Mitsubishi 4DQ50 Service Manual page 37

1) A pneumatic governor, for governing of its speed, consist of diaphragm block
in fuel injection pump and of Venturi unit in inlet manifold, which are
connected together with an air pipe.
2) Now, following the scheme and diagram of operation principle, we will briefly
explain how this governor operates. When intake air passes through Venturi
that closes inlet manifold to some extent, its flow velocity rises but at the same
time, static pressure at that part (to be taken through pipe that opens to its
flow direction at a right angle) falls considerably below the pressure on the area
free from the inflow of air (generally, atmospheric pressure) or in short, turns
into negative. This negative pressure rises, as can be seen in Fig. 3·25, with the
rise of engine speed and consequently of flow velocity of intake air. Through
an air pipe, it is conducted into negative pressure chamber in diaphragm block
to work on diaphragm. The governing force it produces is calculated:
(Venturi negative pressure)x(Diaphragm area)=(Governing force)
Main
sprinC
Diff.,. ... ti ..
~. ~
both sides of
di'-'ecm
by
Yenlui
necativo
Pr_L
Openi"l in idlinl
.:tian
r..,~.~~:::t=====t=:j===:;~=;;~::;'"
Fig. 3·25 Diagramatized principle of pneumatic governor operation
Now suppose that max. engine speed needs to be governed at A (rlp.m.). While,
with Venturi butterfly valve opened 100%, main spring with setting load
equivalent to governing force Fc that is produced by negative pressure C at
point B on Venturi negative curve (Fig. 3·25) is placed on diaphragm. When the
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