Torque Sensor Sleeve Structure for Magnet Stress Control
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Solution Overview
Problem
The existing torque sensors in electric power steering apparatuses face issues with reduced yield due to stress in the magnet when the sleeve is press-fit onto the steering shaft, leading to changes in magnetic properties and deterioration in detection accuracy.
Innovation Solution
A torque sensor design featuring an annular sleeve with a rotating member connecting part and an intermediate member connecting part, where the intermediate member connecting part is shifted axially and has a larger outer diameter than the rotating member connecting part, absorbing stress during press-fitting and preventing deformation, thus maintaining the distance between the magnet and yoke.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the sleeve is press-fit onto the steering shaft with a small step between small diameter part and large diameter part, then the radial size is reduced, but stress occurs in the magnet causing yield reduction
Solution Approach 1:
The sleeve is divided into three distinct parts along the axial direction: a small diameter part for press-fitting onto the steering shaft, a large diameter part for supporting the magnet, and an intermediate part connecting them. This segmentation allows each part to perform its specific function independently, enabling the sleeve to maintain a compact radial size while preventing stress transmission to the magnet during press-fitting.
2Volume of moving object
If the step between small diameter part and large diameter part is made smaller, then the radial size is reduced, but the step cannot be pushed during press-fitting causing stress in the magnet
Solution Approach 1:
The intermediate part acts as a mediator between the small diameter part and the large diameter part. During press-fitting, this intermediate section absorbs the deformation and prevents direct stress transmission to the magnet-supported large diameter part, thereby maintaining manufacturing precision while enabling compact radial dimensions.
3Ease of manufacture
If the tip of the large diameter part is pushed to replace pushing the step, then press-fitting can proceed, but stress occurs in the magnet changing its magnetic properties
Solution Approach 1:
By segmenting the sleeve into distinct diameter sections with an intermediate connecting part, the design allows the small diameter part to be press-fitted onto the steering shaft without directly transmitting stress to the magnet. The intermediate part serves as a stress-absorbing transition zone, enabling ease of manufacture while preserving magnet reliability.
Data Source
AI summary
In a torque sensor (1), a sleeve (21) is an annular member mounted on a first rotating member. An intermediate member (26) is an annular member placed on an outer circumferential face of the sleeve (21). A magnet (25) is an annular member placed on an outer circumferential face of the intermediate member (26). A yoke (35) is mounted on a second rotating member and faces the magnet (25) in a radial direction. A rotating member connecting part (211) of the sleeve (21) is cylindrical and is in contact with the first rotating member. An intermediate member connecting part (215) is at a position shifted with respect to the rotating member connecting part (211) in an axial direction parallel to a central axis Z. An outer diameter (E219) of a sleeve end (219), which is an end of the intermediate member connecting part (215) opposite from the rotating member connecting part (211), is smaller than a minimum inner diameter (125) of the magnet (25).