FR3027350B1 - FUEL INJECTOR - Google Patents

Abstract

A fuel injector includes a needle (72), a two-way solenoid valve (24), such that in the closed position of the solenoid valve and a dynamic leak reducing means (26, 114) preventing the fuel flow directly from the supply channel (146) to a return circuit (148) when the solenoid valve (24) is in the open position.

Description

Fuel injector

TECHNICAL FIELD The invention relates to a fuel injector provided with a means of reducing dynamic leakage.

BACKGROUND OF THE INVENTION

A fuel injector conventionally comprises a needle controlled opening and closing depending on the pressure differential between a control chamber and the injection nozzle. In the control chamber, the pressure is a function of the position of a two-way control solenoid valve, or on-off valve, switching between an open position and a closed position. When the solenoid valve is in the closed position, the high-pressure fuel can enter the control chamber and urge the needle to the closed position and, when the solenoid valve switches to the open position, the fuel previously trapped in the control chamber can exit via a valve. discharge channel allowing the pressure in the control chamber to decrease. During this opening time of the solenoid valve, the high-pressure fuel continues to enter the control chamber but simply passes through it because it comes out directly via the discharge channel. It is known to control this dynamic leak in the injectors equipped with three-way solenoid valve, as in EP2711537, but in the injectors having a two-way valve, this dynamic leakage remains a loss of energy.

SUMMARY OF THE INVENTION

The present invention proposes to at least partially solve these problems by proposing a fuel injector comprising a body in which a needle moves between an open position and a closed position under the influence of the fuel pressure in a control chamber, chamber into which a high pressure supply channel opens, and from which a discharge channel controlled by a two-way solenoid valve returns to a low pressure return circuit.

In the closed position of the solenoid valve the pressure increases in the control chamber urging the needle to the closed position and, in the open position of the solenoid valve, the fuel is discharged from the control chamber in which the pressure decreases, allowing the needle to move in the open position. The injector further includes dynamic leakage-reducing means preventing fuel from flowing directly from the supply channel to the return circuit when the solenoid valve is in the open position. Said dynamic leakage reduction means comprises a movable member moving between an open position and a closed position under the influence of the fuel pressure differential existing between the control chamber and a second control chamber in fluid communication with the channel discharge.

More particularly, the mobile member is a cylindrical piston arranged sliding in a bore of the injector body, the supply channel opening into said bore. The piston moves to an open position when the solenoid valve is in the closed position so that the high pressure fuel can enter the control chamber and it moves to a closed position when the solenoid valve is in the open position so that prevent the entry of high pressure fuel into the control chamber.

More particularly, said bore is coaxial with the bore in which the needle slides.

In one embodiment, the piston comprises an enlarged base surmounted by a cylindrical body of smaller diameter. The lower face of said base is arranged facing the needle and the junction face between the base and the body forms a sealing face cooperating with a seat provided in the injector body. In the closed position of the piston, the sealing face and the seat are in sealing contact preventing the entry of high-pressure fuel into the control chamber and, in the open position of the piston, the sealing face and the seat move away allowing between them fuel at high pressure.

According to this embodiment, the piston is further provided with a channel opening permanently putting in fluid communication the control chamber and the second control chamber. Said channel may be an axial channel. In addition, said opening channel may be provided with a section restriction generating a pressure drop so that the pressure in the control chamber is greater than the pressure in the second control chamber.

In addition, the piston may be provided with a calibrated channel extending radially between the outer cylindrical face of the cylindrical body and said channel opening to establish a hydraulic communication between the high pressure supply and the second control chamber.

In another embodiment, the piston comprises a simple cylindrical body extending axially between a lower face arranged facing the needle, the said lower face forming the ceiling of the control chamber and an upper face opposite the face. lower, said upper face coming into contact against a transverse face of the injector body when the piston has moved to the closed position. In addition, a spring is arranged in the control chamber and compressed between a shoulder secured to the needle and the underside of the piston so as to constantly urge both the needle towards its closed position and the piston towards its position. closed.

More particularly, the piston is provided with a first channel extending from the outer wall of the piston to the upper face and also with a second channel extending between the lower and upper faces, the piston being arranged in its bore so that the supply channel is in permanent fluid communication with the first channel.

The first channel may comprise an annular groove arranged on the outer wall of the piston, the first channel extending from said groove and opening into the upper face of the piston, the supply channel, opening into the space defined by the annular groove .

The piston is further provided on its upper face with a protuberance forming a sealed barrier when the piston is in the closed position, said barrier then being in sealing contact against said transverse face of the injector body, the first channel and the second channel. opening in the upper face of the piston on either side of said barrier, said second control chamber being the space between the transverse face of the injector body and the upper face of the piston and bounded by the side of the barrier where the second channel and the evacuation duct open.

More particularly, the barrier is a circular and closed lip, the first channel opening into the central portion and the second channel opening into the outer portion.

In an alternative to said other embodiment, the injector is provided with a device for generating on the needle a closing force directed towards the tip of the needle, greater than the opening force directed towards the head of the needle. Thus, the fuel pressure injected when the needle is in the open position is equal to the fuel input pressure in the injector.

Said device consists of a piston whose cross section is greater than the cross section of the needle so that the pressurized fuel entering the second control chamber exerts on said piston an increased force.

In a particular embodiment, the piston is sized to contact the needle head as soon as the piston begins to move to the open position. The increased force exerted by the high pressure fuel in the second control chamber is then integrally transmitted to the needle so that the needle is subjected to a closing force of intensity greater than the opening force exerted by the fuel. level of the tip of the needle.

DESCRIPTION OF THE FIGURES

One embodiment of the invention is now described by means of the following figures:

Figure 1 is an axial sectional view of an injector provided with a dynamic leakage reduction means according to the invention.

Figure 2 is a magnified detail in axial section of the injector region comprising said means according to a first embodiment.

Figure 3 is similar to Figure 2 in an even more detailed view of the means.

FIG. 4 is a detail seen from above of the means of FIGS. 2 and 3.

FIG. 5 is an isometric view of a movable piston of the means of FIGS. 2 to 4.

FIG. 6 is an axial section of the piston of FIG.

Figure 7 is an axial section of an alternative to the first embodiment of Figures 2 to 5.

FIG. 8 is a magnified detail in axial section of the region of the injector comprising said means produced according to a second embodiment.

Figure 9 is similar to Figure 8 in an even more detailed view.

FIG. 10 is an isometric view of the movable piston of the means of FIGS. 8 and 9.

FIG. 11 is a schematic graph of operation of the dynamic leakage reduction means, regardless of its embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is an axial section of a fuel injector 10 which extends along a longitudinal axis Al from an injector head 12, drawn at the top of the figure, to an injection nozzle 14, drawn in FIG. bottom of the figure.

For the sake of clarity of the description, the arbitrary orientation of Figure 1 will also be used, terms such as "up, down, above or below" may be used without limiting the description. nor the scope of the invention. The injector 10 comprises the head 12 in which are arranged a high-pressure inlet mouth 16 and partially visible only, a low-pressure outlet mouth 18. The injector head 12 is integral with an actuator body 20, itself secured by an injector nut 22 to a control valve 24, a high guide 26 and the body 28 of the injection nozzle 14 .

The actuator body 20 is generally cylindrical with a longitudinal axis A1 and extends from the head 12 to a lower face 30. It is further provided, on its outer cylindrical face in the vicinity of said lower face 30 , a male thread 32 provided for complementary engagement by screwing the female thread 34 of the injector nut 22 and, it is further provided with a cylindrical inner bore 36 extending along a second axis A2, parallel to the longitudinal axis Al but slightly offset from it. The bore 36 opens into the lower face 30 and, in the bore 36 is arranged fixed the coil 38 of an electromagnet 40 which in the lower part is flush with the lower face 30 of the actuator body 20. From the coil 38 leave in the direction of the injector head 12 electrical connection means 42, such as cables. These means 42 extend in a specific conduit to a connector 44 provided with terminals for connecting the coil 38 to an external control unit not shown. The coil 38 is itself provided with a central bore 46 in which a valve spring 48 is arranged.

The control valve 24 comprises a cylindrical valve body 50 of longitudinal axis revolution A1 extending between an upper face 52 and a lower face 54 and provided with an axial bore 56 comprising two coaxial sections along the second axis A2, the first section opening into said upper face 52 is a wide and shallow countersink forming a low pressure chamber 58, the center of the bottom 60 of which extends towards the lower face 54 the second section forming a hydraulic distributor bore 62. In this boring distributor 62, axially A2 blind, several arrivals of channels open laterally. The set of channels and conduits which is provided with the injector 10 will be detailed further.

Furthermore, the injector represented in FIG. 1 and on which this description is based is only a non-limiting example and, many alternatives of constructions exist and will be mentioned however, the alternatives which would be omitted can not be excluded. the scope conferred by the claims. For example, it has just been specified that the longitudinal axis A1 and the second axis A2 are distinct and parallel. This offset, introduced in patent EP1693563, has many advantages but is not imperative and injectors in which the two axes are confused exist and can easily benefit from the teachings of the present invention.

The control valve 24 further comprises a rod-armature assembly 64 comprising a magnetic armature 66 and a valve stem 68 arranged movable in the axial bore 54. The armature 66 has the general shape of a thick disk which is placed in the low pressure chamber 58 and the valve stem 68 is a cylindrical shaft comprising sections of different diameters and one end of which is embedded and crimped in the center of the armature 66. Thus fixed, the valve stem 68 extends perpendicular to the armature 66 and is arranged in a fair-slip fit in the dispensing bore 62. The valve stem 68 is slidable directly into the dispensing bore 62 or alternatively as shown in FIG. a cylindrical sleeve 70 radially pierced with at least one radial hole, the sleeve 70 being inserted tightly into the dispensing bore 62.

As shown, the coil 38, its central bore 46, the valve spring 48, the axial bore 56 of the valve body, the magnetic armature 66 and the valve stem 68 are coaxial extending along the second axis A2 . The valve spring 48, compressed between the bottom of the central bore 46 of the coil and the valve stem 68 whose head is flush with the center of the armature 66, continuously urges the armature-rod assembly 64 to a position remote from the coil 38, a position called the closed position of the valve PFV in opposition to a position close to the coil called open position of the valve POV.

The injection nozzle 14 comprises the nozzle body 28, the high guide 26, a needle 72 and a needle spring 74. In the example described, the nozzle body 28 and the top guide 26 are two pieces. distinct. In an alternative not shown, injectors whose nozzle body incorporates the high guide exist and can equally benefit from the present invention.

The nozzle body 28 has a tapered cylindrical wall 76 extending along the longitudinal axis Al from an upper face 78 into a first wide section 80 and a narrower second section 82 which is narrowed at its lower end. The outer faces of the two sections 80, 82 are connected in a transverse disc face 84 against which the injector nut 22 bears.

By homothety with the outer faces, the wall 76 defines a continuous interior space 86 divided into a large cylindrical chamber 88 located in the first section 80 and a narrow chamber 90 located in the second section 82.

The large cylindrical chamber 88 opens into the upper face 78 forming a high countersink 92 adapted to receive and position the high guide 26.

The narrow chamber 90 defines at a portion of its lateral cylindrical wall a low sliding guide 94 and the end of the narrow chamber 90 closes similarly to the second section 82 in a female cone forming a seat 96 of the nozzle body circulating a plurality of injection holes 98 passing through the wall 76 of the nozzle body.

The high guide 26 is, in the nonlimiting example described, an independent cylindrical piece of revolution extending along longitudinal axis A1 from a transverse upper face 100 and comprises a large upper cylinder 102 and a narrow lower cylinder 104, the two cylinders 102, 104, joining in a shoulder face 106. The high guide 26 further comprises an axial bore opening 108 passing right through the two cylinders 102, 104, the bore 108 defining in the lower part, located in the a narrow cylinder 104, a top sliding guide 110 and, in the upper part located in the large cylinder 102, a control chamber 112 in which is arranged a movable piston 114 now described.

Said mobile piston 114, particularly detailed in Figures 4, 5 and 6, extends axially between an upper face 116 to a lower face 118, the upper face 116 being provided with a boss rising slightly above said upper face 116, boss at the center of which is formed a high concave housing 120 so that said boss circumscribes the opening of the upper housing 120 forming a circular peripheral lip 122. In the center of its lower face 116, the piston 114 is also provided a low concave housing 124.

The top 120 and bottom 124 are functional centering holes for a particular machining mode. In an alternative not shown corresponding to a different embodiment these housings could not be made.

The piston 114 is further provided on its cylindrical side face with an annular groove 126 and a first channel 128 joining the groove 126 inside the upper housing 120, the opening of said first channel 128 being therefore interior of the lip 122 and, as well as a second channel 130 joining the interior of the lower housing 124 to the upper face 116, the upper opening of said second channel 130 being on the outside of the lip 122. The needle 72, so called by the professionals with reference to its general shape, is an elongated cylindrical shaft extending from a needle head 132 to a conical tip 134 defining a needle seat 136. As particularly visible on Figures 2 and 3, the needle head 132 is provided with a small cylindrical protrusion 138 connected to the body of the needle by a bearing shoulder 140, the body of the needle forming in this part of tê A top needle guide 142 and, opposite the head 116 near the tip 134, the needle 72 has a wider portion forming a low needle guide 144.

As shown in the figures, the nozzle body 28 receives in its high countersink 92 the wide cylindrical portion 102 of the top guide 26, the narrow portion 104 extending into the wide chamber 88 of the nozzle body 28. The face shoulder 106 of the high guide is in sealing abutment against the bottom of the top counterbore 92 and the top guide 26 is radially held by the inner flange of the same counterbore 92.

Since the high guide 26 is thus in place, the top sliding guide 110 and the bottom sliding guide 92 are coaxial along the longitudinal axis A1 and receive the needle 72 in a complementary manner, the high needle guide 142 sliding in the top sliding guide 110 and the bottom guide 144 sliding in the bottom sliding guide 92 of the nozzle body. Above the needle head 116 the needle spring 74 is compressed in the control chamber 112 between the bearing shoulder 104, integral with the needle 72, and the lower face 118 of the movable piston 114.

The upper face 100 of the high guide is maintained in sealed surface contact against the underside of the valve body 54 and the upper face 52 of the valve body itself is in sealed surface contact against the underside 30 of the actuator body. . This integral and impermeable stack is made possible by the injector nut 22 which, threaded around the second narrow section 82 of the nozzle body 28 bears against the disc face 84 of the same nozzle body and extends axially according to FIG. longitudinal axis A1 so as to enclose the high guide 26 and the control valve 24 to screw on the actuator body 20 through the complementary threads 32, 34 previously described. The surface seals are provided on the one hand by the mirror quality of the state of the surfaces in contact and on the other hand by the sufficiently large tightening torque of the nut 22 which generates a strong compression between the lower body of the body. actuator, the valve body, the top guide and the nozzle body.

In the injector 10, it has been previously described that the armature-rod assembly 64, although biased by the valve spring 48, can move axially along the second axis A2 between the closed position PFV valve, or low position wherein the armature-rod assembly 64 is remote from the coil 38 and the valve open position POV, or high position in which the armature-rod assembly 64 is near the coil 38. Similarly, although solicited by the needle spring 74, the needle 72 can move axially along the longitudinal axis A1 between a needle closed position PF A, also commonly referred to as a low position in which the needle seat 136 is in sealing contact against the seat 96 of the nozzle body so as to prevent any injection of fuel and, an open needle position PO A, or high position in which the needle seat 136 is away from the seat 96 of the nozzle body so as to allow the passage and injection of fuel. Similarly, the movable piston 114, also biased by the needle spring 74, can move axially along longitudinal axis A1 between an open position of the piston POP, or low position in which the peripheral lip 122 is remote from the lower face 54 of the valve body and a closed position of the piston PFP, or high position in which the peripheral lip 122 is in sealing contact against the lower face 54 of the valve body. The injector 10 is further provided with channels and conduits comprising complementary sections between the injector elements, these channels and conduits form a high pressure circuit 146 and a low pressure return circuit 148 in which, in use of the fuel circulates.

The high pressure circuit 146 includes a first main conduit 150, extending into the actuator body 20 between the inlet port 16 and the lower face 30 of the actuator body, the main conduit 150 being extended by a second conduit 152 passing through the valve body 50 and then through a third conduit 154 passing through the wide cylindrical portion 102 of the top guide, said third conduit 154 opening into the shoulder face 106 of the top guide between the narrow portion 104 and the inner side face of the wall 76 of the nozzle body, and opening into the wide chamber 88 of the nozzle body 28. The high pressure circuit 146 then continues into the interior space 86 of the nozzle body to the injection holes 98. The high pressure circuit 146 further comprises a fourth conduit 156 provided in the top guide 26 and joining said shoulder face 106 within the axial bore 108 where it opens into the annuli space. area defined by the annular groove 126 of the piston 114.

It is then understood that high-pressure fuel entering through the inlet mouth 16 and flowing in the high-pressure circuit 114 arrives in the space of the annular groove 126 and then flows into the first channel 128 of the piston 114 and fills the high concave housing 120.

In the open position of the piston POP, the high-pressure fuel can follow the path indicated by the arrow F1 in FIG. 3. From the top housing 120, it passes above the lip 122, between said lip 122 and the lower face. 54 of the valve body, then flows into the second channel 130 of the piston so as to fill the control chamber 112.

On the other hand, in the closed position of the piston PFP the high pressure fuel leaving the first channel 128 and having filled the high concave housing 120 can not cross the lip 122 which is in sealing contact against the lower face 54 of the valve body.

The low pressure return circuit 148 comprises a discharge duct 158 provided in the valve body and semitransparently sketched in FIGS. 2 and 3. This exhaust duct 158 extends from the underside 54 of the valve body where it opens on the outer portion of the axial bore 108 of the top guide, outside the lip 122 of the piston 114, and extends to open into the bore hydraulic 62. This space between the outside of the lip 122 of the piston 114 and the lower face 54 of the valve body, space in which the discharge conduit 158 opens out forms a second control chamber 160. As shown , the evacuation duct is made of a first short section 162 opening under the valve body 50, connecting perpendicularly to a second longer section 164 going in a straight line to the bore 62. For reasons of feasibility, the second section 164 opens into the lower face 54 of the valve body but this end is closed on mounting by the upper face 100 of the top guide.

The return circuit 148 then continues in the hydraulic distributor bore 62, or even through the holes of the sleeve 70, then up to the low pressure chamber 58 of which said circuit 148 continues through a main return conduit 166 , not shown, which extends in the actuator body 20 in parallel with the main high-pressure conduit 150 from the lower face 30 to the outlet mouth 18.

The return circuit 148 further comprises a valve leak recovery conduit, said conduit also shown semi-transparent in FIG. 2, extends radially in the valve body 50 from the bottom of the axial bore. 56 to join the lateral cylindrical wall of the valve body where the recovery duct opens into an annular space between said side wall and the injector nut 22, to then rejoin the low pressure chamber 58 and the duct main return 166.

It is then understood when the piston 114 is in the closed position PFP, or high position in which the lip 122 is in sealing contact against the lower face 54 of the valve body, the fuel located in the control chamber 112 comes out of it up through the second channel 130 of the piston and then continue in the return circuit 148 by passing successively through the two sections 162, 164 of the exhaust duct.

The general operation of the injector 10 and the different displacements of the moving parts is now described.

At first the coil 38, is not electrically powered, it does not create a magnetic field and therefore does not attract the magnetic armature 66. The valve spring 48 pushes the frame-rod assembly 64 in the closed position PFV, position in which the valve stem 68 closes the hydraulic communication between the axial bore 56 and the low pressure chamber 58 and thus prevents the fuel from joining the return circuit 148. The high pressure fuel entering permanently into the injector, in the absence of evacuation the pressure increases in the two sections 162, 164 of the discharge duct of the valve body and in particular above the piston 114 in the second control chamber 160. The movable piston 114 is pushed back downward to the POP open position and, as previously described, the high pressure fuel can enter the control chamber 112 where the pressure increases and pushes the needle 72 towards bottom, in closed position PF A. On either side of the piston 114 the pressure is then balanced. The needle 72 moves according to a pressure differential between the head and the tip of the needle. Thus, as the pressure increases in the control chamber 112, for the needle 72 to move downward it is necessary to provide the injector 10 with a device to reduce the pressure on the tip side. Those skilled in the art know injectors whose high pressure circuit is provided with a calibrated orifice arranged between the entrance into the control chamber and the injection holes. Such a function can also be achieved by means of a collar, also called in English "boostflange" or "NMC - needle motion control", secured to the needle and leaving only a small passage to the flow of high pressure fuel said passage generating the desired pressure drop on the tip side.

In a second step, the coil 38 is electrically powered, it then generates a magnetic field which attracts the armature 66 which, despite the solicitation of the valve spring 48, rises and approaches the coil 38 in the open position of the valve POV. The fuel previously trapped in the evacuation duct 162, 164 can be evacuated to the low pressure chamber 58 and the main return duct 16. This rapid evacuation creates a negative pressure in the second control chamber 160, which draws the piston upwards, the movable piston 114 is then placed in the closed position PFP, the lip 122 coming into sealing contact against the lower face 54 of the valve body. As previously described, the high-pressure fuel can no longer exit the top housing 120 of the piston and the one that is trapped in the control chamber 112 can exit via the second channel 130, bypass the lip 122 and join the conduit discharge 162, 164, then the return circuit.

Figure 11 is a two-dimensional graph schematically showing the curve of changes in the pressure in the control chamber 112, as a function of time. Above the curve a table indicates the positions in which the armature rod assembly 64, the movable piston 114 and the needle 72 are placed.

The point P1, intersection of the curve with ordinate axis, axis of the pressures, marks the moment when the coil 38 begins to be energized, the armature rod assembly 64 then moves to the open position POV while the pressure in the control chamber 112 is still high and that the needle 72 is in the closed position PFV. From the point PI, the piston is placed in closed position PFP and the pressure in the control chamber 112 decreases until the needle goes back to the open position POA.

The next point P2 marks the instant when the power supply of the coil 38 is interrupted, the armature-rod assembly 64 being immediately pushed by the valve spring 48 in the closed position PFV while the pressure in the control chamber 112 is still low and that the needle 72 is in the open position POA. Very shortly after the point P2, the piston is placed in open position POP and the pressure in the control chamber 112 re-increases to the point where the needle returns to the closed position PF A.

The cycle starts again and the following points P3 and P4 are similar to the points PI and P2, respectively.

An alternative to the first embodiment is now described in connection with FIG. 7. In this alternative, the piston 114 has an outside diameter substantially greater than the diameter of the needle 72. As shown, the lower housing 124 of the The lower face 118 of the piston can be enlarged into a counterbore of sufficient size to accommodate the head 132 of the needle and the spring 74. The arrangement of such a piston 114 obviously requires that the upper end emerging from the axial bore of the upper guide 108 is itself enlarged to receive the new piston widens. The interest of this alternative of realization appears in the explanation of operation. When the needle 72 is in the open position PO A, high position, and the coil 38 is not energized, the valve closes PFV and the pressure begins to rise in the second control chamber 160 just above the upper face 116 of the piston. This face having a larger area, the force generated by the pressure on the piston 114, force proportional to the surface on which the pressure is exerted, is greater than the force of the in the first embodiment and the piston 114 begins to move downward to the POP open position earlier than in the first embodiment which ensures a faster downward movement of the needle 72 to the closed PF A position.

In addition, in view of the new arrangement of the lower housing 124 receiving the head and the needle spring, the dimensions can easily be selected so that as soon as the piston 114 begins to move downwards it enters into mechanical contact with the needle head and then, the axial force exerted on the upper face 116 of the piston is integrally transmitted to the needle 72.

Alternatively, and without coming into contact, the axial force can be transmitted by hydraulic pressure exerted on the head of the needle. The high pressure now acts on the needle 72 by generating on the head an axial closing force directed towards the tip and on the tip an axial force of opening of weaker intensity directed towards the head. These antagonistic forces are unbalanced, since the surfaces of the needle subjected to the high pressure are unequal, the upper face of the piston being the largest. It is then possible to design injectors 10 without a device artificially drop the pressure on the side of the tip, such as the calibrated orifice or collar mentioned above. Indeed, rather than dropping the pressure and the corresponding force at the tip of the needle, which corresponds to an energy loss, it now appears that the piston widens allows to increase the force on the needle head without any loss of energy, the fuel pressure injected by the injection holes 98 being the pressure at which the fuel enters the injector 10 without there being a voluntary loss of pressure.

A second embodiment of the invention is now described with reference to FIGS. 8, 9 and 10, mainly by way of differences with the first embodiment previously described and, while preserving as far as possible the signs and numbers of the references. already used.

Said differences are structural differences which focus on the high guide 26 and the movable piston 114, the general operation of the injector 10 made according to this second embodiment remaining identical to that of the first mode previously described.

The main difference lies in the shape of the axial bore 108 of the high guide and that of the movable piston 114. The bore 108 is formed in a high section 170 serving only as a sliding guide to the piston 114, said high section 170 being of smaller diameter than the low section which forms the upper sliding guide 110 in which the head of the needle 132. The two sections 170, 110 are connected by a connecting disc surface 172 which can, as is shown in the figures be slightly tapered.

The movable piston 114 comprises a cylindrical body 174, slidably arranged in the upper portion 170 of the axial bore 108, a low flange 176 arranged in the control chamber 112 and a connecting shoulder 178 between the flange 176 and the body 174 of the piston. The piston is further provided with an axial opening opening 180 which, according to the alternative shown, comprises a section restriction 182. In addition, according to the alternative shown, the piston 114 is provided with a small calibrated channel 184 extending radially and joining the outer face of the piston 114 to the axial orifice 180. This calibrated channel 184 establishes a permanent hydraulic connection between the high-pressure inlet and said axial orifice 180.

When the piston 114 is in position in the high guide 26, the fourth high pressure conduit 156 opens into the axial bore 108 just above the collar 176. The mobile piston 114 can, like the previous description, move between a high position or closed position PFP in which the shoulder 178 of the piston is in sealing contact against the disc surface 172 of the bore and a low position, or open position POP in which the shoulder 178 and the surface disc 172 are distant from each other. It is understood that when the piston 114 is in the closed position PFP, the fuel located in the control chamber 112 leaves the latter through the axial orifice 180 and then continues in the return circuit 148. passing as previously described, successively by the two sections 162, 164 of the exhaust duct. In addition, in the closed position PFP piston, a little high pressure fuel can flow through the calibrated channel 184 between the arrival and the upper face of the piston. This allows, at the moment when the valve 24 closes PFV, to accelerate the filling of the second control chamber 160 and its rise in pressure which makes it possible to push the piston towards the open position POP.

In the case where the piston 114 is not provided with the calibrated channel 184, then, when closing the valve PFV, the filling of the second control chamber 160 can be done only by fuel passing between the piston 114 and the top portion 170 of the bore 108. This filling can take a relatively long time and, without this solution can be discarded, the realization of the calibrated channel 184 seems preferred.

It is also understood that in the open position of the piston POP, the high pressure fuel enters the control chamber 112, following the path of the arrow F2, passing between the shoulder 178 and the disc surface 172 and pressurizes said chamber 112 so as to push the needle 72 in the closed position PF A.

The following references were used in the description. 10 fuel injector 12 injector head 14 injection nozzle 16 high pressure inlet port 18 low pressure outlet 20 actuator body 22 injector nut 24 control valve 26 high guide 28 30 face nozzle body actuator body bottom 32 male thread of actuator body 34 female thread of injector nut 36 bore of actuator body 38 coil 40 electromagnet 42 electrical connection means 44 connector 46 central bore of coil 48 spring valve 50 valve body 52 upper surface of the valve body 54 lower face of the valve body 56 axial bore in the valve body 58 low pressure chamber 60 bottom of the low pressure chamber 62 bore hydraulic distributor 64 armature-rod assembly 66 armature magnetic 68 valve stem 70 bushing 72 injector needle 74 needle spring 76 nozzle body wall 78 upper face of nozzle body 80 first wide section 82 second trunk Narrow section 84 Transverse disc face of the nozzle body 86 Inside space of the nozzle body 88 Wide chamber 90 Narrow chamber 92 High counterbore 94 Low sliding guide 96 Nozzle body seat 98 Injection holes 100 Upper side of the guide High 102 Part wide cylindrical of the high guide 104 narrow cylindrical portion of the high guide 106 shoulder face of the high guide 108 axial bore of the high guide 110 high sliding guide 112 control chamber 114 movable piston 116 upper face of the piston 118 lower face of the piston 120 housing top 122 peripheral lip 124 lower housing 126 annular groove 128 first channel 130 second channel 132 needle head 134 needle point 136 needle seat 138 small cylindrical protrusion 140 support shoulder 142 needle guide high 144 guide needle low 146 high pressure circuit 148 low pressure return circuit 150 first main pipe high pressure 152 second HP pipe crossing the body 154 third HP conduit valve crossing the top guide

156 fourth duct HP 158 exhaust duct 160 second control chamber 162 first short section of the exhaust duct 164 second section of the exhaust duct 166 main return duct Specific references to the second embodiment 170 high section of the bore axial axis of the upper guide 172 disc surface of the axial bore of the upper guide 174 cylindrical body of the piston 176 low flange of the piston 178 piston shoulder 180 axial opening opening of the piston 182 restriction of section 184 radial channel

A longitudinal axis A2 second axis PFV closed position e valve POV open position of the valve PFA closed position of the needle POA open position of the needle PFP closed position of the piston POP open position of the piston

Claims (15)

A fuel injector (10) comprising a body in which a needle (72) moves between an open position (POA) and a closed position (PFA) under the influence of fuel pressure in a control chamber (112). ), chamber (112) in which opens a high pressure supply channel. (346, 156, 130) and from which a discharge channel (158, 162, 164) controlled by a two-way solenoid valve (24) is fed back to a low-pressure return circuit (148), so that in the closed position of the solenoid valve (PFV) the pressure increases in the control chamber (112) urging the needle (72) towards the closed position (PFA) and, in the open position of the solenoid valve (POV) the fuel is evacuated from the control chamber (112) in which the pressure decreases allowing the needle (72) to move in the open position (POA), characterized in that the injector (10) further comprises a means ( 26, 114) which prevents the fuel from flowing directly from the feed channel (146) to the return circuit (148) when the solenoid valve (24) is in the open position (POV), said means Dynamic leakage reduction device (26, 114) comprising a movable member (114) moving between an open-position (P) OP) and a closed position (PFP), under the influence of the fuel pressure differential existing between the control chamber (112) and a second control chamber (160) in fluid communication with the evacuation channel (148). ), and wherein the movable member (114) is a cylindrical piston provided on its side cylindrical face with an annular groove (126), the cylindrical piston being slidably disposed in a bore (108) of the injector body, the channel supply (148, 156) opening into the annular space defined by the annular groove (126) into said bore (108), said piston (114) moving to an open position (POP1) when the solenoid valve (24) ) is in the closed position (PFV) so that the high pressure fuel can enter the control chamber (112) and move to a closed position (PFP) when the solenoid valve (24) is in the open position (POV) ) so as to prevent the entry of high fuel p in the control chamber (112). Injector (10) according to claim 1 wherein said bore (108) is coaxial (Al) with the bore (110) in which the needle (72) slides. 3. Injector (10) according to any one of claims 1 or 2 wherein the piston (114) comprises an enlarged base surmounted by a cylindrical body of smaller diameter, the lower face (118) of said base being arranged in view of the needle (72), the junction face between the base and the body forming a sealing face cooperating with a seat provided in the injector body, so that in the closed position of the piston (PFP) the sealing face and the seat are in sealing contact preventing the entry of high pressure fuel into the control chamber. Injector (10) according to claim 3 wherein the piston (114) is further provided with an opening channel (180) permanently communicating in fluid communication the control chamber (112) and the second control chamber ( 160). Injector (10) according to claim 4 wherein said opening channel (180) is provided with a section restriction generating a pressure drop so that the pressure in the control chamber (112) is greater than the pressure in the pressure chamber. the second control chamber (160). 6. Injector (10) according to any one of claims 4 or 5 wherein the piston (114) is provided with a calibrated channel extending radially between the outer cylindrical surface of the cylindrical body and said opening channel (180) so as to establishing a hydraulic communication between the high pressure supply and the second control chamber (160). 7. Injector (10) according to claim 2 wherein the piston (114) comprises a simple cylindrical body extending axially (A1) between a lower face (118) arranged opposite the needle (72), said lower face. (118) forming the ceiling of the control chamber (Π2) and an upper face (116) opposite the lower face (118), said upper face (116) being in contact with a transverse face (54) of the body of the injector when the piston (114) has moved to the closed position (PFP). 8. Injector (10) according to claim 7 further comprising a spring (74) arranged in the control chamber (112) and compressed between a shoulder (140) integral with the needle (72) and the lower face (118). piston (114) so as to permanently urge the needle (72) to its closed position (PFA) and the piston (114) to its closed position (PFP). Injector (10) according to claim 8 wherein the piston (114) is provided with a first channel (128) extending from the outer wall of the piston (114) to the upper face (116) and also a second channel (130) extending between the lower (118) and upper (116) faces, the piston (114) being arranged in its bore so that the feed channel (148, 156) is continuous fluid communication with the first channel (128). Injector (10) according to claim 9 wherein the first channel (128) comprises an annular groove (126) arranged on the outer wall of the piston (114), the first channel (128) extending from said groove (126). ) and opening into the upper face (116) of the piston, the supply channel (148, 156) opening into the space defined by the annular groove (126). 11. Injector (10) according to any one of claims 9 or 10 wherein the piston (114) is further provided on its upper face (116) with a protrusion forming a barrier (122) sealed when the piston (114) ) is in the closed position (PFP), said barrier (122) then being in sealing contact against said transverse face (54) of the injector body, the first channel (128) and the second channel (130) opening in the upper face (116) of the piston on either side of said barrier (122), said second control chamber (160) being the space between the transverse face (54) of the injector body and the upper face (116) piston (14) and delimited by the side of the barrier (122) which open the second channel (130) and the exhaust duct (158). 12. Injector (10) according to claim 11 wherein the barrier (122) is a circular and closed lip, the first channel (128) opening into the central portion and the second channel (130) opening into the outer portion. Injector (10) according to any one of claims 7 to 12 provided with a device for generating on the needle (72) a closing force directed towards the tip (134) of the needle greater than the force aperture directed to the head (132) of the needle so that the fuel pressure injected when the needle is in the open position (POA) is equal to the fuel inlet pressure in the injector (10) . The injector (10) according to claim 13 wherein said device consists of a piston (114) whose cross section is greater than the cross section of the needle (72) so that the pressurized fuel entering the second chamber control device (160) exerts on said piston (114) an increased force. Injector (10) according to claim 14 wherein the piston (114) is dimensioned so that as soon as the piston (114) starts to move to the open position (POP), the increased force exerted by the high pressure fuel in the second control chamber (160) is integrally transmitted to the needle (72), either by mechanical contact between the piston (114) and the needle (72) or by hydraulic pressure exerted on the needle (72), so that the needle (72) experiences a closing force of intensity greater than the opening force exerted by the fuel at the tip (134) of the needle.