Steer-by-Wire Rack Limit Control to Prevent End Impact Noise
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Solution Overview
Problem
Existing steer-by-wire steering systems generate impact noise at the rack end and allow the steering center to deviate from the designed mechanical center, leading to potential collisions and reduced maximum steered angle.
Innovation Solution
A steer-by-wire steering system with a control unit that sets a target steered angle and reaction force to prevent the rack from reaching the end, using a control maximum steered angle smaller than the physical maximum, and applies a steering limit reaction force to notify the operator of the maximum angle, with optional physical stoppers as a fail-safe.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the reaction force actuator generates a reaction force only when the steering wheel is at the rack end position for a prescribed time period, then the load on the steering actuator is reduced, but impact noise is generated at the rack end
Solution Approach 1:
The control unit applies a preliminary reaction force to the steering wheel before the rack reaches the end position. This preliminary action prevents the rack from colliding with the end stop by creating a counteracting force in advance, thereby eliminating impact noise while still reducing the load on the steering actuator during normal operation.
Solution Approach 2:
The system performs preliminary detection of the rack position and pre-applies reaction force before the rack actually reaches the end position. This preliminary action allows the system to prepare the reaction force actuator in advance, ensuring smooth deceleration of the rack without impact while optimizing the timing for load reduction.
2Ease of manufacture
If the steering center deviates from the designed mechanical center due to dimensional errors or assembly errors, then manufacturing and assembly are more flexible, but the rack collides with the rack end before the wheel reaches the design maximum steered angle
Solution Approach 1:
The control unit continuously monitors the actual position of the rack and steering wheel through sensors, and uses this feedback information to dynamically adjust the reaction force application. This feedback mechanism compensates for deviations from the designed mechanical center, ensuring the rack does not collide with the end stop even when assembly variations occur, while maintaining ease of manufacturing.
Solution Approach 2:
The system dynamically changes the control parameters of the reaction force actuator based on the detected steering state and rack position. By adjusting the magnitude and timing of the reaction force according to actual operating conditions rather than fixed design parameters, the system adapts to assembly variations and prevents rack collision while maintaining manufacturing flexibility.
Data Source
AI summary
Provided is a steer-by-wire steering system for a vehicle that can reduce or eliminate the impact noise generated by the rack at the rack end. A control unit of the steering system is configured to determine a target steered angle (αt) according to the steering angle and drive the steering actuator so as to cause the steered angle to coincide with the target steered angle, and to determine a target reaction force (Tt) according to a steered state of the wheels and drive the reaction force actuator so as to cause the reaction force to coincide with the target reaction force. The control unit is further configured to set a maximum limit (αmC) on the target steered angle, the maximum limit being a value smaller than a physical maximum steered angle (αmP) of the wheels imposed by the steering mechanism.