Electric Motor Shielding for Rotor Position Sensor Accuracy

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Solution Overview

Problem

In electric motors for vehicles, the rotor's magnetic field perturbs the measuring magnetic field, affecting the accuracy of rotor position detection, which existing solutions do not entirely eliminate.

Innovation Solution

An electric motor assembly with a high magnetic permeability shield that houses the magnetic field sensor, keeping the rotor's magnetic field lines away from the measuring magnetic field, ensuring precise rotation angle measurement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the magnet and magnetic field sensor are arranged inside the metallic shaft to lessen perturbing influences, then the rotor position detection accuracy is improved, but the perturbing influences of the rotor magnetic field are not entirely eliminated

Engineering Contradiction:

Improverotor position detection accuracyVSAvoidperturbing magnetic field influence

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

A shield with high magnetic permeability is introduced as an intermediary element between the rotor magnetic field and the magnetic field sensor. This shield acts as a mediator that preferentially conducts the rotor's magnetic field lines away from the measuring magnetic field, thereby reducing perturbation while preserving measurement accuracy

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The harmful magnetic field lines are extracted and redirected through the shield, separating them from the measuring magnetic field. The shield effectively pulls the perturbing field lines into itself, removing their harmful influence on the sensor while maintaining the integrity of the measurement field

Inventive Principle:

Principle #2Taking out (Extraction)

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 configuration provides a perturbation-free measurement of the rotor's position and rotation angle, enhancing the accuracy of rotor position detection in electric motors for vehicles.

Implementation Method 1

the shield has high magnetic permeability and is closed in the area of the magnetic field sensor

Methodology Applied

Scientific EffectMagnetic permeability: Magnetic Field

Implementation Method 2

Owing to providing a shield with high magnetic permeability, the magnetic field of the rotor magnetic coil and the magnetic field line run through the shield and may thus be kept away from the measuring magnetic field

Methodology Applied

Scientific EffectMagnetic field shielding: Magnetic Field

Implementation Method 3

the magnet is connected to the rotor and generates a measuring magnetic field, in which the magnetic field sensor is situated

Methodology Applied

Scientific EffectMagnetic field generation: Magnetic Field

Implementation Method 4

The magnetic field sensor may be an MR sensor, based on the magnetoresistive effect

Methodology Applied

Scientific EffectMagnetoresistive effect: Magnetoresistance

Data Source

PatentUS11239731B2Electric motor assembly

Publication Date: 2022.02.01 BAYERISCHE MOTOREN WERKE AG

AI summary

An electric motor assembly (10), in particular for driving a vehicle, comprises an electric motor (12), a magnetic sensor (46) and a shield (14), the electric motor (12) being equipped with a stator (16), a rotor (18) and at least one magnet (28) which is connected to the rotor (18) for conjoint rotation therewith and generates a measuring magnetic field (MM). The magnetic sensor (46) is located in the measuring magnetic field (MM) and is connected to the shield (14), and the shield (14) has high magnetic permeability and is closed in the area of the magnetic sensor (46).