Hammering mechanism for hand-held electric power tool

Abstract

The invention relates to a hammer mechanism (8) for a hand-held electric power tool, comprising a crank mechanism for converting a rotational drive movement of an electric motor (12) into a translatory alternating movement of an exciter piston (13) for axially applying impact energy to the tool by means of a connecting rod (15) driven by a crank disk (14), the connecting rod (15) is provided with a bearing pin section (17) integrally formed on the connecting rod at the piston end, which interacts with the exciter piston (13) to form a pivot bearing, which bearing pin section consists of at least a piston crown (18) and a piston skirt (19), a concave bearing shell section (21) associated with the bearing pin section (17) of the connecting rod (15) is integrally formed on the inner side of the piston crown (18), which bearing shell section interacts with at least one concave bearing shell section (20a, 20b) integrally formed on the inner side of the piston skirt (19) in order to form a pivot bearing.

Description

Technical Field

[0001] The present invention relates to a hammer mechanism for a hand-held electric tool, which includes a crank mechanism for converting the rotational drive motion of an electric motor into a translational alternating motion of an exciter piston for axially applying impact energy to the tool via a connecting rod driven by a crank disk, wherein the connecting rod is provided with a bearing pin section integrally formed on the connecting rod at the end of the piston, the bearing pin section interacting with the exciter piston to form a pivot bearing, the bearing pin section consisting of at least a piston crown and a piston skirt.

[0002] The field of application of the present invention extends primarily to hand-held hammer drills or chisel hammers, which are equipped with an electric motor drive. Such hand-held electric machine tools generate a linear alternating working motion by means of a mechanical hammer mechanism, i.e. a reciprocating motion for striking a tool, which is designed as a mortise chisel in the case of a chisel hammer and as an impact drill in the case of a hammer drill, and is preferably used to work on mineral materials such as stone, concrete, etc. The exciter piston of the hammer mechanism does not act directly on the clamped tool, but rather via a pneumatic coupling. For this purpose, the exciter piston acts on the cylinder chamber from one end via a crank drive, and an impact piston is arranged at its other end, which impact piston acts on the tool in the direction of impact. Therefore, the exciter piston acts indirectly on the tool in a pneumatically damped manner. In addition, it is also conceivable to directly apply the tool or to integrate other components into the operating chain, for example, a rivet die. Background Art

[0003] WO 2015 / 049130 A1 discloses a hand-held electric tool of the type of interest herein with a pneumatic hammer mechanism. The hammer mechanism comprises a striker movable along an impact axis, an exciter piston of a drive device connected to a crank drive via a connecting rod, and a pneumatic cylinder chamber coupling the movement of the striker piston to the exciter piston. The connecting rod is pivotally attached in the exciter piston, for which purpose, in one embodiment disclosed herein, a separate piston pin is used. In another embodiment, a convex bearing shell section is integrally formed on the inner side of the pot-shaped exciter piston on the bottom side, which interacts oppositely with the concave end face of the connecting rod in order to form a pivot bearing. Of course, a forward stroke bearing of the connecting rod can be formed thereby, but not a return stroke bearing. This is achieved by adding a rearward retaining tab. In this prior art, the exciter piston is formed as a single piece.

[0004] In contrast, WO 2017 / 220561 A1 discloses a hammer mechanism for a handheld electric tool having a multi-part exciter piston of interest herein. This consists of a pot-shaped piston crown and an equally pot-shaped piston skirt mounted in an interlocking manner. The connecting rod bearing at the end of the piston is not realized by means of a separate piston pin, but rather by a bearing pin section formed on the end of the connecting rod. The bearing pin section interacts with two inserted bearing shells surrounding the bearing pin section at the end of the piston. The two bearing shells are made of a material different from that of the piston crown and piston skirt of the exciter piston. All components of the exciter piston are made of metal, which generally results in a very high moving mass, which impairs the efficiency of the hammer mechanism.

[0005] It is therefore an object of the present invention to further develop a hammer mechanism for a hand-held electric power tool of generic type in such a way that the efficiency of the hammer mechanism is increased by simple technical measures. Summary of the invention

[0006] This object is achieved by a drill hammer or a chisel hammer in combination with its characterizing features according to the preamble of claim 1. The following dependent claims describe advantageous developments of the invention.

[0007] The present invention includes the following technical teachings: In order to form a pivot bearing when using a multi-part exciter piston, a concave bearing shell section associated with the bearing pin section of the connecting rod is integrally formed on the inner side of the piston crown, and the concave bearing shell section interacts relative to at least one concave bearing shell section integrally formed on the inner side of the piston skirt to form a sliding bearing.

[0008] The formation of the corresponding bearing section directly on the associated component of the exciter piston makes it possible to provide material that fulfills the bearing function only when required. In contrast, separate inserts must be fitted into the inner contours of the piston crown and piston skirt in a constrained and correctly positioned manner, and correspondingly more material is required for this purpose. In contrast, the lighter exciter piston contributes to an increased efficiency of the hammer mechanism. The machine vibrations and wear of the crank drive are also reduced by the reduced mass.

[0009] The solution according to the invention meets the requirement that the connecting rod together with the bearing pin and the multi-part exciter piston together with the integrally formed bearing shell section can be produced from plastic by casting. On the one hand, depending on the material, the movable masses can be further reduced compared to metal materials; on the other hand, casting the components allows efficient production. Preferably, these components are produced by injection molding.

[0010] In particular, in order to further reduce the mass of the connecting rod, according to measures to improve the invention, it is proposed to provide the bearing journal section formed integrally on the connecting rod with at least one recess introduced at the end face for reducing the mass. The recess can be implemented continuously or in the form of a basic hole, depending on the required strength. The recess further contributes to saving material.

[0011] According to a preferred embodiment of the piston crown, it is designed in a pot shape and, thanks to the preferred manufacturing by casting, can be designed with approximately the same wall thickness. The wall thickness is designed to be the minimum size adapted to the load in order to further contribute to weight reduction.

[0012] In the context of this embodiment, it is also proposed that the pot-shaped piston crown of the actuator piston is provided with a U-shaped circumferential groove in the radially outward edge region close to the bottom for receiving an elastomeric sealing ring. For example, a conventional O-ring or the like can be used as an elastomeric sealing ring. The connection point to the piston skirt is located outside the U-shaped circumferential groove. However, it is also conceivable to place the circumferential groove on the piston skirt or to realize the component separation in the region of the circumferential groove.

[0013] According to a further measure for improving the invention, it is proposed that the piston skirt of the actuator piston has a relief recess for further reducing the mass in the region adjacent to the adjacent piston crown. The actual guide surface of the actuator piston is then formed by the edge region of the piston skirt facing away from the piston crown. In terms of further saving of material, this edge region can also be designed to be wavy, thus producing a non-cylindrical piston guide surface.

[0014] According to a further measure to improve the invention, it is proposed that the sleeve-shaped piston skirt has a guide section which at least partially surrounds the connecting rod below the integrally formed bearing pin section. The guide section is designed in such a way that it does not hinder the alternating pivoting movement of the connecting rod, but rather forms a lateral, relatively parallel guide surface. The guided region of the connecting rod has a relative clearance fit with the guide section of the actuator piston.

[0015] Furthermore, it should be noted that the geometric ratio of the length of the bearing pin section of the connecting rod to the diameter of the piston should preferably be ≥0.3 and very preferably ≥0.5. This relatively high ratio results in a correspondingly lower surface pressure and thus advantageously lower wear on the piston bearing.

[0016] In order to reduce the heat generated in the area of ​​the connecting rod bearing during operation, according to another optional measure, it is proposed to arrange a metal sheet between the concave bearing shell section of the piston crown and the bearing pin section of the connecting rod. It should be noted that the use of such a metal sheet is not limited to a multi-part excitation piston of the general type. Such an additional metal sheet can be used in any type of excitation piston and is particularly meaningful when the excitation piston and the connecting rod are made of plastic. Since such a metal sheet, which is preferably composed of steel with a sheet thickness between 0.2 mm and 2 mm, reduces sliding friction, the sliding bearing characteristics are improved, thereby generating less heat. The metal sheet bent into a half-shell shape can be placed or inserted between the components. Preferably, the device is set on the piston crown because it is subjected to the greatest load. The metal sheet in the form of a half shell is preferably fixed in an appropriate position on the piston crown or on the connecting rod by an edge section bent radially inwardly or radially outwardly. A positive locking position fixation is sufficient to achieve this purpose. However, the inserted metal sheet can also be overmolded with plastic so that the metal sheet is constrainedly connected to the piston crown. Furthermore, it is also conceivable to arrange such a metal sheet on a bearing shell section of the piston skirt.

[0017] In view of the multi-part design, in order to reduce the occurrence of exciter piston leakage and clogging in the associated cylinder, it is proposed to design the piston crown as a flat cover (i.e. in contrast to the above-mentioned embodiment), not as a pot-shaped design, but with the above-mentioned bearing pin section integrally formed on the inside. This cover-shaped piston crown covers the sleeve-shaped piston skirt at the end and preferably has a smaller diameter than the maximum diameter of the piston skirt in order to prevent clogging. This design makes it possible to set the component separation in the direction of the piston crown. As a result, the sealing point of the piston seal and the guiding piston section are located in one and the same component, namely the piston skirt, which in this regard assumes the guiding and sealing functions. The connecting rod is closed, held and guided in the piston skirt by the attached cover-shaped piston crown. The diameter of the piston crown is reduced, preferably to 90% to 99% of the diameter of the piston skirt. The latter is provided with a U-shaped circumferential groove for receiving an elastomeric sealing ring in the edge area close to the piston crown.

[0018] In order to further minimize the sliding bearing wear of the piston bearing, according to another measure to improve the present invention, it is proposed that a single bearing shell section of the piston crown forms the forward stroke bearing of the connecting rod, and two bearing shell sections of the piston skirt arranged on both sides of the connecting rod flanks form the return stroke bearing of the connecting rod. In this article, all bearing shell sections can constitute a bearing position of a cylindrical segment with a maximum semicircular encapsulation of the bearing pin section. As a result, the sliding bearing position of the connecting rod in the exciter piston is divided into three bearing shells, which are preferably designed as half shells. The sliding bearing position in the forward stroke bearing and the return stroke bearing is separated so that the forward stroke bearing, which is used for compression and is particularly loaded, can be maximized. Due to the maximum increase in the bearing surface, the surface pressure is correspondingly reduced, thereby reducing wear. In order to achieve an optimal sliding bearing, the one-piece design of the bearing shell sections and the corresponding associated components of the exciter piston meets the requirements for reducing the sliding bearing clearance compared to the prior art described at the beginning.

[0019] In order to further reduce the heat generated in the sliding bearing area of ​​the exciter piston, according to a further measure to improve the invention, it is proposed to introduce at least one lubricating groove into the running-in surface of the bearing shell section of the piston crown as the bearing area subjected to the greatest load. The lubricating groove can be filled with a suitable lubricant as a permanent lubrication point or it can also be connected to a pressure-lubricated lubricant circuit. Thus, the surfaces of the components of the connecting rod bearing that slide on each other are provided with a lubricating film. In this context, a single lubricating groove is sufficient, which is preferably arranged centrally in the longitudinal direction of the bearing shell section and extends in the transverse direction of the curved shape of the bearing shell section. However, it is also conceivable to integrate more than one lubricating groove into the bearing shell section in a functionally appropriate manner. The symmetrical arrangement structure below the connecting rod shaft ensures a uniform supply of lubricant to the sliding bearing surface. Preferably, at least one lubricating groove is designed so that the volume can accommodate 0.02 cm 3 Up to 2cm 3 The at least one lubricating groove may (i.e. alternatively or in addition) be arranged to be independent of the above-mentioned metal sheet and also to be independent of the multi-part actuator piston.

[0020] The component connection between the piston crown and the piston skirt can preferably be realized by welding or adhesive bonding, whereby welding material or excess adhesive is discharged. In order that this does not impair the functionally correct positioning of the components, according to a further measure to improve the invention, it is proposed to provide at least one recess for receiving welding residues or adhesive residues adjacent to at least one welding point or adhesive bonding point on the piston crown and / or on the piston skirt.

[0021] If the welding point or bonding point is in the form of a weld seam, it is recommended to provide groove-shaped recesses on both sides thereof for receiving the residues. The recess should provide sufficient volume to accommodate all discharged welding material or excess adhesive. To achieve this goal, the volume can be in the range of 0.1 to 10 times the volume of the weld seam. Preferably, the cross-section of the groove-shaped recess for receiving the welding residues should be larger than the cross-section of the thickest weld seam. In order to maximize the receiving capacity, the cross-section of the groove-shaped recess can also be shell-shaped.

[0022] In order to achieve the correct installation of the actuator piston consisting of a piston crown and a piston skirt, according to a further measure to improve the invention, it is proposed that at least one centering lug is integrally formed on the piston crown and / or the piston skirt, which extends towards the opposite connecting partner and engages in a corresponding recess. This makes it possible to precisely position the components in rotation during assembly. Before the actuator piston is finally connected, the centering lug positions the two components in the correct rotational position relative to each other.

[0023] The distal section of the centering lug preferably has at least one lead-in chamfer to facilitate assembly. The lead-in angle of the lead-in chamfer is in a preferred range of 5 to 50 degrees. In addition, a recess may also be provided for the centering lug in order to further reduce the mass of this area. This is because the flank side of the centering lug is sufficient to achieve the intended function. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further measures for improving the invention are explained in more detail below together with the description of preferred exemplary embodiments of the invention with reference to the accompanying drawings. In the drawings: Figure 1 A schematic side view of a hand-held electric machine tool designed as a chisel hammer with an integrated pneumatic hammer mechanism is shown, Figure 2 is a longitudinal section of the actuator piston / connecting rod assembly. Figure 3 Another longitudinal section through the actuator piston / connecting rod assembly is shown, Figure 4 A longitudinal section through the piston region is shown, Figure 5 The piston region with the sheet metal insert in the first embodiment is shown. Longitudinal section, Figure 6 The piston region with the sheet metal insert is shown in a second embodiment. Longitudinal section, Figure 7 A longitudinal section through a piston region with an alternative piston crown is shown, Figure 8 A perspective view showing a section through the actuator piston, Figure 9a A detailed cross-sectional view showing the component connection area in a first embodiment, Figure 9b A detailed cross-sectional view showing the component connection area in a second embodiment, Fig.10 shows a longitudinal section through the actuator piston, and Fig.11 A detail of the piston crown with the recess is shown. DETAILED DESCRIPTION

[0025] Figure 1 A hand-held electric power tool is shown in the form of a chisel hammer 1. The chisel hammer 1 has a front tool holder 2, into which a chisel 3 can be inserted and locked along a working axis 4. At the rear end, the electric hammer 1 has a handle 5, which is integrally formed on a housing 6. An additional handle (not shown) can be fastened to the housing 6 near the tool holder 2. For power supply, the mains 7 originates from the housing 6.

[0026] The chisel hammer 1 has an integrated pneumatic hammer mechanism 8 with an impact piston 9 which, during operation, periodically strikes the chisel 3 along the working axis 4 in an impact direction 10. The impact piston 9 is guided movably along the working axis 4 and, in the embodiment shown, strikes the chisel 3 indirectly via a rivet die 11. In this respect, the rivet die 11 is arranged in the impact direction 10 between the impact piston 9 and the tool holder 2.

[0027] The pneumatic hammer mechanism 8 is driven by an electric motor 12 and, by means of a crank drive, moves an exciter piston 13 in alternating translations on the working axis 4. The opposing impact piston 9 is coupled to the exciter piston 13 via a pneumatic spring.

[0028] The hammer mechanism 8 comprises a cylindrical guide tube 14 for pneumatic coupling, in which an exciter piston 13 is guided in a dynamically sealed manner along the working axis 4 . The exciter piston 13 thus closes the guide tube 14 in a gas-tight manner against the striking direction 10 .

[0029] The connecting rod 15 driven by the crank plate 14 forms part of the crank mechanism of the exciter piston 13. The crank plate 14 is driven by the electric motor 12 via a spur gear stage 16.

[0030] according to Figure 2 The connecting rod 15 made of plastic is provided with a bearing pin section 17 integrally formed thereon at the piston end. To form a pivot bearing, the bearing pin section 17 interacts with the exciter piston 13 consisting of a piston crown 18 and a piston skirt 19. Two concave bearing shell sections 20a and 20b arranged on both sides of the connecting rod 15 are integrally formed on the inner side of the piston skirt 19.

[0031] from Figure 3 As can be seen better in FIG, the concave bearing shell section 21 is also integrally formed on the inner side of the piston crown 18. All bearing shell sections 20a, 20b and 21 comprise a bearing pin section 17 of the connecting rod 15 for forming the piston-side pivot bearing of the crank drive, which is designed as a plain bearing.

[0032] according to Figure 4 The bearing pin section 17 of the connecting rod 15 furthermore has two recesses 22 a and 22 b introduced therein on the end face for additional weight reduction and material saving.

[0033] In the exemplary embodiment, the piston crown 18 of the actuator piston 13 is of pot-shaped design and has a substantially uniform wall thickness. For dynamic sealing of the guide tube (not shown here), a U-shaped circumferential groove 23 for receiving an elastomeric sealing ring is provided in the radially outward edge region of the piston crown 18 close to the bottom. In addition, the piston skirt 19 has a circumferential relief recess 25 arranged adjacent to the adjacent piston crown 18 for further weight reduction. In this respect, the piston guidance is achieved by a piston guide surface 26 of the piston skirt 19 adjacent to the relief recess 25.

[0034] Furthermore, the sleeve-shaped piston skirt 19 of the hammer piston 13 is provided with a guide section 27 on the inside which surrounds the connecting rod 15 in the region close to the bearing pin and guides the connecting rod 15 along the alternating pivoting movement by means of a clearance fit on both sides.

[0035] about Figure 5 A metal sheet 28a bent into a half-shell shape and made of steel is arranged between the concave bearing shell section 21 of the piston crown 18 and the bearing pin section 17 of the connecting rod 15, which serves to reduce heat and wear. The metal sheet 28a is fixed to the piston crown 18 by means of a radially outwardly bent edge section 29a and prevents plastic-to-plastic material contact, which generates heat and friction heat when using a highly loaded forward stroke bearing.

[0036] exist Figure 6 In the alternative embodiment shown, a metal sheet 28b bent into a half-shell shape is fastened to the bearing pin section 17 of the connecting rod 15. For this purpose, a radially inwardly bent edge section 29b is used which engages in a corresponding recess in the connecting rod 15 as shown.

[0037] Figure 7The embodiment shown shows a flat cap-shaped piston crown 18' with a concave bearing shell section 21 formed on the inner side, as also present in the above-described embodiments. This cap-shaped piston crown 18' covers a sleeve-shaped piston skirt 19' at the end face and has a diameter that is smaller than the maximum diameter of the piston skirt 19' in order to prevent clogging relative to the guide tube. For dynamic sealing, in the present embodiment of the exciter piston 13', a U-shaped circumferential groove 23' is provided on the piston skirt 19' for receiving an elastomeric sealing ring (not shown here). Here, the circumferential groove 23' is located in the edge region of the piston skirt 19' close to the piston crown.

[0038] from Figure 8 It can be seen that a lubricating groove 30 is introduced into the running-in surface of the bearing shell section 21 of the piston crown 18. The lubricating groove 30 is arranged centrally in the longitudinal direction of the bearing shell section 21 and is introduced in the transverse direction of the curved shape of the bearing shell section 21. The lubricating groove 30 is filled with a lubricant for permanent lubrication of the sliding bearing. According to FIG. 9A , the piston crown 18 (only a part of which is shown here) is integrally connected to the piston skirt 19 via a welding point 31. This welding point 31 takes the form of a weld seam here. Adjacent to it, a groove-like recess 32 extends for receiving welding residues.

[0039] In the embodiment according to Fig. 9B, two mutually adjacent welds 31a and 31b are provided for fastening the components, which are combined with the groove-shaped recesses 32a to 32c arranged on both sides. The groove cross section of the central groove-shaped recess 32b is larger than the groove-shaped recesses 32a and 32c on the two edge sides, because the first welding residues of the welding points 31a and 31b in the form of two welds must be accommodated.

[0040] Fig.10 It is also shown that a centering lug 33 extending away from the piston base is provided on the piston crown 18 here. In the exemplary embodiment, the piston crown 18 has two centering lugs 33 opposite each other, wherein only one of the centering lugs is visible for illustration reasons. Each centering lug 33 engages with a corresponding recess 36 in the piston skirt 19 in order to ensure that the components are correctly positioned. Fig.11 The introduction bevels 34a and 34-5? on the distal end section of the centering lug 33 facilitate assembly. In addition, the centering lug 33' of the present embodiment has a recess 35 for further reducing mass.

[0041] The invention is not limited to the exemplary embodiments described above and their sub-variants. Rather, modifications and other combinations of these exemplary embodiments are also conceivable which fall within the scope of protection of the appended claims or are also independent of the disclosure of the appended claims.

[0042] Thus, for example, at least one lubricating groove can also be arranged in the region of the concave bearing shell section for supplying lubricant to the piston-side plain bearing location of the crank drive, regardless of the shape of the exciter piston, in particular regardless of whether this is designed as a single part or as a plurality of parts. Such an object can be described as follows with regard to the outline of the appended claims: A hammer mechanism for a hand-held electric tool, the hammer mechanism comprising a crank mechanism, which is used to convert the rotational drive motion of an electric motor into a translational alternating motion of an exciter piston for axially applying impact energy to the tool via a connecting rod driven by a crank disk or the like, wherein the connecting rod is provided with a bearing pin section integrally formed on the connecting rod at the end of the piston, the bearing pin section interacting with the exciter piston to form a pivot bearing, wherein at least one concave bearing shell section is arranged on the inner side of the exciter piston, and at least one lubricating groove is introduced into the running-in surface of the bearing pin section.

[0043] In a preferred embodiment, a single lubricating groove is arranged centrally in the longitudinal direction of the bearing shell segment and is positioned to extend transversely to the curved shape of the bearing shell segment. It is also conceivable to provide multiple lubricating grooves, as described above in conjunction with the special actuator piston.

[0044] The same also applies analogously to the wear-reducing sheet metal insert between the piston-side bearing shell section and the bearing pin-side connecting rod. Such a sheet metal, which is preferably bent into a shell form, can also be fixed in position by means of a bent edge section on the actuator piston or on the connecting rod, which is bent radially inwards or radially outwards.

Claims

1. A hammer mechanism (8) for a handheld electric tool, the hammer mechanism comprising a crank mechanism for converting the rotary drive motion of an electric motor (12) via a connecting rod (15) driven by a crank plate (14) into a translational alternating motion of an exciter piston (13) for axially applying impact energy to the tool, wherein: The connecting rod (15) is provided with a bearing pin section (17) integrally formed on the connecting rod at the end of the piston, the bearing pin section interacting with the exciter piston (13) to form a pivot bearing, the bearing pin section consisting of at least a piston crown (18) and a piston skirt (19), characterized in that a concave bearing shell section (21) associated with the bearing pin section (17) of the connecting rod (15) is integrally formed on the inner side of the piston crown (18), and the bearing shell section interacts relative to at least one curved bearing shell section (20a, 20b) integrally formed on the inner side of the piston skirt (19) in order to form the pivot bearing.

2. The hammer mechanism according to claim 1, It is characterized in that The connecting rod (15) with the bearing pin section (17) and / or the multi-part exciter piston (13) with the integrated bearing shell section (20a, 20b, 21) are produced from plastic by casting.

3. The hammer mechanism according to claim 1 or 2, It is characterized in that The bearing pin section (17) formed integrally on the connecting rod (15) is provided with at least one recess (22a, 22b) which is introduced into the end face for weight reduction.

4. Hammer mechanism according to one of the preceding claims, It is characterized in that The piston crown (18) is pot-shaped and has a uniform wall thickness.

5. The hammer mechanism according to claim 4, It is characterized in that The pot-shaped piston crown (18) of the actuator piston (13) is provided with a U-shaped circumferential groove (23) in a radially outward edge region close to the bottom for receiving an elastomeric sealing ring (24).

6. Hammer mechanism according to one of the preceding claims, It is characterized in that The non-cylindrical piston guide surface (26) of the actuator piston (13) is formed by a sleeve-shaped piston skirt (19) and has a relief recess (25) for reducing mass close to an adjacent piston crown (18).

7. Hammer mechanism according to one of the preceding claims, It is characterized in that The sleeve-shaped piston skirt (19) has a guide section (27) which at least partially surrounds the connecting rod (15) below an integrally formed bearing pin section (17).

8. Hammer mechanism according to one of the preceding claims, It is characterized in that At least one metal foil (28a; 28b) for reducing heat and / or wear is arranged between the concave bearing shell section (21) of the piston crown (18) and the bearing pin section (17) of the connecting rod (15).

9. The hammer mechanism according to claim 8, It is characterized in that The metal sheet (28a; 28b) is bent into the form of a half shell and is fixed in position on the piston crown 18 or on the connecting rod 15 by means of edge sections (29a, 29b) bent radially inwards or radially outwards.

10. Hammer mechanism according to one of the preceding claims, It is characterized in that The piston crown (18') is designed as a flat cover with a bearing pin section (21), which is integrally formed on the inner side and covers the sleeve-shaped piston skirt (19') at the end face and has a diameter smaller than the maximum diameter of the piston skirt (19').

11. The hammer mechanism according to claim 10, It is characterized in that The piston skirt (19') is provided with a U-shaped circumferential groove (23') in the edge region close to the piston crown for receiving an elastomeric sealing ring (24).

12. Hammer mechanism according to one of the preceding claims, It is characterized in that The single bearing shell section (21) of the piston crown (18) forms the forward stroke bearing of the connecting rod (15), and the two bearing shell sections (20a, 20b) of the piston skirt (19) arranged on both sides of the connecting rod (15) form the return stroke bearing of the connecting rod (15).

13. The hammer mechanism according to claim 12, It is characterized in that The bearing shell sections (20a, 20b, 21) form a bearing location of the bearing pin section (17) in the form of a cylindrical segment with a maximum semicircular encapsulation.

14. Hammer mechanism according to one of the preceding claims, It is characterized in that At least one lubricating groove (30) is introduced into the running-in surface of the bearing shell section (21) of the piston crown (18).

15. The hammer mechanism according to claim 14, It is characterized in that A single lubricating groove (30) is arranged centrally in the longitudinal direction of the bearing shell segment (21) and extends in the transverse direction of the curved shape of the bearing shell segment (21).

16. Hammer mechanism according to one of the preceding claims, It is characterized in that The piston crown (18) and the piston skirt (19) are connected to each other by welding or gluing, wherein at least one recess (32; 32a, 32b, 32c) for receiving welding residues or adhesive residues is arranged adjacent to at least one welding point or bonding point (31) on the piston crown (18) and / or on the piston skirt (19).

17. The hammer mechanism according to claim 16, It is characterized in that The at least one welding point or bonding point (31) is designed as a weld seam, to which in each case a groove-shaped recess (32a, 32b, 32c) for receiving welding residues is assigned on both sides.

18. Hammer mechanism according to one of the preceding claims, It is characterized in that At least one centering lug (33) is integrally formed on the piston crown (18) and / or on the piston skirt (19), the at least one centering lug extending toward an opposing connection partner and engaging in a corresponding recess therein.

19. The hammer mechanism according to claim 18, It is characterized in that The distal end section of the at least one centering lug (33) is provided with at least one introduction bevel (34a; 34b).

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