Control method for work machine, control system, and work machine

Abstract

To provide a control method, etc., for a work machine by which an abnormality which may cause a circuit failure when a power storage device including a plurality of battery unit groups connected in parallel is used can be speedily and accurately detected by a simple method without using an additional member such as a temperature sensor.SOLUTION: A control method for a work machine includes executing first detection and executing second detection after the first detection. In the first detection, in a first state where a battery unit can be charged or discharged and before an inverter or a battery charger is activated, magnitudes of currents flowing in a plurality of battery unit groups are compared and a first abnormality is detected. In the second detection, in a second state after the inverter or the battery charger is activated, the magnitudes of the currents flowing in the plurality of battery unit groups are compared and a second abnormality is detected.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a control method and system for a work machine, and a work machine. [Background technology]

[0002] 2. Description of the Related Art Conventionally, construction machinery is known that detects an abnormality in an electricity storage device formed of a plurality of cells connected in series by using the differential voltage between a maximum cell voltage and a minimum cell voltage (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 176054 Summary of the Invention [Problem to be solved by the invention]

[0004] Unlike automobiles, construction machinery is subject to significant vibrations and shocks in the environment in which it is used. This makes it easy for fastening members (e.g., screws) to loosen at electrical connections between conductors (e.g., connections between cell terminals of an energy storage device and bus bars). When screws loosen, the contact resistance at the electrical connections increases, making it difficult for current to flow through the electrical connections.

[0005] On the other hand, the power storage device of a construction machine may be configured by connecting multiple battery unit groups, each of which has multiple cells (battery units) connected in series, in parallel, particularly for the purpose of ensuring output or long-term operation. When such a power storage device is used, for example, if a loose screw occurs in the electrical connection of any battery unit group, the total resistance of the battery unit group increases. This makes it difficult for current to flow through the battery unit group, and makes it easier for current to flow through other battery unit groups. In other words, current flows unbalanced among the multiple battery unit groups, resulting in differences in charging voltage.

[0006] In a plurality of battery unit groups, when a difference in the magnitude of the flowing current exceeds a certain level (when a voltage difference exceeding a certain level occurs), it is necessary to detect this as an abnormality. If this abnormality cannot be detected and the output of a device (such as an inverter) electrically connected to the power storage device is not restricted, the power storage device will operate under an overload condition, leading to a failure of the power storage device and ultimately a circuit failure.

[0007] In detecting the above-mentioned abnormality, for example, in the method of detecting the voltage difference of cells as described in Patent Document 1, it takes more than several tens of minutes for the abnormality to appear as a voltage difference of cells. Therefore, with the above method, the abnormality cannot be detected promptly. Also, it is assumed that an irreversible failure has occurred by the time the abnormality is detected.

[0008] On the other hand, when loosening of a screw occurs in an electrical connection part, due to an increase in contact resistance, the electrical connection part generates heat. Therefore, it is also considered that the abnormality can be detected by, for example, detecting the temperature of the electrical connection part with a sensor. However, it takes more than several tens of minutes for the abnormality in the electrical connection part to appear as a temperature rise. Thus, with this method too, the abnormality cannot be detected promptly. Also, it is necessary to arrange a temperature sensor for each electrical connection part, which increases the cost. Furthermore, in the above-mentioned abnormality detection, it is also important to reduce false detection.

[0009] The present invention has been made to solve the above problems, and its object is to provide a control method, a control system, and a working machine for a working machine that can quickly and accurately detect, in a simple manner, an abnormality that leads to a circuit failure when using a power storage device having a plurality of battery unit groups connected in parallel, without using additional members such as temperature sensors.

Means for Solving the Problems

[0010] A control method for a working machine according to one aspect of the present invention includes a power storage device that discharges by supplying power to an electric motor via an inverter or is charged by receiving power from an external power source via a charger. The power storage device has a plurality of battery unit groups connected in parallel, and each battery unit group has a plurality of or one battery unit connected in series. The control method for the working machine is such that the battery unit is chargeable and dischargeable, and in a first state before the inverter or the charger is activated, a first detection is performed to compare the magnitudes of the currents flowing through the plurality of battery unit groups to detect a first abnormality. After performing the first detection, in a second state after the inverter or the charger is activated, a second detection is performed to compare the magnitudes of the currents flowing through the plurality of battery unit groups to detect a second abnormality.

[0011] A control system for a working machine according to another aspect of the present invention includes a power storage device that discharges by supplying power to an electric motor via an inverter or is charged by receiving power from an external power source via a charger. The power storage device has a plurality of battery unit groups connected in parallel, and each battery unit group has a plurality of or one battery unit connected in series. The control system for the working machine is such that the battery unit is chargeable and dischargeable, and in a first state before the inverter or the charger is activated, a first detection unit that compares the magnitudes of the currents flowing through the plurality of battery unit groups to detect a first abnormality, and after the abnormality detection by the first detection unit, in a second state after the inverter or the charger is activated, a second detection unit that compares the magnitudes of the currents flowing through the plurality of battery unit groups to detect a second abnormality.

[0012] A working machine according to still another aspect of the present invention includes the above control system and a display device that displays information based on the detection by at least one of the first detection unit and the second detection unit of the control system.

Advantages of the Invention

[0013] According to the above configuration, when using a power storage device having a plurality of battery unit groups connected in parallel, an abnormality (second abnormality) leading to a circuit failure can be quickly and accurately detected in a simple manner without using an additional member such as a temperature sensor.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0015] The embodiments of the present invention will be described as follows with reference to the drawings.

[0016] 〔1. Working Machine〕 FIG. 1 is a side view showing a schematic configuration of a hydraulic excavator (electric excavator) 1, which is an example of an electric working machine according to the present embodiment. The hydraulic excavator 1 includes a lower traveling body 2, a working device 3, and an upper revolving body 4.

[0017] Here, the directions are defined as follows. The direction in which the operator (driver, operator) sitting in the driver's seat 41a of the upper slewing body 4 faces forward is defined as the front, and the opposite direction is defined as the rear. Therefore, when the upper slewing body 4 is in a non-slewing state (slewing angle 0°) with respect to the lower traveling body 2, the front-rear direction of the upper slewing body 4 coincides with the direction in which the lower traveling body 2 moves forward and backward. Also, the left side as seen from the operator sitting in the driver's seat 41a is defined as "left", and the right side as "right". Further, the gravitational direction perpendicular to the front-rear direction and the left-right direction is defined as the up-down direction, the upstream side of the gravitational direction is defined as "up", and the downstream side as "down". In the drawings, the hydraulic excavator 1 is shown with the upper slewing body 4 in a non-slewing state with respect to the lower traveling body 2. Also, in the drawings, the front is indicated by the symbol "F", the rear by "B", the upper by "U", and the lower by "D".

[0018] The lower traveling body 2 includes a pair of left and right crawlers 21 and a pair of left and right traveling motors 22. Each traveling motor 22 is a hydraulic motor. By driving the left and right crawlers 21 with the left and right traveling motors 22 respectively, the hydraulic excavator 1 can be moved forward and backward. The lower traveling body 2 is provided with a blade 23 for performing leveling work and a blade cylinder 23a. The blade cylinder 23a is a hydraulic cylinder that rotates the blade 23 in the up-down direction.

[0019] The working machine 3 includes a boom 31, an arm 32, and a bucket 33. By driving the boom 31, the arm 32, and the bucket 33 independently, excavation work such as earth and sand can be performed.

[0020] The boom 31, the arm 32, and the bucket 33 are each rotated by a boom cylinder, an arm cylinder, and a bucket cylinder (not shown). The boom cylinder, the arm cylinder, and the bucket cylinder are constituted by hydraulic cylinders.

[0021] The base end portion of the boom 31, that is, the end portion of the boom 31 on the side opposite to the connection side with the arm 32, is swingably connected to the tip end portion 42a of the swing frame 42 via a bracket 34. That is, the hydraulic excavator 1 of the present embodiment has a boom swing function in which the boom 31 swings left and right with the tip end portion 42a as the starting point.

[0022] The upper swing body 4 is located above the lower traveling body 2 and is provided so as to be swingable with respect to the lower traveling body 2 via a swing bearing (not shown). In the upper swing body 4, a control unit 41, a swing frame 42 (machine body frame), a swing motor 43, a machine room 44, etc. are arranged. The upper swing body 4 swings via a swing bearing by the drive of the swing motor 43 which is a hydraulic motor.

[0023] A hydraulic pump 60 (see FIG. 2) is arranged in the upper swing body 4. The hydraulic pump 60 is driven by an electric motor 57 (see FIG. 2) inside the machine room 44. The hydraulic pump 60 supplies hydraulic oil (pressure oil) to hydraulic motors (for example, left and right traveling motors 22, swing motor 43), and hydraulic cylinders (for example, blade cylinder 23a, boom cylinder, arm cylinder, bucket cylinder). The hydraulic motors and hydraulic cylinders driven by the supply of hydraulic oil from the hydraulic pump 60 are collectively called hydraulic actuators.

[0024] A driver's seat 41a is arranged in the control unit 41. Various levers 41b are arranged around the driver's seat 41a. When the operator sits on the driver's seat 41a and operates the lever 41b, the hydraulic actuator is driven. Thereby, traveling of the lower traveling body 2, leveling work by the blade 23, excavation work by the work implement 3, swinging of the upper swing body 4, etc. can be performed.

[0025] In the upper swing body 4, a power storage device 53 is arranged. The power storage device 53 is composed of, for example, a lithium-ion battery unit and is a battery unit (battery pack) that stores electric power for driving the electric motor 57. Details of the configuration of the power storage device 53 will be described later. A power supply port 50 is provided at the rear part of the upper swing body 4. The power supply port 50 and the commercial power supply 51 which is an external power source are connected via a power supply cable 52. Thereby, the power storage device 53 can be charged.

[0026] The hydraulic excavator 1 may have a configuration in which hydraulic devices such as the above-described hydraulic actuator and an actuator driven by electric power are used in combination. Examples of the actuator driven by electric power include an electric travel motor, an electric cylinder, and an electric swing motor.

[0027] 〔2. Electrical System Configuration〕 FIG. 2 is a block diagram schematically showing the electrical system configuration of the hydraulic excavator 1. The hydraulic excavator 1 includes a control system CS. The control system CS includes the above-described power storage device 53, a charger 54, a junction box 55, an inverter 56, an electric motor 57, and a system controller 58. In FIG. 2, the wiring through which current flows is shown by a solid line, and the wiring of the signal input / output to / from the system controller 58 is shown by a two-dot chain line.

[0028] The power storage device 53 discharges by supplying electric power to the electric motor 57 via the inverter 56. Further, the power storage device 53 is charged by receiving electric power from the commercial power supply 51 (see FIG. 1), which is an external power source, via the charger 54.

[0029] The power storage device 53 has a plurality of battery unit groups. Specifically, the power storage device 53 has, as the plurality of battery unit groups, a first battery unit group 53A and a second battery unit group 53B. The first battery unit group 53A and the second battery unit group 53B are connected in parallel (see FIG. 3). The first battery unit group 53A and the second battery unit group 53B are also each referred to as a "string". Note that the number of battery unit groups included in the power storage device 53 is not limited to the above two, and may be three or more.

[0030] A battery unit group has a plurality of battery units. Specifically, the first battery unit group 53A has a first battery unit 53A1 and a second battery unit 53A2. The first battery unit 53A1 and the second battery unit 53A2 are connected in series. The second battery unit group 53B has a third battery unit 53B1 and a fourth battery unit 53B2. The third battery unit 53B1 and the fourth battery unit 53B2 are connected in series. Note that the number of battery units included in one battery unit group is not limited to the above two, and may be one or three or more. That is, the control method of the present embodiment described below can be applied not only when the number of battery units included in one battery unit group is plural, but also when the number is singular.

[0031] A CMU (Cell Management Unit) is incorporated in each battery unit, that is, the first battery unit 53A1, the second battery unit 53A2, the third battery unit 53B1, and the fourth battery unit 53B2. The CMU is a unit that monitors the state of each battery unit (including cell voltage, temperature, etc.). Various types of information acquired by the CMU are output to the system controller 58.

[0032] The charger 54 converts the AC voltage supplied from the commercial power supply 51 shown in FIG. 1 via the power supply cable 52 into a DC voltage. The junction box 55 is configured to include a charger relay, an inverter relay, a battery relay, a fuse, and the like. The voltage output from the charger 54 is supplied to the power storage device 53 via the junction box 55. Thereby, the power storage device 53 is charged.

[0033] The junction box 55 is a battery control unit that controls the input and output of the power storage device 53 by controlling the internal battery relay, and is also called a PDU (Power Distribution Unit). The junction box 55 includes a BMU (Battery Management Unit). The BMU is connected to each CMU of the power storage device 53, and monitors the state of the entire power storage device 53 based on the information output from each CMU. The information acquired by the BMU is output to the system controller 58.

[0034] The junction box 55 includes a first current sensor H1 and a second current sensor H2. The first current sensor H1 and the second current sensor H2 are composed of, for example, Hall elements. The first current sensor H1 is connected in series with the first battery unit group 53A of the power storage device 53, and detects the magnitude of the current flowing through the first battery unit group 53A. The second current sensor H2 is connected in series with the second battery unit group 53B of the power storage device 53, and detects the magnitude of the current flowing through the second battery unit group 53B. The information (current value data) detected by the first current sensor H1 and the second current sensor H2 is output to the system controller 58 via the BMU in the junction box 55.

[0035] Note that the first current sensor H1 and the second current sensor H2 may be provided outside the junction box 55. For example, the first current sensor H1 and the second current sensor H2 may be provided inside the power storage device 53.

[0036] The inverter 56 converts the DC voltage supplied from the power storage device 53 via the junction box 55 into an AC voltage and supplies it to the electric motor 57. As a result, the electric motor 57 rotates. The supply of the AC voltage (current) from the inverter 56 to the electric motor 57 is performed based on the rotation command output from the system controller 58.

[0037] A plurality of hydraulic pumps 60 are connected to the rotating shaft (output shaft) of the electric motor 57. The plurality of hydraulic pumps 60 includes variable displacement pumps and fixed displacement pumps. In FIG. 2, only one hydraulic pump 60 is illustrated as an example. Each hydraulic pump 60 is connected to a hydraulic oil tank (not shown) that stores (retains) hydraulic oil. When the hydraulic pump 60 is driven by the electric motor 57, the hydraulic oil in the hydraulic oil tank is supplied to the hydraulic actuator via the hydraulic pump 60 and a control valve (not shown). As a result, the hydraulic actuator is driven. The above control valve is a direction switching valve that controls the flow direction and flow rate of the hydraulic oil supplied to the hydraulic actuator.

[0038] FIG. 3 is an explanatory diagram showing details of the internal configuration of the power storage device 53 and the junction box 55. The positive terminal of the first battery unit group 53A of the power storage device 53 is connected to the positive-side merging wiring 55a via the first current sensor H1. The positive terminal of the second battery unit group 53B of the power storage device 53 is connected to the positive-side merging wiring 55a via the second current sensor H2. The positive-side merging wiring 55a is connected to the inverter 56 via the main relay MR. Further, a precharge relay PR and a resistor R1 are provided in parallel with respect to the main relay MR. The precharge relay PR and the resistor R1 are connected in series.

[0039] On one hand, the negative terminal of the first battery unit group 53A of the power storage device 53 is connected to the negative-side merging wiring 55b via the first relay K1. The negative terminal of the second battery unit group 53B of the power storage device 53 is connected to the negative-side merging wiring 55b via the second relay K2. The negative-side merging wiring 55b is connected to the inverter 56. The positive-side merging wiring 55a and the negative-side merging wiring 55b are also connected to the capacitor 56C inside the inverter 56.

[0040] Figure 4 is a block diagram showing the detailed configuration of the system controller 58. The system controller 58 is composed of an electronic control unit also called an ECU (Electronic Control Unit). The system controller 58 has a first detection unit 58a and a second detection unit 58b. That is, the control system CS including the system controller 58 has a first detection unit 58a and a second detection unit 58b.

[0041] Both the first detection unit 58a and the second detection unit 58b recognize and compare the magnitudes of the currents flowing through the respective battery unit groups of the power storage device 53 based on the signals output from the above-described first current sensor H1 and second current sensor H2, and thereby detect abnormalities.

[0042] Here, the abnormality detected by the first detection unit 58a is a cross-current abnormality (also referred to as the first abnormality). For example, before the inverter 56 or the charger 54 is started, if the difference in voltage between the respective battery unit groups of the power storage device 53, in other words, the difference in current flowing through the respective battery unit groups is a certain value or more, the current (cross-current) flowing from the battery unit group with a relatively high voltage to the battery unit group with a relatively low voltage increases. The first detection unit 58a determines the above-mentioned difference in current of a certain value or more as a cross-current abnormality. If the cross-current is large (if the voltage difference between the respective battery unit groups is large), there is a possibility that it will affect the abnormality detection by the second detection unit 58b executed after the inverter 56 or the charger 54 is started and cause false detection (false determination). Therefore, the first detection unit 58a determines (detects) the presence or absence of a cross-current abnormality before the second detection unit 58b detects an abnormality.

[0043] On the other hand, the abnormality detected by the second detection unit 58b is an abnormality that leads to a failure of the power storage device 53 and thus a circuit failure. Hereinafter, the above abnormality detected by the second detection unit 58b is also referred to as a circuit abnormality (second abnormality). As the circuit abnormality, loosening of the screws of the electrical connection part caused by vibration or impact can be considered. The electrical connection part is, for example, a connection part between an arbitrary battery unit (cell terminal) of the power storage device 53 and a bus bar. In addition to the loosening of the screws of the electrical connection part, breakage of the cell terminal, loosening of the harness, etc. are also included in the circuit abnormality.

[0044] The system controller 58 further includes a main control unit 58c. The main control unit 58c performs electrical control of each part of the hydraulic excavator 1 of the present embodiment. Therefore, the on / off switching of each relay shown in FIG. 3 is also controlled by the main control unit 58c.

[0045] The above-described first detection unit 58a, second detection unit 58b, and main control unit 58c are all control units within the ECU. And the first detection unit 58a, second detection unit 58b, and main control unit 58c operate according to an operation program stored in a storage unit (not shown) provided inside the system controller 58, for example. Note that the above storage unit may be provided outside the system controller 58.

[0046] The hydraulic excavator 1 of the present embodiment includes a display device 70. The display device 70 displays information (for example, the presence or absence of a cross-flow abnormality, the presence or absence of a circuit abnormality) based on the detection of at least one of the first detection unit 58a and the second detection unit 58b of the control system CS. Such a display device 70 is configured by, for example, a liquid crystal display device.

[0047] 〔3. Regarding the control method〕 Next, the operation of the abnormality detection by the above-described control system CS will be described. FIG. 5 is a flowchart showing the flow of the operation by the control system CS. When a key switch (not shown) of the hydraulic excavator 1 is turned on, the first detection unit 58a executes the first detection (S1). That is, in the first state, the first detection unit 58a compares the magnitudes of the currents flowing through the plurality of battery unit groups (here, the first battery unit group 53A and the second battery unit group 53B) to detect a first abnormality (first detection). At this time, the main relay MR, the first relay K1, and the second relay K2 in FIG. 3 are on. The detection result of the first detection, that is, the information on the presence or absence of the first abnormality, is displayed on the display device 70.

[0048] Here, the first state refers to a state in which each battery unit of the power storage device 53 can be charged and discharged and before the inverter 56 or the charger 54 is activated. As described above, the first detection unit 58a recognizes and compares the magnitudes of the currents flowing through the respective battery unit groups in the first state based on the signals output from the first current sensor H1 and the second current sensor H2, thereby detecting a cross-flow abnormality, which is the first abnormality. Specifically, it is as follows.

[0049] In the first state, the current value detected by the first current sensor H1, that is, the current value flowing through the first battery unit group 53A, is set as Ia1 (A). Also, in the first state, the current value detected by the second current sensor H2, that is, the current value flowing through the second battery unit group 53B, is set as Ib1 (A). The first detection unit 58a determines that there is a first abnormality (cross-flow abnormality) if the absolute value of the difference between Ia1 and Ib1 is equal to or greater than the threshold value X1 (A), and determines that there is no first abnormality if the absolute value is less than the threshold value X1.

[0050] In S1 (the first detection), when the first detection unit 58a detects a first abnormality (Yes in S1), an equalization process is executed to reduce the voltage difference between a plurality of battery unit groups (the first battery unit group 53A and the second battery unit group 53B) (S2). After that, through S3, it proceeds to the second detection in S4. That is, the equalization process in S2 is executed before the second detection in S4. Note that the equalization process, together with the inrush current prevention process in S3 described later, is executed under the control of the main control unit 58c. Also, instead of proceeding to S4 through S3 after S2, it may return to S1.

[0051] Here, as the above-mentioned equalization process, a standby process of not starting the inverter 56 and the charger 54 and waiting for a predetermined time can be considered. The above-mentioned predetermined time can be, for example, several seconds to several minutes, but it can be set arbitrarily. By performing the equalization process (standby process), a cross current is generated during standby, and the voltage difference between a plurality of battery unit groups becomes smaller. That is, among the first battery unit group 53A and the second battery unit group 53B, current flows from the higher voltage side to the lower voltage side, and as a result, the above-mentioned voltage difference approaches zero (ultimately becomes zero).

[0052] When no first abnormality is detected in the first detection (No in S1), and after the above-mentioned equalization process (S2), the main control unit 58c executes an inrush current prevention process (S3). The details of the inrush current prevention process will be described later. After the inrush current prevention process, the second detection unit 58b executes a second detection (S4). That is, the second detection unit 58b compares the magnitudes of the currents flowing through a plurality of battery unit groups (here, the first battery unit group 53A and the second battery unit group 53B) in the second state after the abnormality detection (first detection) by the first detection unit 58a to detect a second abnormality (second detection). At this time, the main relay MR, the first relay K1, and the second relay K2 are on. The detection result of the second detection, that is, the information on the presence or absence of the second abnormality, is displayed on the display device 70.

[0053] Here, the second state refers to the state after the inverter 56 or the charger 54 is activated. As described above, the second detection unit 58b can detect a circuit abnormality, which is a second abnormality, by recognizing and comparing the magnitudes of the currents flowing through each battery unit group in the second state based on the signals output from the first current sensor H1 and the second current sensor H2. Specifically, it is as follows.

[0054] In the second state, let the current value detected by the first current sensor H1, that is, the current value flowing through the first battery unit group 53A, be Ia2 (A). Also, in the second state, let the current value detected by the second current sensor H2, that is, the current value flowing through the second battery unit group 53B, be Ib2 (A). If the absolute value of the difference between Ia2 and Ib2 is equal to or greater than the threshold value X2 (A), the second detection unit 58b determines that there is a second abnormality (circuit abnormality). If the absolute value is less than the threshold value X2, it determines that there is no second abnormality.

[0055] The threshold value X2 is preferably set according to the total current of the power storage device 53. For example, when the total current of the power storage device 53 is large, it is desirable to increase the threshold value X2 as well. This is because the current difference between the battery unit groups increases in proportion to the charge / discharge current in the second state, and if the threshold value X2 is small, it is likely to be determined as a circuit abnormality even within the normal range. Note that the above total current is the sum of the currents output from each battery unit group of the power storage device 53. On the other hand, the threshold value X1 may be a constant value. This is because the first state is the state before the activation of the inverter 56 or the charger 54, and no charge / discharge current occurs.

[0056] In the second detection of S4, if the second detection unit 58b does not detect a second abnormality, the main control unit 58c determines that there is no circuit abnormality (S5). In this case, the processing after S3 is repeatedly performed until the key switch is turned off in S9.

[0057] On the other hand, in the second detection of S4, when the second detection unit 58b detects a second abnormality, the main control unit 58c determines that there is a circuit abnormality (S6). In this case, the main control unit 58c executes first regulation control for regulating the output of the inverter 56 (S7). Note that the first regulation control may be control for immediately stopping the output of the inverter 56, or may be control for reducing the output of the inverter 56 (output derating). In the latter case, the minimum output for moving the hydraulic excavator 1 to a safe location is ensured. The first regulation control is performed based on the rotation command output from the main control unit 58c to the inverter 56.

[0058] Further, after S7, the main control unit 58c executes second regulation control for regulating the drive of the charger 54 (S8). Note that the second regulation control may be control for immediately stopping the drive of the charger 54, or may be control for delaying the stop of the drive of the charger 54. In the former case, the charging of the power storage device 53 is immediately stopped. In the latter case, the charging of the power storage device 53 is executed for a short period and then the charging is stopped. The second regulation control is performed based on the drive signal (control signal) output from the main control unit 58c to the charger 54. Note that S7 and S8 may be performed in the reverse order, or may be performed simultaneously.

[0059] Thereafter, the process proceeds to S9, and the processes after S3 are repeatedly performed until the key switch is turned off. When the key switch is turned off in S9, a series of processes ends.

[0060] As described above, the control method of the present embodiment includes the first detection unit 58a executing the first detection, and after the first detection is executed, the second detection unit 58b executing the second detection (S1, S4). Further, the control system CS of the present embodiment includes the above-described first detection unit 58a and second detection unit 58b.

[0061] If there is a screw loosening (second abnormality, circuit abnormality) in the electrical connection part of the power storage device 53, in the second state after the inverter 56 or the charger 54 is activated, a difference equal to or greater than a certain value immediately occurs in the magnitude of the current flowing through the plurality of battery unit groups of the power storage device 53. In the present embodiment, in the second detection, the second detection unit 58b compares the magnitudes of the currents flowing through the plurality of battery unit groups of the power storage device 53 to detect a circuit abnormality (second abnormality). Therefore, by a simple method of comparing the magnitudes of the currents flowing through the plurality of battery unit groups, the above circuit abnormality can be detected more quickly (than the method of detecting a voltage difference). In addition, in the circuit including the power storage device 53, sensors (first current sensor H1 and second current sensor H2) for detecting the magnitude of the current are usually provided. For this reason, when detecting a circuit abnormality, an additional member such as a temperature sensor (a sensor for detecting a temperature rise at the abnormal location) is unnecessary.

[0062] Also, if each battery unit of the power storage device 53 is chargeable and dischargeable, and there is a difference in the magnitude of the current flowing through the plurality of battery unit groups in the first state before the inverter 56 or the charger 54 is activated, the current difference appears as a cross current. If the second detection is performed while the above current difference is large in the first state, there is a risk of false detection in the second detection. That is, if the second detection is performed while the current difference (the difference between Ia1 and Ib1) is large in the first state, since the current difference is reflected in the current difference (the difference between Ia2 and Ib2) in the second state, there is a risk of false detection that there is a circuit abnormality in the second detection. By performing the first detection before the second detection, after the first detection is performed, if necessary, a process for reducing the cross current (the equalization process in S2) can be performed, and then the second detection can be performed. Thereby, the risk of false detection in the second detection can be reduced.

[0063] That is, according to the control method and the control system CS of the present embodiment, an abnormality (second abnormality) leading to a circuit failure when using the power storage device 53 having a plurality of battery unit groups connected in parallel can be quickly and accurately detected by a simple method without using an additional member such as a temperature sensor.

[0064] In addition, when the control method of this embodiment detects a first abnormality in the first detection, it includes performing an equalization process before the second detection (S2). Since the equalization process is a process of reducing the voltage difference between a plurality of battery unit groups, the cross current becomes small. Therefore, in the second detection (S4) performed after the equalization process, false detection due to the influence of the cross current is surely reduced. That is, the accuracy of detecting a circuit abnormality (second abnormality) is surely improved.

[0065] In particular, the above equalization process includes a standby process. During the standby process, due to the occurrence of cross current, the voltage difference between a plurality of battery unit groups becomes small. That is, the above equalization process is surely and easily realized.

[0066] In this embodiment, when no first abnormality (cross current abnormality) is detected in the first detection, the second detection is performed by omitting the above equalization process (without performing the equalization process) (S4). In this case, after the execution of the first detection, since there is no standby time due to the equalization process, the second detection is performed promptly.

[0067] The control method of this embodiment further includes performing first regulation control for regulating the output of the inverter 56 when a second abnormality (circuit abnormality) is detected in the second detection (S7). By regulating the output of the inverter 56, while driving the electric motor 57 at a low speed (driving the traveling motor 22 (see FIG. 1)) to move the hydraulic excavator 1 to a safe place, the safety of the equipment (including the power storage device 53, the inverter 56, etc.) can be ensured. When ensuring the safety of the equipment as the top priority, in the first regulation control, the output of the inverter 56 may be stopped immediately.

[0068] The control method of this embodiment further includes performing second regulation control for regulating the driving of the charger 54 when a second abnormality is detected in the second detection (S8). In this case, the safety of the equipment (including the power storage device 53, the charger 54, etc.) can be ensured.

[0069] Further, the hydraulic excavator 1 of the present embodiment includes the above control system CS and a display device 70. By displaying information based on abnormal detections (first detection, second detection) in the control system CS on the display device 70, the execution of maintenance is promoted for the user (including the operator). Thereby, the failure of the equipment due to a fatal abnormality is reduced.

[0070] 〔4. About inrush current prevention processing〕 Next, the inrush current prevention processing of S3 described above will be described. In the inrush current prevention processing, the first relay K1 and the second relay K2 in FIG. 3 are turned on, the main relay MR is turned off, and the precharge relay PR is turned on. As a result, a current flows from the power storage device 53 to the capacitor 56C built in the inverter 56 via the resistor R1. At this time, since a current flows through the capacitor 56C via the resistor R1, the value of the flowing current is suppressed lower than when the main relay MR is turned on suddenly.

[0071] When the capacitor 56C reaches the same voltage level as the power storage device 53, it is regarded as the completion of precharge, and the main relay MR is turned on (in some cases, the precharge relay PR is turned off). As a result, a large load current flows through the main relay MR, the first relay K1, and the second relay K2.

[0072] Thus, the control method of the present embodiment further includes executing the inrush current prevention processing of S3 before executing the second detection of S4 described above. By the inrush current prevention processing, when starting the inverter 56 in the second detection, the supply of an excessive inrush current from the power storage device 53 to the inverter 56 is prevented. Thereby, the inverter 56 can be protected. Also, by using a circuit with the resistor R1 to match the voltage levels of the power storage device 53 and the inverter 56 (especially the built-in capacitor 56C), and then turning on the main relay MR without the resistor R1, a large current can be handled without energy loss.

[0073] 〔5. Supplementary explanation〕 In this embodiment, the standby process has been described as an example of the equalization process, but the example is not limited to this. As another equalization process, a process (charging or discharging) of adjusting the voltage of one string (battery unit group) to the voltage of the other string may be performed. For example, one string may be connected to a voltage converter (not shown) to step down the voltage, and by driving a heater or a cooling fan, the power of one string can be consumed to reduce (equalize) the voltage difference between the strings.

[0074] In the above, as an example of an electric working machine, the hydraulic excavator 1 which is a construction machine has been described. However, the working machine is not limited to the hydraulic excavator 1, and other construction machines such as a wheel loader and a compact track loader may be used. Further, the working machine may be an agricultural machine such as a combine or a tractor.

[0075] 〔6. Supplementary Note〕 The control method, control system, and hydraulic excavator 1 of the hydraulic excavator 1 described in this embodiment can also be expressed as follows in the supplementary note.

[0076] The control method of the working machine in Supplementary Note (1) is a control method of a working machine including a power storage device that discharges by supplying power to an electric motor via an inverter or is charged by receiving power from an external power source via a charger, the power storage device having a plurality of battery unit groups connected in parallel, and the battery unit group having a plurality of or one battery unit connected in series, performing a first detection for detecting a first abnormality by comparing the magnitudes of the currents flowing through the plurality of battery unit groups in a first state before the battery unit is chargeable and before the inverter or the charger is activated; and performing a second detection for detecting a second abnormality by comparing the magnitudes of the currents flowing through the plurality of battery unit groups in a second state after the inverter or the charger is activated after performing the first detection.

[0077] The control method of the working machine in Supplementary Note (2) is, in the control method described in Supplementary Note (1), when the first abnormality is detected in the first detection, further including executing an equalization process for reducing the voltage difference between the plurality of battery unit groups before the second detection.

[0078] The control method of the working machine in Supplementary Note (3) is, in the control method described in Supplementary Note (2), the equalization process includes a standby process.

[0079] The control method of the working machine in Supplementary Note (4) is, in the control method described in Supplementary Note (2) or (3), when no first abnormality is detected in the first detection, the second detection is executed by omitting the equalization process.

[0080] The control method of the working machine in Supplementary Note (5) is, in the control method described in any one of Supplementary Notes (1) to (4), when the second abnormality is detected in the second detection, further including executing a first regulation control for regulating the output of the inverter.

[0081] The control method of the working machine in Supplementary Note (6) is, in the control method described in any one of Supplementary Notes (1) to (5), when the second abnormality is detected in the second detection, further including executing a second regulation control for regulating the drive of the charger.

[0082] The control method of the working machine in Supplementary Note (7) is, in the control method described in any one of Supplementary Notes (1) to (6), before executing the second detection, further including executing an inrush current prevention process for preventing the supply of inrush current from the power storage device to the inverter.

[0083] The control system of the working machine in Supplementary Note (8) is A control system for a working machine, comprising a power storage device that discharges by supplying power to an electric motor via an inverter or charges by receiving power from an external power source via a charger, wherein the power storage device has a plurality of battery unit groups connected in parallel, and each battery unit group has a plurality of or one battery unit connected in series. A first detection unit that compares the magnitudes of currents flowing through the plurality of battery unit groups in a first state before the battery unit is chargeable and the inverter or the charger is activated, and detects a first abnormality. A second detection unit that compares the magnitudes of currents flowing through the plurality of battery unit groups in a second state after the inverter or the charger is activated, after the first detection unit has detected an abnormality, and detects a second abnormality.

[0084] The working machine according to supplementary note (9) The control system according to supplementary note (8), And a display device that displays information based on detection by at least one of the first detection unit and the second detection unit of the control system.

[0085] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited thereto, and it can be implemented by expanding or changing without departing from the gist of the invention.

Industrial Applicability

[0086] The present invention can be used for working machines such as construction machines and agricultural machines.

Explanation of Signs

[0087] 1 Hydraulic excavator (working machine) 53 Power storage device 53A First battery unit group 53A1 First battery unit 53A2 Second battery unit 53B Second battery unit group 53B1 Third battery unit 53B2 Fourth battery unit 54 Charger 56 Inverter 57 Electric motor 58a First detection unit 58b Second detection unit 70 Display device CS Control system

Claims

1. A control method for a working machine, comprising a power storage device that discharges by supplying power to an electric motor via an inverter or is charged by receiving power from an external power source via a charger, wherein the power storage device has a plurality of battery unit groups connected in parallel, and each of the battery unit groups has a plurality of or one battery unit connected in series. Performing a first detection to detect a first abnormality by comparing the magnitudes of currents flowing through the plurality of battery unit groups in a first state before the battery units are chargeable and before the inverter or the charger is activated. After performing the first detection, performing a second detection to detect a second abnormality by comparing the magnitudes of currents flowing through the plurality of battery unit groups in a second state after the inverter or the charger is activated.

2. The control method for a working machine according to claim 1, further comprising, when the first abnormality is detected in the first detection, performing an equalization process to reduce the voltage difference between the plurality of battery unit groups before the second detection.

3. The control method for a working machine according to claim 2, wherein the equalization process includes a standby process.

4. The control method for a working machine according to claim 2, wherein when no first abnormality is detected in the first detection, the equalization process is omitted and the second detection is performed.

5. The control method for a working machine according to claim 1, further comprising, when the second abnormality is detected in the second detection, performing a first regulation control to regulate the output of the inverter.

6. The control method for a working machine according to claim 1, further comprising, when the second abnormality is detected in the second detection, performing a second regulation control to regulate the driving of the charger.

7. The control method for a working machine according to any one of claims 1 to 6, further comprising, before performing the second detection, performing an inrush current prevention process to prevent the supply of an inrush current from the power storage device to the inverter.

8. A control system for a working machine, comprising a power storage device that discharges by supplying power to an electric motor via an inverter or is charged by receiving power from an external power source via a charger, wherein the power storage device has a plurality of battery unit groups connected in parallel, and each of the battery unit groups has a plurality of or one battery unit connected in series. A first detection unit that compares the magnitudes of currents flowing through the plurality of battery unit groups in a first state before the battery units are chargeable and before the inverter or the charger is activated, and detects a first abnormality. A second detection unit that compares the magnitudes of currents flowing through the plurality of battery unit groups in a second state after the inverter or the charger is activated after the abnormality detection by the first detection unit, and detects a second abnormality. A control system for a working machine, comprising the second detection unit.

9. The control system according to claim 8, A working machine, comprising a display device that displays information based on detection by at least one of the first detection unit and the second detection unit of the control system.

Images