GB1587611A - Resilient mountings for fluid reciprocated tools - Google Patents

Description

(54) RESILiENT MOUNTING FOR FLUID RECIPROCATED TOOLS (71) 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 fluid power operated tools, particularly those in which an impactor is acted on by a piston reciprocable within a cylinder for example under the action of hydraulic fluid under pressure.

When such impacting equipment is used for heavy duty applications, the reaction forces resulting from sudden reversals of direction of the net driving force on the piston can put a great strain on the mounting for the cylinder, the strain being normally reduced by the incorporation of some form of internal hydraulic cushioning. The size and power requirements of impacting equipment used industrially are however becoming larger and the problem of cushioning reaction forces is therefore becoming more severe. Furthermore, the rapid flow of hydraulic fluid into the cylinder to drive the piston can cause an undesirable transient peak in the fluid pressure, although this effect can to some extent be alleviated by the use of a hydraulic accumulator.

This invention provides a means by which the cylinder is flexibly mounted, the energy stored in the flexible mounting being transferrable to the hydraulic fluid in a manner somewhat analagous to the operation of a hydraulic accumulator.

According to the present invention a fluid power operated tool comprises a cylinder body axially slideable within a frame, a main cylinder formed in the cylinder body, a main piston reciprocable in the main cylinder under the control of a cyclically varying fluid pressure acting in a space within the main cylinder and bounded by one face of the main piston, bias means opposing the action of the said fluid on the main piston, and a reservoir formed between a surface carried on the cylinder body and a surface carried on the frame, the reservoir communicating with the said space and the arrangement being such that the rearward motion of the cylinder body which occurs upon advance of the main piston causes a change in the volume of the reservoir which bears an inverse relationship with the volume of the said space.

By way of example only, two embodiments of the invention will now be described with reference to Figures 1 and 2 of the drawings filed with the Provisional Specification which are, respectively, schematic sectional views of alternative hydraulic drive system for an impactor hammer.

With reference to Figure 1, a main piston 1 is reciprocable within a main cylinder 26 in a cylinder body 2 under the action of alternately high and low hydraulic fluid pressure against a large rear face 4 of the main piston. A volume of gas is retained in the space forward of piston 1 within cylinder 2, to act as a gas spring against a smaller annular front face 6 of the piston, to provide a bias force retracting the piston after it advances under the action of high pressure on the face 4. It will be appreciated that any means such as coil springs, or a constant high pressure bias could be employed to provide the bias force without departing from the invention.

On each advance a forward extension of the main piston is arranged to strike and drive forward an impactor hammer 5 slidably mounted in a sleeve 7; switches (not shown) may be incorporated into the cylinder according to any known arrangement to control fluid connections to a valve 3 through which fluid to the face 4 is arranged to flow.

The valve 3 communicates at its rear end with a secondary cylinder 12 in which a secondary piston 8 is slideable; the piston 8 is rigidly mounted on a frame 9 to the front end of which the sleeve 7 is also rigidly mounted. The body 2 is slideable within a recess 25 in the sleeve 7 coaxial with the body and the cylinder 12, the axial static equilibrium position of the body being determined by the balance of the hydraulic fluid pressure within the cylinder 12 acting against the end face of the cylinder 12, and the force of springs located within the recess 25 and around the forward extension of piston 1.

The cycle of operation is as follows. With the piston 1 in a retracted position, valve 3 is operated so as to connect a high pressure hydraulic fluid supply to cylinder 26, through cylinder 12. High pressure fluid admitted to cylinder 26 urges piston 1 rapidly forward to impact against the hammer 5, and at the same time urges cylinder body rearward. Rearward motion of the cylinder body 2 relative to frame 9 is encouraged by the release of compression in the springs 10. This motion simultaneously results in the advance of piston 8 relative to cylinder 12, hence transferring additional hydraulic fluid at high pressure into cylinder 26 and alleviating the pressure drop occasioned in the high pressure supply by admission of fluid to cylinder 26.

At an appropriate instant during the forward travel of the piston 1, the valve 3 is operated to shut off the supply of high pressure fluid to the cylinder 26, and to connect the cylinder 26 instead with a supply of low pressure hydraulic fluid. The net force acting on the piston 1 is thus at this instant switched to a rearward direction, whilst an equal and opposite pressure force now urges the cylinder body 2 forwards against the action of springs 10 which are thereby compressed again.

At an appropriate instant during retraction of the piston 1, the valve 3 is again operated to connect the high pressure hydraulic supply to the cylinder 26, and the cycle repeats itself.

It will thus be seen that energy which is inevitably transferred to cylinder body 2 during driving of the main piston, instead of being dissipated by impacting the body 2 on the frame 9, is largely put to useful effect. Thus, kinetic energy inherent in rearward motion of the cylinder body 2 is employed through the medium of piston 8 and cylinder 12, to provide an additional flow of high pressure hydraulic fluid when required to drive piston 1 forwards, hence minimising surges and consequent pressure drops in the high pressure fluid supply. The kinetic energy acquired by the body 2 during the part of the cycle when it moves forward is stored as potential energy by compression of springs 10.This potential energy is then returned as kinetic energy to the body 2 during its subsequent rearward movement, and is thus harnessed to assist the action of piston 8 and cylinder 12 in reducing pressure surges etc.

Thus, not only is the harmful energy dissipation by repetitive impacting of body 2 on frame 9 minimised, but the energy is put to useful effect so that a more efficient operation of the tool results.

The embodiment illustrated in Figure 2 operates in a similar way to that of Figure 1. This embodiment comprises a cylinder body 27 having a main cylinder 15 formed therein in which a main piston 13 having a forward extension 31 is reciprocable to strike repeatedly against and drive forward an impactor hammer. The body 27 is slideable axially relative to a frame 29 which may, for example, be rigidly mounted on a vehicle. The body 27 is slideable within the frame 29 in a coaxial cylindrical recess 28 formed in the rear part of the frame, and a further coaxial cylindrical recess 30 in the forward part of the frame. A plurality of compression springs 23 are retained between the end of the recess 28 and the rear end of body 27, and an annular cavity 21 is formed between the wall of the forward recess 30 and a forward extension of the cylinder body 27.Seals are provided on each side of the cavity 21 so that the cylinder body 27 and the wall of the forward recess 30 co-operate in this region to form a secondary piston and a secondary cylinder.

In use of this embodiment, a volume of gas at high pressure is retained in the cylinder 15 to the rear of the piston 13, to act as a gas spring which maintains a continuous biasing force on the rear face 16 of the piston, constantly urging the piston forward. Fluid at high or low pressure can be admitted to annular space 17 in front of the piston 13 under the control of a valve 19, to supply high or low pressure fluid at the forward face 18 of the piston. The valve 19 communicates through a flexible wide bore pipe 20 with the annular cavity 21, which in turn communicates with a source of low pressure hydraulic fluid through a supply line 22. A source of high pressure fluid also communicates with valve 19 through means not shown.

The cycle of operation of this embodiment is as follows. With the main piston 13 in a retracted position, the valve 19 is switched so that the low pressure fluid supply communicates through cavity 21 and pipe 20 with annular space 17. The piston 13 is accordingly urged forward to impact the hammer, under the action of high pressure on its face 16, and the cylinder body 27 is simultaneously urged rearward against the cushioning action of springs 28 and to enlarge the cavity 21. Low pressure fluid ejected from annular space 17 thus passes through wide bore pipe 20 into the expanding cavity 21, so that only a relatively small volume of fluid is ultimately ejected through the low pressure line 22, during the power stroke of the piston 13, and pressure surges are hence reduced considerably. At an appropriate point in the forward travel of the piston 13, the valve 19 is switched to supply high pressure fluid to annular space 17, but not to cavity 21 so that the high pressure acts on the forward face 18 of the piston. The pressure is such as to overcome the effect of high pressure in cylinder 15, so that piston 13 is now urged rearwards, whilst the cylinder body is urged forwards.

At an appropriate instant during retraction of the piston 13, the valve 19 is again switched to connect space 17 with the low pressure supply, and the cycle repeats.

As will be apparent, modifications can be made to this embodiment also without departing from the scope of the invention.

For example, the continuous forward bias force on the piston 13 could be provided by a coil spring or by constantly supplying high pressure fluid to the volume 15, instead of the gas spring arrangement described.

Either embodiment could be constructed to be driven either hydraulically or pneumatically, ie with either liquid or gas as the working fluid supplied to control movement of the main piston.

WHAT I CLAIM TS: 1. A fluid power operated tool comprising a cylinder body axially slideable within a frame, a main cylinder formed in the cylinder body, a main piston reciprocable in the main cylinder under the control of a cyclically varying fluid pressure acting in a space within the main cylinder and bounded by one face of the main piston, bias means opposing the action of the said fluid on the main piston, and a reservoir formed between a surface carried on the cylinder body and a surface carried on the frame, the reservoir communicating with the said space and the arrangement being such that the rearward motion of the cylinder body which occurs upon advance of the main piston causes a change in the volume of the reservoir which bears an inverse relationship with the volume of the said space.

2. A fluid power operated tool according to claim 1 wherein the said surface carried on the cylinder body and the said surface carried on the frame form a sliding seal and co-operate as a secondary piston and a secondary cylinder.

3. A fluid power operated tool according to claim 1 or claim 2 wherein the said space is formed to the rear of the main piston, the arrangement being such that advance of the main piston and consequent rearward motion of the cylinder body results in a reduction in the volume of the said reservoir and an increase in the volume of the said space.

4. A fluid power operated tool according to claim 3 wherein the bias means comprises a quantity of gas sealed within a space bounded by a forward face of the main piston and by the cylinder body.

5. A fluid power operated tool according to claim 3 or claim 4, and including resilient means which can resiliently oppose forward motion of the cylinder body relative to the frame.

6. A fluid power operated tool according to claim 1 or claim 2 wherein the said space is formed to the front of the main piston, the arrangement being such that advance of the main piston and consequent rearward motion of the cylinder body results in an increase in the volume of the reservoir and a reduction in the volume of the said space.

7. A fluid power operated tool according to claim 6 wherein the bias means comprises a quantity of gas sealed within a space bounded by a rearward face of the main piston and by the cylinder body.

8. A fluid power operated tool according to claim 6 or claim 7, and including resilient means which can resiliently oppose rearward motion of the cylinder body relative to the frame.

9. A fluid power operated tool substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the drawings filed with the Provisional Specification.

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

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. supply high pressure fluid to annular space 17, but not to cavity 21 so that the high pressure acts on the forward face 18 of the piston. The pressure is such as to overcome the effect of high pressure in cylinder 15, so that piston 13 is now urged rearwards, whilst the cylinder body is urged forwards. At an appropriate instant during retraction of the piston 13, the valve 19 is again switched to connect space 17 with the low pressure supply, and the cycle repeats. As will be apparent, modifications can be made to this embodiment also without departing from the scope of the invention. For example, the continuous forward bias force on the piston 13 could be provided by a coil spring or by constantly supplying high pressure fluid to the volume 15, instead of the gas spring arrangement described. Either embodiment could be constructed to be driven either hydraulically or pneumatically, ie with either liquid or gas as the working fluid supplied to control movement of the main piston. WHAT I CLAIM TS:

1. A fluid power operated tool comprising a cylinder body axially slideable within a frame, a main cylinder formed in the cylinder body, a main piston reciprocable in the main cylinder under the control of a cyclically varying fluid pressure acting in a space within the main cylinder and bounded by one face of the main piston, bias means opposing the action of the said fluid on the main piston, and a reservoir formed between a surface carried on the cylinder body and a surface carried on the frame, the reservoir communicating with the said space and the arrangement being such that the rearward motion of the cylinder body which occurs upon advance of the main piston causes a change in the volume of the reservoir which bears an inverse relationship with the volume of the said space.

2. A fluid power operated tool according to claim 1 wherein the said surface carried on the cylinder body and the said surface carried on the frame form a sliding seal and co-operate as a secondary piston and a secondary cylinder.

3. A fluid power operated tool according to claim 1 or claim 2 wherein the said space is formed to the rear of the main piston, the arrangement being such that advance of the main piston and consequent rearward motion of the cylinder body results in a reduction in the volume of the said reservoir and an increase in the volume of the said space.

4. A fluid power operated tool according to claim 3 wherein the bias means comprises a quantity of gas sealed within a space bounded by a forward face of the main piston and by the cylinder body.

5. A fluid power operated tool according to claim 3 or claim 4, and including resilient means which can resiliently oppose forward motion of the cylinder body relative to the frame.

6. A fluid power operated tool according to claim 1 or claim 2 wherein the said space is formed to the front of the main piston, the arrangement being such that advance of the main piston and consequent rearward motion of the cylinder body results in an increase in the volume of the reservoir and a reduction in the volume of the said space.

7. A fluid power operated tool according to claim 6 wherein the bias means comprises a quantity of gas sealed within a space bounded by a rearward face of the main piston and by the cylinder body.

8. A fluid power operated tool according to claim 6 or claim 7, and including resilient means which can resiliently oppose rearward motion of the cylinder body relative to the frame.

9. A fluid power operated tool substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the drawings filed with the Provisional Specification.