Tool driving or impacting – Drive controlled by relative axial movement of tool
Patent
1991-10-29
1994-01-11
Yost, Frank T.
Tool driving or impacting
Drive controlled by relative axial movement of tool
173 48, 173109, 173205, B25D 1110
Patent
active
052772594
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is related to a hammer drill having a coupling which is engaged for generating movement to a tool spindle in the drill when the tool is against a work surface.
A motorised hammer drill is already known from German Patent Publication DE-OS 35 06 695 (corresponding to U.S. Pat. No. 4,719,976), the hammer unit of which can be switched off by means of a coupling between a motor-driven intermediate shaft and the motion conversion gear, which produces the reciprocating piston movement. The coupling force is amplified by a lever which is loaded by the reaction forces of the hammer unit. The amplifying force applied to the coupling is absorbed by a pin in the housing and a bearing of the intermediate shaft, which is supported in a special metal bearing bridge. The effectiveness of the force amplification can be reduced by tolerances of the lever, the bearing pin and the bearing bridge. With very adverse conditions during operation, the generation of heat can cause yield of the plastic housing and thus a displacement of the pin. Moreover, any undesirable reduction of the pressing force with such lever designs can lead to a lengthening of the engagement path.
SUMMARY OF THE INVENTION
In contrast, the hammer drill according to the invention includes a first coupling portion being mounted axially to the drive shaft of the hammer drill, a second coupling portion being rotatably mounted to the drive shaft and capable of axial movement along the drive shaft and means for transmitting torque of the drive shaft, the transmitting means coupling the second coupling portion to the drive shaft such that torque of the drive shaft can be transmitted as an axially directed force to the second coupling portion to close the coupling has the advantage that both the pressing force and the pressing path for switch-on of the hammer unit are reduced. This is achieved by an automatically amplifying coupling which utilizes the hammer's motor power to increase the coupling force, or in other words, the axial force for closing the coupling.
Additional and advantageous developments and improvements of the hammer include, for example, gear connections with control faces or contours which extend obliquely in an axial direction to enable a conversion of the rotational movement of the motor-driven shaft to an axial displacement of a control sleeve, so long as this has a different rotation-al speed from that of the shaft. Another feature of the invention facilitates positive engagement of the coupling when the hammer action is actually required.
The design of the hammer has the advantage that the effectiveness of the coupling force amplification is independent of the reactions of non-associated components, such as housings, etc. This is achieved by virtue of the fact that, outwardly, the intermediate shaft is free from coupling forces. This obviates any tolerances originating outside, i.e. from housing parts, levers, and the like, which would impair the function. The plastic housing does not absorb any forces from the amplification of the coupling force. Still another feature of the invention is a brake facility for speedier decoupling.
The present invention both as to its construction so to its mode of operation, together with additional objects and advantages thereof, will be best understood from the following description of preferred embodiments when read with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a longitudinal cross-section of a front portion of a hammer drill constructed in accordance with a first embodiment of the present invention; and
FIG. 2 shows a longitudinal cross-section of a hammer unit of the hammer drill constructed in accordance with a second embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The hammer drill 2 is surrounded by a plastic housing 3 and has a tool holder 4 at the front into which a tool 5 can be inserted. Located within the housing is a motor, not shown here, of which only the mo
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Faelchle Jorg
Laubengaier Walter
Schmid Wolfgang
Rada Rinaldi
Robert & Bosch GmbH
Striker Michael J.
Yost Frank T.
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