JP7495872B2 - Construction Machinery - Google Patents

Description

The present invention relates to a construction machine, and more specifically, to a construction machine equipped with a hydraulic pump driven by a prime mover.

Hydraulic pumps that supply pressurized oil to hydraulic actuators are installed on construction machinery such as hydraulic excavators, hydraulic cranes, and wheel loaders. Hydraulic pumps are driven by a prime mover such as an engine or an electric motor. There are two types of hydraulic pumps: variable displacement, in which the pump capacity can be changed, and fixed displacement, in which the pump capacity is mechanically fixed. With variable displacement hydraulic pumps, the pump flow rate is continuously adjusted by changing the pump capacity while keeping the prime mover rotation speed constant and driving the hydraulic pump at a constant rotation speed. On the other hand, with fixed displacement hydraulic pumps, the pump flow rate is continuously adjusted by changing the hydraulic pump rotation speed by changing the prime mover rotation speed.

In the field of construction machinery, there has been a demand in recent years for semi-automatic control, which assists the operator in controlling the operation of work equipment, etc., and for automatic operation, which eliminates the need for operator operation. To achieve semi-automatic control and automatic operation, there is a demand for improved responsiveness and accuracy of pump flow rate in response to control commands.

A variable displacement hydraulic pump is known in which the pump capacity is adjusted by controlling the tilt angle of the swash plate by driving a servo piston (see, for example, Patent Document 1). In the hydraulic pump capacity control in the construction machinery control device described in Patent Document 1, the hydraulic pump discharge pressure is supplied as the primary pressure to the servo piston via multiple valves to adjust the tilt angle of the swash plate. The tilt angle of the swash plate and the response speed of the change in the tilt angle are adjusted by adjusting the operating pressure supplied to the pressure chamber of the servo piston by switching the position of each valve and the presence or absence of a throttle.

In a configuration in which the pump capacity is adjusted by a servo piston, such as the hydraulic pump mounted on the construction machine described in Patent Document 1, the tilt angle of the swash plate is determined by the balance between the moment generated on the swash plate by the thrust of the servo piston and the moment generated on the swash plate by the hydraulic reaction force of the hydraulic oil received when the multiple pistons of the pump body reciprocate. In this structure, to change to the target tilt angle, it is necessary to adjust the balance position of both moments by switching the position of each valve in the hydraulic system to adjust the pressure in the pressure chamber of the servo piston. In addition, the hydraulic oil in the hydraulic system may pass through a throttle when supplying or discharging it to the servo piston. Such pressure adjustment of the hydraulic system and passing of the hydraulic oil through a throttle may cause response delays and errors in adjusting the pump capacity (adjusting the tilt angle of the swash plate).

In particular, in hydraulic excavators, the temperature of the hydraulic oil changes due to changes in the outside air temperature and changes in the load during excavation operations, and the viscosity of the hydraulic oil changes in response to temperature changes. This change in viscosity causes a change in the flow rate of the hydraulic oil passing through the restriction in the hydraulic system, which in turn causes changes in the control characteristics of the pump capacity, such as the pressure regulation of the hydraulic system (pressure chamber of the servo piston) and the response speed of changes in the tilt angle.

As such, flow control in a variable displacement hydraulic pump can cause response delays and errors due to the structure that adjusts the pump displacement.

Fixed-displacement hydraulic pumps, on the other hand, do not require structures such as pressure regulating mechanisms or throttles in the hydraulic system to adjust the pump capacity, and are driven by a prime mover such as an electric motor whose rotation speed can be freely changed, making it possible to continuously change the pump flow rate according to the rotation speed of the prime mover. In recent years, with the development of battery technology, there have been an increasing number of practical examples of electric motors mounted on vehicles, mainly in the automotive industry. With flow control in fixed-displacement hydraulic pumps, there is no response delay or error caused by structures for adjusting the pump capacity, as occurs with variable-displacement hydraulic pumps.

However, when using a fixed displacement hydraulic pump, there are problems such as the following. In the excavation work of a hydraulic excavator, it is necessary to increase or decrease the pump flow rate according to the work load and the work content while maintaining the discharge pressure of the hydraulic pump at a high pressure. When adjusting the pump flow rate by controlling the rotation speed of the prime mover, in order to ensure a flow rate range similar to that of a variable displacement hydraulic pump, it is necessary to make the rotation speed of the prime mover adjustable over a predetermined range. In order to enable a steep flow rate adjustment from the minimum flow rate to the maximum flow rate for a fixed displacement hydraulic pump, it is necessary to increase the rotation acceleration (angular acceleration) of the prime mover (hydraulic pump) according to the magnitude of the change in the flow rate adjustment. However, in order to increase the rotation acceleration (angular acceleration) of the prime mover, it is necessary to set the maximum power of the prime mover to a large value, which raises concerns about the size of the prime mover. In addition, when a steep flow rate adjustment from the minimum flow rate to the maximum flow rate is required for the hydraulic pump, it is necessary to change the rotation speed of the prime mover from the lower limit to the upper limit of the adjustable range. In this case, there is a concern that the response time until the required pump flow rate (maximum flow rate) is reached will be long.

In contrast to fixed displacement hydraulic pumps, which have the above-mentioned problems, hydraulic pumps are known that can switch the pump capacity to one of several preset capacities (see, for example, Patent Document 2). In the injection molding machine described in Patent Document 2, the pump capacity setting is switched to one of several fixed capacities corresponding to each operation step of the molding cycle, and the rotation speed of the prime mover is variably controlled to control the flow rate of the hydraulic pump.

Japanese Patent Application Laid-Open No. 11-293710 JP 2018-204252 A

As mentioned above, when semi-automatic control or automatic operation is performed in construction machinery, there is a demand for improved responsiveness and accuracy of the pump flow rate in response to the control commands. Furthermore, in hydraulic pump flow rate control in hydraulic excavators, high responsiveness and high accuracy are required with respect to the target hydraulic pump flow rate, even when the operator performs a sudden operation or when a momentary load is input during excavation work.

In a hydraulic pump that can switch the pump capacity to one of multiple fixed capacity stages, as in the technology described in Patent Document 2, the pump capacity is switched to an appropriate fixed capacity stage according to the target flow rate required by the flow control, and the motor speed is adjusted to correspond to the switched fixed capacity. In this flow control, the pump flow rate adjustment range (range from minimum flow rate to maximum flow rate) is covered by multiple fixed capacity stages, so it is considered possible to suppress the amount of change in the motor speed compared to a fixed capacity hydraulic pump in which the pump capacity is completely fixed. Therefore, in the flow control of a hydraulic pump that can switch the pump capacity to one of multiple fixed capacity stages, it is expected that the maximum power of the motor can be reduced and the responsiveness of the pump flow rate can be improved by suppressing the amount of change in the motor speed.

However, in the flow control of the hydraulic pump, when the pump capacity is switched from a fixed capacity of one stage to a fixed capacity of a different stage, the relationship of the hydraulic pump flow rate to the motor rotation speed (flow control characteristics) changes. This can cause the operator to feel uncomfortable when switching the pump capacity. Therefore, in the flow control of the hydraulic pump, an appropriate combination of the pump capacity of the hydraulic pump and the rotation speed of the prime mover is important to suppress the amount of change in the motor rotation speed and to suppress any uncomfortable feeling in operation.

The present invention was made based on the above, and its purpose is to provide a construction machine that can improve responsiveness while suppressing the discomfort of operation in flow control of a hydraulic pump.

The present application includes a number of means for solving the above problem, and one example thereof is a construction machine equipped with a prime mover, a hydraulic pump driven by the prime mover and capable of switching the pump capacity to one of a number of set capacities that differ in stages, a hydraulic actuator driven by pressure oil discharged by the hydraulic pump, an operation device for instructing the operation of the hydraulic actuator, a rotation speed sensor that detects the rotation speed of the prime mover, and a controller that performs flow control to control the flow rate of the hydraulic pump by adjusting the rotation speed of the prime mover and switching the pump capacity of the hydraulic pump, the set capacity of each stage of the hydraulic pump is set so that a common flow rate region is generated in which the adjustable flow rate ranges determined according to the adjustable rotation speed range of the prime mover overlap in part for the set capacity that is one stage different from the set capacity of each stage, and the controller, when changing the flow rate of the hydraulic pump to a predetermined target flow rate, selects one of the combinations of the pump capacity of the hydraulic pump and the rotation speed of the prime mover that can realize the target flow rate, based on either the rotation speed detected by the rotation speed sensor or the operation amount of the operation device, if the target flow rate is in the common flow rate region.

According to the present invention, by making it possible to switch the pump capacity to one of a plurality of set capacities, there is no response delay in capacity control as in a variable capacity hydraulic pump, and the adjustable rotation speed range of the prime mover can be set more limitedly than in a fixed capacity hydraulic pump, thereby making it possible to shorten the response time in the flow control of the hydraulic pump. In addition, by providing a common flow rate region for the flow rate ranges of both the front and rear set capacities, it becomes possible to select from a plurality of options a combination of pump capacity and prime mover rotation speed that can realize a target flow rate in the common flow rate region, and by selecting the combination based on the actual rotation speed of the prime mover or the operation amount of the operating device, it may be possible to shorten the response time and reduce the frequency of switching the pump capacity. Therefore, in the flow control of the hydraulic pump, it is possible to suppress the discomfort of operation while improving the responsiveness.
Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments.

1 is a side view showing a hydraulic excavator to which a first embodiment of a construction machine according to the present invention is applied. 1 is a circuit diagram showing a schematic configuration of a hydraulic system in a first embodiment of a construction machine of the present invention. 3 is a table showing conditions for switching the pump displacement to a set displacement for each stage in the hydraulic pump constituting a part of the first embodiment of the construction machine of the present invention shown in FIG. 2 . 3 is a characteristic diagram showing an example of the relationship between the rotation speed of the electric motor and the flow rate of the hydraulic pump in the construction machine according to the first embodiment of the present invention shown in FIG. 2. 3 is a block diagram showing an example of the functions of a controller constituting a part of the first embodiment of the construction machine of the present invention shown in FIG. 2. FIG. 6 is a flowchart showing an example of a pump flow rate control procedure of a controller according to the first embodiment of the construction machine of the present invention shown in FIG. 5 . FIG. 4 is an explanatory diagram showing a method for selecting a combination of pump displacement and motor rotation speed in pump flow rate control by a controller according to the first embodiment of the construction machine of the present invention. FIG. 11 is a block diagram showing an example of the functions of a controller in a construction machine according to a second embodiment of the present invention. FIG. 11 is a characteristic diagram showing an example of the relationship between the rotation speed of the electric motor and the flow rate of the hydraulic pump in the construction machine according to the second embodiment of the present invention. 9 is a flowchart showing an example of a pump flow rate control procedure of a controller according to the second embodiment of the construction machine of the present invention shown in FIG. 8 . FIG. 11 is an explanatory diagram showing a selection method for finely adjusting a combination of pump displacement and motor rotation speed in pump flow rate control by a controller according to a second embodiment of the construction machine of the present invention.

The following describes an embodiment of the construction machine of the present invention with reference to the drawings. In this embodiment, a hydraulic excavator will be used as an example of the construction machine.

[First embodiment]
First, the configuration of a hydraulic excavator as a first embodiment of a construction machine of the present invention will be described with reference to Fig. 1. Fig. 1 is a side view showing a hydraulic excavator to which the first embodiment of a construction machine of the present invention is applied. Here, the description will be given using the direction as seen by an operator seated in the driver's seat.

In FIG. 1, a hydraulic excavator 1 as a construction machine has a machine body composed of a self-propelled lower traveling body 2 and an upper rotating body 3 mounted so as to be able to rotate on the lower traveling body 2. A front working machine 4 for performing excavation work etc. is provided at the front of the upper rotating body 3 so as to be able to move up and down.

The lower traveling body 2 is equipped with crawler-type traveling devices 11 (only the left side is shown) on the left and right. The left and right traveling devices 11 are each driven by a traveling hydraulic motor 12 that serves as a hydraulic actuator.

The upper rotating body 3 is driven to rotate relative to the lower traveling body 2 by, for example, a hydraulic motor (not shown) as a hydraulic actuator. The upper rotating body 3 includes a rotating frame 21, which is a support structure, a cab 22 installed on the front left side of the rotating frame 21, a counterweight 23 attached to the rear end of the rotating frame 21, and a machine room 24 provided on the rotating frame 21 at a position between the cab 22 and the counterweight 23. Various devices for operating the hydraulic excavator 1, such as an operating device 71 (see FIG. 2 described later), are arranged in the cab 22. The counterweight 23 is for balancing the weight with the front work machine 4. The machine room 24 houses various devices, including a hydraulic pump 51 and an electric motor 52 (see FIG. 2 described later), which will be described later.

The front work machine 4 is a multi-joint type work device composed of multiple link members. For example, it is equipped with a boom 31, an arm 32, and a bucket 33 as an attachment. The base end of the boom 31 is rotatably supported on the front end of the revolving frame 21 of the upper revolving body 3. The base end of the arm 32 is rotatably supported on the tip of the boom 31. The base end of the bucket 33 is rotatably supported on the tip of the arm 32. The boom 31, arm 32, and bucket 33 are driven by a boom cylinder 35, arm cylinder 36, and bucket cylinder 37, respectively. The boom cylinder 35, arm cylinder 36, and bucket cylinder 37 are hydraulic actuators that can be extended and retracted by the supply of pressure oil.

Next, the schematic configuration of the hydraulic system in the first embodiment of the construction machine of the present invention will be described with reference to Figures 2 to 4. Figure 2 is a circuit diagram showing the schematic configuration of the hydraulic system in the first embodiment of the construction machine of the present invention. Figure 3 is a table showing the conditions for switching the pump capacity to the set capacity for each stage in the hydraulic pump constituting part of the first embodiment of the construction machine of the present invention shown in Figure 2. Figure 4 is a characteristic diagram showing an example of the relationship between the rotation speed of the electric motor and the flow rate of the hydraulic pump in the first embodiment of the construction machine of the present invention shown in Figure 2.

In FIG. 2, the hydraulic excavator 1 is equipped with a hydraulic system 50 that drives the lower traveling body 2, the upper rotating body 3, and the front working machine 4 (all see FIG. 1), and a controller 80 that controls the operation of the lower traveling body 2, the upper rotating body 3, and the front working machine 4 via the hydraulic system 50 in response to the operation of the operator.

The hydraulic system 50 includes a hydraulic pump 51 that draws hydraulic oil from a tank 55 and discharges pressure oil, an electric motor 52 as a prime mover that drives the hydraulic pump 51, various hydraulic actuators 53 (only one shown) driven by the pressure oil discharged from the hydraulic pump 51, and various directional control valves 54 (only one shown) that control the flow (direction and flow rate) of the pressure oil supplied from the hydraulic pump 51 to the various hydraulic actuators 53. The structure of the hydraulic pump 51 will be described in detail later. The electric motor 52 is capable of continuously and freely changing the rotation speed. The electric motor 52 is electrically connected to the controller 80, and the rotation speed is controlled according to the rotation speed command of the controller 80. As described above, the various hydraulic actuators 53 are the traveling hydraulic motor 12, the swing hydraulic motor (not shown), the boom cylinder 35, the arm cylinder 36, the bucket cylinder 37, and the like. The various directional control valves 54 correspond to the travel hydraulic motor 12, the swing hydraulic motor (not shown), the boom cylinder 35, the arm cylinder 36, the bucket cylinder 37, etc., and are assembled together to form a control valve unit.

The operator operates the various hydraulic actuators 53 via an operating device 71. The operating device 71 instructs the operation of the various hydraulic actuators 53 corresponding to the operation of the various directional control valves 54 in response to the operator's operation (operation direction and operation amount). The operating device 71 is, for example, an electric lever, and is equipped with a detection device that detects the operation (operation direction and operation amount), and outputs the detected operation to the controller 80.

The hydraulic pump 51 and the directional control valve 54 are connected via a discharge line 56. A pressure sensor 72 is installed in the discharge line 56 to detect the pressure (discharge pressure) of the pressurized oil discharged from the hydraulic pump 51. The pressure sensor 72 outputs the detected discharge pressure (detected pressure P) of the hydraulic pump 51 to the controller 80.

The electric motor 52 is provided with a rotation speed sensor 73 that detects the rotation speed of the electric motor 52. The rotation speed sensor 73 outputs the detected rotation speed of the electric motor 52 (detected rotation speed N) to the controller 80.

The hydraulic pump 51 is capable of switching the pump capacity (displacement volume), which is the discharge flow rate per revolution, to one of a number of different set volumes in a stepwise manner. Specifically, the hydraulic pump 51 is equipped with a pump body 61 having a variable mechanism 61a that allows the pump capacity to be changed by changing the tilt angle, and a capacity switching mechanism 62 that switches the pump capacity to one of a number of set capacities by driving the variable mechanism 61a. Examples of the variable mechanism 61a of the pump body 61 include a swash plate and a slanted shaft. The pump body 61 adjusts the pump capacity by changing the tilt angle of the swash plate or the slanted shaft (variable mechanism 61a). The capacity switching mechanism 62, for example, connects the servo piston 631 of the servo cylinder 63 to the variable mechanism 61a, and structurally restricts the displaceable positions of the servo piston 631 to a number of positions, thereby setting the tilt angle of the variable mechanism 61a only to angles corresponding to the limited positions of the servo piston 631.

The hydraulic pump 51 is configured to be able to switch the pump capacity to one of a number of different set volumes (for example, three stages in FIG. 2). The three set volumes are a first stage set capacity where the pump capacity is the smallest, a third stage set capacity where the pump capacity is the largest, and a second stage set capacity where the pump capacity is intermediate, being larger than the first stage set capacity and smaller than the third stage set capacity.

The capacity switching mechanism 62 includes, for example, a servo cylinder 63 in which a servo piston 631 is displaced using the discharge pressure from the pump body 61 as the operating pressure, and is configured so that the positions to which the servo piston 631 can be displaced are structurally restricted to three positions. Specifically, the servo cylinder 63 has a first piston 631 as a servo piston slidably arranged in a first cylinder tube 633, and a second piston 632 slidably arranged in a second cylinder tube 634.

The first piston 631 is composed of a piston head portion 631a that separates the inside of the first cylinder tube 633 into a first pressure receiving chamber 635 and a second pressure receiving chamber 636, and a piston rod portion 631b that extends from the pressure receiving surface of the piston head portion 631a on the second pressure receiving chamber 636 side and has a smaller cross-sectional area than the piston head portion 631a. The piston head portion 631a of the first piston 631 has a pressure receiving area on the first pressure receiving chamber 635 side that is larger than the pressure receiving area on the second pressure receiving chamber 636 side by the amount of the piston rod portion 631b. The piston rod portion 631b of the first piston 631 is connected to the variable mechanism 61a via a link member 67, and the tilt angle of the variable mechanism 61a is changed depending on the moving position.

The second piston 632 separates the inside of the second cylinder tube 634 into a third pressure receiving chamber 637 and a fourth pressure receiving chamber 638. The tip of the piston rod portion 631b of the first piston 631 is located in the third pressure receiving chamber 637. The second piston 632 is configured so that the pressure receiving portion on the third pressure receiving chamber 637 side can abut against the tip of the piston rod portion 631b of the first piston 631. Here, the area of the fourth pressure receiving chamber 638 side of the second piston 632 is set to be larger than the area of the piston head portion 631a of the first piston 631 on the first pressure receiving chamber 635 side minus the area of the second pressure receiving chamber 636 side.

The capacity switching mechanism 62 further includes a first switching valve 64 that selectively switches between supplying and discharging hydraulic oil (operating pressure) to the first pressure receiving chamber 635 of the servo cylinder 63, and a second switching valve 66 that selectively switches between supplying and discharging hydraulic oil (operating pressure) to the fourth pressure receiving chamber 638 of the servo cylinder 63. The first switching valve 64 and the second switching valve 66 are each electrically connected to the controller 80, and switch positions in response to position commands from the controller 80.

The first switching valve 64 switches the connection destination of the first pressure receiving chamber 635 of the servo cylinder 63 to either the pilot supply line 68 branched off from the discharge line 56 or the pilot discharge line 69 connected to the tank 55. The first switching valve 64 is, for example, a 3-port 2-position solenoid valve, and is configured to be selectively switched to either the first position F or the second position S depending on the presence or absence (ON/OFF) of a position command input. For example, when there is no position command input (OFF), it is switched to the first position F, and when a position command is input (ON), it is switched to the second position S. The first position F is a position where the first pressure receiving chamber 635 is connected to the pilot supply line 68, and the second position S is a position where the first pressure receiving chamber 635 is connected to the pilot discharge line 69.

The second switching valve 66 switches the connection destination of the fourth pressure receiving chamber 638 of the servo cylinder 63 to either the pilot supply line 68 or the pilot discharge line 69. The second switching valve 66 is, for example, a 3-port 2-position solenoid valve, and is configured to be selectively switched to either the first position F or the second position S depending on whether or not a position command is input (ON/OFF). For example, when there is no position command input (OFF), it is switched to the first position F, and when a position command is input (ON), it is switched to the second position S. The first position F is a position that connects the fourth pressure receiving chamber 638 to the pilot discharge line 69, and the second position S is a position that connects the fourth pressure receiving chamber 638 to the pilot supply line 68.

The capacity switching mechanism 62 is configured so that the movement position of the servo piston 631 of the servo cylinder 63 is limited to three positions according to the switching positions (ON or OFF) of the two switching valves 64, 66. This configuration enables the hydraulic pump 51 to switch the pump capacity to three different set capacities (first stage set capacity, second stage set capacity, third stage set capacity) in stages.

In a regulator for a variable displacement hydraulic pump, which can continuously change the pump capacity, the operating pressure in the pressure chamber of the servo cylinder is adjusted through valve operation or a throttle, adjusting the movement position of the servo piston to balance the moment acting on the swash plate and control the pump capacity. In this configuration, the control characteristics of the pump capacity can change when the balance position of the moment acting on the swash plate changes due to factors such as temperature changes in the hydraulic oil.

In contrast, the capacity switching mechanism 62 according to this embodiment does not need to adjust the operating pressure in the pressure-receiving chambers 635, 636, and 638 of the servo cylinder 63 to balance the variable mechanism 61a, and can switch the tilt angle of the variable mechanism 61a to different predetermined angles in stages by displacing the servo piston 631 to a mechanically restricted position. Therefore, the control characteristics of the pump capacity do not change due to changes in the temperature of the hydraulic oil, so there is no decrease in responsiveness or accuracy in the capacity control of the hydraulic pump 51.

In the capacity switching mechanism 62 of this embodiment, as shown in FIG. 3, the pump capacity is switched to one of three set capacity stages (first-stage set capacity, second-stage set capacity, third-stage set capacity) depending on the switching position (ON or OFF) of the two switching valves 64, 66. The details are as follows.

First, when the first switching valve 64 shown in FIG. 2 is in the first position F (OFF) and the second switching valve 66 is in the first position F (OFF), the hydraulic oil (operating pressure) can be supplied to the first pressure receiving chamber 635 of the servo cylinder 63, and the hydraulic oil (operating pressure) can be discharged from the fourth pressure receiving chamber 638. The second pressure receiving chamber 636 is constantly supplied with operating pressure. The force acting on the piston head portion 631a of the first piston 631 is predominantly from the first pressure receiving chamber 635 side to the second pressure receiving chamber 636 side due to the difference in the pressure receiving area on the first pressure receiving chamber 635 side and the pressure receiving area on the second pressure receiving chamber 636 side. As a result, the first piston 631 moves together with the second piston 632 until the piston rod portion 631b abuts against the second piston 632 and presses the second piston 632 against the end wall (stopper) of the fourth pressure receiving chamber 638. That is, the first piston 631 moves to a first position where the movement of the second piston 632 is restricted by the end wall of the fourth pressure receiving chamber 638. When the first piston 631 is displaced to the first position, the tilt angle of the variable mechanism 61a changes to a certain first angle, and the pump capacity switches to the first stage set capacity, which is the minimum capacity.

Secondly, when the first switching valve 64 is in the first position F (OFF) and the second switching valve 66 is in the second position S (ON), the operating pressure can be supplied to the first pressure receiving chamber 635 and the fourth pressure receiving chamber 638 of the servo cylinder 63. The operating pressure is constantly supplied to the second pressure receiving chamber 636, but due to the difference in the pressure receiving area on the first pressure receiving chamber 635 side and the pressure receiving area on the second pressure receiving chamber 636 side, the force acting on the piston head portion 631a of the first piston 631 is predominantly directed from the first pressure receiving chamber 635 side to the second pressure receiving chamber 636 side. As a result, the first piston 631 is displaced to the second position where the piston rod portion 631b abuts against the second piston 632. However, because the operating pressures of the first pressure receiving chamber 635 and the fourth pressure receiving chamber 638 are the same, due to the area difference between the area of the piston head portion 631a of the first piston 631 on the first pressure receiving chamber 635 side and the area of the second piston 632 on the fourth pressure receiving chamber 638 side, which is set to be larger than the area of the piston head portion 631a on the first piston 631 minus the area of the second pressure receiving chamber 636 side, the second piston 632 does not move even when the piston rod portion 631b of the first piston 631 abuts, and functions as a stopper that restricts the movement of the first piston 631. This movement of the first piston 631 to the second position changes the tilt angle of the variable mechanism 61a to a second angle larger than the first angle, and the pump capacity switches to the second stage set capacity, which is an intermediate capacity.

Thirdly, when the first switching valve 64 is in the second position S (ON) and the second switching valve 66 is in the first position F (OFF), the operating pressure can be discharged from the first pressure receiving chamber 635. Operating pressure is constantly supplied to the second pressure receiving chamber 636 of the servo cylinder 63. As a result, the first piston 631 moves to a third position where the piston head portion 631a abuts against the end wall (stopper) of the first pressure receiving chamber 635 and movement is restricted. This movement of the first piston 631 to the third position changes the tilt angle of the variable mechanism 61a to a third angle larger than the second angle, and the pump capacity switches to the third stage set capacity, which is the maximum capacity.

In the hydraulic pump 51 according to this embodiment, the set capacity of each stage and the set capacity one stage different from the set capacity of each stage are set so that the adjustable flow rate ranges determined according to the adjustable rotation speed range of the electric motor 52 create a common flow rate region where they overlap in part. In other words, the adjustable flow rate ranges determined for the set volume of each stage and the adjustable flow rate ranges determined for the set volume one stage different from the set capacity of each stage have a common flow rate region where they overlap in part.

For example, if the pump capacity of the hydraulic pump 51 can be switched to one of three set capacities, as shown in FIG. 4, a characteristic diagram M1 showing the relationship between the adjustable rotation speed of the electric motor 52 and the flow rate of the hydraulic pump is determined for each of the first to third set capacities (minimum capacity, intermediate capacity, maximum capacity). In FIG. 4, the horizontal axis N represents the rotation speed of the electric motor 52, and the vertical axis Q represents the flow rate of the hydraulic pump.

In the characteristic diagram M1, the adjustable rotation speed range of the electric motor 52 by the controller 80 is set according to the specifications of the hydraulic pump 51 and the electric motor 52. Specifically, a first rotation speed range is set as the adjustable rotation speed range, with the minimum rotation speed Nn as the lower limit and the maximum rotation speed Nx as the upper limit. For the set first rotation speed range, adjustable flow rate ranges (first stage flow rate range, second stage flow rate range, third stage flow rate range) are determined for each of the set capacities of the first to third stages of the hydraulic pump 51. In other words, the adjustable flow rate range for the set capacity of each stage is the region from the lower limit of the flow rate corresponding to the minimum rotation speed Nn of the first rotation speed range to the upper limit of the flow rate corresponding to the maximum rotation speed Nx.

The first stage flow rate range determined for the first stage set capacity in this characteristic diagram M1 and the second stage flow rate range determined for the second stage set capacity have a first common flow rate region Fc1 where the flow rate region including the maximum flow rate in the first stage flow rate range and the flow rate region including the minimum flow rate in the second stage flow rate range overlap each other. Also, the second stage flow rate range determined for the second stage set capacity and the third stage flow rate range determined for the third stage set capacity have a second common flow rate region Fc2 where the flow rate region including the maximum flow rate in the second stage flow rate range and the flow rate region including the minimum flow rate in the third stage flow rate range overlap each other.

As shown in this characteristic diagram M1, the entire adjustable flow range of the hydraulic pump 51 is divided into three set capacities. Therefore, compared to a fixed displacement hydraulic pump, it is possible to limit the adjustable rotation speed range of the electric motor 52. By narrowing the adjustable rotation speed range, it is possible to suppress the maximum power of the electric motor 52 and shorten the response time of the rotation speed control of the electric motor 52. In addition, in this characteristic diagram M1, when the flow rate of the hydraulic pump 51 is on the first common flow rate region Fc1 or the second common flow rate region Fc2, it is possible to select the pump capacity of the hydraulic pump 51 from the set capacities that share the common flow rate regions Fc1 and Fc2.

Returning to FIG. 2, the controller 80 is electrically connected to the first switching valve 64 and the second switching valve 66, and controls the switching of the pump capacity of the hydraulic pump 51 via the first switching valve 64 and the second switching valve 66. The controller 80 is also electrically connected to the electric motor 52, and controls the rotation speed of the electric motor 52. The controller 80 according to this embodiment controls the switching of the pump capacity of the hydraulic pump 51 and the rotation speed of the electric motor 52 based on the characteristic diagram M1, thereby performing flow control to adjust the flow rate of the hydraulic pump 51. The controller 80 is configured to perform predetermined calculation processing and comparison judgment in the flow rate control of the hydraulic pump 51 based on the operation detected by the operating device 71, the detected pressure of the pressure sensor 72 (the discharge pressure of the hydraulic pump 51), and the detected rotation speed of the rotation speed sensor 73 (the actual rotation speed of the electric motor 52).

Next, the configuration and functions of the controller constituting the first embodiment of the construction machine of the present invention will be described with reference to Figures 4 and 5. Figure 5 is a block diagram showing an example of the functions of the controller constituting part of the first embodiment of the construction machine of the present invention shown in Figure 2. Note that in Figure 5, the same reference numerals as those shown in Figures 1 to 4 indicate the same parts, and therefore detailed descriptions thereof will be omitted.

In FIG. 5, the controller 80 has, as its hardware configuration, a storage device 81 consisting of a RAM, a ROM, etc., and an arithmetic processing device 82 consisting of a CPU, etc. The storage device 81 stores in advance programs and various information required for flow control of the hydraulic pump 51 and other controls. The arithmetic processing device 82 reads the programs and various information from the storage device 81 as appropriate, and executes processing according to the programs to realize various functions, including those described below.

In the controller 80, a characteristic diagram M1 showing the relationship between the flow rate Q of the hydraulic pump 51 and the rotation speed N of the motor 52 is stored in the storage device 81 in order to control the flow rate of the hydraulic pump 51. As described above, the characteristic diagram M1 defines the flow rate for each set capacity of each stage (first stage set capacity, second stage set capacity, third stage set capacity) relative to the rotation speed (see FIG. 4). In the characteristic diagram M1 of this embodiment, as described above, common flow rate areas Fc1 and Fc2 are provided in which the flow rate ranges determined for the set capacity of each stage overlap with the flow rate ranges determined for the set capacity of each stage that is one stage different from the set capacity of each stage. Therefore, when the flow rate of the hydraulic pump 51 is on the common flow rate areas Fc1 and Fc2 of the characteristic diagram M1, the controller 80 can select one of the set capacities that share the common flow rate areas Fc1 and Fc2 as the pump capacity of the hydraulic pump 51. This allows the controller 80 to select the pump capacity taking into account the responsiveness when controlling the flow rate of the hydraulic pump 51. The details of the function of the controller 80 to control the flow rate of the hydraulic pump 51 are as follows.

The controller 80 has, for example, a target flow rate calculation unit 91, a capacity/rotation speed selection unit 92, a capacity control unit 93, and a rotation speed control unit 94 as functions for executing flow rate control of the hydraulic pump 51.

The target flow rate calculation unit 91 calculates the target pump flow rate Qt of the hydraulic pump 51 based on the operation L of the operating device 71, the detected pressure P of the pressure sensor 72, and the allowable power Wa of the electric motor 52. Specifically, the target flow rate calculation unit 91 calculates the indicated pump flow rate QL based on the operation L of the operating device 71. For example, a characteristic diagram (not shown) that specifies the relationship between the indicated pump flow rate QL and the operation L of the operating device 71 is stored in advance in the storage device 81. Furthermore, the required power of the hydraulic pump 51 is calculated by integrating the indicated pump flow rate QL of the calculation result and the detected pressure P of the pressure sensor 72. In addition, it is determined whether the required power of the hydraulic pump 51 of the calculation result is equal to or less than the allowable power Wa of the electric motor 52. The allowable power Wa of the electric motor 52 is determined by the specifications of the electric motor 52 and is stored in advance in the storage device 81.

If the determination result is equal to or less than the allowable power Wa, the indicated pump flow rate QL of the calculation result is set as the target pump flow rate Qt of the hydraulic pump 51. If the determination result is otherwise, the target pump flow rate Qt is set so that the integrated result of the target pump flow rate Qt and the detected pressure P of the pressure sensor 72 is equal to the allowable power Wa.

The capacity rotation speed selection unit 92 selects a combination of set capacity and rotation speed that can realize the target pump flow rate Qt calculated by the target flow rate calculation unit 91 based on the characteristic diagram M1 (see FIG. 4) in which the flow rate for each set capacity of each stage of the hydraulic pump 51 (in this embodiment, the first stage set capacity, the second stage set capacity, and the third stage set capacity) is determined. Specifically, the capacity rotation speed selection unit 92 refers to the characteristic diagram M1 and extracts all combinations of set capacity and rotation speed that can realize the target pump flow rate Qt. If the target pump flow rate Qt is not on the common flow rate region Fc1, Fc2 of the characteristic diagram M1, only one combination of set capacity and rotation speed that can realize the target pump flow rate Qt is determined, so that combination is selected. On the other hand, if the target pump flow rate Qt is on the common flow rate region Fc1, Fc2 of the characteristic diagram M1, the combination that has the smallest deviation between the rotation speed that can realize the target pump flow rate Qt and the detected rotation speed N of the rotation speed sensor is selected. This aims to improve the responsiveness of the flow control of the hydraulic pump 51 by minimizing the time it takes for the electric motor 52 to change to the target rotation speed.

The capacity control unit 93 outputs a capacity command to the capacity switching mechanism 62 of the hydraulic pump 51, which sets the set capacity selected by the capacity rotation speed selection unit 92 as the target pump capacity of the hydraulic pump 51. Specifically, the capacity control unit 93 sets the set capacity selected by the capacity rotation speed selection unit 92 as the target pump capacity, and outputs an ON or OFF position command to the first and second switching valves 64, 66, respectively, so that the pump capacity becomes the target pump capacity (see FIG. 3).

The rotation speed control unit 94 outputs a rotation speed command to the electric motor 52, which sets the rotation speed selected by the capacity rotation speed selection unit 92 as the target rotation speed of the electric motor 52. This changes the actual rotation speed of the electric motor 52 to the target rotation speed.

Next, an example of a control procedure executed by the controller constituting the first embodiment of the construction machine of the present invention will be described with reference to Figs. 5 to 7. Fig. 6 is a flow chart showing an example of a procedure for pump flow control by the controller of the first embodiment of the construction machine of the present invention shown in Fig. 5. Fig. 7 is an explanatory diagram showing a method for selecting a combination of pump capacity and motor speed in pump flow control by the controller of the first embodiment of the construction machine of the present invention. Note that the characteristic diagram shown in Fig. 7 is the same as the characteristic diagram shown in Fig. 5.

The controller 80 shown in FIG. 5 first receives the operation L detected by the operating device 71 (step S10 shown in FIG. 6) and calculates the command pump flow rate QL (step S20 shown in FIG. 6). Specifically, the target flow rate calculation unit 91 of the controller 80 refers to a characteristic diagram (not shown) pre-stored in the storage device 81 and calculates the command pump flow rate QL of the hydraulic pump 51 according to the operation L of the operating device 71.

Next, the controller 80 takes in the detected pressure P of the pressure sensor 72 (the discharge pressure of the hydraulic pump 51) (step S30 shown in FIG. 6) and determines whether the required power of the hydraulic pump 51 is equal to or less than the allowable power Wa of the electric motor 52 (step S40 shown in FIG. 6). Specifically, the target flow rate calculation unit 91 calculates the required power of the hydraulic pump 51 by multiplying the command pump flow rate QL of the calculation result and the detected pressure P of the pressure sensor 72, and determines whether the required power (P×QL) of the calculation result is equal to or less than the allowable power Wa of the electric motor 52 pre-stored in the storage device 81. If the answer is YES in step S40, the process proceeds to step S50, whereas if the answer is NO, the process proceeds to step S60.

In step S40, if the required power (P x QL) is equal to or less than the allowable power Wa (YES), the target flow rate calculation unit 91 sets the calculated indicated pump flow rate QL as the target pump flow rate Qt (step S50 shown in FIG. 6). On the other hand, in step S40, if the required power (P x QL) is greater than the allowable power Wa (NO), the target pump flow rate Qt is set so that the integrated value of the target pump flow rate Qt and the detected pressure P of the pressure sensor 72 (the power of the hydraulic pump 51) is equal to the allowable power Wa of the electric motor 52 (step S60 shown in FIG. 6). As a result, the calculated target pump flow rate Qt becomes a value smaller than the indicated pump flow rate QL, thereby limiting the power of the hydraulic pump 51.

Following step S50 or step S60, the controller 80 takes in the detected rotation speed N of the rotation speed sensor 73 (the actual rotation speed of the electric motor 52) (step S70 shown in FIG. 6), and selects one of the combinations of the set capacity and rotation speed that can realize the target pump flow rate Qt calculated by the target flow rate calculation unit 91 by referring to the characteristic diagram M1 (see FIG. 4 or FIG. 7) in which the flow rate for the rotation speed is determined for each set capacity of the hydraulic pump 51 at each stage (steps S80 and S90 shown in FIG. 6). Specifically, the capacity rotation speed selection unit 92 of the controller 80 refers to the characteristic diagram M1 (see FIG. 4 or FIG. 7) stored in advance in the storage device 81, and extracts a combination of the set capacity and rotation speed that can realize the target pump flow rate Qt (step S80 shown in FIG. 6). Next, from among the extracted combinations, the set capacity and rotation speed of the combination that minimizes the deviation between the rotation speed that can realize the target pump flow rate Qt and the detected rotation speed N of the rotation speed sensor 73 is selected as the target pump capacity and target rotation speed (step S90 shown in FIG. 6).

The characteristic diagram M1 shown in FIG. 7 has a first common flow rate region Fc1 for the flow rate range of the first stage set capacity and the second stage set capacity, and a second common flow rate region Fc2 for the flow rate range of the second stage set capacity and the third stage set capacity. Therefore, when the target pump flow rate Qt is in the first common flow rate region Fc1 or the second common flow rate region Fc2, there are multiple combinations of selectable set capacity and rotation speed. In this case, the smaller the deviation between the selectable rotation speed in the characteristic diagram M1 and the detected rotation speed N (actual rotation speed of the electric motor 52) of the rotation speed sensor 73, the smaller the power required to match the actual rotation speed of the electric motor 52 with the target rotation speed can be, and the shorter the response time until the actual rotation speed matches the target rotation speed can be.

For example, assume that the actual pump flow rate is Q0 and the pump capacity is the first stage set capacity. In this case, referring to the characteristic diagram M1 shown in FIG. 7, the rotation speed of the electric motor 52 at the control point C0 (the rotation speed N detected by the rotation speed sensor 73) is N0.

In this situation, assume that the pump flow rate is changed to Q1 (target pump flow rate Qt = Q1). In this case, referring to the characteristic diagram M1 shown in FIG. 7, among the set capacities of each stage, only the third stage set capacity has a flow rate range that includes the flow rate Q1. Therefore, the capacity rotation speed selection unit 92 selects the third stage set capacity as the pump capacity, and selects the rotation speed N1 corresponding to the flow rate Q1 in the characteristic diagram of the third stage set capacity as the target rotation speed.

Also, assume that the pump flow rate is changed from Q0 to a new Q2 (target pump flow rate Qt = Q2). In this case, referring to the characteristic diagram M1 shown in FIG. 7, the target pump flow rate Q2 is on the first common flow rate region Fc1 in the flow rate range of the first stage set capacity and the second stage set capacity. In other words, the set capacity of each stage whose flow rate range includes the target pump flow rate Q2 is the first stage set capacity and the second set capacity. Therefore, the capacity rotation speed selection unit 92 can select either the first stage set capacity or the second set capacity as the pump capacity. In other words, the controller 80 can select either one of the two intersection points C2f, C2s for the target pump flow rate Q2 in the characteristic diagram M1 shown in FIG. 7 as the control point.

In this case, the capacity/rotation speed selection unit 92 compares the magnitude of a first deviation amount, which is the deviation amount between the rotation speed N2f corresponding to the first stage set capacity that can realize the target pump flow rate Q2 and the detected rotation speed N0 of the rotation speed sensor 73 (the actual rotation speed of the electric motor 52 at the time of the calculation), and a second deviation amount, which is the deviation amount between the rotation speed N2s corresponding to the second stage set capacity that can realize the target pump flow rate Q2 and the detected rotation speed N0 of the rotation speed sensor 73. The capacity/rotation speed selection unit 92 selects the rotation speed with the smallest deviation amount as the target rotation speed, and selects the set capacity corresponding to the selected rotation speed as the target pump capacity. If the first deviation amount is smaller than the second deviation amount, the second stage set capacity on the characteristic diagram M1 shown in FIG. 7 and the corresponding rotation speed N2s are selected.

Next, the controller 80 outputs a capacity command to the capacity switching mechanism 62, with the set capacity selected by the capacity rotation speed selection unit 92 as the target pump capacity (step S100 shown in FIG. 6). Specifically, the capacity control unit 93 of the controller 80 outputs an ON or OFF position command to each of the first and second switching valves 64, 66 so that the pump capacity becomes the set capacity selected by the capacity rotation speed selection unit 92. As a result, the switching positions of the first and second switching valves 64, 66 shown in FIG. 2 become positions according to the position command. As a result, the supply and discharge of operating pressure occurs to the pressure receiving chambers 635, 638 of the servo cylinder 63 via the first and second switching valves 64, 66, and the position of the servo piston 631 of the servo cylinder 63 is determined to one of three predetermined positions that are mechanically regulated. As a result, the tilt angle of the variable mechanism 61a is set according to the position of the servo piston 631, and the pump capacity becomes the selected set capacity.

Next, the controller 80 outputs a rotation speed command to the electric motor 52, with the rotation speed selected by the capacity/rotation speed selection unit 92 as the target rotation speed (step S110 shown in FIG. 6). This changes the actual rotation speed of the electric motor 52 shown in FIG. 2 to the target rotation speed. As a result, the rotation speed of the hydraulic pump is also changed in conjunction with the change in the rotation speed of the electric motor 52. Therefore, the flow rate of the hydraulic pump 51 is changed according to the selected combination of set capacity and rotation speed, and adjusted to match the target pump flow rate.

In this explanation, the flow rate control of the hydraulic pump 51 by the controller 80 has been described in terms of a case where the flow rate is increased. However, even when the flow rate is decreased, as in the case where the flow rate is increased, the controller 80 selects, from among the combinations of pump capacity and motor speed that can achieve the target pump flow rate, a combination that minimizes the deviation from the rotation speed N detected by the rotation speed sensor 73.

In this embodiment, the hydraulic pump 51 is configured so that the pump capacity can be switched to one of multiple set volumes. Furthermore, common flow ranges Fc1 and Fc2 are provided for both the set capacity of each stage and the set capacity that is one stage different from the set capacity of each stage.

In the flow control of the hydraulic pump 51 with this configuration, the provision of common flow regions Fc1 and Fc2 ensures continuity of the adjustable flow range of the hydraulic pump 51. Furthermore, the provision of common flow regions Fc1 and Fc2 can reduce the frequency of switching the pump capacity.

In addition, the capacity control of the hydraulic pump 51 in this configuration does not have a regulator pressure adjustment process as in a variable capacity hydraulic pump, so the responsiveness of the capacity control (capacity switching) is improved compared to a variable capacity hydraulic pump. Therefore, the responsiveness of the flow control of the hydraulic pump 51 is greatly influenced by the responsiveness of the rotation speed control of the electric motor 52. Therefore, in the flow control of the hydraulic pump 51, the responsiveness is improved by selecting a control point for a combination of pump capacity and rotation speed that minimizes the controlled change in the rotation speed of the electric motor 52.

In the hydraulic excavator 1, loads are placed on the various actuators 53 during excavation, travel, and rotation operations, causing an increase in pressure in the hydraulic circuit. When the discharge pressure of the hydraulic pump is high, if the rotation speed of the electric motor 52 is changed significantly to control the flow rate of the hydraulic pump 51, the required power and torque of the electric motor 52 increase accordingly. By reducing the amount of control change in the rotation speed of the electric motor 52 in the flow rate control of the hydraulic pump 51, the increase in the required power and torque of the electric motor 52 can be suppressed. As a result, it becomes possible to reduce the size of the electric motor 52, etc.

As described above, in the first embodiment of the present invention, the hydraulic excavator 1 as a construction machine includes an electric motor 52 (prime mover), a hydraulic pump 51 driven by the electric motor 52 (prime mover) and capable of switching the pump capacity to one of three (multiple) set capacities that are different in stages, a hydraulic actuator 53 driven by pressure oil discharged by the hydraulic pump 51, an operating device 71 for instructing the drive of the hydraulic actuator 53, a rotation speed sensor 73 for detecting the rotation speed of the electric motor 52 (prime mover), and a controller 80 for performing flow control to control the flow rate of the hydraulic pump 51 by adjusting the rotation speed of the electric motor 52 (prime mover) and switching the pump capacity of the hydraulic pump 51. The set capacity of each stage of the hydraulic pump 51 is set so that common flow rate regions Fc1 and Fc2 are generated in which the adjustable flow rate ranges determined according to the adjustable rotation speed range of the electric motor 52 (prime mover) overlap each other in some areas for the set capacity that is one stage different from the set capacity of each stage. When changing the flow rate of the hydraulic pump 51 to a predetermined target flow rate, if the target flow rate is in the common flow rate region, the controller 80 selects one of the combinations of the pump capacity of the hydraulic pump 51 and the rotation speed of the electric motor 52 (prime mover) that can achieve the target pump flow rate (target flow rate) based on the rotation speed detected by the rotation speed sensor 73.

According to this configuration, by making it possible to switch the pump capacity to one of three (multiple) set capacities, there is no response delay in capacity control as in a variable capacity hydraulic pump, and the adjustable rotation speed range of the electric motor 52 can be set more limitedly than in a fixed capacity hydraulic pump, which makes it possible to shorten the response time in the flow control of the hydraulic pump 51. In addition, by providing common flow ranges Fc1 and Fc2 for both the front and rear set capacity flow ranges, it becomes possible to select from multiple options a combination of pump capacity and electric motor rotation speed that can realize the target pump flow rate (target flow rate) on the common flow ranges Fc1 and Fc2, and by selecting the combination based on the actual rotation speed of the electric motor 52, it may be possible to shorten the response time and reduce the frequency of switching the pump capacity. Therefore, in the flow control of the hydraulic pump 51, it is possible to suppress the discomfort of operation while improving responsiveness.

In addition, when the target pump flow rate (target flow rate) is on the common flow rate region Fc1, Fc2, the controller 80 according to this embodiment is configured to select, from among the combinations of the pump capacity of the hydraulic pump 51 and the rotation speed of the electric motor 52 (prime mover) that can realize the target pump flow rate (target flow rate), the combination that minimizes the deviation between the rotation speed detected by the rotation speed sensor 73 and the rotation speed of the electric motor 52 (prime mover) that can realize the target pump flow rate (target flow rate).

With this configuration, of the rotation speeds of the electric motor 52 that can achieve the target pump flow rate (target flow rate), the selected rotation speed is closest to the rotation speed of the electric motor 52 before the change, so the time (response time) for changing the hydraulic pump 51 to the target pump flow rate (target flow rate) is minimized, and the power required to accelerate and decelerate the electric motor 52 when changing the flow rate of the hydraulic pump 51 to the target flow rate can be reduced.

Furthermore, in this embodiment, the hydraulic pump 51 has a variable mechanism 61a that allows the pump capacity to be changed by changing the tilt angle, and a capacity switching mechanism 62 that switches the pump capacity to one of a plurality of set capacities by driving the variable mechanism 61a. The capacity switching mechanism 62 has a plurality of pressure receiving chambers 635, 638 to which hydraulic oil is supplied and discharged, a servo cylinder 63 having a servo piston 631 that is displaced by supplying and discharging hydraulic oil to the plurality of pressure receiving chambers 635, 638, and a plurality of switching valves 64, 66 that selectively switch the supply or discharge of hydraulic oil to the plurality of pressure receiving chambers 635, 638 of the servo cylinder 63. The servo piston 631 is connected to the variable mechanism 61a, and the servo cylinder 63 is configured so that the position to which the servo piston 631 can be displaced by supplying and discharging hydraulic oil to the plurality of pressure receiving chambers 635, 638 is structurally restricted.

With this configuration, the pump capacity of the hydraulic pump 51 can be reliably switched using the capacity switching mechanism 62 with a simple configuration.

[Second embodiment]
Next, the configuration of a second embodiment of the construction machine of the present invention will be described with reference to Figures 8 and 9. Figure 8 is a block diagram showing an example of the functions of a controller in the second embodiment of the construction machine of the present invention. Figure 9 is a characteristic diagram showing an example of the relationship between the rotation speed of the electric motor and the flow rate of the hydraulic pump in the second embodiment of the construction machine of the present invention. In Figures 8 and 9, the same reference numerals as those in Figures 1 to 7 denote similar parts, so detailed description thereof will be omitted.

The difference between the second embodiment of the construction machine of the present invention and the first embodiment is that the controller 80A shown in FIG. 8 determines whether the operation of the operating device 71 is "fine operation" in the flow control of the hydraulic pump 51, and when it is determined that it is "fine operation", it uses the characteristic diagram M2 (see FIG. 9) in which the adjustable rotation speed range of the electric motor 52 is expanded compared to the characteristic diagram M1 (see FIG. 4) used in cases other than fine operation. Note that "fine operation" in this embodiment means fine adjustment of the flow rate of the hydraulic pump 51, that is, the change in the operation amount of the operating device 71 is small. In other words, the difference is that the adjustable flow rate range of the set capacity of each stage is expanded only when the flow rate adjustment of the hydraulic pump 51 is fine adjustment. In this way, when the flow rate adjustment of the hydraulic pump 51 is fine adjustment, the adjustable flow rate range is expanded in accordance with the expansion of the adjustment margin of the rotation speed of the electric motor 52, thereby suppressing the switching of the pump capacity.

Specifically, in FIG. 8, the controller 80A further includes a function of a fine operation determination unit 96 in addition to a target flow rate calculation unit 91, a capacity rotation speed selection unit 92A, a capacity control unit 93, and a rotation speed control unit 94 as a function for executing flow rate control of the hydraulic pump 51. The fine operation determination unit 96 determines whether the operation of the operating device 71 is a "fine operation", and in this embodiment, whether the change in the operation amount of the operating device 71 is less than a predetermined value. In detail, the fine operation determination unit 96 determines that the difference between the command pump flow rate QL corresponding to the operation of the operating device 71 and the actual flow rate of the hydraulic pump 51 is within 30% of the maximum flow rate of the hydraulic pump 51 is a "fine operation", that is, the change in the operation amount of the operating device 71 is less than a predetermined value (YES), and otherwise determines that the operation is not a "fine operation", that is, the change in the operation amount of the operating device 71 is equal to or greater than a predetermined value (NO). The command pump flow rate QL is calculated based on the operation of the operating device 71 by referring to a characteristic diagram (not shown) previously stored in the storage device 81, similar to the calculation by the target flow rate calculation unit 91. The actual flow rate of the hydraulic pump 51 is calculated by integrating the rotation speed N detected by the rotation speed sensor 73 and the actual pump capacity. The actual pump capacity is estimated as the set capacity corresponding to the capacity command (position command) output to the capacity switching mechanism 62 (each of the switching valves 64, 66) of the hydraulic pump 51. Note that the "fine operation" of the operating device 71 here does not refer to the amount of operation from a reference position (e.g., neutral position) of the operating device 71.

The capacity/rotation speed selection unit 92A selects a combination of set capacity and rotation speed that can realize the target pump flow rate Qt calculated by the target flow rate calculation unit 91 based on a characteristic diagram M2 (see FIG. 9) in which the flow rate versus rotation speed is determined for each set capacity of the hydraulic pump 51 stage (first stage set capacity, second stage set capacity, third stage set capacity). However, the capacity/rotation speed selection unit 92A selects the adjustable rotation speed range of the electric motor 52 in the characteristic diagram M2 shown in FIG. 9 depending on whether or not "fine operation" of the operating device 71 is performed.

When the capacity rotation speed selection unit 92A determines that the operation of the operating device 71 is not a "fine operation" (the change in the amount of operation of the operating device 71 is equal to or greater than a predetermined value), it selects the characteristic diagram M2 in which the first rotation speed range, in which the minimum rotation speed Nn is the lower limit and the maximum rotation speed Nx is the upper limit, is set as the adjustable rotation speed range of the electric motor 52, as in the first embodiment. In this case, as in the first embodiment, the capacity rotation speed selection unit 92A refers to the characteristic diagram M2 in which the first rotation speed range is an adjustable rotation speed range, and extracts all combinations of the set capacity and rotation speed that can realize the target pump flow rate Qt. If the target pump flow rate Qt is not on the common flow rate regions Fc1 and Fc2 of the characteristic diagram M2, only one combination of the set capacity and rotation speed that can realize the target pump flow rate Qt is determined. On the other hand, if the target pump flow rate Qt is on the common flow rate regions Fc1 and Fc2 of the characteristic diagram M2, it selects a combination that minimizes the deviation between the rotation speed that can realize the target pump flow rate Qt and the detected rotation speed N of the rotation speed sensor.

On the other hand, when it is determined that the operation of the operating device 71 is a "fine operation (the change in the amount of operation of the operating device 71 is less than a predetermined value)," the capacity/rotation speed selection unit 92A selects the characteristic diagram M2 (FIG. 9) in which the second rotation speed range, which is obtained by adding a rotation speed expansion region to the first rotation speed range, is set as the adjustable rotation speed range of the electric motor 52. The rotation speed expansion region is composed of a minimum side expansion region from an expansion minimum rotation speed Nne, which is a rotation speed lower than the minimum rotation speed Nn, to the minimum rotation speed Nn, and a maximum side expansion region from an expansion maximum rotation speed Nxe, which is a rotation speed higher than the maximum rotation speed Nx, to the maximum rotation speed Nx. That is, the second rotation speed range has the expansion minimum rotation speed Nne as its lower limit and the expansion maximum rotation speed Nxe as its upper limit. The expansion minimum rotation speed Nne and the expansion maximum rotation speed Nxe are set, for example, based on the allowable values of the specifications of the hydraulic pump 51 and the electric motor 52, and the minimum rotation speed Nn and the maximum rotation speed Nx are set with a margin of error with respect to the allowable values of the specifications of the hydraulic pump 51 and the electric motor 52.

In this characteristic diagram M2, a second rotation speed range expanded by the minimum expansion range and the maximum expansion range is selected as the adjustable rotation speed range of the electric motor 52, and the adjustable flow rate range of the set capacity of each stage (first stage expanded flow rate range, second stage expanded flow rate range, third stage expanded flow rate range) determined according to the second rotation speed range is also expanded. By expanding the adjustable flow rate range of the set capacity of each stage, it is intended to suppress switching of the pump capacity during "fine operation" of the operating device 71.

In this case, the capacity/rotation speed selection unit 92A refers to the characteristic diagram M2, which is the adjustable rotation speed range of the second rotation speed range including the rotation speed extension region, and extracts all combinations of set capacity and rotation speed that can achieve the target pump flow rate Qt. Furthermore, from among the extracted combinations, combinations that do not change the pump capacity are preferentially selected. This is because, since the characteristics of the flow rate relative to the rotation speed differ for each set capacity, there is a concern that switching the pump capacity during "fine operation" of the operating device 71, which corresponds to fine adjustment of the pump flow rate, may change the flow rate characteristics and cause an uncomfortable operation.

Next, an example of the control procedure executed by the controller constituting the second embodiment of the construction machine of the present invention will be described with reference to Figures 8, 10 and 11. Figure 10 is a flow chart showing an example of the procedure of pump flow control by the controller of the second embodiment of the construction machine of the present invention shown in Figure 8. Figure 11 is an explanatory diagram showing a selection method for fine adjustment of the combination of pump capacity and motor speed in the pump flow control of the controller of the second embodiment of the construction machine of the present invention. In Figures 10 and 11, the same reference numerals as those shown in Figures 1 to 9 indicate similar parts, so detailed description thereof will be omitted.

In the controller 80A shown in FIG. 8, the procedure for calculating the target pump flow rate Qt (steps S10 to S60) is the same as in the first embodiment, and therefore a description thereof will be omitted.

Next, the controller 80A takes in the detected rotation speed N (actual rotation speed of the electric motor 52) from the rotation speed sensor 73 (step S70 shown in FIG. 10), calculates the actual flow rate of the hydraulic pump 51 based on the detected rotation speed N of the rotation speed sensor 73 and the actual pump capacity (step S72 shown in FIG. 10), and judges whether the operation of the operation device 71 is "fine operation" or not (step S74). Specifically, the fine operation judgment unit 96 of the controller 80A estimates the set capacity corresponding to the capacity command (position command) output to the capacity switching mechanism 62 (each switching valve) of the hydraulic pump 51 as the actual pump capacity. Furthermore, the estimated actual pump capacity and the detected rotation speed N of the rotation speed sensor 73 are integrated to calculate the actual flow rate of the hydraulic pump 51. Furthermore, it is judged whether the difference between the calculated actual flow rate of the hydraulic pump 51 and the target pump flow rate Qt is 30% or less of the maximum flow rate of the hydraulic pump 51. If the difference is 30% or less of the maximum flow rate, the operation of the operating device 71 is determined to be a "fine operation" (YES), whereas if the difference is more than 30% of the maximum flow rate, the operation of the operating device 71 is determined not to be a "fine operation" (NO). If the answer is YES in step S74, the process proceeds to step S76, whereas if the answer is NO, the process proceeds to step S80. Note that the determination of the presence or absence of the "fine operation" described above is similar to determining whether or not the amount of change in the amount of operation of the operating device 71 is less than a predetermined value.

In step S74, if it is determined that the operation of the operating device 71 is not a "fine operation" (NO), the same control procedure as in the first embodiment is executed. That is, the controller 80A selects and refers to the characteristic diagram M2 (see FIG. 11) in which the first rotation speed range, which has the minimum rotation speed Nn as the lower limit and the maximum rotation speed Nx as the upper limit and has no rotation speed extension region, is an adjustable rotation speed range, to extract a set capacity and rotation speed that can realize the target pump flow rate Qt (step S80 shown in FIG. 10), and selects the set capacity and rotation speed of the combination that minimizes the deviation between the rotation speed that can realize the target pump flow rate Qt and the detected rotation speed N of the rotation speed sensor 73 as the target pump capacity and target rotation speed (step S90 shown in FIG. 10). Thereafter, the selected target pump capacity and target rotation speed are output as control commands to the capacity switching mechanism 62 (each switching valve 64, 66) and the electric motor 52, respectively (steps S100 to S110 shown in FIG. 10).

On the other hand, if it is determined in step S74 that the operation of the operating device 71 is a "fine operation" (YES), the capacity rotation speed selection unit 92A of the controller 80A selects and refers to the characteristic diagram M2 (see FIG. 11) in which the second rotation speed range with the rotation speed extension region, with the extension minimum rotation speed Nne as the lower limit and the extension maximum rotation speed Nxe as the upper limit, is set as an adjustable rotation speed range, thereby extracting the set capacity and rotation speed that can realize the target pump flow rate Qt (step S82 shown in FIG. 10). Next, it is determined whether or not there is a combination that does not change the pump capacity among the extracted combinations (step S84 shown in FIG. 10). If the answer is YES in step S84, the process proceeds to step S92, whereas if the answer is NO, the process proceeds to step S90. The execution of the control procedure in step S90 is the same as in the first embodiment, so a description thereof will be omitted.

If there is a combination in which the pump capacity is not changed (YES) in step S84, the capacity/rotation speed selection unit 92A of the controller 80A selects as the target rotation speed a rotation speed of a combination that can achieve the target pump flow rate Qt without changing the pump capacity (step S92 shown in FIG. 10).

For example, assume that the actual pump flow rate is Q3 and the pump capacity is the first stage set capacity. At this time, referring to the characteristic diagram M2 shown in FIG. 11, the rotation speed N of the electric motor 52 at control point C3 (the value detected by the rotation speed sensor 73) is N3f, which is located near the maximum rotation speed Nx in the rotation speed range that does not include the rotation speed extension region. From this situation, assume that the flow rate of the hydraulic pump 51 is changed to Q4 (target pump flow rate Qt = Q4).

If the characteristic diagram M2 is selected, which sets the first rotation speed range, which has the minimum rotation speed Nn as the lower limit and the maximum rotation speed Nx as the upper limit and does not have a rotation speed expansion region, as the adjustable rotation speed range, that is, if the same characteristic diagram as in the first embodiment is used, the target pump flow rate Q4 is located only in the flow rate range of the second stage set capacity. Therefore, the control point C4s on the characteristic diagram M2 of the second stage set capacity is selected. In other words, the second stage set capacity is selected as the target pump capacity, and the rotation speed N4s corresponding to the control point C4s is selected as the target rotation speed. In this case, the pump capacity is switched from the first stage set capacity to the second stage set capacity, and the rotation speed of the electric motor 52 is changed from N3f to N4s.

If the flow rate adjustment to change the pump flow rate from Q3 to Q4 corresponds to "fine operation" of the operating device 71, there is a concern that switching from the first stage set capacity to the second stage set capacity, which has different flow rate characteristics relative to the rotation speed, will cause an uncomfortable operation due to the change in flow rate characteristics.

In this embodiment, when the operation of the operating device 71 is "fine operation", the characteristic diagram M2 is referenced, which defines the second rotation speed range as an adjustable rotation speed range by adding a rotation speed extension region with the extension minimum rotation speed Nne as the lower limit and the extension maximum rotation speed Nxe as the upper limit. In the characteristic diagram M2, which defines the second rotation speed range including the maximum side extension region and the maximum side extension region as an adjustable range, the flow rate range determined for the set capacity of each stage is expanded. Therefore, unlike the case of selecting the characteristic diagram M2 without the rotation speed range of the extension region, the target pump flow rate Q4 is not only located in the flow rate range of the second stage set capacity, but also in the expanded first stage extension flow rate range at the first stage set capacity.

Therefore, in addition to the combination of the second stage set capacity and the rotation speed N4s (control point C4s), the combination of the first stage set capacity and the rotation speed N4f (control point C4f) is extracted as a combination of the set capacity and the rotation speed that can realize the target pump flow rate Q4. Since the pump capacity at that time is the first stage set capacity, the first stage set capacity and the rotation speed N4f exist as a combination that does not change the pump capacity. Therefore, the first stage set capacity and the rotation speed N4f, which are combinations that do not change the pump capacity, are selected as the target pump capacity and the target rotation speed. As a result, the first stage set capacity is maintained without changing the pump capacity, and the actual flow rate of the hydraulic pump 51 is adjusted to the target pump flow rate Q4 by changing the rotation speed of the electric motor 52 from N3f to N4f.

In this embodiment, when the operation of the operating device 71 is "fine operation", a combination of the set capacity and the rotation speed that can realize the target pump flow rate is selected by referring to the characteristic diagram M2 to which an extension region is added as an adjustable rotation speed range. Therefore, in the flow control of the hydraulic pump 51, when the pump capacity is the first stage set capacity, the adjustment margin of the rotation speed can be extended when the rotation speed of the electric motor 52 is in the vicinity of the maximum rotation speed Nx. Also, when the pump capacity is the second stage set capacity, the adjustment margin of the rotation speed can be extended when the rotation speed of the electric motor 52 is in the vicinity of the minimum rotation speed Nn and in the vicinity of the maximum rotation speed Nx. Also, when the pump capacity is the third stage set capacity, the adjustment margin of the rotation speed can be extended when the rotation speed of the electric motor 52 is in the vicinity of the minimum rotation speed Nn. Therefore, when the flow rate of the hydraulic pump 51 is finely adjusted, the frequency of switching the pump capacity can be reduced. This makes it possible to suppress changes in the flow rate characteristics due to switching of the pump capacity, and therefore to suppress discomfort in operability when the operating device 71 is "finely operated".

In addition, in this embodiment, when the operation of the operating device 71 is "fine operation", a combination of set capacity and rotation speed that does not change the pump capacity is preferentially selected as the target pump capacity and target rotation speed, so that the frequency of switching the pump capacity when the operation of the operating device 71 is "fine operation" can be reduced.

When changing the flow rate of the hydraulic pump 51 from Q3 to Q5 (target pump flow rate Qt = Q5), even if the operation corresponds to "fine operation", it is impossible to maintain the pump capacity at the first stage set capacity and realize the target pump flow rate Q5. This is because the target pump flow rate Q5 is not included in the first stage extension flow rate range of the first stage set capacity in the characteristic diagram M2, which includes an extension region as an adjustable rotation speed range. Therefore, a combination of the second stage set capacity and the rotation speed N5s (control point C5s) that can realize the target pump flow rate Q5 is selected. As a result, the pump capacity is switched from the first stage set capacity to the second stage set capacity, and the rotation speed of the electric motor 52 is changed from N3f to N5s.

According to the second embodiment of the construction machine of the present invention described above, as in the first embodiment described above, by making it possible to switch the pump capacity to one of three (multiple) set capacities, there is no response delay in capacity control as in a variable capacity hydraulic pump, and the adjustable rotation speed range of the electric motor 52 can be set more limitedly than in a fixed capacity hydraulic pump, which makes it possible to shorten the response time in the flow control of the hydraulic pump 51. In addition, by providing common flow ranges Fc1 and Fc2 for the flow ranges of both the front and rear set capacities, it becomes possible to select from multiple options a combination of pump capacity and electric motor rotation speed that can realize the target pump flow rate (target flow rate) on the common flow ranges Fc1 and Fc2, and by selecting the combination based on the operation amount of the operating device 71, it may be possible to shorten the response time and reduce the frequency of switching the pump capacity. Therefore, in the flow control of the hydraulic pump 51, it is possible to suppress the discomfort of operation while improving responsiveness.

In addition, in this embodiment, the controller 80A is configured to determine whether the operation of the operating device 71 is fine operation (the change in the amount of operation is less than a predetermined value), and if it is determined that the operation is not fine operation (the change in the amount of operation is equal to or greater than a predetermined value), select a first rotation speed range in which the minimum rotation speed Nn (first rotation speed) is the lower limit and the maximum rotation speed Nx (second rotation speed) is the upper limit as the adjustable rotation speed range of the electric motor 52 (prime mover), and perform flow control of the hydraulic pump 51, while if it is determined that the operation is fine operation (the change in the amount of operation is less than a predetermined value), select a second rotation speed range in which the adjustable rotation speed range of the electric motor 52 (prime mover) is the lower limit, a rotation speed Nne lower than the minimum rotation speed Nn (first rotation speed), and the upper limit, a rotation speed Nxe higher than the maximum rotation speed Nx (second rotation speed), and perform flow control of the hydraulic pump 51. When the first rotation speed range is selected as the adjustable rotation speed range of the electric motor 52 (prime mover), and the target flow rate is on the common flow rate region Fc1, Fc2, the controller 80A selects one of the combinations of the pump capacity of the hydraulic pump 51 and the rotation speed of the electric motor 52 (prime mover) that can realize the target pump flow rate (target flow rate) based on the rotation speed N detected by the rotation speed sensor 73, and when the second rotation speed range is selected as the adjustable rotation speed range of the electric motor 52 (prime mover), among the combinations of the pump capacity of the hydraulic pump 51 and the rotation speed of the electric motor 52 (prime mover) that can realize the target pump flow rate (target flow rate), if there is a combination that can be maintained without changing the pump capacity of the hydraulic pump 51, the controller 80A is configured to preferentially select a combination of the set capacity and the rotation speed of the electric motor 52 (prime mover) that can maintain the pump capacity of the hydraulic pump 51.

According to this configuration, when the operation of the operating device 71 is fine operation (the change in the amount of operation is less than a predetermined value), the adjustment margin of the rotation speed of the electric motor 52 in the flow control of the hydraulic pump 51 is expanded more than when not fine operation, so that even if the conditions for switching the pump capacity are met when not fine operation, it may be possible to maintain the pump capacity without switching it. Therefore, when the operation of the operating device 71 is fine operation, the frequency of switching the pump capacity can be reduced, and the discomfort in operation caused by the change in flow characteristics due to switching the pump capacity can be suppressed.

The present invention is not limited to this embodiment, but includes various modified examples. The above-mentioned embodiment has been described in detail to explain the present invention in an easy-to-understand manner, and is not necessarily limited to having all of the configurations described. It is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

For example, in the first and second embodiments described above, an example was shown in which the present invention is applied to a hydraulic excavator 1, but the present invention can be widely applied to various types of construction machinery, such as hydraulic cranes and wheel loaders.

In the first and second embodiments described above, an example was shown in which the capacity switching mechanism 62 of the hydraulic pump 51 includes a servo cylinder 63 and first and second switching valves 64, 66. However, the capacity switching mechanism 62 can be configured in any way as long as it is capable of mechanically switching to one of a number of set capacities that differ in stages.

In the above-described embodiment, an example of a configuration in which the operation (operation direction and operation amount) of the operating device 71 is electrically detected and an operation signal is output to the controllers 80, 80A has been shown. However, a configuration in which the operation of the operating device 71 is detected by the operating pilot pressure generated by the operating device 71 is also possible. The operating pilot pressure generated by the operating device 71 is detected by, for example, a pressure sensor.

In the above-described embodiment, an example of a configuration in which an electric motor 52 is used as the prime mover that drives the hydraulic pump 51 has been shown. However, the prime mover that drives the hydraulic pump 51 may be any configuration as long as it is capable of continuously changing the rotation speed.

In the present embodiment, an example has been shown in which the operating pressure supplied to the first, second, and fourth pressure-receiving chambers 635, 636, and 638 of the servo cylinder 63 is supplied via the discharge line 56. However, it is also possible to supply operating pressure to the first, second, and fourth pressure-receiving chambers 635, 636, and 638 using an external hydraulic source, such as a gear pump, whose discharge pressure can be set by a relief valve.

1...hydraulic excavator (construction machine), 51...hydraulic pump, 52...electric motor (prime mover), 53...hydraulic actuator, 61a...variable mechanism, 62...capacity switching mechanism, 63...servo cylinder, 631...servo piston, 635...first pressure receiving chamber (pressure receiving chamber), 638...fourth pressure receiving chamber (pressure receiving chamber), 64...first switching valve (switching valve), 66...second switching valve (switching valve), 71...operating device, 73...rotation speed sensor, 80, 80A...controller

Claims (4)

The prime mover,
a hydraulic pump driven by the prime mover and capable of switching a pump displacement to one of a plurality of set displacements which differ in stages;
a hydraulic actuator driven by pressure oil discharged from the hydraulic pump;
an operating device for instructing driving of the hydraulic actuator;
A rotation speed sensor for detecting a rotation speed of the prime mover;
A construction machine equipped with a controller that performs flow control to control a flow rate of the hydraulic pump by adjusting the rotation speed of the prime mover and switching the pump capacity of the hydraulic pump,
The set capacity of each stage of the hydraulic pump is set so as to generate a common flow rate region in which adjustable flow rate ranges determined according to an adjustable rotation speed range of the prime mover overlap each other in a part of the set capacity of each stage that is different by one stage from the set capacity of each stage,
a control unit for controlling a flow rate of the hydraulic pump from the control unit to a predetermined target flow rate and for controlling a flow rate of the hydraulic pump from the control unit to a predetermined target flow rate, the control unit being configured to control the flow rate of the hydraulic pump from the control unit to a predetermined target flow rate and for controlling a flow rate of the hydraulic pump from the control unit to a predetermined target flow rate. 2. The construction machine according to claim 1,
and when the target flow rate is within the common flow rate region, the controller selects, from among combinations of the pump capacity of the hydraulic pump and the rotational speed of the prime mover that can realize the target flow rate, a combination that minimizes a deviation between the rotational speed detected by the rotational speed sensor and the rotational speed of the prime mover that can realize the target flow rate. 2. The construction machine according to claim 1,
The controller:
determining whether or not a change in an operation amount of the operation device is less than a predetermined value;
When it is determined that the amount of change in the manipulated variable is equal to or greater than the predetermined value, a first rotation speed range in which a first rotation speed is a lower limit and a second rotation speed is an upper limit is selected as an adjustable rotation speed range of the prime mover, and a flow rate control of the hydraulic pump is executed;
when it is determined that the amount of change in the manipulated variable is less than the predetermined value, selecting a second rotation speed range, as an adjustable rotation speed range of the prime mover, the second rotation speed range having a lower limit of a rotation speed lower than the first rotation speed and an upper limit of a rotation speed higher than the second rotation speed, and executing a flow rate control of the hydraulic pump;
The controller:
When the first rotation speed range is selected as an adjustable rotation speed range of the prime mover, and when the target flow rate is within the common flow rate region, one of combinations of the pump capacity of the hydraulic pump and the rotation speed of the prime mover that can realize the target flow rate is selected based on the rotation speed detected by the rotation speed sensor;
when the second rotation speed range is selected as the adjustable rotation speed range of the prime mover, if there is a combination of the pump capacity of the hydraulic pump and the rotation speed of the prime mover that can realize the target flow rate and that can be maintained without changing the pump capacity of the hydraulic pump, a combination of a set capacity and the rotation speed of the prime mover that can maintain the pump capacity of the hydraulic pump is preferentially selected. 2. The construction machine according to claim 1,
The hydraulic pump is
A variable mechanism that enables the pump capacity to be changed by changing the tilt angle;
a displacement switching mechanism that switches the pump displacement to one of a plurality of set displacements by driving the variable mechanism,
The capacity switching mechanism includes:
a servo cylinder having a plurality of pressure receiving chambers to which hydraulic oil is supplied and discharged, and a servo piston that is displaced by supplying and discharging hydraulic oil to and from the plurality of pressure receiving chambers;
a plurality of switching valves that selectively switch between supplying and discharging hydraulic oil to and from the plurality of pressure receiving chambers of the servo cylinder,
The servo piston is connected to the variable mechanism,
The construction machine according to claim 1, wherein the servo cylinder is configured so that a position to which the servo piston can be displaced by supplying or discharging hydraulic oil to or from the plurality of pressure-receiving chambers is structurally restricted.

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