EP3389931A1

EP3389931A1 - Percussive power tool

Info

Publication number: EP3389931A1
Application number: EP16809702.0A
Authority: EP
Inventors: Stefan Schmid; Markus Holubarsch; Markus Hartmann; Eduard Pfeiffer
Original assignee: Hilti AG
Current assignee: Hilti AG
Priority date: 2015-12-15
Filing date: 2016-12-06
Publication date: 2018-10-24
Also published as: US10821589B2; WO2017102418A1; EP3181298A1; US20180370007A1

Abstract

The invention relates to a percussion mechanism (6) containing a guide tube (16), an exciter (13), a hammer (14), a pneumatic chamber (20) for coupling the hammer (14) to the motion of the exciter (13), a striker (15), and a seat (25) for the striker (15). The hammer (14) has a striking point, which is defined by a striking surface (24) of the striker (15) when the striker (15) lies against the seat (25). A check valve (26) has an outlet opening (29) and a closing mechanism (28) for closing the check valve (26) against an air flow from the interior of the guide tube (16). The outlet opening (29) is arranged in such a way that the outlet opening (29) is closed by the hammer (14) during striking operation and otherwise is open.

Description

Beating machine tool

FIELD OF THE INVENTION

The present invention relates to a hitting machine tool, in particular a hand-held pneumatic hammer drill and a hand-held pneumatic electric chisel. A hand-held pneumatic hammer drill has a pneumatic percussion driven by a motor. A pneumatic chamber forms an air spring which couples a racket to an exciter moved by the motor. The hammer mechanism is deactivated if the user does not apply pressure to the tool to protect the hammer from excessive loading. As soon as the user presses the hammer to the tool, the hammer mechanism starts to work again. In high-performance machines, the guiding of the hammer when re-pressing proves to be difficult to control.

DISCLOSURE OF THE INVENTION

The machine tool according to the invention has a tool holder for holding a striking tool on a working axis, a motor and a striking mechanism. The striking mechanism includes a guide tube, a pathogen forcedly moving in the guide tube along the working axis by the motor, a racket slidable in the guide tube along the working axis, a pneumatic chamber closed by the exciter and the racket in the guide tube for coupling the racket to the movement of the pathogen, a striker and a seat for the striker. The striking mechanism has a striking point for the club, which is defined by a striking surface of the striker facing the club when the striker bears against the seat against the direction of impact. A check valve has an outlet opening arranged in the guide tube and a closing mechanism for closing the check valve against an air flow from inside the guide tube. The outlet opening is arranged along the working axis such that the racket closes the outlet opening with respect to the pneumatic chamber when the racket in the direction of impact before The point of impact is such that the pneumatic chamber overlaps the outlet opening when the bat is moved beyond the impact point in the direction of impact.

The outlet opening of the check valve is closed by the bat in the beating operation of the percussion mechanism and is opened when the racket fails. The check valve allows air to flow into the pneumatic chamber and deactivates the air spring of the pneumatic chamber. However, the check valve does not allow air to escape from the pneumatic chamber. This proves to be advantageous when re-attaching the hammer drill. The user must move the tool, the striker and the club against the pressure in the pneumatic chamber. The back pressure allows for better guidance.

An embodiment provides that the closing mechanism has at least one elastic flap. The locking mechanism can open and close quickly and at a low pressure gradient. The closing mechanism based on one or two elastic valves has a low mass, which are quickly actuated even at the low forces due to the low pressure gradient.

One embodiment provides that the flap is biased into a position closing the check valve. Although the check valve is already closed by the club in beating operation, a normally closed locking mechanism proves to be more suitable for the dynamics.

An embodiment provides that the guide tube has a throttle opening. The throttle opening preferably allows a small but continuous air flow between the pneumatic chamber and the environment to ensure pressure equalization. An embodiment provides that the throttle opening has a smaller diameter than the outlet opening of the check valve. The check valve, if opened by the club, dominates the pressure in the pneumatic chamber. An embodiment provides that the cross-sectional area of the throttle opening is less than 6% of the cross-sectional area of the outlet opening. The start of the impact mechanism is hindered by the construction with the check valve. A pressure equalization with the environment lifts the obstruction delayed. The diameter of the throttle opening is preferably adapted as indicated to the air moved by the exciter.

BRIEF DESCRIPTION OF THE FIGURES The following description explains the invention with reference to exemplary embodiments and figures. In the figures show:

Fig. 1 a hammer drill

Fig. 2 shows a striking mechanism on impact, i. 3 the impact mechanism at idle with two positions of the exciter FIG. 4 a striking mechanism with a nonreturn valve FIG. 5 a striking mechanism with a nonreturn valve FIG. 6 a striking mechanism with a non-return valve

Identical or functionally identical elements are indicated by the same reference numerals in the figures, unless stated otherwise.

EMBODIMENTS OF THE INVENTION

Fig. 1 shows an example of a chiseling hand tool 1 schematically a hammer drill 1. The hammer drill 1 has a tool holder 2, in which a shank end 3 of a chisel 4, can be inserted and locked. The bit 4 is an example of beating tools, the hammer drill 1 can also accommodate other beating tools, such as percussive drill bit 4, drill bits, etc. A primary drive of the hammer drill 1 is a motor 5, which drives a striking mechanism 6 and an output shaft 7. A battery pack 8 or a power line supplies the motor 5 with power. A user can lead the hammer drill 1 by means of a handle 9 and take the hammer drill 1 by means of a system switch 10 in operation. In operation, the hammer drill 1 rotates the drill 4 continuously about a working axis 11 and can beat the bit 4 in the direction of impact 12 along the working axis 11 in a substrate. The hammer drill 1 is an example of chiseling hand-held machine tools 1, which are also non-rotating hand tool machines, e.g. may comprise an electric chisel.

The chisel 4 is movably supported in the tool holder 2 along the working axis 11. The chisel 4 is in working mode by a direction of impact 12 on the hammer drill. 1 acting contact pressure held in a working position. The contact pressure can be applied among other things by the user or the own weight of the hammer drill 1. The chisel 4 is in the working position against the direction of impact 12 at a stop. The percussion 6 exerts periodic blows on the bit 4, whereby this is driven from the working position in the direction of impact 12 to remove the substrate. After the strike, the chisel 4 returns to the working position, as long as the contact pressure is maintained. The contact pressure may be absent, for example, if the user lifts the hammer drill 1 including the bit 4 from the ground. In this case, the bit 4 can lie in the direction of impact 12 offset from the working position.

The percussion 6 has along the working axis 11 in the direction of impact 12 successively a pathogen 13, a bat 14 and an anvil 15. The exciter 13 is driven by the motor 5. The bat 14 follows coupled via an air spring the movement of the exciter 13. The bat 14 strikes in the direction of impact 12 on the striker 15. The striker 15 passes the blow on the chisel 4, which is pressed by the contact pressure against the tool-side end of the striker 15.

The percussion 6 has a guide tube 16 which is suspended parallel or coaxial with the working axis 11 in the machine housing 17. The racket 14 and the exciter 13 are arranged in the guide tube 16. The racket 14 and the exciter 13 are piston-shaped, i. its circumference is on the inner surface 18 of the guide tube 16 airtight. Sealing rings can improve the airtight seal of the racket 14 or exciter 13 with the guide tube 16. The guide tube 16 carries bat 14 and exciter 13 along the working axis eleventh

The exciter 13 is forced by the motor 5 along the working axis 11 in a periodic forward and backward movement. The exciter 13 is connected via a mechanical deflection device 19 to the motor 5. The deflection device 19 includes, for example, an eccentric or a wobble finger and converts the rotational movement of the motor 5 in the periodic linear forward and backward movement. The exciter 13 moves as soon as and as long as the system switch 10 is actuated, that is, as long as the motor 5 rotates.

The exciter 13 and the bat 14 close between a pneumatic chamber 20 within the guide tube 16, which acts as an air spring. The air spring couples the bat 14 to the movement of the exciter 13. The forced-motion exciter 13 periodically compresses and decompresses the pneumatic chamber 20. The pressure in the pneumatic chamber 20 acts on one side on a counter to the direction of impact 12 facing rear 21 of the racket 14. On a front side 22 of the racket 14 substantially acts the pressure in the machine housing 17, which is typically equal to the atmospheric pressure of the environment. The front side 22 is ventilated, for example, via large openings 23 at the front end of the guide tube 16. The pressure difference between the rear side 21 and the front side 22 accelerates the racket 14 in the direction of impact 12 or counter to the direction of impact 12. The racket 14 follows the movement of the pathogen 13 with some delay. The racket 14 oscillates between an impact point (see FIG. in which the racket 14 strikes a striking surface 24 of the striker 15, and a turning point near the exciter 13. The distance traveled by the racket 14, ie the relative position of the striking point to the exciter 13, is tuned so that the movement of the Bat 14 is in chiseling operation in synchronism with the movement of the exciter 13. The striker 15 is movable along the working axis 11. The striker 15 is held by means of the contact pressure of the hammer drill 1 in the working position. The bit 4 presses counter to the impact direction 12 on the striker 15. The striker 15 is pushed into the hammer drill 1 until the striker 15 comes to rest on a seat 25 provided for him. The seat 25 may be annular, for example, and the striker 15 abuts the seat 25 with an annular shoulder. The striking surface 24 of the striker 15 lies on the impact point when the striker 15 abuts the seat 25.

The hammer drill 1 automatically switches off the chiseling operation when the user lifts the hammer drill 1 off the ground and thus releases the contact pressure. The striker 15 is no longer forced into the working position, ie adjacent to the seat 25, but may be offset from the working position in the impact direction 12 (FIG. 3). The bat 14 can therefore fly beyond the impact point in the direction of impact 12 before the bat 14 strikes the striker 15. The guide tube 16 is provided with a check valve 26. The check valve 26 has an inlet opening 27, a closing mechanism 28 and an outlet opening 29. The check valve 26 allows an air exchange of the pneumatic chamber 20 with the environment, ie the interior of the machine housing. The outlet port 29 is a radial aperture through the wall of the guide tube 16. The outlet port 29 is offset, for example, at or less than 2 mm from the plane of the back 21 of the racquet 14 when the racquet 14 is in the point of impact. The outlet opening 29 is arranged along the working axis 11 so that the racket 14, the outlet opening 29 during the chiselling operation against the pneumatic chamber 20 closes. Air exchange between the environment and the pneumatic chamber 20 is prevented during chiseling operation. As described above, the bat 14 moves in chiseling operation in the direction of impact 12 only up to the point of impact. The beater 14 preferably partially or completely covers the outlet opening 29 at the point of impact (FIG. 2). The outlet opening 29 is opened relative to the pneumatic chamber 20 when the bat 14 slides in the direction of impact 12 beyond the impact point (FIG. 3). The pneumatic chamber 20 overlaps with the outlet opening 29, corresponding to an exchange of air with the environment is possible. When attaching the hammer drill 1 is still missing the contact pressure, the striker 15 and the bat 14 typically slip in the direction of impact 12, whereby the check valve 26 is opened and an exchange of air is possible.

The check valve 26 has a predetermined flow direction 30 from its inlet opening 27 to its outlet opening 29. An air flow can pass in the flow direction 30, the check valve 26; However, the check valve 26 locks in a flowing against the flow direction 30 air flow. The exciter 13 can thus suck air through the check valve 26 into the pneumatic chamber 20, but do not blow out air from the pneumatic chamber 20. The amount of air in the pneumatic chamber 20 settles after several cycles and remains constant. The amount of air corresponds to the amount of air of the maximum volume of the pneumatic chamber 20 at ambient pressure. The maximum volume of the pneumatic chamber 20 has the exciter 13 in the position facing away from the racket 14 and the bat 14 in its direction of impact 12 at the furthest advanced position. The exciter 13 continues to move, whereby the amount of air is periodically compressed. The mean pressure in the pneumatic chamber 20 is therefore greater than the ambient pressure when the bat 14 is positioned beyond the impact point. The bat 14 is held by the increased pressure in the opposite of the impact point in the direction of impact 12 advanced position. The check valve 26 is kept open by the pressure.

When attaching the bit 4 to the ground of the striker 15 and the bat 14 are pushed into the working position or the point of impact. The bat 14 compresses the amount of air kept constant in the pneumatic chamber 20. The user thus senses a back pressure, which makes it easy to start. The back pressure is maintained for several cycles of the exciter 13. The pressure in the pneumatic chamber 20 hampers start-up of the impact mechanism, since the pressure in the beater 14 in the Holding point. The mean pressure builds up over the duration of several cycles of the exciter 13 continuously down to the ambient pressure. The percussion 6 increasingly begins to move the racket 14, whereby the percussion power increases continuously with decreasing average pressure in the pneumatic chamber 20.

The pressure equalization of the pneumatic chamber 20 with the environment takes place slowly through a throttle opening 31. The throttle opening 31 is a radial opening in the guide tube 16. The typically single throttle opening 31 has a small cross-sectional area. The cross-sectional area is in the range of 0.05% to 0.20% of the area of the rear face 21 of the racquet 14. The small cross-sectional area is sufficient to compensate losses of the air quantity, especially during compression, and sufficiently low to reduce the dynamics of the Air spring not materially affect.

The throttle opening 31 may be arranged along the working axis 11 in different positions. The throttle opening 31 is preferably close to the tool-near

Reversal point of the exciter 13 arranged (Fig. 3, upper half). For example, the

Throttle opening 31 between 2 mm and 5 mm in the direction of impact 12 after the reversal point.

The exciter 13 does not reach the throttle opening 31. The bat 14 hides the

Throttle opening 31 at the compression point, i. in his tool-reversing point. Alternatively, the throttle opening 31 may be at another location before

Be point of at least temporarily overlap with the pneumatic chamber 20 during the beating operation.

A cross-section of the throttle opening 31 is significantly smaller than the cross section of the check valve 26 and its inlet and outlet opening 29. As long as the racket 14 opens the check valve 26 by its position beyond the impact point, the air flow through the check valve 26 dominates the pressure in the The cross-sectional area of the throttle opening 31 is at least a hundredth of the cross-sectional area of the outlet opening 29. The check valve 26 preferably has a plurality of outlet openings 29 whose respective cross sections for comparison with the cross section of the throttle opening 31 are to be summed. The throttle opening 31 has a maximum cross-sectional area of at most 0.20% of the cross-sectional area of the pneumatic chamber 20. The amount of air in the pneumatic chamber 20 preferably halves within a period of 500 milliseconds (ms) to 800 ms depending on the size of the percussion mechanism 6 about ten to fifty cycles of the pathogen 13 equivalent. The Schlagwerk 6 begins its beating effect typically after the amount of air is halved.

The check valve 26 must open and close sufficiently quickly. The closing mechanism 28 of the check valve 26 is formed by two annular, elastic flaps 32, which are arranged in a channel 33 of the check valve 26. The two flaps 32 are at their edge closer to the inlet opening 27, e.g. the radially outer edge, fixed in a carrier 34. The mutually facing inner surfaces of the flaps 32 are spaced in the region of inlet opening 27. The flaps 32 are inclined relative to the flow direction 30 and run in the flow direction 30 towards each other. The inner surfaces of the flaps 32 contact each other in the region of the edges closer to the outlet opening 29, e.g. the radially inner edges. The inner surfaces may abut each other under a bias applied by the flap. The flaps 32 each have an outer surface facing away from the inner surface. The outer surface is exposed in the region of the outlet opening 29 and can be correspondingly flowed. The flaps 32 protrude into the, for example, funnel-shaped channel 33 which widens in the direction of the outlet opening 29. The closing mechanism 28 can alternatively be realized with a flap whose outlet edge 29 comes closer to rest on an inner surface of the channel 33. The two flaps 32 are made of rubber or a synthetic rubber. The flaps 32 are loaded with no spring.

Fig. 4 shows another embodiment of a check valve 35 with an elastic flap 36. The check valve 35 has an inlet opening 27 and an outlet opening 29, in particular the latter is arranged and designed the same as in the embodiment described in connection with FIG. The check valve 35 has a housing 37 which rests airtight on the guide tube 16. The housing 37 has two openings which form the inlet opening 27 and the outlet opening 29. The flap 36 is disposed adjacent to the inlet opening 27 within the cavity of the housing 37. The flap 36 closes and opens the inlet port 27. The flap 36 may be formed of an elastic tube covering the inlet port 27. The flap 36 is entirely made of rubber or a synthetic rubber. The flap 36 is loaded with no spring. An air flow along the flow direction 30 pushes the flap 36 away from the inlet opening 27 and can flow through the housing 37 and the outlet opening 29 into the pneumatic chamber 20. An air flow opposite to the flow direction 30 presses the flap 36 against the inlet opening 27 and blocks the check valve 35. The flap 36 may be resiliently biased against the inlet opening 27. Fig. 5 shows another embodiment of a check valve 38 with an elastic closure element 39. The closure element 39 is, for example, an elastic ring made entirely of rubber or a synthetic rubber. The check valve 38 has a housing 40 which bears sealed against the guide tube 16. The housing 40 forms the inlet opening 27 and the outlet opening 29. The outlet opening 29 is arranged and designed as in the previous embodiments. The housing 40 has a counter to the flow direction 30 tapered channel in which the closure element 39 is arranged. The closure element 39 preferably rests against the inlet opening 27 under its elastic residual stress. The closure element 39 can be elastically deformed radially, ie perpendicular to the working axis 11, whereby the inlet opening 27 is released.

Fig. 6 shows another embodiment of a check valve 41. The check valve 41 has a movable closure element 42. A housing 43 forms the inlet opening 27 and the outlet opening 29. The outlet opening 29 is arranged and designed as in the preceding embodiments. The housing 43 has a counter to the flow direction 30 tapered channel, in which the closure element 42 is arranged. The closure element 42 is movable along the flow direction 30. The closure element 42 is, for example, a ring made of rubber or synthetic rubber. The closure element 42 is acted upon by no spring.

Claims

claims

1 . Beating Machine Tool (1) with

a tool holder (2) for holding a striking tool (4) on a working axis (1 1),

a motor (5)

a percussion mechanism (6) comprising a guide tube (16), an exciter (13) periodically forced in the guide tube (16) along the working axis (1 1) by the motor (5), one in the guide tube (16) along the working axis (1 1) sliding racket (14), one of the exciter (13) and the racket (14) in the guide tube (16)

closed pneumatic chamber (20) for coupling the racket (14) to the movement of the exciter (13), an anvil (15) and a seat (25) for the striker (15), wherein the hammer mechanism (6) for the racket (14) has an impact point which is defined by a striking surface (24) of the striker (15) facing the striker (14) when the striker (15) bears against the seat (25) against the direction of impact (12),

a check valve (26) arranged in the guide tube (16)

Outlet opening (29) and a closing mechanism (28) for closing the

Check valve (26) against an air flow from the inside of the guide tube (16), wherein the outlet opening (29) along the working axis (1 1) is arranged such that the racket (14) the outlet opening (29) relative to the pneumatic chamber (20 ) closes when the bat (14) in the direction of impact (12) before the impact point and that the pneumatic chamber (20) with the outlet opening (29) overlaps when the bat (14) in the direction of impact (12) is moved beyond the impact point ,

2. Beating machine tool (1) according to claim 1, characterized indicates that the closing mechanism (28) has at least one elastic flap (32).

3. Blowing machine tool (1) according to claim 2, characterized indicates that the flap (32) is biased in a check valve (26) closing position.

Characterized in that the closing mechanism (38) has an elastic closure element (39), which abuts due to a residual stress on the inlet opening (27).

5. Beating machine tool (1) according to one of the preceding claims,

characterized in that the guide tube (16) has a throttle opening (31). A hitting machine tool (1) according to claim 5, characterized in that a cross-sectional area of the throttle opening (31) is smaller than a cross-sectional area of the outlet opening (29) of the check valve (26).

Impacting machine tool (1) according to claim 5 or 6, characterized in that the cross-sectional area of the throttle opening (31) is less than 6% of

Cross-sectional area of the outlet opening (29).