Hydraulic system of construction machine

A hydraulic system of a construction machine includes: control valves interposed between a variable displacement main pump and hydraulic actuators; and first solenoid proportional valves connected to pilot ports of the control valves. The hydraulic system further includes: a regulator that changes a displacement of the main pump; and a second solenoid proportional valve connected to an auxiliary pump by a primary pressure line, the second solenoid proportional valve outputting a secondary pressure to the regulator through a secondary pressure line. A switching valve is interposed between the auxiliary pump and the first solenoid proportional valves, and includes a pilot port that is connected to the secondary pressure line by a pilot line.

TECHNICAL FIELD

The present invention relates to a hydraulic system of a construction machine.

BACKGROUND ART

In a hydraulic system installed in construction machines such as hydraulic excavators and hydraulic cranes, control valves are interposed between a main pump and hydraulic actuators. Each of the control valves controls supply and discharge of hydraulic oil to and from a corresponding one of the hydraulic actuators.

Generally speaking, each control valve includes: a spool disposed in a housing; and a pair of pilot ports for moving the spool. In a case where an operation device that outputs an electrical signal is used as an operation device to move the control valve, solenoid proportional valves are connected to the respective pilot ports of the control valve, and the control valve is driven by the solenoid proportional valves.

For example, Patent Literature 1 discloses a configuration for bringing the control valve back to its neutral position when a failure has occurred in the solenoid proportional valves for driving the control valve. In this configuration, a solenoid switching valve is interposed between an auxiliary pump and the solenoid proportional valves for driving the control valve. When a failure has occurred in the solenoid proportional valves for driving the control valve, the solenoid switching valve is switched from an open position to a closed position to stop the supply of the hydraulic oil from the auxiliary pump to the solenoid proportional valves. That is, when a failure has occurred in the solenoid proportional valves for driving the control valve, even if an operator operates the operation device, the control valve is kept in the neutral position and the operation performed on the operation device is invalidated.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, the configuration disclosed in Patent Literature 1 requires a solenoid valve that is dedicated for invalidating an operation performed on the operation device.

In view of the above, an object of the present invention is to provide a hydraulic system of a construction machine, the hydraulic system making it possible to invalidate operations performed on operation devices without using a solenoid valve that is dedicated for invalidating operations performed on the operation devices.

Solution to Problem

In order to solve the above-described problems, the inventors of the present invention have paid attention to the fact that, among various hydraulic systems of construction machines, some of them are configured such that the displacement of a variable displacement main pump thereof is changed by a solenoid proportional valve. Then, the inventors have come up with an idea that it may be possible to use the solenoid proportional valve for invalidating an operation performed on an operation device. The present invention has been made from such a technological point of view.

Specifically, a hydraulic system of a construction machine according to the present invention includes: a variable displacement main pump; control valves interposed between the main pump and hydraulic actuators, each control valve including pilot ports; first solenoid proportional valves connected to the pilot ports of the control valves; operation devices to move the control valves, each operation device outputting an electrical signal corresponding to an operating amount of the operation device; a controller that controls the first solenoid proportional valves based on the electrical signals outputted from the operation devices; a regulator that changes a displacement of the main pump based on a signal pressure; a second solenoid proportional valve connected to an auxiliary pump by a primary pressure line, the second solenoid proportional valve outputting a secondary pressure as the signal pressure to the regulator through a secondary pressure line; and a switching valve interposed between the auxiliary pump and the first solenoid proportional valves, the switching valve including a pilot port that is connected to the secondary pressure line by a pilot line, the switching valve switching between a closed position and an open position in accordance with a pilot pressure led to the pilot port.

According to the above configuration, whether to switch the switching valve, which is interposed between the auxiliary pump and the first solenoid proportional valves, to the closed position or to the open position, i.e., whether to invalidate or validate operations performed on the operation devices, can be switched based on the secondary pressure of the second solenoid proportional valve. Also, the displacement of the main pump can be changed based on the secondary pressure of the second solenoid proportional valve. This allows the second solenoid proportional valve, which is a single valve, to have two functions. Therefore, a solenoid valve dedicated for invalidating operations performed on the operation devices is unnecessary.

For example, the regulator may increase the displacement of the main pump in accordance with increase in the signal pressure, and the switching valve may switch from the closed position to the open position when the pilot pressure led to the pilot port of the switching valve becomes higher than or equal to a setting value.

The above hydraulic system may further include a selector that receives a selection of operation lock, which is a selection to invalidate operations performed on the operation devices, or receives a selection of operation lock release, which is a selection to validate operations performed on the operation devices. While the selector is receiving the selection of operation lock, the controller may control the second solenoid proportional valve, such that the secondary pressure of the second solenoid proportional valve is lower than the setting value. While the selector is receiving the selection of operation lock release, the controller may control the second solenoid proportional valve, such that the secondary pressure of the second solenoid proportional valve is higher than the setting value. According to this configuration, when an operator makes the selection of operation lock with the selector, operations performed on the operation devices are invalidated, whereas when the operator makes the selection of operation lock release with the selector, operations performed on the operation devices are validated.

The setting value may be a first setting value. The regulator may keep the displacement of the main pump to a minimum when the signal pressure is lower than or equal to a second setting value. The first setting value may be lower than the second setting value. According to this configuration, the switching valve can be switched from the closed position to the open position while the displacement of the main pump is kept to the minimum.

The main pump, the auxiliary pump, the regulator, and the second solenoid proportional valve may be integrated together to collectively serve as a pump unit. The switching valve may be connected to the pump unit by a pipe that is a part of a pump line connecting between the switching valve and the auxiliary pump and by a pipe that is a part of the pilot line. This configuration makes it possible to relatively freely determine the position at which to dispose the switching valve in the construction machine

The main pump, the auxiliary pump, the regulator, the second solenoid proportional valve, and the switching valve may be integrated together to collectively serve as a pump unit. According to this configuration, the number of pipes extending from the pump unit and intended for the first solenoid proportional valves may be only one.

Advantageous Effects of Invention

The present invention makes it possible to invalidate operations performed on operation devices without using a solenoid valve that is dedicated for invalidating operations performed on the operation devices.

DESCRIPTION OF EMBODIMENTS

FIG.1shows a hydraulic system1of a construction machine according to one embodiment of the present invention.FIG.2shows a construction machine10, in which the hydraulic system1is installed. Although the construction machine10shown inFIG.2is a hydraulic excavator, the present invention is applicable to other construction machines, such as a hydraulic crane.

The construction machine10shown inFIG.2is a self-propelled construction machine, and includes a traveling unit11. The construction machine10further includes: a slewing unit12slewably supported by the traveling unit11; and a boom that is luffed relative to the slewing unit12. An arm is swingably coupled to the distal end of the boom, and a bucket is swingably coupled to the distal end of the arm. The slewing unit12is equipped with a cabin16including an operator's seat. The construction machine10need not be of a self-propelled type.

The hydraulic system1includes, as hydraulic actuators20, a boom cylinder13, an arm cylinder14, and a bucket cylinder15, which are shown inFIG.2, an unshown pair of left and right travel motors, and an unshown slewing motor. The boom cylinder13luffs the boom. The arm cylinder14swings the arm. The bucket cylinder15swings the bucket.

As shown inFIG.1, the hydraulic system1further includes a main pump22, which supplies hydraulic oil to the aforementioned hydraulic actuators20. InFIG.1, the hydraulic actuators20are not shown for the purpose of simplifying the drawing.

The main pump22is driven by an engine21. Alternatively, the main pump22may be driven by an electric motor. The engine21also drives an auxiliary pump23. The number of main pumps22may be more than one.

The main pump22is a variable displacement pump whose displacement, i.e., the amount of hydraulic oil delivered per rotation of the pump, is variable. The displacement of the main pump22may be controlled by electrical positive control, or may be controlled by hydraulic negative control. Alternatively, the delivery flow rate (i.e., the amount of hydraulic oil delivered per unit time) of the main pump22may be controlled by load-sensing control. In the present embodiment, the main pump22is a swash plate pump including a swash plate22a. Alternatively, the main pump22may be a bent axis pump.

The displacement (delivery flow rate) of the main pump22is changed by a regulator9. The regulator9is fed with a signal pressure, and based on the signal pressure, the regulator9changes the displacement of the main pump22. In the present embodiment, the regulator9increases the displacement of the main pump22in accordance with increase in the signal pressure.

To be more specific, the regulator9includes a servo piston91and an adjustment valve92. The servo piston91is coupled to the swash plate22aof the main pump22. The adjustment valve92is intended for driving the servo piston91. In the regulator9, a first pressure receiving chamber9aand a second pressure receiving chamber9bare formed. The delivery pressure of the main pump22is led into the first pressure receiving chamber9a, and a control pressure is led into the second pressure receiving chamber9b. The servo piston91includes a first end portion and a second end portion. The second end portion has a greater diameter than that of the first end portion. The first end portion is exposed in the first pressure receiving chamber9a, and the second end portion is exposed in the second pressure receiving chamber9b.

The adjustment valve92is intended for adjusting the control pressure led into the second pressure receiving chamber9b. Specifically, the adjustment valve92includes a spool93and a sleeve94. The spool93shifts in a direction to decrease the control pressure (i.e., a displacement-increasing direction; to the left inFIG.1), and also shifts in a direction to increase the control pressure (i.e., a displacement-decreasing direction; to the right inFIG.1). The sleeve94accommodates the spool93therein. The spool93is pressed by a flow rate control piston96to shift in the displacement-increasing direction, and is urged by the urging force of a spring95to shift in the displacement-decreasing direction. The spring95is disposed opposite the flow rate control piston96, with the spool93positioned between the spring95and the flow rate control piston96.

The sleeve94is coupled to the servo piston91by a feedback lever97. In the sleeve94, a pump port, a tank port, and an output port are formed (the output port communicates with the second pressure receiving chamber9b). The output port is blocked from both the pump port and the tank port, or communicates with the pump port or the tank port, in accordance with a positional relationship between the sleeve94and the spool93. When the flow rate control piston96causes the spool93to shift in the displacement-increasing direction or the displacement-decreasing direction, the spool93and the sleeve94are brought into such a positional relationship with each other that forces applied from both sides of the servo piston91(each force=pressure×pressure receiving area of the servo piston) are balanced, and thereby the control pressure is adjusted.

Further, an actuating chamber9c, which applies the aforementioned signal pressure to the flow rate control piston96, is formed in the regulator9. That is, the higher the signal pressure, the more the flow rate control piston96presses the spool93to shift in the displacement-increasing direction.

As shown inFIGS.3A and3B, when the signal pressure is lower than or equal to a setting value β (corresponding to a second setting value of the present invention), the regulator9keeps the displacement of the main pump22to a minimum, whereas when the signal pressure is higher than or equal to a setting value γ, the regulator9keeps the displacement of the main pump22to a maximum. When the signal pressure is between the setting value β and the setting value γ, the displacement of the main pump22changes in accordance with the signal pressure.

Returning toFIG.1, control valves41are interposed between the main pump22and the hydraulic actuators20. In the present embodiment, all the control valves41are three-position valves. Alternatively, one or more of the control valves41may be two-position valves.

All the control valves4are connected to the main pump22by a supply line31, and connected to a tank by a tank line33. Each of the control valves41is connected to a corresponding one of the hydraulic actuators20by a pair of supply/discharge lines. In a case where the number of main pumps22is more than one, the same number of groups of the control valves41as the number of main pumps22are formed. In each group, the control valves41are connected to the corresponding main pump22by the supply line31.

For example, the control valves41include: a boom control valve that controls supply and discharge of the hydraulic oil to and from the boom cylinder13; an arm control valve that controls supply and discharge of the hydraulic oil to and from the arm cylinder14; and a bucket control valve that controls supply and discharge of the hydraulic oil to and from the bucket cylinder15.

The supply line31includes a main passage and branch passages. The main passage extends from the main pump22. The branch passages are branched off from the main passage, and connect to the control valves41. In the present embodiment, a center bypass line32is branched off from the main passage of the supply line31, and the center bypass line32extends to the tank. The control valves41are disposed on the center bypass line32. The center bypass line32may be eliminated.

A relief line34is branched off from the main passage of the supply line31, and the relief line34is provided with a relief valve35for the main pump22. The relief line34may be branched off from the center bypass line32at a position upstream of all the control valves41. Alternatively, the relief line34may be branched off from the center bypass line32at a position between particular control valves41.

Each control valve41includes: a spool disposed in a housing; and a pair of pilot ports for moving the spool. For example, the housings of all the control valves41may be integrated together to form a multi-control valve unit. The pilot ports of each control valve41are connected to respective first solenoid proportional valves43by respective pilot lines42.

Each first solenoid proportional valve43is a direct proportional valve outputting a secondary pressure that indicates a positive correlation with a command current. Alternatively, each first solenoid proportional valve43may be an inverse proportional valve outputting a secondary pressure that indicates a negative correlation with the command current.

All the first solenoid proportional valves43are connected to a switching valve52by a distribution line53. The distribution line53includes a main passage and branch passages. The main passage extends from the switching valve52. The branch passages are branched off from the main passage, and connect to the first solenoid proportional valves43.

The switching valve52is connected to the auxiliary pump23by a pump line51. A relief line54is branched off from the pump line51, and the relief line54is provided with a relief valve55for the auxiliary pump23. The relief pressure of the relief valve55is set sufficiently high (e.g., 4 MPa) so that the spool of each control valve41can move to the stroke end. The relief pressure of the relief valve55is higher, to some extent, than the setting value γ of the regulator9(the signal pressure that brings the displacement of the main pump22to the maximum).

The switching valve52interposed between the auxiliary pump23and all the first solenoid proportional valves43includes a pilot port, and switches between a closed position and an open position in accordance with a pilot pressure led to the pilot port. In the present embodiment, the closed position is the neutral position of the switching valve52. That is, when the pilot pressure becomes higher than or equal to a setting value α (corresponding to a first setting value of the present invention), the switching valve52switches from the closed position to the open position.

When the switching valve52is in the closed position, the switching valve52blocks the pump line51, and brings the distribution line53into communication with the tank. When the switching valve52is in the open position, the switching valve52brings the pump line51into communication with the distribution line53. In other words, in a state where the switching valve52is kept in the closed position, the supply of the hydraulic oil from the auxiliary pump23to the first solenoid proportional valves43is stopped, and the primary pressure of each first solenoid proportional valve43is zero. Accordingly, even when electric currents are fed to the first solenoid proportional valves43, the control valves41do not move.

As shown inFIG.3A, desirably, the setting value α of the switching valve52is set to be lower than the setting value β, which brings the displacement of the main pump22to the minimum, because, with such setting of the setting value α, the switching valve52can be switched from the closed position to the open position while the displacement of the main pump22is kept to the minimum. For example, the setting value α is 0.1 to 0.6 MPa, and the setting value β is 0.7 to 1.0 MPa.

The auxiliary pump23is connected also to a second solenoid proportional valve62by a primary pressure line61, and the second solenoid proportional valve62is connected to the actuating chamber9cof the regulator9by a secondary pressure line63. That is, the second solenoid proportional valve62outputs a secondary pressure as the aforementioned signal pressure to the regulator9through the secondary pressure line63. The upstream portion of the primary pressure line61and the upstream portion of the pump line51merge together to form a shared passage.

In the present embodiment, the second solenoid proportional valve62is a direct proportional valve outputting a secondary pressure that indicates a positive correlation with a command current. The pilot port of the switching valve52is connected to the secondary pressure line63by a pilot line64.

Operation devices44to move the control valves41are disposed in the aforementioned cabin16. Each operation device44includes an operating unit (an operating lever or a foot pedal) that receives an operation for moving a corresponding one of the hydraulic actuators20, and outputs an electrical signal corresponding to an operating amount of the operating unit (e.g., an inclination angle of the operating lever).

For example, the operation devices44include a boom operation device, an arm operation device, and a bucket operation device, each of which includes an operating lever. The operating lever of the boom operation device receives a boom raising operation and a boom lowering operation. The operating lever of the arm operation device receives an arm crowding operation and an arm pushing operation. The operating lever of the bucket operation device receives a bucket excavating operation and a bucket dumping operation. For example, when the operating lever of the boom operation device is inclined in a boom raising direction, the boom operation device outputs a boom raising electrical signal whose magnitude corresponds to the inclination angle of the operating lever.

The electrical signal outputted from each operation device44is inputted to a controller7. For example, the controller7is a computer including memories such as a ROM and RAM, a storage such as a HDD, and a CPU. The CPU executes a program stored in the ROM or HDD.

The controller7controls the first solenoid proportional valves43based on the electrical signals outputted from the operation devices44.FIG.1shows only part of signal lines for simplifying the drawing. For example, when a boom raising electrical signal is outputted from the boom operation device, the controller7feeds a command current to the first solenoid proportional valve43connected to a boom raising pilot port of the boom control valve, and increases the command current in accordance with increase in the boom raising electrical signal.

The controller7controls the second solenoid proportional valve62, such that the secondary pressure of the second solenoid proportional valve62increases in accordance with increase in the operating amount of each operation device44. Accordingly, the displacement (delivery flow rate) of the main pump22increases in accordance with increase in the operating amount of each operation device44.

A selector8is disposed in the cabin16. With the selector8, an operator selects whether to invalidate or validate operations performed on all the operation devices44. The selector8receives a selection of operation lock, which is a selection to invalidate operations performed on the operation devices44, or receives a selection of operation lock release, which is a selection to validate operations performed on the operation devices44.

For example, the selector8may be a micro switch or limit switch including a safety lever, and by shifting or swinging the safety lever, the selection of operation lock or the selection of operation lock release can be made. Alternatively, the selector8may be a push button switch including a button, and by pushing or not pushing the button, the selection of operation lock or the selection of operation lock release can be made.

The controller7controls the second solenoid proportional valve62in accordance with a selection status of the selector8in the following manner.

While the selector8is receiving the selection of operation lock, the controller7controls the second solenoid proportional valve62, such that the secondary pressure of the second solenoid proportional valve62is lower than the setting value α of the switching valve52as shown inFIG.3A. As a result, the displacement of the main pump22is kept to the minimum, and also, the switching valve52is kept in the closed position. At the time, the controller7may feed no command current to the second solenoid proportional valve62, or may feed a command current lower than the electric current value corresponding to the setting value α to the second solenoid proportional valve62.

While the selector8is receiving the selection of operation lock release, the controller7controls the second solenoid proportional valve62, such that the secondary pressure of the second solenoid proportional valve62is higher than the setting value α of the switching valve52. As a result, the switching valve52is switched to the open position.

As described above, while the selector8is receiving the selection of operation lock release, the secondary pressure of the second solenoid proportional valve62increases in accordance with increase in the operating amount of each operation device44. Specifically, when none of the operation devices44are operated, the controller7feeds a standby current to the second solenoid proportional valve62as a command current to keep the secondary pressure of the second solenoid proportional valve62to a predetermined value c, which is higher than the setting value α of the switching valve52. In a case where the setting value α of the switching valve52is lower than the setting value β of the regulator9, the predetermined value c is lower than or equal to the setting value β, and in a case where the setting value α of the switching valve52is higher than the setting value β of the regulator9, the predetermined value c is close to the setting value α. Accordingly, the displacement of the main pump22is kept at, or kept close to, the minimum.

When any one of the operation devices44is operated while the selector8is receiving the selection of operation lock release, the secondary pressure of the second solenoid proportional valve62is adjusted to be higher than the predetermined value ε. Thus, while the selector8is receiving the selection of operation lock release, the secondary pressure of the second solenoid proportional valve62changes between the predetermined value c and the maximum value in accordance with the operating amount of the operation device44.

As described above, in the hydraulic system1of the present embodiment, whether to switch the switching valve52, which is interposed between the auxiliary pump23and the first solenoid proportional valves43, to the closed position or to the open position, i.e., whether to invalidate or validate operations performed on the operation devices44, can be switched based on the secondary pressure of the second solenoid proportional valve62. Also, the displacement of the main pump22can be changed based on the secondary pressure of the second solenoid proportional valve62. This allows the second solenoid proportional valve62, which is a single valve, to have two functions. Therefore, a solenoid valve dedicated for invalidating operations performed on the operation devices44is unnecessary.

Since the present embodiment includes the selector8, when the operator makes the selection of operation lock with the selector8, operations performed on the operation devices44are invalidated, whereas when the operator makes the selection of operation lock release with the selector8, operations performed on the operation devices44are validated.

In general, the main pump22, the auxiliary pump23, the regulator9, and the second solenoid proportional valve62are integrated together to collectively serve as a pump unit. Accordingly, the switching valve52may be connected to the pump unit by a pipe that is a part of the pump line51and a pipe that is a part of the pilot line64. This configuration makes it possible to relatively freely determine the position at which to dispose the switching valve52in the construction machine.

Alternatively, the switching valve52may be integrated with the main pump22, the auxiliary pump23, the regulator9, and the second solenoid proportional valve62, and thereby incorporated in the pump unit. In a case where the switching valve52is a separate component from the pump unit, it is necessary to extend two pipes from the pump unit as pipes for the first solenoid proportional valves43(other than a tank pipe). On the other hand, in a case where the switching valve52is incorporated in the pump unit, the number of pipes extending from the pump unit and intended for the first solenoid proportional valves43may be only one (other than a tank pipe).

The present invention is not limited to the above-described embodiment. Various modifications can be made without departing from the scope of the present invention.

For example, the regulator9may be configured conversely to the above-described embodiment, i.e., the regulator9may decrease the displacement of the main pump22in accordance with increase in the signal pressure. In this case, the switching valve52switches from the open position to the closed position when the pilot pressure becomes higher than or equal to a relatively high setting value. In the case where the regulator9is configured conversely to the above-described embodiment, the second solenoid proportional valve62may be either a direct proportional valve or an inverse proportional valve.

REFERENCE SIGNS LIST