Abstract:
Disclosed is an improved hypocycloidal crank apparatus employing as a stator an internally toothed, continuous, synchronous belt. The apparatus is quiet, easily repaired, and does not require lubrication. It is useful for driving air pumps and the like.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Applicant claims the benefit of provisional U.S. patent application 61/172,815, filed Apr. 27, 2009, which application is incorporated herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an improved hypocycloidal cranking apparatus (Cardan Gear). 
     BACKGROUND OF THE INVENTION 
     A hypocycloidal cranking apparatus converts rotational motion into rectilinear motion. This apparatus can also operate in the reverse, transforming rectilinear motion into rotational motion to drive devices such as reciprocating piston engines. 
     In a typical hypocycloidal cranking apparatus, rotational motion is delivered to the device through an input shaft attached to a power source. A crank arm is affixed to the input shaft such that the crank arm rotates in unison with each rotation of the input shaft. A sprocket shaft is offset from the input shaft and is fixedly mounted within the crank arm. An external toothed orbiting member is rotatably mounted on the sprocket shaft, and the teeth of the orbiting member mesh with the teeth within an internal toothed stator member. An eccentric arm is fixedly mounted on the orbiting gear face such that the eccentric arm rotates in unison with each rotation of the crank arm, but in the opposite rotational direction. An output shaft or rod journal is offset from the eccentric arm. 
     As the input shaft rotates, the crank arm rotates and the sprocket shaft mounted orbiting member rotates within the internal toothed stator member, causing the loci of axis points on the output shaft to transcribe a straight line between the extreme positions of the output shaft. This rectilinear motion can be used to power a variety of devices, including but not limited to, air compressors. 
     In a typical hypocycloidal cranking apparatus the stator member is machined from a single piece of metal. (See e.g. Wiseman U.S. Pat. No. 6,510,831). Because a tight mesh is required between the teeth of the orbiting member and stator member, the teeth on these components are fabricated with high precision. Manufacture of this type of machined gear is costly, difficult, and time consuming. Improper engagement between the metal teeth of the orbiting member and the teeth of the stator member will result in high wear, vibration, noise and eventually fatigue failure of the gear teeth in one or both components. In addition, the metal on metal contact requires lubrication to reduce wear and damage to these components. In the event that the orbiting member or stator member is damaged, it must be replaced with a completely new component. 
     A recent published patent application (U.S. patent application Ser. No. 11/131,819) suggested the use of a chain or belt as a replacement for the conventional machined stator member. In this device, the chain or belt was sandwiched between a front and back ring and was not rigidly fixed on its outer circumference. The application suggested that the flexible chain or belt would prevent or reduce clogging of foreign material within the unit. While this is an appealing idea, a flexible stator member will not work in practice. The stator member must remain rigid in order to synchronize the motion of the orbiting member rotating within it. A hypocycloidal cranking apparatus operating within a flexible stator member would induce destructive oscillations in the device, potentially damaging the crank assembly. 
     The present invention provides an improved hypocycloidal cranking apparatus that avoids the disadvantages of the prior art by providing a stator member that is practical, inexpensive and easy to implement and maintain. 
     SUMMARY OF THE INVENTION 
     In the apparatus of the present invention the stator member is comprised of a continuous synchronous toothed belt seated within an inflexible flange and optionally within a trough in the inner circumference of the flange. The optional trough reinforces the outer circumference of the belt, creating a rigid structure within which the sprocket can rotate. The belt is made of an elastomeric and lubristic material, eliminating the need for lubrication. A sprocket serves as the orbiting member and its metal teeth engage with the elastomeric teeth of the belt. This metal-to-belt contact results in decreased noise, tooth wear and vibration. Because the belt used in the present invention is commercially available and thus need not be specially machined, repair of the stator member is significantly less expensive and time consuming than in conventional metal stator member configurations. 
     The construction and method of operation of the present invention, together with additional objects and advantages thereof, will best be understood from the drawings and detailed description of the invention that follow. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIGS. 1A-1C : Diagrammatic Views of the Present Invention Detailing the Rotary Motion Shaft, Sprocket Shaft and Rod Journal 
         FIG. 2 : Diagrammatic View of the Present Invention Detailing the Crank Arm Assembly, Eccentric Counterweight and Continuous Synchronous Belt 
         FIG. 3 : Diagrammatic View of the Crankcase Housing 
         FIGS. 4A-4B : Diagrammatic Views of the Circular Mounting Flange 
         FIG. 5 : Diagrammatic View of the Circular Mounting Flange Detailing the Inner and Outer Surfaces of the Continuous Synchronous Belt 
         FIGS. 6A-6B : Diagrammatic Views of the Crank Arm Assembly 
         FIG. 7 : Diagrammatic View of the Sprocket 
         FIG. 8 : Diagrammatic View of the Eccentric Counterweight 
         FIG. 9 : Diagrammatic View of Crank Arm Counterweight Mass Positioning 
         FIG. 10 : Diagrammatic View of Eccentric Counterweight Mass Positioning 
         FIGS. 11A-11B : Diagrammatic View of Sprocket Tooth Profile 
     
    
    
     LIST OF REFERENCE NUMBERS USED IN THE FIGURES 
     
         
         
           
               1  rod journal receptacle of eccentric counterweight  2   
               2  eccentric counterweight 
               3  outer surface of continuous synchronous belt  16   
               4  inner toothed surface of continuous synchronous belt  16   
               5  crank arm assembly 
               6  crankcase housing 
               7  circular mounting flange 
               8  output end of rotary motion shaft  18   
               9  input end of rotary motion shaft  18   
               10  recessed area of crankcase housing  6   
               11  back face of circular mounting flange  7   
               12  toothed orbiting sprocket 
               13  rod journal 
               14  sprocket end of sprocket shaft  15   
               15  sprocket shaft 
               16  continuous synchronous belt 
               17  front face of circular mounting flange  7   
               18  rotary motion shaft 
               19  crank arm end of sprocket shaft  15   
               20  center axis of circular mounting flange  7   
               21  inner circumference of circular mounting flange  7   
               22  co-planar trough within the inner circumference  21  of circular mounting flange  7   
               23  counterweight end of crank arm counterweight  30   
               24  centerline of crank arm counterweight  30   
               25  arm end of crank arm counterweight  30   
               26  rotary shaft receptacle of crank arm counterweight  30   
               27  sprocket shaft receptacle of crank arm counterweight  30   
               28  rod journal end of eccentric counterweight  2   
               29  counterweight end of eccentric counterweight  2   
               30  crank arm counterweight 
               31  centerline of eccentric counterweight  2   
               32  counterweight mass of eccentric counterweight  2   
               33  counterweight mass of crank arm counterweight  30   
           
         
       
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1A-1C  and  2  illustrate the fully constructed hypocycloidal cranking apparatus of the invention. The device is comprised of three main assemblies: a synchronous belt assembly, a crank arm assembly, and a rod journal shaft assembly. The configuration and interrelation of each is described below. 
     Synchronous Belt Assembly 
     The synchronous belt assembly is comprised of a circular mounting flange  7  and a continuous synchronous belt  16 .  FIGS. 2-5  illustrate the distinctive details of the synchronous belt assembly. The circular mounting flange  7  has a front face  17 , a back face  11 , and an inner circumference  21 . The back face  11  of the circular mounting flange  7  is secured to a crankcase housing  6  in such a manner to accommodate the rotation of the crank arm assembly  5 . One embodiment, shown in  FIGS. 3-4B , accommodates this rotation by way of a recessed area  10  having sufficient diameter and depth to provide clearance for the rotation of the crank arm assembly  5 . The circular mounting flange  7  has a continuous co-planar trough  22  recessed within the perimeter of its inner circumference  21 . 
     The continuous synchronous belt  16  has an outer surface  3  and an inner toothed surface  4  having a defined pitch diameter and an even tooth count. The outer surface  3  of the continuous synchronous belt  16  is seated and mechanically secured within the trough  22  of the circular mounting flange  7  such that the inner toothed surface  4  of the belt  16  is exposed. The belt should be sufficiently lubristic to eliminate the need for crank case lubrication and should be sufficiently strong to withstand the forces imposed on it during operation. One example of a preferred belt is the Gates Poly Chain GT Carbon Belt system available from the Gates Corporation in Denver, Colo. 
     A rotary motion shaft  18 , having an input end  9  and an output end  8 , is positioned along the center axis  20  of the circular mounting flange  7 . The input end  9  of the rotary motion shaft  18  is mechanically supported by the crankcase housing  6  and is adapted for connection to a power source. In one embodiment, shown in  FIGS. 1A and 1C , the output end  8  of the rotary motion shaft  18  passes through a recessed area  10  within the crankcase housing  6  and terminates within the circular mounting flange  7 . 
     In the embodiment disclosed in the Figures, the circular mounting flange  7  employs a trough  22  to improve the lateral support of the belt and to the root of the belt teeth. It should be noted that a trough  22  is not required; the continuous synchronous belt may be mechanically secured within the inner circumference of a circular mounting flange  7  having no trough. 
     Crank Arm Assembly 
     Referring now to  FIGS. 1 ,  2  and  6 A- 6 B, the crank arm assembly  5  is comprised of a crank arm counterweight  30  and sprocket shaft  15 . The crank arm counterweight  30  has a rotary shaft receptacle  26  and a sprocket shaft receptacle  27  centered on the centerline  24  of the crank arm counterweight  30 . The rotary shaft receptacle  26  is located between the counterweight end  23  and the sprocket shaft receptacle  27  of the crank arm counterweight  30 . The input end  8  of the rotary motion shaft  18  is mechanically affixed within the rotary shaft receptacle  26 . The sprocket shaft  15  has a crank arm end  19  and a sprocket end  14 , the crank arm end  19  being mechanically fixed within the sprocket shaft receptacle  27 . 
     Rod Journal Shaft Assembly 
     Referring now to  FIGS. 1 ,  2 ,  7  and  8 , the rod journal shaft assembly is comprised of a toothed orbiting sprocket  12  and an eccentric counterweight  2 . The toothed orbiting sprocket  12  is rotatably mounted on the sprocket shaft  15 , near the crank arm end  19  of the sprocket shaft  15 . The sprocket  12  has a pitch diameter that is equal to one half the pitch diameter of the teeth of the continuous synchronous belt  16  and consequently has exactly one half the number of teeth as contained in the continuous synchronous belt  16 . 
     The profile of the sprocket teeth is determined through use of an optical comparator. The continuous synchronous belt  16  is mounted within the trough  22  of the circular mounting flange  7  as shown in  FIG. 5 . This component is securely fixed within the comparator and illuminated such that the profile of the inner toothed surface  4  of the continuous synchronous belt  16  appears on a calibrated projection screen. A scaled image of the inner toothed surface  4  is recorded and used to create a scaled drawing of the tooth profile required to properly mate the orbiting sprocket  12 . Proper mating occurs when at least one orbiting sprocket  12  tooth engages with the continuous synchronous belt  16 . 
     The orbiting sprocket  12  tooth profile is a function of the constrained diameter of the continuous synchronous belt  16  fixed within the circular mounting flange  7 ; consequently, a different constrained continuous synchronous belt  16  diameter will produce a different orbiting sprocket  12  tooth profile. For instance, a continuous synchronous belt  16  having a diameter of 4.470 inches would preferably have the orbiting sprocket  12  tooth profile shown in  FIGS. 11A-11B . 
     An eccentric counterweight  2  is fixedly mounted on the sprocket end  14  of the sprocket shaft  15  and has a rod journal end  28 , a counterweight end  29 , and a rod journal receptacle  1 . A rod journal  13  is rotatably mounted within the rod journal receptacle  1  of the eccentric counterweight  2 . 
     The rotation of the eccentric counterweight  2  and crank arm counterweight  30  are interdependent and must be appropriately balanced and positioned to facilitate the proper functioning of the unit. The relationship between these components requires adjustment of the apparatus during final assembly. In order to properly balance the apparatus, a mass or combination of masses is positioned on the counterweight end  29  of the eccentric counterweight  2 . This can be accomplished by affixing a counterweight mass  33  to the eccentric counterweight  2  or by fabricating a one-piece eccentric counterweight  2  with an appropriate mass on the counterweight end  29 . Referring now to  FIG. 11 , in the balancing process, the eccentric counterweight  2  is first rotated about its center of gravity and observed for imbalance. The counterweight mass  33  is increased and/or moved along the centerline  31  of the eccentric counterweight  2  in a trial and error fashion until the component is properly balanced. 
     Prior to initial operation, the device should be oriented such that the centerline  31  of the eccentric counterweight  2  and the centerline  24  of the crank arm counterweight  30  are in alignment when the rod journal  13  arrives at its travel extreme as shown in  FIG. 2 . Once the proper orientation has been achieved, the crank arm counterweight  30  must be balanced. The balancing procedure is similar to that described for the mass  33  of the eccentric counterweight  2 . Referring now to  FIG. 10 , the crank arm counterweight  30  is rotated about its center of gravity and observed for imbalance. The mass  32  is increased and/or moved along the centerline  24  of the crank arm counterweight  30  until balance is achieved. 
     Description of Operation 
     As the rotary motion shaft  18  revolves, the affixed crank arm assembly  5  rotates, allowing the attached sprocket shaft  15  and rotatably mounted sprocket  12  to orbit in the direction of input shaft rotation, while the sprocket engagement drives simultaneous opposite directional rotation of the sprocket  12  within the inner circumference  21  of the circular mounting flange  7 . The teeth of the sprocket  12  engage with the teeth of the continuous synchronous belt  16 , thereby coordinating the motion of the components within the hypocycloidal cranking apparatus. 
     The eccentric counterweight  2  affixed to the sprocket shaft  15  rotates in unison with the sprocket shaft  15 . The rod journal  13 , which is rotatably mounted within the eccentric counterweight  2 , spins as the components behind it orbit within the circular mounting flange  7 . This action allows the rod journal  13  to follow only the horizontal path of the eccentric counterweight  2  motion, thereby completing the translation of rotational motion from the rotary motion shaft  18  into rectilinear motion of the rod journal  13 . 
     It will be apparent to those skilled in the art to which the invention pertains that variations and modifications of the embodiments shown and described herein may be made without departing from the spirit and scope of the invention. Accordingly, it is intended that the invention be limited only to the extent required by the appended claims and the applicable rules of law.