Power Steering Interpolation for Smooth Assist Switching
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Solution Overview
Problem
Existing power steering apparatuses cause a sense of incongruity to drivers when switching between assist characteristics, particularly when transitioning from a high assist quantity to a low assist quantity or vice versa, leading to discomfort during steering wheel operations.
Innovation Solution
A power steering apparatus that calculates an interpolation characteristic intermediate between two assist characteristics and variably controls the characteristic switching time based on steering torque to ensure a smooth transition, aligning the assist torque direction with the driver's steering action, thereby minimizing incongruity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If assist characteristics are switched abruptly between high assist quantity and low assist quantity, then switching responsiveness is improved, but driver comfort deteriorates due to sense of incongruity
Solution Approach 1:
The patent applies dynamics by making the switching time variable rather than fixed. The control unit adjusts the switching time based on the absolute value of steering torque, allowing the transition between assist characteristics to be dynamic and adaptive to the current steering state, thereby resolving the contradiction between fast switching and comfort.
Solution Approach 2:
The patent changes the parameter of switching time based on steering torque conditions. When steering torque is large, switching occurs faster; when steering torque is small, switching occurs more slowly. This parameter change strategy allows the system to optimize both responsiveness and comfort under different operating conditions.
2Loss of time
If switching time between assist characteristics is shortened, then responsiveness is improved, but steering smoothness deteriorates causing driver discomfort
Solution Approach 1:
The patent changes the switching time parameter according to steering torque magnitude. By making switching time conditional rather than fixed, the system achieves fast switching when needed (high torque) while maintaining smoothness when torque is low, resolving the time-stability contradiction.
Solution Approach 2:
The system transitions from static switching time to dynamic switching time that adapts to steering conditions. This dynamic adjustment allows the system to maintain stability during smooth steering while achieving rapid switching during high-torque maneuvers.
3Device complexity
If assist torque direction does not align with steering torque direction during switching, then calculation complexity is reduced, but driver comfort deteriorates due to sense of incongruity
Solution Approach 1:
The patent uses feedback by continuously monitoring the sign of steering torque and using it to determine the appropriate assist torque direction during switching. This feedback mechanism ensures that assist torque always aligns with steering torque direction, maintaining driver comfort while keeping the control logic relatively simple.
Solution Approach 2:
The system changes the assist torque parameter (direction) based on the steering torque sign. When steering torque is positive, assist torque is positive; when steering torque is negative, assist torque is negative. This parameter adaptation ensures comfort without requiring complex calculations.
Data Source
AI summary
A power steering apparatus has a first characteristic which is a characteristic of a command signal with respect to steering torque and a second characteristic which is a characteristic different from the first characteristic. When switching is to be made to a characteristic selected from between the first and second characteristics, an interpolation characteristic intermediate between the first and second characteristics is calculated so that the characteristic used before switching of the characteristics gradually approaches the characteristic to be used after the switching, and a characteristic switching time for switching between the first and second characteristics is variably controlled in accordance with the steering torque.