Electric Machine Torque Control for Drive Train Load Reduction

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Solution Overview

Problem

In vehicles with electric drives, the high mass moment of inertia relative to the output shaft leads to extreme mechanical stress on the drive train during ABS control or full braking, causing premature wear and discomfort due to vibrations, which also impairs ABS control and lengthens the braking distance.

Innovation Solution

The method involves determining the mechanical load on cardan shafts connecting electric machines and drive wheels, and controlling the electric machines to counteract these loads, reducing torsional moments and vibrations, thereby minimizing mechanical stress and improving dynamics and comfort.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If the electric machine is positioned close to the drive wheel to reduce component dimensions, then the mass moment of inertia increases, but this causes extreme mechanical stress and premature wear on the drive train components

Engineering Contradiction:

Improvecomponent dimensionsVSAvoidmechanical stress on drive train

Core Design Contradiction:

Volume of moving objectVSStrength

Solution Approach 1:

The control device applies preliminary counteracting torque through the electric machine before the ABS friction brake is activated. By detecting the upcoming ABS control and pre-positioning the electric machine to counteract the expected inertial loads, the system prevents extreme mechanical stress on the cardan shaft and differential gear stage, thereby reducing premature wear while maintaining compact component dimensions

Inventive Principle:

Principle #9Preliminary anti-action

2Speed

If the friction brake torque is increased to improve braking performance, then the mechanical stress on the drive train increases, but this leads to vibrations and discomfort for occupants

Engineering Contradiction:

Improvebraking performanceVSAvoidvibrations and discomfort

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The system converts the harmful effect of the electric machine's high mass moment of inertia into a beneficial counterbalancing force. During ABS control, the electric machine generates torque in the opposite direction to the friction brake torque, using the inertial properties that cause harm to instead provide mechanical counterbalancing that reduces vibrations and discomfort for occupants

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Object-affected harmful factors

If the cardan shaft is made more rigid to reduce vibrations, then the mechanical stress during ABS control increases, but this causes premature wear on the shaft

Engineering Contradiction:

ImprovevibrationsVSAvoidmechanical stress on cardan shaft

Core Design Contradiction:

Object-affected harmful factorsVSStrength

Solution Approach 1:

The system replaces purely mechanical vibration damping (which would require rigid cardan shafts) with an active control system using the electric machine. The electric machine dynamically adjusts torque to counteract vibrations caused by ABS friction brake interventions, achieving vibration reduction without increasing mechanical stress or rigidity that would lead to premature wear

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 reduces the risk of premature wear, lowers the braking distance, and enhances the safety and comfort of vehicle occupants by minimizing mechanical stress and vibrations, allowing for smaller component dimensions and cost savings.

Implementation Method 1

the electric machine assigned to this drive wheel is controlled in such a way that the mechanical load is counteracted

Methodology Applied

Scientific EffectElectromagnetic torque generation: Electromagnetic Induction

Implementation Method 2

at least one cardan shaft connecting this electric machine and this drive wheel

Methodology Applied

Scientific EffectTorque transmission through rotating shaft: Torque

Implementation Method 3

at least two wheels of the motor vehicle are each assigned a friction brake

Methodology Applied

Scientific EffectFriction braking: Friction

Data Source

PatentEP2758270B1Method for reducing a mechanical load on at least one component of the drive train of a motor vehicle, and corresponding motor vehicle

Publication Date: 2018.03.07 AUDI AG

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Figure 2~3

AI summary

The present invention relates to a method for reducing a mechanical load on at least one component of the drive train of a motor vehicle (10) having at least two wheels, of which at least one is a drive wheel (12a, 12b), wherein the motor vehicle (10) comprises an anti-lock braking system (16), and at least one electrical machine (18) which, in order to drive exactly one drive wheel (12a, 12b) of the motor vehicle (10), is coupled to said drive wheel, wherein a respective friction brake (14a, 14b) is assigned to each of at least two wheels of the motor vehicle (10), said method comprising the following steps: a) provision of the anti-lock braking system (16) in such a manner that it can act individually for each wheel on the friction brakes (14a, 14b) for the wheels of the motor vehicle (10) (step 100); b) during an actuation of the anti-lock braking system (16) (step 110): b1) determining the mechanical load on at least one articulated shaft (20a, 20b) connecting an electrical machine (18a, 18b) and an associated drive wheel (12a, 12b) (step 120); b2) activating the electrical machine (18a, 18b) assigned to the drive wheel (12a, 12b) in such a manner that the mechanical load is counteracted (step 140). The invention additionally relates to a corresponding motor vehicle.