A control method for a steer-by-wire steering system

Abstract

The present application relates to the technical field of steering system, and particularly relates to a control method for a vehicle steer-by-wire system.A control method for a vehicle steer-by-wire system, and the specific control method is as follows: calculating a current steering wheel angle according to an electrical signal input by a steering wheel angle sensor; calculating a current rack position according to an electrical signal input by a rack position sensor; calculating a steering wire angle transmission ratio currently set by an electric power steering system; calculating a deformation variable of a virtual torsion bar by subtracting the current steering wheel angle from the current rack position; calculating a hand feeling feedback request torque according to the deformation variable of the virtual torsion bar and the rigidity of the virtual torsion bar; and calculating a request torque for a steering rack actuator motor by a steering execution torque calculation module according to the hand feeling feedback request torque.Compared with the prior art, the method perceives the force acting on the steering wheel by the steering rack actuator, and simulates the corresponding steering hand feeling in the steering wheel actuator.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steering system, in particular to a control method for a steer-by-wire steering system. BACKGROUND

[0002] With the development of intelligent driving technology, the market demand for steer-by-wire steering system (SbW) is also increasingly strong. However, in today's fully automated driving scheme is not mature, the steer-by-wire steering system still needs to support the driver to manually drive the vehicle, and to perform lateral control. The control method of the traditional electric power steering system (EPS) cannot be applied to the steer-by-wire steering system.

[0003] In the electric power steering system: 1. The steering control unit calculates the corresponding steering assist force according to the torque size of the steering wheel exerted by the driver, and outputs the steering assist force by the servo motor to assist the driver to complete the steering control; 2. The force of the ground on the tire can be transmitted to the steering wheel through the intermediate shaft, and finally to the driver's hand. This force acting on the driver's hand contains information such as the motion state of the vehicle, the road adhesion, and the road surface condition. In principle, part of the mechanical information transmitted to the driver's hands through the above path can assist the driver to better complete the lateral control of the vehicle.

[0004] In the steer-by-wire steering system, the decoupling of the mechanical connection between the steering wheel and the steering rack results in that the steering assist control method and the road feel feedback path of the traditional electric power steering system are no longer applicable. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the present application provides a control method for a steer-by-wire steering system. In order to adapt to the steer-by-wire steering system, the method converts the input of the driver to the steering wheel into the control of the steering rack actuator.

[0006] To achieve the above objectives, a control method for a vehicle steer-by-wire system is designed, comprising a steer-by-wire system, which includes a steering wheel actuator, a steering rack actuator, a controller, and a vehicle bus. The steering wheel actuator is connected to the controller, the controller is connected to the vehicle bus via wires, and the controller is connected to the steering rack actuator. The steering wheel actuator includes a steering wheel, a steering shaft, a steering wheel angle sensor, and a hand feedback motor. The steering wheel is connected to the hand feedback motor via the steering shaft, and the steering wheel angle sensor is connected to the steering shaft. The hand feedback motor is connected to the controller via wires. The steering rack actuator includes a steering control motor, a transmission mechanism, a rack position sensor, a steering rack, a tie rod, and a steering wheel. Both ends of the steering rack are connected to the steering wheel via tie rods. The steering control motor is connected to the controller via wires, and the steering control motor is connected to the steering rack via the transmission mechanism. The rack position sensor is connected to the steering rack. The controller includes a steering wheel angle detection module, a rack position detection module, a steering wheel angle calculation module, a hand feedback torque calculation module, and a steering torque calculation module. The specific control method is as follows:

[0007] S1, the steering wheel angle detection module calculates the current steering wheel angle σ based on the electrical signal input from the steering wheel angle sensor. SW ;

[0008] S2, the rack position detection module calculates the current rack position X based on the electrical signal input from the rack position sensor. Rack ;

[0009] S3, the steering wheel angle calculation module calculates the current rack position X based on the steering line angle transmission ratio currently set in the electric power steering system. Rack Converted to the corresponding steering wheel angle σ Rack2SW ;

[0010] S4, subtracts the current steering wheel angle σ. SW The steering wheel angle σ at the current rack position Rack2SW By taking the difference, the deformation Δσ of the virtual torsion bar is calculated;

[0011] S5, the tactile feedback torque calculation module calculates the tactile feedback request torque τ based on the deformation Δσ and stiffness k of the virtual torsion bar. FeedbackReq ;

[0012] S6, the steering torque calculation module requests torque τ based on the feel feedback. FeedbackReq Calculate the requested torque τ for the steering rack actuator motor. SteeringReq .

[0013] In step S5, the tactile feedback requests torque τ FeedbackReqThe haptic feedback motor is driven by the haptic feedback motor control module, which outputs the haptic feedback motor torque τ. Feedbackmotortorque Then, the signal is transmitted through the steering shaft to the steering wheel and finally to the driver's hands.

[0014] The τ FeedbackReq = k·Δσ.

[0015] In step S6, the requested torque τ of the steering rack actuator motor is... SteeringReq =τ SteeringReqComponent1 +τ SteeringReqComponent2 , where τ SteeringReqComponent1 For the first part of the steering execution request torque, τ SteeringReqComponent2 The second part is the torque requested for steering.

[0016] The first part of the steering execution request torque τ SteeringReqComponent1 Request torque τ through tactile feedback FeedbackReq The power steering curve of the electric power steering system was obtained by looking up a table.

[0017] The second part refers to the steering execution request torque τ. SteeringReqComponent2 The steering torque calculation module calculates the equivalent steering rack actuator motor torque value based on the transmission ratio by converting the driver's hand force.

[0018] The requested torque τ for the steering rack actuator motor SteeringReq The steering control motor is driven by the steering control motor control module, which outputs a torque τ that provides feedback to the steering motor. Feedbackmotortorque The motion is then converted into translational motion of the steering rack via the transmission mechanism, and then transmitted to the steering wheels of the car via the tie rod.

[0019] The controller can be either integrated or separate.

[0020] The transmission mechanism is a worm gear reducer or a ball screw reducer.

[0021] Compared with the prior art, the present invention provides a control method for a car steer-by-wire system. In order to adapt to the steer-by-wire system, the method converts the driver's input to the steering wheel into control of the steering rack actuator; and uses the steering rack actuator to sense the force on the steering wheel and simulates the corresponding steering feel in the steering wheel actuator.

[0022] This invention replicates the force transmission characteristics from the tires to the steering wheel in a steering system with an intermediate shaft. Therefore, it also provides real-time feedback on the self-centering force generated by the suspension's geometry, transmitting it to the steering wheel. As vehicle speed increases, the suspension's self-centering force increases, enhancing the self-centering feel and improving vehicle handling stability. Attached Figure Description

[0023] Figure 1 The structure connection diagram of the electric power steering system of the present application.

[0024] Figure 2 The flow chart of the present application.

[0025] Figure 3 The control flow chart of the steering execution torque calculation module. DETAILED DESCRIPTION

[0026] The present application is further explained below with reference to the accompanying drawings.

[0027] As Figure 1 shown, it is an example of steer-by-wire device applying the control method of the present application, including a steering wheel actuator 1 for collecting driver steering control input and providing driver steering feel feedback, a steering rack actuator 2 for executing steering control, and a controller 3 for controlling the steer-by-wire system. The controller 3 is connected with the vehicle bus 4 through wires to realize communication with the whole vehicle. The steering wheel actuator 1 includes a steering wheel 5, a steering shaft 6 for transmission, a steering wheel angle sensor 7 for collecting driver input, and a feel feedback motor 8; the steering rack actuator 2 includes a steering control motor 9, a transmission mechanism 10 for converting the rotary motion of the motor shaft into the translation of the rack, a rack position sensor 11, a steering rack 12, a tie rod 13 for connecting the steering system with the wheels, and a vehicle steering wheel 14. The controller 3 is connected with the feel feedback motor 8 through wires to control its output power. The controller 3 is connected with the steering control motor 9 through wires to control its output power.

[0028] The controller 3 can be integrated as Figure 1 shown, or can be separated and integrated in the steering wheel actuator 1 and the steering rack actuator 2 respectively.

[0029] The steering shaft 6 can also be a speed reducer for amplifying the torque of the feel simulation motor.

[0030] The steering wheel angle measured by the steering wheel angle sensor 7 can also be indirectly measured by the rotor position sensor in the feel feedback motor 8 with higher precision.

[0031] The rack position sensor 11 can be a displacement sensor for directly measuring the rack position, or can be an angle sensor for indirectly measuring the rack position by measuring the rotation angle of a pinion gear coupled with the steering rack 12. The rack position measured by the rack position sensor 11 can also be indirectly measured by the rotor position sensor in the steering control motor 9 with higher precision.

[0032] The transmission mechanism 10 can be a worm gear speed reducer, a ball screw speed reducer, or other types of transmission mechanisms.

[0033] The above directly or indirectly measured angle or position information, combined with the vehicle speed signal obtained from the vehicle bus 4, is passed as input to the controller 3 for steering control and steering feel simulation.

[0034] The steering control torque of the conventional electric power steering is generated based on the driver input torque calculated from the elastic deformation of the torsion bar. At various vehicle speeds, the motor assistance curve corresponding to different driver input torques is calibrated as the assistance characteristic of the steering system.

[0035] In the online steering system of the present application, the driver input torque corresponding to the current steering wheel angle and the steering wheel angle corresponding to the current rack position is calculated based on the angle difference between the two, combined with the torsion bar stiffness in the conventional electric power steering system. This torque is used as input to the adjusted assistance curve of the conventional electric power steering system, and is output by the steering rack actuator to simulate the top-down force transmission characteristic of the conventional steering and complete the steering control of the online steering system. At the same time, the steering wheel actuator generates a torque of the same size as the steering feel, which is applied to the steering wheel 5 through the steering shaft 6 to simulate the bottom-up force transmission characteristic of the conventional steering.

[0036] The present application replaces the torsion bar and intermediate shaft in the conventional electric power steering system with a virtual intermediate shaft - control device, which is conducive to better restoring the top-down force transmission characteristic from the steering wheel to the tire and the bottom-up force transmission characteristic from the tire to the steering wheel of the conventional steering.

[0037] The steering control and feel simulation method in the present application is executed by the controller 3 controlling the steering wheel actuator 1 and the steering rack actuator 2. As shown in Figure 2 , the control flow of the present application is as follows:

[0038] S1, the steering wheel angle detection module calculates the current steering wheel angle σ SW from the electrical signal input by the steering wheel angle sensor;

[0039] S2, the rack position detection module calculates the current rack position X Rack from the electrical signal input by the rack position sensor;

[0040] S3, the steering wheel angle calculation module converts the current rack position X Rack into the corresponding steering wheel angle σ Rack2SW according to the steering ratio of the electric power steering system currently set;

[0041] S4, the difference between the current steering wheel angle σ SW and the steering wheel angle σ Rack2SW corresponding to the current rack position is calculated by a subtracter to obtain the deformation of the virtual torsion bar Δσ;

[0042] S5, the tactile feedback torque calculation module calculates the tactile feedback request torque τ based on the deformation Δσ and stiffness k of the virtual torsion bar. Feedback Req ;

[0043] S6, the steering torque calculation module requests torque τ based on the feel feedback. Feedback Req Calculate the requested torque τ for the steering rack actuator motor. Steering Req .

[0044] tactile feedback request torque τ Feedback Req The haptic feedback motor 8 is driven by the haptic feedback motor control module, which outputs the haptic feedback motor torque τ. Feedback motor torque Then, it is transmitted through the steering shaft 6 to the steering wheel 5, and then to the driver's hands. Wherein, τ Feedback Req = k·Δσ.

[0045] This invention replicates the force transmission characteristics from the tires to the steering wheel in a steering system with an intermediate shaft. Therefore, it also provides real-time feedback on the self-centering force generated by the suspension's geometry, transmitting it to the steering wheel. As vehicle speed increases, the suspension's self-centering force increases, enhancing the self-centering feel and improving vehicle handling stability.

[0046] This invention also provides real-time feedback on road surface information. For example, when a vehicle enters a low-friction road surface, only a small level of assistance is needed to change the steering wheel angle, meaning the absolute value of the required Δσ is small, resulting in a smaller torque τ generated by the hand-feel feedback motor. Feedback motor torque This decreases accordingly, resulting in a lighter steering feel for the driver, serving as a reminder that the vehicle is on a low-friction surface. Similarly, when the vehicle enters an understeer state and the steering wheel tires lose traction, the steering feel will also become lighter.

[0047] When a vehicle enters an oversteer state, the true zero point of the force on the kingpin of the steering wheel shifts from the zero point corresponding to the straight-line direction of the vehicle. This mechanical characteristic is also reflected in the steering feel to inform the driver of the current vehicle motion status and assist the driver in making the correct steering operation.

[0048] When a vehicle travels over uneven surfaces, random road surface excitations cause changes in the rack position, resulting in variations in the magnitude of Δσ, which in turn causes changes in the tactile feedback torque. In this system, a higher sampling frequency for rack position and steering wheel angle supports a wider tactile feedback response frequency range, enabling the system to deliver more dynamic road surface excitations to the driver, allowing for a clearer understanding of road conditions.

[0049] The steering torque calculation module calculates the steering torque based on the hypothetical driver input torque, i.e., the feel feedback request torque τ. Feedback Req Calculate the requested torque τ for the steering rack actuator motor.Steering Req The torque consists of two parts. The first part is calculated from the power assist characteristic curve of a conventional electric power steering system, and the second part is calculated from the torque of the power assist motor equivalent to the driver's hand force in a conventional electric power steering system. The two requested torques are added together to obtain the rack actuator motor output value required by the decoupled steer-by-wire system.

[0050] like Figure 3 As shown, in the steering torque calculation module, the calculated steering torque τ is the requested torque for steering execution. Steering Req It mainly consists of two parts. The first part is the steering execution request torque τ. Steering Req Component1 The torque input by the hypothetical driver, i.e., the torque requested by the feel feedback, is τ. Feedback Req The power steering assist curve for traditional electric power steering is obtained through table lookup and calculated by the steering torque calculation module in the first part. The assist characteristic curve is calibrated with different values ​​at different vehicle speeds to achieve the characteristic of increasing steering feel with increasing vehicle speed. Multiple curves can be generated for different vehicle speeds. Figure 3 This is merely an example. For steer-by-wire systems, it is also necessary to supplement the portion of the driver's hand force that cannot be transmitted to the steering rack via the intermediate shaft. Therefore, in this invention, a second steering torque calculation module is designed to calculate the equivalent torque of the steering rack actuator motor based on the transmission ratio, which serves as the second steering request torque τ. Steering Req Component2 The two parts of the steering request torque are summed by an adder to obtain the final required request torque τ. Steering Req The requested torque τ Steering Req The steering control motor 9, driven by the steering control motor control module, outputs a hand feel feedback motor torque τ. Feedback motor torque The motion is converted into translational motion of the steering rack 12 by the transmission mechanism 10, and then transmitted to the steering wheel 14 by the tie rod 13, causing it to rotate around the kingpin, thereby achieving lateral control of the vehicle.

Claims

1. A control method for a steer-by-wire steering system, comprising a steer-by-wire steering system, the steer-by-wire steering system comprising a steering wheel actuator, a steering rack actuator, a controller, a vehicle bus, the steering wheel actuator (1) being connected with the controller (3), the controller (3) being connected with the vehicle bus (4) through a wire, the controller (3) being connected with the steering rack actuator (2); the steering wheel actuator (1) comprising a steering wheel, a steering shaft, a steering wheel angle sensor, a feel feedback motor, the steering wheel (5) being connected with the feel feedback motor (8) through the steering shaft (6), the steering wheel angle sensor (7) being connected on the steering shaft (6), the feel feedback motor (8) being connected with the controller (3) through a wire; the steering rack actuator (2) comprising a steering control motor, a transmission mechanism, a rack position sensor, a steering rack, a tie rod, a steering wheel, the steering rack (12) being connected with the steering wheel (14) through the tie rod (13) at both ends, the steering control motor (9) being connected with the controller (3) through a wire, the steering control motor (9) being connected with the steering rack (12) through the transmission mechanism (10), the rack position sensor (11) being connected on the steering rack (12); the controller (3) comprising a steering wheel angle detection module, a rack position detection module, a steering wheel angle calculation module, a feel feedback torque calculation module, a steering execution torque calculation module, characterized in that: The specific control method is as follows: S1, the steering wheel angle detection module calculates the current steering wheel angle σ according to the electrical signal input by the steering wheel angle sensor SW ; S2, the rack position detection module calculates the current rack position X according to the electrical signal input by the rack position sensor Rack ; S3, the steering wheel angle calculation module converts the current rack position X into the corresponding steering wheel angle σ according to the steering line angle transmission ratio currently set by the electric power steering system Rack ; and Rack2SW ; S4, the steering wheel angle σ is calculated by subtracting the current rack position from the current steering wheel angle σ SW and the steering wheel angle σ Rack2SW The deformation amount Δσ of the virtual torsion bar is calculated by subtracting the current rack position from the current steering wheel angle σ S5, the hand feeling feedback torque calculation module calculates the hand feeling feedback requested torque τ according to the deformation amount Δσ of the virtual torsion bar and the stiffness k of the virtual torsion bar FeedbackReq ; S6, the steering execution torque calculation module calculates the requested torque τ based on the steering feel feedback FeedbackReq The requested torque τ for the steering rack actuator motor is calculated SteeringReq .

2. The control method for the steer-by-wire steering system according to claim 1, characterized by: The step S5, the hand feeling feedback request torque τ FeedbackReq The hand feeling feedback motor is driven by the hand feeling feedback motor control module to output a hand feeling feedback motor torque τ Feedbackmotortorque And then transmitted to the steering wheel through the steering shaft and acts on the driver's hand.

3. The control method for the steer-by-wire steering system according to claim 1 or 2, characterized by: The τ FeedbackReq = k Δσ.

4. The control method for the steer-by-wire steering system according to claim 1, characterized by: The request torque τ for the steering rack actuator motor in step S6 SteeringReq = τ SteeringReqComponent1 + τ SteeringReqComponent2 , where τ SteeringReqComponent1 is the first partial steering execution request torque and τ SteeringReqComponent2 is the second partial steering execution request torque.

5. The control method for the steer-by-wire steering system according to claim 4, characterized by: The first part of the steering execution request torque τ SteeringReqComponent1 The hand feeling feedback request torque τ FeedbackReq The power curve table of the electric power steering system is obtained.

6. The control method for the steer-by-wire steering system according to claim 4, characterized by: The second part of the steering execution request torque τ SteeringReqComponent2 The steering rack actuator motor torque value equivalent to the driver hand force is converted by the steering execution torque calculation module according to the transmission ratio.

7. The control method for the steer-by-wire steering system according to claim 1, characterized by: The request torque τ of the steering rack actuator motor SteeringReq The steering control motor output hand feeling feedback motor torque τ is driven by the steering control motor control module Feedbackmotortorque And then converted into the translation of the steering rack by the transmission mechanism, and then transmitted to the automobile steering wheel rotation by the tie rod.

8. The control method for the steer-by-wire steering system according to claim 1, characterized by: The controller (3) is integrated or split structure.

9. The control method for the steer-by-wire steering system according to claim 1, characterized by: The transmission mechanism (10) is worm gear reducer or ball screw reducer.

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