Abstract:
The invention relates to a centrifugal compressor or supercharger with an internal drive mechanism ( 30 ), which operates with great efficiency, higher speed and low noise. The compressor needs no lubrication and has a concentric input-and impeller shaft ( 13 ) for compactness. The compressor has two sets of belt drives ( 36 ) connected to a large sprocket ( 33 ).

Description:
BACKGROUND 
       [0001]    The present invention relates to a centrifugal high-speed compressor, which drives lubrication free, comprising an internal drive mechanism of a compressor with an impeller on an impeller shaft and with an input shaft, which is driven by a motor or other means of power. 
         [0002]    It is well known that a centrifugal compressor is able to compress air to a certain pressure ratio. It is also known that a centrifugal compressor is the most efficient air pump known. The most important part in the centrifugal compressor is the pump wheel or impeller. To work efficiently, however it needs very high rotational speed. 
         [0003]    Therefore, a step-up ratio of minimum 6:1 from an input shaft to the impeller is generally. The internal drive mechanism of such a step-up gear typically consists of planetary gears or planetary gear drives. Because gears need lubrication, an oil supply is needed for the step-up transmission. To separate the compressed media from the oil a high-speed seal is needed between the media and the gear. 
         [0004]    One way to avoid the oil system is to use a transmission that does not need lubrication. One such example is disclosed in U.S. Pat. No. 6,763,812 B2. However, this design limits the maximum ratio to below 4:1, which is not enough for smaller, efficient high-speed impellers. 
         [0005]    The belt drive known from U.S. Pat. No. 6,763,812 B2 has only one cog belt and two sprockets. To cope with the high torque from the input shaft the belt has to be very wide to withstand the high tension in the belt cord. One of the issues in a single belt high-speed belt drive is to evacuate air trapped between the belt and the high-speed sprocket. The wider the belt for increased strength the more difficult is the evacuation of air. If the belt is made narrower and the air can escape to the sides, the belt will not withstand the tension. 
       SUMMARY OF THE INVENTION 
       [0006]    The intension of the invention is to provide a compact compressor or supercharger with an internal drive mechanism, which, as compared to prior internal drive mechanisms, operates with greater efficiency, higher speed, and low noise compared to the compressing noise of the media. In addition, the invented drive needs no lubrication and has a concentric input- and impeller shaft for compactness. 
         [0007]    A more specific object is to provide the drive with synchronous belts and pre-greased bearings. This makes the supercharger easy to install and maintenance free. 
         [0008]    Another object is to provide an internal drive mechanism that incorporates stabilizing design features that reduce stress and tension to the belts. 
         [0009]    The invention incorporates two sets of sprockets mounted on parallel shafts. Each shaft has a large and a small sprocket. The input shaft is connected to the first of the larger sprockets. 
         [0010]    On that sprocket, an endless synchronous belt, preferable with carbon core for reduced elongation, lower weight and higher strength, transfers the torque to the first of the smaller sprockets being positioned on an idler shaft together with the second of the two larger sprockets in a rotatable combined locked manner. The other endless synchronous belt then transfers the torque from the second large sprocket on the idler shaft to the other small sprocket sitting on the impeller shaft concentric with the input shaft. 
         [0011]    The ratio of this internal drive is the ratio of the two drives being multiplied. If as an example, the ratio each of the two drives is 3:1 the final ratio will be 9:1. Since the ratio 3:1 in each step is less than the ratio in U.S. Pat. No. 6,763,812B the belt on the small sprockets engage more teeth, due to the smaller diameter difference of the two sprockets, which reduces the stress in the belt because more teeth are sharing the load. 
         [0012]    Due to the torque conversion of the first stage gear, a belt can be used in the second stage, which is approximately one third the width of the first stage belt width. A second stage belt with one third of the width of the first stage belt will allow the air caught between the belt and the sprocket to escape easily and the belt will only require the same tension as the wider input belt, because the torque is dramatically reduced. 
         [0013]    Normally one of the sprockets in a pair has guiding plates on the sides, to keep the belt in place on the sprockets. When running two pairs of sprockets it is possible to avoid both side plates on the small high-speed sprocket and one of the guide plates on the larger high-speed sprocket. This because the two larger sprockets can be chamfered on the side pointing towards the opposite belt. This design secures the best possible way for the air to escape. 
         [0014]    To further help the air escape during engagement between sprocket and belt a special design at the bottom of the teeth on the high-speed sprockets is used. This could typically be a 1 mm×1 mm axial channel, which is enough for the air that could find itself trapped under the belt, to escape at even very high belt speeds. 
         [0015]    If the high-speed cog-belt has the longitudinal tensioning members made of carbon fibers, the strength is so high compared to conventional belts, that only a thin layer is needed. Since the bending forces on the belts are reduced with a minimized thickness, the heat developed in the belt also is reduced. This improves not only the operational life of the belt but also the efficiency. 
         [0016]    When a normal endless cog belt is used, it is advisable to run idlers on both sides of the belt to prevent vibrations. The very high strength and longitudinal stiffness in the carbon fibers make these costly and complex idlers redundant. 
         [0017]    A further advantage of the design is the possibility to use cheaper high-speed bearings on the output shaft. Since the output shaft is running in bearings situated inside the input shaft, the speed difference between the outer and inner races of the bearings is reduced because of the same rotational direction. 
         [0018]    If the shape of the input shaft, keeping the outer high-speed bearings in place is conical, this will keep dirt away from the bearings due to the centrifugal forces transporting dirt to a larger diameter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Embodiments of the invention will in the following be described referring to the drawing, where 
           [0020]      FIG. 1  is a full longitudinal view of a first embodiment of a compressor, 
           [0021]      FIG. 2  is a cross-section taken along line II-II in  FIG. 1 , 
           [0022]      FIG. 3  is a cross section of the small high-speed sprocket illustrating the axial air channels, 
           [0023]      FIG. 4  is a full longitudinal view of a second embodiment of a two-stage direct drive centrifugal compressor, 
           [0024]      FIG. 5  is a cross-section taken along line V-V in  FIG. 4 . 
           [0025]      FIG. 6  is a third embodiment of a compressor and 
           [0026]      FIG. 7  is a cross-section taken along line VII-VII in  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0027]    Referring now to  FIGS. 1 and 2 , a first embodiment of a double carbon-belt drive compressor will be described. 
         [0028]    The double carbon-belt drive unit includes a compressor  10  having a compressor housing  11  and impeller  12 , an input drive  20  connected to the double carbon-belt drive  30 . 
         [0029]    The input drive  20  has a pulley, clutch or connective coupling  21  connected to the input shaft  22 . The input sprocket  23  is locked to the input shaft  22 . Bearings  24  and  25  are keeping the input shaft  22  rotatable in place. 
         [0030]    The double carbon-belt drive  30  contains an idler shaft  31 . On the idler shaft  31  is a wide sprocket  32 , which has a smaller diameter and is wider in the axial direction than another sprocket  33 , which are positioned in an internally locked rotatable position. The idler shaft  31  runs in bearings  34  and  35 . 
         [0031]    The second large narrow sprocket  33  drives a narrow small sprocket  36  that may for instance have a small diameter and be more or less comparable in width (in the axial direction) to the sprocket  33  but be narrower in width as compared to wide sprocket  32  as shown. The sprocket  36  is positioned on output shaft  13  running in high-speed bearings  37 ,  38  and  39 . High-speed bearing  39  is axially locked to output shaft  13  by screw  44 . High speed bearing  39  is then axially secured by screws  41 . 
         [0032]    Sprockets  33  and  23  have chamfer  45  on the side to guide the belts in axial position. 
         [0033]    Input shaft  22  has a conical shape  46  to reduce dirt and particles reaching the high-speed bearings  37  and  38 . 
         [0034]    A wide tooth belt  42  transfers high torque from input sprocket  23  to wide sprocket  32 . 
         [0035]    A narrow tooth belt  43  transfers lower torque in the high-speed drive from sprocket  33  to sprocket  36 . 
         [0036]      FIG. 3  shows how air channels  14  are machined into the high-speed sprocket  36 . When air is trapped between sprocket and belt in a normal high-speed application, the belt is lifted by the air cushion and will not have the ideal contact path to the sprocket. The channels  14  at the bottom of the grooves between the teeth help the trapped air to escape to the sides. If the sprocket with the highest speed has air channels and no flanges, the belt speed can be very high. 
         [0037]    A second embodiment shown on  FIG. 4  and  FIG. 5  will now be described. 
         [0038]    If very high boost and flow is needed this embodiment is able to provide very high efficiency in an extremely lightweight and quiet solution that runs oil free. Production cost compared to other type of high-pressure compressors is very low. 
         [0039]    In this embodiment, the unit has a second compressor  50 . 
         [0040]    The impeller shaft  13  is in this embodiment extended through the housing  39  and carries a second impeller  52  that runs in compressor housing  51 . 
         [0041]    The process media from compressor  10  is routed to the inlet of compressor  50  for further serial compression. Since the final pressure ratio is the pressure ratios from compressor  10  and compressor  50  multiplied, a total pressure ratio above 10:1 is possible. 
         [0042]    An advantage of this design, since the two impellers compress the same amount of media, is that the axial shaft forces almost outbalance each other. 
         [0043]    Power is supplied to the compressor via belt  61 . Belt  61  drives the input sprocket  60 . Input sprocket  60  then again drives the sprocket  32  on idler shaft  31  through belt  42 . Sprocket  32  is connected to the narrow larger diameter sprocket  33  that again via belt  43  drives a smaller diameter narrow sprocket  46 . Sprocket  46  is fitted to impeller shaft  13 . 
         [0044]    Impeller shaft  13  runs in high-speed bearings  37  and  38 . Bearings  37  and  38  are mounted inside the input sprocket  60 . Impeller shaft  13  and input sprocket  60  rotate in the same direction. Therefore, the demand to the high-speed bearings  37  and  38  can be reduced and cheaper bearings of standard quality can be used. 
         [0045]    Input sprocket  60  runs in bearings  24  and  25 , and has a groove  47  towards the small high-speed sprocket  36  where the air can escape. 
         [0046]    To avoid axial belt guidance on the small high-speed sprocket  36 , the input sprocket  60  has a chamfer  45  and the larger sprocket  33  has on the opposite side a flange  49 . 
         [0047]      FIGS. 6 and 7  show a third embodiment and will now be described. 
         [0048]    If very high durability is needed the load on the high-speed bearings has to be reduced. One way of doing this is by fitting a second idler shaft in an opposite position to the other. Then the forces from the belt pull on the output sprocket can be almost eliminated. 
         [0049]    Further, the load on the inner input-shaft bearing can be almost removed. Then a less space demanding bearing can be used. 
         [0050]    This embodiment is able to provide very high durability in a lightweight and quiet solution that runs oil free. Production cost compared to other type of high-pressure compressors is very low. 
         [0051]    The double carbon-belt drive unit  30  includes a compressor  10  having a compressor housing  11  and impeller  12 , an input drive  20  connected to the double carbon-belt drive  30 . 
         [0052]    The input drive  20  has a pulley, clutch or connective coupling  21  connected to the input shaft  22 . The input sprocket  23  is locked to the input shaft  22 . Bearings  24  and  25  keep the input shaft  22  rotatable in place. 
         [0053]    The double carbon-belt drive  30  contains two idler shafts  31 A and  31 B. The idler shaft  31 A has an oppositely positioned idler shaft  31 B. Sprockets  32 A and  32 B and the larger sprockets  33 A and  33 B are positioned in an internally locked rotatable position on the respective shafts. The idler shaft  31 A runs in bearings  34 A and  35 A. The opposite positioned idler shaft  31 B runs in bearings  34 B and  35 B. This helps to minimize the radial load on the bearings  38  and  39 . 
         [0054]    The two large narrow sprockets  33 A and  33 B drive the common small sprocket  36 . The sprocket  36  is positioned on output shaft  13  running in high-speed bearings  38  and  39 . High-speed bearing  39  is axially locked to output shaft  13  by screw  44 . Screws  41  then axially secure high speed bearing  39 . 
         [0055]    Sprockets  33 A and  33 B have respective chamfers  45 A and  45 B on the sides to guide the belts  43 A and  43 B in axial position. Therefore, no side guides are needed on sprocket  36 . 
         [0056]    Input shaft  22  has a conical shape  46  to reduce dirt and particles reaching the high-speed bearings  39  and  38 . 
         [0057]    The wide tooth belt  42  transfers the high torque from input sprocket  23  to sprockets  32 A and  32 B. 
         [0058]    The narrow tooth belts  43 A and  43 B transfer the lower torque in the high-speed drive from sprockets  33 A and  33 B to common small sprocket  36 .