Nested Ball Joint for Wiper Drive Precision
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Solution Overview
Problem
Conventional ball joint connections for windshield wiper systems, especially those used in large vehicles, face issues with precision and stress distribution due to long lever arm lengths and potential failure under load, particularly when using resilient plastic materials.
Innovation Solution
A single-ball drive connection system with nested sockets and a retainer to secure the ball joint, allowing for closer coupling and improved load distribution between connecting rods and the crank arm, using materials like cast metal or reinforced plastics for durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two ball joints are mounted on a single crank pin, then the connection can accommodate non-parallel wiper arm configurations, but the long lever arm length results in less precise drive and excessive stress on the crank arm
Solution Approach 1:
The patent employs a nested ball joint configuration where an inner ball joint is positioned within an outer ball joint, both sharing a common crank pin. This nesting arrangement reduces the effective lever arm length from the crank pin to the connecting rods while maintaining the ability to accommodate non-parallel wiper arm configurations through the combined angular freedom of both ball joints.
Solution Approach 2:
The invention introduces a vertical dimension by stacking ball joints one above the other on the same crank pin, rather than mounting them side-by-side. This vertical arrangement shortens the horizontal lever arm length, improving drive precision while still providing sufficient angular accommodation for non-parallel wiper arms through the multi-dimensional freedom of the nested ball joint configuration.
2Adaptability or versatility
If two ball joints are mounted on a single crank pin, then the connection can accommodate non-parallel wiper arm configurations, but excessive stress is applied to the eccentric drive crank arm
Solution Approach 1:
The nested ball joint configuration concentrates the load-bearing structures closer to the crank pin, reducing the lever arm length. This shortening of the moment arm directly reduces the bending stress and shear forces applied to the crank arm while maintaining the necessary adaptability through the nested angular freedom.
Solution Approach 2:
By arranging ball joints vertically rather than horizontally, the invention reduces the horizontal distance from the crank pin to the connecting rod attachment points. This dimensional change decreases the lever arm length and consequently reduces the stress on the crank arm while preserving adaptability through the vertical stacking configuration.
3Ease of manufacture
If resilient plastic sockets are used to mate connecting rods to the ball, then the assembly can be easily manufactured, but the connection may separate or fail under load
Solution Approach 1:
The patent employs composite construction where metal components (crank pin, retaining ring, and at least one ball joint) provide structural strength and load-bearing capability, while plastic components may be used for non-critical elements. This composite approach ensures reliability under load while maintaining reasonable manufacturing complexity through the use of standard metal fastening techniques combined with molded plastic parts where appropriate.
Solution Approach 2:
The ball joint's spherical geometry provides inherent load distribution across the contact surfaces. The curved surfaces of the ball and corresponding sockets create point or line contacts that efficiently transmit forces, improving reliability under load while the spherical shape itself is easily manufactured through conventional molding or machining processes.
Data Source
AI summary
An articulating ball joint for connecting a pair of driven members to a driving member such as a crank pin. In one embodiment, a single ball is held in a first, or inner, socket defined by a coupling member having a convex outer surface, and the first socket is held within a second, outer, socket defined in a second coupling member also having a convex outer surface, which is, in turn, engaged by a retainer.