GB2255802A - Pintle fuel injection nozzle. - Google Patents

Abstract

A valve member has a projection which includes a cylindrical portion 17, and a tapered portion 18A of conical or frusto conical form. The cylindrical portion 17 of the projection in the closed position of the valve member extends with clearance within an outlet opening 13B. intermediate the opening 13B and the seating 12 is a stepped portion 13A which forms part of the opening and the edge of the step 20 so formed together with the surface of the tapered portion 18A acts to control the flow of fuel through the opening as the cylindrical portion 17 leaves the opening 13B during the opening movement of the valve member. <IMAGE>

Description

FUEL INJECTION NOZZLE This invention relates to a pintle type fuel injection nozzle for supplying fuel to an internal combustion engine, the nozzle comprising a nozzle body in which there is defined a guide bore, a frusto-conical seating defined in the bore, a valve member slidable in the bore and having a frusto-conical portion for engagement with the seating, the corn angle of the frusto-conical portion being slightly greater than that of the seating, the valve member defining a surface against which fuel under pressure can act to lift the valve member from the seating, an outlet opening positioned downstream of the seating and through which fuel can flow when the valve member is lifted from the seating and a projection on the valve member which extends within said opening, the projection being shaped to modify the flow of fuel through the outlet opening depending upon the axial position of the valve member.

In a typical pintle nozzle the projection has a cylindrical portion adjacent the main portion of the valve member and a tapered portion at its end remote from the valve member, the tapered portion being of conical or frusto-conical form. Moreover, the seating leads directly into the outlet opening which is of cylindrical form and of a diameter slightly larger than the cylindrical portion of the projection to form an annular clearance. In operation, as the valve member is lifted from the seating the control of the flow of fuel through the outlet opening is initially determined by the clearance between the valve member and the seating but quickly as the valve member continues to open, passes to the aforesaid clearance.As the cylindrical portion of the valve member leaves the opening control of the flow of fuel passes to the gap which exists between the junction of the seating and the opening and the conical surface of the conical or frusto-conical portion of the projection. The flow of fuel which when controlled by the clearance is at a low but gradually increasing rate, increases substantially as the aforesaid gap assumes control. For certain engine applications it is required that the rate of increase of the fuel flow when the gap assumes control should be increased and the transition therebetween should be sharper. Some increase in the rate of flow of fuel can be effected by increasing the cone angle of the conical surface.However, the extent of increase is limited by virtue of the fact that the "gap" becomes the gap existing between the junction of the cylindrical and conical portions of the projection and the seating. Instead of altering the cone angle on the portion of the projection, it is possible at least in theory, to increase the cone angle of the seating.

However, this is undesirable because the existing seat angle is chosen for its sealing performance and also its life.

The object of the present invention is to provide a fuel injection nozzle of the kind specified in a simple and convenient form.

According to the invention in a fuel injection nozzle of the kind specified the projection defines a plane cylindrical portion adjacent the main body of the valve member and a tapered portion of conical or frustoconical form at its end remote from the main body of the valve member, and the opening is of stepped cylindrical form with the wider end being adjacent the seating, and the narrower end having a slightly larger diameter than the plane.cylindrical portion of the projection whereby during opening of the valve member the gap between the step defined in the opening and said tapered portion acts to control flow through the outlet opening when the plane cylindrical portion has moved out of the narrower end of the opening.

In the accompanying drawings: Figure 1 shows a known form of pintle fuel injection nozzle, Figure 2 illustrates the flow of fuel through the outlet opening of the nozzle of the example of Figure 1, with increasing movement of the valve member away from its seating, Figure 3 is a view similar to Figure 1 showing the modification in accordance with the invention, and Figure 4 corresponds to Figure 2 in relation to the nozzle shown in Figure 3.

Referring to Figure 1 of the drawings the nozzle includes a nozzle body part of which is seen at 10, the body defining a cylindrical guide bore 11 at the end of which is formed a seating 12 of frusto-conical form. The seating leads into a cylindrical outlet opening 13.

Slidable in the bore is a valve member 14 which adjacent the seating is of reduced diameter to define a space 15 which extends from a fuel supply gallery communicating with a high pressure fuel inlet connected in use to a fuel injection pump. The valve member has a frustoconical portion for cooperation with the seating in the usual manner and it has a projection 16 including a plane cylindrical portion 17 adjacent the valve member, a tapered portion 18 of frusto-conical form and a tapered peg 19. The cone angle of the portion 9 is slightly greater than that of the seating 12 and the cylindrical portion 17 is slightly smaller in diameter than the outlet opening 13. The valve member is shown in Figure 1 lifted from the seating so that fuel can flow though the outlet from the space 15.The valve member in use, is biased to the closed position by means of a spring and it defines a surface against which the fuel pressure in the space 15 can act to lift the valve member against the action of its spring.

In the closed position of the valve member the plane cylindrical portion 17 of the projection will lie within the outlet opening 13. The cylindrical portion of the projection 17 being slightly smaller in diameter than the outlet opening forms an annular clearance and when the valve member starts to move away from the seating the initial flow of fuel through the outlet opening is controlled by the gap between the seating and the shaped end of the valve member. As the valve member continues to move away from the seating control of the fuel flow through the opening passes to the aforesaid clearance which as the valve member further moves away from the seating will reduce in length so that an increased flow of fuel will take place. Nevertheless, the flow of fuel is at a comparatively restricted rate. When the cylindrical portion 17 of the projection leaves the outlet opening 13, the flow of fuel increases substantially and the flow of fuel is controlled by the gap which exists between the junction of the seating 12 and the outlet opening 13 and the surface of the conical or frusto-conical portion 18. The gap is indicated at A in Figure 1 and the gap will increase as the valve member moves away from the seating.

Figure 2 shows how the flow of fuel through the outlet opening varied with the movement of the valve member away from the seating. The initial portion shows a comparatively high rate of increase of flow with increasing lift, this being due to the gap between the seating 12 and the shaped end of the valve member. As will be seen from Figure 2 there follows a fairly flat intermediate portion in which the flow is determined by the aforesaid clearance and then the final portion is determined by the aforesaid gap A with a relatively smooth transition between the control of the flow by the clearance and the control of the flow by the gap.

As mentioned above, in order to increase the rate of increase of fuel flow it is'possible to increase the cone angle of the conical or frusto-conical portion 18 of the projection however, the improvement which can be obtained is limited and the practical effect will be for the "gap" to be defined by the gap indicated at B in Figure 1 that is to say between the junction of the plane cylindrical portion 17 and the tapered portion 18 of the valve member and the seating 12.

Figure 3 illustrates the modification and essentially this comprises increasing the cone angle of the tapered portion 18A of the valve member and forming the outlet opening to stepped cylindrical form with the wider portion 13A being adjacent the valve member and the narrower portion 13B having a diameter generally corresponding to the diameter of the outlet opening 13 of the example shown in Figure 1. The step 20 is generally at right angles.

Figure 4 shows the effect produced by the provision of the step 20. Assuming that the valve member is in the closed position the shapes of the initial and intermediate portions of the flow diagram are substantially the same as is shown in Figure 2 however, when the cylindrical portion 17 of the valve member moves out of the portion 13B of the outlet opening, there is a sharp transition and a rapid increase in the rate of flow of fuel through the outlet opening as control passes to the gap A. If the diameter of the wider portion 13A of the outlet opening is sufficiently great the control of the flow will remain with the gap A during the allowed movement of the valve member. If the diameter of the wider position is reduced control can pass from the gap A to the gap B thereby producing a slower rate of increase as shown at B in Figure 4 followed by a higher rate of increase as shown at C in Figure 4, due to the gap C. If the axial length of the wider portion 13A of the outlet opening is reduced it is possible to arrange for control of the fuel flow to pass directly from gap A to gap C.

Claims (2)

1. A pintle type fuel injection nozzle for supplying fuel to an internal combustion engine comprising a nozzle body in which there is defined a guide bore, a frustoconical seating defined in the bore, a valve member slidable in the bore and having a frusto-conical portion for engagement with the seating, the cone angle of the frusto-conical portion being slightly greater than that of the seating, the valve member defining a surface against which fuel under pressure can act to lift'lithe valve member from the seating, an outlet opening positioned downstream of the seating and through which fuel can flow when the valve member is lifted from the seating and a projection on the valve member which extends within said opening, the projection being shaped to modify the flow of fuel through the outlet opening depending upon the axial position of the valve member, the projection defining a plane cylindrical portion adjacent the main body of the valve member and a tapered portion of conical or frusto-conical form at its end remote from the main body of the valve member, and the opening is of stepped cylindrical form with the wider end being adjacent the seating, and the narrower end having a slightly larger diameter than the plane cylindrical portion of the projection whereby during opening of the valve member the gap between the step defined in the opening and said tapered portion acts to control flow through the outlet opening when the plane cylindrical portion has moved out of the narrower end of the opening.

2. A pintle type fuel injection nozzle substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings.