GB2157220A - Reciprocating percussive device - Google Patents

Abstract

Hydraulic/pneumatic percussive device comprises a double acting piston 60 which is provided with recessed portions 10B, 12B, 14B and contained in a cylinder, a control port 51 and a spaced auxiliary port 104B, a control valve 35 which initiates the hammering action by advancing the piston 60, and an auxiliary valve 102B. Pressure fluid in a port 50 shifts the control valve 35 to initiate the hammering action. The valve 35 is retracted by pressure fluid in the port 51 to commence the return stroke. The auxiliary valve 102B, in its open position, allows ports 51 and 104B to communicate with each other and with a recessed portion 12B to shorten the return stroke. It is maintained in its closed position by a pressure fluid from a conduit 105B. The pressure fluid presses the valve 102B down to shut port 104B. The fluid is vented to release the pressure on the valve 102B. <IMAGE>

Description

SPECIFICATION Reciprocating percussive device This invention relates to hydraulically or pneumatically actuated reciprocating devices such as rock drills, and in particular to such devices in which the reciprocation frequency can readily be altered.

In our earlier patent G.B. 1526048 we describe a reciprocating device in which the frequency of reciprocation may be altered by changing the size of a restricted passage through which hydraulic fluid must pass on the return stroke. The size of this passage can be altered by turning a square-headed adjustment nut projecting externally of the device.

This has the effect of altering the axial movement which a spool valve controlling the passage can undergo. Alternatively the axial movement of the spool valve may be altered by means of interchangeable spacers.

It will be apparent that, when an adjustment nut is provided, a user requiring to alter the reciprocation frequency must stop using the device and effect the alteration. If the spacer method is used a lengthy shut down and substantial dismantling of the device is required.

According to the present invention there is provided a hydraulic or pneumatic percussive device comprising a cylinder containing a double acting piston having recessed portions which during movement of the piston co-operate with a control port, formed in the cylinder wall and leading to a control valve controlling reciprocation of the piston, such that at or near the end of each stroke of the piston there is a change in the fluid pressure acting within the control port and hence on the control valve, which is moved to a position in which it causes the fluid to drive the piston on the other stroke, wherein the cylinder wall is formed with an auxiliary port at a position axially spaced from the control port, the auxiliary and control ports being connectable by opening of an auxiliary valve to allow the recessed portion of the piston to communicate with the control port by way of the auxiliary port near the end of the return stroke, thereby shortening the return stroke, the auxiliary valve being a changeover valve which has a pilot port for connection to a source of pilot pressure to hold the auxiliary valve closed, removal of the pilot pressure allowing the auxiliary valve to open, and the auxiliary valve communicates with the main cylinder such that operating pressure in the cylinder acts on the auxiliary valve at the end of the power stroke of the piston, thereby opening the auxiliary valve unless it is held closed by the pilot pressure.

Shortening of the piston stroke by opening of the auxiliary valve to provide a by-pass to the control port increases the reciprocation frequency.

The pilot pressure may be automatically controlled in response to detected parameters of the operation of the device. Thus it can be electrically or hydraulically interlocked with functions associated with operation of the device, e.g. percussive pressure, rotary pressure or feed pressure.

In a preferred embodiment the piston has first and second recessed portions axially separated by a circumferential timing land, the control port communicating, at the end of the power stroke, with a source of pressurised fluid via the first recessed portion so that the control valve moves to a position in which it causes the pressurised fluid to drive the piston on its return stroke, the control port further communicating, at the end of the return stroke, with a venting outlet via the second recessed portion so that the control valve moves to a position in which it causes pressurised fluid to drive the piston on its power stroke, wherein, when the auxiliary valve is closed, the second recessed portion communicates firstly with the auxiliary port during the return stroke of the piston and, after further movement of the piston, with the control port.

The device preferably further comprises an accumulator for storing pressurised fluid during the return stroke and delivering it on the power stroke.

Whilst the invention may be applied to an impactor (e.g. a paving breaker) in which no rotary motion of the piston is necessary, in preferred embodiments the driven tool is caused to rotate so that blows are delivered in a rotating pattern on the power strokes.

The control valve may be a change-over spool valve.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figures 1A and 1B together show a longitudinal view in partial cross section of a hydraulically operated drill according to the invention; Figure 2 is a longitudinal sectional view of part of the drill, in a plane perpendicular to that of Figures 1A and 1 B; and Figure 3 is the hydraulic circuit of the drill.

The structure and operation of the drill is similar to that of the drill described in G.B. 1526048, to which the reader's attention is directed, in particular for details of the drill which do not bear directly upon the present invention. The reference numerals used in the following description correspond to those used in G.B. 1526048. The reference numerals of newly introduced parts are followed by the letter 'B'.

As shown in Figures 1A and 1B, the drill comprises a hammer piston 60 at its left-hand end for imparting reciprocating motion to a drill rod (not shown) retained by a shank adaptor 90 at its righthand end. The shank adaptor 90 and drill rod are caused to rotate by means of the engagement of a splined portion 86 with an internally splined sleeve 88B which in turn engages a gear 90B via a number of dogs 92B. The gear is rotated by a piston 93B which is fixed to the output shaft of a motor 94B. The rotation is independent of the percussive mechanism.

The reciprocating mechanism with which the invention is concerned, is contained within a hollow backhead block 10. In particular the backhead block contains: most of the length of the piston 60, and in particular that part of the piston whose surface is formed with circumferential increased diameter portions or lands 61 and 62, and with recessed portions 10B, 12B and 14B on either side thereof; a piston sleeve 48 around the piston; a cylinder formed by the bore of the block 10, the cylinder and the sleeve 48 together being formed with axially-spaced ports 49, 50, 51, 104B and 52; a hydraulic accumulatort 23; a spool valve 35 on the top side of the block (see Figure 2); an auxiliary valve 102B, a plug 103B to which remote pilot valve (not shown) is connected, and a hydraulic conduit 105B between the plug 103B and the auxiliary valve 102B.

The hydraulic accumulator 23 has a dished diaphragm cover 22 over a boss 21. Within the chamber formed therebetween is a rubber diaphragm 24 whose edge region is securely trapped between the cover 22 and the boss 21. A perforated portion 26 in the boss 21 leads from the chamber into a passage 97 which communicates with the port 50 in the sleeve 48 and cylinder. The inlet port (not shown for hydraulic fluid is connected via the perforated portion 26 to the pre-charged accumulator.

This has the effect of accomodating pressure fluctuations in the operating fluid, and maintaining the required pressure on the power stroke.

The spool valve 35 (Figure 2), which serves as a control valve controlling reciprocation of the piston, comprises a spool valve sleeve 29 with ports 30, 32 and 33 in respective communication with ports 49, 50 and 51 of the sleeve and cylinder. It further comprises a spool valve member 35' with a head portion 36, a reduced diameter stem portion 37 and an enlarged diameter end portion 38. The head portion 36 and end portion 38 are a close sliding fit in the valve sleeve 29. The head portion 36 has a bore 40 which contains a spool operating piston 41 and passages 42 are provided through the head portion 36 to allow the flow of pressurised fluid to the operating piston from ports 50 and 22.

The auxiliary valve 102B selectively connects the aforesaid port 104B in the piston sleeve and cylinder to the adjacent port 51, via a conduit 106B. The valve 102B has a valve member 107B slidable within a bore. The valve member 107B has a stem 110B and a head 111B. The stem 110B is axially slidable within a bore formed within a valve body 1128 between limits determined by the abutment of one side of the head 111 B with the end of the valve body 112B and by the seating of the other side of the head 111 B over the end of the passage leading from the port 104B.

The end of the valve stem 110B, communicating with the conduit 105B, is of area a4. The end of the passage leading from the port 104B is designated as area a3. The annular shoulder on the head 111B where it adjoins the stem 110B is designated a5.

The notional projected annular area between the outer circumference of the head 111 B and a central area equalling the area a2 is designated a6. The area a4 exceeds the area a2 and the area a6 exceeds the area a5.

The valve member seats over the end of the passage leading from port 104B in order to disconnect the port 104B from the conduit 106B and therefore from the port 51. The valve member 107B is axially movable to seat over the port 104B when the remote pilot valve (not shown) is moved to a position in which it causes pressurised hydraulic fluid to act on the upper surface a4 of the valve stem.

When pressurised hydralic fluid no longer acts on the surface a4 of valve member 107B, because the user has moved the remote pilot valve to a position in which it vents the pressure in the conduit 105B, the valve member 107B is moved upwards at the end of the piston power stroke when port 51 is uncovered, by pressure acting on areas a5 and a6 on the head 111 B of the valve member. Since a6 exceeds a5 the valve member is moved upwards until the shoulder (on the head 111B where it adjoins the stem 11OB) abuts the end of the valve body 112B. Thus the port 104B now communicates with the conduit 106B and hence with port 51. Additional force to move the valve member arises when pressurised fluid also acts on an area on the head equal to a3.

The recessed portion 10B of the piston 60 is recessed more deeply than the recessed portion 12B and so the annular area A2 on the side of the land 60 facing the recessed portion 10B exceeds the annular area A1 on the side facing the recessed portion 12B.

One cycle of the operation of the reciprocating mechanism, with valve 102B disconnecting port 104B from port 51 will now be described.

At the start of the power stroke the piston 60 is in its left-most position and the spool valve member in its right-most position. Pressurised hydraulic fluid acts through the passage 97 and port 50, and thence, via passages 42, on area a1 of the spool operating piston 41. It also acts, via port 50, on the area A, throughout the cycle. In the right-most position of the spool valve member the end portion 38 prevents the admission of hydraulic fluid to the recessed portion 10B of the piston and hence to the area A2. Moreover, timing land 61 covers the openings 51 and 104B and hydraulic fluid is not admitted to act on area a2 formed on the head portion 36 of the spool valve member 35'.

The action of pressurised fluid on a1 moves the spool valve member to the left, opening the connection between the port 49 and the hydraulic fluid, and, at the same time, closing the connection of the port 49 to a return annulus b connected, by a passage not shown, to an outlet for hydraulic fluid. The pressurised fluid thus acts now on the area A2 as well as A, and, because A2 is larger than the area A1, the piston is accelerated to the right on a power stroke. As it moves on the power stroke the timing land 61 uncovers the port 51 and allows pressurised fluid to act, via port 50 and recessed portion 12B, through port 51 and on area a2. Area a2 is greater than a1 and so the spool member 35' is driven to the right, closing the connection of port 49 to the hydraulic fluid and opening its connection to the return annulus b, and venting the pressure acting on area A2.

The piston is not arrested instantaneously as soon as the port 51 is pressurised but after a short distance of further piston travel, when contact with the shank adaptor occurs or when the shank adaptor is not in its drilling position, as shown, but when a damping dashpot is created by the annular recess 14B and a recessed portion of the sleeve 48, once timing land 61 closes off the return port 52 in sleeve 48. Depending on the stroke and frequency requirements the timing land 61 may or may not uncover the port 104B.Even if the port 104B is uncovered the downward force on the valve member 107B due to the fluid pressure acting on areas a4 and a5 exceeds the upward force due to the fluid pressure acting on a6 (through port 51) and a2 (through port 104B), and so the valve member 107B does not lift to connect port 104B to port 51 through the conduit 106B.

The piston finally stops and is driven on it return stroke as a result of the fluid pressure acting on the area A,. The piston is driven slowly on the return stroke relative to the power stroke because of the restricted opening through which fluid must pass in flowing from port 49 to return annulus b.

The leftwards, return movement of the piston is terminated once the timing land 61 has moved past the port 51 to allow the pressure in port 51, acting on area a2 and maintaining the spool valve member in the position shown in Figures 1 or 2, to vent, via the recessed portion 14B and thence port 52. The cycle has now been completed and repeats itself, as the pressure now acting only on a1 again causes the spool valve member to move leftwards and open port 40 and hence area A2 to pressurised fluid.

The remote pilot valve is used to vent the pressure in the conduit 105B when it is desired to change the reciprocation frequency. It will be recalled that pressurised fluid acts on a6 once every cycle, at the end of the power stroke, once the land 61 has uncovered the port 51 and also on area a2 should the land 51 also uncover port 104B. Since the pressure in the conduit 105B is now vented pressure no longer acts on area a4 and the valve member 107B is moved upwards by the pressure on a6, and possibly a2, at the end of the power stroke. The downward force due to pressure acting on the annular surface a5 is overcome. Once the valve member 107B is lifted the conduit 106B and port 1048 are connected together through the valve 102B.Now that the conduit 106B and the port 104B are so connected the return stroke is terminated earlier, when the timing land 61 uncovers the port 104B. The port 51 does not require to be uncovered now because the fluid pressure in port 51, acting on the area a2, is vented via conduit 106B and port 104B as soon as port 104B is uncovered. The stroke length is thus shortened and the reciprocation frequency increased.

The operations described above are easily followed using the hydraulic circuit of Figure 3. The porting formed as between the piston 60 and the piston sleeve 48 and cylinder is schematically denoted as valve 100B. The spool control valve 35, auxiliary valve 102B, remote pilot valve 120B and hydraulic accumulator 23 are all shown.

The spool valve 35 is shown in the position which would appear in Figure 2 as its leftwards position, with no pressure acting on area a2, the piston being at the end of its return stroke and the line 51 being vented. Thus pressurised fluid acts on area A2 and the power stroke occurs. The impetus for the power stroke begins to be lost when pressurised fluid is admitted to line 51, via line 100E of valve 100B in Figure 3 (and in Figures 1 and 2, by the passing of the timing land 61 over the port 51). The valve 35 is now urged to a position in which it causes the pressure acting on area A2 to be vented via the return line b, and pressurised fluid is admitted to act on areas a5 and a6 of the valve 102B.Continuation of the power stroke may then cause pressurised fluid to act, via line 100F on a2, should timing land 61 uncover port 104B.

If pressurised fluid acts in the line 105B the valve 102B remains in the position shown in Figure 3.

However, if the valve is in this position but the pressure in the line 105B has been vented then when the line 51 is pressurised the valve 102B is shunted to connect 104B and 106B, the force on a6 exceeding that on a5 due to the larger area of a6.

The upward force lifting the valve member 107B from its lower position by virtue of the force on a6 may be supplemented by the pressure acting on a2 via the port 104B if that port is uncovered before the valve member has started to lift. It will be appreciated that the initial lifting force on the valve member 107B arises as a result of the pressure acting on the annular area a6. Once the valve member has risen pressure will also act on area a2 irrespective of whether the port 104B has been uncovered.

The return stroke proceeds until the pressure acting in line 51, and hence on the area a2, is vented to the line 52. As is clearly shown n Figure 3, with the auxiliary valve 102B severing the connection between lines 104B and 106B the pressure in line 51 can only vent after the piston has retracted fully, using the line 100C to connect the line 51 to the line 52. On the other hand, when the auxiliary valve connects the lines 104B and 106B the pressure in the line 51 vents when the piston has retracted a shorter distance, the line 51 now being connected to the line 52 via the bypass route provided by valve 102B, through lines 106B, 103B and 100D.

Claims (3)

1. A hydraulic or pnaumatic percussive device comprising a cylinder containing a double acting piston have recessed portions which during movement of the piston co-operate with a control port, formed in the cylinder wall and leading to a control valve controlling reciprocation of the piston, such that at or near the end of each stroke of the piston there is a change in the fluid pressure acting within the control port and hence on the control valve, which is moved to a position in which it causes the fluid to drive the piston on the other stroke, wherein the cylinder wall is formed with an auxiliary port at a position axially spaced from the con trol port, the auxiliary and control ports being connectable by opening an auxiliary valve to allow the recessed portion of the piston to communicate with the control port by way of the auxiliary port near the end of the return stroke, thereby shortening the return stroke, the auxiliary valve being a changeover valve which has a pilot port for connection to a source of pilot pressure to hold the auxiliary valve closed, removal of the pilot pressure allowing the auxiliary valve to open, and the auxiliary valve communicates with the main cylinder such that operating pressure in the cylinder acts on the auxiliary valve at the end of the power stroke of the piston, thereby opening the auxiliary valve unless it is held closed by the pilot pressure.

2. A device as claimed in claim 1 wherein the piston has first and second portions axially separated by a circumferential timing land, the control port communicating, at the end of the power stroke, with a source of pressurised fluid via the first recessed portion so that the control valve moves to a position in which it causes the pressurized fluid to drive the piston on its return stroke, the control port further communicating, at the end of the return stroke, with a venting outlet via the second recessed portion so that the control valve moves to a position in which it causes pressurised fluid to drive the piston on its power stroke, wherein, when the auxiliary valve is closed, the second recessed portion communicates firstly with the auxiliary port during the return stroke of the piston and, after further movement of the piston, with the control port.

3. A device as claimed in claim 1 or 2 further comprising an accumulator for storing pressurised fluid during the return stroke and delivering it on the power stroke.