Electric Power Steering Sensor Abnormality Detection

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Solution Overview

Problem

Existing electric power steering devices face challenges in stably continuing to apply assist force when only one sensor signal remains, due to variations in temperature characteristics and the need for multiplexing sensor signals for precise detection.

Innovation Solution

The electric power steering device incorporates a control mechanism that applies instantaneous motor torque to the steering system, allowing for the detection of sensor signal abnormalities before they become clearly abnormal, and alternately applies positive and negative torque to maintain assist force stability using residual sensor signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If multiple sensor signals are multiplexed for high precision detection, then measurement precision improves, but device complexity increases

Engineering Contradiction:

Improvedetection precision of steering torqueVSAvoidnumber of sensor elements

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The torque sensor is divided into multiple independent sensor elements (first sensor element and second sensor element) that each independently detect torsion of the torsion bar. This segmentation allows the system to use multiple sensor signals for multiplexing and correction processes, improving measurement precision while keeping each individual sensor element simple and manageable

Inventive Principle:

Principle #1Segmentation

2Reliability

If assist continuation control is executed with gradual reduction using residual sensor signal, then reliability is maintained, but productivity decreases

Engineering Contradiction:

Improvestability of assist force applicationVSAvoidsteering response speed

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The system executes abnormality detection before the sensor signal becomes clearly abnormal, using the residual sensor signal to detect potential issues through instantaneous motor torque application. This preliminary detection allows the system to maintain assist force application with full or near-full assistance until actual failure occurs, rather than gradually reducing assistance, thereby maintaining both reliability and steering responsiveness

Inventive Principle:

Principle #10Preliminary action

3Reliability

If instantaneous motor torque is applied for abnormality detection, then reliability improves, but use of energy increases

Engineering Contradiction:

Improvedetection accuracy of sensor abnormalityVSAvoidenergy consumption of motor

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The system applies instantaneous motor torque periodically or at specific intervals to detect sensor abnormalities, rather than continuously. The control device controls the motor to apply instantaneous torque at predetermined timing to generate rotation of the rotation body, enabling abnormality detection while minimizing energy consumption by keeping the motor idle during normal operation periods

Inventive Principle:

Principle #19Periodic action

Data Source

PatentEP2674348B1Electric power steering device and sensor abnormality detection device

Publication Date: 2017.10.04 JTEKT CORP

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AI summary

An ECU controls the operation of an EPS actuator in order to periodically apply instantaneous motor torque to a steering system when assist continuation control is executed using a sensor signal (residual sensor signal) that is output by a sensor element in which an abnormality has not been detected, regardless of the application of an assist force. The ECU also detects an abnormality in the residual sensor signal based on whether the application of instantaneous motor torque is reflected in the residual sensor signal, which is the basis of the assist continuation control.