METHOD AND CONTROL APPARATUS FOR OPERATING A TRANSMISSION OF A MOTOR VEHICLE

Abstract

A transmission is between a drive aggregate and a drive output of a vehicle drivetrain and includes a hydrodynamic starting element and a powershiftable main transmission having a plurality of forward gears and at least one reversing gear. The main transmission has frictional shifting elements, where in each gear a first number of shifting elements are closed and a second number of shifting elements are open. A downstream range group is connected downstream from the main transmission and has at least one interlocking shifting element that can be shifted between first a second driving ranges. With the drive aggregate running, the motor vehicle at a standstill or nearly so, and the main transmission in neutral, a shift request to change the downstream range group is received. The shifting elements of a reversing gear are at least partially closed, and the driving range of the downstream range group is then changed.

Claims

1-14. (canceled)

15. A method for operating a transmission (2) arranged in a drivetrain of a motor vehicle between a drive aggregate (1) and a drive output (14), the method comprising: providing the transmission (2) comprising a hydrodynamic starting element (15, 18); a powershiftable main transmission (2a) having a plurality of forward gears, at least one reversing gear, and a plurality of frictional shifting elements (9, 10, 11, 12, 13), wherein in each gear a first number of shifting elements are closed and a second number of shifting elements are open; and a downstream range group (2b) connected downstream from the main transmission (2a), the downstream range group comprising at least one interlocking shifting element (24, 27) and configured be shifted between a first driving range, a second driving range, and a neutral position; running the drive aggregate (1) with the motor vehicle at a standstill or in a speed range close to standstill and with the main transmission (2a) in neutral; receiving a shift request to change the downstream range group (2b); partially closing the shifting elements (9, 10, 12) of a reversing gear in the main transmission (2a); and subsequently changing the driving range of the downstream range group (2b).

16. The method according to claim 15, comprising: shifting the downstream range group (2b) to the neutral position; determining that a rotation speed of an output shaft (8) of the main transmission (2a) has reached a shifting rotation speed of the downstream range group; and actuating the interlocking shifting element (24, 27) to engage a driving range of the downstream range group (2b).

17. The method according to claim 16, comprising: maintaining the rotation speed of the output shaft (8) of the main transmission (2a) within a defined rotation speed range for engaging a driving range of the downstream range group (2b) by controlled pressurization of a partially closed shifting element (12).

18. The method according to claim 17, comprising: determining that the rotation speed of the output shaft (8) of the main transmission (2b) is within the defined rotation speed range; and actuating the interlocking shifting element (24, 27) of the downstream range group (2b) to engage a driving range of the downstream range group (2b).

19. The method according to any of claim 16, comprising: determining the rotation speed of the output shaft (8) of the main transmission (2a); determining that the rotation speed of the output shaft (8) of the main transmission (2a) is higher than a maximum shifting rotation speed permitted for shifting the downstream range group (2b); and at least partially closing the shifting elements (9, 10, 12) of the reversing gear in the main transmission (2a).

20. The method according to claim 15, comprising: engaging a driving range in the downstream range group (2b); determining that the shifting element is substantially free from load; and actuating the interlocking shifting element (24, 27) of the downstream range group (2b) to disengage the driving range.

21. The method according to claim 15, comprising: determining a transmission condition of the main transmission (2a); determining that the transmission exhibits high drag losses; and at least partially closing the shifting elements (9, 10, 12) of the reversing gear in the main transmission (2a).

22. The method according to claim 15, comprising: varying, as a function of transmission temperature, a pressure of the partially closed shifting element (12) of the main transmission (2a).

23. The method according to claim 15, comprising: determining that a plurality of shifting elements (9, 10, 12) of the main transmission (2a) are closed; partially closing one of the shifting elements (12) of the reversing gear; fully closing another shifting element or shifting elements (9, 10) of the reversing gear; and engaging the reversing gear.

24. The method according to claim 15, comprising: determining that (i) the pressure in the partially closed shifting element (12) of the reversing gear reaches or exceeds a limit value, (ii) a parameter of a vehicle brake reaches or falls below a limit value, (iii) a vehicle speed reaches or exceeds a limit value, (iv) a torque transmitted by the hydrodynamic starting element (15, 18) reaches or exceeds a limit value, or (v) a maximum time duration for shifting the downstream range group (2b) is reached or exceeded; and terminating pressurization of shifting elements (9, 10, 12) of the reversing gear of the main transmission (2a) to assist the shifting of the downstream range group (2b).

25. A control unit (28) configured to carry out a method according to claim 15.

26. A computer program product having executable code configured to carry out the method according to claim 15 when the computer program is executed by a control unit (28).

27. A transmission (2) of a motor vehicle, comprising a main transmission (2a) and a downstream range group (2b) connected downstream from the main transmission (2a), wherein the transmission (2) comprises a control unit (28) configured to carry out the method of claim 15.

28. A motor vehicle comprising the transmission (2) of claim 27.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Below, the invention is explained in greater detail with reference to figures from which further preferred embodiments and features of the invention can be seen. The figures show:

[0037] FIG. 1: An example of a drivetrain scheme of a motor vehicle, with an example of a transmission comprising a main transmission and a downstream range group:

[0038] FIG. 2: A shifting matrix of the main transmission in FIG. 1:

[0039] FIG. 3: A possible design of the downstream range group in FIG. 1:

[0040] FIG. 4: An alternative design of the downstream range group in FIG. 1; and

[0041] FIG. 5: An example of pressure variations in the partially closed shifting element of the main transmission for braking the output shaft of the main transmission to a rotation speed suitable for shifting the downstream range group.

DETAILED DESCRIPTION

[0042] FIG. 1 shows, very schematically, an example of a drivetrain of a motor vehicle. The drivetrain of FIG. 1 comprises a drive aggregate 1, a transmission 2, and a drive output 14, the transmission 2 being connected between the drive aggregate 1 and the drive output 14. The drive aggregate 1 can be, for example, an internal combustion engine or an electric motor.

[0043] The transmission 2 comprises a main transmission 2a, which provides a number of forward gears and a reversing gear, and a downstream range group 2b connected downstream on the drive input side, which provides a first driving range and a second diving range. The first driving range can correspond to a slow driving range and the second gear to a fast driving range. The first driving range can be an all-wheel driving range and the second driving range can be a non-all-wheel driving range.

[0044] Between the drive aggregate 1 and the transmission 2, namelyin the example embodiment shownbetween the drive aggregate 1 and the main transmission 2a, there is connected a hydrodynamic starting element with a converter 15 and a converter bridging cutch 18. A converter comprises a turbine 16, wherein the turbine 16 in the example embodiment shown is coupled rotationally fixed to an input shaft 7 of the main transmission 2a. In addition, a converter 15 comprises a pump 17. The pump 17 is coupled rotationally fixed to the drive aggregate 1. The structure of such a converter 15 is known to those familiar with the subject, to whom this is addressed.

[0045] Between the main transmission 2a of the transmission 2 and the drive output 14 is connected the downstream range group 2b of the transmission 2, this downstream range group 2b being coupled to a drive output shaft 8 of the main transmission 2a.

[0046] In the example embodiment shown, the main transmission 2a of the transmission 2 comprises a plurality of gearsets 3, 4, 5, and 6, and a plurality of frictional shifting elements 9, 10, 11, 12, and 13 which co-operate with the said gearsets 3, 4, 5, and 6, wherein the two shifting elements 9 and 10 are also called shifting elements A and B respectively, and wherein the shifting elements 11, 12, and 13 are also called shifting elements C, D, and E respectively. The shifting elements A and B and also the shifting elements C, D, and E are frictional shifting elements in each case, namely, such that the shifting elements A and B are brakes and the shifting elements C, D. and E are clutches. The shifting elements A and B are disk brakes and the shifting elements C, D. and E are disk clutches.

[0047] In FIG. 1 a control unit 28 is also shown, which serves to actuate the shifting elements A, B, C, D, E of the main transmission 2a and of the downstream range group 2b. Thus, the control unit 28 enables the shifting elements of the transmission 2 to be selectively opened and closed. Thereby, the gear appropriate for the respective situation or the gear called for by a driver of the vehicle is engaged. For that purpose, the requisite information is sent to the control unit 28 by way of the control unit's input. The control unit 28 processes this information and emits corresponding signals for actuating the shifting elements of the transmission 2 by way of the control unit's output. However, it is also conceivable for a respective control unit of its own to be associated with the main transmission 2a and with the downstream range group 2b, which enable the actuation of the shifting elements in the respective parts of the transmission. These control units can then communicate with one another, for example by way of a CAN (Controller Area Network) data bus.

[0048] Among other things, and only as an example, the information signals v_FZG, c_HG and n_AB are sent to the control unit 28. The information signal v_FZG is a speed of the motor vehicle, by way of which a standstill or a speed range close to standstill of the motor vehicle can be recognized. The speed signal v_FZG can be determined, for example, by a speed sensor or from the rotation speed of the output shaft of the downstream range group. The information c_HG is a temperature signal that represents the transmission temperature of the main transmission 2a. The temperature signal c_HG can be determined, for example, by a temperature sensor of the transmission 2. The information n_AB is a rotation speed signal that represents the rotation speed at the output shaft 8 of the main transmission 2a. The control unit 28 is also informed of a shift request to shift the downstream range group 2b when that is called for by the driver of the motor vehicle or by the control unit.

[0049] Usually, the shifting elements of the main transmission 2a are actuated by a pressure medium. For that purpose, each shifting element A, B, C, D, E of the main transmission 2 is associated with an actuation piston that can be acted upon individually by the pressure of the pressure medium. For this, the valves associated with the actuation pistons are operated by the control unit 28. As the pressure medium, with the main transmission 2a shown in FIG. 1 the lubricant of the main transmission 2a (transmission oil) is usually used.

[0050] FIG. 2 shows a shifting matrix for the main transmission 2a of the transmission 2 in FIG. 1. From FIG. 2 it can be seen that with the main transmission 2a of the transmission 2 in FIG. 1 a total of eight frictional and hence traction-force-transmitting forward gears D1 to D8 and one frictional and hence traction-force-transmitting reversing gear R can be obtained. In each of these traction-force-transmitting gears D1 to D8 and R, a defined first number of shifting elements, namely, three shifting elements of the main transmission 2a are closed, whereas on the other hand, a defined second number of shifting elements, namely, two shifting elements of the main transmission 2a are in each case open in each traction-force-transmitting and hence frictional gear.

[0051] The shifting elements of the main transmission 2a which are closed in each respective frictional and hence traction-force-transmitting gear, are indicated by spots in FIG. 2. For example, in forward gear D1 of the main transmission 2a the shifting elements A, B. and C are closed and in forward gear D2 of the main transmission 2a the shifting elements A, B, and E are closed. In the reversing gear R of the main transmission 2a the shifting elements A, B. and D are closed. The shifting elements that are closed in forward gears D3, D4, D5, D6, D7, and D8 of the main transmission 2a can be seen in the same way in the shifting matrix of FIG. 2.

[0052] As already stated, the downstream range group 2b is connected between the output shaft 8 of the main transmission 2a and the drive output 14. In this case, as shown as an example in FIG. 3, the downstream range group 2b can be made such that as in FIG. 3 the downstream range group 2b comprises a planetary gearset 20 and an interlocking shifting element 24. The output shaft 8 of the main transmission 2a is coupled to a sun gear of the planetary gearset 20. The drive output 14 is coupled to a web 23 of the planetary gearset 20 by way of an output shaft 19 of the downstream range group 2b. Depending on the shift position of the interlocking shifting element 24, a ring gear 22 of the planetary gearset 20 is either fixed to the housing in the slow driving range L or coupled to the web 23 in the fast driving range S.

[0053] FIG. 4 shows an alternative design of the downstream range group 2b which, otherwise than shown in FIG. 3, is not of planetary design but rather of spur gear design. Thus, the downstream range group 2b in FIG. 4 comprises two spur gear stages 25 and 26, and an interlocking shifting element 27. Depending on the shift position of the interlocking shifting element 27, the output shaft 8 of the main transmission 2a is coupled to the output shaft 19 of the downstream range group 2b either by way of the spur gear stage 25 or by way of the spur gear stage 26.

[0054] The invention now relates to a method for the safe and reliable shifting of the downstream range group 2b of the transmission 2, which in its the main transmission 2a comprises frictional shifting elements 9, 10, 11, 12, and 13. For this it is provided that when the motor vehicle, with its drive aggregate 1 running, is at a standstill or in a near-standstill speed range, the powershiftable main transmission 2a is in neutral and there is a shift request to shift the downstream range group 2b, first of all the shifting elements 9, 10, and 12 of a reversing gear R of the main transmission 2a are actuated in order to assist the shifting of the downstream range group 2b.

[0055] In this embodiment of the main transmission 2a, for that purpose the shifting elements 9, 10 in the form of disk brakes can be fully closed whereas the other shifting element 12 of the reversing gear R is partially closed in order to brake the output shaft 8 of the main transmission 2a. For this, FIG. 5 shows an example of a pressure variation of the partially closed shifting element 12 of the main transmission 2a for braking the output shaft 8 of the main transmission 2a to a rotation speed n_AB suitable for engaging the driving range of the downstream range group 2b.

[0056] Thus, the frictional shifting element 12 of the main transmission 2a can already be acted upon in neutral with a pressure p_D_init in order to limit the rotation speed n_AB of the output shaft 8 of the main transmission 2a. When a shift request to shift the downstream range group 2b is made the pressure p_D in the shifting element 12 is increased, whereby the output shaft 8 is braked. As shown in FIG. 5 this takes place along a pressure ramp p_D_inc until the rotation speed n_AB of the output shaft 8 has reached a rotation speed n2 that is suitable for shifting the downstream range group 2b, for example 40 rpm. Thereafter, the driving range of the downstream range group 2b is changed.

[0057] The pressure in the partially closed shifting element 12 of the main transmission 2a is maintained until the rotation speed n_AB of the output shaft 8 reaches a lower rotation speed limit value n1, or the driving range to be engaged in the downstream range group 2b is engaged.

[0058] If the rotation speed falls below a lower rotation speed value n1, for example 20 rpm, before the driving range to be engaged in the downstream range group 2b has been engaged, the probability that while engaging the new driving range a tooth-on-tooth position will occur increases. Accordingly, it is provided that when the rotation speed n_AB has reached the said lower limit value n1, the pressure p_D in the partially closed shifting element 12 of the main transmission 2a is reduced. Finally, the result of this is that the rotation speed n_AB of the output shaft 8 of the main transmission 2a increases again and a rotation speed difference desired for engaging the new driving range is produced at the shifting element 24, 27.

[0059] Consequently, by the controlled pressurization of the partially closed shifting element 12 of the main transmission 2a the rotation speed n_AB of the output shaft 8 of the main transmission 2a can be kept within a defined rotation speed range between the rotation speeds n1 and n2, so that the driving range to be engaged can be reliably engaged from neutral.

INDEXES

[0060] 1 Drive aggregate [0061] 2 Transmission [0062] 2a Main transmission [0063] 2b Downstream range group [0064] 3 Gearset [0065] 4 Gearset [0066] 5 Gearset [0067] 6 Gearset [0068] 7 Input shaft of the main transmission [0069] 8 Output shaft of the main transmission [0070] 9 Shifting element A [0071] 10 Shifting element B [0072] 11 Shifting element C [0073] 12 Shifting element D [0074] 13 Shifting element E [0075] 14 Drive output [0076] 15 Converter [0077] 16 Turbine [0078] 17 Pump [0079] 18 Converter bridging clutch [0080] 19 Output shaft of the downstream range group [0081] 20 Planetary gear system [0082] 21 Sun gear [0083] 22 Ring gear [0084] 23 Web [0085] 24 Shifting element [0086] 25 Spur gear stage [0087] 26 Spur gear stage [0088] 27 Shifting element [0089] 28 Control unit