Compression Ratio Mechanism With Oil Buffering Against Cavitation
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Solution Overview
Problem
The plunger pump in crosshead type engines experiences rapid oil suction near the bottom dead center, leading to negative supply pressure and potential cavitation.
Innovation Solution
A compression ratio varying mechanism is implemented with a communication passage allowing the first and second oil storage chambers to communicate through a bypass oil passage with an orifice and check valve, limiting flow from the second to the first chamber, thereby controlling oil flow and preventing cavitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the plunger pump sucks working oil quickly near the bottom dead center to change compression ratio, then the compression ratio can be varied, but the supply pressure becomes negative and cavitation occurs
Solution Approach 1:
The first oil storage chamber stores working oil in advance before the rapid suction phase. This preliminary storage ensures that when the plunger pump needs to suck oil quickly near bottom dead center, the oil is already available in the first storage chamber, preventing negative pressure and cavitation while still enabling compression ratio variation.
Solution Approach 2:
The oil storage system is divided into two separate chambers: the first oil storage chamber for storing working oil in advance, and the second oil storage chamber for the plunger pump's rapid suction. This segmentation allows each chamber to perform its specific function optimally - the first chamber prevents cavitation by providing advance storage, while the second chamber enables quick suction for compression ratio control.
2Productivity
If the plunger pump operates in a very short period near bottom dead center, then compression ratio control is achieved, but the rapid oil suction causes negative supply pressure
Solution Approach 1:
The first oil storage chamber performs preliminary storage of working oil before the rapid suction period. This advance preparation ensures that during the short operational period near bottom dead center, the plunger pump can quickly discharge oil without causing negative supply pressure, as the oil is already positioned and ready for rapid discharge.
Solution Approach 2:
The first oil storage chamber acts as an intermediary between the oil supply system and the plunger pump. It buffers the pressure fluctuations by storing oil in advance, allowing the plunger pump to operate rapidly without experiencing negative supply pressure, thus mediating between the need for fast operation and pressure stability.
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 configuration effectively suppresses cavitation by managing oil flow and pressure, ensuring stable engine operation.
Implementation Method 1
a bypass oil passage configured to connect a side of the first oil storage chamber and a side of the second oil storage chamber of the communication passage with each other with the orifice as a boundary
Implementation Method 2
a check valve, which is provided in the bypass oil passage, and is configured to limit a flow of working oil from the second oil storage chamber to the first oil storage chamber
Implementation Method 3
The plunger pump supplies working oil to a hydraulic chamber formed between the piston rod and the crosshead pin. The plunger pump sucks and discharges the working oil in accordance with a movement of the crosshead pin
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
Provided is a compression ratio varying mechanism, including: a discharge oil passage connected to a first hydraulic chamber (168a); a supply oil passage (182f) connected to a hydraulic pump (P); a pump cylinder (182a) including a first oil storage chamber (182m) connected to the discharge oil passage and the supply oil passage and a second oil storage chamber (182n) partitioned from the first oil storage chamber by a plunger (182b); a branch oil passage (182h)connected to the second oil storage chamber; and an orifice (182i) provided in the branch oil passage.