Fuel injection pumping apparatus

A fuel injection pumping apparatus of the rotary distributor type has cam lobes of a special form in which following the crest of the cam lobe there is a first portion during which limited outward movement of the pumping plunger can take place to relieve pressure in the pipelines connecting the pump with the injection nozzles and this is followed by a second portion which causes slight inward movement is to close any cavities in the fuel contained within the passage of the apparatus.

BACKGROUND OF THE INVENTION 
This invention relates to a fuel injection pumping apparatus for supplying 
fuel to an internal combustion engine and comprising a housing, a rotary 
distributor member mounted in the housing and arranged to be driven in 
use, in synchronism with the associated engine, a bore formed in the 
distributor member and a pumping plunger therein, a delivery passage in 
the distributor member and a plurality of outlet ports in the housing, 
said outlet ports in use being connected to the injection nozzles 
respectively of the associated engine, said outlet ports being positioned 
such that the delivery passage registers in turn therewith as the 
distributor member rotates, inlet port means in the housing, a source of 
fuel under pressure connected to the inlet port means, inlet passage means 
in the distributor member, said inlet passage means being connected to 
said bore, said inlet port means and said inlet passage means being 
arranged to allow fuel flow to said bore during at least part of the time 
said delivery passage is out of register with an outlet port, and cam 
means including a plurality of cam lobes for imparting inward movement to 
the plunger during part of the time the delivery passage is in register 
with an outlet port. 
Such apparatus is well known in the art however, one problem is that the 
amount of fuel delivered through each outlet port can vary even though the 
amount of fuel supplied to the bore at each filling stroke of the 
apparatus is the same. This irregularity of delivery is thought to be due 
to pressure waves which travel up and down the pipelines connecting the 
outlet ports with the injection nozzles. When during the delivery stroke 
the crest of the cam lobe is reached, the supply of fuel to a particular 
nozzle ceases. The plunger is allowed to move outwardly a small amount and 
is then held against movement. The purpose of the outward movement is to 
reduce the pressure in the pipeline and at the nozzle and this allows a 
valve member in the nozzle to close quickly to prevent dribble of fuel 
from the nozzle orifices. The closure of the valve member in the nozzle 
results in a pressure wave which travels back towards the outlet port and 
into the various passages in the distributor member. The wave is reflected 
and travels back towards the nozzle and may be re-reflected many times. 
The purpose of the dwell on the trailing flank of the cam lobe is to 
ensure that a predetermined volume of fuel is relieved from the pipeline 
however, the pressure wave may not have become attenuated by the time the 
delivery passage moves out of register with the outlet port and in this 
situation the pressure in the various passages in the distributor member 
may be low to the extent that there could be a cavity in the fuel. 
Assuming that equal volumes of fuel are supplied to the bore at each 
filling stroke, it is clear that during the following delivery stroke less 
fuel will be delivered. 
It is known to provide in each outlet port a so-called pressurising valve 
and the duty of these valves is to try to ensure that the pressure of fuel 
in the various passages in the distributor member at the instants at which 
the delivery passage moves out of register with the outlets, is 
substantially the same. Such valves are however expensive since they have 
to be carefully made to ensure that their operating characteristics are 
substantially the same. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide an apparatus of the kind 
specified in an improved form. 
According to the invention in an apparatus of the kind specified each cam 
lobe comprises a leading flank extending to the crest of the lobe and a 
trailing flank extending from the crest of the lobe, said trailing flank 
including a first portion adjacent the crest which allows limited outward 
movement of the plunger, a second portion of substantial length and which 
is shaped to impart a small inward movement to the plunger and a third 
portion which extends to the base circle of the cam lobe, the small inward 
movement of the plunger due to the action of the second portion, acting to 
close up any cavities in the fuel contained in the passages in the 
distributor member without causing a significant rise in pressure.

DESCRIPTION OF PREFERRED EMBODIMENT 
Referring to the drawings there is provided a housing 10 in which is 
mounted a rotary cylindrical distributor member 11 which is adapted to be 
driven in timed relationship with the engine with which the apparatus is 
associated. At one end of the distributor member there is provided a 
transversely extending bore 12 in which is mounted a pair of pumping 
plungers 13 which are arranged to be moved inwardly during an injection 
stroke of the apparatus, by a plurality of pairs of cam lobes formed on 
the internal peripheral surface of a cam ring 14 which surrounds the 
distributor member at this point. The cam ring is mounted within the 
housing and is permitted limited angular movement about the axis of 
rotation of the distributor member for the purpose of adjusting the timing 
of delivery of fuel. Interposed between the cam ring and the plungers, are 
rollers 15. 
The bore 13 communicates with a longitudinal passage 16 formed in the 
distributor member and which at one point is in communication with a 
radially disposed delivery passage 17 which is adapted to register in 
turn, as the distributor member rotates with a plurality of outlet ports 
18 formed in the housing. The outlet ports are connected in use, to the 
injection nozzles of the associated engine by respective pipelines and the 
communication between the delivery passage 17 and an outlet port 18 occurs 
whilst the plungers 13 are being moved inwardly by the cam lobes. 
At another point the longitudinal passage 16 is in communication with inlet 
passage means which comprises a plurality of radial inlet passages 19. The 
housing carries inlet port means in the form of an inlet port 20 which is 
positioned to register with the passages 19 so that fuel can be supplied 
to the bore 12. Fuel is supplied to the port 20 by means of a low pressure 
feed pump 21 the rotary part of which is conveniently connected to the 
distributor member. The feed pump has a fuel inlet 22 and a fuel outlet 
23. The quantity of fuel which is supplied to the inlet port is determined 
by an adjustable throttle member 24 and the inlet and outlet of the feed 
pump are interconnected by a relief valve 25. In operation, during a 
filling stroke fuel is supplied by way of the inlet port 20 and an inlet 
passage 19, to the bore 12 to effect outward movement of the plungers. The 
amount of fuel which is supplied through the inlet port is determined by 
the setting of the throttle member 24. As the distributor member rotates 
the inlet passage 19 moves out of register with the inlet port 20 and the 
delivery passage 17 moves into register with an outlet port 18. Whilst 
this communication is established inward movement is imparted to the 
plungers 13 and fuel is supplied to the respective injection nozzle. The 
cycle is repeated as long as the distributor member is rotated. 
The angular adjustment of the cam ring 14 is effected by means of a piston 
26 which is connected to the cam ring by means of a peg 27. Fuel under 
pressure from the output of the low pressure pump is applied to one end of 
the piston and effects movement of the piston against the action of a 
coiled spring. 
Turning now to FIG. 2, this shows a developed view of two cam lobes of 
known form which are referenced 28. Each cam lobe includes a leading flank 
29 and a trailing flank generally indicated at 30. The roller when moved 
by the leading flank of the cam lobe imparts inward movement to the 
plunger and during such movement the delivery passage 17 is in register 
with an outlet 18 the period during which this registration occurs is 
indicated by the reference letter A and it will be noted that this is 
shown in two positions depending upon the position of the cam ring. 
The trailing flank 30 of the cam lobe includes a first portion 31 which 
extends from the crest 32 of the lobe and when the roller 15 engages this 
portion of the trailing flank limited outward movement of the plunger can 
take place. Following the portion 31 there is a dwell portion 31A during 
which the movement of the plunger is prevented. It is whilst the plunger 
is under the control of the dwell portion of the lobe that the delivery 
passage 17 moves out of register with an outlet 18. Following the dwell 
portion there is a further portion 33 which extends down to the base 
circle of the cam this being indicated at 34. There is a period during 
which the passages in the distributor member are out of communication with 
both the inlet port 20 and an outlet 18 but towards the end of the portion 
33, the inlet port 20 is opened to an inlet passage 19. The period during 
which this communication is established is indicated by the reference 
letter B and as with the period during which the delivery passage is in 
register with an outlet, the period is shown in two positions depending 
upon the position of the cam. 
The modified cam profile is shown in FIG. 3 and it will immediately be seen 
that the configuration of the trailing flank now referenced 35, of each 
cam lobe is substantially altered. The leading flank 29 remains unaltered 
and so also does the first portion 31 of the trailing flank although it 
may be permitted to extend a little further towards the base circle of the 
cam. The main difference lies in the extent and shape of the second 
portion 36 of the lobe. Whereas in the case of the standard cam lobe the 
dwell portion 31A is such as to hold the plunger against movement, the 
portion 36 of the modified cam lobe is shaped to impart a small inward 
movement to the plunger. The difference is indicated by the dotted line in 
FIG. 3. The extent of inward movement is small and because the portion 36 
is of substantial length, is gradual. During this movement any cavities 
which may be present in the fuel contained within the passages in the 
distributor member, will be collapsed. The rate of increase of pressure 
which takes place whilst the roller and plunger are controlled by the 
portion 36 of the trailing flank of the cam lobe is so small as not to 
cause any pressure waves in the passages in the distributor member and 
also in the pipeline connecting the outlet to the nozzle. Conveniently the 
portion 36 of the cam lobe terminates in a flat portion 37 during which 
movement of the plunger is halted and the position of the flat portion 37 
corresponds with the portion 31A of the cam lobe shown in FIG. 2. 
Following the portion 37 is a portion 38 which extends down to the base 
circle 39 of the cam. It will also be noted that the period of port 
opening has been substantially modified as compared with the example shown 
in FIG. 2. The communication of the delivery passage with an outlet port 
has been extended and is indicated by the letter C. It will be noted that 
the period extends from just before the roller moves under the control of 
the leading flank 29 to the start of the portion 38 of the trailing flank 
of the lobe. It will further be noted that as soon as the registration of 
the delivery port with an outlet is broken, the inlet port 20 moves into 
register with an inlet passage 19. The communication of the inlet port 20 
with an inlet passage 19 is shown by the reference letter D. It will also 
be noted that as soon as inlet passage 19 moves out of register with the 
inlet port 20, the delivery passage 17 moves into register with an outlet 
18. 
The modification as described above extends the time the delivery passage 
is open to an outlet and therefore it reduces the time which is available 
for filling the bore 12. It is possible to utilize the arrangement in 
pumps for supplying an engine with up to five cylinders but is unlikely 
that there would be enough time for filling of the bore in a pump intended 
for supplying an engine with more than five cylinders.