Power tool

A power tool in the form of an electric disc grinder has a driving motor for driving a grinding wheel that performs a grinding or polishing operation on a workpiece, a motor housing that houses the driving motor, a rear cover that is mounted to a rear end region of the motor housing and forms together with the motor housing a grip to be held by a user, and a power switch including an operating lever that extends longitudinally on both of the motor housing and the rear cover and is operated by gripping with a user's hand, and a switch part that is disposed within the rear cover and actuated by operation of the operating lever to control energization of the driving motor and connected to the operating lever through an opening.

FIELD OF THE INVENTION

The invention relates to a hand-held power tool, and more particularly, to a technique for providing a hand-held power tool which performs a predetermined operation on a workpiece by a tool bit.

BACKGROUND OF THE INVENTION

Japanese Utility Model non-examined laid-open Publication No. H07-33580 discloses a hand-held power tool. This known power tool performs a predetermined operation on a workpiece by a tool bit and has a rear cover which is designed to be held by a user and disposed on a rear end region of a housing in which a motor is housed, on the opposite side from a tool bit mounting part. An operating part which is operated to drive the motor is disposed on the rear cover. With such a construction, the user operates the operating part while holding the rear cover in order to drive the motor to perform the operation. In designing a power tool of this type in which the user operates the operating part while holding a grip such as the rear cover, it is required to provide a technique for enhancing ease of operation of the operating part.

SUMMARY OF THE INVENTION

Object of the Invention

Accordingly, it is an object of the invention to provide a technique for enhancing ease of operation of an operating part which is disposed on a grip provided on a rear end region of a motor housing on the opposite side from a tool bit mounting part, in a power tool which performs a predetermined operation on a workpiece by a tool bit.

Means for Achieving the Object

Above-object is achieved by the claimed invention. A power tool according to the invention is configured as a hand-held power tool and includes at least a driving motor, a motor housing, a tool bit mounting part, a rear cover and a power switch. The power tool according to the invention may be typically represented by an electric disc grinder which performs a grinding or polishing operation on a workpiece. Further, the power tool may include an electric grinding or polishing tool, such as a sander or a polisher, an angle drill to be used for screw tightening operation, a reciprocating saw to be used for cutting operation on a workpiece, and a pneumatic power tool in which a tool bit is driven by an air motor.

The driving motor is configured as a motor for driving a tool bit that performs a predetermined operation on a workpiece. The tool bit driven by the driving motor works on the workpiece so that the predetermined operation is performed. Further, the “tool bit” typically represents a grinding wheel or a blade which performs a grinding or polishing operation on a workpiece, but it also includes a sanding disc or a wire brush. Further, the tool bit may be designed as a component of the power tool or it may be designed as a separate component from the power tool, as necessary. The motor housing is configured as a housing for housing the driving motor. The tool bit mounting part is configured as a section to which the tool bit is attached in a housing front end region of the motor housing. The rear cover includes at least a cylindrical part and an opening. The cylindrical part is a covering which is mounted to a housing rear end region of the motor housing on the opposite side from the tool bit mounting part. The cylindrical part is preferably formed in one piece in order to reduce the number of parts or to ensure its adequate strength by the one-piece structure. The opening is formed in a wall of the cylindrical part. The rear cover together with the motor housing forms a grip to be held by the user.

The power switch includes at least an operating part and a switch part. The operating part extends longitudinally on both of the motor housing and the rear cover and is operated by gripping with a user's hand. Specifically, the elongate operating part extends across the motor housing and the rear cover which both also serve as the grip, along their lengths. The operating part may be configured as a rotating lever which is turned around a predetermined pivot when operated, or it may be configured as a parallel moving lever which moves in parallel or a sliding lever which slides when the switch is operated. When the operating part is of a rotating type, the pivot for the operating part may be provided on the motor housing or on the rear cover. The switch part is disposed within the rear cover and actuated by operation of the operating part to control energization of the driving motor. Further, the switch part is connected to the operating part through the opening.

With the above-described construction of the power tool according to this invention, on the grip formed by the rear cover and the motor housing, the operating part which is operated by gripping with one or both hands of the user is arranged to extend longitudinally on both of the motor housing and the rear cover, so that the operating part can be operated in a wider range of the power tool. Therefore, ease of operation of the operating part can be enhanced.

In a further power tool according to this invention, preferably, the cylindrical part has extending walls which are formed at its both ends in a longitudinal direction of the power tool and extend in a direction transverse to the longitudinal direction, and the opening is defined between the extending walls. Specifically, the opening is formed not to extend to either end of the cylindrical part in the longitudinal direction. With such a construction, the extending walls serve as a reinforcing part of the cylindrical part, so that adequate strength of the rear cover itself can be ensured.

In a further power tool according to this invention, preferably, the motor housing has a pivot for the operating part and the operating part is turned around the pivot by gripping with the user's hand. Thus, the operating part having the pivot on the motor housing is provided.

According to the representative power tool which performs a predetermined operation on a workpiece by a tool bit, particularly, an operating part which is operated by gripping with a user's hand extends longitudinally on both of a motor housing and a rear cover. Further, a switch part is disposed within the rear cover formed by a cylindrical part and connected to the operating part through an opening formed in a wall of the cylindrical part. With such a construction, ease of operation of the operating part can be enhanced.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENT OF THE INVENTION

A representative embodiment of a power tool according to the invention is described with reference toFIGS. 1 to 5. In this embodiment, a hand-held electric disc grinder which performs a grinding or polishing operation on various kinds of workpiece such as metal, concrete or stone by using a disc-like tool bit, is explained as a representative example of the power tool according to the invention.

FIG. 1is a sectional side view showing an entire structure of an electric disc grinder101according to this embodiment. As shown inFIG. 1, the electric disc grinder101according to this embodiment includes a body103that forms an outer shell of the grinder (tool housing). The body103mainly includes a motor housing105, a gear housing107and a rear cover131. A grinding wheel119which performs grinding or polishing operation on a workpiece is disposed in a front (left as viewed inFIG. 1) end region of the body103. The grinding wheel119here is a feature that corresponds to the “tool bit” according to this invention. The electric disc grinder101may include the grinding wheel119as well as the body103as its component, or it may not include the grinding wheel119as its component. Further, in this specification, for the sake of convenience of explanation, the side of the grinding wheel119of the body103(left side as viewed inFIG. 1) is taken as the front and the opposite side (right side as viewed inFIG. 1) as the rear in the longitudinal direction of the body103.

The motor housing105is a cylindrical housing which extends in the longitudinal direction of the body103and houses a driving motor121within its internal space. Further, the motor housing105covers an outer surface of the driving motor121in a direction transverse to the longitudinal direction of the body103and a rear end surface of the driving motor121. The motor housing105together with the rear cover131serves as a grip to be held by a user when the user operates the electric disc grinder101to perform an operation. In the motor housing105of this embodiment, a housing part for covering the outer surface of the driving motor121in the direction transverse to the longitudinal direction of the body103and a housing part for covering the rear end surface of the driving motor121are formed in one piece, but these housing parts may also be separately formed. The motor housing105here is a feature that corresponds to the “motor housing” according to the invention.

The gear housing107is designed as a housing which is coupled to a front end of the motor housing105and houses a power transmitting mechanism111which serves to transmit a rotating output of the driving motor121to the grinding wheel119. The power transmitting mechanism111mainly includes a driving-side gear in the form of a small bevel gear113which is rotationally driven by the driving motor121, a driven-side gear in the form of a large bevel gear115which is engaged with the small bevel gear113, and a spindle117which rotates together with the large bevel gear115. The grinding wheel119is removably attached to a front end of the spindle117. The spindle117(the power transmitting mechanism111) here is designed as a tool bit mounting part to which the grinding wheel119is attached in a front (left as viewed inFIG. 1) end region of the motor housing105, and corresponds to the “tool bit mounting part” according to this invention. The grinding wheel119mounted to the spindle117is disposed at one (front) end in the longitudinal direction of the motor housing105(the longitudinal direction of the body103) such that its axis of rotation extends perpendicularly to an axis of rotation of the driving motor121.

The driving motor121of this embodiment is driven by power which is supplied from a power source (receptacle) via a power cord160. The driving motor121mainly includes an output shaft123, a cooling fan124that rotates together with the output shaft123, an armature125that rotates together with the output shaft123, a stator127fixed to the motor housing105, a commutator129provided on a rear end of the output shaft123(on an opposite side from the cooling fan124), two brushes that are disposed in sliding contact with an outer circumferential surface of the commutator129and serve to pass current, and a brush holder that houses the brushes. The driving motor121is arranged such that an extending direction of the output shaft123coincides with the longitudinal direction of the electric disc grinder101or the longitudinal direction of the body103. The front and rear ends of the output shaft123are rotatably supported by front and rear bearings126,128, respectively. Further, a rotator comprises the output shaft123, the armature125and the commutator129. The driving motor121here is a driving motor for driving the grinding wheel119that performs a grinding or polishing operation on a workpiece, and corresponds to the “driving motor” according to this invention.

The rear cover131is a housing part made of synthetic resin which is connected to the rear end of the motor housing105. The rear cover131here is a feature that corresponds to the “rear cover” according to this invention. The rear cover131is fastened to the motor housing105by a fastening screw132with its front end in the longitudinal direction fitted onto the rear end of the motor housing105. The rear cover131together with the motor housing105forms a grip110to be held by the user. The grip110is long enough in the longitudinal direction to be held with user's both hands set one behind the other in the longitudinal direction. The grip110here is a feature that corresponds to the “grip” according to this invention.

Further, the rear cover131covers the rear end of the motor housing105, and a switch part141for switching the driving motor121between energized state (on state) and de-energized state (off state) is housed within the rear cover131. Further, an operating lever143for turning on and off the switch part141is provided. The operating lever143is provided with a locking member150which can lock the operating lever143. The switch part141and the operating lever143serve as a power switch for driving the driving motor121and form the “power switch” according to this invention. Further, the operating lever143and the switch part141here are features that correspond to the “operating part” and the “switch part”, respectively, according to this invention. The power switch of this type in which the switch part141is turned on and off by gripping the operating lever143with the user's hand, is also referred to as a so-called “paddle switch”.

A further detailed construction of the above-described rear cover131is now described with reference toFIGS. 2 and 3.FIG. 2is a side view of the rear cover131inFIG. 1, andFIG. 3is a perspective view of the rear cover131as viewed from a direction shown by an arrow A inFIG. 2.

As shown inFIGS. 2 and 3, the rear cover131of this embodiment is designed as a cover which is mounted to a rear end region of the motor housing on the opposite side from the tool bit mounting part. The rear cover131comprises a cylindrical part131awhich is generally cylindrically formed in one piece, and an opening133is provided in an underside of the cylindrical part131a. The cylindrical part131ais mounted to the rear (right as viewed inFIG. 1) end of the motor housing105on the opposite side from the spindle117(the power transmitting mechanism111). The cylindrical part131ahas extending walls135,137at its both ends in the longitudinal direction of the power tool and extend in a direction transverse to the longitudinal direction, and the opening133is defined between these extending walls135,137. In other words, the opening133is formed not to extend to either end of the cylindrical part131ain the longitudinal direction. Here, the cylindrical part131aand the opening133are features that correspond to the “cylindrical part” and the “opening”, respectively, according to this invention. Further, the extending walls135,137here form the “extending wall” according to this invention.

The extending walls135,137serve as a reinforcing part of the cylindrical part131aand thus have a function of ensuring adequate strength of the rear cover131itself. The opening133serves to allow connection of the switch part141which is disposed within the rear cover131(the cylindrical part131a) and the operating lever143which is disposed on the outer surface of the rear cover131(the cylindrical part131a). With such a construction, the switch part141can be connected to the operating lever143through the opening133. Further, the opening133also serves as an escape part for allowing rotation of an engagement part150bwhen the locking member150is turned as described below.

Further, a plurality of nonslip ribs138are formed on the outer surface of the cylindrical part131asuch that they extend along the longitudinal direction of the rear cover131or the longitudinal direction of the body103and are spaced substantially evenly in the circumferential direction. Further, a plurality of air vents139are formed in lateral sides of the cylindrical part131ain order to take in air to cool the driving motor121.

By provision of the rear cover131of this embodiment, or particularly by provision of the cylindrical part131awhich is generally cylindrically formed in one piece, the number of parts can be reduced and adequate strength of the rear cover131can be ensured by the one-piece structure. Further, for example, in case of a rear cover consisting of two halves, a space for mounting screws and screw bosses must be provided within the rear cover. Therefore, a sufficient interior space for cooling air to flow through may not be ensured so that dust and dirt tend to accumulate in it, and the overall size of the rear cover may increase. The rear cover131of this embodiment however can effectively overcome such problems.

The detailed constructions of the operating lever143and the locking member150are now described with reference toFIGS. 4 and 5.FIG. 4is a partly enlarged view of the operating lever143inFIG. 1which is placed in a released position andFIG. 5is a partly enlarged view of the operating lever143inFIG. 1which is placed in an operating position.

As shown inFIGS. 4 and 5, the operating lever143of this embodiment is an elongate operating member extending in the longitudinal direction of the body103and is arranged to extend longitudinally on both of the undersides of the motor housing105and the rear cover131. Specifically, in this embodiment, the elongate operating lever143extends across the motor housing105and the rear cover131which both also serve as the grip110, along their lengths. The operating lever143has a projecting front end143aand a projecting rear end143band is mounted to the body103(initial state) by engagement (insertion) of the projecting front end143aand the projecting rear end143binto a recess105aof the motor housing105and a recess105bof the rear cover131, respectively. Further, a plate-like reinforcement member145is mounted to the operating lever143and extends longitudinally along the extending direction of the operating lever143, so that rigidity of the elongate operating lever143can be ensured.

The locking member150has an engagement part150band an operating part150cwhich are arranged on the opposite sides of a rotating shaft150amounted on the operating lever143side and extend transversely to the rotating shaft150aand in opposite directions from the rotating shaft150a. The locking member150is elastically biased in a direction of an arrow20inFIG. 4by a coiled spring member151so that it is held in a locked position (shown inFIG. 4). In the state in which the locking member150is held in the locked position shown inFIG. 4, the engagement part150bengages with (comes in contact with) a projection143cof the operating lever143and is integrally connected to the operating lever143, so that the locking member150is interposed in an operating space of the projection143c. As a result, the operating lever143is prevented from rotating (the operating lever143is locked). Specifically, when the engagement part150bintegrally connected to the projection143ccomes in contact with the motor housing105side, rotation of the operating lever143is prevented. On the other hand, when the operating part150cof the locking member150is turned from the locked position in a direction of an arrow22shown inFIG. 4against the elastic biasing force of the spring member151, the locking member150is placed in an unlocked position (shown inFIG. 5). In the unlocked position, the engagement part150bis disengaged from the projection143c, so that the operating lever143is allowed to rotate. Therefore, in order to place the operating lever143into the operating position, once the locking member150must be turned to the unlocked position.

In the initial state, the operating lever143shown inFIG. 4is elastically biased in a direction of an arrow10inFIG. 4by a spring member (not shown) built into the switch part141which is held in contact with the operating lever143, so that the operating lever143is held in the released position (shown inFIG. 4). When the operating lever143is moved from the released position (shown inFIG. 4) to the operating position (shown inFIG. 5) by gripping operation with user's hand in the unlocked state of the locking member150, the operating lever143is rotated around a pivot (center of rotation) or the front end143aengaged with the recess105a, in the direction of the arrow12shown inFIG. 4against the elastic biasing force of the above-described spring member built into the switch part141. Specifically, the recess105aand the front end143aform a pivot of the operating lever143and form the “pivot” according to this invention. The operating lever143of this embodiment is arranged to extend longitudinally on both of the undersides of the motor housing105and the rear cover131, so that the user can operate the operating lever143in a wider range on the body103. Therefore, ease of operation of the operating lever143can be enhanced.

When the operating lever143is placed into the operating position shown inFIG. 5, the switch part141is pressed, so that the switch part141is turned on. Therefore, by operating the operating lever143to drive the driving motor121while holding the grip110formed by the motor housing105and the rear cover131, the user can rotationally drive the grinding wheel119via the power transmitting mechanism111and appropriately perform a grinding or polishing operation or a cutting operation on a workpiece.

On the other hand, when the user's hand is released and thus the operating lever143which is once placed in the operating position shown inFIG. 5is released, the operating lever143is rotated around the pivot (center of rotation) or the front end143ain the direction of the arrow10shown inFIG. 4by the elastic biasing force of the above-described spring member built into the switch part141. As a result, as being returned to the released position shown inFIG. 4, the operating lever143is disengaged from the switch part141until no longer pressing it so that the switch part141is turned off. Therefore, the driving motor121is stopped, so that rotation of the grinding wheel119via the power transmitting mechanism111is stopped. At this time, when the user releases the operating lever143, the locking member150which is once placed in the unlocked position is returned to the locked position shown inFIG. 4by the elastic biasing force of the spring member151.

In the above-described embodiment, the operating lever143is configured as a rotating lever which is rotated around a predetermined pivot. In this invention, however, an operating part corresponding to the operating lever143may be configured as a parallel moving lever or a sliding lever which moves in parallel or slides when the switch is operated. Further, in the above-described embodiment, the pivot of the operating lever143is described as being provided on the motor housing105, but it may be provided on the rear cover131as necessary.

Further, in the above-described embodiment, the cylindrical part131aof the rear cover131has the extending walls135,137which are formed at its both ends in the longitudinal direction of the power tool and extend in the direction transverse to the longitudinal direction, and the opening133is defined between the extending walls135,137. In this invention, however, the opening133may be formed to extend to the front end of the cylindrical part131awithout providing a part corresponding to the extending wall135, as necessary.

Further, in the above-described embodiment, the electric disc grinder101is explained as a representative example of the power tool. This invention, however, can also be applied to other electric power tools which perform a predetermined operation on a workpiece by a tool bit, including an electric grinding or polishing tool, such as a sander or a polisher, an angle drill to be used for screw tightening operation, a reciprocating saw to be used for cutting a workpiece. Further, this invention can also be applied to a pneumatic power tool in which a tool bit is driven by an air motor. In this case, as the tool bit, a grinding wheel or a blade for performing a grinding or polishing operation on a workpiece are typically used, but then a sanding disc or a wire brush can also be used.

DESCRIPTION OF NUMERALS