Long-piston hydraulic machines

Abstract

Smaller and lighter hydraulic pump/motors are provided with pistons having body portions substantially as long as the axial length of the respective cylinders in which they reciprocate. A plurality of respective lubricating channels, formed circumferentially and radially transecting the walls of each cylinder, is each positioned to be closed at all times by the axial cylindrical body of each respective piston during its entire stroke. Each lubricating channel is interconnected, one to another, to form a single, continuous lubricating passageway entirely within the cylinder block and not connected by either fluid “input” or fluid “output” passageways, being replenished solely by blow-by entering from the valve end of each cylinder. A plurality of sealing members, each located near the open end of each cylinder, substantially eliminates blow-by from this lubricating passageway, thereby significantly increasing volumetric efficiency. The resulting improved lubrication, in combination with unique spring-biased hold-down assemblies, permits use of variable-angle swash-plate arrangements that require neither dog-bones at the outer ends of the pistons nor conventional nutating-only wobblers.

We claim:  
     
         1 . In a hydraulic machine having a plurality of pistons reciprocally mounted in respective cylinders formed in a cylinder block and positioned circumferentially at a first radial distance about the rotational axis of a drive element, each said piston having a body portion and a head end and each respective cylinder having a valve end and an open head portion beyond which said head end of each said piston extends at all times, and said pistons also having a stroke varying up to a predetermined maximum, the improvement comprising: 
 a respective lubricating channel formed in the cylindrical wall of each said cylinder in said cylinder block;    all of said lubricating channels being interconnected to form a continuous lubricating passageway in said cylinder block; and    each said respective lubricating channel being substantially closed by the axial cylindrical body of each respective piston during the entire stroke of each said piston, thereby substantially closing said continuous lubricating passageway at all times.    
     
     
         2 . The hydraulic machine of  claim 1  wherein said closed continuous lubricating passageway is formed entirely within said cylinder block, transecting each said cylinder and being centered circumferentially at substantially the same radial distance as said cylinders are centered about the rotational axis of the drive element.  
     
     
         3 . The hydraulic machine of  claim 1  further comprising a sealing member located in proximity to said open head portion of each said cylinder for substantially eliminating blow-by between each said piston and said open head portion of each respective cylinder.  
     
     
         4 . The hydraulic machine of  claim 1  wherein said closed continuous lubricating passageway is replenished solely by blow-by between said body portion of each piston and said valve end of each respective cylinder.  
     
     
         5 . The hydraulic machine of  claim 1  wherein the primary movement of lubricating fluid in said closed continuous lubricating passageway is the result of at least one of (a) piston motion, (b) changing fluid pressures within said respective cylinders, and (c) blow-by between each said piston and said valve end of each respective cylinder.  
     
     
         6 . The hydraulic machine of  claim 5  in combination with a closed loop of circulating hydraulic fluid and wherein said blow-by between each said piston and said valve end of each respective cylinder is immediately returned to the closed loop without requiring the use of a charge pump.  
     
     
         7 . The hydraulic machine of  claim 1  further comprising a swash-plate with a flat face, said swash-plate having an inclination relative to said rotational axis of the drive element, and wherein said head end of each piston is maintained in effective sliding contact with said flat face of said swash-plate during all relative rotary motions between said pistons and said swash-plate, said stroke of said pistons being determined in accordance with the inclination of said swash-plate, and said body portion of each piston has an axial cylindrical length sufficient to be supported within said respective cylinder to assure minimal lateral displacement of said head end of said piston when in relative sliding contact with said flat face at all times during said stroke.  
     
     
         8 . The hydraulic machine of  claim 7  wherein said cylinder block is fixed in a housing, said swash-plate rotates with said drive element and includes a rotor that rotates and nutates, and said flat face is located on said rotor.  
     
     
         9 . The hydraulic machine of  claim 8  wherein the inclination of said swash-plate is variable, and the stroke of said pistons varies up to said predetermined maximum in accordance with said inclination.  
     
     
         10 . The hydraulic machine of  claim 7  wherein each piston has a spherical head end connected to said piston body by a narrowed neck portion, and said machine further comprises: 
 a respective sliding shoe pivotally affixed to said spherical head end of each said respective piston and maintained in effective sliding contact with said flat face of said swash-plate during all relative rotary motions between said pistons and said flat face; and  
 a hold-down assembly for biasing said sliding shoes toward said flat face of said swash-plate.  
 
     
     
         11 . The hydraulic machine of  claim 10  wherein said hold-down assembly comprises: 
 a hold-down element biased toward said sliding shoes and having a plurality of respective openings, the boundary of each said respective opening in said hold-down plate being located in proximity to said narrowed neck portion of each respective piston; and  
 a respective washer fitted about said narrowed neck portion of each piston between said hold-down plate and each respective sliding shoe, each said respective washer having an extension aligned cylindrically for circumferentially contacting each said respective sliding shoe;  
 said washers being in sliding contact with said hold-down plate for movement relative thereto in response to the changing relative positions of said sliding shoes when said flat face of said rotor is inclined relative to said rotational axis of the drive element.  
 
     
     
         12 . The hydraulic machine of  claim 11  wherein the boundary of each said respective opening in said hold-down plate is designed to be in contact with more than one-half of the outer circumference of each said respective washer at all times during said relative movements.  
     
     
         13 . The hydraulic machine of  claim 11  wherein said machine further comprises a coil spring positioned circumferentially about the rotational axis of said drive element at less than said first radial distance for biasing said hold-down plate against said washers.  
     
     
         14 . The hydraulic machine of  claim 10  wherein said hold-down assembly comprises only: 
 a minimal spring bias sufficient to maintain said effective sliding contact between each said shoe and said flat face of said swash-plate in the absence of hydraulic pressure at said valve end of each respective cylinder.  
 
     
     
         15 . The hydraulic machine of  claim 10  wherein said minimal spring bias is provided by a plurality of springs, each said spring being positioned respectively between said body portion of each respective piston and said valve end of each respective cylinder.