Beltless high velocity air blower

Abstract

A direct drive, single stage, centrifugal compressor air blower assembly for increasing air pressure and air flow for industrial process air applications. The blower assembly consists of a scroll-shaped, single stage, centrifugal compressor air blower housing having an air inlet and an air outlet. The centrifugal air compressor housing contains an impeller that is mounted on an end of a drive shaft of a high speed asynchronous AC induction motor shaft. The drive shaft extends from the asynchronous AC induction motor into the centrifugal compressor blower housing. The compressor blower housing is rotatably attached to the motor housing which enables the direction of the air flow to be changed without repositioning the motor. A Variable Frequency Drive (VFD) is used to control motor RPM and hence blower output. The VFD and asynchronous AC induction motor combination provides 5 to 50 horsepower over an operating RPM range of 10,000 to 30,000 RPM.

Description

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of prior application Ser. No. 10/376,661, filed Feb. 27, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a single stage centrifugal compressor air blower, and, more particularly, to a direct drive single stage centrifugal air compressor controlled by a variable frequency drive (VFD) suitable for various industrial process applications including, but not limited to: forced air cleaning, rapid drying of wet items, blowing dust or fine particles off items, providing a vacuum, an exhauster or as an aeration device.

2. Prior Art

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 20 watts) electric motors normally operate at about 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.

Examples of centrifugal fans which are more or less representative of the prior art are disclosed in 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.

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.

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.

Centrifugal compressor air blowers are used to increase both air pressure and air flow. The resultant increased air pressure and air flow is especially useful in various industrial applications requiring air to be delivered in simultaneously operable pressure ranges of 20 to 200 inches of water (IWG) and flow rates of 20 to 2500 cubic feet per minute (CFM). Process air applications include, but are not limited to: forced air cleaning of parts, rapidly drying wet items such as bottles and cans in bottling plants, blowing off dust or particles such as bottling spices or other fine particulates, various vacuum and exhaust applications, and aeration of water in water treatment facilities.

Heretofore, embodiments of centrifugal compressor air blowers used in the applications previously described consist of a single stage centrifugal compressor housing with an impeller in the compressor housing mechanically coupled to the output drive shaft of a single speed asynchronous AC motor via a belt linking two pulleys of dissimilar size; the primary pulley mounted on the motor drive shaft and the secondary pulley mounted on a separate impeller shaft. The transmission of rotational power in accordance with the prior art requires the presence of supporting and adjustment hardware, including a belt tensioner and belt guard. The AC induction motor of the prior art belt-drive blower has been a single speed motor resulting in a constant impeller speed. The only way to change impeller speed and, consequently, compressor air output has been by changing the ratio between primary and secondary pulley diameters.

In summary, the disadvantages of the prior art belt-drive blowers include:

1. The mechanical complexity of belts, pulleys, and belt tensioner assemblies. Alignment of these components is essential, yet difficult to maintain over time, resulting in a misaligned belt, tensioner, and pulleys that have historically resulted in accelerated wear of the belt with ensuing premature failure.

2. The high radial loads produced by the belt-drive transmission and the required belt tension on the impeller bearing result in rapid bearing wear and ensuing premature failure.

3. The necessity to change the ratio of the primary and secondary pulleys in order to change the RPM of the impeller to attain the prescribed air pressure and air flow rate.

4. The need for multiple sized, standard speed, AC induction motors based on the application horsepower requirements to attain the prescribed air pressure and air flow rate. The standard AC induction motor used in the prior art operates on 60 Hz input, generating a constant motor speed of approximately 3600 RPM, and are sized in the increments 5, 7.5, 10, 15, 20, 25, 30, and 40 horsepower respectively with motor size and weight increasing proportionately with horsepower.

5. The mechanical inefficiencies inherent in the belt-driven transmission linking the impeller with the AC motor. These mechanical inefficiencies result in greater power consumption and higher operating costs.

6. The excessive weight, bulkiness, and overall size of the blower. For example, a prior art 20 HP blower may weigh up 350 lbs and is often too large to fit into assembly line conveyor systems.

7. The danger inherent with the belt-drive transmission, including multiple pinch points and possible injury resulting from belt disintegration.

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 deliver air at a desired and adjustable pressure and flow rate and which can operate at rotational velocities between 15,000 and 100,000 rpm at a relatively low level of noise with minimal mechanical failure.

SUMMARY

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.

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. The above objectives are met by the provision of a direct drive, single stage, centrifugal compressor air blower assembly operable for providing a desired air pressure and air flow for industrial process air applications. Such applications include, but are not limited to: forced air cleaning of parts, rapid drying of wet items, removing dust or particles from items, or as a vacuum or exhauster device. The air blower assembly comprises a centrifugal compressor air blower housing having an axially disposed air intake port and a tangentially disposed air outlet port. A variable high speed, asynchronous AC (alternating current) induction motor having a rotatably mounted drive shaft extending from at least one end thereof is disposed such that the drive shaft extends into the centrifugal compressor blower housing. An impeller housed within the centrifugal compressor air blower housing is mounted on the drive shaft to rotate within the centrifugal compressor blower housing when the drive shaft is caused to rotate. A variable frequency driver is in electrical communication with the motor. The driver is operable for controlling the rotational velocity of the drive shaft and the impeller attached thereto. The centrifugal compressor air blower assembly is rotatably mounted on a substantially circular diffuser plate that is rigidly affixed to the motor such that the centrifugal compressor blower housing is axially rotatable with respect to said motor. The centrifugal compressor blower housing is attached to the diffuser plate by means of a v-band clamp. When said v-band clamp is loosened, the centrifugal compressor blower housing can be rotated 360° about the diffuser plate to change the direction of air output flow.

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. It should be understood that the drawings presented in FIGS. 1-4 are not necessarily to scale. In certain instances details that are not necessary for an understanding of the invention may have been omitted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view taken along a plane through the center of a direct drive, single stage centrifugal compressor air blower assembly controlled with a variable frequency drive according to an embodiment of the present invention.

FIG. 2 is a longitudinal cross-sectional exploded view taken along a plane through the center of a direct drive, single stage centrifugal compressor air blower assembly controlled with a variable frequency drive according to an embodiment of the present invention.

FIG. 3 is an end view (as viewed from the left in FIG. 1) of a single stage, scroll-shaped, compressor housing and impeller of a preferred embodiment of the present invention.

FIG. 4 shows end and side views of a compressor impeller as contained in the single stage, scroll-shaped, compressor housing illustrated in FIG. 1,2, and 3 of a preferred embodiment of the present invention.

FIG. 5 is a graphical representation of the typical air flow vs. air pressure curve for the prior art belt-drive centrifugal compressor blower and for the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As discussed above, 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 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.

Referring to FIG. 1 and FIG. 2, there is provided an illustration of a direct drive, single stage centrifugal compressor air blower assembly controlled with a variable frequency drive according to the present invention, generally indicated at numeral 1. The compressor blower housing 2 is rotatably attached to the motor housing by means of a diffuser plate 5 affixed to the drive end of the motor housing and a v-band clamp 7 which enables the direction of the air flow to be changed without repositioning the motor. Accordingly, the single stage, scroll-shaped, compressor housing 2 contains an annular cavity 2a and is mounted to the diffuser plate 5 by means of the v-band clamp 7. The inner surface of the v-band clamp 7 conforms to and secures over trapezoidal extensions 5c and 2c of the circular diffuser plate 5 and compressor housing 2 respectively. This permits 360° rotation of the compressor housing 2 about the diffuser plate 5 while securing the compressor housing 2 to the diffuser plate 5 and the motor to a supporting substrate. The diffuser plate 5 is bolted to the C-Face of a high speed AC induction motor 11 using four bolts 8 counter-sunk into the diffuser plate 5 and screwed into threaded holes in the motor 11. The single stage compressor housing 2 contains an impeller 3 that is mounted to the drive end of the motor drive shaft 6. The impeller 3 is retained by a retaining bolt 4 bolted through the impeller 3 and into the end of the motor drive shaft 6 and bolted flush against the impeller 3. The rotor 13 of the motor 11 is supported on the drive end of the shaft 6 by means of a hybrid sealed radial roller bearing 9 and on the opposing end of the drive shaft 6 by another hybrid sealed radial roller bearing 10, both bearings being pressed onto the rotor and retained in the motor 11 housing end bells. Contained within the motor 11 housing and encapsulating the motor rotor 13 are the inverter duty motor windings and insulation 12. Extending from the opposite drive end of the motor 11 and mounted to the motor shaft 6 is an external motor cooling fan 14 that is pressed onto the shaft 6. Diagrammatically represented is a variable frequency drive (VFD) 15 used to control the speed (RPM) of the motor 111 by varying the combination of voltage and frequency supplied to the motor 11. Other names used for VFD's include AC Drive and Frequency Inverter.

FIG. 3 is an end-view of the single stage, scroll-shaped, centrifugal compressor blower housing 1 that contains an impeller 3. The impeller 3 is mounted to the motor shaft (not visible in FIG. 3) and retained by an impeller retaining bolt 4. The single stage, scroll-shaped, compressor housing 2 has an axially disposed air intake port 16. When the impeller 3 rotates counterclockwise within the compressor housing 2, negative air pressure is created at the air intake port 16 that is disposed about the axis of the impeller 3. As a result of vortexes created between the impeller blades 22 (FIG. 4) static air pressure is created at the tangentially disposed air outlet port 17. The curved conduit within the wall surfaces of the compressor housing have a radial dimension that progresses from a minimum at the cut-off point 17a of the blower housing, and expands to a maximum at the air outlet port 17.

FIG. 4 shows end and side views of a compressor impeller designed for efficient operation at speeds ranging from 10,000 to 30,000 RPM. The impeller 3 comprises a circular plate 18 supporting: (a) a cylindrical post 19 having an axially disposed bore 20 dimensioned to receive the motor drive shaft 6 (FIGS. 1 and 2) therewithin; and (b) a plurality of blades 21 mounted on an outer surface thereof. Each of the blades 21 has a curvilinear outer edge 22 and a curvilinear inner edge 23 abutting the outer surface of the cylindrical post 19 and affixed thereto. Each blade 21 has a straight top edge 24 and a curvilinear bottom edge 25 affixed to the circular plate 18. The four edges 22, 23, 24, and 25 bound an arcutely contoured blade surface.

FIG. 5 graphically represents the typical air flow and air pressure produced at 20,000 RPM by the prior art belt-drive blowers and the direct drive blower of the present invention. This air flow and air pressure curve is intended to serve as an example of the unique air flow and air pressure combinations required in the industrial process air applications described elsewhere in this disclosure.

In a typical embodiment of the present invention the VFD can accept 3-phase AC input power ranging from 190 to 600 volts at 50 or 60 Hz and perform all motor control functions including, but not limited to: motor startup, acceleration, PWM (pulse width modulation) control, speed (impeller RPM), and deceleration. Voltage and frequency are programmed to change in relation to one another for optimized blower output and motor efficiency at a prescribed air flow and air pressure requirement. The VFD continuously monitors and limits critical motor operating parameters including, but not limited to: current (amperes), Frequency (RPM), and voltage. The motor is thus protected from operating conditions that may result in a motor failure or safety hazard.

Thus the VFD controlled, direct drive centrifugal compressor assembly of the present invention provides significant advantages over the prior art and known belt-drive centrifugal compressors serving the industrial process air market. These advantages have been previously described in this disclosure and include, among others, the elimination of the complicated belt-drive transmission system with their many inherent disadvantages. The VFD controlled, direct drive centrifugal compressor of the present invention greatly increases reliability by reducing the number of assembly components and associated required maintenance and increased failures and safety risk. The resultant reduction in components equate to lower production and maintenance costs. Additionally, inherent in the present invention is improved mechanical and electrical efficiencies over the prior art. The improved efficiencies result in lower energy costs to operate the present invention compared to the prior art. The realization of present invention represents a significant economical and reliability improvement over the prior art. The advantages of the direct drive, single stage centrifugal compressor air blower assembly driven by an integral high speed asynchronous ac induction motor controlled by a variable frequency drive according to the present invention include: (a) the elimination of the belt transmission, with the belt being the most frequent source of failure with the prior art; (b) simplicity of mechanic design, resulting in reduction of approximately 40 components compared with the typical prior art; (c) elimination of high radial loads produced by the belt-drive transmission and required belt tension on the impeller bearing that results in rapid bearing wear and premature failure; (d) improved mechanical efficiencies over the prior art resulting in more air pressure and air flow with less power consumption and hence lower energy and operating costs; (e) ability to use a single sized high speed AC induction motor that operates in the 5 through 20 horsepower and range compared with a separate standard speed AC induction motor used for 5, 7.5, 10, 15, and 20 horsepower versions of the prior art; and (f) compact size allowing more freedom in positioning the blower on assembly lines where space is at a premium compared to the prior art.

As an example: the 20 HP version of the present invention is occupies approximately 30% less space than required by the typical 20 HP version of the prior art belt-drive blower. The reduced weight of the present invention results in safer handling, less structural support for installation and lower transportation costs. As a further example, the 20 HP version of the present invention weighs approximately 140 lbs compared to nearly 300 lbs for a typical 20 HP version of the prior art. The combination of smaller dimensions and lighter weight in comparison to the prior art allow the complete system of the present invention to be shipped by UPS, FedEx, or other ground shipper at much lower costs with faster transit time than the prior art that weighs up to 300 lbs and typically requires a long and costly transit via pallet by a consolidated freight carrier.

The blower of the present invention permits the user to vary the speed of the blower from 0 to 30,000 RPM without the need to alter any of the mechanic design, specifically without the use of a belt transmission and changing primary and secondary pulleys as with the prior art. The inclusion of a VFD into the blower confers the blower with the capabilities inherent in most commercial VFD's which includes feedback control from various sensors or a PLC (Process Logic Controller) that monitors the line process. This enables the VFD to adjust motor speed and blower output automatically in response to sensor or PLC inputs. This advantage of the present invention is significant, extending beyond the simple adjustment of blower RPM to enabling the near instantaneous change air pressure and flow rate based on the requirements of the bottling line or other line application.

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, an AC motor can be employed wherein the drive shaft projects from both ends of the motor housing. Such a motor permits the attachment of compressors to both ends of the drive shaft to provide a dual output. 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 direct drive, single stage, centrifugal compressor air blower assembly operable for providing a desired air pressure and air flow for industrial process air applications including: forced air cleaning of parts, rapid drying of wet items, removing dust or particles from items, or as a vacuum or exhauster device, said air blower assembly comprising:

a. a centrifugal compressor air blower housing having an axially disposed air intake port and a tangentially disposed air outlet port;

b. an integral, variable high speed, asynchronous AC (alternating current) induction motor having a rotatably mounted drive shaft extending from at least one end of said asynchronous AC induction motor into said centrifugal compressor blower housing;

c. an impeller housed within said centrifugal compressor air blower housing and mounted on said drive shaft to rotate within said centrifugal compressor blower housing when said drive shaft is caused to rotate; and

d. a variable frequency drive in electrical communication with said motor operable for controlling the rotational velocity of said drive shaft.

2. A direct drive, single stage, centrifugal compressor air blower assembly according to claim 1 wherein said centrifugal compressor blower housing is rotatably mounted on a substantially circular diffuser plate affixed to said motor such that said centrifugal compressor blower housing is rotatable with respect to said motor.

3. A direct drive, single stage, centrifugal compressor air blower assembly according to claim 2 wherein said centrifugal compressor blower housing is attached to said diffuser plate by means of a v-band clamp and wherein when said v-band clamp is loosened, said centrifugal compressor blower housing can be rotated 360° about said diffuser plate.

4. A direct drive, single stage, centrifugal compressor air blower assembly according to claim 2 wherein said centrifugal compressor blower diffuser plate is mounted directly to the motor C-Face with four bolts of the variable high speed asynchronous AC induction motor.

5. A direct drive, single stage, centrifugal air compressor blower assembly according to claim 1 wherein said variable high speed asynchronous AC induction motor operates at rotational speeds from 12,000 to 30,000 RPM

6. A direct drive, single stage, centrifugal air compressor blower assembly according to claim 1 wherein said variable high speed asynchronous AC induction motor outputs from 5 to 50 horsepower.

7. A direct drive, single stage, centrifugal air compressor blower assembly according to claim 5 wherein said variable high speed asynchronous AC induction motor outputs from 5 to 50 horsepower.

8. A direct drive, single stage, centrifugal air compressor blower assembly according to claim 1 wherein said asynchronous AC induction motor operates from variable voltages and frequencies supplied by said Variable Frequency Drive.

9. A direct drive, single stage, centrifugal air compressor blower assembly according to claim 5 wherein said variable high speed asynchronous AC induction motor RPM is controlled by said Variable Frequency Drive.

10. A direct drive, single stage, centrifugal air compressor blower assembly according to claim 1 wherein said single rotating drive shaft has two sealed radial bearings rotatably mounted about said shaft: one on the drive end (DE) of the motor, between said impeller and the motor rotor and one at the opposite drive end (ODE), each for rotatably supporting the combination of said shaft, said impeller, and the AC induction motor rotor assembly.

11. A direct drive, single stage, centrifugal air compressor blower assembly according to claim 1 wherein said impeller comprises a plurality of blades symmetrically mounted on a circular plate and radiating outwardly from said drive shaft.

12. A direct drive, single stage, centrifugal air compressor blower assembly according to claim 8, each of said impeller blades having an arcuate blade surface, the plurality of the blades being operable for receiving air in a direction parallel to said drive shaft through the air inlet of said centrifugal compressor blower housing and for discharging air through outlet of said centrifugal compressor blower housing.

13. A direct drive, single stage, centrifugal air compressor blower assembly according to claim 1 in which two compressor housings, each containing one impeller, are mounted at opposite ends of a single rotating shaft of the same integral, variable high speed, asynchronous AC induction motor.