the various differences in the power transmission system of the individual motor vehicles, which are due to variations in the manufacture of the vehicles, to external disturbances and to changes in the time of the power transmission system. The engine torque obtained from the updated engine torque card can be

  used for different purposes, for example to control the pressure of the hydraulic circuit

  It can be used to actuate the switching clutches used in the automatic transmission 14. or to control the hydraulic pressure to actuate a lock clutch provided in a torque converter. In such cases. the pressure is controlled according to the engine torque determined by the torque card

updated engine.

  In the torque evaluation routine element of step Q2. the clutch engagement force 12 is reduced until the clutch 12 begins to spin, and the clutch start clutch torque Tslip of the clutch 12 is calculated as the actual transmission torque of the clutch 12. That is to say that the actual transmission torque of the clutch 12, when the latter is substantially fully engaged. is evaluated to be equal to the torque Tslip at the beginning of the clutch 12 slip After the evaluation of the actual transmission torque of the clutch 12. in step Q2. the clutch 12 is brought back to

  the state fully engaged. So, step Q2, in the sub-program of

  engine torque data card teaching thinking. does not influence the

  actual transmission torque of the clutch 12.

  While the present invention has been described in detail in its embodiments,

  currently pre-ferred. it must be understood that it is not limited to the details

  embodiments shown, but that it can take other forms.

  For example, the clutch start clutch torque Tslip of the clutch 12 is still obtained by controlling the clutch pressure P so as to maintain the clutch 12 in an intermediate state between the fully engaged state and the clutch 12. partial skid condition. in such a way that the motor torque Te is obtained on the basis of

  Tslip couple and according to equation (2) above. in the case of a dysfunction

  any element associated with the engine torque card. In addition. the couple

  Slip start clutch Tslip can be used for counter-control

  1 (1 (2 ') - 124 1 reaction of the motor 10, when the driving torque of the driving wheels of the vehicle 10

  is reduced by reducing the output torque of the motor 10.

  The embodiments of FIGS. 2 and 7 are adapted such that the starting slip clutch torque Tslip is determined on the basis of the slip start clutch pressure Pslip. when the affirmative decision (YES) is obtained at step S3. or be determined to be equal to the full clutch torque T (maximum torque transmissible by the clutch) when the affirmative decision (YES) is obtained in step R4. However. the value of the pressure Pslip or the value of the torque T used to determine the slip start clutch torque Pslip can be compensated on the basis of the decrement AP used in the step S1

  or the slip speed AN calculated in step S2 or R3.

  While the illustrated embodiments are adapted to determine the transmission torque of the clutch 12. 50 in a transmission system.

  power of a vehicle driven by the engine 10. The principle of the present invention

  tion is applicable to the determination of a torque transmitted by a transmission system

  power mission of an electric vehicle that is driven by an electric motor

  cudgel. Of course. the present invention is not limited to the embodiments described and shown. and it is susceptible to many variants accessible to

  the person skilled in the art without departing from the spirit of the invention.

Claims (7)

  1. A method for evaluating the transmission torque by a clutch member (12. 50) which is disposed in a power transmission system, and whose braking force is controllable. said transmission torque being a torque transmitted by said clutch member when said clutch member is engaged, said method comprising the steps of: - reducing said clutch force of said clutch member to force said clutch member to be placed in an intermediate state of clutch I (0 between the fully engaged state and the fully disengaged state of the member; - to obtain a critical clutch torque (Tslip) of said clutch member when this last is placed in said intermediate state: and - to determine said transmission torque of said clutch member from of said critical clutch torque.   The method of claim 1 further comprising the step of increasing said clutch force of said clutch member. until the complete clutch of said clutch member is engaged. immediately after that   transmission torque of said clutch member has been determined.   3. A method for evaluating a transmission torque transmitted by a clutch (12, 50) which is disposed in a power transmission system for the   connection and selective disconnection of said power transmission system.   said transmission torque being a torque transmitted by said clutch when the clutch is engaged, said method comprising the steps of:   (a) reducing the clutch force of said clutch which is initially complete;   (b) determining whether said clutch begins to spin as a result of the reduction of said clutch force (c) in calculating a starting slip clutch torque (Tslip) of said clutch at the beginning of said clutch slippage. from the clutch force when said clutch begins to spin; and (d) determining said transmission torque of said clutch such that the determined transmission torque is equal to said start clutch torque skating.   The method of claim 3 further comprising the step of increasing said clutch force of said clutch to cause the clutch to engage fully with said clutch. immediately after said transmission torque   trnsmis by said clutch has been determined.   5. A method of compensating torque data representative of a torque at a predetermined point in a power transmission system including a clutch for selectively connecting or disconnecting said power transmission system and a predetermined physical parameter. said power transmission system, said method comprising the steps of: (a) determining said transmission torque transmitted by said clutch when said clutch is engaged, according to the method defined in claim 3; and (b) compensating a torque data card from the transmission torque evaluated of said clutch.   The method according to claim 5, wherein said physical parameter consists of the load (Oth) of a motor (10) whose output torque is transmitted via said power transmission system, and the speed of rotation ( Ne) of said engine, said method further comprising a step of calculating a torque (Te) of said engine from at least the evaluated transmission torque of said clutch and the inertia (Ie) of said engine, and wherein said step of compensating said torque data card includes compensation of a motor torque data card representative of the engine torque and said load   and speed of said engine, from the calculated torque (Te) of the engine.   7. A device for evaluating transmission torque by a clutch (12, 50) which is arranged in a power transmission system for selective connection and disconnection of said power transmission system, said transmission torque being a transmitted torque. by said clutch when engaged, said apparatus comprising: (a) clutch force control means for controlling the clutch force (T) of said clutch (12, 50); (b) measuring means speed sensor (40, 42) for measuring the input speed (Nin) and the output speed (Nout) of said clutch; (c) control means for controlling said clutch force control means to reduce their said clutch force of said clutch; (d) slip start evaluation means for determining, from said input (Nin) and output (Nout) velocities measured by said R 14300 14387 DOC - 4 Jun 1997 - 27/29 measure of speed if said clutch begins to skate as a result of the reduction of said clutch force by said clutch force control means; and (e) torque evaluation means for calculating a clutch torque. start of slip (Tslip) of said clutch at the beginning of the slipping of said clutch. from the clutch force of said clutch (50) at the beginning of said slip. and to be able to consider said clutch torque of start of slippage. as said transmission torque transmitted by said clutch. 1 È, I) () (- 27 tvler 1)) 7 - 2S)