The present application claims priority under 35 U.S.C. ยง 119 to German Application No. 10 2020 131 410.8, filed on Nov. 26, 2020, the entire contents of which are hereby incorporated herein by reference.
The present disclosure relates to an electric motor.
Electric motors, referred to as internal rotor motors, have a rotor that is connected to a rotor shaft and is rotatably mounted in a housing. The rotor carries permanent magnets. The permanent magnets are arranged around a rotor core and are located on its outer surface. The rotor defines the geometric axes and directions which will also be used herein. A central axis coincides with the axis of symmetry of the rotor and, in the electric motor, also represents the axis of rotation of the rotor. The direction of the axis of rotation is the axial direction of the arrangement. The radial direction is characterized by increasing distance from the central axis. Thus, the permanent magnets of the rotor are located outside in the radial direction. Tangential to the rotor is the circumferential direction, at which each direction vector is oriented perpendicular to a radius of the arrangement. According to the prior art, the electric motor further includes a stator arranged radially outside the rotor and annularly surrounding the rotor on the outside. The side of the rotor closest to the busbar assembly is described as the top of the rotor.
Two bearing systems are usually provided for fixing the rotor. Often these bearings are designed as ball bearings, with the electromagnetic assemblies located between the bearings. For motors with increased noise requirements, the bearings are preloaded with a spring element. This applies an axial force to the end shields accommodating the bearings.
Therefore, the axially acting forces must be introduced into the rotor shaft via bearing inner rings of the ball bearing. The force can be introduced by a frictional or form fit between the outside of the rotor shaft and the bearing inner ring. A design with force introduction via a form fit is often associated with additional costs, since a retaining ring or a retaining washer must also be fitted.
Example embodiments of the present disclosure provide electric motors each including a simple connection of a bearing inner ring to a rotor shaft which absorbs axial forces.
An electric motor according to an example embodiment of the present invention includes a rotor and a stator. The rotor includes a rotor shaft, on which a rotor core is seated, which is adjoined by magnets, in particular permanent magnets, in a radial direction outwards. The rotor shaft is mounted rotatably about an axis of rotation in a ball bearing including a bearing inner ring. The stator surrounds the rotor on an outside. At least the rotor core of the rotor is overmolded in an injection molding process to define the rotor.
On an end surface of the rotor adjacent to the ball bearing, projections are made by injection molding to define an axial support for the bearing inner ring.
Such an example embodiment is particularly cost-effective, since additional components, such as retaining rings, can be dispensed with.
Undersides of the projections are supported on an upper side of the rotor core or an upper side of a laminated core of the rotor. The projections are preferably spaced from a central bore in the radial direction to the axis of rotation, so that the rotor shaft is exposed in a region of the projections. In an example embodiment, the projections each include a projecting base body on which a pin is seated. In this case, the base body includes a larger cross-section than the pin. The bearing inner ring rests on the pins.
The ball bearing preferably is located at the upper side of rotor or the rotor core.
Preferably, the projections extend parallel or substantially parallel to the axis of rotation and are evenly or substantially evenly spaced in the circumferential direction.
In order to ensure reliable force absorption in the axial direction, the projections in the radial direction to the axis of rotation are located exclusively at a level of the bearing inner ring.
Preferably, at least three projections are provided.
It is advantageous if the ball bearing is spring preloaded.
In an example embodiment, the ball bearing supports the rotor shaft on a side away from the stator in the motor housing by a bearing shield.
A magnet holder may be provided to fix a position of the permanent magnets of the rotor in the injection molding process, which is integrally formed with the projections.
There are preferably three projections which preferably have a circular or substantially circular cross-section. It is advantageous if the projections, which are circular or substantially circular in cross-section, are in operative contact with the bearing inner ring at free ends thereof.
The above and other elements, features, steps, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of the example embodiments with reference to the attached drawings.
Example embodiments of the present disclosure are explained in more detail below with reference to the drawings. Similar or similarly acting components are designated in the figures with the same reference signs.
As shown in
By forming the protrusions 8 during the manufacture of the rotor by injection molding, no additional complex manufacturing steps are necessary.
In the example embodiment shown, the projections 8 are formed integrally with the magnet holder 6 of the rotor. However, it is also known to overmold the rotor around the permanent magnets, for example. Regardless of which component of the rotor is formed by injection molding, the projections can be produced in the same step.
While example embodiments of the present disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The scope of the present disclosure, therefore, is to be determined solely by the following claims.
Number | Date | Country | Kind |
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102020131410.8 | Nov 2020 | DE | national |