JP3009822B2 - Construction machine cylinder control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylinder control circuit for a construction machine such as a backhoe shovel or a hydraulic shovel (rotating type).

[0002]

2. Description of the Related Art FIG. 5 shows a conventional hydraulic circuit used in a hydraulic excavator (slewing type), and a lower traveling body (crawler).
Left and right travel motors with brakes 11 for driving
12, a swing motor 13 for turning the upper revolving unit relative to the lower traveling unit, and various hydraulic cylinders for operating a front work machine (hereinafter, referred to as a front linkage) mounted on the upper revolving unit to be controlled. It is assumed that.

As shown in FIG. 6, a front linkage 14 includes a boom 15, an arm 16, and a
The boom 15 is rotated by a boom cylinder 24, the arm 16 is rotated by an arm cylinder 25, and the bucket 17 is rotated by a bucket cylinder 26, respectively. The position of the center of gravity of each member is indicated by a black dot.

Returning to FIG. 5, hydraulic oil discharged from a hydraulic pump 28 driven by an on-board engine 27 is used for various operations corresponding to the hydraulic motors 11, 12, 13 and the hydraulic cylinders 24, 25, 26. Valves (control valves) 111, 121,
Via 131, 241, 242, 251, 252, 261, these are supplied to the respective hydraulic actuators. Ps indicates a hydraulic oil supply line, and T indicates a tank line for hydraulic oil discharge communicating with the tank.

To the head side 25a and the rod side 25b of the arm cylinder 25, hydraulic oil discharged from the left and right hydraulic pumps 28 and passed through the arm primary operation valve 251 and the arm secondary operation valve 252 is combined and supplied. You.

The return line from the rod side 25b of the arm cylinder 25 to the tank (when the arm cylinder is extended) is connected to the arm primary operation valve 251 by the check valve 31 provided on the arm secondary operation valve 252 side. Via The return oil passes through the return throttle 32 in the primary operation valve 251 for the arm.

[0007] Even when the arm primary operation valve 251 has a full stroke, the throttle 32 is considerably narrower than a valve opening area curve having another general opening area. The return flow from the rod side 25b to the tank is strongly restricted. The reason is that arm cylinder 25
This is to prevent head-side voiding due to gravity when performing the stretching operation in the air (e.g., averaging with water).

As described above, even if the opening area in the full stroke and in the intermediate stroke area is suppressed small by the return side throttle 32 in the arm primary operation valve 251, as shown in FIG. When trying to level the soft ground horizontally toward the front from the state of full reach of the front linkage 14 (when light load work is performed on the arm cylinder head side), the arm
The position of the center of gravity (black dot position) of the bucket 16 and the bucket 17 is located at a horizontal distance from the boom tip pin 22, and the rotation moment due to gravity around the boom tip pin 22 is large, so that the rod side 25b of the arm cylinder 25 is held. Pressure is high,
In the return side passage from the rod side 25b to the tank in the arm primary operation valve 251, a passing flow rate is generated with a high gain with respect to the valve stroke.

Therefore, it is difficult to finely control the extension speed of the arm cylinder 25 at the position shown in FIG. 6 (A), the matching with the boom raising inching operation does not work well, and the trajectory of the tip 17a of the bucket becomes wavy. This often leads to operator complaints.

In the position shown in FIG. 6B, on the other hand, the holding pressure on the rod side 25b of the arm cylinder 25 is low, so that the arm primary operating valve 251 returns from the rod side 25b to the tank on the return side passage. The passing flow rate with respect to the valve stroke becomes a low gain, the extension speed of the arm cylinder 25 decreases, and the water averaging at the position shown in FIG. 6 (A) does not match at all, and smooth speed communication cannot be obtained. This water averaging makes the whole work process very difficult.

On the other hand, the primary operation valve 251 for the arm as described above
Due to the aperture 32 set to a small opening area even at full stroke, the head side 25a of the arm cylinder 25 in heavy excavation
When drilling at high speed with high pressure (during heavy load work), this throttle 32 is
However, there is a disadvantage in that an unnecessary high pressure is generated to reduce the speed and the effective work of the cylinder.

[0012]

As described above, conventionally,
Even for the same model, such as the shape of the arm and bucket, the weight is different for each version, which causes a difference in the rod side holding pressure of the arm cylinder. In addition, the difference in the initial posture of the arm also causes a difference in the holding pressure, and at the time of the start of the work by averaging the inching water to the near side, the extension speed of the arm cylinder for controlling the self-weight drop load is likely to be uneven.

For this reason, the balance with the raising of the boom is lost, and when the operation of averaging water is started, the operation of averaging the water from near the full reach is started, and the extension speed of the arm cylinder is too fast to synchronize with the boom cylinder. There was a problem that the tip of the bucket was wavy due to the difficulty, and the horizontal finishing surface of the soil was not finished smoothly.

It is also possible to prevent the bucket tip from waving during the water averaging operation by adding a load pressure compensation function by controlling the return flow rate of the arm cylinder on the rod side. If the pump discharge flow rate is reduced, the oil on the head side of the arm cylinder tends to be insufficient even during the light load airborne water averaging operation, causing voiding and deteriorating controllability.

The present invention has been made in view of the above points, and a cylinder control circuit for a construction machine which can achieve both improvement in operability during light load work and prevention of voiding due to a decrease in pump discharge flow rate. The purpose is to provide.

[0016]

According to the first aspect of the present invention, an arm operating valve provided between a hydraulic pump and a tank and an arm cylinder for operating an arm of a shovel has a head side of an arm cylinder. In a cylinder control circuit of a construction machine that controls supply and discharge of hydraulic oil to a rod side, the rod side of the arm cylinder is branched from a rod side supply line that supplies hydraulic oil through a check valve, and a tank is provided from the rod side of the arm cylinder. A rod-side oil drain line that guides oil back to the line, and a rod-side oil drain line that is provided in this rod-side oil drain line, regulates the return flow from the rod side of the arm cylinder to the tank line by restricting, and returns the rod side to the tank line. A flow control valve with a regeneration function that regenerates part or all of the oil to the head side supply / drain line, and a rod side oil drain line A pressure compensating valve for differential pressure control, which is provided on the arm cylinder side from the flow control valve with function and controls the differential pressure before and after the throttle of the flow control valve with regeneration function, and is provided for the spring of this pressure compensating valve And
A cylinder control circuit for a construction machine comprising a spring adjusting mechanism for directly or indirectly adjusting a set load of a spring by a head side load pressure of an arm cylinder.

According to a second aspect of the present invention, there is provided a flow control valve with a regeneration function according to the first aspect, wherein the arm operation valve is moved by a pilot pressure operating to the arm cylinder extension side to connect with an output line of the pressure compensating valve. In an internal passage communicating with the tank line, a first throttle for flow control and a second throttle for applying back pressure to the return oil from the rod side of the arm cylinder to the tank line are provided in series. An intermediate pressure passage is drawn from between the first and second throttles, and a regeneration check valve and a third throttle are provided in the intermediate pressure passage. The internal passage provided with the regeneration check valve and the third throttle is connected to the arm cylinder. This is a cylinder control circuit for a construction machine configured to move by the extension-side pilot pressure and communicate with a head-side communication line connected to a head-side supply / discharge line.

According to a third aspect of the present invention, there is provided a flow control valve with a regeneration function according to the first aspect, wherein the arm operation valve is moved by a pilot pressure operating toward the arm cylinder extension side to connect with an output line of the pressure compensating valve. A first throttle for flow control is provided in an internal passage communicating with the tank line, and an intermediate pressure passage is drawn from the internal passage on the tank line side from the first throttle, and a regeneration check valve and a third valve are connected to the intermediate pressure passage.
A throttle is provided, and an internal passage provided with the regeneration check valve and the third throttle is moved by the arm cylinder extension-side pilot pressure and communicates with a head-side communication line connected to a head-side supply / discharge line. Further, a cylinder control circuit for a construction machine having a configuration in which a back pressure check valve for applying a back pressure to the return oil from the rod side of the arm cylinder in the tank line is provided.

According to a fourth aspect of the present invention, there is provided the cylinder control circuit for a construction machine according to the first aspect, wherein a pilot signal based on a head-side load pressure of the arm cylinder or the like is indirectly supplied to the spring adjusting mechanism. 4 is a cylinder control circuit having a configuration provided with a controller.

According to a fifth aspect of the present invention, there is provided a cylinder control circuit for a construction machine, wherein the regeneration check valve according to the second aspect is provided in an external head-side communication line.

[0021]

According to a first aspect of the present invention, a return line from the rod side of an arm cylinder of a hydraulic shovel or the like to a tank is provided by a throttle of a flow control valve with a regeneration function and a pressure compensating valve for controlling a differential pressure across the throttle. The arm cylinder is extended at a constant speed even if the holding pressure on the cylinder rod side changes to improve the workability of water averaging work because the load pressure compensation flow rate control function is provided in the apparatus. Also, when the load pressure on the head side of the cylinder is less than a certain value, especially when it is close to voiding, part or all of the return oil from the rod side of the arm cylinder to the tank is regenerated to the head side by the flow control valve with regeneration function. To prevent said voiding. Further, in a high-pressure excavation state in which the head-side load pressure of the arm cylinder is equal to or higher than a certain value, the spring set mechanism is operated by sensing the high-pressure head-side load pressure to adjust the spring set load to the side that increases the pressure. The differential pressure across the first throttle determined by the compensating valve is greatly increased to allow a substantially large flow rate to flow, thereby substantially canceling the load pressure compensating function and reducing the resistance of the return line. .

According to a second aspect of the present invention, the return line from the rod side of the arm cylinder to the tank has a load pressure compensating flow rate control function by the first throttle of the flow rate control valve with the regeneration function and the pressure compensating valve. Water averaging is performed by stable arm cylinder extension operation. The second throttle applies a back pressure to the return oil from the rod side of the arm cylinder to the tank line, and when the load pressure on the head side of the arm cylinder decreases to a state close to voiding, the pressure from the rod side of the arm cylinder to the tank is reduced. A part or all of the return oil is regenerated and supplied to the head through the intermediate pressure passage of the flow control valve with the regeneration function, the regeneration check valve, the third throttle, and the head-side communication line, thereby preventing the voiding. At this time, the regeneration flow from the rod side to the head side is controlled by the third throttle.

According to a third aspect of the present invention, a constant pressure (back pressure) is generated in the return oil by a back pressure check valve having the same function as the second throttle in the second aspect, and the flow rate control with the regeneration function is performed. The return oil from the rod side is regenerated and supplied to the head side through an intermediate pressure passage in the valve.

According to a fourth aspect of the present invention, there is provided an arm cylinder based on a signal output from an external controller to a spring adjusting mechanism based on a load pressure on the head side of the arm cylinder or the number of revolutions of an engine for driving the hydraulic pump. To control the amount of oil that is compensated for the load pressure of the return oil on the rod side.

According to a fifth aspect of the present invention, when the pressure on the cylinder head side is too low, the return oil from the rod side passes through the passage in the flow control valve with the regeneration function and the regeneration check valve in the head side communication line. It is regenerated and supplied to the cylinder head side.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments shown in FIGS. In addition,
Since the basic hydraulic circuit is the same as the conventional circuit shown in FIG. 5, the same reference numerals are given and the description of the basic configuration and operation is omitted.

During the operation of extending the arm cylinder, a pilot pressure is applied to the pilot pressure line 252a to supply / discharge the oil from the hydraulic oil supply line Ps.
Although the pressure oil is merged and supplied to 41 (to the arm cylinder head), the return oil at this time does not return to the operation valve 252 because of the check valve 31, and substantially does not return to the operation valve 252 of FIG. Since the processing is performed by devices such as the pressure compensating valve 45 and the flow control valve 46 with the regeneration function, the following description is omitted.

First, FIG. 1 shows a structure of a first embodiment according to the present invention. One output port of the arm operation valve 251 and the head side 25a of the arm cylinder 25 are connected to the head side supply / discharge line.
The other output port of the arm operation valve 251 and the rod side 25b of the arm cylinder 25 are connected by a rod side oil supply line. The rod-side oil supply line 42 is provided with a check valve 43 that allows oil to flow to the rod side 25b.

From the middle of the line from the check valve 43 to the rod side 25b of the arm cylinder 25, the rod side oil drain line 44
A pressure compensating valve 45 for differential pressure control and a flow control valve 46 with a regeneration function are sequentially provided between the rod side oil drain line 44 and the tank line T.

The means for controlling the flow control valve 46 with the regeneration function comprises a return spring 47 provided on one side and a pilot pressure line 48 provided on the other side. The pilot pressure line 48 is branched from the arm cylinder extension side pilot pressure line 251a of the arm operation valve 251. An arm cylinder contraction side pilot pressure line 251b is guided to the opposite side of the arm operation valve 251.

The internal structure of the flow control valve 46 with the regeneration function includes a first throttle 51 functioning as a main valve orifice for flow control in an internal passage communicating the output line of the pressure compensating valve 45 and the tank line T; A second throttle 52 for applying back pressure to the return oil to the tank from the rod side 25b of the arm cylinder 25 is provided in series, and a rod-side oil drain line 44 is provided between the first throttle 51 and the second throttle 52. To the head side supply / discharge line 41, an intermediate pressure passage 53 is drawn out.
A regeneration check valve 54 and a third throttle 55 for controlling the regeneration flow from the rod side to the head side are provided.

The first diaphragm 51, the second diaphragm 52 and the third diaphragm 55
Are variable throttles which are fully closed in the normal position shown in FIG. 1 but are modulated in accordance with the stroke of the control valve 46.

The internal passage provided with the third throttle 55 is connected to the head side supply / discharge line 41 by the movement of the flow control valve 46 with the regeneration function.
When the pressure in the head-side supply / discharge line 41 is lower than the pressure in the intermediate pressure passage 53 between the first throttle 51 and the second throttle 52, the intermediate pressure passage 53
Accordingly, the rod side 25 of the arm cylinder 25 passes through the regeneration check valve 54, the third throttle 55, and the head side communication line 56.
Part of the return oil from b is regenerated and supplied to the head side 25a.

Next, the flow control mechanism with pressure compensation will be described. By moving the flow control valve 46, the pressure Pa on the upstream side of the first throttle 51 is moved through one differential pressure detecting line 58a to move the pressure compensating valve 45. The intermediate pressure passage 53, the differential pressure detection passage 57 branched from the intermediate pressure passage 53, and the movement of the flow control valve 46 are communicated with one side of the valve body and reduce the pressure Pb downstream of the first throttle 51. Thus, the pressure compensating valve 45 communicates with the other side of the movable valve via the other differential pressure detecting line 58b communicating with the differential pressure detecting passage 57. A set load Kx of a spring 59 is applied to the other side of the movable valve body.

In the pressure compensating valve 45, the effective differential pressure (Pa-Pb) before and after the first throttle 51 detected through the differential pressure detection lines 58a and 58b becomes constant (= Kx / A). The movable valve body is controlled as follows. A is a common pressure receiving area on one side and the other side of the movable valve body.

With respect to the spring 59 of the pressure compensating valve 45,
By changing the set load Kx of the spring 59,
A spring adjusting mechanism 61 for adjusting the effective differential pressure (Pa-Pb) before and after the first throttle 51 is provided.

The spring adjusting mechanism 61 guides a head pressure detecting line 62 branched from the head side communication line 56 to one end of a spring adjusting cylinder 63,
A spring adjustment piston 64 is slidably and liquid-tightly fitted in the cylinder 63, and the piston 64 abuts on the spring 59.

Then, the piston 64 receives the load pressure on the head side 25a of the arm cylinder 25 guided into the cylinder 63 from the head side communication line 56 and the head pressure detection line 62, and the set load Kx of the spring 59 is received. Control.

The spring adjustment cylinder 63 has a cylinder head side load pressure introduction port for operating the piston 64.
65, a first positioning stopper 66 for locking the piston 64 on the introduction port side, and a second positioning stopper 67 for locking the piston 64 on the opposite side.

The differential pressure across the first throttle 51 is controlled to be constant by the left pressure compensating valve 45. The value of the differential pressure is controlled by the piston 64 for controlling the set load of the spring 59, the first stopper 66, It is determined by the second stopper 67 and the like. If the load pressure on the head side 25a is low, the piston 64
Is pressed by the spring 59 and contacts the first stopper 66,
The differential pressure becomes a low differential pressure determined by the first stopper 66, and the head side 25
If the load pressure of a is higher than a certain level, the piston 64
The second stopper 67 abuts against the spring 59, and the differential pressure becomes a high differential pressure determined by the second stopper 67.

Next, the operation of the first embodiment shown in FIG. 1 will be described.

(1) When the arm cylinder extension side pilot pressure is supplied to the pilot pressure lines 251a and 251 and 48, the arm operation valve 251 and the flow control valve with regeneration function 46 are switched to the upper chamber position. Is extended.

During the extension operation of the arm cylinder 25, if the pressure in the head side supply / discharge line 41 is higher than the pressure in the intermediate pressure passage 53, the operating oil on the rod side 25b is applied regardless of the holding pressure on the rod side 25b. For the check valve 43, the entire amount is passed through the differential pressure control pressure compensating valve 45, and the first flow control valve 46 with the regeneration function is operated.
The water flows out to the tank line T via the throttle 51 and the second throttle 52, and a stable water averaging operation is obtained.

(2) During the same operation, when the amount of hydraulic oil discharged and supplied from the hydraulic pump 28 becomes insufficient and voiding starts to occur on the head side 25a, the rod side 25b of the arm cylinder 25
Because part of the return oil from the tank to the tank has a back pressure due to the resistance action of the second throttle 52, the first throttle 51 and the second throttle 52
The pressure in the head-side supply / discharge line 41 is lower than that in the intermediate portion, so that part of the return oil from the rod side 25b to the tank flows through the intermediate pressure passage 53 to the regeneration check valve 54, the third throttle 55, and the head-side communication line. The oil is regenerated and supplied to the head side supply / discharge line 41 via 56, thereby preventing the occurrence of voiding and maintaining the pressure at a low level. At this time, since the cylinder head side load pressure taken out by the head pressure detection line 62 is low enough to prevent voiding, the spring adjustment mechanism is used.
The piston 64 of 61 is at the position of the first stopper 66, and the differential pressure (Pa-Pb) before and after the first throttle 51 is controlled to be relatively small.

(3) In a heavy load state such as excavation, the load pressure on the head side 25a of the arm cylinder 25 becomes high (of course, not in a voiding state), but this high load pressure is applied to the piston 64 by the head pressure detection line 62. Guided, the piston 64 moves from the first stopper 66 to the second stopper 67 and presses the spring 59 to increase the set load Kx.
The differential pressure (Pa-Pb) across the first throttle 51 becomes a high differential pressure.
At this time, the opening degree of the pressure compensating valve 45 becomes large, and the flow resistance of the return oil discharged from the rod side 25b of the arm cylinder 25 to the tank line T becomes substantially small. As a result, the cylinder work can be substantially improved, and the fuel efficiency of the engine that drives the hydraulic power source can be improved.

Next, FIG. 2 shows a second embodiment according to the present invention. In the flow control valve 46 with the regeneration function, the second throttle 52 provided in the first embodiment of FIG. Back pressure check valve to generate a constant back pressure (a kind of relief valve)
71 is installed in the tank line T.

That is, the flow control valve 46 with the regenerating function moves the arm operating valve 251 to the arm cylinder extension side by the pilot pressure to communicate the output line of the pressure compensating valve 45 with the tank line T. Is provided with a first throttle 51 for controlling the flow rate. An intermediate pressure passage 53 is drawn out of the first throttle 51 through an internal passage on the tank line side. A regeneration check valve 54 and a third throttle 55 are inserted into the intermediate pressure passage 53. An internal passage provided with the regeneration check valve 54 and the third throttle 55 is moved by the arm cylinder extension-side pilot pressure to communicate with a head-side communication line 56 connected to the head-side supply / discharge line 41. Is done.

Further, the tank line T is provided with a back pressure check valve 71 for applying a back pressure to the return oil from the rod side 25b of the arm cylinder 25. This back pressure check valve
71 sets the back pressure of the return oil by the set load of the spring that presses the check valve against the valve seat. The other structure is the same as that of the first embodiment shown in FIG.

The operation of the second embodiment will be described. An alternative back pressure check valve 71 generates a constant resistance pressure (back pressure) in the return oil. Thus, if the pressure in the intermediate pressure passage 53 is higher than the opening pressure of the back pressure check valve 71 and higher than the pressure in the head side supply / discharge line 41, a part of the return oil from the rod side 25b Regeneration check valve 5 from 53
4. Reproduced and supplied to the head side 25a via the third diaphragm 55 and the head side communication line 56.

If the pressure in the intermediate pressure passage 53 is lower than the opening pressure of the back pressure check valve 71 and higher than the pressure in the head side supply / discharge line 41, all of the return oil from the rod side 25b will be as described above. Is regenerated and supplied to the head side 25a, which is efficient.

FIG. 3 shows a third embodiment according to the present invention. The head pressure detection lines of the first and second embodiments are shown in FIG.
As a means for introducing a spring adjustment signal pressure to the spring adjustment cylinder 63 of the pressure compensating valve 45 for controlling the differential pressure across the first throttle 51 instead of the cylinder throttle 62, a cylinder head side load pressure or an engine speed is used as an input signal. In this example, a pilot signal pressure is generated by an external controller 81, and the signal pressure is guided to an introduction port 65 of a spring adjusting cylinder 63 by an introduction line 82. The other structure is the same as that of the first embodiment shown in FIG.

The external controller 81 of the third embodiment comprises:
The amount of oil to be compensated for the load pressure of the return oil from the rod side 25b of the arm cylinder 25 depends on the pressure on the head side 25a of the arm cylinder 25 or the rotation speed of the engine 27 (FIG. 5) that drives the hydraulic pump 28. And can be flexibly controlled.

Finally, FIG. 4 shows a fourth embodiment according to the present invention. In the first to third embodiments, the regeneration check valve 54 incorporated in the flow control valve 46 with a regeneration function is replaced with a regeneration check valve 54 according to this embodiment. In the example, it is taken out of the flow control valve with regeneration function 46 and provided in the head side communication line 56 and on the flow control valve 46 side from the branch point of the head pressure detection line 62. In this case, the valve 46 becomes compact, and a similar function can be obtained functionally. The other structure is the same as that of the first embodiment shown in FIG.

[0054]

According to the first aspect of the present invention, the throttle pressure of the flow control valve with the regeneration function and the pressure compensating valve provide the load pressure compensating flow in the return line from the rod side of the arm cylinder of the hydraulic excavator or the like to the tank. Since the control function is provided, a constant return flow which is not affected by the fluctuation of the rod-side holding pressure can be secured, and the workability of the water averaging operation by the rod extension operation of the arm cylinder can be improved. When the load pressure on the cylinder head side is less than a certain value, especially when it is close to voiding, part or all of the return oil from the rod side of the arm cylinder to the tank is transferred to the head side by the internal passage of the flow control valve with regeneration function. The voiding can be prevented by re-supply. Furthermore, in the high pressure excavation state where the cylinder head side load pressure is a certain value or more, the state is detected by the spring adjustment mechanism, and the spring resistance of the pressure compensating valve is changed by changing the spring set load of the pressure compensating valve to release the high resistance of the return line in the pressure compensating valve. As a result, it is possible to improve the cylinder work amount at the time of heavy load work, and to improve the fuel efficiency of the hydraulic drive source.

According to the second aspect of the present invention, the return flow of oil from the rod side of the arm cylinder to the tank can be load-pressure compensated by the first throttle of the flow control valve with the regeneration function and the pressure compensating valve. The workability of the water averaging operation can be improved by the stable arm cylinder extension operation which is not affected by the change of the side holding pressure. When the load pressure on the cylinder head side decreases to a state close to voiding, the back pressure applied to the return oil to the tank by the second throttle regenerates and supplies the return oil to the tank to the head side. Side voiding can be prevented.

According to the third aspect of the present invention, since the back pressure check valve is provided in the tank line, the structure of the flow control valve with the regeneration function can be simplified accordingly.

According to the fourth aspect of the invention, after the external controller processes the load pressure on the head side of the arm cylinder and the like, the load pressure compensating oil amount of the return oil on the rod side of the arm cylinder is adjusted via the spring adjusting mechanism. It is possible to control flexibly.

According to the fifth aspect of the present invention, since the regeneration check valve is provided in the head side communication line, the structure in the flow control valve with the regeneration function can be simplified accordingly.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing a first embodiment of a cylinder control circuit according to the present invention.

FIG. 2 is a hydraulic circuit diagram showing a second embodiment of the cylinder control circuit.

FIG. 3 is a hydraulic circuit diagram showing a third embodiment of the cylinder control circuit.

FIG. 4 is a hydraulic circuit diagram showing a fourth embodiment of the cylinder control circuit.

FIG. 5 is a hydraulic circuit diagram illustrating a cylinder control circuit of a conventional construction machine.

FIG. 6A is an explanatory diagram when the front linkage of the hydraulic excavator is in a full reach state, and FIG. 6B is an explanatory diagram when the linkage is operated with water averaging.

[Description of Signs] 16 Arm 25 Arm Cylinder 25a Head Side 25b Rod Side 251 Arm Operating Valve 28 Hydraulic Pump 41 Head Side Supply / Drain Line 42 Rod Side Oil Supply Line 43 Check Valve 44 Rod Side Oil Discharge Line 45 Pressure Compensation Valve 46 Flow control valve with regeneration function 51 First throttle 52 Second throttle 53 Intermediate pressure passage 54 Regeneration check valve 55 Third throttle 56 Head side communication line 59 Spring 61 Spring adjustment mechanism 71 Back pressure check valve 81 External controller T Tank line

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) E02F 9/22 F15B 11/024

Claims (5)

(57) [Claims] A construction machine that controls supply and discharge of hydraulic oil to a head side and a rod side of an arm cylinder by an arm operation valve provided between a hydraulic pump and a tank and an arm cylinder that operates an arm of the shovel. In the cylinder control circuit, a rod-side oil drain line that branches from a rod-side supply line that supplies hydraulic oil to the rod side of the arm cylinder via a check valve and guides the return oil from the rod side of the arm cylinder to the tank line, This rod-side oil drain line is provided to restrict the return flow from the rod side of the arm cylinder to the tank line by restricting, and a part or all of the return oil from the rod side to the tank line is sent to the head side supply / drain line. A flow control valve with a regeneration function to supply and regenerate, and an arm cylinder side from a flow control valve with a regeneration function in the rod side oil drain A pressure compensating valve for differential pressure control provided by a spring for controlling a differential pressure before and after the throttle of a flow control valve with a regeneration function; and a head side load pressure of an arm cylinder provided for the spring of the pressure compensating valve. And a spring adjusting mechanism for directly or indirectly adjusting the set load of the spring. 2. A flow control valve having a regeneration function, wherein an operation valve for an arm is moved by a pilot pressure operating to an arm cylinder extension side to control a flow rate in an internal passage connecting an output line of the pressure compensation valve and a tank line. First throttle and a second throttle for applying back pressure to the return oil from the rod side of the arm cylinder to the tank line are provided in series, and an intermediate pressure passage is provided between the first throttle and the second throttle. The intermediate pressure passage is provided with a regeneration check valve and a third throttle,
The internal passage provided with the regeneration check valve and the third throttle is moved by the arm cylinder extension-side pilot pressure and communicates with a head-side communication line connected to a head-side supply / discharge line. The construction machine cylinder control circuit according to claim 1. 3. A flow control valve having a regeneration function for controlling a flow rate of an arm operation valve to an internal passage connecting an output line of a pressure compensating valve and a tank line by moving a pilot pressure operating an arm cylinder extension side. A first aperture is provided,
An intermediate pressure passage is drawn from the internal passage on the tank line side from the first throttle, and a regeneration check valve and a third throttle are provided in the intermediate pressure passage, and an internal passage provided with the regeneration check valve and the third throttle is provided. The arm is moved by the arm cylinder extension side pilot pressure, communicates with a head side communication line connected to a head side supply / discharge line, and applies a back pressure to the tank line to the return oil from the rod side of the arm cylinder to the tank line. The cylinder control circuit for a construction machine according to claim 1, further comprising a pressure check valve. 4. The cylinder control of a construction machine according to claim 1, wherein an external controller for indirectly supplying a pilot signal based on a head side load pressure of the arm cylinder or the like is provided to the spring adjustment mechanism. circuit. 5. The cylinder control circuit for a construction machine according to claim 2, wherein the regeneration check valve is provided in an external head-side communication line.