Power tools

It is accordingly an object of the invention to provide a technique of cooling a power tool which further improves cooling effectiveness of the power tool. According to the invention, a power tool is provided that includes a driving motor, a tool bit, a power transmitting mechanism, a tool body and a cooling fan. The power tool further includes first and second cooling air passages. The first cooling air passage is disposed within the tool body and flows cooling air into the tool body by using the cooling fan. The second cooling air passage is provided within the tool body and takes outside air into the tool body by using the flow of the cooling air through the first cooling air passage. The cooling air within the first cooling air passage can be cooled by mixing outside air taken into the tool body via the second cooling air passage and therefore, the cooling air can further effectively cool components within the power tool. As a result, cooling effectiveness of the power tool can be improved.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power tool and more particularly, to a technique of cooling the power tool.

2. Description of the Related Art

Japanese non-examined laid-open patent publication No. 10-201205 discloses a hand-held type electric disc grinder. According to the known grinder, a cooling fan is disposed within a motor housing and driven by a driving motor. Cooling air is introduced from the rear end of the motor housing and led forward by rotation of the cooling fan. Thereafter, the cooling air is discharged to the outside from an air outlet in the vicinity of a gear housing connected to the motor housing. The flow of the cooling air cools the driving motor, the motor housing, the power transmitting mechanism and the gear housing.

While the above-mentioned cooling technique can ensure cooling performance to some degree, further improvement of the cooling effectiveness is desired.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a technique of cooling a power tool which further improves cooling effectiveness of the power tool.

According to the invention, a power tool is provided that includes a driving motor, a tool bit, a power transmitting mechanism, a tool body and a cooling fan. The power tool further includes first and second cooling air passages. The first cooling air passage is disposed within the tool body and flows cooling air into the tool body by using the cooling fan. The second cooling air passage is provided within the tool body and takes outside air into the tool body by using the flow of the cooling air through the first cooling air passage. Outside air taken into the tool body is mixed with the cooling air. Because the cooling air within the first cooling air passage can be cooled by mixing outside air taken into the tool body via the second cooling air passage, the cooling air can further effectively cool components within the power tool. As a result, cooling effectiveness of the power tool can be improved. Other objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.

DETAILED DESCRIPTION OF THE INVENTION

The representative power tool may include a driving motor, a tool bit, a power transmitting mechanism, a tool body, a cooling fan and first and second cooling air passages. The tool bit performs a predetermined operation on a workpiece. The tool bit may typically refer to an electric disc grinder that performs a polishing or grinding operation on a workpiece by rotating a tool bit in the form of a grinding wheel. Further, it also embraces other power tools such as reciprocating saw, chain saw, hammer and hammer drill. The power transmitting mechanism transmits the output of the driving motor to the tool bit. The tool body houses the driving motor and the power transmitting mechanism. The tool body typically includes a motor housing for housing the driving motor and a gear housing for housing the power transmitting mechanism. Preferably in such case, both housings may be fixedly connected to each other. The cooling fan is disposed within the tool body. As the cooling fan, a centrifugal fan or an axial fan may be suitably utilized.

First cooling air passage is disposed within the tool body and flows cooling air into the tool body by using the cooling fan. The second cooling air passage is provided within the tool body and takes outside air into the tool body by using the flow of the cooling air through the first cooling air passage to mix the outside air with the cooling air. According to the invention, the cooling fan causes cooling air to flow within the tool body through the first cooling air passage and outside air is taken into the tool body through the second cooling air passage by utilizing the flow of the cooling air through the first cooling air passage. The outside air taken into the tool body may be mixed with the cooling air in the first cooling air passage. The intake of outside air into the second cooling air passage may be typically achieved by back pressure defined by pressure difference between the atmosphere and the second cooling air passage. Such back pressure may be caused by the flow of the cooling air through the first cooling air passage.

Preferably, the cooling air flowing through the first cooling air passage may flow downstream after cooling the driving motor. The cooling air is heated by cooling the driving motor. In this connection, according to the invention, low-temperature outside air can be taken into the tool body through the second cooling air passage and mixed with the heated cooling air so as to cool the heated cooling air. Thereafter, the cooled cooling air can flow downstream and can cool downstream components of the power tool. The downstream components here may refer to the power transmitting mechanism and the housing that houses the power transmitting mechanism. Thus, entire power tool can be efficiently cooled and the cooling effectiveness can be improved.

Each of the additional features and method steps disclosed above and below may be utilized separately or in conjunction with other features and method steps to provide and manufacture improved power tools and method for using such power tools and devices utilized therein. Representative examples of the present invention, which examples utilized many of these additional features and method steps in conjunction, will now be described in detail with reference to the drawings. This detailed description is merely intended to teach a person skilled in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Only the claims define the scope of the claimed invention. Therefore, combinations of features and steps disclosed within the following detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe some representative examples of the invention, which detailed description will now be given with reference to the accompanying drawings.

First Representative Embodiment

First embodiment of the present invention will be explained with reference toFIGS. 1 to 3. In this embodiment, a hand-held portable electric disc grinder as an example of the representative power tool is provided. The representative disc grinder is used to polish or grind various kinds of workpiece, such as metal, concrete and stone. The disc grinder101includes a body103having a motor housing105and a gear housing107. The body103is a feature that corresponds to the “tool body” according to the invention. The motor housing105is generally cylindrically shaped and houses an electric motor201. The electric motor201includes a rotor203and a stator205. The rotor203is rotatably disposed within the motor housing105and the stator205is fastened within the motor housing105by fastening devices such as screws213. The electric motor201is disposed such that the direction of the axis of rotation of the rotor203corresponds to the longitudinal direction of the disc grinder101. An output shaft207of the motor201extends generally horizontally in the longitudinal direction of the disc grinder101. Bearings211support the rear end and the front end (the right end and the left end, respectively, as viewed inFIG. 1) of the output shaft207. Around the front end portion of the output shaft207, a driving side bevel gear209is integrally formed and a cooling fan217is mounted such that it can rotate together with the output shaft207. Further, other than the electric motor201, the motor housing105houses an electrical device215such as a controller for controlling the motor.

The gear housing107is connected to the front end of the motor housing105and houses a power transmitting mechanism301. The power transmitting mechanism301transmits the output of the driving motor105to a grinding wheel313. The power transmitting mechanism301mainly includes the driving side bevel gear209, a driven side bevel gear305and a spindle303. The spindle303extends generally vertically in a direction perpendicular to the output shaft207of the motor201and is rotatably supported by a bearing307. The driven side bevel gear305is mounted around the upper end portion of the spindle303such that it can rotate together with the spindle303in one piece. The driven side bevel gear305engages the driving side bevel gear209of the output shaft207that extends into the gear housing107. The lower end portion of the spindle303protrudes from the gear housing107. A grinding wheel mounting portion309is formed on the protruded end of the spindle303. The grinding wheel313is mounted to the grinding wheel mounting portion309via a grinding wheel holder311. A cover315covers the rear half of the grinding wheel313. The grinding wheel313is a feature that corresponds to the “tool bit” according to the invention.

The motor housing105is generally cylindrically shaped and forms a handgrip that the user holds during the working (polishing or grinding) operation. A switch knob (not shown) is provided in a predetermined position on the outer periphery of the motor housing105and can be operated to drive the electric motor201. When the motor201is driven by operation of the switch knob, the output of the motor201is transmitted from the output shaft207to the grinding wheel313via the driving side bevel gear209, the driven side bevel gear305and the spindle303. Thus, the grinding wheel313is rotated, so that the operation of polishing or grinding the workpiece can be performed.

Further, an inlet (not shown) is formed in the rear end portion (the right end portion as viewed inFIG. 1) of the motor housing105and air for cooling the electric motor201is taken in through the inlet. When the electric motor201is driven, outside air is allowed to flow into the motor housing105through the inlet by the suction force which is caused by rotation of the cooling fan217. Thus, the cooling fan217causes the cooling air to flow within the motor housing105. The cooling fan217is a centrifugal fan, and a baffle plate221is disposed at the rear of the cooling fan217such that it covers the cooling fan217. The baffle plate221is formed of synthetic resin in one piece and has a generally bowl-like shape. An air hole223(seeFIG. 3) is formed in the center of the baffle plate221.

As shown by arrows inFIG. 1, the cooling air that has been taken into the motor housing105through the inlet by the suction force of the cooling fan217flows forward (toward the gear housing107) through the clearance between the rotor203and the stator205and the clearance between the stator205and the inside wall surface of the motor housing. As a result, the driving motor201is cooled down. The cooling air that has passed along the driving motor201is drawn from the rear side of the baffle plate221into the inside of the baffle plate221via the air hole223. Thus, the cooling air is narrowed via the air hole223. Thus, the amount and pressure of the cooling air in the inside of the baffle plate221increase. With the momentum, the cooling air flows forward along the inside surface of the baffle plate221and is discharged to the outside through an opening225of a retainer317and air outlets227of the gear housing107. The retainer317is disposed in the joint between the gear housing107and the motor housing105when they are butt-joined together. The retainer317retains the bearing211that is disposed on the side of the gear housing107.

The air outlets227are formed in the upper and lower portions of the gear housing107. The cooling air discharged through the upper air outlet227is blown toward a front upper surface107aof the gear housing107. The cooling air discharged through the lower air outlet227is blown onto the upper surface of the cover315that covers the grinding wheel313. Thus, the cooling air that has been taken into the motor housing105through the inlet flows through a passage229defined by the clearance between the rotor203and the stator205of the motor201, the clearance between the stator205and the inside wall surface of the motor housing, the air hole223of the baffle plate221, the openings225and the air outlets227. The passage229is a feature that corresponds to the “first cooling air passage” according to the invention. The passage229is hereinafter referred to as the first passage.

Further, second passages231,233are formed on the upper and lower surface sides of the body103. Outside air is taken in through the second passages231,233and mixed, on the suction side (the upstream side) of the cooling fan217in the first passage229, with the cooling air that has been heated by passing along the driving motor201. As a result, the cooling air is cooled. The second passages231,233are features that correspond to the “second cooling air passage” according to the invention. Specifically, as shown inFIG. 3, the upper second passage231is defined by an air intake231a, a communication passage231band a space235. The air intake231ais formed by notching the retainer317disposed in the joint between the motor housing105and the gear housing107. The communication passage231bis formed by notching the baffle plate221such that it communicates with the air intake231a. The space235is defined between the rear surface of the baffle plate221and the inner wall surface of the motor housing105. Further, the lower second passage233is defined by an air intake233aand the space235between the rear of the baffle plate221and the inner wall surface of the motor housing105. The air intake233ais formed through a bulged front portion105aof the motor housing105. The air intake231aof the retainer317and the air intake233aof the motor housing105have a slit-like shape elongated in the lateral direction of the body103. The second passages231,233communicate with the first passage229between the driving motor201and the baffle plate221on the suction side of the cooling fan217.

Operation and usage of the above-described hand-held electric disc grinder101is now explained. When user hand-holds the motor housing105and operates the switch knob, the electric motor201is driven and the grinding wheel313is rotated, so that the operation of polishing or grinding workpiece can be performed. During the operation by the grinding wheel313, cooling air is drawn into the motor housing105through the inlet by rotation of the cooling fan217. Then, as shown by arrows inFIG. 1, the cooling air is led through the first passage229and discharged to the outside through the air outlets227. The cooling air flowing through the first passage229cools the driving motor201, the motor housing105, the gear housing107and the power transmitting mechanism301.

When the cooling air passes through the first passage229, outside air is taken in through the second passages231,233. This intake of outside air is achieved by utilizing back pressure defined by pressure difference between the first passage229and the atmosphere. Specifically, the suction force of the cooling fan217acts upon the space235between the rear surface of the baffle plate221and the inner wall surface of the motor housing105. By this suction force, outside air is taken into the motor housing105via the air intake231aand the communication passage231bor via the air intake233a. The outside air that has been taken into the motor housing105joins and mixes with the cooling air flowing through the first passage229, on the rear side of the baffle plate221. When the cooling air passes along the driving motor201through the first passage229, the cooling air is heated by the driving motor201. However, as mentioned above, outside air flows in through the second passages231,233and mixes with the heated cooling air, thereby cooling the cooling air. As a result, the gear housing107and the power transmitting mechanism301, which are located downstream of the driving motor201, can also be cooled by the cooled cooling air.

Further, according to this embodiment, the second passages231,233are formed on the suction side of the cooling fan217. In other words, the second passages231,233are formed such that outside air is introduced between the cooling fan217and the driving motor201. With such construction, the outside air is taken into the body103through the second passages231,233and directly contacts with part of the motor housing105and the driving motor201, thereby cooling the motor housing105and the driving motor201. In the above-mentioned manner, the entire hand-held electric disc grinder101, including the body103and the driving motor201and the power transmitting mechanism301disposed within the body103can be efficiently cooled. Thus, the user can perform the operation while holding the motor housing105.

Further, in this embodiment, the air intake231aof the upper second passage231is formed by notching the outer peripheral portion of the retainer317disposed in the joint between the motor housing105and the gear housing107when they are butt-joined together. With this construction, when the body103is viewed from above, only the bottom of the notch is visible through the air intake231a. In other words, the retainer317serves as a screen to hide the inside of the housing, so that the inside of the motor housing105and the gear housing107is not visible or is difficult to see from outside. Thus, the inside of the body103is invisible from outside through the second passage231. Therefore, although the second passage231for air intake is formed in the midsection in the longitudinal direction of the body103, the appearance can be improved. Note that the inside visibility through the lower second passage233does not become a problem as long as it is not peeped into from below.

Second Representative Embodiment

Hand-held electric disc grinder101according to the second representative embodiment of the present invention is now explained with reference toFIGS. 4 and 5. The second representative embodiment is a modification relating to the second passages231,233of the first embodiment. The other components are similarly configured as in the first embodiment and therefore, will be identified by the same numerals and will not be described. In the second embodiment, second passages241,243are formed on the discharge side (the downstream side) of the cooling fan217on the upper and lower surface sides of the body103. The second passages241,243are features that correspond to the “second cooling air passage” according to the invention.

The second passages241,243include air intakes241a,243aand communication passages241b,243b, respectively. The air intakes241a,243aare formed by notching the upper and lower peripheral portions of the retainer317disposed in the joint between the motor housing105and the gear housing107. The communication passages241b,243bare defined by a clearance between the outside surface of an extension221aof the baffle plate221and the inner wall surface of the gear housing107. The baffle plate221corresponds to “baffle member” according to the invention. The extension221aextends forward from the flange (the bowl-like outer circumferential edge region) of the baffle plate221. The exit sides of the communication passages241b,243bface the space in the gear housing107. The air intakes241a,243ahave a slit-like shape elongated in the lateral direction of the body103. Further, the outer circumferential surface of the baffle plate221contacts the inner circumferential surface of the motor housing105at the base of the extension221a, thereby preventing communication between the first passage229and the second passages241,243.

In the electric disc grinder101thus constructed, when the cooling fan217is rotated, cooling air is drawn into the motor housing105through the inlet and flows within the motor housing105through the first passage229. The cooling air is then led into the gear housing107and discharged to the outside through the air outlets227. At this time, the cooling air that has passed through the air hole223of the baffle plate221is accelerated and flows forward in a strong current while being guided by the flange and the extension221aof the baffle plate221. This flow results back pressure to generate a suction force in the second passages241,243, so that outside air is taken in through the second passages241,243. The outside air joins and mixes with the cooling air flowing through the first passage229, thereby cooling the cooling air. As a result, the gear housing107and the power transmitting mechanism301located downstream of the cooling fan127can also be cooled by the cooled cooling air.

Further, the extension221aextends forward from the flange of the baffle plate221and defines the communication passages241b,243bof the second passages241,243. The extension221aserves as a screen to hide the inside of the housing when the body103is viewed from above. In other words, the baffle plate221that defines the second passages241,243also serves as a screen to hide the inside of the body103from view through the second passage231. Therefore, although the air intakes241a,243aare formed in the midsection in the longitudinal direction of the body103, the inside of the motor housing105and the gear housing107is hidden, so that the appearance of he tool can be improved.

Further, the air intakes231a,233amay be formed in the motor housing105in a position where they face the rear surface of the baffle plate221or the vicinity of the front end of the driving motor201. Further, while the above embodiments are explained by using electric disc grinder, this invention can also be applied to power tools having a driving motor, a tool bit and a power transmitting mechanism such as a reciprocating saw, a chain saw, hammer and hammer drill.

DESCRIPTION OF NUMERALS