A control method for switching between EPS power assist mode and return mode

Abstract

The present invention belongs to the field of automotive steering control technology, and in particular, relates to a method for controlling the switching process between an EPS power-assist mode and a return-to-center mode. The method comprises a steering mode switching determination module, a switching time determination module, a torque curve processing module, and a switching compensation torque determination module. The present invention, by designing a switching time length determination module, determines the return-to-center time based on the current steering wheel angle and vehicle speed, thereby better meeting driver expectations. By processing the torque of a Bizier curve, the expected value of the switching compensation torque is calculated based on different switching situations. The switching compensation torque at any switching moment is obtained by tracking the switching torque curve. This makes the steering mode switching process smoother under different vehicle operating conditions, significantly improving the driver's steering comfort, and resolving the frustration experienced by the driver due to sudden changes in hand torque when switching between the power-assist mode and the return-to-center mode in current electric power-steering vehicles, thereby enhancing the driving experience.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile steering control, and in particular to a method for controlling a switching process between an EPS power assist mode and a return mode. Background Art

[0002] With the rapid development of the automotive industry in recent years, consumers have placed higher demands on the steering quality of their vehicles. When it comes to steering, consumers are primarily concerned with stability, steering feel, and the quality of the steering wheel's return to centering when the hands are released (or held onto it). When the driver turns the steering wheel to a certain angle and attempts to maintain that position, even slightly holding onto the wheel can cause a noticeable drag.

[0003] Invention patent CN118270096A discloses a vehicle steering wheel differential return method, device, vehicle, and storage medium. The method includes: determining whether the driver controls the steering wheel by determining whether the hand torque applied to the steering wheel is less than a preset threshold, and performing differential control of the steering wheel based on an active disturbance rejection controller (ADRC); and distributing a target differential return compensation torque to the target wheels of the vehicle to obtain the control torque of the hub motor of the target wheels that meets the preset optimal conditions. However, in actual applications, when the driver is holding the steering wheel, sudden changes in the assist torque may cause a sense of jerkiness, resulting in a poor driving experience.

[0004] Invention patent CN117022430A discloses an EPS system control method, device, electronic device and storage medium. The method includes: according to the steering wheel hand force and the hand force threshold T of the return mode min and Τ max The EPS system operating mode is determined by comparing the results of the manual torque comparison. These modes include steering mode, return mode, and transition mode. In return mode or steering mode, the system determines whether the current hand force control duration gradient is within the range between the hand force rise time gradient and the hand force fall time gradient. If so, the hand force control duration gradient is adjusted based on the rate of change of the manual torque, the torque change coefficient, the manual torque, and the torque coefficient received by the steering wheel until the hand force rise time gradient is reached. This allows the hand force control duration gradient to increase rapidly with the rate of change of the manual torque or the manual torque. However, this method does not consider the control of switching time. The time required for mode switching at different vehicle speeds should be controlled and smoothed to improve the driver's driving experience. Summary of the Invention

[0005] (1) Technical problems solved

[0006] In response to the shortcomings of the existing technology, the present invention provides a method for controlling the switching process between EPS power assist mode and return mode, which solves the problem that when the return mode and power assist mode of the current electric power steering vehicle are switched, the driver may feel a sudden change in steering wheel torque, causing a sense of frustration, thereby affecting the driving experience.

[0007] (2) Technical solution

[0008] In order to achieve the above-mentioned purpose, the present invention specifically adopts the following technical solutions:

[0009] A method for controlling the switching process between an EPS power assist mode and a return mode is provided. The method comprises a steering mode switching judgment module, a switching time determination module, a torque curve processing module, and a switching compensation torque determination module, and includes the following steps:

[0010] Step 1: The steering mode switching judgment module judges the target mode according to the vehicle speed, steering wheel torque, steering wheel angle and steering wheel speed signals. If the current mode is different from the target mode, the steering mode switching state is entered;

[0011] Step 2: The switching time determination module determines the expected switching time length according to the vehicle's motion state before the steering mode is switched;

[0012] Step 3: The switching process torque change curve determination module divides the expected switching time into three equal parts according to different switching situations, uses B-spline to smooth the torque, and obtains the switching process torque change curve;

[0013] Step 4: The switching compensation torque determination module determines the switching compensation torque that the power-assisting motor needs to provide. By switching the compensation torque, the steering wheel torque felt by the driver is prevented from changing suddenly when the steering mode is switched, so that the steering wheel torque felt by the driver can transition smoothly.

[0014] Furthermore, in step 1, when any of the following conditions is met, it is determined that the switching state from the return mode to the power-assisted mode is: (1) the steering wheel torque is greater than a certain threshold value, that is, the driver actively turns the steering wheel; (2) the steering wheel angle and speed are both less than a certain threshold value, that is, the steering wheel returns to the center area.

[0015] Furthermore, the switching state includes switching from active steering to a hands-off or steering-maintaining return state; and switching from a hands-off or steering-maintaining return state to an external active steering state.

[0016] Furthermore, the active steering state includes active outward turning and active inward turning.

[0017] Furthermore, the expected switching time length is divided into: the time required for switching from the power-assisting mode to the return mode and the time required for switching from the return mode to the power-assisting mode.

[0018] Furthermore, in step 2, the switching time is determined according to the motion state of the vehicle at the start time of the switching.

[0019] Furthermore, in step 3, a cubic 4th order B-spline curve is constructed, which requires determining 4 control vertices; the switching time t tar Divide into three equal parts, the torque before switching and the stable torque after switching can determine two of the control vertices, and the other two control vertices can be obtained by the two-circle tangent method;

[0020] Assuming that the coordinates of the four control vertices of the cubic 4th order B-spline curve are P0(x0,y0), P1(x1,y1), P2(x2,y2), and P3(x3,y3), the matrix expression of the B-spline curve is as follows:

[0021]

[0022] The component expressions of the B-spline curve are as follows;

[0023]

[0024] Constructing a B-spline curve requires solving three variables r s , Δt, that is, the design variable X of the B-spline curve optimization model is:

[0025]

[0026] Furthermore, in step 4, after detecting the start of the switching state, the torque in the switching process is controlled to reach the desired position with a size that conforms to the desired curve. It only works when the driver releases the steering wheel, holds the steering wheel and is ready to take over the steering wheel. It does not work when the driver actively steers or actively returns to the center position. At this time, the compensation torque is zero.

[0027] Furthermore, the control method comprises the following specific steps:

[0028] Step 1: Determine whether the steering wheel is in a mode switching state based on the steering wheel torque, steering wheel angle, and speed. If so, proceed to the following steps; otherwise, skip the following steps and the return compensation torque is directly set to zero.

[0029] Step 2: Determine whether the steering wheel is in a switching state based on the vehicle speed, steering wheel torque, steering wheel angle, and steering wheel speed signals, and determine the mode before and after the switching;

[0030] Step 3: According to the situation of the upcoming handover, the handover time is estimated and the desired hand torque is smoothed based on the proposed B-spline curve analysis; B-spline curve equation: Where N is the B-spline basis function and P is the control point;

[0031] Step 4: After determining the desired hand torque curve, the compensation torque curve can be obtained through relationship calculation, so that each switch can achieve the expected comfort; the compensation torque calculation formula is: M exp =M target -M hand .

[0032] (3) Beneficial effects

[0033] Compared with the prior art, the present invention provides a method for controlling the switching process between EPS assist mode and return mode, which has the following beneficial effects:

[0034] The present invention designs a switching time length determination module, determines the return time according to the current steering wheel angle and vehicle speed, and better meets the driver's expectations. Through torque processing of the B-spline curve, the expected value of the switching compensation torque is calculated according to different switching situations. The switching compensation torque at any switching moment is obtained with the goal of tracking the switching torque curve, so that the steering mode switching process under different working conditions of the vehicle is smoother, which greatly improves the driver's comfort when steering. It solves the problem of the driver's feeling of frustration caused by the sudden change of hand torque when switching between the power-assisting mode and the return mode of the current electric power steering vehicle, and improves the driving experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the system of the present invention;

[0036] Figure 2 Schematic diagram of the torque change curve of the switching process of the B-spline of the present invention;

[0037] Figure 3 Schematic diagram of the switching compensation torque calculation architecture of the present invention. DETAILED DESCRIPTION

[0038] 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.

[0039] Example

[0040] like Figure 1-3As shown, an embodiment of the present invention proposes a method for controlling the switching process between the EPS assist mode and the return mode, which comprises a steering mode switching module, a switching time length determination module, a switching process torque change curve determination module, and a switching compensation torque determination module. The specific method includes the following steps:

[0041] Step 1: The steering mode switching judgment module judges the target mode according to the vehicle speed, steering wheel torque, steering wheel angle and steering wheel speed signals. If the current mode is different from the target mode, the steering mode switching state is entered;

[0042] The steering mode switching judgment module judges whether the steering wheel is in a switching state according to the vehicle speed, steering wheel torque, steering wheel angle and steering wheel speed signal, and judges the mode before and after the switching;

[0043] Step 2: The switching time determination module determines the expected switching time length according to the vehicle's motion state before the steering mode is switched;

[0044] The switching time length determination module determines the expected switching time length according to the switching process between the power assist mode and the return mode;

[0045] Step 3: The switching process torque change curve determination module divides the expected switching time into three equal parts according to different switching situations, uses B-spline to smooth the torque, and obtains the switching process torque change curve;

[0046] Step 4: The switching compensation torque determination module determines the switching compensation torque that the power-assisted motor needs to provide. By using the switching compensation torque, a sudden change in the steering wheel torque felt by the driver when the steering mode is switched is avoided, so that the steering wheel torque felt by the driver can have a smooth transition.

[0047] The switching compensation torque determination module determines the expected value of the hand torque felt by the driver at the current speed, and calculates the expected value of the switching compensation torque based on different switching situations. The switching compensation torque at any switching moment is obtained by tracking the switching torque curve, so that the driver's hand force in operating the steering wheel meets the expected requirements.

[0048] As a further technical solution of the present invention: in step 1, when the following conditions are met at the same time, it is determined that the switching state is from the power-assist mode to the return mode: (1) the steering wheel angle and the speed are opposite, that is, the steering wheel is in the return state; (2) the steering wheel torque is less than a certain threshold value, that is, the driver releases the steering wheel; (3) the steering wheel angle is greater than a certain threshold value, that is, the vehicle is not in the center area.

[0049] As a further technical solution of the present invention: in step 1, when any of the following conditions is met, it is judged that the switching state from the return mode to the power-assisted mode is: (1) the steering wheel torque is greater than a certain threshold value, that is, the driver actively turns the steering wheel; (2) the steering wheel angle and speed are both less than a certain threshold value, that is, the steering wheel returns to the center area.

[0050] The switching state includes switching from active steering to hands-off or steering-holding return state; switching from hands-off or steering-holding return state to external active steering state.

[0051] The active steering state includes active outward turning and active inward turning.

[0052] We further divide the expected switching time into the time required to switch from the power-assist mode to the return mode and the time required to switch from the return mode to the power-assist mode.

[0053] In step 2, the switching time is determined according to the motion state of the vehicle at the switching start time.

[0054] In step 3, to construct a cubic 4th order B-spline curve, it is necessary to determine 4 control vertices. tar Divide the solution into three equal parts, and the torque before switching and the stable torque after switching can determine two of the control vertices. The other two control vertices can be obtained by the double circle tangent method.

[0055] Assuming that the coordinates of the four control vertices of the cubic 4th order B-spline curve are P0(x0,y0), P1(x1,y1), P2(x2,y2), and P3(x3,y3), the matrix expression of the B-spline curve is as follows:

[0056]

[0057] The component expressions of the B-spline curve are shown below.

[0058]

[0059] Constructing a B-spline curve requires solving three variables r s , Δt, that is, the design variable X of the B-spline curve optimization model is:

[0060]

[0061] In step 4, after detecting the start of the switching state, the torque in the switching process is controlled to reach the desired position in a size that conforms to the desired curve. It only works when the driver releases the steering wheel, holds the steering wheel, and is ready to take over the steering wheel. It does not work when the driver actively steers or actively returns to the center position. At this time, the compensation torque is zero.

[0062] The specific control method and steps for switching between EPS assist mode and return mode are as follows:

[0063] Step 1: Determine whether the steering wheel is in a mode switching state based on the steering wheel torque, steering wheel angle, and speed. If so, proceed to the following steps; otherwise, skip the following steps and the return compensation torque is directly set to zero.

[0064] Step 2: Determine whether the steering wheel is in a switching state based on the vehicle speed, steering wheel torque, steering wheel angle, and steering wheel speed signals, and determine the mode before and after the switching;

[0065] Step 3: According to the situation of the upcoming handover, the handover time is estimated and the desired hand torque is smoothed based on the proposed B-spline curve analysis; B-spline curve equation: Where N is the B-spline basis function and P is the control point;

[0066] Step 4: After determining the desired hand torque curve, the compensation torque curve can be obtained through relationship calculation, so that each switch can achieve the expected comfort. Compensation torque calculation formula: M exp =M target -M hand .

[0067] The symbolic parameters used in the present invention are shown in Table 1 below.

[0068] Table 1: Symbol parameter description table:

[0069]

[0070]

[0071] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for controlling the switching process between EPS assist mode and return mode, comprising a steering mode switching judgment module, a switching time determination module, a torque curve processing module, and a switching compensation torque determination module, characterized in that: The following steps are involved: Step 1: The steering mode switching judgment module judges the target mode according to the vehicle speed, steering wheel torque, steering wheel angle and steering wheel speed signals. If the current mode is different from the target mode, the steering mode switching state is entered; Step 2: The switching time determination module determines the expected switching time length according to the vehicle's motion state before the steering mode is switched; Step 3: The switching process torque change curve determination module divides the expected switching time into three equal parts according to different switching situations, uses the Bizier curve to smooth the torque, and obtains the switching process torque change curve; Step 4: The switching compensation torque determination module determines the switching compensation torque that the power-assisted motor needs to provide. By using the switching compensation torque, a sudden change in the steering wheel torque felt by the driver when the steering mode is switched is avoided, so that the steering wheel torque felt by the driver can have a smooth transition. The switching state includes switching from active steering to a hands-off or steering-holding return state; switching from a hands-off or steering-holding return state to an external active steering state; In step 3, a 4th-order cubic B-spline curve is constructed, and 4 control vertices need to be determined; the switching time t tar Divide into three equal parts, the torque before switching and the stable torque after switching can determine two of the control vertices, and the other two control vertices can be obtained by the two-circle tangent method; Assuming that the coordinates of the four control vertices of the cubic 4th order B-spline curve are P0(x0,y0), P1(x1,y1), P2(x2,y2), and P3(x3,y3), the matrix expression of the B-spline curve is as follows: The component expressions of the B-spline curve are as follows; Constructing a B-spline curve requires solving three variables r s , Δt, that is, the design variable X of the B-spline curve optimization model is:

2. The EPS power assist mode and return mode switching control method according to claim 1, characterized in that: In step 1, when any of the following conditions is met, it is determined that the switching state from the return mode to the power-assisted mode is: (1) the steering wheel torque is greater than a certain threshold value, that is, the driver actively turns the steering wheel; (2) the steering wheel angle and speed are both less than a certain threshold value, that is, the steering wheel returns to the center area.

3. The EPS power assist mode and return mode switching control method according to claim 1, characterized in that: The active steering state includes active outward turn and active inward turn.

4. The EPS power assist mode and return mode switching control method according to claim 1, characterized in that: The expected switching time length is divided into: the time required to switch from the power-assist mode to the return mode and the time required to switch from the return mode to the power-assist mode.

5. The EPS power assist mode and return mode switching control method according to claim 1, characterized in that: In step 2, the switching time is determined according to the motion state of the vehicle at the switching start time.

6. The EPS power assist mode and return mode switching control method according to claim 1, characterized in that: In step 4, after detecting the start of the switching state, the torque in the switching process is controlled to reach the desired position in a size that conforms to the desired curve. It only works when the driver releases the steering wheel, holds the steering wheel, and is ready to take over the steering wheel. It does not work when the driver actively steers or actively returns to the center position. At this time, the compensation torque is zero.

7. A method for controlling the switching process between an EPS power assist mode and a return mode according to any one of claims 1 to 6, characterized in that: The specific steps are as follows: Step 1: Determine whether the steering wheel is in a mode switching state based on the steering wheel torque, steering wheel angle, and speed. If so, proceed to the following steps; otherwise, skip the following steps and the return compensation torque is directly set to zero. Step 2: Determine whether the steering wheel is in a switching state based on the vehicle speed, steering wheel torque, steering wheel angle, and steering wheel speed signals, and determine the mode before and after the switching; Step 3: According to the situation of the upcoming handover, the handover time is estimated and the desired hand torque is smoothed based on the proposed B-spline curve analysis; B-spline curve equation: Where N is the B-spline basis function and P is the control point; Step 4: After determining the desired hand torque curve, the compensation torque curve can be obtained through relationship calculation, so that each switching can achieve the expected comfort; Formula for calculating compensation torque: M exp =M target -M hand .

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