Work machine

Abstract

This work machine is provided with: a capacitor; a battery connected in parallel to the capacitor; an electric motor to which power is supplied from the capacitor during the discharge of the capacitor and from the battery during the discharge of the battery; a target part driven by the electric motor;

Description

Technical Field

[0001] The present invention relates to a work machine. Background Art

[0002] In the related art field of work machines, a work machine as disclosed in Patent Document 1 is known.

[0003] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2014-139379 Summary of the Invention

[0004] Generally, the higher the energy density of a battery, the lower the power density of the battery. The energy density of a battery refers to the electric energy that can be stored in a unit volume or unit mass of the battery. The power density of a battery refers to the electric energy that can be output from a unit volume or unit mass of the battery. When a work machine operates based on the electricity output from a battery, the higher the energy density of the battery, the longer the work machine can operate. The higher the power density of the battery, the more capable the work machine is of performing instantaneous high-output operations.

[0005] When a work machine operates based on the electric power output from a battery, if a battery is selected according to the electric power required for an instantaneous high-output operation, a too large battery may be mounted on the work machine. In addition, if the load factor of the battery is increased to perform an instantaneous high-output operation, the deterioration of the battery may be promoted. Although the power density of a capacitor is higher than that of a battery, the energy density of a capacitor is lower than that of a battery. Therefore, it is difficult for a work machine to perform a long-term operation only with the electric energy output from a capacitor.

[0006] An object of the present disclosure is to suppress the enlargement and deterioration of a battery when a work machine operates based on the electric power output from a battery.

[0007] According to the present disclosure, there is provided a work machine including: a capacitor; a battery connected in parallel with the capacitor; an electric motor powered by the capacitor during discharge of the capacitor and powered by the battery during discharge of the battery; an object part driven by the electric motor; and a first DC / DC converter that switches discharge and charge of the capacitor during discharge of the battery.

[0008] According to the present disclosure, it is possible to suppress the enlargement and deterioration of a battery when a work machine operates based on the electric power output from a battery. Brief Description of the Drawings

[0009] Figure 1 It is a perspective view showing a work machine according to an embodiment.

[0010] Figure 2 It is a diagram showing a drive system of a work machine according to an embodiment.

[0011] Figure 3 This is a block diagram showing a working machine according to the embodiment.

[0012] Figure 4 It is a diagram for explaining a driving method of the driving system according to the embodiment.

[0013] Figure 5 This is a diagram showing the relationship between the operating state of the operating device and the capacitor according to the embodiment. DETAILED DESCRIPTION

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings, but the present disclosure is not limited to the embodiments. The constituent elements of the embodiments described below can be combined as appropriate. In addition, there are also cases where some constituent elements are not used.

[0015] Operating machinery

[0016] Figure 1 1 is a perspective view showing a working machine 1 according to an embodiment. In the embodiment, the working machine 1 is a hydraulic excavator as a type of construction machinery. Figure 1 As shown, the working machine 1 includes a traveling body 2 , a revolving body 3 supported by the traveling body 2 , a working machine 4 supported by the revolving body 3 , and a working machine cylinder 5 for operating the working machine 4 .

[0017] The traveling body 2 has a driving wheel 2A and a crawler 2B that rotates with the driving wheel 2A. The working machine 1 is able to travel at the working site by rotating the crawler 2B. The rotating body 3 rotates while being supported by the traveling body 2. The working machine 4 includes: a boom 4A connected to the rotating body 3, a dipper arm 4B connected to the boom 4A, and a bucket 4C connected to the dipper arm 4B. The working machine cylinder 5 is a hydraulic cylinder for generating power to move the working machine 4. The working machine cylinder 5 includes: a boom cylinder 5A for moving the boom 4A, a dipper arm cylinder 5B for moving the dipper arm 4B, and a bucket cylinder 5C for moving the bucket 4C.

[0018] Drive system

[0019] Figure 2 This diagram shows a drive system 6 of a working machine 1 according to an embodiment. The drive system 6 includes a capacitor 7, a battery 8 connected in parallel with the capacitor 7, and a pump drive motor 10 and a swing motor 11. The pump drive motor 10 and the swing motor 11 are both electric motors. The capacitor 7 is a lithium-ion capacitor (LiC). The battery 8 is a lithium-ion battery (LiB).

[0020] In addition, the drive system 6 includes: an electric wire 13 connected to the pump drive motor 10 and the rotary motor 11 respectively, a first connecting wire 14 connecting the capacitor 7 to the first part 131 of the electric wire 13, a second connecting wire 15 connecting the battery 8 to the second part 132 of the electric wire 13, a DC / DC converter 16 (first DC / DC converter) connected to the capacitor 7, and a DC / DC converter 17 (second DC / DC converter) connected to the battery 8.

[0021] The pump drive motor 10 operates based on at least the power supplied by the battery 8. During the battery 8 discharge period, which represents the period during which the battery 8 is discharging, the pump drive motor 10 is powered by the battery 8. During the capacitor 7 discharge period, which represents the period during which the capacitor 7 is discharging, the pump drive motor 10 is powered by the capacitor 7. The drive system 6 includes a hydraulic pump 19. The pump drive motor 10 generates power for operating the hydraulic pump 19. The hydraulic pump 19 operates based on the pump drive motor 10 being an electric motor. The hydraulic pump 19 is an example of a target portion of the working machine 1 driven by the electric motor.

[0022] The hydraulic pump 19 discharges hydraulic oil supplied to the working machine cylinder 5. The hydraulic pump 19 also discharges hydraulic oil supplied to the travel motor 2C of the traveling unit 2. The hydraulic oil discharged from the hydraulic pump 19 is supplied to the working machine cylinder 5 and the travel motor 2C via the control valve 20. The hydraulic oil is supplied to the working machine cylinder 5, thereby operating the working machine cylinder 5. The hydraulic oil is supplied to the travel motor 2C, thereby operating the travel motor 2C. The travel motor 2C is a hydraulic motor for rotating the drive wheels 2A of the traveling unit 2.

[0023] The swing motor 11 operates based on at least the power supplied by the battery 8. While the battery 8 is discharging, the swing motor 11 is powered by the battery 8. While the capacitor 7 is discharging, the swing motor 11 is powered by the capacitor 7. The swing motor 11 generates power to rotate the swing unit 3. The swing unit 3 is rotated by the electric motor, i.e., the swing motor 11. The swing unit 3 is an example of a target portion of the working machine 1 driven by the electric motor.

[0024] Electric wires 13 are connected to the pump drive motor 10 and the swing motor 11, respectively. Capacitor 7 and battery 8 are connected in parallel with electric wires 13. Electric wires 13 include a positive line 13A and a negative line 13B. A portion of electric wires 13 is connected to the pump drive motor 10 via an inverter 21. Another portion of electric wires 13 is connected to the swing motor 11 via an inverter 22.

[0025] The first connection line 14 connects the capacitor 7 to the first portion 131 of the electric wire 13. The first connection line 14 includes a positive line 14A and a negative line 14B. The positive line 14A connects the positive electrode of the capacitor 7 to the first portion 131A of the positive line 13A. The negative line 14B connects the negative electrode of the capacitor 7 to the first portion 131B of the negative line 13B.

[0026] The second connection line 15 connects the battery 8 to the second portion 132 of the electric wire 13. The second connection line 15 includes a positive line 15A and a negative line 15B. The positive line 15A connects the positive electrode of the battery 8 to the second portion 132A of the positive line 13A. The negative line 15B connects the negative electrode of the battery 8 to the second portion 132B of the negative line 13B.

[0027] The capacitor 7 can supply power to the pump drive motor 10 and the slewing motor 11 via the first connection line 14 and the electric wire 13 respectively. The battery 8 supplies power to the pump drive motor 10 and the slewing motor 11 via the second connection line 15 and the electric wire 13 respectively.

[0028] The DC / DC converter 16 is connected to the capacitor 7. The DC / DC converter 16 is arranged on the first connection line 14 between the capacitor 7 and the first portion 131 of the electric wire 13. The power from the capacitor 7 is supplied to the pump drive motor 10 and the slewing motor 11 respectively via the DC / DC converter 16, and the DC / DC converter 16 converts the voltage of the capacitor 7. The DC / DC converter 16 boosts the voltage of the capacitor 7 at a specified boost ratio. The voltage of the capacitor 7 boosted by the DC / DC converter 16 is applied to the inverter 21 connected to the pump drive motor 10 and the inverter 22 connected to the slewing motor 11 respectively.

[0029] The DC / DC converter 16 is a bidirectional DC / DC converter that can output power from the primary side to the secondary side and also from the secondary side to the primary side. The primary side of the DC / DC converter 16 is the low voltage side (capacitor 7 side). The secondary side of the DC / DC converter 16 is the high voltage side (electric wire 13 side). The DC / DC converter 16 steps down the regenerative voltage of the slewing motor 11 at a preset step-down ratio. The regenerative voltage of the slewing motor 11 stepped down by the DC / DC converter 16 is applied to the capacitor 7. The capacitor 7 is charged by the regenerative voltage of the slewing motor 11. The capacitor 7 is charged by the regenerative power from the slewing motor 11 supplied via the DC / DC converter 16.

[0030] The DC / DC converter 17 is connected to the battery 8. The DC / DC converter 17 is disposed on the second connection line 15 between the battery 8 and the second part 132 of the electric wire 13. The electric power from the battery 8 is supplied to the pump drive motor 10 and the swing motor 11 respectively via the DC / DC converter 17, and the DC / DC converter 17 converts the voltage of the battery 8. The DC / DC converter 17 boosts the voltage of the battery 8 at a prescribed boost ratio. The voltage of the battery 8 boosted by the DC / DC converter 17 is applied to the inverter 21 connected to the pump drive motor 10 and the inverter 22 connected to the swing motor 11 respectively.

[0031] The DC / DC converter 17 is a unidirectional DC / DC converter that can only output electric power from the primary side to the secondary side. The primary side of the DC / DC converter 17 is the low voltage side (the battery 8 side). The secondary side of the DC / DC converter 17 is the high voltage side (the electric wire 13 side). The capacitor 7 is charged by the voltage of the battery 8. The capacitor 7 is charged by the electric power from the battery 8 supplied via the DC / DC converter 17 and the DC / DC converter 16. In addition, the DC / DC converter 17 can also be a bidirectional DC / DC converter that can output electric power from the primary side to the secondary side and from the secondary side to the primary side.

[0032] The inverter 21 is connected to a part of the electric wire 13. The inverter 21 is used to convert the direct current electricity from the electric wire 13 into three-phase alternating current electricity and supply it to the pump drive motor 10. The pump drive motor 10 is driven based on the three-phase alternating current electricity supplied by the inverter 21.

[0033] The inverter 22 is connected to a part of the electric wire 13. The inverter 22 is used to convert the direct current electricity from the electric wire 13 into three-phase alternating current electricity and supply it to the swing motor 11. The swing motor 11 is driven based on the three-phase alternating current electricity supplied by the inverter 22.

[0034] The power density of the capacitor 7 is higher than that of the battery 8. The responsiveness of the capacitor 7 is better than that of the battery 8. Compared with the battery 8, the capacitor 7 can charge and discharge at a higher speed. The energy density of the battery 8 is higher than that of the capacitor 7.

[0035] The battery 8 is the main power source of the drive system 6. The battery 8 supplies power to the pump drive motor 10 and the swing motor 11 respectively. Both the pump drive motor 10 and the swing motor 11 are driven only by the power supply of the battery 8. Most of the power used to drive the pump drive motor 10 and the swing motor 11 respectively is borne by the power output from the battery 8. The power output from the capacitor 7 is used when the instantaneous responsiveness of the pump drive motor 10 and the swing motor 11 is required.

[0036] Controller

[0037] Figure 3This is a block diagram showing a construction machine 1 of an embodiment. The construction machine 1 includes: a controller 30, a voltage sensor 40, and an operation device 50.

[0038] The controller 30 includes a computer system. The controller 30 has: a processor 31, such as a CPU (Central Processing Unit); a main memory 32, which includes a non-volatile memory such as a ROM (Read Only Memory) and a volatile memory such as a RAM (Random Access Memory); a memory 33; and an interface 34, which includes an input / output circuit. The voltage sensor 40, the operation device 50, the DC / DC converter 16, and the DC / DC converter 17 are respectively connected to the interface 34.

[0039] The voltage sensor 40 is used to detect the voltages respectively applied to the pump drive motor 10 and the swing motor 11. As Figure 2 shown, the voltage sensor 40 is used to detect the voltage between the positive line 13A and the negative line 13B.

[0040] To operate the revolving body 3 and the working machine 4, the operation device 50 is operated by an operator of the construction machine 1. The operation device 50 is arranged in the cab of the construction machine 1. The operation device 50 includes: a left operation lever 51 and a right operation lever 52. As an example, by operating the left operation lever 51 to tilt forward, the revolving body 3 swings to the right, and by operating the left operation lever 51 to tilt backward, the revolving body 3 swings to the left. By operating the left operation lever 51 to tilt to the left, the stick 4B performs a dumping action, and by operating the left operation lever 51 to tilt to the right, the stick 4B performs a digging action. By operating the right operation lever 52 to tilt forward, the boom 4A performs a lowering action, and by operating the right operation lever 52 to tilt backward, the boom 4A performs a raising action. By operating the right operation lever 52 to tilt to the left, the bucket 4C performs a digging action, and by operating the right operation lever 52 to tilt to the right, the bucket 4C performs a dumping action.

[0041] The processor 31 includes: a first control unit 31A, a second control unit 31B, and a monitoring unit 31C. The first control unit 31A outputs a control instruction for controlling the DC / DC converter 16. The second control unit 31B outputs a control instruction for controlling the DC / DC converter 17. The monitoring unit 31C can monitor the load factor of the electric motors (the pump drive motor 10 and the swing motor 11). The load factor of the electric motor refers to the ratio of the actual output of the electric motor to the rated output (100% output in design). The monitoring unit 31C can monitor the load factor of the pump drive motor 10 based on the operating state of the inverter 21. The monitoring unit 31C can monitor the load factor of the swing motor 11 based on the operating state of the inverter 22. In addition, the monitoring unit 31C monitors the detection value of the voltage sensor 40. In addition, the monitoring unit 31C monitors the operating state of the operating device 50. An operation signal is generated by operating the operating device 50. The monitoring unit 31C can monitor the operating state of the operating device 50 based on the operation signal generated in the operating device 50.

[0042] Drive method of the drive system

[0043] Figure 4 It is a diagram for explaining the drive method of the drive system 6 of the embodiment. In Figure 4 the shown graph, the vertical axis represents the load factor, and the horizontal axis represents the time elapsed after the work machine 1 starts working. The line Lm represents the load factor of the electric motors (the pump drive motor 10 and the swing motor 11). The line Lb represents the load factor of the battery 8. The line Lc represents the load factor of the capacitor 7. The load factor of the electric motor corresponds one-to-one with the power consumed by the electric motor. The load factor of the battery 8 corresponds one-to-one with the power discharged from the battery 8. The load factor of the capacitor 7 corresponds one-to-one with the power discharged from the capacitor 7.

[0044] Based on the operation of the work machine 1, the load factor of the electric motor changes. When the work machine 1 performs an operation with a large workload, the load factor of the electric motor becomes high. When the work machine 1 performs an operation with a small workload, the load factor of the electric motor becomes low. For example, when the boom 4A is raised while the excavated material is held in the bucket 4C, a large load is imposed on the work machine 4, so the load factor of the pump drive motor 10 increases. When the slewing body 3 slews, the load factor of the swing motor 11 increases. When the work machine 4 is not operating, the load factor of the pump drive motor 10 becomes low. When the slewing body 3 is not slewing, the load factor of the swing motor 11 becomes low.

[0045] As described above, the battery 8 is the main power source of the drive system 6. During the operation period in which at least a part of the working machine 1 is in operation, the battery 8 continues to discharge. That is, during the operation period of the working machine 1, the battery 8 continues to supply power to the pump drive motor 10 and the swing motor 11, respectively. The operation period of the working machine 1 coincides with the discharge period of the battery 8. In the embodiment, as shown by the line Lb, during the discharge period of the battery 8, the battery 8 is discharged at a fixed power. The second control unit 31B controls the DC / DC converter 17 in such a manner that the battery 8 is discharged at a fixed power. The DC / DC converter 17 causes the battery 8 to discharge at a fixed power during the discharge period of the battery 8.

[0046] Furthermore, the operation period of the working machine 1 may not coincide with the discharge period of the battery 8. Furthermore, during the discharge period of the battery 8, the electric power discharged from the battery 8 may not be constant.

[0047] The first control unit 31A controls the DC / DC converter 16 to switch between discharging and charging the capacitor 7 during the discharge period of the battery 8. The DC / DC converter 16 switches between discharging and charging the capacitor 7 during the discharge period of the battery 8.

[0048] The first control unit 31A controls the DC / DC converter 16 to switch between discharging and charging the capacitor 7 based on the load factor of the electric motor and the power discharged from the battery 8, as monitored by the monitoring unit 31C. When the load factor of the electric motor is greater than a predetermined load factor threshold value Sh, the first control unit 31A controls the DC / DC converter 16 based on the power discharged from the battery 8 to discharge the capacitor 7. Specifically, when the working load of the work machine 1 is large and the load factor of the electric motor is high, the DC / DC converter 16 discharges the capacitor 7 to compensate for the power discharged from the battery 8. When the load factor of the electric motor is high, the electric motor is powered by both the battery 8 and the capacitor 7, thereby preventing power shortages in the electric motor.

[0049] When the load factor of the electric motor is less than the load factor threshold value Sh, the first control unit 31A controls the DC / DC converter 16 to charge the capacitor 7 based on the power discharged from the battery 8. Specifically, when the work load of the working machine 1 is light and the load factor of the electric motor is low, there is excess power discharged from the battery 8. The first control unit 31A controls the DC / DC converter 16 to charge the capacitor 7 using the power discharged from the battery 8. The DC / DC converter 16 charges the capacitor 7 using the excess power from the battery 8.

[0050] Furthermore, the DC / DC converter 16 can also switch between discharging and charging the capacitor 7 based on the detection value of the voltage sensor 40. When the load factor of the electric motor is high, the detection value of the voltage sensor 40 decreases. When the load factor of the electric motor is low, the detection value of the voltage sensor 40 increases. When the detection value of the voltage sensor 40 is below a predetermined voltage threshold, the DC / DC converter 16 discharges the capacitor 7. The power discharged by the capacitor 7 is supplied to the electric motor together with the power discharged by the battery 8. When the detection value of the voltage sensor 40 exceeds the voltage threshold, the DC / DC converter 16 charges the capacitor 7 using the excess power from the battery 8.

[0051] Figure 5 : is a diagram showing the relationship between the operating state of the operating device 50 and the capacitor 7 according to the embodiment. Figure 5 As shown, the DC / DC converter 16 can also switch the discharge and charge of the capacitor 7 based on the operating state of the operating device 50. When the operating device 50 is operated to make the rotating body 3 and the working machine 4 perform a predetermined specific action, the DC / DC converter 16 discharges the capacitor 7. When the operating device 50 is operated to make the rotating body 3 and the working machine 4 perform a non-specific action different from the specific action, the DC / DC converter 16 charges the capacitor 7. The specific action is the action of the working machine 1 with a larger working load. The non-specific action is the action of the working machine 1 with a smaller working load. As a specific action, an example of the action of rotating the rotating body 3 while making the boom 4A rise can be shown. As a non-specific action, an example of the action of stopping the rotating body 3 or rotating at a low speed when the working machine 4 is stopped can be shown.

[0052] Effect

[0053] As described above, in the embodiment, the working machine 1 includes: a capacitor 7, a battery 8 connected in parallel with the capacitor 7, an electric motor (a pump drive motor 10 and a rotary motor 11) which is powered by the capacitor 7 during the discharge period of the capacitor 7 and is powered by the battery 8 during the discharge period of the battery 8, an object part driven by the electric motor, and a DC / DC converter 16 for switching the discharge and charging of the capacitor 7 during the discharge period of the battery 8.

[0054] The energy density of the battery 8 is higher than that of the capacitor 7. Therefore, by continuously discharging the battery 8, the working machine 1 can perform long-term operations. The power density of the capacitor 7 is higher than that of the battery 8. The responsiveness of the capacitor 7 is better than that of the battery 8. Compared with the battery 8, the capacitor 7 can be charged and discharged at a higher speed. Therefore, when the working machine 1 performs a momentary high-output operation during the discharge of the battery 8, the capacitor 7 is discharged in conjunction with the momentary high-output operation of the working machine 1, thereby suppressing the power shortage in the electric motor while suppressing the increase in the load factor of the battery 8. Since the increase in the load factor of the battery 8 is suppressed, the deterioration of the battery 8 can be suppressed. When the working machine 1 performs a momentary high-output operation, the power discharged by the capacitor 7 can be supplemented to the power discharged by the battery 8, so that there is no need to carry an overly large battery 8 on the working machine 1. Therefore, the size of the battery 8 can be suppressed.

[0055] Other Implementations

[0056] In the above embodiment, work machine 1 is a hydraulic excavator. However, work machine 1 may also be a bulldozer with a working mechanism or a wheel loader with a working mechanism. Furthermore, work machine 1 may be a transport vehicle, such as a dump truck. In a dump truck, the battery is charged using regenerative power from the travel motor when traveling downhill.

[0057] Explanation of symbols

[0058] 1…Working machine; 2…Traveling unit; 2A…Drive wheel; 2B…Crawler track; 2C…Travel motor; 3…Swinging unit; 4…Working machine; 4A…Boom; 4B…Arm; 4C…Bucket; 5…Working machine cylinder; 5A…Boom cylinder; 5B…Arm cylinder; 5C…Bucket cylinder; 6…Drive system; 7…Capacitor; 8…Battery; 10…Pump drive motor (electric motor); 11…Swing motor (electric motor); 13…Wire; 13A…Positive line; 13B…Negative line; 14…First connecting line; 14A…Positive line; 14B…Negative line; 15…Second connecting line; 15A…Positive line; 15B…Negative line; 16…DC / DC converter Converter (first DC / DC converter); 17…DC / DC converter (second DC / DC converter); 19…hydraulic pump; 20…control valve; 21…inverter; 22…inverter; 30…controller; 31…processor; 31A…first control unit; 31B…second control unit; 31C…monitoring unit; 32…main memory; 33…storage; 34…interface; 40…voltage sensor; 50…operating device; 51…left operating lever; 52…right operating lever; 131…first part; 131A…first part; 131B…first part; 132…second part; 132A…second part; 132B…second part.

Claims

1. An earthmoving machine, characterized in that, Comprising: A capacitor; A battery connected in parallel with the capacitor; An electric motor powered by the capacitor during discharge of the capacitor and powered by the battery during discharge of the battery; An object part driven by the electric motor; And A first DC / DC converter that switches discharge and charging of the capacitor during discharge of the battery.

2. The working machine according to claim 1, wherein The first DC / DC converter switches discharge and charging of the capacitor based on the load factor of the electric motor and the power discharged from the battery.

3. The working machine according to claim 2, wherein When the load factor of the electric motor is equal to or above a load factor threshold, the first DC / DC converter discharges the capacitor based on the power discharged from the battery; When the load factor of the electric motor is less than the load factor threshold, the first DC / DC converter charges the capacitor based on the power discharged from the battery.

4. The work machine according to claim 1, wherein Comprising: A voltage sensor for detecting the voltage applied to the electric motor, The first DC / DC converter switches discharge and charging of the capacitor based on the detection value of the voltage sensor.

5. The working machine according to claim 4, wherein When the detection value of the voltage sensor is equal to or below a voltage threshold, the first DC / DC converter discharges the capacitor; When the detection value of the voltage sensor is greater than the voltage threshold, the first DC / DC converter charges the capacitor.

6. The work machine according to claim 1, characterized in that, Comprising: A rotating body; A working machine supported by the rotating body; A working machine cylinder for operating the working machine; and A hydraulic pump for discharging hydraulic oil supplied to the working machine cylinder, The object part includes at least one of the rotating body that rotates based on the electric motor and the hydraulic pump that operates based on the electric motor, The working machine is provided with an operating device for operating to move the rotating body and the working machine, The first DC / DC converter switches discharge and charging of the capacitor based on the operating state of the operating device.

7. The working machine according to claim 6, wherein When the operating device is operated to cause the rotating body and the working machine to perform a preset specific action, the first DC / DC converter discharges the capacitor; When the operating device is operated to perform a non-specific action different from the specific action, the first DC / DC converter charges the capacitor.

8. The working machine according to claim 1, wherein The capacitor is charged by at least one of the power from the battery and the regenerative power from the electric motor.

9. The work machine according to claim 1, characterized in that, Comprising: A wire connected to the electric motor; and A first connecting wire connecting the capacitor and a first part of the wire, The first DC / DC converter is arranged on the first connecting wire.

10. The work machine according to claim 1, wherein: During discharging of the battery, the battery discharges with a fixed power.

11. The work machine according to claim 10, characterized in that, Comprises: A second DC / DC converter that causes the battery to discharge with a fixed power during discharging of the battery.

12. The work machine according to claim 11, wherein, Comprises: A wire connected to the electric motor; and A second connection wire connecting the battery and a second portion of the wire, The second DC / DC converter is disposed on the second connection wire.

13. The work machine according to claim 1, wherein: A hydraulic pump is provided, The object portion includes the hydraulic pump that operates based on the electric motor.

14. The work machine according to claim 13, characterized in that, Comprises: A work implement; and A work implement cylinder for operating the work implement, The hydraulic pump discharges hydraulic oil supplied to the work implement cylinder.

15. The work machine according to claim 13, characterized in that, Comprises: A traveling body having drive wheels; and A traveling motor for rotating the drive wheels, The hydraulic pump discharges hydraulic oil supplied to the traveling motor.

16. The work machine according to claim 1, wherein Comprises: A traveling body; and A revolving body supported by the traveling body, The object portion includes the revolving body that revolves based on the electric motor.

17. The work machine according to claim 16, wherein: The capacitor is charged by a regenerative voltage of the electric motor that rotates the revolving body.

18. The work machine according to claim 1, wherein: The capacitor is a lithium-ion capacitor, The battery is a lithium-ion battery.

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