JPH07248004A - Hydraulic circuit for working machine - Google Patents

Abstract

PURPOSE:To easily ensure a lowering speed for crawling in a working machine in accordance with a manipulation degree of a control lever so as to reduce the burden for the manipulation of the operator by connecting a crawling pilot hydraulic circuit to the pilot hydraulic circuit in parallel with the latter, downstream of a mode change-over valve, by way of a mode selector valve. CONSTITUTION:When a mode selecting switch 46 is turned on, a mode selector valve 40 is changed over from a normal control mode position into a crawling control mode position. Hydraulic oil discharged from a pilot pump 18 flows through a crawling pilot hydraulic pipe line 44, that is, the mode selector valve 40 and a pressure reducing valve 42, and are then fed to the upstream side of first and second remote control valves 20, 24. Accordingly, when the first remote control valve 20 is opened, a direction control valve 6 is changed over from a neutral position into a first change-over position 1, and accordingly, hydraulic oil discharged from a hydraulic pump 2 is fed into a boom lowering chamber 14 of the hydraulic cylinder 4. At this time, the pressure of discharge oil is reduced, and accordingly, the stroke of a spool in the direction control valve 6 is limited so as to restrict the opening area of the valve, thereby it is possible to lower the speed for crawling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a working machine hydraulic circuit applied to construction machines such as hydraulic excavators and mobile cranes.

[0002]

2. Description of the Related Art In a construction machine, a working machine such as a boom, an arm or a crane is provided in a turning vehicle body. In order to move these working machines up and down, a working machine hydraulic circuit including a hydraulic cylinder (actuator) is provided. Here, as a conventional technique, a boom hydraulic circuit for a hydraulic excavator will be described as an example. FIG. 2 shows a main part of a conventional hydraulic circuit for a working machine applied to a hydraulic shovel (not shown). The hydraulic pump 2 and a hydraulic cylinder 4 for vertically moving a boom (not shown) which is a working machine are a directional control valve 6 Is connected by the discharge oil passage 8 via. The hydraulic pump 2 is composed of a variable displacement pump driven by an engine (not shown) mounted on a hydraulic excavator. The hydraulic cylinder 4, which is an actuator, is mounted on the vehicle body side, and the piston rod 10
One end of is attached to the boom side. Hydraulic cylinder 4
The inside is divided into two by a piston 12 provided at the other end of the piston rod 10. A chamber 14 on the piston rod 10 side in the hydraulic cylinder 4 forms a boom lowering chamber (working machine lowering chamber), and a chamber 16 on the cylinder head side forms a boom raising chamber (working machine raising chamber). The pilot pump 18 driven by the engine and one end side (the upper end side in FIG. 2) of the directional control valve 6 are connected by a first pilot oil passage 22 via a first remote control valve 20. The pilot pump 18 and the other end side (the lower end side in FIG. 2) of the directional control valve 6 are connected by a second pilot oil passage 26 via a second remote control valve 24.

The first pilot oil passage 22 is located on the upstream side of the first remote control valve 20.
Includes 3. The second pilot oil passage 26 includes the main pilot oil passage 23 on the upstream side of the second remote control valve 24. The first remote control valve 20 and the second remote control valve 24 are open / close controlled by a well-known operation lever (not shown). The directional control valve 6 is composed of a 4-port 3-position switching valve, and is normally positioned at the neutral position shown by springs arranged at both ends thereof. When the first remote control valve 20 is opened by the operation lever, the pressure oil discharged from the pilot pump 18 is discharged through the first remote control valve 20 to the first remote control valve 20.
Is supplied to one end side of the directional control valve 6 by the pilot oil passage 22. As a result, the directional control valve 6 is switched to the first switching position. As a result, the discharge pressure oil of the hydraulic pump 2 is discharged through the discharge oil passage 8 into the hydraulic cylinder 000 lowering chamber 14
And the boom is lowered. The boom raising chamber 16 communicates with the oil tank T via the direction control valve 6. On the other hand, when the second remote control valve 24 is opened by the operation lever, the discharge pressure oil of the pilot pump 18 is transferred to the other end side of the directional control valve 6 by the second pilot oil passage 26 via the second remote control valve 24. Supplied. As a result, the directional control valve 6 is switched to the third switching position. As a result, the discharge pressure oil of the hydraulic pump 2 is supplied to the boom raising chamber 16 of the hydraulic cylinder 4 through the discharge oil passage 8, and the boom raising operation is performed. The boom lowering chamber 14 has a directional control valve 6
Through the oil tank T.

In order to smoothly perform such boom raising and boom lowering operations, the hydraulic circuit is provided with an overload relief valve 30 with a make-up function. That is, the discharge oil passage 8 connecting the directional control valve 6 and the boom lowering chamber 14 of the hydraulic cylinder 4 and the oil tank T are
An oil passage 34 is connected via an overload relief valve 32. Further, the discharge oil passage 8 and the oil tank T have a check valve 36 arranged in parallel with the relief valve 32.
Are connected by an oil passage 38. The overload relief valve 30 with a make-up function is composed of the relief valve 32 and the check valve 36. The discharge oil passage 8a to the boom raising chamber 16 is also provided with another overload relief valve, but it is omitted in the figure.
As described above, during the boom lowering operation, the discharge pressure oil of the hydraulic pump 2 is supplied to the boom lowering chamber 14 of the hydraulic cylinder 4 through the discharge oil passage 8. In this boom lowering operation, if the hydraulic pressure on the boom lowering chamber 14 side exceeds a predetermined value for some reason, the relief valve 32 opens and the boom lowering chamber 14
And the oil tank T are connected via a relief valve 32.
As a result, abnormal pressure rise is prevented and damage to each part is prevented. On the other hand, in this boom lowering operation, when the pressure oil is insufficiently supplied with respect to the lowering of the piston 12, the check valve 36 is opened and the oil is supplied from the oil tank T.
This prevents the generation of vacuum in the boom lowering chamber 14. Such an action of the check valve 36 forms a make-up function in the boom lowering operation.

[0005]

A fine operation mode is selected when the boom is moved up and down at a slow speed. In the fine operation mode, the speed of boom up and down movement is suppressed by reducing the engine speed or the amount of oil discharged by a flow rate control signal to the hydraulic pump 2. When the fine operation mode is selected for the boom lowering operation, the first remote control valve 20 is controlled by operating the operation lever to perform the boom lowering operation. However, the check valve 36 in the above-described overload relief valve 30 with a make-up function is opened, and the oil is supplied from the oil tank T to the boom lowering chamber 14 of the hydraulic cylinder 4. Therefore, the boom lowering speed tends to increase more than the operation amount of the operation lever. Therefore, the operator must always pay attention to such a tendency. As a result, the operator uses more nerve than necessary for the boom lowering operation in the fine operation mode, and requires skill to perform accurate fine operation, which makes the work difficult and the work load is considerable. .

The present invention has been made based on the above facts, and an object thereof is to easily obtain a lowering speed of the working machine according to the operation amount of the operating lever when the working machine is lowered in the fine operation mode. , To provide an improved hydraulic circuit for work implements.

[0007]

In order to achieve the above object, according to the present invention, a hydraulic pump and a hydraulic cylinder of a working machine are connected by a discharge oil passage of the hydraulic pump via a directional control valve, and a pilot is provided. The pump and one end side of the directional control valve are connected by a first pilot oil passage via a first remote control valve, and the pilot pump and the other end side of the directional control valve are connected by a second remote control valve. Connected by a second pilot oil passage, and when the first remote control valve is opened, the directional control valve is switched to the first switching position so that the hydraulic fluid discharged from the hydraulic pump lowers the working machine of the hydraulic cylinder. In the working machine hydraulic circuit configured to be supplied to the chamber, a mode switching valve is arranged in the first pilot oil passage, and a pressure reducing valve is provided downstream of the mode switching valve in the first pilot oil passage. Go through the valve The operation pilot oil passages are provided in parallel, and the mode switching valve includes a normal operation mode position where the discharge pressure oil of the pilot pump is supplied without passing through the fine operation pilot oil passage and a discharge pressure oil of the pilot pump. Is provided to be switched to a fine operation mode position supplied through the fine operation pilot oil passage.

[0008]

In the present invention, the mode switching valve is arranged in the first pilot oil passage. On the downstream side of the mode switching valve in the first pilot oil passage, a fine operation pilot oil passage via the pressure reducing valve is provided in parallel. The mode switching valve has a normal operation mode position where the pressure oil discharged from the pilot pump is supplied without passing through the fine operation pilot oil passage,
The discharge pressure oil of the pilot pump is configured to be switched to a fine operation mode position in which it is supplied through the fine operation pilot oil passage. When the fine operation mode is set, the mode switching valve is switched to the fine operation mode position. The pressure oil discharged from the pilot pump is supplied to the upstream side of the first remote control valve and the second remote control valve through the fine operation pilot oil passage, that is, through the mode switching valve and the pressure reducing valve.
When the operation lever is operated to open the first remote control valve, the discharge pressure oil is supplied to one end of the directional control valve, so that the directional control valve is switched from the neutral position to the first switching position. The hydraulic fluid discharged from the hydraulic pump is supplied to the working machine lowering chamber of the hydraulic cylinder to lower the working machine. In addition,
The work implement raising chamber communicates with the oil tank via the directional control valve. The pressure oil discharged from the pilot pump is decompressed by the pressure reducing valve and supplied to the first remote control valve. As a result, the pilot secondary pressure supplied to the directional control valve via the first remote control valve also becomes the upper limit value of the pressure reduced by the pressure reducing valve. This upper limit pressure is predetermined in consideration of the force of the spring for centering the directional control valve to the neutral position so that the opening area of the directional control valve is not fully opened (for example, about 2/3 times or about half open). As a result, the stroke of the spool included in the directional control valve is limited, and the valve opening area is reduced. This valve opening area is limited in both the discharge oil passage that connects the hydraulic pump in the directional control valve with the working machine lowering chamber of the hydraulic cylinder, and in both the working machine raising chamber of the hydraulic cylinder in the directional control valve and the oil passage to the oil tank. To be As a result, even if an overload relief valve with a make-up function is provided in the discharge oil passage communicating with the working machine lowering chamber of the hydraulic cylinder, there is no tendency for the working machine lowering speed to increase beyond the operation amount of the operating lever. Therefore, no vacuum is generated in the working machine lowering chamber of the hydraulic cylinder, and the working machine lowering speed (fine speed) according to the operation amount of the operating lever can be obtained. The operator can easily and accurately perform the operation of lowering the work implement in the fine operation mode without using too much nerve, so that the work load is remarkably reduced. Further, the lowering speed of the working machine that matches the operation amount of the operating lever is obtained, so that the safety is further improved (for example, a hanging work by a crane).

When the operation lever is operated to open the second remote control valve in the fine operation mode setting, the discharge pressure oil is supplied to the other end side of the directional control valve, so that the directional control valve is neutral. The position is switched to the second switching position.
The hydraulic fluid discharged from the hydraulic pump is supplied to the working machine raising chamber of the hydraulic cylinder, and the working machine is raised. The working machine lowering chamber of the hydraulic cylinder communicates with the oil tank via the directional control valve. The pressure oil discharged from the pilot pump is decompressed by the pressure reducing valve and supplied to the second remote control valve. As a result, the pilot secondary pressure supplied to the directional control valve via the second remote control valve also becomes the upper limit value of the pressure reduced by the pressure reducing valve. As a result, by the same operation as described above, the raising speed (slow speed) of the working machine according to the operation amount of the operation lever can be obtained.

On the other hand, when the normal operation mode is set, the mode switching valve is switched to the normal operation mode position. Since the discharge pressure oil of the pilot pump is supplied without passing through the fine operation pilot oil passage, the discharge pressure oil of the pilot pump is directly passed from the mode switching valve without passing through the pressure reducing valve to the first remote control valve and the second remote control. Supplied upstream of the valve. Therefore, by operating the operating lever, the work machine is vertically moved at a normal speed as in the conventional case.

When the fine operation pilot oil passage including the mode switching valve and the pressure reducing valve is provided on the upstream side of the first remote control valve in the first pilot oil passage, a plurality of works provided on the downstream side thereof. For all operations of the machine hydraulic cylinder, that is, all operations of the plurality of working machines, the operability as the fine operation mode is simultaneously improved. Further, when the fine operation pilot oil passage including the mode switching valve and the pressure reducing valve is provided in the first pilot oil passage on the downstream side of the first remote control valve, only the set working machine is set to the fine operation mode. Therefore, it is possible to form a unique fine operation mode according to the working machine.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a working machine hydraulic circuit constructed according to the present invention will be described with reference to FIG. In FIG. 1, the same parts as those in FIG. A mode switching valve 40 is arranged in the main pilot oil passage 23 that constitutes a part of the first pilot oil passage 22. On the downstream side of the mode switching valve 40 in the main pilot oil passage 23, a fine operation pilot oil passage 44 passing through the pressure reducing valve 42 is provided in parallel. Mode switching valve 4
0 indicates the normal operation mode position in which the discharge pressure oil of the pilot pump 18 is supplied without passing through the fine operation pilot oil passage 44, and the discharge pressure oil of the pilot pump 18 is supplied through the fine operation pilot oil passage 44. It is configured to switch to the fine operation mode position. In this embodiment, the mode switching valve 40 is a 3-port 2-position switching type electromagnetic operation switching valve, and is normally positioned at the normal operation mode position 1 shown in FIG. 1 by a spring provided at one end thereof. A solenoid is provided at the other end of the mode switching valve 40. This solenoid is a power source B,
It is configured to be included in an electric circuit including the mode changeover switch 46, the relay R and the like. The power source B, the mode switching switch 46, and the relay coil portion of the relay R are connected in series, while the power source B, the relay switching portion of the relay R, and the solenoid of the mode switching valve 40 are connected in series. This electric circuit constitutes a mode switching means. When the mode selector switch 46 is in the OFF state,
Since the relay coil portion of the relay R is not energized, the relay switch portion is in the OFF state, and the solenoid of the mode switching valve 40 is not energized. Therefore,
As shown, the mode switching valve 40 is positioned in the normal operating mode position. Mode switch 46 is O
When turned on, the relay coil portion of the relay R is energized, so that the relay switch portion is turned on and the solenoid of the mode switching valve 40 is energized. Therefore, the mode switching valve 40 is switched from the normal operation mode position to the fine operation mode position. An embodiment in which the fine operation pilot oil passage 44 including the mode switching valve 40 and the pressure reducing valve 42 is provided in the first pilot oil passage 22 on the downstream side of the first remote control valve 20 is also conceivable.

Next, the operation of the working machine hydraulic circuit will be described. When the mode selector switch 46 is turned on, the mode selector valve 40 is switched from the normal operation mode position to the fine operation mode position. As a result, the fine operation mode is set. The pressure oil discharged from the pilot pump 18 is supplied to the upstream side of the first remote control valve 20 and the second remote control valve 24 through the fine operation pilot oil passage 44, that is, through the mode switching valve 40 and the pressure reducing valve 42. When the first remote control valve 20 is opened by operating an operation lever (not shown), the discharge pressure oil is supplied to one end side of the directional control valve 6, so the directional control valve 6 is switched from the neutral position shown in the figure to the first position. Switched to position. The hydraulic fluid discharged from the hydraulic pump 2 is supplied to the hydraulic cylinder 4.
It is supplied to the boom lowering chamber 14 and the boom lowering operation is performed. The boom raising chamber 16 is connected to the oil tank T via the direction control valve 6. Since the pressure oil discharged from the pilot pump 18 is reduced in pressure by the pressure reducing valve 42 and supplied to the first remote control valve 20, the pilot secondary oil supplied to one end of the directional control valve 6 via the first remote control valve 20. Regarding the pressure, the pressure reduced by the pressure reducing valve 42 becomes the upper limit value.
This upper limit pressure is predetermined in consideration of the force of the spring that centers the directional control valve 6 to the neutral position so that the opening area of the directional control valve 6 is not fully opened (for example, about 2/3 times or about half open). . As a result, the stroke of the spool included in the directional control valve 6 is limited, and the valve opening area is reduced. This valve opening area is reduced in both the discharge oil passage 8 that connects the hydraulic pump 2 in the directional control valve 6 and the boom lowering chamber 14 and the boom raising chamber 16 in the directional control valve 6 and the oil passage 8a to the oil tank T. To be

As a result, even if the discharge oil passage 8 communicating with the boom lowering chamber 14 is provided with the make-up function overload relief valve 30, the boom lowering speed tends to increase more than the operation amount of the operating lever. Therefore, the vacuum is not generated in the boom lowering chamber 14, and the boom lowering speed (fine speed) corresponding to the operation amount of the operation lever can be obtained. The operator can easily and accurately perform the operation of lowering the boom in the fine operation mode without undue nervousness, which significantly reduces the work load. Further, by obtaining the boom lowering speed that matches the operation amount of the operation lever, the safety is further improved (for example, lifting work by a crane).

When the operation lever is operated to open the second remote control valve 24 in the fine operation mode setting, the pressure oil discharged from the pilot pump 18 is supplied to the other end side of the directional control valve 6. The directional control valve 6 moves from the neutral position to the second position.
To the switching position of. The hydraulic fluid discharged from the hydraulic pump 2 is supplied to the boom raising chamber 16 and the boom raising operation is performed. The boom lowering chamber 14 is connected to the oil tank T via the direction control valve 6. The pressure oil discharged from the pilot pump 18 is reduced in pressure by the pressure reducing valve 42 and supplied to the second remote control valve 24. Therefore, the pilot pressure oil supplied to the other end of the directional control valve 6 via the second remote control valve 24 is used. Regarding the next pressure, the pressure reduced by the pressure reducing valve 42 becomes the upper limit value.
As a result, the boom raising speed (slow speed) according to the operation amount of the operation lever can be obtained by the same operation as described above.

On the other hand, when the mode selector switch 46 is turned off, the mode selector valve 40 is switched from the fine operation mode position to the normal operation mode position. This sets the normal operation mode. Since the pressure oil discharged from the pilot pump 18 is supplied without passing through the fine operation pilot oil passage 44, the pressure oil discharged from the pilot pump 18 does not pass through the pressure reducing valve 42 but directly from the mode switching valve 40 to the first remote controller. It is supplied to the upstream side of the valve 20 and the second remote control valve 24. Therefore, by operating the operating lever, the boom is vertically moved at a normal speed as in the conventional case.

In the embodiment of FIG. 1, the mode switching valve 4
0 and the fine control pilot oil passage 44 including the pressure reducing valve 42 is the first remote control valve 20 in the first pilot oil passage 22.
Is provided on the upstream side of. Therefore, all the operations of other working machine hydraulic cylinders (not shown) controlled by other remote control valves (not shown) and directional control valves (not shown) provided on the downstream side, Operability as an operation mode is improved at the same time. Further, the fine operation pilot oil passage 44 including the mode switching valve 40 and the pressure reducing valve 42 is the first pilot oil passage 22.
In the case where it is provided on the downstream side of the first remote control valve 20 (not shown), only the set working machine can be set to the fine operation mode, and the unique fine operation corresponding to the working machine can be performed. Modes can be formed. In this case, further, an example in which the fine operation pilot oil passage 44 including the mode switching valve 40 and the pressure reducing valve 42 is provided in the second pilot oil passage 26 on the downstream side of the second remote control valve 24 can be considered.
In this case, it becomes possible to set only the set working machine to the fine operation mode in both operations in the vertical direction.

Although the present invention has been described in detail above based on the embodiments, the present invention is not limited to the above embodiments, and various modifications or alterations can be made within the scope of the present invention. is there. In the above embodiments, the boom was used as an example of the working machine, but it goes without saying that the present invention is also applicable to other working machines such as an arm or a crane. Further, in the above embodiment, the mode switching valve is composed of the electromagnetic operation switching valve, but it may be composed of the manual operation switching valve or the pilot operation switching valve.

[0019]

According to the working machine hydraulic circuit constructed in accordance with the present invention, when the working machine is lowered in the fine operation mode, the working machine lowering speed (fine speed) corresponding to the operation amount of the operating lever can be easily increased. can get. The operator can easily and accurately perform the operation of lowering the work implement in the fine operation mode without using too much nerve, so that the work load is remarkably reduced. Further, the lowering speed of the working machine that matches the operation amount of the operating lever is obtained, so that the safety is further improved (for example, a hanging work by a crane).

[Brief description of drawings]

FIG. 1 is a schematic view of a main part showing an embodiment of a hydraulic circuit for a working machine constructed according to the present invention.

FIG. 2 is a schematic view showing a main part of a conventional hydraulic circuit for a working machine.

[Explanation of symbols]

 2 hydraulic pump 4 hydraulic cylinder 6 directional control valve 8 discharge oil passage 10 piston rod 12 piston 14 boom lowering chamber 16 boom raising chamber 18 pilot pump 20 first remote control valve 22 first pilot oil passage 23 main pilot oil passage 24 fourth 2 Remote control valve 26 Second pilot oil passage 30 Overload relief valve with make-up function 32 Overload relief valve 36 Check valve 40 Mode switching valve 42 Pressure reducing valve 44 Fine control pilot oil passage 46 Mode switching switch

Claims (3)

[Claims] 1. A hydraulic pump and a hydraulic cylinder of a working machine are connected by a discharge oil passage of the hydraulic pump via a directional control valve, and the pilot pump and one end side of the directional control valve form a first remote control valve. Through the first pilot oil passage, the pilot pump and the other end of the directional control valve are connected through the second remote control valve by the second pilot oil passage, and the first remote control valve When the valve is opened, the directional control valve is switched to the first switching position so that the hydraulic fluid discharged from the hydraulic pump is supplied to the working machine lowering chamber of the hydraulic cylinder. A mode switching valve is arranged in the first pilot oil passage,
A fine operation pilot oil passage that passes through a pressure reducing valve is provided in parallel on the downstream side of the mode switching valve in the first pilot oil passage, and the mode switching valve uses the fine operation of the pressure oil discharged from the pilot pump. A normal operation mode position supplied without passing through the pilot oil passage, and a fine operation mode position where the discharge pressure oil of the pilot pump is supplied through the fine operation pilot oil passage. Hydraulic circuit for working machine. 2. The work according to claim 1, wherein the fine operation pilot oil passage including the mode switching valve and the pressure reducing valve is provided upstream of the first remote control valve in the first pilot oil passage. Hydraulic circuit for machine. 3. The fine control pilot oil passage including the mode switching valve and the pressure reducing valve is provided in the first pilot oil passage downstream of the first remote control valve. Hydraulic circuit for work equipment.