JP6282941B2 - Hydraulic drive device for work machine - Google Patents

Description

  The present invention relates to a hydraulic drive device for moving a load such as a suspended load in a working machine such as a crane in the same direction as its own weight falling direction.

  Conventionally, as a device for moving a load in the same direction as its own weight falling direction, for example, a lowering drive device for driving a winch for hanging a suspended load by a wire in the lowering direction, described in Patent Document 1 It has been known. The apparatus includes a hydraulic motor for driving the winch, a hydraulic pump for supplying hydraulic oil to the hydraulic motor, and a counter balance valve provided in a meter-out circuit of the hydraulic motor. The counter balance valve opens and closes in response to meter-in pressure, which is the pressure of hydraulic oil introduced into the inlet port of the hydraulic motor. Specifically, it has a function of holding the meter-in pressure at the set pressure by blocking the meter-out circuit only when the meter-in pressure falls below a preset pressure set in advance.

Japanese Patent Laid-Open No. 7-17688

  In the conventional hydraulic drive device, in order to ensure a sufficient meter-in pressure to enable the control by the counter balance valve and supply the hydraulic oil at a sufficient flow rate (meter-in flow rate) to the hydraulic motor, The pump flow rate that is the flow rate of the hydraulic oil discharged from the pump must be larger than the motor flow rate that is the flow rate of the hydraulic oil flowing through the hydraulic motor. Therefore, the required power required for driving the hydraulic pump is large.

  The present invention is a hydraulic drive device for a work machine including a hydraulic pump and a hydraulic motor that is driven by supply of hydraulic oil discharged from the hydraulic pump to move a load in a downward direction, and ensures a sufficient motor flow rate. However, an object of the present invention is to provide an apparatus that can reduce the required power of the hydraulic pump and save energy.

  As means for achieving the above object, the present inventors reduced a part of the hydraulic oil flowing through the meter-out flow path of the hydraulic motor to the meter-in flow path, and merged with the hydraulic oil discharged by the hydraulic pump, It has been conceived to reduce the discharge flow rate required for the hydraulic pump, that is, the pump flow rate, thereby reducing the required power of the hydraulic pump. Furthermore, the present inventors use the function of the counter balance valve for securing the meter-in pressure, that is, the function of maintaining the meter-in pressure at a preset pressure, thereby regenerating the hydraulic oil through the regeneration channel. I came up with a way to make sure.

Specifically, the present invention provides a hydraulic drive device for a work machine that uses hydraulic pressure to move a load in a lowering direction that is the same as the falling direction due to its own weight. A power source for driving the hydraulic pump to discharge the hydraulic oil, an inlet port, and an outlet port. The hydraulic oil discharged from the hydraulic pump is supplied to the inlet port and the hydraulic oil is supplied from the outlet port. A hydraulic motor that operates to move the load in the lowering direction by discharging the oil, and a meter-in for guiding hydraulic oil from the hydraulic pump to the inlet port of the hydraulic motor when the load is moved in the lowering direction and the flow path, and a meter-out flow passage for guiding the tank the hydraulic oil discharged from the outlet port of the hydraulic motor when moving the load to the lowering direction, the An operation device that receives an operation for designating the moving speed of the load and outputs an operation signal according to the operation, and an opening area provided in the meter-in flow path according to the input of the operation signal from the operation device A meter-in throttle valve that opens and closes so as to change, a meter-in flow control valve that opens and closes to maintain the differential pressure across the meter-in throttle valve at a preset meter-in set differential pressure, and the meter-out flow path A counter balance valve that opens and closes to maintain a meter-in pressure, which is a pressure of hydraulic oil introduced into the inlet port of the hydraulic motor, at a preset pressure, and the meter-out flow that flows out of the counter balance valve A part of the hydraulic oil in the passage is reduced to the upstream side of the meter-in throttle valve and the meter-in flow control valve in the meter-in flow path, and the A regeneration channel connected to the meter-out channel and the meter-in channel so as to merge with hydraulic oil discharged from a pressure pump, and the meter-out channel and the regeneration channel in the meter-out channel. A throttle valve provided at a site downstream of the connection site, which generates a back pressure for flowing the hydraulic oil through the regeneration channel, and has an opening area according to an operation signal output from the operation device And a back pressure throttle valve that opens and closes so as to change. And the flow rate of hydraulic oil flowing through the hydraulic motor and the motor flow rate estimated by the opening area of the meter-in throttle valve and the meter-in set differential pressure is the back pressure throttle valve regardless of the operation signal of the operating device. The flow rate of the hydraulic oil flowing through the tank is larger than the tank return flow rate estimated by the opening area of the back pressure throttle valve, the meter-in set differential pressure, and the counter balance valve set pressure. The characteristics of the opening area of the meter-in throttle valve and the characteristics of the opening area of the back pressure throttle valve for the operation signal are set.

  According to this device, the hydraulic oil flowing through the regeneration flow path joins with the hydraulic oil discharged from the hydraulic pump, so that the hydraulic motor is sufficiently capable of suppressing the pump flow rate that is the flow rate of the hydraulic oil discharged from the hydraulic pump. The hydraulic oil can be supplied at a high flow rate. Here, the regeneration flow rate, which is the flow rate of the hydraulic oil flowing through the regeneration flow path, corresponds to the flow rate obtained by subtracting the tank return flow rate from the motor flow rate. By setting the characteristics of the opening areas of the meter-in throttle valve and the back pressure throttle valve for the operation signal so as to exceed the tank return flow rate, the regeneration flow rate can be ensured regardless of the operation signal. .

  This “setting the characteristics of the opening areas of the meter-in throttle valve and the back pressure throttle valve with respect to the operation signal so that the motor flow rate exceeds the tank return flow rate regardless of the operation signal” means that the counter balance valve By utilizing the function of maintaining the meter-in pressure at a preset set pressure and the function of maintaining the differential pressure across the meter-in throttle valve at a preset meter-in set differential pressure by the meter-in flow control valve, Is possible. Specifically, when the opening area of the back pressure throttle valve corresponding to the operation signal is At, the opening area of the meter-in throttle valve is Ami, the meter-in set differential pressure is Pf, and the set pressure of the counter balance valve is Pc. Regardless of the operation signal, for example, by setting the characteristics of the opening areas At and Ami for the operation signal so that the following relational expression is established, the regeneration flow rate can be ensured.

[Equation 1]
At <K · Ami; K ² = Pf / (Pf + Pc) (K <1)

  As described above, according to the present invention, there is provided a hydraulic drive device for a work machine including a hydraulic pump and a hydraulic motor that is driven by supply of hydraulic oil discharged from the hydraulic pump and moves a load in a lowering direction. With respect to the hydraulic motor, it is possible to provide the hydraulic motor capable of reducing the required power of the hydraulic pump and ensuring energy saving while ensuring a sufficient meter-in pressure and meter-in flow rate.

It is a circuit diagram which shows the hydraulic drive device of the working machine which concerns on embodiment of this invention. It is a graph which shows the characteristic of the pump flow volume and motor flow volume in the conventional hydraulic drive unit. 2 is a graph showing characteristics of a pump flow rate, a motor flow rate, and a tank return flow rate with respect to an operation signal in the hydraulic drive device shown in FIG. 1. 2 is a graph showing characteristics of opening areas of a meter-in throttle valve and a back pressure throttle valve with respect to an operation signal in the hydraulic drive device shown in FIG. 1. 2 is a graph showing characteristics of meter-in pressure, upstream pressure of a meter-in throttle valve, and upstream pressure of a counter balance valve with respect to an operation signal in the hydraulic drive device shown in FIG. 1. FIG. 2 is a circuit diagram showing an example in which a neutral shutoff valve is added to the hydraulic drive device shown in FIG. 1.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram showing a hydraulic drive device for a work machine according to the embodiment. This apparatus includes an engine 1, a hydraulic pump 2, a hydraulic motor 4 that is a hydraulic actuator, an operating device, a meter-in flow path 10, a meter-out flow path 20, a regeneration flow path 30, and a meter-in flow controller 12. A counter balance valve 25 and a back pressure throttle valve 23.

  The engine 1 is a power source for the hydraulic pump 2. The hydraulic pump 2 is driven by the engine 1 and thereby discharges hydraulic oil in the tank T.

The hydraulic motor 4 is an example of a hydraulic motor according to the present invention. The hydraulic motor 4 is incorporated in a winch device having a winch drum 5, and the suspended load 7 is a load by rotating the winch drum 5 in both the forward and reverse directions in a specific direction. Raise and lower. Specifically, the hydraulic motor 4 has a first port 4a and a second port 4b, and when the hydraulic oil is supplied to the first port 4a, the winch drum 5 is lowered, that is, the suspended load 7 is moved. Is rotated in a direction in which it is moved downward in the same direction as the falling direction due to its own weight, and the hydraulic oil is discharged from the second port 4b, while when the hydraulic oil is supplied to the second port 4b, the winch drum The hydraulic fluid is discharged from the first port 4a by rotating 5 in the winding direction, that is, the direction in which the suspended load 7 is raised. However, in FIG. 1, for simplification of illustration, only a circuit related to the driving of the hydraulic motor 4 in the lowering direction, that is, the lowering driving for lowering the suspended load 7, which is the subject of the present invention, is shown. In other words, FIG. 1 shows the hydraulic fluid supplied to the first port 4a of the hydraulic motor 4 and discharged from the second port 4b in the hydraulic circuit for rotating the hydraulic motor 4 in both forward and reverse directions. Only the flow path for returning to the tank T is shown.

In the circuit shown in FIG. 1, in order to actually rotate the hydraulic motor 4 in both forward and reverse directions, a control valve such as a direction switching valve is interposed between the hydraulic motor 4 and the hydraulic pump 2, and this control is performed. Any valve may be used as long as it switches between the flow path connecting the hydraulic pump 2 to the first port 4a of the hydraulic motor 4 and the flow path connecting to the second port 4b. However, in the present invention, the hydraulic motor is not limited to being driven in both forward and reverse directions, and may be driven only in the direction in which the load is moved in the downward direction .

  The meter-in flow path 10 is a flow path for supplying hydraulic oil discharged from the hydraulic pump 2 to the hydraulic motor 4 during the lowering drive. Specifically, the meter-in flow path 10 is connected to the discharge port of the hydraulic pump 2. It reaches the first port 4 a of the hydraulic motor 4. The meter-out flow path 20 is a flow path for returning hydraulic oil discharged from the second port 4b of the hydraulic motor 4 to the tank T during the lowering drive. It reaches the tank T from the second port 4b.

  The operating device receives an operation for designating a moving speed in the lowering direction of the suspended load 7 and outputs an operation signal that increases in accordance with the operation. A pilot hydraulic power source and a remote control valve 6 are provided. The remote control valve 6 includes a lever 6a that receives a turning operation, and a valve body 6b that is connected to the lever 6a. The valve body 6b is connected to the pilot hydraulic pressure source, and outputs a pilot signal, which is a hydraulic signal having a pilot pressure having a magnitude corresponding to the operation amount of the lever 6a, as the operation signal. This pilot signal is input to the meter-in flow controller 12 and the back pressure throttle valve 23 through pilot lines 16 and 26, respectively.

  The meter-in flow rate controller 12 is provided in the middle of the meter-in flow channel 10 and controls a meter-in flow rate Qin that is a flow rate of hydraulic oil introduced into the hydraulic motor 4 through the meter-in flow channel 10. This meter-in flow rate Qin corresponds to the motor flow rate Qm flowing through the hydraulic motor 4.

  The meter-in flow controller 12 has a meter-in throttle valve 13 and a meter-in flow control valve 14.

  The meter-in throttle valve 13 is constituted by a variable throttle valve whose opening area changes depending on the pilot pressure of a pilot signal input from the remote control valve 6 through the pilot line 16. Specifically, when the pilot signal is not input, the meter-in throttle valve 13 is held in a closed position by a spring, that is, a position where the meter-in flow path 10 is shut off, whereas when the pilot signal is input, the pilot pressure is reduced. The valve is opened so that the opening area increases in accordance with the size of the hydraulic oil, and the circulation of the hydraulic oil in the meter-in flow path 10 is allowed. That is, the meter-in throttle valve 13 opens so that the opening area of the meter-in throttle valve 13 increases as the lever 6a of the remote control valve 6 is operated in the direction for lowering drive, so that the flow rate is increased. Allow distribution of hydraulic oil.

  The meter-in flow rate adjusting valve 14 is provided in the middle of the bleed-off flow channel from the upstream portion of the meter-in throttle valve 13 in the meter-in flow channel 10 to the tank T, and changes the flow rate of the bleed-off flow channel. The meter-in flow rate Qin can be controlled by opening and closing. The meter-in flow control valve 14 keeps the difference between the upstream pressure and the downstream pressure of the meter-in throttle valve 13, that is, the differential pressure ΔPin across the meter-in throttle valve 13 at a preset meter-in set differential pressure Pf. Open and close. Specifically, an upstream pressure and a downstream pressure of the meter-in throttle valve 13 are introduced into the meter-in flow control valve 14 from opposite sides, and the opening area of the meter-in flow control valve 14 and the meter-in flow are determined by the balance. The flow rate Qin is determined.

  When the hydraulic drive device includes a control valve for switching the drive direction of the hydraulic motor 4 as described above, the meter-in throttle valve 13 may be incorporated in the control valve.

  The counter balance valve 25 is provided in the meter-out flow path 20 and opens and closes so as to keep the meter-in pressure, which is the pressure of the hydraulic oil introduced into the inlet port 4a of the hydraulic motor 4, at a preset set pressure. To do. Specifically, the counter balance valve 25 is given a biasing force in a direction to hold the counter balance valve 25 in a closed state, and a measurement set downstream of the meter-in throttle valve 13 in the meter-in flow path 10. The counter balance valve 25 is opened only when the pressure at the point 15 is introduced on the side opposite to the spring and the pressure, that is, the meter-in pressure exceeds the preset pressure Pc. In other words, the counter balance valve 25 is closed only when the meter-in pressure is equal to or lower than the set pressure Pc, thereby holding the meter-in pressure at the set pressure Pc.

  The regeneration flow path 30 is a part of the hydraulic oil flowing out from the counter balance valve 25 and returned to the tank T through the meter-out flow path 20 upstream of the meter-in throttle 13 in the meter-in flow path 10. It is a flow path for reducing to the side. The regeneration channel 30 includes the meter-in flow rate controller including the inlet end connected to the downstream portion of the counter balance valve 25 in the meter-out channel 20 and the meter-in throttle valve 13 in the meter-in channel 10. 12 and an outlet end connected to the upstream portion. A check valve 32 is provided in the middle of the regeneration flow path 30, and the check valve 32 prevents backflow of hydraulic oil from the meter-in flow path 10 to the meter-out flow path 20.

  The back pressure throttle valve 23 is provided in a flow path downstream from the connection point 34 between the meter-out flow path 20 and the regeneration flow path 30, that is, a tank flow path 36 extending from the connection point 34 to the tank T. It has a function of generating a back pressure upstream of the tank T for ensuring the flow of hydraulic oil from the connection point 34 to the regeneration flow path 30 and changing the flow rate of the hydraulic oil returning to the tank T. . That is, the back pressure throttle valve 23 is constituted by a variable throttle valve whose opening area is changed by the pilot pressure of the pilot signal input from the remote control valve 6 through the pilot line 26. Specifically, the back pressure throttle valve 23 is held in a closed position, that is, a position where the meter-out flow path 20 is shut off by a spring when the pilot signal is not input, and when the pilot signal is input, The valve is opened so that the opening area increases according to the magnitude of the pilot pressure, and the flow of the hydraulic oil in the meter-out flow path 20 is allowed. Thus, the back pressure throttle valve 23 is opened so that the opening area of the back pressure throttle valve 23 increases as the lever 6a of the remote control valve 6 is operated in the direction for driving down. Allow hydraulic fluid to flow at higher return flow rates.

  In this device, when the lever 6a of the remote control valve 6 constituting the operating device is operated, a pilot signal having a pilot pressure of a magnitude corresponding to the operating amount, that is, an operating signal is transmitted through the pilot line 16 to the meter-in flow controller 12. The meter-in throttle valve 13 is opened with an opening area corresponding to the magnitude of the pilot pressure that is input to the meter-in throttle valve 13. The meter-in flow control valve 14 of the meter-in flow controller 12 keeps the differential pressure ΔPin, which is the difference between the upstream pressure and the downstream pressure of the meter-in throttle valve 13, at a preset meter-in set differential pressure Pf. Open and close. Thus, the flow rate of the hydraulic oil introduced from the meter-in throttle valve 13 to the inlet port 4a of the hydraulic motor 4, that is, the meter-in flow rate Qmi is controlled to a flow rate corresponding to the pilot signal. The hydraulic motor 4 rotates at a speed corresponding to the meter-in flow rate Qmi, thereby driving the winch drum 5 in the lowering direction to lower the suspended load 7.

  The hydraulic oil discharged from the second port 4b of the hydraulic motor 4 flows through the counter balance valve 25. The counter balance valve 25 is set to a meter-in pressure that is the pressure of the hydraulic oil introduced into the first port 4a. The meter-in pressure is maintained at the set pressure by closing the valve only when the pressure is not reached.

  The hydraulic oil flowing out from the counter balance valve 25 returns to the tank T through the back pressure throttle valve 23, but the opening area of the back pressure throttle valve 23 is limited to the opening area corresponding to the magnitude of the pilot pressure. Therefore, the back pressure throttle valve 23 generates a back pressure higher than the tank pressure by the throttle action. If the back pressure is ensured up to the pump pressure that is the discharge pressure of the hydraulic pump 2, a part of the hydraulic oil flows through the regeneration flow path 30 and is reduced to the meter-in flow path 10 and is discharged from the hydraulic pump 2. Can merge with hydraulic oil. This reduction and merging of the hydraulic oil makes it possible to reduce the necessary pump flow rate Qp, that is, the flow rate of the hydraulic oil discharged from the hydraulic pump 2, thereby reducing the necessary power for driving the hydraulic pump 2. Energy saving.

  In the case of a conventional circuit having no regeneration flow path 30, in order to enable the meter-in flow rate controller 12 to control the meter-in flow rate Qin, the pump flow rate Qp is larger than the motor flow rate Qm as shown in FIG. It needs to be maintained at a high flow rate. On the other hand, when the hydraulic fluid is reduced through the regeneration flow path 30, a sufficient motor flow rate Qm is secured while reducing the pump flow rate by the flow rate of the reduced hydraulic fluid, that is, the regeneration flow rate Qrc. For example, as shown in FIG. 3, the pump flow rate Qp can be set to a flow rate smaller than the motor flow rate Qm.

  In order to reliably generate such a regeneration flow rate Qrc, that is, to satisfy Qrc> 0, the motor flow rate Qm (= Qmi) is equal to the tank flow regardless of the pilot pressure of the pilot signal output from the remote control valve 6. The characteristics of the opening area Ami of the meter-in throttle valve 13 and the opening area At of the back pressure throttle valve 23 with respect to the pilot pressure may be set so as to exceed the tank return flow rate Qt that is the flow rate in the passage 36. For example, as shown in FIG. 4, the characteristics of both opening areas Ami and At may be set. Since the regeneration flow rate Qrc corresponds to the motor flow rate Qm, that is, the flow rate obtained by subtracting the tank return flow rate Qt from the meter-in flow rate Qmi (= Qmi−Qt), the regeneration flow rate Qrc can be secured by setting the characteristics. it can.

  Here, “the characteristics of the opening areas of the meter-in throttle valve and the back pressure throttle valve with respect to the pilot pressure are set so that the motor flow rate Qm (= meter-in flow rate Qin) exceeds the tank return flow rate Qt regardless of the pilot pressure. “Setting each” means that the counter balance valve 25 holds the meter-in pressure Pin at a preset pressure Pc, and the meter-in flow control valve 14 sets the differential pressure ΔPin across the meter-in throttle valve 13 in advance. This is possible by using the function of maintaining the set meter-in set differential pressure Pf. In other words, the motor flow rate Qm can be estimated from the opening area Ami of the meter-in throttle valve 13 and the meter-in set differential pressure Pf, and the tank return flow rate Qt can be estimated from the opening area At of the back pressure throttle valve 23 and the meter-in set difference. It is possible to estimate from the pressure Pf and the set pressure Pc of the counter balance valve 25. Based on these estimates, the characteristics of the opening areas Ami and At that satisfy the above conditions can be set.

  Specifically, the characteristics of the opening areas At and Ami with respect to the pilot pressure may be set so that the following expression (1) is established.

[Equation 2]
At <K · Ami; K ² = Pf / (Pf + Pc) (∴K <1) (1)

  The reason is as follows. As described above, the regeneration flow path Qrc which is the flow rate of the hydraulic oil in the regeneration flow path 30 is a flow rate of the hydraulic oil discharged from the hydraulic motor 4, that is, a flow rate obtained by subtracting the tank return flow rate Qt from the motor flow rate Qm. Therefore, in order to satisfy Qrc> 0, the following relational expression should be satisfied.

[Equation 3]
Qrc = Qm−Qt> 0 (2)

  Here, since the motor flow rate Qm is equal to the meter-in flow rate Qmi, the flow rate coefficient of the hydraulic oil is represented by the following equation.

[Equation 4]
Qm = Qmi = Cv · Ami · √Pf (3)

  On the other hand, the tank return flow rate Qt, that is, the flow rate of the hydraulic oil flowing through the regeneration throttle valve 23 is expressed by the following equation, where ΔPt is the differential pressure across the regeneration throttle valve 23.

[Equation 5]
Qt = Cv · At · √ΔPt (4)

  Here, the front-rear differential pressure ΔPt of the regeneration throttle valve 23 is equal to the upstream pressure of the regeneration throttle valve 23 as a gauge pressure, and when the regeneration flow rate Qrc is generated, the check valve 32 is opened. Therefore, the front-rear differential pressure ΔPt can be regarded as being equal to the pump pressure Pp. That is,

[Equation 6]
Qt = Cv · At · √Pp (5)

  Substituting Equations (3) and (5) into Equation (2) for transformation yields:

[Equation 7]
At <(√Pf / √Pp) Ami (6)

  Here, the meter-in pressure Pin, that is, the pressure of the hydraulic oil introduced into the first port 4a of the hydraulic motor 4 is a pressure obtained by subtracting the differential pressure ΔPin of the meter-in throttle valve 13 from the pump pressure Pp (= Pp−ΔPi). In addition, the meter-in pressure Pin is maintained at the set pressure Pc by the counter balance valve 25, and the front-rear differential pressure ΔPin is maintained at the meter-in set differential pressure Pf by the meter-in flow control valve 14, so that the pump pressure Pp Can be expressed as:

  Pp = Pin + ΔPin = Pc + Pf (7)

  By substituting Equation (7) into Equation (6), Equation (1) can be obtained.

  In the circuit shown in FIG. 1, the pressure on the upstream side of the counter balance valve 25 (holding pressure for holding the suspended load 7), the pressure on the upstream side of the throttle valve 23 for back pressure (≈pump pressure Pp), and The meter-in pressure Pin (≈Pc) is, for example, as shown in FIG.

  As described above, according to this device, the counter balance valve 25 controls the meter-in pressure Pin to the set pressure Pc, and the meter-in flow control valve 14 converts the front-rear differential pressure ΔPin of the meter-in throttle valve 13 to the meter-in set differential pressure. By utilizing the function of controlling to Pf, the pilot pressure is adjusted so that the hydraulic oil flows through the regeneration passage 30 by the back pressure generated by the back pressure throttle valve 23 regardless of the pilot pressure of the pilot signal output from the remote control valve 6. It is possible to set the characteristics of the opening areas Ami and At of the meter-in throttle valve 13 and the back pressure throttle valve 23 against the above, thereby reducing the necessary pump flow rate Qp and saving energy. In addition, the sum of the pump flow rate Qp and the regeneration flow rate Qrc can be set to a meter-in flow rate Qin controlled by the meter-in flow rate controller 12, that is, the motor flow rate Qm or more. Can be operated. This makes it possible to reliably correspond the motor flow rate Qm to the actual operation amount (pilot pressure) of the lever 6a, and contributes to improvement in operability.

  On the other hand, the presence of the counter balance valve 25 makes it possible to stabilize the meter-in pressure Pin and ensure high safety. For example, when the meter-in pressure rapidly decreases due to, for example, damage to the pipes constituting the meter-in flow path 10, the counter balance valve 25 is fully closed as the meter-in pressure decreases, thereby blocking the meter-out flow path 20. Thus, the sudden drop of the suspended load 7 can be prevented.

  Further, when the device includes at least one of the neutral shutoff valves 40 and 42 as shown in FIG. 6, higher safety can be ensured. These neutral shut-off valves 40 and 42 are provided in the middle of the regeneration flow path 30 and the meter-out flow path 20, respectively, and are opened only when the pilot pressure of the pilot signal output from the remote control valve 6 is a certain level or higher. . In other words, when the lever 6a of the remote control valve 6 is in the neutral position, the valve is closed to block the flow path. The neutral shut-off valves 40 and 42 can reliably stop the hydraulic motor 4 when the lever 6a is in the neutral position due to the valve closing.

  In the present invention, the operation signal input to the meter-in throttle valve or the regeneration throttle valve may be an electrical signal. That is, the operating device according to the present invention may output an electrical signal as an operation signal. In this case, for example, an electrohydraulic pilot type throttle valve may be used as the meter-in throttle valve and the regeneration throttle valve.

1 Engine (Power source)
2 Hydraulic pump 4 Hydraulic motor (hydraulic actuator)
6 Remote control valve (operating device)
7 Suspended load (load)
DESCRIPTION OF SYMBOLS 10 Meter-in flow path 12 Meter-in flow controller 13 Meter-in throttle valve 14 Meter-in flow control valve 15 Counter balance valve measurement point 20 Meter-out flow path 23 Back pressure throttle valve 25 Counter balance valve 30 Regeneration flow path 34 Connection point 36 Tank flow path T tank

Claims (2)

A hydraulic drive device for a work machine for moving a load in a lowering direction in the same direction as a falling direction by its own weight using hydraulic pressure,
A hydraulic pump;
A power source for driving the hydraulic pump to discharge hydraulic oil;
It has an inlet port and an outlet port, and receives the supply of hydraulic oil discharged from the hydraulic pump to the inlet port and discharges the hydraulic oil from the outlet port to operate the load in the downward direction. A hydraulic motor to
A meter-in flow path for guiding hydraulic oil from the hydraulic pump to the inlet port of the hydraulic motor when the load is moved in the lowering direction;
A meter-out flow path for guiding hydraulic oil discharged from the outlet port of the hydraulic motor to the tank when moving the load in the lowering direction;
An operation device that receives an operation for designating the moving speed of the load and outputs an operation signal corresponding to the operation;
A meter-in throttle valve that is provided in the meter-in flow path and opens and closes so that an opening area changes according to the input of the operation signal from the operation device;
A meter-in flow control valve that opens and closes to maintain the differential pressure across the meter-in throttle valve at a preset meter-in differential pressure; and
A counter balance valve that is provided in the meter-out flow path and opens and closes so as to maintain a meter-in pressure that is a pressure of hydraulic oil introduced into an inlet port of the hydraulic motor at a preset pressure;
An operation in which a part of the hydraulic oil in the meter-out flow path flowing out from the counter balance valve is reduced to the upstream side of the meter-in throttle valve and the meter-in flow control valve in the meter-in flow path and discharged from the hydraulic pump. A regeneration channel connected to the meter-out channel and the meter-in channel so as to merge with oil;
A throttle valve provided in a part of the meter-out flow path downstream of the connection part between the meter-out flow path and the regeneration flow path, and generates a back pressure for flowing the hydraulic oil through the regeneration flow path. And a back pressure throttle valve that opens and closes so that the opening area changes according to an operation signal output from the operating device.
Regardless of the operation signal of the operating device, the flow rate of hydraulic oil flowing through the hydraulic motor and the motor flow rate estimated by the opening area of the meter-in throttle valve and the meter-in set differential pressure flows through the back pressure throttle valve. The meter-in to the operation signal is a flow rate of hydraulic oil that is larger than a tank return flow rate estimated by an opening area of the throttle valve for back pressure, the meter-in set differential pressure, and a set pressure of the counter balance valve. A hydraulic drive device for a work machine, wherein a characteristic of an opening area of the throttle valve and a characteristic of an opening area of the back pressure throttle valve with respect to the operation signal are set.
The hydraulic drive device for a work machine according to claim 1, wherein an opening area of the back pressure throttle valve corresponding to the operation signal is At, an opening area of the meter-in throttle valve is Ami, and the meter-in set differential pressure is Pf, The characteristics of the opening areas At and Ami with respect to the operation signal are set so that the following relational expression is satisfied regardless of the operation signal when the set pressure of the counter balance valve is Pc. Hydraulic drive device.
[Equation 8]
At <K · Ami; K ² = Pf / (Pf + Pc) (K <1)

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