Abstract:
A hydraulic axle combination includes a housing having first and second pump chambers containing spaced, axially aligned, first and second hydrostatic pumps with respective pump shafts and input gears; first and second hydraulic motors connected with respective first and second pumps via intermediate manifold blocks thereby enabling closed-loop internal drive systems between the associated pumps and motors and forming first and second independent hydrostatic transmissions wherein the hydraulic motor output shafts serve as first and second axle shafts; an input shaft, extending between the two transmissions, includes a gear for supplying torque to and meshing perpendicularly with the pump shaft input gears and forming, therewith a T-shaped gear box, the housing optionally including: an internal sump serving as an integral combination fluid reservoir for the axle combination, at least one breather cap, a fluid filter assembly and a drain port and plug, all mounted in various housing sides.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 60/676,384, filed Apr. 29, 2005, the disclosure of which is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention pertains to a hydraulic axle combination or transaxle assembly that utilizes spaced, axially aligned, independent hydrostatic transmissions each having respective pump portions thereof located in a housing and having axially aligned hydrostatic pumps operatively interconnected with respective hydraulic motors, where in the motor output shafts serve as opposed axle shafts. An input shaft extending into the housing between the transmissions includes an input gear for supplying torque meshing perpendicularly with opposed pump input shaft gears and forming therewith a T-shaped gear box. Housing options include an integral internal fluid reservoir at least one breather cap, a fluid filter assembly as well as a drain port and plug. 
   BACKGROUND OF THE INVENTION 
   The hydraulic axle combinations of the present invention are, for example, utilized in powered, wheeled, drive units that typically find utility in known, zero-turn-radius (ZTR) vehicles. Such a ZTR vehicle often takes the form of a grass or lawn mowing machine having at least one cutting blade. A ZTR vehicle utilizes a single prime mover or engine that drives a separate, independent transmission for each of its left and right side rear driving wheels. Independent front left and right side wheels are usually caster-type wheels that are free to pivot about their vertical clevis axes, in a manner well known in the art. Today, most commercial ZTR machines are driven by separate, dual, hydrostatic transmissions, for left and right driven wheels. Each such transmission preferably includes its own closed-loop circuit and both transmissions function independently and can, for example, be operated or controlled via their human operator-actuated right and left control levers. In one such mode of operation, each of control levers is linked to a respective trunnion shaft of an associated hydraulic pump and enables the operator to control the direction and amount of fluid flow from each transmission pump. When the operator pushes a lever in one direction, the associated pump delivers fluid flow in one direction of corresponding motor operation. When the operator pushes the lever in the opposite direction, the associated pump delivers fluid flow in the opposite direction of corresponding motor operation. Thus, the use of dual hydrostatic transmissions permits the zero-turn-radius features of these vehicles, which is an important feature, particularly in commercial mowers. 
   The patent literature includes a large number of designs and structures pertaining to hydraulic axle combinations and hydraulic transaxles, including but not limited to the following: U.S. Pat. No. 2,780,424 to Price; U.S. Pat. No. 2,996,135 to Grabow; U.S. Pat. No. 4,280,579 to Zaunberger et al.; U.S. Pat. No. 6,182,784B1 to Pestonik; U.S. Pat. No. 6,457,560B1 to Evans et al.; U.S. Pat. No. 6,705,840B1 to Hauser et al.; and U.S. Pat. No. 6,843,056B1 to Langenfeld et al., some of which will be discussed hereinafter. U.S. Pat. No. 2,780,424 merely shows an application for a “T” gearbox to drive a mechanical system, while U.S. Pat. No. 4,280,579 discloses a control for a tracked vehicle steering system comprised of discrete separate components that also include additional gear reducers that are not required in the structures of the present invention due to its usage of low speed, large displacement, high torque gerotor orbital motors in a purely hydrostatic transmission. U.S. Pat. No. 6,182,784 discloses a drive train that uses a “T” gearbox to drive both axles at the same speed whereas, in the structure of the present invention, a “T” gearbox is used to drive two independent hydrostatic pumps, with each pump being coupled with a hydraulic motor whose output shaft functions as an axle to drive a wheel, thus permitting the two axles to rotate at differing speeds and even in opposite directions, if so desired. U.S. Pat. No. 6,457,560B1 pertains to a gearbox oil pumping system associated with a riding mower, showing a plurality of individual oil conduits connecting dual oil pumps to dual fluid motors as well as an oil radiator, an oil reservoir and dual oil filters. U.S. Pat. No. 6,705,840B1 discloses several embodiments of an inline tandem pump apparatus having a pair of coaxially arranged pump shafts and a separate input shaft that is not coaxial with the pump shafts. The pump outputs are connected to remote hydraulic motors. U.S. Pat. No. 6,843,056B1 pertains to a zero turn transaxle comprised of a hydraulic transmission having a pair of hydraulic pumps connected with axially offset hydraulic motors that drive output axles. However, none of these prior art structures teach or suggest the structural and functional features of the present invention. 
   SUMMARY OF THE INVENTION 
   Accordingly, in order to overcome the deficiencies of the prior art devices, the present invention provides a single unit design and structure of a hydrostatic transaxle including two hydrostatic pumps, two hydraulic motors and a “T” gearbox wherein only one input shaft is used to receive power from a prime mower, operating at high speed and two output shafts are used to drive left and right side wheels at a much lower speed. 
   Specifically, one embodiment of this invention pertains to a hydraulic axle combination comprising: a. a housing having a first pump chamber and a second pump chamber; b. a first hydrostatic pump, having a first pump shaft, rotatably mounted within the first pump chamber; c. a second hydrostatic pump, having a second pump shaft, rotatably mounted within the second pump chamber; d. an input shaft, mounted in and extending into the housing, having a gear, mounted on an intermediate portion thereof, supplying torque to an intermeshing input gear mounted on one end of each of the first and second pump shafts; e. a first hydraulic motor in operative interconnection with the first hydrostatic pump; f. a second hydraulic motor in operative interconnection with the second hydrostatic pump; and g. each of the first and second hydraulic motors including a respective first and second coaxial, rotatably journalled, output shaft, the first and second output shafts serving as respective first and second axle shafts. 
   In one version thereof, each of the operative interconnections includes a respective manifold block structurally and operatively interposed between its associated hydrostatic pump and hydraulic motor, thereby enabling a closed-loop drive system between the associated hydrostatic pumps and hydraulic motors. In a variation thereof, the first hydrostatic pump, together with the first hydraulic motor and their associated manifold block, forms a first, independent hydrostatic transmission. In another variation thereof, the second hydrostatic pump, together with the second hydraulic motor and their associated manifold block, forms a second, independent hydrostatic transmission. In a further variation thereof, the first and second, independent transmissions are substantially similar, coaxial, mirror-image versions of each other. In an additional variation thereof, the input shaft gear is perpendicular to and intermeshes with the input gears and together therewith forms a T-shaped gear box, the gear box being operatively and physically interposed between the first and second independent hydrostatic transmissions and together therewith comprising the hydraulic axle combination. 
   In another version thereof, the first and second pump shafts are perpendicular to the input shaft. 
   In a differing version thereof, the first and second pump shafts are coaxially aligned. 
   In a further version thereof, the housing includes an integral sump, the sump serving as a single, internal, combination fluid reservoir for the first and second hydrostatic pumps as well as the first and second hydraulic motors. A further variation includes at last one case drain port and plug in a bottom side of the housing. An additional variation thereof includes at least one breather cap in a top side of the housing. 
   A still further variation thereof includes a fluid filter assembly operatively interconnected with the sump at a rear side of the housing. 
   A yet additional version thereof further includes a charge pump, mounted on a distal end of the input shaft, operatively interconnected with at least one of the first and second hydrostatic pumps. In a variation thereof, the charge pump is mounted on a bottom side of the housing. 
   In an added version, a top side of the housing includes a cover, with the input shaft extending into the housing through the cover. 
   In yet another added version, each of the first and second hydraulic motors takes the form of a gerotor-type orbital motor. In a variation thereof, the gerotor-type motor is an externally generated gerotor motor. 
   In a still differing version, the input shaft gear is perpendicular to the intermeshing input gears and together therewith forms a T-shaped gear box, with the gear box being physically located intermediate the first and second pumps. 
   Another differing version further includes at least one breather cap in a top side of the housing. 
   A still further version further includes, on a top side of the housing, a plurality of spaced attachment bosses, for attaching the axle combination to a chassis member of a powered, wheeled, drive unit. In a variation thereof, the chassis member includes a plurality of apertures corresponding in location to the plurality of attachment bosses and a plurality of fastening members for uniting the hydraulic axle combination with the chassis member. 
   A further embodiment of this invention pertains to a hydraulic transaxle assembly comprising in combination: a. a central housing having opposed, spaced, axially aligned, first and second pump chambers; b. a first hydrostatic pump, having a first pump shaft, operatively mounted in the first pump chamber; c. a first hydraulic motor axially aligned with and in operative as well as structural interconnection with the first hydrostatic pump, the first hydraulic motor including a first rotatable, coaxial, output shaft serving as a first axle shaft; d. a first manifold block structurally and operatively interposed between the first hydrostatic pump and the first hydraulic motor and together therewith enabling a first closed-loop drive system and forming a first, independent, hydrostatic transmission; e. a second hydrostatic pump, having a second pump shaft, operatively mounted in the second pump chamber; f. a second hydraulic motor axially aligned with and in operative as well as structural interconnection with the second hydrostatic pump, the second hydraulic motor including a second rotatable, coaxial, output shaft serving as a second axle shaft; g. a second manifold block structurally and operatively interposed between the second hydrostatic pump and the second hydraulic motor and together therewith enabling a second closed-loop drive system and forming a second, independent, hydrostatic transmission; and h. an input shaft, mounted in and extending into the housing between the first and second hydrostatic pumps, including a gear mounted on an intermediate portion thereof, supplying torque to and perpendicularly intermeshing with the first and second input gears mounted on respective ones of the first and second pump shafts and forming therewith a T-shaped gear box, the gear box, together with the first and second, independent hydrostatic transmissions comprising the hydraulic transaxle assembly. 
   In one version thereof, the first and second, independent, transmissions are substantially similar, coaxial, mirror-image versions of each other. 
   In another version thereof, the central housing includes an integral, internal sump The sump serves as a single, integral, combination fluid reservoir for at least the first and second hydrostatic transmissions. One variation thereof further includes at least one drain port and plug in the integral sump in a bottom side of the housing. Another variation thereof further includes at least one breather cap in a top side of the housing. A further variation thereof further includes a fluid filter assembly operatively interconnected with the sump at a rear side of the housing. 
   An additional version thereof further includes a charge pump, mounted on a distal end of the input shaft, operatively interconnected with at least one of the first and second hydrostatic pumps. In one variation thereof, the charge pump is mounted on the outside of a bottom surface of the housing. 
   In a further version, a top side of the housing includes a cover, with the input shaft extending into the housing through an aperture in the cover. 
   In a differing version, each of the first and second hydraulic motors takes the form of an externally generated gerotor type orbital motor. 
   A still another version further includes at least one breather cap in a top side of the housing. 
   A yet additional version further includes, on a top side of the housing, a plurality of spaced attachment bosses for attaching the transaxle assembly to a frame of a vehicle. In a variation thereof, the frame member includes a plurality of apertures, each corresponding in location with the plurality of attachment bosses and a further corresponding plurality of fastening members for structurally uniting the transaxle assembly with the frame. 
   Another embodiment of this invention pertains to a powered, wheeled, drive unit for a vehicle including: a. the transaxle assembly of the previous embodiment; b. a frame, with the frame including a plurality of apertures, corresponding in location with the plurality of attachment bosses and a further corresponding plurality of fastening members for structurally uniting the transaxle assembly with the frame; c. a prime mover, affixed to the frame, operatively interconnected with the input shaft gear for supplying the torque; and d. first and second drive wheels, each including a pneumatic tire, affixed to respective ones of the first and second axle shafts. 
   A further embodiment of this invention pertains to a zero-turn-radius vehicle utilizing the powered, wheeled, drive unit of the immediately previously described embodiment. 
   The previously-described advantages and features, as well as other advantages and features, will become readily apparent from the detailed descriptions of the best modes of the preferred embodiments that follow. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of the rear and bottom sides of a powered, wheeled, drive unit in which the hydraulic axle combination of the present invention forms an integral part; 
       FIGS. 2 and 3  are oppositely directed, perspective, views of the front side and chassis of the powered, wheeled, drive unit in which the hydraulic axle combination of the present invention is utilized; 
       FIG. 4  is a perspective view of the front and top sides of the hydraulic axle combination of this invention; 
       FIG. 5  is a perspective view of the rear and top sides of this hydraulic axle combination; 
       FIG. 6  is a top plan view of this hydraulic axle combination; 
       FIG. 7  is a bottom plan view of this hydraulic axle combination; 
       FIG. 8  is an end view of a first end of this hydraulic axle combination; 
       FIG. 9  is an end view of a second end of this hydraulic axle combination; 
       FIG. 10  is a partial sectional view, with parts broken away, taken along line  10 - 10  of  FIG. 8 ; 
       FIG. 10A  is a full sectional view, of a variation of the hydraulic axle combination of  FIG. 10 ; 
       FIG. 11  is an enlarged sectional view, taken along line  11 - 11  of  FIG. 6 , showing a cross section of a sample hydraulic motor power element (gerotor gear set) utilized in this hydraulic axle combination; 
       FIG. 12  is a reduced scale perspective view of the front and bottom sides of this hydraulic axle combination, with the top side thereof being affixed to the outer bottom surface of the driven unit; 
       FIG. 13  is a reduced scale perspective view of the rear and bottom sides of the hydraulic axle combination, with the top side thereof being affixed to the outer bottom surface of the driven unit. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the plurality of drawings, illustrated in  FIGS. 1-3  are several perspective views of a powered, wheeled, drive unit, generally indicated at  20 , in which the hydraulic axle combination or transaxle  22 , of the present invention, forms an integral part. Drive unit  20 , in addition to hydraulic axle combination  22 , mounted on a formed chassis or frame  24 , includes an internal combustion engine  26  mounted on chassis  24 ; an optional, clutch mechanism  27  also mounted on chassis  24 ; and opposed, laterally spaced first, such as left, and second, such as right, drive wheels  28 ,  30 , each equipped with a pneumatic tire  32 . 
   Specifically, drive unit  20 , including hydraulic axle combination  22 , typically finds utility in the previously-described, known, ZTR vehicle. In hydraulic axle combination  22 , engine  26 , via clutch unit  27  and associated belt and pulley drives (not known in detail in order to reduce complexity) drives but a single axle input shaft  50 , as best seen in  FIGS. 4 and 10 . Returning now to  FIGS. 1-3 ,  FIG. 1  is a perspective view of the rear and bottom sides of drive unit  20 , showing the rear side  52  and bottom side  54  of axle combination  22 , while  FIG. 2 , which is a perspective view of the front and bottom sides of drive unit  22 , shows front side  56  and bottom side  54  of axle combination  22 . With  FIG. 3 , which is a perspective view of the rear side and the chassis of axle combination  22 , again shows the front side  56  of axle combination  22  together with clutch unit  27 . All of these structures will be explained in more detail hereinafter. 
     FIGS. 4 and 5  are perspective views of the front and top sides  56 ,  58  and rear and top sides  52 ,  58 , respectively of axle combination  22 . Similarly,  FIGS. 6 and 7  are plan views of top side  58  and bottom side  54 , respectively.  FIGS. 8 and 9  are views of a first, or right, end  60  and a second, or left, end  62  of axle combination  22 , respectively.  FIG. 10  is a partial sectional view, with parts broken away, of  FIG. 8  and illustrates some of the internal components of axle combination  22 . While  FIG. 10A  is a full sectional view of a variation  22 ′ of axle combination  22 .  FIGS. 12 and 13  are reduced scale perspective views of front and bottom sides  56 ,  54  and rear and bottom sides  52 ,  54 , respectively, of axle combination  22 , with the top side  58  thereof (hidden in these views) being affixed to an outer bottom surface  64  of chassis  24 . More detailed explanations will follow. 
   Returning now to  FIGS. 4-6  and  10 , axle combination  22  includes a central or main housing  67  that includes a T-shaped gear box portion  68  having axially spaced, open, ends and a gear box cover  70  that serves to rotatably journal input shaft  50 . Affixed to an intermediate portion of input shaft  50  is a pinion gear  72  that meshes with opposed beveled ring gears  74 L,  74 R, with suffixes L and R referring to Left and Right, since axle combination  22  is comprised of coaxial, allochiral or mirror-image Left and Right transmission portions  22 L,  22 R, housed within main housing  67  on opposite sides of gear box portion  68 . Each of substantially similar transmission portions  22 L,  22 R, includes a closed loop drive system having at least one known hydrostatic pump  76 , for example a swashplate-type piston pump, such as one of the known H1A pump series available from the Parker Hannifin Corporation of Cleveland, Ohio, U.S.A. An input shaft  78  of each of pumps  76  has one of ring gears  74 L,  74 R affixed thereon, as best seen in  FIG. 10 . The axial outer end of each of pumps  76  is connected, via any appropriate manifold block  78 , with a hydraulic motor  80 , for example a externally generated (EGR) gerotor motor, such as one of the known TL gerotor type motors, also available from the Parker Hannifin Corporation. The use of a gerotor orbital motor  80  obviates the use of any additional gear reduction devices.  FIG. 11  illustrates a cross section of a typical EGR motor and shows the internal splines of the gerotor inner rotor or ring gear  82  in orbital mesh with the outer splines of rotatably journalled output shaft  84 . As seen in  FIGS. 4-6 , each of hydrostatic motors  80  is provided, as part of its outer housing  86 , in axle combination top side  58 , with a pair of outwardly-extending, spaced, apertured and threaded bosses or flanges  88  adapted for alignment with similarly spaced apertures  90  ( FIGS. 1-3 ) in chassis bottom portion  66  for bolting together and thus, joining axle combination  22  to and with chassis  24  via bolts  92 . 
   Even though two transmission portions  22 L and  22 R are utilized, preferably only one centralized charge pump  94 , hydraulically interconnected with at least one of main pumps  76 , is used. The charge pump  94  is driven by the distal end of axle input shaft  50  and is located at axle combination bottom side  54 , as best seen in  FIGS. 7 and 10 . Similarly, hydraulic axle combination  22  optionally uses but a single hydraulic fluid filter  96 , preferably of the known spin-on type, located at axle combination rear side  52  for easy access. As shown in  FIG. 10 , a continuous, internal housing sump  97 , which includes gear box housing  70  and the internal housing portions  77  of each piston pump  76 , functions as an integral fluid reservoir  98  for axle combination  22 . Integral reservoir  98  can be drained either by removing fluid filter  96  or by removing an optional drain plug  100  ( FIGS. 1 and 10 ) in axle combination bottom side  54 . Similarly, as best seen in  FIGS. 4 and 6 , at least one and preferably two optional breathers or breather caps  102  can be added to axle combination top surface  58 . 
     FIG. 10A  illustrates a variation  22 ′ of hydraulic axle combination  22  with like parts being denominated by like numerals followed by the suffix prime. In the interest of brevity, no further discussion of such like parts will be made. Axle combination  22 ′ differs from axle combination  22  in that the former does not utilize axle input shaft  50 ′ to also drive a charge pump in addition to driving beveled ring gears  74 L′ and  74 R′. In addition, hydrostatic transmission portions  22 L′ and  22 R′ each utilize an individual internal hydraulic fluid reservoir  108  as well as drain plug  100 ′. If so desired, hydraulic fluid reservoir  110  of gear box housing  70 ′ can also be provided with a drain plug  100 ′. 
   It should be understood, at this time, that the present invention pertains to a single unit design and structure of a hydrostatic transaxle or hydraulic axle combination  22  and  22 ′ that include two hydraulic pumps  76 , two hydraulic motors  80  and a T-shaped intermediate gearbox  68 . Only one axle input shaft  50  is utilized to receive power from one internal combustion engine  26  operating at a preferably constant speed, for example, normally at about 3600 rpm. Two opposed, coaxial, output shafts  84  are used to drive left and right side wheels  28 ,  30  at preferably much lower speeds, for example, normally at about 150 rpm. Thus, the structures of hydraulic axle combinations  22  and  22 ′ are very compact and significantly reduce the assembly time, complexity and efforts for end users by the eliminating the usual hoses, filters, separate reservoirs, as well as the fittings required therefore. 
   Specifically, the single assembly units of axle combinations  22  and  22 ′ include two independent hydrostatic transmissions  22 L,  22 R and  22 L′,  22 R′, respectively. Each of these transmissions includes a closed loop drive system having at least one hydrostatic pump  76  or  76 ′ and one hydraulic motor  80  or  80 ′. Manifold blocks  78  are used to internally connect piston pumps  76  and gerotor motors  80  in a back-to-back orientation, e.g., so that the input shaft of the pump and the output shaft of the motor are at the opposite end of each of transmission portions or segments  221  and  22 R. Thus, the shafts of the two hydrostatic pumps  76  and the two hydraulic motors  80  are of an “in-line” design and configuration, with the two pumps  76  and motors  80  being attached together as but a single unit for ease of assembly. The structure of axle combination  22  includes a sump  97  that serves as an internal, integral, hydraulic fluid reservoir  98  for both transmissions  22 L and  22 R as well as for T-shaped gear box  68 . Associated with reservoir  98  are optional fluid filter  96 , case drain port plugs  100  and breathers  102 . In addition, an optional charge pump  94  is utilized to supply make-up hydraulic fluid flow to avoid possible pump cavitations due to fluid leakages of the transmissions. Furthermore, axle combinations  22 ,  22 ′ are mounted directly onto the frame or chassis  24  of powered, wheeled, drive unit  20 , together with such other parts like an optional clutch mechanism  27  and internal combustion engine or prime mover  26 . The noted mounting of axle combinations  22 ,  22 ′ onto chassis  24  is accomplished via apertured flanges or bosses  88  located on motor housings  80  thereby increasing the overall rigidity of drive unit  20 . 
   It is deemed that one of ordinary skill in the art will recognize that the several embodiments of the present invention fill remaining needs in this art and will be able to affect various changes, substitutions of equivalents and various other aspects of the invention as described herein. Thus, it is intended that the protection granted hereon be limited only by the scope of the appended claims and their equivalents.