Systems And Principle Of Operation; Cr Injector Operation; Injector Valve Types; Solenoid Valves - Hartridge CRi-PC Operating And Servicing Manual

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3. Systems and Principle of Operation

3.1

CR Injector Operation

One of the main differences between Common Rail injectors and traditional mechanical
injectors is the introduction of electrical control; with Common Rail injectors the timing and
duration of injection are controlled using an electrically-operated valve. There are currently
two types of valve, described in section 3.2 below.
In terms of the hydraulic operation, high pressure fuel is supplied to the nozzle body and to a
chamber on top of the control needle. The electrical valve opens/closes a leak off path from
this chamber into the return circuit. When the valve is closed, the high pressure acting on top
of the control needle keeps the injector firmly closed. Opening the valve relieves the high
pressure from the top of the needle, opening the nozzle and starting the injection. Closing the
valve re-establishes the high pressure on top of the control needle, quickly shutting off the
injection.
The volume of fuel delivered is proportional to both the duration of the pulse (pulse width),
and the applied pressure, as shown by the graph in Figure 3.1. Typical pulse widths are in
the range of 200 to 2000s. There is a minimum pressure below which the injector will not
open; this is typically around 200bar.
Figure 3.1 Effect of Pressure and Pulse Width on Delivery
3.2

Injector Valve Types

3.2.1

Solenoid Valves

These are electromagnetic coil valves; Figure 3.2 gives a schematic of the drive signal
(showing current against time). There is a higher "pull-in current" (I
valve, followed by a lower "hold current" (I
(T) is the combined width of the pull-in and hold phases. There is a maximum limit on the
pull-in current to protect the solenoid.
Injectors with solenoid valves are currently manufactured by Bosch, Delphi, and Denso. Each
of these manufacturers uses a different specification for operating voltage and current levels.
HL037 (EN), Issue 13, AT714, 05/14
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CRi-PC Operating and Servicing Manual
bar

s
) to keep the valve open. The overall pulse width
h
) to initially open the
p
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