GB2024315A

GB2024315A - Fuel injection nozzle

Info

Publication number: GB2024315A
Application number: GB7912165A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1978-07-01
Filing date: 1979-04-06
Publication date: 1980-01-09

Abstract

Tension stresses in the injector body 12 in the region of the groove 24 are minimised by a ring 26 about the body, the material of the ring being under tension so that a compressive force is applied to the body. The ring may be a shrink or interference fit. Alternatively a wedge ring moved axially against a corresponding wedge on body 12 by nut 11 may be used (Fig. 3 not shown). <IMAGE>

Description

SPECIFICATION Fuel injection nozzles This invention relates to a fuel injection nozzle of the kind used for supplying fuel to a combustion space of a compression ignition engine and comprising a nozzle head formed by a stepped cylindrical body the larger end of which defines a sealing surface for engagement with a complementary sealing surface formed at one end of a nozzle body, a retaining nut engaging a step on the cylindrical body and having screw thread engagement with the nozzle body to retain said sealing surfaces in sealing engagement, a bore formed in the cylindrical body, a seating defined about the end of the bore remote from said one end of the cylindrical body and a fuel outlet from said end of the bore, a valve member slidable in the bore and shaped for co-operation with the seating to prevent flow of fuel through said outlet, a circumferential groove defined in the wall of said bore, at least one fuel inlet passage extending from said sealing surface to said groove, a clearance defined between the valve member and the wall of the bore between the groove and the seating and resilient means acting to bias the valve member into contact with the seating, fuel under pressure supplied through said passage acting on the valve member to lift the valve member from the seating thereby to allow fuel flow through said outlet.

Such nozzles are well known in the art having been widely used for many years. It has been found that when the fuel pressure is very high, for example, 21 kg/mm2 there is a tendency for fatigue cracking to occur. A crack can occurinthethin section of the cylindrical body between the fuel inlet passage and the bore, the crack starting at the end of the section forming part of the circumferential groove and proceeding along the section towards the sealing face. The risk of cracking can be minimised by moving the passage outwardly but this also requires that the circumferential groove should be deeper and it is not easy from the manufacturing point of view, to increase the depth of the groove.Analysis has also shown that further cracking may take place and extend radially outwardly from the groove at the point where the passage meets the groove. The cracking occurs because of the high tensile stress in the material forming the body in the areas mentioned when fuel under pressure is supplied to the passage.

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

According to the invention in a nozzle of the kind specified a ring is engaged about the cylindrical body, said ring being under tension when engaged with the body so as to generate a compressive stress in the cylindrical body thereby to reduce the tensile stress to which the material of the body in the region of the circumferential groove is subjected when fuel under pressure is supplied through said passage.

The example will now be described with reference to the accompanying drawings in which: Figure lisa sectional side elevation of a known form of fuel injection nozzle, Figure 2 shows one modification of part of the nozzle seen in Figure 1,and Figure 3 shows an alternative modification.

Referring to Figure 1 of the drawings, there is provided a nozzle body 10 to which is secured by means of a cap nut 11, a nozzle head comprising a stepped cylindrical body 12 in which is formed a bore 13. Slidablewithin the bore is a valve member 14 of stepped form.

The narrower portion of the valve member is shaped to co-operate with a seating 20 defined at the end of the bore remote from the nozzle body 10 and downstream of the seating the bore communicates with outlets 21. The outlets 21 constitute orifices through which liquid fuel in use, flows to a combustion chamber of an associated engine.

The opposing faces of the nozzle body 10 and the cylindrical body 12 form sealing surfaces and defined in the surface in the cylindrical body 12 is a circumferential groove 22 which communicates with a fuel inlet passage 23 formed in the nozzle body 10.

Formed in the bore 13 intermediate its ends, is a circumferential groove 24 and this is connected to the groove 22 by a passage 25. As shown only one passage 25 is provided but in practice three such passages may be provided. The cap nut 11 engages a step on the peripheral surface of the cylindrical body 12, the step occurring in the region of the circumferential groove 24.

The valve member 14 has an extension of reduced diameter which extends into one end of the chamber 17 formed in the nozzle body 10. The extension mounts a spring abutment 17a which engages one end of a coiled compression spring 16. The other end of the spring engages a further abutment 18 at the remote end of the chamber 17. Moreover, the abutment 18 is provided with a bore 19 which communicates with a fuel leakage outlet not shown.

An annular clearance is provided between the valve member 14 and the wall of the bore over that portion of the bore extending between the circumferential groove 24 and the seating 20 and in use when fuel under pressure is supplied to the circumferential groove 24 the force acting on the valve member lifts the valve member against the action of the spring 16 to permit fuel flow through the outlets 21.

As previously stated when the fuel supply pressure is extremely high, it has been found that fatigue cracking can occur in the section of the material forming the body 12, between the bore 13 and the passage 25, the crack starting at the end of the section which defines part of the circumferential groove 24. The crack can extend to the sealing surface.

Moreover, analysis indicates that cracking can also occur in a radial direction from the circumferential groove 24 the crack starting in the region where the passage 25 opens into the groove 24.

In order to minimise the risk of cracking occurring it is proposed to subject the body 12 in the region of the circumferential groove 24, to a compressive stress and this is achieved as shown in Figures 2 and 3, by means of a ring which is itself under tension when in position on the body. As shown in Figure 2, the ring 26 is of rectangular section and it is positioned in axial alignment with the circumferential groove 24. In order to provide the desired align ment, the step on the body is moved further back towards the aforesaid sealing surface. The ring 26 may be shrunk onto the body or it may be an interference fit and moved axially along the body by force applied thereto. It will be appreciated that the ring when the nozzle is assembled, is engaged by the cap nut 11.

A slightly different construction is shown in Figure 3 and in this case the ring 27 has a wedge section and the cylindrical body is tapered. As a result when the ring is moved axially compressive stress is imparted to the body again in the region of the circumferential groove 24. As with the example shown in Figure 2, the ring 27 is engaged by the cap nut and the body may be provided with a shoulder 28 to limit the extent of axial movement of the ring on the body.

When the nozzle is inserted into the engine it is the practice to clamp the nozzle by means of a clamp which is applied against the body 10 and which urges the outer end face of the cap nut into engagement with a shoulder defined in the bore in the cylinder head in which the nozzle is located. In both cases therefore the rings 26 and 27 will be subject to an axial stress but at the same time, due to the tensile stress within the rings, they can exert a compressive stress on the cylindrical body 12 in the region of the circumferential groove 24.

Claims

1. A fuel injection nozzle of the kind used for supplying fuel to a combustion space of a compression ignition engine and comprising a nozzle head formed by a stepped cylindrical body the larger end of which defines a sealing surface for engagement with a complementary sealing surface formed at one end of a nozzle body, a retaining nut engaging a step on the cylindrical body and having screw thread engagement with the nozzle body to retain said sealing surfaces in sealing engagement, a bore formed in the cylindrical body, a seating defined about the end of the bore remote from said one end of the cylindrical body and a fuel outlet from said end of the bore, a valve member slidable in the bore and shaped for co-operation with the seating to prevent flow of fuel through said outlet, a circumferential groove defined in the wall of said bore, at least one fuel inlet passage extending from said sealing surface to said groove, a clearance defined between the valve member and the wall of the bore between the groove and the seating, fuel flow through said outlet, and a ring engaged about said cylindrical body, said ring being under tension when engaged with the body so as to generate a compressive stress in the cylindrical body thereby to reduce the tensile stress to which the material of the body in the region of the circumferential groove is subjected when fuel under pressure is supplied through said passage.

2. A nozzle according to claim 1 in which said step is positioned so that the ring is axially aligned with said groove, the ring being located between the step and the retaining nut.

3. A nozzle according to claim 2 in which the ring is of rectangular section.

4. A nozzle according to claim 1 in which the cylindrical body is provided with a taper and said ring has a wedge section, said ring being engaged by the retaining nut and generating the compressive stress in the body as it is moved axially on the tapered portion of the cylindrical body.

5. A nozzle according to claim 4 including a shoulder in the cylindrical body, said shoulder acting to limit the displacement of the ring along the tapered portion of the body.

6. A fuel injection nozzle of the kind used for supplying fuel to a combustion space of a compression ignition engine substantially as described with reference to Figure 1 as modified by Figure 2 of the accompanying drawings.

7. A fuel injection nozzle of the kind used for supplying fuel to a combustion space of a compression ignition engine substantially as described with reference to Figure 1 as modified by Figure 3 of the accompanying drawings.