Torque Sensor Back Yoke Stress Cutout Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing torque sensors in steering devices face errors due to the adhesive peeling away, causing the ring magnet to shift on the back yoke during input shaft rotation, leading to inaccurate torque detection.
Innovation Solution
The torque sensor design incorporates a back yoke with a stress reduction cutout and a ring magnet fixed using an adhesive, where the adhesive is applied between the back yoke and the ring magnet, and the back yoke is press-fitted onto the input shaft, reducing shearing stress and preventing the ring magnet from shifting by using rotation stopping recesses and projecting portions to latch the ring magnet in place.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the ring magnet is fixed to the back yoke using adhesive only, then the structure is simple and easy to manufacture, but the ring magnet may shift position when the adhesive peels away during input shaft rotation
Solution Approach 1:
The patent combines multiple fixation methods: the back yoke is press-fitted onto the input shaft to provide radial clamping force, and rotation stopping recesses are formed in the back yoke to mechanically prevent rotational movement of the ring magnet. This merging of press-fit and mechanical interlocking ensures the ring magnet remains firmly positioned without relying solely on adhesive.
Solution Approach 2:
The back yoke is segmented with rotation stopping recesses that create discrete mechanical barriers against ring magnet rotation. These recesses divide the continuous contact surface into segmented engagement points, providing reliable rotational constraint while maintaining overall structural integrity.
2Reliability
If the back yoke is press-fitted onto the input shaft, then the ring magnet position is stabilized, but shearing stress concentrates at the adhesive interface between the back yoke and ring magnet
Solution Approach 1:
The patent extracts the rotational constraint function from the adhesive interface and relocates it to the rotation stopping recesses formed in the back yoke. By taking out the rotational stopping function from the adhesive bond, the design eliminates shearing stress concentration at the adhesive interface while maintaining reliable position stabilization through the press-fit structure and mechanical recesses.
3Reliability
If the adhesive interface is strengthened to prevent ring magnet shift, then position stability improves, but the structure becomes more complex and manufacturing difficulty increases
Solution Approach 1:
The patent replaces the reliance on adhesive bonding (chemical/mechanical bond) with a mechanical press-fit system and geometric rotation stopping recesses. This mechanics substitution achieves position stability through physical constraints rather than adhesive strength, simplifying the overall structure by eliminating the need for complex adhesive bonding processes and reducing manufacturing complexity.
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 design ensures accurate torque detection by preventing the ring magnet from shifting, maintaining the position of the magnetic flux source and reducing errors in the output signal, even under thermal expansion and adhesive deterioration, thereby maintaining consistent steering assist torque.
Implementation Method 1
a ring magnet 23 formed from a multipolar magnet and fixed to a lower end surface of the back yoke 24 via an adhesive 64
Implementation Method 2
the back yoke 24 is press-fitted onto the input shaft 11, reducing shearing stress
Implementation Method 3
the back yoke 24 is press-fitted onto the input shaft 11
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A torque sensor 2 detects a torque acting on a torsion bar 21 1 provided between a first shaft 11 and a second shaft 12 on the basis of a magnetic flux density led to a rotating magnetic circuit portion 25 from a magnetism generating portion 22. The magnetism generating portion 22 includes a back yoke 24 and a ring magnet 23. The back yoke 24 includes a fitting portion 61D fitted onto the first shaft 11, a joint portion 61A, 61B to which the ring magnet 23 is joined, and a stress reduction cutout 50, 55, 56 that suppresses a transmission of a deformation stress generated in a radial direction of the fitting portion 61D to the joint portion 61A, 61B.