Gear-shifting method for an electric drive system

Abstract

A gear change method for an electric transmission system (1), the electric transmission system (1) including an electric machine (2), a multi-stage transmission (3) drivingly connected downstream from the electric machine (2) and having interruption of tractive force, and at least one brake (4) for braking a vehicle wheel (5), the method including transferring the brake (4) out of an inoperative condition into a readiness condition during a gear change operation of the transmission (3).

Claims

1. A gear change method for an electric transmission system (1), the electric transmission system (1) comprising an electric machine (2), a multi-stage transmission (3) drivingly connected downstream from the electric machine (2) and configured for interruption of tractive force, and at least one brake (4) for braking a vehicle wheel (5), the method comprising: transferring the brake (4) out of an inoperative condition into a readiness condition during a gear change operation of the transmission (3), wherein the brake (4) does not decelerate the vehicle wheel (5) in the inoperative condition, the brake (4) decelerates the vehicle wheel (5) during a braking operation, the brake (4) is adjustable into the braking operation from both the inoperative condition and the readiness condition, and the brake (4) is adjustable into the braking operation more quickly from the readiness condition than from the inoperative condition, and wherein the transmission (3) decouples the electric machine (2) from the vehicle wheel (5) during the gear change operation of the transmission (3) in order to interrupt the tractive force and power flow between the electric machine (2) and the vehicle wheel (5).

2. The gear change method of claim 1, wherein the transfer of the brake (4) into the readiness condition is carried out when no gear is engaged in the transmission (3) or when a gear shift is carried out.

3. The gear change method of claim 1, wherein the gear change operation comprises reducing a load at the electric machine (2), and wherein the transfer into the readiness condition is carried out during the load reduction.

4. The gear change method of claim 3, wherein the gear change operation further comprises: disengaging an engaged gear by disengaging a first shift element after the load reduction; synchronizing a second shift element after disengaging the engaged gear; and engaging a new gear by engaging the second shift element after synchronizing the second shift element, wherein the brake is in the readiness condition during the disengaging of the engaged gear, the synchronizing of the second shift element, and the engaging of the new gear.

5. The gear change method of claim 1, wherein the gear change operation comprises performing a load build-up at the electric machine (2), and wherein the brake (4) is transferred from the readiness condition into the inoperative condition during the load build-up.

6. The gear change method of claim 1, wherein at least one manipulated variable of the brake (4) is changed in order to transfer the brake (4) into the readiness condition.

7. The gear change method of claim 6, wherein the manipulated variable is an actuating travel of a brake component.

8. The gear change method of claim 6, wherein a vehicle acceleration is ascertained and the manipulated variable of the brake (4) is changed depending on the vehicle acceleration.

9. The gear change method of claim 1, wherein the brake (4) is transferred into the readiness condition during the gear change operation when an obstacle is detected with the aid of a detection system.

10. An electric transmission system (1) configured to perform the gear change method of claim 1.

11. An electric vehicle (6), comprising the electric transmission system (1) of claim 10.

12. The gear change method of claim 1, wherein the multi-stage transmission (3) is a two-speed transmission.

13. The gear change method of claim 1, wherein a brake disk of the brake (4) and a brake lining of the brake (4) are spaced apart in the inoperative condition.

14. The gear change method of claim 13, wherein the brake disk of the brake (4) and the brake lining of the brake (4) are spaced further apart in the inoperative condition than in the readiness condition.

15. The gear change method of claim 1, an internal combustion engine is not connected to the electric transmission system (1), and the electric transmission system (1) is configured for electric propulsion only.

16. The electric vehicle (6) of claim 11, wherein the electric vehicle (6) does not include an internal combustion engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The subject of the invention is schematically represented in the figures and is described in the following with reference to the figures, wherein identical or identically operating elements are mostly provided with the same reference characters. Wherein:

(2) FIG. 1 shows a schematic of one portion of an electric vehicle according to the invention, including an electric transmission system according to the invention, and

(3) FIG. 2 shows a shift sequence during a gear change operation.

DETAILED DESCRIPTION

(4) Reference will now be made to embodiments of the invention, one or more examples of which are shown in the drawings. Each embodiment is provided by way of explanation of the invention, and not as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be combined with another embodiment to yield still another embodiment. It is intended that the present invention include these and other modifications and variations to the embodiments described herein.

(5) FIG. 1 shows a portion of an electric vehicle 6. The electric vehicle 6 includes an electric transmission system 1 which includes an electric machine 2, a transmission 3, and brakes 4 for braking vehicle wheels 5. The electric machine 2 is drivingly connected to the transmission 3, wherein the transmission 3 is drivingly connected downstream from the electric machine 2. In the embodiment represented in FIG. 1, the brakes 4 are associated with an axle 7 which is drivable with the aid of the electric machine 2. The gear change method according to the invention functions in the same way when the brakes 4 are arranged on another axle which is not drivable with the aid of the electric machine 2.

(6) The transmission 3 includes a differential gear 8, with the aid of which the electric machine 2 is drivingly connected to vehicle wheels 5. The vehicle wheels 5 are drivingly connected to the axle 7. In this case, one brake 4 is assigned to each vehicle wheel 5.

(7) The transmission 3 is a two-speed transmission including two spur gear stages. In order to implement the two gears, the transmission 3 includes a first shift element A and a second shift element B, which form a double shift element. In this case, a first gear is implemented when the first shift element A is engaged and the second shift element B is disengaged. A second gear is implemented when the first shift element A is disengaged and the second shift element B is engaged. The first shift element A and the second shift element B are form-fit shift elements.

(8) FIG. 2 shows a shift sequence during a gear change operation. In particular, FIG. 2 shows a shift sequence during a gear change from the first gear into the second gear of the transmission shown in FIG. 1. In FIG. 2, the rotational speed curve 9 of the electric machine 2, the torque curve 10 of the electric machine 2, and the curve of the manipulated variable 11 of the brake 4 over the time t are represented. The manipulated variable 11 is, for example, an actuating travel of a brake component, such as a brake shoe or a brake piston. The manipulated is alternatively the curve of a brake pressure.

(9) The shift sequence during the gear change operation includes five phases P1 to P5. Before a first phase P1, the brake 4 is in an inoperative condition in which a brake torque acts on the vehicle wheel 5 associated with the brake 4. In the first phase P1, a load reduction takes place at the electric machine 2, which is the beginning of the interruption of tractive force. Simultaneously, the brake 4 is transferred into a readiness condition. For this purpose, the brake component is displaced in order to reduce the distance between the brake component and a brake disk. Depending on the design of the brake, alternatively or additionally, a low brake pressure is built up. At the end of the first phase P1, the brake 4 is in the readiness condition.

(10) In a second phase P2, the present gear is disengaged by disengaging the first shift element A. In order to disengage the gear, a shift actuator, which is not represented in the figures, is moved. In a third phase P3, an active synchronization of the second shift element B takes place with the aid of the electric machine 2. In a fourth phase P4, the new gear is engaged. In order to engage the gear, the shift actuator (not represented) is moved. For this purpose, the second shift element B is engaged. The brake 4 is in the readiness condition in the second to fourth phases P2 to P4.

(11) In a fifth phase P5, a load build-up of an electric machine 2 takes place, whereby the interruption of tractive force is ended. Simultaneously, the brake 4 is transferred from the readiness condition into the inoperative condition. After the fifth phase, the brake 4 is in its basic condition again.

(12) Modifications and variations can be made to the embodiments illustrated or described herein without departing from the scope and spirit of the invention as set forth in the appended claims.

REFERENCE CHARACTERS

(13) 1 electric transmission system

(14) 2 electric machine

(15) 3 transmission

(16) 4 brake

(17) 5 vehicle wheel

(18) 6 electric vehicle

(19) 7 axle

(20) 8 differential gear

(21) 9 rotational speed curve

(22) 10 torque curve

(23) 11 manipulated variable of the brake

(24) A first shift element

(25) B second shift element

(26) t time

(27) P1 first phase

(28) P2 second phase

(29) P3 third phase

(30) P4 fourth phase

(31) P5 fifth phase