JP2012162878A - Hydraulic drive unit of construction machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic drive unit of a construction machine, capable of inhibiting a delay in the operation of a working device even in a condition of performing a combination of travelling operation at a low speed and working operation of the working device at the same time.SOLUTION: Midway between a travelling direction change-over valve 18 and a hydraulic motor 16 connected to each other via main pipe lines 17A, 17B, a flow control change-over valve 20 is provided for controlling the flow of pressure oil to be supplied to the hydraulic motor 16. The flow control change-over valve 20 has a communication position (a) for causing the main pipe lines 17A, 17B to be in a communicated condition and a throttle position (b) for limiting the flow of the pressure oil in the main pipe lines 17A, 17B. When driving pressure in the boom cylinder 8 rises, the flow control change-over valve 20 is temporarily changed over into the throttle position (b) by a one-direction throttle valve 22, to limit the flow of the pressure oil to be supplied to the hydraulic motor 16. This enables the supply of the sufficient pressure oil to the boom cylinder 8 while inhibiting a sudden increase in the speed of the hydraulic motor 16.

Description

  The present invention relates to a hydraulic drive device for a construction machine that is preferably used for construction machines such as a hydraulic excavator and a crane.

  In general, a hydraulic drive device for a self-propelled construction machine includes a hydraulic source composed of a hydraulic pump and a tank, a travel motor driven by pressure oil discharged from the hydraulic pump, and a pressure discharged from the hydraulic pump. And a working actuator that is driven by oil to drive the working device. Here, the travel motor is connected to a branch pipe branching from a center bypass pipe connected to the hydraulic pump, and the working actuator is connected to another of the center bypass pipes downstream of the branch pipe. By being connected to the branch pipe, pressure oil from the hydraulic pump is supplied to the traveling motor and the working actuator (see, for example, Patent Document 1).

  In this type of conventional technology, the drive of the work actuator is performed when the single travel operation state in which only the low speed travel operation is performed shifts to the combined operation state in which the low speed travel operation and the work operation by the work device are performed simultaneously. If the pressure is higher than the driving pressure of the travel motor, pressure oil is preferentially supplied to the travel motor upstream of the work actuator, and the vehicle speed may increase rapidly against the operator's intention. is there.

  Therefore, in the prior art disclosed in Patent Document 1, when the traveling state is shifted from the single traveling operation state to the combined operation state, the traveling motor is mainly supplied with the pressure oil from the first hydraulic pump and is used for work. Only the pressure oil from the second hydraulic pump is supplied to the actuator.

  According to such a configuration, when shifting from the single traveling operation state to the combined operation state, the pressure oil is supplied from the separate pumps to the traveling motor and the working actuator, respectively. Regardless of this, it is possible to prevent pressure oil from being preferentially supplied to the traveling motor, and to suppress a rapid increase in speed contrary to the operator's intention.

JP-A-9-324446

  In the related art according to Patent Document 1, in a combined operation state in which a traveling operation at a low speed and a work operation by the work device are performed simultaneously, only the pressure oil from the second hydraulic pump is supplied to the work actuator. It has become. For this reason, when performing a combined operation, when the working actuator needs an amount of pressure oil that cannot be supplied by only one hydraulic pump (second hydraulic pump), the working actuator has a sufficient amount. There is a problem that the pressure oil is not supplied and the operation of the working device is slowed down.

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to suppress a delay in the operation of the work device even in a combined operation state in which a traveling operation at a low speed and a work operation by the work device are performed simultaneously. It is an object of the present invention to provide a hydraulic drive device for a construction machine.

  In order to solve the above-described problems, the present invention is to drive a vehicle driven by hydraulic pressure source including a hydraulic pump and a tank, a center bypass passage connected to the hydraulic pump, and pressure oil discharged from the hydraulic pump. The travel motor, a working actuator driven by pressure oil discharged from the hydraulic pump to drive the work device, and a branch passage connected to the center bypass passage and branched from the center bypass passage. A traveling direction switching valve that switches the direction of the supplied pressure oil, and a working direction switch that switches the direction of the pressure oil that is connected to the downstream side of the traveling direction switching valve in the center bypass passage and is supplied to the working actuator. The present invention is applied to a hydraulic drive device for a construction machine provided with a direction switching valve.

  A feature of the configuration adopted by the invention of claim 1 is that the pressure discharged from the hydraulic pump from the low-speed single traveling operation state where the pressure oil discharged from the hydraulic pump is supplied only to the traveling motor. When the driving pressure of the working actuator is higher than the driving pressure of the traveling motor when the oil is supplied to both the traveling motor and the working actuator, and the driving pressure of the working actuator is higher than the driving pressure of the traveling motor The present invention is configured to have a flow rate control means for controlling the flow rate of the pressure oil supplied to the motor.

  According to a second aspect of the present invention, a pressure oil supply line for supplying pressure oil to the traveling motor is connected between the traveling direction switching valve and the traveling motor. A flow rate control switching valve provided in the pressure oil supply line and having a communication position for connecting the pressure oil supply line and a throttle position for restricting the flow rate of the pressure oil flowing through the pressure oil supply line. The flow control switching valve is normally in the communication position, and is temporarily switched to the throttle position when the driving pressure of the working actuator is higher than the driving pressure of the travel motor, and then to the communication position. The configuration is to return.

  According to a third aspect of the present invention, the flow rate control switching valve comprises a hydraulic pilot type switching valve having a first pilot chamber that switches to a communication position and a second pilot chamber that switches to a throttle position. The pilot chamber is connected with first and second pilot pipes for supplying the driving pressure of the working actuator or the pilot pressure of the working direction switching valve, and the first pilot pipe is connected with the first pilot pipe. In order to temporarily lower the pressure in the first pilot chamber as compared with the pressure in the second pilot chamber, the flow rate is limited when pressure oil flows into the first pilot chamber, and the first pilot chamber When pressure oil flows out from the pilot chamber, a one-way throttle valve that communicates is provided.

  According to a fourth aspect of the present invention, the flow rate control means includes a logic valve that is provided in the middle of the branch passage and includes a poppet valve that limits the flow rate of the pressure oil according to the opening area. The fully open operation state in which the opening area of the poppet valve is fully opened and the branch passage is in communication, and the flow area of the pressure oil flowing through the branch passage is reduced by reducing the opening area of the poppet valve from the fully open state. The logic valve is always in a fully open operation state, and is temporarily switched to the limit operation state when the drive pressure of the work actuator is higher than the drive pressure of the travel motor. Then, it is in the structure which returns to a fully open operation state.

  According to a fifth aspect of the present invention, the logic valve has a first pilot chamber that switches to the fully open operation state and a second pilot chamber that switches to the limit operation state, and controls the opening area of the poppet valve. The first and second pilot chambers are connected to the first and second pilot pipes for supplying the driving pressure of the working actuator or the pilot pressure of the working direction switching valve, When pressurized oil flows into the first pilot chamber to temporarily lower the pressure in the first pilot chamber as compared to the pressure in the second pilot chamber. Is a configuration in which a flow rate is limited and a one-way throttle valve that communicates when pressure oil flows out of the first pilot chamber.

  According to the first aspect of the present invention, the flow rate control means controls the flow rate of the pressure oil supplied to the travel motor. Therefore, when the single travel operation state shifts to the composite operation state, the flow restriction means travels. The flow rate of the pressure oil supplied to the motor can be changed gradually. For this reason, it is possible to suppress the pressure oil from being preferentially supplied to the travel motor over the work actuator, and to suppress a rapid increase in the vehicle speed against the operator's intention. In addition, since the change in vehicle speed can be suppressed by the flow rate control means, there is no need to provide a plurality of hydraulic pumps as in the prior art. For this reason, even in a combined operation state in which a traveling operation at a low speed and a work operation by the work device are performed simultaneously, a delay in the operation of the work device can be suppressed.

  According to the invention of claim 2, the flow rate control means is constituted by a flow rate control switching valve provided in the pressure oil supply line and having a communication position and a throttle position. In the single traveling operation state at a low speed, the flow control switching valve is in the communication position, and the pressure oil from the hydraulic pump is supplied to the traveling motor as it is. On the other hand, when the driving pressure of the working actuator is higher than the driving pressure of the traveling motor when the single traveling operation state at the low speed is shifted to the combined operation state in which the traveling operation at the low speed and the work operation by the work device are simultaneously performed. The flow rate control switching valve is temporarily switched to the throttle position. As a result, the flow rate of the pressure oil supplied from the hydraulic pump to the travel motor can be limited to suppress a rapid change in the speed of the vehicle.

  In addition, since the flow rate control switching valve quickly returns from the throttle position to the communication position, when the combined operation state continues, the pressure oil increased by the driving pressure of the work actuator is supplied to the travel motor. The vehicle can be run. As a result, it is possible to prevent loss due to the pressure oil being supplied to the traveling motor while the flow control valve is in the throttle position.

  According to the third aspect of the present invention, when the driving pressure of the working actuator or the pilot pressure of the working direction switching valve rises when shifting from the single traveling operation state to the combined operation state, the increased pressure is controlled by the flow control. It acts on the first pilot chamber and the second pilot chamber of the switching valve. At this time, since the pressure in the first pilot chamber of the flow control switching valve is temporarily lower than the pressure in the second pilot chamber by the one-way throttle valve, the flow control switching valve that is always in the communication position is Temporarily switches to the aperture position. Thereby, the flow control switching valve can limit the flow rate of the pressure oil supplied to the traveling motor. Further, when the pressure in the first pilot chamber and the pressure in the second pilot chamber of the flow control switching valve become equal, the flow control switching valve returns from the throttle position to the communication position. Thereby, pressure oil can be supplied to a traveling motor, without losing pressure.

  According to the invention of claim 4, the flow rate control means is constituted by a logic valve provided with a poppet valve which is provided in the branch passage and limits the flow rate of the pressure oil according to the opening area. In the single traveling operation state at a low speed, the logic valve (poppet valve) is fully opened, and the pressure oil from the hydraulic pump is supplied to the traveling motor as it is. On the other hand, when the driving pressure of the working actuator is higher than the driving pressure of the traveling motor when the single traveling operation state at the low speed is shifted to the combined operation state in which the traveling operation at the low speed and the work operation by the work device are simultaneously performed. The logic valve (poppet valve) is temporarily switched to the limited operation state. As a result, the flow rate of the pressure oil supplied from the hydraulic pump to the travel motor can be limited to suppress a rapid change in the speed of the vehicle.

  Moreover, since the logic valve (poppet valve) quickly returns from the restricted operation state to the fully open operation state, when the combined operation state continues, for example, the pressure valve that has been boosted by the drive pressure of the working actuator travels. The vehicle can be driven by supplying it to the motor. Thereby, it is possible to prevent a decrease in efficiency due to the continued operation while the logic valve (poppet valve) is in the restricted operation state.

  According to the fifth aspect of the present invention, when the driving pressure of the working actuator or the pilot pressure of the working direction switching valve rises when shifting from the single traveling operation state to the combined operation state, the increased pressure is applied to the logic valve. It acts on the first pilot chamber and the second pilot chamber of the pilot valve that controls (opening area of the poppet valve). At this time, since the pressure in the first pilot chamber of the pilot valve is temporarily lower than the pressure in the second pilot chamber due to the one-way throttle valve, the logic valve (poppet valve) that is always in a fully open operation state Is temporarily switched to the limited operation state. Thereby, the logic valve (poppet valve) can restrict | limit the flow volume of the pressure oil supplied to a traveling motor. Further, when the pressure in the first pilot chamber of the pilot valve becomes equal to the pressure in the second pilot chamber, the logic valve (poppet valve) returns from the restricted operation state to the fully open operation state. Thereby, pressure oil can be supplied to a traveling motor, without losing pressure.

1 is an overall view showing a wheeled hydraulic excavator equipped with a hydraulic drive device according to a first embodiment of the present invention. 1 is a hydraulic circuit diagram showing an overall configuration of a hydraulic drive device according to a first embodiment. It is a hydraulic circuit diagram which shows the whole structure of the hydraulic drive device by 2nd Embodiment.

  Hereinafter, a case where a hydraulic drive device for a construction machine according to an embodiment of the present invention is mounted on a wheel-type hydraulic excavator as a construction machine will be described as an example with reference to the accompanying drawings.

  1 and 2 show a first embodiment of the present invention. In the figure, 1 is a wheel-type hydraulic excavator as a construction machine, and the hydraulic excavator 1 is mounted on a self-propelled wheel-type lower traveling body 2 and is pivotably mounted on the lower traveling body 2. The upper revolving body 3 that constitutes a vehicle together with the body 2 and a work device 4 that is provided on the front side of the upper revolving body 3 so as to be able to move up and down are roughly constituted. The wheel-type hydraulic excavator 1 travels, for example, on a general road by a lower traveling body 2 and performs excavation work of earth and sand using a work device 4 described later at a work site.

  Here, the lower traveling body 2 is composed of a track frame 2A and front, rear, left, and right wheels 2B provided on the track frame 2A and driven by a hydraulic motor 16 (see FIG. 2) described later. ing. The lower traveling body 2 is configured to travel on general roads, work sites, and the like by driving the wheels 2B. In addition to the above configuration as a four-wheel drive vehicle, for example, it may be configured as a two-wheel drive vehicle that rotationally drives only the rear wheel side.

  Reference numeral 4 denotes a work device provided on the front side of the upper swing body 3. The work device 4 includes a boom 5 having a base end attached to the upper swing body 3 and an arm 6 attached to the distal end side of the boom 5. A bucket 7 as a work tool attached to the distal end side of the arm 6, a boom cylinder 8 provided between the upper swing body 3 and the boom 5 and moving the boom 5 up and down, and between the boom 5 and the arm 6. The arm cylinder 9 is provided to move the arm 6 up and down, and the bucket cylinder 10 is provided between the arm 6 and the bucket 7 to rotate the bucket 7.

  Here, the boom cylinder 8, the arm cylinder 9, and the bucket cylinder 10 constitute a working actuator for driving the working device 4, and are driven by pressure oil discharged from a hydraulic pump 11 described later. is there.

  Reference numeral 11 denotes a main hydraulic pump provided in the upper swing body 3. The hydraulic pump 11 constitutes a hydraulic source together with a tank 12, and is rotationally driven by a prime mover (not shown) such as a diesel engine. The hydraulic pump 11 discharges hydraulic oil in the tank 12 as high-pressure oil toward a center bypass pipe 13 described later, and this pressure oil is used for a travel direction switching valve 18 and a boom direction switching described later. It is configured to be supplied to the hydraulic motor 16, the boom cylinder 8 and the like via the valve 19 and the like.

  Reference numeral 13 denotes a center bypass pipe serving as a center bypass passage connected to the hydraulic pump 11. In the middle of the center bypass pipe 13, a traveling direction switching valve 18 and a boom direction switching valve, which will be described later, sequentially from the upstream side. 19 is provided. Further, on the upstream side of the traveling direction switching valve 18 in the center bypass pipe 13, a branch pipe 14 </ b> A as a branch path (bridge path) branched from the center bypass pipe 13 is provided, and the branch pipe 14 </ b> A. Is connected to the high-pressure side port of the traveling direction switching valve 18. In addition, another branch pipe 14B is provided in the center bypass pipe 13 on the downstream side of the traveling direction switching valve 18 and on the upstream side of the boom direction switching valve 19, and the branch pipe 14B is provided in the boom direction. The switching valve 19 is connected to the high pressure side port. Further, between the traveling direction switching valve 18 and the boom direction switching valve 19 and the tank 12, tank lines 15A and 15B for returning the return oil from the hydraulic motor 16 and the boom cylinder 8 to the tank 12 side. Is provided.

  In the hydraulic circuit diagram shown in FIG. 2 (and FIG. 3 described later), only the boom cylinder 8 is shown as a working actuator for driving the working device 4, and the direction of the pressure oil supplied to the working actuator is shown. Only the boom direction switching valve 19 is shown as the working direction switching valve to be switched. However, in reality, on the downstream side of the traveling direction switching valve 18 in the center bypass pipe 13, there are an arm direction switching valve, a bucket direction switching valve, etc. (none of which are shown) as working direction switching valves. The pressure oil can be supplied to the arm cylinder 9 and the bucket cylinder 10 through the arm direction switching valve and the bucket direction switching valve.

  Therefore, the following description will be made using a boom cylinder 8 and a boom direction switching valve 19 as representative examples of the working actuator and the working direction switching valve. The arm cylinder 9, the arm direction switching valve, the bucket cylinder 10, A description of the bucket direction switching valve is omitted. However, the arm cylinder 9, the arm direction switching valve, the bucket cylinder 10, and the bucket direction switching valve are the same as the boom cylinder 8 and the boom direction switching valve 19 except that the drive target is different from the arm 6 and the bucket 7. .

  Reference numeral 16 denotes a hydraulic motor as a traveling motor provided in the lower traveling body 2, and the hydraulic motor 16 is driven by pressure oil discharged from the hydraulic pump 11 to drive the vehicle (the lower traveling body 2 and the upper swing body 3). It is intended to run. Here, a pair of main pipes 17A and 17B as pressure oil supply pipes for supplying pressure oil to the hydraulic motor 16 are connected between the hydraulic motor 16 and a travel direction switching valve 18 described later. Is provided. Each of these main pipelines 17A, 17B is connected to the branch pipeline 14A or the tank pipeline 15A according to the switching position of the traveling direction switching valve 18.

  Reference numeral 18 denotes a travel direction switching valve connected to the center bypass pipe 13, which travel direction switching valve 18 is a pressure oil supplied to the hydraulic motor 16 through the branch pipe 14 </ b> A branched from the center bypass pipe 13. The direction is switched. Here, the traveling direction switching valve 18 has left and right hydraulic pilot chambers 18A and 18B, and is normally held at the neutral position (A). The traveling direction switching valve 18 is supplied with pilot pressure generated in response to an operator's operation to the left and right hydraulic pilot chambers 18A and 18B, so that the forward high-speed position (from the neutral position (A)) ( B), forward low speed position (C), reverse high speed position (D), reverse reverse speed position (E).

  Here, when the traveling direction switching valve 18 is held at the neutral position (A), the main pipelines 17A and 17B are connected to the tank 12 via the tank pipeline 15A, and the hydraulic motor 16 does not rotate. At this time, the pressure oil from the hydraulic pump 11 is supplied to the downstream side of the traveling direction switching valve 18 in the center bypass line 13. Thus, pressure oil is supplied to the boom cylinder 8 according to a switching position of a boom direction switching valve 19 described later, and the boom cylinder 8 can be expanded and contracted (the working device 4 can be driven).

  When the traveling direction switching valve 18 is switched to the forward high speed position (B), the pressure oil from the hydraulic pump 11 is branched into the branch line 14A, the traveling direction switching valve 18, the main line 17A, and a flow rate control switching valve 21 described later. Is supplied to the hydraulic motor 16 via the motor, and the hydraulic motor 16 rotates in a direction to advance the vehicle. The pressure oil supplied to the hydraulic motor 16 is discharged to the tank 12 via the main line 17B, the flow rate control switching valve 21, the traveling direction switching valve 18, and the tank line 15A.

  At this time, the pressure oil from the hydraulic pump 11 is not supplied to the downstream side of the traveling direction switching valve 18 in the center bypass pipe 13. For this reason, when the traveling direction switching valve 18 is switched to the forward high speed position (B), the boom cylinder 8 cannot be expanded and contracted (the working device 4 cannot be driven).

  When the traveling direction switching valve 18 is switched to the forward low speed position (C), the pressure oil from the hydraulic pump 11 is supplied to the hydraulic motor 16 and the traveling direction switching valve 18 of the center bypass pipe 13 Pressure oil is also supplied downstream. In this case, the boom cylinder 8 can be expanded and contracted according to a switching position of a boom direction switching valve 19 described later while the vehicle is traveling in the forward direction (the working device 4 can be driven). The forward low speed position (C) is a state in which the operator performs an inching operation between the neutral position (A) and the forward high speed position (B), that is, the spool of the traveling direction switching valve 18 is in the neutral position ( This corresponds to the state in which the operation of moving slightly between A) and the forward high speed position (B) is represented as the switching position of the traveling direction switching valve 18.

  On the other hand, when the traveling direction switching valve 18 is switched to the reverse high speed position (D), the pressure oil from the hydraulic pump 11 is branched into the branch line 14A, the traveling direction switching valve 18, the main line 17B, and a flow rate control switching described later. It is supplied to the hydraulic motor 16 through the valve 21 and the hydraulic motor 16 rotates in the direction of moving the vehicle backward. The pressure oil supplied to the hydraulic motor 16 is discharged to the tank 12 via the main line 17A, the flow rate control switching valve 21, the travel direction switching valve 18, and the tank line 15A.

  At this time, the pressure oil from the hydraulic pump 11 is not supplied to the downstream side of the traveling direction switching valve 18 in the center bypass pipe 13. For this reason, when the traveling direction switching valve 18 is switched to the reverse high speed position (D), the boom cylinder 8 cannot be expanded and contracted (the working device 4 cannot be driven).

  When the traveling direction switching valve 18 is switched to the reverse low speed position (E), the pressure oil from the hydraulic pump 11 is supplied to the hydraulic motor 16 and the traveling direction switching valve 18 of the center bypass pipe 13 Pressure oil is also supplied downstream. In this case, the boom cylinder 8 can be expanded and contracted in accordance with a switching position of a boom direction switching valve 19 described later while the vehicle is traveling in the reverse direction (the working device 4 can be driven). The reverse low speed position (E) is a state in which the operator performs an inching operation between the neutral position (A) and the reverse high speed position (D), that is, the spool of the traveling direction switching valve 18 is in the neutral position ( This corresponds to the state in which the operation of slightly moving between A) and the reverse high speed position (D) is represented as the switching position of the traveling direction switching valve 18.

  Reference numeral 19 denotes a boom direction switching valve as a working direction switching valve connected to the downstream side of the traveling direction switching valve 18 in the center bypass pipe 13. The boom direction switching valve 19 serves as a working actuator. The direction of the pressure oil supplied to the boom cylinder 8 is switched. Here, the boom direction switching valve 19 has left and right hydraulic pilot chambers 19A and 19B, and is normally held in a neutral position (A). The boom direction switching valve 19 is supplied with pilot pressure generated in response to an operator's operation to the left and right hydraulic pilot chambers 19A and 19B, so that the boom direction switching valve 19 is moved from the neutral position (A) to the forward operation position. (B) Switched to the reverse operation position (c).

  Here, a pair of main pipelines 20A and 20B is provided between the boom cylinder 8 and the boom direction switching valve 19, and one of the main pipelines 20A is a bottom-side oil chamber of the boom cylinder 8. 8 A is connected to one pressure oil inflow / outflow port of the boom direction switching valve 19. The other main pipe line 20 </ b> B connects the rod side oil chamber 8 </ b> B of the boom cylinder 8 to the other pressure oil inflow / outflow port of the boom direction switching valve 19.

  When the boom direction switching valve 19 is held at the neutral position (A), the main pipelines 20A and 20B are connected to the tank 12 via the tank pipeline 15B. Further, the pressure oil from the hydraulic pump 11 is supplied to the downstream side of the boom direction switching valve 19 in the center bypass pipe 13 (discharged to the tank 12 through the center bypass pipe 13).

  When the boom direction switching valve 19 is switched from the neutral position (A) to the forward operation position (B), the pressure oil from the hydraulic pump 11 flows through the branch line 14B, the boom direction switching valve 19, and the main line 20A. The pressure oil in the rod side oil chamber 8B is discharged to the tank 12 via the main line 20B, the boom direction switching valve 19, and the tank line 15B. Thereby, the boom cylinder 8 is extended by the pressure oil supplied to the bottom side oil chamber 8A, and the boom 5 is lifted upward.

  When the boom direction switching valve 19 is switched from the neutral position (A) to the reverse operation position (C), the pressure oil from the hydraulic pump 11 passes through the branch line 14B, the boom direction switching valve 19, and the main line 20B. The pressure oil in the bottom side oil chamber 8A is discharged to the tank 12 via the main line 20A, the boom direction switching valve 19, and the tank line 15B. Thereby, the boom cylinder 8 is contracted by the pressure oil supplied to the rod side oil chamber 8B, and the boom 5 is swung downward.

  Next, the flow control switching valve 21 provided between the traveling direction switching valve 18 and the hydraulic motor 16 will be described.

  That is, 21 is a flow control switching valve as a flow control means provided in the middle of the main pipes 17A and 17B between the traveling direction switching valve 18 and the hydraulic motor 16, and the flow control switching valve 21 is a hydraulic motor. The flow rate of the pressure oil supplied to 16 is controlled. Here, the flow rate control switching valve 21 is configured such that the pressure oil discharged from the hydraulic pump 11 is supplied to the hydraulic motor 16 and the boom cylinder from a single traveling operation state where the pressure oil discharged from the hydraulic pump 11 is supplied only to the hydraulic motor 16. 8, the flow rate of the pressure oil supplied to the hydraulic motor 16 is controlled when shifting to the combined operation state of traveling and work supplied to both of the hydraulic pressures 8 and 8.

  More specifically, the flow control switching valve 21 is configured such that, for example, when the traveling direction switching valve 18 is switched to the forward low speed position (C) or the reverse low speed position (E), the drive pressure of the boom cylinder 8 is hydraulic. The flow rate of the pressure oil supplied to the hydraulic motor 16 when the driving pressure of the motor 16 is higher is limited.

  Here, the flow rate control switching valve 21 has a communication position (a) for maintaining the main pipelines 17A and 17B in a communicating state without restricting the flow rate, and a throttle position (b And is always held at the communication position (a). When the flow rate control switching valve 21 is in the communication position (a), the pressure oil from the hydraulic pump 11 is supplied to the hydraulic motor 16 as it is. On the other hand, in a state where the flow control switching valve 21 is switched to the throttle position (b), the pressure oil from the hydraulic pump 11 is supplied to the hydraulic motor 16 via the throttle. Thus, the flow rate of the pressure oil supplied to the hydraulic motor 16 is limited.

  Further, the flow rate control switching valve 21 is temporarily switched to the throttle position (b) when the driving pressure of the boom cylinder 8 is higher than the driving pressure of the hydraulic motor 16, and thereafter, the one-way throttle valve 23 described later. It is configured to return to the communication position (a). For this purpose, the flow control switching valve 21 is configured as a hydraulic pilot type switching valve having a first pilot chamber 21A that switches to the communication position (a) and a second pilot chamber 21B that switches to the throttle position (b). Yes. The flow rate control switching valve 21 is provided with a spring 21C that biases the spool toward the communication position (a), and the spring 21C is switched from the communication position (a) to the throttle position (b). The pressure difference between the first pilot chamber 21A and the second pilot chamber 21B is set.

  The first and second pilot chambers 21A and 21B are connected to first and second pilot pipelines 22A and 22B for supplying the driving pressure of the boom cylinder 8. Here, the first and second pilot pipelines 22 </ b> A and 22 </ b> B are upstream of the traveling direction switching valve 18 in the center bypass pipeline 13 and upstream of the boom direction switching valve 19. The downstream sides are connected to the first and second pilot chambers 21A and 21B, respectively. A one-way throttle valve 23 to be described later is provided in the middle of the first pilot pipeline 22A.

  Reference numeral 23 denotes a one-way throttle valve provided in the middle of the first pilot pipe line 22A. The one-way throttle valve 23 temporarily compares the pressure in the first pilot chamber 21A with the pressure in the second pilot chamber 21B. It is for making it low. Here, the one-way throttle valve 23 includes a throttle 23A that restricts the flow rate when pressure oil flows into the first pilot chamber 21A, and a check valve that communicates when pressure oil flows out of the first pilot chamber 21A. The throttle 23A and the check valve 23B are provided in parallel to the first pilot pipeline 22A. Thereby, when the pressure oil is supplied to the downstream side of the traveling direction switching valve 18 in the center bypass pipe 13, the pressure oil supplied to the first pilot chamber 21A is temporarily restricted by the throttle 23A. By doing so, the pressure in the first pilot chamber 21A is configured to be temporarily lower than the pressure in the second pilot chamber 21B.

  The hydraulic excavator 1 provided with the hydraulic drive device according to the present embodiment has the above-described configuration, and the operation thereof will be described next. Note that this description will focus on the case where the traveling direction is the forward direction, and is omitted when the traveling direction is the reverse direction. However, with respect to the reverse direction, the switching position of the traveling direction switching valve 18 is switched to the reverse high speed position (D) and the reverse low speed position (E), and the flow direction of the pressure oil supplied to the hydraulic motor 16 is changed accordingly. Except for the reverse, it is the same as the forward direction.

  First, a description will be given of a single work state in which the excavator 1 does not travel and only the work by the work device 4 is performed, that is, the travel direction switching valve 18 is in the neutral position (A). In this case, the pressure oil from the hydraulic pump 11 is not supplied to the hydraulic motor 16 but is supplied to the downstream side of the traveling direction switching valve 18 in the center bypass pipe 13. When the boom direction switching valve 19 is switched from, for example, the neutral position (A) to the forward operation position (B), the pressure oil from the hydraulic pump 11 is branched into the branch line 14B, the boom direction switching valve 19, the main pipe. It is supplied to the bottom side oil chamber 8A of the boom cylinder 8 through the path 20A, and the pressure oil in the rod side oil chamber 8B is discharged to the tank 12 through the main pipe line 20B, the boom direction switching valve 19, and the tank pipe line 15B. Is done. Thereby, the boom cylinder 8 can be extended by the pressure oil supplied to the bottom side oil chamber 8A, and the boom 5 can be lifted upward.

  On the other hand, when the boom direction switching valve 19 is switched from the neutral position (A) to the reverse operation position (C), the hydraulic oil from the hydraulic pump 11 is branched into the branch line 14B, the boom direction switching valve 19, and the main line. 20B is supplied to the rod side oil chamber 8B of the boom cylinder 8, and the pressure oil in the bottom side oil chamber 8A is discharged to the tank 12 via the main pipe line 20A, the boom direction switching valve 19, and the tank pipe line 15B. The Thereby, the boom cylinder 8 can be contracted by the pressure oil supplied to the rod side oil chamber 8B, and the boom 5 can be swung downward.

  Next, in a single traveling operation state at high speed, that is, when the traveling direction switching valve 18 is in the forward low speed position (B), the pressure oil discharged from the hydraulic pump 11 is branched from the center bypass line 13. It is supplied to the hydraulic motor 16 via the road 14A via the traveling direction switching valve 18, the main pipeline 17A, and the flow rate control switching valve 21. At this time, the flow control switching valve 21 is held at the communication position (a) by the spring 21C, and the pressure oil from the hydraulic pump 11 is supplied to the hydraulic motor 16 as it is. Thereby, pressure oil can be supplied to the hydraulic motor 16 without losing pressure. During such high speed travel, the pressure oil from the hydraulic pump 11 is not supplied to the downstream side of the travel direction switching valve 18 in the center bypass pipe 13 and work by the work device 4 is performed. I can't.

  On the other hand, when the vehicle is in a single traveling operation state at low speed, that is, when the traveling direction switching valve 18 is in the forward low speed position (C) and the boom direction switching valve 19 is in the neutral position (A), the hydraulic pump 11 The pressure oil discharged from the center is supplied to the hydraulic motor 16 from the center bypass pipe 13 via the branch pipe 14A, through the traveling direction switching valve 18, the main pipe 17A, and the flow rate control switching valve 21. At this time, the flow control switching valve 21 is held at the communication position (a) by the spring 21C, and the pressure oil from the hydraulic pump 11 is supplied to the hydraulic motor 16 as it is. Thereby, pressure oil can be supplied to the hydraulic motor 16 without losing pressure. Further, the pressure oil discharged from the hydraulic pump 11 is also supplied to the downstream side of the traveling direction switching valve 18 in the center bypass pipe 13, but the pressure oil is not supplied to the boom cylinder 8, It is discharged to the tank 12 through the center bypass pipe 13.

  Next, when the single traveling operation state at the low speed is shifted to the combined operation state in which the traveling at the low speed and the work by the work device 4 are simultaneously performed, that is, the traveling direction switching valve 18 is in the forward low speed position (C). When the boom direction switching valve 19 is switched from the neutral position (A) to the forward operation position (B) or the reverse operation position (C), the pressure oil discharged from the hydraulic pump 11 is discharged from the center bypass pipe. The oil is supplied from the passage 13 to the hydraulic motor 16 via the branch conduit 14A via the traveling direction switching valve 18, the main conduit 17A, and the flow rate control switching valve 21.

  At the same time, the pressure oil discharged from the hydraulic pump 11 is also supplied to the downstream side of the traveling direction switching valve 18 in the center bypass pipe 13, and the pressure oil is switched to the boom direction switching valve 19. It is also supplied to the boom cylinder 8 according to the position. At this time, as the boom cylinder 8 starts to expand and contract, the drive pressure of the boom cylinder 8 may increase. When the drive pressure of the boom cylinder 8 is increased in this way, the increased pressure acts on the first pilot chamber 21A through the first pilot pipe line 22A and the second pressure through the second pilot pipe line 22B. Acting on the pilot chamber 21B.

  At this time, since the one-way throttle valve 23 is provided in the first pilot pipe line 22A, the pressure in the first pilot chamber 21A is temporarily lower than the pressure in the second pilot chamber 21B. . For this reason, the flow rate control switching valve 21 that is normally in the communication position (a) is temporarily switched to the throttle position (b). Thereby, the flow control switching valve 21 can limit the flow rate of the pressure oil supplied to the hydraulic motor 16, and the rotational speed (rotational speed) of the hydraulic motor 16 suddenly increases due to the driving pressure of the boom cylinder 8. Can be suppressed.

  When the pressure in the first pilot chamber 21A increases and approaches the pressure in the second pilot chamber 21B, the flow rate control switching valve 21 is returned from the throttle position (b) to the communication position (a) by the spring 21C. To do. Thereby, pressure oil can be supplied to the hydraulic motor 16 without losing pressure.

  As described above, according to the present embodiment, the flow rate of the pressure oil supplied to the hydraulic motor 16 by the flow rate control switching valve 21 can be gradually changed when shifting from the single traveling operation state to the combined operation state. . That is, when the drive pressure of the boom cylinder 8 rises, the pressure in the first pilot chamber 21A of the flow control switching valve 21 is temporarily compared with the pressure in the second pilot chamber 21B by the one-way throttle valve 23. The flow rate control switching valve 21 is temporarily switched to the throttle position (b). For this reason, it can suppress that pressure oil is supplied to the hydraulic motor 16 preferentially rather than the boom cylinder 8, and can suppress that the speed of a vehicle increases rapidly contrary to an operator's intention. .

  In addition, since the change in the speed of the vehicle can be suppressed by the flow rate control switching valve 21, it is not necessary to provide a plurality of hydraulic pumps as in the prior art. For this reason, even in the combined operation state in which the traveling operation at low speed and the work operation by the work device 4 are performed simultaneously, the delay of the operation of the boom cylinder 8 (work device 4) can be suppressed.

  When the pressure in the first pilot chamber 21A and the pressure in the second pilot chamber 21B of the flow control switching valve 21 are equal, the flow control switching valve 21 is moved from the throttle position (b) to the communication position (a Return to). Thereby, pressure oil can be supplied to the hydraulic motor 16 without losing pressure.

  Next, FIG. 3 shows a second embodiment of the present invention. A feature of the present embodiment is that, instead of the flow control switching valve 21 as the flow control means used in the first embodiment, a logic valve 31 as a flow control means is provided in the branch line 14A branched from the center bypass passage 13. It is that it was set as the structure which provides. In the present embodiment, the same components as those in the first embodiment described above are denoted by the same reference numerals, and the description thereof is omitted.

  In the figure, 31 is a logic valve as a flow rate control means provided on the upstream side of the traveling direction switching valve 18 in the middle of the branch line 14A branching from the center bypass line 13, and the logic valve 31 is a hydraulic valve. The flow rate of the pressure oil supplied to the motor 16 is controlled. Here, the logic valve 31 is configured so that the pressure oil discharged from the hydraulic pump 11 is supplied to the hydraulic motor 16 and the boom cylinder 8 from a single traveling operation state where the pressure oil discharged from the hydraulic pump 11 is supplied only to the hydraulic motor 16. When shifting to the combined operation state of traveling and work supplied to both, the flow rate of the pressure oil supplied to the hydraulic motor 16 is controlled.

  More specifically, the logic valve 31 is configured such that, for example, when the traveling direction switching valve 18 is switched to the forward low speed position (C) or the reverse low speed position (E), the drive pressure of the boom cylinder 8 is set to the hydraulic motor 16. This restricts the flow rate of the pressure oil supplied to the hydraulic motor 16 when it is higher than the drive pressure. Here, the logic valve 31 is roughly constituted by a poppet valve 32 and a pilot valve 33 which will be described later.

  Reference numeral 32 denotes a poppet valve that controls the flow rate of the pressure oil in accordance with the opening area. The poppet valve 32 is provided in the middle of the branch line 14A. Here, the poppet valve 32 includes a valve body 32A in which the check valve 32A1 is accommodated, a valve oil chamber (passage) 32B into which pressure oil from the branch pipe 14A flows, and a valve oil chamber 32B across the valve body 32A. And a back pressure chamber 32C provided on the opposite side. The poppet valve 32 increases the opening area by variably adjusting the lift amount (upward and downward displacement in FIG. 3) of the valve body 32A in cooperation with the pilot valve 33 described later ( A fully open operation state in which the branch line 14A is in a communication state (in a fully open state), and a limited operation state in which the flow area of the pressure oil flowing through the branch line 14A is limited by reducing the opening area (decreasing from the fully open state). It is the structure switched to.

  A pilot valve 33 controls the opening area of the poppet valve 32 (the lift amount of the valve body 32A). The pilot valve 33 connects the back pressure chamber 32C of the poppet valve 32 and the outflow side of the branch pipe 14A. It is provided in the middle of the oil passage 34 to be performed. Here, the pilot valve 33 has a communication position (a) for bringing the oil passage 34 into a communication state and a shut-off position (b) for shutting off the pressure oil flowing through the oil passage 34. a).

  When the pilot valve 33 is in the communication position (a), the pressure in the back pressure chamber 32C of the poppet valve 32 decreases to a pressure value relatively lower than the pressure in the valve oil chamber 32B. As a result, the valve body 32A of the poppet valve 32 is displaced in the direction in which the opening area is increased (downward in FIG. 3), and the opening area of the poppet valve 32 is maximized (fully opened). In this case, the pressure oil from the hydraulic pump 11 is supplied to the hydraulic motor 16 via the traveling direction switching valve 18 without the flow rate being limited by the poppet valve 32.

  On the other hand, when the pilot valve 33 is in the shut-off position (b), the back pressure chamber 32C is shut off with respect to the oil passage 34, so that the pressure in the back pressure chamber 32C of the poppet valve 32 and the pressure in the valve oil chamber 32B are The state is almost equal. As a result, the lift amount of the valve body 32A of the poppet valve 32 is suppressed to be small by the pressure in the back pressure chamber 32C (displaced in a direction in which the opening area is reduced), and the opening area of the poppet valve 32 is more than the fully opened state. Reduced state. In this case, the pressure oil from the hydraulic pump 11 is supplied to the hydraulic motor 16 via the traveling direction switching valve 18 in a state where the flow rate is limited by the poppet valve 32.

  The pilot valve 33 is temporarily switched to the cutoff position (b) when the drive pressure of the boom cylinder 8 is higher than the drive pressure of the hydraulic motor 16, and then communicated by a one-way throttle valve 36 described later. The configuration returns to (a). For this purpose, the pilot valve 33 is configured as a hydraulic pilot type switching valve having a first pilot chamber 33A that switches to the communication position (a) and a second pilot chamber 33B that switches to the blocking position (b). The pilot valve 33 is provided with a spring 33C that urges the spool toward the communication position (a), and the spring 33C is the first when the communication position (a) is switched to the cutoff position (b). The pressure difference between the first pilot chamber 33A and the second pilot chamber 33B is set.

  The first and second pilot chambers 33A and 33B are connected to first and second pilot pipes 35A and 35B for supplying the drive pressure of the boom cylinder 8. Here, the first and second pilot pipelines 35 </ b> A and 35 </ b> B are connected to the downstream side of the traveling direction switching valve 18 and the upstream side of the boom direction switching valve 19 in the center bypass pipeline 13. The downstream sides are connected to the first and second pilot chambers 33A and 33B, respectively. A one-way throttle valve 36 to be described later is provided in the middle of the first pilot pipeline 35A.

  A one-way throttle valve 36 is provided in the middle of the first pilot pipe line 35A. The one-way throttle valve 36 temporarily compares the pressure in the first pilot chamber 33A with the pressure in the second pilot chamber 33B. It is for making it low. Here, the one-way throttle valve 36 includes a throttle 36A that restricts the flow rate when pressure oil flows into the first pilot chamber 33A, and a check valve that communicates when pressure oil flows out of the first pilot chamber 33A. The throttle 36A and the check valve 36B are provided in parallel with the first pilot pipe 35A. Thereby, when the pressure oil is supplied to the downstream side of the traveling direction switching valve 18 in the center bypass pipe 13, the pressure oil supplied to the first pilot chamber 33A is temporarily restricted by the throttle 36A. By doing so, the pressure in the first pilot chamber 33A is configured to be temporarily lower than the pressure in the second pilot chamber 33B.

  According to the second embodiment configured as described above, the traveling direction switching valve 18 is in the forward low speed position (C) in the single traveling operation state at low speed, and the boom direction switching valve 19 is located. Is in the neutral position (A), the pressure oil discharged from the hydraulic pump 11 passes through the branch bypass line 14A from the center bypass line 13 and then the logic valve 31, the travel direction switching valve 18, and the main line 17A. Is supplied to the hydraulic motor 16. At this time, the pilot valve 33 is held at the communication position (a) by the spring 33C, so that the logic valve 31 communicates the branch pipe line 14A with the opening area of the poppet valve 32 being maximized (fully opened). It becomes the fully open operation state. In this case, the pressure oil from the hydraulic pump 11 is supplied to the hydraulic motor 16 via the traveling direction switching valve 18 without the flow rate being limited by the poppet valve 32. Thereby, pressure oil can be supplied to the hydraulic motor 16 without losing pressure.

  Further, when the low-speed single traveling operation state shifts to the combined operation state in which the low-speed traveling and the work by the work device 4 are performed simultaneously, that is, the traveling direction switching valve 18 is in the forward low speed position (C), When the boom direction switching valve 19 is switched from the neutral position (A) to the forward direction operation position (B) or the reverse direction operation position (C), the pressure oil discharged from the hydraulic pump 11 is discharged from the center bypass line. 13 is supplied to the hydraulic motor 16 via the branch line 14A, the logic valve 31, the traveling direction switching valve 18, and the main line 17A.

  At the same time, the pressure oil discharged from the hydraulic pump 11 is also supplied to the downstream side of the traveling direction switching valve 18 in the center bypass pipe 13, and the pressure oil is switched to the boom direction switching valve 19. It is also supplied to the boom cylinder 8 according to the position. At this time, as the boom cylinder 8 starts to expand and contract, the drive pressure of the boom cylinder 8 may increase. When the drive pressure of the boom cylinder 8 increases as described above, the increased pressure acts on the first pilot chamber 33A of the pilot valve 33 through the first pilot line 35A and the second pilot line. It acts on the second pilot chamber 33B through 35B.

  At this time, since the one-way throttle valve 36 is provided in the first pilot pipeline 35A, the pressure in the first pilot chamber 33A is temporarily lower than the pressure in the second pilot chamber 33B. . For this reason, the pilot valve 33 which is always in the communication position (a) is temporarily switched to the shut-off position (b), whereby the logic valve 31 reduces the opening area of the poppet valve 32 from the fully open state. Thus, a restricting operation state for restricting the flow rate of the pressure oil flowing through the branch conduit 14A is obtained. In this case, the pressure oil from the hydraulic pump 11 is supplied to the hydraulic motor 16 via the traveling direction switching valve 18 in a state where the flow rate is limited by the poppet valve 32. Thereby, the logic valve 31 can restrict | limit the flow volume of the pressure oil supplied to the hydraulic motor 16, and can suppress that the rotation speed of the hydraulic motor 16 raises rapidly by the drive pressure of the boom cylinder 8. FIG. .

  When the pressure in the first pilot chamber 33A of the pilot valve 33 increases and approaches the pressure in the second pilot chamber 33B, the pilot valve 33 is moved from the shut-off position (b) to the communication position (a) by the spring 33C. Return to. As a result, the logic valve 31 enters the fully open operation state in which the opening area of the poppet valve 32 is maximized (fully opened) and the branch pipe 14A is in communication, and pressure oil is supplied to the hydraulic motor 16 without loss of pressure. can do.

  As described above, according to the second embodiment, the flow rate of the pressure oil supplied to the hydraulic motor 16 by the logic valve 31 can be gradually changed when shifting from the single traveling operation state to the combined operation state. it can. That is, when the drive pressure of the boom cylinder 8 rises, the pressure in the first pilot chamber 33A of the pilot valve 33 temporarily becomes lower than the pressure in the second pilot chamber 33B by the one-way throttle valve 36. The logic valve 31 (poppet valve 32) is temporarily switched to the limited operation state. For this reason, it can suppress that pressure oil is supplied to the hydraulic motor 16 preferentially rather than the boom cylinder 8, and can suppress that the speed of a vehicle increases rapidly contrary to an operator's intention. .

  In addition, since the speed change of the vehicle can be suppressed by the logic valve 31 (poppet valve 32) as described above, it is not necessary to provide a plurality of hydraulic pumps as in the prior art. For this reason, even in the combined operation state in which the traveling operation at low speed and the work operation by the work device 4 are performed simultaneously, the delay of the operation of the boom cylinder 8 (work device 4) can be suppressed.

  When the pressure in the first pilot chamber 33A of the pilot valve 33 becomes equal to the pressure in the second pilot chamber 33B, the pilot valve 33 returns from the shut-off position (b) to the communication position (a). . As a result, the logic valve 31 (poppet valve 32) is fully opened and pressure oil can be supplied to the hydraulic motor 16 without losing pressure.

  In the first embodiment described above, the flow rate control switching valve 21 has a pilot pressure as a driving pressure of the boom cylinder 8 as a working actuator (downstream of the traveling direction switching valve 18 in the center bypass pipe 13). As an example, a case where the hydraulic pressure is used on the side and upstream of the boom direction switching valve 19 is described. However, the present invention is not limited to this, and the switching operation of the flow control switching valve is performed using, for example, the pilot pressure of a working direction switching valve such as a boom direction switching valve, an arm direction switching valve, or a bucket direction switching valve. It is good also as a structure to perform.

  In the second embodiment described above, the pilot valve 33 that controls the poppet valve 32 (the opening area thereof) of the logic valve 31 is used as a pilot pressure for driving the boom cylinder 8 as a working actuator (center bypass pipe). The case where the configuration using the hydraulic pressure at the downstream side of the traveling direction switching valve 18 and the upstream side of the boom direction switching valve 19 in the road 13 is described as an example. However, the present invention is not limited to this, and switching operation of the pilot valve of the logic valve is performed by, for example, the pilot pressure of the working direction switching valve such as the boom direction switching valve, the arm direction switching valve, or the bucket direction switching valve. It is good also as a structure performed using.

  Further, in each of the above-described embodiments, the wheel-type hydraulic excavator 1 has been described as an example of the construction machine. However, the present invention is not limited to this, and may be applied to a crawler-type hydraulic excavator. It can also be applied to various possible construction machines.

1 Excavator (construction machine)
2 Lower traveling body (vehicle)
3 Upper turning body (vehicle)
4 Working device 8 Boom cylinder (working actuator)
9 Arm cylinder (working actuator)
10 Bucket cylinder (working actuator)
11 Hydraulic pump (hydraulic power source)
12 Tank (hydraulic power source)
13 Center bypass conduit (center bypass passage)
14A, 14B Branch pipe (branch passage)
16 Hydraulic motor (travel motor)
17A, 17B Main pipeline (pressure oil supply pipeline)
18 Traveling direction switching valve 19 Boom direction switching valve (working direction switching valve)
21 Flow control switching valve (flow control means)
21A First pilot chamber 21B Second pilot chamber 22A First pilot line 22B Second pilot line 23 One-way throttle valve 31 Logic valve (flow rate control means)
32 poppet valve 33 pilot valve 33A first pilot chamber 33B second pilot chamber 35A first pilot line 35B second pilot line 36 one-way throttle valve

Claims (5)

A hydraulic source comprising a hydraulic pump and a tank, a center bypass passage connected to the hydraulic pump, a travel motor driven by pressure oil discharged from the hydraulic pump, and a vehicle driven by the hydraulic oil, and discharged from the hydraulic pump A driving actuator that is driven by pressure oil to drive a working device, and a traveling actuator that switches the direction of the pressure oil that is supplied to the traveling motor through a branch passage that is connected to the center bypass passage and branches from the center bypass passage. Hydraulic pressure of a construction machine comprising: a direction switching valve; and a working direction switching valve that is connected to a downstream side of the traveling direction switching valve in the center bypass passage and switches a direction of pressure oil supplied to the working actuator. In the drive device,
Pressure oil discharged from the hydraulic pump is supplied to both the travel motor and the working actuator from a single traveling operation state at low speed where the pressure oil discharged from the hydraulic pump is supplied only to the travel motor. A flow control means for controlling the flow rate of pressure oil supplied to the travel motor when the drive pressure of the work actuator is higher than the drive pressure of the travel motor A hydraulic drive device for a construction machine, comprising: Between the traveling direction switching valve and the traveling motor, a pressure oil supply line for supplying pressure oil to the traveling motor is connected and provided.
The flow rate control means is provided in the pressure oil supply line, and has a communication position that brings the pressure oil supply line into a communication state and a throttle position that restricts the flow rate of the pressure oil flowing through the pressure oil supply line. Consists of flow control switching valve,
The flow rate control switching valve is normally in the communication position, and is temporarily switched to the throttle position when the driving pressure of the working actuator is higher than the driving pressure of the travel motor, and then returns to the communication position. The hydraulic drive device for a construction machine according to claim 1. The flow rate control switching valve comprises a hydraulic pilot type switching valve having a first pilot chamber that switches to a communication position and a second pilot chamber that switches to a throttle position,
Connected to the first and second pilot chambers are first and second pilot pipes for supplying a driving pressure of the working actuator or a pilot pressure of the working direction switching valve,
Pressure oil flows into the first pilot chamber for temporarily lowering the pressure of the first pilot chamber as compared with the pressure of the second pilot chamber into the first pilot pipe line. 3. The hydraulic drive device for a construction machine according to claim 2, wherein when the pressure oil flows out of the first pilot chamber, a one-way throttle valve that communicates with the first pilot chamber is provided. The flow rate control means is provided in the middle of the branch passage, and is constituted by a logic valve provided with a poppet valve that limits the flow rate of pressure oil according to the opening area,
The logic valve includes a fully-open operation state in which the opening area of the poppet valve is fully opened and the branch passage is in a communication state; It is configured to switch to a restricted operation state that restricts the flow rate of
The logic valve is normally in a fully open operation state, and is temporarily switched to a limited operation state when the drive pressure of the working actuator is higher than the drive pressure of the travel motor, and then returns to the fully open operation state. The hydraulic drive device for a construction machine according to claim 1. The logic valve has a first pilot chamber that switches to the fully open operation state and a second pilot chamber that switches to the limited operation state, and includes a pilot valve that controls an opening area of the poppet valve,
Connected to the first and second pilot chambers are first and second pilot pipes for supplying a driving pressure of the working actuator or a pilot pressure of the working direction switching valve,
Pressure oil flows into the first pilot chamber for temporarily lowering the pressure of the first pilot chamber as compared with the pressure of the second pilot chamber into the first pilot pipe line. 5. The hydraulic drive device for a construction machine according to claim 4, wherein a flow rate is limited when the pressure oil flows out from the first pilot chamber, and a one-way throttle valve communicating with the pressure oil is provided.

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