High-Pressure Fuel Pump Plunger Structure for Leak Reduction
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Solution Overview
Problem
Cam actuated high pressure pumps in diesel engines experience fuel leaks due to enlarging clearance between the plunger and bore as pressure rises, leading to volumetric loss and inefficient lubrication.
Innovation Solution
A high pressure fuel pump design featuring a plunger with a blind bore and a filler member made of low-density material, such as aluminum or ceramic, which is unfixed and free to move within the chamber, creating a small annular gap that reduces leakage by expanding the bore's peripheral wall to partially close the clearance when pressure increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a recess is provided on the plunger head end to close the clearance, then fuel leaks are reduced, but the compression chamber volume increases causing volumetric loss
Solution Approach 1:
The plunger is segmented into two functional zones: the head end maintains a limited clearance for lubrication, while the body incorporates a blind bore with a filler member that creates a secondary sealing interface. This segmentation allows the clearance to be optimized for lubrication without compromising sealing, as the filler member provides the primary leak prevention mechanism.
Solution Approach 2:
A filler member made of low-density material (aluminum, polymer, or ceramic) is introduced as an intermediary element within the blind bore. This filler member is free to move and is retained by pressure differential and friction, acting as a mediator that enhances sealing between the plunger and bore while maintaining the necessary clearance for lubrication.
2Productivity
If the clearance between plunger and bore is reduced to minimize leaks, then volumetric loss decreases, but lubrication effectiveness deteriorates
Solution Approach 1:
Different clearance characteristics are provided at different locations of the plunger. The head end maintains a larger clearance for effective lubrication, while the blind bore region with the filler member provides a tighter effective sealing clearance. This local differentiation allows both lubrication and leak prevention to be optimized simultaneously.
3Reliability
If a filler member is introduced in the blind bore, then fuel leaks are minimized, but device complexity increases
Solution Approach 1:
The filler member is made from inexpensive, low-density materials such as aluminum, inert polymers, or ceramics. These materials are readily available and easy to manufacture, making the filler member a cost-effective solution that does not significantly increase device complexity despite adding a functional element to the plunger structure.
4Reliability
If the plunger clearance is enlarged for lubrication, then lubrication is maintained, but fuel leaks increase
Solution Approach 1:
The sealing function is extracted from the primary plunger-bore clearance interface and relocated to a secondary interface within the blind bore. By taking out the sealing responsibility from the main clearance zone, the plunger can maintain a larger clearance for lubrication while the filler member provides the sealing function that would otherwise require a tight clearance.
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 minimizes fuel leaks and maintains lubrication by ensuring the filler member remains in place due to fuel suction and pressure forces, reducing volumetric loss and enhancing the pump's efficiency.
Implementation Method 1
when the pressure rises the peripheral wall of the recess slightly expands and closes, at least partially, the clearance
Implementation Method 2
the filler member remains in place due to fuel suction and pressure forces
Data Source
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AI summary
A high pressure fuel pump (10) having a pumping head (16) and a plunger (34) slidably adjusted in a bore (26). The plunger (24) is provided with a blind bore defining a chamber open in the head end of the plunger (34) and in fluid communication with the compression chamber (20), the end face of the plunger being limited to a peripheral annular face surrounding said opening, said bore further defining a peripheral cylindrical wall and a bottom face and a filler member (54) is arranged inside said chamber.