Torque Control for Electric Vehicle Traction Motors

Solution Overview

Problem

Electric vehicles with two independently driving traction motor units face issues due to manufacturing and assembling accuracy variations, leading to torque output differences between left and right wheels, causing discomfort and requiring driver corrections, especially when the motor components' compatibility with inverters is low or when motor output characteristics change due to aging.

Innovation Solution

An electric vehicle system that includes a torque command unit, motor driver, torque difference occurrence determiner, and driving force difference reducer to automatically adjust output torque by determining and reducing differences between the actual driving forces of the left and right traction motor units, using information from torque command values, braking signals, steering angle, and steering torque to maintain stable vehicle performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Weight of moving object

If two independent traction motor units are used to drive left and right drive wheels, then size reduction and weight reduction are achieved, but torque output differences occur between left and right wheels due to manufacturing accuracy variations

Engineering Contradiction:

Improvevehicle weightVSAvoidtorque output consistency

Core Design Contradiction:

Weight of moving objectVSManufacturing precision

Solution Approach 1:

The control unit continuously monitors the actual driving forces of left and right drive wheels and automatically adjusts torque command values to compensate for differences. This feedback mechanism detects torque output variations caused by manufacturing inaccuracies and real-time adjustments ensure consistent vehicle behavior despite component variations

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system dynamically changes torque command parameters for each traction motor unit based on detected performance differences. By adjusting electrical parameters (torque commands) rather than mechanical components, the system compensates for manufacturing variations without requiring higher precision manufacturing

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If high manufacturing and assembling accuracy is required for motor components, then torque output consistency between left and right wheels is improved, but manufacturing cost increases

Engineering Contradiction:

Improvetorque output consistencyVSAvoidmanufacturing cost

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The control unit continuously monitors the actual driving forces of left and right drive wheels and automatically adjusts torque command values to compensate for differences. This feedback mechanism detects torque output variations caused by manufacturing inaccuracies and real-time adjustments ensure consistent vehicle behavior despite component variations

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs self-diagnosis and self-correction by monitoring its own torque output characteristics and automatically adjusting control parameters. This eliminates the need for expensive high-precision manufacturing by allowing the system to compensate for its own manufacturing variations autonomously

Inventive Principle:

Principle #25Self-service

3Device complexity

If the same torque command values are applied to both traction motor units, then control simplicity is maintained, but vehicle behavior deviates from driver intention due to torque differences

Engineering Contradiction:

Improvecontrol system complexityVSAvoidvehicle behavior predictability

Core Design Contradiction:

Device complexityVSEase of operation

Solution Approach 1:

The control unit continuously monitors the actual driving forces of left and right drive wheels and automatically adjusts torque command values to compensate for differences. This feedback mechanism detects torque output variations caused by manufacturing inaccuracies and real-time adjustments ensure consistent vehicle behavior despite component variations

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs preliminary detection of torque differences and pre-adjusts torque command values before vehicle operation. By anticipating and compensating for torque variations in advance, the system ensures accurate vehicle behavior from the start without requiring complex real-time interventions

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentEP2810818B1Electric vehicle

Publication Date: 2019.07.31 NTN CORP

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Figure 2~3
Figure 4~5

AI summary

An electric vehicle is provided which allows an output torque to be automatically adjusted during travelling even when there is a difference in output characteristic between two traction motor units (6, 6) that independently drive left and right drive wheels (2). The electric vehicle includes the motor units; a torque command unit (23) that outputs torque command values to the motor units; a torque difference occurrence determiner (31) that determines that a difference has occurred between actual driving forces TL, TR of the respective drive wheels (2) even when the torque command unit applies the same torque command values TL*, TR* to the motor units; and a driving force difference reducer (32) that, if the determiner determines that a driving force difference not less than a set value has occurred between the drive wheels, causes control of reducing the driving force difference to be performed during travelling.