GB2223804A

GB2223804A - I.C. engine fuel injection pump and nozzle

Info

Publication number: GB2223804A
Application number: GB8922038A
Authority: GB
Inventors: Hermann Kruger
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 1988-10-13
Filing date: 1989-09-29
Publication date: 1990-04-18
Also published as: GB8922038D0

Abstract

The end of the nozzle needle 7 facing the pump piston 3 is in the form of a guide cylinder 11 for the pump piston. The pumping chamber 16 is permanently connected by way of a passage 17 to an injection chamber 10 surrounding the nozzle needle 7. The opening stroke of the needle 7 is limited by the cooperation of the base 15 of the guide cylinder 11 with the 21 facing end face 14 of the piston 3. When the piston 3 undergoes further axial movement, the needle 7 is moved along with it, with the fuel delivery rate being considerably increased. <IMAGE>

Description

DESCRIPTION A PUMP NOZZLE FOR THE INJECTION SYSTEM OF AN INTERNAL COMBUSTION ENGINE.

The invention relates to a pump nozzle for the injection system of an internal combustion engine.

Conventional nozzles of the type in which the needle nozzle opens the injection openings of the nozzle to connect them to the injection chamber during the injection operation only, have the disadvantage of a relatively long overall length, since the pump piston is resiliently sprung for returning the pump piston and for arresting the nozzle needle in its closing position and the nozzle needles are disposed in spatial series within it.

This disadvantage is avoided by the pump nozzles described, for example, in EP 0 260 720, F 02 M1 57/02, in which the nozzle needle is raised from the injection openings outside the injection times, and hence a collection chamber for the quantity of fuel to be injected is formed between it and the injection openings. Pump nozzles having an open nozzle do, however, have functional disadvantages in that, at low internal combustion engine speeds, particularly when starting, injection takes place with very low fuel pressure and there is unsatisfactory fuel atomisation, and, during the return stroke of the needle, that is when the needle is moved away from the injection openings, fuel is pressed back into the pump nozzle by the gas pressures in the combustion chamber (compression stroke).

For these reasons, it is of interest to obtain a pump nozzle of the type described above, that is, one with a nozzle which is closed outside the injection phases, which, in addition to avoiding the disadvantages of pump nozzles having an open nozzle, as is inherent in the system, has the advantage of being smaller than conventional designs.

DE-OS 21 65 443, F 02 M 57/02 discloses a pump nozzle having a closed nozzle, which is suitable in this respect and in which the end of the pump piston facing the nozzle needle has a chamber on the front end which forms a sliding guide for the end of the nozzle needle facing the pump piston. The chamber itself, that is, the space defined by the front end of the nozzle needle, is bled continuously. The spring forces for closing the nozzle needle and for returning the pump piston are obtained through a compression spring which is inserted between the end face of the pump piston and a spring support close to the seat on the nozzle needle so as to surround the region of the nozzle needle outside the above-described chamber.In spatial terms, the spring is parallel to the nozzle needle, thus avoiding the above-described series arrangement comprising the pump piston, spring arrangement and nozzle needle. However, this known design does not afford maximum saving of space, since the defined space in the chamber is continuously bled and hence unused. Rather, a further chamber arrangement, which is equipped with a valve, is provided eccentrically to generate pressure.

It is an object of the present invention to provide a pump nozzle of the generic type, that is, one which provides the functional advantages of a pump nozzle having a closed nozzle, and which has been optimised with regard to the space it requires.

Furthermore, the invention should make it advantageously possible to achieve a particular delivery characteristic using simple means.

In accordance with the present invention there is provided a pump nozzle for the injection system of an internal combustion engine, having a pump piston, which is guided in a housing so as to be axially displaceable against a spring force, and a nozzle needle, which is also guided so as to be axially displaceable against a spring force out of a position in which it closes off the injection openings and which, when fuel pressure is increased by the displacement of the pump piston, performs a stroke movement in an injection chamber into a position in which it opens up the injection openings, wherein the end of the nozzle needle facing the pump piston is in the form of a guide cylinder, which is open at its front end, for the facing end region of the pump piston, the cylinder being provided at various levels with openings for supplying fuel and for conveying fuel into the injection chamber and the area of the nozzle needle which is acted upon in the injection chamber by the fuel pressure in the axial direction being greater than that of the end face of the pump piston.

Advantageously, the pump piston and the nozzle needle are provided with mutually opposite stop faces for limiting the stroke of the nozzle needle during displacement of the pump piston.

In the invention, the nozzle needle (or an additional component connected thereto) forms a cylinder-like chamber for holding the end of the pump piston facing the nozzle needle, wherein this chamber is actively involved in the method of operation of the pump nozzle so that, when the pump piston is moved in the direction of the nozzle needle, the fuel in the cylindrical chamber is compressed and fed into the injection chamber surrounding the nozzle needle. The chamber therefore forms the actual high-pressure pump chamber. Moreover, the design according to the present invention also has the advantage of a short length, especially since one single spring arrangement can be disposed parallel thereto to achieve the closing forces for the nozzle needle (and hence to define the opening pressure required there for in the injection chamber) as well as for returning the pump piston.

The stop faces are preferably formed by the base area of the guide cylinder and the end face of the pump piston.

Advantageously, in order to generate spring forces, a compression spring is connected between the end face of the guide cylinder and a support on the pump piston, so as to surround said pump piston.

The embodiments of the invention incorporating the above features, ensure that the pump nozzle has a delivery characteristic, in which, initially, a relatively small delivery quantity is injected into the combustion chamber in accordance with the relatively low fuel pressure determined by the force of the closing spring, while subsequently, once the stops have become effective as a result of simultaneous movement of the pump piston and the nozzle needle, there is a rapid reduction in the volume of the injection chamber and hence a substantial increase in fuel pressure and in the quantity of fuel injected.

By way of example only, a specific embodiment of the present invention will now be described with reference to the accompanying drawing, which shows an axial section through a pump nozzle in accordance with the present invention.

The active parts of the pump nozzle are located in a housing, which comprises two components 1 and 2, which are fixedly connected to one another. This housing is provided with means for screwing it into a wall of the combustion chamber of an internal combustion engine, which means are conventional and do not therefore have to be described in detail. The most important active components of the pump nozzle are the pump piston 3, which as is known from the above-mentioned EP 0 260 720, comprises a plurality of components 4, 5 and 6, a nozzle needle 7 and a compression spring 8, which is inserted between parts 3 and 7 and which forms both the closing spring for the nozzle needle 7 as well as at least one of the return springs for the pump piston 3. In the closing position shown, the nozzle needle 7 closes off the injection openings 9 from the injection chamber 10, thus preventing any fuel from emerging out of the injection openings 9. This is another advantage of a pump nozzle having a closed nozzle over one having an open nozzle.

On its side facing the pump piston 3, the nozzle needle 7 is in the form of a guide cylinder 11 for the region of the pump piston 3 facing it. The inside wall 12 of this guide cylinder 11 thus forms a sliding guide for the piston component 6 and is in turn slidingly guided by its outer casing 13 in the housing component 2. A chamber 16, which is relatively small given the relative positions shown of the parts 6 and 11, is located between the lower end face 14 of the piston component 6 as shown in the drawing and the base 15 of the cylinder 11 and is in permanent flow connection with the injection chamber 10 by way of the passage 17.

As is known from the above-mentioned European Application for pump nozzles having an open nozzle, the housing 1, 2 has three fuel connections: the fuel to be injected is supplied by way of a fuel supply line 18 and a bore 19 in the cylinder 11 when the piston component 6 has been displaced upwards in the drawing until its end face 14 is above the bore 19.

In the position shown in the drawing, fuel is drawn off by way of the housing opening 20. When the pump piston 3 is in the relatively high position described between the mutually facing end faces of the piston components 4 and 5, that is at 22, a connection 21 serves to form a cushion of fuel whose axial extension defines the commencement of the injection operation.

The greater the axial extension of this cushion, the earlier the commencement of injection (that is, relative to the operating cycle of a cam or lever acting on the pump piston 3).

Assuming that the pump piston 3 is in such a high position that its end face 14 opens up the bore 19, if the method of operation of the pump nozzle is considered, the pump piston 3 initially moves downwards in the drawing under the action of the cam or drive lever and relative to the stationary nozzle needle 11, which is supported on the housing component 2, with the spring 8 becoming increasingly compressed.

During this downwards movement of the pump piston 3, the volume of the cylinder chamber 13 is increasingly reduced and hence there is an increase in pressure in the injection chamber 10. Finally, the fuel pressure in this chamber becomes so great that it exerts an upwardly directed opening pressure on the pressure face 23 on the injection needle 7 which is greater than the force of the spring 8. The nozzle needle 7 then commences its stroke movement, wherein this movement is accelerated by the fact that a conical surface 24 also becomes effective as a surface acted upon by pressure. The stroke movement of the nozzle needle 7 is limited by the fact that the two faces 14 and 15 act as stop faces, so that the nozzle needle 7 also takes part in the further displacement of the pump piston 3 in the downwards direction. The pressure face 23 is larger in dimension than the end face 14 of the pump piston. This joint movement of the pump piston 3 and the nozzle needle 7 ensures a pronounced increase in pressure in the injection chamber 10 and hence that a relatively large quantity of fuel is delivered through the injection openings 9.

The invention thus provides a pump nozzle having a closed nozzle which, in terms of space required, is of an optimum design, and which uses simple means to obtain a desired delivery characteristic.

Claims

1. A pump nozzle for the injection system of an internal combustion engine, having a pump piston, which is guided in a housing so as to be axially displaceable against a spring force, and a nozzle needle, which is also guided so as to be axially displaceable against a spring force out of a position in which it closes off the injection openings and which, when fuel pressure is increased by the displacement of the pump piston, performs a stroke movement in an injection chamber into a position in which it opens up the injection openings, wherein the end of the nozzle needle facing the pump piston is in the form of a guide cylinder, which is open at its front end, for the facing end region of the pump piston, the cylinder being provided at various levels with openings for supplying fuel and for conveying fuel into the injection chamber and the area of the nozzle needle which is acted upon in the injection chamber by the fuel pressure in the axial direction being greater than that of the end face of the pump piston.

2. A pump nozzle as claimed in claim 1, wherein the pump piston and the nozzle needle are provided with mutually opposite stop faces for limiting the stroke of the nozzle needle during displacement of the pump piston.

3. A pump nozzle as claimed in claim 2, wherein the stop faces are formed by the internal base area of the guide cylinder and the end face of the pump piston.

4. A pump nozzle as claimed in any of claims 1 to 3, wherein, in order to generate spring forces, a compression spring is connected between the end face of the guide cylinder and a support on the pump piston, so as to surround said pump piston.

5. A pump nozzle for the injection system of an internal combustion engine, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawing.