Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1998-11-30
2001-02-06
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S211000, C310S262000
Reexamination Certificate
active
06184606
ABSTRACT:
The present invention relates to a solid rotor means of an electric machine in accordance with the preamble of claim
1
. The present invention relates further to a method in accordance with the preamble of claim
9
for improving the characteristics of a solid rotor means.
The electric motors operating in accordance with the principles of an induction machine have usually been machines using so called laminated rotors. Related problems of these are the vibrations which occur already at relatively low rotational speeds and are due to the structure of the rotor, especially due to the poor bending stiffness and partly also due to the poor torsional stiffness thereof, and the changes/wandering in the balance thereof. The so called critical frequency of the laminated rotor is met at relatively low rotational speeds, which are way too low, especially in view of rotational speeds which are raised from the normal. The manufacture of the laminated rotor requires also several working stages and special tools and machines, the manufacture thereof being thus slow and expensive to accomplish.
Therefore, it is prior known to use in the electric motors utilizing high rotational speeds so called solid rotors manufactured from steel, eg. by a lathe from a uniform billet, by means of which an essentially more rigid and stiff structure is achieved. The solid rotor enables also a good and precise balancing, and the rotor also remains in the balance at different rotational speeds This enables the utilization of ball bearings in the rotor bearings.
However, the solid rotor causes also an increase in the rotor resistance and an essential decrease in the power ratio of the machine, this being typically about 0.6-0.7. The coefficient of efficiency for this kind of rotor is poor. The solid rotors, which are manufactured from one piece and in most cases are smooth from the outer periphery thereof, are, however, commonly used in short circuit motors using a rotational speed which is essentially higher than in normal motors, such as up to 200 000 1/min. However, the problem of these is also the above mentioned poor coefficient of efficiency and overheating, even in desired, such as speeds less than 20 000 1/min.
One example of an improved solid rotor application is disclosed by GB patent No. 1 427 818. A rotor means thereof comprises a cylindrical rotor shaft of low carbon iron which is provided with so called copper squirrel cage for decreasing the rotor resistance.
Although the solution provides advantages in the rigidness of the rotor and decreases the resistance, the poor efficiency is, however, still a problem. The losses lead, in addition to the poor efficiency, to a remarkable overheating during the use. Different cooling systems are provided so as to solve the overheating problem, but the power required by them has further decreased the net efficiency. A remarkable problem in view of the manufacture has been the difficulty in attaching the essentially wide semispherical copper portions of the squirrel cage and the fastness thereof in the rotor, especially in higher rotational speeds. In addition, the citation does not disclose or suggest any manner to utilize the disclosed rotor means in other types of motors than in the high speed motors. The disclosed solution has not, eg. due to the above reasons, gained any common success in the field of the electric motors.
FI patent 92114 discloses a rotor for an induction electric machine, the circumference whereof is coated with an electrically conductive coating for the purposes of removing the above mentioned problems. However, the coating is difficult to accomplish and the fastness thereof has proven to be problematic. An additional disadvantage is caused by the fact that in many coating methods the rotor becomes strongly heated, which has a negative effect to the mechanical properties of the rotor. Thus the solution has not been able to solve the problems of the solid rotor machines in a satisfying and economical manner.
The object of the present invention is to overcome the disadvantages of the prior art and to provide a totally new type of solution for improving the characteristics of a solid rotor for an electric machine.
It is also an object of the present invention to provide an induction electric machine solution, which has an essentially improved efficiency and other properties thereof when compared to the known solutions and in which solution there are no significant overheating problems, as is the case with the prior art machines.
It is also an object of the present invention to provide a rotor means having an essentially low rotor resistance.
It is also an object of the present invention to provide a structure and a method for providing a machine which can be used within a wide range of rotational speeds.
An object of the present invention is to provide a solid rotor machine structure having an essentially low field weakening point. This enables eg. loading of the machine by a constant power in an essentially wide range of rotational speeds.
An object of the invention is also to provide a rotor means which is easy to manufacture and thus economical to implement.
An object of the invention is also to provide a machine structure comprising a solid rotor in which an essentially small air gap can be used without any disadvantageous effects, whereby it is possible to increase the efficiency coefficient.
An object of the invention is to provide a electric machine structure having a size and weight which are smaller than those of the known induction machine solutions providing an equivalent power.
The invention is based on that surprising observation that characteristics, which are improved from the prior known solid rotor machines, can be achieved by a solid rotor means which is provided at the end faces thereof with short circuit rings made from material having a good electrical conductivity.
More precisely, the structure according to the present invention is mainly characterized by what is disclosed in appended claims
1
. . .
8
and especially by the characterizing portion of claim
1
. The method according to the present invention is mainly characterized by what is disclosed in appended claims
9
. . .
11
and especially by the characterizing portion of claim
9
.
According to a preferred embodiment of the present invention the apparatus comprises an essentially rigid, from one piece manufactured solid rotor means, the end faces thereof being suitably provided with short circuit ring means which preferably are of copper or similar material having a good electrical conductivity, such as aluminium, bronze, brass, silver, gold etc. material or alloy per se known.
According to one preferred embodiment the end or short circuit ring is essentially deep (high), by means of which an advantage is obtained in the form of a further decrease in the rotor resistance. According to another preferred embodiment the rotor means is manufactured such that the circumferential shape thereof is machined by a lathe from a suitable steel billet, and subsequently a short circuit ring made of a bimetal sheet (eg. FeCu) is attached thereto preferably eg. by electron beam welding (EB welding), friction welding or laser welding or by brazing such that the essentially corresponding steel materials are attached to each other. By this means it is possible to manufacture by a per se known manner a rigid joint which can stand the stresses caused by eg. the high rotational speed in an easy and fast manner. According a still further preferred form rotor bar means provided from a bimetal sheet are used.
Significant advantages are obtained by means of the present invention. The torque output capability and efficiency of a solid rotor machine is essentially improved when compared to the known solutions, while the problem relating to the machine overheating is significantly decreased. By means of the invention the size and weight of the motor are decreased, when compared to known motors having an equal performance. The motor according to the invention gives an essentially even
Arent Fox Kintner & Plotkin & Kahn, PLLC
Dougherty Thomas M.
Perez Guillermo
Rotatek Finland Oy
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