Plastic Shaft Bearing Coupling for High-Load Automotive Actuators
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Solution Overview
Problem
Existing actuators face challenges in coupling metallic bearings with resin or polymeric shafts or tubes due to interference fit limitations, especially under significant axial loads and cyclic fatigue, which are not applicable for non-metallic materials and compromise mechanical stability.
Innovation Solution
An actuator design featuring a plastic shaft or tube with a coupling seat having axial shoulders, co-molded onto a metallic inner ring of a rolling bearing, ensuring axial constraint and using self-lubricating additives like molybdenum disulfide and Teflon to enhance adhesion and prevent plastic flow into the bearing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If interference fit is used to couple bearing inner ring with shaft or tube, then strong mechanical coupling is achieved, but this technique is only applicable between metallic parts and cannot be used with resin or polymeric materials
Solution Approach 1:
The invention changes the coupling mechanism from interference fit (metal-to-metal) to molding process (plastic-to-metal), transforming the physical and chemical parameters of the coupling interface. The plastic material is molded directly onto the bearing inner ring, creating a permanent bond that adapts to non-metallic shaft materials while maintaining coupling strength
Solution Approach 2:
The invention employs composite material coupling by joining plastic (polymer) material with metallic bearing components. The shaft or tube made of resin or polymeric material is coupled to the metallic bearing through the molded plastic, creating a metal-polymer composite structure that achieves both material compatibility and mechanical strength
2Force
If interference fit is used for coupling, then metallic parts are securely connected, but resin or polymeric shafts or tubes cannot be properly coupled except for low torque applications
Solution Approach 1:
The invention transforms the coupling parameter from mechanical interference (pressure-based) to chemical-physical bonding (molding-based). The molding process allows the plastic to chemically and physically bond with the bearing surface, enabling high torque transmission capability that was previously unavailable for polymeric shaft materials
Solution Approach 2:
The invention replaces the mechanical interference fit system with a molding-based bonding system. Instead of relying on mechanical pressure and friction between metallic surfaces, the solution uses the molding process to create a permanent bond between the plastic shaft and metallic bearing, enabling high torque transmission for polymeric materials
3Strength
If shaft or tube is made of resin or polymeric material, then weight is reduced and corrosion resistance is improved, but interference coupling cannot be applied except for low torque transmission
Solution Approach 1:
The invention creates a composite material solution by combining polymeric shaft material with metallic bearing components through molded coupling. The plastic material provides corrosion resistance and weight reduction, while the molded joint with the metallic bearing enables high torque transmission capability that neither material could achieve alone
Solution Approach 2:
The invention changes the coupling parameter from mechanical interference (inapplicable to polymers) to molding bonding (specific for polymers). The molding process parameters are optimized to create strong bonds between the polymeric shaft and metallic bearing, enabling high torque transmission while maintaining the inherent advantages of polymeric materials
4Force
If shaft or tube withstands significant axial loads, then structural integrity is maintained, but the coupling between bearing and shaft or tube is subjected to considerable mechanical stress
Solution Approach 1:
The invention changes the coupling mechanism from mechanical interference (stress-concentrating) to molded bonding (stress-distributing). The molding process creates a large bonding surface area that distributes axial loads across the entire interface between the plastic shaft and bearing, reducing stress concentration and improving coupling reliability under significant axial loads
Solution Approach 2:
The invention adds a dimensional aspect to the coupling by creating a three-dimensional molded joint that envelops the bearing inner ring. This volumetric coupling approach distributes axial stresses across multiple dimensions of the bonding interface, rather than concentrating forces at a single mechanical interface, thereby improving reliability under axial loading
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 achieves strong adhesion and resistance to heavy and cyclic loads, eliminating the need for additional lubricants and maintaining mechanical integrity while reducing maintenance costs.
Implementation Method 1
co-molded onto the inner ring so as to axially constrain the inner ring between said axial shoulders
Implementation Method 2
using self-lubricating additives like molybdenum disulfide and Teflon to enhance adhesion and prevent plastic flow into the bearing
Data Source
AI summary
An actuator comprising a shaft or tube with a coupling seat on an outer side wall, the shaft or tube made by molding of a plastic material, a rolling bearing comprising a metallic inner ring, a metallic outer ring coaxial with respect to the inner ring about a axis of rotation, and rolling bodies interposed between inner ring and outer ring which enable relative rotation of inner ring with respect to outer ring about axis of rotation, wherein the coupling seat comprises a pair of axial shoulders protruding by a radial height, along a radial direction perpendicular and incident to axis of rotation with respect to outer side wall of shaft or tube, axial shoulders being axially spaced apart, along an axial direction parallel to axis of rotation, so as to axially constrain the inner ring with respect to the shaft or tube.