Abstract:
A rotary hammer has a reciprocating piston of a pneumatic impact mechanism driven from a rotatable drive shaft. A coupling element is fixed on, and a drive element slidably mounted on, the drive shaft. These elements have interengageble tapered coupling surfaces and are biased apart by a spring therebetween. The drive element is disposed forwardly of the coupling element and is slidable rearwardly to drivingly engage the coupling surfaces for transmitting drive to the piston. The relative disposition of the drive and coupling elements causes reaction force on the piston, consequential in use upon generation of percussive blows, to urge the drive element into intensified engagement with the coupling element.

Description:
This is a continuation of application Ser. No. 762,715, filed Aug. 5, 1985, now U.S. Pat. No. 4,657,088. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a rotary hammer with a pneumatic impact mechanism which comprises a reciprocating piston driving a beat piece. The impact mechanism is capable of being driven by means of a drive element rotatably mounted on a driven drive shaft. The drive element can be brought into engagement with a coupling element fast on the drive shaft. 
     In a known rotary hammer of this type (see U.S. Pat. No. 4,456,076) there is fixed or non-rotatably formed on the drive shaft a ring-shaped coupling element having an outer surface shaped as a tapering truncated cone. Also on the drive shaft there is rotatably mounted a drive element which carries in an obliquely set annular groove a rotatable ring with a radially projecting pin. This pin is in engagement with the rear end of a piston arranged in a guide tube in which there is also a beat piece between which and the piston a driving excess pressure is built up in operation, as is known for penumatic impact mechanisms of rotary hammers (see U.S. Pat. No. 4,290,492). In order to drive the impact mechanism of the known rotary hammer, the drive shaft carrying the coupling element is axially displaced against spring pressure at the work-piece by contact pressure of the tool held in the tool-holder of the rotary hammer, so that the truncated-cone-shaped peripheral surface of the coupling element is pressed into coupling engagement with a correspondingly truncated-cone-shaped annular surface of the drive element, and thus the drive element is rotated together with the driven drive shaft. 
     This known rotary hammer has a relatively complicatedly constructed drive element which consists of several parts and consequently requires expensive assembly. In addition, on account of the use of an axially displaceable drive shaft, there is also a relatively larger construction expense. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to create a rotary hammer with an improved drive for the penumatic impact mechanism. 
     According to the present invention, there is provided a rotary hammer comprising a pneumatic impact mechanism including a reciprocating piston, a rotatably driven drive shaft for driving the impact mechanism, a coupling element fixed non-rotatably on the drive shaft for rotation therewith, and a drive element rotatably mounted on the drive shaft and optionally engageable with the coupling element by axial displacement relative to the drive shaft. Means, drivingly connecting the drive element to the piston, is provided for reciprocating the piston upon rotation of the drive element, the piston being driven in a forward direction to generate percussive blows and returning in a rearward direction. The drive element and the coupling element have interengageable tapered coupling surfaces. The coupling element is disposed rearward of the drive element with the coupling surface of the coupling element facing in the forward direction and the coupling surface of the drive element facing in the rearward direction. The relative disposition of the drive element and the coupling element cause reaction force on the piston consequential upon generation of the percussive blows to urge the drive element into intensified engagement with the coupling element. 
     In the preferred embodiment, the means for reciprocating the piston comprises a drive fin on the drive element, this drive fin constiuting a cam which extends between two rollers mounted on the rear end of the piston; the two rollers have axes of rotation perpendicular to the longitudinal axis of the piston. 
     In a preferred form of the invention the coupling element has its coupling surface tapering from back to front, which surface can be brought into engagement with a correspondingly formed surface of the drive element, and the drive element is provided between the coupling element and a tool-holder. 
     In a construction of this type the recoil of the tool in operation exerts a force pushing the piston backwards so that the roller fixed at the rear end of the piston and adjacent to the front of the drive fin presses against the drive fin and thereby exerts on the drive element a force which enhances the coupling between the latter and the coupling element. 
     In order to achieve a reliable separtion of the coupling element from the drive element and hence a reliable disconnection of the impact mechanism, there may be provided between the coupling element and the drive element a pressure spring which, on termination of a force pressing the drive element into engagement with the coupling element, effects a reliable separation of the drive element from the coupling element. 
     Since the impact mechanism works only when the tool is engaged with the work-piece but is at other times disconnected, loads on the impact mechanism and its drive occur only for short periods, so that its life is considerably increased. 
     Other objects, features and advantages of 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: 
     FIG. 1 shows in section a gear housing of a rotary hammer according to the invention together with a tool holder thereof; 
     FIG. 2 shows a section on the line II--II of FIG. 1; and 
     FIG. 3 shows an elevational view of the tool holder and the gear housing in which the gear housing is partially cut away in order to show an actuating lever for a pivot pin. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The illustrated gear housing 50 is connected at its rear end, at the right in FIGS. 1 and 3, to a motor housing, not illustrated, from which the armature-shaft spindle 7 of an electric motor extends into the gear housing 50. The armature-shaft spindle 7 is located with its front portion in a needle bearing 35 which is supported in a metal holder-member 29 inset into the gear housing 50 made of for example synthetic material. In this holder-member 29 there is also supported by means of a needle bearing 33 the rear end of a drive shaft 6 whose front end is held in a needle bearing 44 in the gear housing 50 or a metal inset element fixed in this gear housing 50. On the drive shaft 6 there is fixed, non-rotatably and axially non-displaceably, a coupling element 37 which has an external gear-tooth system which meshes with a pinion formed on the armature-shaft spindle 7. 
     In an annular recess open towards the rear in the coupling element 37 there is located a resilient damping ring 34 which has its front side resting against the base surface of the recess and its rear side resting against a disk 31&#39;. Between this disk and a further disk 31&#39; resting against an annular surface of the holder-member 29, there is located an axial-spherical or needle bearing 32 which, on rotation of the coupling element 37 and thus of the damping ring 34 and the disk 31&#39;, prevents rubbing at the disk 31 which is maintained stationary. The damping ring 34 serves to cushion axial impacts which may be transmitted to the drive shaft 6 in operation. 
     On the drive shaft 6 there is also rotatably arranged a drive element 40 whose construction and functioning are explained below. 
     At the front end region of the drive shaft 6 there is formed a toothed gear system 42 which is in meshing engagement with an external toothed gear system 19 of the tool spindle 2 which is held rotatably in bearings 9 and 17. The tool front region of the tool spindle 2 forms a tool holder comprising a casing 3. The tool 1 has the usual axially running grooves in its shank which engage with retaining elements 4. The construction of tool holders of this type for rotatary hammers is known and therefore requires no detailed explanation. 
     Inside the tool spindle there is located a guide sleeve 16 in which the front end region of a beat piece 22 is guided axially and reciprocally so that, through an opening provided in the front end of the guide sleeve 16, its front end surface can impact on the rear end of the tool 1. Between the front end of the guide sleeve 16 and an annular shoulder of the tool spindle 2, there is arranged a resilient damping ring 8, and between an annular shoulder of the gear housing 50 and an annular shoulder of the tool spindle 2 there are located a resilient damping ring 10 and a disk 11. These damping rings serve for cushioning impacts during idling, while a resilient damping ring 13, which is provided between a disk 12 resting against an annular shoulder of guide sleeve 16 and a disk 14 whose displacement motion is limited by pins 15, effects the damping of backwards directed blows during operational impacting. 
     The beat piece 22 is guided with its larger-diameter rear end in a tubular piston 24 which is reciprocally movable axially in the tool spindle 2, an O-ring 23 inset in an annular groove of the beat piece 22 providing a seal at the inner surface of the tool spindle 2. In the prolonged rear end 36 of the tubular piston 24 there are fixed perpendicular to the longitudinal axis of the tubular piston two bearing-pins 25&#39; and 27&#39; which carry at their lower ends rotatable rollers 25, 27 repectively. The rear end 36 is disposed in a U-shaped guide 26 which is fixed in the holder-member 29 (FIG. 2), so that the rear end 36 is movable reciprocally in the guide 26 in the direction of the longitudinal axis of the tubular piston 24. 
     Between the rollers 25 and 27 there extends a drive fin 40&#39; forming a guide cam, which is part of the drive element 40 previously referred to. This drive element is formed in one piece and may for example be a sintered part. The width of the drive fin 40&#39; corresponds essentially with the clear distance between the rollers 25 and 27, so that the external surfaces of these rollers are in engagement with the lateral surfaces of the drive fin 40&#39;. 
     Between the drive element 40, which is arranged rotatably and axially displaceable on the drive shaft 6, and the front end surface of the coupling element 37 there is arranged a pressure spring 39 surrounding the drive shaft 6, a disk 38 being provided between the rear end of the pressure spring 39 and the front end surface of the coupling element 37. From the external periphery of the front end surface of the coupling element 37 there extends a coupling surface 37&#39; which widens towards the rear in the shape of a truncated cone. The drive element 40 has a correspondingly inclined engagement surface, shown in FIG. 1 in engagement with the coupling surface 37&#39;. 
     When the rotary hammer is in the resting state the pressure spring 39 biases the drive element 40 and the drive shaft 6 in FIG. 1 towards the left, i.e. towards the front, so that the coupling surface 37&#39; is not in engagement with the correspondingly shaped engagement surface of the drive element 40. In consequence of this displacement of the drive element 40 the separating disk 21, which has an opening surrounding the tool spindle 2 and an opening surrounding the drive shaft 6, is also displaced forwards, whereby the axial-spherical or needle bearing 20 provided between separating disk 21 and an annular shoulder of the tool spindle 2, and hence also the tool spindle 2, are displaced towards the left in FIG. 1, i.e. towards the front in the rotary hammer. 
     If in this operational setting the rotary hammer is switched on, then the rotating armature-shaft spindle 7 rotates the coupling element 37 via the toothed gear associated therewith, and thus also the drive shaft 6 which, via the meshing toothed gear systems 42 and 19, rotates the tool spindle 2 and thus also the tool 1. When the rotating tool 1 is brought into engagement with a work-piece the contact pressure effects, via the retaining elements 4, an axial displacement of the tool spindle 2 towards the rear, so that the bearing 20, the separating disk 21 and the axial-spherical or needle bearing 41 between the separating disk 21 and the drive element 40 are likewise displaced towards the rear, which leads to a shift of the drive element 40 in the direction of the coupling element 37 and thus to the engagement of coupling surface 37&#39; and associated engagement surface of the drive element 40. By this means the drive element 40, together with the coupling element 37 rigidly fixed to the drive shaft 6, are rotated and the drive fin 40&#39;, which follows essentially the path of an obliquely-set circle, is guided between the rollers 25 and 27. This results in an axial reciprocating motion of the tubular piston 24 carrying the rollers 25 and 27 so that, due to build-up of excess pressure and resulting under-pressure, the beat piece 22 located in the tubular piston is displaced reciprocally in combination with the motion of the tubular piston 24 in the manner described in U.S. Pat. No. 4,290,492, so as to impact on the rear end of the tool. Meanwhile the resulting recoil blows press the tubular piston 24 backwards and thereby intensify the pressure of the roller 25 on the drive fin 40&#39; and thus also the engagement of the drive element 40 and the coupling element 37. 
     As soon as the tool 1 is no longer pressed against the work-piece, the spring 39 effects a separation of the coupling element 37 from the drive element 40 and thereby a stopping of the impact drive, so that the tubular piston 24 is no longer reciprocally displaced and hence the beat piece 22 no longer applies impacts to the rear end of the tool 1. In this connecton it may be mentioned that in consequence of the absence of driving of the impact mechanism in this idling state of operation, no special interception device is required for the beat piece 22. 
     In order to activate or de-activate the impact mechanism at choice there is provided a U-shaped rigid setting element 47 whose limbs pass to either side of the rear end 36 of the tubular piston 24 and are led in recesses in the holder member 29 (FIG. 2). The base of this U-shaped setting element 47 rests against a rounded-off zone 30&#39; (FIG. 1) of the peripheral surface of a setting pin 30 which is supported in the gear housing 50 so as to be rotatable to a limited extend and which extends transversely to the longitudinal axis of the tubular piston. The setting pin 30 has one end projecting from the gear housing 50 and carries at this end a hand lever 46 which is firmly connected by its head 46&#39; with the projecting end of the setting pin 30. 
     As illustrated in FIG. 1, the base of the setting element 47 is embraced by one limb of a spring 28 whose other limb rests against the opposite-lying side of the setting pin 30 and which pulls the base of the setting element 47 towards the setting pin 30. In this way the base of the setting element 47 is always held in engagement with the actual rounded off zone at the periphery of the setting pin 30. 
     At the periphery of the setting pin 30 there are provided two rounded-off zones 30&#39; and 30&#34;, with the rounded-off zone 30&#39; being at a shorter distance from the mid-axis of the setting pin 30 than the rounded-off zone 30&#34;. Hence when the base of the setting element is rested against the rounded-off zone 30&#39; the free ends of the limbs of the setting element 47 are located further to the right in FIG. 1, i.e. further to the rear in gear housing 50, than when the base of the setting element 47 rests against the rounded-off zone 30&#34;. The operational case illustrated in FIG. 1, of the base of the setting element 47 resting against the rounded-off zone 30&#39;, is that in which the impact mechanism is activated, i.e. the impact mechanism is switched on by pressure of the tool 1 on the work-piece. 
     When the hand lever 46 is twisted by 90° (clockwise in FIG. 1), the base of the setting element 47 comes into engagement with the rounded off zone 30&#34;, and in consequence of the greater distance of the rounded-off zone 30&#34; from the mid-axis of the setting pin 30 it becomes displaced towards the left in FIG. 1, i.e. towards the front in the gear housing. This displacement has the result that the free ends of the limbs of the setting element 47 come into engagement with the separating disk 21 and displace it to a frontal end setting, whereby the tool spindle 2 is also brought into this frontal end setting and is held therein. In this frontal end setting the coupling element 37 and the drive element 40 are not in engagement with one another. If now the tool 1 is pressed against a work-piece, then the engagement of the free ends of the limbs of the setting element 47 (resting against the rounded-off zone 30&#34;) with the separating disk 21 prevents displacement of the tool spindle 2 to the rear and hence engagement of drive element 40 and coupling element 37, i.e. the rotary hammer is operating with a pure drilling action and the impact mechanism is de-activated. 
     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.