Abstract:
A centrifugal gas compressor is disclosed that includes an external drive mechanism consisting of a plurality of pulleys arranged to provide an overdrive in rotational speed. The pulleys are connected with belts to provide a reliable, efficient, cost effective, and readily scalable means of power transmission between the associated motor and the compressor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    Not Applicable  
         BACKGROUND  
         [0002]    1. Field of Invention  
           [0003]    This invention is a centrifugal blower with an improved drive mechanism that includes an external overdrive pulley.  
           [0004]    2. Description of Prior Art  
           [0005]    Centrifugal blowers, also known as superchargers, have been used in a number of applications since their introduction in the 19 th  century to move air in forging operations. Centrifugal blowers have a number of applications, including industrial air movers, and power enhancements for internal combustion engine. In addition, they have been used in automotive applications, airplane wing de-icers, snow blowers, food handlers, electronic component dryers, inflation devices, and even military weapons. A centrifugal blower consists of  
           [0006]    (1) a spinning impeller that pulls air in from the center and forces it out radially  
           [0007]    (2) a scroll that guides the air from the center of the impeller to the discharge near the edge  
           [0008]    (3) a drive mechanism to rotate the impeller  
           [0009]    (4) associated hardware to couple the major components  
           [0010]    To increase the output for a given size and configuration supercharger, the impeller is often turned faster than the drive motor. This is typically accomplished by an “overdrive” unit built into the supercharger. The exact overdrive ratio is up to the designer, but input to output speed ratios of 3:1 to 10:1 are common. The input shaft of the overdrive unit is typically turned by a belt system.  
           [0011]    The overdrive can be accomplished in a number of ways. One of the early commercial superchargers by McCulloch and Paxton used a planetary drive system. In this system, an input shaft rotates an array of fingers that in turn rotate a number of balls pressed against an impeller shaft. The rotation of the balls rotates the impeller shaft and, hence, the impeller. A more recent example of friction-type drive was described by Shirai in U.S. Pat. No. 5,158,427. This design used roller pins instead of balls to achieve a comparable overdrive. The amount of overdrive between the input and impeller shafts is dictated by the dimensions of the components. The key to these systems is the high friction between all of the components to prevent slippage. Unfortunately, a system with high internal friction requires significant additional input power to overcome the frictional losses. The frictional loss increases internal temperatures at the expense of efficiency and reliability.  
           [0012]    More recent designs have used gears to achieve the overdrive. See, for example, the U.S. Pat. No. 5,224,459 to Middlebrook (1993). While the gear system results in slightly increased reliability and is simpler to produce, it still has some major drawbacks. The first is that gears make noise, particularly when spinning at the speeds of 30,000 to 50,000 RPM typically run by blowers. It is well known that the noise of a gear system can be reduced by using helical-cut gears instead of straight-cut ones, but helical-cut gears develop an axial thrust that must be absorbed by the bearings causing additional heat generation and wear. Another disadvantage of gear systems is the requirement of an oiling system. This adds to both the cost and complexity of installation. In the case of automotive superchargers, the oiling system for the gears is often plumbed into the engine&#39;s system. This creates an additional risk where debris from the supercharger, e.g., from gear wear, can enter the engine&#39;s oiling system and reduce engine life.  
           [0013]    Another method of driving the impeller is through the use of sprockets and cog belts. The U.S. Pat. No. 5,887,576 to Wheeler (1999) describes one such form of an internal overdrive for superchargers. In this patent, the internal drive mechanism comprises input and output shafts with sprockets that are connected by a cog belt. By making the sprocket on the input shaft larger in diameter than the one on the output shaft, the speed of the output shaft is increased. The input-to-output ratio is similar to that employed with gear overdrives. In theory, the cog belt provides an efficient overdrive mechanism. However, designs such as the one described in the Wheeler patent have a number of shortcomings, many of which are related to the size constraints on the internal drive system. In practice, the space available for the internal overdrive mechanism is about the same size, or more precisely the same diameter, as the supercharger. This dictates that the pulleys are small and the belt is very short. Small pulleys increase the duty on the belt by forcing it to bend around a tighter radius. Short belts increase the number of belt revolutions per pulley revolution and further increase the duty on the belt. The net result of both of these factors is a severely reduced belt life. Air vents to reduce belt temperature, such as those described in U.S. Pat. No. 5,887,576, could theoretically improve the situation, but experience has shown the belt life to be unacceptably short.  
         SUMMARY  
         [0014]    In accordance with the present invention, the supercharger has an external overdrive system comprised of pulleys of optimized size rotationally coupled by an appropriate number of belts in conjunction with a number of other inherent supercharger components and hardware.  
           [0015]    Objects and Advantages  
           [0016]    Accordingly, besides the objects and advantages of superchargers, as described above, several objects and advantages of the present invention are:  
           [0017]    (a) to reduce the size of the supercharger and increase flexibility of design and installation;  
           [0018]    (b) to reduce the noise level of the drive mechanism;  
           [0019]    (c) to reduce the operational duty on the belt and increase belt life;  
           [0020]    (d) to reduce operational temperatures of the belt and increase belt life;  
           [0021]    (e) to improve the overall supercharger reliability; and  
           [0022]    (f) to simplify the design of a supercharger and reduce manufacturing costs.  
           [0023]    Further objects and advantages will become apparent from a consideration of the ensuing description and drawings. 
       
    
    
     DRAWING FIGURES  
       [0024]    [0024]FIG. 1 shows a cut-away view of the supercharger, including the compact bearing case, and the external drive mechanism.  
         [0025]    [0025]FIG. 2 shows a front view of the supercharger and overdrive pulley system attached to a simple drive pulley.  
         [0026]    [0026]FIG. 3 represents one possible arrangement of the invention in a single accessory belt automotive application. 
     
    
       [0027]    [0027]                                                     Reference Numerals in Drawings                                    10   impeller   12   scroll           14   diffuser plate   16   bearing case           17   bearing case bolt   18   main bearing           20   main seal   22   main shaft           24   input pulley   26   supercharger bracket           30   input belt   32   output overdrive pulley           34   input overdrive pulley   36   overdrive bearing           38   overdrive pulley shaft   39   overdrive pulley bracket           40   drive belt   42   drive pulley           50   accessory belt   52   accessory pulley           54   idler pulley   56   tensioner pulley           58   air conditioning pulley   60   alternator pulley           62   power steering pulley   64   water pump pulley                        
       DESCRIPTION  
       [0028]    [0028]FIG. 1—Preferred Embodiment  
         [0029]    A preferred embodiment of the invention is shown in FIGS. 1 and 2. The invention consists of a bearing case  16  and a direct connection from an input pulley  24  to an impeller  10  by means of a main shaft  22  positioned by two main bearings  18 . Main seals  20  are located adjacent to the main bearings  18  to protect them from dust and debris. The impeller  10  rotates inside of a scroll  12 . As the impeller  10  rotates, it draws air from the inlet at the center of the scroll  12 . The centrifugal energy imparted by the rotating impeller  10  pushes the air to the outer diameter of the scroll  12 , compresses it, and forces it out the scroll  12  discharge.  
         [0030]    In centrifugal blower designs, the quantity of gas displaced by the unit is a function of, among other variables, rotational speed of the impeller  10 . Typically, the desired speed of the impeller  10  is higher than the speed of the rotating equipment available to drive it. For this reason, a overdrive of some type is required. The disclosed invention utilizes an external overdrive, as depicted in FIGS. 1 and 2. The overdrive arrangement includes an input overdrive pulley  34  rotationally coupled to an output overdrive pulley  32 . The two pulleys are free to rotate about an overdrive pulley shaft  38  and overdrive bearings  36  supported by an overdrive pulley bracket  39 . The input overdrive pulley  34  is coupled to a drive pulley  42  associated with an internal combustion engine by a drive belt  40  capable of transferring the rotational force from the drive pulley  42  to the input overdrive pulley  34 . By specifying the diameter of the input overdrive pulley  34  to be smaller than the diameter of the drive pulley  42 , the input overdrive pulley  34  will undergo a greater number of revolutions for every drive pulley  42  revolution. The ratio of the rotational speeds is given by the ratio of pulley diameters. The output overdrive pulley  32 , being fixed at the center of the input overdrive pulley  34 , rotates with the same number of revolutions per unit time. The output overdrive pulley  32  is coupled to the input pulley  24  by means of an input belt  30  capable of transferring the rotational force from the output overdrive pulley  32  to the input pulley  24 . The input belt  30  is of the multiple ribbed design to increase grip. Since the diameter of the output overdrive pulley  32  is larger than the diameter of the input pulley  24 , the input pulley  24  undergoes a greater number of revolutions per unit time than the output overdrive pulley  32 . The ratio of the rotational speeds is again given by the ratio of pulley diameters. The net result is that the input pulley  24  can be rotated at a greater speed than the drive pulley  42  associated with the internal combustion engine.  
         [0031]    Additional Embodiment  
         [0032]    One additional embodiment of the invention is its application as an industrial blower. In this case, the invention could be used to compress and transport any industrial gas, including air, in the same manner described in the preferred embodiment. The only practical difference would be that the drive pulley  42  could be coupled to an electric motor or a suitable internal combustion engine.  
         [0033]    Alternative Embodiments  
         [0034]    There are a number of arrangements possible with the current invention. Without wishing to limit the broad and versatile nature of the invention, some representative examples are listed below:  
         [0035]    (a) cogged belts can be used in combination with, or as a replacement for, standard v-belts or multiple ribbed belts;  
         [0036]    (b) two or more overdrive pulley sets can be used to achieve a higher ultimate rotational speed or to reduce the ratio of each overdrive;  
         [0037]    (c) the belts and pulleys of the invention could be enclosed with a separate cover, while maintaining the advantages of an external drive system.  
         [0038]    Advantages  
         [0039]    From the description and drawings above, a number of advantages of the invention become evident:  
         [0040]    (a) The compact size of the supercharger nose piece, or bearing case, provides additional freedom in the design and installation. This is particularly valuable when the available space for a supercharger is limited, as is often the case in automotive applications.  
         [0041]    (b) By utilizing an external overdrive system, the heat generated by the system is not transferred to the supercharger itself and particularly the bearings and seals.  
         [0042]    (c) By using a belt and pulley arrangement rather than gears to achieve the overdrive, the noise generated by the unit can be practically eliminated.  
         [0043]    (d) The external overdrive arrangement allows larger diameter pulleys and greater pulley-to-pulley spacing to be used. Both of these have the effect of increasing belt life.  
         [0044]    (e) In the event that there is a failure of a component of the external overdrive, the component can be repaired or replaced without disassembling the supercharger.  
         [0045]    (f) The external overdrive arrangement also allows greater freedom in the design with regard to size and placement of components. This allows a number of off-the-shelf components to be used which can greatly reduce manufacturing cost.  
         [0046]    Operation—FIG. 3  
         [0047]    The applications of the current invention are very similar to the applications of other supercharger systems in present use. An example of an automotive application is depicted in FIG. 3. The accessory pulley  52  of an automobile rotates an accessory belt  50  that drives the rest of the engine&#39;s accessories, including the air conditioner pulley  58 , the alternator pulley  60 , the power steering pulley  62  and the water pump pulley  64 . Idler pulleys  54  and a tensioner pulley  56  are used to ensure proper power transmission. In this example, the accessory belt  50  is also used to turn the input overdrive pulley  34  that, in turn, rotates the supercharger. The exact types, numbers, and placement of belts and pulleys is determined by the specific design. The same principles apply for both automotive and industrial applications of superchargers.  
         [0048]    Conclusion, Ramifications and Scope  
         [0049]    Accordingly, the reader will see that the supercharger described in this invention has a number of advantages over the prior art in terms of performance, reliability, simplicity, cost of manufacture and flexibility of design.  
         [0050]    Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. For example, sealed bearings could be used to eliminate the need for separate seals and bearings. Also, the volume of the bearing case could be of any size and could thus be used as a reservoir for any oil required by the bearings. On the overdrive pulley shaft, the bearings could just as easily be placed in the overdrive pulley bracket with the pulleys pressed onto the shaft. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.