GB2140080A - Compression ignition engine fuel injection nozzle - Google Patents

Abstract

A valve member 21 is biased by a spring 27 against the action of fuel under pressure supplied to an inlet 15. A further spring 29 acts in opposition to the spring 27 through a piston like push piece 34. The fuel pressure also acts upon the push piece in opposition to the force exerted by the further spring and the extent of movement of the push piece under the action of said further spring is limited. <IMAGE>

Description

SPECIFICATION Fuel injection nozzles This invention relates to fuel injection nozzles for supplying fuel to compression ignition engines the nozzles being of the kind comprising a resiliently loaded fuel pressure actuated valve member which is urged into sealing engagement with a seating by the resilient loading provided by a resilient means, and is lifted from the seating by the action of fuel under pressure supplied to an inlet, to allow fuel flow to an outlet.

Such nozzles are well known in the art. In order to improve the operation of an associated engine it is necessary to control the lift of the valve member away from its seating so that the pressure at the inlet which is required to move the valve member increases during the movement of the valve member from the seating. This can be achieved by the provision of an additional resilient means which is either effective to resist movement of the valve member after the valve member has moved a predetermined distance from the seating or alternatively is arranged to oppose the action of the first mentioned resilient means until the valve member has moved said predetermined distance.

The disadvantage of such an arrangement is that there is a sudden increase in the force acting upon the valve member after it has moved said predetermined distance and the resulting operating characteristics of the nozzle may not be ideal so far as the engine is concerned.

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

According to the invention a fuel injection nozzle of the kind specified comprises further resilient means acting on the valve member in opposition to said first mentioned resilient means, and piston means exposed to the fuel under pressure at said inlet, the force exerted by the fuel under pressure on said piston means acting to oppose the force exerted by said further resilient means, An example of a fuel injection nozzle in accordance with the invention will now be described with reference to the accompanying drawings Fig. 1 of which shows the nozzle in sectional side elevation and Fig. 2 shows to an enlarged scale, part of the nozzle of Fig. 1.

Referring to the drawing the nozzle is generally indicated at 10 being of the socalled outwardly opening type and fuel is supplied to the nozzle by means of fuel injection pump 11. The nozzle comprises a valve body 1 2 which is of generally cylindrical form and which is provided with a peripheral flange 1 3. The nozzle also includes a hollow body portion 1 4 which at one end defines a fuel inlet 1 5 which is connected to the outlet of the pump and which at its other end defines a skirt portion 16.The skirt portion engages a hollow extension 1 6A which is held in sealing engagement with the flange 1 3 by means of a cap nut 1 7 the latter being in screw thread engagement with the body portion 14 and having an aperture in its base wall through which the body 1 2 extends.

Formed in the valve body is an axial bore 1 8 which at its end adjacent the free end of the body 12, is enlarged to define a seating 1 9 of truncated conical form followed by a generally right cylindrical portion 20. Slidable in the bore 1 8 is a valve member which includes a stem 21 of smaller diameter than the bore 18. The stem has a fluted portion 22 and a cylindrical portion 23, these two portions co-operating with the wall of the bore 1 8 to guide the movement of the valve member. In addition, the valve stem carries a valve head 24 which is shaped to co-operate with the seating 1 9 and which defines an annular clearance with the cylindrical portion 20.In addition, the stem extends out of the opposite end of the bore and carries a hollow flanged spring abutment 25 which is retained relative to the stem by means of a retainer 26.

Located between the spring abutment 25 and the flange 1 3 is a first resilient means in the form of a coiled compession spring 27. The interior of the skirt is connected by passages to the inlet 1 5 and the annular clearance defined between the valve stem and the wall of the bore 1 8 communicates with the chamber which contains the spring by way of inlet openings 28 which are formed in the body 12.

The portion of the nozzle thus far described is well known in the art and in operation, when fuel under pressure is supplied to the inlet the fuel pressure acts upon the valve member to move the valve member against the action of the spring 27 and the valve head 24 is lifted from the seating 1 9 to allow fuel flow through the annular clearance defined between the valve head 24 and the cylindrical portion 20 downstream of the seating 1 9. The extent of movement of the valve member is determined by the abutment of the sleeve 25 with the body 1 2. In addition, the valve head is contoured so that the effective area of the aforesaid annular clearance varies as the valve head moves away from the seating.

The nozzle also includes a further coiled compression spring 29 and this is housed within a cylindrical chamber 30 which is defined in an insert 31 which is screwed into position in the skirt portion 16. The insert 31 is provided with passages 32 and ports 32A to permit fuel flow from the inlet 1 5 to the openings 28. The spring 29 constitutes a second or further resilient means and it engages a spring abutment 33 which is formed with an integrai push piece 34 which is slidable within a bore 35 formed in the insert.

The push piece extends into contact with the end of the stem 21 of the valve member and in the closed position of the valve member a small clearance indicated by the letter S exists between the abutment 33 and the end wall of the chamber 30. The spring 29 exerts less force upon the abutment 33 than the force exerted by the spring 27 upon the valve stem 21. The valve member can therefore assume the closed position in which it is shown, with the valve head 24 being in contact with the seating 1 9. The force exerted on the valve stem in the closed position is the difference between the forces exerted by the springs 27 and 29.

When fuel under pressure is supplied to the inlet 1 5 the force exerted by the fluid pressure lifts the valve member from the seating as described. The fuel pressure required to effect the initial movement is less than if an identical spring 27 alone acted upon the valve mem- ber. It is arranged that the spring 27 is stiffer than in a comparable nozzle not having the spring 29, so that the nozzle opening pressure is substantially the same. As the valve member lifts from its seating the spring 29 will continue to assist such movement until the abutment 33 contacts the end wall of the chamber 30. Once this has occurred the continued movement of the valve member is against the force exerted by the spring 27 and an increase in fuel pressure is required.The fuel pressure does however act upon the push piece 34 which forms a piston means to oppose the action of the spring 29 and the practical effect of this arrangement is that the sharp transition which would occur if the push piece 34 did not constitute a piston, is modified.

The preload of the spring 29 can be adjusted by moving an adjustable abutment 36 and the diameter of the push piece 34 can also be varied to adjust the force exerted against the action of the spring 29. It is arranged that the area of contact of the push piece 34 and the valve member is less than the cross-sectional area of the push piece, this conveniently being achieved by providing the valve member with a rounded end which locates in a complementary recess formed in the end face of the push piece, the area of the recess being less than the cross-sectional area of the push piece.

The charnber 30 can be vented to the fuel inlet 1 5 to enable rapid closure of the valve member to take place when the pressure at the inlet falls. The venting is achieved through a one way valve shown as being part of the abutment 36, disposed to prevent flow of fuel from the inlet into the chamber 30 but to permit fuel flow in the opposite direction.

Claims (6)

1. A fuel injection nozzle for supplying fuel to a compression ignition engine, the nozzle comprising a resiliently loaded fuel pressure actuated valve member which is urged into sealing engagement with a seating by the resilient loading provided by a resilient means and is lifted from its seating by the action of fuel under pressure supplied to an inlet to allow fuel flow to an outlet, the nozzle comprising further resilient means acting on the valve member in opposition to said first mentioned resilient means, and piston means exposed to the fuel under pressure at said inlet, the force exerted by the fuel under pressure on said piston means acting to oppose the force exerted by said further resilient means.

2. A nozzle according to Claim 1 in which said piston means forms an abutment for one end of said further resilient means.

3. A nozzle according to Claim 2 including means for limiting the movement of said piston means under the action of the further resilient means.

4. A nozzle according to Claim 2 or Claim 3 in which said piston means is movable into a chamber by the action of the fuel under pressure, and valve means for venting the interior of the chamber to said inlet.

5. A nozzle according to Claim 4 in which said valve means is located in an adjustable abutment for the other end of said further resilient means.

6. A fuel injection nozzle for supplying fuel to a compression ignition engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawing.