Compressors, pumps and fluid motors

DESCRIPTION

This invention relates to compressors, pumps and fluid motors. The invention was originally conceived as a small gas compressor with high volumetric efficiency, but it is also applicable to compressors or pumps (hereinafter referred to simply as compressors) for liquids and to motors driven by fluid pressure. As technology advances there has been an increasing requirement for small compact compressors in many sectors. The computer industry has been seeking small and more efficient cooling systems, the hair styling world is entering into both heating and now cooling to increase longevity of the produced styling. The Peltier module has been utilised in both industries but has performance limitations where the ΔΤ differential is limited to 70°C along the considerable increase in power requirement as greater cooling, or heating performance is required. Conventional refrigeration systems are required to compress the refrigerant gas in order to utilise the compressed and cooled gas to absorb heat at the evaporator stage and therefore provide cooling. The compressor industry has had some difficulty providing a small compressor which is able to provide refrigeration pressures. Most small or so called mini compressors are generally diaphragm type, or in the case of high pressure versions, piston driven diaphragm types. Unfortunately the general size of these still remains too large to be useful in the portable computer industry, or in the portable hair tool industry.

In recent times CPU's have required additional cooling in order for them to either function, or increase their performance, the lack of a powerful cool refrigeration solution having limited performance. These devices include computers, telecommunications relaying equipment, televisions, broadcasting equipment, hairdressing hair straightening irons, hair dryers to mention a few. Most high performance electronics require cooling, sometimes specific components, as well as providing complete air conditioned cabinets. As computer chips have increased in speed so has the heat they exuded in the process. Many CPUs are run below maximum performance having been limited to available cooling capacity. Many manufacturers are therefore seeking to innovate new forms of cooling. The difficulty is that developing a completely new piece of refrigeration technology will take considerable time and will be costly to develop and produce. The computer industry, as well as other industries, requires small efficient cooling systems, at an economical price.

In accordance with a first aspect of the present invention, there is provided a fluid compressor or motor comprising: a structure comprising a tubular wall having a plurality of internal longitudinal dividing walls so as to form a plurality of longitudinal cavities arranged around the inside of the tubular wall; a plurality of pistons each occupying part of the space of a respective one of the cavities and dividing the free space of that cavity into first and second chambers, each piston being mounted for rocking movement relative to the structure so that as the piston rocks in one direction the respective first and second chambers expand and contract, respectively, and as the piston rocks in the opposite direction the respective first and second chambers contract and expand, respectively; a mechanical member mounted so that the mechanical member and the structure can rotate relative to each other; a coupling arrangement operable to transform between (i) rocking movement of the pistons and the structure relative to each other and (ii) rotary movement of the mechanical member and structure relative to each other; a fluid inlet; a fluid outlet; and a valve arrangement to permit fluid (i) to flow from the inlet into each chamber while that chamber is expanding and (ii) to flow from each chamber to the outlet while mat chamber is contracting.

Preferably, each piston has a pair of substantially arcuate side edges with a radius of curvature substantially centred on the rocking axis for that piston; each dividing wall has a pair of substantially arcuate faces each with a radius of curvature substantially centred on the nearmost rocking axis; and the radius of curvature of the side edges of the pistons is substantially equal to and/or slightly less than the radius of curvature of the faces of the dividing walls. This arrangement assists in achieving a good seal between the pistons and dividing walls.

Preferably, each chamber is defined in part by a respective pressure face of the respective piston and a respective pressure portion of the tubular wall; the size and shape of each pressure face of each piston substantially complements the size and shape of the respective pressure portion of the tubular wall; and the coupling arrangement is such that at the extremes of the rocking movement of each piston, one or the other of that piston's pressure faces touches or is closely adjacent its respective pressure portion of the tubular wall. This arrangement assists in minimising waste space in the chambers when they are fully contracted.

Preferably, the pressure portions of the tubular wall are arcuate with a common centre of curvature corresponding to a central axis of the compressor or motor. This assists in design and manufacture because the tubular wall can be substantially circularly-cylindrical. The tubular wall and the dividing walls may be integrally formed, for example by moulding or extrusion.

Each piston may be mounted for its rocking movement on a respective pivot rib fixed relative to the tubular wall, and in this case the tubular wall and the pivot ribs may be integrally formed.

Preferably, each piston has a substantially uniform cross-section along substantially its whole length and/or the tubular wall has a substantially uniform cross-section along substantially the whole length of the pistons and/or each dividing wall has a substantially uniform cross- section along substantially the whole length of the pistons and/or each pivot rib has a substantially uniform cross-section along substantially the whole length of the pistons.

The mechanical member preferably comprises a camshaft, in which case the camshaft and tubular housing are preferably relatively rotatable about a central axis of the compressor or motor. The camshaft preferably has a substantially uniform cross-section along substantially the whole length of the pistons. The coupling arrangement is preferably provided by a cam surface of the camshaft which engages with a cam follower surface on each piston. The cam surface of the camshaft preferably has at least two cam lobes, and the cam lobes are preferably rotationally symmetrical about the centre axis of the compressor or motor.

The number of the pistons is preferably at least three. Preferably neither the number of the cam lobes nor the number of the pistons is an integer multiple of the other. This assists in reducing ripple in the outlet pressure (in the case of a compressor) or the output torque (in the case of a motor).

A second aspect of the invention extends to a method of operation as a fluid compressor, comprising the steps of: providing fluid at the inlet; externally driving the mechanical member and the structure so that they rotate relative to each other; and taking the fluid from the outlet at a higher pressure than at the inlet.

A third aspect of the invention extends to a method of operation as a fluid motor, comprising the steps of: supplying fluid under pressure at the inlet; allowing the fluid to escape from the outlet at a lower pressure than at the inlet; and permitting the mechanical member and the structure to rotate relative to each other.

When configured as a compressor, it is capable of providing a continuous delivery of compressed gas and is suitable to install as part of a small refrigeration circuit, or an arrangement requiring a supply of suitable compressed gas that may be delivered in state of increased enthalpy in order that the gas may be released and so expand within an evaporator thus to absorb ambient or directed heat. The device may be further enhanced by the provision of a thermoelectric module to increase the absorption of heat from an object or area. The compressor and its drive may be small. The compressor may be incorporated into a generally tubular structure facilitating application into relatively low profile computer casings with convenient connectability to ongoing pipe work relative to a refrigeration circuit.

Sealing between the pistons and dividing walls may be further improved by including a lubricant in the refrigerant will contain a lubricant, the lubricant will increase the efficiency of the piston and divider arrangement. Alternatively, a flexible bladder may be provided as provision against more aggressive gasses, or liquids. It may also be convenient to introduce a further mechanical seal. As the cam mechanism works in it own environment it may be convenient to provide the volume of the cam and surrounding space with a permanent lubricating material, the area may require pressure expansion relief in case of pressure build up in the cam casing.

T e rocking piston may be actuated by the same cam mechanism which is utilised in both closing (compression) during its rocking progression with the alternative side of the rocking piston element simultaneously providing the suction stroke. The arrangement provides for several rocking piston elements to be arranged around the inner wall of the tubular housing. The arrangement enables the construction of a small diameter of compressor with sufficient compressor capacity in both flow and volume to compress the gas required to operate a refrigeration system. The arrangement may provide for two power or pumping cycles per piston per rotation. Other arrangements may be provided with a piston and cam arrangements where a greater number of pistons are provided with alternative cam profiles to increase the number of strokes per shaft rotation.

Rather than the cam shaft being the driven prime mover; it may be convenient for the cam shaft to remain static and the piston housing to be the prime driven element.

The piston cam bearing faces may be designed to cause the cam lobes to remain in close proximity at all times to avoid impact wear and any associated mechanical noise also, and to maintain the efficacy of the compressor.

The valve arrangement may be provided in the form of rotary disc valves conveniently attached to either end of the cam mechanism and intended to run at the same rotational speed as the cam arrangement. Valve timing may be adjusted by re-spacing or rearranging the inlet and outlet positions on the disc valves. Valve devices are placed in appropriate positions to either provide for gas to enter the pumping cavity in the case of the suction moment and alternatively to exhaust the gas after compression. The design also provides for adjustment of output by increasing, or decreasing, the overall length of the rocker piston, the cam drive arrangement and the tubular housing.

It is intended that the materials used in the construction of the parts of the compressor may be composite and include metals and their associate alloys, ceramics which exhibit low coefficient of expansion as well to assist dimensional stability, plastic compounds either reinforced or not maybe incorporated into the construction. It may also be convenient to use any of the mentioned in any form in the construction of the compressor.

In larger compressors there may be provided a cam arrangement with several lobes acting on several rocker pistons. In another arrangement more than one core may be provided, the outer housing of a centre core compressor being provided with a cam to means to drive an additional set of pistons in a separate outer tubular housing.

A specific embodiment of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic cross-sectioned view of a compressor;

Fig. 2 is a cross-sectioned view of a tubular housing of the compressor; Fig.3 shows part of Fig. 2 and a piston of the compressor;

Fig. 4 shows the piston and a cam of the compressor;

Fig. 4a shows two of the pistons and the cam in a different position;

Fig. 5 is a schematic iongitudinaliy-sectioned view of the compressor; and

Fig. 6 is a set of isometric, end and side views of the piston. Referring to Fig. 1, a generally tubular body 1 is provided with three cavity walls 2,3 and 4. Also attached to the body 1 are three piston attachment mounts serving as pivot points 5,6 and 7, to which pistons 8,9 and 10 are located. Cam drive 11 is provided to actuate pistons 8,9 and 10. Areas marked "a" enclosed by piston drive faces 8b, 9b and 10b and adjacent T B2012/000135

- 6 - cavity walls 2,3, and 4 provide an enclosure for cam 11 to operate in. (End plates which form the completed enclosure are not shown.) The enclosure are may be lubricated separately to the general lubricant as suspended in a refrigerant gas when the compressor is provided as part of a cooling system. Tubular casing 1 and cam 11 may rotate, either being chosen as the prime mover in the compressor delivery. Both may rotate clockwise or anticlockwise as indicated by arrows 12.

Fig. 2 illustrates the generally tubular housing 13 with cavity separators 14 and piston pivot points 15 being part of a single extrusion or moulding. A wear resistant coating may be applied to all or specific surfaces 13a of the extrusion. Fig. 3 illustrates a section of the tubular housing with one piston 18, in position mounted on its pivot point 17. The radii about the pivot point 17 of the leading face "d" of the piston 18 and of the converging face radius "c" of the cavity separator 16 are substantially the same. An arrangement of seals may be provided on either or both of the elements; in some instances a open ended bladder or tube may be provided where aggressive acids are required to be pumped or compressed.

Fig. 4 illustrates the general principals required for the smooth running of the cam 19 and piston 20. The cam prime mover 19 is acting on the piston 20, and in the shown arrangement the cam is driven anticlockwise shown by arrow T and is causing piston 20 to move in direction ^tt g", pivoting at point "h". The driving cam 19 preferably remains in a substantially constant running tolerance adjusted for heat expansion and contraction relative to piston 20. The purpose is to reduce any uncontrolled motion by the piston 20 and maintain a constant load on the cam 19 and prime mover. During a compression stroke cam 19 makes contact with the back of piston 20, driving it in direction "g". The contour of both the piston drive face T and cam drive profile "j" is designed for a smooth transition and engagement when moving between pistons. The transition is shown in the change of position between Fig. 4, and Fig. 4a. Following engagement surfaces "k" and T formed by the leading edges of the piston 20 are designed to maintain a close contact at points "m" and "n" for the smooth running of the compressor thus avoiding both mechanically generated noise and vibration.

Fig. 5 illustrates a cross section of the compressor showing a typical application and the passage made by a gas through the compressor in a refrigeration circuit, the suction and compression being shown simultaneously by two different pistons 22a and 23. The compressor 22 is positioned in a section of the pipe work 21, which makes up a conventional refrigeration circuit. The compressor is provided with an electrically driven motor 34, in this case a series of rare earth magnets 35, which have been arranged around a skeleton armature 34a, providing what is known as the Halbach effect. The arrangement is powered by electrically powered copper coils 36, arranged in a channel 32 formed in pipe work 21 , so to conveniently provide directional magnetic force on the skeleton armature 34a, the rotational force being transferred to drive shaft 33, to which cam 24 is attached. Shaft 33 is supported by bearing end caps 27 and 28. Rotary valves plates 25 and 26 are attached to cam 24 and contained by end caps 27 and 28. Low pressure gas (LP) is sucked in through the skeleton armature 34, and into the piston chamber 22a, via bearing end plate 27, and rotary valve 26. After being compressed the gas exits through an aperture 29 in rotary valve 25, passing through bearing end cap 28, through exit hole 30 in the direction 31, adding to the high pressure (HP) stage of the refrigeration cycle.

Fig. 6 is an isometric view of one piston, it may be convenient to either reduce or lengthen dimension "o" and its associate housing to increase or decrease the output of the compressor. The overall size and output may be conveniently scaled to produce small or large volumes from a similar cross section "p".

The embodiment of the invention has been described above in terms of a gas compressor. However, it may also be used to pump liquid. In this case, if using rotary plates valves or the like, attention needs to be given to the valve timing to ensure that hydraulic locks do not occur, for example by providing the inlet and outlet valves with a small degree of overlap. Alternatively, other forms of valve may be used such as self-opening poppet, reed or flap valves.

Furthermore, the embodiment of the invention may be used as a motor rather than a compressor, for example by supplying fluid at the high pressure (HP) end in Fig. 5 and releasing it at a lower pressure at the low pressure (LP) end. In this case, the motor may need to be started manually, or by attention to the arrangement of cam lobes and pistons it may be self- starting. When used as a fluid motor, mechanical energy may be output from the shaft 33 or housing 21 (whichever is rotating). Alternatively, the electric motor 34 or the like may instead be deployed as an alternator.

It should be noted that the embodiment of the invention has been described above purely by way of example and that many other modifications and developments may be made thereto within the scope of the present invention.