METHOD AND CONTROL APPARATUS FOR OPERATING A MULTIPLE-SPEED VEHICLE TRANSMISSION

Abstract

Disclosed is a method for operating a multi-speed vehicle transmission having a plurality of shift elements (A, B, C, D, E) for engaging the gears of the vehicle transmission. The method includes decoupling between an input (AN) and an output (AB) of the vehicle transmission in a neutral gear, and coupling the input (AN) and the output (AB) of the vehicle transmission in a drive gear for propelling the vehicle by closing at least one shift element (B). At least one transmission state is determined when the neutral gear is engaged, where a shift element (D) for a reverse gear of the vehicle transmission is closed at least partially if the transmission is in a state with increased drag losses when the neutral gear is engaged.

Claims

1-11. (canceled)

12. A method for operating a multi-speed vehicle transmission, comprising: providing a plurality of shift elements (A, B, C, D, E) for engaging gears of the multi-speed vehicle transmission having an input (AN) and an output (AB); decoupling the input (AN) from the output (AB) in a neutral gear; coupling the input (AN) to the output (AB) in a drive gear for propelling the vehicle by closing at least one shift element (B) of the plurality of shift elements (A, B, C, D, E); determining, when the neutral gear is engaged, at least one transmission state; and closing, at least partially, a shift element (D) for a reverse gear if the multi-speed vehicle transmission is in a state with increased drag losses when the neutral gear is engaged.

13. The method according to claim 12, wherein the further shift elements (A, B, C, E) of the plurality of shift elements (A, B, C, D, E) are ventilated when the neutral gear is engaged and the transmission is in a state with increased drag losses.

14. Method according to claim 12, wherein determining the transmission state with increased drag losses comprises using one or more of (i) a transmission temperature (T), (ii) an operating time of the vehicle transmission since an engine start of a drive engine coupled or capable of being coupled to the vehicle transmission, and (iii) a temperature model of the vehicle transmission.

15. The method according to claim 14, wherein determining the transmission state with increased drag losses comprises using the transmission temperature and wherein using the transmission temperature includes determining a lubricant temperature of the vehicle transmission.

16. The method according to claim 12, comprising: determining an actuation state of a vehicle brake in addition to the transmission state when the neutral gear is engaged; ventilating the shift element (D) for the reverse gear when the neutral gear is engaged and the vehicle brake is actuated; and preloading or prefilling with a pressure medium at least one shift element (B) for a forward gear.

17. The method according to claim 16, comprising: closing first and second shift elements (A, B) of the plurality of shift elements (A, B, C, D, E) when the multi-speed vehicle transmission is in a drive gear; and when the neutral gear is engaged: (I) detecting that the vehicle brake (11) is being released; determining that the vehicle transmission is in the state with increased drag losses; and ventilating a first shift element (B) of the at least two shift elements (A, B); and/or (II) detecting that the vehicle brake (11) is being released; determining that the vehicle transmission is in the state with increased drag losses; determining that the vehicle is rolling; and ventilating a second shift element (A) of the at least two shift elements (A, B); and/or (III) detecting that the vehicle brake (11) is being released; determining that the vehicle transmission is in the state with increased drag losses; determining that the vehicle is rolling despite a ventilated first shift element (B) and a ventilated second shift element (A); and at least partially closing the shift element (D) for the reverse gear.

18. The method according to claim 17, wherein determining that the vehicle is rolling includes using one or more of (i) an output rotation speed (n.sub.AB) of the vehicle transmission, (ii) a wheel rotation speed of the vehicle, and (iii) an acceleration of the vehicle.

19. The method according to claim 17, wherein, when the neutral gear is being engaged and when the vehicle brake (11) is actuated, the method comprises: preloading or prefilling with a pressure medium the first shift element (B) of the at least two shift elements (A, B) for the drive gear, and closing the second shift element (A) of the plurality of shift elements (A, B) for the drive gear.

20. The method according to claim 17, comprising: closing, in the drive gear, at least or exactly three shift elements (A, B, C) of the plurality of shift elements (A, B, C, D, E) of the vehicle transmission; preloading or prefilling with a pressure medium the first shift element (B) of the three shift elements (A, B, C), when the neutral gear is being engaged and the vehicle brake (11) is actuated; closing the second shift element (A) of the three shift elements (A, B, C); and ventilating the third shift element (C) of the three shift elements (A, B, C).

21. The method according to claim 20, wherein the three shift elements (A, B, C) are closed in all travel gears in the vehicle transmission.

22. A transmission control device (10) for actuating a plurality of shift elements (A, B, C, D, E) of a multi-speed vehicle transmission, wherein the transmission control device (10) is configured to carry out the method according to claim 12.

23. A computer-readable storage medium comprising commands which, when executed by a computer, prompt said computer to execute the method according to claim 12.

Description

DETAILED DESCRIPTION

[0063] FIG. 1 shows a schematic illustration of the arrangement of shafts AN, AB, 1, 2, 3, 4, 5, 6, 7, 8 and planetary gear sets RS1, RS2, RS3, RS4 and shift elements A, B, C, D, E of a preferred multi-ratio vehicle transmission having a planetary design. For the sake of clarity, only the upper half of the vehicle transmission is shown. The lower half is in particular configured as a mirror image of this upper half. The structure and the operating principle of the vehicle transmission shown in FIG. 1 correspond to that shown in FIG. 4 of DE 10 2005 002 337 A1. For further details, reference is therefore expressly made to the relevant explanations in this document.

[0064] The drive shaft AN is usually coupled to the drive engine of the vehicle or capable of being coupled to it via a separate clutch, such as in particular via a hydrodynamic torque converter. The output shaft AB is usually coupled or capable of being coupled to drive wheels of the vehicle.

[0065] FIG. 1 also shows a transmission control device 10, which is used to actuate the shift elements A, B, C, D, E of the transmission. The control device 10 thus causes the shift elements A, B, C, D, E to selectively be opened and closed. This engages the gear that is appropriate in the respective situation or is requested by an operator of the vehicle. For this purpose, relevant information is provided to the control device 10 via the control device input. The control device 10 processes this information and outputs corresponding signals for actuating the shift elements A, B, C, D, E via the control device output.

[0066] The control device 10 is in particular provided with the information Br, T and n.sub.AB. The information Br is a brake signal of the service brake of the vehicle, which represents an actuation state of the brake. Of the service brake, only the brake pedal 11 is shown in FIG. 1. The brake signal Br is obtained by means of a position sensor of the brake pedal 11, for example. The information T is a temperature signal, which represents the transmission temperature. The temperature signal T is obtained by means of a temperature sensor of the transmission, for example. The information n.sub.AB is a rotation speed signal, which represents the rotation speed at the output shaft AB.

[0067] The shift elements A, B, C, D, E are usually actuated via pressure medium. Each shift element A, B, C, D, E is assigned an actuating piston, which can be individually pressurized with the pressure medium. To do this, the valves assigned to the actuating pistons are controlled by the control device 10. The used pressure medium is usually the lubricant of the transmission (transmission oil) in the transmission shown in FIG. 1.

[0068] The transmission can be shifted into a neutral gear in which the drive shaft AN is decoupled from the output shaft AB. For this purpose, a sufficient number of the shift elements A, B, C, D, E are opened, in particular the shift elements B, C, D, E, The travel gears of the transmission serve to move the vehicle. Eight forward gears and one reverse gear are therefore available as travel gears.

[0069] In the transmission shown in FIG. 1, three of the five shift elements A, B, C, D, E are always closed in the travel gears and the remaining two shift elements A, B, C, D, E are open.

[0070] The starting gear is used to accelerate the vehicle from a standstill or from very low speeds. The starting gear therefore has a relatively high gear ratio. Depending on the load condition and the desired direction of travel, the first gear (shift elements A, B, C closed and D, E open) or the second gear (shift elements A, B, E closed and C, D open) or the reverse gear (shift elements A, B, D closed and C, E open) is in particular suitable as the starting gear of the transmission.

[0071] A preferred procedure for operating a transmission when the neutral gear is engaged is explained in the following using the transmission in FIG. 1 as an example. This procedure can also be used for other vehicle transmissions. This procedure is carried out by the transmission control device 10, which is specially configured accordingly. As already described above, the engagement of the neutral gear is requested by the operator of the vehicle, for example, or an automatic transmission.

[0072] For the neutral gear, at least the shift elements B, C, D, E are opened. In this example, the first gear is used as the starting gear. For this purpose, the shift elements A, B, C have to be closed and the shift elements D, E have to be open.

[0073] When the neutral gear is engaged, it is first provided that it be determined whether the transmission is in a state with increased drag losses. This can be carried out by the control device 10 comparing the current temperature T of the transmission with a threshold value. The threshold value is 40° C., for example. If the determined temperature T is below this value, the transmission is still relatively cold and the transmission lubricant correspondingly has high viscosity. Therefore, relatively high drag losses are to be expected in the transmission, i.e. the transmission is in the state with increased drag losses. If the determined temperature T is above the threshold value, the transmission is sufficiently warm and the lubricant correspondingly has low viscosity.

[0074] Therefore, low drag losses are to be expected in the transmission, i.e. the transmission is not in the state with increased drag losses. As described above, there are also other ways to determine whether the transmission is in this state.

[0075] If a transmission state with increased drag losses has been detected, it is provided that the shift element D for the reverse gear of the vehicle transmission is closed at least partially. The shift element D is not a shift element A, B, C of the first gear of the vehicle transmission to be actuated. The other shift elements A, B, C, E of the vehicle transmission, on the other hand, are ventilated, i.e. brought into an open state.

[0076] This reverses a direction of torque at the output of the vehicle transmission, as a result of which the increased drag losses of the vehicle transmission are offset and an unwanted rolling state of the vehicle is prevented.

[0077] The shift element D for the reverse gear of the vehicle transmission can, for example, be brought into the partially closed state with a constant pressure. A contact pressure of the shift element D plus an offset, for example, can be set as the pressure. In the partially closed state, the shift element can be closed with a pressure in the range from 2 bar to 8 bar, for example. The shift element D for the reverse gear can, in particular, be pressurized with a pressure of 3 bar to bring it into the partially closed state. In the closed state, on the other hand, the shift element D can be pressurized with a pressure in the range from 10 bar to 12 bar.

[0078] The pressure for closing the shift element D of the reverse gear can alternatively be increased by a pressure regulator to a pressure level that reduces the drag losses of the vehicle transmission in such a way that the unwanted rolling state of the vehicle is prevented. If no distinction is made between “rolling due to drag losses” and “rolling due to a downhill grade” when determining the rolling state of the vehicle, it is further provided that the pressure for closing the shift element D is limited to a maximum value by the pressure regulator.

[0079] In the “rolling due to drag losses” state, rolling of the vehicle would reliably be prevented by adjusting the maximum pressure. In the “rolling due to a downhill grade” state, the pressure regulator would reach the maximum value. The shift element D would, however, not be pressurized beyond the maximum value to prevent rolling downhill.

[0080] In one design of the proposed method for operating the vehicle transmission, it is determined whether the service brake of the vehicle has been released. This is, in particular, accomplished in that the transmission control device 10 receives and evaluates the brake signal Br from the vehicle brake system.

[0081] It is also possible to determine whether the vehicle is in the rolling state. In other words, there is a check to find out whether the vehicle has started when the neutral gear is engaged. For this purpose, it is, in particular, determined whether the rotation speed n.sub.AB>0 is present at the output shaft AB.

[0082] If the service brake is not released, the vehicle is prevented from starting by the service brake. The transmission can therefore be prepared for the gear shift to the starting gear when the neutral gear is engaged. This enables a quick and comfortable subsequent gear shift to the drive gear. The shift element A is therefore closed and the shift element B is prefilled. The shift element C is ventilated or remains ventilated. The shift elements D, E are open.

[0083] If the service brake is released when the neutral gear is engaged, the vehicle can in principle start moving because it is no longer secured against starting. If the transmission is also not in the state with increased drag losses, the above-described preparation for the gear shift to the starting gear can still be carried out or maintained. There is then no increased risk of the vehicle starting, despite the service brake being released and the neutral gear being engaged. If the transmission is in the state with increased drag losses, however, the shift element B is ventilated as a precaution. Any prefilling that may already have occurred in the shift element B is then discharged and the shift element B is brought into the safely open state. In this way, unwanted starting in the neutral gear is prevented at a first safety level. If the rolling state is detected despite the ventilation of the shift element B, the shift element A is ventilated as well. The shift element A is thus also brought into the safely open state. In this way, further unwanted starting in the neutral gear is prevented at a second safety level.

[0084] If it is detected that the vehicle is in the rolling state despite ventilated shift element B and ventilated shift element A, it is provided at a third safety level that the shift element D of the reverse gear of the vehicle transmission is closed at least partially. This reverses a direction of torque at the output of the vehicle transmission and the unwanted rolling state of the vehicle is ended.

[0085] As soon as it is determined later that the service brake is actuated again when the neutral gear is engaged, the above-described preparation for the gear shift to the starting gear can be carried out.

LIST OF REFERENCE NUMERALS

[0086] 1 Shaft [0087] 2 Shaft [0088] 3 Shaft [0089] 4 Shaft [0090] 5 Shaft [0091] 6 Shaft [0092] 7 Shaft [0093] 8 Shaft [0094] 10 Transmission control device [0095] 11 Brake pedal [0096] 100 Step [0097] 200 Step [0098] 300 Step [0099] 400 Step [0100] 500 Step [0101] 600 Step [0102] 700 Step [0103] A Shift element [0104] B Shift element [0105] C Shift element [0106] D Shift element [0107] E Shift element [0108] AN Drive shaft [0109] AB Output shaft [0110] GG Housing [0111] RS1 Planetary gear set [0112] RS2 Planetary gear set [0113] RS3 Planetary gear set [0114] SO3 Sun gear