Fuel Pump Cylinder Clearance to Prevent Plunger Sticking
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Solution Overview
Problem
The high-pressure fuel pump in direct injection engines experiences plunger sticking due to heat-induced deformation of the cylinder, which is caused by the transfer of heat from the pressurized fuel to the press-fitting portion, leading to inward deformation and compression of the plunger.
Innovation Solution
The fuel pump design incorporates a plastically deformable fixing portion that engages with the cylinder, allowing for a clearance to accommodate thermal expansion, preventing the cylinder from pressing against the plunger and reducing deformation, thereby suppressing plunger sticking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cylinder is press-fitted into the pump body to secure the plunger, then the plunger is held in position, but heat from the pressurized fuel causes the cylinder to deform inward and compress the plunger, leading to sticking
Solution Approach 1:
The inner peripheral surface of the cylinder is segmented into multiple regions with different radial clearances relative to the pump body. The first region (opposite the pressurizing chamber) has a larger clearance to accommodate thermal expansion, while the second region (facing the pressurizing chamber) has a smaller clearance to maintain plunger positioning. This segmentation allows different parts of the cylinder to serve different functions under thermal stress.
Solution Approach 2:
Different radial clearance values are applied to different axial positions of the cylinder. The region opposite the pressurizing chamber is designed with larger clearance to prevent heat-induced deformation and plunger compression, while other regions maintain tighter clearances for proper plunger guidance and positioning.
2Stability of the object's composition
If the cylinder is tightly fitted to the pump body to prevent deformation, then structural stability is improved, but heat transfer causes the cylinder to deform and compress the plunger
Solution Approach 1:
The cylinder's inner peripheral surface is divided into zones with different clearance characteristics. The first region has larger radial clearance to act as a thermal buffer zone, absorbing expansion without transmitting deformation to the plunger. The second region maintains smaller clearance for precise plunger positioning, achieving both stability and precision.
Solution Approach 2:
The first region with larger radial clearance acts as an intermediary buffer zone between the heat source (pressurizing chamber) and the plunger positioning region. This buffer absorbs thermal expansion effects, preventing direct transmission of deformation to the plunger and maintaining positioning precision.
3Ease of manufacture
If uniform radial clearance is provided throughout the cylinder, then manufacturing is simplified, but heat-induced deformation causes plunger compression and sticking
Solution Approach 1:
Rather than using uniform clearance throughout, the cylinder is designed with segmented clearance zones. This segmentation, while adding design complexity, actually simplifies manufacturing by allowing the use of standard press-fitting processes for each zone, while avoiding the need for complex adjustable mechanisms to compensate for thermal effects.
Solution Approach 2:
The radial clearance parameter is changed along the axial direction of the cylinder, transitioning from larger clearance in the first region to smaller clearance in the second region. This parameter variation optimizes both manufacturing feasibility and operational reliability under thermal conditions.
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 plunger fixation, maintaining efficient fuel discharge rates and preventing the decrease in flow rate due to thermal expansion, while ensuring reliable operation of the high-pressure fuel pump.
Implementation Method 1
a press-fitting portion press-fitted into the inner peripheral surface of the cylinder insertion hole
Implementation Method 2
a plunger seal that prevents fuel from flowing into the engine
Data Source
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AI summary
The present invention provides a fuel pump capable of suppressing sticking of a plunger. The fuel pump of the present invention includes a plunger 2 that reciprocates, a cylinder 6 in which a guide hole 6a that guides the reciprocating motion of the plunger 2 extends in the axial direction, and a pump body 1 that holds the cylinder 6. The pump body 1 includes a cylinder insertion hole 1g into which the cylinder 6 is inserted, and a pressurizing chamber 11 that communicates with the cylinder insertion hole 1g and has a volume increased or decreased by the reciprocating motion of the plunger 2. The cylinder 6 includes a press-fitting portion 6b press-fitted into the inner peripheral surface of the cylinder insertion hole 1g, and a groove 6d formed at a position corresponding to the press-fitting portion 6b on the inner peripheral surface of the guide hole 6a.