Excavator

Abstract

To provide a shovel including a rotation motor and a power storage system that can appropriately operate even at a lower temperature.SOLUTION: A shovel according to an embodiment of the present invention includes a lower travel body 1, an upper rotation body 3, and a capacitor 19. When temperature information on the capacitor 19 is not in a standard temperature range, the capacitor 19 is shifted to a control mode for a case not in the standard temperature range to control output of the capacitor 19 during power running. When the temperature information on the capacitor 19 is not in the standard temperature range, the shovel may shift the capacitor 19 and a main pump 14 to the control mode for a case not in the standard temperature range.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an excavator equipped with a slewing motor and a power storage system.

Background Art

[0002] Hybrid construction machines equipped with an electric generator connected to a battery, a hydraulic motor rotated by the return oil from a slewing hydraulic motor, a main pump driven by an engine, and an assist pump for assisting the main pump are known (see Patent Document 1). When this hybrid construction machine stops slewing, it generates electricity using the return oil from the slewing hydraulic motor and charges the battery with the generated electricity.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, if regenerative power generation is suppressed, no electric braking force can be obtained.

[0005] In view of the above, it is desirable to provide an excavator equipped with a slewing motor and a power storage system that can operate properly even at low temperatures.

Means for Solving the Problems

[0006] The excavator according to an embodiment of the present invention has a lower traveling body, an upper slewing body, and a capacitor. When the temperature of the capacitor is a predetermined temperature, the discharge power of the capacitor during power running is limited by a discharge limit value adopted in the case of the predetermined temperature. An excavator, wherein the discharge limit value is the maximum value of the power that the capacitor can discharge, and when the temperature of the capacitor is the predetermined temperature, the output of the hydraulic pump is limited by a pump current limit value corresponding to a swing speed limit value adopted when the temperature is the predetermined temperature, the swing speed limit value decreases as the predetermined temperature decreases, and the pump current limit value increases as the swing speed limit value increases .

Effects of the Invention

[0007] By the above means, it is possible to provide an excavator equipped with a swing electric motor and a power storage system that can operate properly even at low temperatures.

Brief Description of the Drawings

[0008]

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Mode for Carrying Out the Invention

[0009] Figure 1 is a side view showing an example of a construction machine to which the present invention is applied, a hydraulic excavator. An upper swing body 3 is mounted on a lower traveling body 1 of the hydraulic excavator via a swing mechanism 2. A boom 4 is attached to the upper swing body 3. An arm 5 is attached to the tip of the boom 4, and a bucket 6 is attached to the tip of the arm 5. The boom 4, the arm 5, and the bucket 6 constitute an excavation attachment, which is an example of a work attachment, and are hydraulically driven by a boom cylinder 7, an arm cylinder 8, and a bucket cylinder 9, respectively. A cab 10 is provided on the upper swing body 3, and a power source such as an engine is mounted.

[0010] Figure 2 is a block diagram showing a configuration example of the drive system of the hydraulic excavator according to an embodiment of the present invention. In Figure 2, the mechanical power system is shown by a double line, the high-pressure hydraulic line is shown by a thick solid line, the pilot line is shown by a broken line, and the electric drive / control system is shown by a thin solid line.

[0011] An engine 11 as a mechanical drive unit and a motor generator 12 as an assist drive unit are respectively connected to two input shafts of a transmission 13. A main pump 14 and a pilot pump 15 as hydraulic pumps are connected to an output shaft of the transmission 13. A control valve 17 is connected to the main pump 14 via a high-pressure hydraulic line 16. The main pump 14 and each valve in the control valve 17 may be connected in parallel.

[0012] The main pump 14 is a component of a hydraulic drive system in an excavator, and in this embodiment, it is a swash plate type variable displacement hydraulic pump.

[0013] A regulator 14a is a device that controls the discharge amount of the main pump 14. In this embodiment, the regulator 14a adjusts the swash plate tilt angle of the main pump 14 according to a command from a controller 30 to control the discharge amount of the main pump 14.

[0014] The control valve 17 is a hydraulic control device that controls the hydraulic system in an excavator. Hydraulic actuators such as a right travel hydraulic motor 1R, a left travel hydraulic motor 1L, a boom cylinder 7, an arm cylinder 8, and a bucket cylinder 9 are connected to the control valve 17 via a high-pressure hydraulic line. Note that the hydraulic system includes the right travel hydraulic motor 1R, the left travel hydraulic motor 1L, the boom cylinder 7, the arm cylinder 8, the bucket cylinder 9, the main pump 14, and the control valve 17.

[0015] The electric generator 12 is connected to a power storage system 120 including a capacitor as a power storage device via an inverter 18 as an electric generator control unit. Further, the power storage system 120 is connected to a swing electric motor 21 as an electric working element via an inverter 20 as an electric generator control unit. A resolver 22, a mechanical brake 23, and a swing speed changer 24 are connected to the rotating shaft 21A of the swing electric motor 21. An operating device 26 is connected to the pilot pump 15 via a pilot line 25. The swing electric motor 21, the inverter 20, the resolver 22, the mechanical brake 23, and the swing speed changer 24 constitute an electric swing system as a load drive system. The swing electric motor 21 has a function of swing drive and rotates the upper swing body 3. The swing system may be configured to include a hydraulic drive and brake system. This embodiment exhibits remarkable effects particularly in a configuration that does not use hydraulic pressure for swing drive. Hereinafter, a configuration that does not use hydraulic pressure for swing drive will be described.

[0016] The operating device 26 generates information related to the operation amount. The information can be supplied directly to the drive device or other devices as it is or after being converted, or indirectly via a controller 30 or the like. The operating device 26 includes a lever 26A, a lever 26B, and a pedal 26C. The lever 26A, the lever 26B, and the pedal 26C are respectively connected to a control valve 17 and a pressure sensor 29 via hydraulic lines 27 and 28.

[0017] The pressure sensor 29 is a sensor that detects the operation content of the operating device 26 in the form of pressure and outputs the detected value to the controller 30.

[0018] The discharge pressure sensor 29A is a sensor that detects the discharge pressure of the main pump 14 and outputs the detected value to the controller 30.

[0019] The temperature sensors M2 and M3 are sensors that detect the temperature of the power storage system 120 and output the detected values to the controller 30. In this embodiment, the temperature sensors M2 and M3 are composed of thermistors and output the detected values to the controller 30.

[0020] The controller 30 is a control device that serves as a main control unit for controlling the operation of the excavator. In this embodiment, the controller 30 is composed of an arithmetic processing unit including a CPU and an internal memory, and realizes various functions by causing the CPU to execute a program for drive control stored in the internal memory.

[0021] In addition, the controller 30 receives detection values from, for example, the pressure sensor 29, the discharge pressure sensor 29A, the temperature sensor M2, and the temperature sensor M3, executes various calculations, and outputs various commands to the engine 11, the regulator 14a, the power storage system 120, and the like. For example, when the controller 30 determines based on the detection value of the temperature sensor M2 that the temperature of the power storage system 120 is lower than a predetermined temperature, the controller 30 starts warming up the power storage system 120. Further, even when the controller 30 determines based on the detection values of the pressure sensor 29 and the discharge pressure sensor 29A that warming up of the hydraulic drive system has started, the controller 30 continues to warm up the power storage system 120. Details regarding the warming up of the hydraulic drive system and the power storage system 120 will be described later.

[0022] FIG. 3 is a block diagram showing the configuration of the power storage system 120. The power storage system 120 includes a capacitor 19 as a first capacitor, a buck-boost converter 100, and a DC bus 110 as a bus line. The first capacitor is a device capable of charging and discharging electric power, and is, for example, a lithium ion capacitor, an electric double layer capacitor, a lithium ion battery, or the like. In this embodiment, the capacitor 19 is a lithium ion capacitor.

[0023] The power storage system 120 is provided with a capacitor voltage detection unit 112 for detecting the capacitor voltage value and a capacitor current detection unit 113 for detecting the capacitor current value. The capacitor voltage value and the capacitor current value are supplied to the controller 30.

[0024] The capacitor voltage value corresponds to the terminal voltage of capacitor 19. Let the open-circuit voltage of capacitor 19 be Vc [V], the internal resistance of capacitor 19 be R [Ω], and the magnitude of the discharge current flowing from capacitor 19 to the buck-boost converter 100 be Id [A]. Then, the terminal voltage V1 during discharge of capacitor 19 is expressed as V1 = Vc - R × Id, and the discharge power W1 of capacitor 19 is expressed as W1 = V1 × Id. Also, if the magnitude of the charging current flowing from the buck-boost converter 100 to capacitor 19 is Ic, the terminal voltage V2 during charging of capacitor 19 is expressed as V2 = Vc + R × Ic, and the charging power W2 of capacitor 19 is expressed as W2 = V2 × Ic.

[0025] In addition, the heat generation amount Q1 during discharge of capacitor 19 is Id 2 × R, and the heat generation amount Q2 during charging is Ic 2 × R.

[0026] Also, the state of charge (SOC) of capacitor 19 is expressed by the following formula, where the minimum voltage of capacitor 19 is Vmin and the maximum voltage is Vmax.

[0027]

Equation

[0028] In addition, the temperature sensor M2 provided in the power storage system 120 detects the temperature of the capacitor 19 (capacitor temperature). The temperature sensor M3 detects the temperature of the buck-boost converter 100. The capacitor temperature may be detected in a manner that allows the relative value of the temperature of the capacitor 19 with respect to an appropriate reference to be known, and is usually directly measured. Information related to the capacitor temperature may also be used. For example, it may be indirectly detected by detecting the temperature of the cooling water used for cooling the capacitor 19. Alternatively, it may be indirectly detected by detecting the temperature of other heat media other than the cooling water that affect the temperature of the capacitor 19. It may also be the ambient temperature such as the air temperature. For example, the temperature sensor M2 is composed of a thermistor attached to the electrode of the capacitor cell, detects the capacitor temperature, and outputs the detected value to the controller 30.

[0029] The buck-boost converter 100 performs control to switch between a boosting operation and a bucking operation so that the DC bus voltage value falls within a certain range according to the operating states of the motor generator 12 and the swing motor 21. Note that the voltage of the DC bus 110 is detected by the DC bus voltage detector 111. The DC bus 110 is disposed between each of the inverters 18 and 20 and the buck-boost converter 100, and conducts power transfer between the capacitor 19, the motor generator 12, and the swing motor 21.

[0030] The controller 30 converts the signal supplied from the pressure sensor 29 into a speed command and controls the drive of the swing motor 21. In this case, the signal supplied from the pressure sensor 29 corresponds to a signal representing the operation amount when the operating device 26 is operated to swing the swing mechanism 2.

[0031] In addition, the controller 30 performs operation control of the motor generator 12 (switching between electric (assist) operation and power generation operation), and performs charge and discharge control of the capacitor 19 by controlling the drive of the buck-boost converter 100. Specifically, the controller 30 performs charge and discharge control of the capacitor 19 corresponding to the charge state of the capacitor 19, the operating state of the motor generator 12 (assist operation or power generation operation), and the operating state of the swing motor 21 (power running operation or regeneration operation).

[0032] In the control of the buck-boost converter 100, the DC bus voltage value, the capacitor voltage value, and the capacitor current value are taken into consideration.

[0033] In the configuration as described above, the electric power generated by the motor generator 12, which is an assist motor, is supplied to the DC bus 110 via the inverter 18 and then supplied to the capacitor 19 via the buck-boost converter 100, or can be supplied to the rotary motor 21 via the inverter 20. Also, the regenerative power generated when the rotary motor 21 performs regenerative operation is supplied to the DC bus 110 via the inverter 20 and then supplied to the capacitor 19 via the buck-boost converter 100, or can be supplied to the motor generator 12 via the inverter 18. Further, the electric power stored in the capacitor 19 can be supplied to at least one of the motor generator 12 and the rotary motor 21 via the buck-boost converter 100 and the DC bus 110.

[0034] In the excavator having the configuration as described above, the controller 30 charges and discharges the capacitor 19 so that the capacitor 19 can maintain or is likely to maintain a predetermined state of charge (SOC). There are advantages, which will be described later, in changing this predetermined SOC within an appropriate range according to the environment surrounding the capacitor 19. At least, the capacitor 19 is maintained within a range such that it does not become overcharged or over-discharged even when it exchanges power with various electrical loads. Furthermore, as an operation of the SOC, the SOC of the capacitor 19 may be maintained at a predetermined SOC level (for example, 70%). The higher this level, the more energy can be retained. However, as will be described later, when the environmental temperature is low and the temperature of the capacitor 19 is low, a relatively low level may be preferable.

[0035] Note that "purposes other than charging the capacitor 19" includes intentionally applying a load to the engine 11. Also, by intentionally applying a load to the engine 11 by causing the motor generator 12 to function as a generator at an arbitrary timing, the controller 30 can increase the output of the engine 11 at an arbitrary timing. This is because the engine 11 increases its output in an attempt to maintain a predetermined rotational speed when the load increases. Therefore, before a hydraulic load is applied to the engine 11, the controller 30 can instantaneously increase the output of the engine 11 to prevent the rotational speed of the engine 11 from decreasing due to insufficient output when the hydraulic load is actually applied.

[0036] The SOC of the capacitor 19 is calculated based on the capacitor voltage value. It may be derived by measuring the internal resistance of the capacitor 19, or may be derived using any other arbitrary known method.

[0037] The controller 30 determines a charge demand value and a discharge demand value based on the current value of the SOC of the capacitor 19, and controls the charge and discharge of the capacitor 19. The controller 30 causes the motor generator 12 to generate electricity with electric power corresponding to the charge demand value (the power generation itself may generate more electric power). The capacitor 19 is charged with electric power corresponding to the charge demand value. The charge demand value may be configured to change according to the current SOC, the state of the motor, and the generator. When the charge demand value is set to zero, the capacitor 19 is not charged. However, it does not prohibit the motor generator 12 from functioning as a generator for other purposes.

[0038] Further, when the turning electric motor 21 is in power running, the controller 30 discharges the power of the capacitor 19 based on the discharge required value (if the power required for turning or assist is low, power equal to or less than the discharge required value may be discharged). The discharge required value may be configured to change according to the current SOC, the states of the electric motor and the generator. If the output [kW] required to drive the turning electric motor 21 is greater than the power corresponding to the discharge required value, the motor generator 12 is made to function as a generator. This is to drive the turning electric motor 21 with the power generated by the motor generator 12 and the power discharged by the capacitor 19. Also, when the controller 30 sets the discharge required value to zero, the capacitor 19 is not discharged.

[0039] Here, referring to FIG. 4, a process in which the controller 30 derives a charge required value and a discharge required value based on the SOC of the capacitor 19 (hereinafter referred to as "required value derivation process") will be described. Note that FIG. 4 is a flowchart showing the flow of the required value derivation process, and the controller 30 repeatedly executes this required value derivation process at a predetermined control cycle.

[0040] First, the controller 30 acquires the SOC of the capacitor 19 (step S1).

[0041] Also, the controller 30 detects the state of the turning electric motor 21 (step S2). The operating state and the stopped state of the turning electric motor 21 are discriminated from the turning speed calculated based on the output of the resolver 22. The power running state and the regenerative operation state of the turning electric motor 21 are discriminated from the turning torque and the turning speed calculated based on the current flowing through the inverter 20.

[0042] Also, steps S1 and S2 may be in any order, and the controller 30 may acquire the SOC of the capacitor 19 after detecting the state of the turning electric motor 21, or may execute the two processes simultaneously.

[0043] Thereafter, the controller 30 derives a charging request value based on the SOC of the capacitor 19 and the state of the turning electric motor 21 (step S3). At this time, the SOC - request value correspondence table stored in the internal memory may be referred to.

[0044] Also, a discharge request value is derived based on the SOC of the capacitor 19 and the state of the turning electric motor 21 (step S4). In this embodiment, the controller 30 may refer to the SOC - request value correspondence table used when deriving the charging request value.

[0045] FIG. 5 is a diagram for explaining an example of the SOC - request value correspondence table. FIG. 5 is a graph showing the relationship between the SOC of the capacitor 19, the discharge request value, and the charging request value. The horizontal axis corresponds to the SOC [%], and the vertical axis corresponds to the request value. In FIG. 5, the discharge request value is set as a positive value, and the charging request value is set as a negative value. Also, the charging request value in FIG. 5 is for causing the motor - generator 12 to function as a generator for charging the capacitor 19. The regenerative power of the turning electric motor 21 is charged to the capacitor 19 separately from the charging by the generated power of the motor - generator 12 corresponding to the charging request value.

[0046] The charging request line CL1 indicated by the broken line in FIG. 5 represents the transition of the charging request value adopted when the turning electric motor 21 is in the power running state. Also, when the SOC is 40 [%] or less, the charging request value becomes the value C1, and even if the SOC further decreases, it remains constant at the value C1. As the SOC exceeds 40 [%] and reaches 45 [%], it gradually approaches zero, and when the SOC is 45 [%] or more, it becomes zero (including the vicinity of zero. The same applies hereinafter). When the charging request line CL1 is adopted, the SOC is more likely to increase when it is 40 [%] or less than when it exceeds 40 [%]. Therefore, the charging rate increases from when the SOC is relatively low and is likely to be maintained between 40 and 45 [%]. Also, since the value C1 is set relatively low even if the SOC further decreases, the generated power is suppressed to a low level, and the engine output is likely to be directed to the hydraulic load and the turning load.

[0047] In addition, the charging requirement line CL2 indicated by the dashed-dotted line in Fig. 5 represents the transition of the charging requirement value adopted when the swing motor 21 is in the regenerative operation state. Also, when the SOC is 40% or less, the charging requirement value becomes the value C2, and even if the SOC further decreases, it remains constant at the value C2. It represents that the value gradually approaches zero as the SOC exceeds 40% and reaches 60%, and becomes zero when the SOC is 60% or more. When the charging requirement line CL2 is adopted, the SOC is more likely to increase when it is 40% or less than when it exceeds 40%. Also, the SOC is likely to be maintained around 45 - 60%. Further, since the value C2 is set relatively low even if the SOC further decreases, the power generation amount is suppressed to a low level, and the engine output is easily directed to the hydraulic load and the swing load. Although it is easier to charge in the case of the value C2 than the value C1, this is because, since the swing is in regeneration, it is not necessary to consider the power generation amount for the swing load so much.

[0048] In addition, the charging requirement line CL3 indicated by the long dashed-dotted line in Fig. 5 represents the transition of the charging requirement value adopted when the swing motor 21 is in the stopped state. Also, when the SOC is 40% or less, the charging requirement value becomes the value C3, and it represents that the value gradually approaches zero as the SOC exceeds 40% and reaches 60%, and becomes zero when the SOC is 60% or more. When the charging requirement line CL3 is adopted, the SOC is more likely to increase when it is 40% or less than when it exceeds 40%. Therefore, it is likely to be maintained between 45 - 60%. Further, since the value C3 is set relatively low even if the SOC further decreases, the power generation amount is suppressed to a low level, and the engine output is easily directed to the hydraulic load and the swing load. The level of the value C3 is lower than the value C2 and higher than the value C1. This is taken into account that the swing is stopped.

[0049] Further, the discharge requirement line DL1 indicated by the dashed line in Fig. 5 represents the transition of the discharge requirement value adopted when the rotary motor 21 is in the power running state. Also, when the SOC is 60% or less, the discharge requirement value becomes zero, and it increases at a constant rate until the SOC exceeds 60% and reaches 100%. When the SOC reaches 100%, it becomes the value D1. When the discharge requirement line DL1 is adopted, the higher the SOC level, the more discharge can be performed, and the driving force of the motor (e.g., for rotation) can be increased. Accordingly, the SOC is more likely to be reduced and is likely to be maintained around 60%.

[0050] Further, the discharge requirement line DL2 indicated by the dash-dotted line in Fig. 5 represents the transition of the discharge requirement value adopted when the rotary motor 21 is in the regenerative operation state. Also, when the SOC is 70% or less, the discharge requirement value becomes zero, and it increases at a constant rate until the SOC exceeds 70% and reaches 80%. When the SOC is 80% or more, it becomes the value D2. When the discharge requirement line DL2 is adopted, the SOC can discharge more when it is 80% or more than when it is less than 80%, and the driving force of the motor (e.g., for assist) can be increased. Accordingly, the SOC is more likely to be reduced and is likely to be maintained between 70% and 80%, particularly around 70%.

[0051] Further, the discharge requirement line DL3 indicated by the double dash-dotted line in Fig. 5 represents the transition of the discharge requirement value adopted when the rotary motor 21 is in the stopped state. Also, when the SOC is 70% or less, the discharge requirement value becomes zero, and it increases at a constant rate until the SOC exceeds 70% and reaches 85%. When the SOC is 85% or more, it becomes the value D3. When the discharge requirement line DL3 is adopted, the driving force of the motor can be increased when the SOC is 85% or more compared to when it is less than 85%, but accordingly the SOC is more likely to be reduced. Therefore, it is likely to be maintained between 70% and 85%, particularly around 70%.

[0052] The graph in Fig. 5 shows that if the current SOC of the capacitor 19 is 70% and the current state of the turning electric motor 21 is the power running state, the charging required value is zero and the discharging required value is D4. If the current SOC of the capacitor 19 is 30% and the current state of the turning electric motor 21 is the regeneration operation state, the charging required value is C2 and the discharging required value is zero. In this way, the charging of the capacitor 19 by the power generation of the motor generator 12 and the turning regeneration, and the discharging of the capacitor 19 for the assist of the motor generator 12 and the turning power running are basically executed according to specific discharge required lines and charging required lines. Regarding discharging, the larger the SOC, the easier it is to discharge, and regarding charging, there are provided an area where the smaller the SOC, the easier it is to be charged, and an area where a certain charging required value is set even if the SOC is small. By setting in this way, the power storage system 120 is made to easily output driving force by discharging and to suppress an increase in the load of the engine 11 by power generation, and is in a highly workable form.

[0053] Next, referring to Fig. 6, when the turning electric motor 21 is in the power running state, a process (hereinafter referred to as "process during turning power running") in which the controller 30 controls the charging and discharging of the capacitor 19 using the charging required value and the discharging required value will be described.

[0054] First, the controller 30 determines whether or not the output required for the turning drive of the turning electric motor 21 (hereinafter referred to as "required output") is less than or equal to the discharging required value (step S11). This is to determine whether the turning electric motor 21 can be driven only by the discharging power. The controller 30 derives the required output from the product of the turning speed calculated based on the output of the resolver 22 and the turning torque calculated based on the current flowing through the inverter 20. Then, the controller 30 compares the required output with the discharging required value derived in the required value derivation process of Fig. 4.

[0055] If it is determined that the required output is less than or equal to the discharging required value (YES in step S11), the controller 30 drives the turning electric motor 21 only with the power (discharging power) by which the capacitor 19 discharges (step S12).

[0056] On the other hand, when it is determined that the required output is greater than the discharge required value (NO in step S11), the controller 30 determines whether the charge required value is zero (step S13). The charge required value of zero may be adopted to control so as not to charge further when the SOC is equal to or higher than a predetermined value based on the used charge required line. In this case, the charging of the capacitor 19 is stopped. When the charge required value is not zero, a part of the generated power is used for charging.

[0057] When it is determined that the charge required value is zero (YES in step S13), the controller 30 determines whether the required output is equal to or less than the sum of the discharge required value and the power generation limit value (step S14). This is to determine whether the rotating electric motor 21 can be driven only by the discharge power and the generated power. Note that the power generation limit value means the maximum value of the power that the motor generator 12 can generate.

[0058] When it is determined that the required output is equal to or less than the sum of the discharge required value and the power generation limit value (YES in step S14), the controller 30 determines whether the discharge required value is zero (step S15). The discharge required value of zero may be adopted to control so as not to discharge further when the SOC is equal to or lower than a predetermined value based on the used discharge required line.

[0059] When it is determined that the discharge required value is zero (YES in step S15), the controller 30 drives the rotating electric motor 21 only with the power generated by the motor generator 12 (generated power) (step S16).

[0060] Also, when it is determined that the discharge required value is not zero (NO in step S15), the controller 30 drives the rotating electric motor 21 with the discharge power discharged from the capacitor 19 and the generated power generated by the motor generator 12 (step S17).

[0061] Also, when it is determined that the required output is greater than the sum of the discharge required value and the power generation limit value (NO in step S14), the controller 30 drives the turning motor 21 with a discharge power greater than the discharge power corresponding to the discharge required value at which the capacitor 19 discharges and the power generation power corresponding to the power generation limit value at which the motor generator 12 generates power (step S19). This is because the required output needed by the turning motor 21 cannot be supplied by the power generation power corresponding to the power generation limit value and the discharge power corresponding to the discharge required value. However, the turning output may be controlled to be suppressed. The discharge from the capacitor 19 can be suppressed to the level corresponding to the discharge required value.

[0062] Also, when it is determined that the charging required value is not zero (NO in step S13), the controller 30 determines whether the required output is greater than or equal to the value obtained by subtracting the charging required value from the power generation limit value (step S18). This is to determine whether the required output needed by the turning motor 21 can be supplied only by the motor generator 12.

[0063] When it is determined that the required output is greater than or equal to the value obtained by subtracting the charging required value from the power generation limit value (YES in step S18), the controller 30 drives the turning motor 21 with a discharge power greater than the discharge power corresponding to the discharge required value at which the capacitor 19 discharges and the power generation power corresponding to the power generation limit value at which the motor generator 12 generates power (step S19). This is because when the capacitor 19 is charged with the power generation power corresponding to the charging required value generated by the motor generator 12, the capacitor 19 cannot discharge, and the required output needed by the turning motor 21 cannot be supplied only by the motor generator 12. However, the turning output may be controlled to be suppressed. The discharge from the capacitor 19 can be suppressed to the level corresponding to the discharge required value.

[0064] On the other hand, when it is determined that the required output is less than the value obtained by subtracting the charging request value from the power generation limit value (NO in step S18), the controller 30 drives the rotation motor 21 only with the power generation power generated by the motor generator 12, and charges the capacitor 19 with the power generation power corresponding to the charging request value generated by the motor generator 12 (step S20). That is, the motor generator 12 generates power corresponding to the required output and power corresponding to the charging request value.

[0065] Next, with reference to FIG. 7, a process in which the controller 30 controls charging and discharging of the capacitor 19 using the charging request value and the discharging request value when the rotation motor 21 is in the regenerative operation state (hereinafter referred to as "regenerative operation during turning process") will be described.

[0066] First, the controller 30 determines whether the discharge request value is zero (step S21).

[0067] When it is determined that the discharge request value is zero (YES in step S21), that is, when the discharge of the capacitor 19 is stopped, the controller 30 determines whether the charging request value is not zero (step S22). This is to determine whether the charging of the capacitor 19 has not been stopped.

[0068] When it is determined that the charging request value is not zero (YES in step S22), the controller 30 charges the capacitor 19 with all of the regenerative power generated by the rotation motor 21 and the power generation power corresponding to the charging request value (step S23).

[0069] Note that when it is determined that the charging request value is zero (NO in step S22), there is no power generation power, and the controller 30 charges the capacitor 19 with all of the regenerative power generated by the rotation motor 21 (step S24).

[0070] Also, when it is determined that the discharge required value is not zero (NO in step S21), the controller 30 determines whether the regenerative power is greater than the discharge required value (step S25). This is to determine whether to charge the capacitor 19. In this embodiment, the regenerative power is represented by a negative value, and the discharge required value is represented by a positive value. Therefore, strictly speaking, the controller 30 determines whether the absolute value of the regenerative power is greater than the discharge required value.

[0071] When it is determined that the regenerative power is greater than the discharge required value (YES in step S25), the controller 30 charges the capacitor 19 by an amount equal to the difference between the regenerative power and the power corresponding to the discharge required value (step S26). In this embodiment, the controller 30 supplies a part of the regenerative power corresponding to the discharge required value from the rotary motor 21 to the motor generator 12 to cause the motor generator 12 to function as a motor, and charges the remaining part of the regenerative power to the capacitor 19.

[0072] On the other hand, when it is determined that the regenerative power is less than or equal to the discharge required value (NO in step S25), the controller 30 directs the sum of the regenerative power and the power corresponding to the discharge required value toward the motor generator 12 (step S27). In this embodiment, the controller 30 supplies all of the regenerative power from the rotary motor 21 to the motor generator 12, and supplies the power corresponding to the discharge required value from the capacitor 19 to the motor generator 12 to cause the motor generator 12 to function as a motor.

[0073] Note that in this embodiment, the power that the motor generator 12 functioning as a motor can receive is limited by a predetermined assist limit value. In this case, the assist limit value means the maximum value of the power that the motor generator 12 functioning as a motor can receive. This is to prevent the engine 11 from stalling due to excessive assist output. Therefore, when the sum of the regenerative power and the power corresponding to the discharge required value exceeds the power corresponding to the assist limit value, the controller 30 reduces the power corresponding to the discharge required value, that is, reduces the power discharged from the capacitor 19, so that the power supplied to the motor generator 12 becomes equal to the power corresponding to the assist limit value.

[0074] By repeatedly executing the above-described turning regeneration process, as shown by the charging demand line CL2 in FIG. 5, when the capacitor 19 indicates an SOC (e.g., 30%) corresponding to a discharge demand value of zero, the controller 30 supplies all of the regenerative power to the capacitor 19 to charge the capacitor 19, and generates power with the motor generator 12 for the power corresponding to the charging demand value, and charges the capacitor 19 with the generated power. In this way, when the SOC of the capacitor 19 is in a low state, the controller 30 causes the motor generator 12 to generate power even during turning regeneration to charge the capacitor 19, thereby returning the SOC to a high state.

[0075] Further, as shown by the discharge demand line DL2 in FIG. 5, the controller 30 prevents overcharging of the capacitor 19. For example, when the capacitor 19 indicates an SOC (e.g., a value greater than 70%) corresponding to a non-zero discharge demand value, if the magnitude of the regenerative power is greater than the magnitude of the discharge demand value, the capacitor 19 is charged with the differential power. Then, the power corresponding to the discharge demand value is supplied from the turning motor 21 to the motor generator 12 to cause the motor generator 12 to function as a motor. In this way, even when a large amount of regenerative power is generated during a 180-degree turn or the like, the controller 30 prevents overcharging of the capacitor 19 by consuming a part of the regenerative power with the motor generator 12.

[0076] Further, when the capacitor 19 indicates an SOC (e.g., a value greater than 70%) corresponding to a non-zero discharge demand value, if the magnitude of the regenerative power is less than or equal to the magnitude of the discharge demand value, the controller 30 causes the motor generator 12 to function as a motor. For example, until the SOC corresponding to the discharge demand value of zero (e.g., 70%) is reached, the sum of the regenerative power and the power corresponding to the discharge demand value is directed to the motor generator 12 to cause the motor generator 12 to function as a motor. In this way, the controller 30 prevents overcharging of the capacitor 19.

[0077] Next, referring to FIG. 8, when the turning electric motor 21 is in a stopped state, a process in which the controller 30 controls the charging and discharging of the capacitor 19 using the charging required value and the discharging required value (hereinafter referred to as the "process during turning stop") will be described. Note that FIG. 8 is a flowchart showing the flow of the process during turning stop, and the controller 30 repeatedly executes this process during turning stop at a predetermined control cycle when the turning electric motor 21 is in a stopped state.

[0078] First, the controller 30 determines whether the discharge required value is zero (step S31). This is to determine whether the discharge of the capacitor 19 has stopped.

[0079] If it is determined that the discharge required value is zero (YES in step S31), that is, if the discharge of the capacitor 19 has stopped, the controller 30 determines whether the charge required value is not zero (step S32). This is to determine whether the charging of the capacitor 19 has not stopped.

[0080] If it is determined that the charge required value is not zero (YES in step S32), that is, if the charging of the capacitor 19 has not stopped, the controller 30 causes the motor generator 12 to function as a generator and charges the capacitor 19 with the generated power generated by the motor generator 12 (step S33).

[0081] Note that if it is determined that the charge required value is zero (NO in step S32), that is, if the charging of the capacitor 19 has stopped, the controller 30 does not charge the capacitor 19. Therefore, the motor generator 12 is not caused to function as a generator only for charging the capacitor 19. However, it is not prohibited to cause the motor generator 12 to function as a generator for other purposes.

[0082] On the other hand, if it is determined that the discharge required value is not zero (NO in step S31), that is, if the discharge of the capacitor 19 has not stopped, the controller 30 drives the motor generator 12 with the power discharged from the capacitor 19 (step S34).

[0083] By repeatedly executing the above-described turning stop processing, the controller 30 prevents over-discharge of the capacitor 19 as shown by the charge request line CL3 in FIG. 5. For example, the capacitor 19 showing an SOC (e.g., 30%) corresponding to a non-zero charge request value is charged to an SOC (e.g., 60%) corresponding to a charge request value of zero. In this way, in a predetermined case, even at the time of turning stop, the controller 30 charges the capacitor 19 to prevent over-discharge of the capacitor 19. The predetermined case includes, for example, a case where the discharge of the capacitor 19 for causing the motor generator 12 to function as a motor to keep the load of the engine 11 constant increases and the SOC of the capacitor 19 is in a low state.

[0084] Also, as shown by the discharge request line DL3 in FIG. 5, the controller 30 discharges the capacitor 19 showing an SOC (e.g., 90%) corresponding to a non-zero discharge request value to an SOC (e.g., 70%) corresponding to a discharge request value of zero. In this way, even when the capacitor 19 is frequently charged, the controller 30 can prevent the SOC of the capacitor 19 from becoming excessively high. The capacitor 19 is frequently charged, for example, when the opportunity for the motor generator 12 to function as a generator to intentionally load the engine 11 or the opportunity for the motor generator 12 to function as a motor to keep the load of the engine 11 constant increases.

[0085] Further, when the capacitor 19 shows an SOC (e.g., 60% or more and 70% or less) at which both the charge request value and the discharge request value are zero, the controller 30 does not charge or discharge the capacitor 19.

[0086] With the above configuration, the controller 30 controls the charging and discharging of the capacitor 19 based on the charge request value and the discharge request value corresponding to the current SOC of the capacitor 19. Therefore, the charging and discharging of the capacitor 19 can be controlled more appropriately.

[0087] Further, the controller 30 changes the charging required value and the discharging required value according to the state of the rotating electric motor 21. Therefore, the charging and discharging of the capacitor 19 can be controlled more appropriately.

[0088] Next, with reference to FIG. 9, when the motor generator 12 functions as a generator or a motor, a process in which the controller 30 increases or decreases the maximum pump output of the main pump 14 (hereinafter referred to as "the process of increasing or decreasing the maximum pump output") will be described. Note that FIG. 9 is a conceptual diagram for explaining the process of increasing or decreasing the maximum pump output. In the present embodiment, the output (absorbed horsepower) of the main pump 14 is calculated as the product of the discharge amount and the discharge pressure of the main pump 14.

[0089] Specifically, the controller 30 derives the engine output EP. In the present embodiment, the controller 30 receives the detection value of an engine speed sensor (not shown), and refers to an engine speed - engine output correspondence map stored in advance in an internal memory to derive the engine output EP.

[0090] Further, the controller 30 derives the assist output AP. In the present embodiment, the controller 30 derives, as the assist output AP, the electric power exchanged between the motor generator 12 and the capacitor 19 based on the detection values of the capacitor voltage detection unit 112 and the capacitor current detection unit 113. Note that in the present embodiment, the assist output AP becomes a positive value when the motor generator 12 functions as a motor (when the capacitor 19 discharges), and becomes a negative value when the motor generator 12 functions as a generator (when the capacitor 19 charges).

[0091] Thereafter, the controller 30 adds the engine output EP and the assist output AP to derive the total output TP. The total output TP becomes a value larger than the engine output EP by the amount of the assist output AP when the motor generator 12 functions as a motor (when the capacitor 19 discharges), and becomes a value smaller than the engine output EP by the amount of the assist output AP when the motor generator 12 functions as a generator (when the capacitor 19 charges).

[0092] After that, the controller 30 derives the pump current PC. In this embodiment, the controller 30 receives the detected value of the engine speed sensor and refers to the total output - pump current correspondence map corresponding to the engine speed pre - stored in the internal memory to derive the pump current PC.

[0093] After that, the controller 30 outputs the pump current PC to the regulator (not shown) of the main pump 14. The regulator is a device that controls the discharge amount of the main pump 14 by adjusting the swash - plate tilt angle of the main pump 14 according to a command from the controller 30. In this embodiment, the smaller the pump current PC is, the lower the discharge amount of the main pump 14 is reduced.

[0094] Therefore, when the engine output EP is constant, the controller 30 increases the pump current PC to increase the maximum pump output of the main pump 14 as the assist output AP increases. That is, when the engine speed is constant, the larger the power consumption of the motor - generator 12 (the discharge amount of the capacitor 19) is, the larger the pump current PC can be increased to increase the maximum pump output of the main pump 14. This is because when the assist output AP increases, the total output TP also increases, creating a margin in the total output TP, and the main pump 14 can efficiently utilize the surplus. As a result, the output (absorbed horsepower) of the main pump 14 is controlled within the range of the increased maximum pump output. On the other hand, when a sudden load is applied to the engine 11, the assist force may be increased without adjusting the regulator to absorb the load of the main pump 14.

[0095] Next, referring to FIG. 10, the process in which the controller 30 adjusts the content of the SOC·required value correspondence table according to the capacitor temperature will be described. Here, the capacitor temperature is adopted, but any temperature of the environment or mechanism that affects the capacitor 19 may be used. Further, FIG. 10 is a diagram showing another example of the SOC·required value correspondence table and corresponds to FIG. 5. Specifically, FIG. 10 is a graph showing the relationship between the SOC of the capacitor 19 and the discharge required value and the charge required value adopted when the rotary motor 21 is in the power running state. The horizontal axis corresponds to the SOC [%], and the vertical axis corresponds to the output [kW].

[0096] Further, the discharge required line DL(20°C) indicated by the broken line in FIG. 10 represents the transition of the discharge required value adopted when the rotary motor 21 is in the power running state and the capacitor temperature is 20°C, and corresponds to the discharge required line DL1 in FIG. 5. Also, the discharge required line DL(0°C) indicated by the broken line represents the transition of the discharge required value adopted when the capacitor temperature is 0°C. Similarly, the discharge required line DL(-10°C) indicated by the broken line represents the transition of the discharge required value adopted when the capacitor temperature is -10°C, and the discharge required line DL(-20°C) indicated by the broken line represents the transition of the discharge required value adopted when the capacitor temperature is -20°C.

[0097] Further, the charge required line CL(20°C) indicated by the dotted line in FIG. 10 represents the transition of the charge required value adopted when the rotary motor 21 is in the power running state and the capacitor temperature is 20°C, and corresponds to the charge required line CL1 in FIG. 5. Also, the charge required line CL(0°C) indicated by the dotted line represents the transition of the charge required value adopted when the capacitor temperature is 0°C. Similarly, the charge required line CL(-10°C) indicated by the dotted line represents the transition of the charge required value adopted when the capacitor temperature is -10°C, and the charge required line CL(-20°C) indicated by the dotted line represents the transition of the charge required value adopted when the capacitor temperature is -20°C.

[0098] Also, the discharge limit line UL(20°C) shown by the solid line in Fig. 10 represents the transition of the discharge limit value when the capacitor temperature is 20°C. The discharge limit value means the maximum value of the power that the capacitor 19 can discharge, and is used to prevent over-discharge of the capacitor 19. Specifically, it is used when restricting the discharge power of the capacitor 19 so that the terminal voltage of the capacitor 19 does not fall below a predetermined lower limit voltage. In Fig. 10, when the SOC is 30 [%], the discharge power of the capacitor 19 is restricted to the value D10, indicating that if the discharge power of the capacitor 19 exceeds the value D10, the terminal voltage may fall below the lower limit voltage. Also, the discharge limit line UL(0°C) shown by the solid line represents the transition of the discharge limit value when the capacitor temperature is 0°C. Similarly, the discharge limit line UL(-10°C) shown by the solid line represents the transition of the discharge limit value when the capacitor temperature is -10°C, and the discharge limit line UL(-20°C) shown by the solid line represents the transition of the discharge limit value when the capacitor temperature is -20°C.

[0099] Also, the charge limit line BL(20°C) shown by the solid line in Fig. 10 represents the transition of the charge limit value when the capacitor temperature is 20°C. The charge limit value means the maximum value of the power that the capacitor 19 can charge, and is used to prevent overcharge of the capacitor 19. Specifically, it is used when restricting the charge power of the capacitor 19 so that the terminal voltage of the capacitor 19 does not exceed a predetermined upper limit voltage. In Fig. 10, when the SOC is 55 [%], the charge power of the capacitor 19 is restricted to the value C10, indicating that if the charge power of the capacitor 19 exceeds the value C10, the terminal voltage may exceed the upper limit voltage. Also, the charge limit line BL(0°C) shown by the solid line represents the transition of the charge limit value when the capacitor temperature is 0°C. Similarly, the charge limit line BL(-10°C) shown by the solid line represents the transition of the charge limit value when the capacitor temperature is -10°C, and the charge limit line BL(-20°C) shown by the solid line represents the transition of the charge limit value when the capacitor temperature is -20°C. Note that hereinafter, the charge limit value and the discharge limit value may also be collectively referred to as the charge / discharge limit value.

[0100] Next, the effect of changing the discharge demand line to be adopted according to the capacitor temperature will be described.

[0101] In the example of FIG. 10, the discharge demand line DL(20°C) becomes zero when the SOC is 60% or less, and increases at a change rate α until the SOC exceeds 60% and reaches 100%. Also, the discharge demand line DL(0°C) becomes zero when the SOC is 48% or less, and increases at a change rate α until the SOC exceeds 48% and reaches 100%. Further, the discharge demand line DL(-10°C) becomes zero when the SOC is 40% or less, and increases at a change rate α until the SOC exceeds 40% and reaches the discharge limit line, and after reaching the level of the discharge limit line UL(-10°C), it increases along the discharge limit line UL(-10°C). Also, the discharge demand line DL(-20°C) becomes zero when the SOC is 25% or less, and increases along the discharge limit line UL(-20°C) until the SOC exceeds 25% and reaches 100%. Note that the change rate α with respect to the SOC of the discharge demand line DL(20°C), the discharge demand line DL(0°C), and the discharge demand line DL(-10°C) is equal in the region below the corresponding discharge limit line.

[0102] In this way, as the capacitor temperature decreases, by reducing the SOC (discharge start charge rate: discharge start SOC) when the discharge required value becomes greater than zero, the controller 30 can reduce the SOC during the power running operation and the regenerative operation of the turning motor 21. Specifically, when the capacitor temperature is, for example, 20°C, the SOC of the capacitor 19 ranges from 60[%] to 80[%] when the power running operation and the regenerative operation are performed by adopting the discharge required line DL(20°C). On the other hand, when the capacitor temperature is, for example, -20°C, the SOC of the capacitor 19 ranges from 25[%] to 45[%] when the power running operation and the regenerative operation are performed by adopting the discharge required line DL(-20°C). Therefore, the controller 30 can suppress the charging power, which is the regenerative power generated by the turning motor 21 during turning regeneration, from exceeding the charge limit line. Specifically, as shown in FIG. 10, when the SOC during the regenerative operation is 55[%], if the capacitor temperature is 20°C, the capacitor 19 can accept the charging power of value C10 while preventing the terminal voltage from exceeding the upper limit voltage. However, if the capacitor temperature is 0°C, the capacitor 19 cannot accept a charging power greater than value C11 in order to prevent the terminal voltage from exceeding the upper limit voltage. Further, if the capacitor temperature is -10°C, it cannot accept a charging power greater than value C12, and if the capacitor temperature is -20°C, it cannot accept a charging power greater than value C13. Thus, the charging power that the capacitor 19 can accept (acceptable charging power) becomes smaller as the capacitor temperature decreases. On the other hand, the acceptable charging power becomes larger as the SOC becomes smaller. From this relationship, the controller 30 reduces the discharge start SOC as the capacitor temperature decreases, thereby reducing the SOC during the power running operation and the regenerative operation of the turning motor 21, and can suppress the regenerative power (charging power) during turning regeneration from exceeding the charge limit line.

[0103] Also, the internal resistance R of the capacitor 19 increases as the capacitor temperature decreases. Furthermore, as the capacitor temperature decreases, the controller 30 lowers the discharge start SOC, thereby also lowering the terminal voltage of the capacitor 19 during charge and discharge. Therefore, to obtain the same discharge power, the discharge current flowing increases, and to obtain the same charge power, the charge current flowing increases. Accordingly, the heat generation amount of the capacitor 19 increases as the capacitor temperature decreases, due to the increase in the internal resistance R and the increase in the charge and discharge currents. As a result, the warm-up of the capacitor 19 can be promoted. Note that the warm-up of the capacitor 19 is a process of forcibly increasing the capacitor temperature by charging and discharging the capacitor 19 when the capacitor temperature is equal to or lower than a predetermined temperature. In this embodiment, when the excavator is in an idle state, even if the engine 11 is idling, the capacitor 19 is charged and discharged using the motor generator 12 or the like, thereby realizing the warm-up.

[0104] Conversely, the internal resistance R of the capacitor 19 decreases as the capacitor temperature increases. Furthermore, as the capacitor temperature increases, the controller 30 raises the discharge start SOC, thereby also raising the terminal voltage of the capacitor 19 during charge and discharge. Therefore, to obtain the same discharge power, the discharge current flowing decreases, and to obtain the same charge power, the charge current flowing decreases. Accordingly, the heat generation amount of the capacitor 19 decreases as the capacitor temperature increases, in response to the decrease in the internal resistance R and the decrease in the charge and discharge currents. As a result, heat loss is reduced, and the capacitor 19 can be utilized with high efficiency.

[0105] Further, the controller 30 equalizes the change rate α with respect to the SOC of each of the discharge demand lines DL(20°C), DL(0°C), and DL(-10°C) in the region below the discharge limit line. This has the effect of maintaining the operating feel of the excavator regardless of the capacitor temperature. Specifically, the smaller the change rate α, the more likely the required output of the swing motor 21 during swing power running will exceed the discharge demand value, the power generation by the motor generator 12 will start earlier, and the pump maximum output of the main pump 14 will be restricted earlier. For example, when boom raising and swinging are performed, the rising speed of the boom 4 decreases at an earlier stage during swing power running. Therefore, maintaining the change rate α regardless of the capacitor temperature means not changing the timing at which the rising speed of the boom 4 decreases. Note that the change rate α may be set to be relatively large particularly in a region where the SOC is relatively high regardless of the capacitor temperature. This is to prevent overcharging during subsequent swing regeneration by increasing the discharge power as much as possible during swing power running. On the other hand, the change rate α is restricted by the discharge limit line in order to protect the capacitor 19. For example, if the change rate is increased at the discharge demand line DL(-20°C) when the capacitor temperature is -20°C, the discharge power will exceed the discharge limit line UL(-20°C) at the discharge start SOC, causing over-discharge. Therefore, the change rate α needs to be appropriately set in consideration of the discharge limit line.

[0106] Note that in FIG. 10, the discharge demand line DL is set to draw a straight line, but it may be set to draw a curve or a broken line.

[0107] Also, in FIG. 10, the discharge demand line DL, the discharge limit line UL, and the charge limit line BL when the capacitor temperature is 20°C, 0°C, -10°C, and -20°C are shown. However, in reality, the discharge demand line DL, the discharge limit line UL, and the charge limit line BL exist at predetermined temperature intervals.

[0108] FIG. 11 is a diagram showing another example of the discharge demand line when the capacitor temperature is -10°C. For clarity, FIG. 11 shows only the discharge limit line UL(-10°C) and the discharge demand lines DLa(-10°C) and DLb(-10°C) when the capacitor temperature is -10°C, and omits the discharge limit line, the discharge demand line, and the charge demand line at other temperatures.

[0109] The dotted discharge demand line DLa(-10°C) is an example of a transition set to draw a broken line, and increases at a relatively small rate of change until the SOC reaches from 30[%] to 47[%]. Then, it increases at a relatively large rate of change until the SOC reaches 55[%], and then increases at a relatively small rate of change until the SOC reaches 100[%]. By adopting such a transition, the controller 30 can prevent the terminal voltage of the capacitor 19 from exceeding the upper limit voltage during subsequent turning regeneration by discharging the capacitor 19 with a relatively large discharge power when the SOC is from 47[%] to 55[%].

[0110] The dashed-dotted discharge demand line DLb(-10°C) is an example of a transition set to draw a straight line without being restricted by the discharge limit line UL(-10°C), and the rate of change is constant until the SOC reaches from 30[%] to 100[%]. By adopting such a transition, the controller 30 can prevent the operation feeling of the excavator from changing suddenly because the discharge demand value does not change suddenly during turning power running as in the case where the transition is set to draw a broken line.

[0111] Next, with reference to FIG. 12, in order to cope with the acceptable charging power that decreases as the SOC of the capacitor 19 increases and as the capacitor temperature decreases, the process in which the controller 30 limits the turning speed during turning power running will be described. Note that FIG. 12 is a diagram showing the relationship between the SOC of the capacitor 19 and the turning speed limit value, where the horizontal axis corresponds to the SOC [%] and the vertical axis corresponds to the turning speed limit value [rpm].

[0112] Specifically, the acceptable charging power of the capacitor 19 is determined according to the SOC of the capacitor 19 at the start of turning and the capacitor temperature. For example, as shown in FIG. 10, when the capacitor temperature is 0°C and the SOC is 55%, referring to the charging limit line BL(0°C), the acceptable charging power is the value C11. And once the acceptable charging power is determined, the maximum braking torque achievable within the range of the acceptable charging power is determined, and the maximum turning speed (turning speed limit value) when the maximum braking torque is required is determined.

[0113] In this embodiment, for the turning speed limit value Ncl, when the charging limit value is Wcl, the maximum braking torque is Tmax, and the power corresponding to the assist limit value is Wa,

[0114] [Number] it is expressed as. Here, ξ1 and ξ2 represent efficiency. Also, at the start of turning, for example, it means the time when the operation amount of the turning operation lever exceeds a predetermined value, the time when the turning speed reaches a predetermined speed, etc. Further, the controller 30 determines the turning speed limit value every time turning starts.

[0115] FIG. 12 shows the transition of the turning speed limit value determined as described above with respect to the SOC. Specifically, the dotted turning speed limit line TL(20°C) represents the transition of the turning speed limit value when the capacitor temperature is 20°C, and the dotted turning speed limit line TL(0°C) represents the transition of the turning speed limit value when the capacitor temperature is 0°C. Also, the dotted turning speed limit line TL(-10°C) represents the transition of the turning speed limit value when the capacitor temperature is -10°C, and the dotted turning speed limit line TL(-20°C) represents the transition of the turning speed limit value when the capacitor temperature is -20°C.

[0116] Also, in this embodiment, the turning speed is electrically or mechanically limited by the upper limit Rmax. Also, when the SOC at the start of turning is 55% or less and the capacitor temperature is 0°C or less, the turning speed limit value when the SOC is 55% is adopted. This is to prevent the turning speed limit value from changing each time the turning operation is performed and the actual maximum turning speed from changing. Specifically, when the SOC at the start of turning is 55% or less and the capacitor temperature is -10°C, the turning speed limit value is set to the value Rb. Also, when the SOC at the start of turning is 55% or less and the capacitor temperature is -20°C, the turning speed limit value is set to the value Ra. Note that if an SOC - required value correspondence table as shown in FIG. 10 is adopted, when the capacitor temperature is 0°C or less, it is normal for the turning operation to be performed in the range where the SOC is 55% or less. Therefore, even if the turning speed limit value changes along the turning speed limit line in the range where the SOC is greater than 55%, the actual maximum turning speed does not change each time the turning operation is performed.

[0117] In this way, the controller 30 limits the maximum turning speed according to the capacitor temperature. Also, the controller 30 gradually releases the limitation of the maximum turning speed as the capacitor temperature rises.

[0118] Next, referring to FIG. 13, the process in which the controller 30 limits the maximum turning torque during turning force application and the pump maximum output of the main pump 14 in accordance with the limitation of the maximum turning speed will be described. Note that FIG. 13(A) is a diagram showing the relationship between the turning speed limit value and the turning torque limit value, where the horizontal axis corresponds to the turning speed limit value [rpm] and the vertical axis corresponds to the turning torque limit value [%]. Also, FIG. 13(B) is a diagram showing the relationship between the turning speed limit value and the pump current limit value, where the horizontal axis corresponds to the turning speed limit value [rpm] and the vertical axis corresponds to the pump current limit value [mA].

[0119] For example, when the SOC at the start of slewing is 55 [%] or less and the capacitor temperature is -10°C, the controller 30 limits the slewing speed limit value to the value Rb. In this case, the controller 30 refers to a correspondence table as shown in Fig. 13(A) and derives the value Sb as the slewing torque limit value. Also, the controller 30 refers to a correspondence table as shown in Fig. 13(B) and derives the value Pb as the pump current limit value.

[0120] Similarly, when the SOC at the start of slewing is 55 [%] or less and the capacitor temperature is -20°C, the controller 30 limits the slewing speed limit value to the value Ra (<Rb). In this case, the controller 30 derives the value Sa (<Sb) as the slewing torque limit value and the value Pa (<Pb) as the pump current limit value.

[0121] Note that the controller 30 determines the slewing torque limit value and the pump current limit value every time slewing starts, similar to the slewing speed limit value.

[0122] The limitation of the slewing torque during slewing operation results in the limitation of the acceleration of the upper slewing body 3, and the limitation of the pump current results in the limitation of the operating speed of the hydraulic actuator. Also, the relaxation of the slewing torque limitation due to the subsequent increase in the capacitor temperature results in the relaxation of the acceleration limitation of the upper slewing body 3, and the relaxation of the pump current limitation results in the relaxation of the operating speed limitation of the hydraulic actuator. Therefore, when the boom raising slewing is performed while the slewing speed limit value is limited to less than the maximum value Rmax, the raising speed of the boom 4 is also limited in accordance with the limitation of the slewing speed. Also, as the slewing speed limit value increases toward the maximum value Rmax due to the subsequent increase in the capacitor temperature, the limitation of the slewing speed is relaxed, and the limitation of the raising speed of the boom 4 is also relaxed in accordance with the relaxation of the slewing speed limitation. As a result, the controller 30 can provide the operator with the operating speed of the hydraulic actuator corresponding to the slewing speed and prevent the operating feeling from being impaired.

[0123] Note that when the controller 30 adopts the maximum value Rmax as the turning speed limit value, it derives the value Smax as the turning torque limit value and derives the value Pmax as the pump current limit value. That is, when the controller 30 does not limit the maximum turning speed, it does not limit the maximum turning torque and the maximum pump output.

[0124] With the above configuration, the controller 30 reduces the charge limit value and the discharge limit value in response to the decrease in the capacitor temperature and changes the discharge demand value. In this embodiment, the changes in the charge limit value and the discharge limit value with respect to the change in the SOC are reduced, and the change in the discharge demand value with respect to the change in the SOC is reduced. Specifically, the limit values of the discharge limit line UL and the charge limit line BL are decreased in response to the decrease in the capacitor temperature. Also, the slope of the discharge demand line DL during turning power running is decreased in response to the decrease in the capacitor temperature. Therefore, even when the controller 30 drives the turning motor 21 in a state where the capacitor temperature is low, overcharge and over-discharge of the capacitor 19 can be prevented. As a result, the controller 30 can drive the turning motor 21 without adversely affecting the capacitor 19 even before the warm-up of the capacitor 19 is completed.

[0125] Further, the controller 30 reduces the lower limit of the charge rate of the capacitor 19 that makes the discharge demand value a value greater than zero in response to the decrease in the capacitor temperature. In this embodiment, the controller 30 reduces the discharge start SOC in response to the decrease in the capacitor temperature. Therefore, the controller 30 can control the charge and discharge of the capacitor 19 during turning power running and turning regeneration so that the SOC of the capacitor 19 changes in a lower range as the capacitor temperature is lower. As a result, as the capacitor temperature is lower, the capacitor 19 can be charged and discharged under conditions that are more likely to generate heat, thereby promoting the warm-up of the capacitor 19. Also, as the capacitor temperature is lower, the SOC at the start of turning regeneration is induced to be lower, so that it is possible to prevent the terminal voltage of the capacitor 19 from reaching the upper limit voltage during turning regeneration and prevent overcharge of the capacitor 19.

[0126] As described above, the preferred embodiments of the present invention have been described in detail. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention.

[0127] For example, in the above-described embodiment, the controller 30 adjusts the content of the SOC·required value correspondence table according to the capacitor temperature when the swing motor 21 is in the power running state. However, the controller 30 does not adjust the content of the SOC·required value correspondence table only when the swing motor 21 is in the power running state, and may also adjust the content of the SOC·required value correspondence table according to the capacitor temperature when the swing motor 21 is in the regeneration operation state and the stop state.

[0128] FIG. 14 is a diagram showing still another example of the SOC·required value correspondence table, corresponding to FIGS. 5 and 10. Specifically, FIG. 14 is a graph showing the relationship between the SOC of the capacitor 19 and the discharge required value and the charge required value employed when the swing motor 21 is in the regeneration operation state.

[0129] As shown in FIG. 14, the controller 30 has not only the SOC·required value correspondence table for swing power running but also the SOC·required value correspondence table for swing regeneration. And, the controller 30 controls the charge and discharge of the capacitor 19 during swing regeneration so that the SOC of the capacitor 19 changes in a lower range as the capacitor temperature is lower, similar to during swing power running.

[0130] Although not shown, the controller 30 has the SOC·required value correspondence table for swing stop, and controls the charge and discharge of the capacitor 19 during swing stop so that the SOC of the capacitor 19 changes in a lower range as the capacitor temperature is lower, similar to during swing power running and swing regeneration.

[0131] Next, referring to FIG. 15, the warm-up of the hydraulic drive system will be described. FIG. 15 is a schematic diagram of the hydraulic circuit mounted on the excavator of FIG. 1. The high-pressure oil passage, the pilot oil passage, and the electric control line are shown by solid lines, broken lines, and dotted lines, respectively.

[0132] In this embodiment, the main pump 14 is composed of two main pumps 14L and 14R, and the regulator 14a is composed of two regulators 14aL and 14aR. Further, the regulator 14aL corresponds to the main pump 14L, and the regulator 14aR corresponds to the main pump 14R.

[0133] The hydraulic circuit circulates the hydraulic oil from the main pumps 14L and 14R to the hydraulic oil tank through the center bypass oil passages 40L and 40R respectively.

[0134] The center bypass oil passage 40L is a high-pressure oil passage passing through the flow control valves 150 to 152. A relief valve 50L is installed upstream of the flow control valve 150. Similarly, the center bypass oil passage 40R is a high-pressure oil passage passing through the flow control valves 153 to 156. A relief valve 50R is installed upstream of the flow control valve 153.

[0135] The flow control valve 150 is a spool valve that controls the flow rate and flow direction of the hydraulic oil flowing through the left travel hydraulic motor 1L. The flow control valve 153 is a spool valve that controls the flow rate and flow direction of the hydraulic oil flowing through the right travel hydraulic motor 1R. Further, the flow control valve 154 is a spool valve that controls the flow rate and flow direction of the hydraulic oil flowing through the bucket cylinder 9. The flow control valves 151 and 155 are spool valves that control the flow rate and flow direction of the hydraulic oil flowing through the boom cylinder 7. The flow control valves 152 and 156 are spool valves that control the flow rate and flow direction of the hydraulic oil flowing through the arm cylinder 8.

[0136] The relief valves 50L and 50R are valves that suppress the pressure of the hydraulic oil in the center bypass oil passages 40L and 40R to a predetermined pressure or less. Specifically, the relief valves 50L and 50R open when the pressure of the hydraulic oil in the center bypass oil passages 40L and 40R reaches the predetermined pressure and discharge the hydraulic oil to the hydraulic oil tank.

[0137] When warming up the hydraulic drive system, the operator of the excavator, for example, continues the closing operation of the bucket 6 in a state where the bucket 6 is fully closed within a range not exceeding a predetermined time (for example, 30 seconds). In this case, since the hydraulic oil discharged from the main pump 14R cannot flow into the bottom-side oil chamber of the bucket cylinder 9, as shown by the thick line in Fig. 15, the pressure of the hydraulic oil in the center bypass oil passage 40R increases. Then, the hydraulic oil discharged from the main pump 14R is discharged into the hydraulic oil tank through the relief valve 50R, generating heat due to the pressure loss caused by the pipeline resistance when passing through the relief valve 50R. As a result, the hydraulic oil circulating in the hydraulic circuit is warmed. After that, the operator warms the hydraulic oil by continuing the opening operation of the bucket 6 in a state where the bucket 6 is fully open within a range not exceeding a predetermined time (for example, 30 seconds) in the same manner as when the bucket 6 is fully closed. In this way, the operator can increase the temperature of the hydraulic oil by repeating the opening and closing of the bucket 6. Note that the operator may increase the temperature of the hydraulic oil by performing operations other than the opening and closing operation of the bucket 6, such as the opening and closing operation of the arm 5.

[0138] Next, with reference to Figs. 16 to 24, the warm-up of the power storage system 120 will be described. Fig. 16 is a diagram for explaining the warm-up start conditions of the power storage system 120. Note that the warm-up start conditions of the power storage system 120 include the conditions for starting the warm-up of the power storage system 120 when the excavator is in the idling state and the conditions for starting the warm-up of the power storage system 120 when the operator is warming up the hydraulic drive system.

[0139] Specifically, the controller 30 starts the warm-up of the power storage system 120 when there is no operation on the operating device 26 by the operator for a predetermined time and the capacitor temperature is equal to or lower than a predetermined warm-up start capacitor temperature Ts. This condition corresponds to the condition for starting the warm-up of the power storage system 120 when the excavator is in an idling state. Note that the capacitor temperature may be a statistical value such as an average value, a median value, or a minimum value at a predetermined time, or may be an instantaneous value. Further, the capacitor temperature may be indirectly detected by detecting the temperature of the cooling water used for cooling the capacitor 19. Alternatively, the controller 30 may start the warm-up of the power storage system 120 when there is no operation on the operating device 26 by the operator for a predetermined time and the temperature of the cooling water detected by a cooling water temperature sensor (not shown) is equal to or lower than a predetermined warm-up start cooling water temperature.

[0140] Further, the controller 30 starts the warm-up of the power storage system 120 when there is no slewing operation or traveling operation by the operator, the capacitor temperature is equal to or lower than Ts, and it is determined based on the detected value of the discharge pressure sensor 29A that the warm-up of the hydraulic drive system is being performed. This condition corresponds to the condition for starting the warm-up of the power storage system 120 when the operator is warming up the hydraulic drive system. Note that the controller 30 may start the warm-up of the power storage system 120 when there is no slewing operation or traveling operation by the operator, the cooling water temperature is equal to or lower than a predetermined warm-up start cooling water temperature, and it is determined based on the detected value of the discharge pressure sensor 29A that the warm-up of the hydraulic drive system is being performed.

[0141] Specifically, when the discharge pressure (first pump pressure) of the main pump 14L detected by the discharge pressure sensor 29AL (see FIG. 15) is substantially the relief pressure, that is, when the open state of the relief valve 50L continues for a predetermined time tr, the controller 30 determines that the warm-up of the hydraulic drive system is being performed. Alternatively, when the discharge pressure (second pump pressure) of the main pump 14R detected by the discharge pressure sensor 29AR (see FIG. 15) is substantially the relief pressure, that is, when the open state of the relief valve 50R continues for a predetermined time tr, the controller 30 determines that the warm-up of the hydraulic drive system is being performed. The predetermined time tr is set to distinguish between the relief state due to excavation operations or the like and the relief state for warming up the hydraulic drive system.

[0142] Next, referring to FIG. 17, the process by which the controller 30 warms up the power storage system 120 (hereinafter referred to as the "power storage system warm-up process") will be described. FIG. 17 is a flowchart showing the flow of the power storage system warm-up process. When the warm-up start condition of the power storage system 120 is satisfied, the controller 30 repeatedly executes this power storage system warm-up process at a predetermined control cycle until the warm-up stop condition (described later) of the power storage system 120 is satisfied.

[0143] Specifically, the controller 30 derives the charge rate (SOC) of the capacitor 19 using a known method, and determines whether the SOC of the capacitor 19 is equal to or higher than a predetermined discharge (assist) / charge (power generation) start determination charge rate (SOC0) (step S41).

[0144] If it is determined that the SOC is equal to or higher than SOC0 (YES in step S41), the controller 30 starts the discharge (assist) process (step S42).

[0145] If it is determined that the SOC is less than SOC0 (NO in step S41), the controller 30 starts the charge (power generation) process (step S43).

[0146] FIG. 18 is a flowchart showing the flow of the discharge (assist) process. When executing the discharge (assist) process, the controller 30 operates the motor generator 12 as a motor by the power discharged from the capacitor 19.

[0147] Specifically, the controller 30 determines whether the capacitor voltage is higher than a predetermined lower limit voltage (Vmin) and the SOC of the capacitor 19 is higher than a predetermined charge transition start charge rate (SOC1) (step S51). Vmin is a value set in advance to prevent over-discharge of the capacitor 19. SOC1 is a value set in advance as an SOC suitable for starting the transition from the discharge state to the charge state. In this embodiment, SOC1 is set stepwise so that it becomes higher as the capacitor temperature is lower.

[0148] If it is determined that the capacitor voltage is higher than Vmin and the SOC is higher than SOC1 (YES in step S51), the controller 30 determines whether the discharge amount is less than a predetermined threshold TH1 (step S52). The discharge amount is the amount of electric power discharged per unit time, and in this embodiment, it is represented by electric power [kW]. Also, in this embodiment, the controller 30 derives the discharge amount based on the detection values of the capacitor voltage detection unit 112 and the capacitor current detection unit 113.

[0149] If it is determined that the discharge amount is less than the threshold TH1 (YES in step S52), the controller 30 increases the discharge amount (step S53). In this embodiment, the controller 30 increases the discharge amount at a predetermined increase rate [kW / s] and then returns the process to step S51.

[0150] Also, if it is determined that the discharge amount is equal to or greater than the threshold TH1 (NO in step S52), the controller 30 returns the process to step S51 without increasing the discharge amount.

[0151] On the other hand, when it is determined that the capacitor voltage is equal to or lower than Vmin or the SOC is equal to or lower than SOC1 (NO in step S51), the controller 30 determines whether the discharge amount is greater than zero (step S54).

[0152] When it is determined that the discharge amount is greater than zero (YES in step S54), that is, when it is determined that discharging is in progress, the controller 30 reduces the discharge amount (step S55). In this embodiment, the controller 30 reduces the discharge amount at a predetermined reduction rate and then returns the process to step S51.

[0153] Also, when it is determined that the discharge amount is zero (NO in step S54), that is, when it is determined that discharging has ended, the controller 30 ends the discharge (assist) process and starts the charging (power generation) process.

[0154] FIG. 19 is a flowchart showing the flow of the charging (power generation) process. When executing the charging (power generation) process, the controller 30 charges the capacitor 19 using the power generated by the motor generator 12 driven as a generator by the engine 11.

[0155] Specifically, the controller 30 determines whether the capacitor voltage is lower than a predetermined upper limit voltage (Vmax) and the SOC of the capacitor 19 is lower than a predetermined charge start rate for discharge transition (SOC2) (step S61). Vmax is a value set in advance to prevent overcharging of the capacitor 19. SOC2 is a value set in advance as an SOC suitable for starting the transition from the charged state to the discharged state. In this embodiment, SOC2 is set stepwise so that it becomes lower as the capacitor temperature is lower.

[0156] When it is determined that the capacitor voltage is lower than Vmax and the SOC is lower than SOC2 (YES in step S61), the controller 30 determines whether the charging amount is less than a predetermined threshold TH2 (step S62). The charging amount is the amount of electric power charged per unit time, and in this embodiment, it is represented by electric power [kW]. Also, in this embodiment, the controller 30 derives the charging amount based on the detection values of the capacitor voltage detection unit 112 and the capacitor current detection unit 113.

[0157] When it is determined that the charging amount is less than the threshold TH2 (YES in step S62), the controller 30 increases the charging amount (step S63). In this embodiment, the controller 30 increases the charging amount at a predetermined increase rate and then returns the process to step S61.

[0158] Also, when it is determined that the charging amount is greater than or equal to the threshold TH2 (NO in step S62), the controller 30 returns the process to step S61 without increasing the charging amount.

[0159] On the other hand, when it is determined that the capacitor voltage is greater than or equal to Vmax or the SOC is greater than or equal to SOC2 (NO in step S61), the controller 30 determines whether the charging amount is greater than zero (step S64).

[0160] When it is determined that the charging amount is greater than zero (YES in step S64), that is, when it is determined that charging is in progress, the controller 30 reduces the charging amount (step S65). In this embodiment, the controller 30 reduces the charging amount at a predetermined reduction rate and then returns the process to step S61.

[0161] Also, when it is determined that the charging amount is zero (NO in step S64), that is, when it is determined that charging has ended, the controller 30 ends the charging (power generation) process and starts the discharging (assist) process.

[0162] In this way, until the warm-up stop condition (described later) of the power storage system 120 is satisfied, the controller 30 alternately repeats the charging (power generation) process and the discharging (assist) process, and warms up the capacitor 19 by self-heating due to the internal resistance of the capacitor 19 accompanying the charging and discharging of the capacitor 19 that is interlocked with the motor generator 12.

[0163] Next, referring to FIG. 20, the transition of various parameters during the warm-up process of the power storage system will be described. Note that FIG. 20 is a diagram showing the transitions of the capacitor input / output, SOC, capacitor voltage, and capacitor current. The capacitor input / output is the amount of electric power that enters and exits the capacitor 19 per unit time, and in this embodiment, it is represented by electric power [kW]. Also, a positive value of the capacitor input / output corresponds to the discharge amount of the capacitor 19, and a negative value of the capacitor input / output corresponds to the charge amount of the capacitor 19.

[0164] Specifically, FIG. 20(A) is a diagram showing the relationship between the capacitor input / output and the SOC. The capacitor input / output is arranged on the vertical axis, and the SOC of the capacitor 19 is arranged on the horizontal axis. Also, FIG. 20(B) is a diagram showing the temporal transition of the capacitor input / output, FIG. 20(C) is a diagram showing the temporal transition of the SOC. Also, FIG. 20(D) is a diagram showing the temporal transition of the capacitor voltage, and FIG. 20(E) is a diagram showing the temporal transition of the capacitor current. Note that the time axes of FIGS. 20(B) to 20(E) are common.

[0165] When the warm-up process of the power storage system is started at time t1, the controller 30 determines that the SOC of the capacitor 19 is equal to or higher than SOC0 and executes the discharging (assist) process.

[0166] Then, the controller 30 determines that the capacitor voltage is greater than Vmin, and the SOC is greater than SOC1, and further determines that the discharge amount is smaller than the threshold value TH1, and increases the discharge amount at a predetermined increase rate.

[0167] After that, when the discharge amount reaches the threshold value TH1 at time t2, the controller 30 stops the increase in the discharge amount and continues the discharge from the capacitor 19 while keeping the discharge amount constant at TH1.

[0168] Thereafter, when the capacitor voltage reaches Vmin at time t3, the controller 30 starts the transition from discharging to charging. Specifically, the controller 30 reduces the discharge amount at a predetermined reduction rate.

[0169] Thereafter, when the discharge amount reaches zero at time t4, the controller 30 ends the discharge (assist) process. Then, the controller 30 determines that the SOC of the capacitor 19 is less than SOC0 and executes the charge (power generation) process.

[0170] Then, the controller 30 determines that the capacitor voltage is less than Vmax and the SOC is less than SOC2, and further determines that the charge amount (absolute value) is less than the threshold value TH2 (absolute value), and increases the charge amount (absolute value) at a predetermined increase rate. Note that hereinafter, the charge amount and the threshold value TH2 represent absolute values.

[0171] Thereafter, when the charge amount reaches the threshold value TH2 at time t5, the controller 30 stops increasing the charge amount and continues to charge the capacitor 19 while keeping the charge amount constant at TH2.

[0172] Thereafter, when the SOC reaches SOC2 at time t6, the controller 30 starts the transition from charging to discharging. Specifically, the controller 30 reduces the charge amount at a predetermined reduction rate.

[0173] Thereafter, when the charge amount reaches zero at time t7, the controller 30 ends the charge (power generation) process. Then, the controller 30 determines that the SOC of the capacitor 19 is equal to or greater than SOC0 and executes the discharge (assist) process again.

[0174] Then, the controller 30 determines that the capacitor voltage is greater than Vmin and the SOC is greater than SOC1, and further determines that the discharge amount is less than the threshold value TH1, and increases the discharge amount at a predetermined increase rate.

[0175] Thereafter, when the discharge amount reaches the threshold value TH1 at time t8, the controller 30 stops the increase in the discharge amount and continues the discharge from the capacitor 19 while keeping the discharge amount constant at TH1.

[0176] Thereafter, when the capacitor voltage reaches Vmin or the SOC reaches SOC1 at time t9, the controller 30 starts the transition from discharge to charge.

[0177] In this way, the controller 30 alternately repeats the charging (power generation) process and the discharging (assist) process until the warm-up stop condition (described later) of the power storage system 120 is satisfied, and warms up the capacitor 19 by self-heating due to the internal resistance of the capacitor 19 accompanying the charge and discharge of the capacitor 19 interlocked with the motor generator 12.

[0178] Next, with reference to FIG. 21, the warm-up stop condition of the power storage system 120 will be described. The warm-up stop condition of the power storage system 120 includes, similar to the warm-up start condition, the condition for stopping the warm-up of the power storage system 120 when the excavator is in the idling state and the condition for stopping the warm-up of the power storage system 120 when the operator is warming up the hydraulic drive system.

[0179] Specifically, when there is an operation on the operation device 26 by the operator, or when the capacitor temperature becomes equal to or higher than a predetermined warm-up stop capacitor temperature Tf, the controller 30 stops the warm-up of the power storage system 120. This condition corresponds to the condition for stopping the warm-up of the power storage system 120 when the excavator is in the idling state. Note that even though the warm-up of the power storage system 120 is being attempted during the warm-up of the hydraulic drive system, the reason for stopping the warm-up of the power storage system 120 when there is an operation on the operation device 26 is as follows. That is, at the time when there is an operation on the operation device 26, it is impossible to determine whether the operation is an operation for starting the warm-up of the hydraulic drive system or a normal operation for excavation work or the like. Also, the capacitor temperature may be indirectly detected by detecting the temperature of the cooling water used for cooling the capacitor 19. Alternatively, when the excavator is in the idling state, the controller 30 may stop the warm-up of the power storage system 120 when the cooling water temperature becomes equal to or higher than a predetermined warm-up stop cooling water temperature.

[0180] Further, when there is a slewing operation or a traveling operation by the operator, when the capacitor temperature becomes equal to or higher than Tf, or when it is determined based on the detected value of the discharge pressure sensor 29A that the warm-up of the hydraulic drive system is not being performed, the controller 30 stops the warm-up of the power storage system 120. This condition corresponds to the condition for stopping the warm-up of the power storage system 120 when the operator is warming up the hydraulic drive system. Note that even when the operator is warming up the hydraulic drive system, the controller 30 may stop the warm-up of the power storage system 120 when the cooling water temperature becomes equal to or higher than a predetermined warm-up stop cooling water temperature.

[0181] Specifically, the controller 30 determines that the warm-up of the hydraulic drive system is not being performed when the discharge pressure (first pump pressure) of the main pump 14L is below the relief pressure, that is, when the relief valve 50L is in the closed state. Alternatively, the controller 30 determines that the warm-up of the hydraulic drive system is not being performed when the discharge pressure (second pump pressure) of the main pump 14R is below the relief pressure, that is, when the relief valve 50R is in the closed state.

[0182] In addition, when the controller 30 stops the warm-up of the power storage system 120 before the capacitor temperature reaches Tf or higher, the controller 30 may limit the movement of the excavator (for example, the swing motor 21) according to the capacitor temperature. This is to prevent the charge and discharge of the power storage system 120 from being unrestricted when the warm-up of the power storage system 120 is insufficient. For example, if the capacitor 19 is used at a low temperature, the internal resistance of the capacitor 19 is large, resulting in the capacitor voltage exceeding the upper limit voltage Vmax or falling below the lower limit voltage Vmin, which may cause the capacitor 19 to deteriorate or be damaged.

[0183] Next, with reference to FIG. 22, the process in which the controller 30 increases or decreases the absorbed horsepower of the main pump 14 (hereinafter referred to as the "absorbed horsepower increase / decrease process") when performing the warm-up of the power storage system 120 while the warm-up of the hydraulic drive system is being performed will be described. Note that FIG. 22 is a conceptual diagram for explaining the absorbed horsepower increase / decrease process. In the present embodiment, the absorbed horsepower of the main pump 14 is calculated as the product of the discharge amount and the discharge pressure of the main pump 14.

[0184] Specifically, the controller 30 derives the engine output EP. In the present embodiment, the controller 30 receives the detection value of an engine speed sensor (not shown), and refers to an engine speed - engine output correspondence map stored in advance in the internal memory to derive the engine output EP.

[0185] In addition, the controller 30 derives the assist output AP. In the present embodiment, the controller 30 derives, as the assist output AP, the power exchanged between the motor generator 12 and the capacitor 19 based on the detection values of the capacitor voltage detection unit 112 and the capacitor current detection unit 113. Note that the assist output AP is a positive value when the motor generator 12 functions as a motor (when the capacitor 19 discharges), and is a negative value when the motor generator 12 functions as a generator (when the capacitor 19 charges).

[0186] Thereafter, the controller 30 adds the engine output EP and the assist output AP to derive the total output TP. The total output TP becomes a value that is larger than the engine output EP by the assist output AP when the motor generator 12 functions as a motor (when the capacitor 19 discharges), and becomes a value that is smaller than the engine output EP by the assist output AP when the motor generator 12 functions as a generator (when the capacitor 19 charges).

[0187] Thereafter, the controller 30 derives the pump current PC. In the present embodiment, the controller 30 receives the detected value of the engine speed sensor and refers to the total output - pump current correspondence map corresponding to the engine speed stored in advance in the internal memory to derive the pump current PC.

[0188] Thereafter, the controller 30 outputs the pump current PC to the regulator 14a. In the present embodiment, the regulator 14a reduces the discharge amount of the main pump 14 as the pump current PC becomes smaller.

[0189] Therefore, if the engine output EP is constant, the controller 30 reduces the pump current PC and the absorbed horsepower of the main pump 14 as the assist output AP becomes smaller. That is, if the engine speed is constant, the controller 30 reduces the pump current PC and the absorbed horsepower of the main pump 14 as the power generation amount of the motor generator 12 (the charge amount of the capacitor 19) becomes larger. This is because when the assist output AP becomes smaller, the total output TP also becomes smaller, and if the absorbed horsepower of the main pump 14 is not reduced, there is a possibility that the absorbed horsepower exceeds the total output TP.

[0190] On the contrary, if the engine output EP is constant, the controller 30 increases the pump current PC as the assist output increases, thereby increasing the absorbed horsepower of the main pump 14. That is, if the engine speed is constant, the pump current PC is increased as the power consumption of the motor generator 12 (the discharge amount of the capacitor 19) increases, thereby increasing the absorbed horsepower of the main pump 14. This is because as the assist output AP increases, the total output TP also increases, creating a margin in the total output TP, and the main pump 14 can efficiently utilize this margin.

[0191] Next, referring to FIG. 23, the temporal changes of various parameters during the warm-up process of the power storage system will be described. FIGS. 23(A) to 23(E) respectively show the temporal changes of the pump discharge pressure, assist output, engine torque, pump load, and pump current, with a common time axis. In this embodiment, the pump discharge pressure is the discharge pressure of the main pump 14R. The assist output is a value corresponding to the above-described assist output AP, and the engine torque is a value corresponding to the above-described engine output EP. The pump load is the absorbed horsepower of the main pump 14R, and the pump current is the value output by the controller 30 to the regulator 14aR (see FIG. 15).

[0192] As shown in FIG. 23(A), the pump discharge pressure changes at a relatively low value before time t10 because the warm-up of the hydraulic drive system has not been performed. Then, when the warm-up of the hydraulic drive system starts at time t10, it rises to the relief pressure Pr and remains at the relief pressure Pr until the warm-up of the hydraulic drive system stops at time t12. After the warm-up of the hydraulic drive system stops at time t12, it changes at the level before the warm-up of the hydraulic drive system starts.

[0193] As shown in FIG. 23(B), before time t10, since the warm-up of the power storage system 120 is being performed, the assist output changes while repeatedly increasing and decreasing across zero. Then, when the warm-up of the hydraulic drive system starts at time t10, it becomes zero. This is because as a result of the bucket 6 being operated to start the warm-up of the hydraulic drive system, the controller 30 stops the warm-up of the power storage system 120 assuming that the warm-up stop condition of the power storage system 120 is satisfied. Specifically, this is because the controller 30 stops the charge and discharge of the capacitor 19 and the operation of the motor generator 12 as a motor or a generator.

[0194] After that, at time t11, the assist output resumes repeating increases and decreases across zero. This is because as a result of the relief state where the pump discharge pressure is approximately the relief pressure continuing for a predetermined time tr, the controller 30 starts the warm-up of the power storage system 120 assuming that the warm-up of the hydraulic drive system is being performed. Specifically, this is because the controller 30 starts the charge and discharge of the capacitor 19 and the operation of the motor generator 12 as a motor or a generator.

[0195] After that, at time t12, the assist output becomes zero again. This is because as a result of the pump discharge pressure becoming less than the relief pressure Pr, the controller 30 stops the warm-up of the power storage system 120 assuming that the warm-up of the hydraulic drive system has stopped.

[0196] After that, at time t13, the assist output resumes repeating increases and decreases across zero. This is because as a result of the state without operation on the operating device 26 continuing for a predetermined time, the controller 30 starts the warm-up of the power storage system 120 assuming that the warm-up start condition is satisfied.

[0197] As shown in Fig. 23(C), before time t10, since the warm-up of the hydraulic drive system has not been performed, the engine torque changes while repeating increases and decreases around the idling torque Ti in accordance with the increase and decrease of the assist output. Then, when the warm-up of the hydraulic drive system starts at time t10, it reaches the allowable maximum torque Tmax. This is because the pump discharge pressure reaches the relief pressure for the warm-up of the hydraulic drive system, resulting in an increase in the pump load.

[0198] After that, the engine torque remains at Tmax except for the period when the assist output is a positive value. During the period when the assist output is a positive value, the engine torque decreases as the assist output increases. The reason why the engine torque decreases during the period when the assist output is a positive value is that the engine 11 is assisted by the motor generator 12 functioning as a motor, and the engine load decreases. On the other hand, during the period when the assist output is a negative value, the engine torque remains at Tmax. This is because the increase in the engine load (engine torque) due to operating the motor generator 12 as a generator is offset by the decrease in the engine load (engine torque) due to reducing the pump load. Specifically, the controller 30 reduces the pump current (see Fig. 23(E)) according to the variation in the negative value region of the assist output (see Fig. 23(B)), and thus reduces the pump load (see Fig. 23(D)) according to the reduction in the pump current.

[0199] Note that the area with the thick dot pattern in Fig. 23(C) represents the increase in the engine load (engine torque) that should have been required to operate the motor generator 12 as a generator if the pump load had not been reduced. Also, the area with the thick dot pattern in Fig. 23(B) represents the amount of power generation by the motor generator 12 during the warm-up of the hydraulic drive system, corresponding to the increase in the engine torque represented by the thick dot pattern in Fig. 23(C). Further, the area with the thick dot pattern in Fig. 23(D) represents the reduction in the pump load, corresponding to the increase in the engine torque represented by the thick dot pattern in Fig. 23(C).

[0200] Next, referring to FIG. 24, another example of the time course of various parameters during the warm-up process of the power storage system will be described. Note that in FIG. 24, the time courses of the engine torque, pump current, and pump load are different from those in FIG. 23, but the time courses of the other parameters are common to those in FIG. 23. Therefore, the description of the common parts will be omitted, and the different parts will be described in detail.

[0201] In FIG. 24(C), unlike FIG. 23(C), during the warm-up of the hydraulic drive system, the engine torque remains at Tmax regardless of the transition of the assist output.

[0202] This is because during the period when the assist output is a positive value, the decrease in the engine load (engine torque) due to the operation of the motor generator 12 as a motor is offset by the increase in the engine load (engine torque) due to the increase in the pump load. Specifically, the controller 30 increases the pump current (see FIG. 24(E)) in response to the variation in the positive value region of the assist output (see FIG. 24(B)), and consequently increases the pump load (see FIG. 24(D)) in response to the increase in the pump current.

[0203] Also, during the period when the assist output is a negative value, the increase in the engine load (engine torque) due to the operation of the motor generator 12 as a generator is offset by the decrease in the engine load (engine torque) due to the reduction in the pump load. Specifically, the controller 30 reduces the pump current (see FIG. 24(E)) in response to the variation in the negative value region of the assist output (see FIG. 24(B)), and consequently reduces the pump load (see FIG. 24(D)) in response to the reduction in the pump current.

[0204] Note that the area of the fine dot pattern in Fig. 24(C) represents the reduction in engine load (engine torque) that should have been reduced by operating the motor generator 12 as a motor if the pump load had not increased. Also, the area of the fine dot pattern in Fig. 24(B) represents the power consumption by the motor generator 12 during warm-up of the hydraulic drive system, corresponding to the reduction in engine torque represented by the fine dot pattern in Fig. 24(C). Further, the area of the fine dot pattern in Fig. 24(D) represents the increase in pump load, corresponding to the reduction in engine torque represented by the fine dot pattern in Fig. 24(C).

[0205] Also, the areas of the thick dot patterns in Figs. 24(B) to 24(D) have the same meaning as the areas of the thick dot patterns in Figs. 23(B) to 23(D).

[0206] With the above configuration, the controller 30 enables the warm-up of the hydraulic drive system and the warm-up of the power storage system 120 to be performed simultaneously. As a result, the controller 30 can efficiently perform the warm-up of the power storage system 120 and the warm-up of the hydraulic drive system, and can shorten the overall warm-up time. Note that the controller 30 may simultaneously perform the warm-up of the engine 11, the warm-up of the hydraulic drive system, and the warm-up of the power storage system 120. Also, since both the warm-up of the hydraulic drive system and the warm-up of the power storage system 120 tend to increase the engine load, they have the effect of accelerating the warm-up of the engine 11.

[0207] Further, when the controller 30 operates the motor generator 12 as a generator for the warm-up of the power storage system 120 during the warm-up of the hydraulic drive system, it reduces the absorbed horsepower of the main pump 14. Therefore, it can prevent the total of the absorbed horsepower of the motor generator 12 (the power generation load on the engine 11) and the absorbed horsepower of the main pump 14 (the hydraulic load on the engine 11) from exceeding the output horsepower of the engine 11. As a result, it can prevent the engine speed from decreasing or the engine 11 from stopping when the warm-up of the power storage system 120 is performed during the warm-up of the hydraulic drive system.

[0208] Further, when the controller 30 operates the motor generator 12 as a motor for warming up the power storage system 120 during the warm-up of the hydraulic drive system, the controller 30 may increase the absorbed horsepower of the main pump 14. Therefore, the absorbed horsepower of the main pump 14 can be maximally increased within a range not exceeding the output horsepower of the engine 11 to further promote the warm-up of the hydraulic drive system. As a result, the warm-up time of the hydraulic drive system can be further shortened.

[0209] Further, the controller 30 determines whether or not the hydraulic drive system is in the warm-up state. In the above-described embodiment, when the relief state in which the discharge pressure of the main pump 14 is substantially the relief pressure continues for a predetermined time, it is determined that the hydraulic drive system is in the warm-up state. Therefore, the controller 30 can reliably discriminate whether the hydraulic drive system is in the warm-up state or in an operation such as excavation. As a result, it is possible to prevent the power storage system 120 from being warmed up during an operation such as excavation.

[0210] Further, the controller 30 starts the warm-up of the power storage system 120 when a predetermined warm-up start condition is satisfied, and stops the warm-up of the power storage system 120 when a predetermined warm-up stop condition is satisfied. In the present embodiment, when the controller 30 determines that the hydraulic drive system is in the warm-up state, the warm-up of the power storage system 120 is started when the capacitor temperature is equal to or lower than the warm-up start capacitor temperature Ts and neither the swing operation nor the traveling operation is performed. Further, when the controller 30 determines that the hydraulic drive system is in the warm-up state, the warm-up of the power storage system 120 is stopped when the capacitor temperature is equal to or higher than the warm-up stop capacitor temperature Tf, or when the swing operation or the traveling operation is performed. As a result, the controller 30 can prevent the warm-up of the power storage system 120 from being started at an inappropriate timing or the warm-up of the power storage system 120 from being stopped at an inappropriate timing.

[0211] As described above, the preferred embodiments of the present invention have been described in detail. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention.

[0212] For example, in the above-described embodiment, the charge transition start charge rate (SOC1) is set stepwise such that it increases as the capacitor temperature decreases, and the discharge transition start charge rate (SOC2) is set stepwise such that it decreases as the capacitor temperature decreases. However, the present invention is not limited to this configuration. For example, at least one of SOC1 and SOC2 may be set continuously according to the capacitor temperature.

[0213] This application also claims priority based on Japanese Patent Application No. 2014-044240 filed on March 6, 2014 and Japanese Patent Application No. 2014-074526 filed on March 31, 2014, and the entire contents of these Japanese patent applications are incorporated herein by reference.

Description of Reference Numerals

[0214] 1 ··· Lower traveling body 1R ··· Hydraulic motor for right-side travel 1L ··· Hydraulic motor for left-side travel 2 ··· Slewing mechanism 3 ··· Upper slewing body 4 ··· Boom 5 ··· Arm 6 ··· Bucket 7 ··· Boom cylinder 8 ··· Arm cylinder 9 ··· Bucket cylinder 10 ··· Cabin 11 ··· Engine 12 ··· Electric generator 13 ··· Transmission 14, 14L, 14R ··· Main pump 14a, 14aL, 14aR ··· Regulator 15 ··· Pilot pump 16 ··· High-pressure hydraulic line 17 ··· Control valve 18 ··· Inverter 19 ··· Capacitor 20 ··· Inverter 21 ··· Slewing electric motor 22 ··· Resolver 23 ··· Mechanical brake 24 ··· Slewing transmission 25 ··· Pilot line 26 ··· Operating device 26A, 26B ··· Lever 26C ··· Pedal 27 ··· Hydraulic line 28 ··· Hydraulic line 29 ··· Pressure sensor 29A, 29AL, 29AR ··· Discharge pressure sensor 30 ··· Controller 40L, 40R ··· Center bypass oil passage 50L, 50R ··· Relief valve 151 - 156 ··· Flow control valve 100 ··· Step-up / step-down converter 110 ··· DC bus 111 ··· DC bus voltage detection unit 112 ··· Capacitor voltage detection unit 113 ··· Capacitor current detection unit 120 ··· Power storage system M2, M3 ··· Temperature sensor

Claims

1. A lower traveling body, an upper slewing body, and a capacitor, and when the temperature related to the capacitor is a predetermined temperature, a hydraulic excavator that limits the discharge power of the capacitor during power running by a discharge limit value adopted in the case of the predetermined temperature, wherein the discharge limit value is the maximum value of the power that the capacitor can discharge, when the temperature related to the capacitor is the predetermined temperature, the output of the hydraulic pump is limited by a pump current limit value corresponding to a slewing speed limit value adopted in the case of the predetermined temperature, wherein the slewing speed limit value decreases as the predetermined temperature decreases, and the pump current limit value increases as the slewing speed limit value increases. Hydraulic excavator.

2. A lower traveling body, an upper slewing body, and a capacitor, and when the temperature related to the capacitor is a predetermined temperature, a hydraulic excavator that limits the discharge power of the capacitor during power running by a discharge limit value adopted in the case of the predetermined temperature, wherein the discharge limit value is the maximum value of the power that the capacitor can discharge, when the temperature related to the capacitor is the predetermined temperature, the maximum slewing speed of the upper slewing body is decreased by a slewing speed limit value adopted in the case of the predetermined temperature, wherein the slewing speed limit value decreases as the predetermined temperature decreases. Hydraulic excavator.

3. The discharge limit value is set for each of a plurality of the predetermined temperatures, and the larger the charge rate of the capacitor, the larger the discharge limit value. The hydraulic excavator according to claim 1 or claim 2.

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