JP2000179504A - Hydraulic control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic control unit which is always able to control the lowering speed of a cylinder as conformed to the shift amount of a selector valve, and that it will not give incompatible feeling to an operator. SOLUTION: This hydraulic control unit is equipped with a pump P, a single- acting cylinder A connected to the pump P, and a selector valve 1 to be installed in space between the pump P and the single-acting cylinder A interconnecting the single-acting cylinder A with the pump P or with a tank T, and controlling a lowering speed in the single-acting cylinder A to be lowered by its own weight and load by the selector valve 1. It is so constituted that a flow control valve R is connected between the single-acting cylinder A and the selector valve 1 or between the valve 1 and the tank T, and in time of the cylinder A going down, a pressure differential in front and in the rear of the selector valve 1 is kept to be constant by the flow control valve R.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control device for controlling a lowering speed of a cylinder used for a forklift or the like.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a hydraulic control device used in a forklift. 3 includes a switching valve 1 for controlling a lift cylinder A which is a single-acting cylinder, a switching valve 2 for controlling a tilt cylinder not shown, and a switching valve 3 for controlling an attachment cylinder also not shown. It has. Switching valve 1
The switching valve 2 is connected to the control flow path 4 in parallel, and the switching valve 3 is connected to the surplus flow path 5. The control flow path 4 and the surplus flow path 5 are connected to a compensator valve 6, and the compensator valve 6 is connected to a pump P via a supply flow path 7. The switching valves 1 and 2 are closed at the neutral position to shut off the control flow path 4 and the tank T side, while the switching valve 3 is opened at the neutral position to connect the surplus flow path 5 and the tank T side. I do.

The compensator valve 6 controls the control flow path 4 of the discharge amount of the pump P depending on the switching position.
And the flow rate to be allocated to the surplus flow path 5 side are determined. The switching position of the compensator valve 6 is determined by the first and second pilot chambers 6a and 6a.
b and the spring force of the spring 6c provided in the second pilot chamber 6b.

[0004] Upstream of the compensator valve 6,
A flow control valve 8 is connected, and a throttle 9 is provided downstream of the flow control valve 8. The upstream side of the throttle 9 is connected to the first pilot chamber 8 a of the flow control valve 8, and the downstream side is connected to the flow control valve 8.
Is connected to the second pilot chamber 8b. In addition, a damper orifice 10 is provided in a flow path leading to the first pilot chamber 8a.
Is provided. The flow control valve 8 thus configured has a throttle 9
Is maintained at a pressure corresponding to the spring force of the spring 8c to supply a constant flow rate downstream thereof.

[0005] A relief valve 12 for generating a pressure on the upstream side by the set pressure is connected downstream of the restrictor 9 to which a constant flow of the pressure oil is supplied. The pressure generated by the relief valve 12 is transmitted to a pilot chamber 1a of each of the switching valves 1, 2, and 3 via a pilot pressure flow path 18.
To 3a and 1b to 3b as pilot source pressures. The pilot source pressure is controlled by proportional electromagnetic pressure reducing valves 1c to 3c and 1d to 3d to act on the spools of the switching valves 1, 2, and 3, respectively. The pilot chambers 1a to 3a and 1b to 3b
Is discharged to the tank T via the discharge passages 19, 19.

The pressure oil upstream of the relief valve 12 is also guided to a first shuttle valve 14. This first shuttle valve 14 connects the second shuttle valve 15,
The second shuttle valve 15 is connected to a first load pressure flow path 16 that guides the load pressure of the lift cylinder A and a second load pressure flow path 17 that guides the load pressure of a tilt cylinder (not shown). Therefore, the first shuttle valve 14 selects the high pressure selected by the second shuttle valve 15 and the pressure on the upstream side of the relief valve 12 and guides the selected pressure to the second pilot chamber 6 b of the compensator valve 6.

The pressure on the upstream side of the switching valves 1 and 2 is led from the control flow path 4 to the first pilot chamber 6a opposite to the second pilot chamber 6b. Therefore, the compensator valve 6 operates with the balance between the pressure on the upstream side of the switching valves 1 and 2 and the set pressure of the relief valve 12, and the same with the pressure on the upstream side of the switching valves 1 and 2 and the lift cylinder A or FIG. The operation may be performed in balance with the load pressure of the tilt cylinder not shown. A damper orifice 13 is provided between the first shuttle valve 14 and the second pilot chamber 6b of the compensator valve 6.

On the other hand, a poppet valve 21 is connected between the lift cylinder A and the switching valve 1. The poppet valve 21 is for completely shutting off the return fluid of the lift cylinder A when the switching valve 1 is at the neutral position. By completely shutting off in this way, even if the return fluid of the lift cylinder A has a high pressure, the stroke position can be maintained. However, when the switching valve 1 moves to the left in the drawing, the poppet valve 21 is opened by the pressure oil of the pump P, and supplies the pressure oil to the lift cylinder A. Also, when the switching valve 1 is moved to the right in the drawing, the switching valve is opened to discharge the return oil from the lift cylinder A to the tank T. At this time, the poppet valve 21 operates as follows.

That is, when the pilot pressure is supplied to the pilot chamber 1a, the switching valve 1 moves rightward in the drawing, and the sub-spool 22 provided inside the switching valve 1 also switches. The flow path f connected to the spring chamber 21a of the poppet valve 21 and the flow path t communicating with the tank T communicate with each other via the sub spool 22. That is, the spring chamber 21a communicates with the tank T.

The spring chamber 21a has a lift cylinder A
Since the pressure is high due to its own weight and load, when it communicates with the tank T via the flow paths f and t as described above, the pressure oil is discharged. Then, the pressure oil of the lift cylinder A flows through the orifice 21b of the poppet valve 21, and a differential pressure is generated before and after the orifice 21b. Therefore, the poppet valve 21 opens, and the return oil of the lift cylinder A is discharged to the tank T via the switching valve 1. The lift cylinder A is connected to the tank via an orifice 25 and a cock 26. This is because the poppet valve 2
Even if 1 cannot be opened due to a malfunction, etc.
This is because the lift cylinder A can be lowered by opening 6. Reference numerals 11 and 20 in the figure are safety valves.

Next, the operation of the conventional device will be described.
While the switching valves 1 and 2 are maintained at the illustrated neutral positions, the pump P
Is driven, since the switching valves 1 and 2 are closed, no flow occurs in the control flow path 4 and the pressure on the upstream side of the switching valves 1 and 2 is increased by the first pilot chamber 6a of the compensator valve 6.
It is led to. The hydraulic oil selected by the first shuttle valve 14 is guided to the second pilot chamber 6 b of the compensator valve 6. At this time, since the switching valves 1 and 2 are closed, the lift cylinder A and the tilt cylinder No load pressure is occurring. Therefore, pressure oil upstream of the relief valve 12 is guided from the first shuttle valve 14 to the second pilot chamber 6b.

As described above, when pressure oil is led to both pilot chambers 6a and 6b, the compensator valve 6
Moves to a position where the action force of the pressure oil and the spring force of the spring 6c are balanced. However, when the switching valves 1 and 2 are closed, the pressure in the first pilot chamber 6a is higher. The compensator valve 6 moves leftward in the figure. Then, most of the pressure oil from the pump P flows to the surplus flow path 5 side. If the switching valve 3 is switched in this state, an attachment cylinder (not shown) operates.

When the switching valve 1 is switched from the above state to, for example, the right position in the figure, the pressure in the control flow path 4 decreases because the control flow path 4 and the lift cylinder A communicate with each other. Then, the pressure in the first pilot chamber 6a decreases, and the compensator valve 6 moves rightward by the spring force of the spring 6c. Therefore, the pressure oil of the pump P is supplied to the control passage 4
The pressure oil is supplied to the lift cylinder A via the switching valve 1 connected to the control flow path 4. At this time, a pressure difference is generated between the upstream side and the downstream side by the opening degree of the switching valve 1. Then, the upstream pressure is guided to the second pilot chamber 6 b of the compensator valve 6, and the downstream pressure is guided to the first shuttle valve 14 via the second shuttle valve 15.

The pressure oil guided to the first shuttle valve 14 corresponds to the load pressure of the lift cylinder A. When this load pressure becomes higher than the pressure on the upstream side of the relief valve 12, a high pressure is selected and the first pilot It is led to the chamber 6a. Therefore, the compensator valve 6 exerts a load sensing function on the lift cylinder A. That is, in this device, the plurality of cylinders are efficiently controlled by the compensator valve 6.

In the conventional apparatus as described above, a flow control valve 27 and a fixed throttle 28 are provided between the poppet valve 21 and the lift cylinder A. The first pilot chamber 27a of the flow control valve 27 is connected between the fixed throttle 28 and the lift cylinder A, and the second pilot chamber 27b is connected between the fixed throttle 28 and the flow control valve 27. A spring 27c is provided on the second pilot chamber 27b side. The flow control valve 27 thus configured is kept fully open at the time of normal operation. When the lift cylinder A is raised, the fully open state is maintained. That is, when the lift cylinder A rises, the high pressure upstream of the fixed throttle 28 is guided to the second pilot chamber 27b of the flow control valve 27, and the low pressure downstream of the fixed throttle 28 is guided to the first pilot chamber 27a. , The acting force on the side of the second pilot chamber 27a is superior. Therefore, when the lift cylinder A rises, the flow control valve 27 maintains the fully open state, and the supply oil to the lift cylinder A passes smoothly.

On the other hand, when lowering the lift cylinder A, the differential pressure generated before and after the fixed throttle 28 is
7c. That is, when the lift cylinder A descends, the first pilot chamber 2 of the flow control valve 27
A high pressure on the upstream side of the fixed throttle 28 is guided to 7a, and a low pressure on the downstream side of the fixed throttle 28 is guided to the second pilot chamber 27b. For this reason, the spool of the flow control valve 27 has the action force on the first pilot chamber 27a side and the second pilot chamber 27b
And the spring force of the spring 27c. Therefore, the differential pressure across the fixed throttle 28 is
The flow rate passing through the fixed throttle 28 is kept constant while maintaining the spring force of c. By keeping the flow rate passing through the fixed throttle 28 constant in this way, the maximum descending speed of the lift cylinder A is kept constant.

The reason why the maximum descending speed of the lift cylinder A is kept constant is as follows. That is,
If the descending speed of the lift cylinder A is too fast, danger may be involved. However, generally, the descending speed of the cylinder depends on the magnitude of the load. Therefore, the descent speed increases as the load increases, and the danger increases as the load increases. In order to avoid such a danger, in the conventional apparatus, when the lowering speed of the lift cylinder A becomes higher than a certain speed, the flow control valve 27 prevents the lowering speed of the lift cylinder A from increasing further. Is regulated. That is, the maximum lowering speed of the lift cylinder A is kept constant. In this manner, the maximum descending speed of the cylinder is kept constant, and the control is performed by the opening of the switching valve 1, that is, the switching amount in a control range equal to or lower than the maximum speed.

[0018]

In the above-mentioned conventional apparatus, when the lowering speed of the lift cylinder A becomes higher than a certain speed, the flow control valve 27 exhibits a function of keeping the maximum lowering speed constant. Becomes larger, the lowering speed of the lift cylinder A may reach the maximum even if the switching amount of the switching valve 1 is small. When the lift cylinder A reaches the maximum descending speed in a state where the switching amount of the switching valve 1 is small, there is a problem that the control range of the switching valve 1 is narrowed.

For example, when the load on the lift cylinder A increases, the pressure upstream of the fixed throttle 28 increases, so that the differential pressure across the fixed throttle 28 increases. Control valve 27 regulates the flow rate therethrough. In the state where the flow control valve 27 regulates the flow rate as described above, if the switching amount of the switching valve 1 on the downstream side is small, no matter how much the opening degree of the switching valve 1 is increased from this state, the flow rate passing therethrough Is the fixed aperture 2
8 is maintained at the maximum flow rate. That is, even if the opening of the switching valve 1 is increased to a certain amount or more, the flow rate passing therethrough does not change. As described above, even if the opening of the switching valve 1 is increased by a certain amount or more, if the flow rate does not change, the control range of the switching valve 1 is narrowed accordingly. And, as the control range of the switching valve 1 becomes narrower, the delicate control thereof becomes more difficult, and there is a problem that a skilled person is required eventually.

When the flow rate of the flow control valve 27 becomes equal to or higher than the set flow rate, the flow rate control valve 27 performs a flow rate control function of controlling the flow rate passing through the fixed throttle 28.
There is also a problem that when the 7 exerts the flow control function, the operator feels strange. That is, before the flow control valve 27 exerts the flow control function, the opening speed of the switching valve 1 controls the lowering speed of the lift cylinder A.
In this state, a fluid force proportional to the flow rate determined by the differential pressure across the switching valve 1 and the opening degree acts on the spool of the switching valve 1.

However, as described above, when the flow rate increases and the flow control valve 27 performs the flow control function, the flow rate passing therethrough is regulated. Thus, the flow control valve 27
Regulates the flow rate, the differential pressure across the flow control valve 27 increases, and the pressure downstream thereof decreases. When the pressure on the downstream side of the flow control valve 27 decreases in this way, the pressure on the upstream side of the switching valve 1 also decreases, and as a result, the differential pressure across the switching valve 1 decreases. When the differential pressure across the switching valve 1 decreases, the flow velocity of the fluid passing through the switching valve 1 decreases, and the fluid force also decreases. That is, when the flow control valve 27 performs the flow control function, the fluid force acting on the spool of the switching valve 1 suddenly decreases, causing a shock.
There has been a problem that this shock gives an uncomfortable feeling to the operator. An object of the present invention is to provide a hydraulic control device that can always control the lowering speed of a cylinder to a speed corresponding to the switching amount of a switching valve and does not give an uncomfortable feeling to an operator.

[0022]

According to a first aspect of the present invention, there is provided a pump, a single-acting cylinder connected to the pump, and a single-acting cylinder provided between the pump and the single-acting cylinder. In a hydraulic control device having a switching valve communicating with the tank or communicating with the tank, and controlling the descending speed of the single-acting cylinder descending by its own weight and load, the switching valve switches between the single-acting cylinder and the switching valve. A flow control valve is connected between the valve and the tank, and the pressure difference before and after the switching valve is kept constant by the flow control valve when the single-acting cylinder descends.

According to a second aspect of the present invention, a valve body, a main spool hole formed in the valve body, a main spool slidably incorporated in the main spool hole, and connected to the main spool hole and connected to a single-acting cylinder. Hydraulic control device that has a cylinder port connected to a main spool hole and a tank flow path that communicates with the main spool hole, and controls the return fluid discharged from the single-acting cylinder to the tank flow path by its own weight and load according to the switching amount of the main spool. Is assumed.

The second aspect of the present invention is based on the above-described apparatus, and a spool hole formed in the valve body and communicating with the cylinder port, is slidably incorporated in the spool hole, and is single-acting in accordance with the switching position. A spool that determines the communication opening between the cylinder and the main spool hole,
A first pilot chamber provided at one end of the spool, a second pilot chamber provided at the other end of the spool, a spring incorporated into the first pilot chamber and applying a spring force to the spool, and a first pilot chamber. A first flow path communicating with the tank; and a second flow path communicating the second pilot chamber with the single-acting cylinder. When the single-acting cylinder descends, the spool operates due to the pressure oil in the first pilot chamber. The main spool is stopped at a position where the total force of the force and the spring force of the spring balances the acting force of the pressure oil in the second pilot chamber, and the differential pressure between the upstream side and the downstream side of the main spool is kept constant. It is characterized by the following.

[0025]

1 and 2 show an apparatus according to an embodiment.
The circuit diagram shown in FIG. 1 omits the flow control valve 27 and the fixed throttle 28 of the above-described conventional example, while providing a flow control valve R between the poppet valve 21 and the switching valve 1. The first pilot chamber Ra of the flow control valve R is connected to the first load pressure passage 16, and the second pilot chamber Rb is connected between the flow control valve R and the switching valve 1. A spring Rc is provided on the first pilot chamber Ra side. Other configurations are the same as those of the related art, and therefore, the same components are denoted by the same reference numerals, and detailed description thereof will be omitted.

The flow control valve R is kept fully open at the time of normal operation. When the lift cylinder A is raised, the fully open state is maintained. That is, when the lift cylinder A is raised, the high pressure on the upstream side of the switching valve 1 is guided to the first pilot chamber Ra of the flow control valve R via the first load pressure flow path 16 and is switched to the second pilot chamber Rb. 1
Low pressure downstream of the first pilot chamber Ra
The working force of the side is superior. Therefore, when the lift cylinder A rises, the flow control valve R maintains the fully open state, and the supply oil to the lift cylinder A passes smoothly.

On the other hand, when lowering the lift cylinder A, the differential pressure generated before and after the switching valve 1 is maintained at an amount corresponding to the spring force of the spring Rc. That is, when the lift cylinder A is lowered, the low pressure downstream of the switching valve 1 is guided to the first pilot chamber Ra of the flow control valve R, and the high pressure upstream of the switching valve 1 is guided to the second pilot chamber Rb. Therefore, the spool of the flow control valve R is located at a position where the sum of the acting force of the pressure oil in the first pilot chamber Ra and the spring force of the spring Rc and the acting force of the pilot pressure in the second pilot chamber Rb are balanced. Is kept. Therefore, the differential pressure across the switching valve 1 is maintained at a level corresponding to the spring force of the spring Rc, regardless of the load on the lift cylinder A. If the differential pressure across the switching valve 1 is kept constant in this way, the lowering speed of the cylinder can always be controlled to a speed corresponding to the switching amount of the switching valve.

According to this embodiment, the flow control valve R
As a result, the differential pressure across the switching valve 1 does not suddenly change, so that the operator does not feel uncomfortable. In this embodiment, the flow control valve R is provided between the poppet valve 21 and the switching valve 1. However, the flow control valve R is provided in the flow path 48 on the downstream side of the switching valve 1, and this switching valve is provided. The pressure difference before and after 1 may be kept constant.

FIG. 2 shows a specific configuration of a range B surrounded by a two-dot chain line in FIG. The configuration will be described below, but the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. A main spool hole M is formed in the valve body V, and caps C1 and C2 are fixed at both ends of the valve body V and coaxially with the main spool hole M. The interiors of the caps C1 and C2 are used as pilot chambers 1a and 1b.

A main spool 33 is slidably incorporated in the main spool hole M, and both ends thereof face the pilot chambers 1a and 1b. Pilot room 1a,
Spring forces of centering springs S1 and S2 are applied to both ends of the main spool 33 facing 1b via spring receivers 35a and 35b, respectively. Then, the illustrated neutral state is maintained. In the pilot chambers 1a and 1b, pressure oil controlled by the proportional electromagnetic pressure reducing valves 1c and 1d is supplied with pilot fluids 34a and 34d, respectively.
34b.

A first annular groove 33a is formed substantially at the center of the main spool 33, and a second annular groove 33a is formed on the right side thereof.
An annular groove 33b is formed, and a third annular groove 33c is formed on the left side. In the illustrated neutral state, the first annular groove 33a communicates with the communication channel 31, the second annular groove 33b communicates with the cylinder port 30, and the third annular groove 33c communicates with the tank channel 32. . The above cylinder port 30
Is connected to the lift cylinder A via the flow control valve R and the poppet valve 21. The flow control valve R will be described below.

The valve body V has a cylinder port 30
Is formed, and an opening thereof is closed by a cap 38. A spool 37 is slidably incorporated in the spool hole 36, and the first pilot chamber Ra and the second pilot chamber R
b. The first pilot chamber Ra communicates with the communication flow path 31 via the first flow path 42, and the second pilot chamber Rb also forms an annular groove formed on the spool 37 via the second passage 43 formed on the spool 37. It communicates with 41.

The spring Rc is incorporated in the first pilot chamber Ra, and the spring force is applied to the spool 37. Therefore, the spool 37 has a stepped portion 40 in which the annular protrusion 39 is formed on the inner periphery of the spool hole 36.
The poppet valve 21 and the cylinder port 30 are communicated through the annular groove 41 while maintaining the state of being pressed against the poppet valve 21. Reference numeral 29 in the figure denotes a supply port communicating with the control flow path 4 shown in FIG. 1, and reference numeral 16 denotes a first load pressure flow path. Reference numeral 46 denotes a discharge port that communicates with the spring chamber 21a of the poppet valve 21 via the flow path f.

When the main spool 33 is moved rightward in the figure from the neutral position shown in the figure by the action of the pilot pressure guided to the pilot chamber 1b, the first annular groove 3
The supply port 29 and the communication channel 31 communicate with each other via 3a. In addition, the communication channel 31 and the cylinder port 30 communicate with each other via the second annular groove 33b. Therefore, the pressure oil of the pump P guided to the supply port 29 is supplied to the supply port 29 →
The communication path 31 → the cylinder port 30 → the annular groove 41 of the spool 37 → the poppet valve 21, and the poppet valve 2.
1 is pushed open to be supplied to the lift cylinder A. At this time, the communication passage 3 is connected to the first pilot chamber Ra of the flow control valve R.
1, the pressure oil of the cylinder port 30 is guided to the second pilot chamber Rb, but the total force of the acting force of the pressure oil on the first pilot chamber Ra side and the spring force of the spring Rc. However, the spool 37 maintains the state shown in the figure and smoothly supplies the pressurized oil to the lift cylinder A side since the action force due to the pressurized oil on the second pilot Rb side is exceeded.

On the other hand, when the main spool 33 is moved to the left in order to lower the lift cylinder A, the supply port 30 and the tank flow path 32 pass through the slit 47 continuously formed in the second annular groove 33b. Communicate. Also,
At the same time, the discharge port 46 and the first control port 44 formed on the main spool 33 communicate with each other. The first control port 44 communicates with the second control port 45 by switching a sub spool (not shown) incorporated in the main spool 33. That is, when pressure oil is supplied to the pilot chamber 1a to move the main spool 33 to the left, the pressure oil also acts on a sub spool (not shown) in the main spool 33. Therefore, the first control port 44 and the second control port 45 communicate with each other, and the discharge port 46 communicates with the tank flow path 32 via the first and second control ports 44 and 45.

When the discharge port 46 communicates with the tank flow path 32 as described above, the spring chamber 21 of the poppet valve 21
The pressure oil of a passes through the passage f → the discharge port 46 → the first control port 4
4 → second control port 45 → tank flow path 32 and discharged to tank T. As a result, a pressure difference occurs before and after the orifice 21b of the poppet valve 21, whereby the poppet 21 valve opens. Therefore, the pressure oil of the lift cylinder A is supplied to the flow control valve R through the opened poppet valve 21.
Guided to the side. Then, the pressure oil guided to the flow control valve R is discharged from the supply port 30 to the tank flow path 32 via the slit portion 47.

When the pressure oil of the lift cylinder A is discharged through the slit 47 as described above, the slit 4
A pressure difference occurs around 7. And this slit part 47
The pressure oil on the upstream side is guided to the second pilot chamber Rb via the second flow path 43, and the pressure oil in the first pilot chamber Ra flows from the first flow path 42 → the communication flow path 31 → the first load pressure flow path 16 Through the tank T. Therefore, the spool 37 is
It stops at a position where the sum of the acting force of the pilot chamber Ra and the spring force of the spring Rc and the acting force of the second pilot chamber Rb due to the pressurized oil balance the main spool 33 of the switching valve 1. Spring R
Keep the spring force equivalent to c. And the main spool 33
If the main spool is switched while the front and rear pressure difference is kept constant, a flow rate corresponding to the switching amount is discharged. That is, the lowering speed of the lift cylinder A can be controlled to a speed corresponding to the switching amount of the main spool 33.

[0038]

According to the present invention, when the single-acting cylinder is lowered, the differential pressure before and after the switching valve is kept constant regardless of the load. The speed can always be controlled according to the speed. Therefore, delicate control of the descending speed is possible without requiring skill. Further, since the differential pressure before and after the switching valve does not suddenly change, the fluid force acting on the spool does not suddenly change. Therefore, the operator does not feel uncomfortable when the single-acting cylinder is lowered.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an apparatus according to an embodiment.

FIG. 2 is a diagram showing a specific structure in a range B of FIG. 1;

FIG. 3 is a circuit diagram of a conventional device.

[Explanation of symbols]

 A lift cylinder corresponding to a single-acting cylinder of the present invention V valve body M main spool hole P pump R flow control valve Ra first pilot chamber Rb second pilot chamber Rc spring T tank 30 cylinder port 32 tank flow path 33 main spool 36 Spool hole 37 Spool 42 First flow path 43 Second flow path

Claims (2)

[Claims] 1. A pump, a single-acting cylinder connected to the pump, and a switch provided between the pump and the single-acting cylinder and communicating the single-acting cylinder to the pump or the tank according to a switching position. A hydraulic control device comprising a valve and controlling the descending speed of the single-acting cylinder descending by its own weight and load by a switching valve, wherein a flow control valve is provided between the single-acting cylinder and the switching valve or between the switching valve and the tank. A hydraulic control device characterized in that the differential pressure across the switching valve is kept constant by a flow control valve when the single-acting cylinder descends. 2. A valve body, a main spool hole formed in the valve body, a main spool slidably incorporated in the main spool hole, and a cylinder port connected to the single-acting cylinder while communicating with the main spool hole. And a tank flow passage communicating with the main spool hole, wherein the hydraulic fluid control device controls the return fluid discharged from the single-acting cylinder to the tank flow passage by its own weight and load according to the switching amount of the main spool. A spool hole which communicates with the cylinder port and which is slidably incorporated in the spool hole and which determines the degree of communication between the single-acting cylinder and the main spool hole according to the switching position; and one end of the spool. And a second pilot chamber provided on the other end of the spool. And a spring incorporated in the first pilot chamber and applying a spring force to the spool, a first flow path for communicating the first pilot chamber with the tank, and a second flow path for communicating the second pilot chamber with the single-acting cylinder. When the single-acting cylinder is lowered, the spool balances the total force of the acting force of the pressure oil in the first pilot chamber and the spring force of the spring and the acting force of the pressure oil in the second pilot chamber. The hydraulic pressure control device is configured to stop at a predetermined position to maintain a constant differential pressure between the upstream side and the downstream side of the main spool.