JP4083963B2 - Hydraulic control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic control device used for a hydraulic working machine including a plurality of actuators such as a forklift.
[0002]
[Prior art]
The conventional example shown in FIG. 3 includes a lift switching valve 2 for controlling a lift cylinder, a tilt switching valve 3 for controlling a tilt cylinder, and an attachment for controlling an attachment cylinder in a supply flow path 1 connected to a pump P. The switching valve 4 is connected in parallel.
These switching valves 2 to 4 keep the closed position when in the neutral position shown in the figure, and shut off the supply flow path 1.
Further, the proportional electromagnetic pressure reducing valves 11 to 16 are connected to the pilot chambers 5 to 10 of the switching valves 2 to 4, respectively, and the proportional solenoids 11a to 16a of the proportional electromagnetic pressure reducing valves 11 to 16 are excited. The pilot pressure is guided to each pilot chamber 5-10.
Note that the switching valve to which the pilot pressure is supplied to the pilot chamber is switched by the pressure action.
[0003]
A first branch channel 17 is connected to the supply channel 1, and a flow control valve 18 is provided in the first branch channel 17. A fixed throttle 19 is provided on the downstream side of the flow control valve 18, and the pressure on the upstream side of the fixed throttle 19 is guided to one pilot chamber 18 a of the flow control valve 18 via the damper throttle 27 to fix the fixed throttle. The pressure on the downstream side of 19 is guided to the other pilot chamber 18 b of the flow control valve 18.
The flow rate control valve 18 configured as described above exhibits a control function that maintains the differential pressure before and after the fixed throttle 19 to be equivalent to the spring force of the spring 20 and keeps the flow rate passing therethrough constant. In other words, the flow rate control valve 18 always supplies a constant flow rate to the first branch flow path 17 side.
[0004]
A relief valve 21 for setting the primary pressure is connected to the downstream side of the first branch channel 17 to which a constant flow rate is supplied as described above, and the pressure on the upstream side is set by the relief valve 21 to the set pressure. I always try to keep it fairly.
The primary pressure corresponding to the set pressure of the relief valve 21 is guided to the proportional electromagnetic pressure reducing valves 11 to 16 through a pilot line 22 connected between the flow control valve 18 and the fixed throttle 19, and this proportional electromagnetic pressure reducing valve The pressure is reduced by the valves 11 to 16 to become a pilot pressure.
[0005]
A second branch channel 23 is connected to the supply channel 1, and a compensator valve 24 is connected to the second branch channel 23.
The compensator valve 24 guides the supply pressure from the pump P through a damper throttle 25 to one pilot chamber 24a. A first shuttle valve 28 is connected to the other pilot chamber 24 b of the compensator valve 24 via a damper throttle 26.
The pilot line 22 and the second shuttle valve 29 are connected to the upstream side of the first shuttle valve 28, and the first load pressure line 31 and the load pressure line 35 are connected to the second shuttle valve 29. . A third shuttle valve 30 is connected to the load pressure line 35, and a second load pressure line 32 and a third load pressure line 33 are connected to the upstream side of the third shuttle valve 30.
The first to third load pressure lines 31 to 33 guide the load pressure generated by the cylinder when the switching valves 2 to 4 are switched. Each load pressure line 31 to 33 is provided with a fixed throttle f so as to control the flow rate passing therethrough.
[0006]
The third shuttle valve 30 has a higher one of the load pressure of the tilt cylinder guided through the second load pressure line 32 and the load pressure of the attachment cylinder guided through the third load pressure line 33. Is selected and led to the second shuttle valve 29.
In addition, the second shuttle valve 29 has a higher pressure of the load pressure selected by the third shuttle valve 30 and the load pressure of the lift cylinder guided through the first load pressure line 31. Select and guide to the first shuttle valve 28.
In other words, the highest load pressure among the load pressures of the cylinders is selected by the second and third shuttle valves 29 and 30 and guided to the first shuttle valve 28.
[0007]
The first shuttle valve 28 selects the higher one of the maximum load pressure of the cylinder and the primary pressure derived from the pilot line 22 and supplies it to the other pilot chamber 24 b of the compensator valve 24. .
Therefore, when the maximum load pressure of the cylinder is guided to the other pilot chamber 24b, the compensator valve 24 controls its opening degree so as to keep the operating speed of the cylinder generating the maximum load pressure constant. To do. That is, the opening degree is adjusted so that the differential pressure before and after the throttle channel formed according to the opening degree of the switching valve is kept high by an amount corresponding to the spring force of the spring 24c.
[0008]
On the other hand, when none of the cylinders is operated, or when the maximum load pressure of the cylinder is lower than the primary pressure, the primary pressure is guided to the other pilot chamber 24b of the compensator valve 24.
Therefore, in this case, the compensator valve 24 is controlled to keep the supply pressure higher than the primary pressure by the amount corresponding to the spring force of the spring 24c. That is, in a state where none of the cylinders are operated, that is, a so-called standby state, the primary pressure is always maintained, and the supply pressure of the pump P is minimized to prevent energy loss.
[0009]
A main relief valve 34 is connected to the second branch flow path 23. The main relief valve 34 controls the maximum load pressure acting on the lift cylinder.
On the other hand, a discharge pressure line 36 is connected to a load pressure line 35 connecting the second shuttle valve 29 and the third shuttle valve 30, and a first pilot relief valve 37 is connected to the discharge flow path 36. Further, a discharge passage 39 is also connected to the third load pressure line 33, and a second pilot relief valve 40 is connected to the discharge passage 39.
[0010]
In addition, among the relief valves, the set pressure of the main relief valve 34 that controls the maximum pressure of the lift cylinder is set to be the highest. Next, the set pressure of the first pilot relief valve 37 that controls the maximum pressure of the tilt cylinder, the set pressure of the second pilot relief valve 40 that controls the attachment cylinder third, and finally the relief valve that sets the primary pressure The order of 21 set pressures is determined.
A fixed throttle 38 is provided upstream of the first pilot relief valve 37, and a fixed throttle 41 is also provided upstream of the second pilot relief valve 40. The fixed throttles 38 and 41 stabilize the operation of the pilot relief valves 37 and 40.
[0011]
The first pilot relief valve 37 determines the highest pressure acting on the tilt cylinder, and the second pilot relief valve 40 determines the highest pressure acting on the attachment cylinder.
For example, when only the tilt cylinder is operated, the load pressure is guided to the other pilot chamber 24 b of the compensator valve 24. Therefore, the compensator valve 24 controls the opening degree so that the differential pressure before and after the throttle passage formed according to the switching amount of the switching valve 3 is always kept constant. That is, the compensator valve 24 exhibits a load sensing control function for the tilt cylinder, and keeps the operating speed of the tilt cylinder constant regardless of load fluctuations.
[0012]
When the load pressure of the tilt cylinder exceeds the set pressure of the first pilot relief valve 37 from the above state, the first pilot relief valve 37 is opened. If the first pilot relief valve 37 is thus opened, the pressure in the pilot chamber 24 b of the compensator valve 24 is maintained at the set pressure of the first pilot relief valve 37.
Therefore, the supply pressure of the pump P is maintained at a magnitude obtained by adding the pressure corresponding to the spring force of the spring 24 c to the set pressure of the first pilot relief valve 37.
Therefore, it is possible to prevent the tilt cylinder from being supplied with a high pressure exceeding the allowable pressure, and the tilt cylinder is not destroyed by the high pressure.
Similarly to the above, the second pilot relief valve 40 prevents the attachment cylinder from being supplied with a pressure higher than the allowable pressure.
[0013]
[Problems to be solved by the invention]
In the above conventional apparatus, for example, when the lift cylinder and the attachment cylinder are operated simultaneously, the attachment cylinder may be destroyed. That is, when the lift cylinder and the attachment cylinder are operated simultaneously and the load pressure of the lift cylinder becomes equal to or higher than the load pressure of the attachment cylinder, the load pressure of the lift cylinder is changed to the other pilot chamber 24b of the compensator valve 24. Led to.
Therefore, the compensator valve 24 exhibits a load sensing control function for the lift cylinder. In other words, the supply pressure is controlled to be higher than the load pressure of the lift cylinder by a certain pressure.
[0014]
At this time, the supply pressure controlled by the compensator valve 24 can be increased to the set pressure of the main relief valve 34. For this reason, the supply pressure may be higher than the allowable pressure of the attachment cylinder. When such a high pressure is supplied to the attachment cylinder, there is a possibility that the supply pressure is destroyed.
An object of the present invention is to provide a hydraulic control device capable of preventing a high pressure exceeding an allowable pressure from acting on an actuator when a plurality of actuators are operated simultaneously.
[0015]
[Means for Solving the Problems]
The present invention is provided with a pump, a supply passage connected to the pump, a plurality of switching valves connected in parallel to the supply passage, an actuator connected to the switching valves, and a pilot chamber of the switching valve. Proportional electromagnetic pressure reducing valve, pilot pressure source for guiding primary pressure to the proportional electromagnetic pressure reducing valve, compensator valve connected to the supply flow path, and load generated when the actuator is operated while connected to each switching valve A load pressure line for introducing pressure to the compensator valve, a discharge line for connecting the load pressure line to the tank, and a pilot relief valve provided in the discharge line. The proportional electromagnetic pressure reduction valve is supplied from a pilot pressure source. It is premised on a hydraulic control device configured to reduce the primary pressure and guide it to the pilot chamber of the switching valve.
[0016]
Assuming the above device, an orifice is provided on the downstream side of the pilot relief valve, and when the pilot relief valve is opened, the pressure generated on the upstream side of the orifice is opposed to the proportional solenoid of the proportional electromagnetic pressure reducing valve. It is characterized in that it is configured to be led to a pilot chamber provided at a position where it is located.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
In the embodiment of the present invention shown in FIG. 1, an orifice 42 is provided on the downstream side of the second pilot relief valve 40 connected to the discharge line 39 of the attachment switching valve 4, and the orifice 42 and the second pilot relief valve are provided. It is characterized in that the pressure generated between it and the pressure chamber 40 is guided to the pilot chambers 46 and 47 of the proportional electromagnetic pressure reducing valves 15 and 16 via the flow path 43 and the shuttle valves 44 and 45.
The configuration of the switching valves 2 and 3 and the configuration of the compensator valve 2 and the flow rate control valve 18 are exactly the same as in the conventional example. Description is omitted.
[0018]
As described above, the orifice 42 is provided on the downstream side of the second pilot relief valve 40.
Therefore, when the second pilot relief valve 40 is opened, a predetermined pressure is generated on the upstream side of the orifice 42, and this pressure is guided to the shuttle valves 44 and 45 via the flow path 43. If the pressure on the upstream side of the orifice 42 is selected by the shuttle valves 44 and 45, the pressure is guided to the pilot chambers 46 and 47 of the proportional electromagnetic pressure reducing valves 15 and 16.
[0019]
The pilot chambers 46 and 47 of these proportional electromagnetic pressure reducing valves 15 and 16 are provided at positions facing the proportional solenoids 15a and 16a.
Therefore, when the pressure upstream of the orifice 42 is guided to the pilot chambers 46 and 47 as described above, the thrust of the proportional electromagnetic pressure reducing valves 15 and 16 is opposed to the thrust provided by the proportional solenoids 15a and 16a. Occurs.
[0020]
Thus, when the thrust which opposes the thrust of a proportional solenoid arises in a spool, the communicating opening degree of a proportional electromagnetic pressure reducing valve will become small. Therefore, the pilot pressure guided to the pilot chamber via the proportional electromagnetic pressure reducing valves 15 and 16 is reduced. When the pilot pressure decreases, the switching valve 4 moves in the neutral direction to reduce the communication opening.
That is, when the second pilot relief valve 40 is opened, the communication opening degree of the switching valve 4 is reduced, and thus the communication opening degree of the switching valve 4 is reduced so that the pressure supplied to the attachment cylinder is within the allowable pressure. I try to keep it down.
[0021]
Next, the operation of this embodiment will be described. Here, a case where the lift cylinder and the attachment cylinder are operated together will be described.
When the proportional solenoid 12a of the proportional electromagnetic pressure reducing valve 12 and the proportional solenoid 16a of the proportional electromagnetic pressure reducing valve 16 are excited to supply pilot pressure to the pilot chambers 6 and 10 of the switching valves 2 and 4, respectively, 2, 4 switches to the right position of the drawing.
Accordingly, the lift cylinder and the attachment cylinder operate.
[0022]
When the lift cylinder and the attachment cylinder are operated as described above, if the load pressure acting on the lift cylinder becomes larger than the load pressure of the attachment cylinder, the load pressure of the lift cylinder is reduced to the other pilot of the compensator valve 24. Guided to chamber 24b. Therefore, this compensator valve 24 exhibits a load sensing control function for the lift cylinder.
[0023]
When the load pressure acting on the lift cylinder further increases from this state and the supply pressure exceeds the set pressure of the second pilot relief valve 40, the second pilot relief valve 40 opens. When the second pilot relief valve 40 is opened, as described above, the pilot pressure introduced into the pilot chamber 10 is reduced, so that the opening degree of the switching valve 4 that controls the attachment cylinder is reduced.
Therefore, it is possible to prevent a high pressure exceeding the allowable pressure from acting on the attachment cylinder.
In this embodiment, a mechanism for reducing the pilot pressure is provided only in the attachment switching valve 4, but this mechanism may be provided in the tilt switching valve 3.
[0024]
FIG. 2 shows a specific structure of the attachment switching valve 4 shown in FIG. 1, and the same components as those in FIG.
A spool hole 51 is formed in the body 50, and a main spool 52 is slidably incorporated in the spool hole 51. In this way, both ends of the spool hole 51 incorporating the main spool 52 are closed with the caps 53, 53, and the pilot chambers 9, 10 are formed on both sides of the main spool 52. Further, centering springs 54, 54 are incorporated in the pilot chambers 9, 10 so that the neutral position of the main spool 52 is maintained. And the switching valve 4 for attachment is comprised by said structure.
[0025]
The body 50 is formed with a pair of pilot lines 22 and 22 and pilot passages 55 and 55, and the proportional electromagnetic pressure reducing valves 15 and 16 are provided between the pilot lines 22 and 22 and the pilot passages 55 and 55. Is incorporated.
In these proportional electromagnetic pressure reducing valves 15 and 16, small spools 57 and 57 are slidably incorporated in spool holes 56 and 56 communicating with the pilot lines 22 and 22 and the pilot passages 55 and 55, respectively. The springs 58 and 58 are incorporated into the lower ends of the small spools 57 and 57, and the other ends of the small spools 57 and 57 are brought into contact with the push rods 59 and 59 of the proportional solenoids 15a and 16a by the elastic force. Yes.
[0026]
When the proportional solenoids 15a, 16a are excited, the proportional electromagnetic pressure reducing valves 15, 16 as described above push the small spools 57, 57 downward from the illustrated state by the push rods 59, 59. Therefore, the pilot lines 22 and 22 communicate with the pilot passages 55 and 55 through the annular grooves 60 and 60 formed in the small spools 57 and 57.
Therefore, the primary pressure introduced through the pilot lines 22 and 22 is reduced in the process of passing through the throttle passage formed by the annular grooves 60 and 60 and is guided to the pilot passages 55 and 55. The pilot pressure introduced to the pilot passages 55 and 55 is introduced to the pilot chambers 9 and 10, respectively.
[0027]
For example, if pilot pressure is introduced into one pilot chamber 10, thrust in the left direction of the drawing is generated in the main spool 52, and the main spool 52 moves rightward while deflecting the centering spring 54.
If the main spool 52 moves to the left in the drawing, one actuator port 61 communicates with the supply port 63 via a notch 64 formed in the main spool 52, and the other actuator port 62 forms a notch 65 formed in the main spool 52. Through the tank port 66a. In this way, the cylinder operates.
[0028]
On the other hand, a second pilot relief valve 40 is incorporated between the proportional electromagnetic pressure reducing valves 15 and 16. The second pilot relief valve 40 includes a hollow cylindrical member 67, a throttle member 68 fixed to the distal end of the cylindrical member 67, a poppet 69 incorporated in the plug member 67, and a spring that imparts an elastic force to the poppet 69. 70 and an adjusting bolt 71 that adjusts the initial elastic force of the spring 70.
A fixed throttle 41 is formed in the throttle member 68, and one side of the fixed throttle 41 communicates with the third load pressure line 33, and the other communicates with the spring chamber 72 in the cylindrical member 67.
However, as shown in the figure, when the poppet 69 is seated on the seat portion 73 of the orifice member 68 by the elastic force of the spring 70, the communication between the fixed throttle 41 and the spring chamber 72 is blocked.
[0029]
Further, the spring chamber 72 and the tank port 66b are connected via a discharge passage 39, and an orifice 42 is provided in the discharge passage 39.
Further, the spring chamber 72 and the pilot chambers 46 and 47 of the proportional electromagnetic pressure reducing valves 15 and 16 are communicated with each other via the flow path 43. Shuttle valves 44 and 45 are incorporated in the flow path 43.
Then, the proportional solenoid pressure reducing valves 15, 16 are set to the higher one of the pilot pressure introduced from the pilot passage 55 by the shuttle valves 44, 45 and the pressure generated upstream of the orifice 42. The pilot chambers 46 and 47 are led to.
[0030]
For example, when the proportional solenoid 16a of the proportional electromagnetic pressure reducing valve 16 is excited and the pilot pressure is guided to the pilot chamber 10 from the neutral state shown in the drawing, the main spool 52 moves to the left in the drawing by the pressure action.
When the main spool 52 is thus switched, as described above, the actuator port 61 and the supply port 63 communicate with each other, and the actuator port 6 and the tank port 66a communicate with each other.
[0031]
In this state, when a high pressure equal to or higher than the set pressure of the relief valve 40 is introduced through the third load pressure line 33, the poppet 69 is separated from the seat portion 73. When the poppet 69 is separated from the seat portion 73, the pressure oil in the third load pressure line 33 is discharged to the tank T through the fixed throttle 41 → the spring chamber 72 → the discharge passage 39 → the orifice 42 → the tank port 66b. The pressure generated on the upstream side of the orifice 42 acts on the shuttle valve 45 via the flow path 43, and the shuttle valve 45 moves to the right in the drawing. When the shuttle valve 45 moves in the right direction in the drawing as described above, the spring chamber 72 and the pilot chamber 47 of the proportional electromagnetic pressure reducing valve 16 communicate with each other, and thrust in the upward direction in the drawing is applied to the small spool 57.
[0032]
Accordingly, the small spool 57 moves upward in the drawing against the push rod 59 of the proportional solenoid 16a, and the opening area between the pilot line 22 and the pilot flow path 55 is reduced. When the opening area between the pilot line 22 and the pilot flow path 55 is reduced in this way, the pilot pressure guided to the pilot chamber 10 decreases, and thereby the main spool 52 moves in the neutral direction. When the main spool 52 moves in the neutral direction in this way, the opening area between the actuator port 61 and the supply port 63 is reduced, so that the pressure supplied to the actuator port 61 is kept low.
As described above, the attachment cylinder is prevented from being supplied with a pressure higher than the allowable pressure.
[0033]
【The invention's effect】
According to the present invention, when the pilot relief valve is opened, the pilot pressure supplied to the pilot chamber is lowered and the switching valve is returned to the neutral direction, so that it is supplied to the actuator connected to the switching valve. Supply pressure can be reduced.
Therefore, it is possible to prevent the actuator having a low allowable pressure from being destroyed when the actuators are simultaneously operated.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an embodiment.
FIG. 2 is a cross-sectional view showing a specific structure of an attachment switching valve 4;
FIG. 3 is a circuit diagram of a conventional example.
[Explanation of symbols]
P Pump 1 Supply flow path 2-4 Switching valve 11-16 Proportional electromagnetic pressure reducing valve 24 Compensator valve 33 Load pressure line 39 Discharge line 40 Pilot relief valve 42 Orifice 15a, 16a Proportional solenoid 46, 47 Pilot chamber

Claims (1)

A pump, a supply flow path connected to the pump, a plurality of switching valves connected in parallel to the supply flow path, an actuator connected to the switching valves, and a proportional electromagnetic pressure reduction provided in a pilot chamber of the switching valve A valve, a pilot pressure source for guiding the primary pressure to the proportional electromagnetic pressure reducing valve, a compensator valve connected to the supply flow path, and each switching valve, and the load pressure generated when the actuator is operated is A load pressure line leading to the valve, a discharge line connecting the load pressure line to the tank, and a pilot relief valve provided in the discharge line, the proportional electromagnetic pressure reducing valve reduces the primary pressure from the pilot pressure source. In the hydraulic control apparatus configured to be guided to the pilot chamber of the switching valve, an orifice is provided on the downstream side of the pilot relief valve. Therefore, when the pilot relief valve is opened, the hydraulic pressure is characterized in that the pressure generated upstream of the orifice is guided to a pilot chamber provided at a position facing the proportional solenoid of the proportional electromagnetic pressure reducing valve. Control device.

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