Working machinery
The hydraulic drive system in hydraulic excavators addresses the issue of pressure differences by using multiple control valves to manage load increases, ensuring efficient operation and preventing hydraulic oil leakage.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- SUMITOMO CONSTRUCTION MACHINERY
- Filing Date
- 2024-12-23
- Publication Date
- 2026-07-03
Smart Images
Figure 2026111379000001_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to a work machine.
Background Art
[0002] Conventionally, a work machine (hydraulic excavator) equipped with a hydraulic pump driven by a drive source (engine) is known (see Patent Document 1). This hydraulic excavator is configured to intentionally increase the load on the engine in order to perform a specific process. The specific process is, for example, a process of raising the temperature of the exhaust gas in order to burn particulate matter collected in the filter of the exhaust gas purification device by the heat of the exhaust gas. Further, this hydraulic excavator is configured to increase the load on the engine by increasing the discharge pressure of the hydraulic pump when the operation lever is not being operated.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] However, the above-described hydraulic excavator is configured to increase the discharge pressure of the hydraulic pump by shutting off the flow of hydraulic oil in the oil passage by a control valve (a control valve that controls the supply and discharge of hydraulic oil related to the hydraulic cylinder) provided in the oil passage connecting the hydraulic cylinder and the hydraulic pump. Therefore, in this hydraulic excavator, during the period in which the process of intentionally increasing the load on the engine is being performed, the pressure of the hydraulic oil on the upstream side of the control valve inevitably increases and becomes higher than the pressure of the hydraulic oil on the downstream side, so there is a risk that leakage of the hydraulic oil from the upstream side to the downstream side of the control valve cannot be suppressed.
[0005] Therefore, it is desirable to provide a work machine that can intentionally increase the load on the drive source while suppressing the increase in the front-to-back pressure difference, which is the difference between the hydraulic fluid pressure on the upstream side and the hydraulic fluid pressure on the downstream side when the hydraulic fluid pressure on the upstream side of the control valve is greater than the hydraulic fluid pressure on the downstream side. [Means for solving the problem]
[0006] An embodiment of the present invention provides a work machine comprising: a lower traveling body; an upper rotating body rotatably mounted on the lower traveling body; a hydraulic actuator; a hydraulic pump capable of supplying hydraulic fluid to the hydraulic actuator; a first control valve provided in a first oil passage connecting the hydraulic pump and a hydraulic fluid tank; a second control valve provided in a second oil passage connecting the hydraulic pump and the hydraulic actuator; and a third control valve provided in the second oil passage between the hydraulic pump and the second control valve, wherein the third control valve is configured to shut off the second oil passage when the first oil passage is shut off by the first control valve. [Effects of the Invention]
[0007] The aforementioned work machine can intentionally increase the load on the drive source while suppressing an increase in the pressure difference across the control valve. [Brief explanation of the drawing]
[0008] [Figure 1] This is a side view of an excavator according to an embodiment of the present invention. [Figure 2] Figure 1 is a schematic diagram showing an example of the configuration of a hydraulic drive system mounted on an excavator. [Figure 3] This flowchart shows an example of the flow of forced high-load processing. [Figure 4] Figure 2 shows an example of the state of the hydraulic drive system. [Figure 5] Figure 2 shows another example of the state of the hydraulic drive system. [Figure 6] This figure shows yet another example of the state of the hydraulic drive system shown in Figure 2. [Figure 7] This figure shows yet another example of the state of the hydraulic drive system shown in Figure 2. [Figure 8] Figure 1 is a schematic diagram showing another example of a hydraulic drive system configuration mounted on the excavator. [Modes for carrying out the invention]
[0009] First, with reference to Figure 1, a working machine 100 according to an embodiment of the present disclosure will be described. Figure 1 is a side view of the working machine 100. The working machine 100 shown in Figure 1 is an excavator (shovel) and has a lower traveling body 1, a slewing mechanism 2, and an upper slewing body 3. The upper slewing body 3 is rotatably mounted on the lower traveling body 1 via the slewing mechanism 2. A boom 4 as a working element is attached to the upper slewing body 3. An arm 5 as a working element is attached to the tip of the boom 4, and a bucket 6 as a working element and end attachment is attached to the tip of the arm 5. The boom 4, arm 5, and bucket 6 constitute an excavation attachment, 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. A cabin 10 is provided on the upper slewing body 3, and a drive source 11 is mounted on it. Furthermore, the work machine 100 may be any other work machine equipped with a hydraulic actuator that can intentionally increase the load on the drive source 11, such as a wheel loader, crane, asphalt finisher, or forklift.
[0010] Figure 2 shows an example of the configuration of a hydraulic drive system mounted on the work machine 100 shown in Figure 1. In Figure 2, mechanical power transmission lines are shown as double lines, hydraulic fluid lines as solid lines, pilot lines as dashed lines, and electrical control lines as dashed lines.
[0011] The hydraulic drive system of the work machine 100 mainly includes a drive source 11, a pump regulator 13, a main pump 14, a pilot pump 15, an operating device 26, a discharge pressure sensor 28, an operating sensor 29, and a controller 30, etc.
[0012] The drive source 11 is the drive source for the work machine 100. The drive source 11 may be an electric motor driven by an external power source, battery, or fuel cell, an internal combustion engine driven by gasoline, diesel fuel, hydrogen, or biofuel, or a hybrid drive source combining an internal combustion engine and an electric motor. In the illustrated example, the drive source 11 is a diesel engine that operates to maintain a predetermined rotational speed. The output shaft of the drive source 11 is connected to the input shafts of the main pump 14 and the pilot pump 15, respectively.
[0013] Intentionally increasing the load on the drive source 11 is done when performing regeneration control of exhaust gas aftertreatment devices such as DPF (Diesel Particulate Filter), thawing and heat retention control of urea solution, freeze prevention control of blow-by gas pipes, air conditioning control (heating control), or warm-up control of the hydraulic drive system. This is because the thermal energy generated by increasing the load on the drive source 11 is used to perform the various processes described above. Furthermore, it is desirable that the load on the drive source 11 be intentionally increased without operating the hydraulic actuator mounted on the work machine 100. Therefore, in the illustrated example, the work machine 100 increases the load on the drive source 11 by blocking the oil passage through which the hydraulic fluid discharged by the main pump 14 flows, thereby increasing the discharge pressure of the main pump 14 and increasing the hydraulic load (pump torque), without operating the attachment.
[0014] The main pump 14 is an example of a hydraulic pump and is configured to supply hydraulic fluid to the control valve unit 17. In the illustrated example, the main pump 14 is a swashplate type variable displacement hydraulic pump and includes a left main pump 14L and a right main pump 14R.
[0015] The pump regulator 13 is configured to control the discharge rate of the main pump 14. In the illustrated example, the pump regulator 13 controls the discharge rate of the main pump 14 by adjusting the swash plate tilt angle of the main pump 14 in response to a command from the controller 30. The pump regulator 13 may output information regarding the swash plate tilt angle to the controller 30. Specifically, the pump regulator 13 includes a left pump regulator 13L that controls the discharge rate of the left main pump 14L, and a right pump regulator 13R that controls the discharge rate of the right main pump 14R.
[0016] The pilot pump 15 is configured to supply hydraulic oil to various hydraulic devices including the operating device 26. In the illustrated example, the pilot pump 15 is a fixed displacement hydraulic pump. However, the pilot pump 15 may be omitted. In this case, the function performed by the pilot pump 15 may be realized by the main pump 14. That is, the main pump 14 may have a function of supplying hydraulic oil to the control valve unit 17, and also a function of supplying hydraulic oil to the operating device 26 etc. after reducing the pressure of the hydraulic oil by means of a throttle or the like.
[0017] The control valve unit 17 is configured to operably accommodate a plurality of control valves. In the illustrated example, the control valve unit 17 includes a plurality of control valves 170 to 177 that control the flow of the hydraulic oil discharged by the main pump 14. The control valve unit 17 is configured to selectively supply the hydraulic oil discharged by the main pump 14 to one or a plurality of hydraulic actuators through those control valves 170 to 177. The plurality of control valves 170 to 177 control the flow rate of the hydraulic oil flowing from the main pump 14 to the hydraulic actuator, and the flow rate of the hydraulic oil flowing from the hydraulic actuator to the hydraulic oil tank T1.
[0018] The hydraulic actuator may be a hydraulic cylinder or a hydraulic motor. The hydraulic cylinder may be a single-rod hydraulic cylinder or a double-rod hydraulic cylinder. In the illustrated example, the hydraulic actuator includes a boom cylinder 7, an arm cylinder 8, a bucket cylinder 9, a traveling hydraulic motor 20, and a slewing hydraulic motor 21. The traveling hydraulic motor 20 includes a left traveling hydraulic motor 20L and a right traveling hydraulic motor 20R.
[0019] The slewing hydraulic motor 21 is a hydraulic motor that slews the upper slewing body 3. An oil passage 21P connected to the port of the slewing hydraulic motor 21 is connected to an oil passage 44 via a relief valve 22 and a check valve 23. Specifically, the oil passage 21P includes a left oil passage 21PL and a right oil passage 21PR. The relief valve 22 includes a left relief valve 22L and a right relief valve 22R. The check valve 23 includes a left check valve 23L and a right check valve 23R.
[0020] The left relief valve 22L opens when the pressure of the hydraulic oil in the left oil passage 21PL reaches a predetermined relief pressure, and discharges the hydraulic oil in the left oil passage 21PL to the oil passage 44. Further, the right relief valve 22R opens when the pressure of the hydraulic oil in the right oil passage 21PR reaches a predetermined relief pressure, and discharges the hydraulic oil in the right oil passage 21PR to the oil passage 44.
[0021] The left check valve 23L opens when the pressure of the hydraulic oil in the left oil passage 21PL becomes lower than the pressure of the hydraulic oil in the oil passage 44, and supplies hydraulic oil from the oil passage 44 to the left oil passage 21PL. The right check valve 23R opens when the pressure of the hydraulic oil in the right oil passage 21PR becomes lower than the pressure of the hydraulic oil in the oil passage 44, and supplies hydraulic oil from the oil passage 44 to the right oil passage 21PR. With this configuration, the check valve 能 supplies hydraulic oil to the suction side port during braking of the slewing hydraulic motor 21.
[0022] The operating device 26 is a device used by the operator to operate the hydraulic actuator. In the illustrated example, the operating device 26 is hydraulic and supplies hydraulic fluid discharged by the pilot pump 15 to the pilot port of the control valve corresponding to each hydraulic actuator via a pilot line. The pilot pressure, which is the pressure of the hydraulic fluid supplied to each pilot port, is a pressure corresponding to the operating direction and amount of the operating lever or operating pedal that constitutes the operating device 26, corresponding to each hydraulic actuator. However, the operating device 26 may also be electric.
[0023] Specifically, the operating device 26 includes a left operating lever, a right operating lever, a left travel operating lever, a right travel lever, a left travel operating pedal, and a right travel pedal, etc. The left operating lever functions as an arm operating lever and a slewing operating lever. The right operating lever functions as a boom operating lever and a bucket operating lever. Hereinafter, at least one of the left operating lever and the right operating lever may be referred to as the "attachment operating device," and at least one of the left travel lever, the right travel lever, the left travel pedal, and the right travel pedal may be referred to as the "travel operating device."
[0024] The discharge pressure sensor 28 is configured to detect the discharge pressure of the main pump 14 and output the detected value to the controller 30. In the illustrated example, the discharge pressure sensor 28 includes a left discharge pressure sensor 28L that detects the discharge pressure of the left main pump 14L, and a right discharge pressure sensor 28R that detects the discharge pressure of the right main pump 14R.
[0025] The operation sensor 29 is a device for detecting the operator's actions using the operating device 26. The actions include, for example, the direction of operation and the amount of operation (operating angle). In the illustrated example, the operation sensor 29 is a pressure sensor that detects the direction of operation and the amount of operation of the lever or pedal that constitutes the operating device 26 corresponding to each hydraulic actuator in the form of pressure, and outputs the detected value to the controller 30. However, the actions of the operating device 26 may also be detected using the output of a device other than a pressure sensor, such as an operating angle sensor, acceleration sensor, angular velocity sensor, resolver, voltmeter, or ammeter.
[0026] The controller 30 is an example of a processing circuit and functions as a control device for controlling the work machine 100. In the illustrated example, the controller 30 consists of a computer equipped with a CPU, a volatile memory device, and a non-volatile memory device, etc.
[0027] The solenoid valve 31 is located in the oil passage connecting the pilot pump 15 and the left pilot port of the control valve 175L in the control valve unit 17, and is configured to change the flow area of the oil passage. In the illustrated example, the solenoid valve 31 is an electromagnetic proportional control valve that operates in response to a control command output by the controller 30. With this configuration, the controller 30 can automatically move the control valve 175L regardless of whether the operator lowers the boom. Also in the illustrated example, the left pilot port of the control valve 175L is configured to be affected by the higher of the pilot pressure generated by the solenoid valve 31 and the pilot pressure generated by the boom operation lever.
[0028] The solenoid valve 32 is located in the oil passage connecting the pilot pump 15 and the left pilot port of the control valve 177 in the control valve unit 17, and is configured to change the flow area of the oil passage. In the illustrated example, the solenoid valve 32 is an electromagnetic proportional control valve that operates in response to a control command output by the controller 30. This configuration allows the controller 30 to automatically operate the control valve 177.
[0029] The center bypass oil passage 40 is a hydraulic fluid line that passes through a control valve located within the control valve unit 17, and includes the left center bypass oil passage 40L and the right center bypass oil passage 40R.
[0030] The control valve 170 is a spool valve that functions as a straight-line travel valve. In the illustrated example, the control valve 170 is configured to switch the flow of hydraulic fluid so that hydraulic fluid is properly supplied from the main pump 14 to the travel hydraulic motor 20 in order to improve the straight-line movement of the lower travel body 1. Specifically, the control valve 170 is configured to switch its valve position between a first valve position (left valve position) and a second valve position (right valve position) in response to a control command from the controller 30.
[0031] More specifically, the valve position of the control valve 170 is the first valve position when only the travel operating device is operated, or when only the attachment operating device is operated, and the valve position is the second valve position when both the travel operating device and the attachment operating device are operated simultaneously.
[0032] The first valve position is the valve position that connects the left main pump 14L to the left travel hydraulic motor 20L and the right main pump 14R to the right travel hydraulic motor 20R. In this state, the left main pump 14L can supply hydraulic fluid to the left travel hydraulic motor 20L, and the right main pump 14R can supply hydraulic fluid to the right travel hydraulic motor 20R.
[0033] The second valve position is the valve position that connects the left main pump 14L to the left travel hydraulic motor 20L and the right travel hydraulic motor 20R, respectively. In this state, the left main pump 14L can supply hydraulic fluid to the left travel hydraulic motor 20L and the right travel hydraulic motor 20R, respectively.
[0034] The control valve 171 is a spool valve that switches the flow of hydraulic fluid to supply the hydraulic fluid discharged by the main pump 14 to the travel hydraulic motor 20 and to discharge the hydraulic fluid discharged by the travel hydraulic motor 20 to the hydraulic fluid tank T1. Specifically, the control valve 171 includes control valve 171L and control valve 171R. The control valve 171L supplies the hydraulic fluid discharged by the left main pump 14L to the left travel hydraulic motor 20L and switches the flow of hydraulic fluid to discharge the hydraulic fluid discharged by the left travel hydraulic motor 20L to the hydraulic fluid tank T1. The control valve 171R supplies the hydraulic fluid discharged by the left main pump 14L or the right main pump 14R to the right travel hydraulic motor 20R and switches the flow of hydraulic fluid to discharge the hydraulic fluid discharged by the right travel hydraulic motor 20R to the hydraulic fluid tank T1.
[0035] The control valve 172 is a spool valve that switches the flow of hydraulic fluid to supply the hydraulic fluid discharged by the left main pump 14L to an optional hydraulic actuator, and to discharge the hydraulic fluid discharged by the optional hydraulic actuator to the hydraulic fluid tank T1. The optional hydraulic actuator is, for example, a grapple drive cylinder or a breaker drive cylinder.
[0036] The control valve 173 is a spool valve that supplies the hydraulic fluid discharged by the left main pump 14L to the swing hydraulic motor 21, and also switches the flow of the hydraulic fluid discharged by the swing hydraulic motor 21 to the hydraulic fluid tank T1.
[0037] The control valve 174 is a spool valve that supplies the hydraulic fluid discharged by the right main pump 14R to the bucket cylinder 9 and discharges the hydraulic fluid in the bucket cylinder 9 to the hydraulic fluid tank T1.
[0038] The control valve 175 is a spool valve that supplies the hydraulic fluid discharged by the main pump 14 to the boom cylinder 7 and switches the flow of hydraulic fluid to discharge the hydraulic fluid in the boom cylinder 7 to the hydraulic fluid tank T1. Specifically, the control valve 175 includes control valve 175L and control valve 175R.
[0039] In the illustrated example, the control valve 175L is configured to switch between a first valve position (left valve position), a second valve position (right valve position), and a third valve position (center valve position) in response to a control command from the controller 30. The valve position of the control valve 175L is set to the first valve position when the boom is lowered, to the second valve position when the boom is raised, and to the third valve position (center valve position) as the initial valve position when neither the boom is raised nor lowered. Specifically, when the boom is lowered, the control valve 175L is set to the first valve position, allowing the hydraulic fluid in the bottom oil chamber of the boom cylinder 7 to flow out into the left center bypass oil passage 40L. Therefore, the control valve 175L can allow the hydraulic fluid flowing out from the bottom oil chamber of the boom cylinder 7 when the boom is lowered to flow into (regenerate) the arm cylinder 8. However, the oil passage in the control valve 175L that allows the hydraulic fluid in the bottom oil chamber of the boom cylinder 7 to flow out into the left center bypass oil passage 40L may be omitted. Between the boom cylinder 7 and the control valve 175, there is a retaining valve (not shown) to prevent the boom 4 from moving due to its own weight when the boom is not being operated (a valve that prevents hydraulic fluid from flowing out of the boom cylinder 7). However, the retaining valve does not stop the flow of hydraulic fluid into the boom cylinder 7. Also, when the boom is raised, the control valve 175L moves to the second valve position, allowing the hydraulic fluid discharged by the left main pump 14L to flow into the bottom oil chamber of the boom cylinder 7. Similar to the case of the control valve 175L, when the boom is raised, the control valve 175R allows the hydraulic fluid discharged by the right main pump 14R to flow into the bottom oil chamber of the boom cylinder 7. Furthermore, when the boom is lowered, the control valve 175R can allow the hydraulic fluid discharged by the right main pump 14R to flow into the rod-side oil chamber of the boom cylinder 7.
[0040] The control valve 176 is a spool valve that supplies the hydraulic fluid discharged by the main pump 14 to the arm cylinder 8 and switches the flow of the hydraulic fluid in the arm cylinder 8 to discharge it to the hydraulic fluid tank T1. Specifically, the control valve 176 includes control valve 176L and control valve 176R.
[0041] Control valve 177 is a spool valve that limits the flow rate of hydraulic fluid that passes through the left parallel oil passage 42L (described later) toward control valve 176L, and is also called a "sub-spool valve" or "cut valve". "Sub-spool valve" is a designation for "main spool valves" such as control valves 170-176 which are located on the center bypass oil passage 40. In the illustrated example, control valve 177 is configured to switch between a first valve position (left valve position), a second valve position (right valve position), and a third valve position (center valve position) in response to a control command from the controller 30.
[0042] Specifically, the valve position of the control valve 177 is the first valve position, which is the initial valve position, when the opening and closing operation of the arm 5 is not performed, and when the opening and closing operation of the arm 5 is performed independently. The valve position of the control valve 177 then becomes the second valve position when processing is performed to intentionally increase the load on the drive source 11, and becomes the third valve position when a combined operation such as opening and closing the arm 5 and rotating the arm is performed.
[0043] More specifically, the control valve 177 is configured to function as a swing-priority valve in the third valve position when a combined operation including opening / closing and swinging of the arm 5 is performed. Therefore, the flow path cross-sectional area of the third fixed throttle AP3, which is provided in the oil passage at the third valve position (center valve position) connecting the upstream and downstream sides of the control valve 177, is smaller than the flow path cross-sectional area of the first fixed throttle AP1, which is provided in the oil passage at the first valve position (left valve position) connecting the upstream and downstream sides of the control valve 177. With this configuration, the third fixed throttle AP3 can, for example, prevent most of the hydraulic fluid discharged by the left main pump 14L from flowing into the arm cylinder 8, which has a lower load pressure, when the arm cylinder 8 and the swing hydraulic motor 21 are operated simultaneously and the load pressure of the arm cylinder 8 is lower than that of the swing hydraulic motor 21. This is because the third fixed throttle AP3 can increase the pressure of the hydraulic fluid upstream of the arm cylinder 8 when the hydraulic fluid flows into the arm cylinder 8 through the control valve 177. Therefore, the hydraulic drive system including the third fixed aperture AP3 can reliably operate not only the arm cylinder 8 with low load pressure but also the slewing hydraulic motor 21 with high load pressure, even when the arm cylinder 8 with low load pressure and the slewing hydraulic motor 21 with high load pressure are operated simultaneously. In the following, the function realized by such a slewing priority valve will also be called the "slewing priority function". Furthermore, the first fixed aperture AP1 and the third fixed aperture AP3 may be realized by a single variable aperture. For example, the oil passage at the first valve position (left valve position) may be provided with a single variable aperture that functions as both the first fixed aperture AP1 and the third fixed aperture AP3. In this case, the third valve position may be omitted.
[0044] In the illustrated example, control valves 170-176 are pilot-operated spool valves, and each pilot port is hydraulically connected to the operating device 26, which is a hydraulic operating device. However, if the operating device 26 is electrically operated, the pilot ports of the control valves 170-176 do not need to be hydraulically connected to the operating device 26. Specifically, if the operating lever of the operating device 26 is an electrically operated lever, the lever operation amount and lever operation direction are input to the controller 30 as electrical signals. In this case, typically, a solenoid valve is placed between the pilot pump 15 and the pilot port of each control valve. The solenoid valve is configured to operate in response to the electrical signal from the controller 30. With this configuration, when manual operation is performed using the operating lever, the controller 30 can move (stroke) each control valve by controlling the solenoid valve with the electrical signal corresponding to the lever operation amount to increase or decrease the pilot pressure. Note that each control valve may be composed of a solenoid spool valve. In this case, the solenoid spool valve operates in response to the electrical signal from the controller 30 corresponding to the lever operation amount of the electrically operated lever.
[0045] The return oil passage 41 is a hydraulic fluid line located within the control valve unit 17 and includes a central return oil passage 41C, a left return oil passage 41L, and a right return oil passage 41R. In the illustrated example, the central return oil passage 41C is a return oil passage connecting the relief valve 55 to the hydraulic fluid tank T1, the left return oil passage 41L is a return oil passage connecting each of the control valves 171L, 172, 173, 175L, and 176L to the hydraulic fluid tank T1, and the right return oil passage 41R is a return oil passage connecting each of the control valves 170, 171R, 174, 175R, and 176R to the hydraulic fluid tank T1.
[0046] The relief valve 55 is a device for maintaining the pressure of the hydraulic fluid in the hydraulic drive system below a predetermined relief pressure. In the illustrated example, the upstream port of the relief valve 55 is connected to the left center bypass oil passage 40L and the right center bypass oil passage 40R via check valves, respectively, and the downstream port is connected to the hydraulic fluid tank T1 via the central return oil passage 41C. The relief valve 55 is kept closed when the pressure of the hydraulic fluid upstream (the pressure of the hydraulic fluid in the hydraulic drive system) is below a predetermined relief pressure, but is configured to open when the pressure of the hydraulic fluid upstream is equal to or greater than the predetermined relief pressure. In the illustrated example, the relief valve 55 is a fixed relief valve with a fixed relief pressure, but it may also be a variable solenoid relief valve with an adjustable relief pressure.
[0047] The parallel oil passage 42 is a hydraulic fluid line running parallel to the center bypass oil passage 40. In the illustrated example, the parallel oil passage 42 includes a left parallel oil passage 42L running parallel to the left center bypass oil passage 40L, and a right parallel oil passage 42R running parallel to the right center bypass oil passage 40R. The left parallel oil passage 42L can supply hydraulic fluid to a control valve further downstream when the flow of hydraulic fluid through the left center bypass oil passage 40L is restricted or blocked by control valves 171L, 172, 173, or 175L. The right parallel oil passage 42R can supply hydraulic fluid to a control valve further downstream when the flow of hydraulic fluid through the right center bypass oil passage 40R is restricted or blocked by control valves 171R, 174, or 175R.
[0048] The throttle 60 is a fixed throttle located upstream of the control valve 176R in the right parallel oil passage 42R, and downstream of the branching point where the oil passage connecting the right parallel oil passage 42R and the control valve 175R branches off from the right parallel oil passage 42R. In the illustrated example, the throttle 60 has the function of preventing most of the hydraulic fluid discharged by the right main pump 14R from flowing into the arm cylinder 8, which has a low load pressure, when the arm cylinder 8, which has a low load pressure, and the hydraulic actuator (at least one of the boom cylinder 7, bucket cylinder 9, and right travel hydraulic motor 20R), which has a high load pressure, are being operated simultaneously. This is because the throttle 60 can increase the pressure of the hydraulic fluid upstream of the arm cylinder 8 when the hydraulic fluid flows into the arm cylinder 8 through the control valve 176R. Therefore, the hydraulic drive system including the throttle 60 can reliably operate not only the arm cylinder 8, which has a low load pressure, but also the boom cylinder 7, which has a high load pressure, even when the arm cylinder 8, which has a low load pressure, and the boom cylinder 7, which has a high load pressure, are being operated simultaneously. The same applies when the arm cylinder 8, which has a low load pressure, and the bucket cylinder 9 or the right-hand travel hydraulic motor 20R, which has a high load pressure, are operated simultaneously.
[0049] Here, we will explain the negative control employed in the hydraulic drive system shown in Figure 2. In the center bypass oil passage 40, a throttle 18 is positioned between each of the control valves 176 at the furthest downstream and the hydraulic oil tank T1. The flow of hydraulic oil discharged by the main pump 14 is restricted by the throttle 18. The throttle 18 then generates a control pressure (negative control pressure) to control the pump regulator 13. Specifically, the throttle 18 is a fixed throttle with a fixed opening area, and includes a left throttle 18L and a right throttle 18R. However, the throttle 18 may also be a variable throttle with a variable opening area. The larger the opening area of the throttle 18, the more stable it tends to be against sudden changes in control pressure. Also, the smaller the opening area of the throttle 18, the more responsive it tends to be to control pressure. The flow of hydraulic oil discharged by the left main pump 14L is restricted by the left throttle 18L. The left throttle 18L then generates a control pressure to control the left pump regulator 13L. Similarly, the flow of hydraulic fluid discharged by the right main pump 14R is restricted by the right throttle 18R. The right throttle 18R then generates a control pressure to control the right pump regulator 13R.
[0050] The control pressure sensor 19 is a sensor that detects the control pressure (negative control pressure) generated upstream of the throttle 18, and includes a left control pressure sensor 19L and a right control pressure sensor 19R. In the illustrated example, the control pressure sensor 19 is configured to output the detected value to the controller 30. The controller 30 outputs a command to the pump regulator 13 according to the control pressure. The pump regulator 13 controls the discharge amount of the main pump 14 by adjusting the swash plate tilt angle of the main pump 14 according to the command. Specifically, the pump regulator 13 decreases the discharge amount of the main pump 14 as the control pressure increases, and increases the discharge amount of the main pump 14 as the control pressure decreases.
[0051] Through negative control, the hydraulic drive system in Figure 2 can suppress wasted energy consumption in the main pump 14 when none of the hydraulic actuators are being operated. This wasted energy consumption includes pumping losses caused by the hydraulic fluid discharged by the main pump 14 in the center bypass oil passage 40. On the other hand, when a hydraulic actuator is being operated, the hydraulic drive system in Figure 2 can reliably supply the necessary and sufficient hydraulic fluid from the main pump 14 to the hydraulic actuator being operated.
[0052] The center bypass oil passage 40 and the return oil passage 41 are connected to the confluence of oil passage 43 downstream of the throttle 18. In the illustrated example, oil passage 43 branches into two downstream of the confluence and connects to oil passages 45 and 46 located outside the control valve unit 17. That is, the hydraulic fluid flowing through the center bypass oil passage 40 and the return oil passage 41 merge in oil passage 43 and then passes through oil passage 45 or oil passage 46 to reach the hydraulic fluid tank T1. Oil passage 43 is also connected to the swing hydraulic motor 21 via oil passage 44, which is a hydraulic fluid line for compensating for any shortage of hydraulic fluid on the suction side of the swing hydraulic motor 21.
[0053] The oil passage 45 is a hydraulic fluid line connecting the oil passage 43 and the hydraulic fluid tank T1. The oil passage 45 is equipped with a check valve 50, an oil cooler 51, and a filter 53.
[0054] The check valve 50 is a valve that opens when the pressure difference between the primary and secondary sides exceeds a predetermined opening pressure difference. In the illustrated example, the check valve 50 is a spring-type check valve that opens when the upstream pressure is higher than the downstream pressure and the pressure difference exceeds the opening pressure difference, allowing the hydraulic fluid in the control valve unit 17 to flow out toward the oil cooler 51. With this configuration, the check valve 50 can maintain the hydraulic fluid pressure in the oil passages 43 and 44 at a level higher than the opening pressure, ensuring that the shortage of hydraulic fluid on the suction side of the swing hydraulic motor 21 is reliably compensated for. In this case, the opening pressure becomes the lower limit of the back pressure relative to the throttle 18. The back pressure relative to the throttle 18 increases as the flow rate of hydraulic fluid passing through the check valve 50 increases. The check valve 50 may be integrated into the control valve unit 17 or it may be omitted. If the check valve 50 is omitted, the pressure loss in the oil passage 45, check valve 50, oil cooler 51, and filter 53 each becomes the back pressure relative to the throttle 18. Furthermore, the back pressure against the throttle 18 increases as the flow rate of the hydraulic fluid passing through the oil passage 45 increases.
[0055] The oil cooler 51 is a device for cooling the hydraulic fluid circulating in the hydraulic drive system. In the illustrated example, the oil cooler 51 is included in a heat exchanger unit that is cooled by a cooling fan driven by the drive source 11. The heat exchanger unit includes a radiator, an intercooler, and the oil cooler 51, etc. In the illustrated example, the oil passage 45 includes an oil passage section 45a connecting the check valve 50 and the oil cooler 51, and an oil passage section 45b connecting the oil cooler 51 and the hydraulic fluid tank T1. A filter 53 is located in the oil passage section 45b.
[0056] The oil passage 46 is a bypass oil passage that bypasses the oil cooler 51. In the illustrated example, one end of the oil passage 46 is connected to the oil passage 43 and the other end is connected to the hydraulic fluid tank T1. One end may be connected to the oil passage 45 between the check valve 50 and the oil cooler 51. A check valve 52 is also located in the oil passage 46.
[0057] The check valve 52, like the check valve 50, is a valve that opens when the pressure difference between the primary and secondary sides exceeds a predetermined opening pressure difference. In the illustrated example, the check valve 52 is a spring-type check valve that opens when the upstream pressure is higher than the downstream pressure and the pressure difference exceeds the opening pressure difference, allowing the hydraulic fluid in the control valve unit 17 to flow out towards the hydraulic fluid tank T1. The opening pressure difference of the check valve 52 is greater than that of the check valve 50. Therefore, the hydraulic fluid in the control valve unit 17 first flows through the check valve 50, and then flows through the check valve 52 if the pressure exceeds the opening pressure due to resistance while flowing through the oil cooler 51. The check valve 52 may be integrated into the control valve unit 17.
[0058] Next, referring to Figure 3, we will explain the process for intentionally increasing the load on the drive source 11 (hereinafter referred to as "forced high-load processing"). Figure 3 is a flowchart showing an example of the flow of forced high-load processing. In the illustrated example, the controller 30 is configured to repeatedly execute this forced high-load processing at a predetermined control cycle while the drive source 11 is in operation. In the following, the function realized by forced high-load processing will also be called the "forced high-load function".
[0059] First, the controller 30 determines whether predetermined conditions for increasing the load on the drive source 11 have been met (step ST1). In the illustrated example, the controller 30 determines that predetermined conditions have been met when a predetermined button is pressed. The predetermined button is a graphic image as a software button displayed on a touch panel monitor, which is a display device provided inside the cabin 10. The predetermined button may be a hardware button attached to the display device provided inside the cabin 10, or it may be a hardware button provided at another location inside the cabin 10.
[0060] Alternatively, the controller 30 may determine that a predetermined condition has been met when a predetermined voice command is received as voice input through an audio input device such as a microphone installed in the cabin 10.
[0061] Alternatively, the controller 30 may determine that a predetermined condition has been met when the work machine 100 is inoperable due to the gate lock lever or the like, and the boom operation lever is operated in the downward direction. Note that the inoperable state means a state in which the hydraulic actuator cannot be operated even if the operating device 26 is operated, for example, a state in which the oil passage between the pilot pump 15 and the pilot port of each control valve is blocked.
[0062] Alternatively, the controller 30 may determine that a predetermined condition has been met when the operating device 26 is not being operated and a predetermined time has arrived, when the ambient temperature is below a predetermined lower limit temperature, when the ambient temperature is above a predetermined upper limit temperature, or when the operating time of the drive source 11 exceeds a predetermined time.
[0063] If the controller determines that the predetermined conditions are not met (NO in step ST1), it terminates the forced high-load processing. This is because it determines that there is no need to intentionally increase the load on the drive source 11.
[0064] On the other hand, if it is determined that a predetermined condition is met (YES in step ST1), the controller 30 increases the discharge pressure of the main pump 14 (step ST2). In the illustrated example, the controller 30 increases the discharge pressure of the left main pump 14L by blocking the left center bypass oil passage 40L. Specifically, the controller 30 outputs a control command to the solenoid valve 31, increasing the pilot pressure acting on the left pilot port of the control valve 175L. When the pilot pressure acting on the left pilot port increases, the control valve 175L switches its valve position to the first valve position (left valve position), and the flow of hydraulic fluid from the left main pump 14L through the left center bypass oil passage 40L to the hydraulic fluid tank T1 is blocked. At this time, hydraulic fluid does not flow out of the bottom oil chamber of the boom cylinder 7. In other words, the boom 4 does not lower. This is because the outflow of hydraulic fluid from the bottom oil chamber of the boom cylinder 7 is prevented by a retaining valve (not shown).
[0065] Figure 4 shows the state of the hydraulic drive system when the controller 30 switches the valve position of the control valve 175L from the third valve position (center valve position) to the first valve position (left valve position). In Figure 4, for the sake of clarity, the increase in the hydraulic fluid pressure in the left center bypass oil passage 40L, which is blocked by the control valve 175L, is shown by a thick solid line.
[0066] Furthermore, when the left center bypass oil passage 40L is shut off by the control valve 175L, the pressure of the hydraulic fluid in the left parallel oil passage 42L, located upstream of the control valve 176L, also increases, as shown in Figure 5. Figure 5 shows the state of the hydraulic drive system when the pressure of the hydraulic fluid in the left parallel oil passage 42L increases. In Figure 5, for the sake of clarity, the increase in the pressure of the hydraulic fluid in the left parallel oil passage 42L, in addition to the increase in the hydraulic fluid in the left center bypass oil passage 40L, is shown by a thick solid line.
[0067] Furthermore, when the pressure of the hydraulic fluid in the left center bypass oil passage 40L and the hydraulic fluid in the left parallel oil passage 42L increases, that is, when the discharge pressure of the left main pump 14L increases, the pressure of the hydraulic fluid in the oil passage 47 connecting the left main pump 14L and the relief valve 55 also increases, as shown in Figure 6. Figure 6 shows the state of the hydraulic drive system when the pressure of the hydraulic fluid in oil passage 47 increases. In Figure 6, for the sake of clarity, the increase in the pressure of the hydraulic fluid in oil passage 47, in addition to the hydraulic fluid in the left center bypass oil passage 40L and the hydraulic fluid in the left parallel oil passage 42L, is shown by a thick solid line.
[0068] Then, when the pressure of the hydraulic fluid in the left center bypass oil passage 40L, the hydraulic fluid in the left parallel oil passage 42L, and the hydraulic fluid in oil passage 47 exceeds a predetermined relief pressure, the hydraulic fluid is discharged through the relief valve 55 into the central return oil passage 41C. The hydraulic fluid discharged from the relief valve 55 then flows through the central return oil passage 41C, oil passage 43, and oil passage 45 to the hydraulic fluid tank T1.
[0069] In this way, the controller 30 can maintain a high hydraulic load (pump torque) of the main pump 14 for a desired period of time, and consequently, maintain a high load on the drive source 11.
[0070] Referring again to Figure 3, we will continue the explanation of the forced high-load processing flow. In the illustrated example, after increasing the discharge pressure of the main pump 14, the controller 30 switches the valve position of the cut-off valve (step ST3). In the illustrated example, the controller 30 outputs a control command to the solenoid valve 32, increasing the pilot pressure acting on the pilot port of the control valve 177. When the pilot pressure acting on the pilot port increases, the control valve 177 shown in Figure 2 switches its valve position to the second valve position (right valve position), and the left parallel oil passage 42L can be shut off. At this time, the oil passage portion PS1 connecting the control valve 177 and the control valve 176L in the left parallel oil passage 42L is connected to the oil passage PS2 connecting the control valve 177 and the left return oil passage 41L. As a result, some of the hydraulic fluid that was in the oil passage portion PS1 is discharged to the left return oil passage 41L through the oil passage PS2, and the pressure of the hydraulic fluid that was in the oil passage portion PS1 is reduced. The oil passage PS2 is also called the bleed oil passage.
[0071] Figure 7 shows the state of the hydraulic drive system when the controller 30 switches the valve position of the control valve 177 to the second valve position (right valve position). In Figure 7, for the sake of clarity, the oil passage section PS1 is represented by a thick dotted line, and the thick arrow indicates that a portion of the hydraulic fluid that was in the oil passage section PS1 has been discharged to the left return oil passage 41L via the oil passage PS2.
[0072] When some of the hydraulic fluid in the oil passage section PS1 is discharged into the left return oil passage 41L, and the pressure of the hydraulic fluid in the oil passage section PS1 decreases, the difference between the hydraulic fluid pressure on the upstream side and the hydraulic fluid pressure on the downstream side of the control valve 176L (the front-to-back pressure difference) decreases. The front-to-back pressure difference is the difference between the hydraulic fluid pressure on the upstream side and the hydraulic fluid pressure on the downstream side when the hydraulic fluid pressure on the upstream side of the control valve 176L is greater than the hydraulic fluid pressure on the downstream side. This decrease in the front-to-back pressure difference has the effect of suppressing the leakage of hydraulic fluid from the upstream side to the downstream side of the control valve 176L through the approximately annular gap between the approximately cylindrical spool section of the control valve 176L and the valve block section which has an approximately cylindrical space for housing the spool section. Furthermore, suppressing hydraulic fluid leakage has the effect of preventing leaked hydraulic fluid from flowing into the rod-side oil chamber and the bottom-side oil chamber of the arm cylinder 8, thereby preventing the pressure in the rod-side oil chamber and the pressure in the bottom-side oil chamber from becoming approximately equal. In addition, preventing the pressure in the rod-side oil chamber and the bottom-side oil chamber of the arm cylinder 8 from becoming approximately equal has the effect of preventing unintended extension of the arm cylinder 8, i.e., unintended arm closing operation. This is because when the pressure in the rod-side oil chamber and the bottom-side oil chamber of the arm cylinder 8 become approximately equal, the piston inside the arm cylinder 8, which is a single-rod hydraulic cylinder, moves in the direction that expands the bottom-side oil chamber due to the difference in pressure-receiving area. In the illustrated example, the pressure-receiving area of the piston facing the bottom-side oil chamber is approximately twice the pressure-receiving area of the piston facing the rod-side oil chamber. Therefore, if the pressure in the rod-side oil chamber and the pressure in the bottom-side oil chamber of the arm cylinder 8 are approximately the same, the thrust that moves the piston toward the cylinder extension side (arm closing side) will be approximately twice the thrust that moves the piston toward the cylinder contraction side (arm opening side). A retaining valve (not shown) (a valve that prevents the outflow of hydraulic fluid from the arm cylinder 8) may be provided between the arm cylinder 8 and the control valve 176 to prevent the arm 5 from moving due to its own weight or other reasons when the arm is not being operated.
[0073] Thus, the hydraulic drive system described above has the effect of preventing the arm cylinder 8 from unintentionally extending due to the hydraulic fluid pressure upstream of the control valve 176L becoming greater than the hydraulic fluid pressure downstream of the control valve 176L during forced high-load processing, for example, when the operating device 26 is not being operated. This is because the controller 30 can avoid maintaining a high pressure in the hydraulic fluid in the oil passage PS1 by returning a portion of the hydraulic fluid in the oil passage PS1 to the hydraulic fluid tank T1, thereby preventing the pressure difference across the control valve 176L from remaining large throughout the forced high-load processing.
[0074] Furthermore, in the above configuration, even if hydraulic fluid leaks from the upstream to the downstream side of the control valve 177 through the approximately annular gap between the approximately cylindrical spool portion and the valve block portion of the control valve 177, the leaked hydraulic fluid is discharged into the left return oil passage 41L through the oil passage PS2. Therefore, the hydraulic fluid leaking through the approximately annular gap around the control valve 177 does not increase the pressure difference across the control valve 176L.
[0075] In the example described above, the controller 30 avoids maintaining a large pressure difference across control valve 176L by switching control valve 177 to the second valve position (right valve position) after switching control valve 175L to the first valve position (left valve position). However, the controller 30 may prevent the pressure difference across control valve 176L from becoming large by switching control valve 177 to the second valve position (right valve position) at the same time as switching control valve 175L to the first valve position (left valve position). Alternatively, the controller 30 may prevent the pressure difference across control valve 176L from becoming large by switching control valve 177 to the second valve position (right valve position) before switching control valve 175L to the first valve position (left valve position).
[0076] Furthermore, the control valve 177 is configured to suppress an increase in the pressure difference across the control valve 177 by connecting the downstream port of the control valve 177 with the return oil passage 41. However, the control valve 177 may be configured not to connect the downstream port of the control valve 177 with the return oil passage 41. For example, if a control system is adopted in which the control valve 177 is switched to the second valve position (right valve position) at the same time as the control valve 175L is switched to the first valve position (left valve position), an increase in the pressure difference across the control valve 177 is prevented. The same applies if a control system is adopted in which the control valve 177 is switched to the second valve position (right valve position) before the control valve 175L is switched to the first valve position (left valve position). Furthermore, even when employing a control system that switches the control valve 177 to the second valve position (right valve position) after switching the control valve 175L to the first valve position (left valve position), the control valve 177 may be configured so that its downstream port does not communicate with the return oil passage 41. This is because the hydraulic drive system can prevent a large pressure difference across the control valve 176L from being maintained for a long period of time, even if the left parallel oil passage 42L is simply blocked by the control valve 177.
[0077] Here, referring to Figure 8, we will describe another example of the configuration of the hydraulic drive system mounted on the work machine 100 in Figure 1. Figure 8 is a diagram showing another example of the configuration of the hydraulic drive system mounted on the work machine 100 in Figure 1, and corresponds to Figure 2. The hydraulic drive system shown in Figure 8 differs from the hydraulic drive system shown in Figure 2 in that it has a control valve 177A instead of the control valve 177, and that the control valve 177A is not connected to the return oil passage 41, but it is the same as the hydraulic drive system shown in Figure 2 in all other respects. Therefore, the explanation of the common parts will be omitted below, and the differences will be explained in detail.
[0078] The control valve 177A is configured to limit the flow rate of hydraulic fluid that flows through the left parallel oil passage 42L towards the control valve 176L. In the illustrated example, the control valve 177A is configured to switch between a first valve position (left valve position), a second valve position (right valve position), and a third valve position (center valve position) in response to a control command from the controller 30.
[0079] More specifically, the valve position of the control valve 177A is the first valve position, which is the initial valve position, when the arm 5 is not being opened or closed, and when the arm 5 is being opened or closed independently. The valve position of the control valve 177A then becomes the second valve position when processing is being performed to intentionally increase the load on the drive source 11, and becomes the third valve position when a combined operation of the arm 5, such as opening / closing and slewing, is being performed. In the illustrated example, the control valve 177A is configured to function as a slewing-priority valve when a combined operation including opening / closing and slewing of the arm 5 is being performed, and it is in the third valve position.
[0080] When predetermined conditions are met to intentionally increase the load on the drive source 11 and the valve is moved to the second valve position, the control valve 177A shuts off the left parallel oil passage 42L. At this time, the oil passage portion PS1 of the left parallel oil passage 42L that connects the control valve 177 and the control valve 176L is not connected to the return oil passage 41, so the pressure of the hydraulic fluid in the oil passage portion PS1 is maintained at the pressure that was present when the control valve 177A was switched to the second valve position.
[0081] Therefore, the controller 30 can prevent the hydraulic fluid pressure in the oil passage PS1 from rising to the relief pressure by switching the control valve 177A to the second valve position before switching the control valve 175L to the first valve position (left valve position). In other words, the controller 30 can avoid maintaining a large pressure difference across the control valve 176L while the forced high-load processing is being performed.
[0082] Thus, the hydraulic drive system shown in Figure 8, like the hydraulic drive system shown in Figure 2, has the effect of suppressing the unintended extension of the arm cylinder 8 due to a large pressure difference across the control valve 176L during forced high-load processing.
[0083] In the hydraulic drive system shown in Figure 2, the control valve 177 is configured such that a swing priority function is realized by switching from the first valve position to the third valve position, and a forced high-load function is realized by switching from the first valve position to the second valve position. However, the swing priority function and the forced high-load function may be realized by separate control valves that are independent of each other. That is, the third valve position of the control valve 177 may be omitted. In this case, the control valve 177 may be located upstream of branching point BP1 (see Figure 2), upstream of branching point BP2 (see Figure 2), or upstream of branching point BP3 (see Figure 2) in the left parallel oil passage 42L. Alternatively, the control valve 177 may be located upstream of the control valve 170 in the left parallel oil passage 42L. Furthermore, the swing priority function may be realized by another control valve in which the second valve position is omitted. The same applies to the control valve 177A in the hydraulic drive system shown in Figure 8.
[0084] In other words, the control valve 177 may be implemented by adding a valve position to an existing control valve (a control valve already incorporated into the hydraulic drive system), such as a swing priority valve. The existing control valve may also be a control valve other than a swing priority valve, such as a regeneration valve or a regenerative valve.
[0085] Furthermore, in the above-described embodiment, the hydraulic drive system increases the load on the drive source 11 by blocking the oil passage through which the hydraulic fluid discharged by the left main pump 14L flows, thereby increasing the discharge pressure of the left main pump 14L and increasing the hydraulic load (pump torque). However, the hydraulic drive system may also increase the load on the drive source 11 by blocking the oil passage through which the hydraulic fluid discharged by the right main pump 14R flows, thereby increasing the discharge pressure of the right main pump 14R and increasing the hydraulic load (pump torque). In this case, the control valve 177 is located in the right parallel oil passage 42R.
[0086] As described above, the work machine 100 according to the embodiment of the present invention, as shown in Figures 1 and 2, comprises a lower traveling body 1, an upper rotating body 3 rotatably mounted on the lower traveling body 1, a hydraulic actuator (arm cylinder 8), a hydraulic pump (main pump 14) capable of supplying hydraulic fluid to the hydraulic actuator (arm cylinder 8), a first control valve (control valve 175L) provided in a first oil passage (center bypass oil passage 40) connecting the hydraulic pump (main pump 14) and the hydraulic fluid tank T1, a second control valve (control valve 176L) provided in a second oil passage (parallel oil passage 42) connecting the hydraulic pump (left main pump 14L) and the hydraulic actuator (arm cylinder 8), and a third control valve (control valve 177) provided between the hydraulic pump (main pump 14) and the second control valve (control valve 176L) in the second oil passage (parallel oil passage 42). Furthermore, the third control valve (control valve 177) is configured to shut off the second oil passage (parallel oil passage 42) when the load on the drive source 11 is intentionally increased. For example, the third control valve (control valve 177) is configured to shut off the second oil passage (parallel oil passage 42) when the first oil passage (center bypass oil passage 40) is shut off by the first control valve (control valve 175L) and the second oil passage (parallel oil passage 42) is shut off by the second control valve (control valve 176L).
[0087] This configuration allows the first control valve (control valve 175L) to be shut off in the first oil passage (center bypass oil passage 40), and the third control valve (control valve 177), which is located upstream of the second control valve (control valve 176L) in the second oil passage (parallel oil passage 42). Therefore, this configuration can increase the hydraulic load (pump torque) of the hydraulic pump (main pump 14). Furthermore, this configuration allows the load on the drive source 11 to be intentionally increased while suppressing the increase in the pressure difference across the second control valve (control valve 176L) in the second oil passage (parallel oil passage 42), that is, forced high-load processing can be performed. In addition, because this configuration can suppress the increase in the pressure difference across the second control valve (control valve 176L), leakage of hydraulic fluid from the upstream side to the downstream side of the second control valve (control valve 176L) in the second oil passage (parallel oil passage 42) can be suppressed. Therefore, this configuration can prevent hydraulic fluid leaking downstream of the second control valve (control valve 176L) from flowing into the hydraulic actuator (arm cylinder 8), and consequently, can suppress unintended movements of the hydraulic actuator (arm cylinder 8) by the operator.
[0088] Furthermore, the third control valve (control valve 177) may be configured to be switchable between a first state and a second state, as shown in Figure 2. In this case, in the first state, the flow of hydraulic fluid from the hydraulic pump (main pump 14) to the second control valve (control valve 176L) may be permitted. In the second state, the flow of hydraulic fluid from the hydraulic pump (main pump 14) to the second control valve (control valve 176L) is blocked, and the flow from the oil passage section PS1 between the third control valve (control valve 177) and the second control valve (control valve 176L) in the second oil passage (parallel oil passage 42) to the hydraulic fluid tank T1 may be permitted. In addition, the third control valve (control valve 177) may be configured to adjust the flow rate of hydraulic fluid flowing from the hydraulic pump (main pump 14) to the second control valve (control valve 176L) when in the first state. For example, the third control valve (control valve 177) may be configured to be switchable between a first valve position (left valve position) and a second valve position (right valve position). In this case, in the first valve position (left valve position), the flow of hydraulic fluid from the hydraulic pump (main pump 14) to the second control valve (control valve 176L) may be permitted. In the second valve position (right valve position), the flow of hydraulic fluid from the hydraulic pump (main pump 14) to the second control valve (control valve 176L) is blocked, and the flow from the oil passage portion PS1 between the third control valve (control valve 177) and the second control valve (control valve 176L) in the second oil passage (parallel oil passage 42) to the hydraulic fluid tank T1 may be permitted. In the illustrated example, the control valve 177 has three valve positions, and the first valve position and the second valve position are configured to be the left valve position and the right valve position, respectively. However, the first valve position and the second valve position may be any of the three valve positions. For example, the control valve 177 may be configured such that the first valve position and the second valve position are the left valve position and the center valve position, respectively, or they may be configured to be the center valve position and the left valve position.
[0089] This configuration has the effect of enabling forced high-load processing while further suppressing the increase in the pressure difference across the second control valve (control valve 176L) in the second oil passage (parallel oil passage 42). This is because the oil passage portion PS1 located upstream of the second control valve (control valve 176L) in the second oil passage (parallel oil passage 42) can be connected to the return oil passage 41. Specifically, this configuration can lower the pressure of the hydraulic fluid in the oil passage portion PS1. Furthermore, this configuration allows the leaked hydraulic fluid to be discharged into the return oil passage 41 even if hydraulic fluid leaks from the upstream to the downstream side of the third control valve (control valve 177) in the second oil passage (parallel oil passage 42). In other words, this configuration can suppress the increase in the pressure of the hydraulic fluid in the oil passage portion PS1 due to hydraulic fluid leaking from the upstream to the downstream side of the third control valve (control valve 177).
[0090] Furthermore, the hydraulic actuator (arm cylinder 8) may be a single-rod type hydraulic cylinder, as shown in Figures 1 and 2.
[0091] This configuration has the effect of suppressing unintended movement of a single-rod hydraulic cylinder. This is because it prevents the hydraulic fluid leaking downstream of the second control valve (control valve 176L) from flowing into the bottom-side oil chamber and the rod-side oil chamber of the single-rod hydraulic cylinder, which would otherwise equalize the hydraulic fluid pressure in both chambers. Specifically, this configuration prevents the single-rod hydraulic cylinder from extending due to the difference in pressure-receiving area on both sides of the piston inside the cylinder when the hydraulic fluid pressure in the bottom-side oil chamber and the rod-side oil chamber becomes equal. In the illustrated example, the hydraulic drive system is configured to suppress unintended movement of the arm cylinder 8, which is an example of a single-rod hydraulic cylinder, but it may also be configured to suppress unintended movement of the boom cylinder 7 or the bucket cylinder 9. Furthermore, the hydraulic drive system may be configured to suppress unintended movement of a double-rod hydraulic cylinder, or to suppress unintended movement of the hydraulic motor.
[0092] Furthermore, the third control valve (control valve 177) may be a swivel-priority valve, as shown in Figure 2. That is, the third control valve (control valve 177) may be located downstream of the branching point BP2.
[0093] This configuration, by adding a valve position to the existing control valve, the swing-priority valve, has the effect of suppressing unintended movements of the hydraulic actuator (arm cylinder 8) during forced high-load processing. In other words, this configuration has the effect of making it easier to introduce a function to suppress unintended movements of the hydraulic actuator (arm cylinder 8) during forced high-load processing into an existing hydraulic drive system.
[0094] Furthermore, as shown in Figure 2, the hydraulic pump (main pump 14) may include a first main pump (left main pump 14L) and a second main pump (right main pump 14R). In this case, the first oil passage (center bypass oil passage 40) may include a first center bypass oil passage (left center bypass oil passage 40L) and a second center bypass oil passage (right center bypass oil passage 40R). Also, the second oil passage (parallel oil passage 42) may include a first parallel oil passage (left parallel oil passage 42L) parallel to the first center bypass oil passage (left center bypass oil passage 40L), and a second parallel oil passage (right parallel oil passage 42R) parallel to the second center bypass oil passage (right center bypass oil passage 40R). Furthermore, the first control valve (control valve 175L) may be located in the first center bypass oil passage (left center bypass oil passage 40L), and the second control valve (control valve 176L) and the third control valve (control valve 177) may each be located in the first parallel oil passage (left parallel oil passage 42L).
[0095] This configuration allows the control valve 175L to be shut off in the left center bypass oil passage 40L, and the control valve 177 located upstream of the control valve 176L in the left parallel oil passage 42L. Therefore, this configuration can increase the hydraulic load (pump torque) of the left main pump 14L. Furthermore, this configuration allows for the intentional increase of the load on the drive source 11 while suppressing the increase in the pressure difference across the control valve 176L in the left parallel oil passage 42L, i.e., forced high-load processing can be performed. In addition, because this configuration can suppress the increase in the pressure difference across the control valve 176L, leakage of hydraulic fluid from the upstream to the downstream side of the control valve 176L in the left parallel oil passage 42L can be suppressed. Therefore, this configuration can prevent hydraulic fluid that has leaked downstream of the control valve 176L from flowing into the arm cylinder 8, and consequently, can suppress unintended movement of the arm cylinder 8 by the operator.
[0096] Furthermore, the hydraulic actuator may include a boom cylinder 7 and an arm cylinder 8, as shown in Figures 1 and 2. In this case, the first control valve (control valve 175L) may be a spool valve that controls the flow rate of hydraulic fluid flowing into the boom cylinder 7. The second control valve (control valve 176L) may also be a spool valve that controls the flow rate of hydraulic fluid flowing into the arm cylinder 8.
[0097] This configuration allows the left center bypass oil passage 40L to be shut off by a control valve 175L that controls the flow of hydraulic fluid driving the boom cylinder 7. Furthermore, this configuration allows the left parallel oil passage 42L to be shut off by a control valve 177 located upstream of the control valve 176L that controls the flow of hydraulic fluid driving the arm cylinder 8, thereby suppressing an increase in the pressure difference across the control valve 176L in the left parallel oil passage 42L. As a result, this configuration can suppress the leakage of hydraulic fluid from the upstream to the downstream side of the control valve 176L in the left parallel oil passage 42L. Moreover, this configuration can prevent hydraulic fluid that has leaked downstream of the control valve 176L from flowing into the arm cylinder 8, and consequently, can suppress unintended movements of the arm cylinder 8 by the operator.
[0098] Preferred embodiments of the present invention have been described above. However, the present invention is not limited to the embodiments described above. Various modifications or substitutions can be applied to the embodiments described above without departing from the scope of the present invention. Furthermore, each of the features described with reference to the embodiments described above may be combined as appropriate, as long as they do not conflict technically. [Explanation of Symbols]
[0099] 1. Lower traveling body 2. Swivel mechanism 3. Upper slewing body 4. Boom 5. Arm 6. Bucket 7. Boom cylinder 8. Arm cylinder 9. Bucket cylinder 10. Cabin 11. Drive source 13. Pump regulator 14. Main pump 15. Pilot pump 17. Control valve unit 18. Throttle 19. Control pressure sensor 20. Hydraulic motor for travel 20L. Hydraulic motor for left travel 20R. Hydraulic motor for right travel 21. Hydraulic motor for slewing 21P. Oil passage 22. Relief valve 23. Check valve 26. Operating device 28. Discharge pressure sensor 29. Operation sensor 30. Controller 31. Solenoid valve 32. Solenoid valve 40...Center bypass oil passage 41...Return oil passage 42...Parallel oil passage 43-47...Oil passage 45a, 45b...Oil passage section 50...Check valve 51...Oil cooler 52...Check valve 53...Filter 55...Relief valve 60...Throttle 100...Working machinery 170-177, 177A...Control valve BP1, BP2, BP3...Branching point PS1...Oil passage section PS2...Oil passage
Claims
1. Lower running body and An upper slewing body is mounted on the lower traveling body so as to be rotatable, Hydraulic actuators and A hydraulic pump capable of supplying hydraulic fluid to the hydraulic actuator, A first control valve is provided in the first oil passage connecting the hydraulic pump and the hydraulic oil tank, A second control valve is provided in the second oil passage connecting the hydraulic pump and the hydraulic actuator, The second oil passage includes a third control valve provided between the hydraulic pump and the second control valve, The third control valve is configured to shut off the second oil passage when the load on the drive source is intentionally increased. A type of machinery used for industrial work.
2. The third control valve has a first state and a second state, In the first state, the flow of hydraulic fluid from the hydraulic pump to the second control valve is permitted. In the second state, the flow of hydraulic fluid from the hydraulic pump to the second control valve is blocked, and the flow from the oil passage portion between the third control valve and the second control valve in the second oil passage to the hydraulic fluid tank is permitted. The work machine according to claim 1.
3. The hydraulic actuator is a single-rod type hydraulic cylinder. The work machine according to claim 1.
4. The hydraulic pump includes a first main pump and a second main pump, The first oil passage includes a first center bypass oil passage and a second center bypass oil passage. The second oil passage includes a first parallel oil passage parallel to the first center bypass oil passage and a second parallel oil passage parallel to the second center bypass oil passage. The first control valve is provided in the first center bypass oil passage, The second control valve and the third control valve are each provided in the first parallel oil passage. The work machine according to claim 1.
5. The hydraulic actuator includes a boom cylinder and an arm cylinder, The first control valve is a spool valve that controls the flow rate of hydraulic fluid flowing into the boom cylinder, The second control valve is a spool valve that controls the flow rate of hydraulic fluid flowing into the arm cylinder. The work machine according to claim 1.
6. The third control valve is a swivel-priority valve. The work machine according to claim 1.