JP2012136344A - Leveling device of high-place working vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a working platform from being tilted further while controlling a negative pressure state in a hydraulic circuit of a leveling device.SOLUTION: The hydraulic circuit has: a first oil passage (a rod-side oil passage 31) which connects the rod side of an upper leveling cylinder 20 and the rod side of a lower leveling cylinder 10; and a second oil passage (a tube-side oil passage 33) which connects the tube side of the upper leveling cylinder 20 and the tube side of the lower leveling cylinder 10. The first and the second oil passages include relief valves 32a and 34a which are connected to a return circuit 35 for returning work oil into a tank T and are opened when the pressure of the first and the second oil passages becomes a predetermined pressure or more. A check valve 45 which can replenish the work oil from the return circuit 35 is provided on only either of the first or the second oil passage.

Description

  The present invention relates to a leveling device for an aerial work platform.

  Conventionally, as a leveling device for maintaining the level of a work table in an aerial work platform, a lower leveling cylinder that operates in conjunction with a boom swinging movement and an upper leveling cylinder that supports the work table in a swingable manner are provided. A leveling device is known in which the upper leveling cylinder operates in conjunction with the operation of the lower leveling cylinder so that the level of the work table can be maintained even when the boom moves up and down. In such a leveling device, for example, a hydraulic circuit is formed by the tube side circuit and the rod side circuit so that the tube side and the rod side of the upper leveling cylinder and the lower leveling cylinder are connected to each other. Then, when the oil pressure in the tube side circuit exceeds a predetermined pilot pressure, the hydraulic oil flows from the rod side of the upper leveling cylinder to the rod side of the lower leveling cylinder, and the oil pressure in the rod side circuit becomes a predetermined pilot pressure. A pilot check valve is provided so that the hydraulic fluid flows from the tube side of the upper leveling cylinder to the tube side of the lower leveling cylinder when the pressure exceeds. As a result, for example, when the lower leveling cylinder is extended in conjunction with the boom raising operation, the hydraulic pressure of the rod side circuit increases accordingly, and the hydraulic pressure of the rod side circuit becomes equal to or higher than the pilot pressure of the pilot check valve. The upper leveling cylinder and the lower leveling cylinder operate in conjunction with each other, such as when the circuit from the tube side of the upper leveling cylinder to the tube side of the lower leveling cylinder is open, and the upper leveling cylinder is contracted. is there.

  In such a conventional leveling device, since the hydraulic circuit is configured as a closed circuit, the volume of the hydraulic oil is reduced due to a change in the oil temperature due to a change in the outside air temperature, and the pressure of the hydraulic oil in the hydraulic circuit is reduced. (So-called negative pressure state). In such a case, in order to raise the hydraulic pressure in the circuit to the pilot pressure of the pilot check valve, it is necessary to expand and contract the lower cylinder more than the normal hydraulic pressure, which causes the operation delay of the upper leveling cylinder. Become.

  Therefore, for example, Patent Document 1 describes a configuration in which a check valve for preventing negative pressure is arranged in both a rod side circuit and a tube side circuit of a cylinder. According to such a configuration, since the hydraulic oil is surely supplied to the negative pressure state of the rod side circuit and the tube side circuit of the cylinder, the volume of the hydraulic oil is reduced due to the oil temperature change. It is thought that it can respond to.

JP 2002-321895 A

  However, for example, when the frequency of suction of the hydraulic oil from the check valve increases, the seat surface of the check valve may be damaged or foreign matter may be caught and the hydraulic oil may leak from the check valve. Therefore, in the configuration according to Patent Document 1, for example, when hydraulic oil leaks from a check valve disposed in the tube side circuit, the work table is tilted and the rod side circuit is in a negative pressure state. Then, the hydraulic oil is supplied from the check valve provided in the rod side circuit, and the hydraulic oil leaks from the check valve arranged in the tube side circuit. When this phenomenon is repeated, the hydraulic oil is supplied from the tube side circuit. Will continue to leak and hydraulic oil will continue to be supplied to the rod side circuit, and the tilt of the work table may continue to advance.

  Therefore, the present invention has been made in view of the above-described circumstances, and an object of the present invention is to prevent the work table from being inclined while suppressing the inside of the hydraulic circuit of the leveling device from being in a negative pressure state. .

  In order to solve the above-mentioned problems, in the invention described in claim 1, a boom that can be raised and lowered on a vehicle body, a workbench that can swing and turn at the tip of the boom, and the workbench A leveling device for an aerial work vehicle comprising: an upper leveling cylinder that swings, a lower leveling cylinder that operates in conjunction with a hoisting operation of the boom, and a hydraulic circuit that connects the upper leveling cylinder and the lower leveling cylinder The hydraulic circuit connects the first oil passage connecting the rod side of the upper leveling cylinder and the rod side of the lower leveling cylinder, and connects the tube side of the upper leveling cylinder and the tube side of the lower leveling cylinder. A second oil passage, and the first oil passage and the second oil passage are connected to a return circuit for returning the working oil to the tank. There is provided a relief valve that opens when the first oil passage and the second oil passage are at a predetermined pressure or higher, and either the first oil passage or the second oil passage is provided. Only, a check valve capable of supplying hydraulic oil from the return circuit is provided.

  The invention according to claim 2 is characterized in that the check valve is opened when the pressure of the oil passage provided becomes smaller than the pressure of the return circuit.

  The invention according to claim 3 is characterized in that the check valve is opened when the pressure of the provided oil passage becomes smaller than the atmospheric pressure.

  According to the first aspect of the present invention, when the oil passage becomes excessively high pressure, the circuit is protected by the relief valve, and when the oil passage becomes negative pressure, the working oil is discharged by the check valve. Supplied. And even if there is a leak from the check valve, hydraulic oil is not supplied to the oil passage on the side where the check valve is not provided, so that it is possible to prevent the tilt of the work table from continuing to proceed.

  According to the second aspect of the present invention, since the hydraulic oil is supplied by the return circuit pressure during the boom operation, even if the work table is inclined due to a leak, the work table is restored to the original state.

  According to the third aspect of the present invention, the working oil is supplied even when there is a decrease in the volume of the working oil caused by a change in the oil temperature, for example, during storage of an aerial work vehicle other than during the boom operation.

It is a side view of an aerial work vehicle according to an embodiment of the present invention. 1 is a hydraulic circuit diagram of a leveling device for an aerial work vehicle according to an embodiment of the present invention. It is a hydraulic-circuit figure of the leveling apparatus of an aerial work vehicle which concerns on other embodiment of this invention.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In addition, the same code | symbol is attached | subjected about the same or equivalent component, and the description is abbreviate | omitted when description overlaps. The present invention can be widely applied to an aerial work vehicle in which various work tables such as a worker boarding bucket and a work manipulator are attached at least to the tip of a boom provided so as to be able to undulate. Here, an example in which the present invention is applied to an aerial work vehicle provided with a bucket for boarding an operator as a work table will be described.

  1 and 2 show an embodiment according to the present invention. FIG. 1 is a side view of an aerial work vehicle. The aerial work vehicle 1 has front wheels 3F, 3F and rear wheels 3R, 3R on a chassis 2. Above the front wheels 3F, 3F, a cab 4 for operating the aerial work vehicle 1 is operated. Is provided. In the vicinity of the rear end of the chassis 2, a swivel base 6 that is swung by hydraulic oil supplied from a pump (not shown) is provided, and on the swivel base 6, a boom 5 is pivotally supported. . The boom 5 is pivotally supported at the rod side end of a hoisting cylinder 8 whose tube side end is pivotally supported by the swivel 6. The boom 5 is raised and lowered by extending and retracting the hoisting cylinder 8. It is like that. The boom 5 is configured to be extendable and retractable in a multistage manner, and a work table 7 is pivotally supported at the tip thereof about a rotation shaft 5a provided in the horizontal direction. The work table 7 can adjust the position in the height direction by expansion and contraction of the boom 5 and expansion and contraction of the hoisting cylinder 8, and can adjust the position in the horizontal direction by turning the swivel base 6. Further, the work table 7 has a pivot shaft so as to be swingable with respect to the boom 5, and the horizontal position can also be adjusted by this. The boom operation valve 50 for operating these operations is located on the swivel base 6. In addition, the raising / lowering apparatus is comprised by the boom P, the raising / lowering cylinder 8, and the pump P which supplies hydraulic fluid to these.

  A lower leveling cylinder 10 is provided between the swivel base 6 and the boom 5. The lower leveling cylinder 10 has a tube side end portion 10a supported on the swivel base 6 and a rod side end portion 10b supported pivotally on the boom 5, respectively, and expands and contracts in conjunction with the hoisting operation of the boom 5. Yes. That is, the lower leveling cylinder 10 is extended when the boom 5 is raised, and contracted when the boom 5 is lowered. Further, an arm 25 extending downward is provided in the vicinity of the rotating shaft 5 a of the work table 7, and an upper leveling cylinder 20 is provided between the arm 25 and the boom 5. The upper leveling cylinder 20 is pivotally supported at its rod-side end 20 a at the lower end of the arm and at the tube-side end 20 b at the tip of the boom 5. In the present embodiment, the upper leveling cylinder 20, the lower leveling cylinder 10 and the leveling circuit 30 connecting them constitute an operation mechanism of the leveling device 100.

  The leveling device 100 in the aerial work vehicle 1 having the above configuration will be further described with reference to the hydraulic circuit diagram shown in FIG. The leveling circuit 30 that connects the upper leveling cylinder 20 and the lower leveling cylinder 10 includes a rod side oil passage 31 that connects the rod side of the upper leveling cylinder 20 and the rod side of the lower leveling cylinder 10, the tube side of the upper leveling cylinder 20, and A closed circuit with a tube side oil passage 33 connecting the tube side of the lower leveling cylinder 10 is provided. A pilot check valve 41 is provided on the upper leveling cylinder 20 side of the leveling circuit 30 (rod side oil passage 31 and tube side oil passage 33), and hydraulic fluid from the lower leveling cylinder 10 to the upper leveling cylinder 20 is predetermined. When the cracking pressure is reached, the flow is allowed. The hydraulic oil from the upper leveling cylinder 20 to the lower leveling cylinder 10 is allowed to flow in the rod side oil passage 31 when the oil pressure in the tube side oil passage 33 exceeds a predetermined pilot pressure. In the path 33, when the oil pressure in the rod side oil path 31 exceeds a predetermined pilot pressure, the flow is allowed.

  When the work platform 7 is in a state such as the aerial work vehicle 1, a force on the contraction side acts on the upper leveling cylinder 20, and the tube side oil passage 33 becomes the high pressure side. First, this case will be described. When the boom 5 is lifted by the leveling device 100 including the leveling circuit 30 as described above, the lower leveling cylinder 10 is extended in conjunction with this, and the pressure in the rod-side oil passage 31 is increased. When the pressure in the rod side oil passage 31 reaches the pilot pressure of the pilot check valve 41, the flow of hydraulic oil from the upper leveling cylinder 20 to the lower leveling cylinder 10 in the tube side oil passage 33 is allowed. The cylinder 20 is contracted. On the other hand, when the boom 5 is tilted, the lower leveling cylinder 10 is contracted in conjunction with this, and the pressure in the tube side oil passage 33 is increased. When the pressure in the tube side oil passage 33 reaches the pilot pressure of the pilot check valve 41, the flow from the upper leveling cylinder 20 to the lower leveling cylinder 10 in the rod side oil passage 31 is allowed, and When the pressure reaches the holding pressure of the upper leveling cylinder 20, the upper leveling cylinder 20 extends. As described above, the upper leveling cylinder 20 operates in conjunction with the lower leveling cylinder 10, so that the work table 7 can maintain a horizontal level within a predetermined range. Further, as described above, the pilot check valve 41 is provided in the rod side oil passage 31 and the tube side oil passage 33, so that even when the leveling circuit 30 is damaged, the upper leveling cylinder 20 can greatly expand and contract. Therefore, the work table 7 can be prevented from being greatly inclined.

  The rod side oil passage 31 and the tube side oil passage 33 are respectively provided with connection oil passages 32 and 34 connected to the return circuit 35, and relief valves 32a and 34a are provided respectively. The return circuit 35 is provided so that hydraulic oil circulates from the boom operation valve 50 for operating the telescopic cylinder of the boom 5 to the tank T. The return circuit 35 has a predetermined back pressure during the pump operation. In the embodiment, a rotary joint 60 is disposed between the tank T and the return circuit 35. Since the relief valves 32a and 34a are provided in the leveling circuit 30 as described above, hydraulic fluid flows from the relief valves 32a and 34a to the return circuit 35 when the hydraulic pressure in the leveling circuit 30 becomes excessively high. The leveling circuit 30 is protected. In addition, a valve 43 and cocks 46 and 47 for correcting the worktable tilt are provided between the connecting oil passages 32 and 34 (tube side oil passage 33, rod side oil passage 31) and the return circuit 35, so that inspection and The inclination of the work table 7 can be corrected during maintenance.

  The return circuit 35 and the leveling circuit 30 are further connected by the negative pressure prevention oil passage 37 not passing through the relief valves 32a and 34a. In the embodiment, the connection oil passage 34 connected to the tube side oil passage 33 and the return circuit 35 are connected by a negative pressure prevention oil passage 37, and the return circuit 35 connects the tube side oil to the negative pressure prevention oil passage 37. A check valve 45 that allows flow to the passage 33 is provided. Thereby, when the oil pressure of the tube side oil passage 33 becomes a negative pressure state, the working oil is supplied via the negative pressure prevention oil passage 37, and the negative pressure state of the tube side oil passage 33 is eliminated. Note that the cracking pressure of the check valve 45 is set to be at least smaller than the back pressure of the return circuit 35, so that hydraulic oil is supplied during the pump operation even if the tube side oil passage 33 is in a negative pressure state. It is what is done. Further, the cracking pressure of the check valve 45 can be set smaller than the atmospheric pressure, for example. In this case, even when the pump P is not operating, the hydraulic oil is replenished if the oil pressure in the tube-side oil passage 33 is in a negative pressure state. The hydraulic oil is also supplied when a negative pressure state occurs. For this reason, it is not necessary to provide a back pressure valve or the like for securing a supply pressure for the return circuit 35.

  As described above, since the negative pressure prevention oil passage 37 and the check valve 45 are provided only in the tube side oil passage 33, even if hydraulic oil leaks from the check valve 45 due to foreign matter being caught, at least during the pump operation. The hydraulic oil is supplied to the tube side oil passage 33. The rod-side oil passage 31 is not provided with the negative pressure prevention oil passage 37 and the check valve 45, and the possibility that the hydraulic oil leaks is low. Therefore, when the hydraulic oil is supplied to the tube-side oil passage 33, The inclination of the work table 7 is restored and returns to a predetermined horizontal level. Even if the hydraulic oil leaks from the check valve 45 of the tube side oil passage 33, the rod side oil passage 31 has no negative pressure prevention oil passage and no check valve, so the hydraulic oil is supplied to the rod side oil passage 31. In addition, the inclination of the work table 7 does not proceed.

  As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to these embodiments, and the design can be changed without departing from the scope of the present invention. Is included in the present invention. For example, the negative pressure prevention oil passage and the check valve are provided only in the tube side oil passage, but the negative pressure prevention oil passage and the check valve are provided only in the rod side oil passage. I do not care.

  In addition, the connection oil passage connected to the tube side oil passage and the return circuit are connected by the negative pressure prevention oil passage, and the check is made to allow the flow from the return circuit to the tube side oil passage to the negative pressure prevention oil passage. Although an example in which a valve is provided is shown, the present invention is not limited to this. For example, as shown in FIG. 3, a pilot check valve 141 is provided in the tube side oil passage 33 and the rod side oil passage 31 in place of the cocks 46 and 47, and one side of the pilot check valve 141 (the same operation as in the embodiment) For example, the cracking pressure of the pilot check valve of the rod side oil passage) can be increased and the cracking pressure on the other side can be set low. In this case, the pilot check valve on the other side functions to prevent negative pressure, and hydraulic fluid is not supplied even if one side is in a negative pressure state, and the same effect as in the first embodiment is achieved. Can be obtained.

DESCRIPTION OF SYMBOLS 1 Aerial work vehicle 5 Boom 7 Worktable 10 Lower leveling cylinder 20 Upper leveling cylinder 31 Rod side oil path (1st oil path)
32a Relief valve 33 Tube side oil passage (second oil passage)
34a Relief valve 35 Return circuit 45 Check valve

Claims (3)

A boom that can be raised and lowered on the vehicle body, a workbench that can be swung and swiveled at the tip of the boom, an upper leveling cylinder that rocks the workbench, and a hoisting operation of the boom. A leveling device for an aerial work vehicle, comprising: a lower leveling cylinder that operates, and a hydraulic circuit that connects the upper leveling cylinder and the lower leveling cylinder,
The hydraulic circuit is
A first oil passage connecting the rod side of the upper leveling cylinder and the rod side of the lower leveling cylinder;
A second oil passage connecting the tube side of the upper leveling cylinder and the tube side of the lower leveling cylinder;
The first oil passage and the second oil passage are connected to a return circuit that returns working oil to the tank, and when the first oil passage and the second oil passage become a predetermined pressure or more. Is provided with a relief valve that opens,
A leveling device for an aerial work vehicle, wherein a check valve capable of supplying hydraulic oil from the return circuit is provided only in one of the first oil passage and the second oil passage.   2. The leveling device for an aerial work vehicle according to claim 1, wherein the check valve is opened when a pressure of an oil passage provided is smaller than a pressure of the return circuit.   2. The leveling device for an aerial work vehicle according to claim 1, wherein the check valve is opened when a pressure of an oil passage provided becomes smaller than an atmospheric pressure.

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