Transfer pump

Transfer pump

1. Transfer pump rotor
2. Brushes
3. Elliptical seal

The transfer pump, which is the volumetric type (inlet and pressurizing), consists of a rotor (1), an elliptical seal (3) and two rigid brushes (2). During rotation, the brushes (2) slide in the rotor (1) following the profile of the elliptical seal (3) offset in relation to the rotor. As the volume in the chamber increases, a vacuum is created, upstream of the brush, which the consequent intake of fuel from the tank; downstream of the vane the volume decreases and therefore there is a supply of fuel under pressure in the circuit.

Hydraulic head

The metering, pumping and distribution functions take place in the main section of the injection pump known as the hydraulic head.

The hydraulic head consists of two groups:

• - the hydraulic head stator;
• - the distributor rotor, consisting of a single element and two pumping pistons.

The distributor rotor is coupled with the housing in the hydraulic head, whilst the pumping pistons are coupled with the seats in the rotor. This means that these parts are not interchangeable, but form a single assembly.

The fuel, subjected to the transfer pressure, enters one of the ports in the hydraulic head; the opening of this port is controlled by the movement of the metering valve connected to the mechanical regulator.

During the pressurizing cycle (stage A), two pressurizing ports in the rotor are aligned with the two head stator filling ports. A metered quantity of fuel, regulated by the metering valve, enters the pumping element and distances the pumping pistons (5), pushing out the unit consisting of the roller (1) and the pad (6).

On rotating, the rotor interrupts the alignment between the pressurizing and filling ports (end of the pressurizing cycle).

As the rotation continues, one of the fuel supply ports coincides with one of the high pressure outlets (stage B).

The cam seal, through the pumping unit, produces the high pressure capable of producing injection. The internal housing of the cam seal has a profile which features four diametrically opposed cams whose shape determines the progress and the duration of the injection stage.

The injection starts when the rollers (4), made to rotate by the drive shaft (1) ramps, come into contact with the seal (7) cams and continues until the top of the cam is reached.

When the cam is exceeded, the fall in pressure allows the compression chamber to be filled once again.