Electronic Power Steering Assist Restriction Control

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Solution Overview

Problem

Conventional electronic power steering apparatuses face issues with unintentional application of assist force due to abnormal sensor signals from torque sensors, leading to unstable steering system assistance.

Innovation Solution

An electronic power steering apparatus with a control means that executes an assist restriction process based on vehicle speed, lateral acceleration, steering angle, and yaw rate, setting upper and lower limits for the assist control variable to prevent unintentional assist force application, even when only one sensor signal is normal, and gradually suspends assist control when no normal signals are detected.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If multiple torque sensors are used to improve detection accuracy and reliability, then the system can continue providing assist force even when one sensor fails, but unintentional assist force may be applied during the period between detecting abnormal signals and suspending assist control

Engineering Contradiction:

Improvecontinuous assist capabilityVSAvoidunintentional assist force application

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The control means immediately executes assist restriction control upon detecting an abnormal sensor signal, before the assist suspension decision is made. This preliminary action of restricting assist force prevents the harmful period of unintentional assist application by proactively limiting the assist control variable within a safe range as soon as abnormality is detected.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention introduces an intermediate control state (assist restriction control) between normal assist control and complete assist suspension. This intermediary mode acts as a buffer, gradually transitioning the system from full assist to no assist, thereby preventing sudden changes and unintentional assist force application during the transition period.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If assist control is suspended immediately when abnormal sensor signals are detected, then unintentional assist force is prevented, but the system cannot provide continuous assist capability when one of multiple sensors fails

Engineering Contradiction:

Improveunintentional assist force applicationVSAvoidcontinuous assist capability

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The control system dynamically adjusts its behavior based on the number of normal sensor signals available. When one sensor is abnormal, the system transitions to assist restriction control with limited assist force. When both sensors are abnormal, it transitions to assist suspension. This dynamic adaptation allows the system to maintain continuous assist capability when possible while preventing unintentional assist when necessary.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The invention changes the assist control variable parameter based on sensor signal status. When abnormal signals are detected, the control means modifies the assist control variable by applying upper and lower limit restrictions, thereby changing the assist force magnitude from normal levels to restricted levels, preventing unintentional assist while maintaining some level of continuous operation.

Inventive Principle:

Principle #35Parameter changes

3Ease of operation

If the assist control variable is not restricted when abnormal sensor signals are detected, then normal assist control is maintained, but assist force may be applied unintentionally to the steering system

Engineering Contradiction:

Improvenormal assist controlVSAvoidunintentional assist force application

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The control means continuously monitors sensor signal status and provides feedback control. When abnormal sensor signals are detected, the feedback mechanism triggers assist restriction control, adjusting the assist control variable within safe limits. This feedback-based control ensures that assist force is restricted precisely when needed, preventing unintentional application while maintaining normal operation during healthy conditions.

Inventive Principle:

Principle #23Feedback

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

Effectively suppresses unintentional assist force application to the steering system, ensuring stable operation by limiting the assist force within predetermined ranges and preventing sudden changes, thus enhancing steering system reliability.

Implementation Method 1

a torsion bar for connecting the input shaft and the output shaft

Methodology Applied

Scientific EffectTorsion: Torsion Spring

Implementation Method 2

magnetic sensors for detecting the density of a magnetic flux generated between the paired magnetic yokes

Methodology Applied

Scientific EffectMagnetic flux detection: Magnetic Field

Data Source

PatentUS9296415B2Electronic power steering apparatus

Publication Date: 2016.03.29 JTEKT CORP

AI summary

When only one of sensor signals generated by the plural systems and output from a torque sensor is normal, a control variable restriction processing part performs an assist restricting process for setting an upper limit value and a lower limit value of a basic assist control variable in accordance with at least one of the lateral acceleration, the steering angle, the steering speed, or the yaw rate.