Steering System Torque-Based Fallback Control
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Solution Overview
Problem
Existing motor vehicle steering systems face reliability challenges, particularly in steer-by-wire and superimposed steering systems, where mechanical malfunctions or sensor failures can lead to loss of steerability, especially when the steering angle sensor fails, making it difficult to control the vehicle safely.
Innovation Solution
A motor vehicle steering system that stores a relationship between handlebar travel speed and torque applied via the steering handle in the control unit, allowing the steering actuator to control handlebar travel speed based on torque detected by the torque sensor in fallback mode, ensuring vehicle maneuverability without relying on handlebar position, thus maintaining steerability even with mechanical blockages or sensor failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the steering angle sensor is used to control the steering actuator in normal operation, then the steering control is precise and responsive, but the system reliability decreases when the sensor fails or mechanical malfunctions occur
Solution Approach 1:
The torque sensor acts as an intermediary backup mechanism that detects driver input through torque application to the steering column. When the primary steering angle sensor fails or mechanical linkages malfunction, the torque sensor provides alternative control information to the control unit, enabling the steering system to maintain functionality without requiring complete system duplication.
Solution Approach 2:
The system switches from controlling steering based on angular position parameters (steering angle sensor) to controlling based on torque parameters (torque sensor). This parameter change allows the system to maintain steering control under different operational conditions, improving reliability without adding redundant sensors.
2Reliability
If a second steering angle sensor is provided to protect the first sensor, then the steering system reliability improves, but the device complexity and cost increase
Solution Approach 1:
The torque sensor serves multiple functions: it normally detects driver torque input for steering control, and additionally acts as a backup sensing mechanism when the steering angle sensor fails. This multi-functionality eliminates the need for a complete sensor duplication while maintaining system reliability.
Solution Approach 2:
The torque sensor acts as an intermediary backup mechanism that detects driver input through torque application to the steering column. When the primary steering angle sensor fails or mechanical linkages malfunction, the torque sensor provides alternative control information to the control unit, enabling the steering system to maintain functionality without requiring complete system duplication.
3Reliability
If the steering actuator is controlled based on torque sensor signals in fallback mode, then the steering system can maintain functionality after sensor failure, but the steering response may be less precise
Solution Approach 1:
The system switches from controlling steering based on angular position parameters (steering angle sensor) to controlling based on torque parameters (torque sensor). This parameter change allows the system to maintain steering control under different operational conditions, improving reliability without adding redundant sensors.
Solution Approach 2:
In fallback mode, the system uses partial information (torque magnitude) rather than complete steering state information (angular position). This partial action approach maintains basic steering functionality and safety while accepting reduced precision, allowing the vehicle to be brought to a safe stop.
4Device complexity
If the steering column module is mechanically coupled to the steering gear, then the steering system is simpler and more direct, but the system becomes vulnerable to mechanical blockages and malfunctions
Solution Approach 1:
The patent replaces direct mechanical coupling with an electrical/control-based steering system. The steering column module and steering gear are decoupled mechanically, with the control unit mediating between driver input (detected via torque sensor) and steering actuator output. This substitution eliminates mechanical blockage vulnerabilities while maintaining steering functionality.
Solution Approach 2:
The steering system is segmented into independent functional modules: steering column module with torque sensor, control unit, and steering gear with actuator. This segmentation allows the system to isolate and compensate for mechanical failures in one module while maintaining functionality in other modules, improving overall reliability.
Data Source
Figure 1~2
Figure 3
AI summary
A motor vehicle steering system (1) comprises a steering column module (10) with a steering handle (11) for inputting a driver-side steering command, a steering angle sensor (12) for detecting a steering angle (ϕ) specified by the steering command, and a torque sensor (13) for detecting a torque (M) applied via the steering handle (11) as part of a steering command; a steering gear (20) with a steering actuator (21) for displaying the steering command at vehicle wheels (2); and a control unit (30) which is configured to control the steering actuator (21) in a main operating mode depending on the steering angle (ϕ) detected by the steering angle sensor (12) and specified via the steering handle (11), and in a fallback mode to control the steering actuator (21) depending on the torque (M) detected by the torque sensor (13) and applied via the steering handle (11).The control unit (30) stores a relationship for a steering rod travel speed (v) for a steering rod (22) of the steering gear (20) as a function of the torque (M) applied via the steering handle (11). The control unit (30) is configured such that, in fallback mode, it sets a steering rod travel speed (v) via the steering actuator (21) as a function of the torque (M) detected by the torque sensor (13) based on the aforementioned relationship. Furthermore, a method for operating such a vehicle steering system is described.