Patent Publication Number: US-10309400-B2

Title: Volumetric compressor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a U.S. National Phase of International Patent Application PCT/IB2015/056764, filed on Sep. 4, 2015, which claims priority to Italian Application No. BO2014A000483, filed on Sep. 4, 2014, each of which is incorporated by reference as if expressly set forth in their respective entireties herein. 
     TECHNICAL FIELD 
     The present invention relates to an electric volumetric Roots-type compressor for gas, in particular air. 
     In particular, the present invention finds advantageous, but not exclusive application to inflate inflatable boats, kite surfing, SUP (acronym for: “Stand Up Paddling”) boards, to which the following description will make explicit reference without thereby losing generality. 
     In particular, the teaching of the present invention advantageously, but not exclusively, applies to a two-stage Roots-type compressor to which explicit reference will be made. 
     BACKGROUND ART 
     As already known, in camping and activities that generally take place during leisure time you often need to inflate a device, such as, for example, rafts, kitesurfing boards, etc. Beside traditional foot pumps, or manual pumps, the use of electric compressors is increasingly widespread. 
     The traditional technology of electric compressors for this type of use contemplates the adoption of an electric turbine plus a piston compressor. 
     While having undoubted advantages with regard to inflation time and reached pressure, the electric compressors currently on the market disadvantageously have a low energy efficiency; moreover, they are very noisy, thus having a disturbing effect in resting places such as campgrounds, beaches etc. 
     DISCLOSURE OF INVENTION 
     Therefore, the main object of the present invention is to provide a two-stage Roots-type air compressor, free from the aforesaid drawbacks and, at the same time, having a simple and economical manufacture. 
     Furthermore, as already known, some special uses require high pressure compressed air with a limited flow rate, as in the case of inflatable boats, kayaks and mattresses, whereas other uses require high flow rates at low pressure, as in the case of kites and SUP boards. 
     Consequently, two different lines for industrially manufacturing two different models should be created to obtain these two types of compressors. 
     Therefore, it would be useful to conceive and design a two-stage Roots-type air compressor where the two types of compressors could respectively be obtained with the same structural elements (although differently assembled), at the manufacturer&#39;s choice according to the market demand; namely a first model at high outlet pressure and with a limited flow rate, and a second model allowing to obtain high flow rates at low outlet pressures. 
     Therefore, the present invention provides a two-stage compressor as claimed in claim  1  or in any one of the claims directly or indirectly dependent from said claim  1 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, it is now described a preferred embodiment, purely by way of non-limiting example and with reference to the accompanying drawings, wherein: 
         FIG. 1  shows an exploded view of a first configuration (with the two stages connected “in series”) of the two-stage compressor of the present invention; 
         FIG. 2  shows an exploded view of a second configuration (with the two stages connected “in parallel”) of the two-stage compressor of the present invention; 
         FIG. 3  shows a three-dimensional rear view of a lid used in the two-stage compressor manufactured according to the teaching of the present invention; 
         FIG. 4  shows a three-dimensional front view of the lid of  FIG. 3 ; 
         FIG. 5  shows a three-dimensional view of a head used in the two-stage compressor according to the present invention; 
         FIG. 6  shows a three-dimensional view of a first cage relative to a first compression stage of the two-stage compressor according to the invention; 
         FIG. 7  shows a three-dimensional view of a second cage relative to a second compression stage of the two-stage compressor according to the invention; 
         FIG. 8  shows a first configuration of two dividing plates comprised in a device for the interconnection of the two compression stages; and 
         FIG. 9  shows a second configuration of the two dividing plates of  FIG. 8 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     In  FIG. 1, 10  indicates, as a whole, a two-stage Roots-type rotary air compressor manufactured according to the teaching of the present invention. 
     The compressor  10  comprises a bottom plate  20  and a head  30 . As shown in  FIG. 1 , a motor (GM) mounted on the side of the head  30  sets in rotation two drive shafts  50  and  60  by using a group of gears (GG) with known systems. 
     From the macroscopic point of view, the compressor  10  has a substantially longitudinally symmetric axis (X), and it is thinkable as if it was divided into a first compression stage (I) and in a second compression stage (II) by means of a pair of dividing plates  70 ,  80 . 
     Incidentally, as better seen later on, the two dividing plates  70  and  80  are identical. Their mutual positioning determines whether the two compression stages (I) and (II) are connected “in series”, or “in parallel” (see below). 
     The combination of the two dividing plates  70  and  80  forms an interconnection device  100  between the two compression stages (I) and (II). 
     As shown in more detail in  FIGS. 3, 4 , the lid  20  comprises a main body  20 A having a substantially ellipsoidal plate shape. 
     Eight through holes have been formed in the main body  20 A, each of them being crossed in use by a respective tie rod  90  ( FIG. 1 ), at least partially threaded, associated to a respective nut (not shown). 
     A groove  20 B ( FIG. 4 ) is arranged on the inner face of the main body  20 A, facing the first compression stage (I). 
     As shown again in  FIG. 4 , also two seats  20 C,  20 D which, in use, accommodate respective end bearings (not shown) for supporting the shafts  50 ,  60 , are arranged on the inner face of the main body  20 A. 
     As shown in more detail in  FIG. 5 , the head  30  comprises, in turn, a main body  30 A having a substantially ellipsoidal plate shape. 
     Eight through holes have been formed in the main body  30 A, each of them being crossed in use by a respective tie rod  90  ( FIG. 1 ). 
       FIG. 5  shows the following openings:
         two centrally arranged circular through holes  30 B and  30 C for air passage;   two circular through holes  30 D,  30 E containing in use two bearings  50 A,  60 A which support the drive shafts  50 ,  60 ; and   two slots  30 F,  30 G for air passage, symmetrically arranged with respect to the circular through hole  30 B.       

     A substantially B-shaped projection is arranged on the face of the main body  30 A facing the second compression stage (II), and it substantially follows the volute of the rotors of the second compression stage (II) (see below). 
     With reference now to  FIGS. 1, 6 , the first compression stage (I) comprises a first cage  110  whose main body  110 A also has a substantially ellipsoidal shape. The edge of the main body  110 A follows the one of the main body  20 A of the lid  20 . 
     Moreover, the main body  110 A ( FIG. 6 ) has:
         an open central volute  110 B receiving two lobe rotors (R 1 ) and (R 2 ) ( FIG. 1 );   a lower opening  110 C ( FIG. 6 ) for air passage;   an upper opening  110 D ( FIG. 6 ) for air passage; and   two lower side slots  110 E and  110 F ( FIG. 6 ) for air passage.       

     Analogously, the second compression stage (II) ( FIGS. 1, 7 ) comprises a second cage  210  whose main body  210 A also has a substantially ellipsoidal shape. The edge of the main body  210 A follows the one of the main body  30 A of the head  30  ( FIG. 1 ). 
     Furthermore, the main body  210 A has:
         an open central volute  210 B receiving two lobe rotors (R 3 ) and (R 4 ) ( FIG. 1 );   a lower opening  210 C ( FIG. 7 ) for air passage;   an upper opening  210 D ( FIG. 7 ) for air passage; and   two lower side slots  210 E and  210 F ( FIG. 7 ) for air passage.       

     The edges of all the openings and of the two volutes formed on the main bodies  110 A,  210 A are surrounded by ribs. 
     In the embodiment shown in  FIG. 1 , the thickness of the main bodies  110 A,  210 A ( FIGS. 6, 7 ) is different because, as later described, the two compression stages (I) and (II) can have different flow rates. However, nothing prevents the two compression stages (I), (II) from having the same thickness. 
     Each main body  110 A,  210 A also has eight through holes which, in use, are crossed by the aforesaid tie rods  90  ( FIG. 1 ). 
     As previously stated, the device  100  for the interconnection between the two compression stages (I) and (II) comprises the two identical dividing plates  70  and  80 . 
     As better seen later on, the two compression stages (I) and (II) are interconnected “in series” or “in parallel” depending on how the two dividing plates  70  and  80  are connected in the interconnection device  100  (see below). 
     As an example of the two forms of connection (“in series”, or “in parallel”) of the two compression stages (I), (II),  FIG. 8  shows an interconnection device  100 * when the two dividing plates  70  and  80  are connected “in series”. 
     On the other hand,  FIG. 9  shows the configuration in which the two dividing plates  70  and  80  are connected “in parallel”, thus forming an interconnection device  100 **. 
     As shown in more detail in  FIGS. 8, 9 , the dividing plate comprises a main body  70 A having a substantially ellipsoidal shape. 
     Two central through holes  70 B,  70 C, respectively corresponding to the aforesaid through holes  30 D,  30 E formed on the head  30 , are formed on the main body  70 A. The two central through holes  70 B,  70 C, in use, are also crossed by the two shafts  50 ,  60 . 
     Four slots  70 D,  70 E,  70 F,  70 G are arranged close to the edge of the main body  70 A, two of them corresponding in use to the slots  30 F,  30 G ( FIG. 5 ). 
     An opening  70 H having a substantially rectangular shape is arranged on the upper edge of the main body  70 A, whereas a longitudinal rectangular recess  70 L extending downwards on the centreline of the main body  70 A is associated to said opening  70 H. 
     The recess  70 L is not a through hole and is actually a simple sunken portion of the plane of the main body  70 A (see below). Analogously, the dividing plate  80  comprises a main body  80 A having a substantially ellipsoidal shape. 
     Two central through holes  80 B,  80 C are formed on the main body  80 A and correspond to said through holes  30 D,  30 E of the head  30 . The two central through holes  80 B,  80 C are also crossed by the two shafts  50 ,  60 . 
     Four slots  80 D,  80 E,  80 F,  80 G are arranged close to the edge of the main body  80 A. 
     Centrally there is a through opening  80 H, having a substantially rectangular shape, to which a longitudinal rectangular recess  80 L extending on the centreline of the main body  80 A is associated. 
     The recess  70 L is not a through hole and is actually a simple sunken portion of the plane of the main body  80 A (see below). Obviously, also the main bodies  70 A and  80 A have eight through holes crossed, in use, by the tie rods  90 . 
     The various elements included in the two-stage rotary compressor  10  are packaged by means of the aforesaid partially threaded tie rods  90 , each of which is provided with a respective nut (not shown). 
     In the embodiment illustrated in  FIG. 9  (connection “in parallel”), the dividing plate  70  has not moved with respect to the configuration of  FIG. 8 , whereas the dividing plate of  FIG. 8  has been ideally rotated by 180° counterclockwise (see arrow in  FIG. 9 ). 
     The two plates  70 ,  80  are then packaged to form said interconnection device  100 **. 
     While the head  30 , the second cage  210  and the first cage  110  are all provided with two respective slots ( 30 F,  30 G;  210 E,  210 F;  110 E,  110 F), each dividing plate  70 ,  80  has four respective slots ( 70 D,  70 E,  70 F,  70 G,  80 D,  80 E,  80 F,  80 G). This is because, in the case of a connection “in series” ( FIGS. 1, 8 ), the slot  80 E must be aligned to the slot  70 E (for the air inlet duct), whereas the slot  70 D must be aligned to the slot  80 D (air outlet duct). 
     On the other hand, in the case of a connection “in parallel” ( FIGS. 2, 9 ) the slot  80 G must be aligned to the slot  70 E (for the air inlet duct), whereas the slot  70 D must be aligned to the slot  80 F (air outlet duct). 
     In the first case (“in series”— FIGS. 1, 8 ) the slots  80 F,  80 G,  70 F,  70 G are not crossed by any airflow; whereas in the second case (“in parallel”— FIGS. 2, 9 ) the slots  80 D,  80 C,  70 F,  70 G are not crossed by the air. 
     The operation “in series” of the two-stage rotary compressor of the present invention will now be described with reference to  FIGS. 1 and 8 . 
     In this case, the outside air to be compressed enters the compressor  10  through the slots  30 F,  30 G formed on the head  30 . 
     Then the air flows through the lower side slots  210 E and  210 F formed in the plate  210  of the second compression stage (II), passing through the slots  70 D and  70 E and  80 D and  80 E which are respectively arranged on the dividing plates  70 ,  80  of the interconnection device  100 *. 
     Therefore, in this case the air bypasses the second compression stage (II) to enter the first compression stage (I). 
     Therefore, the air enters the first compression stage (I) through the lower side slots  110 E and  110 F and, sliding in the groove  20 B ( FIG. 4 ) arranged inside the lid  20 , is conveyed towards the lower opening  110 C actually representing the inlet of the first compression stage (I). 
     Once compressed by the rotors (R 1 ) and (R 2 ), the air is sent to the upper opening  110 D, which can be considered to all effects the outlet of the first compression stage (I). 
     Now the air passes through the opening  70 H ( FIG. 8 ) and finds the recess  70 L which, together with the recess  80 L of the dividing plate  80 , forms a channel  95  having a rectangular cross section. 
     The air then flows downwards along the channel  95  and comes out of the through hole  80 H to move towards the second compression stage (II) through the lower opening  210 C, representing the inlet opening of said second compression stage (II). 
     The air is then compressed by the rotors (R 3 ) and (R 4 ), also rotated by the motor (GM), and exits through the upper opening  210 D, representing the outlet opening of the second compression stage (II). 
     Finally, the air compressed in the two compression stages (I), (II) connected “in series” exits through the circular through hole  30 C and is sent to a user device (not shown). 
     In  FIG. 1 , the airflows entering the two-stage compressor  10  have been indicated by the arrows (F 1 ) and (F 2 ), whereas the outlet airflow is indicated by the arrow (F 3 ). 
     For example, in the case of a connection “in series”, a flow rate of 400 nl/min at a pressure of 500 mbar is supposed in the first compression stage (I), whereas the air undergoes a further compression of 500 mbar in the second compression stage (II). As a result, the air exiting the compressor  10  has a flow rate of 250 nl/min at a pressure of 1000 mbar. 
     On the other hand, in the case of a configuration like the one shown in  FIGS. 2, 9  (“in parallel”), the two openings  70 H,  80 H are disposed one after the other, and the compressed air exiting the first compression stage (I) flows directly towards the upper opening  210 D of the second compression stage (II) and towards the circular outlet through hole  30 C of the head  30 . 
     In this case, as shown in  FIG. 2 , a further airflow fed only to the second compression stage (II) enters the through hole  30 B also formed in the head  30 . This second inlet flow rate, which is added to the first inlet flow rate passing through the two slots  30 G,  30 H, directly reaches the lower opening  210 C (inlet opening) of the second compression stage (II) and, after the compression carried out by the two rotors (R 3 ) (R 4 ) ( FIG. 1 ), is released through the outlet opening represented by the upper opening  210 D. 
     In other words, the two flows from the first compression stage (I) and from the second compression stage (II) add up at the upper opening  210 D. Both flows then come out through the circular through hole  30 C and are sent to a user device (not shown). 
     In  FIG. 2 , the airflows entering the two-stage compressor  10  are indicated by arrows (F 1 ), F 2  (F 4 ), whereas the outlet airflow is indicated by the arrow (F 5 ). 
     For example, in the case of a connection “in parallel”, it can be assumed that 300 nl/min of air at a pressure of 400 mbar enter the first compression stage (I), whereas 200 nl/min of air at a pressure of 400 mbar enter the second compression stage (II). Therefore, a total air flow rate of 500 nl/min at a pressure of 400 mbar comes out of the circular through hole  30 C. 
     Advantageously, the through hole  30 C is provided with a screw cap (not shown) for closing the through hole  30 C when the compressor operates “in series” ( FIGS. 1, 8 ). 
     In the case of  FIG. 2 , the air entering the through hole  30 B is trapped only in the second compression stage (II) and cannot move to the first compression stage (I) because it finds along its path the back of the dividing plate  80  which, in this case, acts as a cap. 
     Furthermore, in the case of a connection “in parallel”, a part of the air entering through the opening  70 H always ends up in the channel  95 , but can come out of said channel  95  always and only passing through the through hole  80 H. 
     In other words, in the case of a connection “in parallel”, the air contained in the channel  95  is substantially stagnant because the main flow of compressed air passes through the openings  70 H,  80 H which are in direct communication between them since, as previously stated, the two dividing plates  70 ,  80  are backed and packaged one on the other. 
     The main advantage of the two-stage volumetric compressor object of the present invention consists in the fact that, by using exactly the same components, in the assembly phase the two compression stages may establish a communication “in series” (with a low flow rate and a high prevalence) or “in parallel” (vice versa, with a high flow rate and a low prevalence).