Method for operating a powertrain

Abstract

A method for operating a powertrain of a motor vehicle with two vehicle axles which can be driven by separate drive assemblies, wherein at least one of the two vehicle axles can be driven by an electromotive drive assembly, and wherein the at least one vehicle axle has two wheels and at least three axle portions, wherein a first axle portion has a first wheel, wherein the first and a second axle portion are coupled by a differential gear, wherein the second and a third axle portion are arranged so they can be connected together by a clutch, and wherein the third axle portion has a second wheel. During drive mode of the motor vehicle with the clutch open, the electromotive drive assembly is held at a standby rotation speed under active regulation by an electric drive control unit, wherein the standby rotation speed tracks a synchronization rotation speed.

Claims

1. A method for operating a powertrain of a motor vehicle with two vehicle axles which can be driven by separate drive assemblies, wherein at least one of the two vehicle axles can be driven by an electromotive drive assembly, and wherein the at least one vehicle axle has two wheels and at least three axleshaft portions, wherein a first axleshaft portion has a first wheel, wherein the first axleshaft portion and a second axleshaft portion are coupled by a differential gear, wherein the second axleshaft portion and a third axleshaft portion are arranged so they can be connected together by a clutch, and wherein the third axleshaft portion has a second wheel, wherein during a drive mode of the motor vehicle with the clutch open, the electromotive drive assembly is held at a standby rotation speed under active regulation by an electric drive control unit, wherein the standby rotation speed tracks a synchronization rotation speed, and wherein the standby rotation speed of the electromotive drive assembly is at least half as great as the synchronization rotation speed.

2. The method as claimed in claim 1, wherein a planet wheel of the differential gear is drivably connected to the electromotive drive assembly.

3. The method as claimed in claim 1, wherein the clutch has a first clutch part which is assigned to the second axle portion, and a second clutch part which is assigned to the third axle portion, wherein one of the two clutch parts can be actuated by a clutch actuator.

4. The method as claimed in claim 1, wherein the clutch is a claw clutch.

5. The method as claimed in claim 1, wherein the standby rotation speed of the electromotive drive assembly is established by the vehicle speed of the motor vehicle and the rotation speed of the wheels.

6. The method as claimed in claim 1, wherein parameters dependent on the vehicle speed are determined from a reference table characterizing the powertrain of the motor vehicle.

7. The method as claimed in claim 1, wherein the standby rotation speed of the electromotive drive assembly is determined from the current vehicle speed and the powertrain parameters dependent on the vehicle speed.

8. The method as claimed in claim 1, wherein the standby rotation speed of the electromotive drive assembly is determined by a predefined nominal value, dependent on the vehicle speed, for a time delay between a signal for engaging the clutch and the end of the clutch engagement process.

9. The method as claimed in claim 1, wherein the standby rotation speed of the electromotive drive assembly is calculated in real time and continuously updated.

10. The method as claimed in claim 1, wherein the at least three axleshaft portions are coaxially aligned with one another.

Description

DRAWINGS

(1) The invention is now explained as an example below with reference to the drawings.

(2) FIG. 1 is a diagrammatic depiction of a powertrain in accordance with the invention.

(3) FIG. 2 illustrates diagrammatically an exemplary rotation speed curve of the electromotive drive assembly.

(4) FIG. 3 illustrates diagrammatically the performance of a method for operating a powertrain in accordance with FIG. 1.

(5) FIG. 4 is a diagrammatic depiction of a powertrain in accordance with the invention illustrating two vehicle axles which can be driven by separate drive assemblies.

DESCRIPTION

(6) FIGS. 1 and 4 illustrate diagrammatically an embodiment of a powertrain which is particularly suitable for performance of the method in accordance with the invention.

(7) A first vehicle axle 2 has a first wheel 16a on a first axleshaft portion 12a. The first axleshaft portion 12a and a second axleshaft portion 12b are coupled by a differential gear 13. A planet wheel 14 of the differential gear 13 is drivably connected to an electromotive drive assembly 20. The electromotive drive assembly 20 is controlled by an electric drive control unit 17 and supplied with power.

(8) The second axleshaft portion 12b is arranged so it can be connected to a third axleshaft portion 12c by a claw clutch 10. The second axleshaft portion 12b has a first clutch part 10a. The third axleshaft portion 12c at one end has a second clutch part 10b and at the other end a second wheel 16b. The clutch part 10a is connected actuatably to a clutch actuator 11, and the clutch actuator 11 is connected via a control line 21 to the electric drive control unit 17. A vehicle control unit 18 is connected firstly via signal lines 22 to wheels 16a, 16b; secondly it is connected via a communication line 23 to the electric drive control unit 17. FIG. 4 illustrates a second vehicle axle 32 having a first wheel 34a on a first axleshaft portion 36a, a second wheel 348 on a second axleshaft portion 36b, and a differential gear 38 drivingly connected to the opposite ends of first axleshaft portion 369 and second axleshaft portion 36b. A second drive assembly 40, such as an internal combustion engine, is driveably connected to differential gear 38.

(9) The depictions in FIG. 2 illustrate diagrammatically different rotation speed curves. The rotation speed values X are shown against time t.

(10) The curve of a synchronization rotation speed simultaneously reflects the curve of the vehicle speed over time t. The curve of the standby rotation speed 27, always lying below the curve of the synchronization speed 28, is determined by the rules and parameters which form the basis for determining the standby rotation speed.

(11) The rotation speed 26 caused by drag moment on an electromotive drive assembly is significantly less than the synchronization rotation speed 28, and also over wide ranges lower than the standby rotation speed 27. Also on steep flanks, i.e. rapid speed changes, because of the large mass of the rotor of the electric drive assembly and the weak coupling in the present powertrain, significant temporal shifts can occur between the rotation speed curve caused by the drag moment in relation to the vehicle speed curve.

(12) FIG. 3 illustrates as an example a flow diagram of the method in accordance with the invention for operating a powertrain. After the start, in a first step S1 the rotation speeds of wheels 16a, 16b, and where applicable further wheels 34a, 34b on second vehicle axle 32 of the motor vehicle, are measured and passed to the vehicle control unit 18. In a step S2, the latter determines the vehicle speed. With the determined value of the vehicle speed, in step S3 speed-dependent parameters of the powertrain may be obtained from a reference table stored in the vehicle control unit 18. In step S4, a standby rotation speed is determined from these parameters and further rules established by the vehicle manufacturer. In step S5, this standby rotation speed is transmitted to the electric drive control unit 17 and applied to the electromotive drive assembly 70. In step S6, the electric motor control unit 17 checks for the presence of a signal for engaging the clutch 10. Such a clutch engagement signal may for example be sent by the vehicle control unit 10. If no clutch engagement signal is present, the standby rotation speed of the electromotive drive assembly 20 is calculated in real time and updated on each run through loops S1 to S6.

(13) If a clutch engagement signal is registered in step S6, the closure of the clutch 10 is initiated in step S7.

(14) In order for the clutch 10 to be closed, the clutch parts 10a and 10b must be synchronized i.e. they must be brought to a substantially equal rotation speed level.

(15) For this, the clutch part 10a, rotating more slowly than the clutch part 10b coupled to the third axleshaft portion 12c, is accelerated by the electromotive drive assembly 20 until the predefined rotation speed difference between the clutch parts 10a, 10b is reached or passed. Then the clutch actuator 11 may be activated to end the clutch engagement 10. The electromotive drive assembly 20 is switched from active speed regulation to active torque regulation.

(16) In other words, first the rotation speed of the first clutch part 10a is synchronized with the rotation speed of the second clutch part 10b, in that the electromotive drive assembly 20 accelerates the first clutch part 10a. Completed synchronization means a state in which the two clutch parts have a predefined speed difference which is usually selected as comparatively small as possible, to allow smooth engagement of the clutch 10. The predefined rotation speed difference is dimensioned in particular such that the engagement process can be carried out without loss of driving comfort, and at the same time the actuation time is kept low.

(17) On disengagement of the clutch 10, for example when a contribution of the electric motor is no longer required to propel the vehicle, the electromotive drive assembly 20 driving the planet wheel 14 is switched from torque regulation to rotation speed regulation, and the clutch 10 then ideally runs without load and can be opened by the clutch actuator 11.

LIST OF REFERENCE SIGNS

(18) 2 First vehicle axle 10 Clutch 10a, 10b Clutch parts 11 Clutch actuator 12a, 12b, 12c Axleshaft portions 13 Differential gear 14 Planet wheel 16a, 16b Wheels 17 Electric drive control unit 18 Vehicle control unit 20 Electromotive drive assembly 21 Control line, clutch actuator 22 Signal line 23 Communication line 26 Rotation speed caused by drag torque 27 Standby rotation speed 28 Synchronization rotation speed 32 Second vehicle axle 34a, 34b Wheels 36a, 36b Axleshaft portions 38 Differential gear 40 Second drive assembly t Time X Rotation speed S1 Measurement of wheel rotation speeds S2 Determination of vehicle speed S3 Parameters from reference table S4 Determine standby speed S5 Apply standby speed S6 Engagement signal S7 Close clutch