GB2274885A

GB2274885A - Fuel pump /injector

Info

Publication number: GB2274885A
Application number: GB9302519A
Authority: GB
Inventors: Lukhbir Singh Panesar
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1993-02-09
Filing date: 1993-02-09
Publication date: 1994-08-10
Also published as: GB9302519D0

Abstract

A pump/injector includes an injection body (14) in which is mounted a pumping plunger (18) coupled to a tappet assembly (19) slidable in the body. The body also carries a two part rocker mechanism (31) the one part (33) of which has an arm engagable with the tappet assembly. The other part (36) of the rocker mechanism carries a roller (37) engagable with an engine driven cam (12) and acting between the parts is an adjustment means (35) so that cam induced movement is transmitted to the tappet assembly and plunger. <IMAGE>

Description

FUEL PUMP This invention relates to a pump/injector for supplying fuel to a combustion chamber of an internal combustion engine, the pump injector being of the kind comprising an injector body on which is mounted a fuel injection nozzle having a fuel pressure actuated valve member for controlling the flow of fuel through an outlet orifice, a bore defined in the body, a reciprocable plunger located in the bore, the plunger at one end extending from the bore and the other end of the plunger forming a pumping chamber with the bore, a passage connecting the pumping chamber with an inlet of the nozzle, a fuel inlet port formed in the wall of the bore and which is covered by the plunger during the initial movement of the plunger in a direction to reduce the volume of the pumping chamber, a valve for controlling the volume of fuel displaced from the pumping chamber during the remaining inward movement of the plunger following closure of the inlet port, a tappet assembly slidable in the body, the extended portion of the plunger being coupled to the tappet assembly and a spring located between the tappet assembly and the body and acting to bias the plunger outwardly.

Pump/injectors of the aforesaid type are well known in the art and in use are mounted on an engine so that the outlet orifices discharge fuel into a combustion chamber of the engine. The tappet is provided with a pressure pad or roller which is engaged by one end of a rocker arm actuated by an engine driven cam and the conventional practice is that the rocker arm is mounted on the engine structure and therefore has to be assembled to the engine after the pump/injector has been secured in place. Once the assembly of the pump/injector and the rocker arm to the engine has been effected it is necessary to adjust the assembly in order to ensure that the plunger covers the inlet port at the correct angular position of the engine thereby to ensure that the start of fuel delivery takes place at the desired engine position.

The object of the invention is to provide a pump/injector of the kind specified in a simple and convenient form.

According to the invention in a pump injector of the kind specified the injector body carries a two part rocker mechanism, one part of which is shaped to engage the tappet assembly and the other part of which carries a roller for engagement with an engine driven cam, the two parts being pivotally mounted relative to each other and the injector body and adjustable means acting between the parts whereby cam and spring induced movement is transmitted between the parts.

An example of a pump/injector in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic side elevation of the pump/injector shown in position in the cylinder head of an engine, and Figure 2 is an exploded perspective view of part of the pump/injector seen in Figure 1.

Referring to the drawings the engine cylinder head is seen at 10 and mounted on the cylinder head is a rotary cam shaft 11 which carries cams 12 for operating the pump/injectors of the engine respectively. The cam shaft also carries valve operating cams. A pump injector is generally indicated at 13 and it comprises an injector body 14 having a cylindrical portion which is located within a stepped bore 15 the narrower end of which opens into a combustion space of the engine. The cylindrical portion of the injector body mounts a nozzle body 16 the narrower end of which projects into the combustion chamber and is provided with the usual fuel outlet orifices. The nozzle includes a fuel pressure actuated valve member which is spring biased to the closed position. Also formed in the body 14 is a blind bore 17 in which is slidably mounted a reciprocable pumping plunger 18.The plunger 18 extends from the bore and is coupled to a generally cup-shaped tappet body 19 which is slidably mounted in an enlarged bore 20 formed in the injector body 14. The tappet body serves as an abutment for a plunger return spring 21 and the tappet body is restrained against rotation by means of a projection 22 which is slidable in a slot 23 formed in the wall of the bore 20. The tappet body 19 carries a roller 24 which is accommodated within a part cylindrical recess 25 formed in the tappet body, the wall of the recess extending through more than 1800 so that the roller is captive within the recess. The length of the roller is slightly less than the overall diameter of the tappet body so as to provide a substantial bearing surface between the roller and the cylindrical surface and the ends of the roller are machined to spherical form.The increased bearing area between the roller and the tappet body as compared with constructions in which the roller is mounted on a bearing pin, enables a simpler lubrication system to be used.

The inner end of the plunger 18 together with the inner portion of the bore 17 form a pumping chamber 26 which is connected by means of a passage to the inlet of the fuel injection nozzle. In addition, the pumping chamber communicates with an electromagnetically operable spill valve generally indicated at 27 which is energised to close the valve and thereby to prevent spillage of fuel from the pumping chamber 26 as will be described.

Formed in the wall of the bore 17 is a port 28 which communicates with a fuel inlet gallery 29 formed in the cylinder head of the engine. The port 28 is covered by the plunger during the initial inward movement thereof and once the port is covered and providing the spill vale 27 is closed the fuel in the pumping chamber will be pressurised to the extent that the valve member in the fuel injection nozzle is lifted from its seating and fuel is supplied to the engine combustion chamber. If during the inward movement of the plunger the valve 27 is opened, the fuel pressure in the pumping chamber will be lowered and flow of fuel to the engine combustion chamber will cease. The fuel which is displaced by the pumping plunger during its continued inward movement will flow by way of the valve 27 to a further gallery 30 formed in the cylinder head of the engine.

Mounted on the pump/injector body 14 is a two part rocker mechanism generally indicated at 31. The rocker mechanism is mounted about a bearing pin 32 which is supported in an extension of the body 14. The rocker mechanism comprises a lever 33 which defines spaced bearing bosses 34 for engagement with the pin 32. One arm of the lever is shaped for engagement with the roller 24 and the other arm of the lever is provided with an aperture to receive a threaded adjustment member 35. The other part of the rocker mechanism comprises a roller housing 36 in which is mounted a roller 37 for engagement with the cam lobe 12. The housing 36 is integral with a bearing boss 38 which is located about the pin 32 and is accommodated within a slot 39 formed in the lever 33.

The housing 36 has an upper surface 40 engagable by the adjustment member 35.

In operation, when the cam lobe 12 engages the roller 37 the roller housing 36 pivots about the pin 32 and through the adjustment member 35 the lever 33 is moved in the same direction about the pin 32 to effect inward movement of the plunger 18.

The fact that the rocker assembly is integral with the pump/injector means that assembly of the pump/injector to the engine is extremely simple.

Once the pump/injector has been assembled to the engine it is necessary to ensure that the plunger 18 is at its correct axial position relative to the engine.

Part of this adjustment process is carried out on assembly of the pump injector. As will be seen from Figure 1 there is provided in an extension of the pump/injector body 14 an aperture which receives a stop 41 in the form of a bar. To achieve adjustment, the inlet port 28 is connected to a source of fuel under pressure and then the arm 33 is moved in the clockwise direction until the flow of fuel through the port 28 ceases. There is then interposed between the stop 41 and the adjacent arm of the lever, a shim 42 and the force on the lever is removed so that the spring 21 urges the tappet outwardly so that the shim is trapped between the stop and the lever. This is the position of the parts shown in the drawing.After the pump/injector has been assembled to the engine and the engine set to a position such that the roller 37 is presented to the base circle of the cam lobe 12, a feeler gauge is inserted between the roller 37 and the base circle of the cam lobe and the adjustment member is adjusted until the feeler gauge is just trapped. The feeler gauge is then removed and the engine rotated so that the cam lobe 12 engages the roller 37 and imparts movement to the rocker assembly. This relieves the pressure on the shim 42 which can then be removed and this will permit further outward movement of the tappet and plunger from the position shown when the roller 37 again engages the base circle of the cam.

Adjustment of the pump/injector once it has been assembled to the engine is therefore very simple and if it should prove necessary to remove the pump/injector the shim 42 can be reinserted so that the plunger assumes the set position determined as explained above, following assembly.

Moreover, the lever ratio of the rocker mechanism does not vary during the process of adjustment of the member 35. Furthermore, the effective cam rate seen by the plunger, can be varied by altering the profile of the cam 12 and altering the profile of the arm of the lever 33 which is engaged by the roller 24.

Claims

1. A pump/injector for supplying fuel to a combustion chamber of an internal combustion engine, comprising an injector body on which is mounted a fuel injection nozzle having a fuel pressure actuated valve member for controlling the flow of fuel through an outlet orifice, a bore defined in the body, a reciprocable plunger located in the bore, the plunger at one end extending from the bore and the other end of the plunger forming a pumping chamber with the bore, a passage connecting the pumping chamber with an inlet of the nozzle, a fuel inlet port formed in the wall of the bore and which is covered by the plunger during the initial movement of the plunger in a direction to reduce the volume of the pumping chamber, a valve for controlling the volume of fuel displaced from the pumping chamber during the remaining inward movement of the plunger following closure of the inlet port, a tappet assembly slidable in the body, the extended portion of the plunger being coupled to the tappet assembly, a spring located between the tappet assembly and the body and acting to bias the plunger outwardly, a two part rocker mechanism carried by the injector body, one part of the rocker mechanism being shaped to engage the tappet assembly and the other part of the rocker mechanism carrying a roller for engagement with an engine driven cam, the two parts being pivotally mounted relative to each other and to the injector body and adjustable means acting between the parts whereby cam and spring induced movement is transmitted between the parts.

2. A pump/injector according to Claim 1, in which said one part defines a pair of axially spaced bearing bosses and said other part defines a single bearing boss which is located between said pair of bearing bosses, the bosses being located about a bearing pin carried by the injector body.

3. A pump/injector according to Claim 1 or Claim 2, in which said adjustable means comprises a screw which is in screw thread engagement with one of said parts and which engages the other of said parts.