Magnetrad

Abstract

A magnetic wheel for an electric motor, comprising a shaft and a disc made of a plastic containing magnetic particles, wherein the disc is arranged on a support hub and the support hub on the shaft, wherein at least one elastic element (4, 6) is arranged between the shaft (2) and the disc (3), characterized in that the at least one elastic element (6) is an O-ring, wherein the at least one O-ring (6) is arranged in a groove (5) and the groove depth is less than the cross-sectional height of the O-ring (6), wherein the O-ring (6) creates an interference fit between the shaft (2) and the support hub, which ensures a tight fit, wherein the magnetic wheel is adjustable in its angular position by rotating the support hub relative to the shaft (2).

Description

The invention relates to a magnetic wheel for an electric motor having a shaft and a disc made of a plastic containing magnetic particles which is integrally formed on a carrier hub by means of injection molding.Magnetic wheels of this type are used, for example, in brushless DC motors or in actuators as a component of position sensors and are therefore known. The disc of the magnetic wheel is produced by injection molding a plastic containing iron particles onto the carrier hub. The carrier hub may be a closed ring of a suitable material such as steel or brass. Subsequently, the carrier hub with the injection-molded disk is pressed onto the shaft. The disadvantage with this design is that, due to manufacturing tolerances of the shaft, considerable stresses sometimes occur in the carrier hub during the pressing-on of the carrier hub, which stresses reduce the service life of the magnetic wheel. In particularly severe cases, adverse effects on the magnetic wheel are imminent, which can lead to malfunctions in the position sensor. It is known from DE 10 2011 089 243 A1 to form the carrier hub as a slotted ring. The slotted design of the carrier hub allows reacting to tolerances of the shaft. The carrier hub thereby surrounds the shaft as a kind of spring and can thereby expand with larger shaft diameters. A disadvantage here is that the position of the carrier hub is determined with the arrangement of the carrier hub on the shaft. If corrections of the angular position of the magnetic wheel are required in the course of test runs, these are possible only with great effort because of the secure fit of the carrier hub on the shaft. In addition, there is a risk of damage when adjusting the magnetic wheel. A smaller press fit between the shaft and the carrier hub is, however, not possible, since due to the motor accelerations occurring during the test run, in conjunction with the tolerances caused by the manufacturing process, no sufficient tight fit is ensured.From DE 195 46 595 A1 a rotational speed and / or rotational direction sensor device is known which comprises a pole wheel which is connected to a shaft via a resilient or elastic intermediate mounting part in the form of an O-ring. The pole wheel does not have a special carrier hub.DE 298 12 803 U1 describes a measuring wheel for a rotary encoder which has on a hub at least one outer magnetic track which is arranged on at least one ring of plastic-bonded magnetic material which is connected to the hub embedded in high-strength plastic. The hub is made of metal and is attached to the shaft by shrinking, axial screwing or axial clamping.JP H06-54 504 A describes a rotor of an electric motor in which a synthetic resin disc interacts with a cylindrical magnet which are arranged on a shaft. The disk is connected to the magnet via corresponding projections.Further prior art is known from DE 10 2006 045 827 A1.The invention is based on the object of creating a magnetic wheel in which, on the one hand, corrections of the angular position are possible with little effort and, on the other hand, a long-term stable connection of magnetic wheel and shaft is ensured during operation.This object is achieved by a magnetic wheel having the features of claim 1.The support hub made of an elastic plastic material allows a long-term stable connection between the shaft and the disk in the form of a tight fit, but at the same time allows the rotation of the magnetic wheel on the shaft in order to adjust the angular position of the magnetic wheel. During the assembly of the magnetic wheel, the carrier hub is deformed and exerts a soft pressure between the shaft and the disk. This achieves the tight fit. At the same time, manufacturing tolerances can be compensated for thereby, whereby the machining quality can be reduced, which leads to a more cost-effective manufacture. On the other hand, the adjustment of the angular position of the magnetic wheel is thus possible without damage to the magnetic wheel.The required elasticity of the carrier hub can be determined in the simplest manner by the choice of material, in that an elastomer is selected as material. Rubber has proven to be a particularly cost-effective material with simultaneously high wear resistance.The invention is explained in more detail on the basis of an exemplary embodiment. The single FIGURE shows a magnetic wheel according to the invention with an elastic carrier hub.The magnetic wheel 1 in the figure consists of a shaft 2, which can be the shaft of an electric motor of an actuator, and a disc 3 made of ferrite-bonded plastic, wherein the disc 3 is formed on a carrier hub 4 by means of injection molding. The carrier hub 4 consists of an elastic plastic material, which on the one hand ensures a sufficient snug fit during operation and on the other hand allows a slight rotation of the carrier hub 4 with the disk 3 relative to the shaft 2 for the correction of the angular position.

Claims

Magnetic wheel for an electric motor, consisting of a shaft and a disc made of a plastic containing magnetic particles, wherein the disc is arranged on a carrier hub and the carrier hub on the shaft, wherein at least one elastic element (4, 6) is arranged between the shaft (2) and the disc (3), characterized in that the at least one elastic element (6) is an O-ring, wherein the at least one O-ring (6) is arranged in a groove (5) and the groove depth is less than the cross-sectional height of the O-ring (6), wherein an interference fit is produced between the shaft (2) and the carrier hub by the O-ring (6) which ensures a secure fit, wherein the magnetic wheel is adjustable in its angular position by rotating the carrier hub relative to the shaft (2).Magnetic wheel according to Claim 1, characterized in that two O-rings (6) are arranged between the shaft (2) and the carrier hub (4).Magnetic wheel according to Claim 1, characterized in that the groove (5) is arranged on the shaft (2).Magnetic wheel according to Claim 1, characterized in that the groove (5) is arranged on the carrier hub (4).Magnetic wheel according to at least one of the preceding claims, characterized in that the elastic element (4, 6) is an elastomer.Magnetic wheel according to at least one of the preceding claims, characterized in that the elastomer is rubber.Magnetic wheel according to at least one of the preceding claims, characterized in that the carrier hub (4) is connected to the shaft (2) by at least one welding point.

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