Integral filter for hydrostatic transmission

Abstract

A hydrostatic transmission having a fluid pump ( 15 ), and a fluid motor ( 17 ) disposed in a housing ( 11 ) which is in fluid communication with a source (C) of low pressure fluid. The housing ( 11 ) defines a recessed area ( 71,85 ) and disposed therein is a piece of filter material ( 83,87 ), the recessed area intersecting the flow path through the transmission at a location between the low pressure source (C) and an inlet ( 65 ) to the pump ( 15 ). The flow area of the recessed area is substantially greater than that of the flow path through the transmission. The piece of filter material ( 83,87 ) is attached directly within the recessed area ( 71,85 ) in a manner sufficient to maintain the filter material therein during flow through the flow path. The invention provides substantial filter capacity without adding to the overall size or cost of any of the transmission components.

What is claimed is:  
     
         1 . A hydrostatic transmission comprising a housing assembly, a variable displacement fluid pump and a fluid pressure operated motor disposed in said housing assembly; said fluid pump including a pump inlet and a pump outlet, and said fluid motor including a motor inlet and a motor outlet, and said housing assembly being in fluid communication with a source of low pressure fluid, said hydrostatic transmission defining a flow path including, in order, said source, said pump inlet, said pump outlet, said motor inlet, and said motor outlet; said hydrostatic transmission further including a filter assembly disposed in series flow relationship in said flow path; characterized by: 
 (a) said housing assembly defining a recessed area intersecting said flow path at a location between said source of low pressure fluid and said pump inlet, the flow area of said recessed area being substantially greater than the flow area of said flow path;    (b) said filter assembly comprising a piece of filter material disposed within said recessed area and attached directly thereto in a manner sufficient to maintain said piece of filter material within said recessed area during flow through said flow path.    
     
     
         2 . A hydrostatic transmission as claimed in  claim 1 , characterized by said fluid pump comprising a radial piston pump and said fluid pressure operated motor comprising a radial piston motor.  
     
     
         3 . A hydrostatic transmission as claimed in  claim 2 , characterized by said housing assembly comprises a pintle assembly including a radially-extending disc-like portion disposed axially between said radial piston pump and said radial piston motor.  
     
     
         4 . A hydrostatic transmission as claimed in  claim 3 , characterized by said radially-extending disc-like portion of said pintle assembly defining said recessed area.  
     
     
         5 . A hydrostatic transmission as claimed in  claim 1 , characterized by said piece of filter material comprises a single piece of pleated filter paper, said piece of filter paper being attached within said recessed area by means of an adhesive material being in contact with both said piece of filter paper and said recessed area of said housing assembly.  
     
     
         6 . A hydrostatic transmission as claimed in  claim 1 , characterized by said housing assembly including a radially-extending disc-like portion disposed axially between said fluid pump and said fluid motor; said disc-like portion defining said recessed area and defining a fluid passage disposed downstream of said recessed area and in fluid communication with said pump inlet.  
     
     
         7 . A hydrostatic transmission as claimed in  claim 6 , characterized by a check valve disposed in said fluid passage and operable to permit flow through said filter assembly, then through said fluid passage and said check valve, and into said pump inlet.  
     
     
         8 . A hydrostatic transmission as claimed in  claim 6 , characterized by radially-extending disc-like portion defining first and second recessed areas, and said filter assembly comprising first and second pieces of filter material disposed in said first and second recessed areas, respectively.