Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
The plesent invelltion relates to a drive arrangement
for the travelling system of a working vehicle, in which pressur-
ized--fluid-driven motors respectively mounted to the right- and
left--hand travelling means of the travelling frame are adapted
to be driven by two pumps mounted to the swivel base.
In a working vehicle, there has been known a travelling
drive system comprising two pumps mounted to a swivel base
adapted to drive pressurized-fluid-driven-motors respectively
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mounted to the right- and left-hand travelling ~ of a
travelling frame, a selector valve mechanism to selectively
provide a low-speed driving condition where fluids from the
pumps are supplied respectively to the motors, or a high-speed
driving condition where fluids from the pumps are serially
supplied in the form of a combined flow to the motors, and
counter balance valves to act on the motors.
In such a conventional drive arrangement, the counter
balance valves have been disposed adjacent the corresponding
pressurized-fluid-driven-motors respectively by usual means, and
the selector valve mechanism has been disposed upstream with
respect to the counter balance valves. In such an arrangement,
in a condition where the selector valve mechanism is operated
to provide a low-speed driving condition or a parallel connection
condition where fluids from the pumps are supplied respectively
to the motors, when the control valve is set to the neutral
position to stop the travelling of the vehicle body, small
amounts of fluids are returned to the respective counter balance
valves. However, in a condition where the selector valve
mechanism is operated to provide a high-speed driving condition
or a series connection condition, when the control valve is set
~o the neutral position, large amounts of fluid are returned to
the respective counter balance valves. Namely, when in the high-
speed driving condition, the control valve is set to the neutral
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position to stop the travelling of the vehicle body, the serially
connected motors serve`as pumps by the inertia of the travelling
vehicle body, thereby to gen`erate in the return lines back pres-
sure higher than that genèrated in the parallel connection. This
presents a problem that such a high back pressure exerts a bad in-
fluence upon the piping system and the counter balance valves
The present invention is proposed in view of the defect
in the prior art above-mentioned and has an object to provide im-
provements in a drive arrangement for the travelling system of
1~ a working vehicle, in which provision is made for counter balance
valves having a small capacity to be used thereby to reduce the
manufacturing cost of the drive arrangement.
Accordingly, the present invention provides a drive
system for working vehicle comprising: pressurized-fluid-driven-
motors adapted to be respectively mounted to right- and left-
hand travelling means of a travelling frame; two pumps adapted
to be mounted to a swivel base for driving said motors; a rotary
joint adapted for connecting the travelling frame to the swivel
base; a driving status selector valve mechanism having parallel
ports and series ports to selectively provide a low-speed driving
status where rlui~s from said pumps are supplied respectively in
parallel to said motors or a high-speed driving status where fluids
from said pumps are serially supplied in the form of a combined
flow to said motors; and a counter balance valves (Va) (Vb) to
act on said motors, said counter balance valves being disposed
upstream with respect to said driving status selector mechanism,
and said counter balance valves and said driving status selector
valve mechanism both being disposed downstream of said rotary
~olnt .
In a drive arrangement for the travelling system of a
w~rking vehicle of the present invention, even if the driving con-
dition selector valve mechanism is operated to provide the high-
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speed driving condition where the both pumps and the both motors
are connected in series, fluids from the pumps combine with each
other after having passed through the counter balance
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valves This means fluids having only a low pressure flow in thecounter balance valves. When a travelling control valve is set
to the neutral position to stop the travelling of the vehicle
body, the serially connected motors are driven and serve as pumps
of the series type by the inertia of the vehicle body, so that a
high back pressure is generated. However, since such a high back
pressure acts on the counter balance valves through branch lines
in the driving condition selector valve mechanism, it means each
of the counter balance valves is subjected to a small back pres-
sure.
As thus discussed hereinbefore, although there is gener-
ated back pressure from the motors when the vehicle body has
stopped travelling, such a peculiar arrangement of the counter
balance valves permits the counter balance valves to be subjected
to reduced back pressure, regardless of the serial or parallel
driving condition provided by the selector valve mechanism. There-
fore, it becomes possible to use respective counter balance valves
having a small capacity corresponding to the capacity of each
motor, thus enabling to reduce the manufacturing cost of the drive
arrangement. Further, the selector valve mechanism and the count-
er balance valves are both mounted downstream of the rotary joint
connecting the frame to the swivel base. This permits the size
of the joint to be reduced.
Although the means by which the desired object is achiev-
ed is simple, it is to be understood that the present invention
will bring notable advantages in view of the industrial utility.
The invention will now be described in more detail, by
way of example only, with reference to the accompanying drawings,
in which:-
Fig. 1 is a general side view of a working vehicle
equipped with a working vehicle drive arrangement in accordance
with the present invention: and
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Fig. 2 i5 a pressurized 1uid circuit in an embodiment
of working vehicle travelling drive system in accordance with the
present invention.
In Fig. 1, a working vehicle is constituted by a tra-
velling frame 2 equipped with right- and left-hand crawler tra-
velling means la and lb, a swivel base 3 mounted to the travelling
frame 2, a prime mover 4 and steering means 5 mounted to the
swivel base 3, and an excavator 6 and a doser 7 mounted on the
swivel base 3 and the travelling frame 2, respectively.
lQ As shown in Fig. 2, a drive arrangement of the travelling
elements la and lb comprises: pressurized-fluid-driven-motors
Ma and Mb respectively mounted to the right- and left-hand
crawler traveIling elements la and lb; two pumps Pa and Pb
mounted to the`swivel base 3, the pumps Pa and Pb connected to the
motors Ma and Mb by lines passing through a rotary joint 8 located
at the swivelling center of the swivel base 3; three-position
selector valves V2 and V3 in the lines for the motors Ma and Mb
to selectively provide a neutral stop, forward travel, or a rear-
ward travel; a driving-condition selector valve mechanism Vl
having parallel p~rts a for supplying respective fluids from the
pumps Pa and Pb to the motors Ma and Mb respectively, thereby to
provide a low-speed driving condition, and series ports _ for
serially supplying fluids from the pumps Pa and Pb to the motors
Ma and Mb in the form of a joined flow, thereby to provide a high-
speed driving condition, the driving condition selector valve
mechanism Vl being disposed downstream with respect to the rotary
joint 8; and counter balance valves Va and Vb respectively
disposed on the lines for the motors Ma and Mb between the rotary
joint 8 and the driving condition selector valve mechanism Vl.
When the travelling frame 2 is stopped with the selector valves
y2 and V3 set to the neutral positions, the
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counter balance valves Va and Vb are adapted to return the fluids
to the supply lines, with the back pressure generated in the
return lines by the dynamic inertia of the travelling frame 2 be-
ing utilized as pilot pressure, thereby to prevent the travelling
frame 2 from being suddenly stopped or an undesirable action from
being exerted onthè piping system.
As thus discussed hereinbefore, since the counter balance
valves Va and Vb are disposed upstream with respect to the driv-
ing condition selector valve mechanism Vl, it is possible to use
the counter balance valves Va and Vb having a relatively small
capacity. That is, if the counter balance valves Va and Vb are
disposed downstream with respect to the selector valve mechanism
Vl, such an arrangement requires to use the counter balance valves
Va and Vb having a capacity sufficiently large to return fluids
from the pumps Pa and Pb in the form of a combined flow at the
time when the selector valve mechanism Vl is operated to provide
the high-speed driving condition.
On the contrary, when the balance valves Va and Vb are
disposed upstream with respect to the selector valve mechanism
Vl, even if the selector valve mechanism Vl is operated to provide
the high-speed driving condition, it is possible to branch the
combined flow and cause the branched flows to act on the counter
balance valves Va and Vb, whereby small-capacity counter balance
valves may be advantageously used.
The valves Va-and Vb have unidirectional valves 9 to
permit only the inflow of fluid to the motors Ma and Mb. In this
connection, the three-position selector valves V2 and V3 have
communicating lines 10 for returning fluids with back pressure
generated by the motors Ma and Mb when the three-position selector
3C valves V2 and V3 are set to the neutral position.
As shown in Fig. 2 since the driving condition selector
val~e mechanism Vl and the counter balance valves Va & Vb are
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disposed downstream from the rotary joint at the side of the tra-
velling frame 2, it is not necessary to dispose at the rotary
joint 8 joint flow lines having a large diameter, thereby advan-
tageously to reduce the size of the rotary joint 8. Thus, the
count:er balance valves Va & Vb, or the driving condition selector
valve mechansim Vl and the counter balance valves Va & Vb may be
disposed at the side of the swivel base 3.
It is to be understood that the drive arrangement sys-
tem of a working vehicle in accordance with the present invention
may be applied to a crane truck of the swivel type or the like.
