Electric power steering system torque sensor failure handling method

Abstract

The application discloses a kind of electric power steering system torque sensor failure processing method, comprising the following steps: step 1, when detecting that vehicle electric power steering system torque sensor completely fails, open torque sensor failure processing procedure;Step 2, electric power steering system real-time acquisition external input signal;Step 3, when torque sensor completely fails, freeze current assist motor torque value;Step 4, to frozen assist motor torque value is safety boundary value limit;Step 5, detect driver steering behavior is straight, turn or change direction;Step 6, according to driver steering behavior determines the processing mode of current assist motor torque value and assist torque decrement slope value, and the assist motor torque value is reduced 0;Step 7, real-time monitoring assist motor torque value, when assist motor torque value is incremental, then cut off assist motor torque value output to 0.

Description

Technical Field

[0001] This invention relates to the field of automotive technology, and in particular to a method for handling the failure of a torque sensor in an electric power steering system. Background Technology

[0002] In automotive systems, the Electric Power Steering (EPS) system, as the primary controller for lateral control, requires a relatively high level of functional safety. Torque and angle sensors are the core signal sources for this system, making fault diagnosis and handling strategies crucial when these sensors malfunction. At the functional safety level of the EPS system, a torque sensor failure renders the torque signal completely unreliable, necessitating a sufficiently high safety level to ensure driver safety. Therefore, fault handling strategies are needed to address the motor's assist torque when the torque sensor fails. Current market research on EPS sensor failures primarily focuses on fault detection, with limited research on corresponding fault handling strategies in practical applications. Current torque handling methods after a steering system torque sensor failure mainly involve rapidly cutting off the power assist motor's torque output within the fault tolerance time, thus disabling EPS assistance. However, this approach doesn't adequately consider the driver's steering behavior, leading to insufficient steering assist and steering lock-up issues. Summary of the Invention

[0003] To solve the above-mentioned technical problems, the present invention provides a method for handling the failure of a torque sensor in an electric power steering system, comprising the following steps:

[0004] Step 1: When the torque sensor of the vehicle's electric power steering system is detected to be completely malfunctioning, the torque sensor failure handling process is initiated.

[0005] Step 2: The electric power steering system acquires external input signals in real time. The external input signals include at least: steering wheel angle, power steering motor speed, power steering motor torque, and sensor status fault setting.

[0006] Step 3: When the torque sensor is not faulty, output the motor torque normally; when the torque sensor is completely faulty, freeze the current boost motor torque value.

[0007] Step 4: Set safety boundary values ​​to limit the frozen torque values ​​of the power assist motor;

[0008] Step 5: Detect the driver's steering behavior as straight, turning, or changing direction based on the frozen power steering motor torque value, steering wheel angle, and power steering motor speed signal;

[0009] Step 6: Determine the processing method for the current power assist motor torque value and the power assist torque reduction slope value based on the driver's steering behavior, and reduce the power assist motor torque value to 0.

[0010] Step 7: Monitor the torque value of the power assist motor in real time. When the torque value of the power assist motor increases, cut off the output of the power assist motor torque value to 0.

[0011] Preferably, in step 1, the method for determining that the torque sensor has completely failed is as follows: obtain the torque sensor status bit signal, and when the fault type of the status bit signal is complete failure, determine that the torque sensor has completely failed.

[0012] Preferably, in step 2, the signals of steering wheel angle, power steering motor speed and power steering motor torque are validated, and invalid signals are filled with invalid values.

[0013] Preferably, the validity verification method is to define upper and lower limit values ​​for the signals of steering wheel angle, power steering motor speed, and power steering motor torque. When the signals of steering wheel angle, power steering motor speed, or power steering motor torque exceed the range of the upper and lower limit values, invalid signals are filled with 0.

[0014] Preferably, in step 4, the specific method for limiting the frozen power assist motor torque value with a safety boundary value is as follows: the power assist motor torque value is compared with a preset safety boundary value; when the power assist motor torque value is greater than or equal to the safety boundary value, the power assist motor torque value is changed to the safety boundary value, and the safety boundary value is used as the safety freeze value; when the power assist motor torque value is less than the safety boundary value, the current power assist motor torque value is directly frozen as the safety freeze value.

[0015] Preferably, the safety boundary value is 0.8 Nm.

[0016] Preferably, in step 5, the method for detecting whether the driver's steering behavior is straight, turning, or changing direction is as follows: when the steering wheel angle is within 15 degrees, the driver is determined to be going straight; when the steering wheel angle is greater than 15 degrees, the driver is determined to be turning; when the direction of the power steering motor speed is opposite to the direction of the steering wheel angle, the driver is determined to be changing direction.

[0017] Preferably, in step 6, the method for determining the current power assist motor torque value based on the driver's steering behavior is as follows: when it is determined that the driver is going straight, the power assist motor torque value is directly cut off to 0; when it is determined that the driver is turning, the power assist motor torque value is reduced from the safety freeze value to 0 according to the first decreasing slope value; when it is determined that the driver is changing direction, the power assist motor torque value is directly cut off to 0; when it is determined that the driver has changed direction during a turn, the power assist motor torque value is reduced to 0 according to the second decreasing slope value.

[0018] Preferably, the first decreasing slope value T ramp1 The calculation formula is: T = T safe -T ramp1 *t, where T is the real-time output motor torque value, and time t is the unit period. safe The value is frozen for safety until T=0.

[0019] Preferably, the second decreasing slope value T ramp2 The calculation formula is: T = T safe -(V rotor *K rotor -K ramp )T ramp2 *t, where V rotor To increase the motor speed, K rotor A value between 0 and 1, related to the speed of the assist motor, K ramp T is the torque decrease slope coefficient, where time t is a unit period. safe The value is frozen for safety until T=0.

[0020] Preferably, in step 7, if the power steering motor torque value is still greater than the safety boundary value within a preset time after the torque sensor fails, or the power steering motor torque value at the previous moment is less than the current power steering motor torque value, then it is determined that the power steering motor torque value does not follow a monotonically decreasing trend, and the electric power steering system is turned off.

[0021] Compared to traditional torque sensor failure handling methods, this invention, considering safety objectives, analyzes the driver's steering behavior and separates the functional safety objectives of the current steering system not violating the sudden loss of assistance and the prevent blocking functional safety objective of ensuring the driver does not violate the steering lock during direction changes. This ensures that the electric power steering torque can better assist the driver in safely and smoothly completing steering actions within the fault tolerance time interval.

[0022] Based on the analysis of driver steering behavior, this invention considers whether the driver is currently driving straight or turning when the EPS torque sensor fails completely. It cuts off the output of the power assist motor torque in a safe way, solving problems such as insufficient power assist when the driver is steering and steering lock when the driver changes direction when the fault occurs. This enhances the safety of the driver and the controllability of the vehicle after the EPS system fails. Attached Figure Description

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0024] Figure 1This is a software system architecture diagram for implementing the electric power steering system torque sensor failure handling method of the present invention;

[0025] Figure 2 This is a flowchart of the method for determining the current torque value of the power steering motor based on the driver's steering behavior according to the present invention;

[0026] Figure 3 It is a graph showing the relationship between the decrease in torque when the speed of the assist motor is within a certain threshold range. Detailed Implementation

[0027] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can fully understand other advantages and technical effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through different specific embodiments, and the details in this specification can also be applied based on different viewpoints, with various modifications or changes made without departing from the overall design concept of the invention. It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. The following exemplary embodiments of the present invention can be implemented in many different forms and should not be construed as being limited to the specific embodiments set forth herein. It should be understood that these embodiments are provided to make the disclosure of the present invention thorough and complete, and to fully convey the technical solutions of these exemplary embodiments to those skilled in the art.

[0028] This specific embodiment provides a method for handling the failure of a torque sensor in an electric power steering system, including the following steps:

[0029] Step 1: When the torque sensor of the vehicle's electric power steering system is detected to be completely malfunctioning, the torque sensor failure handling process is initiated.

[0030] Step 2: The electric power steering system acquires external input signals in real time. The external input signals include at least: steering wheel angle, power steering motor speed, power steering motor torque, and sensor status fault setting.

[0031] Step 3: When the torque sensor is not faulty, output the motor torque normally; when the torque sensor is completely faulty, freeze the current boost motor torque value.

[0032] Step 4: Set safety boundary values ​​to limit the frozen torque values ​​of the power assist motor;

[0033] Step 5: Detect the driver's steering behavior as straight, turning, or changing direction based on the frozen power steering motor torque value, steering wheel angle, and power steering motor speed signal;

[0034] Step 6: Determine the processing method for the current power assist motor torque value and the power assist torque reduction slope value based on the driver's steering behavior, and reduce the power assist motor torque value to 0.

[0035] Step 7: Monitor the torque value of the power assist motor in real time. When the torque value of the power assist motor increases, cut off the output of the power assist motor torque value to 0.

[0036] Specifically, it can be used as follows Figure 1 The software architecture shown implements a method for handling torque sensor failure in an electric power steering system. The software architecture mainly includes the following modules:

[0037] The system comprises the following modules: torque sensor failure state detection module, failure point torque freezing module, safe torque limiting module, signal validity processing module, torque reduction calculation module, driver steering behavior detection module, torque reduction slope calculation module, and torque safety verification module. The signal validity processing module receives steering wheel angle signals, power steering motor speed signals, power steering motor torque signals, and sensor status signals from the vehicle, and connects to input terminal one of the torque reduction calculation module. The torque sensor failure state detection module outputs a sensor invalid signal, which is connected to input terminal one of the torque freezing module and input terminal two of the torque reduction calculation module. The torque freezing module outputs the power steering motor torque signal frozen when a failure occurs, which is connected to input terminal one of the safe torque limiting module. The safe torque limiting module outputs the safe torque value signal after safety limiting, which is connected to input terminal one of the torque reduction calculation module. The driver steering behavior detection module outputs the driver steering behavior signal, which is connected to input terminal one of the torque reduction slope calculation module. The torque reduction slope calculation module outputs the power steering torque reduction slope value, which is connected to input terminal one of the torque reduction calculation module. The torque reduction calculation module outputs a real-time decreasing assist motor torque signal, which is connected to the input of the torque safety verification module. The torque safety verification module outputs the verified assist motor torque value signal, which is connected to the motor control module to control the motor.

[0038] The following is an exemplary description of a method for handling torque sensor failure in an electric power steering system.

[0039] In step 1, the method for determining that the torque sensor is completely failed is as follows: obtain the torque sensor status bit signal, and when the fault type of the status bit signal is complete failure, determine that the torque sensor is completely failed.

[0040] More specifically, if the torque sensor fault status bit is set even once during the period from vehicle ignition to operation, and both channels of the sensor are in a fault state at this time, the sensor is determined to be completely failed. In this embodiment, the torque sensor status bit signal is first acquired. When the status bit of this signal indicates that the sensor fault type is completely failed, it means that the sensor cannot work normally at this time, and the torque processing procedure after the torque sensor failure begins.

[0041] In step 2, the signals for steering wheel angle, power steering motor speed and power steering motor torque are validated, and invalid signals are filled with invalid values.

[0042] More specifically, the system acquires the steering wheel angle signal, power steering motor speed signal, and power steering motor torque signal from the EPS system in real time. The validity of the signals received by the controller is verified, and any invalid signal is filled with an invalid value. In this embodiment, the validity verification mainly defines upper and lower limits for the signal based on its physical meaning. Signals exceeding these limits are considered invalid and pose a safety hazard. Therefore, if the acquired steering wheel angle signal is invalid, it is filled with 0. Similarly, if the power steering motor speed signal is invalid, it is filled with 0. And if the power steering motor torque signal is invalid, it is filled with 0.

[0043] In step 4, the specific method for limiting the frozen power assist motor torque value with a safety boundary value is as follows: the power assist motor torque value is compared with a preset safety boundary value. When the power assist motor torque value is greater than or equal to the safety boundary value, the power assist motor torque value is changed to the safety boundary value, and the safety boundary value is used as the safety freeze value. When the power assist motor torque value is less than the safety boundary value, the current power assist motor torque value is directly frozen as the safety freeze value.

[0044] More specifically, based on the power assist motor torque signal value at the time of the torque sensor failure, this value is compared with the boundary value that ensures the safety and controllability of the EPS system. If this value is greater than or equal to the safety boundary value, the motor torque value is quickly abruptly changed to the boundary value, and this boundary value is used as the safety freeze value T. safe If the motor torque value is less than the safety boundary value, then the current motor torque value is directly frozen as the safety freeze value T. safe In this embodiment, the safety boundary value is set at 0.8 Nm. When the motor torque value at the time of the fault is outside the safety boundary value range, it indicates that the vehicle steering is in an uncontrollable state, and the current motor torque value needs to be abruptly changed to this safety boundary value for processing. If it is within the safety range, the current motor torque value is processed. This safety boundary value can be obtained from the vehicle calibration test.

[0045] In step 5, the method for detecting whether the driver's steering behavior is straight, turning, or changing direction is as follows: when the steering wheel angle is within 15 degrees, the driver is determined to be going straight; when the steering wheel angle is greater than 15 degrees, the driver is determined to be turning; when the direction of the power steering motor speed is opposite to the direction of the steering wheel angle, the driver is determined to be changing direction, otherwise the driver is not changing direction.

[0046] In step 6, the method for determining the current power steering motor torque value based on the driver's steering behavior is as follows:

[0047] When the driver is determined to be going straight, the power assist motor torque is immediately cut off to 0.

[0048] When the driver is determined to be turning, the power assist motor torque value will be reduced from the safety freeze value to 0 according to the first decreasing slope value;

[0049] When the driver is detected to be changing direction, the power assist motor torque is immediately cut off to 0.

[0050] When it is determined that the driver has changed direction during a turn, the torque value of the power assist motor is reduced to 0 according to the second decreasing slope value;

[0051] The first decreasing slope value T ramp1 The calculation formula is: T = T safe -T ramp1 *t, where T is the real-time output motor torque value, and time t is the unit period. safe The value is frozen for safety until T=0.

[0052] The second decreasing slope value T ramp2 The calculation formula is: T = T safe -(V rotor *K rotor -K ramp )T ramp2 *t, where V rotor To increase the motor speed, K rotor A value between 0 and 1, related to the speed of the assist motor, K ramp T is the torque decrease slope coefficient, where time t is a unit period. safe The value is frozen for safety until T=0.

[0053] In this embodiment, the method of the above processing is as follows: Figure 2 As shown, when the vehicle is traveling straight, the EPS motor torque output is cut off. When the driver performs a normal turning maneuver without changing direction, the torque decreases at a fixed first decrease slope value, which can be calibrated on a real vehicle. If the driver changes direction during the torque decrease process, the torque decreases according to a second decrease slope value based on the motor speed. When the motor speed is within a certain threshold range, the degree of torque decrease is as follows: Figure 3 The relationship curve shown in this case indicates that the speed curve starts from 0 and changes at speed V. Min Set to 100 and speed V Max It is 300.

[0054] After a fault occurs, the torque value of the assist motor is monitored in real time. Specifically, the torque change of the motor after the fault occurs is monitored in real time. During this period, the torque value is not allowed to increase. Once the torque value increases, the motor torque output is cut off to 0.

[0055] In this embodiment, the torque verification module monitors torque changes in real time. If the torque is still greater than the safety boundary value within a certain period of time after the sensor fails, or if the torque value at the previous moment is less than the current torque value within a certain period of time after the sensor fails, it is determined that the torque does not follow a monotonically decreasing trend and is prone to commutation lock-up. Therefore, the motor torque output needs to be cut off and the EPS system needs to be shut down.

[0056] The present invention has been described in detail above through specific embodiments and examples, but these are not intended to limit the invention. Many modifications and improvements can be made by those skilled in the art without departing from the principles of the invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. A method for handling torque sensor failure in an electric power steering system, characterized in that, Includes the following steps: Step 1: When the torque sensor of the vehicle's electric power steering system is detected to be completely malfunctioning, the torque sensor failure handling process is initiated. Step 2: The electric power steering system acquires external input signals in real time. The external input signals include at least: steering wheel angle, power steering motor speed, power steering motor torque, and sensor status fault setting. Step 3: When the torque sensor is not faulty, output the motor torque normally; when the torque sensor is completely faulty, freeze the current boost motor torque value. Step 4: Set safety boundary values ​​to limit the frozen torque values ​​of the power assist motor; Step 5: Detect the driver's steering behavior as straight, turning, or changing direction based on the frozen power steering motor torque value, steering wheel angle, and power steering motor speed signal; Step 6: Determine the processing method for the current power assist motor torque value and the power assist torque reduction slope value based on the driver's steering behavior, and reduce the power assist motor torque value to 0. Step 7: Monitor the torque value of the power assist motor in real time. When the torque value of the power assist motor increases, cut off the output of the power assist motor torque value to 0. In step 4, the specific method for limiting the frozen power assist motor torque value with a safety boundary value is as follows: the power assist motor torque value is compared with a preset safety boundary value. When the power assist motor torque value is greater than or equal to the safety boundary value, the power assist motor torque value is changed to the safety boundary value, and the safety boundary value is used as the safety freeze value. When the power assist motor torque value is less than the safety boundary value, the current power assist motor torque value is directly frozen as the safety freeze value. In step 5, the method for detecting whether the driver's steering behavior is straight, turning, or changing direction is as follows: when the steering wheel angle is within 15 degrees, the driver is determined to be going straight; when the steering wheel angle is greater than 15 degrees, the driver is determined to be turning; when the direction of the power steering motor speed is opposite to the direction of the steering wheel angle, the driver is determined to be changing direction. In step 6, the method for determining the current power steering motor torque value based on the driver's steering behavior is as follows: When the driver is determined to be going straight, the power assist motor torque is immediately cut off to 0. When the driver is determined to be turning, the power assist motor torque value will be reduced from the safety freeze value to 0 according to the first decreasing slope value; When the driver is detected to be changing direction, the power assist motor torque is immediately cut off to 0. When it is determined that the driver has changed direction during a turn, the torque value of the power steering motor is reduced to 0 according to the second decreasing slope value.

2. The method for handling torque sensor failure in an electric power steering system according to claim 1, characterized in that, In step 1, the method for determining that the torque sensor is completely failed is as follows: obtain the torque sensor status bit signal, and when the fault type of the status bit signal is complete failure, determine that the torque sensor is completely failed.

3. The method for handling torque sensor failure in an electric power steering system according to claim 1, characterized in that, In step 2, the signals for steering wheel angle, power steering motor speed and power steering motor torque are validated, and invalid signals are filled with invalid values.

4. The method for handling torque sensor failure in an electric power steering system according to claim 3, characterized in that, The validity verification method is to define upper and lower limit values ​​for the signals of steering wheel angle, power steering motor speed and power steering motor torque. When the signals of steering wheel angle, power steering motor speed or power steering motor torque exceed the range of the upper and lower limit values, invalid signals are filled with 0.

5. The method for handling torque sensor failure in an electric power steering system according to claim 1, characterized in that, The safety boundary value is 0.8 Nm.

6. The method for handling torque sensor failure in an electric power steering system according to claim 1, characterized in that, The first decreasing slope value T ramp1 The calculation formula is: T = T safe - T ramp1 *t, where T is the real-time output motor torque value, and time t is the unit period. safe The value is frozen for safety until T=0.

7. The method for handling torque sensor failure in an electric power steering system according to claim 1, characterized in that, The second decreasing slope value T ramp2 The calculation formula is: T = T safe - (V rotor *K rotor -K ramp ) T ramp2 *t, where V rotor To increase the motor speed, K rotor A value between 0 and 1, related to the speed of the assist motor, K ramp T is the torque decrease slope coefficient, where time t is a unit period. safe The value is frozen for safety until T=0.

8. The method for handling torque sensor failure in an electric power steering system according to claim 1, characterized in that, In step 7, if the power steering motor torque value is still greater than the safety boundary value within a preset time after the torque sensor fails, or the power steering motor torque value at the previous moment is less than the current power steering motor torque value, then it is determined that the power steering motor torque value does not follow a monotonically decreasing trend, and the electric power steering system is turned off.

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