KR20110074388A - Hydraulic circuit for construction machinery - Google Patents

Abstract

PURPOSE: A hydraulic circuit for construction machinery is provided to make first and second discharge lines join at an accurate point even if the pressures of the lines change by connecting or blocking the lines according to their pressures. CONSTITUTION: A hydraulic circuit for construction machinery comprises first and second discharge lines(121,122), first and second rod sensing lines(151,152), and first and second joining valves(161,162). The first and second discharge lines connect each of first and second pumps(101,102) to each of first and second control valves(111,112). The first and second rod sensing lines introduces each rod sensing pressure of first and second actuators(131,132) to each of first and second pressure compensation valves(141,142). The first joining valve connects or blocks the first and second rod sensing lines according to operation signals input from an operation unit(191). The second joining valve connects or blocks the first and second discharge lines according to pressures of the first and second discharge lines.

Description

HYDRAULIC CIRCUIT FOR CONSTRUCTION MACHINERY}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a construction machine such as an excavator, and more particularly, to a hydraulic circuit of a construction machine in which hydraulic oil discharged from a plurality of pumps is selectively joined to drive an actuator.

Construction machinery such as an excavator has a plurality of work machines such as a boom, an arm, a bucket, and an upper pivot, each of which is driven by an actuator such as a cylinder or a hydraulic motor. Such actuators are driven by hydraulic oil discharged by a plurality of hydraulic pumps.

Here, the plurality of hydraulic pumps supply hydraulic oil to a plurality of actuators each of which is in charge, and when the required flow rate exceeds the maximum discharge flow rate of any one hydraulic pump, the discharge flow rates of the other hydraulic pumps are joined to the plurality of actuators. Will be supplied to An example thereof is disclosed in Korean Patent No. 0798465.

1 is a view disclosed in the Korean registered patent. Referring to FIG. 1, the hydraulic oil discharged from the first hydraulic pump 2 flows into the first control valve 5 through the first discharge line 10, and the hydraulic oil flowed into the first control valve 5. The flow direction is controlled and supplied to the first actuator 4. In addition, the hydraulic oil discharged from the second hydraulic pump 3 is supplied to the second control valve 8 through the second discharge line 11, and the hydraulic oil supplied to the second control valve 8 is in the flow direction thereof. This is controlled and supplied to the second actuator 7.

Meanwhile, first and second pressure compensation valves 6 and 9 are installed between each of the first and second control valves 5 and 8 and each of the first and second actuators 4 and 7. The first and second load pressure introduction lines 16 and 19 are connected to the hydraulic parts of the first and second pressure compensation valves 6 and 9. The first and second load pressure introduction lines 16 and 19 are joined or blocked by the first confluence valve 21.

In addition, a second confluence valve 13 is installed between the first and second discharge lines 10 and 11, and the first and second discharge lines 10 according to a signal output from the controller 14. Join or block (11).

In the hydraulic system of the construction machine having the configuration as described above, when the operator operates the first operation unit 29, the controller 14 calculates the required flow rate for the first actuator 4 from the operation signal, the calculated required flow rate It is determined whether it is larger than the maximum discharge flow volume of this 1st hydraulic pump 2. As shown in FIG. If the calculated required flow rate is smaller than the maximum discharge flow rate of the first hydraulic pump 2, the first and second confluence valves 21 and 13 are converted to the reverse of FIG. On the other hand, when the calculated required flow rate is larger than the maximum discharge flow rate of the first hydraulic pump 2, the first confluence valve 21 is converted to the state as shown in FIG. Then, pressure compensation is started by the second pressure compensation valve 9, whereby the pressure in the second discharge line 11 rises. Thereafter, the second confluence valve 13 is converted as shown in FIG. 1 at a delayed time to communicate the first and second discharge lines 10 and 11. As a result, the hydraulic oil discharged from the first and second hydraulic pumps 2 and 3 joins. As described above, in the Korean patent, the second confluence valve 13 is opened after a predetermined time after the first confluence valve 21 is completely opened. This is to secure a time for the pressures of the first and second discharge lines 10 and 11 to be the same in order to prevent an impact caused by the pressure difference between the first and second discharge lines 10 and 11. For sake.

If the first and second confluence valves 21 and 13 are opened at the same time, the hydraulic shock in which the flow rate and pressure supplied to the first actuator 4 suddenly decreases as shown in areas A and B of FIG. 2. This will occur. Since the pressure of the first discharge line 10 is high and the pressure of the second discharge line 11 is low, the operating oil of the first discharge line 10 is the second discharge line the moment the second confluence valve 13 is opened. This phenomenon occurs because of the sudden flow to (11). In order to prevent such a shock phenomenon that the pressure and flow rate decreases abruptly, the Korean patent discloses the second confluence valve 13 to be delayed for a predetermined time after the first confluence valve 21 is opened.

However, the time that the pressures of the first and second discharge lines 10 and 11 become equal after the first confluence valve 21 is opened is determined by the hose piping and arrangement, the temperature of the hydraulic oil, the magnitude of the hydraulic oil pressure, and the operation of the operation unit. It depends on various variables such as speed. Therefore, according to the Korean Patent Registration, the case where the second confluence valve 13 is opened in a state where the pressures of the first and second discharge lines 10 and 11 are not the same, may occur. As a result, a hydraulic shock phenomenon in which the flow rate and pressure suddenly decreases as shown in FIG. 2 occurs.

Of course, if the second confluence valve 13 is opened after sufficient time passes after the first confluence valve 21 is opened, the confluence of the pressures in the first and second discharge lines 10 and 11 is the same. Could be. However, in such a case, it takes too much time until the second confluence valve 13 is opened after the first confluence valve 21 is opened, so that the operation speed of the first actuator 4 is lowered. This will occur.

The present invention has been made in view of the above-described point, and an object thereof is to provide a hydraulic circuit of a construction machine capable of joining hydraulic fluids of a plurality of pumps without sudden changes in flow rate and pressure or operation delay.

The hydraulic circuit of the construction machine according to the present invention for achieving the object as described above is discharged from each of the first and second pump 101 (102) and the first and second control valves (111, 112) By supplying the hydraulic fluid controlled by the flow direction to each of the first and second actuators (131, 132) to drive the first and second actuators (131, 132), the first and second pressure compensation valve ( 141, 142 is applied to the construction machinery to compensate the pressure of the front end of the first and second control valves 111 and 112, each of the first and second pumps 101, 102 First and second discharge lines 121 and 122 connected to the first and second control valves 111 and 112, respectively; First and second load sensing lines 151 for introducing load sensing pressures of the first and second actuators 131 and 132 into the first and second pressure compensation valves 141 and 142, respectively. (152); A first confluence valve 161 connecting or blocking the first and second load sensing lines 151 and 152 according to an operation signal input from the operation unit 191; And a second confluence valve 162 for joining or blocking the first and second discharge lines 121 and 122 according to the pressure of the first and second discharge lines 121 and 122.

According to an embodiment of the present invention, the hydraulic circuit selects a larger pressure among the pressures of the first and second discharge lines 121 and 122 so that the first hydraulic part 162a of the second confluence valve 162 is selected. High pressure selection valve 170 for transmitting as a signal pressure to; And a low pressure selection valve for selecting a small pressure among the pressures of the first and second discharge lines 121 and 122 and transmitting the signal pressure to the second hydraulic pressure unit 162b of the second confluence valve 162 as a signal pressure. 180) further.

In addition, the pilot line 181 connecting the low pressure selection valve 180 and the second hydraulic pressure unit 162b is connected or disconnected by the first confluence valve 161 and the first confluence valve 161. When the pilot line 181 is blocked by the second confluence valve 162, the second confluence valve 162 separates the first and second discharge lines 121 and 122, and the first confluence valve 161 is used to separate the first and second discharge lines 121 and 122. When the pilot line 181 is connected and the signal pressures transmitted to the first and second hydraulic parts 162a and 162b are the same, the second confluence valve 162 is the first and second discharge lines 121. Join 122).

According to the problem solving means as described above, the second confluence valve to join or block the first and second discharge line in accordance with the pressure of the first and second discharge line, the hose piping and arrangement, the temperature of the hydraulic oil Even if the pressures of the first and second discharge lines are changed by various variables such as the magnitude of the hydraulic oil pressure and the operation speed of the operation unit, the first and second discharge lines can be joined at an accurate time point. Therefore, it is possible not only to prevent the hydraulic shock at the time of joining due to the pressure difference between the first and second discharge lines, but also to prevent the operation delay caused by the delayed time of joining.

In particular, by connecting and disconnecting the pilot line connected to the second hydraulic pressure section of the second confluence valve through the first confluence valve for controlling the separation and confluence of the first and second load sensing lines, It is possible to configure the joining circuit, thereby reducing the manufacturing cost.

Hereinafter will be described in detail with respect to the hydraulic circuit of the construction machine according to an embodiment of the present invention.

3 and 4, the hydraulic circuit of the construction machine according to an embodiment of the present invention is discharged from each of the first and second pump 101, 102, the first and second control valve 111 ( 112 is applied to a construction machine in which each of the first and second actuators 131 and 132 is driven by hydraulic oil whose flow direction is controlled by each of the first and second discharge lines 121 and 122. , The first and second load sensing lines 151 and 152, the first and second confluence valves 161 and 162, the high pressure selection valve 170, the low pressure selection valve 180 and the controller 190. ).

The first and second pumps 101 and 102 are variable displacement pumps in which the inclination angles of the inclined plates 103 and 104 are adjusted according to the control signal output from the control unit 190, respectively, to control the discharge flow rate. Regulators 105 and 106 are provided in the first and second pumps 101 and 102, respectively, and each of the regulators 105 and 106 is configured according to the signal output from the controller 190. The discharge flow rate is varied by adjusting the inclination angles of the second pumps 101 and 102. Herein, the controller 190 calculates discharge flow rates of the first and second pumps 101 and 102 from the operation signal output from the operation unit 191, and calculates a control signal based on the first and second pumps 101 and 102. And the regulators 105 and 106 of the second pumps 101 and 102, respectively.

The first and second control valves 111 and 112 convert the hydraulic fluid discharged from the first and second pumps 101 and 102 into one or the other side according to a signal output from the controller 190. The flow direction and the flow rate are controlled and supplied to each of the first and second actuators 131 and 132.

The first and second actuators 131 and 132 are for driving a work machine such as a boom, an arm, a bucket, or an upper swinging structure, respectively, and are composed of a hydraulic cylinder or a hydraulic motor. In this figure, each of the actuators 131 and 132 and the control valves 111 and 112 is shown as a single work machine. However, this is not necessarily interpreted as such, and the first and second actuators 131 and 132 may be a group of actuators operated by hydraulic pressure supplied from each of the first pump 101 and the second pump 102. It may also be interpreted as a simplified illustration for convenience of understanding. In this case, although the first and second control valves 111 and 112 may appear to supply hydraulic pressure to only one actuator, respectively, the control valve for controlling the actuators supplied with the hydraulic pressure by the respective pumps may be used. Can be considered as a group. In the control valve group, a control valve that is divided into one speed and two speeds to control hydraulic oil may be installed separately in each of the first and second control valves 111 and 112 to drive one actuator. Considering that the actuators and the control valves are configured as described above, the load sensing lines to be described later may be regarded as a type in consideration of all the load sensing lines of the actuators supplied from the respective pumps. In this case, the confluence between the pumps may take into account the case in which the actuators supplied with hydraulic pressure from each pump are driven in combination. That is, the merging of the pumps may be performed in consideration of a case in which several work machines are driven in combination. In this case, if an additional work order is input in a state in which one pump discharges the maximum discharge amount and a further flow rate is required, it may be understood that the other work machine is driven to increase the discharge flow rate of the remaining pump that is already driven to join. . Hereinafter, for convenience of description, a case in which only individual actuators are connected to each other will be described as an example.

The first and second pressure compensation valves 141 and 142 are connected between the first and second actuators 131 and 132 and the first and second control valves 111 and 112. The first and second pressure compensation valves 141 and 142 are discharged from the first and second pumps 101 and 102 when the first and second actuators 131 and 132 are combined in operation. The pressure is intended to be the same regardless of the load sensing pressures of the first and second actuators 131 and 132. More specifically, the first and second pressure compensation valves 141 and 142 are connected to the first and second load sensing lines 151 and 152, and the first and second pressure compensation valves 141 are connected to each other. The high pressure load sensing pressure is transmitted as a signal pressure to the hydraulic pressure part of the pressure compensation valve in which the load sensing pressure is low, and thus the flow rate of the hydraulic oil supplied to the actuator in which the low pressure load sensing pressure is formed is reduced. As a result, the pressure of the pump discharged from the low pressure pump is increased, whereby the pressure of the hydraulic oil discharged from the pair of pumps 101 and 102 becomes equal. By this principle, the first and second actuators 131 and 132 can be driven according to the operation signal of the operation unit 191 irrespective of the load sensing pressure, thereby improving the operability. That is, the first and second pressure compensation valves 141 and 142 may be formed at front ends of the first and second control valves 111 and 112 when the first and second actuators 131 and 132 are combined in operation. As to compensate for the pressure, a detailed description is omitted since it is a known technique.

The first and second discharge lines 121 and 122 connect each of the first and second pumps 101 and 102 to the first and second control valves 111 and 112, respectively. And hydraulic oil of each of the second pumps 101 and 102 is introduced into each of the first and second control valves 111 and 112. The first and second discharge lines 121 and 122 are interconnected by the joining line 123, and the joining line 123 is connected and disconnected by the second joining valve 162.

Each of the first and second load sensing lines 151 and 152 is withdrawn from a supply line of each of the first and second actuators 131 and 132. Accordingly, when the first and second control valves 111 and 112 are positioned in the neutral state as shown in FIG. 3, the first and second load sensing lines 151 and 152 may be the first and second control valves. The low pressure is formed by connecting to the tank T through the 111 and 112. However, when the first and second control valves 111 and 112 are converted to one side or the other side, the first and second load sensing lines 151 and 152 are connected to the first and second actuators 131. The first and second load sensing lines 151 and 152 communicate with a line for supplying hydraulic oil to the first and second load sensing pressures of the first and second actuators 131 and 132.

The first load sensing line 151 is withdrawn from the supply line of the first actuator 131 and is connected to one side of the first confluence valve 161. In addition, the first load sensing line 151 is branched and connected to one side pressure receiving portion of the first pressure compensation valve 141. On the other hand, the other pressure receiving portion of the first pressure compensation valve 141 is applied to the pressure of the front end of the first pressure compensation valve 141. In addition, a first check valve 153 is installed in the first load sensing line 151 to prevent the load sensing pressure of the first load sensing line 151 from being drained to the tank T.

The second load sensing line 152 is withdrawn from the supply line of the second actuator 132 and is connected to the other side of the first confluence valve 161. In addition, the second load sensing line 152 is branched and connected to one side hydraulic portion of the second pressure compensation valve 142. On the other hand, the pressure of the front end of the second pressure compensation valve 142 is applied to the other pressure receiving portion of the second pressure compensation valve 142. In addition, a second check valve 154 is installed in the second load sensing line 152 to prevent the load sensing pressure of the second load sensing line 152 from being drained to the tank T.

The first confluence valve 161 is connected to the first load sensing line 151 at one side thereof, and the second load sensing line 152 is connected at the other side thereof according to a signal output from the controller 190. The first and second load sensing lines 151 and 152 join or separate. In addition, the first confluence valve 161 is connected to the low pressure selection valve 180 on one side thereof, and the second hydraulic pressure unit 162b of the second confluence valve 162 is connected to the other side thereof to select the low pressure. It also functions to transmit or block the signal pressure selected by the valve 180 to the second pressure receiving portion 162b of the second confluence valve 162. Although the first confluence valve 161 is described as being converted according to the control signal output from the control unit 190, the control unit 190 is the first confluence valve 161 according to the operation signal input from the operation unit 191. Since the first confluence valve 161 may be converted to be converted according to the operation signal of the operation unit 191.

The second confluence valve 162 is installed in the confluence line 123 to block or connect the confluence line 123 to separate or join the first and second discharge lines 121 and 122. Do it. First and second hydraulic pressure parts 162a and 162b are provided at both sides of the second confluence valve 162, respectively, and an output end of the high pressure selection valve 170 is connected to the first hydraulic pressure part 162a. The low pressure selection valve 180 is connected to the second hydraulic pressure unit 162b via the first confluence valve 161.

Meanwhile, a pilot line 181 connecting the second hydraulic pressure unit 162b and the low pressure selection valve 180 is connected to a tank T, and is unloaded between the pilot line 181 and the tank T. Orifice 182 is installed. The unloading orifice 182 drains a small amount of hydraulic oil delivered from the low pressure selection valve 180 when the pilot line 181 is opened by the first confluence valve 161. However, since the amount drained in the tank T is very small, the pressure at the output end of the low pressure selection valve 180 is transmitted to the second hydraulic pressure unit 162b as it is. On the other hand, when the pilot line 181 is blocked by the first confluence valve 161, the hydraulic oil of the second hydraulic pressure unit 162b is drained to the tank T, and a tank ( T) Pressure is applied.

The high pressure selection valve 170 selects a high pressure from the first and second discharge lines 121 and 122 and transmits the signal to the first hydraulic pressure unit 162a of the second confluence valve 162 as a signal pressure. As a shuttle valve, etc. can be used.

The low pressure selection valve 180 selects a low pressure from the first and second discharge lines 121 and 122 and transmits the low pressure to the second water pressure unit 162b of the second confluence valve 162 as a signal pressure. Do it.

The control unit 190 receives an operation signal from the operation unit 191, the first and second control valves 111 and 112, the first and second pumps 101 and 102, and the first confluence valve ( For controlling the 161, the controller 190 will be described in detail in the operation description below.

Hereinafter, the operation of the hydraulic circuit of the construction machine having the configuration as described above will be described.

3 is a circuit diagram schematically showing a state in which a construction machine does not work, that is, an idle state. Referring to FIG. 3, the first confluence valve 161 interrupts the pilot line 181 by a spring 161a and separates the first and second load sensing lines 151 and 152 from each other. Located in In addition, a larger pressure is applied to the first hydraulic pressure unit 162a of the second confluence valve 162 and the tank T is applied to the second hydraulic pressure unit 162b. Pressure is applied. Here, the force of the spring 162c of the second confluence valve 162 to press the second confluence valve 162 is a pressure in a state where the flow rates of the first and second pumps 101 and 102 are minimum. Is set smaller than the force applied to the first hydraulic pressure section 162a. Therefore, the second confluence valve 162 is in a position to block the confluence line 123 as shown in FIG. As a result, the first and second discharge lines 121 and 122 are separated.

In this state, when the operator operates the operation unit 191, the operation signal of the operation unit 191 is input to the control unit 190. Then, the controller 190 calculates a flow rate required for the first and second actuators 131 and 132 from the input operation signal. Thereafter, if the calculated required flow rate is smaller than the maximum flow rate of any one of the first and second pumps 101 and 102, the first confluence valve 161 is maintained in the state as shown in FIG. Then, the second confluence valve 162 maintains a state in which the first and second discharge lines 121 and 122 are separated from each other as shown in FIG. 3. As described above, when the first and second discharge lines 121 and 122 are separated, the hydraulic oil discharged from the first pump 101 is supplied only to the first actuator 131 and discharged from the second pump 102. Hydraulic oil is supplied only to the second actuator 132.

On the other hand, if the required flow rate calculated from the operation signal is greater than the maximum discharge flow rate of any one of the first and second pumps 101 and 102, power is applied to the first confluence valve 161 to join the first confluence. The valve 161 is changed to the state as shown in FIG. As a result, the first and second load sensing lines 151 and 152 are joined to each other.

For example, the operation signal input from the operation unit 191 is an input signal for driving the first actuator 131, and the required flow rate of the first actuator 131 calculated from the operation signal is the maximum discharge of the first pump 101. If the flow rate is greater than the flow rate, the discharge flow rate of the second pump 102 must be supplied to the first actuator 131, and thus the controller 190 converts the first confluence valve 161 as shown in FIG. 4, and the second pump 102. A control signal is outputted to the regulator 106 of) to increase the discharge flow rate of the second pump 102. Then, the discharge flow rate of the second pump 102 is increased to increase the pressure of the second discharge line 122. In addition, when the first and second load sensing lines 151 and 152 are joined together, the low pressure of the first load sensing line 151 passes through the second load sensing line 152 to the first pressure compensation valve. It is delivered to one side of the hydraulic pressure portion of (141). In addition, the other hydraulic part is applied with a high pressure of the hydraulic oil of the first pump 101 supplied through the first control valve 111. As a result, the first pressure compensation valve 141 is converted to the state as shown in FIG. 4, and supplies hydraulic oil passing through the first control valve 111 to the first actuator 131.

On the other hand, when the first confluence valve 161 is converted as shown in FIG. 4, the pilot line 181 of the low pressure selection valve 180 is connected to the second hydraulic part 162b of the second confluence valve 162. do. At this time, a large pressure among the pressures of the first and second discharge lines 121 and 122 is transmitted to the first hydraulic pressure unit 162a of the second confluence valve 162 by the high pressure selection valve 170. do. Therefore, when the first confluence valve 161 is converted, the pressure of the first discharge line 121 is higher than the pressure of the second discharge line 122, and thus the pressure of the first discharge line 121. The pressure is applied to the first hydraulic pressure unit 162a and the pressure of the second discharge line 122 is applied to the second hydraulic pressure unit 162b.

In this state, the discharge flow rate of the second pump 102 is increased so that the pressure of the second discharge line 122 is gradually increased to be the same as the pressure of the first discharge line 121. The confluence valve 162 is converted as shown in FIG. 4 to connect the confluence line 123. As a result, the first and second discharge lines 121 and 122 are joined to each other, and the hydraulic oil discharged from the second pump 102 is transferred to the first pump through the confluence line 123 and the second confluence valve 162. Together with the hydraulic oil of 101, it is supplied to the first actuator 131.

As such, by converting the second confluence valve 162 according to the pressures of the first and second discharge lines 121 and 122, the hose piping and arrangement, the temperature of the hydraulic oil, the magnitude of the hydraulic oil pressure, and the operating speed of the operation unit. The first and second discharge lines 121 and 122 may be joined at the correct time regardless of a change in the pressure of the hydraulic oil that is changed by various variables. Therefore, it is possible not only to prevent the hydraulic shock at the time of joining due to the pressure difference between the first and second discharge lines 121 and 122, but also to prevent the workability from deteriorating due to the delayed joining time. Will be.

In particular, the second hydraulic pressure unit 162b of the second confluence valve 162 through the first confluence valve 161 for controlling the separation and confluence of the first and second load sensing lines 151 and 152. By connecting and disconnecting the pilot line 181 to be connected, it is possible to configure the joining circuit with a minimum of hydraulic components, thereby reducing the manufacturing cost.

1 is a hydraulic circuit diagram schematically showing a hydraulic circuit of a conventional construction machine,

FIG. 2 illustrates the discharge pressure and the flow rate and the flow rate of the first and second hydraulic pumps when the first and second discharge lines are joined when the discharge pressures of the first and second hydraulic pumps are not the same. 1 graph showing the pressure and flow rate of the actuator,

3 is a hydraulic circuit diagram schematically showing a hydraulic circuit of a construction machine according to an embodiment of the present invention;

4 is a hydraulic circuit diagram schematically illustrating a state in which the first and second discharge lines of FIG. 3 are joined.

<Description of Major Reference Marks in Drawings>

101, 102; First and second pumps 111, 112; 1st and 2nd control valve

121, 122; First and second discharge lines 131 and 132; 1st and 2nd actuator

141, 142; First and second pressure compensation valves 151 and 152; First and second load sensing lines

161; First confluence valve 162; 2nd confluence valve

162a, 162b; First and second hydraulic pressure section 170; High Pressure Selection Valve

180; Low pressure selection valve 190; Control

191; Control panel

Claims (3)

The hydraulic fluid discharged from each of the first and second pumps 101 and 102 and whose flow direction is controlled by each of the first and second control valves 111 and 112 is supplied to the first and second actuators 131 and 132. And the first and second actuators 131 and 132 are supplied to the first and second actuators 131 and 132, respectively. Hydraulic circuit of the construction machine to compensate the pressure of the shear of 112, First and second discharge lines 121 and 122 connecting the first and second pumps 101 and 102 to the first and second control valves 111 and 112, respectively; First and second load sensing lines 151 for introducing load sensing pressures of the first and second actuators 131 and 132 into the first and second pressure compensation valves 141 and 142, respectively. (152); A first confluence valve 161 connecting or blocking the first and second load sensing lines 151 and 152 according to an operation signal input from the operation unit 191; And And a second confluence valve 162 for joining or blocking the first and second discharge lines 121 and 122 according to the pressure of the first and second discharge lines 121 and 122. Hydraulic circuit of construction machinery. The method of claim 1, The high pressure selection valve 170 which selects a large pressure among the pressures of the first and second discharge lines 121 and 122 and transmits the signal to the first hydraulic pressure unit 162a of the second confluence valve 162 as a signal pressure. ; And The low pressure selection valve 180 which selects a small pressure among the pressures of the first and second discharge lines 121 and 122 and transmits the signal to the second hydraulic pressure unit 162b of the second confluence valve 162 as a signal pressure. Hydraulic circuit of a construction machine, characterized in that it further comprises a). The method of claim 2, The pilot line 181 connecting the low pressure selection valve 180 and the second hydraulic pressure unit 162b is connected or blocked by the first confluence valve 161. When the pilot line 181 is blocked by the first confluence valve 161, the second confluence valve 162 separates the first and second discharge lines 121 and 122, When the pilot line 181 is connected by the first confluence valve 161 and the signal pressures transmitted to the first and second hydraulic pressure parts 162a and 162b are the same, the second confluence valve 162 is provided. The hydraulic circuit of the construction machine, characterized in that for joining the first and second discharge line (121) (122).

Images