KR800000951B1 - Quiet cooling system for dynamoelectric machines - Google Patents

Abstract

The system comprises at least twenty five short chord axially mounted radial blades disposed on a conical hub which is disposed on the rotor of the dynamoelectric machine. The arrangement and number of blades are such that the coolant folw is increased while the pure tone noises are reduced thus increasing cooling and reducing subjective annoyance. A conical shroud encloses the conical hub defining between a conical annules whose total annular cross-sectional area does not expand to the point where turburance and flow separation would occur. A bell mounted protective grilled inlet is disposed on the conical shroud for conducting a coolant, under the action of the rotating blades, through the bell-mounted inlet and into the conical annulus.

Description

Cooling device without noise of electric motor

1 is a cross-sectional view of one embodiment of the present invention.

2 is an end view with a portion of the grating removed.

The present invention relates to an electric motor provided with a cooling device without noise. One typical example of a motor cooler technology prior to the present invention is a motor cooler that is totally closed and cooled by a fan. The cooling device is disposed on an electric motor provided with cooling fins disposed axially around the motor, a rotor shaft extending out of the motor body, and a hub fixed to the rotor shaft extension. It consists of blades, a case completely enclosing the motor, and a grille attached to the motor case. In such an electric motor, the flow of air enters the axial direction through a grid having a large flow resistance, suddenly rotates 90 ° and radially enters into a large empty space, then rotates 90 ° again in the axial direction and then through the spout to the cooling fins. Go out of the distribution system. The grid with high flow resistance and two 90 ° rotations cause a loss of pressure that reduces the coolant flow rate, resulting in a turbulent flow with low cooling effect. Similarly, the large void at the inlet of the blower causes recycling, turbulence and flow separation, which reduces the cooling effect of the device. Moreover, turbulence and flow separation are directly related to the sound pressure level, so turbulence and flow separation create more noise in the machine.

In addition, the characteristics of the fan of the prior art is that the number of wings is small. Turbulence and flow separation in the prior art not only produce a high level of noise, but also produce fewer coarser noises that can be perceived by hearing due to fewer wings and thus become more unpleasant accordingly.

U.S. Patent No. 3,025,799 describes a drain pump that can be submerged in water, although not specifically dealing with noise treatment. Here the flow of air enters radially about the rotor shaft through the filter and into a large void where turbulence and recirculation takes place. The air then rotates 90 ° into the pump blades. From there, air is directed through an almost radial shape that must rotate rapidly to exit axially. The concave curvature of the hub is against radial flow. The large voids, sharp turns and bumps of the hubs all contribute to noise-turbulent turbulence. This patent does not explain the number or type of wings used.

U. S. Patent No. 2,886, 721 describes the sound processing of an electric motor to reduce the overall noise level and the quality of noise produced by the machine during motor operation. This invention attaches to a motor a distributed silencer, which consists of a number of foods placed in the passage of circulating air used to vent the motor. The twisted passages of this invention are specially designed so that the noise generated by the machine does not have a direct path to the atmosphere. As described in this patent, the fan generates two different kinds of aerodynamic noise. One of them is broadband noise, which includes all frequencies randomly distributed throughout the noise spectrum. Another kind of noise is discrete or pure tone noise, an individual noise of one frequency. Broadband noise is not as unpleasant to the listener as pure noise, because miscellaneous things are mixed and not constant. Pure noise, on the other hand, causes greater discomfort because most of the sound energy is concentrated into a single note at a relatively high frequency. This invention proposes to increase the number of wings from 4 to 21 or 23. The purpose is to increase the number of pure sound waves that are likely to slow the amplitude. Increasing the frequency actually increases the resulting discomfort. However, this invention suggests slowing down this noise. In the present invention, only the pure noise is slowed down, but the method of removing the pure noise is not explained.

U. S. Patent No. 2,881, 337 relates to acoustically processing a motor by providing a resonant sound absorbing device associated with the motor to attenuate frequencies of high sensitivity levels.

An example of a fan chiller is a frame specification 364 60 hp fully enclosed fan cooled 4-pole electric motor manufactured by ASEA, Sweden. The fan is conical in some respects, but the front with inner wings does not provide adequate air inlet to the heat of the wings, resulting in increased noise levels. Similarly, the fan hub's relative position to the motor frame increases the noise level by interfering with the flow of air from the hub rather than directing it to the cooling fin channel. Since the number of vanes is small (10), the fan noise spectrum of this electric motor is characterized by undesired pure noise. In addition, the conical portion of the shroud has no height of the annular portion which decreases with respect to the shroud, so that the proper speed of diffusion is not maintained.

According to the present invention, an electric motor including a cooling device, comprising a hub having a shape installed on the rotor and the rotor in a round shape, and on the hub to circulate the coolant in accordance with the rotation of the rotor Wings are arranged, diverging cover surrounds the hub and form a diverging annular portion therebetween, the distance between the cover and the hub is larger at the inlet side than at the outlet side so that the total annular cross-sectional area is at the inlet side. Larger at the outlet side, the shroud receives the coolant and diffuses through the divergent annulus to a heat sensitive adjacent surface, and a converging member cooperates with the shroud to guide the coolant into the shroud. It is a mechanical device.

The bell-shaped inlet covered by the protective grating provides a large flow area for the coolant through the protective grating and leads the coolant smoothly to the diffuser section. One side of the diffuser portion, which is a conical annulus, is bounded by a smoothly shaped fan hub with an extended edge disposed on the rotor of the motor. The other side of the diffuser section is the cover surrounding the fan hub. The conical annulus is formed such that the total annular cross section is gradually enlarged with a reasonable spreading ratio but remains below the point where turbulence and flow separation occur. Minimal to provide a streamlined mixing passage for generating pressure in the chiller with respect to the inlet and diffuser A trapezoidal radial wing with 25 equally spaced short strings is placed on the fan hub. The arrangement and number of the blades is such that the circulation of the coolant is increased and the pure noise is reduced to increase the cooling effect and thus reduce the discomfort. The shape of the wing is designed to allow maximum throat cross-sectional area for a given minimum hub diameter to increase cooling and reduce noise. Moreover, the shape of the blades allows the entire fan hub to be manufactured by one casting and have the same operating effect in clockwise or counterclockwise rotation.

The objects and advantages of the present invention are mainly aerodynamic in that a large area of recycle flow is eliminated and the coolant moves smoothly without sudden rotation from the inlet grid to the discharge zone. The use of a large number of radial blades on the hub provides the device with maximum pressure and flow, with minimal noise, without loss of minimum hub diameter, tip speed and cooling effects.

The invention will be described in detail with reference to the accompanying drawings.

1 and 2 show an electric motor 10 having a cooling fin 12 and a rotor 14. Attached to the rotor 14 is a conical hub 16 with an edge 18 inclined at an angle of 51 ° with respect to the axis of the rotor 14. On top of the conical hub 16 radial wings 20 with 40 short strings are arranged along with the wing tips 22. The conical cover 24, inclined at 49 ° about the axis of the rotor 14, surrounds the conical hub 16, which forms a conical annulus 26 therebetween. The bell-shaped inlet 28 cooperates with the conical cover 24 to form a minimum cross section, known as throw 30, at their junction. The bell-shaped entrance 28 is provided with an inlet grid 32 of protective mesh.

The coolant (usually air) enters through the inlet grating 32 by the action of the rotating rotor 14, hub 16, wing 20. The bell-shaped inlet 28 leads the coolant through the throat 30 from the inlet grid 32 into the conical annulus 26. The conical annulus then cools the electric motor 10 by diffusing a coolant around a heat sensitive surface, ie around the cooling piece 12.

Turbulence, flow separation, and recirculation increase the sound pressure level of the machine, and this increase is audible as an increase in noise. These factors result in pressure losses and these losses must be compensated for by increasing fan power. The present invention incorporating the streamlined concept can make machines with less noise without losing these cooling effects by reducing these factors.

The streamlined concept of the present invention consists of an inclined conical annulus 26 associated with a mesh grating 32, a bell-shaped inlet 28 and a radial wing 20 with axially attached short strings. Mesh grid 32 acts as a low-resistance shroud that reduces turbulence and pressure loss, allowing the use of smaller fans at the same cooling rate. From the inlet grating, the coolant smoothly enters the conical annulus 26 through the large bell-shaped inlet 28, the throat 30, eliminating turbulence at the inlet by sharp bends and restricted passages. Conical annulus 26 then diffuses the coolant onto the cooling fins 12th place to reduce turbulence and noise associated with high velocity flow. The total annular cross-sectional area of the conical annulus 26 increases from inlet to outlet, while the distance between the conical hub 16 and the conical cover 24 gradually decreases. The rate of increase of the total annular cross-sectional area is such that the coolant diffuses smoothly without the occurrence of turbulent flow and flow separation so as to have an improved cooling effect at low noise levels. Of course, the actual increase in cross-sectional area depends on the size of the motor. The conical annulus also provides a mixing flow passage (i.e., a path that is neither radial nor axial with respect to the motor shaft), the use of the mixing flow passage eliminates sharply dents and voids, thereby reducing noise.

In order to further reduce noise, to prevent recirculation in the throat portion, about half of the wing tip 22 is required to be covered by the conical cover 24. Covering half of the wing tip reduces the size of the throat, thus reducing the coolant flow rate and consequently reducing the cooling effect. The throat portion can be increased by increasing the hub diameter, but this will increase the speed of distribution, making the noise very loud.

However, by using radial vanes with short strings fixed axially, for a given minimum hub diameter the throat of the throat remains at the maximum while the tip can be properly covered, thus reducing noise while maintaining a cooling effect. Moreover, the entire fan hub can be manufactured in a single process of casting and the wings are shaped to achieve the same operating effect in clockwise or counterclockwise rotation.

In addition, the present invention is intended to utilize a large number of wings of at least 25 to 40 or more. Although 40 wings are a practical limit in economic manufacturing, under appropriate conditions the number of wings may exceed 40. More than 40 to 60 wings can be used where economical and cooling effects can guarantee the wings. The use of such a large number of wings absorbs pure noise into a wide band, greatly reducing discomfort. This pure noise begins to be absorbed into a wide band, and with 40 wings, the pure noise is completely eliminated.

The experiment was based on Westinghouse Electric Corp. Standard Lineline-Line Tee. The midwook alternator 326-TS model was implemented using the present invention without a bell shaped inlet. The motor is a two-pole, three-phase type that generates 50 horsepower at 3,600 rpm.

Comparing the results of the electric motor without the present invention with the result of using 40 blades according to the present invention without a bell shaped inlet, the same cooling effect resulted in a noise reduction of 10 dBA and a cooling effect of 10 dBA in the noise reduction of 7 dBA. % Increased. Furthermore, the present invention reduces the pure noise so that the discomfort is lessened. Adding a bell-shaped inlet will further enhance this effect.

As another example of the present invention, the shape of the mesh grid may be changed. Furthermore, it will be appreciated that more than one inlet of the type mentioned above may be used.

Claims (1)

A rotor, a conical hub disposed on the rotor, a plurality of short chords arranged in the axial hub arranged to drive coolant as the rotor rotates, axially disposed around the conical hub, It consists of a truncated conical cover forming a conical annular portion diverging between, wherein the distance at the inlet between the truncated conical cover and the conical hub is greater than at the exit so that the total annular cross section is more at the exit than at the inlet. Large, the wing has a wing tip nearly opposite the inlet such that the cut cone cover covers approximately half of the wing tip while maintaining a substantially constant gap therebetween, and the cut cone cover provides coolant Noise that quietly diffuses through the diverging cone-shaped annulus to the surface sensitive to heat Motor having a cooling device that does not.

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