Magnetrad

Abstract

Magnetic wheel (1) for an electric motor, consisting of a shaft (2) and a disk (3) made of a plastic containing magnetic particles, wherein the disk (3) is arranged on a carrier hub (4) and the carrier hub (4) is pressed onto the shaft (2), characterized in that the carrier hub (4) is designed as a slotted (5) ring around which the disk (3) is formed by injection molding, that the carrier hub (4) has a notch (6) radially on the outside, that the notch (6) is arranged in a region and the ends of the region are arranged at least 90° away from the slot (5), that the notch (6) is designed in the form of at least one impression, that the notch (6) is a single recess (8) in the carrier hub (4) which is arranged opposite the slot (5).

Description

[0001] The invention relates to a 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 is pressed onto the shaft.

[0002] Such magnetic wheels are used in brushless DC motors as components of position sensors and are therefore well known. The magnetic wheel disk is produced by injection-molding a plastic containing iron particles onto the carrier hub. The carrier hub is a closed ring made of a suitable material such as steel or brass. The carrier hub, with the molded-on disk, is then pressed onto the shaft. The disadvantage of this design is that, due to manufacturing tolerances in the shaft, considerable stresses can sometimes occur in the carrier hub when the carrier hub is pressed on, which reduces the service life of the magnetic wheel. In particularly severe cases, this can lead to damage to the magnetic wheel, which can lead to malfunctions in the position sensor.

[0003] The document DE 103 31 961 A1 concerns a ring magnet.

[0004] The invention is therefore based on the object of creating a magnetic wheel in which stresses occurring during production do not lead to an impairment of individual components.

[0005] The object is achieved by the subject matter of claim 1. The carrier hub is designed as a slotted ring around which the disc is formed by means of injection molding.

[0006] The slotted design of the carrier hub allows for significantly better response to shaft tolerances. The carrier hub surrounds the shaft like a spring and can therefore expand for larger shaft diameters. This significantly reduces stresses in the carrier hub, which increases the service life of the magnetic wheel. Due to the greater toughness of the plastic, expanding the carrier hub does not significantly increase stresses in the disk. A further advantage is that the slotted carrier hub also allows for larger manufacturing tolerances in the shaft diameter and hub bore, which simplifies production.

[0007] Production is very cost-effective if the ring for the carrier hub is rolled from strip material.

[0008] In a different design, the ring for the carrier hub can be a turned or stamped part with a slot machined into it. This is particularly advantageous if the ring is subject to further machining prior to overmolding.

[0009] Due to the expansion of the carrier hub, relative movement between the disk and the carrier hub can occur. It has proven advantageous to connect the carrier hub and disk for secure torque transmission by providing the carrier hub with a radially outer notch.

[0010] A secure connection between the carrier hub and the pulley without preventing the carrier hub from expanding is achieved with a notch if the notch is located in an area whose ends are at least 90° away from the slot. Thereafter, no notch is located at least 90° to the left and right of the slot. In this area, relative movement between the pulley and the carrier hub can occur during expansion. This minimizes stresses.

[0011] An intimate connection between the carrier hub and the disc is achieved with a notch in the form of at least one impression, preferably in the form of a knurl.

[0012] In another embodiment, the notch is particularly easy to produce if it is a single recess in the support hub, positioned opposite the slot. A single recess is often sufficient due to the low torque to be transmitted. Another advantage is that this provides large areas of the support hub that allow relative movement between the plastic and the support hub.

[0013] For larger torque transmissions, two to four recesses can be arranged in the carrier hub, which are arranged symmetrically to the slot.

[0014] The invention is explained in more detail using an exemplary embodiment. It shows: Fig. 1 a magnetic wheel in half section, Fig. 2, Fig. 3 further designs of the carrier hub.

[0015] The magnetic wheel 1 consists of a shaft 2, which can be the shaft of an electronically commutated electric motor, and a disk 3 made of ferrite-bonded plastic. The plastic is injection-molded onto a carrier hub 4. The carrier hub has a slot 5, which is arranged in the sectional plane for better visibility. Opposite the slot 5 and thus at a distance of 180°, the carrier hub 4 has a notch 6 in the form of a recess 8 on the radial outside. During injection-molded processing, the ferrite-bonded plastic fills the notch 6 and thereby creates an intimate bond with the carrier hub 4. When the carrier hub 4 with the disk 3 is pressed onto the shaft 2, the carrier hub 4 can expand, whereby relative movements between the carrier hub 4 and the disk 3 can occur in the areas to the right and left of the slot 5.

[0016] In the following figures, the carrier hub 4 is shown without the disc and the shaft. Fig. Figure 2 shows the support hub 4 with a notch 6 in the form of two knurls 7. The knurls 7 are arranged in an area symmetrically opposite the slot 5 and extend over 60°. The knurls 7 each extend over a range of 20° and are spaced 20° apart. The knurls 7 are thus spaced 150° apart from the slot 5. The support hub 4 in Fig. 3 has a notch 6 in the form of three recesses 8 arranged symmetrically to the slot 5, which are spaced apart by 30°.

Claims

[1] Magnetic wheel (1) for an electric motor, consisting of a shaft (2) and a disc (3) made of a plastic containing magnetic particles, wherein the disc (3) is arranged on a carrier hub (4) and the carrier hub (4) is pressed onto the shaft (2), characterized by that the carrier hub (4) is designed as a slotted (5) ring around which the disc (3) is formed by means of injection molding, that the carrier hub (4) has a notch (6) radially on the outside, that the notch (6) is arranged in a region and the ends of the region are arranged at least 90° away from the slot (5), that the notch (6) is designed in the form of at least one impression, that the notch (6) is a single recess (8) in the carrier hub (4) which is arranged opposite the slot (5). [2] Magnetic wheel according to claim 1, characterized by that the carrier hub (4) is rolled from strip material. [3] Magnetic wheel according to claim 1, characterized by that the carrier hub (4) is a turned or stamped part into which a slot (5) is made. [4] Magnetic wheel according to one of the preceding claims, characterized by that the notch (6) is two to four recesses (8) in the carrier hub (4) which are arranged symmetrically to the slot (5).

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