Patent ID: 12209659

DETAILED DESCRIPTION

FIG.1shows schematically an example of a drive-train diagram of a motor vehicle. The drive-train inFIG.1comprises a transmission2and a drive output14, wherein the transmission2is connected between the drive aggregate1and the drive output14.

The transmission2comprises a main transmission group2awhich provides a plurality of forward gears and at least one reversing gear, and a downstream range group2bconnected on its drive input side downstream from the main transmission group2a, which provides a first driving range and a second driving range. The first driving range can be a slow-drive range and the second driving range a fast-drive range. The first driving range can also be an all-wheel driving range and the second driving range can be a non-all-wheel driving range.

Between the drive aggregate1and the transmission2, namely in the example embodiment shown between the drive aggregate1and the main transmission group2a, is connected a hydrodynamic starting element with a converter15and a converter bridging clutch18. A converter15comprises a turbine16, and in the example embodiment shown, the turbine16is coupled in a rotationally fixed manner to an input shaft7of the main transmission group2a. In addition, a converter15has a pump17. The pump17is coupled rotationally fixed to the drive aggregate1. The structure of such a converter15is familiar to a person with knowledge of the field.

The downstream range group2bof the transmission2is connected between the main transmission group2aof the transmission2and the drive output14, and the downstream range group2bis coupled to an output shaft8of the main transmission group2a. Sometimes an upstream splitter group can be connected upstream from the main transmission group2a, this then being located between the hydrodynamic starting element and the main transmission group2a.

In the example embodiment shown, the main transmission group2aof the transmission2comprises a plurality of gearsets3,45, and6and a plurality of frictional shifting elements9,10,11,12, and13that co-operate with the said gearsets, the two shifting elements9and10also being denoted shifting elements A and B. and the shifting elements11,12, and13also being denoted shifting elements C, D, and E. The shifting elements A and B and the shifting elements C, D, and E are in each case frictional shifting elements, namely the shifting elements A and B being brakes and the shifting elements C. D, and E being clutches.

FIG.2shows a shifting matrix of the main transmission group2aof the transmission2inFIG.1. It can be seen fromFIG.2that in the case of the main transmission group2aof the transmission2inFIG.1, a total of eight frictional and thus traction-force-transmitting forward gears D1to D8, and one frictional and thus traction-force-transmitting reversing gear R, can be provided. In each of these traction-force-transmitting gears D1to D8and R, a defined first number of shifting elements, namely three shifting elements of the main transmission group2a, are closed, while in contrast a defined number of shifting elements, namely two shifting elements of the main transmission group2aare open in each traction-force-transmitting and thus frictional gear.

The shifting elements of the main transmission group2a, which are closed in the respective frictional and hence traction-force-transmitting gears, are indicated inFIG.2by a dot. For example, in forward gear D1of the main transmission group2athe shifting elements A, B. and C, and in forward gear D2of the main transmission group2a, the shifting elements A, B. and E are closed. In the reversing gear R of the main transmission group2a, the shifting elements A, B, and D are closed. The shifting elements closed in forward gears D3, D4, D5, D6, D7, and D8of the main transmission group2acan also be seen from the shifting matrix inFIG.2.

The main transmission group2aalso has a parking lock28, such that when the parking lock28is engaged the output shaft8of the main transmission2ais immobilized.

As already mentioned, the downstream range group2bis connected between the output shaft8of the main transmission group2aand the drive output14. In this case the said downstream range group2bcan be designed as shown as an example inFIG.3, wherein inFIG.3the downstream range group2bcomprises a planetary gear system20and a shifting element24. The output shaft8of the main transmission group2ais coupled to a sun gear21of the planetary gear system20. The drive output14is coupled by way of an output shaft19of the downstream range group2bto a web23of the planetary gear system20. Depending on the shift position of the shifting element24, a ring gear22of the planetary gear system20is either fixed to the housing in the slow-drive range L or is coupled to the web23in the fast-drive range S.

FIG.4shows an alternative configuration of the downstream range group2b, which otherwise than inFIG.3, is not of planetary design, but rather, in the form of a spur gear structure. Thus, the downstream range group inFIG.4has two spur gear stages25and26and a shifting element27. Depending on the shift position of the shifting element27, the output shaft8of the main transmission group2ais coupled to the downstream range group2beither via the spur gear stage25or via the spur gear stage26.

The invention now relates to a method for shifting the downstream range group2bof the transmission2, which in its powershiftable main transmission group2acomprises frictional shifting elements9,10,11,12, and13, in a safe and reliable manner, specifically when the motor vehicle is at rest with its drive aggregate1running.

When the motor vehicle is at rest with its drive aggregate1running, to shift the downstream range group2bthe parking lock28of the main transmission group2ais first engaged in order to immobilize the output shaft8of the main transmission group2a. Then, the downstream range group2bis shifted out of a range to be disengaged into neutral. The downstream range group2bcan remain in this neutral position for an arbitrarily long time without any risk that owing to drag losses in the main transmission group2athe output shaft8of the main transmission group2awill accelerate too much so that thereafter, the range to be engaged in the downstream range group2bcan no longer be engaged reliably.

When the motor vehicle is at rest with its drive aggregate1running and with a gear engaged in the main transmission group2a, in a first variant of the invention, the main transmission group2ais shifted into neutral before the parking lock28is engaged. Only after that, once the main transmission group2ahas been shifted to neutral, is the parking lock28of the main transmission2aengaged and the downstream range group2bthen shifted to neutral. To shift the downstream range group2bfrom neutral into a range to be engaged, the parking lock28is then disengaged and the downstream range group2bis then actuated in order to engage the range to be engaged. In that way the range to be engaged can always be engaged reliably in the downstream range group2b.

As a result of the drag torques in the main transmission group2a, when the downstream range group2bis shifted into the range to be engaged, the output shaft8of the main transmission group2ais slightly accelerated, so that even a tooth-on-tooth position sometimes formed at the interlocking shifting element24,27of the downstream range group2bcan be resolved.

When the motor vehicle is stationary with the drive aggregate1running and a gear is engaged in the main transmission group2a, according to a second variant of the invention, it is provided that before and during the engagement of the parking lock28in the main transmission group2athe main transmission group2aremains in the gear concerned. After engaging the parking lock28, the downstream range group2bis then shifted to neutral. For the subsequent shifting of the downstream range group2bfrom neutral into a range to be engaged, the main transmission group2ais then first shifted to neutral and then the parking lock28is disengaged and the downstream range group2bis actuated for engaging the range to be engaged. In this way, too, the range to be engaged in the downstream range group2bcan be engaged safely and reliably, if need be, with automatic resolution of a tooth-on-tooth position at the interlocking shifting element24,27of the downstream range group2bto be shifted.

The release of the parking lock28and the actuation of the downstream range group2bto engage the range to be engaged preferably take place simultaneously, or alternatively immediately after one another, with a time overlap.

When the motor vehicle is stationary with the drive aggregate1running and a gear is engaged in the main transmission group2a, in accordance with a third alternative of the invention, before and during the engagement of the parking lock28in the main transmission group2a, the main transmission group2acan remain in the gear concerned. When thereafter the downstream range group2bis shifted to neutral, then for the subsequent shift of the downstream range group2bfrom neutral into the range to be engaged the downstream range group2b, namely its interlocking shifting element24or27, is actuated in order to engage the said range to be engaged and this is done while the gear in the main transmission group2aand the parking lock28remain engaged.

During this, in accordance with the third alternative of the invention, it is checked whether a tooth-on-tooth position has formed at the interlocking shifting element24or27to be closed. If it is found that a tooth-on-tooth position has formed at the interlocking shifting element24or27of the downstream range group2b, then the main transmission group2ais first shifted to neutral and then the parking lock28is disengaged in order then to resolve the tooth-on-tooth position and shift the downstream range group2binto the range to be engaged. If there is no tooth-o-tooth position at the interlocking shifting element24or27of the downstream range group2b, then after the shifting of the downstream range group2b, i.e. after it has been changed to the range to be engaged, the parking lock28is disengaged and in that case the gear in the main transmission group2aremains engaged throughout the process.

Accordingly, in the method according to the invention, to shift the downstream range group2b, before the range to be disengaged in the downstream range group2bhas been disengaged the parking lock28in the main transmission group2ais engaged in order to immobilize the output shaft8of the main transmission group2a. In that case the main transmission group2acan also previously be shifted to neutral, but alternatively the gear remains engaged in the main transmission group2a. In each case the output shaft8of the main transmission group2ais prevented from accelerating too much when the downstream range group2bis in neutral. Thus, the downstream range group can subsequently be shifted reliably from neutral into the range to be engaged.

The invention also relates to a control unit which is designed to carry out the above-described method automatically. The control unit according to the invention is in particular a transmission control unit, preferably an electric or electronic transmission control unit. When the motor vehicle is at rest with the drive aggregate1running, in order to shift the downstream range group2bthe control unit actuates the parking lock28to engage it in order to immobilize the output shaft8of the main transmission group2a. Thereafter, the control unit actuates an interlocking shifting element24or27of the downstream range group2bin order to shift the downstream range group2bfrom a range to be disengaged, into neutral.

As already mentioned above, the control unit according to the invention is preferably an electronic control unit which has hardware means and software means for carrying out the method according to the invention. The hardware means include data interfaces for exchanging data with the assemblies involved in carrying out the method according to the invention, for example with the parking lock28and the interlocking shifting element24or27of the downstream range group2band the shifting elements of the main transmission group2a. The hardware means also include a processor for data processing and a memory for data storage. The software means include program modules which are implemented in the control unit according to the invention for carrying out the method according to the invention.

INDEXES

1Drive aggregate2Transmission2aMain transmission group2bDownstream range group3Gearset4Gearset7Gearset6Gearset7Input shaft of the main transmission group8Output shaft of the main transmission group9Shifting element AShifting element B11Shifting element C12Shifting element D13Shifting element E14Drive output15Converter16Turbine17Pump18Converter bridging clutch19Output shaft of the downstream range group20Planetary gear system21Sun gear22Ring gear23Web24Shifting element25Spur gear stage26Spur gear stage27Shifting element28Parking lock