Torque Sensor Sleeve Structure to Protect Magnet Accuracy
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Solution Overview
Problem
The existing torque sensors in electric power steering apparatuses face issues with yield reduction due to stress on the magnet when the sleeve is press-fit onto the steering shaft, leading to changes in magnetic properties and detection accuracy deterioration.
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 magnet's position and magnetic properties.
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 magnetic property changes and 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, preventing stress transmission to the magnet while maintaining compact radial dimensions.
Solution Approach 2:
The intermediate part acts as a mediator between the small diameter part and the large diameter part. It absorbs and isolates the stress generated during press-fitting, preventing this stress from being transmitted to the magnet. The intermediate part serves as a buffer zone that protects the magnet's magnetic properties while enabling the press-fit connection.
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 requiring the tip to be pushed which causes magnet stress
Solution Approach 1:
By segmenting the sleeve into distinct diameter parts with a clear intermediate section, the design provides a defined push surface at the tip without compromising the step structure. This allows the sleeve to be pushed during press-fitting without directly transmitting force to the magnet, combining compact radial size with manufacturability.
3Reliability
If the sleeve structure includes distinct small diameter part, large diameter part, and intermediate part, then magnet stress is prevented, but the device complexity increases
Solution Approach 1:
The sleeve integrates three functional parts (small diameter part, intermediate part, large diameter part) into a single monolithic component rather than assembling separate parts. This merging approach maintains the stress-prevention functionality while simplifying manufacturing and assembly, reducing overall device complexity despite the multi-part functional requirements.
Solution Approach 2:
The sleeve serves multiple functions simultaneously: it provides a press-fit connection surface, supports the magnet, absorbs stress during assembly, and maintains structural integrity. This multi-functionality is achieved within a single component design, avoiding the need for additional separate parts and reducing overall system complexity.
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).