JP2005221026A - Hydraulic circuit of hydraulic working machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent inside a hydraulic cylinder from being put in a vacuum state even if a pressing force is applied to a working element for any reason on the way of the sole lowering operation of the working element and allow the working element to make the lowering operation owing to its own weight at the time of the sole lowering operation of the working element. <P>SOLUTION: The hydraulic circuit comprises a main pump 21, a boom 5, a hydraulic cylinder 11 for the boom, a direction control valve 22 to control the flow of pressure oil to the hydraulic cylinder 11, and an operation device 23 to perform the changeover operation of the direction control valve 22, wherein the arrangement further includes a jack-up changeover valve 25 to be changed over when the bottom pressure of the cylinder 11 has attained the specified value, a flow path changing means to change the flow path of the pressure oil supplied to the meter-in of the direction control valve 22 to the opening side or the closing side in association with the changeover operation of the valve 25, and a slow return circuit including a check valve 47 and a throttle valve 46 to control the flow path of the pressure oil for changing over the valve 25. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hydraulic circuit of a hydraulic working machine such as a hydraulic excavator in which working elements such as a boom, an arm, and a bucket are driven by a double-acting hydraulic cylinder, and more particularly to a hydraulic circuit of a hydraulic working machine having a jack-up function.

  Conventionally, as a hydraulic circuit provided in a hydraulic excavator, for example, a hydraulic excavator, a traveling state detecting means for detecting a traveling state of the hydraulic excavator, and a pilot signal for lowering a working element based on a signal from the traveling state detecting means For example, there has been proposed a switch valve having a switching valve for switching to a position where a pilot pipe line for transmitting a pilot signal for lowering a boom for contracting a boom hydraulic cylinder is cut off or communicated. In this hydraulic circuit, when the traveling state detecting means detects the traveling state, by switching the switching valve to a position where the pilot pipe communicates, the combined operation of traveling and boom lowering is performed. Pressure oil from the main pump is supplied to the rod chamber of the boom hydraulic cylinder so that the vehicle body can be jacked up by the boom (see, for example, Patent Document 1).

Conventionally, during the boom lowering operation, pressure oil from the main pump is supplied to the rod chamber of the boom hydraulic cylinder, and return oil from the bottom chamber of the boom hydraulic cylinder is regenerated and supplied to the rod chamber of the boom hydraulic cylinder. There has also been proposed a hydraulic circuit for a hydraulic working machine that can reduce fluctuations in boom operating speed caused by changes in external force acting on the boom hydraulic cylinder while reducing the power consumption of the main pump (for example, patents) Reference 2).
JP-A-6-2344 Japanese Patent Laid-Open No. 5-302604

  In the technique described in Patent Document 1 described above, the pressure oil from the main pump is supplied to the rod chamber of the boom hydraulic cylinder only when the combined operation of traveling and boom lowering is performed. When a pressing force is applied to the boom for some reason, the rod chamber of the boom hydraulic cylinder is evacuated to create a gap, thereby deteriorating the operability of the boom lowering operation.

  Further, the technology described in Patent Document 2 supplies pressure oil from the main pump to the rod side of the boom hydraulic cylinder during the boom lowering single operation, and returns return oil from the bottom chamber of the boom hydraulic cylinder to the boom hydraulic pressure. Since regeneration is supplied to the rod chamber of the cylinder, it is possible to prevent the rod chamber of the boom hydraulic cylinder from being evacuated even if a pressing force is applied to the boom during the boom lowering single operation. However, since the configuration is such that the pressure oil from the main pump is continuously supplied to the boom hydraulic cylinder during the boom lowering operation alone, there is a problem in terms of economy because the pump power consumption is increased. Furthermore, in the combined operation with other work elements such as an arm, the amount of pressure oil supplied to the actuator that drives the other work elements is limited, so that there is a problem that work efficiency is lowered.

  The present invention has been made from the actual state of the above-described prior art, and its purpose is to have a jack-up function of the vehicle body and even if a pressing force is applied to the work element for some reason during the single lowering operation of the work element. An object of the present invention is to provide a hydraulic circuit for a hydraulic working machine that does not make the inside of the hydraulic cylinder in a vacuum state, and enables a lowering operation only by its own weight when the single lowering operation of the working element is performed.

  To achieve the above object, the present invention provides a main pump, a working element, a double-acting hydraulic cylinder that is expanded and contracted by pressure oil discharged from the main pump, and drives the working element, and the main pump. In a hydraulic circuit of a hydraulic working machine comprising: a directional control valve that controls a flow of pressure oil supplied to a bottom chamber and a rod chamber of the hydraulic cylinder from the above; and an operating device that performs a switching operation of the directional control valve. The jack-up switching valve that is switched when the bottom pressure of the hydraulic cylinder reaches a predetermined pressure, and the flow path of the pressure oil that is supplied to the meter-in of the directional control valve in accordance with the switching operation of the jack-up switching valve Or a slow return circuit including a flow path changing means for changing to a closed circuit side and a throttle and check valve for controlling the flow path of the pressure oil for switching the jackup switching valve. When the bottom pressure of the hydraulic cylinder exceeds the predetermined pressure during the element lowering operation, the throttle of the slow return circuit causes the jack-up switching valve to move more time than when the bottom pressure reaches the predetermined pressure. Switching to the first switching position with a delay to switch the flow path changing means to the closed side, without supplying the hydraulic oil discharged from the main pump to the rod chamber of the hydraulic cylinder, and lowering the working element Sometimes when the bottom pressure of the hydraulic cylinder becomes smaller than the predetermined pressure, the jack-up switching valve is switched to the second switching position without a time delay via the check valve of the slow return circuit. The flow path changing means is switched to the open circuit side, and the pressure oil discharged from the main pump is transferred to the rod chamber of the hydraulic cylinder via the direction control valve. It is characterized in that sheet.

  For example, in a boom hydraulic cylinder provided in a hydraulic excavator, the bottom chamber becomes a high pressure due to the weight of booms, arms, etc., which are work elements, when no external force is applied. On the other hand, when a pressing force is applied to the work element, a forcing force, that is, a pulling force is applied to the boom hydraulic cylinder, and the bottom chamber becomes low pressure.

  According to the present invention configured as described above, when the bottom pressure of the hydraulic cylinder becomes lower than a predetermined pressure during the operation of lowering the work element alone, the jack-up switching valve is switched to the second switching position, and accordingly the flow is changed. The road change means is switched to the open circuit side, and the pressure oil discharged from the main pump is supplied to the rod chamber of the hydraulic cylinder via the direction control valve, so that a large pressing force can be generated on the work element. Can be up.

  Also, even if the pressing force acts on the work element for some reason during the single lowering operation of the work element and the bottom pressure becomes smaller than the predetermined pressure, the pressure oil from the main pump is at this time the rod of the hydraulic cylinder as described above. Since the pressure is supplied to the chamber, the inside of the hydraulic cylinder is not in a vacuum state, and therefore the operation stability of the hydraulic cylinder can be maintained.

  When the bottom pressure of the hydraulic cylinder is equal to or higher than the predetermined pressure during the single lowering operation of the working element, the jackup switching valve is switched to the first switching position, and accordingly, the flow path changing means is switched to the closed circuit side, and the main pump Is not supplied to the rod chamber of the hydraulic cylinder. That is, it is possible to realize a lowering operation only by its own weight, save supply of pressure oil to the hydraulic cylinder that drives the work element, and suppress pump power consumption.

  Also, when a lower operation of the hydraulic cylinder that drives the work element is equal to or higher than a predetermined pressure during the operation of lowering the work element, the work element is driven when a combined operation with another work element is performed. Since the hydraulic oil from the main pump is not supplied to the hydraulic cylinder, the pressure oil from the main pump can be supplied to the hydraulic actuator that drives other work elements, and the amount of pressure oil supplied to the hydraulic actuator can be increased. it can.

  Further, when the bottom pressure of the hydraulic cylinder is changed from a state smaller than a predetermined pressure to a pressure higher than a predetermined pressure during the operation of lowering the work element, the jack-up switching valve has a predetermined bottom pressure due to the throttle of the slow return circuit. It is switched to the first switching position later than when the pressure is reached. Thereby, the sensitive switching operation | movement of a jackup switching valve is suppressed, and the hunting of this jackup switching valve can be prevented.

  In the present invention, when the flow path changing means is connected to the meter import of the directional control valve on the upstream side of the directional control valve, and the jackup switching valve is switched to the first switching position. The flow control valve is switched to the open position when the jack up switching valve is switched to the second switching position, and is connected to the center bypass port of the direction control valve on the downstream side of the direction control valve. A center bypass switching valve that is switched to an open position when the jackup switching valve is switched to the first switching position and is switched to a closed position when the jackup switching valve is switched to the second switching position. It is characterized by.

  According to the present invention configured as described above, when the jack-up switching valve is switched to the first switching position, that is, when the work element falls due to its own weight, the flow control valve is switched to the closed position, and the center bypass Since the switching valve is switched to the open position, the pressure oil discharged from the main pump returns to the tank through the center bypass port and center bypass switching valve of the direction control valve, and the supply of pressure oil to the rod chamber of the hydraulic cylinder is not performed. Stopped. Further, when the jackup switching valve is switched to the second switching position, that is, when a pressing force is applied to the work element, the flow control valve is switched to the open position, and the center bypass switching valve is set to the closed position. Since it is switched, the pressure oil discharged from the main pump is supplied to the rod chamber of the hydraulic cylinder through the meter import of the flow control valve and the direction control valve.

  In order to achieve the above object, the present invention provides a first main pump and a second main pump, a first traveling device driven by pressure oil discharged from the first main pump, and the second main pump. A second traveling device driven by pressure oil discharged from the first main control valve; a first directional control valve for controlling a flow of pressure oil supplied from the first main pump to the first traveling device; and the second main pump. The second directional control valve for controlling the flow of pressure oil supplied to the second traveling device from the first, the working element, and expanded and contracted by the pressure oil discharged from the first main pump and the second main pump, A double-acting hydraulic cylinder for driving elements, a third directional control valve for controlling the flow of pressure oil supplied from the first main pump to the bottom chamber and the rod chamber of the hydraulic cylinder, and the second main pump From the bottom chamber and rod chamber of the hydraulic cylinder In a hydraulic circuit of a hydraulic working machine comprising: a fourth direction control valve that controls a flow of supplied pressure oil; and an operation device that performs a switching operation of the third direction control valve and the fourth direction control valve. A jack-up switching valve that is switched when the bottom pressure of the hydraulic cylinder reaches a predetermined pressure, and is supplied from the first main pump to the meter-in of the third directional control valve in accordance with the switching operation of the jack-up switching valve. The working element, comprising: a flow rate changing means for changing a pressure oil flow path to an open circuit side or a closed circuit side; and a slow return circuit including a throttle and a check valve for controlling the pressure oil flow path for switching the jack-up switching valve. When the bottom pressure of the hydraulic cylinder becomes equal to or higher than the predetermined pressure during the lowering operation, the jack-up switching valve is controlled by the throttle of the slow return circuit. Switching to the first switching position with a time delay from the time when the constant pressure is reached, switching the flow path changing means to the closed side, and supplying the pressure oil discharged from the first main pump and the second main pump to the closed position When the bottom pressure of the hydraulic cylinder is lower than the predetermined pressure during the lowering operation of the working element without supplying the rod chamber of the hydraulic cylinder, the jack up switching valve is controlled by the check valve of the slow return circuit. Switch to the second switching position without having a time delay, switch the flow path changing means to the open side, and pressure oil discharged from the first main pump and the second main pump to the third direction control valve, It supplies to the rod chamber of the said hydraulic cylinder through a 4th direction control valve.

  According to the present invention configured as described above, when the bottom pressure of the hydraulic cylinder becomes lower than a predetermined pressure during the operation of lowering the work element alone, the jack-up switching valve is switched to the second switching position, and accordingly the flow path The changing means is switched to the open circuit side, and the pressure oil discharged from the first main pump and the second main pump is supplied to the rod chamber of the hydraulic cylinder via the third direction control valve and the fourth direction control valve, and the working element A large pressing force can be generated, and the vehicle body can be jacked up. At this time, by operating the first traveling device and the second traveling device, a jack-up operation in cooperation with traveling can be realized.

  Further, even if the pressing force acts on the work element for some reason during the single lowering operation of the work element and the bottom pressure becomes smaller than the predetermined pressure, at this time, as described above, the first main pump and the second main pump Since the pressure oil is supplied to the rod chamber of the hydraulic cylinder, the inside of the hydraulic cylinder is not in a vacuum state, and therefore the operation stability of the hydraulic cylinder can be maintained.

  When the bottom pressure of the hydraulic cylinder is equal to or higher than a predetermined pressure during the single lowering operation of the working element, the jack-up switching valve is switched to the first switching position, and accordingly, the flow path changing means is switched to the closed side, Pressure oil from the pump and the second main pump is not supplied to the rod chamber of the hydraulic cylinder. That is, it is possible to realize a lowering operation only by its own weight, save supply of pressure oil to the hydraulic cylinder that drives the work element, and suppress pump power consumption.

  In addition, when a bottom operation of the hydraulic cylinder that drives the work element is equal to or higher than a predetermined pressure during the single lowering operation of the work element, when the combined operation with another work element is performed, the work element is Since the hydraulic oil to be driven is not supplied with the pressure oil from the first and second main pumps, the pressure oil of the first and second main pumps can be supplied to the hydraulic actuators that drive other work elements. The amount of pressure oil supplied to the actuator can be increased.

  Further, when the bottom pressure of the hydraulic cylinder is changed from a state smaller than a predetermined pressure to a pressure higher than a predetermined pressure during the operation of lowering the work element, the jack-up switching valve has a predetermined bottom pressure due to the throttle of the slow return circuit. It is switched to the first switching position later than when the pressure is reached. Thereby, the sensitive switching operation | movement of a jackup switching valve is suppressed, and the hunting of this jackup switching valve can be prevented.

  Further, the present invention is the above invention, wherein the flow path changing means is connected to a meter import of the third directional control valve upstream of the third directional control valve, and the jack-up switching valve is connected to the first switching position. A flow rate control valve that is switched to a closed position when the switch is switched to the open position, and an open circuit position that is switched to the open position when the jack-up switch valve is switched to the second switch position, and the third direction control downstream of the third direction control valve. Connected to the center bypass port of the valve, when the jackup switching valve is switched to the first switching position, it is switched to the open position, and when the jackup switching valve is switched to the second switching position, it is switched to the closed position. And a center bypass switching valve.

  According to the present invention configured as described above, when the jack-up switching valve is switched to the first switching position, that is, when the work element falls due to its own weight, the flow control valve is switched to the closed position, and the center bypass Since the switching valve is switched to the open position, the pressure oil discharged from the main pump returns to the tank through the center bypass port and center bypass switching valve of the third direction control valve, and the pressure oil to the rod chamber of the hydraulic cylinder Supply is stopped. Further, when the jackup switching valve is switched to the second switching position, that is, when a pressing force is applied to the work element, the flow control valve is switched to the open position, and the center bypass switching valve is set to the closed position. Since it is switched, the pressure oil discharged from the main pump is supplied to the rod chamber of the hydraulic cylinder through the meter import of the flow control valve and the third direction control valve.

  Further, the present invention is characterized in that in the above invention, a regeneration circuit is provided for regenerating a part of the meter-out oil discharged from the bottom chamber of the hydraulic cylinder as meter-in oil supplied to the rod chamber of the hydraulic cylinder. Yes.

  In the present invention configured as described above, the pressure oil from the bottom chamber is regenerated and supplied to the rod chamber of the hydraulic cylinder during the single lowering operation of the work element. Even if a pressing force acts on the rod chamber, the rod chamber of the hydraulic cylinder can be reliably prevented from being in a vacuum state.

  The present invention has a function of jacking up the vehicle body, and even if a pressing force is applied to the work element for some reason during the single lowering operation of the work element and the bottom pressure becomes lower than a predetermined pressure, the inside of the hydraulic cylinder is maintained. There is no vacuum, so that the stability of the hydraulic cylinder operation can be maintained. Thereby, the favorable operativity of the lowering operation of the work element driven by this hydraulic cylinder is securable.

  In addition, it is possible to realize a lowering operation only by its own weight during a single lowering operation of the work element, and it is possible to save the supply of pressure oil to the hydraulic cylinder that drives the work element and to suppress the horsepower consumption of the pump. Can be improved.

  In addition, when the operation of lowering the working element is performed and the bottom pressure of the hydraulic cylinder that drives the working element is equal to or higher than a predetermined pressure, when a combined operation with another working element is performed, the other working element It is possible to increase the amount of pressure oil supplied to the hydraulic actuator that drives, and to improve the efficiency of work by the combined operation.

  In addition, it has a slow return circuit including a throttle and a check valve that controls the flow path of the pressure oil that switches the jack-up switching valve, so that hunting associated with the switching operation of the jack-up switching valve can be prevented, and a stable hydraulic circuit can be created. realizable.

  In particular, the present invention including the first traveling device driven by the pressure oil discharged from the first main pump and the second traveling device discharged from the second main pump includes traveling, jacking up work elements, As a result of this cooperation, it is possible to secure a better body jack-up function.

  The best mode for carrying out a hydraulic circuit of a hydraulic working machine according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a side view of a hydraulic excavator cited as an example of a hydraulic working machine provided with a hydraulic circuit according to the present invention.

  As shown in FIG. 1, the hydraulic excavator includes a traveling body 3 composed of a pair of left and right traveling devices 1, 2, a revolving body 4 rotatably mounted on the traveling body 3, and one end of the revolving body 4. A boom 5 that is pivotally connected to a pin, an arm 6 that is pivotally connected to the boom 5 at one end, and a bucket 7 that is pivotally connected to the arm 6 at one end. Further, as the hydraulic actuators, the first traveling hydraulic motor 8 and the second traveling hydraulic motor 9 that respectively drive the traveling devices 1 and 2, the turning hydraulic motor 10 that drives the turning body 4, and the boom 5 are driven. A boom hydraulic cylinder 11, an arm hydraulic cylinder 12 that drives the arm 6, and a bucket hydraulic cylinder 13 that drives the bucket 7 are provided.

  2 is a hydraulic circuit diagram showing a first embodiment of the hydraulic circuit of the present invention provided in the hydraulic excavator shown in FIG. 1, and FIG. 3 is a diagram showing an operating device provided in the hydraulic circuit shown in FIG. The first embodiment shown in FIGS. 2 and 3 includes a hydraulic pilot type switching valve as a jack-up switching valve, and supplies hydraulic oil from one main pump to a hydraulic cylinder.

  That is, as shown in FIG. 2, the first embodiment includes a main pump 21 and a double-acting boom hydraulic cylinder 11 that is expanded and contracted by pressure oil discharged from the main pump 21 to drive the boom 5. A directional control valve 22 that controls the flow of pressure oil supplied from the main pump 21 to the bottom chamber 11a and the rod chamber 11b of the boom hydraulic cylinder 11 and an operating device 23 that performs a switching operation of the directional control valve 22. I have. Further, the pilot pump 24, the jackup switching valve 25 for controlling the flow of the pressure oil discharged from the pilot pump 24, and the meter import of the direction control valve 22 on the upstream side of the direction control valve 22 are connected to the jackup. A flow control valve 26 that is switched by the switching valve 25, a center bypass switching valve 27 that is connected to the center bypass port of the direction control valve 22 downstream of the direction control valve 22 and is switched by the jack-up switching valve 25; And a tank 28.

  The flow control valve 26 described above includes a poppet valve 261 and a pilot-type switching valve 262 that communicates and blocks the back pressure chamber of the poppet valve 261 and the pump port side of the direction control valve 22. The direction control valve 22 includes throttles 29a and 29b and a check valve 29c. Among these, the throttle 29b and the check valve 29c constitute a regeneration circuit that regenerates and supplies the pressure oil discharged from the bottom chamber 11a of the boom hydraulic cylinder 11 to the rod chamber 11b.

  Further, as shown in FIG. 3, the operation device 23 described above includes an operation lever 23a, a boom lowering pressure reducing valve 23b that is switched by the operation lever 23a, and a boom raising pressure reducing valve 23c.

  As shown in FIG. 2, between the main pump 21 and the directional control valve 22, there are an oil passage 31 that leads directly from the main pump 21 to the center bypass port of the directional control valve 22, and a flow control valve 26 from the main pump 21. The oil passages 32 and 33 leading to the meter import of the direction control valve 22 are provided, and between the direction control valve 22 and the boom hydraulic cylinder 11, the oil passage 34 leading to the bottom chamber 11a and the rod chamber 11b are provided. An oil passage 35 is provided. An oil passage 36 for supplying a bottom pressure signal is provided between the bottom chamber 11 a of the boom hydraulic cylinder 11 and the signal port of the jack-up switching valve 25. The oil passage 36 is provided with a slow return circuit in which a throttle 46 and a check valve 47 are juxtaposed.

  Further, the oil passage connecting the direction control valve 22 and the tank 28 is divided into an oil passage 37 on the side of the direction control valve 22 and an oil passage 38 on the side of the tank 28 via the center bypass switching valve 27. Between the directional control valve 22 and the oil passage 38 on the tank 28 side, an oil passage 39 for guiding a part of the pressure oil discharged from the bottom chamber 11a to the tank 28 is provided. Further, a pilot conduit 40 for supplying a boom lowering signal and a pilot conduit 41 for supplying a boom raising signal are provided between the operating device 23 and the signal port of the direction control valve 22. There are provided pilot lines 42 and 43 for supplying a switching signal for guiding the pilot pressure to the center bypass switching valve 27 via the jack-up switching valve 25. In addition, pilot signal lines 44 and 45 for supplying a switching signal are provided between the pilot pump 24 and a signal port of the switching valve 262 constituting the flow control valve 26 via a jack-up switching valve 25. .

  The flow path of the pressure oil supplied to the meter-in of the direction control valve 22 in accordance with the switching operation of the jackup switching valve 27 is changed to the open side or the closed side by the flow control valve 26 and the center bypass switching valve 27 described above. A flow path changing means is configured.

  The operation of the first embodiment configured as described above will be described below.

  When the operation lever 23a is in the neutral position and no tensile force is applied to the boom hydraulic cylinder 11, the direction control valve 22 is in the neutral position 22b as shown in FIG. 2, and the bottom chamber 11a of the boom hydraulic cylinder 11 is placed. Becomes high pressure to support the weight of the boom or the like, the jack-up switching valve 25 is switched to the first switching position 25a via the throttle 46, the switching valve 262 of the flow control valve 26 is switched to the switching position 26a, and the center The bypass switching valve 27 holds the valve position 27a. Accordingly, the pressure oil discharged from the main pump 21 is guided to the tank 28 through the oil passage 31, the center bypass port of the direction control valve 22, the oil passage 37, the center bypass switching valve 27 and the oil passage 38. When the operation lever 23a is returned from the operation position to the neutral position, the signal pressure to the signal port of the jack-up switching valve 25 is applied through the throttle 46 of the slow return circuit. The jack-up switching valve 25 is switched to the first switching position 25a with a time delay from when the pressure reaches a predetermined pressure.

  When the operation lever 23a is operated in the left direction in FIG. 3, that is, in the boom lowering direction from such a neutral state, the pressure oil supplied from the pilot pump 24 is reduced by the pressure reducing valve 23b, and the reduced pilot pressure is reduced. A boom lowering signal is led to the pilot line 40, and the direction control valve 22 is switched to the switching position 22a. A part of the return oil from the bottom chamber 11a is regenerated and supplied to the rod chamber 11b through the throttle 29b, the check valve 29c and the oil passage 35, and the rest is supplied to the tank 28 through the throttle 29a and the oil passage 39. Returned.

  In this case, when the bottom pressure of the boom hydraulic cylinder 11 is equal to or higher than a predetermined pressure set by the spring 25c of the jackup switching valve 25, the switching position of the jackup switching valve 25 is maintained at the first switching position 25a. Therefore, the switching position of the flow control valve 26 is also maintained at the switching position 26a, and the center bypass switching valve 27 is also maintained at the valve position 27a. Therefore, the pressure oil discharged from the main pump 21 is guided to the tank 28 through the oil passage 31, the center bypass port of the direction control valve 22, the oil passage 37, the center bypass switching valve 27, and the oil passage 38, and is used for the boom. Since the pressure oil from the main pump 21 is not supplied to the bottom chamber 11 a and the rod chamber 11 b of the hydraulic cylinder 11, only the regenerated oil is introduced into the rod chamber 11 b, and the boom hydraulic cylinder 11 contracts due to the weight of the boom 5. Then, the boom 5 rotates in the lowering direction. That is, it falls by its own weight.

  On the other hand, when the operation lever 23a is operated in the boom lowering direction, when the bottom pressure becomes lower than the switching pressure of the jack-up switching valve 25, that is, a predetermined pressure, the pressure maintaining the jack-up switching valve 25a is increased. Without any time delay from the check valve 47, it is released instantaneously and becomes low. As a result, the jack-up switching valve 25 is switched to the second switching position 25b, and is supplied from the pilot pump 24 supplied to the signal port of the switching valve 262 of the flow control valve 26 via the pilot conduit 44 and the pilot conduit 45. Since the pressure oil is shut off, the switching valve 262 is switched to the valve position 26b, the back pressure of the poppet valve 261 becomes the same pressure as the pressure in the pipe line 33, and the pressure oil discharged from the main pump 21 is supplied to the oil passage 32. The flow control valve 26 is supplied to the meter import of the direction control valve 22 through the poppet valve 261 and the oil passage 33. In addition, when the jackup switching valve 25 is switched, the pressure oil discharged from the pilot pump 24 passes through the pilot line 40, the pilot line 42, the jackup switching valve 25, and the pilot line 43, and the center bypass is switched. Since the signal is supplied to the signal port of the valve 27, the center bypass switching valve 27 is switched to the switching position 27b, and the downstream of the center bypass of the direction control valve 22 is blocked. Accordingly, the pressure oil from the main pump 21 supplied to the meter import of the direction control valve 22 from the oil passage 33 passes through the oil passage 35 together with the regenerated oil discharged from the bottom chamber 11a, and the rod chamber of the boom hydraulic cylinder 11. 11b and a strong pressing force such as a jack-up force of the vehicle body can be generated.

  Further, for example, when the operation lever 23 a is operated from the neutral state to the right in FIG. 3, that is, in the boom raising direction, the pilot for boom raising is supplied to the pilot line 41 by the pressure oil supplied from the pilot pump 24. The pressure is derived, and the direction control valve 22 is switched to the switching position 22c. As a result, the pressure oil discharged from the rod chamber 11b is returned to the tank 28 through the oil passage 35, the direction control valve 22, and the oil passage 39, so that the bottom pressure is lower than the operating pressure of the jackup switching valve 25. Thus, the jack-up switching valve 25 is switched to the second switching position 25b, and the flow control valve 26 is switched to the switching position 26b. Therefore, the pressure oil from the main pump 21 supplied to the meter import of the direction control valve 22 through the oil passage 32, the flow control valve 26, and the oil passage 33 is supplied to the bottom chamber 11a through the oil passage 34, and the boom. The hydraulic cylinder 11 is extended and the boom 5 is rotated in the raising direction.

  As described above, in the first embodiment configured as described above, when the bottom pressure of the boom hydraulic cylinder 11 becomes smaller than a predetermined pressure during the single lowering operation of the boom 5, the jack-up switching valve 25 is switched to the second switch. As a result, the flow path changing means including the flow control valve 26 and the center bypass switching valve 27 is switched to the open circuit side, and the pressure oil discharged from the main pump 21 passes through the direction control valve 22. It is supplied to the rod chamber 11b of the boom hydraulic cylinder 11, and a large pressing force can be generated on the boom 5, so that the vehicle body can be jacked up.

  Even if the bottom 5 pressure of the boom hydraulic cylinder 11 becomes smaller than a predetermined pressure due to a pressing force acting on the boom 5 for some reason during the single lowering operation of the boom 5, at this time, from the main pump 21 as described above. This pressure oil is supplied to the rod chamber 11b of the boom hydraulic cylinder 11, so that the inside of the boom hydraulic cylinder 11 is not evacuated, so that the operation stability of the hydraulic cylinder can be maintained. As a result, it is possible to ensure good operability of the lowering operation of the boom 5 driven by the boom hydraulic cylinder 11. In the first embodiment, when the boom 5 is lowered, part of the meter-out oil discharged from the bottom chamber 11a of the boom hydraulic cylinder 11 is supplied to the rod chamber 11b of the boom hydraulic cylinder 11. Since the regeneration circuit including the throttle 29b and the check valve 29c that are regenerated as oil is provided, the generation of a vacuum state in the boom hydraulic cylinder 11 can be more reliably prevented.

  Further, when the bottom pressure of the boom hydraulic cylinder 11 is equal to or higher than a predetermined pressure during the single lowering operation of the boom 5, the jack-up switching valve 25 is switched to the first switching position 25a, and accordingly, the flow path changing means is closed. The pressure oil from the main pump 21 is not supplied to the rod chamber 11 b of the boom hydraulic cylinder 11. That is, the lowering operation only by the own weight of the boom 5 can be realized, the supply of the pressure oil to the boom hydraulic cylinder 11 that drives the boom 5 can be saved, the pump consumption horsepower can be suppressed, and the economy can be improved. it can.

  Further, when the bottom pressure of the boom hydraulic cylinder 11 that drives the boom 5 is equal to or higher than a predetermined pressure during the boom lowering operation, when a combined operation with other work elements such as an arm is performed, Since the pressure oil from the main pump 21 is not supplied to the boom hydraulic cylinder 11, the pressure oil from the main pump 21 can be supplied to the hydraulic actuator that drives other work elements, and the amount of pressure oil supplied to the hydraulic actuator can be reduced. It is possible to increase the efficiency of work by complex operation.

  Further, when the bottom pressure of the boom hydraulic cylinder 11 is changed from a state smaller than a predetermined pressure to a predetermined pressure or more during the lowering operation of the boom 5, the jack-up switching valve 25 is moved to the bottom by the throttle 46 of the slow return circuit. The first switching position 25a is switched later than when the pressure reaches a predetermined pressure. Thereby, the sensitive switching operation of the jack-up switching valve 25 is suppressed, hunting of the jack-up switching valve 25 can be prevented, and a stable hydraulic circuit can be realized.

  FIG. 4 is a hydraulic circuit diagram showing a second embodiment of the present invention. The embodiment shown in FIG. 4 is also provided in a hydraulic excavator equivalent to that shown in FIG. In particular, the second embodiment has a configuration in which a boom driving hydraulic circuit and a traveling hydraulic circuit are combined.

  That is, in the second embodiment shown in FIG. 4, the right traveling hydraulic motor 8, the left traveling hydraulic motor 9, the first main pump 21, the second main pump 101, and the first main pump 21 are used for right traveling. A first directional control valve 102 that controls the flow of pressure oil supplied to the hydraulic motor 8 and a second directional control valve that controls the flow of pressure oil supplied from the second main pump 101 to the left travel hydraulic motor 9. 103, a third directional control valve 22 that controls the flow of pressure oil supplied from the first main pump 21 to the bottom chamber 11a and the rod chamber 11b of the boom hydraulic cylinder 11, and boom hydraulic pressure from the second main pump 101. And a fourth direction control valve 104 that controls the flow of pressure oil supplied to the bottom chamber 11a and the rod chamber 11b of the cylinder 11.

  Further, a switching valve 105 for supplying pressure oil supplied from the first main pump 21 to the left travel hydraulic motor 9 side when the boom operation is performed, and a switching valve when the boom operation is performed. A shuttle valve 106 that gives a switching signal to the signal port 105, an oil passage 107 that connects the second main pump 101 and the fourth direction control valve 104, and a center bypass passage that connects the second main pump 101 and the tank 28. 108, an oil passage 109 connecting the fourth direction control valve 104 and the rod chamber 11b of the boom hydraulic cylinder 11, and an oil passage 110 connecting the fourth direction control valve 104 and the bottom chamber 11a of the boom hydraulic cylinder 11. It has.

  Also, a check valve 111 provided in the oil passage 110, an oil passage 112 connecting the first main pump 21 and the switching valve 105, a check valve 113 provided in the oil passage 112, a switching valve 105 and a second valve An oil passage 114 that connects the directional control valve 103, a pilot line 115 that guides a pilot pressure that serves as a boom lowering signal to the jackup switching valve 25, and a pilot that supplies a boom lowering signal to the signal port of the fourth directional control valve 104 A pipeline 116, a pilot pipeline 117 that supplies a boom raising signal to the signal port of the fourth direction control valve 104, and a pilot pipeline 118 that supplies a switching signal to the signal port of the switching valve 105 are provided. Other configurations are the same as those of the first embodiment described above.

  The operation of the second embodiment configured as described above will be described below.

  When the operation lever 23a is in the neutral position, as shown in FIG. 4, the third direction control valve 22 and the fourth direction control valve 104 hold the neutral positions 22b and 104b, respectively, and the jack-up switching valve 25 is the boom hydraulic pressure. The switch is switched to the switching position 25a by the pressure on the bottom side of the cylinder 11. In this state, the pilot line 43 communicates with the tank 28, the center bypass switching valve 27 holds the valve position 27a, and the switching valve 105 holds the valve position 105a. Accordingly, the pressure oil discharged from the first main pump 21 is guided to the tank 28 through the oil passage 31, the center bypass port of the third directional control valve 22, the oil passage 37, the center bypass switching valve 27 and the oil passage 38. It is burned. Further, the pressure oil discharged from the second main pump 101 is guided to the tank 28 through the oil passage 107, the oil passage 108, and the center bypass port of the second directional control valve 102. For this reason, pressure oil is not supplied to the bottom chamber 11a and the rod chamber 11b of the boom hydraulic cylinder 11.

  When the operation lever 23a is operated in the left direction in the figure, that is, in the boom lowering direction from such a neutral state, the pilot pressure supplied from the pilot pump 24 and reduced by the pressure reducing valve 23b is led to the pilot conduit 40, and the third The direction control valve 22 is switched to the switching position 22a. On the other hand, since this pilot pressure is guided to the pilot line 115 and guided to the signal port of the switching valve 262 via the jack-up switching valve 25, the switching valve 262 is switched to the switching position 26a. As a result, part of the return oil from the bottom chamber 11a of the boom hydraulic cylinder 11 is regenerated and supplied to the rod chamber 11b via the throttle 29b, the check valve 29c and the oil passage 35, and the rest is supplied to the throttle 29a and the oil passage. It is returned to the tank 28 via 39.

  In this case, when the bottom pressure of the boom hydraulic cylinder 11 is higher than the operating pressure of the jackup switching valve 25, that is, a predetermined pressure, the jackup switching valve 25 is maintained at the first switching position 25a. The switching position is also maintained at the switching position 26a. The center bypass switching valve 27 is also maintained at the valve position 27a. Accordingly, the pressure oil discharged from the first main pump 21 is guided to the tank 28 through the oil passage 31, the center bypass port of the third directional control valve 22, the oil passage 37, the center bypass switching valve 27 and the oil passage 38. It is burned. Further, the pressure oil discharged from the second main pump 101 is guided to the tank 28 through the oil passage 107, the fourth direction control valve 104, the oil passage 108, and the center bypass port of the second direction control valve 103. As a result, the pressure oil from the first main pump 21 and the second main pump 101 is not supplied to the bottom chamber 11a and the rod chamber 11b of the boom hydraulic cylinder 11, and the rod chamber 11b is discharged from the bottom chamber 11a. Only the regenerated oil is supplied, the boom hydraulic cylinder 11 contracts due to the weight of the boom 5, and the boom 5 falls by its own weight.

  Further, when the operation lever 23a is operated in the boom lowering direction from the neutral state, when the bottom pressure of the boom hydraulic cylinder 11 becomes lower than the operating pressure of the jack up switching valve 25, the jack up switching valve 25 is moved to the second position. Since it is switched to the switching position 25b, the pilot line 45 communicates with the tank 28 via the jack-up switching valve 25, and the switching valve 262 of the flow control valve 26 is switched to the valve position 26b. As a result, the pressure oil discharged from the first main pump 21 is supplied to the meter import of the third direction control valve 22 through the oil passage 32, the flow control valve 26, and the oil passage 33. As the jack-up switching valve 25 is switched, the pilot pressure as a boom lowering signal is supplied to the signal port of the center bypass switching valve 27 through the pilot line 115, the jack-up switching valve 25 and the pilot line 43. Therefore, the center bypass switching valve 27 is switched to the switching position 27b. At the same time, the pilot pressure is supplied to the signal port on the boom lowering side of the fourth direction control valve 104 through the pilot conduit 116, so that the fourth direction control valve 104 is switched to the switching position 104a. Therefore, the pressure oil discharged from the first main pump 21 is supplied to the rod chamber 11b of the boom hydraulic cylinder 11, and the pressure oil discharged from the second main pump 101 is supplied to the fourth direction control valve 104, the oil passage. 109 and the oil passage 35 are supplied to the rod chamber 11 b of the boom hydraulic cylinder 11. In other words, the regenerated oil discharged from the bottom chamber 11a, the pressure oil supplied from the first main pump 21, and the pressure oil supplied from the second main pump 101 are supplied to the rod chamber 11b in a merged manner. As a result, a strong pressing force such as a jack-up force of the vehicle body can be generated.

  Further, since the pilot pressure for boom operation is guided to the switching valve 105 via the shuttle valve 106 and the oil passage 118, the switching valve 105 is switched to the switching position 105b. Here, by operating a travel operation device (not shown) to switch between the first direction control valve 102 and the second direction control valve 103, the pressure oil discharged from the first main pump 21 is changed to the first direction control valve 102, the second direction control valve 102, and the second direction control valve 102. The oil is supplied to the left and right traveling hydraulic motors 8 and 9 through the two-way control valve 103, respectively. Therefore, when the combined operation of the boom 5 and traveling is performed, the hydraulic oil for the boom 11 is supplied with the pressure oil from the second main pump 101, so that the vehicle body can be jacked up by the combined operation of traveling and boom lowering. Is possible.

  In the second embodiment configured as described above, when the bottom pressure of the boom hydraulic cylinder 11 becomes smaller than a predetermined pressure during the single lowering operation of the boom 5, the jack-up switching valve 25 is switched to the second switching position 25b. Accordingly, the flow path changing means is switched to the open circuit side, and the pressure oil discharged from the first main pump 21 and the second main pump 101 is passed through the third direction control valve 22 and the fourth direction control valve 104. It is supplied to the rod chamber 11b of the boom hydraulic cylinder 11, and a large pressing force can be generated on the boom 5, so that the vehicle body can be jacked up. At this time, the left and right traveling hydraulic motors 8 and 9 are actuated to simultaneously perform the traveling, thereby realizing a jack-up operation by a combined operation of the traveling and the boom lowering and securing a more excellent vehicle body jack-up function. it can.

  Even if the pressing force acts on the boom 5 for some reason during the single lowering operation of the boom 5 and the bottom pressure becomes lower than the predetermined pressure, at this time, as described above, the first main pump 21 and the second main pump 101 are used. Is supplied to the rod chamber 11b of the boom hydraulic cylinder 11, so that the inside of the boom hydraulic cylinder 11 is not evacuated, so that the operation of the boom hydraulic cylinder 11 is stable. Can be maintained. Thereby, the favorable operativity of the downward operation of the boom 5 driven with this boom hydraulic cylinder 11 is securable.

  Further, when the bottom pressure of the boom hydraulic cylinder 11 is equal to or higher than a predetermined pressure during the operation of lowering the boom 5 alone, the jack-up switching valve 25 is switched to the first switching position, and accordingly, the flow path changing means is moved to the closed side. The pressure oil from the first main pump 21 and the second main pump 101 is not supplied to the rod chamber 11 b of the boom hydraulic cylinder 11. That is, as in the first embodiment described above, the lowering operation only by the weight of the boom 5 can be realized, the supply of pressure oil to the boom hydraulic cylinder 11 that drives the boom 5 is saved, and the pump power consumption is suppressed. Can improve economy.

  Further, when the boom 5 is lowered and the bottom pressure of the boom hydraulic cylinder 11 is equal to or higher than a predetermined pressure, when a combined operation with other work elements such as an arm is performed, the boom hydraulic pressure Since the pressure oil from the first main pump 21 and the second main pump 101 is not supplied to the cylinder 11, the pressure oil from the first and second main pumps 21 and 101 is transferred to a hydraulic actuator that drives other work elements. It is possible to increase the amount of pressure oil supplied to the hydraulic actuator.

  When the bottom pressure of the boom hydraulic cylinder 11 is changed from a state smaller than the predetermined pressure to a pressure equal to or higher than the predetermined pressure during the lowering operation of the boom 5, as in the first embodiment described above, the slow return circuit. Due to the throttle 46, the jack-up switching valve 25 is switched to the first switching position 25a later than when the bottom pressure reaches the predetermined pressure. Thereby, the sensitive switching operation of the jack-up switching valve 25 is suppressed, hunting of the jack-up switching valve 25 can be prevented, and a stable hydraulic circuit can be realized.

1 is a side view of a hydraulic excavator cited as an example of a hydraulic working machine provided with a hydraulic circuit according to the present invention. FIG. 2 is a hydraulic circuit diagram showing a first embodiment of the hydraulic circuit of the present invention provided in the hydraulic excavator shown in FIG. 1. It is a figure which shows the operating device with which the hydraulic circuit shown in FIG. 2 is equipped. It is a hydraulic circuit diagram which shows 2nd Embodiment of this invention.

Explanation of symbols

1 traveling device 2 traveling device 3 traveling body 5 boom (working element)
6 Arm (other work elements)
8 Hydraulic motor for right travel 9 Hydraulic motor for left travel 11 Boom hydraulic cylinder 11a Bottom chamber 11b Rod chamber 12 Arm hydraulic cylinder 21 Main pump (first main pump)
22 direction control valve (3rd direction control valve)
23 operation device 25 jack-up switching valve 25a first switching position 25b second switching position 26 flow control valve (flow path changing means)
27 Center bypass switching valve (flow path changing means)
28 Tank 29b Aperture (regeneration circuit)
29c Check valve (regeneration circuit)
46 Aperture (slow return circuit)
47 Check valve (slow return circuit)
101 Second main pump 102 First direction control valve 103 Second direction control valve 104 Fourth direction control valve 105 Switching valve 106 Shuttle valve

Claims (5)

A main pump, a working element, a double-acting hydraulic cylinder which is expanded and contracted by pressure oil discharged from the main pump and drives the working element, and is supplied from the main pump to a bottom chamber and a rod chamber of the hydraulic cylinder. In a hydraulic circuit of a hydraulic working machine including a directional control valve that controls the flow of pressure oil and an operating device that performs a switching operation of the directional control valve,
A jack-up switching valve that is switched when the bottom pressure of the hydraulic cylinder reaches a predetermined pressure, and a flow path of the pressure oil that is supplied to the meter-in of the directional control valve when the jack-up switching valve is switched are opened. A slow return circuit including a flow path changing means that changes to a closed side or a closed circuit side, and a throttle and check valve that controls the flow path of the pressure oil that switches the jack-up switching valve,
When the bottom pressure of the hydraulic cylinder becomes equal to or higher than the predetermined pressure during the lowering operation of the working element, the throttle of the slow return circuit causes the jack-up switching valve to move from the time when the bottom pressure reaches the predetermined pressure. Is switched to the first switching position with a time delay to switch the flow path changing means to the closed side, and the pressure oil discharged from the main pump is not supplied to the rod chamber of the hydraulic cylinder. When the bottom pressure of the hydraulic cylinder becomes lower than the predetermined pressure during the lowering operation, the jack-up switching valve is moved to the second switching position without a time delay via the check valve of the slow return circuit. The flow path changing means is switched to the open circuit side to switch the hydraulic oil discharged from the main pump through the directional control valve. A hydraulic circuit of a hydraulic working machine and supplying to the chamber. In the invention of claim 1,
The flow path changing means is connected to the meter import of the directional control valve upstream of the directional control valve, and is switched to a closed position when the jackup switching valve is switched to the first switching position. A flow control valve that is switched to the open position when the switching valve is switched to the second switching position, and a center bypass port of the direction control valve on the downstream side of the direction control valve; And a center bypass switching valve that is switched to the open position when switched to the first switching position and switched to the closed position when the jack-up switching valve is switched to the second switching position. circuit. The first main pump and the second main pump, the first traveling device driven by the pressure oil discharged from the first main pump, and the second traveling driven by the pressure oil discharged from the second main pump. A first direction control valve that controls the flow of pressure oil supplied from the first main pump to the first traveling device, and pressure oil supplied from the second main pump to the second traveling device. A second-direction control valve that controls the flow; a working element; a double-acting hydraulic cylinder that is expanded and contracted by pressure oil discharged from the first main pump and the second main pump, and drives the working element; A third directional control valve that controls the flow of pressure oil supplied from the first main pump to the bottom chamber and rod chamber of the hydraulic cylinder, and from the second main pump to the bottom chamber and rod chamber of the hydraulic cylinder. 4th direction to control the flow of pressure oil And valve, the hydraulic circuit of a hydraulic working machine comprising an operating device for performing a switching operation of these third directional control valve and the fourth directional control valve,
A jack-up switching valve that is switched when the bottom pressure of the hydraulic cylinder reaches a predetermined pressure, and is supplied from the first main pump to the meter-in of the third directional control valve in accordance with the switching operation of the jack-up switching valve. A flow return means for changing the pressure oil flow path to the open circuit side or the closed circuit side, and a slow return circuit including a throttle and a check valve for controlling the pressure oil flow path for switching the jack-up switching valve,
When the bottom pressure of the hydraulic cylinder becomes equal to or higher than the predetermined pressure during the operation of lowering the working element, the throttle of the slow return circuit causes a time delay from the time when the jack-up switching valve reaches the predetermined pressure. Switch to the first switching position and switch the flow path changing means to the closed side, without supplying the pressure oil discharged from the first main pump and the second main pump to the rod chamber of the hydraulic cylinder, When the bottom pressure of the hydraulic cylinder becomes lower than the predetermined pressure during the lowering operation of the working element, the check valve of the slow return circuit performs the second switching of the jack-up switching valve without causing a time delay. Switch to the position, switch the flow path changing means to the open circuit side, and pressure oil discharged from the first main pump and the second main pump in the third direction Valve, a hydraulic circuit of a hydraulic working machine, characterized in that through the fourth directional control valve is supplied to the rod chamber of the hydraulic cylinder. In the invention of claim 3,
The flow path changing means is connected to the meter import of the third direction control valve upstream of the third direction control valve, and is switched to the closed position when the jackup switching valve is switched to the first switching position. A flow control valve that is switched to an open circuit position when the jack-up switching valve is switched to the second switching position, and a center bypass port of the third direction control valve on the downstream side of the third direction control valve, A center bypass switching valve that is switched to an open position when the jackup switching valve is switched to the first switching position, and that is switched to a closed position when the jackup switching valve is switched to the second switching position. A hydraulic circuit for a hydraulic working machine. In the invention according to claim 1 or 2,
A hydraulic circuit for a hydraulic working machine, comprising a regeneration circuit for regenerating a part of meter-out oil discharged from a bottom chamber of the hydraulic cylinder as meter-in oil supplied to a rod chamber of the hydraulic cylinder.

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