Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – With magneto-mechanical motive device
Reexamination Certificate
1999-09-01
2001-11-06
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
With magneto-mechanical motive device
C251S129150, C251S129090
Reexamination Certificate
active
06313726
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns an electromagnet, particularly a proportional magnet for operating a hydraulic valve which is installed within a hydraulic system of a device for varying valve timing in an internal combustion engine, said electromagnet comprising at least one coil winding carried by a hollow cylindrical coil spool which is circumferentially surrounded by a hollow cylindrical magnet housing and limited at each end by a pole shoe, said electromagnet further comprising an axially moveable cylindrical armature which is arranged in a hollow cylinder of the coil spool that is configured as an armature space, the armature being mounted for low friction in rotary, longitudinally moveable axial guides, and electromagnetically produced axial movements of the armature can transmitted to a hydraulic valve piston against the force of a spring via a push rod which is connected to the armature to form an axial extension thereof.
BACKGROUND OF THE INVENTION
A generic proportional or adjusting magnet of the pre-cited type is known from DE-OS 22 55 272. This adjusting magnet essentially comprises a hollow cylindrical coil spool and a coil winding arranged thereon. The coil spool and the coil winding are collectively enclosed circumferentially by a hollow cylindrical magnet housing. The coil spool is limited at its ends by two axially spaced pole shoes, one of which pole shoes is structurally integral with the magnet housing. The adjusting magnet further comprises an axially moveable cylindrical armature which is arranged in the hollow cylinder of the coil spool that is configured as an armature space. The electromagnetically produced axial movements of the armature are transmitted against the force of a compression spring to a hydraulic valve piston via a push rod connected to the armature. The armature is mounted for low friction in rotary, longitudinally moveable axial guides so that a uniform air gap is formed between the outer peripheral surface of the armature and the coil spool, and the radial forces acting on the armature, which increase considerably with an increasing eccentricity of the armature, are reduced to a minimum. The rotary, longitudinally moveable axial guides are configured as two axial ball bearings which are pressed into the pole shoes of the adjusting magnet. The ends of the push rod, which has an extension on one side and which extends axially through the armature, are mounted in these ball bearings. In the interior of each axial ball bearing, there is arranged an axially moveable ball cage with a number of circumferentially uniformly spaced balls whose inner running track is formed by the outer peripheral surface of the push rod, while the outer running track is formed by the inner peripheral surfaces of the two bearing bushings. The armature is mounted in these axial ball bearings for axial movements between the pole shoes, and, for avoiding a seating of the armature on the pole shoes and the concomitant sudden increase of axial force on the armature, so-called anti-stick discs of a non-ferromagnetic material are arranged on the ends of the armature.
A drawback of this prior art adjusting magnet is that, although the axial ball bearings for the rotary, longitudinal axial guidance of the armature have very good friction properties, their complicated structure consisting of bearing bushing, ball cage and balls is relatively cost-intensive, and their assembly is thus likewise complicated and expensive, so that the total manufacturing costs of an adjusting magnet of this type are unreasonably high. Moreover, the wall thicknesses of the bearing bushings of such axial ball bearings, which are generally made by deep drawing, are inherently non-uniform due to the peculiarities of their shaping process and this results in a non-concentricity of their inner peripheral surfaces so that it is only rarely possible to achieve the desired exact, centered mounting of the armature, and undesired radial forces acting on armature cannot be eliminated.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to provide an electromagnet, particularly a proportional magnet for operating a hydraulic valve whose armature is provided with a low-friction rotary, longitudinally moveable axial guide which has an inexpensive simple configuration and assures, in all cases, an exact, centered mounting of the armature.
This and other objects and advantages will become obvious from the following detailed description.
SUMMARY OF THE INVENTION
The invention achieves the above objects by the fact that the rotary, longitudinally moveable axial guides of the armature comprise at least one bushing-less linear ball cage having a number of circumferentially spaced balls while being configured at the same time as an anti-stick means of the armature, an outer peripheral surface of the armature and/or an outer peripheral surface of the push rod is configured as an inner running track for the balls, and an inner peripheral surface of one or more components limiting the reception of the coil spool forms an outer running track for the balls.
In a first embodiment of the electromagnet of the invention, the rotary, longitudinally moveable guides of the armature are preferably formed by two spaced-apart linear ball cages which are made of a plastic or of a non-ferromagnetic material and comprise at least two circulating rows of balls which are uniformly spaced circumferentially. These linear ball cages are arranged opposite the end faces of the armature directly on the push rod which is preferably elongated and extends axially through the armature so that the outer peripheral surface of the push rod, which may also be made up of two parts, serves as the inner running track for the balls of the linear ball cages. The components limiting the reception of the coil spool and formed with the outer running tracks for the balls of the linear ball cages are constituted in this embodiment by the pole shoes of the proportional magnet. Each of these pole shoes is made up preferably of a pole plate and a hollow cylindrical pole core which extends axially away from the pole plate into the reception of the coil spool. Each pole core comprises a larger hollow cylinder and a smaller hollow cylinder, and the inner peripheral surfaces of the smaller hollow cylinders of the pole cores form outer running tracks for the linear ball cages. It has proved to be particularly advantageous to configure the larger hollow cylinders of the pole cores of both pole shoes, which receive at least the end regions of the armature, with a stepped transition to the smaller hollow cylinders of the pole cores of the pole shoes and use the transitions as axial stroke limiters for the armature.
In a further advantageous modification of this first embodiment of the electromagnet of the invention, an annular collar integrally formed on the armature-proximate end of each linear ball cage is arranged in the respective stroke end position of the armature between the end face of the armature and the transition to the smaller hollow cylinder of each pole core. These annular collars are made of the same material as the linear ball cages and are configured as an anti-stick means of the armature. The function of preventing a direct seating of the armature on the transitions of the pole shoes, which is otherwise performed by a separately arranged anti-stick disc, is thus integrated by the annular collars in an economic manner into the two linear ball cages themselves.
As far as materials are concerned, it has been determined that a push rod made preferably of a non-ferromagnetic material has an adequate strength for resisting without deformation, the ball contact pressure of the linear ball cages produced during operation on its outer peripheral surface which is configured as the inner running track for the balls. Due to better osculation conditions, the ball contact pressure on the inner peripheral surface of the smaller hollow cylinders serving as the outer running track for the balls is smaller than in the case of the push ro
Golovatai-Schmidt Eduard
Schafer Jens
Steigerwald Martin
Bierman, Muserlian and Lucas
Donovan Lincoln
Ina Walzlager Schaeffler OHG
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