Tensioner Arm with Radial Damping Element
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Solution Overview
Problem
Existing mechanical tensioners for endless power transmitting elements are costly to manufacture and do not provide consistent damping performance throughout their life, often leading to pulley misalignment due to high forces on pivot bushings.
Innovation Solution
A tensioner assembly featuring a helical coil spring and a damping mechanism with a flexible damping element that expands radially to engage with a brake drum, providing consistent damping and torque while counteracting loads to reduce stress on pivot bushings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional damping tensioners are used, then damping function is provided, but manufacturing cost increases and damping performance becomes inconsistent throughout the life of the tensioner
Solution Approach 1:
The patent employs a simple, inexpensive damping element that can be easily replaced, rather than using a complex, expensive damping mechanism. The damping element is designed to be a consumable component that provides consistent damping performance during its service life and can be economically replaced when worn, resolving the contradiction between reliable damping performance and manufacturing cost.
Solution Approach 2:
The tensioner is divided into functional modules: the arm assembly, the brake drum, and the replaceable damping element. This segmentation allows the damping function to be provided by a simple, inexpensive component that can be independently replaced, rather than requiring a complex integrated damping mechanism, thus reducing manufacturing cost while maintaining damping reliability.
2Reliability
If high damping forces are applied, then damping function is improved, but forces on pivot bushing increase causing pulley misalignment
Solution Approach 1:
The damping function is extracted from the pivot bushing assembly and implemented through a separate brake drum and damping element mechanism. This separation allows the damping forces to be applied independently through friction between the damping element and brake drum, rather than through the pivot bushing, eliminating the harmful effect of high forces on the pivot bushing while maintaining effective damping.
Solution Approach 2:
The brake drum acts as an intermediary component between the arm and the damping element. The damping forces are transmitted through friction at the brake drum-damping element interface, which mediates the interaction and prevents direct transmission of high damping forces to the pivot bushing, thereby avoiding pulley misalignment while maintaining damping effectiveness.
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 tensioner assembly ensures consistent damping and torque throughout its life, reducing pulley misalignment and manufacturing costs by distributing loads effectively and maintaining consistent damping performance.
Implementation Method 1
The helical coil spring is disposed about the stem and has a plurality of coils that are disposed between a first end and a second end. The first end is engaged to the brake drum and the second end is engaged to the spring reaction member. The helical coil spring biases the arm member in a first rotational direction relative to the base. Rotation of the arm member in a second rotational direction opposite the first rotational direction applies a torque to the helical coil spring that causes at least a portion of the plurality of coils to expand in a radial direction.
Implementation Method 2
The damping mechanism includes a damping element that is frictionally engaged with the brake drum. The damping element is received between the helical coil spring and the brake drum. The damping element is arranged along the first axis between the pivot bushing and the wheel and is urged radially outwardly into contact with a surface of the brake drum by at least one of the plurality of coils.
Data Source
AI summary
A tensioner assembly that includes a base, an arm, an opening spring (i.e., a torsion spring that opens or radially expands with increasing torque applied thereto), a spring reaction member, and a pivot bushing. The tensioner assembly is configured to orient various loads in predetermined directions. For example, a spring load can be oriented to counteract a hub load to reduce a bushing load that acts on the pivot bushing. As another example, a spring reaction force exerted by the spring reaction member can be employed by a damping mechanism to generate a grounding force that is parallel to the spring reaction force and is directed to intersect an axis about which the arm pivots relative to the base. A tensioner assembly having improved assembly characteristics is also provided.