Gear pump and manufacturing method of the same

Abstract

A plurality of external teeth of an inner rotor are formed such that an intake-side clearance is larger than a discharge-side clearance. The intake-side clearance denotes a minimum value of a clearance between an external tooth and an internal tooth defining an inter-teeth chamber which communicates with an intake port and in which an amount of change in volume during rotation of the inner rotor by a unit angle is maximized. The discharge-side clearance denotes a minimum value of a clearance between an external tooth and an internal tooth defining the inter-teeth chamber which at least partially overlaps with a partition wall a first discharge port and a second discharge port when the amount of change in volume per unit angle is maximized.

1 . A gear pump including an inner rotor configured to have a plurality of external teeth; an outer rotor configured to have a greater number of internal teeth than number of the external teeth of the inner rotor and arranged to be eccentric with respect to the inner rotor; and a plurality of inter-teeth chambers, each being defined by two adjacent external teeth and two adjacent internal teeth, the gear pump comprising:
 one intake port configured to communicate with the inter-teeth chamber of which volume increases with rotations of the inner rotor and the outer rotor; and   a first discharge port and a second discharge port separated from each other by a partition wall to be independent of each other, each of the discharge ports being configured to communicate with the inter-teeth chamber of which volume decreases with the rotations of the inner rotor and the outer rotor,   wherein an intake-side clearance is larger than a discharge-side clearance, where the intake-side clearance denotes a minimum value of a clearance between the external tooth and the internal tooth defining the inter-teeth chamber which communicates with the intake port and in which an amount of change in volume during rotation of the inner rotor by a unit angle is maximized, and the discharge-side clearance denotes a minimum value of a clearance between the external tooth and the internal tooth defining the inter-teeth chamber which at least partially overlaps with the partition wall between the first discharge port and the second discharge port when the amount of change in volume per unit angle is maximized.   
     
     
         2 . The gear pump according to  claim 1 ,
 wherein each of the external teeth is formed asymmetrical with respect to a tooth profile centerline.   
     
     
         3 . The gear pump according to  claim 1 ,
 wherein the intake-side clearance is at least three or more times larger than the discharge-side clearance.   
     
     
         4 . The gear pump according to  claim 1 ,
 wherein while any one external tooth coming closest to a position where a top of a tooth crest of the external tooth and a top of a tooth crest of the internal tooth are aligned with and opposed to each other is in contact with a corresponding internal tooth, an adjacent external tooth located on a rear side of the any one external tooth in a rotating direction of the inner rotor is in contact with a corresponding internal tooth, during the rotations of the inner rotor and the outer rotor.   
     
     
         5 . The gear pump according to  claim 1 ,
 wherein a tip clearance between any one external tooth and a corresponding internal tooth when a top of a tooth crest of the any one external tooth and a top of a tooth crest of the corresponding internal tooth are aligned is equal to or greater than a minimum value of a clearance between a driving tooth surface of an adjacent external tooth located on a rear side of the any one external tooth in a rotating direction of the inner rotor and a driven tooth surface of a corresponding internal tooth.   
     
     
         6 . The gear pump according to  claim 5 ,
 wherein the tip clearance between the any one external tooth and the corresponding internal tooth is not greater than 200 μm.   
     
     
         7 . The gear pump according to  claim 1 ,
 wherein each of the external teeth of the inner rotor is configured to include:
 a tooth crest formed by an epitrochoid curve obtained by rolling an externally rolling circle having a smaller radius than a radius of a drawing point without sliding while circumscribing the externally rolling circle about a base circle; 
 a first tooth root portion formed by a hypotrochoid curve obtained by rolling an internally rolling circle having a smaller radius than a radius of a drawing point without sliding while inscribing the internally rolling circle with the base circle that is shared by the epitrochoid curve, the first tooth root portion located on a front side of the tooth crest in a rotating direction of the inner rotor; 
 a second tooth root portion formed by a hypotrochoid curve obtained by rolling the internally rolling circle without sliding while inscribing the internally rolling circle with the base circle, the second tooth root portion arranged to be continuous with the first tooth root portion on a rear side in the rotating direction; 
 a first middle portion formed by any curve and located between the tooth crest and the first tooth root portion; and 
 a second middle portion formed by any curve and located between the tooth crest and the second tooth root portion, 
   wherein a length of the curve forming the first middle portion is longer than a length of the curve forming the second middle portion.   
     
     
         8 . The gear pump according to  claim 7 ,
 wherein the first middle portion is formed by at least an involute curve.   
     
     
         9 . The gear pump according to  claim 7 ,
 wherein a range of the second middle portion from an intersection with the base circle to a boundary with the tooth crest is formed by a first curve obtained by rolling the externally rolling circle that is circumscribed about the base circle without sliding while changing the radius of the drawing point of the externally rolling circle, and wherein a range of the second middle portion from the intersection with the base circle to a boundary with the second tooth root portion is formed by a second curve obtained by rolling the internally rolling circle that is inscribed with the base circle without sliding while changing the radius of the drawing point of the internally rolling circle.   
     
     
         10 . The gear pump according to  claim 1 ,
 wherein a teeth profile of the outer rotor defined by the plurality of internal teeth is determined, based on an envelope line drawn with respect to a multiple-teeth profile obtained by revolving a center of rotation of the inner rotor by a predetermined angle on a circle of 2·e+t in diameter about a center of rotation of the outer rotor and rotating the inner rotor by a rotational angle according to the predetermined angle and a number of teeth of the inner rotor during revolution of the center of rotation of the inner rotor by the predetermined angle, where “e” denotes an eccentric amount of the center of rotation of the outer rotor with respect to the center of rotation of the inner rotor, and “t” denotes a clearance between a tooth crest of the external tooth and a tooth crest of the internal tooth when the center of rotation of the inner rotor, the center of rotation of the outer rotor, a top of the tooth crest of the external tooth and a top of the tooth crest of the internal tooth are aligned.   
     
     
         11 . A manufacturing method of a gear pump including an inner rotor configured to have a plurality of external teeth; an outer rotor configured to have a greater number of internal teeth than number of the external teeth of the inner rotor and arranged to be eccentric with respect to the inner rotor; a plurality of inter-teeth chambers, each being defined by two adjacent external teeth and two adjacent internal teeth; one intake port configured to communicate with the inter-teeth chamber of which volume increases with rotations of the inner rotor and the outer rotor; and a first discharge port and a second discharge port separated from each other by a partition wall to be independent of each other, each of the discharge ports being configured to communicate with the inter-teeth chamber of which volume decreases with the rotations of the inner rotor and the outer rotor, the manufacturing method of the gear pump comprising:
 forming the inner rotor such that an intake-side clearance is larger than a discharge-side clearance, where the intake-side clearance denotes a minimum value of a clearance between the external tooth and the internal tooth defining the inter-teeth chamber which communicates with the intake port and in which an amount of change in volume during rotation of the inner rotor by a unit angle is maximized, and the discharge-side clearance denotes a minimum value of a clearance between the external tooth and the internal tooth defining the inter-teeth chamber which at least partially overlaps with the partition wall between the first discharge port and the second discharge port when the amount of change in volume per unit angle is maximized.