Magnet assembly for a fuel injector, and fuel injector

Abstract

The invention relates to a magnet assembly (10) for a fuel injector (100), comprising an armature (26) which is arranged so as to be movable by lifting in the direction of a longitudinal axis (28) and is coupled to a valve element (42), wherein the valve element (42) is intended to open or close a hole (36), formed in a valve plate (35), for a pressure medium in the direction of a low-pressure region, wherein the first end face (43), facing the armature (26), of the valve element (42) abuts the end face (45), facing the first end face of the valve element, of the armature (26), and a pressure spring (20) applies force to the armature (26) towards the first end face (43) of the valve element (42).

Description

[0001] Description

[0002] Solenoid assembly for a fuel injector and fuel injector

[0003] Technical area

[0004] The invention relates to a magnet assembly for a fuel injector, in which a magnet armature and a valve element that opens or closes a bore toward a low-pressure region are designed as separate elements. The valve element is arranged so as to be freely movable relative to the magnet armature in a plane perpendicular to a longitudinal axis of the magnet assembly. Furthermore, the invention relates to a fuel injector with a magnet assembly designed according to the invention.

[0005] State of the art

[0006] From the applicant's EP 3469207 B1, a magnet assembly with a magnetic armature arranged for lifting movement is known. A residual air gap disc is arranged between the magnetic armature and a magnetic core with a magnetic coil arranged therein. To prevent the residual air gap disc from adhering to the magnetic armature due to adhesion forces during a lifting movement toward a closed position of the magnetic armature, the residual air gap disc is provided with a structure.

[0007] Furthermore, DE 102009 003 208 A1 by the applicant discloses a magnet assembly for a fuel injector in which the magnet armature and a valve element are formed as separate components. The valve element is designed in the form of a valve ball that is positively received in a spherical-segment-shaped surface of the magnet armature, so that the valve element is arranged stationary relative to the magnet armature with respect to a plane perpendicular to a longitudinal axis of the magnet armature. Disclosure of the Invention

[0008] The magnet assembly according to the invention for a fuel injector with the features of claim 1 has the advantage that the possibility of relative movement between the valve element and the magnet armature in a plane perpendicular to a longitudinal axis of the magnet armature allows for the installation space of the magnet armature chamber to be optimized, as well as for the material selection of the magnet armature to improve the magnetic force on the one hand, and that of the valve element to optimize the sealing effect and wear on the other. However, for such a solution to function, it is necessary for the valve element to always follow the movement of the magnet armature when the bore in the valve plate is opened to allow pressure medium to flow out toward the low-pressure region.This is critical because, in its position closing the bore, the valve element rests against the valve plate with its end face facing the valve plate, generating adhesion forces that counteract the opening movement of the valve element. These adhesion forces between the valve element and the valve plate should therefore be reduced or minimized while maintaining the sealing effect of the valve element in its lowered, bore-closing position, so that when the bore is opened, the valve element follows the movement of the magnet armature or always rests with its end face facing the magnet armature against the end face of the magnet armature facing it.

[0009] The invention is based on the idea of ​​making this possible by structuring the valve plate on the side facing the valve element. This structuring reduces the contact area between the valve plate and the valve element when the valve element is in the position where it closes the bore, thereby also reducing the adhesion forces between the valve plate and the valve element. Structuring, as defined by the invention, refers to a surface that has regular or irregular depressions or similar surface elements, which can be produced by machining or non-machining.

[0010] Against the background of the above explanations, it is therefore provided according to the invention in a magnet assembly for a fuel injector that this has a magnet armature which is arranged so as to be movable in the direction of a longitudinal axis and which is coupled to a valve element, wherein the valve element is designed to release orServes to close a bore formed in a valve plate for a pressure medium in the direction of a low-pressure region, wherein the valve element rests with its first end face facing the magnet armature against the end face of the magnet armature facing it and the magnet armature is subjected to force in the direction of the first end face of the valve element by a compression spring, wherein the valve element is arranged such that it can move relative to the magnet armature in a plane perpendicular to the longitudinal axis, and wherein a support surface of the valve plate for the valve element facing the valve element is formed with a structure for reducing an adhesion force between the valve element and the valve plate.

[0011] Advantageous further developments of the magnet assembly according to the invention for a fuel injector are listed in the subclaims.

[0012] In a particularly preferred design embodiment of the valve element, which allows for particularly simple and precise manufacture, the valve element is pin-shaped with two flat end faces arranged opposite one another as viewed in the direction of the longitudinal axis, and the second end face of the magnet armature is flat, at least in the area where it overlaps with the valve element. The flat, contacting end faces of the valve element and the magnet armature also make it possible to increase or optimize the adhesion forces between the magnet armature and the valve element as desired. It is important here that the flat end faces of the magnet armature and the valve pin that face one another are, if appropriate, particularly smooth orare designed with low surface roughness in order to support the opening movement of the valve element during an upward movement of the magnet armature or to ensure that the valve element is in constant contact with the magnet armature.

[0013] The structuring on the valve plate comprises at least one groove-like recess. The cross-section of the recess or the cross-sectional shape of the recess is designed according to the manufacturing method chosen for forming the recess and is either rectangular, for example, or with a cross-section that increases or decreases toward the groove base. In particular, such recesses can be produced either by a laser beam device or by machining processes.

[0014] In a geometrically preferred first embodiment of the structuring or the depression, this is designed as a circular arc section or circle arranged concentrically around the longitudinal axis.

[0015] Alternatively or additionally, the recess can also be straight.

[0016] A further embodiment of the invention provides that several recesses are provided which at least partially intersect and thereby form, for example, a grid pattern.

[0017] Such recesses can extend either over the entire surface of the valve plate or merely over a radially inner region of the valve plate. In the first case, in which the recesses also extend over the radially outer region of the valve plate, such recesses can be manufactured particularly easily given the selected manufacturing process. In the second solution, in which the recesses extend in a radially inner region of the valve plate, it is advantageous if this region encompasses the entire area over which the valve element can move in the radial direction (relative to the longitudinal axis).

[0018] Regardless of the shape, arrangement and number of recesses, it is necessary that when the valve element is in contact with the valve plate, the required (hydraulic) sealing of the bore or outflow opening is made possible by the valve element, i.e. that the recesses do not create a direct connection between the bore and the low-pressure area of ​​the fuel injector.

[0019] A further preferred geometric configuration of the at least one recess provides for it to have a width between 10 pm and 300 pm, preferably between 50 pm and 100 pm. Furthermore, the invention also encompasses a fuel injector, in particular a fuel injector for compression-ignition internal combustion engines, with a magnet assembly configured according to the invention as described above.

[0020] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments of the invention and from the drawings.

[0021] Short description of the drawings

[0022] Fig. 1 shows a longitudinal section through a fuel injector in the area of ​​a magnet assembly,

[0023] Fig. 2 to

[0024] Fig. 4 shows plan views of different structures in the area of ​​a valve plate of the magnet assembly and

[0025] Fig. 5a to

[0026] Fig. 5e shows longitudinal sections in the area of ​​differently formed groove-like depressions of the structures.

[0027] Embodiments of the invention

[0028] Identical elements or elements with the same function are provided with the same reference numbers in the figures.

[0029] Fig. 1 shows a portion of a fuel injector 100 (not shown in detail) for a self-igniting internal combustion engine in the region of a magnet assembly 10. The magnet assembly 10 is arranged within a valve housing 12 and comprises a magnet core 14 with an electrically energizable magnet coil 16 arranged in a radially circumferential groove. The magnet core 14 has a stepped bore 18, with a first compression spring 20 being arranged in a section of the stepped bore 18 having a larger diameter. A second compression spring 22 acts on the magnet core 14 on the end face facing it and presses the magnet core 14 in the direction of a spacer ring 24 arranged stationary in the valve housing 12. The spacer ring 24 radially surrounds a magnet armature chamber 25, with a magnet armature 26, which in the exemplary embodiment is flat or disk-shaped, being arranged in the magnet armature chamber 25.The first compression spring 20 rests against the magnet armature 26 with the end face facing the magnet armature 26 and presses the magnet armature 26 in the direction of a longitudinal axis 28 of the magnet armature 25 or toward a closed position. In contrast, when the magnet coil 16 is energized, the magnet armature 26 is moved toward the magnet core 14 against the spring force of the first compression spring 20.

[0030] Viewed in the direction of the longitudinal axis 28, the spacer ring 24 is adjoined, for example, by a guide ring 30 with a through-bore 32 formed concentrically to the longitudinal axis 28. On the side of the guide ring 30 facing away from the spacer ring 24, a valve plate 35 is arranged stationary in the valve housing 12.

[0031] The valve plate 35 has a bore 36 formed concentrically to the longitudinal axis 28, wherein the bore 36 has a first section 37 on the side facing the guide ring 30. The first section 37 is followed by a second section 38, which has a larger diameter than the first section 37. The bore 36 forms, in particular, a control chamber containing pressurized fuel from the fuel injector 100, which serves to move a valve member (nozzle needle) not shown in the figure in order to thereby enable, as is known per se, the injection of fuel into the combustion chamber of the compression-ignition internal combustion engine.

[0032] To close or open and release the bore 36, which serves as an outflow bore in the direction of a low-pressure region or to the magnet armature chamber 25, the valve plate 35 forms a support surface 40 on the end face facing the magnet armature chamber 25, which contact surface interacts with a valve element 42. The valve element 42 is designed as a cylindrical valve element 42 and has a first end face 43 on the side facing the magnet armature 26 and a second end face 44 on the side facing the valve plate 35, each of which runs as flat end faces 43, 44 perpendicular to the longitudinal axis 28.

[0033] The material of the valve element 42 is optimized with regard to wear, for example, by providing the valve element 42 with a coating. In contrast, the magnet armature 26 is made of a different material than the valve element 42, for example, to optimize the magnetic properties in interaction with the magnet core 14 or the magnet coil 16.

[0034] The valve element 42 is arranged with radial play in the through-bore 32 of the guide ring 30, so that the valve element 42 is arranged to be (radially) movable or displaceable in a plane running perpendicular to the direction of the longitudinal axis 28, and only its first end face 43 bears radially movably against the facing end face 45 of the magnet armature 26. Furthermore, the support surface 40 of the valve plate 35 is designed as a sealing area 46 in the region in which the valve element 42 rests with its second end face 44 when the valve element 42 is subjected to the spring force of the first compression spring 20 via the magnet armature 26.

[0035] For the function of the magnet assembly 10, in particular for the controlled release or closing of the first section 37 of the bore 36 when the magnet coil 16 is energized, it is essential that the valve element 42 follows the stroke movement of the magnet armature 26, ie that the valve element 42 always rests with its first end face 43 on the end face 45 of the magnet armature 26.

[0036] For this purpose, it is essential that when the magnet tanker 26 and the valve element 42 move in the direction of the magnetic core 14 from the position closing the bore 36 to release the bore 36, the adhesion force Fi formed as a result of hydraulic effects between the valve element 42 and the magnet armature 26 in the contact area, which acts in the direction of the magnet armature 26, is always greater than the adhesion force F2 formed between the valve plate 35 and the second end face 44 of the valve element 42, which acts in the direction of the valve plate 35. To ensure this, the valve plate 35 has a structuring 50 on the side facing the valve element 42 in the region of the support surface 40.

[0037] In a first embodiment of such a structuring 50, shown in Fig. 2, said structuring has an annular recess 52 relative to the longitudinal axis 28, which is followed by rectilinear recesses 54 extending from the recess 52 in the radial direction and each aligned with the longitudinal axis 28. The rectilinear recesses 54 extend from the recess 52 only over a partial area of ​​the surface of the valve plate 35, i.e. they extend only over a radially inner area of ​​the valve plate 35. The hatched area 56 in Fig. 2 indicates the area of ​​support or the contact surface between the second end face 44 of the valve element 42 and the valve plate 35. In particular, it can be seen that the recesses 54 extend over the entire hatched area 56 when viewed in the radial direction.This ensures that the valve element 42 is always located in the area of ​​the structuring 50 even in the event of a (slight) radial movement due to its mobility relative to the magnet armature 26.

[0038] Fig. 3 shows a further structuring 50a. In addition to the linear recesses 54, the structuring 50a includes a circular recess 58 extending concentrically around the longitudinal axis 28.

[0039] Fig. 4 shows a structuring 50b which has a plurality of rectilinear, intersecting depressions 60 arranged in the form of a grid 62.

[0040] The recesses 54, 58, and 60 are produced as groove-shaped recesses 54, 58, and 60, for example, by means of a laser beam device, by a chemical (deburring) process, or by machining. The cross-sectional shape of the recesses 54, 58, and 60 can be designed in a variety of ways. Preferably, the recesses 54, 58, and 60 have a depth between 10 μm and 30 μm, preferably approximately 20 μm. The groove depth is influenced by the expected wear and the manufacturing process. Furthermore, the groove depth is important with regard to the formation of the adhesion force F2 between the valve element 42 and the valve plate 35 in that at least one recess 54, 58, and 60 must always interrupt the support surface 40. The groove width of the recesses 54, 58 and 60 is essentially determined by the manufacturing process of the recesses 54, 58 and 60 and can therefore have a relatively large fluctuation range.

[0041] Preferably, the recesses 54, 58, and 60 have a width between 10 μm and 300 μm. The groove width is important with regard to the adhesion force F2 between the valve element 42 and the valve plate 35 in that many small residual surfaces enable sufficient robustness against wear while simultaneously maintaining a low adhesion force F2.

[0042] According to Fig. 5a, the recesses 54, 58 and 60 described above can, for example, have a rectangular cross-section. In Fig. 5b, the cross-section of the recesses 54, 58 and 60, in contrast, is formed with a rounded groove base 62. Fig. 5c shows that the cross-section of the recesses 54, 58 and 60 can be formed in the shape of a funnel section. Fig. 5d shows a

[0043] Cross-section of the recesses 54, 58, and 60, which is arranged corresponding to Fig. 5c, but in the opposite arrangement of the funnel-shaped recesses 54, 58, and 60. Finally, Fig. 5e shows a cross-section of triangular recesses 54, 58, and 60.

Claims

Claims 1. Magnet assembly (10) for a fuel injector (100), comprising a magnet armature (26) arranged to be movable in the direction of a longitudinal axis (28), which is coupled to a valve element (42), wherein the valve element (42) is for releasing orThe valve element (42) serves to close a bore (36) formed in a valve plate (35) for a pressure medium in the direction of a low-pressure area, wherein the valve element (42) with its first end face (43) facing the magnetic armature (26) abuts against the end face (45) of the magnetic armature (26) facing it, and the magnetic armature (26) is subjected to force in the direction of the first end face (43) of the valve element (42) by a compression spring (20), wherein the valve element (42) is movably arranged in a plane perpendicular to the longitudinal axis (28) relative to the magnetic armature (26), and wherein a bearing surface (40) of the valve plate (35) facing the valve element (42) is formed with a structure (50; 50a; 50b) to reduce an adhesion force (F2) between the valve element (42) and the valve plate (35).

2. Magnet assembly according to claim 1 characterized in that the valve element (42) is pin-shaped with two flat end faces (43, 44) arranged opposite each other in the direction of the longitudinal axis (28), and that the end face (45) of the magnet armature (26) is flat, at least in the area of ​​overlap with the valve element (42).

3. Magnet assembly according to claim 1 or 2, characterized in that the structuring (50; 50a; 50b) on the valve plate (35) comprises at least one groove-like recess (54, 58, 60). A magnetic assembly according to claim 3, characterized in that the at least one recess (58) is configured as a circular arc segment or circle arranged concentrically around the longitudinal axis (28). A magnetic assembly according to claim 3 or 4, characterized in that the at least one recess (54, 60) is straight. A magnetic assembly according to any one of claims 3 to 5, characterized in that several recesses (60) are provided which at least partially intersect. A magnetic assembly according to claim 6, characterized in that the recesses (54, 58, 60) extend over the entire surface of the valve plate (35) on the side facing the support surface (40). A magnetic assembly according to claim 6, characterized in that the recesses (54, 58, 60) extend only over a radially inner region of the valve plate (35) on the side facing the support surface (40).Magnetic assembly according to any one of claims 3 to 8, characterized in that the at least one recess (54, 58, 60) has a width between 10 pm and 300 pm, preferably between 50 pm and 100 pm. Fuel injector (100) with a magnetic assembly (10) configured according to any one of claims 1 to 9.

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