- BACKGROUND OF THE INVENTION
The present invention relates to a hand machine tool—preferably a hammer drill and/or slide hammer—equipped with a hammer mechanism, which has a hammer that moves axially back and forth in a guide tube; a spring mechanism is provided, which exerts a force on the hammer and can set the hammer into a movement toward a tool that can be inserted into the hand machine tool.
A compression hammer mechanism of this kind, which executes repeating hammering movements and is intended for an electro-pneumatic hammer drill and/or slide hammer of the kind known from DE 198 10 088 C1, is comprised of an eccentric drive unit, a piston, and a hammer. These three elements serve to convert a rotating motion into a hammering motion. The axial back-and-forth motion of the hammer in a guide tube occurs in the following way: the piston, which the eccentric drive unit moves forward, compresses the air cushion between the piston and the hammer, thus causing the hammer to fly freely toward the tool inserted in the machine. The hammer imparts its hammering energy to the tool and from it, receives an impetus in the backward direction. At the same time, the eccentric drive unit also moves the piston backward, which produces a certain vacuum in the air cushion between the piston and the hammer. The moment the piston reaches its reversal point but the hammer is still flying toward the piston, the air cushion between the two is compressed, generating a compression, which, with a renewed forward motion of the piston, then causes the hammer to fly at an even higher speed in the forward direction toward the tool. In a compression hammer mechanism of this kind, the piston and the hammer move with the same frequency. A high individual hammering energy at a low hammering frequency is not possible with a hammer mechanism of this kind. The same is true for a so-called spring buckle hammer mechanism of the kind known from EP 544 865 B1. In it, an eccentric drive unit sets an angle made of spring steel into an oscillating motion and this spring steel piece drives the hammer forward toward the tool or toward an intermediate anvil provided between the tool and hammer. The recoil energy of the hammer is stored in the spring buckle and released again during forward motion as in a pneumatic hammer mechanism.
- SUMMARY OF THE INVENTION
The object of the present invention is to disclose a hammer mechanism of the type mentioned at the beginning, which can be implemented with the simplest possible technical means and is able to generate a high individual hammering energy at a low hammering frequency.
The stated object is attained with the characteristics of claim 1 in that means are provided, which set the hammer into a motion counter to the force of the spring mechanism after each impact in order to place this spring mechanism under stress; after the spring mechanism has been stressed, the means abruptly release the hammer again so that, driven by the spring mechanism, the hammer flies toward the tool. Because the hammer is actively moved counter to the force of the spring mechanism after each impact, a very powerful energy is imparted to the hammer after it is subsequently released for a new impact.
A suitable drive unit for the hammer produces a frictional engagement with the hammer after an impact has been imparted, moves it counter to the force of the spring mechanism, and then releases the frictional engagement again as soon as the hammer has reached a certain position in its movement counter to the force of the spring mechanism.
An advantageous spring mechanism is comprised of a pressure reservoir that is filled with a compressible medium and situated in the guide tube, on the side of the hammer oriented away from the tool. The pressure reservoir can be filled with a gas, for example air, or also a fluid. The compressible medium—gas or fluid—remains in the pressure reservoir on a constant basis and only certain leakage losses from the pressure reservoir need be compensated for. To that end, a pump can be provided, which supplies compressible medium to the pressure reservoir to compensate for leakage losses. The pumping capacity of this pump can be very low because it only needs to compensate for leakage losses in the pressure reservoir. Such a pump, which does not take up much space or weigh much, can be integrated into the hand machine tool.
BRIEF DESCRIPTION OF THE DRAWINGS
Another advantageous spring mechanism can be comprised of one or more compression springs and/or tension springs that are supported against the hammer on the one hand and against a shoulder that is stationary in the movement direction of the hammer on the other hand.
FIG. 1 shows a longitudinal section through a hammer drill and/or slide hammer equipped with a hammer mechanism and a spring mechanism embodied in the form of a pressure reservoir and
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 2 shows a longitudinal section through a hammer drill and/or slide hammer equipped with a hammer mechanism and a spring mechanism embodied in the form of compression/tension springs.
FIG. 1 shows a longitudinal section through a hand machine tool equipped with a hammer mechanism. For example, this hand machine tool is a hammer drill and/or slide hammer. The schematic depiction of the hand machine tool shows only the hammer mechanism, which is the subject of the present invention. All other functional units usually provided in a hand machine tool are not shown.
The hammer mechanism is comprised in an intrinsically known way of a hammer 1 that is supported so that it can move in a reciprocating fashion in a guide tube 2. A tool 3, for example a drill bit or chisel, is inserted into a tool socket of the hand machine tool. If the hammer 1 flies forward toward the tool 3, then the hammer 1 imparts its hammering impetus to the tool 3. Between the tool 3 and the hammer 1, it is also possible for an intermediate anvil (not shown here) to be provided in the guide tube 2, which transmits the hammering impetus from the hammer 1 to the tool 3.
The forward motion of the hammer 1 toward the tool 3 inserted into the hand machine tool is generated by a spring mechanism whose force is directed toward the hammer 1 in the direction of the forward motion. In the exemplary embodiment depicted in FIG. 1, this spring mechanism is a pressure reservoir 4, which is filled with a compressible medium and is situated in the guide tube 2 on the side of the hammer 1 oriented away from the tool. The pressure reservoir 4 is delimited by the side wall of the guide tube 2, the hammer 1 sliding in the guide tube, and a back wall 5 of the guide tube 2 at its end oriented away from the tool 3. A seal 6 is inserted between the hammer 1 and the side wall of the guide tube 2 and prevents the compressible medium from escaping from the pressure reservoir 4.
The compressible medium can be a fluid or a gas. Preferably, the pressure reservoir 4 is filled with air. In order to compensate for leakage losses from the pressure reservoir 4, the pressure reservoir 4 is connected to a pump 7 that can supply compressible medium to the pressure reservoir 4 in order to compensate for leakage losses. Since it is only necessary to compensate for leakage losses of the compressible medium, it is sufficient to provide a small pump 7 with a low pumping capacity, which can easily be accommodated in the hand machine tool because of its low weight and small volume.
The hammer mechanism has a drive unit, which, after each impact with the tool 3, sets the hammer 1 into a motion counter to the force of the spring mechanism, thus stressing the spring mechanism. The aforementioned drive unit is designed so that after the stressing of the spring mechanism, it abruptly releases the hammer 1 again so that, driven by the spring mechanism, the hammer 1 flies toward the tool. Because the spring mechanism is stressed not only by the recoil force of the hammer 1, but also actively by the separate drive unit, which exerts a very high stress on it, a very powerful hammering force is imparted to the hammer 1 upon release of the spring mechanism. Consequently, a very high individual hammering energy can be generated, even at a relatively low hammering frequency.
In the exemplary embodiment shown in FIG. 1, the above-described drive unit is embodied as follows:
The side of the hammer 1 oriented away from the tool 3 is attached to a rod 8, which extends in the direction of the longitudinal axis of the guide tube 2 and passes through the back wall 5 of the guide tube 2. A seal 9 between the rod 8 and the guide opening in the rear wall 5 of the guide tube 2 prevents compressible medium from escaping from the pressure reservoir 4. Outside the pressure reservoir 4, the rod 8 ends in the vicinity of a driving gear 10, which is rotatable around an axis that extends perpendicular to the longitudinal axis of the guide tube 2. The shaft 11 of a motor, not shown, sets the driving gear into rotation, e.g. by means of a parallel shaft gearing (not shown in the drawing). On the driving gear 10, offset from the rotation axis 12 of the driving gear, a pin 13 is provided, which protrudes from the driving gear 10 perpendicular to the plane of the drawing. The end of the rod 8 oriented toward the driving gear 10 is embodied in the form of a hook 14 so that when the driving gear 10 rotates, the pin 13 can travel into the hook 14. If the hammer 1 is moving backward after striking the tool, then the rod with the hook 14 slides toward the driving gear 10. The pin 13 of the rotating driving gear 10 slides into the hook 14 and carries the rod 8 with the hammer 1 toward the driving gear 10—clockwise in the exemplary embodiment—so that the hammer 1 moves toward the back wall 5 of the guide tube 2, thus causing the medium in the pressure reservoir 4 to be compressed. This results in a sharp increase in the pressure on the hammer 1 toward the tool 3. As soon as the driving gear 10 has completed a half rotation and the pin 13 has thus reached a position 13′, which is the furthest from the guide tube 2, then the pin 13 slides back out of the hook 14 again. At this moment, the hammer 1 is released and can move toward the tool 3 to strike it again, driven by the pressure in the pressure reservoir 4. The rotation speed of the driving gear 10 must be set so that whenever the hammer 1 is traveling backward after an impact, the hook 14 at the end of the rod 8 is situated directly over the pin 13 of the driving gear 10.
In lieu of the drive mechanism described above, which pulls the hammer 1 by means of the rod 8 counter to the force of the spring mechanism, it is also possible to provide a drive mechanism that pushes the hammer 1 counter to the force of the spring mechanism. In that case, the drive mechanism would have to be situated on the side of the hammer 1 oriented toward the tool. By contrast with the drive unit for the hammer 1 described above by way of example, it is possible to use any other mechanism that moves the hammer 1 counter to the force of the spring mechanism after each individual impact in order to stress the spring mechanism.
FIG. 2 shows a schematic cross section through a hand machine tool in which the spring mechanism is not comprised of a pressure reservoir as in the exemplary embodiment of FIG. 1, but instead, one or more tension and/or compression springs are used. Aside from the spring mechanism, all other functional elements are the same as in the previously described exemplary embodiment of FIG. 1 and are also provided with the same reference numerals in FIG. 2 as in FIG. 1.
As shown in FIG. 2, the chamber of the guide tube 2 between the hammer 1 and the back wall 5 of the guide tube contains a compression spring 15, which rests against the back wall 5 of the guide tube 2 at one end and against the hammer 1 at the other. Alternatively to this compression spring 15 or in addition to it, it is also possible to provide a tension spring 16 on the side of the hammer 1 oriented toward the tool 3. This tension spring is connected to the hammer 1 at one end and is connected to a shoulder of the guide tube 2 at the other. Instead of only one compression spring 15 and/or tension spring 16, it is also possible for several compression and/or tension springs to be used, which impart the required hammering force to the hammer 1.