Induction motor

Details Induction motor Induction motor

1985-08-07

1987-03-17

Duggan, Donovan F.

Electrical generator or motor structure

Dynamoelectric

Rotary

310 90, 310266, H02K 1700

Patent

active

046510400

DESCRIPTION:

BRIEF SUMMARY
STATE OF THE ART

The invention is based on an induction motor of the type disclosed in the main claim. Such a motor with a permanent magnetically excited rotor has been already suggested (Feinwerktechnik und Messtechnik 87 (1979), page 163 etc). for generating a starting torque between the rotor and the stator the air space is formed with a different width over the circumference of the rotor, so that a definite rest position of the permanent magnetically excited rotor is the result, which is different from the magnetising direction of the stator. When applying the stator field a force is exerted on the rotor in circumferential direction, whereby the rotor comes into synchronism with respect to the stator field and rotates with the stator field, if need be, after one or a plurality of rotary oscillations. However, the start of the motor is possible only if very low forces engage on the rotor, because otherwise the starting torque is not sufficient to accelerate the rotor to the required angle speed, so that it can reach the syncchronism with the stator field. Due to the low starting torques of such motors, their possibility of use is very limited.
A one phase induction motor is known from DE-PS No. 1 999 390, whose rotor is freely rotatable around a defined angle on a drive shaft, before it gets into a force locking connection with the connection with the drive shaft. The rotor is at first axially displaced towards the stator and is simultaneously accelerated in axial direction and in the circumferential direction by magnetic forces, before it gets into a force locking connection with the drive shaft, after overcoming an axial spring force. The starting torque of such types of motors are limited in light of the partial overlapping of rotor and stator and in light of the brake moment by the drive shaft.
Furthermore, shaded-pole motors are useable for pump drives, for example,. However, they to have only small starting torques despite the realtive large structures and their degree of effectiveness is relatively poor.
Induction motors in accordance with the type of the main claim have no defined rotating direction, if no additional measures are taken for defining the rotating direction. A mechanical arrangement for defining a dined rotating direction of the motor is known from GB-PS No. 1 413 782, for example. Other measures for obtaining a defined rotating direction of the motor exist, for example, by installing free running devices with ball or roller clamping elements in corresponding recesses of a free running element, whereby only one rotating direction is transmitted to the drive shaft. Such arrangements are known, for example, from electric ingnitions for motor vehicles.


ADVANTAGES OF THE INVENTION

In contrast thereto, the induction motor in accordance with the invention with the characterizing features of the main claim has the advantage that a high starting moment is obtained with a small, simple and cost efficient mode of structure, so that the high operating moment of the motor is not reduced by too low starting torques from the idle position, In view of the inventive mode of structure one achieves a uniform, synchronous starting of the motor which is free of short circuits with a simple structure and does not cause any mechanical noises, caused by time delayed acting mechanical clutches, and has a high life span because of its lowest number of parts which wear out.
Advantageous further embodiments and improvements of the motor stated in the main claim are made possible by the measures stated in the subclaims. Particularly advantageous is the design of the outer part of the rotor as an electrically conductive hollow cylinder which preferably consists of copper, because it is particularly easy to make and has a very high conductivity.
The rotor may also be made from an interrupted iron cylinder, instead of a good conductive hollow cylinder, whereby copper rods are inserted into the intermediary spaces. Thereby, the iron parts form flow conducting pieces between the rotor and the stator which redu

REFERENCES:
patent: 2159769 (1939-05-01), MacMillan
patent: 2492678 (1949-12-01), Amtsberg
patent: 2974242 (1961-03-01), Apstein
patent: 3866071 (1975-02-01), Hallerback
patent: 4045698 (1977-08-01), Morrill
Feinwerktechnik und Messtechnik 87 (1979), pp. 163-169.

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