Electric Brake Actuator Magnetic Sensor Positioning
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Solution Overview
Problem
Existing electric brake systems face challenges in accurately detecting the pressing force of friction pads due to frictional heat, which affects sensor signal noise and reliability, and require costly noise reduction and leak prevention measures.
Innovation Solution
An electric brake system with a magnetic sensor positioned to receive a reaction force from a linear motion member, using a magnetic pole row with alternating N-poles and S-poles to minimize noise influence and a temperature sensor for signal correction, ensuring accurate detection of pressing force while maintaining system stability and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the strain sensor is provided at the portion of the caliper body where the bridge is joined to one of the opposed pieces to detect the pressing force, then the pressing force can be detected, but the sensor tends to be heated to high temperature by frictional heat, making it impossible to provide a circuit for processing the sensor signal sufficiently close to the strain sensor, which increases noise in the sensor signal
Solution Approach 1:
The magnetic sensor is extracted from the heat-affected zone near the friction pad and bridge connection, and repositioned on the reaction force receiving member or stationary member where temperature is lower, thereby removing the harmful thermal effect while preserving detection capability
Solution Approach 2:
The reaction force receiving member acts as an intermediary element that transmits the pressing force information from the friction pad to the magnetic sensor, allowing indirect measurement that avoids direct exposure to frictional heat
2Measurement precision
If the strain sensor is provided at the portion of the caliper body where the bridge is joined to one of the opposed pieces, then the pressing force can be detected, but when the caliper body is heated to high temperature, the temperature distribution becomes uneven, thus generating thermal strain, and since the strain sensor picks up such thermal strain too, it is difficult to measure only the strain due to the pressing force of the friction pad with high accuracy
Solution Approach 1:
The magnetic sensor is extracted from the high-temperature zone in the caliper body and relocated to the reaction force receiving member or stationary member, which are positioned away from the frictional heat source, thereby avoiding thermal strain interference
Solution Approach 2:
The strain gauge (mechanical sensor) that directly measures strain and is susceptible to thermal strain is replaced with a magnetic sensor system that detects position changes through magnetic field variations, providing immunity to thermal strain effects
3Measurement precision
If the electrodes for detecting the pressing force of the friction pad are provided in the linear motion member, then the pressing force can be detected by measuring electrical resistance, but the electrodes tend to be heated to high temperature, so that it is impossible to provide the signal processing circuit sufficiently close to the electrodes, so that noise in the sensor signal increases
Solution Approach 1:
The sensing function is extracted from the linear motion member where electrodes would be heated, and transferred to the reaction force receiving member or stationary member where the magnetic sensor operates in a cooler environment, eliminating thermal interference
Solution Approach 2:
The electrical resistance measurement method using electrodes is replaced with a magnetic field-based position detection method, which allows for better thermal management and signal processing
4Reliability
If hydraulic fluid in the hydraulic chamber leaks and air enters the hydraulic pressure chamber, then the output of the hydraulic pressure sensor does not correspond to the pressing force of the friction pad any more, but maintaining liquid tightness of the hydraulic pressure chamber with high reliability requires high costs
Solution Approach 1:
The sensing mechanism is extracted from the hydraulic system entirely, replacing hydraulic pressure sensing with magnetic position sensing, thereby eliminating the risk of hydraulic fluid leakage and air entrapment while avoiding the need for expensive seal maintenance
Solution Approach 2:
The hydraulic pressure sensing system is replaced with a magnetic field-based position detection system, eliminating hydraulic components and their associated leakage risks, while reducing manufacturing and maintenance costs
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
The system effectively detects the pressing force of the friction pad with high accuracy and stability, minimizing noise interference and maintaining reliability, while reducing costs associated with noise reduction and leak prevention.
Implementation Method 1
a magnetic sensor mounted to the other of the reaction force receiving member and the stationary member so as to face the magnetic pole row in a direction perpendicular to the axial direction such that the magnetic sensor can detect a change in relative position between the magnetic sensor and the magnetic pole row in the axial direction
Data Source
AI summary
An electric linear motion actuator includes a linear motion mechanism for converting the rotation of a rotary shaft to a linear motion of an outer ring member. The electric linear motion actuator further includes a reaction force receiving member adapted to receive an axially rearward reaction force, and a stationary member provided axially rearward of the reaction force receiving member. A magnetic pole row is mounted to the reaction force receiving member, while the magnetic sensor is mounted to the stationary member.