This invention relates to a fuel pumping apparatus for supplying
fuel to an internal combustion engine and of the kind comprising a plunger reciprocable
within a bore, an outlet from one end of the bore for connection in use to an
injection nozzle of an associated engine, an engine driven cam for imparting inward
movement to the plunger to effect displacement of fuel from said one end of the
bore and a spill valve operable to allow fuel displaced by the plunger to flow
to a drain thereby to control the quantity of fuel delivered through the outlet.
Apparatus of the aforesaid kind is known in which the spill valve
is electrically operated and is controlled by an electronic control system which
allows for the adjustment of the timing and the quantity of fuel delivered to
the associated engine.
It is well known that in a high speed compression ignition engine
the initial delivery of fuel to the engine should be at a restricted rate followed
by the main quantity of fuel at a substantially unrestricted rate. It has been
proposed to provide delivery control devices in or adjacent the injection nozzle
which devices include spring loaded piston elements and restrictors. The piston
elements introduce inertia problems. Moreover, such devices are expensive to manufacture
and are not always consistent in operation throughout their life. Furthermore,
it is not easy to produce a number of such devices which have substantially identical
characteristics for fitment to the injection nozzles of an engine.
The object of the present invention is to provide an apparatus of
the kind specified in a simple and convenient form.
According to the invention a fuel pumping apparatus of the kind specified
comprises a restricted flow path from said one end of the bore, and co-operating
valving edges formed on said plunger and in the wall of the bore whereby said flow
path is open during a predetermined initial portion of the plunger stroke during
the inward movement of the plunger.
An example of a fuel pumping apparatus will now be described with
reference to the accompanying drawings in which:-
- Figure 1 is a diagrammatic illustration of the pumping apparatus and associated
- Figures 2, 3 and 4 show the apparatus of Figure 1 with parts thereof at different
- Figure 5 shows a part of the pump with the axial scale increased.
Referring to the drawings, the pumping apparatus comprises a bore
10 from which extends an outlet 11 which is connected in use, to a fuel injection
nozzle 12 of an associated compression ignition engine. The outlet may be connected
directly to a nozzle as shown or it may be connected through a distributor member
to a plurality of injection nozzles which receive fuel in turn and in timed relationship
with the associated engine. Conveniently the nozzle or nozzles are of the two
stage lift type.
Slidable within the bore 10 is a plunger 13. The plunger is arranged
to be moved inwardly towards the one end of the bore, by means of an engine driven
cam 8 and it can be driven outwardly by means of a coiled compression spring 9
or by a further cam.
Extending from the one end of the bore is a spill passage 14 flow
of fuel through which is controlled by a spill valve generally indicated at 15.
The spill valve is controlled by an electromagnetic device 16 which in turn is
controlled by an electronic control system responsive to various engine operating
parameters and desired operating parameters. The passage 14 conveniently extends
to a low pressure source of fuel not shown which may be a low pressure fuel supply
Opening into the bore at a position spaced from the one end thereof
is a recess 17 which also communicates with the aforesaid source of fuel. For
co-operation with the recess 17, the plunger is provided with a narrow groove 18
which by way of an internal passage 19 in the plunger, communicates with the one
end of the bore. The groove 18 is connected to the passage 19 by drillings 18A
(Figure 5) the flow area of which is comparable to the flow area of the outlet
orifice or orifices of the nozzle 12. The drillings 18A form a restriction to the
flow of fuel. The upper edge of the recess 17 and the lower edge of the groove
18 form valving edges.
Ignoring for the moment the effect of the restricted flow path formed
by the drillings; during the inward movement of the plunger fuel will be displaced
from the one end of the bore. If the valve 15 is open as shown in Figure 1, the
fuel will flow along the passage 14 back to the source of fuel. However, if the
valve 15 is closed as shown in Figure 3, the fuel will be displaced through the
outlet 11 to the injection nozzle. If during the inward movement the valve 15
is opened as shown in Figure 4, then the fuel will again flow along the passage
14 rather than through the outlet 11. The quantity of fuel delivered therefore
depends upon the stroke of the plunger during the time when the valve 15 is closed
and the timing of the delivery of fuel depends on the instant of closure of the
Considering now the operation of the apparatus with the restricted
flow path in operation. With the valve 15 opened as shown in Figure 1, substantially
all the fuel displaced during inward movement of the plunger will flow along the
passage 14. However, if as shown in Figure 2, the valve 15 is closed before the
groove 18 has moved out of register with the recess 17, a restricted flow of fuel
will take place through the groove 18 into the recess 17 and some fuel will flow
through the outlet 11. The flow of fuel through the outlet 11 will be at a lower
rate. With the spill valve 15 maintained in its closed position, as soon as the
valving edge defined by the groove 18 moves beyond the valving edge defined by
the recess 17 as seen in Figure 3, the flow of fuel through the recess 17 will
cease and the rate of flow of fuel through the outlet 11 will increase to its
By the arrangement described it is possible to ensure that the initial
flow of fuel to the associated engine is at a reduced rate and the duration of
delivery at the reduced rate depends on the time in terms of degrees of engine
crankshaft rotation, between the closure of the valve 15 and the closure of the
groove 18 by the plunger.
As the engine speed is reduced, the requirement for a reduced initial
rate of fuel delivery diminishes and the apparatus as described will automatically
achieve this since with reducing engine speed the valve 15 will be closed later
in the stroke of the pumping plunger so that the groove 18 will be covered very
quickly after closure of the valve 15. In addition, because of the reduced engine
speed, the pumping rate of the plunger will be reduced and it may not raise the
pressure within the bore to a sufficient level with the groove 18 open to the
recess, to enable the valve in the injection nozzle to be opened.
It will be understood that different quantities of fuel will be delivered
at high and low engine speeds for equal periods of closure in terms of engine
crankshaft degrees, of the spill valve. The control system 16 however can correct
for this discrepancy by adjusting the closure time of the valve 15.
It will be further understood that the restriction to the flow of
fuel which in the example described is provided by the drillings 18A connecting
the groove 18 with the passage 19 may be in some other form. For example, the
recess 17 can be replaced by a single port elongated in the circumferential direction
so that the equivalent of a valving edge is formed. In this case the axial width
of the groove 18 will have to be increased. Alternatively with a groove 18 of
increased width the single port can be replaced by a plurality of smaller ports.