Sensor Unit Magnetic Field Cancellation for Current Detection

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Solution Overview

Problem

The accuracy of current detection in sensor units is degraded due to magnetic fields generated from bus bars connecting switch elements and motor terminals, which interfere with the magneto-electric conversion device.

Innovation Solution

A sensor unit configuration where the magneto-electric conversion device is positioned between switch and motor terminals in a lateral direction, orthogonal to the bus bar, allowing magnetic fields from these terminals to cancel each other out, thereby reducing interference and maintaining detection accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the magneto-electric conversion device is positioned to face the bus bar for current detection, then current detection function is achieved, but magnetic fields from switch terminals and motor terminals interfere with detection accuracy

Engineering Contradiction:

Improvecurrent detection accuracyVSAvoidmagnetic field interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent positions the magneto-electric conversion device to detect both the magnetic field from the bus bar (useful signal) and the magnetic fields from switch terminals and motor terminals (harmful interference). By strategically placing the device in a location where the harmful magnetic fields from opposite directions can cancel each other out, the interference is converted into a beneficial effect that enhances detection accuracy.

Inventive Principle:

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

Solution Approach 2:

The patent transitions from a conventional one-dimensional arrangement where the sensor faces the bus bar directly, to a three-dimensional spatial configuration where the sensor is positioned to face a middle portion of the bus bar across a clearance. This spatial repositioning allows the sensor to be influenced by magnetic fields from multiple sources (bus bar, switch terminals, motor terminals) in different directions, enabling the harmful fields to cancel each other out.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Measurement precision

If the magneto-electric conversion device is placed close to the bus bar for accurate detection, then detection sensitivity improves, but magnetic field interference from terminals increases

Engineering Contradiction:

Improvedetection sensitivityVSAvoidterminal magnetic field interference

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent strategically positions the magneto-electric conversion device close to the bus bar to maintain high detection sensitivity, while simultaneously placing it in a location where the magnetic fields from switch terminals and motor terminals interfere constructively (cancel each other out). This converts the harmful terminal magnetic fields into a beneficial cancellation effect that protects the sensitive detection.

Inventive Principle:

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

3Measurement precision

If the sensor is positioned between switch terminal and motor terminal in lateral direction, then magnetic field cancellation occurs, but device complexity increases

Engineering Contradiction:

Improvecurrent detection accuracyVSAvoidsensor unit configuration

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent introduces a lateral positioning dimension, placing the magneto-electric conversion device between the switch terminal and motor terminal in a direction orthogonal to the bus bar. This additional spatial dimension enables magnetic field cancellation from the terminals while maintaining a relatively simple overall device structure.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 effectively suppresses the degradation of current detection accuracy by canceling out magnetic fields from switch and motor terminals, ensuring precise current measurement.

Implementation Method 1

The magneto-electric conversion device is disposed to face a middle portion of the bus bar across a clearance in a predetermined direction to detect a magnetic field caused by an electric current flowing through the bus bar

Methodology Applied

Scientific EffectMagnetic field detection: Electromagnetic Induction

Implementation Method 2

the magneto-electric conversion device is located between the switch element and the motor terminal in a lateral direction that is orthogonal to the predetermined direction

Methodology Applied

Scientific EffectMagnetic field cancellation: Magnetic Field

Data Source

PatentUS11333687B2Sensor unit

Publication Date: 2022.05.17 DENSO CORP

AI summary

A sensor unit includes a bus bar and a magneto-electric conversion device. The bus bar connects a plurality of switch elements constituting a part of a power conversion circuit and a motor. The magneto-electric conversion device is disposed to face a middle portion of the bus bar across a clearance in a predetermined direction to detect a magnetic field caused by an electric current flowing through the bus bar, to thereby detects the electric current. The bus bar includes a first end and a second end. The first end of the bus bar is connected to one of a switch terminal extending from the switch elements and a motor terminal extending from the motor, and the second end of the bus bas is connected to the other of the switch terminal and the motor terminal.