METHOD FOR DETERMINING A SERVICE LIFE OF A FRICTION CLUTCH OF A VEHICLE

Abstract

A method for determining a service life of a friction clutch of a vehicle with a clutch actuation system includes setting a maximum torque at the friction clutch of the clutch actuation system. The method also includes incrementing a service life counter when an unintended slip at the friction clutch occurs, determining that wear has occurred on the friction clutch in response to reaching a specific counter value of the service life counter, and multiplying a weighted sensitivity factor by a first absolute vale which increments the counter in response to an unintended slip occurring.

Claims

1. A method for determining a service life of a friction clutch of a vehicle, comprising: setting a maximum torque at the friction clutch; in response to an unintended slip at the friction clutch, incrementing a service life counter; determining that wear has occurred on the friction clutch in response to reaching a specific counter value of the service life counter; and multiplying a weighted sensitivity factor by a first absolute value which increments the service life counter in response to an unintended slip occurring.

2. The method of claim 1, wherein, in order to set the weighted sensitivity factor, a predetermined sensitivity factor is weighted in accordance with thermal effects or with adaptive parameters measured during a clutch control operation or with current quantities to be measured determined a clutch actuating system.

3. The method of claim 2, wherein the predetermined sensitivity factor is reduced when thermal effects occur in a dry friction clutch, whereas the predetermined sensitivity factor is increased when thermal effects occur in a wet friction clutch.

4. The method of claim 3, wherein the method further includes reducing a number of test events to be counted reduced when thermal effects occur at the wet friction clutch.

5. The method of claim 2, wherein the predetermined sensitivity factor is weighted by parameters adapted during a clutch control operation, and these adaptive parameters are evaluated when a maximum torque is acting on the friction clutch, wherein a long-term friction coefficient and/or a long-term bite point of the friction clutch are considered as adaptive parameters.

6. The method of claim 5, wherein the predetermined sensitivity factor is increased when a bite point threshold is exceeded by the long-term bite point, whereas the predetermined sensitivity factor is reduced when the bite point threshold is undershot by the long-term bite point.

7. The method of claim 5, wherein a maximum permissible travel or a maximum permissible pressure of a clutch actuating system for a setting of the maximum torque is calculated from a clutch model, wherein measured quantities to be measured, namely pressure or travel, are compared with model quantities for pressure or travel calculated from a clutch model, and when there is a difference between the measured quantities to be measured and calculated model quantities, the predetermined sensitivity factor is adapted in order to set the weighted sensitivity factor.

8. The method as claimed in claim 7, wherein, when a difference is ascertained between the calculated model quantities and the measured quantities to be measured after a first slip event, the predetermined sensitivity factor selected is smaller, wherein a weighted sensitivity factor is increased in each subsequent measurement when the unintended slip occurs.

9. The method as claimed in claim 8, wherein the weighted sensitivity factor remains at a reduced value until the currently measured adapted quantities to be measured correspond to the calculated model quantities.

10. The method of claim 1, wherein the counter is reduced by a second absolute value when the unintended slip does not occur.

11. A clutch actuating system, comprising: a controller configured to: determine whether a maximum torque has been demanded and set at a clutch; in response to the maximum torque being set at the clutch, determine whether an unintended slip is above a predetermined slip threshold; determine a duration of the unintended slip; and multiply a first absolute value to be used to increment a counter by a sensitivity factor when the duration of the slip exceeds a time threshold.

12. The clutch actuation system of claim 11, wherein the clutch actuating system further includes a sensor configured to determine a pressure of a master cylinder of the clutch actuating system.

13. The clutch actuation system of claim 11, wherein the clutch actuating system further includes a sensor configured to determine a distance traveled by a clutch actuator.

14. The clutch actuation system of claim 11, wherein the clutch actuating system further includes a pressure sensor configured to determine a pressure of a master cylinder of the clutch actuating system, and a displacement sensor configured to determine a distance traveled by a clutch actuator.

15. The clutch actuation system of claim 11, wherein in response to a measured duration exceeds a time threshold, a plausibility check is executed.

16. The clutch actuation system of claim 11, wherein the controller is further configured to determine a rotational speed used when the unintended slip is above a rotational speed threshold.

17. The clutch actuation system of claim 11, wherein the clutch is a wet clutch.

18. A method for determining a service life of a clutch of a vehicle with a clutch actuation system, comprising: setting a maximum torque at the clutch of the clutch actuation system; incrementing a service life counter when an unintended slip at the clutch occurs; determining that wear has occurred on the clutch in response to reaching a specific counter value of the service life counter; and multiplying a weighted sensitivity factor by a first absolute value in response to an unintended slip occurring.

19. The method of claim 18, wherein the first absolute value increments the counter.

20. The method of claim 19, wherein the counter is reduced by a second absolute value when the unintended slip does not occur.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The disclosure allows numerous embodiments. One of these will be explained in greater detail by the figures of the drawing.

[0019] In the drawing:

[0020] FIG. 1 shows a schematic structure of a hydrostatic clutch actuating system,

[0021] FIG. 2 shows an illustrative embodiment of the method according to the disclosure,

[0022] FIG. 3 shows a characteristic for the expected aging behavior of adaptive parameters,

[0023] FIG. 4 shows a characteristic for actuation thresholds of a hydrostatic clutch actuating system.

DETAILED DESCRIPTION

[0024] In FIG. 1, the construction of an automated clutch actuating system 1 is illustrated schematically using the example of a schematically illustrated hydraulic, hydrostatic clutch actuator of the kind used in vehicles. On the master side 2, the hydraulic clutch actuating system 1 comprises a control unit 3, which controls an electric motor 4, which, in turn, drives a mechanism 5 for converting the rotary motion of the electric motor 4 into a translational motion of a piston 6 mounted in an axially movable manner within a master cylinder. If a rotary motion of the electric motor 4 causes a change in the position of the piston 6 in the master cylinder 7 to the right along the actuator path, the volume of the master cylinder 7 is changed, as a result of which a pressure p is built up in the master cylinder 7 and transmitted by a pressure medium 8, via a hydraulic line 9, to the slave side 10 of the hydraulic clutch actuating system 1.

[0025] In respect of its length and shape, the hydraulic line 9 is matched to the installation space situation in the vehicle.

[0026] On the slave side 10, the pressure p of the pressure medium 8 causes a change in the travel in a slave cylinder 11, and this is transmitted to a friction clutch 12 in order to actuate said clutch. The pressure p in the master cylinder 7 on the master side 2 of the hydraulic clutch actuating system 1 can be determined by a sensor 13. The sensor 13 is a pressure sensor. The distance traveled by the clutch actuator is determined by a second sensor 14, which is designed as a displacement sensor.

[0027] FIG. 2 illustrates an illustrative embodiment of the method according to the disclosure which is carried out by the hydraulic clutch actuating system illustrated in FIG. 1. After the start in block 100, where the friction clutch 12 is activated to transmit a maximum torque, the output divides into a check on the clutch actuating system 1 for incorrect functioning in block 201, while, alternatively, in block 301, the clutch actuating system 1 is checked for correct functioning.

[0028] In block 201, the system enquires whether the maximum torque has been demanded and set at the clutch. If this is the case, the system enquires in block 202 whether an unintended slip is above a predetermined slip threshold. Since the slip is represented by a rotational speed at the friction clutch 12, a rotational speed threshold is used as the slip threshold. If the unintended slip is above this rotational speed threshold, the duration of the slip present is checked in block 203. If the measured duration exceeds a time threshold, a plausibility check is performed in block 204, in which a first absolute value to be used to increment a counter is multiplied by a predetermined sensitivity factor. In the plausibility check, adaptive parameters such as a long-term friction coefficient and a long-term bite point, for example, are continuously monitored during the operation of the clutch actuating system 1. It is known that, with increasing wear, the long-term friction coefficient decreases and the long-term bite point rises, this being brought about by abrasion of material from the clutch lining in a dry clutch.

[0029] FIG. 3 illustrates a characteristic for an expected aging behavior of the long-term bite point and of the long-term friction coefficient, showing the torque Trq.sub.CL of the friction clutch 12 against the actuator positions L.sub.CL of the clutch actuator. Here, characteristic A shows the characteristic curve of a new friction clutch 12, while characteristic B illustrates the characteristic curve for a worn friction clutch, wherein the bite point shift TV and the friction coefficient decline RA are illustrated. If, for example, a long-term bite point exceeds a bite point threshold, this confirms that the friction clutch 12 has a corresponding wear and thus a possible end of service life is being reached. In the event of unintended slip, the predetermined sensitivity factor is increased, this corresponding in the case of a high long-term bite point to a high sensitivity. In the case of a lower long-term bite point falling below the bite point threshold, the sensitivity factor selected is smaller than in the case of the high long-term bite point.

[0030] A further plausibility check on the state of wear of the friction clutch 12 can be performed by currently measured quantities to be measured, which are compared with a clutch model. As illustrated in FIG. 4, the actual clutch actuating system 1 is illustrated in regions p.sub.max and L.sub.max, which each represent the maximum pressure in the hydraulic clutch actuating system and the maximum actuator travel traveled by the actuator. When setting the maximum torque at the friction clutch 12, the clutch characteristic, which is subject to hysteresis and which corresponds to normal operation (curve C) must end in the maximum regions p.sub.max and L.sub.max. However, if model deviations lead to a reduced maximum pressure p.sub.max-real leading to a reduced maximum torque of the friction clutch 12, this is described by the model characteristic D. That is to say the maximum pressure p.sub.max, as is supposed to be achieved when the maximum torque is applied, is not achieved in the clutch actuation when there are slip situations. This reduced pressure p.sub.max-real contributes to the actuator travel L.sub.max-Modell being shorter than the expected maximum actuator travel L.sub.max.

[0031] If such a difference between the travel and pressure values calculated from the clutch model and the travel and pressure values measured in the actual system is ascertained, it is assumed that unintended slip in this situation is based on a model error. If, in the checking of the quantities to be measured, it is ascertained that the maximum pressure or the physically permissible travel has not been achieved with the calibratable tolerance, the predetermined sensitivity factor for service life detection of the friction clutch is reduced. This continues until the adaptation of the quantities to be measured reduces the model quantities sufficiently. During this process, the maximum distance L.sub.max-Modell traveled by the actuator is calculated from the actually achieved pressure p.sub.max-real using the clutch characteristic. Thus, wear-independent assessment as to whether the friction clutch 12 is at the end of its service life is possible.

[0032] After the plausibility check, the thermal influences which lead to thermal damage to the lining of the friction clutch 12, e.g. thermal shock or fading, are considered in block 205. In the case of dry friction clutches 12, this thermal damage is healed by abrasion of the lining layer affected. Since an accumulated occurrence of thermal effects, such as fading and thermal shock, delays the detection of a defective clutch when the dry friction clutch 12 is worn, the sensitivity factor in the case of unintended slip with maximum torque applied is reduced. In the case of wet friction clutches, wherein no healing of the affected lining layer is possible, the sensitivity of the wet clutches is increased when fading or thermal shock is detected since damage to the clutch can be expected. That is to say that the predetermined sensitivity factor by which the absolute value is multiplied for incrementation of the counter is increased. In the simplest case, this weighted sensitivity factor can be greater or less than 1. In this case, it is advisable for a number of events to be recorded by the service life counter to be reduced in the case of wet clutches as compared with dry clutches since a defective wet friction clutch 12 can be detected with fewer measurement steps.

[0033] Finally, in block 206, the weighted sensitivity factor is calculated from the influences determined in blocks 204 and 205. After the calculation, a transition is made to block 400, where a check is made to determine whether the slip situation and the torque situation have ended. If this is the case, the service life counter is incremented in block 500 in accordance with the first absolute value multiplied by the weighted sensitivity factor. If the slip situation has not yet ended in block 400, the routine continues to the end in block 600.

[0034] If the enquiries in blocks 201, 202 and 203 receive a negative answer, the routine is interrupted in block 600.

[0035] Beginning with the start 100, where a maximum torque is transmitted by the friction clutch 12, an enquiry is made in block 301 in a test for correct functioning of the friction clutch 12 as to whether the maximum torque is present. If this is the case, the system enquires in block 302 whether the slip is below a slip threshold. If this is the case, the duration of the slip state or adhesion state is determined and the system enquires whether it lasts longer than a predetermined time threshold (block 303). This enquiry as to the duration of the slip is significant since the clutch actuating system 1 settles only over a certain period of time. The observation time begins when a slip below the threshold occurs.

[0036] If the slip is less during the entire duration, there is a transition to block 400, where it is ascertained whether the slip situation has ended. In block 500, the service life counter is reduced by a predetermined second absolute value. If it is ascertained in blocks 301, 302 and 303 that the events have not occurred, the evaluation process is ended in block 600.

LIST OF REFERENCE SIGNS

[0037] 1 clutch actuating system [0038] 2 master side [0039] 3 control unit [0040] 4 electric motor [0041] 5 mechanism [0042] 6 piston [0043] 7 master cylinder [0044] 8 pressure medium [0045] 9 hydraulic line [0046] 10 slave side [0047] 11 slave cylinder [0048] 12 friction clutch [0049] 13 pressure sensor [0050] 14 displacement sensor [0051] p pressure [0052] TV bite point shift [0053] RA friction coefficient decline [0054] A characteristic [0055] B characteristic [0056] C clutch characteristic (normal operation) [0057] D model characteristic [0058] 100, 201-206, 301, 302, 303, 400, 500, 600 step