EP0385398A2

EP0385398A2 - Perfected diesel engine electromagnetic fuel injector

Info

Publication number: EP0385398A2
Application number: EP90103803A
Authority: EP
Inventors: Vincenzo Damiani; Mario Ricco
Original assignee: Weber SRL
Current assignee: Weber SRL
Priority date: 1989-02-28
Filing date: 1990-02-27
Publication date: 1990-09-05
Also published as: EP0385398A3; IT8952903V0; JPH03965A; IT216950Z2

Abstract

A perfected fuel injector comprising an axially-sliding plunger (8) for controlling fuel passage between an injection chamber (13), supplied with fuel under pressure, and at least an injection orifice (9) formed in an injection nozzle (10); which injection chamber (13) is defined by a cylindrical surface (12) coaxial with the plunger (8). According to the present invention, the plunger (8) comprises a cylindrical portion (25) slightly smaller in diameter than the cylindrical surface (12), so as to define, downstream from the cylindrical portion (25), an injection chamber portion (26) of predetermined volume, and so as to define, between the cylindrical portion (25) and cylindrical surface (12), an annular channel (27) enabling fuel passage to the injection chamber portion (26) and along which a predetermined fall in fuel pressure is achieved.

Description

The present invention relates to a perfected electromagnetic fuel injector for Diesel engine application.
Injectors of the aforementioned type usually comprise a plunger for controlling fuel passage between an injection chamber, supplied with fuel under pressure, and at least an injection orifice formed on the injection nozzle; and an electromagnetic fuel metering valve for controlling fuel passage through a drain orifice between a control chamber, supplied with fuel under pressure, and a low-pressure chamber, for reducing the pressure of the fuel in the control chamber by draining the same through said orifice.
The injection and control chambers are partially defined by appropriate surface portions of the plunger, so that the respective pressures inside said chambers and acting on said surface portions displace the plunger when the pressure inside the control chamber falls to a given value.
On injectors of the aforementioned type, the control chamber is normally connected to a fuel supply orifice communicating with a single fitting in turn connected to a supply pipe. In this case, the injection chamber is supplied via a duct branching from the supply orifice and formed inside the injector.
On other types of injectors, the control chamber is likewise connected to a fuel supply orifice communicating with a first fitting in turn connected to a pressurized fuel supply pipe, but, unlike the previous type, fuel is supplied to the injection chamber via a duct communicating with a second fitting in turn connected to a fuel supply pipe.
Injectors of the aforementioned types present numerous drawbacks.
Foremost of these are the high noise level and poor efficiency or combustion of the engine to which they are fitted, which defects have been found to be caused by excessive fuel being injected at the start of each cycle, as a result of too much fuel being accumulated in the injection chamber.
Even in the absence of such defects, by virtue of the correct volume of fuel being accumulated in the injection chamber, this has frequently been found to transmit pressure disturbances to the control chamber on the injector, thus resulting in impaired operation of the electromagnetic fuel metering valve and, consequently, poor metering of the fuel injected at each cycle.
The aim of the present invention is to provide a perfected fuel injector of the aforementioned type designed to overcome the above drawbacks.
With this aim in view, according to the present invention, there is provided a Diesel engine electromagnetic fuel injector comprising an axially-sliding plunger for controlling fuel passage between an injection chamber, supplied with fuel under pressure, and at least an injection orifice formed in an injection nozzle, said injection chamber being defined at least partially by a cylindrical surface coaxial with said plunger; characterised by the fact that said plunger comprises a cylindrical portion located inside and slightly smaller in diameter than said surface, so as to define, downstream from said cylindrical portion, an injection chamber portion of predetermined volume; the diameter and length of said cylindrical portion being so selected as to define, between said cylindrical portion and said cylindrical surface, an annular channel enabling fuel passage to said injection chamber portion and along which a predetermined fall in fuel pressure is achieved.
The present invention will be described in detail with reference to the accompanying drawings, in which:

Fig.1 shows a partial section of an electromagnetic fuel injector perfected according to the present invention;
Fig.2 shows a larger-scale detail of part of the Fig.1 injector;
Fig.3 shows a section of the bottom part of a further injector perfected according to the present invention.

The injector illustrated in Fig.1 and perfected according to the present invention is of the type described in Patent Application n.67134-A/89 filed by the present Applicant on 28 February 1989 and entitled: "Diesel engine electromagnetic fuel injector."
Said injector substantially comprises a body 1 in which are formed an axial hole 2, an axial hole 3 considerably smaller in diameter than hole 2, and a supply orifice 4 substantially perpendicular to holes 2 and 3.
Said hole 2 houses three sleeves 5, 6 and 7 inside which slides a plunger 8, the bottom end of which is designed to control the passage of pressurized fuel through injection orifices 9 formed in an injection nozzle 10 secured to body 1. The top portion 8a of plunger 8 slides inside sleeve 5, whereas, between plunger 8 and the inner surfaces of sleeves 6 and 7 and the inner surface 12 of nozzle 10, there is defined an annular compartment 13 located upstream from injection orifices 9 and thus defining the injection chamber of the injector.
A helical spring 16, located between sleeve 5 and an annular projection 17 on plunger 8, provides for normally securing the bottom end of plunger 8 against a seat on nozzle 10.
Said hole 3 defines the control chamber of the injector, which communicates with a low-pressure chamber (not shown) via a drain orifice 15 controlled by an electromagnetic metering valve 18. Activation of valve 18 opens drain orifice 15 for reducing the pressure inside control chamber 3. Appropriate surface portions of plunger 8 are exposed to the fuel inside injection chamber 13 and control chamber 3, so that, when the pressure inside control chamber 3 falls to a given value, plunger 8 is raised for enabling fuel injection through orifices 9.
The injector according to the present invention presents a single fitting 19 connected to a pressurized fuel supply pipe (not shown) and communicating directly with control chamber 3 via a supply orifice 4. From supply orifice 4, pressurized fuel is supplied to injection chamber 13 along a duct comprising an annular cavity 23, a groove 20, an annular chamber 21 and radial holes 22. According to the present invention, plunger 8 comprises a cylindrical portion 25 (Fig.s 1, 2 and 3) located inside and smaller in diameter than cylindrical surface 12 of nozzle 10, so as to define, downstream from said cylindrical portion, a substantially annular injection chamber portion 26. According to the present invention, the volume of said chamber is specially selected for the purposes indicated later on. The diameter and length of said cylindrical portion are so selected as to define, between said cylindrical portion and cylindrical surface 12, an annular channel 27 (Fig.2) enabling fuel passage to injection chamber portion 26 and along which a predetermined fall in fuel pressure is achieved.
If D represents the diameter of surface 12 and d that of cylindrical portion 25, the radial clearance G between the two equals (D-d)/2. The equation relating the discharge coefficient of the solution according to the present invention and the inflow coefficient e of a restricting disc with a central hole d1 is therefore: DG³/l = Ked₁2, l being the length of cylindrical portion 25.
The injector in the Fig.3 embodiment substantially differs from the previous type by the fact that pressurized fuel is supplied to control chamber 3 along at least one duct 28 located to one side of plunger 8 and supplied via a fitting (not shown) in turn connected to a fuel supply pipe. The Fig.3 injector thus presents two fittings (not shown), one supplying fuel to control chamber 3, and the other to supply ducts 28 to injection chamber 13.
Operation of the injector perfected according to the present invention is as follows.
When metering valve 18 is activated, an appropriate amount of pressurized fuel is drained from control chamber 8 into a low-pressure chamber (not shown) through drain orifice 15, thus reducing the pressure inside control chamber 8. The resultant of the pressures applied on plunger 8 thus raises the latter, detaching the bottom end of plunger 8 from the seat on nozzle 10, and so enabling fuel supply through injection orifices 9.
By virtue of cylindrical portion 25, injection chamber 13 is obviously divided into two parts, one upstream and another 26 downstream from portion 25. The volume of said injection chamber portion may be so selected that the amount of fuel supplied through orifices 9 at each injection cycle increases gradually. Such an improvement has been found to provide for greater efficiency, reduced noise level and improved combustion of the engine. As soon as the fuel in injection chamber portion 26 is injected, further fuel is supplied from injection chamber 13, upstream from cylindrical portion 25, along channel 27 defined between portion 25 and surface 12.
Providing the three parameters: length l, diameter d and diameter D, have been so selected to meet the aforementioned condition, the fuel in injection chamber portion 26 is sufficiently separated from that in the top part of injection chamber 13 to isolate a specific volume of fuel inside said chamber portion 26, while at the same time still being able to flow along channel 27 into injection chamber portion 26 during injection.
The present invention has also been found to prevent pressure disturbances being transmitted by injection chamber portion 26 to control chamber 3, thus providing for efficient operation of metering valve 18 and accurate fuel metering at each cycle. The reason for this lies in the obstruction function performed by cylindrical portion 25 and the very small size of channel 27 along which such pressure disturbances would have to be transmitted.
To those skilled in the art it will be clear that changes may be made to both the design and arrangement of the component parts of the embodiments described and illustrated herein without, however, departing from the scope of the present invention.

Claims

1) - A Diesel engine electromagnetic fuel injector comprising an axially-sliding plunger (8) for controlling fuel passage between an injection chamber (13), supplied with fuel under pressure, and at least an injection orifice (9) formed in an injection nozzle (10), said injection chamber (13) being defined at least partially by a cylindrical surface (12) coaxial with said plunger (8); characterised by the fact that said plunger (8) comprises a cylindrical portion (25) located inside and slightly smaller in diameter than said surface (12), so as to define, downstream from said cylindrical portion (25), an injection chamber portion (26) of predetermined volume; the diameter and length of said cylindrical portion (25) being so selected as to define, between said cylindrical portion (25) and said cylindrical surface (26), an annular channel (27) enabling fuel passage to said injection chamber portion (26) and along which a predetermined fall in fuel pressure is achieved.

2) - An injector as claimed in Claim 1, characterised by the fact that said cylindrical surface (12) is formed inside said injection nozzle (19).

3) - An injector as claimed in one of the foregoing Claims, comprising an electromagnetic fuel metering valve (18) for controlling fuel passage through a drain orifice (15) between a control chamber (3), supplied with fuel under pressure, and a low-pressure chamber, and so reducing the pressure of the fuel in said control chamber (3) by draining the same through said orifice (15); said control chamber (3) being connected to a fuel supply orifice (4) communicating with a single fitting (19) in turn connected to a pressurized fuel supply pipe; characterised by the fact that said injection chamber (13) is supplied via a duct (23, 20, 21, 22) branching from said supply orifice (4).

4) - An injector as claimed in one of the foregoing Claims from 1 to 3, comprising an electronagnetic fuel metering valve (18) for controlling fuel passage through a drain orifice (15) between a control chamber (3), supplied with fuel under pressure, and a low-pressure chamber, and so reducing the pressure of the fuel in said control chamber (3) by draining the same through said orifice (15); said control chamber (3) being connected to a fuel supply orifice (4) communicating with a first fitting in turn connected to a pressurized fuel supply pipe; characterised by the fact that said injection chamber (13) is supplied via at least one duct (28) communicating with a second fitting in turn connected to a fuel supply pipe.