JP2017072171A - Construction machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a construction machine capable of smoothly lifting a base body.SOLUTION: A lever device 35 for a boom is operated by an operator, and switches a direction control valve 31 for the boom. A variable throttle 43 is provided in the halfway of a center bypass pipe passage 27, and variably throttles a flow passage area of the center bypass pipe passage 27. A boom operation determination section 48 of a controller 47 determines on the basis of a bottom pressure output from a bottom pressure sensor 44 and a pilot pressure of boom lowering operation output from an operation pressure sensor 45 whether boom lowering operation is in free lowering operation due to free fall or in vehicle body lifting operation for lifting a vehicle body based on boom lowering operation. A variable throttle control section 49 of the controller 47 controls a variable throttle control valve 46 so as to throttle a flow passage area of the variable throttle 43 when the boom operation determination section 48 determines that the boom is in the vehicle body lifting operation.SELECTED DRAWING: Figure 5

Description

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

  In general, a hydraulic excavator that is a representative example of a construction machine includes a lower traveling body that can be self-propelled, an upper revolving body that is turnably provided on the lower traveling body, and that forms a vehicle body (base body) together with the lower traveling body, And a work device (front) that is rotatably attached to the front portion of the upper swing body. The working device is, for example, a boom that is rotatably attached to the front part of the upper swing body, an arm that is rotatably attached to the tip side of the boom, and a pivotally attached to the tip side of the arm. And a boom cylinder, an arm cylinder, and a bucket cylinder (work tool cylinder) that drive these buckets. Pressure oil is supplied to these boom cylinder, arm cylinder, and bucket cylinder from a hydraulic pump that constitutes a hydraulic power source together with a tank via a direction control valve (control valve).

  Here, the construction machine according to Patent Document 1 is a variable throttle that variably restricts the flow path area of the center bypass pipe downstream of the directional control valve for the boom in the middle of the center bypass pipe connecting the hydraulic pump to the tank. (Center bypass switching valve) is provided. In this case, for example, when performing a vehicle body lifting operation (jacking operation) for lifting the vehicle body based on the boom lowering operation, the flow passage area of the variable throttle is reduced (squeezed). That is, by reducing the opening area of the variable throttle, the flow rate of the center bypass pipe is reduced, and the pressure oil that is diverted from the hydraulic pump to the rod side oil chamber of the boom cylinder is increased. Thereby, the boom lowering force (force for pressing the bucket against the ground) necessary for lifting the vehicle body can be ensured.

  On the other hand, an aerial operation in which the working device (the bucket) for horizontal pulling is not grounded, more specifically, a boom lowering operation is a free lowering operation (boom lowering aerial operation) by free fall (self-weight drop) in the air In this case, the flow area of the variable throttle is increased. That is, by increasing the opening area of the variable throttle, the pressure loss (pressure loss) of the center bypass pipe is lowered, and the flow rate of the center bypass pipe is increased. As a result, the pressure oil flowing from the hydraulic pump into the rod side oil chamber of the boom cylinder is reduced, and the pressure oil can easily flow through the regeneration circuit leading from the bottom side oil chamber of the boom cylinder to the rod side oil chamber. As a result, the reproduction efficiency of the boom lowering operation is improved.

  The variable throttle of the center bypass pipe is a boom lowering operation signal of a boom operating device operated by an operator to operate the boom, specifically, a boom supplied from the boom operating device to the boom direction control valve. Controlled by lowered pilot pressure oil. That is, pilot pressure oil for lowering the boom is supplied from the boom operating device to the variable throttle. The variable throttle has a smaller flow passage area as the pilot pressure for lowering the boom becomes larger, and the flow passage area becomes larger as the pilot pressure for lowering the boom becomes smaller.

  In this case, a meter-in switching valve (jack-up switching valve) that switches according to the pressure (bottom pressure) in the bottom oil chamber of the boom cylinder is provided between the boom operating device and the variable throttle. The meter-in switching valve has a closed position (blocking position) for preventing the boom lowering pilot pressure oil from being supplied to the variable throttle, and an open position for supplying the boom lowering pilot pressure oil to the variable throttle. (Communication position).

  For example, when the boom lowering operation is a free lowering operation in the air, the pressure in the bottom side oil chamber of the boom cylinder increases. At this time, when the pressure in the bottom side oil chamber is equal to or higher than the set pressure of the meter-in switching valve, the meter-in switching valve is in the cutoff position. In this case, the pilot pressure oil for lowering the boom is not supplied to the variable throttle, the flow passage area of the variable throttle is increased, and the flow rate of the center bypass pipe is increased. Thereby, pressure oil flows from the bottom side oil chamber of the boom cylinder to the rod side oil chamber through the regeneration circuit, and the regeneration efficiency of the boom cylinder pressure oil is improved.

  Further, when the boom lowering operation continues and the working device (bucket) comes to ground from the free lowering operation, the pressure in the bottom side oil chamber of the boom cylinder decreases. At this time, when the pressure in the bottom side oil chamber becomes lower than the set pressure of the meter-in switching valve, the meter-in switching valve becomes a communication position, and the pilot pressure oil for lowering the boom is supplied to the variable throttle. In this case, as the pilot pressure for lowering the boom increases, the flow area of the variable throttle becomes smaller, and the flow rate of the center bypass pipe decreases. As a result, the pressure oil flowing from the hydraulic pump into the rod side oil chamber of the boom cylinder increases, and the boom lowering force necessary for lifting the vehicle body can be secured.

JP 2006-292068 A

  The configuration described in Patent Document 1 uses the hydraulic signal as it is for the switching of the spool of the meter-in switching valve and the control of the variable throttle (adjustment of the flow path area). That is, the meter-in switching valve is directly switched by the pressure oil in the bottom oil chamber of the boom cylinder. The variable throttle is directly controlled by pilot pressure oil from the boom operating device. In such a configuration, the lifting speed may fluctuate (hunting) at the start of the lifting operation of the vehicle body.

  That is, when the working device (the bucket) comes into contact with the ground during the boom lowering operation, the pressure in the bottom oil chamber of the boom cylinder decreases, and the meter-in switching valve is switched to the communication position. At this time, the spool of the meter-in switching valve may vibrate (hunting) with a switching shock. When the spool of the meter-in switching valve vibrates, the vibration of the boom lowering pilot pressure oil supplied from the operating device for the boom supplied to the variable throttle pulsates, and the flow passage area of the variable throttle may change. There is. As a result, at the start of the lifting operation of the vehicle body, the lifting speed may fluctuate, and the smooth lifting operation of the vehicle body may be hindered.

  An object of the present invention is to provide a construction machine that can smoothly lift a vehicle body (base).

  A construction machine according to the present invention constitutes a hydraulic pressure source together with a base, a boom rotatably attached to the base, a boom cylinder attached between the base and the boom, and a tank mounted on the base. A hydraulic pump that supplies pressure oil to the boom cylinder, and a boom that is provided in the middle of a center bypass pipe that connects the hydraulic pump to the tank, and that controls the switching of pressure oil supplied from the hydraulic pump to the boom cylinder And a boom operation device that performs an operation of switching the boom direction control valve in order to raise or lower the boom.

  In order to solve the above-described problem, the configuration adopted by the present invention is characterized in that a variable throttle that is provided in the middle of the center bypass pipe and that squeezes the flow passage area variably on the downstream side of the boom direction control valve; A pressure detector for detecting pressure of pressure oil in a bottom oil chamber of the boom cylinder, an operation detector for detecting a boom lowering operation of the boom operation device, and detection of the pressure output from the pressure detector; And a control device that controls a variable operation of the flow passage area by the variable throttle based on a signal and a detection signal of the boom lowering operation output from the operation detector. Based on the pressure detection signal and the boom lowering operation detection signal during the lowering operation, whether the boom lowering operation is in the free lowering operation due to free fall or the boom A boom operation determining unit for determining whether a base lifting operation for lifting the base based on a lowering operation; and when the boom operation determining unit determines that the boom is in the base lifting operation, the hydraulic pump to the boom cylinder The variable throttle control unit is configured to perform control to reduce the flow passage area by the variable throttle so that the pressure oil supplied to the rod side oil chamber increases.

  According to the present invention, the lifting operation of the base body (vehicle body) can be performed smoothly.

The front view which shows the hydraulic excavator by embodiment. The front view which shows the hydraulic shovel during a vehicle body lifting operation | movement. The hydraulic circuit diagram which shows the circuit structure which drives a boom cylinder. FIG. 4 is a hydraulic circuit diagram corresponding to a freely lowering operation in which the boom direction control valve in FIG. 3 is switched. FIG. 4 is a hydraulic circuit diagram corresponding to the vehicle body lifting operation with the boom direction control valve in FIG. 3 switched. The flowchart which shows the process performed in the boom operation | movement determination part in FIG. FIG. 6 is a block diagram showing a configuration of a variable aperture control unit in FIGS. 3 to 5. The block diagram which shows the structure of the pump capacity | capacitance instruction | command part in FIG. 3 thru | or FIG.

  Hereinafter, a construction machine according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings, taking as an example a case where the construction machine is applied to a hydraulic excavator.

  In FIG. 1, a hydraulic excavator 1 which is a typical example of a construction machine is used for excavation work of earth and sand. The hydraulic excavator 1 according to the embodiment is an ultra-large backhoe hydraulic excavator. The hydraulic excavator 1 includes a self-propelled crawler-type lower traveling body 2, an upper revolving body 3 that is provided on the lower traveling body 2 so as to be able to swivel and constitutes a vehicle body (base body) together with the lower traveling body 2, A work device (front) 11 that is attached to the front side of the upper swing body 3 and the front side in the rear direction so as to be rotatable (can be raised and lowered) is configured.

  Here, the upper swing body 3 is attached to the lower traveling body 2 via a swing device 4 including a swing hydraulic motor, a speed reduction mechanism, a swing bearing, and the like, and is swung with respect to the lower traveling body 2 by the swing device. To drive. The upper swing body 3 includes a swing frame 5 on which a working device 11 is attached on the front side in the front and rear directions, and a cab 6 that is mounted on the left front side of the swing frame 5 and forms a driver's cab. A building cover 7 that is located on the rear side of the cab 6 and that houses the engine 22, the hydraulic pump 23, the pilot pump 25, the boom direction control valve 31 (see FIGS. 3 to 5) and the like mounted on the revolving frame 5. And a counterweight 8 that is attached to the rear portion of the revolving frame 5 and balances the weight with the work device 11.

  Here, a driver's seat (not shown) on which an operator is seated is provided inside the cab 6. On the front side of the driver's seat, left and right traveling lever / pedal devices (not shown) operated by an operator are provided. The left and right traveling lever / pedal devices are operated to travel the lower traveling body 2. On the other hand, on both the left and right sides of the driver's seat, left and right working lever devices are provided as operating devices operated by an operator. The left and right working lever devices are operated to turn the upper swing body 3 and rotate the working device 11 (upward / downward movement).

  3 to 5 described later show a boom lever device 35 as the left and right working lever devices. The boom lever device 35 performs an operation of switching the boom direction control valve 31 in order to raise or lower the boom 12 of the work device 11 (extend or reduce the boom cylinder 16). Specifically, the lever operation of the boom lever device 35 corresponds to, for example, the front and rear lever operations of the right working lever device.

  On the other hand, as shown in FIGS. 1 and 2, the work device 11 is pivotably attached (connected) to the front portion of the revolving frame 5 constituting the upper revolving structure 3 (connected). An arm 13 rotatably attached to the distal end side of the boom 12, a bucket 14 as a working tool rotatably attached to the distal end side of the arm 13, A bucket link 15 attached between the tip and the bucket 14 is included.

  A boom cylinder 16 is attached between the revolving frame 5 and the boom 12. An arm cylinder 17 is attached between the boom 12 and the arm 13, and a bucket cylinder 18 is provided between the arm 13 and the bucket link 15. The boom cylinder 16 rotates the boom 12 with respect to the revolving frame 5, and the arm cylinder 17 rotates the arm 13 with respect to the boom 12. Is for rotating the bucket 14 with respect to the arm 13.

  The boom cylinder 16, the arm cylinder 17, and the bucket cylinder 18, each of which is a hydraulic cylinder, change the posture of the work device 11 by expanding and contracting based on pressure oil from a hydraulic pump 23 described later. is there. That is, during excavation work such as earth and sand, the boom cylinder 16, the arm cylinder 17 and the bucket cylinder 18 are expanded and contracted based on the lever operation of the left and right working lever devices, and the boom 12 and the arm 13 are rotated. The bucket 14 is rotated while moving (up and down). Thereby, earth and sand etc. can be excavated by the front end side of the bucket 14.

  Here, as shown in FIGS. 3 to 5, the boom cylinder 16 is slidably inserted into the tube 16A and the tube 16A, and the bottom side oil chamber 16C and the rod side oil chamber 16D are inserted into the tube 16A. And a rod 16E whose proximal end is fixed to the piston 16B and whose distal end protrudes outside the tube 16A.

  Next, the hydraulic circuit 21 for driving the boom cylinder 16 will be described with reference to FIGS.

  The hydraulic circuit 21 is for driving the boom cylinder 16. In addition to the boom cylinder 16, the hydraulic circuit 21 includes an engine 22, a hydraulic pump 23, a tank 24, a pilot pump 25, a boom direction control valve 31, a boom lever device 35, a variable throttle 43, a variable throttle control valve 46, and a controller 47. Etc. are configured.

  The engine 22 is provided on the turning frame 5 between the cab 6 and the counterweight 8. The engine 22 is constituted by a diesel engine, for example, and serves as a prime mover (rotation source) for rotationally driving the hydraulic pump 23, the pilot pump 25, and the like. When the hydraulic excavator 1 is configured as a hybrid hydraulic excavator, the assist power generation motor is also rotationally driven by the engine 22 in addition to the hydraulic pump 23 and the like.

  The hydraulic pump 23 is mounted on the swing frame 5 of the upper swing body 3 and is rotationally driven by the engine 22. The hydraulic pump 23 constitutes a main hydraulic source together with a tank 24 that stores hydraulic oil. On the other hand, the pilot pump 25 is also rotationally driven by the engine 22. The pilot pump 25 constitutes a pilot hydraulic pressure source together with the tank 24. The hydraulic pump 23 discharges the pressure oil to the discharge pipe (delivery pipe) 26. The discharge line 26 branches into a center bypass line 27 and a branch line 28 on the upstream side of the boom direction control valve 31. The pilot pump 25 discharges pilot pressure oil to the pilot pipe line 29. The pilot line 29 branches upstream of the boom lever device 35 and the throttle pilot line 30 for supplying pilot pressure oil to the variable throttle control valve 46 side.

  Here, the hydraulic pump 23 supplies pressure oil to the boom cylinder 16, the arm cylinder 17, the bucket cylinder 18, the traveling hydraulic motor of the lower traveling body 2, and the swing hydraulic motor of the swing device 4. That is, the hydraulic pump 23 is driven by the engine 22 to suck hydraulic oil (oil) from the tank 24 and supply (discharge) the sucked hydraulic oil as pressure oil to the control valve. 3 to 5 show only the boom direction control valve 31 that controls the supply and discharge of the pressure oil to the boom cylinder 16 among the plurality of direction control valves constituting the control valve.

  The hydraulic pump 23 is configured as, for example, a swash plate type, radial piston type or oblique axis type variable displacement hydraulic pump. That is, the hydraulic pump 23 includes a capacity control unit that variably adjusts the displacement volume. Specifically, the hydraulic pump 23 includes a variable capacity portion 23A made of a swash plate or a slanted shaft, and a variable capacity mechanism (tilt actuator) 23B that drives (tilts and drives) the variable capacity portion 23A. ing. The capacity variable mechanism 23 </ b> B drives the capacity variable section 23 </ b> A (tilt drive) based on a command from the controller 47. As a result, the capacity variable portion 23A (tilt angle) changes and the pump capacity (displacement volume) of the hydraulic pump 23 can be increased or decreased (the discharge flow rate of the hydraulic oil can be increased or decreased according to the tilt angle. it can). On the other hand, the pilot pump 25 is configured as a fixed displacement hydraulic pump.

  The boom direction control valve 31 is provided between the hydraulic pump 23 and the boom cylinder 16. In other words, the boom direction control valve 31 is provided in the middle of the center bypass conduit 27 that connects the discharge conduit 26 of the hydraulic pump 23 to the tank 24. The boom direction control valve 31 switches and controls the pressure oil supplied from the hydraulic pump 23 to the boom cylinder 16. That is, the boom direction control valve 31 controls the supply and discharge of pressure oil to the boom cylinder 16.

  The boom direction control valve 31 constitutes a control valve (control valve group) together with various direction control valves (not shown). That is, the boom direction control valve 31 is an arm direction control valve that controls supply and discharge of pressure oil to the arm cylinder 17, a bucket direction control valve that controls supply and discharge of pressure oil to the bucket cylinder 18, and traveling hydraulic pressure. A directional control valve for driving that controls the supply and discharge of pressure oil to the motor, and a directional control valve for rotation that controls the supply and discharge of pressure oil to the swing hydraulic motor (both not shown) constitute a control valve. ing.

  The boom direction control valve 31 is constituted by, for example, a 6-port, 3-position hydraulic pilot type direction control valve. The boom direction control valve 31 is connected to the hydraulic pump 23 via the discharge line 26, and is connected to the tank 24 via the center bypass line 27 and the return line 32. Further, the boom direction control valve 31 is connected to the bottom side oil chamber 16C of the boom cylinder 16 via the bottom side conduit 33, and connected to the rod side oil chamber 16D of the boom cylinder 16 via the rod side conduit 34. Has been.

  The boom direction control valve 31 is operated (switching operation) by the boom lever device 35. For this purpose, a pair of hydraulic pilot portions 31 </ b> A and 31 </ b> B are provided at both ends of the boom direction control valve 31. Pilot pressure (switching signal) based on the operation of the boom lever device 35 is supplied to the hydraulic pilot portions 31A and 31B.

  3 to 5, a direction control valve other than the boom direction control valve 31 and the boom lever device 35 and an operating device for operating the same (for example, an arm direction control valve and an arm lever device for operating the same). The travel direction control valve and the travel lever / pedal device for operating the travel direction control valve are omitted. This is to avoid complication of the drawings. Actually, the excavator 1 also includes a direction control valve other than the boom direction control valve 31 and the boom lever device 35 and an operation device for operating the direction control valve. .

  The boom lever device 35 as the boom operation device is operated by an operator to raise or lower the boom 12 (that is, to extend or reduce the boom cylinder 16). The boom lever device 35 is configured as a pilot operation valve composed of a pressure reducing valve type pilot valve, and has an operation lever 35A operated by an operator. When the operator manually tilts the lever 35A (lever operation), a pilot pressure (switching hydraulic pressure signal) proportional to the operation amount is supplied from the boom lever device 35 to the hydraulic pilot portion 31A of the boom direction control valve 31. To 31B. Thereby, the boom lever device 35 performs an operation of switching the boom direction control valve 31.

  As shown in FIG. 3, when the operation lever 35A is in the neutral position, the pilot pressure is not supplied from the boom lever device 35 to the hydraulic pilot portions 31A and 31B. For this reason, the boom direction control valve 31 is in the neutral position (A). In this case, the pressure oil discharged from the hydraulic pump 23 is discharged to the tank 24 through the center bypass conduit 27. At this time, since the bottom side pipe line 33 and the rod side pipe line 34 are disconnected from the hydraulic pump 23 and the tank 24, the boom cylinder 16 does not move (does not expand or contract).

  On the other hand, when the operation lever 35A is tilted to the side where the boom 12 is raised (the side where the boom cylinder 16 is extended), the pilot pressure oil proportional to the amount of operation is raised from the boom lever device 35 to the raising side pilot pipeline 36. To the hydraulic pilot portion 31A on the raising side. Thereby, the direction control valve 31 for booms is switched from the neutral position (A) of FIG. 3 to the switching position (B) that is the raised position.

  In this case, although not shown, the branch conduit 28 is connected to the bottom conduit 33 and the rod conduit 34 is connected to the return conduit 32. Thereby, the pressure oil discharged from the hydraulic pump 23 is supplied to the bottom side oil chamber 16C of the boom cylinder 16 via the discharge pipe 26, the branch pipe 28, and the bottom side pipe 33, and the rod side oil chamber 16D. Is returned to the tank 24 via the rod side pipe 34 and the return pipe 32 and discharged as return oil. As a result, the boom cylinder 16 extends (the amount of protrusion of the rod 16E from the tube 16A increases).

  On the other hand, as shown in FIGS. 4 and 5, when the operation lever 35A is tilted to the side of lowering the boom 12 (side of reducing the boom cylinder 16), pilot pressure oil proportional to the amount of operation is generated. The boom lever device 35 is supplied to the lower hydraulic pilot section 31B through the lower pilot line 37. Thereby, the direction control valve 31 for booms is switched from the neutral position (A) of FIG. 3 to the switching position (C) that is the lowered position.

  In this case, the branch line 28 is connected to the rod side line 34, and the bottom side line 33 is connected to the return line 32. Here, at the switching position (C) of the boom direction control valve 31, the pressure oil in the bottom side oil chamber 16C is located between the bottom side oil chamber 16C of the boom cylinder 16 and the rod side oil chamber 16D. A regeneration circuit 38 that leads to the side oil chamber 16D is provided. That is, the return path 39 that connects the bottom side pipe line 33 and the return pipe line 32, the branch pipe line 28, and the rod side pipe line 34 are connected to the switching position (C) of the boom direction control valve 31. A supply path 40 is provided. The regeneration circuit 38 is configured as an oil path connecting the return path 39 and the supply path 40 between the return path 39 and the supply path 40. The regeneration circuit 38 permits (opens) the flow of pressure oil from the return path 39 side to the supply path 40 side, and blocks (closes) the flow of pressure oil from the supply path 40 side to the return path 39 side. A check valve 41 is provided. Further, a throttle 42 is provided in the middle of the return path 39 downstream of the branch with the regeneration circuit 38.

  Therefore, when the boom direction control valve 31 is in the switching position (C), the pressure oil discharged from the hydraulic pump 23 is divided into the center bypass pipe 27 and the branch pipe 28. Then, the pressure oil branched to the branch pipe 28 and / or the pressure oil that has flowed from the bottom side oil chamber 16C to the regeneration circuit 38 side via the rod side pipe 34 is connected to the rod side oil chamber 16D of the boom cylinder 16. To be supplied. On the other hand, of the pressure oil in the bottom side oil chamber 16 </ b> C, the pressure oil that has passed through the throttle 42 without flowing to the regeneration circuit 38 side is discharged as return oil to the tank 24 via the return line 32. As a result, the boom cylinder 16 is reduced (the amount of protrusion of the rod 16E from the tube 16A is reduced).

  The variable throttle 43 is provided downstream of the boom direction control valve 31 in the middle of the center bypass conduit 27. The variable restrictor 43 variably restricts the flow passage area of the center bypass conduit 27 on the downstream side of the boom direction control valve 31. The variable throttle 43 is controlled by pilot pressure oil (throttle pilot pressure oil) supplied from the variable throttle control valve 46. The variable throttle 43 has a smaller flow path area (opening area of the variable throttle 43) as the pilot pressure (throttle pilot pressure) of the variable throttle control valve 46 increases, and the flow path area increases as the pilot pressure decreases. Become. The pilot pressure of the variable throttle control valve 46 is variably controlled by the controller 47.

  For example, as shown in FIG. 1, when the lowering operation of the boom 12 is a lowering operation in the air, more specifically, the free lowering operation (the lowering operation of the boom 12) due to the free fall (self-weight dropping) of the boom 12 in the air. ), The pilot pressure oil of the variable throttle control valve 46 is reduced (minimized) based on a command from the controller 47. As a result, the flow area of the variable throttle 43 is increased (maximum), and the flow rate of the center bypass pipe 27 is increased. As a result, the pressure oil flowing from the hydraulic pump 23 into the rod side oil chamber 16D of the boom cylinder 16 is reduced, and the pressure oil easily flows through the regeneration circuit 38. That is, the regeneration circuit 38 supplies the pressure oil in the bottom side oil chamber 16C of the boom cylinder 16 to the rod side oil chamber 16D, thereby improving the regeneration efficiency of the boom lowering operation.

  On the other hand, as shown in FIG. 2, when performing a vehicle body lifting operation (jack-up operation) for lifting the vehicle body (the lower traveling body 2 and the upper swing body 3) based on the lowering operation of the boom 12, a command from the controller 47 is used. Based on this, the pilot pressure oil of the variable throttle control valve 46 increases. As a result, the flow passage area of the variable throttle 43 becomes smaller and is shut off at the end, and decreases until the flow rate of the center bypass conduit 27 becomes zero. As a result, the pressure oil diverted from the hydraulic pump 23 to the rod side oil chamber 16D of the boom cylinder 16 via the branch pipe 28 increases, and the boom lowering force (the force for pressing the bucket 14 against the ground) necessary for lifting the vehicle body is increased. ) Can be secured. At this time, the pressure oil in the bottom side oil chamber 16 </ b> C returns to the tank 24 via the bottom side pipe line 33, the return path 39 and the return pipe line 32.

  By the way, as described above, the prior art described in Patent Document 1 uses the hydraulic signal as it is for switching the spool of the meter-in switching valve and controlling the variable throttle (adjusting the flow path area). Such a configuration may cause the lifting speed to fluctuate (hunting) at the start of the lifting operation of the vehicle body.

  On the other hand, for example, the pressure of the pressure oil in the bottom side oil chamber 16C of the boom cylinder 16 may be detected, and the variable throttle 43 may be controlled based on the detected pressure. That is, whether the free lowering operation or the vehicle body lifting operation is being performed is based on the fact that the pressure in the bottom side oil chamber 16C of the boom cylinder 16 decreases due to the grounding of the working device 11 (the bucket 14) including the boom 12. Can be determined. Therefore, for example, when the pressure in the bottom side oil chamber 16C is smaller than a preset threshold value, it can be determined that the vehicle body is being lifted. However, the pressure in the bottom side oil chamber 16C may fluctuate when shifting from the free lowering operation to the vehicle body lifting operation.

  That is, the pressure oil that has flowed out of the bottom side oil chamber 16C of the boom cylinder 16 during the free lowering operation passes through the regeneration circuit 38 that flows into the rod side oil chamber 16D and the return line that passes through the throttle 42 and flows into the tank 24. Divide into 32. In this case, the pressure loss at the bottom side oil chamber 16C may rise momentarily at the start of the vehicle body lifting operation due to an increase in the pipeline pressure loss caused by the throttle 42. For this reason, if the determination is made only with the pressure in the bottom side oil chamber 16C (the determination is made only by comparing the pressure in the bottom side oil chamber 16C with the threshold value), there is a risk of erroneous determination.

  For example, if the threshold value is set low, the pressure in the bottom side oil chamber 16C rises at the start of the vehicle body lifting operation, so that it may be erroneously determined that the free lowering operation is being performed despite the vehicle body lifting operation. is there. On the other hand, when the threshold value is set high, the pressure in the bottom side oil chamber 16C does not exceed the threshold value when the vehicle body lifting operation is finished and the working device 11 (the bucket 14) including the boom 12 is separated from the ground. there is a possibility. In this case, there is a possibility of erroneous determination that the vehicle body lifting operation is being performed even though the vehicle body lifting operation has been completed.

  On the other hand, in the embodiment, in addition to the detection of the pressure in the bottom side oil chamber 16C, the boom lowering operation of the boom lever device 35 is also detected, and based on the detected pressure and the boom lowering operation, the variable throttle 43 is used. The flow rate control and the discharge amount control by the hydraulic pump 23 are performed. Then, next, the structure for performing the flow control by the variable throttle 43 and the discharge amount control by the hydraulic pump 23 will be described.

  The bottom pressure sensor 44 as a pressure detector detects the pressure of the pressure oil in the bottom side oil chamber 16C of the boom cylinder 16. The bottom pressure sensor 44 is configured, for example, as a pressure sensor that detects the pressure (hydraulic pressure) of the bottom side oil chamber 16C or the bottom side conduit 33. The bottom pressure sensor 44 is connected to the controller 47 via a signal line, and outputs a detection signal (bottom pressure signal) corresponding to the detected pressure (bottom pressure) in the bottom side oil chamber 16C to the controller 47.

  The operation pressure sensor 45 as an operation detector detects a boom lowering operation (lowering operation amount) of the boom lever device 35. For example, the operation pressure sensor 45 is provided in the lowered pilot line 37. The operation pressure sensor 45 is configured as a pressure sensor that detects the hydraulic pressure of the lower pilot line 37, that is, the pilot pressure for lowering the boom. The operation pressure sensor 45 is connected to the controller 47 via a signal line, and detects the boom lowering pilot pressure corresponding to the boom lowering operation amount. The operation pressure sensor 45 outputs a detection signal (boom lowering operation pressure signal) corresponding to the pilot pressure for lowering the boom to the controller 47.

  The variable throttle control valve 46 variably adjusts the flow path area of the variable throttle 43 based on the command current output from the controller 47. The variable throttle control valve 46 can be constituted by, for example, an electromagnetic proportional valve. The variable throttle control valve 46 is connected to the controller 47 and variably adjusts the pilot pressure for the variable throttle 43 to a pressure corresponding to the current value based on a command (current value) from the controller 47. For example, as the command current from the controller 47 increases, the pilot pressure for the variable throttle 43 increases, the flow passage area of the variable throttle 43 decreases, and the amount of oil returned to the tank 24 can be suppressed to zero. .

  The controller 47 as a control device controls the variable operation of the flow passage area by the variable throttle 43 via the variable throttle control valve 46. Further, the controller 47 controls the displacement control unit (the displacement variable unit 23A and the displacement variable mechanism 23B) of the hydraulic pump 23, and variably adjusts the displacement of the hydraulic pump 23 (that is, the displacement that is the discharge amount of the pressure oil). To do. The controller 47 includes, for example, a microcomputer and the input side thereof is connected to the bottom pressure sensor 44 and the operation pressure sensor 45. The output side of the controller 47 is connected to the variable throttle control valve 46 and the variable capacity mechanism 23 </ b> B of the hydraulic pump 23.

  The controller 47 detects a bottom pressure (pressure oil pressure in the bottom side oil chamber 16C) output from the bottom pressure sensor 44 and a boom lowering pilot pressure (boom lowering pilot pressure) output from the operation pressure sensor 45. The variable throttle 43 and the hydraulic pump 23 are controlled based on the detection signal of the oil pressure. For this purpose, the controller 47 includes a boom operation determination unit 48, a variable throttle control unit 49, and a pump capacity command unit 50.

  The boom operation determination unit 48 receives a bottom pressure detection signal from the bottom pressure sensor 44 and a pilot pressure detection signal from the operation pressure sensor 45. The boom operation determination unit 48 operates to lower the boom 12 based on the bottom pressure in the bottom oil chamber 16C and the (boom lowering) pilot pressure in the boom lever device 35 when the boom 12 is performing the lowering operation. Is in a free lowering operation due to a free fall or a vehicle body lifting operation for lifting the vehicle body based on the lowering operation of the boom 12 (that is, from the start to the end of the vehicle body lifting operation) To do. The boom operation determination unit 48 outputs the determination result to the variable throttle control unit 49 and the pump displacement command unit 50.

  Here, in the memory of the controller 47 (boom operation determining unit 48), a processing program for determining the boom lowering operation shown in FIG. 6 is stored. The boom operation determination unit 48 determines whether the lowering operation of the boom 12 is a free lowering operation or a vehicle body lifting operation by the processing of FIG. The determination process of FIG. 6 is repeatedly executed at a predetermined control period while the controller 47 is energized, for example. In FIG. 6, steps in the flowchart are indicated by “S”. For example, “S1” corresponds to step 1.

  When the processing operation of FIG. 6 is started by starting the engine 22 or the like, in S1, it is determined whether or not the vehicle body lifting flag is ON. If it is determined in S1 that “NO”, that is, the vehicle body lifting flag is OFF, the process proceeds to S2. In S <b> 2, it is determined whether or not the operation lever 35 </ b> A of the boom lever device 35 is operated to the side that lowers the boom 12. This determination is made based on the pilot pressure for the boom lowering operation output from the operation pressure sensor 45. For example, when the pilot pressure detected by the operation pressure sensor 45 becomes larger than a preset threshold (for example, 0.7 MPa), it is determined that there is a boom lowering operation. The threshold value is obtained in advance by experiments, simulations, calculations, or the like so that it can be appropriately determined that the boom lowering operation is performed.

  If “NO” in S2, that is, if it is determined that there is no boom lowering operation, the process proceeds to S3, the vehicle body lifting flag and the free lowering flag are turned OFF, and the process returns (returns to the start via the return, and the processes after S1 are performed) repeat). In this case, the boom operation determining unit 48 determines that the boom 12 is not being lowered (the vehicle is not being lifted and is not being freely lowered), and the variable throttle control unit 49 and the pump displacement command unit 50 are notified accordingly. Output to.

  On the other hand, if “YES” in S2, that is, if it is determined that there is a boom lowering operation, the process proceeds to S4. In S4, it is determined whether or not the bottom pressure of the bottom side oil chamber 16C of the boom cylinder 16 detected by the bottom pressure sensor 44 is equal to or less than a preset vehicle body lifting determination threshold (for example, 3 MPa, preferably 1 MPa). The vehicle body lifting determination threshold value can be set as a value corresponding to the bottom pressure when the bucket 14 of the work device 11 is grounded, for example. The vehicle body lifting determination threshold value is obtained in advance by experiment, simulation, calculation, or the like so as to be a value that can appropriately determine that the bucket 14 is grounded.

  If “NO” in S4, that is, if it is determined that the bottom pressure is larger than the vehicle body lifting determination threshold (for example, exceeds 3 MPa), the process proceeds to S5. In S5, the vehicle body lifting flag is turned off and the free lowering flag is turned on, and the process returns. In this case, that is, when the free lowering flag is turned ON, the boom operation determination unit 48 determines that the boom 12 is in the free lowering operation, and outputs that effect to the variable throttle control unit 49 and the pump displacement command unit 50. .

  On the other hand, if “YES” in S4, that is, if it is determined that the bottom pressure is equal to or less than the vehicle body lifting determination threshold (for example, 3 MPa or less), the process proceeds to S6. In S6, the vehicle body lifting flag is turned on, the free lowering flag is turned off, and the process returns. In this case, that is, when the vehicle body lifting flag is turned ON, the boom operation determination unit 48 determines that the boom 12 is in the vehicle body lifting operation, and outputs that effect to the variable throttle control unit 49 and the pump displacement command unit 50. .

  If “YES” in S1, that is, if it is determined that the vehicle body lifting flag is ON, the process proceeds to S7. In S7, it is determined whether or not the boom lever device 35 is operated to be lowered, that is, whether or not the boom lowering operation is being continued. If “YES” in S7, that is, if it is determined that there is a boom lowering operation (continuing), the process returns. In other words, the vehicle body lifting flag is kept ON, and the processes after S1 are repeated. In this case, the boom operation determination unit 48 determines that the boom 12 is in the vehicle body lifting operation, and outputs that effect to the variable throttle control unit 49 and the pump displacement command unit 50. Thereby, even if the bottom pressure fluctuates (increases) after the bottom pressure becomes equal to or less than the vehicle body lifting determination threshold, it is possible to maintain the determination that the vehicle body is being lifted until the lowering operation by the operator is completed. As a result, it is possible to suppress the change in the bottom pressure when the bucket 14 is grounded (when the vehicle body lifting operation is started) from affecting the control of the variable throttle 43, and the vehicle body can be lifted stably. On the other hand, if “NO” in S7, that is, if it is determined that there is no boom lowering operation (continuation end), the process proceeds to S3 via number 1, and the vehicle body lifting flag and the free lowering flag are turned OFF and the process returns.

  The variable throttle control unit 49 of the controller 47 receives the determination result of the boom operation determination unit 48 (that is, the vehicle body lifting flag ON / OFF) and the pilot pressure detection signal from the operation pressure sensor 45. . When the boom operation determination unit 48 determines that the boom 12 starts the vehicle body lifting operation and the variable throttle control unit 49 is currently continuing (vehicle body lifting flag ON), the variable throttle control unit 49 receives the rod side oil of the boom cylinder 16 from the hydraulic pump 23. Control is performed to reduce the flow passage area (opening area) by the variable throttle 43 so that the pressure oil supplied to the chamber 16D increases. Specifically, when the boom operation determination unit 48 determines that the boom 12 starts the vehicle body lifting operation and is still continuing, the variable throttle control unit 49 throttles the flow area of the variable throttle 43. Then, the variable throttle control valve 46 is controlled.

  As shown in FIG. 7, the variable aperture control unit 49 includes a vehicle body lifting operation characteristic unit 49A, a free lowering operation characteristic unit 49B, and a command selection unit 49C. The pilot pressure (boom lowering operation amount) from the operation pressure sensor 45 is input to the vehicle body lifting operation characteristic portion 49A. The vehicle lifting operation characteristic unit 49A calculates a throttle command value (current value) corresponding to the pilot pressure (operation amount) at that time based on the vehicle lifting characteristic indicated by the characteristic line 49A1 in the block, and the calculation The aperture command value thus output is output to the command selector 49C. The vehicle body lifting characteristic (characteristic line 49A1) is the relationship (characteristic) between the pilot pressure when the vehicle body is lifted and the command current value for the variable throttle control valve 46. For example, the command for increasing the pilot pressure (operation amount) The current value can also be increased (for example, a proportional relationship).

  On the other hand, the pilot pressure (boom lowering operation amount) from the operation pressure sensor 45 is input to the free lowering operation characteristic unit 49B, as in the vehicle body lifting operation characteristic unit 49A. The free lowering operation characteristic unit 49B is based on the free lowering characteristic indicated by the characteristic line 49B1 in the block, and the throttle command value (current value) corresponding to the pilot pressure (operation amount) from the operation pressure sensor 45 at that time. And the calculated aperture command value is output to the command selector 49C. The characteristic at the time of free reduction (characteristic line 49B1) is the relationship (characteristic) between the pilot pressure at the time of free reduction and the command current value for the variable throttle control valve 46. For example, the command current value regardless of the pilot pressure (operation amount). Is constant (for example, 0 mA, command value 0, minimum value).

  The command selection unit 49C receives the throttle command value from the vehicle body lifting operation characteristic unit 49A, the throttle command value from the free lowering operation characteristic unit 49B, and the determination result of the boom operation determination unit 48. The command selection unit 49C outputs the throttle command value from the vehicle lifting operation characteristic unit 49A to the variable throttle control valve 46 when the determination result of the boom operation determination unit 48 is during the vehicle lifting operation. Thus, during the vehicle body lifting operation, the larger the pilot pressure (operation amount), the larger the command current value for the variable throttle control valve 46, the smaller the flow passage area of the variable throttle 43, and the amount of oil returned to the tank 24. Is cut off as zero. As a result, the pressure oil diverted from the hydraulic pump 23 through the branch pipe 28 to the rod side oil chamber 16D of the boom cylinder 16 increases, and the boom lowering force (force to press the bucket 14 against the ground) necessary for lifting the vehicle body is increased. Can be secured.

  On the other hand, when the determination result of the boom operation determination unit 48 is during the free lowering operation, the command selection unit 49C outputs the aperture command value from the free lowering operation time characteristic unit 49B to the variable throttle control valve 46. Thereby, during the free lowering operation, the command current value for the variable throttle control valve 46 is constant (for example, 0 mA, command value 0, minimum value) regardless of the pilot pressure (operation amount), and the flow path of the variable throttle 43 The area becomes large (maximum). As a result, the pressure oil easily flows through the regeneration circuit 38, and the regeneration efficiency of the boom lowering operation is improved.

  The pump displacement command unit 50 of the controller 47 receives the determination result signal from the boom operation determination unit 48 and the pilot pressure detection signal from the operation pressure sensor 45. The pump displacement command unit 50 variably adjusts the displacement volume (that is, the discharge capacity) of the hydraulic pump 23 by controlling the displacement control unit (the displacement variable unit 23A and the displacement variable mechanism 23B) of the hydraulic pump 23. Specifically, the pump displacement command unit 50 detects the pilot pressure (boom detected by the operation pressure sensor 45 when the boom operation determination unit 48 determines that the boom 12 is in the vehicle lifting operation (vehicle lifting flag ON). The larger the lowering operation amount), the larger the displacement volume of the hydraulic pump 23, and the more the pressure oil discharge amount is increased.

  As shown in FIG. 8, the pump displacement command unit 50 includes a vehicle body lifting operation characteristic unit 50A, a free lowering operation characteristic unit 50B, a command selection unit 50C, and a command conversion unit 50D. The pilot pressure (boom lowering operation amount) from the operation pressure sensor 45 is input to the body lifting operation characteristic unit 50A. The vehicle lifting operation characteristic unit 50A calculates a target displacement (inclination amount) corresponding to the pilot pressure (operation amount) at that time based on the vehicle lifting characteristic indicated by the characteristic line 50A1 in the block, The calculated target displacement is output to the command selector 50C. The vehicle body lifting characteristic (characteristic line 50A1) is a relationship (characteristic) between the pilot pressure when the vehicle body is lifted and the target displacement of the hydraulic pump 23. For example, when the pilot pressure exceeds a predetermined value, the pilot pressure (operation amount) It is possible to make a relationship (for example, a proportional relationship) in which the target displacement volume increases with respect to the increase of.

  On the other hand, the pilot pressure (boom lowering operation amount) from the operation pressure sensor 45 is input to the free lowering operation characteristic unit 50B. Based on the free lowering characteristic indicated by the characteristic line 50B1 in the block, the free lowering operation characteristic unit 50B calculates a target displacement corresponding to the pilot pressure (operation amount) at that time, and calculates the calculated target displacement. The volume is output to the command selection unit 50C. The characteristic at the time of free lowering (characteristic line 50B1) is the relationship (characteristic) between the pilot pressure and the target displacement of the hydraulic pump 23 at the time of free lowering. For example, the target displacement is constant regardless of the pilot pressure (minimum target value). , Minimum tilt value).

  The command selection unit 50C receives the target displacement from the body lifting operation characteristic unit 50A, the target displacement from the free lowering operation characteristic unit 50B, and the determination result of the boom operation determination unit 48. When the determination result of the boom operation determination unit 48 is during the vehicle body lifting operation, the command selection unit 50C outputs the target displacement volume from the vehicle body lifting operation time characteristic unit 50A to the command conversion unit 50D. On the other hand, when the determination result of the boom operation determination unit 48 is during the free lowering operation, the command selection unit 50C outputs the target displacement volume from the free lowering operation time characteristic unit 50B to the command conversion unit 50D.

  The target displacement volume is input to the command conversion unit 50D from the command selection unit 50C. The command conversion unit 50D calculates a command (command current value) corresponding to the target displacement at that time based on the command characteristics indicated by the characteristic line 50D1 in the block, and the calculated command (command current value). Output to the variable capacity mechanism 23B of the hydraulic pump 23. The command characteristic (characteristic line 50D1) is the relationship (characteristic) between the target displacement volume and the command current value for the variable capacity mechanism 23B. For example, if the target displacement volume exceeds a predetermined value, the increase in the target displacement volume The command current value can also be increased (for example, proportional).

  As a result, during the vehicle body lifting operation, the larger the pilot pressure (operation amount) detected by the operation pressure sensor 45, the larger the command current value for the displacement variable mechanism 23B, and the displacement volume of the hydraulic pump 23 increases. Increase the discharge amount. As a result, the boom lowering force (force for pressing the bucket 14 against the ground) increases rapidly, and the vehicle body lifting speed can be increased.

  The hydraulic excavator 1 according to the embodiment has the above-described configuration, and the operation thereof will be described next.

  First, an operator can board the cab 6 and operate the left and right traveling lever / pedal devices to move the lower traveling body 2 forward or backward. On the other hand, the operator in the cab 6 can perform the excavation work of earth and sand by operating the left and right working lever devices to turn the working device 11 (up and down). For example, when the operator operates (tilts) the operation lever 35A of the boom lever device 35, the boom 12 can be rotated (raised and lowered).

  Here, when the operation lever 35A is tilted from the neutral position to the side of lowering the boom 12 (the side of reducing the boom cylinder 16), the boom direction control valve 31 is shown in FIG. The position is switched from the neutral position (A) shown to the switching position (C) shown in FIGS. At this time, the boom operation determination unit 48 of the controller 47 determines whether the lowering operation of the boom 12 is in the free lowering operation based on the bottom pressure and the pilot pressure (boom lowering operation amount) according to the determination processing of FIG. It is determined whether the vehicle is being lifted.

  The variable throttle control unit 49 of the controller 47 controls the variable throttle control valve 46 so that the flow passage area of the variable throttle 43 is throttled when the boom operation determination unit 48 determines that the boom 12 is in the vehicle body lifting operation. To do. When the boom operation determination unit 48 determines that the boom 12 is in the body lifting operation, the pump capacity command unit 50 of the controller 47 increases the displacement of the hydraulic pump 23 as the pilot pressure (boom lowering operation amount) increases. (Pressure oil discharge amount) is increased. Thereby, the boom lowering force necessary for lifting the vehicle body can be ensured during the vehicle body lifting operation.

  On the other hand, the variable throttle control unit 49 of the controller 47 increases (maximizes) the flow path area of the variable throttle 43 when the boom operation determination unit 48 determines that the lowering operation of the boom 12 is in the free lowering operation. Thereby, the pressure oil can easily flow from the bottom side oil chamber 16C of the boom cylinder 16 to the rod side oil chamber 16D through the regeneration circuit 38, and the regeneration efficiency of the boom lowering operation can be improved.

  Thus, according to the embodiment, the lifting operation of the vehicle body can be performed smoothly.

  (1). That is, according to the embodiment, the boom operation determination unit 48 of the controller 47 detects the pressure detection signal (bottom pressure signal) of the bottom side oil chamber 16C of the boom cylinder 16 and the detection signal of the boom lowering operation of the boom lever device 35. Based on (the boom lowering operation pressure signal), it is determined whether the boom lowering operation is a free lowering operation or a vehicle body lifting operation. For this reason, it is possible to improve the accuracy of the determination as to whether the free lowering operation or the vehicle body lifting operation is being performed, for example, compared with the configuration in which only the pressure in the bottom side oil chamber 16C is used. That is, at the start of the vehicle body lifting operation, for example, even if the pressure in the bottom oil chamber 16C fluctuates (rises) temporarily, the determination that the vehicle body lifting operation is in progress is maintained based on the detection signal of the boom lowering operation. can do. Thereby, erroneous determination can be suppressed.

  Further, the variable aperture control unit 49 of the controller 47 controls the variable aperture 43 based on the determination result of the boom operation determination unit 48. That is, when the boom operation determining unit 48 determines that the boom is in the vehicle body lifting operation, the variable throttle control unit 49 performs control to reduce the flow path area by the variable throttle 43. For this reason, when necessary, the flow passage area of the variable throttle 43 can be reduced, and a stable vehicle body lifting operation can be performed. In other words, for example, a configuration as in Patent Document 1 using the hydraulic signal as it is (directly switched by a meter-in switching valve that is directly switched by the pressure oil in the bottom side oil chamber of the boom cylinder and the pilot pressure oil from the boom operating device). As compared with a configuration including a variable aperture that can be switched, it is possible to suppress fluctuation (hunting) of the lifting speed of the vehicle body. Thereby, the lifting operation of the vehicle body can be performed smoothly.

  (2). According to the embodiment, the regeneration circuit 38 that guides the pressure oil in the bottom side oil chamber 16C to the rod side oil chamber 16D is provided between the bottom side oil chamber 16C and the rod side oil chamber 16D of the boom cylinder 16. . When the boom 12 is being freely lowered, the regeneration circuit 38 supplies the pressure oil in the bottom side oil chamber 16C to the rod side oil chamber 16D. For this reason, when the boom 12 is being freely lowered, the pressure oil can be stably supplied from the bottom side oil chamber 16C to the rod side oil chamber 16D through the regeneration circuit 38, and the pressure oil in the boom cylinder 16 is regenerated. Efficiency can be improved.

  (3). According to the embodiment, the variable throttle control valve 46 that variably adjusts the flow path area of the variable throttle 43 is provided. When the boom operation determination unit 48 determines that the boom 12 is in the vehicle body lifting operation, the variable throttle control unit 49 of the controller 47 controls the variable throttle control valve 46 so as to throttle the flow passage area of the variable throttle 43. It is configured. For this reason, the variable throttle control unit 49 can stably adjust (expand / reduce) the flow passage area of the variable throttle 43 via the variable throttle control valve 46. In this case, the variable throttle control section 49 controls the operation of the boom 12 by controlling the variable throttle control valve 46 and, in turn, the variable throttle 43 in accordance with the detection signal of the boom lowering operation of the boom lever device 35. It is possible to supply (send out) pressure oil having an optimum flow rate according to the pressure to the rod side oil chamber 16D of the boom cylinder 16.

  Moreover, the variable throttle control valve 46 can be constituted by a control valve (electromagnetic valve) that is switched by electric power, more specifically, an electromagnetic proportional valve. That is, the electric signal (command current) output from the variable throttle control unit 49 is converted into a hydraulic signal (pilot pressure) by the variable throttle control valve 46, and the converted hydraulic signal is input to the variable throttle 43. can do. In this case, for example, the change of the characteristic of the variable throttle 43 (control characteristic of the flow path area) is changed without changing the components (for example, the change of the control program of the variable throttle control unit 49, the control parameter) This is only possible by changing the characteristics 49A1 and 49B1. That is, in the case of a configuration in which the hydraulic signal is used as it is, the control characteristic of the hydraulic signal is uniquely determined by the hydraulic component, and when changing the characteristic, the hydraulic component needs to be changed. On the other hand, in the embodiment, the characteristics can be changed without changing the hydraulic parts, and the versatility and the design freedom can be improved. That is, it is advantageous in terms of replacement part costs and replacement work costs.

  (4). According to the embodiment, the hydraulic pump 23 is a variable displacement hydraulic pump including a displacement control unit (a displacement variable unit 23A and a displacement variable mechanism 23B) that variably adjusts the displacement volume. On the other hand, the controller 47 includes a pump capacity command section 50 that controls a capacity control section (capacity variable section 23A, capacity variable mechanism 23B) of the hydraulic pump 23. The pump capacity command unit 50 is configured to increase the displacement volume as the operation amount of the boom lowering operation is larger when the boom operation determining unit 48 determines that the boom is in the body lifting operation. For this reason, when the boom 12 is being lifted, the displacement of the hydraulic pump 23 can be increased in addition to reducing the flow passage area of the variable throttle 43.

  That is, the larger the operation amount of the boom lowering operation, the larger the displacement volume of the hydraulic pump 23, thereby increasing the pressure oil to the rod side oil chamber 16D of the boom cylinder 16. As a result, the boom lowering force (in other words, the force pressing the bucket 14 against the ground) increases rapidly, and the vehicle body lifting speed can be increased. As a result, operability and workability can be improved. Further, the change of the characteristic of the hydraulic pump 23 (the control characteristic of the displacement volume) can be made by changing the software without changing the components (for example, changing the control program of the pump capacity command unit 50, the characteristic 50A1, which is a control parameter). 50B1 and 50D1 can be changed only. For this reason, also from this aspect, versatility and design freedom can be improved.

  In the embodiment, the case where the regeneration circuit 38 is provided integrally with the boom direction control valve 31 has been described as an example. However, the present invention is not limited to this. For example, the regeneration circuit may be provided separately from the boom direction control valve.

  In the embodiment, the boom operation determination unit 48 has been described by taking as an example a case in which two flags, a vehicle body lifting flag and a free lowering flag, are used. However, the present invention is not limited to this. For example, a configuration in which only the vehicle body lifting flag is used (a vehicle body lifting operation when the vehicle body lifting flag is ON and a free lowering operation when it is OFF) may be used.

  In the embodiment, the pilot pressure based on the operation of the boom lever device 35 is supplied to the hydraulic pilot portions 31A and 31B of the boom direction control valve 31, and the operation pressure sensor 45 detects the pilot pressure of the lowering operation. Thus, the case where the amount of operation for lowering the boom lever device 35 is detected has been described as an example. However, the present invention is not limited to this. For example, the operation detector can be configured by a lever sensor (displacement sensor) that directly detects the operation amount of the operation lever of the boom lever device. Further, the boom lever device may be an electric boom operating device, for example. That is, as the operation detector, various sensors can be used as long as they can detect the operation amount of the boom operation device. Also, various operation devices can be used as the boom operation device as long as the boom direction control valve can be switched.

  More specifically, the operation detector only needs to be able to detect the operation amount of the boom operation device, and various sensors, switches, etc., depending on the configuration of the boom operation device and the boom direction control valve. Can be used. Further, for example, when a signal corresponding to the operation amount is input / output from / to the controller from the boom operation device without using the detector, the controller calculates (detects) the operation amount from the signal. It can also be. In other words, the controller can also serve as an operation detector.

  In the embodiment, the case where the hydraulic pump 23 is driven by the engine 22 as a prime mover has been described as an example. However, the present invention is not limited to this, and for example, the hydraulic pump may be driven by an electric motor (electric motor).

  In the embodiment, the super large hydraulic excavator 1 is described as an example of the construction machine. However, the present invention is not limited to this, and the construction machine may be applied to hydraulic excavators of various sizes (large, medium, and small). In addition, the crawler excavator 1 has been described as an example, but the present invention is not limited thereto, and may be applied to, for example, a wheel excavator. Moreover, although the case where the bucket 14 was attached as a working tool was described as an example, for example, a configuration in which a working tool (attachment) other than the bucket such as a gripping tool may be attached. Furthermore, although the backhoe type hydraulic excavator 1 has been described as an example, it may be applied to, for example, a loading type hydraulic excavator. That is, the present invention is not limited to the hydraulic excavator 1 of the embodiment, and can be widely applied to various construction machines.

1 Excavator (construction machine)
2 Lower traveling body (base)
3 Upper swing body (base)
12 Boom 16 Boom Cylinder 16C Bottom Oil Chamber 16D Rod Oil Chamber 23 Hydraulic Pump (Hydraulic Source)
23A Capacity variable section (capacity control section)
23B variable capacity mechanism (capacity controller)
24 tanks (hydraulic power source)
27 Center Bypass Pipeline 31 Boom Direction Control Valve 35 Boom Lever Device (Boom Operation Device)
38 Regenerative circuit 43 Variable throttle 44 Bottom pressure sensor (pressure detector)
45 Operation pressure sensor (operation detector)
46 Variable throttle control valve 47 Controller 48 Boom operation determination unit 49 Variable throttle control unit 50 Pump capacity command unit

Claims (4)

A substrate;
A boom pivotably attached to the substrate;
A boom cylinder attached between the base body and the boom;
A hydraulic pump which is mounted on the base body and constitutes a hydraulic source together with a tank and supplies pressure oil to the boom cylinder;
A boom direction control valve that is provided in the middle of a center bypass pipe that connects the hydraulic pump to the tank, and that controls the switching of pressure oil supplied from the hydraulic pump to the boom cylinder;
In a construction machine comprising a boom operation device that performs an operation of switching the boom direction control valve to raise or lower the boom.
A variable throttle that is provided in the middle of the center bypass pipe and variably throttles the flow path area downstream from the boom direction control valve;
A pressure detector for detecting the pressure of pressure oil in the bottom oil chamber of the boom cylinder;
An operation detector for detecting a boom lowering operation of the boom operating device;
A control device for controlling a variable operation of the flow passage area by the variable throttle based on a detection signal of the pressure output from the pressure detector and a detection signal of the boom lowering operation output from the operation detector. And
In the control device, when the boom is performing a lowering operation, the lowering operation of the boom is in a free lowering operation due to a free fall based on the detection signal of the pressure and the detection signal of the boom lowering operation. Or a boom operation determination unit that determines whether the base is being lifted based on the boom lowering operation,
When the boom operation determining unit determines that the boom is in the base lifting operation, the flow passage area by the variable throttle is reduced so that the pressure oil supplied from the hydraulic pump to the rod side oil chamber of the boom cylinder increases. A construction machine characterized by comprising a variable aperture control section for controlling the aperture. Between the bottom side oil chamber and the rod side oil chamber of the boom cylinder, a regeneration circuit is provided for guiding the pressure oil in the bottom side oil chamber to the rod side oil chamber,
The construction machine according to claim 1, wherein when the boom is in a free lowering operation, the regeneration circuit replenishes the rod side oil chamber with the pressure oil in the bottom side oil chamber. A variable throttle control valve for variably adjusting the flow path area by the variable throttle;
The variable throttle control unit of the control device controls the variable throttle control valve so as to throttle the flow passage area of the variable throttle when the boom operation determining unit determines that the boom is in the base lifting operation. The construction machine according to claim 1 or 2, wherein the construction machine is configured. The hydraulic pump is a variable displacement hydraulic pump including a displacement control unit that variably adjusts the displacement volume.
The control device includes a pump capacity command unit that controls the capacity control unit of the hydraulic pump,
The pump displacement command unit of the control device has a larger operation amount of the boom lowering operation detected by the operation detector when the boom operation determining unit determines that the boom is in the base lifting operation. The construction machine according to claim 1, 2 or 3, wherein the displacement volume is increased.

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