CN111936751A - Hydraulic drive system for construction machine - Google Patents

Abstract

A hydraulic drive system for a construction machine includes a swing motor, a swing operation device that outputs a swing operation signal corresponding to the tilt angle of the operating lever, and one of a neutral position for blocking a pair of supply and discharge lines and for enabling a pair of supply and discharge lines. A swing direction switching valve that switches between operating positions communicated with the pump line and the tank line, and a control device that sends a command current that increases as the swing operation signal becomes larger to the swing direction change valve, the control device When the operating lever of the swing operating device is returned to the neutral state, when the swing speed detected by the speed detector is lower than the first threshold value, the swing direction switching valve is switched from the neutral position to the discharge-side supply and discharge line and the storage tank. In the working position connected to the pipeline, when the rotation speed detected by the speed detector is lower than the second threshold value, the rotation direction switching valve is switched from the working position to the neutral position to control the rotation direction switching valve.

Description

Hydraulic drive system for construction machinery

technical field

The present invention relates to a hydraulic drive system of a construction machine.

Background technique

Construction machines such as a hydraulic shovel and a hydraulic crane are equipped with a hydraulic drive system including a swing motor that swings a swing body (for example, see Patent Document 1). The working fluid is supplied from the pump to the swing motor through the swing direction switching valve.

Specifically, the swing direction switching valve is connected to the swing motor through a pair of supply and discharge lines. The rotation direction switching valve switches between a neutral position for blocking the pair of supply and discharge lines and an operating position for communicating one of the pair of supply and discharge lines with the pump line and the other with the tank line. The swing direction switching valve switches from the neutral position to the operating position when the operation lever of the swing operation device is tilted, and has an opening degree corresponding to the tilt angle (swing operation amount) of the operation lever.

However, when the turning operation lever is returned to the neutral state in order to stop the turning body during turning, the pair of supply and discharge lines are blocked by the turning direction switching valve. Therefore, when the turning speed of the turning body decelerates to zero, a pressure difference may remain between the supply and discharge lines on the discharge side that are in the closed state and the supply and discharge lines on the supply side that flow directly into the hydraulic fluid from the accumulator during turning deceleration. The so-called swing-back phenomenon in which the rotary body is reversed due to the pressure difference, and the magnitude of the pressure difference between the supply and discharge lines is reversed due to the inversion, and the rotary body is further reversed, occurs repeatedly.

In the hydraulic drive system disclosed in Patent Document 1, in order to prevent such a backlash phenomenon, an anti-reverse valve is used.

Prior art literature:

Patent Literature:

Patent Document 1: Japanese Patent Application Laid-Open No. 9-310701.

SUMMARY OF THE INVENTION

The problem to be solved by the invention:

However, in the case of using the anti-reverse valve as in Patent Document 1, the size of the rotary circuit will be large, and the cost will be high.

Therefore, an object of the present invention is to prevent the backlash phenomenon when the rotation is stopped without using an anti-reverse valve.

Means to solve the problem:

In order to solve the above-mentioned problems, the present invention provides, from a first aspect, a hydraulic drive system for a construction machine, comprising: a swing motor that swings a swing body; and an operation lever that outputs a swing corresponding to a tilt angle of the operation lever A swing operation device for operating signals; a swing direction switch valve connected to the swing motor through a pair of supply and discharge lines, the swing direction switch valve includes a spool and a drive part that receives a command current and drives the spool , switch between the neutral position of blocking the pair of supply and discharge lines and the working position of making one of the pair of supply and discharge lines communicate with the pump line and the other with the storage tank line; A larger command current is sent to a control device for the rotation direction switching valve; and a speed detector for detecting the rotation speed of the rotary body; the control device controls the rotation direction switching valve in the following manner : When the operation lever of the swing operation device is returned to the neutral state, when the swing speed detected by the speed detector is lower than the first threshold value, the swing direction switching valve is switched from the neutral position to the discharge side. When the rotation speed detected by the speed detector is lower than a second threshold value smaller than the first threshold value, the rotation direction switching valve is switched from the operation position to the neutral position at the working position where the supply and discharge pipeline and the storage tank pipeline communicate with each other. Location.

According to the above configuration, when the swing is stopped (when the operating lever of the swing operation device returns to the neutral state), the swing direction switching valve is switched to the operating position when the swing speed is lower than the first threshold value. As a result, the pressure of the supply and discharge lines on the discharge side is rapidly decreased, the pressure difference between the supply and discharge lines is decreased, and the reversal of the rotating body is prevented. Therefore, the backlash phenomenon at the time of turning stop can be prevented without using the anti-reverse valve.

Also, the present invention, from a second aspect, provides a hydraulic drive system for a construction machine, comprising: a swing motor for swinging a swing body; An operating device; a slewing direction switching valve connected to the slewing motor through a pair of supply and discharge pipelines, the slewing direction switching valve includes a valve core and a driving part that receives a command current and drives the valve core, and blocks the one Switch between the neutral position of the supply and discharge lines and the working position where one of the pair of supply and discharge lines is connected to the pump line and the other to the storage tank line; the larger the rotation operation signal, the larger the command. a control device for sending current to the swing direction switching valve; a speed detector for detecting the swing speed of the swing body; and a pair of pressure sensors for detecting the inflow pressure and outflow pressure of the swing motor; the The control device controls the swing direction switching valve so that the outflow pressure of the swing motor detected by one of the pair of pressure sensors is lower than the first At the threshold value, the swing direction switching valve is switched from the neutral position to the working position where the supply and discharge line on the discharge side is communicated with the storage tank line, and when the swing speed detected by the speed detector is lower than the second threshold value, all The rotation direction switching valve is switched from the working position to the neutral position.

According to the above configuration, when the swing is stopped (when the operating lever of the swing operating device returns to the neutral state), the swing direction switching valve is switched to the operating position when the outflow pressure of the swing motor is lower than the first threshold value. As a result, the pressure of the supply and discharge lines on the discharge side is rapidly decreased, the pressure difference between the supply and discharge lines is decreased, and the reversal of the rotating body is prevented. Therefore, the backlash phenomenon at the time of turning stop can be prevented without using the anti-reverse valve.

Also, the present invention, from a third aspect, is a hydraulic drive system for a construction machine, comprising: a swing motor for swinging a swing body; and a swing operation including an operation lever that outputs a swing operation signal corresponding to a tilt angle of the operation lever device; a rotary direction switching valve connected to the rotary motor through a pair of supply and discharge lines, the rotary direction switching valve comprising a valve core and a drive part that receives a command current and drives the valve core, and blocks the pair of Switching between the neutral position of the supply and discharge lines and a working position where one of the pair of supply and discharge lines is communicated with the pump line and the other with the storage tank line; the larger the swing operation signal, the larger the command current a control device for sending to the swing direction switching valve; a speed detector for detecting the swing speed of the swing body; and a pair of pressure sensors for detecting the inflow pressure and the outflow pressure of the swing motor; the control The device controls the swing direction switching valve in such a manner that, when the operating lever of the swing operating device returns to a neutral state, when the swing speed detected by the speed detector is lower than a threshold value, the swing direction switching valve is set to Switch from the neutral position to an operating position where the supply and discharge line on the discharge side and the storage tank line communicate with each other, and then set the swing direction switching valve to the pressure difference between the inflow pressure and the outflow pressure of the swing motor detected by the pair of pressure sensors corresponding opening.

According to the above configuration, when the swing is stopped (when the operating lever of the swing operating device returns to the neutral state), the swing direction switching valve is switched to the operating position when the swing speed is lower than the threshold value. As a result, the pressure of the supply and discharge lines on the discharge side is rapidly decreased, the pressure difference between the supply and discharge lines is decreased, and the reversal of the rotating body is prevented. Therefore, the backlash phenomenon at the time of turning stop can be prevented without using the anti-reverse valve. Furthermore, in the above configuration, when the swing direction switching valve is switched to the operating position, the opening degree corresponds to the pressure difference between the inflow pressure and the outflow pressure of the swing motor, so that the pressure difference between the supply and discharge lines can be suppressed as small as possible.

Furthermore, the present invention, from a fourth aspect, provides a hydraulic drive system for a construction machine, comprising: a swing motor for swinging a swing body; An operating device; a slewing direction switching valve connected to the slewing motor through a pair of supply and discharge pipelines, the slewing direction switching valve includes a valve core and a driving part that receives a command current and drives the valve core, and blocks the one Switch between the neutral position of the supply and discharge lines and the working position where one of the pair of supply and discharge lines is connected to the pump line and the other to the storage tank line; the larger the rotation operation signal, the larger the command. a control device for sending electric current to the swing direction switching valve; and a pair of pressure sensors for detecting the inflow pressure and the outflow pressure of the swing motor; the control device controls the swing direction switching valve in the following manner: the When the operating lever of the swing operating device returns to the neutral state, when the outflow pressure of the swing motor detected by one of the pair of pressure sensors is lower than a threshold value, the swing direction switching valve is switched from the neutral position to the discharge pressure. Then, the swing direction switching valve is set to an opening corresponding to the pressure difference between the inflow pressure and the outflow pressure of the swing motor detected by the pair of pressure sensors.

According to the above configuration, when the swing stops (when the operating lever of the swing operating device returns to the neutral state), the swing direction switching valve switches to the operating position when the outflow pressure of the swing motor falls below the threshold value. As a result, the pressure of the supply and discharge lines on the discharge side is rapidly decreased, the pressure difference between the supply and discharge lines is decreased, and the reversal of the rotating body is prevented. Therefore, the backlash phenomenon at the time of turning stop can be prevented without using the anti-reverse valve. Furthermore, in the above configuration, when the swing direction switching valve is switched to the operating position, the opening degree corresponds to the pressure difference between the inflow pressure and the outflow pressure of the swing motor, so that the pressure difference between the supply and discharge lines can be suppressed as small as possible.

In the third and fourth side surfaces, the control device may control the swing direction switching valve in such a manner that the operating lever of the swing operating device returns to a neutral state, and the swing direction switching valve is switched to When the inflow pressure of the swing motor is higher than the outflow pressure after the working position where the supply and discharge lines on the discharge side are communicated with the storage tank lines, the swing direction switching valve is switched to connect the supply and discharge lines on the supply side with the storage tank. The working position where the pipeline is connected. According to this configuration, even if the revolving body is reversed when the rotation is stopped, further reverse rotation can be prevented.

Invention effect:

According to the present invention, it is possible to prevent the swing back phenomenon when the rotation is stopped without using the anti-reverse valve.

Description of drawings

1 is a schematic structural diagram of a hydraulic drive system for a construction machine according to a first embodiment of the present invention;

2 is a side view of a hydraulic excavator as an example of a construction machine;

3A to 3D in FIG. 3 are graphs when the rotation is stopped in the first embodiment, 3A in FIG. 3 shows the time-dependent change in the displacement of the spool of the rotation direction switching valve, and 3B in FIG. 3 shows the time-dependent change in the rotation speed. 3C shows the time change of the inflow pressure of the swing motor, and 3D in FIG. 3 shows the time change of the outflow pressure of the swing motor;

4 is a schematic configuration diagram of a hydraulic drive system according to a modification of the first embodiment;

5A to 5D are graphs when the rotation is stopped in the second embodiment, 5A in FIG. 5 shows the temporal change in the displacement of the spool of the rotation direction switching valve, and 5B in FIG. 5 shows the temporal change in the rotation speed. 5C shows the time change of the inflow pressure of the swing motor, and 5D in FIG. 5 shows the time change of the outflow pressure of the swing motor.

Detailed ways

(first embodiment)

FIG. 1 shows a hydraulic drive system 1 for a construction machine according to a first embodiment of the present invention, and FIG. 2 shows a construction machine 10 on which the hydraulic drive system 1 is mounted. The construction machine 10 shown in FIG. 2 is a hydraulic excavator, but the present invention can also be applied to other construction machines such as a hydraulic crane.

The construction machine 10 shown in FIG. 2 is a self-propelled type, and includes a running body 75 and a revolving body 76 rotatably supported by the running body 75 . The revolving body 76 is provided with a cabin including a driver's seat, and a boom is connected thereto. An arm is connected to the tip of the boom, and a bucket is connected to the tip of the arm. However, the construction machine 10 need not be self-propelled.

The hydraulic drive system 1 includes a boom cylinder 71 , an arm cylinder 72 , and a bucket cylinder 73 (actuator) shown in FIG. 2 , and includes a swing motor 4 shown in FIG. 1 and a pair of left and right travel motors not shown. as a hydraulic actuator. The turning motor 4 turns the turning body 76 . Moreover, as shown in FIG. 1, the hydraulic drive system 1 includes the pump 2 which supplies the hydraulic fluid to these actuators. In addition, in FIG. 1, the hydraulic actuator other than the swing motor 4 is abbreviate|omitted for the simplicity of drawing.

Further, the hydraulic drive system 1 includes a swing direction switching valve 3 that controls supply and discharge of hydraulic fluid to the swing motor 4 , a swing operation device 5 including an operation lever 51 that receives swing operation, and a control device 6 .

The pump 2 is a variable-capacity pump whose tilt angle can be changed. The pump 2 can be a swash plate pump or a slant shaft pump. The tilt angle of the pump 2 is adjusted by a regulator 21 . The regulator 21 may be driven by an electrical signal or by a pilot voltage.

The pump 2 is connected to the rotation direction switching valve 3 through a pump line 11 . A check valve 12 is provided in the pump line 11 . The discharge pressure of the pump 2 is kept below the first upper limit pressure by a relief valve (not shown). Moreover, the rotation direction switching valve 3 is connected to the accumulator via the accumulator line 13 .

Further, the swing direction switching valve 3 is connected to the swing motor 4 through a pair of supply and discharge lines 41 and 42 . A release line 43 is branched from the supply and discharge lines 41 and 42, respectively, and the release line 43 is connected to the storage tank. A safety valve 44 is provided in each release line 43 . That is, the respective pressures of the supply and discharge lines 41 and 42 are kept below the second upper limit pressure by the safety valve 44 . In addition, the second upper limit pressure may be equal to or different from the above-mentioned first upper limit pressure.

In addition, the supply and discharge lines 41 and 42 are connected to the storage tank through the supplementary line 45, respectively. Each supplementary line 45 is provided with a check valve 46 that allows flow to the supply and discharge line ( 41 or 42 ) but prohibits the opposite flow. The supplementary line (41 or 42) functions as a supply and discharge line for direct inflow of the working fluid from the storage tank to the supply side when the rotation is decelerated.

The rotation direction switching valve 3 is in the neutral position where both the supply and discharge lines 41 and 42 are blocked, and the first working position in which the supply and discharge line 41 and the pump line 11 are communicated and the supply and discharge line 42 and the storage tank line 13 communicate with each other (Fig. 1). left position) and a second working position (right position in FIG. 1 ) that communicates the supply and discharge line 42 with the pump line 11 and communicates the supply and discharge line 41 with the tank line 13 .

The rotation direction switching valve 3 is driven by an electric signal. Specifically, the rotation direction switching valve 3 includes a valve body 31 and a drive unit 32 that receives a command current and drives the valve body 31 . For example, the drive unit 32 may be configured as a pair of electromagnetic proportional valves outputting secondary pressures acting on the valve body 31 in opposite directions, or may be a linear motion mechanism including an electric motor and a ball screw connected to the valve body 31 . Furthermore, the opening degree of the swing direction switching valve 3 increases as the command current sent to the drive unit 32 increases, and the supply amount of the working fluid to the swing motor 4 and the discharge amount of the working fluid from the swing motor 4 increase. .

The swing operation device 5 outputs a swing operation signal (a right swing operation signal or a left swing operation signal) corresponding to a tilt angle (a swing operation amount) of the operation lever 51 . That is, the swing operation signal output from the swing operation device 5 increases as the tilt angle of the operation lever 51 increases. In the present embodiment, the swing operation device 5 is an electric joystick that outputs an electric signal as a swing operation signal.

The swing operation signal (electrical signal) output from the swing operation device 5 is input to the control device 6 . For example, the control device 6 includes a memory such as a ROM or a RAM and a CPU, and the program stored in the ROM is executed by the CPU.

The control device 6 sends the command current to the drive unit 32 of the swing direction switching valve 3 , which is larger as the swing operation signal is larger. As a result, the valve body 31 of the swing direction switching valve 3 moves more as the tilt angle of the operation lever 51 of the swing operation device 5 increases.

The control device 6 is electrically connected to a speed detector 65 that detects the rotational speed of the revolving body 76 . The speed detector 65 is, for example, a gyro sensor provided in the revolving body 76 . However, the speed detector 65 may be, for example, an encoder or a revolver attached to the rotary motor 4 .

The control device 6 controls the swing direction switching valve 3 so as to prevent the swing phenomenon when the swing is stopped when the operation lever 51 of the swing operation device 5 is returned to the neutral state. Specifically, the control device 6 makes the command current sent to the drive unit 32 of the swing direction switching valve 3 to be zero when the operation lever 51 of the swing operation device 5 returns to the neutral state. Thereby, as shown to 3A of FIG. 3, the rotation direction switching valve 3 is switched from an operating position (a 1st operating position or a 2nd operating position) to a neutral position. As a result, the inflow pressure of the swing motor 4 (the pressure of the supply and discharge lines on the supply side) as shown in 3C in FIG. pressure) rises.

When the swing direction switching valve 3 is switched to the neutral position, the swing speed of the swing body 76 gradually decreases as shown in 3B in FIG. 3 by the braking action of the discharge side relief valve 44 . When the turning speed of the turning body 76 detected by the speed detector 65 is lower than the first threshold value α, the control device 6 switches the turning direction switching valve 3 from the neutral position to the operation of connecting the supply and discharge line on the discharge side with the tank line 13 In the form of the position, a command current is sent to the drive unit 32 of the rotation direction switching valve 3 . Thereby, the outflow pressure of the swing motor 4 is reduced to zero.

After that, when the rotational speed of the revolving body 76 detected by the speed detector 65 is lower than the second threshold value β smaller than the first threshold value α, the control device 6 switches the rotational direction switching valve 3 from the operating position to the neutral position to The command current is sent to the drive unit 32 of the rotation direction switching valve 3 . Thereby, the rotating body 76 is completely stopped.

The above-mentioned first threshold value α and second threshold value β may be preset fixed values, or may be calculated each time by multiplying the rotation speed before the rotation stop by a coefficient. For example, when the first threshold α and the second threshold β are fixed values, the first threshold α is 5 to 20% of the maximum speed, and the second threshold β is 1 to 10% of the maximum speed.

As described above, in the present embodiment, when the turning is stopped, the turning direction switching valve 3 is switched to the operating position when the turning speed is lower than the first threshold value α. Thereby, the pressure of the supply and discharge lines on the discharge side is rapidly decreased, the pressure difference between the supply and discharge lines 41 and 42 is decreased, and the reversal of the revolving body 76 is prevented. Therefore, the backlash phenomenon at the time of turning stop can be prevented without using the anti-reverse valve. For reference, in 3C and 3D of FIG. 3 , the pressure change when the swing phenomenon occurs without performing the control of the present embodiment is shown by the dotted line.

In addition, in the present embodiment, the timing of reducing the rotation speed and the degree of reduction can be freely set by electronic control adjustment. Therefore, calibration for compensating for the influence of the temperature of the working fluid for each body becomes easy, and the adjustment range of the operability such as adjustment according to the operator's preference, such as turning stop, is widened.

<Variation>

As shown in FIG. 4 , a pair of pressure sensors 61 and 62 may also be provided in the supply and discharge lines 41 and 42 . One of the pressure sensors 61 and 62 detects the inflow pressure of the swing motor 4 , and the other of the pressure sensors 61 and 62 detects the outflow pressure of the swing motor 4 .

In the example shown in 3A in FIG. 3 , when the operation lever 51 of the swing operation device 5 returns to the neutral state and the swing direction switching valve 3 is switched to the operating position, the opening degree of the swing direction switching valve 3 (displacement of the valve body 31 ) is must. On the other hand, when the pressure sensors 61 and 62 are provided, when the rotation direction switching valve 3 is switched to the operating position after the operation lever 51 of the rotation operation device 5 is returned to the neutral state, the rotation direction switching valve 3 may be used as the pressure The control is performed in the form of the opening degree corresponding to the pressure difference between the inflow pressure and the outflow pressure of the swing motor 4 detected by the sensors 61 and 62 . According to this structure, the pressure difference between the supply and discharge lines 41 and 42 can be suppressed as small as possible.

In addition, when the pressure sensors 61 and 62 are provided, after the operation lever 51 of the swing operation device 5 returns to the neutral state, the outflow pressure of the swing motor 4 detected by one of the pressure sensors 61 and 62 may be lower than the first threshold value. At α′, the control device 6 transmits a command current to the driving of the rotation direction switching valve 3 so as to switch the rotation direction switching valve 3 from the neutral position to the operating position in which the supply and discharge line on the discharge side and the storage tank line 13 communicate with each other. Section 32. Also in this structure, the same effect as the said embodiment can be acquired.

In addition, the first threshold value α (or α′) can also be divided into a threshold value α1 for a single swing operation, and a swing operation combined with a swing operation and other operations (eg, boom operation, arm operation, or bucket operation) at the same time. the threshold α2 (<α1).

(Second Embodiment)

Next, the hydraulic drive system of the construction machine according to the second embodiment of the present invention will be described with reference to 5A to 5D in FIG. 5 . The configuration of the hydraulic drive system of the second embodiment is the same as that of the modification of the first embodiment shown in FIG. 4 .

In the present embodiment, the control device 6 controls the swing direction switching valve 3 so as to prevent the swing phenomenon when the swing is stopped when the operation lever 51 of the swing operation device 5 returns to the neutral state. Specifically, the control device 6 makes the command current sent to the drive unit 32 of the swing direction switching valve 3 to be zero when the operation lever 51 of the swing operation device 5 returns to the neutral state. Thereby, as shown in 5A in FIG. 5 , the rotation direction switching valve 3 is switched from the operating position (the first operating position or the second operating position) to the neutral position. As a result, the inflow pressure of the swing motor 4 (the pressure of the supply and discharge lines on the supply side) as shown in 5C in FIG. 5 is zero, and the outflow pressure of the swing motor 4 (the supply and discharge lines of the discharge side) is shown as pressure) rises.

When the turning direction switching valve 3 is switched to the neutral position, the turning speed of the turning body 76 is gradually reduced as shown in 5B in FIG. 5 by the braking action of the relief valve 44 on the discharge side. When the swing speed of the swing body 76 detected by the speed detector 65 is lower than the threshold value γ, the control device 6 switches the swing direction switching valve 3 from the neutral position to the operating position that communicates the supply and discharge line on the discharge side with the tank line 13 . form, a command current is sent to the drive unit 32 of the rotation direction switching valve 3 . Thereby, the outflow pressure of the swing motor 4 is reduced to zero. The threshold value γ may be a predetermined fixed value, or may be calculated each time by multiplying the rotation speed before the rotation stop by a coefficient.

After that, the control device 6 switches the drive unit 32 of the swing direction switching valve 3 to the swing direction switching valve 3 so that the opening degree corresponds to the pressure difference between the inflow pressure and the outflow pressure of the swing motor 4 detected by the pressure sensors 61 and 62 . Send command current. More specifically, the control device 6 increases the opening degree of the swing direction switching valve 3 as the pressure difference between the inflow pressure and the outflow pressure of the swing motor 4 is larger.

After the operating lever 51 of the swing operating device 5 returns to the neutral state, and the swing direction switching valve 3 is switched to the working position where the supply and discharge line on the discharge side and the storage tank line 13 communicate with each other, the control device 6 is set when the inflow pressure of the swing motor 4 is higher than that of the control device 6 . At the time of outflow pressure, the rotation direction switching valve 3 is controlled so that the rotation direction switching valve 3 is switched to an operating position where the supply and discharge line on the supply side and the accumulator line 13 communicate with each other. That is, the rotation direction switching valve 3 is switched from the first working position to the second working position, or from the second working position to the first working position.

As described above, in the present embodiment, when the rotation is stopped, when the rotation speed is lower than the threshold value γ, the rotation direction switching valve 3 is switched to the operating position. As a result, the pressure of the supply and discharge lines on the discharge side is rapidly decreased, the pressure difference between the supply and discharge lines 41 and 42 is decreased, and the reversal of the revolving body 76 is prevented. Therefore, the backlash phenomenon at the time of turning stop can be prevented without using the anti-reverse valve. Furthermore, in the present embodiment, when the swing direction switching valve 3 is switched to the operating position, the opening degree corresponds to the pressure difference between the inflow pressure and the outflow pressure of the swing motor 4, so that the pressure difference between the supply and discharge lines 41 and 42 can be suppressed. as small as possible.

In addition, in the present embodiment, the timing of reducing the rotation speed and the degree of reduction can be freely set by electronic control adjustment. Therefore, calibration for compensating for the influence of the temperature of the working fluid for each body becomes easy, and the adjustment range of the operability such as the adjustment according to the operator's preference, such as the turning stop, is widened.

Further, in this embodiment, when the inflow pressure of the swing motor 4 is higher than the outflow pressure, the operating position of the swing direction switching valve 3 is switched, so that even if the swing body 76 is reversed when the swing is stopped, further reverse rotation can be prevented.

<Variation>

When the outflow pressure of the swing motor 4 detected by one of the pressure sensors 61 and 62 is lower than the threshold value γ′ after the operation lever 51 of the swing operation device 5 returns to the neutral state, the control device 6 may set the swing direction switching valve 3 to neutral. The position is switched to an operating position in which the supply and discharge line on the discharge side and the tank line 13 communicate with each other, and a command current is sent to the drive unit 32 of the rotation direction switching valve 3 . Also in this configuration, the same effects as those of the above-described embodiment can be obtained. In this case, the speed detector 65 may be omitted.

In addition, after the operating lever 51 of the swing operating device 5 is returned to the neutral position, when the swing direction switching valve 3 is switched to the operating position, the swing direction switching valve may be adjusted according to the rate of change of the inflow pressure and/or the outflow pressure of the swing motor 4 3 to adjust the opening.

In addition, the threshold value γ (or γ′) can also be divided into a threshold value γ1 for a single swing operation and a threshold value for a swing combined operation in which the swing operation and other operations (eg, boom operation, arm operation, or bucket operation) are simultaneously performed. γ2 (<γ1).

(Other Embodiments)

The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

For example, the swing operation device 5 need not necessarily be an electric lever, and may be a pilot-operated valve that outputs a pilot pressure as a swing operation signal. In this case, the pilot pressure output from the swing operating device 5 is detected by the pressure sensor and input to the control device 6 .

Symbol Description:

1 Hydraulic drive system

11 Supply line

13 Tank lines

3 Rotation direction switching valve

31 Spool

32 Drive section

4 Rotary motor

5 Rotary operating device

51 Lever

6 Control device

61, 62 Pressure sensor

65 Speed detector.

Claims (5)

1. A hydraulic drive system for a construction machine, comprising: A rotary motor that makes a rotary body rotate; comprising an operating lever and outputting a swivel operation signal corresponding to the tilting angle of the operating lever; A swing direction switching valve connected to the swing motor through a pair of supply and discharge lines, the swing direction switch valve includes a valve body and a drive part that receives a command current and drives the valve body, and blocks the pair of supply and discharge when the pair of supply and discharge is blocked. switching between a neutral position of the line and a working position in which one of the pair of supply and discharge lines communicates with the pump line and the other with the storage tank line; sending a larger command current to the control device of the swing direction switching valve when the swing operation signal is larger; and a speed detector for detecting the rotational speed of the revolving body; The control device controls the swing direction switching valve in such a manner that when the operation lever of the swing operation device returns to the neutral state, when the swing speed detected by the speed detector is lower than the first threshold value, the swing direction switching valve is set to be The swing direction switching valve is switched from a neutral position to an operating position that communicates the supply and discharge line on the discharge side with the tank line, when the swing speed detected by the speed detector is lower than a second threshold value smaller than the first threshold value , so that the rotation direction switching valve is switched from the working position to the neutral position. 2. A hydraulic drive system for a construction machine, characterized in that it has: A rotary motor that makes a rotary body rotate; comprising an operating lever and outputting a swivel operation signal corresponding to the tilting angle of the operating lever; A swing direction switching valve connected to the swing motor through a pair of supply and discharge lines, the swing direction switch valve includes a valve body and a drive part that receives a command current and drives the valve body, and blocks the pair of supply and discharge when the pair of supply and discharge is blocked. switching between a neutral position of the line and a working position in which one of the pair of supply and discharge lines communicates with the pump line and the other with the storage tank line; sending a larger command current to the control device of the swing direction switching valve when the swing operation signal is larger; a speed detector for detecting the rotational speed of the revolving body; and a pair of pressure sensors for detecting the inflow pressure and outflow pressure of the rotary motor; The control device controls the swing direction switching valve in such a manner that the outflow pressure of the swing motor detected by one of the pair of pressure sensors is lower than when the operating lever of the swing operation device is returned to the neutral state. When the first threshold value is used, the swing direction switching valve is switched from the neutral position to the working position where the supply and discharge line on the discharge side is communicated with the storage tank line, and when the swing speed detected by the speed detector is lower than the second threshold value, The rotation direction switching valve is switched from the working position to the neutral position. 3. A hydraulic drive system for a construction machine, characterized in that it has: A rotary motor that makes a rotary body rotate; comprising an operating lever and outputting a swivel operation signal corresponding to the tilting angle of the operating lever; A swing direction switching valve connected to the swing motor through a pair of supply and discharge lines, the swing direction switch valve includes a valve body and a drive part that receives a command current and drives the valve body, and blocks the pair of supply and discharge when the pair of supply and discharge is blocked. switching between a neutral position of the line and a working position in which one of the pair of supply and discharge lines communicates with the pump line and the other with the storage tank line; sending a larger command current to the control device of the swing direction switching valve when the swing operation signal is larger; a speed detector for detecting the rotational speed of the revolving body; and a pair of pressure sensors for detecting the inflow pressure and outflow pressure of the rotary motor; The control device controls the swing direction switching valve so that the swing direction switching valve is caused to swing when the swing speed detected by the speed detector is lower than a threshold value when the control lever of the swing operation device is returned to a neutral state. The directional switching valve is switched from the neutral position to an operating position in which the supply and discharge line on the discharge side and the storage tank line are communicated, and then the turning direction switching valve is set to the inflow pressure and the outflow pressure of the turning motor detected by the pair of pressure sensors. The opening corresponding to the differential pressure. 4. A hydraulic drive system for a construction machine, characterized in that it has: A rotary motor that makes a rotary body rotate; comprising an operating lever and outputting a swivel operation signal corresponding to the tilting angle of the operating lever; A swing direction switching valve connected to the swing motor through a pair of supply and discharge lines, the swing direction switch valve includes a valve body and a drive part that receives a command current and drives the valve body, and blocks the pair of supply and discharge when the pair of supply and discharge is blocked. switching between a neutral position of the line and a working position in which one of the pair of supply and discharge lines communicates with the pump line and the other with the storage tank line; sending a larger command current to the control device of the swing direction switching valve when the swing operation signal is larger; and a pair of pressure sensors for detecting the inflow pressure and outflow pressure of the rotary motor; The control device controls the swing direction switching valve in such a manner that the outflow pressure of the swing motor detected by one of the pair of pressure sensors is lower than when the operating lever of the swing operation device is returned to the neutral state. At the threshold value, the rotation direction switching valve is switched from the neutral position to the operating position where the supply and discharge line on the discharge side and the storage tank line communicate with each other, and then the rotation direction switching valve is set to the rotation detected by the pair of pressure sensors. The opening corresponding to the pressure difference between the inflow pressure and the outflow pressure of the motor. 5. The hydraulic drive system of a construction machine according to claim 3 or 4, characterized in that: The control device controls the swing direction switching valve in such a manner that the operation lever of the swing operating device returns to a neutral state, and the swing direction switching valve is switched to an operation of connecting the supply and discharge line on the discharge side with the tank line. After the position is set, when the inflow pressure of the swing motor is higher than the outflow pressure, the swing direction switching valve is switched to an operating position where the supply and discharge line on the supply side communicates with the tank line.

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