JP5554575B2 - Hydraulic circuit for construction machinery - Google Patents

Description

  The present invention relates to a hydraulic circuit of a construction machine such as a hydraulic excavator.

  For example, Patent Literature 1 discloses a hydraulic circuit 100 of a hydraulic excavator 150 as typified by FIG. This hydraulic circuit 100 is connected to the first and second hydraulic pumps 102 and 104, and switches the direction and flow rate of the pressure oil supplied to the arm hydraulic cylinder 110 according to the operating position of the arm operating lever 120A. First and second switching valves 116 and 118 are provided.

  In the excavator 150 having the hydraulic circuit 100 shown in FIG. 5, when the arm 152 is opened, the arm operating lever 120A is tilted rightward in FIG. 5 and the arm first switching valve 116 is moved to the p side. Then, the second arm switching valve 118 is switched to the q side. As a result, pressure oil is supplied from the first hydraulic pump 102 and the second hydraulic pump 104 to the rod side of the arm hydraulic cylinder 110 via the passages 116a and 118a, and the arm hydraulic cylinder 110 can be contracted. Can open the arm.

  In this arm opening operation, the return oil discharged from the bottom side of the arm hydraulic cylinder 110 is a passage 110a, passages 116b and 118b, arm switching valves 116 and 118, and a discharge passage from the bottom side of the arm hydraulic cylinder 110. 116c and 118c are discharged to the tank T.

JP 2002-4339 A

  Here, in the operation of opening the arm 152, the hydraulic oil is discharged from the bottom side of the hydraulic cylinder 110 for the arm, but the operation is discharged from the bottom side due to the area ratio between the cylinder bottom and the cylinder rod based on the structure of the hydraulic cylinder. Since the oil is discharged in an amount exceeding the same amount as the amount of oil supplied to the rod side, passage pressure loss is likely to occur before the return oil discharged from the bottom side returns to the tank T.

  Further, the cross-sectional area of the passage where the return oil discharged from the bottom side of the arm hydraulic cylinder 110 returns to the tank T is “unique” depending on the switching position of the first arm switching valve 116 and the second arm switching valve 118. Therefore, depending on the work content, there is a risk that a sufficient cross-sectional area of the return oil passage may not be ensured, and the return pressure loss of the return oil may increase. For example, when the arm operation lever 120A is in a “certain operation position”, each passage in the arm first and second switching valves 116 and 118 has “a certain opening”. When the arm 152 reaches the “certain operation position” from the fully closed position and when the arm 152 reaches the same “specific operation position” from the fully open position, the optimum cross-sectional area of the return oil passage is Not necessarily the same.

  The present invention has been made in view of such problems, and is a construction that can appropriately reduce the passage pressure loss until the return oil from the bottom side of the hydraulic cylinder is discharged to the tank according to the work situation. It is an object to provide a hydraulic circuit for a machine.

A first aspect of the present invention is a construction machine including a switching valve that is connected to a hydraulic pump and switches a direction and a flow rate of pressure oil supplied to a hydraulic cylinder that drives a working unit according to an operation position of an operation tool. The hydraulic circuit further includes a discharge passage that is connected in tandem with the switching valve to the hydraulic pump, and that discharges return oil from the bottom side of the hydraulic cylinder to the tank, and returns to the tank through the discharge passage. A discharge switching valve for switching the flow rate of the return oil, and a work state determination means for determining whether or not a specific work state is to promote discharge of return oil from the bottom side of the hydraulic cylinder, When the working state determining means determines that the specific working state is present, the discharge switching valve is switched so that the discharge passage communicates with the bottom side of the hydraulic cylinder; Serial at least part of the return oil from the bottom side of the hydraulic cylinder, a hydraulic circuit of the construction machine to return to the tank through the discharge passage of the discharge switching valve, further wherein said operating member An operation speed detecting means for detecting an operation speed to the contraction side of the hydraulic cylinder is provided, and the work state determination means determines whether or not the specific work state is based on whether or not the operation speed is equal to or higher than a predetermined threshold. The above-described problem is solved by making the determination.
According to a second aspect of the present invention, there is provided a construction machine including a switching valve that is connected to a hydraulic pump and switches a direction and a flow rate of pressure oil supplied to a hydraulic cylinder that drives a working unit according to an operation position of an operation tool. The hydraulic circuit further includes a discharge passage that is connected in tandem with the switching valve to the hydraulic pump, and that discharges return oil from the bottom side of the hydraulic cylinder to the tank, and returns to the tank through the discharge passage. A discharge switching valve for switching the flow rate of the return oil, and a work state determination means for determining whether or not a specific work state is to promote discharge of return oil from the bottom side of the hydraulic cylinder, When the working state determining means determines that the specific working state is present, the discharge switching valve is switched so that the discharge passage communicates with the bottom side of the hydraulic cylinder; A hydraulic circuit for a construction machine in which at least a part of the return oil from the bottom side of the hydraulic cylinder is returned to the tank via the discharge passage of the discharge switching valve, and further the rod of the hydraulic cylinder A contraction speed detection means for detecting the contraction speed of the work state, and the work state determination means determines whether or not the specific work state is based on whether the contraction speed is equal to or higher than a predetermined threshold. It solves the problem.
A third aspect of the present invention is a construction machine comprising a switching valve that is connected to a hydraulic pump and switches the direction and flow rate of pressure oil supplied to a hydraulic cylinder that drives a working unit according to the operating position of the operating tool. The hydraulic circuit further includes a discharge passage that is connected in tandem with the switching valve to the hydraulic pump, and that discharges return oil from the bottom side of the hydraulic cylinder to the tank, and returns to the tank through the discharge passage. A discharge switching valve for switching the flow rate of the return oil, and a work state determination means for determining whether or not a specific work state is to promote discharge of return oil from the bottom side of the hydraulic cylinder, When the working state determining means determines that the specific working state is present, the discharge switching valve is switched so that the discharge passage communicates with the bottom side of the hydraulic cylinder; A hydraulic circuit for a construction machine in which at least a part of the return oil from the bottom side of the hydraulic cylinder is returned to the tank via the discharge passage of the discharge switching valve, and further, a fulcrum of the working unit The working unit includes an angular velocity detecting unit that detects an angular velocity of an angle formed by the working unit in a predetermined direction, and the working state determining unit determines whether the angular velocity when the hydraulic cylinder is operating in the contracting direction is equal to or greater than a predetermined threshold value. The above problem is solved by determining whether or not it is the specific working state depending on whether or not.

  In the present invention, a discharge switching valve having a discharge passage for discharging the return oil from the bottom side of the hydraulic cylinder to the tank is provided, and the discharge switching valve is in a specific work state by the work state determination means. Since the discharge passage is switched so as to communicate with the bottom side of the hydraulic cylinder, the switching position is unique depending on the direction of the pressure oil supplied to the hydraulic cylinder and the operation position of the operation tool for controlling the flow rate. However, the passage pressure loss until the return oil from the bottom side of the hydraulic cylinder is discharged to the tank can be appropriately reduced according to the work situation.

  In the present invention, the “operating tool” is a means having a function of switching the switching valve, and the form is not particularly limited, and is a concept including a lever, a switch, a pedal, and the like.

  Furthermore, a thrust detection means for detecting a thrust force when the rod of the hydraulic cylinder contracts is provided, and the work state determination means determines whether or not the specific work state is based on the thrust. Good.

  Furthermore, pressure difference detecting means for detecting a pressure difference obtained by subtracting the pressure of the pressure oil on the bottom side from the pressure oil pressure on the rod side of the hydraulic cylinder is provided, and the work state determination means is provided with the pressure difference. You may make it judge whether it is the said specific work state.

  According to the present invention, it is possible to appropriately reduce the passage pressure loss until the return oil from the bottom side of the hydraulic cylinder is discharged to the tank according to the work situation.

The figure which shows the structure of the hydraulic circuit of the hydraulic shovel which concerns on 1st Embodiment of this invention. Circuit diagram of an example of a control system for a hybrid excavator The figure which shows the structure of the hydraulic circuit of the hydraulic shovel which concerns on 2nd Embodiment of this invention. The figure which shows the structure of the hydraulic circuit of the hydraulic shovel which concerns on 3rd Embodiment of this invention. The figure which shows an example of a structure of the hydraulic circuit of the conventional hydraulic shovel

  Hereinafter, an example of a preferred embodiment of a hydraulic circuit of a hydraulic excavator according to the present invention will be described in detail based on the drawings.

  FIG. 1 is a diagram showing a configuration of a hydraulic circuit of a hydraulic excavator according to the first embodiment of the present invention.

  The hydraulic circuit 10 includes a first hydraulic pump 12, a second hydraulic pump 14, a first arm switching valve 16, a second arm switching valve 18, a boom switching valve 20, and a discharge switching valve 22. An arm operating lever device 24, a boom operating lever device 26, a pilot pressure sensor 28, a controller 30, an electromagnetic proportional valve 32, and a pilot hydraulic pump 34, and an arm hydraulic cylinder 80 and a boom. The hydraulic oil is supplied to the hydraulic cylinder 82 and the arm (working unit) 84 and the boom 86 are operated to cause the excavator 78 to perform various operations such as excavation work and floor digging work. Reference numeral 88 denotes a bucket. In the present embodiment, the work state that should promote the discharge of the return oil from the bottom side of the arm hydraulic cylinder 80 is referred to as a “specific work state”.

  The first hydraulic pump 12 and the second hydraulic pump 14 are arranged in parallel. A tandem passage 38 is connected to the first hydraulic pump 12. The tandem passage 38 is provided with a discharge switching valve 22 on the upstream side and a first switching valve for arm 16 on the downstream side. The first arm switching valve 16 and the discharge switching valve 22 are connected in tandem. Pressure oil is supplied from the first hydraulic pump 12 to the arm hydraulic cylinder 80 through the tandem passage 38 and the arm first switching valve 16.

  A tandem passage 42 is connected to the second hydraulic pump 14. The tandem passage 42 is provided with a boom switching valve 20 on the upstream side and an arm second switching valve 18 on the downstream side. The second arm switching valve 18 and the boom switching valve 20 are connected in tandem. Pressure oil is supplied from the second hydraulic pump 14 to the arm hydraulic cylinder 80 and / or the boom hydraulic cylinder 82 via the tandem passage 42, the boom switching valve 20, and the arm second switching valve 18.

  The first arm switching valve 16 is a three-position six-port switching valve, and includes three switching positions A, B, and C, and the direction of pressure oil from the first hydraulic pump 12 toward the arm hydraulic cylinder 80. And control the flow rate. Pilot ports 16a and 16b are provided at both ends of the spool of the arm first switching valve 16, and pilot pressure is supplied from the pilot passages 24a and 24b, respectively.

  The spool of the arm first switching valve 16 moves when the operator operates the arm operating lever device 24, and controls the direction and flow rate of the pressure oil supplied from the first hydraulic pump 12 to the arm hydraulic cylinder 80. To do. The pressure oil supplied from the first hydraulic pump 12 to the arm hydraulic cylinder 80 passes through the arm passages 80a and 80b from the parallel passage 40 or the tandem passage 38 and the parallel passage 40 through the arm first switching valve 16. And supplied to the arm hydraulic cylinder 80.

  Further, the first arm switching valve 16 is provided with a discharge passage 16 c for discharging return oil from the bottom side of the arm hydraulic cylinder 80 to the tank T. When the arm first switching valve 16 is in the switching position A, a part of the return oil from the bottom side of the arm hydraulic cylinder 80 is transferred to the tank T via the arm passage 80b, the discharge passage 16c, and the tank passage 16d. Discharged.

  A bypass passage 80 h is provided in parallel with the first arm switching valve 16. The bypass passage 80 h is a passage that connects the branch point 80 g on the arm passage 80 b that is connected to the bottom side of the arm hydraulic cylinder 80 and the port 22 d that is a downstream port of the discharge switching valve 22. The bypass passage 80h communicates with the tank passage 22e communicating with the tank T via the discharge passage 22c of the discharge switching valve 22 when the discharge switching valve 22 is at the switching position I. Thus, when the discharge switching valve 22 is in the switching position I, a part of the return oil from the bottom side of the arm hydraulic cylinder 80 passes through the arm passage 80b, the bypass passage 80h, the discharge passage 22c, and the tank passage 22e. And discharged to the tank T.

  The second arm switching valve 18 is a three-position six-port switching valve, and includes three switching positions D, E, and F, and the direction of the pressure oil from the second hydraulic pump 14 toward the arm hydraulic cylinder 80. And control the flow rate. Pilot ports 18a and 18b are respectively provided at both ends of the spool of the arm second switching valve 18, and pilot pressure is supplied from the pilot passages 24a and 24b, respectively.

  Similarly to the spool of the arm first switching valve 16, the spool of the arm second switching valve 18 moves when the operator operates the arm operating lever device 24, and is supplied to the hydraulic cylinder 80 for arm. Control the direction and flow rate. The pressure oil supplied from the second hydraulic pump 14 to the arm hydraulic cylinder 80 is supplied from the parallel passage 44 or the tandem passage 42 and the parallel passage 44 through the arm second switching valve 18 to the arm joining passages 80c and 80d. , And joins the arm passages 80a and 80b at the joining points 80e and 80f and is supplied to the arm hydraulic cylinder 80.

  Further, the arm second switching valve 18 is provided with a discharge passage 18 c for discharging return oil from the bottom side of the arm hydraulic cylinder 80 to the tank T. When the arm second switching valve 18 is in the switching position D, part of the return oil from the bottom side of the arm hydraulic cylinder 80 is transferred to the tank T via the arm passage 80b, the discharge passage 18c, and the tank passage 18d. Discharged.

  The boom switching valve 20 is a three-position six-port switching valve, and includes three switching positions J, K, and L. The direction and flow rate of the pressure oil from the second hydraulic pump 14 toward the boom hydraulic cylinder 82. To control.

  The discharge switching valve 22 is a three-position six-port switching valve, and includes three switching positions G, H, and I. When the switching position I is provided with the discharge passage 22c, the discharge switching valve 22c passes through the discharge passage 22c. The bypass passage 80h communicates with the tank passage 22e, and the return oil from the bottom side of the arm hydraulic cylinder 80 is guided to the tank T. The switching position H is not provided with a passage through which return oil is discharged to the tank T. At the switching position H, only the tandem passage 38 is communicated, and the pressure oil from the first hydraulic pump 12 is supplied to the tandem passage 38. In this case, the return oil from the bottom side of the arm hydraulic cylinder 80 is not guided to the tank T via the discharge switching valve 22 at the switching position H.

  Pilot ports 22a and 22b are provided at both ends of the spool of the discharge switching valve 22, respectively. The pilot passage 22f that communicates with the pilot port 22a communicates with the tank T, and the pilot pressure supplied to the pilot port 22a is always the tank pressure, and the discharge switching valve 22 does not switch to the switching position G. A pilot pressure is supplied from a pilot hydraulic pump 34 to a pilot passage 34a communicating with the pilot port 22b, and a pilot supplied to the pilot passage 34a by a command from the controller 30 when the arm 84 is in a specific working state, as will be described later. The pressure increases, the pilot pressure supplied to the pilot port 22b increases, and the discharge switching valve 22 switches to the switching position I.

  As described above, the switching position I is provided with the discharge passage 22c through which the return oil from the bottom side of the arm hydraulic cylinder 80 to the tank T passes. For this reason, when the discharge switching valve 22 is switched to the switching position I, part of the return oil from the bottom side of the arm hydraulic cylinder 80 is part of the arm passage 80b, the branch point 80g, the bypass passage 80h, and the discharge passage 22c. Then, it is discharged to the tank T through the tank passage 22e.

  The pilot pressure sensor (pilot pressure detecting means) 28 serves to measure the pilot pressure in the pilot passage 24a supplied to the pilot port 16a of the first arm switching valve 16 and the pilot port 18a of the second arm switching valve 18. The obtained pressure data is sent to the controller 30 via the electric signal line 28a.

  Based on the pressure data sent from the pilot pressure sensor 28, the controller 30 determines whether or not it is a specific working state that should promote the discharge of the return oil from the bottom side of the arm hydraulic cylinder 80. Therefore, the controller 30 is a work state determination unit. Further, the controller 30 operates the electromagnetic proportional valve 32 via the electric signal line 30 a based on the determination result to adjust the opening degree of the pilot passage 34 a, and the pilot hydraulic pump is connected to the pilot port 22 b of the discharge switching valve 22. The pilot pressure supplied from 34 is adjusted to adjust the switching position of the discharge switching valve 22.

  Here, when the pressure data sent from the pilot pressure sensor 28 indicates a large pilot pressure, the switching amount to the position A side of the arm first switching valve 16 and the position D of the arm second switching valve 18 are shown. Therefore, the amount of oil supplied to the rod side of the arm hydraulic cylinder 80 increases, and the amount of return oil from the bottom side of the arm hydraulic cylinder 80 also increases.

  Also, from the structure of the hydraulic cylinder, the pressure receiving area on the bottom side is larger than the pressure receiving area on the rod side, and the amount of oil discharged from the bottom side is the ratio of the pressure receiving area on the bottom side to the pressure receiving area on the rod side. It is an amount obtained by multiplying (the pressure receiving area on the bottom side) / (the pressure receiving area on the rod side) by the amount of oil supplied to the rod side. Therefore, the amount of oil returned from the bottom side of the arm hydraulic cylinder 80 is further larger than the amount of oil supplied to the rod side of the arm hydraulic cylinder 80.

  Therefore, the controller 30 returns oil from the bottom side of the arm hydraulic cylinder 80 when the pilot pressure detected later by the pilot pressure sensor 28 at a predetermined interval indicates a larger value. Is determined to be in a specific working state to be discharged, a command is sent to the solenoid portion 32a of the electromagnetic proportional valve 32 via the electric signal line 30a, and the opening of the pilot passage 34a is increased to switch the discharge. The pilot pressure applied to the pilot port 22b of the valve 22 is increased to switch the discharge switching valve 22 to the position I side. When the pilot pressure detected later by the pilot pressure sensor 28 at a predetermined interval shows a larger value, the switching of the arm first switching valve 16 to the position A side is performed later. As a result, the amount of oil supplied to the rod side of the arm hydraulic cylinder 80 increases and the arm hydraulic cylinder 80 moves to the contraction side. This is because it is considered that the arm operating lever (operating tool) 24A is being operated to the contraction side of the arm hydraulic cylinder 80. Therefore, the pilot pressure sensor 28 and the controller 30 are contraction motion detection means.

  When the discharge switching valve 22 is switched to the position I side, the bypass passage 80h, the discharge passage 22c, and the tank passage 22e communicate with each other. As a result, the return oil discharged from the bottom side of the arm hydraulic cylinder 80 flowing through the arm passage 80b partially flows into the bypass passage 80h at the branch point 80g, and passes through the discharge passage 22c and the tank passage 22e. Is also discharged to the tank T.

  The electromagnetic proportional valve 32 receives an instruction from the controller 30 and adjusts the opening of the pilot passage 34 a to adjust the pilot pressure supplied to the pilot port 22 b of the discharge switching valve 22. It has a role to adjust the switching position. When an electric signal is sent from the controller 30 to the solenoid portion 32a of the electromagnetic proportional valve 32 via the electric signal line 30a, the electromagnetic proportional valve 32 switches the spool of the electromagnetic proportional valve 32 in accordance with the electric signal, and the pilot passage 34a Adjust the opening. Thereby, the pilot pressure supplied to the pilot port 22b of the discharge switching valve 22 is adjusted, and the switching position of the discharge switching valve 22 is adjusted.

  A characteristic point of the configuration of the present embodiment described above is that the controller 30 determines whether or not the controller 30 is in a specific working state based on the pilot pressure detected by the pilot pressure sensor 28 at a predetermined interval. The position of the switching valve 22 is switched, and the sectional area of the return oil discharge passage from the bottom side of the arm hydraulic cylinder 80 depends on the switching positions of the first arm switching valve 116 and the second arm switching valve 118. It is not decided to be “unique”.

  Thus, in this embodiment, the opening degree of the return oil discharge passage from the bottom side of the arm hydraulic cylinder 80 is set regardless of the switching positions of the first arm switching valve 16 and the second arm switching valve 18. It can be changed flexibly according to the working state, and the passage pressure loss until the return oil from the bottom side of the arm hydraulic cylinder 80 is discharged to the tank T can be appropriately reduced according to the working state. it can.

  Here, application of the present invention to a hybrid excavator in which an electric motor is introduced will be described. FIG. 2 is a circuit diagram of an example of a control system of the hybrid excavator, and is a circuit diagram in a case where a turning electric motor 214 is introduced instead of the turning hydraulic motor 252. Reference numeral 202 is an engine, reference numeral 204 is a motor generator, reference numeral 206 is a reduction gear, reference numerals 208 and 210 are inverters, reference numeral 212 is a battery, reference numeral 214 is a motor for turning, reference numeral 216 is a resolver, reference numeral 218 is a mechanical brake, reference numeral 220 Is a turning speed reducer, symbol 222 is a controller, symbol 232 is a main pump, symbol 234 is a pilot hydraulic pump, symbol 236 is an operating device, symbol 238 is a pressure sensor, symbol 240 is a switching valve mechanism, symbol 242 is a boom hydraulic cylinder, Symbol 242A is a boom switching valve, symbol 244 is an arm hydraulic cylinder, symbol 244A is an arm switching valve, symbol 246 is a bucket hydraulic cylinder, symbol 246A is a bucket switching valve, and symbol 248 is a traveling (left) hydraulic motor. 248A is a travel (left) switching valve, and 250 is a travel ( ) Hydraulic motor, reference numeral 250A is traveling (right) switching valve, reference numeral 252A is a swing selector valve.

  The turning hydraulic motor 252 does not actually exist, but is described for convenience of explanation. When the conventional switching valve mechanism is used in the hydraulic system, there is a turning switching valve 252A that is no longer necessary for controlling the supply and discharge of pressure oil to and from the turning hydraulic motor 252. In this case, if the switching valve 252A for turning which is no longer necessary is improved and diverted to be the switching valve 22 for discharge according to the present embodiment, the cost is hardly increased, and the mounting property to the hydraulic excavator 78 is improved. Will not be adversely affected.

  Next, the operation and action of the hydraulic circuit 10 according to the first embodiment configured as described above will be described.

  In FIG. 1, when the operator tilts the operation lever 24A of the arm operation lever device 24 to the left and applies pilot pressure to the pilot ports 16a and 18a via the pilot passage 24a, the arm first switching valve 16 is moved to the position. The arm second switching valve 18 is switched to position D. Thus, the pressure oil from the first hydraulic pump 12 passes through the arm passage 80a from the parallel passage 40, or the tandem passage 38 and the parallel passage 40, through the arm first switching valve 16 (switching position A). Pressure oil supplied from the second hydraulic pump 14 to the rod side of the arm hydraulic cylinder 80 passes through the parallel passage 44 or the tandem passage 42 and the parallel passage 44 to the arm second switching valve 18 (switching position D). Then, the gas is supplied to the rod side of the arm hydraulic cylinder 80 through the arm joining passage 80c, the joining point 80e, and the arm passage 80a. As a result, pressure oil is supplied from both the first hydraulic pump 12 and the second hydraulic pump 14 to the rod side of the arm hydraulic cylinder 80, and the rod of the arm hydraulic cylinder 80 can be greatly contracted. A large opening operation can be performed.

  On the other hand, as described above, due to the structure of the hydraulic cylinder, the pressure receiving area on the bottom side is larger than the pressure receiving area on the rod side, and the amount of return oil discharged from the bottom side is lower than the pressure receiving area on the rod side. It is an amount obtained by multiplying the amount of oil supplied to the rod side by the ratio of the pressure receiving area (pressure receiving area on the bottom side) / (pressure receiving area on the rod side). Therefore, when the arm 84 opens, a large amount of return oil that exceeds the amount of oil supplied to the rod side of the arm hydraulic cylinder 80 is discharged from the bottom side.

  For this reason, the passage pressure loss until the return oil from the bottom side of the arm hydraulic cylinder 80 is discharged to the tank T tends to be large, but in this embodiment, as described above, the bottom side of the arm hydraulic cylinder 80 Regardless of the switching position of the arm first switching valve 16 and the arm second switching valve 18, the opening degree of the discharge passage for the return oil from the engine is flexibly changed according to the working state (the return oil from the bottom side is If there are many, the opening of the return oil discharge passage can be changed), so that the passage pressure loss until the return oil from the bottom side of the arm hydraulic cylinder 80 is discharged to the tank T can be reduced. It can be reduced appropriately according to the working state.

  In the present embodiment, the operation of the arm operation lever 24A toward the contraction side of the arm hydraulic cylinder 80 is performed using the pilot pressure data measured at a predetermined interval by the pilot pressure sensor 28 as a parameter. Whether or not it is a specific work state that should promote the discharge of the return oil from the bottom side of the arm hydraulic cylinder 80 is determined. Other indices may be used as parameters as long as the parameters can be determined.

  For example, an operation speed detecting device for detecting the operation speed to the contraction side of the arm operation lever 24A (the operation speed to the left in FIG. 1) is provided, and the operation speed to the contraction side of the arm operation lever 24A is used as a parameter. The operation speed may be determined to be a specific work state when the operation speed is equal to or higher than a predetermined threshold. Further, for example, a contraction speed detecting device for detecting the contraction speed of the rod of the hydraulic cylinder for arm 80 is provided, and the contraction speed is used as a parameter, and it is determined that the specific working state is obtained when the contraction speed is equal to or greater than a predetermined threshold. May be. Further, for example, an angular velocity detection device that detects an angular velocity of the angle that the arm 84 makes with the boom 86 at the fulcrum 84A of the arm 84 (the direction when the arm hydraulic cylinder 80 contracts is positive) is provided, and the angular velocity is set as a parameter. And when the angular velocity is equal to or greater than a predetermined threshold value, it may be determined that the specific working state is present.

  When operating speed, contraction speed, and angular speed are used as parameters, the discharge switching valve is set such that the larger the contraction speed, the larger the amount of return oil discharged to the tank T through the discharge switching valve 22. You may control so that 22 may be switched.

  Next, a hydraulic circuit 70 for a hydraulic excavator according to a second embodiment of the present invention will be described.

  FIG. 3 is a diagram showing a configuration of a hydraulic circuit 70 of a hydraulic excavator according to the second embodiment of the present invention. The same components as those of the hydraulic circuit 10 according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The hydraulic circuit 70 according to the second embodiment replaces the pilot pressure sensor 28 that measures the pilot pressure in the pilot passage 24a in the hydraulic circuit 10 according to the first embodiment, and pressure oil on the rod side of the hydraulic cylinder 80 for arm. The arm cylinder pressure sensor 52 for detecting the pressure of the oil pressure and the arm cylinder pressure sensor 54 for detecting the pressure of the pressure oil on the bottom side of the hydraulic cylinder for arm 80 are provided. The cylinder pressure data detected by the arm cylinder pressure sensor 52 is sent to the controller 50 via the electric signal line 52a, and the cylinder pressure data detected by the arm cylinder pressure sensor 54 is sent to the controller 50 via the electric signal line 54a. The controller 50 calculates the thrust when the rod of the arm hydraulic cylinder 80 contracts based on the two cylinder pressure data sent.

  The controller 50 determines that it is in a specific working state when the calculated thrust is equal to or greater than a predetermined threshold, and issues a command to the electromagnetic proportional valve 32 via the electric signal line 30a so that the opening degree of the pilot passage 34a is increased. The pilot pressure applied to the pilot port 22b of the feed / discharge switching valve 22 is increased. As a result, the discharge switching valve 22 is switched to the position I side, and the bypass passage 80h, the discharge passage 22c, and the tank passage 22e are communicated to discharge the return oil from the bottom side of the arm hydraulic cylinder 80 to the tank T. The passing pressure loss at the time can be reduced. Here, the larger the calculated thrust, the higher the pilot pressure applied to the pilot port 22b of the discharge switching valve 22 may be. In this case, the discharge switching valve depends on the calculated thrust. The amount of switching to the position I side of 22 is continuously switched, and the opening degree of the return oil discharge passage from the bottom side of the arm hydraulic cylinder 80 is also switched continuously.

  In the hydraulic circuit 70 according to the second embodiment, the controller 50 controls the arm hydraulic pressure based on the cylinder pressure data detected by the arm cylinder pressure sensors 52 and 54 (data on the pressure oil pressure on the rod side and the bottom side). Since the thrust at the time of rod contraction of the cylinder 80 is calculated, the arm cylinder pressure sensors 52 and 54 and the controller 50 can be referred to as thrust detection means.

  In the hydraulic circuit 70 according to the second embodiment, the controller 50 calculates the thrust when the rod of the arm hydraulic cylinder 80 is contracted based on the cylinder pressure data detected by the arm cylinder pressure sensors 52 and 54, and calculates the calculated thrust. Based on the above, it is determined whether or not it is in a specific work state, but without calculating the thrust when the rod of the arm hydraulic cylinder 80 is contracted, the pressure of the pressure oil on the rod side of the arm hydraulic cylinder 80 is determined. Based on the pressure difference obtained by subtracting the pressure of the pressure oil on the bottom side, it may be determined whether or not it is in a specific work state. In this case, the arm cylinder pressure sensors 52 and 54 and the controller 50 can be said to be pressure difference detection means.

  Next, a hydraulic circuit 72 of a hydraulic excavator according to a third embodiment of the present invention will be described.

  FIG. 4 is a diagram showing a configuration of a hydraulic circuit 72 of a hydraulic excavator according to the third embodiment of the present invention. The same components as those of the hydraulic circuit 10 according to the first embodiment or the hydraulic circuit 70 according to the second embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The hydraulic circuit 72 according to the third embodiment includes, in the configuration of the hydraulic circuit 10 according to the first embodiment, an arm cylinder pressure sensor 52 that detects the pressure of pressure oil on the rod side of the arm hydraulic cylinder 80, and an arm hydraulic pressure. This is a configuration in which an arm cylinder pressure sensor 54 for detecting the pressure of the pressure oil on the bottom side of the cylinder 80 is added, and the first embodiment and the second embodiment are combined.

  The pilot pressure data of the pilot passage 24a measured by the pilot pressure sensor 28 is sent to the controller 56 as in the first embodiment, and the cylinders detected by the arm cylinder pressure sensors 52 and 54 as in the second embodiment. Since the pressure data is sent, the controller 56 can comprehensively judge these data to judge whether or not the work state is in a specific state, thereby enabling more accurate judgment. Further, even if either the pilot pressure sensor 28 or the arm cylinder pressure sensors 52 and 54 breaks down, it can be determined whether or not a specific working state is present.

  In the embodiment described above, the discharge switching valve 22 is provided upstream of the first arm switching valve 16 in the tandem passage 38, but the discharging switching valve 22 is provided downstream of the first arm switching valve 16. It may be provided on the side. In the tandem passage 42, the second arm switching valve 18 is provided on the downstream side of the boom switching valve 20, but the second arm switching valve 18 may be provided on the upstream side of the boom switching valve 20.

  In the embodiment described above, the two switching valves, the first switching valve 16 for the arm and the second switching valve 18 for the arm, are used as the switching valve for the arm, but the switching valve for the arm is the first switching valve for the arm. The present invention can also be applied to a hydraulic circuit having only one valve 16. The present invention can also be applied to a hydraulic circuit that does not include the boom switching valve 20. Further, the present invention can also be applied to return oil control on the bottom side of the boom hydraulic cylinder 82.

  Further, the present invention can be applied without depending on a pump control system such as a positive control, a negative control, and an open center.

  For example, it can be suitably used in a hydraulic circuit of a hydraulic excavator, and the passage pressure loss until the return oil from the bottom side of the hydraulic cylinder is discharged to the tank can be appropriately reduced according to the work situation.

  Moreover, it can be used particularly suitably for a hybrid excavator in which an electric motor is introduced.

DESCRIPTION OF SYMBOLS 10, 70, 72 ... Hydraulic circuit 12 ... 1st hydraulic pump 14 ... 2nd hydraulic pump 16 ... 1st switching valve for arms 18 ... 2nd switching valve for arms 20 ... Switching valve for booms 22 ... Switching valve for discharge 16C, 18C, 22C ... discharge passage 24 ... arm operating lever device 24A ... arm operating lever (operating tool)
26 ... Boom operating lever device 26A ... Boom operating lever 28 ... Pilot pressure sensor 30, 50, 56 ... Controller 32 ... Electromagnetic proportional valve 34 ... Pilot hydraulic pump 38, 42 ... Tandem passage 40, 44, 80h ... Parallel passage 52 54 ... Arm cylinder pressure sensor 78 ... Hydraulic excavator 80 ... Hydraulic cylinder for arm 82 ... Hydraulic cylinder for boom 84 ... Arm (working part)
86 ... Boom 88 ... Bucket

Claims (5)

In a hydraulic circuit of a construction machine having a switching valve that is connected to a hydraulic pump and switches a direction and a flow rate of pressure oil supplied to a hydraulic cylinder that drives a working unit according to an operation position of the operation tool.
The hydraulic pump is connected in tandem with the switching valve, and has a discharge passage for discharging the return oil from the bottom side of the hydraulic cylinder to the tank, and switches the flow rate of the return oil to be returned to the tank through the discharge passage. A discharge switching valve;
A working state judging means for judging whether or not it is a specific working state that should promote discharge of return oil from the bottom side of the hydraulic cylinder;
With
When the working state determining means determines that the specific working state is present, the discharge switching valve is switched so that the discharge passage communicates with the bottom side of the hydraulic cylinder;
A hydraulic circuit for a construction machine, wherein at least part of the return oil from the bottom side of the hydraulic cylinder is returned to the tank via the discharge passage of the discharge switching valve ;
Furthermore,
An operation speed detecting means for detecting an operation speed of the operation tool toward the contraction side of the hydraulic cylinder;
The hydraulic circuit for a construction machine, wherein the work state determination means determines whether or not the specific work state is based on whether or not the operation speed is equal to or higher than a predetermined threshold value . In a hydraulic circuit of a construction machine having a switching valve that is connected to a hydraulic pump and switches a direction and a flow rate of pressure oil supplied to a hydraulic cylinder that drives a working unit according to an operation position of the operation tool.
The hydraulic pump is connected in tandem with the switching valve, and has a discharge passage for discharging the return oil from the bottom side of the hydraulic cylinder to the tank, and switches the flow rate of the return oil to be returned to the tank through the discharge passage. A discharge switching valve;
A working state judging means for judging whether or not it is a specific working state that should promote discharge of return oil from the bottom side of the hydraulic cylinder;
With
When the working state determining means determines that the specific working state is present, the discharge switching valve is switched so that the discharge passage communicates with the bottom side of the hydraulic cylinder;
A hydraulic circuit for a construction machine, wherein at least part of the return oil from the bottom side of the hydraulic cylinder is returned to the tank via the discharge passage of the discharge switching valve;
Furthermore,
A contraction speed detecting means for detecting a contraction speed of the rod of the hydraulic cylinder;
The hydraulic circuit for a construction machine, wherein the work state determination means determines whether or not the specific work state is based on whether or not the contraction speed is equal to or higher than a predetermined threshold value . In a hydraulic circuit of a construction machine having a switching valve that is connected to a hydraulic pump and switches a direction and a flow rate of pressure oil supplied to a hydraulic cylinder that drives a working unit according to an operation position of the operation tool.
The hydraulic pump is connected in tandem with the switching valve, and has a discharge passage for discharging the return oil from the bottom side of the hydraulic cylinder to the tank, and switches the flow rate of the return oil to be returned to the tank through the discharge passage. A discharge switching valve;
A working state judging means for judging whether or not it is a specific working state that should promote discharge of return oil from the bottom side of the hydraulic cylinder;
With
When the working state determining means determines that the specific working state is present, the discharge switching valve is switched so that the discharge passage communicates with the bottom side of the hydraulic cylinder;
A hydraulic circuit for a construction machine, wherein at least part of the return oil from the bottom side of the hydraulic cylinder is returned to the tank via the discharge passage of the discharge switching valve;
Furthermore,
An angular velocity detecting means for detecting an angular velocity of an angle formed by the working portion with a predetermined direction at a fulcrum of the working portion;
The working state determining means determines whether or not the specific working state is based on whether or not the angular velocity when the hydraulic cylinder is operating in a contracting direction is equal to or greater than a predetermined threshold value. Hydraulic circuit for construction machinery . In any one of Claims 1-3, Furthermore,
A thrust detecting means for detecting a thrust when the rod of the hydraulic cylinder is contracted;
The hydraulic circuit for a construction machine, wherein the work state determination means determines whether or not the specific work state is based on the thrust. In any one of Claims 1-3 , Furthermore,
Pressure difference detection means for detecting a pressure difference obtained by subtracting the pressure oil pressure on the bottom side from the pressure oil pressure on the rod side of the hydraulic cylinder;
The construction circuit hydraulic circuit according to claim 1, wherein the working state judging means judges whether or not the specific working state is based on the pressure difference.

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