Page 241 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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Engine systems 225

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Figure 2.294 Solenoid valve-controlled radial-piston distributor pump: 1, Sensor (position/
timing); 2, ECU; 3, high-pressure solenoid valve needle; 4, solenoid; 5, outlets to injectors;
6, timing device (ignition advance mechanism); 7, radial-piston high-pressure pump. (Source:
Bosch Media)

Figure 2.295 Electronic diesel control (EDC) unit

A high-pressure solenoid valve is closed by an electrical signal from the pump
ECU. When the valve is closed, fuel under high pressure passes from the
high-pressure pump chamber, through the bores in the rotor and distributor
head, through the return-fl ow throw throttle valve (delivery valve) and out to
the injectors. It is then injected into the engine combustion chambers. The few
microseconds of time during which the valve remains closed is referred to as the
delivery or injection period.
The quantity of fuel that is metered for injection at any time is computed by the
engine ECU ( Fig. 2.296 ), which sends signals to the injection pump ECU for
control of the high-pressure solenoid valve. The electrical current for operating
this valve is high, and the two ECUs are separated to avoid high current
interference in the electronically more vulnerable engine ECU.