Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Reexamination Certificate
1999-12-17
2001-12-25
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
C060S422000
Reexamination Certificate
active
06332316
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a hydraulic control device for a working vehicle capable of adjusting lift force and tractive force of a working machine of the working vehicle such as a wheel loader according to working conditions.
BACKGROUND ART
Japanese Patent No. 2740757, for example, is known as a conventional hydraulic control device for a working vehicle and has such a configuration as shown in
FIG. 6. A
prime mover
1
drives a transmission
3
for making a vehicle travel via a torque converter
2
, and drives a first pump
4
and a second pump
5
. A discharge opening of the first pump
4
is connected to a steering cylinder
8
via a steering circuit
6
, a steering priority valve
7
, and a steering changeover valve
8
a
. A discharge opening of the second pump
5
is connected to a working machine changeover valve
10
via a working machine circuit
9
,
9
a
. An assistance circuit
13
into which part of discharge oil from the first pump
4
flows from the steering priority valve
7
is connected to the working machine circuit
9
,
9
a
. The working machine changeover valve
10
is connected to working machine actuators such as a boom cylinder
11
, a bucket cylinder
12
, and the like. An unloading valve
14
for unloading discharge oil from the second pump
5
is connected to the working machine circuit
9
. A check valve
17
for checking back-flow toward the unloading valve
14
is also connected to the working machine circuit
9
between a portion connected to the assistance circuit
13
and a portion connected to the unloading valve
14
. When inputting an actuating signal from a shift-down switch
15
while the transmission
3
is in a second speed gear, a controller
16
outputs a signal for shifting down the transmission
3
to a first speed gear to the transmission
3
and outputs a signal for unloading the second pump
5
to the unloading valve
14
.
According to the above configuration, when the shift-down switch
15
is operated during low speed work such as excavating work and while the transmission
3
is in the second speed gear, after inputting an actuating signal from the shift-down switch
15
, the controller
16
shifts down the transmission
3
to the first speed gear and unloads the second pump
5
by means of the unloading valve
14
. In this situation, only pressure oil discharged from the first pump
4
(the arrow painted over with black in
FIG. 6
) is supplied to the working machine changeover valve
10
via the steering circuit
6
, the steering priority valve
7
, the assistance circuit
13
, and the working machine circuit
9
a
. At this time, pressure oil in the assistance circuit
13
and the working machine circuit
9
a
never flows into the unloading valve
14
owing to the check valve
17
. Horse power of the prime mover
1
which becomes unnecessary by unloading the second pump
5
as described above is used for tractive horse power of the working vehicle, thereby increasing digging force of a bucket into earth. As a result, the quantity of earth scooped into the bucket is increased and working ability is enhanced.
According to the aforesaid prior art, tractive force can be increased by the force corresponding to motive power which becomes unnecessary by unloading the second pump
5
. However, pressure of the first pump
4
remains unchanged, whereby sufficient working machine lift force such as bucket tilt force or the like can not be obtained. In this case, when earth to be excavated is soft, earth is easy to break even if working machine lift force Fv
1
is small as shown in FIG.
7
A. Therefore, if tractive force Fh is large, the quantity of earth scooped into the bucket increases, which is effective. However, when earth to be excavated is hard, the digging force of the bucket into the earth to be excavated can not be sufficiently obtained even if the tractive force Fh is increased as shown in FIG.
7
B. Hence, the quantity of earth scooped into the bucket does not increase, thus lowering working efficiency. Moreover, a tire slips as shown by the arrow S, thereby causing a disadvantage that abrasion loss is increased, thus shortening the life of the tire. Accordingly, when earth to be excavated is hard, it is requested to increase the tractive force Fh and also increase the working machine lift force like Fv
2
. For this purpose, it is required to increase the quantity of earth scooped into the bucket while the earth is broken by repeatedly performing working machine operation such that bucket tilt force is put forth by rotating a bucket edge upward and that bucket lift force is put forth by lifting a boom to raise the bucket edge.
SUMMARY OF THE INVENTION
The present invention is made in view of the aforesaid disadvantages, and its object is to provide a hydraulic control device for a working vehicle capable of enhancing excavating ability to improve working efficiency even when earth to be excavated is hard and preventing tire slips to thereby lengthen the life of a tire.
To attain the above object, a first configuration of a hydraulic control device for a working vehicle according to the present invention is characterized in that a hydraulic control device for a working vehicle having
a transmission, a first pump, and a second pump which are driven by a prime mover,
a steering circuit for controlling discharge oil from the first pump by a steering priority valve and supplying the same preferentially to a steering changeover valve,
a working machine circuit for supplying discharge oil from the second pump to a working machine changeover valve,
an assistance circuit for making the remainder of discharge oil from the first pump controlled by the steering priority valve join the working machine circuit, and
a shift-down switch for shifting down the transmission to a first speed gear when being operated while the transmission is in a second speed gear, includes
an unloading valve, connected to the working machine circuit upstream of a junction of the working machine circuit and the assistance circuit, for allowing discharge oil from the second pump to be freely drained,
a pressure increasing valve, connected to the working machine circuit downstream of the junction, for increasing a set pressure of pressure oil in the downstream working machine circuit,
a check valve, provided in the upstream working machine circuit between a portion connected to the unloading valve and the junction, for checking back-flow of the pressure oil in the downstream working machine circuit toward the unloading valve, and
a controller for draining discharge oil from the second pump by the unloading valve and increasing the set pressure of the downstream working machine circuit by the pressure increasing valve when the transmission is shifted down from the second speed gear to the first speed gear on receipt of an actuating signal from the shift-down switch.
According to the above configuration, when inputting an actuating signal from the shift-down switch while the transmission is in the second speed gear, the controller shifts down the transmission to the first speed gear, outputs a signal to the unloading valve to unload the second pump, and outputs a signal to the pressure increasing valve to raise the setting of pressure oil in the working machine circuit. At this time, the check valve checks back-flow of the pressure oil in the working machine circuit toward the unloading valve. Hence, tractive force can be increased by the force corresponding to the driving force of the second pump which becomes unnecessary as the result of unload out of prime mover power, and pressure oil in the working machine circuit is raised to thereby increase working machine lift force. Accordingly, even when earth and sand to be excavated are not fully broken by only digging the bucket into the earth and sand with tractive force since the earth to be excavated is hard, the tractive force is increased while working machine lift force such as boom lift force, bucket tilt force, and the like is increased, whereby the earth is fully broken and efficientl
Morimoto Katsuyuki
Nozawa Yasuhiko
Saito Hiroya
Armstrong, Westerman, Hattori, McLeland & Naughton, LLP.
Komatsu Ltd.
Lazo Thomas E.
Lopez F. Daniel
LandOfFree
Hydraulic control device for working vehicle does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hydraulic control device for working vehicle, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydraulic control device for working vehicle will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2557306