Hand-held power tool with pneumatic impact mechanism and a method for its manufacture

Abstract

The invention relates to a hand-held power tool and a method for its manufacture. The hand-held power tool has a motor-driven pneumatic impact mechanism comprising a driven exciter, a guide tube (20), and a piston-shaped striker, wherein the piston-shaped striker and the exciter are guided within the guide tube on its inner circumferential surface, wherein the exciter and the striker are able to seal an air spring chamber within the guide tube (20), and wherein the guide tube (20) has at least one ventilation opening (23) extending substantially radially to a central longitudinal axis (10) of the guide tube (20). According to the invention, at least one circumferential annular groove (30) is provided on the inner circumferential surface (21) of the guide tube (20), into which the at least one ventilation opening (23) opens.

Description

[0001] The invention relates to a hand-held power tool, in particular a hand-held power tool with a motor-driven pneumatic impact mechanism. The invention further relates to a manufacturing method for the hand-held power tool.

[0002] German patent application DE 19 71 31 54 A1 describes the operation of such a striking mechanism. This mechanism comprises a cylinder; a piston that is movably mounted within the cylinder; an air chamber formed adjacent to the piston in the cylinder to generate an air spring; at least one outlet opening formed in the part of the cylinder where the air chamber is located; a striking element contained within the cylinder, which can be moved to engage with the piston via the air spring generated in the air chamber to transmit a striking motion executed by the piston to a tool tip attached to the front end of the striking tool; and an axially displaceable sliding sleeve mounted around the cylinder and biased forward. The sliding sleeve is retracted to close the outlet opening formed in the cylinder when the striking motion is transmitted.The sliding sleeve is moved forward to open the exhaust port during idling operation.

[0003] In a motor-driven pneumatic impact mechanism, a piston is typically accelerated periodically within a guide tube by an air spring and strikes a tool at a forward turning point. The air spring principle requires an airtight seal for the piston within the guide tube. This seal must not fail, even under the high mechanical stress from the recoil or the thermomechanical stresses (the impact mechanism heats up to over 100 degrees Celsius). Furthermore, the piston must move freely within the guide tube to avoid suppressing the relatively weak coupling of the motor drive via the air spring. Therefore, to ensure the necessary mechanical and thermomechanical properties, the guide tube is machined from a solid cylinder or a tube with a smaller inner diameter.

[0004] The publication DE 42 15 288 A1 also describes a pneumatic striking mechanism with a guide tube and a piston contained therein for driving a beater of the striking mechanism.

[0005] The pneumatic impact mechanism requires ventilation openings (such as the outlet openings in the guide tube described in German patent DE 19 71 31 54 A1, or an unspecified air outlet opening as described in German patent DE 42 15 288 A1), the diameters of which are specified with tight tolerances. The openings are drilled into the guide tube from the outside. The resulting sharp edges on the inside must be deburred and honed to prevent damage to seals, such as O-rings, on the impact piston or exciter. Due to the difficult access to the inside of the guide tube, deburring and honing are carried out mechanically and chemically with considerable effort, for example, using EDM processes, where thermal removal is achieved via plasma (spark erosion), or ECM processes, where chemical removal is achieved via anodic metal dissolution.

[0006] Alternatively, the publication EP 2 514 569 B1 proposes a manufacturing process for producing a machine tool in which a sheet metal strip is first provided with the necessary drill holes for ventilating the guide tube, and the sheet metal strip is then formed into a guide tube by bending and joining the longitudinal edges of the strip. The drill can be positioned on the side of the sheet metal strip that will later form the inner circumferential surface of the guide tube.

[0007] Although this method reduces the effort required for post-processing the drilled ventilation openings, it increases the effort required for manufacturing the guide tube, as the guide tube must be bent and joined with tight tolerances to fulfill its guiding function.

[0008] In order to reduce the effort of known post-processing methods for removing the burrs that arise at the ventilation openings in an alternative way, without increasing the effort in the manufacture of the guide tube, the invention proposes a hand-held machine tool with the features of claim 1 and a manufacturing method with the features of claim 6.

[0009] The present invention provides a hand-held power tool comprising a motor-driven pneumatic impact mechanism, including a driven exciter, a guide tube, and a piston-shaped striker. The piston-shaped striker and the exciter are guided within the guide tube on its inner circumferential surface. The exciter and striker are able to seal an air spring chamber within the guide tube. The guide tube has at least one ventilation opening extending substantially radially to a central longitudinal axis of the guide tube. The striker and / or exciter can periodically pass over the at least one ventilation opening to vent and purge the air spring chamber. The invention further provides that at least one circumferential annular groove is provided on the inner circumferential surface of the guide tube, into which the at least one ventilation opening opens.

[0010] Typically, a large number of ventilation openings can be provided, for example two, three or four, or eight ventilation openings, which can be distributed around the circumference of the guide tube, in particular evenly spaced, i.e. at equal intervals from each other.

[0011] The special feature according to the invention can be seen in the internal annular groove, which runs along the inner circumferential surface of the guide tube in such a way that at least one ventilation opening opens into it.

[0012] In principle, the annular groove creates a "relief" for a sealing element or sealing surface of the components of the impact mechanism that slide over the at least one ventilation opening, thus reducing the risk of damage to the sealing element or sealing surface. The inner diameter is increased in the area of ​​the annular groove, preventing any burrs or similar imperfections from rubbing against the sealing element or sealing surface with the same pressure when the sealing element or sealing surface passes over the ventilation opening(s).

[0013] Furthermore, if the annular groove is formed, in particular after drilling, and at least one ventilation opening is introduced into the inner circumferential surface of the guide tube, any burr on the at least one ventilation opening can be easily removed simply by providing the annular groove.

[0014] For the introduction of the ring groove, a machining process, for example grinding, can be used, as will be explained in more detail below in connection with the manufacturing process according to the invention.

[0015] According to an advantageous embodiment, the annular groove, viewed in a longitudinal section along the central longitudinal axis of the guide tube, has an inlet area and an outlet area in the transition region from the annular groove to the inner circumferential surface of the guide tube, wherein the ventilation opening extends in the area between the inlet area and the outlet area of ​​the annular groove. Thus, the width of the annular groove is selected such that it is greater than or equal to the diameter of the at least one ventilation opening opening into it.

[0016] The depth of the annular groove, i.e., the radial extent from the inner circumferential surface of the guide tube, can also be chosen differently depending on the application, depending on whether the primary purpose is to create "relief" for a sealing element or a sealing surface of the components of the impact mechanism that slide over the at least one ventilation opening, or whether the deburring of the incoming ventilation opening is to be achieved by a subsequent introduction of the annular groove.

[0017] A longitudinal section along the central longitudinal axis of the guide tube shows the cross-sectional contour of the annular groove as well as the respective transition areas to the inner circumferential surface, i.e., the inlet and outlet areas. Regardless of the specific cross-sectional contour of the annular groove, it can be designed so that the groove (including its inlet and outlet areas) is wide enough for the entire circumferential edge of the vent opening to open into the annular groove. This ensures that any manufacturing-related burr is mitigated or completely removed during the manufacturing of the annular groove along the entire circumference of the vent opening.

[0018] As already indicated above, it is also possible, in particular, to provide not just a single ventilation opening, but several ventilation openings. Specifically, a first number of at least two or more ventilation openings can be arranged in a first plane perpendicular to the central longitudinal axis of the guide tube, such that these open into a first circumferential annular groove on the inner circumferential surface of the guide tube.

[0019] Furthermore, a second number of at least two or more ventilation openings can be arranged in a second plane perpendicular to the central longitudinal axis of the guide tube, such that these open into a second circumferential annular groove on the inner circumferential surface of the guide tube.

[0020] In some embodiments, a first set of ventilation openings arranged around the circumference of the guide tube in one plane can open into a first common annular groove. If a second set of ventilation openings is provided around the circumference of the guide tube in a second plane (parallel to the first plane), these can open into a second circumferential annular groove on the inner surface of the guide tube.

[0021] Alternatively or additionally, as already indicated above, the annular groove can have a specific cross-sectional contour. For example, when viewed in a longitudinal section along the central longitudinal axis of the guide tube, it can have at least one first radius of curvature. By having this first radius of curvature, the cross-sectional contour of the guide groove is rounded, which allows for improved sliding when a sealing element passes over the annular groove.

[0022] Furthermore, it may be provided that the annular groove in the inlet area and / or in the outlet area has or has a chamfer, a radius opposite to and / or deviating from a radius of curvature of the annular groove or a flattening of the radius of curvature of the annular groove as well as combinations thereof.

[0023] All these measures, individually or in combination, further reduce any sharp transition edges and thus improve the sliding properties for a sealing element that passes over the ventilation opening(s) leading into an annular groove. The risk of damage to an element that periodically moves over the ventilation opening(s), for example a sealing element, is thus advantageously reduced.

[0024] The invention also relates to a manufacturing method for producing a hand-held power tool with the preceding features, comprising the steps of: introducing at least one ventilation opening into the guide tube, for example by means of a drill bit that bores into the outer surface of the guide tube from an outer surface; and introducing at least one circumferential annular groove on the inner circumferential surface of the guide tube, into which the at least one ventilation opening opens.

[0025] The special feature of the manufacturing process is the incorporation of at least one circumferential annular groove on the inner circumferential surface of the guide tube, which brings the advantages already described above and in particular reduces the risk of damage to a sealing element or the like.

[0026] In particular, if the annular groove is so wide that at least one ventilation opening opens into the annular groove with its entire circumferential edge, it can be ensured over the entire circumferential area of ​​the ventilation opening that a manufacturing-related burr around the at least one ventilation opening can be mitigated or completely removed during the subsequent manufacturing of the annular groove.

[0027] It can also be provided that the step of introducing at least one annular groove on the inner circumferential surface of the guide tube is performed after the step of introducing the ventilation openings into the guide tube. In this way, it can be achieved that manufacturing-related burrs in the area of ​​the at least one ventilation opening on the inner circumferential surface of the guide tube are not only mitigated but also removed by introducing the annular groove.

[0028] Alternatively or additionally, it may be provided that the introduction of the at least one annular groove on the inner circumferential surface of the guide tube is carried out by means of a profile grinder which, viewed in cross-section, in particular has a convex grinding contour with at least one first radius of curvature which essentially corresponds to the at least one first radius of curvature of the annular groove viewed in a longitudinal section along the central longitudinal axis of the guide tube.

[0029] Alternatively or additionally, it may be provided that the introduction of the at least one annular groove on the inner circumferential surface of the guide tube further comprises the following steps: introduction of an inlet area upstream of the annular groove in the direction of the central longitudinal axis of the guide tube; and introduction of an outlet area downstream of the annular groove in the direction of the central longitudinal axis of the guide tube, wherein the inlet area and / or the outlet area may be formed with a chamfer, a radius opposite to and / or deviating from the radius of curvature of the annular groove and / or with a flattening of the radius of curvature of the annular groove.

[0030] In particular, it may be provided that the inlet area and / or outlet area is introduced onto the inner circumferential surface of the guide tube by means of a profile grinder which, viewed in cross-section, has in particular a grinding contour with the characteristics of the inlet area and / or the outlet area.

[0031] It is conceivable that the annular groove, including its entry and / or exit sections, could be machined using a single profile grinder whose cross-section corresponds to the contour of the annular groove, including its entry and / or exit sections, as seen in a longitudinal section along the central axis of the guide tube. Alternatively, the annular groove and its entry and / or exit sections could be machined using two or more different profile grinders. For example, the annular groove could be machined with a first profile grinder, and its entry and / or exit sections with a second. Furthermore, although less practical, it is also conceivable to machine the annular groove itself with different profile grinders if it has differently curved sections.

[0032] It should also be noted that terms such as "comprehensive," "exhibit," or "with" do not exclude other characteristics or steps. Furthermore, terms like "a" or "that," which indicate a singular set of steps or characteristics, do not exclude a plurality of characteristics or steps, and vice versa.

[0033] Further features and advantages of the invention will become apparent from the following description of an exemplary embodiment of the invention and from the dependent claims.

[0034] The invention is described in more detail below with reference to the accompanying figures. The figures show several features of the invention in combination with one another. Of course, a person skilled in the art can also consider these features separately and, if necessary, combine them into further meaningful sub-combinations without having to make an inventive step.

[0035] They show schematically: Fig. 1 a state-of-the-art hand-held power tool; Fig. 2 a guide tube of a hand-held power tool according to the invention in a longitudinal section; Fig. 3 the guide tube of the Fig. 2 in a cross-section according to detail AA in Fig. 2; Fig. 4 a detailed view according to detail b in Fig. 2; Fig. 5 a profile grinder according to the invention in a side view; and Fig. 6 the method according to the invention in a section.

[0036] The Fig. Figure 1 shows a hand-held machine tool as known from the prior art, for example EP 2514 569 A1.

[0037] The hand-held power tool 1 shown is an example of a chiseling hand-held power tool, in this case a rotary hammer 1. The rotary hammer 1 has a tool holder 2 into which a shank end 3 of a tool, e.g., a drill bit 4, can be inserted. The primary drive of the rotary hammer 1 is a motor 5, which drives a hammer mechanism 6 and an output shaft 7.

[0038] A user can guide the rotary hammer 1 using a handle 8 and start it up using a system switch 9. During operation, the rotary hammer 1 continuously rotates the drill bit 4 around a working axis 10 and can thereby drive the drill bit 4 into a substrate in the impact direction 11 along the working axis 10.

[0039] The striking mechanism 6 is designed as a pneumatic striking mechanism 6. In a guide tube 20, an exciter 12 and a striker 13 are movably guided along the working axis 10, which also forms the central longitudinal axis 10 of the guide tube 20. The exciter 12 is coupled to the motor 5 via an eccentric 14 or a wobble finger and consequently moves in a periodic, linear motion.

[0040] Within the guide tube, an air spring is formed by a pneumatic chamber 15 between the exciter 12 and the striker 13. This spring couples the movement of the striker 13 to the movement of the exciter 12. The striker 13 can strike the rear end of the drill bit 4 directly or indirectly transfer part of its momentum to the drill bit 4 via a substantially stationary intermediate striker 16 (impact block). The impact mechanism 6 and preferably the other drive components are arranged within a machine housing 17.

[0041] The exemplary exciter 12 is designed as a piston that moves back and forth within the cylindrical guide tube 20. The striker 13 is also designed as a piston. Both the exciter 12 and the striker 13 form an airtight seal with their radial outer surfaces against an inner surface 21 of the guide tube 20. The guide tube 20 can extend to a bearing block 22 for the intermediate striker 16. The guide tube 20 has several ventilation openings 23, 24 radial to the working axis 10. A first set of openings 23 allows for adiabatic pressure equalization of the air spring when the device heats up. A second set of openings 24 vents the pneumatic chamber 15 and deactivates the air spring as soon as the impact mechanism 6 is empty.

[0042] As soon as the openings 23 and 24 are passed over by one of the components of the impact mechanism, there is a risk that a sealing element or a sealing surface of this element or component will be damaged if the ventilation openings 23, 24 still have manufacturing-related burrs or the like.

[0043] The ventilation openings 23, 24 are typically drilled into the guide tube 20 from the outside. The resulting sharp edges on the inside 21 must be deburred and honed to avoid damaging existing seals, sealing elements, or sealing surfaces on the piston. Due to the difficult access to the inside, deburring and honing are performed mechanically and chemically in known solutions, requiring considerable effort.

[0044] The Fig. Figure 2 shows an exemplary guide tube 20 of a hand-held power tool according to the invention. This also has ventilation openings 23 which, in the present invention, open into an annular groove 30 on the inner circumferential surface 21 of the guide tube.

[0045] You can tell by the Fig. 2, Fig. 3 and Fig. 4, that the annular groove 30 has an inlet area 32 and an outlet area 34, as well as a first radius of curvature 36a in the region of its groove contour 36 between the inlet area 32 and the outlet area 34. The ventilation openings 23 open into the annular groove 30 such that their outer edge is completely contained within the area between the inlet area 32 and the outlet area 34 of the annular groove 30. The width 38 of the annular groove 30, which is defined as the area between the inlet area 32 and the outlet area 34 of the annular groove 30, is thus, as shown, larger than the diameter of the incoming ventilation openings 23.

[0046] The annular groove 30 also has a depth 36, which is defined as the maximum radial extent of the annular groove 30 from the inner circumferential surface 21 of the guide tube 20.

[0047] In the illustrated embodiment, the inlet area 32 and the outlet area 34 have a second radius of curvature 32a, 34a, which differs numerically from the first radius of curvature, i.e., is smaller or larger (in this case, the second radius of curvature is smaller) and is curved in the opposite direction. Unlike the rest of the annular groove, whose first radius of curvature 36a is essentially concave inwards, the second radius of curvature 32a, 34a is essentially convex outwards. This provides a particularly smooth, edgeless transition from the annular groove 30 to the adjacent inner circumferential surface 21.

[0048] The second radius of curvature 32a of the inlet area 32 can be identical to the second radius of curvature 34a of the outlet area 34 (as shown here) or differ from it (in its curvature and its orientation).

[0049] The Fig. Figure 5 schematically shows a profile grinder 40 in a side view, with which an annular groove 30 can be produced on the hand-held power tool according to the invention. Viewed in cross-section (analogous to the side view shown), it has a substantially convex grinding contour 52 with a first radius of curvature 56a.

[0050] The inventive method 500 is finally described in excerpts and schematically in Fig. Figure 6 shows that, in a particularly preferred embodiment, steps 510 and 520 are carried out in the sequence shown. In this way, by introducing the annular groove 30 in a subsequent process step 520, manufacturing-related burrs on the circumferential edge of the ventilation openings 23 can be reliably and easily removed.

[0051] This is particularly advantageous when, as in the embodiment shown and in the prior art, several ventilation openings 23 of a first number are arranged in a common plane perpendicular to the central longitudinal axis 10 in a ring-shaped arrangement around the guide tube 20, because the burrs of several ventilation openings can be removed easily and cost-effectively in a single operation.

[0052] Similarly, several ventilation openings (analogous to the ventilation openings 24 according to Fig.1) a second number of rings are attached in a common second plane perpendicular to the central longitudinal axis 10 around the guide tube 20, which open into a second annular groove (not shown) and can be removed easily and safely in a further work step by introducing a second annular groove. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 19 71 31 54 A1 [0002, 0005] DE 42 15 288 A1 [0004, 0005] EP 2 514 569 B1

[0006] EP 2514 569 A1

[0036]

Claims

[1] Hand-held power tool with a motor-driven pneumatic impact mechanism, comprising a driven exciter, a guide tube (20) and a piston-shaped striker, wherein the piston-shaped striker and the exciter are guided within the guide tube on its inner circumferential surface, wherein the exciter is able to close off an air spring chamber with the striker within the guide tube (20), and wherein the guide tube (20) has at least one ventilation opening (23) which extends substantially radially to a central longitudinal axis (10) of the guide tube (20), characterized by , that at least one circumferential annular groove (30) is provided on the inner circumferential surface (21) of the guide tube (20), into which at least one ventilation opening (23) opens. [2] Hand-held power tool according to claim 1, characterized by, that the annular groove (30) viewed in a longitudinal section along the central longitudinal axis (10) of the guide tube (20) has an inlet area (32) and an outlet area (34) in the transition area from the annular groove (30) to the inner circumferential surface (21) of the guide tube (20), wherein the at least one ventilation opening (23) extends in the area between the inlet area (32) and the outlet area (34) of the annular groove. [3] Hand-held power tool according to claim 1 or 2, characterized by , that a first number of at least two or more ventilation openings (23) is arranged in a first plane perpendicular to the central longitudinal axis (10) of the guide tube (20), such that these open into a first circumferential annular groove (30) on the inner circumferential surface (21) of the guide tube (20). [4] Hand-held power tool according to claim 3, characterized by, that a second number of at least two or more ventilation openings is arranged in a second plane perpendicular to the central longitudinal axis of the guide tube, such that these open into a second circumferential annular groove on the inner circumferential surface of the guide tube. [5] Hand-held power tool according to any one of the preceding claims, characterized by , that the annular groove (30) in a longitudinal section along the central longitudinal axis of the guide tube has at least one first radius of curvature (36a). [6] Hand-held power tool according to any one of the preceding claims 2 to 5, characterized by , that the annular groove in the inlet area (32) and / or in the outlet area (34) has or has a chamfer, a radius (32a, 34a) that is opposite to and / or deviates from a radius of curvature (36a) of the annular groove (30) or a flattening of the radius of curvature (36a) of the annular groove (30) as well as combinations thereof. [7] Manufacturing method (500) for manufacturing a hand-held power tool according to any one of claims 1 to 6, comprising the steps: - Introducing (510) at least one ventilation opening (23) into the guide tube, for example by means of a drill bit that bores into the outer surface of the guide tube (20) starting from an outer surface of the guide tube (20); and - Including (520) at least one circumferential annular groove (30) on the inner circumferential surface (21) of the guide tube (20), into which the at least one ventilation opening (23) opens. [8] Manufacturing process (500) according to claim 7, characterized by, that the step (520) of introducing the at least one annular groove on the inner circumferential surface (21) of the guide tube (20) is subsequent to the step (510) of introducing the ventilation openings (23) into the guide tube (20), such that by introducing the annular groove (520) manufacturing-related burrs in the area of ​​the at least one ventilation opening (23) on the inner circumferential surface (21) of the guide tube (20) can be removed. [9] Manufacturing process (500) according to claim 7 or 8, characterized by , that the introduction (520) of the at least one annular groove on the inner circumferential surface (21) of the guide tube (20) is carried out by means of a profile grinder (50) which, viewed in a cross-section, in particular has a convex grinding contour (52) with at least one first radius of curvature (56a) which essentially corresponds to the at least one first radius of curvature (36a) of the annular groove (30) viewed in a longitudinal section along the central longitudinal axis (10) of the guide tube (20). [10] Manufacturing process (500) according to claim 6 or 7, characterized by , that the introduction (520) of at least one annular groove (30) on the inner circumferential surface (21) of the guide tube (20) further comprises the following sub-steps: - Introducing an inlet area (32) upstream of the annular groove (30) in the direction of the central longitudinal axis (10) of the guide tube (20); - Introducing an outlet area (34) downstream of the annular groove (30) in the direction of the central longitudinal axis (10) of the guide tube (20), wherein the inlet area (32) and / or the outlet area (34) have a chamfer, a radius opposite to and / or deviating from the radius of curvature (36a) of the annular groove (30) or a flattening (32a, 34a) of the radius of curvature (36a) of the annular groove (30). [11] Manufacturing process (500) according to claim 8, characterized by, that the introduction of the inlet area and / or the outlet area on the inner circumferential surface of the guide tube is carried out by means of a profile grinder (50) which, viewed in cross-section, in particular has a grinding contour (52) with the characteristics of the inlet area (32) and / or the outlet area (34).

Images