GB2255589A - I.c engine fuel injector. - Google Patents

Abstract

The nozzle body (10) is mounted at the end of an elongated body 22 on the end of which open two fuel supply passages 37, 38. The passages connect with a fuel supply gallery 14 in the nozzle body and the passage 38 contains a restrictor 39A. Also provided is a bypass valve body 25 which locates against the body 22 and it has a passage 39 which connects the passage 38 to a fuel inlet 27. It also 28 houses a pressure responsive valve member 29 which after a predetermined movement under the action of the fuel pressure at the fuel inlet 27 connects the unrestricted passage 37 with the fuel inlet. <IMAGE>

Description

FUEL INJECTOR This invention relates to a fuel injector for supplying fuel to an internal combustion engine and of the kind comprising a nozzle body containing a fuel pressure actuated valve member for controlling the flow of fuel through an outlet orifice, an elongated body to which the nozzle body is secured with a distance piece interposed therebetween, a fuel supply passage extending through the bodies and the distance piece and through which fuel under pressure can be supplied to a fuel supply gallery surrounding a part of the valve member, a spring chamber defined in said elongated body, a coiled compression spring located in said chamber and a spring abutment engaged with said spring and with said valve member whereby the force exerted by the spring opposes movement of the valve member by fuel under pressure.

Such injectors are well known in the art and it is also known to arrange for the injector to supply the initial flow of fuel at a restricted rate. One way of achieving this object is to provide two springs with one spring arranged to provide permanent bias to the valve member and the other spring biasing the valve member only after a predetermined movement thereof. This arrangement has the disadvantage that clamping loads can upset the careful adjustment of the injector and also that any carbon/fuel lacquer deposits in and on the nozzle body can alter the degree of restriction imposed to the flow of fuel during the life of the injector. Another way of achieving the object is to supply fuel initially to the aforesaid fuel supply gallery by way of a restrictor and then to bypass the restrictor using a suitable valve, to allow unrestricted flow of fuel to the gallery.The valve may be responsive to the pressure drop across the restrictor or it may be responsive to the pressure downstream of the restrictor. In the former case the restrictor may be formed in a spring loaded piston member which is moved away from a seating to allow unrestricted fuel flow. In the latter case it is known to use the valve member as the pressure responsive component and to use the movement of the valve member to unseat a bypass valve. The known designs are relatively complex and are not easy to calibrate.

The object of the present invention is to provide an injector of the kind specified in a simple and convenient form.

According to the invention a fuel injector of the kind specified comprises a further fuel supply passage extending through the bodies and the distance piece, a restrictor formed in said further fuel supply passage, the fuel supply passages terminating in the end surface of the elongated body remote from the nozzle body, a bypass valve body located against said end surface, a blind axial bore formed in the bypass valve body and extending from the end thereof located against said surface, a seating defined at the blind end of the bore, a first passage extending from the seating and communicating with a fuel inlet, a second passage in the bypass valve body for placing said further fuel supply passage in communication with said fuel inlet, a third passage in the bypass valve body, said third passage communicating with said first mentioned fuel supply passage and opening into said bore intermediate the ends thereof, a valve member slidable in said bore, a spring biasing the valve member into contact with the seating defined in the bore, the spring being located within a spring chamber defined in said elongated body, the valve member being movable away from the seating by the pressure of fuel at the fuel inlet and after a predetermined movement, placing said first and third passages in communication with each other to allow substantially unrestricted flow of fuel through the injector.

An example of a fuel injector in accordance with the invention will now be described with reference to the accompanying drawing which shows a sectional side elevation of the injector.

Referring to the drawing there is provided a nozzle body 10 of stepped cylindrical form and in which is formed a guide bore 11. At the end of the guide bore within the narrower portion of the body there is defined in the usual manner, a seating 12 leading into a sac volume from which extends a plurality of outlet orifices 13. Intermediate its ends the bore is enlarged to form a fuel supply gallery 14. Slidable within the guide bore is a valve member 15 which is shaped for cooperation with the seating 12 and which intermediate the gallery 14 and the seating, is of reduced diameter so as to define an annular clearance through which fuel can flow from the supply gallery past the seating and through the outlet orifices 13 when'the valve member is lifted from the seating.

Mounted adjacent the nozzle body is a distance piece 16 this being sandwiched between the nozzle body 10 and an elongated body 17. The body 17, the distance piece 16 and the nozzle body 10 are held in assembled relationship by means of a cap nut 18.

Formed in the distance piece is a central aperture through which extends a reduced portion of the valve member and this mounts a spring abutment 19 upon which is mounted one end of a coiled compression spring 20 housed within a spring chamber 21 formed in the elongated body.

The spring at its end remote from the abutment is supported by an integral flange 22 there being interposed between the spring and the flange a shim 23. Formed in the flange is a drain passage 24.

Located against the other end of the elongated body 17 is a bypass valve body 25 and the opposite end of the bypass valve body is engaged by an adaptor 26 which defines a fuel inlet 27 which is connected in use to the output of a fuel injection pump.

Formed in the bypass valve body and extending from the end thereof which engages the elongated body, is a blind bore 28 at the blind end of which there is formed a seating from which extends a first passage 29A which is connected by a passage in the adaptor, with the fuel inlet 27.

Slidable in the bore 28 is a piston like valve member 29 which is shaped to engage with the seating and which is urged into engagement with the seating by means of a spring 30 which is housed within a further spring chamber 31 located in the adjacent end of the elongated body. The spring engages with a spring abutment 32 which in turn is engaged with the piston 29 and at its opposite end engages the flange 22 through the intermediary of a shim 33 and a plate 34 upon which is formed an integral stop peg 35. The peg 35 is provided with drillings which communicate with the passage 24 so that the two spring chambers communicate with each other. A drain outlet 36 is provided in communication with the chamber 31.

A first fuel supply passage 37 is provided, the passage extending within the elongated body 17, the distance piece 16 and the nozzle body 10 and communicating with the gallery 14. A second fuel supply passage 38 is provided which also communicates with the fuel supply gallery 14 but which in the distance piece is provided with a restrictor 39A. The two passages open onto the end surface of the elongated body which is engaged by the bypass valve body 25 and formed in the bypass valve body is a second passage 39 which places the passage 38 in communication with the fuel inlet 27. Also formed in the bypass valve body is a third passage 40 which communicates with the fuel supply passage 37 but opens into the bore 28 intermediate the ends thereof.

The valve member 29 is provided with a peripheral groove 41 intermediate its ends, the groove 41 being in permanent communication with the passage 29A. The groove 41 is brought into register with the passage 40 after a predetermined movement of the valve member 29 away from its seating.

In operation, and assuming that the valve member 15 is in the closed position as shown and the valve member 29 is in engagement with its seating, when fuel under pressure is supplied to the inlet 27, the fuel pressure at the inlet will appear in the supply gallery 14 by way of the passages 39 and 38. As the pressure in the fuel supply gallery increases, so the force developed on the valve member increases and eventually the force developed on the valve member will overcome the force exerted by the spring 20 thereby allowing the valve member to be lifted from its seating to allow fuel flow from the gallery 14 through the outlet orifices 13. The rate of flow of fuel is restricted due to the presence of the restrictor 39A.The fuel pressure at the inlet 27 is also applied to the valve member 29 and when a pressure is attained which is higher than that required to effect movement of the valve member 15, the valve member 29 will be moved away from its seating against the action of the spring 30 until the groove 41 is brought into register with the passage 40. When this occurs fuel can flow from the inlet to the supply gallery 14 through the passages 40 and 37 so that the flow of fuel to the associated engine is at a substantially unrestricted rate.

It will be observed that the valve member 29 is responsive to the pressure developed at the inlet 27 rather than being responsive to the pressure drop across the restriction as in prior art examples. It is therefore not influenced by the density of the fuel.

Furthermore, the spring 30 is of a comparatively large diameter which facilitates the design of the spring and also is of substantial length so that the stress in the spring is kept low. Moreover, the spring 30 is positioned in a chamber which is at a low pressure and is connected to a drain as opposed to prior art arrangements in which the spring is contained in a chamber which contains fuel at high pressure. In the prior art any debris resulting form flexure of the spring may block passages within the nozzle and/or the outlet orifices 13.

Moreover, the spring could be subjected to cavitation erosion due to the formation of cavities in the fuel.

With the spring in a low pressure chamber cavitation is less likely to occur and any debris will be removed to the drain. The pressure at which the valve member moves away from its seating can be adjusted by altering the thickness of the shim 33 and alteration of the thickness of the shim 23 effects a variation in the so called nozzle opening pressure.

The bypass valve body and the adaptor are conveniently held in engagement with each other and with the elongated body 17 by means of a cap nut 42 and it is convenient to incorporate in the fuel inlet, a filter 43 to minimise the risk of obstruction of the restrictor 39A.

Claims (4)

1. A fuel injector for supplying fuel to an internal combustion engine and of the kind comprising a nozzle body containing a fuel pressure actuated valve member for controlling the flow of fuel through an outlet orifice, an elongated body to which the nozzle body is secured with a distance piece interposed therebetween, a fuel supply passage extending through the bodies and the distance piece and through which fuel under pressure can be supplied to a fuel supply gallery surrounding a part of the valve member, a spring chamber defined in said elongated body, a coiled compression spring located in said chamber and a spring abutment engaged with said spring and with said valve member whereby the force exerted by the spring opposes movement of the valve member by fuel under pressure, a further fuel supply passage extending through the bodies and the distance piece, a restrictor formed in said further fuel supply passage, the fuel supply passages terminating in the end surface of the elongated body remote from the nozzle body, a bypass valve body located against said end surface, a blind axial bore formed in the bypass valve body and extending from the end thereof located against said surface, a seating defined at the blind end of the bore, a first passage extending from the seating and communicating with a fuel inlet, a second passage in the bypass valve body for placing said further fuel supply passage in communication with said fuel inlet, a third passage in the bypass valve body, said third passage communicating with said first mentioned fuel supply passage and opening into said bore intermediate the ends thereof, a valve member slidable in said bore, a spring biasing the valve member into contact with the seating defined in the bore, the spring being located within a spring chamber defined in said elongated body, the valve member being movable away from the seating by the pressure of fuel at the fuel inlet and after a predetermined movement, placing said first and third passages in communication with each other to allow substantially unrestricted flow of fuel through the injector.

2. A fuel injector according to Claim 1 in which said chamber and said spring chamber are in communication with a drain outlet.

3. A fuel injector according to Claim 1 or Claim 2 in which said valve member is formed with a circumferential groove for registration with said third passage after said predetermined movement, and a passage in the valve member which connects said groove with said first passage.

4. A fuel injector for supplying fuel to an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawing.