GB2085795A - A hammer drill - Google Patents

Abstract

A hammer drill comprising an air cushion percussive mechanism (18) is proposed which has a cylindrical pot piston (39) reciprocating in a guide. A piston-like striker (41) is arranged in the bore (40) of the pot piston (39) and is entrained by the pot piston (39) through an enclosed air cushion. At its end directed towards the tool (5) the striker has a cylindrical axial extension (43) which has a uniformly large cross section over its entire length. In order to achieve a very small idling path, a trapping device for the striker (41) in its idling position is arranged in the hammer drill. The trapping device includes a slotted brake ring (52) of highly elastic material, such as steel, which, lying in a holder (51), is pushed over the extension (43) of the striker (41) and retains the latter by pure friction. <IMAGE>

Description

SPECIFICATION A hammer drill State ofthe art The invention originates from a hammer drill according to the preamble to the main claim. A hammer drill of that kind has already been proposed in which, in order to achieve a short idling path, the striker of the percussive mechanism is grippingly engaged at the extension in the idling position.

Moreover, the extension is provided with an annular rib. In order to retain the striker rigidly in the idling position, the projection provided with the annular rib must be forced through an O-ring guided in a holder whereby the said O-ring is widened radially elastically. It has been shown that, during the transition of idling to the percussive operation, a relatively large pressure force must suddenly be applied by the operator. However, especially with small easy to handle drill hammers, attempts have been made to provide only a relatively gentle pressure force for the actuation of the striker trapping device.

Advantages of the invention As opposed to this, the hammer drill comprising the characterising features of the main claim has the advantage that only a slight pressure force is required from the operator when he desires to transfer the percussive mechanism from the idling position to percussive operation. Furthermore, by the use of the striker trapping device, a very short idling path can be generated which is required especially when using a percussive mechanism provided with a pot piston which is distinguished by a simple and cheap piston guide and good starting characteristics.

An advantageous further development and improvement of the hammer drill set forth in the main claim is made possible by the measures set forth in the sub-claims. It is especially advantageous for the holderforthe brake ring to be arranged in a fixed sleeve, preferably at its end facing the striker, which extends into the interior of the pot piston at least in its most forward position facing the tool.

Drawing An embodiment of the invention is illustrated in the drawing and is described in detail in the following specification. Figure 1 shows a hammer drill in partial longitudinal section, Figure2 is a longitudinal section through an intermediate shaft of the hammer drill extending parallel to the longitudinal section in Figure 1, Figure 3 is a brake ring and Figures 4, 5and 6 show three further embodiments of a trapping device for the striker of the percussive mechanism.

Description ofthe embodiments The illustrated hammer drill has a gear box 1 consisting of metal which is arranged in an outer plastics shell 2. At its forward end, the plastics shell changes into a cylindrical housing extension 3 which may be designed for rigidly clamping auxiliary apparatus or a handle. At the forward end of the housing extension 3, a tool holder 4 is arranged on the hammer drill and which serves for the reception of a tool - in this case a drill 5. The shank of the drill 5 has two closed longitudinal grooves 6 one on each side in which locking elements - balls 7 - in the tool holder 4 engage radially displaceably. The balls are guided in radial bores in a tool holder tube 8 and are prevented from moving radially by means of a spring loaded sliding sleeve 9.As can be appreciated from Figure 1, the drill 5 can move axially in the tool holder tube 8. The length of this possible axial movement is determined by the axial length of the longitudinal grooves 6.

A pistol grip 10 is moulded onto the plastics housing shell 2 at the rear end remote from the tool holder 4. A switch provided with a trigger 11 through which the hammer drill can be set in operation is incorporated in the pistol grip 10. A current supply cable 12 enters the lower end ofthe pistol grip 10 through a resilient socket.

A bearing seating for a forward bearing of an armature shaft 15 of an electric motor formed as a ball bearing 14 is arranged substantially centrally in a transverse wall 13 of the gear box 1. Thus, the electric motor of which substantially only the front part of the armature shaft 15 is illustrated, is located on the side of the transverse wall 13 of the gear box 1 remote from the tool holder 4. On the side remote from the electric motor, the transverse wall 13 carries a tubular extension 16 in which is arranged a cylindrical guide sleeve 17 for an air cushion percussive mechanism 18. At its forward end facing the tool holder 4, the tubular extension 16 carries a flange 19 which supports the gear box by engaging in an associated fitting 20 on the inside of the plastics shell 2.

The tubular extension 16 and the armature shaft 15 are arranged in the longitudinal central plane of the hammer which is illustrated by the sectional plane of Figure 1. At its forward free end, the armature shaft 15 carries a motor pinion 21 which meshes with a gear wheel 22 which is fixed for rotation to an intermediate shaft 23. The intermediate shaft 23, which is arranged in a plane (Figure 2) which is arranged laterally displaced with respect to the longitudinal central plane (Figure 1) carries an external spline 24 over its entire length. On the one hand, the intermediate shaft 23 is supported in a grooved ball bearing 25 and on the other hand in a needle bearing 26.

A hub member 27 of a swashplate drive for the air cushion percussive mechanism 18, is arranged on the intermediate shaft 23 for rotation therewith. On its outside, the hub member 27 has a single continuous annular track groove 28 for the balls 29 lying in a plane inclined with respect to the axis of the hub member 27.

The hub member 27 and the gear wheel 22 each have an inner spline 30,31 on their bore which engage in the external spline 24 on the intermediate shaft 23. On the one hand, the hub member 27 and the gearwheel 22 are supported in an axial direction against a snap ring 32 inserted in an associated groove in the external spline 24 and on the other hand are supported by the inner ring of the grooved ball bearing 25.

The external spline 24 on the intermediate shaft 23 is in the form of teeth suitable for the transmission of rotary motion, in this case substantially involute teeth. Thus, the forward portion of the spline facing the needle bearing 26 forms the driven pinion 33 of the intermediate shaft 23. This driven pinion 33 meshes with a gear wheel 34 which finally rotates the tool - the drill 5 - held in the tool holder 4.

An outer track 36 cut into the inside of a ring 35 is associated with the track 28 on the hub member 27, the balls 29 being guided between the tracks. In order to retain the balls at a definite spacing, they are guided in a cage 37 known in connection with ball bearings. A swash finger 38 which drives the air cushion percussive mechanism 18 of the hammer drill to and fro is made integral with the ring 35.

The percussive mechanism 18 of the hammer drill is arranged on the interior of the fixed guide sleeve 17 mounted in the tubular extension 16. It consists of a pot piston 39, sealingly and slidingly guided in the guide sleeve 17, in the cylindrical bore 40 of which a striker 41 formed as a freely moving piston is sealingly and slidingly guided. At its end remote from the base 42 of the pot piston 39, the striker 41 has an extension 43 facing the tool 5. Over its entire length, the extension 43 has a uniformly large circular cylindrical cross section. At its forward free end, it is provided with a short transition cone 44.

The rear end of the pot piston 39 remote from the tool holder 4 is made like a fork and carries a rotary pin 45. Atransverse bore in which the swash finger 38 engages with a slight clearance for movement is arranged centrally in the rotary pin 45. Thus, the swash finger 38 can move slightly in an axial direction in the transverse bore. The inner end of a fixed carrier sleeve 46 extends into the forward end region of the bore 40 in the pot piston 39 remote from the swash finger 38. An intermediate dolly 48 is sealingly and slidingiy guided in the axial bore 47 of the carrier sleeve 46 which thus also acts as an intermediate dolly guiding sleeve. The intermediate dolly 48 is formed as a piston and has a cylindrical piston extension 49 extending up to the striker 41.As can be appreciated from Figure 1, the diameter of the piston extension 49 is substantially smaller than the extension 3 on the strikes 41.

The intermediate dolly 48 is prevented from leaving the axial bore 47 in a direction towards the striker 41 by an annular rib 50 projecting into the axial bore 47.

A cylindrical widened portion 51 fashioned as an annular groove and which serves as a holder for a brake ring 52 (see Figure 3 as a detail), is cut into the axial bore 47 of the sleeve 46 at the free end facing the striker 41. The diameter of the widened portion 51 measured at the base of the groove is greater than the diameter of the extension 43 on the striker 41 plus the double thickness of the brake ring 52. The width of the annular groove 51 is greater by a slight movement clearance then the thickness of the brake ring 52. The two groove flanks of the annular groove 51 are axial abutments for the brake ring 52.

The brake ring 52 forms a trapping device for the striker 41 in its idling position. Forthis purpose, the brake ring 52 is slotted (see Figure 3) and consists of a highly elastic material such as steel. The inner diameter of the brake ring illustrated as relieved of stress in Figure 1, is greater by a clearance for movement than the piston extension 49 on the intermediate dolly 48; however, it is once again smaller than the outer diameter of the extension 43 on the striker 1.

The forward rounded end of the intermediate dolly 48 engages the rear end of the drill 5 which is axially displaceable but rotatably held in the tool holder 4.

The carrier sleeve 46 is fixed by a threaded ring 54 inside the tool holder tube 8 where it is supported towards the front by an annular shoulder 53.

The tool holder tube 8 is mounted by means of a needle bearing 55 in the housing extension 3 of the plastics shell 2 wherein the housing extension 3 is reinforced by a metal reinforcing ring 56. The rear end of the tool holder tube 8 is supported by the flange 19 on the tubular extension 16 through an axial needle bearing 57. The tool holder tube 8 is guided in an axial direction at its rear region facing the axial needle bearing 57 on the end of the guide sleeve 17 projecting from the tubular extension 16.

The gearwheel 34 is rotatably guided on the cylindrical outer wall of the tool holder tube 8. The body of the gear wheel 34, which carries coupling claws on its surface facing the motor, is held in engagement with associated coupling claws on the rearflange 60 on thetool holder tube 8 by a compression spring 59 supported by a snap ring 58 which is inserted in an associated groove in the outer surface of the tool holder tube 8. In so doing, the thickness of the compression spring 59 is so calculated that, at normal drilling torques, the gear wheel 34 is retained in engagement with the rear flange of the tool holder tube by the coupling claws.

The rotary connection between the gear wheel 34 and the tool holder tube 8 is only interrupted on reaching the predetermined response torque.

As can be easily seen, a rotary movement of the hub member 27 generates a reciprocating movement ofthe pot piston 39. The striker is likewise subjected to a reciprocating movement by the air cushion, which acts as an energy store, formed between the base 42 of the pot piston 39 and the striker 41. In the position illustrated in Figure 1, the percussive mechanism is positioned for percussive operation: the drill 5 is applied to the wall, for example, to be drilled. Due to the pressure applied by the operator, the shank of the drill 5 is held against the intermediate dolly 48 which is pushed into the axial bore 47 in the carrier sleeve 46 up to the annular rib 50. In this position, the reciprocating striker 41 gives us its energy by striking the piston extension 49 on the intermediate dolly 48 which finally is effective at the tool retained in the tool holder 4 as an axial impact. Moreover, the drill is rotated through the above described safety coupling consisting of the gearwheel 34 and the rear flange 60 on the tool holder tube 8.

If the operator removes the hammer drill from the wall or the like to be drilled whilst the percussive mechanism is operating, then the drill 5 will be driven forwards out of the receiving bore in the tool holder tube until its movement is iimited by the balls 7. During this operation, the extension 43 on the striker 41 enters into the end of the axial bore 47 in the carrier sleeve 46 located inside the pot piston 39.

The slotted brake ring 52 is widened together with an increase in the width of its slot (Figure 3) and is pushed over the extension 43. Since a bore 61 in the wall of the pot piston 39 has now become open, the striker 41 can only be held in its idling position through friction by the trapping device formed by the brake ring 52. The air cushion formed between the striker 41 and the base 42 of the pot piston 39 - as described above - is relieved through the bore 61.

The frictional energy generated by the brake ring 52 is sufficient - at least with a deep entry of the extension 43 - to overcome the maximal achievable rebound energy of the striker 41.

When the operator wishes to transfer the hammer drill from the above described idling position into percussive operation once again, then, with the striker trapping device in accordance with the invention, only a relatively gentle pressure is required by which he must press the hamer drill and with it the drill 5 against the wall to be drilled. In so doing, the extension 43 is then forced out of the brake ring 52 by overcoming the frictional force. Since the bore 61 in the wall of the pot piston 39 is then closed once again, an air cushion is immediately formed once again between the striker 41 and the base 42 of the pot piston 39. The above described percussive operation can begin afresh.

Three further embodiments of the hammer drill illustrated in Figures 1 to 3 are illustrated in Figures 4, 5 and 6. Common to these three embodiments is the fact that, as regards the striker trapping device, which is arranged in front of the percussive mechanism 18, the brake ring 52 is arranged in a carrier sleeve 66 which is decoupled from the intermediate dolly sleeve 67 receiving the intermediate dolly 48.

In the embodiment illustrated in Figure 4, the outer diameter of the intermediate dolly sleeve 67 fits in a bore in the tool holder tube 8 where it is supported towards the front by the annular shoulder 53. At about halfway along the axial length of the intermediate dolly sleeve 67, the sleeve is reduced in diameter at the rear end carrying the annular rib 50.

The carrier sleeve 66, which receives the brake ring 52 in a widened portion 51 formed as an annular groove, is pushed telescopically over the said reduced diameter. An elastic O-ring 69 is inserted between the forward end of the carrier sleeve 66 and the annular shoulder 68 formed at the transition from the reduced to the unreduced diameter of the intermediate dolly sleeve 67. Thereby, the carrier sleeve 66 is supported elastically in the hammer drill at the front. Towards the rear, the carrier sleeve is rigidly supported in the hammer drill by a snap ring 70 arranged in an associated groove in the interior of the bore in the tool holder tube 8.Moreover, the snap ring 70 is so arranged in the axial direction that the forward end of the intermediate dolly sleeve 67 is held against the annular shoulder 53 in the tool holder tube 8 through the O-ring 69 slightly compressed in the axial direction.

The rebound impacts and shockwaves produced by the intermediate dolly 48 on the intermediate dolly sleeve 67 during impact against the annular rib 50 are isolated from the carrier sleeve 66 by the measures used in the embodiment illustrated in Figure 4. In this way, breakages of the brake ring 52 consisting of an elastic material, such as steel for example, which can occur occasionally under unfavourable conditions, are certainly prevented.

The embodiment according to Figure 5 differs from the previous embodiment by another form of widening 51. In the carrier sleeve 76 illustrated in FigureS, the widening 71 in which the brake ring 52 is accommodated is bounded towards the rear towards the striker 41 - by an axial abutment formed as an internal rim 72 applied to the carrier sleeve 76.

Towards the front - towards the tool 5 - the widening 71 is bounded by a resiliently supported axial abutment. The axial abutment is formed, for example, as a washer 73 consisting of steel which is supported through an O-ring 74 by the end 75 of the intermediate dolly sleeve 67 facing the striker 41. In the modified carrier sleeve 76, the widening 71 is represented as a blind bore extending over its entire length with the same or increasing diameter. In so doing, an advantage is provided over the previous embodiment during assembly of the striker trapping device: the brake ring can be inserted in the widening 71 from the tool 5 end without deformation. Tensile stresses at the inner diameter of the brake ring which can occur when incorporating the brake ring 52 in the associated widening 71 of the first two embodiments formed as an annular groove, can be avoided with certainty thereby.As a further advantage, there is provided by the arrangement of the O-ring 74, which acts as a B-impact-damping O-ring, an unloading of the O-ring 69 likewise acting as a B-impact-damping O-ring.

In the embodiment according to Figure 5, the brake ring 52 has a slight axial clearance in the widening 71 in the idling condition. However, during drilling, the O-ring 69 is compressed by the pressure applied by the operator in such a manner that the O-ring 74 then comes to rest against the washer 73 and the brake ring 52 whereupon the brake ring 52 loses its axial freedom of movement. Any shock waves or oscillations due to friction arriving at the brake ring 52 are rapidly damped.

The embodiment illustrated in Figure 6 differs from the previous embodiment by the fact that the washer 83 which corresponds completely to the washer 73 according to Figure 5, lies in a cylindrical recess 84 in the wall of the widening 81. Towards the rear - towards the striker 41 - the washer 83 is supported on a shoulder 85 which forms the base or the rear end of the recess 84 at the transition in the widening 81. Thereby, the brake ring 52 always has a slight axial clearance under all occurring operating conditions as can be seen from Figure 6.

The more simple intermediate dolly 48 according to Figure 1 can of course be used instead of the intermediate dollies 48 illustrated in Figure 4, 5 and 6 which are provided with O-rings 90 inserted in an associated receiving groove for additional sealing.

The same applies to the strikers 41 which, in the embodiments according to Figures 5 and 6, are likewise provided with an additional sealing O-ring 91.

The percussive mechanism itself can of course be constructed in another manner. Thus, instead of the pot piston 39, a normal piston can be used so that the striker 41 then moves in the guide bush 17 which then forms the guide sleeve for the striker. Likewise, the drive for the piston can also be generated by a normal crank drive.

The striker trapping device in accordance with the invention is distinguished by lower production costs, by a compact construction and by a guarantee of faultless operation. Such a striker trapping device is necessary especially with small hammer drills frequently operated above the head since only therewith is a faultless continued operation of the striker guaranteed during idling.

Claims (18)

1. A hammer drill comprising an air cushion percussive mechanism which has a piston-like striker with an extension facing the tool axially striking the tool of the hammer drill, and which is reciprocably driven in a cylindrical guide sleeve, preferably a pot piston, through an enclosed air cushion, wherein a trapping device gripping the extension retains the striker in the idling position of the percussive mechanism, characterised in that, the trapping device comprises a slotted brake ring of highly elastic material such as steel which, lying in a holder provided with axial abutments and pushed over the extension having a uniform circular cylindrical cross section over is entire length, holds the latter, at least predominantly, especially by pure friction.

2. A hammer drill according to claim 1, characterised in that, the holder is formed as a cylindrical widening the diameter of which is greater than the outer diameter of the brake ring mounted on the extension.

3. A hammer drill according to claim 2, characterised in that, the widening is arranged in a carrier sleeve, preferably at is end facing the striker, which extends into the interior of the guide sleeve for the striker, preferably of the pot piston at last in its most forward position facing the tool.

4. A hammer drill according to claim 3, characterised in that, the carrier sleeve is resiliently supported forwardly in the hammer drill, preferably by an O-ring.

5. A hammer drill according to claim 4, characterised in that, the carrier sleeve is rigidly supported in the hammer drill towards the rear, preferably by a snap ring.

6. A hammer drill comprising an axially displaceable intermediate dolly arranged coaxially between the striker and the tool according to claim 1, characterised in that, the intermediate dolly is guided in an intermediate dolly sleeve which is rigidly supported in the hammer drill towards the front.

7. A hammer drill according to claim 6, characterised in that, the intermediate dolly is made like a piston and has a cylindrical piston extension extending towards the striker the diameter of the piston being less than the diameter of the unstressed brake ring.

8. A hammer drill according to claim 6, characterised in that, the intermediate dolly sleeve is resiliently supported in the hammer drill towards the rear, preferably by the O-ring.

9. A hammer drill according to claim 3 and 7, characterised in that, the carrier sleeve and the intermediate dolly sleeve are combined to form a single component and is fixed in an axial direction of the percussive mechanism, preferably by a threaded ring.

10. A hammer drill according to claim 3,4 and 8, characterised in that, the carrier sleeve is pushed telescopically over the intermediate dolly sleeve (67) from the rear together with the O-ring.

11. A hammer drill according to claim 2, characterised in that, the widening is bounded towards the rear - towards the striker by an axial abutment integral with the carrier sleeve and formed as an internal rim.

12. A hammer drill according to claim 11, characterised in that, the widening is bounded towards the front, towards the tool, by an axial abutment likewise integral with the carrier sleeve wherein the widening is represented by an annular groove.

13. A hammer drill according to claim 11, characterised in that, the widening is bounded towards the front - towards the tool - by a resiliently supported axial abutment.

14. A hammer drill according to claim 10 and 13, characterised in that, the axial abutment is formed as a washer which is supported by an O-ring against the end of the intermediate dolly sleeve facing the striker.

15. A hammer drill according to claim 14, characterised in that, the washer lies in a cylindrical recess in the wall of the widening and is supported towards the rear by a shoulder.

16. A hammer drill according to one of the preceding claims, characterised in that, the intermediate dolly sleeve and/or the carrier sleeve are arranged inside a rotatable tool holder tube.

17. A hammer drill according to one of the preceding claims, characterised in that, the percussive mechanism can be driven by an electric motor through a swash plate drive.

18. A hammer drill substantially as herein described with reference to Figures 1 to 3, Figures 3 and 4, Figures 3 and 5 or Figures 3 and 6 of the accompanying drawings.