Diesels are equipped with high-pressure fuel pumps СР3.3 (Figure 1).

The high-pressure fuel pump (HFP) is designed to create a reserve of fuel, maintain and regulate pressure in the fuel accumulator

A fuel priming pump 2, driven by a shaft 9, and an electromagnetic pressure regulator 3 are fixed on the injection pump housing.

Three plungers 5 are located radially with an angle interval of 120° in the injection pump housing (Figure 2), and a cam rotor 4 is eccentrically mounted on the drive shaft 3 (the cams are located 120° apart around the rotor circumference).

The drive shaft of the high-pressure fuel pump with a cam rotor has a gear drive from a gearbox, the input shaft of which is in kinematic communication with the diesel crankshaft through the distribution gears through the drive coupling half.

Fuel that has passed through a coarse fuel filter with a moisture separator is supplied at a pressure of 0.8 ... 0.9 MPa by a fuel priming pump through a fine fuel filter to the inlet fitting of the injection pump.

Lubrication and cooling of high-pressure fuel pump parts is carried out by diesel fuel entering the high-pressure fuel pump.

CP3.3 high pressure fuel pump.

Picture 1 - High pressure fuel pump СР3.3.

Under the influence of the created boost pressure, the protective valve 2 opens access to the fuel through the supply channel 6 to the above-plunger spaces.

The incoming cam of the rotor moves the plunger upwards, while the inlet of the inlet channel is blocked, and as the plunger continues to rise, the fuel is compressed in the space above the plunger.

When the increasing pressure reaches a level corresponding to that maintained in the high pressure accumulator, the outlet valve 7 opens.

Compressed fuel enters the high pressure circuit.

High pressure fuel pump schematic diagram

Figure 2 - Schematic diagram of the high pressure fuel pump.

The plunger delivers fuel until it reaches TDC (delivery stroke). Then the pressure drops, the outlet valve closes.

The plunger starts moving down. For one revolution of the shaft, each (out of three) plunger makes one pumping stroke.

Since the high-pressure fuel pump is designed for a large flow rate, an excess of compressed fuel occurs at idle and at partial loads, which returns to the fuel tank through the pressure control valve 8 and the backflow line.

The pressure control valve sets the pressure in the high pressure accumulator depending on the engine load, engine speed and thermal state of the engine.

If the pressure in the accumulator is too high, the valve opens and part of the fuel from the accumulator is diverted through the backflow line back to the fuel tank.

The pressure control valve is flanged to the injection pump housing.

Anchor 10 presses the valve ball 9 against the seat under the action of the valve spring so as to separate the high and low pressure circuits.

The switched on electromagnet 11 moves the armature, applying additional force to press the ball against the seat.

The entire anchor is washed with fuel, which lubricates the rubbing surfaces and removes excess heat.