Electric motor device and method for controlling a motor braking process of an electric motor

Abstract

The invention relates to a method for controlling a motor braking process of an electric motor (12) which provides a driving torque for a vehicle and is electrically driven via at least two motor connections (Ma) by an inverter circuit (20) having a plurality of switching elements (S1 to S6) and has a rotor (14) which can rotate with a motor speed (n) and which, during the electric motor braking process, is subjected to a speed-dependent braking torque due to the inverter circuit (20) assuming a braking switch position (Sb) and to a braking torque (Nb) which is smaller than the braking torque in the braking switch position (Sb) or to no braking torque (Nb) due to the inverter circuit (20) assuming an open switch position (Sa), wherein, during the motor braking process, the braking switch position (Sb) is assumed in braking switch position intervals which alternate with open switch position intervals of the open switch position (Sa) by means of an alternating switching (S) when the motor speed (n) is below a limiting speed (ng). The invention also relates to an electric motor arrangement (10) which has an inverter circuit (20) for controlling a motor braking process by means of such a method.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for controlling a motor braking process of an electric motor. Furthermore, the invention relates to an electric motor arrangement according to claim 10. BACKGROUND

[0002] DE 10 2017 111 108 A1 describes a method of braking a vehicle in the event of a transmission failure. It describes that a braking process is performed by a wheel brake if a transmission failure occurs.

[0003] A vehicle is in a safe state at least when it is no longer in motion. In addition to the fact that a vehicle brake arranged on a vehicle wheel can be used to brake the vehicle or in the event that the vehicle brake also fails, a braking process can be performed by an electric motor which serves as a drive element of the vehicle. The electric motor has a rotor which can be rotated at a motor speed and is electrically controlled via motor connections by an inverter circuit having a plurality of switching elements.

[0004] A motor braking process can be initiated by adopting a braking switch position of the inverter circuit in which at least two motor connections are short-circuited. The resulting braking torque is dependent on the motor speed of the rotor. At lower motor speeds, an undesirable increase in the motor braking torque can occur, which can lead to an over-braking of the vehicle, which in turn can affect the safety of the vehicle. SUMMARY

[0005] It is an object of the invention to improve motor braking. The motor braking process should be more consistent. The vehicle should be braked more safely.

[0006] At least one of these objects is achieved by a method for controlling a motor braking process having the features according to claim 1. This allows a more consistent application of the braking torque at lower motor speeds. The vehicle can be braked in a more stable and smoother manner. The braking of the vehicle can be performed more safely. A tilting of the vehicle due to motor braking can be prevented.

[0007] The electric motor can be arranged in an electric vehicle. The electric motor can be non-rotatably connected to a vehicle wheel. A transmission can be effectively arranged between the electric motor and the vehicle wheel.

[0008] The electric motor can have several motor phases. The motor phases can each be connected to the inverter circuit by a motor connection. The electric motor can be a brushless direct current motor. The electric motor can have three motor phases.

[0009] The inverter circuit can be a half-bridge circuit. The half-bridge circuit can be a multi-half-bridge circuit, in particular a three-half-bridge circuit.

[0010] The speed limit can be less than or equal to 3000 rpm.

[0011] During motor braking, braking parameters, particularly the alternation frequency, the time intervals between various brake switch positions, and / or the time intervals between various disconnect switch positions, can be specified as a function of the motor speed and can be invoked during vehicle operation. These braking parameters can also be controlled and / or adjusted appropriately based on acceleration information to regulate braking torque.

[0012] Motor braking can be activated during emergency braking.

[0013] In a preferred embodiment of the invention, the time interval between each brake switch position is set according to the motor speed. Below a speed limit, the time interval between each brake switch position can be proportional to the motor speed.

[0014] In a specific embodiment of the invention, the time interval between each disconnect switch position is set according to the motor speed. Below a speed limit, the time interval between each disconnect switch position can be proportional to the motor speed.

[0015] In a preferred embodiment of the invention, the time period of at least one brake switch position interval is different from the time period of at least one subsequent disconnect switch position interval.

[0016] In a particular embodiment of the invention, at least two motors are electrically short-circuited in the brake switch position. In the brake switch position, at least two switching elements with the same voltage potential assigned to the supply voltage can be closed. Alternatively, all switching elements with the same voltage potential assigned to the supply voltage can be closed.

[0017] In a preferred embodiment of the invention, most of the switching elements in the open switch position are in the blocked position. In the blocked position, power transmission is interrupted.

[0018] In a particular embodiment of the invention, all switching elements are in the blocking position when in the open switch position.

[0019] In a preferred embodiment of the invention, the brake switch position is used uninterruptedly during motor braking when the motor speed is higher than the limit speed.

[0020] In a preferred embodiment of the invention, the speed limit corresponds to the motor speed when the voltage induced by the rotor at the switching element due to the open switch position is lower than the limit voltage. Therefore, the voltage load on the switching element can be reduced in the open switch position.

[0021] Furthermore, in order to achieve at least one of the above-mentioned objects, an electric motor arrangement for providing a drive torque for a vehicle is proposed, the electric motor arrangement having an electric motor having a rotatable rotor which is subjected to a braking torque during a motor braking process and which can be rotated at a motor speed, and an inverter circuit for controlling the motor braking process by means of a method having at least one of the above-mentioned features.

[0022] Further advantages and advantageous embodiments of the application are apparent from the description of the drawings and the drawings themselves. BRIEF DESCRIPTION OF DRAWINGS

[0023] The application is described in detail below with reference to the drawings. In the drawings:

[0024] Figure 1 Fig. 1 shows an electric motor arrangement in a specific embodiment of the application.

[0025] Figure 2 Fig. 2 shows a braking torque curve in a method embodiment of the application.

[0026] Figure 3 Fig. 3 shows a detail A in Fig. 1 in an enlarged view. Figure 2 DETAILED DESCRIPTION

[0027] Figure 1 An electric motor arrangement 10 in a specific embodiment of the application is shown. The electric motor arrangement 10 is arranged in a vehicle to provide a drive torque and has an electric motor 12 which enables a rotor 14 to be rotated at a motor speed. The electric motor 12 can output a drive torque for driving the vehicle to vehicle wheels 18 of the vehicle via a transmission 16. The rotor 14 can be connected to the vehicle wheels 18 in a rotationally fixed manner via the transmission 16.

[0028] The electric motor 12 can be a brushless DC motor which can be controlled by an inverter circuit 20. The electric motor 12 can have three motor phases Mp. The individual motor phases Mp are connected to the inverter circuit 20 via motor connections 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.

[0029] ​The inverter circuit 20 is in particular a multi-half-bridge circuit, here a three-half-bridge circuit for driving three motor phases Mp. The inverter circuit 20 has six switching elements S1 to S6. An electric motor braking process for triggering a braking torque by the rotor 14 is preferably set by the inverter circuit 20 in a braking switch position in which at least two motor connections Ma are short-circuited by the inverter circuit 20. In particular, all three motor phases Mp can be short-circuited by switching on three switching elements S1 to S3 or by switching on the other three switching elements S4 to S6.

[0030] When the inverter circuit 20 is in the open switch position, the braking torque caused by the rotor 14 is smaller than the braking torque in the braking switch position or there is no braking torque at all. The open switch position can be adopted when all switching elements S1 to S6 are switched to the blocking position. However, the rotational movement of the rotor 14 can then generate an induced voltage at the switching elements S1 to S6, which loads the switching elements S1 to S6 and is speed-dependent. The induced voltage is proportional to the motor speed.

[0031] Figure 2 A braking torque curve in an embodiment of the method in the specific embodiment of the application is shown. The motor braking process caused by the braking switch position of the inverter circuit, which is adopted completely without interruption via the motor speed n, generates a speed-dependent braking torque Nb on the rotor. The braking torque Nb is inversely proportional to the motor speed n. Thus, at low motor speeds, the braking torque Nb can have a high value.

[0032] Assuming that the electric motor is to be braked by an electric motor braking process starting from a high motor speed n, the braking torque Nb will only change slightly up to a limit speed ng of 3000 rpm here and increase from the limit speed ng with increasingly lower motor speeds n. Thus, the vehicle is braked more strongly at lower motor speeds n and can even tilt due to the excessively large braking torque Nb, depending on the road conditions.

[0033] To this end, during the motor braking process with a motor speed n below the limit speed ng, the braking switch position is adopted by alternating switching S in the braking switch position interval alternately with the open switch position interval. The resulting braking torque curve Nbl is thus adjusted evenly to the braking torque curve Nb0 at motor speeds n above the limit speed ng. Thus, the braking torque Nb can be applied more consistently over the motor speed 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 process of the vehicle can be performed more safely. Tilting of the vehicle due to the motor braking can be prevented.

[0034] Figure 3 An embodiment of the method in the specific embodiment of the application is shown in an enlarged viewFigure 2 The alternating switching S between the braking switch position Sb and the disconnection switch position Sa in relation to the motor speed n is also shown. Starting from the rotor rotating with a motor speed n above the limit speed ng, and the motor braking process initiated by the braking switch position Sb of the inverter circuit is employed without interruption until the limit speed ng is reached, when the braking switch position Sb is replaced by the disconnection switch position Sa. The disconnection switch position Sa is maintained for a first time period t al. During this time, the braking torque Nb is reduced.

[0035] After the first time period t al has elapsed, the disconnection switch position Sa is replaced and the braking switch position Sb is employed for a first time period t bl. Then, for a second time period t a2, the disconnection switch position Sa is again alternating with the braking switch position Sb. After the second time period t a2 has elapsed, the braking switch position Sb is again employed for a second time period t b2. These alternating switchings S take place in particular until the rotor no longer rotates.

[0036] The first time period t al is greater than the subsequent second time period t a2 of the respective disconnection switch position Sa, because the braking torque Nb starting from the motor speed n which has reached the limit speed ng is reduced more than in the further course of the alternating switching S. The respective time periods of the disconnection switch position and the braking switch position and the alternating switching frequency, for example 14 alternating switchings S available here, can be selected from the required profile of the braking torque Nb and for example adapted to environmental conditions.

[0037] List of reference signs

[0038] 10 electric motor arrangement

[0039] 12 electric motor

[0040] 14 rotor

[0041] 16 transmission

[0042] 18 vehicle wheel

[0043] 20 inverter circuit

[0044] Ma motor connection

[0045] Mp motor phase

[0046] n motor speed

[0047] ng limit speed

[0048] Nb braking torque

[0049] Nb0 braking torque profile

[0050] Nb1 braking torque profile

[0051] Nm average braking torque

[0052] S alternating switching

[0053] S1 to S6 switching elements

[0054] Sa open switch position

[0055] Sb braking switch position

[0056] ta1 first time period

[0057] ta2 second time period

[0058] tb1 first time period

[0059] tb2 second time period

[0060] Ub supply voltage

Claims

1. Method for controlling a motor braking process of an electric motor (12) which provides a driving torque for a vehicle and which is electrically driven via at least two motor connections (Ma) by an inverter circuit (20) having a plurality of switching elements (S1 to S6) and which has a rotor (14) which can be rotated at a motor speed (n) and which, during the electric motor braking process, is subjected to a speed-dependent braking torque due to the inverter circuit (20) assuming a braking switch position (Sb) and to a braking torque (Nb) which is smaller than the braking torque of the braking switch position (Sb) or to no braking torque (Nb) at all due to the inverter circuit (20) assuming an open switch position (Sa), characterized in that during the motor braking process, the braking switch position (Sb) is assumed without interruption when the motor speed (n) is above a limit speed (ng), the corresponding braking torque curve being Nb0, and the braking switch position (Sb) is assumed in braking switch position intervals alternating with open switch position intervals of the open switch position (Sa) by means of alternating switching (S) when the motor speed (n) is below the limit speed (ng), the resulting braking torque curve Nb1 being approximately consistent with the braking torque curve Nb0 when the motor speed (n) is above the limit speed (ng) on average.

2. The method of claim 1, wherein, The time period (tb1, tb2) of each braking switch position interval is dependent on the motor speed (n).

3. The method according to claim 1 or 2, characterized in that, The time period (ta1, ta2) of each open switch position interval is set dependent on the motor speed (n).

4. Method according to one of the preceding claims, characterized in that, The time period (tb1, tb2) of at least one braking switch position interval is different from the time period (ta1, ta2) of a subsequent open switch position interval.

5. The method according to one of the preceding claims, characterized in that, In the braking switch position (Sb), at least two motor connections (Ma) are electrically short-circuited.

6. Method according to one of the preceding claims, characterized in that, In the open switch position (Sa), most of the switching elements (S1 to S6) are in a blocking position.

7. The method of claim 6, wherein, In the open switch position (Sa), all of the switching elements (S1 to S6) are in the blocking position.

8. Method according to one of the preceding claims, characterized in that, The limit speed (ng) corresponds to a motor speed (n) at which a voltage induced at the switching elements (S1 to S6) by the open switch position (Sa) of the rotor (14) is below a limit voltage.

9. Electric motor arrangement (10) for providing a driving torque for a vehicle, having an electric motor (12) with a rotatable rotor (14) which is subjected to a braking torque (Nb) during an electric motor braking process and can be rotated at a motor speed (n), and an inverter circuit (20) for controlling the motor braking process by means of a method according to one of the preceding claims.

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