Tool driving or impacting – Impacting devices – Hammer head driven by pulsating fluid pressure
Reexamination Certificate
1999-07-20
2001-04-03
Vo, Peter (Department: 3721)
Tool driving or impacting
Impacting devices
Hammer head driven by pulsating fluid pressure
C173S109000, C173S127000, C173S136000, C173S138000, C173S162100, C173S207000
Reexamination Certificate
active
06209659
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hand drill including a housing, a chuck provided at a front, in a drilling direction, end of the housing for receiving a drill or chisel tool, a rotary drive arranged inside the housing for driving the chuck, together with the drill or chisel tool, a compressed air-operated hammer mechanism for generating axial blows to be applied to the drill or chisel tool and having a pneumatic cylinder with at least one inlet opening and at least one discharge opening, a die member for imparting the axial blows, which are generated by the hammer mechanism, to the drill or chisel tool and extending through a front limiting surface of the pneumatic cylinder, and a percussion piston displaceable in the pneumatic cylinder upon being impinged by compressed air for intermittently applying axial blows to the die member, and a reversing valve for connecting the hammer mechanism with a source of compressed air.
2. Description of the Prior Art
In addition to hand-held drills provided with electro-pneumatic hammer mechanisms or mechanical hammer mechanisms such as ratchet hammer mechanisms, spring-actuated hammer mechanisms and cushioned cam hammer mechanisms, also are used hand-held drills having a compressed air-operated or servo-pneumatic hammer mechanisms which include a pneumatic cylinder in which a percussion piston is arranged. The percussion piston is displaceable by the compressed air and periodically applies axial blows to a die member which transmits the blow to a tool secured in the chuck of the hand-held drill. In the known compressed air-operated hammer mechanisms, a reversing valve is provided between the pneumatic cylinder and the source of the compressed air, e.g., a compressor located in the drill housing. The reversing valve provides for alternating supply of the compressed air to the pneumatic cylinder and the discharge of the compressed air from the pneumatic cylinder for reciprocating the percussion piston in the pneumatic cylinder chamber. The operation of the reversing valve is controlled by end switches which are actuated in front and rear end positions of the percussion piston. The switching of the reversing valve proper is then effected by appropriate mechanical, electrical means or by communicating to the reversing valve the compressed air through control conduits.
The drawback of the known compressed air-operated hammer mechanisms consists in that they have a large dead volume which must be reloaded between each pressurized condition of the pneumatic cylinder and each unpressurized condition of the pneumatic cylinder. This adversely affects timely deceleration of the percussion piston and, thereby, a predetermined blow frequency. Further, the permanent reloading of the large dead volume leads to large energy losses. The known compressed-air operated hammer mechanisms have at least one reversing valve and several end switches. Such an arrangement causes a time delay in switching from one condition of the reversing valve to another condition thereof, which adversely affects the blow power. Further, the energy of a single blow and the frequency of the generated axial blows can only be controlled by the pressure acting on the hammer mechanism to a very small extent.
Accordingly, an object of the present invention is to eliminate the drawbacks of conventional compressed air-operated hammer mechanisms and to provide a hammer mechanism in which the time delay in switching of the pneumatic cylinder between its pressurized and unpressurized conditions is eliminated to a most possible extent.
Another object of the present invention is to provide a hammer mechanism in which the energy necessary for reloading of the dead volume is reduced, and the energy balance for generating axial blows is substantially improved.
A further object of the present invention is to provide a hammer mechanism which would provide greater possibilities for adjusting the energy of single blows and the blow frequency.
SUMMARY OF THE INVENTION
These and other objects of the present inventions, which will become apparent hereinafter, are achieved by providing a hand-held drill including a housing, a chuck provided at a front, in a drilling direction, end of the housing for receiving a drill or chisel tool, a rotary drive arranged inside the housing for driving the chuck, together with the drill or chisel tool receivable in the chuck, and a compressed air-operated hammer mechanism for generating axial blows to be applied to the drill or chisel tool. The hammer mechanism has a pneumatic cylinder with at least one inlet opening and at least one discharge opening, a die member for imparting the axial blows, which are generated by the hammer mechanism, to the drill or chisel tool and extending through a front limiting surface of the pneumatic cylinder, and a percussion piston displaceable in the pneumatic cylinder upon being impinged by compressed air for intermittently applying axial blows to the die member. A reversing valve connects the hammer mechanism with a source of compressed air. The reversing valve is integrated in the percussion piston and has a plurality of recesses and bores alternatively operationally connectable with the at least one inlet opening and the at least one discharge opening of the pneumatic cylinder for feeding the compressed air into the pneumatic cylinder and for discharging the compressed air therefrom.
Because the reversing valve forms an integral part of the percussion piston, the reversing valve is located within the working volume of the pneumatic cylinder. Further, a pressure is permanently applied to the inlet opening of the pneumatic cylinder. The discharge opening of the pneumatic cylinder serves only for discharging the compressed air from the pneumatic cylinder. The recesses and bores, which are formed in the reversing valve, permits to reduce the dead volume which has to be reloaded between the pressurized and unpressurized conditions of the pneumatic cylinder at each complete stroke of the percussion piston. The reduction of the reloadable dead volume permits to reduce the energy necessary for reloading and improves the general energy balance of generation of axial blows. The present invention also reduces the number of necessary conduits, connections and parts due to the fact that the valving function is now performed by the percussion piston itself instead of a separate reversing valve that was the case in the prior art hammer mechanisms. The time delay of switching is eliminated due to the fact that the percussion piston functions as its own end switch.
In accordance with an advantageous embodiment of the present invention, the percussion piston includes an integrated switch piston which forms the reversing valve and which is displaceable between two end pistons for alternatively directing the compressed air into the working chamber of the pneumatic cylinder and discharging the compressed air therefrom. In this embodiment, the percussion piston forms the valve housing in which a cylindrical reversing element, the switch piston, is axially displaceable.
Because the switch piston extends beyond the rebound surface of the percussion piston during the forward stroke of the percussion piston and beyond the rear surface of the percussion piston during the return stroke of the percussion piston, and, respectively, engages the front and rear surfaces of the pneumatic cylinder, the switch piston acts as an end switch for a respective end position of the percussion piston. Thereby, the time delay during switching is eliminated as the switch piston also functions as a reversing valve, and no time delay takes place between the actuation of the end switch and the valve, as it was the case in the prior art hammer mechanisms in which the end switches and the valve were separate elements. Because the switch piston extends beyond the end surface of the percussion piston, it engages the front or rear surface of the pneumatic cylinder before the percussion piston reaches its respective end position, s
Brown & Wood LLP
Calve Jim
Hilti Aktiengesellschaft
Vo Peter
LandOfFree
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