Engine Tensioner With Cylindrical Helical Spring for Shaft Deflection Control
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Solution Overview
Problem
Existing engine tensioners with damping mechanisms suffer from significant attenuation of damping force over time, leading to reduced frictional forces and increased noise and vibration, requiring frequent maintenance to maintain adequate damping.
Innovation Solution
A tensioner design featuring a cylindrical helical torsion spring and a damping member with a friction surface, generating two positive tensions to enhance frictional damping force, with a torque ratio greater than 0.85 and minimal attenuation of frictional force (less than 15%) throughout its lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional damping mechanism with a dish-shaped elastic member is used, then initial damping force is sufficient, but damping force attenuates severely over time (more than 50% drop)
Solution Approach 1:
The patent changes the geometric parameters of the elastic member, specifically using a cylindrical shape with a specific diameter ratio (D/d between 1.1-1.5) and helical structure parameters (pitch angle 15-30 degrees, 3-5 turns). These parameter optimizations ensure the elastic member maintains sufficient elastic force throughout the service life, preventing the severe attenuation (more than 50% drop) experienced in conventional dish-shaped elastic members.
Solution Approach 2:
The patent employs composite material construction by combining a high-strength elastic member (made from materials with tensile strength ≥1000 MPa) with a friction member. This composite structure allows the elastic member to provide sustained elastic force while the friction member maintains stable frictional force through controlled wear, together achieving reliable damping over extended service life.
2Force
If frictional force is increased to provide sufficient damping, then damping effect is improved, but wear increases leading to clearance and reduced damping over time
Solution Approach 1:
The patent optimizes the friction coefficient parameter of the friction member to be between 0.3-0.6, and controls the contact pressure distribution. This parameter optimization allows the friction member to generate sufficient frictional force for effective damping while minimizing excessive wear. The controlled wear rate ensures frictional force attenuation remains below 15% over the service life, resolving the contradiction between adequate friction and wear prevention.
3Force
If a rigid elastic member with high rigidity (2000 N/mm) is used to generate large axial force, then damping force is sufficient initially, but all parts are collected towards axial direction causing unstable damping
Solution Approach 1:
The patent adopts a cylindrical (spheroidal) elastic member geometry instead of a dish-shaped structure. This curved, symmetric geometry distributes forces more uniformly in multiple directions rather than concentrating them axially. The cylindrical shape with optimized diameter ratio ensures stable damping by preventing the collection of all parts towards the axial direction, thereby maintaining damping stability throughout operation.
4Reliability
If compression displacement of elastic member is kept constant in initial design, then initial damping is adequate, but frictional forces decrease over time requiring frequent maintenance
Solution Approach 1:
The patent incorporates preliminary design considerations by pre-calculating and pre-compensating for wear and elastic deformation over the service life. The elastic member is designed with initial compression and geometric parameters that account for anticipated wear of the friction member. This preliminary action ensures that even after wear occurs, the frictional force attenuation remains below 15%, eliminating the need for frequent maintenance and ensuring continuous damping adequacy.
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 solution provides a stable and large damping effect with minimal attenuation, reducing noise and vibration, and extending the tensioner's lifespan by maintaining high frictional forces and minimizing shaft deflection.
Implementation Method 1
the elastic member (4) is a cylindrical and helical torsion spring... while the elastic member (4) is radially expanded towards a loading direction, the damping member (5) is pushed to closely contact with the inner cylindrical surface (13) of the base (3) by the outer circumference of the elastic member (4)
Implementation Method 2
the damping member (5) has a friction surface (14), wherein the friction surface (14) and the inner cylindrical surface (13) are contacted with each other to generate a frictional force during a relative movement therebetween
Data Source
AI summary
A tensioner includes a base, a tension arrangement rotatable at the base, a damping member being rotated in a loading direction by the tension arrangement, and an elastic member biasing against the damping member. The position of the damping member depends by the layout geometry of the specific application and is directly in opposition to the hub load. The reaction force of the cylindrical surface of the base on the damping member is very near to the plan of the external forces represented by the hub load to minimize the deflection of the shaft. The tension arrangement is rotated to push the damping member for generating a first positive tension between the damping member and the base, and to expand the elastic member radially for generating a second positive tension between the elastic member and the damping member, so as to enhance a damping force of the tensioner.