Friction compensation method for automotive electric power steering system

Abstract

The present invention relates to the field of automobile auxiliary drive technology, and proposes a friction compensation method for an automobile electric power steering system, comprising: obtaining a torque demand degree according to a change in input torque; obtaining a compensation start time according to the input torque and a vehicle speed; obtaining a torque process quantity according to the torque demand degree from the compensation start time to a target time; obtaining a steering scenario efficiency according to a cumulative change relationship of the torque process quantity from the compensation start time to the target time; obtaining a dynamic vehicle speed weight; obtaining a mapped torque according to the input torque at the target time, the dynamic vehicle speed weight, and the steering scenario efficiency; obtaining a torque compensation quantity according to the torque demand degree and the mapped torque; obtaining a compensated torque according to the torque compensation quantity, and driving and adjusting a steering motor according to the compensated torque; and in the process of driving and adjusting the steering motor, performing more accurate friction compensation for vehicle driving according to an expected steering angle and an input angle, thereby improving vehicle driving stability.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile auxiliary drive, and in particular to a friction compensation method for an automobile electric power steering system. Background Art

[0002] The electric power steering system in automobiles is a steering technology that uses an electric motor to provide assist torque, replacing traditional hydraulic power steering systems. Its core components include a torque sensor, an electronic control unit (ECU), and a power-assisting motor. When the driver turns the steering wheel, the sensor detects steering torque and vehicle speed in real time. The ECU calculates the required assist force and controls the motor to output the corresponding assist force, making steering easier and more precise. This system offers advantages such as low energy consumption, a compact structure, and the ability to dynamically adjust the assist force based on vehicle speed. It also avoids hydraulic oil leakage, significantly improving energy efficiency and driving safety, and is widely used in modern smart cars.

[0003] To eliminate the non-ideal interference caused by frictional resistance in the mechanical components of the steering mechanism and ensure precise and controllable steering assistance, automotive electric power steering systems require friction compensation. During the steering process, friction can cause a deviation between the actual steering torque and the sensor signal, affecting the ECU's interpretation of the driver's intention and causing problems such as stiff steering feel, offset, or hysteresis. Using a friction compensation algorithm, the ECU dynamically identifies and offsets the effects of friction, ensuring a more accurate match between the motor's power output and the driver's input. This improves steering smoothness, linearity, and feedback fidelity, while also enhancing low-speed steering ease and high-speed stability, ensuring a safe and comfortable driving experience.

[0004] The existing technology combines friction interference from different sources, such as viscous friction, Coulomb friction, and tire-road friction in the electric power steering system, into a comprehensive friction torque model, and uses a linear superposition formula or a static lookup table method for unified compensation. This method has low accuracy in judging the dominant factors affecting friction at each moment while the vehicle is moving, resulting in frequent changes in the direction of the output compensation amount. The compensation amount changes even faster when driving at high speeds, resulting in frequent changes in the direction of the friction torque, affecting the vehicle's driving stability. Summary of the Invention

[0005] The present invention provides a friction compensation method for an automotive electric power steering system to solve the problem that the existing friction torque direction frequently changes and affects the vehicle's driving stability. The technical solution adopted is as follows:

[0006] The present invention provides a friction compensation method for an electric power steering system of an automobile, the method comprising the following steps:

[0007] Obtain the input torque, input angle and vehicle speed at each moment during the vehicle's driving process;

[0008] Based on the change in input torque, the torque demand level at each moment is obtained; the start compensation time is obtained based on the input torque and vehicle speed; any moment in the compensation process after the start compensation time is recorded as the target time; based on the torque demand level from the start compensation time to the target time, the torque process quantity at the target time is obtained; based on the cumulative change relationship of the torque process quantity from the start compensation time to the target time, the steering scenario efficiency at the target time is obtained;

[0009] The dynamic vehicle speed weight at the target moment is obtained based on the vehicle speed at the target moment; the mapped torque at the target moment is obtained based on the input torque at the target moment, the dynamic vehicle speed weight, and the steering scenario efficiency; and the torque compensation amount at the target moment is obtained based on the change in the torque demand level at the target moment and the mapped torque;

[0010] The compensated torque at the target moment is obtained based on the torque compensation amount at the target moment, and the steering motor is driven and adjusted based on the compensated torque at the target moment; the expected turning angle at the target moment is obtained based on the compensated torque at the target moment, and during the steering motor drive adjustment process, the electric power steering system of the vehicle is used to compensate for the friction of the vehicle according to the similarity relationship between the expected turning angle and the input angle.

[0011] Furthermore, the torque requirement at each moment is obtained according to the change of the input torque, including the specific method of:

[0012] At any moment, the ratio of the difference between the input torque at that moment and the input torque at the previous moment and the preset sampling interval is recorded as the torque demand level at that moment.

[0013] Furthermore, the specific method of obtaining the compensation start time according to the input torque and the vehicle speed includes:

[0014] Taking the vehicle speed greater than a preset vehicle speed threshold and the input torque greater than a preset torque threshold as compensation conditions;

[0015] During the driving process of the car, if the current moment meets the compensation condition but the previous moment does not meet the compensation condition, the current moment will be used as the starting compensation moment.

[0016] Furthermore, the torque process quantity at the target moment is obtained according to the torque demand degree from the start compensation moment to the target moment, including the specific method of:

[0017] The mean and standard deviation of the torque demand levels at all times from the start of compensation to the target time are obtained, and the ratio of the difference obtained by subtracting the mean from the torque demand level at the target time to the standard deviation is recorded as the torque process quantity at the target time.

[0018] Furthermore, the steering scenario efficiency at the target moment is obtained based on the cumulative change relationship of the torque process quantity from the start compensation moment to the target moment, including the specific method of:

[0019] The cube of the torque process amount at any moment from the start of compensation to the target moment is recorded as the torque level at that moment;

[0020] The sum of the torque levels at all times from the start of compensation to the target time is recorded as the steering scenario efficiency at the target time.

[0021] Furthermore, the dynamic vehicle speed weight at the target moment is obtained according to the vehicle speed at the target moment, including the specific method of:

[0022] The inverse proportional normalization result of the ratio of the preset collection interval to the vehicle speed at the target moment is recorded as the dynamic vehicle speed weight at the target moment.

[0023] Furthermore, the mapping torque at the target moment is obtained according to the input torque at the target moment, the dynamic vehicle speed weight, and the steering scenario efficiency, including the specific method of:

[0024] The mapping torque at the target moment is calculated as: Where, is the mapping torque at the target moment; is the dynamic vehicle speed weight at the target moment; is the input torque at the target moment; Steering scenario efficiency at the target moment; is the steering scenario efficiency at the moment before the target moment; is a hyperparameter.

[0025] Furthermore, the torque compensation amount at the target moment is obtained according to the change in the torque demand at the target moment and the mapped torque, including the specific method of:

[0026] The calculation method of the torque compensation amount at the target time is: Where, is the torque compensation amount at the target moment; is the torque requirement at the target moment; is the torque demand level at the moment before the target moment; is the preset friction coefficient; is the mapping torque at the target moment; is the absolute value function; is a hyperparameter.

[0027] Furthermore, the method of obtaining the compensated torque at the target moment according to the torque compensation amount at the target moment and driving and adjusting the steering motor according to the compensated torque at the target moment includes the following specific methods:

[0028] The sum of the torque compensation amount at the target time and the input torque at the target time is recorded as the compensated torque at the target time;

[0029] The ratio of the compensated torque at the target moment to the motor torque constant is recorded as the steering motor driving current at the target moment, and the steering motor is driven and adjusted using the steering motor driving current at the target moment to control the vehicle steering.

[0030] Furthermore, during the steering motor drive adjustment process, the electric power steering system of the vehicle is used to perform friction compensation for vehicle driving according to the similarity relationship between the expected steering angle and the input angle, including the following specific methods:

[0031] The expected steering angle at the target moment is obtained by using the compensated torque at the target moment according to the response curve of the steering wheel angle and torque of the moving vehicle;

[0032] At each moment after the compensation starts, the steering control motor is controlled by the steering motor drive current corresponding to each moment until the current input angle is equal to the expected angle. If the car meets the compensation conditions, the current moment is used as the new starting compensation moment, and the friction of the car's electric power steering system is compensated according to the above method. If the car does not meet the compensation conditions, no friction compensation is performed.

[0033] The beneficial effects of the present invention are as follows: when using an electric power steering system for friction compensation in an automobile, it is necessary to determine whether the driver requires the vehicle to steer. The present invention obtains the steering scenario efficiency by using the torque process at the target moment to determine whether the driver's current driving scenario requires steering. When performing friction compensation on the vehicle, the faster the vehicle speed, the greater the deviation will be caused by even a slight steering error. The present invention obtains a dynamic vehicle speed weight and uses it to adjust the input torque, thereby improving the stability of the input torque at higher speeds. When the driver controls the vehicle to steer, the present invention obtains the torque compensation amount at the target moment by using the change in the torque demand level at the target moment and the mapped torque, and then obtains the compensated torque to drive and adjust the steering motor. Thus, the present invention utilizes the torque compensation amount to perform friction compensation using the electric power steering system for automobiles, thereby improving the driving stability of the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 A schematic flow chart of a friction compensation method for an automotive electric power steering system provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0037] See also Figure 1 , which shows a flow chart of a friction compensation method for an automotive electric power steering system provided by one embodiment of the present invention, the method comprising the following steps:

[0038] Step S001: Obtain the input torque, input rotation angle, and vehicle speed at each moment during the vehicle's driving process.

[0039] It should be noted that when performing friction compensation on a car's electric power steering system, the car's driving data must first be collected. Since the electric power steering system primarily assists the driver's steering wheel movements during driving, it is necessary to collect data on the driver's steering wheel movements and the car's driving speed.

[0040] Specifically, the torque sensor is installed on the steering shaft between the steering wheel and the steering gear, close to the steering wheel end, to obtain the driver's input torque on the steering wheel during the vehicle's driving;

[0041] The vehicle speed sensor is installed in the transmission case to obtain the vehicle speed;

[0042] The rotary transformer is installed on the steering knuckle to obtain the steering angle of the car's wheels;

[0043] Using vehicle speed sensor, torque sensor and rotary transformer, The vehicle speed, the driver's input torque on the steering wheel, and the input angle are collected once every second. The input torque and the input angle are calibrated with the steering wheel in the center without deflection as 0, and the clockwise direction is positive and the counterclockwise direction is negative; wherein, To preset the collection interval, this embodiment uses Take this as an example to describe;

[0044] Step S002: Determine the torque demand at each moment based on the change in input torque; determine the start time of compensation based on the input torque and vehicle speed; record any moment in the compensation process after the start time of compensation as the target time; determine the torque process quantity at the target time based on the torque demand from the start time of compensation to the target time; and determine the steering scenario efficiency at the target time based on the cumulative change relationship of the torque process quantity from the start time of compensation to the target time.

[0045] It's important to note that driver control of vehicle behavior takes precedence during driving, so the timing for the electric power steering system to initiate friction compensation is determined based on the driver's steering wheel torque input and the vehicle's speed. Friction compensation is particularly important at high speeds to offset the frictional resistance of the steering system's mechanical components and prevent incomplete steering return or delayed control due to friction interference.

[0046] Specifically, at any moment, the ratio of the difference obtained by subtracting the input torque at the previous moment from the input torque at the moment to the preset collection interval is recorded as the torque demand level at the moment.

[0047] The compensation condition is that the vehicle speed is greater than a preset vehicle speed threshold and the input torque is greater than a preset torque threshold. The preset vehicle speed threshold is 60 km / h and the preset torque threshold is 15 N·m. This embodiment is described using this as an example.

[0048] During the driving process of the car, if the current moment meets the compensation condition but the previous moment does not meet the compensation condition, the current moment will be used as the starting compensation moment.

[0049] It should be noted that after the compensation starts, the electric power steering system needs to be used to start friction compensation. During compensation, it is necessary to make it clear that the driver needs to steer the vehicle. During the process of vehicle torque change, if the torque continuously changes in a certain direction, it means that the greater the degree to which the vehicle currently needs to steer, the more friction compensation is needed.

[0050] Specifically, any moment in the compensation process after the compensation start moment is recorded as the target moment, the mean and standard deviation of the torque demand levels at all moments from the compensation start moment to the target moment are obtained, and the ratio of the difference obtained by subtracting the mean from the torque demand level at the target moment to the standard deviation is recorded as the torque process quantity at the target moment.

[0051] It's important to note that when the torque process at the target moment remains high, the greater the degree of steering required, the more friction compensation the electric power steering system requires. However, if the road is uneven and the driver constantly adjusts the steering wheel to maintain stability, the degree of steering required is not significant. Therefore, the steering efficiency of the current driving scenario can be determined based on the change in torque process after compensation begins.

[0052] Specifically, the cube of the torque process amount at any moment from the start of compensation to the target moment is recorded as the torque level at that moment;

[0053] The sum of the torque levels at all times from the start of compensation to the target time is recorded as the steering scenario efficiency at the target time.

[0054] It should be noted that the greater the steering scene efficiency at the target moment, the greater the need for the vehicle to make a larger turn at the target moment and compensation is required; when the steering scene efficiency at the target moment is smaller, it indicates that although the driver has made continuous adjustments to the vehicle, the direction of the adjustment has been changing, indicating that the driver is trying to maintain vehicle stability during this adjustment process, but there is no substantial need for vehicle steering.

[0055] Step S003: Obtain a dynamic vehicle speed weight at the target moment based on the vehicle speed at the target moment; obtain a mapped torque at the target moment based on the input torque at the target moment, the dynamic vehicle speed weight, and the steering scenario efficiency; and obtain a torque compensation amount at the target moment based on a change in the torque demand level at the target moment and the mapped torque.

[0056] It should be noted that during the friction compensation process, the driver actively inputs torque, and there is a situation of supplementary steering during road driving. That is, if the wheel steering angle is not enough, the driver controls the vehicle to adjust the wheel steering angle. Therefore, the use of the steering scene efficiency is further judged. The input torque jitter changes caused by uneven road surface are analyzed through the steering scene efficiency. After filtering the road jitter, the driver's compensation action is identified and the output torque compensation amount of the compensation action is supplemented, thereby ensuring that the actual output compensation result is more in line with the driver's actual steering demand result.

[0057] It should be further explained that the faster the vehicle speed, the larger the deviation will be caused by even the smallest steering movement. Therefore, the driver's control weight of the steering wheel input torque should be increased to complete the vehicle speed environment assessment during the actual driving process, so as to facilitate the subsequent adjustment of the compensation gain to match the actual driving speed.

[0058] Specifically, the inverse proportional normalization result of the ratio of the preset collection interval to the vehicle speed at the target moment is recorded as the dynamic vehicle speed weight at the target moment;

[0059] The mapping torque at the target moment is calculated as: Where, is the mapping torque at the target moment; is the dynamic vehicle speed weight at the target moment; is the input torque at the target moment; Steering scenario efficiency at the target moment; is the steering scenario efficiency at the moment before the target moment; To prevent the hyperparameter from having a denominator of 0, this embodiment uses Let’s take this as an example.

[0060] The description is that, The larger the value, the greater the change in steering efficiency at the target moment compared to the previous moment. In a scenario where the vehicle speed is relatively slow, the greater the target mapping torque, the greater the steering torque provided by the driver when controlling the steering wheel.

[0061] The calculation method of the torque compensation amount at the target time is: Where, is the torque compensation amount at the target moment; is the torque requirement at the target moment; is the torque demand level at the moment before the target moment; To preset the friction coefficient, this embodiment uses Take this as an example to describe; is the mapping torque at the target moment; is the absolute value function; To prevent the hyperparameter from having a denominator of 0, this embodiment uses Let’s take this as an example.

[0062] What needs to be explained is that The smaller it is, the smaller the input torque controlled by the driver at the target moment is, and the greater the torque compensation required at the target moment. When the torque demand degree at the target moment is more different from the torque demand degree at the previous moment, it means that the driver may need a greater degree of steering, and a larger torque compensation is required at the target moment.

[0063] Step S004: obtaining the compensated torque at the target moment based on the torque compensation amount at the target moment, and driving and adjusting the steering motor based on the compensated torque at the target moment; obtaining the expected turning angle at the target moment based on the compensated torque at the target moment, and during the steering motor drive adjustment process, utilizing the vehicle electric power steering system to perform friction compensation for vehicle driving based on the similarity relationship between the expected turning angle and the input angle.

[0064] It should be noted that after obtaining the torque compensation amount at the target moment, it is necessary to combine the input torque to obtain the compensated torque, and then adjust the steering motor drive current to control the steering.

[0065] Specifically, the sum of the torque compensation amount at the target moment and the input torque at the target moment is recorded as the compensated torque at the target moment;

[0066] The ratio of the compensated torque at the target moment to the motor torque constant is recorded as the steering motor drive current at the target moment, and the steering motor drive current at the target moment is used to drive and adjust the steering motor at the target moment, thereby controlling the vehicle steering; wherein the motor torque constant is 0.1, and this embodiment is described using this as an example.

[0067] It should be noted that there is a corresponding relationship between the steering wheel rotation angle and the torque provided at this rotation angle. During the electric power steering process of a car, if the steering wheel rotation angle is sufficient to provide the torque required for the current steering, friction compensation needs to be stopped to prevent excessive compensation from causing unstable vehicle driving.

[0068] Specifically, the expected steering angle at the target moment is obtained using the compensated torque at the target moment according to a steering wheel angle and torque response curve of the moving vehicle, wherein the steering wheel angle and torque response curve is a functional correspondence between the steering wheel angle and the steering wheel torque, and the steering wheel angle and torque response curve is a priori property of the vehicle;

[0069] At each moment after the compensation starts, the steering control motor is controlled by the steering motor drive current corresponding to each moment until the current input angle is equal to the expected angle. If the car meets the compensation conditions, the current moment is used as the new starting compensation moment, and the friction of the car's electric power steering system is compensated according to the above method. If the car does not meet the compensation conditions, no friction compensation is performed.

[0070] It should be noted that if the vehicle speed is less than a preset stop compensation threshold during the compensation process, friction compensation is stopped. This is to prevent false triggering caused by the driver frequently fine-tuning the steering wheel, such as vibration suppression during frequent turns in a parking lot. The preset stop compensation threshold is 10 km / h, and this embodiment is described using this as an example.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A friction compensation method for an automotive electric power steering system, characterized in that: The method comprises the following steps: Obtain the input torque, input angle and vehicle speed at each moment during the vehicle's driving process; Based on the change in input torque, the torque demand level at each moment is obtained; the start compensation time is obtained based on the input torque and vehicle speed; any moment in the compensation process after the start compensation time is recorded as the target time; based on the torque demand level from the start compensation time to the target time, the torque process quantity at the target time is obtained; based on the cumulative change relationship of the torque process quantity from the start compensation time to the target time, the steering scenario efficiency at the target time is obtained; The dynamic vehicle speed weight at the target moment is obtained based on the vehicle speed at the target moment; the mapped torque at the target moment is obtained based on the input torque at the target moment, the dynamic vehicle speed weight, and the steering scenario efficiency; and the torque compensation amount at the target moment is obtained based on the change in the torque demand level at the target moment and the mapped torque; A compensated torque at a target moment is obtained based on the torque compensation amount at the target moment, and the steering motor is driven and adjusted based on the compensated torque at the target moment; an expected steering angle at the target moment is obtained based on the compensated torque at the target moment, and during the steering motor drive adjustment process, friction compensation for vehicle driving is performed using the vehicle electric power steering system based on a similar relationship between the expected steering angle and the input angle; The specific method of obtaining the compensation start time according to the input torque and vehicle speed is as follows: Taking the vehicle speed greater than a preset vehicle speed threshold and the input torque greater than a preset torque threshold as compensation conditions; During the driving process of the car, if the current moment meets the compensation condition but the previous moment does not meet the compensation condition, the current moment will be used as the starting compensation moment.

2. The friction compensation method for an automotive electric power steering system according to claim 1, characterized in that: The torque requirement at each moment is obtained according to the change of the input torque, including the following specific methods: At any moment, the ratio of the difference between the input torque at that moment and the input torque at the previous moment and the preset collection interval is recorded as the torque demand level at that moment.

3. The friction compensation method for an automotive electric power steering system according to claim 1, characterized in that: The method of obtaining the torque process quantity at the target moment according to the torque demand degree from the start compensation moment to the target moment includes the following specific methods: The mean and standard deviation of the torque demand levels at all times from the start of compensation to the target time are obtained, and the ratio of the difference obtained by subtracting the mean from the torque demand level at the target time to the standard deviation is recorded as the torque process quantity at the target time.

4. The friction compensation method for an automotive electric power steering system according to claim 1, characterized in that: The steering scenario efficiency at the target moment is obtained based on the cumulative change relationship of the torque process quantity from the start compensation moment to the target moment, including the specific method of: The cube of the torque process amount at any moment from the start of compensation to the target moment is recorded as the torque level at that moment; The sum of the torque levels at all times from the start of compensation to the target time is recorded as the steering scenario efficiency at the target time.

5. The friction compensation method for an automotive electric power steering system according to claim 1, characterized in that: The specific method of obtaining the dynamic vehicle speed weight at the target moment according to the vehicle speed at the target moment is as follows: The inverse proportional normalization result of the ratio of the preset collection interval to the vehicle speed at the target moment is recorded as the dynamic vehicle speed weight at the target moment.

6. The friction compensation method for an automotive electric power steering system according to claim 1, characterized in that: The mapping torque at the target moment is obtained according to the input torque at the target moment, the dynamic vehicle speed weight, and the steering scenario efficiency, including the specific method as follows: The mapping torque at the target moment is calculated as: Where T' is the mapping torque at the target moment; γ is the dynamic vehicle speed weight at the target moment; T is the input torque at the target moment; X is the steering scene efficiency at the target moment; X' is the steering scene efficiency at the moment before the target moment; and ε is a hyperparameter.

7. The friction compensation method for an automotive electric power steering system according to claim 1, characterized in that: The method of obtaining the torque compensation amount at the target moment according to the change in the torque demand degree at the target moment and the mapped torque includes the following specific methods: The calculation method of the torque compensation amount at the target time is: Where ΔT is the torque compensation at the target moment; V is the torque demand at the target moment; V' is the torque demand at the moment before the target moment; μ is the preset friction coefficient; T' is the mapped torque at the target moment; || is the absolute value function; and δ is a hyperparameter.

8. The friction compensation method for an automotive electric power steering system according to claim 1, characterized in that: The method of obtaining the compensated torque at the target moment according to the torque compensation amount at the target moment and driving and adjusting the steering motor according to the compensated torque at the target moment includes the following specific methods: The sum of the torque compensation amount at the target time and the input torque at the target time is recorded as the compensated torque at the target time; The ratio of the compensated torque at the target moment to the motor torque constant is recorded as the steering motor driving current at the target moment, and the steering motor is driven and adjusted using the steering motor driving current at the target moment to control the vehicle steering.

9. The friction compensation method for an automotive electric power steering system according to claim 1, characterized in that: In the process of steering motor drive adjustment, friction compensation for vehicle driving is performed using the vehicle electric power steering system according to the similarity relationship between the expected steering angle and the input angle, including the specific method of: The expected steering angle at the target moment is obtained by using the compensated torque at the target moment according to the response curve of the steering wheel angle and torque of the moving vehicle; At each moment after the compensation starts, the steering control motor is controlled by the steering motor drive current corresponding to each moment until the current input angle is equal to the expected angle. If the car meets the compensation conditions, the current moment is used as the new starting compensation moment, and the friction of the car's electric power steering system is compensated according to the above method. If the car does not meet the compensation conditions, no friction compensation is performed.

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