The present invention relates to a fuel injector and more particularly to a pressure sensor able to be arranged on said injector.

BACKGROUND OF THE INVENTION

Control of high pressure fuel injection equipment, such as common rail injection equipment, takes into account fuel pressure measured by a sensor arranged on the common rail. EP2694795, JP2013007341 and EP2188517 further disclose embodiments of fuel injectors comprising a pressure sensor arranged directly in their housing, so that the actual pressure inside the injector is determined and sent to the control unit of the injection equipment. These individual pressure sensor enable control optimization of the equipment and reduction of gas emissions.

The downside is that each injector requires specific machining to accommodate said embedded pressure sensor. Therefore upgrade and retrofit of sensor-less injectors and related injection equipment's cannot be done.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to solve the above mentioned problems in providing a sensor and fixation means assembly wherein the sensor is fixed to the fixation means, said fixation means being fixedly attachable on an external convex curved surface of a fuel injector so that, in use, the sensor delivers a signal varying as a function of the fuel pressure in the injector. This provides the advantage to enable fixation of the sensor without any specific machining to be done in the injector.

The assembly may further comprise an electronic card connected to the sensor, the card processing the signal of the sensor. The assembly may also further comprise an electrical connector to which is connected the sensor, said connector being adapted to receive a complementary connector connected to an electronic control unit. The fixation means comprises a clamp with an adjustable feature enabling to tighten the clamp in place around the curved surface.

In an embodiment, the clamp is metallic, the sensor being bonded onto said clamp.

The assembly may also further comprise an elastomer or polymer overmould advantageously protecting the sensor on the fixation means and forming an integral assembly.

In another embodiment, the fixation means comprises a plastic clamp in which is overmoulded the sensor, said sensor being flush to the inner face of the clamp so that, in use, the sensor contacts with the external convex curved surface of a fuel injector.

The pressure sensor may comprise a strain gauge although other technologies of sensors, such are magneto restrictive sensors, are possible.

The invention also extends to a fuel injector having a housing with a main body and a fuel inlet member extending from said main body. The fuel inlet member has an external convex curved surface and, a sensor and fixation means assembly as set in any of the preceding paragraphs. The assembly is fixedly tightened around said external convex curved surface.

The invention also extends to a fuel injector equipment comprising at least one upgraded fuel injector as set in the preceding paragraph and, an electronic control unit receiving the signal of the sensor.

The invention also extends to a method to upgrade a fuel injector, the method comprising the steps of:

- providing a fuel injector not originally equipped with a pressure sensor, - providing a sensor and fixation means assembly as set in any of the claims to,

- upgrading the fuel injector by fixing said assembly on an external convex curved surface of the injector.

The method to upgrade a fuel injector further may also comprise the step of bonding with an adhesive the sensor and fixation means assembly on an external convex curved surface of the injector.

The method to upgrade a fuel injection equipment may also comprise a plurality of sensor-less injectors, the method comprising the steps of: - upgrading the injectors according to a method as set in claim or,

- connecting the sensors to an electronic control unit controlling the operation of the upgraded injection equipment by taking into account the signals S delivered by the sensors.

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 view of a fuel injector of the prior art.

Figure 2 is the injector of figure 1 to which is connected a fuel inlet pipe.

Figure 3 is a view of a sensor and fixation means assembly according to a first embodiment of the invention.

Figure 4 is a view of a sensor and fixation means assembly according to a second embodiment of the invention.

Figure 5 is an axial view of the fuel injector of figure 2 on which is fixed the assembly of figure 3.

Figure 6 is a section of figure 5 transversal to the sensor and its fixation mean.

Figure 7 is an axial view of the fuel injector of figure 2 on which is fixed the assembly of figure 4.

Figure 8 is a section of figure 7 transversal to the sensor and its fixation mean.

Figure 9 is another view of the sensor and fixation means assembly of figure

3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In reference to figures 1 and 2 is described a fuel injector 10 of the prior art part of a fuel injection equipment 11 adapted to deliver fuel into a combustion chamber of an engine. The injector 10 comprises a housing 12 having a main body 14 and an integral inlet member 16. The main body 14 extends along a main axis A from a nozzle 18, at the bottom of the figure, to a head 20 over which is arranged an electrical connector 22. From said housing head 20 laterally extends the inlet member 16, the extremity of which being threaded 23 for complementary sealing connection of a fuel inlet pipe 24 fixed in place with a nut 26. An inner conduit 27, visible on figures 6 and 8, extends through the inlet member 16 to enable the fuel under pressure to flow from the inlet pipe 24 to the nozzle 18. Externally, the inlet member 16 has a cylindrical surface 28 extending between the head 20 of the main body 14 and the first turns of the thread 23. On figure 2 the nut 26 is tightened in place and, the visible portion of the cylindrical surface 28 solely extends from the head 20 to said nut 26.

A first embodiment of a sensor and clamp assembly 30 is now described in reference to figure 3 where said assembly 30 is represented alone and also in reference to figures 5 and 6 where it is assembled on the injector 10.

The assembly 30 comprises a flexible metallic circular clamp 32 that extends between two extremities 34, 36. The flexibility enables to open the clamp 32 in order to engage the opening created between the two extremities 34, 36, around the cylindrical surface 28. While a first extremity 34 is provided with a through hole enabling passage of a screw 38, the second extremity 36 is provided with a threaded hole 40 enabling tightening of the screw 38 and closing of the clamp 32.

As visible on figure 5, the width W of the clamp 32 is inferior to the length visible portion of the cylindrical surface 28 so that, the sensor and clamp assembly 30 can easily be fixed around said cylindrical surface 28 by tightening the screw 38. When tightened, the clamp 32 generates on the inlet member 16 radial compression forces and, the inner surface on the clamp 32 comes in intimate contact with the external surface 28 of the inlet member.

On the outer face of the clamp 32 is bonded, for instance by gluing, at least one strain gauge 42 electrically connected via wires 44 extending from the gauge 42 to an extremity where a small electrical connector 46 is. A preferred embodiment for the strain gauge 42 is represented by the thick black line on figures 3 and 6 and better visible on figure 9. The gauge 42 is a band extending around a large portion of the circumference, such as 270° or it could have two opposite portions of 90° each.

A polymer, such as a high temperature polyamide, or elastomer, such as a fluorocarbon rubber, overmould 48 is incorporated to the clamp 32 in order to protect the gauge 42, the electrical connections and the wires 44. Also, the assembly 30 could comprise a small electronic card 49 closely connected to the sensor 42, said card processing the signal S delivered by the sensor 42. The card 49 can be in the overmould 48, close to the sensor and the clamp or, as represented on figure 9, in the small electrical connector 46.

In use, the high pressure fuel flowing inside the inner conduit 27 forces the inlet member 16 to radially expand, said expansion being proportional to the fuel pressure. The electrically connected gauge 42 is subject to said expansion and it delivers an electrical signal S that varies as a function to said fuel pressure. The signal S is delivered to a control unit, not represented, which takes it into account as a calculation input for controlling the output parameters of the fuel injection equipment 11.

Multiple constructional alternatives to the sensor and clamp assembly 30 can be derived from the example here above described. For instance, the strain gauge 42, or strain gauges 42 if a plurality, can be replaced by another type of pressure sensor such as a magneto -restrictive or thin- film piezo-electric sensor..

A second embodiment of the assembly 30 is now described in reference to the figures 4, 7 and 8, said second embodiments comprising an integral plastic hook clamp 50, wherein the strain gauge 42 and its electrical wires 44 are overmoulded in the plastic of the clamp 50 so that the gauge 42 is flush with the inner face of the clamp 50 and, when the clamp 50 is hooked on the inlet member 16, the gauge 42 is in direct contact with the external surface 28. In the vicinity of a first extremity 34, the external face of the clamp 50 is provided with external teeth 52 integral with the clamp 50 and symmetrically, internal teeth 54 are provided on the inner face of the clamp 50 in the vicinity of the second extremity 36. When tightening the hook clamp 50 around the cylindrical surface 28, the external 52 and internal teeth 54 complementary engage ensuring closing of the clamp 50.

A known issue with plastic clamps is their lower clamping force, relative for instance to the screw metal clamp 30 of the first embodiment, and their tendency to creep over time which may affect the signal S of the sensor 42. In order to ensure an adequate signal S generation and transmission, it is possible to provide adhesive in order to bond the plastic clamp 50 on the external surface 28 of the inlet member 16. In this respect, the screw clamp 30 of the first embodiment previously described as metallic, can very well be made of plastic material over molding the sensor 42 and its electrical connections 44. In this case the clamp could be bonded onto the cylindrical surface 28 of the inlet member 16.

Another embodiment, not represented, consists in replacing the clamp by elastic ring having an opening enabling to widen it and which, at rest, is smaller than the inlet member external surface 28 so that, it can easily be arranged around the inlet member 16 and, once in place thanks to its elastic properties, the ring closes and tightens on the surface 28. Such ring can be metallic with the gauge 42 and electric wires 44 protected by an overmould or, the ring can be of plastic with sensor embedded in the plastic and flush with the internal face of the ring. In any case, bonding of such elastic ring is also possible ensure longevity of the fixation.

Furthermore, since the injector 10 does not require any modification to receive the assembly 30, 50, said assembly 30, 50, can be arranged on the injectors 10 of fuel injection equipment 11 long after said equipment 11 is in service. Indeed the arrangement of the sensor and clamp assembly 30, 50, can either a standard manufacturing operation or, can also be done as part of a retrofit or an upgrade operation. Afterward, the fuel equipment can operate taking into account the actual fuel pressure inside the injectors 10. This improves the accuracy of the control and, it enables lower fuel emissions.

In case of original mounting or of the retrofit operation requiring disassembly of the injectors 10, a groove 56 could be machined on the external cylindrical surface 28 in order to accommodate, in the groove 56 the clamp of the assembly 30, 50. Such an embodiment is represented on figures 7 and 8. This may be particularly advantageous in case of using a plastic clamp since the groove would enable the sensor 42 to be closer to the inner conduit 27 and be subject to greater radial expansion of the inlet member 16. This is particularly visible when comparing the inlet member 16 of figure 6, without groove, and of figure 8, with groove 56, where the latter diameter is reduced.

Although the external surface 28 has been described as a known cylinder of revolution, any surface having a portion with a convex curved cross section, such as elliptic, oval, oblong or even a frusto-conical surface would be appropriate to implement the invention. The following references have been utilized in this description:

10 fuel injector

11 fuel injection equipment

12 housing of the injector

14 main body of the housing

16 inlet member

18 nozzle

20 head of the injector

22 electrical connector

23 thread

24 fuel inlet pipe

26 nut

27 inner conduit

28 external cylindrical surface

30 sensor and clamp assembly

32 screw type clamp

34 first extremity of the clamp

36 second extremity

38 screw

40 threaded hole

42 strain gauge

44 electrical wires

46 another electrical connector

48 overmould

49 electronic card

50 integral plastic clamp

52 external teeth integral to the clamp

54 internal teeth integral tot he clamp

56 groove

A main axis

W width of the clamp

S electrical signal