Viscous fluid metering device

Abstract

A metering device having two gears and a center plate defining a gear chamber having two major lobes to receive the gears, each of the major lobes defining a diameter and a circular segment having a perimeter extending greater than one hundred eighty degrees. The face surfaces of the first gear, the second gear and the center plate are each machined to be as precisely flat as practical and to be as precisely of equal thickness as practical. The first gear and the second gear are trued on an arbor to eliminate as much runout as practical while at the same time reducing a diameter of the first gear and the second gear to be the substantially the same or slightly larger than the diameter of the major lobes. The first gear and the second gear are press fit into the major lobes; and lapped in the major lobes.

1 . A method for manufacturing a metering device, the metering device comprising two gears, including a first gear and a second gear, and a center plate defining a gear chamber, the gear chamber having two major lobes to receive the gears, each of the major lobes defining a circular segment having a diameter and a perimeter extending greater than one hundred eighty degrees, the first gear, the second gear and the center plate each having two opposing face surfaces, the method comprising the steps of: 
 machining the face surfaces of the first gear, the second gear and the center plate each to be substantially flat and such that the first gear, the second gear and the center plate are substantially of equal thickness;    truing the first gear and the second gear to substantially eliminate runout while at the same time reducing a diameter of the first gear and a diameter of the second gear to be substantially the same as or slightly larger than the diameter of the major lobes;    press fitting the first gear and the second gear into the major lobes; and    lapping in the gears inside the major lobes.    
     
     
         2 . The method as claimed in  claim 1 , in which the machining step comprises grinding.  
     
     
         3 . The method as claimed in  claim 1 , in which the lapping step comprises the use of an abrasive compound.  
     
     
         4 . The method as claimed in  claim 1 , in which the lapping step comprises the use of a viscous adhesive material.  
     
     
         5 . The method as claimed in  claim 1 , in which the center plate further defines at least one minor lobe intersecting the major lobes at two intersections and further comprising the step of machining a break at each of the intersections to prevent interference between the first and second gears and the intersections.  
     
     
         6 . The method as claimed in  claim 1 , further comprising the step of substantially eliminating radiused edges from at least one of the first gear, the second gear and the center plate.  
     
     
         7 . The method as claimed in  claim 6 , in which the first gear and the second gear have a maximum edge break of about 0.002 inches.  
     
     
         8 . A metering device comprising two gears, including a first gear and a second gear, and a center plate defining a gear chamber, the gear chamber having two major lobes to receive the gears, each of the major lobes defining a circular segment having a diameter and a perimeter extending greater than one hundred eighty degrees, the first gear, the second gear and the center plate each having two opposing face surfaces, the metering device being manufactured by a method comprising the steps of: 
 machining the face surfaces of the first gear, the second gear and the center plate each to be substantially flat and such that the first gear, the second gear and the center plate are substantially of equal thickness;    truing the first gear and the second gear to substantially eliminate runout while at the same time reducing a diameter of the first gear and the second gear to be the substantially the same or slightly larger than the diameter of the major lobes;    press fitting the first gear and the second gear into the major lobes; and    lapping in the gears inside the major lobes.    
     
     
         9 . The metering device as claimed in  claim 8 , in which the machining step comprises grinding.  
     
     
         10 . The metering device as claimed in  claim 8 , in which the lapping step comprises the use of an abrasive compound.  
     
     
         11 . The metering device as claimed in  claim 8 , in which the lapping step comprises the use of a viscous adhesive material.  
     
     
         12 . The metering device as claimed in  claim 8 , in which the center plate further defines at least one minor lobe intersecting the major lobes at two intersections and further comprising the step of machining a break at each of the intersections to prevent interference between the first and second gears and the intersections.  
     
     
         13 . The metering device as claimed in  claim 8 , further comprising the step of substantially eliminating radiused edges from the first gear, the second gear and the center plate.  
     
     
         14 . The metering device as claimed in  claim 13 , in which the first gear and the second gear have a maximum edge break of about 0.002 inches.  
     
     
         15 . A metering device comprising: 
 two gears, including a first gear and a second gear,    a center plate defining a gear chamber having two major lobes to receive the gears, each of the major lobes defining a circular segment having a diameter and a perimeter extending greater than one hundred eighty degrees, the first gear, the second gear and the center plate each having two opposing face surfaces;    wherein the face surfaces of the first gear, the second gear and the center plate are each machined to be substantially flat and such that the first gear, the second gear and the center plate are substantially of equal thickness;    further wherein the first gear and the second gear are trued to substantially eliminate runout while at the same time reducing a diameter of the first gear and the second gear to be substantially the same or slightly larger than the diameter of the major lobes; and    further wherein the first gear and the second gear have been press fit into the major lobes and lapped in inside the major lobes.    
     
     
         16 . The metering device as claimed in  claim 15 , in which the face surfaces are machined by grinding.  
     
     
         17 . The metering device as claimed in  claim 15 , in which the gears are lapped with the use of an abrasive compound.  
     
     
         18 . The metering device as claimed in  claim 15 , in which the center plate further defines at least one minor lobe intersecting the major lobes at two intersections and a break at the intersections to prevent interference between the first and second gears and the intersections.  
     
     
         19 . The metering device as claimed in  claim 8 , in which the first gear, the second gear and center plate comprise substantially non-radiused edges.  
     
     
         20 . The metering device as claimed in  claim 13 , in which the first gear and the second gear have a maximum edge break of about 0.002 inches.