ELECTRIC MOTOR DEVICE AND METHOD FOR CONTROLLING A MOTOR BRAKING PROCEDURE FOR AN ELECTRIC MOTOR

Abstract

A motor braking procedure is controlled for an electric motor that provides a drive torque for a vehicle and is driven electrically by an inverter circuit having a plurality of switching elements via at least two motor connections and has a rotor rotateable at a motor speed. A braking switch position is adopted by the inverter circuit in braking switch position intervals. An open switch position is adopted by the inverter circuit in open switch position intervals. The braking switch position intervals are alternately switched with the open switch position intervals based on a motor speed being less than a limit speed during the motor braking procedure. The rotor, during the electric motor braking procedure, is subject to a speed-dependent braking torque based on the inverter circuit adopting a braking switch position and is subject to a braking torque less than that in the braking switch position or no braking torque based on the inverter circuit adopting an open switch position.

Claims

1. A method for controlling a motor braking procedure of an electric motor that provides a drive torque for a vehicle and is driven electrically by an inverter circuit having a plurality of switching elements via a plurality of motor connections and has a rotor rotateable at a motor speed, the method comprising: adopting, via the inverter circuit, a braking switch position in braking switch position intervals, the rotor being subjected to a speed-dependent braking torque when the braking switch position is adopted; adopting, via the inverter circuit, an open switch position in open switch position intervals, the rotor being subjected to no braking torque or a braking torque that is less than the speed-dependent braking torque when the open switch position is adopted; and alternately switching, via the inverter circuit, between the braking switch position intervals and the open switch position intervals based on a motor speed being below a limit speed during the motor braking procedure.

2. The method according to claim 1, wherein a respective time period of each braking switch position intervals is dependent on the motor speed.

3. The method according to claim 1, wherein a respective time period of each open switch position intervals is dependent on the motor speed.

4. The method according to claim 1, wherein a time period of at least one braking switch position interval is different from a time period of the subsequent open switch position interval.

5. The method according to claim 1, wherein at least two of the motor connections are electrically short-circuited in the braking switch position.

6. The method according to claim 1, wherein, in the open switch position, a majority of the switching elements are in a blocking position.

7. The method according to claim 6, wherein, in the open switch position, all of the switching elements are in the blocking position.

8. The method according to claim 1, further comprising, adopting the braking switch position is without interruption based on the motor speed being greater than the limit speed during the motor braking procedure.

9. The method according to claim 1, wherein the limit speed corresponds to a motor speed at which a voltage at the switching elements induced through the open switch position of the rotor is below a limit voltage.

10. An electric motor device for providing a drive torque for a vehicle, comprising: an electric motor having a rotatable rotor which is subject to a braking torque during an electric motor braking procedure and which is able to rotate at a motor speed, and an inverter circuit having a plurality of switching elements in communication with the electric motor via a plurality of motor connections and being configured to, during a motor braking procedure: actuate the plurality of switching elements to adopt a braking switch position in braking switch position intervals, the rotor being subjected to a speed-dependent braking torque when the braking switch position is adopted; actuate the plurality of switching elements to adopt an open switch position in open switch position intervals, the rotor being subjected to no braking torque or a braking torque that is less than the speed-dependent braking torque when the open switch position is adopted; and alternately switch between the braking switch position intervals and the open switch position intervals based on a motor speed being below a limit speed.

11. The method according to claim 1, wherein a time period of one open switch position interval is greater than a time period of a subsequent open switch position interval.

12. The electric motor device of claim 10, wherein a respective time period of each braking switch position interval is dependent on the motor speed.

13. The electric motor device of claim 10, wherein a respective time period of each open switch position interval is dependent on the motor speed.

14. The electric motor device of claim 10, wherein a time period of at least one braking switch position interval is different from a time period of the subsequent open switch position interval.

15. The electric motor device of claim 10, wherein the at least two of the motor connections are electrically short-circuited in the braking switch position.

16. The electric motor device of claim 10, wherein, in the open switch position, a majority of the switching elements are in a blocking position.

17. The electric motor device of claim 16, wherein, in the open switch position, all of the switching elements are in the blocking position.

18. The electric motor device of claim 10, wherein the inverter circuit is further configured to, during the motor braking procedure, adopt the braking switch position without interruption based on the motor speed being greater than the limit speed.

19. The electric motor device of claim 10, wherein the limit speed corresponds to a motor speed at which a voltage at the switching elements induced through the open switch position of the rotor is below a limit voltage.

20. The electric motor device of claim 10, wherein a time period of one open switch position interval is greater than a time period of a subsequent open switch position interval.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The disclosure is described in detail below with reference to the figures. In the figures:

[0023] FIG. 1: shows an electric motor device in an exemplary embodiment of the disclosure.

[0024] FIG. 2: shows a braking torque curve in the embodiment of a method in an exemplary embodiment of the disclosure.

[0025] FIG. 3: shows detail A from FIG. 2 in an enlarged view.

DETAILED DESCRIPTION

[0026] FIG. 1 shows an electric motor device 10 in an exemplary embodiment of the disclosure. The electric motor device 10 is arranged in a vehicle to provide a drive torque and has an electric motor 12 having a rotor 14 able to rotate at a motor speed. The electric motor 12 can output a drive torque for driving the vehicle via a transmission 16 to a vehicle wheel 18 of the vehicle. The rotor 14 can be connected to the vehicle wheel 18 in a rotationally fixed manner via the transmission 16.

[0027] The electric motor 12 can be a brushless DC motor that is controllable by an inverter circuit 20. The electric motor 12 can have three motor phases Mp. The respective motor phase Mp is connected to the inverter circuit 20 via a motor connection Ma. The inverter circuit 20 is fed by a supply voltage Ub, which is preferably a DC voltage. The supply voltage Ub can be provided by a vehicle battery. The vehicle can preferably be an electric vehicle.

[0028] The inverter circuit 20 is in particular a multiple half-bridge circuit, here a triple half-bridge circuit for driving the three motor phases Mp. The inverter circuit 20 has six switching elements S1-S6. An electrical motor braking procedure for triggering a braking torque by rotor 14 is preferably set by the inverter circuit 20 adopting a braking switch position in which at least two of the motor connections Ma are short-circuited via the inverter circuit 20. In particular, all three motor phases Mp can be short-circuited by the three switching elements SI-S3 being switched on or the other three switching elements S4-S6 being switched on.

[0029] When the inverter circuit 20 is in an open switch position, the braking torque caused by the rotor 14 is less than in the braking switch position or no braking torque is present at all. The open switch position can be adopted when all switching elements S1-S6 are switched to a blocking position. However, a rotational movement of the rotor 14 can then produce an induced voltage at the switching elements S1-S6, which loads the switching elements S1-S6 and is speed dependent. The induced voltage is proportional to the motor speed.

[0030] FIG. 2 shows a braking torque curve in the embodiment of a method in an exemplary embodiment of the disclosure. The motor braking procedure brought about by a braking switch position of the inverter circuit adopted entirely without interruption via the motor speed n enacts a speed-dependent braking torque Nb on the rotor. The braking torque Nb is inversely proportional to the motor speed n. At low motor speeds, the braking torque Nb can therefore have high values.

[0031] Assuming that the electric motor is to be braked by the electric motor braking procedure starting from a high motor speed n, then the braking torque Nb will change only slightly up to a limit speed ng of 3000 rpm here and increase from the limit speed ng with increasingly lower motor speeds n. As a result, the vehicle is braked more strongly at lower motor speeds n and can even swerve due to the excessive braking torque Nb, depending on the road conditions.

[0032] For this reason, during the motor braking procedure at motor speeds n below the limit speed ng, the braking switch position is adopted by alternate switching S in braking switch position intervals alternating with open switch position intervals of the open switch position. The resulting braking torque curve Nb1 is thus adjusted on average to the braking torque curve Nb0 at motor speeds n above the limit speed ng. As a result, the braking torque Nb can be applied more consistently over the motor speeds n and a more consistent average braking torque Nbm can be achieved. The vehicle can be braked in a more stable and smoother manner, and the braking procedure of the vehicle can be carried out more safely. The vehicle can be prevented from swerving due to motor braking.

[0033] FIG. 3 shows detail A from FIG. 2 in an enlarged view. The alternate switchings S between the braking switch position Sb and the open switch position Sa, which are dependent on the motor speed n, are also shown. Starting with a rotor rotating at a motor speed n above the limit speed ng and the motor braking procedure initiated by the braking switch position Sb of the inverter circuit being adopted without interruption up to the limit speed ng, the braking switch position Sb is replaced by the open switch position Sa when the limit speed ng is reached. The open switch position Sa is maintained over a first time period ta1. During this time, the braking torque Nb is reduced.

[0034] After the first time period ta1 has elapsed, the open switch position Sa is replaced and the braking switch position Sb is adopted for a first time period tb1. Then, the open switch position Sa alternates with the braking switch position Sb again for a second time period ta2. After the second time period ta2 has elapsed, the braking switch position Sb is adopted again for a second time period tb2. These alternate switchings S take place in particular until the rotor no longer rotates.

[0035] The first time period ta1 is greater than the subsequent second time period ta2 of the respective open switch positions Sa, since the braking torque Nb, starting from the motor speed n that has reached the limit speed ng, is to be reduced more than in the further course of the alternate switching S. The respective time period of the open switch position and the braking switch position, as well as the alternate switching frequency, for example 14 alternate switchings S are available here, can be selected from the required curve for the braking torque Nb and, for example, adapted to ambient conditions.

[0036] List of reference symbols

[0037] 10 Electric motor device

[0038] 12 Electric motor

[0039] 14 Rotor

[0040] 16 Transmission

[0041] 18 Vehicle wheel

[0042] 20 Inverter circuit

[0043] Ma Motor connection

[0044] Mp Motor phase

[0045] n Motor speed

[0046] ng Limit speed

[0047] Nb Braking torque

[0048] Nb0 Braking torque curve

[0049] Nb1 Braking torque curve

[0050] Nm Average braking torque

[0051] S Alternate switching

[0052] S1-S6 Switching element

[0053] S a Open switch position

[0054] Sb Braking switch position

[0055] ta1 First time period

[0056] ta2 Second time period

[0057] tb1 First time period

[0058] tb2 Second time period

[0059] Ub Supply voltage