Fuel injection pump

A fuel injection pumping apparatus has a cam (9) actuated reciprocable plunger (13) housed in a bore (11) into which fuel flows from a fuel supply (7,14). An outlet (12) extends from a pumping chamber (13A) defined by the plunger and bore. A spill passage (19) communicates the pumping chamber with a spill valve (16) so that fuel from the pumping chamber which flows through the passage and spill valve (20) flows into a cylinder (21) containing a resiliently biased piston (17). The fuel which flows into the cylinder is returned to the pumping chamber during outward movement of the plunger and the fuel supply (14,7) ensures that the pumping chamber is completely filled with fuel. A safety valve (30,31) allows fuel to escape from the cylinder (21) in the event that the piston (17) sticks in the cylinder.

BACKGROUND OF THE INVENTION 
This invention relates to a fuel injection pumping apparatus for supplying 
fuel to internal combustion engines. 
Examples of such apparatus are shown in Eurpean patent documents 
EP-A-0343759 (corresponding to U.S. Pat. No. 4,936,755) and 
EP-A-0423958(corresponding to U.S. Pat. No. 5,119,786). In such apparatus 
the maximum stroke of the piston is limited and is arranged to be at least 
just sufficient to absorb the total volume of fuel which can be displaced 
by the pumping plunger during its inward stroke. If in such apparatus the 
piston should seize within its cylinder or if the resilient biasing of the 
piston should fail then in the former case, the piston will be unable to 
move to absorb the spilled fuel and in the latter case if the piston is 
not already at the limit of its stroke, it will very quickly assume its 
limiting position. In both cases therefore irrespective of the operation 
of the spill valve the total volume of fuel displaced by the pumping 
plunger will be delivered to the associated engine. The increase in fuel 
flow to the engine will result in uncontrolled acceleration of the engine 
and the vehicle which is driven by the engine. 
BRIEF SUMMARY OF THE INVENTION 
The object of the present invention is to provide an apparatus of the kind 
specified above in which the aforesaid risk is minimized. 
According to the invention in an apparatus of the kind specified safety 
valve means is provided to allow escape of fuel from the cylinder in the 
event that the fuel pressure in the cylinder increases to a value which 
exceeds the pressure required to move the piston against the action of its 
resilient loading but is less than that required to displace fuel through 
the outlet. 
The apparatus of the invention includes a pumping plunger mounted in a 
bore, the plunger and the bore defining a pumping chamber, a cam operable 
to effect inward movement of the plunger to displace fuel from the pumping 
chamber, an outlet from the pumping chamber through which fuel displaced 
from the pumping chamber can flow to an associated engine, fuel supply 
means for completely filling the pumping chamber with fuel prior to inward 
movement of the plunger by the cam, a spill valve operable to spill fuel 
from the pumping chamber thereby to control the flow of fuel through the 
outlet, an accumulator cylinder into which the fuel which flows through 
the valve flows and a resiliently biased piston in the cylinder, the 
piston being displaced by the spilled fuel flowing into the cylinder and 
acting to return the spilled fuel to the pumping chamber before the next 
inward stroke of the pumping plunger.

DETAILED DESCRIPTION OF THE DRAWING 
Referring to the drawing the apparatus comprises a body 10 in which is 
formed a bore 11. Extending from one end of the bore 11 is an outlet 12 
which in use is connected to a fuel injection nozzle 12A of an associated 
engine. 
Slidable in the bore is a pumping plunger 13 and the inner end of the 
plunger 13 together with the inner end of the bore define a pumping 
chamber 13A from which the outlet 12 extends. 
The plunger is movable inwardly by an engine driven cam 9 and is movable 
outwardly by means of a spring 8. During the outward movement of the 
pumping plunger a port 14 formed in the wall of the bore 11 is uncovered 
by the inner end of the plunger and the port 14 is connected to a source 7 
of fuel under pressure so that the pumping chamber 13A is completely 
filled with fuel prior to the inward movement of the plunger by the cam. 
In order to control the quantity of fuel which is supplied through the 
outlet 12 to the associated engine a spill valve generally indicated at 16 
is provided comprising a valve member 20 engagable with a seating 18 which 
is located about a spill passage 19 extending from the pumping chamber 
13A. The spill valve member 20 is conveniently formed as a projection of a 
piston 17 which is slidable within a cylinder 21 in the end wall 22 of 
which is formed the spill port 19. The piston is biased by resilient means 
in the form of a coiled compression spring 23 so that the valve member 20 
engages with the seating 18. 
Conveniently the valve member in the closed position is arranged to be 
substantially pressure balanced and this is achieved by the provision of a 
bore 25 in the piston, the inner end of the bore being in communication 
with the spill port 19 and the bore being occupied by a plunger 26. The 
end area of the plunger and the area of the bore 25 are slightly less than 
the end area of the valve member 20 which is exposed in the closed 
position of the valve member to the spill port 19. 
The operation of the spill valve is controlled by valve means in the form 
of a spill control valve 27 which comprises a port 28 opening into the 
bore 11 and a helical groove 29 on the periphery of the plunger, the 
groove communicating by way of a passage or groove with the pumping 
chamber 13A. The plunger is movable angularly within the body 10 in known 
manner. In operation, during inward movement of the plunger as soon as the 
port 14 is covered, fuel will be displaced from the pumping chamber 
through the outlet 12. This displacement of fuel will continue until the 
Groove 29 is brought into register with the port 28 whereupon fuel at the 
high pressure within the pumping chamber will be admitted to the cylinder 
21 to act on the piston thereby to lift the valve member 20 from its 
seating to allow the remaining fuel displaced from the pumping chamber 13A 
to flow into the cylinder 21 along the spill passage 19. The position at 
which the groove 29 is brought into register with the port 28 depends upon 
the angular setting of the plunger and this enables the quantity of fuel 
supplied to the associated engine to be varied. When the plunger is moved 
downwardly by the spring 8, the piston 17 under the action of its spring 
23 will force the displaced fuel back into the pumping chamber 13A until 
the valve member engages the seating. The end of the cylinder containing 
the spring 23 is vented by way of a restrictor 35 and the purpose of this 
restrictor is to limit the rate of movement of the piston and therefore 
the rate at which fuel can be spilled. 
The maximum displacement of the piston is slightly more than the maximum 
displacement of the pumping plunger so that it is possible to arrange that 
no fuel is supplied to the associated engine. 
If the piston should stick in its maximum displaced position, the fuel 
which has flowed into the cylinder 21 will not be returned to the pumping 
chamber however, the pumping chamber will be completely filled with fuel 
by way of the inlet port 14, and during the next inward stroke of the 
pumping plunger no fuel will be able to flow through the spill passage 19 
so that all the fuel displaced by the plunger 13 will flow to the 
associated engine. In order to minimize this risk, there is provided a 
safety valve and this comprises a plate like valve element 30 which is 
biased into engagement with the end of the piston remote from the valve 
member conveniently by the spring 23. The valve element closes the 
adjacent ends of a plurality of passages 31 which extend axially within 
the piston and it is arranged that the valve element will be lifted away 
from the piston to permit flow of fuel through the passages 31 when the 
fuel pressure rises above that which is required to effect normal movement 
of the piston but below the pressure required to open the valve in the 
fuel injection nozzle 12A which is connected to the outlet 12. If 
therefore the piston 17 is stuck, the plate valve element 30 will be 
lifted from the piston to allow spillage of fuel so that no fuel will be 
supplied to the associated engine. In the particular example, even if the 
piston sticks with the spill valve member 20 in engagement with the 
seating 18, some spillage of fuel will occur as soon as the groove 29 
opens to the port 28. It is emphasized however that the dimensions of the 
port 28 and the groove 29 are such that in normal operations most of the 
fuel spilled will flow through the spill port 19. 
The arrangement as described is equally applicable to a rotary distributor 
type of fuel pumping apparatus in which the cylinder and piston are formed 
in an extension of the distributor member. In such a case where the fuel 
at high pressure is utilized to actuate the piston some spillage of fuel 
will occur when the spill control valve operates however, as with the 
example described, the dimensions of the various passages associated with 
the spill control valve are limited and the spillage of fuel will not be 
complete. The spill control valve 27 may be in the form of an 
electromagnetically operable valve such as shown at 40 in FIG. 2 connected 
between port 28' and port 41 leading to outlet 12. In the case where the 
initiation of the movement of the piston is effected by fuel derived from 
an additional pair of plungers, the spillage of fuel in the closed 
position of the spill valve member will not occur.