Gear pump

Abstract

A gear pump having a suction port, first and second discharge ports, an inner rotor having external teeth, an outer rotor having internal teeth such that the number of the internal teeth is larger than that of the external teeth of the inner rotor, and inter-tooth chambers defined by the external teeth and the internal teeth. The first and second discharge ports are in communication with the inter-tooth chamber whose volume is decreased along with rotation of the inner rotor etc. An inter-tooth chamber which has been brought out of communication with the second discharge port is brought into communication with the suction port while the volume is decreasing. The volume of the inter-tooth chamber which has been brought out of communication with the second discharge port is increased after at least a part of the inter-tooth chamber has been brought into communication with the suction port.

1 . A gear pump including a suction port, a discharge port, an inner rotor having a plurality of external teeth, an outer rotor which has a plurality of internal teeth such that the number of the internal teeth is larger than that of the external teeth of the inner rotor and which is disposed eccentrically with respect to the inner rotor, and a plurality of inter-tooth chambers defined by the plurality of external teeth and the plurality of internal teeth,
 wherein the discharge port is in communication with the inter-tooth chamber, whose volume is decreased along with rotation of the inner rotor and the outer rotor, the inter-tooth chamber which has been brought out of communication with the discharge port is brought into communication with the suction port while the volume of the inter-tooth chamber is decreasing, and the volume of the inter-tooth chamber which has been brought out of communication with the discharge port is increased after at least a part of the inter-tooth chamber has been brought into communication with the suction port.   
     
     
         2 . The gear pump according to  claim 1 , wherein
 the volume of the inter-tooth chamber which has been brought out of communication with the discharge port starts increasing after the entire inter-tooth chamber is communicated with the suction port.   
     
     
         3 . The gear pump according to  claim 1 , wherein the inner rotor is formed such that a tooth bottom portion that defines the inter-tooth chamber which has been brought out of communication with the discharge port approximates to an inner peripheral edge of the suction port without projecting from the inner peripheral edge toward a center of rotation of the inner rotor as seen in an axial direction of the inner rotor when the volume of the inter-tooth chamber has become smallest. 
     
     
         4 . The gear pump according to  claim 1 , wherein the inner rotor is formed such that the inter-tooth chamber whose volume is decreased is brought into communication with the suction port after a meshing portion between the external tooth and the internal tooth defining the inter-tooth chamber overlaps a peripheral edge of the discharge port as seen in an axial direction of the inner rotor. 
     
     
         5 . The gear pump according to  claim 1 , wherein the inner rotor is formed such that the inter-tooth chamber whose volume is decreased is brought into communication with the suction port before a meshing portion between the external tooth and the internal tooth defining the inter-tooth chamber overlaps a peripheral edge of the discharge port as seen in an axial direction of the inner rotor. 
     
     
         6 . The gear pump according to  claim 1 , wherein each of the external teeth of the inner rotor includes a tooth tip portion formed by an epitrochoid curve obtained by rolling, without sliding, an outer rolling circle having a radius that is smaller than a radius of a drawn point while circumscribing a base circle. 
     
     
         7 . The gear pump according to  claim 6 , wherein:
 each of the external teeth of the inner rotor includes
 a first intermediate portion formed by a desired curve and positioned between the tooth tip portion and a tooth bottom portion positioned on a front side, in a rotational direction of the inner rotor, with respect to the tooth tip portion, and 
 a second intermediate portion formed by a desired curve and positioned between the tooth tip portion and a tooth bottom portion positioned on a rear side, in the rotational direction of the inner rotor, with respect to the tooth tip portion; and 
   a length of the curve which forms the first intermediate portion is longer than a length of the curve which forms the second intermediate portion.   
     
     
         8 . The gear pump according to  claim 7 , wherein the first intermediate portion is formed by at least an involute curve. 
     
     
         9 . The gear pump according to  claim 1 , wherein
 the discharge port includes a first discharge port and a second discharge port separated from the first discharge port by a partition wall and disposed on a front side, in a rotational direction of the inner rotor, with respect to the first discharge port.   
     
     
         10 . The gear pump according to  claim 2 , wherein the inner rotor is formed such that a tooth bottom portion that defines the inter-tooth chamber which has been brought out of communication with the discharge port approximates to an inner peripheral edge of the suction port without projecting from the inner peripheral edge toward a center of rotation of the inner rotor as seen in an axial direction of the inner rotor when the volume of the inter-tooth chamber has become smallest. 
     
     
         11 . The gear pump according to  claim 2 , wherein the inner rotor is formed such that the inter-tooth chamber whose volume is decreased is brought into communication with the suction port after a meshing portion between the external tooth and the internal tooth defining the inter-tooth chamber overlaps a peripheral edge of the discharge port as seen in an axial direction of the inner rotor. 
     
     
         12 . The gear pump according to  claim 2 , wherein the inner rotor is formed such that the inter-tooth chamber whose volume is decreased is brought into communication with the suction port before a meshing portion between the external tooth and the internal tooth defining the inter-tooth chamber overlaps a peripheral edge of the discharge port as seen in an axial direction of the inner rotor. 
     
     
         13 . The gear pump according to  claim 2 , wherein
 each of the external teeth of the inner rotor includes a tooth tip portion formed by an epitrochoid curve obtained by rolling, without sliding, an outer rolling circle having a radius that is smaller than a radius of a drawn point while circumscribing a base circle.   
     
     
         14 . The gear pump according to  claim 13 , wherein:
 each of the external teeth of the inner rotor includes
 a first intermediate portion formed by a desired curve and positioned between the tooth tip portion and a tooth bottom portion positioned on a front side, in a rotational direction of the inner rotor, with respect to the tooth tip portion, and 
 a second intermediate portion formed by a desired curve and positioned between the tooth tip portion and a tooth bottom portion positioned on a rear side, in the rotational direction of the inner rotor, with respect to the tooth tip portion; and 
   a length of the curve which forms the first intermediate portion is longer than a length of the curve which forms the second intermediate portion.   
     
     
         15 . The gear pump according to  claim 14 , wherein the first intermediate portion is formed by at least an involute curve. 
     
     
         16 . The gear pump according to  claim 2 , wherein the discharge port includes a first discharge port and a second discharge port separated from the first discharge port by a partition wall and disposed on a front side, in a rotational direction of the inner rotor, with respect to the first discharge port. 
     
     
         17 . The gear pump according to  claim 10 , wherein the inner rotor is formed such that the inter-tooth chamber whose volume is decreased is brought into communication with the suction port after a meshing portion between the external tooth and the internal tooth defining the inter-tooth chamber overlaps a peripheral edge of the discharge port as seen in an axial direction of the inner rotor. 
     
     
         18 . The gear pump according to  claim 17 , wherein each of the external teeth of the inner rotor includes a tooth tip portion formed by an epitrochoid curve obtained by rolling, without sliding, an outer rolling circle having a radius that is smaller than a radius of a drawn point while circumscribing a base circle. 
     
     
         19 . The gear pump according to  claim 18 , wherein:
 each of the external teeth of the inner rotor includes
 a first intermediate portion formed by a desired curve and positioned between the tooth tip portion and a tooth bottom portion positioned on a front side, in a rotational direction of the inner rotor, with respect to the tooth tip portion, and 
 a second intermediate portion formed by a desired curve and positioned between the tooth tip portion and a tooth bottom portion positioned on a rear side, in the rotational direction of the inner rotor, with respect to the tooth tip portion; and 
   a length of the curve which forms the first intermediate portion is longer than a length of the curve which forms the second intermediate portion.   
     
     
         20 . The gear pump according to  claim 19 , wherein the first intermediate portion is formed by at least an involute curve.