Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-01-14
2001-02-13
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S239000, C310S248000
Reexamination Certificate
active
06188154
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electric motor which is provided with a thermal safety feature.
Electric motors of the above mentioned general type are known in the art. One of such electric motors is disclosed for example in U.S. Pat. No. 5,089,735. The known electric motor has a rotor with a rotor winding. The known rotor is provided with a brush for a current transmission from a stationary current terminal of the electric motor to a rotatably supported rotor winding. The brush is received movably in a case and is spring-loaded against a collector of the rotor. The known electric motor is also a collector motor. The present invention is however not limited to collector motors, but instead can be used for example for sliding ring motors or in general for electric motors in which a current transmission is performed to the rotor winding through a brush or a similar sliding body.
In order to provide the protection from thermal overloading, the known electric motors have a thermal safety means. The thermal safety means include a bimetal-interruption contact which is arranged closely on the brush of the electric motor. During heating of the brush and thereby the bimetal-interruption contact, the bimetal interruption contact opens by a switch-off temperature. Thereby the current supply to the rotor winding is interrupted, and a further thermal heating of the electric motor is prevented.
Another electric motor provided with a thermal safety feature is disclosed for example in the European patent document EP-A 171 446. This electric motor has metal spring tongs composed of a shape memory elements, on which the brushes of the electric motor are mounted. The spring tongs press the brushes against a collector of the electric motor. The shape memory elements change their shape abruptly during exceeding of a threshold temperature. The spring tongs composed of the shape memory elements in the known electric motors are shaped and arranged so that in the event of exceeding the threshold temperature, the brushes are lifted from the collector and thereby the current supply to the rotor winding is interrupted.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an electric motor of the above mentioned general type, which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in an electric motor which has a switch-off contact which is arranged relative to a case so that it is contacted during a thermally-caused length change of the case.
The thermally dependent position change can be a temperature expansion of the case. Also, it is possible that the case is connected with a synthetic plastic part which in response to an undesirably intense heating softens and melts so that the position of the case changes.
The switch-off contact is connected to ground, so that a short circuiting is released when the case supplied with a potential comes in contact with the switch-off contact due to the thermally caused position change. Thereby a melting safety element is burnt through and a current supply to the electric motor is interrupted.
It is possible to lift the case from a counter contact by the thermally caused change of the switch-off contact, and thereby to interrupt the current supply to the electric motor.
The contacting of the switch-off contact can be reversible. Thereby the electric motor after cooling can return back to operation. On the other hand, in the invention the contacting or decontacting of the switch-off contact can be irreversible. Thereby the electric motor can not be brought back into operation after a thermal overloading.
The present invention has the advantage that it provides for a simple and price-favorable thermal safety of the electric motor. The switchoff contact can be formed for example as a tong which is formed of one piece with a housing part of the electric motor and produced by punching. In the predetermined position it is bent relative to the case. Thereby no additional parts or additional working steps are needed during assembly of the electric motor, and the manufacture is not more expensive than the manufacture of an electric motor without the inventive thermal safety feature. The thermal safety is released during a thermal overloading of the electric motor in a reliable manner, and there is no danger of burning.
The inventive electric motor is provided for operation of a secondary air pump (impeller), for oxidation of exhaust gasses of an internal combustion engine. In order to oxidate non-burnt or incompletely burnt hydrocarbons and carbon monoxide secondary air is supplied to hot exhaust gasses of internal combustion engines with such a secondary air pump. The secondary air can be supplied in the internal combustion engines both with and without a catalyst.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 3707694 (1972-12-01), DuRocher
patent: 4034265 (1977-07-01), DuRocher et al.
patent: 4658321 (1987-04-01), Lindner
patent: 4675642 (1987-06-01), Reiferscheid
patent: 5089735 (1992-02-01), Sawaguchi et al.
patent: 5294851 (1994-03-01), Tajima et al.
patent: 5294852 (1994-03-01), Straker
patent: 6028381 (2000-02-01), Yumiyama et al.
patent: 6037685 (2000-03-01), Berfield
patent: 2352823A (1975-04-01), None
patent: 2701884A (1977-07-01), None
patent: 2754939A1 (1978-06-01), None
patent: 0075138A (1983-03-01), None
patent: 0 171 446 A1 (1986-02-01), None
Burg Fabrice
Camphausen Hanno
Luedtke Ulrich
Enad Elvin
Robert & Bosch GmbH
Striker Michael J.
Waks Joseph
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