EP3960379A1 - Manual machine tool - Google Patents

Abstract

The hand-held power tool according to the invention, which has a pneumatic percussion mechanism with a percussion piston that can be moved back and forth along a working axis in a guide tube by means of an air spring, is characterized in that a cylindrical surface of the percussion piston has a plurality of recesses distributed in the circumferential direction, and the recesses have at least 30%, at least 50% and/or at least 70% of the circumference of the cylindrical surface of the percussion piston.

Description

FIELD OF THE INVENTION

The present invention relates to a hand-held power tool.

Percussion or chiseling hand-held power tools, such as rotary hammers, usually have a pneumatic percussion mechanism driven by an electric motor. The pneumatic percussion mechanism has a percussion piston which is moved back and forth in a guide tube by an air spring and which strikes the front end of a tool held in a tool holder via a die or directly. A cylinder surface of the percussion piston is guided in the guide tube, and a gap between the percussion piston and the guide tube can contain a lubricant to reduce friction.

To start impact operation, a breakaway force must be overcome, which is made up of static friction between the impact piston and the guide tube and shearing friction of the lubricant in the lubricating gap. Lubrication, seals, dimensions and tolerances of the hammer mechanism are designed with regard to a typical operating temperature of the rotary hammer, which is typically between 80°C and 150°C due to heating caused by friction of moving components and thermal losses in the air spring. At these temperatures, the breakaway force of the percussion piston is low and can be overcome by the rotary hammer without any problems, so that impact operation can begin immediately when the rotary hammer is switched on.

However, at low temperatures, in particular below freezing point, there is the problem that the viscosity of the lubricant in the gap between the percussion piston and the guide tube and thus the breakaway force is increased and reliable starting of the rotary hammer is prevented. This can mean that the rotary hammer first has to be warmed up for several minutes while idling before the impact mechanism starts and the rotary hammer is fully available.

One to improve the cold start behavior in the EP 3 335 837 A1 The proposed reduction in impact frequency at low temperatures can only be implemented with mechatronic handheld power tools.

Against this background, the object of the present invention is to improve the cold start behavior of a hand-held power tool with an impact mechanism.

DISCLOSURE OF THE INVENTION

Accordingly, a hand-held power tool with a pneumatic percussion mechanism is proposed. The pneumatic percussion mechanism has a percussion piston which can be moved back and forth along a working axis in a guide tube by means of an air spring. A cylindrical surface of the percussion piston has a plurality of recesses distributed in the circumferential direction. The recesses occupy at least 30%, at least 50% and/or at least 70% of the circumference of the cylindrical surface of the percussion piston.

A guide surface of the percussion piston guided in the guide tube is reduced by the recesses. As a result, an expansion of a lubricating gap formed between the guide surface of the percussion piston and the guide tube is reduced. By reducing the expansion of the lubricating gap, a breakaway force of the percussion piston when the hand-held power tool is started up can be reduced. This allows the percussion mechanism to start quickly even at cold temperatures and therefore with very viscous, tough and sticky lubricants. The expansion of the lubricating gap is reduced here in particular without changing the radial tolerances (fit) between the percussion piston and the guide tube. In other words, the expansion of the lubricating gap is reduced without changing a lubricating gap width in the radial direction between the guide surfaces of the percussion piston and the guide tube.

The hand-held power tool is in particular a striking or chiseling hand-held power tool. The hand tool is, for example, a hammer drill.

The pneumatic percussion mechanism serves in particular to percussively drive a tool, such as a drill, into a substrate to be machined. The impact direction is parallel to the working axis. The impact mechanism is driven by a motor of the hand tool. The percussion mechanism has in particular an exciter (z. B. an exciter piston), which is set up by the engine by means of a Eccentric and a connecting rod to be periodically moved back and forth along the working axis. The percussion piston is coupled to the exciter, in particular via the air spring, and is moved by it.

The air spring is formed by a pneumatic chamber between the percussion piston, the exciter and the guide tube. If there is overpressure in the pneumatic chamber (air pressure in the chamber exceeds ambient pressure), a force acts on the percussion piston in the direction of impact. If there is a negative pressure in the pneumatic chamber (air pressure in the chamber is lower than the ambient pressure), a force acts on the percussion piston in the opposite direction to the impact.

The percussion piston has an essentially cylindrical shape. The cylindrical shape has a first end for receiving an impulse from the exciter and a second end for delivering an impulse (via a die or directly) to the tool held in a tool holder. The cylindrical shape also has a lateral surface between the two end faces, which has the cylindrical surface.

Specifically, the circumferential direction of the cylindrical surface is a direction along a circumference of the cylindrical shape in cross section. The circumferential direction is in particular a direction along a circumference of the lateral surface.

In particular, the plurality of recesses are distributed in the circumferential direction in such a way that they are distributed along a circular circumference of the cylindrical lateral surface.

The recesses take up at least 30%, at least 50% and/or at least 70% of the circumference, i. H. the circumferential length of the cylindrical surface of the percussion piston at one or more specific axial positions of the percussion piston.

According to one embodiment, the cylindrical surface of the percussion piston has at least one guide ring area and the recesses take up at least 30%, at least 50% and/or at least 70% of the at least one guide ring area.

In particular, the guide ring surface has the recesses, which represent interruptions in the guide surface, and guide surfaces remaining between the recesses.

According to a further embodiment, the recesses are evenly distributed in the circumferential direction.

As a result, the guide surfaces remaining between the recesses are also distributed uniformly in the circumferential direction, as a result of which good guidance of the percussion piston in the guide tube is achieved.

According to a further embodiment, the recesses have an elongate shape extending parallel to the working axis.

As a result, the guide surface per circular ring can be greatly reduced, as a result of which the cold start behavior of the percussion mechanism can be further improved, while at the same time the risk of the percussion piston tilting can be reduced or prevented.

In particular, the elongated shape of the recesses extends parallel to a longitudinal direction of the percussion piston.

According to a further embodiment, the recesses are indentations, troughs, facets and/or wrench flats.

In particular, the recesses are only arranged in a radial edge area of the cylindrical percussion piston, while a core area of the cylindrical percussion piston forms a solid body. In particular, a depth of the recesses in the radial direction is less than a radius of the cylindrical shape of the percussion piston. For example, the depth of the recesses measured radially from the cylindrical surface (ie measured from the surface of the guide segments remaining between the recesses) is less than 50%, less than 70%, less than 90% of the radius of the cylindrical shape of the percussion piston .

According to a further embodiment, the recesses are produced by means of machining, in particular grinding, milling and/or faceting.

This enables the cutouts to be manufactured easily.

For example, the recesses are made by means of centerless grinding (through grinding, centerless grinding).

According to a further embodiment, the recesses are made by non-cutting deformation.

According to a further embodiment, the recesses are knurls, which are produced by means of knurling and subsequent smooth grinding.

According to a further embodiment, the cylindrical surface of the percussion piston has at least three recesses in the circumferential direction.

In particular, the cylindrical surface of the percussion piston has at least three recesses along a circumference of the cylindrical surface.

According to a further embodiment, the percussion piston has a first end face for receiving an impulse from an exciter, a second end face for delivering an impulse to a tool, and an annular groove arranged adjacent to the first end face for accommodating a sealing ring. Furthermore, the cylindrical surface of the percussion piston has at least two guide ring surfaces which are arranged between the annular groove and the second end face and which have the plurality of recesses. In addition, a radially inwardly offset ring surface is arranged between the at least two guide ring surfaces.

The ring-shaped groove allows a preloaded sealing ring (e.g. O-ring) to be accommodated. The pneumatic chamber of the air spring can be better sealed with the sealing ring. The guide surface of the percussion piston can be further reduced by the annular surface offset radially inwards, which does not constitute a guide surface for guidance in the guide tube. The at least two guide ring surfaces, which are spaced apart by the ring surface offset radially inward, can provide guidance over a large length of the percussion piston (eg the entire length of the percussion piston). As a result, tilting of the percussion piston can be reduced or prevented even more.

The second end face is set up in particular for delivering an impulse to a tool via a snap die and a tool holder.

In some embodiments, the cylindrical surface of the percussion piston can also have a further guide ring surface with the recesses between the annular groove and the first end face.

In embodiments, the recesses of one of the guide ring surfaces can be offset in the circumferential direction to the recesses of another of the guide ring surfaces.

This allows better guidance of the percussion piston in the guide tube and simpler production of the percussion piston, for example by means of through-feed grinding.

According to a further embodiment, the recesses take up at least 30%, at least 50% and/or at least 70% of each of the at least two guide ring surfaces.

According to a further embodiment, the cylindrical surface of the percussion piston is divided in the circumferential direction by the plurality of recesses into a plurality of guide segments for guidance on an inner surface of the guide tube.

According to a further embodiment, the percussion mechanism has an exciter piston, which is set up to be periodically moved back and forth along the working axis in the guide tube by a motor of the handheld power tool, the percussion piston being movably coupled to the exciter piston along the working axis via the air spring .

With such an exciter piston percussion mechanism, in which the lubricating gap is formed between the percussion piston and the passive, static guide tube (instead of between the percussion piston and a positively excited exciter cylinder, as is the case with an exciter cylinder impact mechanism), the improvement of the cold start behavior through the recesses is particularly desirable.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1

eine schematische Ansicht eines Bohrhammers;

Fig. 2

eine schematische Ansicht eines Teils eines pneumatischen Schlagwerks des Bohrhammers aus Fig. 1;

Fig. 3

eine schematische Ansicht eines Schlagkolbens des Schlagwerks aus Fig. 2 gemäß einer ersten Ausführungsform; und

Fig. 4

eine schematische Ansicht eines Schlagkolbens des Schlagwerks aus Fig. 2 gemäß einer zweiten Ausführungsform.

The following description explains the invention using exemplary embodiments and figures. In the figures shows:

1

a schematic view of a rotary hammer;

2

a schematic view of a part of a pneumatic impact mechanism of the rotary hammer 1 ;

3

a schematic view of a percussion piston of the percussion mechanism 2 according to a first embodiment; and

4

a schematic view of a percussion piston of the percussion mechanism 2 according to a second embodiment.

Elements that are the same or have the same function are indicated by the same reference symbols in the figures, unless otherwise stated.

EMBODIMENTS OF THE INVENTION

1 1 schematically shows a hammer drill 1 as an example of a percussive or chiselling hand-held power tool. A motor 5 which drives a percussion mechanism 6 and a drive shaft 7 forms a primary drive of the hammer drill 1 . A battery 8 or a power line supplies the motor 5 with power. A user can hold and guide the hammer drill 1 using a handle 9 . Furthermore, the user can put the hammer drill 1 into operation by means of a main switch 10 . By actuating the main switch 10, the drive shaft 7 coupled to the tool holder 2 causes the tool holder 2 to rotate about a working axis 11. As a result, the tool 4 is rotated about the working axis 11. During operation, the hammer drill 1 can hit the tool 4 in addition to rotating about the working axis 11 in a direction of impact 12 along the working axis 11 into a substrate. In one exemplary embodiment, the hammer drill 1 has an operating selector switch (not shown), by means of which the tool holder 2 can be decoupled from the drive shaft 7, so that the hammer drill 1 can be operated in a purely percussive/chiselling manner.

Impact mechanism 6 is a pneumatic impact mechanism. An exciter piston 13 and an impact piston 14 are movably guided in a guide tube 15 in the impact mechanism 6 along the working axis 11 . The exciter piston 13 is coupled to the motor 5 via an eccentric 16 and is forced to perform a periodic, linear movement. A connecting rod 17 connects the eccentric 16 to the exciter piston 13. An air spring 18 formed by a pneumatic chamber 19 between the exciter piston 13 and the percussion piston 14 couples a movement of the percussion piston 14 to the movement of the exciter piston 13. The percussion piston 14 strikes a die 20, which transmits the impact to the drill 4. The percussion mechanism 6 and preferably the other drive components are arranged inside a machine housing 21 .

2 shows part of the percussion mechanism 6 1 in an enlarged view. As in 2 to see the pneumatic chamber 19 of the air spring 18 of the exciter piston 13, the percussion piston 14 and the guide tube 15 is limited. In particular, both the exciter piston 13 and the percussion piston 14 are guided on an inner surface 24 of the guide tube 15 and coaxially with the working axis 11 . In addition, the percussion piston 14 by means of a preloaded O-ring 22 and the exciter piston 13 by means be sealed against the inner surface 24 of the guide tube 15 by a preloaded O-ring 23 .

3 shows the percussion piston 14 in detail. The percussion piston 14 has an essentially cylindrical shape 25 with a cylindrical surface 26 which is a lateral surface of the cylindrical shape 25 . The two base surfaces of the cylindrical form 25 are defined by an impulse-receiving end face 27 (first end face 27), which faces the exciter piston 13 and forms a boundary of the pneumatic chamber 19, and an impulse-emitting end face 28 (second end face 28), which rests on the die 20 beats, formed (see also figures 1 and 2 ).

As in 3 As can be seen, the percussion piston 14 has an annular groove 29 arranged adjacent to the first end face 27 for receiving the sealing ring 22 ( 2 ) on.

The cylindrical surface 26 of the percussion piston 14 has a plurality of recesses 30 distributed in the circumferential direction U. In 3 only some of the recesses 30 are provided with a reference number for reasons of clarity. The recesses 30 divide the cylindrical surface 26 in the circumferential direction U into a plurality of guide segments 31 for guidance on the inner surface 24 of the guide tube 15 ( 2 ) divided.

In particular, the cylindrical surface 26 of the percussion piston 14 has two guide ring surfaces 32 , 33 arranged between the annular groove 29 and the second end face 28 . Each of the guide ring surfaces 32, 33 has the plurality of recesses 30 distributed in the circumferential direction U and the guide segments 31 lying between them. Between the annular guide surfaces 32, 33, the cylindrical surface 26 has an annular surface 34 offset radially inward. The annular surface 34, which is offset radially inwards, itself has no recesses and does not form a guide surface for guiding on the inner surface 24 of the guide tube 15.

Besides, with that 3 shown example of the percussion piston 14 between the annular groove 29 and the first end face 27 a further annular guide surface 35 with recesses 30 is arranged.

At the in 3 Percussion piston 14 shown, the guide segments 31 of the three guide ring surfaces 32, 33, 35 are guided on the inner surface 24 of the guide tube 15. In particular, there is a gap 36 between the guide segments 31 of the three guide ring surfaces 32, 33, 35 and the inner surface 24 of the guide tube 15 (see enlarged section in 2 ). The gap 36 is filled with a lubricant (not shown).

In order to reduce shearing friction of the lubricant between the percussion piston 14 and the guide tube 15 - especially at low temperatures at which the lubricant is highly viscous and accordingly viscous and sticky - the cylindrical surface 26 of the percussion piston 14 has the recesses 30. These recesses 30 take up at least 30%, at least 50% and/or at least 70% of a circumference C ( 3 ) of the cylindrical surface 26 of the percussion piston 14. In particular, the recesses 30 occupy at least 30%, at least 50% and/or at least 70% of the circumference C of the cylindrical surface 26 of the percussion piston 14 at a specific axial position A1, A2 of a length L of the percussion piston 14. In particular, the recesses 30 occupy at least 30%, at least 50% and/or at least 70% of each of the guide ring surfaces 32, 33, 35.

in the in 3 example shown, the recesses 30 are distributed uniformly in the circumferential direction U. In other examples, the recesses 30 can also be distributed unevenly in the circumferential direction U.

in the in 3 In the example shown, all recesses 30 of the guide ring surface 32 have an elongated shape 37 extending parallel to the working axis 11, ie parallel to a longitudinal direction L of the percussion piston 14. For reasons of clarity, only one of the elongate shapes 37 of the guide ring surface 32 is provided with a reference number. in the in 3 In the example shown, the recesses 30 of the guide ring surfaces 33, 35 do not have an elongated shape extending parallel to the working axis 11. In other examples, the recesses 30 of the guide ring surfaces 33, 35 can also have elongate shapes 37 or the recesses 30 of the guide ring surface 32 can also have no elongate shape 37.

The recesses 30 are in particular indentations or troughs which are deepened radially inwards from an imaginary closed rotationally symmetrical cylindrical shape. The recesses 30 are produced in particular by means of machining, in particular grinding, milling and/or faceting. In other exemplary embodiments, the recesses 30 can also be produced by means of non-cutting deformation and/or by means of knurling and subsequent smooth grinding.

4 shows a percussion piston 114 according to a second embodiment. Only the features of the percussion piston 114 that differ from the percussion piston 14 according to the first embodiment are described below. A cylindrical surface 126 of the percussion piston 114 has three guide ring surfaces 132 , 138 and 133 arranged between an annular groove 129 and a second end face 128 . Each of the guide ring surfaces 132, 138, 133 has a plurality of recesses 130, 230, 330 distributed in the circumferential direction U and guide segments in between (without reference numbers in 4 ) on. Between the annular guide surfaces 138 and 133, the cylindrical surface 126 has an annular surface 134 offset radially inward. The annular surface 134, which is offset radially inwards, itself has no recesses and does not form a guide surface for guiding on the inner surface 24 of the guide tube 15.

In addition, at the in 4 shown example of the percussion piston 114 between the annular groove 129 and a first end face 127 a further guide ring surface 135 with recesses 430 is arranged.

In the percussion piston 114 , the cutouts 130 in the annular guide surface 132 are offset in the circumferential direction U with respect to the cutouts 230 in the annular guide surface 138 . Furthermore, the recesses 330 of the guide ring surface 133 are offset in the circumferential direction U to the recesses 430 of the guide ring surface 135 .

Due to the offset arrangement of the recesses 130 in relation to the recesses 230 and of the recesses 330 in relation to the recesses 430, the percussion piston 114 can be guided uniformly in the guide tube 15 despite the interruptions in the guide surface caused by the recesses.

In addition, the percussion piston 114 can be manufactured particularly easily and inexpensively by means of centerless grinding (centerless grinding, through-feed grinding), since the recesses 130, 230, 330, 430 are arranged in such a way that the percussion piston 114 during manufacture despite the recesses 130, 230, 330, 430 can roll evenly on one level.

REFERENCE LIST

1

hand tool

2

tool holder

3

shaft end

4

tool

5

engine

6

percussion

7

drive shaft

8th

battery

9

handle

10

main switch

11

working axis

12

impact direction

13

pathogen

14

percussion piston

15

guide tube

16

eccentric

17

connecting rod

18

air spring

19

pneumatic chamber

20

Dripper

21

housing

22

sealing ring

23

sealing ring

24

Inner surface

25

cylindrical shape

26

cylindrical surface

27

face

28

face

29

annular groove

30

recess

31

leadership segment

32

guide ring surface

33

guide ring surface

34

ring surface

35

guide ring surface

36

gap

37

elongated shape

114

percussion piston

126

cylindrical surface

128

second face

129

annular groove

130

recess

132

guide ring surface

133

guide ring surface

134

ring surface

135

guide ring surface

138

guide ring surface

230

recess

330

recess

430

recess

A1

axial position

A2

axial position

C

scope

u

circumferential direction

L

length, longitudinal

Claims (13)

Hand-held power tool (1) with a pneumatic percussion mechanism (6) which has a percussion piston (14) which can be moved back and forth along a working axis (11) in a guide tube (15) by means of an air spring (18), characterized in that a cylindrical surface (26) of the percussion piston (14) has a plurality of recesses (30) distributed in the circumferential direction (U), and the recesses (30) at least 30%, at least 50% and/or at least 70% of the circumference (C) of the cylindrical surface (26) of the percussion piston (14). Hand tool machine according to Claim 1, characterized in that the cylindrical surface (26) of the percussion piston (14) has at least one guide ring surface (32, 33, 35) and the recesses (30) are at least 30%, at least 50% and/or at least 70% occupy the at least one guide ring surface (32, 33, 35). Hand-held power tool according to Claim 1 or 2, characterized in that the recesses (30) are evenly distributed in the circumferential direction (U). Hand-held power tool according to one of Claims 1 - 3, characterized in that the recesses (30) have an elongate shape (37) extending parallel to the working axis (11). Hand-held power tool according to one of Claims 1 - 4, characterized in that the recesses (30) are indentations, troughs, facets and/or wrench flats. Hand-held power tool according to one of Claims 1 - 5, characterized in that the recesses (30) are produced by means of machining, in particular grinding, milling and/or faceting. Hand-held power tool according to one of Claims 1 - 5, characterized in that the recesses (30) are produced by means of non-cutting deformation. Hand-held power tool according to one of Claims 1 - 7, characterized in that the recesses (30) are knurls which are produced by means of knurling and subsequent smooth grinding. Hand-held power tool according to one of Claims 1-8, characterized in that the cylindrical surface (26) of the percussion piston (14) has at least three recesses (30) in the circumferential direction (U). Hand-held power tool according to one of Claims 1 - 9, characterized in that the percussion piston (14) has: a first end face (27) for receiving an impulse from an exciter (13), a second end face (28) for delivering an impulse to a tool (4), and an annular groove (29) arranged adjacent to the first end face (27) for receiving a sealing ring (22), wherein the cylindrical surface (26) of the percussion piston (14) has at least two guide ring surfaces (32, 33) arranged between the annular groove (29) and the second end face (28), which have the plurality of recesses (30) and between which a radially inwardly offset annular surface (34) is arranged. Hand machine tool according to Claim 10, characterized in that the recesses (30) occupy at least 30%, at least 50% and/or at least 70% of each of the at least two guide ring surfaces (32, 33). Hand tool according to one of claims 1 - 11, characterized in that the cylindrical surface (26) of the percussion piston (14) in the circumferential direction (U) through the plurality of recesses (30) into a plurality of guide segments (31) for guidance on an inner surface (24) of the guide tube (15) is divided. Hand-held power tool according to one of Claims 1 - 12, characterized in that the hammer mechanism (6) has an exciter piston (13) which is set up to be periodically moved by a motor (5) of the hand-held power tool along the working axis (11) in the guide tube (15 ) to be moved back and forth, the percussion piston (14) being movably coupled along the working axis (11) via the air spring (18) to the exciter piston (13).

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