WO2009132853A1

WO2009132853A1 - Calibrating method for a clutch unit and torque transmission device

Info

Publication number: WO2009132853A1
Application number: PCT/EP2009/003148
Authority: WO
Inventors: Martin Kiessner-Haiden; Bernhard Feier; Jürgen SCHRANZ
Original assignee: Magna Powertrain Ag & Co Kg
Priority date: 2008-04-30
Filing date: 2009-04-30
Publication date: 2009-11-05
Also published as: DE102008021686A1; DE102008021686B4

Abstract

The invention relates to a clutch unit for a drive train of a motor vehicle, comprising a friction clutch for the controlled transmission of a torque from an input element to an output element, and an actuator for actuating the friction clutch. In order to calibrate the clutch unit, a degree of wear of the clutch unit is determined, and a calibrating run of the clutch unit is initiated as a function of the degree of wear determined.

Description

Calibration method for a coupling unit and torque transmission device

The invention relates to a method for calibrating a clutch unit for a drive train of a motor vehicle, wherein the clutch unit has at least one friction clutch for controllably transmitting a torque from an input element to an output element and an actuator for actuating the friction clutch. The invention further relates to a torque transmission arrangement comprising an input element, an output element, a control device and a coupling unit of the aforementioned type.

Such a coupling unit is used for example in a transfer case of a motor vehicle with four-wheel drive for controllably transmitting a driving torque to a primary axis and / or a secondary axis of the motor vehicle. In a so-called "torque on demand" - transfer case, the wheels of the primary axis are permanently driven, while by means of said coupling unit, a part of the drive torque can be optionally transmitted to the wheels of the secondary axis. The transfer case may also be formed as a controllable center differential, wherein the coupling unit is associated with a differential lock to adjust the distribution of the drive torque in the longitudinal direction of the vehicle. A coupling unit of the type mentioned can also be used in a torque transmission arrangement which, in a motor vehicle with a permanently driven front axle, transmits part of the drive torque to the rear axle. axle allowed, wherein the unit is arranged, for example, on the front axle or the rear differential. Such different applications and arrangements are known from US Pat. No. 7,111,716 B2.

A coupling unit of the type mentioned above can also act in the transverse direction of the motor vehicle, for example for a differential lock of an axle differential or in a Drehmomentüberlagerungs- arrangement of an axle differential (so-called "torque vectoring"). In all of the foregoing cases, the clutch unit may frictionally interconnect a rotating input member (e.g., input shaft) and a rotating output member (e.g., output shaft), particularly to transmit a drive torque. Alternatively, the clutch unit may be configured as a brake, with a fixed input member or a fixed output member, in particular to transmit a braking torque.

In the aforementioned applications of the clutch unit, the clutch unit is positioned behind the main transmission of the powertrain (ie, behind the manual or automatic transmission or CVT transmission) with respect to the direction of power flow. The clutch torque - that is, the torque transmitted by the friction clutch - is usually set variably depending on the particular driving situation. Depending on the driving dynamics requirements, which may depend, for example, on the driving situation or environmental influences (eg smooth road surface with occurring slip of the drive wheels), there is thus a change in the torque to be transmitted by the clutch unit. For this purpose, not only a controlled engagement of the friction clutch is required, but often a longer operation with precisely adjusted clutch torque. The coupling unit comprises a friction clutch and an actuator for actuating the friction clutch. The friction clutch is typically a multi-plate clutch, ie a multi-plate clutch. The actuator may include an electric motor. In addition, the actuator may comprise a transmission device for translating a rotational movement of a motor shaft of the electric motor into slow motion. In addition, the actuator may have a deflection device, which deflects a rotational movement of the actuator (eg motor shaft or gear element) into a translational movement of the friction clutch (eg contact pressure piston). Alternatively, however, it is also possible to provide, for example, an electromagnetic, a hydraulic or an electrohydraulic actuator.

A coupling unit of the aforementioned type and a method for calibrating such a coupling unit are known from WO 2003/025422 A1 (corresponding to US Pat. No. 7,032,733 B2), the content of which is expressly included in the disclosure content of the present application. As described in more detail in WO 2003/025422 Al, a direct torque control does not necessarily have to be provided for setting a specific desired clutch torque (with the measured actual clutch torque as controlled variable). But as a result of a corresponding calibration of the coupling unit, the control of the friction clutch can take place via a position control of the actuator. To set the desired torque to be transmitted so, for example, the rotation angle of the electric motor or other position size of the actuator is used as a control variable and set to a value corresponding to the desired clutch torque. For this purpose, a clutch torque / actuator position dependence is determined empirically, which is stored as a characteristic, for example in the form of a table (look up table, LUT) or a function (that is, a calculation rule). Based This dependence is thus determined and adjusted for a specific torque request, the corresponding desired value of the respective position size of the actuator (eg rotation angle). This characteristic (clutch torque / actuator position dependency) can be determined for each individual clutch unit or torque transmission assembly at the factory (end of line) as a so-called initial calibration.

However, due to wear within the clutch unit, the characteristic curve mentioned may change, which must be taken into account when setting a desired clutch torque. Therefore, the characteristic should be adjusted at certain intervals, which is referred to as recalibration in the context of the present invention. For example, a calibration run of the clutch unit can be carried out after each shutdown of the vehicle engine, ie if a control unit associated with the clutch unit receives an "ignition off" signal For example, the electric motor of the clutch unit is driven so that the friction clutch is fully engaged, which corresponds to the maximum clutch torque, and full engagement of the friction clutch results in a detectable increase in the motor current In this calibration position, the actuator position (eg angle of rotation) is measured, and the thus determined clutch torque / actuator position value pair serves as a calibration point for di e recalibration. Alternatively or additionally, a calibration point can be determined, for example, for a complete disengagement of the friction clutch (corresponding to a clutch torque zero). The respective actuator position thus measured is compared with the actuator position measured for the corresponding calibration position of the coupling unit during a previous calibration run (initial calibration or previous recalibration). Depending on the difference between these two measured actuator positions, the clutch characteristic is adjusted, for example by determining and taking into account at least one corresponding correction value (eg offset and / or slope). As a result of each calibration run, such a correction value can be stored so that the correct actuator position setpoint for the currently desired clutch torque can be determined in the subsequent operation of the clutch unit based on the original characteristic using the last determined correction value. However, it is also possible for the clutch characteristic curve to be updated and stored in accordance with the determined correction value, so that during operation of the clutch unit the most recently updated clutch torque / actuator position dependency can be used directly for setting the torque to be transmitted. Preferably, a plurality of calibration points are determined and taken into account during the recalibration in order to bring about a most accurate adaptation of the characteristic curve.

It is an object of the invention to allow a recalibration of a coupling unit of the type described above without unduly stressing the coupling unit as a result.

This object is achieved by a calibration method having the features of claim 1, and in particular by the following steps: determining a state of wear of the coupling unit; and Triggering a calibration run of the coupling unit as a function of the determined state of wear.

In the context of the invention it has been recognized that the recalibration itself can lead to an excessive stress on the coupling unit and thus ultimately to a deterioration of the long-term positioning accuracy of the coupling unit. Apart from the energy expenditure required for a recalibration and the associated load on the electrical system of the motor vehicle, any recalibration of the coupling unit also means an undesired component load, in particular a mechanical component load -for example. on the gear parts of the actuator -, and / or an electrical component load - e.g. on the winding of the electric motor -. This is especially true when a calibration point for the recalibration is generated by fully engaging the friction clutch so that due to the juxtaposition of the clutch plates, the torque applied by the electric motor increases significantly, so that the motor current increases significantly and correspondingly increased torques or forces along the actuator chain (Eg transmission device, deflection) must be transmitted.

According to the invention, recalibrations which are carried out unnecessarily frequently are avoided by determining a state of wear of the coupling unit and triggering a recalibration of the coupling unit as a function of the determined state of wear of the coupling unit. Determining the state of wear of the coupling unit can be carried out regularly, for example due to the exceeding of a predetermined distance, which has covered the motor vehicle since the last determination of the state of wear, or in principle after each shutdown of the vehicle engine ("ignition off" signal). This will takes into account that only a negligible amount of clutch wear may have occurred during a drive of the vehicle, so that a recalibration - despite the receipt of an "ignition off" - signal - is not required at all. Unnecessary calibration and the associated mechanical and electrical loads on the clutch unit are thereby avoided, and the vehicle battery is not unnecessarily burdened.

The determination of the state of wear of the coupling unit can be determined in a simple manner on the basis of the driving state data which is normally present anyway in the motor vehicle, without necessarily requiring an additional sensor system. Since the wear of the clutch unit occurs predominantly on the disks of the friction clutch, an estimate of the state of wear can be carried out in a simple manner by taking into account at least the clutch work introduced into the friction clutch. Other criteria can also be taken into account.

In particular, it is possible for a time integral to be formed via the coupling power during operation of the coupling unit. For example, the clutch performance may be determined as a product of the clutch torque and the speed difference between the input member and the output member of the friction clutch (eg, clutch hub and clutch basket). The said clutch torque can be equated, for example, with a torque request which receives the control unit associated with the clutch unit from a superordinate control unit as reference variable (setpoint value). Alternatively, the said clutch torque may be a calculated torque transmitted by the friction clutch or a measured torque transmitted by the friction clutch. your. Said speed difference can be determined in a simple manner from the signals of the wheel speed sensors, which are usually present anyway, possibly taking into account the transmission ratios present in the drive train.

The explained determination of the state of wear of the coupling unit preferably relates to a change with respect to the state of wear of the coupling unit at the time of the last calibration of the coupling unit. In particular, the aforementioned time integral can be formed from the last recalibration of the coupling unit.

For consideration of the coupling work or the coupling performance, a distinction can also be made according to different load situations or load ranges.

For example, it can be differentiated by using different weighting factors, whether the friction clutch is operated at a high speed difference with a low clutch torque or at a low speed difference with a high clutch torque.

The respective relationship between clutch work or clutch performance on the one hand and clutch wear on the other hand can be determined empirically and then stored permanently in the control unit associated with the clutch unit.

With regard to the triggering of a recalibration, it is preferred that this only takes place when the determined state of wear of the coupling unit reaches or exceeds a predetermined threshold value. However, optional additional conditions may be provided to trigger a recalibration. For example, it can be provided that a recalibration is only triggered when - in addition to the achievement of a certain state of wear - the vehicle has traveled a predetermined distance since the last recalibration.

It is also possible, as an option, to consider other adequate criteria for triggering a recalibration. In other words, it can be provided that a recalibration is already triggered when the vehicle has traveled a predetermined distance since the last recalibration, even if the determined state of wear of the coupling unit is still low and in particular still falls below the aforementioned threshold.

The invention also relates to a torque transmission arrangement having an input element, an output element, a coupling unit of the type described above and a control device, wherein the control device is designed to determine a state of wear of the coupling unit and, depending on the determined state of wear, a recalibration of the Trigger coupling unit.

The coupling unit or torque transmission arrangement according to the invention can be used in different arrangements in order to transmit torque along a drive train of a motor vehicle, as explained in the introduction. The invention will now be described, by way of example only, with reference to the drawings in connection with a "torque on demand" transfer case. Fig. 1 shows a schematic view of a drive train of a motor vehicle.

Fig. 2 shows a schematic view of a transfer case.

FIG. 3 shows a cross-sectional view of the transfer case according to FIG. 2.

4 shows a schematic view of a clutch actuator.

5 shows a flowchart of a calibration method.

Fig. 1 shows schematically a drive train of a motor vehicle with shiftable four-wheel drive. The drive torque generated by an internal combustion engine 1 1 is supplied via a main gear 13 (manual transmission or automatic transmission) to a transfer case 15. A first output of the transfer case 15 is coupled via a propeller shaft 17 with a Hin terachs differential gear 19 coupled. As a result, the wheels 21 of the rear axle 23 are permanently driven. The rear axle 23 thus forms the primary axis of the vehicle. A second output of the transfer case 15 is coupled via a propeller shaft 25 to a front-axle differential 27. In this way, a part of the drive torque of the internal combustion engine 11 can be optionally transmitted to the wheels 29 of the front axle 31. The front axle 31 thus forms the secondary axle of the vehicle. Furthermore, a driving dynamics control unit 33 is shown in FIG. This is connected to wheel speed sensors 35, 37 which are associated with the wheels 21 of the rear axle 23 and the wheels 29 of the front axle 31. The vehicle dynamics control unit 33 is also connected to other sensors 39, for example a yaw rate sensor. Depending on the signals from the sensors 35, 37, 39, the vehicle dynamics control unit 33 generates a control signal which is fed to a transfer device 15 (not shown in FIG. 1) of the transfer case 15, thereby providing a certain distribution of drive torque between the two Set axles 23, 31 of the vehicle. The aforementioned control signal is, in particular, a nominal value of a clutch torque, ie a torque request for a clutch unit of the transfer case 15.

The transfer case 15 has an input shaft 41, a first output shaft 43 and a second output shaft 45. The first output shaft 43 is coaxial with the input shaft 41 and rotatably with this - preferably in one piece - educated. The second output shaft 45 is arranged offset parallel to the input shaft 41.

The transfer case 15 has a clutch unit 47 with a friction clutch 49 and an actuator 51. The friction clutch 49 has a clutch cage 53 which is non-rotatably connected to the input shaft 41 and the first output shaft 43 and carries a plurality of clutch plates. Further, the friction clutch 49 has a rotatably mounted clutch hub 55, which also carries a plurality of clutch plates, which engage in an alternating arrangement in the slats of the clutch basket 53. The clutch hub 55 is rotatably connected to a drive gear 57 of a chain drive 59. An output tooth wheel 61 of the chain drive 59 is rotatably connected to the second output shaft 45. Instead of the chain drive 59, a gear drive may be provided, for example with an intermediate gear between said gears 57, 61.

By actuating the actuator 51 in the direction of engagement of the friction clutch 49, an increasing proportion of the drive torque introduced via the input shaft 41 into the transfer case 15 can be transmitted to the second output shaft 45.

FIG. 3 shows details of the transfer case 15 according to FIG. 2 in a cross-sectional view. In particular, it can be seen that the actuator 51 has a support ring 63 and an adjusting ring 65 which are rotatably mounted with respect to the axis of rotation A of the input shaft 41 and the first output shaft 43. The support ring 63 is axially supported via a thrust bearing on the drive gear 57. The adjusting ring 65, however, is mounted axially displaceable. On the facing sides of the support ring 63 and the adjusting ring 65 each have a plurality of ball grooves 67 and 69th These are with respect to the axis A in the circumferential direction and are ramped with respect to a normal plane to the axis A in the circumferential direction, ie the ball grooves 67, 69 have in the circumferential direction a varying depth. In each case a ball groove 67 of the support ring 63 and a ball groove 69 of the adjusting ring 65 face each other and in this case enclose an associated ball 71. By rotating the support ring 63 and the adjusting ring 65 relative to one another, an axial displacement of the adjusting ring 65 can thus be effected the adjusting ring 65 cooperates via a thrust bearing with a pressure ring 73 of the friction clutch 49. The pressure ring 73 is biased by a plate spring assembly 75 in the disengagement of the friction clutch 49. On the support ring 63 and on the adjusting ring 65, a respective actuating lever 77 and 79 is integrally formed. At the free end of each lever 77, 79 a respective roller 81 and 83 is rotatably mounted. About the rollers 81, 83, the actuating lever 77, 79 cooperate with the two end faces 85, 87 of a control disc 89 which is rotatable relative to an axis C. The end faces 85, 87 have with respect to a normal plane to the axis C a circumferentially inclined course, ie the control disk 89 is wedge-shaped in cross section. By rotating the control disk 89, the actuating lever 77, 79 thus be moved like a scissor to rotate the support ring 63 and the adjusting ring 65 relative to each other. The control disk 89 has an integrally formed plug-in toothed approach 91. Over this, the control disk 89 can be connected to an electric motor and an associated reduction gear drive-effective (not shown in Fig. 3).

Thus, by appropriate control of said electric motor, the control disk 89 are driven to a rotational movement, thereby pivoting the actuating lever 77, 79 relative to each other. The thus caused rotation of the support ring 63 and the adjusting ring 65 relative to each other causes an axial movement of the adjusting ring 65. The pressure ring 73 thus causes engagement of the friction clutch 49 or - supported by the plate spring assembly 75 - a disengagement of the friction clutch 49th

FIG. 4 shows the actuator 51 according to FIGS. 2 and 3 in a schematic view. The actuator 51 has a controllable electric motor 93 with an armature shaft 95, a reduction gear 97 with a worm 99 and a worm wheel 101, and a deflection 103. By means of the deflection 103 is a rotational movement of an output shaft 105 of the reduction gear 97 in a translational, ie linear ge movement of the pressure ring 73 (Fig. 3) implemented. The deflection device 103 includes the control disk 89 and the support ring 63 and the adjusting ring 65 with the operating levers 77, 79 and the balls 71 shown in FIG. 3. At the armature shaft 95 of the electric motor 93, a sensor 107 is arranged, which is formed for example as an incremental encoder , As shown in FIG. 4, the sensor 107 may alternatively also be arranged as a sensor 107 'on the output shaft 105.

The sensor 107 generates a signal that corresponds to an actuator position value. In the exemplary embodiment shown, this is the rotational angle actual value α 'of the armature shaft 95. This signal α' is fed to a control device 109 of the transfer case 15. The control device 109 also receives a torque request M from the vehicle dynamics control unit 33 of the motor vehicle (FIG. 1), that is to say a setpoint value of the clutch torque. From a clutch torque / rotational angle characteristic curve 111 stored in a non-volatile memory 113 of the control device 109, the control device 109 determines a rotational angle desired value α on the basis of the torque request M. In response to the difference between the rotational angle command value α and the rotational angle actual value α ', the control device 109 generates a control signal for the electric motor 93 in order to adjust the friction clutch 49 (FIGS. 2 and 3) accordingly. The control device 109 thus acts as a position controller.

The mentioned clutch torque / angle of rotation characteristic 111 has been created on the basis of an initial calibration of the relevant transfer case 15 and stored in the memory 113. However, due to various influencing factors, the dependence of the coupling torque set by the coupling unit 47 on the actuator position (rotational angle actual value α ') represented by the characteristic curve 111 may change over time. As a result, the characteristic can shift, for example, and / or the slope of the characteristic changes. Therefore, a recalibration of the coupling unit 47 is performed regularly, as explained above. For example, when the vehicle is stationary, the electric motor 93 is actuated in the direction of engagement of the friction clutch 49 until the friction clutch 49 is essentially fully engaged and the motor current of the electric motor 93 finally exceeds a predetermined threshold value due to the increasing load. For the calibration position of the coupling unit 47 defined as a result, the signal α 'of the sensor 107 is determined, which thus corresponds to a rotation angle calibration value. This rotation angle calibration value α 'is compared with a calibration value which has been determined during a preceding calibration run of the coupling unit 47 for the corresponding calibration position. Depending on the difference between these two calibration values, the characteristic curve 111 is adapted. This can be done, for example, by adapting a correction value (eg offset correction value and / or gradient correction value), or by overwriting the characteristic curve 111 stored in the memory 113.

The above-described recalibration of the coupling unit 47 can be performed at fixed predetermined occasions, for example, after each shutdown of the vehicle engine 11, which is the control device 109 transmitted by transmitting an "ignition off" signal. According to the invention, however, the explained recalibration of the clutch unit 47 is controlled as needed, which not only reduces the burden on the electrical system of the motor vehicle, but lessens the overall load on the entire clutch unit 47.

With reference to FIG. 5, the calibration method according to the invention is explained by way of example. In a step S 1, a first calibration of the transfer case 15 takes place with the coupling unit 47 in the manner explained above, for example, in the factory of the manufacturer of the transfer case 15. Subsequently, a value W, which represents the coupling work introduced into the friction clutch 49 and its meaning will be explained below, set to zero (step S2).

If it is determined in a subsequent step S3 that the vehicle has been put into operation (the control device 109 according to FIG. 4 receives the signal "ignition on"), the aforementioned clutch work W is continuously determined in a step S4. The coupling work W introduced into the friction clutch 49 during the operation of the transfer case 15 represents the state of wear of the clutch unit 47. The clutch work W is estimated by forming a time integral over the clutch power during the service life of the transfer case 15. The clutch power, in turn, is calculated as the product of the clutch torque and the speed difference between the input shaft 41 and the second output shaft 45 of the transfer case 15 (FIGS. 2 and 3). With regard to the clutch torque, advantageously the torque request M can be set, which the control device 109 receives from the higher-level vehicle dynamics control unit 33 (FIG. 4). The mentioned speed difference can be calculated in a simple manner from the signals of the wheel speed sensors 35, 37 of the rear axle 23 or the front axle 31 of the vehicle (FIG. 1), since these signals are available anyway via the vehicle data bus (eg CAN) stand.

In order to achieve an even higher accuracy, the calculation of the clutch work W in step S4 can also have other influencing factors or take into account measured values. For example, different torque ranges, different speed ranges and / or different time intervals can be taken into account by means of corresponding weighting factors. Alternatively or additionally, the distance traveled by the vehicle can also be taken into account.

In a step S5 is continuously checked whether the vehicle engine 11 has been stopped. If the control device 109 receives a corresponding signal ("ignition off"), it is checked in a step S6 whether the determined clutch work W exceeds a predetermined threshold value Wmax. This threshold value Wmax can be determined empirically for the relevant type of transfer case 15 and stored in the memory 113. If the check shows that the clutch work W has exceeded the threshold value Wmax, a recalibration is triggered in a step S7, which takes place in the manner described above. Subsequently, the last determined value of the clutch work W is reset to zero (step S2), and it is waited until the vehicle is put back into operation.

If, on the other hand, it has been determined in step S6 that the determined clutch work W has not yet reached the predetermined threshold value Wmax, a recalibration of the clutch unit 47 is generally dispensed with and it is waited until the vehicle engine 11 is put back into operation (step S3 ). The value of the clutching work W determined last is retained in this case, so that this value is available as the initial value for the estimation of the clutch wear as soon as the vehicle is restarted.

Thus, it can be achieved that the transfer case 15 in question is not recalibrated unnecessarily often. Instead, a calibration Run only performed when it is assumed that even a corresponding state of wear of the coupling unit 47 makes this necessary.

As can be seen from FIG. 5, optionally further necessary or sufficient conditions for triggering a recalibration can be taken into account. If the check in step S6 yields a negative result - that is, if the determined clutch work W has not yet reached the predetermined threshold value Wmax - it can be checked in a step S8 whether or not the clutch unit 47 has been running since the last calibration run Vehicle covered distance D has exceeded a predetermined threshold Dmax. If appropriate, a recalibration is triggered in step S7, although this alone does not appear to be absolutely necessary with respect to the coupling work W introduced into the coupling unit 47. The distance traveled by the vehicle can also be easily determined and taken into account by the control device 109 on the basis of the signals available via the vehicle data bus.

While the invention finds particularly advantageous application in a transfer case with electromechanical actuation of the friction clutch, the invention is not limited to the embodiment described above. Other arrangements in the drive train of a motor vehicle are possible, as explained above. Furthermore, the actuator 51 can be designed differently than explained above in connection with the figures. For example, a different type of reduction gear 97 or a different type of deflection 103 may be provided. Instead of the shown electromechanical actuation of the friction clutch 49, for example, an electromagnetic see, be provided a hydraulic or electro-hydraulic actuation.

LIST OF REFERENCE NUMBERS

1 1 internal combustion engine

13 main gearbox

15 transfer cases

17 cardan shaft

19 rear differential

21 wheel

23 rear axle

25 cardan shaft

27 front differential

29 wheel

31 front axle

33 Vehicle dynamics control unit

35 wheel speed sensor

37 wheel speed sensor

39 sensor

41 input shaft

43 first output shaft

45 second output shaft

47 coupling unit

49 friction clutch

51 actuator

53 clutch basket

55 clutch hub

57 drive gear

59 chain drive

61 output gear

63 support ring

65 adjusting ring

67 ball groove

69 ball groove

71 ball

73 pressure ring

75 plate spring assembly

77 operating lever

79 operating lever

81 role

83 role

85 front side

87 front side

89 control disk

91 spline attachment 93 electric motor

95 armature shaft

97 reduction gear

99 snail

101 worm wheel

103 deflecting device

105 output shaft

107 sensor

107 "sensor

109 control device

1 11 Clutch torque / angle of rotation characteristic

1 13 memory

A rotation axis

B rotation axis

C rotation axis α rotation angle setpoint α ¹ rotation angle actual value

M torque request

D distance

W coupling work

Claims

claims

A method of calibrating a clutch assembly (47) for a powertrain of a motor vehicle, the clutch assembly including at least one friction clutch (49) for controllably transmitting torque from an input member (41) to an output member (45) and an actuator (51) for actuating the friction clutch has, with the following steps:

Determining a state of wear of the coupling unit

(47); and

Triggering a calibration run of the coupling unit (47) as a function of the determined state of wear.

2. The method of claim 1, wherein for determining the state of wear of the coupling unit (47) in the friction clutch (49) introduced coupling work is taken into account.

3. The method according to any one of the preceding claims, wherein for determining the state of wear of the coupling unit (47) a time integral over the clutch power during operation of the coupling unit is formed.

4. The method of claim 3, wherein a clutch torque and a rotational speed difference between the input member (41) and the output member (45) are detected, wherein the clutch power is determined from the product of the clutch torque and the speed difference.

5. The method according to claim 4, wherein the clutch torque is determined from a torque request (M), from a calculated torque transmitted by the friction clutch (49) or from a measured torque transmitted by the friction clutch (49).

6. The method according to any one of claims 3 to 5, wherein the time integral from the last calibration run of the coupling unit (47) is formed.

7. The method according to any one of the preceding claims, wherein only then a calibration run is triggered when the determined state of wear reaches or exceeds a predetermined threshold value (Wmax).

8. The method according to any one of the preceding claims, wherein is considered as an additional condition for triggering a calibration run, whether an "ignition off" signal has been received.

9. The method according to any one of the preceding claims, is taken into account as an additional condition for triggering a calibration run, whether the motor vehicle has covered a predetermined distance since the last calibration run.

10. The method according to any one of the preceding claims, is taken into account as an alternative condition for triggering a calibration run, whether the motor vehicle since the last calibration run a predetermined distance (Dmax) has covered.

11. The method according to any one of the preceding claims, wherein for performing the calibration run, the coupling unit (47) by means of the actuator (51) is brought into at least one predetermined calibration position, which is assigned a certain clutch torque, wherein in the calibration position, a control position of the actuator is measured, wherein the difference between the measured positioning position and a positioning position is measured, which was measured in a previous calibration run, and wherein a clutch characteristic is adjusted in response to the determined parking position difference, according to which the coupling unit is controlled during operation of the coupling unit ,

12. The method according to any one of the preceding claims, wherein the actuator (51) comprises an electric motor (93), and wherein the actuator comprises a transmission device (97) for translating a rotational movement of the electric motor into the slow and / or a deflection device (103 ) for deflecting a rotational movement of the actuator in a translational movement of the friction clutch (49).

13. A torque transfer assembly (15) having an input member (41), an output member (45), a clutch unit (47) and a control device (109), wherein the clutch unit at least one friction clutch (49) for controllably transmitting a torque from the input member to the Output element and an actuator (51) for actuating the friction clutch, and wherein the control device (109) is adapted to determine a state of wear of the coupling unit and trigger a calibration run of the coupling unit in dependence on the determined state of wear.