Hydraulic percussive implement

Claim 2

A hydraulically-operated percussive implement which includes: a. a casing, b. first and second Chambers within the casing, c. a striker piston reciprocable within the casing, d. means for introducing pressurised fluid into said chambers and for controlling the fluid pressures in said chambers, e. said striker piston having a relatively large first effective piston area which partly bounds the first chamber and is acted upon when pressurized fluid is introduced into the first chamber to cause the striker piston to execute a working stroke, f. said striker piston also having a relatively small second effective piston area which partly bounds the second chamber is acted upon by pressurized fluid introduced into the second chamber, and when the fluid pressure in the first chamber is reduced, to cause the striker piston to execute a return stroke, g. said second chamber having a wall at the end thereof remote from the first chamber which is formed with a sealed aperture through which an end portion of the striker piston projects, h. the casing including tool holding means for locating a tool so as to be struck by the end of the striker piston towards the end of the working stroke thereof, i. a collar on that portion of the striker piston which passes through the second chamber, said collar having opposing effective surface areas which are normally both exposed to the pressure in the second chamber and being of such dimensions as to permit of passage of fluid in the second chamber around the collar during normal reciprocatory movement of the striker piston, j. an overshoot dashpot cavity situated at the end of the second chamber remote from the first chamber and positioned so that, in the event that the length of the working stroke should exceed a normal length as a result of removal of external resistance to advance of the tool, the collar will enter the cavity to trap fluid therein, k. the effective area of the collar presented to the dashpot cavity being substantially in excess of the second effective piston area of the striker piston, and l. restrictor means provided as the sole path for escape of fluid trapped in the cavity on entry thereinto of the collar.

Claim 3

A hydraulically-operated percussive implement which includes: a. a casing, b. first and second Chambers within the casing, c. a striker piston reciprocable within the casing, d. means for introducing pressurised fluid into said chambers and for controlling the fluid pressures in said chambers, e. said striker piston having a relatively large first effective piston area which partly bounds the first chamber and is acted upon when pressurized fluid is introduced into the first chamber to cause the striker piston to execute a working stroke, f. said striker piston also having a relatively small second effective piston area which partly bounds the second chamber is acted upon by pressurized fluid introduced into the second chamber, and when the fluid pressure in the first chamber is reduced, to cause the striker piston to execute a return stroke, g. said second chamber having a wall at the end thereof remote from the first chamber which is formed with a sealed aperture through which an end portion of the striker piston projects, h. the casing including tool holding means for locating a tool so as to be struck by the end of the striker piston towards the end of the working stroke thereof, i. a collar on that portion of the striker piston which passes through the second chamber, said collar having opposing effective surface areas which are normally both exposed to the pressure in the second chamber and being of such dimensions as to permit of passage of fluid in the second chamber around the collar during normal reciprocatory movement of the striker piston, j. an overshoot dashpot cavity situated at the end of the second chamber remote from the first chamber and positioned so that, in the event that the length of the working stroke should exceed a normal length as a result of removal of external resistance to advance of the tool, the collar will enter the cavity to trap fluid therein, k. the effective area of the collar presented to the dashpot cavity being substantially in excess of the second effective piston area of the striker piston, and l. restrictor means provided as the sole path for escape of fluid trapped in the cavity on entry thereinto of the collar.

Claim 4

A hydraulically-operated percussive implement which includes: a. a casing, b. first and second Chambers within the casing, c. a striker piston reciprocable within the casing, d. means for introducing pressurised fluid into said chambers and for controlling the fluid pressures in said chambers, e. said striker piston having a relatively large first effective piston area which partly bounds the first chamber and is acted upon when pressurized fluid is introduced into the first chamber to cause the striker piston to execute a working stroke, f. said striker piston also having a relatively small second effective piston area which partly bounds the second chamber is acted upon by pressurized fluid introduced into the second chamber, and when the fluid pressure in the first chamber is reduced, to cause the striker piston to execute a return stroke, g. said second chamber having a wall at the end thereof remote from the first chamber which is formed with a sealed aperture through which an end portion of the striker piston projects, h. the casing including tool holding means for locating a tool so as to be struck by the end of the striker piston towards the end of the working stroke thereof, i. a collar on that portion of the striker piston which passes through the second chamber, said collar having opposing effective surface areas which are normally both exposed to the pressure in the second chamber and being of such dimensions as to permit of passage of fluid in the second chamber around the collar during normal reciprocatory movement of the striker piston, j. an overshoot dashpot cavity situated at the end of the second chamber remote from the first chamber and positioned so that, in the event that the length of the working stroke should exceed a normal length as a result of removal of external resistance to advance of the tool, the collar will enter the cavity to trap fluid therein, k. the effective area of the collar presented to the dashpot cavity being substantially in excess of the second effective piston area of the striker piston, and l. restrictor means provided as the sole path for escape of fluid trapped in the cavity on entry thereinto of the collar.

Claim 5

An implement according to claim 1, wherein a bore is formed in the end of the striker piston remote from that intended to strike the tool and a hollow cylindrical member fixed to the casing enters said bore in sealed relationship therewith, the bore and the hollow cylindrical member cooperating to form the first chamber and the end of the bore affording the first effective piston area.

Claim 6

An implement according to claim 2, wherein the end of the striker piston remote from that intended to strike the tool is formed as a piston head which is surrounded by, and has sealing relationship with, a cylinder bore in the casing, the piston head having a first annular face which is bounded by the hollow cylindrical member and the cylinder bore constituting a third effective piston area partly bounding a third chamber which is otherwise bounded by the cylinder bore and the outer surface of the hollow cylindrical member.

Claim 7

An implement according to claim 3, wherein the the hollow cylindrical member provides a passage for the flow of fluid to and from the first chamber and wherein the volumes of the first and third chambers increase and diminish in unison on reciprocation of the striker piston.

Claim 8

An implement according to claim 4, wherein a valve is provided at a location intermediate the first chamber and a low pressure zone, said valve being operable alternatively to a first position in which it admits pressurised fluid to the first chamber and to a second position in which it permits fluid to escape from the first chamber to the low pressure zone.

Claim 9

An implement according to claim 5, which includes an actuating chamber for said valve, a port entering the wall of the cylinder bore at a position at which it is obscured by the piston head for the greater part of the working stroke of the striker piston but is uncovered by the first annular face of the pIston head towards the end of the working stroke and a connection from the valve actuating chamber to said port whereby the valve actuating chamber can be put into communication with the third chamber towards the end of the working stroke of the striker piston to operate the valve to move it to its second position.

Claim 10

An implement according to claim 6, wherein the piston head is formed with a second annular face, said second annular face partly bounding the second chamber and being situated at the end of the piston head remote from the first annular face.

Claim 11

An implement according to claim 7, wherein said port is formed in the cylinder bore at a position at which it is obscured by the piston head for the greater part of the return stroke of the striker piston but is uncovered by the second annular face of the piston head towards the end of the return stroke, and a high pressure zone arranged to communicate with the valve actuating chamber via said port towards the end of the return stroke of the striker piston to operate the valve to move it to its first position.

Claim 12

An implement according to claim 8, which includes a fluid passage communicating with the third chamber and a one-way valve in said passage arranged to permit escape of fluid from the third chamber during the return stroke of the striker piston to permit reduction of the fluid pressure in the third chamber.

Claim 13

An implement according to claim 1, wherein fluid flow restrictor means are provided which are selectively operable to restrict fluid flow from the first chamber but which permit unrestricted flow into the first chamber.

Claim 14

An implement according to claim 8, wherein a recuperation dashpot cavity is located in the second chamber at a position such that it is entered by the collar on the striker piston towards the end of the return stroke of the striker piston, whereby fluid compressed in the recuperation dashpot cavity may pass via said port to the valve actuating chamber to operate the valve to move it into its first position and fluid flow restrictor means being included in said access means.

Claim 15

An implement according to claim 11, wherein a one-way valve is interposed between said port and the valve actuating chamber, said one-way valve being arranged to permit fluid flow from said port to the valve actuating chamber and to prevent return flow.

Claim 16

An implement according to claim 12, wherein a second port enters the cylinder bore, said second port being so positioned that it is uncovered by the first annular face of the piston head at a position in the working stroke of the striker piston before the first annular face reaches the first-mentioned port associated with the one-way valve.

Claim 17

An implement according to claim 8, wherein a single port enters the wall of the cylinder bore to provide communication between said cylinder bore and the valve actuating chamber, this single port being uncovered by the first annular face of the piston head towards the end of the working stroke of the striker piston to operate the valve to move it to its second position, said single port also being uncovered by the second annular face of the piston head towards the end of the return stroke of the striker piston to operate the valve to move it to its first position.

Claim 18

An implement according to claim 14, wherein a recuperation dashpot cavity is provided in the second chamber at a position such that it is entered by the collar on the striker piston towards the end of the return stroke of the striker piston and wherein a by-pass port provides a fluid flow path between the second chamber and the wall of the cylinder bore at position such that, during the return stroke of the striker piston, said by-pass port is uncovered by the second annular face of the piston head before said face uncovers the port leading to the valve actuating chamber, said by-pass port being at such position that it is never uncovered by the first annular face of the piston head during the working stroke of the striker piston nor during any overshoot thereof.

Claim 19

An implement according to claim 1, wherein a recuperation dashpot cavity is located in the second chamber at a position such that it is entered by the collar on the striker piston towards the end of the return stroke of the striker piston.

Claim 20

An implement according to claim 1, which includes a first duct for connection to a source of pressure flow, a second duct for connection to a region of low pressure and on-off valve means operable to connect the first duct to the second duct to immobilise the implement, said on-off valve means being manually operable to break such connection to set the implement in action.

Claim 21

An implement according to claim 1, including a duct for connection to a source of pressurised fluid and on-off valve means operable to block the passage of fluid from said duct to other parts of the implement to immobilise the implement, said on-off valve means being manually operable to unblock said duct to set the implement in action.

Claim 22

An implement according to claim 1, which includes a duct for connection to a region of low pressure and on-off valve means operable to block any passage through which fluid may flow from the first chamber to said duct to immobilise the implement, said on-off valve means being manually operable to permit passage of said fluid from said feed chamber to said duct to set the implement in action.

Claim 23

An implement according to claim 19, wherein the on-off valve means is operable between a first condition in which it blocks the fluid flow from the first chamber to said duct and a second condition in which such flow passes through restrictor means.

Claim 24

A hydraulically-operated percussive implement comprising a casing with tool-holding means, a striker/piston reciprocable within the casing to execute working and return strokes of the striker/piston, and valve means controlling the flow of hydraulic fluid for actuation of the striker/piston, the striker/piston having an annular collar movable in a chamber in the casing in which chamber the hydraulic fluid pressure acts on the striker/piston to produce return strokes thereof, said collar having opposing effective surface areas which are both normally exposed to the pressure in the second chamber, and said chamber having at one end a dashpot cavity entered by said collar over an end portion of the maximum working stroke of the striker/piston whereby trapping of the fluid in said cavity and restricted escape therefrom damps overtravel of the striker/piston beyond a normal length working stroke thereof.

Claim 25

A hydraulically-operated percussive implement comprising a casing with tool-holding means, a striker/piston reciprocable within the casing to execute working and return strokes of the striker/piston, and valve means controlling the flow of hydraulic fluid for actuation of the striker/piston, the striker/piston having an annular collar movable in a chamber in the casing in which chamber the hydraulic fluid pressure acts on the striker/piston to produce return strokes thereof, said collar having opposing effective surface areas which are both normally exposed to the pressure in the second chamber, and said chamber having at one end a dashpot cavity entered by said collar over an end portion of the maximum working stroke of the striker/piston whereby trapping of the fluid in said cavity and restricted escape therefrom damps overtravel of the striker/piston beyond a normal length working stroke thereof.

Claim 26

A percussive implement according to claim 21, wherein the striker/piston has an effective piston area within said chamber, on which the fluid pressure acts to produce said return strokes, which effective piston area is materially less than the effective cross-sectional area of said collar.

Claim 27

A percussive implement according to claim 22, wherein the striker/piston has, in addition to said effective piston area, a further effective piston area on which fluid pressure acts in a further chamber to produce working strokes of the striker/piston.

Claim 28

A percussive implement according to claim 21, wherein the arrangement is such that in operation with a tool held in said tool-holding means the tool is impacted directly by said striker/piston during said working strokes thereof.

Claim 29

A hydraulically-operated percussive implement which includes: a casing providing first and second chambers within the casing, a striker piston reciprocable within the casing and having a relatively large first effective piston area which partly bounds the first chamber and is acted upon when pressurised fluid is introduced into the first chamber to cause the striker piston to execute a working stroke, said striker piston also having a relatively small second effective piston area which partly bounds the second chamber and is acted upon by pressurized fluid introduced into the second chamber, when the fluid pressure in the first chamber is redUced, to cause the striker piston to execute a return stroke; said second chamber having at one end a wall with a sealed aperture through which an end portion of the striker piston projects and the casing including tool holding means for locating a tool so as to be struck by the end of the striker piston towards the end of the working stroke thereof; means for introducing pressurised fluid into said chambers including valve means controlling the flow of fluid to and from said first chamber; a collar on that portion of the striker piston which passes through the second chamber, said collar having opposing effective surface areas which are normally both exposed to the pressure in the second chamber, said collar being of such dimensions as to permit passage of fluid in the second chamber around the collar during normal reciprocatory movement of the striker piston; an overshoot dashpot cavity situated at said one end of the second chamber and positioned so that, in the event that the length of the working stroke should exceed a normal length as a result of removal of external resistance to advance of the tool, the collar will enter the cavity to trap fluid therein; the effective area of the collar presented to the dashpot cavity being substantially in excess of the second effective area of the striker piston; and at least one flow-restrictive passage which interconnects the overshoot dashpot cavity and the second chamber and at least one unrestricted passage which interconnects the lower end of said overshoot dashpot cavity and said second chamber, one-way valve means being provided to prevent the flow of fluid from the overshoot dashpot cavity into the second chamber through any such unrestricted passage but to permit fluid flow into said cavity after the collar on the striker piston has come to rest within said cavity.

Claim 30

A hydraulically-operated percussive implement which includes: a casing providing first and second chambers within the casing, a striker piston reciprocable within the casing and having a relatively large first effective piston area which partly bounds the first chamber and is acted upon when pressurised fluid is introduced into the first chamber to cause the striker piston to execute a working stroke, said striker piston also having a relatively small second effective piston area which partly bounds the second chamber and is acted upon by pressurized fluid introduced into the second chamber, when the fluid pressure in the first chamber is redUced, to cause the striker piston to execute a return stroke; said second chamber having at one end a wall with a sealed aperture through which an end portion of the striker piston projects and the casing including tool holding means for locating a tool so as to be struck by the end of the striker piston towards the end of the working stroke thereof; means for introducing pressurised fluid into said chambers including valve means controlling the flow of fluid to and from said first chamber; a collar on that portion of the striker piston which passes through the second chamber, said collar having opposing effective surface areas which are normally both exposed to the pressure in the second chamber, said collar being of such dimensions as to permit passage of fluid in the second chamber around the collar during normal reciprocatory movement of the striker piston; an overshoot dashpot cavity situated at said one end of the second chamber and positioned so that, in the event that the length of the working stroke should exceed a normal length as a result of removal of external resistance to advance of the tool, the collar will enter the cavity to trap fluid therein; the effective area of the collar presented to the dashpot cavity being substantially in excess of the second effective area of the striker piston; and at least one flow-restrictive passage which interconnects the overshoot dashpot cavity and the second chamber and at least one unrestricted passage which interconnects the lower end of said overshoot dashpot cavity and said second chamber, one-way valve means being provided to prevent the flow of fluid from the overshoot dashpot cavity into the second chamber through any such unrestricted passage but to permit fluid flow into said cavity after the collar on the striker piston has come to rest within said cavity.