EP3076002B1 - Fuel injector - Google Patents

Description

State of the art

The invention relates to a fuel injector according to the preamble of claim 1.

Such a fuel injector is from the post-published DE (R. 356739) A1 the applicant or the DE 10 2010 016 424 A1 known. In the known Kraftstoffinjektor is used to detect the closing time of the nozzle needle, wherein this hits its seat in the injector and thereby at least indirectly closes injection openings formed in the injector, a measuring device with a sensor element which is arranged in the region of a supply bore on the injector. The supply bore supplies a high-pressure space, in which the nozzle needle is arranged, with fuel under high pressure. In particular, the injector housing in the region of the measuring device on a deformation region which is formed elastically deformable in dependence on the fuel pressure in the supply bore. With a pressure increase in the supply bore, the deformation area bulges outwards, which can be detected by means of the sensor element having a piezo element. The sensor element is connected in the known fuel injector by means of an adhesive bond with the deformation region and adapted to detect occurring in the contact region to the injector housing strains or tensile stresses, the size or height of the strains depending on the pressure in the supply bore. Characteristic of the above-mentioned closing of the injection openings through the nozzle needle is that thereby a relatively strong or rapid increase in pressure takes place in the supply bore, since no more fuel is discharged through the injection openings, wherein the pressure increase is detected by means of the sensor element. Since the adhesive connection used in the known fuel injector between the piezoelectric element and the injector, in particular over the life Considering the fuel injector is exposed to external influences or media that can adversely affect the strength or reliability of the adhesive bond, it is provided in the known fuel injector, to act on the sensor element or piezoelectric element in the direction of the adhesive bond with an axial force. This is done by means of a support device, which is connected in the region of a particular blind hole-shaped recess or a flattening with the wall of the recess or flattening in order to be able to apply the required axial force to the piezoelectric element or the adhesive bond. In addition, it is generally known that a piezoelectric element is relatively sensitive to tensile stresses occurring in it, whereas compressive stresses can be relatively absorbed by the piezoelectric element. The supporting device known from the cited document thus fundamentally additionally effects an improved functionality of the piezoelectric element.

When mounting the measuring device, it is necessary to mount or arrange the required components in the region of the recess of the injector. This takes place, for example, with the fuel injector already mounted, or immediately after the production of the injector housing. In any case, it is necessary for the arrangement of the measuring device to connect the corresponding components with the injector, wherein the functionality of the measuring device can only be checked after installation. If, for example, a malfunction occurs or the measuring device does not operate faultlessly, usually not only the measuring device but also the injector housing is to be regarded as waste. In addition, the formation of an adhesive bond is fundamentally a critical manufacturing process, since in particular it must be avoided that the adhesive bond over the service life of the fuel injector in operative connection with the addressed aggressive media (liquids or gases) passes.

Disclosure of the invention

Based on the illustrated prior art, the invention has the object, a fuel injector according to the preamble of the claim 1 such that an optimized manufacturing process is made possible. In the context of the invention, an optimized production process is understood in particular to be the possibility of being able to check the measuring device or the sensor element in a state that has not yet been connected to the injector housing, in order to avoid mounting with the injector housing in the case of a faulty sensor element or faulty measuring device to be able to. In addition, the measuring device should be able to be connected to the injector housing in the deformation area without the use of an adhesive connection, and the sensor or piezo element should be characterized by a high degree of robustness, in particular when tensile stresses possibly occur from it.

This object is achieved in a fuel injector with the characterizing features of claim 1, characterized in that the sensor element is received under axial bias in a sensor housing, wherein the sensor element forms a preassemblable assembly together with the sensor housing, wherein the assembly is connectable to the injector, and wherein the sensor element is separated from the surface of the deformation area by the sensor housing.

In other words, this means that the sensor element or the measuring device after its manufacture or arrangement in the sensor housing is verifiable, without requiring a mounting of the measuring device to the injector is required. In addition, the coupling or connection of the sensor element to the deformation region on the injector housing takes place indirectly via the sensor housing of the sensor device in that the sensor housing is arranged between the surface of the deformation region and the sensor element. The sensor housing makes it possible in particular to arrange the sensor element within the sensor housing under axial prestressing, whereby the above-mentioned advantages in terms of robustness of the sensor element is achieved by avoiding tensile stresses, since any tensile stresses occurring are compensated or overcompensated by the compressive stresses acting on the piezoelectric element ,

According to the invention, the sensor housing is designed as a closed housing. As a result, in particular both the mechanical robustness of the sensor element against external (mechanical) influences is improved, and in particular the entry of media harmful to the piezoelectric element into the sensor housing is prevented.

Advantageous developments of the fuel injector according to the invention are listed in the subclaims.

In order to apply the desired or required axial prestressing to the piezoelectric element, it is provided that the sensor housing has two housing elements with housing walls, between which the sensor element is received, and that the distance between the two housing walls to produce the axial bias on the sensor element adjustable is trained.

In a preferred concrete constructional embodiment for generating the axial preload force by the two housing elements, it is provided that the two housing elements are designed to be displaceable relative to one another in an overlapping region.

The sensor housing can be formed particularly simply or from as few individual parts as possible when the two housing elements are at least substantially pot-shaped, wherein the interior for accommodating the sensor element is formed by two overlapping side walls and two bottom or lid regions arranged parallel to one another. which form the housing walls. The sensor housing thus requires only two components which overlap each other in the overlapping area and receive the sensor or piezoelectric element in their interior.

In order to define the desired or required axial preload force on the piezoelectric element or to maintain it over the service life of the fuel injector, it is provided that the two housing elements in a state in which acts on the sensor element, the desired axial bias, firmly connected are, in particular by a circumferential weld. Such a weld seam can be formed in a particularly simple and accurate manner by a laser beam welding device, wherein a circumferential weld seam in particular reliably prevents the entry or penetration of media into the interior of the sensor housing.

For connecting the sensor housing to the injector housing and thus in particular the possibility of transmitting stresses from the deformation region via the sensor housing to the sensor element is preferably effected by one of the housing elements on the injector housing side facing a flange-like connection region for abutment with the injector.

In particular, it is provided that the housing elements are made of metal and that the connection to the injector by means of a welded joint. Also for this case, the mentioned weld joint between the sensor housing and the injector is preferably formed by means of a laser beam device.

In order to avoid, for example, without additional adhesive layers within the sensor housing electrical insulation between the at least partially made of metal sensor housing and the relevant elements of the piezoelectric element or sensor element, it is provided that the sensor element near the sensor housing via electrically non-conductive insulating layers directly in abutting contact is arranged with the sensor housing.

The fuel injector is exposed to large temperature fluctuations during operation, ranging from, for example, from -30 ° C during cold start up to more than 100 ° C. These temperatures are also transferred to the sensor housing or the sensor element, so that due to different materials for the sensor housing and the sensor element to different (geometric) expansions in the temperature range mentioned can, which lead to the desired axial biasing force on the Sensor element changes. To compensate for this effect at least partially, it is provided in a further embodiment of the invention that the force exerted on the sensor element axial biasing force is at least substantially independent of temperature by a choice of material for the sensor housing and / or a dimensioning of the components.

Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawing.

Fig. 1

eine stark vereinfachte, teilweise geschnittene Seitenansicht eines erfindungsgemäßen Kraftstoffinjektors mit einer Messeinrichtung zur zumindest mittelbaren Fassung des Kraftstoffdrucks im Kraftstoffinjektor und

Fig. 2 und Fig. 3

unterschiedliche Ausführungsbeispiele eines Gehäuses zur Aufnahme eines als Piezoelements ausgebildeten Sensorelements, das mit dem Injektorgehäuse verbunden ist, jeweils im Längsschnitt.

This shows in:

Fig. 1

a greatly simplified, partially sectioned side view of a fuel injector according to the invention with a measuring device for at least indirect version of the fuel pressure in the fuel injector and

Fig. 2 and Fig. 3

different embodiments of a housing for receiving a piezoelectric element designed as a sensor element which is connected to the injector, in each case in longitudinal section.

The same elements and elements with the same function are provided in the figures with the same reference numerals.

The Indian Fig. 1 fuel injector 10 shown greatly simplified is designed as a so-called common rail injector, and is used to inject fuel into the combustion chamber, not shown, of an internal combustion engine, in particular a self-igniting internal combustion engine.

The fuel injector 10 has an injector housing 11, which consists essentially of metal and may have a multi-part design, in which at least one, preferably several injection openings 12 for injecting the fuel are arranged on the side facing the combustion chamber of the internal combustion engine. Within the injector housing 11, this forms a high pressure chamber 15, in which a nozzle needle 16 serving as an injection member is arranged in a liftable manner in the direction of the double arrow 17. In the illustrated, lowered position of the nozzle needle 16, this forms together with the inner wall of the High-pressure chamber 15 and the injector 11 from a sealing seat, so that the injection openings 12 are at least indirectly closed, such that the injection of fuel from the high-pressure chamber 15 is avoided in the combustion chamber of the internal combustion engine. In the other, not shown, lifted from the sealing seat position of the nozzle needle 16, this releases the injection openings 12 for injecting the fuel into the combustion chamber of the internal combustion engine. The movement of the nozzle needle 16, in particular for releasing the injection openings 12, takes place in a manner known per se by means of an actuator, not shown, which can be actuated via a voltage supply line 18 by a control device of the internal combustion engine. The actuator may in particular be a magnetic actuator or else a piezoactuator.

The supply of the high-pressure chamber 15 with fuel under high pressure (system pressure) via a disposed within the injector housing 11 or formed in components of the fuel injector 10 supply bore 19, in particular eccentric to the longitudinal axis 21 of the injector 11 in an edge region of the fuel injector 10, at least Substantially parallel to the longitudinal axis 21, runs. The supply bore 19 is also connected via a fuel connection, not shown, with a fuel line 22, which in turn is coupled to a fuel reservoir 25 (rail).

In one of the injection openings 12 and the combustion chamber axially relatively far-spaced portion of the injector 11 is in the outer wall 23 by way of example a blind hole-shaped recess 24 is formed (in Fig. Fig. 3 ), so that the wall thickness of the injector 11 in the region of the recess 24 is reduced. In addition, it is mentioned that instead of a blind hole-shaped recess 24, the injector housing 11 may also have a flattening, in the region of which the wall thickness of the injector housing 11 is reduced.

The newly formed base 26 of the recess 24 forms part of a deformation region 27. As a result, the fuel pressure currently prevailing in the supply bore 19 also acts in the injector housing 11 on the side facing away from the recess 24. Due to the fact that the wall thickness of the Injector housing 11 is reduced in the region of the recess 24, the wall portion 29 of the injector 11 acts on the recess 24 side facing as a deformation region 27 in the manner of an elastically deformable membrane, the deformation, which forms as a curvature, the higher the higher the instantaneous fuel pressure in the supply bore 19 is.

For detecting the time profile of the fuel pressure in the supply bore 19 and thus also in the high-pressure chamber 15, which is used as an indication of the instantaneous position of the nozzle needle 16 for driving the nozzle needle 16, the fuel injector 10 has a measuring device 30. The measuring device 30 comprises a sensor element 32 designed as a piezo element 31.

The block-shaped or disc-shaped piezoelectric element 31 is covered on its opposite end faces by a respective electrically non-conductive insulating layer 33, 34. The electrodes, not shown in detail, of the piezoelectric element 31 are connected via connecting wires 35, 36, for example, to an evaluation device, not shown, such that electric voltages are generated by the piezoelectric element 31 during a deformation of the deformation region 27, which voltages can be detected via the connecting wires 35, 36 ,

The measuring device 30 is received within a multi-part sensor housing 40, wherein the measuring device 30 together with the sensor housing 40 forms a preassemblable, verifiable separately from the fuel injector 10 assembly 44. The sensor housing 40 has a cover-like or cup-shaped housing upper part 41 with an upper housing wall 42 and a peripheral side wall 43 protruding from the housing wall 42 in the direction of the injector housing. The upper housing part 41 is connected to a lower housing part 45, which consists of a housing bottom 46 and a projecting in the direction of the upper housing part 41, circumferential side wall 47. It is essential that the concentrically arranged to a longitudinal axis 48 side walls 43, 47 of the upper housing part 41 and the lower housing part 45 are arranged to each other or are equipped with such diameters that the side wall 43 at least almost positively protrudes into the opening formed by the side wall 47 of the housing base 47 opening. Further, the two side walls 43, 47 are formed such that they are arranged in the direction of the double arrow 49 relative to each other displaceable. As a result, depending on the position of the side walls 43, 47, between the side walls 43, 47, an overlap region 50 is formed, which serves the connection between the upper housing part 41 and the lower housing part 45. This is done by means of a preferably radially circumferential weld 51, which is preferably formed by a laser beam device, not shown.

It is essential that the piezoelectric element 31 via the insulating layers 33, 34 directly to the housing bottom 46 and the housing wall 42 of the housing upper part 41 is applied, such that a compressive force and thus a compressive stress is generated on the piezoelectric element 31. This is done by applying the upper housing part 41 to the one insulating layer 33, the upper housing part 41, which has a certain flexibility, in particular in the region of the side wall 43 is acted upon by an axial force, such that the side wall 43 moves in the direction of the side wall 47 , After forming the weld seam 51, the desired axial prestressing force on the piezoelectric element 31 takes place via the (elastic) deformation of the housing wall 42 and / or possibly an elastic deformation of the housing bottom 46.

The sensor housing 40 is connected to the housing bottom 46 directly to the deformation region 27. This takes place in that the housing bottom 46 rests on the base 26 of the recess 24, wherein the housing bottom 46, for example, radially outside its side wall 47 has a circumferential flange portion 52 which by another weld 53, which is preferably also produced by means of a laser beam device with the Injector 11 is connected.

In a deformation of the deformation region 27 at a pressure increase in the supply bore 19, the deformation of the deformation region 27 is transmitted via the housing bottom 46 and the insulating layer 34 to the piezoelectric element 31, whereby this generates a voltage signal.

That in the Fig. 3 illustrated sensor housing 40a differs from the sensor housing 40 in that the side wall 43a of the upper housing part 41a radially includes the side wall 47a of the lower housing part 45a. The connection between the two side walls 43a, 47a also takes place by means of a preferably radially completely circumferential weld 51.

The fuel injector 10 described so far can be modified or modified in many ways, without departing from the inventive idea defined by the claims.

Claims (10)

1. Fuel injector (10), in particular common-rail injector, having an injector housing (11), in which there is formed a high-pressure chamber (15) which can be supplied with pressurized fuel via a supply bore (19) arranged in the injector housing (11), having at least one injection opening (12), which is connected at least indirectly to the high-pressure chamber (15) and which is formed in the injector housing (11) and which serves for the injection of fuel into the combustion chamber of an internal combustion engine, having an injection member (16), which opens up or closes off the at least one injection opening (12), and having a measuring device (30) for the at least indirect detection of the pressure in the high-pressure chamber (15) or in the supply bore (19), wherein the measuring device (30) is designed to detect an elastic deformation of a deformation region (27) which is arranged so as to be at least indirectly operatively connected to the supply bore (19) or to the high-pressure chamber (15), and wherein the measuring device (30) has a sensor element (32) which is arranged so as to be operatively connected to the surface (26) of the deformation region (27),
   characterized
   in that the sensor element (32) is accommodated under axial preload in a sensor housing (40; 40a), wherein the sensor element (32) forms a pre-assemblable assembly (44) together with the sensor housing (40; 40a), and in that the assembly (44) is connected to the injector housing (11), wherein the sensor element (32) is separated from the surface (26) of the deformation region (27) by the sensor housing (40; 40a), and the sensor housing (40; 40a) is formed as a closed housing.
2. Fuel injector according to Claim 1,
   characterized
   in that the sensor housing (40; 40a) lies with a housing base (46) directly on the surface (26) of the deformation region (27).
3. Fuel injector according to either of Claims 1 and 2,
   characterized
   in that the sensor housing (40; 40a) has two housing elements (41; 41a, 45; 45a) with a housing base (46) and with a housing wall (42), between which the sensor element (32) is accommodated, and in that the spacing between the housing base (46) and the housing wall (42) is designed to be adjustable in order to generate the axial preload on the sensor element (32).
4. Fuel injector according to Claim 3,
   characterized
   in that the two housing elements (41; 41a, 45; 45a) are formed so as to be adjustable relative to one another in an overlap region (50).
5. Fuel injector according to Claim 3 or 4,
   characterized
   in that the two housing elements (41; 41a, 45; 45a) are at least substantially of pot-shaped form, and in that the interior space for accommodating the sensor element (32) is formed by two overlapping side walls (43; 43a, 47; 47a) and by the housing base (46) and the housing wall (42).
6. Fuel injector according to any of Claims 3 to 5,
   characterized
   in that the two housing elements (41; 41a, 45; 45a) are fixedly connected to one another, in particular by means of an encircling weld seam (51), in a state in which the desired axial preload acts on the sensor element (32).
7. Fuel injector according to any of Claims 3 to 6,
   characterized
   in that one of the housing elements (45; 45a) has, on the side facing toward the injector housing (11), a flange-like connecting region (52) for abutment against the injector housing (11).
8. Fuel injector according to any of Claims 3 to 7,
   characterized
   in that the housing elements (41; 41a, 45; 45a) are composed of metal, and in that the connection to the injector housing (11) is performed by means of a welded connection (53).
9. Fuel injector according to any of Claims 1 to 8,
   characterized
   in that the sensor element (32) is arranged within the sensor housing (40; 40a) so as to be in direct abutting contact with the sensor housing (40; 40a) via electrically non-conductive insulation layers (33, 34).
10. Fuel injector according to any of Claims 1 to 9,
    characterized
    in that, through selection of material for the sensor housing (40; 40a) and/or dimensioning of the components, the axial preload exerted on the sensor element (32) is at least substantially independent of temperature.

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