Rear-Axle Torque Vectoring for Low-Speed Steer-by-Wire Control
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Solution Overview
Problem
Existing steer-by-wire steering systems for motor vehicles lack the ability to enable rear-axle steering at low speeds without modifying the drive system, which hampers maneuverability and turning circle performance.
Innovation Solution
A method for controlling a steer-by-wire steering system that activates rear axle steering by distributing differential drive torque between the rear wheels, using a torque vectoring mechanism to counteract understeer or oversteer, and generates a yaw moment to improve agility and stability, especially during low-speed maneuvers, without modifying the existing drive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If rear-axle steering is activated at low speeds to improve maneuverability, then turning circle and maneuverability are improved, but the drive system requires modification which increases device complexity
Solution Approach 1:
The patent replaces the need for mechanical drive system modifications with a control-based solution. The existing single-wheel drive is controlled to generate differential torques at the rear wheels through brake intervention and torque vectoring, achieving rear-axle steering functionality without mechanical changes to the drive train.
Solution Approach 2:
The patent changes the torque distribution parameters between the rear wheels to achieve steering effect. By dynamically adjusting the differential torque between left and right rear wheels based on steering angle and vehicle speed, the system achieves rear-axle steering without mechanical modifications.
2Speed
If differential drive torque is applied to rear wheels for steering, then steering torque is generated improving low-speed agility, but energy consumption increases
Solution Approach 1:
The patent applies differential drive torque periodically or intermittently rather than continuously. The system activates rear-axle steering only when vehicle speed is below a threshold and steering input is detected, deactivating it when not needed, thereby reducing overall energy consumption while maintaining low-speed agility when required.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances vehicle maneuverability and stability at low speeds by generating a steering torque through differential drive torque distribution, allowing for improved turning performance without the need for mechanical modifications to the drive system.
Implementation Method 1
a braking system for the rear wheel to be braked arranged on the drive train, wherein the braking torque generated by the braking system is transmitted via the drive shaft of the rear-wheel drive to the wheel to be braked
Implementation Method 2
a single wheel drive which is assigned to one of the two axles and drives the two wheels of the corresponding axle via a differential
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a method for controlling a steer-by-wire steering system for a motor vehicle (1), wherein the motor vehicle (1) comprises two axles (10, 20), each having two wheels (RL, RR, FL, FR), wherein the two front wheels (FL, FR) are steerable by means of front wheel steering and the two rear wheels (RL, RR) are steerable by means of rear wheel steering, and the motor vehicle (1) comprises a single wheel drive (2, 6), which is associated with one of the two axles (10, 20) and which drives the two wheels of the corresponding axle via a differential, wherein the motor vehicle (1) comprises an on-board brake system and the method comprises the following steps: checking the motor vehicle speed; activating rear axle steering if a motor vehicle speed is lower than 40 km/h; wherein when the rear axle steering is active the following steps are carried out; deactivating the front wheel steering and the rear wheel steering; determining a setpoint position of the first steering rod (SR, ref) by means of a setpoint wheel steering angle (αRw,ref); determining a differential drive torque (ΔΤ) between the two rear wheels (RL, RR) by means of a control unit in order to reach the setpoint position (SR,ref).