JPH0339601Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an improvement in a speed increasing valve that increases the extension speed of a double-acting cylinder to improve work efficiency.

2. Description of the Related Art In general, double-acting cylinders are sometimes required to be used in such a manner that the reciprocating speed is increased on one side and slowed on the other. For example, in the case of an agricultural front loader, it may be desirable to operate the dump speed faster than the rake speed. In other words, for example, an agricultural front loader
As shown in FIG. 8, the rear end of a lift arm 2 is pivotally connected to a main body 1 of a tractor, etc.
A working machine 3 is attached to the tip of the lift arm 2, a lift cylinder 4 is used to raise and lower the lift arm 2, and a double acting dump cylinder 5 is used to rotate the working machine 3 at the tip of the lift arm 2.

When working with an agricultural front loader such as the one described above, the speed at which workpieces such as agricultural products are scooped out by the work implement 3 is not considered to be as much of a problem, but the speed at which workpieces scooped out by the work implement 3 is It is desired that the speed of discharging to a transport vehicle or the like be increased in order to improve work efficiency.

In response to the above request, the present applicant has developed a speed increasing valve (Utility Model Publication Act 1983-1993-1) that allows a double-acting cylinder to extend at high speed
(See Publication No. 34721).

The speed increasing valve A is disposed between the double-acting cylinder 5 and the directional control valve 6, as shown in FIG. 9, and its structure is as shown in FIG. 10.

In the drawing, the speed increasing valve A is a double-acting cylinder 5.
A first port a connected to the piston front chamber 5a of
and a second port b connected to the piston rear chamber 5b.
and third and fourth ports c and d connected to the directional control valve 6.

The first port a and the fourth port d communicate with each other through a first L-shaped communication oil passage 7 formed in an L-shape within the main body. A check valve 8 that prevents flow of hydraulic oil is provided.

Further, the second port b and the third port c are always in direct communication through a second L-shaped communication oil passage 9 within the main body.

The first and second L-shaped communication oil passages 7,
Between 9 and 9 is a spool that cooperates with the check valve 8 in order to allow the return oil from the piston front chamber 5a when the double-acting cylinder 5 is extended to join the oil supplied to the piston rear chamber 5b. A shaped reflux valve 10 is provided.

The reflux valve 10 is slidably provided in a sliding hole 11 provided parallel to the vertical oil passages of the first and second L-shaped communication oil passages 7 and 9, and its lower end It faces the horizontal oil passage of the L-shaped communication oil passage 7,
It is constantly pushed upward by the spring 12. The sliding hole 11 has first and second L
Branch oil passages 7a and 9a are opened from the letter-shaped communication oil passages 7 and 9, respectively, and circular grooves 13 and 14 are provided on the sliding hole 11 side of these openings, respectively. .

The sliding hole portion between the two annular grooves 13 and 14 forms a valve seat 11a, and correspondingly, an annular communication control groove 15 is formed on the outer periphery of the reflux valve 10.

A horizontal through hole 16 is provided in the middle of the reflux valve 10 corresponding to the annular groove 13 of the branch oil passage 7a of the first L-shaped communication oil passage 7, and a horizontal hole 16 is provided vertically through the center of the reflux valve 10. A pilot oil passage 17 is provided with one end opening into the through-lateral hole 16 and the other end opening into the upper end of the recirculation valve 10;
A throttle passage 18 is opened from 6 to the lower end of the reflux valve 10 via a fixed throttle 19.

The operating procedure of the double-acting cylinder in the above-mentioned speed increasing valve will be explained below.

First, the case where the double-acting cylinder 5 is contracted will be explained with reference to FIGS. 9 and 10. The directional control valve 6 is switched to supply hydraulic oil from the hydraulic pump P to the fourth port d. Then, this hydraulic fluid pushes open the check valve 8 and flows into the first L.
The hydraulic oil passes through the L-shaped communication oil passage 7 and flows into the piston front chamber 5a from the first port a, and the hydraulic oil in the piston rear chamber 5b flows through the second port b, the second L-shaped communication oil passage 9, and the third port. c and returns to the tank T, whereby the double-acting cylinder 5 is contracted at a normal speed. At this time, the working oil pressure from the hydraulic pump P acts on the upper and lower ends of the recirculation valve 10, canceling each other out, and the recirculation valve 10 maintains a state where it is pushed up to the upper end by the upper end force due to the pressing force of the spring 12.

Next, when the double-acting cylinder 5 is extended, the direction control valve 6 is switched and the third port c
When hydraulic oil is supplied from the hydraulic pump P, this hydraulic oil flows into the piston rear chamber 5b via the third port c, the second L-shaped communication oil passage 9, and the second port b, but the hydraulic oil flows into the piston rear chamber 5b. The hydraulic oil in the chamber 5a is
Due to the non-return action of the check valve 8 in the middle of the first L-shaped communication oil passage 7, it cannot return, and is slightly bypassed from the fixed throttle 19 and the throttle passage 18, returning to the tank T from the fourth port d. You will be in a state where you can get it.

Therefore, the pressure of the return oil from the piston front chamber 5a gradually increases, and the oil pressure acts on the upper end of the return valve 10 from the pilot oil passage 17 in the direction opposite to the spring 12, and as shown in FIG. This causes the valve 10 to be pushed down.

As a result, the communication control groove 15 of the recirculation valve 10 straddles the valve seat 11a and communicates the two annular grooves 13 and 14, so that when the double-acting cylinder 5 is extended, some of the return oil in the piston front chamber 5a is is returned to the tank T from the fixed throttle 19 via the throttle passage 18, but most of it is supplied to the piston rear chamber 5b, where it is accelerated and extended.

Problems to be Solved by the Invention The above-mentioned speed increasing valve aims at high work efficiency by extending a double-acting cylinder at high speed.For example, in the agricultural front loader, the double-acting cylinder Due to the high-speed extension operation, the working machine 3 is rapidly rotated downward, and the object to be worked on is rapidly discharged from the working machine 3 to a transport vehicle or the like, thereby performing the work with high efficiency.

By the way, when the double-acting cylinder 5 is extended, the speed increasing valve returns a part of the return oil from the piston front chamber 5a to the tank T through the throttle passage 18, and makes most of the remaining oil join the piston rear chamber 5b. The expansion operation of the double-acting cylinder 5 is accelerated, and the piston front chamber 5a and the piston rear chamber 5 are
b is bypassed, so this extension force is smaller than that of the double-acting cylinder 5 at the normal extension speed, and if a large load is applied to the double-acting cylinder 5 in the direction of contraction, the double-acting cylinder 5 will not extend. .

That is, when a large load is applied against the direction of the expansion operation during the acceleration expansion operation of the double-acting cylinder 5, the hydraulic oil supplied to the third port c is transferred from the branch oil passage 7a to the annular groove 13 and the communication control. Groove 15, annular groove 1
4, passes through the fixed throttle 19, and the throttle oil passage 18, and returns to the tank T from the fourth port d. Also, the pressure of the hydraulic oil at this time acts from the pilot oil passage 17 to the upper end of the reflux valve 10, and this reflux In order to push down the valve 10, the hydraulic oil supplied from the hydraulic pump P to the third port c is bypassed to the fourth port d, flows into the tank T, and does not act on the piston rear chamber 5b, and therefore does not act on the double-acting cylinder. 5 cannot be extended against the above-mentioned large load.

For example, in the above-mentioned agricultural front loader, the tip working device 3 is rotated downward to bite the tip into a hard work object, or the working object discharged to a transport vehicle or the like is moved by the tip working device 3. When compressing by applying pressure at the bottom surface, etc., the double-acting cylinder 5 could not be extended in the above-mentioned speed increasing valve.

Therefore, there is a need for the development of a speed increasing valve that can cause a double-acting cylinder to extend faster than normal when the load is light, and at the normal extension speed when the load is heavy.

Means for Solving the Problems The present invention provides a first port connected to the piston front chamber of a single-rod double-acting cylinder, a second port connected to the piston rear chamber, and a directional control valve connected to the hydraulic pump and tank. between the third and fourth ports that are switched and connected via the communication oil passage, a communication oil passage that constantly communicates the second port and the third port, and a branch oil passage from the first port and the communication oil passage; a reflux valve disposed in the reflux valve for circulating return oil flowing into the first port from the piston front chamber to the first port during the extension operation of the double-acting cylinder; In the speed increasing valve, the speed increasing valve is provided with a throttle passage that allows a part of the return oil from the piston front chamber to flow to the fourth port, and between the communication oil passage and the branch oil passage, there is a connection between the communication oil passage and the branch oil passage. This is a speed increasing valve equipped with a check valve that prevents the flow of hydraulic fluid to.

Function When the load applied to the double-acting cylinder is small, the speed increasing valve according to the present invention, like a conventional speed increasing valve, transfers the return oil from the piston front chamber to the piston rear chamber together with the hydraulic oil from the hydraulic motor. The above-mentioned double-acting cylinder can be extended at a higher speed than usual by merging the supply with the 2nd port and the 3rd port.On the other hand, when the above-mentioned load is large, this The hydraulic oil supplied from the hydraulic pump to the third port is caused to flow through the communication oil passage by the check valve disposed between the branch oil passage branching from the communication oil passage and reaching the return valve. , by ensuring that the oil flows into the piston rear chamber from the second port and returning the entire amount of return oil from the piston front chamber to the tank from the fourth port, the double-acting cylinder is maintained at a normal speed, and the heavy load is maintained. The extension operation speed can be automatically switched depending on the load.

Embodiment FIGS. 1 and 2 show an embodiment in which the present invention is applied to the known speed increasing valve shown in FIGS. 10 and 11, and the components are the same as those of the known speed increasing valve. The same reference numerals or numerals will be given to the same reference numerals, and the explanation thereof will be omitted.

The speed increasing valve B according to the present invention has hydraulic oil flowing from the third port c to the branch oil passage 9a of the second L-shaped communication oil passage 9 at the bent part of the second L-shaped communication oil passage 9. A check valve 30 is provided to prevent flow.

The operation procedure of the double-acting cylinder 5 using the speed increasing valve B according to the present invention will be explained above. It is assumed that the speed increasing valve B is connected to the double acting cylinder 5, the directional control valve 6, the hydraulic pump P and the tank T through the same hydraulic piping as the known speed increasing valve A.

First, in the state shown in FIG. 1, when the double-acting cylinder 10 is contracted, the directional control valve 6 is switched to supply hydraulic oil from the hydraulic pump P to the fourth port d.

The hydraulic oil supplied to the fourth port c pushes open the check valve 8, passes through the first L-shaped communication oil passage 7, flows into the piston front chamber 5a from the first port a, and flows into the piston rear chamber 5b. The hydraulic oil inside is returned to the oil tank T from the third port c through the second L-shaped communication oil passage 9 from the second port b, thereby causing the double-acting cylinder 5 to contract at a normal speed. do. still,
In this case, as described above, the working oil pressure from the hydraulic pump P acts on the upper and lower ends of the recirculation valve 10, canceling each other out, and the recirculation valve 10 is kept pushed up to the upper end by the pressing force of the spring 12.

Next, when the directional control valve 6 is switched to supply hydraulic oil from the hydraulic pump P to the third port c, this hydraulic oil passes through the second L-shaped communication oil passage 9 by the action of the check valve 30. The hydraulic oil in the piston front chamber 5a then flows into the piston rear chamber 5b from the second port b, but the hydraulic oil in the piston front chamber 5a is controlled by the check valve 8 disposed in the middle of the first L-shaped communication oil passage 7. It cannot return freely, is slightly bypassed from the fixed throttle 19 and the throttle passage 18, and is in a state where it can return to the tank T from the fourth port d.

Therefore, the pressure of the return oil in the piston front chamber 5a gradually increases, and the oil pressure acts on the upper end of the return valve 10 from the pilot oil passage 17 in a direction opposite to the spring 12, pushing the return valve 10 down.

As a result, the communication control groove 15 of the reflux valve 10
straddles the valve seat 11a and communicates the two annular grooves 13 and 14, so that part of the return oil in the piston front chamber 5a is returned from the fixed throttle 19 to the tank T through the throttle passage 18 and from the fourth port d. However, most of it flows into the second L-shaped communication oil passage 9 by pushing open the check valve 30, and flows from the second port b to the piston rear chamber 5b together with the hydraulic oil supplied to the fourth port d. The double-acting cylinder 5 is accelerated and extends. In this state, the reflux valve 10
Communication control between the branch oil passages 7a and 9a by the communication control groove 15 is performed by balancing the elastic force of the spring 12 and the return hydraulic pressure from the piston front chamber 5a, and as shown in FIG. The opening degree of the variable throttle part m formed by the upper edge of the annular groove 13 and the lower edge of the communication control groove 15, and the variable throttle part formed by the lower edge of the annular groove 13 and the upper edge of the horizontal through hole 16. The reflux valve 10 is stationary with the opening degree of n maintained in a constant relationship.

If a high load is applied in the direction of contraction of the double-acting cylinder 5 during the extension operation of the double-acting cylinder 5 in the speed increasing state, the extension operation speed of the double-acting cylinder 5 decreases, causing the return from the piston front chamber 5a. As the amount of oil decreases, the hydraulic pressure acting from the pilot oil passage 17 to the upper end of the reflux valve 10 decreases, so the reflux valve 1
0 is pushed upward by the elastic force of the spring 12 and blocks communication between the two annular grooves 13 and 14.

At this time, the hydraulic oil supplied from the third port c flows into the piston rear chamber 10b from the second port b through the second L-shaped communication oil passage 9 due to the action of the check valve 30. The double-acting cylinder 5 is extended by the hydraulic pressure of the hydraulic oil against the large load. Then, as described above, the hydraulic oil in the piston front chamber 5a cannot return freely due to the check valve 8 disposed in the middle of the first L-shaped communication oil passage 7, and is fixed. Aperture 19 and aperture passage 18
The pressure of the return oil in the piston front chamber 5a gradually increases, and this oil pressure flows from the pilot oil passage 17 to the upper end of the return valve 10. act in a direction opposite to the spring 12 to push down the reflux valve 10.

As a result, the communication control groove 15 of the reflux valve 10
Since the two annular grooves 13 and 14 communicate with each other by straddling the valve seat 11a, the return oil from the piston front chamber 5a flows from the annular groove 13 into the annular groove 14. However, in this case, the pressure of the hydraulic oil supplied to the third port c is high in order to cope with the above-mentioned large load, and the check valve 30 is closed by the high pressure of the hydraulic oil. Therefore, the return oil from the piston front chamber 5a is prevented from flowing from the annular groove 14 into the second L-shaped communication oil passage 9 by the check valve 30, and is prevented from flowing from the fixed throttle 19 and the throttle passage 18. It is bypassed and returned to the tank T from the fourth port d.

That is, the hydraulic oil supplied from the hydraulic pump P to the third port c passes through the second L-shaped communication oil passage 9, flows into the piston rear chamber 5b from the second port b, and on the other hand, flows into the piston front chamber 5a. The return oil from
The entire amount of hydraulic oil is transferred from the fourth port d to the tank T without merging with the hydraulic oil supplied to the third port c.
Therefore, the double-acting cylinder 5 extends at the normal extension speed against the large load.

Therefore, if the speed increasing valve B is applied to the dump cylinder 5 of the agricultural front loader shown in FIG. By extending the double-acting dump cylinder 5 at high speed like the speed valve and rotating the tip working device 3 downward, the object to be worked can be rapidly discharged, and the object to be worked can be moved by the rotation of the tip working device 3. When compacting by motion or when the tip working device 3 bites into the workpiece, the double-acting dump cylinder 5 can generate a stronger output than during the above-mentioned high-speed extension operation, and The front part of the main body 1 can be lifted by pressing the tip working device 3 downward, and the front wheel can be easily replaced.

3 to 5 show a second embodiment of the speed increasing valve according to the present invention, and the constituent members corresponding to the first embodiment shown in FIGS. 1 and 2 are the same. A reference number or a reference numeral will be given and the explanation thereof will be omitted.

In the second embodiment, both the first port a and the second port b open in parallel at the upper side of the valve body 40, and the bent portion of the first L-shaped communication oil passage 7 An eccentric cam 41 for forcibly opening the check valve 8 is disposed therein, and the eccentric cam 41 is rotated by a lever 42 disposed at the lower side of the valve body 40.

In the second embodiment, when the lever 42 is operated to rotate the eccentric cam 41 to the position indicated by the solid line in the figure, the function is the same as that of the speed increasing valve in the first embodiment, and the double-acting cylinder If the load applied to 5 is small, it will be extended at a higher speed than usual,
If the load is large, the extension can be operated at a normal speed against the load. On the other hand, when the eccentric cam 41 is rotated to the position indicated by the two-dot chain line in the figure, the eccentric cam 41 forcibly pushes up the check valve 8 and drains the hydraulic oil in the first L-shaped communication oil passage 7. Free distribution becomes possible.

Therefore, when the eccentric cam 41 is rotated to the position indicated by the two-dot chain line in the figure, the hydraulic fluid from the hydraulic pump P is
When supplied to port c, this hydraulic oil flows into the second L
It flows into the piston rear chamber 5b from the second port b through the letter-shaped communication oil passage 9, while the piston front chamber 5
The return oil from port a passes from the first port a through the first L-shaped communication oil passage 7 and from the fourth port d to the tank T.
He is now in a position where he can freely return to.

Therefore, the return oil from the piston front chamber 5a is
Most of it flows through the first L-shaped communication oil passage 7,
Since only a small amount of return oil flows through the fixed throttle 19 and the throttle passage 18, there is almost no increase in the pressure of the return oil upstream of the fixed throttle 19. Therefore, the return valve 10 is closed to the sliding hole by the elastic force of the spring 12. 11, the return oil does not join the hydraulic oil flowing through the first L-shaped communication oil passage 7, and the entire amount returns to the tank T, so that the double-acting cylinder 5 is normal speed,
Moreover, it can be extended even with normal operating force.

6 and 7 show a third embodiment of the speed increasing valve according to the present invention, in which the first port a and the second port b extend perpendicularly to the drawing, and the valve body 50 The third port c and the fourth port d open downward into the lower part of the valve body 50. A reflux valve 52 is slidably housed in a sliding hole 51 formed horizontally in the approximate center of the valve body 50, and is pushed by a spring 53 to be positioned at the left end of the sliding hole 51. The valve body 50 is moved rightward by a solenoid S fixed to the right side of the valve body 50 against the elastic force of a spring 53.

The first port a and the fourth port d are communicated with two annular grooves 54 and 55 formed in the sliding hole 51, respectively. Further, as shown in FIG. 6, when the reflux valve 52 is located at the left end of the sliding hole 51, the annular communication control groove 56 formed on the outer periphery of the reflux valve 52 allows the annular groove 54 to ,5
5 is communicated.

The second port b and the third port c communicate with each other through a bent communication oil passage 57, and a branch oil passage 57a extending from the bent portion of the communication oil passage 57 is formed in the sliding hole 51. It now communicates with one annular groove 58 . Further, between the communication oil passage 57 and the branch oil passage 57a, there is a connection between the communication oil passage 57 and the branch oil passage 57a.
A check valve 59 is provided to prevent the flow to 7a.

In addition, a small diameter throttle passage 60 is formed in the reflux valve 52 from the land portion at the left end of the reflux valve 52 to the communication control groove 56 .

The following is a double-acting cylinder 5 according to the third embodiment.
Explain how it works.

First, in the state shown in FIG. 6, the first port a and the fourth port d, and the second port b and the third port c are in communication with each other. Therefore, when the directional control valve 6 is switched to supply hydraulic oil to the fourth port d, this hydraulic oil flows from the fourth port d through the annular groove 55, the communication control groove 56, and the annular groove 54, and then from the first port a. Flows into the piston front chamber 5a, and flows into the piston rear chamber 5b.
The return oil from the second port b flows through the communication oil passage 57.
, and is returned to the tank T from the third port c, so the double-acting cylinder 5 contracts at a normal speed.

Next, switch the direction control valve 6 to the third port c.
When hydraulic oil is supplied to the piston front chamber 5a, this hydraulic oil passes through the communication passage oil 57 from the third port c, flows into the piston rear chamber 5b from the second port b, and flows into the piston front chamber 5a.
The return oil from the first port a passes through the annular groove 5.
4. Since the gas is returned to the tank T from the fourth port d via the communication control groove 56 and the annular groove 55, the double-acting cylinder 5 is extended at a normal speed.

Next, in order to rapidly extend the double-acting cylinder 5, the solenoid S is actuated to open the reflux valve 52.
is moved to the right end of the sliding hole 51 as shown in FIG. 7, and hydraulic oil is supplied to the third port c.

In the state shown in FIG. 7, the annular groove 54 connected to the first port a and the annular groove 58 connected to the branch oil passage 57a communicate with each other through the communication control groove 56.
Furthermore, the communication control groove 56 and the fourth port d are
They are communicated through a throttle passage 60.

Therefore, the hydraulic oil supplied to the third port c flows into the piston rear chamber 5b from the second port b through the communication oil passage 57, while the return oil from the piston front chamber 5a flows through the first port b. After flowing from a into the communication control groove 56 via the annular groove 54, a portion passes through the throttle passage 60 and flows from the fourth port d into the tank T.
At the same time, most of the oil flows from the annular groove 55 into the branch oil passage 57a and pushes open the check valve 59.
It flows into the second port b from the communication oil passage 57, and flows into the piston rear chamber 5b together with the hydraulic oil supplied to the third port c, causing the double-acting cylinder 5 to rapidly extend.

At this time, when a load is applied to the double-acting cylinder 10 in a direction that causes the double-acting cylinder 10 to contract, the pressure of the hydraulic oil in the piston rear chamber 5b increases due to the pressure of the hydraulic oil in the piston front chamber 5a. Therefore, the pressure of the hydraulic oil in the communicating oil passage 57 becomes higher than the pressure of the hydraulic oil in the branch oil passage 57a, and the check valve 59 acts, so that the piston front chamber 5a
The entire amount of the return oil is returned to the tank T from the fourth port d through the throttle passage 60.

Therefore, all the hydraulic oil flowing into the cylinder rear chamber 5b is the hydraulic oil supplied from the hydraulic pump P, and the double-acting cylinder 5 is extended at a normal speed against the load.

Effects of the invention As explained above, the speed increasing valve according to the invention includes a communication oil passage formed between the second port and the third port, and a branch oil passage that branches from this communication oil passage and reaches the reflux valve. A check valve is installed between the above-mentioned communication oil passage and the branch oil passage to prevent the flow of hydraulic oil from the above-mentioned communication oil passage to the branch oil passage, so when the load applied to the double-acting cylinder is small, it can be used like a conventional speed-up valve. By supplying return oil from the front chamber of the piston to the rear chamber of the piston, the double-acting cylinder is extended at a higher speed than usual. On the other hand, when the load is large, the check valve is checked. The action causes the hydraulic oil supplied from the hydraulic pump to the third port to flow through the communication oil passage,
By ensuring that the oil flows into the piston rear chamber from the second port and returning the entire amount of return oil from the piston front chamber to the tank from the fourth port, the double-acting cylinder can be maintained at normal speed and resist the large load. The extension operation speed can be automatically switched depending on the load.

Therefore, by applying the speed increasing valve according to the present invention, appropriate rotational force and rotational speed can be applied to working machines such as agricultural front loaders operated by double-acting cylinders, depending on the content of the work. This allows for improved work efficiency and diversification of work content.

[Brief explanation of drawings]

1 and 2 are longitudinal cross-sectional views showing one embodiment of the speed increasing valve according to the present invention in each operating state, and FIG.
Figures 5 to 5 show the second speed increasing valve according to the present invention.
FIG. 3 is a front view, FIGS. 4 and 5 are longitudinal sectional views in each operating state, and FIGS. 6 and 7 are diagrams showing an example of the speed increasing valve according to the present invention. FIG. 3 is a vertical cross-sectional view showing the third embodiment in each operating state. FIG. 8 is a schematic side view of an agricultural front loader as an example of the object of the present invention, FIG. 9 is a schematic diagram of the hydraulic circuit of the agricultural front loader, and FIGS.
FIG. 1 is a longitudinal sectional view showing an example of a speed increasing valve in various operating states, which is the premise of the present invention. 5... Double acting cylinder, 5a... Piston front chamber, 5b... Piston rear chamber, a... First port, b... Second port, c... Third port, d...
...Fourth port, 7...First L-shaped communication oil passage, 9
...Second L-shaped communication oil passage, 9a, 57a... Branch oil passage, 10, 52... Reflux valve, 30, 59...
Check valve, 57... communicating oil path.

Claims (1)

[Scope of utility model registration request] A first port connected to the piston front chamber of the single-rod type double-acting cylinder, a second port connected to the piston rear chamber, and a third port and a third port connected to the hydraulic pump and tank via a directional control valve. 4
A communication oil passage that constantly communicates between the port, the second port and the third port, and a branch oil passage from the first port and the communication oil passage, and is arranged between the first port and a branch oil passage from the communication oil passage, and is arranged between the first port and a branch oil passage from the communication oil passage, and is arranged between the first port and a branch oil passage from the communication oil passage, and is arranged between the first port and a branch oil passage from the communication oil passage. a reflux valve that allows return oil flowing into the first port from the front chamber to flow through the communication oil passage; In the speed increasing valve that is provided with a throttle passage that flows to the fourth port, a check valve is provided between the communicating oil passage and this branch oil passage to prevent the flow of hydraulic oil from the communicating oil passage to the branch oil passage. A speed increasing valve characterized by being provided with.