Electric Power Steering Control Device Hands-Off Detection

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Solution Overview

Problem

Conventional electric power steering systems require a significant time lag to determine when a driver has taken their hands off the steering wheel, leading to delayed switching between manual and automatic driving modes due to reliance on torsion bar torque measurements.

Innovation Solution

A control device that calculates steering wheel torque from torsion bar torque and rotation angle, allowing for quicker determination of the hands-off state by comparing the torque with threshold values, thereby reducing the time taken to switch between driving modes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the system uses conventional torsion bar torque measurement to determine hands-off state, then the determination is based on direct torque sensing, but the time lag in detection is significant

Engineering Contradiction:

Improvehands-off state detection accuracyVSAvoiddetection time lag

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent introduces rotation angle as an intermediary parameter to detect hands-off state. Instead of directly measuring torque (which has time lag), the system measures rotation angle changes and infers torque state, thereby reducing detection time lag while maintaining accuracy

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces direct mechanical torque sensing with a computational approach using rotation angle data. By substituting the mechanical measurement method with a computational model that calculates torque from angular position changes, the system achieves faster response

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If the system waits for torque to return to zero to detect hands-off state, then false detection is avoided, but the detection time is delayed

Engineering Contradiction:

Improvehands-off state determination reliabilityVSAvoidswitching response time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent performs preliminary detection by monitoring rotation angle trends before torque actually reaches zero. By detecting the directional change in rotation angle that precedes torque zero-crossing, the system triggers mode switching in advance, reducing time lag while maintaining reliability through threshold-based validation

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Instead of waiting for torque to reach zero (conventional approach), the patent inverts the logic by detecting the approach to zero state through rotation angle changes. The system detects hands-off state when rotation angle change rate indicates torque is approaching zero, rather than waiting for actual zero crossing

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS11787470B2Electric power steering apparatus, control device, control method, and motor module

Publication Date: 2023.10.17 NIDEC CORP(JP)

AI summary

A processor calculates a steering wheel torque which an input shaft receives, from a torsion bar torque applied to a torsion bar between the input shaft to which an operation by a driver is input and an output shaft to which a motor applies a drive force, and a rotation angle of the input shaft, compares a calculated steering wheel torque with a threshold value, and determines that a vehicle is in a hands-off state in which the input shaft receives no input based on the operation by the driver when determining that the calculated steering wheel torque changes from a state in which the steering wheel torque exceeds a threshold value to a state in which the steering wheel torque falls below the threshold value.