Tool driving or impacting – Means to drive tool about an axis – Electric motor
Reexamination Certificate
1999-06-16
2001-04-10
Vo, Peter (Department: 3721)
Tool driving or impacting
Means to drive tool about an axis
Electric motor
C173S170000, C173S216000
Reexamination Certificate
active
06213224
ABSTRACT:
This application claims priority on Japanese Patent Application No. 10-170304, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electric power tools. More particularly, the present invention relates to an electric power tool which has a split two-part housing for encasing a drive unit that includes a motor and a reduction mechanism for transmitting the rotation of the motor to a spindle protruding toward the top end of the tool.
2. Description of the Related Art
Various power screwdrivers and screwdriver/drills have been known in the art, as disclosed in Japan Published Examined Patent Application Nos. S59-52298 and H4-59112, both of which include a description of a split two-part housing made of synthetic resin that encloses a drive unit. Furthermore, the drive unit includes a motor and a reduction mechanism which is coupled to the motor by means of screws and transmits the rotation of the motor to a spindle protruding toward the top end of the housing. Additionally, a torque setting adjuster and a chuck are mounted on the part of the spindle protruding from the front of the housing.
When this arrangement is applied to an electric power screwdriver as in the above examples, the tool is subjected to a large force acting in the axial direction of the spindle when the tool bit is pressed against a screw or other workpiece. The split two-part housing made of synthetic resin sometimes fails to withstand the force, with the result being that the spindle and the housing become distorted or warped. This may in turn adversely affect gear engagement in the reduction mechanism and thus normal rotation of the spindle.
SUMMARY OF THE INVENTION
In view of the above-identified problems, an important object of the present invention is to provide an electric power tool with sufficient rigidity such that the tool can effectively withstand a large axial force applied thereto.
Another object of the present invention is to provide an electric power tool that can maintain normal rotation of the spindle when subjected to a large axial force.
The above objects and other related objects are realized by the invention, which provides an electric power tool, comprising: a spindle having an axis; a drive unit including a motor and a reduction mechanism for transmitting the rotation of the motor to the spindle of the tool; and a housing having a front end for containing the drive unit. In this tool, a portion of the drive unit is made of metal, with the metal portion of the drive unit exposed to the outside of the tool forward of the housing and connected to the front end of the housing. This construction imparts to the tool enhanced rigidity, particularly strength to external force applied in the axial direction, thus preventing the housing from twisting or deforming during operation. In addition, proper engagement, in the reduction mechanism is ensured so as to maintain normal torque transmission.
According to one aspect of the present invention, the metal portion of the drive unit is screwed to the front end of the housing in the axial direction of the spindle. This construction renders the drive unit strong enough to withstand axial external force applied to the unit.
According to another aspect of the present invention, the metal portion of the drive unit is integrally provided with a bearing portion for supporting the spindle. The integral metal bearing portion rigidly supports the spindle such that the spindle does not, easily twist or warp.
According to still another aspect of the present invention, the reduction mechanism is an epicycle reduction gear mechanism, and the drive unit includes a clutch means for interrupting the transmission of the rotation of the motor from the epicycle reduction gear mechanism to the spindle responsive to a load applied to the spindle.
According to yet another aspect of the present invention, the clutch means includes an adjusting member for adjusting the torque at which the transmission of the motor rotation to the spindle is interrupted. Furthermore, the metal portion of the drive unit is disposed between the adjusting member and the housing.
In accordance with another aspect of the present invention, the metal portion of the drive unit has a substantially cylindrical shape, and the tool optionally includes an auxiliary handle with a circular mount that can be fitted around the metal portion of the drive unit.
In a preferred embodiment, the metal portion of the drive unit may have an outer surface that is smoothly and continuously connected with an outer surface of the front end of the housing.
In another preferred embodiment, the metal portion of the drive unit is made of aluminum alloy.
To carry out the invention in one preferred mode, the housing further includes two substantially symmetrical casing halves fitted together in a plane in which the axis of the spindle is located.
Other general and more specific objects of the invention will in part be obvious and will in part be evident from the drawings and descriptions which follow.
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patent: 3734207 (1973-05-01), Fishbein
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patent: 3959677 (1976-05-01), Grieb
patent: 4366403 (1982-12-01), Simpson et al.
patent: 4479555 (1984-10-01), Grossman et al.
patent: 4730134 (1988-03-01), Sistare
patent: 5049012 (1991-09-01), Cavedo
patent: 5339908 (1994-08-01), Yokota et al.
patent: 5531278 (1996-07-01), Lin
patent: 5624000 (1997-04-01), Miller
patent: 59-52298 (1984-12-01), None
patent: 4-59112 (1992-09-01), None
Furuta Takefumi
Mori Shinsuke
Umemura Shingo
Calve Jim
Foley Hoag & Eliot LLP
Makita Corporation
Vo Peter
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