GB2230561A

GB2230561A - I.c engine fuel injection pumping system

Info

Publication number: GB2230561A
Application number: GB9008027A
Authority: GB
Inventors: Karl-Heinz Hoffmann; Walter Putz
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1989-04-21
Filing date: 1990-04-09
Publication date: 1990-10-24
Anticipated expiration: 2010-04-09
Also published as: DE3913062C2; IT9047864A1; GB9008027D0; FR2646210A1; DE3913062A1; FR2646210B1; IT9047864A0; GB2230561B; IT1240087B

Description

1 Fuel-injection device for an internal-combustion engine The invention

relates to a fuel-injection device for an air-compression internal-combustion engine, especially but not exclusively a directinjection engine, with an injection pump, a pump piston of which controls the start of feed and the end of feed of a preinjection and a main injection with an injection intermission between them, and with an injection nozzle connected operatively to the injection pump and having a nozzle needle lifting off from its valve seat counter to the force of a compression spring during the preinjection and during the main injection.

The division of the fuel injection into two separate operations emerges, for example, from U.S. Patent Specification 2,871,796, according to which first only a fuel quantity for initiating combustion is injected, whilst the main fuel quantity is introduced into the cylinder only a little later, that is to say after a period of interruption between the preinjection and main injection. on the pump piston there is therefore a plurality of control edges which interact during a working stroke of the pump piston with control crossarranged in the cylinder of the noises and hiah section recesses injection pump. High combustion fractions of harmful substances in the exhaust gas are to be reduced by the use of a preinjection set off from the main injection. It was shown, however, that injection devices of this type no longer satisfy current requirements as regards the generation of noise and exhaust-gas emissions, since the small injections necessary for the needs of the internal-combustion engine during pilot injection cannot be obtained because of the pronounced change of the pilot quantity which occurs in relation to the engine speed. The cause of this undesirable change of quantity is the behaviour of the 2 nozzle needle which is opened disproportionately wide even under pressure waves which only just reach the opening pressure.

Measures reducing combustion noise, although obtainable by shortening the effective stroke, nevertheless lead to a change of the starting point of the preinjection quantity or start of preinjection, with the result that the pilot injection becomes effective only in the upper speed range, but lapses in the lower speed range, this having an adverse effect on the combustion noises and the exhaust-gas behaviour.

The present invention seeks, therefore, to exert influence on the injection trend by means of special measures which result in a substantial improvement of the noise and exhaust-gas behaviour of the internalcombustion engine.

According to the present invention there is provided a fuel-injection device for an internalcombustion engine, with an injection pump, a pump piston of which controls the start of f eed and the end of f eed of a preinjection and a main injection with an injection intermission between them and with an injection nozzle connected operatively to the injection pump and having a nozzle needle lifting off from its valve seat counter to the force of a compression spring during the preinjection and during the main injection, wherein a stop, provided in the injection nozzle and limiting the peliminary stroke of the nozzle needle during the preinjection, fixes the nozzle needle until the injection intermission, but is such as, after the injection intermission, to be resilient during the main injection comprising the preliminary stroke and the main stroke.

By means of the measures according to the invention, a preinjection with a small fuel quantity can be made constant over the entire speed and load range, as is necessary for ideal values for present-day internalcombustion engines. The nozzle needle is fixed at a very small preliminary stroke as a result of the arrangement 3 of the stop only influencing the pilot quantity, so that a very small pilot quantity virtually constant in relation to the engine speed and insensitive to the fuel temperature, such as is necessary for ideal engine values, can be produced.

DE 3,610,658 A1 makes known an injection nozzle with a nozzle needle, in which valve-opening pressures shape the course of injection in such a way that a main stroke immediately following the preliminary stroke is executed. With this known measure, there is no preinjection set off from the main injection, but on the contrary a shaping of the course of the injection with the aim of making it possible to set the preliminary stroke to a desired value very accurately in a way which is simple in production terms.

Preferably, the resilient stop is formed by a spring plate serving as a support for a main-injection spring, and the spring plate may be guided so as to be longitudinally displaceable and at the same time a guide sleeve for a push rod which interacts with the nozzle needle and which, together with the nozzle needle, during the preinjection stroke counteracts the compression spring serving as a preinjection spring. The end face of the spring plate confronting the needle nay have a recess, into which the nozzle needle penetrates as far as a bottom face limiting the preinjection stroke. Preferably, the preinjection and main-injection springs are arranged coaxially relative to one another.

The invention will now be described in detail by means of an embodiment illustrated in the drawing. In this:

Figure 1 shows the fuel-injection device consisting of an injection pump and injection nozzle, Figures 2a-d show different positions of the pump piston in an enlarged representation, Figure 3 shows a cutout from the injection nozzle in a greatly enlarged representation, Figure 4 shows the trend of the preinjection 4 quantity in relation to the engine speed.

Figure 1 illustrates a fuel-injection device consisting essentially of an injection pump 1 and of an injection nozzle 2 and intended for an aircompression auto-ignition -internal-combustion engine as a directinjection engine. The injection pump 1 contains a pump piston 4 equipped with an upper boss 3 and having control edges for preinjection and main injection which are formed in mutually opposite cross-sectional recesses 5, 6 on the pump piston 3 and f rom control bores 7, 8 in the pump cylinder 9.

As can be taken f rom Figure 2a, the pump piston 4 assumes a position which corresponds to the start of feed of the preinjection and in which the connection between the pump working space 10, the cross-sectional recesses 5, 6 and the control bores 7, 8 is broken.

Figure 2b indicates the end of feed of the preinjection. The upper control edge 5a of the crosssectional recess 5 is located at the same height as the control edge 12 formed by a step 11 in the cylinder 9.

The position of the pump piston 4 in Figure 2c corresponds to the intermediate relief or the injection intermission. Here, the connection between the pump working space 10, the cross-sectional recess 5 and the control bore 7 is restored.

Figure 2d shows the end of the injection intermission, since the cross-sectional recess closes the control bore 7 with its lower control edge 5b. The main injection begins and continues until the oblique control edge Sc opens the connection from the pump working space via a longitudinal groove 13 and an annular space 14 on the pump piston 4 to the control bore 8.

The injection pump 1 is connected via a delivery line 15 to the injection nozzle 2 which i ' s composed of the holding body 16 as a double-spring holder, the nozzle clamping nut 17, the nozzle body 18 and the nozzle needle 19. A compression spring acting as a preinjection spring presses the nozzle needle 19 onto its valve seat via a thrust bolt 21 and a push rod 22. The push rod 22 resting on the rear side of the nozzle needle 19 is guided, on the one hand, by a fixedly located guide disc 23 and, on the other hand, by a spring plate 24 which is designed as a resilient stop and which is provided at the same time as the support for a main-injection spring 25 as a second compression spring. The spring plate 24 rests constantly on the nozzle body 18 and has a needle-confronting recess 26 into which the nozzle needle 19 penetrates when the opening pressure occurs. The bottom face 26a of the recess 26 limits the preliminary stroke of the nozzle needle 19. The main-injection spring 25 supported on the fixedly located guide disc 23 surrounds the push rod 22.

In this design, the preliminary stroke corresponds to the preinjection, whereas after the injection intermission the preliminary stroke and the main stroke immediately following this provide as a total stroke the main injection.

Mode of operation:

As soon as, during the upward stroke, the pump piston 4 reaches the position shown in Figure 2a, corresponding to the first start of feed, the nozzle needle 19 lifts off from its valve seat counter to the force of the upper preinjection spring 20 and after a preliminary stroke VH butts against the spring plate 24 initially acting as a fixed stop. The nozzle needle 19 is thus fixed, during the preinjection, at a very small stroke. As can be taken f rom Figure 4, a constant pre injection quantity, represented by the characteristic tall 1 is thus obtained in relation to the engine speed.

When the pump piston 4 reaches the position shown in Figure 2b, the preinje ' ction is ended (end of f eed) and the intermediate relief or injection intermission (Figure 2c) begins. The preinjection spring 20.brings the nozzle needle 19 into the closing position again. In Figure 2d, there is the end of the injection intermission, and the main injection (second start of feed) begins. The nozzle needle 19 simultaneously executes the preliminary stroke 6 VH counter to the preinjection spring 20 and thereafter the main stroke counter to the main-injection spring 28. The main injection thus corresponds to the total stroke GH composed of the preliminary stroke VH and of the main stroke.

7 claims 1 A fuel-injection device for an internal -combustion engine, with an injection pump, a pump piston of which controls the start of feed and the end of feed of a preinjection and a main injection with an injection intermission between them and with an injection nozzle connected operatively to the injection pump and having a nozzle needle lifting off from its valve seat counter to the force of a compression spring during the preinjection and during the main injection, wherein a stot, provided in the injection nozzle and limiting the preliminary stroke of the nozzle needle during the preinjection, fixes the nozzle needle until the injection intermission, but is such as, after the injection intermission, to be resilient during the main -injection comprising the preliminary stroke and the main stroke.

Claims

2. A fuel-injection device according to Claim 1, wherein the resilient

stop is formed by a spring plate serving as a support for a maininjection spring.

3. A fuel-injection device according to Claim 1 or 2, wherein the spring plate is guided so as to be longitudinally displaceable and is at the same time a guide sleeve for a push rod which interacts with the nozzle needle and which, together with the nozzle needle, during the preinjection stroke counteracts the compression spring serving as a preinjection spring.

4. A fuel-injection device according to any one of Claims 1 to 3, wherein the end f ace of the spring plate confronting the needle has a recess, into which the nozzle needle penetrates as far as a bottom face limiting the preinjection stroke.

8 5. A fuel-injection device according to Claims 1 to 4, wherein the preinjection and main-injection springs are arranged coaxially relative to one another.

6. A fuel-injection device for an internal-combustion engine, substantially as described herein with reference to, and as illustrated in, the accompanying drawings.

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