JP2012112466A - Hydraulic system of construction machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the hydraulic system of a construction machine using a valve of an open center system for a flow rate and directional control valve that controls the flow of pressure oil supplied from first to third hydraulic pumps to actuators, in which when the operation lever device of a plurality of actuators driven by discharged oil of the third hydraulic pump is not operated, an increase in the discharge pressure of the third hydraulic pump by a neutral pressure loss of the flow rate and directional control valve is suppressed and thereby, power consumed by the third hydraulic pump is reduced.SOLUTION: The hydraulic system includes a bypass circuit 53 including a bypass oil passage 51 branched from the third pressure oil supply oil passage 23 of the third hydraulic pump P3 and a bypass selector valve 52 disposed in the bypass oil passage 51; and a switch control device 54 in which the bypass selector valve 52 is switched to an open position when all of the flow rate and directional control valves 37, 38, 39 are at a neutral position I, and the bypass selector valve 52 is switched to a closed position V when the valves are switched to an operation position II or III.

Description

  The present invention has first to third hydraulic pumps (three main pumps), the first and second hydraulic pumps are variable displacement types, the third hydraulic pump is a fixed displacement type, and the third hydraulic pump Equipped with a torque control device that controls to reduce the absorption torque of the first and second hydraulic pumps by the pump discharge pressure, and controls the flow of pressure oil supplied to the actuator using an open center type flow rate / direction control valve The present invention relates to a hydraulic system for construction machinery such as a hydraulic excavator.

  It has first to third hydraulic pumps (three main pumps) and uses an open center type valve for the flow rate and direction control valve that controls the flow of pressure oil supplied from the first to third hydraulic pumps to the actuator. A hydraulic system for construction machinery such as a hydraulic excavator, which is called an open center circuit type three-pump hydraulic system, is described in Patent Documents 1 and 2, for example.

  In the hydraulic systems described in Patent Documents 1 and 2, the first and second hydraulic pumps are variable displacement types, and the third hydraulic pump is a fixed displacement type.

  Moreover, the hydraulic system described in Patent Document 2 includes torque control devices in the first and second hydraulic pumps. This torque control device decreases the first and second hydraulic pump capacities when not only the discharge pressure of the first and second hydraulic pumps but also the discharge pressure of the third hydraulic pump increases. By doing so, the total of the absorption torque (input torque) of the first to third hydraulic pumps is controlled so as not to exceed a preset maximum torque. As a result, the sum of the absorption torques of the first to third hydraulic pumps is controlled within the allowable torque range of the engine, and engine stop (engine stall) due to overload is prevented.

JP-A-2005-331011 Japanese Patent Application Laid-Open No. 07-71055

  In the hydraulic systems described in Patent Documents 1 and 2, since the flow rate / direction control valve is an open center type valve, the operation lever devices of the plurality of actuators driven by the discharge oil of the third hydraulic pump are not operated. When the flow rate / direction control valve is in the neutral position, the oil discharged from the third hydraulic pump is returned to the tank via the flow rate / direction control valve. In addition, since the third hydraulic pump is a fixed displacement type, the third hydraulic pump always discharges a predetermined amount of pressure oil regardless of whether or not the operation lever device of the actuator driven by the discharge oil of the third hydraulic pump is operated. is doing. For this reason, a neutral pressure loss of a magnitude that cannot be ignored is generated in the flow rate / direction control valve when the operation lever device is not operated, and the neutral pressure loss of the flow rate / direction control valve causes a pressure oil supply passage in the third hydraulic pump. The pressure is always on and power is wasted.

  Further, when excavation work is performed with a hydraulic excavator equipped with the hydraulic system described in Patent Documents 1 and 2, the pumps used to drive the actuators related to excavation work are often the first and second hydraulic pumps. . The first and second hydraulic pumps are provided with the torque control device as described above, and the capacities of the first and second hydraulic pumps are determined by the torque control device according to the absorption torque of the first to third hydraulic pumps. The total is controlled so as not to exceed a preset maximum torque. In this way, the capacities of the first and second hydraulic pumps are controlled including the absorption torque of the third hydraulic pump, and whether or not the operation lever devices of the plurality of actuators driven by the discharge oil of the third hydraulic pump are operated. Regardless of the above, the neutral pressure loss of the flow rate / direction control valve causes a constant pressure in the third hydraulic oil supply passage of the third hydraulic pump, and the power is wasted. When the actuator is driven by the discharge oil of the two hydraulic pumps, the capacities of the first and second hydraulic pumps are controlled to decrease by the discharge pressure of the third hydraulic pump, and the absorption torque, that is, the horsepower of the first and second hydraulic pumps is reduced. There is a problem that it decreases.

  A first object of the present invention is to provide an open center type flow rate / direction control valve having first to third hydraulic pumps and controlling the flow of pressure oil supplied from the first to third hydraulic pumps to an actuator. In a hydraulic system of a construction machine such as a hydraulic excavator using a valve, a third hydraulic pump caused by a neutral pressure loss of a flow / direction control valve when an operation lever device of a plurality of actuators driven by discharged oil of the third hydraulic pump is not operated It is to provide a hydraulic system for a construction machine capable of reducing the power consumed by a third hydraulic pump while suppressing an increase in the discharge pressure of the construction machine.

  The second object of the present invention is that the hydraulic system of the construction machine further increases not only the discharge pressure of the first and second hydraulic pumps but also the discharge pressure of the third hydraulic pump. A torque control device that controls the total of absorption torques (input torques) of the first to third hydraulic pumps so as not to exceed a preset maximum torque by reducing the capacities of the first and second hydraulic pumps. A hydraulic system for a construction machine that can suppress a decrease in absorption torque of the first and second hydraulic pumps when operating an operation lever device of an actuator that is driven by discharge oil of the first and second hydraulic pumps. Is to provide.

  (1) In order to achieve the first object, the present invention provides an engine, variable displacement first and second hydraulic pumps driven by the engine, and a fixed displacement pump driven by the engine. A third hydraulic pump; a plurality of first actuators driven by pressure oil discharged from the first hydraulic pump; a plurality of second actuators driven by pressure oil discharged from the second hydraulic pump; A plurality of third actuators driven by pressure oil discharged from the third hydraulic pump, and a plurality of flow rates for controlling the flow of pressure oil supplied from the first hydraulic pump to the plurality of first actuators, respectively. A first valve device including a direction control valve, and a plurality of flow rate / direction controls for respectively controlling the flow of pressure oil supplied from the second hydraulic pump to the plurality of second actuators A second valve device including: a third valve device including a plurality of flow rate and direction control valves that respectively control flow of pressure oil supplied from the third hydraulic pump to the plurality of third actuators; and the engine. A plurality of flow rate / direction controls of each of the first to third valve devices are provided corresponding to the driven pilot pump and the plurality of first to third actuators based on the discharge oil of the pilot pump. A plurality of operation lever devices that generate command pilot pressure for switching the valves, and the plurality of flow rate / direction control valves of the first to third valve devices are respectively the first to third valves. First to third center bypass provided in the valve device, the upstream side being connected to the first to third pressure oil supply oil passages through which the discharge oil of the first to third hydraulic pumps is guided, and the downstream side being connected to the tank oil When the center bypass variable restrictor is above and the plurality of flow rate / direction control valves are respectively in the neutral position, the center bypass variable restrictor is fully opened, and the plurality of flow rate / direction control valves are respectively When the switching operation is performed from the neutral position, the opening area of the center bypass variable restrictor is reduced or completely closed, and the first to first pressure guides led through the first to third pressure oil supply oil passages. In a hydraulic system for a construction machine that is an open center type valve capable of supplying oil discharged from a three hydraulic pump to the plurality of first to third actuators, the third hydraulic pump discharged oil is guided to the third hydraulic pump. A bypass circuit that includes a bypass oil passage that branches off from the pressure oil supply oil passage and that has a downstream side connected to the tank and a bypass switching valve that can be switched between an open position and a closed position. When the passage and the plurality of flow rate / direction control valves of the third valve device are all in the neutral position, the bypass switching valve is switched to the open position, and any of the plurality of flow rate / direction control valves is neutral. And a switching control device that switches the bypass switching valve to the closed position when switched from the position to the operating position.

  In the present invention configured as described above, any one of the plurality of flow rate / direction control valves of the third valve device when the operation lever device of the plurality of third actuators driven by the discharge oil of the third hydraulic pump is operated. Is switched from the neutral position to the operating position, the center bypass variable restrictor is closed, and the switching control device switches the bypass switching valve to the closed position. As a result, the oil discharged from the third hydraulic pump is supplied from the flow rate / direction control valve of the third actuator to the third actuator via the third pressure oil supply oil passage, and the third actuator performs a normal operation.

  On the other hand, when the operation lever device of the plurality of third actuators driven by the discharge oil of the third hydraulic pump is not operated, the plurality of flow rate / direction control valves of the third valve device are all in the neutral position, and the center bypass While the variable throttle is fully opened, the switching control device switches the bypass switching valve to the open position. As a result, most of the oil discharged from the third hydraulic pump circulates directly to the tank via the bypass oil passage and the bypass switching valve. Therefore, the third hydraulic pump is caused by the neutral pressure loss of the plurality of flow rate / direction control valves of the third valve device. The increase in the discharge pressure is suppressed, and the power consumed by the third hydraulic pump can be reduced.

  (2) In order to achieve the first and second objects, the present invention further provides the first to third hydraulic pumps when the discharge pressure of the first to third hydraulic pumps increases. In a hydraulic system for a construction machine including a torque control device that controls the absorption torque of the first and second hydraulic pumps so that the total absorption torque does not exceed a preset maximum torque, the discharge oil of the third hydraulic pump A bypass circuit that branches from the third pressure oil supply oil passage through which the oil is guided and includes a bypass oil passage that is connected to a tank on the downstream side and a bypass switching valve that is disposed in the bypass oil passage and can be switched between an open position and a closed position. And when all of the plurality of flow rate / direction control valves of the third valve device are in the neutral position, the bypass switching valve is switched to the open position, and any of the plurality of flow rate / direction control valves is in the neutral position. From When switched to the turned position is assumed to comprise a switching controller and switching the bypass switching valve in the closed position.

  Thereby, as explained in the above (1), when the operating lever device of the third actuator is not operated and the third actuator is not operating, most of the discharge oil of the third hydraulic pump is the third. Since it flows directly to the tank without passing through the plurality of flow rate / direction control valves of the valve device, an increase in the discharge pressure of the third hydraulic pump due to the neutral pressure loss of the plurality of flow rate / direction control valves of the third valve device is suppressed, The power consumed by the third hydraulic pump can be reduced.

  Further, when operating the operating lever devices of the first and second actuators driven by the discharge oil of the first and second hydraulic pumps to operate the first and second actuators, the capacity of the first and second hydraulic pumps is The torque control device controls the sum of the absorption torques of the first to third hydraulic pumps so as not to exceed the preset maximum torque. At this time, when the operating lever device of the third actuator is not operated and the third actuator is not operating, most of the discharge oil of the third hydraulic pump is directly passed through the bypass oil passage and the bypass switching valve. Since it recirculates to the tank, the increase in the discharge pressure of the third hydraulic pump due to the neutral pressure loss of the plurality of flow rate / direction control valves of the third valve device is suppressed, and the decrease in the absorption torque of the first and second hydraulic pumps is suppressed. it can.

  (3) In the above (1) or (2), preferably, the switching control device outputs the first hydraulic pressure signal when all of the plurality of flow rate / direction control valves of the third valve device are in a neutral position. A neutral position detection device that outputs a second hydraulic pressure signal when any of the plurality of flow rate / direction control valves is switched from the neutral position to the operating position, and the hydraulic pressure output from the neutral position detection device A hydraulic signal transmission oil passage for guiding a signal to the bypass switching valve, the bypass switching valve has a pressure receiving portion connected to the hydraulic signal transmission oil passage, and the bypass switching valve is connected to the pressure receiving portion. When the first hydraulic pressure signal is guided, it is in the open position, and when the second hydraulic pressure signal is guided to the pressure receiving portion, it switches to the closed position.

  Thus, the hydraulic system of the present invention can be configured in a pure hydraulic manner including the switching control device and the bypass circuit, and the hydraulic system can be made inexpensive and highly reliable.

  According to the present invention, an open center type valve is used as a flow rate / direction control valve that has first to third hydraulic pumps and controls the flow of pressure oil supplied from the first to third hydraulic pumps to an actuator. In a hydraulic system of a construction machine such as a hydraulic excavator, due to neutral pressure loss of a plurality of flow rate / direction control valves of a third valve device when an operation lever device of a plurality of actuators driven by discharged oil of a third hydraulic pump is not operated The increase in the discharge pressure of the third hydraulic pump is suppressed, and the power consumed by the third hydraulic pump can be reduced.

  Further, according to the present invention, the hydraulic system for the construction machine further increases not only the discharge pressures of the first and second hydraulic pumps but also the discharge pressures of the third hydraulic pump. A torque control device that controls the total of absorption torques (input torques) of the first to third hydraulic pumps so as not to exceed a preset maximum torque by reducing the capacities of the first and second hydraulic pumps. When provided, it is possible to suppress a decrease in the absorption torque of the first and second hydraulic pumps when operating the operation lever device of the actuator driven by the discharge oil of the first and second hydraulic pumps.

It is a figure which shows the circuit structure of the hydraulic system of the construction machine concerning the 1st Embodiment of this invention. It is a figure which shows the external appearance of a hydraulic shovel. It is a figure which shows the circuit structure of the conventional hydraulic system. It is a figure which shows the change of the instruction | command pilot pressure when operating the operating lever of the operating lever operating device for blades, and the discharge pressure of a 3rd hydraulic pump. It is a figure which shows the change of the maximum absorption torque of the 1st and 2nd hydraulic pump at the time of non-use of a 3rd hydraulic pump, and a use compared with the hydraulic system of this invention, and the conventional hydraulic system. It is a figure which shows the circuit structure of the hydraulic system of the construction machine concerning the 2nd Embodiment of this invention. It is a figure which shows the circuit structure of the hydraulic system of the construction machine concerning the 3rd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<First Embodiment>
FIG. 1 is a diagram showing a circuit configuration of a hydraulic system for a construction machine according to a first embodiment of the present invention.

  1, the hydraulic system according to the present embodiment includes an engine E, a first hydraulic pump (main pump) P1 connected to the engine E, and driven by the engine E, and a second hydraulic pump (main pump) P2. , A pump device 11 including a third hydraulic pump (main pump) P3 and a pilot pump P4, and a plurality of first actuators 12, 13, 14 (travel motor 12) driven by pressure oil discharged from the first hydraulic pump P1. , Boom cylinder 13, bucket cylinder 14), a plurality of second actuators 15 and 16 (travel motor 15, arm cylinder 16) driven by the pressure oil discharged from the second hydraulic pump P 2, and a third hydraulic pump P 3. A plurality of third actuators 17, 18, 19 (swing cylinder 1) driven by pressure oil discharged from , A swing motor 18, a blade cylinder 19) and a first pressure oil supply oil passage 21 of the first hydraulic pump P1, and a plurality of first actuators 12, 13, 14 (travel motor 12, A first valve device CV1 including a plurality of flow rate / direction control valves 32, 33, 34 for controlling the flow (flow rate and inflow / discharge direction) of the pressure oil supplied to the boom cylinder 13 and bucket cylinder 14); A flow (flow rate and flow) of pressure oil connected to the second pressure oil supply oil path 22 of the hydraulic pump P2 and supplied from the second hydraulic pump P2 to the plurality of second actuators 15 and 16 (travel motor 15 and arm cylinder 16). A third hydraulic pump connected to a second valve device CV2 including a plurality of flow rate / direction control valves 35 and 36 for controlling the inflow / discharge direction) and the third pressure oil supply oil passage 23 of the third hydraulic pump P3. A plurality of flow rate / direction controls for controlling the flow (flow rate and inflow / discharge direction) of the pressure oil supplied to the third actuators 17, 18, 19 (swing cylinder 17, swing motor 18, blade cylinder 19) from 3 A third valve device CV3 including valves 37, 38 and 39; a pilot relief valve 25 which is connected to a pilot pressure supply oil passage 24 through which the discharge oil of the pilot pump P4 is guided, and maintains the discharge pressure of the pilot pump P4; Based on the discharge oil of the pilot pump P4 provided corresponding to the plurality of first actuators 12, 13, 14 (travel motor 12, boom cylinder 13, bucket cylinder 14) and guided to the pilot pressure supply oil passage 24. Generates command pilot pressure for switching flow rate / direction control valves 32, 33, 34 according to the amount of lever operation A pilot that is provided corresponding to an operation lever device (not shown) having a built-in remote control valve and a plurality of second actuators 15 and 16 (travel motor 15 and arm cylinder 16) and led to a pilot pressure supply oil passage 24. An operation lever device (not shown) having a built-in remote control valve for generating a command pilot pressure for switching the flow rate / direction control valves 35 and 36 according to the operation amount of the operation lever based on the discharge oil of the pump P4; Based on the discharge oil of the pilot pump P4 provided corresponding to the plurality of third actuators 17, 18, 19 (swing cylinder 17, swing motor 18, blade cylinder 19) and guided to the pilot pressure supply oil passage 24, A command pilot pressure for switching the flow rate / direction control valves 37, 38, 39 according to the operation amount of the operation lever is generated. And an operating lever device 26, 27, 28 with a built-in con valve.

  The first and second hydraulic pumps P1 and P2 are variable displacement hydraulic pumps, and the third hydraulic pump P3 and the pilot pump P4 are fixed displacement hydraulic pumps. The first and second hydraulic pumps P1 and P2 are, for example, split flow type swash plate pumps in which two discharge ports are provided in one pump casing, and have a common variable displacement member (swash plate) 41. is doing.

  Further, the first and second hydraulic pumps P <b> 1 and P <b> 2 have a torque control device 42 connected to a variable capacity member (swash plate) 41. When the discharge pressures of the first to third hydraulic pumps P1 to P3 increase, the torque control device 42 prevents the total absorption torque of the first to third hydraulic pumps P1 to P3 from exceeding a preset maximum torque. The first and second hydraulic pumps P1 and P2 control the absorption torque. When the discharge pressure of the first hydraulic pump P1 is guided and the discharge pressure of the first hydraulic pump P1 rises, the capacity of the variable capacity member 41 is increased. When the discharge pressure of the first hydraulic control piston 42a that operates in the decreasing direction and the second hydraulic pump P2 is guided and the discharge pressure of the second hydraulic pump P2 increases, the second torque that operates the variable capacity member 41 in the capacity decreasing direction. When the discharge pressure of the control piston 42b and the third hydraulic pump P3 is guided and the discharge pressure of the third hydraulic pump P3 rises, the third torque control that operates the variable capacity member 41 in the capacity decreasing direction. A piston 42c, a variable capacitance element 41 is urged in the capacity increasing direction, the first to third hydraulic pumps P1~P3 is a 42d spring to set the maximum torque available.

  The total discharge pressure (or average discharge pressure) of the first to third hydraulic pumps P1 to P3 is not so high, and the total absorption torque of the first to third hydraulic pumps P1 to P3 is greater than the maximum torque set by the spring 42d. When the number is small, the first to third torque control pistons 42a to 42c do not operate, and the capacities of the first and second hydraulic pumps P1 and P2 are maintained at the maximum capacity. The total discharge pressure (or average discharge pressure) of the first to third hydraulic pumps P1 to P3 increases, and the total absorption torque of the first to third hydraulic pumps P1 to P3 exceeds the maximum torque set by the spring 42d. If it does so, the 1st-3rd torque control piston 42a-42c will operate the variable capacity | capacitance member 41 in the capacity | capacitance decreasing direction, and will reduce the capacity | capacitance of 1st and 2nd hydraulic pump P1, P2. Thereby, the torque control device 42 decreases the capacities of the first and second hydraulic pumps P1 and P2 when the total (or average discharge pressure) of the discharge pressures of the first to third hydraulic pumps P1 to P3 increases. Thus, the sum of the absorption torques of the first to third hydraulic pumps P1 to P3 is controlled so as not to exceed the maximum torque set by the spring 42d, and the sum of the absorption torques of the first to third hydraulic pumps is the allowable torque of the engine. The engine stop (engine stall) due to overload is prevented.

  A plurality of flow rate / direction control valves 32, 33, 34 of the first valve device CV1, a plurality of flow rate / direction control valves 35, 36 of the second valve device CV2, and a plurality of flow rate / direction control valves 37 of the third valve device CV3. , 38, 39 are open center type valves, and the plurality of flow rate / direction control valves 32, 33, 34 of the first valve device CV1 are first center bypass provided in the first valve device CV1. A center bypass variable restrictor 32a, 33a, 34a is provided on the oil passage 45, and a plurality of flow rate / direction control valves 35, 36 of the second valve device CV2 are provided in a second center provided in the second valve device CV2. Center bypass variable restrictors 35a and 36a are provided on the bypass oil passage 46, and a plurality of flow rate / direction control valves 37, 38, and 39 of the third valve device CV3 are provided in the third valve device CV3. Center bypass oil passage 47 Have center bypass variable throttle portion 37a, 38a, and 39a on. The upstream sides of the first to third center bypass oil passages 45 to 47 are respectively connected to the first to third pressure oil supply oil passages 21 to 23 through which the pressure oil of the first to third hydraulic pumps P1 to P3 is guided. Each downstream side is connected to a tank T.

  When the flow rate / direction control valves 32, 33, 34 of the first valve device CV1 are in the neutral position I, the center bypass variable restrictors 32a, 33a, 34a are fully open, and the flow rate / direction control valves 32, 33, 34 are open. Are switched from the neutral position I to the operating position II or III, respectively, the center bypass variable throttling portions 32a, 33a, 34a reduce the opening area or become fully closed. Center bypass variable restrictors 35a, 36a; 37a, 38a, 39a of the plurality of flow rate / direction control valves 35, 36 of the second valve device CV2 and the plurality of flow rate / direction control valves 37, 38, 39 of the third valve device CV3 Similarly, when the flow rate / direction control valves 35, 36; 37, 38, 39 are in the neutral position I, the center bypass variable restrictors 35a, 36a; 37a, 38a, 39a are fully open, and the flow rate / direction When the control valves 35, 36; 37, 38, 39 are respectively switched from the neutral position I to the operating position II or III, the center bypass variable restrictors 35a, 36a; 37a, 38a, 39a reduce the opening area or are fully closed. It becomes.

  Thus, when the flow rate / direction control valves 32, 33, 34; 35, 36; 37, 38, 39 are switched from the neutral position I to the operating position II or III, the center bypass variable restrictors 32a, 33a, 34a; , 36a; 37a, 38a, 39a by decreasing or fully closing the opening area, the discharge pressures of the first, second, third hydraulic pumps P1, P2, P3 are increased, and the first, second, second Three hydraulic pumps P1, P2, P3 discharge oil through the first, second and third pressure oil supply oil passages 21, 22, 23, flow rate / direction control valves 32, 33, 34; 35, 36; 37, 38, 39 can be supplied to the first, second and third actuators 12, 13, 14; 15, 16; 17, 18, 19.

  In addition to the above configuration, the hydraulic system according to the present embodiment branches from the third pressure oil supply oil passage 23 of the third hydraulic pump P3, and the bypass oil passage 51 and the bypass oil passage that are connected to the tank T on the downstream side. 51, a bypass circuit 53 comprising a bypass switching valve 52 that can be switched between an open position IV and a closed position V, and a plurality of flow rate / direction control valves 37, 38, 39 of the third valve device CV3 are all in a neutral position. When in I, the bypass switching valve 52 is switched to the open position, and any one of the plurality of flow rate / direction control valves 37, 38, 39 of the third valve device CV3 is switched from the neutral position I to the operating position II or III. And a switching control device 54 for switching the bypass switching valve 52 to the closed position V.

  When all of the plurality of flow rate / direction control valves 37, 38, 39 of the third valve device CV3 are in the neutral position I, the switching control device 54 outputs a tank pressure (first hydraulic pressure signal) as a hydraulic pressure signal. When any of the plurality of flow rate / direction control valves 37, 38, 39 of the three-valve device CV3 is switched from the neutral position I to the operating position II or III, a predetermined control pressure (second hydraulic signal) is output as a hydraulic signal. And a hydraulic signal transmission oil passage 56 that guides a hydraulic signal output from the neutral position detection circuit 55 to the pressure receiving portion 52a of the bypass switching valve 52.

  The neutral position detection circuit 55 has an upstream side connected to the pilot pressure supply oil passage 24 of the pilot pump P4, a downstream side connected to the tank T, and a plurality of flow rate / direction control valves 37, 38, 39 of the third valve device CV3. And a fixed throttle 62 provided upstream of the third valve device CV3 of the hydraulic signal generating oil path 61. The hydraulic signal transmitting oil path 56 is a third valve. The hydraulic signal generating oil passage 61 branches off at a position between the device CV3 and the fixed throttle 62.

  The flow rate / direction control valves 37, 38, 39 are respectively provided with openable / closable signal oil passages 61 a, 61 b, 61 c that constitute a part of the hydraulic signal generation oil passage 61, and the flow rate / direction control valves 37, 38. , 39 are in the neutral position I, the signal oil paths 61a, 61b, 61c are fully opened, and when the neutral position I is switched to the operating position II or III, the signal oil paths 61a, 61b, 61c are fully closed.

  The pressure receiving portion 52a of the bypass switching valve 52 is connected to the hydraulic signal transmission oil passage 56. The bypass switching valve 52 is in the open position when the tank pressure (first hydraulic pressure signal) is guided to the pressure receiving portion 52a, and the pressure receiving portion 52a. When a predetermined control pressure (second hydraulic pressure signal) is introduced to, the switch is switched to the closed position.

  FIG. 2 shows the external appearance of the hydraulic excavator.

  In FIG. 2, the excavator includes an upper swing body 300, a lower traveling body 301, and a swing-type front work machine 302 (boom 306, arm 307, bucket 308). Turning is possible by turning the turning motor 18. A swing post 303 is attached to the front portion of the upper swing body 300, and a front work machine 302 is attached to the swing post 303 so as to move up and down. The front work machine 302 rotates in the vertical direction by expansion and contraction of the boom cylinder 13, the arm cylinder 16, and the bucket cylinder 14. The lower traveling body 301 includes a central frame 304, and a blade 305 that moves up and down by the expansion and contraction of the blade cylinder 19 is attached to the central frame 304, and the lower traveling body 301 travels by the rotation of the traveling motors 12 and 15.

  The upper swing body 300 includes a driver seat 310, and various operation lever devices including the above-described operation lever devices 26, 27, and 28 are arranged around the driver seat 310. As an example, the operation lever device 27 is provided on the left side of the driver's seat 310.

  The engine E and the pump device 11 and the bypass circuit 53 shown in FIG. 1 are arranged in the rear part of the upper swing body 300, and the tank T is a right side portion of the driver seat 310 of the upper swing body 300 when viewed from the operator of the driver seat 310. The valve devices CV <b> 1 to CV <b> 3 are arranged in the lower part of the driver's seat 310 of the upper swing body 300.

  The first to third hydraulic pumps P1, P2, P3 shown in FIG. 1 are connected to the first to third hydraulic pumps P1, P2, P3 and the valve devices CV1, CV2, CV3. The bypass oil passage 51 is also constituted by a pipe connecting the pressure oil supply oil passage 23 and the tank T. On the other hand, the center bypass oil passages 45, 46 and 47 are formed as internal passages in the housings of the valve devices CV1 to CV3, and the center bypass variable restrictors 37a, 38a and 39a of the flow and direction control valves 37, 38 and 39 also have flow It is formed as an internal passage through the spool of the direction control valves 37, 38, 39.

  Next, the operation of the hydraulic system of the present embodiment configured as described above will be described in comparison with the operation of a conventional hydraulic system.

  FIG. 3 is a diagram illustrating a circuit configuration of a conventional hydraulic system. In the figure, elements (members) equivalent to those of the hydraulic system according to the present embodiment shown in FIG. As can be seen from a comparison between FIG. 1 and FIG. 3, the conventional hydraulic system includes a bypass oil passage 51, a bypass switching valve 52, a switching control device 54 (neutral position detection circuit 55) provided in the hydraulic system of the present embodiment. The hydraulic signal transmission oil passage 56) is not provided, and the other configuration is the same as that of the hydraulic system of the present embodiment.

  First, the operation of the conventional hydraulic system shown in FIG. 3 will be described.

  In FIG. 3, when the operation lever devices of the plurality of first actuators 12, 13, 14 (travel motor 12, boom cylinder 13, bucket bucket 14) are not operated and all the operation lever devices are neutral, The flow rate / direction control valves 32, 33, 34 of the first valve device CV1 are in the neutral position I, the center bypass variable restrictors 32a, 33a, 34a are fully open, and the discharge oil of the first hydraulic pump P1 is flow rate / direction. It returns to the tank T through the center bypass variable restrictors 32a, 33a, 34a of the control valves 32, 33, 34 and the center bypass oil passage 45. When one of the operation lever devices is operated, the corresponding one of the flow rate / direction control valves 32, 33, 34 is switched to the operation position II or III, and the center bypass variable restrictor 32a, 33a, 34a is closed, for example. The discharged oil of the first hydraulic pump P1 is supplied from the flow rate / direction control valve 32, 33 or 34 to the corresponding one of the first actuators 12, 13, 14 (travel motor 12, boom cylinder 13, bucket cylinder 14), Corresponding ones of the first actuators 12, 13, 14 (travel motor 12, boom cylinder 13, bucket cylinder 14) are driven.

  Further, when none of the operation lever devices of the plurality of second actuators 15 and 16 (travel motor 15 and arm cylinder 16) are operated and all the operation lever devices are neutral, the flow rate of the second valve device CV2 The direction control valves 35 and 36 are in the neutral position I, the center bypass variable restrictors 35a and 36a are fully open, and the discharge oil of the second hydraulic pump P2 is the center bypass variable restrictor 35a of the flow and direction control valves 35 and 36. , 36a and the center bypass oil passage 46 to return to the tank T. When one of the operation lever devices is operated, the corresponding one of the flow rate / direction control valves 35, 36 is switched to the operation position II or III, and the center bypass variable restrictors 35a, 36a are closed, for example, and the second hydraulic pressure The oil discharged from the pump P2 is supplied from the flow rate / direction control valve 35 or 36 to the corresponding one of the second actuators 15 and 16 (travel motor 15 and arm cylinder 16), and the second actuators 15 and 16 (travel motor 15 and arm). The corresponding one of the cylinders 16) is driven.

  The same applies to the plurality of third actuators 17, 18, 19 (swing cylinder 17, swing motor 18, blade cylinder 19), and the operation lever devices 26, 27, 28 are not operated, and the operation lever devices 26, 27 are not operated. , 28 are neutral, the flow rate / direction control valves 37, 38, 39 of the third valve device CV3 are in the neutral position I, the center bypass variable restrictors 37a, 38a, 39a are fully open, The oil discharged from the three hydraulic pump P3 returns to the tank T via the center bypass variable restrictors 37a, 38a, 39a of the flow rate / direction control valves 37, 38, 39 and the center bypass oil passage 47. When one of the operation lever devices 26, 27, 28 is operated, the corresponding one of the flow rate / direction control valves 37, 38, 39 is switched to the operation position II or III, and the center bypass variable restrictors 37a, 38a, 39a is closed, for example, and the discharge oil of the third hydraulic pump P3 corresponds to the flow rate / direction control valves 37, 38, 39 to the third actuators 17, 18, 19 (swing cylinder 17, swing motor 18, blade cylinder 19). The corresponding ones of the third actuators 17, 18, 19 (swing cylinder 17, turning motor 18, blade cylinder 19) are driven.

  As an example of the operation of the actuator, the expansion / contraction operation of the blade cylinder 17 will be described.

  When the operation lever of the operation lever device 26 of the blade 305 is operated in the right direction in the figure, the command pilot pressure is guided to the flow rate / direction control valve 37, the flow rate / direction control valve 37 is pushed down, and the flow rate / direction control valve 37 is The position is switched from the neutral position I to the upper operating position II in the figure. As a result, the center bypass variable restrictor 37a of the flow rate / direction control valve 37 is closed, for example, and the discharge oil from the third hydraulic pump P3 passes through the oil cylinder 45 provided with the check valve 44 for preventing the backflow from the blade cylinder 17. When the pressure oil in the bottom chamber 17b of the blade cylinder 17 is discharged through the tank line 46 through the flow rate / direction control valve 37, the blade cylinder 17 contracts. On the contrary, when the operation lever of the operation lever device 26 is operated in the left direction in the figure, the command pilot pressure is guided to the flow / direction control valve 37 and the flow / direction control valve 37 is pushed up, and the flow / direction control valve 37 is The position is switched from the neutral position I to the lower operation position III in the figure. As a result, the center bypass variable restrictor 37a of the flow rate / direction control valve 37 is closed, for example, and the discharged oil from the third hydraulic pump P3 flows into the bottom chamber 17b of the blade cylinder 17 from the oil passage 45, and the blade cylinder When the pressure oil in the 17 rod chambers 17 a is discharged through the tank line 46 via the flow rate / direction control valve 37, the blade cylinder 17 extends.

  Incidentally, in the conventional hydraulic system shown in FIG. 3, the operating lever device 26 of the third actuators 17, 18, 19 (swing cylinder 17, turning motor 18, blade cylinder 19) driven by the oil discharged from the third hydraulic pump P3. , 27, 28 are not operated, and the flow rate / direction control valves 37, 38, 39 of the third valve device CV3 are not switched. The directional control valves 37, 38, 39 return to the tank T via the center bypass variable throttles 37 a, 38 a, 39 a and the center bypass oil passage 47.

  As described above, the center bypass oil passage 47 of the valve device CV3 is formed as an internal passage in the housing of the valve device CV3, and the center bypass variable restrictors 37a, 38a, 39a is formed as an internal passage through the spool of the flow rate / direction control valves 37, 38, 39. Therefore, when the oil discharged from the third hydraulic pump P3 returns to the tank T through the center bypass variable restrictors 37a, 38a, 39a and the center bypass oil passage 47 of the flow / direction control valves 37, 38, 39, the flow rate / Pressure loss of a non-negligible magnitude in the center bypass variable restrictors 37a, 38a, 39a and the center bypass oil passage 47 of the direction control valves 37, 38, 39 (hereinafter, neutral pressure loss of the flow rate / direction control valves 37, 38, 39 as appropriate) And the pressure is constantly reached in the third pressure oil supply oil passage 23 of the third hydraulic pump P3, and the power is wasted.

  On the other hand, there is excavation work as an example of work of a hydraulic excavator. This excavation work is normally performed by operating the front work machine 302 (boom 306, arm 307, bucket 308), and the actuator for operating the front work machine 302 is the boom cylinder 13, arm cylinder 16, bucket. Since it is the cylinder 14, the first hydraulic pump P1 and the second hydraulic pump P2 are used for excavation work, and the third hydraulic pump P3 is not used.

  However, the first hydraulic pump P1 and the second hydraulic pump P2 are provided with torque control devices 42, and the capacities of the first and second hydraulic pumps P1 and P2 are adjusted by the torque control device 42 to the first and second. The total absorption torque of not only the hydraulic pumps P1 and P2 but also the third hydraulic pump P3 is controlled so as not to exceed the maximum torque set by the spring 42d. Further, as described above, even when the operation lever device 26, 27, 28 is not operated, a neutral pressure loss having a magnitude that cannot be ignored occurs in the flow rate / direction control valves 37, 38, 39. The pressure is always in the third pressure oil supply oil passage 23 of the third hydraulic pump P3. For this reason, during excavation work, the capacity of the first and second hydraulic pumps P1 and P2 is controlled to be reduced by the discharge pressure of the third hydraulic pump P3, and the absorption torque, that is, the horsepower, of the first and second hydraulic pumps P1 and P2 is controlled. There is a problem that the work efficiency decreases.

  Next, the operation of the hydraulic system according to the present embodiment will be described.

  In FIG. 1, an operation lever device of a plurality of first actuators 12, 13, 14 (travel motor 12, boom cylinder 13, bucket cylinder 14) and a plurality of second actuators 15, 16 (travel motor 15, arm cylinder 16). The operations of the flow rate / direction control valves 32 to 36 and the actuators 12 to 16 when the operation lever device is operated are the same as those of the conventional hydraulic system.

  Further, the operation lever devices 26, 27, 28 of the plurality of third actuators 17, 18, 19 (swing cylinder 17, swing motor 18, blade cylinder 19) are not operated, and the operation lever devices 26, 27, 28 are not operated. When all are neutral, the flow / direction control valves 37, 38, 39 are also in the neutral position I, and the center bypass variable restrictors 37a, 38a, 39a of the flow / direction control valves 37, 38, 39 are fully opened, The signal oil passages 61a, 61b, 61c of the flow rate / direction control valves 37, 38, 39 are also fully opened. For this reason, the discharge oil of the pilot pump P4 supplied to the hydraulic signal generating oil passage 61 via the fixed throttle 62 flows into the tank T, and the hydraulic signal generating oil passage 61 is at the tank pressure (first hydraulic signal). . As a result, the bypass switching valve 52 is in the illustrated open position IV.

  Here, as described above, the center bypass variable restrictors 37a, 38a, 39a and the center bypass oil passage 47 of the flow rate / direction control valves 37, 38, 39 of the valve device CV3 and the center bypass oil passage 47 serve as internal passages in the housing of the valve device CV3. In contrast to this, the pressure oil supply oil passage 23 and the bypass oil passage 51 of the third hydraulic pump P3 are configured by pipes (hose). Therefore, the flow resistance of the center bypass oil passage 47 when the flow rate / direction control valves 37, 38, 39 are in the neutral position I and the flow resistance of the bypass oil passage 51 when the bypass switching valve 52 is in the open position IV are obtained. In comparison, since the flow resistance of the bypass oil passage 51 is smaller than the flow resistance of the center bypass oil passage 47, when the bypass switching valve 52 is in the illustrated open position IV, the discharge oil of the third hydraulic pump P3 Mostly passes through the bypass oil passage 51 and returns to the tank T via the bypass switching valve 52.

  One of the operation lever devices 26, 27, 28 of the plurality of third actuators 17, 18, 19 (swing cylinder 17, swing motor 18, blade cylinder 19), for example, the operation lever of the operation lever device 26 of the blade cylinder 17 Is operated to the right in the figure, the command pilot pressure is guided to the flow rate / direction control valve 37, the flow rate / direction control valve 37 is pushed down to switch from the neutral position I to the operating position II, and the flow rate / direction control valve 37 is operated. The center bypass variable restrictor 37a is closed, for example, and the signal oil passage 61a of the flow rate / direction control valve 37 is also closed. When the signal oil passage 61a is closed, a predetermined control pressure (second hydraulic signal) is generated in the hydraulic signal generation oil passage 61 by the discharge oil of the pilot pump P4 supplied to the hydraulic signal generation oil passage 61 via the fixed throttle 62. This control pressure passes through the hydraulic signal transmission oil passage 56 and is guided to the pressure receiving portion 52a of the bypass switching valve 52, and the bypass switching valve 52 is switched from the open position IV to the closed position V shown in the figure. 51 is closed. When the bypass oil passage 51 is closed, the discharge oil of the third hydraulic pump P3 passes through the third pressure oil supply oil passage 23 and is guided to the flow rate / direction control valve 37, and the blade is passed through the flow rate / direction control valve 37. It flows into the rod chamber 17a of the cylinder 17. The pressure oil in the bottom chamber 17 b of the blade cylinder 17 is discharged through the tank line 46 via the flow rate / direction control valve 37. As a result, the blade cylinder 17 contracts.

  Conversely, when the operation lever of the operation lever device 26 is operated in the left direction in the figure, the command pilot pressure is guided to the flow rate / direction control valve 37, and the flow rate / direction control valve 37 is pushed up from the neutral position I to the operating position III. The center bypass variable restrictor 37a of the flow / direction control valve 37 is closed, for example, and the signal oil passage 61a of the flow / direction control valve 37 is closed. When the signal oil passage 61a is closed, a predetermined control pressure (second hydraulic signal) is generated in the hydraulic signal generation oil passage 61 by the discharge oil of the pilot pump P4 supplied to the hydraulic signal generation oil passage 61 via the fixed throttle 62. This control pressure passes through the hydraulic signal transmission oil passage 56 and is guided to the pressure receiving portion 52a of the bypass switching valve 52, and the bypass switching valve 52 is switched from the open position IV to the closed position V shown in the figure. 51 is closed. When the bypass oil passage 51 is closed, the discharge oil of the third hydraulic pump P3 passes through the third pressure oil supply oil passage 23 and is guided to the flow rate / direction control valve 37, and the blade is passed through the flow rate / direction control valve 37. It flows into the bottom chamber 17b of the cylinder 17. Further, the pressure oil in the rod chamber 17 a of the blade cylinder 17 is discharged through the tank line 46 via the flow rate / direction control valve 37. As a result, the blade cylinder 17 extends.

  FIG. 4 is a diagram showing changes in the command pilot pressure and the discharge pressure of the third hydraulic pump P3 (pressure in the third pressure oil supply oil passage 23) in the above operation.

In FIG. 4, (1) is a command pilot pressure (middle stage), a discharge pressure (upper stage) of the third hydraulic pump P3, and an operation image of the construction machine (hydraulic excavator) when the operation lever of the operation lever device 26 is neutral. (Lower stage), (2) shows the command pilot pressure (middle stage), the discharge pressure (upper stage) of the third hydraulic pump P3 and the operation image of the construction machine (hydraulic excavator) when the operating lever of the operating lever device 26 is operated. (Bottom). When the operation lever of the operation lever device 26 is in the neutral state, in the conventional hydraulic system, all the discharge oil of the third hydraulic pump P3 passes through the flow rate / direction control valves 37 to 39 and circulates to the tank T. The discharge pressure of the third hydraulic pump P3 becomes P0 due to the neutral pressure loss of the flow rate / direction control valves 37 to 39. At this time, P0 is about 10 kgf / cm ^2, for example. On the other hand, in the hydraulic system of the present invention, the bypass switching valve 52 is in the open position IV shown in the figure, and most of the discharge oil of the third hydraulic pump P3 is a bypass circuit comprising the bypass oil passage 51 and the bypass switching valve 52. Since it passes through 53 and circulates to the tank T, the discharge pressure of the third hydraulic pump P3 becomes P1 lower than P0. At this time, P1 is about 3 kgf / cm ^2, for example.

As a result, the neutral pressure loss 10 kgf / cm ² of the flow rate / direction control valves 37 to 39 in the conventional hydraulic system is reduced to about 3 kgf / cm ² of the pressure loss of the bypass circuit 53, and the pressure loss (energy) is reduced by 70%. Become.

  FIG. 5 shows the case of FIG. 4 (1) in which the operating lever device 26 is neutral during excavation work, which is the work of driving the actuators 13, 14, 16 by the discharge oil of the first and second hydraulic pumps P1, P2. The maximum of the first and second hydraulic pumps P1 and P2 in the case of (2) in FIG. 4 (when the third hydraulic pump P3 is not used) and (2) in FIG. It is a figure which shows the change of the absorption torque (The maximum absorption torque of the 1st and 2nd hydraulic pumps P1 and P2 controlled by the torque control apparatus 42) in the hydraulic system of this invention, and the conventional hydraulic system.

  In FIG. 5, T00 is the maximum absorption torque of the first and second hydraulic pumps P1, P2 in the conventional hydraulic system when the operation lever device 26 is neutral (when the third hydraulic pump P3 is not used). T01 is the maximum absorption torque of the first and second hydraulic pumps P1, P2 in the hydraulic system of the present invention when the operation lever device 26 is in a neutral position (when the third hydraulic pump P3 is not used). T11 is the maximum absorption torque of the first and second hydraulic pumps P1, P2 in the conventional and the hydraulic systems of the present invention when the operation lever device 26 is operated (when the third hydraulic pump P3 is used).

  In both the conventional hydraulic system and the hydraulic system of the present invention, in the case of (2) in FIG. 4 where the operation lever device 26 is operated, the discharge pressure of the third hydraulic pump P3 is the load pressure of the third actuator 17 (blade cylinder 17). And the discharge pressure acts on the third torque control piston 42c of the torque control device 42 to operate the variable capacity member 41 in the capacity decreasing direction, so that the maximum of the first and second hydraulic pumps P1, P2 is increased. The absorption torque decreases to T1.

  On the other hand, in the case of (1) in FIG. 4 where the operation lever device 26 is neutral, the discharge pressure of the third hydraulic pump P3 is P0 (conventional) or P1 (present invention) as described above, and the operation lever device 26 is 4 is lower than the discharge pressure of the third hydraulic pump P3 in the case of FIG. 4 (2), the maximum absorption torque of the first and second hydraulic pumps P1 and P2 is T00 (conventional), T01 (present invention). In both the conventional and the hydraulic systems of the present invention, the operating lever device 26 is increased compared to T1 in the case of (2) in FIG.

In addition, in the conventional hydraulic system, all of the discharge oil of the third hydraulic pump P3 passes through the flow rate / direction control valves 37 to 39 and circulates to the tank T, so that the neutral pressure loss due to the neutral pressure loss of the flow rate / direction control valves 37 to 39 occurs. While the discharge pressure of the three hydraulic pump P3 is P0 (for example, about 10 kgf / cm ² ), in the hydraulic system of the present invention, the bypass switching valve 52 is at the open position IV shown in the figure, and the third hydraulic pump P3 Since most of the discharged oil passes through the bypass circuit 53 and circulates to the tank T, the discharge pressure of the third hydraulic pump P3 becomes P1 (for example, about 3 Kgf / cm ² ) lower than P0. Therefore, in the conventional hydraulic system, the maximum absorption torque of the first and second hydraulic pumps P1 and P2 was T00 in FIG. 5, but in the hydraulic system of the present invention, it becomes T01, and the first and second hydraulic pumps. The maximum absorption torque of the pumps P1 and P2 increases compared to T00 of the conventional hydraulic system.

  Thus, when the operating lever devices 26, 27, 28 of the plurality of actuators 17, 18, 19 driven by the discharge oil of the third hydraulic pump P3 are not operated and the actuators 17, 18, 19 are not operating. Because most of the discharge oil of the third hydraulic pump P3 is directly circulated to the tank via the bypass circuit 53, the discharge pressure of the third hydraulic pump P3 due to the neutral pressure loss of the flow rate / direction control valves 37, 38, 39 is reduced. The increase is suppressed, and the decrease in the absorption torque of the first and second hydraulic pumps can be suppressed.

  As described above, according to the present embodiment, the first to third hydraulic pumps P1, P2, and P3 are provided, and the pressure supplied to the actuators 12 to 19 from the first to third hydraulic pumps P1, P2, and P3. In a hydraulic system of a hydraulic excavator using an open center type valve for the flow rate / direction control valves 32 to 39 for controlling the flow of oil, a plurality of actuators 17, 18, 19 driven by discharged oil of the third hydraulic pump P 3 are used. When the operation lever device 26, 27, 28 is not operated, the increase in the discharge pressure of the third hydraulic pump P3 due to the neutral pressure loss of the flow rate / direction control valves 37, 38, 39 is kept low and consumed by the third hydraulic pump P3. Power can be reduced, and the fuel efficiency of the engine E can be improved.

  When the hydraulic system increases not only the discharge pressures of the first and second hydraulic pumps P1, P2 but also the discharge pressure of the third hydraulic pump P3, the first and second hydraulic pressures are increased. Even when the torque control device 42 that controls the total absorption torque of the first to third hydraulic pumps P1 and P2 so as not to exceed the preset maximum torque by reducing the capacity of the pumps P1 and P2 is provided. When operating the operation lever device of the actuators 12 to 16 driven by the oil discharged from the first and second hydraulic pumps P1 and P2, it is possible to suppress a decrease in the absorption torque of the first and second hydraulic pumps P1 and P2. The driving force of the actuators 12 to 16 can be increased and the working efficiency can be improved.

Furthermore, in this embodiment, since the hydraulic system is configured in a pure hydraulic manner including the switching control device 54 and the bypass circuit 53, the hydraulic system can be made inexpensive and highly reliable.
<Second Embodiment>
A second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a diagram illustrating a circuit configuration of a hydraulic system for a construction machine according to the second embodiment. In the figure, elements equivalent to those shown in FIG. The present embodiment shows another example of the neutral position detection circuit 55 of the switching control device.

  In FIG. 6, the hydraulic system according to the present embodiment includes a switching control device 54 </ b> A including a neutral position detection circuit 55 </ b> A and a hydraulic signal transmission oil passage 56.

  The neutral position detection circuit 55A is composed of a plurality of shuttle valves 71a to 71e connected to the tournament system. The shuttle valve 71a selects and outputs the high-pressure side of the command pilot pressure output by the two remote control valves 26a and 26b of the operation lever device 26, and the shuttle valve 71b is provided by the two remote control valves 27a and 27b of the operation lever device 27. The high pressure side of the command pilot pressure to be output is selected and output, and the shuttle valve 71c selects and outputs the high pressure side of the command pilot pressure output by the two remote control valves 28a and 28b of the operation lever device 28. 71d selects and outputs the high pressure side of the output pressure of the shuttle valve 71b and the output pressure of the shuttle valve 71c, and the shuttle valve 71e selects the high pressure side of the output pressure of the shuttle valve 71a and the output pressure of the shuttle valve 71d. Output. The output pressure of the shuttle valve 71 e is guided to the pressure receiving portion 52 a of the bypass switching valve 52 through the hydraulic signal transmission oil passage 56 as a hydraulic signal for switching the bypass switching valve 52.

  When none of the operation lever devices 26, 27, 28 are operated and all of the operation lever devices 26, 27, 28 are neutral, the command pilot pressures output by the respective remote control valves are tank pressures, and the neutral position The detection circuit 55A outputs the tank pressure as a first hydraulic pressure signal, and the first hydraulic pressure signal (tank pressure) is guided to the pressure receiving portion 52a of the bypass switching valve 52. For this reason, the bypass switching valve 52 is in the open position IV shown in the figure, and most of the discharge oil of the third hydraulic pump P3 passes through the bypass oil passage 51 and passes through the bypass switching valve 52 as in the first embodiment. Reflux to tank T.

  When one of the operating lever devices 26, 27, 28, for example, the operating lever of the operating lever device 26 of the blade cylinder 17 is operated rightward in the figure, the command pilot pressure output by the remote control valve 26a of the operating lever device 26 is displayed. Becomes a predetermined pressure corresponding to the operation amount higher than the tank pressure, and the neutral position detection circuit 55A outputs the command pilot pressure of the predetermined pressure as a control pressure (second hydraulic signal) to the pressure receiving portion 52a of the bypass switching valve 52. The control pressure (second hydraulic signal) is derived. For this reason, the bypass switching valve 52 is switched to the closed position V, and the bypass oil passage 51 is closed. As a result, the discharge oil of the third hydraulic pump P3 passes through the third pressure oil supply oil passage 23 and is guided to the flow rate / direction control valve 37, and then to the rod chamber 17a of the blade cylinder 17 via the flow rate / direction control valve 37. It flows in and the blade cylinder 17 contracts.

  Similarly, when the operation lever of the operation lever device 26 is operated in the left direction in the figure, the neutral position detection circuit 55A outputs a command pilot pressure of a predetermined pressure as a control pressure (second hydraulic signal), and the bypass switching valve 52 is Switched to the closed position V, the oil discharged from the three hydraulic pump P3 passes through the third pressure oil supply oil passage 23 and flows into the bottom chamber 17b of the blade cylinder 17 from the flow rate / direction control valve 37, and the blade cylinder 17 extends. .

  Therefore, also in the present embodiment, as in the first embodiment, when the operation lever devices 26, 27, 28 of the plurality of actuators 17, 18, 19 driven by the discharge oil of the third hydraulic pump P3 are not operated. The increase in the discharge pressure of the third hydraulic pump P3 due to the neutral pressure loss due to the flow rate / direction control valves 37, 38, 39 can be kept low, and the power consumed by the third hydraulic pump P3 can be reduced. The fuel efficiency of E can be improved, the decrease in the absorption torque of the first and second hydraulic pumps P1, P2 can be suppressed, the driving force of the actuators 12-16 can be increased, and the working efficiency can be improved. it can.

Further, since the hydraulic system is configured in a pure hydraulic manner including the switching control device 54A and the bypass circuit 53, the hydraulic system can be made inexpensive and highly reliable.
<Third Embodiment>
A third embodiment of the present invention will be described with reference to FIG. FIG. 7 is a diagram showing a circuit configuration of a hydraulic system for a construction machine according to the third embodiment. In the figure, elements equivalent to those shown in FIG. This embodiment shows an example in which an electrical device is interposed in the switching control device.

  In FIG. 7, the hydraulic system according to the present embodiment includes a switching control device 54B including a neutral position detection circuit 55B and a control device 73. The bypass switching valve 52B is an electromagnetic switching valve, and has a solenoid 52b electrically connected to the control device 73.

  The neutral position detection circuit 55B includes a plurality of shuttle valves 71a to 71e connected in a tournament manner similarly to the neutral position detection circuit 55A in the second embodiment, and further includes a pressure sensor 72. The pressure sensor 72 detects the output pressure of the neutral position detection circuit 55B, that is, the output pressure of the shuttle valve 71e at the last stage, and outputs a detection signal to the control device 73. When the detection signal of the pressure sensor 72 is a tank pressure, the control device 73 outputs an OFF electrical signal to the solenoid 52b of the electromagnetic switching valve 52B, and a command for a predetermined pressure at which the detection signal of the pressure sensor 72 is higher than the tank pressure. When the pilot pressure is applied, an ON electrical signal is output to the solenoid 52b of the electromagnetic switching valve 52B. The electromagnetic switching valve 52b is in the open position IV shown when the electric signal output from the control device 73 is OFF, and is switched to the closed position V when the electric signal output from the control device 73 is ON. It is done.

  In the present embodiment configured as described above, as in the first embodiment, the effect of reducing the power consumed by the third hydraulic pump P3 and the effects of the first and second hydraulic pumps P1 and P2 are reduced. An effect of suppressing a decrease in absorption torque can be obtained.

  The above embodiment can be variously modified within the spirit of the present invention. For example, although the case where the construction machine is a hydraulic excavator has been described in the above embodiment, the present invention may be applied to a construction machine other than the hydraulic excavator (for example, a hydraulic crane, a wheeled excavator, etc.). The same effect as the embodiment can be obtained.

E Engine P1 First hydraulic pump P2 Second hydraulic pump P3 Third hydraulic pump P4 Pilot pump CV1 First valve device CV2 Second valve device CV3 Third valve device 11 Pump devices 12, 13, 14 First actuators 15, 16 First 2 Actuators 17, 18, 19 Third actuator 21 First pressure oil supply oil path 22 Second pressure oil supply oil path 23 Third pressure oil supply oil path 24 Pilot pressure supply oil path 25 Pilot relief valves 26, 27, 28 Lever device 32, 33, 34 Flow / direction control valve 32a, 33a, 34a Center bypass variable restrictor 35, 36 Flow / direction control valve 35a, 36a Center bypass variable restrictor 37, 38, 39 Flow / direction control valve 37a, 38a, 39a Center bypass variable restrictor 41 Swash plate 42 Torque control device 42a First torque control pin Ton 42b Second torque control piston 42c Third torque control piston 42d Spring 45 First center bypass oil passage 46 Second center bypass oil passage 47 Third center bypass oil passage 51 Bypass oil passage 52 Bypass switching valve 52a Pressure receiving portion 53 Bypass circuit 54 Switching control device 55 Neutral position detection circuit 56 Hydraulic signal transmission oil passage 61 Hydraulic signal generation oil passages 61a, 61b, 61c Signal oil passages 71a to 71e Shuttle valve 72 Pressure sensor 73 Control device

Claims (3)

Engine,
Variable displacement first and second hydraulic pumps driven by the engine;
A fixed displacement third hydraulic pump driven by the engine;
A plurality of first actuators driven by pressure oil discharged from the first hydraulic pump;
A plurality of second actuators driven by pressure oil discharged from the second hydraulic pump;
A plurality of third actuators driven by pressure oil discharged from the third hydraulic pump;
A first valve device including a plurality of flow rate / direction control valves that respectively control the flow of pressure oil supplied from the first hydraulic pump to the plurality of first actuators;
A second valve device including a plurality of flow rate / direction control valves that respectively control the flow of pressure oil supplied from the second hydraulic pump to the plurality of second actuators;
A third valve device including a plurality of flow rate and direction control valves that respectively control the flow of pressure oil supplied from the third hydraulic pump to the plurality of third actuators;
A pilot pump driven by the engine;
Provided corresponding to the plurality of first to third actuators, and for switching operation of each of the plurality of flow rate / direction control valves of the first to third valve devices based on the discharge oil of the pilot pump. A plurality of operating lever devices that generate command pilot pressure;
The plurality of flow rate / direction control valves of the first to third valve devices are provided in the first to third valve devices, respectively, and the discharge oil of the first to third hydraulic pumps is guided upstream. It has a center bypass variable restrictor on the first to third center bypass oil passages connected to the first to third pressure oil supply oil passages and the downstream side connected to the tank, and the plurality of flow rate / direction control valves are: When in the neutral position, the center bypass variable restrictor is fully opened, and when the plurality of flow rate / direction control valves are respectively switched from the neutral position, the opening area of the center bypass variable restrictor is reduced. The oil discharged from the first to third hydraulic pumps guided through the first to third pressure oil supply oil passages can be supplied to the plurality of first to third actuators. Open center system valve In the construction machine hydraulic system is,
Branched from the third pressure oil supply oil passage through which the discharge oil of the third hydraulic pump is guided, the downstream side is disposed in the bypass oil passage connected to the tank and the bypass oil passage, and can be switched between the open position and the closed position A bypass circuit including a bypass switching valve,
When all of the plurality of flow rate / direction control valves of the third valve device are in the neutral position, the bypass switching valve is switched to the open position, and any of the plurality of flow rate / direction control valves is operated from the neutral position. A hydraulic system for construction machinery, comprising: a switching control device that switches the bypass switching valve to the closed position when switched to a position. Engine,
Variable displacement first and second hydraulic pumps driven by the engine;
A fixed displacement third hydraulic pump driven by the engine;
A plurality of first actuators driven by pressure oil discharged from the first hydraulic pump;
A plurality of second actuators driven by pressure oil discharged from the second hydraulic pump;
A plurality of third actuators driven by pressure oil discharged from the third hydraulic pump;
A first valve device including a plurality of flow rate / direction control valves that respectively control the flow of pressure oil supplied from the first hydraulic pump to the plurality of first actuators;
A second valve device including a plurality of flow rate / direction control valves that respectively control the flow of pressure oil supplied from the second hydraulic pump to the plurality of second actuators;
A third valve device including a plurality of flow rate and direction control valves that respectively control the flow of pressure oil supplied from the third hydraulic pump to the plurality of third actuators;
A pilot pump driven by the engine;
Provided corresponding to the plurality of first to third actuators, and for switching operation of each of the plurality of flow rate / direction control valves of the first to third valve devices based on the discharge oil of the pilot pump. A plurality of operating lever devices that generate command pilot pressure;
The plurality of flow rate / direction control valves of the first to third valve devices are provided in the first to third valve devices, respectively, and the discharge oil of the first to third hydraulic pumps is guided upstream. It has a center bypass variable restrictor on the first to third center bypass oil passages connected to the first to third pressure oil supply oil passages and the downstream side connected to the tank, and the plurality of flow rate / direction control valves are: When in the neutral position, the center bypass variable restrictor is fully opened, and when the plurality of flow rate / direction control valves are respectively switched from the neutral position, the opening area of the center bypass variable restrictor is reduced. The oil discharged from the first to third hydraulic pumps guided through the first to third pressure oil supply oil passages can be supplied to the plurality of first to third actuators. Open center system valve And when the discharge pressures of the first to third hydraulic pumps increase, the first and second hydraulic pumps so that the total absorption torque of the first to third hydraulic pumps does not exceed a preset maximum torque. In a hydraulic system for a construction machine equipped with a torque control device that controls the absorption torque of a hydraulic pump,
Branched from the third pressure oil supply oil passage through which the discharge oil of the third hydraulic pump is guided, the downstream side is disposed in the bypass oil passage connected to the tank and the bypass oil passage, and can be switched between the open position and the closed position A bypass circuit including a bypass switching valve,
When all of the plurality of flow rate / direction control valves of the third valve device are in the neutral position, the bypass switching valve is switched to the open position, and any of the plurality of flow rate / direction control valves is operated from the neutral position. A hydraulic system for construction machinery, comprising: a switching control device that switches the bypass switching valve to the closed position when switched to a position. The hydraulic system for a construction machine according to claim 1 or 2,
The switching control device includes:
When all of the plurality of flow rate / direction control valves of the third valve device are in the neutral position, the first hydraulic pressure signal is output, and any of the plurality of flow rate / direction control valves is switched from the neutral position to the operating position. A neutral position detection device that outputs a second hydraulic pressure signal when
A hydraulic signal transmission oil passage for guiding a hydraulic signal output from the neutral position detection device to the bypass switching valve;
The bypass switching valve has a pressure receiving portion connected to the hydraulic signal transmission oil passage,
The bypass switching valve is in the open position when the first hydraulic pressure signal is guided to the pressure receiving portion, and is switched to the closed position when the second hydraulic pressure signal is guided to the pressure receiving portion. And construction machinery hydraulic system.

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