GB2136725A - Hammer, in particular drill hammer - Google Patents

Abstract

The hammer (2) has an air cushion operated striker (7), in front of which an idle stroke brake (21) is located in the direction of a toolholder (14). This brake (21) has a fixed bush (15) which is conically contracted in the direction of the toolholder (14). A longitudinally slotted brake ring (18), matched to the contraction of the bush 15, is installed with prestress in this bush 15. The displacement path of the ring 18 is limited in the direction of the air cushion striking mechanism 5 by an axial end-stop surface (16) which determines the initial position of the ring. In the case of an idle stroke, the striker 7 comes in contact with the ring 18 and displaces it in the direction of the toolholder 14. Due to the radial prestressing of the ring 18 relative to the bush 15 and the elastic contraction of the ring occurring during the displacement, frictional braking forces occur between the latter and the bush and these bring the striking piece to rest. <IMAGE>

Description

SPECIFICATION Hammer, in particular drill hammer The invention is derived from a hammer, in particular a drill hammer, in accordance with the preamble to Claim 1. A machine tool usable as hammer and drill hammer and guided by hand is known from US Patent 3,170,523. This has an air cushion striking mechanism with a striker operating in the direction of a toolholder and an idle stroke brake with a slotted braking ring for the striker. The striker is shaped as a truncated cone at its end pointing towards the toolholder and this end penetrates into the slotted brake ring, which is formed as a hollow cone in the direction of the striker.The brake ring is displaceable, within a cylindrical guide bore which is located in a housing part of the machine, starting from an annular-type axial end-stop surface adjacent to the guide bore, in the direction of the toolholder and against an elastic cushion ring. In the case of an idle stroke, which occurs if there is no tool in the toolholder or if a tool does not meet any working resistance, the striker penetrates more deeply into the brake ring than during normal operation and presses the brake ring against the cushion ring. As a consequence of the reaction force then occurring at the cushion ring and of the truncated cone-type shape of the striker, the brake ring is expanded and pressed against the cylindrical guide bore.Because of this, a further displacement of the brake ring against the cushion ring by means of the striker causes frictional braking forces along the peripheral surface of the brake ring in addition to the elastic braking forces of the cushion ring. All the forces together finally bring the striker to rest. The machine tool again starts to strike as soon as the striker is pressed sufficiently far out of the brake ring by means of the tool. It is a disadvantage that the length of the braking path is limited by the elastic axial compression which can be tolerated in the long term by the cushion ring. In adaptation to this permissible compression, the braking paths are short and, in consequence, the braking forces undesirably high.

This led, therefore, to the objective of designing an idle stroke brake so that a longer braking path becomes available and so that the braking forces acting on the striker become smaller. Another hammer, in which the idle stroke brake also has an elastic cushion ring and a brake ring, which can be displaced against the cushion ring and presses on it, is known from US Patent 2,260,070. The striking mechanism of this hammer has a striking spring.

Advantages of the invention The hammer, in particular drill hammer, in accordance with the invention and with the characterising features of Claim 1, has the advantage that, because of the conical contraction of the guide bore and the radially acting elastic prestressing of the brake ring, forces are produced which act on the brake ring in the direction of the axial end-stop surface. The brake ring therefore takes up an initial position in which it is in contact with this axial end-stop surface.

Whenever the striker touches the brake ring, braking forces therefore immediately occur between the brake ring and the guide bore. An elastic cushion ring, such as that provided in the previously known hammers, is therefore no longer necessary for producing frictional braking forces. Consequently, there is also no disadvantageous length limitation to the displacement path of the brake ring. This state of affairs is utilised for longer braking paths so that the striker is gently braked.

The design of the hammer in accordance with the characterising feature of Claim 2 has the advantage that the forces acting by means of the brake ring in the direction of the axial end-stop surface, together with vibration forces produced by the hammer, suffice to move the brake ring into its initial position while overcoming frictional forces which occur between the brake ring and the guide bore. This movement occurs without any appreciable excess of displacement forces so that the striker is moved slowly in the direction of the air cushion striking mechanism. By this means, the striker takes up a rest position and only starts to operate again if this is intended by the operator of the machine.The drill hammer with the characterising features of Claim 3 has the advantage that even in the case of changing lubrication conditions between the guide bore and the brake ring, the latter moves safely into its initial position and that, in the process, the striker is not displaced too rapidly in the direction of the striking mechanism and, for this reason, begins to strike undesirably. This embodiment also has advantages if, when a task is completed, a driving motor of the hammer is switched off. The further development in accordance with the characterising features of Claim 4 has the advantage that the striker effects a magnification of the braking force by means of the truncated cone-type extension, which magnification occurs intentionally only during the braking of the striker.By this means, the elastic prestressing of the brake ring and hence also the loading on its material can be reduced. The further developnient in accordance with the characterising features of Claim 5 has the advantage that the guide bore can be provided with a particularly hard-wearing surface and the machine can be manufactured economically despite the conical shape of the guide bore. The further developments in accordance with the characterising features of Claims 6 and 7 have the advantage that the shanks of tools do not penetrate into the brake ring. By this means, the idle stroke brake and the striking mechanism are protected from dirt and attain a long life.

Drawing Three embodiment examples of the invention are shown in the drawing. Figure 1 shows a first embodiment example in longitudinal section, Figure 2 a second embodiment example in longitudinal section and Figure 3 a third embodiment example in longitudinal section.

Description of the embodiment examples The first hammer or drill hammer 2 has a housing part 3 and a housing part 4. An air cushion striking mechanism 5 is located in the housing part 3. The air cushion striking mechanism has a cylinder 6 located in the housing part 3 and a striker 7 longitudinally displaceable in the cylinder 6. The striker 7 and the cylinder 5 (sic), together with another striking mechanism part, not shown, surround an air cushion 8. The cylinder 6 protrudes beyond the housing part 3 and has a flange 9 extending radially outwards at this position. An end surface of this flange is in contact with the housing part 3. The housing part4 is in contact with the flange 9 on the opposite side from this housing part 3.The housing part 4 has a cylindrical bore 10 beginning attheflange9and oriented coaxially with the cylinder 6, which bore 10 ends at an annular end-stop surface 11. At this surface 11, a bore 12, which is made narrower than the bore 10, continues from the former. This bore 12 also ends at an annular-shaped end-stop surface 13.

Continuing from the area within which the end-stop surface 13 is located, the housing part4 is formed as a throat in the direction of a toolholder 14. A bush 15 is inserted in the bore 10. This bush 15 is fixed in the axial direction between the surface 11 and a further surface 16, which is located on the flange 9 and forms an axial end-stop surface. The bush 15 is formed so that it contracts conically starting from the axial end-stop surface 16 in the direction of the toolholder 14 and it has an inner surface 17. A brake ring 18, slotted in its longitudinal direction, is inserted in this bush 15. The brake ring 18 has an end surface 19 directed towards the axial end-stop surface 16 and an external peripheral surface 20, which is directed towards the inner surface 17 and has matched conical contraction.The brake ring 18 is so dimensioned that, in the initial position shown (in which it is in contact with the axial end-stop surface 16), it presses radially against the bush 15 with prestressing. The bush 15, with the surface 17 and the ring 18, form, in common with the axial end-stop surface 16, an idle stroke brake 21 for the striker 7.

The striker 7 has an end surface 22 which is directed towards the end surface 19 of the brake ring 18. An intermediate punch 23 is oriented located coaxially with the striker 7 in the housing part 4. It is guided so as to be axially movable within a cylindrical bore 24 and serves to transmit the impact energy from the striker 7 to a tool 25 inserted in the toolholder 14. The intermediate punch 23 has a peripheral groove 26 in the region of that part which is located within the bore 24. An O-ring 27 in rubber-type elastic material is inserted in the peripheral groove. This O-ring 27 prevents the penetration of stone dust, which may enter the toolholder 14 along the tool 25 in the direction of the striker 7, into the idle stroke brake 21.

The intermediate punch 23 has an end-stop shoulder 28 in a region protruding beyond the bore 24 and in the direction of the idle stroke brake 21. A ring 29 is inserted in the bore 12 aligned with this shoulder.

This ring 29 is followed by a rubber-elastic cushion ring 30 and this in turn is followed by a ring 31. The dimensions of the rings 29,30 and 31 and the length of the bore 12 are so dimensioned that the rings 29 and 31 are in contact with the surface 13 and the bush 15, respectively, with a desired prestress level.

The rings 29, 30 and 31 form an elastic end-stop for the intermediate punch 23 in the direction of the striker 7.

During normal operation of the hammer or drill hammer 2, the striker is set into axial movement by the air cushion 8 by means of a piston, not shown, displaceable within the cylinder 6 and driven by an electric motor via a crank drive. On its path in the direction of the idle stroke brake 21, the striker 7 meets the intermediate punch 23 and, via the latter, imparts impact energy to the tool 25. This procedure is repeated as long as the tool 25 finds sufficient working resistance and the intermediate punch 23 is pressed sufficiently far in the direction of the striker 7 by means of pressure against the housing part 3. If the tool 25 does not find any working resistance or if the hammer or drill hammer 2 is withdrawn from the working position, the striker 7 dispiaces the intermediate punch 23 and the tool 25 further in the direction of a working point of the tool 25.In consequence, the striker 7 also moves further in the direction of the brake ring 18 and finally its end surface 22 comes up against the end surface 19. This causes the brake ring 18 to be displaced within the bush 15 in the direction of the toolholder 14. Since the brake ring is installed with radial prestress in the bush 15, it rubs with its peripheral surface 20 on the inner surface 17 of the bush. Because of the contraction of the bush 15, the ring 18 is elastically contracted along the path in the direction of the toolholder 14 so that the braking force of the ring 18 increases in the direction of the tool holder 14. The ring 31 and the adjacent elastic ring 30 form an elastic emergency stop for the case where the displacement path of the brake ring 18 within the bush 15 is not sufficient to bring the striker 7 to rest.This could, for example, be the case if the drill hammer is lubricated in an uncorrect manner and, in consequence, the coefficient of friction between the ring 18 and the bush 15 is substantially smaller than that planned or if control openings, which are located in the cylinder 6 and control the air cushion 8, become blocked.

The angle enclosed by the surface 17 is so chosen that the displacement component acting in the direction of the axial end-stop surface 16 because of the radial prestressing of the ring 18 is smaller than that friction force arising due to the pressure of the brake ring 18 on the surface 17 of the bush 15.

During vibrations when the drill hammer 2 is in operation, the inertia forces occurring because of these vibrations have the effect that the brake ring 18 moves from a position nearthe ring 31, for example, towards the axial end-stop surface 16. The speed of this movement should, in fact, not exceed a certain magnitude because otherwise the brake ring 18 accelerates the striker 7 too strongly in the direction of the air cushion 8 with the consequence that the striker commences to operate anew. Depending on the type of lubricant used within the drill hammer 2, the angle enclosed by the surface 17 is selected within the order of magnitude of between 4 and 12 degrees, for example.

The second hammer or drill hammer 2a in accordance with Figure 2 differs from that described previously in that the striker 7a has an end surface 38 directed towards the intermediate punch 23. This surface 38 has a smaller diameter than the surface 22 in the previously described example. The striker 7a is formed as a truncated cone in the region adjacent to the surface 38 and has an external surface 39 in this region. As a counterpart to this external area 39, the brake ring 18a has a conical internal surface 40. As the consequence of an idle stroke, the outer surface 39 of the striker 7a meets the inner surface 40 of the ring 18a. Because of this, in addition to the displace mentforces in the direction of the toolholder 15 (sic), forces attempting to expand the brake ring 18a act on the latter.The bush 15 acts against this tendency to expansion so that a magnified braking effect occurs. By this means, the idle stroke brake 21 a acts as a servo-brake. If there is no requirement to fully utilise the possible magnification in force, the radial prestressing of the brake ring 18a can be reduced corresponding to the braking magnification factor.

This makes possible a reduction in the weight of the brake ring 1 8a and the loading on its material. In the first and second examples, the brake rings 18to 18a are slotted open sufficiently wide that the slot boundary surfaces 41 do not meet even if the brake rings press the elastic rings 30 together. By this means, wedging of the brake rings within the bushes 15 is prevented. The movement of the brake rings 18, 18a back into the initial positions shown in Figures 1 and 2 is correspondingly reliable.

The third hammer or drill hammer 2b has a bush 15b and a brake ring 38b in which the opposing surfaces 17b and 20b include a larger angle than that of the first two embodiment examples. This angle is at least 10 degrees and preferably more than 12 degrees. In consequence, the brake ring 18b will move to the axial end-stop surface 16, i.e. towards the striker 7, even without the support of vibrations from the drill hammer 2b. Since this involves the danger that the brake ring 1 8b may accelerate the striker 7 via the surface 22b too rapidly in the direction of the air cushion 8, which could cause the striker to recommence operating when not desired, an additional brake ring 42 is provided. This brake ring 42 is inserted in a peripheral groove 43 so as to be radially movable.This peripheral groove 43 is located in a cylinder 6b, which accepts the striker 7 so that it can be longitudinally displaced, near the axial end-stop surface 16, which is machined on the cylinder 6b. The striker 7 has, adjacent to the end surface 22b, a truncated conical surface 44 which, in the case of idle strokes, meets the ring 42 and expands the latter so that the striker 7 meets the brake ring 18b by passing through this ring 42. The ring 42 also acts as a brake for the striker 7. At the end of an idle stroke, the ring 42 ensures that after a possible acceleration of the striker by means of the brake ring 18b in the direction of the air cushion 8, the striker 7 is brought to rest so that it cannot begin to strike in an undesired manner.

Instead of the pin-type shaped intermediate punch 23, which, together with its O-ring 27, has the duty of preventing the entry of rock dust into the idle stroke brakes 21,21 a, 21 b, a sealed spindle with a toolholder formed in a manner known per se or with a toolholder lining can be installed. This spindle or tool holder, which accelerates the tool in the direction of a working position, can be rotatably supported by means of gearwheels in known manner, for example in the manner described in US Patent 3,170,523, and can be rotated by means of a rotary drive.

Claims (8)

1. Hammer, in particular a drill hammer, having a toolholder (14) and having a striking mechanism, whose striker (7, 7a, 7b) is associated with an idle stroke brake (21,21 a, 21 b), which contains, in a guide bore (17, 17b), a brake ring (18, 18a, 18b) slotted along its total length, which brake ring comes into coaxial contact with the striker (7, 7a, 7b) and alters its diameter elastically and which brake ring is then displaced against resulting increasing frictional braking forces and thereby moves away from an annular axial end-stop surface (16) which is located on the striking mechanism end of the guide bore, characterised in that the guide bore (17, 17b) contracts conically in the direction of the toolholder (14), and that the slotted brake ring (18, 18a, 18b) is also externally conical and so inserted with prestress in the guide bore (17, 17b) that it presses radially against the guide bore (17, 17b) in an initial position determined by the axial end-stop surface (16).

2. Hammer according to Claim 1, characterised in that the contraction includes an angle of approximately 4 to 12 degrees.

3. Hammer according to Claim 1, characterised in that the contraction includes an angle which is greater than 10 degrees and that a second brake ring (42) is provided, which second brake ring can be radially expanded elastically and is fixed in axial direction and into which the striker (7) penetrates with rubbing friction in the case of an idle stroke.

4. Hammer according to one of Claims 1 to 3, characterised in that the striker (7a) has an extension with conical external surface (39) at its end pointing towards the toolholder, with which external surface (39) it penetrates into the slotted brake ring (18a), and that the brake ring (18a) has a corresponding conical inner surface (40).

5. Hammer according to one of Claims 1 to 4, characterised in that the guide bore (17, 17b) is located within an externally cylindrical bush (15, 15b), and that the bush is inserted so as to be axially fixed in a bore (10) in the housing part (4) of the hammer.

6. Hammer according to one of Claims 1 to 5, characterised in that the idle stroke brake (21, 21a, 21) (sic) is secured by sealing means (2) against penetration of dust.

7. Hammer according to Claim 6, characterised in that the sealing means (27) are formed as an O-ring and are adjacent to an intermediate punch (23).

8. A hammer substantially as herein described with reference to Figure 1, Figure 2, or Figure 3 of the accompanying drawings.