Electric Power Steering Torque Shift Control with Dual Low-Pass Filters
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Solution Overview
Problem
Existing electric power steering systems face challenges in providing a comfortable steering feel during transitions between steering states due to sharp changes in assist force, which can lead to noise influence and hunting, especially when improving response performance.
Innovation Solution
An electric power steering system that includes a control unit calculating a basic assist force component and a compensation component, with a low-pass filter process applied to both, where the cutoff frequency of the transition coefficient is set lower than that of the compensation component to suppress sharp changes in the output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the rate of change in the transition coefficient is increased to improve response performance, then the response to steering operation is improved, but noise influence becomes more significant and hunting occurs in the output
Solution Approach 1:
A low-pass filter is introduced as an intermediary element between the transition coefficient calculation and the assist force output. The filter acts as a mediator that allows the transition coefficient to change rapidly for improved response while simultaneously suppressing high-frequency noise and hunting in the final output signal.
Solution Approach 2:
The patent changes the parameter of the transition coefficient by applying a low-pass filter with a specific cutoff frequency. This parameter change allows the system to maintain fast response characteristics while filtering out harmful high-frequency components that cause noise and hunting, thus resolving the contradiction between response speed and output stability.
2Reliability
If the cutoff frequency of the low-pass filter on the transition coefficient is set too high to maintain response performance, then response speed is improved, but hunting occurs in the output; if set too low to suppress hunting, then noise influence is reduced, but response performance deteriorates
Solution Approach 1:
The patent optimizes the cutoff frequency parameter of the low-pass filter to achieve the best balance between response speed and output stability. By carefully selecting this parameter, the system can suppress hunting and noise while maintaining adequate response performance, resolving the contradiction between reliability and speed.
Data Source
AI summary
A steering torque shift control amount calculation unit (31) calculates the steering torque shift control amount (εts) by multiplying the basic shift amount (εts_b) used as the basic compensation component by the transition coefficient (Kss). Then, the steering torque shift control amount (εts) is subjected to the low-pass filter process in an abrupt change prevention processing unit (32). An abrupt change prevention processing unit (40) is provided in the steering torque shift control amount calculation unit (31). The transition coefficient (Kss) is subjected to the low-pass filter process in the abrupt change prevention processing unit (40). The cutoff frequency of the low-pass filter that forms the abrupt change prevention processing unit (40) is set to a value lower than the cutoff frequency of the low-pass filter that forms the abrupt change prevention processing unit (32) that executes the low-pass filter process on the torque shift control amount (εts).