DETERMINING THE ENGAGEMENT POINT OF A CLUTCH

Abstract

A method for determining an engagement point (X) of a clutch (3). The clutch (3) has first and second clutch sides (3a, 3b), which are rotationally decoupled when the clutch (3) is disengaged/open and which are rotationally coupled when the clutch (3) is engaged/closed. The method includes the steps of disengaging the clutch (3) and then engaging the clutch (3), in order to determine the engagement point (X). During this, the first clutch side (3a) is driven in rotation and the second clutch side (3b) is accelerated, for at least part of the time, by an acceleration device (4). A control device actuates the clutch (3) in order determine the engagement point (X) of the clutch (3), and a computer program product with stored commands, brings about the sequence of the method when the program is operated on a suitable control unit.

Claims

1-10. (canceled)

11. A method for determining an engagement point (X) of a clutch (3), the clutch (3) having first and second clutch sides (3a, 3b), which are rotationally decoupled when the clutch (3) is disengaged and rotationally coupled when the clutch (3) is engaged, the method comprising: disengaging the clutch (3) and then engaging the clutch (3) in order to determine the engagement point (X), and during which the first clutch side (3a) is driven in rotation and the second clutch side (3b) is accelerated by an acceleration device (4).

12. The method according to claim 11, further comprising either reducing or increasing a rotational speed (n2) of the second clutch side (3b), with the acceleration device (4), during the acceleration of the second clutch side (3b).

13. The method according to claim 11, further comprising beginning the acceleration of the second clutch side (3b) with the acceleration device (4) either during or after the disengagement (t2) of the clutch and ending the acceleration of the second clutch side (3b) before or during the engagement (t4) of the clutch (3).

14. The method according to claim 11, wherein the clutch (3) is a frictional clutch for a motor vehicle and the clutch (3) is designed to be arranged between a drive motor (1) of the motor vehicle and a transmission (2) of the motor vehicle.

15. The method according to claim 14, wherein when installed in the motor vehicle, arranging the clutch (3) at an inclination (a) relative to a road surface under the motor vehicle.

16. The method according to claim 14, wherein at least one of the acceleration device (4) is a synchronization device of the transmission (2) for synchronizing at least one shifting element of the transmission (2), and the acceleration device (4) is an electric traction machine for driving the motor vehicle.

17. The method according to claim 16, wherein the synchronization device is either a transmission brake, or at least one synchronizing ring of the shifting element.

18. The method according to claim 11, further comprising after determining the engagement point (X): bringing the clutch (3) to a test position (Y) which has been determined on a basis of the engagement point (X) determined and is before the engagement point (X) determined, and then at the test position (Y), bringing the second clutch side (3b) to a defined rotational speed (n2), by the acceleration device (4), and then determining whether, while the first clutch side (3a) is being driven in rotation and the second clutch side (3b) stays in the test position (Y), the rotational speed (n2) of the second clutch side (3b) changes to an unacceptable extent.

19. A control unit for actuating a clutch (3) and for determining an engagement point (X) of the clutch (3), wherein the control unit is designed to carry out the method according to claim 11.

20. A computer program product with stored commands, wherein the commands bring about a sequence of the method according to claim 11 when the computer program product is run on a suitable control unit.

21. A method of determining an engagement point (X) of a clutch (3), the clutch (3) having first and second clutch sides (3a, 3b), which are rotationally decoupled from one another when the clutch (3) is disengaged and are rotationally coupled to one another when the clutch (3) is engaged, the method comprising: disengaging and then engaging the clutch (3) in order to determine the engagement point (X) of the clutch (3), and during such disengagement and engagement of the clutch (3), rotationally driving the first clutch side (3a) while accelerating the second clutch side (3b) by an acceleration device (4).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Below, the invention is explained in greater detail with reference to figures from which further preferred embodiments and features of the invention can emerge. In the form of schematic representations, the figures show:

[0042] FIG. 1: A partial view of a drive-train of a motor vehicle with a drive motor and a multi-stage transmission with a clutch arranged between them,

[0043] FIG. 2: Time variations of a rotational speed at a clutch and of an acceleration device of the clutch, and of an actuation condition of an acceleration device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] According to FIG. 1 the drive-train of a motor vehicle comprises a drive motor 1, in particular such as an internal combustion engine for propelling the motor vehicle. In addition a multi-stage transmission 2 is provided in the drive-train. In this case it can be an automated change-speed transmission but it can also be an automatic transmission. The transmission 2 has an output shaft 2b on its drive output side, by means of which further drive-output-side components of the drive-train are rotationally coupled. Thus, in a manner already known as such, for example wheels of the motor vehicle can be driven by means of the drive motor 1. On the input side, the transmission 2 has a drive input shaft 2a. In particular the transmission 2 has a low drag torque, so its internal frictional torques are relatively low. Accordingly, the input and output shafts 2a, 2b can be rotated particularly easily.

[0045] A frictional clutch 3 is drive-technically connected between the drive motor 1 and the transmission 2. The clutch 3 has two clutch sides 3a, 3b which, depending on the actuation condition of the clutch 3, are rotationally coupled or rotationally decoupled. The clutch 3 is actuated automatically. A driveshaft 1a of the drive motor 1 is coupled rotationally fixed to the first clutch side 3a. The input shaft 2a of the transmission 2 is coupled rotationally fixed to a second clutch side 3b. The clutch 3 can be for example a starter clutch or a converter bridging clutch. When the clutch 3 is open, its clutch sides 3a, 3b are rotationally decoupled from one another. Accordingly, the driveshaft 1a can rotate relative to the input shaft 2a. When the clutch 3 is closed the first and second clutch sides 3a, 3b are rotationally coupled with one another, so that the driveshaft 1a is rotationally coupled to the input shaft 2a.

[0046] In such a drive-train it is already known to determine a so-termed engagement point of the clutch 3 automatically. The engagement point corresponds to that clutch position at which the clutch sides 3a, 3b are just in contact with one another without transmitting any substantial force to one another. Thus, at the engagement point of the clutch 3 no substantial torque transmission yet takes place via the clutch 3.

[0047] A rotational axis of the clutch sides 3a, 3b and of the shafts 1a, 2a, 2b is indexed L in FIG. 1. When the components 1, 2, 3 are correctly installed, the rotational axis L extends at an angle α relative to the horizontal W. Thus, when a motor vehicle fitted with this drive-train is on a horizontal road surface, the components are inclined relative to the road surface by the angle α.

[0048] With such a drive-train it can happed that the determination of the engagement point of the clutch 3 does not take place as it should. This can be attributed to the fact that in practice, one of the clutch sides 3a, 3b is arranged so that it can move axially (i.e. along the rotational axis L) on the shaft 1a, 2a concerned. For example, although the second clutch side 3b can be coupled rotationally fixed to the input shaft 2a, it may be able to be displaced axially on it to some extent. Thus, the second clutch side 3b is arranged in a ‘floating’ manner on the input shaft 2a. Accordingly, when the clutch 3 is closed the second clutch side 3b can come into contact with the first clutch side 3a prematurely. As the clutch continues being closed, the second clutch side 3b is then displaced along the input shaft 2a until the clutch 3 has reached its true engagement point and thereafter begins to grip. If this premature contact takes place while the engagement point of the clutch 3 is being determined, this can be misinterpreted as the actual engagement point. Later actuations of the clutch will be based on this erroneous engagement point, which can result in reduced comfort when the clutch 3 is actuated and/or in increased clutch wear.

[0049] The same applies to an interlocking clutch 3. Even if the installed position of the clutch 3 is horizontal, undesired displacement of one of the two clutch sides 3a, 3b may occur, for example due to vibrations in the drive-train or because the motor vehicle is parked on an inclined road. It is thus not absolutely necessary that the components 1, 2, 3 are actually installed inclined by the angle α.

[0050] To overcome this problem it is proposed that during the determination of the engagement point the second clutch side 3b that can be displaced on the shaft 2a is selectively accelerated positively or negatively by means of an acceleration device 4. This temporarily increases the friction between the second clutch side 3b and the shaft 2a. Slipping of the second clutch side 3b is thereby prevented or at least delayed until it no longer has any appreciable influence on the determination of the engagement point. Furthermore, as is preferable, there is no need to determine the drag torque of the transmission.

[0051] As the acceleration device, for example a transmission brake already present in the transmission in any case would be suitable. This usually serves primarily to synchronize transmission components. By means of it the input shaft 2a can be braked, so that the second clutch side 3b is also braked.

[0052] FIG. 2 shows, in the form of three graphs, the time sequence of a preferred embodiment of the proposed method for determining the engagement point of a clutch. In each of the graphs the time t is plotted along the horizontal axis. Below, the method will be explained in the form of an example relating to the drive-train of FIG. 1. Here, for example, the acceleration device 4 brakes the second clutch side 3b. However, the method can also be used with many other drive-trains.

[0053] FIG. 2 shows, in the topmost graph, a time variation of a rotational speed n1 of the first clutch side 3a and a time variation of a rotational speed n2 of the second clutch side 3b. Thus, the rotational speed n1 corresponds to the rotational speed of the drive motor 1 and the first clutch side 3a in FIG. 1. The rotational speed n2 corresponds to the rotational speed of the input shaft 3a and the second clutch side 3b in FIG. 1. The rotational speeds n1, n2 can be measured for example by means of a motor rotational speed sensor and a transmission input rotational speed sensor.

[0054] In the middle graph FIG. 2 shows a time variation parallel to the above graph, of a clutch position. The clutch position corresponds to the condition of the clutch. The clutch position corresponds to the torque that can be transmitted by the cutch 3. When the clutch position has reached the upper limit, the clutch 3 is fully closed and can then transmit a maximum torque. When the clutch position has reached the lower limit, the clutch 3 is fully open and can then not transmit any torque.

[0055] In the lower graph, FIG. 2 shows a time variation parallel to the above two graphs, of an actuation condition of the acceleration device 4. If the acceleration device 4 is switched on, the line of the graph rises above the base line. The second clutch side 3b is then accelerated together with the input shaft 2a. When the acceleration device 4 is switched off, the line of the graph falls back to the base line. The second clutch side 3b can then rotate freely together with the input shaft 2a.

[0056] The engagement point is now determined as follows:

[0057] At the beginning of the process, i.e. at time t0, the clutch 3 is closed. The first clutch side 3a is driven by the drive motor 1 with a particular constant rotational speed n1 throughout the time interval shown. Throughout the time interval shown, the transmission 2 is idling. Thus, the shifting elements in the transmission 2 are in a shifted condition such that the input shaft 2a is rotationally decoupled from the output shaft 2b.

[0058] At time t1 the opening of the clutch 3 begins. The second clutch side 3b is now rotationally decoupled from the first clutch side 3a.

[0059] At time t2 the clutch 3 is fully opened. The acceleration device 4 is now actuated, i.e. switched on. Consequently the input shaft 2a together with the second clutch side 3b is braked, i.e. accelerated negatively. Due to this acceleration the friction between the input shaft 2a and the second clutch side 3b increases. This prevents an axial sliding of the second clutch side 3b along the input shaft 2a. Thus, the second clutch side 3b maintains the same axial position it was in while the clutch was previously closed. Accordingly, the rotational speed n2 of the second clutch side 3b falls. It is basically possible for the acceleration device 4 to produce a positive acceleration of the second 3b instead of a negative acceleration, so that it is driving the second clutch side instead of braking it. In that case the rotational speed n2 would increase starting at time t2. In particular, to compensate any dead time of the acceleration device 4 it can be provided that the acceleration device 4 is actuated already during the opening of the clutch 3.

[0060] At time t3 the acceleration device 4 is switched off. Thus, the selective braking of the second clutch side 3b ends. Thereafter, the rotational speed n2 still decreases slightly due to the friction in the transmission 2. This switching off of the acceleration device 4 can even be done later if needs be.

[0061] At time t4 the process of closing the clutch 3 in a ramp-like manner begins. This closing serves for the actual determination of the engagement point. During it, in a manner known as such, in particular the torque transmitted by the clutch 3 and the clutch position at the time are recorded. For example, during this the moment when the torque transmitted by the clutch 3 exceeds a particular threshold value is recognized. From this, for example by means of a suitable return method the engagement point can be deduced. This eliminates the need to determine the drag torque of the transmission 2.

[0062] In FIG. 2 the engagement point is reached at time t5 and the corresponding clutch position determined is X. Starting from there, the clutch 3 therefore starts gripping as closing continues. Correspondingly, from time t5 the rotational speed n2 of the second clutch side 3b starts increasing, since the second clutch side 3b is now increasingly coupled to the driven first clutch side 3a. The clutch position X can now be stored in a non-volatile memory of a control unit for actuating the clutch 3, as the determined engagement point for future actuation processes of the clutch 3. This control unit can be the transmission control unit for actuating the transmission 2. Thereafter, the clutch can be closed completely, although that is not imperatively necessary.

[0063] To check the engagement point X just determined, while the first clutch side 3a is still being driven at a constant rotational speed and the transmission 2 is idling, the clutch 3 can now be opened again as far as a test position Y. Starting from the opened clutch 3 the test position Y is located in front of the determined engagement point X. Thus, at the test position Y the two clutch sides 3a, 3b are just rotationally decoupled from one another—assuming that the engagement point X has been determined correctly. The test position Y can be determined for example by deducting or adding a defined offset from or to the previously determined engagement point X. The second clutch side 3b is now braked again by means of the acceleration device 4, in particular down to a standstill. The braking is then terminated. If after this, while the test position Y is maintained, the rotational speed n2 of the second clutch side 3b does not increase or only increases very little over a defined time interval, it can be assumed that the engagement point X has been determined correctly. In that case it can be stored permanently in the non-volatile memory of the control unit for the clutch 3. In that way the engagement point X determined can be verified in a simple manner. In the context of this verification, by means of the acceleration device the second clutch side 3b can also be driven up to a defined rotational speed instead of being braked, i.e. accelerated. Whether it is braked or accelerated for the verification depends on the design of the acceleration device 4 used. For example, if a transmission brake is used as the acceleration device 4, this can only act upon the second clutch side 3b by braking it.

INDEXES

[0064] 1 Drive motor [0065] 1a Driveshaft [0066] 2 Transmission [0067] 2a Input shaft [0068] 2b Output shaft [0069] 3 Clutch [0070] 3a First clutch side [0071] 3b Second clutch side [0072] 4 Acceleration device [0073] L Rotational axis [0074] n, n1, n2 Rotational speed [0075] t, t1 . . . t5 Time point [0076] W Horizontal [0077] X Engagement point [0078] Y Test position [0079] α Angle of inclination