CN111936751B - Hydraulic drive system for construction machinery - Google Patents

Abstract

The hydraulic drive system of construction machinery is equipped with: a rotary motor, a rotary operating device that outputs a rotary operation signal corresponding to the tilting angle of the operating lever, and one of the neutral positions that block a pair of supply and discharge pipelines and the pair of supply and discharge pipelines. A swing direction switching valve that switches between working positions that communicate with the pump line and the other side communicates with the tank line, and a control device that sends a larger command current to the swing direction switching valve as the swing operation signal becomes larger, the control device When the operating lever of the rotary operating device returns to the neutral state, when the rotary speed detected by the speed detector is lower than the first threshold value, the rotary direction switching valve is switched from the neutral position to the discharge pipeline and the storage tank on the discharge side. In the working position where the pipeline is connected, 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 invention relates to a hydraulic drive system of a construction machine.

Background technique

A construction machine such as a hydraulic shovel or a hydraulic crane is equipped with a hydraulic drive system including a rotary motor that rotates a rotary body (for example, refer to Patent Document 1). The working fluid is supplied from the pump to the swing motor through the swing direction switching valve.

Specifically, the rotary direction switching valve is connected to the rotary motor through a pair of supply and discharge pipelines. The rotary directional switching valve switches between a neutral position where a pair of supply and discharge pipelines are blocked (block), and a working position where one of the pair of supply and discharge pipelines communicates with the pump pipeline, and the other communicates with the storage tank pipeline. The swivel direction switching valve is switched from the neutral position to the working position when the operating lever of the rotary operating device is tilted, and has an opening corresponding to the tilting angle (rotation operation amount) of the operating lever.

However, when the turning operation lever is returned to the neutral state in order to stop the turning body in 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 remains between the supply and discharge line on the discharge side that is in the closed state and the supply and discharge line on the supply side that directly flows into the working fluid from the storage tank at the time of turning deceleration. The so-called backswing phenomenon in which the rotor reverses due to the pressure difference and the magnitude of the pressure difference between the supply and discharge lines is reversed due to the reversal occurs repeatedly, causing the rotor to further reverse.

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

Prior art literature:

Patent documents:

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

Contents of the invention

Problems 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 swing 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-rotation valve.

Means to solve the problem:

In order to solve the above problems, the present invention provides a hydraulic drive system for construction machinery from a first aspect, comprising: a rotary motor for rotating a rotary body; A rotary operating device for operating signals; a rotary direction switching valve connected to the rotary motor through a pair of supply and discharge pipelines, the rotary direction switching valve includes a spool and a driving part that receives command current and drives the spool , to switch between the neutral position of blocking the pair of supply and discharge pipelines and the working position of making one of the pair of supply and discharge pipelines communicate with the pump pipeline and the other side communicates with the storage tank pipeline; the rotary operation signal The larger the command current is, the larger the command current is sent to the control device of the rotary direction switching valve; and the speed detector detects the rotary speed of the rotary body; the control device controls the rotary direction switching valve in the following form : When the operating lever of the rotary operating device returns to the neutral state, when the rotary speed detected by the speed detector is lower than the first threshold value, the rotary direction switching valve is switched from the neutral position to the discharge side. The working position where the supply and discharge pipeline communicates with the storage tank pipeline, when the rotation speed detected by the speed detector is lower than the second threshold value smaller than the first threshold value, the rotation direction switching valve is switched from the working position to neutral Location.

According to the above configuration, when the turning is stopped (when the operating lever of the turning operating device returns to the neutral state), the turning direction switching valve is switched to the working position when the turning speed is lower than the first threshold value. As a result, the pressure of the supply and discharge pipeline on the discharge side decreases rapidly, thereby reducing the pressure difference between the supply and discharge pipelines, and preventing the rotary body from reversing. Therefore, it is possible to prevent the swinging phenomenon when the rotation is stopped without using the anti-rotation valve.

Also, from the second aspect, the present invention provides a hydraulic drive system for a construction machine, comprising: a rotary motor for rotating a rotary body; An operating device; a rotary direction switching valve connected to the rotary motor through a pair of supply and discharge pipelines, the rotary direction switching valve includes a valve core and a driving part that receives the command current and drives the valve core. switching between the neutral position of the supply and discharge pipeline and the working position where one of the pair of supply and discharge pipelines communicates with the pump pipeline and the other communicates with the storage tank pipeline; the greater the rotation operation signal, the greater the command A control device that sends current to the slewing direction switching valve; a speed detector that detects the slewing speed of the slewing body; and a pair of pressure sensors that detect the inflow pressure and outflow pressure of the slewing motor; the 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 the first pressure when the operation lever of the swing control device returns to a neutral state. When the threshold value is reached, the rotation direction switching valve is switched from the neutral position to the working position where the supply and discharge pipeline on the discharge side communicates with the storage tank pipeline, and when the rotation speed detected by the speed detector is lower than the second threshold value, the rotation direction switching valve The rotary direction switching valve is switched from the working position to the neutral position.

According to the above configuration, when the turning is stopped (when the operating lever of the turning operating device returns to the neutral state), the turning direction switching valve is switched to the working position when the outflow pressure of the turning motor is lower than the first threshold. As a result, the pressure of the supply and discharge pipeline on the discharge side decreases rapidly, thereby reducing the pressure difference between the supply and discharge pipelines, and preventing the rotary body from reversing. Therefore, it is possible to prevent the swinging phenomenon when the rotation is stopped without using the anti-rotation valve.

In addition, the present invention provides a hydraulic drive system for a construction machine from a third aspect, comprising: a swing motor for turning a swing body; device; a rotary direction switching valve connected to the rotary motor through a pair of supply and discharge pipelines, the rotary direction switching valve includes a spool and a driving part that receives command current and drives the spool, and blocks the pair of switch between the neutral position of the supply and discharge pipeline and the working position in which one of the pair of supply and discharge pipelines communicates with the pump pipeline and the other communicates with the storage tank pipeline; the greater the rotation operation signal, the greater the command current A control device sent to the rotation direction switching valve; a speed detector for detecting the rotation speed of the rotation body; and a pair of pressure sensors for detecting the inflow pressure and outflow pressure of the rotation motor; the control The device controls the slewing direction switching valve in the following form: When the operating rod of the slewing operating device returns to the neutral state, when the slewing speed detected by the speed detector is lower than a threshold value, the slewing direction switching valve is activated. Switch from the neutral position to the working position where the supply and discharge pipeline on the discharge side communicates with the storage tank pipeline, and then set the rotary direction switching valve to the pressure difference between the inflow pressure and the outflow pressure of the rotary motor detected by the pair of pressure sensors. the corresponding opening.

According to the above configuration, when the turning is stopped (when the operating lever of the turning operating device returns to the neutral state), the turning direction switching valve is switched to the operating position when the turning speed is lower than the threshold value. As a result, the pressure of the supply and discharge pipeline on the discharge side decreases rapidly, thereby reducing the pressure difference between the supply and discharge pipelines, and preventing the rotary body from reversing. Therefore, it is possible to prevent the swinging phenomenon when the rotation is stopped without using the anti-rotation valve. Moreover, in the above structure, when the rotary direction switching valve is switched to the working position, the opening degree corresponds to the pressure difference between the inflow pressure and the outflow pressure of the rotary motor, so that the pressure difference between the supply and discharge lines can be suppressed as small as possible.

Also, from the fourth aspect, the present invention provides a hydraulic drive system for a construction machine, comprising: a swing motor for turning a swing body; An operating device; a rotary direction switching valve connected to the rotary motor through a pair of supply and discharge pipelines, the rotary direction switching valve includes a valve core and a driving part that receives the command current and drives the valve core. switching between the neutral position of the supply and discharge pipeline and the working position where one of the pair of supply and discharge pipelines communicates with the pump pipeline and the other communicates with the storage tank pipeline; the greater the rotation operation signal, the greater the command The current is sent to the control device of the rotary direction switching valve; and a pair of pressure sensors for detecting the inflow pressure and the outflow pressure of the rotary motor; the control device controls the rotary direction switching valve in the following form: 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 discharge The working position where the supply and discharge pipeline on the side communicates with the storage tank pipeline, and then the swing direction switching valve is opened 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 turning is stopped (when the operating lever of the turning operating device returns to the neutral state), the turning direction switching valve is switched to the operating position when the outflow pressure of the turning motor is lower than the threshold value. As a result, the pressure of the supply and discharge pipeline on the discharge side decreases rapidly, thereby reducing the pressure difference between the supply and discharge pipelines, and preventing the rotary body from reversing. Therefore, it is possible to prevent the swinging phenomenon when the rotation is stopped without using the anti-rotation valve. Moreover, in the above structure, when the rotary direction switching valve is switched to the working position, the opening degree corresponds to the pressure difference between the inflow pressure and the outflow pressure of the rotary motor, so that the pressure difference between the supply and discharge lines can be suppressed as small as possible.

In the third and fourth sides, the control device may control the rotary direction switching valve in the following manner: the operating rod of the rotary operating device returns to the neutral state, and the rotary direction switching valve is switched to After the working position of connecting the supply and discharge pipeline on the discharge side with the storage tank pipeline, when the inflow pressure of the rotary motor is higher than the outflow pressure, the rotary direction switching valve is switched to connect the supply and discharge pipeline on the supply side to the storage tank. The working position where the pipeline is connected. According to this configuration, even if the revolving body reverses when the revolving stops, subsequent further reversing can be prevented.

Invention effect:

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

Description of drawings

1 is a schematic configuration diagram of a hydraulic drive system of 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 variation of the spool displacement of the rotary direction switching valve with time, and 3B in Fig. 3 shows the variation of the rotation speed with time. Changes, 3C in Figure 3 shows the change with time of the inflow pressure of the rotary motor, and 3D in Figure 3 shows the change with time of the outflow pressure of the rotary motor;

Fig. 4 is a schematic configuration diagram of a hydraulic drive system according to a modified example of the first embodiment;

5A to 5D in Fig. 5 are graphs when the rotation stops in the second embodiment. 5A in Fig. 5 shows the variation of the spool displacement of the rotary direction switching valve with time, and 5B in Fig. 5 shows the variation of the rotation speed with time. 5C in FIG. 5 shows the change with time of the inflow pressure of the swing motor, and 5D in FIG. 5 shows the change with time 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 equipped with the hydraulic drive system 1 . 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 hydraulic cranes.

The construction machine 10 shown in FIG. 2 is self-propelled 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 (cabin) including a driver's seat, and is connected with a boom (boom). An arm is connected to a tip end of the boom, and a bucket is connected to a tip end of the arm. However, the construction machine 10 does not need to 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. As a hydraulic actuator. The turning motor 4 turns the turning body 76 . Also, as shown in FIG. 1 , the hydraulic drive system 1 includes a pump 2 for supplying hydraulic fluid to these actuators. In addition, in FIG. 1 , hydraulic actuators other than the rotary motor 4 are omitted for simplicity of the drawing.

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

The pump 2 is a variable capacity type pump whose inclination angle can be changed. The pump 2 can be a slant plate pump or an inclined axis pump. The tilt angle of the pump 2 is adjusted by a regulator 21 . The regulator 21 can be driven by an electrical signal, or by a pilot pressure.

The pump 2 is connected to the swivel direction switching valve 3 via a pump line 11 . A non-return 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 safety valve (not shown). Also, the rotary direction switching valve 3 is connected to the storage tank through the storage tank line 13 .

In addition, the rotary direction switching valve 3 is connected to the rotary motor 4 through a pair of supply and discharge pipelines 41 , 42 . A release pipeline 43 is branched from the supply and discharge pipelines 41 and 42 respectively, and the release pipeline 43 is connected with the storage tank. A safety valve 44 is provided in each release line 43 . That is to say, 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 pipelines 41 and 42 are respectively connected to the storage tank through the replenishment pipeline 45 . Each supplementary line 45 is provided with a check valve 46 that permits flow to the supply/drain line ( 41 or 42 ) but prohibits flow in the opposite direction. The supplementary pipeline 45 serves as the supply and discharge pipeline (41 or 42) for directly flowing the working fluid from the storage tank to the supply side when the rotation is decelerated.

The rotary direction switching valve 3 is in the neutral position of blocking both the supply and discharge pipelines 41, 42, the first working position of making the supply and discharge pipeline 41 communicate with the pump pipeline 11 and making the supply and discharge pipeline 42 communicate with the storage tank pipeline 13 (Fig. 1 Switch between the left position) and the second working position (the right position in FIG. 1 ) where the supply and discharge pipeline 42 communicates with the pump pipeline 11 and the supply and discharge pipeline 41 communicates with the storage tank pipeline 13 .

The rotary direction switching valve 3 is driven by an electric signal. Specifically, the rotary direction switching valve 3 includes a spool 31 and a driving part 32 that receives command current and drives the spool 31 . For example, the drive unit 32 can be configured as a pair of electromagnetic proportional valves that output secondary pressures that act on the spool 31 in opposite directions, or can be a direct-acting mechanism connected to the spool 31 including an electric motor and a ball screw. Furthermore, the swing direction switching valve 3 has a larger opening degree as the command current sent to the drive unit 32 increases, so that the supply amount of the hydraulic fluid to the swing motor 4 and the discharge amount of the hydraulic fluid from the swing motor 4 are increased. .

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

A 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 has a memory such as ROM or RAM, and a CPU, and the programs stored in the ROM are executed by the CPU.

The control device 6 sends a larger command current to the driving unit 32 of the turning direction switching valve 3 as the turning operation signal becomes larger. Accordingly, the spool 31 of the turning direction switching valve 3 moves more as the tilt angle of the operating lever 51 of the turning operating device 5 increases.

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

The control device 6 controls the turning direction switching valve 3 so as to prevent the swinging phenomenon when turning stops when the operating lever 51 of the turning operating device 5 returns to the neutral state. Specifically, the control device 6 sets the command current sent to the drive unit 32 of the turning direction switching valve 3 to zero when the operating lever 51 of the turning operating device 5 returns to the neutral state. Thus, as shown in 3A in FIG. 3 , the rotary direction switching valve 3 is switched from the working position (the first working position or the second working position) to the neutral position. As a result, the inflow pressure of the rotary motor 4 (the pressure of the supply and discharge pipeline on the supply side) as shown in 3C in FIG. pressure) rises.

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

Afterwards, when the rotational speed of the rotational 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 working position to the neutral position. The command current is sent to the drive unit 32 of the turning direction switching valve 3 . Thereby, the revolving body 76 stops completely.

The above-mentioned first threshold α and second threshold β may be preset fixed values, or may be calculated each time by multiplying the rotation speed before the rotation stops 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 this embodiment, when the rotation is stopped, the rotation direction switching valve 3 is switched to the operating position when the rotation speed is lower than the first threshold value α. As a result, the pressure of the supply and discharge line on the discharge side drops rapidly, thereby reducing the pressure difference between the supply and discharge lines 41 and 42 , and preventing the rotating body 76 from reversing. Therefore, it is possible to prevent the swinging phenomenon when the rotation is stopped without using the anti-rotation valve. For reference, in 3C and 3D of FIG. 3 , the pressure change when the kickback phenomenon occurs without the control of the present embodiment is shown by dotted lines.

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

＜Modifications＞

As shown in FIG. 4 , a pair of pressure sensors 61 , 62 may also be provided in the supply and discharge pipelines 41 , 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 operating rod 51 of the rotary operating device 5 returns to the neutral state, when the rotary direction switching valve 3 is switched to the working position, the opening degree of the rotary direction switching valve 3 (displacement of the spool 31) is must. In this regard, when pressure sensors 61 and 62 are provided, when the operating rod 51 of the rotary operating device 5 returns to the neutral state, when the rotary direction switching valve 3 is switched to the working position, the pressure of the rotary direction switching valve 3 is used as the pressure. The opening degree corresponding to the pressure difference between the inflow pressure and the outflow pressure of the rotary motor 4 detected by the sensors 61 and 62 is controlled. According to this configuration, 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 operating rod 51 of the swing operating 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 is lower than the first threshold value. When α', the control device 6 makes the rotary direction switching valve 3 switch from the neutral position to the working position in which the supply and discharge pipeline on the discharge side communicates with the storage tank pipeline 13, and sends the command current to the drive of the rotary direction switching valve 3 Section 32. Also in this structure, the same effect as that of the above-mentioned embodiment can be obtained.

In addition, the first threshold α (or α') can also be divided into the threshold α1 for single swing operation and the combined swing operation for simultaneous swing operation and other operations (for example, boom operation, arm operation, or bucket operation). The threshold α2 (< α1).

(Second Embodiment)

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

In the present embodiment, the control device 6 controls the swivel direction switching valve 3 so as to prevent the swinging phenomenon when the swivel stops when the operating lever 51 of the swivel operating device 5 returns to the neutral state. Specifically, the control device 6 sets the command current sent to the driving unit 32 of the turning direction switching valve 3 to zero when the operating lever 51 of the turning operating device 5 returns to the neutral state. Thus, as shown in 5A in FIG. 5 , the rotary direction switching valve 3 is switched from the working position (the first working position or the second working position) to the neutral position. As a result, the inflow pressure of the rotary motor 4 (the pressure of the supply and discharge pipeline on the supply side) as shown in 5C in FIG. 5 is zero, and the outflow pressure of the rotary motor 4 (the pressure of the supply and discharge pipeline on the discharge side) pressure) rises.

When the rotary direction switching valve 3 is switched to the neutral position, the rotary speed of the rotary body 76 gradually decreases as shown in 5B in FIG. 5 by the braking action of the safety valve 44 on the discharge side. When the rotation speed of the rotation body 76 detected by the speed detector 65 is lower than the threshold value γ, the control device 6 switches the rotation direction switching valve 3 from the neutral position to the working position where the supply and discharge pipeline on the discharge side communicates with the storage tank pipeline 13. In this form, a command current is sent to the drive unit 32 of the rotary direction switching valve 3 . As a result, the outflow pressure of the swing motor 4 drops to zero. The threshold γ may be a predetermined fixed value, or may be calculated each time by multiplying the rotation speed before the rotation stops by a coefficient.

After that, the control device 6 turns the rotation direction switching valve 3 to the drive unit 32 of the rotation direction switching valve 3 in such a manner that the opening degree of the rotation direction switching valve 3 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 turning direction switching valve 3 as the pressure difference between the inflow pressure and the outflow pressure of the swing motor 4 increases.

The operating lever 51 of the rotary operating device 5 returns to the neutral state, and the rotary direction switching valve 3 is switched to the working position where the supply and discharge pipeline on the discharge side communicates with the storage tank pipeline 13. When the outflow pressure is reached, the rotary direction switching valve 3 is controlled in such a manner that the rotary direction switching valve 3 is switched to the working position where the supply and discharge pipelines on the supply side communicate with the storage tank pipeline 13 . That is to say, the rotary 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 this embodiment, when the rotation is stopped, the rotation direction switching valve 3 is switched to the operating position when the rotation speed is lower than the threshold value γ. As a result, the pressure of the supply and discharge line on the discharge side decreases rapidly, thereby reducing the pressure difference between the supply and discharge lines 41 and 42 , and preventing the rotating body 76 from reversing. Therefore, it is possible to prevent the swinging phenomenon when the rotation is stopped without using the anti-rotation valve. Moreover, in this embodiment, when the rotary direction switching valve 3 is switched to the working position, the opening degree corresponds to the pressure difference between the inflow pressure and the outflow pressure of the rotary motor 4, so that the pressure difference between the supply and discharge lines 41, 42 can be suppressed. into as small as possible.

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

In addition, in this embodiment, when the inflow pressure of the slewing motor 4 is higher than the outflow pressure, the operating position of the slewing direction switching valve 3 is switched, so that even if the slewing body 76 reverses when the slewing stops, it can prevent further inversion thereafter.

＜Modifications＞

It is also possible that after the operating rod 51 of the rotary operating device 5 returns to the neutral state, when the outflow pressure of the rotary motor 4 detected by one of the pressure sensors 61 and 62 is lower than the threshold value γ′, the control device 6 causes the rotary direction switching valve 3 to change from the neutral state to the neutral position. The position is switched to the working position in which the supply and discharge pipeline on the discharge side communicates with the storage tank pipeline 13 , and a command current is sent to the drive unit 32 of the rotary direction switching valve 3 . Also in this structure, the same effect as that of the above-mentioned embodiment can be obtained. In this case, the speed detector 65 may also be omitted.

Also, after the operating rod 51 of the rotary operating device 5 returns to the neutral position, when the rotary direction switching valve 3 is switched to the working position, the rotary direction switching valve is adjusted according to the rate of change of the inflow pressure and/or outflow pressure of the rotary motor 4. 3 to adjust the opening.

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

(Other implementation forms)

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 does not necessarily have to be an electric joystick, 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 a pressure sensor and input to the control device 6 .

Symbol Description:

1 hydraulic drive system

11 Pump lines

13 Tank lines

3 Rotary directional switching valves

31 Spool

32 drive unit

4 swing motor

5 Swivel operating device

51 joystick

6 Controls

61, 62 Pressure sensor

65 Speed detector.

Claims (6)

1. A hydraulic drive system for construction machinery, characterized in that it has: A slewing motor that makes the slewing body turn; including an operating rod, a rotary operating device that outputs a rotary operating signal corresponding to the tilting angle of the operating rod; A rotary direction switching valve connected to the rotary motor through a pair of supply and discharge pipelines, the rotary direction switching valve includes a spool and a driving part that receives command current and drives the spool, when blocking the pair of supply and discharge Switching between a neutral position of the pipeline and an operational position in which one of the pair of supply and discharge lines communicates with the pump pipeline and the other communicates with the storage tank pipeline; 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 rotation speed of the rotating body; The control device controls the turning direction switching valve in such a manner that when the turning speed detected by the speed detector is lower than a first threshold value when the operating lever of the turning operating device is returned to a neutral state, the turning direction switching valve is turned on. The rotation direction switching valve is switched from the neutral position to the working position where the discharge pipeline on the discharge side is connected to the storage tank pipeline, and when the rotation speed detected by the speed detector is lower than the first threshold value and greater than zero When the second threshold is reached, the rotation direction switching valve is switched from the working position to the neutral position. 2. A hydraulic drive system for construction machinery, characterized in that it has: A slewing motor that makes the slewing body turn; including an operating rod, a rotary operating device that outputs a rotary operating signal corresponding to the tilting angle of the operating rod; A rotary direction switching valve connected to the rotary motor through a pair of supply and discharge pipelines, the rotary direction switching valve includes a spool and a driving part that receives command current and drives the spool, when blocking the pair of supply and discharge Switching between a neutral position of the pipeline and an operational position in which one of the pair of supply and discharge lines communicates with the pump pipeline and the other communicates with the storage tank pipeline; Sending a larger instruction current to the control device of the slewing direction switching valve when the slewing operation signal is larger; a speed detector for detecting the revolution speed of the revolution 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 first threshold value is reached, the rotation direction switching valve is switched from the neutral position to the working position where the supply and discharge pipeline on the discharge side communicates with the storage tank pipeline, and when the rotation speed detected by the speed detector is lower than the second threshold value, Switching the rotary direction switching valve from the working position to the neutral position. 3. A hydraulic drive system for construction machinery, characterized in that it has: A slewing motor that makes the slewing body turn; including an operating rod, a rotary operating device that outputs a rotary operating signal corresponding to the tilting angle of the operating rod; A rotary direction switching valve connected to the rotary motor through a pair of supply and discharge pipelines, the rotary direction switching valve includes a spool and a driving part that receives command current and drives the spool, when blocking the pair of supply and discharge Switching between a neutral position of the pipeline and an operational position in which one of the pair of supply and discharge lines communicates with the pump pipeline and the other communicates with the storage tank pipeline; Sending a larger instruction current to the control device of the slewing direction switching valve when the slewing operation signal is larger; a speed detector for detecting the revolution speed of the revolution body; and A pair of pressure sensors for detecting the inflow pressure and outflow pressure of the rotary motor; The control device controls the turning direction switching valve in such a manner that when the turning speed detected by the speed detector is lower than a threshold value when the operating lever of the turning operating device is returned to a neutral state, the turning direction switching valve is turned on and off. The directional switch valve is switched from the neutral position to the working position where the supply and discharge pipeline on the discharge side is connected to the storage tank pipeline, and then the opening between the supply and discharge pipeline on the discharge side and the storage tank pipeline and the supply and discharge pipeline on the supply side are connected to the pump. The opening degree between the pipelines is the opening degree corresponding to the pressure difference between the inflow pressure and the outflow pressure of the rotary motor detected by the pair of pressure sensors. 4. The hydraulic drive system for a construction machine according to claim 3, wherein: The control device controls the rotary direction switching valve in the following manner: the operating rod of the rotary operating device returns to a neutral state, and the rotary direction switching valve switches to the work of connecting the supply and discharge pipeline on the discharge side with the storage tank pipeline. After the position, when the inflow pressure of the slewing motor is higher than the outflow pressure, the slewing direction switching valve is switched to the working position where the supply and discharge pipeline on the supply side communicates with the storage tank pipeline. 5. A hydraulic drive system for construction machinery, characterized in that it has: A slewing motor that makes the slewing body turn; including an operating rod, a rotary operating device that outputs a rotary operating signal corresponding to the tilting angle of the operating rod; A rotary direction switching valve connected to the rotary motor through a pair of supply and discharge pipelines, the rotary direction switching valve includes a spool and a driving part that receives command current and drives the spool, when blocking the pair of supply and discharge Switching between a neutral position of the pipeline and an operational position in which one of the pair of supply and discharge lines communicates with the pump pipeline and the other communicates with the storage tank pipeline; 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 threshold value is reached, the rotary direction switching valve is switched from the neutral position to the working position where the supply and discharge pipeline on the discharge side communicates with the storage tank pipeline, and then the opening between the supply and discharge pipeline on the discharge side and the storage tank pipeline and the supply The opening between the side supply and discharge pipeline and the pump pipeline is the opening corresponding to the pressure difference between the inflow pressure and the outflow pressure of the rotary motor detected by the pair of pressure sensors. 6. The hydraulic drive system for a construction machine according to claim 5, wherein: The control device controls the rotary direction switching valve in the following manner: the operating rod of the rotary operating device returns to a neutral state, and the rotary direction switching valve switches to the work of connecting the supply and discharge pipeline on the discharge side with the storage tank pipeline. After the position, when the inflow pressure of the slewing motor is higher than the outflow pressure, the slewing direction switching valve is switched to the working position where the supply and discharge pipeline on the supply side communicates with the storage tank pipeline.