Patent Publication Number: US-2023144684-A1

Title: Electric work machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Japanese patent application No. 2021-184131 filed with the Japan Patent Office on Nov. 11, 2021, and the entire disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to an electric work machine. 
     Japanese Unexamined Patent Application No. 2016-93854 discloses an electric apparatus in which a control parameter is corrected to reduce a drive current of a motor when the drive current of the motor exceeds a preset current threshold. Thus, the above described electric apparatus avoids the stop of the motor while inhibiting the drive current when the motor receives a momentary large load. 
     SUMMARY 
     The above-described electric apparatus continues to inhibit the drive current when the motor continuously receives a relatively large load. As a result, with an insufficient output torque, it may be impossible to continue to work with the electric apparatus. 
     In one aspect of the present disclosure, it is preferable to achieve an excellent convenience of the electric work machine. 
     The electric work machine in one aspect of the present disclosure includes an output shaft, a motor, a current measuring circuit, and a controller. The output shaft is attached to or is connected to a tool. The motor drives the output shaft. The current measuring circuit measures a current value. The current value corresponds to a magnitude of a drive current flowing through the motor. The controller sets a maximum value and a threshold. The controller calculates the correction value less than or equal to the maximum value so that the drive current decreases, in response to the current value having reached the threshold. The controller subtracts the calculated correction value from the control parameter, thereby correcting the control parameter. The controller drives the motor based on the corrected control parameter. 
     In the above-described electric work machine, the maximum value of the correction value is set, and the correction value less than or equal to the maximum value is calculated. Then, based on the calculated correction value, the control parameter is corrected. Therefore, when the motor momentarily receives a very large load, it is possible to continue to drive the motor while inhibiting the drive current. Furthermore, when the motor continuously receives a relatively large load, it is possible to avoid the drive current from being continuously inhibited and to increase the drive current as necessary. Thus, it is possible to achieve the excellent convenience of the electric work machine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some embodiments of the present disclosure will be described hereinafter by way of example with reference to the accompanying drawings, in which: 
         FIG.  1    shows an outer appearance of an electric work machine according to a first embodiment; 
         FIG.  2    shows a sectional view showing an internal configuration of the electric work machine according to the first embodiment: 
         FIG.  3    is a block diagram showing an electrical configuration of the electric work machine according to the first embodiment; 
         FIG.  4    is a flow chart showing a procedure of a motor drive process according to the first embodiment; 
         FIG.  5 A  is a part of a flow chart showing a procedure of an output limiting process according to the first embodiment: 
         FIG.  5 B  is a remaining part of the flow chart showing the procedure of the output limiting process according to the first embodiment: 
         FIG.  6 A  is one example of a table showing a limit threshold, presence or absence of a maximum limit, a first maximum limit, and a second maximum limit in a drill mode, a clutch mode, a high speed gear mode, and a low speed gear mode according to the first embodiment; 
         FIG.  6 B  is another example of a table showing the limit threshold, the presence or absence of the maximum limit, the first maximum limit, and the second maximum limit in the drill mode, the clutch mode, the high speed gear mode, and the low speed gear mode according to the first embodiment; 
         FIG.  6 C  is another example of a table showing the limit threshold, the presence or absence of the maximum limit, the first maximum limit, and the second maximum limit in the drill mode, the clutch mode, the high speed gear mode, and the low speed gear mode according to the first embodiment; 
         FIG.  7    is a flow chart showing a procedure of an output process according to the first embodiment; 
         FIG.  8    is a map showing a maximum duty ratio and a desired rotational speed associated with a trigger pulled distance in the drill mode and the clutch mode according to the first embodiment; 
         FIG.  9    is a map showing a reference duty ratio associated with the desired rotational speed according to the first embodiment: 
         FIG.  10    is a time chart showing a time variation of a motor rotational speed, a PWM duty ratio, and the drive current according to the first embodiment; 
         FIG.  11    is a time chart showing a time variation of a motor rotational speed, a PWM duty ratio, and a drive current according to a reference example; 
         FIG.  12    is a flow chart showing a procedure of an output process according to a second embodiment; and 
         FIG.  13    is a map showing a desired duty ratio associated with a trigger pulled distance in a drill mode and a clutch mode according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     [Overview of Embodiments] 
     In one embodiment, an electric work machine may include a tool, an output shaft, a motor, a current measuring circuit and/or a controller. The output shaft may be attached to or be connected to a tool. The motor may drive the output shaft. The current measuring circuit may measure a current value, the current value corresponding to a magnitude of a drive current flowing through the motor. The controller may set a maximum value and a threshold. The controller may calculate the correction value less than or equal to the maximum value so that the drive current decreases, in response to the current value having reached the threshold. The controller may subtract the calculated correction value from the control parameter, thereby correcting the control parameter. The controller may drive the motor based on the corrected control parameter. 
     The controller may calculate a variation based on a first difference and a first gain. The controller may integrate the variation calculated, thereby calculating a correction value. The first difference may correspond to a value obtained by subtracting the threshold from the current value measured by the current measurement circuit. In the electric work machine in one embodiment, any of these features may be deleted. 
     When the electric work machine in one embodiment includes all the above-described features, the controller can momentarily inhibit the drive current by calculating the variation based on the first difference and the first gain. Especially, the controller multiplies the first difference by the first gain to calculate the variation, thereby making it possible to momentarily inhibit the drive current in response to the motor momentarily receiving a very large load. 
     The controller also integrate the variation to calculate the correction value, making it possible to continuously inhibit the drive current when the motor continuously receives a relatively large load. Furthermore, the controller also limits the correction value, thereby making it possible to increase the drive current when a torque is insufficient due to the inhibition of the drive current. Thus, the controller can inhibit the torque from being insufficient in the electric work machine. 
     The control parameter may include a rotational speed of the motor, a voltage applied to the motor, or a duty ratio of a pulse voltage applied to the motor. The controller corrects the rotational speed of the motor, the applied voltage, or the duty ratio, thereby making it possible to inhibit the drive current. 
     The electric work machine in one embodiment may further include a mode selector. The mode selector may be manually operated by a user of the electric work machine to select a first mode or a second mode. The controller may (i) change the maximum value and (ii) the controller may drive the motor, depending on the first mode or the second mode selected by the user through the mode selector. 
     It is possible to achieve the excellent convenience of the electric work machine by changing the maximum value depending on the first mode or the second mode. 
     The mode selector may be furthermore manually operated by the user to select a third mode. The controller may allow the correction value to exceed the maximum value in response to the third mode being selected by the user through the mode selector. 
     This allows the controller to continuously inhibit the drive current when the motor continuously receives a relatively large load in the third mode. 
     The first mode may be a drill mode to drill a hole in a workpiece. The second mode may be a clutch mode to fasten a screw. The controller may set a first value for the first mode, and set a second value distinct from the first value for the second mode. The first value may be a maximum value corresponding to the drill mode. The second value may be a maximum value corresponding to the clutch mode. 
     The magnitude of a load received by the motor in the drill mode is different from the magnitude of a load received by the motor in the clutch mode. By differentiating the first value from the second value, it is possible to achieve a more excellent convenience of the electric work machine. 
     The controller may make the first value larger than the second value. The magnitude of the load received by the motor in the drill mode is larger than the magnitude of the load received by the motor in the clutch mode. Thus, by making the first value larger than the second value, the controller can suitably inhibit the momentary large drive current in the drill mode. 
     The controller may set a third value for the first mode, and set a fourth value distinct from the third value for the second mode. The third value may be a threshold corresponding to the drill mode. The fourth value may be a threshold corresponding to the clutch mode. 
     By differentiating the third value from the fourth value, it is possible to achieve a more excellent convenience of the electric work machine. 
     The controller may make the third value smaller than the fourth value. By making the third value smaller than the fourth value, in the drill mode, a difference between the drive current and the third value increases and the correction value promptly reaches the maximum value. This allows the controller, in the drill mode, to promptly increase the drive current as necessary after limiting an output. 
     The electric work machine in one embodiment may further include two or more gears, and/or a deceleration ratio setter. The two or more gears may transmit the rotation of the motor to the output shaft at a first deceleration ratio or a second deceleration ratio. The second deceleration ratio may be larger than the first deceleration ratio. The deceleration ratio setter may be manually operated by the user of the electric work machine, thereby being set at the first deceleration ratio or the second deceleration ratio. The controller may set a fifth value for the first deceleration ratio, and set a sixth value distinct from the fifth value for the second deceleration ratio. The fifth value may be a maximum value corresponding to the first deceleration ratio. The sixth value may be a maximum value corresponding to the second deceleration ratio. 
     When the electric work machine in one embodiment further includes the two or more gears, and the deceleration ratio setter, it is possible to achieve the more excellent convenience of the electric work machine by differentiating the fifth value from the sixth value. 
     The controller may make the fifth value larger than the sixth value. 
     The controller makes the fifth value larger than the sixth value, thereby making it possible to suitably inhibit the momentary large drive current when the first deceleration ratio is set. 
     The controller may set a seventh value for the first deceleration ratio, and set an eighth value distinct from the seventh value for the second deceleration ratio. The seventh value may be a threshold corresponding to the first deceleration ratio. The eighth value may be a threshold corresponding to the second deceleration ratio. 
     By differentiating the seventh value from the eighth value, it is possible to achieve the excellent convenience of the electric work machine. 
     The controller may make the seventh value larger than the eighth value. 
     The controller makes the seventh value larger than the eighth value, thereby making it possible to promptly increase the drive current as necessary after limiting the output when the first deceleration ratio is set. 
     A method for controlling a motor of an electric work machine, the method including: 
     measuring a current value, the current value corresponding to a magnitude of a drive current flowing through the motor; 
     setting a maximum value and a threshold; 
     calculating the correction value less than or equal to the maximum value so that the drive current decreases, in response to the current value having reached the threshold; 
     subtracting the correction value calculated from the control parameter; and 
     driving the motor based on the control parameter from which the correction value is subtracted. 
     The implementation of the above method makes it possible to achieve the same effects as those of the electric work machine described above. 
     In one embodiment, the above-described features may be combined in any way. In one embodiment, any of the above-described feature may be deleted. 
     [1. First embodiment] 
     &lt;1-1. Configuration&gt; 
     Hereinafter, the mechanical configuration of an electric work machine  10  of this embodiment is described with reference to  FIG.  1    and  FIG.  2   . In this embodiment, the electric work machine  10  is a driver drill. 
     The electric work machine  10  includes a housing  11 . The housing  11  stores various components therein. The housing  11  includes a motor container  14 . The motor container  14  is provided in a rear part of the housing  11  (on the left of the figures). 
     The motor container  14  stores a motor  50 . The motor  50  is a three-phase brushless motor. The housing  11  stores a gear case  31  in front of the motor container  14 . The gear case  31  stores a deceleration mechanism  30 . The deceleration mechanism  30  has an output shaft  7 . Details about the deceleration mechanism  30  will be described below. In this embodiment, the deceleration mechanism  30  is one example of the two or more gears of the present disclosure. 
     The electric work machine  10  includes a chuck portion  16 . The chuck portion  16  is arranged to protrude from a leading end of the housing  11  (on the right of the figures). In the chuck portion  16 , a tool bit (or a tool)  80  is attached to the output shaft  7 . 
     The electric work machine  10  includes a torque selector  29 . The torque selector  29  is arranged in a rear part of the chuck portion  16 . The torque selector  29  is a rotatable annular member. The torque selector  29  is rotated by the user to set a magnitude of a torque (i.e. a tightening force) selected by the user. In a below-described clutch mode, the electric work machine  10  outputs a torque having the selected magnitude. 
     The electric work machine  10  includes a mode selector  27 . The mode selector  27  is arranged behind the torque selector  29 . The mode selector  27  is a rotatable annular member. The mode selector  27  is rotated by the user to set one of the operation modes selected by the user. In this embodiment, the operation modes include a drill mode and a clutch mode. The drill mode is an operation mode to drill a hole in a workpiece. The clutch mode is an operation mode to fasten a screw. In a case where the clutch mode is selected, a clutch is disengaged in response to an output torque reaching the magnitude selected through the torque selector  29 . As a result, the electric work machine  10  does not output a torque having a magnitude more than or equal to the selected magnitude. 
     The electric work machine  10  includes a grip  12  to be held by the user. The grip  12  downwardly protrudes from the housing  11 . The grip  12  includes a trigger  21 . The trigger  21  includes a trigger switch  21   a  to be pulled by the user holding the grip  12 . The trigger  21  includes a speed setter  21   b  including a slide resistor. 
     The electric work machine  10  includes a forward/reverse changeover switch  22 . The forward/reverse changeover switch  22  is arranged above the trigger  21  and at the bottom of the housing  11 . The forward/reverse changeover switch  22  is operated by the user to switch a rotation direction of the motor  50  in a forward direction or a reverse direction. Note that the operation modes may include a forward direction rotation mode and a reverse direction rotation mode. In the forward direction rotation mode, the motor  50  rotates in the forward direction. In the reverse direction rotation mode, the motor  50  rotates in the reverse direction. 
     The electric work machine  10  includes a light  23 . The light  23  is arranged above the trigger  21  and at the bottom of the housing  11 . The light  23  includes one or more light emitting diodes (hereinafter, LEDs). In response to the user pulling the trigger switch  21   a , the light  23  shines on an area in front of the electric work machine  10 . 
     The electric work machine  10  includes a sliding connector  28  provided on the under surface of the bottom of the grip  12 . To the connector  28 , a battery pack  160  is connected by sliding over the connector  28 . 
     The battery pack  160  includes a battery  162  having a specified voltage. The battery  162  is a rechargeable battery that is repeatedly rechargeable, such as a lithium-ion battery. 
     On the top surface of the bottom part of the grip  12 , a remaining capacity indicator  24  is arranged. The remaining capacity indicator  24  includes one or more LEDs and indicates a remaining capacity of the battery  162 . 
     Next, details of the deceleration mechanism  30   a  is described with reference to  FIG.  2   . The deceleration mechanism  30  includes internal gears  32 A,  32 B,  32 C, planetary gears  33 A, planetary gears  33 B, and planetary gears  33 C. The internal gears  32 A,  32 B,  32 C are fixed to the inner peripheral surface of the gear case  31 . The planetary gears  33 A revolve in the internal gear  32 A. The planetary gears  33 B revolve in the internal gear  32 B. The planetary gears  33 C revolve in the internal gear  32 C. 
     The internal gears  32 A,  32 B,  32 C are arranged in this order along a rotation axis direction of the motor  50  from the motor  50  to the leading end of the housing  11 . Similarly, the planetary gears  33 A, the planetary gears  33 B, the planetary gears  33 C are arranged in this order along the rotation axis direction of the motor  50  from the motor  50  to the leading end of the housing  11 . The planetary gears  33 A are arranged around the rotation axis at specified angular intervals. The planetary gears  33 B are arranged around the rotation axis at specified angular intervals. The planetary gears  33 C are arranged around the rotation axis at specified angular intervals. 
     The deceleration mechanism  30  includes carriers  34 A,  34 B,  34 C. The carriers  34 A,  34 B,  34 C are arranged in this order along the rotation axis direction of the motor  50  and rotatable around the rotation axis of the motor  50 . The carrier  34 A is arranged between the planetary gears  33 A and the planetary gears  33 B. The carrier  34 A rotatably supports the planetary gears  33 A and is fitted to the planetary gears  33 B. The carrier  34 B is arranged between the planetary gears  33 B and the planetary gears  33 C, and rotatably supports the planetary gears  33 B, and is fitted to the planetary gears  33 C. The carrier  34 C is arranged on the leading end side relative to the planetary gears  33 C, and rotatably supports the planetary gears  33 C. 
     The planetary gears  33 A are fitted to a pinion gear  50 A fixed to the rotation axis of the motor  50 . To the carrier  34 C, the output shaft  7  is fixed. 
     The rotation of the motor  50  is decelerated in three stages by the planetary gears  33 A- 33 C and the carriers  34 A- 34 C and then transmitted to the output shaft  7 . 
     The deceleration mechanism  30  includes a slide ring  35 . The slide ring  35  is movable in the gear case  31  along the rotation axis direction of the motor  50 . The internal gear  32 B is fixed to the slide ring  35 . 
     The slide ring  35  is physically connected to a gear operator  25 . The gear operator  25  is provided on the top surface of the housing  11 . In response to the user moving the gear operator  25  in a front-rear direction, the slide ring  35  moves along the rotation axis direction of the motor  50 . 
     In response to the user operating the gear operator  25  to move the slide ring  35  from a front end position to a rear end position, the planetary gears  33 B are connected to the carrier  34 A by the internal gear  32 B. This allows the carrier  34 A to rotate together with the carrier  34 B. As a result, the deceleration mechanism  30  decelerates the rotation of the motor  50  in two stages by the planetary gears  33 A,  33 C and the carriers  34 A,  34 C, and then, transmits it to the output shaft  7 . 
     Thus, in response to the user moving the gear operator  25  backward, the rotation of the motor  50  is decelerated at a first reduction ratio (i.e. in two stages), whereby the output shaft  7  rotates at a high speed. In response to the user moving the gear operator  25  forward, the rotation of the motor  50  is decelerated at a second reduction ratio (i.e. in three stages), whereby the output shaft  7  rotates at a low speed. The second deceleration ratio is larger than the first deceleration ratio. Hereinafter, a mode in which the first deceleration ratio is selected by the user is referred to as a high speed gear mode, and a mode in which the second deceleration ratio is selected by the user is referred to as a low speed gear mode. In this embodiment, the gear operator  25  is one example of the deceleration ratio setter of the present disclosure. 
     The use can change the speed as appropriate by operating the gear operator  25 . In a low speed rotation, in which the rotation of the motor  50  is decelerated in three stages, a torque corresponding to the drive current increases compared to a case of a high-speed rotation, in which the rotation of the motor  50  is decelerated in two stages. In one embodiment, at least one of the internal gears  32 A,  32 B,  32 C, the planetary gears  33 A, the planetary gears  33 B, the planetary gears  33 C, the carriers  34 A,  34 B,  34 C, and the slide ring  35  may be excluded. 
     Next, the electric configuration of the electric work machine  10  is described with reference to  FIG.  3   . 
     The electric work machine  10  includes a position sensor  51 . The position sensor  51  includes three Hall ICs. The three Hall ICs are arranged to correspond to three-phase stators of the motor  50 . Each time the rotor of the motor  50  rotates by a predetermined angle, the Hall IC outputs a rotation detection signal to a below-described position detection circuit  71 . 
     The electric work machine  10  includes a switch unit  200 . The switch unit  200  includes a power switch  210   a . In response to a pulled distance of the trigger switch  21   a  being more than or equal to a specified distance, the power switch  210   a  outputs a power-on signal to a below-described power supply circuit  41  and a switch input determiner  62 . In response to the pulled distance of the trigger switch  21   a  being less than the specified distance, the power switch  210   a  outputs a power-off signal to the power supply circuit  41  and the switch input determiner  62 . 
     The switch unit  200  includes the speed setter  21   b . The speed setter  21   b  includes the slide resistor and outputs a resistance value corresponding to the pulled distance of the operation part  21   a  to a desired value calculator  61 . 
     The switch unit  200  includes the forward/reverse changeover switch  22 . In a case where the rotation direction is switched to the forward direction, the forward/reverse changeover switch  22  outputs a forward direction signal to a below-described drive controller  65 . In a case where the rotation direction is switched to a reverse direction, the forward/reverse changeover switch  22  outputs a reverse direction signal to the drive controller  65 . 
     To the switch input determiner  62 , a mode selector  27  outputs an operation mode signal corresponding to the selected operation mode (specifically, the drill mode or the clutch mode). The gear operator  25  outputs a gear mode signal corresponding to the selected gear mode to the switch input determiner  62 . 
     The electric work machine  10  includes a work machine circuit  100 . The work machine circuit  100  includes the power supply circuit  41 . The power supply circuit  41  is connected to the battery  162 . The power supply circuit  41  generates a specified power supply voltage Vcc from an input power in response to the receipt of the power-on signal. The power supply circuit  41  supplies the power supply voltage Vcc to various circuits, such as a control circuit  60  in the work machine circuit  100 . 
     The work machine circuit  100  includes a motor driver  42 . The motor driver  42  is a three-phase full-bridge circuit including three high-side switching elements and three low-side switching elements. The motor driver  42  is connected between the battery  162  and the motor  50 . The motor driver  42  receives an electric power from the battery  162  to allow an electric current to flow through the winding of each phase of the motor  50 . Each switching element of the motor driver  42  is turned on or off in accordance with a control command output from the below-described control circuit  60 . 
     The work machine circuit  100  includes a current measuring circuit  43 . The current measuring circuit  43  measures a value of a drive current flowing through the motor  50  and outputs a measurement signal, corresponding to the value of the measured drive current, to a PWM generator  63 . 
     The work machine circuit  100  includes the position detection circuit  71 . The position detection circuit  71  detects the rotational position of the rotor of the motor  50  based on the rotation detection signal input from the position sensor  51 . The position detection circuit  71  outputs a position signal, corresponding to the detected rotational position, to the control circuit  60 . 
     The work machine circuit  100  includes the control circuit  60 . The control circuit  60  includes a CPU  60   a , a ROM  60   b , a RAM  60   c , and I/O. Various functions of the control circuit  60  are realized by the CPU  60   a  executing a program stored in a non-transitory tangible storage medium. In this embodiment, the ROM  60   b  corresponds to the non-transitory tangible storage medium. By the execution of this program, a method corresponding to the program is carried out. Note that a part or all of the functions executed by the CPU  60   a  may be made up of hardware with one or more ICs. The control circuit  60  may be made up of a single microcomputer or may be made up of two or more microcomputers. In this embodiment, the control circuit  60  corresponds to one example of the controller. 
     The control circuit  60  includes, as various functions, the desired value calculator  61 , the switch input determiner  62 , the PWM generator  63 , a rotational speed calculator  64 , the drive controller  65  and an indicator controller  66 . In this embodiment, the control circuit  60  includes all the above-described various functions; however, in one embodiment, any of the above-described various functions may be excluded. 
     The desired value calculator  61  calculates a desired rotational speed of the motor  50  based on an input resistance value. 
     The switch input determiner  62  determines whether the power source is on or off based on the input power-on signal or power-off signal, and outputs the determination result to the PWM generator  63  and the indicator controller  66 . The switch input determiner  62  determines a selected operation mode based on the input operation mode signal, and outputs the determination result to the PWM generator  63  and the indicator controller  66 . The switch input determiner  62  determines a selected gear mode based on the input gear mode signal, and outputs the determination result to the PWM generator  63  and the indicator controller 
     The rotational speed calculator  64  calculates a rotational speed of the motor  50  based on the position signal input from the position detection circuit  71 , and outputs the calculation result to the PWM generator  63 . 
     The PWM generator  63  generates a PWM signal based on (i) the determination result of the power source being on/off, (ii) the determination result of the operation mode, (iii) the determination result of the gear mode, (iv) the detection signal, (v) the measurement signal, and (vi) the calculation result. The PWM generator  63  outputs the generated PWM signal to the drive controller  65 . 
     The drive controller  65  generates a control command based on (i) the PWM signal output from the PWM generator  63  and (ii) the forward direction signal or reverse direction signal output from the forward/reverse changeover switch  22 . The control command instructs each switching element of the motor driver  42  to turn on or off. The drive controller  65  outputs the generated control command to the motor driver  42 . In this way, a pulsed voltage based on the PWM signal is applied to the winding of each phase of the motor  50 . 
     The electric work machine  10  includes a mode indicator  130 . The mode indicator  130  includes at least one LED. The work machine circuit  100  includes an indicator circuit  72 . The indicator controller  66  causes the mode indicator  130  to notify the operation mode through the indicator circuit  72 , based on the determination result of the input operation mode. That is, the indicator controller  66  causes the mode indicator  130  to turn on, blink, and turn off in accordance with the operation mode. The indicator controller  66  also causes the light  23  to turn on, blink, and turn off through the indicator circuit  72  based on (i) the determination result of the power source being on/off, (ii) the determination result of the operation mode, and (iii) the determination result of the gear mode. 
     &lt;1-2. Process&gt; 
     &lt;1-2-1. Motor Drive Process&gt; 
     Next, a motor drive process executed by the control circuit  60  is described with reference to a flowchart of  FIG.  4   . In response to the power source being turned on and activated, the control circuit  60  starts this process. 
     First, in S 10 , the control circuit  60  stops driving the motor  50 . 
     Then, in S 20 , the control circuit  60  clears a present amount to limit the output. That is, the control circuit  50  makes the amount to limit the output zero. The amount to limit the output includes a below-described amount to limit the rotational speed and/or an amount to limit the duty ratio. 
     Then, in S 30 , the control circuit  60  determines whether the trigger switch  21   a  is pulled by a specified distance or more. Upon the determination that the trigger switch  21   a  is pulled by the specified distance or more (S 30 : YES), the control circuit  60  proceeds to a process of S 40 . Upon the determination that the trigger switch  21   a  is not pulled by the specified distance or more (S 30 : NO), the control circuit  60  returns to the process of S 10 . 
     In S 40 , the control circuit  60  obtains the input operation mode and the input gear mode. In this embodiment, the operation mode is the drill mode or the clutch mode, and the gear mode is the high speed gear mode or the low speed gear mode. In a case where the operation mode includes a forward rotation mode and a reverse rotation mode in addition to the drill mode and the clutch mode, the operation mode obtained by the control circuit  60  includes the drill mode or the clutch mode, and the forward rotation mode or the reverse rotation mode. 
     Then, in S 50 , the control circuit  60  obtains a pulled distance of the trigger switch  21   a  based on a resistance value output from the speed setter  21   b.    
     Then, In S 60 , the control circuit  60  executes an output limiting process, thereby limiting an output of the motor  50 . This makes it possible to avoid damage to the motor  50  and/or the work machine circuit  100  due to an excessive increases in the drive current. 
     Then, in S 70 , the control circuit  60  executes an output process. That is, the control circuit  60  controls the output of the motor  50  based on the amount to limit the output calculated in the output limiting process. Details of the output process will be described below. After the process of S 70 , the control circuit  60  returns to the process of S 30 . 
     &lt;1-2-2. Output Limiting Process&gt; 
     Next, the output limiting process executed by the control circuit  60  is described with reference to the flowcharts of  FIG.  5 A  and  FIG.  5 B . 
     First, in S 100 , the control circuit  60  obtains a value of the present drive current (hereinafter, a drive current value) Inow. 
     Then, in S 110 , the control circuit  60  calculates a difference ΔI. The difference ΔI is a value obtained by subtracting a limit threshold Ith from Inow obtained in S 100 . The limit threshold Ith is decided in accordance with the operation mode and the gear mode, and stored in ROM  60   b .  FIG.  6 A  and  FIG.  6 B  each show one example of a first map of the limit threshold Ith in (i) the drill mode, (ii) the clutch mode, (iii) the high speed gear mode and (iv) the low speed gear mode.  FIG.  6 A  and  FIG.  6 B  each show an example in which the operation mode does not include the forward rotation mode and the reverse rotation mode, showing four sets of various parameters decided based on a combination of the four modes (i) through (iv).  FIG.  6 C  shows an example of the first map in which the operation mode includes the forward rotation mode and the reverse rotation mode.  FIG.  6 C  shows eight sets of various parameters decided based on a combination of six modes (i) through (vi). The six modes (i) through (vi) include (i) the forward drill mode, (ii) the reverse drill mode, (iii) the forward clutch mode, (iv) the reverse clutch mode, (v) the high speed gear mode, and (vi) the low speed gear mode. Various parameters include (i) a limit threshold Ith, (ii) a below-described presence or absence of a maximum limit, (iii) a maximum limit of the amount to limit the rotational speed L_smax, and (iv) a maximum limit of the amount to limit the duty ratio L_dmax. 
     As shown in  FIG.  6 A  and  FIG.  6 B , the limit thresholds Ith in the drill mode are different from the limit thresholds Ith in the clutch mode. Specifically, the limit thresholds Ith in the drill mode are smaller than the limit thresholds Ith in the clutch mode. As shown in  FIG.  6 C , the limit thresholds Ith in the forward drill mode is different from the limit thresholds Ith in the reverse drill mode. Specifically, the limit thresholds Ith in the forward drill mode are smaller than the limit thresholds Ith in the reverse drill mode. 
     As shown in  FIG.  6 A  and  FIG.  6 B , the limit thresholds Ith in the drill mode in the high speed gear mode are different from the limit thresholds Ith in the drill mode in the low speed gear mode. Specifically, the limit thresholds Ith in the drill mode in the high speed gear mode are larger than the limit thresholds Ith in the drill mode in the low speed gear mode. As shown in  FIG.  6 C , the limit threshold Ith in the forward drill mode in the high speed gear mode is different from the limit threshold Ith in forward drill mode in the low speed gear mode. Specifically, the limit threshold Ith in the forward drill mode in the high speed gear mode is larger than the limit threshold Ith in forward drill mode in the low speed gear mode. The control circuit  60  sets the limit threshold Ith based on the operation mode, the gear mode and the first map. 
     Then, in S 120 , the control circuit  60  calculates a first variation ΔL_sp and a second variation ΔL_du. Specifically, the control circuit  60  multiplies the difference ΔI calculated in S 110  by a speed gain Gs, thereby calculating the first variation ΔL_sp. The control circuit  60  also multiplies the difference ΔI by a duty gain Gd, thereby calculating the second variation ΔL_du. If the present drive current value Inow is larger than the limit threshold Ith, the first variation ΔL_sp and the second variation ΔL_du are made positive values to further limit the output. On the other hand, if the present drive current value Inow is smaller than the limit threshold Ith, the first variation ΔL_sp and the second variation ΔL_du are made negative values to ease the limitation of the output. 
     Then, in S 130 , the control circuit  60  adds the first variation ΔL_sp calculated in S 120  to the present amount to limit the rotational speed L_sp, thereby updating the amount to limit the rotational speed L_sp. Thus, the amount to limit the rotational speed L_sp corresponds to an integrated value of the first variation ΔL_sp. 
     Then, in S 140 , the control circuit  60  determines whether the amount to limit the rotational speed L_sp updated in S 130  is less than 0 (i.e. negative value). Upon the determination that the amount to limit the rotational speed L_sp is more than or equal to 0 (S 140 : NO), the control circuit  60  proceeds to S 150 . Upon the determination that the amount to limit the rotational speed L_sp is less than 0 (S 140 : YES), the control circuit  60  proceeds to S 145 . 
     In S 145 , the control circuit  60  sets 0 to the amount to limit the rotational speed L_sp, and proceeds to S 150 . 
     In S 150 , the control circuit  60  determines whether there is the maximum limit of the amount to limit the rotational speed L_smax (hereinafter, first maximum limit L_smax). The presence or absence of the first maximum limit L_smax is decided based on the operation mode and the gear mode, and stored in the ROM  60   b . The first map of each  FIG.  6 A  and  FIG.  6 B  shows one example of the presence or absence of the first maximum limit L_smax in (i) the drill mode, (ii) the clutch mode, (iii) the high speed gear mode, and (iv) the low speed gear mode. The first map of  FIG.  6 C  shows one example of the presence or absence of the first maximum limit L_smax in (i) the forward drill mode, (ii) the reverse drill mode, (iii) the forward clutch mode, (iv) the reverse clutch mode, (v) the high speed gear mode, and (vi) the low speed gear mode. In the example shown in  FIG.  6 A , all the combinations of the modes (i) through (iv) include the first maximum limits L_smax. On the other hand, in the example shown in  FIG.  6 B , a combination of the drill mode and the high speed gear mode does not include the first maximum limit L_smax, and other combinations include the first maximum limits L_smax. In the example shown in  FIG.  6 C , a combination of the forward drill mode and the high speed gear mode does not include the first maximum limit L_smax, and other combinations include the first maximum limits L_smax. The presence or absence of the first maximum limit L_smax is decided based of the operation mode and the gear mode, and a type of electric work machine  10  as well.  FIG.  6 A  shows a decided example for a first-type electric work machine  10 .  FIG.  6 B  shows a decided example for a second-type electric work machine  10 .  FIG.  6 C  shows a decided example for a third-type electric work machine  10 . In the example shown in  FIG.  6 B , the drill mode corresponds to one example of the third mode of the present disclosure. In the example shown in  FIG.  6 C , the forward drill mode corresponds to one example of the third mode of the present disclosure. 
     In S 150 , upon the determination that there is the first maximum limit L_smax (S 150 : YES), the control circuit  60  proceeds to S 160 . Upon the determination that there is not the first maximum limit L_smax (S 150 : NO), the control circuit  60  proceeds to a process of S 180 . 
     In S 160 , the control circuit  60  determines where the amount to limit the rotational speed L_sp updated in S 130  is more than or equal to the first maximum limit L_smax. The first maximum limit L_smax is decided in accordance with the operation mode and the gear mode, and stored in the ROM  60   b . The first map of each  FIG.  6 A  and  FIG.  6 B  shows one example of the first maximum limit L_smax in (i) the drill mode, (ii) the clutch mode, (iii) the high speed gear mode, and (iv) the low speed gear mode. The first map of  FIG.  6 C  shows one example of the first maximum limit L_smax in (i) the forward drill mode, (ii) the reverse drill mode, (iii) the forward clutch mode, (iv) the reverse clutch mode, (v) the high speed gear mode, and (vi) the low speed gear mode. 
     As shown in  FIGS.  6 A and  6 B , the first maximum limits L_smax in the drill mode are different from the first maximum limits L_smax in the clutch mode. Specifically, the first maximum limits L_smax in the drill mode are larger than the first maximum limits L_smax in the clutch mode. As shown in  FIG.  6 C , the first maximum limits L_smax in the forward drill mode are different from the first maximum limits L_smax in the reverse drill mode. Specifically, the first maximum limits L_smax in the forward drill mode are larger than the first maximum limits L_smax in the reverse drill mode. The control circuit  60  sets the first maximum limit L_smax based on the operation mode, the gear mode and the first map. 
     In S 160 , upon the determination that the amount to limit the rotational speed L_sp is more than or equal to the first maximum limit L_smax (S 160 : YES), the control circuit  60  proceeds to a process of S 170 . 
     In S 170 , the control circuit  60  sets the first maximum limit L_smax to the amount to limit the rotational speed L_sp. Therefore, even if the drive current Inow is continuously larger than the limit threshold Ith, once the amount to limit the rotational speed L_sp reaches the first maximum limit L_smax, the amount to limit the rotational speed L_sp does not increase any further. 
     Thus, when the motor  50  momentarily receives a very large load, the control circuit  60  can inhibit a momentary increase in the drive current. When the motor  50  continuously receives a relatively large load, the control circuit  60  can increase the drive current as necessary. 
     For example, in a case where the user drills a hole in wood with the electric work machine  10 , the motor  50  momentarily receives a very large load when the tool bit hits a knot in the wood. As a result, the control circuit  60  limits the output of the electric work machine  10 . When the user continues drilling and the hole gets deeper, the motor  50  continuously receives a relatively large load. This relatively large load is smaller than the load when the tool bit hits a knot. If the control circuit  50  continues to limit the drive current of the motor  50 , the electric work machine  10  cannot output a necessary torque, and the work by the electric work machine  10  stops. In contrast, the amount to limit the rotational speed L_sp is set to be less than or equal to the first maximum limit L_smax, whereby the control circuit  60  increases the drive current of the motor  50  as necessary. Therefore, the stop of the work by the electric work machine  10  can be avoided. The control circuit  60  proceeds to a process of S 180  after the process of S 170 . 
     On the other hand, in S 160 , upon the determination that the amount to limit the rotational speed L_sp is less than the first maximum limit L_smax (S 160 : NO), the control circuit  60  proceeds to S 180 . 
     In S 180 , the control circuit  60  adds the second variation ΔL_du calculated in S 120  to the amount to limit the duty ratio L_du, thereby updating the amount to limit the duty ratio L_du. Therefore, the amount to limit the duty ratio L_du corresponds to an integrated value of the second variation ΔL_du. 
     Then, in S 190 , the control circuit  60  determines whether the amount to limit the duty ratio L_du updated in S 180  is less than 0 (i.e. negative value). Upon the determination that the amount to limit the duty ratio L_du is more than or equal to 0 (S 190 : NO), the control circuit  60  proceeds to a process of S 210 . Upon the determination that the amount to limit the duty ratio L_du is less than 0 (S 190 : YES), the control circuit  60  proceeds to a process of S 200 . 
     In S 200 , the control circuit  60  sets 0 to the amount to limit the duty ratio L_du and proceeds to a process of S 210 . 
     In S 210 , the control circuit  60  determines whether there is the maximum limit of the amount to limit the duty ratio L_dmax (hereinafter, second maximum limit L_dmax). As in the case of the presence or absence of the first maximum limit L_dmax, the presence or absence of the second maximum limit L_dmax is decided based on the operation mode and the gear mode, and is stored in the ROM  60   b . In this embodiment, as shown in  FIGS.  6 A,  6 B, and  6 C , the presence or absence of the second maximum limit L_dmax corresponds to the presence or absence of the first maximum limit L_smax. However, the presence or absence of the second maximum limit L_dmax may be decided independently of the presence or absence of the first maximum limit L_dmax. 
     In S 210 , upon the determination that there is the second maximum limit L_dmax (S 210 : YES), the control circuit  60  proceeds to a process of S 220 . Upon the determination that there is not the second maximum limit L_dmax (S 210 : NO), the control circuit  60  ends this process. 
     In S 220 , the control circuit  60  determines whether the amount to limit the duty ratio L_du updated in S 180  is more than or equal to the second maximum limit Ldmax. The second maximum limit L_dmax is decided based on the operation mode and the gear mode, and stored in the ROM  60   b .  FIG.  6 A  and  FIG.  6 B  each show one example of the first map of the second maximum limit L_dmax in (i) the drill mode, (ii) the clutch mode, (iii) the high speed gear mode, and (iv) the low speed gear mode.  FIG.  6 C  shows one example of the first map of the second maximum limit L_dmax in (i) the forward drill mode, (ii) the reverse drill mode, (iii) the forward clutch mode, (iv) the reverse clutch mode, (v) the high speed gear mode, and (vi) the low speed gear mode. 
     As shown in  FIGS.  6 A and  6 B , the second maximum limit L_dmax in the drill mode is different from the second maximum limit L_dmax in the clutch mode. Specifically, the second maximum limit L_dmax in the drill mode is larger than the second maximum limit L_dmax in the clutch mode. Also, as shown in  FIG.  6 C , the second maximum limit L_dmax in the forward drill mode is different from the second maximum limit L_dmax in the reverse drill mode. Specifically, the second maximum limit L_dmax in the forward drill mode is larger than the second maximum limit L_dmax in the reverse drill mode. 
     As shown in  FIG.  6 A , the second maximum limit L_dmax in the drill mode in the high speed gear mode is different from the second maximum limit L_dmax in the drill mode in the low speed gear mode. Specifically, the second maximum limit L_dmax in the drill mode in the high speed gear mode is larger than the second maximum limit L_dmax in the drill mode in the low speed gear mode. 
     In S 220 , upon the determination that the amount to limit the duty ratio L_du is more than or equal to the second maximum limit L_dmax (S 220 : YES), the control circuit  60  proceeds to a process of S 230 . 
     In S 230 , the control circuit  60  sets the second maximum limit L_dmax to the amount to limit the duty ratio L_du. Therefore, even if the drive current Inow is continuously larger than the limit threshold Ith, once the amount to limit the duty ratio L_du reaches the second maximum limit L_dmax, the amount to limit the duty ratio L_du does not increase any further. Thus, when the motor  50  momentarily receives a very large load, the control circuit  60  can inhibit a momentary increase in the drive current. When the motor  50  continuously receives a relatively large load, the control circuit  60  can increase the drive current as necessary. The control circuit  60  ends this process after the process of S 230 . 
     On the other hand, in S 220 , upon the determination that the amount to limit the duty ratio L_du is less than the second maximum limit L_dmax (S 220 : NO), the control circuit  60  ends this process. 
     &lt;1-2-3. Output Process&gt; 
     Next, the output process executed by the control circuit  60  is described with reference to the flowchart of  FIG.  7   . 
     First, in S 300 , the control circuit  60  obtains a maximum duty ratio Max_du based on (i) the mode obtained in S 40 , (ii) the pulled distance obtained in S 50 , and (iii) a second map. The second map shows the maximum duty ratio Max_du associated with the trigger pulled distance in each of the drill mode and the clutch mode, and is stored in the ROM  60   b .  FIG.  8    shows one example of the second map of this embodiment. 
     Subsequently, in S 310 , the control circuit  60  obtains a desired rotational speed Tg_sp based on (i) the mode obtained in S 40 , (ii) the pulled distance obtained in S 50 , and (iii) the second map. The second map shows a desired rotational speed Tg_sp associated with the trigger pulled distance in each of the drill mode and the clutch mode, 
     In S 310 , the control circuit  60  subtracts the amount to limit the rotational speed L_sp from the desired rotational speed Tg_sp obtained from the second map, thereby correcting the desired rotational speed Tg_sp. The amount to limit the rotational speed L_sp is a value calculated in the output limiting process. 
     Then, in S 320 , the control circuit  60  obtains a reference duty ratio Bs_du of the PWM signal in accordance with the corrected desired rotational speed Tg_sp obtained in S 310 . Specifically, the control circuit  60  obtains the reference duty ratio Bs_du based on a third map in which the desired rotational speed Tg_sp is associated with the reference duty ratio Bs_du. The third map is stored in ROM  60   b .  FIG.  9    shows one example of the third map of this embodiment. 
     Then, in S 330  through S 360 , the control circuit  60  calculates a proportional correction amount Off_p and an integral correction amount Off_i to execute a feedback control of the rotational speed of the motor  50  based on the proportional-integral control. The proportional correction amount Off_p and the integral correction amount Off_i are feedback correction amounts. 
     First, in S 330 , the control circuit  60  calculates a speed difference ΔSP. The speed difference ΔSP is a value obtained by subtracting a present actual rotational speed Now_sp from the desired rotational speed Tg_sp. 
     Subsequently, in S 340 , the control circuit  60  multiplies the speed difference ΔSP calculated in S 330  by a proportional gain Gp, thereby calculating the proportional correction amount Off_p. 
     Then, in S 350 , the control circuit  60  adds the speed difference ΔSP calculated in S 330  to a present cumulative difference D_int, thereby updating the cumulative difference D_int. 
     Subsequently, in S 360 , the control circuit  60  multiplies the cumulative difference D_int, which was updated in S 350 , by an integral gain Gi, thereby calculating the integral correction amount Off_i. 
     Then, in S 370 , the control circuit  60  adds (i) the proportional correction amount Off_p calculated in S 340  and (ii) the integral correction amount Off_i calculated in S 360  to the reference duty ratio Bs_du obtained in S 320 , thereby calculating the set duty ratio Set_du. 
     Then, in S 380 , the control circuit  60  determines whether the set duty ratio Set_du calculated in S 370  is larger than the maximum duty ratio Max_du obtained in S 300 . Upon the determination that the set duty ratio Set_du is less than or equal to the maximum duty ratio Max_du (S 380 : NO), the control circuit  60  proceeds to a process of S 400 . Upon the determination that the set duty ratio Set_du is larger than the maximum duty ratio Max_du (S 380 : YES), the control circuit  60  proceeds to a process of S 390 . 
     In S 390 , the control circuit  60  sets the maximum duty ratio Max_du to the set duty ratio Set_du. This inhibits the drive current from exceeding a protection threshold. 
     Then, in S 400 , the control circuit  60  subtracts the amount to limit the duty ratio L_du from the set duty ratio Set_du, thereby calculating the output duty ratio Out_du. The amount to limit the duty ratio L_du is a value calculated in the output limiting process. Then, the control circuit  60  generates a control command based on the output duty ratio Out_du and outputs the control command to the motor driver  42 . 
     &lt;1-3. Operation&gt; 
       FIG.  10    shows a time variation of the actual rotational speed of the motor  50 , the duty ratio of the PWM signal, and the drive current when the control circuit  60  executes the motor drive process of this embodiment. 
     As shown in  FIG.  10   , at a time point t 1 , the motor  50  receives a load and the actual rotational speed begins to decrease. In response to the decrease in the actual rotational speed, the drive current begins to increase to make the actual rotational speed closer to the desired rotational speed. At a time point t 2 , in response to the value of the drive current exceeding the limit threshold, an output is started to be limited. As a result, the duty ratio decreases from 100%, and the drive current decreases following the decrease in the duty ratio. At a time point t 3 , a continuous limitation of the output is started. 
     At a time point t 4 , the motor  50  receives a very large load, and the actual rotational speed rapidly decreases, and the drive current rapidly increases. Due to this rapid increase in the drive current, the amount to limit the output increases and the duty ratio decreases to 50%, and the drive current significantly decreases. With the increase in the amount to limit the output, the amount to limit the output reaches the maximum limit. As a result, the duty ratio is constant at 50%, and is not lower than 50%. 
     At a time point t 5 , in response to the electric work machine  10  requiring a drive current larger than the limited drive current, the duty ratio increases and the drive current increases. That is, the control circuit  60  increases the drive current as necessary while inhibiting a rapid increase in the drive current. 
     As comparison with this embodiment,  FIG.  11    shows a time variation of a rotational speed of a motor  50 , a duty ratio of a PWM signal, and a drive current in a reference example. In the reference example, the control circuit  60  does not set the limit threshold and does not execute the output limiting process. 
     In  FIG.  11   , when the motor  50  receives a load and the actual rotational speed starts to decrease, the drive current starts to increase. At a time point t 10 , when a value of the drive current exceeds the protection threshold, the duty ratio rapidly decreases from 100% to 0%, and the value of the drive current becomes zero and the motor  50  stops. 
     &lt;1-4. Effects&gt; 
     In the first embodiment detailed above, the following effects can be obtained. 
     (1) The first and second maximum limits are set, and upon the determination that the drive current value exceeds the limit threshold, the amounts to limit the rotational speed and the duty ratio, which are less than the first and second maximum limits, are calculated. Then, based on the calculated amounts to limit the rotational speed and the duty ratio, the desired rotational speed and the output duty ratio are corrected. Therefore, when the motor  50  momentarily receives a very large load, the control circuit  60  can inhibit the drive current and continue to drive the motor  50 . Furthermore, when the motor  50  continuously receives a relatively large load, the control circuit  50  can avoid the drive current from being continuously inhibited and increase the drive current as necessary. 
     (2) The control circuit  60  integrates the first and second variations in the limit of each of the rotational speed and the duty ratio, thereby calculating each amounts to limit the rotational speed and the duty ratio. This allows the control circuit  60  to momentarily inhibit the drive current when the motor  50  momentarily receives a very large load. The control circuit  60  can increase the drive current as necessary when the motor  50  continuously receives a relatively large load. 
     (3) The first and second maximum limits in the drill mode is set to be larger than the first and second maximum limits in the clutch mode. This allows the control circuit  60  to suitably inhibit the momentary large drive current in the drill mode. 
     (4) After drilling a hole with the electric work machine  10  in the forward drill mode, the user set the electric work machine  10  in the reverse drill mode to pull the tool bit out of the hole. Thus, in the reverse drill mode, it is assumed that a continuous load is not applied to the motor  50 . Thus, in the reverse drill mode, the first and second maximum limits are set to be relatively small. This improves working efficiency. 
     (5) The limit threshold in the drill mode, or the forward drill mode is set to be smaller than the limit threshold in the clutch mode, or in the reverse drill mode. This increases a difference between the drive current and the limit threshold in the drill mode or the forward drill mode, and each of the amount to limit the rotational speed and the amount to limit the duty ratio quickly reaches the maximum limit. Therefore, in the drill mode or the forward drill mode, the control circuit  60  can promptly increase the drive current as necessary after limiting the output. 
     (6) The second maximum limit in the high speed gear mode is set to be larger than the second maximum limit in the low speed gear mode. This allows the control circuit  60  to suitably inhibit the momentary large drive current in the high speed gear mode. 
     (7) The limit threshold in the high speed gear mode is set to be larger than the limit threshold in the low speed gear mode. This allows the control circuit  60 , in a high speed gear mode, to promptly increase the drive current as necessary after limiting the output. 
     (8) In the drill mode in the high speed gear mode, or in the forward drill mode in the high speed gear mode, the first and second maximum limits are not set. This allows the control circuit  60  to continuously inhibit the drive current when the motor  50  continuously receives a relatively large load in the drill mode in the high speed gear mode, or in the forward drill mode in the high speed gear mode. 
     [2. Second Embodiment] 
     &lt;2-1. Difference from First Embodiment&gt; 
     The basic configuration of a second embodiment is similar to that of the first embodiment, and thus, differences are described hereinafter. The reference numerals same as those in the first embodiment indicate the same configurations and refer to the preceding description. 
     In the above-described first embodiment, the control circuit  60  performed the feedback control of the rotational speed of the motor  50 . In contrast, in the second embodiment, the control circuit  60  is different from the first embodiment in that the control circuit  60  controls the rotational speed of the motor  50  without feedback. That is, the second embodiment is different from the first embodiment in the output process of the motor drive process. 
     In the second embodiment, the control circuit  60  calculates only the amount to limit the duty ratio L_du in the output limiting process and does not need to calculate the amount to limit the rotational speed L_sp. The desired value calculator  61  calculates a desired duty ratio Tg_du based on the resistance value output from the speed setter  21   b  and a determination result of the operation mode output from the switch input determiner  62 . The second embodiment does not necessarily include a function of the rotational speed calculator  64 . 
     &lt;2-2. Output Process&gt; 
     Next, an output process executed by the control circuit  60  is described with reference to the flowchart of  FIG.  12   . 
     First, in S 500 , the control circuit  60  obtains a desired duty ratio Tg_du based on (i) the mode obtained in S 40 , (ii) the pulled distance obtained in S 50 , and (iii) a fourth map. The fourth map shows the desired duty ratio Tg_du associated with the trigger pulled distance in each of the drill mode and the clutch mode, and is stored in the ROM  60   b .  FIG.  13    shows one example of the fourth map of this embodiment. 
     Then, in S 510 , the control circuit  60  determines whether the desired duty ratio Tg_du obtained in S 500  is larger than the presently-set set duty ratio Set_du. Upon the determination that the desired duty ratio Tg_du is less than or equal to the set duty ratio Set_du (S 510 : NO), the control circuit  60  proceeds to a process of S 520 . In S 520 , the control circuit  60  sets the desired duty ratio Tg_du to the set duty ratio Set_du and proceeds to a process of S 540 . 
     Upon the determination that the desired duty ratio Tg_du is larger than the set duty ratio Set_du in S 510  (S 510 : YES), the control circuit  60  proceeds to a process of S 530 . In S 530 , the control circuit  60  adds an incremental duty ratio Inc_du to the set duty ratio Set_du, thereby updating the set duty ratio Set_du and proceeds to a process of S 540 . The incremental duty ratio Inc_du is a constant value set beforehand. 
     Then, in S 540 , the control circuit  60  subtracts the amount to limit the duty ratio L_du from the set duty ratio Set_du, thereby calculating the output duty ratio Out_du. The amount to limit the duty ratio L_du is a value calculated in the output limiting process. Then, the control circuit  60  generates a control command based on the output duty ratio Out_du and outputs the control command to the motor driver  42 . 
     &lt;2-3. Effects&gt; 
     In the second embodiment detailed above, the above-described effects (3) through (6) of the first embodiment can be achieved, and furthermore, the following effects can be achieved. 
     (9) The second maximum limit is set. Upon the determination that the drive current value exceeds the limit threshold, the control circuit  60  calculates the amount to limit the duty ratio that is less than or equal to the second maximum limit, thereby correcting the output duty ratio based on the calculated amount to limit the duty ratio. Therefore, when the motor  50  momentarily receives a very large load, the control circuit  60  can inhibit the drive current and continue to drive the motor  50 . Furthermore, when the motor  50  continuously receives a relatively large load, the control circuit  60  avoids the continuous inhibition of the drive current and can increase the drive current as necessary. 
     (10) The control circuit  60  integrates the second variation, thereby calculating the amount to limit the duty ratio. This allows the control circuit  60  to momentarily inhibit the drive current when the motor  50  momentarily receives a very large load. The control circuit  60  can increase the drive current as necessary when the motor  50  continuously receives a relatively large load. 
     [3. Other Embodiments] 
     Some embodiments of the present disclosure have been described; however, the present disclosure may be embodied in various forms without limited to the above-described embodiments. 
     (a) In the above described embodiments, the electric work machine  10  includes the two operation modes; however, the electric work machine  10  may include three or more operation modes. In the above described embodiments, the electric work machine  10  includes the two gear modes; however, the electric work machine  10  may include three or more gear modes. The operation modes may include an operation mode that does not set the first and/or second maximum limits, and the gear modes may include a gear mode that does not set the first and/or second maximum limit. 
     (b) In the above described embodiments, the control circuit  60  controls the motor  50  by the PWM control; however, the control circuit  60  may control the motor  50  by a method other than the PWM control. For example, the control circuit  60  may control the motor  50  by a pulse voltage amplitude modulation (PAM) control. Examples of control parameters controlling the motor  50  in the PAM control include an applied voltage applied to the motor  50 . When the control circuit  60  controls the motor  50  by the PAM control, in place of the amount to limit the duty ratio L_du, an amount to limit the applied voltage may be calculated, and, in place of the second maximum limit L_du, a maximum limit of the amount to limit the applied voltage may be set. The control circuit  60  may calculate the amount to limit the applied voltage so as to be less than or equal to the set maximum limit of the amount to limit the applied voltage. Then, the control circuit  60  may calculate the value of the applied voltage based on the operation mode and/or the gear mode and/or the pulled distance of the trigger switch  21   a , and may subtract the amount to limit the applied voltage from the calculated applied voltage. 
     (c) The electric work machine  10  is not limited to the driver drill. The electric work machine  10  may be any electric work machine if it includes a tool bit. For example, the electric work machine  10  may be an electric power tools such as reciprocating saws, jigsaws, and hammer drills, or gardening tools such as grass mowers. 
     (d) In place of or in addition to the microcomputer, the control circuit  60  may include a combination of individual various electronic components, and/or may include Application Specified Integrated Circuit (ASIC), Application Specific Standard Product (ASSP), a programmable logic device such as Field Programmable Gate Array (FPGA), and a combination thereof. 
     (e) A plurality of functions of one element of the aforementioned embodiments may be performed by a plurality of elements, and one function of one element may be performed by a plurality of elements. Furthermore, a plurality of functions of a plurality of elements may be performed by one element, and one function performed by a plurality of elements may be performed by one element. A part of the configurations of the aforementioned embodiments may be omitted. Furthermore, at least part of the configurations of the aforementioned embodiments may be added to or replaced with the configurations of the other above-described embodiments.