INDUCTION MOTOR
The present invention relates to an asynchronous electric induction motor with internal rotor providing greatly simplified construction.
An asynchronous electric induction motor typically comprises a stator consisting of a series of metal laminations, which has a cylindrical surface in its central part and inside which there are disposed a number of open slots in which, separated by a number of insulating films, there is accommodated the winding which creates the rotating magnetic field of the motor.
A number of shields or bridging portions are provided on the stator, either directly or via an enclosure which surrounds the stator and is firmly connected therewith. These shields or bridging portions accommodate, in their central part, a number of bearings, on which there revolves the shaft, firmly connected to the rotor, as a result of the action of the rotating magnetic field and the currents induced on the rotor.
The motor is generally secured via an enclosure or by means of the shields or bridging portions, and the load to be actuated is coupled to the shaft.
Motors of the type described exhibit the disadvantage that winding is difficult, for which reason the manufacturing time is undesirably long. Moreover, due to the large number of components which come into play, a very heavy, large assembly is obtained.
The present invention proposes a new arrangement of the component elements with which construction of the assembly is greatly simplified. According to the present invention, the stator pack has a number of slots designed to accommodate the winding, with the special feature that there is an opening in its outer side for introduction of the winding.
Preferably, the insulation between the stator pack and the stator winding for creating the rotating magnetic field is produced by means of an insulating element formed by two components of an electrically insulating material which has a number of suitable mechanical properties. The two components fit together, covering the entire inside of the slot in the stator pack as well as the flat metal surfaces of each one of the two outer end faces of the stator pack.
The insulating components can support a number of bearings, on which there revolves a shaft, which is firmly connected to the rotor, through the action of the rotating magnetic field and the currents induced on the rotor.
The winding can be accommodated in the insulated slots, thereby clamping the insulating component on the stator and holding the assembly totally secure. The bearings, which support the shaft which is firmly connected with the rotor and can be accommodated in the insulating components, ensure that the stator remains mounted concentrically with the rotor.
The stator assembly may include a magnetic pack of metal laminations in the form of a circular yoke. The yoke fits together with the outer profile of the stator pack and winding, completing the motor. The purpose of the yoke is to close the magnetic field and maintain efficiency, as well as providing the assembly with strength.
The two components of the insulating element may be provided with elements for securing the motor, as well as cavities for accommodating terminals for facilitating connection of the enamelled wire of the winding with the supply cables.
Advantageously, there are provided a number of cavities formed in the insulating element, these being designed to accommodate a number of terminals for establishing electrical contact between the winding and said terminals, the latter being capable, at the same time, of connecting an external cable.
Preferably there are provided a number of hollow columns formed in the insulating element, which respectively accommodate fixing screws for the motor.
Optionally, the motor includes a cover or outer enclosure designed to provide greater protection. This enclosure is mounted over the outer yoke of the stator and comprises two half-bodies which fit on the outer profile of the stator yoke, locking the motor inside it. The half-bodies each include orifices allowing exit of the motor shaft, as well as a number of orifices in the flat surface for securing the motor and a number of openings providing access from the outside for cables for connection to the stated terminals.
With the electric motor of the present invention, winding is facilitated, since winding is performed from the outside and there is no need to form bound coil top or bottom end turns, a substantial improvement consequently being achieved in manufacturing time. Moreover, the weight of the assembly is reduced significantly, since there is less weight of copper because the coils are of the type with a virtually diametric path. The motor has a smaller number of components, since the shields or bridging portions are eliminated by securing the bearings to the slot insulators. Finally, it should be pointed out that an assembly is obtained which is of greatly reduced dimensions due to the elimination of components.
The features and advantages of the electric motor of the present invention will become clearer from the detailed description of a preferred embodiment. The description is given, from this point, by way of non-limiting example, with reference to the drawings, in which: Figure 1 is a plan view of an embodiment of an electric motor according to the invention, shown without outer enclosure and without winding; Figure 2 is an elevational view of the embodiment of the electric motor of Figure 1, shown without outer enclosure and without winding; Figure 3 is a sectional view through plane AA' of Figure 1 of the motor without outer enclosure and without winding; Figure 4 is a perspective view of the embodiment of the motor shown without outer enclosure; Figure 5 is a perspective view of the motor without the winding and without the outer enclosure;Figure 6 is a perspective, exploded view of the embodiment of the motor without the winding and without the outer enclosure; Figure 7 is a dismantled perspective view of the motor with outer enclosure from the non-actuation end; Figure 8 is a dismantled perspective view of the motor with outer enclosure from the actuation end; and Figure 9 is a perspective view of the stator assembly with the rotor inside it and with just one coil.
In a first embodiment, in which the motor exhibits an open configuration without outer enclosure, the stator pack (1) is composed of an assembly of metal laminations, which has a series of teeth or vanes (5) connected together by means of the bridging portions (6). At their outer end, the teeth exhibit a number of projections (7) which fit within with a number of cavities (8) formed in a yoke pack (9).
In the surface of the teeth (5), and situated conveniently to achieve a maximum reduction in Foucault losses, there are arranged a number of tie elements (2), by means of which it is possible to hold the metal laminations together.
Between two consecutive teeth (5) there is a space or slot (4) in which is accommodated the winding.
The stator pack (1) has a cylindrical inner surface (10) within which the rotor revolves.
Unlike the laminations at the ends (3), the intermediate laminations (11) do not exhibit a continuous bridging portion (6), because the stator pack (1) exhibits slots (12) dimensioned so as to obtain the desired torque-velocity characteristics.
The rotor (13), like the stator, comprises a number of juxtaposed metal laminations. These metal laminations are provided with a series of internal slots with openings (14) in the outer cylindrical surface (15). The openings (14) are arranged helicoidally to provide smoother operation.
The rotor assembly (13) includes at its end faces two shorting rings (16), which communicate with one another via the slots and are normally diecast in a conductive alloy which is usually aluminium or copper and which constitutes the so-called squirrel cage.
The rotor (13) includes, firmly connected therewith, a shaft (17) which incorporates a circular groove (18) in which is situated a retaining ring (19). The retaining ring serves as a stop for a bearing (20) inserted on the shaft (17), which fits together with a central orifice (21) in the bearing (20). A second bearing (22) is provided, which is also inserted on the shaft (17). However, this second bearing (22) rests on a spring (23) which is compressed between the end face of the rotor and the bearing (22). This makes it possible to compensate the slight variations which may occur in the nominal measurements of the stator pack (1) and the rotor (13) of the motor.
An insulating element (24) is provided which is formed of two plastics components. This insulating element (24) exhibits a flat surface (25), whose outer profile is the same as that of the stator pack. Over its entire periphery, with the exception of the ends, and perpendicular thereto, there extends a wall (26) which covers the side walls of the teeth (5) and of the bridging portion (6), that is to say which covers the slots (4) in the stator pack (1).
In each one of the spaces corresponding to each one of the slots (4), and perpendicularly to the wall (25), the wall (26) is extended cylindrically, forming a closing wall (28) with an outer profile matching the internal profile (17) of the yoke pack (9). This closing wall (28), which extends from the wall (26) which covers a tooth (5), does not extend as far as the following tooth, a slot opening (29) remaining which allows introduction of the wire for producing the stator winding.
In the central part of the surface (25), there extends a conical zone (30) which ends in a flat zone (31) parallel to the flat zone (25). This makes it possible to accommodate a number of shorting rings (16) of the rotor (13), and to leave space free for rotation.
In the centre of the surface (31), and perpendicular thereto, there is a cylindrical wall (32), whose inner part fits together with the outer cylindrical surface of the bearings (20, 22), it being terminated by a flat surface (33) against which rests the flat part of the end face of the bearings (20, 22) under the urging of the extension force of the spring (23).
In the centre of the surface (33) there is an orifice (34) which allows passage of the shaft (17). From the surface (25) and in the zone which covers the teeth there project four hollow posts (60) in which are accommodated the ends of the winding and a terminal (42). From two of the four remaining zones which are situated opposite the teeth there project two cylinders (35) which are slightly taller than the plane (33). The cylinders (35) have a central orifice (36) designed to receive a number of self-tapping screws, with the purpose of securing the motor.
Perpendicularly to the surface (25) a number of walls (38) project, ending in a curved profile (61), which ends exactly where the slot (29) starts and which serves to guide the introduction into the slot (4) of an enamelled wire during winding.
In the assembled state, the walls (26) of the two components of the insulating element (24) fit fully together with the lateral profile (37) of the slots (4) of the stator (1), while the inner part of the wall (25) rests on the flat front surface of the teeth (5) of the stator pack (1 ). Total coverage of the lateral surface (37) of the slots (4) is shared between the two walls (26) of the two components of the insulating element (24).
Between the two components of the insulating element (24) there are arranged a bearing (22), the spring (23), the rotor (13) firmly connected to the shaft (17), on which is mounted the retaining ring (19), and the other bearing (20), the rotor (13) being fully centred axially relative to the stator (1) and the outer surfaces of the rotor (14) and inner surfaces of the stator (10) being fully centred coaxially.
Figure 9 shows an exemplary embodiment of an assembly as described, illustrated with one wound coil (40) of the four which have to be provided.
The coils correspond, in this case, to an asynchronous motor with two poles and two phases for single-phase supply, with a permanent capacitor. The coils are wound directly onto the assembly of Figure 9 described above, the wire passing through the openings (29) to be deposited in the slots (4) of the stator pack (1), conveniently insulated by the insulating element (24). In the stated winding, the two coils (40) are connected together and constitute the main or working phase, while the two coils (41), also connected together, form the auxiliary or starting phase.Each one of the ends of enamelled wire of each one of the phases is directed towards the corresponding cavity (59) in the post (60), so that, with a terminal (42), electrical contact is established between the wire and the terminal, which will also make it possible for an external cable to be connected for connection thereof to the mains power supply. This terminal (42) is a terminal of the type commonly used to effect electrical connection with an enamelled wire by means of the known insulation displacement system.
The arrangement of the above-described winding provides the assembly with good mechanical rigidity, as well as less ohmic resistance, a lower wire weight, better concatenation of the magnetic fields of the main and auxiliary phases and of the rotor. The invention makes it possible to achieve an improvement in efficiency.
The assembly of stator and winding is inserted into the yoke pack (9), causing the projections (7) on the stator pack (1) to match up with the slots (8) in the yoke pack (9) which match up and form a joint, of the dovetail type, the metal laminations of the stator pack thus being totally secure with regard to the mechanical stresses resulting from the magnetic field.
The embodiment described above corresponds to a motor in its open version or without its outer enclosure, which exhibits a number of fixing elements, namely the columns (35) with their orifices (36), the shaft (17) to which the load is applied and a number of elements which allow connection to the mains power supply, namely the terminals (42).
The embodiment of the motor with outer enclosure as described below is intended for instances in which better protection of the motor is desired with regard to the penetration of foreign bodies and water, as well as protection of people against electric shocks.
In such cases, there is incorporated with the motor described above an outer cover or enclosure formed of two components or half-bodies. In particular, the stated enclosure comprises a front half-body (43) and a rear half-body (44). The front half-body (43) consists of a wall (45) cylindrical in form, which on the inside fits together in an interference fit with the outer surface (46) of the yoke pack (9) and which, once assembled, extends as far as half-way along the pack.
The other end of the wall (45) continues, by way of closure, in the form a flat wall or end face (47), which has in its central part an orifice (48) through which the shaft (17) of the motor (17) reaches the outside. In the abovementioned end face (47) there are also two orifices (49) which extend inwards in the form of tubes (50), which each receive self-tapping screws for securing the motor.
The rear half-body (44) of the enclosure is similar to the front half-body. The two half-bodies differ in that, instead of an orifice (48) for passage of the shaft, there are provided four rectangular openings (51) which provide access to the terminals (42) from the outside. This makes it possible to connect the motor to the mains power supply.
When mounting this protective enclosure over the surface (46) of the yoke pack (9), the rectangular openings (51) are fully aligned with the cavities (59) in the posts (60) which accommodate the terminals (42), while axially the outer edge (52) of the rear protector butts against the same outer edge (52) of the front protector (43).
The embodiment of the electric motor of the present invention has been sufficiently described with reference to the attached drawings, and it will be understood that any modifications in detail may be made to the same which are considered advantageous as long as the essential features of the invention summarised in the following claims are not changed.