Patent Publication Number: US-2010107626-A1

Title: Hydraulic variator with adjustable drum plates

Description:
TECHNICAL FIELD  
     The present disclosure is directed to a hydraulic variator and, more particularly, to a hydraulic variator with adjustable drum plates. 
     BACKGROUND  
     Machines such as, for example, dozers, loaders, excavators, motor graders, dump trucks, and other types of machinery typically include a hydro-mechanical power transmission system to transfer power, e.g., torque and rotational speed generated by a power source, to one or more connected loads, e.g., one or more components of the machine. Such power transmission systems often include two transmissions operatively connected to a single power source. 
     One of the two transmissions is typically a fixed ratio transmission configured to convert power into one or more desired power ratios, e.g., one or more desired torque and speed ratios, to operate a connected load. Fixed ratio transmissions usually include one or more discrete gear ratios, through which the power generated by the power source is converted to drive the load in a step-wise manner. The discrete gear ratios are typically manually or automatically selected, via a gear shift, as the load changes. 
     The other transmission is typically a variable ratio transmission connected in parallel to the fixed ratio transmission. The power output of the variable ratio transmission can be adjusted to selectively complement the discrete power ratios of the fixed gear transmission and provide a continuously variable output of torque and speed ratios. Such a power transmission system is commonly referred to as a “step-less” or continuously variable transmission. The variable ratio transmission often includes a variable output pump drivingly connected to a hydraulic motor, which is operatively connected to the fixed ratio transmission. As such, variations in the pump output affect variations in the hydraulic motor output, which is combined with the discrete power ratios of the fixed ratio transmission to provide a continuously variable output of torque and speed ratios. 
     One example of a variable ratio transmission can be found in U.S. Pat. No. 5,642,617 (the &#39;617 patent) issued to Larkin et al. The &#39;617 patent discloses a hydrostatic transmission that includes a hydraulic motor driven by a hydraulic pump. The hydraulic motor and pump each include a plurality of pistons respectively associated with a plurality of sleeves. The pump and motor share a single swash plate, which controls the displacement of both the motor and the pump. As the tilt of the swash plate is adjusted, a ratio between the input received by the pump and the output generated by the motor changes, thereby generating a continuously variable output. 
     Although the hydrostatic transmission disclosed in the &#39;617 patent may generate a continuously variable output, the construction of the piston may limit the efficiency and durability of the transmission. In particular, the fluid seal created by the piston with respect to an associated sleeve, which prevents the fluid from prematurely escaping the associated sleeve, may not be substantially perpendicular to the longitudinal axis of the piston. As such, hydrostatic forces may be unbalanced in both the axial and radial directions. The imbalance of forces in the axial direction may cause some of the pressure energy contained within the fluid to be wasted via frictional losses of a rotor on which the piston is fixed, thereby reducing the efficiency of the energy transfer between the fluid and either the pump or the motor. In addition, the imbalance of forces in the axial direction may exert undesired stresses on the bearings securing the piston to the rotor. Such stresses may reduce the life of the pump or motor and may increase maintenance costs. In addition, a substantial portion of the outer surface of the piston may be in contact with the inner wall of an associated sleeve. As such, the piston may generate substantial frictional losses as it slides relative to the associated sleeve due to the relative high velocity and contact force between the piston and the associated sleeve. 
     The disclosed system is directed to overcoming one or more of the shortcomings set forth above and/or other shortcomings in the art. 
     SUMMARY  
     In one aspect, the present disclosure is directed toward a variator including a first shaft rotatable around a first longitudinal axis associated with the first shaft and a second shaft rotatable around a second longitudinal axis associated with the second shaft. The variator also includes a pump driven by the first shaft. The pump includes a first plurality of drum sleeves attached to a first drum plate titled at a first angle relative to the first longitudinal axis. The drum sleeves are positioned to slidingly receive a first plurality of piston members. Each piston member is configured to form a seal substantially perpendicular to an axis of an associated drum sleeve. The seal substantially prevents fluid from leaking out of a chamber formed by the piston member and the drum sleeve. The variator further includes a motor fluidly coupled to the pump and configured to drive the second shaft. 
     In another aspect, the present disclosure is directed toward a variator including a first shaft rotatable around a longitudinal axis of the first shaft and a second shaft rotatable around a longitudinal axis of the second shaft. The variator also includes a pump driven by the first shaft. The pump has a first plurality of drum sleeves attached to a first drum plate and positioned to slidingly receive a first plurality of piston members. Each piston member includes a contacting surface having a substantially frustro-spherical shape. The variator further includes a motor fluidly coupled to the pump and configured to drive the second shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a diagrammatic illustration of an exemplary disclosed machine; 
         FIG. 2  is a schematic and diagrammatic illustration of an exemplary disclosed powertrain of the machine of  FIG. 1 ; 
         FIG. 3  is a schematic illustration of an exemplary hydrostatic transmission of the powertrain of  FIG. 2 ; 
         FIG. 4  is an exploded view illustration of the hydrostatic transmission of  FIG. 3 ; 
         FIG. 5  is a diagrammatic illustration of an exemplary piston member and associated drum sleeve of the hydrostatic transmission of  FIGS. 3 and 4 ; and 
         FIG. 6  is a schematic illustration of another exemplary hydrostatic transmission of the powertrain of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION  
       FIG. 1  illustrates an exemplary machine  10  having multiple systems and components that cooperate to accomplish a task. The tasks performed by machine  10  may be associated with a particular industry such as mining, construction, farming, transportation, power generation, or any other industry known in the art. For example, machine  10  may embody a mobile machine such as the wheel loader depicted in  FIG. 1 , a bus, a highway haul truck, or any other type of mobile machine known in the art. Machine  10  may include one or more traction devices  12  and a powertrain  14  operatively connected to drive at least one of traction devices  12 . 
     Traction devices  12  may embody wheels located on each side of machine  10  (only one side shown). Alternatively, traction devices  12  may include tracks, belts or other known traction devices. It is contemplated that any combination of the wheels on machine  10  may be driven and/or steered. 
     As shown in  FIG. 2 , powertrain  14  may include components that work together to propel machine  10 . Specifically, powertrain  14  may include a power source  16  drivingly coupled to a transmission  18 . It is contemplated that powertrain  14  may also include a torque converter (not shown) to couple power source  16  and transmission  18 . 
     Power source  16  may provide power output to transmission  18 . Power source  16  may embody an internal combustion engine, such as a diesel engine, a gasoline engine, a gaseous fuel powered engine (e.g., a natural gas engine), or any other type of combustion engine known in the art. Alternatively, power source  16  may embody a non-combustion source of power, such as a fuel cell or a power storage device coupled with an electric motor. 
     Transmission  18  may be driven by an output shaft  20  of power source  16  and may drive traction devices  12  via a shaft  22 . In addition, transmission  18  may include a mechanical portion  24  and a hydrostatic portion  26 , the output of which may be combined using one or more gear assemblies  28  (only one shown in  FIG. 2 ) disposed between mechanical and hydrostatic portions  24 ,  26 , and shaft  22 . Although gear assembly  28  is illustrated as a planetary gear assembly, it is contemplated that gear assembly  28  may include any other type of gear assembly known in the art capable of combining the outputs of mechanical and hydrostatic portions  24 ,  26 . It is further contemplated that mechanical portion  24  and hydrostatic portion  26  may be connected in parallel (as shown in  FIG. 2 ) or, alternatively, in series. 
     Mechanical portion  24  may be operationally connected to output shaft  20  of power source  16  via an input shaft  30  and may be operationally connected to gear assembly  28  via a shaft  32 . Mechanical portion  24  of transmission  18  may embody, for example, a multi-speed, bidirectional, mechanical transmission with a plurality of forward gear ratios, one or more reverse gear ratios, and one or more clutches. Furthermore, the clutches of mechanical portion  24  may be selectively actuated to engage combinations of gears to produce discrete output gear ratios. Mechanical portion  24  may be an automatic-type transmission, wherein shifting is based on a power source speed, a maximum operator selected gear ratio, and a shift map stored within a controller. Alternatively, mechanical portion  24  may be a manual transmission, wherein the engaged gear is manually selected by an operator. It is contemplated that mechanical portion  24  may include any conventional mechanical, e.g., geared, transmission known in the art. 
     Hydrostatic portion  26  may receive an input from output shaft  20  of power source  16  via a gear assembly  34 , which may include a first gear  36  driven by output shaft  20  and a second gear  38  driven by first gear  36 . Hydrostatic portion  26  may include a pump  40  and a motor  42  interconnected by way of a first fluid passage  44  and a second fluid passage  46 . Pump  40  may be driven by second gear  38  via an input shaft  48  and may drive motor  42 . In addition, motor  42  may be operationally connected to gear assembly  28  via an output shaft  50 . A “gear ratio” or “effective gear ratio” of hydrostatic portion  26  may be altered by varying a displacement of pump  40 . For example, if pump  40  is a swashplate-type pump, varying the swashplate angle may vary the displacement of the pump, which may in turn vary the output of an associated hydraulic motor as is know in the art. It is contemplated that motor  42  may be a fixed or variable displacement motor. If variable, the “gear ratio” or “effective gear ratio” of hydrostatic portion  26  may be altered by varying the displacement of motor  42 . It is also contemplated that within the operational limits of pump  40  and/or motor  42 , the fluid displacement of pump  40  and/or motor  42  may be infinitely varied (i.e., any fluid displacement within the operational limits of pump  40  and/or motor  42  may be achievable), thus creating an infinite number of effective gear ratios. 
       FIGS. 3 and 4  illustrate an exemplary embodiment of hydrostatic portion  26 . In particular, hydrostatic portion  26  may include a housing  52  supporting input shaft  48  and output shaft  50  by way of bearings  54 . In addition, housing  52  may at least partially contain pump  40  and motor  42 . Housing  52  may include a central bore  56  having a first axial end  58  and a second axial end  60 . Housing  52  may also contain first and second fluid passages  44 ,  46  configured to direct fluid between pump  40  and motor  42 . For example, pump  40  may be configured to selectively pressurize and direct fluid toward motor  42  via either one of first and second fluid passages  44 ,  46  and receive fluid from motor  42  via the other one of first and second fluid passages  44 ,  46 . Housing  52  may also include ports  62 ,  64  in fluid communication with a makeup pump (not shown) for providing makeup fluid to hydrostatic portion  26  and for removing excess fluid circulating within hydrostatic portion  26 . It is contemplated that hydrostatic portion  26  may also include one or more makeup valves, e.g., one-way valves or pressure biased valves, respectively disposed between ports  62 ,  64  and the make-up pump. It is also contemplated that hydrostatic portion  26  may also include a bypass circuit operatively connected to one or both of first and second fluid passages  44 ,  46  and configured to reduce heat build-up within the circulating fluid. 
     Input shaft  48  and output shaft  50  may support various components of pump  40  and motor  42 , respectively and may be substantially axially aligned with central bore  56 . Bearings  54  may engage interior walls of central bore  56  to support the rotation of input shaft  48  and output shaft  50 . Input shaft  48  may support a pump rotor  66 . Pump rotor  66  may embody a plate-like member fixedly connected to input shaft  48  such that a rotation of input shaft  48  may result in a direct rotation of pump rotor  66 . Pump rotor  66  may be integral to input shaft  48  or, alternatively, joined to input shaft  48  through welding, sintering, a keyed or splined joint or other known joining process. In addition, pump rotor  66  may include a face  68  oriented substantially orthogonal to the axial direction of input shaft  48 . Output shaft  50  may support a motor rotor  70 . Motor rotor  70  may embody a plate-like member fixedly connected to output shaft  50  such that a rotation of output shaft  50  may result in a direct rotation of motor rotor  70 . Motor rotor  70  may be integral to output shaft  50  or, alternatively, joined to output shaft  50  through welding, sintering, a keyed or splined joint or other known joining process. In addition, motor rotor  70  may include a face  72  oriented substantially orthogonal to the axial direction of output shaft  50 . Pump rotor  66  and motor rotor  70  may be respectively supported relative to housing  26  via shafts  55 ,  57  (see  FIG. 4 ) and one or more bearings (not shown). 
     Pump  40  and motor  42  may each include numerous components that interact to direct fluid between first and second fluid passages  44 ,  46 . For example, pump  40  and motor  42  may each include a plurality of piston members  74  respectively connected to faces  68 ,  72  of pump and motor rotors  66 ,  70 . Pump  40  and motor  42  may also each include a plurality of drum sleeves  76 , such that each piston member  74  interacts with a corresponding drum sleeve  76  to form a chamber  78 . 
     Each of drum sleeves  76 , associated with piston members  74  extending from face  68 , may be connected to a drum plate  80 . Each of drum sleeves  76 , associated with piston members  74  extending from face  72 , may be connected to a drum plate  82 . Drum plate  80  may be inclined relative to input shaft  48  and may be configured to rotate therewith. Drum plate  82  may be inclined relative to output shaft  50  and may be configured to rotate therewith. As will be explained in more detail below, the tilt angle of drum plate  80  with respect to input shaft  48  may be adjustable, and the tilt angle of drum plate  82  may or may not be adjustable with respect to output shaft  50 . As input shaft  48  and drum plate  80  rotate piston members  74  may move into and out of drum sleeves  76  as a function of the tilt angle thereof, thereby changing the volume of chambers  78 . Similarly, as output shaft  50  and drum plate  82  rotate, piston members  74  may move into and out of drum sleeves  76  as a function of the tilt angle thereof, thereby changing the volume of chambers  78 . 
     As illustrated in  FIG. 5 , each piston member  74  may have a body portion  84  for securing piston member  74  to either face  68  of pump rotor  66  (as shown in  FIG. 5 ) or face  72  of motor rotor  70 . Body portion  84  may be sized and shaped so that no part of body portion  84  may come into contact with drum sleeve  76  as piston member  74  slides in and out of drum sleeve  76 . In addition, body portion  84  may be integral to face  68  of pump rotor  66  (or face  72  of motor rotor  70 ) or, alternatively, joined to face  68  of pump rotor  66  (or face  72  of motor rotor  70 ) through welding, sintering, or other known joining process 
     Each piston member  74  may also have an interfacing portion  86  connected to body portion  84  and having an outer surface  88  in sliding contact with an inner wall  89  of drum sleeve  76 . The portion of contact surface  88  interfacing with inner wall  89  may form a seal  90 , which may substantially prevent fluid from leaking out of chamber  78  in the direction of pump rotor  66  or motor rotor  70  (see  FIGS. 3 and 4 ). Furthermore, outer surface  88  may be shaped so that seal  90  may be substantially perpendicular to a longitudinal axis  92  of drum sleeve  76  regardless of the position of piston member  74  relative to drum sleeve  76 , i.e., regardless of the tilt angle of either drum plate  80  or drum plate  82 . For example, outer surface  88  may be substantially shaped like a partial sphere, i.e., may include a substantially frustro-spherical shape. It is contemplated that outer surface  88  may contact inner wall  89  at a line contact, which may minimize frictional forces resulting from the interaction between piston member  74  and an associated drum sleeve  76 . It is also contemplated that each piston member  74  may, additionally or alternatively, include a piston ring disposed within interfacing portion  86  and configured to engage inner wall  89  of an associated drum sleeve  76 . 
       FIG. 5  also illustrates an exemplary embodiment of the cross-sectional area of interfacing portion  86 . Interfacing portion  86  may have its maximum cross-sectional area at a location between a first end  94  thereof, furthest from body portion  84 , and a second end  96  thereof adjacent to body portion  84 . It is contemplated that the location of maximum cross-sectional area may be located at a midpoint between first and second ends  94 ,  96 . Body portion  84  may include a relatively larger cross-sectional area at a location adjacent to second end  96  and a relatively smaller cross-sectional area at a location adjacent to plate  68  (as shown in  FIG. 5 ) or plate  70 . As such, piston member  74  may only contact an associated drum sleeve  76  within interfacing portion  86 . 
     Referring back to  FIGS. 3 and 4 , pump  40  and motor  42  may also respectively include face plates  110 ,  112 . Face plate  110  may include a first plurality of distribution passages  102  in fluid communication with first fluid passage  44  and a second plurality of distribution passages  106  in fluid communication with second fluid passage  46 . Face plate  112  may include a first plurality of distribution passages  104  in fluid communication with first fluid passage  44  and a second plurality of distribution passages  108  in fluid communication with second fluid passage  46 . Face plates  110 ,  112  may be fixed with respect to the relative rotation of input and output shafts  48 ,  50  and drum plates  80 ,  82 . As drum plate  80  rotates, distribution holes  98  formed in drum plate  80 , may selectively be in fluid communication with the first plurality of distribution passages  102  or the second plurality of distribution passages  106  of face plate  110 . As drum plate  82  rotates, distribution holes  100  formed in drum plate  82 , may selectively be in fluid communication with the first plurality of passages  104  or the second plurality of distribution passages  108  of face plate  112 . It is contemplated that first and second passages  44 ,  46  may be in fluid communication with approximately half of distribution holes  98 ,  100  via the respective pluralities of distribution passages  102 ,  104 ,  106 ,  108  at any given rotation of input and output shafts  48 ,  50 . 
     Drum plates  80 ,  82  may be inclined with respect to the rotational axes of input and output shafts  48 ,  50  at respective angles β 1 , β 2 . Because of the assembled relationship between face plates  110 ,  112  (which are fixed with respect to the rotation of input and output shafts  48 ,  50 ), drum plates  80 ,  82  (which rotate with input and output shafts  48 ,  50 ), and rotors  66 ,  70  (which also rotate with input and output shafts  48 ,  50 ), piston members  74  may slidingly reciprocate within associated drum sleeves  76 . That is, the rotational movement of input shaft  48  and drum plate  80  may cause the volume of chambers  78  associated with pump  40  and motor  42  to selectively increase and decrease as a function of the respective tilt angle of drum plates  80 ,  82 . The increasing volumes may reduce pressure in chambers  78 , thereby drawing fluid from one of first or second fluid passages  44 ,  46  via a plurality of distribution holes  98  in drum plate  80  or a plurality of distribution holes  100  in drum plate  82 . The decreasing volumes may increase the pressure in chambers  78  thereby forcing fluid into the other one of first and second fluid passages  44 ,  46 . As such, the respective angles β 1 , β 2  may correspond to the volume change of chambers  78  as is known in the art. Furthermore, angle β 1  associated with pump  40  may be different from angle β 2  associated with motor  42 , such that the volume change of chambers  78  associated with pump  40  during a single revolution of pump rotor  66  may be different than the volume change of chambers  78  associated with motor  42  during a similar revolution of motor rotor  70 . 
     To generate a continuously variable output, the displacement settings of pump  40  may be varied. A variable displacement actuator  114 , e.g., a swashplate, may be used to adjust the displacement settings of pump  40 . Variable displacement actuator  114  may include components that adjust angle β 1  of face plate  110  and subsequently the volume change of chambers  78  associated with pump  40 . Specifically, variable displacement actuator  114  may include one or more pistons  116  that may directly or indirectly press against a portion of face plate  110  to urge face plate  110  to tilt relative to the axial direction of input shaft  48 . Pistons  116  may be hydraulically actuated, pneumatically actuated, electrically actuated, or actuated in any other known manner such that face plate  110 , and thus drum plate  80  and pump rotor  66 , may be tilted to a specific desired tilt angle corresponding to a desired characteristic (e.g. flow rate and/or pressure) of the resulting flow of pressurized fluid through first and second fluid passages  44 ,  46 . It is contemplated that angle β 2  may or may not be variable and, if so, may similarly include a variable displacement actuator. It is also contemplated that tilt angle β 1 , may be in a neutral position when perpendicular to the axis of input shaft  48 , may be adjusted in a first direction with respect to being perpendicular so as to supply pressurized fluid to first fluid passage  44  and draw pressurized fluid from second fluid passage  46 , and may be adjusted in a second direction with respect to being perpendicular to supply pressurized fluid to second fluid passage  46  and draw pressurized fluid from first fluid passage  44 . 
       FIG. 6  illustrates another exemplary embodiment of hydrostatic portion  26 . The exemplary embodiment illustrated in  FIG. 6  may include similar components as the exemplary embodiment illustrated in  FIGS. 3 and 4 . However, pump rotor  66  and associated piston members  74  may be located at first axial end  58  of housing  52 . In addition motor rotor  70  and associated piston members  74  may be located at second axial end  60 . Furthermore, drum plates  80 ,  82  and drum sleeves  76  may be positioned at a central location within housing  52 . Such a configuration may reduce the distance between distribution passages  102  and  104  as well as the distance between distribution passages  106  and  108 . This may shorten the lengths of first and second fluid passages  44  and  46 . The shortened passages may reduce the volume of fluid used by hydrostatic portion  26 . In addition, frictional losses associated with first and second fluid passages  44 ,  46  may be reduced. 
     INDUSTRIAL APPLICABILITY  
     The disclosed hydro-mechanical transmission may be applicable for any type of machine performing operations requiring a continuously variable output from the transmission. In particular, the interaction between piston members  74  and drum sleeves  76  may improve the efficiency and durability of the transmission, thereby increasing the variety of environments and applications in which the transmission may be used. 
     The interaction between each piston member  74  and an associated drum sleeve  76  may create a fluid seal  90  that is substantially perpendicular to the axis  92  of an associated drum sleeve  76 . Such an interaction may substantially prevent the hydrostatic forces in the axial direction thereof from becoming unbalanced, which may minimize the portion of pressure energy wasted as frictional losses by the rotor coupled to the respective piston member. In addition, because the hydrostatic forces in the axial direction may be substantially balanced, stresses acting on the connection between the piston member and the rotor may be minimized. Therefore, the efficiency and durability of the transmission may be increased. Furthermore, minimizing the interface between each piston member and the associated drum sleeve may reduce frictional losses which may further improve the efficiency of the transmission. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed system without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.