Excavator

Abstract

To provide a shovel for preventing the occurrence of cavitation in working oil.SOLUTION: The shovel includes an undercarriage, a super structure turnable relative to the undercarriage, a turning hydraulic motor for turning the super structure, a pump for discharging working oil, a control valve for supplying the working oil discharged from the pump to the turning hydraulic motor while switching the flow of the working oil to discharge the working oil discharged by the turning hydraulic motor to a working oil tank, a determination unit for determining whether cavitation occurs or not in an oil path for the working oil, and a control unit for controlling the control valve. The control unit controls the control valve on the basis of the determination result of the determination unit.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a shovel. [Background technology]

[0002] A known work machine includes a lower traveling body, an upper rotating body that can rotate relative to the lower traveling body, an attachment attached to the upper rotating body, a hydraulic swing motor that rotates the upper rotating body, and a hydraulic actuator that drives the attachment. Patent Document 1 discloses a cavitation prevention circuit for a work machine that has a make-up oil passage in a drive circuit that supplies and discharges pressurized oil to a hydraulic actuator, and that includes a negative control circuit that generates negative control pressure by providing a negative control orifice in the oil passage that passes through a control valve that controls the hydraulic actuator, and applies the negative control pressure to a regulator that controls the pump's discharge volume, a negative control pressure switching valve that can switch the negative control pressure to a pseudo-negative control pressure that is a pseudo-reduced negative control pressure and apply it to the regulator, an unloading valve that is provided in parallel with the negative control orifice, and deceleration detection means that detects deceleration of the hydraulic actuator, and that when deceleration of the hydraulic actuator is detected, the negative control pressure switching valve applies the pseudo-negative control pressure to the regulator, thereby increasing the pump's discharge volume and unloading the unloading valve. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-112494 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the rotation speed of the upper rotating body is reduced while the upper rotating body is rotating, the opening of the control valve that supplies hydraulic oil to the swing hydraulic motor narrows, reducing the flow rate of hydraulic oil supplied to the swing hydraulic motor. Meanwhile, the rotating upper rotating body does not suddenly decelerate due to inertia, and the swing hydraulic motor rotates due to the inertial force of the rotating upper rotating body. This results in an insufficient flow rate of hydraulic oil to the swing hydraulic motor, and the hydraulic oil passage that supplies hydraulic oil from the control valve to the swing hydraulic motor becomes low pressure. This can cause cavitation, in which air bubbles are generated in the hydraulic oil in the hydraulic oil passage and then disappear.

[0005] Therefore, an object of the present invention is to provide a shovel that prevents cavitation from occurring in hydraulic oil. [Means for solving the problem]

[0006] An excavator according to an embodiment of the present invention comprises a lower traveling body, an upper rotating body that can rotate relative to the lower traveling body, a swing hydraulic motor that rotates the upper rotating body, a pump that discharges hydraulic oil, a control valve that supplies the hydraulic oil discharged by the pump to the swing hydraulic motor and switches the flow of the hydraulic oil to discharge the hydraulic oil discharged by the swing hydraulic motor to a hydraulic oil tank, a determination unit that determines whether or not cavitation occurs in an oil passage for the hydraulic oil, and a control unit that controls the control valve, The determination unit determines whether or not cavitation will occur based on a deceleration operation amount for decelerating the rotation of an operating device and the rotation speed of the upper rotating body, and when the determination unit determines that cavitation will occur, the control unit restricts a decrease in the spool stroke of the control valve in response to the deceleration operation amount. . [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a shovel that prevents cavitation from occurring in hydraulic oil. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a side view of a shovel according to an embodiment of the present invention. [Figure 2] FIG. 2 is a top view of the excavator of FIG. 1. [Figure 3] FIG. 2 is a diagram showing an example of the configuration of a hydraulic system mounted on the excavator of FIG. 1. [Figure 4] FIG. 2 is a diagram illustrating a hydraulic circuit of a swing hydraulic motor. [Figure 5] 4 is a flowchart illustrating cavity suppression control by a controller. [Figure 6] 10 is a graph illustrating an actual lever operation amount and a lever operation amount control by a controller 0. [Figure 7] 10 is a graph showing an example of a turning speed and a rate limit. DETAILED DESCRIPTION OF THE INVENTION

[0009] First, a shovel 100 as an excavator according to an embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a side view of the shovel 100, and Figure 2 is a top view of the shovel 100.

[0010] In this embodiment, the lower traveling structure 1 of the excavator 100 includes a crawler 1C. The crawler 1C is driven by a traveling hydraulic motor 2M that serves as a traveling actuator mounted on the lower traveling structure 1. Specifically, the crawler 1C includes a left crawler 1CL and a right crawler 1CR. The left crawler 1CL is driven by a left traveling hydraulic motor 2ML, and the right crawler 1CR is driven by a right traveling hydraulic motor 2MR.

[0011] An upper rotating body 3 is rotatably mounted on the lower traveling body 1 via a rotating mechanism 2. The rotating mechanism 2 is driven by a hydraulic swing motor 2A serving as a swing actuator mounted on the upper rotating body 3. However, the swing actuator may also be a swing motor-generator serving as an electric actuator.

[0012] A boom 4 is attached to the upper rotating body 3. An arm 5 is attached to the tip of the boom 4, and a bucket 6 is attached to the tip of the arm 5 as an end attachment. The boom 4, arm 5, and bucket 6 constitute an attachment AT, which is an example of an attachment. The boom 4 is driven by a boom cylinder 7, the arm 5 is driven by an arm cylinder 8, and the bucket 6 is driven by a bucket cylinder 9. The boom cylinder 7, arm cylinder 8, and bucket cylinder 9 constitute an attachment actuator. In the example shown in FIGS. 1 and 2, the bucket 6 is an excavation bucket, but it may also be a skeleton bucket or a (gravel removal bucket). The bucket 6 may also be equipped with a bucket tilt mechanism.

[0013] The upper rotating body 3 is provided with a cabin 10 as a driver's cab, and is equipped with a power source such as an engine 11. Inside the cabin 10, an operating device 26, a controller 30, an operation method switching device SD, etc. are provided. In addition, a space recognition device 70, a rotation angular velocity sensor S5, etc. are attached to the upper rotating body 3. For convenience, in this document, the side of the upper rotating body 3 to which the attachment AT is attached will be referred to as the front, and the side to which the counterweight is attached will be referred to as the rear.

[0014] The spatial recognition device 70 is configured to recognize objects present in the three-dimensional space around the shovel 100. The spatial recognition device 70 may also be configured to calculate the distance from the spatial recognition device 70 or the shovel 100 to the recognized object. The spatial recognition device 70 includes, for example, an ultrasonic sensor, a millimeter-wave radar, an imaging device, a LIDAR, a distance image sensor, an infrared sensor, or any combination thereof. The imaging device is, for example, a monocular camera or a stereo camera. In this embodiment, the spatial recognition device 70 includes a forward sensor 70F attached to the front end of the upper surface of the cabin 10, a rearward sensor 70B attached to the rear end of the upper surface of the upper rotating body 3, a leftward sensor 70L attached to the left end of the upper surface of the upper rotating body 3, and a rightward sensor 70R attached to the right end of the upper surface of the upper rotating body 3. An upward sensor that recognizes objects present in the space above the upper rotating body 3 may be attached to the shovel 100.

[0015] The swing angular velocity sensor S5 is configured to detect the swing angular velocity of the upper swing body 3. In this embodiment, the swing angular velocity sensor S5 is, for example, an inertial measurement unit (IMU) that measures the attitude of the upper swing body 3. The swing angular velocity sensor S5 may also be a resolver, a rotary encoder, or the like. The swing angular velocity sensor S5 may detect a swing speed. The swing speed may be calculated from the swing angular velocity.

[0016] The operating device 26 is a device used by an operator to operate the actuator. The operating device 26 includes, for example, an operating lever and an operating pedal. The actuator includes at least one of a hydraulic actuator and an electric actuator.

[0017] The operation mode switching device SD is configured to be able to switch the operation mode of the operation lever. For example, the operation mode switching device SD includes a push button switch provided on the right console inside the cabin 10, and is configured to be able to switch the operation mode of the operation lever between a first operation mode and a second operation mode each time the push button switch is pressed. For example, the first operation mode is configured so that when the left operation lever 26L (see FIG. 3) is tilted forward, the arm 5 is opened, when the left operation lever 26L is tilted rearward, the arm 5 is closed, when the left operation lever 26L is tilted left, a left turn is performed, and when the left operation lever 26L is tilted right, a right turn is performed. The first operation method is configured so that when the right operation lever 26R (see FIG. 3) is tilted forward, the boom 4 is lowered, when the right operation lever 26R is tilted rearward, the boom 4 is raised, when the right operation lever 26R is tilted left, the bucket 6 is closed, and when the right operation lever 26R is tilted right, the bucket 6 is opened. On the other hand, the second operation method is configured so that when the left operation lever 26L (see FIG. 3) is tilted forward, a right turn is performed, when the left operation lever 26L is tilted rearward, a left turn is performed, when the left operation lever 26L is tilted left, the arm 5 is opened, and when the left operation lever 26L is tilted right, the arm 5 is closed.

[0018] The operator of the shovel 100 may, for example, select the first operation method when performing excavation work using an excavation bucket, and may select the second operation method when performing gravel removal work using a skeleton bucket (gravel removal bucket).

[0019] The controller 30 is a control device for controlling the shovel 100. In this embodiment, the controller 30 is configured as a computer including a CPU, a volatile storage device, a nonvolatile storage device, and the like. The controller 30 reads programs corresponding to each function from the nonvolatile storage device, loads them into the volatile storage device, and causes the CPU to execute the corresponding processing. Each function includes, for example, a machine guidance function that guides the operator in manually operating the shovel 100, and a machine control function that assists the operator in manually operating the shovel 100 or automatically or autonomously operates the shovel 100. The controller 30 may also include a contact avoidance function that automatically or autonomously operates or stops the shovel 100 to avoid contact between the shovel 100 and objects present within a monitoring range around the shovel 100. Monitoring of objects around the shovel 100 is performed not only within the monitoring range but also outside the monitoring range.

[0020] Next, a configuration example of a hydraulic system mounted on the shovel 100 will be described with reference to Fig. 3. Fig. 3 is a diagram showing a configuration example of a hydraulic system mounted on the shovel 100. In Fig. 3, a mechanical power transmission system, a hydraulic oil line, a pilot line, and an electrical control system are indicated by double lines, solid lines, dashed lines, and dotted lines, respectively.

[0021] The hydraulic system of the excavator 100 mainly includes an engine 11, a regulator 13, a main pump 14, a pilot pump 15, a control valve unit 17, an operating device 26, a discharge pressure sensor 28, an operating sensor 29, a controller 30, and the like.

[0022] In FIG. 3, the hydraulic system is configured to circulate hydraulic oil from a main pump 14 driven by an engine 11 through a center bypass line 40 or a parallel line 42 to a hydraulic oil tank.

[0023] The engine 11 is a drive source of the excavator 100. In this embodiment, the engine 11 is, for example, a diesel engine that operates to maintain a predetermined rotation speed. An output shaft of the engine 11 is connected to the input shafts of the main pump 14 and the pilot pump 15.

[0024] The main pump 14 is configured to supply hydraulic oil via a hydraulic oil line to the control valve unit 17. In this embodiment, the main pump 14 is a swash plate type variable displacement hydraulic pump.

[0025] The regulator 13 is configured to be able to control the discharge rate of the main pump 14. In this embodiment, the regulator 13 controls the discharge rate of the main pump 14 by adjusting the tilt angle of the swash plate of the main pump 14 in response to a control command from the controller 30.

[0026] The pilot pump 15 is an example of a pilot pressure generating device, and is configured to supply hydraulic oil to hydraulic control devices via a pilot line. In this embodiment, the pilot pump 15 is a fixed displacement hydraulic pump. However, the pilot pressure generating device may be realized by the main pump 14. That is, the main pump 14 may have a function of supplying hydraulic oil to various hydraulic control devices via a pilot line, in addition to a function of supplying hydraulic oil to the control valve unit 17 via a hydraulic oil line. In this case, the pilot pump 15 may be omitted.

[0027] The control valve unit 17 is a hydraulic control device that controls the hydraulic system in the excavator 100. In this embodiment, the control valve unit 17 includes control valves 171 to 176. The control valve 175 includes a control valve 175L and a control valve 175R, and the control valve 176 includes a control valve 176L and a control valve 176R. The control valve unit 17 is configured to selectively supply hydraulic oil discharged by the main pump 14 to one or more hydraulic actuators via the control valves 171 to 176. The control valves 171 to 176 control, for example, the flow rate of hydraulic oil flowing from the main pump 14 to the hydraulic actuators and the flow rate of hydraulic oil flowing from the hydraulic actuators to a hydraulic oil tank. The hydraulic actuators include a boom cylinder 7, an arm cylinder 8, a bucket cylinder 9, a left traveling hydraulic motor 2ML, a right traveling hydraulic motor 2MR, and a swing hydraulic motor 2A.

[0028] The operating device 26 is configured to allow an operator to operate the actuator. In this embodiment, the operating device 26 includes a hydraulic actuator operating device configured to allow an operator to operate the hydraulic actuator. Specifically, the hydraulic actuator operating device is configured to supply hydraulic oil discharged from the pilot pump 15 to the pilot ports of the corresponding control valves in the control valve unit 17 via pilot lines. The pressure of the hydraulic oil supplied to each pilot port (pilot pressure) is a pressure that corresponds to the operation direction and operation amount of the operating device 26 corresponding to each hydraulic actuator.

[0029] The discharge pressure sensor 28 is configured to be able to detect the discharge pressure of the main pump 14. In this embodiment, the discharge pressure sensor 28 outputs the detected value to the controller 30.

[0030] The operation sensor 29 is configured to detect the details of an operation of the operation device 26 by an operator. In this embodiment, the operation sensor 29 detects the operation direction and operation amount of the operation device 26 corresponding to each actuator, and outputs the detected values ​​to the controller 30.

[0031] The main pump 14 includes a left main pump 14L and a right main pump 14R. The left main pump 14L circulates hydraulic oil to the hydraulic oil tank via a left center bypass line 40L or a left parallel line 42L, and the right main pump 14R circulates hydraulic oil to the hydraulic oil tank via a right center bypass line 40R or a right parallel line 42R.

[0032] The left center bypass line 40L is a hydraulic oil line that passes through control valves 171, 173, 175L, and 176L arranged in the control valve unit 17. The right center bypass line 40R is a hydraulic oil line that passes through control valves 172, 174, 175R, and 176R arranged in the control valve unit 17.

[0033] The control valve 171 is a spool valve that switches the flow of hydraulic oil to supply the hydraulic oil discharged by the left main pump 14L to the left traveling hydraulic motor 2ML and to discharge the hydraulic oil discharged by the left traveling hydraulic motor 2ML to the hydraulic oil tank.

[0034] The control valve 172 is a spool valve that switches the flow of hydraulic oil to supply the hydraulic oil discharged by the right main pump 14R to the right traveling hydraulic motor 2MR and to discharge the hydraulic oil discharged by the right traveling hydraulic motor 2MR to the hydraulic oil tank.

[0035] The control valve 173 is a spool valve that switches the flow of hydraulic oil to supply the hydraulic oil discharged by the left main pump 14L to the swing hydraulic motor 2A and to discharge the hydraulic oil discharged by the swing hydraulic motor 2A to the hydraulic oil tank.

[0036] The control valve 174 is a spool valve that switches the flow of hydraulic oil to supply the hydraulic oil discharged by the right main pump 14R to the bucket cylinder 9 and to discharge the hydraulic oil in the bucket cylinder 9 to the hydraulic oil tank.

[0037] The control valve 175L is a spool valve that switches the flow of hydraulic oil to supply the hydraulic oil discharged by the left main pump 14L to the boom cylinder 7. The control valve 175R is a spool valve that switches the flow of hydraulic oil to supply the hydraulic oil discharged by the right main pump 14R to the boom cylinder 7 and to discharge the hydraulic oil in the boom cylinder 7 to the hydraulic oil tank.

[0038] The control valve 176L is a spool valve that switches the flow of hydraulic oil to supply the hydraulic oil discharged by the left main pump 14L to the arm cylinder 8 and to discharge the hydraulic oil in the arm cylinder 8 to the hydraulic oil tank.

[0039] The control valve 176R is a spool valve that switches the flow of hydraulic oil to supply the hydraulic oil discharged by the right main pump 14R to the arm cylinder 8 and to discharge the hydraulic oil in the arm cylinder 8 to the hydraulic oil tank.

[0040] The left parallel conduit 42L is a hydraulic oil line that runs parallel to the left center bypass conduit 40L. The left parallel conduit 42L can supply hydraulic oil to a downstream control valve when the flow of hydraulic oil through the left center bypass conduit 40L is restricted or blocked by any of the control valves 171, 173, and 175L. The right parallel conduit 42R is a hydraulic oil line that runs parallel to the right center bypass conduit 40R. The right parallel conduit 42R can supply hydraulic oil to a downstream control valve when the flow of hydraulic oil through the right center bypass conduit 40R is restricted or blocked by any of the control valves 172, 174, and 175R.

[0041] The regulator 13 includes a left regulator 13L and a right regulator 13R. The left regulator 13L controls the discharge rate of the left main pump 14L by adjusting the tilt angle of the swash plate of the left main pump 14L in accordance with the discharge pressure of the left main pump 14L. Specifically, the left regulator 13L adjusts the tilt angle of the swash plate of the left main pump 14L in accordance with an increase in the discharge pressure of the left main pump 14L to reduce the discharge rate. The same applies to the right regulator 13R. This is to prevent the absorption power (absorption horsepower) of the main pump 14, which is expressed as the product of the discharge pressure and the discharge rate, from exceeding the output power (output horsepower) of the engine 11.

[0042] The operating device 26 includes a left operating lever 26L, a right operating lever 26R, and a travel lever 26D. The travel lever 26D includes a left traveling lever 26DL and a right traveling lever 26DR.

[0043] The left operating lever 26L is used for swing operation and operation of the arm 5. When the left operating lever 26L is operated in the forward / backward direction, it uses the hydraulic oil discharged from the pilot pump 15 to introduce a control pressure corresponding to the amount of lever operation into the pilot port of the control valve 176. When it is operated in the left / right direction, it uses the hydraulic oil discharged from the pilot pump 15 to introduce a control pressure corresponding to the amount of lever operation into the pilot port of the control valve 173.

[0044] Specifically, when the left operating lever 26L is operated in the arm closing direction, it introduces hydraulic oil into the right pilot port of the control valve 176L and introduces hydraulic oil into the left pilot port of the control valve 176R. When the left operating lever 26L is operated in the arm opening direction, it introduces hydraulic oil into the left pilot port of the control valve 176L and introduces hydraulic oil into the right pilot port of the control valve 176R. When the left operating lever 26L is operated in the left turning direction, it introduces hydraulic oil into the left pilot port of the control valve 173, and when operated in the right turning direction, it introduces hydraulic oil into the right pilot port of the control valve 173.

[0045] In the example shown in FIG. 3, the left operating lever 26L functions as an arm operating lever when operated in the forward / backward direction, and functions as a turning operating lever when operated in the left / right direction.

[0046] The right operating lever 26R is used to operate the boom 4 and the bucket 6. When the right operating lever 26R is operated in the forward / backward direction, it uses the hydraulic oil discharged by the pilot pump 15 to introduce a control pressure corresponding to the amount of lever operation into the pilot port of the control valve 175. When it is operated in the left / right direction, it uses the hydraulic oil discharged by the pilot pump 15 to introduce a control pressure corresponding to the amount of lever operation into the pilot port of the control valve 174.

[0047] Specifically, when the right operating lever 26R is operated in the boom-lowering direction, it introduces hydraulic oil to the left pilot port of the control valve 175R. When the right operating lever 26R is operated in the boom-raising direction, it introduces hydraulic oil to the right pilot port of the control valve 175R and also introduces hydraulic oil to the left pilot port of the control valve 175R. When the right operating lever 26R is operated in the bucket-closing direction, it introduces hydraulic oil to the right pilot port of the control valve 174, and when operated in the bucket-opening direction, it introduces hydraulic oil to the left pilot port of the control valve 174.

[0048] In the example shown in FIG. 3, the right operating lever 26R functions as a boom operating lever when operated in the forward / backward direction, and functions as a bucket operating lever when operated in the left / right direction.

[0049] The travel lever 26D is used to operate the crawler 1C. Specifically, the left travel lever 26DL is used to operate the left crawler 1CL. It may be configured to operate in conjunction with the left travel pedal. When the left travel lever 26DL is operated in the forward / backward direction, it uses hydraulic oil discharged from the pilot pump 15 to introduce a control pressure corresponding to the amount of lever operation into the pilot port of the control valve 171. The right travel lever 26DR is used to operate the right crawler 1CR. It may be configured to operate in conjunction with the right travel pedal. When the right travel lever 26DR is operated in the forward / backward direction, it uses hydraulic oil discharged from the pilot pump 15 to introduce a control pressure corresponding to the amount of lever operation into the pilot port of the control valve 172.

[0050] The discharge pressure sensor 28 includes a discharge pressure sensor 28L and a discharge pressure sensor 28R. The discharge pressure sensor 28L detects the discharge pressure of the left main pump 14L and outputs the detected value to the controller 30. The same applies to the discharge pressure sensor 28R.

[0051] The operation sensor 29 includes operation sensors 29LA, 29LB, 29RA, 29RB, 29DL, and 29DR. The operation sensor 29LA detects the details of the forward / backward operation of the left operation lever 26L by the operator, and outputs the detected value to the controller 30. The details of the operation include, for example, the lever operation direction, the lever operation amount (lever operation angle), etc.

[0052] Similarly, operation sensor 29LB detects the operation of left operation lever 26L in the left-right direction by the operator and outputs the detected value to controller 30. Operation sensor 29RA detects the operation of right operation lever 26R in the forward / backward direction by the operator and outputs the detected value to controller 30. Operation sensor 29RB detects the operation of right operation lever 26R in the left-right direction by the operator and outputs the detected value to controller 30. Operation sensor 29DL detects the operation of left travel lever 26DL in the forward / backward direction by the operator and outputs the detected value to controller 30. Operation sensor 29DR detects the operation of right travel lever 26DR in the forward / backward direction by the operator and outputs the detected value to controller 30.

[0053] The controller 30 receives the output of the operation sensor 29 and outputs a control command to the regulator 13 as necessary to change the discharge rate of the main pump 14. The controller 30 also receives the output of the control pressure sensor 19 provided upstream of the orifice 18 and outputs a control command to the regulator 13 as necessary to change the discharge rate of the main pump 14. The orifice 18 includes a left orifice 18L and a right orifice 18R, and the control pressure sensor 19 includes a left control pressure sensor 19L and a right control pressure sensor 19R.

[0054] A left throttle 18L is disposed in the left center bypass pipe 40L between the hydraulic oil tank and the control valve 176L, which is located most downstream. Therefore, the flow of hydraulic oil discharged from the left main pump 14L is restricted by the left throttle 18L. The left throttle 18L generates a control pressure for controlling the left regulator 13L. The left control pressure sensor 19L detects this control pressure and outputs the detected value to the controller 30. The controller 30 controls the discharge rate of the left main pump 14L by adjusting the swash plate tilt angle of the left main pump 14L in accordance with this control pressure. The controller 30 decreases the discharge rate of the left main pump 14L as this control pressure increases, and increases the discharge rate of the left main pump 14L as this control pressure decreases. The discharge rate of the right main pump 14R is controlled in a similar manner.

[0055] Specifically, as shown in FIG. 3 , when the excavator 100 is in a standby state in which none of the hydraulic actuators are operated, the hydraulic oil discharged from the left main pump 14L passes through the left center bypass pipe 40L and reaches the left throttle 18L. The flow of hydraulic oil discharged from the left main pump 14L increases the control pressure generated upstream of the left throttle 18L. As a result, the controller 30 reduces the discharge rate of the left main pump 14L to the minimum allowable discharge rate, thereby suppressing pressure loss (pumping loss) when the discharged hydraulic oil passes through the left center bypass pipe 40L. On the other hand, when any hydraulic actuator is operated, the hydraulic oil discharged from the left main pump 14L flows into the hydraulic actuator to be operated via the control valve corresponding to the hydraulic actuator to be operated. The flow of hydraulic oil discharged from the left main pump 14L reduces or eliminates the amount of hydraulic oil reaching the left throttle 18L, thereby lowering the control pressure generated upstream of the left throttle 18L. As a result, the controller 30 increases the discharge rate of the left main pump 14L, circulating sufficient hydraulic oil to the hydraulic actuator to be operated and ensuring the drive of the hydraulic actuator to be operated. The controller 30 also controls the discharge rate of the right main pump 14R in a similar manner.

[0056] With the above-described configuration, the hydraulic system of Fig. 3 can suppress unnecessary energy consumption in the main pump 14 in a standby state. The unnecessary energy consumption includes pumping loss caused by the hydraulic oil discharged from the main pump 14 in the center bypass pipe 40. Furthermore, when operating a hydraulic actuator, the hydraulic system of Fig. 3 can reliably supply necessary and sufficient hydraulic oil from the main pump 14 to the hydraulic actuator to be operated.

[0057] In addition, a boom rod pressure sensor S7R and a boom bottom pressure sensor S7B are attached to the boom cylinder 7. An arm rod pressure sensor S8R and an arm bottom pressure sensor S8B are attached to the arm cylinder 8. A bucket rod pressure sensor S9R and a bucket bottom pressure sensor S9B are attached to the bucket cylinder 9. The boom rod pressure sensor S7R, boom bottom pressure sensor S7B, arm rod pressure sensor S8R, arm bottom pressure sensor S8B, bucket rod pressure sensor S9R, and bucket bottom pressure sensor S9B are collectively referred to as "cylinder pressure sensors." In addition, a left swing pressure sensor S10L and a right swing pressure sensor S10R are attached to the swing hydraulic motor 2A.

[0058] The boom rod pressure sensor S7R detects the pressure in the rod-side oil chamber of the boom cylinder 7 (hereinafter referred to as the "boom rod pressure"), and the boom bottom pressure sensor S7B detects the pressure in the bottom-side oil chamber of the boom cylinder 7 (hereinafter referred to as the "boom bottom pressure"). The arm rod pressure sensor S8R detects the pressure in the rod-side oil chamber of the arm cylinder 8 (hereinafter referred to as the "arm rod pressure"), and the arm bottom pressure sensor S8B detects the pressure in the bottom-side oil chamber of the arm cylinder 8 (hereinafter referred to as the "arm bottom pressure"). The bucket rod pressure sensor S9R detects the pressure in the rod-side oil chamber of the bucket cylinder 9 (hereinafter referred to as the "bucket rod pressure"), and the bucket bottom pressure sensor S9B detects the pressure in the bottom-side oil chamber of the bucket cylinder 9 (hereinafter referred to as the "bucket bottom pressure"). The left swing pressure sensor S10L detects the pressure of hydraulic oil in the left port of the swing hydraulic motor 2A. The right swing pressure sensor S10R detects the pressure of hydraulic oil in the right port of the swing hydraulic motor 2A. The values ​​detected by each sensor are transmitted to the controller 30 .

[0059] Next, the hydraulic circuit that supplies hydraulic oil to the swing hydraulic motor 2A will be further described with reference to Fig. 4. Fig. 4 is a diagram illustrating the hydraulic circuit of the swing hydraulic motor 2A.

[0060] The left operating lever 26L is also used to operate the swing mechanism 2. Specifically, the left operating lever 26L uses hydraulic oil discharged by the pilot pump 15 to apply a pilot pressure corresponding to operation in the left or right direction to the pilot port of the control valve 173. More specifically, when the left operating lever 26L is operated in the left swing direction (left direction), it applies a pilot pressure corresponding to the operation amount to the left pilot port of the control valve 173. Furthermore, when the left operating lever 26L is operated in the right swing direction (right direction), it applies a pilot pressure corresponding to the operation amount to the right pilot port of the control valve 173.

[0061] The operation sensor 29LB (see FIG. 3) detects the operation of the left operation lever 26L by the operator in the left and right directions, and outputs the detected value to the controller 30.

[0062] The proportional valve 31AL operates in response to a control command (current command) output by the controller 30. It adjusts the pilot pressure of the hydraulic oil introduced from the pilot pump 15 to the left pilot port of the control valve 173 via the proportional valve 31AL. The proportional valve 31AR operates in response to a control command (current command) output by the controller 30. It adjusts the pilot pressure of the hydraulic oil introduced from the pilot pump 15 to the right pilot port of the control valve 173 via the proportional valve 31AR. The proportional valve 31AL can adjust the pilot pressure so that the control valve 173 can be stopped at any valve position. Similarly, the proportional valve 31AR can adjust the pilot pressure so that the control valve 173 can be stopped at any valve position.

[0063] With this configuration, in response to a left turning operation by the operator, the controller 30 can supply the hydraulic oil discharged by the pilot pump 15 to the left pilot port of the control valve 173 via the proportional valve 31AL. Moreover, regardless of a left turning operation by the operator, the controller 30 can supply the hydraulic oil discharged by the pilot pump 15 to the left pilot port of the control valve 173 via the proportional valve 31AL. In other words, the controller 30 can rotate the swing mechanism 2 left in response to a left turning operation by the operator or regardless of a left turning operation by the operator.

[0064] Furthermore, in response to a right turning operation by the operator, the controller 30 can supply the hydraulic oil discharged by the pilot pump 15 to the right pilot port of the control valve 173 via the proportional valve 31AR. Furthermore, regardless of a right turning operation by the operator, the controller 30 can supply the hydraulic oil discharged by the pilot pump 15 to the right pilot port of the control valve 173 via the proportional valve 31AR. In other words, the controller 30 can rotate the swing mechanism 2 to the right in response to a right turning operation by the operator or regardless of a right turning operation by the operator.

[0065] The hydraulic circuit of the swing hydraulic motor 2A has a hydraulic oil passage 201 connected from the control valve 173 to one port of the swing hydraulic motor 2A, and a hydraulic oil passage 202 connected from the control valve 173 to the other port of the swing hydraulic motor 2A. The hydraulic circuit of the swing hydraulic motor 2A also has a make-up line 203 that supplies back pressure.

[0066] A relief valve 211 and a check valve 221 are provided between the hydraulic oil passage 201 and the makeup line 203. A relief valve 212 and a check valve 222 are provided between the hydraulic oil passage 202 and the makeup line 203.

[0067] The relief valve 211 is a valve that opens when the pressure in the hydraulic oil passage 201 rises above a set pressure. As a result, when the pressure in the hydraulic oil passage 201 becomes higher than the set pressure, the relief valve 211 opens and relieves the hydraulic oil in the hydraulic oil passage 201 to the makeup line 203.

[0068] The relief valve 212 is a valve that opens when the pressure in the hydraulic oil passage 202 rises above a set pressure. As a result, when the pressure in the hydraulic oil passage 202 becomes higher than the set pressure, the relief valve 212 opens and relieves the hydraulic oil in the hydraulic oil passage 202 to the makeup line 203.

[0069] The check valve 221 is a valve that opens when the pressure in the hydraulic oil passage 201 becomes lower than the pressure in the makeup line 203. As a result, when the pressure in the hydraulic oil passage 201 becomes low, the check valve 221 opens and hydraulic oil is supplied from the makeup line 203 to the hydraulic oil passage 201.

[0070] The check valve 222 is a valve that opens when the pressure in the hydraulic oil passage 202 becomes lower than the pressure in the makeup line 203. As a result, when the pressure in the hydraulic oil passage 202 becomes low, the check valve 222 opens and hydraulic oil is supplied from the makeup line 203 to the hydraulic oil passage 202.

[0071] The makeup line 203 is connected to a hydraulic oil passage 204 (204L, R) that is closer to the tank 250 than the throttle 18. The hydraulic oil passage 204 has a hydraulic oil passage 204L and a hydraulic oil passage 204R. The hydraulic oil passage 204R is provided with a back pressure check valve 231 for generating back pressure (a predetermined pressure) in the makeup line 203. The hydraulic oil passage 204R is also provided with an oil cooler 240 that cools the hydraulic oil. The hydraulic oil passage 204L is provided in parallel with the hydraulic oil passage 204R. The hydraulic oil passage 204L is provided with a check valve 232 for protecting the oil cooler 240.

[0072] The hydraulic circuit of the arm cylinder 8 also has a hydraulic oil passage 301 that connects from the control valve 176 to a port on the rod side of the arm cylinder 8, and a hydraulic oil passage 302 that connects from the control valve 176 to a port on the bottom side of the arm cylinder 8. A relief valve 311 and a check valve 321 are provided between the hydraulic oil passage 301 on the rod side of the arm cylinder 8 and the hydraulic oil passage 204. A relief valve 312 and a check valve 322 are provided between the hydraulic oil passage 302 on the bottom side of the arm cylinder 8 and the hydraulic oil passage 204.

[0073] The relief valve 311 is a valve that opens when the pressure in the hydraulic oil passage 301 on the rod side of the arm cylinder 8 rises above a set pressure. As a result, when the pressure in the hydraulic oil passage 301 on the rod side of the arm cylinder 8 becomes higher than the set pressure (overload), the relief valve 311 opens and relieves the hydraulic oil in the hydraulic oil passage 301 on the rod side of the arm cylinder 8 to the hydraulic oil passage 204.

[0074] The relief valve 312 is a valve that opens when the pressure in the hydraulic oil passage 302 on the bottom side of the arm cylinder 8 rises above a set pressure. As a result, when the pressure in the hydraulic oil passage 302 on the bottom side of the arm cylinder 8 becomes higher than the set pressure (overload), the relief valve 312 opens and relieves the hydraulic oil in the hydraulic oil passage 302 on the bottom side of the arm cylinder 8 to the hydraulic oil passage 204.

[0075] Check valve 321 is a valve that opens when the pressure in hydraulic oil passage 301 on the rod side of arm cylinder 8 becomes lower than the pressure in hydraulic oil passage 204. As a result, when the pressure in hydraulic oil passage 301 on the rod side of arm cylinder 8 becomes low, check valve 321 opens and hydraulic oil is supplied from hydraulic oil passage 204 to hydraulic oil passage 301 on the rod side of arm cylinder 8.

[0076] Check valve 322 is a valve that opens when the pressure in hydraulic oil passage 302 on the bottom side of arm cylinder 8 becomes lower than the pressure in hydraulic oil passage 204. As a result, when the pressure in hydraulic oil passage 302 on the bottom side of arm cylinder 8 becomes low, check valve 321 opens and hydraulic oil is supplied from hydraulic oil passage 204 to hydraulic oil passage 302 on the bottom side of arm cylinder 8.

[0077] For example, when the hydraulic oil passage 302 on the bottom side of the arm cylinder 8 becomes high pressure (overload) and the relief valve 312 opens, the hydraulic oil in the hydraulic oil passage 302 on the bottom side of the arm cylinder 8 is relieved to the hydraulic oil passage 204 via the relief valve 312. Furthermore, when the check valve 321 opens, the hydraulic oil is supplied from the hydraulic oil passage 204 to the hydraulic oil passage 301 on the rod side of the arm cylinder 8. This allows the hydraulic oil in the hydraulic oil passage 302 on the bottom side of the arm cylinder 8 to be supplied to the hydraulic oil passage 301 on the rod side of the arm cylinder 8, preventing cavitation from occurring in the hydraulic oil passage 301 on the rod side of the arm cylinder 8.

[0078] Similarly, when hydraulic oil passage 301 on the rod side of arm cylinder 8 becomes high pressure (overload) and relief valve 311 opens, hydraulic oil in hydraulic oil passage 301 on the rod side of arm cylinder 8 is relieved to hydraulic oil passage 204 via relief valve 311. Also, check valve 322 opens, so that hydraulic oil is supplied from hydraulic oil passage 204 to hydraulic oil passage 302 on the bottom side of arm cylinder 8. This allows hydraulic oil in hydraulic oil passage 301 on the rod side of arm cylinder 8 to be supplied to hydraulic oil passage 302 on the bottom side of arm cylinder 8, preventing cavitation from occurring in hydraulic oil passage 302 on the bottom side of arm cylinder 8.

[0079] Although not shown, a relief valve and a check valve may be similarly provided on the bottom side and rod side of the boom cylinder 7 and on the bottom side and rod side of the bucket cylinder 9.

[0080] Here, an example will be described in which the upper swing body 3 rotates in one direction, hydraulic oil is supplied from the hydraulic oil passage 201 to the swing hydraulic motor 2A, and hydraulic oil is discharged to the hydraulic oil passage 202.

[0081] The operator operates the left operating lever 26L to perform a deceleration operation. As a result, the controller 30 controls the proportional valves 31 (31AL, 31AR) to control the spool stroke of the control valve 173. Here, the opening area of ​​the control valve 173 in the flow path from the center bypass pipe 40 to the hydraulic oil path 201 is reduced, and the opening area of ​​the control valve 173 in the flow path from the hydraulic oil path 202 to the hydraulic oil path 204 is reduced.

[0082] Here, the swing hydraulic motor 2A rotates due to the inertial force of the swinging upper swing body 3. As a result, the pressure in the hydraulic oil passage 201 decreases and the pressure in the hydraulic oil passage 202 increases. When the pressure in the hydraulic oil passage 202 reaches the set pressure of the relief valve 212, the relief valve 212 opens.

[0083] Furthermore, a drop in pressure in the hydraulic oil passage 201 may cause bubbles to form in the hydraulic oil in the hydraulic oil passage 201. After that, when the bubbles disappear, cavitation may occur.

[0084] 4, a back pressure check valve 231 is provided in the hydraulic oil passage 204 to generate back pressure in the makeup line 203. As a result, when the pressure in the hydraulic oil passage 201 drops below the pressure (back pressure) in the makeup line 203, the check valve 221 opens. This prevents cavitation from occurring in the hydraulic oil passage 201.

[0085] The same applies to the case where the upper swing body 3 rotates in the opposite direction to the first direction, hydraulic oil is supplied from the hydraulic oil passage 202 to the swing hydraulic motor 2A, and hydraulic oil is discharged to the hydraulic oil passage 201.

[0086] However, providing the back pressure check valve 231 in the hydraulic oil passage 204 increases costs. In addition, the back pressure check valve 231 causes pressure loss, which can worsen the fuel efficiency and heat balance of the excavator 100.

[0087] Furthermore, for example, when the hydraulic oil passage 302 on the bottom side of the arm cylinder 8 becomes high pressure (overload), the check valve 321 opens, and hydraulic oil is supplied from the hydraulic oil passage 204 to the hydraulic oil passage 301 on the rod side of the arm cylinder 8. At this time, the pressure in the hydraulic oil passage 204 drops, and the back pressure check valve 231 may close. When the back pressure check valve 231 closes, the pressure in the hydraulic oil passage 204 becomes low, and air bubbles are generated in the hydraulic oil passage 204. Thereafter, the pressure in the hydraulic oil passage 204 returns to normal and the air bubbles disappear, causing cavitation and generating surge pressure.

[0088] Next, the control of the shovel 100 according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a flowchart illustrating cavity suppression control by the controller 30.

[0089] In step S101, the controller 30 determines whether the swing lever (left operating lever 26L) has been tilted in the deceleration direction (toward the neutral position of the left operating lever 26L) while the upper swing body 3 is swinging. Specifically, the controller 30 detects the operation of the left operating lever 26L by the operator in the left or right direction using the operation sensor 29LB (see FIG. 3). If the swing lever has not been tilted in the deceleration direction (S101: No), the processing of the controller 30 returns to step S101. If the swing lever has been tilted in the deceleration direction (S101: Yes), the processing of the controller 30 proceeds to step S102.

[0090] In step S102, the controller 30 measures the current rotation speed of the upper rotating body 3. Specifically, the controller 30 measures the rotation speed of the upper rotating body 3 using the rotation angular velocity sensor S5. The controller 30 may also measure (estimate) the rotation speed of the upper rotating body 3 based on the pressure difference between the hydraulic oil passages 201 and 202 detected by the left rotation pressure sensor S10L and the right rotation pressure sensor S10R.

[0091] In step S103, the controller 30 calculates a limit value for the amount of decrease in the lever operation amount for the current turning speed based on a rate limit (see FIG. 7, which will be described later). The controller 30 stores in advance a rate limit that stores limit values ​​for turning speeds. The controller 30 calculates a limit value for the current turning speed measured in step S102 based on the rate limit.

[0092] In step S104, the controller 30 compares the amount of deceleration operation with the limit value and selects the smaller value. That is, the amount of deceleration operation of the left operating lever 26L detected in step S101 is compared with the limit value calculated in step S103. Then, the controller 30 selects the smaller value.

[0093] In other words, the controller 30 determines whether or not cavitation will occur in the hydraulic oil passage 201 based on the deceleration operation amount of the left operating lever 26L and the current rotation speed of the upper rotating body 3. Specifically, if the deceleration operation amount of the left operating lever 26L detected in step S101 is greater than the limit value of the decrease in the lever operation amount relative to the current rotation speed, the controller 30 determines that there is a risk of cavitation occurring in the hydraulic oil passage 201. If it is determined that there is a risk of cavitation occurring, the controller 30 selects the limit value. On the other hand, if it is determined that there is no risk of cavitation occurring, the controller 30 selects the deceleration operation amount (actual operation amount).

[0094] In step S105, the controller 30 uses the selected value to control the proportional valve 31. By controlling the proportional valve 31, the controller 30 controls the pilot pressure of the control valve 173 and the spool of the control valve 173.

[0095] 6 is a graph illustrating the actual lever operation amount and the lever operation amount control by the controller 30. In FIG. 6, the horizontal axis represents time, and the vertical axis represents the lever operation amount. This shows the actual lever operation amount when the operator operates the left operating lever 26L. The dashed line shows the lever operation amount when the controller 30 controls the proportional valve 31. Figure 7 is a graph showing an example of the swing speed and rate limit.

[0096] 6, the operator operates the left operating lever 26L in a direction to decelerate the rotation speed from the rotating state of the upper rotating body 3 (see the solid line). That is, the operator operates the left operating lever 26L with a constant lever operation amount until time T1, and then reduces the operation amount of the left operating lever 26L from time T1 until the left operating lever 26L is in the neutral position (zero operation amount) at time T2.

[0097] Here, the controller 30 limits the amount of reduction in the swing speed according to the current swing speed, with reference to the rate limit shown in FIG. 7. In this example, the rate limit increases from RL1 to RL2 as the swing speed decreases. That is, the higher the swing speed, the smaller the rate limit is set to limit the reduction in the swing operation amount. The lower the swing speed, the larger the rate limit is set to ease the restriction on the reduction in the swing operation amount. As a result, the controller 30 controls the proportional valve 31 and the control valve 173 as if the left operating lever 26L had been operated, as shown by the dashed line in FIG. 6. As a result, the controller 30 controls the proportional valve 31 as if the left operating lever 26L had been operated by a constant lever operation amount until time T1, controls the proportional valve 31 as if the operation amount of the left operating lever 26L had been reduced from time T1, and at time T3, which is later than time T2, controls the proportional valve 31 as if the left operating lever 26L had been operated to the neutral position (zero operation amount). Furthermore, from time T1 to time T3 when the amount of operation of the left operating lever 26L is reduced, the turning speed is high and the amount of operation of the lever is reduced gradually in the initial period (for example, immediately after time T1) when the reduction starts. On the other hand, in the final period (for example, immediately before time T3), the turning speed is low and the amount of operation of the lever is reduced more suddenly than in the initial period.

[0098] According to this, when the upper rotating body 3 decelerates, the controller 30 controls the proportional valve 31 to prevent the pressure in the hydraulic oil passage 201 from decreasing and air bubbles from being generated in the hydraulic oil passage 201. In other words, the controller 30 controls the spool stroke of the control valve 173 to prevent the pressure in the hydraulic oil passage 201 from decreasing and air bubbles from being generated in the hydraulic oil passage 201. This makes it possible to prevent cavitation from occurring when the upper rotating body 3 decelerates.

[0099] 5, even if the back pressure check valve 231 in the makeup line 203 is omitted, it is possible to prevent cavitation from occurring in the hydraulic oil passage 201. This makes it possible to prevent pressure loss due to the back pressure check valve 231, thereby improving fuel efficiency and heat balance. Therefore, a hydraulic circuit in FIG. 4 that does not include the back pressure check valve 231 may be employed.

[0100] Furthermore, according to the control shown in FIG. 5, even if the back pressure check valve 231 in the makeup line 203 is omitted, it is possible to prevent the occurrence of cavitation in the hydraulic oil passage 204 during overload. [Explanation of symbols]

[0101] 100 Shovel 1 Undercarriage 2. Swivel mechanism 2A hydraulic swing motor 3 Upper rotating body 4. Boom 5 Arm 6 buckets 7 Boom cylinder 8 Arm Cylinder 9 Bucket cylinder 14 Main pump 15 Pilot pump 17 Control valve unit 171~176 Control valve 18 aperture 26 Operating device 26L Left operating lever 29LB Operation Sensor 30 Controllers 31 Proportional valve (electromagnetic proportional valve) 201,202 Hydraulic oil path 203 Makeup Line 204 Hydraulic oil path 211,212 Relief valve 221,222 Check valve 231 Back pressure check valve 232 Check valve 240 Oil cooler 250 Tank 311,312 Relief valve 321,322 Check valve S5 Turning angular velocity sensor (turning speed sensor)

Claims

1. a lower running body; an upper rotating body that can rotate relative to the lower traveling body; a hydraulic swing motor for swinging the upper swing body; a pump that discharges hydraulic oil; a control valve that switches the flow of hydraulic oil to supply the hydraulic oil discharged by the pump to the swing hydraulic motor and to discharge the hydraulic oil discharged by the swing hydraulic motor to a hydraulic oil tank; a determination unit that determines whether cavitation occurs in an oil passage for hydraulic oil; a control unit that controls the control valve, the determination unit determines whether or not cavitation will occur based on a deceleration operation amount for decelerating the rotation of the operation device and a rotation speed of the upper rotating body, When the determination unit determines that cavitation occurs, the control unit regulates a decrease in the spool stroke of the control valve in response to the deceleration operation amount. Shovel.

2. a make-up line that supplies hydraulic oil discharged from the swing hydraulic motor to the suction side of the swing hydraulic motor does not have a back pressure check valve that generates back pressure; The shovel according to claim 1.

3. The operation device further includes an operation by an operator, The determination unit detects a deceleration operation of the operation device to decelerate the rotation of the upper rotating body. The shovel according to claim 1 or 2.

4. The determination unit detects the rotation speed of the upper rotating body. The shovel according to claim 3.

5. The determination unit The swing speed is detected based on any one of an inertial measurement unit that measures the attitude of the upper swing body, a swing speed sensor of the swing hydraulic motor, and a differential pressure of the swing hydraulic motor. The shovel according to claim 4.

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