Electric tool

Abstract

To provide a cordless electric tool promoting a fastening function or a cutting function by facilitating to control a rotational number of a motor from a low speed region to a high speed region, reducing generation of vibration or noise and achieving small-sized formation and light-weighted formation, there is provided a cordless electric tool constituted by a brushless direct current motor 3 , an output shaft 5 connected to the brushless direct current motor 3 via a speed changing device 4 , a motor driving circuit 7 and a control portion 8 of the driving circuit and using a charge type battery 11 as a drive power source.

Claims

What is claimed is: 1 . An electric tool which is a cordless electric tool comprising a motor, an output shaft connected to the motor via a speed changing device, a motor driving circuit and a control portion of the driving circuit and using a charge type battery as a drive power source: wherein the motor is a brushless direct current motor. 2 . An electric tool comprising: a brushless direct current motor constituting a power source of the electric tool; a first operating member for changing a maximal rotational speed of the brushless direct current motor; a second operating member for changing a rotational speed of the brushless direct current motor within a range of the maximal rotational speed of the brushless direct current motor set by the first operating member; and controlling means for controlling a rotational state of the brushless direct current motor; wherein the controlling means comprises: maximal rotational speed signal outputting means for outputting a maximal rotational speed signal in correspondence with a displacement of the first operating member; and rotational speed signal outputting means for constituting a maximal level by the maximal rotational speed signal outputted from the maximal rotational speed signal outputting means and outputting a rotational speed signal in correspondence with a displacement of the second operating means to thereby drive to rotate the brushless direct current motor. 3 . The electric tool according to claim 1 or 2 : wherein the electric tool is an electric driver, an electric driver drill, an electric impact driver or an electric wrench.
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an electric tool. [0003] 2. Description of the Related Art [0004] Conventionally, there has generally been used an electric tool such as an electric drill or an electric driver of a portable type as an electric tool used for operation of cutting such as drilling or fastening a screw or a bolt. The electric tool is provided with functions of controlling rotational speed or rotational torque of a drive motor and switching a rotational direction and is capable of interchanging a front end tool thereof. [0005] Particularly, in recent years, a cordless electric tool having a direct current motor with brush constituting a power source by a charge type battery, is simple in operation, excellent in operability and spreads also for household use. [0006] An explanation will be given of an outline of an inner constitution (indicated by broken lines) of an example of a conventional cordless electric tool in reference to an outlook view of an electric driver drill 200 capable of using both of a driver and a drill shown in FIG. 7. [0007] The cordless electric driver drill 200 shown in the drawing, is constituted by a driving portion 215 comprising a motor 203 constituting a drive source, a speed changing device 204 containing a gear mechanism for reducing a rotational number of the motor 203 and an output shaft 205 connected to the speed changing device 204 , an operating portion 216 having a motor driving circuit 207 , a control portion 208 thereof and a switch 209 for controlling power supply, and a power source portion 217 comprising a charge type battery 211 and the electric driver drill 200 is formed by a housing 202 . [0008] The operating portion 216 is contained at inside of a grip portion 210 , the charge type battery 211 is attachably and detachably provided at a lower portion of the grip portion 210 , power thereof is transmitted to the driving portion 215 via the control portion 208 and the motor driving circuit 207 by operation of the switch 209 , ON/OFF and the rotational number of the motor 203 are controlled, rotational force is transmitted to a drill (not illustrated) mounted to a chuck 206 provided at a front end of the output shaft 205 , further, at a vicinity of the switch 209 , there is provided a switch 212 for switching a rotational direction of the motor 203 and locking the rotational direction. [0009] According to the above-described conventional electric driver drill 200 , there is used a direct current motor with brush as the motor 203 of the drive source. [0010] The direct current motor with brush is rotated at high speed and therefore, it is difficult to control speed of the motor, it is difficult to continuously control the rotational number of the electric driver drill 200 in a low through high speed region and a range of the rotational number which can be used, is divided into a low speed region and high speed region and a restriction is imposed on use of continuous variable speed over the two speed regions. [0011] Further, control of the rotational number is controlled by switching operation and therefore, the control needs an expensive switch and is inferior in operability since controllability thereof is poor. [0012] Further, since the motor is rotated at high speed, it is necessary to use the motor by increasing a speed reduction ratio by gears and therefore, there poses a problem that vibration or noise is generated significantly, further, the tool is heavy and large since a comparatively large-sized speed changing device is used and the operability is poor. [0013] Further, there poses a problem of noise by generating spark in rotating the brush, noise of a radio, a disturbance of a television screen, generation of noise by sliding movement of the brush and a commutator. Further, the brush is accompanied by service life and there is needed maintenance such as check or interchange of the brush or the motor. [0014] Hence, it is a first object of the invention to provide a cordless electric tool facilitating to control a rotational number of a drive motor from a low speed region to a high speed region, promoting functions of cutting and fastening by selecting a rotational number over a wide range, reducing generation of vibration and noise and achieving small-sized formation, light-weighted formation and long life formation. [0015] Next, FIG. 8 is a view showing an outline of a constitution of an operating portion 301 of the above-described electric tool and FIG. 9 is a circuit diagram showing an electric constitution of a lever switch circuit 304 of the operating portion 301 of the electric tool. [0016] An explanation will be given of the operating portion 301 of the electric tool also in reference to FIG. 8 and FIG. 9. [0017] The operating portion 301 of the electric tool is constituted by including an operating portion main body 302 including a battery, a motor and a motor control circuit, and an operating lever 303 belonging to the operating portion main body 302 and operated by the hand and the finger of an operator. [0018] The operating portion 301 of the electric tool is provided with the lever switch circuit 304 for outputting a pulse width modulated signal (hereinafter, referred to as PWM signal) for driving the motor in correspondence with an operational state of the operating lever 303 . The lever switch circuit 304 is provided with a slide resistor circuit 305 . The slide resistor circuit 305 is provided with a resistor R 1 and a slide terminal 306 and the resistor R 1 is provided between power source voltage Vdd and ground potential. Reference voltage Vth constituting an output of the slide terminal 306 , is inputted to a noninverting input terminal of a comparing circuit 307 and an inverting input terminal of the comparing circuit 307 is inputted with a predetermined triangular wave signal. [0019] An explanation will be given of operation of the lever switch circuit 304 . [0020] Displacement of the operating lever 303 in an arrow mark A 1 direction or an arrow mark A 2 direction, is detected by the slide resistor circuit 305 . At this occasion, when the operating lever 303 is operated in the arrow mark A 1 direction, the rotational speed of the motor is increased and when the operating lever 303 is operated in the arrow mark A 2 direction, the rotational speed of the motor is reduced. [0021] In this case, in correspondence with displacement of the slide terminal 306 in an arrow mark displacement direction A 3 , or the displacement of the slide terminal 306 in an arrow mark A 4 direction in correspondence with the arrow mark A 1 direction or the arrow mark A 2 direction constituting the direction of operating the operating lever 303 , there is outputted the reference voltage Vth an output level of which is increased or reduced from the slide terminal 306 and is inputted to the noninverting input terminal of the comparing circuit 307 . [0022] Thereby, in correspondence with operation of the operating lever 303 in the arrow mark A 1 direction or the arrow mark A 2 direction, there is outputted a rotational speed signal S 1 constituting the PWM signal in which on duty of the triangular wave signal is pertinently controlled from the comparing circuit 307 and the rotational speed signal constitutes the output of the lever switch circuit 304 . The rotational speed signal S 1 drives to rotate the motor via, for example, an inverter circuit including a switching transistor for driving the motor. [0023] In the case of the operating portion 301 of the conventional electric tool, when actual operation is carried out, depending on content of the operation, there is a case in which the operation is carried out at intermediate rotational speed lower than maximal rotational speed of the operating portion 301 of the electric tool. In such a case, the operator carries out the operation not in a state of completely gripping to tighten the operating lever 303 but in a state of gripping the lever intermediately and when the operational time period is prolonged, there causes a drawback that the rotational speed becomes unstable owing to fatigue of the hand and the finger, or fatigue of the operator is increased. [0024] Hence, it is a second object of the invention to provide an electric tool capable of carrying out stable operation by preventing enormous fatigue from being effected to the operator. SUMMARY OF THE INVENTION [0025] According to a first aspect of the invention, there is provided an electric tool which is a cordless electric tool comprising a motor, an output shaft connected to the motor via a speed changing device, a motor driving circuit and a control portion of the driving circuit and using a charge type battery as a drive power source wherein the motor is a brushless direct current motor. [0026] According to a second aspect of the invention, there is provided an electric tool comprising a brushless direct current motor constituting a power source of the electric tool, a first operating member for changing a maximal rotational speed of the brushless direct current motor, a second operating member for changing a rotational speed of the brushless direct current motor within a range of the maximal rotational speed of the brushless direct current motor set by the first operating member, and controlling means for controlling a rotational state of the brushless direct current motor, wherein the controlling means comprises maximal rotational speed signal outputting means for outputting a maximal rotational speed signal in correspondence with a displacement of the first operating member, and rotational speed signal outputting means for constituting a maximal level by the maximal rotational speed signal outputted from the maximal rotational speed signal outputting means and outputting a rotational speed signal in correspondence with a displacement of the second operating means to thereby drive to rotate the brushless direct current motor. [0027] According to a third aspect of the invention, there is provided the electric tool according to the first or the second aspect wherein the electric tool is an electric driver, an electric driver drill, an electric impact driver or an electric wrench. [0028] According to the electric tool of the first aspect of the invention, the drive source is constituted by the brushless direct current motor and therefore, power consumption can be restrained to be small since the motor efficiency is high, further, a control range of the rotational number becomes wide, control of the rotational number of the electric tool from the low speed region to the high speed region is facilitated and therefore, a width of selecting a rotational function of the electric tool becomes wide, the rotational function in accordance with the use can easily be achieved and an expensive switch for controlling the rotational number is dispensed with. [0029] Further, by using the brushless direct current motor, the service life of the tool is prolonged, maintenance is promoted and the problem of generation of spark in rotation is resolved. [0030] Further, the speed ratio by the gears of the rotational number of the motor can be reduced, further, sliding sound of the brush can be eliminated, generation of vibration or noise can be restrained, further, the speed changing device can be made small-sized and therefore, small-sized formation and light-weighted formation of the electric tool can be achieved. [0031] According to the electric tool of the second aspect of the invention, the maximal rotational speed of the brushless direct current motor is changed and set by operating the first operating member. Based on operation of the first operating member, the maximal rotational speed signal is outputted from the maximal rotational speed signal outputting means included in the controlling means. Further, the second operating member is operated in order to change the rotational speed of the brushless direct current motor. [0032] Based on operation of the second operating means, the rotational speed signal outputting means included in the controlling means constitutes the maximal level by the maximal rotational speed signal and the rotational speed signal in correspondence with the displacement of the second operating means is outputted to thereby drive to rotate the brushless direct current motor. [0033] Therefore, when the rotational speed necessary for actual operation is set to the maximal rotational speed of the electric tool by using the first operating means, in the case of operating the second operating means, the rotational speed of the brushless direct current motor is changed within the range of the maximal rotational speed of the brushless direct current motor set by the first operating means and in the case of constituting the maximal rotational speed by maximally operating the second operating means, the rotational speed necessary for the operation is constituted. BRIEF DESCRIPTION OF THE DRAWINGS [0034] [0034]FIG. 1 is an outlook view of an electric driver drill according to a first embodiment; [0035] [0035]FIG. 2 is a block diagram of a motor driving circuit; [0036] [0036]FIG. 3 is a circuit diagram showing an electric constitution of an essential portion of an electric impact driver; [0037] [0037]FIG. 4 is a block diagram showing an electric constitution of the electric impact driver; [0038] [0038]FIG. 5 is a outlook view of an electric impact driver; [0039] [0039]FIG. 6 is a circuit diagram showing an electric constitution of an electric impact driver according to a second embodiment of the invention; [0040] [0040]FIG. 7 is an outlook view of an electric driver drill according to a conventional technology; [0041] [0041]FIG. 8 is a view showing an outline of a constitution of an operating portion of an electric tool according to a conventional technology; and [0042] [0042]FIG. 9 is a circuit diagram showing an electric constitution of a lever switch circuit of the operating portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0043] (First Embodiment) [0044] An explanation will be given of an inner constitution shown by broken lines of an embodiment of the invention in reference to an outlook view of a cordless electric driver drill 1 shown in FIG. 1. [0045] A cordless electric driver drill 1 shown in the drawing, is constituted by a driving portion 15 comprising a brushless direct current motor 3 constituting a drive source, a speed changing device 4 for reducing a rotational number of the brushless direct current motor 3 and an output shaft 5 connected to the speed changing device 4 , an operating portion 16 having a motor driving circuit 7 , a control portion 8 thereof and a switch 9 for controlling power supply, and a power source portion 17 comprising a charge type battery 11 and the electric driver drill 1 is formed by a housing 2 . [0046] According to the driving portion 15 , a drive shaft of the brushless direct current motor 3 is connected with the speed changing device 4 containing a gear mechanism for reducing the rotational number, a front portion of the speed changing device 4 is connected with the output shaft 5 and a front end of the output shaft 5 is provided with a chuck 6 for mounting a front end tool such as a bit or a drill. [0047] The operating portion 16 is constituted by the motor driving circuit 7 and the control portion 8 thereof and the switch 9 for controlling power supply from a power source and the operating portion 16 is contained in a grip portion 10 of the housing 2 . [0048] According to the driving portion 15 and the operating portion 16 , respective parts thereof are fixed at inside of the housing 2 , the driving portion 15 and the operating portion 16 are connected to each other by lead wires, not illustrated, to thereby form the electric driver drill 1 and a vicinity of the drive switch 9 , is provided with a switch 12 for switching a rotational direction of the brushless direct current motor 3 and locking the rotational direction. [0049] The power source portion 17 of the electric driver drill 1 is constituted by the charge type battery 11 provided attachably and detachably at a lower portion of the grip portion 10 and the charge type battery 11 is provided with a cartridge type attaching and detaching means attached to and detached from a bottom portion of the grip portion 10 and electric contacts commonly for supplying power to the electric driver drill 1 and charging the battery. [0050] As shown by a block diagram of FIG. 2, the motor driving circuit 7 is for driving the brushless direct current motor 3 by being supplied with power from the charge type battery 11 and is constituted by an inverter circuit 21 constituted by switching transistors, a logical circuit 22 for controlling the inverter circuit 21 and a rotational speed detecting circuit 24 for detecting the rotational direction by a signal of a position detecting element 23 comprising a Hall element included in the brushless direct current motor 3 . The logical circuit 22 carries out a feedback control to rotate the brushless direct current motor 3 by instructed speed by a speed instructing signal from the control portion 8 and a rotational speed signal from the rotational speed detecting circuit 24 and an output thereof is transmitted to the speed changing device 4 . [0051] The electric driver drill 1 is constituted such that by operating the switch 9 , power of the battery 11 is transmitted to the driving portion 15 via the control portion 8 and the motor driving circuit 7 , ON/OFF and the rotational number of the brushless direct current motor 3 are controlled, driving force is transmitted from the speed changing device 4 to the output shaft 5 , a front end tool (not illustrated) of a bit or a drill mounted to the front end is rotated to thereby carry out cutting such as drilling or chipping or operation of fastening a screw or a bolt. [0052] According to the electric driver drill 1 , the brushless direct current motor 3 is used for the motor constituting the drive source. [0053] According to the brushless direct current motor 3 , a control range of the rotational number of the motor per se becomes wider than that of the conventional direct current motor with brush, control of the rotational number is facilitated and the rotational number from the low speed region to the high speed region can continuously be used variably, there can be facilitated selection of the rotational speed for use at high speed rotation or use at low speed and high torque rotation depending on the use of the electric tool and operability and maneuverability of the electric tool can significantly be promoted. [0054] That is, by controlling a degree of pulling the switch 9 , low speed through high speed rotation can continuously be selected variably by the feedback control of the motor driving circuit, desired rotational torque can be achieved and therefore, a width of selection of the rotational number region becomes wide depending on the use and the content of operation such as drilling operation at high speed rotation or fastening a screw or a bolt at low speed high torque rotation, further, operation can be carried out variably and therefore, the operability is promoted. Further, the switch 9 having a constitution simpler than conventional one can be used and an inexpensive switch can be utilized. [0055] Further, the rotational number of the motor is lower than that of the motor with brush and therefore, the speed reduction ratio of the rotational number by the gear mechanism can be reduced, vibration or noise generated at inside of the speed changing device is reduced, sound emitted by sliding the brush and the commutator is eliminated and vibration or noise of the electric tool can be restrained from being generated than that of the conventional tool. [0056] Further, by reducing the speed reduction ratio, the gear mechanism is simplified, small-sized and light-weighted formation of the speed changing device can be achieved and the operability can be promoted by the light-weighted compact formation of the tool. [0057] Further, maintenance performance is promoted by dispensing with interchanging the brush and checking the motor, which has been needed in the conventional motor with brush, the service life of the electric tool is prolonged and there is also resolved the problem of noise of a radio or a disturbance in a television screen by generating spark in rotating the brush. [0058] An electric tool using the above-described brushless direct current motor is applicable to an electric driver, an electric driver drill, an electric impact driver or an electric wrench and there can be provided an electric tool excellent in operability in cutting or fastening, small sized, light-weighted, having excellent maneuverability and accompanied by low vibration and low noise. [0059] Further, according to the respective electric tools, by providing a vibration generating function or an impact generating function for generating vibration or impact to a drill or a driver of the front end tool, the above-described respective electric tools can be used also for an electric impact driver, a vibration drill or an electric chipping machine. [0060] Further, depending on the use, the electric tool is applicable also to a tool of a stepped variable type by using the brushless direct current motor. [0061] Further, although an explanation has been given of the electric tool using the charge type battery of an attaching and detaching type as the power source according to the above-described embodiment, the electric tool is applicable to an electric tool of a battery fixing type constituting a power source portion by providing a charge type battery at inside of a main body of the electric tool, for example, containing the charge type battery at a lower side portion of a grip portion. [0062] Although a nickel cadmium battery or nickel hydrogen battery is exemplified as the charge type battery, the battery is not limited so far as the battery is the charge type battery. [0063] Further, the electric tool can be used in, for example, a pencil type in a rod-like shape or a type capable of being folded at a central portion other than the pistol type shown in the drawing. [0064] Further, although according to the above-described embodiment, an explanation has been given of the invention in accordance with the electric driver drill of a hand held type, the electric tool of the invention can be used not only for the above-described electric driver, electric impact driver, electric wrench but also electric tools of an electric drill, an electric plane, an electric saw, cutters such as screw cutter and a knife cutter, a plant clipper and polishing machines such as a sander and a polisher and can naturally be used for electric tools of a desk top type such as a drilling machine. [0065] (Second Embodiment) [0066] An explanation will be given of a second embodiment of the invention in reference to FIG. 3 through FIG. 5. [0067] [0067]FIG. 3 is a circuit diagram showing an electric constitution of an essential portion of an electric impact driver 111 of a cordless type according to the embodiment, FIG. 4 is a block diagram showing an electric constitution of the electric impact driver 111 and FIG. 5 is a outlook view of the electric impact driver 111 . [0068] Although in the following embodiment, an explanation will be given by exemplifying the electric impact driver 111 of the cordless type, the invention is not limited to the example but generally and widely embodied to an electric impact driver which is not of a cordless type but is used while being connected to a power source, or other electric tool. [0069] (1) Constitution of the Electric Impact Driver 111 [0070] An explanation will be given of a constitution of the electric impact driver 111 in reference to FIG. 5 as follows. [0071] The electric impact driver 111 is provided with a main body 112 , a tool 113 mounted to one end portion of the main body 112 and a grip portion 114 integrally formed with other end portion of the main body 112 . [0072] The main body 112 is contained with a brushless direct current motor 123 . [0073] The grip portion 114 is formed to be able to be gripped by the hand of an operator and a portion thereof where the finger is disposed in a gripping state, is arranged with a rotational speed switching lever (hereinafter, referred to as speed lever) 115 in a trigger-like shape. Further, a lower portion of the grip portion 114 is provided with a battery 120 of a charge type. The battery 120 is charged by being mounted on a charger 120 a connected to AC100V power source. [0074] A lock switch 116 for fixing a state of pulling the speed lever 115 is provided at a vicinity of the speed lever 115 . [0075] A vicinity of the grip portion 114 of the main body 112 is arranged with a changeover switch 117 for switching rotation of the brushless direct current motor 123 and accordingly, rotation of the tool 113 between predetermined regular rotation and inverse rotation. Further, a top portion of the main body 112 is provided with a maximal speed setting switch (hereinafter, referred to as setting switch) 119 for setting maximal rotational speed of the tool 113 . [0076] (2) Electric Constitution of the Electric Impact Driver 111 [0077] An explanation will be given of an outline of an electric constitution of the electric impact driver 111 also in reference to FIG. 4 as follows. [0078] The electric impact driver 111 is provided with a speed controlling portion 121 , a controller 122 and the brushless direct current motor 123 supplied with power source by the battery 120 . [0079] The speed controlling portion 121 detects operation of the speed lever 115 and the setting switch 119 as described below and outputs a rotational speed signal S 1 subjected to PWM (pulse width modulation) for driving the blushless direct current motor in correspondence with operational states of the lever 115 and the setting switch 119 to the controller 122 . The controller 122 includes a plurality of switching transistors (not illustrated) driven to ON/OFF based on the rotational speed signal S 1 from the speed controlling portion 121 and a drive signal for driving the brushless direction motor 123 is outputted from the switching transistors. [0080] The speed controlling portion 121 is provided with a maximum speed changing lever switch circuit 24 for detecting operation of the setting switch 119 and a rotational speed changing lever switch circuit 125 for detecting operation of the speed lever 115 . A control apparatus is constituted by including the speed controlling portion 121 . [0081] (3) Electric Constitution of the Speed Controlling Portion 121 [0082] An explanation will be given of an example of an electric constitution of the speed controlling portion 121 also in reference to FIG. 3 as follows. [0083] The maximum speed changing lever switch circuit 124 is provided with resistors R 11 and R 12 connected in series between power source voltage vdd and ground potential and a slide terminal 126 for being slidingly moved relative to the resistor R 11 . An output of the slide terminal 126 is outputted to the rotational speed changing lever switch circuit 125 . [0084] The rotational speed changing lever switch circuit 125 is provided with a resistor R 13 inputted with the output from the slide terminal 126 and other end of the resistor R 13 is grounded. [0085] The resistor R 13 is provided with a slide terminal 127 , reference voltage Vth outputted from the slide terminal 127 is inputted to a noninverting input terminal of a comparing circuit 128 and an inverting input terminal of the comparing circuit 128 is inputted with a predetermined triangular wave signal. The rotational speed signal S 1 is outputted from the comparing circuit 128 . [0086] (4) Operation of the Electric Impact Driver 111 [0087] An explanation will be given of operation of the electric impact driver 111 as follows. [0088] First, in correspondence with content of operation, by operating the setting switch 119 , the maximal rotational speed of the electric impact driver 111 is set. According to the embodiment, the maximal rotational speed is set variably. That is, in correspondence with operation of the setting switch 119 , the slide terminal 126 is variably displaced and the maximum speed voltage Vs in correspondence with an operational position of the setting switch 119 stopped at a predetermined position. [0089] Next, in carrying out actual fastening operation, the operator operates the speed lever 115 . Actually, the grip portion 114 shown in FIG. 5 is gripped and the speed lever 115 is gripped by the hand and the finger. According to the embodiment, in correspondence with large or small of a degree of gripping the speed lever 115 , the slide terminal 127 is displaced in an arrow mark B 1 direction or an arrow mark B 2 direction. In correspondence with the direction and the degree of the displacement, the reference voltage Vth from the slide terminal 127 is increased or reduced. The maximum value of the reference voltage vth is the maximum speed voltage Vs. [0090] That is, the maximum speed voltage Vs is divided by the resistor R 13 and the slide terminal 127 and the reference voltage Vth provided by dividing the voltage is inputted to the noninverting input terminal of the comparing circuit 128 . From the comparing circuit 128 , there is outputted the rotational speed signal S 1 subjected to the PWM modulation in which the higher the reference voltage Vth, the higher the on duty. As described above, the rotational speed signal S 1 is outputted to the controller 122 and the brushless direct current motor 123 is driven to rotate. [0091] In this way, according to the embodiment, when the maximal rotational speed of the electric impact driver 111 is set based on operation of the setting switch 119 , even in the case in which the maximal rotational speed by the speed lever 115 is constituted by operating the speed lever 115 , the maximal rotational speed is constituted by the maximal rotational speed set by the setting switch 119 . Thereby, when the rotational speed necessary for actual operation is set by operating the setting switch 119 , the operation can be carried out in a state of operating to maximally gripping the speed lever 115 . [0092] Thereby, there is resolved to eliminate a necessity to carry out operation in the state of intermediately gripping the speed lever 115 to constitute intermediate rotational speed lower than the maximal rotational speed in order to provide the rotational speed necessary for the actual operation and fatigue of the operator can significantly be reduced. Further, there can be resolved to eliminate unstable formation of the rotational speed caused by carrying out the operation in the state of intermediately gripping the speed lever 115 by the operator and stable operation can be carried out. [0093] (Third Embodiment) [0094] [0094]FIG. 6 is a circuit diagram showing an electric constitution of an electric impact driver 111 a according to a third embodiment of the invention. [0095] The embodiment is similar to the second embodiment, corresponding portions are attached with the same reference notations and a further explanation thereof will be omitted. [0096] A characteristic of the embodiment resides in setting the maximal rotational speed of the electric impact driver 111 a in multiple stages. An explanation will be given of an electric constitution of the electric impact driver 111 a as follows. The embodiment is also similarly provided with the constitution explained in reference to FIG. 4 and FIG. 5 in the second embodiment. [0097] (1) Electric Constitution of Speed Controlling Portion 121 a [0098] An explanation will be given of an example of an electric constitution of a speed controlling portion 121 a provided in the electric impact driver 111 a according to the embodiment also in reference to FIG. 6 as follows. [0099] A maximal speed changing lever switch circuit 124 a is provided with a plurality of resistors R 14 , R 15 . . . connected in parallel between the power source voltage Vdd and the ground potential and having resistance values different from each other as an example and a changeover switch 129 . Reference voltage Vth constituting an output of the changeover switch 129 , is outputted to the resistor R 13 of the rotational speed changing lever switch circuit 125 having a constitution similar to the constitution of the first embodiment. [0100] (2) Operation of the Electric Impact Driver 111 a [0101] An explanation will be given of operation of the electric impact driver 111 a according to the embodiment. First, in correspondence with content of operation, by operating the setting switch 119 , the maximal rotational speed of the electric impact driver 111 a is set. [0102] That is, in correspondence with the operation of the setting switch 119 , the changeover switch 129 is connected to any one of the power source voltage Vdd, the resistor R 14 , the resistor R 15 . . . . When the changeover switch 119 is connected to the power source voltage Vdd, the maximal rotational speed of the electric impact driver 111 a is constituted. [0103] Operation of the rotational speed changing lever switch circuit 125 thereafter is similar to that of the above-described embodiment and accordingly, also operation of the electric impact driver 111 a is similar thereto. [0104] Therefore, also according to the embodiment, operation and effect similar to operation and effect explained in the first embodiment are realized. Industrial Applicability [0105] The electric tool according to the first aspect of the invention is the cordless electric tool using the charge type battery as the drive power source of the motor, the motor is brushless direct current motor and therefore, the electric tool can be used by variable speed changing by selecting the rotational number and the rotational torque of the electric tool from wide ranges, further, generation of vibration or noise can be reduced, small-sized and light-weighted formation can be achieved and therefore, there is provided the cordless electric tool having a high function, excellent in maneuverability and capable of achieving an improvement in an operational environment and durable years of the electric tool can be prolonged. [0106] According to the electric tool of the second aspect of the invention, the maximal rotational speed of the brushless direct current motor is set by operating the first operating member and the second operating member is operated within the set maximal rotational speed range to thereby change the rotational speed of the brushless direct current motor. Thereby, when the rotational speed necessary for operation is set to the maximal rotational speed of the electric tool by using the first operating means, even in the case of constituting the maximal rotational speed by maximally operating the second operating means, the rotational speed necessary for the operation is constituted. [0107] Therefore, the operation can be carried out by maximally operating the second operating means by changing the maximal rotational speed in correspondence with content of the operation using the electric tool. Thereby, there is resolved to eliminate a necessity of continuing operation while maintaining the second operating means at an intermediate operational state by the operator, a situation of causing enormous fatigue for the operator is prevented and stable operation can be carried out. [0108] Further, fastening force is made constant, in the case of fastening a screw, fastening torque is made uniform and quality of a product is stabilized.

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