ROTARY HAMMER

Abstract: A rotary hammer with an pneumatic hammering mechanism for driving a reciprocating ram (22) which hammering mechanism is driven by a wobble plate drive (14, 15, 16, 17), has an intermediate shaft (11) for transmitting the torque for the driven rotating tool holder (4). A carrier sleeve (30) is rotatably mounted on the intermediate shaft (11), which is elastically coupled with the intermediate shaft (11) and which has a gear portion (31) for transmitting the driving torque from the intermediate shaft (11) to the tool holder (4). On a suitable portion (35) of the carrier sleeve (30) the hub (14) of the wobble plate drive (14, 15, 16, 17) is mounted non-rotatably in relation to the intermediate shaft (11). By loading hammer bit (7) inserted in the tool holder (4), the carrier sleeves (30) and the intermediate shaft (11) are turned against each other as a result of the elastic coupling, wherein the inclination of the hub body (14) of the wobble plate drive (14, 15, 16, 17) alters and with this the hammering stroke is altered.

Description: The invention relates to a rotary hammer comprising a driven rotating intermediate shaft, a rotating tool holder, a rotatable gear element for transmitting driving torque for the tool holder from the driven rotating intermediate shaft, a reciprocating ram and a pneumatic hammering mechanism with a wobble plate drive having a wobble arrangement and a driven rotating hub body, wherein the reciprocating ram is driven by the wobble plate drive and the driven rotating hub body is mounted on the driven rotating intermediate shaft and wherein the inclination of the circular guiding portion for the wobble plate arrangement provided on said hub body can be adjusted in relation to the longitudinal axis of said intermediate shaft for varying the hammering stroke of said pneumatic hammering mechanism. In a known rotary hammer of this type (DE-A-32 05 141) the hub body of the wobble plate drive is provided non-rotatably on a cylindrical portion of an intermediate shaft, the longitudinal axis of which is inclined in relation to the longitudinal axis of the intermediate shaft. In the inner surface of the hub body recesses are probided, which are engaged with projections on the cylindrical portion of the intermediate shaft, resulting in a positive engagement, by which a non-rotatable coupling between the intermediate shaft and the hub body is achieved. To vary the hammering stroke of the pneumatic hammering mechanism, the hub body can be disengaged from the projections on the cylindrical portion of the intermediate shaft, so that the cylindrical portion can be turned and re-engaged with the projections, resulting in a different position of the hub body on the cylindrical portion of the intermediate shaft, so that the inclination of the hub body of the rubble plate drive is altered in the common plane of the longitudinal axis of the intermediate shaft and of the rubble finger provided on the outer race of the wobble plate drive, whereby the stroke of the wobble finger and thereby also the hammering stroke of the pneumatic hammering mechanism is altered. This known rotary hammer therefore enables the user to preset a larger or smaller hammering stroke and therefore to apply more or less hammering energy when using the rotary hammer. In addition a rotary hammer is known (DE-A-29 17 475), in which the user can alter the hammering stroke of the pneumatic hammering mechanism by adjusting the inclination of a drive plate, mounted so it can be swibelled and rotated about the intermediate shaft, in such a way that the desired hammering stroke is produced for the particular use. The object of the invention is to produce a rotary hammer, the hammering stroke of which automatically adjusts itself dependent on the loading of the rotary hammer, so that a greater hammering stroke is activated for stronger loading of the rotary hammer. To achieve this objective a rotary hammer of the type mentioned in the introduction is designed in such a way that said hub body is held non-rotatably in relation to said intermediate shaft and is mounted rotatably on a carrier sleeve which carrier sleeve is rotatably mounted on said intermediate shaft and connected therewith through a coupling elastic in a circumferential direction and which carrier sleeve is provided with a gear portion for transmitting the driving torque for said tool holder from said intermediate shaft to said rotatable gear element, and that the longitudinal axis of at least the portion of said carrier sleeve holding the hub body is in an inclined position in relation to the longitudinal axis of the intermediate shaft. In the hammer bit according to the invention the hub body is arranged non-rotatably in relation to the intermediate shaft, however, it is arranged rotatably on a carrier sleeve arranged co-axially on the intermediate shaft and coupled elastically therewith, which carrier sleeve transmits the driving torque for the tool holder from the intermediate shaft to a gear element. Therefore as a consequence of stronger loading of the hammer bit there is a corresponding loading on the coupling elements for the transmission of the torque from the intermediate shaft to the tool holder contained by the hammer bit and thereby a distortion of the elastic coupling between the carrier sleeve and the intermediate shaft, with the result that the carrier sleeve is turned in a circumferential direction with respect to the intermediate shaft and thereby also with respect to the hub body of the wobble plate drive, whereby the degree of turning is dependent on the loading of the elastic coupling. As a consequence of this turning, the position of the longitudinal axis of the portion of the carrier sleeve carrying the hub body is altered in relation to the longitudinal axis of the intermediate shaft in the plane of the intermediate shaft and the connection region of the wobble plate drive with the pneumatic hammering mechanism, thereby altering the hammering stroke of the pneumatic hammering mechanism, wherein the greater the turning of the carrier sleeve in relation to the intermediate shaft, the greater the hammering stroke. With the rotary hammer according to the invention, the user does not need to carry out any presetting to alter the amplitude of the hammering stroke, but rather the hammering stroke increases automatically when there is greater loading on the hammer bit corresponding to this loading, so that automatic adaptation of the respective operation conditions occurs. Preferably with the rotary hammer according to the invention, the normal to the plane of the guiding portion of the hub body and the longitudinal axis of the portion of the carrier sleeve carrying the hub body are inclined to each other, at least over a range of the turning, so that a usual arrangement of a wobble plate drive for a rotary hammer can be used, in which an annular body is rotatable, possibly by balls, on the hub body in the plane of the guiding portion, which carries a wobble-finger on its outside, and which is in driving engagement with the pneumatic hammering mechanism. If in this type of arrangement, the inclinations from the normal to the plane of the guiding portion of the hub body and the longitudinal axis of the portion of the carrier sleeve carrying the hub body are equal, then the stroke of the wobble plate drive and with that also the hammering stroke of the pneumatic hammering mechanism is zero, i.e. the result is a plain drilling action of the rotary hammer. The elastic coupling between the intermediate shaft and the carrier sleeve may comprise a coil spring, arranged co-axially in relation to the intermediate shaft, of which one end is connected to the intermediate shaft and the other end is connected to the carrier sleeve, so that loading occurring causes twisting between the carrier sleeve and the intermediate shaft with distortion of the coil spring and against its spring force. The gear portion on the carrier sleeve can be formed as a pinion section, while the gear element can be a gear wheel provided on the drill spindle. In order to couple together non-rotatably the hub body provided rotatably on the carrier sleeve and the intermediate shaft, these can be engaged with each other by coupling projections. The coupling projections can, on the one side be formed on an end surface of the hub body, and on the other side on a driving gear which is fastened non-rotatably on the intermediate shaft. The invention will be described further with reference to the schematic drawings showing an embodiment. Figure 1 is a side view of a rotary hammer. Figure 2 is partially an elevation and partially a sectional view of the gear housing with pneumatic hammer mechanism and the tool holder of the rotary hammer from Figure 1. Figures 3 to 5 are partial elevations of different operating positions of intermediate shaft, carrier sleeve and wobble plate drive with unloaded elastic coupling between the intermediate shaft and the carrier sleeve. Figures 6 to 8 are elevations, corresponding to Figures 3 to 5, of positions with a twisting of the carrier sleeve of 180° in relation to the intermediate shaft, resulting from loading of the elastic coupling. The rotary hammer shown has a usual housing, generally formed from half-shells, with a motor housing 2, in which is located the electric motor - not-shown - and from which a handle 1 extends, out of which usually an actuating element 5 for the trigger switch projects. The handle 1 is provided with an electrical connection line 6 to connect the electric motor with a power source. Towards the front of the motor housing 2, a gear housing 3 is connected, and a usual tool holder 4 serves as a holder for the hammer bit 7 only shown in Figures 1 and 2. As can be seen in Figure 2, an intermediate shaft 11 with a longitudinal axis A is provided in the gear housing 3. The intermediate shaft 11 has its ends housed in the needle bearings 12, 12′, and adjacent to the needle bearing 12 there is a needle bearing 13. A gear 10 is pressed on the end of the intermediate shaft 11 held in the needle bearing 12, which gear meshes with the pinion 9 of the armature shaft 8 of the electric motor (not-shown). A carrier sleeve 30 is mounted on the intermediate shaft 11. On the left-hand end (Figure 2) of carrier sleeve 30 an external gear portion 31 is formed, and carrier sleeve 30 is coupled with the intermediate shaft 11 via a coil spring 34. For this, one end of the coil spring 34 is fastened to a pin 32 extending radially and inserted in the carrier sleeve 30 and the other end of the coil spring 34 is fastened to a pin 33 extending radially and inserted in the intermediate shaft 11, with the result that the carrier sleeve 33, arranged rotatably on the intermediate shaft 11, is kept in its position by the coil spring 34. The gear portion 31 of the carrier sleeve 30 meshes with a gear wheel 29, which is formed on the spindle 27, rotatably mounted in the the bearing 28, which spindle is coupled in the usual way - and therefore not shown - with the tool holder and rotates this in operation. A hub 14 is provided, in a manner yet to be described, on the cylindrical portion 35 of the carrier sleeve 30, which hub has coupling projections 36 on its right-hand end in Figure 2, which engage with coupling projections 37 on the gear 10, such that the hub 14 is non-rotatable in relation to the gear 10 and therefore in relation to the intermediate shaft 11. The outer periphery of the hub 14 forms a tilted, inner race for the balls 15, on which an external race 16 is rotatably mounted. A wobble finger or pin 17, extending in the direction of the tilt, is attached to the external race 16. The plane of the guiding portion defined by the position of balls 15 and the alignment of the pin 17 is shown by the line B. The pin 17 engages with a pivot 18 on the rear end 19 of a hollow piston 20. The type of coupling between the pin 17 and the hollow piston 20 is described, for example, in US-A-4 280 359. In Figure 2 hollow piston 20 is shown in the upper half in its most retracted position, and in the lower half in its most advanced position. The hollow piston 20 is arranged axially movable in a stationary guiding tube 21, and in it there is a cylindrical-shaped ram 22, movable by sliding, which is in air-tight engagement with the inner wall of the hollow piston 20 by means of an O-ring 24 inserted in an annular groove 23 with a reciprocating movement of the hollow piston 20 between the inner end (on the right in Figure 2) of the ram 22 and the interior space of the hollow piston 20 bordered by this end, an overpressure and an underpressure can be built up alternately, which causes the ram to reciprocate in a known manner so as to exert impact on the rear end of the intermediate dolly 25, which transmits these to the rear end of the hammer bit 7. It should be mentioned that when the rotary hammer is idling, that is, if the hammer bit 7 is not engaged with a workpiece ram 22 is held in a known manner by the schematically indicated catching device 26, with its front tapered end in a forward idle position. As already mentioned, the hub 14 of the wobble plate drive formed from this, the balls 15, the race 16 and the pin 17 is mounted on a cylindrical portion 35 of the carrier sleeve 30, which is inclined to the longitudinal axis A of the intermediate shaft 11 and correspondingly also to the longitudinal axis of the carrier sleeve 30, so that it has a central axis C (Figures 4 and 5 as well as 7 and 8). This central axis C runs with an inclination deviating from the inclination of the normal to the plane B, and the angle of this deviation is denoted by γ (e.g. Figure 4). This angle results, as can be seen from Figures 3 to 5 for example, when looking at the plane of the drawing in Figure 2, i.e. that plane, in which the wobble arrangement of the race 16 and the pin 17 is tilted backwards and forwards between the two positions shown in Figure 2, while, in a plane displaced by 90°, the longitudinal axis A of the intermediate shaft 11 and the central axis C of the cylindrical portion 35 of the carrier sleeve 30 coincide with each other, as shown in Figure 3. Considering the operating condition according to Figures 3 and 5, which corresponds to that of Figure 2, then one can recognise that both the pins 32 and 33, which hold the coil spring 34, lie in one plane and on opposite sides of the longitudinal axis A of the intermediate shaft 11. This relates to the essentially unloaded state of the coil spring 34. In this operating state the hub 14 is inclined respectively in both the maximum displacement positions of the pins 17, at the angle β to the vertical, i.e. the maximum angle between the longitudinal axis of the intermediate shaft 11 and the central axis of the hub 14 amounts to β. By rotation of the unit comprising the intermediate shaft 11 and the carrier sleeve 30, this angle continuously changes in the plane of the swivel motion of the pin 17 between +β and -β. The resulting hammering stroke is determined by the value of the angle β and the size of the angle γ, such that the angle γ is negative in the operating state according to Figures 3 and 5, and the stroke of the reciprocating movement of the pin 17 amounts to twice α. If in use, for example as a result of the introduction of heavy loading by the user or as a result of jamming of the hammer bit 7 in the workpiece a higher "braking torque" acts on the hammer bit 7, then this causes a braking of the torque through the spindle 27, the gear wheel 29 and the gear portion 31 of the carrier sleeve 30, while the intermediate shaft 11 is driven further by the armature shaft 8 of the electric motor. As a result of this braking effect the coil spring 34 is loaded and turned in a circumferential direction, so that a relative rotation of the carrier sleeve 30 and the intermediate shaft 11 takes place, such that the rotation is all the greater, the greater the loading of the hammer bit 7. In Figures 6 to 8 an example of loading is represented, in which the carrier sleeve 30 is turned by 180° with respect to the position in Figures 3 to 5 of the intermediate shaft 11, so that both the pins 32 and 33, which hold the coil spring 34, again lie in one plane, however, on the same side of the longitudinal axis A of the intermediate shaft 11. Through this rotation of the carrier sleeve 30 in relation to the intermediate shaft 11, a rotation of the cylindrical portion 35 of the carrier sleeve 30 also takes place relative to the hub 14 of the wobble plate drive, which is coupled non-rotatably to the intermediate shaft 11, so that the hub 14, at the maximum deflection of the pin 17, remains on a region of the cylindrical portion 35, which has the angle β′ in this position (e.g. Figure 7), which is clearly smaller than the angle β in Figures 3 to 5. As, however, in this position the plane B of the guiding portion of the wobble plate drive is "outside" the angle β′, there results a stroke of pin 17 of 2 α′ which as a result of adding of angles β′ and γ′ (Figure 7) is clearly larger than the angle 2 α in Figures 3 to 5, i.e. in the working state in Figures 6 to 8 there is a distinctly increased hammering stroke. As soon as the "braking load" on the hammer bit 7 is reduced or discontinued, the rotation of the intermediate shaft 11 and the carrier sleeve 30 relative to each other is also reduced, as a result of the restoring force of the spring 34, through which the hammering stroke is also automatically reduced. It should be mentioned that the cylindrical portion 35 of the carrier sleeve 30 can also be formed in such a way that by minimal rotation relative to each other of the intermediate shaft 11 and the carrier sleeve 30, i.e. with practically unstressed coil spring 34, no hammering stroke results, if in this position the angle between the longitudinal axis A of the intermediate shaft 11 and the central axis of the cylindrical portion 35, that is, the angle β, is equal to the angle between the normal to plane B and the central axis C, that is equal to the angle γ.

Claims: 1. Rotary hammer comprising a driven rotating intermediate shaft (11), a rotating tool holder (4), a rotatable gear element (29) for transmitting driving torque for the tool holder (4) from the driven rotating intermediate shaft (11), a reciprocating ram (22) and a pneumatic hammering mechanism with a wobble plate drive (14, 15, 16, 17) having a wobble arrangement (16, 17) and a driven rotating hub body (14), wherein the reciprocating ram (22) is driven by the wobble plate drive (14, 15, 16, 17) and the driven rotating hub body (14) is mounted on the driven rotating intermediate shaft (11) and wherein the inclination of the circular guiding portion (15) for the wobble plate arrangement (16, 17) provided on said hub body (14) can be adjusted in relation to the longitudinal axis (A) of said intermediate shaft (11) for varying the hammering stroke of said pneumatic hammering mechanism, characterized in that said hub body (14) is held non-rotatably in relation to said intermediate shaft (11) and is mounted rotatably on a carrier sleeve (30) which carrier sleeve (30) is rotatably mounted on said intermediate shaft (11) and connected therewith through a coupling (32, 33, 34) elastic in a circumferential direction and which carrier sleeve (30) is provided with a gear portion (31) for transmitting the driving torque for said tool holder (4) from said intermediate shaft (11) to said rotatable gear element (29), and that the longitudinal axis (C) of at least the portion (35) of said carrier sleeve (30) carrying said hub body (14) is in an inclined position in relation to the longitudinal axis (A) of said intermediate shaft (11). 2. Rotary hammer according to claim 1, characterized in that the normal to the plane (B) of said circular guiding portion (15) and said longitudinal axis (C) of said portion (35) of the carrier sleeve (30) holding said hub body (14) are in clined in relation to each other, at least within a part of their turned positions. 3. Rotary hammer according to claim 1 or 2, characterized in that the said elastic coupling (32, 33, 34) comprises a coil spring (34) located coaxially in relation to said intermediate shaft (11), one end of said coil spring (34) being connected with said intermediate shaft (11) and the other end of said coil spring (34) being connected to said carrier sleeve (30). 4. Rotary hammer according to one of claims 1 to 3, characterized in that said gear portion (31) is a pinion portion provided on said carrier sleeve (30). 5. Rotary hammer according to one of claims 1 to 4, characterized in that said gear element (29) is a gear wheel provided on the spindle (27) of said rotary hammer. 6. Rotary hammer according to one of claims 1 to 5, characterized in that said hub body (14) and said intermediate shaft (11) are in non-rotatable engagement through coupling projections (36, 37). 7. Rotary hammer according to claim 6, characterized in that said coupling projections (36; 37) on the one hand are provided on an end surface of said hub body (14) and on the other hand are provided on a driving gear (10), non-rotatably mounted on said intermediate shaft (11).

Inventors: WACHE, ROBERT
Applicants: BLACK & DECKER INC.
Application year: 1989
Main classification: B25D11
IPC codes: B23B45, B25D11