Electric Power Steering Hysteresis Control for Assist Stability

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Solution Overview

Problem

In electric power steering systems, low friction causes the assist command to fluctuate with driver torque modulation, making it difficult to maintain a constant steer input.

Innovation Solution

A control system that determines a hysteresis position based on handwheel velocity and torque, and generates a final assist command using an assist curve to stabilize the steering assist, blending between torque and velocity-based compensation at different input velocities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If friction is low in the steering system, then the assist command can respond quickly to driver torque changes, but the assist command fluctuates excessively when the driver modulates torque, making it difficult to maintain constant steer input

Engineering Contradiction:

ImproveResponse speed of assist commandVSAvoidStability of assist command

Core Design Contradiction:

SpeedVSStability of the object's composition

Solution Approach 1:

The patent introduces a hysteresis loop as an intermediary element between the driver torque input and the assist command output. This hysteresis loop acts as a buffer that filters out rapid torque fluctuations while still allowing the system to respond to sustained steering inputs, thereby stabilizing the assist command without sacrificing overall responsiveness

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent dynamically adjusts the hysteresis width based on operating conditions such as vehicle speed and steering angle. By making the hysteresis characteristics adaptive rather than fixed, the system can maintain stability during normal operation while preserving responsiveness when needed, effectively balancing the contradiction between quick response and fluctuation suppression

Inventive Principle:

Principle #15Dynamics

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach helps maintain a consistent assist command, ensuring a steady state input by adapting to changes in driver input, reducing fluctuations and improving steering stability.

Implementation Method 1

a first module that determines a hysteresis position based on handwheel velocity and handwheel torque

Methodology Applied

Scientific EffectHysteresis: Hysteresis

Data Source

PatentEP2489576B1Electric power steering control methods and systems

Publication Date: 2018.05.02 STEERING SOLUTIONS IP HOLDING CORP

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AI summary

A control system (40) for controlling a steering system (12) is provided. The control system (40) includes a first module (44) that determines a hysteresis position based on handwheel velocity and handwheel torque. A second module selectively determines an assist curve based on the hysteresis position. A third module (50) generates a final assist command based on the assist curve.