Fuel Injection Nozzle For Internal Combustion Engines

Abstract

A fuel-injection nozzle for an internal combustion engine is described, which nozzle comprises a valve needle for controlling the flow of fuel via a throttle passage to a pressure chamber for a preliminary fuel injection out of the nozzle and for controlling of the flow of fuel via duct means to the pressure chamber for a main fuel injection out of the nozzle, during the opening stroke of the valve needle, and which nozzle is improved by valve means closed during rest position which valve means are mounted in the duct means and associated with the valve needle to be opened by the needle during its opening stroke; the free cross-sectional area of the nozzle mouth which is traversed by the fuel during the preliminary injection is smaller than the cross-sectional area of said throttle passage.

Description

BACKGROUND OF THE INVENTION

The invention relates to a fuel injection nozzle for internal combustion engines which nozzle has a valve needle controlling a preinjection and a main injection, the fuel for the preinjection being fed into a pressure chamber of the nozzle via a throttle passage and wherein a duct for the main injection of fuel is opened during the opening stroke of the valve needle.

Such pre- and main injection valves are employed in order to reduce the loud ignition noises caused by high speed diesel engines while idling. By means of the preinjection and main injection, of which the former preferably merges into the latter, a combustion of little noise is achieved which sets in smoothly and proceeds slowly in the beginning.

Known fuel injection valves of this type have the drawbacks of being expensive to manufacture and of having a hydrodynamically unfavorable conduit system.

OBJECTS AND SUMMARY OF THE INVENTION

Is is an object of the invention to develop an inexpensive valve means for preinjection and main injection which is free from the above-described drawbacks.

This object is attained, in accordance with the invention, by providing in a fuel injection nozzle of the type initially described, a valve means interposed in the main injection fuel duct, which is in closed position during idling of the engine and which is pushed open by the valve needle during the opening stroke of the latter, and means for producing during the preinjection stroke a throttle effect which is larger at the point of fuel injection than at the throttle passage mentioned further above.

In a preferred embodiment of the invention, the valve is arranged coaxially with the valve needle and comprises a movable valve member having a plug, and the valve needle comprises a return spring and a spring-retaining disc at a distance from the said plug which is as large as the preinjection opening stroke of the needle.

With such an arrangement, it is possible to manufacture an inexpensive valve which requires few closely fitting parts compared with a normal injection valve; only the throttle effect in the preinjection throttle passage and the throttle effect at the opening injection orifice must be exactly proportioned relative to one another.

In another embodiment of the invention, an auxiliary pressure chamber is provided upstream of the main pressure chamber, and these pressure chambers are connected with each other via a throttle passage which is open at all times, and via a valve-controlled fuel line; and a movable valve member of the valve plunges into the auxiliary pressure chamber when the valve is opened against a closing force.

The invention will be better understood and further objects and advantages will become apparent from the ensuing detailed specification of a preferred but merely exemplary embodiment taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING

The drawing shows in axial sectional view a preferred embodiment of the fuel injection nozzle according to the invention.

DETAILED DESCRIPTION OF THE EMBODIMENT

In a nozzle head 1, a valve needle 2 having a throttle plug 3 is mounted to control an injection orifice 4 provided in a pressure chamber 5. The nozzle head 1 is clamped together with three super-imposed discs 8, 9 and 10 in a nozzle holder 7 by means of a clamp bolt 6. Disc 8 has a central bore 13 which houses a locking spring 11 and its spring seat disc 12. In disc 10, a second pressure chamber 14 is provided in the form of a central recess which is connected at its one side via channels 15 and 15a to a line 15b for supplying fuel from the fuel injection pump (not shown), while on its other side recess 14 communicates with pressure chamber 5, on the one hand, via a duct 16 in which throttle 18 is inserted, and which conveys a preliminary fuel amount to the pressure chamber 5, and, on the other hand, via a duct 17 controlled by a valve 19 and serving to convey the main fuel amount. Both ducts 16 and 17 extend through discs 8 and 9 into nozzle head 1. Throttle 18 is mounted in that part of duct 16 which extends through disc 9. Valve 9 comprises a movable valve member 22 which is displaceable for opening against the direction of fuel flow and is biassed by a closing spring 20, which is supported on the end wall of recess 14, so that valve member 22 moves into the recess 14 when opening.

When the injection pump conveys fuel to the nozzle, part of the fuel flows out of pressure chamber 14 and via throttle 18 and duct 16 into the pressure chamber 5, and causes the valve needle 2 to lift from its seat 4a by overcoming the force of the closing spring 11, whereupon preinjection commences. During this first stage of the opening stroke of the valve needle 2, the cross sectional throttling area at the injection orifice 4 is always smaller than the cross sectional area of the throttle passage 18, whereby the valve needle 2 is automatically caused to open further.

During this further opening, the upstream end of valve needle 2 penetrates through a central opening at the upstream end of nozzle head 1 and causes spring seat disc 12 to abut against a pin 21 being a down-stream extension of the movable valve member 22 and thereby lifts the valve member 22 from its seat 23a. This opens a flowpath for the major amounts of fuel via duct 17 to pressure chamber 5 from where the main fuel injection can now begin.

The small amounts of fuel penetrating into central bore 13 housing spring 11, due to leakage along valve needle 2 and pin 21, are led off via channel 23 to a fuel return pipe 23a.

Claims

What is claimed is:

1. In a fuel nozzle for an internal combustion engine, which nozzle comprises a valve needle for controlling the flow of fuel via a throttle passage to pressure chamber means for a preliminary injection out of the mouth of the nozzle and for controlling the flow of fuel via duct means to said pressure chamber means for a main injection out of the mouth of the nozzle, during the opening stroke of the valve needle,

the improvement comprising a valve means closed during rest position which valve means is mounted in said duct means and associated with said needle to be opened by said needle during the opening stroke of the latter; the free cross-sectional area of the nozzle mouth being traversed by the fuel during the preliminary injection being smaller than the cross-sectional area of said throttle passage.

2. The improvement as described in claim 1, wherein the axis of said valve along which the latter opens and closes is disposed coaxially with said valve needle.

3. The improvement as described in claim 2, wherein said valve comprises a movable valve member having a pin extending in downstream direction, a spring biassing said valve member, and a spring seat disc, the distance between the downstream end of said pin and said spring seat disc being as large as the opening stroke of said valve needle during preliminary injection.

4. The improvement as described in claim 1, wherein said pressure chamber means comprise a main chamber, and an auxiliary chamber upstream of said main chamber, and said duct means comprising a first duct from said auxiliary chamber to said main chamber, said throttle passage being located in said first duct and being open at all times, and second duct means from said auxiliary chamber to said main chamber, said valve means being interposed in said second duct.

5. The improvement as described in claim 3, wherein said movable valve member is adapted for penetrating, during opening against the force of said spring, into said auxiliary pressure chamber.