Torque Sensor Integrally Molded Resin Housing
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Solution Overview
Problem
Conventional magnetostrictive torque sensors in electric power steering systems face detection accuracy issues due to temperature-induced backlash and complexity in assembly, resulting from differing coefficients of linear expansion among materials used in the sensor housing, yokes, and shaft, which affects magnetic path stability and output accuracy.
Innovation Solution
The torque sensor employs integrally molded resin to fix coil units and spacers, maintaining a stable distance and eliminating the need for precise dimensional accuracy control, thus preventing backlash and simplifying assembly, while using a spacer with a smaller inner diameter and tapered surfaces for enhanced accuracy and resilience against temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional metal materials with different coefficients of linear expansion are used for sensor housing, yokes, and shaft, then structural strength is improved, but temperature-induced backlash and detection accuracy deteriorate
Solution Approach 1:
The patent applies composite materials by combining resin (housing material) with metal components (yokes and shaft). The resin housing material has a coefficient of linear expansion matched to the metal components, creating a composite structure that maintains dimensional stability across temperature variations while providing adequate structural strength for sensor housing and support functions.
Solution Approach 2:
The patent changes the material parameter (coefficient of linear expansion) by selecting resin as the housing material with a specific expansion coefficient that matches the metal components. This parameter matching eliminates differential thermal expansion, preventing backlash and maintaining detection accuracy across the operating temperature range of -40°C to 80°C.
2Stability of the object's composition
If conventional metal housing with precise dimensional control is used, then structural stability is improved, but manufacturing complexity and assembly time increase
Solution Approach 1:
The patent merges multiple components (housing, coil unit support, and positioning structures) into a single integrally molded resin housing. This consolidation eliminates the need for separate metal housing parts and reduces the number of assembly steps, while the integral structure inherently maintains dimensional stability and positional accuracy of internal components.
Solution Approach 2:
The patent changes the material parameter from metal to resin, which has lower thermal expansion and can be molded with built-in dimensional stability. The resin housing is designed with integrated features that automatically maintain precise spacing and positioning of coil units and spacers, eliminating the need for post-assembly adjustments or additional fastening operations.
3Measurement precision
If spring members are used to prevent backlash, then detection accuracy is improved, but device complexity and component count increase
Solution Approach 1:
The patent converts the potential harm of thermal expansion into a benefit by matching the expansion coefficients of the resin housing and metal components. Instead of using spring members to compensate for expansion differences, the material parameter matching causes all components to expand and contract uniformly with temperature changes, eliminating backlash without requiring additional compensating mechanisms.
Solution Approach 2:
The patent extracts and eliminates the spring members from the sensor structure by addressing the root cause of backlash through material parameter matching. The resin housing and metal components are designed to expand together, making the backlash-prevention function inherent in the material selection rather than requiring separate mechanical compensation elements.
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 stabilizes the sensor's output, improves detection accuracy, reduces component count and assembly time, and enhances productivity by eliminating the need for spring members and precise processing, ensuring accurate torque detection even in severe temperature environments.
Implementation Method 1
a magnetostrictive film (for example, a Ni—Fe alloy film) having magnetic anisotropy is attached on the surface of a shaft. When torque is applied to the shaft from outside, the magnetostrictive torque sensor magnetically detects changes of a magnetic characteristic (magnetic permeability) of the magnetostrictive film, which is generated in accordance with a twisting of the shaft
Data Source
AI summary
The torque sensor includes a plurality of coil units having a substantially cylindrical shape, the coil units including a plurality of detection coils arranged to face a magnetic characteristic change portion formed on a rotary shaft. The coil units include a first coil unit and a second coil unit, and the first coil unit and the second coil unit are disposed in the axial direction of the shaft. The first coil unit and the second coil unit are fixed in an integrally molded resin. Thereby, there is provided a torque sensor having a high productivity and an easy configuration and a method of manufacturing the torque sensor.