Downward Angle Hydraulic Tensioner Sealing
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Solution Overview
Problem
Conventional hydraulic tensioners set at a downward angle suffer from oil leakage, leading to reduced damping force, air accumulation, and increased oil consumption, resulting in backlash and abnormal sounds in timing chains, especially after prolonged engine shutdown.
Innovation Solution
A hydraulic tensioner design featuring a plunger with a hollow sleeve and a check valve unit, including a ball seat and bell-shaped retainer, which forms labyrinthine gaps to prevent air entry and maintain oil pressure, ensuring full damping force upon engine start-up and reducing oil consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the conventional hydraulic tensioner is set at a downward angle, then proper tension can be maintained in the timing chain during engine operation, but oil leaks downward through the gap between the plunger and the plunger-accommodating hole when the engine is stopped, causing air accumulation and loss of damping force
Solution Approach 1:
A seal member is introduced as an intermediary component between the plunger and the plunger-accommodating hole to prevent oil leakage. The seal member fills the gap that causes oil to leak downward when the engine is stopped, thereby maintaining oil pressure and preventing air accumulation in the high pressure chamber while allowing the tensioner to maintain proper tension during operation.
Solution Approach 2:
The seal member is pre-installed in the plunger-accommodating hole before the plunger is assembled, creating a preliminary barrier against oil leakage. This preliminary sealing action prevents oil from leaking downward before the engine is even started, ensuring that the high pressure chamber remains sealed and maintains its damping force.
2Loss of substance
If the clearance between the plunger and the plunger-accommodating hole is reduced to prevent oil leakage, then oil consumption is reduced, but manufacturing precision becomes more difficult to achieve due to various factors including size and measurement errors, surface finishing, and materials
Solution Approach 1:
The seal member serves as an intermediary that eliminates the need for tight clearance control between the plunger and the plunger-accommodating hole. By providing a dedicated sealing component, the design allows for larger, more tolerant clearances while still preventing oil leakage, thereby simplifying manufacturing requirements.
Solution Approach 2:
The invention changes the sealing mechanism from relying on precise dimensional parameters (clearance between plunger and hole) to using a dedicated seal member with its own sealing parameters. This parameter change allows for more relaxed tolerance requirements in the plunger and hole dimensions while maintaining effective sealing.
3Reliability
If air accumulates in the high pressure chamber due to oil leakage, then the tensioner cannot exert adequate damping force and the timing chain experiences backlash and abnormal sounds, but increasing the seal tightness to prevent air entry makes the device more complex
Solution Approach 1:
The seal member is a simple intermediary component that effectively prevents air from entering the high pressure chamber through the gap. By using this single sealing element, the design achieves reliable prevention of air accumulation and maintains damping force without introducing complex multi-component sealing systems.
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 suppresses backlash and abnormal sounds by maintaining hydraulic damping force and optimizing oil balance, even after prolonged engine shutdown, while minimizing oil leakage and consumption.
Implementation Method 1
The plunger has a cylindrical hollow portion with one end open, and accommodates a plunger-biasing spring, which urges the plunger in a protruding direction.
Implementation Method 2
A check valve unit permits flow of oil into the high pressure oil chamber, but blocks reverse flow of oil.
Implementation Method 3
The check valve unit comprises a ball seat, a check ball facing the ball seat, a ball-biasing spring, which urges the check ball into engagement with the ball seat
Implementation Method 4
When the conventional hydraulic tensioner is set at a downward angle, when the engine is stopped and left standing for a long period of time, oil in the high pressure oil chamber leaks downward by gravity, through a slight gap between the plunger-accommodating hole of the housing and the outer circumferential surface of the plunger
Implementation Method 5
A hollow sleeve having an open first end is fixed at the bottom end of the plunger-accommodating hole and communicates with the oil supply passage. The sleeve extends into the hollow interior portion of the plunger and has a second end opposite from its first end. The sleeve has a cylindrical outer circumferential surface in sliding contact with the cylindrical inner wall of the plunger
Data Source
AI summary
The hollow plunger of a hydraulic tensioner for an engine timing chain protrudes from a tensioner housing in an oblique downward direction. An inner sleeve fixed to the housing slidably protrudes into the interior of the plunger, and has a ball check valve at its protruding end. Oil is supplied though the sleeve and the check valve to a high pressure oil chamber formed inside the plunger, and flows outward through a two-part leakage path formed by a gap between the sleeve and the interior of the plunger and a gap between the exterior of the plunger and an interior wall of a plunger-accommodating hole in the housing. Any air that enters the tensioner accumulates in a region surrounding the upper end of the sleeve, rather than in the high oil pressure chamber inside the plunger.