Electric Power Steering Stroke-End Control for Bounce-Back Stability
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Solution Overview
Problem
Existing electric power steering devices experience impact noise and unintended steering wheel rotation due to the rack bar abutting against structure members at the stroke end, with existing solutions failing to address bouncing back after the stroke end.
Innovation Solution
A control device that adjusts steering force by reducing it before the stroke end and increasing it after bouncing back, using proportional integral control to correct the assist torque based on the steering wheel angle difference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the steering force is reduced before the stroke end to prevent impact noise, then the impact at abutment is reduced, but the operation feeling before and after the stroke end deteriorates
Solution Approach 1:
The steering force is dynamically adjusted based on the real-time position of the rack bar. The control unit continuously monitors the rack bar position and modulates the electric motor output accordingly, transitioning from high steering force during normal operation to reduced steering force near the stroke end, and then increasing it again after bounce-back. This dynamic adjustment resolves the contradiction by adapting the steering force to different operational phases.
Solution Approach 2:
The system employs feedback control by detecting the rack bar position and using this information to adjust the steering force. The control unit receives feedback about the rack bar's proximity to the stroke end and the bounce-back condition, then appropriately modifies the electric motor output. This feedback mechanism enables the system to maintain good operation feeling while preventing impact noise through intelligent force modulation.
2Object-affected harmful factors
If the steering force is reduced before the stroke end, then the abutment impact is suppressed, but the rack bar bounce-back causes unintended steering wheel rotation
Solution Approach 1:
The system applies preliminary anti-action by detecting when the rack bar reaches the stroke end and preemptively adjusting the steering force to prevent excessive impact. The control unit reduces the electric motor output before significant bounce-back occurs, and then increases it again to counteract the bounce-back effect, thereby preventing unintended steering wheel rotation while still suppressing abutment impact.
3Object-affected harmful factors
If the upper limit of target current value is set to prevent excessive assist force, then the impact noise is reduced, but the bouncing back after stroke end is not addressed
Solution Approach 1:
Instead of using a static upper limit for the target current value, the system dynamically adjusts the current command to the electric motor based on the rack bar position and bounce-back detection. The control unit modifies the current limit in real-time, reducing it near the stroke end to prevent impact noise, then increasing it after bounce-back to maintain steering control reliability and prevent unintended steering wheel rotation.
Data Source
AI summary
Provided is a control device to be used for a vehicle including: a steering wheel configured to steer the vehicle; a steering member configured to steer steered wheels in accordance with rotation of the steering wheel; and a steering actuator configured to apply a steering force to the steering member, the control device including a control unit configured to output, to the steering actuator, a drive signal for applying the steering force based on steering information on the steering wheel. The control unit is configured to output, to the steering actuator, a drive signal for reducing the steering force until the steering member reaches a stroke end after a rotation angle of the steering wheel reaches a predetermined control start angle and increasing the steering force when the steering member reaches the stroke end and then bounces back.