Impact mechanism arrangement

Abstract

The invention relates to an impact mechanism arrangement for a rotary hammer or chipping hammer, comprising an impact mechanism unit (1) for converting a rotary drive motion of an electric motor (2) into a linearly reciprocating working motion for a tool (3), wherein the impact mechanism unit (1) acts on an adjacent striker body (10) which is made of a steel material and applies rearward impacts to the tool (3), wherein the steel striker body (10; 10'; 10'', 10''') has, on the end face (11a) facing at least the tool (3), a contact element (13; 13'; 13'', 13''', 13'''') which is integrally bonded to the steel striker body (10; 10'; 10", 10''') and has a preferably convex impact surface, wherein the contact element (13; 13'; 13'', 13''', 13'''') is made of a metal-matrix composite material.

Description

[0001] 2023P00163EP

[0002] Hilti Aktiengesellschaft

[0003] Principality of Liechtenstein

[0004] PERCENTAGE ARRANGEMENT

[0005] DESCRIPTION

[0006] The present invention relates to an impact mechanism for a drill or chisel hammer, comprising an impact unit for converting a rotary drive movement of an electric motor into a linear alternating working movement for a tool, wherein the impact unit acts on an adjacent impact body made of a steel material, which strikes the tool from behind.

[0007] The application area of ​​the invention extends primarily to hand-held power tools, such as in particular impact drills, chiseling machines, rotary hammer machines or combination hammer machines, which have in common an impact mechanism unit integrated into the drive train.

[0008] A percussion unit serves to convert a rotary drive movement into an alternating working movement for striking the tool, primarily a percussion drill or chisel. Between the percussion unit and the tool, a percussion element according to the invention, a so-called impactor, is arranged which, due to its inertia, generates a sufficiently large impulse.

[0009] State of the art

[0010] According to generally known technology, the combination of high mechanical stress and high abrasive wear on an impactor leads to considerable wear of the impactor's contact surface, even when using high-grade steels. This, in turn, results in increased contact stiffness, which increases the overall stress on the tool and can thus lead to premature tool failure. Furthermore, high-grade steels require a complex and energy-intensive heat treatment process. Since an impactor in an impact mechanism typically comes into contact with a large number of tools over its service life, the wear of the contact surface is more severe than the typical wear of the tool contact points.While there is a user tolerance for the need to replace tools due to wear, the impact elements of an impact mechanism are expected to have a long service life. Furthermore, a deformed impact element due to wear leads to increased tool wear, resulting in a poor sustainability profile.

[0011] DE 10 2010 043 837 A1 discloses a generic striking mechanism arrangement, the striking unit of which acts on a striking body which in turn acts on a tool.

[0012] The impact mechanism transmits the impulse via a front-facing contact surface to the coaxially arranged tool and is subjected to particularly high loads. This also applies, to a lesser extent, to the second contact surface on the opposite front face of the impact mechanism, which interacts with the impact unit.

[0013] To withstand high impulse loads, the striking surface of the striking mechanism is arranged on a first striking mechanism part made of a different material than the rest of the striking mechanism part. The material of both striking mechanism parts is the same, but they differ in their heat treatment. This allows the striking mechanism part with the striking surface to be manufactured with higher impact toughness.

[0014] Against this background, the object of the present invention is to further improve the striking element of a striking mechanism in such a way that a low-wear striking surface can be produced with minimal manufacturing effort. Disclosure of the invention

[0015] The problem is solved starting from a percussion mechanism according to the preamble of claim 1 in conjunction with its characterizing features. The following dependent claims describe advantageous embodiments of the invention. Dependent claim 13 relates to an electric drill or chisel hammer equipped with a percussion mechanism according to the invention.

[0016] The invention includes the technical teaching that a steel striking body has a contact element, preferably convex, joined to the steel striking body on an end face facing the tool, wherein the contact element consists of a metal matrix composite material. This allows for the production of a low-wear impact surface with minimal manufacturing effort.

[0017] In other words, a contact element made of metal matrix composite material with a preferably convex, i.e. outwardly curved, contact surface is attached to a main body produced conventionally by turning, forging, extrusion or the like on the end face facing at least the tool.

[0018] Thanks to this special choice of material and the geometric design, an almost constant tool load can be achieved over the entire service life of the hand-held power tool, as end-face wear of the impact body is minimized.

[0019] In a particularly advantageous embodiment of the invention, it is provided that the steel impact body has a three-dimensional joining zone, in particular a recess, on an end face facing the tool during operation, in which the contact element is at least partially arranged.

[0020] The contact element, consisting of a metal matrix composite material, preferably incorporates a cemented carbide material. This results in very high impact strength. In contrast, the steel material of the remaining impact body can be conventional case-hardening steel, heat-treatable steel, or tool steel. For example, a tungsten carbide-cobalt cemented carbide (WC-Co) is suitable as the cemented carbide material used within the metal matrix composite. The WC to Co ratio is preferably greater than 6, and particularly preferably greater than 10, to achieve the desired workpiece properties.

[0021] According to a preferred embodiment, the contact element is rotationally symmetrical, with its maximum diameter D being larger than its height H, and the ratio of the maximum diameter D to the height H preferably being between 1 and 8, more preferably between 1.4 and 3.5, and most preferably between 1.4 and 2.2. Particularly in the latter range, an optimum is achieved in terms of the largest possible force transmission area with a sufficiently large joining zone. Fundamentally, two opposing requirements must be met. On the one hand, there is the impact load, which is relevant for the joining zone. For this purpose, the contact element or the carbide insert should preferably be lightweight, and the joining zone on the circumference should be sufficiently large, with the remaining ring of the steel body not being too weak. On the other hand, there is the impact load, which is relevant for the contact element.The height of the contact element should not be too small to prevent exceeding permissible tensile stresses at its base. Tests have shown that the specified diameter-to-height ratio surprisingly achieves a very good compromise that fulfills both of the aforementioned requirements.

[0022] The contact element according to the invention preferably has a cylindrical or conical basic shape. In particular, with a conical basic shape, a self-centering effect is generated in the impact direction, although this results in a high contact gap load on the outer surface.

[0023] To optimize the joint gap load-bearing capacity, a further measure improving the invention proposes that the contact element has several centering stiffeners or spacers arranged along the circumferential surface at intervals from each other and projecting upwards from the surface.

[0024] Alternatively or additionally, it may be provided that the striking body has several centering strips or spacers arranged at intervals, particularly in the circumferential direction, and which protrude in a raised manner, in the area of ​​the recess.

[0025] Alternatively or additionally, axial spacers can be provided on the striking mechanism body and / or the contact element. These axial spacers allow for the adjustment of the distance between the contact element and the striking mechanism body, relative to the centering strips.

[0026] The centering strips or spacers can, for example, be interrupted or otherwise designed and ensure a defined gap for receiving the bonding agent. To guarantee a uniform gap, the number of centering strips, preferably equidistant from each other along the circumference, should be greater than 3. The centering strips can, for example, also be designed as knurling or ribbing.

[0027] Preferably, the contact element is bonded to the recess of the striking mechanism body. According to a preferred embodiment, the bond is produced by soldering.

[0028] Preferably, the soldered joint is provided both in the area of ​​an end face between the contact element and the striking body, and in the area of ​​a lateral surface between the contact element and the striking body. Preferably, the soldered joint covers the entire end-face and lateral contact area between the contact element and the recess in order to achieve maximum holding force through the three-dimensional joining zone thus created.

[0029] To achieve a particularly good hold between the contact element and the striking body, it has proven advantageous if a solder gap arranged in the end-face and / or mantle-side contact area between the contact element and the recess is between 0.05 mm and 0.5 mm, in particular between 0.05 mm and 0.2 mm.

[0030] The ratio of the soldering area to the centering areas created by the centering strips should be > 80%, preferably > 90%, and most preferably > 95%. The centering areas are sufficiently large to ensure that the intended function of maintaining the solder gap is guaranteed even under adverse stress conditions, while maximizing the soldering area.

[0031] Preferably, the centering strips of the contact element and / or the striking body are designed such that, in the assembled state, a sliding or press fit exists between the contact element and the striking body. In a cost-effective embodiment, the centering strips are part of the contact element, with the circumscribed circle around the centering strips preferably being slightly larger than the diameter of the recess in the striking body. Alternatively or additionally, the centering strips can be designed, for example, as knurling, embossing, or as an element produced by an extrusion process within the recess of the striking body, with the circumscribed circle around the centering strips preferably being slightly smaller than the outer diameter of the contact element.

[0032] According to a preferred embodiment of the invention, the striking body has a contact element on each of its end faces, which is bonded to the steel striking body and preferably has a convex impact surface. In this embodiment, wear of the contact point towards the striking piston can also be prevented, which additionally results in a constant shock wave over the service life of the hand tool.

[0033] The percussion unit used in the percussion arrangement according to the invention is preferably designed in the manner of a pneumatic percussion mechanism and comprises an eccentric drive for converting the rotary drive movement into a linear alternating movement by means of coupling to an exciter piston with a connecting rod, which is guided slidably in a guide tube, in order to interact with a striking piston arranged opposite it in the guide tube via the compressed air column generated between them. The striking piston in turn corresponds to the striking body designed according to the invention.

[0034] In an advantageous embodiment of the invention, the impact piston has a contact element on an end face facing the impact body, which is bonded to the steel impact piston and has a preferably convex impact surface, wherein the contact element consists of a metal matrix composite material.

[0035] With such a design, a nearly constant load can be achieved on the impact piston over the entire service life of the hand-held power tool, similar to the impact body, since wear on the end face of the impact piston is minimized.

[0036] The contact body of the piston can be designed in a similar way to the contact body of the impact body and can be connected to it.

[0037] If both the impact piston and the impact body have contact elements that interact with each other on their facing end faces during operation, wear is particularly low and service life is increased.

[0038] Furthermore, an electric drill or chisel hammer is proposed, comprising a percussion mechanism as described above.

[0039] In an advantageous embodiment of an electric hammer drill or chisel, a tool is provided which interacts with the impact element during operation of the electric hammer drill or chisel. This tool has a contact element on an end face facing the impact element, the contact element being bonded to a steel tool and preferably having a convex contact surface. The contact element is made of a metal matrix composite material. In such an embodiment, a nearly constant load can be achieved on the tool over the entire service life of the power tool, similar to the impact element, since end-face wear of the tool is minimized.

[0040] The contact body of the tool can be designed and connected in a similar way to the contact body of the impact body and / or the contact body of the impact piston.

[0041] If both the tool and the impactor have contact elements that interact with each other on their facing end faces during operation, wear is particularly low and service life is increased.

[0042] In a particularly preferred embodiment, both the tool and the impact piston have a contact element that interacts with a contact element of the impact body during operation. This preferably results in the entire impact chain, consisting of the tool, impact body, and impact piston, being made of hard metal on both sides at all impact points, thus minimizing wear.

[0043] Detailed description based on drawing

[0044] Further measures improving the invention are described in more detail below, together with a description of preferred embodiments, with reference to the figures. The figures show:

[0045] Fig. 1 shows a schematic longitudinal section through a percussion mechanism of a chisel hammer with a tool inserted.

[0046] Fig. 2 shows a schematically detailed longitudinal section through the percussion mechanism to illustrate the impact chain.

[0047] Fig. 3 shows a longitudinal section through an impactor according to a first embodiment,

[0048] Fig. 4 shows a detailed view of the longitudinal section according to Fig. 3.

[0049] Fig. 5 shows a longitudinal section through an impactor according to a second embodiment,

[0050] Fig. 6 shows a detailed view of the longitudinal section according to Fig. 5.

[0051] Fig. 7 shows a longitudinal section through an impactor according to a third embodiment,

[0052] Fig. 8 shows a detailed view of the longitudinal section according to Fig. 7.

[0053] Fig. 9 shows a longitudinal section through a tool, a striking element, and a striking piston according to a fourth embodiment. According to Fig. 1, a striking mechanism for an exemplary chisel hammer essentially consists of a striking unit 1 for converting a rotary drive movement of a drive unit designed as an electric motor 2 into a linear alternating working movement for a tool 3, which here is designed as a chisel. The pneumatic striking unit 1 comprises an eccentric drive 4 for converting the rotary drive movement generated by the drive motor 2 into the linear alternating movement by coupling it to an exciter piston 5 with a connecting rod 6. The exciter piston 5 is guided slidably in a guide tube 7, forming a piston-cylinder unit. Opposite the exciter piston 5, a striking piston 8 is arranged, also slidably in the guide tube 7.A damping column of air is generated between the exciter piston 5 and the impact piston 8 as a result of the linearly alternating movement.

[0054] The impact unit 1 acts on an adjacent impact body 10, made of a steel material, which is also slidably housed in an extension 9 of the guide tube 7. The impact body 10 has a rotationally and longitudinally symmetrical shape and acts in a backward-percussive manner on the tool 3 within the action chain.

[0055] As shown in Fig. 2, the two end faces 11a and 11b of the impactor 10 are provided with a convex impact surface. Along the chain of action, the global stress on the impacting components is minimized. However, the local stress on the impacting components at the contact points is very high. The convexly shaped impact surfaces 11a and 11b of the impactor 10 reduce the contact stiffness of the impact transmission and stretch the temporal contact force profile, which has a stress-reducing effect.

[0056] As shown in Fig. 3, the steel impactor 10 has a recess 12 for receiving a contact element 13 with a preferably convex contact surface. In this embodiment, the contact element 13, which is cylindrical in its basic form, consists of a metal matrix composite material containing a tungsten carbide-cobalt cemented carbide to increase its impact strength. As shown in Fig. 4, the contact element 13 is bonded to the recess 12 of the impactor 10 by means of a soldered connection. A solder gap 14 exists between the recess 12 and the contact element 13. The contact element 13 is rotationally symmetrical with a diameter D that is larger than its height H.

[0057] According to Fig. 5, the contact element 13' in the second embodiment is conical in design, to which the shape of the recess 12' is also adapted.

[0058] As shown in Fig. 6, the conical contact element 13' has several centering strips 16 or spacers (exemplary) arranged circumferentially spaced apart from one another along the cylindrical surface 15 and projecting upwards from the cylindrical surface 15. Alternatively or additionally, spacers can also be provided in the area of ​​an end face 17.

[0059] According to Fig. 7, in the third embodiment of a striking body 10", this is also provided with a contact element 13" which is cylindrical in its basic form, as in the first embodiment.

[0060] In contrast to the first embodiment, the cylindrical contact element 13" in Fig. 8 has several centering strips 16' arranged circumferentially spaced apart from one another along the outer surface 15'. Spacers may also be provided in the area of ​​the end face 17'.

[0061] Fig. 9 shows a fourth embodiment of a striking body 10'", wherein the striking body 10'" has a contact element 13'" both in the area of ​​the end face 11 a and in the area of ​​the end face 11b.

[0062] Furthermore, the tool 3 has a contact element 19 on an end face 18 facing the striking body 10'" which interacts with the contact element 13'" of the striking body 10'" during operation. The striking piston 8 also has a contact element 21 on an end face 20 facing the striking body 10'" which interacts with the contact element 13"" of the striking body 10'" during operation. Both the contact element 19 of the tool 3 and the contact element 21 of the striking piston 8 can be designed in a similar manner to the contact element 13 of the striking body 10 and can be connected to their respective bodies.

[0063] The invention is not limited to the preferred embodiments described above. Rather, variations thereof are also conceivable and are included within the scope of protection of the following claims. For example, it is also conceivable that, under suitable geometric conditions, a press fit is created between the contact element and the impact body, piston, or tool to join the two components. If a material-bonded connection is chosen, it is also conceivable to implement this, for example, as an adhesive bond.

[0064] Reference symbol list

[0065] 1 percussion unit

[0066] 2 electric motors

[0067] 3 tools

[0068] 4 eccentric drives

[0069] 5 exciter pistons

[0070] 6 connecting rods

[0071] 7 Guide tube

[0072] 8 impact pistons

[0073] 9 Extension of the guide tube

[0074] 10 striking devices

[0075] 11 Front

[0076] 12 Exclusion

[0077] 13 Contact element

[0078] 14 Joining gap

[0079] 15 lateral surface area

[0080] 16 centering strips

[0081] 17 Front surface

[0082] 18 Front

[0083] 19 Contact element

[0084] 20 Front

[0085] 21 Contact element

[0086] Diameter

[0087] H height

Claims

REQUIREMENTS 1. Impact mechanism for a drill or chisel hammer, comprising an impact unit (1) for converting a rotary drive movement of a drive device (2) into a linear alternating working movement for a tool (3), wherein the impact unit (1) acts upon an adjacent impact body (10) made of a steel material, which acts backwards on the tool (3), characterized in that the steel impact body (10; 10'; 10", 10'") has on its end face (11a) facing at least the tool (3) a contact element (13; 13'; 13", 13', 13"") joined to the steel impact body (10; 10'; 10", 10'") with a preferably convex impact surface, wherein the contact element (13; 13'; 13", 13', 13"") is made of a It consists of a metal matrix composite material.

2. Impact mechanism arrangement according to claim 1, characterized in that the steel impact body (10; 10'; 10“, 10'“) has a three-dimensional joining zone, in particular a recess (12), on an end face (11a) facing the tool (3) during operation, in which the contact element (13; 13'; 13“) is at least partially arranged.

3. Impact mechanism arrangement according to one of claims 1 or 2, characterized in that the contact element (13; 13'; 13“, 13'“, 13““) consisting of a metal matrix composite material comprises a hard metal material, preferably a tungsten carbide-cobalt hard metal, wherein the ratio of tungsten carbide to cobalt is preferably greater than 6, and particularly preferably greater than 10.

4. Striking mechanism arrangement according to one of the preceding claims, characterized in that the contact element (13; 13'; 13“, 13'“, 13““) is rotationally symmetrical, wherein its maximum diameter (D) is dimensioned larger than its height (H), wherein a ratio of the maximum diameter (D) to the height (H) is preferably between 1 and 8, preferably between 1.4 and 3.5 and particularly preferably between 1.4 and 2.

2.

5. Percussion arrangement according to one of the preceding claims, characterized in that the contact element (13; 13'; 13“, 13'“, 13““) has a cylindrical or conical basic shape, wherein the contact element (13; 13'; 13“, 13'“, 13““) in particular has several centering strips (16; 16') or spacers arranged spaced apart from each other in the circumferential direction, particularly along the lateral surface (15) and projecting upwards from the lateral surface (15; 15').

6. Striking mechanism arrangement according to one of the preceding claims, characterized in that the striking body (10; 10'; 10") has several centering strips or spacers arranged in the area of ​​the recess (12), in particular spaced apart from each other in the circumferential direction and projecting in a raised manner.

7. Striking mechanism arrangement according to one of the preceding claims, characterized in that axial spacers are provided on the striking mechanism body (10; 10'; 10") and / or the contact element (13, 13', 13").

8. Striking mechanism according to one of the preceding claims, characterized in that the contact element (13; 13'; 13“, 13'“, 13““) is materially bonded to the recess (12) of the striking body (10; 10'; 10“, 10'“), wherein the materially bonded connection is in particular designed as a soldered connection, wherein the soldered connection is further advantageously provided both in the area of ​​an end face (17) between the contact element (13; 13'; 13“, 13'“, 13““) and the striking body (10; 10'; 10“, 10'“) and in the area of ​​a lateral surface between the contact element (13; 13'; 13“, 13'“, 13““) and the striking body (10; 10'; 10“, 10'“).

9. Striking mechanism according to one of the preceding claims, characterized in that a gap between the contact element (13; 13'; 13“, 13'“, 13““) and the striking body (10; 10'; 10“, 10') is between 0.05 mm and 0.5 mm, in particular between 0.05 mm and 0.2 mm.

10. Impact mechanism arrangement according to one of the preceding claims, characterized in that the centering strips (16, 16') of the contact element (13, 13', 13“, 13'“, 13““) and / or of the impact body (10; 10'; 10“, 10'“) are designed such that in the assembled state there is a sliding fit or press fit between the contact element (13, 13', 13“, 13'“, 13““) and the impact body (10; 10'; 10“, 10'“).

11. Impact mechanism arrangement according to one of the preceding claims, characterized in that the impact body (10; 10'; 10“, 10'“) has on both end faces (11a, 11b) a contact element (13'“, 13'“) which is bonded to the steel impact body (10“') and has a preferably convex impact surface.

12. Impact mechanism arrangement according to one of the preceding claims, characterized in that the impact mechanism unit (1) has an impact piston (8) provided for interaction with the impact body (10; 10'; 10“, 10'“), wherein the impact piston (8) has on an end face (20) facing the impact body (10; 10'; 10“, 10'“) a contact element (21) joined to the steel impact piston (8) in a material-bonded manner with the preferably convex impact surface, wherein the contact element (21) consists of a metal matrix composite material.

13. Percussion mechanism according to one of the preceding claims, characterized in that the percussion unit (1) is designed in the manner of a pneumatic percussion mechanism, comprising an eccentric drive (4) for converting the rotary drive movement into a linear alternating movement by means of coupling to an exciter piston (5) with connecting rod (6), which is guided slidably in a guide tube (7) in order to interact with an opposing percussion piston (8) via an intermediately generated compressible column of air.

14. Electric drill or chisel hammer comprising a percussion mechanism according to any of the preceding claims.

15. Electric hammer drill or chisel, characterized in that a tool (3) is provided which, in the operation of the electric drill or chisel hammer, interacts with the impact body (10; 10'; 10“, 10'“), wherein the tool (3) has on an end face (18) facing the impact body (10; 10'; 10“, 10'“) a contact element (19) joined to a steel tool (3) in a material-bonded manner with a preferably convex impact surface, wherein the contact element (19) consists of a metal matrix composite material.

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