Abstract:
The casing ( 1 ) of a positive displacement machine has a cylindrical internal surface ( 3 ) delimiting an operating chamber which accommodates an orbiting piston ( 4 ) having a cylindrical external surface. At least one of the said surfaces, e.g. the internal surface ( 3 ), is at least partly constituted by a peripheral wall ( 2 ) having a front surface facing the operating chamber and a rear surface. The peripheral wall ( 2 ) having through-slots ( 22 ) which extend parallel to one another and accommodate respective compliant strips ( 24 ) extending from the front surface to the rear surface. The strips ( 22 ) are retained in the slots ( 22 ), against pressure in the operating chamber, by a retaining device such as a clamping member ( 28 ). An assembly of three positive displacement machines and engines comprising first and second positive displacement machines are also described.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    This invention relates to rotary positive displacement machines, in particular orbiting piston machines, and engines which make use of positive displacement machines. 
         [0003]    2. Background Art 
         [0004]    Rotary positive displacement machines with orbiting pistons have been described by the present inventor in WO 03/062604 and WO 2004/031539, the contents of which are hereby incorporated by reference. Engines using positive displacement machines have been described by the present inventor in WO 2005/124106, the contents of which are hereby incorporated by reference. 
       SUMMARY OF INVENTION 
       [0005]    In one aspect the present invention provides a rotary positive displacement machine comprising: a casing having a cylindrical internal surface delimiting an operating chamber; and an orbiting piston in the operating chamber, having a cylindrical external surface; wherein at least one of the said external and internal surfaces is at least partly constituted by a peripheral wall having a front surface facing the operating chamber and a rear surface, the peripheral wall having through-slots which extend parallel to one another, the through-slots accommodating respective compliant strips extending from the front surface to the rear surface, retaining means being provided to retain the strips in the slots against pressure in the operating chamber. 
         [0006]    In another aspect the invention provides an assembly comprising three rotary positive displacement machines, each machine comprising a casing having a cylindrical internal surface delimiting an operating chamber and an orbiting piston in the operating chamber, having a cylindrical external surface, the casings being connected together and the orbiting pistons being kinematically linked. 
         [0007]    In another aspect the invention provides an engine comprising: a first positive displacement machine; a second positive displacement machine; an inlet duct connected to the first positive displacement machine; an intermediate duct connected between the first and second positive displacement machines; an outlet duct connected to the second positive displacement machine; a heater for raising the temperature and pressure of a gaseous working fluid in the intermediate duct; and a kinematic connection between the first and second positive displacement machines; the arrangement being such that, in operation of the engine, the first positive displacement machine causes the working fluid to flow through the intermediate duct to the second positive displacement machine, the heated working fluid drives the second positive displacement machine, and the second positive displacement machine drives the first positive displacement machine via the kinematic connection; the engine further comprising a heat pump circuit through which a refrigerant flows, including, in sequence, a compressor, a condenser which constitutes at least part of the said heater, an expander, and an evaporator; wherein the heat pump circuit includes means for supplying heat to the refrigerant between the evaporator and the compressor. 
         [0008]    The various aspects of the invention will be described further, by way of example only, with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a cut-away perspective view of a rotary positive displacement machine with an orbiting piston; 
           [0010]      FIG. 2  is a perspective view of a peripheral wall portion of the machine; 
           [0011]      FIG. 3  is a perspective view of one part of the peripheral wall portion; 
           [0012]      FIG. 4  is a perspective view of another part of the peripheral wall portion; 
           [0013]      FIG. 5  is a perspective view of a clamping member; 
           [0014]      FIG. 6  is a perspective view of an assembly of three rotary positive displacement machines, with outer casings removed; 
           [0015]      FIG. 7  is a diagram of one embodiment of fluid interconnection of the three machines. 
           [0016]      FIG. 8  is a diagram showing the assembly of  FIG. 6  connected to an internal combustion engine; 
           [0017]      FIG. 9  is a perspective view of an assembly of three rotary positive displacement machines, constituting a three-stage compressor; 
           [0018]      FIG. 10  corresponds to  FIG. 9  with parts of the assembly removed; 
           [0019]      FIG. 11  is a diagrammatic representation of the layout of an engine as described in WO 2005/124106; 
           [0020]      FIG. 12  is a diagrammatic representation of the layout of one embodiment of the engine according to the present invention; and 
           [0021]      FIG. 13  is a diagrammatic representation of the layout of another embodiment of the engine according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0022]    The type of rotary positive displacement machine which is shown in  FIGS. 1 to 5  is more fully described in WO 03/062604 and WO 2004/031539. It comprises a casing  1  with a peripheral wall  2  having a circular cylindrical internal surface  3 . An orbiting piston  4  (also referred to as a rolling piston) comprises a rotating inner part  4   a , which is eccentrically mounted on an input/output drive shaft  9  and which may carry at one or both ends a shutter in the form of a flange or disc (not visible), and a non-rotating outer part  4   b  which orbits about the axis of the internal surface  3 . The outer part  4   b  of the orbiting piston  4  has a circular cylindrical external surface  11 , one generatrix of which is spaced from the internal surface  3 . 
         [0023]    A vane member  17  is accommodated in an aperture in the casing  1  and this aperture can function as a fluid inlet/outlet. The vane member  17  has a passageway  17   a  communicating between the exterior of the casing  1  and the operating chamber, an arcuate end wall  17   b , transverse walls  17   c  extending from the respective ends of the end wall  17   b  and being pivotally mounted on the casing  1 , and a tip face (not visible) which is a sealing surface with respect to a recess in the external surface  11  of the orbiting piston  4 . A fixed appendage  71  to the outer part  4   b  is connected to the vane member  17  by a bearing (not visible) at a position between the pivot axis of the vane member  17  and its arcuate end wall  17   b.    
         [0024]    The outer part  4   b  of the orbiting piston  4  comprises an extruded body which may be made of light metal, e.g. an aluminium alloy. It may be provided with a plurality of compliant strips extending in the axial direction and being equally spaced apart. Each strip may be made of an elastomer, e.g. Viton or butyl rubber, and mounted in a groove. 
         [0025]    The casing  1  includes a peripheral wall portion  21  having through-slots  22  which extend in the axial direction and are equally spaced apart. A belt  23  of compliant material (such as the elastomer mentioned above) is fitted on the peripheral wall portion  21 . The belt  23  consists of a plurality of compliant strips  24  integrally connected by a ribbon  26 . The strips  24  fill the slots  22  and project slightly into the operating chamber. The ribbon  26  is retained against the rear surface  27  of the peripheral wall portion  21  by a clamping member  28 , which prevents the strips  24  from being pushed out of the slots  22 . 
         [0026]    In the same way, compliant strips  24  may be provided in the peripheral wall of the outer part  4   b  of the orbiting piston  4 . 
         [0027]    Various embodiments of compressors and expanders (rotary positive displacement machines) require different circumferential lengths of peripheral wall portions (between inlets and outlets, e.g. ranging from 90° to 290°, and different axial lengths of compliant strips. The belt  23  described above can be made in any convenient length and width and can be cut to the (circumferential and axial) size required. The belt may be manufactured flat and then bent to the required shape during fitting. The orbiting piston  4  exerts a rolling, sliding, and squeezing action on the surface of the complaint strips  24 ; in addition, any pressure in the operating chamber will try to push the strips out. A typical clamp to prevent this is shown in the drawings by way of example. The clamping member  28  may be hinged to a casing appendage and/or retained by a side plate. 
         [0028]      FIG. 6  shows an assembly of three rotary positive displacement machines A, B, C in which the orbiting pistons  4  are mounted on a common shaft  9 . 
         [0029]    WO 2004/031539 describes an assembly of two rotary positive displacement machines, one of which is a compressor and the other an expander (expansion turbine). This produces an out-of-balance couple that has to be reduced by adding a counter-balancing weight. 
         [0030]    The use of an assembly of the type shown in  FIG. 6  allows the compression to be carried out in two stages, e.g. by machines A and B in sequence, the remaining machine (C) being used as the expander. By selecting the appropriate size and weight of each orbiting piston  4 , the assembly can be balanced without the need for an additional balancing weight. 
         [0031]    As described above the first stage compressor is interposed between the second stage compressor and the expander. Various arrangements of compressor and expander stages can be devised to optimise balance and bearing life. 
         [0032]    When the assembly is only used for compression, two of the machines (e.g. B and C) can be used for first-stage compression and can be fluidly connected in parallel to the remaining machine (A). 
         [0033]    Alternatively, the machines A-C can be fluidly connected in series to provide three stages of compression, for example as indicated in  FIG. 7 . If air is to be compressed, the air can enter the first machine A and exit to the second machine B, and air entering the second machine B can exit to the third machine C. The air can be vented from the casing of one or more of the machines to vary the air mass flow. 
         [0034]    By having the ability to compress air in three stages and to vent air from any or all of the compression stage, the final pressure and mass flow rate can be adjusted to give similar conditions to those created by the control system of an internal combustion engine, so as to enable the cylinder of a four-stoke internal combustion engine to provide the power and exhaust strokes only. The induction and compression are carried out by the three-stage compressor assembly. In this way the relatively high pressure and temperature of combustion can be separated from the air induction and compression strokes. In the case of a petrol (gasoline) engine there would be no throttling or pumping losses. 
         [0035]      FIG. 8  shows the three-stage compression assembly  29  connected to the intake manifold  30  of two cylinders  31 ,  32  of an internal combustion engine having a crankshaft  33  which drives the shaft  9  via a pair of pulleys  34 . The piston in the first cylinder  31  is just commencing the power stroke and the piston in the second cylinder  32  is just commencing the exhaust stroke. At the end of the exhaust stroke the intake valve opens so that an air/fuel mixture is introduced at a sufficiently high pressure to cause the next power stroke to immediately follow the exhaust stroke. 
         [0036]    Modern car engines may have too little heat in the engine-cooling system to provide heat for the passenger. Inter-coolers (heat exchangers) associated with the three-stage compressor assembly can be used for the passengers. Inter-cooling between the compression stages can keep the temperatures in the assembly sufficiently low that it can be made from aluminium. 
         [0037]    If refrigerant from the air conditioning system of a car is used in the inter-coolers they can be made smaller than if ambient air was used and the air flowing into the engine could be made cooler. 
         [0038]      FIGS. 9 and 10  show a three-stage compressor assembly  29  with two inter-coolers (heat exchangers)  36 ,  37 . The inter-coolers are integrated with an air conditioning unit (not shown) and use the air conditioning refrigerant for cooling the air as it transfers from one stage of compression to the next. The three-stage compressor assembly  29  can provide a range of air mass flow rates and pressures from idle to 2 bar boost, for example, before the air is injected into the internal combustion engine (as explained above). 
         [0039]    In  FIG. 10  some components are removed to expose a typical vent position and means for allowing automatic adjustment of the running clearance of the orbiting piston in the second-stage compressor B. The peripheral wall  2  of the compressor B has an air-venting orifice  38  controlled by a valve (not shown). the air is selectively vented to provide additional control of air mass flow. One or more vent orifices may be provided in each compression stage. Wear-away strips  39  in grooves in the internal surface  3  of the casing  1  ensure a minimum running clearance for the orbiting piston. (Such strips may instead be constituted by the compliant strips  24  described above.) 
         [0040]    An engine as described in WO2005/124106 is shown diagrammatically in  FIG. 11 . It includes a heat pump comprising a circuit in which a suitable refrigerant circulates as indicated by the broken arrows. The heat pump circuit includes a combined compressor/expander  101  (each constituted by a rotary positive displacement machine with an orbiting piston), a condenser  102 , and an evaporator  103 . The condenser  102  serves as a heater and the evaporator  103  serves as a cooler for a Sterling engine including a first rotary positive displacement machine  104  with one orbiting piston and a second rotary positive displacement machine  106  with two orbiting pistons. 
         [0041]    An inlet duct  107  for atmospheric air leads through the evaporator  103  (heat exchanger) to the first positive displacement machine  104 . An intermediate duct  108  leads from there, through the condenser  102  (heat exchanger), before arriving at the second positive displacement machine  106 . The machines  104  and  106  are linked by a suitable kinematic connection  111 , which may comprise at least one shaft, a belt or chain, or gears, for example. The second machine  106  is linked to the compressor/expander  101  by a suitable kinematic connection  112  and to an electrical generator/motor  113  (or a power offtake) by a suitable kinematic connection  114 . An outlet duct  109  leads from the second positive displacement machine  106  to a hot exhaust or heat exchanger  116 . 
         [0042]    Air enters the evaporator  103  and evaporates the refrigerant for the heat pump compressor  101  to compress and pass to the condenser  102 . Condensed refrigerant passes back from the condenser  102  to the heat pump expander  101  for expansion and return to the evaporator  103 . After passing through the evaporator  103  some or all the inlet air passes to the orbiting piston in the cold part  104  of the Stirling engine and the orbiting piston transfers the cold air via the hot condenser  102  to the orbiting pistons in the hot part  106  of the Stirling engine. As the cold air rises in temperature as it passes through the condenser  102 , it rises in pressure. Pressure energy is expanded by the hot orbiting pistons and exhausted to provide heating. 
         [0043]    As the ambient temperature falls the above system quickly becomes impractical, and as the ambient temperature rises a point is reached where only cooling is required. To extend the range over which it is practical to provide heating, a supplementary heater  118  is provided to heat the air before entering the second positive displacement machine  106 . The heater  118  may provide heat by anything known in the art, but probably most conveniently by electricity or gas. 
         [0044]    Under conditions where cooling is required the system is designed such that the mass of air used to evaporate the refrigerant in the evaporator  103  is more than the mass of air taken by the Stirling cycle engine, the difference is the mass of air available for cooling at  117 . 
         [0045]    Under cold conditions an external source of mechanical energy will be required to supplement the Stirling cycle engine power. This is most conveniently provided by changing the electrical generator to a motor at  113 . Under these conditions the system will not generate electricity. 
         [0046]    For further details of the operation of the engine, and possible modifications, the reader is referred to WO2005/124106, the contents of which are hereby incorporated by reference. 
         [0047]    The overall efficiency of the system may be improved by superheating the refrigerant at a suitable point in the heat pump circuit ( 101 - 103 ). This can be done by passing the refrigerant through a superheater (heat exchanger) before entry to the compressor/expander  101 . 
         [0048]      FIG. 12  shows a heat exchanger  121  through which passes a first line  122 , connecting the evaporator  103  and the compressor  101 , and a second line  123 , connecting the condenser  102  and the expander  101 . A diverter valve  124  is provided for selectively by-passing the heat exchanger  121  in the second line  123 . 
         [0049]    The heat available in the refrigerant before entry to the expander  101  or the evaporator  103  may be used for heating either directly or by supplying the heat to the working fluid before exiting the Stirling cycle at  116 .  FIG. 13  shows direct heating with a heat exchanger  126  between the condenser  102  and expander  101 , and superheating by the heat exchanger  121  before exit of the working fluid (air) at  116 .