Pole tube for electromagnets and magnetic valves, and method as well as apparatus for its manufacture

1. A method for manufacturing a pole tube, having two magnetic pole tube parts and a center axis, for an electromagnet, the electromagnet comprising a magnetic valve of an automatic transmission in an automobile, comprising the following steps:

(a) arranging the pole tube parts on a centering arbor with a mutual axial distance such that the pole tube parts form a gap sufficient for a magnetic separation,

expanding the centering arbor so that in the region of the gap, a lateral surface of the centering arbor closes the gap with a respective inner surface of each of the pole tube parts without any offset; and

(b) connecting, by insert molding and/or casting, an outer lateral area of the pole tube parts with a nonmagnetic material so that, together with the pole tube parts, the nonmagnetic material forms the inner surface of the pole tube;

wherein the centering arbor is an expansion arbor with a radially expandable cylinder surface which is closed even in the expanded state.

2. The method according to claim 1 , further comprising:

inserting a pole core in one of the pole tube parts at one end of the pole tube.

3. A pole tube having a center axis for an electromagnet, the electromagnet comprising a magnetic valve of an automatic transmission in an automobile, comprising a nonmagnetic material that fills a axial gap between two magnetic pole tube parts,

wherein the pole tube parts are arranged in a mutually axial and concentric relationship,

wherein outer lateral surfaces of the pole tube parts are cast-in or insert-molded with the nonmagnetic material, and

wherein together with the pole tube parts the nonmagnetic material forms a planar and offset-free inner surface, so that portions of the inner surface of the pole tube which are formed by the nonmagnetic material in the gap and, respectively, the part of the inner surface of the adjacent pole tube part have an identical inside diameter at each transition between the nonmagnetic material and the adjacent pole tube part.

4. The pole tube according to claim 3 , wherein the nonmagnetic material is a plastic.

5. The pole tube according to claim 3 , wherein the pole tube parts are manufactured from a magnetically conducting steel material, by machining, or as a sintered part or as an extruded part.

6. The pole tube according to claim 3 , wherein one of the pole tube parts has a pole core at one end of the pole tube or is connected, by joining, with a pole core.

7. The electromagnet for a magnetic valve according to claim 3 , wherein a coil, in particular a copper wire winding, is arranged on a winding carrier, which is formed by the nonmagnetic material surrounding the lateral surface of the pole tube parts.

8. An apparatus for manufacturing a pole tube, having two magnetic pole tube parts, for an electromagnet, the electromagnet comprising a magnetic valve of an automatic transmission in an automobile, comprising: a centering arbor for arranging the pole tube parts; and an injection mold which can enclose the pole tube parts arranged on the centering arbor to connect the pole tube parts by insert molding and/or casting an outer lateral surface of the pole tube parts by means of an injection molding or casting material;

wherein:

the centering arbor is an expansion arbor with a radially expandable cylinder surface which is closed even in the expanded state, and

the apparatus is configured to radially expand the centering arbor before the insert molding and/or casting so that in the region of a gap between the pole tube parts a lateral surface of the centering arbor terminates the gap flush with the respective adjacent inner surfaces of the pole tube parts.

9. A method of manufacturing the pole tube of claim 3 , wherein the method comprises:

(a) arranging the pole tube parts on a centering arbor with a mutual axial distance such that the pole tube parts form the axial gap such that the axial gap has a size sufficient for a magnetic separation,

expanding the centering arbor so that in the region of the gap, a lateral surface of the centering arbor closes the gap with a respective inner surface of each of the pole tube parts without any offset; and

(b) connecting, by insert molding and/or casting, an outer lateral area of the pole tube parts with the nonmagnetic material so that, together with the pole tube parts, the nonmagnetic material forms the inner surface of the pole tube;

wherein the centering arbor is an expansion arbor with a radially expandable cylinder surface which is closed even in the expanded state.