A design method of variable transmission ratio coefficient of a steer-by-wire system

Abstract

The application discloses a variable transmission ratio coefficient design method of a steer-by-wire system, and belongs to the technical field of steer-by-wire systems of electric vehicles, and comprises the following steps: establishing a human-vehicle comprehensive evaluation index under a specific transmission ratio; obtaining a fitting curve of vehicle speed and the transmission ratio coefficient; obtaining, through experiments, a yaw angular velocity gain, a lateral acceleration gain, a roll angle gain corresponding to different steering wheel angles under a fixed vehicle speed, and an ideal steering gain under each vehicle speed; calculating the variable transmission ratio coefficient under the ideal steering gain; calculating the weight of the variable transmission ratio coefficient under the ideal steering gain; and combining the yaw angular velocity gain, the lateral acceleration gain, the roll angle gain and the steering gain weight coefficient to obtain the variable transmission ratio coefficient considering the comprehensive vehicle steering gain. Finally, the variable transmission ratio coefficient of the steer-by-wire system is introduced into a fuzzy neural network for training to obtain a model of the variable transmission ratio coefficient of the steer-by-wire system with respect to the vehicle speed and the steering wheel rotation angle. The application can maintain the steering gain of the vehicle and improve the stability and safety of the vehicle.

Description

Technical Field

[0001] The present invention relates to the technical field of electric vehicle wire control, and more particularly to a method for designing a variable transmission ratio coefficient of a wire control steering system. Background Art

[0002] With the continuous advancement of automotive technology, steering systems play a crucial role in vehicle handling and safety, primarily by controlling the front wheel angle to improve steering response. With the increasing popularity of electric vehicles and the development of intelligent driving technologies, steer-by-wire technology has rapidly developed in the field of vehicle steering control. Steer-by-wire systems eliminate the mechanical connection between the steering wheel and steering mechanism, thereby expanding the steering angle transfer characteristics and enabling flexible design of the gear ratio. Variable gear ratio technology not only helps drivers more easily turn the steering wheel at low speeds, improving vehicle maneuverability, but also provides a larger gear ratio at high speeds, increasing vehicle stability and thus improving driving safety.

[0003] The Chinese invention patent application, CN 114312751A, discloses a variable angle transmission ratio control method for a 4WID / S electric vehicle. The method comprises the following steps: introducing an objective multi-objective evaluation index function for vehicle handling stability, combining the four evaluation index functions into a comprehensive evaluation index function through weighting, and determining the angular rotation ratio corresponding to the comprehensive evaluation index of vehicle handling stability at different vehicle speeds in an open-loop serpentine operating condition experiment using the comprehensive evaluation index function; deriving a mathematical model for a conventional vehicle fixed transmission ratio within a speed range of 100 km / h, a fixed k ratio, and a control method for the vehicle steering ratio within a speed range of 100 km / h using a vehicle dynamics model and a mathematical model for the steering motor. γ The mathematical model of the ideal transmission ratio i1 and the constant k ay The invention combines the steering angle transmission ratio corresponding to a constant yaw rate gain with the steering angle transmission ratio corresponding to a constant lateral acceleration gain. A speed range variable weight fitting method is used to fit the vehicle's angular transmission ratio curve to control 4WID / S electric vehicles and improve vehicle handling stability. However, this patent only considers the yaw rate gain and lateral acceleration gain when designing the steering angle transmission ratio coefficient, sacrificing some roll angle gain and resulting in reduced vehicle safety. Summary of the Invention

[0004] The present invention provides a method for designing a variable transmission ratio coefficient of a steer-by-wire system, so as to overcome the shortcomings of existing steer-by-wire variable transmission ratio control that only considers yaw rate gain and lateral acceleration gain, resulting in reduced vehicle safety.

[0005] The present invention adopts the following technical solutions:

[0006] A method for designing a variable transmission ratio coefficient of a steer-by-wire system, characterized by comprising the following steps:

[0007] S1. Collect vehicle information, including vehicle speed, steering wheel angle, yaw rate, lateral acceleration, and roll angle;

[0008] S2. Establishing comprehensive evaluation index of human-vehicle under specific transmission ratio;

[0009] S3, calculate the optimal value of the transmission ratio coefficient at a fixed speed, and get the speed by fitting v With variable transmission ratio coefficient The relationship curve of

[0010] S4: Substitute the relationship curve between vehicle speed and transmission ratio coefficient obtained in step S3 into the steering wheel angle step input test to obtain the corresponding yaw rate gain under different steering wheel angles at a fixed vehicle speed. , lateral acceleration gain , roll angle gain and steering angle gain 、 、 , in the small turning angle area, each vehicle speed corresponds to a basically unchanged gain, which is the ideal steering gain at that speed: the ideal yaw rate gain is , the ideal lateral acceleration gain is , the ideal roll angle gain is ;

[0011] S5. Calculate the variable transmission ratio coefficient under the ideal steering gain, including the variable transmission ratio coefficient of the ideal yaw rate gain , variable transmission ratio coefficient of ideal lateral acceleration gain , variable transmission ratio coefficient of ideal roll angle gain ;

[0012] S6: Under the condition of fixed vehicle speed and steering wheel angle, the variable transmission ratio coefficient of step S3 is changed. The coefficients of variation are calculated by comparing the three variable transmission ratio coefficients under the ideal steering gain in step S5 to obtain the coefficients of variation. , for ; Then determine the weight coefficient according to the coefficient of variation:

[0013]

[0014] Where, is the weight;

[0015] By changing the vehicle speed and steering wheel angle, the steering gain weight coefficient under different vehicle speeds and steering wheel angles can be obtained;

[0016] S7, the step S5 obtained 、 、 The variable transmission ratio coefficient considering the comprehensive vehicle steering gain is obtained by weighted combination with the steering gain weight coefficients obtained in step S6:

[0017]

[0018] Where, 、 、 is the weight coefficient;

[0019] S8. Import the corresponding data of vehicle speed, steering wheel angle and variable transmission ratio coefficient into the fuzzy neural network for training, and obtain a model of the variable transmission ratio coefficient of the wire control steering system with respect to vehicle speed and steering wheel angle.

[0020] Furthermore, between step S1 and step S2, the above step also includes deriving a formula for changing the transmission ratio of the steering-by-wire system:

[0021]

[0022] Where, is the transmission ratio from the steering wheel to the front wheels of the vehicle, is the steering wheel angle, is the front wheel turning angle, is the steering actuator angle, is the variable transmission ratio coefficient, i.e. the design target, It is a fixed transmission ratio of the mechanical structure.

[0023] Furthermore, the specific process of step S2 is as follows:

[0024] S201. Establish vehicle path tracking error evaluation index :

[0025]

[0026] Where, For the test time, is the lateral displacement deviation between the actual vehicle trajectory and the expected path, is the threshold value of lateral displacement deviation;

[0027] S202. Establishing Driver Burden Indicators :

[0028]

[0029] Where, For the test time, is the steering wheel angular velocity, The steering wheel rotation angular velocity threshold;

[0030] S203. Establish vehicle stability index :

[0031]

[0032] Where, For the test time, is the lateral acceleration, is the lateral acceleration threshold;

[0033] S204. Establish vehicle safety indicators :

[0034]

[0035] Where, For the test time, is the vehicle roll angle, is the vehicle roll angle threshold;

[0036] S205, the above 、 、 、 A weighted combination is performed to obtain a comprehensive human-vehicle evaluation index that considers vehicle maneuverability, stability, and safety. :

[0037]

[0038] Furthermore, the specific process of step S3 is as follows:

[0039] S301, starting from 20 km / h, the simulation speed is selected in sequence with 20 km / h intervals: 20 km / h, 40 km / h, 60 km / h, and 80 km / h, a total of four speed groups;

[0040] S302, variable transmission ratio coefficient =0.1, and select the transmission ratio coefficient value in intervals of 0.1;

[0041] S303. Set up a double lane-shifting operating condition test, calculate the comprehensive evaluation index of different transmission ratio coefficients at different vehicle speeds, obtain the transmission ratio coefficient value corresponding to the minimum comprehensive evaluation index at a fixed vehicle speed, fit the relationship curve between vehicle speed and variable transmission ratio, and set the minimum transmission ratio coefficient and the maximum transmission ratio coefficient as constraints.

[0042] Furthermore, the coefficient of variation of each item in step S6 is calculated using the following formula:

[0043]

[0044]

[0045] ;

[0046] Where, is the coefficient of variation, is the standard deviation, is the mean, for .

[0047] It can be seen from the above description of the present invention that, compared with the prior art, the present invention has the following advantages:

[0048] 1. The present invention adopts a variable transmission ratio coefficient design method that comprehensively considers yaw rate gain, lateral acceleration gain, and roll angle gain, thereby maintaining the steering gain of the vehicle and improving the stability and safety of the vehicle.

[0049] 2. The ideal value data of the steering gain of the present invention is obtained by an experimental method, which can effectively reflect the nonlinear characteristics of the steering system.

[0050] 3. The present invention considers both the human-vehicle comprehensive evaluation index and the vehicle steering gain in a variable transmission ratio generation method, and proposes a weight distribution coefficient design method to link the weight distribution coefficient with the vehicle speed and steering wheel angle.

[0051] 4. The calculation of the weight of the fusion method of the present invention is to adjust the size of the weight according to the size of the change difference, which can ensure the stability of the three gains without sacrificing any gain. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a design flow chart of the present invention.

[0053] Figure 2 This is a curve diagram showing the relationship between vehicle speed and variable transmission ratio of the present invention. DETAILED DESCRIPTION

[0054] Refer to the following Figure 1 The following describes specific embodiments of the present invention. Numerous details are provided below to provide a comprehensive understanding of the present invention, but those skilled in the art will appreciate that the present invention can be implemented without these details. Well-known components, methods, and processes are not described in detail below.

[0055] The present invention proposes a design method for a variable transmission ratio coefficient of a wire-controlled steering system. The implementation process is shown in the attached figure. Figure 1 , mainly including the following steps:

[0056] Step 1: Collect vehicle information, including vehicle speed, steering wheel angle, yaw rate, lateral acceleration, and roll angle.

[0057] Step 2: Derive the formula for changing the transmission ratio of the wire-controlled steering system:

[0058]

[0059] Where, is the transmission ratio from the steering wheel to the front wheels of the vehicle, is the steering wheel angle, is the front wheel turning angle, is the steering actuator angle, is the variable transmission ratio coefficient, i.e. the design target, It is a fixed transmission ratio of the mechanical structure.

[0060] Step 3: Establish comprehensive evaluation index of human-vehicle under specific transmission ratio. The details are as follows:

[0061] Step 3.1: Establish vehicle path tracking error evaluation index :

[0062]

[0063] Where, For the test time, is the lateral displacement deviation between the actual vehicle trajectory and the expected path, is the threshold value of lateral displacement deviation;

[0064] Step 3.2: Establish driver burden indicators :

[0065]

[0066] Where, For the test time, is the steering wheel angular velocity, The steering wheel rotation angular velocity threshold;

[0067] Step 3.3: Establish vehicle stability index :

[0068]

[0069] Where, For the test time, is the lateral acceleration, is the lateral acceleration threshold;

[0070] Step 3.4: Establish vehicle safety indicators :

[0071]

[0072] Where, For the test time, is the vehicle roll angle, is the vehicle roll angle threshold.

[0073] Step 3.5, the above 、 、 、 A weighted combination is performed to obtain a comprehensive human-vehicle evaluation index that considers vehicle maneuverability, stability, and safety. :

[0074]

[0075] Step 4: Calculate the optimal value of the variable transmission ratio coefficient at a fixed vehicle speed. The details are as follows:

[0076] Step 4.1, starting from 20 km / h, select the simulation speed in intervals of 20 km / h: 20 km / h, 40 km / h, 60 km / h, 80 km / h, a total of four speed groups;

[0077] Step 4.2: Variable transmission ratio coefficient =0.1, and select the transmission ratio coefficient value in intervals of 0.1;

[0078] Step 4.3: Set up a double lane change test, calculate the comprehensive evaluation index of different transmission ratio coefficients at different vehicle speeds, obtain the transmission ratio coefficient value corresponding to the minimum comprehensive evaluation index at a fixed vehicle speed, fit the relationship curve between vehicle speed and variable transmission ratio, and set the minimum transmission ratio coefficient and the maximum transmission ratio coefficient as restrictions, as shown in the attached figure. Figure 2 shown.

[0079] Step 5: Substitute the speed-variable transmission ratio curve obtained in step 4.3 into the steering wheel angle step input test to obtain the corresponding yaw rate gain at different steering wheel angles at a fixed speed. , lateral acceleration gain , roll angle gain and steering angle gain 、 、 , where: is the yaw rate gain of the steering wheel, is the lateral acceleration gain of the steering wheel, is the steering wheel roll angle gain, is the yaw rate gain of the steering actuator angle, is the lateral acceleration gain of the steering actuator angle, The roll angle gain of the steering angle of the steering actuator. In the small steering angle region, each vehicle speed corresponds to a substantially constant gain, which is the ideal steering gain at that vehicle speed, the ideal yaw rate gain is , the ideal lateral acceleration gain is , and the ideal roll angle gain is .

[0080] Step 6, calculate the variable transmission ratio coefficient under the ideal steering gain. Specifically, it includes:

[0081] Step 6.1, variable transmission ratio coefficient based on ideal yaw rate gain:

[0082]

[0083] Step 6.2, variable transmission ratio coefficient based on ideal lateral acceleration gain:

[0084]

[0085] Step 6.3, variable transmission ratio coefficient based on ideal roll angle gain:

[0086]

[0087] Step 7, calculate the weight of the variable transmission ratio coefficient under the ideal steering gain.

[0088] Step 7.1, at a fixed vehicle speed and steering wheel angle, the variable transmission ratio coefficient of step 4 is respectively calculated with the three variable transmission ratio coefficients of step 6 , , to determine the variable coefficients:

[0089]

[0090]

[0091]

[0092] In the formula, is the variable coefficient, is the standard deviation, is the mean, is .

[0093] Step 7.2, determine the weight coefficient:

[0094]

[0095] In the formula, is the weight.

[0096] Step 7.3: By changing the vehicle speed and steering wheel angle, the steering gain weight coefficient under different vehicle speeds and steering wheel angles can be obtained.

[0097] Step 8: 、 、 The variable transmission ratio coefficient considering the comprehensive vehicle steering gain is obtained by weighted combination:

[0098]

[0099] Where, 、 、 is the weight coefficient.

[0100] Step 9: Import the corresponding data of vehicle speed, steering wheel angle and variable transmission ratio coefficient into the fuzzy neural network for training, and obtain a model of the variable transmission ratio coefficient of the steer-by-wire system with respect to vehicle speed and steering wheel angle.

[0101] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited to this. Any non-substantial changes to the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A method for designing a variable transmission ratio coefficient of a steer-by-wire system, characterized in that: The following steps are involved: S1. Collect vehicle information, including vehicle speed, steering wheel angle, yaw rate, lateral acceleration, and roll angle; S2. Establishing comprehensive evaluation index of human-vehicle under specific transmission ratio; S3, calculate the optimal value of the transmission ratio coefficient at a fixed speed, and get the speed by fitting v With variable transmission ratio coefficient The relationship curve of S4: Substitute the relationship curve between vehicle speed and transmission ratio coefficient obtained in step S3 into the steering wheel angle step input test to obtain the corresponding yaw rate gain under different steering wheel angles at a fixed vehicle speed. , lateral acceleration gain , roll angle gain and the yaw rate gain of the steering actuator angle , lateral acceleration gain of steering actuator angle , Roll angle gain of steering actuator angle , in the small turning angle area, each vehicle speed corresponds to a basically unchanged gain, which is the ideal steering gain at that speed: the ideal yaw rate gain is , the ideal lateral acceleration gain is , the ideal roll angle gain is ; S5. Calculate the variable transmission ratio coefficient under the ideal steering gain, including the variable transmission ratio coefficient of the ideal yaw rate gain , variable transmission ratio coefficient of ideal lateral acceleration gain , variable transmission ratio coefficient of ideal roll angle gain ; S6: Under the condition of fixed vehicle speed and steering wheel angle, the variable transmission ratio coefficient of step S3 is changed. The coefficients of variation are calculated by comparing the three variable transmission ratio coefficients under the ideal steering gain in step S5 to obtain the coefficients of variation. , for ; Then determine the weight coefficient according to the coefficient of variation: Where, is the weight coefficient; By changing the vehicle speed and steering wheel angle, the steering gain weight coefficient under different vehicle speeds and steering wheel angles is obtained; The coefficient of variation of each item was calculated using the following formula: ； Where, is the coefficient of variation, is the standard deviation, is the mean, for ; S7, the step S5 obtained 、 、 The variable transmission ratio coefficient considering the comprehensive vehicle steering gain is obtained by weighted combination with the steering gain weight coefficients obtained in step S6: Where, 、 、 is the weight coefficient; S8, importing the corresponding data of vehicle speed, steering wheel angle, and variable transmission ratio coefficient into a fuzzy neural network for training, and obtaining a model of the variable transmission ratio coefficient of the steer-by-wire system with respect to vehicle speed and steering wheel angle; represents the yaw angular velocity, represents the lateral acceleration, Indicates the roll angle.

2. The method for designing a variable transmission ratio coefficient of a steer-by-wire system according to claim 1, wherein: The step between step S1 and step S2 also includes deriving a formula for changing the transmission ratio of the steering-by-wire system: Where, is the transmission ratio from the steering wheel to the front wheels of the vehicle, is the steering wheel angle, is the front wheel turning angle, is the steering actuator angle, is the variable transmission ratio coefficient, i.e. the design target, It is a fixed transmission ratio of the mechanical structure.

3. The method for designing a variable transmission ratio coefficient of a steer-by-wire system according to claim 2, wherein: The specific process of step S2 is as follows: S201. Establish vehicle path tracking error evaluation index : Where, For the test time, is the lateral displacement deviation between the actual vehicle trajectory and the expected path, is the threshold value of lateral displacement deviation; S202. Establishing Driver Burden Indicators : Where, For the test time, is the steering wheel angular velocity, The steering wheel rotation angular velocity threshold; S203. Establish vehicle stability index : Where, For the test time, is the lateral acceleration, is the lateral acceleration threshold; S204. Establish vehicle safety indicators : Where, For the test time, is the vehicle roll angle, is the vehicle roll angle threshold; S205, the above 、 、 、 A weighted combination is performed to obtain a comprehensive human-vehicle evaluation index that considers vehicle maneuverability, stability, and safety. : .

4. The method for designing a variable transmission ratio coefficient of a steer-by-wire system according to claim 3, wherein: The specific process of step S3 is as follows: S301, starting from 20 km / h, the simulation speed is selected in sequence with 20 km / h intervals: 20 km / h, 40 km / h, 60 km / h, and 80 km / h, a total of four speed groups; S302, variable transmission ratio coefficient =0.1, and select the transmission ratio coefficient value in intervals of 0.1; S303. Set up a double lane-shifting operating condition test, calculate the comprehensive evaluation index of different transmission ratio coefficients at different vehicle speeds, obtain the transmission ratio coefficient value corresponding to the minimum comprehensive evaluation index at a fixed vehicle speed, fit the relationship curve between vehicle speed and variable transmission ratio, and set the minimum transmission ratio coefficient and the maximum transmission ratio coefficient as constraints.

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