Abstract:
A hydrostatic transmission including a variable displacement pump including an input shaft and a pump cylinder barrel rotatably coupled to the input shaft, the pump cylinder barrel having a plurality of cylinder chambers arranged in parallel with other and distributed about the input shaft axis of rotation. Each cylinder chamber has a reciprocating piston therein which bears against a pivotable swashplate, the displacement of the pump being varied in response to changes in the position of the swashplate. A gerotor motor is attached to the pump and has an output shaft. The motor includes an engaged pair of inner and outer members, the outer member being eccentric relative to the inner member. The inner member is rotatably driven relative to the outer member by fluid received between the inner and outer members from the pump, the inner member being drivingly connected to the output shaft. A plurality of fluid conduits extend between the pump to the motor, through which the motor is in fluid communication with the pump.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60/314,030, filed Aug. 21, 2001 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to hydrostatic transmissions for use in lawn and garden implements, such as, for example, wide area and zero turn radius mowers, and garden tractors.  
           [0004]    2. Description of the Related Art  
           [0005]    The use of hydrostatic transmissions including a system of communicating hydrostatic pumps and motors in lawn and garden implements is well-known with such hydrostatic systems often providing ease of control and component replacement. One prior art transmission, the Model 778 by Eaton Corporation, utilizes a ball piston pump and ball piston motor combination, and a set of double planetary reduction gears. Such reduction gearing usually requires additional moving parts which add cost and complexity to the hydrostatic transmission, could malfunction, and require packaging space within the transmission. Furthermore, the use of ball piston pumps and ball piston motors adds to the cost and complexity of the transmission, thereby increasing the cost and complexity of the implement in which the transmission is used. Additionally, the ball piston pump and ball piston motor combination is rather large, thereby failing to provide packaging flexibility desired by many manufacturers.  
           [0006]    To solve the problem of a lack of packaging flexibility, other prior art transmissions use external hoses or tubes to allow fluid movement between the motor and the pump, as well as to and from the sump. However, the connection of the external hoses or tubes to the motor, pump, and sump creates junctions from which the fluid could easily leak, since those junctions may not have a tight seal between the hose and the motor, pump, or sump. An example of the problems resulting from such leakage is found when the prior art transmissions are used in a riding greens mower, which are typically used to maintain golf course greens. If the mower has connections that leak, the fluid may drip onto the green surface, thereby destroying a portion of the golf course green and requiring possibly thousands of dollars in repairs. Additional problems with the prior art transmissions and the leaking connections is the loss of fluid, thereby potentially allowing the operator to operate a hydrostatic transmission with low fluid levels and causing damage to the hydrostatic transmission. Thus, a hydrostatic transmission, which would minimize the connections, thereby minimizing the possibility of leaks therefrom, is desirable.  
           [0007]    In response to the problem with leakage from the connections between the hoses or tubes and the transmission, prior art integrated hydrostatic transmissions were created which generally prevent leakage of fluid; however, these transmissions have the same problem as the Model 778 transmission, described above, in that they are rather large, expensive, and complex. Like the Model 778 transmission, the previous integrated transmissions cause the vehicles to be more expensive, more complex, and much larger to accommodate the transmission. Additionally, previous integrated hydrostatic transmissions may include reduction gearing, further increasing the cost and complexity of the transmission, as described above. Thus, prior art transmissions may solve one problem, that of leakage or the large size and lack of packaging flexibility, but not the other.  
           [0008]    An additional problem experienced with some previous transmissions is that they were designed and manufactured differently to fit either a horizontal or a vertical shaft engine; a common transmission often could not be coupled to both types of engines. This inflexibility creates greater expense for the original equipment manufacturer (OEM) since the prior art hydrostatic transmissions may be used with only one type of engine, thereby requiring an OEM to have a supply of transmissions which work only with vertical shaft engines and a supply of transmissions which only work with horizontal shaft engines. Alternatively, the OEM may be limited to using only one type of engine in the lawn and garden products.  
           [0009]    What would be desirable is a hydrostatic pump and motor system which is inexpensive and compact in design, and yet provides the flexibility of usage with a horizontal or vertical crankshaft engine. A hydrostatic pump and motor system which minimizes leakage and enables multiplication of torque and speed reduction without the use of reduction gearing is also desirable. Inclusion of a differential in such a pump and motor system would also be desirable.  
         SUMMARY OF THE INVENTION  
         [0010]    In overcoming the problems of the prior art designs, the present invention provides a hydrostatic transmission which is inexpensive and compact in design since no reduction gearing is required, and which minimizes leakage since no additional hoses or tubes are required to connect the pump to the motor. Furthermore, the inventive transmission is modular and may be rotated 90° to accommodate either a vertical shaft or a horizontal shaft engine, thereby providing flexibility lacking in prior art transmissions.  
           [0011]    The present invention provides a hydrostatic transmission including a variable displacement pump including an input shaft and a pump cylinder barrel rotatably coupled to the input shaft, the pump cylinder barrel having a plurality of cylinder chambers arranged in parallel with other and distributed about the input shaft axis of rotation. Each cylinder chamber has a reciprocating piston therein which bears against a pivotable swashplate, the displacement of the pump being varied in response to changes in the position of the swashplate. A gerotor motor is attached to the pump and has an output shaft. The motor includes an engaged pair of inner and outer members, the outer member being eccentric relative to the inner member. The inner member is rotatably driven relative to the outer member by fluid received between the inner and outer members from the pump, the inner member being drivingly connected to the output shaft. A plurality of fluid conduits extend between the pump to the motor, through which the motor is in fluid communication with the pump.  
           [0012]    The present invention also provides for the orientation of the transmission during operation to be with its input shaft rotational axis being substantially vertical and its output shaft rotational axis being substantially horizontal, its input shaft rotational axis being substantially horizontal and its output shaft being substantially horizontal, or its input shaft rotational axis being substantially horizontal and its output shaft rotational axis being substantially vertical. Thus, the present invention provides a transmission which facilitates packaging flexibility.  
           [0013]    The present invention also provides for its motor to be one of a plurality of interchangeable motors having different inner member lengths, the displacement of each interchangeable motor being different. Speed reduction between the pump&#39;s input shaft and the motor&#39;s output shaft may thus be altered by assembling a different one of the interchangeable motors to the pump.  
           [0014]    The present invention further includes an axle housing attached to the pump and motor, the axle housing having an axle rotatably disposed therein which is operatively coupled to the motor output shaft. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The above mentioned and other features and objects of this invention will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:  
         [0016]    [0016]FIG. 1 is a side view of a first embodiment of the inventive transmission;  
         [0017]    [0017]FIG. 2 is a top view of the transmission of FIG. 1;  
         [0018]    [0018]FIG. 3 is a top view of the center section of the transmission of FIG. 2;  
         [0019]    [0019]FIG. 4 is a front view of the transmission of FIG. 2;  
         [0020]    [0020]FIG. 5 is a top view of an alternative embodiment of the inventive transmission of FIG. 1;  
         [0021]    [0021]FIG. 6 is a sectional view of the motor of the transmission of FIG. 2 along line  6 - 6 , the motor being shown without the motor mounting surface;  
         [0022]    [0022]FIG. 7 is a view of the geroller stator and rotor of the motor of FIG. 6;  
         [0023]    [0023]FIG. 8 is a view of a zero turn radius mower having a pair of the inventive transmissions therein;  
         [0024]    [0024]FIG. 9 is a top view of a transaxle incorporating the inventive transmission of FIG. 1, the transmission being attached to an axle housing;  
         [0025]    [0025]FIG. 10 is a side view of the transaxle of FIG. 9; and  
         [0026]    [0026]FIG. 11 is a view of a tractor having the inventive transaxle of FIG. 9 therein. 
     
    
       [0027]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.  
       DETAILED DESCRIPTION  
       [0028]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.  
         [0029]    Referring first to FIG. 1, inventive transmission  34  is shown in a side view. Transmission  34  includes pulley  36  and fan  38  keyed to input shaft  40  of pump  56  through key  42 . Pulley  36  is in communication with the engine of an implement such as, for example, the mower of FIG. 8 or the garden tractor of FIG. 11, to provide drive input to pump  56 . Pump  56 , which is an axial piston pump, is disposed within housing  50  of transmission  34 . Pump  56  includes a plurality of axially aligned cylindrical chambers with a reciprocating piston disposed in each chamber, as is known in the art. Such a pump is disclosed, for example, in U.S. Pat. Nos. 6,301,885, issued Oct. 6, 2001, 6,378,300, issued Apr. 30, 2002, and 6,422,109, issued Jul. 23, 2002, all of which are assigned to the assignee of the present invention, the complete disclosures of which are all expressly incorporated herein by reference. Included in housing  50  is flange  64  which extends beyond the outer edges of housing  50 . Attached to housing  50 , motor mounting surface  52  has a plurality of bores  54  for receipt of a plurality of bolts when a hydrostatic motor is mounted thereto.  
         [0030]    Attached to exterior of housing  50  of transmission  34  is fluid reservoir  46  having opening  44  through which fluid may be poured. A cap (not shown) is sealably closed onto opening  44 . Fluid reservoir  46  serves to maintain a constant quantity of fluid moving throughout the fluid system of transmission  34 , as is known in the art. Check valve  48  is located between the fluid system of transmission  34  and reservoir  46  to prevent fluid from entering reservoir  46  from the fluid circuit. The fluid system of transmission  34  includes two conduits or passages  58  and  60  from pump  56 , which will be fluidly connected to a motor when the motor is mounted to motor mounting surface  52 , such that displacement of fluid by pump  56  will force the fluid through passages  58  or  60  to the motor. The fluid system further includes passage  62  from passages  58  and  60  to valve  48 . The displacement of pump  56 , and which of fluid passages  58  and  60  fluid flows from the pump, is controlled by varying the angle of a swashplate assembly by rotating a control, or shift, lever attached to pump control shaft  72  (FIG. 2), as is known in the art. The direction of rotation in which the motor is driven is dependent upon which of passages  58  and  60  fluid flows through from the pump to the motor. The rate at which the pumped fluid flows through the motor determines the speed of the motor.  
         [0031]    With reference to FIG. 2, a top view of transmission  34  is shown. Flange  64  further includes central bore  74  for receipt of pump input shaft  40 . Further shown in this view, motor  66  has been attached to motor mounting surface  52  to provide a complete hydrostatic transmission  34 . It is to be noted that passages  58  and  60  for fluid communication with motor  66  are curved in a 90° angle. Such casting may be done through one of a variety of known methods such as lost wax casting, sand casting or others. With the use of the conduits or passages in housing  50  of transmission  34 , no hoses or tubes are needed to provide fluid communication between pump  56  and motor  66 . Rather, motor  66  is directly mounted to motor mounting surface  52  thus placing pump  56  and motor  66  in fluid communication through passages  58  and  60 , without the need for any additional or external tubing. If external tubing were to be used, leaks could occur at the junctions of the tubing and the pump and motor. However, such leaks are prevented as fluid flow occurs through the cast passages. Also shown at the respective ends of passages  58  and  60  are openings  68  and  70  which provide the direct fluid communication to motor  66 .  
         [0032]    Straight passages  58 ′ and  60 ′ of the embodiment of transmission  34 , shown in FIG. 5, are cast or bored at approximately a 45° angle, relative to the front of transmission  34 , from pump  56  to motor  66 . Again with the 45° angle structure, no hoses or tubes are required and these passages may be cast within the housing of transmission  34 . In either the embodiment with the curved 90° angle fluid passages  58  and  60 , or the embodiment with the 45° angle fluid passages  58 ′ and  60 ′, hydrostatic fluid is passed between pump  56  and motor  66  for operation through these passages.  
         [0033]    With reference to FIG. 3, a view of center section  51  of transmission  34  is provided, and as such, pump  56 , motor mounting surface  52 , and motor  66  have been removed. Pump mounting surface  80  includes arcuate openings  82  and  84 , as is generally known in the art, through which fluid flows to or from pump  56  through passages  58  and  60 . Bore  86  is included in pump mounting surface  80  to allow insertion of pump input shaft  40 . On the underside of pump mounting surface  80  are two passages  76  and  78  in communication with passages  58  and  60 , respectively. In operation, pump  56  is mounted on pump mounting surface  80  and movement of a swash plate assembly (not shown) displaces fluid through arcuate openings  82  or  84  into passages  76  or  78 . From passages  76  or  78 , the fluid travels through passages  58  or  60 , through openings  68  or  70 , to motor  66  for operation of motor  66 .  
         [0034]    Referring now to FIG. 4, a front view of transmission  34  is shown with both pump  56  and motor  66  attached. The operation of the swash plate assembly would be done in a known manner, whereby movement of the shift lever would cause the swash plate to pivot in either a forward or reverse direction. This movement causes the fluid in the fluid system of transmission  34  to move in a manner to convey a driving force to motor  66  in either the forward or reverse direction with varying the pressure of the fluid changing the output speed of the transmission.  
         [0035]    Referring now to FIGS. 6 and 7, a view of motor  66  and a perspective view of a section of motor  66  are shown. Motor  66  is a low speed, high torque motor, such as those disclosed in U.S. Pat. Nos. 4,545,748 and 4,699,577, assigned to Parker-Hannifin Corporation, the complete disclosures of which are expressly incorporated herein by reference. Motor  66  may also be the commercially available TC Series Motor of the Torqlink™ Series of motors, available from Parker-Hannifin Corporation of Greeneville, Tenn. Alternatively, motor  66  may be a motor such as that disclosed in U.S. Pat. No. 6,086,344, assigned to White Hydraulics, Inc, the complete disclosure of which is expressly incorporated herein by reference, or a commercially available RS or HB Series Motor, available from White Hydraulics, Inc. of Hopkinsville, Ky.  
         [0036]    Motor  66  includes casing  67  and has at least one bore  124  therein for mounting of motor  66  to motor mounting surface  52 . Further included in motor  66 , specifically in first section  66   a , is outer member or stator  118  having inner member or rotor  120  rotatably disposed therein. Stator  118  also includes rollers  122  which rotor  120  engages as rotor  120  rotates about axis  119  of stator  118 . Such a structure may be the Roller Stator®, which is produced by White Hydraulics, Inc. of Hopkinsville, Ky., or another suitable geroller type of gerotor device. Alternatively, motor  66  may comprise a gerotor device that does not include rollers  122 .  
         [0037]    In first section  66   a  of motor  66  is wobble or “dog bone” shaft  116  which is fixedly engaged with rotor  120  through the intermeshing of teeth  115  and  117 . Wobble shaft  116  further extends into second section  66   b  of motor  66  where it engages output shaft  128  through the intermeshing of teeth  130  and  132 . Pressurized fluid flows from pump  56  and enters motor  66 , specifically first section  66   a , where it flows into varying size chambers  126  and causes rotor  120  to orbit about common axis  119  of stator  118  and output shaft  128  and to abut rollers  122  during the orbital motion. Through engagement with rotor  120 , one end of wobble shaft  116 , is orbiting axis  119  causing the other end to rotate, thereby rotating output shaft  128 . Therefore, the orbital motion of rotor  120  is converted by the wobble shaft  116  into rotational motion of the output shaft  128 . Output shaft  128  may serve as an axle, or drive a differential as described below.  
         [0038]    It is to be noted that the length of motor  66  may be varied and the volume of cells  126  increased or decreased, thereby requiring more or less fluid from the fluid system to rotate motor  66 . When more fluid is needed to rotate motor  66 , more work is required, thus the input speed from input shaft  40  is greater than the axle speed resulting in speed reduction. When the volume of cells  126  is decreased, less fluid is used and the speed reduction will be decreased. Thus, by adjusting the length of motor  60 , and in particular the axial lengths of outer and inner members  118 ,  120 , an adjustment in the volume of cells  126  results. The speed reduction ratio between the input speed and the output speed at the axle may thus be adjusted to a desired ratio without the use of reduction gearing. One of ordinary skill in the art will now appreciate that different ones of a plurality of motors  60  having various length outer and inner members  118 ,  120  can be assembled to the pump to alter the speed reduction between the pump input shaft and the motor output shaft.  
         [0039]    It is further to be noted that as input shaft  40  of pump  56  is at a 90° angle to the output shaft  128 , transmission  34  may be rotated 90° to accommodate either a vertical shaft engine or a horizontal shaft engine.  
         [0040]    With reference to FIG. 8, zero turn radius mower  22  is shown as having a plurality of ground engaging wheels  24  and mower deck  26  mounted to the underside of the mower frame. Zero turn radius mower  22  utilizes two transmissions  34 , each having an independent control mechanism  32  and associated with separate axles  30 . Furthermore, each transmission  34  engages a separate axle  30  that is connected to a ground engaging wheel  24 .  
         [0041]    Although not shown, zero turn radius mower  22  may instead be a greens mower and utilize three separate motors  66  associated with each wheel  24  and a single pump, similar to pump  56 , for all three motors  66  in place of a pump for each motor, as in the zero turn radius mower. The third wheel, at the rear of the mower, would be the drive wheel and would be moved by a control mechanism, such as a steering wheel, associated with the mower. Since the three motors  66 , associated with the three wheels, share a common pump, all would be driven at the same speed and through the action of the rear drive wheel would move in the same direction.  
         [0042]    Referring now to FIG. 9, a view of inventive transmission  34  is shown as a part of transaxle  35 . Transmission  34  is connected to axle housing  92 , which has two halves  93  and  108 , to provide transaxle  35  as shown. As in the previously described embodiment, pump  56  is included and has flange  64  with bore  74  therein and pump control shaft  72  for attachment of a shift lever. Like motor  66 , motor  66 ′ is attached to motor mounting surface  52  through bolts  110  and is in fluid communication with pump  56 ; however, motor  66 ′ differs from motor  66  of the previous embodiments in that bevel gear  98 , rather than output shaft  128 , extends therefrom. Bevel gear  98  has a portion within motor  66 ′ (not shown) engaging wobble shaft  116  and intermeshes with another bevel gear  100  disposed within axle housing  92  and connected to differential housing  104  through bolts  112 .  
         [0043]    Within differential housing  104  is differential mechanism  102 , which is of the type known in the art and is used to drive two axle portions  30   a  and  30   b  extending therefrom. Each axle portion  30   a  and  30   b  is supported by a boss  106 , one of which is in each respective casing half  93  and  108 . Axle portions  30   a  and  30   b  are further supported by casing  96  which is mounted to each respective casing half  93  and  108  by bolts  114 . In operation, when pump  56  operates motor  66 ′, bevel gear  98  rotates, thereby rotating bevel gear  100  to cause differential mechanism  102  to operate in a known manner and drive axles  30   a  and  30   b.    
         [0044]    With reference to FIG. 10, a side view of transaxle  35  of FIG. 9 is shown. as can be seen, housing  92  requires a plurality of bolts to connect halves  93  and  108  together. It is also to be noted with reference to FIG. 10 that with transmission  34  connected to axle housing  92  to create transaxle  35 , transaxle  35 , like transmission  34 , is compact in size.  
         [0045]    Referring to FIG. 11, garden tractor  20  is shown as having engine  28  and transaxle  35  mounted in the frame of garden tractor  20 . Garden tractor  20  further includes two pairs of ground engaging wheels  24  and mower deck  26  mounted on the underside of tractor  20 . At the rear of garden tractor  20  is located transaxle  35  which drives two rear ground engaging wheels  24 . Transaxle  35  is controlled by a single control lever  32  which engages the swash plate of pump  56  to vary the direction of motion and the speed of the transaxle.  
         [0046]    While this invention has been described as having exemplary structures, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.