Electric Power Steering Control With Frequency-Band Torque Compensation

Solution Overview

Problem

Existing electric power steering systems face a trade-off between stability, disturbance suppression, and responsiveness, making it difficult to improve the steering feeling for the driver.

Innovation Solution

A control device with a reaction force controller and an assist controller, incorporating high-pass and low-pass filters, to generate correction torque based on a nominal model, and a disturbance compensation value calculator to compensate for self-aligning torque, thereby improving steering feel.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional control elements are adjusted to improve stability, then disturbance suppression improves but responsiveness deteriorates

Engineering Contradiction:

ImprovestabilityVSAvoidresponsiveness

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The control device segments the control bandwidth into multiple frequency bands using a first cutoff frequency and a second cutoff frequency. The assist controller operates in a first bandwidth (below first cutoff frequency) to improve stability and disturbance suppression, while the reaction force controller operates in a second bandwidth (above first cutoff frequency, below second cutoff frequency) to maintain responsiveness. This frequency-based segmentation allows both stability and responsiveness to be optimized in their respective domains without trade-off.

Inventive Principle:

Principle #1Segmentation

2Object-generated harmful factors

If disturbance suppression is enhanced, then steering smoothness improves but responsiveness deteriorates

Engineering Contradiction:

Improvedisturbance suppressionVSAvoidresponsiveness

Core Design Contradiction:

Object-generated harmful factorsVSSpeed

Solution Approach 1:

The control device segments the control bandwidth into multiple frequency bands using a first cutoff frequency and a second cutoff frequency. The assist controller operates in a first bandwidth (below first cutoff frequency) to improve stability and disturbance suppression, while the reaction force controller operates in a second bandwidth (above first cutoff frequency, below second cutoff frequency) to maintain responsiveness. This frequency-based segmentation allows both stability and responsiveness to be optimized in their respective domains without trade-off.

Inventive Principle:

Principle #1Segmentation

3Measurement precision

If multiple control controllers are added to improve steering feeling, then control precision improves but device complexity increases

Engineering Contradiction:

Improvecontrol precisionVSAvoiddevice complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The control device segments the control bandwidth into multiple frequency bands using a first cutoff frequency and a second cutoff frequency. The assist controller operates in a first bandwidth (below first cutoff frequency) to improve stability and disturbance suppression, while the reaction force controller operates in a second bandwidth (above first cutoff frequency, below second cutoff frequency) to maintain responsiveness. This frequency-based segmentation allows both stability and responsiveness to be optimized in their respective domains without trade-off.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The control device dynamically switches between different control modes based on frequency bands. The assist controller provides disturbance suppression for low-frequency components, while the reaction force controller handles high-frequency components for responsive steering feel. This dynamic frequency-based control allocation optimizes steering performance across different operating conditions without requiring overly complex hardware architecture.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS12377909B2Control device, electric power steering device, and control method

Publication Date: 2025.08.05 NIDEC CORP(JP)

AI summary

A control device includes a reaction force controller to generate an input torque input to a control target and control a reaction force transmitted to a steering person and an assist controller to generate a correction torque to correct the input torque based on an output of the control target and a nominal model. The assist controller includes a high-pass filter with a first cutoff frequency, a low-pass filter with a second cutoff frequency higher than the first cutoff frequency, and a disturbance compensation value calculator. When a transfer function of the low-pass filter is Q(s) and a transfer function of the high-pass filter is HPF(s), a transfer function of a control target is constrained by a transfer function of the nominal model in a frequency band in which a gain in a gain characteristic of Q(s)·HPF(s) is 1.