Hydraulic drive unit of construction machine

Abstract

To secure favorable workability by preventing the abrupt deceleration of a traveling speed irrespective of an engine rotation number, and also preventing an operation of a front working machine from becoming sluggish at a start of a traveling / front complex operation.SOLUTION: A hydraulic drive unit of a construction machine comprises a traveling communication valve 30 in which a first flow passage Oa for introducing oil discharged from a second hydraulic pump P3 to a center bypass passage CB3 of a second valve group V2, and a second flow passage Ob for introducing the oil discharged from the second hydraulic pump P3 to a plurality of front direction changeover valves 7, 10 and 11 of a first valve group V1 are formed. When the traveling communication valve 30 is not in a traveling / front complex operation, the traveling communication valve takes a first position in which the first flow passage Oa is fully opened, and the second flow passage Pb is fully closed, and when the traveling / front complex operation is started, the traveling communication valve takes a second position in which the first flow passage Oa is throttled, and an opening area of the second flow passage Ob is set larger than an opening area of the first flow passage Oa. The second position is changed according to a rotation number of an engine 1, and the opening area of the first flow passage Oa is set small following the lowering of the rotation number of the engine 1.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a hydraulic drive system for construction machinery such as a hydraulic excavator, and in particular to a hydraulic drive system for construction machinery that has multiple hydraulic pumps driven by a prime mover and drives multiple actuators with pressurized oil discharged from the multiple hydraulic pumps. [Background technology]

[0002] For example, Patent Document 1 describes a hydraulic drive system for construction machinery such as a hydraulic excavator, which drives multiple actuators with pressurized oil discharged from three hydraulic pumps (hereinafter referred to as pumps P1, P2, and P3).

[0003] In the hydraulic drive system described in Patent Document 1, pump P1 is connected to the travel motor (right or left) and a part of the first actuator other than the travel motor (e.g., boom cylinder, bucket cylinder) via an open center type directional control valve of a first valve group, and pump P2 is connected to the travel motor (left or right) and a part of the second actuator other than the travel motor (e.g., arm cylinder) via an open center type directional control valve of a second valve group. The directional control valves of the right and left travel motors are both located at the most upstream position so as to preferentially supply the discharge oil of pumps P1 and P2 to the right and left travel motors.

[0004] The pump P3 is connected to the remaining third actuators other than the traveling motor (e.g., swing motor, swing cylinder, blade cylinder) via an open center type directional control valve of the third valve group, and a traveling communication valve is arranged upstream of these directional control valves. The traveling communication valve drives the front work equipment (boom, arm, bucket) while traveling, and when the traveling / front combined operation starts, it switches from the normal position to the operating position, blocking the communication passage between the pump P3 formed in the traveling communication valve and the center bypass passage of the third valve group, so that the entire amount of oil discharged from the pump P3 can be supplied to the boom cylinder, arm cylinder, and bucket cylinder, thereby preventing the operation of the front work equipment from slowing down and ensuring good workability.

[0005] Patent Document 2 describes a hydraulic drive device that includes two hydraulic pumps (hereinafter referred to as pumps P1 and P2) and drives a plurality of actuators with pressure oil discharged from the two hydraulic pumps.

[0006] In the hydraulic drive system described in Patent Document 2, pump P1 is connected to the right travel motor and the first work actuators (boom cylinder and bucket cylinder) via an open center type directional control valve of the first valve group, and pump P2 is connected to the left travel motor and the second work actuators (arm cylinder and swing motor) via an open center type directional control valve of the second valve group. The directional control valves of the right and left travel motors are both located at the most upstream positions within the first and second valve groups so that the discharge oil of pumps P1 and P2 is preferentially supplied.

[0007] In addition, a straight-line travel valve is disposed between pumps P1, P2 and the first valve group, and this straight-line travel valve is in a neutral position when travelling operations and front work equipment operations are performed separately, connecting the pressurized oil supply path of pump P1 to the first valve group and blocking communication between pump P2 and the first valve group, so that the discharge oil of pump P1 is supplied to the first valve group and the pressurized oil of pump P2 is supplied to the second valve group.

[0008] In addition, when the front work implement is driven while traveling and the combined traveling operation is started, the straight traveling valve switches to an intermediate position or a straight traveling position depending on the engine speed at that time, preventing a sudden deceleration of traveling when the combined traveling operation starts and preventing the operation of the front work implement from becoming sluggish during the combined traveling operation.

[0009] More specifically, when the combined traveling operation is started while traveling, if the engine speed is equal to or higher than the set speed, the straight traveling valve switches from the neutral position to an intermediate position, and in this intermediate position, pump P2 is connected to the first valve group, pump P1 is connected to the directional control valve for work of the second valve group, and pump P1 is also connected to the first valve group via a communication passage (throttle) in the straight traveling valve, so that a portion of the discharge oil of pump P1 can also be supplied to the directional control valve for right traveling of the first valve group, thereby preventing sudden deceleration of traveling when the combined traveling operation is started.

[0010] In addition, when the combined traveling operation is started when the engine speed is a relatively low speed below the set speed, the straight traveling valve switches from the neutral position to the straight traveling position, pump P2 is connected to the first valve group, the communication passage (throttle) in the straight traveling valve is closed to block communication between pump P1 and the first valve group, and pump P1 is connected only to the work directional control valve of the second valve group so that the entire amount of oil discharged from pump P1 can be supplied to the work directional control valve of the second valve group, thereby preventing the operation of the front work equipment from becoming sluggish when the combined traveling operation is started. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2005-291217 A [Patent Document 2] Patent No. 4380643 Summary of the Invention [Problem to be solved by the invention]

[0012] Hydraulic drive systems for construction machinery such as hydraulic excavators are generally equipped with a torque control regulator that performs torque limit control by reducing the capacity of the hydraulic pump as the discharge pressure rises when the discharge pressure of the hydraulic pump exceeds a predetermined value. This torque limit control suppresses overload on the prime mover (engine) that drives the hydraulic pump, preventing engine stall.

[0013] Although not mentioned in Patent Documents 1 and 2, it is essential that such a torque control regulator be installed in an actual machine equipped with the hydraulic drive system described in Patent Documents 1 and 2, and in that case, the following problems arise.

[0014] In the hydraulic drive system described in Patent Document 1, when the front work machine is driven during traveling to start the combined traveling / front operation and the travel connecting valve is switched from the normal position to the operating position, the travel connecting valve blocks the communication passage between the pump P3 and the center bypass passage in the third valve group, so that the entire amount of oil discharged from the pump P3 can be supplied to the boom cylinder, the arm cylinder, and the bucket cylinder, thereby preventing the operation of the front work machine from becoming sluggish. However, if the communication passage between the pump P3 of the travel connecting valve and the center bypass passage of the third valve group is blocked, the discharge pressure of the pump P3 rises suddenly when the travel connecting valve is switched, generating a surge pressure. This surge pressure of the pump P3 is led to the torque control regulator, and the discharge flow rate of the pumps P1 and P2 is suddenly reduced by the torque limit control, which causes the travel speed to suddenly decrease at the start of the combined traveling / front operation, deteriorating the workability.

[0015] In the hydraulic drive system described in Patent Document 2, when the front work machine is driven during traveling and a combined traveling / front operation is started, if the engine speed is a low speed below the set speed, the straight traveling valve switches to the straight traveling position, closing the communication passage (throttle) in the straight traveling valve for pump P1 to cut off communication between pump P1 and the first valve group. Therefore, as in Patent Document 1, surge pressure is generated in pump P1 when the straight traveling valve switches, and the discharge flow rate of pumps P1 and P2 is reduced by torque limit control, so that the traveling speed drops sharply at the start of the combined traveling / front operation, deteriorating workability.

[0016] The object of the present invention is to provide a hydraulic drive system for construction machinery which prevents a sudden deceleration in the traveling speed due to torque limiting control of the hydraulic pump when starting a combined traveling / front working operation to drive the front working equipment while traveling, regardless of the engine speed, and which prevents the operation of the front working equipment from becoming sluggish, thereby ensuring good workability. [Means for solving the problem]

[0017] In order to achieve the above object, the present invention provides a hydraulic system comprising a prime mover, a variable displacement first pump device and a fixed displacement second pump device driven by the prime mover, a plurality of actuators driven by pressure oil discharged from the first and second pump devices, and a plurality of open center type directional control valves for controlling the flow of pressure oil supplied from the first and second pump devices to the plurality of actuators, the plurality of actuators including a travel motor driven by the pressure oil discharged from the first pump device and driving a lower travel body, a front cylinder driven by the pressure oil discharged from the first pump device and driving a front work machine, and actuators other than the travel motor and the front cylinder driven by the pressure oil discharged from the second pump device, the plurality of directional control valves including a first directional control valve for controlling the flow of pressure oil supplied from the first pump device to the travel motor, a second directional control valve for controlling the flow of pressure oil supplied from the first pump device to the front cylinder, and a plurality of directional control valves for controlling the flow of pressure oil supplied from the second pump device to the actuators other than the travel motor and the front cylinder. and a third direction switching valve for controlling the flow of pressure oil supplied to the first pump, the first direction switching valve and the second direction switching valve constituting a first valve group, and the third direction switching valve constituting a second valve group, and when an average discharge pressure of the first pump device and the second pump device exceeds a predetermined value, the capacity of the first pump is reduced as the average discharge pressure increases. A hydraulic drive device for a construction machine is provided with a travel communicating valve having a first flow path, an inlet port of which is connected to the pressure oil supply path of the second pump device and an outlet port of which is connected to a center bypass passage of the second valve group, and a second flow path, an inlet port of which is connected to the pressure oil supply path of the second pump device and an outlet port of which is connected to a bypass passage connected to the second direction switching valve of the first valve group, the travel communicating valve being in a first position where the first flow path is fully opened and the second flow path is fully closed when the travel / front combined operation in which the travel motor and the front cylinder are simultaneously driven is not being performed, andand a second position that narrows the first flow path and makes the opening area of ​​the second flow path larger than the opening area of ​​the first flow path, and the second position of the traveling connecting valve is set so that the opening area of ​​the first flow path becomes smaller as the rotation speed of the prime mover decreases. Effect of the Invention

[0018] According to the present invention, when the combined traveling / front operation of driving the front work implement while traveling begins, a sudden deceleration of the traveling speed due to the torque limiting control of the first pump device is prevented regardless of the engine speed, and the operation of the front work implement does not become sluggish, ensuring good workability. [Brief description of the drawings]

[0019] [Figure 1] 1 is a diagram showing the appearance of a hydraulic excavator, which is a representative example of a construction machine according to the present invention. [Diagram 2] 1 is a diagram showing a hydraulic drive system for a construction machine according to an embodiment of the present invention. [Diagram 3] 3 is an enlarged view of a portion of the travel connecting valve shown in FIG. 2. [Figure 4] FIG. 13 is a diagram showing torque characteristics of torque limiting control by a regulator of the first pump unit. [Diagram 5] 5 is a diagram showing the relationship (output characteristics) between the engine speed and a second signal pressure which is an output pressure of a speed detection valve. FIG. [Figure 6] 5 is a diagram showing the relationship (opening area characteristic) between the spool stroke of the travel connection valve and the opening areas of the first flow passage and the second flow passage of the travel connection valve. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0021] <Construction machinery> First, the present invention will be described using a hydraulic excavator as an example of a construction machine.

[0022] FIG. 1 is a diagram showing the external appearance of a hydraulic excavator.

[0023] 1, a hydraulic excavator, which is well known as a construction machine, has a lower running body 300, an upper rotating body 301 rotatably mounted on the lower running body 300, and a front working machine 302 attached to the front of the upper rotating body 301 so as to be able to tilt up and down. A blade 304 is attached to the front of the central frame of the lower running body 300, and a swing post 303 is attached to the front of the upper rotating body 301, and the front working machine 302 is attached to this swing post 303 so as to be able to move up and down. The front working machine 302 is composed of a boom 306, an arm 307, and a bucket 308.

[0024] The upper rotating body 301 can rotate relative to the lower running body 300 by the rotation of the swing motor 13. The swing post 303 can rotate horizontally relative to the upper rotating body 301 by the extension and retraction of the swing cylinder 14 (see Figure 2), and the boom 306, arm 307 and bucket 308 of the front working machine 302 can rotate vertically by the extension and retraction of the boom cylinder 18, arm cylinder 15 and bucket cylinder 19, respectively. The lower running body 300 travels by driving the right and left tracks 310, 311 by the rotation of the right and left running motors 16, 17. The blade 304 moves up and down relative to the central frame of the lower running body 300 by the extension and retraction of the blade cylinder 12. The hydraulic excavator shown in the figure is a small hydraulic excavator such as a mini-excavator, and in particular, a mini-excavator with a body specification called an ultra-small swing machine or a rear small swing machine. An ultra-small swing machine is defined as a mini-excavator with a body specification in which no part of the upper rotating body 301 protrudes beyond the vehicle width of the right and left tracks 310, 311 when the upper rotating body 301 rotates, and a rear small swing machine is defined as a mini-excavator with a body specification in which the rear part of the upper rotating body 301 does not protrude beyond the vehicle width of the right and left tracks 310, 311 when the upper rotating body 301 rotates.

[0025] <Hydraulic drive unit> ~Overall composition~ FIG. 2 is a diagram showing a hydraulic drive system for a construction machine in one embodiment of the present invention.

[0026] In Figure 2, the hydraulic drive system of this embodiment comprises a prime mover (e.g., a diesel engine, hereinafter referred to as the engine) 1, a variable displacement first pump unit 101 driven by the engine 1, a fixed displacement second pump unit 102 and a pilot pump 103, the above-mentioned multiple actuators 12-19 driven by pressurized oil discharged from the first and second pump units 101, 102 and driving the lower running body 300, the upper rotating body 301, the front work machine 302, and the blade 304 and swing post 303 (and other driven bodies), and multiple open center type directional control valves 3-5, 7-11 which control the flow of pressurized oil supplied from the first and second pump units 101, 102 to the multiple actuators 12-19.

[0027] As shown in FIG. 1, actuator 12 is a blade cylinder, actuator 13 is a rotation motor, actuator 14 is a swing cylinder, actuators 15 and 17 are right and left travel motors, actuator 16 is an arm cylinder, actuator 18 is a boom cylinder, and actuator 19 is a bucket cylinder.

[0028] The right and left travel motors 16, 17, arm cylinder 15, boom cylinder 18 and bucket cylinder 19 are driven by pressurized oil discharged from a first pump unit 101, and the rotation motor 13, swing cylinder 14 and blade cylinder 12 are driven by pressurized oil discharged from a second pump unit 102. Hereinafter, the arm cylinder 15, boom cylinder 18 and bucket cylinder 19 may be referred to as front cylinders.

[0029] The multiple directional control valves 3-5, 7-11 include right and left traveling directional control valves 8, 9 (first directional control valves) that control the flow of pressurized oil supplied from the first pump device 101 to the right and left traveling motors 16, 17, and multiple front directional control valves 7, 10, 11 (second directional control valves) that control the flow of pressurized oil supplied from the first pump device 101 to the multiple front cylinders 15, 18, 19, and a slewing directional control valve 4, a swing directional control valve 5, and a blade directional control valve 3 (third directional control valve) that control the flow of pressurized oil supplied from the second pump device 102 to the slewing motor 13, the swing cylinder 14, and the blade cylinder 12, and the right and left traveling directional control valves 8, 9 and the multiple front directional control valves 7, 10, 11 constitute a first valve group V1, and the slewing directional control valve 4, the swing directional control valve 5, and the blade directional control valve 3 constitute a second valve group V2.

[0030] The front directional control valves 7, 10, 11 are the arm directional control valve 7, the boom directional control valve 10, and the bucket directional control valve 11, which control the flow of pressurized oil supplied to the arm cylinder 15, the boom cylinder 18, and the bucket cylinder 19, respectively.

[0031] As described below, the first valve group V1 is composed of a first sub-valve group V1-1 including a directional control valve 9 for left traveling, a directional control valve 10 for the boom, and a directional control valve 11 for the bucket, and a second sub-valve group V1-2 including a directional control valve 7 for the arm and a directional control valve 8 for right traveling.

[0032] In this embodiment, the first pump device 101 is a variable displacement split flow type hydraulic pump SP equipped with two discharge ports P1, P2 and a common regulator 105. Hereinafter, the two discharge ports P1, P2 of the hydraulic pump SP are referred to as the first hydraulic pump P1 and the first hydraulic pump P2, respectively. The pressure oil discharged from the first hydraulic pump P1 is supplied to the left traveling motor 17, the boom cylinder 18, and the bucket cylinder 19 via the directional control valves 9, 10, and 11 of the first sub-valve group V1-1, and the pressure oil discharged from the first hydraulic pump P2 is supplied to the arm cylinder 15 and the right traveling motor 16 via the directional control valves 7 and 8 of the second sub-valve group V1-2.

[0033] The second pump device 102 is a fixed displacement hydraulic pump equipped with a discharge port P3, and hereinafter the second pump device 102 will be referred to as the second hydraulic pump P3.

[0034] In this embodiment, the first pump device 101 is configured with two split-flow type hydraulic pumps P1 and P2, but the first pump device 101 may be configured with one hydraulic pump having one discharge port. Also, the first pump device 101 is configured with two split-flow type hydraulic pumps P1 and P2, but the first pump device 101 may be configured with two separate, independent hydraulic pumps.

[0035] The directional control valves 9-11 of the first sub-valve group V1-1, the directional control valves 7 and 8 of the second sub-valve group V1-2, and the directional control valves 3-5 of the second valve group V2 are disposed on center bypass passages CB1, CB2, and CB3, respectively, which are connected to pressure oil supply passages 101a, 101b, and 102a of the first hydraulic pumps P1 and P2 and the second hydraulic pump P3, respectively. In addition, the pump ports of the directional control valves 9-11 of the first sub-valve group V1-1 and the directional control valves 7 and 8 of the second sub-valve group V1-2 are connected to the center bypass passages CB1 and CB2, and the pump ports of the directional control valves 3-5 of the second valve group V2 are connected to the pressure oil supply passage 102a via a bypass passage 102b.

[0036] When the directional control valves 9-11, directional control valves 7, 8, and directional control valves 3-5 are in the neutral position, they open the center bypass passages CB1, CB2, and CB3, respectively, and return the pressure oil supplied from the first hydraulic pumps P1, P2, and the second hydraulic pump P3 to the tank T. When the directional control valves 9-11, directional control valves 7, 8, and directional control valves 3-5 are switched from the neutral position, they throttle or block the center bypass passages CB1, CB2, and CB3, respectively, and allow the oil discharged from the first hydraulic pumps P1, P2, and the second hydraulic pump P3 to be supplied to the actuators 12-19. The pressure oil supply passages 101a, 101b, and 102a are connected to main relief valves 26, 27, and 28, which set the upper limit of the discharge pressure of the first hydraulic pumps P1, P2, and the second hydraulic pump P3, respectively.

[0037] As described above, the hydraulic drive system according to this embodiment is configured as an open center system equipped with the open center type directional control valves 3-5, 7-11.

[0038] The plurality of directional control valves 3 to 5 and 7 to 11, the travel connection valve 30, and the main relief valves 26, 27, and 28 are disposed in a valve housing VH of the control valve 2.

[0039] ~Operation system~ An operation system for switching the directional control valves 3 to 5 and 7 to 11 by an operator will be described below.

[0040] In FIG. 2, the hydraulic drive device of this embodiment further includes a pilot oil passage 103b connected to a discharge oil passage 103a of the pilot pump 103 via a rotation speed detection valve 250 described later, to which the discharge oil of the pilot pump 103 is guided, a pilot relief valve 29 provided in the pilot oil passage 103b and forming a pilot hydraulic source 110 by maintaining the pressure of the pilot oil passage 103b constant, and operating devices 20a, 20b, 21a, 21b, 22, 23a, 23b, 24 connected to the pilot oil passage 103b and equipped with remote control valves that generate operating pilot pressures a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p for switching the directional control valves 3-5, 7-11 using the hydraulic pressure of the pilot oil passage 103b as the source pressure. The operating devices 20a, 20b and the operating devices 21a, 21b are configured as operating lever devices 20, 21 arranged on the right and left in front of the driver's seat, the operating device 22 is arranged on the right side of the driver's seat, the operating devices 23a, 23b are configured as a pedal device 23 arranged in front of the driver's seat, and the operating device 24 is arranged on the front right side of the driver's seat.

[0041] ~Torque Control Regulator~ The torque control regulator (hereinafter simply referred to as regulator) 105 of the first hydraulic pumps P1, P2 (split-flow type hydraulic pumps SP) will be described.

[0042] The regulator 105 includes torque control (horsepower control) pistons 111, 112, 113 to which the discharge pressures of the first hydraulic pumps P1, P2 and the second hydraulic pump P3 are guided and which reduce the displacement (capacity) of the first hydraulic pumps P1, P2 as the pressures increase, and a spring 114 which sets the maximum torque available to the first hydraulic pumps P1, P2 and the second hydraulic pump P3.

[0043] FIG. 4 is a diagram showing the torque characteristics of the torque limiting control by the regulator 105, where the horizontal axis represents the average value of the discharge pressures of the first hydraulic pumps P1, P2 (average discharge pressure), and the vertical axis represents the capacity (tilt angle) of the first hydraulic pumps P1, P2.

[0044] When none of the swing motor 13, the swing cylinder 14, and the blade cylinder 12 are driven and no actuator load is acting on the second hydraulic pump P3, the biasing force of the torque control piston 113 is minimum, and the maximum torque of the regulator 105 is set by the spring 114 as shown by the solid line TA. In this state, when any of the right and left travel motors 16, 17, the arm cylinder 15, the boom cylinder 18, and the bucket cylinder 19 is driven by the discharge oil of the first hydraulic pumps P1, P2, and the average discharge pressure of the first hydraulic pumps P1, P2 rises and exceeds the threshold value PA, the biasing force of the torque control pistons 111, 112 controls the capacity of the first hydraulic pumps P1, P2 to decrease along the solid line TA as the average discharge pressure increases, and the discharge flow rate of the first hydraulic pumps P1, P2 also decreases accordingly. As a result, the absorption torque of the first hydraulic pumps P1, P2 is controlled so as not to exceed the maximum torque set by the spring 114, and engine stall can be prevented.

[0045] When the rotation motor 13, the swing cylinder 14, or the blade cylinder 12 is driven by the discharge oil of the second hydraulic pump P3 and an actuator load acts on the second hydraulic pump P3, the maximum torque of the regulator 105 decreases from the solid line TA to the dashed line TB due to the action of the torque control piston 113 to which the discharge pressure of the second hydraulic pump P3 is introduced. In this state, when the right or left travel motor 16, 17, the arm cylinder 15, the boom cylinder 18, or the bucket cylinder 19 is driven by the discharge oil of the first hydraulic pumps P1, P2 and the average discharge pressure of the first hydraulic pumps P1, P2 increases and exceeds a threshold value PB lower than the threshold value PA, the capacity of the first hydraulic pumps P1, P2 is controlled to decrease along the dashed line TB as the average discharge pressure increases due to the biasing force of the torque control pistons 111, 112, and the discharge flow rate of the first hydraulic pumps P1, P2 also decreases accordingly. As a result, the total absorption torque of the first hydraulic pumps P1, P2 and the second hydraulic pump P3 is controlled so as not to exceed the maximum torque set by the spring 114, thereby making it possible to prevent engine stall.

[0046] ~Characteristic composition~ Returning to FIG. 2, the hydraulic drive system according to this embodiment has the following characteristic configuration in addition to the configuration described above.

[0047] First, the hydraulic drive system of this embodiment is provided with a travel connecting valve 30 having a first flow path Oa whose inlet port is connected to the pressurized oil supply path 102a of the second hydraulic pump P3 (second pump device 102) and whose outlet port is connected to the center bypass passage CB3 of the second valve group V2, and which guides the oil discharged from the second pump P3 to the directional control valves 12, 13, 14 of the second valve group V2, and a second flow path Ob whose inlet port is connected to the pressurized oil supply path 102a of the second hydraulic pump P3 (second pump device 102) and whose outlet port is connected to bypass passages 31, 32 connected to the multiple front directional control valves 7, 10, 11 of the first valve group V1, and which guides the oil discharged from the second hydraulic pump P3 to the multiple front directional control valves 7, 10, 11 of the first valve group V1. The travel connecting valve 30 has a first position in which the first flow path Oa is fully opened and the second flow path Ob is fully closed when a travel / front combined operation in which the right and left travel motors 16, 17 and at least one of the multiple front cylinders 15, 18, 19 are simultaneously driven is not being performed, and a second position in which the first flow path Oa is narrowed and the opening area of ​​the second flow path Ob is made larger than the opening area of ​​the first flow path Oa when at least one of the multiple front cylinders 15, 18, 19 is driven during travel and the right and left travel motors 16, 17 are driven and a travel / front combined operation has been started, and the second position changes according to the rotational speed of the engine 1, and is set so that the opening area of ​​the first flow path Oa in the second position becomes smaller as the rotational speed of the engine 1 decreases.

[0048] Moreover, the second position of the traveling communication valve 30 is set so that the opening area of ​​the second flow passage Ob becomes larger as the rotation speed of the engine 1 becomes lower.

[0049] The hydraulic drive system further includes a traveling / front combined operation detection circuit 200 that detects the traveling / front combined operation and generates a first signal pressure Pa, and a rotation speed detection valve 250 that generates a second signal pressure Pe that decreases as the rotation speed of the engine 1 decreases, and when the traveling / front combined operation is not being performed, the traveling connecting valve 30 is held in the first position by the second signal pressure Pe, and when the traveling / front combined operation is started, the traveling connecting valve 30 is switched from the first position to the second position by the first signal pressure Pa and reduces the opening area of ​​the first flow path Oa by the second signal pressure Pe as the rotation speed of the engine 1 decreases.

[0050] Furthermore, the traveling / front combined operation detection circuit 200 and the rotation speed detection valve 250 are arranged within the valve housing VH of the control valve 2 in which the multiple directional control valves 3-5, 7-11, the traveling communication valve 30 and the main relief valves 26, 27, 28 are arranged.

[0051] The characteristic configuration will be described in detail below.

[0052] [Driving / front combined motion detection circuit] The traveling / front combined operation detection circuit 200 includes on-off valves 8t, 9t provided integrally with the spools of the directional control valves 8, 9 for right and left traveling, a first detection oil passage 200a having one end connected to the pilot oil passage 103b (pilot hydraulic source 110) and the other end connected to the tank T and passing through the on-off valves 8t, 9t, on-off valves 7f, 10f, 11f provided integrally with the spools of the directional control valves 7, 10, 11 for the front, a second detection oil passage 200b having one end connected to the pilot oil passage 103b (pilot hydraulic source 110) and the other end connected to the tank T and passing through the on-off valves 7f, 10f, 11f, and a third detection oil passage 200c having one end connected to the pilot oil passage 103b (pilot hydraulic source 110) and the other end connected to the first pressure receiving portion 30a of the traveling connecting valve 30.

[0053] When at least one of the directional control valves 8, 9 for right / left driving and the directional control valves 7, 10, 11 for the front is not operated and is in the neutral position, at least one of the first detection oil passage 200a and the second detection oil passage 200b is not blocked, so that the third detection oil passage 200c is connected to the tank T via at least one of the first and second detection oil passages 200a, 200b, and the pressure in the third detection oil passage 200c becomes the low tank pressure.

[0054] When at least one of the right / left travel directional control valves 8, 9 and at least one of the front directional control valves 7, 10, 11 are simultaneously operated and switched from the neutral position, both the first detection oil passage 200a and the second detection oil passage 200b are blocked, so that the pressure in the third detection oil passage 200c rises to the pressure of the pilot hydraulic source 110, and a first signal pressure Pa is generated, which indicates that a combined travel / front operation has been performed. This first signal pressure Pa is led to the first pressure receiving portion 30a of the travel communicating valve 30.

[0055] In this way, when at least one of the right / left traveling directional control valves 8, 9 and at least one of the front directional control valves 7, 10, 11 are simultaneously switched from the neutral position, the traveling / front combined operation detection circuit 200 generates a first signal pressure Pa indicating that a traveling / front combined operation has been performed to simultaneously drive the lower traveling body 300 and the front work machine 302 based on the pressure of the pilot hydraulic source 110.

[0056] The first signal pressure Pa is the same pressure as that of the pilot hydraulic source 110, for example, 4.5 Mp.

[0057] [Rotational speed detection valve] The rotation speed detection valve 250 is composed of a fixed throttle 250a, a throttle valve 250b, and a differential pressure generating valve 250c. The fixed throttle 250a is formed in the discharge oil passage 103a of the pilot pump 103, and the throttle valve 250b is connected in parallel to the fixed throttle 250a. The throttle valve 250b is for adjusting the differential pressure before and after the fixed throttle 250a, and increases the opening area in response to an increase in the differential pressure before and after the fixed throttle 250a. The differential pressure before and after the fixed throttle 250a increases in response to an increase in the flow rate of pressurized oil passing through the fixed throttle 250a (in other words, an increase in the rotation speed of the engine 1).

[0058] The differential pressure generating valve 250c uses the pressure in the pilot oil passage 103b downstream of the fixed throttle 250a (the pressure of the pilot hydraulic source 110) as the base pressure, and generates the differential pressure across the fixed throttle 250a as an absolute pressure.

[0059] More specifically, the pressure upstream of the fixed orifice 250a acts on the left end (pressure receiving portion) of the differential pressure generating valve 250c in the figure, and the pressure downstream of the fixed orifice 250a (pressure in the pilot oil passage 103b) and the output pressure of the differential pressure generating valve 250c act on the right end (pressure receiving portion) of the differential pressure generating valve 250c in the figure, and when the output pressure of the differential pressure generating valve 250c is greater than the differential pressure before and after the fixed orifice 250a, the differential pressure generating valve 250c operates in the pressure reducing direction. As a result, the differential pressure generating valve 250c generates a pressure equal to the differential pressure before and after the fixed orifice 250a as an absolute pressure, and outputs the absolute pressure to the detection oil passage 250e as the second signal pressure Pe.

[0060] FIG. 5 is a diagram showing the relationship (output characteristics) between the rotation speed of the engine 1 and the second signal pressure Pe which is the output pressure of the rotation speed detection valve 250. As shown in FIG.

[0061] When the engine 1 speed is at the rated maximum speed Nmax, the speed detection valve 250 operates at point Na, and the second signal pressure Pe output by the speed detection valve 250 at this time is the maximum pressure Pemax. When the engine 1 speed drops to the minimum speed Nmin, the speed detection valve 250 operates at point Nb, and the second signal pressure Pe output by the speed detection valve 250 at this time is the minimum pressure Pemin. As the engine 1 speed drops from the maximum speed Nmax to the minimum speed Nmin, the second signal pressure Pe drops from the maximum pressure Pemax to the minimum pressure Pemin.

[0062] The second signal pressure Pe is a pressure lower than the pressure of the pilot hydraulic source 110, and for example, the maximum pressure Pemax is 2.0 Mp and the minimum pressure Pemin is, for example, 1.0 Mp. In other words, there is a relationship Pa>Pe.

[0063] [Travel communication valve] FIG. 3 is an enlarged view of the traveling communication valve 30 shown in FIG.

[0064] 2 and 3, the travel connecting valve 30 has a first flow path Oa that guides the pressurized oil discharged from the second hydraulic pump P3 (second pump device 102) to the center bypass passage CB3 of the second valve group V2, and a second flow path Ob that guides the pressurized oil discharged from the second hydraulic pump P3 to the front directional control valves 7, 10, 11 of the first valve group V1.

[0065] In addition, the traveling connecting valve 30 has a pump port 30p which is an inlet port, a center bypass port 30c which is an outlet port, and two front ports 30f1, 30f2, and the first flow path Oa is formed as a connecting passage with a variable throttle between the pump port 30p and the center bypass port 30c, and the second flow path Ob is formed as a connecting passage with a variable throttle between the pump port 30p and the front ports 30f1, 30f2. The pump port 30p is connected to the pressurized oil supply passage 102a of the second hydraulic pump P3, the center bypass port 30c is connected to a center bypass passage CB3 of the second valve group V2, the front ports 30f1, 30f2 are connected to the first and second bypass passages 31, 32, respectively, the first bypass passage 31 is connected to the center bypass passage CB1 of the first sub-valve group V1-1, between the directional control valve 9 for left traveling and the directional control valve 10 for the boom, and the second bypass passage 32 is connected to the center bypass passage CB2 of the second sub-valve group V1-2, between the directional control valve 8 for right traveling and the directional control valve 7 for the arm.

[0066] The traveling connecting valve 30 is a hydraulically operated spool valve having a first pressure receiving portion 30a and a second pressure receiving portion 30b at both ends of the spool valve body, and as described above, the first signal pressure Pa of the traveling / front combined operation detection circuit is guided to the first pressure receiving portion 30a, and the second signal pressure Pe of the rotation speed detection valve is guided to the second pressure receiving portion 30b.

[0067] When the combined running and front operation is not performed, the first signal pressure Pa is not generated, so the first pressure receiving section 30a is tank pressure, and the running connecting valve 30 is held in the illustrated first position by the second signal pressure Pe and the biasing force of the weak spring 30s. In this first position, the first flow path Oa is fully open, and the second flow path Ob is fully closed. When the combined running and front operation is started, the first signal pressure Pa is introduced to the first pressure receiving section 30a, and the differential pressure ΔP (= Pa-Pe) between the first signal pressure Pa and the second signal pressure Pb switches the running connecting valve 30 to the illustrated upper second position. In this second position, the first flow path Oa is narrowed, and the opening area of ​​the second flow path Ob becomes larger than the opening area of ​​the first flow path Oa.

[0068] Furthermore, as the rotation speed of the engine 1 decreases (ie, as the differential pressure ΔP increases), the opening area of ​​the first flow path Oa of the traveling connection valve 30 in the second position decreases and the opening area of ​​the second flow path Ob increases.

[0069] 6 is a diagram showing the relationship (opening area characteristics) between the spool stroke of the traveling connection valve 30 and the opening areas of the first flow path Oa and the second flow path Ob of the traveling connection valve 30. In the following, the spool stroke of the traveling connection valve 30 is referred to as the stroke of the traveling connection valve 30 and is denoted by the symbol S. In addition, the right vertical axis of FIG. 6 shows the rotation speed of the engine 1 as auxiliary information.

[0070] 6, when the traveling connection valve 30 is in the first position, the stroke of the traveling connection valve 30 is zero, and when the traveling connection valve 30 switches to the second position, the stroke of the traveling connection valve 30 changes within the range of S2min and S2max according to the rotation speed of the engine 1. S2min is the stroke when the rotation speed of the engine 1 is at the maximum Nmax, and S2max is the stroke when the rotation speed of the engine 1 is at the minimum Nmin.

[0071] In Fig. 6, when the stroke S of the travel connecting valve 30 is zero, the opening area of ​​the first flow path Oa is at its maximum, A1ful, and the second flow path Ob is fully closed. As the stroke S of the travel connecting valve 30 increases, the opening area of ​​the first flow path Oa decreases, and when the stroke S increases to a position Sc just before the spool stroke end, the first flow path Oa is fully closed. When the stroke S of the travel connecting valve 30 increases to Sa, the second flow path Ob opens, and as the stroke S increases further, the opening area of ​​the second flow path Ob increases.

[0072] Furthermore, when the engine 1 speed is at its maximum Nmax and the stroke of the traveling connecting valve 30 is S2min, the opening area of ​​the first passage Oa decreases from the maximum Aafull to Aa2max, which is less than 1 / 4 of the maximum Aafull, and the opening area of ​​the second passage Ob increases to Ab2min, which is more than twice the opening area Aa2max of the first passage Oa. When the engine 1 speed is at its minimum Nmin and the stroke of the traveling connecting valve 30 is S2max, the opening area of ​​the first passage Oa decreases to Aa2min, which is less than half of Aa2max, and the opening area of ​​the second passage Ob increases to Ab2max.

[0073] ~Operation~ The operation of the hydraulic drive system according to this embodiment configured as above will now be described.

[0074] [Actuator 17, 18, 19] When neither the operation levers of the operation devices 20a, 20b nor the operation pedal of the operation device 23b are operated, the directional control valves 9, 10, 11 are in the neutral position, and the oil discharged from the first hydraulic pump P1 flows back to the tank T via the center bypass passage CB1. When either the operation levers of the operation devices 20a, 20b or the operation pedal of the operation device 23b is operated, the corresponding one of the directional control valves 9, 10, 11 switches, and the oil discharged from the first hydraulic pump P1 is supplied to the corresponding actuator (either the travel motor 17, the boom cylinder 18, or the bucket cylinder 19), and the driving direction and driving speed of that actuator are controlled.

[0075] [Actuator 15, 16] When neither the operation lever of the operation device 21a nor the operation pedal of the operation device 23a is operated, the directional control valves 7, 8 are in a neutral position, and the oil discharged from the first hydraulic pump P2 flows back to the tank T via the center bypass passage CB2. When either the operation lever of the operation device 21a or the operation pedal of the operation device 23a is operated, the corresponding one of the directional control valves 7, 8 switches, and the oil discharged from the first hydraulic pump P2 is supplied to the corresponding actuator (either the arm cylinder 15 or the travel motor 16), and the drive direction and drive speed of that actuator are controlled.

[0076] [Actuator 12, 13, 14] When neither the operation levers of the operation devices 21b, 22 nor the operation pedal of the operation device 24 are operated, the directional control valves 3, 4, 5 are in the neutral position. At this time, when the operation pedals of the operation devices 23a, 23b and the operation levers of the operation devices 20a, 20b, 21a are operated and the traveling / front combined operation is not being performed, the traveling connection valve 30 is in the first position, the first flow path Oa is fully opened, and the discharge oil of the second hydraulic pump P3 flows back to the tank T via the center bypass passage CB3. In this state, when either the operation lever of the operation lever devices 21b, 22 or the operation pedal of the operation pedal device 24 is operated, the corresponding one of the directional control valves 3, 4, 5 is switched, and the discharge oil of the second hydraulic pump P3 is supplied to the corresponding actuator (either the blade cylinder 12, the swing motor 13, or the swing cylinder 14), and the driving direction and driving speed of the actuator are controlled.

[0077] [Driving and front combined movement] During travel in which the right travel motor 16 and the left travel motor 17 are driven by operating the operation pedals of the operation devices 23a and 23b, when any of the operation levers of the operation devices 20a, 20b, and 21a is operated to start the combined travel and front operation, the corresponding directional control valve 7 for the arm, directional control valve 10 for the boom, and directional control valve 11 for the bucket are switched.

[0078] In addition, in the combined driving / front operation, at least one of the directional control valves 8, 9 and at least one of the directional control valves 7, 10, 11 are switched, and both the first detection oil passage 200a and the second detection oil passage 200b are blocked, so that a first signal pressure Pa is generated in the third detection oil passage 200c, and the driving connecting valve 30 is switched to the second position at the top as shown in the figure.

[0079] When the engine 1 speed is at its maximum Nmax, the stroke S of the travel connecting valve 30 is S2min, the opening area of ​​the first flow path Oa decreases to Aa2max, the second flow path Ob opens, and the opening area becomes Ab2min. In addition, the center bypass port 30c of the travel connecting valve 30 communicates with the tank T via the center bypass passage CB3 of the second valve group V2. Therefore, when the travel connecting valve 30 is switched to the second position, the pressure oil discharged from the second hydraulic pump P3 bleeds off into the center bypass passage CB3, suppressing the occurrence of surge pressure that causes the discharge pressure of the second hydraulic pump P3 to suddenly rise.

[0080] Here, when the travel connecting valve 30 is switched to the second position, if the first flow path Oa is fully closed, the discharge pressure of the second hydraulic pump P3 rises suddenly and a surge pressure occurs. This surge pressure of the second hydraulic pump P3 is led to the torque control piston 113 of the regulator 105 of the first hydraulic pumps P1, P2 (first pump device 101), and the torque limit control of the regulator 105 causes a sudden decrease in the discharge flow rate of the first hydraulic pumps P1, P2.

[0081] That is, in the torque characteristic diagram of the torque limit control shown in Fig. 4, when the average value (average discharge pressure) of the discharge pressure of the first hydraulic pumps P1, P2 when the right and left traveling motors 16, 17 are driven by the discharge oil of the first hydraulic pumps P1, P2 is Pt, the capacity of the first hydraulic pumps P1, P2 is limited to qt1 by the torque limit control of the regulator 105. From this state, the combined traveling and front operation is started, and as described above, the discharge pressure of the second hydraulic pump P3 rises suddenly, generating a surge pressure, and when this surge pressure is led to the torque control piston 113 of the regulator 105, the maximum torque of the regulator 105 decreases from the solid line TA to the broken line TB. Therefore, the capacity of the first hydraulic pumps P1, P2 decreases from qt1 to qt2 by the torque limit control of the regulator 105, and the discharge flow rate of the first hydraulic pumps P1, P2 decreases suddenly.

[0082] This causes a sudden drop in travel speed at the start of combined travel and front-wheel motion, making workability worse.

[0083] In this embodiment, as described above, when the travel connecting valve 30 is switched to the second position, the pressure oil discharged from the second hydraulic pump P3 bleeds off into the center bypass passage CB3, and the occurrence of surge pressure in which the discharge pressure of the second hydraulic pump P3 rises suddenly is suppressed. Therefore, as shown by the dashed line TC, the decrease in the maximum torque of the regulator 105 caused by the discharge pressure of the second hydraulic pump P3 being led to the torque control piston 113 of the regulator 105 is smaller than when surge pressure occurs, and the decrease in the capacity of the first hydraulic pumps P1 and P2 is also small, from qt1 to qt3, and the decrease in the discharge flow rate of the first hydraulic pumps P1 and P2 is small, so that a sudden decrease in the travel speed can be prevented.

[0084] In addition, since the opening area of ​​the second flow path Ob of the travel connecting valve 30 is larger than twice Aa2max, the discharge oil of the second hydraulic pump P3 flows smoothly into the boom directional control valve 10, the bucket directional control valve 11, or the arm directional control valve 7, and is supplied to the boom cylinder 18, the arm cylinder 15, or the bucket cylinder 19. This allows the front work implement 302 to operate with good responsiveness, and prevents the operation of the front work implement 302 from becoming sluggish.

[0085] When the engine 1 speed is at the minimum Nmin, the stroke S of the travel connecting valve 30 is S2max, the opening area of ​​the first flow path Oa decreases to Aa2min, and the opening area of ​​the second flow path Ob increases to Ab2max. When the engine 1 speed is at the minimum Nmin, the opening area of ​​the first flow path Oa decreases accordingly, but the discharge amount of the second hydraulic pump P3 decreases, so that the pressure oil discharged from the second hydraulic pump P3 bleeds off into the center bypass passage CB3, and the generation of surge pressure in which the discharge pressure of the second hydraulic pump P3 rises suddenly is suppressed. In addition, the opening area of ​​the second flow path Ob increases, so that the discharge oil of the second hydraulic pump P3 is smoothly supplied to the front directional control valves 7, 10, and 11. Therefore, just as when the engine 1 speed is at its maximum Nmax, at the start of the combined travel / front operation in which the front work equipment is driven while traveling, a sudden deceleration in the travel speed due to torque limiting control of the first hydraulic pumps P1, P2 is prevented, and the operation of the front work equipment is prevented from becoming sluggish.

[0086] When the rotation speed of the engine 1 is between the maximum Nmax and the minimum Nmin, the stroke S of the traveling connecting valve 30 is between S2min and S2max according to the rotation speed of the engine 1, the first flow path Oa has an opening area between Aa2max and Aa2min, and the second flow path Ob has an opening area between Ab2min and Ab2max. Therefore, in this case as well, for the same reasons as when the rotation speed of the engine 1 is Nmax or Nmin, the front working implement 302 operates with good responsiveness, and the operation of the front working implement 302 is prevented from becoming sluggish.

[0087] ~Effects~ 1. As described above, in this embodiment, the travel communicating valve 30 is provided with a first flow path Oa having an inlet port connected to the pressure oil supply path 102a of the second hydraulic pump P3 (second pump device 102) and an outlet port connected to the center bypass passage CB3 of the second valve group V2, and guiding the discharge oil from the second pump P3 to the directional control valves 12, 13, 14 of the second valve group V2, and a second flow path Ob having an inlet port connected to the pressure oil supply path 102a of the second hydraulic pump P3 (second pump device 102) and an outlet port connected to the bypass passages 31, 32 connected to the multiple front directional control valves 7, 10, 11 of the first valve group V1, and guiding the discharge oil from the second hydraulic pump P3 to the multiple front directional control valves 7, 10, 11 of the first valve group V1. The travel communicating valve 30 is provided with a first flow path Oa having an inlet port connected to the pressure oil supply path 102a of the second hydraulic pump P3 (second pump device 102) and an outlet port connected to the bypass passages 31, 32 connected to the multiple front directional control valves 7, 10, 11 of the first valve group V1, and guiding the discharge oil from the second hydraulic pump P3 to the multiple front directional control valves 7, 10, 11 of the first valve group V1. When a combined traveling / front operation in which one of the front cylinders is driven at the same time is not being performed, the first position is set to fully open the first flow path Oa and fully close the second flow path Ob, and when at least one of the multiple front cylinders 15, 18, 19 is driven during traveling while the right and left traveling motors 16, 17 are driven and a combined traveling / front operation is started, the first position is switched to a second position in which the first flow path Oa is narrowed and the opening area of ​​the second flow path Ob is made larger than the opening area of ​​the first flow path Oa, and the second position of the traveling connecting valve 30 is set so that the opening area of ​​the first flow path Oa becomes smaller as the rotation speed of the engine 1 decreases, so that at the start of a combined traveling / front operation in which the front work equipment is driven while traveling, a sudden deceleration of the traveling speed is prevented by the torque limit control of the first hydraulic pumps P1, P2 regardless of the engine rotation speed, and the operation of the front work equipment does not become sluggish, thereby ensuring good workability.

[0088] 2. In construction machinery such as hydraulic excavators, when detecting engine revolutions to control the hydraulic circuit, it is common to use a rotation speed sensor such as a pickup sensor as a rotation speed detector, input the detection signal of this rotation speed sensor to a controller, and control the valve by the control signal from the controller. Also, when the hydraulic circuit is the main hydraulic circuit that supplies pressure oil from the pump to the directional control valve, the pressure oil supplied from the pump to the directional control valve is a large flow rate, so it is difficult to directly control the main hydraulic circuit with a proportional solenoid valve, and it is necessary to drive the proportional solenoid valve with a controller to generate a hydraulic signal, and drive a hydraulic pilot type switching valve with this hydraulic signal to control the hydraulic circuit.

[0089] In this regard, for example, in the hydraulic drive device of Patent Document 2, a straight travel valve, which is a hydraulic pilot type switching valve, is arranged in the main hydraulic circuit that supplies pressurized oil from pumps P1 and P2 to multiple directional control valves, and a proportional solenoid valve called a straight travel proportional valve is driven by a control signal from a controller, and the straight travel valve is switched by a hydraulic signal from this proportional solenoid valve.

[0090] In this way, conventionally, controllers and proportional solenoid valves have been used to switch the hydraulic pilot-operated switching valve in the main hydraulic circuit, and in the case of small hydraulic excavators such as mini excavators, which do not normally use controllers, it is necessary to newly install expensive parts such as controllers and proportional solenoid valves, making the vehicle expensive.

[0091] Furthermore, when a proportional solenoid valve is used to control the main hydraulic circuit, it is most compact and preferable to place the proportional solenoid valve in the same valve housing VH as multiple directional control valves, but the solenoid part of the proportional solenoid valve generally has low heat resistance because it contains a magnetic material, and so it must be placed away from the control valve, which is a heat source. For this reason, in mini excavators, especially those with vehicle specifications known as ultra-small swing machines or small rear swing machines, the inside of the vehicle becomes overcrowded with parts, limiting the mounting position of the proportional solenoid valve where the environmental temperature will be high, and restricting the layout design.

[0092] In this embodiment, the traveling / front combined operation and the rotation speed of the engine 1 are hydraulically detected by the traveling / front combined operation detection circuit 200 and the rotation speed detection valve 250, and the first signal pressure Pa and the second signal pressure Pb are led to the pressure receiving portions 30a, 30b of the traveling connecting valve 30, which is a hydraulic pilot type switching valve, so that the switching and stroke control of the traveling connecting valve 30 are performed by hydraulic control alone, which eliminates the need for a controller or proportional solenoid valve, reduces the number of parts and makes them inexpensive, and avoids high costs for the vehicle body.

[0093] In addition, because it does not require a controller or proportional solenoid valve and can be constructed using only hydraulic components, the component layout can be designed without worrying about heat resistance, which not only increases the freedom of layout design but also improves robustness against the equipment installation environment.

[0094] Furthermore, in this embodiment, the rotation speed detection valve 250, together with the traveling / front combined operation detection circuit 200, is arranged within the valve housing VH of the control valve 2 in which the multiple directional control valves 3-5 and the traveling communication valve 30 are arranged, thereby making it possible to make the overall configuration of the hydraulic drive system compact.

[0095] ~Other~ In the above embodiment, the prime mover is a diesel engine, but the prime mover may be an electric motor. Also, the construction machine may be a wheel loader, bulldozer, or other construction machine other than a hydraulic excavator, and the same effects can be obtained in that case. [Explanation of symbols]

[0096] 1. Engine 2. Control valve 3~5,7~11 Multiple directional control valves 4. Directional control valve for turning (third directional control valve) 8,9 Right / left driving directional control valve (first directional control valve) 7, 10, 11 Front directional control valve (second directional control valve) 12~19 Multiple Actuators 12 Blade Cylinder 13 Swivel motor 15 Arm cylinder (front cylinder) 16,17 Right and left drive motors 18 Boom cylinder (front cylinder) 19 Bucket cylinder (front cylinder) 20, 21, 22 Operating lever device 23,24 Operation pedal device 30 Travel communication valve 30a First pressure receiving part 30b 2nd pressure receiving part 30c Center bypass port (exit port) 30f1, 30f2 Front port (outlet port) 30p pump port (inlet port) 31,32 Bypass Passage 101 First pump device 102 Second pump device 102a Pressure oil supply path 105 Torque control regulator 200 Running / front combined operation detection circuit 250 Speed ​​detection valve 300 Undercarriage 301 Upper rotating body 302 Front Work Machine 306 Boom 307 Arm 308 Bucket P1, P2 First hydraulic pump P3 No. 2 hydraulic pump V1 First valve group V1-1 1st sub-valve group V1-2 Second sub-valve group V2 2nd valve group CB1, CB2, CB3 Center bypass passage Oa 1st flow path Ob 2nd Stream VH valve housing

Claims

1. A prime mover, a variable displacement type first pump device and a fixed displacement type second pump device driven by the prime mover, a plurality of actuators driven by pressure oil discharged from the first and second pump devices, and a plurality of open center type direction switching valves for controlling the flow of pressure oil supplied from the first and second pump devices to the plurality of actuators. The plurality of actuators include a travel motor driven by pressure oil discharged from the first pump device to drive a lower traveling body, a front cylinder driven by pressure oil discharged from the first pump device to drive a front work implement, and actuators other than the travel motor and the front cylinder driven by pressure oil discharged from the second pump device. The plurality of direction switching valves include a first direction switching valve for controlling the flow of pressure oil supplied from the first pump device to the travel motor and a second direction switching valve for controlling the flow of pressure oil supplied from the first pump device to the front cylinder, and a third direction switching valve for controlling the flow of pressure oil supplied from the second pump device to actuators other than the travel motor and the front cylinder. The first direction switching valve and the second direction switching valve constitute a first valve group. The third direction switching valve constitutes a second valve group. In a hydraulic drive device for a construction machine that reduces the capacity of the first pump device as the average discharge pressure of the first pump device and the second pump device exceeds a predetermined value and increases with the increase of the average discharge pressure. A travel communication valve including a first flow path with an inlet port connected to the pressure oil supply path of the second pump device and an outlet port connected to the center bypass passage of the second valve group, and a second flow path with an inlet port connected to the pressure oil supply path of the second pump device and an outlet port connected to a bypass passage connected to the second direction switching valve of the first valve group. The travel communication valve has a first position in which the first flow path is fully opened and the second flow path is fully closed when a travel / front combined operation in which the travel motor and the front cylinder are simultaneously driven is not being performed, and a second position in which the first flow path is throttled and the opening area of the second flow path is made larger than the opening area of the first flow path when the travel / front combined operation in which the front cylinder is driven during travel when the travel motor is driven is started. The hydraulic drive device for construction machinery is characterized in that the second position of the traveling communication valve is set such that the opening area of the first flow path decreases as the rotational speed of the prime mover decreases.

2. In the hydraulic drive device for construction machinery according to Claim 1, The hydraulic drive device for construction machinery is characterized in that the second position of the traveling communication valve is set such that the opening area of the second flow path increases as the rotational speed of the prime mover decreases.

3. In the hydraulic drive device for construction machinery according to Claim 1, A traveling / front combined operation detection circuit that detects the traveling / front combined operation and generates a first signal pressure, and a rotational speed detection valve that generates a second signal pressure that decreases as the rotational speed of the prime mover decreases are further provided. When the traveling / front combined operation is not being performed, the traveling communication valve is held at the first position by the second signal pressure. When the traveling / front combined operation is started, the traveling communication valve is switched from the first position to the second position by the first signal pressure, and the opening area of the first flow path is decreased as the rotational speed of the prime mover decreases by the second signal pressure. The hydraulic drive device for construction machinery is characterized by this.

4. In the hydraulic drive device for construction machinery according to Claim 3, The hydraulic drive device for construction machinery is characterized in that the traveling / front combined operation detection circuit and the rotational speed detection valve are arranged within a valve housing of a control valve in which the plurality of direction switching valves and the traveling communication valve are arranged.

5. In the hydraulic drive device for construction machinery according to Claim 1, The first pump device is a variable displacement split flow type hydraulic pump having first and second discharge ports and a common regulator. The first direction switching valve is a direction switching valve for left traveling and a direction switching valve for right traveling, and the second direction switching valve is a plurality of direction switching valves for the front. The first valve group includes a first sub-valve group including the direction switching valve for left traveling and a part of the plurality of direction switching valves for the front, and a second sub-valve group including the direction switching valve for right traveling and the other part of the plurality of direction switching valves for the front. The pressure oil supply passage of the first discharge port is connected to the center bypass passage of the first sub-valve group, the pressure oil supply passage of the second discharge port is connected to the center bypass passage of the second sub-valve group, and the pressure oil supply passage of the second pump device is connected to the center bypass passage of the second valve group via the travel communication valve. A hydraulic drive device for a construction machine, characterized in that.

Images