Abstract:
A double-lobe type rotor design process includes a process for forming a defined rotor and a process for forming a conjugate rotor, wherein the defined rotor and the conjugate rotor intermesh and conjugate to each other. The rotor profile curves suitably for the completed operation period of carryover, suction and exhaust could be well defined by proper parameters, thereby optimizing rotor performance, enhancing compression ratio, providing a smooth suction and exhaust process and avoiding noise and vibration.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Field of the Invention  
         [0002]     This application is a continuation-in-part application of U.S. Pat. No. 6,776,594 filed Jun. 2, 2003 entitled “Rotor Mechanism”.  
         [0003]     The present invention relates to a double-lobe type rotor design process which is able to create a defined rotor and a conjugate rotor intermeshing and conjugating to each other from carryover to suction and from exhaust to the end of the completed operation period by different parameters, and evaluate optimal rotor profiles to be used for some systems like a vacuum pump, an air booster, a compressor and a supercharger, enhancing compression ratio, providing a smooth suction and exhaust process and avoiding noise and vibration.  
         [0004]     A double-lobe type rotor used in multistage type vacuum pumps, compressors, air boosters or superchargers generally comprise a defined rotor and a conjugate rotor intermeshing to each other. A pair of lobes of each rotor provides periodic compression operation of gas suction and gas exhaust. Therefore, the meshing mechanism of two lobes of the rotors is very important. If the meshing mechanism of the two lobes of the rotors is not good enough, noise and vibration may occur during the periodic gas suction, gas exhaust, and carry over processes of the rotors. Moreover, wear may occur due to the improper intermeshing of the rotors thereby reducing the durability of operation.  
         [0005]     U.S. Pat. Nos. 1,426,820, 4,138,848, 4,224,016, 4,324,538, 4,406,601, 4,430,050 and 5,149,256 disclose relevant rotors. Referring to  FIG. 9 , lobes of a pair of rotors 8, 9 of U.S. Pat. No. 5,149,256 include a tip portions 82, 92 formed at ajunctions between the concave portions 80, 90 and the arcuate surfaces 81, 91 so that there is discontinuity of the rotors 80, 90&#39;s curves. Therefore, during the moments from inefficient compression period to the period of air&#39;s starting intake, the top portions 83, 93 of the rotors 8, 9 will operate unsmoothly at the tip portion 82, 92 thereby resulting in noise and vibration.  
         [0006]     To overcome the defects mentioned above, U.S. Pat. No. 6,776,594 provides two rotors with smooth operation curve and conjugate to each other. The main feature is that the operation curve provided by the rotors from the carryover period to the period of starting suction and from the exhaust period to the end is defined by a couple of smoothly connected curves rather than a couple of connected arc and concave curve, thereby avoiding noise and vibration during the periodic operation of suction, exhaust, and carryover, etc  
       SUMMARY OF THE INVENTION  
       [0007]     Accordingly, an object of the present invention is to provide a double-lobe type rotor design process which is able to create a defined rotor and a conjugate rotor intermeshing and conjugating to each other from carryover to suction and from exhaust to the end of the completed operation period by different parameters, and evaluate optimal rotor profiles to be used for some systems like a vacuum pump, an air booster, a compressor and a supercharger, enhancing compression ratio, providing a smooth suction and exhaust process and avoiding noise and vibration.  
         [0008]     A double-lobe type rotor design process of the present invention is adapted for forming a defined rotor and a conjugate rotor intermeshing to each other. The rotor profile curves suitably for the completed operation period of carryover, suction and exhaust could be well defined by proper parameters, thereby optimizing rotor performance, enhancing compression ratio, providing a smooth suction and exhaust process and avoiding noise and vibration. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a sketch view of forming a tip conjugate curve of a lobe type rotor design process of the present invention.  
         [0010]      FIG. 2  is a sketch view of forming a defined rotor profile of a lobe type rotor design process.  
         [0011]      FIG. 3  is a sketch view of forming a conjugate rotor profile of a lobe type rotor design process.  
         [0012]      FIG. 4  is an example of a lobe type rotor design process, where the maximum diameter R of the defined rotor is 60 mm, width D thereof is 85 mm, central angle α thereof is 3°, central angel β is 6°.  
         [0013]      FIG. 5  is a sketch view of the defined rotor profile varying, where width D thereof is 52, 55, 60, 65, 75, 80 mm.  
         [0014]      FIG. 6  is a sketch view of the defined rotor profile varying, where central angle α thereof is 3°, 6°, 9°, 12°.  
         [0015]      FIG. 7  is a sketch view of the defined rotor profile varying, where central angle β thereof is 3°, 6°, 9°, 12°.  
         [0016]      FIG. 8  is a list of different values of the lobes of the defined rotor and the conjugate rotor according to different parameters in  FIGS. 4, 6  and  7 .  
         [0017]      FIG. 9  is the planar view of a rotor mechanism of the U.S. Pat. No. 5,149,256. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     A double-lobe type rotor design process in accordance with the present invention designs the profile of a defined rotor  1  by suitable parameters, and then get the profile of conjugate rotor  2  with conjugate theory. With reference to  FIGS. 1 and 2 , designing process for forming the profile of defined rotor  1  comprises the following steps:  
         [0019]     1. Specifying maximum radius R and width D of the defined rotor  1 , pitch circles of the defined rotor  1  and the conjugate rotor  2  with a pitch circle radius Rp and centers t 1  and t 3  respectively, wherein Rp is smaller than R by the ratio of R=3Rp/2.  
         [0020]     2. The first pitch circle center t 1  is designated as the center of the defined rotor  1 . A reference horizontal line h 1  is defined through the first center t 1  and the third center t 3  as assistant line. A base point p 0  on the reference horizontal line h 1  is spaced a distance R apart from the first center t 1 . Referring to  FIG. 1 , a conjugate curve E′ is created when the base point p 0  rotating about the first center t 1 . Referring to  FIGS. 1 and 2 , a curve E is drawn symmetrically to the conjugated curve E′ about the tangent point p 7  of the two pitch circles of the defined rotor  1  and the conjugate rotor  2 . The curve E serves as a portion of a first lobe of the defined rotor  1 . A third point p 3  is an intersection of the curve E and the horizontal line h 1 .  
         [0021]     3. A first point p 1  on the profile of the defined rotor  1  is defined by a first central angle α and a circle with a center of t 1  and a radius of R. A first arc A is defined between the base point p 0  and the first point p 1  and with a center of t 1  and a radius of R.  
         [0022]     4. A second line h 2  is defined by the reference horizontal line h 1  and the first central angle α. A second center t 2  is designated on the second line h 2  and is spaced a distance r B  apart from the first point p 1 .  
         [0023]     5. The r B  is defined by following equation, wherein R is the maximum radius of the defined rotor  1 , namely, the distance between the first center t 1  and the first point p 1 .  
           r   B     +       (     R   -     r   B       )     ⁢   sin   ⁢           ⁢   α       =     D   2         
         r   B     =         D   /   2     -     R   ⁢           ⁢   sin   ⁢           ⁢   α         1   -     sin   ⁢           ⁢   α             
 
         [0024]     6. The second arc B is defined by a circle with a center of t 2  and a radius of r B , and connecting with the first point p 1  and a second point p 2 . The second point p 2  is located on a vertical line through the second center t 2  and above the center point t 2 .  
         [0025]     7. The third center t 3  of the pitch circle of the conjugate rotor  2  is located on the reference horizontal line h 1 , and is spaced a distance 2Rp apart from the first center t 1 . A fourth point p 4  is defined by a second central angle β and a circle with a center of t 3  and a radius of R. A third arc F is defined by connecting with the third point p 3  and the fourth point p 4 .  
         [0026]     8. A third line h 3  is defined by the reference horizontal line h 1  and the second central angle β. A fourth center t 4  is located on the third line h 3  and is spaced a distance r C  apart from the fourth point p 4 .  
         [0027]     9. The radius r C  is defined by the following equation, wherein R is the maximum radius of the defined rotor  1 , namely, the distance between the center t 3  and the fourth point p 4 .  
           r   C     +       (     R   +     r   C       )     ⁢   sin   ⁢           ⁢   β       =     D   2         
         r   C     =         D   /   2     -     R   ⁢           ⁢   sin   ⁢           ⁢   β         1   +     sin   ⁢           ⁢   β             
 
         [0028]     10. A fourth arc C is defined with a circle center of t 4  and a radius of r C , and connecting with the fourth point p 4  and a fifth point p 5 . The fifth point p 5  is located on a vertical line through the fourth center t 4  and below the fourth center t 4 .  
         [0029]     11. A second horizontal line Y is defined by connecting the second point p 2  and a seventh point p 6  which is symmetric to the fifth point p 5  about the first center t 1 .  
         [0030]      12 . Smoothly connecting the curve E, the first arc A, the second arc B, the third arc F, the fourth arc C and the horizontal line Y forms a profile of a first lobe of the defined rotor  1 . A profile of a second lobe of the defined rotor  1  is drafted symmetrically to that of the first lobe about the first center t 1 , as shown by broken line in  FIG. 2 .  
         [0031]     Thus, a profile of the defined rotor  1  with two lobes is completed through the design process described above.  
         [0032]     Referring to  FIG. 3 , a profile of the conjugate rotor  2  is created by connecting the respective conjugate curves of the profile of the defined rotor  1 , including the respective conjugate curves of the curve E, the first arc A, the second arc B, the third arc F, the fourth arc C and the horizontal line Y  
         [0033]      FIG. 4  shows an application of the present design process, where the maximum radius R of the defined rotor  1  is 60 mm, width D of the defined rotor  1  is 85 mm, the first central angle α is 3° and the second central angle β is 6°. The defined rotor  1  and the conjugate rotor  2  have generally identical profile, and therefore have similar mechanical characteristics.  
         [0034]      FIG. 5  shows some applications of the present design process, where the maximum radius R of the defined rotor  1  remains 60 mm, while the width of the defined rotor  1  is 52, 55, 60, 65, 70, 75, 80 mm, respectively. Based on conjugate characteristic, a profile of the defined rotor  1  with minimum width S 1  corresponds to a profile of the conjugate rotor  2  with maximum width L 1 . The width D may be subject to variation in accordance with different practical applications.  
         [0035]     Referring to  FIGS. 6 and 7 , the maximum radius R of the defined rotor  1  is 60 mm, and the width of the defined rotor  1  is 85 mm, while the first central angle α and the second central angle β are 3°, 6°, 9°, 12°, respectively. The profile of the defined rotor  1  varies with different first central angle α and second central angle β. As clearly shown in  FIG. 6 , with the first central angle α becoming larger, outward sides of the lobes of the defined rotor  1  become larger, and outward sides of the lobes of the conjugate rotor  2  become smaller. As clearly shown in  FIG. 7 , with the second central angle β becoming larger, another outward sides of the lobes of the defined rotor  1  become larger, and another outward sides of the lobes of the conjugate rotor  2  become smaller.  FIG. 8  is a table collecting applications of the defined rotor  1  and the conjugate rotor  2  in  FIGS. 5 through 7 , where the design parameters of width D, the first central angle α and second central angle β vary, resulting in different radius r B  and r C , and correspondingly profiles of the defined rotor  1  and the conjugate rotor  2  vary.  
         [0036]     During the design process described above the defined rotor  1  and the conjugate rotor  2  intermesh to each other from carryover to suction and from exhaust to the end of the completed operation period, operation curves of the defined rotor  1  and the conjugate rotor  2  smoothly connect, eliminating noise and vibration and enhancing compression ratio and transporting volume.  
         [0037]     It is understood that the invention may be embodied in other forms without departing from the spirit thereof. Thus, the present examples and embodiments are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein.