A method and device for calculating steering wheel tactile assist torque based on sliding mode control

Abstract

The present invention provides a method and device for calculating steering wheel haptic assist torque based on sliding mode control. The method comprises the following steps: Step 1: Establishing a dynamic model of the arm, steering wheel, and steering column; Step 2: Defining sliding mode input; Step 3: Designing a sliding mode function; Step 4: Establishing a driver preview model; and Step 5: Calculating the haptic assist torque. Based on the error between the driver's steering wheel output and the output of an expert driver model, the present invention utilizes a sliding mode algorithm to calculate the appropriate assist torque in real time. When the error between the two outputs is excessively large or small, the assist torque is applied to guide the driver to perform more appropriate maneuvers, thereby improving vehicle safety and stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of automobile steering systems, and in particular relates to a method and device for calculating steering wheel tactile auxiliary torque based on sliding mode control. Background Art

[0002] The steering system is a key component of the vehicle chassis, and its performance is closely related to the vehicle's handling stability, safety, and comfort. Currently, steering assistance systems primarily include electronically controlled hydraulic power steering, electric power steering (EPS), and active front-wheel steering (AFS). These assisted steering systems control the hydraulics or electric motors to apply additional steering force to the steering system based on driver input, thereby reducing the driver's operational burden. However, these power steering systems only change the steering force transmitted to the ground, while the steering feedback force transmitted to the driver remains unchanged. The driver still needs to focus on the driving task, so they are essentially assisted driving systems.

[0003] Human-machine co-driving is a transitional technology between assisted and autonomous driving. It brings the driver into the control loop of the autonomous driving system, allowing them to supervise and participate in the driving task. Through intelligent algorithms, human-machine operations are integrated, fully leveraging the respective strengths of the driver and the autonomous vehicle while satisfying subjective feelings. Haptic assistance (also known as tactile guidance) is a typical human-machine co-driving system. It transmits tactile information to the driver by controlling the feedback force / torque interacting with the driver, guiding the driver's operation and achieving human-machine collaborative control. Existing torque design methods for haptic assistance primarily rely on proportional-integral control (PI) and proportional-integral-derivative control (PID). However, due to the system uncertainty introduced by the driver in the loop, current haptic assistance designs suffer from poor control effectiveness, low system stability, and poor driving comfort. Sliding mode control is a special nonlinear control method that can quickly adjust the control output according to the current state of the system so that the system state moves according to a pre-designed sliding mode. The design of the sliding mode is independent of the control object parameters and disturbances. Therefore, it has the advantages of fast response, strong robustness, and easy physical implementation. Summary of the Invention

[0004] Purpose of the invention: The technical problem to be solved by the present invention is to address the deficiencies of the existing technology and provide a method for calculating the steering wheel tactile assist torque based on sliding mode control. While ensuring the system response speed and stability, the method improves the driver's driving comfort and helps the driver to control the vehicle more effectively. The method comprises the following steps:

[0005] Step 1: Establish the dynamic model of the arm, steering wheel, and steering column;

[0006] Step 2, define synovial input;

[0007] Step 3, designing the synovial function;

[0008] Step 4: Establish a driver preview model;

[0009] Step 5: Calculate the tactile assist torque.

[0010] Step 1 includes: establishing the following dynamic models of the arm, steering wheel, and steering column:

[0011]

[0012] Among them, J a is the moment of inertia of the arm; J c is the steering wheel-steering column moment of inertia; is the steering wheel angular acceleration; B a is the arm damping coefficient; B c is the steering wheel-steering column damping coefficient; is the steering wheel speed; K a is the arm stiffness; θ sw is the corner; T h is the steering wheel torque applied by the driver; T s is the steering resistance torque of the steering wheel; T sa is the tactile assist torque.

[0013] Step 2 includes defining the synovial input as:

[0014]

[0015] Where, e is the steering wheel angle error; is the steering wheel speed error; θ swd is the desired steering wheel angle; is the desired steering wheel speed.

[0016] Step 2 also includes: writing equation (1) into the state equation form about synovial input:

[0017]

[0018] Among them, x1 is the first-order synovial input, x1=e, is the first derivative of the first-order sliding mode function; x2 is the second-order sliding mode input, is the first derivative of the second-order sliding mode function; f is the state function, is the desired steering wheel angular acceleration; g is the input function, u is the state equation input, u=T sa .

[0019] Step 3 includes: the synovial function s is designed as:

[0020]

[0021] Where α is the parameter of the first sliding mode function, α>0; β is the parameter of the second sliding mode function, β>0; γ1 is the parameter of the third sliding mode function, γ1>γ2; γ2 is the parameter of the fourth sliding mode function, 1<γ2<2; sgn(x) is the sign function;

[0022] The sliding mode control rate is designed as:

[0023]

[0024] Among them, K1 is the first sliding mode reaching rate parameter, K1>0; K2 is the second sliding mode reaching rate parameter, K2>0.

[0025] Step 3 also includes: When using the sliding mode control rate of formula (5), the sliding mode approach rate for:

[0026]

[0027] In order to suppress the sliding mode chattering phenomenon, the saturation function sat(x) is used to replace the sign function sgn(x) in Equations (4), (5), and (6). The saturation function is expressed as:

[0028]

[0029] Where b is the saturation function parameter, b>0;

[0030] Substituting the saturation function into equation (5) gives the tactile assist torque:

[0031]

[0032] By changing the sliding mode parameters: α, β, γ1, γ2, K1, K2, the actual control effect of the sliding mode can be adjusted.

[0033] Step 4 includes: establishing the following driver preview model:

[0034]

[0035] Where l is the Laplace operator, (l) represents l in the Laplace domain; θ swd (l) is the desired steering wheel angle; τ L is the leading time constant; τ d1 is the delay time constant; τ d2 is the driver's reaction delay time; G h Driver steering proportional gain; ΔY(l) is the lateral deviation between the vehicle's current position and the preview point, expressed as:

[0036]

[0037] in, is the lateral position coordinate of the desired path at the preview point; Y(l) is the lateral position coordinate of the current vehicle; φ(l) is the vehicle heading angle; L is the preview distance, expressed as:

[0038] L=v x τ p

[0039] Among them, v x is the current speed of the vehicle; τ p Preview time for the driver;

[0040] Write equation (8) in the form of state equation:

[0041]

[0042] Where c is the delay time operator, T d is the total delay time, T d = d1 + d2 ;T p is the total preview time, T p = L + p .

[0043] Step 4 also includes: using the sensor to obtain the longitudinal vehicle speed v x , vehicle heading angle φ, lateral position deviation Y d -, using the driving characteristic parameter G of the expert driver h , τ L , τ d1 , τ d2 , τ p , according to formula (9), the desired steering wheel angle θ is obtained swd , expected steering wheel speed Expected steering wheel angular acceleration

[0044] Step 5 includes: using the sensor to obtain the steering wheel angle θ sw , steering wheel speed Combine the results of step 4 to calculate the sliding membrane input of formula (2); use the sensor to obtain the steering wheel torque T applied by the driver h , steering wheel steering resistance torque T s , the actual value of the above data is substituted into formula (7) to finally calculate the tactile assist torque T sa .

[0045] The present invention also provides a steering wheel haptic assist torque calculation device based on sliding mode control, comprising:

[0046] Dynamic model building module, used to build dynamic models of arms, steering wheels, and steering columns;

[0047] A driver preview model building module is used to build an expert driver preview model;

[0048] Synovial input definition module, used to define and calculate synovial input;

[0049] Synovial function design module, used to design and calculate synovial function;

[0050] The tactile assistance torque calculation module is used to calculate the tactile assistance torque.

[0051] The present invention also provides a storage medium storing a computer program or instruction. When the computer program or instruction is executed, the above-mentioned method for calculating the steering wheel haptic auxiliary torque based on sliding mode control is implemented.

[0052] The beneficial effects of the present invention are:

[0053] 1. The present invention can calculate the appropriate assist torque in real time using a sliding membrane algorithm based on the error between the driver's steering wheel output and the output of the expert driver model. When the output error between the two is too large or too small, the assist torque can be applied to guide the driver to output a more appropriate operation, thereby improving the safety and stability of vehicle driving.

[0054] 2. By applying tactile assistance, the expert driver's operations can be transmitted to the driver in the form of force feedback, realizing the transfer of expert driver's driving skills and helping drivers, especially novice drivers, to quickly improve their driving skills. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more apparent.

[0056] Figure 1 It is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0057] The present invention provides a method for calculating steering wheel haptic assist torque based on sliding mode control, comprising the following steps:

[0058] Step 1) Establish the arm-steering wheel-steering column dynamic model:

[0059]

[0060] Where, J a is the moment of inertia of the arm; J c is the steering wheel-steering column moment of inertia; is the steering wheel angular acceleration; B a is the arm damping coefficient; B c is the steering wheel-steering column damping coefficient; is the steering wheel speed; K a is the arm stiffness; θ sw is the corner; T h is the steering wheel torque applied by the driver; T s is the steering resistance torque of the steering wheel; T sa is the tactile assist torque;

[0061] 2) Define synovial input as:

[0062]

[0063] Where, e is the steering wheel angle error; is the steering wheel speed error; θ swd is the desired steering wheel angle; is the desired steering wheel speed;

[0064] Formula (1) is written as the state equation for synovial input:

[0065]

[0066] Among them, x1 is the first-order synovial input, x1=e, is the first derivative of the first-order sliding mode function; x2 is the second-order sliding mode input, is the first derivative of the second-order sliding mode function; f is the state function, is the desired steering wheel angular acceleration; g is the input function, u is the state equation input, u=T sa ;

[0067] 3) The synovial function is designed as follows:

[0068]

[0069] Where s is the sliding mode function; α is the parameter of the first sliding mode function, α>0; β is the parameter of the second sliding mode function, β>0; γ1 is the parameter of the third sliding mode function, γ1>γ2; γ2 is the parameter of the fourth sliding mode function, 1<γ2<2; sgn(x) is the sign function;

[0070] The sliding mode control rate is designed as:

[0071]

[0072] Where, K1 is the first sliding mode approaching rate parameter, K1>0; K2 is the second sliding mode approaching rate parameter, K2>0;

[0073] When using the sliding mode control rate of formula (5), the sliding mode approach rate is:

[0074]

[0075] In order to suppress the sliding mode chattering phenomenon, the saturation function sat(x) is used to replace the sign function sgn(x) in Equation (4), Equation (5) and Equation (6). The saturation function is expressed as:

[0076]

[0077] Where b is the saturation function parameter, b>0;

[0078] Substituting the saturation function into equation (5) gives the tactile assist torque:

[0079]

[0080] By changing the sliding mode parameters: α, β, γ1, γ2, K1, K2, the actual control effect of the sliding mode can be adjusted;

[0081] 4) Expected steering wheel angle θ in the present invention swd , expected steering wheel speed Expected steering wheel angular acceleration Methods for obtaining include but are not limited to: a driver preview model method based on expert driving characteristic parameters, a neural network black box driver model method based on expert driving data, etc. The driver preview model method based on expert driving characteristic parameters is described as follows:

[0082] Build a driver preview model:

[0083]

[0084] Where l is the Laplace operator, (l) represents the variable in the Laplace domain; θ xwd (l) is the desired steering wheel angle; τ L is the leading time constant; τ d1 is the delay time constant; τ d2 is the driver's reaction delay time; G h Driver steering proportional gain; ΔY(l) is the lateral deviation between the vehicle's current position and the preview point, expressed as:

[0085] ΔY(l)=(l)e τpl -(l)-φ(l)

[0086] Where, is the lateral position coordinate of the desired path at the preview point; Y(l) is the lateral position coordinate of the current vehicle; φ(l) is the vehicle heading angle; L is the preview distance, expressed as:

[0087] L=v x τ p

[0088] Where, v x is the current speed of the vehicle; τ p Preview time for the driver;

[0089] Write equation (8) in the form of state equation:

[0090]

[0091] Where c is the delay time operator, T d is the total delay time, T d = d1 + d2 ;T p is the total preview time, T p = L + p ;

[0092] Use the sensor to obtain the longitudinal vehicle speed v x , vehicle heading angle φ, lateral position deviation Y d -, using the driving characteristic parameter G of the expert driver h , τ L , τ d1 , τ d2 , τ p , the desired steering wheel angle θ can be obtained according to formula (9) swd , expected steering wheel speed Expected steering wheel angular acceleration

[0093] 5) Use the sensor to obtain the steering wheel angle θ sw , steering wheel speed Combine the results of 4) to calculate the sliding membrane input of formula (2); use the sensor to obtain the steering wheel torque T applied by the driver h , steering wheel steering resistance torque T s ; Substitute the actual values ​​of the above data into formula (7) to finally calculate the tactile assist torque T sa .

[0094] Example

[0095] The flow chart of this embodiment is as follows Figure 1 As shown in the figure, for steer-by-wire vehicles, an arm-steering wheel-steering column dynamics model and an expert driver model are established, and a sliding mode algorithm is designed. At the same time, the wheel speed sensor, vehicle position sensor, steering wheel angle sensor, steering wheel speed sensor, and steering wheel force sensor information are used to determine the input of the sliding mode control system and calculate the assist torque, specifically:

[0096] 1. Get the driver's steering wheel angle input θ through the sensor sw is 0.616rad, and the steering wheel speed input is 0.913 rad / s, and the longitudinal speed v x is 15m / s, the vehicle heading angle φ is -0.106rad, and the lateral position deviation Y d - is 0.332m, which is obtained through the Simulink, Carsim, and PreScan hardware-in-the-loop co-simulation platform established based on the hardware steering wheel system and Matlab software. The output of the expert driver model at this time is calculated:

[0097]

[0098] In the formula, the characteristic parameters of the expert driver are set to G h =0.607, τ L =0.12, τ d1 =0.05, τ d2 =0.086, τ p =0.931, that is, T d =0.136, c=0.232, T p =1.051;

[0099] The desired steering wheel angle θ at this time swd is 0.401rad; expected steering wheel speed 0.370rad / s; expected steering wheel angular acceleration -1.236 rad / s 2 ;

[0100] 2. Calculate the sliding mode input:

[0101]

[0102] Design the sliding mode function parameters and calculate the sliding mode function based on the error:

[0103]

[0104] Where, α is the parameter of the first sliding mode function, 3.2; β is the parameter of the second sliding mode function, 1.75; γ1 is the parameter of the third sliding mode function, 2.15; γ2 is the parameter of the fourth sliding mode function, 1.9; is a saturation function, b=10;

[0105] At this time, the sliding mode function s is 0.859;

[0106] Design the sliding film approach rate parameters and calculate the sliding mode output according to the sliding film function value:

[0107]

[0108] Where, J a is the moment of inertia of the arm, 0.064; J c is the steering wheel-steering column moment of inertia, 0.172; B a is the arm damping coefficient, 0.56; B c is the steering wheel-steering column damping coefficient, 0.57; K a is the arm stiffness, 3.8; K1 is the sliding mode approach rate parameter, 1.5; K2 is the sliding mode approach rate parameter, 3.2;

[0109] Through the above calculation, the tactile assist torque T can be obtained sa , which is 1.369 N·m. This proves that this method can provide the driver with appropriate auxiliary torque, guide the driver to output more appropriate operations, and thus improve the safety and stability of vehicle driving.

[0110] In a specific implementation, the present application provides a computer storage medium and a corresponding data processing unit, wherein the computer storage medium is capable of storing a computer program that, when executed by the data processing unit, can execute the invention content of the method for calculating steering wheel tactile assist torque based on sliding mode control provided by the present invention and some or all of the steps in each embodiment. The storage medium can be a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM).

[0111] Those skilled in the art can clearly understand that the technical solutions in the embodiments of the present invention can be implemented by means of computer programs and their corresponding general hardware platforms. Based on this understanding, the technical solutions in the embodiments of the present invention, in essence or in other words, the part that contributes to the prior art, can be embodied in the form of a computer program, i.e., a software product. The computer program software product can be stored in a storage medium and includes several instructions for enabling a device including a data processing unit (which can be a personal computer, a server, a single-chip microcomputer, a MUU, or a network device, etc.) to execute the methods described in various embodiments of the present invention or certain parts of the embodiments.

[0112] The present invention provides a method and apparatus for calculating steering wheel haptic assist torque based on sliding mode control. While there are numerous methods and approaches for implementing this technical solution, the foregoing description represents only a preferred embodiment of the present invention. It should be noted that those skilled in the art may make improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Components not specified in this embodiment may be implemented using existing technologies.

Claims

1. A method for calculating steering wheel tactile assist torque based on sliding mode control, characterized in that: The following steps are involved: Step 1: Establish the dynamic model of the arm, steering wheel, and steering column; Step 2, define synovial input; Step 3, designing the synovial function; Step 4: Establish a driver preview model; Step 5, calculating and obtaining the tactile assist torque; Step 1 includes: establishing the following dynamic models of the arm, steering wheel, and steering column: Among them, J a is the moment of inertia of the arm; J c is the steering wheel-steering column moment of inertia; is the steering wheel angular acceleration; B a is the arm damping coefficient; B c is the steering wheel-steering column damping coefficient; is the steering wheel speed; K a is the arm stiffness; θ sw is the corner; T h is the steering wheel torque applied by the driver; T s is the steering resistance torque of the steering wheel; T sa is the tactile assist torque; Step 2 includes defining the synovial input as: Where, e is the steering wheel angle error; is the steering wheel speed error; θ swd is the desired steering wheel angle; is the desired steering wheel speed; Step 2 also includes: writing equation (1) into the state equation form about synovial input: Among them, x1 is the first-order synovial input, x1=e, is the first derivative of the first-order sliding mode function; x2 is the second-order sliding mode input, is the first derivative of the second-order sliding mode function; f is the state function, is the desired steering wheel angular acceleration; g is the input function, u is the state equation input, u=T sa ; Step 3 includes: the synovial function s is designed as: Where α is the parameter of the first sliding mode function, α>0; β is the parameter of the second sliding mode function, β>0; γ1 is the parameter of the third sliding mode function, γ1>γ2; γ2 is the parameter of the fourth sliding mode function, 1<γ2<2; sgn(x) is the sign function; The sliding mode control rate is designed as: Among them, K1 is the first sliding mode approaching rate parameter, K1>0; K2 is the second sliding mode approaching rate parameter, K2>0; Step 3 also includes: When using the sliding mode control rate of formula (5), the sliding mode approach rate for: In order to suppress the sliding mode chattering phenomenon, the saturation function sat(x) is used to replace the sign function sgn(x) in Equations (4), (5), and (6). The saturation function is expressed as: Where b is the saturation function parameter, b>0; Substituting the saturation function into equation (5) gives the tactile assist torque: By changing the sliding mode parameters: α, β, γ1, γ2, K1, K2, the actual control effect of the sliding mode can be adjusted; Step 4 includes: establishing the following driver preview model: Where l is the Laplace operator, (l) represents l in the Laplace domain; θ swd (l) is the desired steering wheel angle; τ L is the leading time constant; τ d1 is the delay time constant; τ d2 is the driver's reaction delay time; G h Driver steering proportional gain; ΔY(l) is the lateral deviation between the vehicle's current position and the preview point, expressed as: in, is the lateral position coordinate of the desired path at the preview point; Y(l) is the lateral position coordinate of the current vehicle; φ(l) is the vehicle heading angle; L is the preview distance, expressed as: L=v x t p Among them, v x is the current speed of the vehicle; τ p Preview time for the driver; Write equation (8) in the form of state equation: Where c is the delay time operator, T d is the total delay time, T d =τ d1 +τ d2 ;T p is the total preview time, T p =τ L +τ p ; Step 4 also includes: using the sensor to obtain the longitudinal speed v x , vehicle heading angle φ, lateral position deviation Y d -Y, use the driving characteristic parameters G of the expert driver h , τ L , τ d1 , τ d2 , τ p , according to formula (9), the desired steering wheel angle θ is obtained swd , expected steering wheel speed Expected steering wheel angular acceleration Step 5 includes: using the sensor to obtain the steering wheel angle θ sw , steering wheel speed Combine the results of step 4 to calculate the sliding membrane input of formula (2); use the sensor to obtain the steering wheel torque T applied by the driver h , steering wheel steering resistance torque T s , the synovial input and the steering wheel torque T applied by the driver h , Steering wheel steering resistance torque T s Substituting into formula (7), the tactile assist torque T is finally calculated. sa .

2. A steering wheel tactile assist torque calculation device based on sliding mode control implemented by the method according to claim 1, characterized in that: include: Dynamic model building module, used to build dynamic models of arms, steering wheels, and steering columns; A driver preview model building module is used to build an expert driver preview model; Synovial input definition module, used to define and calculate synovial input; Synovial function design module, used to design and calculate synovial function; The tactile assistance torque calculation module is used to calculate the tactile assistance torque.

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