GB2070692A - Improvements in or relating to power tools - Google Patents

Abstract

The invention proposes a drive apparatus for a fluid actuated power tool 31 comprising a control unit including a pressure fluid driving circuit, a pressure fluid driven circuit isolated from said driving circuit and connectable to a power tool, and a pressure varying device 11 driven by pressure fluid in said driving circuit to maintain a fluid pressure and flow rate in said driven circuit suited to effective drive of the tool. The pressure varying device conveniently comprises a piston and cylinder arrangement 11, 12, reciprocated by the driving circuit, and a piston and cylinder arrangement 22, 21 driving the driven circuit, the two pistons being linked for mutual displacement and the bores of the cylinders being of different diameters. The control unit can be driven by any available fluid power source to deliver to a fluid actuated tool a tool operating fluid at a pressure and flow rate suited to the tool. <IMAGE>

Description

SPECIFICATION Improvements in or relating to power tools This invention relates to power tools, that is to say tools actuated by a power source, such as a prime mover mounted on the tool or a pressure fluid supply to the tool.

Power tools are well known in the art and are available for a wide variety of uses but a difficulty with such tools resides in the limitations imposed by the power sources available therefore. Thus, and by way of examples, pneumatically operated tools must be designed for actuation by the pressures obtainable from commercially available compressors, electrically operated tools must be designed for drive by one of the standard drive electric motors commercially available and, thereby, the practice has been to design a power tool for actuation by a given commercially available power source rather than by a power source most suited for the tool.

A further difficulty with conventional power tools resides in the fact that because such tools are designed to be operated by a predetermined available power source it is essential to supply the tool with an individual power source even locations where an alternative power source is available and this requirement imposes severe restrictions on the use of the tools in special locations, such as in mines.

The present invention seeks to provide a control apparatus for a pressure fluid actuated power tool and whereby the pressure fluid circuit for the tool can be driven from any locally available fluid pressure supply.

According to the present invention there is provided a drive apparatus for a fluid actuated power tool comprising a control unit including a pressure fluid driving circuit, a pressure fluid driven circuit isolated from said driving circuit and connectable to the power tool, and a pressure varying device arranged to be driven by pressure fluid in said driving circuit and to maintain a fluid pressure and flow rate in said driven circuit suited to effective drive of the tool.

The invention further envisages a drive ap paratus in combination with a fluid actuated power tool, said drive apparatus comprising a control unit including a driving circuit, a driven circuit, isolated from said driving circuit, connected to the fluid drive for the tool, and a pressure varying device arranged to be driven by pressure fluid in said driving circuit to generate in said driven circuit a pressure fluid supply effective to drive the tool.

It will now be seen that by the combination proposed by the present invention a fluid pressure actuated power tool can be supplied with a pressure fluid most suited to operation of the tool from virtually any available fluid pressure source differing in pressure or flow rate from the pressure and flow rate desired for effective operation of the tool.

Preferably said driving and driven circuits are of the same type, that is to say both circuits are pneumatic or, more preferably, hydraulic.

Preferably said drive apparatus comprises a piston and cylinder arrangement forming part of the driving circuit with a valve arrangement for ducting driving pressure fluid to and from said piston and cylinder arrangement to effect reciprocation of the piston within the cylinder.

Preferably said drive apparatus includes a piston and cylinder arrangement forming part of the driven circuit and said piston, when reciprocated within the cylinder, serves to supply pressure fluid to the tool circuit.

Preferably said two piston and cylinder arrangements are in axial alignment and the two pistons are rigidly linked together for mutual displacement whereupon, when the piston of the driving circuit is reciprocated by the driving pressure fluid, the piston of the driven circuit is reciprocated to deliver driving pressure fluid to the tool.

Preferably the driven circuit includes an accumulator.

In a preferred embodiment in accordance with the invention the cylinder of the driven circuit is supplied with hydraulic fluid from a reservoir and pressure fluid from said cylinder is directed to an accumulator which supplies pressure fluid, as and when required, at the desired pressure and flow rate to effect tool actuation and, conveniently, said driven circuit includes a by-pass duct back to the reservoir via a pressure relief valve.

Whilst many tools require an actuating fluid at a pressure in excess of atmosphere it is possible to actuate other tools by a driven circuit fluid pressure less than atmospheric pressure. Further, when the driving circuit is required to reciprocate a double acting piston and cylinder arrangement such reciprocation may be obtained from a fluid supply at a pressure less than atmosphere. Thus, in this specification, the term "pressure fluid" means a fluid at a pressure above or below but different from atmosphere pressure.

The invention will be described further by way of example with reference to the accompanying drawings in which the single figure shows, diagrammatically, one drive arrangement for a power tool in accordance with the invention.

In the illustrated example a cylinder 11, with a piston head 1 2 slidably disposed therein, has hydraulic fluid supplied to, and exhausted from, its ends by ducts 1 3 and 1 4 in dependence upon the setting of a four-way valve 1 5. Valve 1 5 receives pressure fluid via a duct 16, including an on/off valve 1 7 and a pressure adjusting valve 18, from a pressure fluid ring main 19.With such an arrangement the valve 15, in one position, allows fluid flow from ring main 1 9 via duct 1 6 and through valves 1 7 and 1 8 to duct 1 3 for discharge into the left hand side of the cylinder 11 (as viewed in the figure) whilst valve 1 5 is ducting hydraulic fluid from duct 14 to an exhaust duct 20, whereby the pressure difference on the two radial faces of piston head 12 will cause the piston head 1 2 to be displaced towards the right as viewed in the figure.By reversing the position of valve 1 5 duct 1 3 is in open communication with exhaust duct 20 and duct 14 is connected with the pressure fluid supply from duct 1 6 so that the piston head 1 2 moves towards the left as viewed in the figure.

The piston and cylinder arrangement 11, 1 2 is thus double acting acting and the arrangement 11 to 20 inclusive comprises a driving circuit, adapted to reciprocate piston head 1 2 in cylinder 11 in accordance with the switching programme applied to valve 1 5.

A cylinder 21, co-axially arranged with respect to cylinder 11, has a piston head 22 slidably disposed therein and piston head 22 is rigidly linked for mutual displacement, with piston 1 2 by a piston rod 23. When piston head 22 is displaced towards the right (as viewed in the figure) hydraulic fluid is drawn from a reservoir 24 via a duct 25, including a one-way valve 26, which communicates with a duct 27 opening to the cylinder 21 so that the right hand side of cylinder 21 is charged with fluid. When the piston head 22 is displaced towards the left (as viewed in the figure) valve 26 closes and hydraulic fluid is displaced from cylinder 21 via the duct 27 and through a pressure relief valve 28 to an accumulator 29 which extends a constant fluid pressure via its outlet duct 30 to a tool 31.Tool 31 exhausts hydraulic fluid via a duct 32, which extends to the reservoir 24. As the piston head 22 is rigidily linked to piston head 12, and is displaced therewith, the arrangement 21 to 32 defines a driven fluid circuit, including the tool 31.

It will be observed that in the illustrated example the cross-sectional area of the cylinder 11 is many times greater than the crosssectional area of the cylinder 21 and, thereby, the pressure of the fluid delivered from the cylinder 21 may be many times greater than the fluid pressure at the ring main 1 9.

With the illustrated system the pressure fluid from cylinder 21 discharges to the accumulator 29, which thereby affords a constant supply of hydraulic fluid for driving the tool 31. In some arrangements the working pressure from accumulator 29 relative to the pressure in ring main 1 9 may be such that once the accumulator 29 is fully charged an hydraulic lock will occur in the piston and cylinder arrangements 11, 12 and 21, 22 but in other arrangements it is advantageous to have a pressure relief duct 33, with a pressure relief valve 34 therein, in communication with duct 27, between cylinder 21 and valve 28, and the reservoir 24 so that, with accumulator 29 topped up and the piston and cylinder arrangements 11, 12 and 21, 22 actuating, excess hydraulic fluid from cylinder 21 is ducted back to reservoir 24.

The tool 31 may comprise any tool effecting a rotary movement, such as is required for a drill, or a reciprocating movement, suchtas is required for a hammering, chiselling, shearing, cropping, riveting, or jacking operations.

When the tool is to be used continuously, as for drilling, the accumulator 29 is most advantageous but for reciprocating tools, which may only perform intermittently and require only a small volume of pressure fluid for actuation, the accumulator 29 may be omitted from the driven circuit.

The on-off valve 1 7 may include a connection by which the control apparatus may be removed from the connection with ring main 19, valve 1 7 being closed, and by providing a plurality of ducts 16, each with an on-off valve 1 7 and a connection thereto, spaced along the ring main 1 9 the control apparatus, and the tool, can be selectively connected to any one of the outlets 16/17 along tiering main 1 9. At the same time, of course, a number of tools, each having its control apparatus, can be connected to the ring main 19, each control apparatus being attached to an outlet 16/17 individual thereto, and, subject to the output of the driven circuit being adequate, a number of tools 31 can be driven from the same control apparatus.

Whilst in the above described embodiment the pressure fluid supplied by ring main 1 9 and the pressure fluid of the driven circuit are both hydraulic fluids it will be appreciated that the apparatus will work effectively when the ring main 1 9 supplies pressure air, whereupon the system 11 to 20 will be a pneumatic system and, for many types of tool 31, the driven circuit may also be a pneumatic circuit.

Further, whilst the arrangement 11 to 20 of the specific embodiment has been described as actuated by hydraulic pressure fluid, the driving circuit 11 to 20 inclusive can be worked by a low pressure air supply (less than atmospheric pressure) from ring main 19, in which case when one side of the cylinder .11 is in open communication with the low pressure supply in duct 1 9 the other end of the cylinder 11 will be open to atmosphere whereupon the atmosphere side of the cylinder 11 will comprise the driving side for displacing the piston 1 2.

Thus, whilst the present invention has been described by way of example with reference to a specific embodiment the invention is not restricted thereto and many modifications and variations will be apparent to persons skilled in the art and, by way of example, it will be appreciated that when the tool 31 is a simple reciprocating tool worked by a single acting piston and cylinder arrangement the driven circuit may be limited to the piston and cylinder arrangement 21, 22, the piston and cylinder arrangement in tool 31, and a single fluid line between cylinder 21 and the cylinder of the tool 31.

Claims (11)

1. A drive apparatus, for a fluid actuated power tool, comprising a control unit including a pressure fluid driving circuit, a pressure fluid driven circuit isolated from said driving circuit and connectable to a power tool, and a pressure varying device arranged to be driven by pressure fluid in said driving circuit and to maintain a fluid pressure and flow rate in said driven circuit suited to effective drive of the tool.

2. A drive apparatus as claimed in claim 1 in which said driving and driven circuits are both hydraulic or pneumatic.

3. A drive apparatus as claimed in claim 1 or 2 in which the pressure varying device includes a piston and cylinder arrangement and said driving circuit includes a valve arrangement for ducting driving pressure fluid to and from said piston and cylinder arrangement to effect reciprocation of the piston within the cylinder.

4. A drive apparatus as claimed in claim 3 in which said piston and cylinder arrangement is double acting.

5. A drive apparatus as claimed in claim 3 or 4 in which the pressure varying device includes a piston and cylinder arrangement forming part of the driven circuit and said piston, when reciprocated within the cylinder, serves to supply pressure fluid to the tool.

6. A drive apparatus as claimed in claim 5 in which said piston and cylinder arrangement is single acting.

7. A drive apparatus as claimed in claim 5 or 6 in which the piston of said two piston and cylinder arrangements are linked for mutual displacement.

8. A drive apparatus as claimed in claim 7 in which said cylinders are in axial alignment and the two pistons are rigidly linked together by a common piston rod.

9. A drive apparatus as claimed in claim 5, 6, 7 or 8 in which the bores of the cylinders are of different diameters.

10. A drive apparatus as claimed in any preceeding claim in which the driven circuit includes an accumulator.

11. A drive apparatus as claimed in claim 5, 6, 7, 8, 9 or 10 in which the cylinder of the driven circuit is supplied with hydraulic fluid from a reservoir and wherein said driven circuit includes a by-pass duct, between the said cylinder and the tool, back to the reservoir via a pressure relief valve.

1 2. A drive apparatus as claimed in any preceding claim in which the fluid pressure in the driving circuit is always in excess of atmospheric pressure.

1 3. A drive apparatus as claimed in any preceeding claim in combination with a fluid actuated power tool.

1 4. A drive apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.