The present invention relates to a fuel injector and more particularly to the arrangement to control the displacement of the valve needle.

BACKGROUND OF THE TNVENTION

In modern high pressure fuel injection equipment, such as diesel common rail systems, statically leak less injectors are commonly used. These injectors use simple unbalanced nozzle control valves to control pressure acting on the nozzle control piston. The control valve has no stem through which high pressure fuel can leak and therefore an unbalanced nozzle control valve does not leak when the injector is idle and not injecting.

However when the needle lifts away from the seat and injection is occurring there is a continuous flow of fuel out through the open nozzle control valve seat. This loss of high pressure fuel represents a loss of potential energy from the system and, to compensate said loss the fuel pump has to supply additional fuel which demands extra power from the engine. This reduces engine efficiency.

SUMMARY OF THE FNVENTION

Accordingly, it is an object of the present invention to solve the above mentioned problem by providing a fuel injector for injecting fuel into a combustion chamber of an internal combustion engine. A supply channel arranged in the body of the injector is adapted to flow high pressure fuel from an inlet to at least one injection hole. The injector comprises a control valve hydraulically controlling the displacements of a valve needle arranged within an axial main bore of the body. The needle reciprocally displaces between a closed position, wherein fuel injection is prevented and, a fully open position wherein fuel injection through the injection holes is enabled. The main bore axially extends from a pointy tip provided with the injection holes to an upper extremity forming a control chamber in which protrudes the upper extremity of the valve needle. The control chamber is in fluid communication with the high pressure supply channel via a supply conduit and with, a low pressure return channel via another conduit controlled by the control valve.

The needle is provided with an internal conduit extending between its upper face and its side wall where it opens in the control chamber.

In an embodiment, the internal conduit comprises a diametral through hole having its both ends diametrally opposed, each end opening in the control chamber and, an axial hole extending from the through hole to the upper face of the needle.

Additionally, the supply conduit is provided with an inlet orifice creating a first restriction.

The internal conduit arranged in the needle is provided with a second restriction. That has a smaller cross section than the first restriction.

The section of the second restriction is between 75% and 25% of the section of the first restriction and, preferably half of the section of the first restriction.

The control chamber has a transversal ceiling in which is arranged another recess, the central conduit opening in said recess. When the needle is in said fully open position the upper face of the needle abuts against the ceiling on a peripheral surface surrounding said another recess. In this upper position, the internal conduit arranged in the needle opens as well in said another recess and, the control chamber forms an annulus volume surrounding the upper extremity of the valve needle.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figures 1 is a schematic axial section of the control valve of a fuel injector as per the invention, the valve being in a closed position.

Figure 2 is the injector of figure 1 in a fully open position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description, similar elements will be designated with the same reference numbers. Also, to ease and clarify the description the top-down orientation the figures will be followed. Therefore, words and expressions such as "top, upper, lower, over, under"... may be utilized without any intention to limit the scope of the invention.

An injector 10 is now described in reference to the figures. The injector 10 extends along a main axis A. Its body 12 comprises, fixedly arranged from top to bottom, an upper actuator body 14, a valve plate 16 and a lower nozzle body 18. A supply channel 20 extends downwardly from a top inlet arranged in the actuator body 14 then, through the valve plate 16 and in the nozzle body 18. High pressure fuel flows in said channel 20 to be ultimately injected in a combustion chamber of an internal combustion engine.

The upper body 14 is provided with an upper cylindrical space 22 from which downwardly extends an upper valve bore 24 opening in an enlarged cylindrical recess 26. In said spaces, the upper body 14 receives an

electromagnetic actuator 28 that commands the displacements of an armature 30, arranged in the cylindrical space 22, having an integral valve stem 32 reciprocally sliding in the valve bore 24 along the main axis A and protruding in the recess 26.

The lower nozzle body 18 is provided with a main bore 34 axially extending from top to bottom. Known in the art are injectors having the main bore 34 coaxial to the valve bore 24, as represented on the figures, or having an offset between the two axes. The non-represented lowest part of the bore 34 narrows into a closed tip-end provided with a valve seat with injection holes, while the represented top part of the bore 34 enlarges into a cylindrical recess forming a control chamber 36.

A valve needle 38 is slidably guided in the bore 34 and is constantly downwardly solicited by a spring 39 compressed between a face of the nozzle body 18 and a spring seat 41 integral to the needle 38. The spring 39 generates on the needle 38 a first downwardly oriented force FDl . The upper part of the needle 38 forms a cylindrical piston 40 that protrudes in the control chamber 36 and, the lowest end of the needle 38 cooperates with the seat in order to enable or prohibit fuel injection through the injection holes. The cylindrical piston 40 is provided with a diametral through-hole 42 and with an axial hole 44 upwardly extending inside the needle 38 from the hole 42 to the upper face 46 of the piston 40 where it opens. The axial hole 44 comprises an intermediate orifice 48 having a restricted cross-section S48 relative to the section of the hole 44. As can be observed on the figures, both ends of the diametral hole 42 open into the control chamber 36. The diametral hole 42 with the axial hole 44 constitute an internal conduit creating fluid communication between the compression chamber 36 and the upper face 46 of the piston 40. Alternative embodiments are possible such as a direct straight conduit arranged at an angle.

Arranged between the actuator body 14 and the nozzle body 18, the valve plate 16 has an upper face 50 in surface contact with the lower face 52 of the actuator body 14 and, a lower face 54 in surface contact with the upper face 56 of the nozzle body 18. Centrally, the lower face 54 of the plate 16 covers the control chamber 36 and constitutes a ceiling 58 to said control chamber 36.

The valve plate 16 is provided with a supply conduit 60 wherein part of the high pressure fuel can flow from the high pressure supply channel 20 to the control chamber 36 in passing through an inlet orifice 62 creating a restriction in the supply conduit 60. For reasons that are detailed after, the section S62 of the inlet orifice 62 is larger than the section S48 of the intermediate orifice 48.

The valve plate 16 is also provided with a return conduit 64 wherein low pressure fuel can flow from the cylindrical recess 26, provided in the upper body 14, toward a return outlet not represented.

The valve plate 16 is further provided with a central conduit 66 axially extending between its lower 54 and the upper 50 faces. In the lower face 54 of the plate 16 is formed a shallow cylindrical recess 68 wherein centrally opens said central conduit 66.

In the exemplary embodiment represented on the figures, the supply conduit 60 comprises an inwardly radially extending upper groove 70 provided in the upper face 50 of the valve plate 16 and, a complementary radially extending lower groove 72 provided in the lower face 54 of the valve plate 16. The restricted inlet orifice 62 is axially arranged between the upper and lower grooves 70, 72. Also, the return channel 64 is another upper groove outwardly radially extending in the upper face 50.

In figure 1, the valve stem 32 is in its utmost downward position where it closes the central conduit 66. The needle 38 is in downward position cooperating with the valve seat, preventing injection events. This downward position is also known as a closed position.

In figure 2, the valve stem 32 is moved upward opening the central conduit 66 into the cylindrical recess 26. The valve needle 38 is in its utmost upper position, also known as a fully open position and, the upper face 46 of the piston 40 abuts against the ceiling 58 of the control chamber 36. As can be seen, the diameter D68 of the shallow recess 68 is smaller than the diameter D40 of the piston 40 therefore, in this upper position, the piston 40 contacts the valve plate 16 along an annular surface 74 set at the peripheral edge of the shallow recess 68. As the piston 40 is in contact with the ceiling 58 of the chamber 36, the control chamber 36 is limited to an annulus volume surrounding the piston 40.

The operation of the injector 10 is now described.

In figure 1, the armature 30 and integral valve stem 32 are moved downward; the central conduit 66 is closed by the stem 32 and high pressure fuel pressurizes the volume consisting of the control chamber 36, the diametral through hole 42, the small axial hole 44, the central conduit 66 and, the shallow recess 68. The high pressure built up the control chamber 36 generates on the upper face 46 of the piston 40 a second downwardly oriented force FD2 which adds to the first downward force FD1 and maintains the needle 38 in a downward position cooperating with the valve seat to close the injection holes and to prevent injection event.

In figure 2, the armature 30 and integral stem 32 are in upward position; the central conduit 66 is open in fluid communication with the return channel 64. Pressurized fuel contained in the control chamber 36, the diametral through hole 42 and in the small axial hole 44 flows through the shallow recess 68 and the central conduit 66 to reach the cylindrical recess 26 and the return channel 64. As pressure decreases in the control chamber 36, the needle 38 is no longer subject to the second force FD2 but, to an opposite upward force FU generated by the high pressure fuel acting on the lower extremity of the needle 38. Said upward force FU is superior to the first downward force FDl of the spring 39 and consequently the needle 38 moves upward, enabling injection events. During the final upward displacement of the needle 38, the fuel present inside the shallow recess 68 gets trapped and slightly damps said final displacement. When in its utmost upward position, the upper face 46 of the piston abuts against the ceiling 58 of the chamber 36 and therefore, a unique path of fuel remains open from the supply channel 20 to the return channel 64. Said unique path consist of the upper groove 70, the inlet orifice 62, the lower groove 72, the annulus control chamber 36, the diametral through hole 42, the axial hole 44 and its intermediate restriction 48, the shallow recess 68, the central conduit 66, the cylindrical recess 26 and finally the return channel 64. The pressure of the fuel, that is high by the entry in this unique path decreases a first time when passing through the restriction of the inlet orifice 62, then decreases further when passing through the intermediate restriction 48. Therefore the fuel leak, occurring when the needle 38 is up, is minimized. The intermediate restriction 48 having a cross section S48 smaller than the cross section S62 of the inlet orifice 62 generates a second pressure drop, the pressure being higher in the through hole 42 than above, in the central conduit 66 and the shallow recess 68. While the section S48 should be between 75% and 25% of the inlet orifice section S62, a preferred value is around 50%> where said section S48 is only about half the inlet orifice section S62.

In a following step, the armature 30 and integral stem 32 are back in downward position again closing the central conduit 66, as in figure 1. At the instant conduit 66 is closed the needle 38 is still in its upward position. The high pressure rapidly built-up again in the annulus control chamber 36, the diametral through hole 42, the small axial hole 44 and its intermediate restriction 48, the shallow recess 68 and the central conduit 66. The high pressure in the shallow recess 68 re-generates on the upper face 46 of the piston the second downwardly oriented force FD2 which balances the upward force FU. The hydraulic forces applied on the needle 38 are balanced and the first downward force FDl of the spring 39 becomes predominant downwardly displacing the needle 38. In the above description the following references have been utilized: injector 58 ceiling of the control chamber body 60 supply conduit

upper actuator body 62 inlet orifice

valve plate 64 return conduit

lower nozzle body 66 central conduit

supply channel 68 shallow recess

upper cylindrical space 70 upper groove

upper valve bore 72 lower groove

cylindrical recess 74 annular surface

actuator

armature

valve stem A main axis

main bore D40 diameter of the piston control chamber D68 diameter of the shallow recess valve needle S48 section of the restriction 48 spring S62 section of the inlet orifice piston FD1 first downward force spring seat FD2 second downward force through hole FU upward force

axial hole

upper face of the piston

intermediate restriction

upper face of the valve plate

lower face of the actuator body

lower face of the valve plate

upper face of the nozzle body