A method for generating a variable angular transmission ratio for a steer-by-wire system

Abstract

The present invention discloses a method for generating a variable angular transmission ratio for a steer-by-wire system, comprising: collecting vehicle speed, vehicle stability factor, and steering wheel angle signals; obtaining yaw rate sensitivity and lateral acceleration sensitivity; calculating an ideal angular transmission ratio based on yaw rate and an ideal angular transmission ratio based on lateral acceleration sensitivity; weighted adjustment of the angular transmission ratio; correcting the adjusted angular transmission ratio by a steering wheel angle coefficient; limiting the corrected angular transmission ratio; and generating a target angular transmission ratio. This invention can reduce the nonlinear characteristics of vehicle steering at low and medium speeds, improving road tracking capability and maneuverability; and at high speeds, it can slow the change in front wheel angle in response to steering wheel input, improving maneuverability safety and vehicle lateral stability. It can also achieve changes in the angular transmission ratio with steering wheel angle at the same vehicle speed, effectively reducing the driver's operating burden in low-speed, large-angle scenarios such as parking and U-turns.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile steering control, and in particular to a method for generating a variable angular transmission ratio for a steer-by-wire system. Background Art

[0002] Steer-by-Wire (SBW) systems are an evolution of the widely used Electric Power Steering (EPS) system. These systems convert driver inputs into electrical signals, transmitting them to the steering actuator via CAN communication without the need for mechanical connections. This allows for flexible design of the steering system's angular and force transfer characteristics. Compared to EPS systems, SBW offers greater vehicle design flexibility, fewer mechanical connection constraints, and the ability to decouple the steering system from the steering wheel assembly. This system is highly compatible with the demands of autonomous driving and represents a key technology for achieving high-level autonomous vehicles and intelligent connected vehicles. It also represents the future development direction of automotive steering systems.

[0003] The steer-by-wire system consists of a road feel simulator assembly and a steering actuator assembly. The road feel simulator primarily includes components such as the steering wheel, a road feel motor, a torque angle sensor, and a road feel simulation controller. It provides simulated road feel feedback to the driver when manipulating the steering wheel, while converting the driver's control signal into a target front wheel angle signal. The steering actuator primarily includes components such as the steering actuator motor, a steering controller, an angle sensor, and a steering mechanism. The steering controller receives the target front wheel angle request from the road feel simulator via private CAN communication, controls the steering actuator motor, and drives the front wheels to the target angle through the steering mechanism, thereby achieving front-wheel steering.

[0004] Flexible angular transfer characteristics are a key advantage of steer-by-wire systems compared to EPS and a key design consideration. This angular transfer characteristic is reflected in the angular transmission ratio—the ratio of the steering wheel angle to the front wheel angle—which directly impacts the vehicle's steering stability and maneuverability. In EPS, the angular transmission ratio is fixed due to the mechanical connection between the steering column and the steering gear. In SBW, the angular transmission ratio is variable, enabling high steering flexibility at low speeds and high stability at higher speeds.

[0005] Currently, many steer-by-wire variable-angle transmission ratio designs are based on methods that maintain a constant steady-state steering gain, minimizing the impact of nonlinear characteristics of components such as the steering system, suspension system, and tires on vehicle handling. For vehicles with a fixed steering angle transmission ratio, the response of the vehicle's yaw rate gain to a steering wheel angle step signal varies with vehicle speed: the faster the speed, the more violent the oscillation of the yaw rate gain, the closer the vehicle approaches an unstable state, and the more difficult and unsafe it becomes for the driver to operate. Therefore, designing a variable angle ratio from the perspective of maintaining a constant vehicle yaw rate gain ensures a similar response at different speeds, reducing driving difficulty and providing better adaptability for different drivers. Patent CN202210248910.6 designates that when the vehicle speed is between 30 and 120 km / h, the steering system's angular transmission ratio is calculated based on a fixed yaw rate gain. The yaw rate gain is collected by the vehicle's yaw rate sensor and calculated in the electronic control unit. Patent CN202010004877.3 establishes a handling stability evaluation index value based on the variable angle transmission ratio formula based on the yaw rate gain, thereby obtaining the vehicle handling performance evaluation index. The design selects yaw rate gain values ​​at equal intervals (0.1, 0.15, 0.2...0.5), calculates the handling stability index under each yaw rate gain and vehicle speed, and obtains the optimal yaw rate gain value at each vehicle speed through quadratic polynomial fitting, which is finally used to calculate the target angular transmission ratio. Patent CN202111382718.8 first determines the base transmission ratio based on the steering wheel parameters, and then determines the vehicle speed gain coefficient and steering sensitivity correction coefficient by looking up the preset vehicle speed gain model based on the vehicle speed, corrects the base transmission ratio, and obtains the target variable transmission ratio.

[0006] Another approach to variable angular transmission ratio design utilizes early-stage simulations to design the angular transmission ratio as a function of parameters such as yaw rate, vehicle speed, lateral acceleration, and steering wheel angle, directly generating a mapping relationship (MAP). During actual vehicle operation, the relevant signals are collected, processed in real time, and the current angular transmission ratio is retrieved from the mapping relationship (MAP). Currently, a three-dimensional MAP mapping of vehicle speed and steering wheel angle to the target angular transmission ratio is widely used.

[0007] The two existing methods for generating target angular transmission ratios have the following shortcomings:

[0008] (1) When the target transmission ratio is calculated using a given yaw rate gain, the overall trend of the target transmission ratio changing with vehicle speed is: it increases first, then decreases after reaching the maximum value, and then decreases as the vehicle speed increases further, such as Figure 1 As shown. Figure 1For example, when the vehicle speed exceeds 80 km / h, the target angular transmission ratio begins to decrease. However, the reduced angular transmission ratio at high speeds will lead to increased steering sensitivity at high speeds. Specifically, the vehicle is very sensitive to steering wheel angle input. Even a small turn of the steering wheel or a misoperation by the driver will cause a large change in the front wheel angle, which can easily lead to loss of control at high speeds.

[0009] At the same time, when calculating the target transmission ratio using a given yaw rate gain, the lateral acceleration steady-state gain value at the same steering wheel angle will gradually increase with increasing vehicle speed. Due to the limitation of tire adhesion, excessive lateral acceleration may cause the vehicle to skid, making it difficult to control and affecting the vehicle's handling stability.

[0010] (2) In existing designs using the above calculation method, to avoid the problem of the target angular transmission ratio decreasing at high vehicle speeds, the target angular transmission ratio is generally set to a fixed value, i.e., the maximum target angular transmission ratio, after the vehicle speed reaches a certain higher threshold (e.g., 100 km / h or 120 km / h). However, directly setting the maximum value may result in a small target angular transmission ratio, resulting in still high steering sensitivity; or the target angular transmission ratio is set too high, making it impossible to achieve a smooth transition to low vehicle speeds.

[0011] (3) Regarding the method of directly obtaining the target value from the three-dimensional mapping MAP of vehicle speed, steering wheel angle and diagonal transmission ratio, the shape characteristics of the three-dimensional mapping MAP are complex and involve multiple important performance indicators such as vehicle steering stability and handling sensitivity. It is difficult to directly obtain it during the actual vehicle calibration process and is difficult to implement. Summary of the Invention

[0012] The purpose of the present invention is to address the problems in the prior art and provide a method for generating a variable angular transmission ratio for a steer-by-wire system. The method combines yaw rate sensitivity and lateral acceleration sensitivity, and performs weighted adjustment and correction based on vehicle speed and steering wheel angle to generate a target angular transmission ratio.

[0013] In order to achieve the above object, the technical solution adopted by the present invention is:

[0014] A method for generating a variable angular transmission ratio for a steer-by-wire system comprises the following steps:

[0015] S1, collect vehicle speed u, vehicle stability factor K and steering wheel angle δ sw signal, and perform low-pass filtering on the vehicle speed u signal;

[0016] S2, obtain the yaw rate sensitivity at different vehicle speeds and lateral acceleration sensitivity

[0017] S3, calculate the ideal angular transmission ratio i based on the yaw rate yaw and the ideal angular transmission ratio i based on lateral acceleration sensitivity ay ;

[0018] S4, weighted adjustment of the angular transmission ratio. The calculation formula of the angular transmission ratio after weighted adjustment is i vsr_weighted =p·i yaw +(1-p)·i ay , p is the preset weighted adjustment factor, ranging from 0 to 1;

[0019] S5, performing steering wheel angle coefficient correction on the weighted angular transmission ratio. The calculation formula of the corrected angular transmission ratio is: vsr =G sw ·i vsr_weighted , G sw is the steering wheel angle coefficient;

[0020] S6, limiting the corrected angular transmission ratio. The target angular transmission ratio after limiting is calculated as follows:

[0021] Among them, u1 and u2 are vehicle speed thresholds;

[0022] S7, generate target angular transmission ratio i vsr .

[0023] Preferably, in step S2, a mapping diagram of yaw rate sensitivity versus vehicle speed and a mapping diagram of lateral acceleration sensitivity versus vehicle speed are preset first, and then simulation correction is performed by simulation software, or correction is performed by actual vehicle test calibration to obtain the final mapping diagram of yaw rate sensitivity versus vehicle speed and the mapping diagram of lateral acceleration sensitivity versus vehicle speed, thereby obtaining the yaw rate sensitivity at different vehicle speeds. and lateral acceleration sensitivity

[0024] Preferably, in step S3, the ideal angular transmission ratio i based on the yaw angular velocity yaw The calculation formula is: L is the wheelbase, L=lf+lr, lf and lr are the distances from the front and rear axles to the center of mass of the vehicle respectively.

[0025] Preferably, in step S3, the ideal angular transmission ratio i based on the lateral acceleration ay The calculation formula is: L is the wheelbase, L=lf+lr, lf and lr are the distances from the front and rear axles to the center of mass of the vehicle respectively.

[0026] Preferably, in step S4, when the vehicle speed is less than 40 km / h, the p value is 1; when 40 km / h≤vehicle speed≤160 km / h, the p value gradually decreases; when the vehicle speed is greater than 160 km / h, the p value is 0.

[0027] Preferably, in step S5, the steering wheel angle coefficient G sw The method for determining is:

[0028] (1) When the steering wheel angle increases from 0 and is not greater than the first angle threshold P0, the steering wheel angle coefficient G sw The value is the maximum value Cmax, Cmax ≥ 1;

[0029] (2) When the steering wheel angle increases from the first threshold value P0 and is less than the second threshold value P1, the steering wheel angle coefficient G sw Decrease linearly;

[0030] (3) When the steering wheel angle increases to the second threshold value P1 and continues to increase, the steering wheel angle coefficient G sw Maintain at the minimum value Cmin, Cmin≤1.

[0031] Furthermore, the maximum value Cmax and the minimum value Cmin are different at different vehicle speeds. The higher the vehicle speed, the smaller the maximum value Cmax and the closer it is to 1, and the larger the minimum value Cmin and the closer it is to 1.

[0032] Furthermore, when the steering wheel is rotated in different directions, the steering wheel angle coefficient G sw The changing trend is the same.

[0033] Preferably, in step S6, when the vehicle speed is zero, the ideal angular transmission ratio minimum value i is determined by the ratio of the desired maximum steering wheel angle to the maximum front wheel angle. vsr_min Under the conditions of double lane change simulation at a speed of 120 km / h, the ideal angular transmission ratio maximum value i is determined based on the ratio of the expected steering wheel angle to the front wheel angle. vsr_max .

[0034] Preferably, in step S1, the vehicle speed u signal and the vehicle stability factor K are obtained from the vehicle controller via the CAN bus, or the vehicle stability factor K is set to a fixed value and the steering wheel angle δ is collected from the steering wheel angle sensor. sw Signal.

[0035] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0036] (1) The present invention combines yaw rate sensitivity and lateral acceleration sensitivity, which can significantly improve the existing problem that when a given yaw rate gain is used to calculate the target transmission ratio, the vehicle lateral acceleration continues to increase at medium and high speeds, which may lead to instability such as loss of control and sideslip. By adjusting the preset weighted diagonal transmission ratio, it can be achieved that at medium and low speeds, the yaw rate sensitivity preset value is mainly changed, thereby reducing the nonlinear characteristics of the vehicle during steering, the driver has a stronger sense of control during operation, and the road feel tracking ability and maneuverability are improved; at high speeds, the lateral acceleration sensitivity preset value is mainly changed, and the lateral acceleration sensitivity is controlled within a safe limit that is easy for the driver to operate, so that the front wheel angle changes slowly in response to the steering wheel input, thereby improving the maneuverability safety and the lateral stability of the vehicle.

[0037] (2) The present invention can achieve the change of the angular transmission ratio with the steering wheel angle at the same vehicle speed. For low-speed and large-angle scenarios such as parking and U-turns, it can effectively reduce the driver's operating burden and give full play to the advantages of wire-controlled steering.

[0038] (3) Compared with the method of directly obtaining the target value from the three-dimensional mapping MAP of vehicle speed, steering wheel angle and diagonal transmission ratio, this scheme provides the steps for generating the target angular transmission ratio. The mapping relationship involved in each step can be preset in a simple and feasible way, and is easy to calibrate and adjust, which has good implementation feasibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Attachment Figure 1 This is a schematic diagram of the target transmission ratio changing with vehicle speed in the prior art;

[0040] Attachment Figure 2 A flow chart of steps for generating a target variable angle transmission ratio of the present invention;

[0041] Attachment Figure 3 Generate a flow chart for the target variable angle transmission ratio of the present invention;

[0042] Attachment Figure 4 is a mapping relationship diagram of yaw rate sensitivity and vehicle speed according to the present invention;

[0043] Attachment Figure 5 is a mapping relationship diagram of lateral acceleration sensitivity and vehicle speed according to the present invention;

[0044] Attachment Figure 6 A mapping diagram of the weighted adjustment coefficient and vehicle speed of the present invention;

[0045] Attachment Figure 7 Schematic diagram of determining the rotation angle correction coefficient of the present invention. DETAILED DESCRIPTION

[0046] The present invention addresses the shortcomings of the existing methods for calculating the target angular transmission ratio and proposes a method for generating the target angular transmission ratio by combining yaw rate sensitivity and lateral acceleration sensitivity and performing weighted adjustment and correction based on vehicle speed and steering wheel angle. The implementation steps and flow chart are shown in the figure. Figure 2 and Figure 3 The specific implementation steps are as follows:

[0047] S1, signal acquisition and processing.

[0048] The road feel simulator assembly controller in the steer-by-wire system obtains the vehicle speed signal u and vehicle stability factor K from the vehicle controller via the CAN bus. The steering wheel angle signal δ is collected from the steering wheel angle sensor. sw , and perform low-pass filtering on the vehicle speed signal u.

[0049] Optionally, the vehicle stability factor K may be selected as a constant value that can reflect the understeering characteristic of the entire vehicle and used for calculating the target angular transmission ratio.

[0050] In this embodiment, a first-order digital low-pass filter is used to obtain the low-frequency signal of the vehicle speed, and the calculation method is shown in the following formula:

[0051] Y(n)=α·X(n)+(1-α)·Y(n-1) (1)

[0052] Where X(n) is the input vehicle speed signal value at time n; Y(n) and Y(n-1) are the output vehicle speed signal values ​​at time n and n-1; α is the filter coefficient, which can be obtained through calibration.

[0053] S2, obtain steering sensitivity at different vehicle speeds and

[0054] The mapping diagrams of yaw rate sensitivity and vehicle speed, and lateral acceleration sensitivity and vehicle speed are preset, and simulation correction is performed through simulation software, or correction is performed through actual vehicle test calibration to obtain the final yaw rate sensitivity-vehicle speed mapping diagram, and lateral acceleration sensitivity-vehicle speed mapping diagram. According to the above mapping diagrams, the yaw rate sensitivity at different vehicle speeds is obtained. and lateral acceleration sensitivity

[0055] As a preset reference, for general drivers, the yaw rate sensitivity The value ranges from 0.16 to 0.37 seconds -1 For experienced drivers, the yaw rate sensitivity The value ranges from 0.22 to 0.41 seconds -1 In this embodiment, the yaw rate sensitivity The value range is from 0.30 to 0.18s as the vehicle speed increases. -1 Linearly decreasing, such as Figure 4 shown.

[0056] Lateral acceleration sensitivity The value is related to the lateral acceleration increment generated by each 100-degree rotation of the steering wheel. This increment is generally in the range of 0.9 to 1.4 g / 100 degrees. In this design, the value range is preset to increase linearly from 1.2 to 1.3 g / 100 degrees as the vehicle speed increases. Figure 5 shown.

[0057] S3, calculate the ideal angular transmission ratio i based on the yaw rate yaw and the ideal angular transmission ratio i based on lateral acceleration sensitivity ay .

[0058] The linear two-degree-of-freedom vehicle dynamics model in steady state is written in state space as follows:

[0059]

[0060]

[0061]

[0062] Where m is the vehicle mass; r is the yaw rate; β is the sideslip angle of the center of mass; δ f is the front wheel turning angle; C f and C r are the front and rear wheel cornering stiffness respectively; l f and l r The distance between the front and rear axles and the center of mass of the vehicle, respectively. Wheelbase L = l f +l r ;I zz is the yaw moment of inertia of the vehicle.

[0063] The yaw rate sensitivity can be derived from equation (2) as follows:

[0064]

[0065] Ratio of steering wheel angle to front wheel angle Therefore, the ideal angular transmission ratio expression based on the yaw rate is obtained as follows:

[0066]

[0067] Similarly, the ideal angular transmission ratio expression based on lateral acceleration is derived:

[0068]

[0069] Get the filtered vehicle speed u, stability factor K, and mapped yaw rate sensitivity and lateral acceleration sensitivity Then, the ideal angular transmission ratio i based on the yaw angular velocity is calculated by formula (4): yaw The ideal angular transmission ratio i based on lateral acceleration sensitivity is calculated by formula (5): ay .

[0070] S4, performing weighted adjustment on the ideal angular rotation ratio.

[0071] To ensure linear and controllable handling at low speeds for steer-by-wire vehicles, the angular transmission ratio in the low and medium speed range should be primarily based on the ideal angular transmission ratio based on yaw rate. To ensure appropriate steering sensitivity at high speeds, the angular transmission ratio in the high-speed range should be primarily based on the ideal angular transmission ratio based on lateral acceleration sensitivity.

[0072] The angular transmission ratio after weighted adjustment of the present invention is calculated by the following expression:

[0073] i vsr_weighted =p·i yaw +(1-p)·i ay (6)

[0074] Among them, p is a preset weighted adjustment factor, and its value ranges from 0 to 1. The weighted adjustment factor designed by the present invention has the following mapping relationship with the vehicle speed: when the vehicle speed is low, such as the vehicle speed is less than 40km / h, p takes a value of 1, and the angular transmission ratio design is mainly based on maneuverability; when the vehicle speed is in a medium to high range, such as 40km / h≤vehicle speed≤160km / h, p takes a value that gradually decreases, and the angular transmission ratio design gradually transitions to stability; when the vehicle speed is higher than a certain value, such as the vehicle speed is greater than 160km / h, p takes a value of 0, and the angular transmission ratio design is mainly based on stability. The mapping relationship diagram of the weighted adjustment coefficient p and the vehicle speed is shown in the figure below. Figure 6 shown.

[0075] S5, performing steering wheel angle coefficient correction on the weighted angular transmission ratio.

[0076] At low speeds, the driver may need to turn the steering wheel at large angles. By modifying the angular transmission ratio, the angular transmission ratio decreases with increasing steering wheel angles at the same speed. Compared to before the modification, a smaller steering wheel angle is required to achieve the same front wheel steering angle, reducing the driver's operational burden in situations such as parking and U-turns.

[0077] At high speeds, vehicles are extremely sensitive to steering wheel angle input. Even a slight turn or misoperation by the driver can cause a significant change in the front wheel angle, easily leading to loss of control at high speeds. By adjusting the angle coefficient based on the diagonal transmission ratio, a larger steering wheel rotation is required to achieve the same front wheel angle, reducing steering wheel sensitivity and improving vehicle stability and safety.

[0078] The steering wheel angle coefficient G designed by the present invention sw , the corrected angular transmission ratio is calculated by the following expression:

[0079] i vsr =G sw ·i vsr_weighted (7)

[0080] Steering wheel angle coefficient G sw The preset value can be determined by the following method, as follows: Figure 7 shown.

[0081] When the steering wheel angle increases from 0 and is not greater than the first angle threshold P0, the steering wheel angle coefficient G sw The value is Cmax, that is, the steering wheel angle coefficient G sw In this embodiment, the maximum value Cmax is greater than or equal to 1. This design can reduce the sensitivity of the steering wheel within a small turning angle range, which is used to improve stability and safety at medium and high vehicle speeds.

[0082] When the steering wheel angle increases from the first threshold value P0 and is less than the second threshold value P1, the steering wheel angle coefficient G sw Decreases linearly.

[0083] When the steering wheel angle increases to reach the second threshold value P1 and continues to increase, the steering wheel angle coefficient G sw It no longer decreases and remains at the minimum value Cmin of the steering wheel angle coefficient. In this embodiment, the minimum value Cmin is less than or equal to 1. This design enables the steering system to reduce the driver's operating burden when the steering wheel is at a large angle.

[0084] When the steering wheel is turned in different directions, the steering wheel angle coefficient G sw The changing trend is the same as above.

[0085] For different vehicle speeds, in this embodiment, the steering wheel angle coefficient G sw The maximum value Cmax and the minimum value Cmin are designed to be variable values, and the specific change rule is: the higher the vehicle speed, the smaller the maximum value Cmax and the closer it is to 1, and the larger the minimum value Cmin and the closer it is to 1.

[0086] S6, limits the ideal angular transmission ratio.

[0087] In order to avoid the situation where the ideal angular transmission ratio is zero or too large, and a smooth transition to a low vehicle speed cannot be achieved, the minimum and maximum values ​​of the ideal angular transmission ratio are respectively limited.

[0088] The minimum value of the ideal angular transmission ratio is determined by: determining the minimum value based on the ratio of the desired maximum steering wheel angle to the maximum front wheel angle when the vehicle speed is zero, and determining the corresponding vehicle speed threshold u1. In this embodiment, the vehicle speed threshold u1 is 30 km / h.

[0089] The maximum value is determined as follows: Under the conditions of 120 km / h vehicle speed and double lane change simulation, the front wheel angle is generally about 1.5°. The maximum value i is determined based on the ratio of the expected steering wheel angle to the front wheel angle. vsr_max The corresponding vehicle speed threshold u2 is determined. In this embodiment, the vehicle speed threshold u2 is 100 km / h.

[0090] The target angular transmission ratio after limiting is:

[0091]

[0092] S7, generate the target angular transmission ratio i according to formula (8) vsr .

[0093] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for generating a variable angular transmission ratio for a steer-by-wire system, characterized by: The steps include: S1, collect vehicle speed u, vehicle stability factor K and steering wheel angle δ sw signal, and perform low-pass filtering on the vehicle speed u; S2, obtain the yaw rate sensitivity at different vehicle speeds and lateral acceleration sensitivity The details are as follows: First, preset the mapping diagram of yaw rate sensitivity and vehicle speed, and the mapping diagram of lateral acceleration sensitivity and vehicle speed, and then perform simulation correction through simulation software, or perform correction through actual vehicle test calibration, to obtain the final mapping diagram of yaw rate sensitivity-vehicle speed, and the mapping diagram of lateral acceleration sensitivity-vehicle speed, so as to obtain the yaw rate sensitivity at different vehicle speeds. and lateral acceleration sensitivity S3, calculate the ideal angular transmission ratio i based on the yaw rate sensitivity yaw and the ideal angular transmission ratio i based on lateral acceleration sensitivity ay ; S4, weighted adjustment of the angular transmission ratio, the calculation formula of the angular transmission ratio after weighted adjustment is i vsr_weighted =p·i yaw +(1-p)·i ay , p is the preset weighted adjustment factor, ranging from 0 to 1; S5, performing steering wheel angle coefficient correction on the weighted angular transmission ratio. The calculation formula of the corrected angular transmission ratio is: vsr =G sw ·i vsr_weighted , G sw is the steering wheel angle coefficient, the steering wheel angle coefficient G sw The method for determining is: (1) When the steering wheel angle increases from 0 and is not greater than the first angle threshold P0, the steering wheel angle coefficient G sw The value is the maximum value Cmax, Cmax ≥ 1; (2) When the steering wheel angle increases from the first threshold value P0 and is less than the second threshold value P1, the steering wheel angle coefficient G sw Decrease linearly; (3) When the steering wheel angle increases to the second threshold value P1 and continues to increase, the steering wheel angle coefficient G sw Maintain at the minimum value Cmin, Cmin≤1; S6, limiting the corrected angular transmission ratio. The target angular transmission ratio after limiting is calculated as follows: Among them, u1 and u2 are vehicle speed thresholds; S7, generate target angular transmission ratio i vsr .

2. The method for generating a variable angular transmission ratio for a steer-by-wire system according to claim 1, wherein: In step S3, the ideal angular transmission ratio i based on the yaw rate sensitivity is yaw The calculation formula is: L is the wheelbase, L=lf+lr, lf and lr are the distances from the front and rear axles to the center of mass of the vehicle respectively.

3. The method for generating a variable angular transmission ratio for a steer-by-wire system according to claim 1, wherein: In step S3, the ideal angular transmission ratio i based on the lateral acceleration sensitivity is ay The calculation formula is: L is the wheelbase, L=lf+lr, lf and lr are the distances from the front and rear axles to the center of mass of the vehicle respectively.

4. The method for generating a variable angular transmission ratio for a steer-by-wire system according to claim 1, wherein: In step S4, when the vehicle speed is less than 40 km / h, the p value is 1; when 40 km / h≤vehicle speed≤160 km / h, the p value gradually decreases; when the vehicle speed is greater than 160 km / h, the p value is 0.

5. The method for generating a variable angular transmission ratio for a steer-by-wire system according to claim 1, wherein: When the vehicle speed is different, the maximum value Cmax and the minimum value Cmin are different. The higher the vehicle speed, the smaller the maximum value Cmax and the closer it is to 1, and the larger the minimum value Cmin and the closer it is to 1.

6. The method for generating a variable angular transmission ratio for a steer-by-wire system according to claim 1 or 5, characterized in that: When the steering wheel is turned in different directions, the steering wheel angle coefficient G sw The changing trend is the same.

7. The method for generating a variable angular transmission ratio for a steer-by-wire system according to claim 1, wherein: In step S6, when the vehicle speed is zero, the ideal angular transmission ratio minimum value i is determined by the ratio of the desired maximum steering wheel angle to the maximum front wheel angle. vsr_min Under the conditions of double lane change simulation at a speed of 120 km / h, the ideal angular transmission ratio maximum value i is determined based on the ratio of the expected steering wheel angle to the front wheel angle. vsr_max .

8. The method for generating a variable angular transmission ratio for a steer-by-wire system according to claim 1, wherein: In step S1, the vehicle speed u signal and the vehicle stability factor K are obtained from the vehicle controller via the CAN bus, or the vehicle stability factor K is set to a fixed value and the steering wheel angle δ is collected from the steering wheel angle sensor. sw Signal.

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