Patent Description:
A screw-tightening power tool is disclosed in <CIT> and <CIT>.

As disclosed in <CIT>, a screw-tightening power tool comprises a rotary-drive part having, at a front-end part of a housing that houses a motor, a first spindle rotationally driven by the motor and a second spindle capable of holding a tip tool, the rotary-drive part being configured to be capable of tightening a screw by the transmission of the rotation of the first spindle to the second spindle when the second spindle has retracted.

Document <CIT> discloses a screw-tightening tool with a motor disposed downward of the clutch. The motor is in an inclined orientation in parallel to the grip part what leads to a bulky shape of the tool.

In the above-mentioned, previously existing screw-tightening power tool, a commutator motor is used as the motor; however, this causes a durability problem owing to wear of brushes and, moreover, also risks impeding miniaturization.

Accordingly, an object of the present invention is to provide a screw-tightening power tool wherein suitable durability is obtained and miniaturization also can be achieved.

To achieve the aforementioned object, a screw-tightening power tool according to claim <NUM> is provided.

According to the present invention, the miniaturization is improved.

Embodiments of the present teachings are explained below, with reference to the drawings.

<FIG> is an external view of a screwdriver <NUM>, which is one example of a screw-tightening power tool, and <FIG> is a longitudinal cross-sectional view thereof. In a housing <NUM> of the screwdriver <NUM>, left and right half housings 2a, 2b are assembled together by screws <NUM>, and a front housing <NUM> (right sides in <FIG>, <FIG> are forward), which houses an output part <NUM> and a brushless motor <NUM> described below, and a rear housing <NUM>, which is coupled in a loop rearward of the front housing <NUM>, are formed. Reference numeral <NUM> is a hook provided on a rear surface of the front housing <NUM>. A grip part <NUM> is formed in an up-down direction at a rear end of the rear housing <NUM>, and a trigger switch <NUM>, from which a trigger <NUM> projects forward, is housed inside the grip part <NUM>. A forward/reverse switching button <NUM> is provided upward of the trigger switch <NUM>.

In addition, a battery pack <NUM>, which constitutes a power supply, is attachably and detachably mounted to a mounting part <NUM>, which is formed downward of the grip part <NUM>. The battery pack <NUM> comprises a pair of left and right sliding rails <NUM>, <NUM> on an upper surface of a case <NUM> that houses a plurality of storage batteries, and the battery pack <NUM> is capable of being mounted to the mounting part <NUM> by mating, from the rear, the sliding rails <NUM>, <NUM> to and in between a pair of guide rails, which are not shown, provided on the mounting part <NUM> and then sliding the sliding rails <NUM>, <NUM> rearward. In this mounted state, a terminal plate <NUM> of a terminal block <NUM> provided in the mounting part <NUM> advances into the case <NUM> and is electrically connected with terminals, which are not shown, inside the case <NUM>. Reference numeral <NUM> is a latching hook that is provided inside the case <NUM> such that it protrudes and is biased upward, latches in a recessed part <NUM>, which is provided in the mounting part <NUM>, in the mounted state, and thereby acts to lock the battery pack <NUM>.

Furthermore, a control circuit board <NUM>, which is molded of resin and on which a capacitor <NUM>, a microcontroller, etc., are installed, is provided on an upper side of the terminal block <NUM>. The control circuit board <NUM> and the trigger switch <NUM> are electrically connected by cords <NUM>, <NUM>,.

The brushless motor <NUM> is an inner-rotor-type that comprises a stator <NUM> and a rotor <NUM>, and is disposed on a lower side of the front housing <NUM>. First, the stator <NUM> comprises: a stator core <NUM>; a front insulating member <NUM> and a rear insulating member <NUM>, which are provided forward and rearward of the stator core <NUM>; and a plurality of coils <NUM>, <NUM>,. , which are wound around the stator core <NUM> via the front insulating member <NUM> and the rear insulating member <NUM>. In addition, the rotor <NUM> comprises: a rotary shaft <NUM> located at an axial center; a tubular rotor core <NUM> disposed around the rotary shaft <NUM>; tubular permanent magnets <NUM><NUM>,. disposed on an outer side of the rotor core <NUM> and whose polarities alternate in a circumferential direction; and a plurality of sensor permanent magnets <NUM>, disposed radially on a front side thereof. As shown in <FIG>, a sensor-circuit board <NUM>, whereon are installed three rotation-detection devices <NUM>, <NUM>,. , which detect the positions of the sensor permanent magnets <NUM> of the rotor <NUM> and output rotation-detection signals, and six switching devices <NUM>, <NUM>,. , which switch the coils <NUM>, is fixed to a front end of the front insulating member <NUM>. Reference numerals <NUM> are screws that affix the sensor-circuit board <NUM>; reference numerals <NUM> are projections, which are provided such that they project from a front end surface of the front insulating member <NUM>, that mate with small holes of the sensor-circuit board <NUM>; reference numerals <NUM> are coil-connection parts; and reference numeral <NUM> is a tongue part, which is provided such that it projects downward facing; therein, a plurality of cords <NUM>, <NUM>,. (including power-supply lines 40a for transmitting electric power from the control circuit board <NUM> and signal lines 40b for transmitting signals from the control circuit board <NUM>) for electrically connecting with the control circuit board <NUM> is connected to the tongue part <NUM>.

Furthermore, the stator <NUM> is held, with an attitude such that its axis line is oriented in the front-rear direction, inside a chamber <NUM> formed by ribs <NUM> uprightly provided on an inner surface of the front housing <NUM>; the rotary shaft <NUM> is rotatably supported by a bearing <NUM>, which is held by the rib <NUM> on the front side of the chamber <NUM>, and by a bearing <NUM>, which is held by the ribs <NUM> on a rear side of the chamber <NUM>. A centrifugal fan <NUM> for cooling the motor is securely mounted forward of the bearing <NUM> on the rotary shaft <NUM>, a plurality of air-suction ports <NUM>, <NUM>,. is formed in an outer-side region in the radial direction of the sensor-circuit board <NUM> in the front housing <NUM>, and a plurality of air-exhaust ports <NUM>, <NUM>,. is formed in an outer-side region in the radial direction of the centrifugal fan <NUM>.

Furthermore, a rear end of the rotary shaft <NUM> protrudes rearward from the chamber <NUM> and a first gear <NUM> is securely mounted thereon. Upward of the rotary shaft <NUM>, a gear shaft <NUM> is axially supported, parallel to the rotary shaft <NUM>, by front and rear bearings <NUM>, <NUM>, and a second gear <NUM>, which is provided at a rear end of the gear shaft <NUM>, meshes with the first gear <NUM>. A third gear <NUM>, the diameter of which is smaller than that of the second gear <NUM>, is formed at a front end of the gear shaft <NUM>.

Furthermore, the output part <NUM> is disposed upward of the brushless motor <NUM>. The output part <NUM> comprises: a first spindle <NUM>, which is axially supported, via a bearing <NUM>, by the front housing <NUM>; and a second spindle <NUM>, which is provided such that it extends from the front housing <NUM> to a tubular tip housing <NUM> coupled forward of the front housing <NUM>, that serves as a tip-tool retaining part axially supported via a bearing <NUM>. A fourth gear <NUM> is integrally and securely mounted to a rear part of the first spindle <NUM>, and the fourth gear <NUM> is meshed with the third gear <NUM> of the gear shaft <NUM>. In addition, a cam <NUM> is integrally joined, in a rotational direction, to the front of the fourth gear <NUM> via a ball <NUM>.

Moreover, the second spindle <NUM> is coaxially disposed forward of the first spindle <NUM> such that it is capable of forward-rearward movement; a mount hole <NUM>, wherein a driver bit that is a tip tool can be inserted and mounted, is formed at a front end of the first spindle <NUM>; and a cam part <NUM>, which opposes the cam <NUM>, is formed at a rear end of the first spindle <NUM>. The cam part <NUM> meshes with the cam <NUM> in the forward rotational direction, and therefore a coil spring <NUM> is interposed between the cam <NUM> and the cam part <NUM>. That is, a clutch (cam <NUM>, cam part <NUM>), through which the rotation of the second spindle <NUM> is transmitted when the first spindle <NUM> has retracted, is formed between the first spindle <NUM> and the second spindle <NUM>.

Furthermore, a tip of the first spindle <NUM> is inserted into a bottomed hole <NUM>, which is formed in a rear part of the second spindle <NUM>, and a one-way clutch <NUM>, which engages in a reverse rotational direction, is provided between both of the spindles <NUM>, <NUM>. Reference numeral <NUM> is a cap for adjusting the depth with which a front-rear position thereof is modifiably fitted to a front end of the tip housing <NUM>.

In addition, a cap-shaped cover housing <NUM> is fixed to a front-end lower part of the front housing <NUM> forward of the brushless motor <NUM>, and an LED <NUM>, which serves as a light, is housed, with an attitude such that it faces diagonally frontward, downward inside the cover housing <NUM> and is electrically connected to the control circuit board <NUM> via a cord <NUM>.

In the screwdriver <NUM> configured as above, when the driver bit mounted in the second spindle <NUM> is pressed against a screw-to-be-tightened and the second spindle <NUM> is retracted, the cam part <NUM> engages with the cam <NUM> of the first spindle <NUM>. When the trigger switch <NUM> is turned ON by an operation of depressing the trigger <NUM> in this state, power is supplied from the battery pack <NUM>, and thereby the brushless motor <NUM> is driven. That is, the microcontroller of the control circuit board <NUM> acquires the rotational state of the rotor <NUM> by receiving rotation-detection signals, which are output from the rotation-detection devices <NUM> of the sensor-circuit board <NUM> and indicate the positions of the sensor permanent magnets <NUM> of the rotor <NUM>, sequentially supplies electric current to each of the coils <NUM> of the stator <NUM> by controlling the ON/OFF state of each of the switching devices <NUM> in accordance with the acquired rotational state, and thereby causes the rotor <NUM> to rotate. However, an amount of manipulation (press-in amount) of the trigger <NUM> is transmitted as a signal to the microcontroller, and the rotation of the rotor <NUM> is controlled in accordance with the amount of manipulation. Furthermore, another method of use is also possible wherein the second spindle <NUM> is caused to retract in a state in which the operation of depressing the trigger <NUM> has been performed beforehand and the brushless motor <NUM> has been caused to rotate.

Thus, when the rotor <NUM> rotates, the rotary shaft <NUM> and the first gear <NUM> rotate and the gear shaft <NUM> is rotated via the second gear <NUM> at a slower speed; furthermore, the first spindle <NUM> is rotated via the third gear <NUM> and the fourth gear <NUM> at a slower speed. Thereby, the second spindle <NUM>, which engages with the cam <NUM>, rotates, enabling the driver bit to perform screw tightening. As the screw tightening progresses, the second spindle <NUM> advances, and, when the cam part <NUM> disengages from the cam <NUM>, the rotation of the second spindle <NUM> stops and the screw tightening terminates.

Moreover, in the case of loosening a screw, when the forward/reverse switching button <NUM> is switched to the reverse-rotation side, the rotor <NUM> rotates in reverse under the control of the microcontroller, and the first spindle <NUM> rotates in reverse. Because the one-way clutch <NUM> is provided between the first spindle <NUM> and the second spindle <NUM>, the second spindle <NUM> also rotates in reverse, enabling the driver bit to loosen the screw.

Furthermore, when the centrifugal fan <NUM> rotates together with the rotary shaft <NUM>, air drawn from the air-suction ports <NUM> into the chamber <NUM> passes between the sensor-circuit board <NUM> and the stator <NUM> and between the sensor-circuit board <NUM> and the rotor <NUM> and is discharged from the air-exhaust ports <NUM>. Thereby, the sensor-circuit board <NUM> and the brushless motor <NUM> are cooled.

In addition, upon turning ON the trigger switch <NUM>, the LED <NUM> is energized by the control circuit board <NUM> and turns ON. Thereby, the area ahead of the driver bit is illuminated and thus work efficiency can be maintained even in a dark location.

Furthermore, the brushless motor <NUM> and the LED <NUM> are proximate to one another, and therefore wiring is easy.

Thus, according to the screwdriver <NUM> of the above-mentioned first embodiment, the adoption of the brushless motor <NUM> can be expected to increase motive-power-transmission efficiency and miniaturization, thereby enabling screw tightening at low power. In addition, durability is also improved because brushes are not used.

Furthermore, because the brushless motor <NUM> is disposed downward of the clutch, the brushless motor <NUM> is balanced with respect to the battery pack <NUM> to the rear, thereby excelling ergonomically.

In addition, because the sensor-circuit board <NUM> is not sandwiched between the brushless motor <NUM> and the first gear <NUM> and the like, durability with regard to heat, vibration, etc. is further increased.

Furthermore, because the tongue part <NUM> of the sensor-circuit board <NUM> is formed such that it faces downward, wiring from the control circuit board <NUM> to the tongue part <NUM> is efficient.

Furthermore, in the above-mentioned first embodiment, although the switching devices <NUM> are provided on the sensor-circuit board <NUM>, they can also be provided on the control circuit board <NUM>, as shown in <FIG>. Reference numeral <NUM> in <FIG> is a microcontroller.

In addition, the speed-reducing mechanism from the rotary shaft to the first spindle likewise can be suitably modified; for example, the number of gear shafts can be increased, the gear shafts conversely can be omitted, or the like.

Next, another embodiment of the present invention will be explained. However, constituent parts identical to those in the above-mentioned first embodiment are assigned the same reference numbers, and redundant explanations thereof are omitted.

A screwdriver 1A shown in <FIG> differs from the first embodiment in that the orientation of the brushless motor <NUM> is reversed in the front-rear direction, the sensor-circuit board <NUM> is located on the rear side of the stator <NUM>, and the centrifugal fan <NUM> is located on the front side of the stator <NUM>. Thereby, here, the air-suction ports <NUM> are disposed on the rear side of the housing <NUM>, and the air-exhaust ports <NUM> are disposed on the front side of the housing <NUM>.

In addition, a partition part 42a for spacing apart the cord <NUM> for the LED <NUM> and the outer circumference of the centrifugal fan <NUM> is formed, which makes it possible to supply the draft of the centrifugal fan <NUM> more efficiently.

Thus, in the screwdriver 1A of the above-mentioned second embodiment, too, the adoption of the brushless motor <NUM> can be expected to increase motive-power-transmission efficiency and miniaturization, thereby enabling screw tightening at low power. In addition, effects the same as those in the first embodiment are obtained, such as the improvement also of durability because brushes are not used.

In particular, the sensor-circuit board <NUM> is closer to the control circuit board <NUM> than it is in the first embodiment, which is advantageous because it is possible to get by with a shorter run of wiring.

In a screwdriver 1B shown in <FIG>, <FIG>, the housing <NUM> has a shape of an L turned on its side and comprises: a motor housing <NUM>, which houses the brushless motor <NUM> and the output part <NUM> and extends in the front-rear direction, and a grip housing <NUM>, which extends from a rear end of the motor housing <NUM> in the downward direction; furthermore, the mounting part <NUM> of the battery pack <NUM> is formed at a lower end of the grip housing <NUM>. The LED <NUM> is housed, upward of the terminal block <NUM>, such that it faces diagonally upward from the mounting part <NUM>.

In addition, the control circuit board <NUM> herein is provided integrally with a lower part of the trigger switch <NUM> to form a switch assembly <NUM>; the control circuit board <NUM> of the switch assembly <NUM> and the sensor-circuit board <NUM> are electrically connected via cords <NUM>, <NUM>,. ; and the control circuit board <NUM> and the LED <NUM> are electrically connected via cords <NUM>, <NUM>. The control circuit board <NUM> is equipped with an IPM (Intelligent Power Module) <NUM> in addition to the microcontroller <NUM>, the capacitors <NUM>, etc. The IPM contains switching devices (IGBTs) and is encapsulated with a driver for driving, which is for driving the switching devices.

Furthermore, in the brushless motor <NUM>, a connecting piece <NUM>, which protrudes toward the outer side in the radial direction, is provided on the rear insulating member <NUM> of the stator <NUM> such that it protrudes therefrom, and a cord <NUM> that supplies electric power to the coils <NUM> is connected to the coils <NUM> through the connecting piece <NUM>.

Furthermore, a pinion <NUM> is securely mounted to a front end of the rotary shaft <NUM>, and the pinion <NUM> directly meshes with the first spindle <NUM> and an integrated gear <NUM>.

Thus, in the screwdriver 1B of the above-mentioned third embodiment, too, the adoption of the brushless motor <NUM> can be expected to increase motive-power-transmission efficiency and miniaturization, thereby enabling screw tightening at low power. In addition, effects the same as those in the first embodiment are obtained, such as the improvement also of durability because brushes are not used.

Here in particular, the adoption of the switch assembly <NUM> is advantageous in that the time and labor needed for assembly are reduced and in that the wiring procedure is easier because the wiring is concentrated in one location.

Furthermore, because the centrifugal fan <NUM> is located between the brushless motor <NUM> and the gear <NUM>, direct and indirect cooling of the gear <NUM> is also possible, in addition to the cooling of the brushless motor <NUM>.

Furthermore, although the positional information of the rotor <NUM> is output from the sensor-circuit board <NUM> via the signal lines 40b, the sensor-circuit board <NUM> is located on the rear side, and therefore the connection to the control circuit board <NUM> is easy. In addition, because the connecting piece <NUM> of the rear insulating member <NUM> is also on the rear side, the connection to the control circuit board <NUM> is easy.

In a screwdriver 1C shown in <FIG>, the orientation of the brushless motor <NUM> is the reverse in the front-rear direction of that of the third embodiment, and therefore the sensor-circuit board <NUM> is on the front side and the centrifugal fan <NUM> is on the rear side.

Thereby, in the screwdriver 1C of the above-mentioned fourth embodiment, too, the adoption of the brushless motor <NUM> can be expected to increase motive-power-transmission efficiency and miniaturization, thereby enabling screw tightening at low power. In addition, effects the same as those in the third embodiment are obtained, such as the improvement also of durability because brushes are not used.

In a screwdriver 1D shown in <FIG>, the control circuit board <NUM> is provided not on the trigger switch <NUM> but rather above the terminal block <NUM> as in the first embodiment, and therefore power is supplied to the coils <NUM> via the sensor-circuit board <NUM>, not via the insulating members.

In addition, here, an operation panel <NUM> shown in <FIG> is provided on an upper surface of the mounting part <NUM> and rearward of the LED <NUM>. The operation panel <NUM> is provided with a light switch <NUM>, a remaining-capacity-display switch <NUM>, and a battery indicator <NUM>, and is electrically connected to the control circuit board <NUM>; furthermore, the luminous flux intensity of the LED <NUM> changes in steps every time the operation of pressing the light switch <NUM> is performed and, when the operation of pressing the remaining-capacity-display switch <NUM> is performed, the battery indicator <NUM> lights up a number of gradations in accordance with the remaining capacity of the storage battery of the battery pack <NUM>.

Thus, in the screwdriver 1D of the above-mentioned fifth embodiment, too, the adoption of the brushless motor <NUM> can be expected to increase motive-power-transmission efficiency and miniaturization, thereby enabling screw tightening at low power. In addition, effects the same as those in the first embodiment are obtained, such as the improvement also of durability because brushes are not used.

Here in particular, the illumination mode of the LED <NUM> can be changed by the light switch <NUM>, and the remaining capacity of the battery is made evident at a glance by the remaining-capacity-display switch <NUM>, thereby excelling in user-friendliness.

In a screwdriver 1E shown in <FIG>, the orientation of the brushless motor <NUM> is the reverse in the front-rear direction of that in the fifth embodiment, that is, the sensor-circuit board <NUM> is on the rear side and the centrifugal fan <NUM> is on the front side.

Thereby, in the screwdriver 1E of the above-mentioned sixth embodiment, too, the adoption of the brushless motor <NUM> can be expected to increase motive-power-transmission efficiency and miniaturization, thereby enabling screw tightening at low power. In addition, effects the same as those in the fifth embodiment are obtained, such as the improvement also of durability because brushes are not used.

Furthermore, because the sensor-circuit board <NUM> is on the rear side, it is advantageous in that the wiring run is shorter than that in the fifth embodiment.

Furthermore, in common with the third through sixth embodiments, the reduction of speed from the rotary shaft to the first spindle is performed by the pinion and the gear, but it is also possible to achieve a reduction in speed with a planetary-gear mechanism disposed coaxially with the rotary shaft and the first spindle.

Claim 1:
A screw-tightening power tool, comprising
a housing (<NUM>) having a L-shape, wherein the housing (<NUM>) comprises
a motor housing (<NUM>) extending in a front-rear-direction, and
a grip housing (<NUM>) extending from a rear end of the motor housing (<NUM>) in the downward direction,
a brushless motor (<NUM>) comprising a stator (<NUM>) fixed to the motor housing (<NUM>) and a rotor (<NUM>) rotatable with respect to the stator (<NUM>), wherein the brushless motor is housed in the motor housing (<NUM>), wherein an axis line of the stator (<NUM>) is oriented in the front-rear-direction,
a tip-tool retaining part (<NUM>, <NUM>) capable of holding a bit,
a mounting part (<NUM>) formed at a lower part of the grip housing (<NUM>) for detachably mounting a battery pack, wherein a terminal block (<NUM>) is provided in the mounting part,
a control circuit board (<NUM>) provided upward of the battery pack, when mounted,
wherein the control circuit board is provided on an upper side of the terminal block (<NUM>) and
a clutch (<NUM>, <NUM>) disposed between the rotor and the tip-tool retaining part (<NUM>, <NUM>), wherein
the brushless motor is disposed downward of the clutch.