Fluid device output shaft with coating

Abstract

A fluid device includes a housing defining a central bore, a plurality of commutator holes that extend radially outward from the central bore and a plurality of axial passages in fluid communication with the commutator holes. A fluid displacement assembly is in fluid communication with the housing. The fluid displacement assembly includes volume chambers in fluid communication with the axial passages of the housing. An output shaft includes a valving portion disposed in the central bore of the housing. The valving portion includes a first and second lands and a valving land disposed between the first and second lands. The first land cooperates with the central bore to define a first journal bearing and the second land cooperates with the central bore to define a second journal bearing. A coating is applied to the first and second lands of the output shaft. The coating includes a polyamide 11 material.

What is claimed is: 
     
         1 . A fluid device comprising:
 a housing defining a central bore, a plurality of commutator holes that extend radially outward from the central bore and a plurality of axial passages in fluid communication with the commutator holes;   a fluid displacement assembly in fluid communication with the housing, the fluid displacement assembly including a plurality of volume chambers in fluid communication with the axial passages of the housing;   an output shaft having a valving portion disposed in the central bore of the housing, the valving portion having a first land, a second land and a valving land disposed between the first and second lands, wherein the first land cooperates with the central bore of the housing to define a first journal bearing and the second land cooperates with the central bore of the housing to define a second journal bearing; and   a coating applied to the first and second lands and the valving land of the output shaft, the coating including a polyamide 11 material.   
     
     
         2 . The fluid device of  claim 1 , wherein the polyamide 11 material is at least 50% by weight of the coating. 
     
     
         3 . The fluid device of  claim 1 , wherein a thickness of the coating is greater than or equal to about 0.1 mm. 
     
     
         4 . The fluid device of  claim 3 , wherein the thickness of the coating is less than or equal to about 0.2 mm. 
     
     
         5 . The fluid device of  claim 1 , wherein the coating is applied to the valving portion of the output shaft. 
     
     
         6 . The fluid device of  claim 1 , wherein the valving portion of the output shaft includes a first groove disposed between the first land and the valving land and a second groove disposed between the second land and the valving land. 
     
     
         7 . The fluid device of  claim 6 , wherein the first and second journal bearings are lubricated by fluid from the first and second grooves, respectively, during operation of the fluid device. 
     
     
         8 . The fluid device of  claim 1 , wherein the housing defines a fluid inlet port and a fluid outlet port. 
     
     
         9 . A fluid device comprising:
 a housing defining a central bore, a plurality of commutator holes that extend radially outward from the central bore and a plurality of axial passages in fluid communication with the commutator holes;   a fluid displacement assembly in fluid communication with the housing, the fluid displacement assembly including a plurality of volume chambers in fluid communication with the axial passages of the housing;   an output shaft having a valving portion disposed in the central bore of the housing, the valving portion having a first land and an oppositely disposed second land, wherein the first land cooperates with the central bore of the housing to define a first journal bearing and the second land cooperates with the central bore of the housing to define a second journal bearing; and   a coating applied to the first and second lands of the output shaft, the coating including a material selected from the group consisting of polyamide, polytetrafluoroethylene and combinations thereof.   
     
     
         10 . The fluid device of  claim 9 , wherein the material is at least 50% by weight of the coating. 
     
     
         11 . The fluid device of  claim 9 , wherein a thickness of the coating is greater than or equal to about 0.1 mm. 
     
     
         12 . The fluid device of  claim 11 , wherein the thickness of the coating is less than or equal to about 0.2 mm. 
     
     
         13 . The fluid device of  claim 9 , wherein the output shaft includes a valving land disposed between the first and second lands, the valving land defining a first plurality of slots that extend axially outward from a first groove disposed between the first land and the valving land and a second plurality of slots extends outwardly from a second groove disposed between the valving land and the second groove. 
     
     
         14 . The fluid device of  claim 13 , wherein the first and second journal bearings are lubricated by fluid from the first and second grooves, respectively, during operation of the fluid device. 
     
     
         15 . The fluid device of  claim 14 , wherein the coating is applied to the valving land. 
     
     
         16 . The fluid device of  claim 9 , wherein the coating is applied to the valving portion of the output shaft. 
     
     
         17 . A fluid device comprising:
 a housing defining a central bore, a plurality of commutator holes that extend radially outward from the central bore and a plurality of axial passages in fluid communication with the commutator holes;   a fluid displacement assembly in fluid communication with the housing, the fluid displacement assembly including a plurality of volume chambers in fluid communication with the axial passages of the housing;   an output shaft having a valving portion disposed in the central bore of the housing, the valving portion having a first land, a second land and a valving land disposed between the first and second lands, the first land cooperating with the central bore of the housing to define a first journal bearing and the second land cooperating with the central bore of the housing to define a second journal bearing, the valving portion of the output shaft defining a first groove disposed between the first land and the valving land and a second groove disposed between the second land and the valving land, wherein the first and second journal bearings are lubricated by fluid from the first and second grooves, respectively, during operation of the fluid device; and   a coating applied to the first and second lands and the valving land of the output shaft, the coating including a material selected from the group consisting of polyamide, polytetrafluoroethylene and combinations thereof.   
     
     
         18 . The fluid device of  claim 17 , wherein the material is at least 50% by weight of the coating. 
     
     
         19 . The fluid device of  claim 17 , wherein a thickness of the coating is greater than or equal to about 0.1 mm. 
     
     
         20 . The fluid device of  claim 17 , wherein a thickness of the coating is less than or equal to about 0.2 mm. 
     
     
         21 . A method for manufacturing an output shaft for a fluid device comprising:
 machining a first land and second land of a valving portion of an output shaft of a fluid device;   heat treating the output shaft;   performing a first grinding operation on the output shaft;   applying a coating to the first land and second land of the output shaft, the coating including a material selected from the group consisting of polyamide, polytetrafluoroethylene and combinations thereof; and   performing a second grinding operation on the first land and second land of the output shaft.   
     
     
         22 . The method of  claim 21 , wherein the thickness of the coating on the first land and second land of the output shaft after the second grinding operation is in a range of about 0.1 mm to about 0.2 mm. 
     
     
         23 . The method of  claim 21 , wherein the material includes polyamide 11. 
     
     
         24 . The method of  claim 23 , wherein the material is at least 50% by weight of the coating. 
     
     
         25 . The method of  claim 21 , wherein a valving land that is disposed between the first land and the second land of the valving portion of the output shaft is coated with the coating. 
     
     
         26 . A method for manufacturing an output shaft for a fluid device comprising:
 machining an interface portion, a sealing portion and a valving portion of an output shaft, the sealing portion being disposed between the interface portion and the valving portion, wherein the valving portion includes a first land, a second land and a valving land, the valving land being disposed between the first and second lands;   heat treating the output shaft;   performing a first grinding operation on the output shaft;   applying a coating to the first land and the second land of the output shaft, the coating including a polyamide material; and   performing a second grinding operation on the first land and second land of the output shaft following the application of the coating.   
     
     
         27 . The method of  claim 26 , wherein the polyamide material includes polyamide 11. 
     
     
         28 . The method of  claim 26 , wherein the valving land of the valving portion of the output shaft is coated with the coating. 
     
     
         29 . The method of  claim 26 , wherein the thickness of the coating on the output shaft after the second grinding operation is in a range of about 0.1 mm to about 0.2 mm.