FUEL INJECTOR TECHNICAL FIELD

The present invention relates to a fuel injector and more particularly to a nozzle assembly provided with a contact-less electrical switch enabling determination of a valve member location. BACKGROUND OF THE FNVENTION

In fuel injectors a needle shape valve member reciprocally commutes in a nozzle body between a fully closed position where sloped seating faces are in contact and, a fully open position where said sloped seating faces are lifted away from each other.

Furthermore, recent injectors are provided with electrical switch means informing a control unit of the needle position.

Said switch means comprise electrical insulation of the valve member relative to the nozzle body, especially of the valve guiding faces that slide against faces of the body, the sloped seating faces remaining uncoated to enable closing of the switch when they are in contact, the closed position meaning that fuel injection is prevented, and open of the switch as soon as the needle lifts and the seating faces split, the open position meaning that fuel injection occurs.

Unfortunately, physical contact induces wear of the seating and damages of the faces and furthermore, incorrect information may be sent to the control unit since, when the seating faces are away from each other by a short distance of few microns, since they are no more, or not yet, in contact the electrical circuit is open informing the control unit that fuel injection occurs when in reality fuel does not flow yet through the gap of few microns. SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a nozzle assembly of a fuel injector adapted to be arranged in a fuel injection equipment of an internal combustion engine. The nozzle assembly comprises a nozzle body provided with a bore extending along a main axis and a valve member having an elongated needle shape extending from a head extremity to a pointy extremity.

The needle is slidably guided in said bore between lower and upper guiding means wherein in use, fuel pressure variations in a control chamber, wherein protrudes the head extremity of the needle, force the needle to reciprocal displacements in the bore between a fully closed position forbidding injection via spray holes, where a male seating face provided at the pointy extremity of the needle abuts in sealing contact against a complementary female seating face of the nozzle body and, a fully open position enabling said injection events, said male and female seating faces being away from each other. The lower guiding means is arranged in the vicinity of the seating faces and, the upper guiding means is arranged in the vicinity of the control chamber, said guiding means comprising the sliding fit of male needle faces with female body faces.

Advantageously, the nozzle assembly is further provided with a contact- less switch means adapted to commute between an open state and a closed state in order to enable electrical detection of the position of the needle.

Also, said switch means comprises electrical insulation of the needle relative to the nozzle body, said insulation being provided by insulation coating covering at least one of the male needle faces or female body faces of each guiding means and, at least one of the seating faces, to the exception of a needle uncoated zone and of a bore uncoated zone, the electrical circuit being in a closed state only when said uncoated zones are facing each other without contact.

Also, the uncoated zones are arranged so that the switch means commutes around a needle position where the seating faces are away from each other by a predetermined gap.

Furthermore, the switch means is in closed state when the distance between the seating faces is smaller than said predetermined gap, and wherein the switch means commutes to the open state when the distance between the seating faces is superior to said predetermined gap.

More precisely, said predetermined gap is approximately 10 μιη and preferably 5μιη.

Also, the uncoated zones are preferably arranged on the sliding faces of the lower guiding means. Also, between the upper and the lower guiding means the needle has an elongated thin core narrower than its male face of the lower guiding means and, the body has a larger section than the female face of the lower guiding means.

Furthermore, said needle male face of the lower guiding means axially extends from an upper edge to a lower edge, a needle shoulder face joining said upper edge to the thin core and, said body female face of the lower guiding means axially extends from an upper edge to a lower edge, a body shoulder face joining said upper edge to said larger section of the bore.

Also, the uncoated zones extend on said male and female faces of the lower guiding means.

Moreover, the upper edges of the needle and of the body are sharp edges.

In fully closed position of the needle, the upper edge of the needle male face is substantially aligned to the upper edge of the body female face.

The needle uncoated zone extends from said upper edge of the needle male face. Also, the needle uncoated zone further extends on the peripheral area of the needle shoulder face.

To the exception of the uncoated zone, the insulation coating only covers the needle male face of the lower guiding means, the body female face being uncoated.

In fully closed position of the needle, the uncoated zone of the needle faces the uncoated body female face of the lower guiding means.

The invention further extends to a fuel injector comprising a nozzle assembly as described above. BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 is an axial section of a diesel fuel injector.

Figure 2 is a magnified section of a portion of the injector of figure 1. Figure 3 is a transverse section of figure 2.

Figure 4 is a further magnified view of a switch means on the injector of figures 1 and 2. Figures 5, 6 and 7 are three sequence of operation of the injector of figure 1 and the switch means of figure 4.

Figures 8 and 9 are two embodiments of the switch means of figure 4. Figure 10 is a plot of the injector needle movement in relation to the switch means state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In reference to figure 1 is represented an section of a diesel fuel injector 10 along a main axis X. In the bottom part, as per the arbitrary and non- limiting orientation of the figure, the injector 10 is provided with a nozzle assembly 12 comprising a nozzle body 14 in which is slidably arranged a needle-like valve member 16.

The lower extremity of said nozzle assembly 12 is magnified on figure 2 and a transverse section is presented on figure 3. As can be observed the nozzle body 14 has a wall 18 defining an inner bore 20 which, from top to bottom of figure 2, comprises a cylindrical upper face 22 of diameter D22 ending on a shoulder face 24 which extends and narrows the section of the bore toward a circular sharp upper edge 25 joining an axial cylindrical guiding face 26 of smaller diameter D26 than the upper face 22. The shoulder face 24 can be planar and transverse or alternatively slightly sloped as represented. The guiding face 26 downwardly extends from said sharp upper edge 25 to a bottom tip end 28 of the nozzle body where the inner face of the wall defines a female sloped seating face 30 which smallest section opens in a sac 32 wherefrom depart spray holes 34 extending through said tip end of the wall. Alternatively, the guiding face 26 could extend from the upper edge 25 down to a lower edge 35, not represented, wherefrom the bore section could enlarge again.

The needle-like valve member 16 is complementary arranged in the bore 20 and it has an elongated body extending from a head end 36, protruding in a control chamber 38, a thin core 40 of diameter D40 downwardly extending from said head 36 toward a needle sloped shoulder face 42, that alternatively to the sloped representation, could be planar and transverse, and which enlarges the section of the needle from said thin diameter D40 toward a peripheral circular upper edge 44 wherefrom downwardly extends a cylindrical male guiding face 46 of diameter D46, said male guiding face 46 axially extending from said upper edge 44 to a sharp lower edge 48 wherefrom the needle narrows again in one or several portions as represented. The ultimate ending portion forms a male sloped seating face 50. Furthermore, the cylindrical male guiding face 46 is provided with three flats 52 enabling in use fuel flow toward the spray holes 34. The flats 52 limit the male guiding face 46 to three circular 46a, 46b, 46c, portions better visible on the transverse section of figure 3. Alternatively, the male guiding face could be provided with only one flat or two or four or any other number of flats.

As shown on the figure, once slidably arranged in place in the nozzle body, the three portions 46a, 46b, 46c, of the male guiding face 46 of the needle cooperates with the female guiding face 26 of the bore, thus forming lower guiding means 54, the nozzle assembly 12 also comprising upper guiding means 56 arranged between the head end 36 and the control chamber 38.

In use, a command unit (ECU) 58 controls fuel flow in the injector 10 and, upon fuel pressure variations occurring in the control chamber 38 and imparting forces on the needle 16, the needle 16 reciprocally translates in the bore guided by the upper guiding means 56 and the lower guiding means 54, between a fully closed position CP where the male seating face 50 abuts in sealing contact against the female seating face 30, thus preventing fuel injection through the spray holes 34 and, a fully open position OP where said seating faces 30, 50 are distant from each other, enabling fuel injection event. This indirect control of the needle motion is typical of diesel fuel injector wherein the fuel pressure reaches 2000 bars or more. In such diesel injector an electro -magnetic actuator operates a control valve which in turn controls the inner pressure of the control chamber enabling hydraulic control of the needle motions.

In order to vary an electrical signal S informing the ECU 58 of the needle position in the bore, the injector is further provided with switch means 59 that commute in a closed position CS when the needle is in closed position CP and that opens OS when the needle has left the closed position. The switch means 59 is arranged within an electrical circuit 60 comprising the metallic core of the needle, the metallic nozzle body and also, coating of the needle 16 with an electrically insulating material 61 on said faces which cooperate in close contact with faces of the bore, to the exception of an uncoated zone 62 where the metal of the needle is exposed. Specifically, although not limited to these faces, in the lower part of the nozzle body shown on figure 2, the needle 16 is coated on its circular portion of the male guiding face 46a, 46b, 46c, and also on the sloped male seating face 50, the uncoated zone 62 extending over said coated faces. Other faces than those of the lower guiding means 54 of the needle are coated, for instance in the area of the upper guiding means 56. Alternatively to the uncoated zone 62 wherein the metal is exposed, said zone could be coated with a conductive coating and, in this alternative what is identified in this description as the "uncoated zone" should be referred to a "conductive zone". This alternative might be more complex to implement than just reserving an "uncoated zone" but, this would allow the system to operate at lower voltage for the switch signal since, there would be no, or minor, thickness differences between the insulation coating and the conductive coating and therefore, the coated conductive face would be closer to the opposite conductive face. Further magnified in figure 4 is now detailed the upper area of the lower guiding means 54 where the male guiding face 46 of the needle, covered with said insulating coating 61 having a thickness T61, slides against the female guiding face 26 of the bore and, as it is represented, the uncoated zone 62 extends on both sides of said upper edge 44, downwardly on the top of the male guiding face 46 and also upwardly on the periphery of the shoulder face 42. The bore faces are not coated and, in fully closed position CP of the uncoated zone 62 faces the upper edge 25 of the bore and the top part of the female guiding face 26 of the bore. In operation the faces of the lower guiding means 54 slide against each other and the metallic part of it remain at a distance from each other equal to the thickness T61 of the coating.

Conclusive tests have been performed in coating a needle with insulation coating made of Aluminum oxide, Zirconium oxide in thickness varying from 1 to 5 μιη. Other type of coating such as DLC or commercial coating known under the names of Diaforce, SiCon, could also be used, in thickness superior to 2 μιη. Requirement for the insulation coating 61 is to have low conductivity versus gap (62) conductivity, and resistance to wear, in order to avoid degradation of the insulation over time and high resistance to wear. Gap conductivity qualifies the electrical conductivity of an exposed zone, uncoated, which is typically filled with fuel. The coating is expected to prevent flow of electrical current relative to this uncoated case.

The uncoated zone 62 operates as a contact-less switch 64 now detailed in reference to the figures 5, 6 and 7.

In figure 5, the needle is open, either in fully open position OP or in ballistic mode between said extreme closed and open positions, the uncoated zone 62 does not face any face of the bore, the switch 59 is in open state OS and no signal S is received by the ECU 58 which interprets this as an open position of the needle, enabling fuel injection through the spray holes 34.

In figure 6, the needle has downwardly travelled and the uncoated zone 62 has moved to face the upper edge 25 of the bore. Electrical field in the electrical circuit 60 has concentrated around the sharps edges 25, 44, of the bore and of the needle and, even in absence of physical contact, the seating faces 30, 50, still being distant from each other, the switch 59 closes CS and current flows between the needle and the bore as it is sketched by the arrows A. The closing of the switch 59 occurs before the needle reaches the fully closed position CP, when a predetermined gap G remains between the seating faces 30, 50. This gap G is too narrow and not sufficient to enable fuel passage between the seating faces and consequently fuel injection. The ECU advantageously interprets the early closing of the switch 59 as a signal that fuel injection has ended.

Electrical field concentration is known a geometrical effect. All the field lines have a trend to connect to the closest opposite point, between two surfaces at different voltage. In the case of two parallel plates, all distances are equal and field is then uniform. If there is a peak in the surface, or a sharp edge, this edge can be the "closest" opposite point, for many location of the opposite surface, and therefore, the field will then have a concentration on this edge.

In figure 7, the needle is in fully closed position CP and the switch 59 remains in closed state CS, the electrical current passing via the uncoated zone 62 and the sharp edges 25, 44 and the rest of the surface, below edge 25

When the needle opens, travelling in the reverse direction from the figures 7 to figure 5, the switch 59 remains closed CS during a short period after the needle has started to lift and, the switch commutes in open position once the sharp edges 25, 44, are distant enough so the electrical current can no longer pass, or "flows", from one edge to the other, this distance corresponding to the lift of the needle where the gap G is between the seating faces 30, 50.

Subsequent figures 8, 9 and 10 have to be observed together, figure 8 being the case of a first embodiment where the uncoated zone 62 is a short uncoated zone, now referenced 62S, corresponding to a small gap G and, figure 9 being a second embodiment where the uncoated zone is an extended uncoated zone referenced 62E for a more important gap G.

As this is sketched in comparison of the figures 8 and 9, the extended uncoated zone 62E is larger and axially extends on a wider area of the male guiding face 46 of the needle.

Figure 10 is a double plot representing the needle lift, on the top curve, in relation to the switch 59 position on the bottom curve. The plots represent the needle position and switch state along the time one injection event. The case of the short uncoated zone 62S and the case of the extended uncoated zone 62E are overlaid on the plot of figure 10.

Following the case of the short uncoated zone 62S of figure 8 the plots progress as follow:

- in an initial opening phase PI, from time tO to time tl, the ECU 58 commands a lift of the needle. The needle is in fully closed position CP and, the switch is in closed position CS.

- in a second phase P2S, from time tl to time t2S, the needle initiates a lift movement. The distance between the seating faces 30, 50, remains smaller than the predetermined gap, here referenced GS and, the switch 59 remains closed CS. At time t2S, the needle rises so the distance between the seating faces 30, 50, is now superior to the predetermined gap GS and the switch 59 opens OS.

- in a third phase P3S, the needle continues to lift toward the fully open position OP, the top plot of said lift raising and the switch 59 remains open OS.

As it is represented on the figure, the nozzle assembly is provided with another switch means that closes when in fully open position of the needle. There, the signal communicated to the ECU 58 commutes back to the closed position while the plot of the needle lift reaches a plateau indicating the fully open position OP of the needle. - in a fourth phase P4S, the pressure in the control chamber continues to rise and the needle moves toward the closed position CP this move being indicated by the decreasing slope of the top plot. Actually, the pressure in the control chamber starts to rise before the fourth phase. Beginning of said fourth phase is the moment when the needle begins its ballistic movement downwards, the pressure in control chamber having reached the level high enough to push the needle downward. The switch 59 remains open OS, until a time t4S where, the needle being very close from the fully closed position CP, the switch 59 closes CS again, the seating phases 30, 50 being apart by the gap GS.

In the final fifth phase P5S, the needle continues its downward move toward the fully closed position CP, closing the gap G and, the switch 59 remains closed CS.

The plot corresponding to the extended uncoated zone 62E is similar to the above description for the short zone as the behavior of the needle and of the switch as similar. The predetermined gap is chosen to be larger and is now references GE. The differences are that the second phase, now identified P2E, extends from time tl to a time t2E occurring later than the time t2S because it takes a longer time for the needle to raise so the extended uncoated zone 62E is moved away from the bore face 26 of the lower guiding means. Symmetrically, at the end of the cycle, in the case of the extended uncoated zone 62E, the switch 59 closes CS at an earlier time t4E than the time t4S, simply because the needle in its closing displacement reaches earlier said predetermined gap GE and, the uncoated zone 62E faces earlier the bore face 26 of the lower guiding means.

Conclusive tests have been performed where the gap G was between

A preferred location for the uncoated zone 62 is as previously described by the upper edges 44 of the lower guiding means 54. Other location can be chosen to create a contact-less switch 59, such as the lower edge 48 of the same lower guiding means 54.

In this alternative, the female guiding face 26 needs to be ended into a lower shoulder face or an annular groove in order to create a sharp groove at the lower end of the female guiding face. Therefore, in fully closed position CP of the needle the uncoated zone 62 faces said annular groove beneath the female guiding face 26 of the bore and the switch means 59 is in open state OS. When the needle lifts up and reaches an altitude equal to the gap G, the uncoated zone 62 faces the female guiding face and the switch 59 closes. The signal S received by the ECU 58 is reversed: closed state CS of the switch corresponds to open position OP of the needle and open state OS of the switch means closed position CP of the needle, at least a smaller gap than gap G and no fuel injection.

Another alternative to the main description is to coat the surfaces of the bore rather than those of the needle or, both the faces of the bore and of the needle. In this case of double insulation, the switch means would require to reserve a needle uncoated zone and a bore uncoated zones, said two uncoated zones facing each other to commute the switch in closed state CS.

Also, the contact-less switch means could be implemented in the vicinity of the upper guiding means, by the head end 36 of the needle. LIST OF REFERENCES

A arrows

CP fully closed position of the needle

CS closed state of the switch

D22 diameter of the upper face of the bore

D26 diameter of the female guiding face

D46 diameter of the male guiding face

G gap

OP fully open position of the needle

OS open state of the switch

S electrical signal

T61 thickness of the coating

X main axis

10 injector

12 nozzle assembly

14 nozzle body

16 needle - valve member

18 wall of the nozzle body 20 bore

22 upper face of the bore

24 bore shoulder face

25 peripheral circular upper edge of the bore

26 female guiding face

28 tip end of the nozzle

30 female sloped seating face

32 sac

34 spray holes

35 lower edge of the female guiding face

36 head end of the needle - head extremity

38 control chamber

40 thin core of the needle

42 needle shoulder face

44 peripheral circular upper edge of the needle

46 male guiding face of the needle

46a circular portion of the male guiding face

46b circular portion of the male guiding face

46c circular portion of the male guiding face

48 lower edge of the male guiding face

50 male seating face

52 fiat

54 lower guiding means

56 upper guiding means

58 command unit - ECU

59 switch means

60 electrical circuit

61 insulation coating

62 uncoated zone

62S short uncoated zone

62E extended uncoated zone