JP2011225287A - Forklift - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption of an operating-oil pump while eliminating danger such as oil leakage due to very high operating-oil pressure.SOLUTION: A forklift includes: a fork 6 raised/lowered for cargo handling operation; a lift cylinder 7 vertically extended so as to raise/lower the fork 6 by operating-oil and divided by a piston into an upper chamber and a lower chamber so as to store the operating oil in the upper chamber and the lower chamber respectively; an operating-oil pump 21 and an operating-oil tank 20, which supply/discharge the operating oil to/from the lower chamber in order to raise/lower the fork 6; and a selector valve 28 for switching the upper chamber and the lower chamber between a communicating state and a non-communicating state. The selector valve 28 is a hydraulic pilot type that is switched according to pressure of the operating oil in the lower chamber. When the fork 6 is raised, the selector valve is made non-communicable if the fork 6 is used for the cargo handling operation, and also, made communicable if the fork 6 is not used for the cargo handling operation.

Description

  The present invention relates to a forklift provided with a fork for lifting and lowering cargo handling.

  The reach-type forklift is provided with a fork for raising and lowering the cargo handling (see Patent Document 1, etc.), and as shown in FIG. 8, a reach cylinder 9 for allowing the fork to move forward and backward, and a fork to be tilted. Tilt cylinder 8 and a lift cylinder 7 for raising and lowering the fork.

  As shown in FIG. 7, the lift cylinder 7 extends in the up-down direction, and a rod portion 70 and a piston portion 71 are provided therein. The conventional lift cylinder 7 is divided into an upper chamber 7a and a lower chamber 7b via a piston portion 71, and hydraulic oil is supplied to and discharged from the lower chamber 7b through a port 72 provided on the bottom side. .

  As shown in FIG. 8, the conventional hydraulic circuit includes a hydraulic oil tank 20, a hydraulic oil pump 21, a lift control valve 27, and the like. When the fork is raised, the hydraulic oil pump 21 supplies the hydraulic oil from the hydraulic oil tank 20. The hydraulic oil is supplied to the lower chamber 7b of the lift cylinder 7, and the fork is pushed up via the piston portion 71 by the hydraulic pressure. When the fork is lowered, the piston portion 71 is pushed down by its own weight such as the fork, and the hydraulic oil in the lower chamber 7 b of the lift cylinder 7 is discharged to the hydraulic oil tank 20.

  As described above, the hydraulic oil is supplied to the lower chamber 7b of the lift cylinder 7 and the fork is raised by pushing up the piston portion 71. Therefore, if the lift cylinder 7 has a large diameter, the flow rate of the required hydraulic oil increases. Since the operation time of the hydraulic oil pump 21 becomes longer, the power consumption is large. Therefore, by reducing the diameter of the lift cylinder 7, it is possible to reduce the required flow rate of the hydraulic oil. However, when raising the cargo handling (at the time of loading), the hydraulic oil in the pipeline of the hydraulic circuit and the control valve The pressure becomes very high (high pressure) and the risk of oil leakage increases.

Japanese Patent Laid-Open No. 10-147499

  Therefore, the problem to be solved by the present invention is to provide a forklift that can reduce the power consumption of the hydraulic oil pump without risk of oil leakage due to high pressure.

In order to solve the above-described problems, the forklift according to the present invention is:
A fork for raising and lowering cargo handling, and a vertical extension for raising and lowering the fork with hydraulic oil, divided into an upper chamber and a lower chamber by a piston portion, and hydraulic oil is stored in the upper chamber and the lower chamber A lift cylinder, a hydraulic oil pump and hydraulic oil tank for supplying and discharging hydraulic oil to and from the lower chamber to raise and lower the fork, and a switching valve for switching the upper chamber and the lower chamber between communication and non-communication. This is a hydraulic pilot type that switches according to the pressure of hydraulic oil in the lower chamber. When the fork is lifted, it is disconnected when the fork has a cargo handling, and communicates when the fork has no cargo handling.

  Preferably, when the hydraulic circuit descends the fork, the hydraulic oil discharged from the lower chamber is supplied to the upper chamber, and the remainder of the hydraulic oil is discharged to the hydraulic oil tank.

  Preferably, the switching valve includes a check valve, and when the fork has no cargo handling, the check valve enables flow from the upper chamber to the lower chamber of the lift cylinder, and allows flow from the lower chamber to the upper chamber. Stop.

  Preferably, the switching valve is provided in the piston part.

  As described above, in the forklift according to the present invention, the lift cylinder is divided into the upper chamber and the lower chamber by the piston portion. The lift cylinder contains hydraulic oil in an upper chamber and a lower chamber, and the upper chamber and the lower chamber are switched between communication and non-communication by a switching valve. When the fork is lifted, the switching valve becomes non-communication when the fork has cargo handling and communicates when the fork has no cargo handling.

As a result, when the fork has cargo handling (loading), the upper chamber and the lower chamber are disconnected from each other by the switching valve when the fork is lifted, and the hydraulic oil corresponding to the inner diameter of the cylinder is supplied to and discharged from the lower chamber as in the conventional case. Therefore, there is no danger of oil leakage due to high pressure. Furthermore, when the fork has no cargo handling (no load), the upper chamber and the lower chamber communicate with each other by the switching valve. Supply only hydraulic oil to the lower chamber. Therefore, since it is only necessary to supply a lower amount of hydraulic oil to the lower chamber than in the prior art, the power consumption of the hydraulic oil pump can be reduced, and the lifting speed of the fork can be increased. In this way, when the load is high, there is a risk of oil leakage when the pressure is increased, and the same amount of hydraulic oil as before is supplied and discharged. Since a small amount of hydraulic oil is supplied and discharged, the power consumption of the hydraulic oil pump can be reduced and the risk of oil leakage can be avoided.
Further, since the switching valve is configured by a hydraulic pilot operation system, it has a very simple configuration and is very excellent in terms of cost and productivity.

It is a perspective view which shows a reach type forklift. It is a perspective view for demonstrating a lift cylinder, a reach cylinder, and a tilt cylinder. It is sectional drawing which shows the lift cylinder of this invention. It is a hydraulic circuit diagram regarding the lift cylinder when a fork has a cargo handling (at the time of load), (a) is when the fork is raised (lift up), (b) is when the fork is lowered (lift down). It is a hydraulic circuit diagram regarding a lift cylinder when there is no cargo handling on the fork (no load), (a) is when the fork is raised (lift up), (b) is when the fork is lowered (lift down). . It is a partially expanded sectional view which shows the lift cylinder of 2nd embodiment of this invention. It is sectional drawing which shows the conventional lift cylinder. It is a hydraulic circuit diagram regarding the conventional lift cylinder, reach cylinder, and tilt cylinder.

  Hereinafter, an embodiment of a forklift according to the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the reach forklift includes a vehicle body 1 having left and right straddle arms 2 extending forward. The reach-type forklift includes a carriage 4 that can be moved back and forth along the left and right straddle arms 2. A mast 3 is erected on the carriage 4 in the vertical direction. The reach forklift includes a lift bracket 5 that is guided up and down along the mast 3. A pair of left and right forks 6 are supported on the lift bracket 5 so as to be tiltable. A lift cylinder 7 is erected on the carriage 4 along the mast 3, and the fork 6 moves up and down together with the lift bracket 5 by the expansion and contraction of the lift cylinder 7. Further, the lift bracket 5 is provided with a tilt cylinder 8 (FIG. 2), and the tilt cylinder 8 is expanded and contracted, whereby the fork 6 is tilted. A reach cylinder 9 is provided between the vehicle body 1 and the carriage 4 (FIG. 2). The reach cylinder 9 is extended and retracted, whereby the carriage 4 is advanced and retracted.

  The left rear portion of the vehicle body 1 is a device storage chamber 10 that is closed by an openable / closable door, and a hydraulic oil tank 20, a hydraulic oil pump 21, a motor 22 and the like to be described later are mounted in the device storage chamber 10. Yes. A right rear portion of the vehicle body 1 is a driver seat 11 that is formed to be opened rearward, and is covered with a top cover 12 from the upper part of the device storage chamber 10 to the front of the driver seat 11. On the top cover 12, a handle 13 for steering is provided at the left position of the driver's seat 11, and various operation levers 14 for performing a cargo handling operation and an accelerator operation are provided at a position in front of the driver's seat 11. Is provided. A head guard 15 is provided above the vehicle body 1.

  As shown in FIG. 2, the carriage 4 includes left and right side plates and a bottom plate that connects these lower edges. A guide roller (not shown) rotatably supported on the outer side of each side plate of the carriage 4 is brought into rolling contact with a U-shaped guide rail formed on the inner side of the straddle arm 2 so that the carriage 4 is moved to the straddle arm 2. It is designed to move forward and backward. A mast 3 is fixed to the front end of the side plate of the carriage 4, and a lift cylinder 7 is supported on the bottom plate on the rear side of the mast 3.

  As shown in FIG. 3, the lift cylinder 7 includes therein a rod portion 70 extending in the axial direction and a piston portion 71 provided at the lower end of the rod portion 70. In the lift cylinder 7, an upper chamber 7 a and a lower chamber 7 b are formed via a piston portion 71. The lift cylinder 7 contains hydraulic oil in an upper chamber 7a and a lower chamber 7b. In addition, Preferably, hydraulic fluid is accommodated so that the upper chamber 7a and the lower chamber 7b may be filled. The lift cylinder 7 includes a top port 72 provided on the upper end side and a bottom port 73 provided on the lower end side, and a pipe 30 for supplying and discharging hydraulic oil to and from the upper chamber 7a is provided in the top port 72. Is connected, and the bottom port 73 is connected to a pipeline 31 for supplying and discharging hydraulic oil to and from the lower chamber 7b.

  As shown in FIGS. 4 and 5, the hydraulic circuit of the reach forklift rotates the hydraulic oil tank 20 that stores hydraulic oil, the hydraulic oil pump 21 that discharges hydraulic oil from the hydraulic oil tank 20, and the hydraulic oil pump 21. And a motor 22 to be driven. The hydraulic circuit includes a lift control valve 27 that controls supply and discharge of hydraulic oil to and from the lift cylinder 7. The hydraulic circuit includes a switching valve 28 that switches between the conduit 30 and the conduit 31 connected to the upper chamber 7a and the lower chamber 7b of the lift cylinder 7 between communication and non-communication. In the present embodiment, the switching valve 28 is provided outside the lift cylinder 7.

  The switching valve 28 includes a spring 18 provided on one end side and a hydraulic pilot 17 provided on the other end side. The spring 18 is a compression spring and biases the switching valve 28 in one direction (right direction in FIGS. 4 and 5). The hydraulic pilot 17 is connected to the pipeline 31 and applies the pressure of the hydraulic oil in the pipeline 31 to drive the switching valve 28 using the pressure as a pilot pressure (hydraulic pilot operation switching valve). The hydraulic pilot 17 presses the switching valve 28 in the other direction (the left direction in FIGS. 4 and 5) when the pressure of the hydraulic oil in the pipeline 31 is greater than a predetermined pressure (the urging force of the spring 18). . Accordingly, the switching valve (i) is operated by the pressing force of the hydraulic pilot 17 when the hydraulic oil pressure in the pipe line 31 is higher than a predetermined pressure, so that the pipe line 30 and the pipe line 31 are not communicated. (Ii) When the pressure of the hydraulic oil in the pipe line 31 is lower than a predetermined pressure, the pipe line 30 and the pipe line 31 are communicated with each other by operating by the biasing force of the spring 18 (see FIG. 4). 5). When lifting and lowering the cargo handling with the fork 6, the pressure of the hydraulic oil in the lower chamber 7 b (pipe line 31) of the lift cylinder 7 becomes higher than a predetermined pressure due to a downward load caused by the cargo handling. 30 and the pipe line 31 are made non-communication (FIG. 4). When only the fork 6 is moved up and down, there is no load due to cargo handling (no load), and therefore the hydraulic oil pressure P in the lower chamber 7b (pipe 31) of the lift cylinder 7 is smaller than a predetermined pressure. 28 communicates the conduit 30 and the conduit 31 (FIG. 5). In this embodiment, the switching valve 28 includes a check valve, and when there is no cargo handling, the hydraulic oil can flow from the pipe line 30 to the pipe line 31, but can flow from the pipe line 31 to the pipe line 30. As a result, the upper chamber 7a is not filled with hydraulic oil and air is mixed therein, so that it does not flow backward even if there is a pressure difference between the upper chamber 7a and the lower chamber 7b. It has become. Note that the switching valve 28 may not include a check valve, and the hydraulic oil may be able to flow through the pipe line 30 and the pipe line 31 in both directions.

  Based on FIG. 4, the hydraulic circuit when the fork 6 is loaded (when loaded) will be described. As shown in FIG. 4A, when the fork 6 is lifted (lifted up), the operation lever 14 is operated to switch the lift control valve 27 via a link mechanism or the like (not shown). The lift control valve 27 communicates a pipe line 32 connected to the hydraulic oil pump 21 and a pipe line 31 connected to the lower chamber 7 b of the lift cylinder 7. Furthermore, the switching valve 28 does not communicate the conduit 30 connected to the upper chamber 7a of the lift cylinder 7 and the conduit 31 connected to the lower chamber 7b. Further, the switching valve 28 communicates the pipe line 30 and the pipe line 33. The pipe 33 is connected to a pipe 34 that leads to the hydraulic oil tank 20. Then, the hydraulic oil from the hydraulic oil tank 20 is sent to the lower chamber 7 b of the lift cylinder 7 through the pipeline 32 and the pipeline 31 by the hydraulic oil pump 21. By supplying the hydraulic oil to the lower chamber 7b of the lift cylinder 7, the piston portion 71 is pushed up and lifted up. As a result, the hydraulic oil accommodated in the upper chamber 7a of the lift cylinder 7 is pushed out through the conduit 30 and discharged, further flows through the conduit 33 through the switching valve 28, and then enters the hydraulic tank 20 through the conduit 34. Return.

  As shown in FIG. 4B, when the fork 6 is lowered (lifted down), the operation lever 14 is operated to switch the lift control valve 27 via a link mechanism or the like. The lift control valve 27 communicates the conduit 31 connected to the lower chamber 7 b of the lift cylinder 7 with the conduit 33 and the conduit 34. Furthermore, the switching valve 28 makes the pipe line 30 and the pipe line 31 non-communication and connects the pipe line 30 and the pipe line 33. The pipeline 33 is connected to the pipeline 34. Then, the hydraulic oil accommodated in the lower chamber 7 b of the lift cylinder 7 is pushed out through the pipe 31 and discharged by the dead weight of the fork 6 and the cargo handling, and further flows into the pipe 33. This hydraulic oil is supplied from the pipe 33 to the upper chamber 7 a of the lift cylinder 7 through the pipe 30. Here, the total amount of hydraulic oil discharged from the lower chamber 7b is not supplied to the upper chamber 7a, but the volume difference between the upper chamber 7a and the lower chamber 7b (= movement distance of the piston portion 71 × rod portion). 70) is returned to the hydraulic oil tank 20 through the pipe 34.

  Based on FIG. 5, the hydraulic circuit when the fork 6 has no cargo handling (no load) will be described. As shown in FIG. 5A, when the fork 6 is raised (lifted up), the operation lever 14 is operated to switch the lift control valve 27 via a link mechanism or the like. The lift control valve 27 communicates the pipe line 32 and the pipe line 31. Further, the switching valve 28 communicates the pipe line 30 and the pipe line 31. Then, the hydraulic oil from the hydraulic oil tank 20 is sent to the lower chamber 7 b of the lift cylinder 7 through the pipeline 32 and the pipeline 31 by the hydraulic oil pump 21. Further, since the pipe line 30 and the pipe line 31 communicate with each other via the switching valve 28, the hydraulic oil stored in the upper chamber 7a of the lift cylinder 7 is pushed out of the pipe line 30 and discharged to be switched. It is supplied to the lower chamber 7 b through the valve 28 and the pipe line 31. Here, due to the volume difference between the upper chamber 7a and the lower chamber 7b, it is not sufficient to supply hydraulic oil discharged from the upper chamber 7a to the lower chamber 7b. Therefore, the insufficient amount of hydraulic oil due to the volume difference is lifted by being supplied from the hydraulic oil tank 20 to the lower chamber 7b of the lift cylinder 7 through the pipe line 32 and the pipe line 31.

  As shown in FIG. 5B, when the fork 6 is lowered (lifted down), the operation lever 14 is operated to switch the lift control valve 27 via a link mechanism or the like. The lift control valve 27 communicates the pipe line 31, the pipe line 33, and the pipe line 34. Further, the switching valve 28 communicates from the pipe line 30 to the pipe line 31, but does not flow from the pipe line 31 to the pipe line 30 by the check valve. The pipeline 33 is connected to the pipeline 34 and the pipeline 30. Then, the hydraulic oil accommodated in the lower chamber 7 b of the lift cylinder 7 is pushed out through the pipe 31 and discharged by the dead weight of the fork 6 and the cargo handling, and further flows into the pipe 33. This hydraulic oil is supplied from the pipe 33 to the upper chamber 7 a of the lift cylinder 7 through the pipe 30. Here, the entire amount of hydraulic oil discharged from the lower chamber 7 b is not supplied to the upper chamber 7 a, and an extra amount due to the volume difference between the upper chamber 7 a and the lower chamber 7 b is passed through the pipe 34. Return to 20.

  As described above, when the fork 6 is loaded (when loaded), the upper chamber 7a and the lower chamber 7b of the lift cylinder 7 are not in communication with each other (FIG. 4). For this reason, the hydraulic oil supplied to the lower chamber 7b of the lift cylinder 7 at the time of lift-up has the same pressure as the conventional one. It is unnecessary. Further, when the lift is down, the hydraulic oil discharged from the lower chamber 7b of the lift cylinder 7 is supplied to the upper chamber 7a of the lift cylinder 7, so that the hydraulic oil is accommodated (filled) in the lift cylinder 7 very efficiently. be able to.

  Further, as described above, when the fork 6 has no cargo handling (no load), the upper chamber 7a and the lower chamber 7b communicate with the lift cylinder 7 (FIG. 5). Therefore, at the time of lift-up, the hydraulic oil supplied to the lower chamber 7b of the lift cylinder 7 has a flow rate that is only the volume difference between the upper chamber 7a and the lower chamber 7b, and the area of the rod portion 70 becomes the pressure receiving area, which is conventional. However, since there is no load due to cargo handling, a configuration such as a pipeline or a control valve considering the pressure at the time of loading may be used, and a specially configured pipeline or control valve is unnecessary. Moreover, since it is sufficient to supply a smaller amount of hydraulic oil than in the past, the hydraulic oil pump 21 can be made smaller and the power consumption of the motor 22 can be reduced. In addition, since a small amount of hydraulic oil is supplied and discharged, lift-up and down can be speeded up.

  Based on FIG. 6, the forklift of the second embodiment will be described. A configuration different from the above-described embodiment will be described in detail. In the present embodiment, the switching valve 28 is incorporated in the piston portion 71 of the lift cylinder 7. The upper chamber 7 a of the lift cylinder 7 and the switching valve 28 are connected by a pipe line 40, and the lower chamber 7 b and the switching valve 28 are connected by a pipe line 41. When the fork 6 is loaded (when loaded), the switching valve 28 is not in communication between the upper chamber 7a and the lower chamber 7b of the lift cylinder 7 and when the fork 6 is not loaded (unloaded). The upper chamber 7a and the lower chamber 7b of the lift cylinder 7 communicate with each other.

  As described above, when the fork 6 is loaded (when loaded), the switching chamber 28 makes the upper chamber 7a and the lower chamber 7b non-communication so that the hydraulic oil corresponding to the inner diameter of the cylinder 7 is supplied to the lower chamber as in the conventional case. Since it is supplied to and discharged from 7b, there is no danger of oil leakage due to high pressure. Further, when the fork 6 has no cargo handling (no load), the switching chamber 28 communicates the upper chamber 7a and the lower chamber 7b, so that the hydraulic oil in the upper chamber 7a moves to the lower chamber 7b during lift-up. At the same time, only insufficient hydraulic oil is supplied to the lower chamber 7b. Therefore, since it is only necessary to supply and discharge a smaller amount of hydraulic oil to and from the lower chamber 7b than before, the power consumption of the motor 22 of the hydraulic oil pump 21 can be reduced, and the raising / lowering speed of the fork 6 can be increased. In this way, when the load is high, there is a risk of oil leakage when the pressure is increased, and the same amount of hydraulic oil as before is supplied and discharged. Since a small amount of hydraulic oil is supplied and discharged, the power consumption of the motor 22 of the hydraulic oil pump 21 can be reduced and the risk of oil leakage can be avoided.

6 Fork 7 Lift cylinder 7a Upper chamber 7b Lower chamber 70 Rod portion 71 Piston portion 72 Top port 73 Bottom port 17 Hydraulic pilot 18 Spring 27 Lift control valve 28 Switching valve 20 Hydraulic oil tank 21 Hydraulic oil pump 22 Motor

Claims (4)

  A fork for raising and lowering the cargo handling; and a vertical extension for raising and lowering the fork with hydraulic oil; the piston chamber is divided into an upper chamber and a lower chamber; the hydraulic oil is provided in the upper chamber and the lower chamber; The lift cylinder in which the engine is housed, the hydraulic oil pump and hydraulic oil tank for supplying and discharging the hydraulic oil to and from the lower chamber in order to raise and lower the fork, and the upper chamber and the lower chamber are switched between communication and non-communication. The switching valve is a hydraulic pilot type that switches according to the hydraulic oil pressure in the lower chamber, and when the fork is lifted, it is disconnected when the fork has cargo handling. A forklift that communicates when there is no cargo handling.   The hydraulic circuit supplies the hydraulic oil discharged from the lower chamber to the upper chamber when the fork is lowered, and discharges the remainder of the hydraulic oil to the hydraulic oil tank. Item 2. The forklift according to item 1.   The switching valve includes a check valve, and the check valve allows the lift cylinder to flow from the upper chamber to the lower chamber when the fork has no cargo handling. The forklift according to claim 1 or 2, wherein distribution to the upper chamber is prevented.   The forklift according to any one of claims 1 to 3, wherein the switching valve is provided in the piston portion.

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