Tappet Air-Vent Passage Design for Hydraulic Oil Retention
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Solution Overview
Problem
In internal combustion engines, tappets with incorporated hydraulic lash adjusters face the issue of hydraulic oil leakage from the low pressure chamber during long-period engine stops, leading to air entrainment in the high pressure chamber upon restart, which affects the valve clearance and engine performance.
Innovation Solution
A tappet design with an internal lash adjuster and an upwardly oriented air-vent passage to discharge air between the tappet case and the lash adjuster, preventing hydraulic oil leakage and ensuring a sufficient oil reservoir, thereby avoiding air entrainment in the high pressure chamber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an air-vent passage is provided in a lower end portion of the tappet to discharge air, then air removal is effective, but hydraulic oil leaks from the low pressure chamber during long-period stops
Solution Approach 1:
The air-vent passage is configured with asymmetric orientation, opening upward rather than laterally. This asymmetric design allows air to be discharged effectively while preventing hydraulic oil from leaking out during long-period engine stops, as the upward orientation creates a barrier against downward gravitational flow of the oil.
Solution Approach 2:
Instead of opening the air-vent passage laterally as in conventional designs, the invention inverts the opening direction to upward. This inversion changes the flow dynamics so that air can still escape during assembly while hydraulic oil is retained in the low pressure chamber during operation and storage.
2Adaptability or versatility
If the tappet incorporates a hydraulic lash adjuster, then valve clearance can be eliminated, but air entrainment occurs during restart after long stops due to oil loss
Solution Approach 1:
The upwardly oriented air-vent passage creates an asymmetric configuration that maintains hydraulic oil in the low pressure chamber during long-period stops. This prevents air entrainment during engine restart while preserving the valve clearance adjustment capability provided by the hydraulic lash adjuster.
3Ease of manufacture
If a lateral air-vent passage is used, then assembly is simple, but hydraulic oil is discharged to the outside during long-period stops
Solution Approach 1:
Changing the air-vent passage orientation from lateral to upward creates a simple yet effective solution that maintains hydraulic oil volume in the low pressure chamber during long-period stops, while still allowing for straightforward assembly procedures.
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 effectively maintains hydraulic oil in the low pressure chamber during extended engine stops, preventing air entrainment and ensuring reliable engine operation upon restart, while also reducing the weight and manufacturing costs of the valve gear mechanism.
Implementation Method 1
an inner peripheral surface of the tappet case is provided with an air-vent passage through which air existing between the tappet case and the lash adjuster is discharged upward when the lash adjuster is being assembled
Implementation Method 2
the hydraulic oil stored in the low pressure chamber (reservoir chamber) of the lash adjuster can be prevented from leaking through the air-vent passage when the internal combustion engine is stopped for a long period of time
Data Source
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AI summary
In a tappet with a built-in lash adjuster, hydraulic oil is prevented from leaking from a low pressure chamber during a long-period stop. A tappet (10) includes a hydraulic lash adjuster (11) which supports a lower end portion of a push rod (96) and a tappet case (12) to which the lash adjuster (11) is internally fitted and which is reciprocally displaced in a vertical direction according to a rotating cam (85). An inner peripheral surface of the tappet case (12) is provided with an air-vent passage (34) through which air existing between the tappet case (12) and the lash adjuster (11) can be discharged upward when the lash adjuster (11) is being assembled.