JPH0540299U - Load lifting device - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to prevent the rod side chamber 5 from being in a vacuum state when the load W is lowered by contracting the cylinder 1 while keeping the switching valve 4 in the neutral position. An object of the present invention is to provide a load lifting device. [Structure] A bottom side passage 3 between a counter balance valve 7 and a bottom side chamber 2 is connected to a tank via a return passage 12. An operation check valve 14 and a throttle 15 are provided in the return passage, and the operation check valve is opened by the pressure action of the hand pump 16 to make the flow from the bottom passage to the tank a free flow. Further, between the operating check valve and the throttle, a regenerative passage 17 connecting to the rod side chamber is provided, and a check valve 18 which allows only the flow from the tank to the rod side passage is provided in the regenerating passage.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a load lifting device that is optimal for use in, for example, an aerial work vehicle.

[0002]

[Prior Art]

 FIG. 2 is a circuit diagram of a conventionally known load lifting device for use in an aerial work vehicle. A cylinder 1 of the load lifting device has a bottom chamber 2 and a switching valve 4 via a bottom passage 3. The rod-side chamber 5 is connected to the other actuator port of the switching valve 4 via the rod-side passage 6. A pump P is connected to the pump port of the switching valve 4, and a tank T is connected to the tank port. The switching valve 4 thus configured is of a normally closed type and is configured to be closed when it is in the neutral position shown in the figure, and to connect the passage 3 or 6 to the pump P or the tank T when switched to the left or right. ..

A counter balance valve 7 is provided in the bottom side passage 3. The counter balance valve 7 comprises a check valve 7a and a control valve 7b connected in parallel. The check valve 7a is configured to allow only the flow from the switching valve 4 to the bottom side chamber 2. The control valve 7b is closed in the normal state shown in the drawing and opened by the action of pilot pressure introduced from the pilot passage 8, but its opening is proportional to the pilot pressure.

The pilot passage 8 communicates with the hand pump 10 and the rod-side passage 6 via a shuttle valve 9. Therefore, when the hand pump 10 is operated, or when the pressure in the rod side passage 6 is increased, the control valve 7b is opened. Further, an operation check valve 11 is connected to the bottom side passage 3 between the counter balance valve 7 and the switching valve 4, and the operation check valve 11 is opened by the discharge pressure of the hand pump 10. Speak.

Now, when the switching valve 4 is switched to the left side position from the state shown in the figure, the discharge fluid of the pump P flows from the switching valve 4 to the bottom side chamber 2 of the cylinder 1 via the bottom side passage 3 and the check valve 7a. Supplied. At this time, the working fluid in the rod side chamber 5 is returned from the rod side passage 6 to the tank T via the switching valve 4. Therefore, the cylinder 1 extends to increase the load W. When the switching valve 4 is switched to the right side position which is the opposite side to the above, the discharge fluid of the pump P is supplied to the rod side chamber 5 via the rod side passage 6. At this time, the pressure in the rod side passage 6 rises, so that the pressure is guided to the pilot passage 8 via the shuttle valve 9. When the pressure is introduced into the pilot passage 8 in this manner, the control valve 7b opens due to the pressure action. Therefore, at this time, the working fluid in the bottom side chamber 2 is returned to the tank T from the control valve 7b via the bottom side passage 3 and the switching valve 4.

Further, when the switching valve 4 is kept in the neutral position shown in the figure with the cylinder 1 extended and the load W is maintained at a high place, for example, when an engine trouble occurs, the load W is urged. I have to lower it. At this time, the hand pump 10 is operated to generate the pilot pressure while maintaining the switching valve 4 in the neutral position. This pilot pressure is guided from the shuttle valve 9 to the pilot passage 8, so that the control valve 7b opens. At the same time, this pilot pressure also acts on the operating check valve 11 to open it. Therefore, the cylinder 1 automatically contracts under the action of the load W and lowers it.

[0007]

[Problems to be solved by the device]

 In the conventional load lifting device as described above, the supply of the working fluid to the rod side chamber 5 of the cylinder 1 is completely cut off when the load W is lowered in an emergency. Therefore, there is a problem that the inside of the rod side chamber 5 is in a vacuum state and the seal of the rod portion of the cylinder 1 is damaged. Further, when the inside of the rod side chamber 5 is in a vacuum state as described above, there is a problem that the load does not come down because the cylinder 1 does not contract when the load W is light. An object of the present invention is to provide a load elevating device that prevents the rod side chamber from being in a vacuum state when the load is lowered by contracting the cylinder while keeping the switching valve in the neutral position.

[0008]

[Means for Solving the Problems]

 This invention comprises a cylinder for raising and lowering a load, a bottom side passage connected to the bottom side chamber of the cylinder, a rod side passage connected to the rod side chamber, and a counter balance valve provided in the bottom side passage. Is based on a load elevating device configured to communicate with a pump or tank via a switching valve. Based on the above device, the present invention connects the bottom side passage between the counter balance valve and the bottom side chamber to the tank via the return passage, and the return passage has an operation check valve and a throttle. This operating check valve is configured to open by the pressure action of the hand pump so that the flow from the bottom side passage to the tank can flow freely.Furthermore, between the operating check valve and the throttle, there is a rod side chamber. It is characterized in that a regenerative passage connected to is provided and a check valve that allows only the flow from the tank to the rod side passage is provided in the regenerative passage.

[0009]

[Action]

 Since the present invention is configured as described above, when the hand pump is operated to open the operate check valve, the working fluid in the bottom side chamber is returned to the tank via the throttle. Since the fluid is returned to the tank while the throttling resistance is applied in this way, the fluid having a volume difference between the bottom side chamber and the rod side chamber is supplied to the rod side chamber of the cylinder from the regenerative passage having a small resistance.

[0010]

[Effect of the device]

 According to the load elevating device of the present invention, when the hand pump is operated to suddenly lower the load, a fluid having a volume difference between the bottom side chamber and the rod side chamber is supplied to the rod side chamber, so that the rod side chamber is in a vacuum state. It doesn't become. Therefore, unlike the conventional case, the problem that the seal of the rod portion is damaged or the cylinder does not operate does not occur.

[0011]

【Example】

 In the embodiment of FIG. 1 showing a load lifting device used for an aerial work vehicle, each of the bottom side chamber 2 and the rod side chamber 5 of the cylinder 1 is provided with a switching valve 4 via a bottom side passage 3 and a rod side passage 6. 2 and the provision of the counter balance valve 7 in the bottom side passage 3 are the same as in the conventional case shown in FIG.

Then, the difference of this embodiment from the conventional one is as follows. That is, the return passage 12 connected to the tank T is connected to the bottom passage 3 that connects the bottom chamber 2 and the counterbalance valve 7. The return passage 12 is provided with a descending speed control throttle 13, an operating check valve 14 and a fixed throttle 15 in this order from the bottom passage 3 side. Further, a hand pump 16 is connected to the operate check valve 14, and the operation check valve 14 is opened by the action of pilot pressure from the hand pump 16. When the operation check valve 14 is closed, the passage of fluid from the bottom side passage 3 is blocked.

The return passage 12 between the operation check valve 14 and the fixed throttle 15 is connected to the rod-side passage 6 via the regeneration passage 17. The regenerative passage 17 is provided with a check valve 18 which allows only the flow from the regenerative passage 17 to the rod side passage 6.

Next, the operation of this embodiment will be described. The operation of switching the switching valve 4 and expanding and contracting the cylinder 1 is the same as in the case of the Jurai shown in FIG. Only the case of lowering the load W while maintaining the standing position will be described. When the hand pump 16 is operated with the switching valve 4 kept in the neutral position shown in the figure, the discharge pressure of the hand pump 16 acts on the operate check valve 14 to open it. Then, the working fluid in the bottom side chamber 2 of the cylinder 1 passes from the bottom side passage 3 through the descending speed control throttle 13 and the operation check valve 14.

At this time, since resistance is imparted to the fluid flowing in the tank T by the fixed throttle 15, most of the fluid in the bottom side chamber 2 that has passed through the operation check valve 14 is mostly in the regeneration passage 17 and the check valve. It is supplied to the rod side chamber 5 via 18. Then, only the excess fluid corresponding to the volume difference between the bottom side chamber 2 and the rod side chamber 5 is returned to the tank T via the fixed throttle 15. As described above, according to the load elevating / lowering device of this embodiment, even when the load W is suddenly lowered, the inside of the rod side chamber 5 is not in a vacuum state, so that the seal of the rod portion is damaged as in the conventional case, or If the load is light, there is no problem that it does not drop.

[Brief description of drawings]

FIG. 1 is a circuit diagram of this device.

FIG. 2 is a circuit diagram of a conventional load lifting device.

[Code]

 P Pump T Tank 1 Cylinder 2 Bottom side chamber 3 Bottom side passage 4 Switching valve 5 Rod side chamber 6 Rod side passage 7 Counterbalance valve 12 Return passage 14 Operate check valve 15 Fixed throttle 16 Hand pump 17 Regeneration passage 18 Check valve

Claims (1)

[Scope of utility model registration request] 1. A cylinder for raising and lowering a load, a bottom side passage connected to a bottom side chamber of the cylinder, a rod side passage connected to a rod side chamber, and a counterbalance valve provided in the bottom side passage, both of which are provided. In a load lifting device configured to communicate the passage with a pump or a tank via a switching valve, a bottom side passage between a counterbalance valve and a bottom side chamber is connected to a tank via a return passage, and the return passage is connected to the tank. An operating check valve and a throttle are provided in the passage, and this operating check valve is
The valve is opened by the pressure action of the hand pump to make the flow from the bottom side passage to the tank a free flow.In addition, a regenerative passage is provided between the operate check valve and the throttle to connect it to the rod side chamber. A load lifting device with a check valve in the regenerative passage that allows only flow from the tank to the rod-side passage.