Adjusting the start of pressing

The beginning of pressing is recorded as a map of characteristics as a function of engine rotational speed and fuel dose as a measure of the engine load.. The engine and intake air temperatures as well as the ambient pressure are used as correction factors. The most important sensors are: sensor
crankshaft position and the rotation angle sensor in the pump. Based on the latter, the controller determines the exact position of the pump shaft and the injection timer. The injection start regulator circuit in the pump control unit constantly compares the actual injection start with a predetermined nominal value and if a difference is detected – changes the control signal sent to the solenoid valve. The information about the actual injection start value is the signal of the rotation angle sensor or the signal of the needle lift sensor in the injector holder..

The spray needle lift sensor is not necessary. This sensor has been dispensed with in Ford and Opel engines, while it is present in BMW and Audi engines.

The start of delivery is initiated by the closure of the high pressure solenoid valve. High pressure builds up in the injection line. When the injector opening pressure is reached, the sprayer needle rises and the injection begins.

During operation, the fuel pressure in the pump interior is regulated by a pressure regulating valve, depending on speed. This fuel pressure is transferred as control pressure via the throttle to an annular chamber around the hydraulic buffer (13) and the solenoid valve of the injection timer is closed (15) moves the control piston (12), against the direction of the control piston spring force (10), accelerating injection (in fig. right). As a result, an adjusting slider (5), moving in the direction of accelerating the injection, opens the inflow channel (4) into the space behind the piston in the injection actuator. This allows the fuel to pass through this channel and move the injection actuator piston to the right, in the direction of accelerating the injection. The axial movement of the injection actuator piston is transmitted through the projection (2) on the cam ring (1) high pressure pumps, causing it to rotate through a certain angle. Rotation of the cam ring relative to the pump drive shaft causes, in the case of a change in the direction of acceleration of injection, earlier entry of the rollers on the lobes of the cams of the ring and earlier start of injection. Possible lead up to 20 ° camshaft rotation angle (which corresponds to 40 ° rotation of the crankshaft).

The injection is delayed, when the control piston (12) will move under the action of the spring force (10) in the direction of delaying the injection (in fig. left). It is happening, when the solenoid valve on the injection actuator (15) will open on control signal from the pump controller. Then the pressure in the annular chamber of the hydraulic buffer drops (13). When the adjusting slider (5) it will open the opening leading to the drainage channel, the fuel from the space behind the setting device's piston will be able to drain away and allow the settinger's piston to move. The force of the spring (11) and reaction torque, acting on the cam ring, by pressing the plunger of the adjuster in the direction of injection delay, they move it to the starting position.

The injection actuator valve can be continuously opened and closed by the controller by specifying the appropriate pulse duty factor. The greater the factor, the later start of pressing, smaller – earlier.