The present invention relates to a fuel injector and more particularly to means improving the gain curve linearity.

BACKGROUND OF THE INVENTION

In hydraulically controlled fuel injectors, typically diesel injectors having an electro-valve with a solenoid cooperating with a magnetic armature integral to a valve spool, fuel event are indirectly commanded by energizing said solenoid attracting the armature-and-spool assembly. This opens a control chamber spill orifice through which fuel pressurized expels enabling lift of a needle valve and spray of fuel via injection holes. A theoretical linear gain curve rules the fuel injection quantity as a function of solenoid power timing and duration. Problem occurs as unequal fuel pressures around armature generate forces disrupting the displacements and said theoretical linearity of the gain curve. SUMMARY OF THE FNVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a control valve assembly of a fuel injector adapted to be arranged between a nozzle assembly and an actuator assembly. The control valve assembly has a body extending along a main axis between a transverse first face and an opposed transverse second face and being provided with a recess dug in said second face and a bore opening in the bottom face of said recess and axially extending to the first face of the body. The control valve assembly further comprises an armature-and-stem-assembly arranged within said recess and bore and being actionable between open and closed positions via a magnetic field generated by a powered solenoid arranged in the body of the actuator assembly. The recess forms a chamber in which the armature is, the stem forming a sliding valve spool in the bore. Advantageously, the control valve assembly further comprises a check valve arranged to prevent flow between the first face of the body and the bottom face of the recess and, to enable flow in the opposite direction.

Also, said check valve comprises a valve member biased by a spring against a seating face that controls a narrow passage.

Also, said valve member is a ball and the seating face is a conical face and, said narrow passage extending from the tip of said conical face to the bottom face of the recess.

The invention further extend to a solenoid of a fuel injector provided with a control valve assembly as described above, the solenoid having an over- moulded core around which is wand a coil defining a central bore axially extending from a transverse lower face of the solenoid toward an end-shoulder face adapted to receive in abutment a pin against which, in use, a valve spring compresses.

The solenoid is further provided with a channel extending inside the over-moulding from said end-shoulder face toward a lateral face of the solenoid.

Also, a second check valve is provided within said channel said check valve preventing, in use fuel flow from said central bore toward the outer lateral face of the solenoid.

Also, the channel comprises an axial portion, and a radial portion joining together in a substantially right angle elbow, the axial portion extending from the end-shoulder face toward said elbow and the radial portion extending from said elbow to said outer lateral face of the solenoid.

Also, said second check valve comprises a valve member biased by a spring against a valve seat controlling a narrow passage joining said elbow.

Also, said valve member is a ball and the seat is a conical face and wherein, said narrow passage joining said elbow extends from the tip of said conical face.

The invention further extends to a fuel injector comprising a control valve assembly as described previously.

Also, the fuel injector further comprises a solenoid as described previously. 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 according to a first embodiment of the invention.

Figure 2 is similar to figure 1 with a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In reference to the figures is described a fuel injector 10 comprising a nozzle assembly 12, a control valve assembly 14 and an actuator assembly 16 firmly held together by a capnut 18 that engages and bears on the body 20 of the nozzle assembly 12 and that is tightened on the body 22 of the actuator assembly 16.

The nozzle assembly 12 comprise the body 20 and an upper guide member 24 provided having a bore 26 defining an upper guiding means aligned with a lower guide means, not represented, and defined directly in said body 20.

For clarity and simplification purposes, the orientation of the figures is utilized to support the description and so, without any limiting intention words such as "upper, lower, above," are utilized.

A needle valve member 28, extending from a head 30 to a tip end, not represented, is slidably arranged between said two guiding means and adapted to translate about a main axis X between a closed position CP and, an open position OP. In use, the needle 28 translates under the influence of pressure variations in a control chamber 32 that is defined in the bore 26, above the needle head 30. When pressure in said control chamber 32 is high, the needle 28 is urged in the closed position CP and, when said pressure drops the needle 28 lifts in open position OP further compressing a needle spring 34 arranged between a shoulder face of the needle 28 and an under face of the upper guide member 24.

The control valve assembly 14 has a body 36 axially X extending from an lower face 38 that is in surface contact against the upper guide member 24 to, an opposed upper face 40 that is in surface contact against the lower face 42 of the body 22 of the actuator assembly. Although the body 36 of the control valve could be in arranged in direct contact against the upper guide member 24, in the embodiment presented on the figures, an intermediate plate member 44 is arranged between said body 22 and member 24. The body 36 is provided with a recess 46 dug in its upper face 40 and also with a hydraulic bore 48 extending between the bottom face 50 of said recess 46 and the lower face 38 of the body. In the embodiment presented said hydraulic bore 48 further extends through the intermediate plate member 44 to open right above the opening of a return conduit 52 provided in the upper guide member 24. The return circuit 52 extends from the guide member 24 to an outlet provided in the head of the injector.

In said recess and hydraulic bore is arranged an armature-and-stem- assembly 54, the stem 56 forms a valve spool 56 slidably arranged in the hydraulic bore 48 and, the armature 58 is a thick disc crimped on said stem 56 and arranged in the recess 46 that forms an armature chamber 46.

In the embodiment presented the stem 56 extends above the armature 58. The lower end the stem forms a valve seat 60 cooperating with the opening of the return conduit 52.

Parallel to said hydraulic bore 48, the control valve assembly 14 is provided with a check valve 62 arranged between the bottom face 50 of the armature chamber 46 and the body's lower face 38. Said check valve 62, or non- return valve, enables downward flow and prohibits upward flow and, it comprises a channel having an upper narrow portion 64 that joins, via a enlarging tapered seating face 65, a lower wider portion 66. In said wider portion 66 are arranged a compression spring 68 biasing a ball 70 against said seating face 65. Alternatively to this spring and ball arrangement, the check valve 62 can be of a different embodiment such as a reed valve, or the ball replaced by a plate...

The intermediate plate 44 is provided with several grooves dug in its upper face and also through channels creating necessary fluid communications for the operation of the injector.

The actuator assembly 16 has its body 22 axially X extending from a lower face 42, that is in surface contact with the upper face 40 of the control valve, to an injector head, not represented, wherein are arranged a fuel inlet, the fuel return outlet and an electric connector. Said body 22 is provided with a bore 74 opening in said lower face 42 and upwardly extending right above the armature 58.

Through the body's 20, 22, 36 of the injector extend a high pressure (HP) channel 76 from the fuel inlet to spray holes provided in the lower end of the nozzle body.

In the bore 74 of the actuator body 22 is arranged an over-moulded solenoid 78 having a coil wand around a core, said over-moulded solenoid extending in the bore 74 from a lower face 80, flush in surface with the lower face 42 of the actuator's body and in abutment against the body 36 of the control valve, to a top end wherefrom electrical leads upwardly extend and electrically connect the coil to the connector.

Said over-moulded solenoid 78 further defines an inner bore 82 in which a coil spring 84 is compressed between a pin 86 urged against the top end of the bore 82 and, the armature 58. The upper part of the stem 56 extending above the armature 58 and axially engaging in the coil spring 84 inside said bore 82.

In operation, fuel pressurized at to a level higher than 2000 bar enters the injector via the inlet and flows in the HP channel 76 toward the spray holes. The HP fuel fills all possible empty spaces and, via grooves and channels arranged in the intermediate plate 44, the fuel fills the control chamber 32. When the solenoid is not energized, the stem downwardly pushed by the coil spring 84 closes the valve seat 60 and the return conduit. Fuel at high pressure then leaks through the functional clearance provided between the stem 56 and the hydraulic bore 48 and, said leaks enter and fill the armature chamber 46 as well as the bore 82 arranged in the solenoid. When the solenoid is energized it generates a magnetic field that upwardly attracts the armature 58, further compressing the coil spring 84 and also lifting the valve seat 60. This opens the return conduit 52 and HP fuel contained in the control chamber 32 is enabled to expel said chamber 32 and flow in the return conduit 52, via other grooves and channels of the intermediate plate 44. Also, because of the armature 58 lifting up, fuel contained in the solenoid bore 82 is forced to exit said bore 82 and to flow around the armature wherefrom it can exit the armature chamber 46 by pushing the ball 70 of the check valve 62, and then the fuel can return to the return circuit 52. Thanks to said check valve 62 pressure around the armature tend to equalize cancelling forces on said armature. In use, as mentioned above, all empty spaces are filled with fuel and, the fuel not sprayed via the injection holes has to return to the outlet. For instance, inside the capnut 18 the annular space SI surrounding the control valve 14 and, the second annular space S2 around the solenoid 78 and inside the bore 74 provided in the actuator body are filled with the fuel and are fluidly connected to the outlet.

In a second embodiment of the invention represented on figure 2, in addition to the check valve 62 provided in the body's 36 control valve, a second check valve 88 is arranged inside the solenoid 78 for controlling a fluid connection provided between the inner bore 82, wherein is compressed the coil spring 84, and said second annular space S2. Said second check valve 88 forbids a flow from the bore 82 to said second annular space S2 while enabling flow in the opposite direction.

Models and conclusive tests have been performed with check valves having balls of 1.5 mm diameter and springs compressed to generate a force of 0.5 N.

As visible on the figure, said fluid communication arranged in the solenoid 78 comprises a upward channel having a wide portion 90 extending from the top end of the inner bore 82 and which end tapers forming a valve seat 92 at the tip of which is a narrow portion 94 that connects into a radial channel 96 extending to the lateral face of the solenoid so that it opens in said second space S2. Similarly to the first check valve 62 provided in the body's 36 control valve, in said wide portion 90 are arranged a compression spring 98 biasing a ball 100 against said seating face 92. In the embodiment presented, said controlled fluid communication further comprises an orifice 102 axially arranged in the pin 86.

Alternatively to this spring and ball arrangement, the check valve 88 can also be of a different embodiment such as a reed valve, or the ball replaced by a plate. Also, alternatively to the representation of the figure, the radial channel 94 can be made at an angle

In use, said second check valve 88 maintains a pressure in the inner bore

82 and tends to further maintain the equal pressures around the armature 58 so that when said armature moves it does not have to overcome additional forces generated by fuel having unequal pressures and that is captured in the inner bore 82 or in the armature chamber 46. Thanks to said check valves 62, 88, the gain curve linearity improves.

LIST OF REFERENCES

X main axis

CP closed position

OP open position

51 first annular space

52 second annular space

10 fuel injector

12 nozzle assembly

14 control valve assembly

16 actuator assembly

18 capnut

20 body of the nozzle assembly

22 body of the actuator assembly

24 upper guide member

26 bore

28 needle valve member

30 neede head

32 control chamber

34 needle spring

36 body of the control valve

38 lower face, first face, of the body of the control valve

40 upper face, second face, of the body of the control valve

42 lower face of the body of the actuator assembly

44 intermediate plate member

46 recess - armature chamber

48 hydraulic bore

50 bottom face of the recess

52 return conduit

54 armature-and-stem-assembly stem - valve spool

armature

valve seat

check valve in the control valve upper narrow portion seating face

lower wider portion

spring

ball

bore

high pressure channel solenoid

lower face of the solenoid bore in the coil

coil spring

pin

second check valve

wide portion

valve seat

narrow portion

radial channel

compression spring

ball