Control method for automobile steer-by-wire system

Abstract

The invention relates to the technical field of steering systems, in particular to a control method for an automobile steer-by-wire system. The invention discloses a control method for an automobile steer-by-wire system. The control method specifically comprises the following steps: calculating a current steering wheel turning angle according to an electric signal input by a steering wheel angle sensor; the current rack position is calculated according to an electric signal input by a rack position sensor; the steering line angle transmission ratio is set at present according to the electric power steering system; calculating the deformation quantity of a virtual torsion bar according to the difference between the current steering wheel angle and the steering wheel angle at the current rack position; calculating a hand feeling feedback request torque according to the deformation quantity of the virtual torsion bar and the rigidity of the virtual torsion bar; the steering execution torque calculation module calculates the request torque of a steering rack actuator motor according to the hand feeling feedback request torque. Compared with the prior art, the steering rack actuator is used for sensing the acting force borne by the steering wheel, and the corresponding steering hand feeling is simulated in the steering wheel actuator.

Description

Technical Field

[0001] The invention relates to the technical field of steering systems, in particular to a control method for an automobile wire-controlled steering system. Background Art

[0002] With the development of intelligent driving technology, the market demand for steer-by-wire (SbW) systems is also growing. However, as fully autonomous driving solutions are not yet mature, steer-by-wire systems still need to support drivers to manually drive the vehicle and perform lateral control. The traditional control method of the electric power steering system (EPS) is no longer applicable to the steer-by-wire product form.

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

[0004] In the steer-by-wire system, the decoupling of the mechanical connection between the car's steering wheel and the steering rack causes the above-mentioned traditional electric power steering system's steering assist control method and road feel feedback path to no longer be applicable. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a control method for a steer-by-wire system of an automobile, and a method for converting a driver's input to a steering wheel into control of a steering rack actuator in order to adapt the steer-by-wire system.

[0006] To achieve the above purpose, a control method for a car wire steering system is designed, including a wire steering system, the wire steering system 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 through a wire, 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-feel feedback motor, the steering wheel is connected to the hand-feel feedback motor through the steering shaft, the steering wheel angle sensor is connected to the steering shaft, and the hand-feel feedback motor is connected to the controller through a wire; 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, the two ends of the steering rack are respectively connected to the steering wheel through a tie rod, the steering control motor is connected to the controller through a wire, the steering control motor is connected to the steering rack through a transmission mechanism, and 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-feel feedback torque calculation module, and a steering execution torque calculation module, characterized in that: the specific control method is as follows:

[0007] 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 ;

[0008] S2, the rack position detection module calculates the current rack position X according to the electrical signal input by the rack position sensor Rack ;

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

[0010] S4, through the subtractor to the current steering wheel angle σ SW and the steering wheel angle σ at the current rack position Rack2SW Make a difference and calculate the deformation Δσ of the virtual torsion bar;

[0011] S5, the hand-feel feedback torque calculation module calculates the hand-feel feedback request torque τ according to the deformation variable Δσ of the virtual torsion bar and the stiffness k of the virtual torsion bar FeedbackReq ;

[0012] S6, the steering execution torque calculation module requests torque τ according to the hand feel feedback FeedbackReq Calculate the requested torque τ for the steering rack actuator motor SteeringReq .

[0013] In step S5, the hand-feel feedback request torque τ FeedbackReqThe hand-feel feedback motor control module drives the hand-feel feedback motor to output the hand-feel feedback motor torque τ Feedbackmotortorque , and then transmitted to the steering wheel through the steering shaft and acts on 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 The requested torque for the first partial steering operation, τ SteeringReqComponent2 Request torque for the second partial turn execution.

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

[0017] The second part of the steering execution request torque τ SteeringReqComponent2 The steering execution torque calculation module converts the steering rack actuator motor torque value equivalent to the driver's hand force according to the transmission ratio.

[0018] The requested torque τ of the steering rack actuator motor SteeringReq The steering control motor control module drives the steering control motor to output the hand-feel feedback motor torque τ Feedbackmotortorque , which is then converted into the translational motion of the steering rack through the transmission mechanism, and then transmitted to the steering wheel rotation of the car through the tie rod.

[0019] The controller is of integrated or split structure.

[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 present invention converts the driver's input to the steering wheel into a method for controlling a steering rack actuator; utilizes the steering rack actuator to sense the force acting on the steering wheel, and simulates the corresponding steering feel in the steering wheel actuator.

[0022] The present invention restores the force transmission characteristics from the tire to the steering wheel of the intermediate shaft steering system, so the self-centering force generated by the geometric characteristics of the suspension is also fed back in real time and transmitted to the steering wheel. When the vehicle speed increases, the self-centering force of the suspension increases, the self-centering feel is enhanced, and the stability of vehicle control is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structural connection of the electric power steering system of the present invention.

[0024] Figure 2 It is a flow chart of the present invention.

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

[0026] The present invention will be further described below with reference to the accompanying drawings.

[0027] like Figure 1 As shown, it is an example of a wire-controlled steering device applicable to the control method of the present invention, including a steering wheel actuator 1 for collecting the driver's steering control input and providing the driver with steering feel feedback, a steering rack actuator 2 for performing steering control, and a controller 3 for controlling the wire-controlled steering system. The controller 3 is connected to the vehicle bus 4 through a wire to achieve communication with the entire 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 the driver's 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 rotational motion of the motor shaft into rack translation, a rack position sensor 11, a steering rack 12, a tie rod 13 for connecting the steering system and the wheel, and a car steering wheel 14. The controller 3 is connected to the feel feedback motor 8 through a wire to control its output power. The controller 3 is connected to the steering control motor 9 through a wire to control its output power.

[0028] The controller 3 may be as follows Figure 1 The integrated type shown can also be a split type, which is integrated into 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 tactile simulation motor.

[0030] The steering wheel angle measured by the steering wheel angle sensor 7 may also be indirectly measured by a rotor position sensor in the hand-feel feedback motor 8 with higher accuracy.

[0031] The rack position sensor 11 may be a displacement sensor that directly measures the rack position, or may be an angle sensor that measures the rotation angle of a pinion coupled to the steering rack 12 to indirectly measure the rack position. The rack position measured by the rack position sensor 11 may also be indirectly measured by a rotor position sensor in the steering control motor 9 with higher accuracy.

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

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

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

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

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

[0037] The steering control and hand feeling simulation method of the present invention is executed by the controller 3 controlling the steering wheel actuator 1 and the steering rack actuator 2. Figure 2 As shown, the control process of the present invention is as follows:

[0038] 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 ;

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

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

[0041] S4, through the subtractor to the current steering wheel angle σ SW and the steering wheel angle σ at the current rack position Rack2SW Make a difference and calculate the deformation Δσ of the virtual torsion bar;

[0042] S5, the hand-feel feedback torque calculation module calculates the hand-feel feedback request torque τ according to the deformation variable Δσ of the virtual torsion bar and the stiffness k of the virtual torsion bar Feedback Req ;

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

[0044] Hand feedback request torque τ Feedback Req The hand-feel feedback motor control module drives the hand-feel feedback motor 8 to output the hand-feel feedback motor torque τ Feedback motor torque , and then transmitted to the steering wheel 5 through the steering shaft 6, acting on the driver's hands. Feedback Req =k·Δσ.

[0045] The present invention restores the force transmission characteristics from the tire to the steering wheel of the intermediate shaft steering system, so the self-centering force generated by the geometric characteristics of the suspension is also fed back in real time and transmitted to the steering wheel. When the vehicle speed increases, the self-centering force of the suspension increases, the self-centering feel is enhanced, and the stability of vehicle control is improved.

[0046] The present invention will also provide real-time feedback of road surface information. For example, when a vehicle enters a low-friction road surface, only a small level of power assistance is required to change the steering wheel angle, that is, the absolute value of the required Δσ is small, and the resulting hand-feel feedback motor torque τ Feedback motor torque The steering feel will also decrease accordingly, which will be reflected in the driver's hand as a lighter steering feel, reminding the driver that the vehicle is driving on a low-friction road. Similarly, when the vehicle enters an understeering state and the steering wheel tire loses grip, the steering feel will also become lighter accordingly.

[0047] When the vehicle enters an oversteer state, the actual zero position of the steering wheel kingpin force will be offset from the corresponding zero position in the straight direction of the vehicle. This mechanical characteristic will also be reflected in the steering feel to inform the driver of the current vehicle movement status and assist the driver in making correct steering operations.

[0048] When the vehicle passes through an uneven road surface, random road excitation will cause the rack position to change, resulting in a change in the size of Δσ, which in turn causes a change in the hand-feel feedback torque. In the system, a higher sampling frequency of the rack position and steering wheel angle supports a larger hand-feel feedback response frequency range, which can feedback a more dynamic road excitation to the driver's hand, allowing the driver to understand the road conditions more clearly.

[0049] The steering execution torque calculation module calculates the torque τ based on the assumed driver input torque, that is, the hand-feel feedback request torque τ Feedback Req Calculate the requested torque τ for the steering rack actuator motorSteering Req The torque consists of two parts. The first part is calculated from the power-assistance characteristic curve in the traditional electric power steering system, and the second part is calculated from the torque of the power-assistance motor equivalent to the driver's hand force in the traditional electric power steering system. The two parts of the requested torque are added together to become the output value of the rack actuator motor required by the upper and lower decoupled wire control steering system.

[0050] like Figure 3 As shown, in the steering execution torque calculation module, the steering execution request torque τ is calculated Steering Req It mainly consists of two parts. The first part is the first part of the steering execution request torque τ Steering Req Component1 , the imaginary driver input torque, that is, the hand-feel feedback request torque τ Feedback Req The traditional electric power steering assist curve is obtained by looking up the table and calculated by the first part of the steering execution torque calculation module. The assist characteristic curve is calibrated with different values ​​at different vehicle speeds to achieve the characteristic that the steering feel becomes heavier as the vehicle speed increases. There can be more curves at different vehicle speeds. Figure 3 It is only used as an example. For the wire control steering system, it is also necessary to make up for the driver's hand force that cannot be transmitted to the steering rack through the intermediate shaft. Therefore, in the present invention, a second part of the steering execution torque calculation module is designed to convert the steering rack actuator motor torque equivalent to the driver's hand force according to the transmission ratio as the second part of the steering execution request torque τ Steering Req Component2 The above two parts are turned into the requested torque by the adder to obtain the final required requested torque τ Steering Req The requested torque τ Steering Req The steering control motor control module drives the steering control motor 9 to output the hand-feel feedback motor torque τ Feedback motor torque , which is converted into translational motion of the steering rack 12 through the transmission mechanism 10, and then transmitted to the vehicle steering wheel 14 by the tie rod 13 to make it rotate around the kingpin, thereby realizing lateral control of the vehicle.

Claims

1. A control method for a car steering-by-wire system, comprising a steering-by-wire system, the steering-by-wire system comprising a steering wheel actuator, a steering rack actuator, a controller, and a vehicle bus, the steering wheel actuator (1) being connected to the controller (3), the controller (3) being connected to the vehicle bus (4) via a wire, and the controller (3) being connected to the steering rack actuator (2); the steering wheel actuator (1) comprising a steering wheel, a steering shaft, a steering wheel angle sensor, and a hand-feel feedback motor, the steering wheel (5) being connected to the hand-feel feedback motor (8) via a steering shaft (6), a steering wheel angle sensor (7) being connected to the steering shaft (6), and the hand-feel feedback motor (8) being connected to the controller (3) via a wire The steering rack actuator (2) comprises a steering control motor, a transmission mechanism, a rack position sensor, a steering rack, a tie rod, and a steering wheel. The two ends of the steering rack (12) are connected to the steering wheel (14) through tie rods (13), respectively. The steering control motor (9) and the controller (3) are connected through wires. The steering control motor (9) is connected to the steering rack (12) through a transmission mechanism (10). A rack position sensor (11) is connected to the steering rack (12). The controller (3) comprises 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 execution torque calculation module, and is characterized in that: The specific control methods are 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 calculates the current rack position X according to the steering line angle transmission ratio currently set by the electric power steering system Rack Converted into the corresponding steering wheel angle σ Rack2SW ; S4, through the subtractor to the current steering wheel angle σ SW and the steering wheel angle σ at the current rack position Rack2SW Make a difference and calculate the deformation Δσ of the virtual torsion bar; S5, the hand-feel feedback torque calculation module calculates the hand-feel feedback request torque τ according to the deformation variable Δσ of the virtual torsion bar and the stiffness k of the virtual torsion bar FeedbackReq ; S6, the steering execution torque calculation module requests torque τ according to the hand feel feedback FeedbackReq Calculate the requested torque τ for the steering rack actuator motor SteeringReq .

2. A control method for a vehicle steer-by-wire system according to claim 1, characterized in that: In step S5, the hand-feel feedback request torque τ FeedbackReq The hand-feel feedback motor control module drives the hand-feel feedback motor to output the hand-feel feedback motor torque τ Feedbackmotortorque , and then transmitted to the steering wheel through the steering shaft and acts on the driver's hands.

3. A control method for a vehicle steer-by-wire system according to claim 1 or 2, characterized in that: The τ FeedbackReq =k·Δσ.

4. The control method for a vehicle steer-by-wire system according to claim 1, characterized in that: In step S6, the requested torque τ of the steering rack actuator motor is SteeringReq =τ SteeringReqComponent1 +τ SteeringReqComponent2 , where τ SteeringReqComponent1 The requested torque for the first partial steering operation, τ SteeringReqComponent2 Request torque for the second partial turn execution.

5. The control method for a vehicle steer-by-wire system according to claim 4, characterized in that: The first part of the steering execution request torque τ SteeringReqComponent1 Request torque τ through hand feel feedback FeedbackReq The power assist curve of the electric power steering system is obtained by looking up the table.

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

7. The control method for a vehicle steer-by-wire system according to claim 1, characterized in that: The requested torque τ of the steering rack actuator motor SteeringReq The steering control motor control module drives the steering control motor to output the hand-feel feedback motor torque τ Feedbackmotortorque , which is then converted into the translational motion of the steering rack through the transmission mechanism, and then transmitted to the steering wheel rotation of the car through the tie rod.

8. The control method for a vehicle steer-by-wire system according to claim 1, characterized in that: The controller (3) is of an integrated or split structure.

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

Images