JP2013163907A - Hydraulic circuit for boom cylinder of construction machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve fuel efficiency by lowering the delivery pressure of a hydraulic pump which is a pressure oil supply source or a boom cylinder when moving a boom upward, in a construction machine which moves up and down the boom vertically by a telescopic operation of the boom cylinder.SOLUTION: A hydraulic circuit for a boom cylinder 8 of a construction machine is configured in such a manner that: a booster 15 equipped with a pre-compressed spring 15d is disposed in a head side oil path 13 which connects a control valve 12 and a head side oil chamber 8a of the boom cylinder 8 to each other; when moving up the boom 5, the delivery pressure of a hydraulic pump 10 is boosted by an accumulated energizing force of the spring 15d of the booster 15 to supply oil to the head side oil chamber 8a of the boom cylinder 8; and when moving down the boom 5, the spring 15d of the booster 15 is made to accumulate energizing force by discharge oil from the head side oil chamber 8a of the boom cylinder 8.

Description

  The present invention relates to a technical field of a hydraulic circuit for a boom cylinder of a construction machine having a boom such as a hydraulic excavator.

Generally, in construction machines such as hydraulic excavators, an arm or bucket is attached to the tip of the boom that is supported by the machine so that it can swing up and down. Some boom cylinders are provided, and a hydraulic pump is provided as a pressure oil supply source for the boom cylinder. In such a construction machine, the head side oil chamber of the boom cylinder requires a high holding pressure to hold the weight of the front working part, and when the boom is moved up, a pressure oil higher than the holding pressure is supplied to the head side. It is necessary to supply the oil chamber. For this reason, when the boom is moved upward, the hydraulic pump must discharge high-pressure oil, resulting in a high output state and hindering fuel efficiency. On the other hand, when the boom is lowered, oil is discharged from the oil chamber on the head side of the boom cylinder, and the lowering speed of the boom is adjusted by controlling the discharge flow rate with a control valve. High pressure discharged oil from the head-side oil chamber is throttled by the throttle of the control valve, and the loss of heat energy generated by the throttle also becomes a factor in hindering fuel consumption reduction.
Therefore, conventionally, the oil discharged from the head side oil chamber of the boom cylinder when the boom is lowered is accumulated in the accumulator, and the accumulated oil in the accumulator is increased by the pressure increasing cylinder, and the increased pressure oil is supplied to the boom. There is known a technique of supplying the oil to the head side oil chamber of the boom cylinder at the time of upward movement (see, for example, Patent Document 1). In this system, oil discharged from the boom cylinder head side oil chamber when the boom is moved down can be reused to reduce the discharge flow rate of the hydraulic pump when the boom is moved up, thereby reducing fuel consumption. ing.

JP 2009-150462 A

  However, in the above-mentioned Patent Document 1, the oil discharged from the head-side oil chamber of the boom cylinder is supplied to the accumulator and the rod-side oil chamber of the pressure increasing cylinder when the boom is lowered, while the accumulator pressure is accumulated when the boom is moved up. Since the oil is supplied to the head side oil chamber of the pressure increasing cylinder, the pressure oil in the rod side oil chamber of the pressure increasing cylinder is increased and supplied to the head side oil chamber of the boom cylinder. The output oil amount of the booster oil from the booster cylinder is less than half the amount of oil discharged from the side oil chamber. For this reason, the flow rate that can be supplied from the booster cylinder to the head side oil chamber of the boom cylinder when the boom moves up is only a part of the total flow rate supplied to the head side oil chamber, and the remaining flow rate is from the hydraulic pump. Therefore, when the boom is moved upward, the hydraulic pump still has to discharge high pressure oil, and further reduction in fuel consumption is desired. There are issues to be addressed.

The present invention has been created in order to solve these problems in view of the above-described circumstances, and the invention of claim 1 includes a boom supported by an airframe in a vertically swingable manner, and the boom. In a construction machine, comprising: a boom cylinder that expands and contracts to vertically move the hydraulic cylinder; a hydraulic pump that serves as a hydraulic pressure supply source of the boom cylinder; and a control valve that performs oil supply / discharge control on the boom cylinder. A booster with a pre-compressed spring is installed in the oil passage connecting the cylinder head side oil chamber, and when the boom moves up, the discharge pressure of the hydraulic pump is controlled by the stored energy of the spring of the booster. While boosting the pressure and supplying it to the boom-side oil chamber of the boom cylinder, the spring of the booster is stored by the oil discharged from the head-side oil chamber of the boom cylinder when the boom moves down. A hydraulic circuit for a construction machine of the boom cylinder, characterized.
A second aspect of the present invention is the construction machine according to the first aspect, wherein when the boom is moved downward, the pressure booster functions as a pressure decreaser for reducing the pressure of the oil discharged from the head side oil chamber and flowing it to the control valve. It is a hydraulic circuit for boom cylinders.
According to a third aspect of the present invention, in the first or second aspect, the booster is connected to the first oil chamber connected to the control valve and the head side oil chamber of the boom cylinder on both sides of the piston moving in the cylinder. A second oil chamber is formed, and the first oil chamber is provided with a pre-compressed spring, while the second oil chamber has a maximum capacity equivalent to the maximum capacity of the head-side oil chamber of the boom cylinder. A hydraulic circuit for a boom cylinder of a construction machine.
According to a fourth aspect of the present invention, in the method according to any one of the first to third aspects, the hydraulic pump discharge oil supplied from the control valve is supplied to the boom-side oil chamber of the boom cylinder without passing through the booster. Provided with a side bypass oil passage and an upper motion side bypass valve that opens and closes the upper motion side bypass fluid passage, and the spring of the booster extends to the maximum of the movable range when the boom is moved upward. In this case, the boom cylinder hydraulic circuit of the construction machine is configured to open the ascending-side bypass oil passage.
A fifth aspect of the present invention is directed to any one of the first to fourth aspects, wherein the lower side bypass oil passage for flowing the oil discharged from the head side oil chamber of the boom cylinder to the control valve without passing through the booster; A lower-side bypass valve that opens and closes the lower-side bypass oil passage, and the lower-side bypass valve moves downward when the pressure in the rod-side oil chamber of the boom cylinder is equal to or higher than a preset pressure. It is the hydraulic circuit for boom cylinders of the construction machine characterized by opening a side bypass oil path.

According to the first aspect of the present invention, the discharge pressure of the hydraulic pump necessary for the upward movement of the boom can be reduced by the stored energy of the booster spring, and thus the boom requiring high pressure oil is required. Even when the engine is moved upward, the discharge pressure of the hydraulic pump can be kept low, which can greatly contribute to the improvement of fuel consumption.
According to the second aspect of the present invention, the pressure on the inflow side of the throttle formed in the control valve so as to control the flow rate of the oil discharged from the head side oil chamber can be reduced. Compared with the case where high-pressure exhaust oil from the oil passes through the throttle as it is, the throttle can be widened, energy loss in the throttle can be reduced, and further fuel efficiency can be reduced.
By setting it as invention of Claim 3, the whole quantity of the pressure oil supplied to a head side oil chamber at the time of an upward movement of a boom can be supplied from a pressure | voltage riser.
By setting it as invention of Claim 4, even after the spring of a pressure | voltage riser has extended to the maximum of the movable range, a boom can be moved up without trouble.
According to the fifth aspect of the present invention, when a strong force is required to move down the boom, such as excavation work, the lower power of the boom can be increased by flowing the oil discharged from the head side oil chamber to the booster. It can prevent reliably that it falls.

It is a side view of a hydraulic excavator. It is a hydraulic circuit diagram for boom cylinders.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 1 denotes a hydraulic excavator that is an example of a construction machine, and the body of the hydraulic excavator 1 includes a crawler type lower traveling body 2 and an upper portion that is pivotably supported above the lower traveling body 2. Further, the front working unit 4 that is mounted on the upper swing body 3 includes a boom 5 whose base end is supported by the upper swing body 3 so as to be able to swing up and down, and the boom 5. The arm 6 is supported at the tip by swinging back and forth, and the bucket 7 is attached to the tip of the arm 6.

  Further, 8 is a pair of left and right boom cylinders that extend and contract to swing the boom 5 up and down, and the boom cylinder 8 holds the weight of the front working unit 4 by the pressure of the head side oil chamber 8a. The boom 5 is moved upward by the pressure oil supply to the head side oil chamber 8a and the oil discharge from the rod side oil chamber 8b, and the pressure oil supply to the rod side oil chamber 8b and the head side oil chamber 8a are extended. The boom 5 is configured to move down by reducing the oil discharged from the vehicle.

  Next, the hydraulic circuit of the boom cylinder 8 will be described with reference to FIG. 2. In FIG. 2, 9 is an engine, 10 is a hydraulic pump driven by the engine 9, 11 is an oil tank, and 12 is oil for the boom cylinder 8. It is a control valve that performs supply and discharge control. The hydraulic pump 10 is a hydraulic pressure supply source for the boom cylinder 8 and other hydraulic actuators provided in the hydraulic excavator 1 (not shown in FIG. 2, for example, a traveling motor, a turning motor, an arm cylinder, etc. , Bucket cylinders, etc.).

  The control valve 12 includes upper moving side and lower moving side pilot ports 12a and 12b and ports connected to the hydraulic pump 10, the oil tank 11, the head side oil passage 13, and the rod side oil passage 14, respectively. This is a three-position switching spool valve. And in the state where pilot pressure is not inputted to both pilot ports 12a and 12b on the upper moving side and the lower moving side, the discharge oil of the hydraulic pump 10 is not supplied to the head side oil passage 13 and the rod side oil passage 14, In addition, although the oil in the head-side oil passage 13 and the rod-side oil passage 14 is located at the neutral position N where the oil does not flow into the oil tank 11, the hydraulic pump is input by the pilot pressure being input to the upward movement-side pilot port 12a. 10 discharge oil is supplied to the head-side oil passage 13 and the rod-side oil passage 14 is switched to the upward movement position X where the oil in the oil tank 11 flows. Further, when the pilot pressure is input to the lower moving side pilot port 12b, the oil discharged from the hydraulic pump 10 is supplied to the rod side oil passage 14, and the oil in the head side oil passage 13 is supplied to the oil via the throttle 12c. It is configured to switch to the lower movement position Y that flows into the tank 11. The head side oil passage 13 is an oil passage connecting the control valve 12 and the head side oil chamber 8 a of the boom cylinder 8, and the rod side oil passage 14 is a rod of the control valve 12 and the boom cylinder 8. It is an oil path which connects the side oil chamber 8b.

  Here, the upward and downward movement pilot ports 12a and 12b of the control valve 12 are connected to the boom operation lever based on the upward and downward movement operations of the boom operation lever (not shown). The pilot pressure that is controlled to increase or decrease according to the operation amount is input, the movement stroke of the spool of the control valve 12 increases or decreases according to the increase or decrease of the input pilot pressure, and further according to the increase or decrease of the spool movement stroke. The flow rate passing through the control valve 12 is configured to increase or decrease. Thus, by switching the control valve 12 based on the operation of the boom operation lever, the supply / discharge switching and the supply / discharge flow rate control for the head side oil chamber 8a and the rod side oil chamber 8b of the boom cylinder 8 are performed. It has become.

  Further, in the head side oil passage 13 connecting the control valve 12 and the head side oil chamber 8a of the boom cylinder 8, a booster for increasing the discharge pressure of the hydraulic pump 10 and supplying it to the head side oil chamber 8a. 15 is arranged. The booster 15 has a first oil chamber 15b connected to the control valve 12 and a first oil chamber 8a connected to the head side oil chamber 8a of the boom cylinder 8 on both sides of a piston 15a that is movably fitted in the cylinder. The two oil chambers 15c are formed, and the first oil chamber 15b is internally provided with a pre-compressed spring (compression coil spring) 15d that presses the piston 15a toward the second oil chamber 15c by the stored energy. Has been. As the spring 15d, a strong spring that can store a large pressing force (for example, 10 Mpa) that is slightly smaller than the holding pressure of the weight of the front working unit 4 is used. The second oil chamber 15c has a maximum capacity when the piston 15a is moved to the first oil chamber 15b side. The maximum capacity of the second oil chamber 15c is that of the left and right boom cylinders 8. It is designed to be equivalent to the maximum capacity of the head side oil chamber 8a.

  When the boom 5 is moved upward, that is, when the boom operating lever is operated to the upward movement side and the control valve 12 is switched to the upward movement position X, the oil discharged from the hydraulic pump 10 is controlled as described above. The oil supplied from the hydraulic pump 10 to the head side oil passage 13 is supplied to the first oil chamber 15 b of the booster 15 through the valve 12. The oil discharged from the hydraulic pump 10 input to the first oil chamber 15b presses the piston 15a toward the second oil chamber 15c, whereby pressure oil is output from the second oil chamber 15c, and the boom cylinder 8 head. The hydraulic pump 10 is supplied to the side oil chamber 8a. In this case, the stored force of the spring 15d provided in the first oil chamber 15b presses the piston 15a toward the second oil chamber 15c. A pressure obtained by adding the stored force (pressing force) of the spring 15 d to the discharge pressure of the oil is output from the second oil chamber 15 c and supplied to the head-side oil chamber 8 a of the boom cylinder 8. That is, the discharge pressure of the hydraulic pump 10 is boosted by the booster 15 by the amount of the stored force of the spring 15d and supplied to the head side oil chamber 8a. The discharge pressure of the hydraulic pump 10 can be lowered by the amount of stored energy of the spring 15d. The flow rate supplied from the second oil chamber 15c to the head-side oil chamber 8a is equal to the flow rate supplied from the control valve 12 to the first oil chamber 15b, and thus the flow rate is controlled by the control valve 12. The pressure oil is supplied to the head side oil chamber 8a. When the boom 5 is moved upward, the oil discharged from the rod side oil chamber 8b of the boom cylinder 8 is discharged to the oil tank 11 via the rod side oil passage 14 and the control valve 12 at the upper movement side position X. Is done. In the figure, reference numeral 20 denotes a relief oil passage that branches off from the head-side oil passage 13 between the booster 15 and the head-side oil chamber 8a of the boom cylinder 8 and reaches the oil tank 11, and the relief oil passage The maximum pressure in the head-side oil passage 13 is limited by a relief valve 21 disposed at 20.

  On the other hand, when the boom 5 is moved downward, that is, in a state where the boom operation lever is operated to the downward movement side and the control valve 12 is switched to the downward movement side Y, the oil discharged from the head side oil chamber 8a is boosted. Input to the second oil chamber 15 c of the vessel 15. The oil discharged from the head-side oil chamber 8a is high-pressure oil that maintains the weight of the front working unit 4, but the piston 15a is moved to the first oil chamber 15b side by the oil discharged from the high-pressure head-side oil chamber 8a. As a result, the oil is discharged from the first oil chamber 15b and flows to the control valve 12. In this case, the piston 15a moves toward the first oil chamber 15b, and the spring 15d is stored. The oil whose pressure has been reduced by the amount stored in the spring 15d is discharged from the first oil chamber 15b. That is, the oil discharged from the head-side oil chamber 8a accumulates the spring 15d of the booster 15 and is reduced in pressure by the accumulated amount of the spring 15d and flows to the control valve 12, and the restriction 12c of the control valve 12 is It passes through and is discharged to the oil tank 11. Thus, when the boom 5 is moved downward, the pressure booster 15 functions as a pressure decreaser that lowers the oil discharged from the head side oil chamber 8a. As a result, the inflow side pressure is reduced, and as a result, the throttle 12c can be widened (the opening area of the throttle 12c is wide) compared to the case where high-pressure discharged oil from the head-side oil chamber 8a passes through the throttle as it is. Thus, the energy loss in the diaphragm 12c can be reduced. Further, the flow rate flowing from the head side oil chamber 8a to the second oil chamber 15c is equal to the flow rate flowing from the first oil chamber 15b to the control valve 12, so that the oil whose flow rate is controlled by the control valve 12 is the head side. It is configured to be discharged from the oil chamber 8a. When the boom 5 is moved downward, the oil discharged from the hydraulic pump 10 is supplied to the rod-side oil chamber 8b of the boom cylinder 8 via the control valve 12 and the rod-side oil passage 14 at the lower-side position Y.

Further, an upper moving side bypass oil path 16 and a lower moving side bypass oil path 17 are connected to the head side oil path 13 in parallel with the booster 15.
The upper moving side bypass oil passage 16 supplies the discharge oil of the hydraulic pump 10 supplied from the control valve 12 to the head side oil chamber 8a of the boom cylinder 8 without passing through the booster 15 when the boom 5 moves up. The upper moving side bypass oil path 16 is provided with an upper moving side bypass valve 18 that opens and closes the upper moving side bypass oil path 16. The upper moving side bypass valve 18 includes an ammunition machine 18a that presses the upper moving side bypass valve 18 toward the non-operating position, and an operating portion 18b that presses toward the operating position side. The pressure booster 15 is inserted into the second oil chamber 15c and faces the piston 15a. When the spring 15d of the booster 15 is not extended to the maximum of the preset movable range, the piston 15a is separated from the operation portion 18b and does not press the operation portion 18b. The side bypass valve 18 is located at a non-operating position that closes the upstream side bypass oil passage 16, but the spring 15d is extended to the maximum of the movable range (the spring 15d is pre-compressed, so the maximum of the movable range). The piston 15a abuts against the operation portion 18b and presses the operation portion 18b, so that the upper moving side bypass valve 18 causes the upper moving side bypass oil passage 16 to pass through. It is configured to switch to an open operating position. That is, the oil in the head side oil passage 13 is relieved from the relief valve 21, or the oil in the head side oil chamber 8 a of the boom cylinder 8 passes through the lower side bypass oil passage 17 when the boom 5 is lowered as will be described later. As a result, the total oil amount of the head side oil chamber 8a and the second oil chamber 15c of the booster 15 decreases, and the head side oil chamber is moved from the booster 15 when the boom 5 is moved upward. The amount of oil supplied to 8a may be insufficient. In this case, when the spring 15d extends to the maximum movable range, the upper moving side bypass valve 18 is switched to the operating position and the upper moving side bypass oil passage 16 is opened, whereby the discharge oil of the hydraulic pump 10 is discharged. It is supplied to the head side oil chamber 8a of the boom cylinder 8 without going through the booster 15, and as a result, the boom 5 can be moved upward without any trouble even after the spring 15d has been extended to the maximum movable range. You can continue.

  On the other hand, the lower-side bypass oil passage 17 is an oil passage that allows the oil discharged from the head-side oil chamber 8a to flow to the control valve 12 without going through the booster 15 when the boom 5 moves downward. The lower moving side bypass oil passage 17 is provided with a lower moving side bypass valve 19. The lower moving side bypass valve 19 opens and closes the lower moving side bypass oil passage 17 and also includes a booster 15. The head side oil passage 13 is also connected to the head side oil passage 13 to open and close the head side oil passage 13 between the boom cylinder 8 and the head side oil chamber 8a. The lower moving side bypass valve 19 includes an elastic machine 19a that presses the lower moving side bypass valve 19 to the non-operating position side, and a pilot port 19b that receives a pilot pressure that presses the lower moving side bypass valve 19 to the operating position side. The pressure of the rod side oil chamber 8b of the boom cylinder 8 is input to the pilot port 19b via the rod side oil passage 14. When the pressure in the rod side oil chamber 8b input to the pilot port 19b is less than a preset set pressure, the lower side bypass valve 19 opens the head side oil passage 13 and lowers the lower side. Although it is located at the non-operating position for closing the bypass oil passage 17, when the pressure in the rod-side oil chamber 8b input to the pilot port 19b becomes equal to or higher than the set pressure, the head-side oil passage 13 is closed and moved downward. The side bypass oil passage 17 is configured to be switched to an operating position for opening. Here, the set pressure is a pressure set in advance as the pressure of the rod-side oil chamber 8b during work that requires a strong force to move the boom 5 downward, such as excavation work. That is, when the front working unit 4 is not in contact with the ground, the weight of the front working unit 4 acts as a force for moving the boom 5 downward, so the pressure in the rod-side oil chamber 8b may be low. A strong force is required to move the boom 5 downward, and the rod-side oil chamber 8b has a high pressure. At this time, if the oil discharged from the head-side oil chamber 8a is flowed to the booster 15, the spring 15d of the booster 15 acts as a force against the downward movement of the boom 5, so that the lower power of the boom 5 is correspondingly increased. Get smaller. In order to avoid this, in the case of work that requires a strong force to move the boom 5 down, such as excavation work, the pressure on the rod side oil chamber 8b becomes lower than the set pressure. The moving side bypass valve 19 is switched to the operating position to open the lower moving side bypass oil passage 17, and the head side oil passage 13 between the booster 15 and the head side oil chamber 8a is closed. As a result, oil discharged from the head side oil chamber 8a can be allowed to flow to the control valve 12 without going through the booster 15.

  In the present embodiment configured as described, the hydraulic excavator 1 includes a boom 5 that is swingably supported by the airframe, a boom cylinder 8 that expands and contracts to move the boom 5 up and down, and a hydraulic pressure of the boom cylinder 8. A hydraulic pump 10 serving as a supply source and a control valve 12 for performing oil supply / discharge control on the boom cylinder 8 are provided. Further, a head connecting the control valve 12 and the head side oil chamber 8a of the boom cylinder 8 is provided. The side oil passage 13 is provided with a booster 15 having a spring 15d. When the boom 5 is moved upward, the discharge pressure of the hydraulic pump 10 is increased by the stored force of the spring 15d of the booster 15. While the pressure is increased and supplied to the head side oil chamber 8a of the boom cylinder 8, when the boom 5 moves downward, the oil discharged from the head side oil chamber 8a of the boom cylinder 8 is discharged. The spring of the booster 15 is to be prestressed.

  As a result, the discharge pressure of the hydraulic pump 10 necessary for the upward movement of the boom 5 can be reduced by the stored force of the spring 15d of the booster 15, and thus the weight of the front working unit 4 is held. Even when the boom 5 requires high pressure oil higher than the pressure, the discharge pressure of the hydraulic pump 10 can be kept low, which can greatly contribute to the improvement of fuel consumption.

  Moreover, the booster 15 reduces the pressure of the oil discharged from the head side oil chamber 8a as much as the spring 15d is stored by the oil discharged from the head side oil chamber 8a of the boom cylinder 8 when the boom 5 is moved downward. Since it functions as a step-down device that steps down and flows to the control valve 12, the pressure on the inflow side of the throttle 12c formed in the control valve 12 to control the flow rate of the discharged oil can be lowered, and thus Compared with the case where high-pressure exhaust oil from the head-side oil chamber 8a passes through the diaphragm as it is, the diaphragm 12c can be widened (the opening area of the diaphragm 12c is widened), and the energy loss in the diaphragm 12c is reduced. Can contribute to further fuel efficiency.

  Further, the booster 15 has a first oil chamber 15b connected to the control valve 12 and a second oil chamber connected to the head side oil chamber 8a of the boom cylinder 8 on both sides of the piston 15a moving in the cylinder. 15c, and a pre-compressed spring 15d is built in the first oil chamber 15b. Thus, when the boom 5 is moved upward, the control valve 12 moves to the first oil chamber 15b. The supplied discharge pressure of the hydraulic pump 10 can be increased by the accumulating force of the spring 15 and supplied from the second oil chamber 15c to the head side oil chamber 8a, while the boom 5 is moved downward from the head side oil chamber 8a. The spring 15d can be stored by supplying the discharged oil to the second oil chamber 15c. Further, the second oil chamber 15c has a maximum equivalent to the maximum capacity of the head side oil chamber 8a of the boom cylinder 8. Capacity And has, by Thus, the substantially entire amount of the hydraulic fluid supplied to the head-side oil chambers 8a when upward movement of the boom, so that can be supplied from the booster 15.

  Further, in the head side oil passage 13 connecting the control valve 12 and the head side oil chamber 8a of the boom cylinder 8, the boom discharged from the hydraulic pump 10 supplied from the control valve 12 without passing through the booster 15 is supplied. An upper moving side bypass oil passage 16 to be supplied to the head side oil chamber 8a of the cylinder 8 is connected, and the upper moving side bypass oil passage 16 is connected to an upper moving side bypass oil passage 16 that opens and closes the upper moving side bypass oil passage 16. A valve 18 is provided. The upward movement bypass valve 18 opens the upward bypass oil passage 16 when the spring 15d of the booster 15 extends to the maximum movable range when the boom 5 moves upward. Can be supplied to the head side oil chamber 8a of the boom cylinder 8 without going through the booster 15, and thus the boom 5 can be moved upward without any trouble even after the spring 15d has been extended to the maximum movable range. Can be continued.

  Further, the head-side oil passage 13 is connected with a lower-side bypass oil passage 17 for flowing oil discharged from the head-side oil chamber 8a of the boom cylinder 8 to the control valve 12 without going through the booster 15. In addition, a lower movement side bypass valve 19 for opening and closing the lower movement side bypass oil path 17 is disposed in the lower movement side bypass oil path 17. The lower moving side bypass valve 19 opens the lower moving side bypass oil passage 17 when the pressure in the rod side oil chamber 8b of the boom cylinder 8 is equal to or higher than a preset set pressure, whereby the head side oil chamber 8a. The oil discharged from the engine can flow to the control valve 12 without going through the booster 15. Thus, when a strong force is required to move down the boom 5 during excavation work or the like, and the pressure in the rod side oil chamber 8b becomes equal to or higher than the set pressure, the oil discharged from the head side oil chamber 8a. It is possible to reliably prevent the lower motive power of the boom 5 from being lowered by causing the booster 15 to flow.

  The present invention is applied to various construction machines such as a hydraulic excavator provided with a boom supported by the machine body so as to be swingable up and down, and a boom cylinder that extends and contracts using a hydraulic pump as a hydraulic supply source to move the boom up and down. be able to.

DESCRIPTION OF SYMBOLS 5 Boom 8 Boom cylinder 8a Head side oil chamber 8b Rod side oil chamber 10 Hydraulic pump 12 Control valve 13 Head side oil passage 15 Booster 15a Piston 15b First oil chamber 15c Second oil chamber 15d Spring 16 Upper moving side bypass oil passage 17 Lower moving side bypass oil passage 18 Upper moving side bypass valve 19 Lower moving side bypass valve

Claims (5)

  A boom supported by the machine body so as to swing up and down, a boom cylinder that expands and contracts to move the boom up and down, a hydraulic pump that serves as a hydraulic pressure supply source of the boom cylinder, and a control that controls oil supply / discharge to the boom cylinder In a construction machine comprising a valve, a booster having a precompressed spring is disposed in an oil passage connecting the control valve and the head side oil chamber of the boom cylinder, and when the boom is moved up, While the discharge pressure of the hydraulic pump is increased by the accumulating force of the booster spring and supplied to the head side oil chamber of the boom cylinder, when the boom is moved downward, the pressure of the booster is reduced by the oil discharged from the head side oil chamber of the boom cylinder. A hydraulic circuit for a boom cylinder of a construction machine, characterized by storing a spring.   2. The boom cylinder hydraulic circuit for a construction machine according to claim 1, wherein, when the boom is moved downward, the pressure booster functions as a pressure decreaser for reducing the pressure of the oil discharged from the head side oil chamber and flowing it to the control valve.   3. The booster according to claim 1, wherein the booster has a first oil chamber connected to the control valve and a second oil chamber connected to the head side oil chamber of the boom cylinder on both sides of the piston moving in the cylinder. The first oil chamber is formed with a precompressed spring, and the second oil chamber has a maximum capacity equivalent to the maximum capacity of the head side oil chamber of the boom cylinder. Hydraulic circuit for boom cylinder of construction machinery.   In any 1 paragraph of Claims 1 thru / or 3, Upside bypass oil passage which supplies the discharge oil of the hydraulic pump supplied from a control valve to the head side oil room of a boom cylinder without going through a pressure booster, An upper-side bypass valve that opens and closes the upper-side bypass oil passage, and the upper-side bypass valve is configured to lift the bypass-side bypass oil when the booster spring extends to the maximum movable range when the boom moves up. A hydraulic circuit for a boom cylinder of a construction machine, characterized by being configured to open a path.   5. The lower movement side bypass oil path according to claim 1, wherein the lower movement side bypass oil path for flowing the oil discharged from the head side oil chamber of the boom cylinder to the control valve without passing through the booster, and the lower movement side bypass oil path And a lower-side bypass valve that opens and closes the lower-side bypass oil passage when the pressure in the rod-side oil chamber of the boom cylinder is equal to or higher than a preset pressure. A hydraulic circuit for a boom cylinder of a construction machine.

Images