PORTABLE WORKING DEVICE

Description

[0001] The invention relates to a portable working device according to the preamble of claim 1. Such a working device is known from FR 2 163 286 A5.

[0002] Portable work devices are known which have a housing, a drive motor arranged in the housing, and a tool driven by the drive motor. The drive motor is designed as an electric motor, in particular as a direct current motor. Such direct current motors are versatile and commercially available as mass-produced items. Such a direct current motor has a motor housing and a drive shaft which is mounted on the motor housing via a bearing and extends from the motor housing. The drive shaft is also designed as the rotor of the electric motor. Such direct current motors are usually designed as internal rotors, with the rotor windings connected via a commutator. Sliding contacts, which can be designed as metal or carbon brushes, are in contact with the commutator.

[0003] It has been shown that with such implements, even short operating times can cause damage to the drive motor, which may limit or even prevent the operation of the implement.

[0004] The object of the invention is to provide a portable working device that enables a long service life.

[0005] The object is achieved by a portable working device having the features according to claim 1.

[0006] The invention is based on the observation that, in the case of portable work tools known from the prior art, increased sparking occurs between the brushes and the commutator during operation. The intensity of the sparking depends on the load of the work tool. The drive shaft is subject to bending vibrations during operation of the work tool, which constantly changes the position of the sliding contacts relative to the commutator and results in increased sparking. The invention is based on the finding that, in order to reduce sparking, the drive shaft should be mounted with as little vibration as possible to enable uniform contact between the sliding contacts and the commutator.

[0007] The portable working device according to the invention comprises a housing, wherein the housing extends from a first end to a second end, a tool, a drive motor arranged in the housing between the first end and the second end and having a drive shaft for driving the tool, wherein the drive motor has a first bearing and a second bearing, wherein the drive shaft is rotatably mounted relative to the housing by means of the first bearing and the second bearing, a drive transmission unit, wherein the drive transmission unit is functionally arranged between the drive motor and the tool, wherein the working device comprises an additional bearing mounted on the drive shaft for supporting the drive shaft relative to the housing of the working device.

[0008] The use of the additional bearing stiffens the drive shaft bearing. Loads are absorbed by the additional bearing. The bending vibrations of the drive shaft are reduced or even completely eliminated by the additional bearing. In other words, the vibration amplitudes of the bending vibrations are reduced by the additional bearing. As a result, the drive shaft rotates with increased concentricity, resulting in even contact between the sliding contacts and the commutator. Sparking is reduced, thus extending the service life of the drive motor.

[0009] In addition, the additional bearing is also particularly advantageous for other drive motors, such as brushless electric motors or combustion engines, since the reduction of bending vibrations can prevent damage to drive shaft bearings, motor mounts and the gearbox.

[0010] The additional bearing is preferably designed as a floating bearing. The motor's own bearing is preferably designed as a fixed floating bearing. By designing the additional bearing as a floating bearing, over-determination of the drive shaft bearing and the resulting distortions can be avoided. The additional bearing is designed, in particular, as a radial bearing. The additional bearing is preferably a ball bearing. This allows axial forces acting on the drive shaft in the direction of the rotational axis to be absorbed in addition to radial forces.

[0011] It is advantageously provided that the drive motor is fastened to the housing in such a way that the drive motor is firmly connected to the housing in the direction of its axis of rotation. The drive motor is preferably fastened to the housing via a fastening unit. The additional bearing preferably rests directly on the fastening unit with its bearing outer ring. It is advantageously provided that a pinion is held in a rotationally fixed manner on the drive shaft of the drive motor, wherein the pinion is part of the drive transmission unit. The additional bearing preferably rests with its inner ring on a receiving section of the pinion. As a result, the forces acting on the pinion, in particular radial forces, are transmitted directly via the additional bearing into the fastening unit.

[0012] Furthermore, it has been observed that resonant vibrations can occur on the drive shaft in the area of ​​the additional bearing. The cause of these resonant vibrations is a phenomenon known as knocking, meaning that the balls of the additional bearing deform the bearing rings when passing through the load range, which in turn leads to resonant vibrations in the drive shaft. To prevent deformation of the bearing rings and the associated resonant vibrations, the additional bearing must be dimensioned such that the bearing rings no longer deform. Therefore, the outer diameter of the outer ring of the additional bearing is preferably at least as large as the maximum outer diameter of the pinion.

[0013] It is advantageous that the drive transmission unit is designed as a gear unit free of axial forces. Accordingly, the drive transmission unit is designed such that no axial forces act on the drive shaft in the direction of the rotational axis of the drive motor. This eliminates the need for a radial bearing for the drive shaft. Advantageously, the pinion is preloaded in the direction of the rotational axis of the drive motor by means of a spring unit. By using the spring unit, the drive shaft is axially preloaded, thereby counteracting manufacturing tolerances. This sets a targeted backlash in the drive transmission unit. Excessive or insufficient backlash in the drive transmission unit can be avoided.

[0014] The drive transmission unit preferably has a gear ratio of 3. This allows a drive motor rotating at high speed, in particular a brushed DC motor, to be used in the work device with a speed adapted to the tool.

[0015] It is provided that the drive motor comprises a motor housing, wherein the drive shaft is rotatably mounted directly relative to the motor housing by means of the first bearing and the second bearing.

[0016] Further features of the invention will become apparent from the following description and the exemplary embodiments illustrated in the drawings. They show: Fig. 1 shows a perspective view of an embodiment of a portable working device with a guide tube and a tool at one end and a power source at the other end of the guide tube, Fig. 2 shows a side view of the portable working device according to the invention with a schematically indicated guide tube, Fig. 3 shows a plan view of the portable working device according to Fig. 2 , Fig. 4 in a side sectional view of the portable working device according to Fig. 2 , Fig. 5 in a sectional view in a view from above the portable working device according to Fig. 2 , Fig. 6 in a partial sectional view in a view from above the portable working device according to Fig. 2 and Fig. 7 in a partial sectional view in a view from above of an alternative embodiment of the working device with spring unit according to the invention.

[0017] In the figures, identical components are provided with the same reference symbols.

[0018] In Fig. 1 The portable tool 1 is shown, which is designed as a pole pruner. The portable tool 1 can also be designed as a power chainsaw, hedge trimmer, circular saw, or similar tool. The portable tool 1 comprises a housing 2, a drive motor 5 arranged in the housing 2, and a tool 9 drivable by the drive motor 5.

[0019] As in the Figures 4 and 5 As shown, the drive motor 5 is designed as an electric motor. In the exemplary embodiment, the electric motor is designed as a DC motor, in particular as a brush motor. Alternatively, the electric motor can also be designed as a brushless DC motor. In an alternative embodiment of the portable working device, the drive motor can also be designed as an internal combustion engine.

[0020] As in Fig. 1As shown, the portable working device 1 comprises a guide tube 51 with a first end 52 and a second end 53. The housing 2 of the working device 1 is held at the first end 52 of the guide tube. A second housing 54 is held at the second end 53 of the guide tube 51. The second housing 54 has a receiving shaft 55 for receiving a battery or similar energy source. It may be expedient to use a stationary power grid as the energy source, which is connected via an electrical line to the second housing 54 or to control electronics arranged in the second housing 54. In the exemplary embodiment shown, an operating handle 56 with operating elements is provided at the second end 53 of the guide tube 51. In the exemplary embodiment shown, the operating elements provided are an operating element referred to as an operating lever 57 or throttle lever and a locking lever 58. The operating lever 57 serves to control the drive motor 5.The locking lever 58 is intended to secure the operating lever 57.

[0021] As in Fig. 1 As shown, in the exemplary embodiment the guide tube 51 is preferably designed to be telescopic. The guide tube 51 comprises a first tube section 62 with the first end 52 of the guide tube 51 and a second tube section 63 with the second end 53 of the guide tube 51. The guide tube 51 comprises a clamping device 59. The clamping device 59 is preferably fastened to the second tube section 63. The clamping device 59 serves to fix the first tube section 62 to the second tube section 63. In an alternative embodiment the guide tube 51 is not telescopic. In such an embodiment the clamping device 59 serves to connect the first tube section 62 and the second tube section 63. Further extension pieces can also be provided.

[0022] As in Fig. 2As shown, the housing 2 of the portable power tool 1 extends in a longitudinal direction 10 from a rear end 3 to a front end 4. The tool 9 is arranged at the front end 4 of the housing. The tool 9 is designed in the exemplary embodiment as a saw chain 33. The saw chain 33 is connected to the chain drive wheel 38 ( Fig. 5) is driven in rotation around a guide rail 32 in a running direction 37. The running direction 37 of the saw chain 33 is the direction of movement of the saw chain 33 intended for the intended operation of the work device 1 for chip removal. The chain drive wheel 38 is driven in rotation via the drive motor 5. The guide rail 32 is arranged at the front end 4 of the housing 2 and extends in a longitudinal direction 34 which corresponds to a direction from the rear end 3 to the front end 4 of the housing 2. The saw chain 33 spans a tool plane 30, with both the saw chain 33 and the guide rail 32 lying in the tool plane 30.

[0023] As in Fig. 2As shown, the guide bar 32 comprises an upper side 35 and a lower side 36. During normal operation of the portable tool 1, the saw chain 33 runs along the upper side 35 of the guide bar 32 in the direction away from the front end 4 of the housing 2. During normal operation of the portable tool 1, the saw chain 33 runs along the lower side 35 of the guide bar 32 in the direction toward the front end 4 of the housing 2. Both the upper side 35 of the guide bar 32 and the lower side 36 of the guide bar 32 lie in the tool plane 30.

[0024] As in the Figures 2 and 3As shown, the housing 2 extends along its longitudinal direction 10 from its rear end 3 to its front end 4. The rear end 3 forms the first end face 39 of the housing 2. The front end 4 of the housing 2 forms the second end face 40 of the housing 2. The housing 2 comprises an upper side 26 and a lower side 27. In addition, the housing 2 comprises a first longitudinal side 28 and a second longitudinal side 29. The first end face 39 and the second end face 40 of the housing 2 are connected to one another via the upper side 26, the lower side 27, the first longitudinal side 28 and the second longitudinal side 29 of the housing 2. During normal operation of the working device 1, the upper side 26 of the housing 2 lies above the lower side 27 of the housing 2. A vertical direction 45 running from the lower side 27 to the upper side 26, together with the longitudinal direction 10 or with the axis of rotation 6 of the drive motor 5, defines a longitudinal plane 46 of the housing 2.The housing 2 comprises a transverse plane 47, which is oriented orthogonally to the longitudinal plane 46 and the vertical direction 45. The longitudinal sides 28, 29 are arranged opposite one another with respect to the longitudinal plane 46. The top side 26 and the bottom side 27 are arranged opposite one another with respect to the transverse planes 47. In the exemplary embodiment, the longitudinal plane 46 of the housing 2 is oriented parallel to the tool plane 30.

[0025] As in the Figures 4 to 6As shown, the drive motor 5, designed as an electric motor, is arranged in the housing 2 between the rear end 3 of the housing 2 and the front end 4 of the housing 2. The drive motor 5 comprises an axis of rotation 6, which in the exemplary embodiment corresponds to the longitudinal direction 10 of the housing 2. The drive motor 5 comprises a motor housing 11, which extends along the axis of rotation 6 of the drive motor 5 from a front-side first end 21 to a front-side second end 22 of the motor housing 11. The first end 21 of the motor housing 11 faces the rear end 3 of the housing 2. The second end 22 of the drive motor 5 faces the front end 4 of the housing 2.

[0026] As in the Figures 4 to 6As shown, the drive motor 5 comprises a drive shaft 7. The drive shaft 7 projects with a drive section 20 at the second end 22 of the motor housing 11 from the motor housing 11 in the direction of the front end 4 of the housing 2. The drive motor 5 comprises a first bearing 12 and a second bearing 13. The drive shaft 7 is rotatably mounted on the motor housing 11 via the first bearing 12 and the second bearing 13. The first bearing 12 is arranged at the first end 21 of the motor housing 11. The second bearing 13 is arranged at the second end 22 of the motor housing 11. The first bearing 12 is designed as a loose bearing. The second bearing 13 is designed as a fixed bearing. The first bearing 12 and the second bearing 13 thus form a fixed-loose bearing between the drive shaft 7 and the motor housing 11. The first bearing 12 and the second bearing 13 are in the Figures 4 to 6 only indicated schematically.

[0027] As particularly in Fig. 6As shown, the portable work device 1 has a drive transmission unit 8. The drive transmission unit 8 is designed to transmit the energy of the drive motor 5 to the tool 9 to be driven. In the present exemplary embodiment, the drive transmission unit 8 is designed as a gear, since both the speed and the torque are converted from the drive motor 5 to the tool 9. In the present exemplary embodiment, the drive transmission unit 8 comprises a pinion 18, a bevel gear 23, and the chain drive wheel 38. In an alternative embodiment of the work device 1, it may also be expedient to design the drive transmission unit 8 differently.

[0028] As particularly in Fig. 6As shown, the pinion 18 is arranged in a rotationally fixed manner on the drive section 20 of the drive shaft 7. The pinion 18 is held on the drive shaft 7 by a press fit. Alternatively, the pinion 18 can also be held in a form-fitting manner, in particular by a tongue and groove connection on the drive shaft 7. The pinion 18 is operatively connected to the bevel gear 23. The working device 1 has an output shaft 24, wherein the bevel gear 23 is held in a rotationally fixed manner on the output shaft 24. The output shaft 24 is rotatably mounted in the housing 2. The chain drive gear 38 is held in a rotationally fixed manner on the output shaft 24. The pinion 18 arranged on the drive shaft 7 of the drive motor 5 drives the bevel gear 23. The output shaft 24 and thus also the chain drive gear 38 are in turn driven via the bevel gear 23.

[0029] During operation of the working device 1, forces are transmitted from the operative connection between the bevel gear 23 and the pinion 18 to the drive shaft 7 via the pinion 18, which can lead to bending vibrations of the drive shaft 7. To counteract these bending vibrations, the working device 1 comprises an additional bearing 14, as shown in the Figures 4 to 6shown. The additional bearing 14 supports the drive shaft 7 at least indirectly against the housing 2. The additional bearing 14 is a radial bearing. The drive shaft 7 is thus supported in three bearings, whereby the amplitudes of the bending vibrations of the drive shaft 7 are considerably reduced, or can even be avoided entirely. This circumstance has a beneficial effect on the service life of the drive motor 5. The additional bearing 14 is designed as a ball bearing, whereby the additional bearing 14 can support not only radial forces but also axial forces, i.e. forces that act against the housing 2 in the direction of the axis of rotation 6. The pinion 18 has a receiving section 19. In the exemplary embodiment, the additional bearing 14 is arranged directly on the receiving section 19 of the pinion 18. Accordingly, the additional bearing 14 rests with its bearing inner ring 17 directly on the receiving section 19 of the pinion 18.Thus, the forces acting on the pinion 18 are transmitted directly to the additional bearing 14 in the housing 2. The force flow does not run via the drive shaft 7. In an alternative embodiment of the implement 1, it may be expedient to arrange the additional bearing 14 directly on the drive shaft 7. It should be ensured that the arrangement of the additional bearing 14 is as close as possible to the point of force introduction into the drive shaft 7 in order to be able to transmit the forces to the housing 2 with little bending stress on the drive shaft 7. Accordingly, in such an alternative embodiment, the additional bearing 14 is attached adjacent to the pinion 18 directly on the drive section 20 of the drive shaft 7.

[0030] As in Fig. 6As shown, the additional bearing 14 has an outer diameter a measured radially to the axis of rotation 6, an inner diameter b measured radially to the axis of rotation 6 and a bearing width c measured in the direction of the axis of rotation 6. The outer diameter a of the additional bearing 14 is at least as large as a maximum outer diameter d of the pinion 18. Preferably, the outer diameter a of the additional bearing 14 is larger than the outer diameter of the first bearing 12 and the second bearing 13. Preferably, the outer diameter a of the additional bearing 14 is at least 15 mm, preferably at least 20 mm, in particular approximately 22 mm. Preferably, the inner diameter b of the additional bearing 14 is at least 5 mm, in particular at least 7, preferably approximately 8 mm. Preferably, the width c of the additional bearing 14 is at least 5 mm, in particular at least 6 mm, preferably approximately 7 mm.

[0031] The force to be transmitted from the pinion 18 to the bevel gear 23 is supported on the housing 2 via the additional bearing 14. When the implement 1 is in operation, the drive shaft 7 rotates, with the balls of the additional bearing 14 repeatedly passing through a range of maximum force transmission, i.e., at a ball passing frequency. In the range of maximum force transmission, deformations of the bearing inner ring 17 and / or the bearing outer ring 16 can even occur, thus also causing deformation of the drive shaft 7. If the ball passing frequency corresponds to an excitation frequency of the drive shaft 7 or of the entire drive motor 5, the drive motor 5 can be damaged.The oversizing of the additional bearing 14 described above results in the bearing outer ring 16 and the bearing inner ring 17 of the additional bearing 14 no longer deforming and consequently no longer noticeably affecting the drive shaft 7 with the ball passing frequency.

[0032] As in the Figures 4 to 6As shown, the working device 1 comprises a fastening unit 15. The fastening unit 15 is designed to fasten the drive motor 5 to the housing 2. The drive motor 5, in particular the motor housing 11 of the drive motor 5, is preferably fastened directly to the fastening unit 15. In the exemplary embodiment, the drive motor 5 is screwed to the fastening unit 15 via a plurality of screws 25, in particular via four screws 25. In an alternative embodiment of the portable working device 1, it may be expedient to provide a different number of screws 25 in order to fasten the drive motor 5 to the fastening unit 15. In the preferred exemplary embodiment, the fastening unit 15 is connected to the housing 2 of the working device 1 via anti-vibration elements (not shown in detail).In an alternative embodiment of the implement 1, it can also be provided to fasten the fastening unit 15 directly to the housing 2 of the implement 1. The fastening unit 15 is preferably formed from a metal plate. The metal plate is preferably formed from a magnesium alloy, in particular from an aluminum alloy. The additional bearing 14 contacts the fastening unit 15 with its outer ring 16. The additional bearing 14 is designed as a loose bearing in the exemplary embodiment in order to avoid tension between the drive motor 5 and the fastening unit 15. Since the motor housing 11 is firmly screwed to the fastening unit 15, designing the additional bearing 14 as a fixed bearing would lead to over-determination of the system and, if the drive shaft 7 expands during operation of the implement 1, would lead to tension in the system and possibly even damage to the drive motor 5.

[0033] As in the Figures 4 to 6 As shown, the bevel gear 23 and the pinion 18 are engaged. Such bevel gears typically generate high axial forces that act on the drive pinion in the direction of the drive shaft. Such axial forces must be supported by appropriate radial bearings or adjusted bearings. The drive motor 5 used in the present embodiment is a simple, commercially available brushed DC motor. Such drive motors 5 are provided with a fixed-loose bearing on their drive shaft 7, with the individual bearings 12, 13 being designed as ball bearings. These are not suitable for supporting high axial forces. The additional bearing 14 is also not suitable for supporting high axial forces.

[0034] Therefore, in the preferred embodiment, the drive transmission unit 8 is designed as an axial force-free gear. The term "axial force-free" is to be understood such that only forces less than 10 N, preferably less than 5 N, and in particular less than 2 N, act on the drive shaft 7 via the drive transmission unit 8 in the direction of the rotational axis 6. The drive transmission unit 8 is an axial force-free gear both during normal operation of the implement 1 and during malfunction of the implement 1. Malfunction is operation of the implement 1 in which, for example, the chain is blocked by a particularly hard object. In the exemplary embodiment, the drive transmission unit 8 has a transmission ratio of 3. The DC motor provided in the exemplary embodiment has a speed of approximately 20,000 rpm.The gear ratio of 3 allows the speed for operating implement 1 to be reduced.

[0035] In an alternative embodiment of the working device 1 according to Figure 7the working device 1 comprises a spring unit 50. The spring unit 50 is designed such that it preloads the pinion 18 in the direction of the axis of rotation 6 towards the bevel gear 23. Because the pinion 18 and the bevel gear 23 are designed such that no axial forces are transmitted from the bevel gear 23 to the pinion 18, there is axial play in the drive shaft 7. The variable axial play is overcome by the use of the spring unit 50. The spring unit 50 is preferably designed as a compression spring. The spring unit 50 is supported on the motor housing 11 and / or on the second bearing 13 of the drive motor 5 and acts on the additional bearing 14. The spring unit 50 presses the drive shaft 7 with the pinion 18 against the bevel gear 23, whereby the axial play of the drive shaft 7 is overcome.The tolerance of the tooth play between the bevel gear 23 and the pinion 18 is reduced, resulting in a longer service life and a reduction in the noise emissions of the drive transmission unit 8.

Claims

1. Portable implement, comprising - a housing (2), wherein the housing (2) extends from a first end (3) to a second end (4), - a tool (9), - a drive motor (5), which is arranged in the housing (2) between the first end (3) and the second end (4) and has a drive shaft (7) for driving the tool (9), wherein the drive motor (5) is an electric motor, wherein the drive motor (5) has a first bearing (12) and a second bearing (13), wherein, by means of the first bearing (12) and the second bearing (13), the drive shaft (7) is mounted rotatably in relation to the housing (2), - a drive-transmission unit (8), wherein the drive-transmission unit (8) is functionally arranged between the drive motor (5) and the tool (9), characterized in that the implement (1) comprises an additional bearing (14), which is arranged on the drive shaft (7) and serves for supporting the drive shaft (7) in relation to the housing (2) of the implement (1), and in that the drive motor (5) comprises a motor housing (11), wherein, by means of the first bearing (12) and the second bearing (13), the drive shaft (7) is directly mounted rotatably in relation to the motor housing (11).

2. Implement according to Claim 1, characterized in that the additional bearing (14) is designed as a floating bearing.

3. Implement according to Claim 1 or 2, characterized in that the additional bearing (14) is a ball bearing.

4. Implement according to one of Claims 1 to 3, characterized in that the drive motor (5) is fastened to the housing (2) in such a way that the drive motor (5) is connected fixedly to the housing (2) in the direction of its axis of rotation (6).

5. Implement according to one of Claims 1 to 4, characterized in that the drive motor (5) is fastened to the housing (2) via a fastening unit (15).

6. Implement according to Claim 5, characterized in that the additional bearing (14) directly bears against the fastening unit (15) by way of its bearing outer ring (16).

7. Implement according to one of Claims 1 to 6, characterized in that a pinion (18) is held rotationally conjointly on the drive shaft (7) of the drive motor (5), wherein the pinion (18) is part of the drive-transmission unit (8).

8. Implement according to Claim 7, characterized in that the additional bearing (14) bears on a receiving portion (19) of the pinion (18) by way of its bearing inner ring (17).

9. Implement according to Claim 7 or 8, characterized in that an outer diameter (a) of the bearing outer ring (16) of the additional bearing (14) is at least as large as the maximum outer diameter (d) of the pinion (18).

10. Implement according to one of Claims 7 to 9, characterized in that the pinion (18) is preloaded in the direction of the axis of rotation (6) of the drive motor (5) by means of a spring unit (50).

11. Implement according to one of Claims 1 to 10, characterized in that the drive-transmission unit (8) is designed as an axial-force-free gear mechanism.

12. Implement according to one of Claims 1 to 11, characterized in that the drive-transmission unit (8) has a transmission ratio of three.