JP2005106124A - Hydraulic system for forklift truck - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydraulic system as an object for a forklift truck, which has a working machine driven by oil pressure, capable of preventing a temperature rise of an operating oil in advance in response to motions of a working machine. <P>SOLUTION: The hydraulic system for a forklift truck comprises a hydraulic actuator driving the working machine, a variable delivery hydraulic pump supplying operating oil to the hydraulic actuator, a load-sensing type direction and flow control valve inserting into an oil passage connecting between the hydraulic pump and the hydraulic actuator, a sub-oil passage connecting between the hydraulic pump and the hydraulic actuator by no way of the direction and flow control valve, and a selector valve inserted into the sub-oil passage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

    The present invention relates to a hydraulic device for a forklift truck provided with a working machine driven by hydraulic pressure.

    FIG. 3 shows an example of a very general forklift (forklift truck) including a working machine driven by hydraulic pressure.

  The forklift A is provided with a work machine C in front of a vehicle body (vehicle body) B. The work machine C is provided with a fork along a mast M that is erected vertically based on the operation of a mast lift cylinder R. F is configured to move up and down.

  Further, the working machine C tilts forward over the range of the angle α and tilts backward over the range of the angle β by the operation of the tilt cylinder T interposed between the vehicle body B and the mast M. Thus, during the cargo handling operation, for the purpose of preventing the collapse of the articles loaded on the fork F, it is required to travel with the working machine C (mast M) tilted last. .

  Here, as a means for tilting the working machine C, a hydraulic device is provided in which an oil passage connecting a tilt cylinder (hydraulic actuator) and a hydraulic pump is interposed with a direction / flow rate control valve ( For example, see Patent Document 1, Patent Document 2, and Patent Document 3.)

  That is, the conventional hydraulic apparatus O shown in FIG. 4 includes a tilt cylinder (hydraulic actuator) T that drives a work machine (see FIG. 3), and a fixed displacement gear pump (hydraulic pump) that supplies hydraulic oil to the tilt cylinder T. ) P, and an open center type direction / flow rate control valve V is interposed in an oil passage W connecting the tilt cylinder T and the gear pump P.

When the operator operates the operation lever L, the direction / flow rate control valve V is switched to the three positions of the backward tilt position Vb, the neutral position Vn, and the forward tilt position Vf. Is supplied to the cap side of the tilt cylinder T through the oil passage a, the oil passage b, and the oil passage c, and the hydraulic oil discharged from the head side is supplied through the oil passage d and the oil passage e. Drained.
Japanese Utility Model Publication No.59-123097 Japanese Utility Model Publication No.59-22298 Japanese Utility Model Publication No. 61-171799

    By the way, in the forklift A as described above, when traveling with an article loaded, it is necessary to keep the working machine C (mast M) in the last tilted state as described above. The occurrence of so-called natural forward tilt, which moves forward due to oil leaks, could not be avoided.

  Therefore, when the article is transported over a long distance, the operator operates the operation lever L of the hydraulic device O at an appropriate timing, and the working machine C (mast M) tilted naturally forward to the last tilt position. It was necessary to repeat the backward tilting operation.

  A similar problem can be seen in a forklift that is mounted with a clamp device that is an attachment instead of a fork. The leakage of hydraulic oil inside the hydraulic device that operates the clamp causes the clamping force to drop and the article falls off. In order to prevent this, it is necessary for the operator to operate the clamper operating lever at an appropriate timing and repeatedly perform so-called additional tightening of the article.

  In order to eliminate the operational inconvenience due to the hydraulic oil leakage as described above, for example, in the case of the hydraulic device O that operates the tilt cylinder T shown in FIG. 4, the direction / flow rate control valve V is set to the backward tilt position Vb. A method is conceivable in which the rearward tilting operation of the work machine C (mast M) is continuously performed while maintaining the above state.

  However, when the direction / flow rate control valve V is maintained at the rearward tilt position Vb, after the hydraulic oil is supplied to the tilt cylinder T to operate the work machine C (mast M) to the last tilt position, the oil passage W When the pressure of the hydraulic oil at the pressure rises to the relief pressure set in the relief valve (pressure safety valve) S, the total amount of hydraulic oil fed from the gear pump P flows into the relief valve S via the oil passage a and the oil passage f Then, after passing through the relief valve S, it is drained through the oil passage g.

  Here, a large amount of hydraulic fluid is pumped from the fixed displacement type gear pump P based on the engine rotation during traveling, and when this large amount of hydraulic fluid passes through the relief valve S, energy (pressure x flow rate) is generated. Changing to heat caused the oil temperature to rise, and this caused various inconveniences such as adversely affecting the sealing material.

  In view of the above circumstances, an object of the present invention is to provide a hydraulic device for a forklift truck that can prevent an increase in the temperature of hydraulic oil accompanying the operation of a work machine.

    In order to achieve the above object, a hydraulic device for a forklift truck according to claim 1 is a hydraulic device for a forklift truck provided with a working machine driven by hydraulic pressure, a hydraulic actuator for driving the working machine, and the hydraulic actuator A variable displacement hydraulic pump for supplying hydraulic oil to the vehicle, a load sensing type direction / flow rate control valve interposed in an oil passage connecting the hydraulic pump and the hydraulic actuator, and the direction / flow rate control valve. It is characterized by comprising a secondary oil passage that connects the hydraulic pump and the hydraulic actuator without passing through, and a switching valve interposed in the secondary oil passage.

  A hydraulic device for a forklift truck according to a second aspect of the invention is the hydraulic device for a forklift truck according to the first aspect of the invention, wherein the switching valve maintains a state where hydraulic oil is supplied from a hydraulic pump to a hydraulic actuator. An operation lock means is provided.

    According to the hydraulic device for a forklift truck related to the invention of claim 1, the hydraulic oil is supplied to the hydraulic actuator by adopting the variable displacement type hydraulic pump as the hydraulic pump for supplying the hydraulic oil to the hydraulic actuator. Other than the above, it becomes possible to set the flow rate of the hydraulic oil from the hydraulic pump to the minimum necessary, and thus it is possible to prevent an increase in the temperature of the hydraulic oil accompanying the operation of the work machine.

  According to the configuration of the hydraulic device for a forklift truck according to the invention of claim 2, in the same manner as the hydraulic device for a forklift truck according to the invention of claim 1, the temperature rise of the hydraulic oil accompanying the operation of the work machine is increased. This can be prevented in advance, and the operator's work when operating the hydraulic actuator continuously can be facilitated.

Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments.
In the following first and second embodiments, an example in which the present invention is applied to a hydraulic device that drives a tilt cylinder of a forklift truck will be described. Except for the above configuration, there is basically no difference from the conventional forklift truck described with reference to FIG.

    FIG. 1 shows a first embodiment of a hydraulic device for a forklift truck according to the present invention. The hydraulic device 1 is a tilt for tilting a forklift truck working machine (see FIG. 3) forward / backward. A cylinder (hydraulic actuator) 2 and a piston pump (hydraulic pump) 3 for supplying hydraulic oil to the tilt cylinder 2 are provided.

  The piston pump 3 is a variable displacement swash plate type piston pump, and as is well known, is configured to adjust the discharge amount of hydraulic oil by changing the inclination angle of a swash plate (not shown). .

  A load sensing type direction / flow rate control valve 5 is interposed in the oil passage 4 (4a, 4b) connecting the tilt cylinder 2 and the piston pump 3. This direction / flow rate control valve 5 is a lever-operated manual valve, and when the operator operates the operation lever 5L, the direction / flow rate control valve 5 is switched to three positions: a backward tilt position 5B, a neutral position 5N, and a forward tilt position 5F. When the hand is released from the operation lever 5L, the spring 5s returns to the neutral position 5N.

  Here, throttle passages 5t are respectively provided at the backward tilt position 5B and the forward tilt position 5F of the direction / flow rate control valve 5, and at the rear tilt position 5B, the neutral position 5N, and the forward tilt position 5F, respectively. The pilot passages 5p are respectively provided.

  The hydraulic device 1 includes a bypass oil passage (sub-oil passage) 6 that bypasses the direction / flow rate control valve 5 and connects the oil passage 4a and the oil passage 4b of the oil passage 4, and a bypass oil passage. A switching valve 7 is interposed between 6a and 6b.

  The switching valve 7 is a normally closed type manual valve. When the operator operates the lever 7L, the switching from the closed position 7C to the open position 70 is performed, and when the operator releases the lever 7L. Is configured to return to the closed position 7C by a spring 7s.

  Further, the switching valve 7 includes an operation lock means 8 comprising a notch 8A formed in the operation lever 7L, a ball 8B fitted into the notch 8A, and a spring 8S for biasing the ball 8B. ing.

  The operation lock means 8 is configured such that when the operator operates the operation lever 7L to set the switching valve 7 to the open position 70, the ball 8B biased by the spring 8S is fitted into the notch 8A. 7 is held in the open position 70, and bypass oil passages 6a and 6b connecting the piston pump 3 and the tilt cylinder 2 are communicated to maintain a state where hydraulic oil is supplied from the piston pump 3 to the tilt cylinder 2. It is.

  Further, the hydraulic apparatus 1 has a shuttle valve 9, and the shuttle valve 9, the direction / flow rate control valve 5, the piston pump 3, and the bypass oil passage 6b are connected to pilot oil passages 6c, 6d, and 6e, respectively. Connected through.

  Even when the direction / flow rate control valve 5 is in the neutral position 5N by the bypass oil passages 6a and 6b, the switching valve 7, the shuttle valve 9, and the pilot oil passages 6c, 6d, 6e, Sub-operating means for communicating hydraulic oil 4 from the piston pump 3 to the tilt cylinder 2 by connecting the oil passage 4 connecting the tilt cylinder 2 is configured.

  The direction / flow rate control valve 5 is normally positioned at the neutral position 5N, and when the operator operates the operation lever 5L to set the rearward tilt position 5B, the hydraulic oil discharged from the piston pump 3 is oil The hydraulic fluid supplied to the cap side of the tilt cylinder 2 through the passage 4a, the throttle passage 5t, and the oil passage 4b and discharged from the head side of the tilt cylinder 2 is drained from the oil passage 4c through the oil passage 4d. The

  Here, after the hydraulic oil fills the cap side of the tilt cylinder 2, the pressure of the hydraulic oil supplied from the pilot passage 5p through the pilot oil passage 6d, the shuttle valve 9, and the pilot oil passage 6e increases. The inclination angle of a swash plate (not shown) in the piston pump 3 is adjusted based on the pressure (pilot pressure), and the flow rate of the hydraulic oil discharged from the piston pump 3 becomes extremely small.

  Therefore, in order to cope with the natural forward tilt of the work machine (see FIG. 3) in the forklift truck, the state / flow control valve 5 is maintained in the rearward tilt position 5B, and the backward tilting operation of the work machine is continued. Even if it is performed, since the flow rate of the hydraulic oil discharged from the piston pump 3 is extremely small, there is no increase in the oil temperature due to the flow of a large amount of hydraulic oil.

  Further, the necessary pressure is continuously supplied to the cap side of the tilt cylinder 2 by a small amount of hydraulic oil discharged from the piston pump 3, thereby preventing the natural forward tilt of the work machine. Become.

  Further, in this hydraulic apparatus 1, even when the direction / flow rate control valve 5 is in the neutral position 5N, the lever 7L of the switching valve 7 in the sub-operating means described above is operated to tilt the work implement backward. The action can be performed.

  That is, by operating the lever 7L to bring the switching valve 7 into the open position 70, the hydraulic oil discharged from the piston pump 3 is supplied to the tilt cylinder 2 via the bypass oil passage 6a, the switching valve 7 and the bypass oil passage 6b. If the pressure of the hydraulic oil supplied through the pilot oil passage 6c, the shuttle valve 9 and the pilot oil passage 6e increases after the hydraulic oil is filled on the cap side of the tilt cylinder 2, this high pressure (pilot The inclination angle of a swash plate (not shown) in the piston pump 3 is adjusted based on the pressure), so that the flow rate of hydraulic oil discharged from the piston pump 3 is extremely small.

  For this reason, in order to cope with the natural forward tilt of the work machine (see FIG. 3) in the forklift truck, it is assumed that the switching valve 7 is maintained in the open position 70 and the backward tilting operation of the work machine is continued. However, since the flow rate of the hydraulic oil discharged from the piston pump 3 is extremely small, the oil temperature does not rise appreciably due to the flow of a large amount of hydraulic oil.

  Further, the necessary pressure is continuously supplied to the cap side of the tilt cylinder 2 by a small amount of hydraulic oil discharged from the piston pump 3, thereby preventing the natural forward tilt of the work machine. Become.

  Further, in the hydraulic apparatus 1, the switching valve 7 can be maintained at the open position 7O without the operator continuing to operate the operation lever 7L of the switching valve 7 by the operation of the operation lock means 8 described above. Therefore, the operator's work when dealing with the natural forward tilt of the work machine can be made extremely easy.

  Further, in the hydraulic apparatus 1 according to the present embodiment, the switching valve 7 in the sub operation means can be installed away from the direction / flow rate control valve 5, so that the operator can easily access, for example, a front console in the cab. By installing the switching valve 7 so that the lever is located at the place, the operator's work for dealing with the natural forward tilt of the work machine becomes extremely easy.

  In this embodiment, the switching valve 7 in the sub-operating means is constituted by a lever-operated manual valve. However, it is also possible to employ an electromagnetic valve that opens and closes in response to an electric switch signal. According to the configuration, since the degree of freedom of the mounting location in the electric switch is extremely large, the operability of the operator with respect to the sub operation means can be greatly improved by adopting an appropriate layout.

  In this embodiment, the operation locking means 8 for the switching valve 7 is composed of a notch 8A, a ball 8B, and a spring 8S. By adopting an electromagnetic valve as the switching valve 7, the ball 8B Needless to say, the operation lock means can be constituted by a drive mechanism of an electromagnetic valve without requiring a mechanical operation lock means having elements such as.

    FIG. 2 shows a second embodiment of a hydraulic device for a forklift truck according to the present invention. This hydraulic device 10 is a tilt for tilting a forklift truck working machine (see FIG. 3) forward / backward. A cylinder (hydraulic actuator) 12 and a piston pump (hydraulic pump) 13 for supplying hydraulic oil to the tilt cylinder 12 are provided.

  The piston pump 13 is a variable displacement swash plate type piston pump, and is configured to adjust the discharge amount of the hydraulic oil by changing the inclination angle of a swash plate (not shown) as is well known. .

  A load sensing type direction / flow rate control valve 15 is interposed in an oil passage 14 (14 a, 14 b) connecting the tilt cylinder 12 and the piston pump 13.

This direction / flow rate control valve 15 is a lever-operated manual valve, and when the operator operates the operation lever 15L, it is switched to three positions, that is, a backward tilt position 15B, a neutral position 15N, and a forward tilt position 15F. When the hand is released from the operation lever 15L, the spring 15s returns to the neutral position 15N.

  Here, throttle passages 15t are respectively provided at the backward tilt position 15B and the forward tilt position 15F of the direction / flow rate control valve 15, and at the rear tilt position 15B, the neutral position 15N, and the forward tilt position 15F, respectively. The pilot passages 15p are respectively provided.

  The direction / flow rate control valve 15 has a function as the switching valve 15 by having the switching position 15C, and the oil passage 14 ( 14a, 14b) are auxiliary oil passages 14 that connect the tilt cylinder 12 and the piston pump 13 without passing through the substantial direction / flow rate control valve 15 (the backward tilt position 15B, the neutral position 15N, and the forward tilt position 15F). (14a, 14b).

  Here, at the switching position 15C in the switching valve 15, a throttle passage 15t and a pilot passage 15p are provided in the same manner as the backward tilting position 15B in the direction / flow rate control valve 15.

  The switching valve 15 includes an operation lock means 16 including a notch 16A formed in the operation lever 15L, a ball 16B fitted into the notch 16A, and a spring 16S for biasing the ball 16B. ing.

  The operation lock means 16 is configured so that when the operator operates the operation lever 15L to set the switching valve 15 to the switching position 15C, the ball 16B urged by the spring 16S is fitted into the notch 16A. 15 is held at the switching position 15C, and the auxiliary oil passage 14 (14a, 14b) that connects the piston pump 13 and the tilt cylinder 12 is communicated, so that hydraulic oil is supplied from the piston pump 13 to the tilt cylinder 12. To maintain.

  The direction / flow rate control valve 15 is normally positioned at the neutral position 15N, and when the operator operates the operation lever 15L to the rearward tilt position 15B, the hydraulic oil discharged from the piston pump 13 is oil The hydraulic fluid supplied to the cap side of the tilt cylinder 12 through the passage 14a, the throttle passage 15t, and the oil passage 14b and discharged from the head side of the tilt cylinder 12 is drained from the oil passage 14c through the oil passage 14d. The Rukoto.

  Here, until the hydraulic oil fills the cap side of the tilt cylinder 12, the inclination of the piston pump 13 is increased based on the low pressure (pilot pressure) of the hydraulic oil supplied from the pilot passage 15p via the pilot oil passage 14e. A tilt angle of a plate (not shown) is adjusted, and a large amount of hydraulic oil is discharged from the piston pump 13.

  On the other hand, when the hydraulic oil supplied from the pilot passage 15p through the pilot oil passage 14e increases after the hydraulic oil is filled on the cap side of the tilt cylinder 12, the piston pump is based on this high pressure (pilot pressure). The inclination angle of a swash plate (not shown) at 13 is adjusted, and the flow rate of hydraulic oil discharged from the piston pump 13 is extremely small.

  Therefore, in order to cope with the natural forward tilt of the work machine (see FIG. 3) in the forklift, the state / flow control valve 15 is maintained in the rearward tilt position 15B, and the work machine is continuously tilted backward. Even if it is set, the flow rate of the hydraulic oil discharged from the piston pump 13 is extremely small, so that the oil temperature does not rise appreciably due to the flow of a large amount of hydraulic oil.

  Further, a small amount of hydraulic oil discharged from the piston pump 13 continuously supplies the necessary pressure to the cap side of the tilt cylinder 12, thereby preventing the natural forward tilt of the work implement. Become.

  Further, in the hydraulic apparatus 10, the work implement can be tilted backward by operating the direction / flow rate control valve 15, in other words, the operation lever 15L of the switching valve 15.

  In other words, by operating the operation lever 15L to set the switching valve 15 to the switching position 15C, the hydraulic oil discharged from the piston pump 13 is passed through the auxiliary oil passage 14a, the throttle passage 15t, and the auxiliary oil passage 14b through the tilt cylinder. After the hydraulic oil is supplied to the tilt cylinder 12 on the cap side and the pressure of the hydraulic oil supplied from the pilot passage 15p through the pilot oil passage 14e increases, the high pressure (pilot pressure) is applied. Thus, the inclination angle of a swash plate (not shown) in the piston pump 13 is adjusted, and the flow rate of the hydraulic oil discharged from the piston pump 13 becomes extremely small.

  For this reason, it does not cause a drastic increase in the oil temperature due to the flow of a large amount of hydraulic oil, and is necessary on the cap side of the tilt cylinder 12 by a small amount of hydraulic oil discharged from the piston pump 13. The pressure is continuously supplied, so that the natural forward tilt of the work implement is prevented in advance.

  In the hydraulic apparatus 10, the switching valve 15 can be maintained at the switching position 15C without the operator continuing to operate the operation lever 15L of the switching valve 15 by the operation of the operation locking means 16 described above. Therefore, the operator's work when dealing with the natural forward tilt of the work machine can be made extremely easy.

  Here, in this embodiment, the switching valve 15 is constituted by a lever-operated manual valve, but an electromagnetic valve that opens and closes in response to a signal from an electrical switch can also be employed.

  In the present embodiment, the operation locking means 16 for the switching valve 15 is composed of a notch 16A, a ball 16B, and a spring 16S. However, by adopting an electromagnetic valve as the switching valve 15, the ball 16B Needless to say, the operation lock means can be constituted by a drive mechanism of an electromagnetic valve without requiring a mechanical operation lock means having elements such as.

  In the first and second embodiments described above, a swash plate type piston pump is employed as a variable displacement hydraulic pump that supplies hydraulic oil to the tilt cylinder. The present invention is not limited, and various types of hydraulic pumps such as a variable displacement vane pump can be employed.

  In the first and second embodiments described above, an example in which the present invention is applied to a hydraulic device that operates a tilt cylinder of a forklift truck has been described. However, a forklift mounted by replacing a clamping device as an attachment with a fork. Needless to say, the present invention can also be effectively applied to a hydraulic apparatus for operating a track clamp.

The circuit diagram which shows the 1st Example in the hydraulic device of the forklift truck concerning this invention. The circuit diagram which shows the 2nd Example in the hydraulic device of the forklift truck concerning this invention. The whole side view which shows a forklift truck notionally. The circuit diagram which shows the hydraulic device of the conventional forklift truck.

Explanation of symbols

1 ... hydraulic device,
2 ... Tilt cylinder (hydraulic actuator),
3. Cylinder pump (hydraulic pump)
4 ... Oil channel,
5. Direction / flow rate control valve,
6 ... Bypass oil passage (sub oil passage),
7 ... Switching valve,
8 ... Operation lock means,
10 ... hydraulic device,
12 ... Tilt cylinder (hydraulic actuator),
13 ... Cylinder pump (hydraulic pump),
14: Oil passage / sub-oil passage,
15: Direction / flow rate control valve / switching valve,
16: Operation lock means.

Claims (2)

A hydraulic device for a forklift truck having a working machine driven by hydraulic pressure,
A hydraulic actuator for driving the working machine, a variable displacement hydraulic pump for supplying hydraulic oil to the hydraulic actuator, and load sensing interposed in an oil passage connecting the hydraulic pump and the hydraulic actuator A directional / flow rate control valve, a secondary oil passage connecting the hydraulic pump and the hydraulic actuator without passing through the directional / flow rate control valve, and a switching valve interposed in the secondary oil passage. A hydraulic system for a forklift truck. 2. The hydraulic apparatus for a forklift truck according to claim 1, wherein the switching valve includes an operation lock means for maintaining a state in which hydraulic oil is supplied from the hydraulic pump to the hydraulic actuator.

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