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A powertrain module for a zero turn radius vehicle, such as a tractor or mower, the powertrain module generally including a structural member or mounting plate to which an engine, a pair of hydrostatic transmission modules, and a pair of axle drive units are attached to form a self-contained powertr

A powertrain module for a zero turn radius vehicle, such as a tractor or mower, the powertrain module generally including a structural member or mounting plate to which an engine, a pair of hydrostatic transmission modules, and a pair of axle drive units are attached to form a self-contained powertrain module which may be shipped as a single packaged unit for installation into the zero turn radius implement. The mounting plate provides structural rigidity between the powertrain components attached thereto, and the mounting plate of the powertrain module may be attached directly to the frame of the vehicle, or alternatively, may itself serve as a structural frame member for the vehicle.

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1. A self-contained powertrain module, comprising:a structural member;an engine attached to said structural member, said engine including an output shaft;first and second hydrostatic transmission modules connected to said structural member, each said hydrostatic transmission module comprising a tran

1. A self-contained powertrain module, comprising:a structural member;an engine attached to said structural member, said engine including an output shaft;first and second hydrostatic transmission modules connected to said structural member, each said hydrostatic transmission module comprising a transmission housing, a rotating fluid pump disposed within said housing, and a rotatable fluid motor disposed within said housing and in fluid communication with said pump, said pump being driven by said engine output shaft and being of variable displacement, each said motor being rotated at various speeds and in forward and reverse directions in response to changes in pump displacement. the displacement of each said pump being variable independent of the displacement of the other said pump;first and second axle drive units connected to said structural member, each said axle drive unit comprising a housing and a speed reduction gear train disposed within said housing, each said speed reduction gear train having an input and an output, said first hydrostatic transmission module motor being operably coupled to said first axle drive unit gear train input, said second hydrostatic transmission module motor being operably coupled to said second axle drive unit gear train input; andfirst and second axles, said first axle being operably coupled to said first gear train output, said second axle being operably coupled to said second gear train output, said first and second axles respectively extending through said first and second axle drive unit housings. 2. The powertrain module of claim 1, further comprising a bearing supported by said structural member, said bearing supporting an end of a said axle. 3. The powertrain module of claim 1, wherein said first and second axles are coaxial. 4. The powertrain module of claim 1, wherein ends of said first and second axles are adjacent. 5. The powertrain module of claim 4, wherein said adjacent ends of said first and second axles abut. 6. The powertrain module of claim 4, further comprising a bearing supported by said structural member, said bearing rotatably supporting both of said adjacent ends of said first and second axles. 7. The powertrain module of claim 6, wherein said bearing is disposed between said first and second axle drive unit housings. 8. The powertrain module of claim 7, further comprising a support member extending from said structural member, said bearing being attached to said support member. 9. The powertrain module of claim 1, wherein said housings of said first and second axle drive units each comprise attached first and second portions, said first and second housing portions of said first and second drive units being respectively identical. 10. The powertrain module of claim 1, wherein said first and second hydrostatic transmission module pumps have an input shaft, said pump input shafts being coupled to said engine output shaft. 11. The powertrain module of claim 10, further comprising a pulley attached to said engine output shaft and to each of said pump input shafts, and a drive belt in driving engagement around said pulleys. 12. The powertrain module of claim 1, wherein said first and second hydrostatic transmission modules are mirror-images of one another. 13. The powertrain module of claim 1, wherein said structural member comprises a plate to which said engine and said first and second axle drive unit housings are fixed. 14. The powertrain module of claim 13, wherein said engine is disposed above said plate and said axle drive unit housings are disposed below said plate. 15. The powertrain module of claim 14, wherein said engine is located forwardly of said axles. 16. The powertrain module of claim 1, further comprising a brake mechanism attached to each of said first and second axle drive units. 17. In combination with the powertrain module of claim 1, a zero turn radius vehicle comprising a frame to which said support member is attached, and ground-engaging wheels att ached to said first and second axles. 18. A self-contained powertrain module, comprising:a structural member;an engine attached to said structural member, said engine including an output shaft;first and second hydrostatic transmission modules connected to said structural member, each said hydrostatic transmission module comprising a transmission housing, a rotating fluid pump disposed within said housing, and a rotatable fluid motor disposed within said housing and in fluid communication with said pump, said pump being driven by said engine output shaft and being of variable displacement. each said motor being rotated at various speeds and in forward and reverse directions in response to changes in pump displacement;first and second axle drive units connected to said structural member, each said axle drive unit comprising a housing and a speed reduction gear train disposed within said housing, each said speed reduction gear train having an input and an output, said first hydrostatic transmission module motor being operably coupled to said first axle drive unit gear train input, said second hydrostatic transmission module motor being operably coupled to said second axle drive unit gear train input; andfirst and second axles, said first axle being operably coupled to said first gear train output, said second axle being operably coupled to said second gear train output, said first and second axles respectively extending through said first and second axle drive unit housings, wherein said first hydrostatic transmission module is connected to said structural member through said first axle drive unit, and said second hydrostatic transmission module is connected to said structural member through said second axle drive unit. 19. The powertrain module of claim 18, wherein said first hydrostatic transmission module is affixed to said first axle drive unit housing, and said second hydrostatic transmission module is affixed to said second axle drive unit. 20. The powertrain module of claim 18, wherein said structural member comprises a plate to which said engine and said first and second axle drive unit housings are fixed. 21. The powertrain module of claim 20, wherein said first and second axle drive unit housings each comprise attached first and second portions, each said first housing portion being substantially planar and affixed to said structural member. 22. In combination with the powertrain module of claim 18, a zero turn radius vehicle comprising a frame to which said support member is attached, and ground-engaging wheels attached to said first and second axles. 23. A self-contained powertrain module, comprising:a structural member;an engine attached to said structural member, said engine including an output shaft;first and second hydrostatic transmission modules connected to said structural member, each said hydrostatic transmission module comprising a transmission housing, a rotating fluid pump disposed within said housing, and a rotatable fluid motor disposed within said housing and in fluid communication with said pump, said pump being driven by said engine output shaft and being of variable displacement, each said motor being rotated at various speeds and in forward and reverse directions in response to changes in pump displacement;first and second axle drive units connected to said structural member, each said axle drive unit comprising a housing and a speed reduction gear train disposed within said housing, each said speed reduction gear train having an input and an output, said first hydrostatic transmission module motor being operably coupled to said first axle drive unit gear train input, said second hydrostatic transmission module motor being operably coupled to said second axle drive unit gear train input; andfirst and second axles, said first axle being operably coupled to said first gear train output, said second axle being operably coupled to said second gear train output, said first and second axles respectively e xtending through said first and second axle drive unit housings, wherein said first and second axle drive unit housings each comprise attached first and second portions, each said first housing portion being substantially planar and affixed to said structural member. 24. The powertrain module of claim 23, wherein said axle drive unit second housing portions are located between said axle drive unit first housing portions. 25. The powertrain module of claim 23, wherein each said axle drive unit housing first portions defines a cavity in which a said speed reduction gear train is disposed. 26. The powertrain module of claim 25, wherein said cavity is grease-filled. 27. The powertrain module of claim 25, wherein said axle drive unit second housing portions are metal stampings. 28. In combination with the powertrain module of claim 23, a zero turn radius vehicle comprising a frame to which said support member is attached, and ground-engaging wheels attached to said first and second axles. 29. A self-contained powertrain module, comprising:a structural member;an engine attached to said structural member, said engine including an output shaft;first and second hydrostatic transmission modules connected to said structural member, each said hydrostatic transmission module comprising a transmission housing, a rotating fluid pump disposed within said housing, and a rotatable fluid motor disposed within said housing and in fluid communication with said pump, said pump being driven by said engine output shaft and being of variable displacement, each said motor being rotated at various speeds and in forward and reverse directions in response to changes in pump displacement;first and second axle drive units connected to said structural member, each said axle drive unit comprising a housing and a speed reduction gear train disposed within said housing, each said speed reduction gear train having an input and an output, said first hydrostatic transmission module motor being operably coupled to said first axle drive unit gear train input, said second hydrostatic transmission module motor being operably coupled to said second axle drive unit gear train input; andfirst and second axles, said first axle being operably coupled to said first gear train output, said second axle being operably coupled to said second gear train output, said first and second axles respectively extending through said first and second axle drive unit housings, wherein each said fluid motor is provided with an output shaft, and further comprising a brake disk rotatably couple to and coaxial with said motor output shaft, said brake disk being selectively operatively engaged by a said brake mechanism. 30. The powertrain module of claim 29, wherein said motor output shafts are located rearwardly of said axles. 31. A zero turn radius vehicle, comprising:a first frame portion;a second frame portion comprising a powertrain module separably attached to said first frame portion and comprising:a substantially rigid structural member attached to said first frame portion,an engine attached to said structural member, said engine having an output shaft,first and second hydrostatic transmission modules connected to said structural member, each said hydrostatic transmission module comprising: a transmission housing, a rotating fluid pump and a rotatable fluid motor disposed in said transmission housing, said pump connected in driving relationship with said engine output shaft, said motor being in fluid engagement with said pump, said pump being of variable displacement, each said motor being rotated at various speeds and in forward and reverse directions in response to changes in pump displacement,first and second axle drive units connected to said structural member, each including a housing and a speed reduction gear train disposed within said axle drive unit housing, each said speed reduction gear train having an input and an output, said first hydrostatic transmission module motor bein g operably coupled to said first axle drive unit gear train input, said second hydrostatic transmission module motor being operably coupled to said second axle, drive unit gear input, wherein said first hydrostatic transmission module is connected to said structural member through said first axle drive unit, and said second hydrostatic transmission module is connected to said structural member through said second axle drive unit; andfirst and second independently rotatable axles, said first axle being operably coupled to said first gear train output, said second axle being operably coupled to said second gear train output, said first and second axles respectively extending through said first and second axle drive unit housings; anda ground-engaging wheel attached to each said axle.