Electric tool comprising a pneumatic percussion mechanism, comprising a damped guide tube

Abstract

The invention relates to an electric power tool comprising a pneumatic percussion mechanism (3) for alternately applying impacts to a tool, comprising an exciter piston (8) which is driven by an electric motor via an eccentric drive (2) and which cooperates with an opposing striking piston (9), wherein the exciter piston and the striking piston (8, 9) are guided in a dynamically sealed manner in a guide tube (10) which is received, at a drive-side tube end (11), by a gear housing part (12) and which is received, at a tool-side tube end (13), by a guide housing part (14) which is detachably fastened to the gear housing part (12), wherein a first annular bearing device (15a), which acts elastically in the radial direction and in the axial direction, is arranged between the tool-side tube end (13) of the guide tube (10) and the guide housing part (14) surrounding the guide tube, and / or a second annular bearing device (15b), which acts elastically in the radial direction and in the axial direction, is arranged between the drive-side tube end (11) of the guide tube (10) and the gear housing part (12) which surrounds the guide tube.

Description

[0001] Hilti Aktiengesellschaft

[0002] Principality of Liechtenstein

[0003] POWER TOOL WITH A PNEUMATIC PERCUSSION MECHANISM,

[0004] COMPREHENSIVELY A DAMPED GUIDE TUBE

[0005] DESCRIPTION

[0006] The present invention relates to a power tool with a pneumatic impact mechanism for alternately striking a tool, comprising an exciter piston driven by an electric motor via an eccentric drive, which interacts with an opposing impact piston, wherein the exciter and impact pistons are dynamically sealed in a guide tube, which is received at a drive-side tube end by a gearbox housing part and which is received at a tool-side tube end by a guide housing part, which is detachably attached to the gearbox housing part.

[0007] The invention's application area extends primarily to handheld power tools, such as, in particular, rotary hammers, demolition hammers, and the like. A common feature of these power tools is a pneumatic impact mechanism for applying impact energy to the tool, for example, a hammer drill, chisel drill, or chisel. In addition to the desired axially directed impact energy for the tool, a pneumatic impact mechanism also generates radial and axial vibrations due to the drive mechanism, which manifest themselves as disruptive vibrations.

[0008] State of the art

[0009] WO 2021 / 198023 A1 describes a power tool with a pneumatic impact mechanism, driven by an electric motor. The motor's rotary motion is converted via an eccentric drive into an alternating linear motion of the pneumatic impact piston. The excitation piston is dynamically sealed within a guide tube and, via an internal column of compressed air, acts on an opposing impact piston. This piston, in the direction of action, strikes a coaxial impactor, whose mass-related impact energy is then transferred coaxially to the tool, which is detachably mounted in a tool holder.

[0010] In this state of the art, the gearbox housing fully accommodates the guide tube and is longitudinally divided into a main shell and a cover shell for this purpose. To secure the guide tube to the gearbox housing, it has retaining collars at both ends, ensuring a positive-locking connection.

[0011] Pneumatic impact mechanisms also emerge from the general state of the art, the guide tube of which is received by a gearbox housing part of the eccentric drive on the one hand and by a guide housing part of the dopper on the other, which corresponds to a transverse division of the housing.

[0012] The housing structures that accommodate the guide tube are usually made of steel, plastic, or are designed as metallic sintered bushings and transmit the mechanical loads emitted by the guide tube, such as bending loads, torsional loads, or even impact / collision loads, to the surrounding housing structure through direct contact. This manifests itself, among other things, in the disruptive vibrations already mentioned above.

[0013] It is therefore the object of the present invention to further improve an electric tool of the generic type in such a way that the mechanical loads emitted by a pneumatic impact mechanism are compensated in a simple manner.

[0014] Disclosure of the invention

[0015] The problem is solved starting from a power tool according to the preamble of claim 1 in conjunction with its characterizing features. The following dependent claims describe advantageous embodiments of the invention. The invention includes the technical teaching that a first bearing arrangement, elastically acting in the radial and axial directions, is arranged between the tool-side tube end of the guide tube of a pneumatic impact mechanism and the guide housing part surrounding it, and / or that a second bearing arrangement, elastically acting in the radial and axial directions, is arranged between the drive-side tube end of the guide tube and the gear housing part surrounding it.

[0016] The inventive measure achieves at least partial elastic decoupling of the guide tube of the pneumatic impact mechanism from the surrounding housing structure, thus significantly damping the mechanical loads emitted by the guide tube. The elastic mounting according to the invention and the damping properties of the at least one elastic bearing arrangement reduce the transmission of vibrations from the guide tube to the surrounding housing structure. The vibrations of the guide tube arise primarily from the pressure peaks of the air spring. Furthermore, vibrations caused by play in a guide tube mounting with play are prevented. The bearing arrangement according to the invention can be easily and compactly positioned between the guide tube and the surrounding housing structure.For sufficient damping, it is adequate to implement an elastic bearing device at only one of the two tube ends of the guide tube. This at least one elastic bearing device also compensates for manufacturing-related geometric tolerances, prevents play in the guide tube's mounting, and allows minor relative movements between the guide tube and the surrounding housing structure, in particular a slight tilting movement caused by bending loads introduced via the tool during operation.

[0017] In a structurally simple embodiment, the first bearing assembly is designed as an annular first bearing bushing and / or the second bearing assembly as an annular second bearing bushing. According to a preferred embodiment, the at least one elastic bearing bushing is essentially hollow cylindrical and is arranged on the outer surface of the associated tube end of the guide tube such that there is an elastic clearance in the radial direction relative to the guide housing part or the gearbox housing part. In this way, the guide tube together with the bearing bushing(s) can be pre-assembled to simplify the subsequent final assembly within the housing structure. The elastic clearance enables the aforementioned tolerance compensation as well as tilt compensation.

[0018] To ensure elastic movement in the axial direction, the elastic bearing bushing preferably interacts with at least one housing-side axial stop. In other words, axial movement is achieved via an end-face contact of the hollow cylindrical bearing bushing against a stationary housing stop, which is preferably formed on both end faces of the elastic bearing bushing, i.e., in both directions of movement.

[0019] In an advantageous embodiment, the first bearing assembly and / or the second bearing assembly is designed with several bearing elements arranged circumferentially distributed on the guide tube. The bearing elements are arranged on the outer surface of the associated tube end of the guide tube in such a way that there is elastic radial clearance relative to the gearbox housing part or the guide housing part. It is possible for two, three, four, five, six, or any larger number of bearing elements to be provided, which are arranged, in particular, uniformly distributed around the circumference of the guide tube. Preferably, the guide tube has a receiving device for each bearing element, which is designed, in particular, as radially outwardly projecting elements with which the bearing assembly interacts to secure its position, especially in the axial and circumferential directions.

[0020] To form a circumferentially annular bearing bushing, the bearing elements can be connected to each other circumferentially. To ensure the aforementioned pre-assembly of the at least one elastic bearing assembly on the guide tube, it is proposed that the component connection be material-fit or form-fit, for example, by vulcanization or bonding. Alternatively, it is also conceivable that the elastic bearing assembly is simply elastically pressed onto the guide tube, provided that this results in a reliable component connection at least until final assembly.

[0021] According to a further improvement of the invention, it is proposed that the guide housing part and / or the gearbox housing part be designed as a die-cast part made of light metal. Such a housing structure ensures sufficient housing stability and can be designed to be lightweight. The housing structure can, for example, be made of aluminum, an aluminum alloy, a magnesium alloy, or the like. The elastic mounting according to the invention reliably prevents deformation or even tearing of the housing structure surrounding the guide tube.

[0022] Preferably, the elastic bearing assembly is designed with regard to installation space, material stiffness, and preload such that axial and radial displacement or deformation of the guide tube of up to 1 mm is permitted during operation. This elastic movement ensures sufficient damping and prevents damage to the surrounding housing structure from the occurring mechanical loads.

[0023] According to a preferred embodiment of the invention, an elastic bearing arrangement is assigned to both the tool-side and the drive-side tube ends. This bilateral elastic bearing arrangement ensures maximum damping. It should be noted, however, that a bearing arrangement of the guide tube on either the tool-side or drive-side alone is sufficient for adequate damping.

[0024] Preferably, the elastic bearing assembly consists of a temperature-stable elastomer material, for example, hydrogenated acrylonitrile butadiene rubber (HNBR) or fluorocarbon rubber (FPM). In this case, the elastic properties are primarily determined by the material. However, it is also conceivable to manufacture the elastic bearing assembly from a fiber-reinforced plastic, such as polyamide 66 (PA66), and to achieve the desired elastic properties relative to the surrounding housing structure through the component geometry, for example, by molding small, resilient tabs.

[0025] Detailed description based on drawing

[0026] Further measures improving the invention are described in more detail below, together with a description of a preferred embodiment of the invention, with reference to the figures. The figures show:

[0027] Fig. 1 shows a schematic, partially cut-away side view of a power tool, here in the form of a rotary hammer.

[0028] Fig. 2 shows a partial longitudinal section through the power tool in the area of ​​the pneumatic impact mechanism;

[0029] Fig. 3 shows a three-dimensional representation of a first embodiment of a bearing device in a state arranged on a guide tube, wherein the bearing device is designed as an annular bearing bushing; and

[0030] Fig. 4 shows a three-dimensional representation of a second embodiment of the bearing device, in a state arranged on a guide tube, wherein the bearing device is designed with several bearing elements.

[0031] According to Fig. 1, a power tool designed in the form of a rotary hammer essentially consists of an electric motor 1, the rotary motion of which is transmitted via an eccentric drive 2 into a linear alternating working motion on a pneumatic impact mechanism 3. The pneumatic impact mechanism 3 acts on a striker 4, the impact mass of which in turn acts backwards on a tool 6 clamped in a tool holder 5.

[0032] The aforementioned drive components, including the pneumatic impact mechanism 3, are housed in a machine housing 7.

[0033] As shown in Fig. 2, the pneumatic impact mechanism 3 consists of an exciter piston 8 driven by the eccentric drive 2, which interacts with an opposing impact piston 9 via an air column. The exciter piston 8 and the impact piston 9 are dynamically sealed within a common guide tube 10. The guide tube 10 is received at the drive-side tube end 11 by a gearbox housing part 12 of the machine housing. At the tool-side tube end 13, the guide tube 10 is received by a guide housing part 14. The guide housing part 14 is detachably flanged to the gearbox housing part 12.

[0034] Between the tool-side tube end 13 of the guide tube 10 and the surrounding guide housing part 14, a first bearing assembly 15a, shown in more detail in Fig. 3, is arranged, acting elastically in the radial and axial directions. The first bearing assembly is designed as an annular first bearing bushing 15a. Opposite this, between the drive-side tube end 11 of the guide tube 10 and the surrounding gearbox housing part 12, a second annular bearing assembly 15b, also acting elastically in the radial and axial directions, is arranged, designed as an annular second bearing bushing 15b. Both elastic bearing assemblies 15a and 15b consist of a temperature-resistant elastomer material and provide damping support for the guide tube 10 within the surrounding housing structure.

[0035] The two bearing devices 15a and 15b can each be designed as hollow cylindrical elastic bearing bushings 15a and 15b and arranged on the outer surface of the associated tube end 11 or 13 of the guide tube 10 such that there is an elastic clearance in the radial direction relative to the gearbox housing part 12 or to the guide housing part 14. To ensure the elastic clearance in the axial direction, the elastic bearing devices 15a and 15b attached to the outer surface of the guide tube 10 interact with at least one housing-side axial stop 16 (exemplary).

[0036] In the embodiment shown in Fig. 2, an elastic bearing device 15a or 15b is assigned to both the drive-side tube end 11 and the tool-side tube end 13.

[0037] The bearing devices shown in Fig. 3 and Fig. 4 can be arranged in any combination in the area of ​​the drive-side tube end 11 and / or in the area of ​​the tool-side tube end 13.

[0038] The bearing assembly 15a according to Fig. 3 comprises four bearing elements 151, 152, 153, and 154, which are arranged evenly distributed around the circumference of the guide tube 10. Two circumferentially adjacent bearing elements 151, 152, 153, 154 are connected to each other by webs such that the bearing elements 151, 152, 153, 154, together with the webs, form an annular bearing bushing 15a. The bearing elements 151, 152, 153, and 154 interact with the guide tube 10 in such a way that they are secured circumferentially against the guide tube 10. Furthermore, they are supported against the guide tube 10 by an axial stop 16.

[0039] Fig. 4 shows an alternative embodiment of the bearing assembly 15a. In this embodiment, the bearing assembly 15a comprises four separate bearing elements 151, 152, 153, which are arranged evenly distributed around the circumference of the guide tube 10. For the arrangement of the bearing elements 151, 152, 153, a receiving element in the form of a radially outwardly projecting element 100 is provided on the guide tube 10 for each bearing element 151, 152, 153, with which the bearing elements 151, 152, 153 interact in a positive-locking manner. The bearing elements 151, 152, 153 are defined and fixed to the elements 100 in the circumferential and axial directions, so that the bearing elements 151, 152, 153 are secured in their position relative to the guide tube 10. The invention is not limited to the preferred embodiment described above. Rather, variations are also conceivable that are included in the scope of protection of the following claims.For example, it is also conceivable to arrange an elastic bearing device 15a only at one of the two tube ends, preferably at the tool-side tube end 13, in order to achieve significant vibration damping of the guide tube 10. Reference numeral list.

[0040] 1 electric motor

[0041] 2 eccentric drives

[0042] 3 pneumatic percussion instruments

[0043] 4 Döpper

[0044] 5 Tool holder

[0045] 6 tools

[0046] 7 machine housings

[0047] 8 exciter pistons

[0048] 9 impact pistons

[0049] 10 guide tube

[0050] 100 elements of the guide tube

[0051] 11 drive-side pipe end

[0052] 12 Gearbox housing part

[0053] 13 Tool-side pipe end

[0054] 14 Guide housing part

[0055] 15a First elastic bearing device 15b Second elastic bearing device 16 Axial stop

[0056] 151 Bearing element

[0057] 152 Bearing element

[0058] 153 Bearing element

Claims

REQUIREMENTS 1. Power tool with a pneumatic impact mechanism (3) for alternately striking a tool, comprising an exciter piston (8) driven by an electric motor via an eccentric drive (2), which interacts with an opposing impact piston (9), wherein the exciter and impact pistons (8, 9) are dynamically sealed in a guide tube (10), which is received at a drive-side tube end (11) by a gearbox housing part (12), and which is received at a tool-side tube end (13) by a guide housing part (14), which is detachably attached to the gearbox housing part (12), characterized in that a first bearing device (15a) acting elastically in the radial and axial directions is arranged between the tool-side tube end (13) of the guide tube (10) and the guide housing part (14) surrounding it, and / or that a second bearing device (15b) acting elastically in the radial and axial direction is arranged between the drive-side tube end (11) of the guide tube (10) and the gearbox housing part (12) surrounding it.

2. Power tool according to claim 1, characterized in that the first bearing device (15a) is designed as an annular first bearing bushing (15a) and / or the second bearing device (15b) is designed as an annular second bearing bushing (15b).

3. Power tool according to claim 2, characterized in that the at least one elastic bearing bushing (15a; 15b) is designed as a hollow cylinder and is arranged on the outer surface of the associated tube end (11; 13) of the guide tube (10) in such a way that there is an elastic movement clearance in the radial direction relative to the gearbox housing part (12) or to the guide housing part (14).

4. Power tool according to claim 3, characterized in that the elastic bearing bushing (15a; 15b) cooperates with at least one housing-side axial stop (16) to ensure elastic movement in the axial direction.

5. Power tool according to one of the preceding claims, characterized in that the first bearing device (15a) and / or the second bearing device (15b) is designed with several bearing elements (151, 152, 153) arranged circumferentially distributed on the guide tube (10), wherein the bearing elements (151, 152, 153) are arranged on the outer surface of the associated tube end (11; 13) of the guide tube (10) such that there is an elastic clearance in the radial direction relative to the gearbox housing part (12) or to the guide housing part (14).

6. Power tool according to one of the preceding claims, characterized in that the elastic bearing bushing (15a; 15b) is connected to the outer surface of the guide tube (10) by a material-locking or form-locking connection.

7. Power tool according to one of the preceding claims, characterized in that the gearbox housing part (12) and / or the guide housing part (14) is designed as a die-cast part made of light metal.

8. Power tool according to claim 7, characterized in that the gearbox housing part (12) or the guide housing part (14) is made of aluminium or an aluminium alloy or a magnesium alloy.

9. Power tool according to one of the preceding claims, characterized in that the elastic bearing device (15a; 15b) is designed with regard to the design parameters installation space, material stiffness and preload such that an axial as well as radial Displacement or axial and radial deformation of the guide tube (10) by up to 1 mm is present.

10. Power tool according to one of the preceding claims, characterized in that both the drive-side tube end (11) and the tool-side tube end (13) are each assigned an elastic bearing device (15a; 15b).

11. Power tool according to one of the preceding claims, characterized in that the elastic bearing device (15a; 15b) consists of a temperature-stable elastomer material selected from an elastomer material group comprising hydrogenated acrylonitrile butadiene rubber (HNBR), fluorocarbon rubber (FPM), wherein the elastic properties result predominantly from the material.

12. Power tool according to one of the preceding claims, characterized in that the elastic bearing device (15a; 15b) consists of a synthetic fiber reinforced plastic selected from a plastic group comprising polyamide 66 (PA66), polyphenylene sulfide (PPS), wherein the elastic properties result predominantly from the shape.

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