When the engine is started and the rotor turns
within the sleeve, the rotor port at the control stop end becomes coincident
with the port in the sleeve leading to the fuel reservoir in the body casting.
Fuel at high pressure enters the rotor bore and drives the shuttle to the right
(i.e., towards the fixed stop end of the rotor). This movement of the shuttle
displaces fuel in the rotor bore through the ports in the rotor and sleeve to
the injector serving No. 1 cylinder.
A further 180 degree rotation of the rotor
(Fig. 8B) causes the rotor ports at the fixed stop end to align with the sleeve
port leading to the fuel reservoir. Fuel now enters at the fixed stop end of the
rotor and drives the shuttle back towards the control stop end. An identical
quantity of fuel is displaced, by the shuttle as it moves to the left, by way of
the outlets in the rotor and sleeve to No. 2 injector.
In this way the shuttle continually moves between the two stops displacing an
accurate amount of fuel to each cylinder in turn.
The quantity of fuel delivered at each injection is dependent
upon the distance the shuttle travels, this distance is adjusted by the control
PRINCIPLES OF SHUTTLE-METERING
Before considering the design features
of the metering distributor, it will probably be advantageous to discuss
the principles of shuttle-metering. Figure 8 shows a metering distributor
for a twin cylinder engine. It consists essentially of two parts; the
rotor and the sleeve. The rotor has two radial ports, which lead to a
centre bore containing a shuttle - which is movable between two stops (one
fixed and the other adjustable). The sleeve has fuel inlet and outlet
ports. The rotor fits inside the sleeve and is connected to, and driven
by, the engine.
As the rotor turns, the port at the
control stop end of the rotor becomes coincident with the fuel inlet port
in the sleeve (see Figure 8, top diagram).
Pressurised fuel then enters the bore
and drives the shuttle towards the fixed stop. This causes fuel to be
discharged through the ports in the rotor and sleeve at the fixed stop
end, and hence into the first cylinder through the appropriate injector.
The lower diagram shows the result of turning the rotor
through 180 degrees. Fuel now enters the bore through the port at the fixed stop
end of the rotor, driving the shuttle towards the control stop. An
identical amount of fuel is then delivered to the second cylinder.
As the rotor turns, the pressurised fuel drives the shuttle
between the two stops, ensuring that an accurately metered quantity of fuel is
injected into the appropriate cylinder at the right time. The low mass of the
shuttle ensures a rapid response at high engine speeds.
The quantity of fuel injected is the product of the surface
area of the shuttle end face and its length of travel. The length of travel is
determined by the position of the control stop. The metering distributor shown
is for two-cylinder engines. However, the same principles of shuttle-metering
can be adapted for four, six and eight cylinder engines, by altering the
position and the number of ports in the rotor and sleeve assemblies.