Power tool

A power tool is disclosed. The power tool has a striker, which is guided along an axis in a guide tube. A pneumatic chamber has a volume which varies with a movement of the striker. The pneumatic chamber is closed by the striker, the guide tube and a valve device. The valve device has in a flow channel a sealing element that is moveable between two positions in a bearing along the axis. The flow channel has a first cross-sectional area in a first of the two positions of the sealing element adjacent to a first mating surface of the bearing, and the flow channel has a second cross-sectional area in a second of the two positions of the sealing element adjacent to second mating surface of the bearing offset from the first mating surface along the axis. The second cross-sectional area is greater than the first cross-sectional area.

This application claims the priority of German Patent Document No. 10 2010 029 918.9, filed Jun. 10, 2010, the disclosure of which is expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a power tool, in particular a hand-operated chiseling power tool.

In the case of hand-held chiseling power tools, chiseling action is supposed to be suspended when a chisel is lifted off a workpiece. In the case of striking mechanisms that operate pneumatically, a pneumatic spring can be deactivated by means of additional ventilation openings, which are only opened if the chisel is disengaged. A striker, also called an intermediate striking device or anvil, is supposed to remain away from the ventilation openings for this purpose after an empty impact. However, this is not the case to some extent due to the rebound of the striker on a forward limit stop.

A power tool according to the invention has a striker, which is guided along an axis in a guide. A pneumatic chamber has a volume which varies with a movement of the striker along the axis. A pneumatic chamber is closed by the striker, the guide and a valve device actuated by its own medium. The volume of the pneumatic chamber varies with a movement of the striker along the axis. The valve device actuated by its own medium has, in a flow channel between the striker and the guide, a sealing element that is moveable between two positions in a bearing along the axis. The flow channel has a first cross-sectional area in a first of the two positions of the sealing element adjacent to a first mating surface of the bearing, and the flow channel has a second cross-sectional area in a second of the two positions of the sealing element adjacent to a second mating surface of the bearing offset from the first mating surface along the axis. The second cross-sectional area is greater than the first cross-sectional area. The valve device actuated by its own medium may have, for example, a groove embedded in the striker or in the guide, and a sealing element. The sealing element is moveable in the groove along the axis between a first and a second groove wall. The flow channel of the valve device has the first cross-sectional area in a first position of the sealing element adjacent to the first groove wall and the second cross-sectional area in a second position of the sealing element adjacent to the second groove wall, which is greater than the first cross-sectional area. Adjacent to the first groove wall, the sealing element closes or throttles an air flow into or out of the pneumatic chamber. The striker experiences a braking effect because of the closed pneumatic chamber when it slides back into the tool receptacle. Adjacent to the second groove wall, a greater air flow through the second cross-sectional area of the flow channel is possible. In the case of a movement in the impact direction, the valve device makes a pressure equalization possible in the pneumatic chamber, which is why no braking effect occurs.

One embodiment provides that a volume of the pneumatic chamber is increasing in the case of a movement of the striker in the impact direction and the first mating surface of the bearing is facing the pneumatic chamber, e.g., the groove with the second groove wall is arranged facing the pneumatic chamber. In the case of an air flow out of the pneumatic chamber, the sealing element is pushed in the direction of the mating surface of the bearing facing the pneumatic chamber. With this first variant, air is able to flow into the pneumatic chamber, when the striker moves forward and the volume increases. When the volume of the pneumatic chamber is decreasing in the case of a movement of the striker in the impact direction, the second mating surface of the bearing is facing the pneumatic chamber, e.g., the groove with the first groove wall is arranged facing the pneumatic chamber. A further embodiment provides for two pneumatic chambers, which are connected by the valve device actuated by its own medium.

One embodiment provides that the flow channel runs between the first mating surface of the bearing and a first mating surface of the sealing element assigned to the first mating surface of the bearing and between the second mating surface of the bearing and a second mating surface of the sealing element assigned to the second mating surface of the bearing. The first cross-sectional area of the flow channel is determined by the space between the first mating surfaces of the bearing and the sealing element, when these are adjacent to each other. The second mating surface of the bearing and/or a mating surface, that is the second mating surface, of the sealing element assigned to the second mating surface of the bearing may have narrow channels running at least in part radially, i.e., perpendicularly, to the axis. The narrow channels define a second cross-sectional area that is greater than zero and make an air exchange possible into or out of the pneumatic chamber, even if the sealing element is adjacent to the second groove wall. The two second mating surfaces of the bearing and of the sealing element close flush only in part, e.g., due to the narrow channels. The second cross-sectional area is not equal to zero and an airflow may flow through the flow channel. If the two first mating surfaces are flush with each other, the first cross-sectional area is equal to zero. The groove and the sealing element may run annularly around the axis and, in the first position, the sealing element touches the guide and the striker respectively along a closed line around the axis.

One embodiment provides that a channel runs from the first groove wall to the second groove wall between a groove base of the groove and the sealing element. The flow channel of the valve runs between the sealing element and the body in which the groove is introduced.

In one embodiment, the first groove wall is inclined with respect to the axis by less than 60 degrees and the second groove wall is inclined with respect to the axis by at least 80 degrees.

One embodiment provides that the first cross-sectional area of the flow channel is a maximum of one tenth of the second cross-sectional area of the flow channel.

One embodiment provides that the striker has a prismatic first section and a second section with a larger cross-sectional area as compared to the first section, wherein the valve device is arranged in the second section of the striker. Bodies having a cross-section that is constant along an axis, e.g., cylinders, are prismatic.

One embodiment provides that a seal between the striker and the guide and that is offset from the valve device actuated by its own medium along the axis for sealing the pneumatic chamber is provided, wherein the valve device actuated by its own medium and the seal are arranged at different distances from the axis.

One embodiment has a throttle, which connects the pneumatic chamber with an air reservoir. An effective cross-sectional area of the pneumatic chamber, defined by the differential of the volume of the pneumatic chamber in the impact direction is greater than one hundred times a cross-sectional area of the throttle. The striker is moved parallel to the axis, whereby a volume change of the pneumatic chamber is produced proportional to the displacement along the axis and the effective cross-sectional area. The effective cross-sectional area can be determined by the mathematical operation of differentiation in the movement or impact direction. In the case of a cylindrical guide and a cylindrical striker, the effective cross-sectional area corresponds to the largest cross-sectional area perpendicular to the axis. The ratio of the effective cross-sectional area of the pneumatic chamber to the cross-sectional area of the throttle determines a relative flow speed of the air in the throttle related to the speed of the striker. Starting at this relative flow speed, the air can escape quickly enough from the pneumatic chamber without a drop in pressure developing with respect to the environment. It was recognized that an absolute speed of the air in the throttle cannot be exceeded. However, the throttle appears to block a limit value of the absolute speed. The ratio of a hundred times, preferably three-hundred times, is selected so that, in the case of a striker driven by the striking mechanism, the absolute speed of the air in the throttle is reached; in the case of a striker moved manually, the absolute speed is fallen short of considerably. As a result, the throttle blocks when the striker strikes, and opens when the striker is moved manually.

In one embodiment, the valve device may be configured as a throttle valve device. An effective cross-sectional area of the pneumatic chamber defined by the differential of the volume of the pneumatic chamber in the impact direction is greater than a hundred times of a cross-sectional area of the flow channel. The first mating surface of the bearing and/or a mating surface of the sealing element assigned to the first mating surface of the bearing may have narrow channels running radially perpendicularly to the axis at least in part. A total of their cross-sectional area is less than one hundredth of the effective cross-sectional area of the pneumatic chamber.

One embodiment has a pneumatic striking mechanism, which is arranged percussively with its impacting piston in the impact direction on the striker. The striker is an impact body or an anvil moveable along the axis, which is arranged between a striking device of a pneumatic striking mechanism and a tool inserted into a tool receptacle.

The following description explains the invention on the basis of exemplary embodiments and figures.

DETAILED DESCRIPTION OF THE DRAWINGS

Unless otherwise indicated, the same or functionally equivalent elements are identified in the figures by the same reference numbers.

FIG. 1shows a hammer drill1as an embodiment for a chiseling power tool. The hammer drill1has a machine housing2, in which a motor3and a pneumatic striking mechanism4driven by the motor3are arranged, and a tool receptacle5is preferably fastened in a detachable manner. The motor3is an electric motor, for example, which is supplied with electricity by a cable-based power supply6or a chargeable battery system. The pneumatic striking mechanism4drives a tool7inserted into the tool receptacle5, e.g., a boring tool or a chisel, away from the hammer drill1along an axis8in the impact direction9into a workpiece. The hammer drill1optionally has a rotary drive10, which can rotate the tool7around the axis8in addition to the impacting movement. One or two hand grips11are fastened on the machine housing2, which make it possible for a user to operate the hammer drill1. A purely chiseling embodiment, e.g., a chisel hammer, differs from the hammer drill1essentially only by the lack of the rotary drive10.

The pneumatic striking mechanism4depicted exemplarily has an impacting piston12, which is induced by an excited pneumatic spring13to move forward, i.e., in the impact direction9, along the axis8. The impacting piston12hits a striker20and thereby releases a portion of its kinetic energy to the striker20. Because of the recoil induced by the pneumatic spring13, the impacting piston12moves backward, i.e., against the impact direction9, until the compressed pneumatic spring13again drives the impacting piston12forward. The pneumatic spring13is formed by a pneumatic chamber, which is closed axially at the front by a rear face surface21of the impacting piston12and axially at the rear by an exciter piston22. In the radial direction, the pneumatic chamber can be closed circumferentially by an impacting tube23, in which the impacting piston12and the exciter piston22are guided along the axis8. In other designs, the impacting piston12may slide in a cup-shaped piston, wherein the exciter piston closes the hollow space of the pneumatic chamber in the radial direction, i.e., circumferentially. The pneumatic spring13is excited by a forced, oscillating movement along the axis8of the exciter piston22. An eccentric drive24, a wobble drive, etc., can convert the rotational movement of the motor3into the linear, oscillating movement. A period of the forced movement of the exciter piston22is coordinated with the interplay of the system of the impacting piston12, pneumatic spring13and striker20and their relative axial distances, in particular a predetermined impact point25of the impacting piston12with the striker20in order to excite the system resonantly and thus optimally for energy transmission from the motor3to the impacting piston12.

The striker20is a body, preferably a rotating body, with a front impact surface26exposed in the impact direction9and a rear impact surface27exposed against the impact direction9. The striker20transmits an impact on its rear impact surface27to the tool7adjacent to its front impact surface26. In terms of its function, the striker20may also be designated as an intermediate striking device.

A guide28guides the striker20along the axis8. In the depicted example, the striker20dips partially with a rear end into a rear guide section29. The rear end is adjacent with its radial outer surface to the guide section29in the radial direction. A forward guide section30can likewise enclose a forward end of the striker20and restrict its radial movement. The rear and forward guide sections29,30together form two limit stops, which limit an axial movement of the striker20on a path between the rear limit stop29and the forward limit stop30situated in the impact direction9(striker limit stop). The striker20has a thickened center section33, whose face surfaces strike against the guide sections29,30. The guide28depicted exemplarily has, for example, a cylindrical, circumferentially closed guide tube31, in which is the striker20. The thicker section33of the striker20is spaced apart radially with its lateral surface34, i.e., radial outer surface, at least in sections or along its entire circumference from an inner wall32of the guide tube31. A channel-like or cylindrical gap35between the striker20and the guide tube31runs over the entire axial length of the center thickened section33. The gap35may have a radial dimension of between 0.5 mm and 4 mm for example.

During chiseling, the tool7supports itself on the forward impact surface26of the striker20, whereby the striker20is kept engaged on the rear limit stop29(FIG. 2). The striking mechanism4is designed for the engaged position of the striker20. The predetermined impact point25(FIG. 2) of the impacting piston12and the reversal point in the movement of the impacting piston12is determined by the rear impact surface27of the engaged striker20.

As soon as a user removes the tool7from the workpiece, the impacting function of the pneumatic striking mechanism4is supposed to be interrupted, because otherwise the hammer drill1will idle percussively. When the impacting piston12impacts the striker20, the striker20slides to the forward limit stop30and preferably stands still in its vicinity. The impacting piston12may move forward beyond the predetermined impact point25in the impact direction9up to the preferably dampening limit stop30. In the advanced position beyond the impact point25, the impacting piston12frees a ventilation opening36in the impact tube23, through which the pneumatic chamber of the excited pneumatic spring13is connected and ventilated with preferably the environment in the machine housing2. The effect of the pneumatic spring13is reduced or reversed, which is why the impacting piston12stands still because of the weakened or missing connection to the exciter piston22. The striking mechanism4is reactivated, if the striker20is engaged up to the rear limit stop29and the impacting piston12closes the ventilation opening36.

So that the striker20remains preferably in the vicinity of the forward limit stop30after an empty impact, the striker20can essentially move unchecked in the impact direction9to the forward limit stop30; in the opposite direction from the rear limit stop29, the movement occurs, however, against a spring force of at least one pneumatic spring40. The spring force of the pneumatic spring40is controlled as a function of the movement direction of the striker20related to the guide28.

An at least partially radially running surface of the striker20and an at least partially radially running surface of the guide28form inner surfaces of the pneumatic chamber40, which are oriented perpendicularly or inclined to the axis8. An axial distance of the two radially running surfaces changes with the movement of the striker20, and therefore, the volume of the pneumatic chamber40. The change in volume causes a change in the pressure within the pneumatic chamber40.

A rear bounce surface41of the thicker section33that points opposite from the impact direction9can form the first radially running inner surface of the pneumatic chamber40. A rear bounce surface42of the guide28pointing in the impact direction9, which together with the rear bounce surface41of the thicker section33defines the rear limit stop29, can be the second radially running inner surface of the pneumatic chamber40.

In the radial direction, the pneumatic chamber40is closed on one side by the guide28and on the other side by the striker20. A hermetic air-tight seal between the striker20and the guide28is realized by a first sealing element43and a second sealing element44. The sealing elements43,44are arranged offset from one another along the axis8. The first sealing element43is arranged, for example, between the two limit stops29,30, and the second sealing element44is arranged axially outside of the two limit stops29,30, i.e., of the respective bounce surfaces42. Located between the two sealing elements43,44are the radially running inner surfaces of the pneumatic chamber40. In the depicted embodiment, the sealing elements43,44are arranged on sections of the striker20having different cross-sections, whereby the distances of the sealing elements43,44to the axis8are different sizes. In other embodiments, at least sections of the sealing elements43,44are at different distances from the axis8. In a projection onto a plane perpendicular to the axis8, the two seals do not overlap or at least not in sections.

The dependence of the pneumatic spring40on the movement direction of the striker20is achieved in that at least one of the sealing elements43,44is configured as a valve50. An air channel45links the pneumatic chamber40to an air reservoir in the environment, e.g., the machine housing2. The valve50, which controls an air flow through the channel45, is arranged in the channel45. Control takes place as a function of the movement of the striker20. When the striker20moves in the impact direction9, the valve50opens and air can flow in from the reservoir through the channel45into the enlarging volume of the pneumatic chamber40; the pneumatic spring is herewith deactivated. The valve50blocks the channel45when the striker20moves against the impact direction9. The pressure in the pneumatic chamber40rises with the reducing volume of the pneumatic chamber40, whereby the pneumatic spring40works against the movement of the striker20.

In one embodiment, the valve50is configured as an automatic valve or a valve50actuated by its own medium, e.g., a check valve or a throttle check valve. The valve50is actuated by an air flow, which flows into the valve50. The air flow is a result of the pressure difference between the pneumatic chamber40and the space51connected to it via the valve50. The connected space51may be a very large air reservoir, e.g., the environment, the inside of the machine housing51, or another closed, pneumatic chamber with a limited volume.

In the depicted embodiment, the pneumatic spring40presses a sealing closure body52of the valve50against a valve opening53or valve seat of the valve50, thereby hermetically closing the valve opening53. When the pressure within the space51linked by the valve50overcomes the pneumatic spring40, i.e., exceeds the pressure within the pneumatic chamber40, the closure body52is pressed away from the valve opening53. Air can flow through the valve opening53along the air channel45into the pneumatic chamber40.

With the movement of the striker20, the volume of the pneumatic chamber40changes in proportion to the speed of the striker20and to the annular cross-sectional area of the volume enclosed by the pneumatic chamber40. In an opened state, the valve50has at its narrowest point perpendicular to the flow direction an opening with a cross-sectional area (hydraulic cross section), which preferably does not fall short of 1/30, e.g., 1/20, or 10% of the effective cross-sectional area of the pneumatic chamber40. The displaced air flows through the opened valve50with approximately 30-times, respectively 20-times, 10-times the speed of the striker20.

A throttle opening54can ventilate the pneumatic chamber40. The throttle opening54can be a borehole through the wall of the guide tube31for example. The surface of a flow cross-section (hydraulic cross-section) of the throttle opening54is smaller by at least two orders of magnitude than the annular cross-sectional area of the pneumatic chamber40, e.g., less than 0.5 percent. The throttle opening54is, for example, greater than 1/2000 or 1/1500 of the annular cross-sectional area in order to make a manual insertion of the striker20possible. The flow cross-section or the cross-sectional area of the throttle opening54is determined at its narrowest point perpendicular to the flow direction. If the throttle54is supposed to equalize the volume change without a pressure change, the displaced air must pass through the throttle54at a speed that is at least a hundred times the speed of the striker. The flow characteristics of air set an upper limit for the flow speed, which is why a pressure equalization is possible with a slow moving but not with a rapidly moving striker20.

The speed of the striker20in the impact direction9is approximately in the range of 1 m/s to 10 m/s in the case of an empty impact. The volume of the pneumatic chamber40increases correspondingly rapidly. Air flows through the opened valve50into the pneumatic chamber40at a high rate so that a pressure equalization quickly adjusts. When the striker20is reflected on the striker limit stop30, its speed against the impact direction9can be in the same order of magnitude. The valve50closes and the compression of the closed pneumatic chamber40brakes the striker20. The throttle opening54allows only a low airflow to escape, thereby maintaining the overpressure in the pneumatic chamber40. In the case of a slow movement of less than 0.2 m/s against the impact direction9, typical for a new application of the chisel, the air may escape through the throttle opening54at a rate adequate to facilitate a pressure equalization. As an alternative to a separate throttle opening54, the valve50may be designed as a throttle valve, which leaves open an appropriate throttle opening in a closed/throttling position.

FIG. 3andFIG. 4show an exemplary embodiment with a valve60in a closed or open state.FIG. 5andFIG. 6are cross-sections through the valve60of planes V-V or VI-VI. The valve60has as the closure body52a sealing ring61, i.e., an annular sealing element, which is inserted into a circumferentially running groove62in the thicker section33of the striker20. The gap35between the striker20and guide tube31is divided by the sealing ring61and the groove62into two sections along the axis8, which corresponds to the air channel45divided by the valve50. Depending upon the position of the sealing ring61, air can flow along the gap35. The sealable valve opening is defined by a seat for the sealing ring61in the region of a forward groove wall63of the groove62, i.e., situated in the impact direction9.

The sealing ring61is, for example, an elastic O-ring made of natural or synthetic rubber. A surface pointing radially outwardly, called the radial outer surface64of the sealing ring61in the following, consistently abuts the inner wall32of the guide tube31along the entire circumference of the sealing ring61so that the sealing ring61and the guide tube31are hermetically sealed together. The sealing ring61may be used in the guide tube31in a radially pre-tensioned manner in order to support the airtight seal. A thickness65of the sealing ring61, i.e., a difference from the outer radius to the inner radius, is preferably less than a depth66of the groove62. A surface pointing radially inwardly, called the radial inner surface67of the sealing ring61in the following, is spaced apart in the radial direction from a groove base68of the groove62at least in a section along the circumference of the thicker section33. Situated between the groove base68and the sealing ring61is a gap69, through which air may flow along the axis8.

In the closed or hermetically sealed state of the valve60, the sealing ring61is adjacent with a forward face surface70, i.e., pointing in the impact direction9, to the forward groove wall63of the groove62(FIG. 3). The forward groove wall63and the forward face surface70touch each other at least along an annular closed line around the axis8. The forward face surface70may be flattened, for example, in order to terminate on a surface of the groove wall63with the same inclination, e.g., perpendicular, to the axis8. A hermetic seal of the valve60is produced by the pairwise hermetic sealing of the sealing ring61with the groove wall63, i.e., with the striker20, or with the guide tube31, i.e., with the guide28. The movement of the striker20against the impact direction9stabilizes the valve60in the closed state. In the pneumatic chamber40closed by the valve60, the pressure increases as compared with the environment, thereby pressing the sealing ring61against the forward groove wall63.

In the opened state, the sealing ring61is adjacent with a rear face surface71, i.e., pointing against the impact direction9, to the rear groove wall72of groove62(FIG. 4). A distance of the forward groove wall63to the rear groove wall72is dimensioned in such a way that the sealing ring61disengages from the forward groove wall63at least in sections along the circumference, when the sealing ring61is adjacent to the rear groove wall72. For example, the distance between the groove walls is greater than a dimension of the sealing ring61along the axis8. The sealing ring61moves along the axis8from the forward groove wall63to the rear groove wall72.

The rear groove wall72and/or the rear face surface70of the sealing ring61are structured in such a way that a contact surface along which they touch is interrupted by at least one continuous channel lying in the contact surface from the groove base68to the guide tube31. For example, one or more radially running narrow channels73are provided in the rear face surface71. The sealing ring61touches the rear groove wall72only in sections along the circumference and air can flow through the narrow channels73. A channel through the open valve60therefore runs along the forward face surface72, the radial inner surface67and the narrow channels73. The movement of the striker20in the impact direction9stabilizes the valve60in the open state. In the pneumatic chamber40, the pressure drops below the ambient pressure, e.g., in the space51, and the pressure gradient causes air to flow in and press the sealing ring61on the rear groove wall72. As an alternative or addition to the narrow channels73in the sealing ring61, radially running narrow channels may be embedded in the rear groove wall72. The air may flow along these narrow channels, and bridges between the narrow channels prevent the narrow channels from being sealed by the sealing ring61.

The rear face surface71may have other structures instead of narrow channels73, which define channels from the radial inner surface67to the radial outer surface64. The channels may run strictly radially or in addition partially along the circumference of the sealing ring61. For example, rigid knobs may be provided which maintain the channels against the forces occurring with a forward movement of the striker20.

The sealing ring61may have narrow channels74on one of its radial inner surfaces (FIG. 7). This makes it possible to use a sealing ring61adjacent to the groove base.

In one embodiment, the sealing ring61has a throttling effect when the forward face surface70is adjacent to the forward groove wall63. A low air flow can flow through between the face surface70and the forward groove wall63. Thin radial channels may be introduced in the forward face surface70for this. The effective total cross-sectional area of the channels is less than the effective total cross-sectional area of the channels73in the rear face surface71. A cross-sectional area perpendicular to the air flow of the thin channels is restricted to a maximum of one hundredth of all perpendicular cross-sectional areas of the narrow channels73added up over all narrow channels73to be the air flow.

The first sealing element43in the embodiment is realized by the valve60moved between the limit stops29,30. The second sealing element44is arranged axially offset from the rear limit stop29against the impact direction9and, for example, is mounted in a stationary manner in the guide28. The second sealing element44is preferably configured to be annular, e.g., as an O-ring made of rubber. The striker20has a cylindrical rear section75, which is guided through the second sealing element44consistent with its inner radial surface. The length76of the rear cylindrical section75is preferably dimensioned in such a way that at least one portion of the rear section75sticks into the second sealing element44when the striker20is adjacent to the forward limit stop30in order to hermetically seal the pneumatic chamber40in every position of the striker20. The length76of the rear section75is at least longer than the path of the striker20between the forward limit stop30and the rear limit stop29.

The second sealing element44may be inserted, for example, in a cylindrical sleeve77, which is then introduced into the guide tube31. The forward face surfaces of the sleeve77may form the mating surfaces42for the rear limit stop29. The cross-sectional area of the sleeve77may essentially determine the cross-sectional area of the pneumatic chamber40. The second sealing element44may alternatively be fastened on the rear section75of the striker20, e.g., in an annular groove. The sleeve77is provided with a preferably smooth cylindrical inner wall along which the second sealing element44slides.

A diameter of the rear section75is less than a diameter of the thicker section33, whereby the valve device60is arranged at a greater distance from the axis8than the second sealing element44.

The forward groove wall70may be inclined with respect to the axis8, e.g., by between 45 degrees and 70 degrees. The inclined groove wall70can spread the sealing ring61in order to support a tight fit on the forward groove wall70.

FIG. 8andFIG. 9show an exemplary embodiment with a valve80in a closed or open state.FIG. 10andFIG. 11are cross-sections through the valve80of planes X-X or XI-XI. The valve80has as the closure body a sealing ring81, which is inserted into a circumferentially running groove82in the thicker section33of the striker20. The gap35between the striker20and guide tube31forms the channel45, which is divided by the groove82and the sealing ring81along the axis8. In the region of a forward groove wall84of the groove82, the sealing ring81can seal the channel45.

The groove82can accommodate the sealing ring81in such a way that the sealing ring81is spaced apart from the inner wall32of the guide tube31(FIG. 8), i.e., there is an air gap84between the sealing ring81and the guide tube31. To this end, a depth85of the groove82may be at least as great as a thickness86of the sealing ring81. A length87of a groove base88may be selected to be at least as great as a length89of the sealing ring81along the axis8. The groove base88essentially runs parallel to the axis8and is cylindrical. Air may flow in along the gap35into the pneumatic chamber40.

A forward groove wall90is inclined with respect to the axis8and preferably defines a conical surface whose radius increases in the impact direction9. In a closed state of the valve80, the sealing ring81is slid onto the conical forward groove wall90. The sealing ring81in this case is spread radially and its outside diameter increases at least enough that the radial outer surface91of the sealing ring81touches the inner wall32of the guide tube31(FIG. 9). A hermetic seal is produced between the striker20and the guide28by its pairwise, hermetically sealing contact with the sealing ring81.

The pressure conditions with a backward movement of the striker20push the sealing ring81onto the conical forward groove wall90and thereby cause the valve80to close automatically. In the case of a forward movement, the sealing ring81disengages from the conical forward groove wall90, relaxes into its basic form with a smaller outside diameter and releases the air gap84to open the valve80.

The sealing ring81is, for example, an elastic O-ring made of natural or synthetic rubber. The sealing ring81may be formed to be symmetrical to a plane perpendicular to the axis8, i.e., having identical face surfaces.

The second sealing element44may be arranged axially offset from the rear limit stop29against the impact direction9and, for example, may be a sealing ring mounted in a stationary manner in the guide28. Alternatively, the second sealing element44may be mounted on the rear section75of the striker20.

FIG. 12shows an embodiment with the valve60, which pneumatically couples the forward pneumatic chamber120and the rear pneumatic chamber40. Reference is made to the embodiments in connection with the valve60for a description of the elements, particularly those related to the rear pneumatic chamber40. The air channel134between the two pneumatic chambers40,120is completely arranged within the guide28.

A forward bounce surface of the thicker section33of the striker20forms the rear inner wall132of the forward pneumatic chamber120and the rear bounce surface of the thicker section33forms the forward inner wall41of the rear pneumatic chamber40. The forward inner wall131of the forward pneumatic chamber120may be formed by a region of the guide28defining the forward limit stop30. An elastic damping element30made of rubber, e.g., an O-ring, may also be arranged in the forward pneumatic chamber120, which damping element softens an impact of the striker20in the forward limit stop30. Projections of the two inner walls131,132of the forward pneumatic chamber120onto a plane perpendicular to the axis8are essentially the same. The rear inner wall42of the rear pneumatic chamber40may be formed by a surface of the guide28defining the rear limit stop29. Projections of the two inner walls41,42of the rear pneumatic chamber40onto a plane perpendicular to the axis8are essentially the same. In the case of a movement of the striker20, the axial distances between the inner walls of each of the pneumatic chambers40,120change and consequently their volumes. The total of the two volumes may be constant, wherefore the surfaces of the forward inner walls projected onto the plane perpendicular to the axis8and the correspondingly projected surfaces of the rear inner walls are the same size.

The gap35between the striker20and the guide tube31forms the air channel134between the pneumatic chambers40,120. Narrow channels running along the axis8in the lateral area34of the thicker section33may form additional air channels.

The valve60on the thicker section33blocks against an air flow from the rear pneumatic chamber into the forward pneumatic chamber120and opens for an air flow from the forward pneumatic chamber into the rear pneumatic chamber40. The design of the valve60may be taken from the foregoing descriptions.

The third sealing element may be a sealing ring142made of rubber, which is arranged axially offset from the forward limit stop30in the impact direction9. The third sealing element133may be inserted, for example, into a groove in the guide tube31. The striker20has a cylindrical, forward section143, which is consistently guided through the third sealing element133with its inner radial surface144. The length145of the forward cylindrical section143is preferably dimensioned such that at least one portion of the forward section143sticks in the third sealing element133, when the striker20is adjacent to the rear limit stop29in order to hermetically seal the forward pneumatic chamber120in every position of the striker20. When the striker20is adjacent to the forward limit stop30, the forward section143projects over the third sealing element133in the impact direction9by at least a length corresponding to the path of the striker20between the forward limit stop30and the rear limit stop29. A diameter of the forward section143is less than the diameter of the thicker section33.

In an alternative embodiment, the sealing ring146is fastened on the forward section143of the striker20, e.g., in an annular groove (as shown inFIG. 13). The sealing ring146slides within a cylindrical sleeve147in the guide28and with it seals in every position of the striker20. An outer radial surface of the sealing ring146touches the sleeve147.

Instead of or in addition to the one-way valve60with an axially floating sealing ring61, other one-way valve systems may be arranged on the thicker section33, e.g., those described with a conical connecting member for a sealing ring80, a flap valve, a gap sealing valve.

FIG. 14andFIG. 15show another embodiment with a valve150in a longitudinal section or a cross-section of plane XVIII-XVIII. The valve150is mounted in a stationary manner in the guide28and forms the second sealing element44. The alignment of the valve150with respect to the impact direction9is altered when compared to the previous embodiments, because the valve150is arranged as viewed from the tool behind the pneumatic chamber40.

The design of the valve150corresponds to a large extent to the design of the embodiment explained in conjunction with valve50embodiment. The single essential difference is the opposite orientation of the valve150with respect to the impact direction9as compared to the valve50. Both valves50make it possible for air to flow into the pneumatic chamber40and prevent air from flowing out. The valve150has a sealing ring151, which is mounted in a circumferential groove152in the guide28. The sealing ring151encloses the rear section75of the striker20in a flush and air-tight manner.

There is a gap154between a groove base153of the groove152and the sealing ring151, through which gap air can flow in along the axis8. The groove152is wider than the sealing ring151in order to make movement of the sealing ring151along the axis8possible. A forward groove wall155and a forward face surface156of the sealing ring are structured in such a way that, when the sealing ring151is adjacent to the forward groove wall155, radial channels157remain free between the sealing ring151and the forward groove wall155. The channels157may be stamped into the forward face surface156of the sealing ring151as narrow channels for example. The rear groove wall158of the groove152and the rear face surface159of the sealing ring151may be hermetically sealed together along a closed circular line around the axis8. In the case of the forward movement of the striker20, the sealing ring151is pressed against the forward groove wall155, also supported by the air flowing along the rear section75of the striker20into the pneumatic chamber40, whereby the valve150is opened or kept open. In the case of a backwards movement of the striker20, the sealing ring151is pressed against the rear groove wall158, also supported by the overpressure building up in the pneumatic chamber40, whereby the valve150is closed or kept closed.

The first sealing element43between the limits stops may be realized, for example, by a sealing ring made of rubber, e.g., an O-ring, which is inserted into an annular groove160in the thicker section33so that it cannot move. Alternatively, a valve, for example, the valve60from the previous embodiment, may form the first sealing element43.

FIG. 16shows a longitudinal section of another embodiment with a valve170arranged in a stationary manner. The first sealing element43may be a sealing element that seals permanently or a valve. The valve170forms the second sealing element44by means of a groove171, which is embedded in an inner wall172of the guide28, and an annular sealing element173, which is inserted into the groove171, and encloses the rear section75of the striker20. The groove171is arranged axially against the impact direction9of the rear limit stop29. A forward groove wall174of the groove171is essentially perpendicular to the axis8, while the rear groove wall175of the groove171is inclined with respect to the axis8. The rear groove wall175runs radially inwardly against the impact direction9radial. The valve170blocks when air flows out of the pneumatic chamber40, in that the sealing ring173is compressed radially by the diagonal rear groove wall175and presses against the striker20.

FIG. 17shows another embodiment with a differently designed striker200and an associated guide201. The guide201has, for example, a cylindrical guide tube202, in which the striker200slides. Inserted into the guide tube202is a sleeve203, which locally reduces the inner cross-section of the guide tube202. The striker200has a tapered center section206along the axis8between a forward section204and a rear section205. The forward section204and the rear section205may form the impact surfaces26,27. The diameter of the center section206is adapted to the sleeve203. The diameters of the forward and rear sections204,205, which are preferably equal in size, are adapted to the larger inner diameter of the guide tube201. The forward section204is after the sleeve in the impact direction9and the rear section205is in front of the sleeve203in the impact direction9. A radially running surface207of the forward section204pointing against the impact direction9together with a surface208of the sleeve203pointing in the impact direction9form the rear limit stop. The forward limit stop is formed by the rear section205and its radially running surface209pointing in the impact direction9and the surface210of the sleeve203pointing against impact direction.

The guide201is connected in an air-tight manner with the forward section204or the rear section205of the striker200in the radial direction by a forward sealing ring211and a rear sealing ring212. A one-way valve60is arranged in the sleeve203, which can seal the sleeve203with respect to the center section206of the striker200depending upon the movement direction of the striker200. A forward pneumatic chamber214and a rear pneumatic chamber215are hereby defined, which are coupled via the valve60. As in the foregoing embodiments, the valve60opens in the case of a movement of the striker200in the impact direction9and closes or throttles in the case of a movement of the striker200against the impact direction9. The one-way valve60may be, for example, the valve60with a slotted, axially floating sealing ring61, the valve80with a conical connecting member for a sealing ring, the valve with a flap valve, the valve with a gap sealing valve.

In one embodiment, only one pneumatic chamber is provided, wherefore the forward211or the rear sealing ring212is omitted or is arranged in a non-hermetically sealed manner for example.

FIG. 18shows another embodiment, in which two independent valves for two pneumatic chambers40,120are provided. The pneumatic chambers40,120are not linked.

In the depicted embodiment, the forward pneumatic chamber120is linked to the environment via a first valve270. The first valve270blocks against air flowing into the forward pneumatic chamber120. A second valve271links the rear pneumatic chamber40to the environment and is blocked for air flowing out of the rear pneumatic chamber40. The two pneumatic chambers40,120are separated by the first sealing element in the exemplary embodiment of a sealing ring272, which is arranged axially between the two valves270,271. The two valves270,271may be formed, for example, by the depicted one-way valve160or by other one-way valves.

FIG. 19shows another embodiment with a valve280in a longitudinal section through the striking mechanism4,FIG. 20shows a cross-section through the valve280in plane XX-XX andFIG. 21shows an enlarged detailed representation. The thicker center section33has a radially projecting rib283, which, for example, runs around the circumference in a closed manner. The sealing ring281, which spans the center section33, is put over the rib283. The sealing ring281has a groove282, in which the rib283engages. The groove282is wider than the rib283and a groove base287is spaced apart from a roof area286of the rib283. The sealing ring281is preferably adjacent to a lateral area293of the center section33offset from the rib283. Introduced in the sealing ring281are several axial running narrow channels290in a surface291facing the striker20such that the surface291together with the groove292forms at least one continuous axially running channel between the striker20and the sealing ring281. Air may flow through the valve280along the axial narrow channels290and the groove282.

The striker20may move along the axis8opposite from the sealing ring281. In a first position, a forward face surface284of the rib283may be adjacent to a forward groove wall288of the groove282. Several radially running narrow channels292are introduced in the groove wall288. A flush closure of the forward face surface284and the forward groove wall288is hereby prevented. Between the forward groove wall288and the forward face surface284, the radial narrow channels292form an air channel with a cross-sectional area that is not equal to zero. In the depicted embodiment, the forward face surface284of the rib283and the forward groove wall288are perpendicular to the axis8. As an alternative, they may also be inclined with respect to the axis8. In a second position, a rear face surface285of the rib283may be adjacent to a rear groove wall289of the groove282. The rear face surface285and the rear groove wall289are preferably form-fitting, whereby an airflow between the two surfaces in the second position may be prevented.

The sealing ring281is axially moveable in the guide28, i.e., the guide tube31. In the case of a forward-moving striker20, the sealing ring281is carried along, whereby the forward face surface284is adjacent to the forward groove wall288(first position). In the pneumatic chamber40, air may flow along a flow channel, which is formed by the axial narrow channels290, the radial narrow channels292along the forward groove wall288and the forward face surface284, the hollow space between the groove base287and the roof area286of the rib283, and the spaced-apart rear groove wall289and rear face surface285of the rib283. In the case of a backward-moving striker20, the sealing ring281is likewise carried along, whereby the rear face surface285is now adjacent to the rear groove wall289. The sealing ring281is preferably flush, hermetically sealed, on the inner wall32of the guide tube31, thereby constricting the flow channel of the valve280. The cross-section of the flow channel is now determined by the two adjacent rear surfaces.

In one embodiment, the radially running narrow channels292are arranged alternatively or additionally in the forward face surface284of the rib283.

The pneumatic chamber40may be closed by the second sealing element44, preferably a permanently sealing, immobile sealing ring, which encloses a rear end75of the striker20.

FIG. 22shows a detailed view of a stationary valve300on the sleeve77. The sleeve77has a projecting rib303, over which a moveable sealing ring301with a groove302is put. As opposed to the embodiment depicted inFIGS. 19 to 21, the arrangement of the sealing ring301is disposed in a mirrored manner to a plane perpendicular to the axis8. A groove wall308with radially running narrow channels312is opposite from a rear face surface304of the rib303. The rear face surface304points away from the pneumatic chamber40. A forward groove wall309is preferably smooth and is opposite from a flush-terminating forward face surface305of the rib303. The sealing ring301is moved by the airflow into and out of the pneumatic chamber40. An airflow into the pneumatic chamber40pushes the sealing ring in the direction of the pneumatic chamber40, whereby the rear surfaces with the radial narrow channels312are adjacent to one another. The valve300is open. An airflow out of the pneumatic chamber40pushes the sealing ring301away from the pneumatic chamber40, whereby the two flush-terminating forward surfaces305,309are adjacent to one another. The valve300is closed.