Abstract:
A rotary vane compressor having features for reducing sound emitted from the compressor during operation. The sound reduction features include and relate to specific components of the compressor. Specifically the features relate to (1) the compressor motor; (2) a non-vented motor housing and back or closure; (3) the inlet ring; (4) the bearing system; (5) the rotor and vane positioning and vane weight or mass; (6) the mass of the body within which the rotor and vane rotate; and (7) a shroud which surrounds the body which is solid and non-vented solid and may be formed of a laminated material having a sound dampening core layer.

Description:
FIELD 
   This invention relates to rotary vane compressors and more particularly to an improved compressor which exhibits low sound emission due to a combination of improved elements. 
   BACKGROUND 
   Rotary vane compressors are used in a variety of applications. One such compressor includes a rotor having vane receiving slots with a vane in each slot. The rotor is rotated, in an eccentric manner, in a cavity within a body to produce compressed gas. One major application is in home sewage treatment. There the rotary vane compressor is used to pump air into home sewage treatment tanks to provide bacteria growth, which in turn, will break down the effluent in the tank. The compressor is typically located outside, next to the house and operates continuously. 
   A typical rotary vane compressor is sold by Gast Manufacturing, Inc. of Benton Harbor, Mich., 49023-0097 as its “23 Series”. These compressors usually include the following components: (1) a motor in a vented housing having a bearing mounted drive shaft; (2) a vented back plate or closure for the motor housing; (3) a rear plate mounted to the housing and though which the shaft extends; (4) an inlet ring between the motor housing and rear plate; (5) a rotor with vanes mounted to the drive shaft, and positioned within a body; (6) a vented shroud surrounding the body which abuts the motor housing; (6) a front plate that bears against the body and rotor; and (7) a muffler box positioned against the front plate and through which air enters and exits the compressor. 
   The muffler box, front plate, body, rear plate and motor housing are secured together. The major moving parts are the motor, drive shaft, bearings and rotor with vanes all of which produce sound. However, vibration of the non-moving parts is also important. The compressor emits sound during operation, which due to its 24-hour operation can become irritating over time. 
   It is an object of this invention to reduce the sound of the compressor when it operates. 
   This and other objects of the invention will become apparent from the following description and independent claims. 
   SUMMARY 
   The compressor of this invention is quieter in operation and exhibits reduced sound emission. The compressor operates at sound levels of less than about 50 dBA (decibels) at one meter. This low sound level has been achieved by various improvements taken in combination. These include improvements relate to the motor, a shorter non-vented motor housing, a non-vented back plate for the motor housing, improved bearings for the drive shaft, and a change in the rotor carrying body such as an increased mass, a solid or non-vented shroud made of a laminated material that surrounds the body, modifications in the vane carrying rotor and optionally an improved muffler box made out of a cast iron, zinc or magnesium casting. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric view of a sound-reduced rotary vane compressor; 
       FIG. 2  is a back view of the compressor of  FIG. 1 ; 
       FIG. 3  is an exploded isometric view of components of the compressor of  FIG. 1 ; 
       FIG. 4  is a top or elevational and exploded view of components shown in  FIG. 3 ; 
       FIG. 5  is a front view of an improved inlet ring used in the compressor of  FIG. 1 ; 
       FIG. 6  is a perspective view of the body used in the compressor of  FIG. 1 ; 
       FIG. 7  is a top view of the body of  FIG. 6 ; 
       FIG. 8  is a front view of the body of  FIG. 6 ; 
       FIG. 9  is a front view of the vane-carrying rotor used in the compressor of  FIG. 1 ; 
       FIG. 10  is a side view of the rotor used in the compressor of  FIG. 1 ; 
       FIG. 11  is a perspective view of a non-vented cylindrical shroud used in the compressor of  FIG. 1 ; 
       FIG. 12  is a sectional view of the shroud taken along line  12 — 12  of  FIG. 11  and showing the laminated construction of the shroud. 
   

   DESCRIPTION 
   The compressor  10  is shown in  FIG. 1 . Externally the compressor has a solid, non-vented motor housing  12 , a non-vented back  13 , a rear plate  14 , a solid non-vented shroud  16 , a front plate  18  and a muffler box  20 . The components are bolted together so as to form a unit. Two ports  22  and  24  are provided in the muffler box for the entry of air and exit of compressed air. Muffler constructions  26  and  28  are provided for use in the muffler box. The rear or back  13  of the compressor is shown in  FIG. 2  and includes a solid non-vented plate. 
   Referring now to  FIG. 3 , an exploded view of the compressor is shown and the internal mechanism can be seen. In the housing there is positioned an electric motor which can be generally characterized as a one-sixth horsepower motor, having a four pole stator and a six pole rotor. The housing  12  has a maximum length of about 5.22 inches so as to reduce the vibrations. The motor&#39;s rotor drives a drive shaft  30  which is mounted on a plurality of deep groove ball bearings  32 . 
   An inlet ring  34  is positioned against the motor housing  12 . There is provided the rear plate  14  which includes a centrally positioned bolting and bearing support section  38  which is held in position by a plurality of webs such as  40 . It is seen that the drive shaft  30  is also supported by a second set of bearings  42  which is secured to the section  38 . The rear plate  14  is secured to the motor housing with the inlet ring  34  positioned therebetween like a gasket. Bolts such as  44  from the motor housing are secured to the periphery of the rear plate  14 . The shroud  16  is non-vented and made of a laminated material and fits against the rear plate  14 . 
   The body  36  defines a rotor cavity  46  therein, fits within the shroud  16 , has a radius of at least about 2.62 inches, a minimum weight of about 4.63 pounds, and is made of a gray iron casting, more specifically SAE J4321 G2500. A rotor and vane assembly  48  is positioned within the cavity  46 . The drive shaft  30  extends to and engages the rotor and rotates the assembly  48 . The assembly  48  includes the rotor  50  and four vane receiving slots such as  52  within each of which there is a positioned a vane  54 . It will be appreciated that the motor rotates the drive shaft which, in turn, rotates the assembly  48  for compressing incoming air and expelling compressed air. When the rotor is rotated, each vane can slide within a rotor slot and can engage the cavity wall or body  36 . The front plate  18  engages the front face of the body  36  and is divided into two chambers or sections  58  and  60  by the by a central rib  62  and peripheral edge  64 . The muffler box  20  which is preferably made from a gray iron, but can be made from die cast aluminum, is secured against the front end plate. The muffler box defines the exit and inlet ports  22  and  24  and each communicates with a chamber  58  or  60 . The muffler box is deep enough to receive the muffler elements  26  and  28 . 
   Elements or components of the compressor are also seen in  FIG. 4  and include the motor housing  12 , the drive shaft  30 , the inlet ring  34 , the rear plate  14 , the shroud  16 , the rotor assembly  48 , the body  36 , the front plate  18  and muffler box  20 . 
   Inlet Ring 
   The inlet ring  34  is seen in  FIG. 5 . The ring  34  has a small wall thickness  66  [i.e., the difference between the outside diameter (OD) and inside diameter (ID)] of about 1.25 inches and is made of 20 gage cold rolled steel. The ring is positioned between the motor housing  12  and the rear plate  14 . The ring is crushable and acts like a gasket to seal against both the housing and plate. The ring OD is fixed by the compressor size and the ID is increased as much as possible so as to reduce vibration and maintain sealing. 
   The Body 
   The body  36  is shown in  FIGS. 6 ,  7  and  8 . The body  36  has a positioning groove  62  located at the top thereof, has an increased mass or, a weight of about 4.63 pounds, as well as an increased outer radius  68  of about 2.62 inches. The body  36  is fabricated from a first sound dampening material, which in a preferred embodiment,is gray iron, as specified hereinbefore, which exhibits good sound-dampening characteristics. In addition, the size, weight and mass of the body is maximized so as to maximize sound dampening. The outside diameter is increased, but is limited by the size of the compressor. The inside diameter or cavity is maintained for cooperation with the rotor assembly. 
   Rotor 
   The rotor body  50  which has vane-carrying slots such as  52  is shown in  FIGS. 3 and 9 . Each of the slots carries a vane, extends into the rotor body, is at right angles to an adjacent vane slot and forms a chord-like construction which extends from the circumference or periphery of the rotor into the rotor body as shown. The positioning of the slot relative to the center and relative to the other slots is important in reducing the sound of operation. The angular relation between the centerline of a vane receiving slot and a line passing through the rotor center and the center of the vane slot opening at the periphery of the rotor is about 24°. The angular relation can vary between 23° and 25°. This angular relationship is important as it permits vane movement in the slot and reduces vane bounce during rotation. The mass or weight of each vane is important to maximize radial force. The weight of the vane herein is about 6.75 grams. The combination of vane mass and angular relation also reduces vane bounce and noise. 
   The Shroud 
     FIGS. 10 ,  11  and  12  show the shroud  16 . The shroud  16  is a cylindrical member which fits about the body  18  and engages the rear plate  14  and the front plate  56 . The shroud is a solid non-vented member which can be made of a laminated structure seen in  FIG. 12 . The laminated structure may include at least one of an outer metal layer  70  and an inner metal layer  72 . Also, the laminated structure includes and an intermediate viscous layer  74  made from a second sound dampening material.The solid or non-vented structure and the laminated structure contributes to the dampening or sound reduction. The inner and outer layers are 24 to 26 gauge Galvaneal steel (Galvaneal steel is electro-galvanized steel which is made for painting) and the sound dampening material is a viscous material such as Acrylic pressure sensitive adhesive. The laminate can be purchased from Roush Anatrol Main Office, 11953 Market Street, Livonia, Mich. 48100, under the trade name Anatrol 980. 
   Bearings 
   The bearings such as  32  and  42  are referred to as deep groove ball bearings (See NSK catalog, Rolling Bearings, Cat. No. A 140b, 19933-10 Printed in Japan, Copyright NSK Ltd. 1989) are sealed and utilize a grease or lubricant to dampen sound. This grease or lubricant is a polyurea grease (available as POLYREX EM, from Exxon Mobile Corporation, 3225 Gallows Road, Fairfax, Va. 22037. The combination of the deep groove bearing and grease reduce the sound of operation. 
   Motor and Housing 
   The motor itself is one-sixth horse power, 6-pole rotor and 4-pole stator type. The motor housing is less than about 5.22 inches in length and is solid or non-vented. Sound emanating from the motor during operation has been minimized. 
   The back or closure  13  for the motor housing  12  is a solid non-vented member which is secured to the housing. The fact that the back is solid and non-vented minimizes sound emanating from the rear of the compressor. 
   Summary 
   The combination of above-identified factors reduces the sound emitted from the compressor during operation to about 50 dB at 1 meter. Those factors include the solid non-vented motor housing  12 , the solid non-vented housing back  13 , the 6-pole rotor 4-pole stator motor, the deep groove bearings  32  and  42  and lubricant, the rotor-vane angular relationship and vane weight or mass, the increased body size and mass  18  and the non-vented solid or laminated shroud  16 . In addition, the muffler  20  can be made of various materials so as to enhance the sound deadening property. 
   It will be appreciated that numerous changes and modifications can be made to the embodiments detailed above.