GB1563121A - Hydraulic seciprocatory tools - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO HYDRAULIC RECIPROCATORY TOOLS I, SECRETARY OF STATE FOR INDUSTRY, London do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to hydraulically operated reciprocatory tools such as impact devices, and in particular is concerned with hand-held tools such as paving breakers.

Paving breakers have a piston which is reciprocable within a cylinder. It is important in such tools that the acceleration of their handles and hence the vibration experienced by their operators be kept to a minimum. For this to be so, for a given energy output per stroke of the piston, the mass of the whole machine should be as large as possible relative to the mass of the piston, and the stroke length of the piston should be as great as possible.

In practice, however, the mass of the machine is limited to that which an operator can carry and the mass of the piston assembly must be sufficient to act as an effective hammer. It is desirable therefore to arrange for the length of the stroke of the piston assembly to be as great as possible.

According to the present invention there is provided a reciprocatory tool driveable by flow of hydraulic fluid and comprising (a) a stepped piston having a recess spanning the step in its cylindrical surface, the piston being slideable in and in fluid-tight contact on both sides of the recess with a stepped cylinder formed in the housing, the piston being reciprocable between a forward position in which the relatively large diameter portion of the stepped recess and the relatively small diameter portion of the cylinder overlap and are in fluidtight contact and a rearward position in which these said portions are spaced from one another, (b) a first signal bore formed in the housing and able to communicate with the stepped recess in the piston at a location in the cylinder wall forward of its step, (c) a second signal bore formed in the housing and communicating with the cylinder rearwardly of its step at a location such that it communicates with the stepped recess in the piston when the piston is in a rearward position and with a part of the cylinder rearward of the stepped recess and separated from it in substantially fluidtight manner when the piston is in a forward position, (d) a fluid passage for supply of hydraulic fluid to the stepped recess, (e) a valve in the second signal bore to allow fluid flow into the cylinder but not out of the cylinder along the second signal bore, and (f) means actuable by the pressure of hydraulic fluid in the first and second signal bores for actuation of the reciprocatory movement of the piston.

In preferred embodiments of the apparatus of the invention, high fluid pressure acts, in use, against a drive rod reciprocable within a bore in a housing, the rod extending forwardly from the rear end of the cylinder and thus urged against the piston to drive it forward.

By way of example, one embodiment of the invention will now be described with reference to the drawings filed with the provisional specification, in which: Figure 1 is a section of the rear end of a tool in accordance with the invention, and Figure 2 is a section along the line Il-Il of Figure 1.

The tool shown in the drawings has a body 1 comprising a main cylinder housing within which a driving piston 2 is axially slideable. A spool valve 3 in the body 1 is operable on depression of a spring loaded control button 4 to urge forward (in a manner explained below) a drive rod 5 which in turn bears on and causes advance of the driving piston 2. As such, the spool valve 3 constitutes a means for actuation of the reciprocatory movement of the piston.

At the forward end of its motion, the driving piston 2 is arranged to strike the rear end of a tool bit (not shown).

A first signal recess 30 (Fig 1) is located in the body 1 in the main cylinder wall near its forward end and a second signal recess 32 is located in the main cylinder wall intermediate the first signal recess 30 and the rear end of the cylinder. The first and second signal recesses are connected to a fluid passage 29 through first and second signal bores 41 and 42 respectively.

In the second signal bore 42 is a non-return valve 31 which permits flow of the fluid only into the cylinder. The cylinder has a step 35, and is connected to low and high pressure fluid supply lines (not shown) through fluid passages (not shown) to respectively a peripheral recess 33 at the rear end of the cylinder and a peripheral recess 34 located between the first and second signal recesses and rearward of the step 35. The cylinder is generally of constant diameter between its rear and the step 35. From the step 35 to its forward end the cylinder is generally of constant but slightly smaller diameter.

The driving piston 2 is generally cylindrical rearward of a tapered front portion, and its diameter immediately rearward of the front portion provides a sliding and substantially fluid-tight fit with the cylinder forward of the step 35. A short portion 35 of enlarged diameter at the rear end of the piston 2, rearward of a shoulder 40, provides a sliding and substantially fluid-tight fit with the cylinder rearward of the said step 35. The piston 2 can move between a rearward position in which the second signal recess is forward of shoulder 40 and a forward position in which the second signal recess communicates with a part of the cylinder rearward of the piston 2. A circumferential groove 37 on the piston 2 near its forward end extends from forward of signal recess 30 to rearward of the step 35 in the cylinder wall when the piston is in its rearmost position.It will be seen that the piston 2 has in effect a stepped recess extending from the forward end of the groove 37 to the shoulder 40, with the rearward end of the groove 37 constituting the step of the recess.

A drive rod bore 26 in the body 1 is aligned with a guide bore 26a extending through a tubular housing 38 which extends axially forwardly from the rear of the cylinder. A drive rod 5 is a close fit with the guide bore 26a so that pressurised fluid which urges the drive rod 5 forward cannot pass between the rod 5 and the guide bore 26a. The piston 2 has an axial bore 39, formed in its rear end, to accommodate the housing 38 and is of sufficient size to provide a clearance round the housing to permit flow of hydraulic fluid out from the bore 39 to the recess 33 during retraction of the piston 2.

In Figure 2, depression of the control button 4 causes a sleeve 7 to slide in a control bore 8 in the body 1 so as to sever communication between two recesses 9 and 10 in the wall of the control bore 8, the recesses 9 and 10 being respectively in communication with a line for supply of high pressure and a line for supply of low pressure hydraulic fluid (not shown). A spool valve 3 consists of a spool out 12 is reciprocable between end faces 13 and 14 under the action of the differential force produced by pressurised fluid contained in large and small diameter bores 15 and 16 respectively located within the spool and closed by rods 17 and 18 slideable within bores 15 and 16 respectively and urged by the fluid against the respective end faces 13 and 14.The spool 12 is further provided with ducts 19 and 20 respectively interconnecting the bores 15 and 16 with the outer surface of the spool 12 on either side of a peripheral groove 21 in the spool surface.

The spool bore 11 is provided with three circumferentially extending recesses 22, 23 and 24, and a duct 25 connecting a point on the bore 11 between recesses 22 and 23 with the rear of the drive rod bore 26 within which the drive rod 5 is slideable. The recess 22 is connected to the recess 9 in the control bore 8 through a duct 27 and communicates with the duct 20 at all positions of the spool 12, and the recess 23 is connected to the recess 10 in the control bore 8 through a duct 28. The duct 25, and hence the drive rod bore 26 communicates through the groove 21 with either the duct 27 or the duct 28, depending on the axial position of the spool 12. Communicating with the recess 24 is the fluid passage 29. The recess 24 communicates with the ducts 19 at all positions of the spool 12.

The tool is primed by application of fluid to the high and low pressure fluid supply lines which latter is normally the fluid return line. The priming causes hydraulic fluid to enter the control bore 8 at recess 9 and immediately exhaust via recess 10. Actuation of the tool by depression of the control button 4, however, causes the sleeve 7 to prevent direct flow of the fluid from recess 9 to recess, 10, so that fluid at high pressure occupies the duct 27 and hence the ducts 20 and the small diameter bore 16. The effect of this is for the high pressure fluid to act on the small diameter rod 18 and on the spool 12 to urge the spool 12 towards the right of Figure 2.

The drive rod bore 26 is thus open to exhaust through duct 25, groove 21, recess 23 and bore 28, so that, if it has not already done so, the driving piston 2 retracts fully under the action of high pressure fluid entering the cylinder at groove 34 and acting against the shoulder 40. At this piston position, the fluid passage 29 is at high pressure, as the recesses 30 and 34 are in communication via the groove 37, so that the wide diameter bore 15 receives the same high pressure as the pressure in the narrow diameter bore 16. The net force on the high pressure fluid in the bore 15 acting against the spool 12 is therefore greater than the net force of the high pressure fluid in the bore 16 acting against the spool 12 in the opposite direction and the spool 12 therefore switches towards the left of Figure 2.After the spool has passed its mid-position, the groove 21 comes into communication with the recess 22 which is at high pressure, whereupon the drive rod 5 is urged forward by the fluid flowing to it through duct 25. Since the cross-sectional area of the drive rod is considerably greater than that of the step 40, the piston 2 is urged forward by the drive rod 5 to strike the tool bit.

On advance of the piston 2, communication between the high pressure supply at recess 34 and the first signal recess 30 is broken when the step formed by the rear wall of the groove 37 passes the step 35 in the cylinder wall. However, leakage from the fluid passage 29 is too slow for the pressure of the fluid in it to fall sufficiently for switching off the spool 12 to occur. As soon as the rear end of the piston passes the second signal recess 32, fluid from the passage 29 passes through the non-return valve 31 into the part of the cylinder behind the piston and hence to the low pressure line via recess 33. With low pressure in the passage 29 and hence bore 15, the force on the spool 12 from the high pressure fluid in the narrow diameter bore 16 is sufficient to switch the spool 12 towards the right in the drawing.

On this switching, the drive rod bore 26 reverts to low pressure, and the piston again retracts. On retraction, the non-return valve 31 prevents high pressure fluid from entering the fluid passage 29 when the shoulder 40 passes the recess 32. Sudden changes of pressure in the passage 29 only occur when the piston is near the end of its retraction, when the rear end of the groove 37 ceases to overlap the step 35.

Reciprocation of the piston 2 continues as described until the control button 4 is released, whereupon the supply of high pressure fluid to the small diameter bore 16 is ended so that the spool 12 stays at the extreme of its motion, to the left of the drawing. If the high pressure supply is discontinued, so removing any driving force, reciprocation of the piston 2 will also cease.

WHAT WE CLAIM IS:1. A reciprocatory tool drivable by flow of hydraulic fluid and comprising: a. a stepped piston having a recess spanning the step in its cylindrical surface, the piston being slideable in and in fluid tight contact on both sides of the recess with a stepped cylinder formed in a housing, the piston being reciprocable between a forward position in which the relatively large diameter portion of the stepped recess and the relatively small diameter portion of the cylinder overlap and are in fluid-tight contacts and a rearward position in which these said portions are spaced from one another; b. a first signal bore formed in the housing and able to communicate with the stepped recess in the piston at a location in the cylinder wall forward ofits step; c. a second signal bore formed in the housing and communicating with the cylinder rearwardly of its step, at a location such that it communicates with the stepped recess in the piston when the piston is in a rearward position and with a part of the cylinder rearward of the stepped recess and separated from it in substantially fluid-tight manner when the piston is in a forward position; d. a fluid passage for supply of hydraulic fluid to the stepped recess; e. a valve in the second signal bore to allow fluid flow into the cylinder but not out of the cylinder along the second signal bore; and f. means actuable by the pressure of hydraulic fluid in the first and second signal bores for actuation of the reciprocatory movement of the piston.

2. A reciprocatory tool as claimed in claim 1, wherein the means for actuating piston movement comprises a spool valve and a fluid passage for conveying hydraulic pressure to the spool valve from the ends of the first and second signal bores remote from the cylinder.

3. A reciprocatory tool as claimed in claim 1 or 2 wherein the means for actuating piston movement includes a drive rod slideable in a drive rod bore in the housing, which drive rod can be urged into contact with the stepped piston by hydraulic fluid supplied to the drive rod bore.

4. A reciprocatory tool substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   has passed its mid-position, the groove 21 comes into communication with the recess 22 which is at high pressure, whereupon the drive rod 5 is urged forward by the fluid flowing to it through duct 25. Since the cross-sectional area of the drive rod is considerably greater than that of the step 40, the piston 2 is urged forward by the drive rod 5 to strike the tool bit.

   On advance of the piston 2, communication between the high pressure supply at recess 34 and the first signal recess 30 is broken when the step formed by the rear wall of the groove 37 passes the step 35 in the cylinder wall. However, leakage from the fluid passage 29 is too slow for the pressure of the fluid in it to fall sufficiently for switching off the spool 12 to occur. As soon as the rear end of the piston passes the second signal recess 32, fluid from the passage 29 passes through the non-return valve 31 into the part of the cylinder behind the piston and hence to the low pressure line via recess 33. With low pressure in the passage 29 and hence bore 15, the force on the spool 12 from the high pressure fluid in the narrow diameter bore 16 is sufficient to switch the spool 12 towards the right in the drawing.

   On this switching, the drive rod bore 26 reverts to low pressure, and the piston again retracts. On retraction, the non-return valve 31 prevents high pressure fluid from entering the fluid passage 29 when the shoulder 40 passes the recess 32. Sudden changes of pressure in the passage 29 only occur when the piston is near the end of its retraction, when the rear end of the groove 37 ceases to overlap the step 35.

   Reciprocation of the piston 2 continues as described until the control button 4 is released, whereupon the supply of high pressure fluid to the small diameter bore 16 is ended so that the spool 12 stays at the extreme of its motion, to the left of the drawing. If the high pressure supply is discontinued, so removing any driving force, reciprocation of the piston 2 will also cease.

   WHAT WE CLAIM IS:1. A reciprocatory tool drivable by flow of hydraulic fluid and comprising: a. a stepped piston having a recess spanning the step in its cylindrical surface, the piston being slideable in and in fluid tight contact on both sides of the recess with a stepped cylinder formed in a housing, the piston being reciprocable between a forward position in which the relatively large diameter portion of the stepped recess and the relatively small diameter portion of the cylinder overlap and are in fluid-tight contacts and a rearward position in which these said portions are spaced from one another; b. a first signal bore formed in the housing and able to communicate with the stepped recess in the piston at a location in the cylinder wall forward ofits step; c. a second signal bore formed in the housing and communicating with the cylinder rearwardly of its step, at a location such that it communicates with the stepped recess in the piston when the piston is in a rearward position and with a part of the cylinder rearward of the stepped recess and separated from it in substantially fluid-tight manner when the piston is in a forward position; d. a fluid passage for supply of hydraulic fluid to the stepped recess; e. a valve in the second signal bore to allow fluid flow into the cylinder but not out of the cylinder along the second signal bore; and f. means actuable by the pressure of hydraulic fluid in the first and second signal bores for actuation of the reciprocatory movement of the piston.
2. 2. A reciprocatory tool as claimed in claim 1, wherein the means for actuating piston movement comprises a spool valve and a fluid passage for conveying hydraulic pressure to the spool valve from the ends of the first and second signal bores remote from the cylinder.
3. 3. A reciprocatory tool as claimed in claim 1 or 2 wherein the means for actuating piston movement includes a drive rod slideable in a drive rod bore in the housing, which drive rod can be urged into contact with the stepped piston by hydraulic fluid supplied to the drive rod bore.
4. 4. A reciprocatory tool substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.