GB2135021A - Rectangular piston for pneumatic vibrator - Google Patents

Abstract

A piston and working chamber arrangement, for example for a pneumatically operated vibrator, wherein the working chamber (11a, 11b) is rectangular in cross-section over at least that part of its axial length along which a piston (20) of corresponding cross-section is disposed to slide. <IMAGE>

Description

SPECIFICATION Piston and working chamber arrangement This invention relates to a piston and working chamber arrangement.

Previously, such pistons and working chambers have been of a cylindrical construction, the piston being a close fit with the wall bounding the working chamber, and/or being provided with circular piston rings to effect good seal with said boundary wall. It has been convenient to provide the working chamber by drilling the chamber in a solid block, or enlarging a preformed opening in a solid block by drilling.

However, such cylindrical piston and working chamber arrangements are not efficient for their external size. The working force developed by the piston due to the pressure exerted on a working end face of the piston by-a working fluid, such as pressurised air, expanding combustion gases, or other pressurised fluid, such as hydraulic fluid, depends on the cross-sectional area of the working end force, and the pressure of the working fluid. To increase the working force for a given working fluid pressure, it is this necessary to increase the diameter of the piston, which increases the external size of the arrangement in all directions. This is disadvantageous where size is restricted.

Accordingly, it is one object of the invention to provide a new or improved piston and working chamber arrangement.

According to one aspect of the invention, we provide a piston and working chamber arrangement wherein the working chamber is rectangular in cross-section over at least that part of its axial length along which a piston of corresponding cross-section is disposed to slide.

It has been found that the force developed by a rectangular piston for a given working fluid pressure and external size of such an arrangement is considerably improved because the cross-sectional area of the working end face of the piston on which the working fluid acts is increased, compared with a cylindrical piston and working chamber arrangement of corresponding external size. Thus the external size of the arrangement according to the invention may be decreased compared with known arrangements, without any loss of working force.

For example, for a cylindrical piston having a round working end face with a diameter of one inch, the cross-sectional area of the working end of the piston is 0.7854 square inches. Thus, for a pressure of 201bs per square inch on the working end face, the force developed by the piston is 1 5.701bs.

For a square piston of one inch size, the area of the working end of the piston is one square inch, and thus for the same pressure, i.e. 201bs per square inch, the force developed by the square piston would be 201bs, which is an improvement in developed working force of approximately 27%.

The cross-section of the working chamber may be square, where space permits, wherein all sides of the rectangle are of the same length, but if required the pairs of sides of the rectangle may be of differing lengths so that the width and breadth of the piston and working chamber are different. Thus the piston and working chamber arrangement may be used in applications in which there is only limited space in one dimension available. For example, where only a limited width is available, the breadth of the arrangement may be increased to give the piston the required cross-sectional area of end working face to develop a desired working force. This would not of course be possible with known cylindrical piston and working chamber arrangements which are restricted by their round shape.

Preferably, the sides of the working chamber are provided by plate members connected together by any desired means, at least one of the open ends of the construction being closed by an end cap, to provide a substantially fluid-tight working chamber at that end, with an inlet and outlet for working fluid provided where required. For example, the plate members, and cap or caps may be connected together by bolts or other fasteners, or the plates may be merely clamped together by an outer casing surrounding the plates.

The invention is particularly applicable to a vibratory device of the kind operated by fluid pressure, and more particularly to such a device of the free piston type, i.e. wherein a piston is free to oscillate in a working chamber along an axial path under the pressure of fluid acting on a working end face of the piston, to cause a vibration.

In this case, where plate members are connected together to provide the sides of the working chamber, an end cap may be provided at the other end also so that first and second working chambers are provided, one at either end of the piston, the piston having two end working faces on which the working fluid acts.

Preferably, the side plate members which form the sides of the working chambers provide a bearing sleeve located within a casing, with which bearing sleeve the piston co-operates, and the end caps may provide end parts of the casing.

The bearing sleeve and the casing may together define at least one passageway therebetween, into which passageway coolant may be passed to cool the device during operation.

The coolant may comprise the working fluid, although if required, an alternative, separate coolant may be provided.

The working fluid may pass into such a passageway prior to inlet into a working chamber, i.e. prior to use to move the piston, and/or the working fluid may pass into the passageway prior to outlet from the device, i.e. subsequent to use in moving the piston.

Of course, where inlet and outlet working fluid is used as a coolant, the inlet fluid would flow in a different passageway or passageways to the outlet fluid.

Preferably, a plurality of outlet openings are provided in the bearing sleeve for the outlet of pressurised fluid at the end of the piston stroke, the openings being positioned so that at the end of the piston stroke in each direction, fluid may pass from the working chamber into said at least one coolant passageway.

The casing may be provided with at least one outlet port spaced from the outlet openings of the bearing sleeve so that the coolant is caused to flow around the bearing sleeve in the passageway, before passing from the device through the outlet port. Thus, optimum cooling is achieved.

It will be appreciated that the pressurised working fluid, as it passes into the passageway, will undergo an expansion because the pressure will decrease, which expansion will produce a cooling effect. Thus the passageway or passageways acts as a condensing chamber.

Preferably, an inlet opening is provided in the bearing sleeve which is connected to a source of pressurised working fluid via an inlet port of the vibratory device, and the piston may have two ducts, one of which extends from a first aperture in a side of the piston to one working end face of the piston, and the second duct, from a second aperture in the side of the piston to the other working end face, the first and second apertures being positioned so that as the piston oscillates, the apertures are each in turn moved into and out of alignment with the inlet opening of the bearing sleeve.These openings, and the outlet opening or openings may be arranged so that as the piston is moved by fluid entering the first working chamber the outlet opening or openings of the second working chamber are not blocked by the piston, and as the piston reaches the end of its stroke, said first aperture is blocked and the second aperture opened, whilst the outlet openings of the first working chamber are opened and the outlet openings of the second working chamber are closed, whereby fluid enters the second working chamber to move said piston in an opposite direction. Thus the piston oscillates.

Preferably, said inlet opening is in one side of the working chamber and outlet openings are provided for each working chamber in each of the remaining three sides of the working chamber.

It has been found that in such an arrangement, the wear which can occur by outrushing fluid around the outlet openings, is considerably reduced because of the presence of more than one opening relatively spaced from one another. Generally in such a vibratory device, the fluid flow characteristics through the vibratory device are improved compared with known vibrators, such as described in Patent No. 1,452,888, turbulence and degra- dation of air pressure which can reduce the working force developed by the vibratory device and the frequency of the vibrations, being minimised.

The invention will now be described with the aid of the accompanying drawings, in which: Figure 1 is a side view through a pneumatic vibratory device embodying the invention, showing the walls bounding a working chamber in section; Figure 2 is a plan view of the vibratory device of Fig. 1 with an end cap removed; Figures 3, 4 and 5 are views of one side, the end and the opposite side of the piston respectively of the vibratory device of Figs. 1 and 2; Figure 6 is an end view of the vibratory device of Figs. 1 and 2 with the piston and end caps removed.

Referring to the drawings, a vibratory device 10 has first and second working chambers 11 a, 11 b defined by four side walls 12, 13, 14 and 15, which side walls comprise plate members which provide a bearing sleeve 16, and an end cap 1 7 to close the upper end of the bearing sleeve 1 6 to provide an end wall for the first working chamber 11 a, and also comprises an upper casing part, and an end cap 1 8 to close an opposite end of the bearing sleeve 1 6 to provide an end wall for the second working chamber 11 b, and which cap 1 8 also provides a base which extends outwardly of the device 10 and has apertures 1 9 to enable the vibratory device to be secured to, for example, a conveyor or other apparatus to which it is desired to impart a vibration. Of course any other securing means may be provided to enable the vibratory device 10 to be secured to an apparatus for use.

A piston 20 is disposed to freely oscillate in the bearing sleeve 1 6 under the power of pressurised air, as hereinafter described. As shown in Fig. 1, the piston 20 is in a midway position moving from left to right.

It can be seen that the working chambers 11a, 11bdefined by the walls 12, 13, 14 and 1 5 and end caps 1 7 and 18, which are in the present example connected together by bolts 21, are both square in cross-section over their entire lengths, and that the piston 20 is of corresponding section. Thus the sides of the piston 20 co-operate with the plate members 12, 13, 14 and 1 5 during slide movement.

The plate members 12, 13, 14 and 1 5 are in sealing engagement with one another, and the end caps 18, 1 9. If necessary, an adhe sive or other jointing compound may be used to ensure good sealing.

Surrounding the bearing sleeve 16 is a casing 22 of which the end caps 1 7 and 18 form a part, the casing 22 otherwise having side walls 23, 24, 25 and ?6 surrounding the bearing sleeve 16.

Although as described, the parts of the bearing sleeve are connected together by bolts 21, if desired plate members 12, 13, 14 and 1 5 could be secured in any other way, for example they may merely be clamped together by the surrounding casing 22 particularly where the mating surfaces are a precision fit.

It can be seen that the plate members 12, 13, 14 and 15 each have bosses 28 with which the bolts 21 engage, the bosses 28 also having the effect of spacing the members 12, 13, 14 and 15 from the side walls 23, 24, 25 and 26 of the casing. Thus four passageways 30, 31, 32 and 33 are formed between the plate members and side walls 12, 26; 13, 23; 14, 24; 15, 25 respectively, the passageways 30 and 32 communicating with passageway 33 via one of two communication ducts 34, 35.

To enable pressurised air to be fed into the working chambers 11 a, 11 b, the side wall 23 of the casing 22 has an inlet port 36 which opens into passageway 31, and the plate member 1 3 of the bearing sleeve 1 6 has an aligned inlet opening 37.

The piston 20 has first and second ducts 38, 39 to convey the air from opening 37 to the first 11 a and second 11 b working chambers respectively.

The first duct 38 extends from a first aperture 40 in a side 43 of the piston 20. to a first working end face 41 thereof, whilst the second duct 39 extends from a second aperture 42 in the piston side 43 axially spaced from the first aperture 40, to an opposite second end working face 45 of the piston 20.

The ducts 38 and 39 are L-shaped, each having an axially extending portion and a radially extending portion. The radial portions are each inclined at an angle to a transverse plane perpendicular to the axial portions but in opposite directions.

To enable pressurised air to pass from the vibrator device 10, the wall 26 of the casing 22 is provided with a single outlet port 50 in the same axial plane as the inlet port 36, so that air in each of the communicating passageways 30, 32 and 33 can pass from the device through the port 50.

The plate members 12, 14, and 1 5 each have two outlet openings, one associated with each working chamber 11 a, 11 b. Thus in all, working chamber 11 a has three outlet openings 51 a, 52a and 53a and working chamber 11 b has three outlet openings 51 b, 52b and 53b. Each of the outlet openings enable air to exhaust from the working chamber 11 a, 11 b into the passageways 30 or 32 or 33.

The inlet opening 37 of plate member 13, apertures 40 and 42 of the piston 20, the axial length of the piston (which in the example described is equal to the width and breadth of the piston so that the piston is cubic), and the outlet openings 51 a, 52a, 53a; 51 b, 52b, 53b are all arranged to enable the following sequence of operation to be achieved, whereby the piston oscillates in the bearing sleeve 1 6.

Operation of the Vibratory Device Commencing with the piston moving from left to right, as seen in Fig. 1, pressurised air from port 36 enters passageway 31 and passes into opening 37. From there, the air is directed via first aperture 40 in the piston 20 and duct 38 to the first working chamber 11 a, to act on the end working face 41 of the chamber 11 a to move the piston to the right.

The second aperture 42 of the piston side wall is closed due to the misalignment of the aperture 42 and the inlet opening 37, by the plate member 1 3 of the bearing sleeve 1 6.

The outlet openings 51 b, 52b and 53b from the second working chamber 11 b are open and thus air may freely exhaust from chamber 11 b into passageways 30, 32 and 33 respectively, flow around the bearing sleeve 1 6 and pass from the device through outlet port 50.

However, as the piston reaches the end of its left to right stroke, the openings 51 b, 52b and 53b will become blocked by the piston 20 and thus further movement of the piston will be resisted by a cushion of air within the chamber 11 b.

Furthermore, the first aperture 40 of the piston will become misaligned with opening 37 and is thus blocked by the plate member 1 3 of the bearing sleeve 16, whilst the second aperture 42 will become aligned with the inlet opening 37. Thus air will be directed to the second working chamber 11 b whilst the flow of air into the first working chamber 11 a will be arrested. Also, the outlet openings 51 a, 52a and 53a of working chamber 11 a will become opened and thus during the return stroke, whilst air in chamber 11 b acts on the working end face 45 of the piston 20, air is freely exhausted from chamber 11 a via openings 51 a, 52a, 53a into passageways 30732 and 33 respectively and hence to outlet port 50 of the casing.

At the end of the right to left stroke, the openings 51 a, 52a, 53a will be closed by the piston 20 so that movement of the piston is arrested on a cushion of air within the chamber 11 a and second aperture 42 is again closed due to misalignment of the aperture 42 and the inlet opening 37, whilst the first aperture becomes again aligned with the inlet opening 37, and openings 51 b, 52b and 53b are again opened so that the piston again moves from the left to right and so on. Thus the piston 20 oscillates in the bearing sleeve 16.

Due to the mass of the piston 20, this movement will impart a vibration from the vibrator to any apparatus to which the vibratory device is connected, along an axial path along which the piston oscillates.

The strength of the vibration will depend on the frequency of vibration which in turn depends on the air pressure applied to the vibratory device 10 and the mass and hence inertia of the piston 20.

In a pneumatic vibrator, it is not essential for there to be a very close tolerance fit between the piston 20 and walls of the working chamber, as in for example a piston and working chamber arrangement in an internal combustion engine. It is preferred for there to be a small gap in the present example, so that lubrication between the piston sides and working chamber wall of the vibratory device will only need to be minimal, as an air barrier is formed between the two as the piston 20 slides. However, there is a need for some lubrication such a fine oil lubricant which may be mixed with the pressurised air to provide an oil mist lubrication.

Due to the relative movement of the piston 20 and working chamber walls, friction heating occurs. In the present example, the air flowing through passageways 30, 31, 32 and 33 acts as a coolant for the bearing sleeve 1 6. It will be appreciated that as the pressurised air passes out of the working chambers 11 a and 11 b, the air will expand, which expansion will produce a cooling effect in the passageways 30, 32 and 33 which, because of their communication via ducts 34 and 35, together act as a condensing chamber.

In other examples, a separate coolant may be provided for passageways around the bearing sleeve 16, although the arrangement described has been found to be very efficient.

In a variant, a vibratory device similar to device 10 may have two passageways into which inlet air passes, and two passageways into which outlet air passes, or even three inlet passageways and only one outlet passageway, although the arrangement shown in the drawings is preferred.

Although as described, the working chambers 11 a and 11 b are formed by plate members 12, 13, 14 and 15 and end caps 17, 18 which together provide a bearing sleeve 16, if desired any other arrangement may be provided. For example, a separate casing need not be provided but the working chambers 11 a and 11 b may be provided solely by a casing, or in any other construction as required.

The end caps need not be as shown but may be integral with one or more of the sides of the working chamber, or be parts of the bearing sleeve. Other means than apertures 19 could be provided to enable the device to be secured to an apparatus such as a tang or the like.

However, although the square working chamber described may be provided by alternative means, the described construction is preferred because the casing 22 and sleeve 16 can be easily dismantled for maintenance thereby giving the device prolonged life.

It will be appreciated that although the working chamber and piston arrangements described have been of square cross-section, any other rectangular shape could be provided. In some applications it may be preferred to make the working chamber so that opposite pairs of sides are of different lengths, so that a vibrator with a piston of a selected cross-sectional area to develop a selected working force may be used, whilst only a restricted external width/breadth is available.

Thus the piston need not be cubic as in the example described. Furthermore the length of the piston can be longer or smaller than shown, with a corresponding re-arrangement of inlet and outlet openings to provide a piston of the required strength.

Instead of providing a single inlet opening 37 and ducts 38, 39 in the piston 20 as described, to enable air to be fed alternately to working chamber 11 a or 11 b, if desired more than one inlet opening may be provided with a suitable valve arrangement or the like to direct the air to the respective working chamber 11 a or 11 b.

Similarly, the three exhaust openings for each chamber 11 a, 11 b need not be provided, although this is preferred to reduce the wear which can occur at a single outlet opening.

Instead of connecting port 36 to a supply of pressurised air as a working fluid, it will be appreciated that if required a similar construction could be used where the working fluid is another gas, or even a liquid such as a hydraulic fluid, although some modification may be required in the latter case because of the properties of liquids that they do not flow so readily as gases and are not compressible.

In prior cylindrical piston and working chamber arrangements, in a vibratory device 10 of the type in which the piston is free to oscillate in the working chamber, it has not been possible to constrain the piston from rotating about the oscillating axis. Thus it has been necessary to provide a circumferential groove around the piston (or cylinder) into which inlet fluid passes and from which groove the fluid has to search for the ducts or other passage means, which lead to the working end faces of the piston. This searching by the fluid results in turbulence.

In the vibratory device described, because the working chambers 11 a, 11 b are rectangular, e.g. square, turbulence through the device is minimised. This is because the piston is located due to its non-circular shape so that the inlet opening or openings of the bearing sleeve is or are always opposite the inlet port and the inlet fluid is fed axially into the chambers 11 a, 11 b by the ducts in the piston. Thus the fluid does not need to search.

Although the invention has been described with reference to a vibrator device in which a piston is free to oscillate in and between two working chambers, it will be appreciated that the principle of using a rectangular, e.g.

square piston and working chamber, could be applied in any other piston and working chamber arrangement.

For example, only one working chamber may be provided and the piston may be connected via a connecting rod as is well known, to drive a crankshaft or other member. For example, the piston and working chamber arrangement may comprise one of a plurality of such arrangements within a multipiston and working chamber internal combustion engine. In this case, the working fluid would be expanding combustion gases which could be ignited in the working chamber at the end of the piston stroke when compressed by spark ignition as in the case of a petrol engine, or on compression of air as in a diesel engine.

Claims (20)

1. A piston and working chamber arrangement wherein the working chamber is rectangular in cross-section over at least that part of its axial length along which a piston of corresponding cross-section is disposed to slide.

2. An arrangement according to Claim 1 wherein the working chamber is square in cross-section.

3. An arrangement according to Claim 1 wherein the width and breadth of the piston and working chamber are different.

4. An arrangement according to any one of Claims 1 to 3 wherein the sides of the working chamber are provided by plate members connected together, at least one of the open ends of the construction being closed by an end cap, to provide a substantially fluidtight working chamber at that end, with an inlet and outlet for working fluid provided.

5. An arrangement according to any one of Claims 1 to 4 wherein the arrangement is part of a vibratory device of the kind operated by fluid pressure.

6. An arrangement according to Claim 5 wherein the device is of the free piston type having a piston free to oscillate in a working chamber along an axial path under the pressure of fluid acting on a working end face of the piston, to cause a vibration.

7. An arrangement according to any one of Claims 4 to 6 wherein an end cap is provided at the other end also so that first and second working chambers are provided, one at either end of the piston, the piston having two end working faces on which the working fluid acts.

8. An arrangement according to Claim 7 wherein the slide plate members which form the sides of the working chambers provide a bearing sleeve located within a casing, with which bearing sleeve the piston co-operates, the end caps providing end parts of the cas ing.

9. An arrangement according to Claim 8 wherein the bearing sleeve and the casing together define at least one passageway there between for coolant to cool the device during operation.

10. An arrangement according to Claim 9 wherein the coolant comprises the working fluid.

11. An arrangement according to Claim 10 wherein the working fluid passes into the passageway prior to inlet into the or a work ing chamber.

1 2. An arrangement according to Claim 10 wherein the working fluid passes into the passageway prior to outlet from the device.

1 3. An arrangement according to Claim 10 wherein a plurality of outlet openings are provided in the bearing sleeve for the outlet of pressurised fluid at the end of the piston stroke, the openings being positioned so that at the end of the piston stroke in each direc tion, fluid may pass from the working cham ber into said at least one coolant passageway.

14. An arrangement according to Claim 1 3 wherein the casing is provided with at least one outlet port spaced from the outlet openings of the bearing sleeve so that the coolant is caused to flow around the bearing sleeve in the passageway, before passing from the device through the outlet port.

1 5. An arrangement according to any one of Claims 8 to 14 wherein an inlet opening is provided in the bearing sleeve which is con nected to a source of pressurised working fluid via an inlet port of the vibratory device.

1 6. An arrangement according to Claim 1 5 wherein the piston has two ducts, one of which extends from a first aperture in a side of the piston to one working end face of the piston, and the second duct, from a second aperture in the side of the piston to the other working end face, the first and second aper tures being positioned so that as the piston oscillates, the apertures are each in turn moved into and out of alignment with the inlet opening of the bearing sleeve.

1 7. An arrangement according to Claim 1 6 wherein the openings, and the outlet opening or openings are arranged so that as the piston is moved by fluid entering the first working chamber the outlet opening or open ings of the second working chamber are not blocked by the piston, and as the piston reaches the end of its stroke, said first aper ture is blocked and the second aperture opened, whilst the outlet openings of the first working chamber are opened and the outlet openings of the second working chamber are closed, whereby fluid enters the second working chamber to move said piston in an opposite direction.

1 8. An arrangement according to any one of Claims 1 5 to 1 7 wherein said inlet opening is in one side of the working chamber and outlet openings are provided for each working chamber in each of the remaining three sides of the working chamber.

1 9. A piston and working chamber arrangement substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

20. Any novel feature or novel combination of features disclosed herein and/or shown in the accompanying drawings.