SUPPLY PUMP <4M4>

Construction Diagram

After drawing the fuel from the fuel tank, the supply pump pressurizes the fuel maximum 180 MPa <Europe STEP 4>, maximum 135 MPa <Europe STEP 3> and delivers it to the common rail. It consists of the following parts and functions.

Feed pump: Draws fuel from the fuel tank.
Regulator valve: Opens when the fuel pressure between the feed pump and the suction control valve exceeds a predetermined value, and returns excess pressure to the fuel tank.
Suction control valve: Regulates the amount of fuel that is delivered to the common rail in accordance with the actuation signals received from the engine-ECU.
Plunger: Pressurizes the fuel that is stored in the high-pressure chamber. The plunger moves constantly at full stroke.
Suction valve: Prevents the fuel in the high-pressure chamber from flowing backwards.
Delivery valve: Prevents the fuel in the common rail from flowing back towards the supply pump.

CONSTRUCTION DESCRIPTION

The drive force for the supply pump travels from the gear that is mounted on the crankshaft, via an idler gear, to the supply pump camshaft. The rotational movement of the supply pump camshaft drives the feed pump and the plungers. The driving of the feed pump causes the fuel to be drawn up from the fuel tank. The driving of the plungers pressurizes the fuel that is stored in the high-pressure chamber. There are two plungers, which are arranged in such a way that when one is in the suction stroke, the other is in the pumping stroke.
Operation Diagram

The fuel that is delivered from the feed pump is drawn into the high-pressure chamber, which is located at the side of the plunger that is in the suction stroke. Then, as the camshaft rotates, it starts the pumping stroke and pressurizes the fuel in the high-pressure chamber. When this exceeds the fuel pressure in the common rail, the delivery valve opens, pumping the fuel into the common rail. The two plungers repeat these strokes alternately. Consequently, as the injectors inject fuel twice per revolution of the engine, the supply pump also pumps twice. Thus, it is able to maintain a constant fuel pressure in the common rail.

SUCTION CONTROL VALVE

Suction control valve is installed in the fuel passage between the feed pump and the suction valve. A type of solenoid valve in which the opening of the valve varies in accordance with the amount of the actuating current, the suction control valve regulates the amount of fuel that is delivered by the feed pump to the high-pressure chamber.
When the amount of actuating current is small, the opening of the suction control valve becomes large, thus increasing the amount of fuel that is delivered to the high-pressure chamber. As a result, the amount of fuel that is pumped to the common rail is increased.
When the amount of actuating current is large, the opening of the suction control valve becomes small, thus reducing the amount of fuel that is delivered to the high-pressure chamber. As a result, the amount of fuel that is pumped to the common rail is reduced.
By varying the amount of actuating current to the solenoid valve in accordance with the running conditions of the engine, the engine-ECU controls the amount of fuel that is delivered to the high-pressure chamber.