Transmission for a working vehicle

#The present invention relates to a transmission for driving front and rear wheels of a running vehicle. More specifically, the invention relates to, a transmission in which is provided in a housing unit thereof: a hydrostatic transmission (hereinafter referred to as an HST), a front wheel driving construction, a restraint mechanism for rearward speed change, a power transmission system linking an input shaft of a power take-off shaft of the transmission with a power take-off clutch and a power take-off braking unit, and a brake operating construction which enables left and right braking units to provide oil to the vehicle independently with left and right turn brake pedals or simultaneously by a master brake pedal.

#A transmission equipped with an HST and for driving front wheels and rear wheels is well-known, as disclosed in, for example, U.S. Pat. No. 5,544,547. With this technique, an engine transmits power through an input shaft to drive a hydraulic pump of the HST. The input shaft transmits the power from the rear end of the hydraulic motor of the HST to a differential gear unit, which in turn drives a gear-type speed changing unit. This unit drives the rear and front wheels through a universal joint by a fore end of the output shaft forwardly projecting from a housing.

#This technique is constructed so that both the hydraulic pump and hydraulic motor are housed in the housing and the front wheels are directly driven by the output shaft of the hydraulic motor of the HST. Thus, when the speed of the gear-type speed changing unit is changed, the speed ratio between the front wheels and the rear wheels is not synchronized. In order to avoid this occurrence, a restraint mechanism must be provided which restrains the front wheels from being driven when the gear-type speed changing unit is switched to the high speed setting.

#These and other objects, features and advantages of the invention will become more apparent upon a reading of the following detailed specification and drawings.

#FIG. 1 is a side view of a working vehicle incorporating the present invention;

#FIG. 2 is a schematic diagram of the power transmission of a running system and a PTO system of the present invention;

#Explanation will be given on the entire construction of a mid-mount mower type working vehicle in accordance with FIG. 1, in which: an engine E is mounted on a vehicle body frame in a bonnet 1 in the front of the vehicle body; a dashboard 2 is disposed behind the bonnet 1; a handle 3 is disposed on the dashboard 2; steps 4 are disposed at both sides below and between the dashboard 2 and a seat 6; brake pedals 5L and 5R are disposed on the left side of step 4; a forward running pedal 8F and a rearward running pedal 8R, to be discussed below, are juxtaposed on the right side step 4; and at the lateral side of the seat 6 are disposed a sub-speed-changing lever 7 and a PTO switching lever 9.

#Under the seat 6 is disposed a transmission of the present invention. The transmission comprises a hydrostatic transmission (hereinafter referred to as HST), a gear-type speed changing unit and a PTO transmission unit housed in a front casing 10 and a rear casing 11. An input shaft 12, a front wheel driving shaft 13, and a mid-PTO shaft 14 forwardly project from the front casing 10. With the input shaft 12 are interlocked a crank shaft of the engine E through a damper and a transmission shaft 16 in a vehicle body frame 15. The front wheel driving shaft 13 connects through a universal joint 17 with an input shaft 19 projecting from the front axle casing 18 through a universal joint 17. Thus, power is transmitted from the front wheel driving shaft 13 to the input shaft 19 which in turn drives front wheels 20 journalled to the left and right sides of front axle casing 18. Reference numeral 22 designates a hydraulic cylinder which expands and contracts by operating a handle 3 so as to steer the front wheels 20. The mid-PTO shaft 14 interlocks through a universal joint 23 with an input shaft 26 projecting from a gear box 25 of a mower 24, which is constructed to elevate and fall by a lift (not shown) with respect to the ground surface in a space between the front wheels 20 and the rear wheels 21.

#Rear axle boxes 127L and 127R are mounted at both side surfaces at the rear of the rear casing 11. Axles 27L and 27R laterally project and pivotally support rear wheels 21 for driving. On the upper surface of the rear casing 11 is mounted a hydraulic cylinder casing 29 for a hydraulic lift. A pair of left and right lift arms 30 rearwardly project from the cylinder casing 29. Lower links 31 are pivotally supported at the front portions thereof onto the rear surface of the rear casing 11. A plate provided with a draw bar hitch 32 is mounted to the lower end of the same. A working machine is mountable in relation of freely raising and lowering the lift arms 30, lower links 31 and top links (not shown), and a traction working machine is mountable to the draw bar hitch 32.