JP7588483B2 - Electric small mobile crane - Google Patents

Description

The present invention relates to a small mobile crane with a relatively small body size. More specifically, it relates to an electrically powered small mobile crane that uses a battery and an external AC power source as a driving power source.

A type of mobile crane known to be electric is one that is powered by a battery. In this type of mobile crane, hydraulic actuators for operating and traveling the crane are driven by pressurized oil generated by a hydraulic pump driven by an electric motor. When the battery runs low, it is charged using a commercial power source.

Conventional electric mobile construction machines are capable of selectively switching between a drive mode and a charging mode (Patent Documents 1 and 2). In addition, they are configured so that they cannot travel or perform work while the power cable is connected to a commercial power source (Patent Document 2).

Patent No. 5737598 Japanese Utility Model Application Publication No. 5-62104 Japanese Utility Model Application Publication No. 4-108302

Among mobile cranes, there are small mobile cranes with a relatively small body size and a lifting load of approximately 8 tons or less. Because the body size of small mobile cranes is small, there is naturally a limit to the size of the battery that can be loaded, and therefore the battery capacity. If the capacity of the onboard battery is small, the continuous operating time of the electric small mobile crane will be short, the battery will need to be charged frequently, and work efficiency will decrease.

Crane operations using small mobile cranes are generally performed in a stationary position with the outriggers extended. It is therefore conceivable that crane operations can be performed while obtaining drive power from an external power source via a power cable. When the workload during crane operations is heavy, the electric motor consumes a lot of power, and the external power source alone may not be enough to provide the power required, so the shortage of power may have to be supplied from the battery. When the battery capacity is small, the operating mode must be frequently switched from work mode to charging mode to charge the battery, and crane operations may not be possible for long periods of time.

In view of these circumstances, the object of the present invention is to provide an electric small mobile crane that can perform crane work and the like continuously for long periods of time even if the installed battery is small and has a small capacity.

In order to achieve the above object, the mini mobile crane of the present invention comprises:
A hydraulic pump that generates pressure oil for driving hydraulic actuators for traveling and crane operation;
an electric motor that drives the hydraulic pump;
A battery;
a charger that, when power is supplied from an external AC power source, converts the power supplied from the external AC power source into a DC current of a constant current within a specified voltage range and outputs the DC current;
a key switch that is operated to an on position and an off position;
The battery includes a control device that controls the power supply to the electric motor and the charging of the battery.

The control device includes:
When the key switch is in the ON position and there is no power supply from the external AC power source, an output current of the battery is supplied to the electric motor;
When the key switch is in the ON position and power is being supplied from the external AC power source, an output current of the charger is supplied to the battery and the electric motor;
When power is being supplied from the external AC power source, if the current consumption of the electric motor exceeds the output current of the charger, a current deficiency, which is the difference between the current consumption and the output current, is supplied from the battery to the electric motor.

In the small mobile crane of the present invention, when no power is supplied from the outside, the battery is used as the driving power source to drive the electric motor and perform travel, etc. When power is supplied from the outside, the electric motor is driven using the external power source as the driving power source to perform crane work, etc. In parallel with this, the on-board battery is charged using the external power source.

In this way, when the battery charge level drops while connected to an external power source, the electric motor is driven and the battery is charged in parallel. This makes it possible to avoid frequent battery insufficiency and the resulting drop in work efficiency. Also, unlike conventional battery-equipped mobile cranes, there is no need for the operator to switch from drive mode to charge mode and interrupt work in order to charge the battery.

In addition, unlike typical large, electrically powered mobile cranes, small mobile cranes have a narrow travel and working range, and lifting work is generally a stationary task performed with outriggers extended. Therefore, even if the power cable is connected to an external power source, there are few practical restrictions or hindrances to crane work.

1A and 1B are a side view and a perspective view showing a small mobile crane to which the present invention is applied, respectively, and a working state. FIG. 2 is a schematic block diagram showing a control system of the small mobile crane. 4 is a schematic flowchart showing a battery charge/discharge control operation. FIG. 4 is a characteristic curve diagram showing an example of the charge/discharge characteristics of a battery.

Below, an embodiment of a battery-powered small mobile crane to which the present invention is applied will be described with reference to the drawings. Note that the embodiment described below shows an example of the present invention, and the present invention is not intended to be limited to the configuration of the embodiment.

Figure 1(a) is a schematic side view of a small mobile crane 1 according to this embodiment, and Figure 1(b) is a schematic perspective view showing an example of a stationary state with outriggers extended for crane operation. The small mobile crane 1 comprises a crawler-type lower traveling body 2 and an upper frame 3 mounted thereon. The lower traveling body 2 is, for example, a hydraulically driven traveling body. The upper frame 3 is equipped with a crane boom 4. Four outriggers 5 are attached to the four corners of the lower traveling body 2. A traveling operation unit 6 for the lower traveling body 2 is disposed at one end of the lower traveling body 2, and a crane operation unit 8 equipped with a monitor 7 is disposed at the other end of the lower traveling body 2. When traveling, as shown in Figure 1, the operator stands at the side of the traveling operation unit 6 and operates the operation levers, etc. to travel the small mobile crane 1.

The crane boom 4 is a multi-stage boom, and is raised and extended by hydraulic actuators such as the elevation cylinder 9 and a telescopic cylinder (not shown). From the stored state, the outriggers 5 are rotated and extended outward by the outrigger extension cylinders, etc., and the lower traveling body 2 is raised above the ground surface and fixed in a stable state. In this state, the crane boom 4 is raised and extended to perform crane work. In this case, the worker stands next to the crane operation unit 8 and performs screen input operations on the monitor 7, operation of the operation lever, etc. to extend the outriggers 5 and rotate, raise, lower, and extend the crane boom 4.

The lower traveling body 2 is equipped with a hydraulic pump 11 that generates pressurized oil to drive hydraulic actuators such as the hoisting cylinder 9 for crane operation, and an electric motor 12 to drive the hydraulic pump 11. The upper frame 3 is equipped with a battery 13 that is the driving power source for the electric motor 12 and the like. A charger 14 that charges the battery 13 is also mounted inside the upper frame 3. A power cable (see Figure 2) is drawn out from the charger 14. The charger 14 converts the power supplied from an external AC power source into DC of a constant voltage (e.g., 54 V). The output current of the charger 14 is used as the charging current for the battery 13 and the driving current for the electric motor 12. A control device 15 that controls the driving of each part is also mounted inside the upper frame 3.

Figure 2 is a schematic block diagram of the control system of the small mobile crane 1, focusing on the drive power supply system. The control device 15 has a control function for the electric motor 12, a travel control function, a crane operation control function, a power supply control function for the electric motor 12, a charging control function for the battery 13, and other control functions. When the key switch 21 arranged on the travel operation unit 6 or the crane operation unit 8 is switched on, power is supplied from the battery 13 to each unit, and the unit becomes operable. When the power supply port 22 is connected to an external AC power source via the power cable 23, the AC current supplied via the power cable 23 is supplied to the charger 14, and is converted to a constant current (e.g., 50 A at 38 V to 66 V) in a specified voltage range in the charger 14. The battery 13 is charged by the output current of the charger 14. The output current of the charger 14 is also used as the drive power for the electric motor 12 via the motor driver 24. When not connected to an external AC power source, the battery 13 is used as the drive power source for the electric motor 12.

The hydraulic oil generated by the hydraulic pump 11 driven by the electric motor 12 is supplied to the hydraulic actuators 26 for traveling on the lower traveling body 2 and the hydraulic actuators 27 for crane operation such as the boom hoisting cylinders on the upper frame 3 via the hydraulic control circuit 25 equipped with a directional control valve, etc. In response to the operation of the various operating levers arranged on the traveling operation unit 6 and the crane operation unit 8, the hydraulic control circuit 25 is controlled by the control device 15, and the necessary hydraulic actuators are driven to perform the specified traveling operation and crane operation.

Figure 3 is a schematic flow chart showing the charge/discharge control operation of battery 13, and Figure 4 is a characteristic curve diagram showing an example of the charge/discharge characteristics of battery 13.

Referring to these figures, when the operator operates the key switch 21 to switch from the OFF position to the ON position (ST1 in FIG. 3), the power supply lines from the battery 13 to each part are switched to a connected state (ST2 in FIG. 3).

When the power cable 23 is connected to an external AC power source and power is supplied from the external AC power source to the charger 14 (ST3 in FIG. 3), if the key switch 21 is in the OFF position, control ends (ST4→ST5 in FIG. 3). If the key switch 21 is in the ON position, a constant current is supplied from the charger 14 to the battery 13 and charging begins (ST6 in FIG. 3, time t1 in FIG. 4). In addition, the output current of the charger 14 can be supplied as part of the drive current of the electric motor 12.

In advance, the rated current is read from the commercial power plug or breaker, and the input current value is selected on the monitor 7 of the crane operating unit 8 (see Figure 2), and the upper limit current input to the charger 14 is set.

After charging starts, the control device 15 monitors the cell voltage of the battery 13. When it detects that the maximum cell voltage is equal to or greater than a preset value, for example, 2.7 V, charging of the battery 13 by the charger 14 is stopped (ST7→ST8 in FIG. 3). After this, an error message is displayed on the monitor 7, and the process ends (ST9, ST10 in FIG. 3).

On the other hand, if charging is normal, the state of the key switch 21 during charging is monitored (ST11 in FIG. 3), and if the key switch 21 is on, charging continues until the remaining battery capacity (SOC) reaches a certain value, after which charging is terminated (ST12, ST13 in FIG. 3, time points t1 to t2 in FIG. 4). For example, charging is terminated when the remaining battery capacity reaches 90%.

When the key switch 21 is on and connected to an external AC power source, the output current of the charger 14 is supplied to the electric motor 12 as the drive current. When the current consumed by the electric motor 12 exceeds the output current supplied from the charger 14, the control device 15 controls the supply of the shortage current from the battery 13. When the key switch 21 is on and not connected to an external AC power source, the output current of the battery 13 is supplied to the electric motor 12 as the drive current.

For example, when the key switch 21 is on and connected to an external AC power source, if the electric motor 12 is driven (times t3 to t5 in FIG. 4), a drive current is supplied from the charger 14 to the electric motor 12. Also, when necessary, the battery 13 replenishes the shortage current, gradually decreasing the remaining capacity of the battery 13. When the remaining capacity of the battery 13 falls below a preset lower limit, for example, 50% (time t4 in FIG. 4), charging of the battery 13 is resumed (ST14 → ST3, ST4, ST6 in FIG. 3).

On the other hand, when the key switch 21 is off and connected to an external AC power source (ST11 → ST15 in Figure 3), charging is performed until the battery remaining capacity reaches 100%, and control ends (ST16, ST17, ST18 in Figure 3)

As described above, in the small mobile crane 1, charging control of the battery 13 and power supply control of the electric motor 12 are performed under the control of the control device 15. When the key switch 21 is switched on and the power is on, and there is no power supply from an external AC power source, the battery 13 is used as the drive power source for the electric motor 12. On the other hand, when there is power supply from an external AC power source with the power on, the battery 13 is charged by the charger 14, and the output current of the charger 14 is used as the drive current for the electric motor 12. Also, when the current consumed by the electric motor 12 exceeds the output current of the charger 14 during high-load operation such as crane work, the shortage current is supplied from the battery 13 to the electric motor 12.

The battery 13 is automatically charged in parallel with the driving of the electric motor 12. Therefore, even if a small-capacity battery 13 is installed, crane operation can be performed without interruption.

In addition, when the key switch 21 is switched off and the power is off, the control device 15 charges the battery 13 until the remaining capacity reaches 100%. In contrast, when the key switch 21 is switched on and the power is on, the control device 15 ends charging when the remaining capacity is less than 100%. This makes it possible to suppress a decrease in the lifespan of the battery 13.

Reference Signs List 1 Small mobile crane 2 Lower travel unit 3 Upper frame 4 Crane boom 5 Outriggers 6 Travel operation unit 7 Monitor 8 Crane operation unit 9 Drawer cylinder 11 Hydraulic pump 12 Electric motor 13 Battery 14 Charger 15 Control device 21 Key switch 22 Power supply port 23 Power cable 24 Motor driver 25 Hydraulic control circuit 26 Travel hydraulic actuators 27 Crane operation hydraulic actuators

Claims (2)

A hydraulic pump that generates pressure oil for driving hydraulic actuators for traveling and operating the crane;
an electric motor that drives the hydraulic pump;
A battery;
a charger that, when power is supplied from an external AC power source, converts the power supplied from the external AC power source into a DC current of a constant current within a specified voltage range and outputs the DC current;
a key switch that is operated to an on position or an off position and that switches a power supply line from the battery to the electric motor to a connected state when the key switch is switched from the off position to the on position ;
a control device that controls power supply to the electric motor and charging of the battery;
It has
The control device includes:
When power is being supplied from the external AC power source, and the key switch is operated to switch from the OFF position to the ON position, an output current of the charger is supplied to the battery and the electric motor, charging of the battery is started using the output current of the charger, the output current of the charger is used as a drive current for the electric motor, and when a current consumed by the electric motor exceeds the output current of the charger, a deficit current which is the difference between the current consumed and the output current is supplied from the battery to the electric motor ,
In the charging control of the battery,
monitoring the state of the key switch;
When the key switch is in the ON position, charging of the battery is terminated if the remaining battery capacity exceeds a predetermined upper limit value that is less than 100%, and charging of the battery is initiated if the remaining battery capacity falls below a predetermined lower limit value;
When the key switch is switched from the ON position to the OFF position, charging is performed until the remaining battery capacity reaches 100%, and control is then terminated . In the mini mobile crane according to claim 1,
The control device includes:
The small mobile crane stops charging the battery when the maximum voltage value of the battery cells reaches or exceeds a predetermined set value.

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