GB2349670A - Unit fuel injector with a filtration path between the plunger and its bore - Google Patents

Abstract

The injector comprises a pump housing 22 having a bore 24 within which a plunger 26 is reciprocated by a cam (not shown) to pressurise fuel in a pump chamber 32 which receives fuel via a spill valve 34. The housing 22 includes an annular step 40 which defines, with the plunger 26, an annular clearance 46 through which fuel flows from the pump chamber 32 to a recess 38 which communicates with the nozzle body 10 via a passages 42, 44. The annular clearance 46 is of such a size, eg 60 žm for a bore diameter of 8 mm, as to ensure that the passage of particulate contaminants is prevented. Unlike known injectors in which filtration is provided on entry of the fuel to the injector, the invention thus provides filtration of particles originating from within the injector itself The annular clearance 46 also helps to damp pressure waves within the injector. In a modification, fig.3, fuel can flow though passages 56, 58 in the plunger to a second annular clearance 52, thus increasing the flow area and reducing the pressure drop.

Description

FUEL INJECTOR The invention relates to a fuel injector of the type having a filter arrangement for removing particulate contaminants from a flow of fuel.

In fuel injector systems for compression ignition internal combustion engines the presence of particulate contaminants in the fuel has undesirable effets. In particular, particulate contaminants can result in small openings in the injector becoming blocked, excessive wear or seizure of close fitting guides can occur and impact surfaces can become damaged. Such contaminants may include dirt swarf, loose burrs and other debris in the fuel supply pipes which contaminate the fuel prior to its supply to the fuel injector. In addition, contamination of the fuel can occur within the body of the fuel injector itself.

It is known to provide a fuel filter in the fuel flow path in order to remove contaminants from the fuel supplied to the fuel injector. However, the provision of such filters can restrict the rate of supply of fuel to the injector and it is often not then possible to supply fuel at a sufficiently high rate for efficient operation. In particular, this can be a problem when using pump injectors which require fuel to be supplied at a relatively high rate for efficient operation.

European Patent Application No 98309996.1 describes a fuel injector having a filter arrangement which permits a greater fuel flow rate to be used. The fuel injector inclues a nozzle body having a blind bore within which a valve needle is reciprocable, the valve needle being biased towards a seating by means of a compression spring. Movement of the valve needle away from the seating is controlled by applying fuel pressure to valve needle thrust surfaces which acts against the spring force, controlled movement of the valve needle away from the seating providing a means of controlling fuel injection. A filtration path for fuel is provided on entry to the fuel injector by forming annular recesses in the compression spring housing and a cap nut of the fuel injector housing.

This shaping of the spring housing and the cap nut presents a flow path of reduced area to fuel as it enters the fuel injector. Any particulate contaminants present in the fuel entering the fuel injector cannot pass through the restricted flow path and are therefore prevented from passing into the internal chambers and passages of the fuel injector.

However, problems can arise if contamination of fuel originates from within the fuel injector itself. Such contamination can lead to the blockage of small openings in the fuel injector, a degradation of performance and possible fuel injector failure. The provision of a fuel filter on entry to the fuel injector does not have any effect on contaminants originating from within the fuel injector.

It is an object of the present invention to provide a fuel injector having a filter arrangement which serves to filter particulate contaminants originating from within the fuel injector, as well as filtering any contaminants present in the fuel supplied thereto.

According to the present invention there is provided a fuel injector comprising a fuel injector housing part having a bore within which a plunger member is reciprocable, the plunger member acting on fuel introduced to a pump chamber defined within the bore to control fuel injection, the housing part being arranged to define, with the plunger member, a filtration path for fuel flowing from the pump chamber.

The fuel injector provides the advantage that any particulate contaminants originating from within the fuel injector are filtered from the fuel flow by the filtration path, thereby preventing damage or blockage occurring downstream in chambers, passages or openings of the fuel injector.

The filtration path is conveniently of annular form, the filtration path being defined by a clearance between the housing part and the plunger member. The clearance is conveniently defined by an annular step, formed on the bore of the housing part, and the plunger member.

The housing part may have a first annular recess formed therein, the first annular recess being in communication with a fuel passage for supplying fuel to a fuel injector nozzle body, fuel passing through the filtration path to the first annular recess and through the fuel passage to the nozzle body.

The fuel injector housing part may include a second filtration path defined by the housing part and the plunger member, the second filtration path being in fluid communication with the pump chamber by means of fuel passages formed within the plunger member.

The provision of a second flow route for fuel, having a second filtration path, provides the advantage that the fuel flow area is increased and therefore any decrease in fuel pressure due to the restricted filtration paths is minimised.

The second filtration path is conveniently of annular form, being defined by a second clearance between the housing part and the plunger member.

The second clearance is conveniently defined by a second annular step, formed on the bore of the housing part, and the plunger member.

The invention will now be described, by way of example only, with reference to the following figures in which: Figure 1 is a view, in section, of an embodiment of the invention; Figure 2 is a view, in section, of an alternative embodiment of the invention; and Figure 3 shows an enlarged view of a part of the fuel injector shown in Figure 2.

Referring to Figure 1, the fuel injector inclues a nozzle body 10 including a blind bore within which a valve needle 20 is reciprocable, an end of the valve needle 20 being engageable with a seating (not shown) defined adjacent the blind end of the bore. The valve needle 20 inclues thrust surfaces which are orientated such that the application of fuel under pressure thereto applies a force to the valve needle 20 urging the needle away from its seating. The movement of the valve needle away from the seating permits fuel delivered to the nozzle body 10 to flow past the seating to one or more outlet openings provided in the nozzle body 10 downstream of the seating.

The nozzle body 10 engages a spring housing 12 defining a spring chamber 14 within which a compression spring 16 is located. The spring 16 engages an abutment member 18, carried by an end of the valve needle remote from the end which engages with the seating, to bias the valve needle 20 towards the seating.

The upper end of the spring housing 12 engages a pump housing 22 having a bore 24 within which a plunger member 26 is reciprocable. The plunger member 26 is driven by a cam arrangement (not shown), a return spring 28 being provided to withdraw the plunger member 26 from the bore 24. An end face 30 of the plunger member 26, the bore 24 and the upper end of the spring housing 12 define a pump chamber 32 for receiving fuel from a spill valve arrangement 34. The spill valve arrangement 34 inclues an electromagnetically actuated spill valve 35, reciprocable within a bore 37, which communicates with the pump chamber 32 by means of a supply passage 36. The spill valve arrangement 34 serves to supply fuel from a reservoir (not shown) to the pump chamber 32.

The housing 22 is provided with an enlarged annular recess 38 spaced axially from the pump chamber 32. The housing 22 is also provided with an annular step 40, the annular step defining, with the plunger 26, an annular clearance 46 through which fuel flows from the pump chamber 32 to the enlarged annular recess 38. The annular recess 38 is iocated above the clearance 46 and communicates with the nozzle body 10 by means of fuel passages 42,44 formed by drillings in housings 22,12 respectively.

The annular clearance 46 is of an appropriate dimension to ensure that fuel is able to flow therethrough, whilst preventing the passage of any particulate contaminants present within the fuel. Thus, the clearance 46 provides a means of filtering fuel passing from the pump chamber 32 to the nozzle body 10, and therefore provides a means of filtering particulate contaminants which may have originated from within the fuel injector itself. The fuel injector therefore provides an advantage over known fuel injectors in which a filtration path is provided on entry of the fuel to the injector.

Typically, for a plunger bore diameter of 8 mm, the clearance 46 will be of 60 um. An arrangement of this size provides the same flow area as a 1 mm diameter orifice.

In use, with the plunger member 26 starting in its outermost position and with the spill valve 35 open, fuel will flow from the pump chamber 32 through the spill valve arrangement 34 to the fuel reservoir as the plunger member 26 commences inward movement under the action of the cam arrangement. When fuel injection is to be commenced, the spill valve 35 is closed so that fuel cannot return from the pump chamber 32 through the spill valve arrangement 34. Continued inward movement of the plunger member 26 from an outer position pressurises fuel within the pump chamber 32 and in the passages 42,44. As the fuel pressure increases during continued inward movement of the plunger member 26, the pressure applied to the thrust surfaces of the valve needle 20 of the nozzle body 10 increases until such time as the valve needle 20 is urged away from the seating against the biasing force of the spring 16. Fuel injection then takes place.

To terminate fuel injection, the spill valve arrangement 34 is actuated once more to open the spill valve 35. Fuel under pressure within the pump chamber 32 and the passages 42,44 therefore returns through the open spill valve 35 to a fuel reservoir through passages 42,44, through the clearance 46 and through the supply passage 36. The pressure applied to the thrust surfaces of the valve needle 20 is therefore reduced and the valve needle, under the force of the spring 16, is returned into engagement with the seating, thereby closing the openings in the nozzle body 10 to cease fuel injection. The return flow of fuel through the annular clearance 46 has the effect of cleaning out the clearance 46, thereby reducing the risk of the filtration flow path becoming blocked.

The annular clearance 46 also helps to damp pressure waves which occur within the fuel injector and which can cause problems with low fuel rate deliveries. Problems due to pressure waves are particularly evident when mechanical pilot devices are included in the fuel injection system.

It is inevitable that a slight decrease in fuel pressure will occur due to the restricted flow passage presented by the clearance 46. For many applications, however, the reduction in fuel pressure will not be significant. Furthermore, referring to Figures 2 and 3, an alternative embodiment of the invention enables a higher fuel pressure to be maintained, whilst still providing the advantages of having a filtration path within the body of the fuel injector. The housing 22 is provided with a second annular step 50 which defines, with the plunger member 26, a second clearance 52 above the first clearance 46. In addition, the plunger member 26 has flow passages 56,58 formed therein through which fuel can flow from the pump chamber 32, to a second enlarged annular recess 54 and then through the second clearance 52.

The second enlarged annular recess 54 is of relatively large axial extent, the length of the recess 54 being sufficient to ensure that the recess 54 is in constant communication with the flow passages 56,58 and the pump chamber 32.

Inward movement of the plunger member 26, with the spill valve 35 closed, results in a proportion of fuel within the pump chamber 32 passing through the flow passages 56,58 in the plunger member 26 to the second enlarged annular recess 54, whilst other fuel can pass through the clearance 46 to the lower annular recess 38. Thus, fuel in the pump chamber 32 is presented with two possible flow routes; upwards through the passages 56,58 in the plunger member 26, through the annular recess 54 and the second clearance 52, or through the first clearance 46.

The second clearance 52 provides a second filtration path for preventing particulate contaminants within the fuel following the second flow route from reaching the nozzle body 10. By providing a second flow route for fuel, the flow area is increased such that any decrease in fuel pressure, due to the restricted flow paths provided by the first and second clearances 46,52, is minimised.

It will be appreciated that other filtering means may be provided in addition to the filtration paths in the fuel injector housing. For example, it may be desirable to provide an initial filtering stage for fuel externally to the fuel injector.

Claims (9)

1. CLAIMS 1. A fuel injector comprising a fuel injector housing part having a bore within which a plunger member is reciprocable, the plunger member acting on fuel introduced to a pump chamber defined within the bore to control fuel injection, the housing part being arranged to define, with the plunger member, a filtration path for fuel flowing from the pump chamber.
2. 2. The fuel injector as claimed in Claim 1, wherein the filtration path is of annular form.
3. 3. The fuel injector as claimed in Claim 2, wherein the filtration path is defined by a clearance between the housing part and the plunger member.
4. 4. The fuel injector as claimed in Claim 3, wherein the clearance is defined by an annular step, formed on the bore of the housing part, and the plunger member.
5. 5. The fuel injector as claimed in any of the preceding claims, wherein the housing part has a first annular recess formed therein, the first annular recess being in communication with a fuel passage for supplying fuel to a fuel injector nozzle body, fuel passing through the filtration path to the first annular recess and through the fuel passage to the nozzle body.
6. 6. The fuel injector as claimed in Claim 5, wherein the fuel injector housing part includes a second filtration path defined by the housing part and the plunger member, the second filtration path being in fluid communication with the pump chamber by means of fuel passages formed within the plunger member.
7. 7. The fuel injector as claimed in Claim 6, wherein the second filtration path is of annular form and is defined by a second clearance between the housing part and the plunger member.
8. 8. The fuel injector as claimed in Claim 7, wherein the second clearance is defined by a second annular step, formed on the bore of the housing part, and the plunger member.
9. 9. A fuel injector as herein described with reference to the accompanying drawings.