GB1592134A

GB1592134A - Apparatus for injecting fuel in air-compression internal combustion engines

Info

Publication number: GB1592134A
Application number: GB8626/78A
Authority: GB
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1977-03-03
Filing date: 1978-03-03
Publication date: 1981-07-01
Also published as: FR2382586A1; FR2382586B1; HU176285B; DD134558A1; CH629872A5; IT1092930B; IT7820688A0; IN148168B; DE2709162A1; JPS53109016A; SU784807A3; SE7802448L; RO77290A

Abstract

The device contains an injection pump element (1) with a pump delivery valve (2), a spring-loaded injection valve (5) and a fuel feed line (3) connecting the pump delivery valve (2) to the nozzle needle annular orifice (12) of the injection valve (5), in which line a relief valve (4) is arranged close to the nozzle needle annular orifice (12). In such a device it is desirable to shorten the closing sequence of the injection valve (5) as much as possible in the upper speed and load range. In order to achieve this an additional outlet bore (15) is connected to the nozzle needle annular orifice (12), by means of which bore the pressure still prevailing in the nozzle annular orifice (12) is rapidly reduced following closure of the pump delivery valve (2) and the relief valve (4). The cross-sectional area of the piston (8) in the injection pump element (1) is selected to be sufficiently large for the quantity of fuel flowing out through the outlet aperture (15) during the injection sequence to be additionally available without prolonging the injection period. A shut-off element (17) can be automatically actuated as a function of the engine speed and/or the engine load in order to close the outlet aperture (15) in the lower speed or load range. In this range the stroke of the pump (8) in the injection pump element (1) can then be reduced. <IMAGE>

Description

(54) APPARATUS FOR INJECTING FUEL IN AIR-COMPRESSION INTERNAL COMBUSTION ENGINES (71) We, MASCHINENFABRIK AUGSBURG NURNBERG AKTIENGESELLSCHAFT, Katzwanger Strasse 101, 8500 Nurnberg, Germany (Fed. Rep.), a German body Corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to apparatus for injecting fuel in an air-compression internal combustion engine.

Such apparatus is known comprising at least one injection pump member having a pump delivery valve, a spring-loaded injection valve, a return pipe for oil leakage around the injection valve and a fuel delivery pipe connecting the injection pump member and the pump delivery valve to the injection valve, a pressure-reducing valve being provided in the fuel delivery pipe adjacent the injection valve.

In such known apparatus the pressurereducing valve is arranged close to the injection valve e.g. to an annular clearance around the nozzle needle of the injection valve, The pressure-reducing valve accelerates the pressure decrease in the annular clearance during closing of the nozzle needle.

It is a well-known fact that the closing motion of the nozzle needle in the case of direct fuel injection in internal combustion engines is an important factor for the engine performance. Thus, for instance, there is a reduction in exhaust smoke as the rate of closing is increased, mainly because dribbling of the nozzle is minimized. The closing motion of the nozzle needle is initiated at the end of injection by pressure drop at the injection pump member. In other words, the nozzle needle motion is influenced by the length and design of the injection pipe, the pressure waves occurring in it and their reflections as well as by the flexibility of the whole system.

In order to avoid these drawbacks and to ensure quick closing of the nozzle needle, generally known means are to select the correct unloading volume at the pump delivery valve, to minimize the passage volume between the pump member and the injection valve, to reduce the moving masses in the injection valve and to increase the valve spring force by increasing the effective annular clearance area on the needle guide (small needle seat diameter).

However, since all these means have failed to produce a substantial improvement, it has been proposed to install an additional pressure-reducing valve. While this brings about an accelerated pressure drop in the nozzle needle annular clearance, there remain certain disadvantages when considering the effect over the whole speed and load ranges of an engine.

An object of the present invention is to provide apparatus for the injection of fuel in which fuel atomization is improved at lower engine speeds and loads, and in which above all the time for closing the injection valve is reduced at upper engine speeds and loads, whereby improved performance may be expected over the complete operating range of the engine.

The invention provides apparatus for injecting fuel in an air-compression internal combustion engine comprising at least one injection pump member having a. plunger and a pump delivery valve, a spring-loaded injection valve having a nozzle hole or holes, a return passage to the injection pump member for fuel leakage from the injection valve, a fuel delivery passage connecting the injection pump member and the pump delivery valve with the injection valve, a pressure-reducing valve provided in the fuel delivery passage adjacent the injection valve, a discharge passage leading from the injection valve and through which a proportion of the fuel fed to the injection valve via the fuel delivery passage may flow away, so that interruption of fuel supply to the injection valve may produce a substantially instantaneous fuel-pressure drop therein resulting in substantially instantaneous closing of the injection valve, the cross sectional area of the plunger of the injection pump member being at least large enough to supply addi tionally the proportion of the fuel flowing away through the discharge passage without prolonging the injection time.

The higher fuel pressure now obtainable at low engine speed and load results in improved atomization, while the additional facility of discharging fuel with practically no back-pressure enables the nozzle needle to close at a very rapid rate and pressure waves remain ineffective.

Preferably, the fuel delivery passage leads directly to an annular clearance around a nozzle needle of the injection valve.

The discharge passage is preferably disposed so that it terminates directly in the nozzle needle annular clearance whereby a minimum length of the discharge path is provided. In order to return the fuel in an advantageous manner without any great expense back to the injection pump member, preferably the discharge passage communicates with the return passage via a passage bypassing the injection valve.

Preferably, the free cross sectional area of the discharge passage is equivalent to the free cross sectional area of the nozzle hole or.holes. It appears relevant to mention that deviations resulting from the fact that the discharge passage is not valve controlled such as is the nozzle hole can of course be taken into consideration and should be taken into consideration.

Preferably, an optionally operable shut-off valve is provided directly downstream of the discharge passage. The shut-off valve is closed preferably only during engine idling and at low engine speeds and loads, actuation being conveniently as a function of the engine speed and/or engine load.

As briefly mentioned initially it is an established fact that the design of injection apparatus to match a engine operating at higher speeds and loads, will result in unfavourable conditions for operation at lower speeds or loads. This applies especially to idling. The given nozzle hole in conjunction with the diminished injection rate at reduced speed of the plunger in the injection pump member enables only a relatively low pressure to be attained in the passages. This adversely affects fuel atomization which is crucial for effective mixture formation at idling and applies especially to engines with a wide speed range.The proposed shut-off directly downstream of the discharge passage in conjunction with an increase diameter of the plunger in the pump member enhances the delivery rate at the low plunger speed so that pressure build-up and fuel atomization at the nozzle hole are improved.

The invention will now be described with reference to two embodiments shown schematically in the accompanying drawing, in which: Figure 1 shows in section the general layout of injection apparatus according to the invention with the position of the pump member at higher and lower engine speeds and loads shown separately; and Figure 2 is a view similar to Figure 1 of modified apparatus and also showing the position of the pump member at higher and lower engine speeds and loads separately.

In the drawing, fuel-injection apparatus comprises an injection pump member 1 provided with a pump delivery valve 2, a fuel delivery passage 3, a pressure-reducing valve 4, an injection valve 5, and a oilleakage return passage 6.

The injection pump member 1 essentially comprises a plunger 8 which is axially slidable in a barrel 7 and has a variable stroke depending on the speed and load range of the engine, the stroke attainable at full load being denoted by H and the reduced stroke at idling being denoted by h. The pump delivery valve 2 and the pressure reducing valve 4 ensure that no fuel can flow back along the passage 3 into the barrel 7, and above all that the fuel supply to the injection valve 5 is instantly interrupted every time the pressure drops. The pressure reducing valve 4 furthermore prevents any pressure waves occurring in the fuel delivery passage 3, and their reflections, from reaching the injection valve 5. The valve 5 has a nozzle needle 11 which is axially slidable in a nozzle body 9, shown diagrammatically, and is maintained in a closed position by a spring 10.The nozzle needle 11 controls the passage of fuel from a nozzle needle annular clearance 12 to a nozzle hole 13 as a function of the pressure.

Inevitable oil leakage seeping from around the nozzle needle 11 and from other parts which are difficult to seal, is collected in the spring chamber of the injection valve 5 and returned through the return passage 6 together with new fuel 14 to the injection pump member 1.

Furthermore, a discharge passage 15 is provided extending to the annular clearance 12 through which a proportion of the fuel introduced into the clearance 12 is discharged immediately through a, bypass 16 into the return passage 6. The diameter of the plunger 8 of the injection pump member 1 is of such a size that this amount of fuel directly discharged from the annular clearance 12 through the passage 15 will be additionally supplied via the passage 3. This amount of fuel can be readily determined in Figure 1 because the free cross sectional area of the discharge passage 15 is equal to the free cross sectional area of the nozzle hole 13.

Now as soon as the pressure produced by the injection pump member 1 decreases, the pump delivery valve 2 and the pressure reducing valve 4 will close instantly. The pressure still prevailing in the annular clearance 12 is rapidly dissipated through the discharge passage 15 since no new fuel is being supplied. Thus, the nozzle needle 11 closes substantially instantly.

Figure 2 shows an additional shut-off valve 17 arranged directly between the discharge passage 15 and the bypass 16. The valve 17 is brought into a closed position (shown on the right-hand side of Figure 2) by any suitable means (not shown) as a function of engine speed and load at lower loads and speeds. The valve 17 causes an increased pressure to build-up in the injection valve 5 at low speeds and loads when little fuel is admitted. Thus, improved atomization of the fuel is obtained. As can be seen from the injection pump member 1 shown diagrammatically on the right hand side of Figure 2 it is possible with a plunger 8 of increased diameter, for the stroke of the plunger at idling of the engine to be kept at only about half the normal stroke.

WHAT WE CLAIM IS:- 1. Apparatus for injecting fuel in an aircompression internal combustion engine comprising at least one injection pump member having a plunger and a pump delivery valve, a spring-loaded injection valve having a nozzle hole or holes, a return passage to the injection pump member for fuel leakage from the injection valve, a fuel delivery passage connecting the injection pump member and the pump delivery valve with the injection valve, a pressure-reducing valve provided in the fuel delivery passage adjacent the injection valve, a discharge passage leading from the injection valve and through which a proportion of the fuel fed to the injection valve via the fuel delivery passage may flow away, so that interruption of fuel supply to the injection valve may produce a substantially instantaneous fuelpressure drop therein resulting in substantially instantaneous closing of the injection valve, the cross sectional area of the plunger of the injection pump member being at least large enough to supply additionally the proportion of the fuel flowing away through the discharge passage without prolonging the injection time.

2. Apparatus as claimed in claim 1, wherein the fuel delivery passage leads directly to an annular clearance around a nozzle needle of the injection valve.

3. Apparatus as claimed in claim 2, wherein the discharge passage extends from the nozzle-needle annular clearance.

4. Apparatus as claimed in claim 1, 2 or 3, wherein the discharge passage communicates with the return passage via a passage bypassing the injection valve 5. Apparatus as claimed in any one of claims 1 to 4, wherein the free cross sectional area of the discharge passage is equal or substantially equal to the free cross sectional area of the nozzle hole or holes.

6. Apparatus as claimed in any one of claims 1 to 5, wherein an optionally operable shut-off valve is provided directly downstream of the discharge passage.

7. Apparatus as claimed in claim 6, wherein the shut-off valve is arranged to be closed only during idling and at low engine speeds and loads.

8. Apparatus as claimed in claim 6 or 7, wherein actuation of the shut-off valve is effected as a function of the engine and/or engine load.

9. Apparatus as claimed in claim 6, 7 or 8, wherein the stroke of the plunger in the injection pump member with the shut-off valve closed at idling and at low engine speeds and loads is sized so as to amount to only substantially half the plunger stroke if there were no shut-off valve directly downstream of the discharge passage.

10. Apparatus as for injecting fuel for an air compression internal combustion engine substantially as herein described with reference to Figure 1 or 2 of the accompanying drawing.

11. An internal combustion engine provided with apparatus for injecting fuel as claimed in any one of the preceding claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. pressure still prevailing in the annular clearance 12 is rapidly dissipated through the discharge passage 15 since no new fuel is being supplied. Thus, the nozzle needle 11 closes substantially instantly. Figure 2 shows an additional shut-off valve 17 arranged directly between the discharge passage 15 and the bypass 16. The valve 17 is brought into a closed position (shown on the right-hand side of Figure 2) by any suitable means (not shown) as a function of engine speed and load at lower loads and speeds. The valve 17 causes an increased pressure to build-up in the injection valve 5 at low speeds and loads when little fuel is admitted. Thus, improved atomization of the fuel is obtained. As can be seen from the injection pump member 1 shown diagrammatically on the right hand side of Figure 2 it is possible with a plunger 8 of increased diameter, for the stroke of the plunger at idling of the engine to be kept at only about half the normal stroke. WHAT WE CLAIM IS:-

1. Apparatus for injecting fuel in an aircompression internal combustion engine comprising at least one injection pump member having a plunger and a pump delivery valve, a spring-loaded injection valve having a nozzle hole or holes, a return passage to the injection pump member for fuel leakage from the injection valve, a fuel delivery passage connecting the injection pump member and the pump delivery valve with the injection valve, a pressure-reducing valve provided in the fuel delivery passage adjacent the injection valve, a discharge passage leading from the injection valve and through which a proportion of the fuel fed to the injection valve via the fuel delivery passage may flow away, so that interruption of fuel supply to the injection valve may produce a substantially instantaneous fuelpressure drop therein resulting in substantially instantaneous closing of the injection valve, the cross sectional area of the plunger of the injection pump member being at least large enough to supply additionally the proportion of the fuel flowing away through the discharge passage without prolonging the injection time.

4. Apparatus as claimed in claim 1, 2 or 3, wherein the discharge passage communicates with the return passage via a passage bypassing the injection valve

5. Apparatus as claimed in any one of claims 1 to 4, wherein the free cross sectional area of the discharge passage is equal or substantially equal to the free cross sectional area of the nozzle hole or holes.