Pneumatic percussion mechanism for a hammer drill or chisel hammer

Abstract

The invention relates to a pneumatic percussion mechanism for a hammer drill or chisel hammer, comprising a striker (6) which is acted on by a percussion piston (5) and is intended for acting on the rear of a tool (7), wherein the striker (6) is longitudinally guided in an associated guide tube (4) which is provided with damping means at the end face thereof for damping a bouncing or an idle stroke of the striker (6); the damping means comprise an insert sleeve (9), which is provided in the tool-side region of the guide tube (4), for forming an additional mass for the idle stroke damping function, the insert sleeve being captively inserted into the guide tube (4) in that a guide tube (4) drill shoulder, which is formed by an undercut portion (11a), forms a rear end stop (12) for the insert sleeve (9); and the guide tube (4) undercut portion (11a) is formed by a rear diameter (D1) which is greater than an adjacent guide tube (4) front diameter (D2), formed by a mouth portion (11b). Furthermore, the rear diameter (D1), together with an associated outer diameter (D3) of the insert sleeve (9), forms a clearance fit, and the front diameter (D2), together with the outer diameter (D3) of the insert sleeve (9), forms a press fit.

Description

[0001] 2024P00080WQ

[0002] Hilti Aktiengesellschaft

[0003] Principality of Liechtenstein

[0004] Pneumatic percussion mechanism for a drill or chisel hammer

[0005] DESCRIPTION

[0006] 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 on a tool, wherein the hammer is arranged longitudinally in an associated guide tube which is equipped with end-side damping means for the rebound and impact damping of the hammer.

[0007] The invention's application area extends primarily to hand-held power tools, in particular rotary hammers or demolition hammers, which are equipped with a pneumatic impact mechanism for generating impact impulses acting on the tool. An electropneumatic impact mechanism, driven by an electric motor of the power tool, is particularly suitable for this purpose. The pneumatic impact mechanism comprises a so-called impactor, which is arranged in the impact chain between a piston of the pneumatic impact mechanism and the tool, and which, by virtue of its mass, delivers the impact impulses to the tool.

[0008] State of the art

[0009] German patent DE 10 2011 081 617 A1 discloses a generic pneumatic impact mechanism for a hand-held 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, which 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, 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 acts on a tool, designed here as a drill bit, from the rear. Elastomeric stops are used for end-position damping of the striker, absorbing some of the kinetic energy at the striker's end positions.The elastomeric stop on the tool side serves to dampen the initial impact, while the elastomeric stop on the piston side serves to dampen the rebound. The initial impact of the piston, during which the tool is no longer in contact with the workpiece, is called the initial impact. Due to the lack of resistance, the impact of the piston propels the tool and the hammer towards the tool-side stop during the initial impact. The hammer's guide tube acts as the front stop. The initial impact damping ensures controlled deceleration of the hammer when the power tool is stopped, preventing excessive rebound and impact. The rebound damping reduces machine vibrations generated by a rebounding hammer during chiseling.

[0010] To prevent the impactor from colliding with the guide tube at full speed, it first strikes the stationary damping element. However, the impactor moves more slowly than before the impact, while the damping element moves faster than the impactor did before the impact. Consequently, the damping element strikes the guide tube, which has a significantly larger mass than the damping element and therefore remains stationary, while the damping element is reflected, thus reversing its direction of motion. Due to this reversal of direction, the damping element and impactor move towards each other, resulting in another collision, the outcome of which depends on the masses and velocities of the colliding objects. Ideally, the damping element reverses its direction once again, and another collision occurs between the guide tube and the damping element.This process repeats until the impactor and the damping material strike the guide tube together, or until the damping material reflected from the guide tube forces the impactor to reverse direction. Since this sequence of successive impacts is practically a semi-elastic collision, some of the kinetic energy is converted into heat or deformation with each impact. This gradually dissipates the impactor's original kinetic energy, and the impactor is progressively slowed down until it either comes to a stop or reverses direction and moves back at a lower speed, which is insufficient to return the piston to its operating point.Furthermore, the gradual reduction of the kinetic energy of the dopper has the positive effect that the guide tube can be dimensioned smaller, since thanks to the damping means it is not only subjected to a very high load once and thus the maximum component stresses are lower.

[0011] The damping elements to be integrated between the guide tube and the end cap are usually multi-part and consist of elastomer elements as well as additional masses for dimensioning the vibration system. These active components must be positioned within the guide tube with the required clearance, necessitating additional fastening devices such as snap rings or similar securing elements.

[0012] CN 102 554 877 A describes a pneumatic impact mechanism of the type relevant here, featuring damping elements for recoil and idle damping of a tapping mechanism. These damping elements are implemented by corresponding insert sleeves within a tapping mechanism housing located upstream of the guide housing. The two insert sleeves provide additional mass for idle and recoil damping, respectively, and are securely held in place within the tapping mechanism housing. Undercut sections of the housing form a rear end stop for the trapezoidal insert rings. These undercut sections of the housing are characterized by a progressively smaller inner diameter. The insert ring is mounted behind this undercut and positively locked in place by the undercut section. When the insert rings are installed, an elastomer ring positioned upstream in the direction of action is pre-tensioned, resulting in a backlash-free assembly.

[0013] The previously known positive-locking connection between the insert ring and the dopper housing has the disadvantage that assembly is only possible with a multi-part design of either the dopper housing or the insert sleeve, in order to position the latter behind the undercut section. The design illustrated in Fig. 5, in contrast to the purely schematic Fig. 2, shows a possibility in which the dopper housing is closed with a cover and the internal components are inserted sequentially. It is also evident that the undercut section is not formed as part of the housing, but rather constitutes a separate ring component. Overall, this results in a multitude of interacting individual components.

[0014] It is therefore the object of the present invention to further improve a pneumatic impact mechanism of the type described above in such a way that the damping means provided for the tapping mechanism, in particular for idle impact damping, are implemented in a component-saving and assembly-friendly manner.

[0015] Disclosure of the invention

[0016] 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 10 specifies a hand-held power tool comprising the pneumatic impact mechanism according to the invention. The dependent claims refer to preferred embodiments of the invention.

[0017] The invention includes the technical teaching that the damping means for a dopper comprise an insert sleeve arranged in the tool-side area of ​​the guide tube to form an additional mass for the idle impact damping, which is inserted into a guide bore of the guide tube in a captive manner, in that a bore shoulder of the guide tube formed by an undercut section forms a rear end stop for the insert sleeve, wherein a front diameter of the guide tube forms an interference fit with an outer diameter of the insert sleeve.

[0018] The undercut section of the guide tube is formed by a rear diameter D1 (in the direction of impact) which is larger than an adjacent front diameter D2 of the guide tube (in the direction of impact). The rear diameter D1 forms a clearance fit with an associated outer diameter D3 of the insert sleeve for axial guidance of the insert sleeve. In contrast, the front diameter D2 forms an interference fit with the outer diameter D3 of the insert sleeve according to the invention.

[0019] Preferably, the press fit between the front diameter D2 of the guide tube and the outer diameter D3 of the insert sleeve is dimensioned according to the following tolerance range:

[0020] -0.0028 * D2 - 0.0281 < (D3 - D2) < 0, preferably:

[0021] -0.0019 * D2 - 0.0272 < (D3 - D2) < -0.0002 * D2 - 0.0122, especially preferably:

[0022] -0.0015 * D2 - 0.0027 < (D3 - D2) < -0.0002 * D2 - 0.0122.

[0023] Particularly preferred is the press fit as an H7 / u6 fit or as a

[0024] H7 / g6 fit is formed.

[0025] These fitting pairings are minor interference fits, in which the shaft is dimensioned slightly larger than the bore. In the application according to the invention, the aim is not to achieve a press fit between the two components, but rather a retaining mechanism. The letter "H" stands for the tolerance range of the bore, which has a fixed upper limit but a variable lower limit, while the term "u6" indicates the tolerance of the shaft, which here extends into the negative range. From a manufacturing perspective, the front diameter D2 of the guide tube can be produced by reaming, while the tolerance on the insert sleeve side can be produced by grinding.

[0026] The solution according to the invention is based on the realization that the tolerance pairing actually intended for creating an interference fit between two components can be used to implement a retention mechanism between two components that are not pressed together. In the application described in the invention, only a small overlap is required to create a rear axial stop for the additional mass of the insert sleeve. This offers the advantage that no radial installation space is lost for the arrangement of the insert sleeve. The guide tube can be made thinner, and the insert mass can be maximized. Furthermore, the tolerance chain required to maintain a constant gap between the insert sleeve, which provides the additional mass, and the guide tube is minimal, since only the insert sleeve and the guide tube are involved.The additional mass can be designed in such a way that all or at least most of it lies behind the undercut section, thus preventing any life-threatening tensile stresses from arising due to the collision.

[0027] In the solution according to the invention, the function of a locking element for the insert sleeve is integrated into the guide tube, thereby functionally and spatially separating the dry-fire damping from the recoil damping without individual fastening elements. Since the dopper is guided longitudinally by the one-piece guide tube in the solution according to the invention, larger and therefore heavier doppers can be accommodated in the available installation space.

[0028] To install the insert sleeve in the guide tube, the additional mass representing the insert sleeve must be pressed through the press fit until the insert sleeve is only connected to and guided by the clearance fit of the guide tube. Once this state is reached, the insert sleeve is axially secured in the direction of the impact piston, as it can only be removed with a very high force when perfectly centered, a force that never occurs during operation.

[0029] According to a further measure improving the invention, it is proposed that the outer diameter D3 of the insert sleeve is provided with a relief section to separate the assignment to the rear diameter D1 of the guide tube on the one hand and to the front diameter D2 on the other.

[0030] Preferably, the insert sleeve interacts with the guide tube for impact damping via an elastomer ring arranged on its end face in the area of ​​a corresponding diameter shoulder. The diameter shoulder ensures reliable positioning of the elastomer ring relative to the insert sleeve. In the installed state of the insert sleeve, the elastomer ring is preferably pre-tensioned against the rear end stop. This allows the insert sleeve to be moved for impact damping only by a shock impulse from the plunger.

[0031] According to a preferred design of the insert sleeve, it consists of a front hollow cylinder section with an outer diameter D3, which interacts with the undercut guide bore of the guide tube, and a rear, relatively larger, externally radial rim section adjoining this on the piston side. Thus, the insert sleeve as a whole has at least a single-stepped cylindrical shape. Preferably, the externally radial rim section of the insert sleeve is at least partially conical and provided with a funnel-shaped opening for the centered reception of a correspondingly shaped stop section of the thumper. This ensures coaxial interaction between the thumper and the insert sleeve during idle impact damping, which relieves stress on the longitudinal guide of the thumper during this peak load.

[0032] According to an alternative embodiment of the inventive recoil damping system, it is proposed that the press fit is located on the outer radial edge section of a guide sleeve, which interacts with a corresponding undercut section of the guide tube. The insert sleeve consists of the rear outer radial edge section with outer diameter D3' and a relatively smaller, front hollow cylinder section with outer diameter D5, adjoining this on the tool-receiving side. The insert sleeve is guided by this, in conjunction with an inner diameter of the guide sleeve. In this embodiment, the guiding and holding functions are thus advantageously further separated.

[0033] According to a preferred embodiment, a dopper suitable for the solution according to the invention comprises coaxially formed rod sections of smaller diameter on both sides of the conical stop section, wherein a tool-side rod section is guided longitudinally through the hollow cylinder section of the insert sleeve. The stop section, on the other hand, comes into sliding contact with the inner wall of the guide tube with its outer circumference.

[0034] According to a further measure improving the invention, it is provided that the axial end stop on the tool side between the guide tube and the outer radial edge section of the insert sleeve is also conically designed for self-centering.

[0035] Detailed description based on drawing

[0036] 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:

[0037] Fig. 1 shows a schematic side view of a pneumatic impact mechanism of a hand-held power tool.

[0038] Fig. 2 shows a detailed longitudinal section of the pneumatic percussion mechanism in the area of ​​the hammer,

[0039] Fig. 3 shows a longitudinal section through a guide tube for the dopper,

[0040] Fig. 4 shows a side view of an insert sleeve arranged in the guide tube,

[0041] Figs. 5 to 5d show a sequence of longitudinal sections to illustrate the assembly of the damping elements for idle vibration damping in the guide tube.

[0042] Fig. 6 shows an enlarged detail view of the damping means for idle vibration damping in the assembled state.

[0043] Fig. 7 shows a functional diagram of the spring mass system of the idle impact damping, and Fig. 8 shows a detailed longitudinal section of the pneumatic impact mechanism in the area of ​​the thumper according to a second embodiment.

[0044] According to Fig. 1, a pneumatic impact mechanism of a rotary hammer (not shown) 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. An opposing impact piston 5, also guided in the guide tube 4, acts in the usual manner on an adjacent striker 6, which in turn strikes a tool 7 in the form of a chisel from the rear.

[0045] According to the schematic diagram in Fig. 2, an insert sleeve 9 is arranged in the guide tube 4, which also surrounds the dopper 6. Together with an elastomer ring 8 arranged at its end face between the insert sleeve 9 and an inner shoulder of the guide tube 4, the insert sleeve 9 forms a damping element for damping the dopper 6 during idle impact. The elastomer ring 8 schematically forms a spring, while the adjacent longitudinally movable insert sleeve 9 represents a mass in the dynamic mass-spring system.

[0046] According to the constructive drawing in Fig. 3, for a captive mounting of the insert sleeve 9 (not shown) in the guide tube 4, a bore shoulder formed by an undercut section 11a constitutes a rear end section 12 for the insert sleeve 9. The undercut section 11 of the guide tube 4 has a larger diameter than an adjacent end section 11b of the guide tube 4.

[0047] According to Fig. 4, the insert sleeve 9 for the guide tube 4 described above consists of a hollow cylinder section 13, which interacts with the undercut section of the guide tube (not shown here) and has an outer diameter for the clearance or press fit, and an outer radial edge section 14 adjoining this on the piston side, which has a funnel-shaped opening 16. The outer circumference of the hollow cylinder section 13 is further provided with a relief groove section 15 to separate the different diameters of the guide tube 4.

[0048] As shown in Fig. 5a, before the insert sleeve 9 is installed in the guide tube 4, the elastomer ring 8 is positioned against an inner shoulder of the guide tube 4. As shown in Fig. 5b, the insert sleeve 9 is then pressed in over the narrow opening section 11b. During this phase, an interference fit exists between the components. Once the opening section 11b has been traversed, the outer diameter of the insert sleeve 9 reaches the larger diameter undercut section 11a, as shown in Fig. 5c. This undercut section, together with the outer diameter of the insert sleeve 9, forms a clearance fit. However, when the insert sleeve 9 is not yet fully inserted, the interference fit with respect to the opening section 11b continues. This interference fit is released, as shown in Fig. 5d, when the insert sleeve 9 is fully inserted into the guide tube 4, at which point the elastomer ring 8 is placed under preload.

[0049] As shown in Fig. 6, in the fully assembled state, the rear end section 12, formed between the undercut section 11a and the opening section 11b, prevents the insert sleeve 9 from sliding out of the guide tube 4. The preload applied by the elastomer ring 8 presses the insert sleeve 9 against the rear end stop 12. In this assembled state, there is a clearance fit between the undercut section 11a and the adjacent opening section 11b with respect to the outer diameter of the insert sleeve 9. The insertion depth is limited by the conical edge section 14 of the insert sleeve 9, which forms an axial end stop for the idle damping on the tool side.

[0050] In the manufacturing process, the opening section 11b is introduced into the front area of ​​the guide tube 4 by means of an H7 bore, creating an edge opposite the adjoining undercut section 11a. Conversely, the insert sleeve 9 has a u6 fit for interaction with the undercut section 11a, which would form an interference fit with the opening section 11b in the guide tube 4. This is followed by a functional surface with a g6 fit corresponding to the opening section 11b, which is separated by the relief section 15 and forms a clearance fit with the opening section 11b of the guide tube 4. When joining the components, the insert sleeve 9 must be pressed into the guide tube 4, preferably after expansion by heating, through the interference fit, until the insert sleeve 9 is only connected to and guided by the guide tube 4 via the clearance fit.

[0051] Once this state is reached, the insert sleeve 9 is axially secured against loss, as it can only be dislodged from its intended position with a large force when centrally aligned, which, however, never occurs during operation. Consequently, the insert sleeve 9 is trapped and pre-tensioned against the undercut section 11a by the elastomer ring 8, which is designed as an O-ring. As a result of this arrangement, the insert sleeve 9 can only be deflected in the tool-side direction by the impact of the plunger.

[0052] Fig. 7 illustrates the functional diagram of the spring mass system of the dry-fire damping, where the guide tube 4 has the diameter D1 of the undercut section, the adjacent smaller diameter D2 of which designates the muzzle section. The difference in diameter forms the rear end stop for the insert sleeve 9 with the outer diameter D3. The insert sleeve 9 simultaneously provides a guide for the coaxially penetrating hammer 6, which is also guided into the shoulder of the guide tube 4 as shown. In the sequence of the impact chain S, the impact piston 5 acts on the hammer 6, which in turn acts on the tool 7.

[0053] The schematic diagram illustrates that the inner diameter D1 of the guide tube 4 is larger than the outer diameter D3 of the insert sleeve 9, resulting in a clearance fit with a gap of < 0.12 mm. In contrast, the diameter D2 of the muzzle section on the guide tube 4 is smaller than the outer diameter D3 of the insert sleeve 9, thus forming an interference fit. The interference in this embodiment is < 0.06 mm, which is sufficient for adequate retention. The axial length L1 of the insert sleeve 9 is shorter than the axial length L2, which is defined by the inner diameter D1 of the guide tube 4, representing the undercut section. This creates an axial clearance in the range of 0.1 to 2.5 mm, which, in conjunction with the spring action of the elastomer element 8, is sufficient to achieve effective recoil damping.

[0054] According to the second embodiment illustrated in Fig. 8, the insert sleeve 9' has a rear outer radial edge section 13' with an outer diameter D3' which interacts with the undercut section 11a' of the guide tube 4', thereby realizing the holding function in conjunction with the end stop 12'. Adjoining this, on the tool-receiving side, is a front hollow cylinder section 14' with a smaller diameter and an outer diameter D5, which guides the insert sleeve 4' in conjunction with a corresponding inner diameter D4 of the guide sleeve 4'.

[0055] The invention is not limited to the preferred embodiment described above. Rather, variations thereof are also conceivable, which are included in the scope of protection of the following claims. For example, it is also conceivable that the axial length of the insert sleeve is greater and that, corresponding to the muzzle section, a smaller diameter than diameter D3 is connected, which also ensures a clearance fit with respect to the muzzle section. Furthermore, it remains possible to combine the recoil damping for the dopper according to the invention with a recoil damping arranged in the piston-side area of ​​the guide tube.

[0056] Reference symbol list

[0057] 1 electric motor

[0058] 2 Crank drive

[0059] 3 exciter pistons

[0060] 4 / 4' guide tube

[0061] 5 impact pistons

[0062] 6 Döpper

[0063] 6a Stop section

[0064] 6b first rod section

[0065] 6c second bar section

[0066] 7 tools

[0067] 8 elastomer ring

[0068] 9 / 9' Insert sleeve

[0069] 11a Undercut section

[0070] 11b Mouth section

[0071] 12 / 12' End stop

[0072] 13 / 13' hollow cylinder section / rim section

[0073] 14 / 14' edge section / hollow cylinder section

[0074] 15 Free stitch

[0075] 16 Opening

[0076] D1 inner diameter of the undercut section

[0077] D2 inner diameter of the mouth section

[0078] D3 outer diameter of the hollow cylinder section of the insert sleeve

[0079] L1 axial length of the insert sleeve

[0080] L2 axial length of the undercut section of the guide tube

[0081] S shock chain

Claims

REQUIREMENTS 1. Pneumatic impact mechanism for a drill or chisel hammer, comprising a hammer (6) acted upon by a piston (5) for the rear impact of a tool (7), wherein the hammer (6) is arranged longitudinally guided in an associated guide tube (4) which is equipped with end-end damping means for rebound and dry-blow damping of the hammer (6), which comprise an insert sleeve (9) arranged in the tool-side region of the guide tube (4) for forming an additional mass for dry-blow damping, which is inserted into the guide tube (4) in a captive manner by a bore shoulder of the guide tube (4) formed by an undercut section (11a) forming a rear end stop (12) for the insert sleeve (9), wherein the undercut section (11a) of the guide tube (4) is formed by a rear diameter (D1) which is larger than an adjacenta front diameter (D2) of the guide tube (4) formed by a muzzle section (11b), wherein the rear diameter (D1) also forms a clearance fit with an associated outer diameter (D3) of the insert sleeve (9), characterized in that the front diameter (D2) forms an interference fit with the outer diameter (D3) of the insert sleeve (9).

2. Pneumatic impact mechanism according to claim 1, characterized in that the press fit between the front diameter (D2) of the guide tube (4) and the outer diameter (D3) of the insert sleeve (9) is dimensioned according to the following tolerance range: -0.0028 * D2 - 0.0281 < (D3 - D2) < 0, preferably: -0.0019 * D2 - 0.0272 < (D3 - D2) < -0.0002 * D2 - 0.0122, especially preferably: -0.0015 * D2 - 0.0027 < (D3 - D2) < -0.0002 * D2 - 0.0122.

3. Pneumatic impact mechanism according to claim 1, characterized in that the interference fit is designed as an H7 / u6 fit.

4. Pneumatic impact mechanism according to claim 2, characterized in that the outer diameter (D3) of the insert sleeve (9) is provided with a relief section (15) for separating the connection to the rear diameter (D1) of the guide tube (4) on the one hand and to the front diameter (D2) on the other.

5. Pneumatic impact mechanism according to any one of the preceding claims, 5. Pneumatic impact mechanism according to claim 2, characterized in that the insert sleeve (9) interacts with the guide tube (4) for idle impact damping via an elastomer ring (8) arranged on the end face in the area of ​​a corresponding diameter step.

6. Pneumatic impact mechanism according to one of the preceding claims, characterized in that the insert sleeve (9) consists of a front hollow cylinder section (13) with outer diameter (D3) cooperating with the undercut section (11a) of the guide tube (4) and a rear, relatively larger outer radial edge section (14) adjoining it on the impact piston side, so that the insert sleeve (9) has an overall cylindrical shape of at least a single stepped shape.

7. Pneumatic impact mechanism according to one of claims 1 to 5, characterized in that the insert sleeve (9') consists of a rear outer radial edge section (13') with outer diameter (D3') cooperating with the undercut section (11a') of the guide tube (4') and a front, relatively smaller hollow cylinder section (14') with outer diameter (D5) adjoining it on the tool receiving side, whereby the insert sleeve (4') is guided in conjunction with an inner diameter (D4) of the guide sleeve (4').

8. Pneumatic impact mechanism according to claim 6 or 7, characterized in that the outer radial edge section (13'; 14) of the insert sleeve (9) is at least partially conical and is equipped with a 16 funnel-shaped opening (16) for the centering reception of a correspondingly shaped stop section (6a) of the dopper (6) is provided.

9. Pneumatic impact mechanism according to claim 8, characterized in that the hammer (6) has coaxially formed rod sections (6b, 6c) of smaller diameter on both sides of the conical stop section (6a), wherein a tool-side rod section (6b) is guided longitudinally through the hollow cylinder section (9) of the insert sleeve (9).

10. Pneumatic impact mechanism according to any one of the preceding claims, characterized in that the tool-side axial end stop between the guide tube (4) and the outer radial edge section (14) of the insert sleeve (9) is conically formed.

11. Hand-held power tool, in particular a rotary hammer or chisel hammer, comprising a pneumatic impact mechanism according to any one of the preceding claims.

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