METHOD FOR CONTROLLING GEAR CHANGES IN A TRANSMISSION OF A MOTOR VEHICLE DRIVETRAIN

Abstract

A method is disclosed for controlling gearshifts in a transmission of a motor vehicle. Devising a shifting strategy of the gearshift takes into account the operation of a sustained-action braking device (10). To organize gearshifts in an optimum way having regard to the operation of the sustained-action braking device (10), at the beginning of the operation of the sustained-action braking device (10) it is examined with what starting criterion the operation of the sustained-action braking device (10) was initiated. Depending on the starting criterion identified, a current workload of the sustained-action braking device (10) is compared against an associated threshold value. Alternately, a gearshift is carried out directly to a lowest possible gear of the motor vehicle transmission (4). If the comparison of the current workload of the sustained-action braking device (10) exceeds the threshold value, then the shifting strategy is adapted.

Claims

1-11. (canceled)

12. A method for controlling gearshifts in a transmission (4) of a motor vehicle drivetrain (1), wherein a shifting strategy is based at least in part on operation of a sustained-action braking device (10), the method comprising: initiating actuation of the sustained-action braking device; determining, after initiating use of the sustained-action braking device, a starting criterion for initiating actuation of the sustained-action braking device (10); and executing, based on the starting criterion, an operation selected from (i) comparing a current workload (x.sub.Ausl_Ret) of the sustained-action braking device (10) with an associated threshold value (x.sub.Grenz1, x.sub.Grenz2), and (ii) shifting a gear directly to a lowest possible gear of the motor vehicle transmission (4).

13. The method according to claim 12, further comprising: determining that the current workload (x.sub.Ausl_Ret) of the sustained-action braking device (10) exceeds the threshold value (x.sub.Grenz1, x.sub.Grenz2); and modifying the shifting strategy.

14. The method according to claim 13, wherein modifying the shifting strategy comprises: determining a reference parameter (z.sub.ref) based on the current workload (x.sub.Ausl_Ret) of the sustained-action braking device (10); selecting an actuation level (a.sub.Bet) of the sustained-action braking device (10) from stored characteristics; and modifying the shifting strategy based on the reference parameter (z.sub.ref).

15. The method according to claim 14, comprising determining an adjustment parameter (z.sub.Stell) based on the reference parameter (z.sub.ref) and based on a current actuation level (a.sub.Betrbrems) of a service brake (12) of the motor vehicle.

16. The method according to claim 15, wherein the adjustment parameter (z.sub.Stell) is further based in part on an additional stored characteristic and based in part on a previously selected shifting characteristic of the gearshift.

17. The method according to claim 16 comprising selecting, based on the adjustment parameter (z.sub.Stell), a further shifting characteristic from the stored characteristics.

18. The method according to claim 17, comprising displacing the further shifting characteristic based on the adjustment parameter (z.sub.Stell).

19. The method according to claim 14, wherein modifying the shifting strategy comprises decreasing an actuation level of a service brake and increasing the actuation level of the sustained-action braking device.

20. The method according to claim 14, wherein modifying the shifting strategy comprises increasing a current actuation level of a service brake of the motor vehicle and decreasing the current workload of the sustained-action braking device.

21. The method according to claim 14, wherein modifying the shifting strategy comprises increasing a downshift rotation speed.

22. The method according to claim 12, wherein determining the starting criterion comprises: determining that actuation of the sustained-action braking device (10) was initiated by an action of the vehicle driver; determining that an actuation level (a.sub.Bet) of the sustained-action braking device (10) is a highest actuation level; and shifting into the lowest possible gear of the transmission (4).

23. The method according to claim 12, wherein determining the starting criterion comprises: determining that actuation of the sustained-action braking device (10) was initiated by a driver-assistance system; and comparing the current workload (x.sub.Ausl_Ret) of the sustained-action braking device (10) with the associated threshold value (x.sub.Grenz1, x.sub.Grenz2).

24. The method according to claim 23, wherein the driver-assistance system is one of an adaptive speed control, an adaptive speed limiting system, and a speed restriction system.

25. A transmission control unit (5) configured to take into account operation of a sustained-action braking device (10) when devising a shifting strategy for gearshifts in a transmission (4) of a motor vehicle, the control unit configured to: (i) initiate actuation of a sustained-action braking device; (ii) determine, after initiating actuation of the sustained-action braking device, a criterion for initiating actuation of the sustained-action braking device (10); (iii) execute, based on the starting criterion, an operation selected from (i) comparing a current workload (x.sub.Ausl_Ret) of the sustained-action braking device (10) with an associated threshold value (x.sub.Grenz1, x.sub.Grenz2), and (ii) shifting a gear directly to a lowest possible gear of the motor vehicle transmission (4); and (iv) adapt the shifting strategy if the current workload (x.sub.Ausl_Ret) of the sustained-action braking device (10) exceeds the threshold value (x.sub.Grenz1, x.sub.Grenz2).

26. The transmission control unit (5) according to claim 25, further configured to determine a reference parameter (z.sub.ref) based on the current workload (x.sub.Ausl_Ret) of the sustained-action braking device (10); select an actuation level (a.sub.Bet) of the sustained-action braking device (10) from stored characteristics; and adapt the shifting strategy based on the reference parameter (z.sub.ref).

27. The transmission control unit (5) according to claim 26, further configured to determine an adjustment parameter (z.sub.Stell) based on the reference parameter (z.sub.ref) and based on a current actuation level (a.sub.Betrbrems) of a service brake (12) of the motor vehicle.

28. The transmission control unit (5) according to claim 27, further configured to displace a shifting characteristic based on the adjustment parameter (z.sub.Stell).

29. The transmission control unit (5) according to claim 27, further configured to change a ratio of an actuation level of a service brake and the actuation level of the sustained-action braking device.

30. The transmission control unit (5) according to claim 29, further configured to increase a downshift rotation speed.

31. A computer program product containing executable code that, when executed by a transmission control unit for a motor vehicle, executes the method of claim 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] An advantageous embodiment of the invention, which is explained below, is illustrated in the drawings, which show:

[0023] FIG. 1: A schematic representation of a motor vehicle drivetrain; and

[0024] FIG. 2: A flow chart of a method according to the invention for controlling gearshifts in a transmission of the motor vehicle drivetrain shown in FIG. 1.

DETAILED DESCRIPTION

[0025] FIG. 1 shows a schematic representation of a motor vehicle drivetrain 1, this being in particular the drivetrain of a utility vehicle such as a truck. The motor vehicle drivetrain 1 comprises a drive machine 2 which is in the form of an internal combustion engine and is connected on its drive output side, via an intermediate torsion fluctuation damper 3, to a transmission input of a downstream transmission 4. The torsion fluctuation damper 3, and if necessary a starter element provided on the input side of the transmission 4, are in this case integrated in a housing of the transmission 4.

[0026] In the present case the transmission 4 is in the form of an automated manual transmission or an automatic transmission, in which gearshifts are carried out automatically. For that purpose, a control unit is associated with the transmission 4, which controls gearshifts in the transmission 4. On its drive output side, the transmission 4 is connected to an axle differential 6, by way of which drive power of the drive machine 2 geared by the transmission 4 is distributed to drive wheels 7 and 8 of a drive axle 9 of the motor vehicle.

[0027] In the motor vehicle drivetrain 1, connected between the drive machine 2 and the transmission 4, there is also a sustained-action braking device 10 in the form of a retarder 11, which is preferably in the form of a hydrodynamic retarder and is connected in a rotationally fixed manner to the drive output side of the drive machine 2. Within the motor vehicle drivetrain 1 the retarder 11 serves during a braking operation to supply a braking torque in order to assist a service brake 12 by means of which the drive wheels 7 and 8, and also further wheels of the motor vehicle—no more of which are shown in this case—can be braked. In the retarder 11 various actuation levels and consequently various braking torques can be produced, which are transmitted via the downstream transmission 4 to the drive wheels 7 and 8 of the drive axle 9. The particular actuation level is in this case set by a control unit 13 of the retarder 11, which selects the actuation level concerned either in accordance with a choice made by a vehicle driver using an input element 14, or in accordance with a specification by a driver-assistance system. The driver-assistance system can in this case be an adaptive speed control (ACC) or an adaptive speed limitation system (ASL), or even a speed limitation system.

[0028] During the course of a braking operation by the retarder 11, the control unit 5 of the transmission 4 checks whether a shifting strategy for the organization of gearshifts in the transmission 4 should be adapted in order to achieve an optimum integration of the retarder 11. This checking procedure is carried out in accordance with a method according to the invention, whose flow chart is shown in FIG. 2.

[0029] At the beginning of the method according to the invention, in a first step S1 it is first examined whether an operation of the retarder 11 has been initiated and is still active. If not, then the method is terminated, whereas otherwise the system progresses to a step S2 in which it is examined whether, as the starting criterion for the operation of the retarder 11, there was a request by the driver of the vehicle. If not, then a change to a step S3 takes place in which, as the starting criterion for the operation of the retarder 11, a specification by a driver-assistance system is recognized.

[0030] On the other hand if in step S2 it is found that the retarder 11 is operating because of a command by the vehicle driver, then in a step S4, after the lapse of a specified time it is examined which actuation level of the retarder 11 has been chosen by the vehicle driver by way of the input element 14. In a subsequent step S5 it is then checked whether the actuation level is the highest actuation level, and if so the system advances to a step S6, whereas otherwise step S5 is followed by a step S7.

[0031] In step S6 the control unit 5 initiates a downshift in the transmission 4 to the lowest gear, i.e. the gear with the highest transmission ratio. Then the system springs back to step S1 so that it is checked again whether the retarder 11 is still operating and thereafter whether the driver of the vehicle might perhaps have changed his choice of the actuation level.

[0032] In contrast, in step S7 a current workload x.sub.Ausl_Ret of the retarder 11 is checked, such that in particular a percentage workload of the retarder 11 relative to a maximum obtainable braking power is determined. In a step S8 the current workload determined is compared against a threshold value x.sub.Grenz1 which is permanently stored. If the current workload x.sub.Ausl_Ret of the retarder 11 is found in step S8 to exceed the said threshold value x.sub.Grenz1 then the system changes to a step S9, whereas otherwise, in a step S10 the current shifting strategy in the transmission 4 is maintained and the system then reverts to step S1.

[0033] In step S9, with reference to the current workload x.sub.Ausl_Ret of the retarder 11 and the selected actuation level a.sub.Bet, a reference parameter z.sub.ref from a characteristic diagram is determined and the system then changes to a step S1 in which, in a further characteristic diagram and with reference to the reference parameter z.sub.ref from step S9 and a current actuation level a.sub.Betrbrems of the service brake 12, an adjustment parameter z.sub.Stell is determined. For this purpose, the current actuation level a.sub.Betrbrems of the service brake 12 is determined in advance. After that, with reference to the adjustment parameter z.sub.Stell and in a step S12 the shifting strategy in the transmission 4 is implemented by the control unit 5, in that with reference to the adjustment parameter z.sub.Stell the control unit 5 makes a selection from various stored characteristic curves and if necessary also displaces the shifting characteristics. In this case the shifting characteristics are chosen and if necessary their displacement is calculated in such manner that with increasing adjustment parameter z.sub.Stell higher downshift rotation speeds are obtained in the transmission 4. After step S12 the system springs back to step S1 and thereby a new check is carried out to see whether the retarder 11 is still operating and whether its operation might have changed.

[0034] In contrast, if the system has changes from step S2 to step S3 in which it has been found that as the starting criterion a command to operate the retarder 11 was issued by a driver-assistance system, then a change to a step S13 takes place in which a current workload x.sub.Ausl_Ret of the retarder 11 is determined, as was also done in step S7. With this current workload x.sub.Ausl_Ret of the retarder 11, in a step S14 a comparison with a threshold value x.sub.Grenz2 is carried out, wherein x.sub.Grenz2 is different from the threshold value x.sub.Grenz1 is step S8. If in step S14 the current workload x.sub.Ausl_Ret of the retarder 11 is found to be lower then the associated threshold value x.sub.Grenz2, then the system changes to step S10, whereas if the current workload x.sub.Ausl_Ret of the retarder 11 is found to be higher then the associated threshold value x.sub.Grenz2, then the system changes to step S9. In this case, however, for the determination of the reference parameter z.sub.ref from the characteristic diagram the currently chosen actuation level a.sub.Bet of the retarder 11 is set to zero. After step S9 or step S10, the process continues as described earlier.

[0035] By means of the procedure according to the invention the organization of gearshifts in the transmission can be adapted to the operation of a sustained-action braking device in an optimum manner.

INDEXES

[0036] 1 Motor vehicle drivetrain [0037] 2 Drive machine [0038] 3 Torsion fluctuation damper [0039] 4 Transmission [0040] Control unit [0041] 6 Axle differential [0042] 7 Drive wheel [0043] 8 Drive wheel [0044] 9 Drive axle [0045] Sustained-action braking device [0046] 11 Retarder [0047] 12 Service brake [0048] 13 Control unit [0049] 14 Input element [0050] x.sub.Ausl_Ret Workload [0051] x.sub.Grenz1 Threshold value [0052] x.sub.Grenz2 Threshold value [0053] a.sub.Bet Actuation level [0054] z.sub.ref Reference parameter [0055] z.sub.Stell Adjustment parameter [0056] a.sub.Betrbrems Actuation level of the service brake [0057] S1 to S14 Individual steps