JP3161965B2 - Timer valve of mechanical brake device for hydraulic motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanical valve for a hydraulic motor for driving a large inertial load and a timer valve associated with the mechanical brake.

[0002]

2. Description of the Related Art Hydraulic motors are used in construction machines and civil engineering machines, such as hydraulic excavators and backhoes, for driving the vehicle and rotating the revolving unit. As is well known to those skilled in the art, such a hydraulic motor is provided with a mechanical brake so that a driven part operatively connected to its output shaft, for example, a revolving body, does not inadvertently turn under its own weight during traveling on a slope, for example. Equipment.

[0003] Typically, this mechanical brake device is normally pressed against an output shaft or a rotating element of a hydraulic motor by a spring biasing force to prevent its rotation, and thus inadvertent turning of the rotating body. Including brake plate. When the hydraulic lever is operated by the operating lever to rotate the revolving structure, pressurized oil is supplied into the cylinder chamber of the mechanical brake device, the piston is retracted against the urging force of the spring, and the brake plate attached to this is retracted. Disengagement, thereby quickly releasing the mechanical brake device from the hydraulic motor. Conversely, when the revolving unit is stopped, the operation of the revolving lever shuts off the supply of pressure oil to the hydraulic motor to stop the operation. During this operation, the hydraulic oil in the cylinder chamber of the mechanical brake device is drained, and as a result, the piston is urged by a spring and the brake plate is pressed against the rotating element of the hydraulic motor, thereby returning the mechanical brake device to the operating state. I do. Such an operation type mechanical brake device is generally called a “pressurized release type (negative type)”. Generally, the supply or cutoff of the pressure oil to the mechanical brake device is often performed in conjunction with the operation of the hydraulic motor control switching valve operatively connected to the operation lever.

By the way, in the technical field, a driven portion, for example, a shovel tends to rotate the hydraulic motor for a while due to its relatively large inertia force even when the supply of the pressure oil to the hydraulic motor is stopped. . If the mechanical brake device returns to operation before the hydraulic motor is completely stopped, the rotating elements of the hydraulic motor continue to rotate against the pressing force of the brake plate,
Noise and heat may be generated due to friction with the brake plate.

Conventionally, in order to solve such inconvenience, a timer valve (also referred to as a "delay valve") for delaying the return of the operation of the mechanical brake device until the hydraulic motor is completely stopped after the supply of the hydraulic oil to the hydraulic motor has been used. Have been. One example of such a timer valve is disclosed in Japanese Patent Application Laid-Open No. 6-307415 of the present applicant, and the structure and operation thereof will be described with reference to FIG.

A conventional timer valve 1 shown in FIG. 5 is related to a mechanical brake 3 of a hydraulic motor 2. The mechanical brake 3 is a brake plate 4 that normally comes into frictional engagement with a rotating element or an output shaft of the hydraulic motor 2.
Is shown as a pressurized release type. The timer valve 1 includes a spool 6 slidably moving between a pressure oil supply position to a mechanical brake and a drain position in the longitudinal bore of the valve body 5. The first port P1 of the valve body can be connected to a hydraulic source via a switching valve 7 that is interlocked with the operation of the operation lever.
2 is connected to the pilot hydraulic pressure source 8 and the third port P
Numeral 3 communicates with the cylinder hydraulic chamber 9 of the mechanical brake device, and a fourth port P4 communicates with the drain tank 10. The timer valve includes a throttle device 11 in a hydraulic circuit associated with the cylinder hydraulic chamber 9 of the mechanical brake, and the throttle device is associated with a check valve 12 for supplying pressure oil to the cylinder hydraulic chamber of the mechanical brake. It is provided. The expansion device includes a cylindrical spacer 13 provided in a hydraulic path, and a narrow annular gap 14 is formed between the hydraulic path and the spacer.

When the port P1 is pressurized by operating the operation lever, the spool 5 moves to the right against the urging force of the spring as seen in FIG. Then, the pilot pressure oil of the port P2 flows into the flow path 15 through the circumferential groove of the spool, opens the check valve, is supplied to the hydraulic chamber 9 of the mechanical brake 3 through the port P3, and releases the mechanical brake. Let it. Thus, the rotation of the hydraulic motor becomes possible. When the supply of the pressure oil to the port P1 is shut off, the spool returns to the original position, the pilot pressure oil is shut off, and the check valve 12 is closed. Then, the hydraulic oil in the cylinder chamber 9 of the mechanical brake 3 flows into the timer valve 1 through the port P3, and then reaches the flow path 15 while being subjected to a throttle action when passing through the narrow annular gap 14 on the outer periphery of the spacer. , And gradually drains into the tank 10 through the port P4 through the passage inside the spool.

Thus, with the timer valve having such a configuration, it is possible to obtain a certain delay time after the supply of the hydraulic oil to the hydraulic motor is stopped until the mechanical brake is actually activated effectively. Premature operation of the mechanical brake for the motor can be avoided.

[0009]

However, in such a conventional structure, the delay time mainly depends on the internal volume of the cylinder chamber of the mechanical brake, that is, the working oil supply amount, the gap size of the expansion device through which the drain flow passes, and the delay time in the mechanical brake. It is determined by the provided spring force and hydraulic oil viscosity. The cylinder chamber volume is 2cc depending on the specifications of the hydraulic motor used.
The delay time varied greatly depending on the amount of hydraulic oil supplied into the cylinder chamber. In addition, it was very difficult in manufacturing to control the gap size according to the difference in the volume of the thin cylinder in order to obtain a desired delay time. Further, the hydraulic oil in the cylinder chamber is gradually drained from start to end by the delaying action of the throttle device until the operation of the mechanical brake is returned, and it is difficult to accurately set the delay time. Finally, in the case where the retarding action is achieved by the action of narrowing the gap as described above, the delay time is not stable because it may be affected by the viscosity of the oil.

An object of the present invention is to solve the above-mentioned problems, and to provide a timer valve capable of delaying the operation of the mechanical brake for a predetermined time regardless of the volume of the cylinder chamber of the mechanical brake device. It is in.

[0011]

DISCLOSURE OF THE INVENTION In view of the above object, the present invention
The gist of the explanation is that the mechanical brake device of the hydraulic motor
It is used continuously to delay the return of operation from its released state.
To the longitudinal bore and hydraulic power source
Connectable first port, second pilot pressure oil port
G, through the cylinder hydraulic chamber of the mechanical brake device
Third port and a fourth drain leading to the oil tank
A valve body with a port and a slide in the longitudinal bore of the valve body
A second port and a third port movably provided;
Are in fluid communication with each other, thereby providing mechanical brake
The first position to release the position, the third port and the fourth port.
Boards are in fluid communication with each other, thereby
In axial movement between the second position to activate the keying device
A switching valve means comprising a
The lube further controls the movement of the spool of the switching valve means to provide
Control means for delaying the operation of the mechanical brake device
The control means is filled with a predetermined amount of working fluid
The closed cylinder chamber and the closed cylinder chamber are divided into a first chamber and a second chamber.
Chamber and a closed cylinder chamber
Are reciprocally movable, and piston locks are
A piston provided with a valve, and a piston provided in the closed cylinder chamber.
Normally, the piston is oriented toward the second position.
The spring that is once biased and the piston
Means for bringing the first chamber and the second chamber into fluid communication with each other.
The working surfaces of opposite axial end faces of the piston
The products are equal and one of the piston rods is
The piston lock is guided axially in the closed cylinder chamber.
The other one of the blades abuts or is in contact with the spool.
Body, the spool is supplied with pressurized oil in the first port
Then, this causes the second force against the urging force of the piston spring.
From the position to the first position, and pressurized oil to the first port
When the supply is stopped, the piston moves due to the spring biasing force.
Moves from the first position to the second position.
And the fluid communication means supplies pressure oil to the first port.
Connection of piston motion by spring biasing force in response to supply stop
Resulting in the first chamber and the second chamber during contraction
Restricts the flow of the working fluid from one to the other being expanded,
Movement of the piston, thus moving to the second position.
Activate the mechanical brake device by controlling the movement of the pool
To include Hisage providing throttle means a desired delay time to return
The feature is the timer valve.

The timer valve of the present invention exerts a braking delay effect by using a predetermined amount of working fluid contained in a closed chamber separated from a hydraulic oil supply circuit or a drain circuit to the mechanical brake device. , The delay time can be controlled accurately. Thus, with the timer valve of the present invention, the delay time can be set independently of the volume of the cylinder interior of the mechanical brake device.

Preferably, the throttle means is at least one orifice provided in a piston movable in the closed chamber, and the delay time until the mechanical brake device returns to operation is substantially determined by the spool of the switching valve means. This is the time from the first position to the second position. This is because as soon as the spool reaches the second position, the hydraulic oil in the cylinder chamber of the mechanical brake device is quickly discharged into the oil tank, and at the same time, the braking action on the hydraulic motor is obtained. . Thus, the delay time is substantially a function of the spring force of the spring biasing the piston and the size of the orifice opening, given the internal volume of the closed cylinder chamber of the control means, by controlling these delay times Can be set relatively easily.

Preferably, the fluid communication means is provided on the piston, and moves from the contracting chamber to the expanding chamber upon movement of the piston accompanying movement of the spool from the second position to the first position. To reverse the flow of the working fluid from the contracting chamber to the expanding chamber upon movement of the piston with movement of the spool from the first position to the second position. A stop valve is further included. Thereby, when the pressure oil is supplied to the first port, the spool is quickly moved from the second position to the first position against the urging force of the spring of the piston. Therefore, the mechanical brake device is released almost simultaneously with the start of operation of the hydraulic motor, so that there is no heat generation or noise due to friction due to a delay in release.

According to an embodiment of the present invention, preferably, the piston of the control means and the spool of the switching valve means are separate members, and the spool member of the switching valve means has one end at one end of the axial rod of the piston member. Is spring-pressed toward the piston member so as to always contact the piston member. A central internal axial passage is provided in each of the spool member of the switching valve means and the piston member of the control means, and the central internal axial passage is provided at one of ends of the spool member and the piston member which are in contact with each other. Being in communication with each other via the provided throttle portion and being able to communicate with the first port,
In addition, a groove is provided on the end face of the end portion so as to communicate with the central internal axial passage across the throttle portion, and the groove preferably communicates with the oil tank through a fourth port.

[0016] Preferably, a check valve is disposed at the first port of the valve body, and the compression spring is connected to the spool member by the first port.
It is arranged between the port and the check valve. Preferably, the spring of the piston member of the control means has a substantially greater spring force than the spring of the spool member of the switching valve means, so as to minimize the effect of the latter on the delay time.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, FIGS. 1 and 2 show a timer valve 20 of the present invention associated with a mechanical brake device 3 in an activated state and a released state with respect to a hydraulic motor 2, respectively. The internal configuration is shown in a cross-sectional view so as to be clear. The hydraulic motor 2 illustrated as an example is of a type that rotationally drives a large inertial load, for example, an upper excavator of a hydraulic shovel. Although the mechanical brake device 3 is shown as the same type with a built-in hydraulic motor as that of the conventional configuration shown in FIG. 5, it may be one that can be externally connected to the hydraulic motor.

The timer valve 20 has a preferably single valve body 22 forming the switching valve means and its control means. The valve body has a central longitudinal bore 24 as shown,
A first port P1 that can be connected to the hydraulic pressure source 28 by operating the switching valve 26, a second port P2 that is in communication with the pilot pressure oil source 30, and a third port that communicates with the cylinder chamber 9 of the mechanical brake device. P3 and a fourth port P4 communicating with the drain oil tank 32. Switching valve 2
Numeral 6 is interlocked with the operation of a turning lever (not shown) for operating a switching valve (not shown) for supplying hydraulic oil to a hydraulic motor from a driving hydraulic source (not shown).
It will be understood by those skilled in the art that the hydraulic pressure source for driving the hydraulic motor may be used as the pilot pressure oil source 30. A switching valve spool 34 is provided in the longitudinal bore 24 of the valve body. The spool 34 communicates with a port P3 communicating with the cylinder chamber 9 of the mechanical brake device and a port P4 communicating with the oil tank 32 through a circumferential groove 36 provided in the inner peripheral portion of the bore, as shown in FIG. Through the circumferential recess 38 between the lands of the spool and the pilot pressure oil port P2 and the cylinder chamber 9 of the mechanical brake device.
2 (hereinafter, may be referred to as a "brake release position") where the port P3 communicating with the port P3 communicates. The valve body 22 has a plug 42 defining a port P1 and having a check valve 40. The check valve 40 closes the port P1 when the supply of the pressure oil to the hydraulic motor is shut off. One end 44 of the spool
Is a spring receiver for the compression spring 46 of the check valve. The spool 34 has a central through oil passage 48 for receiving pressure oil from the oil pressure source 28 to the port P1. A throttle portion 52 is provided near the tip of the other end 50 of the spool.

Also, as best seen in FIG. 3, the end of the spool end 50 extends across the throttle
Is provided. Thus, the spool passageway 48 communicates with the interior of the longitudinal bore 24 of the valve body 22 via the constriction 52 and the groove 54.

Referring to FIG. 1, control means for controlling the movement of the spool of the switching valve means to delay the operation of the mechanical brake device will be described.
Is provided adjacent to the longitudinal bore 24 and has a bore having a considerably larger inner diameter, and a plug 56 is sealingly attached to an end of the valve body to form a sealed cylinder chamber 58 having a predetermined internal volume. Have been. The closed cylinder chamber 58 is filled with a predetermined amount of a working fluid, preferably a working oil. As shown, a piston 60 is reciprocally mounted within a closed cylinder chamber 58 and separates it into two chambers 62 and 64 (see also FIG. 2). The rod portion 66 of the piston 60 fits into the guide recess of the plug 56 as shown. Also, a rod portion 68 opposite the piston 60 hermetically projects from the closed cylinder chamber 58 and extends into the bore 24 of the switching valve means. Piston 6
0 is normally biased rightward by a spring 70, and the tip of the piston rod 64 abuts the end 50 of the switching valve spool 34 in the bore 24 to press the spool 34 to the braking position. The spring 70 of the piston 60 is the spring 4 of the spool 34.
It should be noted that the spring force is substantially greater than 6. The reason will be described later. Preferably, an axial through oil passage 72 is provided inside the center of the piston 60, and this passage 68
8 and is always in communication therewith via a stop 52.

As shown, the piston 60 includes a chamber 62.
At least one throttle means, preferably an orifice 74, is provided for communicating the chamber and the chamber 64. Also, the piston preferably includes at least one check valve 76 diametrically opposite the orifice. With such a configuration,
When the timer valve is operated, the spring 7 is moved from the position shown in FIG.
During the leftward movement of the piston (movement of the switching valve spool 34 to the braking release position) against the urging force of 0, the oil in the contracting chamber 62 opens the check valve 76 to open the expanding valve. It flows into the chamber 64. On the other hand, when the piston 70 moves to the right (moves the switching valve spool 34 to the braking position) by the spring 70 from the position shown in FIG.
The flow of working fluid from 4 to the expanding chamber 62 has a throttle effect, which results in a reduction in piston movement and thus a delay in the movement of the switching valve spool 34 to the braking position. . During this operation, the piston 6
It goes without saying that the zero check valve 76 is closed. As described above, since the spring 70 is stronger than the spring 46, the effect of the spring 46 on such a delay action is negligible.

In the embodiment of the timer valve of the present invention, the spool 34 and the piston 60
Are arranged separately from each other, but as will be appreciated by those skilled in the art, as a variant, the valve body of the timer valve comprises a plurality of mutually connectable parts and comprises a piston arranged in a closed cylinder chamber. Alternatively, a single spool may be used. In this case, the central through passage 48, the throttle portion 52, the spring 46, and the check valve 40 in this embodiment will not be required. Further, a throttle means comprising an orifice is used as a means for communicating the two divided chambers of the closed cylinder chamber. However, as another throttle means, for example, a gap between the cylindrical inner circumference of the closed cylinder chamber and the outer circumference of the piston is used. However, an orifice that is not affected by the viscosity of the hydraulic oil is desirable.

The operation of the timer valve according to the present invention will be described below. Now, it is assumed that the timer valve is at the braking position shown in FIG. When pressure oil is supplied from the hydraulic pressure source 28 to the port P1 of the valve body 22 by operating the switching valve 26, the check valve 40 is opened and the pressure oil acts on the switching valve spool 34 to move the spool 34 to the braking release position. , And the piston 60 also starts to move leftward against the urging force of the spring 70. The supplied pressure oil passes through the passage 48 and passes through the throttle portion 52 while exerting a driving force on the spool.
The oil is drained to the oil tank 32 through the lateral groove 54 and the port P4. Also, the hydraulic oil present in the passage 72 of the piston 60 is discharged to the oil tank 32 through the lateral groove 54. As described above, the chamber 62 of the closed cylinder chamber 58 is
0, the hydraulic oil in the chamber 62 is discharged by the check valve 76.
To quickly flow into the expanding chamber 64. Preferably, the check valve is configured such that the resistance due to the flow of hydraulic oil passing through the check valve is so small that it does not substantially impede the movement of the piston. During this operation, substantially no hydraulic fluid flow through the orifice 74 will occur. When the spool 34 reaches the braking release position shown in FIG. 2, at the same time, the pilot pressure oil of the port P2 flows into the cylinder chamber 9 of the mechanical brake device 3 through the port P3 from around the circumferential recess 38 of the spool, As a result, the brake plate 4 is disengaged from the rotating element of the hydraulic motor 2, and thus the mechanical brake device is quickly released, and the hydraulic motor becomes rotatable.

When the supply of the pressure oil to the port P1 is stopped by operating the switching valve 26 in conjunction with the stop of the supply of the pressure oil to the hydraulic motor, the check valve 40 is closed. Then, the piston 60 starts to move rightward from the position shown in FIG. 2 along with the piston 34 in contact with the spring 70 in the closed cylinder chamber 58. The movement of the piston 60 causes the hydraulic oil in the contracting chamber 64 to gradually flow into the expanding chamber 62 through the orifice 74 while undergoing a throttling action during its passage. During this operation, the check valve 76 remains closed.
Thus, the spool 34 slowly moves toward the braking position shown in FIG. 1, thereby obtaining a delay operation required for a mechanical brake device for a hydraulic motor driving a large inertial load. Importantly,
From the brake release position in FIG. 2 to the brake position in FIG. 1, the hydraulic oil in the cylinder chamber 9 of the mechanical brake device is held essentially as it is and is not drained.
As soon as a certain delay time elapses after the supply of the pressure oil to the port P1 and the spool reaches the braking position, the operating oil in the cylinder chamber 9 passes through the port P3 to the bore 24 formed by the groove 36. The oil passes through the gap between the inner peripheral portion and the outer peripheral portion of the spool, is quickly drained to the oil tank 32 through the port P4, and the mechanical brake device 3 is activated.

The profile of the operation delay effect of the mechanical brake device obtained by the experiment of the timer valve of the present invention will be described with reference to the graph of FIG. FIG. 4A shows the pressure at the port P1 on the vertical axis and the time on the horizontal axis.
(B) is drawn with the pressure at port P3 on the vertical axis and time on the horizontal axis. When the pressure oil is supplied to the port P1 after the start of the operation, the port pressure of the port P3 increases almost at the same time (in this embodiment, the port pressures of the ports P1 and P3 are about 4).
0 kgf / cm ² ). When the supply of the pressure oil to the P1 port is cut off, the P1 port pressure disappears, but the P3 port pressure is maintained as shown in FIG. 4 (B). The section indicated by section a shows the P3 port pressure state from the time when the spool receives the delay action from the braking release position in FIG. 2 to the position immediately before the braking position in FIG. It can be seen that during the period a, the hydraulic oil in the brake cylinder chamber 9 is kept substantially in its normal state and is in a non-drain state. The section indicated by section b shows a state in which the spool is further moved and the port P4 is partially connected to the port P4 via the circumferential groove 36. Thus, the hydraulic oil in the cylinder chamber 9 is gradually drained linearly into the oil tank in accordance with the movement of the piston, and when the spool reaches the complete braking position shown in FIG. It is 0.

In the configuration of the present invention, the delay time from the release state to the operation state of the mechanical brake device is practically a + b, and is about 6.5 seconds in this experimental example. In the configuration of the present invention, the delay time is essentially a function of the spring force of the spring 70 biasing the piston 60 and the opening size of the orifice 74 for a given internal volume of the closed cylinder chamber. It will be appreciated by those skilled in the art that the setting of is easy.

On the other hand, the broken line shown in FIG. 4 (B) indicates the operation delay effect of the conventional timer valve shown in FIG. In such a conventional configuration, the hydraulic oil in the cylinder chamber 9 is drained as “sloppy” from start to stop until the signal is completely drained after the signal to the port P1 is completely shut off. Therefore, it is difficult to set or predict the delay time. It is also clear that it is not stable.

[0028]

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an internal structure of a timer valve of the present invention when a mechanical brake device is in a braking state.

FIG. 2 is a longitudinal sectional view showing the internal structure of the timer valve of the present invention when the mechanical brake device is in a braking release state.

FIG. 3 is a cross-sectional view taken along line 3-3 in FIG.

FIGS. 4A and 4B are graphs comparing the delay effect of the timer valve of the present invention and the timer valve of the conventional configuration, wherein FIG.
The change in measured pressure over time at three ports is shown.

FIG. 5 is a sectional view of a conventional timer valve having a built-in gap type throttle device.

[Explanation of symbols]

 2 Hydraulic motor 3 Mechanical brake device 4 Friction braking plate 9 Brake cylinder hydraulic chamber 20 Timer valve 22 Valve body 24 Bore 30 Pilot pressure oil source 32 Oil tank 34 Switching valve spool 36 Peripheral groove 58 Closed cylinder chamber 60 Piston 62, 64 Classification Chamber 70 Spring 74 Orifice 76 Check valve P1, P2, P3, P4 Port

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-26205 (JP, A) JP-A-6-307415 (JP, A) JP-A-1-266379 (JP, A) JP-A-7-207 167317 (JP, A) Japanese Utility Model Sho 62-194172 (JP, U) Japanese Utility Model Sho 51-26349 (JP, Y2) Japanese Utility Model Utility Model 47-22316 (JP, Y1) (58) Fields investigated (Int. Cl. ⁷ , DB name) F15B 11/08 F15B 21/10 F16K 21/14

Claims (3)

(57) [Claims] 1. A timer valve for use in connection with a mechanical brake device of a hydraulic motor, for delaying operation return from a released state, comprising: a longitudinal bore, a first port connectable to a hydraulic pressure source, and a second port. A valve body having a pilot pressure oil port, a third port communicating with the cylinder hydraulic chamber of the mechanical brake device, and a fourth drain port communicating with the oil tank; and a slidable slide in a longitudinal bore of the valve body. A first position in which the second port and the third port are in fluid communication with each other, thereby releasing the mechanical brake device; and a third port and a fourth port in fluid communication with each other, A switching valve means comprising: a spool movable in an axial direction between a second position for actuating the mechanical brake device by the control valve and a timer valve. Control means for controlling the movement of the spool of the means to delay the operation of the mechanical brake device, the control means including a closed cylinder chamber filled with a predetermined amount of working fluid, and a closed cylinder chamber in the first position. A piston provided with a piston rod on the opposite side, and provided in the closed cylinder chamber, and provided in the closed cylinder chamber in a normal state. A spring biasing the piston toward the second position, and means provided on the piston for fluidly communicating the first chamber and the second chamber with each other; The working areas of the axial end faces are equal, one of the piston rods is guided axially in the closed cylinder chamber, and the other of the piston rods abuts the spool. When the pressure oil is supplied to the first port, the spool moves from the second position to the first position against the urging force of the spring of the piston, When the supply of the pressurized oil to the first port is stopped, the port moves from the first position to the second position with the movement of the piston by the spring urging force. Restricting the flow of working fluid from one of the first and second chambers, which is contracting, to the other, which is expanding, resulting from movement of the piston by a spring biasing force in response to a stop of supply of hydraulic oil to the port. ,
Whereby the piston movement, thus saw including a throttle means for providing a desired delay time operation return of the mechanical braking device to control the movement of the spool toward the second position,
In this way, the delay function is
It is possible to set an accurate delay time because it is independent of the road.
Timer valve, characterized in that. 2. The fluid communication means is provided on the piston, and moves from the contracting chamber to the expanding chamber upon movement of the piston accompanying movement of the spool from the second position to the first position. To reverse the flow of the working fluid from the contracting chamber to the expanding chamber upon movement of the piston with movement of the spool from the first position to the second position. Further comprising a stop valve, whereby the spool
2. The system according to claim 1, wherein when the pressure oil is supplied to the first port, the piston moves quickly from the second position to the first position against the urging force of the spring of the piston. The described timer valve. 3. The spool of the switching valve means and the piston of the control means are each provided with a central internal axial passage, and the central internal axial passage is provided at a contact portion between the spool and the other piston rod of the piston. 3. The timer valve according to claim 2, wherein the timer valve is in communication with each other via the throttle portion and can communicate with the first port.