Patent ID: 12221769

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of a work machine according to the present invention will be described with reference to the drawings. In the description of the drawings, identical elements are denoted by identical reference signs, and repeated description thereof will be omitted. Although the following description illustrates an example in which the work machine is a hydraulic excavator, the present invention is not limited thereto, and is also applicable to work machines other than hydraulic excavators. Further, in the following description, the directions and positions indicated by upper, lower, right, left, front, or rear are based on the state in which the hydraulic excavator is used in the ordinary way, that is, a traveling body touches the ground.

First Embodiment

FIG.1is a side view illustrating a hydraulic excavator according to a first embodiment. A hydraulic excavator1according to the present embodiment includes a traveling body2that travels with crawler belts provided on its right and left side portions driven, and a swivel body3provided above the traveling body2in a swivellable manner. The swivel body3includes an operator's cab4, an engine room5, a counterweight6, and a work implement7. The operator's cab4is provided in the left side portion of the swivel body3. The engine room5is provided behind the operator's cab4. The counterweight6is provided behind the engine room5, that is, in the rearmost portion of the swivel body3.

The work implement7includes a boom8, an arm9, a bucket10, a boom cylinder11afor driving the boom8, an arm cylinder11bfor driving the arm9, and a bucket cylinder11cfor driving the bucket10. The proximal end of the boom8is rotatably attached to the front portion of the swivel body3via a boom pin. The proximal end of the arm9is rotatably attached to the distal end of the boom8via an arm pin. The proximal end of the bucket10is rotatably attached to the distal end of the arm9via a bucket pin.

Each of the boom cylinder11a, the arm cylinder11b, and the bucket cylinder11cis a hydraulic actuator driven with pressure oil. Thus, in the following description, the boom cylinder11ais referred to as a “hydraulic actuator11a,” the arm cylinder11bis referred to as a “hydraulic actuator11b,” and the bucket cylinder11cis referred to as a “hydraulic actuator11c.”

The swivel body3has a swivel motor11ddisposed in its center (seeFIG.4). When the swivel motor11dis driven, the swivel body3rotates with respect to the traveling body2. In addition, the traveling body2has a right travel motor11eand a left travel motor11fdisposed therein (seeFIG.4). When the travel motors are driven, the right and left crawler belts are driven. Accordingly, the traveling body2can move forward or backward. Each of the swivel motor11d, the right travel motor11e, and the left travel motor11fis a hydraulic actuator that is driven with pressure oil. Thus, in the following description, the swivel motor11dis referred to as a “hydraulic actuator11d,” the right travel motor11eis referred to as a “hydraulic actuator11e,” and the left travel motor11fis referred to as a “hydraulic actuator11f.”

The engine room5has disposed therein an engine16, a main hydraulic pump17, and a pilot hydraulic pump18(seeFIG.2). Each of the main hydraulic pump17and the pilot hydraulic pump18is driven by the engine (i.e., a prime mover)16. It should be noted that each of the main hydraulic pump17and the pilot hydraulic pump18may also be driven by an electric motor (i.e., a prime mover).

FIG.2is a configuration diagram illustrating a system of the hydraulic excavator according to the first embodiment. As illustrated inFIG.2, the hydraulic actuators11ato11fare driven with pressure oil that has been discharged from the main hydraulic pump17and further supplied through flow rate control valves25ato25f, respectively. The flow rate control valves25ato25fare adapted to control the flow rate of pressure oil to be supplied from the main hydraulic pump17to the hydraulic actuators11ato11f, respectively, and are driven with control pilot pressures output from an operating device14.

The main hydraulic pump17and the pilot hydraulic pump18are variable-displacement hydraulic pumps driven by the engine16. The displacement (i.e., pump tilt) of each of the main hydraulic pump17and the pilot hydraulic pump18is controlled based on a control command from a controller15. More specifically, a control signal from the controller15is sent to a regulator17a, and then, the regulator17acontrols the tilt of the main hydraulic pump17, thereby adjusting the discharge flow rate of the main hydraulic pump17. Similarly, a control signal from the controller15is sent to a regulator18a, and then, the regulator18acontrols the tilt of the pilot hydraulic pump18, thereby adjusting the discharge flow rate of the pilot hydraulic pump18. The main hydraulic pump17supplies pressure oil to the flow rate control valves25ato25f, and the pilot hydraulic pump18supplies pilot pressure oil to the operating device14.

The operating device14includes hydraulic pilot levers that are adapted to reduce the pressure of pilot pressure oil supplied from the pilot hydraulic pump18in accordance with the operation amounts of the pilot levers, and then output control pilot pressures to the flow rate control valves25ato25f, respectively. Each hydraulic pilot lever has attached thereto an operation amount detection device, which will be described in detail later. The operation amount detection device detects the operation amount of the operating device14, and outputs the detection result to the controller15.

The controller15computes a control command for each of the flow rate control valves25ato25ffrom each operation amount output from the operating device14based on the detection result of each operation amount detection device, and computes the control amount for each of the main hydraulic pump17and the pilot hydraulic pump18based on the control command for each of the flow rate control valves25ato25fand the number of revolutions of the engine16output from the engine, and then outputs the computed control amount.

FIG.3is a diagram illustrating a hydraulic circuit of the hydraulic excavator according to the first embodiment. As illustrated inFIG.3, the operating device14includes a boom operating lever22a, an arm operating lever22b, a bucket operating lever22c, a swivel operating lever22d, a right-travel operating lever22e, and a left-travel operating lever22f. The boom operating lever22ahas attached thereto a boom operation amount detection device23afor detecting its operation amount. The arm operating lever22bhas attached thereto an arm operation amount detection device23bfor detecting its operation amount. The bucket operating lever22chas attached thereto a bucket operation amount detection device23cfor detecting its operation amount. The swivel operating lever22dhas attached thereto a swivel operation amount detection device23dfor detecting its operation amount. The right-travel operating lever22ehas attached thereto a right-travel operation amount detection device23efor detecting its operation amount. The left-travel operating lever22fhas attached thereto a left-travel operation amount detection device23ffor detecting its operation amount. Each of the operation amount detection devices23ato23foutputs its detection result to the controller15. It should be noted that each of the operation amount detection devices23ato23fmay be a device, such as a potentiometer or a stroke sensor, that electrically measures the driven amount of each of the operating levers22ato22f, and may also be a pressure sensor that detects a control pilot pressure generated as a result of operating each of the operating levers22ato22f.

Though not illustrated, each of the operating levers22ato22fis provided with a pilot valve. The pilot valve is adapted to reduce the pressure of pilot pressure oil supplied from the pilot hydraulic pump18in accordance with the operation direction and the operation amount of each of the operating levers22ato22f, and output a control pilot pressure to each of the flow rate control valves25ato25f.

More specifically, the boom operating lever22aoutputs a boom lowering control pilot pressure24aand a boom raising control pilot pressure24b, the arm operating lever22boutputs an arm dump control pilot pressure24cand an arm crowd control pilot pressure24d, the bucket operating lever22coutputs a bucket dump control pilot pressure24eand a bucket crowd control pilot pressure24f, the swivel operating lever22doutputs a right-swivel control pilot pressure24gand a left-swivel control pilot pressure24h, the right-travel operating lever22eoutputs a right-travel forward movement control pilot pressure24iand a right-travel backward movement control pilot pressure24j, and the left-travel operating lever22foutputs a left-travel forward movement control pilot pressure24kand a left-travel backward movement control pilot pressure24l.

In addition, a relief valve21is provided in the discharge oil passage of the pilot hydraulic pump18. The relief valve21is adapted to prevent the pressure of pilot pressure oil from increasing to greater than or equal to a preset pressure of the relief valve21.

FIG.4is a diagram for illustrating a hydraulic circuit of the hydraulic actuators and the flow rate control valves. As described above, the hydraulic actuators11ato11fare driven with pressure oil that has been discharged from the main hydraulic pump17and further supplied through the flow rate control valves25ato25f, respectively. Among the flow rate control valves25ato25f, the flow rate control valve25ais a boom flow rate control valve, the flow rate control valve25bis an arm flow rate control valve, the flow rate control valve25cis a bucket flow rate control valve, the flow rate control valve25dis a swivel flow rate control valve, the flow rate control valve25eis a right-travel flow rate control valve, and the flow rate control valve25fis a left-travel flow rate control valve.

That is, the boom flow rate control valve25acontrols the flow rate of pressure oil to be supplied to the hydraulic actuator (i.e., the boom cylinder)11a, the arm flow rate control valve25bcontrols the flow rate of pressure oil to be supplied to the hydraulic actuator (i.e., the arm cylinder)11b, the bucket flow rate control valve25ccontrols the flow rate of pressure oil to be supplied to the hydraulic actuator (i.e., the bucket cylinder)11c, the swivel flow rate control valve25dcontrols the flow rate of pressure oil to be supplied to the hydraulic actuator (i.e., the swivel motor)11d, the right-travel flow rate control valve25econtrols the flow rate of pressure oil to be supplied to the hydraulic actuator (i.e., the right-travel motor)11e, and the left-travel flow rate control valve25fcontrols the flow rate of pressure oil to be supplied to the hydraulic actuator (i.e., the left travel motor)11f.

For example, the boom flow rate control valve25ais driven with the boom lowering control pilot pressure24aor the boom raising control pilot pressure24boutput from the operating device14. For example, when the boom lowering control pilot pressure24aacts on the boom flow rate control valve25a, the boom flow rate control valve25ais driven to the right inFIG.4. This allows the pressure oil supplied from the main hydraulic pump17to be supplied to the rod chamber side of the boom cylinder11aand allows oil on the bottom chamber side of the boom cylinder11ato be discharged to a tank. Consequently, the boom cylinder11aoperates in the retracting direction, and the boom8operates in the downward direction.

Meanwhile, when the boom raising control pilot pressure24bacts on the boom flow rate control valve25a, the boom flow rate control valve25ais driven to the left inFIG.4. This allows the pressure oil supplied from the main hydraulic pump17to be supplied to the bottom chamber side of the boom cylinder11a, and allows oil on the rod chamber side of the boom cylinder11ato be discharged to the tank. Accordingly, the boom cylinder11aoperates in the extending direction, and the boom8operates in the upward direction.

FIG.5is a block diagram illustrating the controller related to the control of the pilot hydraulic pump. As illustrated inFIG.5, the controller15includes a flow rate control valve command computing unit39, a requested pilot flow rate computing unit29, and a target pump displacement computing unit30. The flow rate control valve command computing unit39computes a control command for each of the flow rate control valves25ato25fbased on the operation amount output from each of the operating levers22ato22f, and outputs the computed control command. In the present embodiment, the operating device14includes hydraulic pilot levers. Therefore, in practice, a control command output to each of the flow rate control valves25ato25fis a pilot pressure generated by each pilot valve. The flow rate control valve command computing unit39estimates the actually generated pilot pressure based on the operation amount of the operating device14.

The requested pilot flow rate computing unit29computes a requested pilot flow rate for the pilot hydraulic pump18from the control commands for the respective flow rate control valves25ato25f. That is, the requested pilot flow rate computing unit29obtains a requested pilot flow rate determined in accordance with the control commands for the respective flow rate control valves25ato25f. Meanwhile, the target pump displacement computing unit30computes the target pump displacement of the pilot hydraulic pump18by dividing the requested pilot flow rate output from the requested pilot flow rate computing unit29by the number of revolutions of the engine, and further outputs a control command for attaining the computed target pump displacement.

FIG.6is a diagram for illustrating computation of the requested pilot flow rate computing unit. As illustrated inFIG.6, the requested pilot flow rate computing unit29computes a requested pilot flow rate for each of the flow rate control valves25ato25from a control command for each of the flow rate control valves25ato25fbased on a conversion table, and determines the sum of the value of the requested pilot flow rate and a value, which is obtained by passing the requested pilot flow rate through a high-pass filter and multiplying the filtered value by a constant number, thereby temporarily increasing the requested pilot flow rate only while each of the flow rate control valves25ato25fstarts to move.

Then, the requested pilot flow rate computing unit29selects the maximum value between the requested pilot flow rate and the filtered value thereof, thereby preventing a filtering process from being applied when the requested pilot flow rate falls. After that, the requested pilot flow rate computing unit29determines the sum of the requested pilot flow rates of the flow rate control valves25ato25f, and then outputs the sum of the determined sum and a preset standby flow rate as a requested pilot flow rate of the pilot hydraulic pump.

Herein, the standby flow rate means a pilot flow rate consumed per flow rate control valve of the flow rate control valves25ato25fthat control the flow rate of pressure oil to be supplied to the hydraulic actuators11ato11f, respectively. It should be noted that the hydraulic excavator1according to the present embodiment includes a plurality of hydraulic actuators (i.e., six hydraulic actuators11ato11f) as described above, and the standby flow rate is set for the hydraulic actuators11ato11fwhen they are sequentially driven in a time-series manner.

For example, when an operator moves the boom8, the arm9, and the bucket10in turn to load earth and sand on the hydraulic excavator, for example, the operator sequentially drives the hydraulic actuator (i.e., the boom cylinder)11afor driving the boom8, the hydraulic actuator (i.e., the arm cylinder)11bfor driving the arm9, and the hydraulic actuator (i.e., the bucket cylinder)11cfor driving the bucket10. At this time, a standby flow rate is set for each of the hydraulic actuators11a,11b, and11c(seeFIG.8). The standby flow rate set for each of the hydraulic actuators11a,11b, and11cmay be either the same or different.

Meanwhile, when the traveling body2is moved forward or backward, the hydraulic actuator (i.e., the right-travel motor)11eand the hydraulic actuator (i.e., the left travel motor)11fare driven concurrently. At this time, one standby flow rate is set for the hydraulic actuators11eand11fthat have received drive commands.

FIG.7is a graph illustrating the relationship between a control command for each flow rate control valve and a requested pilot flow rate. As illustrated inFIG.7, the requested pilot flow rate is set such that it monotonically increases with respect to the control command for each flow rate control valve. The relationship is determined by the properties of each hydraulic pilot lever and the properties of each flow rate control valve. The relationship may differ for each hydraulic actuator, and need not be a monotonical increase.

FIG.8is a graph illustrating a change in the discharge flow rate of the pilot hydraulic pump with time. InFIG.8, the alternate long and short dash line indicates the sum of the requested pilot flow rates before subjected to dynamic flow rate compensation, the dashed line indicates the sum of the requested pilot flow rates after subjected to dynamic flow rate compensation, and the solid line indicates the discharge flow rate of the pilot hydraulic pump. In the example illustrated inFIG.8, operator's work of sequentially driving the boom8, the arm9, and the bucket10to load earth and sand on the hydraulic excavator is supposed, for example.

As illustrated inFIG.8, in the present embodiment, only while the flow rate control valves25ato25fstart to move, the requested pilot flow rate is temporarily higher than the sum of the requested pilot flow rates corresponding to the control commands for the respective flow rate control valves25ato25f(i.e., the sum of the requested pilot flow rates before subjected to dynamic flow rate compensation as indicated by the alternate long and short dash line) due to the filtering process performed. Thus, a command for dynamic flow rate compensation is output (i.e., the sum of the requested pilot flow rates after subjected to dynamic flow rate compensation as indicated by the dashed line). In the present embodiment, a flow rate, which is obtained by adding a preset standby flow rate to the sum of the requested pilot flow rates after subjected to dynamic flow rate compensation, is output as the discharge flow rate of the pilot hydraulic pump (see the portion of the solid line).

That is, in the hydraulic excavator1according to the present embodiment, the controller15controls the discharge flow rate of the pilot hydraulic pump18such that it becomes equal to the sum of the requested pilot flow rates determined in accordance with the control commands for the respective flow rate control valves25ato25fand a preset standby flow rate. Therefore, since the pilot hydraulic pump18supplies a pilot flow rate that is higher than the pilot flow rate necessary for driving the hydraulic actuators11ato11fby the standby flow rate, it is possible to reduce the energy consumption of the pilot hydraulic pump18, and prevent response delay of the hydraulic actuators11ato11fas well as temporal deceleration or stop of the hydraulic actuators11ato11f, which would otherwise occur due to an insufficient supply of the pilot flow rate, and thus maintain excellent operability.

Second Embodiment

Hereinafter, a second embodiment of a work machine will be described with reference toFIGS.9and10. The hydraulic excavator of the present embodiment differs from that of the aforementioned first embodiment in that the pilot hydraulic pump is driven by an electric motor and in the structure of the controller. The other structures are similar to those of the first embodiment. Thus, overlapped description will be omitted.

FIG.9is a configuration diagram illustrating a system of a hydraulic excavator according to the second embodiment. In the present embodiment, the pilot hydraulic pump18is a fixed displacement hydraulic pump driven by an electric motor31. The electric motor31is driven by a battery32, and the number of revolutions of the electric motor31is controlled in accordance with a control command from a controller15A. The electric motor31and the battery32are disposed in the engine room5, for example.

FIG.10is a block diagram illustrating the controller related to the control of the pilot hydraulic pump. As illustrated inFIG.10, the controller15A includes the flow rate control valve command computing unit39, the requested pilot flow rate computing unit29, and a target electric motor rotation computing unit33. The flow rate control valve command computing unit39and the requested pilot flow rate computing unit29are the same as those described in the first embodiment. Meanwhile, the target electric motor rotation computing unit33computes the target number of revolutions of the electric motor by dividing the requested pilot flow rate output from the requested pilot flow rate computing unit29by the pump displacement of the pilot hydraulic pump18, and outputs a control command.

In addition, the controller15A controls the discharge flow rate of the pilot hydraulic pump18such that it becomes equal to the sum of the requested pilot flow rates determined in accordance with the control commands for the respective flow rate control valves25ato25fand a standby flow rate as in the first embodiment.

With the hydraulic excavator according to the present embodiment, it is possible to reduce energy consumed by the pilot hydraulic pump and maintain excellent operability as in the aforementioned first embodiment.

Third Embodiment

Hereinafter, a third embodiment of a work machine will be described with reference toFIGS.11to15. The hydraulic excavator of the present embodiment differs from that of the aforementioned first embodiment in that the operating device includes electric levers and the hydraulic excavator further includes a proportional solenoid valve. The other structures are similar to those of the first embodiment. Thus, overlapped description will be omitted.

FIG.11is a configuration diagram illustrating a system of the hydraulic excavator according to the third embodiment. An operating device14A of the present embodiment includes electric levers including a boom operating lever, an arm operating lever, a bucket operating lever, a swivel operating lever, a right-travel operating lever, and a left-travel operating lever. The boom operating lever outputs a boom lowering operation amount and a boom raising operation amount to a controller15B. The arm operating lever outputs an arm dump operation amount and an arm crowd operation amount to the controller15B. The bucket operating lever outputs a bucket dump operation amount and a bucket crowd operation amount to the controller15B. The swivel operating lever outputs a right-swivel operation amount and a left-swivel operation amount to the controller15B. The right-travel operating lever outputs a right-travel forward movement operation amount and a right-travel backward movement operation amount to the controller15B. The left-travel operating lever outputs a left-travel forward movement operation amount and a left-travel backward movement operation amount to the controller15B.

The hydraulic excavator according to the present embodiment further includes a proportional solenoid valve (i.e., a pressure-reducing valve)34. The proportional solenoid valve34is adapted to reduce the pressure of pressure oil supplied from the pilot hydraulic pump18based on a control command from the controller15B, and generate a pilot pressure for driving each of the flow rate control valves25ato25f, and then output the pilot pressure to each of the flow rate control valves25ato25f.

FIG.12is a diagram illustrating a hydraulic circuit of the hydraulic excavator according to the third embodiment. As illustrated inFIG.12, the proportional solenoid valve34includes a boom lowering proportional solenoid valve35a, a boom raising proportional solenoid valve35b, an arm dump proportional solenoid valve35c, an arm crowd proportional solenoid valve35d, a bucket dump proportional solenoid valve35e, a bucket crowd proportional solenoid valve35f, a right-swivel proportional solenoid valve35g, a left-swivel proportional solenoid valve35h, a right-travel forward movement proportional solenoid valve35i, a right-travel backward movement proportional solenoid valve35j, a left-travel forward movement proportional solenoid valve35k, and a left-travel backward movement proportional solenoid valve35l.

The boom lowering proportional solenoid valve35aoutputs a boom lowering control pilot pressure37ato the boom flow rate control valve25a, and the boom raising proportional solenoid valve35boutputs a boom raising control pilot pressure37bto the boom flow rate control valve25a. The arm dump proportional solenoid valve35coutputs an arm dump control pilot pressure37cto the arm flow rate control valve25b, and the arm crowd proportional solenoid valve35doutputs an arm crowd control pilot pressure37dto the arm flow rate control valve25b. The bucket dump proportional solenoid valve35eoutputs a bucket dump control pilot pressure37eto the bucket flow rate control valve25c, and the bucket crowd proportional solenoid valve35foutputs a bucket crowd control pilot pressure37fto the bucket flow rate control valve25c.

The right-swivel proportional solenoid valve35goutputs a right-swivel control pilot pressure37gto the swivel flow rate control valve25d, and the left-swivel proportional solenoid valve35houtputs a left-swivel control pilot pressure37hto the swivel flow rate control valve25d. The right-travel forward movement proportional solenoid valve35ioutputs a right-travel forward movement control pilot pressure37ito the right-travel flow rate control valve25e, and the right-travel backward movement proportional solenoid valve35joutputs a right-travel backward movement control pilot pressure37jto the right-travel flow rate control valve25e. The left-travel forward movement proportional solenoid valve35koutputs a left-travel forward movement control pilot pressure37kto the left-travel flow rate control valve25f, and the left-travel backward movement proportional solenoid valve35loutputs a left-travel backward movement control pilot pressure37lto the left-travel flow rate control valve25f.

FIG.13is a block diagram illustrating the controller related to the control of the pilot hydraulic pump. As illustrated inFIG.13, the controller15B includes a maximum flow rate computing unit36, the flow rate control valve command computing unit39, the requested pilot flow rate computing unit29, the target pump displacement computing unit30, and a flow rate control valve command limiting unit38.

The maximum flow rate computing unit36computes the maximum flow rate of the pilot hydraulic pump18based on the number of revolutions of the engine and the maximum displacement of the pilot hydraulic pump18, and outputs the computation result to the requested pilot flow rate computing unit29. The flow rate control valve command computing unit39computes control commands for the respective flow rate control valves25ato25fin accordance with the operation amounts of the respective operating levers output from the operating device14A, and outputs the computed control commands. The requested pilot flow rate computing unit29outputs the requested pilot flow rate of the pilot hydraulic pump18and7the limited control amounts for the respective control valves25ato25fbased on the maximum flow rate of the pilot hydraulic pump18output from the maximum flow rate computing unit36and the flow rate control valve control commands output from the flow rate control valve command computing unit39. It should be noted that the details of the requested pilot flow rate computing unit29will be described later.

The target pump displacement computing unit30computes the target displacement of the pilot hydraulic pump18based on the number of revolutions of the engine and the requested pilot flow rate output from the requested pilot flow rate computing unit29, and outputs a control command to the pilot hydraulic pump18.

The flow rate control valve command limiting unit38computes a control command for the proportional solenoid valve34based on the control amount for each of the flow rate control valves25ato25foutput from the flow rate control valve command computing unit39and the limited control amount for each of the flow rate control valves25ato25foutput from the requested pilot flow rate computing unit29, and outputs the control command. Specifically, the flow rate control valve command limiting unit38selects the smaller one between the control amount for each of the flow rate control valves25ato25foutput from the flow rate control valve command computing unit39and the limited control amount for each of the flow rate control valves25ato25foutput from the requested pilot flow rate computing unit29, and outputs a proportional solenoid valve command that is necessary for the control amount for each of the flow rate control valves25ato25f.

FIG.14is a flowchart illustrating a control process of the controller. First, in step S1, the requested pilot flow rate computing unit29computes a requested pilot flow rate to be consumed by each of the flow rate control valves25ato25ffrom a control command for each of the flow rate control valves25ato25foutput from the flow rate control valve command computing unit39. The method of computing the requested pilot flow rate from the control command for each of the flow rate control valves25ato25fis similar to that described in the first embodiment.

In step S2following step S1, the controller15B determines that the hydraulic actuators are ON if their requested pilot flow rates are greater than zero, and determines that the hydraulic actuators are OFF if their requested pilot flow rates are zero. In step S3following step S2, the controller15B sets the operation numbers allocated to the hydraulic actuators, which have been determined to be OFF, to zero.

In step S4following step S3, the controller15B sequentially renumbers, starting with 1, the operation numbers for the hydraulic actuators, which have been determined to be ON in the current operation and have had operation numbers other than zero in the previous computation, in ascending order of previous operation number. In step S5following step S4, the controller15B sequentially renumbers the operation numbers for the hydraulic actuators, which have been determined to be ON and have had an operation number of zero in the previous computation, starting with the number following the last number allocated in step S4.

In step S6following step S5, if there is a plurality of hydraulic actuators that has been determined to be ON and has had an operation number of zero in the previous computation, the controller15B allocates the operation numbers in accordance with a preset priority of the hydraulic actuators. Then, the controller15B selects a hydraulic actuator with the smallest operation number among the allocated operation numbers.

In step S7following step S6, the controller15B determines if the requested pilot flow rate corresponding to the selected hydraulic actuator is less than or equal to the maximum flow rate of the pilot hydraulic pump output from the maximum flow rate computing unit36. If the requested pilot flow rate of the selected hydraulic actuator is less than or equal to the maximum flow rate, the controller15B outputs the requested pilot flow rate of the selected hydraulic actuator as it is (see step S8). Meanwhile, if the requested pilot flow rate of the selected hydraulic actuator is greater than the maximum flow rate, the controller15B outputs the maximum flow rate as the requested pilot flow rate of the selected hydraulic actuator (see step S9).

In step S10following step S8or step S9, the controller15B subtracts the output requested pilot flow rate from the maximum flow rate, and updates the maximum flow rate for use in the next computation with the subtraction result. In step S11following step S10, the controller15B determines if there is any hydraulic actuator for which a requested pilot flow rate has not been determined. If there is a hydraulic actuator for which a requested pilot flow rate has not been determined, the control process proceeds to step S12. In step S12, the controller15B selects a hydraulic actuator with the second smallest operation number. After that, the control process proceeds to step S7so that the aforementioned control process of from step S7is repeated. Meanwhile, if it is determined that there is no hydraulic actuator for which a requested pilot flow rate has not been determined in step S11, the series of the control processes ends.

According to the aforementioned control process of the controller15B, it is possible to compute the requested pilot flow rate for each of the hydraulic actuators11ato11fbased on the control amount for each of the flow rate control valves25ato25f, and to, even if a plurality of hydraulic actuators is requesting a pilot flow rate at a time, limit a requested pilot flow rate of a hydraulic actuator that has received a drive command at a later timing.

In addition, the controller15B outputs the sum of the requested pilot flow rates of the hydraulic actuators computed in accordance with the control flow and a preset standby flow rate as the requested pilot flow rate of the pilot hydraulic pump. Further, the controller15B computes the limited control amount for each flow rate control valve by converting the computed requested pilot flow rate of each hydraulic actuator into the control amount for each flow rate control valve used in step S1in terms of the requested pilot flow rate, and outputs the computed limited control amount.

FIG.15is a graph illustrating a change in the discharge flow rate of the pilot hydraulic pump with time. The alternate long and short dash line, the dashed line, and the solid line inFIG.15indicate the same values as those inFIG.8. As illustrated inFIG.15, when the discharge flow rate of the pilot hydraulic pump is less than or equal to the maximum flow rate of the pilot hydraulic pump, the discharge flow rate is output such that it becomes equal to the sum of the requested pilot flow rates corresponding to the control amounts for the respective flow rate control valves (i.e., the requested pilot flow rates determined in accordance with the control commands for the respective flow rate control valves) and a standby flow rate. Meanwhile, when the discharge flow rate of the pilot hydraulic pump is over the maximum flow rate of the pilot hydraulic pump, the maximum flow rate of the pilot hydraulic pump is output as the discharge flow rate of the pilot hydraulic pump. In addition, when the sum of the requested pilot flow rates corresponding to the control amounts for the respective flow rate control valves is over the maximum flow rate of the pilot hydraulic pump, the sum of the pilot flow rates consumed by the respective flow rate control valves is limited such that it becomes equal to the maximum flow rate of the pilot hydraulic pump.

With the hydraulic excavator according to the present embodiment, it is possible to obtain the effects of reducing energy consumed by the pilot hydraulic pump and maintaining excellent operability as in the aforementioned first embodiment, and further obtain the following operational advantage. That is, when a plurality of hydraulic actuators is sequentially controlled, even if a pilot flow rate consumed by a proportional solenoid valve has exceeded the maximum flow rate of the pilot hydraulic pump, the outputs of the other proportional solenoid valves that have received control commands at later timings are limited, that is, the requested pilot flow rates of the hydraulic actuators that have received drive commands at later timings are limited. Thus, it is possible to prevent deceleration or stop of the hydraulic actuators, which would otherwise occur due to an insufficient supply of the pilot flow rate, and allow the hydraulic actuators, which have received drive commands so far, to continue operation.

That is, when a requested pilot flow rate that is necessary for driving a hydraulic actuator has exceeded the maximum flow rate of the pilot hydraulic pump, it is possible to, by limiting the outputs of the proportional solenoid valves other than the proportional solenoid valve that had been operating before the requested pilot flow rate has exceeded the maximum flow rate of the pilot hydraulic pump, prevent deceleration or stop of the hydraulic actuator that has been operating so far, and thus maintain excellent operability.

Fourth Embodiment

Hereinafter, a fourth embodiment of a work machine will be described with reference toFIGS.16and17. The hydraulic excavator of the present embodiment differs from that of the aforementioned first embodiment in that the pilot hydraulic pump is driven by an electric motor and the hydraulic excavator further includes a proportional solenoid valve. The other structures are similar to those of the first embodiment. Thus, overlapped description will be omitted.

FIG.16is a configuration diagram illustrating a system of the hydraulic excavator according to the fourth embodiment. In the present embodiment, the pilot hydraulic pump18is a fixed displacement hydraulic pump driven by the electric motor31. The electric motor31is driven by the battery32, and the number of revolutions of the electric motor31is controlled in accordance with a control command from a controller15C. The electric motor31and the battery32are disposed in the engine room5, for example.

The hydraulic excavator according to the present embodiment further includes the proportional solenoid valve34. The proportional solenoid valve34is adapted to reduce the pressure of pressure oil supplied from the pilot hydraulic pump18based on a control command from the controller15C, and generate a pilot pressure for driving each of the flow rate control valves25ato25f, and then output the pilot pressure to each of the flow rate control valves25ato25f. It should be noted that the configuration of the proportional solenoid valve34is similar to that described in the third embodiment.

FIG.17is a block diagram illustrating the controller related to the control of the pilot hydraulic pump. As illustrated inFIG.17, the controller15C includes the maximum flow rate computing unit36, the flow rate control valve command computing unit39, the requested pilot flow rate computing unit29, the target electric motor rotation computing unit33, and the flow rate control valve command limiting unit38. The maximum flow rate computing unit36computes the maximum flow rate of the pilot hydraulic pump18from the displacement of the pilot hydraulic pump18and the maximum number of revolutions of the electric motor31, and outputs the computed maximum flow rate.

The target electric motor rotation computing unit33computes the target number of revolutions of the electric motor31from the displacement of the pilot hydraulic pump18and the requested pilot flow rate of the pilot hydraulic pump18output from the requested pilot flow rate computing unit29, and outputs a control command. The configurations of the requested pilot flow rate computing unit29, the flow rate control valve command computing unit39, and the flow rate control valve command limiting unit38are similar to those described in the third embodiment.

With the hydraulic excavator according to the present embodiment, it is possible to obtain the effects of reducing energy consumed by the pilot hydraulic pump and maintaining excellent operability as in the aforementioned first embodiment, and further obtain the following operational advantage. That is, when a plurality of hydraulic actuators is sequentially controlled, even if a pilot flow rate consumed by a proportional solenoid valve has exceeded the maximum flow rate of the pilot hydraulic pump, the outputs of the other proportional solenoid valves that have received control commands at later timings are limited. Thus, it is possible to prevent deceleration or stop of the hydraulic actuators, which would otherwise occur due to an insufficient supply of the pilot flow rate, and thus allow the hydraulic actuators, which have received drive commands so far, to continue operation.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited thereto, and various design changes are possible within the spirit and scope of the present invention recited in the appended claims.

REFERENCE SIGNS LIST

1Hydraulic excavator2Traveling body3Swivel body4Operator's cab5Engine room6Counterweight7Work machine8Boom9Arm10Bucket11ato11fHydraulic actuators14,14A Operating devices15,15A,15B,15C Controllers16Engine (prime mover)17Main hydraulic pump17a,18aRegulators18Pilot hydraulic pump25ato25fFlow rate control valves29Requested pilot flow rate computing unit30Target pump displacement computing unit31Electric motor33Target electric motor rotation computing unit34Proportional solenoid valve (pressure-reducing valve)36Maximum flow rate computing unit38Flow rate control valve command limiting unit39Flow rate control valve command computing unit