Damping arrangement for rebound impacts in a hand-held electric power tool equipped with a striking mechanism

Abstract

The invention relates to a damping arrangement for rebound impacts in a hand-held electric power tool equipped with a striking mechanism (10), comprising a housing-side axial stop (11; 11a, 11b) and a counter-stop (12; 12a, 12b) formed on a component that is axially movable relative thereto, wherein at least one damping ring (13; 13'; 13") which is composed of an elastomer material is arranged between the axial stop (11; 11a, 11b) and the counter-stop (12; 12a, 12b), the damping ring having a non-rotationally symmetrical shape, wherein the damping ring (13; 13`; 13") has, along the entire circumference, a substantially constant cross-sectional area which runs along a circumferential line that is corrugated at least in the axial direction (X), such that a bilinear spring stiffness can be produced.

Description

[0001] 2023P00254EP

[0002] Hilti Aktiengesellschaft

[0003] Principality of Liechtenstein

[0004] Damping arrangement for recoil impacts in an electric hand tool equipped with a percussion mechanism

[0005] DESCRIPTION

[0006] The present invention relates to a damping arrangement for recoil impacts in an electric hand tool equipped with an impact mechanism, comprising a housing-side axial stop and a counter-stop formed on the side of a component axially movable relative thereto, wherein at least one damping ring made of an elastomer material is arranged between the housing-side axial stop and the counter-stop, which is designed with a non-rotationally symmetric shape.

[0007] The application area of ​​the invention extends primarily to electric hand tools, such as rotary hammers or demolition hammers, which are equipped with an impact mechanism to subject the tool – a hammer drill or chisel – to impact impulses from the rear. For this purpose, the highest possible force impulses are desirable; however, these force impulses must be dampened with respect to the tool housing and also to protect adjacent components that are not part of the force flow.

[0008] Conventional electropneumatic impact mechanisms employ highly dynamically moving masses for impact generation, such as an exciter piston, a striking piston, a so-called "dopper," as well as guide tubes or tool holders. The movement of these masses must remain within predetermined installation space limits, inevitably causing adjacent components to collide. This results in high accelerations, which negatively impact the service life of the components and also the handling of the tool. Therefore, such contact points are usually equipped with damping elements of interest here, which dampen the impact, thereby significantly reducing the force peaks and accelerations. State of the art

[0009] According to generally known prior art, such damping elements take the form of elastomeric damping rings with a rotationally symmetrical shape. This results in a cross-sectional area that remains constant along the entire circumference and can be circular, oval, or rectangular.

[0010] Although such rotationally symmetrical damping rings are easy to manufacture and prove to be very robust under alternating stress due to their homogeneous geometry, on the other hand, such damping rings exhibit a relatively high and linear spring stiffness in their working range.

[0011] For the application described in the invention, however, vibration reduction is desirable in addition to pure impact damping, for which a relatively low spring stiffness would be required. Only for very high forces, such as those resulting from misuse with an exceptionally high contact force or from a recoil impact, is a high spring stiffness desirable in order to absorb such high loads without overloading the elastomer component.

[0012] EP 3 683 021 A1 discloses a generic damping arrangement with a damping ring made of an elastomeric material, which provides both low and high spring stiffness. The elastomeric damping ring consists of a rectangular ring with axially projecting material protrusions on both ends, arranged in a ring-like pattern alternating with cutouts. For integration into the impact mechanism, additional adjacent components, such as a stop ring for the impact mechanism, are provided. The damping ring is quite bulky, requiring a correspondingly large amount of installation space.

[0013] EP 3 335 838 A1 discloses an elastomeric damping ring intended for a damping arrangement of the same type, which is more compact in comparison. For this purpose, the damping ring is formed from several elastic beads arranged in a circumferential sequence. This allows for an initially low spring stiffness. An increase in load leads to a progressive compression of the damping ring, which, due to its shape, offers a correspondingly increased spring stiffness in response to the load. However, the transition areas between adjacent beads form constrictions, which can prove to be weak points as a result of alternating stress.

[0014] It is therefore the object of the present invention to extend and improve a generic damping arrangement with a damping ring made of an elastomeric material in such a way that an elastomeric damping ring with bi-linear spring stiffness is realized in a manufacturing-technically simple manner and in an application-oriented robust design.

[0015] Disclosure of the invention

[0016] The problem is solved starting from a damping arrangement according to the preamble of claim 1 in conjunction with its characterizing features. With regard to an electric hand tool comprising such a damping arrangement, reference is made to claim 9. The respective dependent claims refer back to advantageous embodiments of the reply.

[0017] The invention includes the technical teaching that a non-rotationally symmetric elastomeric damping ring has a substantially constant cross-sectional area AR along its entire circumference, which runs along a circumferential line UL that is corrugated at least in the axial direction X, in order to generate a bi-linear spring stiffness.

[0018] The advantage of the solution according to the invention lies in the fact that, in the sense of a bi-linear spring stiffness, a low spring stiffness is provided at initial loads to reduce vibrations, while at the same time a high spring stiffness is provided at high loads, which can occur, for example, due to misuse such as falls or extremely high contact forces resulting from impacts, in order to prevent damage. For this purpose, the design of the damping ring according to the invention is such that the deformation direction of the elastomer changes depending on the load level. At initially low loads, the damping ring stretches primarily in the circumferential direction, since it tends to compensate for the axially acting load by smoothing the corrugated circumferential line UL.After the damping ring has utilized its axially directed waviness through flattening, further increasing loads cause the damping ring to stretch, primarily in the axial direction X. During this phase of bilinear spring stiffness, the shape of the damping ring no longer has an effect; instead, its inherent spring action becomes significant. This results in both a reduction of vibrations and the compensation of impacts. Thanks to the essentially constant cross-sectional area AR along its entire circumference, the damping ring proves to be extremely robust under alternating stress.

[0019] According to a preferred embodiment of the damping ring, its circumferential line UL, which is corrugated in the axial direction X, is sinusoidally corrugated. This allows for a largely linear spring characteristic to be achieved under axial stress during the initial loading phase. The number of sine cycles along the circumferential circle can preferably be between three and six. While the minimum number of sine cycles results in a particularly low spring stiffness, a higher spring stiffness can be achieved with the maximum number of sine cycles. The number of sine cycles achievable around the circumferential circle naturally also depends on the diameter of the damping ring. Regardless of the diameter, however, the minimum number ensures stable three-point contact on both sides.While increasing the diameter allows for more than six sine cycles along the circumference, in the present application of impact damping, a maximum of six proves to be the limiting factor for achieving effective vibration damping, given the typical diameter ratios of the components used. For effective vibration damping under initially low loads on the damping ring, a height H of the damping ring of 1.5 to 2 times the length L of the cross-section proves to be an optimal range for effective vibration damping in this application, with regard to compensating the resulting vibration amplitudes.

[0020] Preferably, the damping ring has a rectangular cross-section with rounded corner areas, which, with regard to axial contact in the unloaded state, allows for a linear contact surface that contributes to the linearity of the spring characteristic compared to the point contact surface of a circular cross-section. The rounded corner areas can also be designed with a very small radius and are primarily due to the design constraints.

[0021] According to a further improvement of the invention, it is proposed to arrange several identical damping rings in series in order to achieve the lowest possible spring stiffness. In contrast to a one-piece elastomer damper, this multi-part solution achieves minimal stiffness with maximum material utilization, while requiring comparable installation space and using the same Shore hardness of the elastomer material.

[0022] A damping ring suitable for the application according to the invention preferably consists of an elastomer material selected from a group of materials comprising: styrene-butadiene rubber (SBR), nitrile rubber or acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), fluoropolymer rubber (FKM), butadiene rubber (BR), ethylene propylene diene monomer rubber (EPDM), hydrogenated acrylonitrile butadiene rubber (HNBR) or the like.

[0023] The damping ring according to the invention described above can be used in conjunction with electropneumatic impact mechanisms, in which the housing-side axial stop is preferably arranged both on the tool housing of the electric hand tool opposite the impact mechanism and within a damper housing of the impact mechanism opposite the damper. At both locations of the electric hand tool, it is necessary to dampen force peaks and accelerations of moving masses, which occur on the one hand from the impact mechanism itself opposite the tool housing and on the other hand from the damper integrated in the impact mechanism opposite the housing part surrounding it, which represents a continuation of the guide tube.

[0024] Detailed description based on drawing

[0025] Further measures improving the invention are described in more detail below, together with a description of a preferred embodiment, with reference to the figures. The figures show:

[0026] Fig. 1 shows a schematic longitudinal view of a percussion mechanism integrated into an electric hand tool with a damping arrangement for recoil impacts,

[0027] Figs. 2a to 2c show different perspective views of a damping ring designed according to the invention with bi-linear spring stiffness.

[0028] Figures 3a to 3b illustrate the behavior of the damping ring under initially low load.

[0029] Figures 4a to 4b illustrate the behavior of the damping ring under high load.

[0030] Figs. 5a to 5d show several embodiments of damping rings with a different number of sine periods along the circumferential circle, and

[0031] Fig. 6 shows a multiple arrangement of the damping ring according to the invention in series connection.

[0032] According to Fig. 1, an electric hand tool in the form of a chisel hammer (not shown in detail here) comprises an electric drive motor 2 integrated within a tool housing 1. The rotary drive movement of the motor is converted via an eccentric gear 3 with a connecting rod 4 coupled to it into a linear alternating movement of an exciter piston 5. The exciter piston 5, as part of a piston-cylinder unit, is guided within a guide tube 6 and interacts in a known manner with a striking piston 7, which is also guided opposite it in the guide tube 6. The striking piston 7, in turn, acts on a striker 8, which ultimately transmits the resulting impact impulse to a tool 9. The striker 8 is guided in its own guide tube section 6a.

[0033] The impact mechanism 10 of the power tool, consisting essentially of the components connecting rod 4, exciter piston 5, guide tube 6, impact piston 7 and stop 8, abuts an axial stop 11 formed on the housing 1 of the power tool. The guide tube 6 of the impact mechanism 10 is a component axially movable relative to the axial stop 11, with a corresponding counter-stop 12. In the area of ​​the stop 8, the guide tube section 6a forms an axial stop 11a and 11b on both sides of the housing, with corresponding shoulders on the stop 8 forming the counter-stops 12a and 12b, respectively.

[0034] A damping ring 13, 13', 13" made of an elastomer material is arranged between the respective axial stop 11, 11a and 11b and the respective corresponding counter-stop 12, 12a and 12b.

[0035] Figures 2a to 2c show different perspective views of the same exemplary damping ring 13 to illustrate its geometry. The damping ring 13 has four sine periods of a wavy circumferential line UL along its circumference. It is evident that the damping ring 13 has a cross-sectional area AR that remains essentially constant along its entire circumference. The height H of the damping ring is approximately 1.5 times the length L of the cross-section.

[0036] According to the load situation illustrated in Figs. 3a and 3b, a progressive flattening of the exemplary sealing ring 13 occurs as a result of an initially low load according to Fig. 3a. In this phase, the damping ring 13 expands primarily in the circumferential direction. According to Fig. 3b, this leads to a low spring stiffness in the corresponding load situation A, as illustrated by the flat section of the spring characteristic curve.

[0037] As shown in Fig. 4a, after the exemplary damping ring 13 has completely flattened with a further increasing load, a further progressive load leads to elongation primarily in the axial direction. This elongation, which is no longer due to shape but solely due to material properties, is associated in this load situation B with a higher spring stiffness, which can be seen in the steep section of the spring characteristic curve.

[0038] Overall, the damping ring designed according to the invention is associated with a bilinear spring stiffness.

[0039] According to Figures 5a to 5d, the initial spring stiffness of the exemplary damping ring 13 can also be adjusted by the number of sine periods of the corrugated circumferential line UL. Figure 5a shows three sine periods, Figure 5b shows four sine periods, Figure 5c shows five sine periods, and Figure 5d shows six sine periods.

[0040] To further increase the spring stiffness, especially in the area of ​​material-related spring action, a multiple arrangement of damping rings 13a to 13c is realized according to Fig. 6, which are connected in series, wherein the same wave shape of the damping rings 13a to 13c allows a positive interlocking.

[0041] The invention is not limited to the 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 possible to design the damping ring with a different cross-sectional shape, such as a circular cross-section. [List of reference numerals]

[0042] 1 tool housing

[0043] 2 Drive motor

[0044] 3 eccentric gears

[0045] 4 connecting rods

[0046] 5 exciter pistons

[0047] 6 guide tube

[0048] 7 impact pistons

[0049] 8 Döpper

[0050] 9 tools

[0051] 10 percussion instruments

[0052] 11 housing-side axial stop

[0053] 12 Counterattack

[0054] 13 Damping ring

[0055] X Axial direction

[0056] AR cross-sectional area

[0057] UL perimeter line

[0058] H height

[0059] Length L

Claims

REQUIREMENTS 1. Damping arrangement for recoil impacts in an electric hand tool equipped with an impact mechanism (10), comprising a housing-side axial stop (11; 11a, 11b) and a counter-stop (12; 12a, 12b) formed on the side of a component axially movable relative thereto, wherein at least one damping ring (13; 13'; 13") made of an elastomer material is arranged between the axial stop (11; 11a, 11b) and the counter-stop (12; 12a, 12b), which has a non-rotationally symmetric shape, characterized in that the damping ring (13; 13'; 13") has a substantially constant cross-sectional area (AR) along its entire circumference, which runs along a circumferential line (UL) that is corrugated at least in the axial direction (X), so that a bi-linear spring stiffness can be generated.

2. Damping arrangement according to claim 1, characterized in that the corrugated circumferential line (UL) is sinusoidally corrugated.

3. Damping arrangement according to claim 2, characterized in that the number of sine periods along the circumferential circle is between 3 and 6.

4. Damping arrangement according to one of the preceding claims, characterized in that the height (H) of the damping ring (13; 13'; 13") is 1.5 to 2 times the length (L) of the cross-section.

5. Damping arrangement according to one of the preceding claims, characterized in that the damping ring (13; 13'; 13") has a rectangular envelope cross-section with rounded corner areas.

6. Damping arrangement according to one of the preceding claims, characterized in that several similar damping rings (13a, 13b, 13c) are arranged in series.

7. Damping arrangement according to one of the preceding claims, characterized in that the damping ring (13; 13'; 13") changes its direction of deformation depending on the load level due to the elastomer material in conjunction with the geometry such that an initial load causes an elongation in a predominantly circumferential direction, followed by an elongation in a predominantly axial direction when the load is increased.

8. Damping arrangement according to one of the preceding claims, characterized in that the damping ring (13; 13'; 13") consists of an elastomer material selected from a group of materials comprising: styrene-butadiene rubber (SBR), nitrile rubber or acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), fluoropolymer rubber (FKM), butadiene rubber (BR), ethylene propylene diene monomer rubber (EPDM), hydrogenated acrylonitrile butadiene rubber (HNBR).

9. Electric hand tool, in particular chisel hammer, with an electropneumatic impact mechanism (10) which is equipped with a damping arrangement for rebound impacts according to one of the preceding claims.

10. Electric hand tool according to claim 9, characterized in that the housing-side axial stop (11; 11a, 11b) is arranged in a tool housing (1) of the electric hand tool opposite the impact mechanism (10) and / or in a guide tube part (6a) of the impact mechanism (10) opposite a hammer (8).

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