DD 15 – Section 3.6 High Pressure Pump

Section 3.6
High Pressure Pump

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1. Intake Valve‪	5. High Pressure Piston‪
2. High Pressure Connection‪	6. Compression Spring‪
3. High Pressure Valve‪	7. Roller Tappet‪
4. High Pressure Pump Housing‪	8. Camshaft‪

The camshaft (8) for the high pressure fuel pump is driven by the pinion gear drive.‪

The fuel is compressed by two high pressure pistons (5) and feeds the high pressure connection (9) and corresponding high pressure lines to the rail. The two roller tappets (7) on the double cams of the camshaft (8) are pressed together by two push springs (6) which are offset by 90°. With this configuration, two pressure strokes occur for one camshaft revolution for each high pressure piston (5). If the high pressure piston (5) is in a downward movement, the fuel can flow over the corresponding intake valve (1) into the clearance volume of the high pressure piston (5). If the high pressure piston (5) now changes to an upward movement, the corresponding intake valve (1) is closed by the compression pressure rising and the fuel in compressed until the high pressure valve (3) opens a transfer duct between the high pressure compartment and the corresponding high pressure connection (9). The highly compressed fuel can now flow into the rail. If the high pressure piston (5) again changes to a downward movement, the transfer duct is closed again by the spring-loaded high pressure valve (3) and new fuel can flow through the opened intake valve (1) into the clearance volume.‪

Section 3.6.1
Two–Stage Valve

Internal to the high pressure fuel pump is a two-stage valve. The excess fuel from the quantity control valve and high pressure fuel pump is routed past the two-stage valve. ‪

The two-stage valve has a number of tasks:‪

• It is closed at pressures in the low pressure circuit below 3 bar relative to high pressure pump backflow pressure. This will ensure best filling for the pumping elements under cranking speed where low pressure pump flow is low.
• It guarantees lubrication of the high pressure fuel pump components if the pressure in the low pressure circuit is above 3 bar relative to high pressure pump backflow pressure. The lubrication path is fully open at 3.5 bar.
• It ensures that in overrun conditions the pressure at the inlet to the high pressure pump is limited by opening of the backflow path. This function avoids pressures above burst pressure level of the filter module. If the pressure at the high pressure pump inlet exceeds 4.7 bar relative to backpressure, excess fuel is routed to the return path.