Abstract
A hydraulic percussion device comprising a piston mounted for reciprocal motion within a cylinder to impact a percussion bit and a control valve to control reciprocation of the piston. A valve pilot line is arranged to switch the control valve based on the position of the piston within the cylinder, wherein the valve pilot line is alternately connected, by the reciprocal movement of the piston, to high and low pressure lines (P, T) via an undercut in the piston. The undercut is located at a portion of the piston having a diameter less than the maximum sealing diameter of the piston.
Claims
1. A hydraulic percussion device comprising: a piston mounted for reciprocal motion within a cylinder to impact a tool, the piston including a first undercut disposed at least partially about a circumferential surface of the piston, wherein the first undercut is provided at a rear end of the piston; a control valve to control reciprocation of the piston, the control valve alternately connecting a rear driving chamber of the piston to high pressure and low pressure lines, such that when the rear driving chamber is connected to the high pressure line, the piston is driven towards the tool, and wherein the first undercut is provided at a portion of the piston which is rearward of the rear driving chamber of the piston during an entire piston cycle; and a valve pilot line arranged to switch the control valve based on the position of the piston within the cylinder, wherein the valve pilot line is alternately connected, by the reciprocal movement of the piston, to high and low pressure lines via the first undercut in the piston, wherein the first undercut is a portion of the piston having a smaller diameter than adjacent portions of the piston forward and rear of the first undercut, the adjacent portions of the piston forward and rear of the first undercut having a diameter less than the maximum sealing diameter of the piston.
2. A hydraulic percussion device as claimed in claim 1, wherein the first undercut is provided at a portion of the piston which is forward of a rear seal disposed between the piston and the cylinder during the entire piston cycle.
3. A hydraulic percussion device as claimed in claim 1, further comprising: a port provided in the cylinder for connection of the valve pilot line to the v pressure line via the undercut; wherein the port further provides seal drainage for a seal disposed between the piston and cylinder.
4. A hydraulic down-the-hole hammer comprising: a hydraulic percussion device as claimed in claim 1; and a percussion bit.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1a is a schematic representation of a prior art valve piloting arrangement for a hydraulic percussion device;
(2) FIG. 1b is a schematic representation of the hydraulic percussion device of FIG. 1a in a return stroke;
(3) FIG. 1c is a schematic representation of the hydraulic percussion device of FIG. 1a at the top of stroke;
(4) FIG. 2a is a schematic representation of an alternate prior art valve piloting arrangement for a hydraulic percussion device, in which the device is in a return stroke;
(5) FIG. 2b is a schematic representation of the hydraulic percussion device of FIG. 2a at the top of stroke;
(6) FIG. 3 is a schematic representation of the hydraulic percussion device of FIG. 1a showing typical leakages;
(7) FIG. 4a is a schematic representation a valve piloting arrangement for a hydraulic percussion device according to a first embodiment of the invention, in a return stroke;
(8) FIG. 4b is a schematic representation of the hydraulic percussion device of FIG. 4a at the top of stroke;
(9) FIG. 5a is a schematic representation of a valve piloting arrangement for a hydraulic percussion device according to a second embodiment of the invention, in a return stroke;
(10) FIG. 5b is a schematic representation of the hydraulic percussion device of FIG. 5a at the top of stroke;
(11) FIG. 6a is a schematic representation a valve piloting arrangement for a hydraulic percussion device according to a third embodiment of the invention, in a return stroke; and
(12) FIG. 6b is a schematic representation of the hydraulic percussion device of FIG. 6a at the top of stroke.
DETAILED DESCRIPTION OF THE DRAWINGS
(13) A valve piloting arrangement for a hydraulic percussion device according to a first embodiment of the invention is illustrated in FIGS. 4a and 4b. The device comprises a cylinder 101, a piston 102 mounted for reciprocal motion within the cylinder to impact a percussion bit or tool 103 located at a forward end of the device and a control or shuttle valve 104 to control reciprocation of the piston. The control valve alternately connects rear driving chamber 105, 106 of the piston to high pressure and low pressure lines P, T of the device to cause the reciprocal movement of the piston. The switching of the control valve is controlled by the position of the piston, that is, position feedback control. A valve pilot line 107 is arranged to switch the control valve based on the position of the piston within the cylinder.
(14) FIG. 4a shows the device in a return stroke, where the piston is being driven away from the tool in the direction shown by the arrow. The valve pilot line 107 is connected between the right side 114 of the valve and an undercut 108 in a rear end of the piston 102, that is, in the piston tail 111. The left side of the valve 115 is connected to the high pressure line P by line 116. As shown in FIG. 4a, the portion of the piston at which the undercut 108 is provided has a minimum piston diameter m which is less than the maximum sealing diameter M of the piston.
(15) In FIG. 4a, the valve pilot line 107 is connected to the high pressure line P via the undercut 108 and cylinder ports 117 and 118. Because the area on the right side of the valve on which the high pressure acts is greater than that on the left side of the valve, the hydraulic forces acting on the valve have moved the valve to the left which in turn connects the rear chamber 106 with the low pressure line T. The front chamber 105 is continuously connected to high pressure so that the piston is driven away from the tool 103.
(16) As the piston moves to the right, the undercut moves from a position in which it connects the valve pilot line to the high pressure line P, to a position in which it connects the valve pilot line to the low pressure line T. FIG. 4b shows the piston in a position in which the undercut 108 in the piston connects the valve pilot line 107 with the low pressure line T via cylinder ports 117 and 119. As the left side 115 of the valve is connected to the high pressure line P, the valve 104 is forced to switch to the right position which in turn connects the rear chamber 106 with the high pressure line P. Since the piston area 112 of the rear chamber is greater than the piston area 113 of the front chamber, the net hydraulic force drives the piston towards the tool 103. Just before the piston impacts the tool, the valve pilot line is once again connected to the high pressure line and the control valve moves to the left to repeat the cycle. As shown in FIGS. 4a and 4b, the undercut 108 is provided at a portion of the piston which is rearward of the rear chamber 106 during the entire piston cycle. The undercut 108 is provided at a portion of the piston which is forward of a rear seal 110 during the entire piston cycle. Cylinder port 119 provides seal drainage for the rear seals 110, so that no dedicated seal drainage ports are required.
(17) FIGS. 5a and 5b show a valve piloting arrangement for a hydraulic percussion device according to a second embodiment of the invention, in which both front and rear chambers have alternating pressures. The valve is piloted in exactly the same manner as described in relation to FIGS. 4a and 4b.
(18) A third embodiment of the invention is illustrated in FIGS. 6a and 6b. In this embodiment, the undercut 208 is located at a forward end of the piston. As shown in FIGS. 6a and 6b, the undercut is located at a portion of the piston having a diameter D which is less than the maximum sealing diameter M of the piston. The valve pilot line 107 is connected between the left side 115 of the valve and the undercut 208 in the forward end of the piston 102. The right side of the valve 114 is connected to the high pressure line P by line 116.
(19) FIG. 6a shows the device in a return stroke, where the piston is being driven away from the tool in the direction shown by the arrow. The valve pilot line 107 is connected to the low pressure line T via the undercut 208 in the forward end of the piston 102 and cylinder ports 120 and 121. Hydraulic forces acting on the valve have moved the valve to the left which in turn connects the rear chamber 106 with the low pressure line T. The front chamber 105 is continuously connected to high pressure so that the piston is driven away from the tool 103.
(20) FIG. 6b shows the piston in a position in which the undercut 208 in the piston connects the valve pilot line 107 with the high pressure line P via cylinder port 120 and the front chamber, forcing the valve 104 to switch to the right position which in turn connects the rear chamber 106 with the high pressure line P. Since the piston area 112 of the rear chamber is greater than the piston area 113 of the front chamber, the net hydraulic force drives the piston towards the tool 103. Just before the piston impacts the tool, the valve pilot line is once again connected to the low pressure line and the control valve moves to the left to repeat the cycle.
(21) Cylinder port 121 provides seal drainage for the forward seals 110, so that no dedicated seal drainage ports are required.
(22) The words “comprises/comprising” and the words “having/including” when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.
(23) It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.
