Steer-by-wire torque control via actuator current

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Solution Overview

Problem

The existing steer-by-wire system for vehicle steering control is ineffective in maintaining optimal steering reaction under adverse loading conditions such as bumps and potholes, leading to unpleasant sensations for the driver due to fluctuations in steering reaction torque.

Innovation Solution

A steering apparatus with a driver operating unit, a turning unit, a backup mechanism, a steering reaction actuator, and a controller that controls the wheel turning actuator and steering reaction actuator based on the operating parameter of the wheel turning actuator, reducing friction torque effects by using the driving current of the second motor to calculate the steering reaction command value, thereby suppressing torque fluctuations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If steering reaction torque is calculated based on steering angle from a sensor, then the steering reaction control can be implemented, but the steering reaction torque fluctuates under adverse loading conditions such as bumps and potholes

Engineering Contradiction:

Improvesteering reaction control reliabilityVSAvoidsteering reaction torque stability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent replaces the mechanical sensor-based steering angle measurement system with an electrical control system that calculates steering reaction torque based on the operating parameters (such as driving current) of the wheel turning actuator. This substitution eliminates the direct mechanical connection between the steering angle sensor and the reaction torque calculation, thereby preventing road surface disturbances from directly affecting the steering reaction torque.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces the wheel turning actuator's operating parameters as an intermediary variable between the steering input and the steering reaction torque calculation. Instead of directly using steering angle from a sensor, the system uses the actuator's current or power consumption as a mediator to estimate the steering reaction torque, which filters out the direct impact of road surface disturbances.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the backup mechanism is used to mechanically connect the driver operating unit to the turning unit, then reliable steering is provided, but friction torque from the backup mechanism causes unwanted fluctuations in steering reaction torque

Engineering Contradiction:

Improvesteering reliabilityVSAvoidfriction torque fluctuations

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent replaces the mechanical friction-based backup mechanism with an electrical control system. Instead of relying on the mechanical connection through the backup mechanism to determine steering reaction torque, the system uses electrical parameters (driving current) of the wheel turning actuator to calculate the reaction torque, thereby eliminating the harmful friction effects from the backup mechanism.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent uses the wheel turning actuator's electrical parameters as an intermediary to bypass the mechanical friction path. By calculating steering reaction torque based on the actuator's driving current rather than through the mechanical backup mechanism, the system filters out friction-induced fluctuations while maintaining steering reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If steering reaction torque is based on steering angle that is not affected by loading conditions, then the control system is simple, but it is difficult to effect optimum steering reaction control

Engineering Contradiction:

Improvecontrol system complexityVSAvoidsteering reaction control effectiveness

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent changes the parameter basis for steering reaction torque calculation from steering angle (spatial parameter) to wheel turning actuator operating parameters such as driving current or power consumption (electrical parameter). This parameter change allows the system to respond to adverse loading conditions while maintaining relatively simple control logic through direct measurement of actuator performance.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS7900742B2Vehicle steering control

Publication Date: 2011.03.08 NISSAN MOTOR CO LTD

AI summary

A steer-by-wire system is provided with a driver operating unit, a turning unit, a backup mechanism, a steering reaction actuator, a wheel turning actuator and a controller. The backup mechanism mechanically connects the driver operating unit to the turning unit via a first shaft to transmit an input torque from the driver operating unit to the turning unit when the driver operating unit and the turning unit are mechanically connected by the backup mechanism. The steering reaction actuator applies a steering reaction torque to the driver operating unit. The wheel turning actuator applies a wheel turning torque to the turning unit via a second shaft. The controller controls the wheel turning actuator and the steering reaction actuator. The controller is configured to control the steering reaction actuator based on an operating parameter of the wheel turning actuator.