JP2011021688A - Hydraulic driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve favorable operability by restraining a speed change in turn by preferentially supplying a pressurized oil to a swivel motor even if a saturated condition arises when the swivel motor and other actuator are simultaneously operated and by restraining a shock at the start of turn even in turn-only operation. <P>SOLUTION: In a hydraulic driving device, a flow control valve 6a for turn comprises a fixed restriction 20 setting a maximum demand flow rate for turn and an open center type directional control valve 40, an output pressure identical to an output pressure introduced from an engine speed detecting valve 13 to a pump tilting control part 17a as a target differential pressure for LS control is introduced to a pressure compensation valve 7a, a target compensated differential pressure is set therefor, and other pressure compensation valves 7b, 7c, ... are set by a differential pressure between a pump discharge pressure which is an output pressure from a detecting valve 11 and the highest load pressure. Shuttle valve 9a, ... detects a pressure between the fixed restriction 20 and the directional control valve 40 as a load pressure of the swivel motor 3a. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a hydraulic drive device used in construction machinery such as a hydraulic excavator, and more particularly to a hydraulic drive device that performs load sensing control so that a discharge pressure of a hydraulic pump is higher than a maximum load pressure of a plurality of actuators by a target differential pressure. .

  An example of this type of hydraulic drive device is disclosed in Patent Document 1. In the hydraulic drive device described in Patent Document 1, as the target compensation differential pressure of the pressure compensation valve related to the actuator other than the swing, the differential pressure between the discharge pressure of the hydraulic pump and the maximum load pressure is derived to compensate the pressure related to the swing. The output pressure from the engine speed detection circuit is introduced as the target compensation differential pressure of the valve, so that in the combined operation of the swing motor and another actuator, the discharge flow of the hydraulic pump is controlled simultaneously with the other Even if a saturation state that is insufficient with respect to the required flow rate of the actuator occurs, pressure oil is preferentially supplied to the swing motor so that the speed change can be suppressed.

Japanese Patent No. 3907040

  In the hydraulic drive device that performs load sensing control described in Patent Document 1, pressure oil is preferentially supplied to the swing motor even when a saturation state of the pump discharge flow rate occurs during simultaneous operation of the swing motor and other actuators. Thus, the speed change of the swing motor can be suppressed. However, in a single operation of the swing motor, the swing body that is rotationally driven by the swing motor is an inertial body, so that the load pressure of the swing motor suddenly increases at the start of the movement (when the swing is started). For this reason, the differential pressure between the discharge pressure of the hydraulic pump and the maximum load pressure (load pressure of the slewing motor) decreases, and the tilt angle of the hydraulic pump switches suddenly in the direction of increasing the flow rate. There was a problem that the shock suddenly entered the turning motor and the shock at the start of turning was great.

  For example, when excavation / loading work and swiveling start with excavated soil or liquid concrete in a bucket, if a shock occurs as described above, the excavated soil or liquid concrete of the load will be spilled. There was a case.

  The object of the present invention is to suppress the change in the turning speed by preferentially supplying pressure oil to the turning motor even when the hydraulic pump discharge flow rate saturation occurs during simultaneous operation of the turning motor and other actuators. It is also possible to provide a hydraulic drive device for a construction machine that can suppress shock at the time of turning start and realize good operability in independent operation of the turning motor.

  (1) In order to achieve the above object, the present invention includes a plurality of engines, a variable displacement hydraulic pump driven by the engine, and a swing motor driven by pressure oil discharged from the hydraulic pump. Actuators, a plurality of flow control valves that control the flow rate of pressure oil supplied from the hydraulic pump to the plurality of actuators, and a plurality of pressure compensations that respectively control the differential pressure across the throttle portions of the plurality of flow control valves A valve, a maximum load pressure detecting means for detecting a maximum load pressure among the load pressures of the plurality of actuators, and a discharge pressure of the hydraulic pump being a target difference from a maximum load pressure detected by the maximum load pressure detecting means. Pump control means for load sensing control to increase only the pressure, and depending on the engine speed to decrease as the engine speed decreases. An engine speed detector that outputs the pressure to be output, the output pressure of the engine speed detector is guided to the pump control means, and the target differential pressure of the load sensing control depends on the engine speed In the hydraulic drive apparatus set as above, each target compensation differential pressure of the pressure compensation valve related to the actuator other than the swing motor is set by the differential pressure between the discharge pressure of the hydraulic pump and the maximum load pressure of the plurality of actuators. The pressure compensation valve related to the swing motor is led to the same output pressure as the target pressure difference of the load sensing control from the engine speed detection unit to the pump control means, and the target compensation is performed by the output pressure. A differential pressure is set, and the flow control valve for the swing motor is set to the maximum required flow rate of the swing motor. A fixed throttle and an open center type directional control valve arranged downstream of the fixed throttle, and a pressure compensation valve related to the swing motor is configured to control a differential pressure across the fixed throttle, The maximum load pressure detecting means is configured to detect the pressure between the fixed throttle and the direction switching valve as the load pressure of the swing motor.

  In this way, when the flow control valve for the swing motor is composed of a fixed throttle and an open center type directional switching valve, by detecting the pressure between the fixed throttle and the directional switching valve as the load pressure of the swing motor When the swing motor is operated, since the pressure between the fixed throttle and the direction switching valve is detected as the load pressure of the swing motor, the discharge flow rate of the hydraulic pump can be increased by load sensing control.

  The flow control valve related to the swing motor is composed of a fixed throttle and an open center type directional switching valve, and the pressure compensation valve related to the swing motor is configured to control the differential pressure across the fixed throttle. When the swing motor and other actuators are operated simultaneously, the differential pressure across the fixed throttle is controlled to be constant by the pressure compensation valve, so that the swing motor has no relation to the behavior of other actuators or the saturation state of the hydraulic pump. A certain flow rate is preferentially supplied (priority is maintained), and a change in turning speed can be suppressed.

  In addition, even when the swing motor is operated independently, the load pressure of the swing motor temporarily increases and the hydraulic pump increases the discharge flow rate by load sensing control. The center type directional control valve can control the flow rate of pressure oil to the swing motor while letting a part of the pressure oil to escape to the tank. Can do.

  (2) In the above (1), preferably, the pump control means is configured so that the minimum discharge flow rate of the hydraulic pump is greater than the maximum required flow rate of the swing motor set by the fixed throttle. Set the tilt.

  This eliminates the instability of the system due to the interference between the load sensing control of the hydraulic pump and the control of the pressure compensation valve when the swing motor is operated, and the swing operability can be further improved.

  (3) In the above (1) or (2), preferably, the pressure compensation valve related to the swing motor reduces the differential pressure across the fixed throttle as the load pressure of the swing motor increases. It has a load-dependent characteristic that reduces the passage flow rate.

  This makes it possible to reduce the horsepower consumed by the swing motor when the load pressure of the swing motor temporarily increases at the time of turning start, thereby reducing the horsepower consumed by the turning motor, turning, boom raising, etc. Even if a saturation state occurs during the simultaneous operation, the flow rate that can be used by other actuators is increased correspondingly, and a good combined operability can be realized, such as ensuring the amount of raising the boom.

  According to the present invention, at the time of simultaneous operation of the swing motor and other actuators, even when a saturation state of the discharge flow rate of the hydraulic pump occurs, pressure oil is preferentially supplied to the swing motor, and the high priority of the swing motor is maintained. Thus, it is possible to suppress a change in the turning speed and obtain a good combined operability.

  In addition, when the swing motor is operated alone, the load pressure of the swing motor temporarily increases at the start of swing, and even if the hydraulic pump increases the discharge flow rate by load sensing control, the pressure oil supplied to the swing motor By performing the flow rate control with an open center type directional control valve, it is possible to suppress a shock at the time of start-up due to a rapid flow rate increase and realize a smooth turning operability.

  In addition, since the minimum tilt of the hydraulic pump is set so that the minimum discharge flow rate of the hydraulic pump does not become smaller than the maximum required flow rate of the swing motor set by the fixed throttle, the load sensing control of the hydraulic pump and the control of the pressure compensation valve The instability of the system due to the interference can be eliminated, and the turning operability can be further improved.

  In addition, since the pressure compensation valve related to the swing motor has a load-dependent characteristic, when the load pressure of the swing motor is increased at the start of swing, the supply flow rate to the swing motor is reduced and the horsepower consumed by the swing motor is reduced. In addition, even if a saturation state occurs during simultaneous operations such as turning and boom raising, the flow rate that can be used by other actuators is increased accordingly, and a good combined operability such as securing the boom raising amount is realized. Can do.

It is a figure which shows the system configuration | structure of the hydraulic drive device of the construction machine in one embodiment of this invention. It is a PQ characteristic figure of the main pump by a tilt angle control part. It is a figure which shows the external appearance of the hydraulic excavator by which the hydraulic drive device of this invention is mounted.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
~Constitution~
FIG. 1 shows a system configuration of a hydraulic drive apparatus according to the first embodiment of the present invention. In the present embodiment, the present invention is applied to a hydraulic drive device of a front swing type hydraulic excavator.

  In FIG. 1, a hydraulic drive apparatus according to the present embodiment includes an engine 1, a variable displacement hydraulic pump 2 and a fixed displacement pilot pump 30 as a main pump driven by the engine 1, and a main pump 2. And a plurality of actuators 3a, 3b, 3c... Driven by the pressure oil discharged from the oil passages 8a, 8b, 8c corresponding to the actuators 3a, 3b, 3c. Are connected to the plurality of flow control valves 6a, 6b, 6c, and the flow control valves 6a, 6b for controlling the flow rate and direction of the pressure oil supplied from the main pump 2 to the actuators 3a, 3b, 3c,. , 6c... Are connected to the oil passages 8a, 8b, 8c..., And are pressure compensation valves 7 for controlling the differential pressure across the throttle portions of the flow control valves 6a, 6b, 6c. , 7b, 7c..., Shuttle valves 9a, 9b, 9c... (Maximum load pressure detecting means) for selecting and outputting the highest pressure among the load pressures of the actuators 3a, 3b, 3c. The differential pressure reducing valve 11 that outputs the differential pressure between the pressure and the maximum load pressure as an absolute pressure to the oil passage 12d and the supply oil passage 5 of the main pump 2 are connected to the maximum discharge pressure (maximum circuit pressure) of the main pump 2. The main relief valve 14 for limiting the discharge pressure of the main pump 2 when the differential pressure between the discharge pressure of the main pump 2 and the maximum load pressure exceeds a certain value set by the spring 15a. And an unload valve 15 for limiting the pressure rise of the main pump 2 is provided.

  The actuator 3a is a swing motor for a hydraulic excavator, and the actuators 3b and 3c are a boom cylinder and an arm cylinder of the hydraulic excavator, respectively. It is for. For convenience of illustration, other actuators such as a bucket cylinder, a boom swing cylinder, a traveling motor, and circuit elements related to these actuators are omitted.

  The flow control valve 6a for turning is disposed on the downstream side of the pressure compensation valve 7a in the oil passage 8a for supplying pressure oil to the turning motor 3a, and a fixed throttle 20 (throttle part) for setting the maximum required flow rate of the turning motor 3a. ) And an open center type directional switching valve 40 that controls the flow direction and flow rate of the pressure oil that is disposed downstream of the fixed throttle 20 and is supplied to the turning motor 3a.

  The pressure compensation valve 7a includes an opening direction pressure receiving portion 21a through which an output pressure of an engine speed detection valve 13, which will be described later, is introduced as a target compensation differential pressure via an oil passage 12e and an oil passage 12f, and a fixed throttle 20 (throttle). .., And controls the differential pressure across the fixed throttle 20 based on the output pressure of the engine speed detection valve 13. As will be described later, the output pressure of the engine speed detection valve 13 is also guided to the pump control means (tilt angle control unit 17) as a target differential pressure for load sensing control. In other words, the pressure receiving portion 21a of the pressure compensating valve 7a related to the swing motor 3a has the same output pressure as the output pressure led from the engine speed detection valve 13 to the switching valve 17b of the pump control means as the target differential pressure for load sensing control. The pressure is derived, and the target compensation differential pressure is set by the output pressure. As will be described later, the pressure compensation valve 7a preferably has a load-dependent characteristic.

  For the open center type directional switching valve 40, at the neutral position 40a, the neutral circuit 41 for returning the pressure oil supplied via the pressure compensation valve 7a and the fixed throttle 20 to the tank, and at the switching position 40b or 40c. A feeder circuit 42 for supplying pressure oil via the pressure compensation valve 7a and the fixed throttle 20 is provided, and a check valve 60 is provided in the feeder circuit 42.

  The fixed throttle 20 is for setting the maximum required flow rate of the swing motor 3a. The engine 1 is at the maximum rated speed, and the pressure compensation valve 7a causes the differential pressure across the fixed throttle 20 to change between the engine speed detection valve 13 and the engine. When controlled to be equal to the output pressure, the opening degree is set so that the passage flow rate of the fixed throttle 20 matches the maximum required flow rate of the turning motor 3a.

  The flow rate control valves 6b, 6c,... Are composed of one closed type valve as in the conventional case. The pressure compensating valves 7b, 7c,... Are pressure sensing parts 21b, 21c, which are operated in the opening direction, and the flow rate control valves 6b, 6c through which the output pressure of the differential pressure reducing valve 11 is guided through the oil passage 12d. Are pressure receiving portions 22b, 23b,..., 22c, 23c,... That detect the differential pressure before and after the meter-in throttle portion, and the differential pressure before and after the meter-in throttle portions of the flow control valves 6b, 6c,. The pressure is controlled to be equal to the pressure (the differential pressure between the discharge pressure of the main pump 2 and the maximum load pressure of the actuators 3a, 3b, 3c...). That is, the actuators 3b, 3c,... Other than the swing motor 3a set their target compensation differential pressures by the differential pressure between the discharge pressure of the main pump 2 and the maximum load pressure of the actuators 3a, 3b, 3c,.

  Further, in the pressure compensating valve 7a for turning, the pressure receiving area of the pressure receiving portion 22a for detecting the pressure on the downstream side of the fixed throttle 20 is larger than the pressure receiving area of the pressure receiving portion 23a for detecting the pressure on the upstream side of the fixed throttle 20, The urging force generated by the pressure on the downstream side of the fixed throttle 20 acting on the difference in the pressure receiving area is configured to act in the valve closing direction opposite to the urging force generated in the pressure receiving portion 21a, and thereby the swing motor 3a. As the load pressure increases, the differential pressure across the fixed restrictor 20 is reduced to reduce the passing flow rate (load dependent characteristics). The specific configuration is detailed in Japanese Patent Application Laid-Open No. 2000-227103.

  The shuttle valve 9a selects and outputs the high pressure side of the load pressure of the swing motor 3a and the load pressure of the boom cylinder 3b, and the shuttle valve 9b selects the high pressure side of the output pressure and the load pressure of the arm cylinder 3c. The shuttle valve 9c selects and outputs the high pressure side between the output pressure and the output pressure of another similar shuttle valve (not shown). In this way, the maximum load pressure of the load pressures of the actuators 3a, 3b, 3c... Is output from the shuttle valve 9c, and the shuttle valves 9a, 9b, 9c... Serve as maximum load pressure detecting means for detecting the maximum load pressure. Function.

  The flow control valve 9a for turning has a load pressure take-out part 42a between the fixed throttle 20 and the direction switching valve 40, and the pressure of the load pressure take-out part 42a (the direction of the fixed restrictor 20 and the direction) as the load pressure of the turning motor 3a. Pressure with respect to the switching valve 40) is guided to the shuttle valve 9a. That is, the maximum load pressure detecting means including the shuttle valves 9a, 9b, 9c,... Is configured to detect the pressure between the fixed throttle 20 and the direction switching valve 40 as the load pressure of the swing motor 3a.

  When the direction switching valve 40 is in the neutral position 40a, the load pressure extraction unit 42 communicates with the tank via the direction switching valve 40 and the neutral circuit 41. Therefore, the load pressure extracted from the load pressure extraction unit 42 becomes the tank pressure. . The other flow control valves 6b, 6c... Have load pressure detection ports 42b, 42c..., And pressures taken out from these load pressure detection ports 42b, 42c. . The load pressure detection ports 42b, 42c, ... are configured to communicate with the tank when the flow control valves 6b, 6c, ... are in the neutral position, and output the tank pressure as the load pressure.

  The pressure of the load pressure extracting portion 42a of the flow control valve 9a for turning (pressure between the fixed throttle 20 and the direction switching valve 40) is a tank pressure when the direction switching valve 40 is in the neutral position 40a, and the direction When the switching valve 40 is operated at a full stroke and switched to the switching position 40b or 40c, the load pressure of the swing motor 3a becomes equal, and the direction switching valve 40 is at an intermediate position between the neutral position 40a and the switching position 40b or 40c. Is an intermediate pressure between the tank pressure and the load pressure of the swing motor 3a in accordance with the opening area (opening) of the meter-in throttle portion of the direction switching valve 40.

  Flow control valve 6a (fixed throttle 20, direction switching valve 40, check valve 60) and flow control valves 6b, 6c, pressure compensation valves 7a, 7b, 7c, shuttle valves 9a, 9b, 9c,. The differential pressure reducing valve 11, the main relief valve 14, and the unload valve 15 are respectively installed inside the control valve 4.

  The hydraulic drive apparatus according to the present embodiment is further connected to the supply oil passage 31a of the pilot pump 30, and outputs an engine speed detection valve 13 that outputs a pressure corresponding to the discharge flow rate of the pilot pump 30, and the engine speed. Connected to the pilot oil passage 31c on the downstream side of the detection valve 13 and operated by the pilot relief valve 32 for keeping the pressure of the pilot oil passage 31c constant and the gate lock lever 24, the pilot pressure supply oil passage 31b on the downstream side is piloted. A gate lock valve 100 that selectively communicates with one of the oil passage 31c and the tank is provided. The pilot pressure supply oil passage 31b is used as a hydraulic pressure source of a hydraulic device such as a remote control valve built in the operation lever devices 122 and 123 (FIG. 2) for operating the direction switching valve 40 and the flow control valves 6b and 6c. The The gate lock lever 24 is disposed on the entrance / exit side of the driver's seat 121 (FIG. 2), and can be selectively operated by an operator between a raised position (gate lock release position) and a lowered position (gate lock position). When the gate lock lever 24 is operated to the raised position (gate lock release position), the gate lock valve 100 is switched to the position shown in the figure, the pilot pressure supply oil passage 31b is communicated with the tank, and the direction by the operation of the operation lever device. The operation of the switching valve 40 and the flow rate control valves 6b, 6c,.

  The engine speed detection valve 13 has a variable throttle 50 having a characteristic that its throttle amount is variable in accordance with the flow rate supplied from the pilot pump 30, and a differential pressure reducing pressure that outputs the differential pressure across the variable throttle 50 as an absolute pressure. And a valve 51. As will be described later, the output pressure of the engine speed detection valve 13 (the differential pressure across the variable throttle 50) is guided to the pump control means (tilt angle control unit 17) as the target differential pressure for load sensing control. Thus, by using the differential pressure across the variable throttle 50 as the target differential pressure for load sensing control, the saturation phenomenon can be improved according to the engine speed, and fine operability can be achieved when the engine speed is set low. Is obtained. This point is detailed in JP-A-10-196604. The engine speed detection valve 13 constitutes an engine speed detection unit that outputs a pressure depending on the speed of the engine 1 so as to decrease as the speed of the engine 1 decreases.

  The main pump 2 has a pump tilt changing unit 90 such as a swash plate, and a tilt angle control unit 17 that acts on the pump tilt changing unit 90 and controls the tilt angle (capacity or displacement) of the main pump 2. have. The tilt angle control unit 17 is configured so that when the discharge pressure of the main pump 2 is introduced and the discharge pressure of the main pump 2 increases, the absorption torque of the main pump 2 does not exceed a certain value. 2, the tilt angle control piston 17a for controlling the tilt angle of the main pump 2 to be reduced as the discharge pressure of the main pump 2 increases, the load sensing control switching valve 17b, and the output pressure of the switching valve 17b are led. The tilt angle control piston 17c controls the tilt angle of the main pump 2 in accordance with the output pressure of the switching valve 17b (required flow rate of each actuator). The switching valve 17b has pressure receiving portions 17d and 17e through which the output pressure of the engine speed detection valve 13 and the output pressure of the differential pressure reducing valve 11 are guided to face each other through the oil passages 12e and 12g. The pressure output to the tilt angle control piston 17c (the output pressure of the switching valve 17b) is controlled so that the output pressure of 11 is equal to the output pressure of the engine speed detection valve 13. Specifically, when the output pressure of the differential pressure reducing valve 11 becomes higher than the output pressure of the engine speed detection valve 13, the switching valve 17b increases the output pressure. When the output pressure of the switching valve 17b increases, the tilt angle control piston 17c decreases the tilt angle of the main pump 2 to decrease the discharge flow rate of the main pump 2, and decreases the output pressure of the differential pressure reducing valve 11. When the output pressure of the differential pressure reducing valve 11 becomes lower than the output pressure of the engine speed detection valve 13, the switching valve 17b reduces the output pressure. When the output pressure of the switching valve 17b decreases, the tilt angle control piston 17c increases the tilt angle of the main pump 2 to increase the discharge flow rate of the main pump 2, and increases the output pressure of the differential pressure reducing valve 11.

  As described above, the switching valve 17b and the tilt angle control piston 17c have the engine speed detection valve based on the maximum load pressure at which the discharge pressure of the main pump 2 is detected by the shuttle valves 9a, 9b, 9c. It functions as a pump control means for performing load sensing control of the discharge flow rate of the main pump 2 so as to increase by 13 output pressures (target differential pressure). The output pressure of the engine speed detection valve 13 is guided to the switching valve 17b of the pump control means, and the target differential pressure of the load sensing control is set as a variable value depending on the engine speed.

  The tilt angle control unit 17 further includes a stopper 91 that limits the minimum tilt of the main pump 2 when it hits the pump tilt changing unit 90 of the main pump 2 and regulates the minimum discharge flow rate of the main pump 2. The stopper 91 is configured so that the minimum tilt of the main pump 2 can be adjusted by changing the position where the stopper 91 comes in and out of the pump case by a screw mechanism and hits the pump tilt changing portion 90, for example. The casting of the pump case itself may have a shape that can limit the minimum tilt, and the minimum tilt may be set as a basic specification of the pump.

  Here, the minimum tilt of the main pump 2 is the maximum required flow rate of the swing motor 3a (more strictly speaking, the opening degree and pressure compensation of the fixed throttle 20) in which the minimum discharge flow rate of the main pump 2 is set by the fixed throttle 20 described above. The maximum required flow rate of the swing motor 3a determined by the valve 7a) is set to be larger.

  FIG. 2 is a PQ characteristic diagram of the main pump 2 by the tilt angle control unit 17. The horizontal axis is the discharge pressure (P) of the main pump 2, and the vertical axis is the discharge flow rate (Q) of the main pump 2. A characteristic line H is a pump horsepower control diagram set by the tilt angle control piston 17a. Qmin is the minimum discharge flow rate of the main pump 2, and Qsmax is the maximum required flow rate of the swing motor 3a determined by the opening of the fixed throttle 20 and the pressure compensation valve 7a. A control region of the discharge flow rate of the main pump 2 by the tilt angle control unit 17 is a shaded portion. The minimum tilting of the main pump 2 is limited by the stopper 91, and the minimum discharge flow rate Qmin of the main pump 2 is set to be larger than the turning maximum required flow rate Qsmax.

  FIG. 3 is a diagram showing an external appearance of a hydraulic excavator on which the hydraulic drive device according to the present embodiment is mounted.

  The hydraulic excavator includes a lower traveling body 101, an upper revolving body 102 that is turnably mounted on the lower traveling body 101, and a top portion of the upper revolving body 102 that rotates in the vertical and horizontal directions via a swing post 103. And a front work machine 104 that is movably connected. The lower traveling body 101 is a crawler type, and a blade 106 for earth removal that can move up and down is provided on the front side of the track frame 105. The upper swivel body 102 includes a swivel base 107 having a basic lower structure, and a canopy type cab 108 provided on the swivel base 107. The front work machine 104 includes a boom 51, an arm 112, and a bucket 113. The base end of the boom 51 is pin-coupled to the swing post 103, and the tip of the boom 51 is pin-coupled to the base end of the arm 112. The tip of each is pin-coupled to the bucket 113.

  The upper turning body 101 is driven to turn by the turning motor 3a with respect to the lower traveling body 100, and the boom 51, the arm 112, and the bucket 113 are rotated by extending and retracting the boom cylinder 3b, the arm cylinder 3c, and the bucket cylinder 3d, respectively. To do. The lower traveling body 101 is driven by left and right traveling motors 3f and 3g. The blade 106 is driven up and down by a blade cylinder 3h. In FIG. 1, illustration of the bucket cylinder 3d, the left and right traveling motors 3f and 3g, the blade cylinder 3h, and their circuit elements is omitted.

The driver's cab 108 is provided with a driver's seat 121, operation lever devices 122 and 123 (shown only on the right side in FIG. 2), and a gate lock lever 24.
~ Operation ~
Next, the operation of the present embodiment will be described.

<When all control levers are neutral>
When the operation levers of all the operation lever devices are neutral, the flow rate control valves 6b, 6c,... Of the actuators 3b, 3c, etc. other than the swing motor 3a are in the neutral positions, and the supply oil passages 8b, 8c,. Are blocked by the flow control valves 6b, 6c... And are not supplied to the actuators 3b, 3c.

  On the other hand, regarding the supply oil passage 8a of the turning motor 3a, even if the operation lever of the turning operation lever device (for example, the operation lever device 122) is neutral, the pressure oil is the pressure compensation valve 7a, the fixed throttle 20, the direction switching valve 40 ( Return to the tank via the neutral switching position 40a) and the neutral circuit 41. At this time, since the flow rate through which the pressure compensation valve 7a passes is controlled so that the differential pressure across the fixed throttle 20 is constant, the flow rate returning to the tank is constant.

  On the other hand, the minimum flow rate of the main pump 2 is set to be larger than the flow rate flowing through the supply oil passage 8a defined by the fixed throttle 20 and the pressure compensation valve 7a by the stopper 91 provided in the tilt switching unit 90. Therefore, the flow rate flowing from the supply oil passage 5 of the main pump 2 through the supply oil passages 8a, 8b, 8c of the actuator is only the flow rate flowing out to the tank via the supply oil passage 8a of the turning motor 3a. The pressure in the supply oil passage 5 increases.

  When all the operation levers are neutral, the tank pressure is detected by the shuttle valves 9a, 9b, 9c... As the maximum load pressure and guided to the differential pressure reducing valve 11. The differential pressure reducing valve 11 outputs the difference between the discharge pressure of the main pump 2 (pressure of the supply oil passage 5) and the tank pressure as an absolute pressure. The output pressure from the differential pressure reducing valve 11 and the output pressure of the engine speed detection valve 13 are guided to the switching valve 17 b of the flow rate control unit 17 of the main pump 2. When the pressure in the supply oil passage 5 increases as described above, the output pressure of the differential pressure reducing valve 11 becomes higher than the output pressure from the engine speed detection valve 13, the output pressure of the switching valve 17b increases, and the main pressure increases. The tilt angle control piston 17c of the pump 2 controls the tilt angle of the main pump 2 to be small. Therefore, the main pump 2 is maintained at the minimum tilt angle position, that is, the minimum flow rate.

  In addition, an unload valve 15 is provided in the supply oil passage 5 of the main pump 2, and the unload valve 15 is a constant in which a difference between the discharge pressure of the main pump 2 and the maximum load pressure is defined by a spring 15a. Control to be a value. The tank pressure detected as the maximum load pressure by the shuttle valves 9a, 9b, 9c. Therefore, when the pressure in the supply oil passage 5 rises, the unload valve 15 is activated, and the discharge pressure of the main pump 2 (pressure in the supply oil passage 5) is maintained at a constant pressure defined by the spring 15a. .

<When turning alone>
As described above, when the operation lever of the turning operation lever device is neutral, the direction switching valve 40 provided in the supply oil passage 8a of the turning motor 3a is defined by the fixed throttle 20 and the pressure compensation valve 7a. A certain flow rate is supplied. When the operation lever for turning is input, the direction switching valve 40 is switched. If the direction switching valve 40 is switched to the switching position 40b, the neutral circuit 41 is blocked and the pressure is applied to the oil passage 70a connecting the turning motor 3a and the control valve 4 via the check valve 60. Oil is supplied and the turning motor 3a is driven. The return oil from the swing motor 3a passes through the oil passage 70b connecting the swing motor 3a and the control valve 4, passes through the direction switching valve 40, and returns to the tank. At this time, the pressure compensating valve 7a provided in the supply oil passage 8a of the swing motor 3a has a characteristic (load dependent characteristic) for reducing the flow rate when the load pressure is high. When the load pressure of the swing motor 3a is high, such as during startup, the pressure compensation valve 7a is switched to the closing direction, and the supply flow rate to the direction switching valve 40 decreases.

  On the other hand, the load pressure of the swing motor 3a (pressure between the fixed throttle 20 and the direction switching valve 40) is detected by the shuttle valves 9a, 9b, 9c... As the maximum load pressure, and the differential pressure reducing valve 11 and the unloading valve 15 are detected. Led to. When the load pressure of the swing motor 3a is guided to the unload valve 15, the unload valve 15 increases the discharge pressure of the main pump 2 (pressure of the supply oil passage 5) by a pressure set by the spring 15a. Control its pressure.

  On the other hand, the differential pressure reducing valve 11 outputs the difference between the pressure (pump discharge pressure) of the supply oil passage 5 from the main pump 2 and the tank pressure as an absolute pressure. The output pressure from the differential pressure reducing valve 11 and the output pressure from the engine speed detecting valve 13 are guided to the switching valve 17 b of the flow rate control unit 17 of the main pump 2.

  When the discharge pressure of the main pump 2 rises at the beginning of the turning movement, the output pressure from the differential pressure reducing valve 11 becomes higher than the output pressure from the engine speed detection valve 13, and the output pressure of the switching valve 17b increases. The tilt angle control piston 17c of the main pump 2 controls the tilt angle of the main pump 2 to be small.

  As described above, even in the case of a single turn operation, the main pump 2 is maintained at the minimum tilt angle position, that is, the minimum flow rate, and so-called load sensing control is not performed.

<When an actuator other than turning is operated>
When an operation lever device for operating an actuator other than a turn, for example, an operation lever device for a boom operation lever device (for example, the operation lever device 123) is operated, the flow control valve 6b is switched and pressure oil is applied to the boom cylinder 3b. Supplied.

  The flow rate flowing through the flow rate control valve 6b is controlled by the pressure compensation valve 7b so that the differential pressure across the flow rate control valve 6b becomes equal to the output pressure of the differential pressure reducing valve 11.

  Further, the load pressure of the boom cylinder 3b is detected as the maximum load pressure by the shuttle valves 9a, 9b, 9c... And is guided to the unload valve 15, so that the pressure of the supply oil passage 5 is the maximum load pressure. Adjustment is made so that the pressure set by the spring 15a is higher than (the load pressure of the boom cylinder 3b).

  When the boom cylinder 3b starts to move, pressure oil is temporarily supplied from the supply oil passage 5 of the main pump 2 to the boom cylinder 3b via the supply oil passage 8b of the boom cylinder 3b. descend.

  On the other hand, the load pressure of the boom cylinder 3b is detected as the maximum load pressure by the shuttle valves 9a, 9b, 9c. The differential pressure reducing valve 11 outputs the difference between the pressure of the supply oil passage 5 of the main pump 2 (discharge pressure of the main pump 2) and the load pressure of the boom cylinder 3b as an absolute pressure. The output pressure from the differential pressure reducing valve 11 and the output pressure from the engine speed detecting valve 13 are guided to the switching valve 17 b of the flow rate control unit 17 of the main pump 2. When the discharge pressure of the main pump 2 decreases due to the beginning of the movement of the boom cylinder 3b as described above and the output pressure of the differential pressure reducing valve 11 becomes smaller than the output pressure of the engine speed detection valve 13, the switching valve 17b As the output pressure decreases, the tilt angle control piston 17c of the main pump 2 controls to increase the tilt angle of the main pump 2, and the discharge flow rate of the main pump 2 increases. The increase in the discharge flow rate of the main pump 2 continues until the output pressure of the differential pressure reducing valve 11 becomes equal to the output pressure of the engine speed detection valve 13. With these series of operations, the discharge flow rate of the main pump 2 is controlled so that the flow rate required by the flow rate control valve 6b flows through the boom cylinder 3b.

  Thus, when an actuator other than turning is operated, so-called load sensing control is performed.

<When turning and other actuators are operated simultaneously>
When the operation lever of the turning operation lever device and the actuator other than the turning operation, for example, the operation lever of the boom operation lever device are operated at the same time, the direction switching valve 40 provided in the supply oil passage 8a of the turning motor 3a, the boom The flow rate control valve 6b provided in the supply oil passage 8b of the cylinder 3b is switched.

  In the supply oil passage 8a of the swing motor 3a, when the operation lever is neutral, a fixed flow rate flows to the tank via the neutral circuit 41 of the direction switching valve 40 by the action of the fixed throttle 20 and the pressure compensation valve 7a. The flow rate is supplied to the turning motor 3a when the direction switching valve 40 is switched.

  Further, when the operating lever of the boom operating lever device is operated in this state, the flow control valve 6b for controlling the boom cylinder 3b is switched, and the pressure oil is supplied to the boom cylinder 3b via the supply oil passage 8b. . At this time, the higher load pressure of the swing motor 3a and the boom cylinder 3b is detected as the maximum load pressure by the shuttle valves 9a, 9b, 9c, and is guided to the unload valve 15, so that the unload valve 15 is supplied. The pressure in the oil passage 5 is adjusted to be higher than the maximum load pressure (load pressure of the boom cylinder 3b) by the pressure set by the spring 15a.

  Further, the higher load pressure of the swing motor 3a and the boom cylinder 3b is detected as the maximum load pressure by the shuttle valves 9a, 9b, 9c, and guided to the differential pressure reducing valve 11.

  On the other hand, the pressure generated in the supply oil passage 5 of the main pump 2 (discharge pressure of the main pump 2) temporarily decreases as the pressure oil flows out from the supply oil passage 5 to the supply oil passages 8a and 8b. As described above, when the maximum load pressure increases and the discharge pressure of the main pump 2 decreases, the output pressure of the differential pressure reducing valve 11 temporarily decreases. The output pressure from the differential pressure reducing valve 11 and the output pressure from the engine speed detecting valve 13 are guided to the switching valve 17 b of the flow rate control unit 17 of the main pump 2. When the output pressure of the differential pressure reducing valve 11 becomes smaller than the output pressure of the engine speed detecting valve 13, the output pressure of the switching valve 17 b decreases, and the tilt angle control piston 17 c of the main pump 2 tilts the main pump 2. Control is made to increase the turning angle, and the discharge flow rate of the main pump 2 increases. The increase in the discharge flow rate of the main pump 2 continues until the output pressure of the differential pressure reducing valve 11 becomes equal to the output pressure of the engine speed detection valve 13.

  In this way, even when the swing motor 3a and other actuators are operated simultaneously, a certain flow rate is supplied to the swing motor 3a, and a so-called load that supplies the flow rate required by the actuator to the other actuators. Sensing control is performed.

<When turning and other actuators are operated simultaneously to reach saturation>
Temporarily, the total flow rate of the flow rate flowing out to the supply oil passage 8a of the swing motor 3a and the flow rate flowing out to the supply oil passages 8b, 8c,. When the flow rate is larger than the flow rate, that is, when the saturation state is reached, the pressure compensation valve 7a that controls the supply oil path 8a of the swing motor 3a to keep the differential pressure across the fixed throttle 20 constant is maintained. A certain flow rate flows. The remaining flow rate obtained by subtracting the flow rate supplied to the supply oil passage 8a of the turning motor 3a from the maximum flow rate that can be discharged from the main pump 2 is supplied to the supply oil passages 8b, 8c.

  In the saturation state, the pressure oil supplied from the main pump 2 is insufficient with respect to the flow rate required by the actuator other than the swing motor 3a. As a result, the oil is generated in the supply oil passage 5 of the main pump 2. Pressure (discharge pressure of the main pump 2) decreases, and the output pressure of the differential pressure reducing valve 11 also decreases. As a result, the main pump 2 is controlled to discharge the maximum flow rate within the dischargeable range by the action of the switching valve 17b and the tilt angle control piston 17c of the tilt angle control unit 17.

  The output pressure of the differential pressure reducing valve 11 is guided to the respective pressure compensation valves 7b, 7c,... Provided in the supply oil passages 8b, 8c, etc. of the actuators other than the swing motor 3a as target compensation differential pressures. Therefore, the pressure compensation valves 7b, 7c,... Are controlled so as to restrict the flow rates that pass through the ratios of the required flow rates determined by the open areas of the flow rate control valves 6b, 6c,.

  On the other hand, since the output pressure of the engine speed detection valve 13 acts as a target compensation differential pressure on the pressure compensation valve 7a provided in the supply oil passage 8a of the turning motor 3a, the pressure compensation is performed even in the saturation state. The flow rate through which the valve 7a passes is not reduced.

  Thus, the pressure oil is preferentially supplied to the swing motor 3a even in the saturation state.

  Further, since the pressure compensation valve 7a of the swing motor 3a has a load-dependent characteristic (a characteristic that the flow rate decreases when the load pressure is high), when the load pressure is temporarily high, such as when the swing motor 3a starts moving, Since the flow rate flowing through the supply oil passage 8a of the swing motor 3a is decreased, the flow rate that can be used by an actuator (such as the boom cylinder 3b) other than the swing motor 3a is increased accordingly.

<When the engine speed is lowered>
The above operation is performed when the engine 1 is at the maximum rated speed. When the rotational speed of the engine 1 is lowered to a low speed, the output pressure of the differential pressure reducing valve 51 decreases accordingly. Therefore, the target differential pressure of the load sensing control of the tilt angle control unit 17 and the target of the pressure compensating valve 7a. The compensation differential pressure also decreases. For this reason, when not in a saturation state by the turning combined operation when the engine speed is reduced, both the target compensation differential pressure Pc1 of the pressure compensation valve 7a and the target compensation differential pressure of the pressure compensation valves 7b, 7c. There is no such thing as turning too fast. Further, when the saturation state is achieved by the combined turning operation, only the target compensation differential pressure of the pressure compensation valves 7b, 7c. Thus, appropriate turning priority can be maintained regardless of the setting of the engine speed.
~effect~
According to the present embodiment configured as described above, when the swing motor 3a and the other actuators 3b, 3c,... Are operated simultaneously, even if a saturation state of the discharge flow rate of the main pump 2 occurs, the swing motor 3a has priority. The pressure oil is supplied to the swivel motor 3a so that the high priority of the swivel motor 3a is maintained, the swiveling speed change can be suppressed, and good composite operability can be obtained.

  Further, when the swing motor 3a is operated alone, the load pressure of the swing motor 3a is temporarily increased at the start of the swing, and the main pump 2 is supplied to the swing motor 3a even if the discharge flow rate is increased by load sensing control. By performing the flow control of the pressure oil to be performed by the open center type directional control valve 40, it is possible to suppress a shock at the time of start-up due to a sudden increase in the flow rate, and to realize smooth turning operability.

  Further, since the minimum tilt of the main pump 2 is set so that the minimum discharge flow rate of the main pump 2 does not become smaller than the maximum required flow rate of the swing motor 3a set by the fixed throttle 20, the load sensing control and pressure of the main pump 2 are set. The instability of the system due to interference with the control of the compensation valve 7a can be eliminated, and the turning operability can be further improved.

  Further, since the pressure compensation valve 7a related to the swing motor 3a has a load-dependent characteristic, the supply flow rate to the swing motor 3a decreases when the load pressure of the swing motor 3a increases at the start of the swing and is consumed by the swing motor 3a. In addition to reducing the horsepower required, even if saturation occurs during simultaneous operations such as turning and boom raising, the amount of flow that can be used by other actuators is increased, and the amount of boom raised can be secured. Can be realized.

Further, when the rotational speed of the engine 1 is lowered to a low speed, the output pressure of the differential pressure reducing valve 51 decreases accordingly, and the target differential pressure of the load sensing control of the tilt angle control unit 17 and the pressure compensation valve 7a. Since the target compensation differential pressure also decreases in the same manner, appropriate turning priority can be maintained regardless of the setting of the engine speed.
-Other embodiments-
In the above embodiment, the differential pressure between the discharge pressure of the main pump 2 and the maximum load pressure is output as an absolute pressure by the output pressure of the differential pressure reducing valve 11, and the pressure receiving portions 21b of the pressure compensating valves 7b, 7c,. 21c ... and the pressure receiving portion 17e of the switching valve 17b, but the pressure compensating valves 7b, 7c, ... and the switching valve 17b are provided with pressure receiving portions facing each other in place of the pressure receiving portions 21b, 21c, ... and the pressure receiving portion 17e, respectively. The two discharge pressures and the maximum load pressure may be separately guided to those pressure receiving portions.

  In the above embodiment, the pressure compensation valve 7a related to the swing motor 3a has a load-dependent characteristic. However, when the load pressure of the swing motor 3a temporarily increases, the supply flow rate to the swing motor 3a is reduced. When it is not necessary to decrease the pressure, or when a similar function is provided by other means, the pressure compensation valve 7a may be a normal pressure compensation valve having no load dependent characteristics.

  Further, in the above embodiment, the stopper 91 is provided in the pump tilt changing unit 90, and the main pump 2 is set so that the minimum discharge flow rate of the main pump 2 is larger than the maximum required flow rate of the turning motor 3a set by the fixed throttle 20. If the system instability due to interference between the load sensing control of the hydraulic pump and the control of the pressure compensation valve can be resolved by another means, the minimum discharge flow rate of the main pump 2 is reduced. A normal value smaller than the maximum required flow rate of the swing motor 3a may be set.

1 Engine 2 Hydraulic pump (Main pump)
3a Rotating motor 3b, 3c ... Actuator 4 Control valve 5 Supply oil passages 6a, 6b, 6c Flow control valves 7a, 7b, 7c Pressure compensation valves 8a, 8b, 8c Oil passages 9a, 9b, 9c Shuttle valve 11 Differential pressure reducing valve 12d, 12e, 12g Oil passage 13 Engine speed detection valve 14 Main relief valve 15 Unload valve 15a Spring 17 Tilt angle control unit 17a Tilt angle control piston 17b Switching valve 17c Tilt angle control pistons 17d, 17e Pressure receiving unit 20 Fixed throttle 21a, 21b, 21c Pressure receiving portion 22a, 23a Pressure receiving portion 22b, 23b Pressure receiving portion 22c, 23c Pressure receiving portion 24 Gate lock lever 30 Pilot pump 31a Supply oil passage 31b Pilot pressure supply oil passage 31c Pilot oil passage

32 Pilot Relief Valve 40 Direction Switching Valve 41 Neutral Circuit 42 Feeder Circuit 42a Load Pressure Extracting Unit 50 Variable Throttle Unit 51 Differential Pressure Reducing Valve 60 Check Valve 90 Pump Tilt Changing Unit 91 Stopper 100 Gate Lock Valve

Claims (3)

An engine, a variable displacement hydraulic pump driven by the engine, a plurality of actuators including a swing motor driven by pressure oil discharged from the hydraulic pump, and the hydraulic pump supplied to the plurality of actuators A plurality of flow control valves for controlling the flow rate of pressure oil, a plurality of pressure compensation valves for controlling differential pressures before and after the throttle portions of the plurality of flow control valves, and a maximum load among the load pressures of the plurality of actuators A maximum load pressure detecting means for detecting pressure, a pump control means for performing load sensing control so that a discharge pressure of the hydraulic pump is higher by a target differential pressure than a maximum load pressure detected by the maximum load pressure detecting means, An engine speed detector for outputting a pressure dependent on the engine speed so as to decrease as the engine speed decreases; Provided, leads to the output pressure of the engine speed detecting unit to said pump control means, the hydraulic drive apparatus to set the target differential pressure of the load sense control as a variable value depending on the rotational speed of the engine,
The target compensation differential pressure of each pressure compensation valve related to the actuator other than the swing motor is set by the differential pressure between the discharge pressure of the hydraulic pump and the maximum load pressure of the plurality of actuators, and the pressure compensation related to the swing motor The valve is configured to introduce the same output pressure as the target pressure of load sensing control from the engine speed detector to the pump control means and set the target compensation differential pressure by the output pressure. ,
The flow control valve related to the swing motor is composed of a fixed throttle for setting the maximum required flow rate of the swing motor and an open center type directional switching valve arranged downstream of the fixed throttle,
A pressure compensation valve related to the swing motor is configured to control a differential pressure across the fixed throttle,
The hydraulic drive device for a construction machine, wherein the maximum load pressure detecting means is configured to detect a pressure between the fixed throttle and the direction switching valve as a load pressure of the swing motor. The hydraulic drive device for a construction machine according to claim 1,
The construction machine characterized in that the pump control means sets a minimum tilt of the hydraulic pump so that a minimum discharge flow rate of the hydraulic pump is larger than a maximum required flow rate of the swing motor set by the fixed throttle. Hydraulic drive device. The hydraulic drive device for a construction machine according to claim 1,
The pressure compensation valve related to the swing motor has a load-dependent characteristic that reduces the passage flow rate by reducing the differential pressure across the fixed throttle as the load pressure of the swing motor increases. Hydraulic drive device for the machine.

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