GB2034405A

GB2034405A - Fuel injector for an internal combustion engine

Info

Publication number: GB2034405A
Application number: GB7937360A
Authority: GB
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1978-10-28
Filing date: 1979-10-29
Publication date: 1980-06-04
Also published as: HU181453B; IT1126304B; AT368250B; SU1034615A3; DE2847058A1; IN153196B; RO78220A; IT7926777A0; DD147134A1; JPS5560656A; GB2034405B; CH640308A5; SE7908855L; ATA680079A; FR2439876A1

Abstract

A nozzle needle (2) slidable in a nozzle body (1) terminates in a pintle (4) slidable in a central outlet bore (5). A pressure space (7) is arranged between the valve seat (3) and the pintle (4). The pintle (4) has a longitudinal bore (8) and a transverse port or bore (9) communicating therewith, and an annular gap (6) between the wall of the central bore (5) and the pintle (4) provides an atomised spray at low speeds and/or loads. The transverse port or bore (9) terminates within the central bore (5) when the nozzle needle is closed and connects the space (7) with the bore (4) after a predetermined lift of the nozzle needle (2) to provide a compact fuel jet at higher speeds and/or loads. The pintle (4) extends over substantially the full length of the central outlet bore (5) when the nozzle needle (2) is fully open, thereby preventing an increase in atomised spray. <IMAGE>

Description

SPECIFICATION Fuel injector This invention relates to a fuel injector for a self-ignition or spark-ignition internal combustion engine having a nozzle needle axially slidable in a nozzle body and terminating in a pintle movable in a central bore of the nozzle body, a pressure space being arranged between a valve seat and the pintle, the pintle having a longitudinal bore and a transverse port or bore communicating therewith.

An injector of this type is disclosed in German Utility Patent 7538 166. Here, the transverse port connected to the longitudinal bore communicates with the pressure space when the nozzle needle is in the closed position, and the pintle slides in the central bore to provide a sealing action. When the nozzle needle is lifted only slightly off its seat, fuel penetrates into the pressure space, and a pilot amount of fuel is injected through the transverse port and the longitudinal bore into the combustion chamber in the form of a compact fuel jet. As the nozzle needle is opened further, an annular gap is formed between the wall of the central bore and the conicallyformed pintle, through which gap the amount of fuel injected increases. Only when the nozzle needle is fully open and the pintle withdrawn from the central bore is the full injection area free and the main charge injected.

Since the lift of the nozzle needle is a function of the specific speed and/or load of the engine, the fuel is injected in all operating modes in the form of a more or less compact jet, the important feature being whether the pintle is fully withdrawn or not.

Now in the greater proportion of directinjection internal combustion engines on the market today combustion air fed into the combustion chamber in the piston is given a pronounced turbulence and/or caused to rotate about the longitudinal axis of the combustion chamber. The fuel is then applied in the form of a film directly onto the combustion chamber wall or at least close to it. Because of a compact solid fuel jet, this system enables almost optimum motor characteristics to the attained at upper speeds and/or loads with smooth running and good exhaust gas quality. However, if at upper speeds and/or loads the pintle is fully withdrawn from the central bore, it is no longer possible to achieve the desired optimum injection cycle and the desired compactness of the fuel jet.

This is particularly true of small high speed engines for which the smallest nozzle bores or central bores that are technologically possible would still be too large. Thus the need arises for the cross-sectional area of the central bore to be decreased by the tip of the pintle remaining in the central bore so that the fuel jet is injected with a sufficient momentum into the combustion chamber. As a result, the fuel jet is emitted through an annular gap also at full load of the engine which produces an undesirable excessive atomization. The conse quences of this are higher smoke levels at a given load and relatively rough running of the engine.

At no load and at lower speed and/or loads, however, poor combustion with blue smoke formation and uneven running occur, particularly in cold conditions. These deficien cies can be overcome by introducing the fuel in a well atomized condition into the combus tion air so that better and faster mixture formation takes place. Thus, with the known injector exactly the opposite is achieved of what is desired.

An object of the present invention is to provide a fuel injector capable of meeting the specified requirements, i.e. to provide good atomization of the fuel at no load and at lower speeds and/or loads, and injection into the combustion chamber as a compact fuel jet at upper speeds and/or loads.

The invention provides a fuel injector for a self-ignition or spark-ignition internal combus tion engine and comprising a nozzle needle axially slidable in a nozzle body and terminat ing in a pintle slidable in a central outlet bore of the nozzle body, a pressure space being arranged between the valve seat and the pintle and/or central bore, the pintle having a longitudinal bore and a transverse port or bore communicating therewith, wherein there is an annular gap between the wall of the central bore and the pintle and the transverse port or bore terminates a predetermined distance within the central bore when the nozzle needle is closed and connects the pressure space with the longitudinal pintle bore only after a predetermined lift of the nozzle needle, the pintle extending over substantially the full length of the central outlet bore even when the nozzle needle is fully open.

Thus, as soon as the nozzle needle slightly lifts off its valve seat, fuel flows into the pressure space, passes through the annular gap between the wall of the central bore and the pintle, is atomized as an annular spray and fed into the combustion chamber with a relatively large surface. The large surface pro vides a large area of contact with the air for combustion and thus promotes fast direct mix ing with the air. In other words, mixture formation proceeds at a faster rate than previ ously. As the engine speed and/or load in creases, more fuel is injected, the nozzle nee dle lifts further off its valve seat until the upper edge of the transverse port reaches the bottom edge of the pressure space and, even tually, at full load opens with its full area into the pressure space.At this stage, the fuel will be injected through the transverse port and the longitudinal bore as a compact jet into the combustion chamber and, if this is desired, can penetrate to the combustion chamber wall to spread there as a thin film. The fact that the pintle still extends substantially over the full length of the central bore even when the nozzle needle is fully open, prevents an in crease in the scattered spray.

The transverse port may be formed with different shapes in order to improve the transition from injection through the annulus to injection through the longitudinal bore. By way of example, a rectangular cross-section may be provided in order to obtain a faster transition. The distance between the pressure space and the edge of the transverse port facing the pressure space, which is the so called overlap, with the nozzle needle closed, amounts to anything between 0.1 and 0.5 mm depending on the desired conditions.

In so far as greater amounts of fuel are desired to be injected, preferably the pintle tapers conically inwards from the transverse port to its outer end, or it is stepped with a reduced diameter from the transverse port to its outer end. As a result, an enhanced annular injection will be produced at upper speeds and/or loads but, because of the great amount of fuel and the pressure in conjunction with the jet emitted through the longitudinal bore, this will again produce a substantially compact fuel jet.

Four embodiments of the invention will now be described with reference to the accompanying drawings, wherein: Figures 1 to 4 each show a longitudinal section through the combustion chamber end part of a fuel injector according to the invention, Figure 5 is a section along the line V-V of Fig. 1, and Figure 6 is a section along the line VI-VI of Fig. 2.

In Figs. 1 to 4, a nozzle needle 2 is axially slidable in a nozzle body 1, and has a valve surface contacting a valve seat 3 or the nozzle body 1 in the closed position. The nozzle needle 2 has a pintle 4 into a centre bore 5 of the nozzle body 1 so that there is an annular gap 6 between the pintle 4 and the wall of the bore. Between the valve seat 3 and the centre bore 5 or the pintle 4 there is an annular pressure space 7. The pintle 4 is formed with a longitudinal bore 8 which terminates in a transverse port 9, which in the closed position of the nozzle needle 2 has an upper edge opening into the bore 5 at a distance 10 below the pressure space 7.

As can be seen from Figs. 1 and 5, the transverse port 9 has a circular cross-section.

In Figs. 2 and 6, the transverse port 9 has a rectangular cross-section, so that when thenozzle needle 2 opens, a rapid transition from injection through the annulus 6 to injection through the longitudinal bore 8 is possible.

The embodiment of Fig. 3 differs from the injectors of Figs. 1 and 2 in that the diameter of the pintle 4 is stepped inwardly with a reduced diameter from the transverse port 9 down to its free end. This gives the advantage that, with the nozzle needle 2 opened, a greater amount of fuel can be injected into the combustion chamber.

The same effect is achieved by the injector of Fig. 4 in which the pintle 4 tapers inwardly from the transverse port 9 down to its free end.

It should also be noted that all the pintles 4 extend through the nozzle body 1 by such a length that they substantially fill the centre bore 5 even when the nozzle needle 2 is in the open position.

Claims

1. A fuel injector for a self-ignition or spark-ignition internal combustion engine and comprising a nozzle needle axially slidable in a nozzle body and terminating in a pintle slidable in a central outlet bore of the nozzle body, a pressure space being arranged between the valve seat and the pintle and/or central bore, the pintle having a longitudinal bore and a transverse port or bore communicating therewith, wherein there is an annular gap between the wall of the central bore and the pintle and the transverse port or bore terminates a predetermined distance within the central bore when the nozzle needle is closed and connects the pressure space with the longitudinal pintle bore only after a predetermined lift of the nozzle needle, the pintle extending over substantially the full length of the central outlet bore even when the nozzle needle is fully open.

2. A fuel injector as claimed in Claim 1, wherein the transverse port has a rectangular cross-section.

3. A fuel injector as claimed in Claim 1 or 2, wherein the axial distance between the pressure space and the edge of the transverse port adjacent the pressure space is 0.1 to 0.5 mm when the nozzle needle is closed.

4. A fuel injector as claimed in Claim 1, 2 or 3, wherein the diameter of the pintle tapers inwardly towards its outer end away from the transverse port.

5. A fuel injector as claimed in Claim 1, 2 or 3, wherein the pintle is stepped inwardly to provide a portion of reduced diameter from the transverse port to its outer end.

6. A fuel injector substantially as herein described with reference to any one of the embodiments shown in the accompanying drawings.

7. An internal combustion engine provided with a fuel injector as claimed in any one of the preceding claims.