Powertrain diagnostics for electric vehicles including brake torque compensation

By switching short circuits between the front axle and rear axle motor of an electric vehicle and using acceleration torque to compensate for the braking torque, the problem of thermal state detection of the motor under low speed driving is solved, and driving comfort and the availability of diagnostic functions are improved.

CN112666457BActive Publication Date: 2025-01-03AUDI AG
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Patent Information

Application Number
CN202010918302.2
Authority / Receiving Office
CN · China
Patent Type
Patents(China)
Current Assignee / Owner
Priority Date
2019-09-30
Filing Date
2020-09-02
Publication Date
2025-01-03
Estimated Expiration
2040-09-02

AI Technical Summary

Technical Problem

The prior art is difficult to effectively check the thermal state of the electric vehicle motor at low driving speeds, and active short circuit diagnosis will affect the driving comfort of the vehicle.

Method used

In pure electric vehicles, undesired swings are avoided by switching short circuits between two permanently magnetized synchronous motors on the front axle and the rear axle, and using another motor to generate acceleration torque to compensate for braking torque generated by the short circuit. Torque, realizes the detection of the thermal state of the motor.

Benefits of technology

It can accurately detect the motor thermal state when driving at low speeds, improve driving comfort and avoid problems of sudden and yaw torque caused by short circuit diagnosis.

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Abstract

The invention relates to a method for checking the thermal state of an electric motor of a vehicle, which is driven by at least two electric motors. In this method, a phase of one of the at least two electric motors is short-circuited during driving and the resulting current is measured, wherein at the same time the braking torque of the electric motor generated by the short circuit is compensated by an acceleration torque generated by at least one other of the at least two electric motors. The invention also relates to a device for checking the thermal state of an electric motor of a vehicle, which is driven by at least two electric motors.
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Description

Technical Field

[0001] The invention relates to a method and a device for checking the thermal state of an electric machine of a vehicle driven by at least two electric machines. Background Art

[0002] In electric vehicles, the state of an electric machine, in particular a permanently excited synchronous machine (PSM), can be checked by switching the machine to an active short circuit for a very short time during driving. In the case of an active short circuit, the three phases of the electric machine are short-circuited via semiconductors of the power electronics. The thermal state of the electric machine can be determined from the current that occurs.

[0003] The disadvantage here is that the active short circuit generates a speed-dependent braking torque. At high driving speeds, this leads to jerking in the vehicle, while at low speeds the braking torque is so great that the short circuit diagnosis cannot be used.

[0004] A drive device for a motor vehicle is known from DE 10 2014 214 541 A1, wherein the motor vehicle has two mechanically coupled electric machines on one axle, which are controlled in such a way that a torque difference of the first electric machine is compensated by a counter-torque of the second electric machine.

[0005] Document DE 10 2015 207 368 A1 discloses a stator for an electric motor and an electric motor. The electric motor is equipped with a plurality of phases, wherein an error torque generated by a short-circuit current in one phase is compensated by the reaction torque of the other two phases of the electric motor.

[0006] Document DE 11 2013 006 972 T5 relates to a control device and a control method for a hybrid vehicle. The hybrid vehicle is equipped with two power devices that generate torque, wherein one of the power devices is designed as an electric motor, which is used to generate a reaction torque during the switching process of the transmission of the hybrid vehicle, and the reaction is beneficial to counteract the torque of the other power device. Summary of the invention

[0007] Against this background, the object of the present invention is to provide a method and a device by means of which the thermal state of an electric machine of an electric vehicle can be determined even at low driving speeds without impairing driving comfort.

[0008] According to the invention, this object is achieved by a method having the following features and by a device having the following features.

[0009] In one embodiment of the invention, in a pure electric vehicle (BEV) with two electric machines, one electric machine each located on the front axle and the rear axle, the second electric machine compensates the braking torque of the first electric machine which is switched into a short circuit. For example, when the front axle is switched into a diagnostic short circuit, the rear axle simultaneously and additionally provides the same positive torque.

[0010] The subject of the invention is a method for checking the thermal state of an electric machine of a vehicle driven by at least two electric machines. According to the invention, during driving, a phase of one of the at least two electric machines is short-circuited and the resulting current is measured, wherein at the same time the braking torque of the electric machine resulting from the short circuit is compensated by an acceleration torque generated by at least one other of the at least two electric machines.

[0011] In one specific embodiment of the method, the at least two electrical machines are permanently excited synchronous machines.

[0012] In one specific embodiment of the method, the at least two electrical machines each have three phases.

[0013] In one specific embodiment of the method, at least one of the electric machines drives a front axle of the vehicle and at least one other of the electric machines drives a rear axle of the vehicle.

[0014] In another embodiment of the method, the vehicle has four electric machines, each of which drives a wheel of the vehicle. In another embodiment of the method, the braking torque generated by the short circuit of the electric machine is compensated by the acceleration torque generated by another electric machine assigned to the wheel on the same side of the vehicle. This avoids the generation of undesired yaw torques.

[0015] In another embodiment of the method, two electric machines assigned to the wheels of an axle of the vehicle are checked simultaneously, thereby also avoiding the generation of undesired yaw moments.

[0016] The subject matter of the invention also includes a device for checking the thermal state of an electric motor of a vehicle driven by at least two electric motors. The device is designed on the one hand to control the torque generation of the at least two electric motors, that is, to act as a drive control. On the other hand, the device is designed to short-circuit the phases of one of the at least two electric motors during driving. The current that occurs is measured and the thermal state of the electric motor is determined. In this case, the device controls at least one other of the at least two electric motors in such a way that an acceleration torque is generated, which compensates for the braking torque generated by the short circuit.

[0017] In one specific embodiment, the device is designed to individually control a plurality of electric motors, each of which drives a wheel of the vehicle.

[0018] In one specific embodiment, the device is designed to control the at least two electric machines in such a way that no additional yaw torque is generated during the short circuit.

[0019] The drive control makes the request to the motor to be checked, i.e. switches to the diagnostic short circuit. At the same time, it sends a request to the other drive to set a compensation torque that matches the speed. The thermal state of the motor can thus be detected by means of the short circuit, thereby avoiding potential disadvantages.

[0020] Advantages of the method and device according to the invention include improved driving comfort, since no jerking of the drive train occurs when diagnosing one of the electric machines. In addition, the short-circuit diagnostic function can also be used at low speeds.

[0021] Further advantages and embodiments of the present invention are apparent from the description. It is obvious that the above-mentioned features can be used not only in the respectively specified combination but also in other combinations or alone without departing from the scope of the present invention.

Claims

1. A method for checking the thermal state of an electric machine of a vehicle, the vehicle being driven by at least two electric machines, wherein: During driving, phases of one of the at least two electric machines are short-circuited and the resulting current is measured, wherein at the same time a braking torque of the electric machine generated by the short circuit is compensated by an acceleration torque generated by at least one other of the at least two electric machines, wherein at least one of the electric machines drives a front axle of the vehicle and at least one other of the electric machines drives a rear axle of the vehicle.

2. The method according to claim 1, wherein: The at least two electric machines are permanently excited synchronous machines.

3. The method according to claim 1 or 2, wherein: The at least two electric machines each have three phases.

4. The method according to claim 1 or 2, wherein: The vehicle has four electric machines, each of which drives one wheel of the vehicle.

5. The method according to claim 4, wherein: The braking torque generated by the short circuit of the electric motor is compensated by the acceleration torque generated by the other electric motor assigned to the wheels on the same side of the vehicle.

6. The method according to claim 4, wherein: Both motors assigned to the wheels on one axle of the vehicle are checked simultaneously.

7. A device for checking the thermal state of an electric motor of a vehicle, the vehicle being driven by at least two electric motors, the device being designed to control the torque generation of the at least two electric motors, and being further designed to short-circuit the phases of one of the at least two electric motors during driving, and to measure the current occurring and to determine the thermal state of the electric motor, and to control at least one other of the at least two electric motors in such a way that an acceleration torque is generated, which compensates for the braking torque generated by the short circuit, wherein: At least one of the electric machines drives a front axle of the vehicle and at least one other of the electric machines drives a rear axle of the vehicle.

8. The device according to claim 7, which is designed to individually control a plurality of electric motors that respectively drive individual wheels of the vehicle. 9 . The device according to claim 7 , wherein the at least two electric machines are controlled in such a way that no additional yaw torque is generated during a short circuit.