JPH0141921Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a cushion device for a hydraulic cylinder that unloads oil discharged from a pump at a stroke end portion of the cylinder.

As a device of this kind, one disclosed in Japanese Utility Model Publication No. 39-28946 has been known for some time, and this device will be explained with reference to FIG.

The conventional device described above has ports 2 and 3 formed at both ends of the cylinder 1, and protrusions 5 and 6 provided on both sides of the piston 4 are inserted into the ports 2 and 3, thereby controlling the spool 8 of the control valve 7. It is what activates it.

That is, when the piston 4 now moves in the direction of the arrow 9 and its protrusion 6 enters the port 3, the pressure inside the port 3 increases. The pressure within the port 3 that has increased in this way acts on the left side of the flange 10 of the spool 8, causing the spool 8 to move rightward in the drawing. When the spool 8 moves to the right, the ports 11 and 12 of the control valve 7 are brought into communication, and the supply passage 13 at this time is brought into communication with the tank 14, and the oil discharged from the pump 15 is unloaded.

When the piston 4 moves in the opposite direction to the arrow 9, the pressure in the port 2 acts on the right side of the flange 10 and moves the spool 8 to the left,
At this time, the supply side passage 16 is communicated with the tank 19 via ports 17 and 18, and the oil discharged from the pump 15 is unloaded.

The biggest problem with this conventional device is that it is not possible to form an appropriate circuit in consideration of the situation when a counter load is applied to the cylinder.

That is, if a counter load is applied, the piston 4 may run away, which is dangerous, so the counter balance valves 20 and 21 must be provided at the positions shown in FIG. However, in this device now the arrow 9
If a counter load is applied in the direction, P ₁
As the pressure on the P2 side decreases, the counterbalance valve 21 closes to prevent it from escaping, but as the pressure on the _P2 side increases, the spool 8 moves and connects the passage 13, which is the supply side, to the tank 14. Put it away. Therefore, no matter how long the pressure on the _P1 side does not rise, the counterbalance valve 21 will no longer open, and the cylinder will no longer be able to operate.

This idea unloads the oil discharged from the pump at the end of the stroke, prevents it from escaping even if a counter load is applied, and allows the cylinder to operate immediately when the counter load is removed. This is what I did.

The embodiment shown in FIG. 2 will be described below.

Piston 2 slidably installed inside cylinder 22
A protruding portion 26 is provided on the rod 24 side of No. 3, and the protruding portion 25 projects into the control port 26 at the stroke end portion, so that the two together form a differential pressure detecting portion. In other words, when the protrusion 25 enters the control port 26, a slight gap is formed between them, and this gap functions as an orifice.

In the figure, reference numeral 27 is a piston side chamber, and 28 is a rod side chamber.

Further, the control valve 29 has first to second parts in its main body 30.
Three ports 31 to 33 are formed, and a spool 34 is installed inside.

The first port 31 is connected to the piston side chamber 27.
It is connected via a passage 37 to a passage 36 through which the directional control valve 35 and the directional switching valve 35 communicate with each other. Also, the second port 3
2 is a passage 3 that communicates the directional control valve 35 with the rod side chamber 28 and the outside of the control port 26;
8 through a passage 39. A counterbalance valve 40 is provided in the passage 38, and the counterbalance valve 40 is located closer to the directional control valve 35 than the intersection of the passages 38 and 39. Furthermore, the third port 33 is
It communicates with the rod side chamber 28 slightly inward from the control port 26 via a passage 41.

Note that the passages 36 and 38 are connected to the directional control valve 3.
Depending on the switching position of 5, the passage becomes a supply side passage or a return side passage.

Further, the first and second ports 31 and 32 open into the first and second annular grooves 42 and 43, and the third port 33 opens into the pilot pressure chamber 44.

On the other hand, the spool 34 is held by the action of a spring 45 in the illustrated position where the first annular groove 42 and the second annular groove 43 are normally disconnected from each other. In this normal position, the pressure receiving protrusion 46 projects into the pilot pressure chamber 44 and forms a balance chamber 47. Further, this spool 34 is formed with a communication hole 49 that communicates the spring side chamber 48 and the balance chamber 47, and this communication hole 49 is connected to the second annular groove 43, that is, the second port through the communication hole 50. 32 is always in communication.

In the spool 34 thus constructed, the pressure receiving area of the spring side chamber 48 is made equal to the pressure receiving area of both the balance chamber 47 and the pilot pressure chamber 44.

However, when the directional control valve 35 is set to the left position as shown in the figure, the oil discharged from the pump 51 flows into the piston side chamber 27 via the passage 36, and the counterbalance valve 40 is opened by the increase in pressure. Therefore, the oil in the rod side chamber 28 is returned to the tank 52, and the piston 23 moves toward the arrow 53.
move in the direction.

At this time, when a counter load in the direction of arrow 53 acts, the pressure in the supply passage 36 decreases, the counterbalance valve 40 closes, and the return passage 38 is cut off, thereby preventing the piston 23 from escaping.
In this state, the pressure in the rod side chamber 28 is introduced into the pilot pressure chamber 44 from the third port 33 and also into the second port 32. The pressure introduced into the second port 32 is also introduced into the spring side chamber 48 and the balance chamber 47 via the communication hole 49. Therefore, the same pressure acts on both end surfaces of the spool 34, and as described above, the pressure-receiving areas of both end surfaces are equal, so the spool 34 is held in its original position as shown in the figure by the action of the spring 45. The oil discharged from the pump 51 is not unloaded. Since unloading is not performed in this manner, when the counter load is removed, the pressure in the supply side passage 36 increases again, so the counter balance valve 40 opens and normal operation continues thereafter.

When the piston 23 further moves in the direction of the arrow 53 and the protrusion 25 enters the control port 26, the protrusion 25 and the control port 26 together constitute a differential pressure detection section. As mentioned above, this differential pressure detection part has a small gap and functions as an orifice, so when the piston 23 moves as described above and the hydraulic oil in the rod side chamber 28 flows out, this differential pressure detection part has a small gap and functions as an orifice. A pressure difference occurs before and after the pressure detection section.

Note that, as described above, the protrusion 25 is connected to the control port 2.
6, the pressure inside the piston side chamber 27, that is, the pressure inside the passage 36, also becomes quite high, so the counterbalance valve 40 maintains an almost fully open state.

Therefore, a higher pressure is introduced into the pilot pressure chamber 44 than in the spring side chamber 48 and the balance chamber 47, so that the spool 34 is moved against the spring 45. When the spool 34 moves in this way, the first annular groove 42 opens and communicates each of the first and second ports 31 and 32, so that the oil discharged from the pump 51 is almost fully open as described above. Returns to tank 52 via counterbalance valve 40. In other words, since the pump discharge oil is unloaded, the desired cushioning effect can be obtained.

Note that when the pump discharge oil is unloaded, the pressure on the passage 36 side decreases and the opening degree of the counterbalance valve 40 also decreases, but the pressure on the passage 36 side and the counterbalance valve 40 decrease.
Since the opening degree is almost proportional to the opening degree, there is no influence on the cushion effect.

Note that the second port 32 and a portion of the rod side chamber 28 outside the control port 26 may be directly connected. However, in this case, the pump discharge oil will be unloaded via the rod side chamber 28.

Further, the first port 31 and the piston side chamber 27 may be directly connected, but in this case, the pump discharge oil will be unloaded via the piston side chamber 27.

Next, if you switch the directional control valve 35 to the right position,
The oil discharged from the pump 51 flows into the rod side chamber 28 via the supply side passage 38, and then flows into the piston side chamber 27.
The oil returns to the tank 52 via the return passage 36, and the piston 23 moves to the opposite side of the arrow 53.

As is clear from the above explanation, this idea is
A protrusion is formed on the piston inserted into the cylinder, and at the stroke end of the piston, the protrusion enters a control port formed in the cylinder, and the protrusion and control port together form a differential pressure detection section. A directional switching valve is provided between the cylinder and the pump, which directs the oil discharged from the pump to one of the chambers of the cylinder and communicates the oil in the other chamber to the tank. A counterbalance valve is provided between the valve and one of the chambers of the cylinder, while a spool is installed in the control valve, and a pilot pressure chamber is formed that communicates with the high pressure side before and after the differential pressure detection section, The pressure receiving protrusion of the spool is inserted into this pilot pressure chamber, and the pressure on the low pressure side before and after the differential pressure detection part is applied to both end surfaces of the spool excluding the pressure receiving protrusion. It is characterized in that the spool of the control valve moves in accordance with the differential pressure that occurs, and the supply side passage that communicates with the pump communicates with the tank.

With the above configuration, when a counter load acts on the cylinder, the counter balance valve functions, while the control valve maintains its original position and prevents unloading of pump discharge oil.

Furthermore, when the protrusion provided on the piston enters the control port, the control valve is switched and the pump discharge oil is unloaded.

Therefore, an appropriate cushioning effect can be obtained at the stroke end portion, and a counterbalance valve can be connected to prevent the piston from running away when a counterload is applied to the cylinder. That is, even if a counterbalance valve is provided as in the prior art, there is no need to worry about the balance valve not opening after it closes due to the action of the counterload.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional device, in which a control valve is shown in cross section, other elements are shown by symbols,
FIG. 2 is a circuit diagram similar to FIG. 1 showing one embodiment of this invention. 22...Cylinder, 23...Piston, 25...
...Protruding portion, 26...Control port, 29...Control valve, 34...Spool, 36, 38...Passway serving as supply side or return side, 40...Counter balance valve, 44...Pilot pressure chamber, 51... ...pump, 52...tank.

Claims (1)

[Scope of utility model registration request] A protrusion is formed on the piston inserted into the cylinder, and at the stroke end of the piston, the protrusion enters a control port formed in the cylinder, and the protrusion and control port together constitute a differential pressure detection section. A directional switching valve is provided between the cylinder and the pump to guide the oil discharged from the pump into one of the chambers of the cylinder and to communicate the oil in the other chamber to the tank. A counterbalance valve is provided between the valve and one of the chambers of the cylinder, while a spool is installed in the control valve, and a pilot pressure chamber is formed that communicates with the high pressure side before and after the differential pressure detection section, The pressure receiving protrusion of the spool is inserted into this pilot pressure chamber, and the pressure on the low pressure side before and after the differential pressure detection part is applied to both end surfaces of the spool excluding the pressure receiving protrusion. A hydraulic cylinder cushioning device that moves the spool of a control valve in response to the differential pressure that occurs, allowing the supply side passage that communicates with the pump to communicate with the tank.