JPH0419038Y2 - - Google Patents

Description

[Detailed Description of the Invention] A. Field of Industrial Application The present invention relates to a table lifter, and more particularly to a descending speed control mechanism for avoiding rapid descent of a table that is lifted and lowered by hydraulic operation.

B. Prior art When raising and lowering a table that is hydraulically operated, by injecting hydraulic oil into the cylinder using a pump, it is possible to easily lift objects from light to heavy to the desired height. It is. However, when lowering the table, a valve is opened to lower the oil pressure and the weight of the table and the loaded object causes the table to descend naturally, making it extremely difficult to control the lowering speed. In other words, the descending speed varies depending on the opening degree of the valve and the load on the table, and if a heavy load is loaded, the table may descend to the bottom all at once just by opening the valve slightly. It can happen. Therefore, in such a case, there is a risk that the table may collide with the frame and cause the load to collapse, or the loaded object may fly up due to the reaction and be thrown outside the table, thereby damaging the precious cargo. It was hot. Therefore, when the table was lowered, the valves were operated with special care to prevent the table from descending suddenly.

A control valve described in Japanese Patent Publication No. 38-21149 is known as a device that enables such throttle control.

C. Problems to be Solved by the Invention The conventional control valve described above has a complicated orifice mechanism in the inverted cup-shaped spool to perform throttle control, and also incorporates multiple springs to gradually move the spool using pressure differences. Due to the complicated structure of moving it toward the discharge path, it was not only difficult to adjust, but also difficult to use with a cylinder device that operates at low pressure, such as a table lifter.

D. Means for Solving the Problems In view of the above-mentioned drawbacks of conventional control valves, the present invention has a simple structure and allows the spool to be operated directly with less pressure.
The structure is such that a cylindrical injection passage with a smaller diameter than the oil reservoir is provided on one side of an oil reservoir provided in the housing, and a discharge passage with an even smaller diameter than the injection passage is coaxially disposed on the other side. an inverted cup-shaped spool with an internal cavity, the tip of which is brought into contact with the opening of the discharge passage and projected into the oil reservoir chamber by the force of a spring provided in the injection passage; loosely fit into the contact surface of the spool with the discharge passage opening,
In addition to forming an oil groove in the direction perpendicular to the discharge path, a through hole communicating with the cavity inside the spool is bored in the side of the spool that extends into the oil reservoir chamber, and the spool is opened by hydraulic pressure on the discharge port side. The control valve, which is forced into the injection path and performs a throttle operation, is arranged in series with the hydraulic circuit of the table lifter.

E. Effect Since the diameter of the discharge passage and injection passage is smaller than the diameter of the spool, even if the pressure is low, changes in pressure act on the spool appropriately, and during injection, the spool remains pressed toward the discharge passage by the spring. It communicates through the through hole and the oil groove, and at the time of discharge, the discharge pressure acts directly on the spool and pushes the spool back toward the injection path against the spring force, causing a throttling operation.

F. Embodiment Next, an embodiment of the present invention will be described with reference to the drawings.

In FIG. 1 showing the hydraulic circuit of the table lifter, a control valve 5 which is throttled by hydraulic pressure in the opposite direction is inserted and connected to a main conduit 4 through which oil from an oil tank 1 is sent to a cylinder 3 by operation of a pump 2. Further, the main pipe line 4 is provided with a branch line 7 that returns the water to the ortank via a return valve 6. Sho 8,
8' is a check valve, and 9 is a safety valve. As shown in the third figure, the control valve 5 has an injection passage 11 in the housing 10,
An internally hollow cup-shaped spool 14 is loosely fitted into a cylindrical injection path 11, which is a communicating path in which an oil reservoir chamber 12 and a discharge path 13 are provided coaxially. The inner wall of the cylinder has a smaller diameter than the chamber 12, and the discharge passage 13 on the opposite side
is formed within the joint member 15 to have a smaller diameter than the injection path 11 by screwing the joint member 15 together. The spool 14 is loosely fitted into the injection path 11 in a state where it is pushed out into the oil reservoir chamber 12 by a coil spring 16.
is positioned in the oil reservoir chamber 12, and its tip is in contact with the opening of the discharge passage 13. Also spool 14
As shown in the second figure, an oil groove 17 is carved on the tip of the head, that is, on the contact surface with the discharge passage 13, and is perpendicular to the discharge passage and forms a flow passage on the corresponding contact surface. , a small through hole 18 communicating with the intermediate interior is provided on the side of the portion of the spool that extends into the oil reservoir chamber 12.
Multiple holes have been drilled. In the drawings, 19 is a washer.

When the table is to be raised, the pump 2 is operated to pump hydraulic oil from the oil tank 1 into the cylinder 3, which causes the piston rod to extend and lift the table. Conversely, in order to lower the table, by opening the return valve 6, the hydraulic oil in the cylinder 3 is returned to the oil tank 1, the piston rod retracts, and the table naturally lowers.

In the above operation, when the pump is operated, the control valve 5 maintains the tip of the spool 14 in contact with the opening of the discharge passage 13 as shown in the third figure when the table is raised. The hydraulic oil flows from the injection path 11 into the cavity of the spool 14, passes through the small through hole 18, flows into the oil reservoir chamber 12, and from there passes through the oil groove 17 to the discharge path 13 and then to B. be. On the other hand, when the return valve 6 is opened to lower the table, the control valve 5 operates in two ways depending on the opening degree of the return valve and the load on the table. When the return pressure of the hydraulic oil is low, it flows in the opposite direction from the flow path from A to B, but when the return pressure exceeds a predetermined value (when the force of the coil spring 16 is exceeded), the return pressure The spool 14 is pushed into the injection path 11, and the small through hole 18 is closed. A higher return pressure means that the amount of hydraulic oil returned increases and the table descends faster.
8 is blocked, the flow path is blocked, and rapid descent of the table is prevented. The control valve of the invention is
Since the spool is loosely fitted into the cylindrical injection path, the inner surface of the injection path and the outer surface of the spool are not in close contact, and the hydraulic oil flows little by little from B to A, and the table descends at a very slow speed. be. This operation works because when a heavy object is loaded, a large return pressure is always applied to the spool, so even if the return valve is opened wide by mistake when lowering the table,
The table descends slowly from the beginning. Also, if the table is accelerated while descending and reaches a predetermined speed during the descent, the spool is pushed into the injection path and the mode is switched to slow descent. If the rapid descent of the table is prevented, when unloading the load,
There is no need to be particularly careful in operating the return valve, and the operation can be handled by simply closing the valve.

Effects As described above, according to the present invention, by arranging a control valve with a simple structure and an accurate throttling operation even at low pressure in series with the hydraulic circuit of the table lifter, the table lowering speed of the table lifter can be maintained at a constant speed. If this occurs, the conduit is throttled and the load is automatically lowered at a slow speed to keep the load safe, so table lifters have superior operability compared to those using conventional control valves. Less maintenance required,
The benefits are enormous.

[Brief explanation of drawings]

FIG. 1 is a hydraulic circuit of a table lifter, FIG. 2 is a perspective view showing the internal structure of the spool with a portion thereof cut away, and FIGS. 3 and 4 are sectional views showing the operation of a control valve. 1...Oil tank, 2...Pump, 3...Cylinder, 4...Main pipe, 5...Control valve, 6...Return valve, 7...Branch passage, 8, 8'...Check valve ,9...
...Safety valve, 10...Housing, 11...Injection path, 12...Oil reservoir chamber, 13...Discharge path, 14...
... Spool, 15 ... Joint member, 16 ... Coil spring, 17 ... Oil groove, 18 ... Small through hole, 1
9...Washer.

Claims (1)

[Scope of utility model registration request] A cylindrical injection path with a smaller diameter than the oil storage chamber is provided on one side of an oil reservoir provided in the housing, and a discharge path with an even smaller diameter than the injection path is provided coaxially on the other side. A communicating path is formed, and an inverted cup-shaped spool with an internal cavity is moved into the injection path by the force of a spring provided in the injection path, the tip of which touches the opening of the discharge path and extends into the oil reservoir chamber. and forming an oil groove in a direction orthogonal to the discharge passage on the contact surface of the spool with the discharge passage opening,
A through hole that communicates with the cavity inside the spool is drilled in the side of the spool that is tipped into the oil sump chamber, and the spool is pushed into the injection path by hydraulic pressure on the discharge port side to perform a throttle operation. A table lowering speed control mechanism for a table lifter, characterized in that a valve is arranged in series with a hydraulic circuit of the table lifter.