Body frame structure for crawler type working vehicle

A frame structure for a working vehicle having crawler running devices includes main frames extending longitudinally along right and left sides of a vehicle body. The crawler running devices have track frames extending below and along the main frames, respectively. An oil tank is disposed between the main frames for rigidly interconnecting forward positions of the main frames and rigidly interconnecting the track frames. The frame structure includes an engine supporting frame for supporting an engine rearwardly of the oil tank. The engine supporting frame is connected to the oil tank through a reinforcing beam, and is curved downwardly with an intermediate portion thereof lying substantially level with the bottom of the oil tank.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a body frame structure for a working 
vehicle having right and left crawler running devices, with a working 
implement connected to the front of body frames and an engine mounted on a 
rear portion thereof. 
2. Description of the Related Art 
In a conventional body frame structure as noted above, the right and left 
crawler running devices have track frames secured to the body frames 
extending along upper positions of the crawler running devices, and the 
engine and an oil tank are mounted on the body frames. A working vehicle 
having such a frame structure is designed to have a space between the 
right and left crawler running devices located at a high level above the 
ground, to avoid the vehicle body becoming bogged down in the mud when 
running over a wet field or other unleveled grounds. Since the body frames 
lie at a high level above the ground and heavy components are mounted on 
the body, the vehicle has an elevated center of gravity. The elevated 
center of gravity brings about a serious problem of reduced running 
stability when such a frame structure is applied to a lawn mower which 
engages in a grass cutting operation on riverbeds or undulating grassy 
terrains. The right and left crawler running devices must be wide apart to 
compensate for the low running stability due to the high center of 
gravity, but this would result in a large overall size of the working 
vehicle. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a working vehicle having 
a low center of gravity while securing a sufficient height above the 
ground of the space between the right and left crawler running devices. 
The above object is fulfilled, according to the present invention, by a 
frame structure comprising main frames extending longitudinally along 
right and left sides of a vehicle body, track frames of crawler running 
devices extending below and along the main frames, respectively, and an 
oil tank disposed between the main frames for rigidly interconnecting 
forward positions of the main frames and rigidly interconnecting the track 
frames. 
In the above structure, the large and heavy oil tank is disposed in a low 
level, which is made possible by rigidly interconnecting the right and 
left track frames through the oil tank. Thus, the oil tank acts also as a 
connecting member for interconnecting the main frames and interconnecting 
the track frames. Such use of the oil tank allows part of frames to be 
omitted without reducing the strength of the frame structure. 
This frame structure may include an engine supporting frame extending 
between the right and left main frames to allow the engine to be disposed 
in a free space rearwardly of the oil tank. The engine supporting frame 
may be connected to the oil tank through a reinforcing beam. Such a frame 
structure has an increased rigidity, and at the same time achieves 
efficient use of the free space. A still more efficient use of space may 
be made by arranging drive units of the running devices in right and left 
spaces across the reinforcing beam between the oil tank and the engine. 
Thus, the present invention may be applied to a working vehicle having 
crawler running devices for running over undulating grassy terrains or 
other unleveled grounds, to allow the large and heavy oil tank and engine 
to be arranged in low levels while securing a sufficient vehicle height. 
This structure realizes a working vehicle having a low center of gravity 
for an excellent running stability without increasing spacing between the 
right and left crawler running devices. 
Other features and advantages of the present invention will be apparent 
from the following description of the preferred embodiment to be had with 
reference to the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
An embodiment of the present invention will be described with reference to 
the drawings. 
FIGS. 1 and 2 are a side view and a plan view, respectively, of a lawn 
mower remote-controlled by radio, which is one example of working vehicles 
according to the present invention. This lawn mower has a flail mower type 
grass cutting implement 1 connected to the front of a vehicle body for 
vertical movement and sideways rolling through a three-point link 
mechanism 2. The vehicle body has right and left crawler running devices 
3, and carries an engine 4 in a rear position of the vehicle body, a fuel 
tank 5 disposed in a left forward position relative to the engine 4, and a 
control unit 6 in a right forward position relative to the engine 4. 
The crawler running devices 3 are hydraulically driven by hydrostatic 
stepless transmissions 40, respectively. Rotation of the grass cutting 
implement 1, and vertical movement and rolling of the link mechanism 2 are 
all effected by hydraulic drive. A large quantity of pressure oil is 
required to enable this all hydraulic type drive structure, and a far 
greater quantity of oil than the required minimum is needed to check 
temperature increase of the pressure oil. The lawn mower has a large oil 
tank 7 to store the great quantity of pressure oil. It is an important 
feature of the present invention to use the oil tank 7 also as part of a 
body frame structure. 
Radiators 8 are disposed at opposite sides of the engine 4 having a 
forwardly extending output shaft. The radiators 8 are cooled by fans 10 
driven by electric motors 9, respectively. Each of the radiators 8 has a 
dust net 11 secured to a side cover 12 of a motor section including the 
engine 4. The side cover 12 is removably and elastically supported at two 
upper and two lower positions thereof by a body frame. Specifically, as 
shown in FIGS. 3 and 4, the side cover 12 to which the dust net 11 is 
secured has rubber elements 14 attached through support brackets 13 to 
lower forward and rearward positions thereof. The rubber elements 14 
define vertical through holes therein. The body frame has support pins 14 
extending vertically into the through holes of the rubber elements 14, 
respectively. Further, the side cover 12 has rubber elements 17 attached 
through support brackets 16 to upper forward and rearward positions 
thereof. These rubber elements 17 define sideways oriented through holes 
therein. The body frame has support pins 14 extending sideways into the 
through holes of the rubber elements 17, respectively. In this way, the 
side cover 12 is elastically supported to be readily detachable and free 
of clattering. 
The body frame structure will be described next. As shown in FIGS. 5 
through 7, the oil tank 7 includes an upper tank portion 7a and a lower 
tank portion 7b, and is located between the right and left crawler running 
devices 3. The crawler running devices 3 have track frames 19 fixed to 
opposite lateral positions of the lower tank portion 7b. Body frames 20 
extending longitudinally and acting as main frames of the lawn mower are 
fixed at forward ends thereof to opposite lateral positions of the upper 
tank portion 7a. Thus, the oil tank 7 acts as a cross beam for the track 
frames 19 and body frames 20. Further, the upper tank portion 7a has a 
mounting bracket 7c fixed to a top surface thereof to connect thereto the 
three-point link mechanism 2 for the grass cutting implement 1. The body 
frames 20 are interconnected at rearward positions thereof through a pair 
of forward and rearward connecting beams 21 and 22 curved downwardly in a 
shape resembling letter U. The respective connecting beams 21 and 22 carry 
engine support brackets 23 fixed thereto. The connecting beams 21 and 22 
are interconnected and reinforced by right and left connecting rods 24 to 
form an engine supporting framework 25 recessed downwardly. The engine 
supporting framework 25 is rigidly connected at a center front position 
thereof to a center rear position of the oil tank 7 through a reinforcing 
beam 26. 
Hydraulic motors 41 and reduction mechanisms 27 for driving the right and 
left crawler running devices 3 are arranged in spaces rearwardly of the 
oil tank 7 and laterally of the reinforcing beam 26. 
In this way, the heavy and rigid oil tank 7 and engine 4 are arranged 
between the right and left body frames 20, to realize a body structure 
having a low center of gravity for steady running while maintaining a 
sufficient space from the ground between the crawler running devices 3. 
In the foregoing embodiment, the oil tank 7 stores the pressure oil for 
driving the hydraulic devices. This oil tank may be divided into two 
chambers, one for storing the pressure oil and the other for storing fuel. 
In this case, the fuel tank 5 mounted in the left forward position of the 
engine 4 is omitted. Where this frame structure is employed for a working 
vehicle without hydraulic devices, the oil tank 7 may be adapted for use 
as the fuel tank 5.