JPH076525B2 - Swing hydraulic circuit of construction machinery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a swing hydraulic circuit for a construction machine such as a hydraulic crane.

(Prior Art) Conventionally, a directional control valve that enables flow rate control and pressure control in a swing hydraulic circuit of a hydraulic crane (see, for example, Japanese Patent Laid-Open Publication No.
Those using JP-A 57-29860 and JP-A-58-50369) are known.

However, the above-mentioned directional control valve is provided with a set of a flow control throttle portion and a pressure control throttle portion on both sides of the spool, and the flow control and the pressure control are performed within a limited stroke range of the spool. In order to do this, increasing the axial length of the flow control throttle to make it convenient for work where speed control is important for speed control such as crane work Since the length becomes small, it is not suitable for work such as bucket work in which pressure control for torque control is important. On the contrary, if the axial length of the pressure control throttle is increased to make it convenient for bucket work, the axial length of the flow control throttle becomes smaller, making it unsuitable for crane work. It is difficult to improve both operability and controllability of pressure control at the same time.

Further, in order to improve the controllability of the flow rate control in the low pilot pressure range, the spring force of the neutral return spring of the spool is increased to change the opening area of the flow control throttle portion corresponding to the change of the pilot pressure. It is desirable to reduce the amount, but if the spring force is increased in this way, the pilot pressure introduced to the large pressure chamber formed at one end of the spool is controlled when the pilot pressure is controlled in the high pressure range. Not only load pressure on the other end of the spool, but also large spring force (reaction force)
Therefore, it becomes impossible to sufficiently increase the acceleration pressure and the deceleration pressure only by controlling the pilot pressure. On the contrary, in order to improve the controllability of the pressure control, if the spring force is reduced so that only the load pressure faces the pilot pressure, the spring does not work during the flow rate control,
It becomes impossible to finely control the opening area.

Moreover, in the transient position where the flow rate control is switched to the pressure control, the load pressure is suddenly introduced into the small pressure chamber at the other end of the spool that was in communication with the tank during the flow rate control, and the load pressure causes the large pressure chamber at one end of the spool to flow. The spool is pushed back against the pilot pressure that is guided to, then the spool is pushed back by the pilot pressure, the load pressure is guided again to the small pressure chamber, and the spool is pushed back again. As a result, the spool position is unstable and hunting may occur.

Further, since the directional control valve is a neutral flow valve that connects the flow passages on both sides of the motor to each other, when the motor is decelerated and stopped, so-called reverse lever operation is required, which is troublesome and difficult to operate. There are problems such as poor responsiveness at time.

(Object of the Invention) The present invention has been made in order to solve such a problem, and can efficiently perform both flow rate control and pressure control, and reduce the load on the motor such as during crane work. When the accelerating pressure is in the low pressure range, delicate speed control is possible by controlling the flow rate, and inching can be improved to improve operability.In the bucket work, the load on the motor is large and the accelerating pressure is in the high range. A wide range of pressure control according to the lever operation angle is possible, the acceleration pressure can be accurately controlled to improve work efficiency, and the deceleration pressure can be controlled by lever operation even during deceleration stop, allowing smooth deceleration stop. The present invention provides a swing hydraulic circuit for a construction machine that can smoothly carry out work by reducing load sway and the like.

(Structure of the Invention) The present invention relates to a turning remote control valve in which pilot pressure to the secondary side is controlled by lever operation, a directional control valve that is switched by pilot pressure from the remote control valve, and switching of this directional control valve. A swirling hydraulic motor whose flow rate is controlled by a hydraulic pump by means of the directional control valve having a bleed-off passage to the tank, and blocking both side flow paths of the motor at a neutral position. The pump discharge pressure is controlled in proportion to the pilot pressure in which the discharge pressure of the pump and the pilot pressure from the remote control valve are input to the discharge flow path of the pump and the pilot pressure exceeds a set value. A pressure control valve is connected, and a switching valve for taking out the pressure of the motor discharge side flow path between the both side flow paths of the motor and the discharge side flow path taken out by the switching valve. A second pressure control valve for inputting the pressure and the pilot pressure and controlling the pressure of the discharge side flow path in inverse proportion to the pilot pressure when the sum of the discharge side flow path pressure and the pilot pressure exceeds a set value. It is characterized by being provided.

With this configuration, when the load on the motor is small and the accelerating pressure is low, such as during crane work, the bleed-off control of the directional control valve that is operated by the pilot pressure from the remote control valve is given priority, and the operation amount of the remote control valve is By proportionally controlling the spool opening of the directional control valve, the flow rate into the motor can be controlled over a wide range, and the flow rate can be finely controlled to improve the inching performance.

Further, when the load on the motor is large and the accelerating pressure is high, such as during bucket work, the first pressure control valve provided in the pump discharge flow path is balanced by the balance between the pilot pressure from the remote control valve and the pump discharge pressure. Is activated, the pressure control by the first pressure control valve is prioritized over the bleed-off control by the directional control valve, and the pump discharge pressure, that is, the motor acceleration pressure is controlled in a wide range according to the lever operation angle. Accelerating pressure is accurately controlled to improve work efficiency.

Further, when the hydraulic motor decelerates and stops, the second pressure control valve provided between the flow passages on both sides of the hydraulic motor is operated by the pilot pressure from the remote control valve and the pressure on the motor discharge side, and the operation amount of the remote control valve is increased. Inversely, the pressure on the motor discharge side, that is, the deceleration pressure is accurately controlled, and the motor is smoothly stopped.

(Embodiment) FIG. 1 is a hydraulic circuit diagram showing an embodiment of the present invention. In this drawing, a hydraulic motor 6 is provided in a discharge passage 3 of a hydraulic pump 2 driven by an engine 1 via a direction control valve 4. The both side flow paths 5a, 5b and the return oil flow path 7 to the tank 8 are switchably connected. The directional control valve 4 has a bleed-off passage, blocks both side flow paths 5a, 5b of the motor 6 at a neutral position, and is of a neutral brake type that returns the oil discharged from the pump 2 to the tank 8 side.

The remote control valve 10 is a pair of variable pressure reducing valves in which the pilot pressure Pi guided to the secondary side is controlled in proportion to the operating angle of the lever 10c.
10a, 10b, a pilot hydraulic pressure source 9 is connected to the primary side of both variable pressure reducing valves 10a, 10b, and a pilot flow path 11a,
11b through pilot portions 4a at both ends of the directional control valve 4,
4b is connected.

A flow path 13 is connected to the pilot flow paths 11a and 11b via a shuttle valve 12, and the flow paths 13 are connected to the primary sides of first and second constant difference source pressure valves 14 and 15, respectively. Each constant difference source pressure valve 1
4,15 is for guiding the secondary pressure proportional to the pressure on the primary side to the secondary side when the pressure on the primary side exceeds a set value, and more specifically, the variable pressure reducing valve 10a or the variable pressure reducing valve 10a on the primary side. 1
The pilot pressure Pi from 0b is introduced, and from that pressure Pi the spring
Initial setting pressure by 14a, 15a Pressure Pi minus Pa ₁ , Pa ₂ Pi
It leads ₁ and Pi ₂ to the secondary side.

The first pressure control valve 16 is for controlling the pressure (acceleration pressure) during acceleration of the motor 6, and is provided between the discharge passage 3 of the pump 2 and the return oil passage 7 to the tank 8, Spring 16c
The _first set pressure reducing valve 1 is urged in the direction of closing the valve passage by the initial set pressure Pr ₁ by
The secondary pressure Pi _{1 of} 4 is introduced, and the pump discharge pressure Pp is introduced to the pilot portion 16a on the side where the valve passage is opened.
The opening area is controlled by the initial set pressure Pr ₁ and the secondary pressure Pi ₁ , the bypass flow rate from the pump 2 to the tank 8 is controlled, and the pump discharge pressure Pp is controlled.

The second pressure control valve 17 is for controlling the pressure (deceleration pressure) at the time of deceleration of the motor 6, and both side flow paths 5a, 5 of the motor 6 are controlled.
It is provided between b and is urged in the direction to close the valve passage by the set pressure Pc by the spring 17c, and has a pair of pilot portions 17a, 17b on the side that opens the valve passage, and one of the pilot portions 17a has the variable decompression pressure. The discharge side pressure Pb of the motor 6 is guided through a pilot switching valve 18 that is switched by the pilot pressure Pi from the valves 10a and 10b, and the secondary pressure Pi ₂ of the second constant pressure reducing valve 15 is supplied to the other pilot portion 17b. Is being guided. The set pressure Pc of the second pressure control valve 17 is set higher than the initial set pressure Pr ₁ of the first pressure control valve 16 (Pc> Pr ₁ ).

In the figure, 19a and 19b are check valves, 20a and 20b are overload relief valves, 21a and 21b are cavitation prevention check valves, and 22 is a back pressure valve.

Next, the operation will be described.

When the lever 10c of the remote control valve 10 is operated in the direction of arrow a,
The pilot pressure Pi proportional to the lever operation angle θ is guided from the variable pressure reducing valve 10a in the arrow B direction, and the directional control valve 4 is switched to the right side in the drawing by the pilot pressure Pi, and the discharge oil of the pump 2 is guided in the arrow C direction. The oil is discharged and flows into the motor 6, the motor 6 is accelerated, and the oil discharged from the motor 6 is guided in the direction of arrow D and returned to the tank 8.

At the time of this acceleration, first, the pilot pressure Pi from the variable pressure reducing valve 10a is controlled according to the operation angle θ of the lever 10c,
The spool opening of the directional control valve 4 is controlled according to the pilot pressure Pi, the flow rate of the pump 2 flowing into the motor 6 through the directional control valve 4 is controlled, and the excess oil from the pump 2 is directional controlled. Bleed off to the tank 8 via the valve 4, and by this bleed-off control, the pressure (acceleration pressure) Pm of the suction side flow path 5a of the motor 6 is controlled to be a pressure corresponding to the load of the motor 6.

Here, during normal work, that is, when the engine 1 is driven in medium load operation and the discharge flow rate of the pump 1 is medium, when the lever operation angle θ is gradually increased, as shown by the solid line I in FIG. The bleed-off control is performed by the directional control valve 4 from the time when the lever operation angle θ exceeds the angle θ ₁₁ to the angle θ _{13 at the} intermediate point, and the acceleration pressure Pm of the motor 6 follows the solid line I by this bleed-off control. Controlled to rise.

On the other hand, the discharge pressure Pp of the pump 2 rises according to the acceleration pressure Pm of the motor 6, and the discharge pressure Pp is the first pressure control valve 16
Is guided to the pilot portion 16a (in the direction of arrow E) and is controlled to be equal to or lower than the set pressure Pr of the first pressure control valve 16. At this time,
The set pressure Pr of the first pressure control valve 16 is controlled as shown by the solid line II in FIG.

That is, during the acceleration, the pilot pressure Pi corresponding to the lever operation angle θ passes through the shuttle valve 12 and the first constant pressure reducing valve 14
Is led to the primary side (direction of arrow). From the neutral lever operation angle θ to the angle θ ₁₂ , the pilot pressure Pi
Since the pressure is low, no pressure is introduced to the secondary side of the first constant difference pressure reducing valve 14, and the set pressure Pr of the first pressure control valve 16 is the spring 16
It is maintained at the initial set pressure Pr ₁ by c (low pressure in the lower horizontal part of the solid line II, constant). After that, when the lever operation angle θ is increased to the angles θ ₁₂ to θ ₁₅ , the pilot pressure Pi
Becomes high, and as the pilot pressure Pi rises, the first constant pressure reducing valve 14 moves from the secondary side to the first pressure control valve.
The pilot pressure Pi on the primary side of the 16 pilot section 16b
Secondary pressure proportional to the lever operating angle θ
Pi ₁ (Pi ₁ = Pi−Pa ₁ ) is guided (in the direction of arrow G), and the secondary pressure Pi ₁ and the initial set pressure Pr ₁ by the spring 16c cause the set pressure Pr of the first pressure control valve 16 to rise. It is variably controlled (inclined portion of solid line II above). The lever operation angle θ
Exceeds the angle θ ₁₅ , the pilot pressure Pi becomes the upper limit value (high pressure, constant), and the secondary pressure Pi ₁ of the first constant pressure reducing valve 14 and the set pressure Pr of the first pressure control valve 16 are Also becomes the upper limit (high pressure in the upper horizontal part of the solid line II, constant).

In this way, the set pressure Pr of the first pressure control valve 16 is controlled according to the lever operation angle θ along the solid line II in FIG.

By the above control, until the lever operation angle θ is up to the angle θ ₁₃ ,
The motor accelerating pressure Pm and the pump accelerating pressure Pp corresponding to the accelerating pressure Pm are equal to or lower than the set pressure Pr of the first pressure control valve 16 shown by the solid line II, and therefore the first pressure control valve 16 is not operated. Instead, the bleed-off control is performed by the directional control valve 4, and the motor 6 is controlled by this bleed-off control.
The acceleration pressure Pm is controlled, the flow rate into the motor 6 is controlled, and the rotation speed of the motor 6 is controlled.

In this case, since the first pressure control valve 16 does not operate, the entire discharge flow rate of the pump 2 is guided to the directional control valve 4, and in this state, the bleed-off control is performed by the directional control valve 4, and the lever The inflow flow rate to the motor 6 is appropriately controlled according to the operation angle θ, the rotation speed of the motor 6 is smoothly controlled as the lever operation, and the controllability and operability of speed control (flow rate control) are improved.

Next, when the lever operation angle θ exceeds the angle θ ₁₃ , the bleed-off passage of the directional control valve 4 is throttled, and the motor acceleration pressure Pm tends to rapidly increase in the extension line (broken line portion) of the solid line I. However, at this time, the pump discharge pressure Pp also rises as the motor acceleration pressure Pm rises.
Pp exceeds the set pressure Pr of the first pressure control valve 16 that is controlled along the solid line II according to the lever operation angle θ, so that part of the pump discharge flow rate is part of the first pressure control valve. While being bypassed to the tank 9 by 16, the pump discharge pressure Pp is controlled to be a pressure corresponding to the set pressure Pr, and accordingly, the motor acceleration pressure Pm is also set to a pressure corresponding to the set pressure Pr. Controlled.

That is, after the angle θ ₁₃ is exceeded, the control by the first pressure control valve 16 has priority over the bleed-off control by the directional control valve 4, and the pump discharge pressure Pp and the motor acceleration pressure are controlled by the first pressure control valve 16. Pm is controlled so as to rise along the solid line II. As a result, even when the accelerating pressure Pm is in the high pressure range, the accelerating pressure Pm can be arbitrarily controlled according to the lever operation angle θ, and the pressure control range in the high pressure range is enlarged to improve controllability and manufacturability during high torque operation. .

By the way, during the above control, the work content and the motor 6
The rotation speed of the engine 1 that drives the pump 2 may fluctuate due to fluctuations in the load, etc., and the discharge flow rate Q of the pump 2 may fluctuate.

For example, when the load on the motor 6 is small, such as during crane work, the engine 1 generally has a low load and rotates at high speed to increase the pump discharge flow rate, and the bleed-off control curve corresponding to the lever operation angle θ has a second curve. One-dot chain line II in the figure
It becomes a gentle curve like I.

Such a low load operation, the first pressure control valve 16 lever operation angle theta until large angle theta ₁₄ than the angle theta ₁₃ during the normal working does not operate, the range of the angle theta ₁₄ from the angle theta ₁₁ Then, the bleed-off control is performed by the directional control valve 4 according to the lever operation angle θ along the one-dot chain line III, and the flow rate control region (θ _{11 to} θ ₁₄ ) becomes large. And lever 10
By minute operation of c, minute control of the rotation speed of the motor 6, that is, minute speed control of the motor 6 becomes possible, and inching performance is greatly improved. Further, if the lever operation angle θ is increased, the switching amount of the directional control valve 4 increases, the flow rate of the flow into the motor 6 increases, and the rotation speed of the motor 6 increases. As a result, the inflow flow rate to the motor 6, that is, the motor rotation speed is controlled in a wide range, and very good turning operability is obtained.

When the load on the motor 6 is large, such as during bucket work, the engine 1 has a high load and rotates at a low speed to reduce the pump discharge flow rate, and the bleed-off control curve corresponding to the lever operation angle θ has a second value. It becomes a sharp curve as indicated by the chain double-dashed line IV in the figure.

Such During high load operation, with the lever operation angle theta is less angle theta ₁₂ than the angle theta ₁₃ during the normal working, the motor acceleration pressure Pm and the pump discharge pressure Pp is set pressure of the first pressure control valve 16 Pr will be exceeded, and for this reason,
The first pressure control valve 16 operates so that the control by the first pressure control valve 16 has priority over the bleed-off control by the directional control valve 4, and the two-dot chain line IV in the range of the angle θ ₁₂ to the angle θ ₁₅
The pressure control is performed by the first pressure control valve 16 according to the lever operation angle θ, and the pressure control region (θ _{12 to} θ ₁₅ ) increases. Then, even when the driving and stopping of the motor 6 are frequently repeated by this pressure control as in the bucket work, the set pressure Pr of the first pressure control valve 16 is controlled according to the lever operation angle θ, The discharge pressure Pp of the pump 2 is controlled, and the acceleration pressure Pm of the motor 6 is properly controlled, the motor 6 is prevented from being overloaded, shock is reduced, and smooth turning work is performed.

At the time of acceleration, the pilot pressure Pi from the variable pressure reducing valve 10a is guided in the arrow H direction, and the pilot switching valve 18
Is switched to the right position, and the pressure on the discharge side of the motor 6 becomes the second
It is guided to the pilot portion 17a of the pressure control valve 17. The pilot pressure Pi is also introduced to the primary side of the second constant difference pressure reducing valve 15 (direction of arrow D) via the shuttle valve 12,
When the lever operation angle θ is increased, the second constant difference pressure reducing valve 15
Pi ₂ (Pi ₂ = Pi-Pa ₂ ) is introduced to the secondary side of the second pressure control valve, and the secondary pressure Pi ₂ is introduced to the pilot portion 16b of the second pressure control valve 16 (direction indicated by the arrow). However, during this acceleration, the pressure Pb on the motor discharge side is low, and the set pressure Pc of the second pressure control valve 16 is equal to the initial set pressure Pr ₁ of the first pressure control valve 15.
Since it is set higher, the second pressure control valve 17 remains biased to the shut-off position side, and therefore the pressure oil on the suction side of the motor 6 is not bypassed to the discharge side, and the motor 6 is The rotation is surely accelerated.

Next, when the lever 10c is gradually operated to return to neutral after the acceleration, the pilot pressure P from the variable pressure reducing valve 10a is changed.
i gradually decreases, and the directional control valve 4 is gradually returned from the right position to the neutral position. Along with this, the return oil passage from the motor discharge side flow path 5b of the direction control valve 4 to the tank 8 is gradually narrowed, and the return oil flow rate from the motor 6 to the tank 8 is narrowed.
Along with this, the pressure (deceleration pressure) Pb on the motor discharge side gradually rises, and the motor 6 is gradually decelerated.

During this deceleration, during normal work, as shown by the solid line I ′ in FIG. 3, from the time when the lever 10c is returned to a certain angle θ ₂₅ , the flow rate control by the throttle action of the return oil passage of the directional control valve 4 is performed. Is started, the deceleration pressure Pb of the motor 6 changes from the angle θ ₂₅ to the intermediate point angle θ ₂₃ by the flow rate control by the directional control valve 4 according to the lever operation angle θ.
Controlled along.

On the other hand, during this deceleration, the spring 17 of the second pressure control valve 17
The secondary pressure Pi ₂ of the second constant differential pressure reducing valve 15 is introduced to the pilot portion 17b on the side opposite to c, and the secondary pressure Pi ₂ remains constant at a high pressure until it returns from the full lever position to an angle θ _24. There, then the secondary pressure Pi ₂ becomes gradually low pressure according to decrease the lever operation angle theta, then an angle theta ₂₁
In the following cases, the secondary pressure Pi ₂ is not guided, and the secondary pressure Pi ₂ and the spring 17c cause the second pressure control valve 1
The set pressure Pc of 7 is controlled as shown by the solid line II 'in FIG. That is, the set pressure Pc of the second pressure control valve 17 is controlled in inverse proportion to the lever operation angle θ.

The pressure on the motor discharge side is introduced to the pilot portion 17a of the second pressure control valve 17, and the pressure on the motor discharge side, that is, the deceleration pressure Pb, exceeds the set pressure Pc of the second pressure control valve 17. Then, the deceleration pressure Pb is controlled by the second pressure control valve 17.

That is, when the lever 10c is returned from the acceleration position to the neutral position during normal work, the motor deceleration pressure Pb is the set pressure of the second pressure control valve 17 while the lever operation angle θ is between the angle θ ₂₅ and the angle θ _23. The pressure is lower than Pc, the second pressure control valve 17 does not operate, and the motor deceleration pressure Pb is controlled by the directional control valve 4 to control the return oil flow rate to the tank 8.
Controlled along.

Next, when the lever operation angle θ becomes equal to or less than the angle θ ₂₃ , the return oil passage of the directional control valve 4 to the tank 7 is greatly throttled, the motor deceleration pressure Pb rapidly rises, and the set pressure Pc of the second pressure control valve 17 is increased. Try to cross. At this time, the second pressure control valve 17 has a pressure Pb on the motor discharge side that is guided to the pilot portion 17a and the second constant differential pressure reducing valve 1 that is guided to the pilot portion 17b.
It is switched to the lower position side by the secondary pressure Pi ₂ from 5 and its valve opening is controlled, and the pressure oil on the motor discharge side is passed through the second pressure control valve 17 to the motor suction side (direction of arrow). The pressure Pb on the motor discharge side is controlled (pressure control) while being partially bypassed.

As a result, until the lever operation angle θ is returned from the angle θ ₅ to the neutral position, the control by the second pressure control valve has priority over the control by the direction control valve 4, and the deceleration pressure by the second pressure control valve 17 is given. Pb is controlled along line II 'in FIG. Further, as the lever 10c is returned to the neutral state by this control, the deceleration pressure is controlled by the pressure control by the second pressure control valve 17.
Pb is controlled so as to gradually increase along the solid line II ', and the motor 6 is smoothly decelerated and stopped with less shock.

During deceleration, when the load on the motor 6 is small, the engine 1 is under a low load and rotates at high speed, and the pump discharge flow rate, that is, the motor return oil flow rate is large, such as during crane work, the lever operation angle θ is set. The control curve of the motor deceleration pressure Pb based on the flow rate control by the corresponding directional control valve 4 becomes a gentle curve as indicated by the one-dot chain line III 'in FIG. As a result, the flow rate control region (angles θ _{25 to} θ ₂₂ ) by the directional control valve 4 is increased even during deceleration, wide range control of the deceleration speed and fine deceleration are possible during deceleration, and inching performance is greatly improved.

Further, when the load on the motor 6 is large, such as during bucket work, and the engine 1 has a high load and rotates at a low speed and the pump discharge flow rate, that is, the motor return oil flow rate is small, the directional control valve 4 according to the lever operation angle θ is used. The control curve of the motor deceleration pressure Pb based on the flow rate control is the chain double-dashed line IV ′ in FIG.
It becomes a sharp curve like. Thus the flow control region (angle theta ₂₅ through? ₂₄₎ pressure control region by the second pressure control valve 17 than the (theta ₂₄ through? ₂₁₎ increases, the deceleration pressure Pb is the lever operation angle of the motor 6 by the pressure control The control is performed more appropriately according to θ, the controllability of the pressure control is greatly improved, the shock is greatly suppressed, and the vehicle is decelerated and stopped extremely smoothly.

In the above embodiment, the pilot pressure Pi from the remote control valve 10 is reduced by the first constant difference pressure reducing valve 14 and the second constant difference pressure reducing valve 15, respectively, and the pilot portion 16b of the first pressure control valve 16 and the second pressure control valve 16 are controlled. Although the pilot pressure 17 is introduced to the pilot portion 17b of FIG.
May be directly guided to the pilot portions 16b and 17b of the pressure control valves 16 and 17, respectively.

As described above, according to the present invention, when the load on the motor is small and the acceleration pressure is low, such as during crane work,
The bleed-off control of the directional control valve operated by the pilot pressure from the remote control valve is prioritized and its flow rate control area is enlarged, so that the flow rate into the motor can be controlled in a wide range according to the lever operation angle, and A delicate flow rate control is possible and inching can be greatly improved.

When the load on the motor is large and the acceleration pressure is high, such as during bucket work, the first pressure control valve is activated by the balance between the pilot pressure from the remote control valve and the pump discharge pressure, and the directional control valve Since the pressure control by the first pressure control valve is prioritized over the bleed-off control and the pressure control area becomes large, the pump discharge pressure, that is, the motor acceleration pressure can be controlled in a wide range according to the lever operation angle. Acceleration pressure can be accurately controlled by pressure control. In this way, optimum control characteristics can be obtained according to the load, and the controllability and operability of turning can be greatly improved.

Further, when the motor discharge side pressure becomes higher than the set pressure of the second pressure control valve when the motor decelerates and stops, this second pressure control valve causes the pressure on the motor discharge side, that is, the deceleration pressure, in inverse proportion to the operation amount of the remote control valve. Can be controlled accurately, and the motor can be smoothly decelerated and stopped.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of the present invention, FIG. 2 is a control diagram showing the relationship between the lever operating angle of a remote control valve and the acceleration pressure of a motor, and FIG. 3 is the lever operating angle and the motor. It is a control diagram which shows the relationship with deceleration pressure. 1 ... Engine, 2 ... Hydraulic pump, 4 ... Direction control valve, 6 ... Turning hydraulic motor, 8 ... Tank, 10 ... Remote control valve, 10a, 10b ... Variable pressure reducing valve, 11a, 11b ... … Pilot channel, 12 …… Shuttle valve, 14 …… First constant difference pressure reducing valve,
15 …… Second constant difference pressure reducing valve, 16 …… First pressure control valve, 17 ……
2nd pressure control valve, 18 …… Pilot switching valve.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location // B66C 23/86 9037-3F E02F 9/22 C

Claims (1)

[Claims] 1. A turning remote control valve whose pilot pressure is controlled to a secondary side by operating a lever, a directional control valve which is switched by pilot pressure from the remote control valve, and a hydraulic pump which is switched by switching the directional control valve. And a slewing hydraulic motor whose supply flow rate is controlled, the directional control valve has a bleed-off passage to the tank, and is configured to block both side flow passages of the motor in a neutral position. First pressure control for inputting the discharge pressure of the pump and the pilot pressure from the remote control valve to the discharge flow path of the pump and controlling the pump discharge pressure in proportion to the pilot pressure when the pilot pressure exceeds a set value Valve is connected,
A switching valve for extracting the pressure of the motor discharge side flow path between both side flow paths of the motor, and a discharge side flow path pressure for inputting the pressure of the discharge side flow path and the pilot pressure extracted by the switching valve. A swing hydraulic circuit for a construction machine, further comprising: a second pressure control valve that controls the pressure in the discharge side flow path in inverse proportion to the pilot pressure when the sum with the pilot pressure exceeds a set value. .