Plastic Rotary Shaft for Wiper Drive Assembly
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Solution Overview
Problem
Conventional windshield wiper assemblies using steel rotary shafts are heavy, large, and costly to manufacture, with complex and time-consuming tapping operations.
Innovation Solution
A wiper arm drive assembly featuring a rotary shaft made of plastic materials, comprising a hollow tube and a pinion part, with a self-tapping screw mechanism for attachment to the wiper arm head, allowing for reduced weight and simplified manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a steel rotary shaft is used in the wiper assembly, then the mechanical strength and torque transmission are sufficient, but the weight and manufacturing complexity increase
Solution Approach 1:
The patent changes the material parameter from steel to plastic (specifically POM - polyoxymethylene), which fundamentally alters the density and weight characteristics while maintaining sufficient mechanical strength for the application. This material substitution resolves the contradiction by providing adequate strength with significantly reduced weight.
Solution Approach 2:
The rotary shaft is constructed as a composite structure combining plastic material with reinforcing elements (such as fiberglass or metal inserts in critical areas). This composite approach maintains the necessary mechanical strength and torque transmission capability while keeping the overall weight lower than a solid steel shaft.
2Strength
If a steel rotary shaft with threaded bore is used, then the connection strength is sufficient, but the manufacturing time and cost increase
Solution Approach 1:
The patent replaces the traditional mechanical threading process with an injection molding process that integrates the threaded bore directly into the plastic shaft during manufacturing. This substitution eliminates complex post-processing operations while maintaining connection strength through the self-tapping screw mechanism designed for plastic materials.
Solution Approach 2:
The manufacturing process merges the shaft formation and thread creation into a single injection molding operation. The threaded bore is formed directly during molding using a specialized mold insert, combining what would traditionally be separate machining operations into one efficient process step.
3Device complexity
If a plastic rotary shaft is used, then the weight and manufacturing complexity are reduced, but the torque transmission capability must be maintained
Solution Approach 1:
The plastic shaft incorporates reinforcing materials (such as glass fibers or metal embeds) within the plastic matrix to enhance torsional strength and stiffness. This composite construction allows the shaft to transmit the required torque while maintaining the weight and manufacturing advantages of plastic materials.
Solution Approach 2:
The shaft design applies local reinforcement only in the critical torque transmission zones, such as the pinion gear area and connection points. The plastic material is used in non-critical areas where weight reduction is prioritized, creating a locally optimized structure that balances torque transmission needs with overall weight reduction.
Data Source
Figure 1~2
Figure 3~4
AI summary
A drive assembly according to the invention is particularly used in window-wiping assemblies for motor vehicles. A wiper-arm head (204) is driven by a rotating shaft (206) to which said wiper-arm head (204) is attached by fastening means (208), said rotating shaft (206) being driven by an output shaft (214) of an actuator. According to the invention, the rotating shaft (206) is made from at least one plastic material.