Technical Field

The invention relates to a hydraulic hammer with two handles connected to the outer side of a cylinder being continuously passed by a hydraulic liquid when the ham¬ mer is in use, and being provided with a piston which is displaced upwards and downwards by means of the hy¬ draulic liquid when the hammer is activated, said piston during its upward and downward displacement driving a tool such as a chisel projecting from the cylinder.

Background Art

It is known to activate a hydraulic hammer by a mecha¬ nically operating connection between one of the hammer' s handles and a remote-controlled valve located within the cylinder. This remote-controlled valve interrupts the direct flow of hydraulic liquid from the inlet duct of the cylinder to the outlet duct of the cylinder in such a manner that the hydraulic liquid drives the pis¬ ton. Attempts to vibration dampen the handles relative to the cylinder are rendered difficult by the presence of said mechanical activating connection between the handle and the remote-controlled valve, for which reasons said attempts have been given up previously in connection with hydraulic hammers.

Disclosure of Invention

The object of the invention is therefore to provide a hammer which may be activated without employing mecha¬ nical connections, so that a possibility of vibration dampening the handles relative to the cylinder is pro- vided.

The hydraulic hammer according to the invention is char¬ acterised in that the hammer comprises a manually oper¬ able activating valve located on one of the handles, the inlet of said valve communicating with a space present in the cylinder and partly defined by a movable slider and partly by portions of the cylinder, the outlet of said valve communicating with the outlet duct for the liquid in the cylinder, that the space partly defined by the slider communicates with the inlet duct of the li- quid in the cylinder through a throttle opening, that the slider is shaped in such a manner that the liquid force downwardly influencing the slider -towards an in¬ creasing size of the space is greater than the oppo¬ sitely directed force when the connection between the inlet and the outlet of the activating valve is interrupted, and lower when said connection is open, and that the slider when the space is greatest, is adapted to close the direct communication between the inlet -duct and the outlet- duct of the liquid. In this manner a hammer is obtained which in a simple manner permits a hydraulic activation only by opening the activating valve, where¬ by the liquid present in the space may flow through the activating valve and back to the hammer and then through the outlet duct. As a result, the pressure in the space decreases and becomes substantially lower than the pres¬ sure in the liquid present outside said space, i.e. in the liquid flowing into the cylinder. This pressure dif¬ ference and the dimensioning of the various surfaces of the slider implies that the pressure in the liquid flow- ing into the 'cylinder presses the slider in a direction towards a reduced space size and thereby opens the di¬ rect connection between the inlet duct and the outlet duct of the liquid, whereby the movement of the piston is stopped. By closing the activating valve, the liquid

flowing into the cylinder now flows through the throttle opening in the slider and into the space, wherein it is prevented from flowing further, for which reason the pressure in the space is increased. Therefore and as a result of the above dimensions, the slider is displaced in such a manner by the liquid that the size of the space is increased and the direct connection between the inlet duct and the outlet duct is finally interrupted, whereby the liquid is made influencing the piston. In order to activate the hammer, the user thus only need to influence the activating valve in such a manner that the connection between its inlet and outlet is interrupted.

According to the invention it is preferred that the slider is a sleeve-shaped cylindrical body coaxially lo- cated relative to the cylinder and adapted to be dis¬ placed in the axial direction of the cylinder axis, and that the throttle opening is shaped in the cylindrical wall of the slider.

Furthermore according to the invention the space may ex- tend about the outer side of the slider, and the slider may comprise a flange projecting radially outwards and co-operating with the cylinder wall on one side of an outlet opening, through which the space communicates with the inlet of the activating valve, whereas a first, usually upper end of the slider co-operates with an axi- ally extending surface on a portion projecting inwards of the cylinder over the outlet opening in the space, and a second opposite end is adapted to slidingly engage an axially extending surface on a projection projecting inwards of the cylinder when the size of the space is greater than a predetermined size, whereby the di¬ rect flow of liquid to the outlet duct is interrupted. As a result a particularly simple embodiment of the sli¬ der is obtained which reacts particularly quickly to the

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closing of the activating valve by the user. This is due to the fact that some of the surface(s) co-operating in making the slider being displaced in a direction towards a smaller space size, are present on the flange of the slider. As the opposite end of the slider approaches the projection on the cylinder which projects inwards and co-operates with said slider, these surfaces are prevent ed from being influenced by the relatively high pressure in the liquid flowing in.

Moreover according to the invention the slider may be a solid, plug-shaped body, and the throttle opening may be shaped in the cylinder wall, whereby a second advanta¬ geous embodiment of the invention is provided.

This plug-shaped body may according to the invention be adapted to close an opening when the space has reached its maximum size, said opening forming a direct connec¬ tion between the inlet duct and the outlet duct of the liquid in the cylinder. As a result a particularly simpl hammer is obtained.

Furthermore according to the invention, the connection between the activating valve and the cylinder may be provided by means of resilient conduits, whereby the hammer is particularly suited for being provided with dampening handles.

According to a particularly preferred embodiment of the invention the activating valve may comprise a slider bar acting as valve body and being displaceably mounted in the valve chamber, one end of said slider bar projecting out of the valve chamber of the activating valve and abutting a manually and downwardly pressable pawl, through which the slider bar is made interrupting the connection between the inlet and the outlet of the valve

when the hammer is desired to be activated.

Moreover according to the invention, the inlet opening of the activating valve may extend into the valve cham¬ ber at a place directly filled out by the slider bar when the hammer is desired to be activated, whereas its outlet opening is always located under the action field of the slider bar. In this manner the activating valve is automatically opened when the user stops influencing the slider bar. This is due to the fact that the end of the slider bar is always subjected to a certain liquid pressure.

According to the invention it is particularly preferred that the handles with the activating valve are secured on a cylindric housing displaceably located about the upper end of the hammer cylinder, and that one or more dampening springs are provided between the cylindric housing and the upper end of the hammer cylinder. As a result, a relatively slender hammer provided with hand¬ les and with a nice appearance is obtained.

Finally according to the invention, the cylindric housing may surround a dampening spring located substantially coaxially relative to the cylinder and apdated so as to surround an accumulator connected to said cylinder.

Brief Description of Drawing

The invention will be described below with reference to the accompanying drawing, in which

Fig. 1 is a sectional view through the upper portion of a hammer according to the invention,

Fig. 2 is a diagrammatic, sectional view through the up-

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per portion of the cylinder in a hammer according to the invention, as well as a sectional view through the acti¬ vating valve of the hammer,

Fig. 3 is a diagrammatic, sectional view through the up- per end of the cylinder and the activating valve in a second embodiment of the invention, and

Fig. 4 is a sectional view perpendicular to the section¬ al view of Fig. 1 through part of a hammer according to the invention.

Best Mode for Carrying Out the Invention.

The portion of the hammer illustrated in Fig. 1 comprises a double-acting cylinder provided with a cylinder wall 2. The cylinder wall 2 surrounds a cylinder chamber 3, in which a piston 4 comprising a piston rod 5 is located. In the common use position of the hammer, this piston rod 5 extends downwards and out through the bottom wall (-not shown) of the cylinder. The lower outer end of the piston rod is in the illustrated embodiment provided with a ham¬ mer head and in a manner known per se, but not shown, adapted to abut a chisel or another appropriate tool du¬ ring the upward and downward movement of the piston when the hammer is activated. The lower end of the piston rod and the piston head and the upper end of the chisel may be surrounded by a tubular portion, which at the bottom end is adapted to receive the upper end of the chisel in such a manner that said chisel may be dis¬ placed forwards and backwards without falling out du¬ ring the activation of the hammer.

The cylinder chamber 3 comprises a lower cylinder chamber 10 located below the piston 4 , and an upper cylinder chamber 7 located above the piston . Through an inlet duct 8

shaped in the upper portion of the cylinder wall, the upper cylinder chamber 7 communicates with an inlet gate 9 formed by a pipe stub 10 secured on the cylinder wall for connecting a hose supplying hydraulic pressurized liquid. The lower portion of the cylinder wall is pro¬ vided with two mutually connected outlet ducts, viz. a longitudinal outlet duct 11 and a transverse outlet duct 12. The transverse outlet duct communicates with an outlet gate 13 formed by a pipe stub 14 secured on the cylinder wall for connecting a hose draining off the hydraulic liquid to a reservoir or a reception tank. The longitu¬ dinal outlet duct 11 communicates with the transverse outlet duct within the cylinder wall 2. -At the bottom, the lower cylinder chamber 6 comprises an opening 15, through which the lower cylinder chamber 6 communicates permanently with a longitudinal connection duct 16. The upper end of this connection duct 16 is by means of a control means 17, cf. the detailed description below, alternately connected to the upper cylinder chamber for supply of hydraulic liquid to the lower cylinder cham¬ ber and to the longitudinal outlet duct 11 for draining off hydraulic liquid from the lower cylinder chamber.

The control means 17 comprises a change-over bar 18 co- axially arranged with the piston rod. This change-over bar 18 is displaceably located in a sleeve-shaped change-over slider 19 and in a circumferential project¬ ion 20 projecting radially inwards on the inner wall of the cylinder. The cylinder bar which is integrally shaped with or secured on the piston 4 comprises a first inner duct 21 forming a connection between an opening 22 at the end of the change-over bar and one or more openings 23 in the side of the change-over bar. In addition, the change-over bar comprises a second duct 24 forming a connection between an upper, indicated by dotted lines, and a lower set of openings 25 and 26, respectively, in

the side of the change-over bar. These two sets of open¬ ings are mutually spaced in axial direction on the change-over bar 18 from the first duct 21 and the piston 4, respectively. Their precise location appears from the following.

The sleeve-shaped change-over slider 19 comprises an up¬ per and a lower flange 27, 28 projecting radially out¬ wards. The upper flange is adapted to co-operate with a circumferential projection 29 on the cylinder wall pro- jecting radially inwards relative to the change-over slider in such a manner that the slider sealingly abuts this projection when the slider is in its bottom posi¬ tion, whereas it clears this projection when it is in its top position. The lower flange 28 of the change-over slider 19 is adapted to abut the top side of the lower projection 20 projecting inwards when it is in its bot¬ tom position and to abut an intermediate circumferential projection 30 on the cylinder wall projecting inwards when the change-over slider is in its top position. The intermediate projection 30 on the inner wall of the cy¬ linder and the projection 29 located uppermost relative to the slider 19 defines a circumfe ential recess 31. At the bottom of this recess 31, an opening 32 is shaped, through which the recess 31 communicates with the upper end of the above longitudinal connection duct 16 forming the connection to the lower cylinder chamber 6. Between the intermediate projection 30 and the lower projection 20, a further recess 33 is shaped immediately under the intermediate projection. At the bottom of this recess 33, an opening 34 is provided, through which the recess 33 communicates with the longitudinal outlet duct 11. The axial extension of the recess 33 and the lower flange 28 of the change-over slider is so that the lower flange 28 of the slider completely covers the recess 33 when the change-over slider is in its top po-

sition, in which it abuts the intermediate projection 30, whereas when the change-over slider 19 is in its bottom position, the lower flange 28 is completely re¬ moved from the recess 33. The intermediate projection 30 furthermore comprises such a radial extension that free passage for a liquid flow is permitted between the change-over slider and this projection from the recess 31 with the opening into the vertical connection duct 16 and the recess 33 with the opening into the longitu- dinal outlet duct 11 when the change-over slider 19 is in its bottom position. Therefore, in the bottom posi¬ tion of the change-over slider, a connection is provided between the vertical connection duct 16 and the longi¬ tudinal outlet duct 11 and consequently between the lower cylinder chamber 6 and the outlet gate 13. Hereby, the hydraulic liquid may flow from the lower cylinder chamber 6 when the piston 4 is moved downwards and the change-over slider 19 is maintained in its bottom posi¬ tion.

When the change-over slider is in its top position, the lower flange 28 thereof abuts the intermediate projection 30, whereby the connection between the vertical connec¬ tion duct 16 and the outlet duct 11 is interrupted. How¬ ever, in this position the upper flange 27 of the change- over slider 19 clears the sealing connection with the upper projection 29 on the cylinder wall, whereby the portion of the cylinder chamber located above the change¬ over slider 19 and the change-over bar 18 is connected to the longitudinal connection duct 16. As a result, the hydraulic liquid may flow from the upper cylinder cham¬ ber to the lower cylinder chamber.

The slider 19 furthermore comprises a circumferential . inner recess 35, cf. the dotted lines, at the end clo¬ sest to the piston 4. The radial extension of this re-

cess 35 as well as the axial extension of both the first duct 21 and the second duct 24 in the change-over bar 18 are so that the openings 23 of the first duct 21 in the side of the change-over bar open on to the inner recess 35 in the change-over slider 19 when the piston and the change-over bar connected thereto are in their bottom position. When the piston 4 and the change-over bar are adjacent their top position, the upper set of openings 25 to the second duct 24 open on to the recess, 35 in the change-over slider 19 at the same time as the lower set of openings 26 to the second duct open on below the lower projection 20 on the cylinder wall. Therefore, when the piston 4 is in its top position, the. top side of the pistion 4 and the opposite bottom side of the projection 20- projecting inwards are spaced a predetermined distance the lower set of openings 26 in the second duct 24 in the change-over bar opening on to the space between these opposing sides. Through an opening 36 in the cylinder wall this space communicates permanently with the trans- verse outlet duct 12 in the cylinder wall.

A remote-controlled valve 37 is situated at the top end of the upper cylinder chamber above the opening of the inlet duct 8. This remote-controlled valve comprises a slider 38 in the form of a substantially sleeve-shaped, cylindrical body displaceably located within the cylin¬ der. This body comprises a flange 39 projecting radially outwards into a circumferential recess 40 in the inner wall of the cylinder. This flange 39 is adapted to seal- ingly slide along the axial bottom surface of the above inner wall of the cylinder within said circumferential recess. At the upper and lower end of the circumferen¬ tial recess 40, an upper and a lower groove 41 and 42, respectively, are shaped.

As illustrated in the drawing, the upper, first end 43

of the cylindric slider 38 is adapted to co-operate with the cylinder wall 2 in such a manner that it sealingly abuts said cylinder wall in any position during its slid¬ ing movement. The lower, second end of the slider 38 is adapted to co-operate with the cylinder wall below the lower groove 42. The slider 38 and this co-operating part of the cylinder wall are dimensioned in such a manner that the second lower end 44 of the slider sealingly slides against the cylinder wall within the lower por- tion of its movement path. The movement path is defined downwardly by the abutment of the flange 39 against the cylinder wall at the lower end of the groove 42. Thus a circumferential space 45 is defined between the slider and the cylinder wall above the flange 39 projecting ra- dially outwards. The size of the space 45 varies during the movement of the slider in such a manner that it reaches its maximum when the flange 39 abuts the cylin¬ der wall in the bottom position of the slider, cf. the drawing. As indicated by dotted lines, an outlet duct 46 is shaped andextends from the lower groove 42. This out¬ let duct 46 communicates in an apppropriate manner with the longitudinal outlet duct 11 within the cylinder wall 2. Furthermore, as indicated by dotted lines, both the upper groove 41 and the lower groove 42 communicate with an activating valve 47 through a conduit 48 and 49, re¬ spectively. These conduits 48 and 49 extend in an appro¬ priate manner through the cylinder wall 2. The activat¬ ing valve 47 is secured on one of the hammer's handles 50, e.g. by bolts 51, only one bolt appearing from the drawing.

In the illustrated embodiment the activating valve com¬ prises a valve chamber 52, in which a slider bar 53 is displaceably located. This slider bar 53 extends upwards through an opening 54 in the handle 50 and abuts a ma- nually, downwardly pressable activating pawl 55. By means

of this activating pawl 55, the slider bar is made mov¬ ing downwards into a lower position when the user pres¬ ses the pawl downwards towards the handle. In Fig. 1, in which the slider bar is illustrated in its top posi- tion, the conduit 48 communicating with the upper groove 41 at the remote-controlled valve 37, opens under the lower end of the slider bar on to the valve chamber 56, in which the slider bar 53 is displaceably located. The opening of the conduit 48, below referred to as the in- let opening 57 of the activating valve, is located so that the slider bar closes said inlet opening when it by the pawl is pressed downwards into its bottom posi¬ tion. Furthermore as indicated in the drawing, the con¬ nection between the valve chamber 56 and the conduit 49 connected to the lower groove 42 at the remote-controlle valve 37, is located at the lower end of the valve cham¬ ber below the inlet opening 57.. The opening correspond¬ ing to this connection, below referred to as the outlet opening 58 of the activating valve, is located under the lower end of the slider bar in any of the positions of the bar.

Furthermore, a throttle opening 59 is shaped between the inner side of the sleeve-shaped slider 38 and the side facing the space 45, cf. Figs. 1 and 2.

In order to ensure a correct function of the remote-con¬ trolled valve, the slider is shaped and dimensioned so that the force influencing the slider in a downward di¬ rection towards an increasing size of the space 45, is higher than the ^" oppositely directed force when the con- nection between the inlet opening 57 and the outlet opening 58 of the activating valve is interrupted, but lower when said connection is open.

Fig. 2 illustrates more diagrammatically the above sli-

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der and activating valve for the sake of clarity. When the activating valve is open, i.e. a liquid connection is provided between the inlet opening 57 and the outlet opening 58 of said valve, liquid is allowed to flow from the space 45 through the activating valve and back to the lower groove 42 and further through the outlet duct 46 to the outlet duct 12. When the hydraulic liquid under a predetermined pressure flows into the upper cy¬ linder chamber 7 through the inlet duct 8, and when the slider is in the position illustrated in Fig. 1, the li¬ quid flows through the throttle opening 59. As a conse¬ quence of the throttling and the open connection between the conduits 48 and 49 through the activating valve, the pressure within the space is substantially lower than the pressure within the upper cylinder chamber. Further¬ more, since the area of the surface 60 turning downwards at the lower end of the slider is a short distance greater than the area of the surface 61 turning upwards at the upper end of the slider, the force influencing the slider in a downward direction is lower than the force influenc¬ ing the slider in an upward direction, the first-men¬ tioned force influencing the slider in a downward direc¬ tion being a consequence of both the relatively high li¬ quid pressure present within the cylinder chamber, said liquid pressure influencing the surface 61, and the rela¬ tively low liquid pressure influencing the surface 62 turning in the opposite direction as to the surface 61 on the flange of the slider within the cylinder chamber. The other force influences the slider in an upward direc- tion as a consquence of pressure acting on the surface 60 assisted by optionally located, inclined transition surfaces 63. Due to the above, the slider moves upwards relative to Fig. 1 and provides an open, direct connec¬ tion between the upper cylinder chamber 7 and the lower groove 42 and consequently the outlet duct 12. Therefore the movement of the hammer is interrupted when the slider

is in this position, said position almost corresponding to the position illustrated in Fig. 2.

When activating the hammer by manually pressing the pawl 55 towards the handle 50, the slider bar 53 interrupts the connection between the inlet opening 57 and the out¬ let opening 58 of the activating valve. As a consequence thereof, the liquid flowing through the throttle opening 59 implies that the pressure rises within the space 45 and in the conduit 48. The pressure within the space 45 gradually becomes sufficiently high so as to make the force deriving from the pressure against the upward sur¬ face 62 of the flange and the upward surface 61 at the end of the slider, sufficiently high for overcoming the force directed upwards and deriving from the pressure influencing the downwardly turning surface 60 and the optionally provided inclined ^surfaces 63 as well as the downwardly turning side 64 on the flange. Since the surface 64 on the flange 39 turning downwards is located immediately adjacent the outlet duct 46, this surface 63 is subjected to a pressure a little lower than the pres¬ sure within the upper chamber 7 of the cylinder. Thus when the force directed downwards has grown greater than the force directed upwards, the slider is displaced downwards towards its bottom position. As the lower end approaches the mesh with the cylinder wall, i.e. the surface 60 levels with the lower end of the recess 40, into which the flange 39 of the slider projects, the pressure influencing the downward surface 64 of the flange, gradually decreases. Therefore, the velocity of the slider gradually increases during its downward move¬ ment. When the lower end of the slider 38 engages the cylinder wall, the direct connection between the cylin¬ der chamber 7 and the outlet duct 12 is interrupted by the slider, for which reason the hydraulic pressurized liquid subsequently is available for the driving of the

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piston of the hammer, cf. the explanation below.

Fig. 3 illustrates a second embodiment of a remote-con¬ trolled valve 65. This remote-controlled valve 65 com¬ prises a plug-shaped solid slider 66, which at its upper end comprises a flange 67 projecting radially outwards. The slider 66 is displaceably located in a separately shaped cylinder chamber 68, from which its main portion 69 projects through an opening 70. The main portion 69 of the slider 66 is shaped in such a manner that the lower end may sealingly pass through an opening 71 form¬ ing a connection between the upper cylinder chamber 7 of the hammer and a duct extending to the outlet duct 12 when the slider 66 is in its bottom position within ^' the separate cylinder chamber 68. A space 72 is defined by the upper end of the slider 66 and the surrounding cy¬ linder wall, said space communicating with the inlet duct 8 of the hammer through a throttle opening 73 shaped in the cylinder wall of the hammer . Furthermore, the space 72 is connected to the inlet opening 56 of an acti- vating valve through the conduit 48-, said activating valve corresponding to the above described valve, the outlet opening 58 of the activating ^' valve being connect¬ ed to the outlet duct 52 of the hammer through the con¬ duit 49.

The plug-shaped slider 66 is dimensioned in such a man¬ ner, cf. Figs. 1 and 2, that the force influencing the slider in a downward direction towards an increasing space size, is greater than the oppositely directed force when the connection between the inlet opening 56 and the outlet opening 58 of the activating valve is interrupted, but lower when said connection is open. When the connec¬ tion between the inlet opening 56 and the outlet open¬ ing 58 of said activating valve is open, hydraulic li¬ quid flows through the throttle opening 73. into the space

72 and further through the activating valve to the out¬ let duct 21 of the hammer. The pressure within the space 72 is as a consequence of the throttling lower than the pressure within the inlet duct 8 and the cylinder cham- ber 7, for which reason the slider moves upwards on account of the high pressure influencing its lower end. When the plug-shaped slider reaches its top position, a direct connection is provided between the upper cylinder chamber 7 and the outlet duct 12, for which reason the hammer is inactivated in this position. When the activa¬ ting valve is activated and the connection between its inlet opening 57 and outlet opening 58 is interrupted, a pressure is produced within the space 72 which finally is sufficiently high to overcome the oppositely directed pressure. The slider is subsequently displaced downwards for closing the passage through the opening 71. When this opening 71 is closed, the liquid pressure within the cylinder chamber 7 is available for driving the piston 4 of the hammer, as mentioned above.

The outlet opening 58 of the activating valve 47 is as previously mentioned located in such a manner that it is always located below the lower end of the slider bar 53, the bottom position of which being indicated by a dotted line between the inlet opening 57 and the outlet opening 58 in Figs. 2 and 3. Therefore the lower end of the slider bar is always subjected to the pressure in the conduit 49, i.e. the pressure in the outlet ducts of the hammer, for which reason the slider bar 53 is automatically displaced upwards into the open position when the user ceases pressing down the pawl towards the handle. Thereby the slider 66 also moves automatically backwards into its top position, in which the direct connection between the upper cylinder chamber 7 and the outlet duct 12 is present, the hammer thereby also being automatically stopped when the user no longer presses

the pawl 55 downwards.

On the outer side of the cylinder wall two accumulators are secured. The first accumulator 74 communicates with the upper cylinder chamber 7 through a duct 75, whereas the second (not shown for the sake of clarity) accumula¬ tor communicates with the outlet ducts of the hammer. These accumulators may be of any desired type. The func¬ tion of the accumulators is to support the hydraulic li¬ quid during the driving of the piston of the hammer.

The hammer operates in the following manner:

When the hammer is inactivated, the remote-controlled valve 37 is in its top position, in which the opening to the longitudinal duct 11 of the hammer communicates with the upper cylinder .chamber 7. When the inlet gate 9 and the outlet gate 14 of the hammer are connected to the supply hose and the draining off hose, respectively, for hydraulic liquid, and hydraulic liquid is supplied under pressure to the hammer, the liquid flows continuously through the inlet duct 8 and into the upper cylinder - chamber 7. From this cylinder chamber 7 the liquid flows directly upwards under the slider 38 and out through the duct 46 to the outlet duct 12 and out of the hammer through the return hose carrying the liquid to a recep¬ tion tank or a reservoir. In this position the accumula- tors are almost in an uncharged state.

When the hammer is activated by manually pressing down the pawl 55, the slider bar 53 of the activating valve 47 is pressed axially downwards from the top of the ac¬ tivating valve, whereby the inlet opening 57 of said ac- tivating valve and consequently its connection with the remote-controlled valve 37 is interrupted. As a result, the slider is pressed downwards into its bottom posi-

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tion, whereby the connection between the upper cylinder chamber 7 and the direct duct 46 to the outlet duct 12 is interrupted. Initially the pressure within the upper cylinder chamber 7 is increased at the same time as the accumulator 74 is charged. The rise in pressure within the upper cylinder chamber 7 implies that the piston 4 is immediately pressed downwards, since the upper end of the change-over bar 18 is influenced by the pressure within the upper cylinder chamber 7, said upper end act- ing as the upper piston area of the piston. During this movement, the change-over slider 19 is located in its bottom position, cf. Fig. 1. In this position, a connec¬ tion is provided between the lower cylinder chamber 6 and the longitudinal outlet duct 11, whereby the ^• ydrau- lie liquid present in the lower cylinder chamber 6 is pressed out of the hammer during the downward movement of the piston. Since the space 76 between the lower projection 20 on the inner wall of the cylinder and the top side of the piston 4 during the outflow of liquid is expanded, the outlet ducts are subjected to suction. This suction would imply heavy pulsations within the drain hose if the accumulator (not shown) was not pre¬ sent. These pulsations are, however, avoided since the accumulator supplies the outlet duct with hydraulic liquid. The supply of hydraulic liquid to the hammer continues, of course, constantly during any position of the remote-controlled valve, and for this reason the upper cylinder chamber is continuously provided with hydraulic liquid. Immediately after the charging of the accumulator 74, cf. the drawing, this accumulator also supplies hydraulic liquid, during the downward movement of the piston. Adjacent the predetermined bot¬ tom position of the piston 4, the opening 23 of the first duct 21 of the change-over bar 18 reaches the area adjacent the circumferential inner recess 35 in the change-over slider 19, whereby the liquid flows

down into the space defined by the recess 35, the change-over bar 18 and the lower projection 20 on the cylinder wall. As a result the change-over slider 19 starts to slide upwards, thus permitting passage of the hydraulic liquid betwen the underside of the lower flange 28 of the change-over slider 19 and the top side of the lower projection 20 on the cylinder projecting inwards, which results in a faster upward displacement of the slider.

Adjacent the lower position of the piston, the hammer head impacts on the chisel not shown and releases its energy thereto. Hereby the downward movement of the piston is stopped. At this moment the accumulator (not shown) has supplied all the liquid stored therein and is now completely uncharged, whereas the accumulator 74 is in a state between completely uncharged and com¬ pletely charged.

Since the liquid is supplied under pressure to the un¬ derside of the change-over slider 19 through the first duct 21, the change-over slider 19 impacts on the in¬ termediate projection 30 on the inner wall of the cy¬ linder projecting inwards and is subsequently stopped in its top position. As previously mentioned, the connection between the lower cylinder chamber 6 and the outlet duct 11 through the slider 19 ^' is interrupted in this top position of the slider. In stead, the con¬ nection between the lower cylinder chamber 6 and the upper cylinder chamber 7 is opened, whereby hydraulic ^■ liquid flows under pressure from the upper cylinder chamber 7 down to the lower cylinder chamber 6. This implies in turn, that the piston 4 and consequently the change-over bar 18 are displaced upwards towards the top of the cylinder. The individual parts are dimen¬ sioned in such a manner that the connection between

the upper and the lower cylinder chamber is provided almost at the same time as the piston reaches a bottom position spaced a predetermined distance from the bot¬ tom of the cylinder. In this manner the hydraulic liquid present under the piston is able to alleviate the down¬ ward movement of the piston if the hammer for some rea¬ son should not have been provided with a chisel.

Hydraulic liquid flows, of course, constantly into the upper cylinder chamber 7 from the supply source through the supply hose. The accumulator (not shown) is in this position still uncharged whereas the accumulator 74 com¬ municating with the upper cylinder chamber is being charged.

On a place between the bottom and the top position of the piston and during its return strokes, the connection between the upper cylinder chamber 7 and the underside of the change-over slider 19 is interrupted, whereby hy¬ draulic liquid is confined in the space defined by the change-over slider 19, the change-over bar 18, and the inner wall of the cylinder between the lower flange 28 of the slider 19 and the lower projection 20 on the cy¬ linder wall. Therefore, the slider is still maintained in its top position so that hydraulic liquid is able to flow continuously from the upper cylinder chamber 7 down into the lower cylinder chamber 6. During the return strokes of the piston 4, liquid is also pressed out of the space 76 between the top side of the piston 4 and the lower projection 20 on the inner wall of the cylin¬ der. In this manner liquid is partly drained off through the return hose and partly pressed into the accumulator (not shown) . The accumulator 74 is also being charged by the liquid supplied.

The change-over slider 19 is maintained in its top posi-

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tion until the piston 4 and consequently the change-over bar 18 reach the vicinity of their top positions . Then the second duct 24 in the change-over bar 18 provides a connection to the liquid confined under the slider 19 so that this liquid may flow into the space 76 between the top side of the piston 4 and the underside of the lower projection 20 on the inner wall of the cylinder, and therefore out through the transverse outlet- duct 12. ■ This implies that the change-over slider 19 is no longer locked in its top position by the confined liquid, but starts to move downwards as a consequence of the influ¬ ence of the pressure present in the upper cylinder cham¬ ber 7 and presses the confined liquid out through the second duct 24 in the change-over bar 18.

As soon as the slider 19 reaches its bottom position, the connection between the upper cylinder chamber 7 and the lower cylinder chamber 6 is interrupted, for which reason the upward movement of the piston 4 is stopped _. in a state corresponding substantially to the situation illustrated in Fig. 1. Both acculumators have now been charged and are ready for entering into function. As long as the remote-controlled valve 37 is maintained in its bottom position, this cycle of operation is con¬ tinuously repeated. The desired movements of the mov- able parts are ensured by an appropriate dimensioning of the surfaces of said movable parts , such as the change-over bar 18, the piston 4, and the slider 19, to be influenced by the hydraulic liquid.

When the user wants to interrupt the upward and down- ward movement of the hammer, he releases the pawl 55, whereby the pressure within the inner cylinder chamber 7 automatically presses the slider 38 of the remote- controlled valve 37 upwards as a consequence of the difference in pressure between the upper cylinder cham-

ber 7 and the space 45 defined by the slider 38. In this manner the direct connection between the upper cylinder chamber 7 and the outer duct 46 is established, and the movements of the hammer are stopped.

The handle of the hammer is secured on a cylindrical housing 77, cf. Fig. 1. This housing coaxially surrounds the upper end of the cylinder and is displaceably locat¬ ed about the upper end of the cylinder. An appropriate spring 78 is located between the upper end of the cylin- der and the upper, inner end of the cylindrical housing 77, said spring also extending coaxially with the cylin¬ der and surrounding the accumulator 74 located at the upper end of the cylinder. The cylindrical housing 77 is, cf. Fig. 4, adapted to move in axial direction relative to the cylinder within a predetermined range determined by means of appropriate control and stopping means. In the illustrated embodiment, these control and stopping means are formed by a bar 79 secured to the cylindrical housing and extending parallel to the axis of the hous- ing. This bar 79 is furthermore displaceably received in a projecting portion 81 on the cylinder wall provided with an appropriate opening. The lower end of the bar 79 is as illustrated provided with a thread 82 receiving a nut 83, by means of which the displaceability of the cylindrical housing 77 may be adjusted. If desired, the hammer may be provided with several such control and stopping means . Through the adjustability of these con¬ trol and stopping means, the user may provide an appro¬ priate pre-tightening of the spring 78 between the upper end of the cylinder 1 and the cylindrical housing 77. During the use of the hammer, the spring provides an appropriate vibration dampening of the handles rela¬ tive to the cylinder, whereby the use of the hammer is considerably more pleasant than when the handles are directly secured on the cylinder of the hammer.

When it is a question of vibration dampened handles, the connections between the inlet opening 57 and the outlet opening 58 of the activating valve on one hand and the cylinder on the other hand are appropriately provided by means of resilient hoses forming said conduits 48 and 49, respectivel .

The invention may be varied in many ways without thereby deviating from the scope thereof. Many other known types of activating valves may for instance be used, as well as several springs may be used for providing the vibra¬ tion dampening in stead of the single spring shown.