JP2009190538A - Circuit for operation fluid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit for an operation fluid suppressing generation of cavitation in a suction flow passage of an emergency pump. <P>SOLUTION: The circuit 1 for the operation fluid is provided with: a first pump 11 for feeding the operation fluid to a steering device 3; a second pump 12 for feeding the operation fluid to the other device 10 other than the steering device 3; the emergency pump 13 driven by rotation motive force of a wheel 101a and feeding the operation fluid to the steering device 3; a return flow passage 14 for returning the operation fluid fed to the other device 10 to a tank 2; a first suction flow passage 15 provided between the tank 2 and the emergency pump 13; a first check valve 16 provided on the first suction flow passage 15 and shutting off flow of the operation fluid to the tank 2; and a second suction flow passage 17 branched from the return flow passage 14 and connected to the emergency pump 13 side from the first check valve 16 in the first suction flow passage 15. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a working fluid circuit provided in a vehicle such as a wheel crane. In particular, the present invention relates to a working fluid circuit provided in a vehicle including a steering device.

2. Description of the Related Art Conventionally, a hydraulic circuit described in Patent Document 1 is known as a working fluid circuit provided in a vehicle. This hydraulic circuit is driven by the rotational power of the steering pump for supplying hydraulic oil to the steering valve via the hydraulic supply flow path, sucks the hydraulic oil in the tank, and supplies the hydraulic oil to the steering valve Possible emergency pumps. And a return flow path for returning the hydraulic oil discharged from the emergency pump to the tank, an emergency supply flow path for flowing the hydraulic oil discharged from the emergency pump to the hydraulic pressure supply path, and the return flow path and the emergency flow path. And an emergency switching valve for switching to any one of the supply flow paths. The emergency switching valve is switched by the discharge side pressure of the steering pump.
According to this, even when an abnormality occurs in the steering pump, the hydraulic oil can be supplied to the steering cylinder by the operation of the emergency pump. You can turn to

JP 2001-171505 A

  However, in the hydraulic circuit described in Patent Document 1, the emergency pump is configured to suck up the hydraulic oil only from the tank and supply it to the steering valve. Therefore, when the vehicle is traveling at a high speed, the emergency pump is operated by the rotational power of the wheels rotating at a high speed, so that a large amount of hydraulic fluid is sucked up from the tank. In this case, there is a problem that cavitation is likely to occur in the suction flow path for sucking the hydraulic oil up to the emergency pump, and the inner wall of the suction flow path and the emergency pump are likely to be damaged.

  In view of the above circumstances, an object of the present invention is to provide a working fluid circuit capable of suppressing the occurrence of cavitation in a suction flow path of an emergency pump.

Means and effects for solving the problems

The present invention relates to a working fluid circuit provided in a vehicle such as a wheel crane. In particular, the present invention relates to a working fluid circuit provided in a vehicle including a steering device.
The working fluid circuit according to the present invention has the following features to achieve the above object. In other words, the working fluid circuit of the present invention includes the following features alone or in combination.

  In order to achieve the above object, a first feature of a working fluid circuit according to the present invention is a working fluid circuit in a vehicle including a steering device that operates by supplying the working fluid. A first pump that supplies a working fluid to a device, a second pump that supplies working fluid from a tank to another device other than the steering device, and an emergency device that is driven by the rotational power of wheels and supplies the working fluid to the steering device A pump, a return flow path for returning the working fluid supplied to the other device by the second pump to the tank, a first suction flow path provided between the tank and the emergency pump, and the first Provided in the suction flow path to block the flow of working fluid from the emergency pump to the tank and to operate from the tank to the emergency pump. A first check valve that allows fluid flow, and a second suction flow that branches off from the return flow path and is connected to the emergency pump side of the first suction flow path relative to the first check valve. Road.

According to this configuration, the emergency pump can suck the working fluid flowing through the return flow path via the second suction flow path. In this case, it is possible to suppress the occurrence of cavitation in the suction flow path for sucking the working fluid up to the emergency pump by sucking the working fluid in the return flow path having back pressure. This makes it possible to prevent damage to the suction flow path and the emergency pump. Moreover, the piping which forms a suction flow path can be made thin, and piping space can be reduced.
In addition, by having a 1st check valve, it can prevent that the working fluid which flows in into a 1st suction flow path via a 2nd suction flow path from a return flow path returns to a tank.

  The second feature of the working fluid circuit according to the present invention is that, in the second suction channel, the flow of the working fluid from the first suction channel to the return channel is interrupted, and the return flow A second check valve having a cracking pressure higher than that of the first check valve, which allows a working fluid to flow from the passage to the first suction flow path.

Here, when an abnormality occurs and the first pump and the second pump are stopped, the flow of the working fluid to the tank from another device to which the working fluid is supplied from the second pump is stopped. . In this case, when the emergency pump is activated by the rotation of the wheel, the working fluid may be sucked into the emergency pump from the tank via the return flow path and the second suction flow path. That is, backflow may occur from the tank side to the second suction channel in the return channel. Due to the occurrence of the back flow, for example, when a filter for removing foreign matter is installed in the flow path from the tank to the second suction flow path, there is a possibility that the foreign matter attached to the filter flows into the emergency pump. This leads to breakage of the emergency pump and the steering device and causes a problem.
However, according to the configuration having the second feature, the first check valve opens before the second check valve because the cracking pressure of the second check valve is larger than that of the first check valve. The working fluid can be sucked up to the emergency pump using only the first suction flow path. Thereby, it is possible to prevent a back flow from occurring from the tank side to the second suction channel in the return channel.

  Further, the third feature of the working fluid circuit according to the present invention is that the working fluid flows from the tank to the branch position on the tank side of the return flow path from the branch position to the second suction flow path. And a third check valve that allows the flow of the working fluid from the branch position to the tank.

  According to this configuration, the third check valve can reliably prevent a backflow from occurring from the tank side to the second suction flow path in the return flow path.

  A fourth feature of the working fluid circuit according to the present invention is that the third check valve has an urging member for applying a predetermined cracking pressure.

  According to this configuration, a back pressure corresponding to the urging force by the urging member of the third check valve can be applied to the working fluid that flows from the other device through the return flow path to the third check valve. It becomes possible. Thereby, it becomes possible to suck in the working fluid having a larger back pressure with the emergency pump, and it is possible to more reliably suppress the occurrence of cavitation in the suction flow path.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is an overall view showing a wheel crane 100 (vehicle) provided with a hydraulic circuit (working fluid circuit) according to a first embodiment of the present invention.

  The wheel crane 100 includes a lower traveling body 102 provided with wheels 101a and 101b, an upper revolving body 104 mounted on the lower traveling body 102 via a swivel bearing 103 so as to be rotatable about a vertical axis, A cab 105 provided on the revolving structure 104 and serving as a cab during traveling and a cockpit during crane operation; a main jib 106 provided on the upper revolving structure 104 and extending toward the front of the cab 105; And a supplemental jib 107 connected to the leading end of the jib 106 in the extending direction. Note that FIG. 1 shows a state in which the lower traveling body 102 is supported from the ground by an outrigger 102a driven by hydraulic pressure during crane work.

  In the wheel crane 100, the main jib 106 is formed by extending and contracting a hydraulic cylinder device 106 a configured such that a cylinder body is fixed to the upper swing body 104 and a piston rod tip protruding from the cylinder body is fixed to the main jib 106. The undulation operation is performed. The outrigger 102a that supports the lower traveling body 102 has the cylinder body fixed to the lower traveling body 102, and the piston rod protrudes from the cylinder body toward the ground by the action of hydraulic pressure, so that the vehicle body is removed from the ground. It is lifted upward and supported. In the case of traveling, the piston rod is pulled back into the cylinder body, and the lower traveling body 102 is supported from the ground by the wheels 101a and 101b.

  The wheel crane 100 is configured such that a pair of left and right wheels 101a and 101a connected by an axle is rotated by an engine power to run. When the vehicle travels, the steering wheel (not shown in FIG. 1) provided on the cab 105 is operated to turn left or right through a hydraulic steering device (not shown in FIG. 1) driven by hydraulic pressure. It is possible to operate the pair of left and right wheels 101a and 101a so as to face the left or the right direction as possible.

  As described above, the wheel crane 100 is provided with a plurality of hydraulic devices (hydraulic cylinder device 106a, outrigger 102a, hydraulic steering device, etc.) driven by hydraulic pressure, and supplies hydraulic oil to the plurality of hydraulic devices. A hydraulic circuit 1 is provided. FIG. 2 is a diagram schematically showing the hydraulic circuit 1 provided in the wheel crane 100.

As shown in FIG. 2, the hydraulic circuit 1 is provided with a first pump 11, a second pump 12, and an emergency pump 13.
The first pump 11 can supply hydraulic oil from the tank 2 to the hydraulic steering device 3. The hydraulic oil in the hydraulic steering device 3 can be discharged to the tank 2.
The second pump 12 can supply hydraulic oil from the tank 2 to the hydraulic device 10 other than the hydraulic steering device 3 (for example, the hydraulic cylinder device 106a, the outrigger 102a, etc.).

  Here, the output shaft 6 a of the engine 6, the propeller shaft 5, and the drive shaft 7 a for driving the first pump 11 and the second pump 12 include a power divider 7 having a plurality of gears and the like. It is connected by. The power divider 7 is configured such that the rotational power of the engine 6 is transmitted to the propeller shaft 5 and the drive shaft 7a. Since the axles 4 of the wheels 101a and 101a are connected so as to rotate in accordance with the rotation of the propeller shaft 5, the wheels 101a and 101a are driven via the propeller shaft 5 and the axle 4 by driving the engine 6. Can be rotated. As a result, the wheel crane 100 can travel. Further, the first pump 11 and the second pump 12 are driven by the driving of the engine 6, and hydraulic oil can be supplied to the hydraulic steering device 3 and the hydraulic device 10.

  Since the emergency pump 13 is connected to the propeller shaft 5, the emergency pump 13 is driven by the rotation of the propeller shaft 5. The emergency pump 13 performs an operation according to the rotation speed of the propeller shaft 5. Therefore, even when the engine 6 is not driven, the emergency pump 13 is driven by the rotation of the propeller shaft 5 by the rotational power of the wheels 101a and 101a. The emergency pump 13 can supply hydraulic fluid to the hydraulic steering device 3 by being driven. That is, according to this configuration, the emergency pump 13 is driven and hydraulic oil is supplied to the hydraulic steering device 3 regardless of whether the engine 6 is driven or stopped while the vehicle is traveling.

  In the case where the first pump 11 is normally driven to supply hydraulic oil to the hydraulic steering device 3, the hydraulic oil supplied from the emergency pump 13 to the hydraulic steering device 3 is operated by the hydraulic steering device 3. Without being contributed to the tank 2. On the other hand, when the supply of hydraulic fluid from the first pump 11 to the hydraulic steering device 3 is cut off, for example, when the first pump 11 is stopped, the operation supplied from the emergency pump 13 to the hydraulic steering device 3 The hydraulic steering device 3 is configured to operate by the action of oil.

  The hydraulic steering device 3 includes, for example, a steering cylinder. The switching valve for switching the hydraulic oil supply flow path is switched based on the operation of the steering handle 8 so that the piston rod of the steering cylinder moves forward and backward. The piston rod is connected to the axle 4, and the wheels 101a and 101a can be moved to the left and right turn positions by moving forward and backward.

  The hydraulic circuit 1 is provided in the return flow path 14 between the tank 2 and the hydraulic device 10, the first suction flow path 15 between the tank 2 and the emergency pump 13, and the first suction flow path 15. The first check valve 16 and the second suction flow path 17 between the return flow path 14 and the first suction flow path 15 are provided.

  The return flow path 14 is a flow path provided between the tank 2 and the hydraulic apparatus 10, and includes a flow path 14a on the hydraulic apparatus 10 side and a flow path 14b on the tank 2 side. The hydraulic oil supplied to the hydraulic device 10 by the second pump 12 can be returned to the tank 2 through the return flow path 14. A return filter 19 is provided in the flow path 14b on the tank 2 side. The return filter 19 can remove foreign matters mixed in the hydraulic fluid flowing from the hydraulic device 10 to the tank 2.

  The first suction flow path 15 is a flow path provided between the tank 2 and the emergency pump 13, and includes a flow path 15 a communicating with the emergency pump 13 and the flow path 15 a to the first check valve 16. A flow path 15b to be connected and flow paths 15c and 15d communicating from the first check valve 16 to the tank 2 are provided. The hydraulic oil in the tank 2 can be supplied to the emergency pump 13 via the first suction flow path 15.

  The first check valve 16 is provided in the first suction flow path 15 to block the flow of hydraulic oil from the emergency pump 13 to the tank 2 and to flow the hydraulic oil from the tank 2 to the emergency pump 13. It is an acceptable valve.

The second suction flow path 17 branches from the return flow path 14 and is connected to a flow path 15 a located on the emergency pump 13 side of the first check flow path 15 in the first suction flow path 15. The second check valve 18 is provided.
The The second suction flow path 17 communicates the flow path 17 a that communicates the flow path 15 a of the first suction flow path 15 and the second check valve 18, and the second check valve 18 and the return flow path 14. And a flow path 17b. The hydraulic oil in the return flow path 14 can be supplied to the emergency pump 13 via the second suction flow path 17.

  The second check valve 18 blocks the flow of hydraulic oil from the first suction flow path 15 to the return flow path 14 in the second suction flow path 17 and from the return flow path 14 to the first suction flow path 15. This valve allows the flow of hydraulic oil. The second check valve 18 includes a spring that biases the valve to a closed state so that the cracking pressure is higher than that of the first check valve 16. Here, the cracking pressure refers to a pressure at which the hydraulic oil pressure in the flow path connected to the check valve increases and the valve starts to open.

Hereinafter, the operation of the hydraulic circuit 1 having the above-described configuration will be described.
During normal traveling of the wheel crane 100, the axle 4 is rotationally driven by the engine 6 via the power divider 7. The hydraulic steering device 3 is supplied with hydraulic oil from a first pump 11 driven by the engine 6. Thereby, the steering operation which changes direction of wheel 101a * 101a using the hydraulic steering device 3 is possible. At this time, the emergency pump 13 installed on the propeller shaft 5 connected to the axle 4 is also driven.

  Here, at the branch position of the return flow path 14 to the second suction flow path 17, the pressure loss when the hydraulic oil passes through the return filter 19 or the pipe pressure loss in the flow path 14b on the tank 2 side from the branch position. Thus, a pressure higher than at least the pressure in the tank 2 (hereinafter referred to as tank pressure) is generated. Therefore, the hydraulic oil is supplied from the return flow path 14 side to the first suction flow path 15 side by setting the cracking pressure of the second check valve 18 lower than the pressure generated on the return flow path 14 side. . As a result, hydraulic oil is supplied from the return flow path 14 to the suction port of the emergency pump 13 via the second suction flow path 17 and the flow path 15 a of the first suction flow path 15. In this way, the pressure of the hydraulic oil supplied to the suction port of the emergency pump 13 is configured to be higher than the tank pressure by using a pressure higher than the tank pressure generated in the return flow path 14. Thus, the occurrence of cavitation in the suction flow path for sucking the working fluid up to the emergency pump 13 is suppressed.

Next, the case where hydraulic fluid is not flowing from the hydraulic apparatus 10 to the tank 2 via the return flow path 14 will be described below.
An example will be described in which the wheel crane 100 is pulled by another vehicle in a state where the driving of the first pump 11 and the second pump 12 is stopped due to a failure of the engine 6. In this case, the hydraulic oil does not flow from the hydraulic apparatus 10 to the tank 2 via the return flow path 14 due to the stop of the second pump 12. However, the emergency pump 13 is driven via the axle 4 and the propeller shaft 5 by being pulled and the wheels 101a and 101a are rotated. As a result, hydraulic oil is supplied from the emergency pump 13 to the hydraulic steering device 3. During towing, since the connection between the propeller shaft 5 and the engine 6 is usually removed in order to reduce the towing load, the first pump 11 and the second pump 12 are driven by the rotational power of the propeller shaft 5. There is no.

  At this time, the pressure in the flow path on the return flow path 14 side of the second check valve 18 is substantially equal to the tank pressure. That is, the pressure of the flow path 17b on the return flow path 14 side connected to the second check valve 18 and the flow path 15c on the side opposite to the second check valve 18 connected to the first check valve 16 (first The pressure on the suction flow path side of the pump 11 and the second pump 12 is substantially equal. In this case, since the cracking pressure of the second check valve 18 is configured to be higher than that of the first check valve 16, the first check valve 16 is not opened without opening the second check valve 18. The hydraulic oil is opened and supplied to the emergency pump 13. That is, hydraulic fluid is not supplied to the emergency pump 13 from the return flow path 14 side. Thereby, the reverse flow (flow from the tank 2 to the 2nd suction flow path 17) of the return flow path 14 can be prevented.

  During towing, since a normal speed limit is provided, the rotation of the propeller shaft 5 does not become excessively high. Therefore, the flow rate sucked by the emergency pump 13 that is driven in conjunction with the propeller shaft 5 is not excessively increased. Therefore, cavitation in the suction flow path is unlikely to occur.

  As described above, the hydraulic circuit 1 according to the present embodiment is a hydraulic circuit in a vehicle including the hydraulic steering device 3 that operates by supplying hydraulic oil. The hydraulic circuit 1 includes a first pump 11 that supplies hydraulic oil from the tank 2 to the hydraulic steering device 3, and a second pump that supplies hydraulic oil from the tank 2 to another hydraulic device 10 other than the hydraulic steering device 3. 12, the emergency pump 13 that is driven by the rotational power of the wheels 101a and 101a and supplies hydraulic oil to the hydraulic steering device 3, and the hydraulic oil supplied to the other hydraulic device 10 by the second pump 12 is supplied to the tank 2. Return channel 14, a first suction channel 15 provided between the tank 2 and the emergency pump 13, and an operation from the emergency pump 13 to the tank 2 provided in the first suction channel 15. A first check valve 16 that cuts off the flow of oil and allows the flow of hydraulic oil from the tank 2 to the emergency pump 13 and a return flow path 14 are branched to form a first suction line. In ® emission passage 15 includes a second suction passage 17 connected to the emergency pump 13 side of the first check valve 16, the.

  According to this configuration, the emergency pump 13 can suck the hydraulic oil flowing through the return flow path 14 via the second suction flow path 17. In this case, cavitation occurs in the suction flow path (second suction flow path 17 and flow path 15a) for sucking the hydraulic oil to the emergency pump 13 by sucking the hydraulic oil in the return flow path 14 having back pressure. It becomes possible to suppress. This makes it possible to prevent damage to the inner wall of the suction flow path and the emergency pump 13.

  Further, since the pressure of the hydraulic oil flowing through the suction flow path can be increased, the pipes that form the first suction flow path 15 and the second suction flow path 17 and the like are narrowed while suppressing the occurrence of cavitation. Is possible. Thereby, piping space can be reduced.

  In addition, since the first check valve 16 is provided, the hydraulic oil that flows from the return flow path 14 to the first suction flow path 15 via the second suction flow path 17 passes through the flow paths 15b and 15c and the tank 2. Can prevent backflow.

  Further, the hydraulic circuit 1 according to the first embodiment interrupts the flow of hydraulic oil from the first suction flow path 15 to the return flow path 14 in the second suction flow path 17 and from the return flow path 14 to the first flow path. A second check valve 18 having a cracking pressure larger than that of the first check valve 16 and allowing the flow of hydraulic oil to the suction flow path 15 is provided.

  According to this configuration, since the cracking pressure of the second check valve 18 is larger than that of the first check valve 16, the second reverse valve is applied even when the back pressure larger than the tank pressure does not act on the return flow path 14. The first check valve 16 is opened before the stop valve 18, and the hydraulic oil can be sucked up to the emergency pump 13 using only the first suction flow path 15. Thereby, it is possible to prevent a back flow from occurring from the tank 2 side to the second suction channel 17 in the return channel 14. As a result, foreign matter adhering to the return filter 19 can be prevented from flowing into the emergency pump 13, and the emergency pump 13 and the hydraulic steering device 3 can be prevented from being damaged due to the foreign matter flowing in.

(Second Embodiment)
Next, the hydraulic circuit 20 according to the second embodiment of the present invention will be described. FIG. 3 is a diagram schematically illustrating the hydraulic circuit 20 according to the second embodiment. In addition, the same code | symbol is attached | subjected to the same member as the hydraulic circuit 1 which concerns on the said 1st Embodiment, and description is abbreviate | omitted.

  As shown in FIG. 3, the hydraulic circuit 20 is provided with a third check valve 21 on the tank 2 side with respect to the branch position X to the second suction flow path 17 in the return flow path 14. In the hydraulic circuit 20, a check valve 28 having no spring blocks the flow in the same direction as the second check valve 18 instead of the spring-loaded second check valve 18 in the hydraulic circuit 1. It is installed to do. In these points, the hydraulic circuit 20 in the second embodiment is different from the hydraulic circuit 1 in the first embodiment.

  The third check valve 21 is provided to block the flow of hydraulic oil from the tank 2 to the branch position X and to allow the flow of hydraulic oil from the branch position X to the tank 2. The third check valve 21 includes a spring that applies a predetermined cracking pressure.

  According to this configuration, since the third check valve 21 blocks the flow of hydraulic oil from the tank 2 to the second suction flow path 17, the return flow path 14 from the tank 2 side to the second suction flow path 17. It is possible to reliably prevent the occurrence of backflow. As a result, foreign matter adhering to the return filter 19 can be reliably prevented from flowing into the emergency pump 13, and the emergency pump 13 and the hydraulic steering device 3 can be reliably prevented from being damaged due to the foreign matter flowing in.

  In the second embodiment, the check valve 28 does not have a biasing member that applies a predetermined cracking pressure. Therefore, the cracking pressure of the check valve 28 is substantially equal to the cracking pressure of the first check valve 16. However, since the third check valve 21 is provided, for example, even when the wheel crane 100 is pulled when the engine 6 is stopped, the emergency pump 13 passes from the tank 2 through the check valve 28. There is no flow of hydraulic oil.

  In addition, since the third check valve 21 is configured as a check valve with a spring, the third check valve 21 is configured to prevent the hydraulic oil flowing from the hydraulic device 10 through the return flow path 14 to the third check valve 21. It becomes possible to give the back pressure corresponding to the urging | biasing force with the spring which 3 check valve 21 has. As a result, the emergency pump 13 can suck hydraulic oil having a larger back pressure, and can more reliably suppress the occurrence of cavitation in the suction flow path. The predetermined cracking pressure is applied not only when the predetermined cracking pressure is applied to the check valve by the biasing force of the spring but also by applying the biasing force of another elastic member or the pilot pressure of the pilot flow path. You can also

  In addition to the above configuration, a large back pressure is applied to the hydraulic oil passing through the return flow path 14 by forming a throttle flow path with a partially reduced pipe diameter in the flow path 14 b of the return flow path 14. It is possible. Further, by making the return filter 19 fine or providing a plurality of filters, it is possible to apply a large back pressure to the hydraulic oil passing through the return flow path 14.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims.

  In the present embodiment, the vehicle (wheel crane 100) configured to travel by rotating the propeller shaft 5 by driving the engine 6 is exemplified, but the present invention is not limited to this, and the vehicle travels by a hydraulic motor or an electric motor. Even if it exists, this invention is applicable similarly.

1 is an overall view showing a wheel crane including a hydraulic circuit according to a first embodiment of the present invention. It is a figure which shows typically the hydraulic circuit provided in the wheel crane. It is a figure which shows typically the hydraulic circuit which concerns on 2nd Embodiment.

Explanation of symbols

1,20 Hydraulic circuit (working fluid circuit)
2 Tank 3 Hydraulic steering device (steering device)
10 Hydraulic equipment (other equipment)
11 First pump 12 Second pump 13 Emergency pump 14 Return flow path 15 First suction flow path 16 First check valve 17 Second suction flow path 18 Second check valve 21 Third check valve 100 Wheel crane ( vehicle)
101a wheels

Claims (4)

A working fluid circuit in a vehicle including a steering device that operates by supplying a working fluid,
A first pump for supplying a working fluid from a tank to the steering device;
A second pump for supplying a working fluid from a tank to a device other than the steering device;
An emergency pump that is driven by the rotational power of the wheels and supplies the working fluid to the steering device;
A return flow path for returning the working fluid supplied to the other device by the second pump to the tank;
A first suction channel provided between the tank and the emergency pump;
A first check valve that is provided in the first suction flow path, blocks a flow of the working fluid from the emergency pump to the tank, and allows a flow of the working fluid from the tank to the emergency pump;
A second suction flow path branched from the return flow path and connected to the emergency pump side of the first check flow path with respect to the first check valve;
A working fluid circuit comprising:   In the second suction channel, the flow of the working fluid from the first suction channel to the return channel is blocked, and the flow of the working fluid from the return channel to the first suction channel is allowed. The working fluid circuit according to claim 1, further comprising a second check valve having a cracking pressure higher than that of the first check valve.   The flow of the working fluid from the tank to the branch position is blocked and the flow of the working fluid from the branch position to the tank is closer to the tank than the branch position to the second suction flow path in the return flow path. The working fluid circuit according to claim 1, further comprising a third check valve that allows   The working fluid circuit according to claim 3, wherein the third check valve includes a biasing member that applies a predetermined cracking pressure.

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