METHOD FOR OPERATING A MOTOR VEHICLE COMPRISING A POWER TAKE-OFF UNIT

Abstract

The present invention relates to a method for operating a motor vehicle. A request for coupling a power take-off is detected. It is checked (12) whether relevant boundary conditions for coupling the power take-off are fulfilled. If the boundary conditions are fulfilled, a system pressure for actuating the power take-off clutch is built up (16). It is checked (18) whether sufficient system pressure to actuate the power take-off clutch has been built up. When sufficient system pressure has been built up, a confirmation signal is produced (20). In reaction to the confirmation signal, a driving transmission control unit is modified (34) in order to actuate the at least one shifting element of the driving transmission with a higher actuation pressure than with an unmodified driving transmission control unit.

Claims

1-12. (canceled)

13. A method of operating a motor vehicle with a motor, a driving transmission having at least one shifting element, a power take-off and a power take-off clutch by which the power take-off can be coupled to the driving transmission, the method comprising at least the following steps: detecting (10) a request to couple the power take-off; checking (12) whether respective boundary conditions for coupling the power take-off are fulfilled; if the respective boundary conditions are fulfilled, building-up (16) a system pressure sufficient for actuating the power take-off clutch; checking (18) whether a system pressure sufficient for actuating the power take-off clutch has been built up; if sufficient system pressure has been built up, producing (20) a confirmation signal that actuation of the power take-off clutch is permitted; and modifying (34) a driving transmission control unit in reaction to the confirmation signal, in order to actuate the at least one shifting element of the driving transmission with a higher actuation pressure than with an unmodified driving transmission control unit.

14. The method according to claim 13, further comprising, with the modification of the driving transmission control unit, in addition deactivating (30) a learning function for an actuation pressure when actuating the at least one shifting element of the driving transmission.

15. The method according to claim 13, further comprising, in reaction to the confirmation signal, modifying (32) a motor control unit with at least one of the following functions: specification of at least one rotation speed limit for the motor; and specification of a limit for the power drawn from the motor.

16. The method according to claim 13, further comprising, along with the modification of the transmission control unit, in addition activating (36) a different shifting program for the driving transmission.

17. The method according to claim 13, further comprising the following steps: checking (22) whether the power take-off has been coupled, within a predetermined time interval, after producing the confirmation signal; and reducing (24) the system pressure for actuating the power take-off clutch and cancelling (14) the confirmation signal, if the power take-off has not been coupled within the predetermined time interval.

18. The method according to claim 13, further comprising the following steps: after the power take-off has been coupled, checking (28) whether the relevant boundary conditions for coupling the power take-off are still fulfilled; and while the power take-off is currently coupled, cancelling (14) the confirmation signal if the relevant boundary conditions are no longer fulfilled.

19. The method according to claim 13, further comprising, even after the confirmation signal has been cancelled, maintaining the system pressure for actuating the power take-off clutch at least until the power take-off has been decoupled.

20. The method according to claim 13, further comprising, for the modification of the driving transmission control unit in reaction to the confirmation signal, determining a value for increasing the actuation pressure compared with an unmodified actuation pressure as a function of the following factors: a rotation speed applied at the drive input of the driving transmission; and a torque applied at the drive input of the driving transmission.

21. The method according to claim 12, further comprising calculating an actual torque at a drive input of the driving transmission as a function of at least one of the following parameters: a torque provided at the crankshaft of the motor; a consumer loss; a motor braking force when driving downhill; and a calculated torque applied on the power take-off.

22. The method according to claim 21, further comprising calculating a torque at the power take-off in each case once as a function of a characteristic of the power take-off and once as a function of the converter slip, and if the torque calculated as a function of the converter slip is the smaller, using that torque for control purposes.

23. A control unit designed to carry out the method according to claim 13.

24. A computer program designed to enable a control unit to carry out the method according to claim 13, when the computer program is run on the control unit.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0031] The sole FIG. clearly but schematically illustrates, in the form of a flow chart, a method for operating a motor vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The sole FIG. clearly but schematically illustrates, in the form of a flow chart, a method for operating a motor vehicle. The motor vehicle has a motor, a driving transmission with at least one shifting element, a power take-off and a power take-off clutch by means of which the power take-off can be connected to the driving transmission. The method can be, for example, provided in the form of a computer-implemented program product. For this, a corresponding software code and a non-volatile data carrier can be provided. The method can be, for example, implemented on a transmission control unit of the motor vehicle, which is connected to the CAN bus of the motor vehicle.

[0033] Step 10 is the start of the method. In step 10 a request to couple the power take-off is detected. For example, the driver of the motor vehicle can actuate a corresponding operating element whereby the transmission control unit receives an actuation signal.

[0034] In step 12, it is checked whether respective boundary conditions for coupling and if need be operating the power take-off are fulfilled. Example boundary conditions are that the motor is running, a drive input rotation speed is within an acceptable range, a parking brake is activated, if the power take-off is a stationary one, a selector lever is in N or P, if the power take-off is a stationary one, a transmission oil temperature is in the acceptable range, no relevant error messages are active, another power take-off is switched completely on or off, and the actuation signal is present and still valid.

[0035] If the check shows that respective boundary conditions are not fulfilled, step 14 follows. In step 14, a signal is generated to the effect that the operation is not permitted and, alternatively or in addition, a confirmation signal, which can be produced in step 20, is cancelled. If the power take-off clutch is not engaged, its engagement is blocked in step 14. Since step 14 was reached from step 12, this signal or the cancellation of the confirmation signal can be supplemented by the information that some, or even which particular, boundary conditions are not fulfilled.

[0036] If the said check shows that the respective boundary conditions are fulfilled, this is followed by step 16. In step 16, a system pressure sufficient to actuate the power take-off clutch is built up. For this, a corresponding control signal to open a valve, for example, is produced.

[0037] In step 18, it is checked whether a system pressure sufficient to actuate the power take-off clutch has been built up. That check can take place after a predetermined time interval following the beginning of the pressure build-up in step 16, so that in the event of a fault, the method can be interrupted and, alternatively or in addition, a corresponding signal can be emitted. If no sufficient system pressure has been or can be built up, step 14 is repeated and a signal is generated to the effect that the operation of the auxiliary aggregate is not permitted. That signal, or the cancellation of the confirmation signal, can be supplemented by the information that the system pressure could not be built up.

[0038] If a sufficient system pressure is built up, the process moves on to step 20. In step 20, the confirmation signal is produced to show that the actuation of the power take-off clutch is permitted. For this, the transmission control unit can send the confirmation signal to a clutch control unit, for example via the CAN bus. The confirmation signal can be a change of a variable in the software, for example from zero to one. If the confirmation signal is cancelled, the value of the variable can then be correspondingly restored to zero.

[0039] After the confirmation signal has been produced in step 20, in step 22 it can be checked after a predetermined time interval whether the power take-off clutch has been engaged and the power take-off coupled thereby. For this, a corresponding signal can be received by the control unit via the CAN bus. If the power take-off has not been coupled, then in step 24, the system pressure is reduced, for example, to its initial value before passing through step 16. In addition, step 14 is carried out again in order to cancel the confirmation signal. This can be supplemented with the information that the power take-off has not been coupled within the predetermined time interval.

[0040] Step 26 relates to the case when, after step 20, the power take-off has been coupled. This can be notified to the transmission control unit by way of the CAN bus. Now, in step 28, it is checked quasi-continuously, continuously or intermittently whether the respective boundary conditions for operating the power take-off or for the power take-off to be coupled are fulfilled. In this, the boundary conditions can be the same as for the check in step 12 with the same or different values, or they can be different boundary conditions. If the required boundary conditions are still fulfilled, the confirmation signal is maintained. This is indicated by the arrow leading from step 28 to step 20. If the check, in step 28, shows that the boundary conditions are not fulfilled, the confirmation signal is cancelled in accordance with step 14. This can be supplemented with the information that some boundary conditions for coupling the power take-off or for its operation despite the already effected coupling or start of operation, are no longer fulfilled. In reaction to that information, the system pressure can be maintained until the power take-off clutch has been again disengaged. As soon as the confirmation signal has been cancelled and the power take-off clutch has been disengaged, in step 14 the system pressure built up in step 16 can, in contrast, be lowered again, analogously to step 24.

[0041] When step 26 of the method has been reached and the power take-off clutch has been engaged so that the power take-off is coupled and in operation, then at least one of steps 30 to 36 can in addition be carried out.

[0042] In step 30, in a driving transmission control unit a learning function for an actuation pressure of the shifting elements concerned is deactivated. During the operation of the power take-off, some assumed input torques are often too imprecise to achieve proper fine adjustment with the learning function.

[0043] In step 32 a motor control unit is modified by at least one function. For example, new rotation speed limits for the motor can be specified. Alternatively or in addition, new limits for a power take-up at the motor can be specified.

[0044] In step 34, a driving transmission control unit is modified in order that at least one shifting element of the driving transmission is actuated with a higher actuation pressure than if the driving transmission control unit had not been modified. An unmodified actuation pressure can already take into account a characteristic of the auxiliary aggregate and alternatively or in addition a take-off capacity drawn by the power take-off, in that the respective loads of the at least one shifting element are designed for a lower pressure. Thanks to the modification, an offset to a higher actuation pressure can be provided in order to take account of uncertainties in a determination of a power take-up by the auxiliary aggregate and to avoid slip at the shifting elements concerned in the driving transmission. In an embodiment the offset can be determined in the form of a current rotation speed of the power take-off and alternatively or in addition a torque of the power take-off, in order to adapt it as closely as possible to requirements.

[0045] In step 36, a modified shifting program for the driving transmission is activated. In this, some shifting points at which a gearshift takes place can be modified. For example, the shifting strategy can be adapted so that owing to the coupled power take-off, there are smaller input torques.

[0046] In step 38, an input torque can be determined as a function of a power take-off torque characteristic. The calculation of an input torque can thus be modified by taking account of the said power take-off torque characteristic. The control of the relevant shifting elements of the driving transmission, in particular their actuation pressure, can therefore be achieved as a function of a more precisely calculated input torque.

INDEXES

[0047] 10 Request to couple the power take-off [0048] 12 Checking of boundary conditions [0049] 14 Blocking of the operation of the power take-off [0050] 16 System pressure build-up [0051] 18 Checking the system pressure [0052] 20 Production of the confirmation signal [0053] 22 Checking whether the power take-off has been coupled [0054] 24 Reduction of the system pressure [0055] 26 Power take-off has been coupled [0056] 28 Further checking of boundary conditions [0057] 30 Deactivation of the learning function of the driving transmission control unit [0058] 32 Modification of the motor control unit [0059] 34 Modification of the respective actuation pressures of the shifting elements of the driving transmission [0060] 36 Activation of the modified shifting program [0061] 38 Calculation of the input torque as a function of the power take-off torque characteristic