GB2223270A

GB2223270A - I.C. engine fuel infection nozzle

Info

Publication number: GB2223270A
Application number: GB8817800A
Authority: GB
Inventors: Geoffrey Carpenter
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1988-07-26
Filing date: 1988-07-26
Publication date: 1990-04-04
Also published as: GB8817800D0

Abstract

The entrances to the spray holes 14 are formed in a conical or frusto-conical internal wall 10 of the sac 13 which is displaced axially from the frusto-conical valve seat 9. The semi-vertical angle of the wall 10 is at least as large as that of the seat 9. The valve member 5 is spaced from the wall 10 in all positions and the wall thickness in the region of the wall can be chosen to provide the required length for the spray holes without prejudicing the strength of the injection nozzle body in the region of the valve seat line. <IMAGE>

Description

FUEL INJECTION NOZZLES FOR INTERNAL COMBUSTION ENGINES This invention relates to fuel injection nozzles for internal combustion engines.

According to the present invention, there is provided a fuel injection nozzle comprising a valve member having a tapered end which is biased to seat on a frusto-conical seating surface in an injection nozzle body at the entry to a sac at the end of the nozzle body, the sac being formed with one or more outlet spray holes, wherein the entry to each spray hole is formed in a further, conical or frusto-conical surface forming an internal wall of the sac, the said further surface being displaced from the first mentioned conical surface in the direction axially towards the vertex thereof, the semi-vertical angle of the additional surface being not less than that of the first mentioned frusto conical surface, the said second surface being spaced from the tip of the valve member in the fully closed position of the latter.

The semi-vertical angle of a conical or frusto-conical surface is the angle subtended between any generator line on the surface and the axis of the surface. The semi-vertical angle is thus one-half of the included angle, at the vertex of the surface, between two diametrically opposite generators of the surface.

With this construction, the portion of the nozzle body formed with the spray holes can be well spaced from the seat-line on which the valve member seats on the valve body, thereby avoiding the risk of fracture around the spray holes as the result of repeated impacts between the valve member and its seat. Further, the wall thickness of the body in the region presenting the said second surface can be chosen to provide the desired length for the spray holes (in accordance with the fuel-spray penetration required for the combustion chamber) without prejudicing the wall thickness of the injection nozzle' body in the region of the valve seat line. At the same time, the volume enclosed between the said second surface and the valve member tip can be sufficiently small to minimize the residue of fuel remaining in the sac below the seat line after the valve has seated.Where the volume of the residue is substantial, there is a tendency for it to enter the combustion chamber in an uncontrolled manner as a result of the high combustion pressures and temperatures during a combustion phase, with the result that the residual fuel does not burn completely and can be exhausted through the exhaust port as unburnt or partially burnt hydrocarbons, resulting in pollution problems. In the construction provided by the invention, the tip of the valve member in the closed position masks the entry to the or each spray hole thereby restricting access between the residual fuel space and the combustion chamber.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which the single figure is an axial sectional view of the tip portion of a fuel injection nozzle.

The tip portion of the fuel injector nozzle shown in the drawing comprises a hollow injection nozzle body 1 having a tubular portion 2 terminating at its outlet end in a generally conical tip portion 3, and a valve member 4 formed by a cylindrical rod 5 having a tapered end portion defined by a frusto conical surface 6 and a conical tip surface 7 the semi-vertical angle of which is greater than that of the surface 6 so that a convex circular seating line 8 is defined at the junction of the surfaces 6 and 7 for engagement with a frusto conical seating surface 9 in the nozzle tip 3.The semi-vertical angle x of the frusto conical surface 9 is slightly less than that 2 of the conical tip surface 7 of the valve member 4 (by between a half and one degree) so that at the end of a closing movement of the valve member 4 onto its seat 9, the liquid fuel between the surfaces 7 and 9 exerts a damping or dashpot effect.

Beyond the frusto conical seating surface 9, the end portion of the inner wall surface of the tip 3 is defined by a further frusto conical wall surface 10 which is connected to the surface 9 by a short cylindrical step 11 and at its narrower end merges into a short counter bore 12 which is required to facilitate the formation of the other surfaces in the tip 3 during manufacture.

The end portion of the nozzle tip 3 which is formed with the surfaces 10 and 12 forms a nozzle sac 13 formed with the required number of spray nozzles 14. As the result of the step 11, a wall thickness of the sac 13 is less than that of the base of the tip 3 in the region of the surface 9. Thus, the wall thickness of the sac 13 can be chosen to provide the desired length for the spray orifaces 14 without compromising the ability of the base portion of the tip 3 formed with the surface 9 to withstand the repeated closing shocks applied to it by the valve member 4 under its powerful closing spring at the termination of any injection pulse.

The difference between the semi-vertical angles of the surfaces 7 and 9 has been exagerated in the drawing for reasons of clarity. Thus, in practice, the tip of the valve member will extend further into the sac chamber 15 than is shown in the drawing, thereby reducing still further the volume of residual fuel in the chamber 15 at the termination of an injection pulse while at the same time masking the entries to the spray nozzles 14. As shown in the drawing, the semi-vertical angles of the surfaces 10 and 9 are equal but by increasing somewhat the semi-vertical angle of the surface 10, the residual volume of fuel is further reduced provided, of course, that there is always adequate clearance between the tip of the valve member 4 and the surface 10.

Claims

1. A fuel injection nozzle comprising a valve member having a tapered end which is biased to seat on a frusto-conical seating surface in an injection nozzle body at the entry to a sac at the end of the nozzle body, the sac being formed with one or more outlet spray holes, wherein the entry to each spray hole is formed in a further conical or frusto-conical surface forming an internal wall of the sac, the said further surface being displaced from the frusto-conical seating surface in the direction axially away from the valve member, the semi-vertical angle of the further surface being not less than that of the frusto-conical seating surface, the said further surface being spaced from the tapered end of the valve member in the fully closed position of the latter.

2. A fuel injection nozzle according to claim 1 in which the portion of the internal wall of the sac between the frusto-conical seating surface and the said further conical or frusto-conical surface is defined by a substantially cylindrical surface.

3. A fuel injection nozzle according to claim 1 or 2 in which the entrances to the outlet spray holes are covered and substantially closed by the tapered end of the valve member in the fully closed position thereof.

4. A fuel injection nozzle according to claim 1,2 or 3, in which the wall of the sac bounded internally by the seating surface is thicker than the wall of the sac bounded internally by the further conical or frusto-conical surface and through which one or more outlet spray holes pass.

5. A fuel injection nozzle substantially as described herein with reference to the drawing.