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An axle driving apparatus in which a hydraulic pump and a hydraulic motor which constitute a hydrostatic transmission are disposed on a center section. In a horizontal portion of the center section are provided a pair of linear oil passages in parallel to each other. A pair of arcuate ports are prov

An axle driving apparatus in which a hydraulic pump and a hydraulic motor which constitute a hydrostatic transmission are disposed on a center section. In a horizontal portion of the center section are provided a pair of linear oil passages in parallel to each other. A pair of arcuate ports are provided on a pump mounting surface formed on the horizontal portion of the center section. The pair of arcuate ports are substantially perpendicular with respect to the direction in which the oil passages extend. The axis of slanting movement of a movable swash plate of the hydraulic pump extends laterally of the vehicle body on which the axle driving apparatus is provided. The rotating direction of an arm provided on a control shaft for slantingly operating the movable swash plate is coincident with the operating direction of a control rod connected with a speed changing member. Thus, the link mechanism for connecting the speed changing member and the control arm for the movable swash plate is simplified.

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1. A hydrostatic transmission comprising:a housing; an oil sump formed in said housing; a center section having a horizontal surface and a vertical surface disposed in said housing; a hydraulic pump having a cylinder block which is rotatably, slidably disposed on said horizontal surface of said cent

1. A hydrostatic transmission comprising:a housing; an oil sump formed in said housing; a center section having a horizontal surface and a vertical surface disposed in said housing; a hydraulic pump having a cylinder block which is rotatably, slidably disposed on said horizontal surface of said center section; a hydraulic motor having a cylinder block which is rotatably, slidably disposed on said vertical surface of said center section; a pair of oil passages provided in said center section; a first pair of arcuate ports opened on said vertical surface of said center section and communicating with said pair of oil passages; a second pair of arcuate ports opened on said horizontal surface of said center section, wherein each of said second pair of arcuate ports has a length and a depth substantially perpendicular to each other, wherein the depth of one of said second pair of arcuate ports is shallow at a first end and gradually deepens to a second end which fluidly communicates with one of said pair of oil passages and the depth of the other of said second pair of arcuate ports is shallow at a first end and gradually deepens to a second end which fluidly communicates with the other of said pair of oil passages, whereby feed oil discharged from said cylinder block of said hydraulic pump is introduced into said one of said pair of oil passages and feed discharge oil in said other of said pair of oil passages from said cylinder block of said hydraulic motor is introduced into said cylinder block of said hydraulic pump; oil holes branched from said pair of oil passages formed in said center section, opened on an opposite surface of said center section which is opposite to, said horizontal surface of said center section; a valve casing inserted into each of said oil holes, wherein an outer portion of each of said valve casings projects from said opposite surface of said center section to said oil sump; a valve body inserted into each of said valve casings; openings provided in said respective projecting outer portions of said valve casings, wherein said openings are closed by said valve bodies and are freely opened and closed so as to constitute a check valve with said oil sump; and an oil filter disposed in said oil sump so as to cover said projecting outer portions of said valve casings on said opposite surface of said center section so that said oil filter divides said oil sump into an inner oil sump and an outer oil sump, wherein said openings of said valve casing directly communicates with said inner oil sump. 2. The hydrostatic transmission as set forth in claim 1, wherein said respective second ends of each of said pair of arcuate ports communicates with said respective oil passages where each of said second pair of arcuate ports is overlapped with each of said pair of oil passages.3. The hydrostatic transmission as set forth in claim 1, further comprising:an axle disposed within said housing; a drive train for transmitting power from said hydraulic motor to said axle disposed within said housing; a plurality of pistons reciprocally disposed in said cylinder block of said hydraulic pump; a movable swash plate abutting against the heads of said pistons; and a control shaft for slantingly operating said movable swash plate disposed substantially in parallel to said axle.