Hydraulic actuator

Abstract

To provide a hydraulic actuator which enables reduction of a load applied to a cylinder at a stroke end.SOLUTION: In a double-acting type hydraulic actuator 1, a piston 4 includes: an oil passage which allows a head side oil chamber 21 and a rod side oil chamber 22 to communicate with each other; a relief valve 5 which is disposed in the oil passage and opens when a pressure in the rod side oil chamber 22 reaches a predetermined pressure; and a proximity activator member 6 which is pressed by an inner surface 23a of a rod cover 23 to open the relief valve 5 at a closet position to a stroke end.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a hydraulic actuator that reduces the load on a cylinder by discharging oil just before a piston reaches a stroke end. [Background technology]

[0002] One of the problems with conventional hydraulic actuators is the load on the piston and cylinder caused by pressure buildup at the end of the piston's stroke. In many actuators, pressure buildup at the end of the piston's stroke is unnecessary. For example, in the case of a compression head actuator, compression is completed when the upper and lower dies touch, so pressurization at the end of the stroke is unnecessary. Therefore, compression operations without dies, which would cause load buildup at the end of the stroke, are prohibited. For example, in a pole crusher such as that described in Patent Document 1, which uses a hydraulic actuator to drive a chisel into a concrete pillar to crush it, pressure is applied at the stroke end due to the structure, even though pressure is not required after crushing the pole. The same can be said for hydraulic cutters for electric wires. Therefore, a cylinder and piston strong enough to withstand the load at the stroke end are required. This has led to problems such as the device becoming larger and heavier. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 6-31841 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a hydraulic actuator that can mechanically open an oil passage at a position immediately adjacent to the stroke end of the piston to release pressure inside the cylinder, thereby reducing the load on the cylinder at the stroke end. [Means for solving the problem]

[0005] In the following description, reference will be made to the reference numerals in the accompanying drawings, but the present invention is not limited thereto. In order to solve the above problems, in the double-acting hydraulic actuator 1 of the present invention, the piston 4 is provided with an oil passage that connects the head-side oil chamber 21 and the rod-side oil chamber 22, a relief valve 5 that is interposed in the oil passage and opens when the rod-side oil chamber 22 reaches a predetermined pressure, and a proximity actuation member 6 that is pressed by the inner surface 23a of the rod cover 23 at a position just near the stroke end to open the relief valve 5. [Effects of the Invention]

[0006] According to the hydraulic actuator of the present invention, the oil passage is mechanically opened at a position immediately adjacent to the stroke end of the piston to release pressure inside the cylinder, thereby reducing the load on the cylinder at the stroke end. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a perspective view of a concrete pillar crushing device in use. [Figure 2] 2 is a cross-sectional view of a hydraulic crusher constituting the crushing device of FIG. 1, showing a state in which the piston rod of the hydraulic actuator is in a retracted position. [Figure 3] 2 is a cross-sectional view of a hydraulic crusher constituting the crushing device of FIG. 1, showing a state in which the piston rod of the hydraulic actuator is in an extended position. [Figure 4] 3 is a partially cutaway plan view of the hydraulic crusher of FIG. 2, showing the piston rod of the hydraulic actuator in an extended position. [Figure 5] FIG. 4 is an enlarged view of part V in FIG. 3. [Figure 6] FIG. 10 is a cross-sectional view showing another embodiment of the actuator in the hydraulic crusher. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment in which a hydraulic actuator of the present invention is applied to a concrete pillar crushing device will be described with reference to the drawings. As shown in Figure 1, the concrete pillar P crushing device 101 is equipped with four identical hydraulic crushers 102 arranged on all four sides, at 90° intervals, around the outer periphery of the upright concrete pillar P to be crushed, and four connecting metal fitting assemblies 103 that connect adjacent hydraulic crushers 102 to surround the concrete pillar P, and is a device that crushes the concrete pillar P from all four sides simultaneously using the four hydraulic crushers 102.

[0009] As clearly shown in Figures 2 to 4, the hydraulic actuator 1 of the hydraulic crusher 102 is equipped with a hydraulic cylinder 2, a piston rod 3, and a piston 4, which are arranged with their axis oriented horizontally at the center of the concrete column P. A crushing blade 105 is fixed to the tip of the piston rod 3. A frame assembly 104 is attached to the rod cover 23 of the hydraulic cylinder 2.

[0010] The frame assembly 104 is provided with a pair of ball lock pins 106 for attaching and detaching the connecting fitting assembly 103 .

[0011] The piston rod 3 has a through-hole 31 in a direction perpendicular to the axis at a position adjacent to the piston 4. In the illustrated embodiment, the piston rod 3 is provided with a hollow portion 32 for weight reduction, which forms an internal oil chamber. The internal oil chamber 32 communicates with the head-side oil chamber 21 via the relief valve 5, and also communicates with the rod-side oil chamber 22 via the through-hole 31. In the illustrated embodiment, a pair of through-holes 31 open at opposing positions in the direction perpendicular to the axis on the outer circumferential wall 33 of the internal oil chamber 32.

[0012] The piston 4 is fitted with a relief valve 5 disposed in an oil passage (inflow passage 51a, valve chamber 51b, outflow passage 51c, through hole 31) communicating between the rod side oil chamber 22 and the head side oil chamber 21 of the cylinder 2.

[0013] The relief valve 5 includes a casing 51 having an oil inlet passage 51a, a valve chamber 51b, and an oil outlet passage 51c, and a stem 52 and a spring 53 housed in the valve chamber 51b. The inlet passage 51a communicates with the head-side oil chamber 21. The outlet passage 51c communicates with the rod-side oil chamber 22 via a through-hole 31. The tip of the stem 52 protrudes from the outlet passage 51c toward the through-hole 31.

[0014] A proximity actuating member 6 is provided on the piston rod 3 adjacent to the piston 4 for opening the relief valve 5 when pressed by the inner surface 23a of the rod cover 23 of the cylinder 2 at a position immediately adjacent to the stroke end of the piston 4.

[0015] The proximity actuation member 6 consists of a spring pin 61 and a guide ring 62. The spring pin 61 passes loosely through the through hole 31 and moves freely in the axial direction of the piston rod 3 within the range of the inner diameter of the through hole 31. Both ends of the spring pin 61 protrude beyond the outer periphery of the piston rod 3, and the middle part of the spring pin 61 abuts against the tip of the stem 52 of the relief valve 5 that protrudes into the through hole 31 (internal oil chamber 32).

[0016] The guide ring 62 is fitted onto the piston rod 3 and engaged with both ends of the spring pin 61, so that it can move freely in the axial direction of the piston rod 3 together with the spring pin 61 within the range of the inner diameter of the through hole 31.

[0017] The guide ring 62 is pressed by the inner surface 23a of the rod cover 23 at a position immediately adjacent to the stroke end of the piston 4, and pushes the stem 52 to the open position via the spring pin 61. This opens the relief valve 5, and the head-side oil chamber 21 and the rod-side oil chamber 22 communicate with each other via the inlet passage 51a, the valve chamber 51b, the outlet passage 51c, and the through-hole 31. Therefore, the hydraulic pressure in the rod-side oil chamber 22 is released just before the piston 4 reaches the stroke end, reducing the load on the cylinder 2.

[0018] In addition, when oil is sent to the head side oil chamber 21 without the rod side oil chamber 22 being connected to the hydraulic pump, the pressure in the rod side oil chamber 22 increases due to the operation of the piston 4, the relief valve 5 opens at the set pressure, and the rod side oil chamber 22 and the head side oil chamber 21 are balanced.

[0019] Also, if high pressure is mistakenly applied to the rod-side oil chamber 22 by mistake, the relief valve 5 opens at the set pressure and oil is released into the oil tank via the head-side oil chamber 21.

[0020] 6 shows an embodiment of a hydraulic actuator in which no cavity (internal oil chamber 32) is provided in the piston rod 3. Note that the same components as those in the previous embodiment are given the same reference numerals and their explanation will be omitted.

[0021] The above has been described taking as an example the case where the hydraulic actuator 1 of the present invention is applied to the hydraulic crusher 102, but the present invention is not limited to this and can also be applied to actuators of other equipment, such as compression heads, electric wire cutting devices, etc. [Explanation of symbols]

[0022] 1 Hydraulic Actuator 2 hydraulic cylinders 21 Head side oil chamber 22 Rod side oil chamber 23 Rod cover 23a Inside surface 3 Piston rod 31 Through hole 32 Cavity (internal oil chamber) 33 Outer wall 4 pistons 5 Relief valve 51 Casing 51a Inlet channel 51b Valve chamber 51c Outflow channel 52 stem 53 Spring 6 Proximity activation member 61 Spring pin 62 Guide ring 101 Crushing equipment 102 Hydraulic crusher 103 Connecting metal fitting assembly 104 Frame assembly 105 Crushing blade 106 Ball lock pin P Concrete pillar

Claims

1. A double-acting hydraulic actuator, wherein a piston comprises: an oil passage connecting a head-side oil chamber and a rod-side oil chamber; a relief valve that is interposed in the oil passage and opens when the rod-side oil chamber reaches a predetermined pressure; and a proximity actuation member that is pressed by the inner surface of the rod cover at a position immediately adjacent to the stroke end to open the relief valve.

2. the oil passage of the piston includes a through hole that is adjacent to the piston and penetrates the piston rod in a direction perpendicular to the axis, and both ends of which communicate with the rod-side oil chamber, The relief valve is provided so that a tip end of a stem projects in an axial direction into the through hole, the proximity actuation member includes a guide ring fitted onto the piston rod adjacent to the piston so as to be movable in the axial direction, and a spring pin loosely inserted into the through hole, both ends of which are engaged with the guide ring and an intermediate portion of which abuts against a tip of the stem of the relief valve, 2. The hydraulic actuator according to claim 1, wherein the guide ring is pressed against the inner surface of the rod cover at a position immediately adjacent to the stroke end to push the stem to an open position via the spring pin, thereby connecting the head-side oil chamber and the rod-side oil chamber via the through hole.

3. the through hole included in the oil passage of the piston is provided to penetrate a peripheral wall of an internal oil chamber formed in the piston rod in a direction perpendicular to the axis and to communicate with the rod-side oil chamber, 3. The hydraulic actuator according to claim 2, wherein the relief valve is provided so that the tip of the stem projects axially into the internal oil chamber.

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