Pneumatic striking mechanism for a drill hammer or chisel hammer

Abstract

Pneumatic impact mechanism for a drill or chisel hammer, comprising a hammer (6) actuated by a piston (5) for the rear actuation of a tool (7), wherein the hammer (6) is arranged longitudinally in an associated guide tube (4), wherein end-side damping means are provided at least for damping the idle impact of the hammer (6), the damping means comprising a first contact element (8) and an adjacent second contact element (9), wherein the contact elements (8, 9) are designed for force transmission in the longitudinal direction between the hammer (6) and the guide tube (4) and the contact elements (8, 9) have different stiffness and damping, wherein both contact elements (8, 9) respond successively during an idle impact due to a coaxial arrangement.

Description

[0001] The present invention relates to a pneumatic impact mechanism for a drill or chisel hammer, comprising a hammer actuated by a piston for the rearward impact of a tool, wherein the hammer is arranged longitudinally guided on an associated guide tube which is equipped with end-side damping means for at least the idle impact damping of the hammer.

[0002] The invention primarily applies to handheld rotary hammers or demolition hammers equipped with an electric motor drive. Such power tools generate a linear, alternating working motion—a back-and-forth movement—via a mostly pneumatic impact mechanism to actuate the tool. In the case of a rotary hammer, this tool is designed as a hammer drill, and in the case of a demolition hammer, as a chisel for working preferably mineral materials such as stone, concrete, and the like. A power tool that drives a tool by impact typically exhibits complex vibration behavior due to interactions with the workpiece, the operator's hand-arm system, and the internal mass and stiffness distribution. This vibration behavior must be largely suppressed.

[0003] In the context of the power tools of interest here, the impact mechanism is particularly susceptible to so-called dry hits and impacts. Dry hits occur when tools are accelerated by impact impulses from the impact mechanism, but this impact energy cannot be transferred to the workpiece because the tool is not in contact with it. In this case, the impact impulse cannot be transmitted from the impact piston via the hammer and the tool to the workpiece; instead, the impact impulse is at least temporarily directed through the tool and / or the hammer into internal stops. Thus, in this operating state, the impact impulse must be absorbed by the power tool itself. Impacts occur when the tool is in contact with too much force and / or a workpiece that is too hard, so that the impact impulses from the impact mechanism essentially rebound onto the machine.The present invention is dedicated in particular to damping the idle sound. State of the art

[0004] WO 2021 / 094214 A1 discloses a pneumatic impact mechanism with a tool holder. The impact mechanism has an axially displaceable hammer that acts on the tool. The hammer is mounted to the tool holder via two bearings. The impact mechanism also has a zero-impact damping element, which is positioned between the hammer and the tool holder to dampen zero-impact movements. An additional zero-impact damping element is also provided, which is arranged between the tool holder and the guide housing. Both damping elements act in parallel and thus simultaneously.

[0005] German patent DE 10 2011 081 617 A1 discloses a pneumatic impact mechanism for an electric power tool, driven by an electric motor. The rotary drive energy of the electric motor is converted by means of a crank mechanism into an alternating translational movement of an exciter piston of the pneumatic impact mechanism. The exciter piston is arranged in a guide tube to form a piston-cylinder unit. Opposite the exciter piston, separated by a column of air, is an impact piston, which is also arranged in the guide tube. Further along the impact chain, the impact piston acts on a striker guided in an extension of the guide tube, which in turn strikes a tool, designed here as a drill bit, from the rear.

[0006] Elastomeric damping elements are used for end-position damping of the impactor, absorbing a portion of the kinetic energy at the impactor's end positions. The elastomeric damping element located on the tool side provides damping during idle impact, while the elastomeric damping element located on the piston side provides impact damping. All damping elements are manufactured as single units.

[0007] In particular, dry hits cause high stresses on the machine components, which depend on the moving mass and the approach speed of the impactor. The damping solutions described above are intended to reduce the maximum forces acting upon them. The usual elastomeric damping elements consist of HNBR (hydrogenated acrylonitrile butadeine rubber) or FKM (fluorocarbon rubber). Due to the temperature dependence of the mechanical properties of such damping materials, an undesirable temperature-dependent functionality of the impact mechanism can also occur.

[0008] The object of the present invention is to further improve a generic pneumatic percussion mechanism with damping means for at least the idle impact damping of a hammer in such a way that a temperature-independent functionality of the percussion mechanism and increased robustness over the service life are achieved using simple technical means. Disclosure of the invention

[0009] The problem is solved starting from a pneumatic impact mechanism according to the preamble of claim 1 in conjunction with its characterizing features. Dependent claim 15 specifies a hand-held power tool comprising the pneumatic impact mechanism according to the invention; the dependent claims relating back to it are directed to preferred embodiments of the invention.

[0010] The invention includes the technical teaching that the damping means comprise a first contact element and an adjacent second contact element, wherein the contact elements are designed for force transmission in the longitudinal direction between the dopper and the guide tube and the contact elements have different stiffness and damping, wherein both contact elements respond one after the other as a result of a coaxial arrangement during a dry strike.

[0011] In other words, the impact damping according to the invention is designed such that the impactor transfers its kinetic energy to two different components, which are characterized by different stiffness and damping properties and optionally also by different lengths, and thus are fundamentally made of different materials. Furthermore, the impact on the two contact elements, which act as contact partners, occurs sequentially, so that the kinetic energy to be transferred by the impactor is distributed depending on the specific design.

[0012] The solution according to the invention offers the advantage that the specific properties of the different contact elements are used synergistically. The maximum elongation of the less rigid contact element can also be adjusted and controlled. Lower elongation also results in less heat generation due to the material damping. The high material damping of the second contact element leads to a slow springback and relaxation of the contact element after it has been loaded. The first contact element, on the other hand, transfers some of its kinetic energy directly into the impactor during contact, causing it to rebound. This means that the second contact element preferably transfers practically no energy back to the impactor, because it is already rebounding before the springback occurs.Furthermore, the solution according to the invention is characterized by lower noise levels compared to the prior art.

[0013] According to a preferred embodiment of the invention, the first contact element has a higher stiffness and lower damping than the second contact element. The impact of the impact preferably strikes the second, softer contact element first, before the harder first contact element comes into effect. The damping effect of the combined damping means thus decreases with increasing damping distance, with the impact of the impact on the stiffer first contact element generating a strong jump until the impact stops.

[0014] According to a preferred embodiment, the first contact element has at least ten times the stiffness and at least ten times the damping of the second contact element. Under these conditions, maximum damping is achieved while maintaining high robustness of the damping elements.

[0015] For example, the first contact element can be a steel component, for example 16MnCr5, and the second contact element can be an elastomer component, preferably FKM.

[0016] According to a further improvement of the invention, it is proposed that, to ensure that the second contact element impacts the first contact element sequentially, an axial gap is provided between the first contact element and the first contact element in the direction of impact, both with the dopper and with the guide tube. This axial gap preferably corresponds to 0.15 to 0.5 times the axial length of the second contact element. For example, the dopper undergoes a displacement of a few millimeters after coming into contact with the second contact element, before coming into contact with the first contact element. The claimed ratio corresponds to the maximum impact strain.

[0017] According to a further improvement of the invention, it is proposed that the first contact element has a mean contact radius that is smaller than the mean contact radius of the second contact element. This easily ensures that a desired high damping effect is generated by a correspondingly large volume of material. Alternatively or additionally, both contact elements can be designed as hollow cylindrical components, with the first contact element having a smaller diameter than the second. Since the first contact element can generate the desired high damping effect by means of a correspondingly large volume of material, a correspondingly larger component design is advantageous.

[0018] According to an advantageous embodiment of a pneumatic impact mechanism according to the invention, the first contact element is integrally formed with the guide tube and serves as a stop for the impactor. This reduces the number of components required to implement the desired functionality in a structurally simple manner.

[0019] Alternatively, the second contact element can be a separate component mounted on the guide tube. This can be achieved, for example, via an undercut, a retaining ring, or similar means. It is also possible for the second contact element to be mounted on the dopper. This can be done, for example, via a clip connection, an undercut, vulcanization, or similar means. Another possibility is to mount the second contact element so that it can move freely in the longitudinal direction between the dopper and the guide tube.

[0020] According to another improvement of the invention, it is proposed that the first contact element has at least one circumferential groove on its inner surface for receiving an associated sealing ring for dynamic sealing against a rod section of the dopper. Preferably, two axially spaced circumferential grooves are provided to prevent the ingress of damaging moisture or dirt particles from the environment into the guide tube. The first contact element is pressed into a corresponding receiving diameter of the guide tube and comes to rest against an associated stop shoulder of the guide tube. Similarly, the second contact element is also inserted into the guide tube and comes to rest against an associated stop shoulder. The guide tube can also be integrally designed to receive a tool.Alternatively, the tool holder can be implemented using a component different from the guide tube.

[0021] 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: Fig. 1 a schematic side view of a pneumatic impact mechanism of a hand-held power tool, Fig. 2 a detail from the longitudinal section according to Fig. 1 In the area of ​​damping means for idle vibration damping, Fig. 3 shows a schematic vibration damping system to illustrate the mode of operation of the damping means according to the invention; and Figs. 4-6 show highly simplified side views of sections of a pneumatic guide tube in various embodiments.

[0022] According to Fig. 1A pneumatic impact mechanism of a chisel hammer (not shown in detail) essentially consists of an eccentric drive 2, driven by an electric motor 1, for converting the rotary drive motion of the electric motor 1 into an alternating translational motion for an excitation piston 3, which is guided longitudinally in a guide tube 4. In this particular design, the guide tube 4 also serves as a tool holder. In an alternative design, this functionality can be achieved using different components.

[0023] A striking piston 5, also guided in the guide tube 4, acts in the usual manner on an adjacent striker 6, which in turn strikes a chisel-shaped tool 7 from behind. Damping elements are housed in the guide tube 4 at the end positions of the striker 6 to dampen the impact and recoil of the impact.

[0024] The detailed view of Fig. 2Figure 1 shows the tool-side damping elements for idle impact damping. These comprise a first contact element or damping element 8 and an adjacent second contact element or damping element 9, which bear against a corresponding stop shoulder 10 or 11 of the guide tube 4, respectively. The first damping element 8 has two axially spaced circumferential grooves 12a and 12b on its inner surface, which serve to receive a corresponding sealing ring. These sealing rings provide a dynamic seal against a rod section 13 of the dopper. A piston section 14 with a larger diameter is positioned upstream of the end rod section 13 of the dopper 6. A transition section 15 is located between the rod section 13 and the piston section 14. The diameter of this transition section is larger than that of the rod section 13 but much smaller than that of the piston section 14.

[0025] According to the invention, the first damping element 8 has a higher stiffness and lower damping than the second damping element, with both damping elements 8 and 9 responding sequentially during a dry strike due to their coaxial arrangement. This means that the impact 6 first strikes the second damping element 9 and then the first damping element 8. The first damping element is designed as an unhardened steel component and consists here of 16 MnCr5, whereas the second damping element is an elastomer component made of FKM.

[0026] To ensure that the second damping element 9, which is acted upon by the Döpper 6 in the end position, impacts the first damping element 8 sequentially, the two damping elements 8 and 9 are arranged while maintaining an axial gap 16.

[0027] The Fig. 3Figure 1 illustrates the vibration and damping system of the damping element arrangement described above. The damping elements are arranged between a stationary contact surface A on the left side and extend towards the impulse mass M on the top side. This mass first encounters the second damping element – ​​here C2 in the model – and after overcoming the axial gap dX, also the first damping element C1. Both contact elements, or damping elements, or spring-damper elements C1 and C2, have different vibration damping characteristics with respective damping paths X1 and X2. The first damping element C1 is characterized by a material-related elasticity E1 and damping D1, whereas the second damping element C2 has a different elasticity E2 and damping D2.

[0028] In Figs. 4 to 6Further embodiments of the pneumatic percussion mechanism according to the invention are shown, with the differences to the embodiment according to the invention being discussed below. Fig. 2 The above statements are otherwise referred to.

[0029] In the Figs. 4 to 6 In the illustrated embodiments, the first contact element 8 is integrally formed with or by the guide tube 4. Alternatively, the first contact element 8 can also be designed as a separate contact element 8, as is the case, for example, in Fig. 2 is shown.

[0030] The statements according to the Figures 4 to 6 differ essentially in the arrangement of the second contact element 9.

[0031] When executed according to Fig. 4The second contact element 9 is mounted on the guide tube 4 and is located in a recess 20 of the guide tube 4. The second contact element 9 can be held on the guide tube 4 by means of securing devices not shown in detail. Alternatively, the second contact element 9 can also be vulcanized onto the guide tube 4.

[0032] The axial gap 16 is defined here by a distance in the direction of impact between a first contact surface 17 of the first contact element 8 and a second contact surface 18 of the second contact element 9.

[0033] Furthermore, in Fig. 4 The mean radii R1 and R2 are shown, which are defined by the effective area of ​​the respective contact element 8 or 9 for interaction with the dopper 6. It is evident that the mean radius R1 of the first contact element 8 is smaller than the mean radius R2 of the second contact element 9.

[0034] The execution according to Fig. 5 differs from the design according to Fig. 4 by the fact that the second contact element 9 is mounted on the dowel 6. For example, it may be provided that the second contact element 9 is vulcanized onto the dowel 6 or held on the dowel 6 by a corresponding locking device, which is not shown in detail.

[0035] The execution according to Fig. 6 differs from the statements according to Fig. 4 and Fig. 5by the fact that the second contact element 9 is arranged so as to be freely movable in the direction of impact between the dopper 6 and the guide tube 4. The axial gap 16 results from the difference between the distance of the first contact element 8 and the contact surface with the dopper 6, and in the illustrated embodiment, the distance between the contact surface of the second contact element 9 with the guide tube 4 and the contact surface of the second contact element 9 with the dopper 6, minus the length of the second contact element 9 in the direction of impact.

[0036] The invention is not limited to the preferred embodiment described above. Rather, variations thereof are also possible, which are included in the scope of protection of the following claims. For example, it is also conceivable to manufacture the two damping elements from other materials, provided that a correspondingly different stiffness and damping are achieved to adapt to the dopper mass and the impact impulse. Reference symbol list

[0037] 1 Electric motor 2 Crank drive 3 Exciter piston 4 Guide tube 5 Impact piston 6 Dopper 7 Tool 8 First contact element 9 Second contact element 10 First stop shoulder 11 Second stop shoulder 12 Circumferential groove 13 Rod section 14 Piston section 15 Transition section 16 Axial gap 17 First contact surface 18 Second contact surface 20 Recess C1 First contact element (schematic) C2 Second contact element (schematic) dX Axial gap Fixed contact surface Impulse mass E1 Elasticity of first contact element D1 Damping of first contact element X1 Effective length of first contact element R1 Mean contact radius of the first contact element E2 Elasticity of second contact element D2 Damping of second contact element X2 Effective length of second contact element R2 Mean contact radius of the second contact element

Claims

1. Pneumatic impact mechanism for a drill or chisel hammer, comprising a hammer (6) acted upon by a piston (5) for the rear actuation of a tool (7), wherein the hammer (6) is arranged longitudinally guided in an associated guide tube (4), wherein end-side damping means are provided at least for damping the idle impact of the hammer (6), characterized by the fact that The damping means comprise a first contact element (8) and an adjacent second contact element (9), wherein the contact elements (8, 9) are designed for force transmission in the longitudinal direction between the dopper (6) and the guide tube (4) and the contact elements (8, 9) have different stiffness and damping, wherein both contact elements (8, 9) respond sequentially during a dry strike as a result of a coaxial arrangement.

2. Pneumatic percussion mechanism according to claim 1, characterized by the fact thatthe first contact element (8) has a higher stiffness and lower damping than the second contact element (9), wherein the dopper (6) in the empty strike in the direction of impact first hits the second contact element (9) and then the first contact element (8).

3. Pneumatic percussion mechanism according to claim 2, characterized by the fact that the first contact element (8) has at least ten times higher stiffness and at least ten times lower damping than the second contact element (9).

4. Pneumatic percussion mechanism according to one of claims 2 or 3, characterized by the fact that the first contact element (8) is designed as a steel component and the second contact element (9) as an elastomer component.

5. Pneumatic percussion mechanism according to one of the preceding claims, characterized by the fact thatIn the state of contact between the second contact element (9) and both the dopper (6) and the guide tube (4) an axial gap (16) exists between the first contact element (8) and the dopper (6) in the direction of impact.

6. Pneumatic percussion mechanism according to claim 5, characterized by the fact that the axial gap (16) corresponds to 0.15 to 0.5 times the axial length of the second contact element (9).

7. Pneumatic percussion mechanism according to one of the preceding claims, characterized by the fact that the first contact element (8) has a mean contact radius (R1) that is smaller than the mean contact radius (R2) of the second contact element (9).

8. Pneumatic percussion mechanism according to one of the preceding claims, characterized by the fact that Both contact elements (8, 9) are hollow cylindrical in their envelope geometry, with the first contact element (8) having a smaller diameter than the second contact element (9).

9. Pneumatic percussion mechanism according to one of the preceding claims, characterized by the fact that the first contact element (8) is integral with the guide tube (4) and forms a stop for the dopper (6).

10. Pneumatic percussion mechanism according to one of the preceding claims, characterized by the fact that the second contact element (9) is mounted on the guide tube (4).

11. Pneumatic percussion mechanism according to one of claims 1 to 9, characterized by the fact that the second contact element (9) is mounted on the dowel (6).

12. Pneumatic percussion mechanism according to one of claims 1 to 9, characterized by the fact that the second contact element (9) is mounted to be freely movable in the longitudinal direction between the dopper (6) and the guide tube (4).

13. Pneumatic percussion mechanism according to one of the preceding claims, characterized by the fact thatthe first contact element (8) has at least one circumferential groove (12a, 12b) on the inner surface for receiving an associated sealing ring for dynamic sealing against a rod section (13) of the dopper (6).

14. Pneumatic percussion mechanism according to one of the preceding claims, characterized by the fact that the first damping element (8) and the second damping element (9) come into contact with a respective assigned stop shoulder (10, 11) of the guide tube (4).

15. Hand-held power tool, in particular a drill and chisel hammer, comprising a pneumatic impact mechanism according to one of the preceding claims.

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