Steering Torque Control for Low Friction Stability
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Solution Overview
Problem
Existing vehicle steering systems fail to effectively mitigate the risk of accidents caused by sudden reductions in friction coefficients, particularly during aquaplaning, where the coefficient of friction between tires and the road surface drops significantly due to water, ice, or snow, leading to loss of control.
Innovation Solution
The method employs a power steering device, such as an electric servomotor, to manipulate steering torque by increasing resistance in one direction and applying counter-steering torque to guide the driver in correcting the steering angle, thereby preventing further instability and restoring drivability by bringing the steerable wheels to a neutral position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the power steering device generates support torque to assist steering, then steering effort is reduced, but the driver receives insufficient feedback about hazardous steering movements on low-friction surfaces
Solution Approach 1:
The system introduces tactile feedback through modified steering torque that informs the driver about hazardous steering movements. When low friction is detected, the power steering device generates increased resistance torque in steering directions that would worsen the situation, providing the driver with sensory information about the dangerous condition while still allowing corrective steering actions.
Solution Approach 2:
The system applies preliminary counteracting torque before the driver can make harmful steering corrections. When aquaplaning or low-friction conditions are detected, the control unit preemptively increases steering resistance in directions that would exacerbate instability, preventing the driver from making dangerous steering adjustments before they occur.
2Reliability
If the power steering device increases steering resistance to prevent hazardous steering movements, then driver control is restricted, but the driver's ability to perform necessary corrective steering actions is reduced
Solution Approach 1:
The system applies different steering resistance characteristics to different steering directions based on the specific hazard. When aquaplaning is detected during cornering, increased resistance is applied only to steering movements that would increase the steering angle further (which would worsen instability), while resistance is reduced or eliminated for steering movements in the opposite direction (which would be corrective).
Solution Approach 2:
The steering resistance is dynamically adjusted based on real-time driving conditions, steering angle, and detected friction levels. The system continuously modifies the torque characteristics to provide appropriate assistance or resistance, transitioning between support mode and warning mode based on the severity and type of hazardous condition detected.
3Loss of information
If the system provides tactile feedback through increased steering torque, then the driver is informed of hazardous conditions, but the steering system complexity increases
Solution Approach 1:
The power steering device performs multiple functions: it provides steering assistance torque to reduce steering effort, generates warning torque to inform the driver of hazardous conditions, and applies counteracting torque to prevent dangerous steering movements. These different functions are achieved through a single integrated control system that adjusts torque characteristics based on detected conditions and steering state.
Solution Approach 2:
The system combines the steering assistance function with the hazard warning function in a single power steering device controlled by one control unit. The same actuator that provides support torque is used to generate warning torque, eliminating the need for separate warning mechanisms and reducing overall system complexity despite the multifunctional requirements.
Data Source
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AI summary
In a method for influencing the steering torque in a vehicle steering system, the torque generated in a power steering device is changed such that a steering movement in at least one steering direction meets with increased resistance in case the coefficient of friction between at least one vehicle wheel and the road falls below a threshold value.