JP6757238B2 - Hydraulic drive system - Google Patents

Description

The present invention relates to a hydraulic drive system mounted on, for example, a construction machine.

In hydraulic drive systems used in industrial machinery and construction machinery, hydraulic oil is supplied from a pump to a plurality of hydraulic actuators. Specifically, a center bypass line extends from the pump to the tank, and a plurality of control valves are arranged on the center bypass line. Each control valve controls the supply and discharge of hydraulic oil to the corresponding actuator.

Generally, the above pump is a variable displacement pump that discharges hydraulic oil at a flow rate according to the tilt angle, and the tilt angle of the pump is adjusted by a regulator. Regulators include flow control that changes the discharge flow rate of the pump according to the operating speed of the actuator, and horsepower control that limits the discharge flow rate of the pump so that the load of the pump does not exceed the output of the engine that drives the pump. is there.

For example, Patent Document 1 describes a regulator that controls the discharge flow rate of a pump by a negative control method, and includes a flow rate control piston and a horsepower control piston. The flow rate control piston and the horsepower control piston are for driving a spool for adjusting the control pressure for the servo piston, and the smaller the discharge flow rate of the pump is preferentially configured to function.

More specifically, the flow rate control piston moves the spool in the flow rate reduction direction as the negative control pressure, which is the pressure between the control valve located on the most downstream side in the center bypass line and the throttle, increases. The horsepower control piston moves the spool in the direction of reducing the flow rate as the discharge pressure of the pump increases.

Japanese Patent No. 5965502

However, in the regulator as described above, two pistons, a flow rate control piston and a horsepower control piston, are required as a spool driving means, and the structure is complicated.

Therefore, an object of the present invention is to provide a hydraulic drive system capable of performing both flow rate control and horsepower control while simplifying the structure of the regulator.

In order to solve the above problems, the hydraulic drive system of the present invention is arranged on a variable displacement pump that discharges a flow rate of hydraulic oil according to the tilt angle and a center bypass line extending from the pump to the tank. , At least one control valve for controlling the supply and discharge of hydraulic oil to the actuator, an operating device including an operating lever for operating the at least one control valve, and a regulator for adjusting the tilt angle of the pump. A servo piston having a first end exposed to the first pressure receiving chamber into which the discharge pressure of the pump is introduced and a second end having a diameter larger than that of the first end exposed to the second pressure receiving chamber. A spool that moves in a flow rate reducing direction that raises the control pressure introduced into the second pressure receiving chamber and a flow rate increasing direction that lowers the control pressure, and a common piston that moves the spool in the flow rate reducing direction as the signal pressure increases. A regulator including, and an electromagnetic proportional valve that outputs a secondary pressure according to a command current, a direct proportional electromagnetic proportional valve in which the secondary pressure increases as the command current increases, and at least the above in the center bypass line. A high-pressure selection valve that selects the higher of the negative control pressure, which is the pressure on the most downstream side of one control valve, and the secondary pressure output from the electromagnetic proportional valve, and supplies it as the signal pressure to the common piston. , The pressure sensor that detects the discharge pressure of the pump and the horsepower control characteristic line that is the relationship line between the discharge pressure of the pump and the discharge flow rate are stored in advance, and correspond to the discharge pressure of the pump detected by the pressure sensor. It is characterized by comprising a control device for supplying a command current to the electromagnetic proportional valve so that the pump discharges hydraulic oil having a discharge flow rate determined by the horsepower control characteristic line.

According to the above configuration, when the negative control pressure is higher than the secondary pressure output by the electromagnetic proportional valve, the flow rate can be controlled by the negative control pressure becoming the signal pressure of the common piston, and the electromagnetic proportional valve outputs. When the secondary pressure is higher than the negative control pressure, the secondary pressure output by the electromagnetic proportional valve becomes the signal pressure of the common piston, so that the horsepower can be controlled. Moreover, since the regulator includes one common piston as a spool driving means, the structure of the regulator can be simplified. Further, if a plurality of horsepower control characteristic lines are stored in the control device and one of them is selected according to the situation, the horsepower control can be made variable.

The regulator is connected to the first operating chamber for applying the signal pressure to the common piston, which is connected to the high pressure selection valve by a signal pressure line, and to the common piston, which is connected to the center bypass line by a fail-safe line. The hydraulic drive system including a second operating chamber on which the discharge pressure of the pump acts is a switching valve provided in the fail-safe line, and the secondary pressure output from the electromagnetic proportional valve is a set pressure. When it is lower than, the fail-safe line is opened to guide the discharge pressure of the pump to the second operating chamber, and when the secondary pressure output from the electromagnetic proportional valve is higher than the set pressure, the fail-safe A switching valve that blocks the line and communicates the second operating chamber with the tank may be further provided. According to this configuration, when the electromagnetic proportional valve operates normally, the fail-safe line is blocked and the second operating chamber communicates with the tank, so that both flow rate control and horsepower control can be performed as described above. it can. On the other hand, when a problem occurs in which the secondary pressure of the electromagnetic proportional valve is maintained lower than the set pressure due to a disruption of the electrical system or a failure of the electromagnetic proportional valve, the discharge pressure of the pump is superimposed on the negative control pressure as the signal pressure of the common piston. Can be made to. As a result, when a problem occurs, the discharge flow rate of the pump is limited when the relationship between the discharge pressure of the pump and the discharge flow rate exceeds the horsepower control characteristic line predetermined for each operation amount of the operating device while controlling the flow rate. be able to. Therefore, it is possible to reliably prevent the engine from stopping due to overload.

Alternatively, the regulator includes an operating chamber in which the signal pressure is applied to the common piston, which is connected to the high pressure selection valve by a signal pressure line, and the signal pressure line includes the high pressure selection valve to the operating chamber. A check valve is provided that allows forward flow but prohibits reverse flow, and the hydraulic drive system branches off the center bypass line to the tank on the most upstream side of at least one control valve. A fail-safe line provided with a pair of throttles and a switching valve provided on the fail-safe line on the upstream side of the pair of throttles, and the secondary pressure output from the electromagnetic proportional valve is the set pressure. A switching valve that opens the fail-safe line when it is lower than the value and blocks the fail-safe line when the secondary pressure output from the electromagnetic proportional valve is higher than the set pressure, and the signal pressure line. A flow from the fail-safe line to the signal pressure line connecting the portion between the working chamber and the check valve and the portion between the pair of throttles in the fail-safe line is allowed, but vice versa. A relay line provided with a check valve that prohibits flow may be further provided. According to this configuration, when the electromagnetic proportional valve operates normally, the fail-safe line is blocked, so that both flow rate control and horsepower control can be performed as described above. On the other hand, when a problem occurs in which the secondary pressure of the electromagnetic proportional valve is maintained lower than the set pressure due to a disruption of the electrical system or a failure of the electromagnetic proportional valve, the signal pressure of the common piston becomes a pair of negative control pressure and fail-safe line. The higher the pressure between the throttles. As a result, when a problem occurs, the discharge flow rate of the pump can be limited when the relationship between the discharge pressure of the pump and the discharge flow rate exceeds a predetermined horsepower control characteristic line while controlling the flow rate. Therefore, it is possible to reliably prevent the engine from stopping due to overload.

According to the present invention, both flow rate control and horsepower control can be performed while simplifying the structure of the regulator.

It is a schematic block diagram of the hydraulic drive system which concerns on 1st Embodiment of this invention. It is a graph which shows the relationship between the negative control pressure and a pump discharge flow rate when the signal pressure to a common piston is a negative control pressure. (A) is a graph showing the horsepower control characteristic line, and (b) shows the relationship between the command current to the electromagnetic proportional valve and the pump discharge flow rate when the signal pressure to the common piston is the secondary pressure of the electromagnetic proportional valve. It is a graph. It is a schematic block diagram of the hydraulic drive system which concerns on 2nd Embodiment of this invention. It is a schematic block diagram of the hydraulic drive system which concerns on 3rd Embodiment of this invention.

(First Embodiment)
FIG. 1 shows a hydraulic drive system 1A according to a first embodiment of the present invention. The hydraulic drive system 1A is mounted on, for example, a construction machine such as a hydraulic excavator or a hydraulic crane, or an industrial machine. The construction machine may be self-propelled, may be mounted on a ship such as a dredger, or may be installed in a port as a fixed loader or unloader.

Specifically, the hydraulic drive system 1A includes a variable displacement main pump 12 that discharges hydraulic oil at a flow rate according to the tilt angle, and a regulator 2 that adjusts the tilt angle of the main pump 12. The main pump 12 is driven by the engine 11. The engine 11 also drives the auxiliary pump 13. However, the main pump 12 and the sub pump 13 may be driven by an electric motor.

A center bypass line 14 extends from the main pump 12 to the tank, and at least one control valve 31 is arranged on the center bypass line 14. Further, the center bypass line 14 is provided with a throttle 15 on the most downstream side of at least one control valve 31. Further, a throttle bypass line is connected to the center bypass line 14 so as to bypass the throttle 15, and a relief valve 16 is provided in the throttle bypass line.

The control valve 31 controls the supply and discharge of hydraulic oil to the hydraulic actuator 32. The hydraulic actuator 32 may be a hydraulic cylinder or a hydraulic motor. The number of sets of the hydraulic actuator 32 and the control valve 31 may be one or a plurality.

For example, when the hydraulic drive system 1A is mounted on a self-propelled hydraulic excavator, the boom cylinder, arm cylinder, bucket cylinder, swivel motor and traveling motor are hydraulic actuators 32. In this case, two main pumps 12 may be provided.

The control valve 31 is operated by an operating device 33 including an operating lever. In the present embodiment, the operating device 33 is a pilot operating valve that outputs a pilot pressure according to the tilt angle of the operating lever, and is connected to the pilot port of the control valve 31 by a pair of pilot lines. However, the operating device 33 is an electric joystick that outputs an electric signal according to the tilt angle of the operating lever, and a pair of electromagnetic proportional valves may be connected to the pilot port of the control valve 31.

In the present embodiment, the main pump 12 is a swash plate pump whose tilt angle is defined by the angle of the swash plate 12a. However, the main pump 12 may be an oblique shaft pump whose tilt angle is defined by the angle formed by the drive shaft and the cylinder block.

The regulator 2 includes a servo piston 21 that changes the tilt angle of the main pump 12 and a regulating valve 23 for driving the servo piston 21. The regulator 2 is formed with a first pressure receiving chamber 2a into which the discharge pressure Pd of the main pump 12 is introduced and a second pressure receiving chamber 2b into which the control pressure Pc is introduced. The servo piston 21 has a first end portion and a second end portion having a diameter larger than that of the first end portion. The first end portion is exposed to the first pressure receiving chamber 2a, and the second end portion is exposed to the second pressure receiving chamber 2b.

The regulating valve 23 is for adjusting the control pressure Pc introduced into the second pressure receiving chamber 2b. Specifically, the adjusting valve 23 provides a spool 24 and a spool 24 that move in a flow rate reducing direction (to the left in FIG. 1) for increasing the control pressure Pc and a flow rate increasing direction (to the right in FIG. 1) for decreasing the control pressure Pc. Includes a sleeve 25 to accommodate.

The servo piston 21 is connected to the swash plate 12a of the main pump 12 so as to be movable in the axial direction of the servo piston 21. The sleeve 25 is connected to the servo piston 21 by a feedback lever 22 so as to be movable in the axial direction of the servo piston 21. The sleeve 25 is formed with a pump port, a tank port, and an output port (the output port communicates with the second pressure receiving chamber 2b), and the output port is a pump port and a tank depending on the relative position between the sleeve 25 and the spool 24. It is either shut off from the port or communicated with either the pump port or the tank port. Then, when the spool 24 is moved in the flow rate decreasing direction or the flow rate increasing direction by the common piston 26 described later, the spool 24 and the sleeve 25 are balanced so that the forces acting from both sides of the servo piston 21 (pressure × servo piston pressure receiving area) are balanced. The relative position with and is determined, and the control pressure Pc is adjusted.

Further, the regulator 2 includes a common piston 26 for driving the spool 24 and a spring 27 arranged on the opposite side of the spool 24 from the common piston 26. The common piston 26 is used for both flow control and horsepower control. The spool 24 is pressed by the common piston 26 and moves in the flow rate decreasing direction, and is moved in the flow rate increasing direction by the urging force of the spring 27.

Further, the regulator 2 is formed with an operating chamber 2c that causes a signal pressure Pp to act on the common piston 26. That is, the common piston 26 moves the spool 24 in the flow rate reduction direction as the signal pressure Pp increases.

The operating chamber 2c is connected to the high pressure selection valve 41 by a signal pressure line 42. In the present embodiment, the high pressure selection valve 41 is arranged outside the regulator 2, but the high pressure selection valve 41 may be incorporated in the regulator 2. In this case, the electromagnetic proportional valve 51 described later may also be incorporated in the regulator 2. Alternatively, the high-pressure selection valve 41 may not be incorporated in the regulator 2, and only the electromagnetic proportional valve 51 may be incorporated in the regulator 2.

The high-pressure selection valve 41 is connected by a flow rate control line 43 to a portion between the control valve 31 and the throttle 15 located on the most downstream side of at least one control valve 31 in the center bypass line 14, and has horsepower. It is connected to the electromagnetic proportional valve 51 by a control line 44. The electromagnetic proportional valve 51 is connected to the auxiliary pump 13 described above by a primary pressure line 52. A relief line branches off from the primary pressure line 52 and is connected to the tank, and a relief valve 53 is provided in this relief line.

The electromagnetic proportional valve 51 is controlled by the control device 6. That is, the command current I is supplied from the control device 6 to the electromagnetic proportional valve 51, and the electromagnetic proportional valve 51 outputs the secondary pressure Ps corresponding to the command current I. The electromagnetic proportional valve 51 is a direct proportional type (normally closed type) in which the secondary pressure Ps increases as the command current I increases.

The high-pressure selection valve 41 is a pressure between the secondary pressure Ps output from the electromagnetic proportional valve 51 and the pressure between the control valve 31 and the throttle 15 located on the most downstream side of at least one control valve 31 in the center bypass line 14. (The pressure on the most downstream side of at least one control valve 31), whichever is higher of the negative control pressure Pn, is selected. The pressure (Ps or Pn) selected by the high pressure selection valve 41 is supplied to the common piston 26 as a signal pressure Pp through the signal pressure line 42.

When the signal pressure Pp is the negative control pressure Pn, the discharge flow rate Q of the main pump 12 decreases as the negative control pressure Pn increases, as shown in FIG. On the other hand, when the signal pressure Pp is the secondary pressure of the electromagnetic proportional valve 51, the discharge flow rate Q of the main pump 12 is shown in FIG. 3B because the electromagnetic proportional valve 51 is of the direct proportional type as described above. As described above, the larger the command current I is, the lower the value is. That is, the discharge flow rate Q becomes the minimum when the command current I is the second command current I2 or more, and the discharge flow rate Q becomes the maximum when the command current I is the first command current I1 or less.

Further, the center bypass line 14 is provided with a pressure sensor 61 that detects the discharge pressure Pd of the main pump 12. The pressure sensor 61 is electrically connected to the control device 6. However, in FIG. 1, only some signal lines are drawn for the sake of simplification of the drawing.

For example, the control device 6 has a memory such as a ROM or RAM and a CPU, and the program stored in the ROM is executed by the CPU. The metric horsepower control characteristic line as shown in FIG. 3A is stored in the control device 6 in advance. The horsepower control characteristic line is a relationship line between the discharge pressure Pd of the main pump 12 and the discharge flow rate Q. The horsepower control characteristic line is determined based on the output of the engine 11, or is set to be lower than the output of the engine 11 in order to improve fuel efficiency. As shown in FIGS. 3A and 3B, the control device 6 applies hydraulic oil having a discharge flow rate Qx determined by a horsepower control characteristic line according to the discharge pressure Pdx of the main pump 12 detected by the pressure sensor 61. The command current Ix is supplied to the electromagnetic proportional valve 51 so that the main pump 12 discharges.

As described above, in the hydraulic drive system 1A of the present embodiment, when the negative control pressure Pn is higher than the secondary pressure Ps output by the electromagnetic proportional valve 51, the negative control pressure Pn becomes the signal pressure Pp of the common piston 26. Therefore, the flow rate can be controlled, and when the secondary pressure Ps output by the electromagnetic proportional valve 51 is higher than the negative control pressure Pn, the secondary pressure Ps output by the electromagnetic proportional valve 51 is the signal pressure Pp of the common piston 26. The horsepower can be controlled by becoming. Moreover, since the regulator 2 includes one common piston 26 as a driving means for the spool 24, the structure of the regulator 2 can be simplified. Further, if a plurality of horsepower control characteristic lines are stored in the control device 6 and one of them is selected according to the situation, the horsepower control can be made variable.

(Second Embodiment)
FIG. 4 shows a hydraulic drive system 1B according to a second embodiment of the present invention. In this embodiment and the third embodiment described later, the same components as those in the first embodiment are designated by the same reference numerals, and duplicate description will be omitted.

In the present embodiment, the regulator 2 is formed with a first operating chamber 2d and a second operating chamber 2e as operating chambers for the common piston 26. The first operating chamber 2d is connected to the high pressure selection valve 41 by a signal pressure line 42, similarly to the operating chamber 2c of the first embodiment. That is, the first operating chamber 2d is an operating chamber in which the signal pressure Pp is applied to the common piston 26. On the other hand, the second operating chamber 2e is connected to the center bypass line 14 by a fail-safe line 71. The second operating chamber 2e is an operating chamber in which the discharge pressure Pd of the main pump 12 acts on the common piston 26. That is, the fail-safe line 71 branches from the center bypass line 14 on the most upstream side of at least one control valve 31 and is connected to the second operating chamber 2e.

The fail-safe line 71 is provided with a switching valve 72. The switching valve 72 is connected to the tank by a tank line 74.

The switching valve 72 has a pilot port, which is connected to the horsepower control line 44 by a pilot line 73. When the secondary pressure Ps output from the electromagnetic proportional valve 51 is lower than the set pressure Pt, the switching valve 72 opens the fail-safe line 71 to guide the discharge pressure Pd of the main pump 12 to the second operating chamber 2e. When the secondary pressure Ps is higher than the set pressure Pt, the fail-safe line 71 is blocked and the second operating chamber 2e is communicated with the tank.

As the set pressure Pt, the first command current I1 which is the maximum of the command currents (0 to I1 in FIG. 3B) that maximizes the discharge flow rate Q of the main pump 12 is supplied to the electromagnetic proportional valve 51. Sometimes it is set to a value lower than the secondary pressure Ps1 output from the electromagnetic proportional valve 51. For example, when the secondary pressure Ps1 is 1 MPa, the set pressure Pt is 0.3 to 1.0 MPa.

In the hydraulic drive system 1B of the present embodiment, when the electromagnetic proportional valve 51 operates normally, the fail-safe line 71 is blocked and the second operating chamber 2e communicates with the tank, so that the flow rate is the same as that of the first embodiment. Both control and horsepower control can be performed. On the other hand, when a problem occurs in which the secondary pressure Ps of the electromagnetic proportional valve 51 is maintained lower than the set pressure Pt due to a disruption of the electric system or a failure of the electromagnetic proportional valve 51, the negative control pressure Pn is used as the signal pressure Pp of the common piston 26. The discharge pressure Pd of the main pump 12 can be superimposed on the main pump 12 (Pp = Pn + Pd × Ad / An). Here, An is the pressure receiving area of the common piston 26 in the first operating chamber 2d, and Ad is the pressure receiving area of the common piston 26 in the second operating chamber 2e. As a result, when a problem occurs, the relationship between the discharge pressure Pd of the main pump 12 and the discharge flow rate Q is determined in advance for each operation amount of the operating device 33 while controlling the flow rate (discharge pressure Pd and discharge flow rate). The discharge flow rate Q of the main pump 12 can be limited when the line (relationship line with Q) is crossed. Therefore, it is possible to reliably prevent the engine 11 from stopping due to an overload.

(Third Embodiment)
FIG. 5 shows a hydraulic drive system 1C according to a third embodiment of the present invention. In the present embodiment, the regulator 2 has one operating chamber 2c as the operating chamber for the common piston 26, as in the first embodiment.

Further, in the present embodiment, the fail-safe line 81 branches from the center bypass line 14 on the most upstream side of at least one control valve 31 and is connected to the tank. The fail-safe line 81 is provided with a pair of diaphragms 82 and 83. Further, the fail-safe line 71 is provided with a switching valve 84 on the upstream side of the pair of throttles 82 and 83.

The switching valve 84 has a pilot port, which is connected to the horsepower control line 44 by a pilot line 85. The switching valve 84 opens the fail-safe line 81 when the secondary pressure Ps output from the electromagnetic proportional valve 51 is lower than the set pressure Pt, and the fail-safe line 81 when the secondary pressure Ps is higher than the set pressure Pt. To block.

The set pressure Pt is a secondary output from the electromagnetic proportional valve 51 when the first command current I1 which is the maximum of the command currents that maximize the discharge flow rate Q of the main pump 12 is supplied to the electromagnetic proportional valve 51. It is set to a value lower than the pressure Ps1. For example, when the secondary pressure Ps1 is 1 MPa, the set pressure Pt is 0.3 to 1.0 MPa.

Further, in the present embodiment, the check valve 45 is provided on the signal pressure line 42. The check valve 45 allows a flow from the high pressure selection valve 41 toward the operating chamber 2c, but prohibits the reverse flow.

The portion of the fail-safe line 81 between the pair of throttles 82 and 83 is connected by the relay line 86 to the portion of the signal pressure line 42 between the working chamber 2c and the check valve 45. The relay line 76 is provided with a check valve 87. The check valve 87 allows a flow from the fail-safe line 81 to the signal pressure line 42, but prohibits the reverse flow.

In the hydraulic drive system 1C of the present embodiment, the fail-safe line 81 is blocked when the electromagnetic proportional valve 51 operates normally, so that both flow rate control and horsepower control can be performed as in the first embodiment. it can. On the other hand, when a problem occurs in which the secondary pressure Ps of the electromagnetic proportional valve 51 is maintained lower than the set pressure Pt due to a disruption of the electric system or a failure of the electromagnetic proportional valve 51, the signal pressure Pp of the common piston 26 becomes the negative control pressure Pn. The pressure Pm between the pair of throttles 82 and 83 at the fail-safe line 81 and the fail-safe line 81 is higher. As a result, when a problem occurs, the relationship between the discharge pressure Pd and the discharge flow rate Q of the main pump 12 exceeds the predetermined horsepower control characteristic line (relationship line between the discharge pressure Pd and the discharge flow rate Q) while controlling the flow rate. At that time, the discharge flow rate Q of the main pump 12 can be limited. Therefore, it is possible to reliably prevent the engine 11 from stopping due to an overload.

That is, in the present embodiment, when the above-mentioned trouble occurs, the discharge flow rate with respect to the discharge pressure Pd of the main pump 12 regardless of the size of the flow rate control, in other words, regardless of the size of the tilt angle of the operation lever of the operation device 33. Since the upper limit of horsepower control can be set only by the relationship of Q, the engine horsepower can be used more effectively.

(Other embodiments)
The present invention is not limited to the first to third embodiments described above, and various modifications can be made without departing from the gist of the present invention.

For example, in the second embodiment, instead of the fail-safe line 71 and the switching valve 72, the fail-safe line 81 and the switching valve 84 provided with the same pair of throttles 82 and 83 as in the third embodiment are adopted and fail. The portion of the safe line 81 between the pair of diaphragms 82 and 83 may be connected to the second operating chamber 2e by a relay line. According to this configuration, when a problem occurs in which the secondary pressure Ps of the electromagnetic proportional valve 51 is maintained lower than the set pressure Pt, the pressure Pm between the pair of throttles 82 and 83 in the fail-safe line 71 becomes the second operating chamber. Guided to 2e.

1A to 1C Hydraulic drive system 12 Main pump 14 Center bypass line 2 Regulator 21 Servo piston 24 Spool 26 Common piston 2a 1st pressure receiving chamber 2b 2nd pressure receiving chamber 2c Operating chamber 2d 1st operating chamber 2e 2nd operating chamber 31 Control valve 41 High-pressure selection valve 42 Signal pressure line 45 Check valve 51 Electromagnetic proportional valve 6 Control device 61 Pressure sensor 71 Fail-safe line 72 Switching valve 81 Fail-safe line 82, 83 Squeezing 84 Switching valve 86 Relay line 87 Check valve

Claims (3)

A variable displacement pump that discharges hydraulic oil with a flow rate according to the tilt angle,
At least one control valve located on the center bypass line extending from the pump to the tank to control the supply and discharge of hydraulic oil to the actuator.
An operating device including an operating lever for operating the at least one control valve,
A regulator that adjusts the tilt angle of the pump, which is larger than the first end exposed to the first pressure receiving chamber into which the discharge pressure of the pump is introduced and the first end exposed to the second pressure receiving chamber. The servo piston having the second end of the diameter, the spool moving in the flow rate decreasing direction for increasing the control pressure introduced into the second pressure receiving chamber and the flow rate increasing direction for decreasing the control pressure, and the higher the signal pressure, the more the said. A regulator that includes a common piston that moves the spool in the flow rate reduction direction,
An electromagnetic proportional valve that outputs a secondary pressure according to the command current, and a direct proportional type electromagnetic proportional valve that increases the secondary pressure as the command current increases.
The higher of the negative control pressure, which is the pressure on the most downstream side of the at least one control valve in the center bypass line, and the secondary pressure output from the electromagnetic proportional valve is selected and used as the signal pressure of the common piston. High-pressure selection valve to supply to
A pressure sensor that detects the discharge pressure of the pump and
The horsepower control characteristic line, which is the relationship line between the discharge pressure of the pump and the discharge flow rate, is stored in advance, and the operation of the discharge flow rate determined by the horsepower control characteristic line according to the discharge pressure of the pump detected by the pressure sensor. A control device that sends a command current to the electromagnetic proportional valve so that the pump discharges oil, and
A hydraulic drive system. The regulator is connected to the first operating chamber for applying the signal pressure to the common piston connected to the high pressure selection valve by a signal pressure line, and to the common piston connected to the center bypass line by a fail-safe line. Includes a second working chamber on which the discharge pressure of the pump acts.
A switching valve provided in the fail-safe line, and when the secondary pressure output from the electromagnetic proportional valve is lower than the set pressure, the fail-safe line is opened and the pump is sent to the second operating chamber. A claim that guides the discharge pressure and further includes a switching valve that blocks the fail-safe line when the secondary pressure output from the electromagnetic proportional valve is higher than the set pressure and communicates the second operating chamber with the tank. Item 1. The hydraulic drive system according to item 1. The regulator comprises an operating chamber that acts the signal pressure on the common piston, which is connected to the high pressure selection valve by a signal pressure line.
The signal pressure line is provided with a check valve that allows the flow from the high pressure selection valve to the operating chamber but prohibits the reverse flow.
A fail-safe line with a pair of throttles that branches off from the center bypass line and connects to the tank on the most upstream side of the at least one control valve.
A switching valve provided on the fail-safe line on the upstream side of the pair of throttles, and the fail-safe line is opened when the secondary pressure output from the electromagnetic proportional valve is lower than the set pressure. A switching valve that blocks the fail-safe line when the secondary pressure output from the electromagnetic proportional valve is higher than the set pressure.
The flow from the fail-safe line to the signal pressure line connecting the portion between the working chamber and the check valve in the signal pressure line and the portion between the pair of throttles in the fail-safe line The hydraulic drive system according to claim 1, further comprising a relay line provided with a check valve that allows but prohibits the reverse flow.

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