Hydraulic circuit for turning excavator

Description

SPECIFICATION

1. Field of the Art

The present invention r elates to a hydraulic circuit system having at least three hydraulic pumps for supplying hydraulic actuators of a turning excavator with pressure oil, wherein working arms consisting of a boom, an arm and a bucket are operated and a turning excavator body is turned by the respective hydraulic actuators.

2. Background Art

Conventionally, it is a well-known technique for a turning excavator having a turning excavator body (a main body) and working arms consisting of a boom, an arm and a bucket to provide the hydraulic circuit system thereof with three hydraulic pumps for supplying hydraulic actuators for respectively driving the boom, the arm, the bucket and the main body with pressure oil, wherein each actuator is supplied with pressure oil by one of the pumps whether the actuators are driven one by one at different times (individually) or more than one of those are driven simultaneously.

For increasing the operation speed of each of the working arms like the boom, Japanese Laid Open Gazette No. Hei 8-134960 discloses a conventional turning excavator provided with a purpose-built hydraulic circuit having a hydraulic pump for it, wherein the circuit can be joined with chosen one of hydraulic circuits for the respective hydraulic actuators like a boom cylinder. Furthermore, Japanese Laid Open Gazette No. Hei 8-113961 discloses a joining circuit including a check valve interposed between a hydraulic circuit for turning the main body and a hydraulic circuit for driving the boom, thereby making the erecting operation of the boom faster than the turning operation of the main body when they are driven simultaneously.

Especially in various operations of the boom, the arm and the bucket of the working arms for excavation, the erecting operation of the boom and the pulling operation of the arm are hoped to be as swift as possible. However, with respect to the conventional hydraulic system, each hydraulic actuator is supplied with pressure oil from a single hydraulic pump, thereby being too low in quantity of pressure oil to be operated at such a hopeful speed. The hydraulic circuit system disclosed in Japanese Laid Open Gazette No. Hei 8-134960 is further provided with such purpose-built circuit for increasing the operation speed, thereby being complicated and expensive. Moreover, the check valve in the joining circuit cannot limit the amount of joined oil flow for restricting the increasing of the operation speed.

In some working conditions, more than one of the main body and the working arms are driven simultaneously. For example, a horizontal motion of the bucket for horizontal excavation requires the simultaneous erecting operation of the boom and pulling operation of the arm. In this case, making the pulling operation of the arm faster than the erecting operation of the boom is effective. However, there is no conventional hydraulic circuit system designed with said case in mind so as to give the arm priority over the boom when the both are operated simultaneously.

Supposing the turning excavator raises sand and moves it to a truck, the erecting operation of the boom must be prior to the turning of the main body. The above said conventional hydraulic circuit system of Japanese Laid Open Gazette No. Hei 8-113961 is designed with this situation in mind. However, one of the three hydraulic pumps thereof is for pilot operation, so that each actuator is substantially supplied with pressure oil from either of only the other two pumps. Also, supposing a small excavator employs this hydraulic circuit system, the hydraulic pressure for turning operation of the main body is to be limited low. However, as the pressure oil for turning the main body flows into the hydraulic circuit for driving the boom, the boom may be moved too fast. The operation speed of the boom cannot be limited because the oil flowing from the above said joining circuit to the hydraulic circuit for the hydraulic actuator for the boom cannot be shut off.

SUMMARY OF THE INVENTION

A hydraulic circuit for a turning excavator according to the present invention is provided with first, second and third hydraulic pumps for supplying pressure oil to respective hydraulic actuators for driving a boom, an arm, a bucket and a turning main body of the turning excavator.

During the individual driving of them, an actuator for the boom is supplied with pressure oil from the first and third pumps, an actuator for the arm from the second and third pumps, an actuator for the bucket from the first pump, and an actuator for the main body from the third pump.

For simultaneously driving the boom and the arm, the third pump supply pressure oil to the actuator for the arm prior over that for the boom.

During the simultaneous driving of the boom and the arm, the hydraulic circuit, which makes the above mentioned pressure oil supplying patterns by the first, second and third hydraulic pumps thereof, preferentially supplies the actuator for the arm with pressure oil from the third pump. When the boom and the main body are operated simultaneously, it additionally supplies the actuator for the boom with a part of the pressure oil to the actuator for the main body from the third pump through a branching circuit.

The branching circuit toward the actuator for the boom may be a bleed-off-circuit.

Additionally, the pressure oil from the third pump to the actuator for the arm is partly bled off.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1

is a diagram showing a pressure oil supplying pattern in a turning excavator having a three pump type hydraulic circuit system according to the present invention, during the individual driving of a boom;

FIG. 2

is a similar diagram during the individual driving of an arm;

FIG. 3

is a similar diagram during the individual driving of a bucket;

FIG. 4

is a similar diagram during the individual driving of a turning main body;

FIG. 5

is a similar diagram during the simultaneous driving of the boom and the arm;

FIG. 6

is a similar diagram during the simultaneous driving of the arm and the bucket;

FIG. 7

is a similar diagram during the simultaneous driving of the boom, the arm and the turning main body;

FIG. 8

is a similar diagram during the simultaneous driving of the boom and the turning main body;

FIG. 9

is a hydraulic circuit diagram of the turning excavator for making the pressure oil supplying patterns shown in

FIGS. 1 through 8

, and

FIG. 10

is the same hydraulic circuit diagram, wherein a boom accelerating circuit shown in

FIG. 9

can bleed off and an arm accelerating circuit shown in the same bleeds off a part of the pressure oil flowing therethrough.

BEST MODE FOR PRACTICING THE INVENTION

At first, explanation will be given on a general construction of a turning excavator of the present invention. As shown in

FIGS. 1 through 8

, a main body

4

is rotatably mounted over a crawler type travelling device

5

. A boom

1

is pivoted at the basic end thereof onto the front end of the main body

4

. An arm

2

is pivoted at the basic end thereof onto the utmost end of the boom

1

. A bucket

3

is pivoted at the basic end thereof onto the utmost end of the arm

2

. The boom

1

, arm

2

and bucket

3

, serving as working arms, are driven by hydraulic actuators of a boom cylinder CY

1

, an arm cylinder CY

2

and a bucket cylinder CY

3

, respectively. The main body

4

is turned about the travelling device

5

by a turning motor M serving as a hydraulic actuator.

In addition to the above mentioned hydraulic driving means, the travelling device

5

is provided with left and right hydraulic travelling motors ML and MR, which can be driven independently to each other. As shown in

FIG. 4

or others, a blade

6

is provided on the travelling device

5

. The blade

6

is vertically moved by a hydraulic cylinder CY

4

. A boom bracket

4

a, which is disposed on the front end of the main body

4

for pivoting the basic end of the boom

1

, is laterally rotated by a hydraulic swinging cylinder CY

5

connected to the bottom of the main body

4

. The boom

1

or arm

2

is provided with an oil extracting portion for PTO, to which a separate hydraulic driving means can be attached. The hydraulic motors ML and MR and cylinders CY

4

and CY

5

are shown in FIG.

10

.

Next, explanation will be given on a series of pressure oil supplying patterns made by a three pump type hydraulic circuit system in the turning excavator of the present invention having the above various hydraulic driving means in accordance with

FIGS. 1 through 8

. At first, the hydraulic circuit system is basically provided with main a first hydraulic main pump P

1

and a second hydraulic main pump (a second pump) P

2

, and a hydraulic sub pump (a third pump) P

3

, occasionally more than one. The first, second and third pumps P

1

, P

2

and P

3

are driven by an engine E. Fundamentally, the first pump P

1

is connected to the boom and bucket cylinders CY

1

and CY

3

, the second pump P

2

to the arm cylinder CY

2

, and the third pump P

3

to the turning motor M, through respective hydraulic circuits for supplying the hydraulic actuators with pressure oil. During the individual driving of the bucket

3

or the individual turning of the main body

4

, only the first or third pump P

1

or P

3

supplies pressure oil as shown in

FIGS. 3 and 4

.

Additionally, joining circuits are extended from the third pump P

3

to the boom cylinder CY

1

and the arm cylinder CY

2

, respectively. During the individual operation of the boom cylinder CY

1

, the pressure oil from the third pump P

3

joins that from the first pump P

1

as shown in

FIG. 1

, thereby supplying the boom cylinder CY

1

with the joined increased pressure oil, thereby enabling the erecting motion of the boom

1

to be accelerated. During the individual operation of the arm cylinder CY

2

, the pressure oil from the third pump P

3

joins that from the second pump P

2

as shown in

FIG. 2

, so that the arm cylinder CY

2

is supplied with the joined increased pressure oil, thereby moving the arm

2

swiftly. Thus, the third pump

3

supply pressure oil for acceleration of the boom

1

and the arm

2

unless it is not used for turning the main body

4

. The boom

1

and the arm

2

can be accelerated by such simple and low costing hydraulic circuit system which uses the unused hydraulic pump P

3

as a pressure oil source for the accelerating operation thereof without an additional hydraulic pump or hydraulic circuit.

In the same construction which supplies pressure oil as the above during the individual driving of the hydraulic actuators, the cases of simultaneous driving of more than one of the hydraulic actuators will be described in accordance with

FIGS. 5 through 8

. At first, during the simultaneous driving of the boom

1

and arm

2

as shown in

FIG. 5

, while the boom cylinder CY

1

is supplied with the pressure oil from the first pump P

1

, and the arm cylinder CY

2

from the second pump P

2

, there is such a problem that which cylinder CY

1

or CY

2

is additionally supplied with the pressure oil from the unused third pump

3

. The simultaneous driving of the boom

1

and arm

2

is required when the working arms are folded. In this situation, the foremost desired operation is that the arm

2

, which has been expanded apart from the main body

4

, is pulled swiftly into a safe range, so that priority should be given to the operation of the arm

2

. Accordingly, the pressure oil from the third pump P

3

is joined to the hydraulic circuit from the second pump P

2

to the arm cylinder CY

2

for supplying the arm cylinder CY

2

with the joined pressure oil, thereby accelerating the arm

2

.

As shown in

FIG. 6

, during the simultaneous driving of the arm

2

and bucket

3

, the bucket cylinder CY

3

is supplied with pressure oil from the first pump P

1

, and the arm cylinder CY

2

is supplied with joined pressure oil from the second pump P

2

and the third pump P

3

in consideration that the operating range of the arm

2

is larger than that of the bucket

3

, thereby accelerating the arm

2

.

When the main body

4

is turned during the simultaneous driving of the boom

1

and arm

2

, the third pump P

3

supplies pressure oil into the turning motor M, which is an original object to be supplied by the third pump P

3

. In other words, the pressure oil is supplied from the first pump P

1

to the boom cylinder CY

1

, from the second pump P

2

to the arm cylinder CY

2

, and from the third pump P

3

to the turning motor M, respectively.

During the simultaneous driving of the boom

1

and turning of the main body

4

, a slow turning of the main body

4

is allowed or preferred, and the boom

1

is desired to be erected as soon as possible. Then, as shown in

FIG. 8

, the hydraulic circuit between the third pump P

3

and the turning motor M is throttled and branches toward the boom cylinder CY

1

so as to join the pressure oil from the third pump P

3

with the original pressure oil flow from the first pump P

1

to the boom cylinder CY

1

. Due to the addition of the slight pressure oil from the third pump P

3

to that for the boom cylinder CY

1

, the acting speed of the boom

1

is increased so much. The turning speed of the main body

4

is reduced because of the throttling of the pressure oil flow for the turning motor M.

Next, explanation will be given on the hydraulic circuit system shown in

FIG. 9

, which makes the above mentioned various patterns of pressure oil supplying to the hydraulic actuators (the hydraulic cylinders CY

1

through CY

3

and turning motor M) for driving the working arms (the boom

1

, arm

2

and bucket.

3

) and for turning the main body

4

. In this regard, it is assumed that each of hydraulic valves V

1

through V

8

is neutral and not a pilot pressure Pa for accelerating the boom

1

but a pilot pressure Pb is applied onto a hydraulic accelerating valve V.

A hydraulic left travelling valve V

5

L is supplied with the pressure oil from the first pump P

1

for driving the left travelling motor ML, and a hydraulic right travelling valve V

5

R from the second pump P

2

for driving the right travelling motor MR. The pressure oil from the first pump P

1

passing the left travelling valve V

5

L is supplied to a hydraulic boom valve V

1

for controlling the boom cylinder CY

1

, and further to a hydraulic bucket valve V

3

for controlling the bucket cylinder CY

3

. The pressure oil from the second pump P

2

passing the right travelling valve V

5

R is supplied to a hydraulic arm valve V

2

for controlling the arm cylinder CY

2

through a hydraulic swinging valve V

7

for controlling the lateral rotation of the boom bracket

4

a

supporting the basic end of the boom

1

, and a hydraulic PTO valve V

8

. The pressure oil from the third pump P

3

is supplied to a hydraulic turning valve V

4

through a hydraulic blade valve V

6

for controlling the hydraulic cylinder for vertical motion of the blade

6

, and the accelerating valve V.

From the accelerating valve V is extended a boom accelerating circuit R

1

to the boom valve V

1

, and a throttling circuit R

2

to the turning valve V

4

. When the pilot pressure Pa is applied onto the accelerating valve V, the pressure oil from the third pump P

3

passing the accelerating valve V (through the blade valve V

6

) is divided into the boom accelerating circuit R

1

and the throttling circuit R

2

. The boom accelerating circuit R

1

joins the hydraulic circuit to the boom cylinder CY

1

. The throttling circuit V

4

joins the hydraulic circuit to the turning motor M. Unless the main body

4

is turned, the turning valve R

2

is neutral, so that the hydraulic circuit to the boom cylinder CY

1

is supplied with the formal quantity of pressure oil from the third pump P

3

through the boom accelerating circuit R

1

without flowing to the turning valve V

4

through the throttling circuit R

2

, thereby accelerating the boom

1

, or making the condition shown in FIG.

1

.

When the boom

1

is driven and the main body

4

is turned simultaneously, the turning valve V

4

is supplied with the reduced pressure oil through the throttling circuit R

2

, thereby turning the main body

4

slowly. The remaining pressure oil from the third pump P

3

flows into the boom accelerating circuit R

1

. This condition is shown in FIG.

8

.

The pilot pressure Pa is applied only when the boom

1

is accelerated during the individual driving of the boom

1

or during the simultaneous driving of the boom

1

and the main body

4

. At all other times, the pilot pressure Pa is not applied so that the pressure oil from the third pump P

3

does not flow into either the boom accelerating circuit R

1

or the throttling circuit R

2

. In case of driving the boom cylinder CY

1

together with another hydraulic driving means as shown in

FIG. 5

or

7

, the boom cylinder CY

1

is supplied with only the pressure oil from the first pump P

1

.

During the simultaneous driving of the boom

1

and arm

2

as shown in

FIG. 5

in the condition that not the pilot pressure Pa but the pilot pressure Pb is applied onto the accelerating valve V, the acceleration of the arm

2

is prior to that of the boom

1

, so that the pressure oil from the third pump P

3

through the accelerating valve V passes the neutral turning valve V

4

and an arm accelerating circuit R

3

joining the hydraulic circuit between the second pump P

2

and the arm valve V

2

, whereby the arm cylinder CY

2

is supplied with the joined pressure oil, thereby accelerating the arm

2

. Additionally, a PTO accelerating circuit R

4

is interposed between the arm accelerating circuit R

3

and the PTO valve V

8

. Unless the arm

2

is driven(when the arm valve V

2

is in neutral), the pressure oil through the arm accelerating circuit R

3

flows into the PTO accelerating circuit R

4

, thereby enabling a PTO driving device to be driven.

As shown in

FIG. 7

, when the main body

4

is rotated simultaneously with the driving of the boom

1

and arm

2

, the turning valve V

4

is set in the acting position, thereby shutting off the pressure oil flow to the arm accelerating circuit R

3

. Thus, the arm cylinder CY

2

is supplied with only the pressure oil from the second pump P

2

, so that the arm

2

is driven without being accelerated.

The hydraulic circuit system shown in

FIG. 9

such constructed as the above mentioned can make every hydraulic driving pattern of them shown in

FIGS. 1 through 8

. However, a small excavator employing the system occasionally requires no acceleration or requires the reduction of the increased operation speed. The hydraulic circuit system shown in

FIG. 10

answers to such requirements. In this case, the boom accelerating circuit R

1

extended from the accelerating circuit V can constitute a bleed-off-circuit R

1

′ without joining the hydraulic circuit between the first pump P

1

and the boom valve V

1

, so that the boom

1

is not accelerated, thereby preventing the erecting of the boom

1

from being badly operated at excessive high speed.

The hydraulic circuit shown in

FIG. 10

also limits the increasing speed of the arm

2

. In this regard, the arm accelerating circuit R

3

, through which the pressure oil from the third pump P

3

flows, branches so as to constitute a cut-off circuit R

3

a having an orifice toward a bleed-off(draining) circuit R

5

extended from the arm valve V

2

. Accordingly, a part of the pressure oil from the third pump P

3

flows into the bleed-off circuit R

5

through the cut-off circuit R

3

a, thereby being bled off. The remaining discharged pressure oil therefrom enters the arm accelerating circuit R

3

, so that the arm cylinder CY

2

is supplied with pressure oil less than that in the case shown in FIG.

9

. Thus, the increasing speed of the arm

2

is limited so as to prevent the arm

2

from being badly operated at excessive high speed. Additionally, when the hydraulic circuit for PTO as shown in

FIG. 9

is provided in the hydraulic circuit shown in

FIG. 10

, the whole of pressure oil toward the arm accelerating circuit R

3

flows through the PTO accelerating circuit R

4

. Thus, the providing of the cut-off circuit R

3

a enables the the increasing of the PTO operation speed to be limited.

The hydraulic circuit system for a turning excavator such constructed as the above according to the present invention is advantageous as follows:

The above various pressure oil supplying patterns are made by the first and second main pumps P

1

and P

2

and the third pump P

3

without another additional hydraulic pump for acceleration. Particularly, during the individual driving of the hydraulic actuator for the boom or arm, the pressure oil for acceleration thereof can be supplied from the third pump P

3

, which is not used for turning of the main body, so that the boom or arm can be operated at an increased speed by such simple and low-costing system, thereby improving the efficiency of working.

When the system is provided with a plurality of the third pumps P

3

, the pressure oil for acceleration of the individual driving of the boom or arm can be increased, thereby driving it more swiftly.

Referring to the simultaneous driving of the boom and arm, since the operation speed of the arm is higher than that of the boom because of the preferential supplying of the hydraulic actuator for the arm with pressure oil from the third pump P

3

, the horizontally excavating motion of the bucket, for example, can be swift and smooth, and when folding the working arms, the arm expanded apart from the main body can be pulled swiftly so as to be firstly placed in the safe range of the excavator.

Referring to the simultaneous driving of the bucket and arm, since the operation speed of the arm is higher than that of the bucket because of the preferential supplying of the hydraulic actuator for the arm with pressure oil from the third pump P

3

, the arm can be pulled swiftly into the safe range when the arm and bucket are folded toward the arm or in other cases.

Referring to the simultaneous driving of the boom and turning of the main body, the turning speed of the main body is limited while the operation speed of the boom is increased because of the actuator for the boom additionally supplied with a part of pressure oil flowing between the third pump P

3

and the actuator for the main body, so that, when the excavator raises sand and move it to a truck, the erecting motion of the boom is relatively faster than the turning speed of the main body, whereby the excavator can do it swiftly and smoothly.

On the precondition that the branching circuit to the hydraulic actuator for the boom can communicate with the draining circuit, if the acceleration of the boom is unnecessary in such a case that the hydraulic system is applied on a small turning excavator or so on, the branching circuit is made to be a bleed-off-circuit, so that the actuator for the boom is always supplied with only pressure oil from the first pump P

1

without additional pressure oil from the third pump P

3

, thereby preventing the boom from being badly operated too fast. It means that the hydraulic circuit system can be applied on either of small and large excavators, thereby reducing the manufacturing cost thereof.

Additionally, on the precondition that a part of pressure oil between the third pump P

3

and the hydraulic actuator for the arm is introduced into the draining circuit, even if the acceleration of the arm is not necessary so much, the amount of pressure oil from the third pump P

3

to the actuator for the arm is limited because of the partly bleeding-off of pressure oil between the third pump P

3

and the actuator for the arm is bled off, so that the increased operation speed of the arm is limited, thereby preventing the arm from being badly operated too fast. It means that the hydraulic circuit system can be applied on either of small and large excavators, thereby reducing the manufacturing cost thereof.

Field of Industrial Use

The hydraulic circuit system of the present invention is suitable to a turning excavator having respective hydraulic actuators for driving working arms and turning a main body, the hydraulic actuators being supplied with pressure oil from at least three hydraulic pumps, which has the capacity of accelerating a boom or an arm for improving efficiency of works.

Claims

1. A hydraulic circuit system for a turning excavator, comprising:a first hydraulic pump and a second hydraulic pump, wherein one of said first and second hydraulic pumps is fluidly connected to a first hydraulic circuit that supplies pressure oil for driving a boom; and at least one hydraulic third pump for supplying pressure oil fluidly connected to a second hydraulic circuit for turning an excavator body, wherein, while said boom is driven and said excavator body is turned simultaneously, said at least one hydraulic third pump is also fluidly connected to said first hydraulic circuit so as to additionally provide a part of the pressure oil supplied for turning said excavator body to said first hydraulic circuit, thereby accelerating operation of said boom.
2. The hydraulic circuit system for a turning excavator as set forth in claim 1, further comprising:a branching circuit extended from said second hydraulic circuit, wherein, while said boom is driven and said excavator body is turned simultaneously, said branching circuit is fluidly connected to said first hydraulic circuit so as to additionally supply a part of the pressure oil supplied for turning said excavator body to said first hydraulic circuit, thereby accelerating operation of said boom; and a draining circuit fluidly connected to said branching circuit, wherein a part of the pressure oil through said branching circuit is introduced into said draining circuit.
3. The hydraulic circuit system for a turning excavator as set forth in claim 2, further comprising:a PTO hydraulic circuit fluidly connected to said branching circuit for supplying pressure oil for driving a PTO device, wherein a part of the pressure oil through said PTO hydraulic circuit is introduced into said draining circuit.
4. A hydraulic circuit system for a turning excavator, comprising:a first hydraulic pump for supplying pressure oil fluidly connected to a first hydraulic circuit for driving a boom; a second hydraulic pump for supplying pressure oil fluidly connected to a second hydraulic circuit for driving an arm; and a hydraulic third pump for supplying pressure oil fluidly connected to a third hydraulic circuit for turning an excavator body, wherein said hydraulic third pump is also selectively fluidly connected to one of said first and second hydraulic circuits for providing additional pressure oil to said one of said first and second hydraulic circuits to accelerate operation of one of said boom and said arm.
5. A hydraulic circuit system for a turning excavator, comprising:a first hydraulic pump for supplying pressure oil fluidly connected to a first hydraulic circuit for driving a boom; a second hydraulic pump for supplying pressure oil fluidly connected to a second hydraulic circuit for driving an arm; and a plurality of hydraulic third pumps for supplying pressure oil, wherein at least one of said hydraulic third pumps is fluidly connected to a third hydraulic circuit for turning an excavator body, and wherein said plurality of hydraulic third pumps are also selectively fluidly connected to one of said first and second hydraulic circuits for providing additional pressure oil to said one of said first and second hydraulic circuits to accelerate operation of one of said boom and said arm.
6. A hydraulic circuit system for a turning excavator, comprising:a first hydraulic pump for supplying pressure oil fluidly connected to a first hydraulic circuit for driving a boom; a second hydraulic pump for supplying pressure oil fluidly connected to a second hydraulic circuit for driving an arm; and at least one hydraulic third pump for supplying pressure oil fluidly connected to a third hydraulic circuit for turning an excavator body, wherein, unless said excavator body is turned, said at least one hydraulic third pump is selectively fluidly connected to one of said first and second hydraulic circuits for providing additional pressure oil to said one of said first and second hydraulic circuits to accelerate operation of one of said boom and said arm, and wherein said hydraulic third pump is fluidly connected to said second hydraulic circuit to preferentially accelerate operation of said arm during the simultaneous driving of said boom, and said arm without turning said excavator body.
7. The hydraulic circuit system for a turning excavator as set forth in claim 6, further comprising:a branching circuit extended from said third hydraulic circuit and selectively fluidly connected to one of said first and second hydraulic circuits for accelerating one of said boom and said arm, wherein said branching circuit is fluidly connected to said second hydraulic circuit to preferentially accelerate operation of said arm during the simultaneous driving of said boom and said arm without turning said excavator body; and a draining circuit fluidly connected to said branching circuit, wherein a part of the pressure oil through said branching circuit is introduced into said draining circuit.
8. A hydraulic circuit system for a turning excavator, comprising:a first hydraulic pump for supplying pressure oil fluidly connected to a first hydraulic circuit for driving a boom and a bucket; a second hydraulic pump for supplying pressure oil fluidly connected to a second hydraulic circuit for driving an arm; and at least one hydraulic third pump for supplying pressure oil fluidly connected to a third hydraulic circuit for turning an excavator body, wherein, unless said excavator body is turned, said at least one hydraulic third pump is selectively fluidly connected to one of said first and second hydraulic circuits for providing additional pressure oil to said one of said first and second hydraulic circuits to accelerate operation of one of said boom and said arm, and wherein said hydraulic third pump is fluidly connected to said second hydraulic circuit for preferentially accelerating said arm during the simultaneous driving of said arm and said bucket without turning said excavator body.

Priority Claims (1)

Number	Date	Country	Kind
8-247883	Sep 1996	JP

PCT Information

Filing Document	Filing Date	Country	Kind	102e Date	371c Date
PCT/JP97/03288		WO	00	3/4/1999	3/4/1999

Publishing Document	Publishing Date	Country	Kind
WO98/12391	3/26/1998	WO	A

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3686862	Grider et al.	Aug 1972
3723026	Soyland et al.	Mar 1973
3922855	Bridwell et al.	Dec 1975
3998053	Johnson	Dec 1976
4000616	Symmank	Jan 1977
4210061	Bianchetta	Jul 1980
4526085	Morizur et al.	Jul 1985
4649705	Williamson	Mar 1987
4928488	Hunger	May 1990
4961371	Takashima	Oct 1990
4986075	Shimoie	Jan 1991
5136846	Arii et al.	Aug 1992
5832729	Reid et al.	Nov 1998

Hydraulic circuit for turning excavator

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

PCT Information

US Referenced Citations (13)