Work vehicle

A work vehicle comprising a stepless hydraulic speed change apparatus, a radiator for cooling hydraulic fluid for the said apparatus, a hydraulic cylinder for actuating a work implement, and a hydraulic pump provided with a suction portion. A return flow path is provided for supplying hydraulic fluid from the radiator to the suction portion of the oil pump.

BACKGROUND OF THE INVENTION 
This invention relates to a work vehicle such as a tractor having a 
stepless hydraulic speed change apparatus, a radiator through which 
hydraulic fluid from the stepless hydraulic speed change apparatus is 
circulated to be cooled, and a hydraulic cyclinder for actuating a work 
implement. 
FIG. 3 shows a hydraulic circuit of a prior art tractor having the elements 
mentioned above. In the prior art construction a return flow path 4' for 
the hydraulic fluid from a radiator 2 is connected to a transmission case 
7. A hydraulic actuating system for travelling and an hydraulic actuating 
system for a work implement are constituted separately in the prior art, 
thus requiring a separate hydraulic pump having an appropriate and high 
capacity for positively actuating the work implement. In FIG. 3, the other 
elements are the same as those of this invention and accordingly 
description concerning the elements indicated by numerals is omitted here 
since such will be understood from the following detailed description of 
this invention. 
SUMMARY OF THE INVENTION 
The objects of this invention are to provide an improved hydraulic supply 
system utilizing the above mentioned elements or apparatus, and enable a 
minimum or small capacity hydraulic pump to be employed for actuating the 
work implement, and, also to increase efficiency of the hydraulic pump. 
To achieve the above objects, a work vehicle of this invention comprises a 
stepless hydraulic speed change apparatus, a radiator for cooling 
hydraulic fluid from the apparatus, a hydraulic cylinder for actuating a 
work implement, a hydraulic pump for supplying pressurized hydraulic fluid 
to the hydraulic cylinder, this pump being provided with a suction portion 
connected to the radiator, and a return flow path connected to the suction 
portion and at the other end to the stepless hydraulic speed change 
apparatus whereby the hydraulic pump is supplied with cooled and 
pressurized hydraulic fluid pumped by the hydraulic speed change 
apparatus. 
Namely, the efficiency of the hydraulic pump is increased by supplying the 
pump with hydraulic fluid under pressure pumped by the stepless hydraulic 
speed change apparatus via the return flow path. As a result, sufficient 
pressure and flow of hydraulic fluid to the hydraulic cylinder is 
obtained, even if a minimum or small capacity hydraulic pump is utilized.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in the drawings, a stepless hydraulic speed change apparatus 1 is 
disposed rearwardly of a prime mover unit 6, comprising a radiator 6A, a 
cooling fan 6B, and an engine 6C which are arranged in that order from the 
front of a tractor to the rear thereof. A transmission case 7 is attached 
to the rear of the stepless hydraulic speed change apparatus 1. 
Lubricating oil in the transmission case 7 is used as the hydraulic fluid 
for the stepless hydraulic speed change apparatus 1, the transmission case 
7 being utilized as a storage tank for the hydraulic fluid used for the 
stepless hydraulic speed change apparatus 1. A radiator 2 is disposed in 
front of the radiator 6A to cool the oil pumped by the stepless hydraulic 
speed change apparatus 1. The prime mover unit 6 drives a hydraulic pump 5 
which supplies hydraulic fluid under pressure to a hydraulic cylinder 3 of 
single action type which is employed for raising and lowering a rotary 
cultivator or other ground work implement 8 mounted on the rear portion of 
the tractor. A return flow path 4 extends between a suction portion 5a of 
the hydraulic pump 5 and the radiator 2. A flow path 9 is provided to 
supply hydraulic fluid from the stepless hydraulic speed change apparatus 
1 to the radiator 2. A return flow path 10 is provided to connect the 
transmission case 7 with the suction portion 5a of the hydraulic pump 5. A 
supply flow path 11 provided with a control valve 11a connects the 
hydraulic pump 5 with the hydraulic cylinder 3. In the drawings, 12 and 13 
show front wheels and rear wheels respectively. 14 is a driver's seat, and 
15 is an operating lever for the stepless hydraulic speed change apparatus 
1. 
According to the construction as described above, when the volume of 
hydraulic fluid from the stepless hydraulic speed change apparatus 1 via 
the radiator 2 is greater than the output of the hydraulic pump 5, any 
excess of hydraulic fluid flowing into the suction portion 5a from the 
radiator 2 directly returns into the transmission case 7 via the flow path 
10. Further, when the volume of hydraulic fluid from the stepless 
hydraulic speed change apparatus 1 to the radiator 2 is less than the 
output of the hydraulic pump 5, hydraulic fluid in the transmission case 7 
flows reversely along the flow path 10 and any lack of hydraulic fluid for 
the hydraulic pump 5 is supplied. In either case, hydraulic fluid under 
pressure is supplied to the hydraulic pump 5 by the stepless hydraulic 
speed change apparatus 1. 
In the prior art construction the circuit for the radiator 2 and the 
circuit for the hydraulic cylinder 3 are independent of each other and 
therefore greater power is required to circulate hydraulic fluid through 
the two separate circuits. This invention, however, minimizes the power 
required for hydraulic fluid circulation by decreasing a total amount of 
the circulating hydraulic fluid and utilizing the hydraulic fluid supplied 
to the radiator 2 as the supply for the hydraulic cylinder 3, while 
additionally effecting cooling of the hydraulic fluid. 
Additionally, it is possible to simplify the hydraulic fluid return path 
and to cut a cost down by making the return flow path 4 from the radiator 
2 to the transmission case 7 shorter than that in the prior art.