Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1992-01-03
1992-09-22
Stephan, Steven L.
Electrical generator or motor structure
Dynamoelectric
Rotary
310 58, H02K 906, H02K 900
Patent
active
051499975
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a fan for an electrically operated machine, comprising a propeller arranged axially about the machine and including a hub and several blades attached to it and projecting substantially radially from it; and a cover surrounding the propeller in the front and on the sides and comprising a suction opening on the suction side of the propeller, and an opening on the pressure side for passing ventilation air into the machine parts to be cooled.
Fans of this type are known e.g. from U.S. Pat. No. 2,479,233 and German Offenlegungsschrift 32 07 448, of which the former relates to an axial fan and the latter to a radial fan.
To operate properly, a typical axial fan has to be provided with a hood around the propeller and a guide vane assembly on one or both sides of the propeller for the control of the air flow. The size of the propeller and the blade angles of the blades have to be dimensioned to relatively accurately correspond to the dimensions of the intended place of application. Due to leakage losses, the gaps between the blades and the hood and between the blades and the hub have to be minimized. By means of the guide vanes, part of the tangential flow component created by the propeller, i.e. its dynamic pressure, can be converted into static or so-called effective pressure. If no guide vanes are provided, this relatively great flow component turns into losses, which involves a corresponding reduction in the static pressure created by the fan and the efficiency of the fan.
In most cases it is not possible to construct an axial fan in connection with an electrically operated machine in the best possible way. Space in the axial direction is usually limited so that no guide vanes can be used and the hood too has to be short. The other dimensions cannot be optimized either. In addition, the flow has to turn or disperse abruptly on the pressure side of the propeller in most applications, which in this type of fan involves considerable losses.
The radial fan of German Offenlegungsschrift 32 07 448 can be more easily fitted in an electrically operated machine without having to substantially compromise over its theoretical structural principles. This kind of radial fan, however, creates considerable turbulent currents in the forward and backward portions of the cover, which reduces efficiency.
The object of the present invention is to provide a fan for an electrically operated machine, by means of which the above-mentioned problems can be overcome and achieve a structurally simple fan of high efficiency and low noise level. The fan of the invention is characterized by the combination of the following features: the blades have a radius of curvature and they are attached to the hub at a blade angle between 25.degree. and 70.degree.; a gap defined between the suction opening or its cylindrical extension and the blades of the propeller in the axial direction is no more than 20% of the outer diameter of the propeller; the inner diameter of the suction opening before the propeller is 0.8 to 1.6 times the outer diameter of the propeller; and the inner diameter of the cover is at least 1.2 times the outer diameter of the propeller or the inner diameter of the suction opening, depending on which one of them is larger.
The fan of the invention, which is mainly an intermediate between an axial and radial fan, operates in one direction only. Therein the blade angle .alpha., width 1 and radius of curvature R of the blades of the fan propeller are selected so that the blades give the flow a relatively strong radial speed component. By displacing the blades onwards in the direction of rotation, this property can be made more effective and the noise level and losses can be reduced. The obtained radial flow, which both rotates in the direction of the propeller and is turbulent, acts similarly as an ejector, taking with it air from the relatively large gap defined between the propeller and the air guide. This flow increases the total air flow of the fan while decreasing the flow through the propeller, so that
REFERENCES:
patent: 2479233 (1949-08-01), Haas
ABB Stromberg Drives OY
LaBalle C.
Stephan Steven L.
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