Electric Power Steering Filter Constant Adjustment
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Solution Overview
Problem
Conventional electric power steering (EPS) systems experience degraded steering feel when the steering state transitions directly from 'holding' or 'returning' to 'turning' without sufficient neutral position time, due to excessive assist force reduction caused by sharp change prevention filtering processes.
Innovation Solution
An EPS apparatus with a controller that adjusts the filtering effect of the low pass filter based on the steering state, reducing the filtering effect when transitioning to 'turning' to prevent excessive assist force reduction and maintain favorable steering feel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low pass filter is applied to prevent sharp changes in assist force, then steering feel is improved during holding and returning, but the assist force reduction is retarded when transitioning to turning, causing excessive assist force and degraded steering feel
Solution Approach 1:
The filter constant is made dynamically adjustable based on the detected steering state. When turning is detected, the filter constant is increased to reduce filtering effect and accelerate assist force reduction. When holding or returning is detected, the filter constant is decreased to maintain smooth steering feel. This dynamic adjustment resolves the contradiction by adapting the filtering strength to the current operational context.
Solution Approach 2:
The filter constant parameter is changed according to the steering state to optimize performance. By increasing the filter constant during turning transitions, the system reduces the filtering effect and accelerates assist force reduction. By decreasing the filter constant during holding and returning, the system maintains smooth steering feel. This parameter change strategy resolves the time delay issue while preserving steering feel quality.
2Speed
If the filter constant is increased to reduce filtering effect during turning, then assist force reduction is accelerated, but steering feel may become unstable during holding and returning
Solution Approach 1:
Different filter constant values are applied locally to different steering states. A larger filter constant is applied specifically during turning transitions to accelerate assist force reduction. A smaller filter constant is applied during holding and returning to maintain stability. This localized parameter adjustment resolves the contradiction by optimizing performance for each specific operational context without compromising overall stability.
Solution Approach 2:
The filter constant is dynamically adjusted based on real-time detection of steering state. When turning is detected, the filter constant increases to accelerate response. When holding or returning is detected, the filter constant decreases to maintain stability. This dynamic adaptation allows the system to achieve fast response when needed while maintaining stability during critical steering phases.
Data Source
AI summary
An electric power steering (EPS) apparatus 1 includes a motor 12, an EPS actuator 10, a torque sensor 14, and an ECU 11. The EPS actuator 10 uses the motor 12 as a drive source to apply assist force to a steering system, thereby assisting a steering operation. The torque sensor 14 detects a steering torque τ of the steering system. The ECU 11 controls the operation of the EPS actuator 10. Based on the steering torque τ detected by the torque sensor 14, the ECU 11 computes a basic shift amount εts_b of the assist force applied to the steering system. The ECU 11 determines which one of returning, holding, and turning is the state of the steering operation. When the state of the steering operation is returning or holding, the ECU 11 executes compensation control for correcting the steering torque τ, which is used in the computation of the basic shift amount εts_b of the assist force, thereby increasing the assist force applied to the steering system. The ECU 11 subjects the steering torque shift control amount εts to a filtering process using a low pass filter, thereby inhibiting the steering torque shift control amount εts from sharply changing. When the state of the steering operation is turning, the ECU 11 changes a filter constant of the low pass filter so as to reduce the filtering effect.