1. Not used at present in the M67. Will instead be used in future CR systems in which pressure control is provided by a system of suction-end volume control.
2. Element filling
3. The CP3 is suitable for operation with restricted suction. However, the M67 version does not utilize this special feature of the gear pump to the fullest extent possible.
In addition to the CP1, the CP3 is also being equipped with the following components:
• Gear pump fitted as a fuel delivery pump
• Solenoid valve for suction end flow rate control
(in the M67 currently only available in conjunction with the “ELAB” function. In future CR systems, pressure control will be handled by a solenoid valve, used to control flow rates at the suction end)
Task
The high pressure pump is the interface between the low pressure and the high pressure sections. It has the task of ensuring that there is always enough fuel delivered at a sufficient pressure in every operating mode over the entire service life of the vehicle. This includes the delivery of spare fuel, required for a rapid start and pressure increase in the rail.
Structure
Fuel is delivered via the filter to the HPP intake (13) and the safety valve (14) situated behind it. It is forced through the throttle bore into the low pressure duct (15). This duct is connected to the lubrication and coolant circuit of the high pressure pump.
It is therefore not connected to an oil circuit.
The drive shaft (1) is driven via the chain drive at more than half of the engine speed (max. 3300 rpm). It moves the three pump pistons (3) up and down with its eccentric cam (2), depending on the cam shape.
If the pressure in the low-pressure duct exceeds the opening pressure of the suction valve (5) (0.5 -1.5 bar), the advance delivery pump can force fuel into the element chamber where the pump piston moves downwards (suction stroke). If the dead centre point of the pump piston is exceeded, then the intake valve closes. The fuel in the element chamber (4) can no longer escape. It is then compressed in the intake line by the delivery pressure. The accumulating pressure opens the exhaust valve (7) as soon as the pressure in the rail is achieved. The compressed fuel enters the high pressure system.
The pump piston delivers fuel until the upper dead centre point is reached (delivery stroke). The pressure then falls again, which closes the outlet valve. The remaining fuel is no longer subject to pressure. The pump piston moves downwards.
If the pressure in the element chamber falls below the pressure in the low pressure duct, then the intake valve opens again. The whole process is repeated from the beginning.
The high pressure pump constantly generates the system pressure for the high pressure accumulator (rail). The pressure in the rail is determined by the pressure control valve.
The high pressure is generated by means of three pump pistons arranged radially within the high pressure pump. Three delivery strokes per revolution ensure low injection torque and uniform load over the pump drive. At 16 Nm, the average torque is only approx. 1/9 of the drive torque required for a comparable distributor pump.
The power required for the pump drive increases proportionally
• to the set pressure in the rail and
• to the pump speed (delivery volume).
On a 2 litre engine (rated speed, rail pressure 1350 bar), the high pressure pump (at approx. 90 % mechanical efficiency) has a power intake of 3.8 kW (compared to a distributor-type injection pump: 2.5 kW at the rated output point). The higher power requirement is attributed to the leakage and control volumes in the fuel injector and the fuel return via the pressure control valve.
Since the high pressure pump is designed for large delivery quantities, there is an excess of compressed fuel when the vehicle is idling or only subject to partial load. Since the compressed fuel is no longer subject to pressure once the excess fuel flows away, the energy generated by compression is lost and/or heats the fuel.
This excess delivered fuel is returned to the fuel tank via the pressure control valve and the fuel cooler.
