GB2321089A - Hand machine tool with torque responsive safety clutch - Google Patents

Abstract

A hand machine tool, eg a drill, impact drill, drilling hammer etc, comprises a safety clutch with latch-over torque disengagement and having first and second clutch parts 181, 182 drivenly connected by coupling elements 19, 20 in the form of a elastically compliant wavy spring ring 27 and balls 21 respectively. The wavy spring ring 27 has troughs 272 which engage in cavities 26 in the first clutch part 181 and crests 271 that bear against the balls 21. If a pre-set latch over torque is exceeded the balls 21 will deform the crests 271 of the wavy spring 27 thereby allowing the two clutch parts 181, 182 to rotate relative to one another. When used with drilling hammers the second clutch part 182 comprises a thin wall sleeve having shallow blind bores 22 for the balls 21. To prevent the balls 21 from jamming or rotating out of the bores 22, due to their shallowness, a web 30 is provided.

Description

2321089 1 Hand machine tool

Background art

The invention relates to a hand machine tool, such as a drillm'g or impact drilling machine, as well as a drilling hammer or the like, of the type deffied in the preamble of claim 1.

In such hand machine tools, the safety clutch is used in the event of blocking of the tool to prevent the transmission of torques, which are no longer supportable by the operator without injury, to the machine housing with its handle held by the operator.

In a known hand machine tool with a safety clutch of said-type (DE 38 32 202 Cl), the safety clutch inserted in the drive train between electric motor and chuck comprises three clutch parts and an operating device for adjusting latch-over torques of varying magnitudes. To said end, two discshaped clutch parts are disposed coaxially inside a third, hollowcylindrical clutch part which is provided with an external gearing and is supported in a freely rotatable manner on a shaft. Of the two disc-shaped clutch parts, one is non-rotatably connected to the shaft and the other may be fastened by means of the operating device non-rotatably to the other disc-shaped clutch part. The transmission means acting between the clutch parts has a plurality of transmission elements which are disposed between the opposmig peripheral surfaces of the outer clutch part and each of the inner clutch parts. Each transnuission element comprises a cylindrical body, which lies in a radial blind bore of the inner, discshaped clutch parts, and a helical compression spring, which is supported between the base of the bore and the cylindrical body and presses the cylindrical body into one of detent cavities 2 formed mi the peripheral surface of the outer clutch part. Thus, each cylindrical body establishes a positive connection between the outer and the two inner clutch parts. When a specific torque, the so-called latch- over torque, is exceeded, the cylindrical bodies are pushed by the flanks of the detent cavities counter to the action of the helical compression springs so far into the blind bores that the cylindrical bodies move out of the detent cavities and lie against the annular surface of the outer clutch part lying between the detent cavities. The outer clutch part and the two inner clutch parts may then rotate past one another.

In a known drilling machine with a safety clutch (DE 38 44 311 AI), the two clutch parts arranged coaxially with one another have two axially opposing flanges, lymig between which is a transmission means comprising a plurality of transmission elements. Each transmission element is formed by a cylinder, the cylinders projecting into radially extending detent cavities lying opposite one another in the two clutch part flanges. A clutch spring in the form of a helical compression spring exerts upon the one clutch pait an axial force directed towards the other clutch part and thereby clamps the cylinders between the clutch part flanges. In the event of a torque exceeding the latch-over torque, the cylinders via the flanks of the detent cavities displace the one clutch part counter to the action of the helical compression spring and move out of the detent cavities in said clutch part. Thus, the two clutch parts are uncoupled and may rotate past one another.

In both hand machine tools, the torque transmission is effected by rigid transmission elements, namely the cylinders, which may Yield only radially or axially counter to spring action. This has the drawback that the yieldmig motion of the transmission elements after extended use of the hand machine tool is hampered, e.g. as a result of clogging with oil or accumulated dirt, and so the tripping torque of the safety clutch becomes unacceptably high in older hand 3 machine tools. But even in new machines there is a wide variation of the latchover torque within a production batch.

Advantages of the invention In contrast, the hand machine tool according to the invention having the charactenizing features of claim 1 has the advantage that, by virtue of designing the transmission elements so as to be elastically compliant mi direction of rotation and not in a radial or axial direction - when the latch-over torque is reached and/or exceeded, it is not only possible to keep within a very low tolerance of the latchover torque m the production process of new machines but also the latch-over torque remains substantially constant with extended use of the hand machine tool. The wear of the transmission means, which preferably comprises a plurality of elastically compliant transmission elements with two coupling elements fixed in each case to one of the clutch parts, is relatively low with the result that the safety clutch has a long service life.

Advantageous developments and improvements of the hand machine tool indicated in claim 1 are possible by virtue of the measures outlied in the further claims.

According to an advantageous embodiment of the invention, the elasticity of the transmission elements is achieved in that one of the two coupling elements is of an elastically compliant design, its stiffness being fixed in such a way that at torque values equal to or above the latch-over torque the two coupling elements are able, with simultaneous elastic deformation of the one coupling element, to rotate past one another.

4 According to a preferred embodiment of the invention, the elastically compliant coupling element is realized by at least one spring bow and the other coupling element is realized as a cylindrical or spherical capshaped protuberance projecting from the clutch part and pressing in at least one direction of rotation against the spring bow. Preferably, a spring bow is provided on either side of each protuberance and the two spring bows are integrally connected to one another by a connecting bow lying positively in the one clutch part. In a manner which is particularly advantageous in terms of production engineering, this may be realized in that the spring bows and connecting bows are formed by an alternating sequence of wave crests and wave troughs of a closed, wave- form spring ring. The wave troughs representing the connecting bows are at least partially positively received in a cavity profile formed on the one clutch part. The spring ring thus representing the one coupling element of all of the transmission elements is easy and quick to assemble and allows a reduction in the cost of assembly of the safety clutch.

In a preferred embodiment of the invention, the two clutch parts are disposed concentrically with one another and the coupling elements are disposed in surfaces of the clutch pails which are concentric with one another. The spring ring is so designed that the axes of symmetry of the wave crests and wave troughs lie on radial lines of the spring ring. The spring ring is preferably made by bending spring steel strip and welding the two strip ends to one another. The cavity profile for positively holding the spring ring is formed at the radial base of an annular groove, which is provided mi the outer clutch part and is open towards the firont of the clutch part. The protuberances forming the other coupling elements of the transmission elements are disposed at the peripheral surface of the inner clutch part.

According to a preferred embodiment of the invention, each protuberance is formed by the projecting region of a cylinder or ball, which lies partially in a groove or blind bore introduced axially into the inner clutch part.

Given said construction of the other coupling elements of the transmission elements, according to an advantageous embodiment of the ffivention there is provided, in the region of each connecting bow lying opposite a cylinder or ball, a web which projects axially into the annular groove and overlaps the cylinder or ball with slight radial clearance. Said webs prevent the cylinders or balls from escaping or jamming and thereby ensure trouble-free operation of the safety clutch.

Drawings There follows a detailed description of the invention with reference to embodiments which are illustrated in the drawings. The drawings show:

Fig. 1 in a cutout manner a longitudinal section of a hand machine tool with a rotating tool, Fig. 2 an enlarged view of the section II-11 in Fig. 1 with an additional cutout of a modified safety clutch, Fig. 3 a section of the modified safety clutch according to cutting line IllIll in the cutout of Fig. 2, Fig. 4 an enlarged view of the cutout IV in Fig. 3.

6 Deschiption of the embodiments The impact drilling machine shown, as an embodiment of a hand machine tool with a rotating tool, mi a cutout manner in the longitudinal section of Fig. 1 has in its machine housing 10 a non-visible electric motor, the drive shaft 11 of which drives an intermediate shaft 12. Engaging mito a gear wheel 13 with external gearing, which is disposed non-rotatably on the intermediate shaft 12, is a ring gear 14 which is rotatably mounted on an output shaft 15 supported in the machine housing 10. The output shaft 15 drives a chuck denoted by 16, in which a drillmg tool or an impact drilling tool may be inserted.

Seated non-rotatably on the output shaft 15 is a coaxial ring 17 which is overlapped by the pot-shaped I'Mig gear 14 so that the outer annular surface of the ring 17 and the inner peripheral surface of the rmig gear 14 lie opposite one another with radial clearance. The ring gear 14 forms the first clutch part 181 and the ring 17 the second clutch part 182 of a safety clutch 18 in the drive train between the drive shaft 11 driven by the electric motor and the chuck 16 holding the tool. Acting between the two clutch parts 181, 182 for the purpose of transmitting a torque is a transmission means, which comprises a plurality of transmission elements 183 and, at torque values equal to or above a so-called latch-over torque, enables a relative movement between the two clutch parts 181 and 182. In the embodiment of Fig. 1, a total of two transmission elements 183 are provided between the clutch parts 181, 182 and are arranged offset by identical angles at periphery - here, therefore, by 1800 - relative to one another. As is evident in particular from the sectional view in Fig. 2, each transmission element 183 comprises a first coupling element 19 fixed to the first clutch part 181 and a second coupling element 20 fixed to the second clutch part 182. The first coupling element 19 is designed so as to be elastically compliant in direction of rotation, to 7 which end its stiffiess is fixed 'm such a way that, at an effective torque above the preset latch-over torque, the two coupling elements 19, 20 are able, with simultaneous elastic deformation of the first coupling element 19, to rotate past one another. To said end, the second coupling element 20 takes the form of a ball 2 1, which is received in a blind bore 22 introduced radially in the second clutch part 182 and projects with a projecting region from the blind hole 22 beyond the outer annular surface of the second clutch part 182 and into an annular groove 23 introduced in the inner peripheral surface of the first clutch part 18 1. As Fig. 1 reveals, the annular groove 23 is open towards the front of the pot-shaped clutch part 181 situated at the pot opening.

The coupIffig element 19 of the transmission elements 183 which is designed so as to be elastically compliant in direction of rotation comprises two spring bows 24, which are integrally connected to one another by a connecting bow 25. The two spring bows 24 are disposed on either side of the balls 21 and are supported, offset from the radial centre of the ball 2 1, agamist said ball. The connecting bow 25 lies partially positively in a cavity 26 formed at the radial base of the annular groove 23 in the first clutch part 18 1. The spring bows 24 and connecting bows 25 are formed by an alternating sequence of wave crests 271 and wave troughs 272 of a closed, wave-form spring ring 27. The wave troughs 272 of the spring ring 27 are received in a cavity profile comprising a plurality of equidistantly arranged cavities 26 formed at the radial base of the annular groove 23 in the first clutch part 18 1. The radii of curvature of the wave crests 271 and wave troughs 272 are of equal size. The spring ring 27 is preferably made by bending spring steel strip 'm such a way that the axes of symmetry of the wave crests 271 and wave troughs 272 lie on radial lines of the spring ring 27. The two strip ends are welded to one another. By means of said spring ring 27 the number of elastically compliant coupling elements 19 fixed to the outer clutch part 181 is considerably 8 increased. Each of said coupling elements 19 together with the two coupling elements 20 in the form of balls 21 may form the two transmission elements 183. The two clutch parts 181 and 182 may therefore be coupled to one another rotated through small angular increments relative to one another, in the embodiment having twelve wave troughs 272 and twelve wave crests 273, through angular increments of 30'.

Upon switching on of the electric motor, the latter's drive shaft 11 via the gear wheel 13 on the intermediate shaft 12 drives the ring gear 14, the torque of which is transmitted via the safety clutch 18 to the output shaft 15 and the tool. When the impact drilling mode is switched on, an impact mechanism denoted by 28 periodically strikes the end of the output shaft 15 remote ftom the chuck 16. In the event that the torque to be transnuitted between the two clutch parts 181 and 182 and the transnfission elements 183 of the safety clutch 18 exceeds a preset socalled latch-over torque, e.g. as a result of seizing of the drilling tool, the first coupling elements 19 realized by the spring rmig 27, with simultaneous deformation of the two spring bows 24 pressing 'm direction of rotation directly against the two balls 2 1, slide past the spring bows 24 and the spring ring 27 slides as a whole over the two balls 21. Said process is repeated at each subsequent connecting bow 25 with the result that the two clutch parts 181 and 182 rotate past one another. The latch-over torque, at which the safety clutch 18 responds, is determined by the outside and inside diameter of the spring ring 27, the depth of the cavities 26, the radii of the wave crests 271 and wave troughs 272 and by the thickness and width of the spring steel strip.

The cutout bordered by a dash-dot line in Fig. 2 and Figs. 3 and 4 show a modification of the safety clutch 18 such as is preferably used in socalled drilling hammers. Here, the second clutch part 182 is designed, not as a ning, but as a 9 fifin-walled sleeve 29 which is connected non-rotatably to the output shaft 15. The ring gear 14 with external gearing is seated rotatably on the sleeve 29 and locked against axial displacement by means of a disc 32 and two retaining rings 3 1. Because the sleeve 29 is thin-walled, the balls 21 forming the second coupling element 20 of the transmission elements 183 project to a far greater extent from the blind bore 22 in the sleeve 29. To prevent the balls 21 from rotating out of the blind bores 22 or from becoming jammed, 'm front of each cavity 26 opposite a ball 21 there is a web 30, which projects integrally from the front wall of the annular groove 23 and axially into the annular groove 23 in the first clutch part 18 1. The web 3 0 is aligned in a radially symmetric manner relative to the cavity 26 and overlaps the ball 21 with slight radial clearance (Fig. 4).

The invention is not restricted to the descnbed embodiment. Thus, instead of only two transmission elements 183, it is possible to provide three transmission elements 183 offset in each case by 120' relative to one another or an even higher number of transmission elements, which are all of the described construction. Instead of the balls 2 1, cylinders may be used. It is also possible entirely to dispense with the separate balls 21 and cylinders inserted 'm blind holes 22 and provide cylindrical or spherical cap-shaped protuberances on the outer periphery of the ring 17 foriming the second clutch part 182.

Instead of the plurality of transnuission elements 183, the transmission means may comprise a single spring ring which may take the same form as the spring ring 27 in Fig. 2, Le. a closed, wave-form ring with an alternating sequence of wave crests and wave troughs, which are bent out at right angles to the ring shape. In said case, the outer annular clutch part at its inner periphery and the inner clutch part at its outer peniphery carry cavities or depressions, which are uniformly distributed over the pefiphery and have a contour adapted to the shape of the wave crests and wave troughs. The spring ring in turn lies, in each case Positively, with the outer portions of the wave troughs mi the cavities of the inner clutch part and with the outer portions of the wave crests in the cavities of the outer clutch part. Depending on the magnitude of the required latch-over torque and the stiffness of the spring ring, the depth of immersion of the portions of the wave crests and wave troughs into the cavities is more or less great.

In each of the embodiments, a radially acting safety clutch is described, in which the two clutch parts 181, 182 are connected to one another in a radial direction by the transmission elements 183. The construction according to the invention of the safety clutch 18 may however also be translated to axially acting safety clutches, m which the two clutch parts 181, 182 are connected mi an axial direction by the transmission elements 183. Such an axially acting safety clutch is described, for example, in the initially cited DE 3 8 44 3 11 A 1. In said case, the blind bores 22 would have to be introduced axially in the second clutch part and the spring ring 27 would have to be bent mi such a way that the wave crests 271 and wave troughs 272 extend in the wall plane of a cylinder envelope and so are likewise axially aligned.

Any toolholder may be used as chuck 16. The chuck may, for example, be a toolholder, in which the tool is clamped firmly between clamping jaws. It may however alternatively be a toolholder, into which the tool is inserted and axially interlocked.

11

Claims (1)

1. Claims

   1.

   2.

   Hand machine tool, such as a drilling or impact drillmig machine as well as a drilling hammer or the like, having a safety clutch (18) disposed in the drive train between an electric motor and a toolholding chuck (16) and comprising two clutch parts (181, 182) and at least one transmission means (183), which acts between said clutch parts and, when torque values below a latch-over torque are effective at one of the two clutch parts (181, 182), effects a positive rotary coupling of the other clutch part (182, 18 1) and, given torque values above the latch-over torque, enables a relative movement between the clutch parts (181, 182), characterized 'm that the at least one transmission means (183) is designed so as to be elastically compliantmi the direction of rotation of the clutch parts (181, 182) at torque values equal to or greater than the latch-over torque.

   Machine according to claim 1, characterized mi that the transmission means has at least one transmission element (183), which comprises a coupling element (19) fixed to the one clutch part (181) and a coupling element (20) fixed to the other clutch part (182), and that one of the two coupling elements (19, 20) is designed so as to be elastically compliant in direction of rotation.

   Machine according to claim 2, characterized mi that the stiffness of the elastically compliant coupling element (19) is fixed 'm such a way that, at torque values equal to or greater than the latch-over torque, the two coupling elements (19, 20) are able, with 12 simultaneous elastic deformation of the one coupling element (19), to rotate past one another.

   4.

   5.

   6.

   7.

   Machine according to claim 2 or 3, characterized mi that the elastically compliant couplmg element (19, 20) takes the form of a spring bow (24).

   Machine according to claim 4, characterized in that the other coupImig element (20) takes the form of a cylindrical or spherical cap-shaped protuberance (ball 21), which projects from the other clutch part (182) and in at least one direction of rotation presses against the spring bow (24).

   Machine according to claim 5, characterized in that, viewed in a peripheral direction of the clutch parts (181, 182), a spring bow (24) is disposed on either side of each protuberance (ball 21) for contacting by the protuberance (ball 21) in inverse directions of rotation and that the two sprmg bows (24) are integrally connected to one another by a connecting bow (25) which lies at least partially positively in the one clutch part (18 1).

   Machine according to claim 6, characterized in that the spring bows (24) and connecting bows (25) are formed by an alternating sequence of wave crests (27 1) and wave troughs (272) of a closed, wave-form spring ring (27) and that the wave troughs (272) representing the connecting bows (25) are at least partially positively received in a cavity profile (26) formed on the one clutch part ( 18 1).

   8.

   9.

   10.

   12.

   13 Machine according to claim 7, characterized in that the radii of curvature of the wave crests (271) and wave troughs (272) are of equal size.

   Machine according to claim 7 or 8, characterized in that the two clutch parts (181, 182) are disposed concentrically with one another and the coupling elements (19, 20) are disposed on surfaces of the clutch parts (181, 182) which are concentric with one another and that the spring ring (27) is so designed that the axes of symmetry of the wave crests (271) and wave troughs (272) lie on equidistant radial lines of the spring ring (27).

   Machine according to one of claims 7 - 9, characterized in that the spring ring (27) is formed by bending spring steel strip and welding the two strip ends to one another.

   Machine according to one of claims 7 - 10, characteri zed in that the cavity profile (26) is formed at the radial base of an annular groove (23) provided in the one clutch part (181) and preferably that the annular groove (23) is open towards the firont of the clutch part (181).

   Machine according to one of claims 5 - 11, characterized in that each protuberance on the other clutch part (182) is formed by the projecting region of a cylinder or ball (2 1), which lies partially 'm a slot or blind bore (22) mitroduced in the clutch parts (181, 182).

   14 13.

   14.

   15.

   16.

   Machine according to claim 12, characterized in that disposed 'm front of each cavity (26) lying opposite a cylinder or ball (2 1) is a web (30), which projects axially into the annular groove (23) and overlaps the cylinder or ball (2 1) of the other clutch part ( 182) with slight radial clearance.

   Machine according to one of claims 2 - 13, characterized mi that provided over the periphery of the clutch parts (181, 182) are at least two, preferably three transmission elements (183) which are arranged offset by identical angles at periphery relative to one another.

   Machine according to one of claims 1 - 14, characterized in that the one clutch part ( 18 1) takes the form of a driven ring gear ( 14) and the other clutch part (182) takes the form of a rmig (17) or sleeve (29), which is connected non-rotatably to the chuck (16) and is concentric therewith.

   Machine according to claim 1, characterized in that the at least one transmission means (183) takes the form of a closed, wave-form spring ring (27) having an alternating sequence of wave crests (27 1) and wave troughs (272) bent out at right angles to the ring shape and that at least portions of the wave troughs (272) lie positively mi cavities or depressions formed in the inner periphery of the one clutch part (181) and at least portions of the wave crests (271) lie positively in cavities or depressions formed mi the outer periphery of the other clutch part (182).

   17.

   A hand machine tool substantially as heremi described with reference to the accompanying drawings.