GB2139697A

GB2139697A - Compression ignition engine fuel injection nozzles

Info

Publication number: GB2139697A
Application number: GB08408427A
Authority: GB
Inventors: Donald Worby
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1983-05-13
Filing date: 1984-04-02
Publication date: 1984-11-14
Also published as: GB8408427D0

Abstract

A nozzle body 26 is secured to a holder 11 with a spacer member 28 therebetween, by means of a sleeve 27. The opposite ends of the sleeve have screw threads which engage complementary threads on the nozzle body and holder. The threads at the opposite ends of the sleeve can be of opposite hand or the same hand with different pitches. <IMAGE>

Description

SPECIFICATION Fuel injection nozzles This invention relates to fuel injection nozzles for supplying fuel to a compression ignition engine, the nozzle being of the kind comprising a nozzle body of generally cylindrical form, a valve member slidable within a bore in the body to control fuel flow through an outlet orifice formed in one end of the body, from a fuel supply passage which extends from the other end of the body, a nozzle holder in which is formed a fuel inlet for connection in use to the outlet of an injection pump or some other source of fuel at high pressure, a fuel passage in the holder connected with said fuel inlet and communicating with said supply passage and means for holding said nozzle body and said holder in assembled relationship.

The conventional way of securing the nozzle body to the holder is by means of a cap nut which is of cup-shaped form having an aperture in its base wall through which a reduced portion of the nozzle body can extend. The skirt portion of the cap nut is provided with internal screw threads for engagement with complementary threads on the holder.

The present trend in engine design is.to require increased injection pressures and to accommodate the increased pressures the fuel injection nozzles must be of stronger construction. At the same time however engine manufacturers do not wish to increase the space available in the cylinder head of the engine for accommodating the injection nozzles. The nozzle body in use is disposed adjacent to the combustion chamber and a substanstial portion of the overall diameter of the injection nozzle at this position, is constituted by the wall thickness of the skirt portion of the cap nut. The thickness of the cap nut must be sufficient to withstand the clamping force which in any case, is increased if the injection pressure is increased.Moreover, in order to withstand the increased fuel pressure, the wall thickness about at least the supply passage in the nozzle body must be increased.

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

According to the invention in a fuel injection nozzle of the kind specified said means comprises a sleeve member having internal screw thread formations at opposite ends thereof, said holder and nozzle body having complementary screw thread formations.

According to a further feature of the invention said screw thread formations are of opposite hand.

According to another feature of the invention said screw thread formations are of the same hand but have different pitch.

In the accompanying drawings: Figure 1 is a part sectional side elevation of a conventional form of fuel injection nozzle, Figure 2 shows one example of a fuel injection nozzle modified in accordance with.

the invention, and Figure 3 shows another example of a fuel injection nozzle modified in accordance with the invention.

Referring to Figure 1 of the drawings, the fuel injection nozzle includes a nozzle body 10 and a nozzle holder 11. The nozzle body is of stepped cylindrical form and in order to retain the nozzle body relative to the holder, a cap nut 1 2 is provided. This is of generally cup shaped form having an aperture in its base wall through which extends the reduced portion of the nozzle body. The step defined on the nozzle body engages with the base wall of the cap nut and the skirt portion of the cap nut is provided with a screw thread for engagement with a complementary screw thread formed on the periphery of the nozzle holder.

Interposed between the nozzle body and the holder is a distance member 1 3.

Formed in the nozzle body is a bore 14 having an open end presented to the distance piece 1 3 and at its other end, a seating defined about a discharge orifice 1 5. Intermediate its ends the bore is provided with an enlargement 1 6 which is in communication with one end of a supply passage 1 7 formed in the body and opening onto the face thereof presented to the distance piece. In the nozzle holder there is formed a further passage 18 which is connected to a fuel inlet on the holder and which opens onto the face of the nozzle holder presented to the distance piece 1 3. The distance piece 1 3 is provided with a connecting passage 1 9 to place the passage 18 in communication with the passage 17.

Slidable in the bore 14 is a valve member 20 which defines an annular clearance with the portion of the bore intermediate the enlargement 1 6 and the orifice 1 5. The valve member is shaped for co-operation with the seating and the main body of the valve member when in the closed position as shown, terminates short of the end of the bore adjacent the distance piece. The valve member is provided with a small extension 21 which is engaged by a spring abutment 22 located in a recess formed in the distance piece and forming an extension of a spring chamber 23 formed in the nozzle holder. The abutment 22 is engaged by a coiled compression spring 24 located in the chamber and the other end of the spring engages a further abutment 25 also accommodated in the chamber.A passage is formed in the abutment 25 for connection to a drain outlet on the nozzle holder whereby in use, the spring chamber is at a low pressure.

In operation, when fuel under pressure is admitted to the enlargement 16, a force acts upon the valve member against the action of the force exerted upon the valve member by the spring. When the force due to fuel under pressure is sufficient, the valve member is lifted from the seating to allow fuel flow through the outlet orifice 1 5, the maximum movement of the valve member being limited by its abutment with the distance piece 1 3.

When the fuel pressure supplied to the injection nozzle falls, the valve member under the action of the spring, returns to the seating to prevent further flow of fuel to the orifice 1 5.

The cap nut 1 2 provides a clamping force to ensure that there is no leakage of fuel from the passages 17, 1 8 and 1 9 at the interfaces between the distance piece 1 3 and the nozzle body 10 and the holder 11.

It will be noted that the wall thickness between the passage 1 7 and the exterior surface of the nozzle body 10 is small. If the pressure of fuel delivered to the nozzle is increased then there is the possibiiity that failure of the nozzle body in this region may occur.

Referring now to Figures 2 and 3 it will be seen that the nozzle body 26 has a larger diameter although the diameter of the reduced portion is substantiaily the same as the nozzle body of Figure 1. Increasing the diameter of the nozzle body allows the wall thickness between the passage 1 7 and the external surface of the body, to be increased. The nozzle body 26 and the holder 11 are maintained in assembled relationship by means of a sleeve.

In the example of Figure 2, the sleeve 27 on its internal peripheral surface, is provided at opposite ends respectively with thread formations for engagement with corresponding thread formations on the holder 11 and the nozzle body 26. Intermediate the thread formations the sleeve defines a plain cylindrical portion which has a sliding fit with the distance piece 28 which in this example is of right cylindrical form. The thread formations are of opposite hand so that as the sleeve is rotated in one direction with the nozzle body and the holder held against rotation, the body will move towards the holder and vice versa.

A dowel 29 is provided to secure the angular relationship between the holder, the distance piece and the nozzle body. In assembling the nozzle, the distance piece may be located by the dowel relative to the nozzle body and in facial contact therewith. The sleeve 27 is partly threaded onto the holder 11 and the nozzle body partly threaded into the sleeve.

The sleeve is then rotated while the holder and body are held against rotation. As the distance piece moves towards the holder, some slight angular movement may need to be imparted to the body to ensure that the dowel locates within the aperture provided in the holder.

In the example of Figure 3, the sleeve 30 in its internal peripheral surface, is provided at opposite ends respectively with thread formations for engagement with corresponding thread formations on the holder 11 and the nozzle body 26, the distance piece 28 is again of right cylindrical form. The thread formations are of the same hand but are of different pitch so that as the sleeve is rotated in one direction with the nozzle body and the holder held against rotation, the body will move towards the holder and vice versa. The dowel 29 is provided to secure the angular relationship between the holder, the distance piece and the nozzle body.

In the example of Figure 3 the nozzle holder 11 is provided with the coarser thread and in assembling the nozzle the sleeve 30 is first of all engaged fully with the nozzle body 26 as shown in Figure 3. The distance piece 28 together with the dowel 29, is located between the holder and the body and the dowel is made sufficiently long to allow its opposite ends to be engaged within the respective recesses in the body and holder. The sleeve is then rotated relative to the holder, distance piece and body. The sleeve is in effect unscrewed from the body but screwed onto the holder. However, because of the difference in the pitches of the thread formations the sleeve is screwed onto the holder at a greater rate than it is unscrewed from the body and as a result the holder, distance piece and body are moved into engagement. It will be understood that the threads may be left hand threads and the coarser thread may be on the body in which case assembly starts with the sleeve on the body.

The larger diameter of the nozzle body 26 also allows an increased wall thickness between the bore 14 which accommodates the valve. member and the passage 1 7 particularly in the region of the enlargement 1 6 in the bore. Moreover, because of the larger diameter of both the distance piece and the nozzle body at their contact faces, the sealing area available for sealing against fuel leakage from the passages 1 7 and 1 9 is increased.

Claims

1. A fuel injection nozzle for supplying fuel to a compression ignition engine, the nozzle being of the kind comprising a nozzle body of generally cylindrical form, a valve member slidable within a bore in the body to controi fuel flow through an outlet orifice formed in one end of the body, from a fuel supply passage which extends from the other end of the body, a nozzle holder in which is formed a fuel inlet for connection in use to the outlet of an injection pump or some other source of fuel at high pressure, a fuel passage in the holder connected with said fuel inlet and communicating with said supply passage, means for holding said nozzle body and said holder in assembled relationship, said means comprising a sleeve member having internal screw thread formations at opposite ends thereof, said holder and nozzle body having complementary screw thread formations.

2. A nozzle according to Claim 1 in which said screw thread formations are of opposite hand.

3. A nozzle according to Claim 1 in which said screw thread formations are of the same hand but have different pitch.

4. A nozzle according to any one of the preceding claims in which said nozzle includes a dowel extending between the nozzle body and the holder to maintain the angular relationship thereof.

5. A nozzle according to any one of the preceding claims including a spacer member located between the nozzle body and the holder said spacer member being of right cylindrical form, said sleeve member having a plain cylindrical portion intermediate the thread formations, said spacer member being a sliding fit with said plain cylindrical portion.

6. A fuel injection nozzle for supplying fuel to a compression ignition engine comprising the combination and arrangement of parts substantially as herein defined with reference to Figure 1 as modified by Figures 2 or 3 or the accompanying drawings.