Power tool with an impact mechanism

Abstract

A power tool with an impact mechanism in particular, an impact wrench or a hammer drill, comprising an outer housing and an inner housing at least partly surrounded by the outer housing; an motor installed in the inner housing, and an impact mechanism connected to the motor and fixedly mounted to the inner housing, to define an integrated inner sub-assembly comprising the motor and the impact mechanism; the inner housing and outer housing are elastically connected to each other in axial direction by at least two elastic elements pre-tensioned against each other, the inner housing floating received in the outer housing in axial direction, thereby reducing the vibration suffered by the user from the impact mechanism and motor of the power tool.

Description

TECHNICAL FIELD

[0001] The present invention relates to a power tool with an impact mechanism comprising a hammer mass oscillating in axial direction, in particular, an impact wrench or a hammer drill.BACKGROUND ART

[0002] During operation, power tools with impact mechanisms (such as impact wrenches or rotary-hammer for drilling) will generate vibration, which affects components and users and might even cause premature failure of the power tool or damage to the user's health. Daily exposure limits for hand-arm vibration (HAV value) and limits for duration of use are formulated according to international standards for electrical. If these limits are reached, further work is prohibited. People are becoming more and more aware of the negative effects of vibration on ergonomics and health, and it has thus become a competitive differentiation factor in the market of electric tools.

[0003] Impact mechanism comprising a hammer mass oscillating in axial direction in impact wrenches or hammer drills, as well as transmission gears and motor movement, generate excitations in form of vibrations during operation. Due to the axial movement of the hammer, the excitations occur for the most part in the axis of rotation of the tangential impact mechanism. These excitations are transferred to the housing, in which the motor and impact mechanism are mounted. These excitations are transmitted to the user in form of vibrations via the handle integrated in the housing or other housing surfaces touched by the user. These vibrations are measured and calculated according to an international standard for electrical devices and claimed by a hand-arm vibration value (HAV). This standard includes a certain filtering setting the focus of HAV on rather low frequencies around 14Hz.

[0004] US6318479 B disclosed a vibration isolated power tool wherein an impact mechanism and a motor assembly are arranged into a cartridge assembly. An elastomeric member resiliently connects the cartridge assembly with a housing. The cartridge assembly is free to move axially and rotationally within the housing. The elastomeric member absorbs axial vibration and torsional vibration, reducing the vibration transmitted to an operator. However, US6318479B disclosed a "one-sided" suspension of the cartridge assembly so that it does not really work for reducing axial vibration, because a certain contact force has to be applied to push the cartridge assembly into its working point from where it can swing in both directions.SUMMARY OF THE INVENTION

[0005] An objective of the present invention is to provide a power tool comprising an impact mechanism with a floating suspension of an inner housing relative to an outer housing, thereby reducing the vibrations transmitted to the user generated by the impact mechanism and motor of the power tool.

[0006] According to an embodiment of the present invention, a power tool with an impact mechanism comprises an outer housing and an inner housing at least partly surrounded by the outer housing; a motor accommodated in the inner housing, and the impact mechanism received in a gearbox that is connected to the motor and fixedly coupled to the inner housing; the outer housing coupling a handle at its lower side. The inner housing and outer housing are elastically connected to each other in axial direction by at least two elastic elements pre-tensioned against each other, whereby the inner housing is floatingly received in the outer housing in axial direction. Hence, no axial application force needed to bring sub-chassis into an effective working point. The vibration transmitted from the power tool with an impact mechanism to the user's hands and arms during application is reduced effectively.

[0007] The inner housing is substantially cylindrical, having a frontward open first end and a rearward closed second end. The outer housing has a frontward open front end and a rearward open or at least partially closed rear end. A radial gap is created between the inner housing and the outer housing and at least one axial support is provided in inner housing or outer housing extending into the radial gap. The at least two elastic elements are received in the radial gap and each of elastic elements is pre-tensioned supported by the at least one axial support and the outer housing or inner housing in axial direction. Therefore, the axial support is connected to the respective other housing by the elastic elements, so that the inner housing is axially floatingly connected to the outer housing. Vibration during the application would be absorbed by the floating of the inner sub-assembly.

[0008] According to one embodiment of the present invention, the axial support is provided in the outer surface of the inner housing between the first end and the second end. A first radial protrusion close to the front end extends radially inward from the outer housing. A second radial protrusion close to the rear end extends radially inward from the outer housing. The elastic elements comprise at least one first elastic element and at least one second elastic element, the first elastic element being supported between the first radial protrusion and the axial support while the second elastic element being supported between the axial support and the second radial protrusion of the outer housing. The elastic elements are pretensioned, pressing against the axial support. During application, the first elastic element is pushing the inner housing to the rear side and the second elastic element is pushing the inner housing to the forward side. With no application force, the forces of the first elastic element and second elastic elements are in balance and keep the inner housing in a "floating" middle position.

[0009] According to the other embodiment of the present invention, the axial support is provided in inner surface of the outer housing between the front end and the rear end. The inner housing comprises a first end stop and a second end stop extending radially outward from the first end and the second end respectively. The elastic elements comprise at least one first elastic element and at least one second elastic element, the first elastic element being supported between the first end stop and the axial support while the second elastic element being supported between the axial support and the second end stop. Similarly, the forces of the first elastic element and second elastic elements are in balance and keep the inner sub assembly in a "floating" middle position within the outer housing, therefore no additional contact forces are needed to bring the inner sub assembly into working point.

[0010] The axial support can be a portion projecting from the inner housing or the outer housing. Alternatively, the axial support can be a separate part that fixed to the inner housing or the outer housing. The axial support could be designed as various types and structures, depending on the structure and / or assembly of the inner housing and outer housing.

[0011] According to another embodiment of the present invention, the axial support extends circumferentially in the radial gap. There is only one axial support which is a ring-like shape extending around the outer surface of the inner housing or the inner surface of the outer housing.

[0012] Alternatively, more than one axial support is distributed around the inner housing in the circumferential direction. In this embodiment, the axial support is not a continuous ring, but there are several separated axial supports distributed around the inner housing in circumferential direction. This would help ease of assembly of inner housing and outer housing.

[0013] According to an exemplary embodiment of the present invention, the elastic element is a coil spring. A coil spring has a quite linear characteristic and low damping. That makes it easy for simulating / calculating its decoupling behaviour.

[0014] According to an embodiment of the present invention, at least one anti-rotation structure is provided between the inner housing and the outer housing generating a form fit between outer housing and inner housing to prevent a rotational displacement of the inner housing towards the outer housing. Due to the radial gap between the inner housing and outer housing, there might be a rotational displacement of the inner housing towards the outer housing. In order to prevent such a rotation of the inner towards the outer housing, an anti-rotation structure generating a form fit is provided.

[0015] The anti-rotating structure comprises at least one rotational support surface formed on the inner surface of the outer housing and / or outer surface of the inner housing; The rotational support surface is formed in the outer surface of inner housing and / or the inner surface of the outer housing. Preferably, the rotational support surface is formed in the outer surface of inner housing and the inner surface of the outer housing respectively, and they are parallel surfaces which can get in contact to stop a rotational movement between inner and outer housing in either clockwise or anti clockwise direction.

[0016] The rotational support surface can be made of a sliding-optimized material different to the housing material (e.g. peace of hardened sheet metal) to reduce friction between the inner and outer housing and, if necessary, to adjust the gap size. To realize this the anti-rotating structure of one embodiment of the present invention comprises at least one insert placed in a cavity formed in the inner housing and / or the outer housing. The insert blocks the relative rotation between the inner housing and the outer housing. Preferably, these cavities are deeper than two times the radial gap so that in assembled condition these inserts cannot get lost / fall out.

[0017] According to a preferred embodiment of the present invention, these inserts are elastic and thus decoupling / damping vibrations in rotational direction.

[0018] According to another embodiment of the present invention, the anti-rotating structure comprises at least one groove extending in axial direction formed in the outer housing and one projection formed in the inner housing, the projection received in the groove. Therefore, the inner housing can float in the axial direction within the outer housing, but it cannot rotate in the circumferential direction within the outer housing.

[0019] According to another yet embodiment of the present invention, the anti-rotating structure is formed on at least one of the radial protrusions and / or end stops, thereby simplifying the structures of the power tool.BRIEF DESCRIPTION OF THE DRAWINGS

[0020] A better understanding of the embodiments mentioned can be gained from the following detailed description with reference to the drawings. It is emphasized that the various components are not necessarily drawn to scale. In fact, dimensions may be increased or decreased at will for the purpose of clear description. In the drawings, identical reference numerals denote identical elements. Fig. 1 is a partial front view of a power tool with an impact mechanism in an embodiment of the present invention. Fig. 2 is a partial explosion view of a power tool with an impact mechanism shown in Fig.1. Fig.3 is a partial section view of the power tool shown in Fig. 1. Fig. 4a is a simplified sketch drawing of the power tool in rearward deflection according to one embodiment of the present invention. Fig. 4b is a simplified sketch drawing of the power tool in frontward deflection according to one embodiment of the present invention. Fig. 5a is a simplified sketch drawing of the power tool in rearward deflection according to the other embodiment of the present invention. Fig. 5b is a simplified sketch drawing of the power tool in frontward deflection according to the other embodiment of the present invention. Fig. 6 is a radial sectional view of A-A line of a power tool shown in Fig. 1 Fig. 7 is a partial enlarged drawing of details B of a power tool shown in Fig. 6 in one embodiment of the present invention. Fig. 8 is a partial enlarged drawing of details B of a power tool shown in Fig. 6 in the other embodiment of the present invention. Fig. 9 is a partial enlarged drawing of details B of a power tool shown in Fig. 6 in another embodiment of the present invention. Fig. 10 is a partial enlarged drawing of details B of a power tool shown in Fig. 6 in another yet embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] The power tool of the present invention is described below with reference to Figs. 1-10.

[0022] The following description is merely exemplary, and does not limit the disclosed content of the present application or the applications or uses of the present invention. In the description of the present invention, it should be understood that orientations or positional relationships indicated by terms such as "centre", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "axial", "radial", and "circumferential" are based on orientations or positional relationships shown in the drawings, which are only for facilitating the description of the present invention and simplifying the description, rather than indicating or implying that devices or elements referred to must have a specific orientation or be constructed and operated in the specific orientation, and therefore cannot be construed as limiting the present invention.

[0023] Figs. 1 - 3 show an exemplary power tool with an impact mechanism, e.g. an impact wrench 1. The impact wrench 1 comprises an outer housing 2 and an inner housing 3 at least partly surrounded by the outer housing 2. A motor 4 is accommodated in the inner housing 3. A gearbox 10 with an impact mechanism 5 connected to the motor 4 and fixedly mounted to the inner housing 3. The impact mechanism 5 comprises a hammer mass that may oscillate in axial direction. In front of the hammer there is an output shaft 6, wherein the impact mechanism 5 can apply an impact to the output shaft 6 lying on a work axis 7 in a direction of rotation about the work axis 7 under the driving action of the motor 4. A handle 29 extends from below the outer housing 2, and a user can grip and guide the impact wrench 1 by means of the handle 29 during operation. A trigger is provided on the handle 29, and the motor 4 can be turned on or off by means of the trigger. A battery or an AC power supply may be connected to a lower side of the handle 29, and an electronic component (not shown) connecting the power supply and the motor is accommodated in the handle 29. Preferably, the lower side of the handle 29 has an expanded part to serve as an interface for battery connection; the electronic component is deployed close to the battery connection interface, to simplify the wiring layout and improve heat dissipation. Alternatively, the electronic components could be arranged behind the motor. In this case, the sucked in cold air would be first guided to flow through the motor and secondly over the electronics.

[0024] The outer housing 2 may be injection-moulded from a suitable composite material. In some embodiments, the outer housing 2 may comprise two substantially symmetric half-shells; these have an upper part 20 extending substantially in the axial direction of the work axis 7, and a half part which, from an upper part, gradually changes into the handle 29 formed by downward extension. The two half-shells are fitted together by fasteners such as screws, forming a hollow tube shape extending substantially in the axial direction. An upper part of the tube shape of the outer housing 2 comprises a front end 21 facing towards the output shaft 6, and a rear end 22 which is opposite the front end 21 and remote from the output shaft 6. The front end 21 is open, and has a substantially annular sectional profile. Preferably, an inner surface 23 of the outer housing 2 is substantially round; a suitable shape is chosen for an outer surface 24 according to the requirements of industrial design of the tool. According to an embodiment of the present invention shown in Figs. 1-3, the rear end 22 is open, so as to keep the power tool short. It can be understood that the rear end 22 can be at least partly closed, even fully closed.

[0025] Similar to the outer housing 2, the inner housing 3 may also be injection-moulded from a suitable composite material. For example, the inner housing 3 is substantially cylindrical, which could be formed by one cup-shaped part with motor to be installed into it from front. The inner housing 3 may also comprise two substantially symmetric half-shells, which are fitted together to form a cylindrical structure. It will be understood that the inner housing 3 may also be integrally formed. The inner housing 3 has a frontward open first end 31 and a rearward closed second end 32; a second end face 33 substantially perpendicular to the work axis 7 is formed at the closed second end 32. The motor 4 is accommodated in the inner housing 3 at a side close to the second end 32.

[0026] The motor 4 connects to a drive shaft 9, which extends to a region in front of the motor and is connected to the impact mechanism 5. According to an embodiment of the present invention, the impact mechanism 5 comprises a gear transmission component, a main shaft, a hammer and the output shaft 6, as well as a gearbox 10 accommodating these components. The gear transmission component and hammer mentioned above have the following well-known structure: the gear transmission mechanism is meshed with the drive shaft 9, converts high-speed rotation of the drive shaft 9 of the motor 4 to rotation of the output shaft 6 by speed reduction, and transmits torque to the hammer, which repeatedly engages with and disengages from the output shaft 6, thereby producing impacts in the direction of rotation.

[0027] The impact wrench shown in the Figs. 1-3 is just an exemplary embodiment of the power tool with an impact mechanism. The power tool with an impact mechanism could also be other power tool with an impact mechanism, for example, a hammer drill. Though the impact mechanism in various power tool may provide different impact, the hammer mass of the impact mechanism is always move forward and backward in the axial direction, thereby creating oscillations in axial direction.

[0028] According to the exemplary embodiment of impact wrench 1 of the present invention, the gearbox 10 is a tubular body, a rear part thereof being inserted into the inner housing 3 and engaged with a bearing seat of the gear transmission component installed in the inner housing 3, while a front part of the gearbox 10 that is exposed at the first end 31 of the inner housing 3 has a tapered shape pointed at the front and may be covered by a shroud made of synthetic resin. The output shaft 6 is supported at a front end of the gearbox 10 and protrudes towards the front. Mounting holes are provided on an outer periphery of the gearbox 10 at the position where it is exposed at the first end 31 of the inner housing 3, so that the gearbox 10 may be fixedly mounted to the first end 31 of the inner housing 3 by fasteners.

[0029] Referring to Fig. 3, the outer housing 2 has substantially the same shape as the inner housing 3 in the axial direction, and the inner surface 23 of the outer housing 2 has a larger diameter than the outer surface 34 of the inner housing 3. Therefore, a radial gap 8 is created between the inner housing 3 and the outer housing 2. Now referring to Fig. 2, 4a, 4b and 5a, 5b, the inner housing 3 and outer housing 2 are elastically connected to each other in axial direction by at least two elastic elements 12 pre-tensioned against each other. The inner housing 3 is floating received in the outer housing 2 in axial direction. Hence, no axial application force needed to bring the inner sub-assembly into an effective working point. The vibration transmitted from the impact wrench to the user's hands and arms during use is reduced effectively.

[0030] At least one axial support 13 is provided in inner housing 3 or outer housing 2 extending into the radial gap 8. The axial support 13 can be provided either in the outer surface 34 of the inner housing 3 or the inner surface 23 of the outer housing 2. The at least two elastic elements 12 comprise at least one first elastic element 121 and at least one second elastic element 122. The first elastic element 121 and the second elastic element 122 are pre-tensioned supported by the at least one axial support 13 and the outer housing 2 or inner housing 3 in axial direction. Therefore, the inner sub-assembly is suspended within the outer housing. The vibration during the application would be absorbed by the floating of the inner sub-assembly.

[0031] According to one embodiment of the present invention as shown in Figs. 4a and 4b, the axial support 13 is provided in the outer surface 34 of the inner housing 3 between the first end 31 and the second end 32. A first radial protrusion 25 close to the front end 21 extends radially inward from the outer housing 2. A second radial protrusion 26 close to the rear end 22 extends radially inward from the outer housing 2. The first elastic element 121 is supported between the first radial protrusion 25 and the axial support 13 while the second elastic element 122 is supported between the axial support 13 and the second radial protrusion 26 of the outer housing 2. Both elastic elements 12 are pretensioned, pressing against the axial support 13 in axial direction. During application, as shown in fig. 4a, the first elastic element 121 is pushing the inner housing 3 to the rear side when the output shaft 6 is applied a rearward reaction force from working piece, and the second elastic element 122 is pushing the inner housing to the forward side when the output shaft is applied a rearward reaction force from working piece. With no force from user towards application in axial direction, the forces of the first elastic element 121 and second elastic element 122 are in balance and keep the inner housing 3 in a "floating" middle position of the outer housing 2.

[0032] According to the other embodiment of the present invention as shown in Figs. 5a and 5b, the axial support 13 is provided in inner surface 23 of the outer housing 2 between the front end 21 and the rear end 22. The inner housing 3 comprises a first end stop 35 and a second end stop 36 extending radially outward from the first end 31 and the second end 32 respectively. The first elastic element 121 is supported between the first end stop 36 and the axial support 13 while the second elastic element 122 is supported between the axial support 13 and the second end stop 37. Similarly, the forces of the first elastic element 121 and second elastic element 122 are in balance and keep the inner sub assembly in a "floating" middle position within the outer housing, therefore no additional contact forces are needed to bring the inner housing and output shaft into working point.

[0033] The axial support 13 could be designed as various types and structures, depending on the structure and / or assembly of the inner housing and outer housing. The axial support 13 can be a portion projecting from the inner housing 3 or the outer housing 2. For example, the axial support 13 extends circumferentially in the radial gap 8. There is only one axial support which is a ring-like shape extending around the outer surface 34 of the inner housing 3 or the inner surface 23 of the outer housing 2. Alternatively, the axial support 13 can be a separate part that fixed to the inner housing or the outer housing. Anyhow, the axial support 13 should be shorter than the radial gap in radial direction so that it won't fix the inner housing 3 to the outer housing 2.

[0034] According to an alternative embodiment, more than one axial support 13 is distributed around the inner housing in the circumferential direction. In this embodiment, the axial support is not a continuous ring, but there are several separated axial supports distributed around the inner housing in circumferential direction. For example, as shown in fig. 1, the outer housing 2 is not a complete cylindrical shape, it is kind of a square-like shape with round side. Four axial supports 13 are distributed in the corners of the outer housing 2. Moreover, the axial support 13 is not a portion of outer housing, but it is fixed to the inner surface of outer housing by fasteners 14. This would help ease of assembly of inner housing and outer housing.

[0035] Many types of material may be used for the elastic element. Preferably, the elastic element is a coil spring. A coil spring has a quite linear characteristic and low damping. That makes it easy for simulating / calculating its decoupling behaviour. According to an exemplary embodiment of the present invention, referring to the Fig. 2, in this exemplary embodiment, there are four axial supports 13 distributed around the radial gap 8 between the inner housing 3 and outer housing 2. There are four coil springs as the first elastic elements are held between the first end stop 35 and the four axial support 13 respectively. The other four coil springs are held between the four axial supports and the second end stop 36 respectively. Each coil spring is preloaded, therefore, every two coil springs arranged in the front and rear side of every axial support 12 are pre-tensioned against each other, the inner housing 3 floating received in the outer housing 2 in axial direction.

[0036] Alternatively, the elastic element is formed of a non-metal material capable of elastic deformation. More preferably, the elastic element is formed of polyurethane foam. Of course, the material, density or thickness, etc. of the elastic element is altered appropriately according to the strength required for attenuation of the striking vibration transmitted from the inner sub-assembly.

[0037] As the inner housing 3 is floating received in the outer housing 2, the inner housing 3 can not only move in the axial direction, but also rotate relative to the outer housing in circumferential direction, which is not anticipated to occur in the application of the power tool. In order to prevent rotation of the inner towards the outer housing in both directions, at least one anti-rotation structure 11 is provided between the inner housing 3 and the outer housing 2.

[0038] Referring to Figs. 2, 6 and 7, according to one exemplary embodiment, the anti-rotating structure 11 comprises at least one rotational support surface 110 formed on the inner surface 23 of the outer housing 2 and / or outer surface 34 of the inner housing 3. Preferably, rotational support surface 110 are two parallel surfaces formed on the inner surface 23 of the outer housing 2 and outer surface 34 of the inner housing 3 respectively, which can get in contact to stop a rotational movement between inner housing 3 and outer housing 2 in either clockwise or anti clockwise direction. To better stop both directions of rotational movement, there are four the two anti-rotating structures 11 provided in every corner of the outer housing.

[0039] Preferably, the rotational support surface is formed in the outer surface of inner housing and the inner surface of the outer housing respectively, and they are parallel surfaces which can get in contact to stop a rotational movement between inner and outer housing. More preferably, the rotational support surface is made of a sliding-optimized material different to the housing material (e.g. hardened sheet metal) to reduce friction between the inner and outer housing and, if necessary, to adjust the gap size.

[0040] According to an alternative embodiment of the present invention, as shown in Fig. 8, the anti-rotating structure comprises at least one insert 112 placed in a cavity 111 formed in the inner housing 3 and / or the outer housing 2. The insert 112 block the relative rotation between the inner housing 3 and the outer housing 2. Preferably, as shown in Fig.8, these cavities 111 are deeper than two times the radial gap 8 and the INSERTS 112 should have at least a thickness of two times the radial gap 8 so that in assembled condition these inserts 110 cannot get lost / fall out. More preferably, these inserts 112 are elastic and thus decoupling / damping vibrations in rotational direction, as shown in fig. 9.

[0041] According to another embodiment of the present invention, referring to fig. 10, the anti-rotating structure comprises at least one groove 114 extending in axial direction formed in the outer housing and one projection 113 formed in the inner housing, the projection 113 received in the groove 114. Therefore, the inner housing 3 can float in the axial direction within the outer housing 2, but it cannot rotate in the circumferential direction within the outer housing 2.

[0042] According to another yet embodiment of the present invention, the anti-rotating structure is formed on at least one of the first or second radial protrusions 25, 26 and / or first or second end stops 35, 36, thereby simplifying the structures of the power tool.

[0043] As stated above, although exemplary embodiments of the present invention have been explained herein with reference to the drawings, the present invention is not limited to the specific embodiments described above and may have many other embodiments. The scope of the present invention should be defined by the claims and their equivalent meaning.

Claims

1. A power tool with an impact mechanism comprising an outer housing and an inner housing at least partly surrounded by the outer housing; a motor accommodated in the inner housing, and a gearbox with the impact mechanism connected to the motor and fixedly coupled to the inner housing; the outer housing coupling a handle at its lower side, characterized in that the inner housing and outer housing are elastically connected to each other in axial direction by at least two elastic elements pre-tensioned against each other, wherein the inner housing is floatingly received in the outer housing in axial direction.

2. Power tool according to Claim 1, characterized in that the inner housing is substantially cylindrical, having a frontward open first end and a rearward closed second end, the outer housing having a frontward open front end and a rearward open or at least partially closed rear end; a radial gap created between the inner housing and the outer housing; at least one axial support being provided in inner housing or outer housing extending into the radial gap; the at least two elastic elements being pre-tensioned supported by the at least one axial support and the outer housing or inner housing in axial direction.

3. Power tool according to Claim 2, characterized in that the axial support is provided in outer surface of the inner housing between the first end and the second end; a first radial protrusion close to the front end extending radially inward from the outer housing; a second radial protrusion close to the rear end extending radially inward from the outer housing; the elastic elements comprising at least one first elastic element and at least one second elastic element, the first elastic element being supported between the first radial protrusion and the axial support and the second elastic element being supported between the axial support and the second radial protrusion.

4. Power tool according to Claim 2, characterized in that the axial support is provided in inner surface of the outer housing between the front end and the rear end; the inner housing comprising a first end stop and a second end stop extending radially outward close from the first end and second end respectively; the elastic elements comprising at least one first elastic element and at least one second elastic element, the first elastic element being supported between the first end stop and the axial support and the second elastic element being supported between the axial support and the second end stop.

5. Power tool according to Claim 3 or 4, characterized in that the axial support is a portion projecting from the inner housing or the outer housing or a separate part that fixed to the inner housing or the outer housing.

6. Power tool according to Claim 5, characterized in that the axial support extends circumferentially in the radial gap.

7. Power tool according to Claim 5, characterized in that more than one axial support is distributed around the inner housing in circumferential direction.

8. Power tool according to any one of Claims 1-7, characterized in that the elastic element is a coil spring.

9. Power tool according to any one of Claims 1- 8, characterized in that at least one anti-rotation structure is provided between the inner housing and the outer housing generating a form fit between outer housing and inner housing to prevent a rotational displacement of the inner housing towards the outer housing.

10. Power tool according to Claim 9, characterized in that the anti-rotating structure comprises at least one rotational support surface formed on the inner surface of the outer housing and / or outer surface of the inner housing.

11. Power tool according to Claim 10, characterized in that wherein the rotational support surface is made of a sliding-optimized material different to the housing material.

12. Power tool according to Claim 9, characterized in that the anti-rotating structure comprises at least one insert placed in a cavity formed in the inner housing and / or the outer housing.

13. Power tool according to Claim 12, characterized in that these inserts are elastic and thus decoupling / damping vibrations in rotational direction.

14. Power tool according to Claim 9, characterized in that the anti-rotating structure comprises at least one groove extending in axial direction formed in the outer housing and one projection formed in the inner housing, the projection received in the groove.

15. Power tool according to any one of Claims 9-14, characterized in that the anti-rotating structure is formed on at least one of the radial protrusions and / or end stops.

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