GB2295347A

GB2295347A - Hammer drill and/or percussion hammer

Info

Publication number: GB2295347A
Application number: GB9523099A
Authority: GB
Inventors: Ulrich Bohne; Wilfried Kabatnik; Joachim Hecht
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1994-11-24
Filing date: 1995-11-10
Publication date: 1996-05-29
Anticipated expiration: 2015-11-10
Also published as: IT1277215B1; ITMI952376A1; FR2727341A1; ITMI952376A0; DE4441820A1; DE4441820B4; NL1001737A1; FR2727341B1; GB9523099D0; GB2295347B; NL1001737C2

Description

I- Hammer drill and/or vercussion hammer 2295347

Prior art

The invention starts from a hammer drill and/or percussion hammer according to the precharacterizing clause of Claim 1.

From DR 42 31 986 Al an apparatus in already known in which, after the motor has been switched on, the percussion mechanism is put into action when the tool is pressed against a place where machining is to be done. An adjustable eccentric clutch is here provided, the eccentricity of which in varied from zero to a maximilyn value by translatory movement, or combined translatory and rotational movement, of an outer eccentric part relative to an inner eccentric part. owing to the fact that the parts always remain in engagement with one another, the coupling operations take place noiselessly and without wear. The reaction forces of the percussion mechanism on the eccentric clutch and the mass inertia forces act in such a manner that the movement of the clutch to the maximum position is assisted. The spring force for return to the no-load position (zero eccentri city) or for holding a position with a particular eccentricity should be sufficiently great to prevent the clutch from spontaneously moving in the direction of maximum eccentricity. It is a disadvantage that either this spring force must be very great, so that the pres sure force to be applied by the operator is.inereased, or the spring force is too weak, thus leading to dis advantageous no-load behaviour comprising the spontaneous movement of the eccentric clutch in the direction of increasing eccentricity.

Advantages of the invention The him-or drill and/or percussion hanner according to the invention, which has the characterizing features of Claim 1, has in contrast thereto the advantage that the pressure force which must be exerted by the operator to bring the clutch into the maximum position in kept low and the no-load behaviour is improved.

Owing to the fact that only the inner, smaller eccentric part is axially movable, the manses which tend to displace the clutch in the direction of the maximum position are smaller. Because the outer eccentric part in axially fixed in relation to the shaft, the reaction forces of the percussion mechanism, which unavoidably is occur during percussion operation, are taken by the outer eccentric part and by the shaft and therefore do not lead to a displacement of the clutch. in addition, the distance, from the tilting axis, of the articulation point between the driver element and the drive element remains constant, so that uniform force transmission behaviour between the eccentric clutch and the percussion mechanism is achieved.

Through the measures specified in the dependent claims advantageous developments and improvements of the

Claims

hammer drill and/or percussion hammer indicated in Claim 1 are possible. It is particularly simple and inexpensive for the rotational driving of the eccentric parts to be affected by means of a pin, which in received in a hole extending transversely to the axial direction of the shaf t, and for the inner eccentric part to have an axially extending slot by which this eccentric part is guided on the pin. If a control element axially movable relative to the shaft is provided for the movement of the inner eccentric part, the fact that the inner eccentric part makes a purely axial movement ensures that no friction occurs between the adjusting elment and the inner eccentric part. The rotatable mounting of the articulation sleeve on the outer eccentric part may advantageously be in the form of a ball bearing. Axial support of the articulation sleeve, for example by means of a collar or a dine, can be dispensed with, no that frictional loosen are avoided. Drawing Three exemplary embodlincints of the Invention are illustrated in the drawing and explained in more detail in the following description. Figure 1 shown an enlarged longitudinal section through a hammer drill, Figure 2 shown a detail of Figure 1, and Figure 3 shown the inner eccentric part in a front view from the right in Figure 2. Figures 4 and 5 show respectively a second and a third exemplary embodiment of an eccentric clutch. Description of the exemplary embodiments In Figure 1 a part of a hammer drill 1 comprising is a caning 2 and a motor 3 situated at the rear in shown. The motor 3 drives a percussion mechanism 5 by means of a shaft 4. Said mechanism has a striker 6, which with the aid of a dolly 7 acts on a tool 9 mounted at the front in a tool holder e. The striker 6 in driven reciprocatingly by a resiliently stiff driver element 11. The latter in mounted for tilting about a tilting axis 12 by means of a drive lever 15 and is provided with another lover 14 coupled to a drive element 13. The tilting axis 12 extends transversely to and in offset relative to the axis of movement of the striker 6. An shown on a larger scale in Figure 2, the drive element 13 consists of an articulation alcove 16, which has a downwardly directed extension 17 provided with an aperture 18. The aperture 18 has a shape such that its surfaces facing the lever 14 have on both sides a frustoconical shape with an elliptical base. This has the consequence that in every possible eccentric position of the drive element 13 the lover 14 is guided with only slight play in such a manner that it is in contact in an ideal manner with the aperture 18 at top and bottom. The main element of the drive consists of two eccentric parts 20, 21 which lie against or engage in one another and are capable of limited translation relative to one another. An inner eccentric part 20 in mounted on the shaft 4. This eccentric part has a cylindrical Annular surface 22, which in Inclined obliquely relative to the axis of the shaf t 4. An outer eccentric part 21 lion with its Inner cylindrical annular surface 23 on the annular surface 22. The articulation &leave 16 in rotatably mounted by means of a ball bearing 25 on the circumference of the eccentric part 21, said circum ference extending parallel to the axis of the shaft 4. By means of a pin 59, which in Inserted with a sliding fit Into a through hole 62 extending transversely through the shaft 4, the outer eccentric part 21 in connected to the shaft 4 in such a manner an to be incapable of axial and is rotational movement but capable of radial movement thereon. The pin 59 In secured against falling out by means of a circlip 60. The inner eccentric part 20 has a radial slot 24, which has dimensions ouch that in every axial position of the inner eccentric part 20 It in in engagement on both aides with the pin 59. For the axial movement of the inner eccentric part 20 against the force of a spring 28, a flange bush 41 axially movable on the shaf t 4 in provided an an adjusting element. A hammer tube 29 joined fast to the tool holder 8 and capable of limited axial movement carries a gear 30 which mashes with a second gear 31 mounted on the shaft 4. The hammer tube 29 also carries a thrust bearing 32 provided with a disc 33 which initiates the translatory movement of the inner eccentric part 20, by moving the flange bush 41 and thus also the inner eccentric part 20 towards the rear, that is to say towards the left In Figures 1 and 2, through the pressure force applied by the operator of the machine. The end position in reached when the flange bush 41 is supported on the outer eccentric part 21 and thus, via the pin 59, on the shaft 4. A further movement of the inner eccentric part 20 against the action of the spring 28, an the result of any reaction forces of the percussion mechanism that may occur, in prevented by the circlip 61 which in fastened on the shaft and against which the inner eccentric part 20 in supported with the aid of a washer Ss. When the tool 9 in f irmly pressed against a place where machining In to be carried out, the inner eccentric part 20 in situated in the position shown in Figure 2, in which it cannot be further displaced relative to the outer eccentric part 21. The total eccentricity of the drive element 13, produced by the two eccentric parts 20 and 21, has now reached its maximum value. The lover 14 of the driver element 11 In moved up and down with maximum amplitude. The drive lover 15 of the driver element 11 thus acts on the percussion mechanism 5 in such a manner that maximil- striking power in reached. is When the tool 9 in jected to lens heavy pressure, the compression spring 28 moves the inner eccentric part 20 axially a little to the right. The total eccentricity In thereby reduced. If the tool 9 is completely removed from the workpiece, the inner eccentric part 20 passes Into its front end position, the bottom of the radial slot 24 coming to bear against the pin 59. In this position, which in not shown In the figures, the total eccentricity of the drive element 13 is zero and the percussion mechanism is thus switched off. The second examplary embodiment according to Figure 4 in in principle constructed like the first. Functionally Identical component parts shown in Figure 4 are given reference numerals increased by 100. Where they are not mentioned hereinbelow, designations can be taken from the first exemplary embodiment. in this exemplary emb odiment, the eccentric parts 120 and 121 and also the pin connection are arranged as the mirror image of the embodiment shown in Figures 1 to 3, in relation to a plane normal to the shaft 104 and extending through the ball bearing 125. In this embodiment the circlip 61 provided in the exemplary embodiment according to Figures 1 to 3 can be dispensed with. In the position shown in Figure 4, in which the total eccentricity of the drive element 113 is maximum, the base of the radial slot 124 in the inner eccentric part 120 lies against the pin 159. The third exemplary embodiment according to Figure 5 has in principle the same construction an the previous embodiments. Functionally identical component parts are given reference nil-orals increased by 200 in relation to the first exemplary embodiment and have the same designations. Where they are not mentioned below, the latter can be taken from the first exemplary embodi ment. The inner eccentric part 220 is axially movable on the shaft 204 and is secured against rotation of one relative to the other by a feather (not shown) inserted into longitudinal grooves in the shaft 204 and the inner eccentric part 220. The annular surfaces 222 and 223 also have longitudinal grooves into which in inserted a feather (not shown) which makes a connection between the eccentric parts 220 and 221 preventing rotation of one relative to the other. Two bushes 270 and 271, which are axially fixed on the shaft 204, support the outer eccentric part 221 axially. The bush 271 in in turn supported against the gear 231 and in its shoulder has apertures 272 for the rear and (the lef t end in Figure 5) of the f lange bush 241, this end being divided in this exemplary embodiment. The rear end of the f lange bush 241 in in contact with the end face of the inner eccentric part 220 on the f lange side. On that side of the f lange of the f lange bush 241 which is rem to from the eccentric parts 220 and 221 is provided a thrust bearing 232, which is in contact with the bearing disc 233 with the interposition of a washer 234. When the tool is firmly pressed against a place where machining in to be effected, the rear end of the f lange bush 241 lies against the outer eccentric part 221, and the rear end face of the inner eccentric part 220 is supported against a shoulder of the flange bush 270 to prevent further axial movement. When the pressure force applied is relaxed, the compression spring 228 - 7 moves the inner eccentric part 220 back to the zero position. The invention is not restricted to the exemplary embodiments illustrated. In particular, other possible ways of driving the two eccentric parts by means of the shaft, apart from the pin connection illustrated or a feather, are also conceivable, for example in the form of longitudinal toothing. A plurality of pins distributed over the circumference may be provided, and these need not extend right through. The pin can be secured in the shaft in a different manner, for example by being pressed in. Instead of having the shape of a lateral surface of a cylinder, the annular surfaces may also be noncircular, for example polygonal, or may have some other profile. In this case the longitudinal grooves in the annular surfaces are also unnecessary. The compression spring 28, 128 may also be supported directly on the inner eccentric part 20, 120. Instead of the circlip 61, a flange may be provided on the shaft 4. Instead of the ball bearing 25, 125, 225, a different bearing, for example a needle bearing, may also be provided.

1 - a - Claims Hammer drill and/or percussion hammer having a percussion mechanism (5), whose striker (6) cooperates with a driver element (11), which is tiltable about a tilting axis (12), in such a manner that the striker (6) is accelerated approximately in its axial direction and periodically directly or indirectly impinges axially on the shank of a tool (9), which driver element (11) in reciprocatingly driven by a drive element (13) which in turn in rotated by a drive (3) with the aid of a shaft (4), the drive element (13) having inter-engaging is eccentric parts (20, 21) which are axially movable relative to one another such that the eccentricity of the drive element (13), acting on the driver element (11), relative to the shaft is adjustable between zero and a maximum value, characterized in that the inner eccentric part (20) in axially movable relative to the shaft (4) and the outer eccentric part (21) is heldaxially immovable relative to the shaft.

2. Hammer drill and/or percussion hammer according to Claim 1, characterized in that the two eccentric parts (20, 21) are each provided with annular surfaces (22, 23) surrounding the shaft (4), arranged asymmetrically relative to the latter and in contact with one another.

3. Hammer drill and/or percussion ba-mer according to Claim I or 2, characterized in that the annular surfaces (22, 23) extend obliquely to the axial direction of the shaft (4).

4. Hammer drill and/or percussion hammer according to one of Claims 1 to 3, characterized in that the annular surfaces (22, 23) have the shape of the lateral surface of a cylinder.

5. Hammer drill and/or percussion bnz=er according to one of the preceding claims, characterized in that the outer eccentric part (21) in. secured against rotation relative to the shaft (4).

6. Hammer drill and/or percussion hammer according to Claim 5, characterized in that the outer eccentric part (21) is connected to the shaf t (4) by means of at least one driving element (59).

7. Hammer drill and/or percussion hanmer according 10 to Claim 6, characterized in that the driving element in a pin (59) which is received in a hole (62) extending transversely to the axial direction of the shaft (4) and engages in holes (63, 64) in the outer eccentric part (21).

S. Hammer drill and/or percussion hammer according to Claim 6 or 7, characterized in that the inner eccentric part (20) is guided for axial movement on the driving element (59).

9. En-er drill and/or percussion hamomer according 20 to Claim 8, characterized in that the inner eccentric part (20) cooperates with the driving element or elements (59) with the aid of at least one axially extending slot (24).

10. Hn-mer drill and/or percussion hammer according to one of Claims 1 to 5, characterized in that the outer eccentric part (221) in secured against rotation on the inner eccentric part (220) and the inner eccentric part (220) is secured against rotation on the shaft (204), in each case by means of positive connection elements, particularly feathers or profiled contact surfaces.

11. Hanmer drill and/or percussion hammer according to Claim 10, characterized in that the outer eccentric part (221) is supported axially relative to the shaft by means of support elements, particularly bushes (270, 271).

12. H--er drill and/or percussion hammer according to one of the preceding claims, characterized in that for the movement of the inner eccentric part (20) an adjusting element (41) movable axially relative to the shaft in provided.

13. Hammer drill and/or percussion hammer according to Claim 12, characterized in that the adjusting element is a flange bush (41) whose flange in supported, preferably by means of a thrust bearing (232), against a bearing disc (33) connected to a tool holder (9) axially movable when pressure in applied against it.

14. Hammer drill and/or percussion hammer according to one of the preceding claims, characterized in that the drive element (13) has an articulation sleeve (16) which in rotatably mounted on the outer eccentric part (21).

15. Hamer drill and/or percussion hawmer, according to Claim 14, characterized in that for the rotatable mounting of the articulation sleeve (16) on the outer eccentric part (21) a ball bearing (25) in provided.

16. Any of the hammer drills and/or percussion is hammers substantially as herein described with reference to the accompanying drawings