VN 2.120
1. Fuel injection pump (M41)
2. Fuel quantity control valve (Y94)
3. Fuel temperature sensor (B50)
4. High pressure fuel line
VN 2.121
Fuel injection pump. Placement and design
1. Fuel injection pump
2. Electrical connector
VN 2.122
Fuel injection pump. Operating principle
a. Throttle valve closed:
3. High pressure channels
4. Eccentric cam
5. Eccentric shaft
6. Input channel
9. Plungers
10. Plunger springs
12. Throttle valve spring
b. Throttle valve open:
13. Throttle valve piston
14. Throttle valve metering hole
16. Return flow
VN 2.123
Fuel injection pump. Operating principle
a. Incoming flow
b. High pressure channel
C. Pressure from the fuel pump
D. High pressure
1. High pressure fuel line
2. Fuel inlet line
3. High pressure channels
4. Eccentric cam
5. Eccentric shaft
6. Input shaft
7. Valve disc
8. Valve spring
9. Plungers
10. Plunger return springs
15. Ball valve
16. Return flow
Purpose
Creation and maintenance of high pressure in the fuel manifold, the required fuel pressure (from 20 to 135 MPa (from 200 to 1350 bar).
Accommodation
The high-pressure fuel pump is located on the front cover of the cylinder head.
Design
The high-pressure fuel pump is a three-plunger cam-type pump with a radial arrangement of plunger pairs in a star-shaped pattern. The injection pump rotates at a speed approximately 1.3 times higher than the camshaft rotation speed.
Functioning
Low pressure circuit
Fuel is supplied from the fuel pump through the inlet channel (6) to the throttle valve (13). Any remaining air in the fuel is carried away by the fuel flow directed through the throttle opening (14) into the return flow cavity (16). At a pressure above 0.04 MPa (0.4 bar), the piston of the valve (13) is displaced, opening access for fuel into the annular channel for supplying fuel to the plungers (9),
The eccentric shaft (5) with the eccentric cam (4) pushes the plungers (9) of the three pump elements. The plungers are returned using springs (10). Fuel leaks through the plunger pairs are collected in the return cavity.
High pressure circuit
a. Filling the cylinder
The plunger (9), under the action of the return spring (10), moves towards the eccentric shaft. Fuel from the fuel pump is supplied through the low pressure annular channel (6), the valve disk (7) and the valve spring (3) into the cavity of the pressure cylinder. The ball valve (15) prevents the backflow of fuel from the high-pressure channel (3) into the low-pressure cavity.
b. Creating high pressure
The plunger (9), pushed by the eccentric cam (5), displaces the fuel into the high-pressure channel (3) through the ball valve (15). In this case, the pumped volume of fuel is cut off from the low-pressure cavity (6) by means of the valve disk (6).