The present invention relates to a chiseling handheld power tool, which includes an absorber for reducing vibrations.
The handheld power tool includes a tool holder for holding a tool on a working axis, a pneumatic striking mechanism for striking the tool and an absorber, which includes a bending spring situated transversely to the working axis and a mass body. A countershaft is driven by the motor around a rotation axis, which runs in parallel to the working axis. A wobble drive is situated on the countershaft for driving the pneumatic striking mechanism. A cam disk, which includes a cam projecting in a start-up direction, which runs in parallel to the working axis, is also situated on the countershaft. The bending spring has a counterpiece provided with respect to the cam. The cam, which abuts the counterpiece, pretensions the bending spring in the start-up direction.
The absorber is struck by the rotating cam. The striking action takes place in the idle position of the bending spring, which is assumed when the absorber is stopped, or if the absorber has not yet fully reached the steady state. The cam periodically forces a minimum deflection of the absorber. However, the absorber may also be deflected to a greater degree, excited by the vibrations and the handheld power tool. The striking action takes place synchronized with the movement of the striking mechanism and thus the vibrations of the handheld power tool.
One embodiment provides that the cam disk is contact-free with respect to the bending spring when the cam and the counterpiece are in a diametrical angular position with respect to the rotation axis. The cam disk becomes detached from the bending spring each time the cam rotates once around the rotation axis, so that the absorber is able to oscillate freely at least during this phase. The absorber preferably oscillates freely for at least 50% of an oscillation, i.e. without contact with the cam and driven only by the inertia of the mass.
One embodiment provides that the mass body is guided by the bending spring on a curved path. The bending spring may be fastened to the power tool housing by a first end and be fastened to the mass body on a second end, the first end and the second end being situated diametrically to the countershaft. The projection may be from the first end at a distance corresponding to between 30% and 50% of the distance between the first end and the second end.
One embodiment provides that a maximum deflection of the bending spring from an idle position due to the cam abutting the counterpiece is between 1 degree and 5 degrees.
One embodiment provides that the cam has a helical edge facing the bending spring, which ascends in the start-up direction over a central angle between 30 degrees and 90 degrees. The counterpiece may have a helical edge facing the cam, which ascends counter to the start-up direction over a central angle between 30 degrees and 90 degrees. The force introduced onto the absorber during the striking action is preferably kept low. Excitations of higher harmonic oscillations in the bending spring are avoided hereby.
The pneumatic chamber of the striking mechanism achieves maximum compression in an angular position of the countershaft. At this point in time, the cam assumes a special position relative to the projection, which depends on the arrangement of the cam upstream or downstream from the bending spring. If the cam is upstream from the bending spring, the cam and the projection are in the same angular position with respect to the rotation axis, i.e. the cam may deflect the projection to the maximum extent. If the cam is situated downstream from the bending spring, the cam and projection are offset diametrically to the rotation axis, i.e. by 180 degrees. The absorber is optimally excited, tuned to the movement of the striking mechanism.
The wobble drive is at a dead center facing away from the tool in a first angular position of the countershaft. The cam is in an angular position which deflects the bending spring to the maximum extent in a second angular position. If the cam is situated on the side of the bending spring facing away from the tool, the second angular position may advantageously follow the first angular position between 95 degrees and 115 degrees. If the cam is situated on the side of the bending spring facing the tool, the first angular position may advantageously follow the second angular position between 65 degrees and 85 degrees.
The following description explains the present invention based on exemplary specific embodiments and the figures.
Unless otherwise indicated, identical or functionally equivalent elements are identified by identical reference numerals in the figures.
Hammer drill 1 includes a switchable gear drive having a countershaft 11. Countershaft 11 is rotatably supported around a rotation axis 12. Rotation axis 12 is in parallel to working axis 3. Motor 5 meshes with a driving pinion 13 on countershaft 11 and continuously drives countershaft 11. Countershaft 11 transmits the torque to a wobble drive 14 for striking mechanism 6 and a rotary drive 15 for tool holder 2. The exemplary gear drive makes it possible to turn the rotary drive of tool holder 2 on and off. A shift sleeve 16 is axially movable on countershaft 11 between a first position and a second position. In the first illustrated position, an inner toothing of shift sleeve 16 engages with a toothing 17 of countershaft 11; in a second position, shift sleeve 16 is disengaged. Shift sleeve 16 is in continuous engagement with a sprocket 18, which is coupled with rotary drive 15 and tool holder 2. A shift knob enables the user to move shift sleeve 16 between the two positions. A similar shift sleeve may be situated on countershaft 11 for turning the wobble drive on and off.
Wobble drive 14 converts the rotational movement of countershaft 11 into a periodic, linear movement for striking mechanism 6. Wobble drive 14 includes a wobble plate 19 and a wobble finger 20. Exemplary wobble plate 19 includes a rolling bearing having an inner ring driven by countershaft 11 and an outer ring connected to wobble finger 20. The outer ring is rotatable in relation to the inner ring around an inclined axis with respect to rotation axis 12 but is prevented from rotating around rotation axis 12 by wobble finger 20 abutting striking mechanism 6. The driven inner ring forces the outer ring and wobble finger 20 to a periodic swiveling movement in a plane E spanned by rotation axis 12 of countershaft 11 and working axis 3 around a swivel axis, which runs through rotation axis 12 and is perpendicular to spanned plane E.
Pneumatic striking mechanism 6 includes an exciter piston 21 and a striker 22, both of which are guided in a guiding tube 23 of striking mechanism 6 coaxially to working axis 3. Exciter piston 21 is connected to wobble finger 20. The swiveling movement of wobble finger 20 is translated into a periodic, linear movement of exciter piston 21. An air spring, formed by a pneumatic chamber 24 between exciter piston 21 and striker 22, couples a movement of striker 22 to the movement of exciter piston 21 (
The periodically acting striking mechanism 6 generates shocks in power tool housing 9, which the user perceives as vibrations of handle 10. The vibrations result in an early fatigue of the user and may cause health problems in the case of excessive exposure. Handle 10 may be connected to power tool housing 9 via damping elements 26 to mitigate the vibrations. Damping elements 26 reduce, in particular, high frequency portions of the vibrations and convert them into heat. Damping elements 26 are preferably made from open-pore polymer foams. The effectiveness of damping elements 26 is limited. The guidance of handheld power tool 1 requires a stable and rigid connection of handle 10 to power tool housing 9, while a loose and soft connection would be advantageous for an ideal damping.
Exemplary hammer drill 1 includes an absorber 27 to reduce the vibrations. Absorber 27 includes a mass body 28 and a bending spring 29. Mass body 28 is held only by bending spring 29 and is otherwise preferably unguided. Mass body 28 may move back and forth along working axis 3 on a curved path, an approximately circular path. The curved path is preferably in a plane E spanned by working axis 3 and rotation axis 12 of countershaft 11 (image plane of
Absorber 27 is tuned to striking mechanism 6. The natural frequency is selected to be approximately equal to the number of strikes of striking mechanism 6, for example between 100% and 105% the number of strikes. Inertial mass body 28, which is coupled to power tool housing 9 only via bending spring 29, dynamically counteracts the vibrations of striking mechanism 6, whereby the vibrations of power tool housing 9 acting upon handle 10 are reduced. Due to its inertia, inertial mass body 28 begins to independently move relative to power tool housing 9, once striking mechanism 6 is activated and vibrations occur. Excited by striking mechanism 6, mass body 28 oscillates between two reversal points, which are illustrated in
A cam disk 36 facilitates the steady state of absorber 27, in particular when striking mechanism 6 is initially accelerated to the provided number of strikes. Cam disk 36 deflects absorber 27 onto a side of its idle position 30 in a start-up direction 37; cam disk 36 situated upstream from absorber 27, for example in striking direction 7, deflects absorber 27 onto the side of idle position 30 facing away in striking direction 7. Cam disk 36 does not come into contact with absorber 27 when absorber 27 oscillates to the other side of idle position 30 (
Cam disk 36 is situated on countershaft 11, adjacent to bending spring 29. Cam disk 36 may be integrated into driving pinion 13, integrated into wobble plate 19 or be designed as an independent disk. Countershaft 11 drives cam disk 36 at the same rotational speed as wobble plate 19, whereby the wobbling movement of wobble plate 19 and the rotational movement of cam disk 36 have a constant angle offset. Cam disk 36 may be coupled to or decoupled from countershaft 11 together with wobble plate 19 to activate or deactivate striking mechanism 6.
Cam disk 36 includes a single cam 39, which projects toward bending spring 29 in a start-up direction 37 which runs in parallel to working axis 3. Exemplary cam 39 includes an apex 40, a rising edge 42 up to apex 40 in circumferential direction 41 and a falling edge 43 downstream from apex 40 (
Bending spring 29 has a projection 46 projecting toward cam disk 36 counter to start-up direction 37, which may be struck by cam 39. Projection 46 projects into rotation volume passed over by cam 39 when bending spring 29 is in the idle position. Projection 46 may have the same design as cam 39. Exemplary projection 46 has an apex 47 which projects in the direction of cam disk 36. Projection 46 has a rising edge 48 in the clockwise direction toward apex 47 and a falling edge 49 following apex 47. A central angle 50 of rising edge 48 is, for example, in the range between 45 degrees and 90 degrees. Apex 47 is preferably situated in plane E between mass body 28 and countershaft 11.
Cam disk 36 rotates around rotation axis 12, driven by countershaft 11. Cam 39 approaches projection 46 of bending spring 29. Cam 39 moves past idle position 30 of projection 46 with rising edge 42 in start-up direction 37. For example, cam 39 moves past idle position 30 at an angular position 52 of −45 degrees. Angular position 52 results from the axial distance between cam disk 36 and idle position 30. If absorber 27 is unmoved and thus projection 46 is in idle position 30, cam 39 begins to deflect and clamp absorber 27 in start-up direction 37. Maximum deflection 38 forced by cam 39 is achieved when apex 40 of cam 39 has an angular position 53 aligned with apex 47 of projection 46. Aligned apexes 40, 47 are both at 0 degrees, for example. The two apexes 40, 47 are in plane E with mass body 28 and the oscillation plane of absorber 27. Maximum forced deflection 38 is in the range between 1 degree and 5 degrees.
Following maximum forced deflection 38, cam 39 moves away from projection 46 by falling edge 43. Cam 39 does not apply any more force onto bending spring 29 in start-up direction 37. Accordingly, bending spring 29 relaxes and accelerates mass body 28 counter to start-up direction 37 in the direction of idle position 30. Projection 46 moves at increasing velocity counter to start-up direction 37. The rate of descent of falling edge 48 at the rotational speed of countershaft 11 is selected to be greater than the velocity of projection 46. Accordingly, a gap opens between bending spring 29 and cam disk 36. The movement of absorber 27 is now predefined solely by the inertia of mass body 28 and the rigidity of bending spring 29. The free movement lasts for at least 75% of one revolution of countershaft 11 (270 degrees).
Absorber 27 oscillates over idle position 30 and reaches its maximum deflection 31 counter to start-up direction 37 when cam 39 is at approximately 180 degrees. Cam 39 is again in plane E but on the side of countershaft 11 facing suspension 32 of bending spring 29. Cam 39 and projection 46 are situated diametrically to rotation axis 12. A recess 54 of bending spring 29 is preferably situated opposite cam 39 along rotation axis 12, and recess 45 of cam disk 36 is preferably situated opposite projection 46 along rotation axis 12. Cam disk 36 and bending spring 29 do not touch each other in diametrical angular position 55, regardless of the amplitude of deflection 31 of bending spring 29. Amplitude 38 illustrated in
Maximum forced deflection 38 of absorber 27 preferably takes place simultaneously with the maximum compression of pneumatic chamber 24. Countershaft 11 synchronously drives wobble finger 20 and thus indirectly striking mechanism 6 as well as cam disk 36. Wobble finger 20 periodically reaches its dead center 56 facing away from the tool at an angular position 57, for example at 255 degrees (−105 degrees). Wobble finger 20 subsequently moves itself and exciter piston 21 in striking direction 7. Pneumatic chamber 24 of striking mechanism 6 is compressed. The maximum compression is reached between 95 degrees and 115 degrees after dead center 56. The fixed angle offset of wobble drive 14 with respect to cam disk 36 is selected in such a way that aligned angular position 53 of cam 39 in relation to projection 46 follows dead center 56 of wobble drive 14 facing away from the tool between 95 degrees and 115 degrees. The angle offset shifts by 180 degrees if cam disk 36 is situated on the tool side of bending spring 29.
Already oscillating absorber 27 is to be interfered with as little as possible by cam 39. Projection 46 is designed to quickly leave the area over which cam 39 passes. Apex 47 is situated on a side of countershaft 11 facing away from suspension 32. The distance between apex 47 and suspension 32 is between 30% and 50% of length 34 of bending spring 29.
Bending spring 29 may be reinforced perpendicularly to the plane. Width 58 of bending spring 29 is preferably greater than its thickness 35 and less than its length 34. Exemplary bending spring 29 is designed as a sheet-like leaf spring (
Number | Date | Country | Kind |
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14196018.7 | Dec 2014 | EP | regional |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2015/078122 | 12/1/2015 | WO | 00 |