Steering Control Apparatus Torque Limiting for End-Striking Impact
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Solution Overview
Problem
Existing electric power steering systems struggle to adequately reduce end-striking impact on low-μ roads, where small surface resistance allows wheels to turn easily with minimal torque, leading to insufficient inertia attenuation and increased end-striking impact despite current command value limitations.
Innovation Solution
A steering control apparatus that computes a steering angle limit value reducing with increased rotation angle and sets a torque command value limit, incorporating a damping control amount based on angular velocity exceeding a threshold, to limit motor torque and reduce end-striking impact, especially on low-μ roads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the current command value is limited to reduce end-striking impact, then the impact reduction is improved, but on low-μ roads the inertia attenuation becomes insufficient and end-striking impact increases
Solution Approach 1:
The patent implements dynamic adjustment of the current command value limit based on steering angular velocity. When the absolute value of steering angular velocity exceeds a predetermined threshold, the limit is set to a first value; otherwise, it is set to a second value (smaller than the first). This dynamic switching allows the system to provide sufficient inertia attenuation on low-μ roads while maintaining impact reduction on normal roads.
Solution Approach 2:
The patent changes the parameter of current command value limit based on the steering angular velocity condition. By monitoring whether the steering angular velocity exceeds the threshold and adjusting the limit parameter accordingly, the system adapts to different road conditions without requiring direct μ detection, resolving the contradiction between impact reduction and inertia attenuation.
2Object-affected harmful factors
If the steering angle threshold is set near the end to limit motor torque, then end-striking impact is reduced, but steering feel may be unnecessarily reduced on other road surfaces
Solution Approach 1:
The patent dynamically adjusts the torque limitation strategy based on steering angular velocity. By switching between different current command value limits based on whether the angular velocity exceeds the threshold, the system provides appropriate torque limitation only when necessary (high velocity conditions), preserving steering feel during normal operations while still protecting against end-striking impact during rapid steering movements.
Solution Approach 2:
The patent applies preliminary anti-action by detecting high steering angular velocity as an indicator of potential end-striking conditions and preemptively applying torque limitation before the rack end actually strikes. This prevents impact while avoiding unnecessary limitation during normal steering operations, maintaining steering feel when not needed.
Data Source
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AI summary
A steering control apparatus (6) for a steering system (1) includes a controller (41). The controller sets a limit value to less than or equal to a steering angle limit value, the limit value being an upper limit of an absolute value of a torque command value, and controls a motor such that a motor torque follows the torque command. When the absolute value of a rotation angle of a rotary shaft (11) exceeds a steering angle threshold, the controller computes a damping control amount such that the damping control amount increases with an increase in an excess of an angular velocity of the rotary shaft over a first upper limit angular velocity. The controller computes the torque command value based on a value obtained by combining the basic command value and the damping control amount such that an absolute value of the basic command value is reduced.