阅读说明：本技术 建筑机械的液压回路及液压回路 (Hydraulic circuit of construction machine and hydraulic circuit ) 是由 小野纯弥 松山博志 荫山侃杜 岩崎仁 塚原七海 于 2020-03-06 设计创作，主要内容包括：本发明提供一种液压回路,建筑机械的液压回路使来自固定容量型泵的压力油与从可变容量型泵至油箱的中央旁通油路汇合而使致动器驱动,能够根据致动器的要求流量来控制从固定容量型泵向中央旁通油路流动的流量。分配用方向切换阀(64)具有：从固定容量型泵(62)至油箱(T)的第一油路(64a)、以及从固定容量型泵(62)至第一中央旁通油路(61c)的第二油路(64b),且该分配用方向切换阀(64)具有：使阀芯在形成第一油路(64a)的方向上滑动的第一信号接收部(641)、以及使阀芯在形成第二油路(64b)的方向上滑动的第二信号接收部(642),根据第一信号接收部(641)和第二信号接收部(642)接收到的信号的大小差异,来确定向第一油路(64a)和第二油路(64b)流动的压力油的分配率,第一信号接收部(641)接收基于负控制信号的信号。(The invention provides a hydraulic circuit for a construction machine, which enables a pressure oil from a fixed capacity type pump to be merged with a central bypass oil path from a variable capacity type pump to an oil tank to drive an actuator, and can control the flow rate flowing from the fixed capacity type pump to the central bypass oil path according to the required flow rate of the actuator. The direction switching valve (64) for distribution has: a first oil passage (64a) from the fixed displacement pump (62) to the tank (T), and a second oil passage (64b) from the fixed displacement pump (62) to the first center bypass oil passage (61c), wherein the distribution direction switching valve (64) includes: a first signal receiving section (641) for sliding the valve body in the direction of forming the first oil path (64a) and a second signal receiving section (642) for sliding the valve body in the direction of forming the second oil path (64b) determine the distribution ratio of the pressure oil flowing to the first oil path (64a) and the second oil path (64b) according to the difference in the magnitude of the signals received by the first signal receiving section (641) and the second signal receiving section (642), and the first signal receiving section (641) receives a signal based on a negative control signal.)

1. A hydraulic circuit for a construction machine, comprising: an engine; a variable displacement pump and a fixed displacement pump driven by the engine; a center bypass oil passage from the variable capacity pump to an oil tank; and a negative control throttle valve disposed at the most downstream side of the center bypass oil passage, the hydraulic pressure on the upstream side of the negative control throttle valve being monitored as a negative control signal, the variable displacement pump being controlled based on the negative control signal,

the hydraulic circuit of a construction machine is characterized in that,

the hydraulic circuit is provided with a direction switching valve, and the direction switching valve is provided with: a first oil passage from the fixed displacement pump to the tank and a second oil passage from the fixed displacement pump to the center bypass oil passage, the first oil passage and the second oil passage being formed by sliding of a spool,

the direction switching valve includes: a first signal receiving portion that receives a signal to slide the spool in a direction in which the first oil passage is formed; and a second signal receiving portion that receives a signal to slide the spool in a direction in which the second oil passage is formed, the first signal receiving portion receiving a signal based on the negative control signal, and determining a distribution ratio of the pressure oil flowing to the first oil passage and the second oil passage based on a difference in magnitude of the signals received by the first signal receiving portion and the second signal receiving portion.

2. The hydraulic circuit of a construction machine according to claim 1,

the hydraulic circuit is provided with: a center bypass oil passage different from the center bypass oil passage from the variable capacity pump to the oil tank,

the center bypass oil passage includes: a first travel motor; and a work machine actuator disposed downstream of the first travel motor,

the other center bypass oil passage has a second travel motor,

the second oil passage communicates with the center bypass oil passage between the first travel motor and the work machine actuator.

3. The hydraulic circuit of a construction machine according to claim 2,

the second signal receiving unit receives a signal based on a first monitor signal for monitoring driving of the work machine actuator and a second monitor signal for monitoring driving of the first travel motor or the second travel motor.

4. The hydraulic circuit of a construction machine according to claim 3,

the direction switching valve includes: a third oil passage that is formed when the second signal receiving portion receives a signal and that is from the fixed capacity type pump to an oil passage on an inlet throttle side of the work machine actuator.

5. A hydraulic circuit is characterized by comprising:

a variable displacement pump driven by an engine;

a fixed displacement pump driven by the engine;

a center bypass oil passage from the variable capacity pump to an oil tank;

a negative control throttle valve that is disposed in the center bypass oil passage, monitors an upstream hydraulic pressure as a negative control signal, and controls the variable displacement pump based on the negative control signal; and

and a direction switching valve having a first oil passage through which the pressure oil from the fixed displacement pump reaches the tank, and a second oil passage through which the pressure oil from the fixed displacement pump reaches the center bypass oil passage.

6. The hydraulic circuit of claim 5,

the negative control throttle valve is disposed at the most downstream of the center bypass oil passage.

7. The hydraulic circuit according to claim 5 or 6,

the directional control valve switches the pressure oil from the fixed displacement pump between the first oil passage and the second oil passage according to a position of the spool.

8. The hydraulic circuit of claim 7,

the direction switching valve includes: a first signal receiving portion that receives a signal to move the spool in a direction in which the first oil passage is formed; and a second signal receiving portion that receives a signal to move the spool in a direction in which the second oil passage is formed.

9. The hydraulic circuit of claim 8,

determining a distribution ratio of the pressure oil flowing to the first oil passage and the second oil passage according to a difference in magnitude of the signals received by the first signal receiving portion and the second signal receiving portion, the first signal receiving portion receiving a signal based on the negative control signal.

Technical Field

The present invention relates to a hydraulic circuit for a construction machine and a hydraulic circuit for a working vehicle such as a construction machine.

Background

Patent document 1 below discloses a technique of reducing a discharge flow rate of a pump and reducing a flow rate of a first neutral full open bypass by performing Negative control using a Negative control pressure on a low pressure side of a first Negative control pressure detected in a first neutral full open bypass and a second Negative control pressure detected in a second neutral full open bypass in a hydraulic circuit of a construction machine in which Negative control (hereinafter, also referred to as "Negative control") of a bypass-type variable displacement piston pump is performed, and when the first Negative control pressure is higher than the second Negative control pressure, discharging oil in an amount corresponding to a pressure difference between the first Negative control pressure and the second Negative control pressure from a first unloading valve provided upstream of the first neutral full open bypass, thereby reducing the discharge flow rate of the pump.

Patent document 2 below discloses a technique for suppressing the discharge amount of a fixed displacement hydraulic pump by providing a bypass selector valve forming a bypass oil passage to an oil tank upstream of a center bypass oil passage from the fixed displacement hydraulic pump to the oil tank, and switching the bypass selector valve to the bypass oil passage to the oil tank when the flow direction control valve provided in the center bypass oil passage is in the neutral state, in a hydraulic system of a construction machine in which a flow direction control valve for controlling the flow of pressurized oil supplied to an actuator from the variable displacement hydraulic pump and the fixed displacement hydraulic pump is provided with a valve of an open center (open center) type.

Documents of the prior art

Patent document

Patent document 1: international publication No. 2009/123047

Patent document 2: japanese patent laid-open publication No. 2012-112466

Disclosure of Invention

In the hydraulic circuit disclosed in patent document 1, in order to compensate for the insufficient amount of oil when performing a combined operation of the work implement actuator and the travel motor, if the center bypass passage is merged with the pressure oil of the fixed displacement hydraulic pump provided separately from the split flow type variable displacement piston pump, the flow rate flowing through the center bypass passage is designed to be as small as possible, and therefore, the split flow opening of the directional control valve provided in the center bypass passage is set to be small. Therefore, when the required flow rate of the work machine actuator is to be reduced in the combined operation, the pressure in the center bypass flow path abnormally rises, so that the energy loss increases, and in general, in a construction machine such as a hydraulic excavator, in order to prevent an engine stall, control is performed such that the pressure in the hydraulic circuit is input to the regulator of the variable displacement piston pump, and when the pressure in the hydraulic circuit rises, the discharge flow rate of the variable displacement piston pump is reduced.

The technique of patent document 2 can virtually control the discharge amount of the fixed displacement hydraulic pump, but cannot control the discharge amount in accordance with the required flow rate of the actuator.

In view of the above problems, an object of the present invention is to provide a hydraulic circuit for a construction machine, including: the pressure oil from the fixed displacement pump is joined to a center bypass oil passage from the variable displacement pump to the oil tank to drive the actuator, and the flow rate of the pressure oil flowing from the fixed displacement pump to the center bypass oil passage can be controlled in accordance with the required flow rate of the actuator.

The hydraulic circuit of a construction machine according to the present invention includes: an engine; a variable displacement pump and a fixed displacement pump driven by the engine; a center bypass oil passage from the variable capacity pump to an oil tank; and a negative control throttle valve disposed at the most downstream side of the center bypass oil passage, the hydraulic pressure on the upstream side of the negative control throttle valve being monitored as a negative control signal, the variable displacement pump being controlled based on the negative control signal,

in the hydraulic circuit of the construction machine,

the hydraulic circuit is provided with a direction switching valve, and the direction switching valve is provided with: a first oil passage from the fixed displacement pump to the tank and a second oil passage from the fixed displacement pump to the center bypass oil passage, the first oil passage and the second oil passage being formed by sliding of a spool,

the direction switching valve includes: the hydraulic pump includes a first signal receiving portion that receives a signal to slide the spool in a direction in which the first oil passage is formed, and a second signal receiving portion that receives a signal to slide the spool in a direction in which the second oil passage is formed, and the first signal receiving portion receives a signal based on the negative control signal, and determines the distribution ratio of the pressure oil flowing to the first oil passage and the second oil passage based on a difference in magnitude of the signals received by the first signal receiving portion and the second signal receiving portion.

According to the present invention, in a hydraulic circuit of a construction machine in which pressure oil from a fixed capacity pump and a center bypass oil passage from a negatively controlled variable capacity pump to a tank are merged and an actuator is driven, a part of the pressure oil flowing from the fixed capacity pump to the center bypass oil passage is returned to the tank based on the magnitude of a negative control signal generated by a negative control throttle valve downstream of the center bypass oil passage, whereby the flow rate flowing from the fixed capacity pump to the center bypass oil passage can be controlled in accordance with the required flow rate of the actuator.

Drawings

Fig. 1 is a perspective view showing a construction machine according to an embodiment of the present invention.

Fig. 2 is a diagram showing a hydraulic circuit of a construction machine according to an embodiment of the present invention.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[ Structure of construction machine ]

As shown in fig. 1, a construction machine 1 includes: a lower traveling structure 2; an upper revolving structure 3 provided above the lower traveling structure 2 so as to be able to revolve; a boom bracket 4 that is a swing body supported by the upper swing body 3 so as to be horizontally rotatable; and a working machine 5 supported by the boom bracket 4 so as to be vertically rotatable. The construction machine 1 is configured as an excavator (backhoe) with a boom swing function. In general, a boom swing function is provided in a small excavator which requires workability in a narrow place.

The lower traveling structure 2 is driven by power from the engine 31 to travel or turn the construction machine 1. The lower carrier 2 includes: a pair of left and right crawler belts 21, and a pair of left and right running motors 22, 22 for driving them (the right running motor 22 is not shown in fig. 1). The construction machine 1 can be moved forward or backward by driving the left and right crawler belts 21, 21 by the left and right traveling motors 22, 22 as hydraulic motors, respectively. The lower carrier 2 is provided with a blade 23 and a blade cylinder 24 as a hydraulic actuator for vertically rotating the blade 23.

The upper slewing body 3 is configured to: can perform a turning motion around an axis extending in the vertical direction at the center portion thereof. The upper revolving structure 3 is provided with an engine 31, a revolving motor 32, an operation portion 33, and the like. The control unit 33 is provided with a driver's seat, a control device, and the like.

Boom bracket 4 is attached to the tip end portion of upper revolving unit 3 via attachment portion 35. The boom bracket 4 is supported by the mounting portion 35 so as to be horizontally rotatable (i.e., so as to be swingable leftward and rightward). A swing cylinder 40 (not shown in fig. 1) that extends and contracts in the front-rear direction is provided between the upper revolving structure 3 and the boom bracket 4. The horizontal rotation of the boom bracket 4 operates in accordance with the expansion and contraction of the swing cylinder 40.

Work implement 5 is driven by receiving power from engine 31, and performs an excavation operation of earth and sand in accordance with an operation of operation unit 33. The work implement 5 is supported by the boom bracket 4 so as to be vertically rotatable. The boom bracket 4 is provided with a pivot pin 54 having an axis directed in the horizontal direction. The base end portion of the work implement 5 (a base end portion of a boom 51 described later) is supported by: the pivot pin 54 is vertically rotatable. Further, the working implement 5 can perform a swing operation in conjunction with the horizontal rotation of the boom bracket 4.

The working machine 5 includes: boom 51, arm 52, and bucket 53. The boom 51 is attached to the boom bracket 4 so as to be vertically rotatable. The boom 51 extends in the vertical direction from a base end portion supported by the boom bracket 4, and is bent so as to have a boomerang shape in a side view. A boom cylinder 51a that is movable in a telescopic manner is provided between the boom bracket 4 and the middle portion of the boom 51. The boom 51 rotates up and down with respect to the boom bracket 4 and operates in accordance with expansion and contraction of the boom cylinder 51 a.

The arm 52 is attached to the boom 51 so as to be vertically rotatable. A pivot pin 55 having an axis directed in the horizontal direction is provided at the distal end of the boom 51. The base end portion of the arm 52 is supported as: the pivot pin 55 is rotatable up and down (forward and backward). An arm cylinder 52a that is movable in a telescopic manner is provided between a middle portion of the boom 51 and a base end portion of the arm 52. The vertical rotation of the arm 52 with respect to the boom 51 is performed in accordance with the expansion and contraction of the arm cylinder 52 a.

Bucket 53 is attached to arm 52 so as to be rotatable up and down. A pivot pin 56 having an axis directed in the horizontal direction is provided at the tip end of the arm 52. The base end portion of the bucket 53 is supported as: the pivot pin 56 is rotatable up and down (forward and backward). Bucket link 57 is interposed between the tip end of arm 52 and bucket 53. The bucket link 57 is configured as a link that transmits a driving force to the bucket 53. A bucket cylinder 53a that is movable in an extendable and retractable manner is provided between the bucket link 57 and the base end portion of the arm 52. The vertical rotation of bucket 53 with respect to arm 52 operates in accordance with the extension and contraction of bucket cylinder 53 a.

The upper slewing body 3 is configured to: an engine 31, a battery, a fuel tank, and the like are placed on revolving frame 30, these components are covered with an engine cover 34, and a manipulation unit 33 is disposed at the front thereof. A hydraulic pump is connected to the engine 31, and the hydraulic pump is driven by the engine 31 to discharge hydraulic oil. The hydraulic oil discharged from the hydraulic pump is supplied to the boom cylinder 51a, the arm cylinder 52a, the bucket cylinder 53a, the travel motors 22, the blade cylinder 24, the swing motor 32, the swing cylinder 40, and the like via a hydraulic hose, a control unit, and the like.

[ construction of Hydraulic Circuit ]

The hydraulic circuit 6 included in the construction machine 1 will be described with reference to fig. 2. The hydraulic circuit 6 includes: first travel motor 22a and second travel motor 22b (either one of left travel motor 22 and right travel motor 22), first work implement actuator 50a and second work implement actuator 50b, third work implement actuator 50c (either one of boom cylinder 51a, arm cylinder 52a, and bucket cylinder 53 a), blade cylinder 24, swing motor 32, swing cylinder 40, variable displacement pump 61, fixed displacement pump 62, pilot pump (pilot pump)63, and distribution direction switching valve 64.

The variable displacement pump 61 and the fixed displacement pump 62 are driven by the engine 31 to discharge pressure oil supplied to the hydraulic actuators (the first work machine actuator 50a, the second work machine actuator 50b, the third work machine actuator 50c, the first travel motor 22a, the second travel motor 22b, the blade cylinder 24, the swing motor 32, and the swing cylinder 40). The variable displacement pump 61 supplies pressure oil to and drives the first work implement actuator 50a, the second work implement actuator 50b, the third work implement actuator 50c, the first travel motor 22a, and the second travel motor 22 b. The fixed displacement pump 62 supplies pressure oil to the squeegee cylinder 24, the swing motor 32, and the swing cylinder 40 to drive them.

The variable displacement pump 61 is capable of controlling the discharge flow rate of the pressure oil by changing the inclination angle of the movable swash plate 61b by driving the pump regulator 61 a. The pump regulator 61a is driven by a first negative control pressure or a second negative control pressure described later.

The variable displacement pump 61 is: a so-called bypass hydraulic pump having a first discharge port P1 and a second discharge port P2. The pressure oil discharged from the first discharge port P1 is supplied to a first traveling direction switching valve 65a, a first working machine direction switching valve 65c, and a second working machine direction switching valve 65d, which will be described later, via the first center bypass oil passage 61c, and the pressure oil discharged from the second discharge port P2 is supplied to a second traveling direction switching valve 65b and a third working machine direction switching valve 65e, which will be described later, via the second center bypass oil passage 61 d. The first center bypass oil passage 61c and the second center bypass oil passage 61d finally reach the tank T.

The pressure oil discharged from the fixed displacement pump 62 is supplied to a blade direction switching valve 65f, a turning direction switching valve 65g, and a swinging direction switching valve 65h, which will be described later, via a third center bypass oil passage 62 a.

A first negative control throttle valve 61e is provided at the most downstream of the first center bypass oil passage 61 c. The first negative control throttle valve 61e restricts the flow of the pressure oil flowing through the first center bypass oil passage 61c such that a first negative control pressure is generated upstream of the first negative control throttle valve 61 e. Similarly, a second negative control throttle 61f is provided at the most downstream side of the second center bypass oil passage 61 d. The second negative control throttle valve 61f restricts the flow of the pressure oil flowing through the second center bypass oil passage 61d such that the second negative control pressure is generated upstream of the second negative control throttle valve 61 f. The first negative control pressure or the second negative control pressure is set as a negative control signal, and the pump regulator 61a is driven based on the negative control signal, thereby controlling the discharge flow rate of the pressurized oil from the variable displacement pump 61. Specifically, the lower the first negative control pressure and the second negative control pressure, the larger the discharge flow rate of the variable displacement pump 61.

The hydraulic actuators (the first work machine actuator 50a, the second work machine actuator 50b, the third work machine actuator 50c, the first travel motor 22a, the second travel motor 22b, the blade cylinder 24, the swing motor 32, and the swing cylinder 40) are provided with corresponding direction switching valves 65, respectively. The direction switching valve 65 is: a pilot-operated directional control valve capable of switching the direction and the capacity of the pressure oil pumped from the variable displacement pump 61 and the fixed displacement pump 62 to the hydraulic actuator. The direction switching valve 65 can be switched between a plurality of positions by sliding the spool. When the pilot signal pressure is not applied to any of the 2 pilot ports of the direction switching valve 65, the direction switching valve 65 is held at the neutral position by the biasing force of the spring. When the direction switching valve 65 is in the neutral position, the pressure oil is not supplied to the corresponding hydraulic actuator. On the other hand, when the pilot signal pressure is applied to any of the pilot ports of the direction switching valve 65, the direction switching valve 65 is switched from the neutral position to another position, and the pressure oil is supplied to the corresponding hydraulic actuator.

In the present embodiment, the direction switching valve 65 includes: a first travel direction switching valve 65a corresponding to the first travel motor 22a, a second travel direction switching valve 65b corresponding to the second travel motor 22b, a first work machine direction switching valve 65c corresponding to the first work machine actuator 50a, a second work machine direction switching valve 65d corresponding to the second work machine actuator 50b, a third work machine direction switching valve 65e corresponding to the third work machine actuator 50c, a blade direction switching valve 65f corresponding to the blade cylinder 24, a turning direction switching valve 65g corresponding to the turning motor 32, and a turning direction switching valve 65h corresponding to the turning cylinder 40. These directional control valves are collectively referred to as control valves.

The pilot pump 63 discharges pilot oil as a command mainly input to the direction switching valve 65. However, in fig. 2, an oil passage from the pilot pump 63 to the direction switching valve 65 is not shown. The pilot pump 63 is driven by the engine 31, and discharges pressure oil so that a pilot signal pressure is generated in an oil passage.

An oil passage 63a connected to the pilot pump 63 branches into a work machine detection oil passage 63b and a travel detection oil passage 63 c. The working machine detection oil passage 63b is returned to the oil tank T by a third working machine detection direction switching valve 66e that operates in conjunction with the third working machine direction switching valve 65e, a second working machine detection direction switching valve 66d that operates in conjunction with the second working machine direction switching valve 65d, and a first working machine detection direction switching valve 66c that operates in conjunction with the first working machine direction switching valve 65 c. The travel detection oil passage 63c is returned to the tank T by a first travel detection direction switching valve 66a that operates in conjunction with the first travel direction switching valve 65a and a second travel detection direction switching valve 66b that operates in conjunction with the second travel direction switching valve 65 b.

The first work machine detection direction switching valve 66c is integrated with the first work machine direction switching valve 65c, and operates in conjunction with the first work machine direction switching valve 65 c. The first work machine detection directional control valve 66c can be switched between a plurality of positions by sliding the valve body. When the first working machine direction switching valve 65c is held at the neutral position, the first working machine detection direction switching valve 66c is also held at the neutral position. When the first working machine direction switching valve 65c is switched from the neutral position to another position, the first working machine detection direction switching valve 66c is also switched from the neutral position to another position in conjunction with this.

When the first work implement detection direction switching valve 66c is in the neutral position, the first work implement detection direction switching valve 66c does not block the work implement detection oil passage 63 b. Therefore, the pressure oil can be circulated through the work machine detection oil passage 63 b. On the other hand, when the first work machine detection direction switching valve 66c is at a position other than the neutral position, the first work machine detection direction switching valve 66c closes the work machine detection oil passage 63 b. That is, the first work implement detection direction switching valve 66c can be switched to a communication position for communicating the work implement detection oil passage 63b or a blocking position for blocking the work implement detection oil passage 63 b.

Similarly, the second and third work machine detection direction switching valves 66d and 66e can also be switched to a communication position at which the work machine detection oil passage 63b is communicated or a blocking position at which the work machine detection oil passage 63b is blocked. Similarly, the first and second travel detection direction switching valves 66a and 66b can be switched to a communication position for communicating the travel detection oil passage 63c and a blocking position for blocking the travel detection oil passage 63 c.

The working machine detection oil passage 63b branches into a first signal oil passage 63d at a position upstream of the third working machine detection direction switching valve 66 e. The first signal oil passage 63d is connected to a second signal receiving portion 642 of the distribution direction switching valve 64, which will be described later. By operating the work implement operation lever so that the first work implement detection direction switching valve 66c that is interlocked with the first work implement direction switching valve 65c, the second work implement detection direction switching valve 66d that is interlocked with the second work implement direction switching valve 65d, or the third work implement detection direction switching valve 66e that is interlocked with the third work implement direction switching valve 65e is changed from the neutral position to a position other than the neutral position, the work implement detection oil passage 63b is blocked and the first monitor pressure is generated in the work implement monitor 63h downstream of the first monitor pressure generation throttle 63 f. That is, the work implement monitoring unit 63h can monitor the driving of the first work implement actuator 50a, the second work implement actuator 50b, or the third work implement actuator 50c and output the first monitored pressure. The first monitor pressure is input as a first monitor signal to the second signal receiving unit 642 via the first signal oil passage 63 d.

Similarly, the travel detection oil passage 63c branches into a second signal oil passage 63e at a position upstream of the first travel detection direction switching valve 66 a. The second signal oil passage 63e is connected to a second signal receiving portion 642 of the distribution direction switching valve 64, which will be described later. By operating the travel lever so that the first travel direction switching valve 66a that is interlocked with the first travel direction switching valve 65a or the second travel direction switching valve 66b that is interlocked with the second travel direction switching valve 65b is changed from the neutral position to a position other than the neutral position, the travel detection oil passage 63c is blocked and the second monitor pressure is generated in the travel monitor unit 63i downstream of the second monitor pressure generation throttle valve 63 g. That is, the travel monitoring unit 63i can monitor the driving of the first travel motor 22a or the second travel motor 22b and output the second monitored pressure. The second monitor pressure is input as a second monitor signal to the second signal receiving unit 642 via the second signal oil passage 63 e.

The third center bypass oil passage 62a includes a distribution-purpose direction switching valve 64 on the downstream side of the swing-purpose direction switching valve 65 h. Downstream of the distribution directional control valve 64, there are provided: a first oil passage 64a connected to the tank T, a second oil passage 64b connected to the first center bypass oil passage 61c, and a third oil passage 64c connected to the first working machine direction switching valve 65c and the second working machine direction switching valve 65 d. Thus, the pressure oil flowing through the third center bypass oil passage 62a is supplied to the tank T, the first center bypass oil passage 61c, the first working machine direction switching valve 65c, or the second working machine direction switching valve 65d via the distribution direction switching valve 64.

The second oil passage 64b is connected to a first center bypass oil passage 61c between the first travel motor 22a and the first working implement actuator 50a, and more specifically, to a first center bypass oil passage 61c between the first travel direction switching valve 65a and the first working implement direction switching valve 65 c.

The third oil passage 64c is connected to a first meter-in oil passage 500a of the first working machine actuator 50a via a first working machine direction switching valve 65c, and is connected to a second meter-in oil passage 500b of the second working machine actuator 50b via a second working machine direction switching valve 65 d.

The distribution direction switching valve 64 can be switched to the position 64X, the position 64Y, or the position 64Z by sliding the spool. When the distribution direction switching valve 64 is at the position 64X shown in fig. 2, the third center bypass oil passage 62a and the first oil passage 64a communicate with each other. When the distribution direction switching valve 64 is at the position 64Y, the third center bypass oil passage 62a communicates with the second oil passage 64b and the third oil passage 64 c. When the distribution direction switching valve 64 is at the position 64Z, the third center bypass oil passage 62a communicates with the first oil passage 64a, the second oil passage 64b, and the third oil passage 64 c. Accordingly, the distribution direction switching valve 64 can be formed by sliding the spool: a first oil passage 64a from the fixed displacement pump 62 to the tank T, a second oil passage 64 from the fixed displacement pump 62 to the first center bypass oil passage 61c, and a third oil passage 64c from the fixed displacement pump 62 to the first meter-in oil passage 500a of the first working machine actuator 50a and the second meter-in oil passage 500b of the second working machine actuator 50 b.

The distribution direction switching valve 64 includes a first signal receiving unit 641 and a second signal receiving unit 642. The first signal receiving portion 641 receives a signal for sliding the spool in a direction in which the first oil passage 64a is formed, that is, in a direction for switching to the position 64X or the position 64Z. The second signal receiving portion 642 receives a signal for sliding the spool in a direction in which the second oil passage 64b is formed, that is, in a direction for switching to the position 64Y or the position 64Z.

The first signal oil passage 63d and the second signal oil passage 63e are connected to the second signal receiving portion 642. The second signal receiving unit 642 can receive a signal based on: a first monitoring signal that monitors driving of the first work machine actuator 50a, the second work machine actuator 50b, or the third work machine actuator 50 c; and a second monitoring signal for monitoring driving of the first travel motor 22a or the second travel motor 22 b. When the second signal receiving unit 642 receives the first monitor signal and the second monitor signal, that is, when the work implement actuators (the first work implement actuator 50a, the second work implement actuator 50b, and the third work implement actuator 50c) and the travel motors (the first travel motor 22a and the second travel motor 22b) are operated in combination, the distribution direction switching valve 64 is switched to the position 64Y or the position 64Z.

The first negative control pressure is input to the first signal receiving part 641. The first signal receiving part 641 can receive the first negative control pressure as the negative control signal. When the first signal receiving unit 641 receives a signal based on the negative control signal, the distribution direction switching valve 64 is switched to the position 64X or the position 64Z.

The distribution direction switching valve 64 switches to the position 64X, the position 64Y, or the position 64Z in accordance with a difference in magnitude between the negative control signal received by the first signal receiving unit 641 and the first monitor signal and the second monitor signal received by the second signal receiving unit 642.

For example, in the case of a complex operation in which the first work implement actuator 50a or the second work implement actuator 50b is operated relatively largely, the second signal receiving unit 642 receives the first monitor signal and the second monitor signal, and the distribution direction switching valve 64 is switched to the position 64Y because the first negative control pressure is low and the negative control signal received by the first signal receiving unit 641 is small. At this time, a second oil passage 64b is formed from the fixed displacement pump 62 to the first center bypass oil passage 61c, and a third oil passage 64c is formed from the fixed displacement pump 62 to the first meter-in oil passage 500a of the first working machine actuator 50a and the second meter-in oil passage 500b of the second working machine actuator 50 b. Therefore, a large amount of pressure oil can be supplied from the fixed displacement pump 62 to the first work machine actuator 50a and the second work machine actuator 50 b.

On the other hand, during the combined operation and when the first work implement actuator 50a or the second work implement actuator 50b is operated relatively small, the second signal receiving unit 642 receives the first monitor signal and the second monitor signal, and the distribution direction switching valve 64 is switched to the position 64X because the first negative control pressure is high and the negative control signal received by the first signal receiving unit 641 is large. At this time, a first oil passage 64a is formed from the fixed displacement pump 62 to the tank T. Therefore, the pressure oil from the fixed displacement pump 62 is not supplied to the first work machine actuator 50a or the second work machine actuator 50 b.

Further, during the combined operation, when the first work implement actuator 50a or the second work implement actuator 50b is operated to a medium level, the distributing direction switching valve 64 is switched to the position 64Z. At this time, a first oil passage 64a from the fixed displacement pump 62 to the tank T, a second oil passage 64b from the fixed displacement pump 62 to the first center bypass oil passage 61c, and a third oil passage 64c from the fixed displacement pump 62 to the first meter-in oil passage 500a of the first working machine actuator 50a and the second meter-in oil passage 500b of the second working machine actuator 50b are formed. Therefore, a part of the pressure oil from the fixed displacement pump 62 is returned to the tank T, and a part of the pressure oil is supplied to the first working machine actuator 50a and the second working machine actuator 50 b.

As described above, the hydraulic circuit 6 of the present embodiment includes: an engine 31; a variable displacement pump 61 and a fixed displacement pump 62 driven by the engine 31; a first center bypass oil passage 61c from the variable capacity pump 61 to the tank T; and a first negative control throttle valve 61e disposed most downstream of the first center bypass oil passage 61c, monitors a first negative control pressure on an upstream side of the first negative control throttle valve 61e as a negative control signal, controls the variable displacement pump 61 based on the negative control signal,

in the hydraulic circuit 6 of the construction machine 1,

the hydraulic circuit 6 includes a distribution directional control valve 64, and the distribution directional control valve 64 includes: a first oil passage 64a from the fixed displacement pump 62 to the tank T; and a second oil passage 64b from the fixed displacement pump 62 to the first center bypass oil passage 61c, and the first oil passage 64a and the second oil passage 64b are formed by sliding of the spool,

the distribution direction switching valve 64 includes: the first signal receiving portion 641 that receives a signal for sliding the spool in the direction in which the first oil passage 64a is formed and the second signal receiving portion 642 that receives a signal for sliding the spool in the direction in which the second oil passage 64b is formed determine the distribution ratio of the pressure oil flowing to the first oil passage 64a and the second oil passage 64b based on the difference in magnitude of the signals received by the first signal receiving portion 641 and the second signal receiving portion 642, and the first signal receiving portion 641 receives a signal based on the negative control signal.

According to this configuration, in the hydraulic circuit 6 of the construction machine 1 in which the hydraulic oil from the fixed capacity pump 62 is joined to the first center bypass oil passage 61c from the negatively controlled variable capacity pump 61 to the tank T to drive the working machine actuator, the flow rate flowing from the fixed capacity pump 62 to the first center bypass oil passage 61c can be controlled in accordance with the flow rate requested by the working machine actuator by returning a part of the hydraulic oil flowing from the fixed capacity pump 62 to the first center bypass oil passage 61c to the tank T based on the magnitude of the negative control signal generated by the first negative control throttle 61e downstream of the first center bypass oil passage 61 c.

In addition, the present embodiment includes: a second center bypass oil passage 61d which is different from the first center bypass oil passage 61c from the variable capacity pump 61 to the tank T,

the first center bypass oil passage 61c has: a first travel motor 22 a; and a first work machine actuator 50a and a second work machine actuator 50b disposed downstream of the first travel motor 22a,

the second center bypass oil passage 61d has the second travel motor 22b,

the second oil passage 64b communicates with the first center bypass oil passage 61c between the first travel motor 22a and the first and second work implement actuators 50a and 50 b.

According to this configuration, the first travel motor 22a and the first and second work implement actuators 50a and 50b are disposed upstream of the first center bypass oil passage 61c, and the pressure oil from the fixed capacity pump 62 is merged between the first travel motor 22a and the first and second work implement actuators 50a and 50b, so that the pressure oil from the fixed capacity pump 62 flowing into the first center bypass oil passage 61c is not consumed by the first travel motor 22 a. Therefore, the negative control signal detected from the first center bypass oil passage 61c becomes the required flow rate of the first work implement actuator 50a and the second work implement actuator 50b, and therefore the flow rate of the fluid flowing from the fixed capacity pump 62 to the first center bypass oil passage 61c can be controlled in accordance with the required flow rate of the first work implement actuator 50a and the second work implement actuator 50 b.

In the present embodiment, second signal receiving unit 642 receives a signal based on a first monitor signal for monitoring driving of first work implement actuator 50a, second work implement actuator 50b, or third work implement actuator 50c, and a second monitor signal for monitoring driving of first travel motor 22a or second travel motor 22 b.

When the first work implement actuator 50a, the second work implement actuator 50b, or the third work implement actuator 50c (work implement actuator), and the first travel motor 22a or the second travel motor 22b (travel motor) are subjected to combined operation, the pressure oil from the fixed displacement pump 62, the pump flow rate of which cannot be controlled, is merged with the first center bypass oil passage 61c extending from the variable displacement pump 61, the negative control of which is provided with the work machine actuator, and the circuit is designed so as to satisfy the flow rate required by the work machine actuator during a large operation, even in this case, according to the above configuration, a part of the pressure oil flowing from the fixed displacement pump 62 to the first center bypass oil passage 61c is returned to the tank T based on the magnitude of the negative control signal monitored by the first negative control throttle 61e downstream of the first center bypass oil passage 61c, whereby the required flow rate of the work machine actuator during a small operation can be satisfied.

In the present embodiment, the distribution direction switching valve 64 includes: the first meter-in oil passage 500a from the fixed capacity pump 62 to the first work machine actuator 50a and the third oil passage 64c from the fixed capacity pump 62 to the second meter-in oil passage 500b of the second work machine actuator 50b are formed when the second signal receiving portion 642 receives the signal.

According to this configuration, the pressure oil from the fixed-capacity pump 62 is joined to the meter-in oil passage of the work implement actuator, and the pressure oil from the fixed-capacity pump 62 is directly sent to the work implement actuator, whereby the operation of the work implement actuator can be ensured when the work implement actuator and the travel motor are subjected to combined operation.

The hydraulic circuit 6 of the present embodiment includes: a variable displacement pump 61, the variable displacement pump 61 being driven by the engine 31; a fixed displacement pump 62, the fixed displacement pump 62 being driven by the engine 31; a first center bypass oil passage 61c from the variable capacity pump 61 to the tank T; a first negative control throttle valve 61e disposed in the first center bypass oil passage 61c, monitoring a first negative control pressure on the upstream side as a negative control signal, and controlling the variable displacement pump 61 based on the negative control signal; and a distribution directional control valve 64, the distribution directional control valve 64 having a first oil passage 64a through which the pressurized oil from the fixed displacement pump 62 reaches the tank T, and a second oil passage 64b through which the pressurized oil from the fixed displacement pump 62 reaches the first center bypass oil passage 61 c.

In the present embodiment, the first negative control throttle 61e is disposed at the most downstream side of the first center bypass oil passage 61 c.

In the present embodiment, the distribution direction switching valve 64 switches the pressure oil from the fixed displacement pump 62 between the first oil passage 64a and the second oil passage 64b in accordance with the position of the spool.

In the present embodiment, the distribution direction switching valve 64 includes: a first signal receiving portion 641 that receives a signal to move the spool in a direction in which the first oil passage 64a is formed; and a second signal receiving portion 642 that receives a signal to move the spool in a direction in which the second oil passage 64b is formed.

In the present embodiment, the distribution ratio of the pressure oil flowing through the first oil passage 64a and the second oil passage 64b is determined based on the difference in magnitude between the signals received by the first signal receiving unit 641 and the second signal receiving unit 642, and the first signal receiving unit 641 receives a signal based on the negative control signal.

[ other embodiments ]

In the above-described embodiment, the variable displacement pump is a split type variable displacement pump 61 including the first discharge port P1 and the second discharge port P2, but the present invention is not limited thereto. For example, the variable displacement pump may be a tandem type variable displacement pump including a first variable displacement pump having a first discharge port P1 and a second variable displacement pump having a second discharge port P2. In the tandem variable displacement pump, the discharge flow rates of the 2 variable displacement pumps may be controlled by one pump regulator, or may be controlled by the respective pump regulators.

Although the hydraulic circuit 6 provided in the construction machine 1 has been described in the above embodiment, the hydraulic circuit according to the present invention may be applied to a work vehicle or the like other than the construction machine.

Although the embodiments of the present invention have been described above with reference to the drawings, the specific configurations should not be construed as being limited to these embodiments. The scope of the present invention is shown not only by the description of the above embodiments but also by the claims, and includes all modifications equivalent in meaning and scope to the claims.

Description of the reference numerals

1 construction machine

2 lower traveling body

3 upper slewing body

5 working machine

6 hydraulic circuit

22a first traveling motor

22b second traveling motor

50a first work machine actuator

50b second work machine actuator

50c third work machine actuator

31 engine

61 variable displacement pump

61c first center bypass oil passage

61d second center bypass oil passage

61e first negative control throttle valve

62 fixed displacement pump

62a third center bypass oil passage

64 distribution directional control valve

64a first oil path

64b second oil path

64c third oil path

641 first signal receiving part

642 second signal receiving part

T-shaped oil tank