Driving system of electric construction machine

Abstract

To provide a driving system of an electric construction machine which keeps a long life of a residual amount of stored power of a power storage device, and is operable over a long time.SOLUTION: After operation devices 21 to 26 are in an inoperable state to lower the rotational speed of an electric motor 11 from reference rotational speed and the electric motor 11 is driven at low rotational speed, a controller 33 determines an upper limit torque of the electric motor 11 on the basis of a residual amount of stored power of the battery 10 wen the operation devices 21 to 26 are operated, and executes restoration control of restoring the rotational speed of the electric motor 11 to the reference rotational speed while restricting the output torque of the electric motor 11 to the upper limit torque.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a drive system for electric construction machinery that performs control to reduce the rotation speed of an electric motor from a reference rotation speed to a predetermined low-speed rotation speed when a predetermined time has elapsed since the operating device was not operated. [Background technology]

[0002] Many construction machines such as hydraulic excavators are powered by diesel engines, and perform work by operating hydraulic actuators with pressurized oil supplied from a hydraulic pump connected to the diesel engine. The operation of the hydraulic actuator is commanded by operating an operating device. In the drive system of such construction machines, as described in Patent Document 1, for example, a technology is adopted in which, when a predetermined time has elapsed since the operating device was not operated, auto-idle control is performed to reduce the engine speed from a reference speed commanded by an engine speed command device to a low idle speed, and then, when the operating device is operated, the engine speed is controlled to return from the low idle speed to the reference speed.

[0003] On the other hand, in recent years, from the standpoint of improving fuel efficiency, improving exhaust gas characteristics, and reducing noise, work machines such as electric hydraulic excavators have been developed and put into practical use, which are equipped with an energy storage device (battery) as a driving source, and use the electricity from the energy storage device to drive an electric motor, which in turn drives a hydraulic pump.

[0004] In such electric construction machinery, Patent Document 2 discloses that, similar to construction machinery that uses a diesel engine to drive a hydraulic pump, when a predetermined time has elapsed since the operating device has been left unoperated, the rotation speed of the electric motor is controlled to be reduced from a reference rotation speed to a predetermined low-speed rotation speed, and then, when the operating device is operated, the rotation speed of the electric motor is returned from the predetermined low-speed rotation speed to the reference rotation speed indicated by the rotation speed indicating device. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 60-038561 [Patent Document 2] Patent No. 5389100 Summary of the Invention [Problem to be solved by the invention]

[0006] In the electric construction machine described in Patent Document 2, when a predetermined time has elapsed since the operating device was not operated, the rotation speed of the electric motor is controlled to be reduced from the reference rotation speed indicated by the rotation speed indicating device to a predetermined low-speed rotation speed, thereby reducing power consumption when the operating device is not being operated.

[0007] However, in Patent Document 2, when the rotation speed of the electric motor is lowered to a predetermined low speed and then the operating device is operated to return the rotation speed of the electric motor from the predetermined low speed to the reference speed, the output torque of the electric motor increases sharply even when the remaining charge (SOC) of the power storage device is low, and the ratio of power consumption to the remaining charge becomes large. This causes the remaining charge of the power storage device to decrease more quickly, making it impossible to prolong the remaining charge of the power storage device, and there is a problem that the construction machine cannot be operated for a long time on a single charge.

[0008] An object of the present invention is to provide a drive system for electric construction machinery that can extend the remaining charge in a power storage device and operate for long periods of time. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides a drive system for an electric construction machine comprising an electric motor driven by power from a power storage device, a hydraulic pump driven by the electric motor, a hydraulic actuator driven by pressurized oil discharged from the hydraulic pump, an operating device for operating the hydraulic actuator, a rotation speed indicating device for setting a reference rotation speed of the electric motor, and a controller for driving the electric motor at the reference rotation speed set by the rotation speed indicating device and reducing the rotation speed of the electric motor from the reference rotation speed when the operating device is not operated, wherein, when the operating device is operated after the operating device is not operated and the rotation speed of the electric motor is reduced from the reference rotation speed, the controller determines an upper limit torque of the electric motor based on the remaining amount of stored power in the power storage device, and executes return control for returning the rotation speed of the electric motor to the reference rotation speed while limiting the output torque of the electric motor to the upper limit torque.

[0010] By providing a controller in this manner, when the operating device is operated after the electric motor's rotation speed has been reduced from the reference rotation speed, an upper limit torque of the electric motor is determined based on the remaining charge in the power storage device, and return control is executed to return the electric motor's rotation speed to the reference rotation speed while limiting the output torque of the electric motor to the upper limit torque. This reduces the amount of power consumed when returning the electric motor's rotation speed to the reference rotation speed when the remaining charge in the power storage device becomes low, extends the remaining charge in the power storage device, and enables long-term operation on a single charge. Effect of the Invention

[0011] According to the present invention, the remaining charge in the power storage device can be made to last longer, enabling long-term operation. [Brief description of the drawings]

[0012] [Figure 1] 1 is a side view of an electric construction machine equipped with a drive system according to a first embodiment of the present invention. [Diagram 2]FIG. 1 is a diagram showing a drive system of an electric hydraulic excavator according to an embodiment of the present invention. [Diagram 3] This is a view of the inside of the hydraulic excavator's cabin (operator's cab) as seen from the operator's seat side. [Figure 4] FIG. 2 is a diagram showing an outline of the overall configuration of a hydraulic system for driving a lower traveling body, an upper rotating body, and a working machine. [Diagram 5] FIG. 4 is a functional block diagram showing the processing function of a vehicle body controller. [Figure 6] FIG. 13 is a diagram showing an example of a relationship between the SOC of a battery and an upper limit torque of return control, which is set in a table of a motor torque calculation unit. [Figure 7] 4 is a flowchart showing the overall flow of processing by a vehicle body controller. [Figure 8] FIG. 7 is a diagram showing the change in output torque of the electric motor under return control when the SOC of the battery falls below the first threshold shown in FIG. 6 and reaches, for example, the second threshold, in comparison with the case where return control is not performed. [Figure 9] FIG. 7 is a diagram showing the change in the rotation speed of the electric motor under return control when the battery SOC falls below the first threshold shown in FIG. 6 and reaches, for example, the second threshold, in comparison with the case where return control is not performed. [Figure 10] FIG. 11 is a diagram showing an example of a relationship between the SOC of a battery and an increment value of an upper limit torque of return control in the second embodiment of the present invention. [Figure 11] 10 is a flowchart showing an overall flow of processing by a vehicle body controller in a second embodiment. [Figure 12] FIG. 11 is a diagram showing the change in output torque of the electric motor in the return control of the second embodiment when the SOC of the battery falls below the first threshold and becomes, for example, the second threshold, in comparison with the case where the return control is not performed. [Figure 13] FIG. 13 is a diagram showing a drive system for an electric hydraulic excavator according to a third embodiment of the present invention, illustrating a case in which an electric motor is driven by battery power. [Figure 14]FIG. 13 is a diagram showing a drive system for an electric hydraulic excavator according to a third embodiment, illustrating a case in which an electric motor is driven while a battery is being charged with electric power from an external power source. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0014] <First embodiment> A first embodiment of the present invention will be described.

[0015] ~Construction machinery~ 1 is a side view of an electric construction machine equipped with a drive system according to a first embodiment of the present invention. In this embodiment, the electric construction machine is a track-type hydraulic excavator, which is a representative example of construction machines.

[0016] In FIG. 1, the electric hydraulic excavator in this embodiment includes a lower traveling body 101, an upper rotating body 102, and a front work unit 103.

[0017] The lower traveling body 101 includes left and right crawlers 101a, 101b, and the left and right traveling motors 1a, 1b are rotated to drive the traveling devices 101a, 101b, thereby causing the vehicle to travel.

[0018] The upper rotating body 102 can rotate relative to the lower running body 101 by rotating a rotation motor 1c provided on the rotating ring 102a. The upper rotating body 102 is equipped with a cabin 105 forming a driver's cab. A swing post 104 is attached to the front of a rotation frame 102c of the upper rotating body 102, and a front working machine 103 is attached to this swing post 104 so that it can move up and down. The swing post 104 rotates left and right by extending and retracting a swing cylinder 1g, and the front working machine 103 rotates left and right relative to the upper rotating body 102.

[0019] The front work implement 103 is equipped with a boom 103a, an arm 103b, and a bucket 103c. By extending and contracting a boom cylinder 1d, an arm cylinder 1e, and a bucket cylinder 1f, the boom 103a, the arm 103b, and the bucket 103c are driven and the posture of the front work implement 103 changes.

[0020] A blade 106 is attached to a central frame between the left and right crawlers 101a, 101b, and the blade 106 moves up and down by extending and contracting a blade cylinder 1h.

[0021] ~Drive System~ FIG. 2 is a diagram showing a drive system of the electric hydraulic excavator according to this embodiment.

[0022] In FIG. 2, the drive system of this embodiment includes a battery 10 which is a power storage device, an electric motor 11 which is driven by the power of the battery 10 (power storage device), a hydraulic pump 12 and a pilot pump 13 which are driven by the electric motor 11, the above-mentioned travel motors 1a, 1b, a swing motor 1c, a boom cylinder 1d, an arm cylinder 1e, a bucket cylinder 1f, a swing cylinder 1g, and a blade cylinder 1h which are hydraulic actuators driven by the pressure oil discharged from the hydraulic pump 12, and directional control valves 16a to 16h (FIG. 4) which control the flow of the pressure oil supplied from the hydraulic pump 12 to the hydraulic actuators 1a to 1h. The hydraulic actuators 1a-1h are provided with an operating device 21-26 (see Figs. 3 and 4) that generate operation signals for switching the directional control valves 16a-16h and operate the hydraulic actuators 1a-1h by switching the directional control valves 16a-16h, a motor rotation speed dial 32 that is a rotation speed indicating device that sets a reference rotation speed Nset of the electric motor 11, and a vehicle controller 33 (controller) that drives the electric motor 11 at the reference rotation speed Nset set by the motor rotation speed dial 32 (rotation speed indicating device) and reduces the rotation speed of the electric motor 11 from the reference rotation speed Nset when the operating devices 21-26 are not operated.

[0023] When the operating devices 21-26 are in an unoperated state, the control that reduces the rotation speed of the electric motor 11 from the reference rotation speed Nset corresponds to the auto-idle control when the prime mover is a diesel engine, and in this specification, this control is referred to as low-speed rotation speed control.

[0024] The drive system of this embodiment also includes an inverter 31 that controls the power supplied from the battery 10 to the electric motor 11, a battery controller 10a that is provided in the battery 10 and functions as a battery charge remaining charge monitoring device that controls the inside of the battery 10 and acquires the battery temperature, as well as monitors the state of charge (hereinafter referred to as SOC) which indicates the remaining charge or charging rate of the battery 10 and outputs an SCO signal, an operation detection device 35 that detects whether or not the operation devices 21-26 are operated and outputs an operation pilot pressure signal as an operation information signal, a mode selection switch 36 that outputs a mode selection signal (ON / OFF signal) that selects either a normal control mode or a low speed rotation speed control mode, and a rotation sensor 37 that detects the rotation speed of the electric motor 11 and outputs a motor rotation speed detection signal.

[0025] The signals from the motor rotation speed dial 32, the battery controller 10a, the operation detection device 35, the mode selection switch 36, and the rotation sensor 37 are input to the vehicle body controller 33, which performs predetermined calculation processing (described later) based on these signals and commands the inverter 31 to control the rotation speed and torque of the electric motor 11.

[0026] The inverter 31 and battery 10 are electrically connected via a high-voltage power supply line 41, and the inverter 31 and electric motor 11 are electrically connected via a high-voltage power supply line 42. The vehicle body controller 33 commands the inverter 31 to have a torque and rotation speed. Based on the commands, the inverter 31 converts the high-voltage DC current output from the battery 10 into a high-voltage AC current, and controls the power supplied from the battery 10 to the electric motor 11, thereby controlling the rotation speed and torque of the electric motor 11.

[0027] The hydraulic pump 12 is of a variable displacement type, and is equipped with a regulator 15 for controlling the pump displacement (capacity) so that the pump absorption torque is limited to a maximum torque. The regulator 15 has a regulator piston 15a to which the discharge pressure of the hydraulic pump 12 is introduced, and a spring 15b positioned opposite the regulator piston 15a, and when the discharge pressure of the hydraulic pump 12 rises beyond the biasing force of the spring 15b, the regulator 15 reduces the displacement (capacity) of the hydraulic pump 12, and controls so that the absorption torque of the hydraulic pump 12, which is the product of the displacement (capacity) of the hydraulic pump 12 and the discharge pressure of the hydraulic pump 12, is limited to the maximum torque set by the spring 15b.

[0028] ~Inside the cabin~ FIG. 3 is a view of the interior (driver's compartment) of the hydraulic excavator's cabin 105 as seen from the driver's seat side.

[0029] In Figure 3, within the cabin 105 are arranged a driver's seat 20 where the operator sits, operation devices 21, 22 that command the operation of the upper rotating body 102 and the front work machine 103 (boom 103a, arm 103b, bucket 103c), operation devices 23, 24 that command the operation of the lower running body 101 (left and right crawlers 101a, 101b), an operation device 25 that commands the operation of the swing post 104, and an operation device 26 that commands the operation of the blade 106.

[0030] The operating devices 21, 22, 23, 24, and 26 are of a lever type, and the operating device 25 is of a pedal type. Although not shown in the figure, pedals are attached to the bases of the levers of the operating devices 23 and 24, respectively, so that the operating devices 23 and 24 can also instruct the traveling operation of the lower traveling body 101 by pedal operation.

[0031] The operating devices 21, 22 are provided on the left and right in front of the driver's seat 20, and their respective operating levers can be operated in cross directions, left and right and front and rear. The left operating device 21 commands the movement of the arm 103b when the operating lever is operated in the left and right direction, and commands the movement of the upper rotating body 102 when it is operated in the front and rear direction. The right operating device 22 commands the movement of the bucket 103a when the operating lever is operated in the left and right direction, and commands the movement of the boom 103a when it is operated in the front and rear direction.

[0032] The operating devices 23, 24 are arranged side by side in the center of the floor in front of the driver's seat 20, and the left operating device 23 instructs the left crawler 101a to move forward / reverse when the operating lever is operated in the forward / reverse direction, and the right operating device 24 instructs the right crawler 101b to move forward / reverse when the operating lever is operated in the forward / reverse direction.

[0033] The operating device 25 is provided on the floor in front of the driver's seat 20, to the right of the operating device 24 for traveling, and when the operating pedal is operated in the forward / backward direction, it commands the left / right swinging movement of the swing post 104. The operating device 26 is provided to the right of the operator seated in the driver's seat 20, and when the operating lever is operated in the forward / backward direction, it commands the up / down movement of the blade 106.

[0034] A console box 27 is provided at the base end portion of the operating device 22 on the right side of the driver's seat 20, to the right of the operator seated in the driver's seat 20, and the console box 27 is provided with the above-mentioned mode selection switch 36.

[0035] ~Hydraulic System~ FIG. 4 is a diagram showing an outline of the overall configuration of a hydraulic system for driving the lower traveling body 101 (left and right crawlers 101a, 101b), the upper rotating body 102, and the front working implement 103 (boom 103a, arm 103b, bucket 103c).

[0036] In Figure 4, the operating device 21 is illustrated divided into a portion 21a that instructs the movement of the arm 103b and the upper rotating body 102, and a portion 21b that instructs the movement of the upper rotating body 102, and the operating device 22 is illustrated divided into a portion 22a that instructs the movement of the boom 103a, and a portion 22b that instructs the movement of the bucket 103c.

[0037] The operating devices 21-26 are hydraulic pilot systems that generate operating pilot pressure as an operating signal based on the discharge pressure of the pilot pump 13. When an operating lever or an operating pedal is operated, the discharge pressure of the pilot pump 13 (see FIG. 2) is reduced according to the operating direction and amount to generate operating pilot pressure. These operating pilot pressures are led to the control valve 16 via the respective pilot lines shown by dotted lines. The spools of the above-mentioned directional control valves 16a-16h are arranged within the control valve 16, and each spool within the control valve 16 strokes according to the operating pilot pressure sent from the operating devices 21-26, controlling the flow rate and flow direction of the pressure oil supplied from the hydraulic pump 12 to the multiple actuators 1a-1h.

[0038] In addition, a shuttle block 16j is disposed within the control valve 16, and the shuttle block 16j selects the highest pressure among the operation pilot pressures sent from the operation devices 21-26 and outputs it to the operation detection device 35. The operation detection device 35 is a pressure sensor that detects the pressure selected by the shuttle block 16j (the highest operation pilot pressure) and transmits an operation signal to the vehicle body controller 33.

[0039] ~Car Controller 33~ FIG. 5 is a functional block diagram showing the processing functions of the vehicle body controller 33.

[0040] The vehicle body controller 33 has a SOC information acquisition unit 33a, a pressure conversion unit 33b, an operating pilot pressure determination unit 33c, a motor torque calculation unit 33d, and a motor rotation speed calculation unit 33e.

[0041] The SOC information acquisition unit 33a acquires SOC information (information on remaining charge) from the SOC signal sent from the battery controller 10a, and sends the SOC information to the motor torque calculation unit 33d.

[0042] The pressure conversion unit 33b converts the operation signal sent from the operation detection device 35 (pressure sensor) into an analog value of the operation pilot pressure, and sends the analog value of the operation pilot pressure to the operation pilot pressure determination unit 33c.

[0043] The operating pilot pressure determination unit 33c determines whether the analog value of the operating pilot pressure sent from the pressure conversion unit 33b is lower than a preset threshold value as a determination value for whether or not an operation is performed, and when any of the operating devices 21-26 is operated (operated) and the analog value of the operating pilot pressure is equal to or higher than the threshold value, it sends an operation ON signal to the motor torque calculation unit 33d and the motor rotation speed calculation unit 33e.

[0044] When none of the operating devices 21-26 are operated (no operation) and the analog value of the operating pilot pressure is lower than the threshold value, the operating pilot pressure determination unit 33c sends an operation OFF signal to the motor torque calculation unit 33d and the motor rotation speed calculation unit 33e.

[0045] Furthermore, the operation pilot pressure determination unit 33c counts the no-operation time by a counter provided in the operation pilot pressure determination unit 33c. Then, when the no-operation time exceeds a predetermined time that is preset as a value for determining whether or not low-speed rotation speed control is required, in addition to an operation OFF signal, a predetermined time lapse signal is sent to the motor torque calculation unit 33d and the motor rotation speed calculation unit 33e.

[0046] In addition to the SOC information sent from the SOC information acquisition unit 33a and the operation ON signal or operation OFF signal and a specified time elapse signal sent from the operation pilot pressure determination unit 33c, the motor torque calculation unit 33d receives a motor rotation speed detection signal from the rotation sensor 37, a mode selection signal (ON / OFF signal) from the mode selection switch 36, and a reference rotation speed signal from the motor rotation speed dial 32.

[0047] In addition to the above-mentioned operation ON signal or operation OFF signal and a specified time elapse signal transmitted from the operation pilot pressure determination unit 33c, the motor rotation speed calculation unit 33e receives a mode selection signal (ON / OFF signal) from the mode selection switch 36 and a reference rotation speed signal from the motor rotation speed dial 32.

[0048] The motor torque calculation unit 33d and the motor rotation speed calculation unit 33e each operate as follows depending on whether the mode selection signal sent from the mode selection switch 36 is OFF or ON.

[0049] <When the mode selection signal is OFF> When the mode selection signal sent from the mode selection switch 36 is OFF and the normal control mode is indicated, the motor torque calculation unit 33d and the motor rotation speed calculation unit 33e perform only normal control and do not perform low speed rotation speed control, regardless of the operation ON signal, operation OFF signal, and specified time elapse signal sent from the operation pilot pressure determination unit 33c.

[0050] In normal control, the motor torque calculation unit 33d commands the inverter 31 an upper limit torque Tmax-N (first upper limit torque) for normal control of the electric motor 11, and controls the output torque of the electric motor 11 so as not to exceed the upper limit torque Tmax-N for normal control. In addition, the motor rotation speed calculation unit 33e commands the inverter 31 a reference rotation speed Nset specified by the motor rotation speed dial 32, and controls the rotation speed of the electric motor 11 to be the reference rotation speed Nset.

[0051] <When the mode selection signal is ON> When the mode selection signal sent from the mode selection switch 36 is ON and the low speed rotation speed control mode is selected, if an operation ON signal is sent from the operation pilot pressure determination unit 33c, the motor torque calculation unit 33d and the motor rotation speed calculation unit 33e each perform the normal control described above. That is, the motor torque calculation unit 33d commands the upper limit torque Tmax-N of the normal control of the electric motor 11 to the inverter 31, and controls the output torque of the electric motor 11 not to exceed the upper limit torque Tmax-N of the normal control. Also, the motor rotation speed calculation unit 33e commands the reference rotation speed Nset specified by the motor rotation speed dial 32 to the inverter 31, and controls the rotation speed of the electric motor 11 to be the reference rotation speed Nset.

[0052] In addition, even if the mode selection signal sent from the mode selection switch 36 is ON, an operation OFF signal is sent from the operation pilot pressure determination unit 33c, and no specified time elapse signal is sent, the motor torque calculation unit 33d and the motor rotation speed calculation unit 33e each perform the above-mentioned normal control.

[0053] On the other hand, when the mode selection signal sent from the mode selection switch 36 is ON and both an operation OFF signal and a specified time elapse signal are sent from the operation pilot pressure determination unit 33c, the motor torque calculation unit 33d and the motor rotation speed calculation unit 33e each perform low-speed rotation speed control.

[0054] In this low-speed rotation speed control, the motor torque calculation unit 33d commands the inverter 31 to an upper limit torque Tmax-idle (second upper limit torque) for the low-speed rotation speed control of the electric motor 11, which is smaller than the upper limit torque Tmax-N (first upper limit torque) for the normal control of the electric motor 11 described above, and controls the output torque of the electric motor 11 so as not to exceed the upper limit torque Tmax-idle for the low-speed rotation speed control. Also, the motor rotation speed calculation unit 33e commands the inverter 31 to a predetermined low-speed rotation speed Nidle, which is lower than the reference rotation speed Nset specified by the motor rotation speed dial 32, and controls the rotation speed of the electric motor 11 to be the low-speed rotation speed Nidle.

[0055] Here, when the reference rotation speed Nset indicated by the motor rotation speed dial 32 is the maximum rotation speed of 2000 rpm, the predetermined low speed rotation speed Nidle is preferably 400 to 600 rpm, and in this embodiment is, for example, 450 rpm.

[0056] In addition, when low-speed rotation speed control is being performed, if at least one of the multiple operating devices 21-26 is operated and the signal sent from the operating pilot pressure determination unit 33c switches from an operation OFF signal to an operation ON signal, the motor torque calculation unit 33d and the motor rotation speed calculation unit 33e each perform control to return from low-speed rotation speed control to normal control (hereinafter sometimes referred to as return control).

[0057] In this return control, the motor torque calculation unit 33d calculates an upper limit torque Tmax-R that is smaller when the SOC (remaining charge) of the battery 10 is less than the first threshold value E1 (see FIG. 6) than when it is more than the first threshold value E1, and commands this upper limit torque Tmax-R to the inverter 31, thereby controlling the output torque of the electric motor 11 to be limited to the upper limit torque Tmax-R. The motor rotation speed calculation unit 33e commands the reference rotation speed Nset designated by the motor rotation speed dial 32 to the inverter 31, and controls the rotation speed of the electric motor 11 to be the reference rotation speed Nset.

[0058] In this embodiment, when the operating devices 21-26 are operated after the operating devices 21-26 are in an unoperated state and the rotation speed of the electric motor 11 has been reduced from the reference rotation speed Nset, the vehicle body controller 33 determines the upper limit torque Tmax-R of the electric motor 11 based on the SOC (remaining charge) of the battery 10, and executes return control to return the rotation speed of the electric motor 11 to the reference rotation speed Nset while limiting the output torque of the electric motor 11 to the upper limit torque Tmax-R. In addition, in this embodiment, the vehicle body controller 33 determines the upper limit torque Tmax-R so that it is smaller when the SOC of the battery 10 is less than the first threshold E1 than when it is more than the first threshold E1, and more preferably, determines the upper limit torque Tmax-R so that it is smaller as the SOC of the battery 10 becomes lower.

[0059] <Relationship between SOC and upper limit torque Tmax-R> Next, the relationship between SOC and upper limit torque Tmax-R will be described.

[0060] The vehicle body controller 33 stores a table that sets the relationship between the SOC of the battery 10 and the upper limit torque Tmax-R of the electric motor 11. When the motor torque calculation unit 33d returns the rotational speed of the electric motor 11 to the reference rotational speed Nset, based on the SOC of the battery 10 and the table, it determines the upper limit torque Tmax-R when executing the return control.

[0061] FIG. 6 is a diagram showing an example of the relationship between the SOC of the battery 10 set in the above table and the upper limit torque Tmax-R of the return control. The unit of SOC is %.

[0062] In FIG. 6, in the table stored in the vehicle body controller 33, while the SOC is more than the first threshold value E1, the upper limit torque Tmax-R becomes a constant first torque T1. Between when the SOC is from the first threshold value E1 to the second threshold value E2 set lower than the first threshold value E1, the upper limit torque Tmax-R decreases from the first torque T1 to the second torque T2. While the SOC is less than the second threshold value E2, the upper limit torque Tmax-R is set to be constant at the second torque T2.

[0063] Also, in the present embodiment, in the above table, while the SOC decreases from the first threshold value E1 to the second threshold value E2, the upper limit torque Tmax-R is set to continuously decrease from the first torque T1 to the second torque T2. As a result, when the SOC becomes less than or equal to the first threshold value E1 and the output torque of the electric motor 11 changes gently when shifting from normal control to return control, it is possible to shift to return control without making the operator feel uncomfortable.

[0064] The table stored in the vehicle body controller 33 may be set to a certain SOC between the first threshold value E1 and the second threshold value E2 as the first threshold value, and may be set so that the upper limit torque Tmax-R decreases in a stepped manner when the SOC of the battery 10 decreases to the first threshold value.

[0065] Here, the first torque T1 is preferably set to a value equal to the upper limit torque Tmax-N of the normal control described above. The second torque T2 is set to a value between the upper limit torque Tmax-idle of the low speed rotation speed control described above and the upper limit torque Tmax-N of the normal control, for example, such that the rotation speed of the electric motor 11 smoothly increases from the low speed rotation speed to the reference rotation speed Nset during the return control.

[0066] Specifically, taking into consideration the responsiveness of the return control, when the difference Tmax-N-Tmin-L between the upper limit torque Tmax-idle of the low speed rotation speed control and the upper limit torque Tmax-N of the normal control is ΔT, the second torque T2 is preferably set to a value smaller than the upper limit torque Tmax-N of the normal control by 30% to 60% of the difference ΔT. In this embodiment, the second torque Tmin is set to a value smaller than the upper limit torque Tmax-N of the normal control by 40% of the difference ΔT.

[0067] Furthermore, the first threshold E1 is preferably set to a value within the range of SOC 50% to 30%, and the second threshold E2 is preferably set to a value within the range of SOC 30% to 10%; in this embodiment, the first threshold E1 is set to SOC 40%, and the second threshold E2 is set to SOC 25%.

[0068] <Overall processing flow of the vehicle body controller 33> 7 is a flowchart showing the overall flow of processing by the vehicle body controller 33. The processing contents of the vehicle body controller 33 will be further explained below with reference to FIG.

[0069] <Normal control mode> First, a process flow when the operator turns off the mode selection switch 36 and selects the normal control mode will be described.

[0070] 7, the vehicle body controller 33 first determines whether the mode selection switch 36 is ON based on a signal transmitted from the mode selection switch 36 (step A). ​​Here, since the mode selection switch 36 is OFF, the vehicle body controller 33 denies the determination in step A and transitions to normal control (step H).

[0071] As described above, in normal control, the vehicle controller 33 commands the inverter 31 to use the upper limit torque Tmax-N for normal control and the reference rotation speed Nset indicated by the motor rotation speed dial 32, and controls the torque and rotation speed of the electric motor 11 so that the output torque of the electric motor 11 is limited to the upper limit torque Tmax-N for normal control (first upper limit torque) and the rotation speed of the electric motor 11 becomes the reference rotation speed Nset.

[0072] Thereafter, the vehicle controller 33 repeats the normal control from step A to step H until the mode selection switch 36 is turned ON.

[0073] <Low speed control mode> Next, the flow of processing when the operator turns on the mode selection switch 36 and selects the low speed rotation speed control mode will be explained by dividing the processing into cases according to examples of operation of the operating devices 21 to 26.

[0074] <<(1) When none of the operation devices 21 to 26 are operated>> When the operator turns on the mode selection switch 36, the vehicle body controller 33 makes an affirmative determination in step A, and determines whether or not all of the operating devices 21 to 26 are in a non-operated state (neutral state) (step B).

[0075] In this operation example, since all of the operating devices 21 to 26 are not operated, the vehicle body controller 33 makes a positive determination in step B, and further determines whether the rotation speed commanded to the inverter 31 in the previous calculation cycle was the rotation speed for low-speed rotation speed control (step C). In this operation example, since the previous calculation cycle was in normal control mode and the rotation speed commanded to the inverter 31 was the reference rotation speed Nset, the vehicle body controller 33 makes a negative determination in step C, and further determines whether a predetermined time has elapsed since all of the operating devices 21 to 26 became unoperated (step D). In this operation example, since the previous calculation cycle was also in normal control mode and the time of no operation was not counted, the vehicle body controller 33 makes a negative determination in step D, and transitions to normal control in step H.

[0076] In normal control, as described above, the vehicle body controller 33 commands the inverter 31 to use the upper limit torque Tmax-N for normal control and the reference rotation speed Nset indicated by the motor rotation speed dial 32, and controls the torque and rotation speed of the electric motor 11 so that the output torque of the electric motor 11 is limited to the upper limit torque Tmax-N for normal control and the rotation speed of the electric motor 11 becomes the reference rotation speed Nset.

[0077] Thereafter, the vehicle body controller 33 repeats the process of steps A→B→C→D→H until any of the operating devices 21-26 is operated and the judgment in step B is denied, or a predetermined time has elapsed with all of the operating devices 21-26 not being operated and the judgment in step D is affirmed.

[0078] <<(2) When none of the operation devices 21 to 26 is operated and any of the operation devices 21 to 26 is operated before a predetermined time has elapsed>> If none of the operating devices 21-26 are operated and the operator operates any of the operating devices 21-26 before the lapse of a predetermined time, the vehicle body controller 33 denies the determination in step B, clears the count of the non-operation time of the low-speed rotation speed control (step F), and then determines whether the rotation speed commanded to the inverter 31 in the previous calculation cycle was the rotation speed for low-speed rotation speed control (step G). In this operation example, the previous calculation cycle was normal control, and the rotation speed commanded to the inverter 31 was the reference rotation speed Nset for normal control, so the vehicle body controller 33 denies the determination in step G and transitions again to normal control in step H.

[0079] Thereafter, the vehicle body controller 33 repeats the process of steps A→B→F→G→H until all of the operating devices 21 to 26 are again unoperated and the determination in step B becomes positive.

[0080] <<(3) When a predetermined time has elapsed without any operation of the operation devices 21 to 26>> If the predetermined time has elapsed without any operation of the operating devices 21 to 26, the vehicle body controller 33 makes an affirmative determination in step D and proceeds to step E of low speed rotation speed control.

[0081] In the low-speed rotation speed control, as described above, the vehicle body controller 33 commands the inverter 31 to set an upper limit torque Tmax-idle (second upper limit torque) for the low-speed rotation speed control of the electric motor 11, and controls the output torque of the electric motor 11 to be limited to the upper limit torque Tmax-idle for the low-speed rotation speed control. Also, the vehicle body controller 33 commands the inverter 31 to set a rotation speed Nidle for the low-speed rotation speed control that is lower than the reference rotation speed Nset specified by the motor rotation speed dial 32, and controls the rotation speed of the electric motor 11 to be the predetermined low-speed rotation speed Nidle.

[0082] In the next calculation cycle, since the rotation speed commanded to the inverter 31 in the previous calculation cycle was the rotation speed Nidle for low-speed rotation speed control, the vehicle body controller 33 judges in step C as positive, and proceeds directly to the low-speed rotation speed control of step E.

[0083] Thereafter, the vehicle body controller 33 repeats the process of steps A→B→C→E until any of the operating devices 21 to 26 is operated again and the determination in step B is negative.

[0084] <<(4) When none of the operating devices 21 to 26 are operated, a predetermined time has passed and the system has transitioned to low-speed rotation speed control, and then any of the operating devices 21 to 26 is operated>> If none of the operating devices 21-26 are operated and a predetermined time has elapsed to transition to low-speed rotation speed control, and then any of the operating devices 21-26 is operated, the vehicle body controller 33 denies the determination in step B, clears the count of the non-operation time of the low-speed rotation speed control (step F), and then determines whether the rotation speed commanded to the inverter 31 in the previous calculation cycle was the rotation speed Nidle for low-speed rotation speed control (step G). In this operation example, the low-speed rotation speed control has been performed up until now, and the rotation speed commanded to the inverter 31 was the predetermined low-speed rotation speed Nidle, so the vehicle body controller 33 affirms the determination in step G and transitions to control to return from low-speed rotation speed control to normal control.

[0085] In this recovery control, the vehicle body controller 33 first acquires SOC information from the SOC signal sent from the battery controller 10a (Step I), then determines the upper limit torque Tmax-R of the electric motor 11 based on the SOC (remaining charge) of the battery 10 (Step J), and commands this upper limit torque Tmax-R and the reference rotation speed Nset indicated by the motor rotation speed dial 32 to the inverter 31 (Step K), thereby controlling the torque and rotation speed of the electric motor 11.

[0086] Next, the vehicle body controller 33 judges whether the detected rotation speed of the electric motor 11 has reached the reference rotation speed Nset based on the motor rotation speed detection signal from the rotation sensor 37 (step L), and if the rotation speed of the electric motor 11 has not reached the reference rotation speed Nset, it performs the processing of steps J and K again, and repeats the processing of steps J → K → L until the rotation speed of the electric motor 11 reaches the reference rotation speed Nset. As a result, the output torque of the electric motor 11 is controlled to be limited to the upper limit torque Tmax-R of the return control, and the rotation speed of the electric motor 11 is controlled to become the reference rotation speed Nset while suppressing the rate of increase in the rotation speed of the electric motor 11.

[0087] Next, when the rotation speed of the electric motor 11 reaches the reference rotation speed Nset, the process shifts to normal control in which the processing of steps A→B→F→G→H is carried out.

[0088] ~Effects~ Figure 8 is a diagram showing the change in output torque of the electric motor 11 during recovery control when the SOC of the battery 10 in this embodiment falls below the first threshold E1 shown in Figure 6 and becomes, for example, the second threshold E2, in comparison with a case where the SOC of the battery 10 falls below the first threshold E1 but remains constant at Tmax and the recovery control of this embodiment is not performed.

[0089] Figure 9 is a diagram showing the change in rotation speed of the electric motor 11 under return control when the SOC of the battery 10 falls below the first threshold E1 shown in Figure 6 and becomes, for example, the second threshold E2, in comparison with a case where the return control of this embodiment is not performed.

[0090] In addition, the change in output torque of the electric motor 11 when the SOC of the battery 10 remains constant at Tmax and the return control of this embodiment is not performed corresponds to the change in output torque of the electric motor when the SOC of the battery 10 is equal to or greater than the first threshold value E1 shown in Figure 6 and the return control is performed in this embodiment.

[0091] In Figure 8, if the return control of this embodiment is not performed, when returning from low-speed rotation speed control to normal control, the upper limit torque of the return control of the electric motor 11 remains the upper limit torque Tmax-N (=T1) of normal control, so the output torque of the electric motor 11 increases sharply to the upper limit torque Tmax-N (=T1) of normal control, as shown by the dotted line TA in Figure 8, and then, after the peak of the output torque of the electric motor 11 exceeds the upper limit torque Tmax-N (=T1) due to the inertia of the load, it changes to converge to the upper limit torque Tmax-N (=T1).

[0092] For this reason, the rotation speed of the electric motor 11 changes so that the peak of the rotation speed greatly exceeds the reference rotation speed Nset indicated by the motor rotation speed dial 32 before converging to the reference rotation speed Nset, as shown by the dotted line in FIG.

[0093] In contrast, when the return control of this embodiment is performed, if the SOC of the battery 10 falls below the first threshold E1 and becomes, for example, E2, the upper limit torque Tmax-R of the return control of the electric motor 11 is calculated as T2, which is smaller than the upper limit torque Tmax-N (=T1) of the normal control (see FIG. 6), and when returning from the low speed rotation speed control to the normal control, the output torque of the electric motor 11 is limited by the upper limit torque Tmax-R (=T2). Therefore, as shown by the solid line TB in FIG. 8, the output torque of the electric motor 11 rises to the upper limit torque Tmax-R (=T2) of the return control, which is smaller than the upper limit torque Tmax-N (=T1) of the normal control, and then the peak of the output torque of the electric motor slightly exceeds the upper limit torque Tmax-R (=Tmin) due to the inertia of the load, and then changes to converge to the upper limit torque Tmax-R (=T2).

[0094] Therefore, the rotation speed of the electric motor 11 is controlled so as to gradually increase to the reference rotation speed Nset as shown by the solid line in FIG. 9, slightly exceed the reference rotation speed Nset, and then converge to the reference rotation speed Nset.

[0095] When the rotation speed of the electric motor 11 reaches the reference rotation speed Nset at time Ta, the control shifts from the recovery control to the normal control, and the upper limit torque switches to the upper limit torque Tmax-N (=T1) of the normal control.

[0096] In this manner, in this embodiment, the upper limit torque Tmax-R of the electric motor 11 is determined based on the SOC (remaining charge) of the battery 10, and this upper limit torque Tmax-R is commanded to the inverter 31, and return control is executed to return the rotation speed of the electric motor 11 to the reference rotation speed Nset while limiting the output torque of the electric motor 11 to the upper limit torque Tmax-R. Therefore, when the SOC of the battery 10 becomes lower than the first threshold value E1, the amount of power consumption when returning the rotation speed of the electric motor 11 from the predetermined low speed rotation speed Nidle to the reference rotation speed Nset is suppressed, the remaining charge of the battery 10 is prolonged, and it is possible to operate for a long time on a single charge.

[0097] In addition, the operating site of an electric hydraulic excavator may be far away from the charging device, which is an external power source, and the charging device cannot be easily moved.

[0098] In this embodiment, even if the SOC remains during the return control, the upper limit torque of the return control of the electric motor 11 is lowered at an early stage, thereby reducing power consumption, thereby reducing the possibility that the remaining charge in the battery 10 will be depleted before the electric hydraulic excavator reaches the charging device when the electric hydraulic excavator moves to the charging device.

[0099] <Second embodiment> A second embodiment of the present invention will be described with reference to FIGS.

[0100] In the first embodiment, in the return control, the vehicle body controller 33 determines the upper limit torque Tmax-R based on a table showing the relationship between the battery SOC and the upper limit torque Tmax-R of the return control shown in FIG. 6 so that the upper limit torque Tmax-R is smaller when the SOC (remaining charge) of the battery 10 is less than the first threshold E1 than when it is more than the first threshold E1, and controls the output torque of the electric motor 11 to be limited to the upper limit torque Tmax-R, but the method of determining the upper limit torque Tmax-R of the return control is not limited to this.

[0101] FIG. 10 is a diagram showing an example of the relationship between the SOC of the battery and the increment value of the upper limit torque of the return control, which is set in a table stored in the vehicle body controller 33, in the second embodiment of the present invention. In this embodiment, the table stored in the vehicle controller 33 sets the relationship between the SOC of the battery 10 and the increment value ΔT of the upper limit torque Tmax-R, in which the parameters on the vertical axis of FIG. 6 are replaced with the increment value ΔT of the upper limit torque Tmax-R, as shown in FIG. 10. That is, in FIG. 10, the table stored in the vehicle body controller 33 is set so that while the SOC (remaining charge) of the battery 10 is greater than the first threshold value E1, the upper limit torque increment value ΔT is constant at the first torque increment value ΔT1, and while the SOC is between the first threshold value E1 and the second threshold value E2 which is set lower than the first threshold value E1, the upper limit torque increment value ΔT decreases from the first torque increment value ΔT1 to a second torque increment value ΔT2 which is set smaller than the first torque increment value ΔT1, and while the SOC is less than the second threshold value E2, the upper limit torque increment value ΔT is constant at the second torque increment value ΔT2. In addition, preferably, the table is set so that the upper limit torque increment value ΔT continuously decreases from the first torque increment value ΔT1 to the second torque increment value ΔT2 while the SOC decreases from the first threshold value E1 to the second threshold value E2.

[0102] FIG. 11 is a flowchart showing the overall flow of processing by the vehicle body controller in the second embodiment.

[0103] In this embodiment, the vehicle body controller 33 determines the upper limit torque increment value ΔT when returning the rotation speed of the electric motor 11 to the reference rotation speed Nset by the return control, for each specified calculation cycle (each specified time) as shown in step J1 of Figure 11, based on a table that sets the relationship between the SOC of the battery 10 shown in Figure 10 and the upper limit torque increment value ΔT of the return control, and determines the upper limit torque Tmax-R of the return control by adding the upper limit torque increment value ΔT to the upper limit torque Tmax-R calculated previously. In addition, the vehicle body controller 33 adds the increment value ΔT of the upper limit torque Tmax-R to the upper limit torque Tmax-idle (second upper limit torque) of the low speed rotation speed control to determine the initial upper limit torque Tmax-R of the return control, and then continues to add the increment value ΔT of the upper limit torque until the upper limit torque Tmax-R of the return control reaches the upper limit torque Tmax-N (first upper limit torque) of the normal control. Here, since the relationship between the battery SOC and the upper limit torque increment value ΔT in Figure 10 is obtained by replacing the parameters on the vertical axis of Figure 6 with the upper limit torque increment value ΔT of the return control, the upper limit torque Tmax-R of the return control calculated at each specified time is smaller when the SOC (remaining charge) of the battery 10 is less than the first threshold E1 than when it is more than the first threshold E1.

[0104] Next, as shown in step K of FIG. 11, the vehicle body controller 33 commands the upper limit torque Tmax-R and the reference rotation speed Nset of the return control to the inverter 31 at predetermined time intervals, thereby controlling the output torque of the electric motor 11.

[0105] As shown in step M of Figure 11, the vehicle body controller 33 determines at predetermined time intervals whether the upper limit torque Tmax-R of the return control has reached the upper limit torque Tmax-N (first upper limit torque) of the normal control, and adds the upper limit torque increment value ΔT until the upper limit torque Tmax-R reaches the upper limit torque Tmax-N (first upper limit torque) of the normal control.

[0106] Figure 12 is a diagram showing the change in output torque of the electric motor under the return control of this embodiment when the battery SOC falls below the first threshold E1 and becomes, for example, the second threshold E2, in comparison with the case where return control is not performed.

[0107] In this embodiment, as described above, the increment value ΔT of the upper limit torque is calculated at every predetermined time, the upper limit torque Tmax-R of the return control is calculated until the upper limit torque reaches the upper limit torque Tmax-N of the normal control, and the output torque of the electric motor 11 is controlled, so that the output torque of the electric motor 11 can be increased while limiting the increase speed of the output torque of the electric motor 11 until the upper limit torque Tmax-R of the return control reaches the upper limit torque Tmax-N of the normal control, as shown by the solid line TC in Fig. 12. Therefore, in this embodiment as well, the amount of power consumption when returning to the reference rotation speed Nset can be reduced. Furthermore, according to this embodiment, it is possible to return to normal control more quickly than in the first embodiment.

[0108] <Third embodiment> A third embodiment of the present invention will be described with reference to FIGS.

[0109] Figures 13 and 14 are diagrams showing the drive system of an electric hydraulic excavator according to the third embodiment, where Figure 13 shows the case where the electric motor 11 is driven by power from a battery 10, and Figure 14 shows the case where the electric motor 11 is driven while the battery 10 is being charged by power from an external power source 73.

[0110] 13 and 14, the drive system of this embodiment further includes a power supply connector 71 that is connected to a power supply line 41 via a power supply line 70 and can be connected to the power supply line 41 via a charger 72 to an external power source 73. The charger 72 is connected to the power supply connector 71 via a power supply line 74, and the charger 72 supplies power from the external power source 73 to the inverter 31, and can charge the battery 10 while driving the electric motor 11.

[0111] In FIG. 13, when the SOC of the battery 10 is sufficient, as indicated by the white arrow 76, power from the battery 10 is supplied to the inverter 31 via the power supply line 41, and the electric motor 11 is driven by the inverter 31.

[0112] When the SOC of the battery 10 drops and the battery 10 needs to be charged, as shown in Fig. 14, a charger 72 is connected to a power supply connector 71 via a power supply line 74, and an external power source 73 is connected to the power supply connector 71. When the operator turns on the start switch of the hydraulic excavator in this state, power from the external power source 73 is supplied from the charger 72 to the battery 10, as shown by arrow 77a, which is one of two white arrows 77a, 77b. At this time, the charger 72 outputs a current according to the SOC of the battery 10 to charge the battery 10, and when the voltage of the battery 10 reaches a set voltage, charging ends.

[0113] In addition, when the electric motor 11 is driven while the battery 10 is being charged, as shown by the other white arrow 77b, the inverter 31 receives the current necessary to drive the electric motor 11 from the charger 72, and the battery 10 is charged with the remaining current from the charger 72, allowing the electric motor 11 to be driven and work to be performed while the battery 10 is being charged.

[0114] Furthermore, as explained in the first embodiment, when the SOC of the battery 10 is equal to or lower than the first threshold value E1, the upper limit torque Tmax-R of the return control is smaller than the first torque T1, for example, the second torque T1 (see FIG. 6), and therefore the power consumption of the electric motor 11 driven while the battery 10 is being charged is reduced by the amount that the upper limit torque Tmax-R is reduced. The same is true in the second embodiment. Therefore, when the electric motor 11 is driven while the battery 10 is being charged, the reduced power consumption can be diverted to charging the battery 10, thereby shortening the charging time of the battery 10 by the amount that the power consumption of the electric motor 11 is reduced.

[0115] In this manner, in this embodiment, by connecting the charger 72 and the external power source 73 to the inverter 31 and the battery 10 via the power supply connector 71, the electric motor 11 can be driven while the battery 10 is being charged.

[0116] Furthermore, even if the electric motor 11 is driven while charging the battery 10, the power consumption of the electric motor 11 is reduced by reducing the upper limit torque of the return control, and therefore the charging time of the battery 10 can be shortened by the amount of the reduced power consumption of the electric motor 11.

[0117] <Other> 1. In addition, in the above embodiment, the electric construction machine is described as a track-type hydraulic excavator, but the electric construction machine may be a construction machine other than a track-type hydraulic excavator (for example, a wheel-type hydraulic excavator, a hydraulic crane, a wheel loader, etc.).

[0118] 2. In addition, in the above embodiment, a pressure sensor was used to detect whether the operating lever or operating pedal of the operating device 21-26 is being operated, but a position sensor may be used to detect whether the operating lever or operating pedal is being operated.

[0119] 3. Furthermore, in the above embodiment, the operating devices 21 to 26 are of a hydraulic pilot type that generates an operating pilot pressure as an operating signal, but the operating devices 21 to 26 may be of an electric lever type that generates an electric signal as an operating signal. In this case, the operating signals (electrical signals) of the operating devices 21 to 26 are sent directly to the vehicle body controller 33, and the vehicle body controller 33 judges the presence or absence of operation from those operating signals. [Explanation of symbols]

[0120] 1a~1h Multiple hydraulic actuators 10 Battery (energy storage device) 10a Battery controller (remaining battery charge monitor) 11 Electric motor 12 Hydraulic pump 16a~16h Multiple directional control valves 21-26 Multiple operating devices 31 Inverter 32 Motor speed dial (speed indicator) 33 Vehicle Controller (Controller) 35 Operation detection device 36 Mode selection switch 37 Rotation Sensor 41 Power supply line 71 Power supply connector 72 Charger 73 External power supply SOC State of charge (remaining charge or charging rate) Tmax-N Upper limit torque for normal control Tmax-idle Upper limit torque for low speed rotation control Tmax-R Upper limit torque for return control Nset Reference speed Nidle: Predetermined low speed (low speed control speed) E1 First threshold E2 Second Threshold T1 First torque T2 Second torque ΔT Upper limit torque increment ΔT1 First torque increment value ΔT2 Second torque increment value

Claims

1. an electric motor driven by power from the power storage device; a hydraulic pump driven by the electric motor; a hydraulic actuator driven by the pressure oil discharged from the hydraulic pump; an operating device for operating the hydraulic actuator; a rotation speed indicator for setting a reference rotation speed of the electric motor; A drive system for an electric construction machine comprising: a controller that drives the electric motor at a reference rotation speed set by the rotation speed indicator device, and reduces the rotation speed of the electric motor from the reference rotation speed when the operating device is not operated, The controller A drive system for electric construction machinery characterized in that, when the operating device is operated after the operating device is in an unoperated state and the rotation speed of the electric motor has been reduced from the reference rotation speed, an upper limit torque of the electric motor is determined based on the remaining amount of electricity stored in the electricity storage device, and return control is executed to return the rotation speed of the electric motor to the reference rotation speed while limiting the output torque of the electric motor to the upper limit torque.

2. 2. The drive system for an electric construction machine according to claim 1, A drive system for an electric construction machine, wherein the controller determines the upper limit torque so that the upper limit torque is smaller when the remaining amount of stored electricity in the electricity storage device is less than a first threshold value than when the remaining amount of stored electricity is more than a first threshold value.

3. 2. The drive system for an electric construction machine according to claim 1, A drive system for an electric construction machine, wherein the controller determines the upper limit torque so that the upper limit torque decreases as the remaining amount of electricity stored in the electricity storage device decreases.

4. 2. The drive system for an electric construction machine according to claim 1, The controller a table that sets a relationship between the remaining amount of stored electricity of the electricity storage device and the upper limit torque of the return control; A drive system for an electric construction machine, characterized in that the upper limit torque when the rotation speed of the electric motor is returned to the reference rotation speed by the return control is determined based on the remaining amount of storage in the storage device and the table.

5. 5. The drive system for an electric construction machine according to claim 4, The table stored in the controller is set so that while the remaining amount of stored power is greater than a first threshold, the upper limit torque of the return control is constant at a first torque, while while the remaining amount of stored power is between the first threshold and a second threshold set lower than the first threshold, the upper limit torque of the return control decreases from the first torque to a second torque set lower than the first torque, and while while the remaining amount of stored power is less than the second threshold, the upper limit torque of the return control is constant at the second torque.

6. 6. The drive system for an electric construction machine according to claim 5, A drive system for an electric construction machine, characterized in that the table stored in the controller is set so that the upper limit torque of the return control continuously decreases from the first torque to the second torque while the remaining amount of stored power decreases from the first threshold to the second threshold.

7. 2. The drive system for an electric construction machine according to claim 1, The controller a table that sets a relationship between the remaining amount of electricity stored in the electricity storage device and an increment value of the upper limit torque of the return control; A drive system for an electric construction machine, characterized in that the increment value of the upper limit torque when returning the rotation speed of the electric motor to the reference rotation speed by the return control is determined at every predetermined time based on the remaining amount of storage in the storage device and the table, and the upper limit torque for the return control is determined by adding the increment value of the upper limit torque to the upper limit torque calculated previously.

8. 8. The drive system for an electric construction machine according to claim 7, The controller When the operating device is not operated and the rotation speed of the electric motor is reduced from the reference rotation speed, the electric motor is driven at a predetermined low rotation speed, controlling the electric motor so that an output torque of the electric motor does not exceed a first upper limit torque when the electric motor is driven at the reference rotation speed, and controlling the electric motor so that an output torque of the electric motor does not exceed a second upper limit torque that is smaller than the first upper limit torque when the electric motor is driven at the low rotation speed; When executing the return control, an increment value of the upper limit torque is added to the second upper limit torque to determine an initial upper limit torque of the return control, and then the increment value of the upper limit torque is added until the upper limit torque of the return control reaches the first upper limit torque.

9. 8. The drive system for an electric construction machine according to claim 7, The table stored in the controller is set so that while the remaining amount of stored power is greater than a first threshold, the upper limit torque increment value of the return control is constant at a first torque increment value, while while the remaining amount of stored power is between the first threshold and a second threshold set lower than the first threshold, the upper limit torque increment value of the return control is decreased from the first torque increment value to a second torque increment value set smaller than the first torque increment value, and while while the remaining amount of stored power is less than the second threshold, the upper limit torque increment value of the return control is constant at the second torque increment value.

10. 10. The drive system for an electric construction machine according to claim 9, The table stored in the controller is set so that the upper limit torque increment value of the return control continuously decreases from the first torque increment value to the second torque increment value while the remaining amount of stored power decreases from the first threshold value to the second threshold value.

11. 2. The drive system for an electric construction machine according to claim 1, an inverter that controls the power supplied from the power storage device to the electric motor based on a command from the controller; a power supply connector connected to a power supply line connecting the inverter and the power storage device and connectable to an external power supply via a charger, A drive system for an electric construction machine, characterized in that the power supply connector is capable of supplying power to the inverter and driving the electric motor while charging the power storage device with power from the external power source.

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