198002674 - INTRODUCTION - INJECTORS AND PIPES

DESCRIPTION OF COMPONENTS

INJECTORS

The injectors are fitted on the cylinder head and controlled by the injection control unit.

The injector can be divided into two sections:

  • actuator/spray consisting of pressure rod (1), pin (2) and nozzle (3);
  • control solenoid consisting of coil (4) and pilot valve (5).
Injector operation is divided into three stages.REST POSTION - the coil (4) is deactivated and the plunger (6) is in the closed position to prevent fuel from being introduced into the cylinder Fc > Fa (Fc: due to line pressure acting on control area 7 of rod 1; Fa: due to line pressure acting on feed volume 8).START OF INJECTION - the coil (4) is energised and causes the plunger (6) to rise.Control volume fuel (9) flows out towards the return manifold (10) to bring about a pressure drop on the control area (7). Simultaneously, the line pressure flowing through the intake duct (12) exercises a force Fa > Fc in the supply volume (8) to cause the pin (2) to lift and allow fuel into the cylinders.END OF INJECTION - the coil (4) is deactivated and causes the plunger (6) to return to closed position. This rebalances the forces so that the pin (2) returns to the closed position and the injection ends.

Ima classification

During the test stage the injectors are checked with the specifications verified in different pressure/flow rate conditions. All the injectors that do not meet a certain standard are rejected; the remaining ones are classified using a 9-character alphanumerical code, known as an IMA code, imprinted by laser on the top part of the magnet.During fitting on the vehicle the control unit should memorise the individual code and, if one or more injectors is replaced in a service situation, the alteration to the code should be made during the diagnosis using the appropriate equipment.
1. Pressure rod2. Pin3. Nozzle4. Coil5. Pilot valve6. Ball plunger7. Control area8. Feed volume9. Control volume10. Fuel return - low pressure11. Control duct12. Feed duct13. Electrical connection14. Fuel return connector - high pressure15. Spring16. IMA code

COMMON RAIL

The common rail is fitted to the intake side of the cylinder head.

With a volume of around 33 cm³, this damps fuel pressure fluctuations due to:

  • pressure pump operation
  • injector opening.
The fuel pressure sensor is fitted at the left-hand end of the delivery manifold.The hydraulic connections (high pressure) between manifold-pump and manifold-injectors are via steel pipes with a bore of 2 mm and external diameter of 6 mm.