Electric Power Steering Reverse Steering Detection and Gain Control

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Solution Overview

Problem

Existing electric power steering devices face issues with accurate detection of reverse steering and insufficient suppression of steering torque variation, leading to driver discomfort and instability in the control system, due to noise interference and incorrect detection conditions.

Innovation Solution

An electric power steering device with a motor rotational speed detection unit, acceleration calculation unit, and reverse steering detection unit that determines the start of reverse steering based on the magnitude and direction of motor rotational speed and acceleration, and adjusts the transfer gain for current command control to accurately detect and suppress steering torque variation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If the torque proportional gain is increased to reduce steering torque and improve driver feeling, then the steering torque is reduced, but the control system stability deteriorates causing oscillation

Engineering Contradiction:

Improvesteering torqueVSAvoidcontrol system stability

Core Design Contradiction:

Ease of operationVSStability of the object's composition

Solution Approach 1:

The torque proportional gain is made dynamically adjustable based on operating conditions. The control device switches between a first torque proportional gain (higher) for low vehicle speeds and a second torque proportional gain (lower) for high vehicle speeds, allowing the system to optimize both steering effort and stability according to the driving situation.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control device changes the parameter (torque proportional gain) based on vehicle speed. By detecting vehicle speed and selecting appropriate gain values, the system adapts the assist torque characteristics to different operating conditions, resolving the trade-off between steering lightness and stability.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If the transfer gain is increased to suppress disturbance torque, then the disturbance suppression is improved, but the control system stability deteriorates

Engineering Contradiction:

Improvedisturbance torqueVSAvoidcontrol system stability

Core Design Contradiction:

Object-affected harmful factorsVSStability of the object's composition

Solution Approach 1:

The control device applies different transfer gains for different steering conditions. A first transfer gain (higher) is used when the steering wheel rotation direction reverses to suppress disturbance torque, while a second transfer gain (lower) is used during normal operation to maintain stability. This localized adjustment of gain based on specific conditions resolves the contradiction.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The transfer gain is dynamically adjusted based on steering wheel rotation direction detection. The system monitors for reversals in rotation direction and switches between high and low gain modes accordingly, allowing disturbance suppression only when necessary while maintaining overall system stability.

Inventive Principle:

Principle #15Dynamics

3Difficulty of detecting and measuring

If reverse steering detection is based on motor rotational speed sign reversal, then reverse steering can be detected, but erroneous detection or chattering occurs due to noise

Engineering Contradiction:

Improvereverse steering detectionVSAvoiddetection accuracy

Core Design Contradiction:

Difficulty of detecting and measuringVSReliability

Solution Approach 1:

The control device introduces an intermediary mechanism by detecting the rotation direction of the steering wheel through steering torque sign changes rather than directly monitoring motor rotational speed sign reversals. This intermediary detection method filters out noise and prevents erroneous detection while still accurately identifying reverse steering events.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The control device applies beforehand cushioning by implementing a determination period threshold. Reverse steering is only detected when the steering torque maintains the same sign for a predetermined period, cushioning against noise-induced false detections while still capturing genuine reverse steering maneuvers.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentUS11364948B2Electric power steering device

Publication Date: 2022.06.21 MITSUBISHI ELECTRIC MOBILITY CORP

AI summary

There is provided an electric power steering device, including: a reverse steering detection unit configured to determine start of reverse steering when a magnitude of a rotational speed of a motor is equal to or smaller than a set speed, a rotational acceleration of the motor is in a direction of causing the rotational speed of the motor to become 0, and a magnitude of the rotational acceleration of the motor is equal to or larger than a set acceleration; and a current command control unit configured to output a current command for the motor based on the steering torque or the rotational speed of the motor, in which the current command control unit is configured to increase a transfer gain from input to output by the current command control unit when the reverse steering detection unit determines start of the reverse steering.