The present invention relates to a cooling device for an electric motor such as a switched reluctance motor in which a coil is wound on each of a plurality of projected poles of a stator.
In general, there are four types of cooling devices for electric motors as follows:
(a) Free cooling device: constructed such that a plurality of fins are provided on the outside of a housing of an electric motor. PA1 (b) Compulsive cooling device: constructed such that a fan is provided inside or outside a housing of an electric motor so as to exhaust high temperature air outside the electric motor housing. PA1 (c) Water cooling device: constructed within a housing of an electric motor. PA1 (d) Oil spray cooling device: constructed such that an amount of oil is sprayed from an output shaft of an electric motor for cooling the same.
However, the foregoing four devices are not satisfactory at all. In detail, the fins are not expected to be practical especially when no winds blow or a heat generation source is isolated from the fins. The compulsive cooling device is widely used but its cooling ability is not very good. The reason is that the electric motor has to be located in a sealed construction when it is placed under wet or humid conditions and therefore, the generated heat in the sealed motor housing has no passages to escape outside. In addition, the water cooling device is often spaced from a heat generation source so that the cooling ability is inefficient. Furthermore, to form water passages in the housing of the electric motor, the thickness of the housing becomes inevitably thick and therefore the total weight of the motor and castings for forming the housing are very large, expensive and complex. In the oil spray cooling device, foreign matter or particles are generated due to oil deterioration and the resultant foreign matter or particles may clog or plug an oil passage. Thus, it is difficult to achieve satisfactory cooling using the oil spray cooling device.