Steering Torque Sensor Sleeve Assembly Using Ultrasonic Welding
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Solution Overview
Problem
Conventional methods for connecting a ring magnet or stator holder to a shaft in torque sensors for motor vehicle steering systems face challenges such as low strength welds, high production costs, and susceptibility to cracks due to difficulties in achieving precise tolerances and serrations during injection molding.
Innovation Solution
The solution involves using a thermoplastic material for the ring magnet sleeve or stator holder, which is formed onto the steering shaft via ultrasonic forming, ensuring a torque-proof connection and avoiding high stresses by employing knurling for a positive lock, and using ultrasonic welding for assembly, eliminating the need for pressing and injection molding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pressing-fit or injection molding methods are used to connect the ring magnet sleeve to the steering shaft, then the connection can be established, but the manufacturing precision and reliability deteriorate due to difficulty in achieving tight tolerances for serrations and susceptibility to cracking
Solution Approach 1:
The patent replaces conventional mechanical pressing-fit or injection molding methods with ultrasonic welding technology. The ultrasonic welding device generates high-frequency vibrations that locally melt and fuse the thermoplastic material of the ring magnet sleeve to the metal steering shaft, eliminating the need for precision serrations and pressing operations. This substitution of mechanical assembly with ultrasonic welding resolves the contradiction by achieving reliable connections without requiring tight manufacturing tolerances for serrations.
Solution Approach 2:
The patent changes the physical state of the thermoplastic material during connection by applying ultrasonic energy. The high-frequency vibrations temporarily raise the temperature and alter the viscosity of the thermoplastic material at the interface, enabling it to flow and bond with the metal shaft. After cooling, the material solidifies to create a strong, crack-resistant connection. This parameter change approach eliminates the need for precision mechanical features while ensuring connection reliability.
2Ease of manufacture
If conventional pressing-fit methods with serrations are used, then the connection can be established, but the device complexity and production costs increase due to the need for precise tolerances and additional manufacturing steps
Solution Approach 1:
The patent replaces complex mechanical pressing-fit operations with ultrasonic welding. Instead of requiring precision serrations, tight tolerances, and multi-step assembly processes, the ultrasonic welding device directly fuses the ring magnet sleeve to the steering shaft through high-frequency vibrations. This simplifies the manufacturing process by eliminating unnecessary mechanical features and reducing the number of production steps, thereby improving ease of manufacture while reducing device complexity.
Solution Approach 2:
The patent combines the ring magnet sleeve and steering shaft into a single integrated assembly through ultrasonic welding. The thermoplastic material of the sleeve is fused directly to the metal shaft, creating a unified structure that eliminates the need for separate pressing-fit operations and precision-machined serrations. This merging of components simplifies the overall manufacturing process and reduces production complexity.
3Strength
If high pressing forces are applied during conventional welding or pressing operations, then the connection strength can be improved, but the components become susceptible to high stresses and cracking
Solution Approach 1:
The patent replaces conventional pressing-fit or cold-welding methods with ultrasonic welding. The high-frequency vibrations generate localized heat at the interface between the ring magnet sleeve and steering shaft, melting the thermoplastic material and creating a strong bond without requiring high pressing forces. This eliminates the stress concentration and cracking problems associated with mechanical pressing operations while maintaining connection strength.
Solution Approach 2:
The patent utilizes the phase transition of the thermoplastic material from solid to molten state during ultrasonic welding. The high-frequency vibrations temporarily raise the temperature of the thermoplastic material at the interface, causing it to melt and flow. When the vibration stops, the material cools and solidifies, creating a strong, stress-free connection. This phase transition approach allows for strong bonding without applying high pressing forces that would cause cracking.
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 method simplifies production, reduces costs, and enhances the reliability of the connection between the plastic and metal components, preventing cracks and ensuring a strong, stress-free coupling while maintaining precise alignment.
Implementation Method 1
the ring magnet sleeve and/or the stator holder is/are made of a thermoplastic material and is/are formed into the steering shaft in an area for mounting on the steering shaft by means of ultrasonic forming
Implementation Method 2
introducing a high-frequency mechanical vibration in the ultrasonic range into the corresponding steering shaft
Data Source
Figure 1~3
Figure 4~6
Figure 7~9
AI summary
The invention relates to an electromechanical power steering system (1) for a motor vehicle, comprising an integral structural unit (8) with a torque sensor unit (9) which detects the rotation of the upper steering shaft (3) with respect to the lower steering shaft (4), wherein the torque sensor unit (9) has a ring magnet (11), which is connected fixedly to the upper steering shaft (3) so as to rotate with it, and a magnetic flux conductor (12) which is connected to the lower steering shaft (4), and wherein a magnetic sensor (18) detects the rotation of the shaft (3) which is connected to the ring magnet (11) with respect to the lower shaft (4) which is connected to the magnetic flux conductor (12), and wherein the ring magnet (11) is supported by a ring magnet sleeve (11') which is seated on the upper steering shaft (3), is manufactured from a thermoplastic, and is formed by means of ultrasonic reshaping into the upper steering shaft (3) in a region for mounting on the upper steering shaft (3).