Daewoo G15S-2, Руководство по обслуживанию, Страница: 21 / 88

G420E/G424E
Tier
LP Engine System Operational Overview 20
MI-04 N-CA55-500TR Mixer
Vapor propane fuel is supplied to the N-CA55-500TR
mixer by the N-2001 pressure regulator/converter.
The N-CA55-500TR mixer uses a piston type air
valve assembly to operate a gas-metering valve
inside the mixer. The gas-metering valve is normally
closed, requiring a negative pressure (vacuum) signal
from a cranking or running engine to open. This is the
third of the three safety locks in the MI-04 system. If
the engine stops or is turned off, the air valve
assembly closes the gas-metering valve, stopping
fuel flow past the mixer. The gas-metering valve
controls the amount of fuel to be mixed with the
incoming air at the proper ratio. The air/fuel mixture
then travels past the throttle, through the intake
manifold and into the engine cylinders where it is
compressed, ignited and burned.
(Figure 16) shows the N-CA55-500TR mixer installed
with the electronic throttle.
N-CA55-500-TR Air/Fuel Mixer
Theory of Operation
The air/fuel mixer is mounted in the intake air stream
between the air cleaner and the throttle. The design
of the main body incorporates a cylindrical bore or
mixer bore, fuel inlet (1) and a gas discharge jet (2).
In the center of the main body is the air valve
assembly, which is made up of the piston air valve (3),
the gas-metering valve (4), and air valve sealing ring
(5), air valve spring (6) and the check valve plate (7).
The gas-metering valve is permanently mounted to
the piston air valve with a face seal mounted between
the two parts.
When the engine is not running this face seal creates
a seal against the gas discharge jet, preventing fuel
flow with the aid (upward force) of the air valve spring.
The outer surface of the piston air valve forms the
venturi section of the mixer while the inner portion of
the piston is hollow and forms the air valve vacuum
chamber. The check valve plate seals off the bottom
of the air valve vacuum (AVV) chamber and the air
valve sealing ring seals the top portion of the AVV
chamber as the piston moves against the air valve
spring.
Figure 16
1
2
5
4
3
6
7
Figure 17
Air Intake
Gas-Metering
Valve open
View of Venturi Air
Valve Piston
Figure 18