Electric Power Steering Gain Control for Rack End Shock
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Solution Overview
Problem
Conventional electric power steering apparatuses generate uncomfortable shock and noise when reaching the maximum steering angle due to high assist torque, leading to potential system locking and unpleasant driving experiences.
Innovation Solution
An electric power steering apparatus that calculates a current command value based on steering torque and adjusts it by multiplying with a gain or clipping a target current limit-value, which changes corresponding to the steering angle, to reduce torque near the rack end, thereby attenuating shock energy and suppressing uncomfortable sounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If high assist torque is applied at maximum steering angle, then steering assistance is improved, but shock and noise increase causing uncomfortable driving experience
Solution Approach 1:
The patent applies dynamics by making the current command value dynamic based on steering angle. A gain factor is calculated that varies with steering angle, and this gain is applied to the current command value to reduce assist torque near the rack end. This dynamic adjustment allows the system to provide high assist torque when needed (at normal steering angles) while reducing it when approaching maximum steering angle, thereby preventing shock and noise without sacrificing steering assistance during normal operation.
Solution Approach 2:
The patent changes the parameter of current command value based on steering angle. By calculating a gain factor that depends on the steering angle and multiplying it with the current command value, the system adjusts the assist torque parameter dynamically. This parameter change ensures that assist torque is reduced when the steering angle approaches the rack end, preventing the harmful shock and noise while maintaining adequate assistance during normal steering operations.
2Object-affected harmful factors
If assist torque is reduced near rack end, then shock and noise are suppressed, but steering assistance may be insufficient
Solution Approach 1:
The patent applies local quality by making the assist torque characteristic different in different steering angle regions. In the normal steering angle region, full assist torque is provided. In the region near the rack end (maximum steering angle), the assist torque is reduced through the gain factor. This localized differentiation ensures that shock and noise are suppressed only where necessary (near rack end) while maintaining full steering assistance in the normal operating region.
Solution Approach 2:
The system dynamically adjusts the current command value based on the steering angle by applying a gain factor. This dynamic control ensures that assist torque is maintained at appropriate levels for each steering condition: full assistance during normal steering and reduced assistance near the rack end to prevent shock and noise, thereby resolving the contradiction between maintaining assistance and suppressing harmful effects.
3Object-affected harmful factors
If gain is reduced to zero at rack end, then shock and noise are eliminated, but steering feeling becomes unnatural
Solution Approach 1:
The patent applies partial action by reducing the gain factor to a small positive value rather than zero when the steering angle exceeds the rack end. This partial reduction is sufficient to suppress shock and noise (the harmful effect) while maintaining a small amount of assist torque that preserves natural steering feeling. The gain is not completely eliminated, allowing the system to achieve the beneficial effect without the detrimental side effect.
Data Source
AI summary
An electric power steering apparatus that calculates a current command value based on at least a steering torque and assist-controls a steering system by driving a motor based on the current command value, the apparatus having a function to detect a steering angle on a steering and includes a gain section having a gain characteristic that a gain changes corresponding to the steering angle, such that a new current command value is generated by multiplying the current command value with the gain outputted from the gain section corresponding to the steering angle, and the gain characteristic is a constant value “1.0” till a steering angle θ1 short of a rack end, gradually decreases till a steering angle θ2 (>θ1) exceeding the rack end and holds a constant value G (>0) in a region that the steering angle is equal to or more than the steering angle θ2.