Worm Shaft Retainer Overmolding for Stiff, Low-Noise Steering Columns
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Solution Overview
Problem
Existing electromechanical power steering systems face issues with dimensional stability, stiffness, and noise due to the use of elastic preloading methods in worm gear mechanisms, which lead to unwanted play and complex assembly processes.
Innovation Solution
A retainer with a main body made of injection-molded thermoplastic, integrating a bearing ring through overmolding, providing a durable and form-fitting connection, and incorporating a pivoting bearing and a damper element for improved stability and vibration damping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If an elastic preloading method is used to preload the worm shaft against the worm wheel, then smooth running and noise reduction are improved, but dimensional stability and connection stiffness deteriorate
Solution Approach 1:
The patent changes the physical state and mechanical properties of the retainer material by using thermoplastic polymer instead of elastic materials. This parameter change eliminates the elastic deformation and dimensional instability while maintaining the preloading function through the rigid connection of the bearing ring to the retainer body.
Solution Approach 2:
The patent employs composite construction by integrating the bearing ring into the retainer body made of thermoplastic polymer through overmolding. This composite structure combines the load-bearing capability of the metal bearing ring with the rigid, dimensionally stable polymer retainer, eliminating elastic play while maintaining structural integrity.
2Strength
If a force-fitting connection is used to fix the bearing ring in the retainer, then the connection firmness is improved, but assembly complexity and manufacturing difficulty increase
Solution Approach 1:
The patent merges the bearing ring and retainer into a single integrated component through overmolding. The bearing ring is embedded directly into the retainer body during the molding process, eliminating the need for separate assembly steps and force-fitting operations while maintaining strong mechanical connection.
Solution Approach 2:
The bearing ring is pre-positioned and integrated into the retainer body during the molding process before final assembly. This preliminary action of incorporating the bearing ring during manufacturing eliminates the need for complex post-assembly force-fitting operations and simplifies the overall assembly process.
3Ease of manufacture
If an elastically flexible intermediate element is introduced between the bearing ring and retainer, then the assembly is simplified, but stiffness and long-term stability deteriorate
Solution Approach 1:
The patent removes the elastically flexible intermediate element from the system and replaces it with a rigid thermoplastic retainer body that directly supports the bearing ring. This extraction of the elastic intermediate element eliminates the source of dimensional instability and play while maintaining assembly simplicity through the integrated overmolded structure.
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 solution enhances dimensional stability, stiffness, and long-term performance, reducing noise and assembly complexity while ensuring smooth operation and reliable attachment of the worm shaft to the worm wheel.
Implementation Method 1
The retainer (4) has a main body (41), which is formed as an injection-molded part made of thermoplastic, in which the bearing ring (16) is overmolded.
Implementation Method 2
a spring, which acts on the retainer and presses the worm shaft elastically without play against the toothing of the worm wheel
Implementation Method 3
The actuating drive has an electric motor for producing an auxiliary torque, which is coupled into the steering shaft. According to the generic type, the auxiliary torque is coupled in via a worm gear mechanism
Implementation Method 4
the worm shaft is rotatably mounted at its end remote from the motor in a bearing which is accommodated in a retainer
Data Source
AI summary
An electromechanical power steering system for a motor vehicle includes a worm shaft which can be driven by an electric motor and which meshes with a worm wheel coupled to a steering shaft. The worm shaft is rotatably mounted in a bearing which has at least one bearing ring fitted in a retainer that can be displaced relative to the worm wheel. In order to specify an electromechanical power steering system having an improved retainer, which has higher dimensional stability and increased stiffness, according to the invention the retainer has a main body of plastic, which is injection-molded onto the bearing ring as an injection-molded part.