Electric Power Steering Feedback Gain Adjustment

Solution Overview

Problem

Conventional electric power steering systems can cause an uncomfortable feeling for drivers due to rigid steering operations when current feedback control is executed with a held detected steering torque value, leading to a fixed assist force.

Innovation Solution

The system reduces this discomfort by implementing a smaller feedback gain during current feedback control when the detected steering torque value is held, allowing the motor's actual current value to follow the command value more moderately, and includes a redundant torque sensor design for continuous malfunction monitoring and adaptive control modes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If current feedback control is executed with a held detected steering torque value, then the system can maintain continuous control during sensor malfunction diagnosis periods, but the assist force becomes fixed and causes rigid steering operation feeling

Engineering Contradiction:

Improvecontinuous control during sensor diagnosisVSAvoidsteering operation smoothness

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The feedback gain is dynamically adjusted based on the operational state: a first (larger) feedback gain is used during normal operation to ensure responsive current control, while a second (smaller) feedback gain is applied when the steering torque value is held during sensor diagnosis periods. This dynamic adjustment prevents rigid steering feeling while maintaining continuous control reliability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the feedback gain parameter according to the control mode. During normal operation, a larger feedback gain is applied for responsive current control. When the detected steering torque value is held during magnetic field application periods, a smaller feedback gain is applied to prevent the assist force from becoming fixed, thereby maintaining steering smoothness while ensuring continuous control.

Inventive Principle:

Principle #35Parameter changes

2Speed

If a larger feedback gain is used for responsive current control, then the motor current follows the command value quickly, but the assist force becomes fixed when torque value is held, causing rigid steering feeling

Engineering Contradiction:

Improvecurrent response speedVSAvoidsteering operation comfort

Core Design Contradiction:

SpeedVSEase of operation

Solution Approach 1:

The feedback gain is dynamically adjusted based on the operational state: a first (larger) feedback gain is used during normal operation to ensure responsive current control, while a second (smaller) feedback gain is applied when the steering torque value is held during sensor diagnosis periods. This dynamic adjustment prevents rigid steering feeling while maintaining continuous control reliability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the feedback gain parameter according to the control mode. During normal operation, a larger feedback gain is applied for responsive current control. When the detected steering torque value is held during magnetic field application periods, a smaller feedback gain is applied to prevent the assist force from becoming fixed, thereby maintaining steering smoothness while ensuring continuous control.

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 ensures a smooth steering mechanism operation and reduces driver discomfort by preventing the fixation of output torque to a constant value, even when the detected steering torque value is held, while continuously monitoring for sensor malfunctions.

Implementation Method 1

The torque sensor includes a Hall IC and a magnetic circuit that applies magnetic flux corresponding to steering torque applied by a driver to the Hall IC

Methodology Applied

Scientific EffectHall Effect: Hall Effect

Implementation Method 2

the system includes a magnetic field generator that periodically applies a magnetic field to the torque sensor

Methodology Applied

Scientific EffectMagnetic Field: Magnetic Field

Data Source

PatentEP2842837B1Electric power steering system

Publication Date: 2017.05.31 JTEKT CORP

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AI summary

There is provided an electric power steering system that makes it possible to reduce an uncomfortable feeling given to a driver even when current feedback control is executed in a state where a detected steering torque value is held. The electric power steering system includes a torque sensor (6) that outputs a detection signal (SÄ) corresponding to a steering torque; and a controller (5) that controls driving of a motor (30). The controller (5) computes a detected steering torque value (Ä) based on the detection signal (SÄ) from the torque sensor (6), and executes current feedback control for causing an actual current value (I) of the motor (30) to follow a current command value (I*) based on the detected steering torque value (Ä). When the detected steering torque value (Ä) is held, the controller (5) makes a feedback gain of the current feedback control smaller than a feedback gain that is used when the detected steering torque value (Ä) is not held.