Beltless high velocity air blower

Abstract

A direct drive, high velocity, high power centrifugal air blower. The blower employs a high-speed electric motor (>15,000 rpm) having an output drive shaft that is directly coupled to an impeller rotatably housed within a volute. The assembly enables the impeller to rotate at speeds up to 100,000 rpm without the need for either step-up gears or belts and pulleys interposed between the motor output drive shaft and the impeller. The elimination of an indirect coupling assembly between the motor ouput shaft and the impeller provides a high power, high velocity blower/vacuum with greater reliability than indirectly coupled assemblies.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a centrigugal air blower and, more particularly, to a high-speed (˜100,000 rpm) air blower employing a high-speed electric motor directly coupled to an impeller.

[0003] 2. Prior Art

[0004] A centrifugal fan in accordance with the current art includes a motor and a motor-driven impeller comprising a plurality of fan blades arranged at a predetermined pitch around a rotation axis. By rotating the plurality of the blades on the rotation axis, air is taken in the direction of the rotation axis and discharged in a direction that is both tangential to the rotation of the plurality of the blades and orthogonal to the rotation axis. A volute (housing) is disposed around the impeller and directs the flow of air through the fan. In order to move a large volume of air through the fan in a relatively short period of time, it is desirable to operate the impeller at a high rotational rate (˜20,000 rpm or higher). Since higher power (greater than about three kilowatts ) electric motors normally operate at a maximum of 3600 rpm, a “V” belt and pulley assembly or gearing is employed between the motor output shaft and the impeller in order to rotate the impeller at a higher velocity than the motor's rotational velocity.

[0005] Examples of centrifugal fans in accordance with the prior art are disclosed U.S. Pat. Nos. 6,210,118; 5,964,576; 5,813,834; 5,707,209; 5,478,201; 5,474,422; 5,324,167; 5,165,857; 5,156,524; 5,141,397; 4,913,621; 4,874,293; 4,662,830; 4,531,890; 4,265,592 and 4,061,441. These representative disclosures of prior art centrifugal fans, while not exhaustive, teach a centrifugal fan comprising either a low-speed direct coupled motor-impeller assembly or a high-speed indirectly coupled motor-impeller assembly.

[0006] Noise is a common problem with centrifugal fans. One source of noise is the impeller. Miyazawa, in U.S. Pat. No. 6,488,472, discloses a low-noise axial fan having an impeller comprising a plurality of blades arranged around a rotation axis at predetermined and varied layout pitches. For instance, the layout pitch between the two adjacent blades may be different from the layout pitch between the remaining blades. Miyazawa asserts that the arrangement of blades controls the whirring sound of the fan, which whirring sound is increased when the blades are arranged at an equal layout pitch.

[0007] Fujita, et al., in U.S. Pat. No. 5,964,576 disclose an impeller for a centrifugal fan having fifty or more blades of not larger than 250 mm in outer diameter which has a casing and a multi-blade impeller rotatably supported in the casing. A centrifugal force is applied to air entering an inlet formed on the casing when the impeller is rotated, and high pressure air is ejected through an outlet formed on a portion of the casing. An outer peripheral surface of the impeller is inclined or curved so as to have an inlet side large diameter portion and a blade holding base side small diameter portion, or is stepped so as to have an inlet side cylindrical outer peripheral surface of large diameter and a blade holding base side cylindrical outer peripheral surface of small diameter connected to the inlet side cylindrical outer peripheral surface. The inlet side cylindrical outer peripheral surface and the blade holding base side cylindrical outer peripheral surface are substantially the same height

[0008] A drive belt and pulley assembly interposed between the output drive shaft of the motor and the impeller, which is in accordance with the prior art fan assemblies operating at rotational velocities above 15,000 rpm, is yet another source of both mechanical failure and noise. In addition, at high rotational velocities, the impeller must be perfectly balanced in order to maintain its structural integrity and produce a low level of noise. There remains a need for a centrifugal fan that can operate at rotational velocities between 15,000 and 100,000 rpm at a relatively low level of noise with minimal mechanical failure.

SUMMARY

[0009] It is an object of the present invention to provide a direct-drive centrifugal fan operable at rotational velocities between 15,000 and 100,000 rpm.

[0010] It is a further object of the invention to provide a centrifugal fan meeting the above objective and further comprising an efficient, low-noise impeller.

[0011] The features of the invention believed to be novel are set forth with particularity in the appended claims. However the invention itself, both as to organization and method of operation, together with further objects and advantages thereof may be best understood by reference to the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a longitudinal cross-sectional view of a centrifugal fan assembly in accordance with the present invention.

[0013] FIG. 2 is a perspective view of an impeller for a centrifugal fan in accordance with the present invention.

[0014] FIG. 3 is a transverse cross-sectional view of the impeller of FIG. 2 taken along section line 3-3.

[0015] FIG. 4 is an end view (viewed from the right in FIG. 1) of the impeller illustrated in FIGS. 2 and 3, rotatably housed within a volute. The motor is not visible in the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Prior art high-speed centrifugal fans employ mechanical amplification to cause an impeller to rotate at speeds greater than the rotational speed of the motor which, in accordance with the prior art, operates at 3600 rpm. The term “high-speed motor”, as used herein, refers to an electric motor operating at speeds greater than 3600 rpm and, most preferably, at speeds greater than 15,000 rpm. The interposition of mechanical amplification means such as pulleys and a drive belt or gears disposed between the motor output shaft and the impeller in order to increase the rotational velocity of the impeller introduces a source of potential failure into the assembly.

[0017] FIG. 1 is a longitudinal cross-sectional view of a direct-drive high-speed centrifugal fan assembly, indicated at numeral 10, in accordance with the present invention. The centrifugal fan 10 includes a high-speed motor 11 having an axial output shaft 12, a distal end 12a of shaft 12 being directly attached to an impeller 13. A volute 14 having an air output port 15 substantially encloses the impeller 13. In operation, air is drawn into an air intake port 16 of the volute 14 by the rotating blades of the impeller 13 and forced through the air output port 15 to generate a high-velocity working air stream adjacent the output port 15 which may be used, for example, for ventilating moisture or a volatile solvent from a work area. The term “ventilating” means that the centrifugal fan may be employed either as a blower or as a vacuum.

[0018] An impeller suitable for efficient operation at high velocities is illustrated in perspective view in FIG. 2 and in transverse cross-section in FIG. 3. The impeller 13 comprises a circular plate 20 supporting: (a) a cylindrical post 21 having an axially disposed bore 21a dimensioned to receive the motor drive shaft 12a (FIG. 1) therewithin; and (b) a plurality of blades 22 mounted on an outer surface thereof. Each of the blades 22 has a curvilinear outer edge 23 and a curvilinear inner edge 24 abutting the outer surface of the cylindrical post 21 and affixed thereto. Each blade 22 further has a straight top edge 25 and a curvilinear bottom edge 26 affixed to the circular plate 20. The four edges 23, 24, 25 and 26 bound an arcuately contoured blade surface 27.

[0019] While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. For example, the centrifugal fan in accordance with the present invention may be employed either as a blower or as a vacuum. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims

1. A centrifugal fan consisting essentially of: (a) an electric motor operable for rotating a drive shaft at rotational velocities greater than 15,000 rotations per minute; (b) an impeller affixed to said drive shaft; and (c) a volute substantially enclosing said impeller, said volute having an axially disposed air intake port and a tangentially disposed air output port.

2. The centrifugal fan of claim 1 wherein said impeller comprises a plurality of blades symmetrically mounted on a circular plate and radiating outwardly from an axially disposed rotation axis, each of said blades having an arcuately contoured blade surface, the plurality of the blades being operable for receiving air in a direction of the rotation axis through said air intake port and for discharging the air tangentially through said air outlet port in said volute.