Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Reexamination Certificate
2001-02-23
2001-11-27
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
C060S449000
Reexamination Certificate
active
06321535
ABSTRACT:
TECHNICAL FIELD
The present invention relates to oil pressure control for a working vehicle, and the invention particularly relates to a hydraulic circuit for a loader vehicle and to a pump capacity control device for a working vehicle.
BACKGROUND ART
A loader vehicle, for example, a wheel loader (hereinafter, simply called “the vehicle”) has a working machine at the front portion of the vehicle body. The working machine has a boom, with the rear end of the boom being coupled to the front portion of the vehicle body via pivot pins, and a bucket, coupled at the front end of the boom via pivot pins. As shown in
FIG. 18
, the boom is rotatable around the pin coupling at the rear end of the boom via the operation of the boom cylinder
11
, and the bucket is rotatable around the pin coupling at the front end of the boom via operation of the bucket cylinder
12
. Specifically, the vehicle has a working machine hydraulic circuit
10
. It is normal to include a steering hydraulic circuit
20
together with the hydraulic circuit
10
.
Incidentally, the steering circuit, as well as the brake, is a safety element of a vehicle. For this reason, in some vehicles, the working machine hydraulic circuit
10
receives pressurized oil discharged from a working machine hydraulic pump
30
at a flow rate Qw, and the steering hydraulic circuit
20
receives pressurized oil discharged from a steering hydraulic pump
40
at a flow rate Qst, whereby the circuits
10
and
20
are independent from each other. Such a vehicle further has an auxiliary hydraulic pump
50
and a flow dividing valve
60
, which is connected to the pumps
40
and
50
and to the circuits
10
and
20
in order to use the engine torque efficiently. The operation of the flow dividing valve
60
is as follows.
At a medium or higher speed of the engine
70
, the flow Qst of pressurized oil, discharged from the steering hydraulic pump
40
, is sufficient for the steering hydraulic circuit
20
. Accordingly, at this time, the flow dividing valve
60
supplies pressurized oil at a flow Qs from the auxiliary hydraulic pump
50
to the working machine hydraulic circuit
10
. However, when a steering operation is carried out at a low speed of the engine
70
(at so-called minimum idling engine speed), the oil flow rate Qst is not sufficient for the steering hydraulic circuit
20
, and a quick steering operation cannot be conducted. The flow dividing valve
60
then supplies pressurized oil, discharged from the auxiliary pump
50
, to the steering hydraulic circuit
20
at the flow rate Qs. Incidentally, oil which has flowed through either of the circuits
10
and
20
returns to a tank
90
by way of a drain circuit
80
. Each of the hydraulic pumps
30
,
40
, and
50
is a fixed displacement type. Some vehicles are equipped with variable displacement type hydraulic pumps, but their variable control does not serve the purpose of the present invention, the details of which will be described below; therefore, in the present invention such a variable displacement type hydraulic pump is considered as a fixed displacement type.
In the vehicle, the operating oil pressure Pw becomes lower during an operation with a low load (for example, when the boom is being raised with a load in the bucket). At this time, the higher the oil flow in the working machine hydraulic circuit
10
, the higher the boom ascending speed becomes, and the higher the working speed becomes. On the other hand, during an operation with a high load (for example, during rock excavation by the bucket), the oil pressure of the working machine hydraulic circuit
10
(hereinafter referred to as “operating oil pressure Pw”) becomes higher. At this time, the necessary flow of pressurized oil in the working machine hydraulic circuit
10
may be smaller. Then there is an example having an unload circuit
100
to which the oil flow Qs, heading for the working machine hydraulic circuit
10
from the flow dividing valve
60
, is drained to the tank
90
when the operating oil pressure Pw exceeds a previously specified oil pressure Pu (hereinafter referred to as “unloaded condition starting pressure Pu”), and is raised to be higher (specifically “Pmax≧Pw>Pu”). Here, “Pmax” is the relief oil pressure of the working machine hydraulic circuit
10
. The details are as follows.
For example, the unloaded circuit
100
in
FIG. 18
has: a check valve
101
, which opens in one direction toward the working machine hydraulic circuit
10
from the flow dividing valve
60
; an oil passage
102
, branching from a portion between the flow dividing valve
60
and the check valve
101
and connecting to the tank
90
; and an on-off valve
103
, provided in the oil passage
102
. The on-off valve
103
has a spring
104
, which is initially set with momentum corresponding to the unloaded condition starting pressure Pu. The on-off valve
103
is a two position switching valve which can be switched according to the magnitude of the operating oil pressure Pw by receiving the operating oil pressure Pw from the working machine hydraulic circuit
10
to oppose the momentum given to the spring
104
. Specifically, when the operating oil pressure Pw is defined by “Pw≦Pu”, the on-off valve
103
cuts off the oil passage
102
and supplies the oil quantity Qs from the flow dividing valve
60
to the working machine hydraulic circuit
10
(non-unloaded condition). On the other hand, when the operating oil pressure Pw is defined by “Pmax≧Pw>Pu”, the on-off valve
103
provides communication from the flow dividing valve
60
to the oil passage
102
, and drains the oil quantity Qs into the tank
90
from the flow dividing valve
60
(unloaded condition). Irrespective of the magnitude of the operating oil pressure Pw, when a steering operation is effected at the minimum idling engine speed, the flow dividing valve
60
supplies the oil quantity Qs into the steering hydraulic circuit
20
.
The operation of the aforesaid conventional art will be explained with reference to
FIGS. 19A
,
19
B,
19
C, and
20
. In order to make the explanation easier, it is assumed that the oil flow Qs flows to the working machine hydraulic circuit
10
side and that the reduction ratio from the engine
70
to each of the hydraulic pumps
30
,
40
, and
50
is “1”, unless otherwise specified.
In
FIG. 19A
, the operating oil pressure Pw is plotted in the axis of ordinates, and the displacement volume Vw of the working machine hydraulic pump
30
per one rotation of the engine
1
is plotted in the axis of abscissa. In
FIG. 19B
, the operating oil pressure Pw is plotted in the axis of ordinates, and the displacement volume Vs of the auxiliary hydraulic pump
50
per one rotation of the engine
1
is plotted in the axis of abscissa. In
FIG. 19C
, the steering oil pressure Pst is plotted in the axis of ordinates, and the displacement volume Vst of the steering hydraulic pump
40
per one rotation of the engine
1
is plotted in the axis of abscissa. The relief pressures of the circuits
10
and
20
are not necessarily the same, but in the present embodiment both of them have the same pressure Pmax.
FIG. 19A
shows the oil pressure torque Tw (=Pw*Vw) of the working machine hydraulic pump
30
per one rotation of the engine
70
.
FIG. 19B
shows the oil pressure torque Ts (=Pw*Vs) of the auxiliary hydraulic pump
50
per one rotation of the engine
70
. The oil pressure torque Tws (not illustrated) is the total of the oil pressure torque Tw and the oil pressure torque Ts, i.e., “Tws=Tw+Ts”. This can be also considered as “Tws=Pw*(Vw+Vs)” in a non-unloaded condition (Pw≦Pu). The maximum value of the oil pressure torque Tws in a non-unloaded condition occurs at the time when “Pw=Pu” (“hatched portions shown by the diagonal lines extending upwardly to the right in FIGS.
19
A and
19
B). On the other hand, in an unloaded condition (Pmax≧Pw>Pu), the oil flow Qs discharged from the auxiliary hydraulic pump
50
is drained into the tank
90
by means of the unload circui
Ikari Masanori
Oba Motoki
Komatsu Ltd.
Lazo Thomas E.
Look Edward K.
Sidley Austin Brown & Wood
LandOfFree
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