Method of and apparatus for preventing shifts of reference positions of friction clutches

A method of and an arrangement for preventing a shift of the reference position of a clutch which is operated by an actuator and is installed in the power train of a motor vehicle. Such shift of reference position can be caused in response to axial displacements between the input and output shafts of the clutch. The method includes the steps of routinely ascertaining the reference position, memorizing and thus actualizing the information pertaining to the ascertained reference position, ascertaining an operational parameter which is the cause of axial displacements between the input and output shafts of the clutch, and altering the routine determination and the memorizing of the reference position when the operational parameter exceeds a predetermined threshold value.

BACKGROUND OF THE INVENTION

The present invention relates to a method of and to an arrangement or apparatus for reducing the likelihood of malfunctioning, or of less than optimal functioning, of clutches in the power trains of motor vehicles. More particularly, the invention relates to improvements in methods of and in arrangements for preventing or reducing the likelihood of malfunctioning, such as shifts of reference positions, of actuator-operated friction clutches which are engageable and disengageable to transmit, or to interrupt the transmission of, torque between the prime movers (such as internal combustion engines) and the change-speed transmissions in the power trains of motor vehicles.

The reference position of a clutch in the power train of a motor vehicle is likely or bound to change as a result of axial shifting of at least one of the input and output shafts of the clutch relative to the other shaft. Such changes or shifts of reference position can cause extensive discomfort to the occupant(s) of the motor vehicle (for example, during starting of the vehicle and/or during shifting of the transmission into a different gear) and/or extensive damage to the clutch and/or to other constituents of the power train. Heretofore known attempts to overcome the above outlined problems have met with no success or with limited success.

On the other hand, motor vehicles embodying automated (actuator operated) clutches have gained widespread acceptance in the industry. Such vehicles are preferred by many motorists, not only due to their increased comfort but also because the utilization of automated clutches entails substantial savings in fuel.

OBJECTS OF THE INVENTION

An object of the present invention is to provide a novel and improved power train for use in motor vehicles.

Another object of the invention is to provide a power train which affords pronounced comfort to the occupant(s) of the vehicle and can be operated satisfactorily for long periods of time with substantial savings in fuel.

A further object of this invention is to provide a novel and improved operative connection between the control unit and the clutch in a power train which employs an actuator-operated friction clutch.

An additional object of the invention is to reduce the likelihood of damage to the power train of a motor vehicle as a result of undesirable changes of reference positions of an actuator-operated friction clutch due to axial shifts between the input and output shafts of the clutch.

Still another object of the instant invention is to provide a novel and improved method of compensating for axial shifting of at least one of the input and output shafts of an automatic clutch relative to the other shaft.

A further object of our invention is to provide a novel and improved control unit for the arrangement which controls the actuator for the clutch in the power train of a motor vehicle.

Another object of the invention is to provide a novel and improved fluid-operated connection between the control circuit and the actuator for the friction clutch in the power train of a motor vehicle.

An additional object of the invention is to provide a novel array of sensors for the transmission of signals to the control unit which operates the actuator for the automatic clutch in the power train of a motor vehicle.

SUMMARY OF THE INVENTION

One feature of the present invention resides in the provision of a method of ascertaining and regulating shifts of reference position of an actuator-operated clutch in the power train of a motor vehicle wherein the shifts are caused by axial displacements of at least one of the input and output shafts of the clutch relative to the other shaft. The improved method comprises a first step of routinely ascertaining the reference position of the clutch, a second step of routinely memorizing and thus actualizing information pertaining to the ascertained reference position, a third step of determining operational parameters which initiate shifts of reference position of the clutch, and a fourth step of conforming the first and second steps to the shifted reference position when the determined operational parameter exceeds a predetermined threshold value.

The method can further comprise the steps of continuing to memorize and actualize, in the course of and subsequent to the fourth step, that information which is obtained in the second step, ascertaining and memorizan emergency reference position while the determined operational parameter is in the process of exceeding the predetermined threshold value, and regulating the actuator for the clutch as a function of the emergency reference position.

If the method is resorted to in order to ascertain and regulate shifts of reference position of an actuator-operated clutch in the power train of a motor vehicle in which the output shaft of the clutch is the torque-transmitting input shaft of a change-speed transmission, the third step can include determining the torque which is being transmitted by the output shaft of the clutch.

The method can further comprise the step of establishing a hydraulic force transmitting path between the actuator and the clutch. The first step of such method can include a snifting operation and the first and second steps can be carried out at regular intervals as long as the operational parameter is below the predetermined threshold value. Such method can comprise the additional step of carrying out at least one emergency snifting operation to thus ascertain an emergency engagement condition of the clutch when the operational parameter exceeds the predetermined threshold value. The third step of the just discussed modified method can include determining the torque which is being transmitted by the output shaft of the clutch, and such method can include the additional steps of (a) ascertaining and memorizing an emergency reference position while the determined operational parameter is in the process of exceeding the predetermined threshold value and (b) setting the engagement stage of the clutch to coincide with the emergency reference position when the torque decreases below the predetermined threshold value. Such method can further comprise the additional steps of memorizing at least one torque being transmitted by the output shaft of the clutch while the determined operational parameter is below the predetermined threshold value and reactivating the memorized at least one torque upon renewed drop of the torque below the predetermined threshold value.

Another feature of the present invention resides in the provision of an arrangement for regulating the shift of a reference position of an actuator-operated torque-transmitting clutch in the power train of a motor vehicle wherein the shift is caused by axial movements of at least one of an input shaft of the clutch and an output shaft of the clutch relative to the other shaft. The improved arrangement comprises a connection between a mobile multiple-position force-transmitting operating member (such as a piston in a master cylinder of the actuator) and a displaceable clutch setting member (e.g., a pivotable lever which can change the condition of a diaphragm spring in the clutch); a control unit for the actuator; a plurality of signal-transmitting monitoring devices which are operatively connected with the control unit and include a sensor arranged to transmit to the control unit signals denoting the positions of the operating member; means for ascertaining the force being transmitted by the operating member to displace the setting member; and means for monitoring the torque being transmitted by the clutch. The control unit is arranged to routinely ascertain the reference position of the clutch, to routinely memorize and to thus actualize information pertaining to the ascertained reference position, to determine operational parameters which initiate shifts of reference position of the clutch, and to conform the reference position and the memorized information to the shifted reference position when the determined operational parameter exceeds a predetermined threshold value.

The output shaft of the clutch can constitute the input shaft of a change-speed transmission in the power train of the motor vehicle.

The aforementioned connection can comprise a hydraulic system between a mobile motor-operated member (such as a piston rod for the aforementioned piston)and a clutch-operating member (such as a piston rod for the aforementioned lever) of the actuator.

The hydraulic system can further include a master cylinder which reciprocably receives the aforementioned piston and exhibits a snifting orifice adjacent a path for the piston. The aforementioned motor for the mobile member can be arranged to move the piston relative to the orifice; such motor can include or constitute a stepping motor.

The aforementioned sensor can include means for transmitting to the control unit signals denoting the position of the motor-operated member relative to the orifice.

The clutch can constitute a friction clutch, and the power train can further comprise an internal combustion engine having a rotary output member (such as a crankshaft) which is connected with the input shaft of the clutch.

The control unit can include at least one memory for signals from the monitoring devices, and such at least one memory can include means for storing regularly transmitted signals which are generated by the monitoring devices and signals generated by at least one of the monitoring devices under special circumstances of operation of the clutch.

The novel features which are considered as characteristic of the invention are set for in particular in the appended claims. The improved arrangement itself, however, both as to its construction and the modes of assembling, installing and operating the same, together with numerous additional important and advantageous features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1illustrates certain relevant component parts of a power train in a motor vehicle wherein the power train employs an automated friction clutch4arranged to transmit torque between a prime mover2(such as an internal combustion engine) and a change-speed transmission or gearing6. The output shaft8of the transmission6is arranged to transmit torque to the driven wheels (not shown) of the motor vehicle, e.g., by way of a customary differential. The transmission6can constitute a manually shiftable automated gearing. The reference character9denotes a transmission actuating device which can cause a gear selector10to shift the transmission6into a selected one of several gears including those denoted by the reference characters P, R, N, D,2and1. The gear selector10includes a customary lever12which can be actuated by hand in a well known manner. The position of the lever12is monitored by a sensor26which transmits signals to the corresponding input of a control unit14; the latter has several outputs one of which is connected to the transmission actuating device9.

The clutch4can constitute a standard component having a clutch disc which operates between an input shaft17adapted to receive torque from the output shaft (such as a crankshaft) of the prime mover2and an output shaft18. The latter can transmit torque to the input shaft of the transmission6or can include or constitute such input shaft. The means for actuating the clutch4includes an electric, hydraulic, hydroelectric or other suitable actuator (e.g., a novel and improved actuator16of the type shown inFIG. 2) which is connected to and can receive signals from the corresponding output of the control unit14. The input shaft17can be rigidly connected to the crankshaft of the prime mover2, and (if it is a separately produced part) the output shaft18can be rigidly connected with the input shaft of the transmission6.

In addition to the sensor26, the control unit14receives signals from a plurality of additional monitoring means including a sensor19which monitors the pressure in the suction pipe (not shown) of the prime mover2, an RPM sensor20which ascertains the rotational speed of the crankshaft of the prime mover, a sensor22which ascertains the position (extent of depression) of a gas pedal24, and an RPM sensor28which monitors the rotational speed of the output shaft8of the transmission6.

The control unit14can comprise a standard microprocessor with associated memory or memories29for storage of characteristic fields or programs for the regulation of actuator means such as an actuator30serving to select the load upon the prime mover2, the aforementioned actuator16for the clutch4, the aforesaid actuating device9for the transmission6and, if necessary, one or more additional actuators which is or which are directly or indirectly connected with the corresponding output(s) of the control unit14and serve to operate additional consumers (not shown) which are directly or indirectly operated by the prime mover. The individual actuators can be constructed in such a way that their positions or settings are directly known in the control unit14; alternatively, the power train can comprise additional or discrete position or condition indicators such as a position indicator32for the determination of a parameter which is relevant for the setting or position of the clutch4.

The heretofore described constituents of the power train, as well as the manner in which they cooperate with each other, are known from the field of motor vehicles and, therefore, the exact details of their construction, interconnection and mode of operation will be described in detail only to the extent which is necessary for adequate comprehension of the present invention. It is to be understood that the illustrated power train is but one of numerous arrangements which can embody the present invention. By way of example only, the aforedescribed clutch4and/or the aforedescribed transmission6can be replaced with any one of numerous other types of clutches and/or transmissions without departing from the spirit of the present invention.

The memory29of the control unit14preferably stores a characteristic curve which establishes a desired or required setting of the clutch4, as selected by the actuator16, in dependency upon the magnitude of torque to be transmitted by the clutch. In order to enhance the quality of regulation, to reduce the extent of wear upon the clutch4and/or to reduce the energy consumption of the actuator16, the transmittable clutch torque should not exceed the absolutely necessary minimum value. Such minimum value is dependent upon the desire of the operator of the motor vehicle (such as the operator-selected position of the gas pedal24) as well as, for example, upon the load being ascertained by the sensor31for the prime mover2and, if desired or necessary, one or more additional parameters such as the signals from the sensor20denoting the RPM of the crankshaft of the prime mover2.

The characteristic curve which is stored in the control unit14and which determines the desired position of an operating member54(here shown as a pivotable lever, seeFIG. 2) of the actuator16as a function of the ascertained torque to be transmitted to the input shaft of the transmission6, exerts the greatest influence upon the comfort of starting the motor vehicle as well as upon the ease of carrying out the gear shifting operatons. Such characteristic curve undergoes (a) short-lasting changes, for example, as a result of changes of temperature; and (b) long-lasting changes during the life of the clutch4, e.g., as a result of wear. This is the reason that the characteristic curve is continuously actualized (adjusted or updated) in accordance with different strategies whenever the sensors of the power train ascertain the presence of predetermined operating conditions.

FIG. 2illustrates the details of a presently preferred fuid-operated (hydraulic) actuator16for the clutch4. This actuator comprises a liquid-filled master cylinder36containing a reciprocable piston38connected with a piston rod40which extends from the master cylinder and has external gear teeth mating with those of an internal gear41. The latter further meshes with the external teeth of a driver pinion42on the output shaft of an electric motor43. This motor is operated by signals being transmitted by the corresponding output of the control unit14. For example, the electric motor43can be of the type adapted to be operated by PWM (pulse width modulation) signals. A presently preferred motor43is a stepping motor.

The master cylinder36is provided with a snifting or equalizing orifice44which is connected with a liquid storage vessel (not shown) by way of a hydraulic line or conduit45. Reference may be had, for example, toFIG. 1Bof commonly owned U.S. Pat. No. 5,632,706 granted May 27, 1997 to Kremmling et al. for “MOTOR VEHICLE WITH ELECTRONIC CLUTCH MANAGEMENT SYSTEM”. The plenum chamber46of the master cylinder36is connected with the plenum chamber of a slave cylinder50by a hydraulic conduit48, and the piston52of the slave cylinder is articulately connected to the aforesaid clutch disengaging lever54, e.g., a lever which can act upon the customary diaphragm spring of the clutch4by way of a release bearing or the like. A friction clutch which can be operated by a release bearing or an equivalent clutch engaging/disengaging arrangement is disclosed, for example, in commonly owned U.S. Pat. No. 5,409,091 granted Apr. 25, 1995 to Reik et al. for “AUTOMATICALLY ADJUSTABLE FRICTION CLUTCH”.

The location A, which is known as the snifting location, determines that position of the piston38which the latter assumes on its way toward pressurizing of hydraulic fluid in the plenum chamber46of the master cylinder36. At such time, the chamber46is sealed from the adjacent end of the conduit45and from the liquid-containing vessel which is in communication with the other end of this conduit. The pressure of fluid in the plenum chamber46is communicated to that in the slave cylinder50and causes the piston52to change the position of the clutch operating member or lever54.

The aforementioned sensor32(shown inFIGS. 1 and 2) is an incremental position indicator which serves to furnish signals denoting the axial position of that component of the actuator16that includes the piston rod40and piston38of the slave cylinder36. The sensor32can monitor the axial position of the internal gear41which, as already explained hereinbefore, can mate with external teeth of the exposed end of the piston rod40. The exact construction of the sensor32forms no part of the present invention; it suffices to say that this sensor monitors the axial positions of the parts38,40and thus indicates the position of the piston38relative to the location A and the snifting or equalizing orifice44. The indicator32can be arranged to count the number of gear teeth on the piston rod40, while the latter moves relative to the slave cylinder36, and to thus ascertain the distance which is covered by the piston38relative to the slave cylinder. Signals or impulses which are generated by the indicator or sensor32are transmitted to the corresponding input of the control unit14. The number of such impulses can be a direct indication of the extent of axial displacement of the piston38in the slave cylinder36of FIG.2. Furthermore, and if the piston38is located to the right of the location or position A shown inFIG. 2, the characteristics of signals from the sensor or indicator32are directly proportional to (i.e., indicative of) the angular position of the clutch operating lever54and hence of the extent of engagement of the clutch4.

The piston38of the slave cylinder36is or can be combined or associated or made integral with a check valve (not shown inFIGS. 1 and 2) which opens when the pressure of hydraulic fluid in the left-hand portion of the slave cylinder (i.e., at the left-hand side of the piston38, as viewed inFIG. 2) rises to a predetermined value. This causes the piston38to advance in a direction to the left and beyond the snifting position A. Consequently, the fluid-containing space between the pistons38,52is free to communicate with the conduit45and the fluid in such space is not pressurized. This enables the lever54to assume a position in which the clutch4is fully engaged.

If the control unit14thereupon transmits to the motor43a signal which causes the latter to initiate a rightward movement of the piston rod40, the fluid in the slave cylinder50causes the respective piston52to pivot the lever54as soon as the piston38advances to the position A. Such position of the piston38can be ascertained, for example, in that the energy consumption of the motor43increases. That one (A) of its positions in which the piston38overlies the snifting orifice at A is memorized in the control unit14(at29) by memorizing the number of gear teeth which are counted at32and such position of this sensor corresponds to the engaged or operative condition of the clutch4.

In addition to knowing the engaged or closed condition or position of the clutch4, it is also necessary to ascertain at least one other position or condition of the clutch, e.g., that condition in which the clutch transmits or is set to transmit a torque of 4 Nm. Knowledge of the fully engaged condition of the clutch4is necessary because it plays an important role during starting of the motor vehicle as well as during shifting of the transmission6into different gears. The input and output shafts17,18of the clutch4are fully separated from each other only when the clutch is disengaged or opened beyond the position of engagement. Furthermore, a comfortable shifting of the transmission6into a different gear or a shifting without endangering the transmission is possible only if the aforementioned prerequisites are fully met. Moreover, the motor vehicle exhibits a pronounced creeping action if the clutch is not fully disengaged for starting and/or for shifting of the transmission into a different gear.

The condition of engagement of a clutch is normally selected in that, in certain conditions of the power train (for example, when the motor vehicle is at a standstill, the operator applies the brake and the transmission is in gear), the clutch is fully disengaged and is thereupon slowly engaged while one measures the engine torque. When, during gradual engagement of the clutch, the engine torque (which, for one, is given with engine idling regulation by the position of an adjusting member for the idling regulation) reaches a predetermined value, the information furnished by the incremental position indicating (distance monitoring) sensor32is ascertained and the corresponding information is memorized as the engagement position or condition of the clutch. This renders it possible to rapidly reach such condition of engagement and to utilize it as an orientation value for the carrying out of the starting or for a shifting into different gears. An adaptation or actualization of the condition of engagement takes up about 5 seconds and is normally carried out at least once during each drive of the motor vehicle.

Individual points of the distance-torque curve of the clutch4which curve is memorized in the control unit14can be actualized in a similar fashion in that one ascertains the clutch torque and the corresponding position of the position indicating sensor32is read and memorized as an actualized new position. The torque being transmitted by the clutch4while the latter is still operated with slip is ascertained by determining the torque of the prime mover2by taking into consideration the change of its RPM and the moment of inertia. In this manner, the characteristic curve of the clutch, which furnishes the transmittable torque in dependency upon the position of the clutch actuating lever54of the actuator16, can be ascertained in a point-by-point fashion. An adaptation of the characteristic curve of the clutch is required due to changes of friction value.

The scanning and engagement positions of the clutch4and/or of the clutch actuating lever54, which are indicative of the torque being transmitted by the clutch as a function of the position of the lever54, are of maximum importance for a rapid, proper and comfortable actuation of the clutch. In order to ensure that such positions can be determined independently of the changes of the hydraulic path in46and48, it would be necessary to carry out routinely a series of snifting operations so that the snifting positions and the corresponding readings of the counter could furnish a reliable reference value.

A problem concerning the actual and accurate monitoring of information pertaining to the closed position, position of engagement and the positions of transmission of a predetermined torque is attributable to the following: The position of the lever54when the clutch4is fully engaged is the same as the snifting position of the piston38which latter can be read directly into the control unit14by way of the sensor32. This basic reference position of the clutch4is continuously actualized (updated), for example, each 60 seconds while the clutch is fully engaged and, therefore, is actually available in a continuous manner. Any changes of the geometry of the hydraulic path which is established by the parts46,48(e.g., due to temperature changes) are thus compensated for, the same as eventual leakages of the hydraulic system.

Actual changes of the clutch4itself, such as those attributable to wear, are relatively slow to develop so that an adaption of the condition of engagement or of those positions of the clutch actuating lever54(namely the characteristic curve of the clutch) which correspond to predetermined or selected torques being transmitted by the clutch are necessary at infrequent intervals.

If the transmission6is to transmit pronounced torque, its input shaft (such as the output shaft18of the clutch4) is likely to move axially owing to the obliqueness of teeth of helical gears which are connected therewith (the extent of such axial displacement can be in the range of one or more millimeters). This causes an axial shifting of the clutch disc between the shafts17,18and entails a shifting of the partial and full engagement positions of the clutch4and of the therein oriented characteristic curve of the clutch. This, in turn, results in discomfort to the occupant(s) of the motor vehicle during starting as well as during shifting of the transmission6into a different gear because the actuation of the clutch takes place with reference positions which were actualized and memorized while the input shaft of the transmission was called upon to transmit a high torque and such high torque no longer exists.

As already stated hereinbefore, an important object of the present invention is to overcome the just discussed problems which arise in conventional power trains.

In accordance with a feature of the invention, the aforediscussed problems are overcome by a method which renders it possible to avoid those shifts of reference positions which are caused by axial displacements between the input shaft and the output shaft of a clutch which is installed in the power train of a motor vehicle and is operated by an actuator. In accordance with the novel method, the reference position is ascertained in routine fashion and the results of such ascertainment are memorized (stored) and thus actualized. An operational parameter which leads to an axial shifting of the input and output shafts of the clutch is ascertained and the routine ascertainment and memorizing of the reference position are altered when the operational parameter exceeds a predetermined threshold value.

For example, a routine ascertainment can be fully dispensed with when the operational parameter exceeds the predetermined threshold value, or it can be considered in a manner different than when the operational parameter is below the predetermined threshold value.

It is of advantage if, when the threshold value is exceeded, the previously actualized reference position remains memorized while the threshold value is being exceeded so that, when the threshold value drops below the predetermined value, the memorized reference value is again available. It is also of advantage if, while the threshold value is being exceeded, one ascertains and memorizes an emergency reference position and, when the threshold value is exceeded, the operation of the actuator is regulated as a function of such emergency reference position.

The novel method can be practiced in connection with all clutches wherein axial shifting between the input and output shafts of the clutch takes place in dependency upon at least one operational parameter, namely or such as an axial shifting which entails a shifting of reference positions.

The method can be resorted to with advantage when the output shaft of the clutch constitutes the input shaft of the transmission in the power train of the motor vehicle (wherein the clutch is located immediately ahead of the transmission, as seen in the direction of transmission of torque from the prime mover to the wheels) and the operational parameter is the torque which is being transmitted by the input shaft of the transmission. In the embodiment ofFIG. 1, torque which is being transmitted by the input shaft of the transmission6corresponds to that which is being transmitted by the prime mover2provided, of course, that the clutch4is fully engaged.

Furthermore, the novel method is preferably resorted to when the clutch4and the actuator16are connected to each other by a hydraulic arrangement (46,48) and the reference position (such as that corresponding to the fully engaged condition of the clutch) is ascertained by resorting to a snifting operation (at A).

In accordance with a further presently preferred embodiment, the improved method is carried out in such a way that, if the torque acting upon the input shaft of the transmission is below a predetermined threshold value, a shifting operation is carried out at predetermined intervals, for example, every 60 seconds or, when the transmission is in neutral and the clutch is engaged, every 180 seconds. Such snifting operation is performed in order to ascertain and actualize the normal closed or engaged condition of the clutch4. If the torque is above the predetermined threshold value, at least one emergency snifting operation is carried out in order to ascertain the emergency engaged condition of the clutch, and the actuator16is operated in accordance therewith while the torque is above the threshold value.

It is of additional advantage if the actual engagement condition of the clutch is set to match the condition prior to exceeding the threshold value if the torque decreases below the predetermined threshold value.

Still further, it is preferred to memorize at least one torque (and the corresponding position) which can be transmitted by the clutch when the torque being transmitted by the clutch is below the predetermined value and to reactivate when the torque drops below the predetermined value.

The illustrated arrangement for avoiding or preventing, as a result of axial shifting between the input and output shafts of a clutch, shifts of reference positions of a clutch4which is operated by an actuator16comprises a hydraulic device46,48between the piston38and the lever54, the control unit14for the actuator16, sensors (19,20, etc.) which are operatively connected with the control unit14and include at least one distance monitoring sensor (such as32) which ascertains the position of the member54of the actuator16, an arrangement for ascertaining the force being applied by the clutch actuator16to move the member54, and an arrangement for ascertaining the torque being transmitted by the clutch4. The control unit14is designed to carry out at least one of the aforediscussed embodiments of the improved method.

The following is an example of practicing the improved method by resorting to the improved apparatus. This example will be described with reference to the flow chart or flow diagram ofFIG. 3wherein the step100includes ascertaining whether or not the torque being applied to the output shaft18of the clutch4(i.e., to the input shaft of the transmission) is below a threshold value GW. If the torque being applied to the output shaft18is below the threshold value GW, the step102includes an actualization of the snifting position (closing position) SP in that the arrangement which is shown inFIG. 2or an equivalent thereof performs a snifting operation and that position of the piston38which the latter assumes during movement past the snifting orifice44is memorized as a count furnished to the control unit14by the sensor32. A snifting operation renders it possible to ensure that the snifting position actually corresponds to that position of the actuating arrangement38,40which is indicative of the fully engaged position or condition of the clutch4. This, in turn, ensures that the snifting operation does not alter that setting of the counter which corresponds to the fully engaged condition of the clutch4.

The step104ofFIG. 3is carried out in order to ascertain whether or not the information furnished by a counter Z1of snifting operations (this information exceeds by one that which was obtained during the preceding actualization of the closing position) exceeds a predetermined value n1. If such is not the case, the system reverts back to the step100. If the value n1is exceeded, i.e., if a snifting operation was carried out n1times, the next step106is carried out to actualize and memorize the position of engagement (GP) in the aforedescribed manner.

The next step108involves a determination whether or not a counter Z2(the setting of which is raised by one after each actualization) has reached the setting n2. If such is not the case, the system reverts to the step100. However, if such is the case, the next step110involves an actualization of a position RP of the clutch4; such position corresponds to the transmission of the then applied torque and is characteristic of the actual friction value of the clutch. The system reverts back to the step100. In this manner, the control unit14memorizes actual counter readings, namely those which correspond to the reference position of the clutch4and are thus ready to be utilized. It will be appreciated that the snifting (i.e., the actualizing of the engaged position as well as the actualization of the gripping position and friction value) can be carried out in a different, logical, pulse sequence so that the durations of pulses and the counter stands or the counter switchings can be selected accordingly.

If the carrying out of the step100results in a determination that the torque is above the threshold value GW, the step112is carried out to perform an emergency snifting operation (NSP) which involves conforming the hydraulic path to an altered clutch engaging position of the lever54. The steps114,116,118and120are thereafter carried out in correspondence with the respective steps104,106,108,110but the counter readings, timing intervals and switchings, etc. can be different. The memory or memories29of the control unit14can be different. In this manner, the memory or memories29of the control unit memorizes or memorize an actual emergency engagement position (NGP) and an emergency friction value (NRP) of clutch4, namely a value corresponding to that operation of the clutch when the input shaft of the transmission6transmits high torque.

If the torque at 100 drops below the predetermined threshold value GW, the apparatus immediately carries out a snifting operation and proceeds with the last actualized values GP and RP.

It will be seen that the improved method involves a change of the normally progressing actualization routine whenever the engine torque GW is exceeded.

However, and in order to correct, during a long trip of the motor vehicle at an elevated load, the expansion effects of the hydraulic path, the apparatus carries out emergency snifting operations at intervals which, for example, are much longer than the intervals of normal cyclical snifting. Those emergency positions which are ascertained during the steps116and120can remain memorized so that they are immediately preferentially available at elevated torques following an emergency snifting operation.

The actualizations can progress in their entirety or with limitations.

To summarize:

(a) the actual friction value of the clutch4is memorized;

(b) the long-range snifting point is no longer adapted;

(c) the friction value adaptation as well as the adaptation of the short-lasting and medium-length scanning point continue to proceed; and

(d) as soon as a snifting operation takes place below the threshold value GW, the actual friction value is set and the adaptions of the long-range scanning point are again permissible.

If the torque of the power train drops below the threshold value GW, a snifting operation is carried out as long as the conditions which are required therefor (the clutch must be fully engaged) exist. The next operation involves the customary snifting cycle with additional actualizations.

Referring again toFIG. 3, the term GW is intended to denote that threshold value of the extent of engagement of the clutch4(between its fully engaged and fully disengaged positions or conditions) at which the friction linings of the clutch disc come in contact with the pressure plate and/or with the counterpressure plate of the clutch so that the clutch begins to transmit torque. The term SP denotes that position or condition of the clutch in which the latter transmits torque without slip. The term “reference position” (RP) denotes that specific position or condition which the clutch assumes when it is calibrated, preferably when the clutch is fully disengaged.

The disclosures of the patents which are identified in this specification are incorporated herein by reference.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of the above outlined contribution to the art of operating friction clutches in the power trains of motor vehicles and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the appended claims.