Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Magnet structure or material
Reexamination Certificate
1999-08-02
2001-07-10
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Magnet structure or material
C335S306000
Reexamination Certificate
active
06259343
ABSTRACT:
The invention relates to a high-grade plastic component, e.g. a permanent magnet, which is fixed to a basic body with the basic body showing at least one strap-shaped part for the purpose of fixing the plastic component.
With high-grade plastic components, it is a matter of parts with a material embedded in a plastic matrix. As embedding material, permanent magnetic particles for the manufacture of a plastic-bonded permanent magnet, soft magnetic particles the magnetic properties of which are determined by the surrounding electromagnetic fields, ceramic powder—e.g. for the manufacture of sealing washers—as well as other powder or particle shaped materials can be considered. High-grade plastic components of such kind are mostly manufactured through injection moulding with the plastic component being fixed to the basic body either by injection or after its manufacture by frictional connection or glueing. In many cases, the fixing is subject to particular safety requirements which exclude the application of frictional connection or glueing.
With positive connections, in particular when the plastic part is injected to the basic body, contraction strains occur with the cooling of the high-grade plastic which may result in the plastic part tearing off the basic body in the connecting area.
This problem, for instance, occurs with plastic-bonded permanent magnets which need to be fixed to a shaft as motor or sensor magnets. For this purpose, the basic body, to which the plastic-bonded permanent magnet is fixed, is placed on the captioned shaft by press fitting. The permanent magnets are applied as motor or sensor magnets and mostly laid out as ring or disk magnets which are fixed to a ring- or bush-shaped basic body.
Such plastic-bonded permanent magnets are increasingly applied in many technical fields. The automobile industry, for instance, is changing support functions like e.g. power steering for energy saving reasons from hydraulic to electromotive mode. The fixing of the sensor magnets to the captioned shaft, e.g. the steering wheel column, is subject to particular safety requirements. Accordingly, the technical surveyance associations require a frictional or positive connection as glued connections do not guarantee a permanent safe fixing.
From DE-PS 704 000, a permanent magnet is known which is fixed to a basic body by means of bended straps, possibly compensating measure tolerances of the permanent magnet towards the basic body.
If such a permanent magnet is laid out as a high-grade plastic component, the aforementioned problems will occur. I.e. during cooling of a thermoplastic bonded magnetic material a contraction occurs which may make up e.g. 5% of the volume. Due to the related contraction strains, the magnet may tear off the basic body.
The U.S. Pat. No. 5,530,344 discloses an encoder for a ball bearing which cooperates with a sensor for the purpose of determining the rotary speed of the bearing. This is performed by means of a axially magnetized dipolar ring which is equipped with radially running projections evenly distributed along the circumference. The permanent magnet is held by a ring disk-shaped basic body with window-like recesses taking up the projections. In addition, the permanent magnet is fixed to the basic body by means of a sealing device.
From DE-PS 966 719, a permanent magnet is known, particularly for bicycle dynamos, which is connected to a shaft by a separate operating cycle. For this purpose, a space between the permanent magnet and the shaft is moulded with metal. The central boring of the permanent magnet shows indentations at one or both ends which are filled by flanges building up when moulding with metal thus forming a safety device against shifting in lengthwise direction of the shaft.
In DE-AS 1 043 540, a permanent magnet is described which consists of a porous material and shows in its boring a bush made of non-sintered ceramic material which is fixed by means of synthetic resin cement. The bush is fixed to a shaft with ethoxylene resin cement. In this case too the permanent magnet, bush and shaft are connected to each other in separate operating cycles.
In DE-OS 1 614 183, a plastic-bonded hollow cylinder-shaped permanent magnet is described which shows a longitudinal slot as elastic fixing out of and/or in a hollow cylinder-shaped basic body. Here as well the connection between the permanent magnet and the basic body is done in a separate operating cycle. The permanent magnet is not fixed to the basic body and accordingly can tear off the basic body.
The DE 92 16 750 U1 discloses a rotor magnet of plastic-bonded magnetic material with an injected bush-shaped basic body. In order to reduce the strains occurring when the rotor magnet is pressed onto a shaft, the basic body shows a constriction in the center area of its outside circumference.
With the designs described above, permanent magnets made of plastic-bonded magnetic material show the problem of tearing off the basic body due to the contraction strains which occur during cooling.
As was mentioned before, this problem applies to the positive connection between a high-grade plastic component and a basic body in general.
Therefore, the invention is based on the task to create a tearproof positive connection between the permanent magnet and the basic body.
The task is solved as per the invention by arranging the strap-shaped part, which is surrounded by the high-grade plastic during manufacture of the plastic component, within the high-grade plastic in such a way that the contraction strains of the high-grade plastic occurring after the manufacture of the plastic component are at least partly taken up by bending.
Due to the measure as per invention, contraction strains occurring during cooling in the high-grade plastic surrounding the strap-shaped parts are completely or at least partly eliminated to such an extent that the plastic component a tearing off the basic body is avoided. In particular in such case, when the high-grade plastic component is a matter of a motor magnet or sensor magnet. The plastic component is preferably laid out as ring or disk magnet with the basic body showing a bush-shaped part for being fixed to a shaft and a flange part extending to the outside. The strap-shaped part/s are arranged in such a way that they incline towards the lengthwise direction of the basic body. Due to such arrangement of the strap-shaped part/s, contraction strains of the plastic-bonded magnetic material are taken up by bending these parts.
Advisably, several strap-shaped parts are provided and preferably distributed evenly along the circumference of the flange part.
In a preferred further development of the invention, the flange part consists of an approximately radially running ring-shaped area adjoining the bush-shaped part which shows openings distributed along the circumference at the radially inside or outside located edges of which the strap-shaped parts are arranged. Advisably, the openings are filled with the high-grade plastic, thus improving the positive connection of the plastic component to the basic body. During cooling, contraction strains occur in the area of the openings towards the outside volume of the high-grade plastic which, however, are taken up by the bendable straps and consequently are compensated.
In another version, the flange part adjoining the bush-shaped part shows a mainly radially running ring-shaped area where the strap-shaped parts are distributed along the circumference.
Starting from the ring-shaped area, the strap-shaped parts incline towards the lengthwise direction of the basic body in radial arrangement with recesses in between.
The openings and/or recesses guarantee the torsional strength of the plastic component on the basic body. Further, the openings surrounded by the ring-shaped area present a better guard against radial forces. The axial fixing strength is guaranteed by means of the radially running ring-shaped area and the connecting strap-shaped parts extending radially in a component, too.
With the aforementioned version, the strap-shap
Donovan Lincoln
Max Baermann GmbH
Nixon & Vanderhye P.C.
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