JP6815267B2 - Hydraulic system - Google Patents

Description

The present invention relates to an electric positive control type hydraulic system.

Conventionally, electric positive control type hydraulic systems have been adopted in construction machinery and industrial machinery. For example, Patent Document 1 discloses a hydraulic system 100 as shown in FIG.

In this hydraulic system 100, the tilt angle of the variable displacement pump 110 is adjusted by the regulator 120. The regulator 120 includes a flow rate control piston 121 and a horsepower control piston 122, and the tilt angle of the pump 110 increases as the control pressure acting on the flow rate control piston 121 increases or the pump discharge pressure acting on the horsepower control piston 122 decreases. (Discharge flow rate) is increased. The regulator 120 is configured so that the one that limits the discharge flow rate of the flow rate control piston 121 and the horsepower control piston 122 to a small value preferentially functions.

The regulator 120 is connected to the electromagnetic proportional valve 140 by a secondary pressure line 130. The electromagnetic proportional valve 140 outputs a higher secondary pressure to the regulator 120 as the above-mentioned control pressure as the operation amount of the pilot-operated valve, which is the operation device (not shown), increases.

The secondary pressure line 130 is provided with a pilot type switching valve 150. When the electromagnetic proportional valve 140 is normal, the switching valve 150 is positioned at the operating position (right position in FIG. 9) by the secondary pressure of the electromagnetic proportional valve 140, and the secondary pressure of the electromagnetic proportional valve 140 is controlled by the flow rate control piston. It acts on 121. On the other hand, when the electromagnetic proportional valve 140 does not function normally due to a failure or the like and its secondary pressure becomes zero, the switching valve 150 switches to the neutral position (left position in FIG. 9) and is a pilot operated valve. The pilot pressure output from is applied to the flow control piston 121. As a result, even if the electromagnetic proportional valve 140 does not function normally, the discharge flow rate of the pump 110 can be increased according to the operation amount of the pilot operated valve.

However, when the electromagnetic proportional valve 140 does not function normally, the switching valve 150 applies the primary pressure of the electromagnetic proportional valve 140 to the horsepower control piston 122, so that the power shift is superimposed on the horsepower control. Therefore, the horsepower control works more strongly than when the electromagnetic proportional valve 140 is working normally, so that the upper limit of the discharge flow rate of the pump 110 for each discharge pressure becomes lower.

Japanese Patent No. 4041789

However, the configuration shown in FIG. 9 requires a relatively long line connecting the pilot operation valve (operation device) located at a position away from the pump 110 (for example, the cab in the construction machine) and the switching valve 150. In addition, the regulator 120 requires two pressure receiving chambers for the flow rate control piston 121 and the horsepower control piston 122, and the structure is complicated.

Therefore, according to the present invention, even if the electromagnetic proportional valve that outputs the secondary pressure as the control pressure to the regulator does not function normally and the secondary pressure becomes zero, the discharge flow rate of the pump is secured to some extent with a simple structure. The purpose is to provide a hydraulic system that can be used.

In order to solve the above problems, the hydraulic system of the present invention includes an operation device that outputs an operation signal according to the amount of operation to the operation unit, a variable displacement main pump, and a flow control piston, and includes the flow control piston. A regulator that increases the tilt angle of the main pump as the control pressure acting on the main pump increases, an auxiliary pump, the regulator are connected by a secondary pressure line, and the auxiliary pump is connected by a primary pressure line. In an emergency, an electromagnetic proportional valve that outputs a higher secondary pressure as the control pressure to the regulator as the operation signal output from the device becomes larger, and a pair of throttles that branch from the primary pressure line and connect to the tank. The line and the secondary pressure line are divided into a first flow path on the electromagnetic proportional valve side and a second flow path on the regulator side, and the emergency line is divided into an upstream flow path between the pair of throttles. It is a switching valve provided so as to separate from the downstream flow path, and blocks the first flow path at the neutral position and communicates the upstream flow path with the downstream flow path and the second flow path. When the secondary pressure of the electromagnetic proportional valve exceeds the set value, the operation of communicating the first flow path with the second flow path and blocking the upstream flow path and the downstream flow path by the secondary pressure. The electromagnetic proportional valve outputs a secondary pressure between a minimum value and a maximum value larger than the set value according to the switching valve that can be switched to the position and the operation signal output from the operating device. It is characterized by including a control device for supplying a command current to an electromagnetic proportional valve.

According to the above configuration, when the electromagnetic proportional valve is normal, the switching valve is located at the operating position, so that the secondary pressure of the electromagnetic proportional valve acts on the flow control piston of the regulator through the secondary pressure line. Therefore, the tilt angle (discharge flow rate) of the pump can be controlled by the electromagnetic proportional valve. On the other hand, when the electromagnetic proportional valve does not function normally and its secondary pressure becomes zero, the switching valve is switched to the neutral position, and hydraulic oil flows from the auxiliary pump to the tank through the emergency line. As a result, the intermediate pressure between the pair of throttles in the emergency line acts on the flow control piston of the regulator through the second flow path of the secondary pressure line. As a result, the discharge flow rate of the pump can be secured to some extent. The emergency line passing through the switching valve may be relatively short, and the regulator does not require a conventional horsepower control piston and only needs a pressure receiving chamber for the flow rate control piston, which is simple. The above effect can be obtained with the structure.

The hydraulic system further includes an engine controlled by the control device that drives the main pump and the sub-pump, and the control device monitors the command current supplied to the electromagnetic proportional valve to the electromagnetic proportional. When it is determined that the valve does not function normally, the engine speed may be adjusted to the vicinity of the engine speed at which the engine torque is maximized. According to this configuration, the maximum value of the pump torque with respect to the pump discharge pressure when the electromagnetic proportional valve does not function normally can be set to a certain high value. Therefore, the intermediate pressure between the pair of throttles can be increased to some extent to secure a large discharge flow rate of the pump when the electromagnetic proportional valve does not function normally.

The set value is a first set value, and the maximum value of the secondary pressure of the electromagnetic proportional valve corresponding to the operation signal output from the operating device is a second set pressure lower than the discharge pressure of the auxiliary pump. When the secondary pressure of the electromagnetic proportional valve exceeds the second set value, the switching valve blocks the first flow path and sets the upstream flow path to the downstream flow path and the second set value. It may communicate with two flow paths. According to this configuration, even if the electromagnetic proportional valve does not function normally and its secondary pressure becomes equal to the primary pressure, the discharge flow rate of the pump can be secured to some extent.

According to the present invention, even if the electromagnetic proportional valve that outputs the secondary pressure as the control pressure to the regulator does not function normally and the secondary pressure becomes zero, the discharge flow rate of the pump is secured to some extent with a simple structure. can do.

It is a schematic block diagram of the hydraulic system which concerns on 1st Embodiment of this invention. It is a graph which shows the relationship between the operation amount with respect to the operation part of the operation device, and the command current to an electromagnetic proportional valve. It is a graph which shows the relationship between the command current to an electromagnetic proportional valve, and the secondary pressure of an electromagnetic proportional valve. It is a graph which shows the relationship between the control pressure to a regulator, and the discharge flow rate of a main pump. (A) and (b) are graphs relating to the main pump in the modified example, (a) is a graph showing a discharge flow rate limit line, and (b) is a graph showing a relationship between a pump discharge pressure and a pump torque. It is a graph which shows the relationship between the engine speed and the engine torque. It is a schematic block diagram of the hydraulic system which concerns on 2nd Embodiment of this invention. It is a graph which shows the relationship between the command current to an electromagnetic proportional valve, and the secondary pressure of an electromagnetic proportional valve. It is a schematic block diagram of the conventional hydraulic system.

(First Embodiment)
FIG. 1 shows a hydraulic system 1A according to a first embodiment of the present invention. The hydraulic system 1A is mounted on a construction machine such as a hydraulic excavator or a hydraulic crane, a civil engineering machine, an agricultural machine or an industrial machine.

Specifically, the hydraulic system 1A includes a hydraulic actuator 24 and a main pump 22 that supplies hydraulic oil to the hydraulic actuator 24 via a control valve 3. In the illustrated example, the hydraulic actuator 24 and the control valve 3 are set in one set, but a plurality of sets of the hydraulic actuator 24 and the control valve 3 may be provided.

The main pump 22 is driven by the engine 21. The engine 21 also drives the auxiliary pump 23.

The main pump 22 is a variable displacement pump whose tilt angle can be changed. In this embodiment, the main pump 22 is a swash plate pump. However, the main pump 22 may be an oblique shaft pump. The tilt angle of the main pump 22 is adjusted by the regulator 5.

The main pump 22 is connected to the control valve 3 by a supply line 11. The discharge pressure of the main pump 22 is kept below the relief pressure by the relief valve 12.

In the present embodiment, the hydraulic actuator 24 is a double-acting cylinder, and the control valve 3 is connected to the hydraulic actuator 24 by a pair of supply / discharge lines 31. However, the hydraulic actuator 24 may be a single-acting cylinder, and the control valve 3 may be connected to the hydraulic actuator 24 by a single supply / discharge line 31. Alternatively, the hydraulic actuator 24 may be a hydraulic motor.

The control valve 3 is moved from the neutral position to the first position (the position where the hydraulic actuator 24 is operated in one direction) or the second position (the position where the hydraulic actuator 24 is operated in the opposite direction) when the operating device 4 is operated. Can be switched. In this embodiment, the control valve 3 is a hydraulic pilot type and has a pair of pilot ports. However, the control valve 3 may be an electromagnetic pilot type.

The operation device 4 has an operation unit 41 and outputs an operation signal according to the amount of operation for the operation unit 41. That is, the operation signal output from the operation device 4 increases as the operation amount increases. The operation unit 41 is, for example, an operation lever, but may be a foot pedal or the like.

In the present embodiment, the operation device 4 is a pilot operation valve that outputs a pilot pressure as an operation signal. Therefore, the operating device 4 is connected to the pilot port of the control valve 3 by a pair of pilot lines 42. Then, as the pilot pressure (operation signal) output from the operation device 4 increases, the opening area of the passage through which the control valve 3 supplies the hydraulic oil to the hydraulic actuator 24 increases. However, the operation device 4 may be an electric joystick that outputs an electric signal as an operation signal. In this case, each pilot port of the control valve 3 is connected to the secondary pressure port of the electromagnetic proportional valve.

The regulator 5 described above includes the flow rate control piston 56, and the tilt angle of the main pump 22 increases as the control pressure Pc acting on the flow rate control piston 56 increases. The regulator 5 is connected to the secondary pressure port of the electromagnetic proportional valve 61 by a secondary pressure line 62, and the primary pressure port of the electromagnetic proportional valve 61 is connected to the secondary pump 23 by a primary pressure line 65. The discharge pressure of the auxiliary pump 23 is maintained at the relief set pressure by the relief valve 13.

More specifically, the regulator 5 includes a servo piston 51 that changes the tilt angle of the main pump 22, and a regulating valve 53 for driving the servo piston 51. The regulator 5 is formed with a first pressure receiving chamber 5a into which the discharge pressure of the main pump 22 is introduced and a second pressure receiving chamber 5b into which the control pressure is introduced. The servo piston 51 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 5a, and the second end portion is exposed to the second pressure receiving chamber 5b.

The regulating valve 53 is for adjusting the control pressure introduced into the second pressure receiving chamber 5b. Specifically, the regulating valve 53 includes a spool 54 that moves in a direction of decreasing the control pressure (flow rate increasing direction, leftward in FIG. 1) and a direction of increasing the control pressure (flow rate decreasing direction, rightward in FIG. 1). Includes a sleeve 55 for accommodating 54. The spool 54 is pressed by the flow rate control piston 56 described above and moves in the flow rate increasing direction, and moves in the flow rate decreasing direction by the urging force of the spring 57 arranged on the opposite side of the flow rate control piston 56.

The servo piston 51 is connected to the swash plate 22a of the main pump 22 so as to be movable in the axial direction of the servo piston 51. The sleeve 55 is connected to the servo piston 51 by a feedback lever 52 so as to be movable in the axial direction of the servo piston 51. The sleeve 55 is formed with a pump port, a tank port, and an output port (the output port communicates with the second pressure receiving chamber 5b), and the output port is a pump port and a tank depending on the relative position between the sleeve 55 and the spool 54. It is either blocked from both ports or the output port communicates with either the pump port or the tank port. Then, when the spool 54 is moved by the flow rate control piston 56 in the flow rate increasing direction or the flow rate decreasing direction, the spool 54 and the sleeve 55 are relative to each other so that the forces acting from both sides of the servo piston 51 (pressure × servo piston pressure receiving area) are balanced. The position is fixed and the control pressure is adjusted.

Further, the regulator 5 is formed with an operating chamber 5c for applying a control pressure Pc to the flow rate control piston 56. That is, the flow rate control piston 56 moves the spool 54 in the flow rate increasing direction as the control pressure Pc increases. The secondary pressure line 62 extending from the electromagnetic proportional valve 61 described above is connected to the working chamber 5c.

As shown in FIG. 3, the electromagnetic proportional valve 61 is of a direct proportional type in which the command current sent to the electromagnetic proportional valve 61 and the secondary pressure output by the electromagnetic proportional valve 61 show a positive correlation. The electromagnetic proportional valve 61 is controlled by the control device 9.

The control device 9 also controls the engine 21. Specifically, the control device 9 outputs a command to the engine control device of the engine 21 so as to keep the rotation speed of the engine 21 at a predetermined value.

For example, the control device 9 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 control device 9 may be a single device or may be divided into a plurality of devices (for example, a pump control device and an engine control device).

The control device 9 is electrically connected to the pressure sensors 91 provided in each of the pair of pilot lines 42 described above. However, in FIG. 1, only some signal lines are drawn for the sake of simplification of the drawing.

The pressure sensor 91 detects the pilot pressure output from the operating device 4. Then, as shown in FIG. 2, the control device 9 increases the command current supplied to the electromagnetic proportional valve 61 as the pilot pressure output from the operating device 4 increases. That is, the electromagnetic proportional valve 61 outputs a higher secondary pressure to the regulator 5 as the above-mentioned control pressure Pc as the pilot pressure (operation signal) output from the operation device 4 increases. As a result, the discharge flow rate of the main pump 22 increases as the amount of operation of the operating device 4 with respect to the operating unit 41 increases.

More specifically, as shown in FIG. 2, the control device 9 sets the command current supplied to the electromagnetic proportional valve 61 to the minimum value I1 slightly higher than zero according to the pilot pressure output from the operating device 4. Change with the maximum value I2. Therefore, as shown in FIG. 3, the secondary pressure of the electromagnetic proportional valve 61 also changes between the minimum value P1 and the maximum value P2 larger than zero. That is, the electromagnetic proportional valve 61 outputs a secondary pressure between the minimum value P1 and the maximum value P2 according to the operation signal output from the operation device 4.

In the present embodiment, as shown in FIG. 4, the discharge flow rate of the main pump 22 is minimized when at least the secondary pressure output from the electromagnetic proportional valve 61 is the minimum value P1, and is output from at least the electromagnetic proportional valve 61. When the secondary pressure is the maximum value P2, the discharge flow rate of the main pump 2 becomes maximum. However, the range in which the discharge flow rate of the main pump 22 is maintained to the minimum does not necessarily have to coincide with the range in which the control pressure Pc is from zero to the minimum value P1, and may be narrower than that range. Similarly, the range in which the discharge flow rate of the main pump 22 is maintained at the maximum does not necessarily have to coincide with the range in which the control pressure Pc is the maximum value P2 or more, and may be narrower than that range.

An emergency line 71 is branched from the primary pressure line 65 between the electromagnetic proportional valve 61 and the auxiliary pump 23, and this emergency line 71 is connected to the tank. The emergency line 71 is provided with a pair of diaphragms 74 and 75.

A switching valve 8A is provided on the secondary pressure line 62 and the emergency line 71 between the electromagnetic proportional valve 61 and the regulator 5. The switching valve 8A divides the secondary pressure line 62 into a first flow path 64 on the electromagnetic proportional valve 61 side and a second flow path 63 on the regulator 5 side, and divides the emergency line 71 into a pair of throttles 74 and 75. It is provided so as to divide between the upstream flow path 72 and the downstream flow path 73.

The switching valve 8A is a pilot type that operates in response to the secondary pressure of the electromagnetic proportional valve 61. The switching valve 8A blocks the first flow path 64 of the secondary pressure line 62 at the neutral position (the position on the left side in FIG. 1), and the upstream flow path 72 of the emergency line 71 is connected to the downstream flow path 73 and the secondary flow path 73. It communicates with the second flow path 63 of the pressure line 62.

When the secondary pressure of the electromagnetic proportional valve 61 exceeds the set value α, the switching valve 8A is switched to the operating position (right position in FIG. 1) by the secondary pressure. At the operating position, the switching valve 8A communicates the first flow path 64 of the secondary pressure line 62 with the second flow path 63 and blocks the upstream flow path 72 and the downstream flow path 73 of the emergency line 71.

As shown in FIG. 3, the set value α is set smaller than the minimum value P1 of the secondary pressure of the electromagnetic proportional valve 61 corresponding to the pilot pressure output from the operating device 4. That is, when the electromagnetic proportional valve 61 is normal, the switching valve 8A is located at the operating position.

As described above, in the hydraulic system 1A of the present embodiment, when the electromagnetic proportional valve 61 is normal, the switching valve 8A is located at the operating position, so that the secondary pressure of the electromagnetic proportional valve 61 is the secondary pressure line 62. It acts on the flow control piston 56 of the regulator 5 through. Therefore, the tilt angle (discharge flow rate) of the pump can be controlled by the electromagnetic proportional valve 61. On the other hand, when the electromagnetic proportional valve 61 does not function normally and its secondary pressure becomes zero, the switching valve 8A switches to the neutral position, and the hydraulic oil flows from the auxiliary pump 23 to the tank through the emergency line 71. It flows. As a result, the intermediate pressure Pm between the pair of throttles 74 and 75 in the emergency line 71 acts on the flow control piston 56 of the regulator 5 through the second flow path 63 of the secondary pressure line 62. As a result, the discharge flow rate of the main pump 22 can be secured to some extent (Qm in FIG. 4). The emergency line 71 passing through the switching valve 8A may be relatively short, and the regulator 5 does not require a conventional horsepower control piston and only needs a pressure receiving chamber 5c for the flow rate control piston 56. Therefore, the above effect can be obtained with a simple structure. As a result, the regulator 5 can be made smaller than the conventional one, and the cost can be reduced as compared with the conventional one.

<Modification example>
The control device 9 can determine whether or not the electromagnetic proportional valve 61 functions normally from the monitoring of the command current supplied to the electromagnetic proportional valve 61. Here, the case where the electromagnetic proportional valve 61 does not function normally means that the electromagnetic proportional valve 61 itself fails (disconnection), the electrical wiring extending to the electromagnetic proportional valve 61 is disconnected, the control device 9 or the electromagnetic proportional valve 61 This is the case when a poor contact (non-energized) occurs in the connector of. The control device 9 does not have to change the rotation speed of the engine 21 even when it is determined that the electromagnetic proportional valve 61 does not function normally. However, when the control device 9 determines that the electromagnetic proportional valve 61 does not function normally, the rotation speed of the engine 21 is set to the vicinity of the rotation speed Na where the engine torque is maximum (for example, of Na), as shown in FIG. It may be adjusted within the range of ± 20%). This modification can also be applied to the second embodiment described later.

Depending on the type of machine on which the hydraulic system 1A is mounted, a selection switch for selecting the rotation speed of the engine 21 kept constant by the control device 9 from a plurality of values may be provided. Therefore, when the electromagnetic proportional valve 61 does not function normally, the rotation speed of the engine 21 may be near the rated rotation speed Nr, or may be a considerably low rotation speed Nb.

As shown in FIG. 5A, a discharge flow rate limiting line is defined in the main pump 22 so that the pump torque of the main pump 22 does not exceed the engine torque. The discharge flow rate limit line is highest when the engine torque is maximum as shown by the solid line in FIG. 5 (a), and when the engine torque is low, it is correspondingly as shown by the alternate long and short dash line in FIG. 5 (a). Only the discharge flow rate limit line becomes lower. Therefore, when the rotation speed of the engine 21 is not changed when the electromagnetic proportional valve 61 does not function normally, the discharge flow rate becomes constant as shown by the alternate long and short dash line in FIG. In order to match the minimum value of the discharge flow rate limit line, the maximum value of the pump torque with respect to the pump discharge pressure must be set considerably low as shown by the alternate long and short dash line in FIG. 5 (b).

On the other hand, if the rotation speed of the engine 21 when the electromagnetic proportional valve 61 does not function normally is adjusted to the vicinity of the rotation speed Na where the engine torque is maximized as in this modification, the result is shown in FIG. 5 (b). As shown by the broken line, the maximum value of the pump torque with respect to the pump discharge pressure when the electromagnetic proportional valve 61 does not function normally can be set to a certain degree. Therefore, the intermediate pressure Pm between the pair of throttles 74 and 75 is increased to some extent, and as shown by the broken line in FIG. 5A, the discharge flow rate of the pump when the electromagnetic proportional valve 61 does not function normally is increased. Can be secured.

(Second Embodiment)
FIG. 5 shows a hydraulic system 1B according to a second embodiment of the present invention. In the present embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and duplicate description will be omitted.

In the first embodiment, the switching valve 8A which is a two-position valve is adopted, but in this embodiment, the switching valve 8B which is a three-position valve is adopted. Other configurations in the second embodiment are the same as those in the first embodiment.

The switching valve 8B is switched between the neutral position (left position in FIG. 7) and the operating position (center position in FIG. 7), similarly to the switching valve 8A in the first embodiment. That is, the switching valve 8B is switched from the neutral position to the operating position when the secondary pressure of the electromagnetic proportional valve 61 exceeds the set value α (corresponding to the first set value of the present invention).

Further, in the present embodiment, when the secondary pressure of the electromagnetic proportional valve 61 exceeds the set value β (corresponding to the second set value of the present invention), the switching valve 8B reaches the limit position (right position in FIG. 7). Can be switched. As shown in FIG. 8, the set value β is equal to or greater than the maximum value P2 of the secondary pressure of the electromagnetic proportional valve 61 according to the pilot pressure (operation signal) output from the operating device 4, and the auxiliary pump 23. It is lower than the discharge pressure.

At the limit position, the switching valve 8B blocks the first flow path 64 of the secondary pressure line 62 as well as the neutral position, and also blocks the upstream flow path 72 of the emergency line 71 with its downstream flow path 73 and the secondary pressure. It communicates with the second flow path 63 of the line 62.

Also in this embodiment, the same effect as that of the first embodiment can be obtained. Further, in the present embodiment, even if the electromagnetic proportional valve 61 does not function normally and its secondary pressure becomes equal to the primary pressure, the switching valve 8B is switched to the limit position which performs the same function as the neutral position. , The discharge flow rate of the main pump 22 can be secured to some extent.

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

For example, the pair of throttles 74, 75 may be built in the switching valve (8A or 8B). Further, the switching valve (8A or 8B) and the electromagnetic proportional valve 61 may be incorporated in the regulator 5.

1A, 1B Hydraulic system 21 Engine 22 Main pump 23 Sub pump 4 Operating device 41 Operating unit 5 Regulator 56 Flow control piston 61 Electromagnetic proportional valve 62 Secondary pressure line 63 Second flow path 64 First flow path 65 Primary pressure line 71 Emergency Time line 72 Upstream flow path 73 Downstream flow path 74,75 Squeezing 8A, 8B Switching valve 9 Control device

Claims (3)

An operation device that outputs an operation signal according to the amount of operation on the operation unit,
Variable capacity type main pump and
A regulator that includes a flow control piston and increases the tilt angle of the main pump as the control pressure acting on the flow control piston increases.
With the auxiliary pump
An electromagnetic wave that is connected to the regulator by a secondary pressure line and is connected to the auxiliary pump by a primary pressure line, and outputs a higher secondary pressure as the control pressure to the regulator as the operation signal output from the operation device becomes larger. Proportional valve and
An emergency line with a pair of throttles that branches off from the primary pressure line and connects to the tank.
The secondary pressure line is divided into a first flow path on the electromagnetic proportional valve side and a second flow path on the regulator side, and the emergency line is divided into an upstream flow path and a downstream flow path between the pair of throttles. It is a switching valve provided so as to be divided into the above, and in the neutral position, the first flow path is blocked and the upstream flow path is communicated with the downstream flow path and the second flow path, and the electromagnetic proportional valve is provided. When the secondary pressure of the above exceeds the set value, the secondary pressure switches the first flow path to the operating position that communicates with the second flow path and blocks the upstream flow path and the downstream flow path. Switching valve and
A command current is sent to the electromagnetic proportional valve so that the electromagnetic proportional valve outputs a secondary pressure between a minimum value and a maximum value larger than the set value according to an operation signal output from the operation device. Control device to supply and
A hydraulic system. Further including an engine controlled by the control device for driving the main pump and the sub pump.
The control device adjusts the engine speed to the vicinity of the maximum engine torque when it is determined from the monitoring of the command current supplied to the electromagnetic proportional valve that the electromagnetic proportional valve does not function normally. The hydraulic system according to claim 1. The set value is the first set value.
The maximum value of the secondary pressure of the electromagnetic proportional valve according to the operation signal output from the operating device is equal to or less than the second set pressure lower than the discharge pressure of the auxiliary pump.
When the secondary pressure of the electromagnetic proportional valve exceeds the second set value, the switching valve blocks the first flow path and uses the upstream flow path as the downstream flow path and the second flow path. The hydraulic system according to claim 1 or 2, which communicates with each other.

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