Tool driving or impacting – Impacting devices – With impact cushioning means
Reexamination Certificate
2002-04-19
2004-07-20
Rada, Rinaldi I. (Department: 3721)
Tool driving or impacting
Impacting devices
With impact cushioning means
C173S090000, C173S201000, C173S211000, C173S162200
Reexamination Certificate
active
06763897
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to hand held electrically powered hammers, and in particular to demolition hammers.
Such hammers generally comprise a housing within which is located an electric motor and a gear arrangement for converting the rotary drive of the motor to a reciprocating drive to drive a piston within a hollow spindle, which spindle is located within the hammer housing. The spindle may be formed from a single part or from more than one part, for example from a rearward hollow cylinder, within which a piston and ram reciprocate and a forward cylindrical tool holder body, within which a tool or bit may be releasably mounted. A ram is located in front of the piston within the spindle so as, in normal operating conditions, to form a closed air cushion within the spindle between the piston and the ram. The reciprocation of the piston reciprocatingly drives the ram via the air cushion. A beatpiece is generally located within the spindle and transmits repeated impacts that it receives from the ram to a tool or bit releaseably mounted for limited reciprocation in front of the beatpiece in a tool holder portion of the spindle. The impacts on the tool or bit are transmitted to a workpiece against which the tool or bit is pressed in order to break up or make a bore in the workpiece.
Some hammers may also be employed in combination impact and drilling mode in which the spindle, and hence the bit inserted therein, will be caused to rotate at the same time as the bit is struck by the beatpiece. The present invention is also applicable to such rotary hammers.
One problem with such hammers is that the reciprocating parts and repeated impacts between the parts cause large vibrations to be transmitted via the handles of the hammer to the user. This is uncomfortable for the user, particularly over prolonged periods of use and can contravene safety standards.
This problem has been solved in the past by forming a vibration damping linkage between the handles of the hammer and the main housing of the hammer. However, the linkages have to be rigid enough for the handles to guide the hammer while also providing damping. Also, the user of the hammer tensions the linkage when the hammer is urged against a workpiece and this changes the damping effect of the linkage. This means that such linkages tend to be relatively complex.
This problem has also been solved for a pneumatic hammer, for example as disclosed in DE815,179 by mounting masses on opposing sides of the spindle, with each mass mounted between two springs so that each of the masses can oscillate parallel to the axis of the spindle due to the forces from the two springs. The masses oscillate in phase and in the same direction as the ram and are arranged to oscillate as near to resonance as possible. However, this gives rise to the problem of synchronising movement of the masses. If the masses are not exactly synchronised then a torque at right angles to the direction of mass vibration is generated which is transmitted to the user of the hammer via the hammer housing. This problem has been addressed in DE31 22 979 which describes an electrically powered hammer to which a dampening housing is attached. The dampening housing comprises two moveable masses each connected to a compression spring. The channels in which the masses are located are interconnected so that generation of an over pressure in one channel results in a corresponding over pressure in the other channel in order to synchronise movement of the masses. However, the arrangement disclosed in DE31 22 979 is relatively complex and takes up a lot of space.
The problem of synchronising masses can also be overcome for a pneumatic hammer by using a single mass as described in DE24 03 074 in which there is described a hammer housing which is enclosed by a handle housing. Around the hammer housing is located a cylindrical mass which is able to reciprocate along the hammer housing on the end of a coil spring. Optimum vibration reduction is achieved if the spring constant of the coil spring is adapted to the beat frequency of the hammer.
A second problem is that the reciprocating parts and repeated impacts cause heat generation within the hammer and some means is required to transfer the generated heat away from the spindle and the parts within the spindle. If the parts within the spindle are operating at high temperatures then they are more prone to wear and eventually to failure. In particular any seals between the piston and the spindle and the ram and the spindle are susceptible to damage at higher temperatures. Hammers are generally operated in very dusty environments and it is critical to the prolonged operation of the hammer that there is no dust ingress into the spindle. As there are several ports in the spindle through which air can flow into and out of the spindle, cooling of the spindle using air flows can easily introduce dust into the spindle.
Therefore, cooling of the spindle is generally achieved by passive heat transfer from the metal spindle either via air pockets or directly to metal housing parts surrounding the spindle. However, the cooling achieved by such passive heat transfer is relatively limited.
SUMMARY OF THE INVENTION
The present invention aims to overcome the problems discussed above by providing a system which both reduces the vibration of the hammer housing and cools the spindle, without taking up much space within the hammer housing.
According to the present invention there is provided a hand held electrically powered hammer, comprising a housing within which is located:
a motor;
hollow spindle within which is located for reciprocation therein a piston and forwardly of the piston a ram;
a hammer drive arrangement which converts the rotary drive of the motor to a reciprocating drive to the piston;
a tool holder body located at the forward end of the spindle in which a tool or bit may be releasably mounted for limited reciprocation;
wherein the reciprocation of the piston reciprocatingly drives the ram via a closed air cushion such that repeated impacts from the ram are transmitted to a tool or bit mounted in the tool holder body, wherein the hammer additionally comprises:
a metal casing which encloses at least part of the spindle so as to form an air filled chamber between the spindle and the casing;
a damping mass, which is located within the chamber, which damping mass is connected to the hammer housing via at least one spring element so as to oscillate back and forth along the spindle to minimise the vibration of the hammer housing; and
at least one spacer element for positioning the damping mass with respect to the spindle and the metal casing so that a small gap is present between the mass and the spindle and a small gap is present between the mass and the casing such that oscillation of the damping mass within the chamber generates air turbulence within the chamber for facilitating heat transfer from the spindle to the metal casing.
The use of a damping mass oscillating within a chamber surrounding the spindle for reducing the vibration of the hammer housing is also used according to the present invention for generating air turbulence between the spindle and a metal casing part surrounding the spindle. When the damping mass moves forwardly along the spindle an overpressure is generated in front of the mass which causes air to flow rearwardly through the gaps between the mass and the spindle and the mass and the metal housing. When the damping mass moves rearwardly along the spindle an overpressure is generated rearwardly of the mass which causes air to flow forwardly through the gaps between the mass and the spindle and the mass and the metal housing. This air turbulence between the spindle and the metal casing can facilitate a three times increase in heat transfer away from the spindle as compared to passive heat transfer via an air pocket in which no turbulence occurs. According to the present invention the same components are used for the dual purpose of reducing the vibration transmitted to a user of the tool from the h
Becht Reimund
Faatz Heinz-Werner
Gensmann Stefan D.
Hanke Andreas
Plietsch Reinhard
Black & Decker Inc.
Leary Michael P.
Lopez Michelle
Rada Rinaldi I.
Shapiro Bruce S.
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