Excavator

Abstract

To provide a shovel that suppresses an increase in negative control pressure.SOLUTION: A shovel has a lower traveling body, an upper revolving body that can rotate relative to the lower traveling body, a pump that discharges hydraulic oil, a hydraulic actuator, a control valve that controls the hydraulic oil flowing to the hydraulic actuator, a negative control restriction with variable opening, and a control unit. The control unit changes the opening of the negative control restriction and increases a standby flow rate of the pump.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] There is known an excavator that includes a pump for supplying hydraulic oil, a control valve, and a hydraulic actuator. Patent Document 1 discloses an excavator that, when performing lifting work using an attachment, sets the standby flow rate of the hydraulic pump to be larger than when performing work other than lifting work. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-165268 Summary of the Invention [Problem to be solved by the invention]

[0004] However, as the load on the hydraulic actuator increases and the load pressure of the hydraulic actuator rises, the spool stroke of the control valve before the hydraulic actuator starts to move increases. In response to this, increasing the standby flow rate of the pump changes the pressure characteristics of the control valve, reducing the spool stroke of the control valve before the hydraulic actuator starts to move. However, increasing the standby flow rate raises the issue of an increase in negative control pressure.

[0005] Therefore, an object of the present invention is to provide a shovel that suppresses an increase in negative control pressure. [Means for solving the problem]

[0006] A shovel according to an embodiment of the present invention includes a lower traveling body, an upper rotating body that can rotate relative to the lower traveling body, a pump that discharges hydraulic oil, Multiple A hydraulic actuator; Multiple the hydraulic actuator Each of Controls the hydraulic oil flow to Multiple A control valve; a hydraulic oil tank; and a hydraulic oil line passing through the plurality of control valves in series, the hydraulic oil line including a center bypass line through which hydraulic oil flows from the pump to the hydraulic oil tank; and a center bypass line provided in the center bypass line between the hydraulic oil tank and the most downstream control valve of the plurality of control valves, The apparatus includes a negative control diaphragm capable of changing an aperture, and a control unit, A load pressure of the hydraulic actuator is detected, and if the load pressure is greater than a threshold value, The opening of the negative control aperture Make it bigger , and increasing the standby flow rate of the pump. [Effects of the Invention]

[0007] According to the present invention, a shovel can be provided that suppresses an increase in negative control pressure. [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] 4 is a graph showing an example of the opening area and pressure characteristics of a control valve. [Figure 5] 10 is an example of a graph showing the relationship between negative control pressure and pump flow rate. [Figure 6] 10 is a flowchart illustrating the control of the controller. [Figure 7] 4 is an example of a graph showing the relationship between negative control pressure and pump flow rate in control of the shovel according to the first embodiment. [Figure 8] 10 is an example of a graph showing the relationship between negative control pressure and pump flow rate in control of a shovel according to a second embodiment. 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, 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 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.

[0016] 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.

[0017] 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).

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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 (negative control pressure) of a control pressure sensor 19 provided upstream of the throttle (negative control throttle) 18 and outputs a control command to the regulator 13 as necessary to change the discharge rate of the main pump 14. The throttle 18 includes a left throttle 18L and a right throttle 18R, and the control pressure sensor 19 includes a left control pressure sensor 19L and a right control pressure sensor 19R.

[0053] Here, the throttles 18 (18L, 18R) are configured so that their opening degrees can be changed. The throttle 18 has a throttle 181, a throttle 182, an on-off valve 183, and a relief valve 184. The throttles 181, 182, and relief valve 184 are arranged in parallel. The on-off valve 183 is a solenoid valve that can be opened and closed by the controller 30, and is arranged in series with the throttle 182. By closing the on-off valve 183, it is possible to switch between a state in which the throttle 181 generates negative control pressure and a state in which the on-off valve 183 generates negative control pressure using the throttles 181 and 182 arranged in parallel. The relief valve 184 opens when the pressure of the hydraulic oil reaches or exceeds a predetermined relief pressure.

[0054] Although the above description has been given of an example in which the throttle 18 has a plurality of throttles 181, 182 arranged in parallel, and the opening degree of the throttle 18 is changed by opening and closing the on-off valve 183, the present invention is not limited to this. The throttle 18 may also have a configuration including a throttle whose opening degree is adjustable, and a relief valve arranged in parallel with the throttle.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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 .

[0060] Next, the characteristics of the control valves (171 to 176) and the throttle 18 will be described with reference to FIGS.

[0061] FIG. 4 is a graph showing an example of the opening area and pressure characteristics of the control valves (171-176). In FIG. 4, the horizontal axis represents the spool stroke of the control valves (171-176). The vertical axis represents the opening area and pressure (circuit pressure) of the control valves (171-176). The solid line represents the opening area of ​​the control valves (171-176). The dashed line represents the pressure characteristics of the circuit pressure when the standby flow rate of the main pump 14 is Q1 [L / min]. The dashed line represents the pressure characteristics of the circuit pressure when the standby flow rate of the main pump 14 is Q2 [L / min]. Here, the flow rate Q2 is greater than the flow rate Q1 (Q2>Q1). An example of the load pressure of the hydraulic actuator is shown by the two-dot chain line. Here, the standby flow rate refers to the flow rate of hydraulic oil discharged from the main pump 14 flowing into the hydraulic circuit before the hydraulic actuator starts operating (standby state).

[0062] As shown in Figure 4, as the spool stroke of the control valve increases, the circuit pressure in the pressure characteristics (see dashed line and dashed line) increases. Then, the increased pressure (circuit pressure) due to the pressure characteristics exceeds the load pressure, causing the hydraulic actuator to start moving. Therefore, as the load on the hydraulic actuator increases and the load pressure of the hydraulic actuator rises, the spool stroke of the control valve before the hydraulic actuator starts moving increases.

[0063] In response to this, by increasing the standby flow rate of the main pump 14, the pressure characteristics of the control valves (171-176) can be changed, and the spool stroke amount of the control valves until the hydraulic actuators start to operate can be reduced. In the example shown in Fig. 4, at the load pressure indicated by the two-dot chain line, by increasing the standby flow rate indicated by the dashed line from flow rate Q1 (see dashed line) to flow rate Q2 (see dashed line), the pressure characteristics can be changed, and the spool stroke amount of the control valves until the hydraulic actuators start to operate can be reduced from S1 to S2.

[0064] FIG. 5 is an example of a graph showing the relationship between negative control pressure and pump flow rate. The horizontal axis represents negative control pressure, and the vertical axis represents the flow rate of hydraulic oil. The solid line represents the pump flow rate of the main pump 14 relative to the negative control pressure when the standby flow rate is flow rate Q1 and flow rate Q2. The dashed line represents the flow rate (negative control flow rate) through the throttle 18 relative to the negative control pressure. The difference between the pump flow rate of the main pump 14 and the negative control flow rate represents the flow rate (PC flow rate) supplied to the hydraulic actuator. In the example of FIG. 5, the throttle 18 has a throttle 181 and a relief valve 184.

[0065] As shown by the solid line in Figure 5, the controller 30 controls the pump flow rate of the main pump 14 based on the negative control pressure detected by the control pressure sensor 19. The pump flow rate and the negative control flow rate are balanced at the intersection of the pump flow rate characteristics of the main pump 14 shown by the solid line and the negative control flow rate characteristics shown by the dashed line. When the standby flow rate is at flow rate Q1 and the negative control pressure is at pressure P1, the pump flow rate and the negative control flow rate are balanced.

[0066] Here, by increasing the standby flow rate from flow rate Q1 to flow rate Q2, the negative control pressure at which the pump flow rate and the negative control flow rate are balanced increases from pressure P1 to pressure P2.

[0067] As the negative control pressure increases from pressure P1 to pressure P2, the pressure in the hydraulic circuit increases. This increases the pressure on the various valves in the hydraulic circuit, which may reduce the durability of the valves. In addition, the standby flow rate increases, and the negative control pressure increases, which increases the noise generated by the hydraulic oil passing through the restriction 18.

[0068] Furthermore, the negative control flow rate, shown by the dashed line, increases as the negative control pressure increases, and above a certain negative control pressure (pressure P5), the relief valve 184 operates, causing a change in the characteristics (slope) of the negative control flow rate relative to the negative control pressure. When the negative control pressure rises from pressure P1, which is smaller than pressure P5, to pressure P2, which is larger than pressure P5, the relief valve 184 operates, causing a change in characteristics, which creates the problem of making it difficult to control the hydraulic pressure.

[0069] Next, the control by the controller 30 of the shovel 100 according to this embodiment will be described with reference to Fig. 6. Fig. 6 is a flowchart illustrating the control by the controller 30.

[0070] In step S101, the controller 30 measures the load pressure (holding pressure) of the hydraulic actuator after the operation of the operation levers (left operation lever 26L, right operation lever 26R) and before the hydraulic actuator starts moving (standby state). For example, when raising the boom 4, the bottom pressure of the boom cylinder 7 is measured as the load pressure. When lowering the boom 4, the rod pressure of the boom cylinder 7 is measured as the load pressure. For example, when closing the arm 5, the bottom pressure of the arm cylinder 8 is measured as the load pressure, and when opening the arm 5, the rod pressure of the arm cylinder 8 is measured as the load pressure. The same applies to the opening and closing of the bucket 6 and the rotation of the upper rotating body 3.

[0071] In step S102, the controller 30 determines whether to switch control. Specifically, the controller 30 determines whether the load pressure measured in step S101 is equal to or greater than a predetermined threshold. If the load pressure is equal to or greater than the predetermined threshold (S102: Yes), the process by the controller 30 proceeds to step S103. If the load pressure is not equal to or greater than the predetermined threshold (S102: No), the process by the controller 30 proceeds to step S106.

[0072] In step S103, after the operation lever is operated and before the hydraulic actuator starts to move (standby state), the controller 30 increases the opening area of ​​the throttle 18 and increases the standby flow rate (for example, flow rate Q2). For example, the on-off valve 183 is opened, and the opening area of ​​the throttle 18 is set to the sum of the opening areas of the throttles 181 and 182 arranged in parallel.

[0073] In step S104, the controller 30 measures the load pressure of the hydraulic actuator. In step S105, the controller 30 determines whether to switch control. Specifically, the controller 30 determines whether the load pressure measured in step S104 is equal to or greater than a predetermined threshold. If the load pressure is equal to or greater than the predetermined threshold (S105: Yes), the process of the controller 30 returns to step S104. If the load pressure is not equal to or greater than the predetermined threshold (S104: No), the process of the controller 30 proceeds to step S106.

[0074] In step S106, after the operation lever is operated and before the hydraulic actuator starts to move (standby state), the controller 30 reduces the opening area of ​​the orifice 18 and reduces the standby flow rate (for example, flow rate Q1). For example, the on-off valve 183 is closed and the opening area of ​​the orifice 18 is set to only the opening area of ​​the orifice 181.

[0075] Thereafter, the control of the controller 30 returns to step S101, and the control of the diaphragm 18 is repeated.

[0076] FIG. 7 is an example of a graph showing the relationship between negative control pressure and pump flow rate in the control of the excavator 100 according to the first embodiment. The horizontal axis represents the negative control pressure, and the vertical axis represents the flow rate of hydraulic oil. The solid line represents the pump flow rate of the main pump 14 relative to the negative control pressure when the standby flow rate is flow rate Q1 and flow rate Q2. The dashed line represents the flow rate (negative control flow rate) through the throttle 18 relative to the negative control pressure when the negative control throttle is small. The dashed line represents the flow rate (negative control flow rate) through the throttle 18 relative to the negative control pressure when the negative control throttle is large. The difference between the pump flow rate of the main pump 14 and the negative control flow rate represents the flow rate (PC flow rate) supplied to the hydraulic actuator. In the example of FIG. 7, when the negative control throttle is small, the on-off valve 183 is closed, and the opening area of ​​the throttle 18 is set to the opening area of ​​the throttle 181 only. When the negative control throttle is large, the on-off valve 183 is opened, and the opening area of ​​the throttle 18 is set to the sum of the opening areas of the throttles 181 and 182 arranged in parallel.

[0077] As shown in FIG. 5, by increasing the standby flow rate from flow rate Q1 to flow rate Q2, the negative control pressure increases from pressure P1 to pressure P2.

[0078] In contrast to this, as shown in Fig. 7, in the control of the shovel 100 according to the first embodiment, the standby flow rate is increased from flow rate Q1 to flow rate Q2, and the opening area of ​​the throttle 18 is increased from small negative control throttle to large negative control throttle. This allows the negative control pressure at the standby flow rate Q2 to be set to pressure P3, and the increase in the negative control pressure can be suppressed.

[0079] As a result, even if the load pressure of the hydraulic actuator increases, it is possible to suppress an increase in the spool stroke amount of the control valve until the hydraulic actuator starts to move.

[0080] In addition, an increase in negative control pressure can be suppressed. This suppresses the pressure applied to the various valves in the hydraulic circuit, preventing a decrease in the durability of the valves. In addition, by suppressing the negative control pressure, noise generated by the hydraulic oil passing through the orifice 18 can be suppressed. In addition, the operation of the relief valve 184 can be suppressed.

[0081] In the description of steps S103 and S106, the controller 30 controls the opening area of ​​the throttle 18 and the standby flow rate of the main pump 14, but the present invention is not limited to this.

[0082] FIG. 8 is an example of a graph showing the relationship between negative control pressure and pump flow rate in the control of the excavator 100 according to the second embodiment. The horizontal axis represents the negative control pressure, and the vertical axis represents the flow rate of hydraulic oil. The solid line represents the pump flow rate of the main pump 14 relative to the negative control pressure when the standby flow rate is flow rate Q1 and flow rate Q2. The dashed line represents the flow rate (negative control flow rate) through the throttle 18 relative to the negative control pressure when the negative control throttle is small. The dashed line represents the flow rate (negative control flow rate) through the throttle 18 relative to the negative control pressure when the negative control throttle is large. The difference between the pump flow rate of the main pump 14 and the negative control flow rate represents the flow rate (PC flow rate) supplied to the hydraulic actuator. In the example of FIG. 8, when the negative control throttle is small, the on-off valve 183 is closed, and the opening area of ​​the throttle 18 is set to the opening area of ​​the throttle 181 only. When the negative control throttle is large, the on-off valve 183 is opened, and the opening area of ​​the throttle 18 is set to the sum of the opening areas of the throttles 181 and 182 arranged in parallel.

[0083] In controlling the excavator 100 according to the second embodiment, the standby flow rate is increased from flow rate Q1 to flow rate Q2, and the opening area of ​​the throttle 18 is increased from small negative control throttle to large negative control throttle. In addition, the characteristics of the pump flow rate of the main pump 14 relative to the negative control pressure are changed. Here, the characteristics are changed so as to suppress the increase in the pump flow rate relative to a drop in the negative control pressure. In other words, the slope at which the pump flow rate decreases relative to an increase in the negative control pressure is made smaller (more gradual). This allows the negative control pressure at the standby flow rate Q2 to be pressure P4, thereby suppressing the increase in the negative control pressure.

[0084] As a result, even if the load pressure of the hydraulic actuator increases, it is possible to suppress an increase in the spool stroke amount of the control valve until the hydraulic actuator starts to move.

[0085] In addition, an increase in negative control pressure can be suppressed. This suppresses the pressure applied to the various valves in the hydraulic circuit, preventing a decrease in the durability of the valves. In addition, by suppressing the negative control pressure, noise generated by the hydraulic oil passing through the orifice 18 can be suppressed. In addition, the operation of the relief valve 184 can be suppressed. [Explanation of symbols]

[0086] 100 Shovel 1 Undercarriage 2A Swing Hydraulic Motor (Hydraulic Actuator) 2. Swivel mechanism 3 Upper rotating body 4. Boom 5 Arm 6 buckets 7 Boom cylinder (hydraulic actuator) 8 Arm cylinder (hydraulic actuator) 9 Bucket cylinder (hydraulic actuator) 15 Pilot pump 17 Control valve unit 171~176 Control valve 18 aperture (negative control aperture) 181,182 aperture 183 On-off valve 184 Relief valve 26 Operating device 30 Controllers 31 Proportional valve (electromagnetic proportional valve)

Claims

1. a lower running body; an upper rotating body that can rotate relative to the lower traveling body; a pump that discharges hydraulic oil; A plurality of hydraulic actuators; a plurality of control valves that control hydraulic oil flowing to each of the plurality of hydraulic actuators; A hydraulic oil tank; a hydraulic oil line passing through a plurality of the control valves in series, the hydraulic oil being a center bypass line through which hydraulic oil flows from the pump to the hydraulic oil tank; a negative control throttle having a variable opening, the negative control throttle being provided in the center bypass pipe between the hydraulic oil tank and the most downstream control valve among the plurality of control valves; a control unit; The control unit Detecting a load pressure of the hydraulic actuator, and if the load pressure is greater than a threshold, increasing the opening of the negative control throttle and increasing the standby flow rate of the pump. Shovel.

2. The negative control throttle is arranged in series with a plurality of the control valves. The shovel according to claim 1.

3. The control unit detects the load pressure of the hydraulic actuator, and when the load pressure is greater than a threshold value, increases the opening of the negative control throttle, increases the standby flow rate of the pump, and changes the pump characteristic, which is the relationship between the negative control pressure formed by the negative control throttle and the pump flow rate of the pump, to a characteristic that reduces the slope of the decrease in the pump flow rate with respect to an increase in the negative control pressure; The shovel according to claim 1 or 2.

4. The negative control diaphragm is a variable negative control diaphragm whose opening area is variable. The shovel according to any one of claims 1 to 3.

5. The negative control throttle has a first throttle, a second throttle arranged in parallel to the first throttle, and an on-off valve arranged in series with the second throttle, and the opening area is changed by opening and closing the on-off valve. The shovel according to any one of claims 1 to 3.

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