Unsymmetrical profile threads for use in a positive displacement motor housing

Abstract

The present invention provides an unsymmetrical thread profile used to connect stator housings of a positive displacement motor. The unsymmetrical thread profile comprises one or more non-load bearing flanks angled with respect to the longitudinal axis of the thread profile such that the root radius is greater than the root radius of a symmetrical thread profile having substantially the same pitch and first angle.

1 . An unsymmetrical thread profile used to connect stator housings of a positive displacement motor, comprising: 
 one or more load bearing flanks angled with respect to the longitudinal axis of the thread profile at a first angle;    one or more non-load bearing flanks angled with respect to the longitudinal axis of the thread profile at a second angle; and    a root radius between the non-load bearing flanks and the load bearing flanks;    wherein the second angle is less than the first angle such that the root radius is greater than the root radius of a symmetrical thread profile having substantially the same pitch and first angle.    
   
   
       2 . The unsymmetrical thread profile of  claim 1 , wherein the thread profile is a pin-side profile.  
   
   
       3 . The unsymmetrical thread profile of  claim 1 , wherein the thread profile is a box-side profile.  
   
   
       5 . A method of providing a larger root radius for a thread profile, comprising: 
 providing a load bearing flank having a first angle; and    providing a non-load bearing flank having a second angle less than the first angle.    
   
   
       6 . A method of reducing the fatigue experienced by a threaded connection, comprising: 
 reducing the angle of the non-load bearing flank to increase the root radius.