Method for steering wheel and front wheel angle coupling alignment for steer-by-wire systems

Abstract

The present application relates to the technical field of steering system, and particularly relates to a method for coupling and aligning a steering wheel and a front wheel steering angle for a steer-by-wire system.A method for coupling and aligning a steering wheel and a front wheel steering angle for a steer-by-wire system includes a steering wheel alignment state machine.Compared with the prior art, the method for coupling and aligning a steering wheel and a front wheel steering angle for a steer-by-wire system can solve the problem of how to realign the coupling after the up-down decoupling of the steer-by-wire system; the method is automatically powered and operated, and does not need to be activated by a human key, thereby improving the flexibility and comfort of the alignment function; when the up-down steering coupling is performed after the completion of the steering wheel alignment, the abnormal sound caused by the large fluctuation of the down steering torque can be avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steering systems, in particular to a method for coupling and aligning the steering wheel and front wheel steering angle of a steer-by-wire system. BACKGROUND

[0002] With the popularization of new energy vehicles and the rapid development of intelligent driving technology, the diversification and intelligentization of vehicle use requirements have become an inevitable trend for future vehicle development. The steering system is a key system for intelligent driving, and will evolve from traditional mechanical steering, hydraulic steering, and electric power steering to steer-by-wire to adapt to higher levels of autonomous driving and future intelligent transportation scenarios.

[0003] Steer-by-wire eliminates the mechanical intermediate shaft that connects the traditional electric power steering system, controls the steering execution motor through an electric control signal, and drives the front wheels to complete steering by the execution motor, thereby achieving mechanical decoupling of the steering wheel and the steering front wheels of the vehicle.

[0004] Without the mechanical intermediate shaft constraint of the steer-by-wire system, the steering wheel mechanism and the front wheel drive mechanism will be separated into two independent control systems, each controlled by its own controller, which can achieve software decoupling and software coupling of the steering wheel mechanism and the front wheel steering angle mechanism. When the upper and lower steering systems are decoupled, steer-by-wire can achieve more functions than traditional steering, such as game mode, steering wheel silence mode, etc. When the steering wheel and the front wheel steering angle are coupled, steer-by-wire can achieve normal steering driving experience as traditional steering. A steering wheel alignment method is needed to achieve coupling between decoupling and coupling of the upper and lower steering. SUMMARY

[0005] The present application overcomes the shortcomings of the prior art and provides a method for coupling and aligning the steering wheel and front wheel steering angle of a steer-by-wire system, allowing the steer-by-wire system to complete the upper and lower coupling action more quickly and comfortably.

[0006] To achieve the above-mentioned purpose, a method for coupling and aligning the steering wheel and front wheel steering angle of a steer-by-wire system is designed, including a steering wheel alignment state machine, characterized in that: the method flow is as follows:

[0007] S1, the steering wheel alignment state machine determines whether the vehicle has been unlocked, and if so, enters the steering wheel alignment angle closed control mode, and the central control screen prompts that the steering wheel enters the alignment mode; otherwise, waits for the opening condition to be met;

[0008] S2, the steering wheel alignment initialization state determines whether to enter the steering wheel alignment execution state according to the condition; when the condition is met, the steering wheel alignment mode is executed;

[0009] S3, if the angle difference between the current steering wheel and front wheel steering angle is less than or equal to 1°, skip step S2 steering wheel alignment execution state, and directly enter the steering wheel alignment completion state;

[0010] S4, if the steering wheel torque is greater than 3Nm during the steering wheel alignment execution process, the steering wheel alignment is interrupted, the system enters the steering wheel alignment interruption state, the central large screen prompts that the steering wheel alignment is interrupted, and enters the steering wheel vibration output control mode, the steering wheel produces vibration to remind the driver to release the steering wheel, and when the steering wheel torque is less than 3Nm, the steering wheel alignment mode is re-executed;

[0011] S5, if the steering wheel alignment process is interrupted more than 3 times, the system exits the steering wheel alignment mode, and prompts on the central large screen that the steering wheel alignment mode is exited;

[0012] S6, after the steering wheel alignment fails, the vehicle needs to be powered on and off again, and the steering wheel alignment mode is executed again.

[0013] S7, after the steering wheel alignment is completed, if it is detected that the vehicle mode starts the game mode or the steering wheel silent mode, jump to the steering wheel alignment start state.

[0014] The steer-by-wire system comprises a steering wheel, a TAS sensor, a steering column, a feel simulation motor, a SAS, a steering execution motor, an upper steering controller, a lower steering controller, a central control screen and vehicle communication. The SAS is an angle sensor, and the TAS sensor is an angle torque sensor. The upper and lower steering controllers communicate with the vehicle communication through a public CAN bus, and the driver controls the switches of several modes through the central control screen. The upper and lower steering controllers transmit their own angle signals and mode signals through a private CAN, and independently control the torque output of the feel simulation motor and the steering execution motor to realize several steer-by-wire driving modes.

[0015] In step S1, it is judged whether the vehicle has been unlocked for the first power-on in the current power-on period or whether the decoupling mode has been exited.

[0016] In step S1, the flow of the steering wheel alignment angle closing control is as follows:

[0017] S11, the current angle of the steering wheel is subtracted from the lower steering angle, and the target angular velocity is obtained by the angle difference curve;

[0018] S12, the target angular velocity is subtracted from the current angular velocity difference, and the target steering wheel alignment motor request torque is obtained by PID control.

[0019] The steering wheel alignment angle closing control module has two sets of configuration parameters corresponding to two alignment scenes:

[0020] (1) Fast alignment: when the vehicle is unlocked by the Bluetooth key, the vehicle detects that the driver is not seated on the seat, and the fast alignment parameter is selected, the purpose is to ensure that the steering wheel is aligned before the driver enters the vehicle;

[0021] (2) Slow alignment: when the game mode or steering wheel mute mode is exited, the vehicle detects that the driver is seated on the seat, and the slow alignment parameter is selected, the purpose is to gently align the steering wheel, not to frighten the driver, and to improve the seniority of the vehicle.

[0022] In step S2, the judgment condition of the alignment initialization state is: (1) the difference between the steering wheel angle and the front wheel turning angle is greater than 1°; (2) whether the current steering wheel torque is less than 2Nm; (3) whether the current steering wheel speed is less than 50° / s; all three conditions are met to execute steering wheel alignment.

[0023] In step S4, the steering wheel vibration output control is calculated by a cosine function to obtain the motor torque M=Acos(ωt+φ)=Acos(2πft+φ)=Acos(360ft+φ), wherein A is the amplitude of the motor output torque, f is the vibration frequency, t is the running time, and φ is the initial phase angle.

[0024] Compared with the prior art, the present application provides a method for coupling and aligning the steering wheel and the front wheel turning angle of a steer-by-wire system, which can solve the problem of how to re-align the coupling after decoupling up and down in the steer-by-wire system; the method is automatically run after power-on, without the need for manual button activation, improving the flexibility and comfort of the alignment function; when the steering wheel is aligned and the up and down steering is coupled, the abnormal noise caused by the large fluctuation of the down turning torque can be avoided. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a schematic diagram of the connection of the steer-by-wire system.

[0026] Figure 2 It is a flowchart of the up and down coupling alignment control strategy of the steering wheel.

[0027] Figure 3 It is a flowchart of the steering wheel alignment state machine.

[0028] Figure 4 It is a flowchart of the steering wheel alignment control strategy.

[0029] Figure 5 It is an angle difference single-loop PID control flowchart.

[0030] Figure 6 It is a vibration output control flowchart.

[0031] Figure 7 It is a relationship curve diagram of the angle difference and the target angular velocity. DETAILED DESCRIPTION

[0032] The application is further described below with reference to the accompanying drawings.

[0033] After the decoupling of the steering wheel mechanism and the front wheel drive mechanism of the steer-by-wire system, the steering wheel mechanism and the front wheel drive mechanism are controlled by the respective controllers to control the respective functions. When the driver enters the driving mode, the angle alignment of the up and down steering needs to be completed, so that the angle sensors of the up and down steering remain consistent, and the coupling of the system can be completed. There are two typical application scenarios:

[0034] 1. Vehicle unlocking and starting: when the vehicle is unlocked by the Bluetooth key, the steering wheel will be coupled and aligned in the up and down angle to ensure that the steering wheel angle and the front wheel angle are consistent when the driver gets on the vehicle. Because the steering wheel may be tilted by the driver during the process of getting off the vehicle after parking.

[0035] 2. Exit of decoupling mode: when the game mode or the steering wheel silent mode exits, the steering wheel angle and the front wheel angle are probably misaligned. The up and down coupling of the steering wheel needs to be performed again.

[0036] The hardware part of the steer-by-wire system mainly includes: steering wheel, TAS sensor (angle and torque sensor), steering column, feel simulation motor, SAS (angle sensor), steering execution motor, up steering controller, down steering controller, central control screen and vehicle communication. The up and down steering controllers communicate with the vehicle through the public CAN bus, and the driver controls the mode switch through the central control screen. The up and down steering controllers transmit the angle signals and mode signals through the private CAN, and independently control the torque output of the feel simulation motor and the steering execution motor to realize different steer-by-wire driving modes.

[0037] Therefore, the application provides a method for coupling and aligning the steering wheel and the front wheel angle of a steer-by-wire system, as shown in Figure 1 , Figure 2 The flow of the method is as follows:

[0038] 1. The steering wheel alignment state machine first determines whether the vehicle has been unlocked, i.e. the first power-on in the current power-on period, or whether the decoupling mode (game mode, steering wheel silent mode, etc.) is exited. The signal is sent by the driver through the central control screen or the voice control system, and is sent to the steering system through the vehicle communication. The steering system determines whether to enter the steering wheel alignment initialization state according to the current conditions (such as whether the vehicle speed signal meets the switching condition), and the central control screen will prompt the steering wheel to enter the steering wheel alignment mode, and please do not hold the steering wheel.

[0039] 2. The steering wheel alignment initialization state determines whether to enter the steering wheel alignment execution state according to the conditions, mainly: (1) the steering wheel angle and the front wheel angle difference is greater than 1° (the limit can be changed according to the requirements); (2) the current steering wheel torque is less than 2Nm (the limit can be changed according to the requirements); (3) the current steering wheel speed is less than 50° / s (the limit can be changed according to the requirements), all the above three conditions are met to execute the steering wheel alignment mode. If the current steering wheel and the front wheel angle difference is less than or equal to 1°, the steering wheel alignment execution state is skipped, and the steering wheel alignment completion state is directly entered.

[0040] 3. If the steering wheel torque is greater than 3Nm during the steering wheel alignment execution process, the steering wheel alignment will be interrupted, the system enters the steering wheel alignment interruption state, the central control large screen will prompt that the steering wheel alignment is interrupted and the steering wheel will vibrate to remind the driver to release the steering wheel. When the steering wheel torque is below 3Nm, the steering wheel alignment mode is re-executed.

[0041] 4. If the steering wheel alignment is interrupted more than 3 times during the steering wheel alignment process, the system will exit the steering wheel alignment mode, and the central control large screen will prompt that the steering wheel alignment mode is exited. After the steering wheel alignment fails, the vehicle needs to be powered on and off again to execute the steering wheel alignment mode again.

[0042] 5. In the steering wheel alignment completion state, if it is detected that the vehicle mode is started in the game mode or the steering wheel is in the silent mode, the state will jump to the steering wheel alignment start state.

[0043] The state signal of the steering wheel alignment state machine will be sent to the central control panel through the vehicle communication to synchronously display the current state. At the same time, it will also be used as one of the conditions for the vehicle mode switching. Only in the alignment completion state, the vehicle can enter the driving mode, and the steering execution motor can execute the steering according to the current angle of the steering wheel.

[0044] Actual case:

[0045] (1) When the steering wheel alignment is completed, the driver can feel that the vehicle movement direction is consistent with the steering direction, which meets the normal driving habit.

[0046] (2) When the steering wheel alignment fails, for example, the steering wheel and the front wheel angle have a 100° angle difference. At this time, if the driver still maintains the steering wheel in the middle position according to the driving habit, expecting to drive straight. Due to the existence of the steering wheel and the front wheel angle difference, the vehicle will deviate to one side. The vehicle running direction is inconsistent with the driver's subjective intention, which will cause the driver's panic and greatly increase the probability of traffic accidents.

[0047] When the state machine is in the alignment execution state, the angle difference single loop PID is used for control, and when the state machine is in the alignment interruption state, the vibration output control is used.

[0048] 1. The angle difference single loop PID control process is as follows:

[0049] (1) The current angle of the steering wheel is subtracted from the next steering angle, and the angle difference curve is obtained to obtain the target angular velocity;

[0050] (2) The target angular velocity is subtracted from the current angular velocity to perform PID control, and the target steering wheel alignment motor request torque is obtained.

[0051] There are two sets of configuration parameters under this control logic, which correspond to the alignment scenarios described above:

[0052] (1) Fast alignment: When the vehicle is unlocked by the Bluetooth key, the vehicle detects that the driver is not seated, and the fast alignment parameters are selected, which aims to ensure that the steering wheel is aligned before the driver enters the vehicle.

[0053] (2) Slow alignment: When the game mode or steering wheel is silent, the vehicle detects that the driver is seated, and the slow alignment parameters are selected, which aims to gently align the steering wheel and not startle the driver, improving the overall sense of seniority.

[0054] 2. The vibration output control is constructed by a cosine function: M=Acos(ωt+φ)=Acos(2πft+φ)=Acos(360ft+φ), where A is the amplitude of the motor output torque, f is the vibration frequency, t is the running time, and φ is the initial phase angle.

[0055] In the vibration output control algorithm, the running logic is as follows: after the steering wheel alignment is completed, the system can enter the driving mode, and the central control screen will prompt the driver to take over the vehicle. When entering the human driving mode, the lower steering system enters the driving mode from the alignment mode by judging the steering wheel alignment state machine, and the lower steering angle ring control will increase a torque buffer strategy, i.e. the angle ring torque in this state is increased within a certain gradient limit. In order to prevent a large instantaneous force from appearing in the control when entering the driving mode, a small angle difference will cause some abnormal noise. When the lower steering angle responds to the upper steering angle, the system enters the human driving mode, and the steering wheel alignment coupling is completed.

[0056] The present application can solve the problem of how to re-align and couple after decoupling of the steer-by-wire system; the steering wheel alignment method automatically runs after power-on, without the need for manual button activation, improving the flexibility and comfort of the alignment function; and when the steering wheel alignment is completed and the upper and lower steering is coupled, the abnormal noise caused by large fluctuations in the lower steering torque can be avoided.

Claims

1. A method for steering wheel to front wheel steering angle coupling alignment for a steer-by-wire system, comprising a steering wheel alignment state machine, characterized by: The method flow is as follows: S1, the steering wheel alignment state machine judges whether the whole vehicle has been unlocked, yes, enter the steering wheel alignment angle closed control mode, and the central control large screen prompts that the steering wheel enters the alignment mode; otherwise, wait for the opening condition to be met; S2, the steering wheel alignment initialization state judges whether to enter the steering wheel alignment execution state according to the condition; when the condition is met, the steering wheel alignment mode is executed; S3, if the angle difference between the current steering wheel and the front wheel rotation angle is less than or equal to 1°, skip step S2 steering wheel alignment execution state, and directly enter the steering wheel alignment completion state; S4, if the steering wheel torque is greater than 3Nm during the steering wheel alignment execution process, the steering wheel alignment is interrupted, the system enters the steering wheel alignment interruption state, the central control large screen prompts that the steering wheel alignment is interrupted and enters the steering wheel vibration output control mode, the steering wheel produces vibration to remind the driver to release the steering wheel, and when the steering wheel torque is below 3Nm, the steering wheel alignment mode is re-executed; S5, if the steering wheel alignment is interrupted more than 3 times during the steering wheel alignment process, the system exits the steering wheel alignment mode, and prompts on the central control large screen that the steering wheel alignment mode is exited; S6, after the steering wheel alignment fails, the whole vehicle needs to be powered on and off again, and step S1 steering wheel alignment mode is executed again; S7, after the steering wheel alignment is completed, if it is detected that the whole vehicle mode opens the game mode or the steering wheel silent mode, jump to the steering wheel alignment start state.

2. A method of steering wheel to front wheel steering angle coupling alignment for a steer-by-wire system according to claim 1, characterized in that: The steer-by-wire system comprises a steering wheel, a TAS sensor, a steering column, a feel simulation motor, a SAS, a steering execution motor, an upper steering controller, a lower steering controller, a central control screen and whole vehicle communication. The SAS is an angle sensor, and the TAS sensor is an angle torque sensor. The upper and lower steering controllers communicate with the whole vehicle through a public CAN bus, and the driver controls the opening and closing of several modes through the central control screen. The upper and lower steering controllers transmit their own angle signals and mode signals through a private CAN, and independently control the torque output of the feel simulation motor and the steering execution motor to realize several steer-by-wire driving modes.

3. The method for steering wheel to front wheel angle coupling alignment for a steer-by-wire system of claim 1, wherein: In step S1, it is judged whether the whole vehicle has been unlocked for the first power-on period or whether the decoupling mode is exited.

4. The method for steering wheel to front wheel angle coupling alignment for a steer-by-wire system of claim 1, wherein: In step S1, the steering wheel alignment angle closed control flow is as follows: S11, difference between the current angle of the steering wheel and the lower steering angle is obtained, and the angle difference curve is used to obtain the target angular velocity; S12, PID control is performed on the difference between the target angular velocity and the current angular velocity to obtain the target steering wheel alignment motor request torque.

5. The method for steering wheel to front wheel angle coupling alignment for a steer-by-wire system of claim 1, wherein: The steering wheel alignment angle closed control module has two sets of configuration parameters corresponding to two alignment scenes: (1) fast alignment: when the whole vehicle is unlocked through the Bluetooth key, the whole vehicle detects that the driver is not sitting on the seat, and the fast alignment parameters are selected, the purpose is to ensure that the steering wheel is aligned before the driver enters the vehicle; (2) slow alignment: when the game mode or the steering wheel silent mode is exited, the whole vehicle detects that the driver is on the seat, and the slow alignment parameters are selected, the purpose is to align the steering wheel smoothly and not to surprise the driver, and to improve the seniority of the whole vehicle.

6. The method for steering wheel to front wheel steering angle coupling alignment for a steer-by-wire system of claim 1, wherein: The judgment condition of the alignment initialization state in the step S2 is: (1) the difference between the steering wheel angle and the front wheel turning angle is greater than 1°; (2) the current steering wheel torque is less than 2Nm; (3) the current steering wheel rotating speed is less than 50° / s. All the three conditions are met to execute the steering wheel alignment.

7. The method for steering wheel to front wheel angle coupling alignment for a steer-by-wire system of claim 1, wherein: In the step S4, the steering wheel vibration output control is calculated by a cosine function to obtain the motor torque M=Acos(ωt+φ)=Acos(2πft+φ)=Acos(360ft+φ), wherein A is the amplitude of the motor output torque, f is the vibration frequency, t is the running time, and φ is the initial phase angle.

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