Patent Description:
A work machine such as a hydraulic excavator includes: a machine body including a swing structure; and a work device (front device) attached to the swing structure. The work device includes: a boom (front-implement member) connected vertically rotatably to the swing structure; an arm (front-implement member) connected vertically rotatably to the tip of the boom; a boom cylinder (actuator) that drives the boom; an arm cylinder (actuator) that drives the arm; a bucket connected rotatably to the tip of the arm; and a bucket cylinder (actuator) that drives the bucket. To operate the front-implement members of the work machine by their corresponding manual operation levers to excavate a predetermined area is not easy, and operators are required to have high operation skills. In view of this, technologies for making such work easy have been proposed (Patent Documents <NUM> and <NUM>).

An area limiting excavation controller of a construction machine described in Patent Document <NUM> includes: sensing means that senses the position of a front device; a controller including a calculating section that calculates the position of the front device on the basis of signal from the sensing means, a setting section that sets an off-limits area where the front device is prohibited from entering, and a calculating section that computes a control gain of an operation lever signal on the basis of the off-limits area and the position of the front device; and actuator control means that control the action of actuators on the basis of the computed control gain. According to such a configuration, since lever operation signals are controlled in accordance with distances to the boundary line of an off-limits area, the locus of a bucket tip is controlled to move along the boundary automatically even if an operator tries, by mistake, to move the bucket tip into the off-limits area. Thereby, any operator can perform precise and stable work without being affected by his/her operation skill level.

On the other hand, in a hydraulic drive system described in Patent Document <NUM>, pressure-compensating valves that compensate for pressures of directional control valves of actuators are arranged in series with the directional control valves. Thereby, it becomes possible for an operator to supply flows to the actuators at rates according to lever operation amounts without being influenced by load variations. In Patent Document <NUM>, a region is set in advance in which a front unit can be moved. Further, Patent Document <NUM> shows a mode switch and a target speed vector, wherein the mode switch can be switched on or off. This enables an operator to choose between an accuracy priority working mode and a speed priority working mode. Patent Document <NUM> shows a posture computing apparatus for a work machine based on information about a posture angle. Further, Patent Document <NUM> shows a detection apparatus that is provided to the work machine and a first posture angle computing unit that is provided to the detection apparatus. Furthermore, Patent Document <NUM> shows a second posture angle computing unit.

If it is supposed, about the construction machine described in Patent Document <NUM>, that switching is performed between a manual operation function for manual operation of a work device by an operator and an automatic control function for a machine body controller in accordance with work contents, there are the following problems.

It is important to move the tip of the front device accurately along a target locus in a case where automatic control of the front device is performed in accordance with commands from the controller, and, for this purpose, it is necessary to supply flows to the actuators accurately at target rates. However, in the area limiting excavation controller of Patent Document <NUM>, since targets to be controlled in accordance with lever operation amounts are the openings of the directional control valves, the rates of flows supplied to the actuators become unstable in some cases due to changes in the differential pressures across the valves accompanying load variations of the actuators.

On the other hand, according to the technology of Patent Document <NUM>, by controlling not only the openings of the directional control valves in accordance with input amounts of operation levers, but also the differential pressures across the directional control valves via the pressure-compensating valves, it becomes possible to supply flows to the actuators at accurate rates without depending on the loads of the actuators. Accordingly, by applying the technology of Patent Document <NUM> to the area limiting excavation controller of Patent Document <NUM>, presumably it becomes possible in automatic control also to supply flows to actuators accurately at target rates without being affected by load variations.

However, changes in the operation of actuators caused by load variations are one of important factors for decision making by an operator in operating a machine body via operation levers. Implementing a function to make it possible to supply flows to actuators accurately at target rates without being affected by load variations as mentioned above means the loss of operational changes of the actuators accompanying the load variations. Accordingly, there is a fear that an operator feels a significant sense of discomfort in a feeling about operation of a machine body, and deterioration of the operability of the machine body occurs.

In this way, different types of performance are demanded for an operator manual operation function and a machine body automatic control function of work machines such as hydraulic excavators, and hydraulic system configurations suited therefor are also different. Accordingly, even if these two functions can be switched to each other in the hydraulic system of one work machine, it is difficult to realize both the different types of performance demanded for those functions.

The present invention has been contrived in view of such circumstances, and an object of the present invention is to provide a work machine that makes it possible to drive actuators faster and more accurately by supplying flows to the actuators accurately at target rates without depending on load variations in a case where the machine body is controlled automatically by command inputs of a controller, while high operability is ensured for manual operation by an operator.

In order to achieve the object, the present invention provides a work machine including: a machine body; a work device attached to the machine body; a plurality of hydraulic actuators that drive the machine body or the work device; a hydraulic pump; a plurality of directional control valves that are connected in parallel to a delivery line of the hydraulic pump, and adjust a flow of a hydraulic fluid supplied from the hydraulic pump to the plurality of hydraulic actuators; an operation lever for giving an instruction to operate the plurality of hydraulic actuators; a machine control switch for giving an instruction to activate or deactivate a machine control function that prevents the work device from going into a preset area; and a controller that executes the machine control function in a case where the machine control function is selected via the machine control switch. The work machine includes auxiliary flow rate control devices that are arranged upstream of the plurality of directional control valves, and limit the flow rate of the hydraulic fluid supplied from the hydraulic pump to the plurality of directional control valves in accordance with pressure variations at the plurality of hydraulic actuators. In a case where the machine control function is cancelled via the machine control switch, the controller cancels limitation of the flow rate of the hydraulic fluid supplied to the directional control valves, the limitation being performed by the auxiliary flow rate control devices, and in a case where the machine control function is selected via the machine control switch, the controller causes the auxiliary flow rate control devices to limit the flow rate of the hydraulic fluid supplied to the directional control valves.

According to the thus-configured present invention, in a case where the machine control function is cancelled, the flow rate control of pilot lines of the auxiliary flow rate control devices is deactivated, and the auxiliary flow rate control devices maintain openings according to an input amount of operation by an operator, and generates branch flows to a plurality of actuators. In this case, it becomes easier for the operator to feel changes of actuator operation according to the load variations of the actuators, thus the operability of the work machine at the time of operator operation is ensured. On the other hand, in a case where the machine control function is selected, the auxiliary flow rate control can supply flows to the actuators highly responsively and surely at rates according to target flow rates in accordance with commands by the controller, without depending on the load variations of the actuators, thus the automatic control precision of the actuators can be improved. Thereby, in each of two types of operation mode at the time of manual operation by an operator or at the time of automatic control by the controller, switching of hydraulic-system characteristics suited for the operation mode is performed, thus different types of performance demanded in those operation modes can both be realized.

According to the present invention, it becomes possible to drive actuators faster and more accurately in a work machine such as a hydraulic excavator by supplying flows to the actuators accurately at target rates without depending on load variations in a case where the machine body is controlled automatically by command inputs of a controller, while high operability is ensured for manual operation by an operator.

In the following, a hydraulic excavator is explained as an example of work machines according to embodiments of the present invention with reference to the drawings. Note that equivalent members are given the same reference characters through the drawings, and overlapping explanation is omitted as appropriate.

<FIG> is a side view illustrating a hydraulic excavator according to the present embodiments.

As illustrated in <FIG>, a hydraulic excavator <NUM> includes: a track structure <NUM>; a swing structure <NUM> that is arranged on the track structure <NUM>, and forms a machine body; and a work device <NUM> that is attached to the swing structure <NUM>, and performs earth and sand excavation work and the like. The work device <NUM> includes: a boom <NUM> attached vertically rotatably to the swing structure <NUM>; an arm <NUM> attached vertically rotatably to the tip of the boom <NUM>; a bucket <NUM> attached vertically rotatably to the tip of the arm <NUM>; a boom cylinder 204a that drives the boom <NUM>; an arm cylinder 205a that drives the arm <NUM>; and a bucket cylinder 206a that drives the bucket <NUM>. A cab <NUM> is provided at a position located on the front side on the swing structure <NUM>, and a counter weight <NUM> that ensures the balance of weight is provided at a position on the rear side on the swing structure <NUM>. A machine room <NUM> that houses an engine, hydraulic pumps and the like is provided between the cab <NUM> and the counter weight <NUM>, and a control valve <NUM> is installed in the machine room <NUM>.

Hydraulic drive systems explained in the following embodiments are mounted on the hydraulic excavator <NUM> according to the present embodiment.

<FIG> and <FIG> are circuit diagrams of a hydraulic drive system in a first embodiment of the present invention.

As illustrated in <FIG>, a hydraulic drive system <NUM> in the first embodiment includes three main hydraulic pumps driven by the unillustrated engine which are a first hydraulic pump <NUM>, a second hydraulic pump <NUM> and a third hydraulic pump <NUM> each including a variable displacement hydraulic pump, for example. In addition, the hydraulic drive system <NUM> includes a pilot pump <NUM> driven by the unillustrated engine, and includes a hydraulic operation fluid tank <NUM> that supplies a hydraulic fluid to the first to third hydraulic pumps <NUM> to <NUM>, and the pilot pump <NUM>.

The tilting angle of the first hydraulic pump <NUM> is controlled by a regulator provided in association with the first hydraulic pump <NUM>. The regulator of the first hydraulic pump <NUM> includes a flow-rate-control command pressure port 1a, a first hydraulic pump self-pressure port 1b and a second hydraulic pump self-pressure port 1c. Similarly, the tilting angle of the second hydraulic pump <NUM> is controlled by a regulator provided in association with the second hydraulic pump <NUM>. The regulator of the second hydraulic pump <NUM> includes a flow-rate-control command pressure port 2a, a second hydraulic pump self-pressure port 2b and a first hydraulic pump self-pressure port 2c. In addition, similarly, the tilting angle of the third hydraulic pump <NUM> is controlled by a regulator provided in association with the third hydraulic pump <NUM>. The regulator of the third hydraulic pump <NUM> includes a flow-rate-control command pressure port 3a and a third hydraulic pump self-pressure port 3b.

The first hydraulic pump <NUM> is first connected with a right-travel directional control valve <NUM> that controls the driving of an unillustrated right travel motor of a pair of travel motors that drive the track structure <NUM>. The right-travel directional control valve <NUM> is in turn connected with: a bucket directional control valve <NUM> that is connected to the bucket cylinder 206a, and controls the flow of the hydraulic fluid; a second arm directional control valve <NUM> that controls the flow of the hydraulic fluid supplied to the arm cylinder 205a; and a first boom directional control valve <NUM> that controls the flow of the hydraulic fluid supplied to the boom cylinder 204a. These bucket directional control valve <NUM>, second arm directional control valve <NUM> and first boom directional control valve <NUM> are connected to a line <NUM> connected to the right-travel directional control valve, and connected in parallel to the line <NUM> via lines <NUM>, <NUM> and <NUM> connected to the line <NUM>.

The second hydraulic pump <NUM> is connected with: a second boom directional control valve <NUM> that controls the flow of the hydraulic fluid supplied to the boom cylinder 204a; a first arm directional control valve <NUM> that controls the flow of the hydraulic fluid supplied to the arm cylinder 205a; a first attachment directional control valve <NUM> that controls the flow of the hydraulic fluid supplied to an unillustrated first actuator that drives a first special attachment such as a secondary crusher provided instead of the bucket <NUM>, for example; and a left-travel directional control valve <NUM> that controls the driving of an unillustrated left travel motor of the pair of travel motors that drive the track structure <NUM>. These second boom directional control valve <NUM>, first arm directional control valve <NUM>, first attachment directional control valve <NUM> and left-travel directional control valve <NUM> are connected to a line <NUM> connected to the second hydraulic pump <NUM>, and connected in parallel to the line <NUM> via lines <NUM>, <NUM>, <NUM> and <NUM> connected to the line <NUM>. In addition, the line <NUM> is connected to the line <NUM> via a confluence valve <NUM>.

The third hydraulic pump <NUM> is connected with: a swing directional control valve <NUM> that controls the flow of the hydraulic fluid supplied to an unillustrated swing motor that drives the swing structure <NUM>; a third boom directional control valve <NUM> that controls the flow of the hydraulic fluid supplied to the boom cylinder 204a; and a second attachment directional control valve <NUM> that controls the flow of the hydraulic fluid supplied to an unillustrated second actuator when a second special attachment including two hydraulic actuators, a first actuator and a second actuator, is attached in addition further to the first special attachment or instead of a first special actuator.

The swing directional control valve <NUM>, the third boom directional control valve <NUM> and the second attachment directional control valve <NUM> are connected to a line <NUM> connected to the third hydraulic pump <NUM>, and connected in parallel to the line <NUM> via lines <NUM>, <NUM> and <NUM> connected to the line <NUM>.

The boom cylinder 204a is provided with a pressure sensor 71a that senses the bottom-side pressure, and a pressure sensor 71b that senses the rod-side pressure. Similarly, the arm cylinder 205a is provided with a pressure sensor 72a that senses the bottom-side pressure, and a pressure sensor 72b that senses the rod-side pressure. In addition, similarly, the bucket cylinder 206a is provided with a pressure sensor 73a that senses the bucket-side pressure, and a pressure sensor 73b that senses the rod-side pressure. In addition, for the purpose of acquiring the operation state of the machine body, a stroke sensor <NUM> that senses the stroke amount of the boom cylinder 204a, a stroke sensor <NUM> that senses the stroke amount of the arm cylinder 205a, and a stroke sensor <NUM> that senses the stroke amount of the bucket cylinder 206a are provided. Note that a wide variety of means for acquiring the operation state of the machine body, such as inclination sensors, rotation angle sensors or IMUs can be used, and the stroke sensors mentioned above are not the only means therefor.

The line <NUM> connected to the bucket directional control valve <NUM>, the line <NUM> connected to the second arm directional control valve <NUM>, and the line <NUM> connected to the first boom directional control valve <NUM> are respectively provided with auxiliary flow rate control devices <NUM> to <NUM> that limit the flow rate of the hydraulic fluid supplied from the first hydraulic pump <NUM> to the corresponding directional control valves at the time of combined operation.

The line <NUM> connected to the second boom directional control valve <NUM>, and the line <NUM> connected to the first arm directional control valve <NUM> are respectively provided with auxiliary flow rate control devices <NUM> and <NUM> that limit the flow rate of the hydraulic fluid supplied from the second hydraulic pump <NUM> to the corresponding directional control valves at the time of combined operation. In the first embodiment, the auxiliary flow rate control device <NUM> includes: a seat-shaped main valve <NUM> that forms an auxiliary variable restrictor; a feedback restrictor 31b as a control variable restrictor having an opening area that changes in accordance with the movement amount of a valve body 31a of the main valve <NUM>, and is provided to the valve body 31a; a hydraulic variable restrictor valve <NUM> as a pilot variable restrictor; and a pressure-compensating valve <NUM>. A housing in which the main valve <NUM> is housed has: a first pressure chamber 31c formed at a connecting portion between the main valve <NUM> and the line <NUM>; a second pressure chamber 31d formed at a connecting portion of a line <NUM> between the main valve <NUM> and the second boom directional control valve <NUM>; and a third pressure chamber 31e formed to communicate with the first pressure chamber 31c via the feedback restrictor 31b. The third pressure chamber 31e and the pressure-compensating valve <NUM> are connected to each other by a line 59a, the pressure-compensating valve <NUM> and the hydraulic variable restrictor <NUM> are connected to each other by a line 59b, the hydraulic variable restrictor <NUM> and the line <NUM> are connected to each other by a line 59c, and these lines 59a, 59b and 59c form a pilot line <NUM>.

On a side of the pressure-compensating valve <NUM> where force is applied in the direction to cause the pressure-compensating valve spool to open the hydraulic line, a pressure signal port 32e receives the second-hydraulic-pump delivery pressure of the line <NUM>, a pressure signal port 32c receives a pressure of the line 59c, and a pressure signal port 32d receives a function switching signal pressure transmitted from a solenoid selector valve <NUM> via a line <NUM>. On a side of the pressure-compensating valve <NUM> where force is applied in the direction to cause the pressure-compensating valve spool to close the hydraulic line, a pressure signal port 32b receives a pressure of the line 59b, and a pressure signal port 32a receives a highest load pressure that a high-pressure selecting valve <NUM> selects from a load pressure of the bucket cylinder 206a sensed from the bucket directional control valve <NUM>, a load pressure of the boom cylinder 204a sensed from the first boom directional control valve <NUM>, the second boom directional control valve <NUM> and the third boom directional control valve <NUM>, a load pressure of the arm cylinder 205a sensed from the first arm directional control valve <NUM> and the second arm directional control valve <NUM>, and the load pressure of the swing directional control valve <NUM>.

The supply port of the solenoid selector valve <NUM> is connected with the pilot pump <NUM>, and the tank port of the solenoid selector valve <NUM> is connected with the hydraulic operation fluid tank <NUM>.

A pressure signal port 33a of the hydraulic variable restrictor <NUM> is connected with the output port of a proportional solenoid pressure-reducing valve <NUM>. The supply port of the proportional solenoid pressure-reducing valve <NUM> is connected with the pilot pump <NUM>, and the tank port of the proportional solenoid pressure-reducing valve <NUM> is connected with the hydraulic operation fluid tank <NUM>.

Note that although some illustrations are omitted for simplification and convenience of explanation, all of the auxiliary flow rate control devices <NUM> to <NUM>, and surrounding equipment, lines and wires have the same configurations.

The hydraulic drive system <NUM> in the first embodiment includes: an operation lever 17a and a pilot valve 18a that are capable of switching operation of each of the first boom directional control valve <NUM>, the second boom directional control valve <NUM>, the third boom directional control valve <NUM> and the bucket directional control valve <NUM>; and an operation lever 17b and a pilot valve 18b that are capable of switching operation of each of the first arm directional control valve <NUM> and the second arm directional control valve <NUM>. Lines <NUM> that connect the pilot valves 18a and 18b of the operation levers 17a and 17b with a selector valve unit <NUM> are provided with pressure sensors <NUM> that sense that the boom <NUM>, the arm <NUM> and the bucket <NUM> are operated. Note that, in order to avoid complexity of explanation, illustrations of a swing operation device that performs switching operation of the swing directional control valve <NUM>, a right travel operation device that performs switching operation of the right-travel directional control valve <NUM>, a left travel operation device that performs switching operation of the left-travel directional control valve <NUM>, a first attachment operation device that performs switching operation of the first attachment directional control valve <NUM>, and a second attachment operation device that performs switching operation of the second attachment directional control valve <NUM> are omitted.

The selector valve unit <NUM> is connected to the pilot port of each directional control valve by a line <NUM>, and to the flow rate control command ports of the first to third hydraulic pumps <NUM> to <NUM> by lines <NUM>, and also is connected to a solenoid proportional valve unit <NUM> by lines <NUM> and <NUM>.

<FIG> is a configuration diagram of the selector valve unit <NUM>. As illustrated in <FIG>, the selector valve unit <NUM> houses a plurality of solenoid selector valves 19a that are subjected to switching control by a command from a controller <NUM>. When a machine control function is cancelled via a machine control switch <NUM>, the solenoid selector valves 19a are switched to Positions A illustrated in the figure, and when the machine control function is selected via the machine control switch <NUM>, the solenoid selector valves 19a are switched to Positions B illustrated in the figure. When the solenoid selector valves 19a are at Positions A illustrated in the figure, pilot pressure signals input from the lines <NUM> are output to the flow-rate-control command pressure ports 3a, 3b and 3c of the first to third hydraulic pumps <NUM> to <NUM>, or the pilot ports of directional control valves via the lines <NUM> or <NUM>. On the other hand, when the solenoid selector valves 19a are at Positions B, pilot pressure signals input from the lines <NUM> are output to the solenoid proportional valve unit <NUM> via the lines <NUM>. Simultaneously, pilot pressure signals input from the solenoid proportional valve unit <NUM> via the lines <NUM> are output to the flow-rate-control command pressure ports 3a, 3b and 3c of the first to third hydraulic pumps <NUM> to <NUM>, or the pilot ports of directional control valves via the lines <NUM> or <NUM>.

<FIG> is a configuration diagram of the solenoid proportional valve unit <NUM>. As illustrated in <FIG>, the solenoid proportional valve unit <NUM> houses a plurality of proportional solenoid pressure-reducing valves 20a having openings that are controlled in accordance with commands from the controller <NUM>. Pilot pressure signals input from the lines <NUM> are corrected by the proportional solenoid pressure-reducing valves 20a, and output to the selector valve unit <NUM> via the lines <NUM>.

The hydraulic drive system in the first embodiment includes the controller <NUM>, and output values of the pressure sensors <NUM>, 71a, 71b, 72a, 72b, 73a and 73b, output values of the stroke sensors <NUM>, <NUM> and <NUM>, and a command value of the machine control switch <NUM> are input to the controller <NUM>. In addition, the controller <NUM> outputs commands to selector valves provided to the selector valve unit <NUM>, each solenoid valve provided to the solenoid proportional valve unit <NUM>, the proportional solenoid pressure-reducing valves <NUM> and <NUM> (and unillustrated proportional solenoid pressure-reducing valves), and the solenoid selector valve <NUM>.

<FIG> is a functional block diagram of the controller <NUM>. In <FIG>, the controller <NUM> has an input section 21a, a control activation deciding section 21b, a machine-body-posture calculating section 21c, a demanded-flow-rate calculating section 21d, a target-flow-rate calculating section 21e, a pressure-state deciding section 21f, a differential-pressure rate-of-decrease calculating section <NUM>, a corrected-target-flow-rate calculating section <NUM>, a current-flow-rate calculating section 21i, and an output section 21j.

The input section 21a acquires a signal of the machine control switch <NUM>, and sensor output values. On the basis of a signal of the machine control switch <NUM>, the control activation deciding section 21b decides whether to activate or deactivate area limiting control. On the basis of sensor output values, the machine-body-posture calculating section 21c calculates the postures of the machine body <NUM> and the work device <NUM>. On the basis of sensor output values, the demanded-flow-rate calculating section 21d calculates demanded flow rates of actuators. On the basis of the posture of the machine body, and demanded flow rates, the target-flow-rate calculating section 21e calculates target flow rates of actuators. On the basis of sensor output values, the pressure-state deciding section 21f decides the pressure states of hydraulic pumps and actuators. On the basis of the pressure states of hydraulic pumps and actuators, the differential-pressure rate-of-decrease calculating section <NUM> calculates the rates of decrease in the differential pressures between the delivery pressures of the hydraulic pumps and a highest load pressures of the actuators. On the basis of target flow rates from the target-flow-rate calculating section 21e, and rates of decrease in differential pressures from the differential-pressure rate-of-decrease calculating section <NUM>, the corrected-target-flow-rate calculating section <NUM> calculates corrected target flow rates of actuators. On the basis of sensor output values, the current-flow-rate calculating section 21i computes the current flow rates of actuators. On the basis of results of decision from the control activation deciding section 21b, corrected target flow rates from the corrected-target-flow-rate calculating section <NUM>, and current flow rates from the current-flow-rate calculating section 21i, the output section 21j generates command electric signals, and outputs the command electric signals to the selector valve unit <NUM>, the solenoid proportional valve unit <NUM> and the proportional solenoid pressure-reducing valves <NUM> and <NUM>.

<FIG> is a flowchart illustrating a calculation process of the controller <NUM> in the first embodiment. The controller <NUM> decides whether or not the machine control switch <NUM> is turned on (Step S100). In a case where it is decided that the machine control switch <NUM> is turned off (NO), the controller <NUM> executes a control deactivation process (Step S200), and in a case where it is decided that the machine control switch <NUM> is turned on (YES), the controller <NUM> executes a control activation process (Step S300).

<FIG> is a flowchart illustrating details of Step S200 (control deactivation process). The controller <NUM> switches off the selector valve unit <NUM> (Step S201), outputs a command electric signal to the solenoid selector valve <NUM> for generation of pressure-compensation-function switching signals (Step S202), generates a pressure-compensation-function switching signal pressure at the solenoid selector valve <NUM> (Step S203), and turns off a pressure compensation function by causing the pressure-compensation-function switching signal pressure to be applied to the pressure-compensating valves <NUM> and <NUM> (Step S204). Subsequent to Step S204, it is decided whether or not an operation lever input is absent (Step S205).

In a case where it is decided at Step S205 that an operation lever input is absent (YES), the control deactivation process (Step S200) is ended.

In a case where it is decided at Step S205 that an operation lever input is not absent (NO), pilot command pressures according to the amount of the operation lever input are generated at the pilot valves 18a and 18b (Step S206), directional control valves are opened in accordance with the pilot command pressures (Step S207), and the hydraulic fluid is fed to actuators to operate the actuators (Step S208). Subsequent to Step S208, it is decided whether or not branch flows for a plurality of actuators are necessary (Step S209).

In a case where it is decided at Step S209 that branch flows are not necessary (NO), command electric signals are outputted from the controller <NUM> to the proportional solenoid pressure-reducing valves <NUM> and <NUM> (Step S210), the pilot variable restrictors <NUM> and <NUM> are fully opened (Step S211), the main valves <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> and <NUM> are fully opened in accordance with the pilot-variable-restrictor openings (Step S212), and the control deactivation process (Step S200) is ended.

In a case where it is decided at Step S209 that branch flows are necessary (YES), command electric signals are outputted from the controller <NUM> to the proportional solenoid pressure-reducing valves <NUM> and <NUM> (Step S213), the pilot variable restrictors <NUM> and <NUM> are opened in accordance with command pressures from the proportional solenoid pressure-reducing valves <NUM> and <NUM> (Step S214), the main valves <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> and <NUM> are opened in accordance with the pilot-variable-restrictor openings (Step S215), the flow rates of the hydraulic fluid having been fed from directional control valves to actuators are limited (Step S216), and the control deactivation process (Step S200) is ended.

<FIG> is a flowchart illustrating details of Step S300 (control activation process). The controller <NUM> switches the selector valve unit <NUM> to the on state (Step S301), outputs a command electric signal to the solenoid selector valve <NUM> for generation of pressure-compensation-function switching signals (Step S302), cuts a pressure-compensation-function switching signal pressure at the solenoid selector valve <NUM> (Step S303), and turns on the pressure compensation function by causing the pressure-compensation-function switching signal pressure not to be applied to the pressure-compensating valves <NUM> and <NUM> (Step S304). Subsequent to Step S304, it is decided whether or not an operation lever input is absent (Step S305).

In a case where -it is decided at Step S305 that an operation lever input is absent (YES), the control activation process (Step S300) is ended.

In a case where it is decided at Step S305 that an operation lever input is not absent (NO), pilot command pressures according to the amount of the operation lever input are generated at the proportional solenoid pressure-reducing valves 20a of the solenoid proportional valve unit <NUM> (Step S306), directional control valves are opened in accordance with the pilot command pressures (Step S307), and the hydraulic fluid is fed to actuators to operate the actuators (Step S308).

Subsequent to Step S308, target flow rates of actuators are computed at the target-flow-rate calculating section 21e of the controller <NUM> (Step S309), target command electric signals are computed from a target-flow-rate/electric-signal table at the output section 21j of the controller <NUM> (Step S310), and the command electric signals are output at the output section 21j of the controller <NUM> to the proportional solenoid pressure-reducing valves <NUM> and <NUM> (Step S311). Thereby, the proportional solenoid pressure-reducing valves <NUM> and <NUM> generate command pressures to the pilot variable restrictors <NUM> and <NUM> (Step S312), and the pilot-variable-restrictor openings become openings Aps according to the command pressures (Step S313). In addition, the differential pressures across the pilot variable restrictors are compensated for by the pressure-compensating valves <NUM> and <NUM> with target compensation differential pressures ΔPpc (Step S314), and the flow rates Qm of the main valves <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> and <NUM> are controlled by the pilot-variable-restrictor openings Aps and the target compensation differential pressures ΔPpc (Step S316). Subsequent to Step S316, it is decided whether or not the state where the flow rates of the hydraulic fluid that the hydraulic pumps <NUM> to <NUM> actually can deliver are lower than demanded delivery flow rates demanded for the hydraulic pumps <NUM> to <NUM> (saturation state) has occurred (Step S316).

In a case where it is decided at Step S316 that the saturation state has not occurred (NO), the control activation process (Step S300) is ended.

In a case where it is decided at Step S316 that the saturation state has occurred (YES), the target compensation differential pressures ΔPpc of the pressure-compensating valves <NUM> and <NUM> are reduced (Step S317), the flow rates Qm of the main valves <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> and <NUM> are reduced correspondingly (Step S318), and the control activation process (Step S300) is ended.

Note that the processes of the flowcharts explained with reference to <FIG> are applied to all the directional control valves, auxiliary flow rate control devices and solenoid proportional valves including those that are not illustrated.

The thus-configured hydraulic drive system <NUM> in the first embodiment is capable of operation and control like the ones mentioned below. Note that, for simplification and convenience of explanation, operation is explained by mentioning about a case where triple combined operation of the boom <NUM>, the arm <NUM> and the bucket <NUM> is performed.

When a signal to deactivate the area limiting control of the hydraulic excavator <NUM> is sent from the control activation switch <NUM> to the controller <NUM>, the controller <NUM> switches hydraulic lines in the selector valve unit <NUM> such that pilot command pressures generated via the pilot valves 18a and 18b from inputs to the operation levers 17a and 17b are caused to be applied directly to the pilot ports of directional control valves of actuators. Thereby, it becomes possible to drive each actuator in accordance with an operation amount input by an operator.

Simultaneously, the controller <NUM> sends a command to the solenoid selector valve <NUM>, and establishes communication between a line <NUM> and the line <NUM> such that the hydraulic fluid of the pilot pump <NUM> is guided to the line <NUM>. Thereby, by causing force to be applied in the direction to open the pressure-compensating valve spool, the pressure-compensating valve <NUM> fully opens the circuit, and the pressure compensation function becomes deactivated.

In this state, the relationship between the opening area Am of the main valve <NUM> of the auxiliary flow rate control device <NUM>, and the opening area Aps of the hydraulic variable restrictor valve <NUM> as a pilot variable restrictor is: <MAT> * K is a coefficient determined on the basis of the shape of the main valve <NUM>.

Therefore, when the opening area Aps is determined by the controller <NUM> driving the proportional solenoid pressure-reducing valve <NUM>, and inputting a signal pressure input to a pressure signal port 36a of the pilot variable restrictor <NUM>, the opening area Am of the main valve <NUM> can be determined in accordance with Equation <NUM>.

Thereby, for example when an operator inputs combined operation of the boom, the arm and the bucket, and, as a result, it becomes necessary to cause the delivery flow of the second hydraulic pump <NUM> to branch into the boom cylinder 204a and the arm cylinder 205a, the main valves of the auxiliary flow rate control devices are controlled to have openings determined in accordance with the operation amounts of actuators, and it becomes possible to cause the flow to branch.

Here, the opening of the main valve <NUM> is determined only on the basis of the opening area Aps without depending on the loads of cylinders. Accordingly, when the load of an actuator varies in a state in which an operator maintains an input amount of an operation lever, the differential pressure across the main valve <NUM> changes, and the flow rate of a branch flow to the actuator generated by the main valve <NUM> changes. This flow rate change is well reflected by the behavior of the actuator, an input of the operation lever is adjusted by an operator who recognizes the change, and operation as intended by the operator can be performed.

Although operation of the auxiliary flow rate control device <NUM> has been explained thus far, the other auxiliary flow rate control devices operate likewise.

When a signal to activate the area limiting control of the hydraulic excavator <NUM> is sent from the machine control switch <NUM> to the controller <NUM>, the controller <NUM> switches hydraulic lines in the selector valve unit <NUM> such that pilot command pressures generated via the pilot valves 18a and 18b from inputs to the operation levers 17a and 17b are guided to the solenoid proportional valve unit <NUM>. The signal pressures guided to the solenoid proportional valve unit <NUM> are guided again to the selector valve unit <NUM> by being controlled by solenoid valves included in the solenoid proportional valve unit <NUM>, and a command of the controller <NUM>. The signal pressures having been guided to the selector valve unit <NUM> are then caused to be applied to the pilot ports of directional control valves of actuators.

Thereby, it becomes possible to drive the actuators under the control of the controller <NUM>, and the area limiting control of the hydraulic excavator <NUM> can be performed.

Simultaneously, the controller <NUM> sends a command to the solenoid selector valve <NUM>, and interrupts the communication between the line <NUM> and the line <NUM>. Thereby, the pressure-compensating valve <NUM> stops receiving the pressure guided to the pressure signal port 35d by the line <NUM>. Accordingly, force having been applied in the direction to open the pressure-compensating valve spool stops being applied thereto, and the pressure compensation function becomes activated.

In this state, the relationship among the flow rate Qm of the main valve <NUM> of the auxiliary flow rate control device <NUM>, the target compensation differential pressure ΔPpc of the pressure-compensating valve <NUM>, and the opening area Aps of the pilot variable restrictor <NUM> is:<MAT> * L is a coefficient determined on the basis of the shape of the main valve <NUM> and a liquid type.

Therefore, when the opening area Aps is determined by the controller <NUM> driving the proportional solenoid pressure-reducing valve <NUM>, and inputting a signal pressure to the pressure signal port 36a of the pilot variable restrictor <NUM>, the flow rate Qm of the main valve <NUM> can be determined in accordance with Equation <NUM>.

Thereby, for example when an operator inputs combined operation of the boom, the arm and the bucket, and, as a result, it becomes necessary to cause the delivery flow of the second hydraulic pump to branch into the boom and the arm, the main valves of the auxiliary flow rate control devices are controlled to have demanded flow rates determined in accordance with the operation amounts of actuators, and it becomes possible to cause the flow to branch.

Here, the flow rate of the main valve <NUM> is determined on the basis of the opening area Aps without depending on the loads of cylinders. Accordingly, even when the load of an actuator varies in a state in which an operator maintains an input amount of an operation lever, the flow rate of a branch flow to the actuator generated by the main valve <NUM> does not vary, and a flow can be fed to the actuator accurately at the demanded rate. Furthermore, because the target compensation differential pressure ΔPpc includes the component of the differential pressure between the delivery pressure Ps of the second hydraulic pump <NUM> and a highest load pressure PLmax of actuators, in a case where the delivery flow rate of the second hydraulic pump becomes lower than the total of the demanded flow rates of the actuators, the flow rate that can be caused to flow with respect to an opening condition of the main valves of the auxiliary flow rate control devices decreases. Accordingly, the pressure difference between the delivery pressure Ps of the second hydraulic pump <NUM> and the highest load pressure PLmax of the actuators decreases. Thereby, ΔPpc also decreases, which results also in a decrease in the flow rate Qm of the main valve <NUM>. It should be noted however that because the amounts of decrease of ΔPpc at the auxiliary flow rate control devices <NUM> and <NUM> that limit the flow rates of the boom cylinder 204a and the arm cylinder 205a are equal to each other, the rate of branch flows can be maintained in accordance with the rate of the opening areas Aps of the main valves <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> and <NUM>.

Thereby, even in a case where the state where the flow rates that the hydraulic pumps <NUM> to <NUM> can actually deliver are lower than the demanded delivery flow rates demanded for the hydraulic pumps <NUM> to <NUM>, which state is a so-called saturation state, has occurred, the rate of branch flows to actuators can be maintained, and it becomes possible to perform automatic control without causing deterioration of the control precision of the actuators.

Although operation of the auxiliary flow rate control devices <NUM> and <NUM> has been explained thus far, the other auxiliary flow rate control devices operate likewise.

In the first embodiment, in the hydraulic excavator <NUM> including: the machine body <NUM>; the work device <NUM> attached to the machine body <NUM>; the plurality of hydraulic actuators 204a, 205a and 206a that drive the machine body <NUM> or the work device <NUM>; the hydraulic pumps <NUM> to <NUM>; the plurality of directional control valves <NUM> to <NUM>, <NUM> and <NUM> that are connected in parallel to the delivery lines of the hydraulic pumps <NUM> to <NUM>, and adjust the flow of the hydraulic fluid supplied from the hydraulic pumps <NUM> to <NUM> to the plurality of hydraulic actuators 204a, 205a and 206a; the operation levers 17a and 17b for giving an instruction to operate the plurality of hydraulic actuators 204a, 205a and 206a; the machine control switch <NUM> for giving an instruction to activate or deactivate the machine control function that prevents the work device <NUM> from going into a preset area; and the controller <NUM> that executes the machine control function in a case where the machine control function is selected via the machine control switch <NUM>, the hydraulic excavator <NUM> includes the auxiliary flow rate control devices <NUM> to <NUM> that are each arranged upstream of the plurality of directional control valves <NUM> to <NUM>, <NUM> and <NUM>, respectively, and limit the flow rate of the hydraulic fluid supplied from the hydraulic pumps <NUM> to <NUM> to the plurality of directional control valves <NUM> to <NUM>, <NUM> and <NUM> in accordance with pressure variations at the plurality of hydraulic actuators 204a, 205a and 206a, and in a case where the machine control function is cancelled via the machine control switch <NUM>, the controller <NUM> cancels the limitation of the flow rate of the hydraulic fluid supplied to the plurality of directional control valves <NUM> to <NUM>, <NUM> and <NUM>, the limitation being performed by the auxiliary flow rate control devices <NUM> to <NUM>, and in a case where the machine control function is selected via the machine control switch <NUM>, the controller <NUM> causes the auxiliary flow rate control devices <NUM> to <NUM> to limit the flow rate of the hydraulic fluid supplied to the plurality of directional control valves <NUM> to <NUM>, <NUM> and <NUM>.

In addition, the hydraulic excavator <NUM> includes: the pilot pump <NUM>; the pilot valves 18a and 18b that reduce the pressure of the hydraulic fluid supplied from the pilot pump <NUM> in accordance with operation instruction amounts from the operation levers 17a and 17b, and output the reduced pressure as operating pressures for the plurality of directional control valves <NUM> to <NUM>, <NUM> and <NUM>; the solenoid proportional valve unit <NUM> that corrects the operating pressures from the pilot valves 18a and 18b; and the selector valve unit <NUM> that switches the operating pressures from the pilot valves 18a and 18b between to be guided to the pressure signal ports of the plurality of directional control valves <NUM> to <NUM>, <NUM> and <NUM> and to be guided to the solenoid proportional valve unit <NUM>. The auxiliary flow rate control devices <NUM> to <NUM> have: the seat-shaped main valves <NUM> and <NUM> forming auxiliary variable restrictors; the control variable restrictors 31b and 34b having opening areas that change in accordance with movement amounts of the seat valve bodies of the main valves <NUM> and <NUM>; the pilot variable restrictors <NUM> and <NUM> that are arranged on the pilot lines <NUM> and <NUM> that determine movement amounts of the seat valve bodies in accordance with passing flow rates, and have openings that change in accordance with commands from the controller <NUM>; and the pilot flow rate control devices <NUM> and <NUM> that control passing flow rates of the pilot variable restrictors <NUM> and <NUM> in accordance with commands from the controller <NUM>. In a case where the machine control function is cancelled via the machine control switch <NUM>, the controller <NUM> performs switch control of the selector valve unit <NUM> such that the operating pressures from the pilot valves 18a and 18b are guided directly to the plurality of directional control valves <NUM> to <NUM>, <NUM> and <NUM>. In a case where the machine control function is selected via the machine control switch, the controller <NUM> executes the machine control function by performing switch control of the selector valve unit <NUM> such that the operating pressures from the pilot valves 18a and 18b are guided to the plurality of directional control valves <NUM> to <NUM>, <NUM> and <NUM> via the solenoid proportional valve unit <NUM>, and controlling the solenoid proportional valve unit <NUM> such that pilot pressure signals guided from the selector valve unit <NUM> are corrected, and limits passing flow rates of the auxiliary flow rate control devices <NUM> to <NUM> by limiting the passing flow rates of the pilot variable restrictors <NUM> and <NUM> in accordance with pressure variations at the plurality of hydraulic actuators 204a, 205a and 206a.

In addition, the pilot variable restrictors <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM> include hydraulic variable restrictor valves. The hydraulic excavator <NUM> further includes the proportional solenoid pressure-reducing valves <NUM> and <NUM> that reduce the pressure of the hydraulic fluid supplied from the pilot pump <NUM> in accordance with commands from the controller <NUM>, and outputs the reduced pressure as operating pressures for the hydraulic variable restrictors <NUM> and <NUM>. The pilot flow rate control devices <NUM> and <NUM> include the hydraulic pressure-compensating valves <NUM> and <NUM> arranged upstream of the pilot variable restrictors <NUM> and <NUM> on the pilot lines <NUM> and <NUM>. Upstream pressures of the pilot variable restrictors <NUM> and <NUM> are guided to a first pressure signal port 35b that drives the pressure-compensating valves <NUM> and <NUM> in closing directions. A highest load pressure of the plurality of hydraulic actuators 204a, 205a and 206a is guided to the second pressure signal ports 32a and 35a that drive the pressure-compensating valves <NUM> and <NUM> in closing directions. Downstream pressures of the pilot variable restrictors <NUM> and <NUM> are guided to third pressure signal ports 32c and 35c that drive the pressure-compensating valves <NUM> and <NUM> in opening directions. The delivery pressures of the hydraulic pumps <NUM> to <NUM> are guided to the fourth pressure signal ports 32e and 35e that drive the pressure-compensating valves <NUM> and <NUM> in the opening directions. The fifth pressure signal ports 32d and 35d that drive the pressure-compensating valves <NUM> and <NUM> in the opening directions, and the delivery line <NUM> of the pilot pump <NUM> are connected to each other via the solenoid selector valve <NUM> that is opened and closed in accordance with a command from the controller <NUM>. In a case where the machine control function is cancelled via the machine control switch <NUM>, the controller <NUM> keeps the pressure-compensating valves <NUM> and <NUM> at full-open positions, and disables operation of the pressure-compensating valves <NUM> and <NUM> by opening the solenoid selector valve <NUM>, and causing the delivery pressure of the pilot pump <NUM> to be applied to the fifth pressure signal ports 32d and 35d. In a case where the machine control function is cancelled via the machine control switch <NUM>, the controller <NUM> enables the operation of the pressure-compensating valves <NUM> and <NUM> by closing the solenoid selector valve <NUM>, and causing the delivery pressure of the pilot pump <NUM> not to be applied to the fifth pressure signal ports 32d and 35d.

According to the thus-configured first embodiment, in a case where the machine control function is cancelled, the flow rate control of pilot lines <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM> is deactivated, and the auxiliary flow rate control devices <NUM> to <NUM> maintain openings according to an input amount of operation by an operator, and generates branch flows to a plurality of actuators. In this case, it becomes easier for the operator to feel changes of actuator operation according to the load variations of the actuators, thus the operability of the hydraulic excavator <NUM> at the time of operator operation is ensured. On the other hand, in a case where the machine control function is selected, the auxiliary flow rate control devices <NUM> to <NUM> can supply flows to the actuators highly responsively and surely at rates in accordance with target flow rates according to commands by the controller <NUM>, without depending on the load variations of the actuators, thus the automatic control precision of the actuators can be improved. Thereby, in each of two types of operation mode at the time of manual operation by an operator or at the time of automatic control by the controller, switching of hydraulic-system characteristics suited for the operation mode is performed, thus different types of performance demanded in those operation modes can both be realized.

<FIG> and <FIG> are circuit diagrams of a hydraulic drive system in a second embodiment of the present invention.

As illustrated in <FIG> and <FIG>, the configuration of a hydraulic drive system 300A in the second embodiment is almost the same as the hydraulic drive system <NUM> in the first embodiment (illustrated in <FIG> and <FIG>), but is different in the following respects.

In the auxiliary flow rate control device <NUM>, a line 94a, a line 94b and a line 94c that are formed around the main valve <NUM> form a pilot line <NUM>, the line 94a connecting a third pressure chamber 34e with the hydraulic variable restrictor <NUM>, the line 94b connecting the hydraulic variable restrictor <NUM> with a pressure-compensating valve <NUM>, the line 94c connecting the pressure-compensating valve <NUM> with a line <NUM>.

On a side of the pressure-compensating valve <NUM> where force is applied in the direction to cause the pressure-compensating valve spool to open the hydraulic line, a pressure signal port 88b receives a pressure of the line 94b, and a pressure signal port 88c receives a function switching signal pressure transmitted from the solenoid selector valve <NUM> via the line <NUM>. On a side of the pressure-compensating valve <NUM> where force is applied in the direction to cause the pressure-compensating valve spool to close the hydraulic line, a pressure signal port 88a receives a highest load pressure that the high-pressure selecting valve <NUM> selects from a load pressure of the bucket cylinder 206a sensed from the bucket directional control valve <NUM>, a load pressure of the boom cylinder 204a sensed from the first boom directional control valve <NUM>, the second boom directional control valve <NUM> and the third boom directional control valve <NUM>, a load pressure of the arm cylinder 205a sensed from the first arm directional control valve <NUM> and the second arm directional control valve <NUM>, and the load pressure of the swing directional control valve <NUM>.

Note that although some illustrations are omitted for simplification and convenience of explanation, all of the auxiliary flow rate control devices <NUM> to <NUM>, and surrounding equipment, lines and wires have the same configurations. In addition, the calculation process of the controller <NUM> is similar to that in the first embodiment (illustrated in <FIG>, <FIG> and <FIG>).

In the second embodiment, the pilot variable restrictors <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM> include hydraulic variable restrictor valves. The hydraulic excavator <NUM> further includes the proportional solenoid pressure-reducing valves <NUM> and <NUM> that reduce the pressure of the hydraulic fluid supplied from the pilot pump <NUM> in accordance with commands from the controller <NUM>, and outputs the reduced pressure as operating pressures for the hydraulic variable restrictor valves <NUM> and <NUM>. The pilot flow rate control devices <NUM> and <NUM> include the hydraulic pressure-compensating valves <NUM> and <NUM> arranged downstream of the pilot variable restrictors <NUM> and <NUM> on the pilot lines <NUM> and <NUM>. A highest load pressure of the plurality of hydraulic actuators 204a, 205a and 206a is guided to first pressure signal ports 84a and 88a that drive the pressure-compensating valves <NUM> and <NUM> in closing directions. Downstream pressures of the pilot variable restrictors <NUM> and <NUM> are guided to second pressure signal ports 84b and 88b that drive the pressure-compensating valves <NUM> and <NUM> in opening directions. The third pressure signal ports 84c and 88c that drive the pressure-compensating valves <NUM> and <NUM> in the opening directions, and the delivery line <NUM> of the pilot pump <NUM> are connected to each other via the solenoid selector valve <NUM> that is opened and closed in accordance with a command from the controller <NUM>. In a case where the machine control function is cancelled via the machine control switch <NUM>, the controller <NUM> keeps the pressure-compensating valves <NUM> and <NUM> at full-open positions, and disables operation of the pressure-compensating valves <NUM> and <NUM> by opening the solenoid selector valve <NUM>, and causing the delivery pressure of the pilot pump <NUM> to be applied to the third pressure signal ports 84c and 88c. In a case where the machine control function is selected via the machine control switch <NUM>, the controller <NUM> enables the operation of the pressure-compensating valves <NUM> and <NUM> by closing the solenoid selector valve <NUM>, and causing the delivery pressure of the pilot pump <NUM> not to be applied to the third pressure signal ports 84c and 88c.

According to the thus-configured second embodiment, effects similar to those in the first embodiment can be attained, and the hydraulic drive system can have a simpler configuration because fewer pressure signals are caused to be applied to the pressure-compensating valves of the auxiliary flow rate control devices <NUM> to <NUM>.

<FIG> and <FIG> are circuit diagrams of a hydraulic drive system in a third embodiment of the present invention.

As illustrated in <FIG> and <FIG>, the configuration of a hydraulic drive system 400B in the third embodiment is almost the same as the hydraulic drive system <NUM> in the first embodiment (illustrated in <FIG> and <FIG>), but is different in the following respects.

The line <NUM> connected to the second hydraulic pump is provided with a pressure sensor <NUM>.

In the auxiliary flow rate control device <NUM>, a line 111a connecting the third pressure chamber 34e with a solenoid proportional restrictor valve <NUM>, a line 111b connecting the solenoid proportional restrictor valve <NUM> with the line <NUM> form the pilot line <NUM>.

The main valve <NUM> is provided with a stroke sensor <NUM>.

The line <NUM> is provided with a pressure sensor <NUM>.

The controller <NUM> receives inputs of output values of the pressure sensors <NUM>, <NUM> and <NUM> (and output values of pressure sensors attached to the other auxiliary flow rate control devices), and output values of the stroke sensors <NUM> and <NUM> (and output values of stroke sensors attached to the main valves of the other auxiliary flow rate control devices). The controller <NUM> outputs commands to solenoids 102a and 104a of the solenoid variable restrictor valves <NUM> and <NUM> (and solenoids of solenoid variable restrictor valves of the other auxiliary flow rate control devices).

<FIG> is a flowchart illustrating a calculation process of the controller <NUM> in the third embodiment. In <FIG>, the third embodiment is different from the first embodiment (illustrated in <FIG>) in that a control deactivation process S200A is included instead of the control deactivation process S200, and a control activation process S300A is included instead of the control activation process S300.

<FIG> is a flowchart illustrating details of Step S200A (control deactivation process). In <FIG>, the third embodiment is different from the first embodiment (illustrated in <FIG>) in that Steps S202 to S204 are not included, and Steps S210A and S213A are included instead of Steps S210 and S213. At Step S210A, command electric signals to the pilot variable restrictors <NUM> and <NUM> are not output. At Step S213A, command electric signals to the pilot variable restrictors <NUM> and <NUM> are output in accordance with input amounts of the operation levers 17a and 17b.

<FIG> is a flowchart illustrating details of Step S300A (control activation process). In <FIG>, the third embodiment is different from the first embodiment (illustrated in <FIG>) in that Steps S302 to S304 and S314 are not included, Steps S310A to S312A are included instead of Steps S310 to S312, and Steps S317A to S324A are included instead of Steps S317 and S318.

Subsequent to Step S309, the current flow rate of the actuator is computed at the current-flow-rate calculating section 21i of the controller <NUM> (Step S310A), a target command electric signal is computed at the output section 21j of the controller <NUM> such that the difference between the target flow rate and the current flow rate decreases (Step S311A), and command electric signals are output at the output section 21j of the controller <NUM> to the pilot variable restrictors <NUM> and <NUM> (Step S312A).

In a case where it is decided at Step S316 that the saturation state has occurred (YES), a differential pressure ΔPsat between a pump pressure Ps and a highest load pressure PLmax in the saturation state (current) is computed at the pressure-state deciding section 21f of the controller <NUM> (Step S317A), the rate of decrease in the differential pressure is computed from a differential pressure ΔPnonsat between the pump pressure Ps and a highest load pressure PLmax in the non-saturation state, and ΔPsat at the differential-pressure rate-of-decrease calculating section <NUM> of the controller <NUM> (Step S318A), a corrected target flow rate is computed at the corrected-target-flow-rate calculating section <NUM> of the controller <NUM> by multiplying the target flow rate by the rate of decrease in the differential pressure (Step S319A), the current flow rate of the actuator is computed at the current-flow-rate calculating section 21i of the controller <NUM> (Step S320A), a target command electric signal is computed at the output section 21j of the controller <NUM> such that the difference between the corrected target flow rate and the current flow rate decreases (Step S321A), and command electric signals are output at the output section 21j of the controller <NUM> to the pilot variable restrictors <NUM> and <NUM> (Step S322A). Thereby, the pilot-variable-restrictor openings become the openings Aps according to the command electric signals (Step S323A), and the flow rates Qm of the main valves <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM> are controlled (Step S324A).

The thus-configured hydraulic drive system 400B in the third embodiment is capable of operation and control like the ones mentioned below. Note that, for simplification and convenience of explanation, operation is explained by mentioning about a case where triple combined operation of the boom <NUM>, the arm <NUM> and the bucket <NUM> is performed.

When a signal to deactivate the area limiting control of the hydraulic excavator <NUM> is sent from the machine control switch <NUM> to the controller <NUM>, the controller <NUM> switches hydraulic lines in the selector valve unit <NUM> such that pilot command pressures generated via the pilot valves 18a and 18b from inputs to the operation levers 17a and 17b are caused to be applied directly to the pilot ports of directional control valves of actuators. Thereby, it becomes possible to drive the actuators in accordance with an operation amount input by an operator.

The controller <NUM> computes target displacements of main valves on the basis of operation amounts of the boom <NUM>, the arm <NUM> and the bucket <NUM>, simultaneously acquires the current displacement of the main valve <NUM> from an output value of the stroke sensor <NUM> of the main valve <NUM> of the auxiliary flow rate control device <NUM> corresponding to the first arm directional control valve <NUM>, for example, and controls the opening of the solenoid proportional restrictor valve <NUM> such that the difference between the target displacement and the current displacement decreases.

Here, the displacement of the main valve <NUM> is determined only on the basis of input amount of operation by an operator without depending on the loads of cylinders. Accordingly, when the load of an actuator varies in a state in which an operator maintains an input amount of an operation lever, the differential pressure across the main valve changes, and the flow rate of a branch flow to the actuator generated by the main valve changes. This flow rate change is well reflected by the behavior of the actuator, an input of the operation lever is adjusted by an operator who recognizes the change, and operation as intended by the operator can be performed.

When a signal to select the machine control function of the hydraulic excavator <NUM> is sent from the machine control switch <NUM> to the controller <NUM>, the controller <NUM> switches hydraulic lines in the selector valve unit <NUM> such that pilot command pressures generated via the pilot valves 18a and 18b from inputs to the operation levers 17a and 17b are guided to the solenoid proportional valve unit <NUM>. The signal pressures guided to the solenoid proportional valve unit <NUM> are guided again to the selector valve unit <NUM> by being controlled by solenoid valves included in the solenoid proportional valve unit <NUM>, and a command of the controller <NUM>. The signal pressures having been guided to the selector valve unit <NUM> are guided to the pilot ports of directional control valves of actuators.

The controller <NUM> computes a target flow rate of an auxiliary variable restrictor on the basis of the operation amounts of the boom <NUM>, the arm <NUM> and the bucket <NUM>, and the operation state of the machine body acquired from each pressure sensor or stroke sensor, simultaneously acquires the current flow rate of the main valve <NUM> by using an output value of the stroke sensor <NUM> of the main valve <NUM>, and the differential pressure across the main valve <NUM> acquired from the pressure sensors <NUM> and <NUM>, and controls the opening of the solenoid proportional restrictor valve <NUM> such that the difference between the target flow rate and the current flow rate decreases.

In the third embodiment, the pilot variable restrictors <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM> include solenoid variable restrictor valves having openings that change in accordance with commands from the controller <NUM>. The hydraulic excavator <NUM> further includes: the first pressure sensor <NUM> provided on the delivery line of the hydraulic pump <NUM>; the second pressure sensors <NUM> and <NUM> provided on the hydraulic lines connecting the directional control valves <NUM> to <NUM>, <NUM> and <NUM> with the main valves <NUM> and <NUM>; and the valve displacement sensors <NUM> and <NUM> provided to the main valves <NUM> and <NUM>. In a case where the machine control function is cancelled via the machine control switch <NUM>, the controller <NUM> computes target displacements of the main valves <NUM> and <NUM> on the basis of operation instruction amounts from the operation levers 17a and 17b, and controls the openings of the solenoid variable restrictor valves <NUM> and <NUM> such that the differences between current displacements of the main valves <NUM> and <NUM> sensed by the valve displacement sensors <NUM> and <NUM>, and the target displacements decrease. In a case where the machine control function is selected via the machine control switch <NUM>, the controller <NUM> computes target flow rates of the main valves <NUM> and <NUM> on the basis of operation instruction amounts from the operation levers 17a and 17b, acquires the openings of the main valves <NUM> and <NUM> on the basis of displacements of the main valves <NUM> and <NUM> sensed by the valve displacement sensors <NUM> and <NUM>, and the opening characteristics of the main valves <NUM> and <NUM>, computes the current flow rates of the main valves <NUM> and <NUM> on the basis of the openings, and differential pressures across the main valves <NUM> and <NUM> sensed by the first pressure sensor <NUM>, and the second pressure sensors <NUM> and <NUM>, and controls the openings of the solenoid variable restrictor valves <NUM> and <NUM> such that the differences between the target flow rates and the current flow rates decrease.

According to the thus-configured third embodiment, in addition to effects similar to those in the first embodiment, the following effects can be attained.

The control of the auxiliary flow rate control devices <NUM> to <NUM> can be performed as electronic control, and switching of the flow rate control characteristics of the auxiliary flow rate control devices <NUM> to <NUM> is possible at the time of operator operation and at the time of automatic control in accordance with commands of the controller <NUM> to the solenoid variable restrictor valves <NUM> and <NUM>. Accordingly, it is not necessary to provide separate function switching signal means or circuit, and the hydraulic drive system can have a simpler configuration. In addition, by computing the passing flow rates of the main valves <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM> from displacements of and the pressures across the main valves, and performing feedback control of main-valve displacements, it is possible to correct errors caused by disturbance or the like, and supply flows to actuators more accurately at target rates.

<FIG> and <FIG> are circuit diagrams of a hydraulic drive system in a fourth embodiment of the present invention.

As illustrated in <FIG> and <FIG>, the configuration of a hydraulic drive system 400C in the fourth embodiment is almost the same as the hydraulic drive system 400B in the third embodiment (illustrated in <FIG> and <FIG>), but is different in the following respects.

The main valve <NUM> of the auxiliary flow rate control device <NUM> corresponding to the first arm directional control valve <NUM> is not provided with a stroke sensor.

The solenoid variable restrictor valve <NUM> of the auxiliary flow rate control device <NUM> is provided with a stroke sensor <NUM>.

The line 111a connecting the solenoid variable restrictor valve <NUM> with the third pressure chamber 34e (or a feedback variable restrictor 34b) is provided with a pressure sensor <NUM>.

The controller <NUM> receives inputs of an output value of the stroke sensor <NUM> (and output values of stroke sensors provided to solenoid variable restrictor valves of auxiliary flow rate control devices), and the pressure sensor <NUM> (and pressure sensors provided to the pilot lines of the auxiliary flow rate control devices). The controller <NUM> outputs commands to the solenoid variable restrictor valves <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM>.

Note that the calculation process of the controller <NUM> is similar to that in the third embodiment (illustrated in <FIG>, <FIG> and <FIG>).

In the fourth embodiment, the pilot variable restrictors <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM> include solenoid variable restrictor valves having openings that change in accordance with commands from the controller <NUM>. The hydraulic excavator <NUM> further includes: the first pressure sensor <NUM> provided on the delivery line of the hydraulic pump <NUM>; the second pressure sensors <NUM> and <NUM> provided on the hydraulic lines connecting the directional control valves <NUM> to <NUM>, <NUM> and <NUM> with the main valves <NUM> and <NUM>; the third pressure sensors <NUM> and <NUM> provided on the hydraulic lines connecting the solenoid variable restrictor valves <NUM> and <NUM> with the control variable restrictors 31b and 34b; and the valve displacement sensors <NUM> and <NUM> provided to the solenoid variable restrictor valves <NUM> and <NUM>. In a case where the machine control function is cancelled via the machine control switch <NUM>, the controller <NUM> computes target openings of the solenoid variable restrictor valves <NUM> and <NUM> on the basis of operation instruction amounts from the operation levers 17a and 17b, computes the current openings of the solenoid variable restrictor valves <NUM> and <NUM> on the basis of displacements of the solenoid variable restrictor valves <NUM> and <NUM> sensed by the valve displacement sensors <NUM> and <NUM>, and the opening characteristics of the solenoid variable restrictor valves <NUM> and <NUM>, and controls command values given to the solenoid variable restrictor valves <NUM> and <NUM> such that the differences between the target openings and the current openings decrease. In a case where the machine control function is selected via the machine control switch <NUM>, the controller <NUM> computes target flow rates of the main valves <NUM> and <NUM> on the basis of operation instruction amounts from the operation levers 17a and 17b, computes target openings of the main valves <NUM> and <NUM> on the basis of the target flow rates of the main valves <NUM> and <NUM>, and differential pressures across the main valves <NUM> and <NUM> sensed by the first pressure sensor <NUM>, and the second pressure sensors <NUM> and <NUM>, acquires target openings of the solenoid variable restrictor valves <NUM> and <NUM> on the basis of the relationship between the opening characteristics of the main valves <NUM> and <NUM>, and the opening characteristics of the solenoid variable restrictor valves, computes target flow rates of the solenoid variable restrictor valves <NUM> and <NUM> on the basis of the target openings of the solenoid variable restrictor valves <NUM> and <NUM>, and differential pressures across the solenoid variable restrictor valves <NUM> and <NUM> sensed by the second pressure sensors <NUM> and <NUM>, and the third pressure sensors <NUM> and <NUM>, computes the current flow rates of the solenoid variable restrictor valves <NUM> and <NUM> on the basis of the openings of and the differential pressures across the solenoid variable restrictor valves <NUM> and <NUM>, and controls the openings of the solenoid variable restrictor valves <NUM> and <NUM> such that the differences between the target flow rates and the current flow rates decrease.

According to the thus-configured fourth embodiment, effects similar to those in the third embodiment can be attained, and the hydraulic drive system can have a simpler configuration because displacement sensing means such as stroke sensors are not attached to the main valves <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM>.

<FIG> and <FIG> are circuit diagrams of a hydraulic drive system in a fifth embodiment of the present invention.

As illustrated in <FIG> and <FIG>, the configuration of a hydraulic drive system 300D in the fifth embodiment is almost the same as the configuration of the hydraulic drive system 400C in the fourth embodiment (illustrated in <FIG> and <FIG>), but is different in the following respects.

The solenoid variable restrictor valve <NUM> of the auxiliary flow rate control device <NUM> corresponding to the first arm directional control valve <NUM> is not provided with a stroke sensor.

The controller <NUM> outputs commands to the solenoid variable restrictor valves <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM>.

In the fifth embodiment, the pilot variable restrictors <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM> include solenoid variable restrictor valves having openings that change in accordance with commands from the controller <NUM>. The hydraulic excavator <NUM> further includes: the first pressure sensor <NUM> provided on the delivery line of the hydraulic pump <NUM>; the second pressure sensors <NUM> and <NUM> provided on the hydraulic lines connecting the directional control valves <NUM> to <NUM>, <NUM> and <NUM> with the main valves <NUM> and <NUM>; and the third pressure sensors <NUM> and <NUM> provided on the hydraulic lines connecting the control variable restrictors 31b and 34b with the solenoid variable restrictor valves <NUM> and <NUM>. In a case where the machine control function is cancelled via the machine control switch <NUM>, the controller <NUM> computes target openings of the solenoid variable restrictor valves <NUM> and <NUM> on the basis of operation instruction amounts from the operation levers 17a and 17b, acquires the current openings of the solenoid variable restrictor valves <NUM> and <NUM> on the basis of the opening characteristics of the solenoid variable restrictor valves <NUM> and <NUM>, and command values to the solenoid variable restrictor valves <NUM> and <NUM>, and controls the openings of the solenoid variable restrictor valves <NUM> and <NUM> such that the differences between the target openings and the current openings of the solenoid variable restrictor valves <NUM> and <NUM> decrease. In a case where the machine control function is selected via the machine control switch <NUM>, the controller <NUM> computes target flow rates of the main valves <NUM> and <NUM> on the basis of operation instruction amounts from the operation levers 17a and 17b, computes target openings of the main valves <NUM> and <NUM> on the basis of the target flow rates of the main valves <NUM> and <NUM>, and differential pressures across the main valves <NUM> and <NUM> sensed by the first pressure sensor <NUM>, and the second pressure sensors <NUM> and <NUM>, acquires target openings of the solenoid variable restrictor valves <NUM> and <NUM> on the basis of the relationship between the opening characteristics of the main valves <NUM> and <NUM>, and the opening characteristics of the solenoid variable restrictor valves <NUM> and <NUM>, computes target flow rates of the solenoid variable restrictor valves <NUM> and <NUM> on the basis of the target openings, and differential pressures across the solenoid variable restrictor valves <NUM> and <NUM> sensed by the second pressure sensors <NUM> and <NUM>, and the third pressure sensors <NUM> and <NUM>, acquires the openings of the solenoid variable restrictor valves <NUM> and <NUM> on the basis of the opening characteristics of the solenoid variable restrictor valves <NUM> and <NUM>, and command values to the solenoid variable restrictor valves <NUM> and <NUM>, computes the current flow rates of the solenoid variable restrictor valves <NUM> and <NUM> on the basis of the openings, and differential pressures across the solenoid variable restrictor valves <NUM> and <NUM> sensed by the second pressure sensors <NUM> and <NUM>, and the third pressure sensors <NUM> and <NUM>, and controls the openings of the solenoid variable restrictor valves <NUM> and <NUM> such that the differences between the target flow rates and the current flow rates of the solenoid variable restrictor valves <NUM> and <NUM> decrease.

According to the thus-configured fifth embodiment, effects similar to those in the fourth embodiment can be attained, and the hydraulic drive system can have a simpler configuration because displacement sensing means such as stroke sensors are attached to none of the solenoid variable restrictor valves <NUM> and <NUM> and the main valves <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM>.

<FIG> and <FIG> are circuit diagrams of a hydraulic drive system in a sixth embodiment of the present invention.

As illustrated in <FIG> and <FIG>, the configuration of a hydraulic drive system 400E in the fifth embodiment is almost the same as the hydraulic drive system 400B in the third embodiment (illustrated in <FIG> and <FIG>), but is different in the following respects.

The pilot line of the auxiliary flow rate control device <NUM> corresponding to the first arm directional control valve <NUM> is provided with a hydraulic variable restrictor valve <NUM> instead of the solenoid proportional restrictor valve <NUM> in the third embodiment (illustrated in <FIG>).

A line <NUM> connecting the pressure signal port of the hydraulic variable restrictor valve <NUM> with the delivery port of the pilot pump <NUM> is provided with the proportional solenoid pressure-reducing valve <NUM>.

The controller <NUM> outputs a command to a solenoid 38a of the proportional solenoid pressure-reducing valve <NUM>.

Note that although some illustrations are omitted for simplification and convenience of explanation, all of the auxiliary flow rate control devices <NUM> to <NUM>, and surrounding equipment, lines and wires have the same configurations. In addition, the calculation process of the controller <NUM> is similar to that in the third embodiment (illustrated in <FIG>, <FIG> and <FIG>).

In the sixth embodiment, the pilot variable restrictors <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM> include hydraulic variable restrictor valves. The hydraulic excavator <NUM> further includes: the first pressure sensor <NUM> provided on the delivery line of the hydraulic pump <NUM>; the second pressure sensors <NUM> and <NUM> provided on the hydraulic lines connecting the directional control valves <NUM> to <NUM>, <NUM> and <NUM> with the main valves <NUM> and <NUM>; the valve displacement sensors <NUM> and <NUM> provided to the main valves <NUM> and <NUM>; and the proportional solenoid pressure-reducing valves <NUM> and <NUM> that reduce the pressure of the hydraulic fluid supplied from the pilot pump <NUM> in accordance with commands from the controller <NUM>, and output the reduced pressure as operating pressures for the hydraulic variable restrictors <NUM> and <NUM>. In a case where the machine control function is cancelled via the machine control switch <NUM>, the controller <NUM> computes target displacements of the main valves <NUM> and <NUM> on the basis of operation instruction amounts from the operation levers 17a and 17b, and controls the openings of the hydraulic variable restrictor valves <NUM> and <NUM> via the proportional solenoid pressure-reducing valves <NUM> and <NUM> such that the differences between the target displacements of the main valves <NUM> and <NUM>, and current displacements of the main valves <NUM> and <NUM> sensed by the valve displacement sensors <NUM> and <NUM> decrease. In a case where the machine control function is selected via the machine control switch <NUM>, the controller <NUM> computes target flow rates of the main valves <NUM> and <NUM> on the basis of operation instruction amounts from the operation levers 17a and 17b, acquires the current openings of the main valves <NUM> and <NUM> on the basis of the opening characteristics of the main valves <NUM> and <NUM>, and current displacements of the main valves <NUM> and <NUM> sensed by the valve displacement sensors <NUM> and <NUM>, computes the current flow rates of the main valves <NUM> and <NUM> on the basis of the current openings, and differential pressures across the main valves <NUM> and <NUM> sensed by the first pressure sensor <NUM>, and the second pressure sensors <NUM> and <NUM>, and controls the openings of the hydraulic variable restrictor valves <NUM> and <NUM> via the proportional solenoid pressure-reducing valves <NUM> and <NUM> such that the differences between the target flow rates and the current flow rates decrease.

According to the thus-configured sixth embodiment, in addition to effects similar to those in the third embodiment, the following effects can be attained.

The flow rate control of the pilot lines <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM> can be performed indirectly as electronic control, and switching of the flow rate control characteristics of the auxiliary flow rate control devices <NUM> to <NUM> is possible at the time of operator operation and at the time of automatic control in accordance with commands of the controller <NUM> to the proportional solenoid pressure-reducing valves <NUM> and <NUM>. Accordingly, it is not necessary to provide separate function switching signal means or circuit, and the hydraulic drive system can have a simpler configuration.

In addition, by computing the passing flow rates of the main valves <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM> from displacements of and pressures across the main valves <NUM> and <NUM>, and performing feedback control of main-valve displacements, it is possible to correct errors caused by disturbance or the like, and supply flows to actuators more accurately at target rates.

<FIG> and <FIG> are circuit diagrams of a hydraulic drive system in a seventh embodiment of the present invention.

As illustrated in <FIG> and <FIG>, the configuration of a hydraulic drive system 400F in the seventh embodiment is almost the same as the configuration of the hydraulic drive system 400C in the fourth embodiment (illustrated in <FIG> and <FIG>), but is different in the following respects.

The pilot line <NUM> of the auxiliary flow rate control device <NUM> corresponding to the first arm directional control valve <NUM> is provided with the hydraulic variable restrictor valve <NUM> instead of the solenoid proportional restrictor valve <NUM> in the fourth embodiment (illustrated in <FIG>).

The line <NUM> connecting the pressure signal port of the hydraulic variable restrictor valve <NUM> with the delivery port of the pilot pump <NUM> is provided with the proportional solenoid pressure-reducing valve <NUM>.

The controller <NUM> outputs a command to the solenoid 38a of the proportional solenoid pressure-reducing valve <NUM>.

In the seventh embodiment, the pilot variable restrictors <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM> include hydraulic variable restrictor valves. The hydraulic excavator <NUM> further includes: the first pressure sensor <NUM> provided on the delivery lines of the hydraulic pumps <NUM> to <NUM>; the second pressure sensors <NUM> and <NUM> provided on the hydraulic lines connecting the directional control valves <NUM> to <NUM>, <NUM> and <NUM> with the main valves <NUM> and <NUM>; the third pressure sensors <NUM> and <NUM> provided on the hydraulic lines connecting the hydraulic variable restrictor valves <NUM> and <NUM> with the control variable restrictors 31b and 34b; the valve displacement sensors <NUM> and <NUM> provided to the hydraulic variable restrictor valves <NUM> and <NUM>; and the proportional solenoid pressure-reducing valves <NUM> and <NUM> that reduce the pressure of the hydraulic fluid supplied from the pilot pump <NUM> in accordance with commands from the controller <NUM>, and output the reduced pressure as operating pressures for the hydraulic variable restrictor valves <NUM> and <NUM>. In a case where the machine control function is cancelled via the machine control switch <NUM>, the controller <NUM> computes target openings of the hydraulic variable restrictor valves <NUM> and <NUM> on the basis of operation instruction amounts from the operation levers 17a and 17b, acquires the current openings of the hydraulic variable restrictor valves <NUM> and <NUM> on the basis of the opening characteristics of the hydraulic variable restrictor valves <NUM> and <NUM>, and displacements of the hydraulic variable restrictor valves <NUM> and <NUM> sensed by the valve displacement sensors <NUM> and <NUM>, and controls the openings of the hydraulic variable restrictor valves <NUM> and <NUM> via the proportional solenoid pressure-reducing valves <NUM> and <NUM> such that the differences between the target openings and the current openings decrease. In a case where the machine control function is selected via the machine control switch <NUM>, the controller <NUM> computes target flow rates of the main valves <NUM> and <NUM> on the basis of operation instruction amounts from the operation levers 17a and 17b, computes target openings of the main valves <NUM> and <NUM> on the basis of the target flow rates of the main valves <NUM> and <NUM>, and differential pressures across the main valves <NUM> and <NUM> sensed by the first pressure sensor <NUM>, and the second pressure sensors <NUM> and <NUM>, acquires target openings of the hydraulic variable restrictor valves <NUM> and <NUM> on the basis of the relationship between the opening characteristics of the main valves <NUM> and <NUM>, and the opening characteristics of the hydraulic variable restrictor valves <NUM> and <NUM>, computes target flow rates of the hydraulic variable restrictor valves <NUM> and <NUM> on the basis of the target openings of the hydraulic variable restrictor valves <NUM> and <NUM>, and differential pressures across the hydraulic variable restrictor valves <NUM> and <NUM> sensed by the second pressure sensors <NUM> and <NUM>, and the third pressure sensors <NUM> and <NUM>, acquires the openings of the hydraulic variable restrictor valves <NUM> and <NUM> on the basis of the opening characteristics of the hydraulic variable restrictor valves <NUM> and <NUM>, and displacements of the hydraulic variable restrictor valves <NUM> and <NUM> sensed by the valve displacement sensors <NUM> and <NUM>, computes the current flow rates of the hydraulic variable restrictor valves on the basis of the openings of and the differential pressures across the hydraulic variable restrictor valves, and controls the openings of the hydraulic variable restrictor valves via the proportional solenoid pressure-reducing valves such that the differences between the target flow rates and the current flow rates decrease.

According to the thus-configured seventh embodiment, effects similar to those in the sixth embodiment can be attained, and the hydraulic drive system can have a simpler configuration because displacement sensing means such as stroke sensors are not attached to the main valves <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM>.

<FIG> and <FIG> are circuit diagrams of a hydraulic drive system in an eighth embodiment of the present invention.

As illustrated in <FIG> and <FIG>, the configuration of a hydraulic drive system <NUM> in the eighth embodiment is almost the same as the configuration of the hydraulic drive system 400D in the fifth embodiment (illustrated in <FIG> and <FIG>), but is different in the following respects.

The pilot line <NUM> of the auxiliary flow rate control device <NUM> corresponding to the first arm directional control valve <NUM> is provided with the hydraulic variable restrictor <NUM> instead of the solenoid proportional restrictor valve <NUM> in the fifth embodiment (illustrated in <FIG>).

The line <NUM> connecting the pressure signal port of the hydraulic variable restrictor <NUM> with the delivery port of the pilot pump <NUM> is provided with- the proportional solenoid pressure-reducing valve <NUM>.

In the eighth embodiment, the pilot variable restrictors <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM> include hydraulic variable restrictor valves. A hydraulic excavator <NUM> further includes: the first pressure sensor <NUM> provided on the delivery line of the hydraulic pump <NUM>; the second pressure sensors <NUM> and <NUM> provided on the hydraulic lines connecting the directional control valves <NUM> to <NUM>, <NUM> and <NUM> with the main valves <NUM> and <NUM>; the third pressure sensors <NUM> and <NUM> provided on the hydraulic lines connecting the hydraulic variable restrictor valves <NUM> and <NUM> with the control variable restrictors 31b and 34b; and the proportional solenoid pressure-reducing valves <NUM> and <NUM> that reduce the pressure of the hydraulic fluid supplied from the pilot pump <NUM> in accordance with commands from the controller <NUM>, and output the reduced pressure as operating pressures for the hydraulic variable restrictor valves <NUM> and <NUM>. In a case where the machine control function is cancelled via the machine control switch <NUM>, the controller computes target openings of the hydraulic variable restrictor valves <NUM> and <NUM> on the basis of operation instruction amounts from the operation levers 17a and 17b, acquires the current openings of the hydraulic variable restrictor valves <NUM> and <NUM> on the basis of the opening characteristics of the hydraulic variable restrictor valves <NUM> and <NUM>, and operating pressures from the proportional solenoid pressure-reducing valves <NUM> and <NUM>, and controls the openings of the hydraulic variable restrictor valves <NUM> and <NUM> via the proportional solenoid pressure-reducing valves <NUM> and <NUM> such that the differences between the target openings and the current openings of the hydraulic variable restrictor valves <NUM> and <NUM> decrease. In a case where the machine control function is selected via the machine control switch <NUM>, the controller computes target flow rates of the main valves <NUM> and <NUM> on the basis of operation instruction amounts from the operation levers 17a and 17b, computes target openings of the main valves <NUM> and <NUM> on the basis of differential pressures across the main valves <NUM> and <NUM> sensed by the first pressure sensor <NUM>, and the second pressure sensors <NUM> and <NUM>, and the target flow rates of the main valves <NUM> and <NUM>, acquires target openings of the hydraulic variable restrictor valves <NUM> and <NUM> on the basis of -the opening characteristics of the main valves <NUM> and <NUM> in relation to the openings of the hydraulic variable restrictor valves <NUM> and <NUM>, and the target openings of the main valves <NUM> and <NUM>, computes target flow rates of the hydraulic variable restrictor valves <NUM> and <NUM> on the basis of the target openings of the hydraulic variable restrictor valves <NUM> and <NUM>, and differential pressures across the hydraulic variable restrictor valves <NUM> and <NUM> sensed by the second pressure sensors <NUM> and <NUM>, and the third pressure sensors <NUM> and <NUM>, acquires the openings of the hydraulic variable restrictor valves <NUM> and <NUM> on the basis of the opening characteristics of the hydraulic variable restrictor valves <NUM> and <NUM>, and operating pressures outputted from the proportional solenoid pressure-reducing valves <NUM> and <NUM>, computes the current flow rates of the hydraulic variable restrictor valves <NUM> and <NUM> on the basis of the openings of and the differential pressures across the hydraulic variable restrictor valves <NUM> and <NUM>, and controls the openings of the hydraulic variable restrictor valves <NUM> and <NUM> via the proportional solenoid pressure-reducing valves <NUM> and <NUM> such that the differences between the target flow rates and the current flow rates decrease.

According to the thus-configured eighth embodiment, effects similar to those in the seventh embodiment can be attained, and the hydraulic drive system can have a simpler configuration because displacement sensing means such as stroke sensors are attached to none of the main valves <NUM> and <NUM>, and the hydraulic variable restrictor valves <NUM> and <NUM> of the auxiliary flow rate control devices <NUM> to <NUM>. Ninth Embodiment.

As a ninth embodiment of the present invention, an application example of the third to eighth embodiments are explained.

The configuration of a hydraulic drive system in the ninth embodiment is almost the same as the configurations of the third to eighth embodiments.

The hydraulic excavator <NUM> according to the ninth embodiment further includes: the regulators 1a, 1b, 1c, 2a, 2b, 2c, 3a and 3b that perform horse-power control of the hydraulic pumps <NUM> to <NUM>; and the fourth pressure sensors 71a, 71b, 72a, 72b, 73a and 73b that sense the load pressures of the plurality of hydraulic actuators 204a, 205a and 206a. In a case where the machine control function is selected via the machine control switch <NUM>, and saturation has occurred in which the delivery flow rate of the hydraulic pump <NUM> decreases due to an effect of horse-power control along with an increase in the load pressures of the plurality of hydraulic actuators 204a, 205a and 206a, the controller <NUM> computes the differential pressure between the delivery pressure of the hydraulic pump <NUM> sensed by the first pressure sensor <NUM>, and a highest load pressure of the plurality of hydraulic actuators 204a, 205a and 206a sensed by the fourth pressure sensors 71a, 71b, 72a, 72b, 73a and 73b, computes a rate of decrease from a differential pressure before the occurrence of the saturation that has been acquired in advance, and reduces a target flow rate of the main valves of the auxiliary flow rate control devices <NUM> to <NUM> in accordance with the rate of decrease.

According to the thus-configured ninth embodiment, effects similar to those in the third to eighth embodiments can be attained, and even in a case where the saturation state has occurred, the rates of branch flows to actuators can be maintained, and it becomes possible to perform automatic control without causing deterioration of the control precision of the actuators.

Although embodiments of the present invention have been mentioned in detail thus far, the present invention is not limited to the embodiments described above, but includes various modification examples within the scope of the invention as defined by the claims. For example, the embodiments described above illustrate aspects in which, in a case where the machine control function is cancelled via the machine control switch, the selector valve units are controlled such that the operating pressures from the pilot valves are guided directly to the plurality of directional control valves, and in a case where the machine control function is selected via the machine control switch, the selector valve units are controlled such that the operating pressures from the pilot valves are guided to the plurality of directional control valves via the solenoid proportional valve units. However, aspects of the present invention are not particularly limited as long as objects of the present invention can be attained within the scope of the invention as defined by the claims. For example, in a possible aspect, in both the case where the machine control function is cancelled, and the case where the machine control function is selected, pilot pressures are controlled via electric levers, that is, selector valve units are not provided.

Claim 1:
A work machine comprising:
a machine body (<NUM>);
a work device (<NUM>) attached to the machine body (<NUM>);
a plurality of hydraulic actuators (204a, 205a, 206a) that drive the machine body (<NUM>) or the work device (<NUM>);
a hydraulic pump (<NUM> - <NUM>);
a plurality of directional control valves (<NUM> - <NUM>, <NUM>, <NUM>) that are connected in parallel to a delivery line of the hydraulic pump (<NUM> - <NUM>), and adjust a flow of a hydraulic fluid supplied from the hydraulic pump (<NUM> - <NUM>) to the plurality of hydraulic actuators (204a, 205a, 206a);
an operation lever (17a, 17b) for giving an instruction to operate the plurality of hydraulic actuators (204a, 205a, 206a);
a controller (<NUM>) that executes a machine control function that prevents the work device (<NUM>) from going into a preset area, and
auxiliary flow rate control devices (<NUM> - <NUM>) that are arranged upstream of the plurality of directional control valves (<NUM> - <NUM>, <NUM>, <NUM>), and limit the flow rate of the hydraulic fluid supplied from the hydraulic pump (<NUM> - <NUM>) to the plurality of directional control valves (<NUM> - <NUM>, <NUM>, <NUM>) in accordance with pressure variations at the plurality of hydraulic actuators (204a, 205a, 206a), wherein
the controller (<NUM>) is configured to cause the auxiliary flow rate control devices (<NUM> - <NUM>) to limit the flow rate of the hydraulic fluid supplied to the plurality of directional control valves (<NUM> - <NUM>, <NUM>, <NUM>),
characterized in that
the work machine comprises a machine control switch (<NUM>) for giving an instruction to activate or deactivate the machine control function, and
the controller (<NUM>) is configured to,
in a case where the machine control function is cancelled via the machine control switch (<NUM>), cancel limitation of the flow rate of the hydraulic fluid supplied to the plurality of directional control valves (<NUM> - <NUM>, <NUM>, <NUM>), the limitation being performed by the auxiliary flow rate control devices (<NUM> - <NUM>), and
in a case where the machine control function is selected via the machine control switch (<NUM>), cause the auxiliary flow rate control devices (<NUM> - <NUM>) to limit the flow rate of the hydraulic fluid supplied to the plurality of directional control valves (<NUM> - <NUM>, <NUM>, <NUM>), thereby executing the machine control function.