EP0731270A1

EP0731270A1 - Fuel injection nozzle

Info

Publication number: EP0731270A1
Application number: EP96301084A
Authority: EP
Inventors: Paul Buckley; Gordon M. Reid; John R. Jefferson; Marc-Andre Charbonnier
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1995-02-24
Filing date: 1996-02-16
Publication date: 1996-09-11
Also published as: GB9503733D0

Abstract

A fuel injection nozzle of the pintle type includes a valve member (14) movable against the force exerted by a spring (17) by fuel under pressure in a chamber (20) from which fuel can flow to an outlet (19). The chamber (20) increases in volume as the valve member is moved against the action of the spring and decreases in volume as the valve member moves under the influence of the spring. In order to effect some compensation for the change in volume a further chamber (26) is provided which decreases in volume as the valve member moves against the action of the spring. Both chambers are connected to the fuel inlet passage (21). One wall of the further chamber (26) is movable with the valve member and the area of the wall is slightly less than the area of the valve member exposed within the first chamber.

Description

This invention relates to a fuel injection nozzle for supplying fuel to an internal combustion engine and of the kind comprising a nozzle body defining a bore, a valve member slidable in the bore, resilient means biasing the valve member into engagement with a seating defined at one end of the bore, an outlet extending from said one end of the bore, a projection on the valve member, said projection extending beyond the seating and through said outlet and acting to control the flow area of said outlet as the valve member is lifted from the seating, a fuel inlet passage communicating with the bore adjacent the seating and a thrust area defined on the valve member, the pressure of fuel in said fuel inlet passage acting in use, on said thrust area to lift the valve member from the seating to allow fuel flow through said outlet.
Such a nozzle is known in the art as a pintle nozzle and as with all fuel injection nozzles of the inwardly opening type, as the valve member is lifted from the seating, the volume within the nozzle which contains fuel at high pressure increases.
A pintle nozzle has a high flow rate when the valve member is lifted from the seating and this together with the increase in volume results in a reduction of the fuel pressure which can in extreme cases, allow the valve member to re-close onto the seating. Even if re-closure of the valve member does not take place, the fuel may not be properly atomised. Moreover, when the valve member closes onto the seating it tends to act as a pump and displaces fuel at a low rate through the outlet into the engine with an adverse effect on engine emissions.
The object of the invention is to provide such a nozzle in a simple and convenient form in which the above described effects are reduced.
According to the invention a fuel injection nozzle of the kind specified comprises a chamber defined in the nozzle body, said chamber being connected to said fuel inlet passage and having a wall which is movable with the valve member, the area of said wall being less than the thrust area of the valve member and being arranged so that as the valve member moves to the closed position the wall moves to increase the volume of the chamber and vice versa.
Examples of fuel injection nozzles 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 known form of pintle nozzle, and
Figures 2-4 show modifications in accordance with the invention.

Referring to Figure 1 of the drawings the fuel injection nozzle includes a nozzle body 10 of stepped cylindrical form which is clamped by means of a cap nut not shown, to a nozzle holder of the general type seen at 11 in Figure 5. Interposed between the nozzle holder and the nozzle body is a distance piece 12. Formed in the nozzle body is a bore 13 in which is slidably mounted a valve member 14. The valve member has a reduced end portion 15 which extends with clearance through an opening in the distance piece, and it carries a spring abutment 16 which is engaged by one end of a coiled compression spring 17.
At its end opposite to the reduced portion the valve member is shaped for engagement with a seating 18 which is positioned upstream of an outlet in the form of an opening 19 which is more clearly seen in Figure 2. The valve member and the wall of the bore adjacent the seating, are of enlarged size to define a fuel inlet chamber 20 and this is connected by way of a fuel inlet passage 21 formed in the nozzle body and continuing in the distance piece and the holder, to a fuel inlet 22 seen in Figure 5, and which in use is connected to the outlet of a fuel injection pump. The spring 17 is housed within a chamber 23 defined in the nozzle holder and the chamber communicates with a drain passage 24.
The valve member has an extension 25 which extends with clearance through the opening 19 and which is contoured so that as the valve member is lifted from its seating, the cross-sectional area of the opening 19 varies. The reduced portion of the valve member within the inlet chamber 20 defines a thrust face against which the fuel pressure in the chamber can act to lift the valve member away from its seating. In use therefore when fuel is delivered from the fuel injection pump the pressure of fuel in the chamber 20 acts upon the thrust face and when the force developed is sufficient to overcome the force exerted by the spring, the valve member is lifted from its seating to allow fuel flow through the opening 19.
As previously explained when the valve member moves away from the seating the effective volume of the chamber 20 increases and as a result there is a reduction in the pressure of fuel within the chamber 20 which may allow movement of the valve member towards the seating. The opening period of the nozzle is therefore uncertain and can lead to poor atomisation of the fuel flowing into the combustion space of the associated engine. Moreover, when the valve member moves to the closed position fuel is displaced from the chamber 20 and whilst some of this fuel will flow back along the fuel inlet passage 21, some of the fuel flows through the opening but at a much reduced rate so that poor combustion takes place in the combustion chamber.
Referring now to Figure 2 there is defined in the nozzle body a further chamber 26 which is in communication with the fuel inlet passage 21. This chamber is defined by means of a sleeve 27 which is a sliding fit on a reduced portion 14A of the valve member. The sleeve 27 is located with clearance within an enlarged portion of the bore 13 and the fuel pressure within the chamber 26 urges it into sealing engagement with the end surface of the distance piece 12. A light spring may be provided to ensure that it remains in engagement with the surface between the periods of fuel delivery and when the engine is not in use. Part of the wall of the chamber 26 is defined by the step between the main portion of the valve member and the reduced portion 14A and in use therefore when the valve member is lifted from the seating whilst the volume of the chamber 20 increases, the volume of the chamber 26 decreases. It is to be noted however that the area of the step on the valve member which is exposed to the pressure in the chamber 26 must be less than the area of the thrust face of the valve member which is exposed to the pressure in the chamber 20. With this arrangement a weaker spring is required to maintain the valve member in engagement with the seating. As compared with the nozzle shown in Figure 1 the increase in the total volume which contains fuel at high pressure as the valve member moves to the open position, is reduced.
In the arrangement shown in Figure 3 the valve member 14 is provided with a counter bore 29 in which is slidably mounted a plunger 30 which by means of a thrust pin 31 which engages an end wall of the spring chamber in the holder, is restrained against movement out of the counter bore. The inner end 26A of the counter bore 29 defines the further chamber and it communicates with a circumferential groove 32 which is connected to the fuel inlet passage 21. The end area of the counter bore defines the aforesaid wall of the further chamber and as with the example of Figure 2, its end area must be less than that of the thrust face which is exposed to the pressure within the chamber 20. The spring abutment in the example of Figure 3, is of annular form and has a skirt portion 33 for engagement with the valve member. The arrangement which is shown in Figure 4 is basically the same as the arrangement shown in Figure 3 except that in this case the valve member extends with clearance through the distance piece and the spring abutment 34 is of annular form without the skirt portion.
Referring now to Figure 5 the nozzle body and the distance piece are of standard form as shown in Figure 1 but in this case the spring abutment 35 is provided with an integral push rod 36 which extends into engagement with a plunger 37 slidably mounted in a bore 38 formed in the nozzle holder. The end of the plunger is exposed within a chamber 26B formed by an extension of the fuel inlet 22. The end area of the plunger 37 exposed to the pressure at the inlet 22 constitutes the aforesaid wall and again the area of the plunger must be less than that of the aforesaid thrust face of the valve member 14. In order to reduce the total volume of fuel at high pressure within the nozzle, a fluted plug 39 is forced into the fuel inlet to adjacent the plunger 37. As an alternative to the arrangement shown in Figure 5, the push rod 36 may be formed integrally with the plunger 37 and merely located within a recess formed in the spring abutment. Alternatively the rod 36 may be a separate item which is guided adjacent its opposite ends.
In order to avoid the need for the plug 39, the bore 38 may be machined from the spring chamber the length of the bore being sufficient so that it just breaks into the inclined portion of the fuel inlet passage 21. In this case the end of the bore forms the stop.

Claims

A fuel injection nozzle for supplying fuel to an internal combustion engine comprising a nozzle body (10) defining a bore (13), a valve member (14) slidable in the bore, resilient means (17) biasing the valve member into engagement with a seating (18) defined at one end of the bore, an outlet (19) extending from said one end of the bore, a projection (25) on the valve member (14), the projection extending through the outlet and acting to control the flow area of the outlet as the valve member is lifted from the seating, a fuel inlet passage (21) communicating with the bore (13) adjacent the seating and a thrust area defined on the valve member, the pressure of fuel in the fuel inlet passage acting in use, on said thrust area to lift the valve member from the seating to allow fuel flow through the outlet (19) characterised by a chamber (26, 26A, 26B) connected to the fuel inlet passage, the chamber having a wall which is movable with the valve member (14), the area of said wall being less than the thrust area of the valve member and being arranged so that as the valve member moves to the closed position the wall moves to increase the volume of the chamber and vice versa.
A fuel injection nozzle according to Claim 1, characterised in that said chamber (26) is defined in the nozzle body (10) and said wall is constituted by a part of the valve member.
A fuel injection nozzle according to Claim 1, in which said nozzle body is held in sealing engagement with a distance piece (12) the valve member defining a reduced end portion (15) which passes with clearance through an opening in said distance piece, characterised in that the valve member defines a reduced intermediate portion (14A) which forms a step with the main portion of the valve member, a sleeve (27) slidable upon the intermediate portion, said sleeve being engageable with the distance piece to form a fuel tight seal therewith, the sleeve being located in a wider portion of the bore which forms the chamber (26) and said step defining the wall movable with the valve member.
A fuel injection nozzle according to Claim 1, characterised by a counter bore (29) extending into the end of the valve member (14) remote from the projection (25), a plunger (30) extending into said counter bore, the inner end of the plunger (30) and the counter bore defining the chamber (26A), and stop means (31) for restraining the plunger (30) against movement in the direction out of said counter bore.
A fuel injection nozzle according to Claim 4, characterised in that said stop means comprises a thrust pin (31) positioned intermediate said plunger and an end wall of a spring chamber (23) formed in a nozzle holder (11) to which the nozzle body is secured.
A fuel injection nozzle according to Claim 1, characterised in that said chamber (26B) is defined in a nozzle holder (11) to which the nozzle body is secured, the nozzle holder defining a bore (38), a plunger (37) slidable in the bore, a push rod (36) interposed between one end of the plunger (37) and the valve member (14), the opposite end of the plunger forming said wall.
A fuel injection nozzle according to Claim 6, characterised by a fuel inlet (22) in the nozzle holder, said chamber (26B) being formed as an extension of the fuel inlet and a plug (39) in the fuel inlet to reduce the volume of fuel within the nozzle.
A fuel injection nozzle according to Claim 7, characterised in that said push rod (36) is formed integrally with a spring abutment (35) which is mounted on the valve member.