Frustoconical Bushing Wear Compensation in Belt Tensioner
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Solution Overview
Problem
Conventional tensioners for flexible drives, such as serpentine belts, suffer from wear at the pivot attachment, leading to off-axis movement of the pulley, which can result in damage to the flexible drive and slippage, due to the large forces carried by the tensioner arm.
Innovation Solution
A tensioner design featuring a frustoconical bushing and a wear take-up mechanism that biases the bushing towards the pivot surface to maintain contact and prevent off-axis movement, combined with a thrust plate and thrust washer to inhibit such movement and provide consistent dampening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional tensioner arm with pivot attachment is used, then the tensioner can provide dampening force through friction, but wear at the pivot causes off-axis movement of the pulley
Solution Approach 1:
The patent employs a frustoconical bushing with a curved conical surface instead of a conventional cylindrical pivot. This curved geometry provides self-aligning properties that resist off-axis movement of the pulley while maintaining the necessary dampening friction. The conical shape allows the bushing to compensate for wear by maintaining contact pressure on the curved surface, preventing the pulley from moving to an off-axis position.
2Reliability
If a frustoconical bushing is used to resist off-axis movement, then wear compensation is achieved, but device complexity increases
Solution Approach 1:
The frustoconical bushing is designed to be self-adjusting through its geometry. As wear occurs on the conical surface, the bushing naturally maintains contact pressure through its tapered shape without requiring external adjustment mechanisms. The self-aligning property of the conical surface automatically compensates for wear, eliminating the need for complex adjustment devices while maintaining reliability.
3Force
If the tensioner arm pivots with large forces, then the tensioner can maintain constant belt tension, but wear at the pivot attachment increases
Solution Approach 1:
The frustoconical bushing serves as an intermediary element between the tensioner arm and the pivot attachment. It distributes the large forces across its conical surface area, reducing stress concentration and wear at any single point. The bushing material and geometry are selected to handle the high forces while minimizing wear, protecting the pivot attachment from direct contact with high-stress loads.
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 effectively compensates for wear, prevents off-axis movement, and maintains consistent dampening, reducing wear and failure risks in flexible drives by ensuring the pulley remains aligned and properly engaged.
Implementation Method 1
a bushing having an outer frustoconical surface and an inner surface complementary to the shape of the spindle shaft, the bushing receiving the shaft in its inner surface; a tensioner arm having a pivot surface complementary to and engaging the outer frustoconical surface of the bushing
Implementation Method 2
a wear take up mechanism to bias the bushing towards the pivot surface to compensate for wear of the bushing and/or pivot surface
Implementation Method 3
A thrust plate is mounted to the end of the spindle shaft and rides in a thrust washer, the thrust plate and thrust washer being held captive in the tensioner arm such that the tensioner arm can pivot about the bushing and the spindle and the thrust plate and thrust washer assist in inhibiting off-axis movement of the tensioner arm
Data Source
AI summary
A novel tensioner for use with flexible drives, such as serpentine accessory belts on automobiles includes a tensioner arm to spindle pivot design which employs a frustoconical bushing between an inner pivot surface of the tensioner arm and a spindle shaft. The frustoconical design of the bushing resists off axis movement of the tensioner arm and a wear take up mechanism biases the bushing into contact with the inner pivot surface to compensate for normal wear of the bushing and/or pivot surface. A thrust plate is mounted to the end of the spindle shaft and rides in a thrust washer, the thrust plate and thrust washer being held captive in the tensioner arm such that the tensioner arm can pivot about the bushing and the spindle and the thrust plate and thrust washer assist in inhibiting off-axis movement of the tensioner arm. In one embodiment, the biasing force which biases the bushing against the inner pivot surface of the tensioner arm can be varied to change the amount of dampening of the tensioner.