Electric machine and method of making an electric machine

An electric machine includes an external rotor rotatable about a rotation axis, and a stator arranged in coaxial relationship to the rotation axis in the external rotor. The stator is comprised of a first stator portion to define a core element, and a second stator portion arranged in the form of a ring in surrounding relationship to the core element and including radially inwardly directed teeth to define a comb-shaped configuration with slots which taper towards the rotation axis for receiving a stator winding. The comb teeth have free ends which are supported on the core element.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of German Patent Application, Serial No. 102 59 090.7, filed Dec. 17, 2002, pursuant to 35 U.S.C. 119(a)–(d), the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates, in general, to an electric machine, and to a method of making such an electric machine.

External rotor motors are generally known to have an external rotor which is rotatable about a rotation axis. Disposed in coaxial relationship to the rotation axis inside the external rotor is a stator having slots for receiving the stator winding, whereby the slots taper in a direction to the rotation axis. The stator is formed about its outer circumference with small openings in the slots for wrapping the winding to the stator. In the event, it is desired to fill the slot with winding as much as possible, the winding operation become cumbersome because the stator winding must be wound through the narrow openings.

The coils of the stator winding may hereby be mounted by means of needle winding technique, flyer technique, draw-in technique, or manual guiding-in technique, into the slots. Using a needle arrangement to wind a copper coil results only in a limited slot filling degree so that the power density in the motor is decreased. The draw-in technique requires a prolongation of the winding end portion so that the coil exhibits a higher electrical resistance, accompanied by greater losses in the motor. The manual guiding-in technique is labor-intensive and thus expensive.

In particular when exciter coil windings are involved, the broad tooth tips of the slots require a flexible copper coil. Thus, the winding quality becomes substandard, when the winding operation is carried out automatically.

It would therefore be desirable and advantageous to provide an improved electric machine and method of making an electric machine to obviate prior art shortcomings.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, an electric machine includes an external rotor rotatable about a rotation axis, and a stator arranged in coaxial relationship to the rotation axis in the external rotor, wherein the stator includes a first stator portion to define a core element, and a second stator portion arranged in surrounding relationship to the core element in the form of a ring and including radially inwardly directed teeth to define a comb-like configuration with slots which taper towards the rotation axis for receiving a stator winding, wherein the comb teeth have free ends supported on the core element.

The present invention resolves prior art problems by making the stator stack of two stator portions, namely a stator core and a comb-shaped stator element. In this way, the stator winding can be mounted to the stator in a simple and cost-efficient manner. Suitable, the comb-shaped stator element can be laid or bent around the stator core.

According to another feature of the present invention, adjacent ends of the annularly shaped comb-like stator element are securely fixed to one another.

According to another feature of the present invention, the first stator portion can be constructed as a laminated core shaped in the form of a cylindrical shaft, and the second stator portion can be constructed as a stack of laminations, with the teeth being disposed equidistantly and constructed for attachment of the stator winding, before assembly of the stator. Manufacture of comb-like laminations is generally inexpensive. Suitably, connectors can be provided for securing the individual stacks of laminations of the second stator portion with one another. An example of a suitable connector includes registration members for aligning and securing the laminations.

According to another feature of the present invention, the teeth of the comb-shaped stator element may be so supported on the core element as to provide a magnetic yoke therebetween forming a closed magnetic loop.

The stability of the stator can be enhanced by configuring the free ends of the comb teeth in a pointed manner for placement in complementary grooves of the core element during assembly. Suitably, the pointed free ends of the comb teeth lock into the grooves.

According to another aspect of the present invention, a method of making an electric machine includes the steps of placing a stator winding in tapered slots between radially inwardly extending teeth of a comb-shaped stator portion, shaping the comb-shaped stator portion into a ring, placing the ring in surrounding relationship to a stator core such that free ends of the comb teeth are supported on the stator core to thereby form a stator; and positioning the stator in an external rotor in coaxial relationship to a rotation axis thereof.

According to still another aspect of the present invention, a method of making a stator of an electric machine, includes the steps of placing a stator winding in slots between radially inwardly extending teeth of a comb-shaped stator portion, and wrapping the comb-shaped stator portion about a stator core such that free ends of the comb teeth are supported on the stator core.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Turning now to the drawing, and in particular toFIG. 1, there is shown a schematic front, top and side perspective view of one stator potion according to the present invention, generally designated by reference numeral1and forming part of a stator, generally designated by reference numeral2and shown in more detail inFIG. 4. The stator2is the fixed component of an external rotor motor and is received inside an external rotor, indicated by broken line12, in coaxial relationship to a rotation axis13about which the rotor12is rotatable. As is generally known, the stator2is hereby placed at a distance to the rotor12at formation of an air gap.

As shown inFIG. 1, the stator portion1is comprised of plural stacks of sheet metal laminations in parallel side-by-side relationship to define a comb-like configuration with comb teeth4,5arranged at regular intervals, whereby the comb teeth4have a width which is greater than a width of the comb teeth5. Connectors6in spaced-apart relationship secure adjacent stacks of laminations in circumferential direction at their upper ends, and registration members14in the form of dents or bumps in the metal sheets secure the stacks of laminations of the stator portion1to one another, as shown inFIG. 1, so as to realize the comb structure. Although registration members6are shown here to implement the connection of the stacks of laminations of the stator portion1, it is, of course, possible to use other types of connections, such as, e.g., riveting, gluing, or welding. As shown inFIG. 1, the stator portion1is so configured that the wider comb teeth4alternate with the narrower comb teeth5.

Referring now toFIG. 2, there is shown a schematic front view of the stator portion1, with a coil7attached to each of the wider comb teeth4so that each comb tooth4is wrapped on both sides with a coil7. The coils7have a V-shaped configuration which are tapered in the direction of the rotation axis13. Although not shown in the drawing, the coils7are each wound on an insulating plastic body before being attached to the comb teeth4, whereby the attachment of the coils7onto the comb teeth4may be carried out automatically by a suitable inserting machine. All coils7form together the stator winding of the stator2.

As shown inFIG. 3, the stator2further includes another stator portion3in the form a cylindrical core element comprised of laminations. The core element3has an outer perimeter formed with notches8,9to complement the configuration of the pointed teeth ends of the comb teeth4,5. In other words, the core element3has wider notches8and narrower notches9in alternating sequence.

FIG. 4is a schematic illustration of the fully assembled stator2according to the present invention. The assembly of the stator2is as follows: The stator portion1ofFIG. 1, after being provided with the stator winding, as described above, is shaped into a ring and wrapped around the laminated core3. Depending on the configuration of the connectors6, the stator portion1may also be bent into the ring shape. The adjacent ends10of the ring-shaped stator portion1abut hereby one another and are securely fixed to each other. The width of both ends10corresponds hereby to the width of the narrow comb tooth5. In the assembled state, the radially inwardly directed comb teeth4,5are supported on the laminated core3, with the ends of the comb teeth4,5engaging the complementary notches8,9. In other words, the wider comb teeth5engage the notches8and the narrower comb teeth4engage the notches9. Although not shown in the drawing, the comb teeth4,5may also be constructed in a way to lock in the respective notches8,9. In any event, the engagement of the comb teeth4,5in the notches8,9of the laminated core3results in a superior magnetic yoke.

In the assembled state of the stator2, as shown inFIG. 4, the coils7and thus the stator winding almost completely fill the slots11formed between the comb teeth4,5and tapered in the direction of the rotation axis13.