Anti-Notch Filter for Steering Wheel Nibble
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Solution Overview
Problem
Existing electric power steering systems face challenges in effectively canceling undesirable vibrations such as steering wheel nibble and brake judder, which can lead to customer complaints and increased costs due to the need for costly chassis modifications and potential instability when using resonator filters for disturbance rejection.
Innovation Solution
The implementation of an anti-notch filter and a lag-lead compensation filter in the electric power steering system, which calculates an active nibble-canceling torque based on detected wheel speed, reduces amplification and maintains stability by shifting filter zeros and adding phase lag without causing pole-zero cancellation, thereby enhancing disturbance rejection without affecting steering feel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If resonator filters are used for disturbance rejection, then steering wheel nibble and brake judder are reduced, but system stability deteriorates and costly tuning is required
Solution Approach 1:
The patent changes the filter design parameters from resonator filters to anti-notch filters, modifying the frequency response characteristics to provide disturbance rejection without the stability issues. This parameter change allows the system to reject vibrations at specific frequencies while maintaining overall system stability and avoiding the need for costly tuning procedures
2Object-affected harmful factors
If resonator filters are used for disturbance rejection, then steering wheel nibble and brake judder are reduced, but device complexity and tuning costs increase
Solution Approach 1:
The patent simplifies the filter design by using anti-notch filters instead of resonator filters, changing the approach from complex tuned resonators to simpler filters with fixed characteristics that are easier to implement and tune, thereby reducing device complexity and tuning costs while maintaining disturbance rejection effectiveness
3Object-affected harmful factors
If chassis modifications are made to reduce nibble and judder, then vibration reduction is achieved, but manufacturing cost increases
Solution Approach 1:
The patent replaces mechanical chassis modifications with an electronic control solution using anti-notch filters in the power steering system. This substitution allows vibration reduction to be achieved through software/filter tuning rather than expensive mechanical modifications to the chassis, thereby maintaining ease of manufacture while effectively reducing nibble and judder
Data Source
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AI summary
An active nibble control (ANC) includes an anti-notch filter that increases the gain margin of the control and, therefore, greater disturbance rejection. The closed loop frequency response of the ANC is further enhanced by the addition of a lag-lead phase compensator filter. The addition of the lag-lead compensation filter allows use of the higher ANC gains at higher wheel frequencies to increase disturbance rejection, thereby compensating for anti-notch filter gain reduction with increasing wheel frequency. Similar results are obtained by adding a lag-lead phase compensator filter to a resonator filter in an active ANC.