Magnet Unit Thermal Stress Reduction via Segmented Connecting Elements
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Solution Overview
Problem
Generic magnet units for detecting the rotational state of a motor vehicle's steering shaft face issues with thermally induced stresses leading to crack formation due to the brittleness of magnetic elements and differing thermal expansion coefficients between the sleeve and magnet element, especially when directly injection molded or glued together.
Innovation Solution
A magnet unit design featuring a sleeve with a socket-shaped fastening section and a radially extending connecting flange with recesses, where the magnet element has connecting elements that form a positive connection with the sleeve in the tangential and axial directions, allowing for unhindered contraction and expansion without radial interference, thus reducing thermally induced stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the magnet element is injection molded directly onto the sleeve or glued to the sleeve, then a non-rotatable connection is achieved, but thermally induced stresses occur due to different thermal expansion coefficients leading to crack formation
Solution Approach 1:
The connection between the magnet element and sleeve is segmented into multiple discrete connecting elements (protrusions) distributed around the circumference, rather than a continuous rigid connection. This segmentation allows localized stress distribution and reduces the risk of crack propagation through the entire magnet element.
Solution Approach 2:
The connecting elements are designed with elastic deformation capability, allowing them to flex and accommodate thermal expansion differences between the magnet element and sleeve. The plastic material of the connecting elements can elastically deform under thermal stress, preventing rigid stress concentration that would lead to cracking.
2Strength
If the magnet element is made with high magnetic particle filling to achieve sufficient magnetic strength, then the magnetic performance is improved, but the plastic becomes more brittle and susceptible to thermal cracking
Solution Approach 1:
The magnet element exhibits local quality differences: the connecting elements are made of more elastic plastic material compared to the main body of the magnet element. This local variation in material properties allows the connecting regions to handle thermal stress while the main body maintains high magnetic particle filling for sufficient magnetic strength.
Solution Approach 2:
The magnet element is a composite material consisting of plastic matrix filled with magnetic particles. The connecting elements use a plastic composition optimized for elasticity and stress resistance, while the main body uses a composition optimized for magnetic properties, creating a composite structure with spatially varying material characteristics.
3Reliability
If the magnet element is designed as a separate piece connected to the sleeve, then thermal expansion stresses are reduced, but the device complexity increases
Solution Approach 1:
The magnet element and connecting elements are merged into a single integrated component manufactured in one piece using injection molding. The connecting elements are formed as integral parts of the magnet element body, eliminating the need for separate connecting components and reducing assembly steps while still providing the benefits of stress reduction.
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 design ensures a play-free, non-rotatable connection and significantly reduces the risk of crack formation in the magnet element by allowing for unimpeded thermal expansion and contraction, maintaining a secure attachment even under temperature fluctuations.
Implementation Method 1
a magnet element (12) connected to the sleeve (11) with a magnetically effective magnet section (12A)
Implementation Method 2
Due to the different thermal expansion coefficients of the sleeve and magnetic element, thermally induced shrinkage stresses can occur when the plastic melt cools
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The invention relates to a magnet unit (10) for a sensor device for sensing a measurement variable which characterizes a state of rotation of a steering shaft of a motor vehicle, a sensor device and a motor vehicle, wherein the magnet unit (10) has a sheath (11) and a magnet element (12) which is connected in a positively locking fashion to the sheath (11), wherein the sheath has a connecting flange (11B) which extends outward in the radial direction and has a recess (11C) with a radial outer face (14) for connecting to the magnet element (12), and the magnet element (12) has a connecting element (12B) which extends in the axial direction and has a radial inner face (13) for connecting to the sleeve (11), wherein the connecting element (12B) extends through the recess (11C) in the connecting flange (11B) and is embodied in such a way that the connecting element (12B) forms a positively locking connection to the connecting flange (12B) in the tangential direction and in the axial direction, wherein the magnet unit (10) is embodied in such a way that the radial inner face (13) of the connecting element (12B) is arranged spaced apart, in the radial direction, from the radial outer face (14) of the associated recess (11C).