JPH02291399A - Oil full cylinder device - Google Patents

Abstract

PURPOSE:To prevent sudden rising of an oil level in an oil tank and damage of a cylinder when a piston is lowered by disposing a relief valve between a branch portion in a drain circuit and the oil tank. CONSTITUTION:A relief valve 1 is interposed in a drain circuit 33 extending from an oil control valve 5 to an oil tank 20. A discharge pipe 39 is also disposed between the relief valve 1 and the oil tank 20. A branch portion 40 is provided on the upstream side from the relief valve 1, and a suction and exhaust circuit 34 is connected between the branch portion 40 and the upper chamber 41 of a cylinder 4. A return pipe 37 adapted to circulate oil from an oil pump 23 to the oil tank 20 during the time except rising of a piston 45 is disposed between an oil control valve 5 and the oil tank 20.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an oil-filled cylinder device used for lifting a forklift truck, etc.

[Prior art]

For forklift trucks. A lift cylinder is provided to raise and lower the fork. and. In the lift cylinder. To prevent rust, there is a type of oil-full cylinder that keeps both the upper and lower chambers divided by the piston filled with operating oil at all times.

That is, as shown in Figure 3. The oil full cylinder device is. A cylinder 4 having an upper chamber 41 and a lower chamber 42 divided by a piston 45, an oil pump 23 that supplies oil 21 to the lower chamber 42 via an oil control valve 5, and a space between the lower chamber 42 and the oil tank 20. and a drain circuit 33 provided through the oil control valve 5.

Also. In the drain circuit 33, a branch part 40 is provided between the oil control valve 5 and the oil tank 20, and a suction/discharge circuit 34 is provided between the branch part 40 and the upper chamber 41 of the cylinder 4. Note that the code 22 is . It is a suction filter.

However. In the cough device, when raising and lowering the piston 45, the oil control lever 5 is
The oil pump 23 is supplied to the lower chamber 42 via the vibrator 32 through the vibrator 31 and check valve 35. As a result, the piston 4
5 rises. On the other hand, the oil in the upper chamber 41 flows through the suction and exhaust circuit 34 to the branch section 40. It returns to the oil tank 20 via the drain circuit 33.

Also, to lower the piston 45, operate the oil control valve 5 in the D direction. Lower chamber 42
The oil inside the vibrator 32 and oil control valve 5. It is returned to the oil tank 20 via the drain circuit 33. At this time. The oil that is constantly sent from the oil pump 23 is supplied to the oil control valve 5. It returns to the oil tank via a pipe 36 and a drain circuit 33.

Therefore, at the branch part 40 of the drain circuit 33, the oil discharged from the lower chamber 42 and the oil discharged from the lower chamber 42. The oil sent from the oil pump 23 joins.

On the other hand, the upper chamber 41 becomes a negative pressure because the piston 45 descends. Therefore, the upper chamber 41 sucks some of the oil in the drain circuit 33 from the branch section 40 via the suction circuit 34. Therefore, the upper chamber 41 of the cylinder. Lower chamber 42
will be filled with oil at all times.

[Problems to be Solved] However, the suction/exhaust circuit 34 has piping resistance, and there is also a henodic pressure based on the height difference H between the branch section 40 and the upper chamber 41. When the piston descends, the upper chamber 41
There may be cases where sufficient oil cannot be sucked into the tank. In such a case, a portion of the oil that should be sucked into the tree upper chamber 41 returns into the oil tank 20. Therefore. The oil level in the oil tank 20 would temporarily rise sharply, and sometimes the oil would blow out to the outside.

Further, as described above, when the amount of oil sucked into the upper chamber is small, the inside of the upper chamber 41 is in a reduced pressure state. Therefore,
The piston has finished descending. When the amount of oil from the lower chamber 42 decreases, the oil 21 in the oil tank 20. It may be sucked up from the lower end of the drain circuit 33. At this time, since there is no filter at the lower end of the drain circuit 33, dirt in the oil tank 20 may be sucked into the upper chamber 41 and damage the inner surface of the cylinder. The present invention has been developed in view of these conventional problems. It is an object of the present invention to provide an oil-full cylinder device which can prevent the oil level of an oil tank from rising sharply at -L when the piston descends, and which does not cause the above-mentioned damage to the cylinder.

[Means for solving the problem] The present invention provides a cylinder having an upper chamber and a lower chamber partitioned by a piston. An oil pump for supplying operating oil to the lower chamber via an oil control valve, a drain circuit provided between the lower chamber and the oil tank, and a branch portion provided in the middle of the drain circuit.
33. In an oil full cylinder device having a suction and exhaust circuit provided between a branch part and the upper chamber, and in which both the upper chamber and the lower chamber are filled with oil, the branch part in the drain circuit and the oil The oil full cylinder device is characterized by having a relief valve disposed between the oil tank and the tank.

In the present invention, what is a relief valve? This control valve prevents the oil in the drain circuit from flowing out toward the oil tank when the oil pressure in the drain circuit is below a certain pressure.

The cent pressure in the 8-bar relief vanole is. When the piston is descending. When oil from the lower chamber flows into the upper chamber. Set the pressure above the pressure required to follow the downward speed of the piston.

[Effect]

In the present invention, the oil discharged from the lower chamber when the piston descends tries to return to the oil tank via the drain circuit, and the cough drain circuit is provided with a relief valve.

Therefore, when the oil pressure in the drain circuit is lower than the set pressure of the relief valve, the entire amount of oil in the drain circuit enters the upper chamber from the branch section through the suction and discharge circuit. Note that when the oil pressure at the branch portion becomes higher than the set pressure, the oil in the drain circuit pushes open the relief valve and is discharged to the oil tank until the set pressure is reached.

On the other hand, when the piston rises, the oil in the upper chamber enters the drain circuit via the suction and exhaust circuit and the branch section. At this time, the oil in the suction and exhaust circuit. The pressure is high because it is forcibly discharged as the piston rises. Therefore, the relief valve opens. Oil in the upper chamber is easily drained.

However, as mentioned above. When the piston descends, oil is stably supplied into the upper chamber from the branch in front of the relief valve, so the upper chamber does not become depressurized like in the past. (Effect) Therefore. According to the present invention, the pressure in the upper chamber does not become reduced, so the oil level in the oil tank does not rise suddenly. Furthermore, it is possible to provide an oil flush cylinder device that does not suck dirt and the like in the oil tank into the cylinder. [Embodiment] An oil-filled cylinder device according to a first embodiment will be explained with reference to FIG.

The zero example device is. This is applied to the oil full lift cylinder of a forklift, and the oil control valve 5
to the drain circuit 33 leading from the oil tank 2o. Relief valve 1 is installed. Also, between the relief valve 1 and the oil tank 2o. A discharge pipe 39 is provided. A branch section 4o is provided on the upstream side of the relief valve 1, and a suction/exhaust circuit 34 is connected between the branch section 40 and the upper chamber 41 of the cylinder 4.

Also, oil control valve 5 and oil tank 20
, except when the piston 45 rises. A return pipe 37 is provided for circulating oil from the oil pump 23 between it and the oil tank 20. Other than that,
This is similar to the prior art (FIG. 3).

The relief valve 1 has a set pressure of, for example, approximately 15
It is set to kg/cd.

In the above device, when the piston 45 is lowered, the oil control valve 5 is operated in the D direction, and the oil in the lower chamber 42 is transferred to the pipe 32. The oil is discharged through the oil control valve 5 and the drain circuit 33. At this time, if the oil in the drain circuit 33 is below the set pressure of the relief valve 1, the entire amount of oil is sucked into the upper chamber 41 via the suction/discharge circuit 34. Therefore, the oil volume discharged from the lower chamber 42 is
This is larger than the oil capacity sucked into the upper chamber 41. Therefore, the oil pressure in the drain circuit 33 eventually increases and becomes higher than the set pressure of the relief valve 1. Then, the relief valve 1 is activated, and the oil is discharged (drained) into the oil tank 20 through the discharge pipe 39, and the pressure in the drain circuit 33 is lowered to the set pressure. Due to this. The inside of the upper chamber 41 will not be in a reduced pressure state.
, Filled with oil in a stable state.

On the other hand, when raising the piston 45, the oil control valve 5 is operated in the U direction to force the oil sent from the oil pump 23 into the lower chamber 42. Accordingly, the oil in the upper chamber 41 is discharged through the suction and discharge circuit 34. Since this oil discharge is forced, the oil pressure in the suction and discharge circuit 34 is . It becomes higher than the cent pressure of relief valve 1. Therefore. Eight hours later, I pushed open the relief valve. It is immediately discharged into the oil tank 2o.

As described above, according to the device of this example, the pressure inside the upper chamber 41 does not become reduced even when the piston descends. Therefore,
Unlike the conventional oil tank 2o, the oil does not blow out from the oil tank 2o, and the upper chamber 41 does not suck in dirt in the oil tank 2o together with the oil. Second Embodiment The oil full cylinder device of this example is. As shown in FIG. 2, in the first embodiment. The oil control valve 5 is provided with a drain circuit i55 and a supply circuit 56. The rest is the same as the first embodiment.

The drain circuit 55 drains oil from the upper chamber 41 when the piston 45 rises. Suction circuit 34, drain circuit 33
It is provided so that it communicates with the return vibe 37 through the. Also. The supply circuit 56 is a circuit for feeding oil from the oil pump 23 into the lower chamber 42 in order to raise the piston 45. Thus, both circuits 55 and 56 are connected to each of the above circuits by operating the oil control valve 5. According to this example.
When the piston is rising. The oil discharged from the upper chamber 41 is
It returns to the oil tank 20 through the drain circuit 55 of the oil control valve and the return pipe 37 without passing through the relief valve 1. Therefore, there is no need to push open the relief valve 1 for the discharged oil. Therefore, the pressure loss in this discharge path can be reduced, and smooth drainage can be performed. Furthermore, the same effects as in the first embodiment can be obtained.

[Brief explanation of the drawing]

Figure 1 is an oil circuit diagram in the first embodiment, and Figure 2 is an oil circuit diagram in the second embodiment. FIG. 3 shows an oil circuit diagram in a conventional example. 1. ．． ．． Relief valve, 20. ．． , oil tank, 4. ．． ．． cylinder, 40. ．． ．． Branch, 4 1. ．． ．． Upper chamber, 42. ．． ．． Lower chamber, 45. ．． ．． piston

Claims (1)

[Claims] A cylinder having an upper chamber and a lower chamber partitioned by a piston, an oil pump for supplying operating oil to the lower chamber via an oil control valve, and a cylinder provided between the lower chamber and the oil tank. The drain circuit includes a drain circuit provided in the middle of the drain circuit, a branch part provided in the middle of the drain circuit, and a suction/exhaust circuit provided between the branch part and the upper chamber, wherein both the upper chamber and the lower chamber are filled with oil. An oil full cylinder device characterized in that a relief valve is disposed between the branch portion of the drain circuit and the oil tank.