Vehicle Steering Centering Torque for Low-Speed Stability
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Solution Overview
Problem
Existing power assisted steering systems struggle to maintain steering stability, particularly at low speeds and high motor torque, leading to instability and potential loss of control.
Innovation Solution
Applying a centering torque that urges the steered wheels to a central position, combining it with driver assistance torque to stabilize steering, using a controller to determine the assistance torque based on driver input and wheel rotation, and implementing a small, imperceptible torque to enhance steering stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If power assisted steering systems operate at low speeds with high motor torque, then the vehicle can achieve sufficient driving force, but steering stability deteriorates and loss of control may occur
Solution Approach 1:
The controller continuously monitors steering wheel angle, driver torque input, and vehicle speed to dynamically adjust the assistance torque. This closed-loop feedback mechanism ensures that the assistance torque is optimized for each operating condition, preventing steering instability at low speeds while maintaining high motor torque capability.
Solution Approach 2:
The assistance torque is varied as a function of steering wheel angle, driver torque, and vehicle speed. By changing the torque parameters dynamically based on operating conditions, the system maintains steering stability across different speed-torque regimes, resolving the contradiction between high power delivery and steering stability.
2Reliability
If centering torque is applied to urge wheels to central position, then steering stability is improved, but driver effort may be increased if not properly coordinated with driver input
Solution Approach 1:
The controller monitors driver torque input and steering wheel angle to determine the appropriate centering torque magnitude. The feedback mechanism ensures that centering torque is applied only when necessary (e.g., when wheels deviate from central position without driver input) and is adjusted to complement rather than conflict with driver intentions, maintaining ease of operation.
Solution Approach 2:
The centering torque is made dynamic rather than static, varying with steering wheel angle, driver torque input, and vehicle speed. This dynamic adjustment allows the system to provide gentle centering assistance when needed while being completely transparent to driver input, preserving ease of operation while improving steering stability.
3Reliability
If assistance torque is increased to stabilize steering, then steering stability improves, but the system complexity and control difficulty increase
Solution Approach 1:
The assistance torque system performs multiple functions through a unified control architecture: it provides centering torque for stability, compensates for driver input, and adapts to varying operating conditions. This multi-functional approach reduces overall system complexity by consolidating control functions rather than requiring separate systems for each function.
Solution Approach 2:
The control system uses parameter-based adjustment of assistance torque rather than complex control algorithms. By varying torque magnitude based on simple thresholds and relationships (steering angle, driver torque, vehicle speed), the system achieves stable steering without requiring complex control logic, reducing computational and system complexity.
Data Source
AI summary
A vehicle includes a motor coupled to steered wheels by a differential. A steering mechanism is coupled to the steered wheels and changes the steering angle of the steered wheels in response to torque applied to a steering column. A power assistance actuator facilitates turning of the steered wheels, such as by amplifying torque applied by the driver to the steering wheel, which amplified torque is converted into a transverse force to turn the steered wheels. The assistance torque commanded from the power assistance actuator may be determined based on (a) a driver torque applied by the drive to steering wheel and (b) a small (e.g., less than 4 Nm) centering torque that urges the steered wheels to a central position. The centering torque may increase with increasing motor torque, increase with increasing steering wheel angle, and decrease with increasing vehicle speed.