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This invention relates to a fuel injection pump for supplying fuel to an internal combustion engine, the pump comprising a body in which or in a part secured in the body, is defined a bore the inner end of which forms a pumping chamber, a port formed in the wall of the bore, a plunger extending into the bore and movable towards the inner end of the bore, said plunger during its inward movement covering said port to allow fuel to be displaced from said pumping chamber to the associated engine during continued inward movement while a spill path from said pumping chamber is closed and the plunger at its outer end mounting a spring abutment between which and the body is located a spring which biases the plunger outwardly.

Such a pump can be mounted on an engine and be actuated by an engine driven cam through for example, a rocker mechanism which will incorporate an adjuster. It is essential that each pump of a number of pumps of a multi-cylinder engine should have as near as possible the same delivery characteristic in order that the engine operates as efficiently as possible. The pumps are therefore assembled into the engine with the plungers thereof in a so called datum position from which a predetermined inward movement of the plunger will be required before the port is covered. For each pump the rotary parts of the engine are set at a predetermined position for that pump and the adjuster is adjusted until movement of the plunger is about to take place. The adjuster is then adjusted a known amount so that a known inward movement of the plunger takes place from the datum position which however is less than the predetermined inward movement of the plunger necessary to cover said port. Each pump of the engine is adjusted in the same manner.

SUBSTITUTE SHEET The object of the present invention is to provide in a pump of the kind specified means for setting the datum position.

According to the invention the body is shaped to provide an annular portion through which the plunger extends, a screw thread formed on the external surface of the annular portion, an inwardly extending step defined on the plunger, a cup shaped member having an internal screw thread for engagement about said annular portion, said cup shaped member having an aperture formed in its base wall through which the plunger can be passed, an annular shim located against the end of said annular portion and a divided stop plate located intermediate the shim and said base wall of the cup shaped member and which is clamped in position by tightening the cup shaped member relative to the body said stop plate defining portions for engagement by said step to limit the outward movement of the plunger.

An example of a fuel pump in accordance with the invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a part sectional side elevation of a portion of the pump, and

Figure 2 is a view on the line B-B of • Figure 1.

The pump forms part of a so called unit injector and has a pump body 10 to which is secured a fuel
injection nozzle not shown. The pump body 10 is adapted to be secured within the cylinder head 9 of an engine so that fuel flowing through the outlet of the nozzle will be directed, into a combustion chamber of the engine.
Within the pump body 10 or in a part secured in the body, is defined a bore 11 the inner end of which forms a

SUBSTITUTE SHEET pumping chamber 12 to which the inlet of the nozzle is connected. Formed in the wall of the bore is a port 13 which is connected to a source of fuel under pressure and communicating with the pumping chamber is a spill passage 14 the flow through which is controlled by an electro- magnetically operable spill valve 15.

Slidable within the bore is a plunger 16 and this has a reduced portion 17 extending from the bore and which at its end is provided with a head 18.
Intermediate the reduced portion of the plunger and the main portion thereof there is defined a step 19.

Also provided is an annular spring abutment 20 in the base wall of which is formed an aperture through which the head of the plunger and the plunger itself, can pass. A circlip 21 is carried by the spring abutment and engages the head 18 of the plunger and the spring
abutment is engaged by one end of a coiled compression spring 22 the other end of which is engaged with the pump body. The spring abutment also carries a pressure pad 23 which engages with the head 18 of the plunger and which in use is engaged by an engine cam actuated rocker.

The plunger is shown in Figure 1 in a so called datum position in which the port 13 is partly covered by the inner end of the plunger. The datum position is determined by the engagement with the step 19 of the parts 24 of a divided stop plate. The parts 24 are of C-shaped form so that they can be located about the reduced portion 17 of the plunger but can engage with the step 19. The parts of the stop plate are located against the base wall of a cup shaped member 25 having an internal screw thread which is engaged with a complementary thread formed on an annular portion 26 of the pump body. The base wall of the cup shaped member 25 is provided with an aperture through which the plunger 16 can be passed and

SUBSTITUTE SHEET in order to determine the position of the stop plates an annular shim 27 is provided. As will be observed from Figure 2, the periphery of the cup shaped member 25 is of non-circular section so that it can be engaged by a spanner.

In operation, during inward movement of the plunger with the spill valve 15 closed, fuel will be displaced from the pumping chamber through the port 13" until the latter is covered and thereafter until the spill valve is opened, fuel will be displaced from the pumping chamber through the injection nozzle and will be supplied to the associated engine. During outward movement of the plunger under the action of the spring 22, fuel will flow into the pumping chamber 12 once the port 13 is uncovered.

The datum position of the pump must be set
following assembly, before the pump can be assembled into the engine. The adjustment of the datum position is carried out before the spring and the spring abutment are located in position and is determined by choosing a shim 27 of appropriate thickness. Once the datum position has been determined the spring and spring abutment are assembled and the pump is ready for assembly to the engine. In order to adjust the rocker mechanism
associated with the pump, the engine parts are first set to a position appropriate for that pump, the rocker is then adjusted so that the pressure pad 23 is just engaged by the rocker part and then the adjuster is rotated through a predetermined number of turns during which the plunger moves inwardly a small amount. The port 13 remains open to the pumping chamber so that in use there is a predetermined movement of the plunger before the port 13 is closed, which movement is less than the
required movement of the plunger from the datum position, to achieve closure of the port.

SUBSTITUTE SHEE" It will be seen that the setting of the datum position is achieved in a particularly convenient manner using few additional parts which in themselves are easy to manufacture .