Electromagnetic actuator with composite core assembly

Abstract: A core assembly for an electromagnet includes a plurality of stacked laminations extending along a stacking axis. The laminations each having generally the same thickness in a direction along the stacking axis. A solid core member has opposing ends. The core member is disposed generally centrally with respect to the plurality of stacked laminations such that each end of the core member contacts a lamination of the plurality of laminations. The core member has a thickness in a direction along the stacking axis substantially greater than the thickness of a lamination. The core member also has an aperture therethrough disposed generally perpendicular to the stacking axis for receiving a shaft of an armature assembly.

Description: FIELD OF THE INVENTION This invention relates to an electromagnetic actuator for a vehicle engine and, more particularly, to a core assembly of a solenoid-type actuator having a plurality of stacked laminations and a moving armature. BACKGROUND OF THE INVENTION A conventional electromagnetic actuator for opening and closing a valve of an internal combustion engine generally includes "open" and "close" electromagnets which, when energized, produce an electromagnetic force on an armature. The armature is biased by a pair of identical springs arranged in parallel. The armature is coupled with a gas exchange valve of the engine. The armature rests approximately half way between the open and close electromagnets when the springs are in equilibrium. When the armature is held by a magnetic force in either the closed or opened position (at rest against the open or close electromagnet), potential energy is stored by the springs. If the magnetic force is shut off with the armature in the opened position, the spring's potential energy will be converted to kinetic energy of the moving mass and cause the armature to move towards the close electromagnet. If friction is sufficiently low, the armature can then be caught in the closed position by applying current to the close electromagnet. Generally, each electromagnet of a conventional electromagnetic actuator comprises a plurality of stacked laminations joined to define the core of the actuator. This core design offers the advantage of high efficiency by minimizing eddy current loses in the magnetic material. However, a disadvantage of this design is that machining of the laminations must be performed in a plane perpendicular to the orientation of the laminations which tends to cause the laminations to spread apart. This may result in poor dimensional control and burr formation. Furthermore, an aperture is generally provided through the core to receive a press-fit bushing to support a reciprocating shaft of the actuator. The stacked lamination core design cannot support the press-fit bushing due to the spreading of the individual laminations. JP 02 240 473 A discloses a core assembly comprising a metal plate material of large thickness which is sandwiched by two or more sheets of metal plate materials of equal circumference shape when compared with the thick metal plate material. The centre thick metal plate material has a hole for guiding a shaft of an armature. EP 0 795 881 A discloses in its description of the related art a core assembly comprising thin magnetic plates stacked at both right and left positions of a thicker central plate in which plate a hole is formed for insertion of a push rod. DE 297 12 502 U discloses an electromagnetic actuator assembly having an upper and a lower electromagnetic device. An armature is located between the upper and lower electromagnetic devices, and is operated by the devices. With respect to the cited state of the art there is a need to provide an electromagnetic actuator having a core assembly which minimizes eddy currents yet is capable of receiving a bushing to support a reciprocating shaft carrying an armature, and wherein the shaft is guided such that it is presented from twisting around its longitudinal axis. It is an object of the present invention to fulfil the need referred to above. SUMMARY OF THE INVENTION According to a first aspect of the present invention there is provided a core assembly for an electromagnetic actuator, the core assembly comprising: a plurality of stacked laminations extending along a stacking axis, said laminations each having generally the same thickness in a direction along the stacking axis, and a solid core lamination member having opposing ends, said core member being disposed generally centrally with respect to said plurality of stacked laminations such that each end of said core member contacts a lamination of said plurality of laminations, said core member having a thickness in a direction along said stacking axis substantially greater than the thickness of a lamination, said core member having a center aperture therethrough disposed generally perpendicular to said stacking axis, characterised in that the core member includes at least one pin extending from said solid member in a direction generally perpendicular to said stacking axis which pin is to prevent twisting of a reciprocating armature. According to a second aspect of the present invention there is provided an electromagnetic actuator for mounting to a cylinder head of an engine, the actuator comprising: first and second electromagnets disposed in spaced relation, each said electromagnet including a core assembly and a coil associated with the core assembly, each core assembly comprising: a plurality of stacked laminations extending along a stacking axis, said laminations each having generally the same thickness in a direction along said stacking axis, a solid core member having opposing ends, said core member being disposed generally centrally with respect to said plurality of stacked laminations such that each end of said core member contacts a lamination of said plurality of laminations, said core member having a thickness in a direction along said stacking axis substantially greater than the thickness of a lamination, said core member having a centeraperture therethrough disposed generally perpendicular to said stacking axis, and a bushing in said aperture, an armature mounted for reciprocal movement between said electromagnets, and a shaft coupled to said armature and supported for reciprocal movement via said bushings, characterised in that said solid core member includes at least one pin extending therefrom in a direction perpendicular to said stacking axis and said armature includes at least one aperture to receive said pin such that said pin may guide said armature upon movement thereof According to a third aspect of the present invention there is provided a method of providing a core assembly for an electromagnetic actuator, the method comprising: providing a solid centre core member having first and second ends and having a certain thickness defined between said ends, said core having top and bottom surfaces and a center aperture therethrough extending from said top surface to said bottom surface, stacking a plurality of laminations so as to extend outwardly from each end of said core member, each of said plurality of laminations having a thickness substantially less than said certain thickness, and joining said plurality of laminations together and to said core member to define said core assembly, characterised in providing at least one pin extending from the core member in a direction perpendicular to a stacking axis and providing in an armature at least one aperture to receive said pin such that said pin may guide said armature upon movement thereof. Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of an electromagnetic actuator having electromagnet core assemblies provided in accordance with the principles of the present invention; and FIG. 2 is a perspective view of a core assembly of a lower electromagnet of the electromagnetic actuator of FIG. 1, provided in accordance with the principles of a first embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, an electromagnetic actuator is shown, generally indicated 10, having electromagnet core assemblies provided in accordance with the principles of the present invention. The electromagnetic actuator 10 includes an upper housing assembly, generally indicated at 12, containing an upper electromagnet 14, and a lower housing assembly, generally indicated at 16, containing a lower electromagnet 18. Each electromagnet 14 and 18 includes a core assembly, generally indicated at 20, and a coil assembly 22. A generally rectangular armature 24 is arranged for movement between the electromagnets 14 and 18. The armature 24 is carried by a reciprocating shaft 26 The shaft 26 is configured to be coupled to a stem of a gas exchange valve (not shown) of an engine of a vehicle in the conventional manner. In the conventional manner, a pair of opposing springs are associated with the armature 24. One spring 27 is shown in FIG. 1. The other spring (not shown) is disposed near the cylinder valve. The invention will be described with regard to the lower electromagnet 18. It will be appreciated, however, that the principles of the invention are applicable to the structure of the upper electromagnet 14 as well. Thus, with reference to FIG. 2, the core assembly 20 is shown provided in accordance with the principles of the present invention. The core assembly 20 comprises a plurality of laminations 28 stacked with respect to a stacking axis A. The laminations generally have the same thickness B in a direction along the stacking axis A and are preferably composed 29 gage M15 C5 soft magnetic material. Other suitable materials of various gages may be employed for the lamination. Two laminations of the plurality laminations 28 contact opposing ends 31 and 33 of a solid center core member 30 such that the core member 30 is disposed generally centrally between the plurality of laminations 28. Each lamination 28 is generally E-shaped defining channels 32 to receive the associated coil assembly 22 (FIG. 1). In accordance with the invention, the solid center core member 30 has ends 31 and 33, a top surface 38 and a bottom surface 40. A thickness C of the core member 30 as defined between ends 31 and 33 or in a direction along the stacking axis, is substantially greater than a thickness B of the individual laminations 28. The center core member 30 is also of E-shape, is composed of silicon iron, and has a thickness C of about 8-12 mm. In the illustrated embodiment, the center core member 30 is composed of 2.5% silicon iron and has a thickness of about 10 mm. The core member 30 also includes a center aperture 32 therethrough extending from the top surface 38 to the bottom surface 40. The aperture 32 receives a bushing 34, press-fitted therein. Thus, the aperture 32 is disposed generally perpendicular to the stacking axis A. The bushing 34 supports the reciprocating shaft 26 (FIG. 1). The core member 30 may also include one or more apertures 36 for receiving a support pin 37. The support pin(s) are received in apertures in the armature 24 to provide additional support of the reciprocating armature 24 and thus prevent twisting thereof. The laminations 28 and core member may be secured together by a weld 42 on each side thereof. It can be appreciated that the laminations 28 may be joined in any other conventional manner, such as, for example, an interlocking or mechanical upset arrangement, gluing, riveting or a combination of these techniques. After assembly, surfaces 38 and 40 of the core assembly are machined so as to be substantially parallel. Pins 39 are disposed through apertures 41 in the core assembly 20 to secure the core assembly 20 to the housing assembly 16. It can be appreciated that with the composite structure of the core assembly of the invention, the stacked laminations 28 provide a high efficiency core by minimizing eddy current losses, while the solid core member allows for easy machining of surfaces 38 and 40 and provides good support of the press-fit bearing 34 disposed in the aperture 32 of the core member 30. The solid core member 30 may include oil passages therein to lubricate the bearing 34 via oil galley 43.

Claims: A core assembly for an electromagnetic actuator, the core assembly (20) comprising: a plurality of stacked laminations (28) extending along a stacking axis (A), said laminations each having generally the same thickness (B) in a direction along the stacking axis, and a solid core lamination member (30) having opposing ends (31, 33), said core member being disposed generally centrally with respect to said plurality of stacked laminations such that each end of said core member contacts a lamination of said plurality of laminations, said core member having a thickness (C) in a direction along said stacking axis substantially greater than the thickness of a lamination, said core member having a center aperture (32) therethrough disposed generally perpendicular to said stacking axis, characterised in that the core member includes at least one pin (37) extending from said solid are in a direction generally perpendicular to said stacking axis which pin is to prevent twisting of a reciprocating armature (24). The core assembly according to claim 1, further comprising a bushing (34) disposed in said first aperture. The core assembly according to claim 1, wherein each of said laminations and said core member is of generally E-shape. The core assembly according to claim 1, wherein said core member is composed of silicon iron. The core assembly according to claim 1, wherein ends of said core assembly which are perpendicular to said stacking axis are machined to be substantially parallel. An electromagnetic actuator for mounting to a cylinder head of an engine, the actuator (10) comprising:first and second electromagnets (14, 18) disposed in spaced relation, each said electromagnet including a core assembly (20) and a coil (22) associated with the core assembly, each core assembly comprising:a plurality of stacked laminations (28) extending along a stacking axis (A), said laminations each having generally the same thickness (B) in a direction along said stacking axis, a solid core member (30) having opposing ends (31, 33), said core member being disposed generally centrally with respect to said plurality of stacked laminations such that each end of said core member contacts a lamination of said plurality of laminations, said core member having a thickness (C) in a direction along said stacking axis substantially greater than the thickness of a lamination, said core member having a center aperture (32) therethrough disposed generally perpendicular to said stacking axis, and a bushing (34) in said aperture, an armature (24) mounted for reciprocal movement between said electromagnets, and a shaft (26) coupled to said armature and supported for reciprocal movement via said bushings, characterised in that said solid core member includes at least one pin (37) extending therefrom in a direction perpendicular to said stacking axis and said armature includes at least one aperture to receive said pin such that said pin may guide said armature upon movement thereof. The electromagnetic actuator according to claim 6, wherein each of said laminations and said core member is of generally E-shape. The electromagnetic actuator according to claim 7, wherein said center aperture is disposed in a central leg of said E-shape. The electromagnetic actuator according to claim 6, wherein said core member is composed of silicon iron. The electromagnetic actuator according to claim 6, wherein ends of said core assembly which are perpendicular to said stacking axis are machined to be substantially parallel. A method of providing a core assembly for an electromagnetic actuator the method comprising: providing a solid centre core member (30) having first and second ends (31, 33) and having a certain thickness (C) defined between said ends, said core having top and bottom surfaces (38, 40) and a center aperture (32) therethrough extending from said top surface to said bottom surface, stacking a plurality of laminations (28) so as to extend outwardly from each end of said core member, each of said plurality of laminations having a thickness (B) substantially less than said certain thickness (C), and joining said plurality of laminations together and to said core member to define said core assembly, characterised in providing at least one pin (37) extending from the core member in a direction perpendicular to a stacking axis (A) and providing in an armature at least one aperture to receive said pin such that said pin may guide said armature upon movement thereof. The method according to claim 11, wherein said joining includes performing a welding operation along a stacking direction of said laminations. The method according to claim 11, further including machining top and bottom surfaces of said core assembly so as to be substantially parallel. The method according to claim 11, further including placing a bushing in said aperture in the core member.

Inventors: NITKIEWICZ JAMES ANTHONY, SAILER HANS J, NITKIEWICZ, JAMES ANTHONY, SAILER, HANS J.
Applicants: SIEMENS VDO AUTOMOTIVE CORP, SIEMENS VDO AUTOMOTIVE CORPORATION
Application year: 1998
Main classification: H01F7
IPC codes: H01F3, F16K31, H01F7, H01F27, F01L9