DESCRIPTION

ELECTRIC POWER TOOL

Technical Field

The present invention relates to an electric power tool which has a compact size which using a brushless DC motor as a drive source .

Background Art

Recently, a brushless DC motor has been used in an electric power tool which rotates a tool such as a drill or a driver by a motor thereby to perform the required work. The brushless DC motor is a DC (Direct-Current) motor having no brush (brush for communication) , which uses coils (windings) on the stator side, and a permanent magnet on the rotor side, and applies the electric power driven by an inverter to the predetermined coil in order thereby to rotate a rotor. As an example of the brushless DC motor, for example, a brushless DC motor described in PTL 1 has been known. In this PTL 1, a switching element for switching on/off the current application to a coil wounded on a stator is arranged on a circular circuit board attached to the rear end side (the side opposite to an output shaft) of a motor. All the switching elements are mounted on a one-sided surface (surface on the

rear side) of the circuit board, and abut on a heat radiating member fixed to a stator core separately from the circuit board for radiating the heat generated in the switching elements.

Citation List

Patent Literature

PTL 1: JP-A-2004-357371

Summary of Invention Technical Problem

In a method of mounting all the switching elements on the rear surface of the circuit board, in view of a relation between a cooling surface and the mounting space, the switching elements are arranged so that the height direction of each switching element becomes parallel to a rotational shaft of the motor. However, such the arrangement enables realization of good cooling performance, but space corresponding to the heights of the circuit board and the switching element is required on the rear end side of the motor and in the axial direction thereof. Therefore, application of this motor to the electric power tool causes increase in length in a front-rear direction of a housing.

On the other hand, in order to prevent the length in the front-rear direction of the housing from increasing, it is also thought that the circuit board is not provided at the rear of

the motor but provided in another position. However, in this case, due to not only a disadvantage that wiring for connecting the coil of the motor and the switching element becomes long but also a disadvantage on heat-radiation of the switching element that is easy to generate the heat, it is difficult to arrange the board in another place.

An object of the invention, in view of the above backgrounds, is to provide an electric power tool which can make a full length of the electric power tool compact by shortening the length in a front-rear direction of a housing.

Another object of the invention is to provide an electric power tool which can make a full length of the electric power tool compact while providing a board mounting a switching element thereon on the rear side of a motor. Still another object of the invention is to provide an electric power tool which can cool a switching element satisfactorily.

Solution to Problem Of the invention disclosed in this application, the typical features will be described below.

According to one feature of the invention, in an electric power tool which includes a housing, a brushless direct-current type motor accommodated in the housing and a drive circuit that supplies drive power to the motor, and which

rotates or drives a tool, the drive circuit includes plural switching elements and is mounted on a board provided on the rear end side of the motor, and the switching elements are mounted on the board so that at least a part of the switching elements overlaps with the motor in an axial direction. The board is arranged in a perpendicular direction to the axial direction of this motor. The switching elements arranged in the overlapped state are mounted on the board so as to be located on the peripheral side of the motor and in the left-right direction thereof. Therefore, the board has the shape having a protrusion part which protrudes from a circular board having the substantially same diameter as the outer diameter of the motor. It is better that the switching element arranged in the overlapped state is fixed to the protrusion part. According to another feature of the invention, an air intake and an air outlet are formed in the housing, a fan which generates air flow from the air intake to the air outlet is provided inside the housing, and the air intake and the air outlet are formed so that the switching element is arranged in the flowing passage of the air flow. Plural ribs are formed inside the housing, and these ribs provide a gap between the housing and the motor.

According to still another feature of the invention, in an electric power tool which includes a brushless direct-current type motor and a drive circuit that supplies

drive power to the motor, and rotates or drives a tool, the drive circuit includes plural switching elements and is mounted on a board provided on the rear end side of the motor perpendicularly to the rotational shaft direction of the motor, the switching elements are mounted separately on the motor side of the board and on the opposite side to the motor side, and the switching element mounted on the opposite side to the motor side is arranged so as to become parallel to the board.

Advantageous Effects of Invention

According to the first aspect of the invention, the drive circuit includes the plural switching elements and is mounted on the board provided on the rear end side of the motor, and the switching elements are mounted on the board so that at least a part of the switching elements overlaps with the motor in the axial direction. Therefore, in order to secure the space for mounting the switching elements, it is not necessary to extend the rear end portion of the housing, with the result that it is possible to realize an electric power tool in which a full length (front-rear length) of the housing is made compact .

According to the second aspect of the invention, since the board is arranged in the perpendicular direction to the axial direction of the motor, the board can be attached in the small space on the rear end side of the motor. Further, the

distance from the board to the stator windings of the motor is short, which helps in size-reduction and weight-reduction of the motor.

According to the third aspect of the invention, the air intake and the air outlet are formed in the housing, the fan which generates air flow from the air intake to the air outlet is provided inside the housing, and the air intake and the air outlet are formed so that the switching element is arranged in the flowing passage of the air flow. Therefore, it is not necessary to install separately a heat radiating unit for cooling at the switching element.

According to the fourth aspect of the invention, the plural ribs are formed inside the housing, and these ribs provide the gap between the housing and the motor. Therefore, when the electric power tool falls or is hit on something, it is possible to prevent the switching element from breaking. Further, since the ribs provide the gap, there is no fear that the air flowing passage is occluded.

According to the fifth aspect of the invention, the switching elements arranged in the overlapped state are mounted on the board so as to be located in the left and right directions on the peripheral side of the motor. Therefore, it is possible to realize an electric power tool in which a full length (front-rear length) of the housing is made compact without changing the height in the top-bottom direction of the

housing .

According to the sixth aspect of the invention, the board has the shape having the protrusion part which protrudes from the circular board having the substantially same diameter as the outer diameter of the motor, and the switching element arranged in the overlapped state is fixed to the protrusion part. Therefore, without changing the conventional attachment method of fixing the board to the motor, by only changing the shape of the board, the constitution of the invention can be readily realized.

According to the seventh aspect of the invention, in the electric power tool which includes the brushless direct-current type motor and the drive circuit that supplies drive power to the motor, and which rotates or drives a tool, the drive circuit includes plural switching elements, the drive circuit is mounted on the board provided on the rear end side of the motor perpendicularly to the rotational shaft direction of the motor, the switching elements are mounted separately on the motor side of the board and on the opposite side to the motor side, and the switching element mounted on the opposite side to the motor side is arranged so as to become parallel to the board. Therefore, by the switching element mounted on the opposite side to the motor side, it is possible to prevent the front-rear length of the housing from becoming large. Further, since the switching elements are arranged on

the both sides of the board, the constitution of the invention can be realized also in a brushless DC motor that is smaller in diameter.

According to the eighth aspect of the invention, the switching element mounted on the motor side is arranged so as to overlap with the motor in the axial direction. Therefore, it is possible to realize an electric power tool in which a full length (front-rear length) of the housing is made compact According to the ninth aspect of the invention, since the switching element mounted on the motor side is arranged on the peripheral portion of the motor, it is not necessary to fix the board apart from the motor.

The above and other objects of the invention and new features thereof will be apparent from the following description and the accompanying drawings.

Brief Description of Drawings

Fig. 1 is a diagram showing the internal structure of an impact driver according to an embodiment of the invention. Figs. 2A to 2C are diagrams showing a drive circuit board 7 shown in Fig. 1, in which Fig .2A is a rear view seen from the rear side, Fig. 2B is a side view seen from the side, and Fig. 2C is a front view seen from the front side.

Fig. 3A is a sectional view taken along a line A-A in Fig. 1, which is seen from the rear side of its section.

Fig. 3B is a sectional view taken along a line B-B in Fig. 1, which is seen from the rear side of its section.

Fig. 4 is a block diagram showing the configuration of a drive control system of a motor 3. Fig. 5 is a side view showing the inner shape of a housing 6 of the impact driver 1 according to the embodiment of the invention.

Fig. 6 is an enlarged view near the rear end portion of the impact driver 1 in Fig. 1.

Description of Embodiments

An embodiment of the invention will be described below with reference to Figs. 1 to 3. It should be noted that an top-bottom direction and a front-rear direction in the following description represent directions shown in Fig. 1. Fig. 1 is a diagram showing the internal structure of an impact driver 1 as one embodiment of an electric power tool according to the invention. The impact driver 1, with a chargeable battery 2 as a power source, drives a rotary impact mechanism 4 by means of a motor 3 as a drive source, and gives rotational force and impact force to an anvil 5 that is an output shaft, thereby to deliver intermittently the rotary impact force to a not-shown tool such as a driver bit held by a sleeve 15 and perform the screwing or bolting operation. The above motor 3 is a brushless DC motor, which is

accommodated in a cylindrical body portion 6a of a housing 6 having the nearly T-shape in side view. A rotational shaft of the motor 3 is held rotatably by a bearing 17a provided on the rear end side of the body portion 6a and a bearing 17b provided near the central portion of the body portion 6a. In front of the motor 3, a fan 18 is provided, which is attached to the rotational shaft of the motor and rotates in synchronization with the motor 3. At the rear of the motor 3, a drive circuit board 7for driving the motor 3 is disposed. On the drive circuit board 7, plural switching elements 21a, 21b and 21c are mounted, and inverter control is performed by these switching elements thereby to rotate the motor 3. The details of the drive circuit board 7 and the switching element will be described later. At the upper portion inside a handle portion 6b extending integrally from the body portion 6a of the housing 6 at a substantially right angle, a trigger switch 8 is disposed. A trigger operating portion 8c which is urged by a not-shown spring and protrudes from the handle portion 6b is provided for the trigger switch 8. At the lower portion inside the handle portion 6b, a control circuit board 9 is accommodated, which has a function of controlling the speed of the motor 3 by the pulling operation of the trigger operating portion 8c. This control circuit board 9 is electrically connected to the battery 2 and the trigger switch 8. To a battery retaining

portion 6c located at the lower portion of the handle portion 6b, the battery 2 is detachably attached.

The rotary impact mechanism 4 includes a planetary gear reduction mechanism 10, a spindle 11, and a hammer 12. When the trigger operating portion 8c of the trigger switch 8 is pulled and the motor 3 is actuated, the rotation of the motor 3 is speed-reduced by the planetary gear reduction mechanism 10 and the speed-reduced rotation is transmitted to the spindle

11, whereby the rotation of the spindle 11 is driven at the predetermined speed. The spindle 11 and the hammer 12 are coupled to each other by a cam mechanism. This cam mechanism includes a V-shaped spindle cam groove 11a formed on the outer peripheral surface of the spindle 11, a hammer cam groove 12a formed on the inner peripheral surface of the hammer 12, and a ball 13 which engages with these cam grooves 11a and 12a. The hammer 12 is always urged forward by a spring 14, and located, in the static time, by the engagement between the ball 13 and the cam grooves 11a, 12a in a position spaced from the end surface of the anvil 5. At two places on each of rotary planes of the hammer 12 and the anvil 5 opposed to each other, not-shown convex portions are formed symmetrically.

When the rotation of the spindle 11 is driven, its rotation is transmitted through the cam mechanism to the hammer

12. Before the hammer 12 rotates half, the convex portion of the hammer 12 engages with the convex portion of the anvil 5,

whereby the anvil 5 is rotated. When relative rotation is produced between the spindle 11 and the hammer 12 by engagement reaction at that time, the hammer 12 starts to retreat to the motor 3 side along the spindle cam groove 11a of the cam mechanism while compressing the spring 14.

When the convex portion of the hammer 12 gets over the convex portion of the anvil 5 by the retreat of the hammer 12 and their convex portions are disengaged, the hammer 12, while being rapidly accelerated in the rotational direction and in the forward direction by elastic energy stored in the spring 14 and the action of the cam mechanism in addition to the rotational force of the spindle 11, moves forward by the urging force of the spring 14, and the convex portion of the hammer 12 engages with the convex portion of the anvil 5 again, whereby the hammer 12 and the anvil 5 start to rotate integrally. Since the strong rotary impact force is applied to the anvil 5 at this time, the rotary impact force is transmitted to a screw through a not-shown tool attached to the anvil 5.

Afterward, the similar operation is repeated and the rotary impact force is repeatedly transmitted from the tool to the screw intermittently, so that the screw is fastened into a not-shown fastened material such as wood.

Figs. 2A to 2C are diagrams showing the drive circuit board 7 shown in Fig. 1, in which Fig. 2A is a rear view seen from the rear side, Fig. 2B is a side view seen from the side,

and Fig. 2C is a front view seen from the front side. On the drive circuit board 7, six switching elements 21a, 21b, 21c, 22a, 22b and 22c are mounted. A feature in this embodiment is that: the two switching elements 21c and 22c of the six switching elements are attached on the rear side (the opposite side to the motor 3 side) of the drive circuit board 7 so as to become parallel to the drive circuit board 7; and the other four switching elements 21a, 21b, 22a and 22b are attached to the front side (the same side as the motor 3 side) of the drive circuit board 7 so that each arrangement direction becomes the front-rear direction (direction perpendicular to the drive circuit board 7) .

The drive circuit board 7 is a known board such as an epoxy board or a glass composite board, and can use a single sided board or a double sided board. The base of the drive circuit board 7 is formed in the shape of a circuit board having the substantially same diameter as the diameter of the motor 3, and the drive circuit board 7 has at its peripheral portion four protrusions 25a, 25b, 25c and 25d for mounting the switching elements thereon. Between the protrusions 25a and 25b, and between the protrusions 25c and 25d, V-shaped notches are formed in order to make cooling wind flow easily. In the central portion of the drive circuit board 7, a hole 7a into which the rotational shaft of the motor 3 is inserted is formed. Four screw holes 24a, 24b, 24c and 24d are formed in the drive

circuit board 7, and the drive circuit board 7 is fixed to the rear side of the motor by fastening screws to the screw holes.

At the lower portion of the drive circuit board 7, a connector 23 is provided as shown in Fig. 2C, to which a switching element drive signal is input from a control signal output circuit which will be described later. Further, to the drive circuit board 7, two lead wires for the plus and minus poles are connected, through which the electric power is supplied from the battery 2 to the drive circuit board 7. Fig. 3A is a sectional view taken along a line A-A in Fig. 1, which is seen from the rear side of its section. Fig. 3B is a sectional view taken along a line B-B in Fig. 1, which is seen from the rear side of its section. The motor 3 includes a stator 3a in which a stator winding 30 is wound on a stator core 32 formed by laminating electromagnetic steel sheets, and a rotor 3b which is rotatably attached to the inside of the stator 3a and to which two-pole magnets are fixed. As understood from these figures, on the outer surface side of the stator 3a, plane portions are partially formed. At the four plane portions provided in the circumferential direction, the stator 3a comes into good contact with plane holding portions (described later) formed on the inner circumferential side of the housing 6a and is fixed thereto. In these figures, the motor 3 is so constituted so as to have space between the motor 3 and the housing 6a, at the upper and lower sides of

the motor 3, and near the central portions of the left and right of the motor 3 (Note: on the basis of the direction seen from an operator holding the tool, the "left and right" are defined. Therefore, in this figure, the directions shown in Fig. 3A represent the left and right) . In that space, two ribs 38 shown in Fig. 3A and four ribs 39 shown in Fig. 3B are provided, and these ribs 38 and 39 are brought into contact with the outer peripheral portion of the motor 3 or brought close to the outer peripheral portion of the motor 3 at a slight interval. Thus, the impact driver 1 is so constituted so as to have the predetermined gaps between the motor 3 and the housing 6a. Therefore, since the air generated by the fan 18 can flow in the space of these gaps, the switching elements 21a, 21b, 22a and 22b can be satisfactorily cooled. Further, by the ribs 38 and 39, that space is prevented from being crushed. Therefore, when the impact driver 1 falls or the housing 6a is hit on something, without applying the excessive load to the switching element, it is possible to prevent the switching element from breaking, so that the electric power tool which is high in reliability can be provided.

Next, the configuration and working of a drive control system of the motor 3 will be described with reference to Fig. 4. Fig. 4 is a block diagram showing the configuration of the motor drive control system. In the embodiment, the motor 3 is composed of a three-phase brushless DC motor. This

brushless DC motor is a so-called inner rotor type, which includes the rotor 3b including a permanent magnet (magnet) including plural sets (two sets in the embodiment) of N-pole and S-pole, the stator 3a composed of star-connected three-phase stator winding U, V, W, and three rotary position detecting elements (hall elements) 42 which are arranged in the circumferential direction at predetermined intervals, for example, at intervals of an angle of 60° in order to detect the rotary position of the rotor 3b. On the basis of position detecting signals from these rotary position detecting elements 42, the power input direction and power input time to the stator windings U, V, W are controlled, and the rotor 3 rotates. It is better that the rotary position detecting element 42 is arranged on the drive circuit board 7. As the elements mounted on the drive circuit board 7, six switching elements Ql to Q6 such as FET' s (Field Effect Transistors) connected in three-phase bridge are included. Each gate of the six bridge-connected switching elements Ql to Q6 is connected to the drive circuit board 7, each drain or each source of the six switching elements Ql to Q6 is connected to the star-connected stator windings U, V, W. Hereby, the six switching elements Ql to Q6 perform the switching operation on the basis of switching element drive signals (drive signals of H4, H5, H6 and the like) inputted from the drive circuit board 7, and transform the

direct-current voltage of the battery 2 applied to the drive circuit board 7 into three-phase (U-phase, V-phase and W-phase) voltages Vu, Vv, Vw to supply the electric power to the stator windings U, V and W. Of the switching element drive signals (three-phase signal) which drive each gage of the six switching elements Ql to Q6, the drive signals H4, H5 and H6 are supplied as pulse width modulation signals (PWM signals) to the three switching elements Q4, Q5 and Q6 on the negative power source side. By an arithmetic part 41 mounted on the control circuit board 9, the pulse width (duty ratio) of the PWM signal is changed on the basis of a detection signal of the operating amount (stroke) L of the trigger operating portion 8a of the trigger switch 8, whereby the power supplying amount to the motor 3 is adjusted, and start/stop and rotational speed of the motor 3 are controlled.

Here, the PWM signals are supplied to either the positive power source side switching elements Ql to Q3 on the drive circuit board 7 or the negative power source side switching elements Q4 to Q6, thereby to subject the switching elements Ql to Q3 or the switching elements Q4 to Q6 to the high-speed switching operation, with the result that the electric power to be supplied to each stator winding U, V, W on the basis of the direct-current voltage of the battery 2 is controlled. In the embodiment, since the PWM signals are supplied to the

negative power source side switching elements Q4 to Q6, the electric power to be supplied to each stator winding U, V, W can be adjusted by controlling the pulse width of the PWM signal thereby to control the rotational speed of the motor 3. A regular/reverse switching lever 51 for switching the rotational direction of the motor 3 is provided for the impact driver 1. A rotational direction setting circuit 50, every time it detects the change of the regular/reverse switching lever 51, switches the rotational direction of the motor, and transmits its control signal to the operating portion 41. The operating portion 41 includes a central processing unit (CPU) for outputting a drive signal on the basis of a processing program and data, ROM for storing the processing program and control data, RAM for storing temporarily the data, and a timer, which are not shown.

The operating portion 41 forms a drive signal for switching the predetermined switching elements Ql to Q6 alternately on the basis of the output signals from the rotational direction setting circuit 50 and the rotator position detecting circuit 43, and outputs the drive signal to a control signal output circuit 46. Hereby, the electric power is supplied alternately to the predetermined windings of the stator windings U, V, W, thereby to rotate the rotor 3b in the set rotational direction. In this case, the drive signal to be applied to the negative power source side switching

elements Q4 to Q6 on the drive circuit board 7 is output as a PWM signal on the basis of the output control signal from an applied voltage setting circuit 49. A value of current to be supplied to the motor 3 is measured by a current detecting circuit 48, and its measured value is fed back to the operating portion 41, whereby the electric current to be supplied to the motor 3 is adjusted so as to become the set drive electric power . The PWM signal may be applied to the positive power source side switching elements Ql to Q3. Fig. 5 is a side view showing the inner shape of the housing 6 of the impact driver 1 according to the embodiment of the invention. At the rear end of the body portion 6a of the housing 6, there are provided an air intake 53 opening in the axial direction, and plural slits 54 opening in the circumferential direction with respect to the axial direction. Further, near the attaching portion of the switching element arranged in an overlapped state with the motor 3, plural slits 55 that are opening portions are formed. In the housing 6, there are formed not only the slit but also the ribs 38, 39 and 40 for fixing the motor 3, and a plane holding portion 57 for holding the plane portions formed in the plural places on the periphery of the motor 3. The plane holding portion 57 has several ribs formed in the circumferential direction, by which contact performance with the planes at the periphery of the motor 3 is made good. A slit 55 is an opening portion formed

on the outside in the circumferential direction of the fan 18, and the air inside the housing 6 is exhausted through the slit 56 to the outside. In the housing 6, an attachment portion 48 for attaching the trigger switch 8 is formed. In Fig. 5, although only the one-sided shape of the housing 6 divided in the axial direction is shown, the other-sided shape of the housing 6 is also similar. By fastening screws to screw bosses 59, 60, the left and right housings are fixed together.

Fig. 6 is an enlarged view near the rear end portion of the impact driver 1 in Fig. 1, in which air flow for cooling is shown. As understood from the figure, a length Wm in the front-rear direction (axial direction) of the motor 3 overlaps in the front-rear direction with a length Ws necessary for arrangement of the switching element. Accordingly, compared with the conventional arrangement method, the length of the body portion 6a of the housing 6 can be shortened by length corresponding to the height of the switching element 21a, 21b, so that the compact power tool can be realized. Further, with execution of this overlapped arrangement method, the width in the left-right direction (lateral direction) of the body portion 6a becomes slightly large. However, since the height in the top-bottom direction of the body portion 6a is the same as that in the conventional power tool, it is seldom that an operator is conscious that the body portion 6a becomes thick. In Fig. 6, a part of the air inhaled from the air intake

53 and the slit 54 (Fig. 6) passes through the upside of the motor 3 through a passage shown by an arrow 61, is sucked by the fan 18, and is exhausted from the slit 56 (Fig. 5) to the outside. Similarly, a part of the air (not shown by an arrow) inhaled from the lower air intake 53 passes through the bottom side of the motor 3, is sucked by the fan 18, and is exhausted from the slit 56 (Fig. 5) to the outside.

Further, the air inhaled mainly from the slits 54 and 55 (Fig. 5) pass around the switching elements 21a and 21b through a passage shown by an arrow 62, is sucked by the fan 18, and is exhausted from the slit 56 (Fig. 5) to the outside. At this time, since the slit is formed near the switching element, the air sucked from the outside by the fan 18 blows in the switching element soon, so that the switching element can be effectively cooled, and a heat radiating plate does not need to be provided for the switching element separately. The flow of air on the switching elements 22a and 22b is also similar. Further, in case that it is necessary to enhance particularly the cooling performance, for example, in case that the impact driver is used under a high-temperature environment, another heat radiating unit may be attached to a heat radiating plate for the switching element.

As described above, according to the invention, it is possible to realize an electric power tool which can make its full length compact by shortening the length in the front-rear

direction of a housing while using a brushless DC motor.

In the above embodiment, though the example in which the electric power tool of the invention is applied to the impact driver has been described, the invention can be similarly applied also to another arbitrary power tool which can use a brushless DC motor as a motor that is a drive source. Further, in the above embodiment, though the example in which FET is used as the switching element has been described, also in case that another type output transistor element such as IGBT (Insulated Gate Bipolar Transistor) is used, the invention can be similarly applicable.

The present application is based on Japanese Patent Application No. 2008-141514, filed on May 29, 2008, the entire contents of which are incorporated herein by reference.