WO2017170352A1

WO2017170352A1 - Shovel

Info

Publication number: WO2017170352A1
Application number: PCT/JP2017/012303
Authority: WO
Inventors: 圭二本田; 塚根　浩一郎; 英祐松嵜; 匠伊藤
Original assignee: 住友重機械工業株式会社
Priority date: 2016-03-29
Filing date: 2017-03-27
Publication date: 2017-10-05
Also published as: JP2019094608A

Abstract

This shovel is provided with: hydraulic pumps (14L, 14R); an engine (11) which drives the hydraulic pumps (14L, 14R); a variable displacement regenerative hydraulic motor (14A) which drives the hydraulic pumps (14L, 14R); a transmission (13) which is connected to the output shaft of the engine (11) and the output shaft of the regenerative hydraulic motor (14A) and which transmits power from the engine (11) and power from the regenerative hydraulic motor (14A) to the hydraulic pumps (14L, 14R); a boom cylinder (7) to which a work oil discharged from the hydraulic pumps (14L, 14R) is supplied; a line (45) which connects the boom cylinder (7) and the regenerative hydraulic motor (14A); a line (46) which branches from the line (45); and a first accumulator (85L) which accumulates the working oil that is emitted from the boom cylinder (7) and flows through the line (45) and the line (46).

Description

Excavator

The present invention relates to an excavator provided with an accumulator.

An excavator that accumulates pressure in an accumulator by increasing the pressure of hydraulic oil flowing out from the bottom oil chamber of the boom cylinder with a pump motor when the boom is lowered is known (see Patent Document 1). This shovel makes a pump motor act as a motor when supplying hydraulic oil accumulated in an accumulator to a bottom side oil chamber of a boom cylinder.

Japanese Patent No. 5412077

However, the above-described excavator increases the engine load because the pump motor acts as a pump when accumulating pressure in the accumulator.

In view of the above, it is desired to provide an excavator that can more efficiently use hydraulic oil flowing out from the bottom oil chamber of the boom cylinder when the boom is lowered.

An excavator according to an embodiment of the present invention includes a hydraulic pump that discharges hydraulic oil, an engine that drives the hydraulic pump, a variable displacement hydraulic motor that drives the hydraulic pump, an output shaft of the engine, and the hydraulic pressure A pump drive connected to an output shaft of the motor and transmitting the power of the engine and the power of the hydraulic motor to the hydraulic pump; a hydraulic actuator for a boom to which hydraulic oil discharged from the hydraulic pump is supplied; A first pipe connecting the boom hydraulic actuator and the hydraulic motor; a second pipe branched from the first pipe; and the first pipe and the second pipe discharged from the boom hydraulic actuator. And an accumulator for accumulating hydraulic fluid flowing through the path.

The above-described means provides an excavator that can more efficiently use the hydraulic oil flowing out from the bottom oil chamber of the boom cylinder when the boom is lowered.

It is a side view of the shovel which concerns on the Example of this invention. It is a figure which shows the structural example of the drive system mounted in the shovel of FIG. It is a figure which shows another structural example of the drive system mounted in the shovel of FIG.

FIG. 1 is a side view showing an excavator (excavator) as a construction machine to which the present invention is applied. An upper swing body 3 is mounted on the lower traveling body 1 of the excavator via a swing mechanism 2. A boom 4 is attached to the upper swing body 3. An arm 5 is attached to the tip of the boom 4, and a bucket 6 is attached to the tip of the arm 5. The boom 4, the arm 5, and the bucket 6 as work elements constitute a drilling attachment that is an example of an attachment, and are hydraulically driven by the boom cylinder 7, the arm cylinder 8, and the bucket cylinder 9, respectively. The upper swing body 3 is provided with a cabin 10 and is mounted with a power source such as the engine 11 and a controller 30.

The controller 30 is a control device as a main control unit that performs drive control of the excavator. In the example of FIG. 1, the controller 30 includes an arithmetic processing unit that includes a CPU and an internal memory, and realizes various functions by causing the CPU to execute a drive control program stored in the internal memory.

FIG. 2 is a schematic diagram showing a configuration example of a hydraulic circuit mounted on the excavator of FIG. In the example of FIG. 2, the hydraulic circuit mainly includes a first pump 14L, a second pump 14R, a regeneration hydraulic motor 14A, a control valve 17, a first accumulator 85L, a second accumulator 85H, and a hydraulic actuator. The hydraulic actuator mainly includes a boom cylinder 7, an arm cylinder 8, a bucket cylinder 9, and a turning hydraulic motor 21. The hydraulic actuator may include a left traveling hydraulic motor (not shown) and a right traveling hydraulic motor (not shown).

The turning hydraulic motor 21 is a hydraulic motor for turning the upper turning body 3, and has

ports

21L and 21R. The

ports

21L and 21R are connected to the first accumulator 85L via the

relief valves

22L and 22R, connected to the hydraulic oil tank T and the first accumulator 85L via the

check valves

23L and 23R, and the

check valves

24L and 24R. To the second accumulator 85H and the regenerative hydraulic motor 14A.

The relief valve 22L opens when the pressure on the port 21L side reaches a predetermined relief pressure, and can discharge the hydraulic oil on the port 21L side to the first accumulator 85L. The relief valve 22R opens when the pressure on the port 21R side reaches a predetermined relief pressure, and can discharge the hydraulic oil on the port 21R side to the first accumulator 85L.

The check valve 23L opens when the pressure on the port 21L side becomes lower than the pressure on the opposite side, and can supply hydraulic oil from the hydraulic oil tank T or the first accumulator 85L to the port 21L side. The check valve 23R opens when the pressure on the port 21R side becomes lower than the pressure on the opposite side, and can supply hydraulic oil from the hydraulic oil tank T or the first accumulator 85L to the port 21R side. In this manner, the

check valves

23L and 23R constitute a supply mechanism that can supply hydraulic oil to the suction side port when the hydraulic motor 21 for turning is braked.

The check valve 24L opens when the pressure on the port 21L side becomes higher than the pressure on the opposite side, and can supply hydraulic oil to the second accumulator 85H or the regenerative hydraulic motor 14A from the port 21L side. The check valve 24R opens when the pressure on the port 21R side becomes higher than the pressure on the opposite side, and can supply hydraulic oil from the port 21R side to the second accumulator 85H or the regenerative hydraulic motor 14A. In this manner, the

check valves

24L and 24R can supply hydraulic oil at the discharge port to at least one of the second accumulator 85H and the regenerative hydraulic motor 14A during braking of the turning hydraulic motor 21.

The proportional valve 22G is a valve that controls the flow rate by adjusting the size of the opening in accordance with a command from the controller 30. In the example of FIG. 2, the proportional valve 22G is a 1-port 2-position electromagnetic proportional valve capable of switching between communication and blocking between the turning hydraulic motor 21 and the second accumulator 85H. Specifically, the proportional valve 22G can communicate between the turning hydraulic motor 21 and the second accumulator 85H with a maximum opening when in the first position, and can block the communication when in the second position.

The first pump 14L is a hydraulic pump that sucks and discharges hydraulic oil from the hydraulic oil tank T. In the example of FIG. 2, it is a swash plate type variable displacement hydraulic pump. The first pump 14L is connected to a regulator (not shown). The regulator changes the swash plate tilt angle of the first pump 14L in accordance with a command from the controller 30, and controls the displacement volume (discharge amount per rotation) of the first pump 14L. The same applies to the second pump 14R.

The regenerative hydraulic motor 14 A is a hydraulic motor that assists the engine 11 by regenerating energy of hydraulic oil flowing out from the hydraulic actuator. In the example of FIG. 2, a swash plate type variable displacement hydraulic motor, the discharge side port of which is connected to the hydraulic oil tank T. Therefore, the hydraulic oil discharged by the regeneration hydraulic motor 14A can be returned to the hydraulic oil tank T when the boom is lowered.

The regenerative hydraulic motor 14A is connected to a regulator in the same manner as the first pump 14L and the second pump 14R. The regulator changes the swash plate tilt angle of the regenerative hydraulic motor 14A in accordance with a command from the controller 30 to control the displacement of the regenerative hydraulic motor 14A. The regulator may be capable of setting the displacement volume (swash plate tilt angle) of the regeneration hydraulic motor 14A to zero. This is because the hydraulic oil can be rotated without being consumed (sucked and discharged), and the flow of the hydraulic oil passing through the regeneration hydraulic motor 14A can be blocked.

The first accumulator 85L is a hydraulic device that accumulates hydraulic fluid discharged from the boom cylinder 7. In the example of FIG. 2, in the first accumulator 85 L, the accumulation / release of hydraulic oil is controlled by the switching valve 86. Further, the working pressure of the first accumulator 85L is higher than the pressure of the working oil in the working oil tank T, and is, for example, in the range of 0.2 to 5 MPa. This is because it is possible to prevent the occurrence of cavitation by reliably supplying hydraulic oil to the suction side port of the turning hydraulic motor 21 at the time of turning deceleration. Further, when the hydraulic oil discharged from the discharge side port of the turning hydraulic motor 21 during turning deceleration is accumulated in the second accumulator 85H, the hydraulic oil discharged from the discharge side port does not circulate to the suction side and cavitation occurs. This is because it becomes easier.

The switching valve 86 is a valve that operates in response to a command from the controller 30. In the example of FIG. 2, the switching valve 86 is a 1-port 2-position electromagnetic valve that can switch communication / blocking between the first accumulator 85 L and the turning hydraulic motor 21. Specifically, the switching valve 86 communicates between the first accumulator 85L and the turning hydraulic motor 21 when in the first position, and shuts off the communication when in the second position.

The relief valve 90 opens when the pressure of the hydraulic oil in the first accumulator 85L reaches a predetermined relief pressure, and discharges the hydraulic oil to the hydraulic oil tank.

A second accumulator 85H is arranged via a switching valve 87 on the upstream side (suction side) of the regeneration hydraulic motor 14A.

The second accumulator 85H is a hydraulic device that accumulates hydraulic oil flowing out from the discharge side port of the turning hydraulic motor 21. In the example of FIG. 2, in the second accumulator 85H, the accumulation of hydraulic oil is controlled by the proportional valve 22G, and the discharge of hydraulic oil is controlled by the switching valve 87. Further, the working pressure of the second accumulator 85H is higher than the working pressure of the first accumulator 85L, and is, for example, in the range of 15 to 30 MPa. However, the working pressure of the second accumulator 85H is lower than the relief pressure of the

relief valves

22L and 22R.

The switching valve 87 is a valve that operates in response to a command from the controller 30. In the example of FIG. 2, the switching valve 87 is a 1-port 2-position electromagnetic valve that can switch communication / blocking between the second accumulator 85 H and the regenerative hydraulic motor 14 A. Specifically, the switching valve 87 communicates between the second accumulator 85H and the regenerative hydraulic motor 14A when in the first position, and shuts off the communication when in the second position.

In the example of FIG. 2, the drive shafts of the first pump 14L, the second pump 14R, and the regenerative hydraulic motor 14A are mechanically coupled. Specifically, each drive shaft is connected to the output shaft of the engine 11 at a predetermined gear ratio via a transmission 13 as a pump drive. That is, the transmission 13 is connected to the output shaft of the engine 11 and the output shaft of the regenerative hydraulic motor 14A, and the power of the engine 11 and the power of the regenerative hydraulic motor 14A are transferred to the first pump 14L and the second pump 14R. Can communicate. Therefore, if the engine speed is constant, each speed is also constant. However, the first pump 14L, the second pump 14R, and the regenerative hydraulic motor 14A are connected to the engine 11 via a continuously variable transmission or the like so that the rotational speed can be changed even if the engine rotational speed is constant. May be.

The first pump 14L and the second pump 14R circulate the hydraulic oil to the hydraulic oil tank T via the

center bypass pipelines

40L and 40R, the

parallel pipelines

42L and 42R, or the

return pipelines

43L, 43R and 43C.

The center bypass conduit 40L is a hydraulic oil line that passes through the

flow control valves

170, 172L, and 173L disposed in the control valve 17. The center bypass conduit 40 R is a hydraulic oil line that passes through the

flow control valves

171, 172 R, and 173 R disposed in the control valve 17.

The parallel pipeline 42L is a hydraulic oil line parallel to the center bypass pipeline 40L. The parallel pipe line 42L can supply the hydraulic oil to the flow control valve further downstream when the flow of the hydraulic oil passing through the center bypass pipe 40L is restricted or blocked by the flow control valve 170 or the flow control valve 172L. The parallel pipeline 42R is a hydraulic oil line parallel to the center bypass pipeline 40R. The parallel pipe line 42R can supply the hydraulic oil to the downstream flow rate control valve when the flow of the hydraulic oil passing through the center bypass pipe line 40R is restricted or blocked by the flow rate control valve 171 or the flow rate control valve 172R.

The return pipeline 43L is a hydraulic oil line parallel to the center bypass pipeline 40L. The return line 43L distributes hydraulic oil flowing from the hydraulic actuator through the flow

rate control valves

170, 172L, and 173L to the return line 43C. The return pipeline 43R is a hydraulic oil line parallel to the center bypass pipeline 40R. The return line 43R distributes hydraulic oil flowing from the hydraulic actuator through the flow

rate control valves

171, 172R, 173R to the return line 43C.

The

center bypass pipelines

40L and 40R include negative control throttles 18L and 18R and

relief valves

19L and 19R between the hydraulic control tanks T and the

flow control valves

173L and 173R located on the most downstream side. The flow of hydraulic oil discharged from the first pump 14L and the second pump 14R is limited by the negative control throttles 18L and 18R. The negative control throttles 18L and 18R generate a control pressure (negative control pressure) for controlling the regulator. The

relief valves

19L and 19R are opened when the negative control pressure reaches a predetermined relief pressure, and the hydraulic oil in the

center bypass pipes

40L and 40R is discharged to the hydraulic oil tank T.

A check valve 20 with a spring is installed on the most downstream side of the return pipe 43C. The check valve 20 with a spring fulfills the function of increasing the pressure of the hydraulic oil in the conduit 44 that connects the turning hydraulic motor 21 and the return conduit 43C. With this configuration, it is possible to reliably supply hydraulic oil to the suction-side port of the turning hydraulic motor 21 during turning deceleration to prevent cavitation.

The control valve 17 is a hydraulic control device that controls a hydraulic drive system in the excavator. The control valve 17 mainly includes

flow control valves

170, 171, 172L, 172R, 173L, and 173R.

The

flow control valves

170, 171, 172L, 172R, 173L, and 173R are configured to control the direction and flow rate of the hydraulic oil flowing into and out of the hydraulic actuator. In the example of FIG. 2, each of the

flow control valves

170, 171, 172 L, 172 R, 173 L, and 173 R has a pilot pressure generated by an operating device (not shown) such as a corresponding operating lever. A three-port, three-position spool valve that receives and operates at the port. The operating device causes the pilot pressure generated according to the operation amount (operation angle) to act on the pilot port on the side corresponding to the operation direction.

Specifically, the flow control valve 170 is a spool valve that controls the direction and flow rate of the hydraulic oil flowing into and out of the turning hydraulic motor 21, and the flow control valve 171 is the hydraulic oil flowing into and out of the bucket cylinder 9. A spool valve that controls the direction and flow rate.

The

flow control valves

172L and 172R are spool valves that control the direction and flow rate of the hydraulic oil flowing into and out of the boom cylinder 7, and the

flow control valves

173L and 173R are the direction and flow rate of the hydraulic oil flowing into and out of the arm cylinder 8. It is a spool valve that controls.

Here, the boom lowering regeneration circuit in the hydraulic circuit of FIG. 2 will be described. The boom lowering regeneration circuit mainly includes a pipe 45, a pipe 46, a proportional valve 70, and a switching valve 71.

The pipe line 45 is configured to connect the bottom side oil chamber of the boom cylinder 7 and the upstream side (suction side) of the regenerative hydraulic motor 14A. The pipe 46 is configured to branch from the pipe 45 and connect the pipe 45 and the first accumulator 85L.

The proportional valve 70 is configured to control the flow rate by adjusting the size of the opening in accordance with a command from the controller 30. In the example of FIG. 2, the proportional valve 70 is a 1-port 2-position electromagnetic proportional valve capable of switching communication / blocking between the bottom oil chamber of the boom cylinder 7 and the first accumulator 85 L. The proportional valve 70 is provided in the pipe 46. Specifically, when the proportional valve 70 is in the first position, the bottom side oil chamber of the boom cylinder 7 and the first accumulator 85L communicate with each other at the maximum opening, and when in the second position, the proportional valve 70 communicates with the communication. Can be blocked.

The switching valve 71 is configured to operate in accordance with a command from the controller 30. In the example of FIG. 2, the switching valve 71 is an electromagnetic proportional one-port and two-position that can switch communication / blocking between the bottom oil chamber of the boom cylinder 7 and the upstream side (suction side) of the regenerative hydraulic motor 14 A. It is a valve. The switching valve 71 is provided in the pipeline 45. Specifically, when the switching valve 71 is in the first position, the switching valve 71 communicates between the bottom side oil chamber of the boom cylinder 7 and the upstream side (suction side) of the regenerative hydraulic motor 14A and is in the second position. In that case, the communication is cut off.

When the controller 30 detects that the boom lowering operation has been performed based on the outputs of various sensors, the controller 30 outputs a command to the switching valve 71. Upon receiving the command, the switching valve 71 switches to the first position, and communicates between the bottom oil chamber of the boom cylinder 7 and the upstream side (suction side) of the regeneration hydraulic motor 14A.

Further, the controller 30 outputs a command to the regulator of the regeneration hydraulic motor 14A. The regenerative hydraulic motor 14 A directly receives hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 and rotates to assist the engine 11.

In this way, the regenerative hydraulic motor 14A can directly regenerate the hydraulic energy of the hydraulic oil flowing out from the boom cylinder 7 (the potential energy of the boom 4) when the boom is lowered. Therefore, it is possible to save energy by effectively using the energy that was discarded as heat (pressure loss) when the boom is lowered. In addition, the hydraulic oil flowing out of the boom cylinder 7 is temporarily stored in the accumulator, and then it is more efficient than indirectly regenerating the hydraulic energy of the hydraulic oil flowing out of the accumulator.

Further, the controller 30 may output a command to the proportional valve 70 when the flow rate of the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 exceeds the flow rate acceptable by the regenerative hydraulic motor 14A. . Receiving the command, the proportional valve 70 switches to the first position, and communicates between the bottom side oil chamber of the boom cylinder 7 and the first accumulator 85L. Therefore, the first accumulator 85L can accumulate the hydraulic oil that cannot be absorbed by the regenerative hydraulic motor 14A among the hydraulic oil flowing out from the boom cylinder 7 when the boom is lowered. That is, hydraulic oil that cannot be sucked by the regenerative hydraulic motor 14A can be accumulated in the first accumulator 85L.

Further, the controller 30 can adjust the pressure of the hydraulic oil in the pipe 45 by adjusting the opening degree of the proportional valve 70 when the boom is lowered. That is, it is possible to adjust the back pressure due to the working oil from the bottom oil chamber of the boom cylinder 7 toward the regeneration hydraulic motor 14A. Therefore, the back pressure that increases due to the response delay of the regenerative hydraulic motor 14A can be adjusted, and the responsiveness and fine operability of the boom operation can be ensured.

Further, when it is not necessary to assist the engine 11, the controller 30 adjusts the opening degree of the proportional valve 70 to be larger when the boom is lowered, so that the hydraulic oil that flows out from the bottom side oil chamber of the boom cylinder 7. Most of the pressure can be accumulated in the first accumulator 85L. Therefore, it is possible to prevent engine overspeed due to excessive assist.

Next, another configuration example of the hydraulic circuit mounted on the excavator in FIG. 1 will be described with reference to FIG. FIG. 3 is a schematic view showing another configuration example of a hydraulic circuit mounted on the excavator of FIG. The hydraulic circuit of FIG. 3 differs from the hydraulic circuit of FIG. 2 mainly in that the control valve 17 includes variable load check valves 51 to 53, a merging valve 55, and unified bleed-off

valves

56L and 56R. It is common in. Therefore, description of common parts is omitted, and different parts are described in detail. FIG. 3 clearly shows the

regeneration valves

7a, 8a and 9a and the holding

valves

7b and 8b.

The

ports

21L and 21R of the turning hydraulic motor 21 are connected to the hydraulic oil tank T via

relief valves

22L and 22R, connected to the proportional valve 22G via a shuttle valve 22S, and via

check valves

23L and 23R. And connected to the hydraulic oil tank T.

The relief valve 22L is opened when the pressure on the port 21L side reaches a predetermined relief pressure, and the hydraulic oil on the port 21L side can be discharged to the hydraulic oil tank T. The relief valve 22R is opened when the pressure on the port 21R side reaches a predetermined relief pressure, and the hydraulic oil on the port 21R side can be discharged to the hydraulic oil tank T.

The shuttle valve 22S can supply hydraulic oil having higher pressure on the port 21L side and the port 21R side to the proportional valve 22G.

The proportional valve 22G is configured to operate in accordance with a command from the controller 30. In the example of FIG. 3, the proportional valve 22 G is a 1-port 2-position electromagnetic valve that can switch communication / blocking between the swing hydraulic motor 21 (shuttle valve 22 S) and the second accumulator 85 H.

check valves

The variable load check valves 51 to 53 are configured to operate in response to a command from the controller 30. In the example of FIG. 3, the variable load check valves 51 to 53 can switch communication / blocking between each of the flow control valves 171 to 173 and at least one of the first pump 14L and the second pump 14R. It is a solenoid valve at the port 2 position. The variable load check valves 51 to 53 have a check valve that blocks the flow of hydraulic oil returning to the pump side at the first position. Specifically, when the variable load check valve 51 is in the first position, the flow control valve 173 communicates with at least one of the first pump 14L and the second pump 14R and is in the second position. In that case, the communication is cut off. The same applies to the variable load check valve 52 and the variable load check valve 53.

The merging valve 55 is an example of a merging switching unit, and is configured to operate in accordance with a command from the controller 30. In the example of FIG. 3, the merging valve 55 is hydraulic oil discharged from the first pump 14L (hereinafter referred to as “first hydraulic oil”) and hydraulic oil discharged from the second pump 14R (hereinafter referred to as “second operation”). It is a 1-port 2-position solenoid valve that can be switched to join or not. Specifically, the merging valve 55 merges the first hydraulic oil and the second hydraulic oil when in the first position, and merges the first hydraulic oil and the second hydraulic oil when in the second position. Do not let it.

The unified bleed-off

valves

56L and 56R are configured to operate in response to a command from the controller 30. In the example of FIG. 3, the unified bleed-off valve 56 L is a 1-port 2-position electromagnetic valve that can control the discharge amount of the first hydraulic oil to the hydraulic oil tank T. The same applies to the unified bleed-off valve 56R. With this configuration, the unified bleed-off

valves

56L and 56R can realize the combined opening of the associated flow control valves among the flow control valves 170 to 173. Specifically, when the merging valve 55 is in the second position, the unified bleed-off valve 56L can realize a combined opening of the flow control valve 170 and the flow control valve 173, and the unified bleed-off valve 56R includes the flow control valve 171 and A synthetic opening of the flow control valve 172 can be realized. The unified bleed-off valve 56L functions as a variable throttle that adjusts the opening area of the synthetic opening in accordance with a command from the controller 30 when in the first position, and opens the synthetic opening when in the second position. Cut off. The same applies to the unified bleed-off valve 56R.

Each of the variable load check valves 51 to 53, the merging valve 55, and the unified bleed-off

valves

56L and 56R may be pilot pressure driven spool valves.

The check valve 89 shuts off the flow of hydraulic oil flowing out to the hydraulic oil tank T. In the example of FIG. 3, the check valve 89 can prevent a part of the hydraulic oil flowing from the second accumulator 85H to the regenerative hydraulic motor 14A from flowing out to the hydraulic oil tank T. The check valve 89 does not block the flow of hydraulic oil from the hydraulic oil tank T to the third pump when the regenerative hydraulic motor 14A functions as the third pump.

Here, the boom lowering regeneration circuit in the hydraulic circuit of FIG. 3 will be described. The boom lowering regeneration circuit mainly includes a pipe 45, a pipe 46, a proportional valve 70, and a switching valve 71.

The pipe line 45 is configured to connect the bottom side oil chamber of the boom cylinder 7 and the upstream side (suction side) of the regenerative hydraulic motor 14A. The pipe line 46 is configured to connect the pipe line 45 and the first accumulator 85L.

The proportional valve 70 is configured to operate in response to a command from the controller 30. In the example of FIG. 3, the proportional valve 70 is a 1-port 2-position electromagnetic proportional valve capable of switching communication / blocking between the bottom oil chamber of the boom cylinder 7 and the first accumulator 85 L. The proportional valve 70 is provided in the pipe 46. Specifically, the proportional valve 70 communicates between the bottom oil chamber of the boom cylinder 7 and the first accumulator 85L when in the first position, and blocks communication when in the second position.

The switching valve 71 is configured to operate in accordance with a command from the controller 30. In the example of FIG. 3, the switching valve 71 is an electromagnetic proportional one-port and two-position capable of switching communication / blocking between the bottom side oil chamber of the boom cylinder 7 and the upstream side (suction side) of the regenerative hydraulic motor 14 A. It is a valve. The switching valve 71 is provided in the pipeline 45. Specifically, when the proportional valve 70 is in the first position, it communicates between the bottom side oil chamber of the boom cylinder 7 and the upstream side (suction side) of the regenerative hydraulic motor 14A, and is in the second position. In that case, the communication is cut off.

Further, the controller 30 may output a command to the proportional valve 70 when the flow rate of the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 exceeds the flow rate acceptable by the regenerative hydraulic motor 14A. . Receiving the command, the proportional valve 70 switches to the first position, and communicates between the bottom side oil chamber of the boom cylinder 7 and the first accumulator 85L. Therefore, the first accumulator 85L can accumulate the hydraulic oil that cannot be absorbed by the regenerative hydraulic motor 14A among the hydraulic oil flowing out from the boom cylinder 7 when the boom is lowered.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the above-described embodiments. Various modifications and substitutions may be applied to the embodiments described above without departing from the scope of the present invention.

For example, the above hydraulic circuit may be mounted on other construction machines such as a forklift and a wheel loader that move up and down by a hydraulic cylinder.

This application claims priority based on Japanese Patent Application No. 2016-066693 filed on Mar. 29, 2016, the entire contents of which are incorporated herein by reference.

DESCRIPTION OF SYMBOLS 1 ... Lower traveling body 2 ... Turning mechanism 3 ... Upper turning body 4 ... Boom 5 ... Arm 6 ... Bucket 7 ... Boom cylinder 8 ... Arm cylinder 9 ...

Bucket cylinders

7a, 8a, 9a ...

regenerative valves

7b, 8b ... holding valves 10 ... cabin 11 ... engine 13 ... transmission 14L ... first pump 14R ... second Pump 14A ... Regenerative hydraulic motor 17 ...

Control valve

18L, 18R ...

Negative control throttle

19L, 19R ... Relief valve 20 ... Check valve with spring 21 ... Hydraulic motor for turning 21L, 21R ... Port 22G ...

Proportional valve

22L, 22R ... Relief valve 22S ...

Shuttle valve

23L, 23R, 24 , 24R ... check valve 30 ...

controller

40L, 40R ...

center bypass conduit

42L, 42R ...

parallel conduit

43C, 43L, 43R ... return

conduit

44, 45, 46 ...

Pipe line

50, 51, 52, 53 ... Variable load check valve 55 ...

Junction valve

56L, 56R ... Unified bleed-off valve 70 ... Proportional valve 71 ... Switching valve 85L ... First accumulator 85H:

Second accumulator

86, 87 ... Switching valve 89 ... Check valve 90 ...

Relief valve

170, 171, 172, 172L, 172R, 173, 173L, 173R ... Flow control valve T ..Working oil tank

Claims

A hydraulic pump that discharges hydraulic oil;
An engine for driving the hydraulic pump;
A variable displacement hydraulic motor for driving the hydraulic pump;
A pump drive connected to an output shaft of the engine and an output shaft of the hydraulic motor, and transmitting power of the engine and power of the hydraulic motor to the hydraulic pump;
A boom hydraulic actuator to which hydraulic oil discharged from the hydraulic pump is supplied;
A first pipe connecting the boom hydraulic actuator and the hydraulic motor;
A second pipe branching from the first pipe;
An accumulator for accumulating hydraulic fluid discharged from the boom hydraulic actuator and flowing through the first pipe line and the second pipe line;
Excavator.
Supplying hydraulic oil discharged from the boom hydraulic actuator directly to the hydraulic motor when the boom is lowered, and accumulating pressure in the accumulator via the first pipe and the second pipe;
The excavator according to claim 1.
The hydraulic oil accumulated in the accumulator is supplied to the suction side port of the turning hydraulic actuator during turning deceleration.
The excavator according to claim 1.
Comprising another accumulator for accumulating hydraulic fluid discharged from the discharge side port of the turning hydraulic actuator during turning deceleration;
The excavator according to claim 1.
The hydraulic oil discharged from the hydraulic motor is returned to the hydraulic oil tank when the boom is lowered.
The excavator according to claim 1.