Electric Power Steering Handle-Returning Control Deviation

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Solution Overview

Problem

Conventional electric power steering apparatuses experience excessive handle-returning control deviations, leading to uncomfortable feelings for drivers, especially during steering interventions, due to large differences between target and actual steering angular velocities.

Innovation Solution

An electric power steering apparatus that calculates a target steering angular velocity using a virtual vehicle model, limits this value to prevent excessive deviations, and employs a handle-returning control current to adjust the motor current command value, incorporating proportional, integral, and differential control calculations to ensure smooth handle-returning and reduce driver discomfort.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If handle-returning control is performed without limiting the target steering angular velocity, then the steering returns to neutral position, but excessive deviation between target and actual steering angular velocity causes driver discomfort

Engineering Contradiction:

Improvehandle-returning smoothnessVSAvoiddriver discomfort

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The patent applies parameter changes by dynamically adjusting the target steering angular velocity based on vehicle speed and steering angle. The control device calculates appropriate target values that vary with operating conditions, ensuring smooth handle-returning at low speeds while preventing excessive deviations at high speeds, thereby eliminating driver discomfort.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements feedback control by continuously monitoring the actual steering angular velocity and comparing it with the target value. The control device adjusts the motor output based on the deviation between target and actual values, creating a closed-loop system that maintains optimal handle-returning characteristics across different driving conditions.

Inventive Principle:

Principle #23Feedback

2Device complexity

If target steering angular velocity is calculated without considering vehicle speed and steering angle, then control is simplified, but excessive deviations occur causing uncomfortable feeling

Engineering Contradiction:

Improvecontrol calculation complexityVSAvoidsteering comfort

Core Design Contradiction:

Device complexityVSEase of operation

Solution Approach 1:

The patent applies dynamics by making the control parameters adaptive rather than fixed. The target steering angular velocity is dynamically calculated based on real-time vehicle speed and steering angle inputs, allowing the system to automatically adjust its behavior to match current driving conditions, thereby maintaining comfort without excessive complexity.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control device changes parameters (target steering angular velocity) based on operating conditions (vehicle speed and steering angle). This parameter adaptation allows the system to optimize handle-returning characteristics for each specific situation, balancing control complexity with steering comfort.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If excessive handle-returning control current is applied, then steering returns quickly to neutral position, but driver feels uncomfortable due to over-correction

Engineering Contradiction:

Improvehandle-returning speedVSAvoiddriver discomfort

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the control current parameters dynamically based on vehicle speed and steering angle. At high speeds, the system reduces the target steering angular velocity to prevent excessive correction, while at low speeds it allows faster return. This parameter adaptation resolves the contradiction between return speed and comfort.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The control device applies preliminary anti-action by preemptively limiting the target steering angular velocity before excessive deviations can occur. By anticipating potential over-correction based on current operating conditions, the system prevents driver discomfort before it happens.

Inventive Principle:

Principle #9Preliminary anti-action

Data Source

PatentUS10919567B2Electric power steering apparatus

Publication Date: 2021.02.16 NSK LTD

AI summary

An electric power steering apparatus that drives a motor based a current command value and assist-controls a steering system by a driving-control of the motor. The apparatus includes a handle-returning control section that calculates a target steering angular velocity by using a steering angle, the vehicle speed, the steering torque and the current command value, calculates a handle-returning control current by using a limit-target steering angular velocity which is obtained by limiting the target steering angular velocity depending on steering angular velocity, and drives the motor by a compensated current command value which is obtained by adding the handle-returning control current to the current command value.