Electric Power Steering Angle Estimation via Regenerative Current

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Solution Overview

Problem

Conventional electric power steering systems using brushless motors face challenges in accurately estimating motor rotational angles, especially in low-speed steering conditions, leading to inaccurate torque generation and differing steering feelings for drivers, which can impact safety when the angle detecting system fails.

Innovation Solution

The system employs an angle estimating section that fixes phase duties to 0% or 100% to detect regenerative currents, allowing for accurate angle estimation and continued assist-control even when the angle detecting system fails, using motor regenerative currents and dual-system windings to ensure reliable steering assistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If motor back-EMF is used to estimate motor rotational angle, then angle estimation can be performed, but sufficient voltage amplitude cannot be obtained in low-speed steering region leading to inaccurate angle estimation

Engineering Contradiction:

Improvemotor rotational angle estimation accuracyVSAvoidsteering speed

Core Design Contradiction:

Measurement precisionVSSpeed

Solution Approach 1:

The patent changes the detection parameter from motor back-EMF voltage to motor regenerative current. By fixing phase duties to 0% or 100% and detecting the current flowing through the motor during regenerative braking, the system obtains sufficient signal amplitude even at low steering speeds, resolving the accuracy issue in low-speed region

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Instead of using the motor's generated back-EMF voltage during normal operation, the patent inverts the approach by intentionally allowing regenerative braking and detecting the current flow in reverse direction. This inversion provides sufficient voltage amplitude for accurate angle estimation in low-speed conditions

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If angle detecting system fails, then system reliability is compromised, but accurate angle estimation is needed to continue assist-control

Engineering Contradiction:

Improvesteering assist continuityVSAvoidmotor rotational angle detection accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent introduces motor regenerative current as an intermediary parameter to estimate motor rotational angle when the primary angle detecting system fails. By using the current detection during regenerative braking as a mediator, the system can continue assist-control with accurate angle information even without the primary sensor

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent prepares an alternative angle estimation method using motor regenerative current in advance, so that when the primary angle detecting system fails, the system can immediately switch to the backup method without interruption, ensuring continuous and reliable steering assist

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Device complexity

If conventional angle estimation methods are used, then system complexity is reduced, but inaccurate torque generation occurs leading to differing steering feelings

Engineering Contradiction:

Improveangle estimation system complexityVSAvoidsteering feel consistency

Core Design Contradiction:

Device complexityVSEase of operation

Solution Approach 1:

The patent changes the detection parameter from motor back-EMF voltage to motor regenerative current, and changes the duty cycle to fixed 0% or 100%. This simple parameter change provides sufficient signal amplitude for accurate angle estimation across all steering speeds, ensuring consistent steering feel without adding system complexity

Inventive Principle:

Principle #35Parameter changes

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 enables accurate angle estimation and continued assist-control during low-speed steering, preventing sudden steering torque changes and maintaining vehicle stability, thus enhancing driver safety and steering feel.

Implementation Method 1

fixes the respective phase duties to 0% or 100% in order to detect a regenerative current of the motor

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentEP3351456B1Electric power steering device

Publication Date: 2020.03.04 NSK LTD

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AI summary

[Problem] An object of the present invention is to provide an electric power steering apparatus that can perform an angle estimating by using a motor regenerative current so as to accurately perform an angle estimating even in a low speed steering. [Means for solving the problem] The present invention is the electric power steering apparatus that calculates a current command value based on at least a steering torque, driving-controls a motor, which applies an assist torque to a steering system based on the current command value, by an inverter with respective phase duties of a PWM, and detects an angle of the steering system or the motor, comprising: an angle estimating section to estimate the angle when a detecting system of the angle is failed, wherein the electric power steering apparatus performs an assist-control based on an estimating angle that is estimated at the angle estimating section. The present invention can be also adapted to the control of the motor having multi-system windings.