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Title:
BEARINGS FOR A WALL SAW
Document Type and Number:
WIPO Patent Application WO/2014/168535
Kind Code:
A1
Abstract:
A wall saw comprising: - a carriage (2); - a saw arm (11) pivotally mounted to the carriage; - a radial bearing (23) provided between the saw arm and the carriage; - a first axial bearing (21) provided between the saw arm and the carriage, this axial bearing comprising a flat and ring-shaped first sliding element (38); - a second axial bearing (22) provided between the saw arm and the carriage, this axial bearing comprising a flat and ring-shaped second sliding element (41) clamped between a contact surface (42) of the saw arm and a clamping member (43) fixed to the carriage. The clamping member comprises an axially springy part (43b) which is pre-tensioned against the second sliding element (41) so as to keep the second sliding element clamped between the clamping member and said contact surface (42) under the effect of a spring force exerted by the clamping member.

Inventors:
JOHNSEN, Anders (Alderbäcken 72, Borlänge, S-781 93, SE)
Application Number:
SE2013/050406
Publication Date:
October 16, 2014
Filing Date:
April 12, 2013
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
JOHNSEN, Anders (Alderbäcken 72, Borlänge, S-781 93, SE)
International Classes:
B28D1/04; B23D45/04; B23D47/00; B23Q1/48; B23Q5/38; B23Q9/00; B27B5/38
Domestic Patent References:
WO2012105876A1
WO1990012222A1
Foreign References:
US20070163412A1
Attorney, Agent or Firm:
LÖFGREN, Jonas et al. (Bjerkéns Patentbyrå KB, Box 1274, Gävle, SE-801 37, SE)
Download PDF:
Claims:
CLAI MS

1 . A wall saw comprising :

- a carriage (2), which is to be mounted to a guide rail (3) so as to be moveable along the guide rail;

- a saw arm (1 1 ) pivotally mounted to the carriage (2) so as to be pivotable in relation to the carriage about a pivot axis (A3), the saw arm ( 1 1 ) comprising an external housing (20) and a ring gear (24) connected to the housing (20);

- a gear wheel (26) which is rotatably mounted to the carriage (2) and in engagement with the ring gear (24);

- an actuating device (27) , by means of which said gear wheel (26) is rotatable in order to rotate the ring gear (24) and thereby pivot the saw arm (1 1 ) in relation to the carriage (2) about the pivot axis (A3);

- a radial bearing (23) provided between the saw arm ( 1 1 ) and the carriage (2);

- a rotatable spindle (10) configured for connection to a saw blade (9), the spind le (10) being rotatably mounted to the saw arm housing (20); and

- a drive motor (1 3) for rotating the spindle ( 10),

characterized in :

- that the wall saw (1 ) comprises a first axial bearing (21 ) provided between the saw arm (1 1 ) and the carriage (2), this first axial bearing (21 ) comprising a flat and ring-shaped first sliding element (38) clamped between a first contact surface (39) of the saw arm (1 1 ) and a corresponding contact surface (40) of the carriage (2);

- that the wall saw (1 ) comprises a second axial bearing (22) provided between the saw arm (1 1 ) and the carriage (2), this second axial bearing (22) comprising a flat and ring-shaped second sliding element (41 ) clamped between a second contact surface (42) of the saw arm ( 1 1 ) and a clamping member (43) fixed to the carriage (2); and

- that the clamping member (43) comprises an axially springy part (43b) which is pre-tensioned against the second slid ing element (41 ) so as to keep the second sliding element clamped between the clamping member (43) and said second contact surface (42) of the saw arm (14) under the effect of a spring force exerted by the clamping member, wherein the first contact surface (39) of the saw arm (14) is pressed towards the corresponding contact surface (40) of the carriage (2) under the effect of the clamping member (43).

A wall saw according to claim 1 , characterized in that the clamping member (43) is ring-shaped and comprises an outer part (43a), through which the clamping member is fixed to the carriage (2), said axially springy part (43b) of the clamping member (43) extending radially inwards from the outer part (43a) and bearing against the second sliding element (41 ) in a pre-tensioned manner.

A wall saw according to claim 1 or 2, characterized in that the clamping member (43) is a flat ring of metallic material.

A wall saw according to any of claims 1 -3, characterized in that the radial bearing (23) is located between the first sliding element (38) and the second slid ing element (41 ), as seen in a d irection perpendicular to the pivot axis (A3).

A wall saw according to any of claims 1 -4, characterized in that the first slid ing element (38) has an outer diameter that is smaller than the inner diameter of the second sliding element (41 ).

A wall saw according to any of claims 1 -5, characterized in that the radial bearing (23) is provided between an outer peripheral surface (45) of a circular cylindrical part (58) included in the carriage (2) and an inner peripheral surface (46) of a circular cylindrical recess provided in the saw arm ( 1 1 ) .

A wall saw according to claim 6, characterized in that the radial bearing (23) comprises a slid ing element (47) in the form of a band of plastic material arranged between said outer peripheral surface (45) and said inner peripheral surface (46).

8. A wall saw according to claim 6 or 7, characterized in that said first contact surface (39) of the saw arm ( 14) constitutes a bottom surface of said circu lar cylindrical recess, whereas the correspond ing contact surface (40) of the carriage (2) is provided on an outer side of an end wall (32) of said circu lar cylindrical part (58) of the carriage (2).

9. A wall saw according to any of claims 6-8, characterized in that the second sliding element (41 ) and the clamping member (43) surround said circular cylindrical part (58) of the carriage (2).

10. A wall saw according to any of claims 6-9, characterized in that the ring gear (24) surrounds said circular cylindrical part (58) of the carriage (2). 1 1 . A wall saw according to any of claims 1 -10, characterized in that a lateral surface on the ring gear (24) constitutes said second contact surface (42) of the saw arm (1 1 ).

12. A wall saw according to any of claims 1 -1 1 , characterized in that the first sliding element (38) is a disc of plastic material.

13. A wall saw according to any of claims 1 -12, characterized in that the second sliding element (41 ) is a ring of plastic material.

Description:
BEARINGS FOR A WALL SAW

FI ELD OF THE I NVENTION AND PRIOR ART The present invention relates to a wall saw according to the preamble of claim 1 .

A wall saw is a sawing machine primarily used for cutting walls, ceilings or floors made of concrete or similar materials. A con- ventional wall saw comprises a carriage which is moveable along a guide rail by means of a feeding device. A saw blade is mounted to a spindle, which is rotatably mounted to a saw arm . The saw arm is in its turn pivotally mounted to the carriage. The spindle is rotated by means of a drive motor, which is mounted to the carriage and operatively connected to the spindle through a transmission mechanism accommodated in the saw arm. When the saw arm is pivoted , the saw blade is moved upwards or downwards for adjustment of the depth of the cut. The saw arm may be pivoted by means of a motor or a manually operated ac- tuating device mounted to the carriage.

Wall saws of the above-mentioned type are for instance disclosed in US 3 722 497 A and US 2007/0163412 A1 . The saw arm of these previously known wall saws is pivotally mounted to the associated carriage through two rad ial bearings in the form of ball bearings or the similar.

OBJECT OF THE I NVENTION The object of the present invention is to provide a wall saw having a new and favourable design .

SUMMARY OF THE I NVENTION According to the invention , said object is achieved by a wall saw having the features defined in claim 1 . The wall saw according to the invention comprises:

- a carriage, which is to be mounted to a guide rail so as to be moveable along the gu ide rail;

- a saw arm pivotally mounted to the carriage so as to be pivo- table in relation to the carriage about a pivot axis, the saw arm comprising an external housing and a ring gear connected to the housing ;

- a gear wheel which is rotatably mounted to the carriage and in engagement with the ring gear;

- an actuating device, by means of which said gear wheel is ro- tatable in order to rotate the ring gear and thereby pivot the saw arm in relation to the carriage about the pivot axis;

- a rotatable spindle configured for connection to a saw blade, the spindle being rotatably mounted to the saw arm housing ;

- a drive motor for rotating the spindle,

- a radial bearing provided between the saw arm and the carriage;

- a first axial bearing provided between the saw arm and the carriage, this first axial bearing comprising a flat and ring-shaped first slid ing element clamped between a first contact surface of the saw arm and a correspond ing contact surface of the carriage; and

- a second axial bearing provided between the saw arm and the carriage, this second axial bearing comprising a flat and ring- shaped second sliding element clamped between a second contact surface of the saw arm and a clamping member fixed to the carriage.

The clamping member comprises an axially springy part which is pre-tensioned against the second sliding element so as to keep the second slid ing element clamped between the clamping member and said second contact surface of the saw arm under the effect of a spring force exerted by the clamping member, wherein the first contact surface of the saw arm is pressed towards the corresponding contact surface of the carriage under the effect of the clamping member. There is a certain play in the engagement between the teeth of a gear wheel and the teeth of a ring gear. Due to this play, the saw arm will pivot somewhat to and fro about its pivot axis when the saw blade is driven through the material to be cut and the saw blade is thereby subjected to vibrations in its own plane. If the saw arm is pivotally mounted to the carriage by means of on ly ball bearings or other bearings with neglig ible friction , the bearings will not be capable of damping these vibrations and the saw blade will be subjected to increased and peripherally irregular wear due to these vibrations. The use of axial bearings with flat and ring-shaped sliding elements will make it possible, by a su itable setting of the clamping force acting on the slid ing elements, to achieve a friction between the saw arm and the carriage that is sufficiently low to allow the saw arm to be pivoted by the torque transmitted to the ring gear from the associated gear wheel and at the same time sufficiently high to allow the bearings to efficiently dampen the above-mentioned vibrations. The dampening of these vibrations will result in a reduced wear on the saw blade.

Furthermore, the use of axial bearings with flat and ring-shaped sliding elements will make it possible to ach ieve simple, inexpensive and space-saving bearings between the saw arm and the carriage and a very good lateral stability of the saw arm in rela- tion to the carriage.

Owing to the fact that the clamping member acts on the second sliding element in a pre-tensioned manner through an axially springy part of the clamping member, the clamping member will be capable of exerting an appropriate and evenly distributed press force on the second slid ing element during the sawing operations without requ iring any adjustments of the clamping member. Furthermore, by using pre-tensioned axial bearings with flat and ring-shaped sliding elements, the static friction coefficient between the saw arm and the carriage will be larger than the kinetic friction coefficient, which is favourable with respect to the damping of the above-mentioned vibrations. Further advantages as well as advantageous features of the wall saw according to the invention will appear from the following description and the dependent claims.

BRI EF DESCRI PTION OF THE DRAWI NGS

With reference to the appended drawings, a specific description of preferred embod iments of the invention cited as examples follows below. In the drawings:

Fig 1 is a perspective view of a wall saw accord ing to an embod iment of the present invention Fig 2 is a perspective view of the wall saw of Fig 1 , as seen from another direction and with a saw blade mounted to the wall saw,

Fig 3 is a perspective view of a carriage and a saw arm included in the wall saw of Fig 1 ,

Fig 4 is a partially sectioned lateral view of the carriage and saw arm included in the wall saw of Fig 1 , Fig 5 shows a part from Fig 4 in a larger scale

Fig 6 shows another part from Fig 4 in a larger scale

Fig 7 is a sectioned front view of the saw arm included in the wall saw of Fig 1 ,

Fig 8 is a perspective view of an actuating device included in the wall saw of Fig 1 , Fig 9 is a perspective view of a chassis included in the carriage of the wall saw of Fig 1 , Fig 10 is a perspective view of the chassis of Fig 9, as seen from another direction ,

Fig 1 1 is an exploded view of a motor module and the car- riage included in the wall saw of Fig 1 ,

Fig 12 is a longitudinal section through a safety clutch included in the wall saw of Fig 1 , Fig 13 is an exploded view of the safety clutch of Fig 12, and

Fig 14 is an exploded view of components included in the wall saw of Fig 1 . DETAI LED DESCRI PTION OF EMBODI MENTS OF THE I NVENTION

A wall saw 1 accord ing to an embod iment of the present invention is illustrated in Figs 1 and 2. This wall saw 1 is primarily in- tended to be used for cutting walls, ceilings or floors made of concrete or similar materials. The wall saw 1 comprises a carriage 2, which is to be mounted to an elongated gu ide rail 3 so as to be moveable along the guide rail . The guide rail 3 is mounted to a floor or other supporting surface by means of support mem- bers 4, wh ich are secured to the guide rail 3.

Guide rollers 5a-5d are rotatably mounted to the carriage 2. These guide rollers 5a-5d are in engagement with guide tracks 6a, 6b on the guide rail 3 and are arranged to keep the carriage 2 in place on the guide rail 3, while allowing the carriage 2 to move along the guide rail 3 in the longitudinal direction thereof. In the illustrated embodiment, the guide rail 3 is provided with an upper guide track 6a and a lower guide track 6b, wh ich extend in parallel with each other along the guide rail. In the illustrated embod iment, two guide rollers 5a, 5b are in engagement with the upper guide track 6a from above and two other guide rollers 5c, 5d are in engagement with the lower gu ide track 6b from below. A cog track 7 is fixed to the gu ide rail 3 and extends in the longitudinal direction thereof in parallel with the guide tracks 6a, 6b. The carriage 2 is moveable along the cog track 7 by means of a feeding device, which comprises a feed gear wheel 8 (see Fig 3) rotatably mounted to the carriage 2. The feed gear wheel 8 is in engagement with the cog track 7. The feeding device also comprises a feed motor (not shown) mounted to the carriage 2, by means of which the feed gear wheel 8 is rotatable in order to move the carriage 2 along the guide rail 3. The feed motor is preferably an electric motor, but could alternatively be a hydraulic motor.

A circu lar saw blade 9 (see Fig 2) is to be attached to a rotatable spindle 10. I n Fig 1 , the wall saw is shown without any saw blade attached to the spind le 10. The saw blade 9 is detachably attachable to the spindle 10 by means of a suitable coupling . The spindle 10 is rotatably mounted to a saw arm 1 1 by means of suitable bearings 12 (see Fig 4) and is rotatable about a first axis of rotation A1 . The spind le 10 is driven in rotation by means of an electric drive motor 13, which is mounted to the carriage 2. Driving torque is transmitted from an output shaft 14 of the drive motor 13 to the spindle 10 through a transmission mechanism 15 (see Figs 4 and 7). Thus, the spindle 10 is rotatable under the effect of the drive motor 13 via the output shaft 14 and the transmission mechanism 15. The transmission mechanism 15 comprises a set of gear wheels acting between the output shaft 14 of the drive motor and the spind le 10. One gear wheel 16 of the transmission mechanism 1 5 is non-rotatably fixed to the out- put shaft 14 of the drive motor 13 and another gear wheel 1 7 of the transmission mechanism 1 5 is non-rotatably fixed to the spindle 10. These gear wheels 16, 1 7 are operatively connected to each other via a number of intermed iate gear wheels 18a, 18b, 18c rotatably mounted in an external housing 20 of the saw arm 1 1 . In the illustrated example, two of said intermed iate gear wheels 18b, 18c are non-rotatably connected to each other. As an alternative to gear wheels, the transmission mechanism 15 could be provided with a driving chain or driving belt for transmitting driving torque from the output shaft 14 of the drive motor to the spindle 1 0. The output shaft 14 of the drive motor 13 is rotatable about a second axis of rotation A2, which extends in parallel with and at a distance from said first axis of rotation A1 . The saw arm 1 1 is pivotally mounted to the carriage 2 by means of bearings 21 , 22, 23 and is pivotable about a pivot axis A3, which is perpendicular to the longitud inal axis of the guide rail 3 and coincides with said second axis of rotation A2. The saw arm 1 1 is adjustable into different rotational positions in relation to the carriage 2 by being pivoted about the pivot axis A3. A ring gear 24 (see Figs 4 and 6) is non-rotatably fixed to the saw arm housing 20 by means of fastening members 25 in the form of screws. A gear wheel 26 (see Fig 8) is rotatably mounted to the carriage 2 and in engagement with the ring gear 24. The wall saw 1 comprises an actuating device 27 (see Fig 8), by means of which said gear wheel 26 is rotatable in order to rotate the ring gear 24 and thereby pivot the saw arm 1 1 in relation to the carriage 2 about the pivot axis A3. The actuating device 27 comprises a motor 28 mounted to the carriage 2, by means of wh ich said gear wheel 26 is rotatable. Said motor 28 is preferably an electric motor, but could alternatively be a hydraulic motor. The actuating device 27 also comprises a transmission mechanism 29 for transmitting torque from the output shaft of said motor 28 to said gear wheel 26. In the illustrated example, this transmission mechanism 29 comprises a worm screw 30a non-rotatably connected to the output shaft of the motor 28 and a number of intermediate gear wheels 30b, 30c, 30d acting between the worm screw 30a and said gear wheel 26. The gear wheel 26 is non-rotatably connected to the last one 30d of said intermediate gear wheels.

In the illustrated embodiment, the drive motor 13 and the saw arm 1 1 are carried by a chassis 31 included in the carriage 2. The chassis 31 is vertically oriented and is preferably of metallic material, such as for instance steel. The chassis 31 comprises a vertical wall 32 (see Figs 4, 9 and 10) and a flange 33 protruding in a horizontal direction from this wall 32. This vertical wall 32 and the flange 33 are preferably formed in one piece, but are alternatively formed as separate pieces which are rigid ly joined to each other by welding . The saw arm 1 1 is pivotally mounted to the chassis 31 on a first side of said wall 32 and a motor cavity 34 is provided in the chassis 31 on an opposite second side of said wall 32. In the following , said first side of the wall 32 is denominated the outer side of the wall, whereas said second side of the wall 32 is denominated the inner side of the wall. The motor cavity 34 is delimited in one axial direction by said wall 32 and in the rad ial direction by said flange 33, which forms a cylindrical inner wall of the motor cavity 34. The stator 35 and rotor 36 of the drive motor 13 are accommodated in the motor cavity 34. Thus, the stator 35 and rotor 36 of the drive motor 13 are protected by said wall 32 and flange 33 of the chassis 31 . The output shaft 14 of the drive motor extends through an open ing 37 in the wall 32. A first axial bearing 21 and a second axial bearing 22 are provided between the saw arm 1 1 and the carriage 2, as illustrated in Figs 4 and 6. The first axial bearing 21 comprises a flat and ring-shaped first slid ing element 38, preferably in the form of a disc of plastic material, clamped between a first contact surface 39 of the saw arm 1 1 and a correspond ing contact surface 40 of the carriage 2. The second axial bearing 22 comprises a flat and ring-shaped second slid ing element 41 , preferably in the form of a ring of plastic material, clamped between a second contact surface 42 of the saw arm 1 1 and a clamping member 43 fixed to the carriage 2. Said first contact surface 39 of the saw arm 1 1 is pressed towards the correspond ing contact surface 40 of the carriage 2 under the effect of the press force exerted by the clamping member 43 against the second sliding element 41 . Thus, the clamping member 43 also keeps the first sliding element 38 clamped between the first contact surface 39 of the saw arm 1 1 and the corresponding contact surface 40 of the carriage 2. In the illustrated embod iment, the first slid ing element 38 has an outer diameter that is smaller than the inner diameter of the second sliding element 41 .

In the illustrated embodiment, a lateral surface on the ring gear 24 constitutes said second contact surface 42 of the saw arm 1 1 .

The clamping member 43 comprises an axially springy part 43b which is pre-tensioned against the second sliding element 41 so as to keep the second sliding element 41 clamped between the clamping member 43 and said second contact surface 42 of the saw arm 1 1 under the effect of a spring force exerted by the clamping member. The saw arm 1 1 is retained in engagement with the chassis 31 of the carriage 2 under the effect of the spring force exerted by the clamping member 43. Thus, the clamping member 43 keeps the saw arm 1 1 secured to the carriage 2 in a pre-tensioned manner.

In the illustrated embod iment, the clamping member 43 is ring- shaped and comprises an outer part 43a, through which the clamping member is fixed to the chassis 31 of the carriage 2. Said axially springy part 43b of the clamping member extends radially inwards from the outer part 43a and bears against the second sliding element 41 in a pre-tensioned manner. The outer part 43a of the clamping member is fixed to the chassis 31 by means of fastening members 44 in the form of screws. The clamping member 43 is preferable a flat ring of metallic material.

A rad ial bearing 23 is also provided between the saw arm 1 1 and the carriage 2. The radial bearing 23 is preferably located be- tween the first slid ing element 38 and the second slid ing element 41 , as seen in a direction perpendicular to the pivot axis A3. The radial bearing 23 is provided between an outer peripheral surface 45 of a circu lar cylindrical part 58 (see Figs 4, 6 and 1 0) included in the carriage 2 and an inner peripheral surface 46 of a circular cylindrical recess provided in the saw arm 1 1 . In the illustrated example, said circular cylindrical part 58 forms part of the chassis 31 of the carriage 2. I n the illustrated embodiment, the radial bearing 23 comprises a third sliding element 47, preferably in the form of a band of plastic material, arranged between said outer peripheral surface 45 and said inner peripheral surface 46. In the illustrated example, said first contact surface 39 of the saw arm 1 1 constitutes a bottom surface of said circular cylindrical recess, whereas the correspond ing contact surface 40 of the carriage 2 is provided on the outer side of the above-mentioned wall 32 of the chassis 31 , which constitutes an end wall of the above- mentioned circu lar cylindrical part 58 of the carriage 2. The second slid ing element 41 , the clamping member 43 and the ring gear 24 surround said circular cylindrical part 58 of the carriage 2. In the illustrated embod iment, the ring gear 24 is received in an annular recess 50 (see Figs 6 and 10) in the chassis 31 and the outer part 43a of the clamping member 43 is fixed to a part 51 of the chassis which surrounds said recess 50. Furthermore, the guide rollers 5a-5d and the feed gear wheel 8 are rotatably mounted to the chassis 31 , and the feed motor and the motor 28 of the actuating device 27 are received in a cavity 52 (see Fig 9) provided in the chassis 31 .

The carriage 2 may be lifted and carried by means of handles 54 mounted to the chassis 31 .

A lid 55 is fixed to the flange 33 of the chassis at the outer free end thereof by means of fastening members 57 (see Figs 3 and 1 1 ) in the form of screws or bolts. In the illustrated embod iment, the lid 55 and the drive motor 13 form part of a motor module 60 (see Fig 1 1 ) which is detachably mounted to the chassis 31 . The motor module 60 comprises a cylindrical sleeve 61 which is rigidly connected to the lid 55 and projects therefrom into the motor cavity 34, the stator 35 of the drive motor 13 being fixed to the sleeve 61 on the inner side thereof. An outer peripheral surface of the sleeve 61 abuts against an inner peripheral surface of the above-mentioned flange 33 of the chassis 31 . A channel 62 for cooling fluid is provided in the interface between the outer peripheral surface of the sleeve 61 and the inner peripheral surface of the flange 33, as illustrated in Fig 4. In the illustrated embodiment, the rotor 36 of the drive motor 13 comprises a rotor hub 66 (see Figs 4 and 5) , which is rotatably mounted in the carriage 2 through at least one first bearing 72, for instance in the form of a ball bearing or a roller bearing , provided on the outer side of the rotor hub 66 at a first end thereof and at least one second bearing 74, for instance in the form of a ball bearing or a roller bearing , provided on the outer side of the rotor hub 66 at an opposite second end thereof. In the illustrated example, said at least one first bearing 72 is provided between a flange 73 on the inner side of the lid 55 and an outer peripheral surface at the first end of the rotor hub 66, and said at least one second bearing 74 is provide between a flange 75 on the inner side of the wall 32 of the chassis 31 and an outer peripheral surface at the second end of the rotor hub 66. In the illustrated embod iment, the stator 35 of the drive motor 13 is located on the outside of the rotor 36. As an alternative, the stator 35 of the drive motor 13 may be located between an outer part of the rotor 36 and the rotor hub 66. In the latter case, the stator 35 is fixed to the lid 55 of the motor module 60.

In the illustrated embod iment, the rotor hub 66 is operatively connected to the output shaft 14 of the drive motor through a safety clutch 67 so as to allow torque to be transmitted from the rotor hub 66 to the output shaft 14 via the safety clutch 67. The safety clutch 67 is configured to allow mutual rotation between the rotor hub 66 and the output shaft 14 when said torque reaches a given threshold value. The safety clutch 67 is accommodated in a space inside the rotor hub 66 and comprises one or more first clutch members 68 (see Figs 5, 12 and 13), each of which being non-rotatably fixed to the rotor hub 66, and one or more second clutch members 69 each of which being non-rotatably fixed to the output shaft 14. Said first and second clutch members 68, 69 are pressed towards each other under the effect of a spring member 70 so as to allow torque to be transmitted from the rotor hu b 66 to the output shaft 14 via these clutch members 68 , 69. The spring member 70 is also accommodated in the space inside the rotor hub 66. Said first and second clutch members 68, 69 and the spring member 70 are located between an inner peripheral surface of the rotor hub 66 and an outer peripheral surface of a part 14a of the output shaft 14 surrounded by the rotor hub 66. The above-mention threshold value is given by the spring force of the spring member 70.

In the illustrated embodiment, said first and second clutch members 68, 69 have the form of ring-shaped discs and are arranged side by side in frictional engagement with each other. The output shaft 14 extends through a central opening in each clutch member 68, 69. The clutch members 68, 69 are moveable in the axial direction of the output shaft 14 and the rotor hub 66. In the illustrated example, each first clutch member 68 is provided with teeth 76 on its outer periphery, which teeth 76 are in engagement with internal splines in the rotor hub 66 so as to force the clutch member 68 to rotate together with the rotor hub 66, while at the same time allowing the clutch member 68 to slide axially in relation to the rotor hub 66. Each second clutch member 69 is provided with teeth 77 on its inner periphery, which teeth 77 are in engagement with external splines 78 on the output shaft 14 so as to force the clutch member 69 to rotate together with the output shaft 14, while at the same time allowing the clutch member 69 to slide axially on the output shaft 14. The first and second clutch members 68, 69 are arranged alternately side by side and are pressed towards each other by the spring member 70 so as to allow torque to be transmitted from the rotor hub 66 to the output shaft 14 by the frictional engagement between the clutch members. In the illustrated embod iment, the spring member 70 is clamped between an internal shoulder 79 (see Fig 5) on the rotor hub 66 and an axially outermost one of said clutch members 68, 69. The spring member 70 preferably comprises one or more Belleville washers 71 , the output shaft 14 extending trough a central opening in each Belleville washer. In the illustrated example, the spring member 70 comprises four Belleville washers 71 arranged side by side.

The spring force of the spring member 70 is adjustable by means of an adjustment member 86, which is provided with an external thread 87 that is in engagement with a corresponding internal thread 88 in the rotor hub 66 at the above-mentioned first end of the rotor hub, as illustrated in Fig 5. The adjustment member 86 abuts against an axially outermost one 68' of the first clutch members (see Fig 1 2). The position of the adjustment member 86 in the axial direction of the rotor hub 66, and thereby the axial pre-tensioning and spring force of the spring member 70, is adjustable by screwing the adjustment member 86 in either direction in relation to the rotor hub 66. At least one locking screw 90 is received in an axial through hole 91 in the adjustment member 86. An inner end 90a of this locking screw 90 is engageable in a recess 93 in the last-mentioned clutch member 68' in order to lock the adjustment member 86 to this clutch member 68' and thereby prevent mutual rotation between the adjustment member 86 and the rotor hub 66. Thus, when the end 90a of the locking screw 90 is received in a recess 93 in the clutch member 68' , the adjustment member 86 will be locked in its prevailing position in relation to the rotor hub 66. The locking screw 90 is provided with an external thread 89a that is in engagement with a corresponding internal thread 89b in said through hole 91 , as illustrated in Fig 12. In the illustrated example, two such locking screws 90 are used . To make possible an accurate adjustment of the position of the adjustment member 86, the clutch member 68' is provided with several recesses 93 distributed around the centre axis of the clutch member and/or the adjustment member 86 is provided with several threaded through holes 91 distributed around the centre axis of the adjustment member. The above-mentioned space inside the rotor hub 66 is limited in a first axial direction by the above-mentioned shoulder 79 on the rotor hub 66 and in the opposite axial direction by the adjustment member 86.

At the above-mentioned first end of the rotor hub 66, the output shaft 14 of the drive motor 13 is rotatably mounted to the rotor hub 66 through the adjustment member 86. In the illustrated example, a stub shaft 94 fixed to the output shaft 14 is rotatably re- ceived in an axial recess 95 in the centre of the adjustment member 86. The stub shaft 94 is mounted in a recess 97 at the end of the output shaft 14, for instance by press fit. In the illustrated example, the adjustment member 86 is ring-shaped and the above-mentioned recess 95 is formed as an axial through hole in the adjustment member 86.

At the above-mentioned second end of the rotor hub 66, the output shaft 14 of the drive motor 13 is rotatably mounted to the rotor hub 66 through a sleeve-shaped sliding element 98 provided between the rotor hub 66 and the output shaft 14. This sliding element 98 is clamped between a shoulder 96 on the output shaft 14 and a Belleville washer 71 of the spring member 70, as illustrated in Fig 12. As an alternative, the output shaft 14 and the rotor 36 of the drive motor 13 may be non-rotationally connected to each other directly without any intermediate safety clutch .

The wall saw 1 also comprises an electronic unit 63, which com- prises electron ic components for controlling the power supply to the stator 35 of the drive motor 13. In the illustrated embod iment, the electronic unit 63 is fixed to the lid 55 on the side thereof facing away from the motor cavity 34. The adjustment member 86 is accessible through an opening 99 (see Fig 5) in the lid 55 when the electronic unit 63 has been detached from the lid . The drive motor 13 is preferably a switched reluctance motor, but may alternatively be a permanent magnet motor or any other suitable motor. The invention is of course not in any way restricted to the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention such as defined in the appended claims.