EP1815947A2

EP1815947A2 - Rotary hammer

Info

Publication number: EP1815947A2
Application number: EP07105981A
Authority: EP
Inventors: Reinhard Plietsch; Michael Stirm
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 1999-04-30
Filing date: 2000-04-14
Publication date: 2007-08-08
Also published as: EP1048415A3; ATE368552T1; GB9909987D0; DE60035732T2; EP1048415B1; EP1815947A3; EP1048415A2; JP2000326263A; DE60035732D1

Abstract

A hammer that is capable or receiving a tool bit (30) for acting on a workpiece, and includes an air cushion hammering mechanism that comprises a cylinder (2), a piston (6) that can be caused to reciprocate within the cylinder, and an impact member (12) that is slidably located within the cylinder and can be caused to move in response to reciprocation of the piston by means of an air cushion between the piston and the impact member so that the impact member can strike the end of a bit (30) that is held in the hammer. The hammer includes a web (22) of flexible impervious material that extends from the impact member to prevent ingress of dust from the region of the bit to the cylinder. A hammer is also provided which includes an arrangement for arresting the impact member in its forward position, which comprises a resilient ring (52) that is located within the cylinder and extends around the impact member, the impact member (12) having an intermediate portion (100) of varying diameter so that, at a given position of the impact member in the cylinder, the intermediate portion (100) of the impact member touches the resilient ring (52) and a substantially closed chamber is formed within the cylinder (2) that extends around the resilient ring (52), further forward movement of the impact member reducing the volume of the chamber (70) and causing the resilient ring (52) to constrict the impact member. A hammer is also provided which includes a housing (1) and a tool holder (4) that can receive a tool bit (30) for acting on a workpiece, in which the bit (30) is retained in the tool holder by means of one or more locking elements (42) and the hammer includes one or more cushioning elements (34, 36) located between the tool holder (4) and the housing (1) so that impacts that are reflected by the workpiece back along the bit (30) are transmitted to the housing via the tool holder (4) and the cushioning element(s) (34, 36).

Description

This invention relates to rotary hammers, and, in particular to hammers that incorporate an air cushion hammering mechanism.
Such hammers will normally include a tool holder that can hold a hammer bit or chisel bit for acting on a workpiece, and an air cushion hammering mechanism which comprises a piston, a ram and a beat piece that are slidably located in a cylinder so that reciprocation of the piston in the cylinder will cause the ram to reciprocate in the cylinder by virtue of the air cushion between the piston and ram. The ram strikes the beat piece and the beat piece hits the rear or proximal end of the hammer or chisel bit inserted in the tool holder, thereby transferring the impact from the ram to the bit. The beat piece generally has a considerably smaller stroke within the cylinder than does the piston or ram, usually only moving a few millimetres when the hammer is employed in its working mode.
The beat piece has a number of purposes. One reason for the presence of the beat piece is to provide a barrier against ingress of dust from the workpiece to the air cushion mechanism via the tool holder. This is a particularly important function since considerable quantities of dust are generated from the workpiece by the action of the hammer, and it is important for the dust to be kept out of the air cushion mechanism since otherwise the seal between the reciprocating components and the cylinder will be degraded and friction between the components and the cylinder will be increased. However, the presence of the beat piece has the disadvantage that it causes a reduction in the impact energy transmitted to the tool. For example, it is estimated that approximately 20 to 30% of the impact energy may be lost due to the presence of the beat piece.
It has been proposed to provide hammers that do not include any beat piece, and in which the ram strikes the end of the bit inserted in the tool holder, for example as described in CA-950288 to Hilti AG . However, such forms of hammer have the disadvantage that it is necessary to provide a seal between the ram and the cylinder sufficient to prevent dust ingress to the air cushion, which seal will inevitably cause frictional deceleration of the ram and thereby reduce the magnitude of the impact on the bit held in the tool holder. The effect of the seal in reducing the magnitude of the impact is greater than the effect of seals located between the beat piece and the cylinder due to the considerably greater stroke of the ram compared to that of the beat piece.
According to one aspect, the present invention provides a hammer that includes an air cushion hammering mechanism that comprises a cylinder, a piston that can be caused to reciprocate within the cylinder, and an impact member that is slidably located within the cylinder and can be caused to move in response to reciprocation of the piston by means of an air cushion between the piston and the impact member so that the impact member can strike the end of a bit that is held in the hammer, characterised in that the hammer includes a web of flexible impervious material that extends from the impact member to prevent ingress of dust from the region of the bit to the cylinder.
The web of flexible material preferably extends radially from the impact member to the cylinder, although it may extend to part of the housing forward of the cylinder, or even the rear end of the tool holder if more convenient, provided that it acts as a barrier to the flow of dust rearwardly from the tool holder to the cylinder. In addition, the web of material should have sufficient slack, i.e. excess length, to allow the impact member to slide axially within the cylinder to its full extent. Such axial movement will, in general, correspond to the stroke of the ram in conventional hammers rather than to the stroke of the beat piece. In view of this, the impact member may be referred to hereafter as a ram. Such excess length is most conveniently provided by folding the web, for example in the manner of a concertina.
The hammer according to the present invention has the advantage that the impact energy applied to the bit is not reduced by the presence of the beat piece, nor is it reduced due to the presence of sliding sealing elements located between the ram and the cylinder, so that the impact energy may be maximised. This form of seal will obviate the need to provide any other seal such as a sliding seal between the impact member and the cylinder which would reduce the impact strength on the bit, and so the web preferably forms the only seal against dust ingress to the cylinder. Such an arrangement is particularly advantageous in the case of hammers that are powered by batteries rather than by mains power, in view of the more efficient use of power and therefore the increase in operation time of the hammer between battery charges.
Another problem that is relevant to hammers that employ air cushion hammer mechanisms is that of arresting the impact member in its forward position when the hammer is released from the workpiece. Typically, it is desired for the hammer mechanism to continue to operate while the hammer bit is applied to the workpiece, but when the bit is disengaged from the workpiece the hammer mechanism should stop, even though the piston continues to reciprocate within the cylinder. The impact member will strike the beat piece if a beat piece is present, or will strike the bit if no beat piece is present to move the beat piece and/or the bit to the forward position, and should itself be arrested and preferably also held in that position. In that position, a vent hole in the cylinder is normally exposed in order to deactivate the air cushion, so that the hammer action will continue only when the tool bit is engaged once more in the workpiece.
This is achieved according to another aspect of the invention in which there is provided a hammer that is capable or receiving a tool bit for acting on a workpiece, and includes an air cushion hammering mechanism that comprises a cylinder, a piston that can be caused to reciprocate within the cylinder, and an impact member that is slidably located within the cylinder and can be caused to move by the piston by means of an air cushion between the piston and the impact member, characterised in that the hammer includes an arrangement for arresting the impact member in its forward position, which comprises a resilient ring that is located within the cylinder and extends around the impact member, the impact member having an intermediate portion of varying diameter so that, at a given position of the impact member in the cylinder, the intermediate portion of the impact member touches the resilient ring and a substantially closed chamber is formed within the cylinder that extends around the resilient ring, further forward movement of the impact member reducing the volume of the chamber and causing the resilient ring to constrict the impact member.
The intermediate portion of the impact member preferably increases in diameter in a rearward direction, so that forward movement of the impact member causes the resilient ring to expand radially. This radial expansion against the resilience of the ring will cause the ring to oppose the forward motion of the impact member, and the radially inward force due to the raised air pressure exerted on the radially outward surface of the ring will enhance the action of the ring in constricting the impact member. Preferably the impact member has a waist portion, for example in the form of a circumferentially extending groove, that can receive the resilient ring when the impact member is in its forward position to allow the resilient ring to hold the impact member in that position until the hammer re-engages the workpiece.
It is preferable for the forward motion of the impact member to be damped when it is arrested and for the impact member not to fly back rearwardly by the pressure of the air in the chamber since that would cause re-actuation of the hammer mechanism. Accordingly a bleed hole may be provided in the cylinder to allow venting of the air in the chamber when the impact member is in its forward position.
The need to arrest and retain the impact member applies whether the impact member acts on a beat piece that transfers impact energy from the impact member to the bit, or whether the impact member strikes the bit directly without the presence of an intermediate beat piece, and this aspect of the invention applies to both forms of hammer.
Another problem that occurs, especially with hammers that do not include a separate beat piece, is that of shocks or impacts that are reflected by the workpiece back along the tool bit. It is highly desirable to cushion such impacts so that they are damped in order to prevent discomfort or injury to the operator of the hammer and to reduce the risk of damage to the hammer. Thus, according to yet another aspect of the invention, there is provided a hammer which includes a housing and a tool holder that can receive a tool bit for acting on a workpiece, in which the bit is retained in the tool holder by means of one or more locking elements, characterised in that the hammer includes one or more cushioning elements located between the tool holder and the housing so that impacts that are reflected by the workpiece back along the bit are transmitted to the housing via the tool holder and the cushioning element(s). The reverse impact is preferably transferred from the bit to the tool holder by the locking element(s).
One form of rotary hammer will now be described by way of example, with reference to the accompanying drawing which is a schematic sectional elevation through part of a hammer along the cylinder axis of the hammer.
Referring to the accompanying drawing, a rotary hammer comprises a housing 1, a cylinder 2 located within the housing, and a tool holder 4 attached to the front of the housing. Many of the elements of the housing, tool holder and other parts of the hammer are known per se and are not reproduced for the sake of clarity. The cylinder contains a piston 6 that is coupled, via a trunnion 8 housed in it and a crank arm 10 to the spindle of a vertically oriented electric motor (not shown). The cylinder 2 also houses an impact member or ram 12 that serves the function of a combined ram and beat piece, and is coupled to the piston 6 by means of an air cushion formed between them and is thus able to slide along the axis of the cylinder 2 under the action of the piston. An annular seal 14 formed from polytetrafluoroethylene is located on an annular recess at the rear end of the ram 12. The seal has a generally "L" shaped cross-section in its radial plane, and is referred to as an "L-seal".
The ram 12 has a forward portion 16 of relatively small diameter, a rear portion 18 of relatively large diameter, so that it will fit slidably within the cylinder 2, and an intermediate portion 20 having a diameter between the two. A tapering web 22 of flexible impervious material, for example plastics elastomer extends from the forward end of the forward portion 16 of the ram 12 to the forward end of the cylinder, and is held at each end to the ram 12 and the cylinder 2 respectively by means of a pair of clips 24 and 26 so that the arrangement is substantially impervious to air and dust. The web 22 has a length that enables the ram 12 to slide within the cylinder between its rearmost position in which the front ends of the ram and cylinder are relatively close to one another, and its forwardmost position as shown in which they are axially separated from one another by the length of the forward portion 16 of the ram. The web is shown schematically in two alternative forms above and below the cylinder axis in which (as shown above the cylinder axis) the web 22a is folded with folds substantially parallel to the axis, while, as shown below the cylinder axis, the web 22b concertinas with folds substantially normal to the cylinder axis. In either form, the web will provide a seal with substantially no hindrance to axial sliding of the ram 12.
A tool holder 4 (only part of which is shown) is located at the front of the housing 1, and is clamped in a chamber in the housing, the front end of which is closed by means of a front plate 27 secured to the housing by means of bolts 26. The tool holder comprises a cylinder 28 having a bore that is capable of accepting the shank of a bit 30, which cylinder increases in radius at its rearward end 32 to fill the chamber formed in the housing 1 and to accommodate the forward portion 16 of the ram 12 and the web 22. The rearward end 32 of the cylinder forming the tool holder is seated in the chamber by means of a pair of resilient cushioning rings 34 and 36, one of which is located between the rearward end 32 and the front plate 27 of the housing, and the other of which is located between the rear end thereof and the rest of the housing, thereby allowing the tool holder to move axially by a small extent. The bit shown is a standard form of bit having a pair of retaining recesses 38 and a pair of grooves 40 for receiving splines to enable the bit to be rotated, such a form of bit being described in DE-A-25 51 125 and sold under the designation "SDS Plus". The bit is retained in the bore of the tool holder 4 by means of one or more locking elements 42 that can be moved radially outwardly through apertures 44 in the tool holder to allow the bit to be inserted and removed, and can be moved radially inwardly to the position shown, and locked in that position by means not shown in order to retain the bit in the tool holder but to allow it to move axially to a limited extent.
The cylinder 2 has a two arrays of vent holes 46 and 48 in the side wall thereof, and further holes 50 in the front end of thereof. In addition the cylinder 2 contains a resilient ring 52 formed from an elastomeric material that is held in place against an internal shoulder 54 of the cylinder by means of a retaining ring 56 that is itself held in place by snap ring 58. The retaining ring 56 is so shaped, for example by means of a number of cut-out portions, that is allows free movement of air past it in the axial direction. The intermediate portion 20 of the ram 12 has a front end 100 that is frusto-conical so that it gradually increases in diameter, to that of the intermediate portion, and has a waist portion 101 whose outer profile generally complements the inner profile of the resilient ring 52. The diameters of the waist portion 101 of the ram 12 and the resilient ring 52 are such that the resilient ring is required to expand radially in order to pass over frusto-conical part 100 of the ram into the waist portion 101.
In operation, the electrical motor will cause the piston 6 to reciprocate within the cylinder 2. While the ram 6 and the bit 30 are in their forwardmost positions as shown in the figure, reciprocation of the piston 6 will not cause the ram 12 to move because air located in the cylinder 2 will be vented or replenished via vent hole 48. When the bit 30 is caused to engage a workpiece, the bit will move rearwardly (to the right as shown in the drawing) into engagement with the front end of the ram 12, and push the ram rearwardly to release the ram from the resilient ring 52 until the vent holes 48 are blocked by the rear portion of the ram. The ram 12 and the piston are then coupled by an air cushion between them, so that reciprocation of the piston will cause the ram to strike the rear end of the bit 30, and cause the bit to strike the workpiece. During this operation, dust formed from the workpiece is prevented from entering the cylinder 2 by means of the flexible web 22 that seals the front end of the air cushion mechanism while allowing movement of the ram over the full length of its stroke. If desired, the motor can cause a flow of air in a forward direction into the chamber via apertures 60 and out of the chamber via apertures 62, in order to reduce the quantity of dust in the chamber.
As the bit strikes the workpiece, reflection of the impact back along the bit will cause the forward ends 64 of the retaining grooves to strike the forward ends of the locking elements 42. The locking elements 42 transfer this impact to the tool holder 4 and thence to the body 1 of the hammer, but the impact is cushioned by means of the cushioning rings 36 and 34, which act to dampen any impacts.
As the ram 12 reciprocates within the cylinder 2, air is forced through vent holes 46 in the side of the cylinder and through holes 50 in the front of the cylinder, so that the air pressure in front of the ram 12 and within the web 22 is maintained relatively constant (at least compared with the air pressure between the piston and the ram) so that movement of the ram 12 is not hindered and the flexible web 22 is not damaged.
When the bit 30 is removed from the workpiece, and it is desired that the hammer action stops, the ram 12 will strike the bit 30 and cause it to move into the forwardmost position as shown in the drawing. As the rear portion 18 of the ram passes the forward vent holes 46 the ram prevents any further aspiration or venting of air through the vent holes. At about the same time the forward end of the frusto-conical portion 100 touches the rearward side of the resilient ring 52, thereby forming a closed annular chamber 70 defined by the intermediate portion 20 of the ram, the forwardly directed surface of the rear portion 18 of the ram, the bore of the cylinder 2 in the region of the intermediate portion of the ram, and the radially outwardly oriented surface 72 of the resilient ring. As the ram 12 continues to move in the forward direction, the resilient ring 52 is caused to ride up the frusto-conical portion and thereby expand radially against its elastic resilience. This radial expansion thus provides resistance to further forward movement of the ram 12. In addition, the volume of the annular chamber 70 reduces, due to the forward movement of the ram 12, and the pressure in the annular chamber increases. The pressure in the regions lying forward of the resilient ring 52 and in the centre thereof, however, remains generally unchanged since the air is able to vent through the holes 50 into the region forward of the cylinder that is enclosed by the web 22. The pressure difference between the annular chamber 70 and the region lying to the centre of the resilient ring 52 thus causes the ring 52 to exert an additional radially inwardly directed force on the ram that augments the force caused by the resilience of the ring, and assists the resilient ring in stopping the ram. As the ram 12 continues to move forwardly, the resilient ring 52 rides over the annular ridge 102 that separates the frusto-conical portion 100 from the waist 101, and then becomes seated in the waist 101 as shown in the drawing, where it retains the ram in position. A small bleed hole 74 is provided to allow air to bleed out of the chamber 70 once the ram 12 has been caught, thus acting as a damping mechanism so that the ram is not urged rearwardly out of position by the air pressure in chamber 70.

Claims

A hammer that is capable or receiving a tool bit (30) for acting on a workpiece, and includes an air cushion hammering mechanism that comprises a cylinder (2), a piston (6) that can be caused to reciprocate within the cylinder, and an impact member (12) that is slidably located within the cylinder and can be caused to move by the piston by means of an air cushion between the piston and the impact member, characterised in that the hammer includes an arrangement for arresting the impact member in its forward position, which comprises a resilient ring (52) that is located within the cylinder and extends around the impact member, the impact member (12) having an intermediate portion (100) of varying diameter so that, at a given position of the impact member in the cylinder, the intermediate portion (100) of the impact member touches the resilient ring (52) and a substantially closed chamber is formed within the cylinder (2) that extends around the resilient ring (52), further forward movement of the impact member reducing the volume of the chamber (70) and causing the resilient ring (52) to constrict the impact member.
A hammer as claimed in claim 1, characterised in that the intermediate portion (100) of the impact member increases in diameter in a rearward direction, so that forward movement of the impact member (12) causes the resilient ring (52) to expand radially.
A hammer as claimed in claim 1 or claim 2, characterised in that the impact member has a waist portion (101) that can receive the resilient ring (52) when the impact member (12) is in its forward position to allow the resilient ring (52) to hold the impact member.
A hammer as claimed in any one of claims to 3, characterised in that the cylinder has a bleed hole (74) to allow air in the chamber (70) to vent when the impact member is in its forward position.
A hammer as claimed in any one of claims 1 to 4, characterised in that the resilient ring (52) is held in place by a retaining ring (56) which is formed with cut out portions which allow air to flow axially past the retaining ring (56).
A hammer which includes a housing (1) and a tool holder (4) that can receive a tool bit (30) for acting on a workpiece, in which the bit (30) is retained in the tool holder by means of one or more locking elements (42), characterised in that the hammer includes one or more cushioning elements (34, 36) located between the tool holder (4) and the housing (1) so that impacts that are reflected by the workpiece back along the bit (30) are transmitted to the housing via the tool holder (4) and the cushioning element(s) (34, 36).
A hammer as claimed in claim 6, characterised in that reverse impacts from the bit are transferred from the bit to the tool holder (4) by the locking element(s).
A hammer as claimed in claim 6 or claim 7, characterised in that a first cushioning ring (34) is located between the front of the tool holder (4) and the housing (1) and a second cushioning ring (36) is located between the rear of the tool holder and the housing (1).