Injection Timing Control System
The injection timing control system controls injection proportional to the injection pump speed. Although the feed pump fuel pressure is controlled by the regulating valve, fuel pressure in the pump housing increases with injection pump speed. The timer piston moves perpendicularly to the drive shaft after overcoming the timer spring force. Timer movement causes the roller ring to rotate in the opposite direction to drive shaft rotation. This causes the roller to come in contact with lobes on cam plate earlier in the cycle.
Fuel pressure in the pump housing is controlled by the injection timing control solenoid valve which is incorporated in the injection pump. When the control lever is moved to a point where the accelerator switch is turned on, the solenoid valve is energized by the accelerator switch, and the fuel return passage to the injection pump fuel inlet is closed.
As a result, fuel pressure in the pump housing is increased, resulting in injection timing being advanced. When the solenoid valve is de-energized by the accelerator switch (which is turned off with the control lever movement), the fuel return passage is opened so that excess fuel in the injection pump is returned to the injection pump fuel inlet. Fuel pressure in the pump housing is decreased, resulting in injection pump timing being retarded.
Injection timing is also advanced at high altitude to prevent excessive exhaust smoking. At high altitude the vacuum switch is turned on resulting from reduced barometric pressure applied to 1 side of the diaphragm of the vacuum switch. The injection timing control solenoid valve is then energized.