Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-07-30
2001-05-08
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S064000, C310S160000
Reexamination Certificate
active
06229232
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an electric motor with a frequency converter for speed control, a casing of the frequency converter being provided with a cooler or dissipator.
The term converter is understood to mean a transformer, which transforms the mains voltage with constant frequency and voltage into a three-phase voltage system with a variable frequency and variable voltage. This three-phase voltage system is supplied to the three-phase motor (asynchronous machine) to be driven, so as in this way to predetermine the electric motor speed by a corresponding choice of the output frequency of the converter.
Unlike in the conventional arrangement, in which the converter is arranged as a separate unit in a switch cabinet and supplies the electric motor by means of a motor lead with a length of up to 100 m, electric motors are already known in which the electric motor-controlling signal and power electronics is integrated as a mechanical unit into the electric motor. This economizes on the previously necessary switch cabinet space requirement and also reduces EMC problems, which were caused in the conventional arrangement by radiation as a result of the long motor leads with a length of up to 100 m. For integrating the frequency converter into the electric motor the electronics thereof are installed in one of the terminal boxes of the electric motor. The connecting elements such as terminals and/or plugs for the supply and signal lines are also located within the terminal box. Particularly with regards to the manufacturing technology and the associated manufacturing costs, such an arrangement in which the frequency converter and electric motor are constructionally interconnected offers numerous advantages. However, problems arise with the cooling of the frequency converter, because in particular the power output stage of the power electronics produces high waste heat levels. In order to dissipate the frequency converter waste heat, on the B side of the electric motor (the B side is the side remote from the driven motor shaft end) a separate fan cowl with fan must be fitted, said fan being driven by the electric motor or by an additional, separate fan motor.
In place of integrating the frequency converter into the terminal box, the frequency converter casing can also be fitted to the electric motor on the B side. Here again for dissipating the frequency converter waste heat a fan must be fitted to the electric motor on the B side and is here again driven by the electric motor or by a separate fan motor. In this variant only the connecting elements such as terminals and/or plugs for the supply and signal lines are housed in one or more terminal boxes, so that they maintain their standard size. However, through the incorporation of the electronics on the B side end of the electric motor, the overall length of the electric motor is now increased. A further increase in the overall length results from the necessary special fan cowl. If no fan is provided, the electronics must be designed for high temperatures and special high temperature resistant, electronic components are used.
As a result of the described special parts when integrating the converter into the electric motor, it is not possible to use a simple standard motor. For the fitting of the frequency converter and special fan cowl and optionally fan motor special structures are required on the electric motor. Apart from the space requirement caused by the additional fan, additional disturbing fan noise arises and the energy costs for the fan as an active cooling element is extremely high. The separate motor required for the fan is also an expensive component.
SUMMARY OF THE INVENTION
Therefore, the problem of the present invention, based on an electric motor in which the frequency converter forms a constructional unit with the motor, is to provide an electric motor, which is simple and inexpensive to manufacture and in which the frequency converter can be integrated into the electric motor without requiring expensive special parts.
According to the invention, the set problem is solved by an electric motor of the aforementioned type, which is characterized by an intermediate part replacing a terminal box and receiving the connecting elements and by means of which the frequency converter casing is fitted in thermally decoupled manner with respect to the electric motor.
Conventional electric motors are provided with a terminal box or connectors for the same. In the electric motor according to the invention with integrated frequency converter the latter is connected by means of an intermediate part replacing the terminal box and as a result the frequency converter casing and the intermediate part casing are separate from one another. Thus, such a frequency converter can be fitted by means of the intermediate part to a conventional electric motor, because there is now no need for additional components, such as fans and a separate fan motor. The cooling and therefore dissipation of the waste heat now takes place by means of a cooler or dissipator provided on the frequency converter casing. Thus, there is no longer a need to adapt the entire motor component for cooling the frequency converter and in particular for dissipating the waste heat of the power output stage by means of special structures and instead corresponding measures need only be taken on the frequency converter casing, e.g. the adaptation of the effective cooling surface of the cooler to the power electronics.
Conventional B side attachments such as motors, e.g. fans, pick-ups, brakes and/or combinations thereof can consequently be fitted without restriction. As a result of the design according to the invention, there is no need for the frequency converter to have an additional fan or a special construction of the fan or fan cowl. The connecting elements such as terminals and/or plugs for supply and signal lines are now housed in the intermediate part and can easily be reached following the disassembly of the frequency converter casing. In order not to unnecessarily increase the construction space requirement for the electric motor with integrated frequency converter, according to a further development the frequency converter casing projects over the intermediate part in the longitudinal direction and the cooler can be positioned below the casing laterally of the intermediate part. Preferably the signal electronics of the frequency converter are positioned above the intermediate part and the power electronics above the cooler in the casing. Thus, the waste heat from the power electronics, particularly its power output stage, can be directly transferred to the cooler by heat conduction. Due to the resulting temperature conditions in the casing of the frequency converter, in the vicinity of the signal electronics which are extremely sensitive, it can be kept very cool. In the prior art electric motors with integrated frequency converter all parts are at the same heat level, because they are thermally well coupled by screwing down and using aluminium alloys for the frequency converter casing. In order to bring about a good thermal coupling of the cooler with the frequency converter power output stage and consequently dissipate the waste heat of the power output stage, the cooler is preferably made from a high thermal conductivity material. Correspondingly the power semiconductors of the power output stage can be made very high without damaging the signal electronics. The volume and effective cooling surface of the cooler can be very compact. According to a further development, the frequency converter casing is also made from a high thermal conductivity material. Thus, the dissipation of the waste heat of the integrated frequency converter firstly takes place via the frequency converter casing surface and secondly via the cooler and thirdly by means of natural convection and radiation. Thus, the frequency converter waste heat which cannot be dissipated by means of the cooler, can be efficiently emitted to the ambient air via the frequency converter
Roth-Stielow Jorg
Schmidt Josef
Antonelli Terry Stout & Kraus LLP
Sew-Eurodrive GmbH & Co.
Waks Joseph
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