Fuel injector with a control rod controlled by the fuel pressure in an control chamber

ES 2 284 558 T3

DESCRIPTION

Fuel injector with a control rod controlled by the fuel pressure in a control chamber.

The present invention relates to a fuel injector, in particular for an internal combustion engine, with a control rod controlled by the fuel pressure in a control chamber.

Known fuel injectors typically include a nozzle having an injection chamber fed with pressurized fuel for injection; the nozzle has injection ports that are normally closed by a pin connected to the control rod and are activated by the fuel pressure in the injection chamber; and the control chamber has a calibrated fuel intake duct, and a normally closed, calibrated control chamber discharge duct, controlled by a metering valve controlled in turn by an electromagnet, which is energized for a variable time interval depending on the amount of fuel for injection.

In known injectors, the control rod is normally mechanically stopped by a fixed stop after sufficient travel to open the nozzle orifices and before fuel injection is complete. The rod is normally stopped by the end wall of the cylindrical rod guide, but, to eliminate precision machining of the end wall of the rod guide, the rod of the known injector is provided with an annular protrusion which is stopped against the edge of the cylindrical guide supported by the conventional metering valve body.

In both of the above cases, mechanical arrest poses several drawbacks. In particular, it produces a certain amount of shock-induced wear; and, to obtain a predetermined travel, the fixed stop member and the rod stop member involve precision machining, complex assembly work, and various provisions to ensure fluid tightness between the rod and the guide.

From EP 0 753 659 A1 a fuel injector of the above type is known, where a rod is movable in a control sleeve forming a control chamber. The rod is provided with a protruding end adapted to abut against a front protrusion arranged on an end wall of the sleeve. The projection of the rod is provided with a slit hole towards the control chamber, in order to have the control chamber always in communication with a discharge conduit.

An object of the present invention is to provide a fuel injector of the above type, which is cheap to produce, highly reliable, and allows to eliminate said drawbacks typically associated with known injectors.

According to the present invention, a fuel injector as defined in claim 1 is provided.

A preferred non-limiting embodiment of the invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 represents a mid-section of a fuel injector of an internal combustion engine according to the present invention.

Figure 2 represents a detail on a larger scale of Figure 1.

Figure 3 represents another detail on a larger scale of figure 1.

Figure 4 represents a flow chart of the injector.

The number 7 in figure 1 indicates as a whole a fuel injector for an internal combustion engine, for example diesel. Injector 7 includes a hollow body 11 connected by an annular nut 12 to a nozzle 13; the nozzle 13 has an axial hole 15 and ends with a conical seat 14 (see also figure 2) having injection holes 16; and the body 11 has an axial hole 25 into which a control rod 17 slides.

The hollow body 11 also has an appendix 26 into which is inserted an intake adapter 27 connected to a pressurized fuel supply conduit. The appendix 26 has a hole 28, which, through a feed conduit 29 in the body 11 and a feed conduit 30 in the nozzle 13, communicates with an annular injection chamber 31 formed in the nozzle 13 and communicates with the hole axial 15.

One end of the rod 17 engages an appendix 18 of a pin 19 to close holes 16 and which slides into the axial hole 15. More specifically, the pin 19 has a tapered end 21 that engages a tapered seat 14 of the nozzle 13, and includes a fluid tightly guided portion 20 within a portion 33 of hole 15 in nozzle 13.

Portion 20 ends at one end with a ring 22 that supports appendix 18 and is guided within a cylindrical seat 23 in body 11; ring 22 is normally biased towards seat 14 by a spring 24 which helps to keep holes 16 closed; and, at the other end, the portion 20 ends with a projection 32 pushed by the fuel into the chamber 31 pressurized at a predetermined injection pressure causing the joint 19 to engage the rod 17.

With respect to the inner wall of the hole 15 in the nozzle 13, the pin 19 has a given clearance to ensure rapid flow of fuel from the chamber 31 to the holes 16 of the nozzle 13. In known injectors, the volume of chamber 31 is normally less than the maximum amount of fuel to be injected by injector 7, so that supply lines 29 and 30 are dimensioned to also allow the supply of fuel to chamber 31 during injection.

Injector 7 also includes a metering valve indicated in conjunction with 34 and which is activated by an electromagnet 36 that controls an armature 37. Armature 37 includes a disk 38 that has indentations 39 and is connected to a stem 40, which is pushed toward down by a compression spring 41 housed in a central hole 42 in electromagnet 36.

The metering valve 34 includes a body 43 having a flange 44 normally held by resting on a projection of the body 11 of the injector 7 by an annular nut 46 and by means of a flange 45 of a guide 50 to guide the stem 40. Flange 45 has holes 47 that communicate with a discharge chamber 48 of metering valve 34; and, through slits 39 in disk 38 and central hole 42, discharge chamber 48 communicates with a discharge adapter (not shown in FIG. 1) that communicates with the fuel tank.

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The body 43 of the metering valve 34 has an axial control chamber 52 (see also FIG. 3) that communicates with a guide cylinder 53 in the body 43 of the valve 34. A piston-shaped portion 54 of the rod 17 slides fluid-tight within cylinder 53, which terminates with an end wall 55 adjacent an end surface 56 of portion 54 of rod 17.

The body 43 includes a calibrated radial fuel inlet passage 57 which communicates with the hole 28 in the appendix 26 via an annular groove 58; and a calibrated axial discharge conduit 59 for discharging pressurized fuel from control chamber 52 and communicating with discharge chamber 48.

Rod 17 has a ring 64 housed in a larger diameter portion 66 of hole 25. Ring 64 is locked by valve body 43 within portion 66 of hole 25, and cooperates with an edge 67 of valve body 43 to avoid in any case that the surface 56 contacts the end wall 55 of the cylinder 53.

The pressurized fuel in the control chamber 52 acts on the end surface 56 of the portion 54 of the rod 17; and, since the surface 56 of the rod 17 has a larger area than the projection 32, the one resulting from the pressure of the fuel in the portions 54 and 20, with the aid of the spring 24, normally holds the rod 17 in the position. lowered, the end 21 of the pin 19 contacting the conical seat 14 of the nozzle 13 to close the injection ports 16.

The discharge conduit 59 of the control chamber 52 is normally closed by a plug in the form of a ball 61, which rests on a contact surface of a conical surface 62 of the flange 44, where the discharge conduit 59 ends The ball 61 is hooked by a guide plate 63 on which the rod 40 of the armature 37 acts.

When electromagnet 36 is energized, armature 37 moves stem 40 in opposition to spring 41; and the pressure of the fuel in the control chamber 52 releases the ball 61 to discharge the fuel from the chamber 52 to the discharge chamber 48 and return it to the tank. Obviously, the intake conduit 57 is unable to restore the pressure in the chamber 52, so the fuel in the chamber 52 remains at a low pressure, and the fuel pressure in the injection chamber 31 exceeds the residual pressure in the end surface 56 of rod 17 to raise pin 19 so that fuel in chamber 31 is injected through holes 16.

When electromagnet 36 is de-energized, spring 41 lowers stem 40 together with armature 37. Stem 40 also restores ball 61 to the closed position that closes discharge conduit 59, and the pressurized fuel restores pressure in the intake chamber. control 52 so that pin 19 closes holes 16.

According to the invention, the injector 7 is dimensioned so that the rod 17 and the pin 19 are moved from the closed position of the nozzle 13 (as shown in Figures 1-3) and are held hydraulically balanced in a position that fully opens holes 16 and that constitutes the maximum actual lift of rod 17 and pin 19. This is accomplished by properly sizing pin 19 and rod 17, as well as intake conduit 57 and discharge conduit 59.

Advantageously, the hydraulic balance of the rod 17 and the pin 19 can be achieved by selecting a diameter D1 of 3 to 5 mm for the portion 20 of the pin 19, and necessarily the same or a greater diameter D2, for example, from 3 to 6 , 5 mm, for portion 54 of rod 17. With a spring 24 exerting a predetermined force on pin 19, and with a predetermined pressure of fuel in chamber 31 during injection, the ratio D2 / D1 between diameter D2 of portion 54 of rod 17 and diameter D1 of the portion 20 of the pin 19 may be in the range of 1 to 1.3.

When the metering valve 34 is opened, the flow of fuel in the control chamber 52 can be such that it maintains the control chamber 52 at a given low pressure and, with the help of the spring 24, balances the fuel pressure in the projection. 32 of the pin 19. For this purpose, the diameter D3 of the discharge conduit 59 may advantageously be in the range of 0.2 to 0.4 mm. Alternatively, the conduit 59 can be defined by multiple holes, the total area of ​​which must equal the sectional area of ​​the conduit 59.

With a spring 24 exerting a predetermined force on pin 19, and with a predetermined inlet fuel pressure in control chamber 52, the ratio D3 / D4 between the diameter D3 of the discharge duct 59 and the diameter D4 of the intake duct 57 can be in the range 0.8 to 1.5. Obviously, the ratio D2 / D1 between the diameters of the portions 54 and 20 and the ratio D3 / D4 between the diameters of the conduits 59 and 57 can be selected accordingly.

If t0 (figure 4) is the time when electromagnet 36 is energized, the injection begins at time t1 with a predetermined delay or out of phase with respect to time t0. The rod 17 (see also Figures 1 and 3) is hydraulically stopped at time t2, when the forces acting on the rod 17-pin 19 assembly reach an equilibrium state, and the path of the rod 17 depends on the D2 / D1 ratio between the diameters of the portions 54 and 20 and the D3 / D4 ratio between the diameters of the discharge and intake ducts 59 and 57. This position of the rod 17 corresponds substantially to the end 21 of the pin 19 that fully opens the holes 16, that is, the maximum lifting position of the rod 17 and the pin 19.

The time interval that the electromagnet 36 is energized may be shorter or longer than the time interval t2-t0. If it is less than the interval t2t0, the quantity of fuel Q injected, from the beginning of the opening stroke to the end of the corresponding closing stroke of the rod 17 and the pin 19, increases substantially constantly from the duration that ends at time t1 to the duration that ends at time t2, as represented by a first graphic segment 68 indicated by the solid line in figure 4, and which, therefore, is right and is inclined at a given angle with respect to the abscissa axis.

If the length of time that the electromagnet 36 is energized ends after time t2, the increase in the amount of fuel Q injected decreases, as represented by the much less inclined graph segment 69, to form a bend P in the du3

ES 2 284 558 T3 ration that ends at the instant t2 in which the rod 17 stops. Segment 69 extends to a point F, which defines the total amount of fuel injected and corresponds to a duration that ends at time t3.

The tolerances of the diameters D1-D4 displace the elbow P along the segment 68, and thus displace the segment 69 parallel to itself. In Figure 4, the dotted line segment 69 'represents the situation where the rod 17 passes through the position of the segment 69, and the dotted line segment 69 "the situation where the rod 17 is stopped before segment 69 position.

The advantages, with respect to the known technology, of the injector 7 according to the invention will be clear from the above description. In particular, the rod 17 does not experience impact, each time the injector is activated, thus reducing wear and deformation; neither the stop ring 64 nor the rim 67 of the valve body 43 need precision machining; and any difficulty involved in assembling and regulating the stroke of the rod 17 is eliminated.

Clearly, changes can be made to the injector described herein without, however, departing from the scope of the accompanying claims. For example, intake conduit 57 may be located in control chamber 52 as opposed to cylinder 53.

Furthermore, the travel of the pin 19 and the rod 17 can be mechanically limited in any way other than that described. For example, the travel of the pin 19, as opposed to the ring 64 of the rod 17, can be limited in the same way.