ACTUATION OF A CONVERTER LOCK-UP CLUTCH OF A HYDRODYNAMIC TORQUE CONVERTER BY MEANS OF A SAFETY FUNCTION

Abstract

The invention relates to the actuation of a converter lock-up clutch (44) of a hydrodynamic torque converter (4) in a vehicle drive-train by means of a safety function where, in addition to a driving strategy function, the safety function can actuate the converter lock-up clutch (44) by issuing a clutch actuation command. For this purpose, at least one rotation speed at the torque converter (4) is monitored. If the monitored rotation speed is below a rotation speed threshold, the safety function commands an actuation of the converter lock-up clutch (44) in its opening direction.

Claims

1-9. (canceled)

10. A method for actuating a converter lock-up clutch (44) of a hydrodynamic torque converter (4) in a vehicle drive-train by means of a safety function, the method comprising: providing a vehicle drive-train having a safety function configured to actuate a converter lock-up clutch (44) and to actuate a driving strategy function by issuing a clutch actuation command; monitoring at least one rotation speed at the torque converter (4) to determine a monitored rotation speed; and issuing the clutch actuation command, if the monitored rotation speed falls below a rotation speed threshold, to actuate the converter lock-up clutch (44) in its opening direction.

11. The method according to claim 10, wherein monitoring the at least one rotation speed comprises monitoring the input rotation speed and/or monitoring the output rotation speed at the torque converter (4).

12. The method according to claim 10, wherein monitoring the at least one rotation speed comprises monitoring a rotation speed ratified by a plausibility check.

13. The method according to claim 12, wherein the plausibility check comprises: comparing the input rotation speed of the converter with an engine rotation speed; and determining a plausibility of the input rotation speed based on comparing the input rotation speed of the converter with the engine rotation speed.

14. The method according to claim 13, comprising opening the lock-up clutch if the plausibility of the input rotation speed is determined to be implausible.

15. The method according to claim 12, wherein the plausibility check comprises comparing the output rotation speed with a quotient between the transmission output rotation speed and a gear ratio of an engaged gear.

16. The method according to claim 15, comprising opening the lock-up clutch if the plausibility of the output rotation speed is determined to be implausible.

17. The method according to claim 10, wherein the rotation speed threshold is in a range of an idling rotation speed of a drive engine (1) coupled on an input side to the torque converter.

18. The method according to claim 10, wherein the converter lock-up clutch (44) is actuated by a hydraulic pressure, and wherein the safety function commands the actuation of the converter lock-up clutch (44) by generating a corresponding hydraulic actuation pressure in order to actuate the converter lock-up clutch (44).

19. The method according to claim 18, wherein each of the driving strategy function and the safety function is configured to call for an actuation of the converter lock-up clutch (44) by issuing the clutch actuation demand to a hydraulic control unit (24) for the converter lock-up clutch (44), and the method comprises: the hydraulic control unit (24) actuating the converter lock-up clutch (44) by applying an actuation pressure to a hydraulic actor of the converter lock-up clutch (44); the safety function checking whether the monitored rotation speed is below a predetermined rotation speed threshold when the driving strategy function issues to the hydraulic control unit (24) a clutch actuation command to close the converter lock-up clutch (44); and the safety function issuing a clutch actuation command to the hydraulic control unit (24) to open the converter lock-up clutch (44) if the safety function recognizes that the monitored rotation speed is below the rotation speed threshold.

20. The method according to claim 10, wherein the safety function is activated continuously.

21. The method according to claim 10, wherein the safety function is deactivated above a predetermined threshold for a speed of the vehicle or a rotation speed, and the safety function is activated below the predetermined threshold.

22. A vehicle control unit (23) for actuating a converter lock-up clutch (44) of a hydrodynamic torque converter in a vehicle drive-train, wherein the vehicle control unit (23) is configured to carry out the method according to claim 10.

23. A computer-readable storage medium with a stored program code that, when executed by a vehicle control unit (23) for actuating a converter lock-up clutch (44) of a hydrodynamic torque converter, carries out the method according to claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Below, the invention is explained in greater detail with reference to figures showing further preferred embodiments of the invention. These show, in each case represented schematically:

[0034] FIG. 1: A vehicle drive-train,

[0035] FIG. 2: A flow-chart of a method.

DETAILED DESCRIPTION

[0036] FIG. 1 shows a vehicle drive-train viewed from above, for example for a passenger car or a truck.

[0037] The drive-train comprises a drive engine 1, for example in the form of an internal combustion engine, and a multi-gear transmission 2. The transmission 2 is for example in the form of an automatic transmission. With the transmission 2 a selection of gears can be engaged in order to convert the rotation speed and torque of the drive engine 1 in accordance with the driving situation. On the drive output side of the transmission 2 the drive power is transmitted to drive wheels 3. In drive-connection between the drive engine 1 and the transmission 2 a hydrodynamic torque converter 4 is provided. Alternatively, the converter 4 can be provided inside the transmission 2 so that it forms an integral part of the transmission 2.

[0038] The structure of such a converter 4 is already known as such, so here the said structure will only be outlined in brief. The converter comprises a pump wheel 41 and a turbine wheel 42 that can be driven hydrodynamically by the pump wheel 41. Optionally, an additional guide wheel 43 can be provided. The pump wheel 41 forms the drive-technological drive/input of the converter 4. The turbine wheel forms the drive-technological drive/output of the converter 4. The force transmission taking place by virtue of the pump wheel 41 and the turbine wheel 42 can be bridged across mechanically by closing a converter lock-up clutch 44 arranged inside the converter 4. Thus, optionally the clutch 44 forms or releases a rotationally fixed mechanical coupling between the input and output of the converter 4. In particular, the clutch 44 is in the form of a disk clutch. To actuate the clutch 44, an actor (not shown) is provided inside the converter 4. In this case, the said actor is in particular hydraulically actuated, for example a hydraulic cylinder.

[0039] The input of the converter 4 is coupled rotationally fixed to the drive engine 1. Thus, the input rotation speed of the converter 4 corresponds to the motor rotation speed of the drive engine 1. The output of the converter is coupled rotationally fixed to the transmission input shaft 21. Thus, the output rotation speed of the converter 4 corresponds to the input rotation speed of the transmission 2.

[0040] The converter 4 serves at least as a starting clutch. When the vehicle is staring off and driving slowly, it transmits the drive power from the drive engine 1 to the transmission 2, largely by hydrodynamic means. When starting, the transmission input shaft 21 and thus the output of the converter 4 are at first stationary. At the same time, the drive engine 1 is turning the input of the converter 4. Then, there is a relative rotation between the pump wheel 41 and the turbine wheel 42, which produces the hydrodynamic force transmission in the converter 4. In such a case the clutch 44 must be open far enough for the rotation speed of the drive engine 1 not to be reduced too much. The same applies during slow maneuvering of the vehicle.

[0041] At higher speeds (this corresponds to higher rotation speed of the transmission input shaft 21 and the transmission output shaft 22) the clutch 44 is normally closed in order to bridge mechanically across the hydrodynamic force transmission in the converter 4, which is substantially affected by losses.

[0042] The actuation of the clutch 44 is controlled by a control unit 23. For that purpose, the control unit 23 issues respective actuation commands for the clutch 44 to a hydraulic control unit 24. The hydraulic control unit 24 transforms the command from the control unit 23 into an associated actuation pressure for the actor of the clutch 44, for example by means of one or more electrically actuated valves. The actuation pressure can for example be passed into the converter 4 and on to the actor of the clutch 44 via a shaft bore.

[0043] Preferably, the control unit 23 and the hydraulic control unit serve not only to actuate the clutch 44, but also to actuate shifting elements of the transmission 2 with which gears of the transmission 2 can optionally be engaged and disengaged.

[0044] The regular actuation of the clutch 44, i.e. when nothing is wrong, takes place by virtue of a driving strategy function stored in the control unit 23. The driving strategy function can also be provided in order to bring about the actuation of the shifting elements of the transmission 2. In that way a mode of operation of the drive-train is made possible which is coordinated between the converter 4 and the transmission 2. Preferably, for that purpose the control unit 23 processes rotation speeds and/or the speed of the vehicle. A measure for the vehicle speed is in particular the rotation speed of the transmission output shaft 22. The command to actuate the clutch 44 and the transmission shifting elements is issued in particular with reference to characteristic curves and/or diagrams stored in the control unit 23. Correspondingly, during regular operation the opening of the clutch 44 in order to hold the vehicle still and for slow maneuvering of the vehicle is brought about by the driving strategy function.

[0045] During operation, problems can arise, for example, due to the failure of a sensor or if the driving strategy function is carried out incorrectly. It can then happen that the opening of the clutch 44 is erroneously not called for. When the vehicle is at rest or maneuvering, the rotation speed of the drive engine 1 is then reduced due to the closed clutch 44 until the idling speed control is brought into play. The idling speed control seeks to maintain the motor rotation speed required for the engine 1 to keep operating. If the idling speed control is set too high the vehicle will accelerate unintentionally, while if it is set too low the motor rotation speed will decrease further until the engine 1 stalls.

[0046] An extra safety function is now provided in the control unit 23, which reliably brings about the opening of the clutch 44 for holding the vehicle at rest or maneuvering it even when this is not done by the driving strategy function. In particular, the safety function only intervenes when irregular operation is taking place.

[0047] The procedure of the safety function is illustrated in FIG. 2. In this procedure it is assumed that the speed of the vehicle is relatively low. For example, the vehicle is actually stopped or is maneuvering. Accordingly, the rotation speeds at the transmission output shaft 22 and the transmission input shaft 21 are relatively low. The rotation speed of the transmission input shaft 21 has fallen to just below the idling speed of the drive engine 1.

[0048] Step 100: As a result of irregular operation the driving strategy function calls for closing of the clutch 44. It issues a corresponding clutch actuation command, in particular to the hydraulic control unit 24.

[0049] Step 200: The safety function recognizes that the driving strategy function has issued the command to close the clutch 44.

[0050] Step 300: The safety function monitors the rotation speed at the input of the converter 4 (this corresponds to the motor rotation speed) and the rotation speed at the output of the converter 4 (this corresponds to the rotation speed at the transmission input shaft 21). This monitoring takes place continuously, i.e. at least always when the safety function is activated. Or else, the monitoring only takes place when the safety function has recognized that the driving strategy function has issued a command to close the clutch 44. The safety function checks whether either the rotation speed at the input of the converter 4 or the rotation speed at the output of the converter 4 is below a rotation speed threshold stored in the control unit 23. In particular, this rotation speed threshold is in the region of the idling speed of the engine 1.

[0051] Step 400: Decision path Y: If the safety function recognizes that one of the two monitored rotation speeds (or even both of them) is/are below the rotation speed threshold, the safety function for its part commands the opening of the clutch 44. Thus, independently of the driving strategy function, it issues a corresponding clutch actuation command of its own, in particular to the hydraulic control unit 24.

[0052] In practice there is a slight time delay between the command by the driving strategy function to close the clutch 44 (Step 100) and the command by the safety function to open the clutch 44 (Step 400). Thus, the command to open the clutch 44 reverses the immediately preceding command to close it, still in time before the clutch actor can close the clutch 44.

[0053] Step 500: Decision path N: If the safety function recognizes that neither of the two monitored rotation speeds is below the rotation speed threshold, no separate command to actuate the clutch 44 is issued by the safety function. In such a case the rotation speeds are still high enough for the clutch 44 to be closed without risk on the basis of the command from the driving strategy function (Step 100). Preferably, however, the safety function still remains active. Thus, it still monitors the said rotation speeds and carries out the check as in Step 300 continuously, so as to be able to react promptly by opening the clutch 44 if the rotation speeds should fall to an unacceptable extent.

[0054] To prevent the procedure shown in FIG. 2 from being carried out unnecessarily at relatively high rotation speeds or vehicle speeds, the safety function can then be deactivated. In particular it is only activated when the rotation speeds at the input or output of the converter 4 are low enough. In FIG. 2, for example, before Step 100 the safety function can have been activated because one of the rotation speeds or the speed of the vehicle has fallen below a threshold for activating the safety function.

INDEXES

[0055] 1 Drive engine [0056] 2 Transmission [0057] 21 Transmission input shaft [0058] 22 Transmission output shaft [0059] 23 Control unit, transmission control unit [0060] 24 Hydraulic control unit [0061] 3 Drive wheel [0062] 4 Hydrodynamic torque converter [0063] 41 Pump wheel [0064] 42 Turbine wheel [0065] 43 Guide wheel [0066] 44 Converter lock-up clutch [0067] 100 Process step [0068] 200 Process step [0069] 300 Process step [0070] 400 Process step [0071] 500 Process step