GB2147240A

GB2147240A - Hammer drill

Info

Publication number: GB2147240A
Application number: GB08424629A
Authority: GB
Inventors: Horst Grossmann; Stefan Schmidt
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 1983-10-01
Filing date: 1984-09-28
Publication date: 1985-05-09
Also published as: GB2147240B; DE3335795A1; CA1233377A; FR2552696B1; IT1176850B; GB8424629D0; IT8422896A0; DE3335795C2; AU3368784A; FR2552696A1

Abstract

A hammer drill with an air cushion impact mechanism has a latch device, comprising a resilient annular body (50; 50a), for the ram (27), and an annular resilient damping element (50; 50b) for damping the recoils of the beat piece (29). The annular body (50; 50a) and the damping element (50; 50b) are located within the rotationally driven spindle (39) of the tool bit holder (3) in a plane normal to the spindle axis, and are held against axial displacement between an annular plate 51 and a washer 52 (51,52) common to them both. The latch device and the damping element are preferably O-rings, one inside the other, and may be integral (50) or separate (50a and 50b). The damping element (50b) is preferably thicker axially than the latch device (50a). Recoil blows from the beat piece are transmitted to the plate 51 and from there to the member 50 which is compressed to damper the blow. At idle the ram 27 moves forward sufficiently for the inner ring of the member 50 to engage a groove 35 of the ram 27 to latch the ram. <IMAGE>

Description

SPECIFICATION Hammer drill Field of the invention This invention relates to hammer drills of the air cushion type having a ram reciprocally driven via an air cushion inside a cylindrical member. The invention particularly relates to damping and latching arrangements for components of such drills.

Background of the invention Hammer drills of the air cushion type usually have an air cushion impact mechanism which contains a piston type striker ram having an axial extension pointing towards the tool holder. The ram is usually driven with a reciprocating motion in a cylindrical guide sleeve via an enclosed air cushion and drives a beat piece against the rear end of the tool bit when inserted in a hollow spindle. This spindel may have a latch device, comprising a rubber-elastic annular body which is located within the spindle, and holds the striker in an idling position by engagement with an annular groove present in the extension of the ram.An annular, rubber-elastic damping element may be provided in the internal space of the spindle for damping axial recoils of the beat piece, the side of which damping element facing towards the tool holder being in contact with a positioning region which can move axially in the direction away from the tool holder.

German Offenlegungsschrift 3,120,326 discloses a hammer drill of this type in which the annular body and the damping element each consist of an O-ring. The damping element is located between the inner surface of the spindle and the outer surface of a step in a sleeve so that one of its sides is in contact with the annular shoulder, formed by the step, of the sleeve. On the opposite side, the damping element is in contact with the front surface of a support sleeve which has, in the inner surface of its rear end region, an extension for accepting the annular body. A circlip located in the spindle serves to position the support sleeve.

In this above arrangement, therefore, two sleeve parts of relatively complicated construction, and hence expensive to manufacture, are necessary in order to position the damping element and the annular body and, in addition, the assembly is expensive.

German Offenlegungsschrift 3,120,326 also discloses designing the annular body as a steel ring and providing a continuous smooth surface extension on the striker in order, in this manner, to obtain a frictional engagement between the extension and the steel ring in the latch position. In this case, however, the positioning of the steel ring occurs in the same manner as the positioning of the O-ring so that the manufacturing and assembly costs are not reduced.

Summary of the invention An object of the present invention is to arrange both the damping element for damping axial recoils of the beat piece and the annular body of the latch device in the hammer drill in such a way that they can be positioned by parts which are constructed as simply as possible and can be assembled without large expense.

In order to achieve this object, a hammer drill of the air cushion type is so designed, in accordance with the invention, that the annular body and the damping element are located in a common plane normal to the longitudinal axis of the spindle, the annular body being located radially further inwards than the damping element, and the annular body and the damping element being retained against axial displacement by positioning regions common to them both.

In a hammer drill in accordance with the invention, therefore, the damping element and the annular body are located in common plane instead of being located, as previously usual, with an axial distance between them along the spindle. By this means, common positioning regions, which can be designed in a particularly simple manner, are present on each side of the annular body and the damping element. As an example, the positioning region remote from the tool holder may be formed by means of a washer held by a circlip and the positioning region near to the tool holder may comprise an annular plate which is in contact with an annular shoulder of the spindle. Such components require only slight machining, or none at all, so that the manufacturing costs are substantially reduced.In addition, the insertion of the damping element and the annular body in a common plane is very simple and can take place practically in one assembly step.

In order to attain adequate damping of the recoils of the beat piece, the axial extension of the damping element can be greater than the axial extension of the annular body, and the dampng element can be compressed between the positioning regions in order to generate pre-stress so that it will, in this way, act as a relatively stiff spring.

In one embodiment of the invention, the damping element and the annular body can each consist of an O-ring. It is, however, also possible to form the damping element and the annular body in one piece.

The transition between the extension and the main body of the striker ram may be formed by an annular surface located normal to the longitudinal axis of the ram, and the annular groove is then preferably in the immediate vicinity of this annular surface. In this way, the damping element will also provide damping of the shocks from the ram when the ram moves forward during idling of the percussive mechanism.

Other objects, features and advantages df the present invention will become more fully apparent from the following detailed description of the preferred embodiment, the appended claims and the accompanying drawings.

Brief description of the drawings In the accompanying drawings: Figure 1 shows a partial side view of the front portion of a hammer drill according to the invention, mainly in section but with some internal parts not sectiond, and showing some of the moving parts in two positions; Figure 2 shows a portion of Figure 1 but with a different construction of damping element and latching element.

Figure 3 shows an arrangement similar to Figure 2 but with a different construction of the ram.

Detailed description of the preferred embodiments The hammer drill shown in Figure 1 corresponds in its general construction to the hammer drill described and shown in German Patent Application P 32 24 050.3 published December 29, 1983.

In Figure 1, the hammer drill has a housing 1 consisting of two plastic clam-shells, this housing having a chuck 3 at its front end for accepting the partially shown drill bit 2. A fan 7 is mounted on the armature shaft of the electric motor (not shown), the armature shaft being rotatably supported at its forward end in a bearing supported in an aluminum casting 4 positioned inside the housing 1. The forward end of the armature shaft forms a pinion, which is concealed in Figure 1, and which drivingly engages with a gear wheel 13 carried by an intermediate shaft 10. The ends of the intermediate shaft 10 are rotatably mounted in bearings 11 and 24. The bearing 11 is mounted in the casting 4, and the bearing 24 in sheet metal part 5 inserted in the casing 1. A plate spring 12 is located between the gear 13 and the bearing 11.The gear 13 can be displaced axially to a limited extent on the shaft 10 in the direction of the bearing 11, but it is held against rotation relative to the shaft 10. Such displacement of the gear 13 compresses the spring 12.

A drum 14, 14', which has a peripheral groove 15, is mounted rotatably on and relative to the intermediate shaft 10. The peripheral groove 15 is in the form of an obliquely set circle and produces the reciprocating movement, to be described later, of the piston of the impact mechanism. On the end remote form the gear 13, the drum 14, 14' has axial dog clutch teeth which engage with correspondingly shaped axial clutch teeth on a bush 16 secured to the intermediate shaft 10 and rotatable therewith. A spring 18 surrounds a forward part of the bush 16 and is compressed between a washer 19 and a rear flange of the bush 16 to effect driving engagement of the dog clutch teeth.The bush 16 can, by means of an arrangement not shown, be so displaced from outside the housing 1 that the teeth of the bush 16 come out of engagement with the teeth of the drum 14, 14', i.e.the bush 16 can be displaced to the left in Figure 1 against the pressure of the spring 18. In this latter position, the rotational movement of the intermediate shaft 10 is no longer transmitted from the bush 16 to the drum 14, 14' and the drive for the impact mechanism is, therefore, interrupted.

A gear wheel 37 is located on the intermediate shaft 10 between the washer 19 and an axial thrust bearing 23. This gear 37 engages with a gear wheel 38 secured on a chuck spindle 39 and thus effects rotation thereof to rotate the drill bit 2. The chuck spindle 39 is supported at its inner end on an axial bearing 40 and is rotatably mounted on a guide tube 25. The gear 38, so that it can accept shocks, is axially movable to a limited extent against flexing of a plate spring 41 retained by an inset ring 42. In addition, the gear 38 can be rotated relative to the spindle 39 when a specified driving torque is exceeded so forming an overload clutch.

A tubular piston 26, in which a ram 27 is reciprocally located, reciprocates in the guide tube 25 to generate the percussive movement of the drill bit 2. For the method of operation of such a percussive mechanism, reference should be made to United States Patent 4,290,492 which also explains the function and position of venting provided in the tubular piston 26 and the guide tube 25.

It should be noted that two different operating positions are shown above and below the axial centre line of the guide tube 25 in Figure 1 in order to illustrate the various operating positions of the percussion mechanism. In the operating position shown below the centre line, the tubular piston 26 is located in its almost fully withdrawn position while the ram 27 is in the position occupied during idling, i.e. when the drill bit 2 is not present or where there is no resistance on the front end of the drill bit 2. Above the centre line, the tubular piston 26 is shown in its most forward position, while the ram 27 is in a position in which it strikes the rear end of a beat piece 29 disposed intermediate the ram 27 and the drill bit 2. Two lugs 28 are formed on the rear outer end of the tubular piston 26, and these lugs have central holes for accepting a trunnion 30.The trunnion 30 is rotatably supported about its longitudinal axis and has a central hole, in and through which one end of a lever 31 extends. The lever 31 is rotatably supported at its lower end 133 on a pin 134 extending from the housing 1 or the casting 4. Intermediate the two ends of the lever 31 is secured another trunnion which extends into the groove 15 of the drum 14, 14' so that, when the groove 15 rotates, the lever 31 pivots about the pin 134; in consequence, the upper end of the lever 31 is moved reciprocally in the direction of the central axis of the guide tube.

A duct 45, which is open towards the rear and acts to supply cooling air, is located in the upper region of the casting structure 4.

As indicated in Figure 1, the striker ram 27 can be moved reciprocally in the tubular piston 26 and is sealed against the inner wall of the latter by means of an O-ring 36. An extension at the front end of the ram 27 consists of a truncated coneshaped section 33 forwardly from which extends a short cylindrical section 34. A peripheral annular groove 35 is located between the two sections 33 and 34.

An internal, rearwardly facing annular shoulder 60 is formed in the spindle 39, and an annular metallic plate 51 abutts this shoulder 60. Next to this annular plate 51 is a damping and latching member 50 of elastic material, preferably a ring-like element consisting of rubber. The member 50 is retained on one side by the annular plate 51 and on the other side by a washer 52, the latter being retained by a circlip 53 inserted in an internal groove in the spindle 39. The member 50 has the shape of two concentric rings, one inside the other and connected to one another by means of an integral intermediate web region. The radially outside ring has a larger cross-section (in radial planes through its central axis, i.e. the axis of ratation of the spindle 39) than the ring located radially further inwards.This causes the outer ring to be compressed between the annular plate 51 and the washer 52. The member 50 is so located in the spindle 39, that in normal operation (shown at the top in Figure 1) it lies in front of the annular groove 35 of the ram 27. In other words, the beat piece 29 is located so far back, when the drill bit 2 is pressed in, that the annular groove 35 of the ram 27 is prevented from moving into the region occupied by the member 50. Also, in this position a chamfered rear end region 62 of the beat piece 29 enters through and comes into engagement with the annular plate 51; recoil blows exerted by the beat piece 29 are transmitted to the annular plate 51 and from the latter to the resilient member 50, so that the outer ring of the member 50 is compressed and dampens these blows or shocks.

At idle, that is when there is either no drill bit 2 in the chuck 3 or when the drill bit 2 is not pushed into the spindle by contact with a work piece, the beat piece 29 is displaced forwards by being struck by the ram 27 (see lower part of the central diagram in Figure 1). The ram 27 can thus move sufficiently far forwards for the inner ring of the resilient member 50 to come into engagement with the groove 35. By this means, the ram 27 is held "captured" in this forward position and further drive movements of the tubular piston 26 cause no reciprocating movement of the ram 27, i.e. the ram is latched.

It will be appreciated, therefore, that the outer ring of the member 50 functions in dampening return of the beat piece, and may also function in dampening forward movement of the ram, whereas the inner ring of the member 50 functions as a latch for the ram during idling. Although these two rings perform separate functions, as will be appreciated there is a certain degree of interaction between them.

The section shown in Figure 2 corresponds to the corresponding region of the hammer drill shown in Figure 1, and the same parts are indicated by the same reference numbers with the addition of'.

The arrangement in Figure 2 differs from that of Figure 1 in that the elastic arrangement provided between the annular plate 51' and the washer 52' consists of two discrete rubber O-rings 50a and 50b, of which the outer O-ring 50b has larger cross-sectioned diameter (i.e. is a thicker ring) and is compressed between the annular plate 51' and washer 52. This outer O-ring 50b acts to dampen the recoils of the beat piece 29'.

When the hammer drill is idling, the inner O-ring 50a comes into engagement with the annular groove 35' of the ram 27' and so holds the ram 27' latched in this position.

The arrangement shown in Figure 3 corresponds substantially to the arrangement of Figure 2 and the same parts are indicated by the same reference numbers as in Figure 2.

The striker ram 27'shown in Figure 3 has an annular, forwardly facing surface 54 extending normal to the longitudinal axis of the ram, the surface 54 being located at the junction between the main body of the ram 27' and the reduced forward extension thereof. The annular groove 35' for engagement with the O-ring 50a continues inwardly directly from this annular surface 54. If the ram 27' moves forward during idle, its annular surface 54 strikes the washer 52' and the shock is accepted and dampened mainly by the thicker O-ring 50b. In this process, the thinner inner O-ring 50a is also elastically deformed. This deformation of the 0ring 50a reinforces its latching engagement with the annular groove 35'.

The two separate O-rings 50a, 50b are preferably made of the same resilient material, but could be made from different resilient materials, e.g. rubber and plastic material. The O-rings preferably have a solid cross-section.

It will be appreciated that although in the preferred embodiments above the hollow spindle is rotatable for rotation of the tool bit with or without percussion, the invention is applicable to a hammer drill having a non-rotatable hollow spindle and only capable of percussive action.

The above described embodiments, of course, are not to be construed as limiting the breadth of the present invention. Modifications, and other alternative constructions, will be apparent which are within the spirit and scope of the invention as defined in the appended claims.

Claims

1. A hammer drill, comprising: an air cushion impact mechanism having a piston type ram with an axial extension pointing towards a tool bit holder; the ram, in use, being driven with a reciprocating motion via an air cushion and in turn driving a beat piece against the rear end of a tool bit when inserted in the tool bit holder; a hollow spindle connected to the tool bit holder and in which said beat piece is mounted; an annular resilient body located within the hollow spindle for latching the ram in an idling position by engagement in an annular groove in the extension of the ram; an annular resilient damping element located within the spindle for damping axial recoils of the beat piece, a side of the damping element facing towards the tool bit holder being in contact with a first positioning region which is movable axially in a direction away from the tool bit holder; the annular body and the damping element being located in a common plane normal to the longitudinal axis of the spindle, the annular body being located radially further inward towards said axis than the damping element; and the annular body and the damping element both being retained against axial displace ment by and between said first positioning region and a second positioning region.

2. The hammer drill of Claim 1, wherein the axial dimension of the damping element is greater than the axial dimension of the annular body, and the damping element is compressed between said positioning regions in order to generate pre-stress therein.

3. The hammer drill of Claim 1 or 2, wherein the damping element and the annular body each comprise an O-ring.

4. The hammer drill of Claim 1 or 2, wherein the damping element and the annular body are formed in one piece.

5. The hammer drill as claimed in any preceding claim, wherein said second positioning region comprises a washer held by a circlip.

6. The hammer drill as claimed in any preceding claim, wherein the transition between the extension and the main body of the ram comprises an annular surface located normal to the longitudinal axis of the ram, and the annular groove is located in the immediate vicinity of said annular surface.

7. The hammer drill as claimed in any preceding claim, wherein said first positioning region comprises an annular plate in abutment with an annular internal shoulder of said hollow spindle.

8. The hammer drill as claimed in any preceding claim, wherein the beat piece has a rearwardly extending portion of reduced diameter connected to a forward portion of the beat piece by a chamfered region.

9. The hammer drill as claimed in any preceding claim, wherein said annular resilient body is a first rubber O-ring of solid cross-section and said damping element is a second rubber O-ring circumscribing said first O-ring and having a larger solid cross-section.

10. The hammer drill substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

11. A hammer drill having latching and damping arrangements substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

12. A hammer drill having latching and damping arrangements substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.