GB2324485A

GB2324485A - Overload clutch

Info

Publication number: GB2324485A
Application number: GB9807918A
Authority: GB
Inventors: Helmut Wanek; Markus Heckmann
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-04-25
Filing date: 1998-04-14
Publication date: 1998-10-28
Anticipated expiration: 2018-04-14
Also published as: GB9807918D0; DE19717465A1; CH692776A5; ITMI980799A1; GB2324485B; DE19717465B4; IT1299092B1

Abstract

An electric tool machine for rotary and/or impact tools, e.g. an impact drilling machine or hammer drill, has a spindle sleeve (11), driven by an electric motor. A toolholder (12) attached is the spindle sleeve (11) and coupled non-rotatably by locking elements (19) to the spindle sleeve (11). The locking elements (19) for rotary driving of the toolholder (12) are simultaneously designed as load-limiting clutch elements of the overload clutch (20) acting between spindle sleeve (11) and toolholder (12). The elements (19) are loaded by a conical ring member (21) which is biased by spring (22).

Description

1 Electric tool machine

Background art

2324485 The invention relates to an electric hand tool machine for rotary and/or impact tools, in particular an impact drilling machine or hammer drill, of the type defined m the preamble of claim, 1.

Such a hand-guided electric tool machine is known from DE 34 43 186 C2. The toolholder is mounted by means of a hollow cylindrical shank onto the spindle sleeve and fastened thereon by means of the roller-shaped locking elements, which engage through axial slots in the shank into corresponding pockets formed m the spindle sleeve. The flinction of the locking elements is, on the one hand, rotary driving of the toolholder and, on the other hand, axially displaceable mounting of the toolholder on the spindle sleeve. The header lying in an axially displaceable manner inside the spindle sleeve is guided with a reduced-diameter portion m an axially displaceable manner in the toolholder and, under the action of the striker of the impact mechanism, hammers upon the end face of a tool such as a hammer drill clamped in a firictionally connected manner in the toolholder by means of clamping jaws, With the result that the toolholder and the tool clamped in the toolholder during operation execute a rotating and percussive (hammering) motion as a result of the rotating spindle sleeve and the acceleration of the striker in the direction of the header.

From DE 38 44 3 11 A1 it is known to equip a drilling machine with an overload clutch in order to safeguard the operator holding the drilling machine in the event of seizing of the drill in the machining surface. The overload clutch in said case is disposed between a gear wheel driven by an output shaft of an electric motor and the spindle sleeve carrying the toolholder and is realized by working, M the end face of the gear wheel seated in a freely rotating manner on the spindle sleeve,detent recesses into which roller-shaped detent bodies with 2 radially directed body axes engage at least halfway and by pressing the gear wheel by means of a clutch spring in the form of a compression spring against a disc, which is connected non-rotatably to the spindle sleeve and has detent cavities, which correspond to the detent recesses in the ring gear, for receiving the detent bodies. In the event of seizing of the drill during operation of the drilling machine, e.g. as a result of reinforcing iron in reinforced concrete, the detent bodies move out of the detent cavities but remain in the detent recesses of the gear wheel. Thus, the gear wheel is displaced towards the clutch springs and continues to rotate, since it i's still driven by the output shaft, without driving the disc and hence the spindle sleeve.

Advantages of the invention The electric tool machine according to the invention having the characterizing features of claim 1 has the advantage of realizing an overload clutch for the drilling and hammering mode of the machine m a simple manner using few -additional structural elements. The mounting for tile toolholder on the spindle sleeve and the overload clutch forin.an integrated structural unit, in which the locking elements of the mounting additionally perform the function of the clutchor detent elements of the overload clutch. Thus, the design of the electric tool machine despite an additional overload clutch remains simple and as a result of reducing the number of parts and tile assembly time a cost benefit is achieved in terms of manufacturing costs.

Advantageous developments and improvements of the electric tool machine indicated in claim 1 are possible by virtue of the measures outlined in the finiher claims.

According to a preferred embodiment of the invention, the integration of the mounting of the toolholder on the spindle sleeve and the overload clutch between spindle sleeve and toolholder is realized in a particularly 3 sIMPle manner in that the spindle sleeve overlaps a hollow cylindrical shank of the toolholder and in the overlap region has radial openings, which are distributed over the periphery and penetrate the sleeve wall. Countersunk in the shank of the toolholder are pockets radially aligned with the openings, and the locking elements take the form of rolling bodies, which are guided in the openings and may engage into the pockets and be supported against the pocket base, it being preferred that the rolling bodies take the form of balls and the openings in the spindle sleeve take the form of radial bores. The overload clutch in said case is supplemented by a supporting ring, which embraces the rollmg bodies projecting from the openings, and by a clutch. spring preferably in the form of a compression spring which is mounted on the spindle sleeve. The supporting ring has an axially aligned inner ring surface, which overlaps the rolling bodies with radial clearance, and a conical support surface, which lies against the rolling bodies and forms an obtuse angle with the inner ring surface. The clutch spring is supported, on the one hand, against the supporting ring and, on the other hand, against an abutment fixed in an axially non-displaceable manner on the spindle sleeve. To guarantee the axial mobility of the toolholder, the supporting ring is applied under the action of the clutch spring against a stop fixed in an axially non-displaceable manner on the spindle sleeve, its support surface touching but not clamping the rolling bodies.

According to an advantageous embodiment of the invention, the shank portion of the toolholder containing the pockets is reduced in diameter and the radial clearance of the inner ring surface from the rolling bodies is less than the sum of the radial depth of the pockets and the difference in radius between the shank portion having the pockets and the shank portion immediately adjacent to said operating end remote from the toolholder. By virtue of the radial annular shoulder thus formed at least at the rear pocket end and by virtue of limiting the maximurn radial rolling body travel to a value which does not exceed said annular shoulder, the toolholder in the event of blocking of the tool is reliably prevented from being torn out.of the spindle sleeve because the rolling bodies are supported 4 against the rear annular radial shoulder.

Drawings There follows a detailed description of an embodiment of the invention which is illustrated in the drawings. The drawings show:

Fig. 1 in a cutout manner a longitudinal section of a hammer drill, Fig. 2 an enlarged view of the cutout 11 m Fig. 1, Fig. 3 a section along the line III-III M Fig. 2.

Description of the embodiment

The harnmer drill, which is illustrated in a cutout manner and in longitudinal section in Fig. I as an embodiment of a general, in particular handguided electric tool machine for rotary and/or irnpact tools, comprises a housing 10, In which a spindle sleeve 11 driven via a gearing by an electric motor (not shown here) is rotatably supported. Attached to the front end of the spindle sleeve I I is a toolholder 12, which projects from the housing 10 and with a protective cap 13 overlaps the front end of the housing 10 with clearance. The toolholder 12 comprises a chuck body 121 with a central location bore 14 for the insertion of a shank of a tool 15 and, as an integral extension thereof, a hollow cylindrical shank 122 which inside the housing 10 is overlapped with slight clearance by the front end of the spindle sleeve 11. The tool to be inserted into the location bore 17 is fixed in a non-rotatable manner in the chuck body 121 and prevented from unintentionally sliding axially out of the chuck body 121 by means of a quickrelease locking element 16. The toolholder 12 is coupled to the spindle sleeve I I in a non-rotatable and, to a limited extent, axially displaceable manner. To said end, the spindle sleeve 11 has, in its region of overlapping of the shank 122, a plurality of radial bores 17 which are distributed over the periphery and fully penetrate the sleeve wall, and there are countersunk in the shank 122 of the toolholder 12 axial pockets 18, which are radially aligned with the radial bores 17 and whose axial length is a multiple of the bore diameter of the radial bores 17. Guided in the radial bores 17 are locking elements in the form of balls 19, which project from the inside and outside of the spindle sleeve 11 and may be supported against the pocket base 181 of the pockets 18. The balls 19 lying with slight clearance m the radial bores 17 and engaging into the pockets 18 guarantee the rotary driving of the toolholder 12 during rotation of the spindle sleeve 11 and at the same time allow a limited axial displacement of the toolholder 12 by a displacement distance predetermined by the axial length of the pockets 18.

Disposed between the spindle sleeve 11 and the toolholder 12 is an overload clutch 20 which, m the event of blocking of the tool in the machining surface e.g. as a result of reinforcing iron in reinforced concrete, automatically uncouples the toolholder 12 from the spindle sleeve 11 so that the latter may rotate freely while the toolholder 12 is stationary. Said overload clutch 20 utilizes the locking elements in the form of balls 19 provided for the non-rotatable and axially displaceable mounting of the toolholder 12 on the spindle sleeve 11 as loadlimiting clutch- or detent elements and additionally comphses a supporting ring 21 and a clutch spring 22 in the form of a compression spring, which is mounted onto the spindle sleeve 11 and supported, on the one hand, against the supporting ring 21 and, on the other hand, against an abutment 23 fixed m an axially nondisplaceable manner on the spindle sleeve 11. The supporting ring 21, which embraces the balls 19 projecting from the radial bores 17, has an axially aligned inner ring surface 211 overlapping the balls 19 with radial clearance and a conical support surface 212, which lies against the balls 19 and forms an obtuse angle with the inner ring surface 211 (Fig. 2). To guarantee the axial mobility of the 6 toolholder 12, a stop for the supporting nng 21 is formed by means of a snap ring 24, which is'inserted into a peripheral groove in the spindle sleeve 11, and prevents the clutch spring 22 from clamping the balls 19 firmly over the support surface 212. The position of the snap ring 24 is so selected that the conical support surface 212 just touches the balls 19 without exerting an axial displacement force upon the balls 19. The lateral boundary walls 182 of the pockets 18 pointing in a peripheral direction of the shank 122 and extending in axial direction are inclined relative to the radial plane so that they form an obtuse angle with the pocket base 181 (Fig. 3). Said inclination of the lateral boundary walls 182 facilitates the disengagement of the balls 19 from the pockets 18 in the event of overload.

In the event of overload, the torque at the spindle sleeve I I is greater than the detent moment applied by the balls 19 and the clutch spring 22 between spindle sleeve I I and toolholder 12. The balls 19 then slide radially outwards over the lateral boundary walls 182 and, in so doing, displace the supporting ring 24 via the latter's support surface 212 counter to the action of the clutch spring 22.

The moment the balls 19 are fiilly disengaged from the pockets 18, the overload clutch 20 is released and the spindle sleeve 11 may rotate relative to the toolholder 12. To enable ftffl disengagement of the balls 19 from the pockets 18 in the event of overload, the radial clearance of the inner ring surface 211 of the support ring 21 from the surface of the balls 19 is made slightly greater than the difference between the ball diameter of the balls 19 and the radial depth or height h (Fig. 2) of the pockets 18; in other words, the radial distance of the inner ring surface 2 11 from the pocket base 181 is slightly greater than the sum of ball diameter and pocket - depth h.

As Figs. 2 and 3 reveal, the shank portion 122a, containing the pockets 18, of the hollow cylindrical shank 122 of the toolholder 12 is slightly reduced in diameter. The axial length of said shank portion 122a corresponds exactly to the axial length of the pockets 18. The radius of the outer surface of the 7 reduced-diameter shank portion 122a is denoted in Fig. 3 by r, and the radius of the outer surface of the remaining shank 122 is denoted by r2. The radial clearance of the inner surface 211 of the supporting ring 21 from the balls 19 is additionally made smaller than the swn of the radial depth h of the pockets and the radius difFerence i, - r, between the radius r, of the shank portion having the pockets 18 and the radius r, of the two shank portions 122b immediately adjacent thereto. By virtue of said radius difference r2- r, a radial shoulder is formed at each of the two end faces of the pockets 18, which end faces are aligned at right angles to the axial direction. In an overload situation, the balls 19 are supported against the rear annular shoulder (not Visible in Fig. 2) lying closer to the free shank end remote from the toolholder 12 and prevent the toolholder 12 from being tom out of the spindle sleeve 11. The above- mentioned dimensioning of the radial clearance of the inner ring swface 2 11 of the supporting ring 2 1 from the balls 19 prevents said radial annular shoulders from being surmounted by the balls 19.

Me hammer drill has, for additional axial drivmg of the rotating tool 15, an impact mechanism 25 of which Fig. 1 shows m a cutout manner a striker 26, which is guided m an axially displaceable manner inside the spindle sleeve 2 1, and a header 27, which lies in an axially displaceable manner inside the hollow cylindrical shank 122 of the toolholder 12 and is applied by its front end 271 remote from the striker 26 against the opposing end face of the tool 15 held in the toolholder 12. The striker 26 is accelerated in axial direction by a drive (not shown here) and strikes against the header 27, which transnuts said impact force directly to the tool 15. The toolholder 12 is, as a result of the tool contact pressure exerted by the operator, shifted in the direction of its end position of deeper engagement into the spindle sleeve 11. A sealing ring 28, which is mserted into a peripheral groove of the header 27 and supported against the inner wall of the shank 122 of the toolholder 12, prevents lubricant from escaping in a forward direction.

The invention is not linuted to the embodiment described above.

8 Thus, the balls 19 used simultaneously as clutch- or detent elements of the overload clutch 20 and as locking elements for rotary driving and axial guidance of the toolholder 12 by the spindle sleeve 11 may alternatively be replaced by other forms of rolling body, e.g. by rollers having roller axes aligned parallel to the spindle sleeve axis. The hollow cylindrical shank of the toolholder may alternatively overlap the front end of the spindle sleeve, in which case the pockets for engagement of the rolling bodies are disposed m the spindle sleeve 11 and the radial openings for guiding the rolling bodies are disposed m the hollow cylindrical shank of the toolholder. The supporting ring of the overload clutch is then seated, like the clutch spring, on the shank of the toolholder. Furthermore, it is possible to dispense with the displaceability of the toolholder 12 in an axial direction relative to the spindle sleeve 11 and to couple the toolholder 12 exclusively m a nonrotatable manner to the spindle sleeve 11. In said case, the length of the axial pockets 18 is substantially reduced so that the balls 19 or rolling bodies engage only with slight clearance into the pockets 18.

9

Claims

1. Electric tool machine for rotary and/or impact tools, in particular an impact drilling machine or harnmer drill, having a spindle sleeve (11) driven by an electric motor, having a toolholder (12) attached to the spindle sleeve (11) and coupled non-rotatably by locking elements to the spindle sleeve (11), characterized in that the locking elements (rolling bodies 19) are simultaneously designed as load-linUting clutch elements of an overload clutch (20) acting between spindle sleeve (11) and toolholder (12).

2. Machine according to claim 1, charactenzed in that the spindle sleeve (11) overlaps a hollow cylindrical shank (122) of the toolholder (12) and in the overlap region has radial openings (17), which are distributed over the periphery and penetrate the sleeve wall, that axial pockets (18) are countersunk in the shank (122) of the toolholder (12) and radially aligned with the openings (17) and that the locking elements take the form of rolling bodies (19), which are guided in the openings (17) and engage into the pockets (18).

3. Machine according to claim 2, characterized in that the rolling bodies (19) projecting from the openings (17) are embraced by a supporting ring (2 1), which forms a part of the overload clutch (20) and has an axially aligned inner ring sur---face (211) overlapping the rolling bodies (19) with radial clearance and a conical support surface (212), which rests against the rolling bodies ( 19) and forms an obtuse angle with the inner ring surface (211), and that the supporting ring (2 1) enclosing the spindle sleeve ( 11) is applied by an axially directed spnng force against a stop (24) fixed m an axially non-displaceable manner on the spindle sleeve (11).

4.

Machine according to claim 3, characterized in that the overload clutch (20) has a clutch spring (22) in the form of a compression spring, which is seated on the spindle sleeve ( 11) and supported between the supporting ring (2 1) and an abutment (23) fixed in an axially non- displaceable manner on the spindle sleeve (11).

5. Machine according to claim 3 or 4, characterized in that the stop is formed by a snap ring (24) inserted m a peripheral groove in the spindle sleeve (11).

6. Machine according to one of claims 2 to 5, characterized m that the lateral boundary walls (182) of the pockets (18), which walls are directed m a peripheral direction of the shank (122) of the toolholder (12) and extend m axial direction, form an obtuse angle with the pocket base (18 1).

7. Machine according to one of claims 1 to 6, characterized in that the radial clearance of the inner ring surface (211) of the supporting ring (2 1) from the rolling bodies (19) is slightly greater than the difference between the radial dimension of the rolling bodies (19) and the radial depth (h) of the pockets (18).

8. Machine according to one of claims 3 to 7, characterized m that the shank portion (122a), containing the pockets (18), of the shank (122) of the toolholder (12) is reduced in diameter and that the radial clearance of the inner ring surface (211) of the supporting ring (2 1) from the rolling bodies (19) is less than the sum of the radial depth (h) of the pockets (18) and the radius difference (r2- rj) between the radius (r,) of the shank portion (122a) having the pockets (18) and the radius (r) of the shank portion (122b) immediately adjacent to said shank portion (122a) in the direction of the end of the shank (122) remote from the tool.

9.

Machine according to one of claims 2 to 8, characterized in that, for 11 limited axially displaceable coupling of the toolholder (12) to the spindle sleeve (11), the axial length of the pockets (18) is substantially greater than the dimension, directed in a longitudinal direction of the pockets (18), of the engagement region of the rolling bodies (19).

10. Machine according to one of claims 2 to 9, characterized in that the rolling bodies take the form of balls (19) and the openings M the spindle sleeve (11) take the form of radial bores (17).

11. Machine according to one of claims 1 to 10 having an impact mechanism (25) for axial displacement of the tool (15) held in the toolholder (12), characterized in that the impact mechanism (25) comprises a striker (26) accommodated m an axially displaceable manner m the spindle sleeve (11), a drive accelerating the striker (26) in axial direction and a header (27) transnutting the striker impacts to the tool (15) and that the header (27) is accommodated m an axially displaceable manner m the hollow cylindrical shank (122) of the toolholder (12).

12. An electric machine tool substantially as herein described with reference to the accompanying drawings.