Method for damping load-change shocks in a drive arrangement

Abstract

Method for damping load-change shocks in a drive arrangement (1) for a motor vehicle comprising a drive unit (2) and a transmission (3) with an input shaft (4), an output shaft (5) and at least two gear stages that can be selectively switched via a switching unit (6), namely a first gear stage (7) and a second gear stage (8), wherein the switching unit (6) has a first positive-locking switching element (9) for switching the first gear stage (7) and a second positive-locking switching element (10) for switching the second gear stage (8), wherein the output shaft (5) can be effectively connected via a torque-vectoring unit (11) to a drive shaft (12) of the motor vehicle, namely to a first half-shaft (13) of the drive shaft (12) and / or a second half-shaft (14) of the drive shaft (12),wherein the torque vectoring unit (11) has a first friction-fit switching element (15) for the effective drive connection of the output shaft (5) with the first half-shaft (13) and a second friction-fit switching element (16) for the effective drive connection of the output shaft (5) with the second half-shaft (14), characterized in that a switching operation from the first gear stage (7) to the second gear stage (8) or vice versa is only carried out if a slip corresponding to the damping of the load change shock is set in the first friction-fit switching element (15) and / or in the second friction-fit switching element (16) of the torque vectoring unit (11).

Description

Field of the InventionThe present invention relates to a method for damping load change impacts during a shifting process in a drive arrangement for a motor vehicle comprising a drive unit, an at least two-speed transmission and a torque vectoring unit.Prior ArtIn the prior art, drive trains for motor vehicles with automated manual transmissions are disclosed, which use form-locking shift elements for shifting gear stages, with which, however, only traction-force-interrupted shifts are possible. Furthermore, drive trains with powershift transmissions are described, such as dual clutch transmissions and automatic transmissions, in which frictional shift elements are used to perform shifts without interruption of the tractive force.The publication DE 199 17 724 A1, for example, discloses a drive train for a motor vehicle having an electric motor and a two-speed transmission, which has two idler gears rotatably mounted on a shaft, which gears can be shifted without interruption of the tractive force by two assigned multiplate clutches, in order to transmit a torque to an interaxle differential. However, arrangements of this type often result in increased drag losses and thus a lower efficiency of the electric motor.Positive shifting devices are almost loss-free, but, as already mentioned above, can at least not conveniently represent a shifting process free of interruptions of the tractive force without additional components. In particular, in the case of at least two-speed gear transmissions with positively locking shift elements, a dynamic torque increase occurs as a result of the principle-dependent high rotational speed gradient during a shift operation as a result of the system-intrinsic mass moments of inertia of the (electric) drive unit and of the gear stages, which increase is manifested in a shift jerk which can be perceived by the driver.The requirements for drive arrangements for motor vehicles in modern vehicle technology are manifold. For example, drive arrangement concepts comprising electrical "high-performance" drive arrangements with an at least two-stage transmission free of traction force interruptions and / or a torque vectoring system are often required. If both an at least two-stage transmission and a torque vectoring system are installed together, synergies can be used advantageously.The document US 2016 / 0 207 396 A1, for example, describes a drive arrangement for a motor vehicle having a drive unit and a transmission, which has an input shaft and an output shaft. A shift unit serves for selectively shifting two gear stages. The shift unit has a first form-fitting shift element for shifting the first gear stage and a second form-fitting shift element for shifting the second gear stage. The output shaft is connected in a drive-effective manner via a torque vectoring unit to a drive shaft of the motor vehicle, namely to a first half shaft of the drive shaft and a second half shaft of the drive shaft. The torque vectoring unit has a first frictional shifting element for drive-effective connection of the output shaft to the first half shaft and a second frictional shifting element for drive-effective connection of the output shaft to the second half shaft.SUMMARY OF THE INVENTIONIt is an object of the invention to specify an improved method for damping load change impacts for a motor vehicle having a drive arrangement for a motor vehicle having an at least two-speed transmission and a torque vectoring system.This need can be met by the subject matter of the present invention according to independent claim 1. The method according to the invention serves for damping load change impacts in a drive arrangement for a motor vehicle comprising a drive unit and a transmission.The transmission has an input shaft, an output shaft which drives the two half shafts of the vehicle by means of two friction clutches, and at least two gear stages which can be selectively shifted via a shift unit, namely a first gear stage and a second gear stage.The shift unit has a first form-fitting shift element for shifting the first gear stage and a second form-fitting shift element for shifting the second gear stage. By using form-locking shift elements for shifting the gear stages, a loss-optimized operation of the transmission and thus of the drive arrangement is ensured.The output shaft is drive-effectively connectable to a drive shaft of the motor vehicle via a torque vectoring unit, namely to a first half shaft of the drive shaft and / or a second half shaft of the drive shaft.The torque vectoring unit has a first frictional shifting element for drive-effective connection of the output shaft to the first half shaft and a second frictional shifting element for drive-effective connection of the output shaft to the second half shaft. By means of the torque vectoring unit, a "decoupling" as well as a differential functionality can be represented, among other things.The design of the drive arrangement, in particular the functional coupling of a transmission with form-locking shift elements for shifting between at least two gear stages and a torque vectoring unit with frictional shift elements, allows, in addition to a shift process free from interruption of the tractive force, also a shift process with reduced load change shock by damping the high rotational speed gradient caused by the shift process by the torque vectoring unit, more precisely its frictional shift elements. In this way, an efficient switching system is presented in conjunction with a torque vectoring system and synergies can be optimally utilized.The frictional shift elements of the torque vectoring unit can thus be used advantageously, for example, in a sport mode of the motor vehicle for damping the load change shock with a shift between the gear stages without interruption of the tractive force. In addition, the frictional shift elements of the torque vectoring unit can be fully released in a comfort mode of the motor vehicle and a comfort shift with traction force interruption can be presented.The drive unit can be, for example, an electric machine.The switching unit can have, for example, a single actuator for the optional actuation of the first form-fitting switching element and for the optional actuation of the second form-fitting switching element. The actuator can be designed, for example, as an electric motor and the actuation of the two form-fitting shift elements is thus effected by an electric motor. However, it is also conceivable to choose the actuator such that a pneumatic, hydraulic or electromagnetic actuation of the form-fitting shift elements of the shift unit takes place. In this way, a particularly space- and cost-optimized construction is achieved. By using form-fitting shift elements, the actuator can also be represented in a space-optimized manner, since only low actuation forces are required.The torque vectoring unit can have, for example, two actuators, namely an actuator for the selective actuation of the first frictional shifting element and a further actuator for the selective actuation of the second frictional shifting element. In this case, too, the actuators can each be designed, for example, as an electric motor and the actuation of the two frictionally engaging shift elements is thus effected by an electric motor. However, it is also conceivable here to choose the actuators such that a pneumatic or hydraulic actuation of the frictional shift elements of the torque vectoring unit takes place.The two form-fitting shift elements can be designed, for example, as claw clutches.The two frictional shift elements can be designed, for example, as multiplate clutches.According to the invention, a shifting process from the first gear stage to the second gear stage or vice versa is carried out only when a slip corresponding to the damping of the load change shock is set in the first frictional shifting element and / or in the second frictional shifting element of the torque vectoring unit.By using the frictional shift elements of the torque vectoring unit, the load change shock during a shift operation can be compensated by means of form-locking shift elements, resulting in a transmission architecture that is optimized with regard to its operating and efficiency properties.Brief Description of the DrawingsThe invention is described below by way of example with reference to the drawings. FIG. 1 shows a schematic illustration of a drive arrangement. FIG. 2 shows a flow chart of a shifting process of a drive arrangement in the course of a full load acceleration. FIG. 3 shows an idealised curve of transmitted torque, the rotational speed at the transmission output and the axle torque over time in a shifting process without damping means. FIG. 4 shows an idealised curve of transmitted torque, the rotational speed at the transmission output and the axle torque over time in a shifting process with damping means.DETAILED DESCRIPTION OF THE INVENTIONFig. 1 shows a schematic representation of a drive arrangement 1 according to the present invention.The drive arrangement 1 comprises a drive unit 2, a transmission 3 and a torque vectoring unit 11.In the present exemplary embodiment, the drive unit 2 is designed as an electric machine and can be operated both by electric motor and by generator. The electric machine is operatively connected to an input shaft 4 of the transmission 3.The transmission 3 has the input shaft 4, an output shaft 5 and two gear stages, namely a first gear stage 7 and a second gear stage 8. The gear stages 7, 8 represent transmission stages of different transmission ratios and are each designed as spur gear stages.The gear stages 7, 8 are assigned a shifting unit 6. The switching unit 6 has two form-fitting switching elements, namely a first form-fitting switching element 9 and a second form-fitting switching element 10, and an actuator 17, namely an electric motor, for the selective actuation of the first form-fitting switching element 9 and the second form-fitting switching element 10. The two form-locking shift elements 9, 10 are each designed as a claw clutch in the present exemplary embodiment. The first form-locking shifting element 9 is assigned to the first gear stage 7 and serves for shifting the first gear stage 7. the second form-locking shifting element 10 is assigned to the second gear stage 8 and serves for shifting the second gear stage 8. Depending on the design of the transmission 3 and the gear stages 7, 8, the shift unit 6 can, however, also be arranged on the output shaft 5.A loose wheel of the first gear stage 7 and a loose wheel of the second gear stage 8 are assigned to the input shaft 4. The loose wheel of the first gear stage 7 can be connected to the input shaft 4 in a drive-effective manner via the first form-fitting shifting element 9, and the loose wheel of the second gear stage 8 can be connected to the input shaft 4 in a drive-effective manner via the second form-fitting shifting element 10.A fixed wheel of the first gear stage 7 and a fixed wheel of the second gear stage 8 are assigned to the output shaft 5. The output shaft 5 is drive-effectively connectable via the torque vectoring unit 11 to a drive shaft 12 of the motor vehicle, more precisely to a first half shaft 13 and / or a second half shaft 14 of the drive shaft 12.The torque vectoring unit 11 has a first frictional shifting element 15 and a second frictional shifting element 16 as well as two actuators 17, 18, namely electric motors, wherein one actuator 17, 18 is assigned to each frictional shifting element 15, 16 and serves for the actuation of the respective frictional shifting element 15, 16.FIG. 2 shows, based on the drive arrangement 1 according to the invention shown in FIG. 1, a flow diagram of a shifting process from the first gear stage 7 into the second gear stage 8 in the course of a full load acceleration.In the case of a request for full load acceleration, it is first checked whether the first gear stage 7 is engaged. The first gear stage 7 represents the shorter transmission stage and is thus optimized with respect to drive torque. The second gear stage 8 represents the longer transmission stage and is thus optimized with respect to efficiency and is necessary to achieve the maximum vehicle speed. If the first gear stage 7 is not engaged, the actuating force on the two frictionally engaging shift elements 15, 16 of the torque vectoring unit 11 is first regulated until a defined slip is present. The first gear stage 7 is then engaged. Subsequently, during acceleration of the motor vehicle, the two frictional shift elements 15, 16 are overlocked until the optimum shifting time for shifting from the first gear stage 7 to the second gear stage 8 is reached. Once this is reached, the actuating force on the two frictionally engaging shift elements 15, 16 of the torque vectoring unit 11 is regulated until a defined slip is present. Only then is the shift from the first gear stage 7 to the second gear stage 8. After a positive check as to whether the second gear stage 8 is engaged, the actuating force on the two frictional shifting elements 15, 16 of the torque vectoring unit 11 is regulated until no slip is present. The requirement for full load acceleration is then fulfilled.FIG. 3 shows the profile of an input shaft torque T output, the transmitted torque of the output shaft in the first gear stage T gear1 and in the second gear stage T gear2 and the rotational speed at the transmission output n output over time. The dynamic torque superelevation as a result of the system-intrinsic mass moments of inertia of the electric machine and the transmission stage can be seen as a deflection in the course of the drive shaft torque T output. This dynamic torque increase manifests itself in a perceptible shift jerk without countermeasures for the motor vehicle driver.FIG. 4 shows the curve of the drive shaft torque T output over time using the method according to the invention. The dynamic torque increase, i.e. the load change shock, is completely damped.During the shifting process, the frictional shifting elements 15, 16 of the torque vectoring unit 11 are controlled to the slip limit. As a result, torque elevations as a result of the inertia in the frictional shift elements 15, 16 of the torque vectoring unit 11 are converted into frictional work and are thus damped (FIG. 4, "Slip_TV_Clutch").List of reference characters1 Drive arrangement 2 Drive unit 3 Transmission 4 Input shaft 5 Output shaft 6 Shift unit 7 First gear stage 8 Second gear stage 9 First positively locking shifting element 10 Second positively locking shifting element 11 Torque vectoring unit 12 Drive shaft 13 First half shaft 14 Second half shaft 15 First frictionally locking shifting element 16 Second frictionally locking shifting element 17, 18, 19 Actuators T output Axle torque T gear1 Torque T gear2 transmitted via the first gear stage Torque n output Rotational speed at the transmission output transmitted via the second gear stage

Claims

Method for damping load changes in a drive arrangement (1) for a motor vehicle comprising a drive unit (2) and a transmission (3) having an input shaft (4), an output shaft (5) and at least two gear stages which can be selectively shifted via a shift unit (6), namely a first gear stage (7) and a second gear stage (8), wherein the shift unit (6) has a first positively locking shift element (9) for shifting the first gear stage (7) and a second positively locking shift element (10) for shifting the second gear stage (8), wherein the output shaft (5) can be connected via a torque vectoring unit (11) in a drive-effective manner to a drive shaft (12) of the motor vehicle, namely to a first half shaft (13) of the drive shaft (12) and / or to a second half shaft (14) of the drive shaft (12), wherein the torque vectoring unit (11) has a first frictional shifting element (15) for the drive-effective connection of the output shaft (5) to the first half shaft (13) and a second frictional shifting element (16) for the drive-effective connection of the output shaft (5) to the second half shaft (14), characterized in that a shifting process from the first gear stage (7) to the second gear stage (8) or vice versa is carried out only when a slip corresponding to the damping of the load change shock is set in the first frictional shifting element (15) and / or in the second frictional shifting element (16) of the torque vectoring unit (11).

Images