High pressure fuel pump (HPFP) construction: types of fuel pumps, how it works
The high-pressure fuel pump has the abbreviation (HPFP) performs the following main functions:
- deliver high-pressure fuel to the fuel system of the internal combustion engine;
- To regulate the moments of fuel injection.
The fuel pump is of the most important devices for gasoline and diesel engines.
HPFP are usually use in diesel engines. The using of a high-pressure pump in gasoline engines is impractical, because it does not require such high pressures as in a diesel engine.
There are following main structural elements of the high-pressure fuel pump:
Plunger (piston) + Cylinder (bushing) = Plunger system (pair)
Plunger system is made of high-strength steel on high-tech equipment (machine tools), due to the need for high precision.
There are three main types of fuel pump that we will consider:
- Fuel injection pump;
- high pressure inline fuel pump;
- Mechanical fuel pump.
High-pressure inline fuel pump
The in-line high-pressure fuel pump is equipped with plunger pairs that are arrange with each other. Their number depends on the number of working cylinders of the engine and corresponds to it. One piston pair provides fuel for only one cylinder.
Pairs are installing in the pump casing, which has inlet and outlet channels. A camshaft driven by a crankshaft drives the plunger.
When the camshaft of the fuel pump is rotating, the cams act on the plunger pushers, causing them to move inside the pump bushings. Due to the inlet and outlet openings start to open and close in sequence. When the plunger moves upward, a pressure creates in the sleeve, which leads to the opening of the discharge valve, through which fuel is supply to the nozzle through the fuel line.
The moment of fuel supply is regulating by a special device (centrifugal clutch). The work of the centrifugal clutch is bases on the movement of weights under the action of centrifugal force.
The centrifugal force changes as the engine’s crankshaft rotates (or decreases), as a result of which the weights diverge to the outer edges of the coupling, or approach the axis. There is a shift of the camshaft relative to the drive, which leads to a change in the operation of the plungers.
When the crankshaft speed increases – there is an early fuel injection, when they decrease – late fuel injection.
Inline fuel pumps have proven themselves reliable. They are not picky at all to the quality of the fuel and the lubrication of the injection pump is carried out with ordinary engine oil.