External-Pin Hydraulic Tensioner for Thermal Clearance Stability
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Solution Overview
Problem
Current hydraulic tensioners face challenges in integrating a ratchet mechanism due to piston-to-bore clearance changes with temperature, caused by differing thermal expansion coefficients of steel and aluminum, and viscosity reduction of oil, leading to unstable performance.
Innovation Solution
A hydraulic tensioner design featuring a body, rod, hollow piston, moveable sleeve, external spring, ratchet clip, and check valve, where the body, floating sleeve, and rod are made of aluminum, and the piston is made of steel, reducing clearance variations with temperature and stabilizing tensioner performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional materials (steel piston in aluminum body) are used, then the tensioner provides adequate strength, but the piston-to-bore clearance increases with temperature due to differential thermal expansion
Solution Approach 1:
The patent applies homogeneity by making both the piston and body from aluminum alloy, eliminating the material interface that causes differential thermal expansion. This ensures both components expand at the same rate with temperature changes, maintaining stable piston-to-bore clearance throughout the operating temperature range while providing sufficient strength through proper aluminum alloy selection and design.
2Stability of the object's composition
If aluminum materials are used for body and piston, then thermal expansion stability is improved, but strength may be reduced compared to steel
Solution Approach 1:
The patent employs composite materials by using aluminum alloy for both the piston and body, leveraging the favorable properties of aluminum (low thermal expansion differential, adequate strength-to-weight ratio) while accepting the trade-off of reduced absolute strength compared to steel. The design compensates through optimized geometry and aluminum alloy selection to achieve the required strength levels.
3Temperature
If oil viscosity reduces with temperature, then fluid flow increases, but tensioner performance becomes unstable
Solution Approach 1:
The patent addresses oil viscosity changes with temperature by incorporating a compensating spring mechanism that adjusts the piston preload based on temperature. As oil viscosity decreases and flow increases with temperature, the spring force increases to maintain proper tensioner pressure and performance, effectively compensating for the fluid property changes across the operating temperature range.
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
This design provides a stable tensioner performance across varying engine temperatures, reducing dependency on high-performance control devices to compensate for flow variability, as evident in reduced flow rates at elevated temperatures.
Implementation Method 1
The external spring is between the first end of the moveable sleeve and the shoulder of the collar of the hollow piston, providing a force between the moveable sleeve and the shoulder of the collar of the hollow piston, biasing the hollow piston outwardly relative to the body.
Implementation Method 2
the check valve is received within the bore of the hollow piston and within the first end of the rod to control fluid flow between the low pressure chamber and the high pressure chamber
Implementation Method 3
Many prior art tensioner designs have a piston to bore clearance that increases when oil temperatures in the engine rise... this hydraulic tensioner configuration makes it challenging to use most traditional ratchet mechanisms
Implementation Method 4
The hollow piston is slidably received around the outer surface of the rod, such that the piston slides relative to the outer surface of the rod.
Data Source
AI summary
A hydraulic tensioner having a piston sliding around an outside surface of a pin or rod, so that the high pressure chamber for chain control is created by the area between the piston internal diameter and the rod outside diameter. A spring around the outside of the rod presses against the bottom of the piston, biasing the piston outward during low oil pressure conditions. Preferably, the piston is steel and the rod is aluminum, the reverse of prior art designs, which means that as temperature increases, the piston to bore clearance reduces. This can offset the oil viscosity reduction and maintain the same performance over operating temperatures.