JP4795682B2 - Hydraulic circuit for forklift - Google Patents

Description

  The present invention relates to a hydraulic circuit for a forklift.

In a conventional forklift, a hydraulic circuit is known in which hydraulic oils from two pumps are joined to increase the extension speed (lift speed) of a lift cylinder. As a hydraulic circuit of a hydraulic excavator having a boom, there has been proposed one in which hydraulic oils from two pumps are merged to extend a boom cylinder (see Patent Document 1).
JP-A-9-78635

  However, in the forklift described above, when the engine is idling, if the lift and travel are operated simultaneously, the engine load becomes excessive, and travel may not be possible. That is, when the engine is running at a low speed, both the lift function and the traveling function may not be fully exhibited.

  On the other hand, in the above-mentioned Patent Document 1, in the hydraulic excavator, when the operation lever is finely operated in the boom raising direction, the hydraulic oil is supplied to the boom cylinder from only one pump with respect to the boom cylinder. A technique for moving the machine at low speed and high accuracy is described. However, no method has been proposed for solving the problem that the engine cannot run at low speeds. Or, when the traveling speed of the vehicle is low, it has been impossible to solve problems such as difficulty in traveling if the lift cylinder is extended.

The object of the present invention is to solve the above-mentioned problems and ensure both a lift function and a traveling function when the engine is running at a low speed. the sufficiently fast, or Ru near the corresponding other operating conditions of the vehicle of the forklift and provides a forklift hydraulic circuit capable of obtaining a proper lift speed reliably.

The present invention includes a first pump and a second pump, a first supply path for supplying hydraulic oil from the first pump to a lift cylinder via a first control valve, and hydraulic oil from the second pump. In the forklift hydraulic circuit comprising a second supply passage for supplying the engine to the lift cylinder via the second control valve, the detection means for detecting the engine speed and the engine speed is less than a predetermined value. If there is a command means for outputting a signal and a switching valve for switching one of the pilot pressures of the first and second control valves according to the signal, the engine speed is detected and the engine speed is Under one of the first and second control valves, the lift cylinder is extended only with the other one of the first and second supply passages under the condition of a predetermined value or less. To those having a switching means.

In addition, the present invention includes a first pump and a second pump, a first supply path for supplying hydraulic oil from the first pump to the lift cylinder via the first control valve, and a second pump from the second pump. In a forklift hydraulic circuit comprising a second supply passage for supplying hydraulic oil to the lift cylinder via a second control valve, the detection means for detecting the traveling speed and the traveling speed are less than a predetermined value Command means for outputting a signal and a switching valve for switching one of the pilot pressures of the first and second control valves according to the signal, and the traveling speed is detected and the traveling speed is less than a predetermined value. Switching means for setting one of the first and second control valves to a neutral position under the above conditions and extending the lift cylinder only in the other of the first and second supply paths. It is intended to Bei.

In addition, the present invention includes a first pump and a second pump, a first supply path for supplying hydraulic oil from the first pump to the lift cylinder via the first control valve, and a second pump from the second pump. In the forklift hydraulic circuit comprising a second supply passage for supplying hydraulic oil to the lift cylinder via the second control valve, a detecting means for detecting the connection / disconnection state of the vehicle travel clutch and the clutch A command means for outputting a signal when a disengagement state is detected, and a switching valve for switching one of the pilot pressures of the first and second control valves according to the signal, and the disengagement state of the clutch In the clutch connected state, one of the first and second control valves can be switched to the neutral position, and the lift series is switched only in the other of the first and second supply paths. With a Da which is extendable working, in the clutch disengaged state Ru der those having a switching means for switching so as to extend operating the lift cylinder in the working oil from both of the first and second supply path.

The forklift hydraulic circuit according to the present invention can appropriately maintain the forklift travel function and the lift function. For example, when the engine is idling at low speed, the lift function is also slowed down, and both functions can be secured by reducing the engine load.
When the engine is running at high speed, the lift speed can be sufficiently increased by the amount of oil merged from the two pumps. In short, that Do and to obtain achieving smooth effective use and forklift operations of the engine output.

Hereinafter, the present invention will be described in detail based on the illustrated embodiment.
1, 2 and 3 show an embodiment of a hydraulic circuit for a forklift. FIG. 1 shows a state in which the lift cylinder 10 is stopped, and FIG. 2 shows a high speed at which the lift cylinder 10 extends at a high lift speed V ₂ . FIG. 3 shows a low-speed operation state in which the lift cylinder 10 extends at a small lift speed V ₁ .

Reference numeral 1 denotes a first pump, 2 denotes a second pump, and 3 denotes a tank. As shown in FIG. 2, a first supply passage 21 that supplies hydraulic oil from the first pump 1 to the lift cylinder 10 via the first control valve 11, and hydraulic oil from the second pump 2 to the second control. And a second supply path 22 for supplying the lift cylinder 10 via the valve 12.
The first supply path 21 and the second supply path 22 merge at the junction 4 and are connected to the lift cylinder 10. 1 to 3 show the case of two lift cylinders 10 and 10. Even if there is only one lift cylinder 10, it is free.

Then, one of the first and second control valves 11, 12—in FIG. 3, the first control valve 11—is switched to the neutral position as shown in FIGS.・ The other of the second supply passages 21 and 22—in FIG. 3, only the second supply passage 22—provides hydraulic oil (pressure oil) to the lift cylinder 10 and extends the lift cylinder 10. Switching means Z is provided.
A third pump 13 generates a pilot pressure, and the pilot pressure is maintained at a constant value by returning to the tank 3 via the relief valve 5. That is, in FIG. 1, when the set pressure is reached through the relief valve 5 in the middle of the supply path 6 from the third pump 13, the hydraulic oil is returned to the tank 3 through the reflux path 7.
Reference numeral 8 denotes a remote control valve, which is composed of two valve portions 8a and 8b that are switched to opposite open / close states. Switch. Pressure oil from the third pump 13 is connected to the remote control valve 8 through the supply path 6.

  One valve portion 8 a is connected to the pilot pressure receiving portions of the first and second control valves 11 and 12 through a pilot pressure transmission path 14. The pilot transmission path 14 is branched into two first and second transmission paths 14a and 14b at a branching section 15. The first transmission path 14a is a first control valve composed of a three-position pilot switching valve. 11 is connected to one pilot pressure receiving part, and the second transmission path 14b is connected to one pilot pressure receiving part of the second control valve 12 constituted by a three-position pilot switching valve. As is apparent from FIG. 2, if pilot pressure acts on one pilot pressure receiving portion of the first control valve 11 via the first transmission path 14a, the first pump 1 via the first supply path 21 The first control valve 11 is switched so that the pressure oil is sent to the lift cylinder 10. Further, if the pilot pressure acts on one pilot pressure receiving portion of the second control valve 12 via the second transmission path 14b, the pressure oil from the second pump 2 will be lift cylinder via the second supply path 22. The second control valve 12 is switched so as to be sent to 10 (see FIGS. 2 and 3).

  The other valve portion 8 b of the remote control valve 8 is connected to the other pilot pressure receiving portion of the first and second control valves 11 and 12 via another pilot pressure transmission path 16. The pilot pressure transmission path 16 is branched into two first and second transmission paths 16a and 16b at a branching portion 17, and the first transmission path 16a is a first control valve 11 comprising a three-position pilot switching valve. And the second transmission path 16b is connected to the other pilot pressure receiving portion of the second control valve 12 including a three-position pilot switching valve.

If the pilot pressure acts on the other pilot pressure receiving portion of the first control valve 11 via the first transmission path 16a, the operation of the first pump 1 and the lift cylinder 10 via the first return path 31 is performed. The oil returns to tank 3. If the pilot pressure acts on the other pilot pressure receiving part of the second control valve 12 via the second transmission path 16b, the operation of the second pump 2 and the lift cylinder 10 via the second return path 32 The oil returns to tank 3.
And the switching valve 20 which opens and closes the above-mentioned 1st flow path 14a and the 1st flow path 16a simultaneously is provided. This switching valve 20 has illustrated the 2-position solenoid valve in FIGS. 1-3.

The switching means Z will be described below with specific examples.
Reference numeral 23 denotes detection means, and 24 denotes command means. For example, the detection means 23 is a rotation detector that detects the rotational speed of the engine of the forklift vehicle. 2 to FIG. 3, for example, a switch for outputting a switching signal I ₀ . Therefore, in this case, the switching means Z includes a detecting means 23 comprising an engine speed detector, a switch for outputting a signal I ₀ when the engine speed is equal to or lower than a predetermined value (specifically, the idling speed), etc. Command means 24, a two-position switching valve 20 for switching the pilot pressure from the contact state to the disconnection state in FIG. 2 by this signal I ₀ , pilot pressure transmission paths 14 and 16, the first control valve 11, and the like. ing.

As described above, when the detecting means 23 detects that the engine speed has become equal to or lower than the predetermined value (the engine speed in the idling rotation state) by the switching means Z, the first and second control valves 11, 12 are controlled. Only one of the first control valves 11 is switched to the neutral position (switched from FIG. 2 to FIG. 3), the first supply path 21 is closed, and the pressure oil of the first pump 1 is transferred from the first return path 31 to the tank 3. And the lift cylinder 10 is extended only by the other second supply path 22 (only by the second pump 2) (see FIG. 3). Thus, when the engine speed is low and the output torque of the engine is not high, it is possible to use only one pump to reduce the engine load and thus enable the vehicle to travel.
In the example shown in the figure, the detection means 23 and the command means 24 are divided and shown in a block diagram. However, in practice, the detection means 23 and the command means 24 may be integrally configured by a rotation limiter or the like.

Further, the detecting means 23 is a speedometer for detecting the traveling speed of the forklift vehicle, and the command means 24 is a signal I ₀ for switching as shown in FIGS. 2 to 3 when the traveling speed of the vehicle becomes a predetermined value or less. Is a limiter that outputs Thus, the switching means Z outputs the signal I ₀ and transmits it to the solenoid of the switching valve 20 when the traveling speed is below a predetermined value (low speed state). a command means 24, this signal I ₀ and the switching valve 20 for switching the pilot pressure from 2 to 3, the pilot pressure transmission path 14, 16, the first control valve 11 and the like, configured.

As described above, when the detecting means 23 detects that the traveling speed is lower than the predetermined value by the switching means Z, only the first control valve 11 is switched to the neutral position (switched from FIG. 2 to FIG. 1). The first supply path 21 is closed and the pressure oil of the first pump 1 is returned from the first return path 31 to the tank 3, and the lift cylinder is only in the other second supply path 22 (only in the second pump). 10 is extended (see FIG. 3). Therefore, it extends at a low speed V ₁ .
The engine output can be prioritized for traveling until the vehicle reaches a predetermined speed from the vehicle stop state, and when the predetermined speed is exceeded, the discharge flow rates of the two pumps 1 and 2 are combined at a high speed V ₂ . By extending (raising) the lift cylinder 10, it is possible to eliminate the slack at the start of the vehicle.
In the example shown in the drawing, the detection means 23 and the command means 24 are drawn separately. However, in practice, the travel speed detection device may be configured integrally.

Next, another specific example will be described. It is also preferable that the detection means Z is configured as follows. In other words, the detecting means 23 detects the connection / disconnection state of the vehicle traveling clutch. When the clutch is engaged, one of the first and second control valves 11 and 12 (first control valve 11 in the illustrated example) can be switched to the neutral position. In other words, the configuration is such that it is not possible to forcibly switch to the neutral position. In other words, when the clutch connection state is detected by the detection means 23, the lift cylinder 10 can be extended only in one of the first and second supply paths 21 and 22, but the vehicle speed is When the desired speed is reached, the lift cylinder 10 can be extended at a high speed (large lift speed) V ₂ .

However, when the clutch disengagement state is detected by the detection means 23, a signal is issued from the command means 24 so that the lift cylinder 10 is extended by hydraulic oil from both the first and second supply passages 21 and 22. Then, it automatically switches to the state of FIG.
Thus, it is the structure controlled by the presence or absence of the connection of the vehicle travel clutch.

When the vehicle is stopped in the clutch disengaged state (transmission is in the neutral state), there is an advantage that all the output of the engine can be utilized for the extension operation of the lift cylinder 10. That is, when all the clutches are in the off state, the discharge flow rates of the first and second pumps 1 and 2 can be merged, and the lift cylinder 10 can be extended at a large lift speed V ₂ (see FIG. 2). When the clutch is in the engaged state, according to the engine speed and the vehicle traveling speed described above or the method described later, only one of the first and second pumps 1 and 2 and the two pumps 1 , 2 it is desirable to combine the operator's preferences and conditions so that it can be switched to.

Next , a reference example will be described. The switching means Z sets one of the first and second control valves 11 and 12 as a neutral position under the condition that the fork lift set value is not more than a predetermined value ( In the illustrated example, the first control valve 11 is switched to the neutral position as shown in FIGS. 2 to 3), and only one of the first and second supply paths 21 and 22 (in the illustrated example, only the second supply path 22). Thus, the lift cylinder 10 is extended.
More specifically, for example, when a container is stacked on a forklift, the lift height is high, but on the contrary, when the container is stacked on a trailer, the lift height is low. An operator (driver) can set (select) the above-mentioned lift by using a lift-value input or a height switch, but in the present invention, for example, as the command means 24, the above-mentioned lift-value input value Is set to a preset value or less, a command signal I ₀ (see FIG. 3) is output so that the switching valve 20 is switched (the detection means 23 is omitted), and the switching means Z is configured. Alternatively, the command means 24 may be configured so that the signal I ₀ is output when the high / low selector switch is switched to “low”.

In this way, when loading on a trailer with a low loading platform height, a small lift speed V ₁ is sufficient, so the state shown in FIG. 3 is used, and the lifting height is increased as when stacking many layers of containers. If it is higher, the state is switched to the state shown in FIG. This can improve work efficiency and prevent unnecessary lift speed.

Next , another reference example will be described. In FIGS. 1 to 3, the detection means 23 is omitted, and the command means 24 is a manual electric switch. The electric switch is manually turned on and off. The switching valve 20 may be switched.
Alternatively, the switching means Z may be configured to switch between the state shown in FIGS. 2 and 3 by changing the switching valve 20 itself to a manually operated valve and manually connecting and disconnecting.

By using the switching means Z that can be manually operated in this way, if it is possible to select travel priority and lift increase priority at the discretion of the operator (driver), work efficiency, safety, and smooth work can be achieved. It becomes easy. In particular, it is also preferable to combine the switching means Z that can be manually operated with one or more switching means Z such as the engine speed, the traveling speed of the vehicle, the clutch engagement state, and the lift height as described. In this case, in FIG. 1 to FIG. 3, a plurality of switching valves 20 may be arranged in series along the first transmission paths 14a and 16a, or processed by the command means 24 ( It is also possible to configure to output the signal I _{0 (} for example, by an OR circuit).
1 to 3 show only an example of the hydraulic circuit, and the pumps 1 and 2 may be used for branching pipes (including a distribution valve, a diversion valve, etc.) to various other actuators. Besides, other design changes are free.

The present invention is configured as described above. When the remote control valve (pilot valve) 8 as a lift operation valve is switched as shown in FIG. 1 to FIG. 2 or FIG. Since one of the valves 11 and 12 is in a neutral position, the lift cylinder 10 can be extended by only one of the first and second supply passages 21 and 22, thus reducing the engine load when the engine is idling. Thus, the vehicle can be easily driven. That is, both the lift function and the travel function can be ensured. On the other hand, the engine is at a high rotation extending action is possible in large lift speed V _2.

It is a hydraulic circuit diagram of a lift cylinder stop state showing an embodiment of the present invention. It is a hydraulic circuit diagram of a state where a lift cylinder extends at a large lift speed. It is a hydraulic circuit diagram of the state where a lift cylinder extends at a small lift speed.

1 1st pump 2 2nd pump 8 Remote control valve
10 Lift cylinder
11 First control valve
12 Second control valve
20 selector valve
21 First supply channel
22 Second supply channel
23 Detection means
24 Command means
I ₀ signal Z switching means

Claims (3)

A first supply comprising a first pump (1) and a second pump (2) and supplying hydraulic oil from the first pump (1) to a lift cylinder (10) via a first control valve (11) A forklift having a passage (21) and a second supply passage (22) for supplying hydraulic oil from the second pump (2) to the lift cylinder (10) via a second control valve (12) In the hydraulic circuit for
The detection means (23) for detecting the engine speed, the command means (24) for outputting a signal (I ₀ ) if the engine speed is equal to or less than a predetermined value, and the signal (I ₀ ) 2 A control valve (20) for switching one pilot pressure of the control valves (11) and (12), and a condition in which the engine speed is detected and the engine speed is less than a predetermined value With one of the first and second control valves (11) and (12) in the neutral position, the lift cylinder (only in the other of the first and second supply passages (21) and (22)) 10) A hydraulic circuit for a forklift comprising switching means (Z) for extending the operation 10). A first supply comprising a first pump (1) and a second pump (2) and supplying hydraulic oil from the first pump (1) to a lift cylinder (10) via a first control valve (11) A forklift having a passage (21) and a second supply passage (22) for supplying hydraulic oil from the second pump (2) to the lift cylinder (10) via a second control valve (12) In the hydraulic circuit for
The detection means (23) for detecting the traveling speed, the command means (24) for outputting a signal (I ₀ ) if the traveling speed becomes a predetermined value or less, and the first and second control valves (by the signal (I ₀ )). 11) A switching valve (20) for switching one of the pilot pressures of (12), and the above-mentioned first and second conditions under the condition that the traveling speed is detected and the traveling speed becomes a predetermined value or less. One of the second control valves (11) and (12) is set to the neutral position, and the lift cylinder (10) is extended only by the other of the first and second supply passages (21) and (22). A hydraulic circuit for a forklift characterized by comprising switching means (Z). A first supply comprising a first pump (1) and a second pump (2) and supplying hydraulic oil from the first pump (1) to a lift cylinder (10) via a first control valve (11) A forklift having a passage (21) and a second supply passage (22) for supplying hydraulic oil from the second pump (2) to the lift cylinder (10) via a second control valve (12) In the hydraulic circuit for
A detecting means (23) for detecting the engagement / disengagement state of the clutch for driving the vehicle, a command means (24) for outputting a signal when the engagement state of the clutch is detected, and the first and second control valves ( 11) a switching valve (20) for switching one of the pilot pressures of (12), and detecting the clutch engagement / disengagement state, and in the clutch engagement state, the first and second control valves (11 ) (12) while the a freely switched to the neutral position of the said first and second supply path (21) (22 above the lift cylinder (10 other at only of the)) can elongation operation In addition, there is provided switching means (Z) for switching so that the lift cylinder (10) is extended by hydraulic oil from both the first and second supply paths (21) and (22) when the clutch is disengaged. A hydraulic circuit for a forklift characterized by that.

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