Steer-By-Wire Emergency Steering via Front Brake Torque Vectoring
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Solution Overview
Problem
Existing steer-by-wire steering systems in motor vehicles lack an effective emergency steering mode that does not impair steering behavior and do not require costly mechanical fallback systems.
Innovation Solution
Implement a method for controlling a steer-by-wire steering system using brake-based torque vectoring, where a control unit determines a target wheel steering angle and brake pressure to achieve emergency steering by selectively braking one front wheel, with an open or partially open differential to compensate for vehicle speed loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical fallback function is provided for emergency steering, then steering reliability is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical fallback steering system with an electrical/electronic solution using brake-based torque vectoring. The control system uses the existing braking system to generate differential braking forces on the front wheels, creating a yaw moment that enables emergency steering without any mechanical connection between the steering wheel and wheels. This substitution eliminates the need for costly mechanical fallback components while maintaining emergency steering capability.
Solution Approach 2:
The patent makes the braking system serve a dual function: its primary function of decelerating the vehicle and its secondary function of enabling emergency steering through differential torque application. By using the same braking components for both purposes, the system eliminates the need for separate mechanical fallback steering components, reducing overall system complexity and cost while maintaining reliability.
2Device complexity
If brake-based torque vectoring is used for emergency steering, then device complexity is reduced, but vehicle speed is reduced due to braking
Solution Approach 1:
The patent applies partial braking force only to one front wheel rather than braking both wheels equally. This differential braking creates the necessary yaw moment for steering while minimizing the overall deceleration effect on the vehicle. The braking torque is carefully controlled to be just sufficient for steering purposes without excessively reducing vehicle speed.
Solution Approach 2:
The patent dynamically adjusts the braking torque parameter based on the steering demand and vehicle operating conditions. By modulating the magnitude of the braking force applied to the individual wheel, the system optimizes the balance between generating sufficient yaw moment for effective emergency steering and minimizing the adverse effect on vehicle speed.
3Measurement precision
If differential braking is applied to achieve target steering angle, then steering precision is improved, but steering behavior is impaired due to speed loss
Solution Approach 1:
The patent implements a closed-loop control system that continuously monitors the actual wheel steering angle and compares it with the target steering angle. Based on this feedback, the control system adjusts the differential braking torque in real-time to achieve and maintain the desired steering angle, ensuring precise steering control while compensating for any speed variations caused by braking.
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
Enables improved emergency steering without a mechanical fallback system, ensuring vehicle control and maintaining speed during failures, while reducing costs and complexity.
Implementation Method 1
braking the front wheel to be braked
Implementation Method 2
the wheel drive is a front-wheel drive with an open differential which drives the unbraked front wheel in emergency steering mode
Data Source
Figure 1~2
Figure 3~5
AI summary
The invention relates to a method for controlling a steer-by-wire steering system in an emergency steering mode, 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 are connected to each other by a steering rod (3) of a steering system (4) of the front wheel steering, and the motor vehicle (1) comprises a single wheel drive, which is associated with one of the two axles (10, 20) and which drives the two wheels of the corresponding axle by means of a differential, wherein the wheel drive comprises a single actuator (2), and wherein the motor vehicle (1) comprises a brake system and the method comprises the following steps: examining the steering system for the presence of an error state; carrying out the emergency steering mode in the event that an error state has been detected and carrying out the following steps: determining a target position of the steering rod (SR,ref) by means of a target wheel steering angle (αRW,ref); determining a front wheel (FL, FR) to be braked and a brake pressure for achieving the target position (SR,ref) by means of a control unit; transmitting the front wheel (FL, FR) to be braked and the brake pressure to the brake system and braking the front wheel (FL, FR) to be braked; increasing a torque provided by the wheel drive in order to compensate for a loss of speed of the vehicle (1) caused by the braking of the front wheel (FL, FR) to be braked.