CA1233377A

CA1233377A - Hammer drill

Info

Publication number: CA1233377A
Application number: CA000464396A
Authority: CA
Inventors: Horst Grossmann; Stefan Schmidt
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 1983-10-01
Filing date: 1984-10-01
Publication date: 1988-03-01
Also published as: AU3368784A; DE3335795A1; FR2552696B1; IT1176850B; FR2552696A1; GB2147240B; GB2147240A; IT8422896A0; DE3335795C2; GB8424629D0

Abstract

ABSTRACT OF THE DISCLOSURE

A hammer drill with an air cushion impact mechanism has a resilient ring for latching a reciprocating ram-in an idle position, and another resilient ring for damping recoil blows of a beat piece driven by the ram.
The rings are disposed one inside the other in a plane normal to the axis of reciprocation of the ram, and are disposed between and axially retained by two spaced apart annular retaining members. Preferably the outer ring is thicker than the inner ring.

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Description

~333 case 4551 IMMURE 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 invent10n particularly relates to damping and latching arrangements for come pennants of such drills.

BACKGROUND OF TIRE 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 point-in towards the tool holder. The ram is usually driven with a reciprocating motion in a cylindrical glide sleeve via an enclosed air cushion and drives a beat piece against the rear end of the tool bit when inserted in a a hollow spindle. This spindle 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 o-f 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 Of~enlegungsschrift 3,120,326 discloses a hammer drill of this type in which the annular body and the I.

~33~ to damping element each consist of an O-ring. The damping element is located between the inner surface of the spindle and -the outer surface ox a step in a sleeve so that one of its sides is in contact with the amlular shoulder, formed by the step, ox the sleeve. On the opposite side, the damping element is in contact with the front surface ox a support sleeve which has, in the inner surface ox its rear end region, an extension or accepting the annular body. A oirclip located in the spindle serves to position the support sleeve.

In this above arrangement, therefore, two sleeve parts ox 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 Of'fenlegungsschri:t't 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 cots are not reduced.

SUMMARY OF THE INVENTION
An object ox the present invention is -to arrange both the damping element for damping axial recoils of' the beat piece and the annular body ox the latch device in the-hammer Trill 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.

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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 ox 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 thy invention, therefore, the damping element and the annular body are located in a common plane instead of being located, as was previously usual, with an axial distance between them along the spindle. By this means, common position in 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 -prom the tool holder may be wormed by means of a washer held by a circlip and the positioning regioll 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 manu~ac-tur-in 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 practice ally in one assembly step.

In order to attain adequate damping owe the recoils ox the beat piece, the axial extension of the damping eye-mint can be greater than the axial extension of the annular body, and the damping element can be compressed between the positioning regions in order to generate preceptors so that i-t will, in this way, act as a relative-lye stir spring.

3~7 In one embodiment of -the invention, the damping eye mint and the annular body can each consist of an O-ring.
It is, however, also possible to Norm the damping element and the annular body in one piece.

The transition between the extension and the main body ox the sink or ram may be wormed by an annular Sirius located normal to the longitudinal axis ox -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 ox` the shocks from the ram when the ram moves forward during idling ox the percussive mechanism.

Other objects, features and advantages ox the present invention will become more sully apparent Rome the hollow-lung detailed description of the preferred embodiment, the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:
FIG. 1 shows a partial side view ox the frost portion of a hammer drill according to the invention, mainly in section but with some internal parts not section, and showing some of the moving parts in two positions;
FIG. 2 shows a portion of Fig. 1 but with a differ-en construction damping element and latching element.
FIG. 3 shows an arrangement similar to Fix. 2 bolt with a different construction of the ram.

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DETAILED Description OF THE PREFERRED ~ODIMENTS

The hammer drill shown in Fig. 1 corresponds in its general construction to the Henry drill described and shown in German Patent Application P 32 24 050.3 published December 29, 1983.

In Fig. 1, the hummer drill has a housing 1 consisting ox two plastic clam-shells, this housing having a chuck 3 at its front end or accepting the partially shown drill bit 2. A fan 7 is mounted on the armature shaft owe the -10 electric motor (not shown), the armature shalt being rotatable supported at its -forward end in a bearing supported in an aluminum casting 4 positioned inside the housing 1. The forward end o e the armature shut worms a pinion, which is concealed in Fig. 1, and which drivingly engages with a gear wheel 13 carried by an intermediate shalt 10. The ends ox the intermediate shaft 10 are rotatable 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 shalt 10 in the direction of the bearing 11, but i-t is held against rotation relative to the shalt 10. Such displacement ox the gear 13 compresses the spring 12.

A drum 14, wish has a peripheral groove 15, is mounted rotatable on and relative to the intermediate shaft 10. The peripheral groove 15 is in the Crimea of an obliquely set circle and produces the reciprocating movement, to be described later, ox the piston ox the impact mechanism. On the end remote prom the gear 13, the drum 14$ 14? has axial dog clutch teeth which engage I

with correspondingly shaped axial clutch teeth on a bush 16 secured to the intermediate shut 10 and rotatable therewith. A spring 18 surrounds a fevered part of the bush 16 and is compressed between a washer 19 and a rear Lange of the bush 16 to effect driving engagement of the dog clutch teeth. The bush 16 can, by means ox an arrangement not shown be so displaced from outside the housing 1 that the teeth of the bush 16 come out of en-gngement with the teeth ox the drum 14, 14', i.e.$he bush 16 can be displaced to the left in Fig. 1 against the pressure o-f the spring 18. In this latter position, the rotational movement of the intermediate shalt 10 is no longer transmitted from the bush 16 to the drown 14, 14' and the drive or the impact mechanism is, therefore, interrupted A gear wheel 37 is located on the intermediate shaft 10 between the washer 19 and an axial th~lst bearing 23.
This gear 37 engages with a gear wheel 38 secured on a chuck spindle 39 and thus effects rotation thereon to rotate the drill bit 2. The chuck spindle 39 is support Ed at its inner end on an axial bearing 40 and it rotate ably mounted on a guide tube 25. The gear 38, Jo that it can accept shocks, is axially movable to limited extent against flexing ox 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 worming 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 ox the drill bit 2. For the method ox operation o-f such a percussive mechanism, no-erroneous should be mode to United States Patent 4,290,492 which also explains the junction and position ox venting provided in the tubular piston 26 and the guide tube 25.

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It should be noted that two die rent operating positions are shown above and below -the axial center line ox the guide tube 25 in Fig-. 1 in order to illustrate the various operating positions ox the percussion mechanism.
In the operating position shown below the center line, the tubular piston 26 is located in its almost -sully 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 center 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 ox a beat piece I disposed intermediate the ram 27 and the drill bit 2. Two lugs 28 are wormed on the rear outer end ox the tubular piston 26, and these lugs have central holes or accepting a trunnion 30. The t~lnnion 30 is rotatable 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 rotatable supported 20 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 ox-tends into -the groove 15 of the drum 14, 14' so that, when the groove 15 rotates, the lever 31 pivots about the 25 pin 134; in consequence, the upper end ox the lever 31 is moved reciprocally in the direction ox the central axis ox 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 Fix. 1, the striker ram 27 can be moved reciprocally in the tubular piston 26 and is sealed against the inner wall owe the latter by means of an 33'~

0-ring 36. An extension at the front end o-f -the ram 27 consists of a truncated cone-shaped section 33 forwardly Eros which extends a short cylindrical section 34. A
peripheral annular groove 35 it located between the two sections 33 and 34.

An internal, rearwardly racing annular shoulder 60 is Wormed in the spindle 39, and an annular metallic plate 51 abuts 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 top shape owe two 16 concentric rings, one inside the other and connected -to one another by means o-f 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 o-E rotation ox the spindle 39~ than the rip 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 Jo located in the spindle 39, that in normal operation (shown at the top in Figure 1) -it lies in front o-E the annular groove 35 owe the ram 27. In other words, the beat piece 29 is located so Lear back, when the drill bit 2 is pressed in, that the annular grove 35 o-E the ram I it prevented from moving into the region occupied by the member 50. Also, on this position a chamfered rear end region 62 ox the beat I 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 prom the latter to the resilient member 50, $0 that the outer rirlg o- the member 50 is compressed and dampen 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 no pushed into the spindle by contact with a work piece, the beat piece 29 is displaced forwards by being struck by the rum 27 (see lower part owe the central diagram in ~1g 1).
The ram 27 own thus move su~iciently jar forwards or the inner ring of the resilient member 50 to come into engagement with the groove 35. By this means, the ram I
is held "captured" in this ~oru~ard position and further drive movements of the tubular piston 26 cause no foci-prorating movement of the ram 27, i.e. the ram is latched It will be appreciated, therefore, that the outer ring of the member 50 junctions in dampening return of the beat piece, and may also junction in dampening forward movement of the ram, whereas the inner ring of the member 50 junctions as a latch for the rum during fling Al-though these two rings perform separate junctions, as will be appreciated there is a certain degree ox interaction between them.

The section shown in Fig. 2 corresponds to the correspond-in region TV the hammer drill shown in Fig. 1, and the same parts are indicated by the sole reference numbers with the addition ox '.

The arrangement in Fig. 2 divers prom that of Fig. 1 in that the elastic arrangement provided between the annular plate 51' and the washer 52' consists ox two discrete rubber 0-rings aye and 50b, ox which the outer 0-ring 50b has a larger cross-sectioned diameter (i.e. is a .
thicker ring) and is compressed between the annular plate I, 51' and washer 52. This outer 0-ring 50b arts to dampen the recoils ox the beat piece 29'.

1~3 r~3~7t~

When the hammer drill is idling the inner 0-ring aye comes into engagement with the annular groove 35' o-the ram I and so holds the ram 27' latched in -this position The arrangement shown in Fig. 3 corresponds substantially to the arrangement of Fig. 2 and the same parts are in-dilated by the same reference numbers as in Fig. 2.

The striker ram Sheehan in Fig. 3 has an annular, for-warmly aqualung surface 54 extending normal to the long-tudinal axis of the ram, the surface 54 being located at the ~un~tlon between the main body ox the Al I and the reduced forward extension thereon. The annular groove 35' for engagement with the 0-ring aye continues inwardly directly prom this annular surface 54. If the ram 27' moves coward during idle, its annular surface 54 strikes the washer 52' and the shock is accepted and dampened mainly by the thicker 0-ring 50b. In this pro-Swiss the thinner inner 0-ring aye is also elastically deformed. This deformation of the 0-ring aye reinforces its latching engagement with the annular groove 35', The two separate 0-rings aye, 50b are preferably made ox the same resilient material, but could be made from die rent resilient materials, erg, rubber and plastic ~at0rial. The 0-rings preferably have a solidcross-section.
It will be appreciated that although in the preferred embodiments above the hollow spindle is rotatable or 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 active.

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

Claims

CLAIMS:

1. A hammer drill, comprising:
a hollow spindle defining a longitudinal axis;
a beat piece axially movable in said hollow spindle for imparting percussive blows to a tool bit when present, a ram driven with reciprocating motion in a cylinder via an air cushion for imparting percussive blows to said beat piece;
said ram having a circumferential groove therearound;
two retaining members located inside said hollow spindle, said retaining members being spaced apart along said axis;
first and second rings of resilient material disposed between and retained by said two retaining members, said rings being coaxial with respect to said axis;
said first ring being disposed inside said second ring and functioning to engage in said circumferential groove for latching said ram in an idle position;
said second ring being thicker than said first ring and being compressed between said two retaining members to generate a pre-stress condition therein; and said second ring functioning to dampen recoil blows imparted by said beat piece to one of said retaining members.

2 . The hammer drill of Claim 1, wherein said first and second rings are integrally connected by a web.

3. The hammer drill of Claim 1, wherein said first and second rings are separate O-rings, and said one of said retaining members comprises an annular plate which is displaceable by said beat piece towards the other of said retaining members .

4. A hammer drill, comprising:
a hollow spindle defining a longitudinal axis about which said spindle can be rotatable driven;
a beat piece movable axially in said spindle for imparting percussive blows to a tool bit, when present, rotatable via said spindle;
a ram reciprocally driven along said axis via an air cushion for imparting percussive blows to said beat piece;
said ram having a reduced portion extending towards said beat piece, said reduced portion having an annular peripheral groove therein;
said spindle having an internal shoulder therein against which abuts an annular retaining plate;
an annular retaining member spaced along said axis from said retaining plate in a direction away from said drill bit;
a first resilient ring disposed inside said spindle and juxtaposed between said retaining plate and said retaining member, said first ring engaging in said peripheral groove for latching said ram in an idle position; and a second resilient ring also juxtaposed between said retaining plate and said retaining member and surrounding said first resilient ring, said second ring having a thickness in said direction greater than that of said first ring and being compressed between said retaining plate and said retaining member to a pre-stressed condition, said second ring functioning to dampen recoil blows by said beat piece against said retaining plate.

5. The hammer drill of claim 4, wherein said first and second rings are integrally connected.

6. The hammer drill of claim 4, wherein said first and second rings are separate rubber o-rings and are coplanar.

7. The hammer drill of claim 4, wherein said re-taining member comprises a washer retained against displacement in said direction by a circlip engaged in said spindle.