Magnet Unit Sleeve Form-Fitting Connection Thermal Stress
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Solution Overview
Problem
Existing magnet units for steering shaft sensors face challenges in maintaining a non-rotatable, backlash-free connection while minimizing the risk of cracking due to thermal stresses, which are exacerbated by the brittleness of plastic magnetic elements and differing thermal expansion coefficients between the sleeve and magnet material.
Innovation Solution
A magnet unit design featuring a sleeve with a sleeve connecting section and a magnet element with a magnetically active section, where the magnet element is connected to the inside of the sleeve via form-fitting connections, ensuring compressive stresses are induced in the magnet element, reducing the risk of cracking and maintaining a non-rotatable connection through carefully designed recesses and projections.
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 the sleeve is injection molded with the magnetic material, then a non-rotatable connection is achieved, but thermally induced shrinkage stresses occur leading to cracking in the magnetic element
Solution Approach 1:
The connection between sleeve and magnet element is divided into multiple form-fitting connections through recesses and projections distributed around the circumference, rather than a single monolithic connection. This segmentation allows thermal stresses to be distributed and absorbed locally at each connection point, preventing crack propagation through the entire magnet element.
Solution Approach 2:
The design changes the geometric parameters of the connection interface by creating overlapping axial sections with complementary recesses and projections. This geometric configuration enables the connection to accommodate thermal expansion and contraction by allowing controlled movement and stress redistribution, reducing the risk of cracking while maintaining rotational stability.
2Reliability
If the magnet element is connected via an intermediate element made of elastic material, then thermal stresses are reduced, but the device complexity and cost increase
Solution Approach 1:
The functional elements of the connection system are merged into a single integrated structure. The recesses and projections are formed directly as part of the magnet element and sleeve geometry, eliminating the need for separate intermediate elastic elements while achieving the same stress-absorbing function through the form-fitting connection design.
Solution Approach 2:
The magnet element and sleeve themselves provide the stress-absorbing function through their own geometric features (recesses and projections). The structure is self-sufficient, using its own form-fitting geometry to accommodate thermal stresses without requiring additional specialized components, thereby reducing complexity while maintaining reliability.
3Reliability
If the magnet element is connected via separate production and form-fitting connection with tabs and recesses, then cracking risk is reduced, but manufacturing complexity increases
Solution Approach 1:
The recesses and projections are pre-formed as integral features of the magnet element and sleeve during their respective manufacturing processes. This preliminary formation of connection features allows the components to be manufactured separately using optimized processes, then assembled through a simple form-fitting connection, reducing overall manufacturing complexity while maintaining cracking resistance.
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 effectively reduces the risk of cracking in the magnet element and ensures a secure, non-rotatable connection by managing thermal stresses, maintaining the integrity of the sensor signal and the magnet unit's functionality across temperature variations.
Implementation Method 1
the magnetic flux that occurs in the magnetic element and is dependent on the rotational state of the shaft can be passed on to a magnetic sensor, for example a Hall sensor, via a flux conductor
Implementation Method 2
when the plastic melt cools, thermally induced shrinkage stresses can occur, which can lead to the formation of cracks in the magnetic element
Implementation Method 3
temperature fluctuations occurring during operation can lead to thermally induced stresses in the magnet unit due to the different thermal expansion coefficients of the sleeve and magnet element
Data Source
Figure 1~2a
Figure 2b~2d
AI summary
The invention relates to a magnetic unit (20) for a sensor device for detecting a measured quantity characterizing a rotational state of a steering shaft of a motor vehicle, as well as a sensor device and a motor vehicle with such a magnetic unit (20), wherein the magnetic unit (20) comprises a sleeve (13) and a magnetic element (12) positively connected to the sleeve (13), wherein the sleeve (13) comprises an axially extending sleeve connection section (13B) with an inner surface for connection with the magnetic element (12) and a socket-shaped sleeve fastening section (13A) for connecting the magnetic unit (20) to a first part of the steering shaft, wherein the magnetic element (12) comprises an axially extending magnetic element connection section (12B) with an outer surface for connection with the sleeve (13) and a magnetically effective magnetic section (12A).wherein the magnetic element (12) and the sleeve (13) are connected by means of at least one positive-locking connection between the magnetic element connection section (12B) and the sleeve connection section (13B), wherein the sleeve connection section (13B) and the magnetic element connection section (12B) are arranged overlapping in the axial direction and the outer surface of the magnetic element connection section (12B) rests against the inner surface of the sleeve connection section (13B).