A method for protecting a motor from stall in an electric power assisted steering system

Abstract

The application discloses a kind of motor's stall protection method in electric power steering system, specifically includes: S1, the maximum current limiting value and the lowest protection value of motor output current are determined;S2, the steering torque and steering angular velocity of steering wheel connected with electric power steering system and the motor output current are detected, if the detected steering torque is not less than set torque threshold, steering angular velocity is zero, and motor output current is not less than maximum current limiting value in the first set time, it is detected continuously, it is turned to S3, otherwise it is turned to S5;S3, according to the current reduction strategy set, reduce motor output current, and continuously detect whether steering torque is less than set torque threshold, if yes, it is turned to S5, otherwise it is turned to S4;S4, detect whether motor output current is greater than the lowest protection value, if yes, it is turned to S3, otherwise, motor output current is kept at the lowest protection value;S5, according to the current control strategy of electric power steering system, motor output current is determined.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of motor control, in particular to a motor stall protection method in an electric power steering system. BACKGROUND

[0002] The electric power steering system EPS is a power steering system relying on a motor to provide auxiliary torque. The EPS collects torque and angle signals through sensors inside the EPS according to the required steering force, and then controls the motor to provide appropriate assistance by an ECU. After a dead steering, the motor of the electric power steering system EPS stalls, and the motor stall current is usually 5-10 times the rated current. Without protection, the circuit and related components will be burned out, and improper protection will result in poor steering assistance experience and no assistance. SUMMARY

[0003] In view of the above problems, the present application provides a motor stall protection method in an electric power steering system to overcome the above problems or at least partially solve the above problems. The technical solution is as follows:

[0004] A motor stall protection method in an electric power steering system, comprising:

[0005] S1, determining the maximum current limiting value and the minimum protection value of the motor output current;

[0006] S2, detecting the steering torque and steering angular velocity of a steering wheel connected to the electric power steering system and detecting the motor output current, if the detected steering torque is not less than a set torque threshold, the steering angular velocity is zero, and the motor output current is detected to be not less than the maximum current limiting value for a first set time, go to S3, otherwise go to S5;

[0007] S3, reducing the motor output current according to a set current reduction strategy, and continuously detecting whether the steering torque is less than the set torque threshold, if yes, go to S5, otherwise go to S4;

[0008] S4, detecting whether the motor output current is greater than the minimum protection value, if yes, go to S3, otherwise keep the motor output current at the minimum protection value;

[0009] S5, determining the motor output current according to the current control strategy of the electric power steering system.

[0010] The above method, optionally, the current control strategy of the electric power steering system comprises:

[0011] Obtaining a function relationship between the motor output current and the steering torque of the steering wheel, bringing the detected steering torque into the function relationship between the motor output current and the steering torque of the steering wheel, and determining the corresponding motor output current.

[0012] Optionally, when it is detected that the motor output current is not less than the maximum current limiting value but does not last for the first set time, the motor output current is maintained at the maximum current limiting value.

[0013] Optionally, the maximum current limiting value of the motor output current is set according to the power of the motor.

[0014] Optionally, the maximum current limiting value of the motor output current is 60A, the minimum protection value is 20A, and the set torque threshold value is 8Nm.

[0015] Optionally, the set current reduction strategy includes:

[0016] An initial current reduction speed v0 and a current reduction acceleration a are set, and an actual current reduction speed v = v0 + at is determined.

[0017] The motor output current is reduced according to the determined actual current reduction speed v from the maximum current limiting value, and the motor output current is reduced to not less than the minimum protection value.

[0018] Optionally, the initial current reduction speed v0 is 0.05A / ms, and the acceleration a is 2A / ms. 2 .

[0019] Optionally, when it is detected in the step S3 that the steering torque is less than the set torque threshold value for the second set time, the step S5 is turned to.

[0020] Optionally, the first set time is 3s, and the second set time is 0.2s.

[0021] Optionally, in the step S2, the steering torque and the steering angular velocity of the steering wheel connected with the electric power steering system and the output current of the motor are detected through the sensors arranged in the electric power steering system.

[0022] Compared with the prior art, the application has the following advantages: in the scheme provided by the application, the motor output current is kept in a suitable range through specific control of the motor output current, so that the circuit or related components are prevented from being damaged after exceeding the range, and motor stall protection is achieved; in the embodiment, the problem of rebounding and shaking hands caused by too much current reduction is solved by gradually reducing the current, so that the safety of the whole vehicle during steering is ensured while comfort is also taken into account.

[0023] The above description is only a summary of the technical scheme of the application, in order to more clearly understand the technical means of the application, and to be implemented in accordance with the content of the specification, and in order to make the above and other purposes, features and advantages of the application more obvious and easy to understand, the following specific embodiments of the application are described. BRIEF DESCRIPTION OF DRAWINGS

[0024] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are intended to depict only preferred embodiments of the application, and therefore should not be considered to narrow the scope of the present application in any way. Instead, they are included to provide illustration of the preferred embodiments of the application. In the drawings:

[0025] Figure 1 A method flowchart of a motor stall protection method provided by an embodiment of the application in an electric power assisted steering system,

[0026] Figure 2 A setting schematic diagram of an electric power assisted steering system when applying the motor stall protection method provided by an embodiment of the application in the electric power assisted steering system. DETAILED DESCRIPTION

[0027] Exemplary embodiments of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it is understood that the present disclosure can be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0028] Reference Figure 1 A method flowchart of a motor stall protection method provided by an embodiment of the application in an electric power assisted steering system, Figure 1 The method execution process is a feasible implementation scheme of the motor stall protection method provided by an embodiment of the application in an electric power assisted steering system. The method can be applied in various system platforms, and the execution subject can be a server arranged in the system platform. The motor stall protection method provided by an embodiment of the application specifically includes:

[0029] S1, determining a maximum current limiting value and a minimum protection value of a motor output current;

[0030] In the method provided by the embodiment of the application, the maximum current limiting value I MA and the minimum protection value I Z of the motor output current are set, and the motor output current is limited between I Z and I MAX when the motor is normally working, so as to avoid damaging the circuit or related components.

[0031] Further, the maximum current limiting value I MAX of the motor output current is set according to the power of the motor, and I MAX is set too high, which may cause a safety hazard and too slow entering of the stall; in some embodiments, the maximum current limiting value I MAX may be set to 60 A, and the minimum protection value I Z may be set to 20 A.

[0032] S2, detecting a steering torque and a steering angular velocity of a steering wheel connected with the electric power steering system and detecting the motor output current, and if the detected steering torque is not less than a set torque threshold, the steering angular velocity is zero, and the motor output current is not less than the maximum current limiting value for a first set time, proceeding to S3, otherwise proceeding to S5.

[0033] In the method provided by the embodiment of the application, whether the motor stall occurs is determined by detecting the steering torque and the steering angular velocity of the steering wheel connected with the electric power steering system and detecting the motor output current; after the steering wheel is dead-steered, if the detected steering torque reaches the set torque threshold T, the detected steering angular velocity is 0, the detected motor output current is not less than the maximum current limiting value I MAX and the first set time is lasted, it is considered that the motor stall occurs, the motor output current needs to be reduced, and the motor output current is reduced according to the set current reduction strategy in step S3; if the above situation is not detected, the motor output current is determined according to the normal current control strategy of the electric power steering system.

[0034] Further, the set torque threshold T and the first set time can be set according to actual conditions; in some embodiments, the set torque threshold T is set to 8 Nm, and the first set time is set to 3 seconds; if the detected steering torque reaches 8 Nm, the steering angular velocity is 0, and the motor output current reaches 60 A and lasts for 3 seconds, the stall protection is started, and the motor output current is reduced according to the set current reduction strategy in S3.

[0035] Reference Figure 2A schematic diagram of a setting of an electric power steering (EPS) on a vehicle is shown, the electric power steering 2 is connected with a steering wheel assembly 1, the electric power steering 2 includes a motor 3, a sensor 4 and an EPS controller, the steering wheel is connected with a steering column, the sensor 4 is arranged on the steering column, the steering torque and the steering angular velocity of the steering wheel are collected by the sensor 4 inside the EPS and are transmitted to the EPS controller, and the motor 3 is controlled by the EPS controller to provide appropriate assistance; the electric power steering 2 also acquires the output current of the motor for control.

[0036] S3, reducing the motor output current according to a set current reduction strategy, and continuously detecting whether the steering torque is less than a set torque threshold, if yes, going to S5, otherwise going to S4;

[0037] The motor locked-rotor current is 5-10 times of the rated current, and if no control is added, the circuit and related parts can be burned out, in the method provided in the embodiment of the application, when it is detected that the motor locked-rotor occurs and the motor output current reaches the maximum current limiting value I MAX and lasts for a first set time, a set current reduction strategy is used to reduce the motor output current.

[0038] Further, if the current is reduced too much at once, it can cause rebound and hand shock, and the steering assistance hand feeling experience is poor and the comfort is low. Optionally, the set current reduction strategy used in the method provided in the embodiment of the application includes: setting an initial current reduction speed v0 and a current reduction acceleration a, determining an actual current reduction speed v=v0+at; the motor output current starts from the maximum current limiting value, and is reduced according to the determined actual current reduction speed v, and the motor output current is not less than the lowest protection value after being reduced.

[0039] In the method provided in the embodiment of the application, an initial current reduction speed v0 can be optionally set, and the acceleration a is set on the basis of v0 to gradually increase the actual current reduction speed v, in this way, the rebound and hand shock problem caused by too much current reduction at once is avoided, the safety during the steering of the whole vehicle is ensured, and the comfort is also taken into account.

[0040] Optionally, in some embodiments, the initial current reduction speed v0 is set to 0.05 A / ms, and the acceleration a is set to 2 A / ms 2 , and the motor output current is reduced according to the following formula:

[0041]

[0042] Further, the motor output current can be reduced by changing the duty ratio of the input voltage.

[0043] When the motor output current is reduced according to the set current reduction strategy, it is continuously detected whether the steering torque is lower than the set torque threshold T, and if yes, the reduction of the motor output current is stopped, and the current control strategy of the electric power steering system is used to determine the motor output current.

[0044] S4, it is detected whether the motor output current is greater than the minimum protection value, and if yes, it is transferred to S3, otherwise the motor output current is kept at the minimum protection value;

[0045] If the steering torque is not lower than the set torque threshold T all the time, the motor output current is continuously reduced according to the set current reduction strategy, but when the motor output current is reduced according to the set current reduction strategy, the motor output current cannot be reduced to be lower than the minimum protection value I Z Therefore, when the current is reduced, it is continuously detected whether the motor output current is greater than the minimum protection value, and if the motor output current is reduced to the minimum protection value I Z , the motor output current is kept at the minimum protection value I Z and is not continuously reduced.

[0046] Further, to avoid false triggering, in the step S3, it is optionally set that when the steering torque is detected to be less than the set torque threshold for a second set time, it is transferred to S5; and in the step S4, it is optionally set that when the motor output current is detected to be lower than the minimum protection value I Z for a second set time, the motor output current is kept at the minimum protection value I Z and is not continuously reduced. In some embodiments, the second set time is optionally set to be 0.2s.

[0047] S5, the motor output current is determined according to the current control strategy of the electric power steering system.

[0048] In the method provided by the embodiments of the application, the current control strategy of the electric power steering system can include: obtaining a functional relationship between the motor output current and the steering torque of the steering wheel, bringing the detected steering torque into the functional relationship between the motor output current and the steering torque of the steering wheel, and determining the corresponding motor output current. The current control strategy of the electric power steering system can set the corresponding motor output current according to the actually detected torque, and the motor output current is set by using the strategy in the case where the motor does not stall, and the current reduction strategy set by the embodiments of the application is used to reduce the motor output current in the case where the motor stalls, so that the motor output current is guaranteed to be between I Z and I MAX .

[0049] The motor stall protection method provided by the embodiments of the application adjusts the actual output torque by controlling the motor output current, and the motor output current is continuously reduced according to the set current reduction strategy when the motor output current is reduced according to the set current reduction strategy.Figure 1 If the motor does not stall, i.e. if the conditions that the detected steering torque reaches the set torque threshold T, the steering angular velocity is 0, and the motor output current reaches the maximum current limit I MAX are not met simultaneously, the motor output current is determined according to the current control strategy of the electric power steering system, i.e. optionally according to the actually detected steering torque. If the conditions that the detected steering torque reaches the set torque threshold T, the steering angular velocity is 0, but the motor output current reaches the maximum current limit I MAX for the first set time, the motor output current is optionally set to remain I MAX . According to the motor output current I MAX , the power assistance is provided. After the steering torque reaches the set torque threshold T, the steering angular velocity is 0, and the motor output current reaches the maximum current limit I MAX for the first set time, the current reduction protection is started, and the motor output current is reduced according to the speed v = v0 + at. During the process of reducing the motor output current, if the detected steering torque is less than the set torque threshold T, the motor output current is switched from the set current reduction strategy to the current control strategy of the electric power steering system, and the motor output current is determined according to the actually detected steering torque. If the steering torque is not less than the set torque threshold T, the motor output current continues to be reduced according to the set current reduction strategy, but if the motor output current is not greater than the minimum protection value I Z , the current reduction is stopped, and the motor output current is kept at the minimum protection value I Z . Further optionally, if the steering torque is subsequently detected to be less than the set torque threshold T, the motor output current is determined according to the actually detected steering torque.

[0050] The above embodiments are only used to illustrate the technical solutions of the present application, and are not used to limit the present application. Although the present application has been described in detail, it should be understood that those skilled in the art can make various modifications and changes without departing from the spirit and scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A method for protecting a motor against stall in an electric power assisted steering system, characterized in that, The method comprises: S1, determining a maximum current limiting value and a minimum protection value of a motor output current; S2, detecting a steering torque and a steering angular velocity of a steering wheel connected with the electric power steering system and detecting the motor output current, and if the detected steering torque is not less than a set torque threshold, the steering angular velocity is zero, and the motor output current is detected to be not less than the maximum current limiting value for a first set time, going to S3, otherwise going to S5; S3, reducing the motor output current according to a set current reduction strategy, and continuously detecting whether the steering torque is less than the set torque threshold, if yes, going to S5, otherwise going to S4; S4, detecting whether the motor output current is greater than the minimum protection value, if yes, going to S3, otherwise keeping the motor output current at the minimum protection value; S5, determining the motor output current according to a current control strategy of the electric power steering system; The set current reduction strategy comprises: setting an initial current reduction speed v0 and a current reduction acceleration a, and determining an actual current reduction speed v = v0 + at; The motor output current is reduced according to the determined actual current reduction speed v from the maximum current limiting value, and the motor output current is not less than the minimum protection value.

2. The method of claim 1, wherein the motor is a motor of an electric power steering system. The current control strategy of the electric power steering system comprises: obtaining a functional relationship between the motor output current and the steering torque of the steering wheel, bringing the detected steering torque into the functional relationship between the motor output current and the steering torque of the steering wheel, and determining the corresponding motor output current.

3. The method of claim 2, wherein the motor is a motor of an electric power steering system. When the motor output current is detected to be not less than the maximum current limiting value but not for the first set time, the motor output current is kept at the maximum current limiting value.

4. The method of claim 1 or 3, wherein the motor is a motor of an electric power steering system. The maximum current limiting value of the motor output current is set according to the power of the motor.

5. The method of claim 4, wherein the motor is a motor of an electric power steering system. The maximum current limiting value of the motor output current is 60A, the minimum protection value is 20A, and the set torque threshold is 8Nm.

6. The method of claim 1, wherein the motor is a motor of an electric power steering system. The initial current reduction speed v0 is 0.05A / ms, and the acceleration a is 2A / ms2.

7. The method of claim 1, wherein the motor is a motor of an electric power steering system. When the steering torque is detected to be less than the set torque threshold for a second set time in the step S3, going to S5.

8. The method of claim 7, wherein the motor is a motor of an electric power steering system. The first set time is 3s, and the second set time is 0.2s.

9. The method of claim 1, wherein the motor is a motor of an electric power steering system. In the step S2, the steering torque and the steering angular velocity of the steering wheel connected with the electric power steering system are detected by a sensor arranged in the electric power steering system, and the motor output current is detected.

Images