GB2099076A - A fuel injection nozzle for combustion engines - Google Patents

Abstract

The injection nozzle has valve needle (20) opened by fuel pressure against the direction of flow of the fuel and provided with sealing cone (22) and throttle needle (24) which projects into injection outlet (16) and bounds narrowest throttle cross- section (28) at the outlet region on its combustion chamber side. This is widened upstream towards sealing cone (22) so that throttle needle (24) has conical transition section (30), the narrowest cross-section (d) is located near to sealing cone (22). Due to this arrangement, the reduction in pressure of the fuel along the throttle gap is reduced and the fuel is introduced into the narrowest throttle cross-section (28) without any deviation losses to speak of. <IMAGE>

Description

SPECIFICATION A fuel injection nozzle for combustion engines State of the art The invention originates from an injection nozzle according to the preamble to the main claim. With such injection nozzles, the pressure drop in the fuel flow along the throttle gap is removed by the axial shortening of the narrowest throttle gap region over a partial length of the injection opening and by the widening of the throttle cross-section over the remaining length region of the injection opening so that the fuel can be injected at a higher pressure and the inclination to coking at the opening from the throttle gap on the combustion chamber side is thereby reduced.

With known injection nozzles of the above kind, (German Specification 894 789) the injection opening is made conical whereby the narrowest cross-section is located at the outlet from the injection opening on the combustion chamber side. The throttle pin likewise narrows towards the combustion chamber of the engine wherein its angle of cone is less than that of the injection opening. When the injection nozzle is closed, the throttle needle projects out of the injection opening by a distance corresponding substantially to the needle stroke so that in any position of the valve needle, the narrowest throttle cross-section at the time always remains at the outlet from the injection opening on the combustion chamber side.The pressure drop in the fuel flow along the throttle gap is of course likewise reduced with this known injection nozzle since the narrowest crosssectional region of the throttle gap is maintained axially very short and the throttle gap is widened upstream of the valve seat. However, there is the disadvantage that not only the throttle needle but also the injection outlet is made conical and requires an increased manufacturing outlay.

Furthermore, the known arrangement is restricted to those injection nozzles in which not only the pilot injection quantity but also the main injection quantity of the fuel and the injection jet shape are determined exclusively by the gap between the throttle needle and the injection outlet wall and by the formation of the parts at the particular narrowest throttle gap region.

For reducing the pressure drop in the fuel flow along the throttle gap in the injection outlet it has already been proposed with injection nozzles of the type in accordance with the preamble to make the injection outlet cylindrical and to provide the throttle needle with a transition section smaller in diameter which connects the sealing cone of the valve needle to a cylindrical flange of larger diameter at the end of the throttle needle which, in the closed position of the valve needle, closes the opening from the injection outlet on the combustion chamber side up to the narrowest cross-section of the throttle gap.With this arrangement, the throttle gap is indeed widened in the region of the weakened transition section of the throttle needle but comparatively high flow losses due to deviations and vortex formation occur at the comparatively sharp transistion from this region into the narrowest throttle gap cross section determined by the greater diameter of the flange. These flow losses compensate to some extent the reduction in pressure loss sought by the widening of the throttle gap in the region of the weakened transition section of the throttle needle.

Advantages of the invention As opposed to this, the arrangement in accordance with the invention comprising the characterising features of the main claim has the advantage that the fuel passing through the throttle gap approaches and enters the narrowest throttle gap region with the lowest possible friction losses so that the pressure loss reduction sought by the partial cross-section widening of the throttle gap is completely retained as an advantage having regard to the coking behaviour of the injection nozzle.Furthermore, due to the cylindrical formation of the injection outlet, manufacture is simplified and moreover the throttle needle can leave the injection outlet completely at the end of a first portion of the stroke during which a substantially equal or only slightly varying small quantity of fuel is injected, and completely open the injection outlet crosssection for the injection of the main quantity of the fuel.

In many cases, it can be preferable to bunch or form the injection jet to a certain extent even at the beginning of the pilot injection. A form of injection nozzle according to the features of claim 2 is proposed for this purpose.

Drawing Two embodiments of the invention are illustrated in the drawing and are described in detail in the following specification. Figure 1 shows a considerably enlarged partial longitudinal section through the first embodiment. The second embodiment is enlarged in Figure 2 and illustrated in section. Figure 3 shows the behaviour of the outlet cross-section from the injection nozzle according to Figure 2 over the stroke of the valve needle.

Description of the embodiments The injection nozzle according to Figure 1 has a nozzle body 10 which encloses a pressure chamber 12 into which the fuel can be introduced under pressure. The pressure chamber 12 is bounded downwardly by a conical valve seat 14 which continues as an injection outlet 1 6 arranged as a cylindrical bore which issues at the end wall 1 8 of the nozzle body 10 on the combustion chamber side.

A valve needle 20 is displaceably guided in the nozzle body 10 and is provided with a sealing cone 22 and is under the influence of a closure spring (not shown) which forces the sealing cone 22 against the valve seat 14 when pressure is relieved in the pressure chamber 1 2. In the region of the pressure chamber 1 2, the valve needle 20 has an exposed shoulder, known per se and therefore not illustrated, to which the fuel pressure is applied in the opening direction of the valve needle 20.

A throttle needle illustrated generally by the reference numeral 24 extends from the sealing cone 22 of the valve needle 20 and projects through the injection outlet 1 6 and in the illustrated closed position of the injection nozzle, projects beyond the end wall 18 of the nozzle body 10. The throttle needle 24 has a cylindrical section 26 with the diameter D which, with the injection nozzle closed, is located in the region of the opening from the injection outlet 1 6 and in that position bounds a narrowest throttle crosssection 28. Moreover, the cylindrical section 26 can project to some extent out of the injection outlet 1 6.

At the beginning of the injection operation, the fuel pressure in the pressure chamber 12 rises until it exceeds the opposing force of the closure spring and raises the valve needle 20 from the valve seat 14. The fuel then arrives in the throttle gap 36, 28 and from there proceeds into the combustion chamber of the engine. During a first portion of the stroke of the valve needle 20, the cylindrical section 26 on the throttle needle 24 is moved within the injection outlet 1 6 whereby the narrowest throttle cross-section 28 remains the same size, but, together with the throttle needle 24, it moves upstream with respect to the valve seat 1 4. During this first partial stroke, only a limited quantity of fuel is injected, as desired, which acts advantageously on the smooth running of the machine in the low speed range and on other criteria.During the remainder of the stroke of the valve needle 20, the cylindrical section 26 on the throttle needle 24 leaves the injection outlet 1 6 upwards whereupon the injection opening 16 is made available for the unthrottled passage of the main fuel jet.

During the first portion of the stroke of the valve needle 20, a portion of the fuel pressure reduces along the throttle gap 36, 28 whereupon the injected quantity of fuel is correspondingly reduced. Due to the widening of the throttle gap 36 in the region.

During the first portion of the stroke of the valve needle 20, a portion of the fuel pressure reduces along the throttle gap 36, 28 whereupon the injected quantity of fuel is correspondingly reduced. Due to the widening of the throttle gap 36 in the region of the conically converging transistion section 30, the reduction in the fuel pressure is, however, held within limits and due to the continuous transition towards the narrowest throttle cross-section 28 pressure losses are completely prevented due to deviations and the formation of vortices. Thus, at the narrowest throttle cross-section 28 there is still a sufficiently high fuel pressure to prevent effectively the inclination to coking-at this location.

The injection nozzle according to Figure 2 corresponds completely to the previously described injection nozzle according to Figure 1 up to the constructive feature that the cylindrical section 26' of throttle needle 24' projects slightly beyond the end wall 18 of the nozzle body 10 on the combustion chamber side in the closed position of the valve needle 20'. Thus, in the closed position, a throttle cross-section 28' is formed between the outlet edge 40 at the injection outlet 1 6 and the edge 42 on the valve needle 20' limiting the cylindrical section 26' upstream and which is slightly greater than the narrowest cross-section which is provided between the wall of the injection outlet 16 and the section 26' entering the injection outlet after a short stroke.

Due to this formation of the throttle needle 24', the behaviour of the opening cross-section A illustrated in Figure 3 and which can act positively on the combustion behaviour, is provided during the opening stroke of the valve needle 20'. Due to the throttle cross-section 28', the injection of the pre-injection quantity then takes place whereafter, during the entry of the cylindrical section 26' into the injection outlet 16, the cross-section and with it the injection quantity is reduced. When the section 26' has passed through the injection outlet 1 6 the cross-section increases once again whereupon the main injection takes place.

Claims (3)

1. A fuel injection nozzle for combustion engines, comprising a valve needle displaceably guided in a nozzle body and raisable by the fuel pressure against the direction of flow of the fuel and the force of a closure spring, from a conical valve seat which continues downstream in an injection outlet into which projects a throttle needle of the valve needle in the closed position and during a first partial stroke for producing a throttled pre-injection jet, wherein the throttle needle and the injection outlet are so formed and matched to one another that, in the closed position of the valve needle, the throttle gap at the opening from the injection outlet on the combustion chamber side has a narrowest crosssectional region which is shorter than the entire length of the throttle gap, characterised in that, in a manner known per se, the injection outlet is made cylindrical and that the section of the throttle needle bounding the narrowest crosssectional region of the throttle gap is connected to the sealing cone on the valve needle by a section converging conically upstream.

2. An injection nozzle according to claim 1, characterised in that, the section of the throttle needle bounding the narrowest cross-section of the throttle gap, has a cylindrical outer surface which projects at least to some extent out of the injection outlet in the closed position of the valve needle.

3. A fuel injection nozzle substantially as herein described with reference to Figure 1 or Figures 2 and 3 of the accompanying drawings.