Striking mechanism for an electric hand-held power tool

Abstract

The invention relates to a striking mechanism (8) for an electric hand-held power tool, comprising a crank drive for converting a rotational drive movement of an electric motor (12) into a translationally alternating movement of an exciter piston (13), via a connecting rod (15) driven by a crank disc (14), in order to axially apply a tool with impact energy, wherein the connecting rod (15) is provided with a bearing pin section (17) formed thereon on the piston side, which cooperates with the exciter piston (13) to form a pivot bearing, formed at least by a piston base part (18) and a piston casing part (19), wherein a concave bearing shell section (21) that is associated with the bearing pin section (17) of the connecting rod (15) is formed inside the piston base part (18), which cooperates with an oppositely arranged at least one concave bearing shell section (20a, 20b) formed inside the piston casing part (19) in order to form the pivot bearing.

Description

[0001] Impact mechanism for an electric hand tool

[0002] DESCRIPTION

[0003] The invention relates to a percussion mechanism for an electric hand-held power tool, comprising a crank drive for converting a rotary drive movement of an electric motor via a connecting rod driven by a crank disk into a translatory alternating movement of an exciter piston for axially applying impact energy to a tool, wherein the connecting rod is provided with a bearing journal section formed thereon on the piston side, which cooperates with the exciter piston to form a pivot bearing, which is composed of at least a piston head part and a piston skirt part.

[0004] The field of application of the invention extends primarily to handheld rotary hammers or chisel hammers equipped with an electric motor drive. Such electric hand tools generate a linearly alternating working movement via a mechanical percussion mechanism, i.e., a back-and-forth movement to act on the tool, which in the case of a chisel hammer is designed as a chisel, and in the case of a hammer drill as an impact drill for machining preferably mineral materials - such as stone, concrete, and the like. The exciter piston of the impact mechanism does not act directly on the clamped tool, but rather via a pneumatic coupling. For this purpose, the exciter piston acts via the crank drive from one side on a cylinder chamber. On the opposite side of the cylinder chamber - pneumatically damped by the cylinder chamber - a percussion piston is arranged, which acts on the tool in the direction of impact.This results in indirect, pneumatically damped loading of the tool by the excitation piston. It is also conceivable to apply direct loading to a tool or to integrate additional components into the process chain, such as a die head. This is state-of-the-art technology.

[0005] WO 2015 / 049130 A1 discloses an electric hand-held power tool of the type of interest here, comprising a pneumatic percussion mechanism. The percussion mechanism comprises a striker movable along the percussion axis, an exciter piston connected to the drive via a crank drive by a connecting rod, and a pneumatic cylinder chamber that couples the movement of the striker piston to the exciter piston. The connecting rod is pivotally suspended in the exciter piston, for which purpose, in one embodiment disclosed here, a separate piston pin is used. In another embodiment, a convex bearing shell section is formed on the inside of a pot-shaped exciter piston at the bottom, which interacts with a concave end of the connecting rod to form the pivot bearing. While this allows for a forward stroke bearing of the connecting rod, it does not allow for a return stroke bearing. This is achieved via additional rear retaining tongues.In this state of the art, the excitation piston is formed in one piece.

[0006] In contrast, WO 2017 / 220561 A1 discloses a percussion mechanism of a hand-held electric power tool with a multi-part exciter piston of interest here. This is composed of a pot-shaped piston crown part and a likewise pot-shaped piston skirt part, which are mounted in an interlocking manner. The connecting rod bearing on the piston side is not provided by a separate piston pin, but rather by a bearing journal section formed integrally on the end of the connecting rod. This bearing journal section interacts with two inserted bearing shells on the piston side, which enclose the bearing journal section. The two bearing shells are made of a different material than the piston crown part and the piston skirt part of the exciter piston. All components of the exciter piston are made of metal, which results in a relatively high moving mass overall, which impairs the percussion mechanism's efficiency.

[0007] It is therefore the object of the present invention to further improve an impact mechanism for an electric hand-held power tool of the generic type in such a way that the impact mechanism efficiency is increased by simple technical measures.

[0008] Disclosure of the invention

[0009] The object is achieved by a percussion mechanism according to the preamble of claim 1 in conjunction with its characterizing features. The following dependent claims describe advantageous developments of the invention.

[0010] The invention includes the technical teaching that, in order to form a pivot bearing in a multi-part exciter piston, a concave bearing shell section associated with the bearing journal section of the connecting rod is formed on the inside of the piston head part, which bearing shell section cooperates oppositely with at least one concave bearing shell section formed on the inside of the piston skirt part to form a plain bearing.

[0011] The design of the respective bearing sections directly on the associated components of the exciter piston makes it possible to provide material for the bearing function only where it is needed. In contrast, separate inserts would have to be fitted securely and accurately into the inner contour of the piston crown and piston skirt sections, which would require correspondingly more material. The lightweight exciter piston, in contrast, contributes to increasing the impact mechanism's efficiency. The reduced mass also reduces device vibration and wear on the crank mechanism.

[0012] The solution according to the invention provides the prerequisite for the connecting rod including the bearing journal, as well as the multi-part exciter piston including the molded-on bearing shell sections, to be manufactured by casting from a plastic. Firstly, due to the material, the moving mass can be further reduced compared to a metal material; secondly, the casting of said components opens up efficient production. The components are preferably manufactured by injection molding. In order to further reduce the mass of the connecting rod in particular, a measure improving the invention proposes that the bearing journal section molded onto the connecting rod be provided with at least one hollow introduced into the end face thereof to reduce mass. This hollow can be continuous or designed in the manner of blind bores, depending on the required strength.The hollowing out makes a further contribution to saving material.

[0013] According to a preferred embodiment of the piston crown part, it is cup-shaped and, thanks to its preferably cast-based production, can be designed with a wall thickness of approximately the same thickness. The wall thickness is minimized to accommodate the load, further contributing to mass reduction.

[0014] Within the scope of this embodiment, it is further proposed that the cup-shaped piston crown part of the exciter piston be provided with a U-shaped circumferential groove in the outer radial edge region near the crown for receiving an elastomer sealing ring. A conventional O-ring or the like can be used as the elastomer sealing ring. The connection point to the piston skirt part is located outside the U-shaped circumferential groove. However, it is also conceivable to place the circumferential groove on the side of the piston skirt part or to realize the component separation in the region of the circumferential groove.

[0015] According to a further measure improving the invention, it is proposed that the piston skirt part of the exciter piston has a relief recess in the area adjacent to the adjacent piston crown part for further mass reduction. The actual guide surface of the exciter piston is then formed by the edge area of ​​the piston skirt part remote from the piston crown. This edge area can also be designed in a wave-like manner to further save material, resulting in a non-cylindrical piston guide surface.

[0016] According to a further measure improving the invention, it is proposed that the sleeve-shaped piston skirt part has a guide section that at least partially surrounds the connecting rod below the integrally formed bearing journal section. This guide section is designed in such a way that it does not impede the alternating pivoting movement of the connecting rod, but forms parallel, opposite lateral guide surfaces. The guided region of the connecting rod has a clearance fit with respect to the guide section of the exciter piston.

[0017] Furthermore, it should be noted that the length of the connecting rod's journal section and the piston diameter should have a geometric ratio of preferably > 0.3, most preferably > 0.5. This relatively large ratio leads to a correspondingly lower surface pressure and thus, advantageously, less wear on the piston bearings.

[0018] In order to reduce heat development during operation in the area of ​​the connecting rod bearing, a further optional measure proposes that a metal sheet be arranged between the concave bearing shell section of the piston crown part and the bearing journal section of the connecting rod. It should be noted that the use of such a metal sheet is not limited to multi-part exciter pistons of the generic type. Such an additional metal sheet can be used with any type of exciter piston and is particularly useful for exciter pistons and connecting rods that are made of plastic. Since such a metal sheet, preferably made of steel with a sheet thickness of between 0.2 and 2 mm, reduces sliding friction, the plain bearing properties are improved, which leads to less heat development. The half-shell-shaped bent metal sheet can be inserted or placed between the aforementioned components.Preferably, the arrangement should be on the piston crown part, as this is where the highest load is present. The half-shell-shaped metal sheet is preferably fixed in position on the piston crown part or the connecting rod via edge sections bent radially inward or radially outward. A positive positional fixation is sufficient for this. However, an inserted metal sheet can also be overmolded with plastic to permanently bond it to the piston crown part. It is also conceivable to arrange such a metal sheet on the bearing shell section of the piston skirt part.In order to reduce leakage and jamming of the exciter piston in the associated cylinder barrel due to the multi-part design, it is proposed that the piston crown part be designed as a flat cover - i.e., not pot-shaped in contrast to the embodiment described above - but with the bearing journal section molded onto the inside as described above. This cover-shaped piston crown part covers the sleeve-shaped piston skirt part at the end face and preferably has a smaller diameter than the maximum diameter of the piston skirt part to prevent jamming. This design shifts the component separation towards the piston crown. As a result, the sealing point of the piston seal and the leading piston portion are located in one and the same component, namely the piston skirt part, which in this respect assumes the guiding and sealing function.The connecting rod is enclosed, held, and guided in the piston skirt by the attached, cap-shaped piston crown. The reduced diameter of the piston crown is preferably 90 to 99% of the diameter of the piston skirt. The latter is provided with a U-shaped circumferential groove in the edge area near the piston crown to accommodate the elastomer sealing ring.

[0019] To further minimize plain bearing wear on the piston bearings, a further measure improving the invention proposes that the single bearing shell section of the piston crown part forms a pre-stroke bearing for the connecting rod, and two bearing shell sections of the piston skirt part, arranged on either side of the connecting rod flanks, form a return-stroke bearing for the connecting rod. All bearing shell sections can be cylinder-segment-shaped bearing positions with a maximum semicircular surround of the bearing journal section. As a result, the plain bearing position of the connecting rod in the exciter piston is divided into three bearing shells, which are preferably designed as half-shells. Separating the plain bearing position into pre-stroke and return-stroke bearings enables maximization of the particularly stressed pre-stroke bearing for compression. Thanks to the maximization of the bearing surfaces, the surface pressure is reduced accordingly, which leads to less wear.The one-piece design of the bearing shell sections with the respective associated components of the exciter piston provides the prerequisite for reducing the plain bearing clearance compared to the state of the art described at the beginning in order to achieve optimal plain bearing support.

[0020] In order to further reduce heat development in the area of ​​the plain bearing of the exciter piston, a further measure improving the invention proposes that at least one lubrication groove be introduced into the running surface of the bearing shell section of the piston crown part, as the most heavily loaded bearing zone. This lubrication groove can be filled with a suitable lubricant as a permanent lubrication point or can be connected to a lubricant circuit of a pressure lubrication system. This supplies the component surfaces of the connecting rod bearing that slide against one another with a lubricating film. A single lubrication groove is sufficient, which is preferably arranged centrally in the longitudinal direction of the bearing shell section and runs transversely along the curved shape of the bearing shell section. However, it is also conceivable to functionally integrate more than one lubrication groove into the bearing shell sections.A symmetrical arrangement below the connecting rod shaft ensures a uniform lubricant supply to the plain bearing surfaces. The at least one lubrication groove should preferably be designed to provide a volume of 0.02 to 2 cm. 3 Lubricant is available. This at least one lubrication groove can be provided independently of the aforementioned metal sheet, i.e. instead of or in addition to it, and is also not tied to a multi-part exciter piston.

[0021] The component connection between the piston crown part and the piston skirt part can preferably be achieved by welding or gluing, whereby expelled weld metal or excess adhesive is generated. To prevent this from impairing functionally precise component positioning, a further measure improving the invention proposes that at least one recess for receiving welding or adhesive residues be arranged adjacent to the at least one welding or gluing point on the piston crown part and / or the piston skirt part.

[0022] If the welding or bonding point is formed as a weld seam, it is recommended to provide a groove-shaped recess on either side of the recess to absorb the residues. The recess should offer sufficient volume to completely absorb the expelled weld metal 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. The cross-section of the groove-shaped recess for absorbing welding residues should preferably be larger than the cross-section of the thickest weld seam. To maximize absorption capacity, the cross-section of the groove-shaped recess can also be bowl-shaped.

[0023] To ensure the correct assembly of an exciter piston composed of a piston crown part and a piston skirt part, a further measure improving the invention proposes that at least one centering lug be formed on the piston crown part and / or the piston skirt part, extending toward the opposite connecting partner and engaging into a corresponding recess therein. This allows for precise positioning of the components during assembly. The centering lugs position the two components in the correct rotational position relative to each other before the exciter piston is finally joined.

[0024] Preferably, the distal end sections of the centering lug have at least one lead-in bevel to facilitate assembly. The lead-in bevel has a lead-in angle in the preferred range of 5 to 50 degrees. Furthermore, the centering lug can be provided with a recess to further reduce mass in this area, as the flank sides of the centering lug are sufficient for the intended function.

[0025] Detailed description based on the drawing

[0026] Further measures improving the invention are described in more detail below, together with the description of preferred embodiments of the invention, with reference to the figures. Fig. 1 shows a schematic side view of an electric hand-held power tool designed as a chisel hammer with an integrated pneumatic percussion mechanism.

[0027] Fig. 2 a longitudinal section through the exciter piston-connecting rod assembly,

[0028] Fig. 3 shows another longitudinal section through the exciter piston-connecting rod assembly,

[0029] Fig. 4 a longitudinal section through the piston area,

[0030] Fig. 5 a longitudinal section through the piston area with sheet metal insert in a first

[0031] embodiment,

[0032] Fig. 6 a longitudinal section through the piston area with sheet metal insert in a second

[0033] embodiment,

[0034] Fig. 7 a longitudinal section through the piston area with an alternative piston crown part,

[0035] Fig. 8 is a perspective view of a sectioned excitation piston,

[0036] Fig. 9a shows a detailed section in the area of ​​the component connection in a first embodiment,

[0037] Fig.9b a detailed section in the area of ​​the component connection in a second embodiment,

[0038] Fig. 10 a longitudinal section through the excitation piston, and

[0039] Fig. 11 shows a detailed view of a piston crown section with a recess. Fig. 1 shows an electric hand tool in the form of a chisel hammer 1. The chisel hammer 1 has a front tool holder 2, in which a chisel 3 can be inserted and locked along a working axis 4. The electric hammer 1 has a handle 5 at its rear end, which is integrally formed on a machine housing 6. An additional handle—not shown in detail—can be attached to the machine housing 6 near the tool holder 2. An electrical mains power supply 7 is provided from the machine housing 6 for power supply.

[0040] The chisel hammer 1 has an integrated pneumatic impact mechanism 8 with a percussion piston 9, which, during operation, periodically applies impacts in the impact direction 10 to the chisel 3 along the working axis 4. The percussion piston 9 is movably guided along the working axis 4 and, in the illustrated embodiment, strikes the chisel 3 indirectly via a striker 11. The striker 11 is arranged in the impact direction 10 between the percussion piston 9 and the tool holder 2.

[0041] The pneumatic percussion mechanism 8 is driven by an electric motor 12 and moves an excitation piston 13 by means of a crank drive in a translational alternating manner on the working axis 4. The opposite percussion piston 9 is coupled to the excitation piston 13 via an air spring.

[0042] The impact mechanism 8 comprises a cylindrical guide tube 14 for pneumatic coupling, in which the excitation piston 13 is guided in a dynamically sealed manner along the working axis 4. Thus, the excitation piston 13 seals the guide tube 14 airtight against the impact direction 10.

[0043] The crank drive for the exciter piston 13 includes a connecting rod 15 driven by a crank disk 14. The crank disk 14 is driven by the electric motor 12 via a spur gear stage 16.

[0044] According to Fig. 2, the plastic connecting rod 15 is provided with a bearing journal section 17 directly molded onto the piston side. The bearing journal section 17 cooperates with an exciter piston 13 consisting of a piston crown part 18 and a piston skirt part 19 to form a pivot bearing. Two concave bearing shell sections 20a and 20b are molded onto the inside of the piston skirt part 19, arranged on either side of the connecting rod 15.

[0045] As can be better seen in Fig. 3, a concave bearing shell section 21 is also formed on the inside of the piston crown part 18. All bearing shell sections 20a, 20b, and 21 encompass the bearing journal section 17 of the connecting rod 15 to form a piston-side pivot bearing of the crank drive designed as a plain bearing.

[0046] According to Fig. 4, the bearing journal section 17 of the connecting rod 15 additionally has two hollows 22a and 22b formed therein on each end face for additional mass reduction and material savings.

[0047] In this embodiment, the piston crown portion 18 of the exciter piston 13 is cup-shaped and has approximately the same wall thickness. In the outer radial edge region of the piston crown portion 18 near the crown, a U-shaped circumferential groove 23 is provided for receiving an elastomer sealing ring for dynamic sealing against the guide tube (not shown here). Furthermore, the piston skirt portion 19 has a circumferential undercut recess 25 arranged adjacent to the adjacent piston crown portion 18 for further mass reduction. The piston is guided via a piston guide surface 26 of the piston skirt portion 19 adjacent to the undercut recess 25.

[0048] The sleeve-shaped piston skirt part 19 of the exciter piston 13 is further provided on the inside with a guide section 27 surrounding the connecting rod 15 in the area near the bearing journal, which guides the connecting rod 15 along the alternating pivoting movement via a clearance fit on both sides.

[0049] With reference to Fig. 5, a half-shell-shaped, bent steel metal sheet 28a is arranged between the concave bearing shell section 21 of the piston crown part 18 and the bearing journal section 17 of the connecting rod 15. This sheet serves to reduce heat and wear. The metal sheet 28a is fixed in position to the piston crown part 18 by radially outwardly bent edge sections 29a and prevents plastic-to-plastic material contact, which causes wear and frictional heat, during the highly loaded pre-stroke bearing.

[0050] In the alternative embodiment illustrated in Fig. 6, a half-shell-shaped bent metal sheet 28b is attached to the bearing journal portion 17 of the connecting rod 15. For this purpose, radially inwardly bent edge portions 29b are used, which engage in corresponding recesses on the connecting rod 15 as shown.

[0051] The embodiment shown in Fig. 7 shows a flat, lid-shaped piston crown part 18' with a concave bearing shell section 21 formed on the inside, as is also present in the embodiment described above. This lid-like piston crown part 18' covers the sleeve-shaped piston skirt part 19' at the end and has a smaller diameter than the maximum diameter of the piston skirt part 19' in order to avoid jamming against the guide tube. For dynamic sealing, in this embodiment of an exciter piston 13', a U-shaped circumferential groove 23' is provided on the side of the piston skirt part 19' for receiving an elastomer sealing ring (not shown here). The circumferential groove 23' is located here in the edge region of the piston skirt part 19' near the piston crown part.

[0052] As can be seen from Fig. 8, a lubrication groove 30 is formed in the running surface of the bearing shell section 21 of the piston crown part 18. The lubrication groove 30 is arranged centrally in the longitudinal direction of the bearing shell section 21 and is formed in the transverse direction along the curved shape of the bearing shell section 21. The lubrication groove 30 is filled with a lubricant for permanent lubrication of the plain bearing. According to Fig. 9A, the piston crown part 18, shown here only in section, is integrally connected to the piston skirt part 19 via a weld 31. This weld 31 is designed as a weld seam. Adjacent to this extends a groove-like recess 32 for receiving welding residues.

[0053] In the embodiment according to Fig. 9B, two adjacent weld seams 31a and 31b are provided for component fastening, which are combined with groove-shaped recesses 32a to 32c arranged adjacent thereto on both sides. The central groove-shaped recess 32b has a larger groove cross-section than the two edge-side groove-shaped recesses 32a and 32c, since the former must accommodate welding residues from both welds 31a and 31b formed as a weld seam.

[0054] Fig. 10 further shows that centering lugs 33 extending away from the piston crown are provided on the piston crown part 18. In this embodiment, the piston crown part 18 has two opposing centering lugs 33, of which only one is visible due to the nature of the illustration. Each centering lug 33 engages a corresponding recess 36 on the piston skirt part 19 to ensure correct component positioning. According to Fig. 11, run-in bevels 34a and 34b on the distal end section of the centering lug 33 facilitate assembly. Furthermore, the centering lug 33' of this embodiment has a recess 35 for further mass savings.

[0055] The invention is not limited to the above-described embodiments and their sub-variants. Rather, modifications and other combinations thereof are also conceivable, which either fall within the scope of the following claims or are also disclosed independently thereof.

[0056] For example, it is also possible, regardless of the shape of the exciter piston, in particular whether it is constructed in one or more parts, to arrange at least one lubrication groove in the area of ​​an internal concave bearing shell section to supply lubricant to the piston-side plain bearing point of the crankshaft drive. Such a generalized object, as compared to the following claims, can be described as follows:

[0057] Impact mechanism for an electric hand-held power tool, comprising a crank drive for converting a rotary drive movement of an electric motor via a connecting rod driven by a crank disk or the like into a translationally alternating movement of an exciter piston for axially applying impact energy to a tool, wherein the connecting rod is provided with a bearing journal section formed thereon on the piston side, which cooperates with the exciter piston to form a pivot bearing, wherein at least one concave bearing shell section is arranged on the inside of the exciter piston, on the running surface of which at least one lubrication groove is introduced. In a preferred embodiment, a single lubrication groove is arranged centrally in the longitudinal direction of the bearing shell section and is positioned running transversely along the curved shape of the bearing shell section.It is also conceivable to provide several lubricant grooves, as described above in connection with the special exciter piston.

[0058] The same applies analogously to the wear-reducing sheet metal inserts between the piston-side bearing shell section and the connecting rod on the journal side. Such a sheet metal insert, preferably bent in a shell-shaped manner, can also be secured in position via bent edge sections on the exciter piston or connecting rod side, which are bent radially inward or radially outward.

Claims

CLAIMS 1. Impact mechanism (8) for an electric hand-held power tool, comprising a crank drive for converting a rotary drive movement of an electric motor (12) via a connecting rod (15) driven by a crank disk (14) into a translatory alternating movement of an exciter piston (13) for axially applying impact energy to a tool, wherein the connecting rod (15) is provided with a bearing journal section (17) formed thereon on the piston side, which cooperates with the exciter piston (13) to form a pivot bearing, which is composed of at least a piston head part (18) and a piston skirt part (19), characterized in that on the inside of the piston head part (18) a concave bearing shell section (21) is formed which is associated with the bearing journal section (17) of the connecting rod (15), which, to form the pivot bearing, is connected oppositely to at least one concave bearing shell section formed on the inside of the piston skirt part (19). (20a,20b) interacts., 2. Percussion mechanism according to claim 1, characterized in that the connecting rod (15) including the bearing journal section (17) and / or the multi-part excitation piston (13) including the integrated bearing shell sections (20a, 20b, 21) are made by casting from a plastic.

3. Percussion mechanism according to one of claims 1 or 2, characterized in that the bearing journal section (17) formed on the connecting rod (15) is provided with at least one hollow (22a, 22b) made therein on the end face for reducing mass.

4. Percussion mechanism according to one of the preceding claims, characterized in that the piston head part (18) is cup-shaped and has a uniform wall thickness.

5. Percussion mechanism according to claim 4, characterized in that the pot-shaped piston head part (18) of the exciter piston (13) is provided in the outer radial edge region near the base with a U-shaped circumferential groove (23) for receiving an elastomer sealing ring (24).

6. Percussion mechanism according to one of the preceding claims, characterized in that a non-cylindrical piston guide surface (26) of the exciter piston (13) is formed by the sleeve-shaped piston skirt part (19) and has a free-cut recess (25) for mass reduction adjacent to the adjacent piston head part (18).

7. Percussion mechanism according to one of the preceding claims, characterized in that the sleeve-shaped piston skirt part (19) has a guide section (27) which at least partially surrounds the connecting rod (15) below the molded-on bearing journal section (17).

8. Percussion mechanism according to one of the preceding claims, characterized in that at least one metal sheet (28a; 28b) for reducing heat and / or wear is arranged between the concave bearing shell section (21) of the piston head part (18) and the bearing journal section (17) of the connecting rod (15).

9. Percussion mechanism according to claim 8, characterized in that the metal sheet (28a; 28b) is bent in the shape of a half-shell and is fixed in position on the piston head part (18) or on the connecting rod (15) by means of edge sections (29a, 29b) bent radially inward or radially outward.

10. Percussion mechanism according to one of the preceding claims, characterized in that the piston head part (18') is designed as a flat cover with a bearing pin section (21) formed on the inside, which covers the sleeve-shaped piston skirt part (19') on the end face and has a smaller diameter than the maximum diameter of the piston skirt part (19').

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

12. Percussion mechanism according to one of the preceding claims, characterized in that the single bearing shell section (21) of the piston head part (18) forms a pre-stroke bearing of the connecting rod (15) and two bearing shell sections (20a, 20b) of the piston skirt part (19) arranged on both sides of the connecting rod (15) form a return stroke bearing of the connecting rod (15).

13. Percussion mechanism according to claim 12, characterized in that the bearing shell sections (20a, 20b, 21) form cylinder-segment-shaped bearing points with a maximum semicircular enclosure of the bearing journal section (17).

14. Percussion mechanism according to one of the preceding claims, characterized in that at least one lubricating groove (30) is introduced into the running surface of the bearing shell section (21) of the piston head part (18).

15. Percussion mechanism according to claim 14, characterized in that the single lubrication groove (30) is arranged centrally in the longitudinal direction of the bearing shell section (21) and runs in the transverse direction along the curved shape of the bearing shell section (21).

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

17. Percussion mechanism according to claim 16, characterized in that the at least one weld or bonding point (31) is formed as a weld seam, to which a groove-shaped recess (32a, 32b, 32c) for receiving welding residues is assigned on each side.

18. Percussion mechanism according to one of the preceding claims, characterized in that at least one centering lug (33) extending to the opposite connecting partner and engaging in a corresponding recess therein is formed on the piston crown part (18) and / or the piston skirt part (19).

19. Percussion mechanism according to claim 18, characterized in that the distal end portion of the at least one centering lug (33) is provided with at least one inlet bevel (34a; 34b).

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