Friction force identification and compensation method for steering-by-wire system

Abstract

The invention discloses a friction force identification and compensation method for an upper steering-by-wire system. The friction force identification and compensation method specifically comprises the following steps: step 1, designing a steering wheel rotation angle time sequence based on a dynamics principle; 2, based on a steering wheel rotation angle time sequence, an upward steering wheel rotates; 3, torque data of the rotation process of the upward steering wheel are obtained through calculation; 4, performing data fitting by using the torque data to obtain a rotation torque periodic function; and 5, compensating the friction torque by using the fitting parameters of the autorotation torque periodic function. The friction force of different upper steering columns can be recognized and compensated, and the problem of different hand feels caused by the difference between the friction force is solved.

Description

Technical Field

[0001] This invention relates to the field of vehicle steer-by-wire (SBW) systems, specifically to a method for friction identification and compensation in steer-by-wire systems. Background Technology

[0002] With the development of intelligentization and electronics in the automotive industry, traditional steering systems can no longer meet the diverse needs of advanced autonomous driving and intelligent vehicles. As a new type of steering, steer-by-wire systems have the structural characteristics of vertical decoupling, making them an important actuator in intelligent vehicle chassis and beginning to serve as the most important actuator in advanced intelligent driving and intelligent cockpits.

[0003] The steer-by-wire system is divided into an upper steering system and a lower steering system. The upper steering system mainly includes a power supply, steering wheel, upper steering column mechanism, steering angle and torque sensor, road feel motor, and upper steering control processing unit. The friction of the upper steering column mechanism is closely related to the user's feel, and the friction of each upper steering column mechanism is also different. Therefore, it is necessary to identify and compensate for the friction to eliminate the difference in friction and improve the feel. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for identifying and compensating for friction in a steer-by-wire system, which can solve the problem of differences in friction in the upper steering column mechanism that affect the user's feel.

[0005] To address the aforementioned problems, the present invention provides a method for friction identification and compensation in a steer-by-wire system, which specifically includes the following steps:

[0006] Step 1: Design the steering wheel rotation angle timing based on dynamic principles;

[0007] Step 2: Based on the timing of the steering wheel rotation angle, the steering wheel rotates when the steering wheel is turned upwards;

[0008] Step 3: Calculate and obtain the torque data during the upward rotation of the steering wheel;

[0009] Step 4: Use the torque data to perform data fitting to obtain the rotation torque periodic function;

[0010] Step 5: Compensate for frictional torque using the fitting parameters of the periodic function of the rotation torque.

[0011] Furthermore, in step 1, a dynamic model of the steer-by-wire system is first established to obtain the relationship between the frictional torque of the steer-by-wire system and the output torque of the steer-by-wire road feel motor when the driver takes his hands off the steering wheel and the steering wheel rotates at a low speed and constant speed.

[0012] Furthermore, when the driver takes their hands off the steering wheel and the steering wheel is rotating at a low speed and near constant speed, the frictional torque of the upper steering system is equal in magnitude and opposite in direction to the output torque of the upper steering road feel motor.

[0013] Furthermore, in step 1, the steering wheel rotation angle timing sequence includes a right turn acceleration segment, a right turn constant speed segment, a right turn deceleration segment, a left turn acceleration segment, a left turn constant speed segment, and a left turn deceleration segment.

[0014] Furthermore, in step 2, when the steering wheel rotates upwards, the speed is first increased to the target speed in the acceleration phase, the target speed is maintained in the constant speed phase to learn the friction torque, and the speed drops from the target speed to 0 in the deceleration phase.

[0015] Furthermore, the target rotational speed is determined by looking up a table based on the angle difference between the current actual angle of the steering wheel and the target angle of the steering wheel.

[0016] Furthermore, in step 3, based on the feedback control method, the current control torque is calculated according to the difference between the current actual angular velocity of the steering wheel and the target angular velocity of the steering wheel.

[0017] Furthermore, the control torques of the acceleration and deceleration segments are removed to obtain the torque data for the left turn constant speed segment and the right turn constant speed segment, and then a first-order low-pass filter is performed to obtain the torque data.

[0018] Furthermore, in step 4, a polynomial fitting method is used to perform curve fitting on the torque data to obtain the rotation torque periodic function.

[0019] Furthermore, during the left or right turn of the steering wheel, the angle of the steering wheel corresponding to the minimum absolute value in the torque data is taken as the starting point StrAng1 of the periodic fitting, and the ending point of the periodic fitting is StrAng1+360°, thus obtaining the self-rotation torque periodic function within one cycle.

[0020] Compared with the prior art, the present invention designs the steering wheel rotation timing based on the dynamic principle, and obtains the friction torque data of the constant speed segment when the steering wheel rotates according to the timing. Based on the meshing characteristics of the road feel motor and the upper steering column, the friction torque data is fitted to finally obtain the periodic function of the friction torque. In this way, the friction force of different upper steering columns can be identified and compensated, eliminating the problem of different feel caused by the difference between friction forces. Attached Figure Description

[0021] Figure 1 This is a flowchart of the present invention;

[0022] Figure 2 This is a timing diagram of the steering wheel rotation angle according to the present invention;

[0023] Figure 3This is a schematic diagram of polynomial fitting;

[0024] Figure 4 This is a data fitting graph of the steering wheel rotation torque. Detailed Implementation

[0025] The embodiments of the present invention are described below with reference to the accompanying drawings and specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Specific details are set forth in the following description to provide a thorough understanding of the present invention; however, the present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be based on different viewpoints and applications. Those skilled in the art can make various similar extensions and substitutions without departing from the spirit of the present invention.

[0026] This invention provides a method for friction identification and compensation in a steer-by-wire system, such as... Figure 1 As shown, the specific steps include the following:

[0027] Step 1: Design the steering wheel rotation angle timing based on dynamic principles;

[0028] Step 2: Based on the timing of the steering wheel rotation angle, the steering wheel rotates when the steering wheel is turned upwards;

[0029] Step 3: Calculate and obtain the torque data during the upward rotation of the steering wheel;

[0030] Step 4: Use the torque data to perform data fitting to obtain the rotation torque periodic function;

[0031] Step 5: Compensate for frictional torque using the fitting parameters of the periodic function of the rotation torque.

[0032] In step 1, a dynamic model of the steer-by-wire system is first established to obtain the relationship between the frictional torque of the steer-by-wire system and the output torque of the steer-by-wire road feel motor when the driver takes their hands off the wheel and the steering wheel rotates at a low, constant speed. Here, the low speed of steering wheel rotation is typically defined as between 10 deg / s and 15 deg / s.

[0033] Specifically, a dynamic model of the steer-by-wire system is established:

[0034]

[0035] In equation (1), JB is the equivalent moment of inertia and damping coefficient, θ is the actual steering angle of the steering wheel, and T mot It is the output torque of the road feeler motor, T fri G1 is the equivalent transmission ratio of the frictional torque of the upper steering column, G2 is the equivalent transmission ratio of the frictional torque of the upper steering column, and T is the equivalent transmission ratio of the frictional torque of the upper steering column. driverIt is the torque applied to the steering wheel by the driver.

[0036] When the driver releases their hands, that is, stops operating the steering wheel, the dynamic model is as shown in equation (2):

[0037]

[0038] Based on dynamic analysis, when the driver takes their hands off the steering wheel and the steering system rotates at a low speed and near a constant speed, the torque output by the steering feel motor is used to overcome the frictional torque of the steering column. At this time, the frictional torque of the steering system is equal in magnitude and opposite in direction to the torque output by the steering feel motor, as shown in equation (3).

[0039] G2T fri =G1T motor Equation (3)

[0040] A low-speed self-rotation algorithm (e.g., angle control based on PID algorithm) is constructed for the upper steering system to meet the requirement of near-uniform steering wheel rotation at a low speed. To achieve self-learning of the upper steering system, a steering wheel rotation angle timing sequence based on steering wheel speed is first constructed, such as... Figure 2 As shown.

[0041] In step 2, in order to obtain the frictional torque of the upper steering column throughout the entire stroke, it is necessary to set the speed increase segment and the speed constant segment. Specifically, the speed changes with the steering wheel angle rotation sequence as follows:

[0042] When turning right: S2 to S3 (acceleration phase), S3 to S5 (constant speed phase), S5 to S6 (deceleration phase).

[0043] When turning left: S6 to S7 (acceleration phase), S7 to S9 (constant speed phase), S9 to S2 (deceleration phase).

[0044] in accordance with Figure 2 The steering wheel rotation angle timing shown is as follows: taking a right turn as an example, during the acceleration phase of the entire learning process, the steering wheel speed is first increased to the target speed. During the constant speed phase, the steering wheel speed is maintained at the target speed to learn the value of friction torque. During the deceleration phase, the steering wheel speed is reduced to 0. The same applies to a left turn.

[0045] In the self-learning process described above, a table of correspondence between angle difference and target angle can be established based on the rotational speed corresponding to each segment in the time series. The target rotational speed corresponding to the current actual angle of the steering wheel can be obtained by looking up the table according to the angle difference DiffAngle between the current actual angle of the steering wheel and the target angle.

[0046] In step 3, based on the feedback control method, the current control torque is calculated according to the angular velocity difference between the current actual angular velocity of the steering wheel and the target angular velocity of the steering wheel. Specifically, as shown in equation (4), the current control torque T ctrl for

[0047]

[0048] Where P, I, and D are the three parameters of feedback control, e diff This is the difference between the current actual angular velocity of the steering wheel and the target angular velocity of the steering wheel.

[0049] To ensure subsequent curve fitting, the aforementioned control torque is processed. Specifically, the control torque of the acceleration segment (including right turn acceleration and left turn acceleration) and deceleration segment (including right turn deceleration and left turn deceleration) is removed to obtain the torque data of the constant speed segment of the steering wheel turning left and the constant speed segment of the steering wheel turning right. The control torque of the constant speed segment is then subjected to a first-order low-pass filter to obtain the torque data of the constant speed segment.

[0050] In the steer-by-wire system, the road feel motor and the upper steering column are connected by a worm gear meshing mechanism. When these two mesh, surface forces result in friction. Due to the unique meshing structure of the worm gear, the meshing surfaces during forward rotation are different from those during reverse rotation. This leads to a difference in the magnitude of friction when the upper steering column rotates clockwise versus counterclockwise. Furthermore, since each revolution of the worm gear constitutes a cycle, the friction exhibits a periodic variation.

[0051] Based on the aforementioned periodic variation characteristics, in step 4, a polynomial fitting method is used to perform curve fitting on the processed torque data to obtain the periodic function of the rotation torque in the uniform speed segment, as shown below. Figure 3 As shown, the polynomial function can be expressed as:

[0052] f(x) = a n x n +a n-1 x n-1 +…+a1x+a0 Equation (5)

[0053] Where n represents the order of the polynomial function.

[0054] Based on this, the loss function can be designed as follows:

[0055]

[0056] Where M is the number of sampling points, a0……a n y represents the fitting parameters, and y represents the processed torque data.

[0057] By taking the partial derivative of the loss function and solving the system of linear equations, the corresponding fitting parameters a0……a can be obtained. n .

[0058] When fitting the friction torque using the processed torque data, taking a right turn as an example, the angle of the steering wheel corresponding to the minimum absolute value in the torque data is identified as the starting point StrAng1 of the periodic fitting, and the ending point of the periodic fitting is StrAng1+360°. This yields the periodic function f(StrAng) of the rotation torque within one cycle. The same principle applies to left turns. The data fitting graph of the steering wheel rotation torque is shown below. Figure 4 As shown.

[0059] After the steer-by-wire system is decommissioned, the aforementioned process can be used to identify the friction force of the upper steering column. By learning the friction torque data through sequential operation, and performing offline processing, the periodic function f(StrAng) and fitting parameters of the friction torque of each upper steering column can be obtained. Finally, the fitting parameters are written into the software to compensate for the friction torque generated by the upper steering system during vehicle operation.

[0060] This invention can use this process to identify and compensate for the friction force of each upper steering column, thereby eliminating the friction force difference between different products and avoiding the difference in feel that users perceive.

[0061] The present invention has been described in detail above through specific embodiments. These embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to the above-described implementation methods. Equivalent substitutions and improvements made by those skilled in the art without departing from the principles of the present invention should be considered within the scope of the technology protected by the present invention.

Claims

1. A method for identifying and compensating for friction in a steer-by-wire system, characterized in that, Specifically, the steps include the following: Step 1: Design the steering wheel rotation angle timing based on dynamic principles; Step 2: Based on the timing of the steering wheel rotation angle, the steering wheel rotates when the steering wheel is turned upwards; Step 3: Calculate and obtain the torque data during the upward rotation of the steering wheel; Step 4: Use the torque data to perform data fitting to obtain the rotation torque periodic function; Step 5: Compensate for frictional torque using the fitting parameters of the periodic function of the rotation torque.

2. The friction force identification and compensation method for a steer-by-wire system according to claim 1, characterized in that, In step 1, a dynamic model of the steer-by-wire system is first established to obtain the relationship between the frictional torque of the steer-by-wire system and the output torque of the steer-by-wire road feel motor when the driver takes his hands off the steering wheel and the steering wheel rotates at a low speed and constant speed.

3. The friction force identification and compensation method for a steer-by-wire system according to claim 2, characterized in that, When the driver takes their hands off the steering wheel and the steering wheel is rotating at a low speed and near constant speed, the friction torque of the upper steering system is equal in magnitude and opposite in direction to the output torque of the upper steering road feel motor.

4. The friction force identification and compensation method for a steer-by-wire system according to claim 1, characterized in that, In step 1, the steering wheel rotation angle timing sequence includes a right turn acceleration segment, a right turn constant speed segment, a right turn deceleration segment, a left turn acceleration segment, a left turn constant speed segment, and a left turn deceleration segment.

5. The friction force identification and compensation method for a steer-by-wire system according to claim 1, characterized in that, In step 2, when the steering wheel rotates upwards, the speed is first increased to the target speed in the acceleration phase, and then the target speed is maintained in the constant speed phase to learn the friction torque. In the deceleration phase, the speed drops from the target speed to 0.

6. The friction force identification and compensation method for a steer-by-wire system according to claim 5, characterized in that, The target rotational speed is determined by looking up a table based on the angle difference between the current actual angle of the steering wheel and the target angle of the steering wheel.

7. The friction force identification and compensation method for a steer-by-wire system according to claim 4, characterized in that, In step 3, based on the feedback control method, the current control torque is calculated according to the difference between the current actual angular velocity of the steering wheel and the target angular velocity of the steering wheel.

8. The method for friction identification and compensation in a steer-by-wire system according to claim 7, characterized in that, The control torques of the acceleration and deceleration segments are removed to obtain the torque data for the left turn constant speed segment and the right turn constant speed segment. Then, a first-order low-pass filter is applied to obtain the torque data.

9. The method for friction identification and compensation in a steer-by-wire system according to claim 1, characterized in that, In step 4, a polynomial fitting method is used to perform curve fitting on the torque data to obtain the rotation torque periodic function.

10. The method for friction identification and compensation in a steer-by-wire system according to claim 9, characterized in that, During the left or right turn of the steering wheel, the angle of the steering wheel corresponding to the minimum absolute value of the torque data is taken as the starting point StrAng1 of the periodic fitting, and the ending point of the periodic fitting is StrAng1+360°, thus obtaining the self-rotation torque periodic function within one cycle.

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