Fuel Pump Tappet Return Circuit Hydraulic Force
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Solution Overview
Problem
Existing fuel pump assemblies for compression ignition engines face challenges in maintaining sufficient force to hold plunger-tappet-cam rider components together at high speeds, leading to potential separation and malfunction, due to packaging restraints on the return spring within the tappet.
Innovation Solution
A fuel pump assembly design featuring a return circuit where the internal volumes of two tappets are constantly in communication, supplemented by a large expansion chamber and top-up ports to enhance hydraulic force and fuel replenishment, preventing separation of parts during the return stroke.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the tappet internal volume is connected to the cam box interior to cool components and minimize fuel displacement force, then cooling effect and fuel displacement force are improved, but the return spring force is insufficient at high speeds causing part separation
Solution Approach 1:
The invention divides the fuel circulation path into separate functions: the cam box interior provides cooling, while a dedicated return circuit with expansion chamber provides the hydraulic force for tappet return. This segmentation allows each system to optimize its function without compromising the other.
Solution Approach 2:
The return circuit acts as an intermediary system between the tappet and cam box, providing the necessary hydraulic force through fuel pressure while allowing the cam box to focus on cooling functions. The expansion chamber serves as a mediator to accumulate and regulate the hydraulic force.
2Productivity
If the pump operates at increasingly higher speeds to reduce emissions, then productivity is improved, but the return spring force becomes insufficient causing part separation and malfunction
Solution Approach 1:
The invention uses hydraulic principles by utilizing fuel pressure within the return circuit to provide the force necessary for tappet return at high speeds. The expansion chamber accumulates hydraulic energy that supplements the return spring force, ensuring reliable operation at increased pump speeds.
Solution Approach 2:
The invention changes the physical parameters of the fuel system by introducing an expansion chamber that increases fuel volume and pressure in the return circuit. This parameter change provides additional hydraulic force to maintain part contact at high operating speeds.
3Device complexity
If packaging restraints limit the return spring size within the tappet, then device complexity is reduced, but the return spring force is insufficient to hold parts together at high speeds
Solution Approach 1:
The invention merges the return spring mechanism with an external hydraulic assistance system. The return spring remains compact within the tappet while the expansion chamber and return circuit provide additional force, combining mechanical and hydraulic systems to achieve the required return force.
Solution Approach 2:
The invention moves part of the force-generating mechanism from the one-dimensional space within the tappet to the three-dimensional space of the external return circuit and expansion chamber. This dimensional expansion allows for greater force generation without increasing tappet complexity.
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 ensures that the fuel pump assembly can operate reliably at higher speeds by providing a supplementary hydraulic force to the return spring, minimizing part separation and wear, while damping pressure waves and replenishing fuel lost due to leakage.
Implementation Method 1
A cam follower in the form of a tappet cooperates with the cam rider, and in turn a foot of the plunger cooperates with the tappet. The tappet is driven to perform a forward stroke, during which the plunger is driven inwardly within the bore to perform a pumping stroke and pressurise fuel within a pumping chamber by reducing the volume of the pumping chamber. The tappet performs a return stroke in which the plunger is withdrawn from the bore to expand the volume of the pumping chamber and fuel is delivered to the pumping chamber. A tappet return spring effects the return stroke of the tappet.
Implementation Method 2
A return circuit is provided by which the internal volume of the first tappet is in constant communication with the internal volume of the second tappet so that fuel displaced from the internal volume during the pumping stroke of the first tappet fills the internal volume of the second tappet so as to aid the return stroke of the second tappet
Implementation Method 3
supplemented by a large expansion chamber and top-up ports to enhance hydraulic force and fuel replenishment, preventing separation of parts during the return stroke. The solution ensures that the fuel pump assembly can operate reliably at higher speeds by providing a supplementary hydraulic force to the return spring, minimizing part separation and wear, while damping pressure waves and replenishing fuel lost due to leakage.
Data Source
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AI summary
A fuel pump assembly for use in an internal combustion engine comprises a pump housing (10), at least first and second pumping plungers (16a, 16b) for pressurising fuel within a respective one of first and second pumping chambers (20a, 20b); and first and second tappets (22a, 22b), each being associated with a respective one of the pumping plungers and being driven, in use, by an engine-driven cam, so as to drive a pumping stroke of the tappet and the associated plunger during which fuel within the associated pumping chamber is pressurised. Each tappet (22a, 22b) defines an internal volume (24a, 24b) for housing, at least in part, an associated return spring (34a) which drives a return stroke of the tappet and the associated plunger during which the associated pumping chamber is filled with fuel. A return circuit (50a, 50b, 52a, 52b, 54) is provided by which the internal volume (24a) of the first tappet (22a) is in constant communication with the internal volume (24b) of the second tappet (22b) so that fuel displaced from the internal volume during the pumping stroke of the first tappet fills the internal volume of the second tappet so as to aid the return stroke of the second tappet.