Procedure for calibrating a clutch control

Abstract

Method for calibrating a clutch control of a drive train of a motor vehicle, wherein the drive train has a motor (14) designed as an electric motor and wherein the method comprises at least the following steps: - blocking (32) an output of the drive train; - operating (36) the motor (14) with a value for a first operating variable; - actuating (54, 66) the clutch with a first value for a clutch control variable; - detecting a first value of a second operating variable of the engine (14) when the clutch is actuated with the first value; characterized by the steps: - actuating (64) the clutch with a second value for the clutch control variable; - detecting a second value of the second operating variable of the engine (14) when the clutch is actuated with the second value; and - Determining (42) clutch characteristic data as a function of the detected first value and the detected second value of the second operating variable.

Description

Technical area

[0001] The present invention relates to a method for calibrating a clutch control of a drive train of a motor vehicle, wherein the drive train has a motor designed as an electric motor. State of the art

[0002] Calibration routines are used to optimize the control of vehicle transmissions. These are intended to compensate for component and manufacturing tolerances, for example. This is intended to compensate for the fact that different clutches of the same series can transmit very different torques when actuated in the same way. Due to respective tolerances, the clutches can otherwise close with different strengths even with the same control. However, the actual contact pressure at the clutch is usually not recorded, as measuring this is very complex. In motor vehicles, the necessary sensors are usually not even installed. Instead, for calibration, only a filling equalization pressure is determined.To do this, a clutch is actuated at different pressure levels, and based on a detected speed, it is determined at what point the clutch begins to transmit a torque greater than the drag torque. However, the relationship determined in this way between clutch actuation and the transmittable torque is weak. Furthermore, calibration, for example, can only be performed using a single operating point.

[0003] Alternatively, calibration can also be performed on a test bench directly after the clutch or transmission is manufactured. However, such calibration is inherently complex and expensive. Furthermore, recalibration can only be performed at the factory, for example, during vehicle maintenance. For example, recalibration by the vehicle itself cannot be used to address the aging of a clutch oil.

[0004] In this context, DE 602 26 285 T2 discloses a clutch calibration for vehicle main clutches, preferably for wet friction clutches used in partially or fully automated mechanical transmission systems. In particular, DE 60 226 285 T2 describes a clutch control system / method that has a motion or creep point calibration logic that uses an electronic data link.

[0005] DE 102 32 491 A1 proposes a method for determining the motion state of a clutch actuator in a vehicle, wherein the clutch actuator is driven by an electric motor. According to DE 102 32 491 A1, the armature resistance of the electric motor is determined in a stationary state of the electric motor. Using the determined armature resistance and the applied motor voltage as well as the measured motor current, a current and / or an induced voltage induced in the electric motor is calculated. The motion state of the clutch actuator is determined from the induced current and / or the induced voltage, which are proportional to the motor speed.

[0006] DE 196 52 244 A1 comprises the combination of a drive motor and a transmission with a number of selectable gear ratios. An adjustable automated torque transmission system is equipped with a number of different engagement states. A mechanism automatically regulates the torque transmission of the system. The mechanism includes a control unit that generates output signals that indicate the magnitude of the torque to be transmitted and are dependent on a number of parameters. The control unit adjusts the system in response to the output signals. The transmission system may include a clutch. One of the numerous parameters may be the engagement position of the torque transmission system. The engagement positions may include a starting position or a starting point at which the system generally begins to transmit torque.The control unit can perform at least one of the operations of detecting, calculating and storing the starting position at least at one operating point of the vehicle.

[0007] DE 10 2017 220 029 A1 proposes a method for operating a work machine, in particular an agricultural or construction machine, in which an actual torque is detected in a drive train of the work machine using at least one torque measuring device. The torque is analyzed and / or processed by a control unit, and / or at least one component of the drive train is controlled by the control unit, taking into account the analyzed and / or processed actual torque.

[0008] DE 103 45 906 A1 discloses a method for controlling a drive train of a motor vehicle. The drive train comprises a drive motor and a manual transmission automated by a transmission actuator, as well as a clutch arranged in the power path between the drive motor and the manual transmission and operable automatically by an actuating device. The clutch is controlled depending on at least one specific operating state of the drive motor and / or the transmission actuator and / or the actuating device. Description of the invention

[0009] A first aspect relates to a method for calibrating a clutch control of a drive train. The calibration can require a change in the control parameters of one or more clutches of the drive train. The drive train has at least one clutch. The clutch can be designed, for example, as a multi-plate clutch. The clutch can be actuated, for example, by means of an electro-hydraulic pressure control valve. By energizing the pressure control valve, a proportional actuation pressure of the clutch can be set. However, depending on manufacturing tolerances, for example, the proportional relationship between energization and actuation pressure can vary for similar clutches. The drive train can be designed to generate and transmit drive power for a motor vehicle. The drive train has a motor designed as an electric motor.The electric motor can be designed, for example, as a synchronous or asynchronous motor. The engine can be, for example, a traction motor of the motor vehicle. The motor vehicle can be designed, for example, as a passenger car, construction machine, or agricultural machine.

[0010] The method involves blocking an output of the drivetrain. The output can be, for example, a driven axle or an output shaft of a transmission of the drivetrain. Blocking can be achieved, for example, using a parking brake or a service brake. If multiple clutches are present, all clutches in the power flow from the engine to the output that are not to be calibrated can also be fully closed. These clutches can, for example, be subjected to maximum pressure, thus providing a virtually non-rotatable connection.

[0011] The method comprises operating the motor with a value for a first operating variable. The value can be a predetermined value, for example. The operating variable can be, for example, a power output, a speed, or a torque of the motor. In the case of an electric motor, respective operating variables can be recorded and specified with a high degree of quality. For example, in the case of an electric motor, a torque can be set with a high degree of accuracy and maintained even under different loads. The torque of the electric motor can, for example, be available as a measured variable in an inverter of the drive train. This means that no additional sensors are necessary. The operating variable can, for example, be transmitted to an ECU, such as a transmission ECU, via a data bus of the motor vehicle, such as a CAN bus. In order to carry out the calibration method, a structural adaptation of the drive train and additional elements which are assigned to the drive train during regular clutch operation orDriving operations are not required and may be unnecessary.

[0012] The method includes actuating the clutch with a first value for a clutch control variable. The clutch can be actuated, for example, while the engine is operating at the value for the operating variable. The clutch control variable can be a control variable used to actuate the clutch. For example, the clutch control variable can be a voltage or a current flow used to energize the pressure control valve of the clutch. Actuating the clutch causes the clutch to be actuated with a pressure corresponding to the first value.

[0013] Accordingly, the clutch is then partially closed, for example. The clutch can then transmit a torque corresponding to the first value for the clutch control variable.

[0014] The method comprises detecting a first value of a second operating variable of the engine when the clutch is actuated with the first value. The second operating variable can be a variable corresponding to a power of the engine, which differs from the first operating variable. This makes it possible to infer a state of the clutch during actuation with the first value of the clutch control variable. The state can, for example, be a transmittable torque, which corresponds to the first value of the clutch control variable. The detection can be carried out, for example, using the drive train. For example, a torque can be detected by means of the engine and, alternatively or additionally, the inverter, which is required to maintain the specified speed. Due to the blocked output of the drive train, this torque corresponds to the transmittable torque of the clutch, optionally less any drag torques in the drive train.Alternatively, for example, a speed can be recorded, which is achieved by the engine at a given torque. This allows the overall degree of clutch actuation to be determined.

[0015] The method comprises actuating the clutch with a second value for the clutch control variable. The second value of the clutch control variable differs from the first value. The second value of the clutch control variable can, for example, be greater than the first value. The method comprises detecting a second value of the second operating variable of the engine when the clutch is actuated with the second value. In this way, a second operating point of the clutch can be determined. Even when the clutch is actuated with the second value of the clutch control variable and the second value of the second operating variable of the engine is detected, the output of the drive train can be blocked and the engine can be operated with the value for its first operating variable.

[0016] Optionally, additional operating points can also be considered for calibration. For example, the clutch can be actuated with a third value and, optionally, additional values ​​for the clutch control variable. A corresponding third value and, optionally, additional values ​​for the second operating variable of the engine can then be recorded during the corresponding actuation of the clutch.

[0017] Optionally, the process can be repeated with different values ​​for the first operating variable. For example, transmittable torques can be determined at a first engine speed level and at a different second engine speed level. This allows additional operating points to be determined and further data to be generated and considered for calibration. Furthermore, different clutch control parameters or clutch control curves can be calibrated for different speeds.

[0018] The method comprises determining clutch characteristics as a function of the detected first value and the detected second value of the second operating variable. These clutch characteristics can be used to calibrate the clutch control. For example, a relationship between the clutch control variable and the transmissible torque of the clutch can be determined by interpolation and, if more than two operating points are determined, by a compensation curve. This relationship can be stored and used for clutch control, for example, by a transmission control system. The clutch characteristics can accordingly have a characteristic curve. For example, a clutch control characteristic curve can be changed depending on the determined clutch characteristics.To determine clutch characteristics, additional parameters can optionally be taken into account, such as the value for the first operating variable of the engine, the first value for the clutch control variable and the second value for the clutch control variable.

[0019] In a further embodiment of the method, the first operating variable can be a motor speed and the second operating variable a motor torque. The motor can therefore be speed-controlled, at least during calibration. For example, a transmittable torque through the clutch can be determined based on the current flow required to maintain the motor speed. Calibration can thus be particularly simple and precise.

[0020] In a further embodiment of the method, the first operating variable can be a motor torque and the second operating variable a motor speed. The motor can thus be torque-controlled, at least during calibration. This reliably prevents overloading of the clutch during calibration.

[0021] In a further embodiment of the method, it can be provided that when the clutch is actuated, respective values ​​for the clutch control variable are controlled in order to achieve respective predetermined target values ​​for the second operating variable. Therefore, instead of measuring, for example, the torque required to maintain a predetermined speed at a predetermined value for the clutch control variable, the clutch control variable is controlled in order to achieve, for example, a predetermined torque for the engine at a predetermined speed. Such a calibration method can result in a particularly low load for the engine. For example, this control can be used for only one value, such as the first value or the second value, of the clutch control variable. However, this control can also be used for several or all values ​​for the clutch control variable.

[0022] In a further embodiment of the method, it can be provided that before the clutch is actuated with one of the respective values ​​for the clutch control variable, a rapid filling of the clutch takes place. Rapid filling can be filling a hydraulic actuator of the clutch before the actual actuation. This allows the actuator to be vented. During rapid filling, the pressure control valve can, for example, be opened particularly wide. Rapid filling can allow particularly fast calibration. In addition, standardized actuation procedures that are also used in normal operation can be used to actuate the clutch during calibration. A time duration for the rapid filling can, for example, be fixed or determined as part of the calibration procedure. Rapid filling can take place before each actuation of the clutch during the calibration process or only during some of the actuations.After rapid filling, for example, a clutch piston may not yet be in contact with the clutch plates and, alternatively or additionally, a fan clearance may not yet be eliminated.

[0023] In a further embodiment of the method, it can be provided that before the clutch is actuated, a fill leveling of the clutch takes place using one of the respective values ​​for the clutch control variable. This can, for example, take into account any residual oil quantities remaining in the clutch actuator. The fill leveling can be a filling of a hydraulic actuator of the clutch before the actual actuation and after the quick fill. A time duration can also be specified for the fill leveling. During the fill leveling, the pressure control valve can, for example, be opened less wide than during quick fill in order to prevent unintentional actuation and the onset of friction in the clutch. After the fill leveling, a clutch piston can be applied at minimal clutch torque. The blocking of the output can, for example, only occur after the first fill leveling.In a further embodiment of the method, it can be provided that the clutch is actuated a first time with the first value for the clutch control variable starting from a less strongly actuated clutch and a second time with the first value for the clutch control variable starting from a more strongly actuated clutch. The first value can be smaller than the second value and the clutch is thus actuated less strongly. For example, the clutch can be actuated the first time after a fill equalization with the first value and the second time after actuating the clutch with the second value of the clutch control variable. This allows hysteresis to be detected during calibration, whereby only three instead of four measurements of operating points may be necessary.Depending on whether the clutch is being adjusted toward its open or closed position, the relationship between the manipulated variable and the torque that can be transmitted to the clutch can vary. Accordingly, the relationship can be determined for both adjustment directions with little effort. Two corresponding characteristic curves can then be determined, or, for example, one characteristic curve with a hysteresis loop.

[0024] In a further embodiment of the method, it can be provided that the method comprises a step of detecting a further value of the second operating variable of the engine when the clutch is not actuated. This can, for example, determine a drag torque. The drag torque can be caused by friction in the drive train and, alternatively or additionally, a minimum torque transmission when the clutch is fully disengaged. The drag torque does not correspond, for example, to any transmittable torque at the clutch and can, for example, be subtracted for clutch control. Clutch characteristics can be determined depending on the detected further value of the second operating variable. For example, the further value can be subtracted from the other detected values ​​of the second operating variable in order to determine the torque transmittable by the clutch.The respective characteristic curves for the clutch control can thus be offset or corrected by the drag torque.

[0025] In a further embodiment of the method, it can be provided that the method includes a step of changing a clutch control system depending on the determined clutch characteristics. For example, respective control parameters and, alternatively or additionally, control characteristics of the clutch control system can be changed. For example, the clutch control system can be calibrated once when the motor vehicle is put into operation. However, the clutch control system can also be adapted over its lifetime. For example, the calibration process can be carried out periodically. Calibration can take place, for example, after a specified mileage, after a specified time, or each time the vehicle is started.

[0026] In a further embodiment of the method, the clutch can be monitored using the calibration method. For this purpose, the determined clutch characteristics can be compared with previously determined clutch characteristics or target clutch characteristics. If deviations exceed a threshold value, an output can be generated, for example, as an error message. This can signal to the user, for example, the need for clutch maintenance. For example, clutch wear can also be determined based on the determined clutch characteristics or a change in the determined clutch characteristics.

[0027] In a further embodiment of the method, the clutch characteristics may include a relationship between the clutch control variable and a torque that can be transmitted by the clutch. This allows the clutch to be controlled according to the desired transmittable torque.

[0028] In a further embodiment of the method, the clutch characteristics may include a friction coefficient. For example, the calibration method can be used to determine the clutch's current friction coefficient. This allows changes in the clutch oil and clutch friction linings to be taken into account.

[0029] In a further embodiment of the method, it can be provided that the clutch characteristics include a clutch hysteresis. This allows the clutch control to be calibrated to match the adjustment direction of the clutch. In a further embodiment of the method, it can be provided that the clutch characteristics include a clutch wear characteristic value. The clutch wear characteristic value can, for example, be proportional to the transmittable torque and calculated as a percentage deviation from a target value. The clutch wear characteristic value can, for example, be determined based on an average deviation across all operating points determined during calibration or based on a maximum deviation across all operating points determined.

[0030] In a further embodiment of the method, the method may further comprise a step of detecting a clutch temperature, and determining clutch characteristics based on the detected clutch temperature. This allows the calibration to take into account the fact that the clutch temperature has a significant influence on the friction in the clutch and thus on the transmittable torque. Furthermore, the calibration and clutch control can also be temperature-dependent. The clutch temperature can be, for example, a friction lining temperature or an oil temperature in the clutch.

[0031] A second aspect relates to a transmission control unit which is designed to carry out the method according to the first aspect. Respective further features, embodiments and advantages can be found in the descriptions of the first aspect. Conversely, features, embodiments and advantages of the second aspect also represent features, embodiments and advantages of the first aspect. The transmission control unit can be designed to actuate respective clutches of a motor vehicle. The transmission control unit can be designed to transmit respective control signals to a clutch actuator, to an engine control unit of the motor vehicle and to a braking system of the motor vehicle. The transmission control unit can thus, for example, block the output of the drive train of the motor vehicle, specify a value for the first operating variable of the engine and specify a value for the clutch control variable for actuating the clutch.In addition, the transmission control unit can be configured to receive status signals from the engine control unit. For example, currently detected values ​​of the second operating variable of the engine can be transmitted to the transmission control unit. Furthermore, the transmission control unit can be configured to determine clutch characteristics based on the detected first value and the detected second value of the second operating variable.

[0032] A third aspect relates to a system configured to perform the method according to the first aspect. Further features, embodiments, and advantages can be found in the descriptions of the first aspect. Conversely, features, embodiments, and advantages of the third aspect also represent features, embodiments, and advantages of the first aspect. Short description of the characters Fig. 1 shows a schematic system by means of which a clutch control of a drive train of a motor vehicle can be calibrated. Fig. 2 schematically illustrates a method for determining an operating point when calibrating the clutch control. Fig. 3 illustrates in a diagram an actuation of a clutch for calibrating its control. Detailed description of embodiments

[0033] Fig. 1 shows a system 10 designed to calibrate a clutch control of a drive train of a motor vehicle. The system 10 has a brake 12 designed to block an output of the drive train. The system 10 has an engine 14 designed as an electric motor and a transmission 16 designed to transmit a drive force from the engine 14 to the output. In the example shown, the transmission 16 has only a single clutch, which in the example shown is designed as a multi-plate clutch. The system 10 has an inverter 18, which controls a power supply to the engine 14 via an energy source 20. The inverter 18 is also designed to detect respective uncontrolled operating variables of the engine 14. In addition, the system 10 has a transmission control unit 22 designed as an ECU.The transmission control unit 22 is configured to control the clutch of the transmission 16 by adjusting a current flow for a pressure control valve. Furthermore, in one embodiment, the transmission control unit 22 is configured to detect a clutch temperature. Furthermore, the transmission control unit 22 can specify a target value for an engine speed and, alternatively or additionally, an engine torque to the inverter 18. Furthermore, the transmission control unit 22 can receive a current value for the engine speed and, alternatively or additionally, the engine torque from the inverter 18.

[0034] In the example shown, motor 14 is speed-controlled. Inverter 18 thus provides motor 14 with a speed value as the first operating variable and regulates the power supply accordingly. From the required power supply, inverter 18 derives a motor torque value as the second operating variable. If motor 14 is operated at a fixed speed, which is specified by transmission control unit 22 during calibration, and brake 12 blocks the output, the detected motor torque corresponds to a torque transmittable by the clutch in transmission 16.

[0035] Fig. 2 illustrates a method for determining an operating point during a calibration of a clutch control of the clutch of the transmission 16. In a step 30, the calibration is activated. In a step 32, the output is blocked by means of the brake 12. In a step 34, a quick fill and a fill equalization calibration takes place. The quick fill and fill equalization can bring a piston of the clutch into contact with plates while the clutch remains fully open. In a step 36, the transmission control unit 22 specifies a fixed target speed for the motor 14. In response, the inverter 18 controls a power supply such that the motor 14 maintains this target speed. In a step 38, the motor torque generated is detected by the inverter 18 and transmitted to the transmission control unit 22. This determined motor torque corresponds to a drag torque when the clutch is open.In a step 40, the clutch is controlled by the transmission control unit 22 using a value for a clutch control variable in order to actuate the clutch accordingly. The torque generated by the engine 14 when the clutch is actuated using the value of the clutch control variable is also recorded. This results in a corresponding operating point at which the torque that can be transmitted by the clutch, corresponding to a value of the clutch control variable, was recorded. Step 40 can be repeated several times to determine corresponding data for additional operating points. The data collected in this way is used in a step 42 to determine clutch characteristics. In a simple embodiment, the data from two operating points is used to generate a straight line as the clutch control characteristic curve. The determined clutch characteristics, or the clutch control calibrated therewith, is stored by the transmission control unit 22 in a step 44.

[0036] Fig. Figure 3 illustrates a diagram of an embodiment for actuating the clutch, or rather, energizing the pressure control valve to actuate the clutch for clutch control calibration. The current flow is plotted on the ordinate in mA. The time curve is plotted on the abscissa in seconds.

[0037] During calibration, the motor 14 is operated with a predetermined value for the engine speed as the first operating variable. In area 48, the clutch is disengaged and the output is blocked by the brake 12. The drag torque is determined. An initial rapid filling takes place in an area 50, and a fill equalization takes place in an area 52. The clutch is then actuated in an area 54 with a first value for the clutch control variable, i.e. a specific level of current flow through the pressure control valve. The torque required to maintain the predetermined value for the engine speed is recorded as the first value for the second operating variable of the motor 14. Subsequently, in an area 56, the clutch is energized again with the value of the clutch control variable for the fill equalization, and the clutch is thus disengaged again. One piston of the clutch remains in contact with the plates.In one embodiment, the torque required to maintain the predetermined value for the engine speed is detected as a value for the second operating variable of the engine 14 in order to determine a point of hysteresis of the clutch control.

[0038] Subsequently, in an area 58, a clutch actuator is completely emptied and a waiting period occurs. After that, rapid filling occurs again in an area 60 and fill equalization occurs in an area 62. The clutch is then actuated in an area 64 with a second value for the clutch control variable, which is greater than the first value of the clutch control variable. The torque required to maintain the predetermined value for the engine speed is recorded as the second value for the second operating variable of the engine 14. Subsequently, in an area 66, the clutch is actuated again with the first value of the clutch control variable and the clutch is thus slightly opened again. The torque required to maintain the predetermined value for the engine speed is recorded in one embodiment as a further value for the second operating variable of the engine 14 in order to determine a further point of a hysteresis of the clutch control.Subsequently, in a region 68, the clutch is again energized with the value of the clutch control variable for fill compensation, thus fully opening the clutch again. A clutch piston remains in contact with the plates. In one embodiment, the torque required to maintain the specified value for the engine speed is recorded as a value for the second operating variable of the engine 14 in order to determine a further point of clutch control hysteresis.

[0039] Subsequently, a clutch actuator is completely emptied in a region 70. In one embodiment, the calibration measurements are then completed. In another embodiment, a waiting period occurs, and then further operating points are determined at a different speed level. After the waiting period, the engine 14 is operated with a different predetermined value for the engine speed as the first operating variable, and the previously described regions 50 to 68 are run through again. In one embodiment, this is repeated for several different speed levels. Reference symbol 10 systems 12 Brake 14 Engine 16 gearboxes 18 inverters 20 Energy source 22 Transmission control unit 30 step activation calibration 32 step output blocking 34 step calibration quick fill and fill equalization 36 Step Specifying a fixed target speed 38 Step Transmission of engine torque to transmission control unit 40 step control clutch with value 42 Step Determine clutch characteristics 44 Step storage of clutch characteristics 48 Area clutch open, output blocked 50 Area first quick fill 52 Filling compensation area 54 Range actuation clutch with first value 56 Area opening clutch 58 Area Complete emptying actuator including waiting time 60 area refill quickly 62 Filling compensation area 64 Range actuation clutch with second value 66 Area actuation clutch with first value 68 Area complete opening clutch 70 Area Complete Emptying Actuator

Claims

[1] Method for calibrating a clutch control of a drive train of a motor vehicle, wherein the drive train has a motor (14) designed as an electric motor and wherein the method comprises at least the following steps: - blocking (32) an output of the drive train; - operating (36) the motor (14) with a value for a first operating variable; - actuating (54, 66) the clutch with a first value for a clutch control variable; - detecting a first value of a second operating variable of the engine (14) when the clutch is actuated with the first value; characterized by the steps: - actuating (64) the clutch with a second value for the clutch control variable; - detecting a second value of the second operating variable of the engine (14) when the clutch is actuated with the second value; and - Determining (42) clutch characteristic data as a function of the detected first value and the detected second value of the second operating variable. [2] Method according to claim 1, characterized by that the first operating variable is a speed of the motor (14) and the second operating variable is a torque of the motor (14). [3] Method according to claim 1, characterized by that the first operating variable is a torque of the motor (14) and the second operating variable is a speed of the motor (14). [4] Method according to one of the preceding claims, characterized by that when the clutch is actuated, respective values ​​for the clutch control variable are regulated in order to achieve respective predetermined target values ​​for the second operating variable. [5] Method according to one of the preceding claims, characterized bythat before the clutch is actuated with one of the respective values ​​for the clutch control variable, a quick filling (50, 60) of the clutch takes place. [6] Method according to one of the preceding claims, characterized by that before the clutch is actuated with one of the respective values ​​for the clutch control variable, a filling compensation (52, 62) of the clutch takes place. [7] Method according to one of the preceding claims, characterized by that the clutch is actuated a first time with the first value for the clutch control variable starting from a less strongly actuated clutch and a second time with the first value for the clutch control variable starting from a more strongly actuated clutch. [8] Method according to one of the preceding claims, characterized bythat the method comprises a step of detecting a further value of the second operating variable of the engine (14) when the clutch is not actuated and the determination of clutch characteristics takes place as a function of the detected further value of the second operating variable. [9] Method according to one of the preceding claims, characterized by that the method comprises a step of changing a clutch control depending on the determined clutch characteristics. [10] Method according to one of the preceding claims, characterized by that the clutch is monitored using the calibration procedure. [11] Method according to one of the preceding claims, characterized by that the coupling characteristics include at least one of the following data: - A relationship between the clutch control variable and a torque that can be transmitted by the clutch; - A coefficient of friction; - A clutch hysteresis; and - A clutch wear index. [12] Method according to one of the preceding claims, characterized by that the method further comprises a step of detecting a clutch temperature and determining clutch characteristics as a function of the detected clutch temperature.

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