Electric tool with a pneumatic striking mechanism, comprising a striking piston valve

Abstract

Power tool with a pneumatic impact mechanism (3) for alternately striking a tool (6), comprising a guide tube (9) received by a guide housing part (8) of the machine housing (7), in which an exciter piston (10) and an opposing impact piston (11) are dynamically sealed, wherein an impact piston valve (15) for overpressure venting of the movement space (14) in the case of idle impact is arranged in a tool-side annular gap (13) between the guide housing part (8) and the guide tube (9), which is part of a movement space (14) of the impact piston (11) located in the direction of impact in front of the impact piston (11).

Description

[0001] The present invention relates to a power tool with a pneumatic impact mechanism for alternatingly striking a tool, comprising a guide tube received by a guide housing part of the machine housing, in which an exciter piston and an opposing impact piston are dynamically sealed and guided.

[0002] The invention's scope of application 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. Mechanical loads generated during drilling and / or chiseling typically act back on the drive components, manifesting themselves, among other things, as disruptive vibrations. State of the art

[0003] EP 3 181 298 A1 discloses a generic power tool with a pneumatic impact mechanism. The rotary drive motion of this mechanism, generated by an electric motor, is converted via an eccentric drive (referred to here as a deflection device) into a linearly alternating drive motion of an exciter piston of the pneumatic impact mechanism. The exciter piston is dynamically sealed and separated from a striking piston within a guide tube by an air column. Continuing the coaxial chain of action, a so-called impactor is connected to the striking piston. This impactor applies shock impulses to the rear of the tool held in a tool holder. The impactor is guided by a guide housing component, which, in this prior art, is directly integrally formed with the guide tube in a coaxial extension.

[0004] A ring-shaped check valve is arranged on the guide tube. This valve is aligned with an outlet opening in the outer surface of the guide tube and features a closing mechanism to prevent airflow from inside the guide tube. During impact operation, the outlet opening in the guide tube is closed by being covered by the impact piston; otherwise, it is open. This allows the check valve to open when the impact piston performs a so-called "dry strike." The air spring of the pneumatic impact mechanism is deactivated by the inflow of air into the intermediate piston area. However, the check valve prevents air from escaping from this area, ensuring immediate operational readiness when the tool is repositioned. This valve mechanism thus contributes to increased user comfort.

[0005] In this known power tool, the impactor can be re-excited by the tool even after a period of inactivity. This is caused by a change in the so-called impulse coefficient, the ratio of the impactor's approach velocity to its return velocity. The impact piston is re-excited by the impactor, in this case again passing over the outlet openings in the guide tube and being drawn back in by the exciter piston. This causes the power tool to re-excite, producing an unpleasant noise accompanied by high vibrations.

[0006] The object of the present invention is to further improve a generic power tool with a pneumatic impact mechanism in such a way that re-striking is avoided using simple technical means. Disclosure of the invention

[0007] 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.

[0008] The invention includes the technical teaching that a piston valve for overpressure venting of the movement space in the case of a dry strike is arranged in an annular gap on the tool side between the guide housing part and the guide tube, which is part of a movement space of the piston located in the direction of impact in front of the piston.

[0009] According to the invention, the air volume located in front of the piston opens the piston valve in the preferred direction by means of overpressure. The piston valve closes when pressure equalization occurs, i.e., when pressure equilibrium exists before and after the piston valve. For this purpose, the piston valve is preferably connected via a venting annular gap running along the guide tube between the guide tube and the guide housing part to a space arranged radially outside the guide housing part, in particular a striking mechanism and / or gear chamber.

[0010] According to a further improvement of the invention, the guide tube has at least one vent hole connected to the annular vent gap in the tool-side end region. This vent hole is closed by the impact piston during idle operation. The at least one vent hole, preferably designed as a series of vent holes along the circumference of the guide tube, is only open during operation. This virtually eliminates the possibility of the impact piston rebounding, which would otherwise occur due to the exciter piston's excitation. This ensures that no losses occur through the valve during normal operation. During idle operation, the valve generates a braking effect during the impact piston's return stroke, preventing rebound or aiding in shutting down the piston.

[0011] In this arrangement, the circulated air volume flows exclusively through the vent holes during operation. The piston valve only becomes active during idle operation.

[0012] The piston valve is preferably designed in the manner of a groove ring or shaft seal and comprises a rigid retaining ring on which a radially resilient, obliquely extending sealing lip made of an elastomeric material is formed.

[0013] According to a first embodiment, the piston valve housing is fixedly arranged on the guide housing part, for example pressed in, and comes into radial sealing contact with the outer surface of the guide tube in an elastic manner.

[0014] According to a second embodiment, the piston valve can also be attached to the outer surface of the guide tube, for example pressed on, and comes into radial sealing contact with the guide housing part in an elastic manner.

[0015] As an alternative to designing the piston valve as an additional component, it can also be integrated into a radial damping element of the guide tube. Such a radial damping element consists of an elastomer material and is arranged on the tool mounting side between the guide tube and the guide housing part. Detailed description based on drawing

[0016] 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: Fig. 1 a schematic, partially cutaway side view of a power tool, here in the form of a rotary hammer, Fig. 2 a schematic longitudinal section in the tool-holder side area of ​​the pneumatic impact mechanism in a first piston position, Fig. 2 a schematic longitudinal section in the tool-holder side area of ​​the pneumatic impact mechanism in a second piston position, Fig. 3 a schematic longitudinal view in the area of ​​the pneumatic impact mechanism with a tool holder arranged thereon with an integrated impact piston valve as an additional component in a first piston position, Fig. 3 a schematic longitudinal view in the area of ​​the pneumatic impact mechanism with a tool holder arranged thereon with an integrated impact piston valve as an additional component in a second piston position, Fig.Fig. 4a shows a schematic longitudinal view in the area of ​​the pneumatic impact mechanism with a tool holder arranged thereon and an impact piston valve integrated in a radial damping element in a first piston position, and Fig. 4b shows a schematic longitudinal view in the area of ​​the pneumatic impact mechanism with a tool holder arranged thereon and an impact piston valve integrated in a radial damping element in a second piston position.

[0017] According to Fig. 1 A power tool in the form of a rotary hammer essentially consists of an electric motor 1, whose rotary motion is converted into a linear alternating working motion via an eccentric drive 2 and transmitted to a pneumatic impact mechanism 3. The pneumatic impact mechanism 3 acts on a striker 4, whose impact mass in turn acts backward on a tool 6 inserted in a tool holder 5. The aforementioned drive components, including the pneumatic impact mechanism, are housed in a machine casing 7, from which the tool holder 5 protrudes.

[0018] According to Fig. 2a A guide housing part 8 of a machine housing 7 (not shown here) surrounds a guide tube 9 of the pneumatic impact mechanism 3, in which an exciter piston 10 and an opposing impact piston 11 are dynamically sealed and separated from a working pressure chamber 12.

[0019] In an axially located annular gap 13 on the tool side, situated between the hammer 4 and the impact piston 11, and radially extending between the guide housing part 8 and the guide tube 9, and forming part of a movement space 14 of the impact piston 11 located in the direction of impact, an impact piston valve 15 is arranged for overpressure venting of the movement space 14 located in the direction of impact in the event of a dry strike. The impact piston valve 15 is, on the other hand, connected via a venting annular gap 16 running along the guide tube 9 between the tube and the guide housing part 8 to a space arranged radially outside the guide housing part 8, in particular a striking mechanism and / or gear chamber. The impact piston valve 15 is designed as a check valve that blocks airflow towards the movement space 14.

[0020] The guide tube 9 is provided in the tool-side end area with several venting bores 17 connected to the venting annular gap 16, which are closed in the case of idle striking by being covered by the striking piston 11 in the piston position shown.

[0021] According to Fig. 2b In contrast, the vent holes 17 are open in the operating state, in which the exciter piston 10 is in the retracted drive-side position and pulls the striking piston 11 along via the pressure in the working chamber 12. The exciter piston 10 is driven directly via the eccentric drive 2 and the connecting rod. In the operating state, the striking piston 11, driven by the air spring, moves back and forth between the striking piston 11 and the exciter piston 10, striking the tumbler 4 at the forward point, which then transfers the energy to the tool 6. The in Fig. 2b The position shown corresponds to the forwardmost position of the striking piston 11 just before impact with the striker 4. The holes 17 prevent any braking effect from the valve 15, which would otherwise undesirably reduce the striking power during normal operation. In the case of a dry strike, the striker 4 can move further forward, allowing the striking piston 11 to also travel further forward. As soon as the striking piston 11 passes over or covers the holes 17, the valve 15 becomes active and allows air in area 14 to escape into the striking mechanism housing. When the striking piston 11 attempts to retract after impact with the striker 4, it is slowed by the building-up negative pressure in area 14. This facilitates the shutdown of the striking mechanism 3.

[0022] According to Fig. 3a The impact piston valve 15 is designed as an additional component and is fixed to the guide tube 9 in the housing. The impact piston valve 15 seals radially against the guide housing part 8. During normal operation, the front vent holes 17a are open, so that the movement chamber 14 of the impact piston 11 is directly connected via the vent annular gap 16 to a radially externally arranged chamber, in particular a striking mechanism and / or gear chamber, i.e., it is vented in the piston position shown.

[0023] In the Fig. 3b The impact piston 11 is in the tool-mounting side stop position, so that the series of vent holes 17 vent the working pressure chamber 12.

[0024] The piston valve 15 consists of a rigid ring element 18 made of a hard elastomer, which also dampens the guide tube 9 relative to the guide housing part 8. In addition, the ring element 18 forms the support structure for a sealing lip section 19 for air passage to the outside, thus fulfilling the check valve function described above.

[0025] According to the alternative embodiment as follows Fig. 4a The impact piston valve 15' is directly integrated into a radial damping element 20, in which the impact piston valve 15' is integrally formed as an axial extension of the radial damping element 20. The radial sealing element 15 acts between the tool holder 5 and the guide housing part 8 to dampen mechanical loads applied on the tool side. The movement chamber 14 of the impact piston 11 is connected via the front vent bores 17a and the vent annular gap 16 to the radially outer chamber, in particular a percussion mechanism and / or gear chamber, and is thus vented in the piston position shown.

[0026] According to Fig. 4b The impact piston 11 is in the stop position on the tool holder side. Venting of the movement chamber 14 takes place via the impact piston valve 15'. Bezugszeichenliste

[0027] 1 Electric motor 2 Eccentric drive 3 Impact mechanism 4 Dropper 5 Tool holder 6 Tool 7 Machine housing 8 Guide housing part 9 Guide tube 10 Exciter piston 11 Impact piston 12 Working pressure chamber 13 Annular gap 14 Movement chamber 15 Impact piston valve 16 Venting annular gap 17 Venting holes 18 Ring element 19 Sealing lip section 20 Radial damping element

Claims

1. Power tool with a pneumatic impact mechanism (3) for alternately striking a tool (6), comprising a guide tube (9) received by a guide housing part (8) of the machine housing (7), in which an exciter piston (10) and an opposing impact piston (11) are dynamically sealed and guided, characterized by the fact that In a tool-side annular gap (13) between the guide housing part (8) and the guide tube (9), which is part of a movement space (14) of the impact piston (11) located in the direction of impact in front of the impact piston (11), an impact piston valve (15) is arranged for overpressure venting of the movement space (14) in the case of a dry impact.

2. Power tool according to claim 1, characterized by the fact thatthe impact piston valve (15) is connected via a venting annular gap (16) running along the guide tube (9) between this and the guide housing part (8) to a radially outside space, in particular an impact mechanism and / or gear room.

3. Power tool according to claim 2, characterized by the fact that the guide tube (9) has at least one venting bore (17) connected to the venting annular gap (16) in the tool-side end area, which is closed in the case of idle firing by being covered by the impact piston (11).

4. Power tool according to one of the preceding claims, characterized by the fact that the piston valve (15) is designed in the manner of a single-acting internally or externally sealing groove ring.

5. Power tool according to claim 4, characterized by the fact that the piston valve (15) is fixed to the housing on the guide housing part (8) and comes into elastic contact with the outer surface of the guide tube (9) in a radially sealing manner.

6. Power tool according to claim 4 or 5, characterized by the fact that the piston valve (15) is attached to the outer surface of the guide tube (9) and comes into elastic contact with the guide housing part (8) in a radially sealing manner.

7. Power tool according to claim 5 or 6, characterized by the fact that the piston valve (15) consists of a rigid ring element (18) for connecting to the guide housing part (8) or the guide tube (9) and of a sealing lip section (19) for air passage in the direction of the radially outside space.

8. Power tool according to one of the preceding claims, characterized by the fact that the impact piston valve (15') is integrated into a radial damping element (20) of the guide tube (9).

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