The present invention relates to manufacture of a nozzle tip for a fuel injector such as a diesel fuel injector, and more particularly to a manufacture of a nozzle body seat in a nozzle tip.

BACKGROUND OF THE INVENTION

Known nozzle tips for fuel injectors comprise a nozzle body, and a frustoconical nozzle body seat against which a needle abuts, wherein the nozzle can be opened and closed by moving the needle towards and away from the seat, thereby to selectively allow fuel to pass the seat and enter a nozzle sac, from which the fuel is injected into a combustion chamber via one or more spray holes. Known methods of manufacturing a nozzle body seat involve the use of a grinding wheel. Due to the dimensions of the frustoconical seat and the speed of the grinding wheel, tangential speed of the grinding wheel on the seat may be low. Low tangential speeds of the grinding wheel often lead to a poor finish of the seat, i.e. the seat has a higher degree of roughness and straightness than required.

A poor surface finish of the nozzle body seat can lead to poor geometry of contact between a needle and the nozzle body seat, and thereby a reduction in the performance of the injector.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of manufacturing a nozzle tip which at least mitigates the problems encountered with nozzle body seats of known embodiments. Accordingly the present invention provides, in a first aspect, a pin for use in a process for honing a seat of a nozzle body tip, according to claim 1.

In one embodiment of the present invention, the end portion of the pin is frustoconical, and the flatted sections each comprise a flat which extends axially partially along the main shaft portion and partially into the end portion;

and wherein a maximum diameter of the end portion is less than a maximum diameter of the shaft portion and wherein the at least one shoulder comprises shoulders formed by junctions, at the non-flatted sections, of the main shaft portion and the end portion.

In an alternative embodiment, the flatted sections are provided by a slot provided in the end portion;

and the end portion comprises a first frustoconical section, a second frustoconical section, further away from the main shaft portion than the first frustoconical section, and an intermediate section, between the first frustoconical section and the second frustoconical section;

wherein the first frustoconical section and the second frustoconical section decrease in diameter moving away from the main shaft portion, and wherein the intermediate section is of a constant diameter equal to a minimum diameter of the first frustoconical section and a maximum diameter of the second frustoconical section;

and wherein the at least one shoulder is formed by the intermediate section.

Preferably, the pin is formed of an erosion-resistant material.

In a further aspect, the present invention comprises an assembly comprising the pin of claim 1, and a nozzle body tip comprising a nozzle body; wherein the pin is located within the nozzle body such that a peripheral edge of each shoulder abuts a seat of the nozzle body, and wherein an annular frustoconical channel is formed between the pin end portion and the seat. In the above assembly, the peripheral edges of the pin may abut the seat of the nozzle body at a maximum diameter of the seat, or at a minimum diameter of the seat. In one embodiment, an outer surface of the end section of the pin may be at an angle relative to a longitudinal axis of the pin, said angle being substantially the same as an angle at which the nozzle body seat is to a longitudinal axis of the nozzle tip which is coincident with the longitudinal axis of the pin, such that there is a constant separation between the nozzle body seat and the outer surface of the end portion.

In the alternative embodiment above, an outer surface of the first frustoconical section may be at an angle relative the a longitudinal axis of the pin, said angle being substantially the same as an angle at which the nozzle body seat is to a longitudinal axis of the nozzle tip which is coincident with the longitudinal axis of the pin, such that there is a constant separation between the nozzle body seat and the outer surface of the first section of the pin.

In a further aspect, the present invention comprises a method of honing a seat of a nozzle tip, the nozzle tip comprising a nozzle body provided with a bore, a sac, and a frustoconical portion located between the bore and the sac;

wherein the seat comprises a surface of the frustoconical portion;

the method comprising steps of:

inserting a pin as described above into the bore of the nozzle tip until a peripheral edge of the or each shoulders abuts the surface of the frustoconical section of the nozzle tip;

inserting abrasive fluid into the bore of the nozzle body from an end remote from the sac;

wherein the abutment of the peripheral edges of the shoulders of the pin with the surface of the frustoconical section forms a restriction which prevents the abrasive fluid from flowing from the bore into the sac at the non- flatted sections; and wherein a flow of abrasive fluid through a channel formed between the pin and the nozzle body acts to erode the surface of the seat; wherein the abrasive fluid subsequently flows into the sac at the flatted sections;

and wherein abrasive fluid flowing into the sac is subsequently evacuated from the sac via one or more spray holes provided through the nozzle body.

In a further alternative embodiment, the present invention comprises a pin for use in a process for honing a seat of a nozzle tip;

the pin comprising a main body portion and a valve portion, the valve portion comprising a first section, and a second, extending section, wherein the extending section of the valve portion is located within a bore defined by an inner wall of the main body portion,

wherein an outer surface of the main body portion and an outer surface of first section of the valve potion are frustoconical;

and wherein a void is provided between the extending section of the valve portion and the inner wall of the main body portion;

and wherein an annular channel, provided between the main body portion and the first section of the valve potion provides a fluid communication between the void and the frustoconical outer surfaces of the main body portion and the first section of the valve portion.

The valve portion may be fixedly located with respect to the main body portion or the valve portion may be moveable with respect to the main body portion. The present invention also comprises an assembly comprising the alternative pin as described above and a nozzle body tip comprising a nozzle body;

wherein the pin is located within the nozzle body, and wherein a maximum diameter section of the main body portion of the pin abuts a minimum diameter section of a seat of the nozzle body;

and wherein an annular frustoconical channel is formed between the pin and the seat. The invention also includes a method of honing a seat of a nozzle tip comprising a nozzle body provided with a bore, a sac, and a frustocomcal section located between the bore and the sac;

wherein the seat comprises a surface of the frustocomcal section;

the method comprising steps of:

inserting the alternative pin as described above into the bore of the nozzle body until a maximum diameter section of the main body portion of the pin abuts a minimum diameter section of the seat;

inserting abrasive fluid into the void;

wherein abrasive fluid flows from the void into a tapered frustocomcal annular channel between the pin and the seat;

wherein the abrasive fluid subsequently flows into the sac;

and wherein abrasive fluid flowing into the sac is subsequently evacuated from the sac via one or more spray holes provided through the nozzle body.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is a partially cross-sectional view of an assembly in accordance with a first embodiment of the present invention; Figure 2 is a detailed partial view of the assembly of Figure 1;

Figure 3 is a partial view of the pin of the assembly of Figure 1 ;

Figure 4 is a partially cross-sectional view of an assembly in accordance with a second embodiment of the present invention; Figure 5 is a cross-sectional view of an assembly in accordance with a third embodiment of the present invention; and

Figure 6 is a detailed view of the assembly of Figure 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 illustrates a step of a manufacturing process in accordance with the present invention. An assembly 2, comprises a nozzle tip and a pin 20. The nozzle tip comprises a nozzle body 4 provided with a bore 6, a nozzle sac 8, and spray holes 50. Between the nozzle bore 6 and the sac 8 is provided a frustoconical portion 10. Part of the frustoconical portion 10 forms a nozzle body seat 14, i.e. a surface against which a frustoconical portion of a needle will contact in a closed position after the nozzle has been fully assembled.

The nozzle body 4, sac 8 and spray holes 50 are each formed in a known manner.

Prior to a method step of calibrating the spray holes 50, the pin 20, formed of an erosion-resistant material, is inserted into the bore 6 of the nozzle body 4. The pin 20 comprises a main shaft portion 22, and an end portion 24. The end portion 24 is frustoconical, and has an external diameter which decreases moving away from the main shaft portion 22, to a minimum diameter at an end 42 remote from the main shaft portion 22. An outer surface 26 of the end portion 24 has an angle relative to a longitudinal axis A of the pin 20, which is substantially the same as the angle of the nozzle body seat 14 relative to a longitudinal axis B of the nozzle body 2, wherein axes A, B are coincident. In other words, the angle of the outer surface 26 of the pin end portion 24 is the same as, or within a few degrees of, the angle of the nozzle body seat 14. The pin 20 is provided with at least one flatted section 28, each comprising a flat 30 which extends partially axially along the main shaft portion 22, and partially into the end portion 24. Between each flatted section 28 is provided a non-flatted section 32.

At the non- flatted sections 32, the main shaft portion 22 and the end 24 portion meet at a junction 34. At the junction 34, the main shaft portion 22 and the end portion 24 are offset slightly from one another (the offset is indicated at 18 in Figure 3), i.e. the maximum diameter of the end portion 24 is slightly less than the maximum diameter of the shaft portion 22, such that a shoulder 36 (see Figure 3) is formed at the junction 34.

The pin 20 is inserted into the nozzle body bore 6, end portion 24 first. The pin 20 is inserted until a peripheral edge 38 (Figure 3) of each of the shoulders 36 of the non-flatted sections 32 abut an area of the nozzle body seat 14 having the highest diameter.

During the honing process, abrasive fluid is inserted into the bore 6 of the nozzle body 4 from an end remote the nozzle sac 8, (i.e. from the top in the orientation of Figure 1).

The abutment of the peripheral edges 38 of the shoulders 36 of the non- flatted sections 32 of the pin 20 with the nozzle body seat 14 form a restriction, such that at these points, abrasive fluid cannot flow from the nozzle bore 6 to the nozzle body seat 14. The flats 30 provide non-restricted areas, i.e. at the flatted sections 28, abrasive fluid is permitted to flow to the nozzle body seat 14.

Due to the offset between the main shaft portion 22 and the end portion 24 of the pin 20, a frustoconical annual channel 40 (indicated on Figure 2), is provided between the outer surface 26 of the end portion 24, and the nozzle body seat 14. Abrasive fluid flows through the channel 40, into the nozzle sac 8, from where it is subsequently evacuated from the nozzle tip 2 through the spray holes 50. As the angle of the outer surface 26 of the pin end section 24 to the pin longitudinal axis A is substantially the same as the angle of the nozzle body seat 14 to the pin longitudinal axis A, there is a constant separation between the nozzle body seat 14 and the outer surface 26 of the end portion 24.

The channel 40 acts as a restriction; the flow speed of the abrasive fluid flowing through the channel 40 therefore acts to hone the nozzle body seat 14, i.e. to erode the surface of the nozzle body seat 14 thereby reducing the roughness of the surface. The surface finish of the surface of the nozzle body seat 14 is thereby improved.

As the pin 20 is formed of an erosion-resistant material, the abrasive fluid does not erode the pin 20.

Second and third alternative embodiments of the present invention are illustrated in Figures 4 and 5. Like features are numbered according to the first embodiment above. Referring to Figure 4, the alternative restrictive pin 220 of the second embodiment is illustrated as part of an assembly 202. The pin 220 comprises a main, cylindrical shaft portion 222 of substantially uniform cross-sectional area, and an end portion 224. The end portion 224 comprises a frustoconical first section 260, adjacent the cylindrical section 222, a frustoconical second section 264, remote from the main shaft portion 222, and an intermediate section 262, between the first and second sections 260, 264. The first section 260 of the end portion 224 of the pin 220 decreases in diameter moving away from the main shaft portion 222, to a minimum diameter adjacent the intermediate section 262. The intermediate section 262 is of a constant diameter, which is equal to the minimum diameter of the first section 260. The second section 264 decreases from a minimum diameter adjacent the intermediate section 262, which is equal to the diameter of the intermediate section 262, to a minimum diameter at an end 242 remote from the intermediate section 262.

Due to the above construction, the intermediate section 262 forms shoulders, in a similar manner to the first embodiment.

The end portion 224 of the pin 220 is provided with a slot 266, extending into the pin 220 along the longitudinal axis A of the pin 220. The slot 266 extends fully through the second section 264 and the intermediate section 262, and partially into the first section 260 of the end portion 224.

The slot 266 extends radially across the pin 220 such that the sides of the slot form flatted sections, in a similar manner to those of the first pin embodiment. Accordingly, the pin 220 is provided with two flatted sections, where the slot 266 is provided at either side of the pin 220, and with non- flatted sections, around the remainder of the end portion 224. Peripheral edges 238 are provided at a junction of the second portion 264 and the intermediate portion 262 in the non-flatted section, i.e. either side of the slot 266.

The pin 220 is inserted into the nozzle body bore 6, end portion 224 first. The pin 220 is inserted until the peripheral edges 238 abut an area of the nozzle body seat 14 having the smallest diameter.

In a similar manner to the first embodiment, during the honing process, abrasive fluid is inserted into the bore 6 of the nozzle body 4 from an end remote the nozzle sac 8.

Due to the offset between the first section 260 and the second section 264 which is provided by intermediate section 262, a frustoconical annual channel 240 is provided between the outer surface 226 of the first section 260, and the nozzle body seat 14.

Abrasive fluid is free to flow into the channel 240 formed between the pin 220 and the nozzle body seat 14, thereby honing the nozzle body seat in the same manner as the first embodiment.

The abutment of the peripheral edges 238 with the smallest-diameter section of the nozzle body seat 14 causes a restriction, such that abrasive fluid cannot exit the channel 240 at these points. However, the flatted portions formed at the sides of the slot 266, allow abrasive fluid to flow from the channel 240 into the nozzle sac 8, from where it is subsequently evacuated from the nozzle tip 2 through the spray holes 50. As the angle of the outer surface 226 of the first section 260 of the end portion 224 to the longitudinal axis A of the pin is substantially the same as the angle of the nozzle body seat 14 to the longitudinal axis B of the nozzle tip (axes A and B again being coincident), there is a constant separation between the nozzle body seat 14 and the outer surface 226 of the first section 260 of the pin 220.

Referring to Figures 5 and 6, an alternative restrictive pin 320 in accordance with a third embodiment of the present invention, as part of an assembly 302, comprises a main body portion 370, which comprises a frustoconical outer surface, and a valve portion comprising an outward valve 372. The valve 372 comprises a first section 376 having a frustoconical outer surface 378, and a second, extending section 380, which extends away from the first section 376 in axis A,B. The pin 320 is assembled such that the second, extending section 380 of the valve 372, is located within a bore 374 of the main body portion 370 defined by an inner wall 394. The valve 372 may be located moveably or fixedly located with respect to the main body portion 370. The pin 320 is inserted into the bore of the nozzle body 4, until a maximum diameter section of the main body portion 370 abuts a minimum diameter section of the seat 14.

To effect a honing operation, abrasive fluid is inserted into the bore of the pin 320,370, and flows into an annular void 390 provided between the inner wall 394 of the main body portion 370, and the extending section 380 of the valve 372, From the void 390, abrasive fluid exits the pin 320 via an annular channel 392, provided between the main body 370 and the valve 372, wherein the channel 392 communicates the void 390 with the nozzle body seat 14.

Abrasive fluid flowing over the nozzle body seat 14, i.e. in a frustoconical channel 340 between the nozzle body seat 14 and pin 320, (i.e. between the nozzle body seat 14 and the outer surface 396 of the main body portion 370, and between the nozzle body seat 14 and the outer surface 378 of the vale portion 376).

the frustoconical outer surface 378 of the first section 376 of the valve 372, erodes the surface of the seat 14 in the same manner as the first and second embodiments. Abrasive fluid subsequently flows into the sac 8 and is evacuated via spray holes 50 in the same manner as the first and second embodiments.

The angle of the frustoconical outer surface 378 of the first section 376 of the valve 372 to the pin longitudinal axis A is slightly higher than that of the nozzle body seat 14, such that the channel formed 340 between the frustoconical outer surface 378 of the valve first section 376 and the nozzle body seat tapers, from a maximum width closest to the sac 8, to a minimum width furthest away from the sac 8.

The angle of the frustoconical outer surface 378 of the valve first section 376, and therefore the geometry of the channel 340, is selected to optimise honing of the nozzle body seat 14. The present invention provides an assembly for, and a method of, manufacturing a fuel injector nozzle tip. By the present invention, the prior art problems of high roughness and straightness of the nozzle body seat are solved by using an additional honing process, using a flatted pin to enable abrasive fluid to improve the surface finish of the surface of the nozzle body seat, i.e. to significantly decrease the roughness of the nozzle body seat.

The present invention provides an improved surface finish of nozzle body seat compared to prior art methods wherein only a grinding operation is used to machine the nozzle body seat. The present invention therefore enables manufacture of a nozzle body seat which is less rough than prior art embodiments, therefore leading an improved geometry of contact between a needle and the nozzle body seat, lower wear of any coating on the needle, and lower Minimum Drive Pulse (MDP) of the injector to open and inject the fluid) after the first injection test cycle.

REFERENCES

nozzle tip 2

nozzle body 4

bore 6

sac 8

frustoconical portion 10

nozzle body seat 14

offset 18

restrictive pin 20

pin main shaft portion 22

pin end portion 24

end portion outer surface 26

flatted section 28

flat 30

non-flatted section 32

junction 34

shoulder 36

shoulder peripheral edge 38

frustoconical annual channel 40 end of end portion 42

spray holes 50

pin longitudinal axis A

the nozzle longitudinal axis B Second embodiment:

pin 220

pin main, cylindrical shaft portion 222 pin end portion 224

end portion first section outer surface 226 peripheral edges 238

frustoconical annual channel 240 end of end portion 242

end portion first section 260 end portion intermediate section 262

end portion second section 264

end portion slot 266 Third embodiment:

pin 320

frustoconical annual channel 340

pin main body portion 370

pin valve portion / outward valve 372 main body portion bore 374

valve first section 376

valve first section frustoconical outer surface 378 valve second, extending section 380

void 390

annular channel 392

pin main body inner wall 394

main body portion outer wall 396