JP6094754B2 - Electric tool - Google Patents

Description

  The present invention relates to an electric tool having a switching element for motor control.

  In recent years, brushless motors have been increasingly used in electric tools such as circular saws. In order to supply driving power to the brushless motor, a switching element such as an FET is required. The switching element generates heat due to a large current for driving the brushless motor. For this reason, a fan is attached to the rotating shaft of a brushless motor, and the switching element is cooled by an air flow generated by the fan. It is also known to have an overheat protection function in order to prevent the switching element from becoming excessively hot. The overheat protection function is a function to stop energization of the brushless motor when the switching element reaches a certain temperature or higher.

JP 2011-5555 A

  In general, when the overheat protection function is activated and the brushless motor is stopped, the switching element cannot be restarted unless the temperature is lower than a predetermined temperature. For this reason, with natural cooling alone, there was a problem that it took a long time before restarting was possible, and work efficiency was poor. Such a problem is common in a brushed motor that controls an applied voltage by a switching element.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide an electric tool capable of speeding up cooling after the motor is stopped by an overheat protection function.

One embodiment of the present invention is a power tool. This electric tool
A motor, a cooling fan rotated by the motor, and an operation unit that switches between driving and stopping the motor,
After the motor is stopped by the overheat protection function, when the operation unit is operated to switch the motor from stop to drive, the motor is driven in a low load limited mode ,
In the low load limited mode, the effective value of the voltage applied to the motor is reduced while the set value of overcurrent protection is reduced .

  The motor may be a brushless motor.

  The effective value may be reduced by reducing the duty of the PWM signal applied to the switching element for driving control of the motor.

  You may provide the alerting | reporting means to alert | report outside in the period until the temperature conditions which can cancel | release the overheat protection by the said overheat protection function after the said low load limitation mode is started.

  The low load limiting mode may be terminated when a condition for canceling overheat protection by the overheat protection function is satisfied.

  The release condition may be that a temperature condition capable of releasing overheat protection by the overheat protection function is satisfied, and the operation unit is operated so as to switch the motor from stop to drive thereafter.

  In a predetermined temperature range before the overheat protection function works, in a low power mode in which the effective value of the voltage applied to the motor is lower than that in the low load limited mode when the temperature is lower than the temperature range. The motor may be driven.

  You may provide the alerting | reporting means to alert | report outside that it is the said low power mode.

  Temperature detection means for detecting the temperature of the switching element for driving control of the motor may be provided, and overheat protection by the overheat protection function may be activated or canceled according to the temperature detected by the temperature detection means.

  It should be noted that any combination of the above-described constituent elements, and those obtained by converting the expression of the present invention between methods and systems are also effective as aspects of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the electric tool which can speed up the cooling after a motor stops with an overheat protection function can be provided.

This top view of the cordless circle which concerns on embodiment of this invention. The same side view. The rear view. The front view. The 1st top view which made this a part of this cordless circle a section. The 2nd top view. AA sectional drawing of FIG. This functional block diagram of the cordless circle shown in FIG. FIG. 9 is a flowchart (No. 1) of control by the control unit 27 shown in FIG. The example time chart of this operation | movement of the cordless circle of embodiment when the control shown in the flowchart of FIG. 9 is performed. FIG. 9 is a flowchart (part 2) of control by the control unit 27 shown in FIG. The example time chart of this operation | movement of the cordless circle of embodiment when the control shown in the flowchart of FIG. 11 is performed.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or equivalent component, member, process, etc. which are shown by each drawing, and the overlapping description is abbreviate | omitted suitably. In addition, the embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

  1 is a plan view of the cordless circle according to the embodiment of the present invention, FIG. 2 is a side view thereof, FIG. 3 is a rear view thereof, and FIG. 4 is a front view thereof. FIG. 5 is a first plan view, partly in section, of the cordless circle of FIG. FIG. 6 is a second plan view of the same. 7 is a cross-sectional view taken along the line AA in FIG.

  The cordless circular saw of the present embodiment includes a base 1 and a main body 2. The base 1 is a substantially rectangular plate made of metal such as aluminum. The longitudinal direction of the base 1 coincides with the cutting direction. The bottom surface of the base 1 is a sliding surface with the work material. As will be described later, the main body 2 is connected to the base 1 at two places in the front and rear, and is rotatable with respect to the base 1 and tilted to the left and right. The main body 2 includes a motor housing 3, a handle portion 4, a gear cover 5, a saw cover 6, a protective cover 7, and a circular saw blade 8 (rotating tool). The motor housing 3 is made of resin, for example, and incorporates a brushless motor 9 (FIGS. 5 and 6). The brushless motor 9 rotates the circular saw blade 8. The handle portion 4 is made of the same material as the motor housing 3 and extends in the front-rear direction above the motor housing 3. The handle portion 4 is provided with a main trigger switch 18 (main switch) as an operation portion for switching the driving and stopping of the brushless motor 9 by the user. As shown in FIGS. 3 and 4, the handle portion 4 is composed of a left part integrally provided with the motor housing 3 and a right part sandwiched between the motor housing 3 and the gear cover 5. A battery pack mounting portion 4a to be described later is configured by a combination of the component and the right side component, and a control circuit board storage portion 4b to be described later is provided on the right side component of the handle portion 4 located on the circular saw blade 8 side. . Note that the boundary between the left part and the right part of the handle part 4 is a line appearing at the center of the handle part 4 in FIGS. 1, 3, 4, and the like.

  A battery pack attachment portion 4a (battery attachment portion) and a control circuit board storage portion 4b are integrally provided at the lower rear end of the handle portion 4. The battery pack 20 (storage battery) is detachably mounted on the battery pack mounting portion 4a by sliding it from the rear. A mode change switch 16 (for example, a tact switch) and an LED 29 are provided below the handle portion 4 and on the upper surface of the battery pack mounting portion 4a. The user can select, for example, either the normal mode or the eco mode with the mode switch 16. The battery pack 20 supplies driving power to the brushless motor 9. As shown in FIG. 1, the left side surface of the battery pack 20 attached to the battery pack mounting portion 4 a and the left side surface of the motor housing 3 are on substantially the same plane. That is, the distance from the circular saw blade 8 to the left side surface of the motor housing 3 and the distance from the circular saw blade 8 to the left side surface of the battery pack 20 are substantially the same, and the left side surface of the battery pack 20 and the left side of the motor housing 3 are the same. The cordless circular saw can be placed with the surface facing down, and the replacement operation of the circular saw blade 8 can be easily performed. The control circuit board storage portion 4 b is provided on the right side of the battery pack 20. The control circuit board 21 is housed and held in the control circuit board housing portion 4b. The control circuit board 21 is equipped with a control unit (controller) that controls the operation of the brushless motor 9. The control circuit board 21 is substantially perpendicular to the rotation axis of the brushless motor 9 (rotation axis of the circular saw blade 8). The left side of the control circuit board 21, that is, the control circuit board 21 and the battery pack 20, is partitioned by a controller cover 22 made of, for example, resin.

  The gear cover 5 is provided on the right side of the handle portion 4. The gear cover 5 is made of metal, for example, and incorporates a rotation transmission mechanism between the brushless motor 9 and the circular saw blade 8. The rotation transmission mechanism includes a known speed reduction mechanism. The saw cover 6 is attached to the gear cover 5 and covers the upper half of the circular saw blade 8 together with the gear cover 5. The saw cover 6 may be formed of the same material as the gear cover 5 and integrally. The front end portions of the gear cover 5 and the saw cover 6 are rotatably connected by a rotation support portion 14. The protective cover 7 is made of resin, for example, and is provided on the rear side of the gear cover 5 so as to be rotatable along the outer edges of the gear cover 5 and the saw cover 6. A spring (not shown) is interposed between the gear cover 5 and the protective cover 7. This spring urges the protective cover 7 against the gear cover 5 in the circumferential direction of the gear cover 5 and the saw cover 6 and in the direction covering the lower half of the circular saw blade 8 (counterclockwise in FIG. 2). . Therefore, when the cutting operation is not performed, the protective cover 7 covers the lower half of the circular saw blade 8 (a portion protruding downward from the bottom surface of the base 1) except for a part of the front.

  A bevel plate 12 is erected in front of the base 1. The bevel plate 12 stands upright in a short direction substantially orthogonal to the cutting direction. The bevel plate 12 is provided with a long hole 13. The long hole 13 has an arc shape centered on the first tilting shaft portion 15a extending in the cutting direction and orthogonal to the first tilting shaft portion 15a. The rotation support portion 14 is supported so as to be tiltable to the left and right with respect to the base 1 with the first tilt shaft portion 15a as a center. The tilting position of the rotation support unit 14 is adjusted with the tilt angle adjustment lever 11 loosened, and is fixed by tightening the tilt angle adjustment lever 11. The rotation support unit 14 rotatably supports the front end portion of the saw cover 6 with an axis parallel to the rotation axis of the brushless motor 9 (the rotation axis of the circular saw blade 8). Adjustment and fixing of the rotational position of the saw cover 6 will be described later.

  A link 10 is provided behind the base 1 so as to be rotatable about a tilting shaft portion 15b coaxial with the first tilting shaft portion 15a, and extends along the left side surface of the gear cover 5. The link 10 is made of a metal such as aluminum. In a state where the cutting depth adjusting lever 19 is loosened, the link 10 and the gear cover 5 can slide relative to each other, and the rotational position of the saw cover 6 relative to the base 1, that is, the cutting depth can be adjusted. And the rotation position of the gear cover 5 can be fixed by tightening the cutting depth adjusting lever 19.

  As shown in FIG. 6, the brushless motor 9 has a rotor core 9b around the output shaft 9a. The output shaft 9 a is parallel to the rotational axis of the circular saw blade 8. The rotor core 9b rotates integrally with the output shaft 9a. A rotor magnet 9c is inserted and supported in the rotor core 9b. The stator core 9d is provided so as to surround the outer peripheral surface of the rotor core 9b. The stator core 9d is provided with a stator coil 9f with an insulator 9e interposed therebetween. A switching substrate 23 is fixed to the left end side of the stator core 9d. The switching substrate 23 is substantially perpendicular to the output shaft 9a. As shown in FIG. 7, six switching elements 23 a (such as FETs) are mounted on the switching substrate 23 in a state where the main body portion is tilted. The switching element 23 a switches the supply voltage from the battery pack 20. As shown in FIG. 5, the terminal portion 20 a of the battery pack 20 and the switching substrate 23 are electrically connected to each other by a wiring 24. The wiring 25 electrically connects the terminal portion 20a of the battery pack 20 and the control circuit board 21 to each other. The wiring 26 electrically connects the control circuit board 21 and the switching board 23 to each other. A control signal from the controller of the control circuit board 21 is applied to the control terminal (gate) of the switching element 23a on the switching board 23 through the wiring 26, and the on / off of the switching element 23a is controlled. A cooling fan 33 is attached to the output shaft 9a of the brushless motor 9 and rotates together with the output shaft 9a. The brushless motor 9 and the switching element 23a are cooled by the airflow generated by the cooling fan 33.

  FIG. 8 is a functional block diagram of the cordless circle according to the embodiment of the present invention. The control unit 27 is mounted on the control circuit board 21 shown in FIG. The inverter unit 28 is a circuit in which the switching elements 23a shown in FIGS. 6 and 7 are bridge-connected. The LED 29 is an example of a notification unit that notifies the user of this state of the cordless circle by lighting or blinking, for example. The remaining amount display unit 30 displays the remaining capacity of the battery pack 20. The temperature sensor 31 includes a temperature detection element such as a thermistor provided in the vicinity of the switching element 23a of the inverter unit 28, and detects the temperature of the switching element 23a. The detection resistor 32 is provided in the drive current path of the brushless motor 9. The control unit 27 can detect the drive current based on the terminal voltage of the detection resistor 32. When the main trigger switch 18 is turned on, the control unit 27 sends a PWM signal to each switching element 23a of the inverter unit 28 according to the mode set by the mode change switch 16 (for example, either the normal mode or the eco mode). Applied to control driving of the brushless motor 9.

  FIG. 9 is a flowchart (No. 1) of control by the control unit 27 shown in FIG. This flowchart starts when the user turns on the main trigger switch 18. The control unit 27 confirms the value of the flag K of the overheat protection function (S1). The flag K is “1” when the overheat protection function is in operation and “0” when it is not in operation. If K = 0 (S1: YES), the control unit 27 sets the duty of the PWM signal applied to each switching element 23a of the inverter unit 28 (hereinafter also simply referred to as “duty”) to 100%, turns off the LED 29, The brushless motor 9 is driven with the overcurrent protection threshold (set value) set to 70A (S2). The duty in step S2 corresponds to the mode set by the mode switch 16 and 100% is an example in the normal mode. Until the temperature of the switching element 23a exceeds T1, the control unit 27 continues to drive the brushless motor 9 under the driving condition of step S2 (in the mode set by the mode switch 16) (S3: NO).

  When the temperature of the switching element 23a exceeds T1 (S3: YES), the control unit 27 activates the overheat protection function. That is, the control unit 27 stops the brushless motor 9 (duty is set to 0), turns on the LED 29 to notify the user, and sets the overcurrent protection threshold to 10A (S4). The control unit 27 also sets the value of the overheat protection function flag K to “1” (S5). Thereafter, when the main trigger switch 18 is turned off (S6: YES), the control unit 27 checks the temperature of the switching element 23a (S7), and when the temperature becomes T3 or less (S7: NO), the LED 29 is turned off. The user is notified (S8), and the value of the flag K of the overheat protection function is set to “0” (S9). The temperature check in step S7 is continued until the main trigger switch 18 is turned on again (S10: NO). Thereafter, when the main trigger switch 18 is turned on (S10: YES), the control unit 27 returns to step S1 and performs control according to the value of the flag K of the overheat protection function.

  If K = 1 (S1: NO), the controller 27 checks the temperature of the switching element 23a (S11), and if the temperature exceeds T3 (S11: YES), the brushless motor in the low load limited mode. 9 is driven. That is, the control unit 27 drives the brushless motor 9 by setting the duty to 30%, turning on the LED 29, and setting the overcurrent protection threshold to 10A (S12). The control unit 27 continues to drive the brushless motor 9 under the driving condition in step S12 while the temperature of the switching element 23a exceeds T3 (S13: YES). Thereafter, when the temperature of the switching element 23a becomes equal to or lower than T3 (S13: NO), the control unit 27 turns off the LED 29 to notify the user (S14), and when the main trigger switch 18 is turned off (S15: YES), The value of the overheat protection function flag K is set to "0" (S16), and the brushless motor 9 is stopped (S17). Thereafter, when the main trigger switch 18 is turned on (S18: YES), the control unit 27 returns to step S1 and performs control according to the value of the flag K of the overheat protection function. If the temperature of the switching element 23a is equal to or lower than T3 in step S11 (S11: NO), the control unit 27 turns off the LED 29 (S19), and sets the value of the overheat protection function flag K to “0” (S20). ), The process returns to step S1.

  FIG. 10 is an exemplary time chart of this operation of the cordless circle of the embodiment when the control shown in the flowchart of FIG. 9 is performed. When the user turns on the main trigger switch 18 at time t0, the control unit 27 drives the brushless motor 9 with a duty of 100% (drives the brushless motor 9 in the mode set by the mode switch 16). At this time, the threshold for overcurrent protection is 70 A, and the LED 29 is turned off. During the driving of the brushless motor 9, the temperature of the switching element 23a rises. After that, at time t10, the temperature of the switching element 23a exceeds T1 that is the overheat protection threshold (set value), the control unit 27 stops the brushless motor 9 (duty is set to 0), and sets the overcurrent protection threshold to 10A. The LED 29 is turned on. The user knows the operation of the overheat protection function by stopping the brushless motor 9 and turning on the LED 29, turns off the main trigger switch 18 once, and turns on the main trigger switch 18 again at time t11. During the period from time t10 to time t11, the brushless motor 9 is stopped, but the temperature of the switching element 23a rises due to the influence of the cooling fan 33 being stopped.

  When the main trigger switch 18 is turned on again at time t11, the control unit 27 resumes the driving of the brushless motor 9 with the overcurrent protection threshold 10A and the duty of 30% (resuming the driving of the brushless motor 9 in the low load limited mode). To do). In the low load limiting mode, the overcurrent protection threshold is 10 A, so that no substantial load can be applied. However, the cooling of the brushless motor 9 and the switching element 23 a can be promoted by rotating the cooling fan 33 (naturally). Cooling speed can be increased compared to cooling only). The two-dot chain line in the temperature time chart shows the case of natural cooling only for comparison. During a period from time t11 to time t12 (period in which the brushless motor 9 is driven in the low load limited mode), the cooling effect by the cooling fan 33 exceeds the heat generation effect by driving the brushless motor 9, and the temperature of the switching element 23a is It goes down. At time t12, the temperature of the switching element 23a becomes equal to or lower than T3 (a temperature condition that can cancel overheat protection by the overheat protection function is satisfied), and the control unit 27 turns off the LED 29. A user who knows that the temperature has dropped by turning off the LED 29 turns off the main trigger switch 18 and then turns it on again. Then, the control unit 27 returns the overcurrent protection threshold value to 70 A, and drives the brushless motor 9 with a duty of 100% (drives the brushless motor 9 in the mode set by the mode switch 16). It should be noted that the duty reduction due to the main trigger switch 18 being temporarily turned off at time t12 is not shown.

  FIG. 11 is a flowchart (part 2) of control by the control unit 27 shown in FIG. This flowchart is different from that shown in FIG. 9 in that a function of reducing the duty to 70% (that is, a low power mode) is added when the temperature of the switching element 23a exceeds T2. , Otherwise match. Hereafter, the part regarding a difference is demonstrated. When the temperature of the switching element 23a exceeds T2 while driving the brushless motor 9 under the driving condition of step S2 (S21: YES), the control unit 27 continues until the temperature of the switching element 23a exceeds T1 (S3: NO), the LED 29 is blinked to notify the user, and the brushless motor 9 is driven with a duty of 70% (S22). The overcurrent protection threshold at this time may remain at 70A. Thus, when the temperature T2 lower than the temperature T1 at which the overheat protection function operates is exceeded, the duty is reduced (the effective value of the voltage applied to the brushless motor 9 is reduced), and the low power mode is set. Thus, the temperature rise speed of the switching element 23a can be slowed down to ensure a long working time until the overheat protection function is activated.

  FIG. 12 is an exemplary time chart of this operation of the cordless circle of the embodiment when the control shown in the flowchart of FIG. 11 is performed. In FIG. 12, the temperature T2 for shifting to the low power mode and the temperature T3 at which the overheat protection by the overheat protection function can be canceled are the same, but they may be different.

  When the user turns on the main trigger switch 18 at time t0, the control unit 27 drives the brushless motor 9 with a duty of 100% (drives the brushless motor 9 in the mode set by the mode switch 16). At this time, the threshold for overcurrent protection is 70 A, and the LED 29 is turned off. During the driving of the brushless motor 9, the temperature of the switching element 23a rises. After that, at time t20, the temperature of the switching element 23a exceeds T2, and the control unit 27 blinks the LED 29 to notify the user and reduce the duty to 70% (set to the low power mode). The duty should be lowered gradually. When the duty is decreased, the temperature rise speed of the switching element 23a is decreased. After that, at time t21, the temperature of the switching element 23a exceeds T1, which is the overheat protection threshold, the control unit 27 stops the brushless motor 9 (duty is set to 0), lowers the overcurrent protection threshold to 10A, and the LED 29 Lights up. The user knows the operation of the overheat protection function by stopping the brushless motor 9 and turning on the LED 29, turns off the main trigger switch 18 once, and turns on the main trigger switch 18 again at time t22. During the period from time t21 to time t22, the brushless motor 9 is stopped, but the temperature of the switching element 23a rises due to the influence of the cooling fan 33 being stopped.

  When the main trigger switch 18 is turned on again at time t22, the control unit 27 resumes the driving of the brushless motor 9 with the overcurrent protection threshold 10A and the duty of 30% (resuming the driving of the brushless motor 9 in the low load limited mode). To do). In the period from time t22 to time t23 (period in which the brushless motor 9 is driven in the low load limited mode), the cooling effect by the cooling fan 33 exceeds the heat generation effect by driving the brushless motor 9, and the temperature of the switching element 23a is It goes down. Then, at time t23, the temperature of the switching element 23a becomes equal to or lower than T3 (a temperature condition that can cancel overheat protection by the overheat protection function is satisfied), and the control unit 27 turns off the LED 29. Here, unlike the case of FIG. 10, even if the LED 29 is turned off, the user keeps the main trigger switch 18 on until time t24. For this reason, the control unit 27 continues to drive the brushless motor 9 with a duty of 30% until time t24, and the temperature of the switching element 23a further decreases from T3. At time t24 thereafter, the user turns off the main trigger switch 18 once and turns it on again. Then, the control unit 27 returns the overcurrent protection threshold value to 70 A and drives the brushless motor 9 with a duty of 100%. In addition, illustration of the fall of the duty by the main trigger switch 18 once turning off at the time t24 is abbreviate | omitted. After that, at time t25, the temperature of the switching element 23a exceeds T2, and the control unit 27 blinks the LED 29 to notify the user and reduce the duty to 70% (set to the low power mode).

  According to the present embodiment, the following effects can be achieved.

(1) After the temperature of the switching element 23a exceeds T1 and the brushless motor 9 is stopped by the overheat protection function, when the main trigger switch 18 is turned off and then turned on again, the driving of the brushless motor 9 is resumed in the low load limited mode. Therefore, the switching element 23a can be cooled at a faster speed than natural cooling due to the cooling effect of the cooling fan 33. For this reason, the time until the temperature of the switching element 23a becomes T3 or less and the work can be resumed can be shortened, and the work efficiency can be improved.

(2) Since the overcurrent protection threshold (set value) is set low in the low load limited mode, the switching element 23a is instead driven by driving at a high load such that the heat generation effect by the brushless motor 9 exceeds the cooling effect by the cooling fan 33. Can be prevented from rising.

(3) Since the duty is lower in the low load limited mode than in the case of not in the low load limited mode, the circular saw blade 8 has a lower rotational speed than usual, and thus the user is in the low load limited mode. It is convenient to know.

(4) Since the LED 29 is lit to notify the user until the temperature of the switching element 23a after the activation of the overheat protection function becomes a temperature T3 or less at which the overheat protection by the overheat protection function can be canceled, the temperature of the switching element 23a is It is possible to prevent the user from erroneously performing a high-load work before T3 or less, and the trouble of checking whether the work can be resumed by turning the main trigger switch 18 on and off many times is eliminated.

(5) When the temperature of the switching element 23a exceeds T2, as shown in the control example of FIG. 11, when the duty is reduced to 70% (that is, the low power mode is set), the temperature of the switching element 23a exceeds T2 It is possible to secure a long working time until the overheat protection function is activated by slowing the temperature rise speed. Further, since the LED 29 blinks in the low power mode, it is convenient for the user to know that the mode is the low power mode.

  The present invention has been described above by taking the embodiment as an example. However, it is understood by those skilled in the art that various modifications can be made to each component and each processing process of the embodiment within the scope of the claims. By the way. Hereinafter, modifications will be described.

  The duty and overcurrent protection threshold values are not limited to the specific numerical values exemplified in the embodiment, and can be arbitrarily set. The notification means is not limited to a light notification means (light emission means) like the LED 29, and may be a speaker (sound generation means) for notification by sound, for example. Further, in the above-described embodiment, the low load limited mode is configured to be released when the main trigger switch 18 is turned off and then turned on again after the temperature condition capable of releasing the overheat protection is satisfied. The configuration may be such that the low load limiting mode is automatically canceled when the temperature condition that can cancel the overheat protection is satisfied without turning off the switch 18. The power tool is not limited to the cordless circular saw illustrated in the embodiment, and may be another power tool such as a grinder or an electric planer. The power tool is not limited to the cordless type, and may be a type that is connected to an external AC power source. The motor serving as the drive source is not limited to the brushless motor illustrated in the embodiment, and may be a motor with a brush.

1 base, 2 main body, 3 motor housing, 4 handle part, 4a battery pack mounting part, 4b control circuit board storage part, 5 gear cover, 6 saw cover, 7 protective cover, 8 circular saw blade, 9 brushless motor, 9a output shaft , 9b Rotor core, 9c Rotor magnet, 9d Stator core, 9e Insulator, 9f Stator coil, 10 link, 11 Inclination angle adjustment lever, 12 Bevel plate, 13 Long hole, 14 Rotating support part, 15a Tilt shaft part, 15b Tilt shaft part , 16 mode change switch, 18 main trigger switch, 19 cutting depth adjustment lever, 20 battery pack, 20a terminal, 21 control circuit board, 22 controller cover, 23 switching board, 23a switching element, 24-26 wiring, 27 control Part 28 Inverter unit, 29 LED, 30 remaining amount display unit, 31 temperature sensor, 32 detection resistor, 33 cooling fan

Claims (9)

A motor, a cooling fan rotated by the motor, and an operation unit that switches between driving and stopping the motor,
After the motor is stopped by the overheat protection function, when the operation unit is operated to switch the motor from stop to drive, the motor is driven in a low load limited mode ,
In the low load limited mode , the power tool that reduces the effective value of the voltage applied to the motor while reducing the set value of overcurrent protection .   The power tool according to claim 1, wherein the motor is a brushless motor. Electric tool according to claim 1 or 2 to reduce the effective value by reducing the duty of the PWM signal applied to the switching element for driving control of the motor. According to any one of claims 1-3 comprising informing means for informing outside the period from when the low load limit mode is started until the thermal protection releasable temperature overheating protection are met Power tools. The power tool according to any one of claims 1 to 4 , wherein the low load limiting mode is terminated when a condition for canceling overheat protection by the overheat protection function is satisfied. The release condition, the superheated releasable temperature overheating protection by the protective function is fulfilled, and is that subsequent to the said operating unit to switch the drive from stopping the motor is operated, in claim 5 The electric tool described. In a predetermined temperature range before the overheat protection function works, in a low power mode in which the effective value of the voltage applied to the motor is lower than that in the low load limited mode when the temperature is lower than the temperature range. The power tool according to any one of claims 1 to 6 , which drives the motor. The power tool according to claim 7 , further comprising notification means for notifying the outside that the low power mode is set. The temperature detection means for detecting the temperature of the switching element for driving control of the motor is provided, and the overheat protection by the overheat protection function is activated or canceled according to the temperature detected by the temperature detection means. 8 power tool according to any one of.