Material or article handling – Vertically swinging load support – Shovel or fork type
Reexamination Certificate
2000-09-20
2003-05-13
Underwood, Donald W. (Department: 3652)
Material or article handling
Vertically swinging load support
Shovel or fork type
C091S520000
Reexamination Certificate
active
06561751
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device which performs the drive control of two hydraulic actuators. In addition, the present invention relates to a device which performs the drive control of a boom hydraulic actuator and a bucket hydraulic actuator such that a posture of the bucket provided in the hydraulic drive machine is held constant.
2. Description of the Related Art
Booms and buckets are provided as work devices in construction machine such as wheel loaders and skid-stair loaders and so on.
By way of example, using a wheel loader, work is performed in which, following the excavation of the earth and sand with the bucket, the boom is raised whereby the earth and sand within the bucket is loaded into a dump truck. For the boom to be actuated in the upward direction during this work operation, the bucket must be actuated in the dumping direction in such a way that the posture of the bucket is held in a constant horizontal state with respect to the ground surface. This horizontal hold control is indispensable in preventing the earth and sand and so on within the bucket from spilling.
However, when the above-noted horizontal hold control is entrusted to the manual operation of the operator only, the dual operation of a boom operation unit and bucket operation unit must be performed. This dual operation places a large burden on the operator and requires experience. For this reason, an invention in which the abovementioned horizontal hold control can be performed without burden on the operator, and for which no experience is required, has been hitherto well known. That is to say, an invention in which the boom and the bucket are simultaneously actuated by the boom operation unit to perform horizontal hold control has been hitherto well known.
By way of example, an invention in which the boom and arm of a wheel loader are linked by a linking mechanism and, the posture of the bucket is held horizontal by the actuation of the bucket at a constant relationship established by the link mechanism in response to the actuation of the boom has been hitherto well known.
However, according to this invention, a special link mechanism must be manufactured in accordance with the type of work device. In addition, the link mechanism cannot be installed easily in existing construction machine and new work devices must be manufactured. For this reason, there are problems in that this lacks versatility.
In addition, Japanese Patent Application Laid-Open No. 10-219730 describes an invention in which return pressured oil discharged from a boom hydraulic cylinder is, in such a way that the posture of the bucket is held horizontal, branched by a branching valve to be supplied to a bucket hydraulic cylinder.
However, the abovementioned branching valve must be provided between an operation valve and the hydraulic cylinder. For this reason, the laying of the pressured oil conduits is complicated. In addition, a problem arises in that the hydraulic apparatus, through which a large flow rate of pressured oil of high pressure passes, is of large scale. In addition, because the flow rate which drives the actuator is branched, changes in the flow rate are dependent on the load. For this reason the operator must, to maintain the horizontal posture, be constantly carrying out minute operations. In other words, there are the problems that, because control is difficult, the burden on the operator is large and experience is required.
SUMMARY OF THE INVENTION
Thereupon, the present invention, which has excellent versatility, in which the pipe laying can be configured easily, in which the hydraulic apparatus can be compacted by the manipulation of pilot pressured oil, and in which no burden is placed on the operator, was designed to resolve these problems.
A first invention of the present inventions provides, in order to achieve the above-noted resolution of the problems, a hydraulic drive machine which comprises: a hydraulic pump (
1
), and at least two hydraulic actuators (
2
,
3
) driven by supply of discharged pressured oil from the hydraulic pump (
1
); operation means (
4
,
5
) provided correspondent with the hydraulic actuators (
2
,
3
); and operation valves (
6
,
7
) connected between each of the operation means and each of its correspondent hydraulic actuator which respectively change opening amounts thereof in accordance with operating amounts of the operation means (
4
,
5
), and which supply pressured oil to the hydraulic actuators (
2
,
3
) correspondent with the operation means (
4
,
5
), at a flow rate according to the respective opening amounts, wherein
the machine comprises front-to-rear differential pressure constant means (
8
,
9
) connected between the hydraulic pump and each of the operational valves which equalize a difference in pressure between a pressure of pressured oil on an upstream side and a pressure of pressured oil on a downstream side of the operation valves (
6
,
7
) respectively, and wherein
when one of the operation means (
4
) of the operation means (
4
,
5
) is operated, by changing the opening amount of the other operation valve (
7
) correspondent with the other operation means (
5
) in accordance with the operation amount of the operation means (
4
), the other hydraulic actuator (
3
) correspondent with the other operation valve (
7
) is driven.
A description of the first invention is given below with reference to FIG.
1
and FIG.
3
.
Based on the general formula for a hydraulic circuit, the following formula (1) is established, when Q is the flow rate which passes through the diaphragm of the operation valve, c is the flow rate coefficient, A is the opening surface area of the diaphragm, and &Dgr;P is the front-to-rear differential pressure of the diaphragm
Q=c·A·{square root over ( )}&Dgr;P
) (1)
Here, by constantly making the differential pressure &Dgr;P identical, a flow rate is obtained which is proportional to a drive command value (opening surface area A) issued by the operator.
According to the first invention, the differential pressure &Dgr;P between the pressure of the pressured oil on the upstream side and the pressure of the pressured oil on the downstream side of the operation valves
6
,
7
is equalized by the front-to-rear differential pressure constant means
8
,
9
. As a result, from the above-noted formula (1), the flow rates Q
1
, Q
2
of the operation valves
6
,
7
are, irrespective of load fluctuations, determined univocally in accordance with the opening surface areas (opening amounts) A
1
, A
2
of the operation valves
6
,
7
.
When one of the operation means
4
,
5
, the operation means
4
for example is operated, the opening amount A
2
of the other operation valve
7
correspondent with the other operation means
5
is altered in accordance with the operation amount S
1
of said operation means
4
, and the other hydraulic cylinder
3
correspondent with said other operation valve
7
is driven.
That is to say, the ratio of the opening amount A
1
of the operation valve
6
and the opening amount A
2
of the operation valve
7
with respect to the operation amount S
1
of the one operation means
4
is, as shown in FIG.
3
(
b
), set to a constant relationship (b:a). For this reason, the ratio of the flow rate Q
1
supplied to the hydraulic cylinder
2
correspondent with the operation valve
6
, and the flow rate Q
2
supplied to the hydraulic cylinder
3
correspondent with the operation valve
7
, form the above-noted constant relationship (b:a).
According to the first invention as described above, by way of example, a boom hydraulic cylinder
2
and bucket hydraulic cylinder
3
can be simultaneously driven at a constant flow rate ratio by the operation of the boom operation unit
4
only.
In this case, since the ratio of the opening amount A
1
of the operation valve
6
and the opening amount A
2
of the operation valve
7
with respect to the operation amount S
1
of the operation means
4
only needs to be set to a constant relationship, the devic
Hori Shuuji
Ishizaki Naoki
Nagura Shinobu
Komatsu Ltd.
Underwood Donald W.
Varndell & Varndell PLLC
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