A FAN COVER FOR A ROTATING ELECTRIC MACHINE Background of the Invention Field of the Invention

The present invention refers to rotating electric machines and, more specifically, to a fan cover particularly designed to reduce the noise generated by the rotating electric machine and to improve the cooling performance of the electric machine. Description of the Prior Art

The fan cover, together with the fan rotor, are responsible for cooling the rotating electric machine by suitably directing and distributing the air flow generated by the fan rotor along the frame of the rotating electric machine.

Typically, a fan cover is mounted upon a rotating electric machine in such a manner as to simultaneously cover the fan rotor and the back cover of the rotating electric machine, the fan cover comprising a grid on its front end to allow for the admission of air and a curved side wall designed for directing the flow of air generated by the fan rotor along the frame of the rotating electric machine, said air flow being responsible for exchanging heat between the rotating electric machine and the environment.

The fan cover has been conceived with specific characteristics and features for reducing the noise level and the losses generated by the cooling system, thus increasing the cooling system performance and consequently increasing the rotating electric machine performance.

It is still within the scope of the present invention to present a fan cover for the reduction of the noise level and for the increase

of the rotating electric machine's eficiency with very low costs for its industrial operational feasibility, summing up the requisites of strength, safety and reliability, reassuring its usage practicality providing the industry of rotating electric machinery with an additional freedom as well as choices of option in this market sector, thus offering a variety of possibilities and benefits with regards to the design and to the performance of rotating electric machines which becomes a specific model of great expectations for this market sector. Rotating electric machines play the role of transforming electric energy into mechanic energy or vice-versa. Despite the fact these machines are a kind of equipment with very high productivity, during the conversion process part of the energy transformed is converted into thermal energy. For the good performance of a rotating electric machine it is necessary for this very energy to be removed from the rotating electric machine so that the integrity of its components and its performance are well kept and maintained. One of the methods used to remove part of said heat is to increase the air speed over the external portion of the rotating electric machine structure. One technique used to obtain said air speed increase is the coupling of a ventilation system to the rotating electric machine. Said ventilation system can be activated by the very shaft of the rotating electric machine or by a secondary machine. Independently from and regardless of the kind of activating manner, the ventilation system is composed of a fan's rotor and a fan cover which in its turn is composed of a fan cover body and an air inlet grid. The fan's rotor is fixed to the main machine or to the

secondary machine' s shaft and the fan cover is fixed to the rotating electric machine.

The manufacturers of rotating electric machines are constantly trying to increase more and more the competitiveness of its products in order to meet the market demands and the norms which regulate the manufacturing of rotating electric machinery.

Amongst these very factors in order to improve the competitiveness of a rotating electric machine one may find the reduction of noise level (which is specified in sound power level) and the increase of performance. One way to obtain some improvement of both these two features and/or characteristics is through an optimized ventilation system design.

The main function and role of a fan cover in a rotating electric machine is to direct the air flow towards the structural portion, this air being used for cooling the very rotating electric machine. Said orientation is characterized in the following manner: the fan cover has an opening designated as an air inlet grid whereby the air flow begins its trajectory; after this step the air flow passes by the fan rotor being sequentially directed by the fan cover' s body to the air outlet, of the fan cover which is the interface region situated in between the fan cover and the posterior lid. After going through the fan cover's air outlet, the air flow moves towards the rotating electric machine structure'.

One of the negative features and/or characteristics of this type of ventilation system, the system that uses a straight blade centrifugal fan rotor, is the very high noise level when compared to other types of fan rotors. The additional level of noise is related

to the recirculation and to the turbulent exhausting of air which takes place within the fan rotor and the fan cover.

Another negative feature and/or characteristic obtained through experimental data and through pertinent literature refer to the low efficiency of this type of ventilation system.

The main causes for this low efficiency are:

1. The need for a design of a fan rotor which can operate on both rotational directions, clockwise and counterclockwise, thus meeting the main requisite of its operational function which is the cooling of the rotating electric machine. In order to meet this very design requisite it is necessary to use a straight blade centrifugal fan rotor type.

2. In some cases one may use the same fan cover with distinct fan rotors thus invalidating a design whereupon the fan cover and the fan rotor are coupled together, which is recommended by the literature of fan designs. Summary of the Invention

Considering the technical aspects with regards to the great level of noise generated by the ventilation system of the rotating electric machines and also considering an improved heat exchange between the rotating electric machine and the environment, the inventors have designed and developed the fan cover according to the present invention, particularly designed to reduce the noise generated by the rotating electric machine and to improve the cooling performance of the electric machine.

According to the present invention, these advantages are provided by a fan cover for a rotating electric machine, particularly

designed to reduce the level of noise generated by the rotating electric machine and to improve the cooling performance of the rotating electric machine, said fan cover having a front end having a first diameter and a back end having a second diameter bigger than said first diameter, said front and back ends being connected to each other through a structural side wall having an inner surface defined by, from said front end to said back end, a first convex side wall portion having a first curvature and a second concave side wall portion having a second curvature. According to the present invention, said first and second curvatures can be the same or can be different, and said structural side wall can be made integral or in more than one piece. Also, it does not interfere with the performance of the fan cover whether or not said front and back ends are circular, elliptical, square or have different shapes, provided the geometry of the inner surface of the structural side wall is not altered. Brief Description of the Drawings

The principles of the present invention will be better understood from the following detailed description, made with reference to the accompanying drawings, which are provided as a non- limitative illustration of an exemplary fan cover incorporating the features of the present invention. In the drawings:

Fig. 1 is cross-sectional side elevational view of a rotating electric machine incorporating a fan cover according to the present invention;

Fig 2 is an isometric perspective view of the fan cover according to the present invention;

Fig. 3 is a partially cut-away view of the fan cover according to the present invention showing the geometry of the fan cover;

Fig. 4 is a front elevational view showing the air inlet grid at the front end of the fan cover according to the present invention; and

Fig. 5 is a back elevational view of the fan cover according to the present invention showing the back end of the rotating electric machine and of the fan cover.

Detailed Description of the Preferred Embodiment The following description and the embodiment described therein are provided only to illustrate an example of a particular embodiment of the principles of the present invention. This example is provided for the purposes of explanation, and not of limitation, of those principles and of the invention. In the description, like parts are identified throughout the specification and the drawings with the same respective reference numbers. The drawings are not necessarily to scale and in some instances proportions may have been exaggerated in order more clearly to depict certain features of the invention.

Figures 1 - 5 illustrate a fan cover used for cooling a rotating electric machine, particularly designed to reduce the noise generated by the rotating _, electric machine and to improve the cooling performance of the electric machine.

Fig. 1 shows the main parts' of a rotating electric machine, which basically comprises an electrical rotor 2 concentrically positioned relative to a stator 3. The set formed by the rotor 2 and the stator 3 being housed in a frame 4 having front and back covers

5, 6, both rigidly mounted upon the frame 4 by mechanical fixtures.

The rotor 2 is supported by the shaft 7 which is centrally positioned within the rotor 2 and stator 3 set by forward and back bearings 8, 9 mounted at its ends, said forward and back bearings 8, 9 being also positioned within said front and back covers 5, 6. The cooling system for the rotating electric machine comprises a fan rotor 11 mounted upon the back end 7a of said shaft 7 and a fan cover 10 having an air inlet grid 10a at its front end and a structural side wall 10b ^' having a special geometry at its inner surface, said fan cover 10 being mounted upon the back cover 6 of the machine.

The purpose of the fan cover 10 in the cooling system of a rotating electric machine is to direct the flow of air 1 required for cooling the rotating electric machine. Typically, the fan cover 10 has an opening at its outer face defining an air inlet grid 10a through which the fan rotor 11 collects the air to create a flow of air 1 having a trajectory through air inlet grid 10a and the fan rotor 11, which flow of air is sequentially directed by the geometry 10b of the inner surface of the fan cover to an air outlet 10c of the fan cover 10 which is the interface region situated between the fan cover 10 and the back cover 6. After passing by the air outlet 10c of the fan cover 10,. the air flow 1 moves towards the frame 4 of the rotating electric machine.

The present invention is characterized by the aerodynamic format of the geometry 10b of the inner surface of the structural side wall of the fan cover 10, which provides smaller levels of recirculation of the flow of air, thereby resulting in a reduced level of noise and in a bigger efficiency of the cooling system of the machine.

The fan cover 10 for a rotating electric machine according to the present invention has a front end 10a having a first diameter 1Od and a back end having a second diameter 1Oe bigger than said first diameter 1Od, said front and back ends being connected to each other through a structural side wall 10b having an inner surface defined by, from said front end 10a to said back end, a first convex side wall portion 1Of having a first curvature and a second concave side wall portion 1Og having a second curvature.

While not shown in the drawings, it will be obvious to any person skilled in the art that said first curvature and said second curvature can be the same or can be different, and that said structural side wall can be made integral, in one piece or in more than one piece.

Also, it does not interfere with the performance of the fan cover whether or not both said front end and said back end are equally circular, elliptical or square or may have different shapes.

With particular reference to mounting the fan cover 10 to the frame 4 of the rotating electric machine, the fan cover is formed with mounting means for fixing it to the rotating electric machine through any type of mechanic fixing element, such as rivets, adhesives or nuts and screws. Also, the fan cover is formed with through bores to allow for inspection, wiring passing or fixing components to the rotating electric machine.

Another feature of the fan cover according to the present invention that provides for an increased reduction of the noise level and in the performance the cooling of the rotating electric machine is the configuration of the air inlet grid 10a at the front end of

the fan cover .

Said grid 10a is formed with a plurality of concentric ring elements 1Oh interconnected by at least two sinuous connecting members 1Oi radially extending from the center of the grid, in an arrangement that contributes for reducing the level of noise.

Preferably, said sinuous connecting members 1Oi are "S" shaped.

These concentric rings 1Oh and the "S" shaped connecting members 1Oi can be incorporated into any fan cover known in the state of the art. While the invention has been described in terms of its preferred embodiments. Those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims.