NZ565810A

NZ565810A - A congeneration system

Info

Publication number: NZ565810A
Application number: NZ56581008A
Authority: NZ
Inventors: Donald Murray Clucas; Vinod Kumar
Original assignee: Whisper Tech Ltd
Priority date: 2008-02-08
Filing date: 2008-02-08
Publication date: 2009-12-24
Also published as: WO2009099343A1

Abstract

A cogeneration system is disclosed which includes: an external or internal combustion engine that includes at least one piston reciprocally movable in a cylinder; at least two balancing rotors mounted for oscillating rotational movement about an axis or axes transverse to the axis of motion of the piston; one balancing rotor having a centre of mass on one side of and another balancing rotor having a centre of mass on an opposite side of the axis or axes of motion of the rotors; and at least one connecting member or mechanism between the piston and rotors so that the rotors move in opposition to the reciprocal movement of the piston. A generator driven by the engine produces electricity, and an electronic control system is provided which controls the electrical and/or heat output of the cogeneration system by controlling piston motion of the engine.

Description

565810 *10056925028* NEW ZEALAND PATENTS ACT, 1953 No: 565810 Date: 8 February 2008 COMPLETE SPECIFICATION A COGENERATION SYSTEM We, DONALD MURRAY CLUCAS , a New Zealand citizen of 7 Matisse Place Ilam, Christchurch, New Zealand and VINOD KUMAR, a New Zealand citizen of 1/291 Barbadoes Street, Christchurch, New Zealand do hereby declare this invention to be described in the following statement: 565810 FIELD OF INVENTION The invention a comprises a cogeneration system which includes an electronic control system arranged to control the electrical and/or heat output of the cogeneration system by controlling motion of piston(s) or piston(s) and a displacer of the engine.

Conventionally, Stirling engine based microCHP systems are not controllable. That is, the system turns on at a set temperature of the primary coolant and then shuts down when the coolant temperature has increased to the set value. Power and heat are output at near a Fixed ratio.

Electricity is generated when the system is running. Primary control is via a heat demand signal, which starts and stops the engine. MicroCHP systems are typically sized to handle the average thermal load of a house. An auxiliary or a boost burner maybe provided in the microCHP system to increase thermal output when required. The boost burner is often coupled to the main exhaust heat exchanger and is turned on to increase the heat output. Turning the boost burner on and off enables some control of heat output. A disadvantage is that energy going into the boost burner is not generating electricity and this part of the system works like a conventional boiler. When the boost burner operates the overall system efficiency of producing electricity decreases.

The electrical efficiency of a microCHP system is typically 10 to 20%. Homes are becoming better insulated and have lower heat loads. Greater electrical output for the heat generated is therefore required to achieve any worthwhile electricity generation in the shorter run time. This would translate to the need of a higher overall electrical efficiency.

The householder does not always have the incentive to export power to the grid if there is not a system of fair compensation for power exported. In this case it is not cost effective for the householder to generate any more electricity than is absolutely necessary for his own use.

On the other hand, the engine must be able to respond to larger transient heat loads (eg heat up from cold) for the sake of the householder comfort. Maximum electrical efficiency is not necessarily required in this condition.

In at least some applications such as where a microCHP system is mounted on the wall of 5658: a home or workplace for example, the engine must generate very low vibration levels. SUMMARY OF INVENTION In broad terms the invention comprises a cogeneration system including: an external or internal combustion engine including at least one piston reciprocally movable in a cylinder, at least two balancing rotors mounted for oscillating rotational movement about an axis or axes transverse to the axis of motion of the piston, one balancing rotor having a centre of mass on one side of and another balancing rotor having a centre of mass on an opposite side of the axis or axes of motion of the rotors, and at least one connecting member or mechanism between the piston and rotors so that the rotors move in opposition to the reciprocal movement of the piston; a generator driven by die engine for producing electricity; and an electronic control system arranged to control the electrical and/or heat output of the cogeneration system by controlling piston motion of the engine.

The control system may be arranged to control the electrical and/or heat output of the cogeneration system by controlling any one or more of piston or displacer stroke length on swept area, velocity, phase, position, or dwell time of the piston(s) at either or both of top dead centre and bottom dead centre of piston motion for example, and/or by controlling piston motion to cause the piston(s) to move with a non-sinusoidal motion.

The engine may comprise a stator comprising multiple windings and the control system may be arranged to control piston motion by controlling energising power to the stator windings. The engine may be an external or internal combustion engine and may be a heat engine such as a Stirling engine with the system comprising a combustion chamber having a burner for supplying heat to the engine. The engine may be a single cylinder or multi-cylinder engine as will be further described.

In one embodiment each of the rotors may comprise a permanent magnet or an electromagnet and the engine may comprise a stator associated with the rotors — movement of the rotors generates an emf in the stator. In another embodiment a stator or stators may comprise a permanent or electromagnet and the rotors a winding or windings - movement of the rotors generates an emf in the rotor winding(s). In a farther stator-less embodiment one rotor may comprise a permanent or electromagnet and another rotor may comprise a winding or 565810 windings - relative movement between the rotors generates an emf in the winding or windings.

In this specification and claims the term "generator" includes electrical engines which generate either dc or ac power.

For the avoidance of doubt, in this specification and claims the term "piston" includes both a piston which is moved within a cylinder by internal combustion or external combustion such as in a heat engine i.e. a power piston, and a piston which is moved alternatively, by a mechanical linkage for example, to expel a fluid from a cylinder or draw a fluid into a cylinder, such as a displacer piston (sometimes referred to simply as a displacer) in a Stirling engine for example, and "pistons" and "piston(s)" have a similar meaning.

The term 'comprising' as used in this specification and claims means 'consisting at least in part of, that is to say when interrupting independent claims including that term, the features prefaced by that term in each claim will need to be present but other features can also be present.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is further described with reference to the accompanying drawings, by way of example and without intending to be limiting, in which: Figure 1 schematically shows a first embodiment of an engine of a cogeneration system of the invention, Figures 2 and 3 schematically show a second embodiment of an engine of a cogeneration system of the invention, Figure 4 schematically shows an embodiment of similar to that of Figures 2 and 3 also showing a stator, Figure 5 schematically shows a further embodiment also showing a stator, from one side and partially cut away, Figure 6 schematically shows the embodiment of Figure 5 in the direction of arrow A in Figure 5, 565316 - Figure 7 schematically shows drive circuitry for the embodiment of Figures 5 and 6, Figure 8 schematically shows a parallel twin cylinder engine which may be used in a cogeneration system of the invention, Figure 9 schematically shows an opposed twin cylinder engine which may be used in a cogeneration system of the invention, Figure 10 schematically shows an opposed six cylinder engine which may be used in a cogcneration system of the invention, Figure 11 schematically shows another embodiment of an engine which may be used in a cogeneration system of the invention, Figure 12 shows a further embodiment of engine which may be used in a cogeneration system of the invention, and Figure 13 schematically shows a partial embodiment of a cogeneration system of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The engine of Figure 1 is shown as a single cylinder engine for simplicity and comprises a piston 1 which moves reciprocally in a cylinder 2. The piston and cylinder may be of a heat engine such as a Stirling engine or Rankine cycle machine, or of an internal combustion engine. Two balancing rotors 3 are mounted about axes transverse to the axis of motion of the piston, at bearings 4. The piston 1 and rotors 3 are coupled by connecting rods 6. The major part of the mass of each of the rotors 3 are on opposite sides of the pivot axes 4, and the connecting rods 6 couple to minor parts 3a of the rotors 3 on the other side as shown.

A spring may be fitted between the oscillating piston or displacer and the body of the machine, between the rotors or other part to store reciprocating energy and reduce the power consumption of the electric machine. Gas springs may also be used. 565810 The configuration is such that during operation of the engine, reciprocal linear motion of the piston 1 in the cylinder 2 drives or is driven by oscillating rotational motion of the rotors 3, with the majority of the rotor mass moving in opposition to the movement of the piston 1. That is, during downward movement of the piston 1 in the direction of arrow PI in Figure 1, the rotors 3 move in the direction of arrows R1. During upward movement of the piston in the direction of arrow P2 in Figure 1 the rotors move in the direction of arrows R2.

The connecting rods 6 can be either flexible in the plane of the engine but stiff axially, or have articulation joints where the connecting rods couple to the piston and/or to the rotors 3, to accommodate a small rotational motion of the connecting rods.

The engine can be substantially dynamically balanced. The rotors can be formed to have a mass distribution that will substantially balance the reciprocating mass of the piston, and to also have near equal rotary moments of inertia so that the rotating inertia of the two cranks substantially balances and negates each other. The mass of the two rotors and piston should lie in substantially the same plane to avoid out of balance moments. The sum of the rotary inertia moments of the two connecting rods will be zero due to the opposite direction of their rotation. A high degree of balance can be obtained whilst the stroke is short in comparison to the lever arm length of the two contra-rotating rotors. Also, because the contra-rotating cranks are dynamically balancing the piston inertia and are fixed in unison, the motion of the piston can vary away from sinusoidal motion whilst maintaining the high degree of balance. That is non-sinusoidal piston motion can be used without compromising engine balance.

In one form the rotors 3 may comprise magnets particularly around the curved periphery of each rotor, and a stator (not shown in Figure 1) may be associated with the rotor on either side so that movement of the rotors will generate an emf in windings of the stator(s). The rotor magnets may be permanent magnets or electromagnets, the windings of which are connected to a power source via brushes, springs or flexible wires for example. Alternatively the stators may comprise permanent or electromagnets and the rotors may carry windings in which an emf is generated as the rotors move relative to the stator(s), with the current generated in the rotor windings being connected to an external circuit again via brushes, springs or flexible wires.

Should the electrical load be lost at any time during operation, the inherently balanced nature of the mechanism means the engine would not violently shake. 565813 " Figures 2 and 3 show an embodiment in which the contra-oscillating rotors oscillate about a common axis at pivot 4. Downward movement of the piston 1 as indicated by arrow PI causes movement of rotors 3c and 3d in the direction of arrows R2 and R1'respectively, and upward movement of the piston in the direction of arrow P2 causes movement of the rotors in the direction of arrows R1 and R2'.

As shown in Figure 3 which shows the engine with rotor 3d removed, connecting rod 6a connects to rotor 3c on one side of the axis 4, and connecting rod 6b connects to the rotor 3d on the other side of the axis 4 (in Figure 3 the end of connecting rod 6b is shown but not the rotor 3d). Each of the rotors 3c and 3d is symmetrically and oppositely balanced about the common axis of motion 4. In this embodiment the rotors are circular-shaped about the axis 4 as shown, and weight part 3e of rotor 3c causes the centre of mass of the rotor to be to one side of the axis 4, and rotor 3d (not shown in Figure 3) has a similar weight part on the opposite side of the axis 4.

Also in the embodiment shown in Figures 2 and 3 the connecting rods 6a and 6b connect to a bridge part 9 which in turn is connected to the piston 1, as shown. Alternatively the connecting rods 6a and 6b may connect directly to the piston 1 (without part 9) .

The rotors 3 may comprise peripheral permanent magnets or electromagnets, and a surrounding stator, or alternatively (but less preferably) the stator may comprise a permanent magnet or electromagnet, the flux of which is cut by windings on the rotors. Figure 4 shows a stator 10 in an embodiment of Figures 2 and 3 configured as a generator or alternator. In a preferred form the magnet polarities of the two rotors 3c and 3d are chosen such that when the rotor magnets contra-rotate past the output stator winding, the direction of the emf generated by each moving magnet will develop in-phase series voltages in the output winding. This increases generator voltage and simplifies stator winding.

In a further embodiment the two moving rotors may each comprise a compound wound winding connected to the output connectors through brushes, springs, flexible wires or similar.

In a yet further embodiment similar to the embodiment of Figures 2 and 3, one rotor may comprise the magnet(s) and the other a winding in which the emf is generated. Alternatively again a combination of magnets and windings may be provided on each of ./Ut ■ vV this embodiment is that a separate surrounding stator as shown at 10 a^Figure 4 is not required, ( i e m ) "V ""lb—I jw» ft- * 565810 and the generator is more compact than where a separate stator surrounding the rotor(s) is provided. Another advantage is that the flux cutting speed of the generator is doubled.

Figure 5 shows another embodiment from one side with one rotor shown in phantom outline and stator 10 bisected. Figure 6 shows the engine in direction of arrow A in Figure 5. The engine is similar to that of Figures 2 to 4, and comprises rotors 3c and 3d which oscillate about a common axle 4, to which the rotors are mounted via bearings 20. Connecting rod 6a connects to the rotor 3c on one side of the axle 4 and connecting rod 6b connects to the rotor 3d (shown in phantom outline) on the other side of the axle 4. The connecting rods 6a and 6b connect to a bridge part 9 which in turn is connected to the piston by connecting rod 6c. To make the engine as compact as possible, in this embodiment each of connecting rods 6a and 6b connects to it's respective rotor through an arcuate slot 21 in the other rotor. And each of the connecting rods 6a and 6b passes through an aperture 22 in the stator 10 (see Figure 6), or alternatively a slot may be formed across the top of the stator between the connecting rods. As in the embodiment of Figure 1, a major part of each of the rotors has a curved periphery on one side of the axis of the motion of the rotors, and each rotor has a minor part on the other side to which the connecting rods 6a and 6b couple respectively, via pivot joints 23. Each of the rotors 3c and 3d is symmetrically and oppositely balanced about the common axis of motion 4 as before. The peripheral parts of the rotors comprise permanent magnets (or alternatively electromagnets) and the engine comprises a surrounding stator 10 mounted to the body of the machine, (not shown).

In a further embodiment the generator may be a linear generator. The moving element of the linear generator, which may be a permanent magnet and which moves reciprocally through or within a wound stator, is connected to the piston, or multiple pistons of the engine may drive multiple linear generators with their outputs electrically coupled. In such embodiments the rotors may act as balancing rotors only or may also comprise peripheral permanent magnets or electromagnets, and a surrounding stator.

The engine may be an external or internal combustion engine and may be a heat engine such as a Stirling engine with the system comprising a combustion chamber supplied with air and fuel and having a burner for supplying heat to the engine. The hot end of the Stirling engine is placed in the combustion chamber of the burner. Typically the heater head or hot end heat exchanger of the Stirling engine is positioned at the lower end of the combustion chamber. Alternatively the combustion chamber may surround the hot heat exchanger. The cogeneration 565810 system comprises a generator driven by the engine for producing electricity. The generator output may be alternating or direct current and may be supplied to the electricity network or an electric energy storage device such as a batter}', for example. Exhaust gas from the combustion chamber is directed to a heat exchanger for thermal energy recovery.

An electronic control system is arranged to control the electrical and/or heat output of the cogeneration system by in accordance with the invention controlling piston or piston and displacer motion of the engine. The electronic control system supplies electric power to the generator to cause the generator to act as a motor during a part or parts of the engine cycle, to modify piston motion. The control system comprises for example a micro-processor, optionally with one or more sensors on piston and/or rotor position and/or movement, which may be arranged to control piston motion such as the effective capacity or swept area of the cylinder(s) by the piston(s), by controlling the or each piston so that the piston(s) op crate (s) only in an upper part of the cylinder(s) for example. The electronic control system may supply electric power back into the generator before BDC in each piston cycle to cause the piston(s) to stop and reverse direction before BDC, to thereby reduce effective capacity or swept area. Reducing the effective capacity or swept area of the cylinder(s) by the piston(s) from maximum will reduce the electrical output of the generator. Subsequently the control system may control piston motion to increase the effective capacity or swept area of the cylinder(s) by the piston(s) to increase the electrical output of the generator for example when electrical demand increases. The control system may also or alternatively operate to control piston motion to cause the pistons to move with a non-sinusoidal morion. The electronic control system may supply electric power back into the generator during a part or parts of the engine cycle to cause piston motion to be non-sinusoidal and/or control piston velocity. Controlling piston motion to cause the pistons to move with a non-sinusoidal motion may be used to control or alter the waveform shape to thereby vary the electrical output of the generator. Alternatively or additionally again, the electronic control system may be arranged to in response to reduced electrical and/or heat output demand to control piston motion so that a piston or piston(s) moves with motion of a different phase. For example in a twin cylinder alpha or gamma Stirling engine or a single cylinder beta configuration engine the control system may cause the phase between the pistons or piston and displacer to vary, to vary the cogeneration system output.

Using this system the ratio of heat to electricity may be modified as required to give the best conditions for the user, owner or power company. 5658-iki) - In principle the thrust required for moving the piston at the desired velocity and/or to the desired top dead centre (TDC) and/or bottom dead centre (BDC) position (s) is calculated for different crank angles. The magnetic circuit and the electric circuit of the engine are designed to generate the force required.

The cogeneration system may be a micro-combined heat and power (microCHP) unit, in which engine and engine exhaust heat are exchanged for water or space heating. The microCHP unit may be suitable for wall mounting as the engine can be configured to have low or minimal vibration.

Optionally the system may receive information via radio, wire, internet, time of day or telephone line that the microprocessor or user will use to decide on the mode of operation which will give the best performance. For example the electricity supplier may advise spot price tariff information, which the microprocessor use to identify electrical power generation by the microCHP as beneficial to the supplier or the customer, and may operate the microCHP at high electricity efficiency to produce as much electricity as possible. Alternatively if the information received indicates low electricity payback the micro processor may operate the system to produce as much heat as possible without or with lower electricity production. In each case the controller operates to modify the piston and/or displace motion of the engine. The microprocessor will also take information from water temperature and outdoor temperatures in deciding the starting/run time and required heat output rate.

Figure 13 systematically shows an embodiment of a co-generation system of the invention. Reference numerals 1, 2, and 3, as before indicate the piston or pistons, cylinder or cylinders of a heat engine, and rotors 3 connected to the pistons. A burner 30 is provided to drive the heat engine. Stator coils are indicated at 10. An electronic controller receives piston position information from one or more piston position sensors, and may receive inputs such as referred to immediately above for example manual user inputs, electricity supplier inputs, time of day, water temperature, outdoor and/or indoor temperature inputs. The cogeneration system also comprises power electronics through which electrical energy generated in the stator windings 10 as the rotors 3 move is extracted. Output power may be supplied to for example a domestic dwelling in which the co-generation is situated, the utility grid, or to a battery for example. Heat is extracted from engine cooling fluid and/or an exhaust gas heat exchanger. The controller operates as described above to control piston motion to control the el^^Slf®J&(f|«^^at output of the co-generation system. 565810 The cogeneration system may optionally also comprise an auxiliary combustion chamber located in or near the exhaust gas heat exchanger for to provide additional heat output when required. Hot exhaust gas from the engine includes some oxygen and is directed to the auxiliary chamber where the necessary amount of additional fuel and air is added and burnt via an auxiliary burner, to generate additional heat. Alternatively a separate air supply to the auxiliary burner may be provided. The combined hot exhaust gas from the engine combustion and auxiliary burner is then directed to the exhaust gas heat exchanger or boiler.

The engine may be implemented as a stepper engine, BLDC engine, induction engine, reluctance engine, synchronous engine, limited angle torque engine, servo engine, vernier hybrid engine, or a PM synchronous engine for example, in single or (some cases) multiphase.

A prototype engine of the embodiment shown in Figures 5 and 6 was wired as a two phase stepper motor. The two phases were connected across two full bridges as shown in Figure 7. The bridges were fed from a DC source. A control system 25 drives the H bridges/operates the power switching to the stator windings, to control any of the duty cycle, dwell time, speed, starting thrust and a regenerative braking profile of the engine. The stator was wired similar to a two-phase stepper motor, with four stator poles 26 — 29. The design is short stator type. Each pole covered two slots in the stator former. Each rotor travelled 30° from TDC to BDC, which equated to a 25mm stroke. The resolution of this prototype engine was 5° or 4.17mm in equivalent stroke.

TDC State 1 State 2 State 3 State 4 State 5 BDC In normal operation the mechanism has a natural rest position at state 3 above, and in one full cycle the rotors can oscillate to BDC, then to TDC, and then return to state 3. The stroke of rotor movement was is 15° on either side of state 3.

To control the stroke length, the cycle in one mode can be limited to between state 5 and state 1 on either side, instead of between BDC and TDC. This limits the stroke to 20° or 16.7mm. Alternatively in another mode the stroke length can be limited to 10° or 8.35mm stroke. For stroke control in the prototype, the minimum resolution achievable was 10°. 565810 Another control variable is the DC level or bias. With a stroke of 10°, the natural rest position can be at any of the five states above. For example, state 1 can be the natural rest position and the engine can then in operation oscillate between TDC and state 2. Alternatively when the natural rest position is state 2, then the engine can in operation oscillate between state 1 and state 3 for a 10° stroke or between TDC and state 5 for a 20° stroke. In general, when the natural rest position is state 2 or state 4, stroke lengths of 20° and 10° are possible. When the natural rest position is state 1 or state 5, a stroke of 10° is possible.

The dwell time of the piston at TDC or BDC or both can be controlled to obtain nonlinear or non-sinusoidal travel of the piston ie the piston can be controlled to pause at TDC and BDC to generate a trapezoidal motion profile.

The instantaneous position of the piston can be determined by a position sensing system such as for example an encoder to provide a piston position input signal to the engine controller 25. The position signal(s) are used for generating drive signals to the power electronic switches S1-S8 driving the individual stator coils 26-29 to achieve the desired piston motion. The prototype engine was driven in a closcd loop with the position sensing system providing the feedback to decide the instant for commutation (changing between the stator poles 26-29 by operating switches S1-S8 to redirect the current into a different set of stator poles). The position sensing system also helps in controlling the modulation level to obtain the appropriate control parameters (for example-speed and dwell). The control system 25 may be arranged to drive the stator windings to achieve a flux profile to achieve accurate motion profile (similar to the micro stepping of stepper motors). The waveform can be a non-linear one with individual power control to achieve any non-linear motion profile required.

The power electronic circuitry is switched according to piston position and the energy generated in the windings is extracted. Energy can be extracted by non-switching methods also. Alternatively, it can be designed as any other electrical engine with suitable grid tie electronics to export the power generated.

The electrical engine may be connected to a utility grid without any power electronics by designing it as an induction engine or a synchronous engine. The generator may produce an output wave form which is non-sinusoidal by controlling the piston motion to be non-sinusoidal. 565810 Figure 8 shows a twin-cylinder embodiment essentially comprising the engine of Figures 2 and 3 duplicated side-by-side in a parallel twin configuration as could be used as an alpha or gamma configuration- Stirling engine for example. The engine comprises displacer or piston la which operates within cylinder 2a and is connected to a pair of rotors 3e which contra-oscillate relative to one another during operation of the engine in the same way as described in relation to Figures 2 and 3. Piston lb operates in a cylinder 2b and is connected to contra-oscillating rotor pair 3f. Both pairs of rotors 3e and 3f oscillate about an axis as indicated at 4 (but their axes could be separate). The rotor pairs are not connected at a mechanical level but provide a common electrical output or could be configured via a microprocessor or other control system which switches or modulates the power flow to or from the windings. Alternatively the engine may again be an electric motor driving two pistons.

Figure 9 shows an opposed twin cylinder embodiment of the engine. Piston la operates in cylinder 2a and is connected to a contra-oscillating rotor pair comprising rotors 3c and 3d via connecting rods 6 through bridge part 9, as described with reference to Figures 2 and 3. Piston lb operates in second cylinder 2b, in opposition to piston la. Connecting member 11 passes between the rotors 3c and 3d and couples the piston lb to bridge part 9. Other reference numbers indicate the same parts as before. Fleat is applied to the top of cylinder 2a.

Figure 10 shows a six cylinder embodiment comprising three adjacent opposed twin cylinder units each of which operates as described in relation to in Figure 9. Opposed pistons la and lb operate in cylinders 2a and 2b and are coupled by connecting element 11a through bridge 9a, pistons coupled by connecting element lib similarly operate in cylinders 2c and 2d, and pistons coupled by connecting element 11c operate in cylinders 2e and 2f.

In all embodiments very preferably for each oscillating rotor the distance between the axis about which the rotor moves, and the axis at which the connecting rod from the piston attaches to the rotor, is less than the distance from the same axis of motion of the rotor to the external peripheries of the rotors, so that the linear speed of the magnets and/or windings is greater than the linear speed of the piston(s). This makes it possible to increase the output voltage and simultaneously reduce the output current for the same output power, enabling in a lighter and more economic rotor design.

A further benefit of the invention is that conventional stator lamination construction may be used in preferred embodiments (which comprise stator(s)), whereas prior art linear alternator 565810 electrical engines have unconventional stator lamination construction, which increases manufacturing costs.

Figures 11 and 12 schematically show in single cylinder form for simplicity, embodiments of engines of the invention comprising alternative mechanisms for connecting between the piston (or pistons) and rotors. In Figure 11 rotors 14 have gears 15 formed on a part of the periphery of each rotor, which engage a rack 16 on either side of the connecting rod 6 to the piston 1, so that as the piston moves in the direction of arrow PI the rotors will move in the direction of arrows R1 and as the piston moves in the direction P2 the rotors move in the direction R2.

In a further embodiment (not shown) but similar to that of Figure 11, coupling between the connecting rod and the rotors may be by friction or a pinch engagement, rather than a rack and gears as shown. For example the portions of the peripheries of the rotors shown as carrying gears 15 in Figure 11 may carry a thin layer of rubber or similar synthetic material or any other material which will cause an effective friction engagement with the connecting rod 6, as may the contact surface or surfaces of the connecting rod.

In the embodiment of Figure 12 the connecting rod 6 between the piston 1 and the rotors 14 are connected by four flexible connecting elements such as belts or chains or similar (herein referred to as belts for convenience). In particular belts B1 and B2 connect from the peripheries of the rotors 14 respectively, to a lower part of the connecting rod 6 and belts B3 and B4 connect from the peripheries of the rotors to an upper part of the connecting rod 6. For example where the piston drives the rotors, belts B1 and B2 are in tension during downward movement of the piston as indicated by arrow PI, causing the rotors to pivot in the direction of arrows R1, while during upward movement of the piston P2 belts B3 and B4 are in tension causing the rotors to move in the direction of arrows R2. Alternatively where the rotors drive the piston as in. an electric motor applica tion, movement of the rotors in the direction of arrows R1 causes belts B3 and B4 to be in tension, causing upward movement of the piston in the direction of arrow R2, and when the rotors reverse their direction and move in the direction of arrows R2 belts B1 and B2 are in tension causing downward movement of the piston in the direction of arrow P2.

This is further described by way of example, in relation to the embodiment of Figures 5 to 7 arranged as a motor driving the piston(s). 565810 In all embodiments described above a biasing arrangement, of for example a mechanical spring or springs, may be provided to bias the rotors to a neutral position (a position at which the piston is intermediate of its stroke length in the cylinder). A spring arrangement may operate between the two rotors or each pair of rotors, or separately between one or more rotors and a fixed (non-moving) part of the engine. The bias arrangement may be configured to create a natural working frequency of the engine. Alternative to a mechanical spring arrangement the bias arrangement may utilise gas cylinders or similar, or magnetic force. Alternatively the spring, magnet or gas spring could act on the piston or piston rod. Springs may be used to store energy from one part of the cycle and release during another to reduce the power requirement of the electric drive motor.

The foregoing describes the invention including a preferred form thereof. Alterations and modifications as would be obvious to those skilled in the art are intended to be incorporated within the scope hereof as defined in the accompanying claims. 565810

Claims

CLAIMS 1. A cogeneration system including: an external or internal combustion engine including at least one piston reciprocally movable in a cylinder, at least two balancing rotors mounted for oscillating rotational movement about an axis or axes transverse to the axis of motion of the piston, one balancing rotor having a centre of mass on one side of and another balancing rotor having a centre of mass on an opposite side of the axis or axes of motion of the rotors, and at least one connecting member or mechanism between the piston and rotors so that the rotors move in opposition to the reciprocal movement of the piston; a generator driven by the engine for producing electricity; and an electronic control system arranged to control the electrical and/or heat output of the cogeneration system by controlling piston motion of the engine.
2. A cogeneration system according to claim 1 wherein the electronic control system is arranged to in response to reduced electrical and/or heat output demand reduce electrical and/or heat output of the cogeneration system by controlling piston motion of the engine.
3. A cogeneration system according to claim 2 wherein the electronic control system is arranged to in response to reduced electrical output demand reduce electrical output of the cogeneration system by controlling piston motion of the engine.
4. A cogeneration system according to claim 2 wherein the electronic control system is arranged to in response to reduced heat output demand reduce heat output of the cogeneration system by controlling piston motion of the engine.
5. A cogeneration system according to any one of claims 2 to 4 wherein the electronic control system is arranged to control piston motion so that a piston or piston(s) of the engine move only over a reduced swept area of the cylinder(s) of the engine.
6. A cogeneration system according to claim 5 wherein the electronic control system is arranged to control piston motion so that a piston or piston(s) of the engine move only over a reduced swept area in an upper part of the cylinder(s) of the engine. 565810 -17- 7. A cogeneration system according to any one of claims 2 to 6 wherein the electronic control system is arranged to control piston motion so that a piston or piston(s) of the engine move at a reduced velocity. 8. A cogeneration system according to any one of claims 2 to 7 wherein the electronic control system is arranged to control piston motion so that a piston or piston(s) of the engine move with a non-sinusoidal motion, 9 A cogeneration system according to any one of claims 2 to 8 wherein the electronic control system is arranged to control piston motion so that a piston or piston (s) of the engine move with motion of a different phase. 10. A cogeneration system according to any one of claims 2 to 9 wherein the electronic control system is arranged to control dwell time of a piston or pistons of the engine at either or both of top dead centre and bottom dead centre of piston motion, 11. A cogeneration system according to claim 1 wherein the electronic control system is arranged to in response to increased electrical and/or heat output demand to increase electrical and/or heat output of the cogeneration system by controlling piston motion of the engine. 12. A cogeneration system according to claim 11 wherein the electronic control system is arranged to in response to increased electrical output demand to increase electrical output of the cogeneration system by controlling piston motion of the engine. 13. A cogeneration system according to claim 13 wherein the electronic control system is arranged to in response to increased heat output demand to increase heat output of the cogeneration system by controlling piston motion of the engine, 14. A cogeneration system according to any one of claims 11 to 13 wherein the electronic control system is arranged to control piston motion so that a piston or piston(s) of the engine move with a non-sinusoidal motion. 15. A cogeneration system according to any one of claims 1 to 14 including one or more sensors arranged to sense piston motion and/or position and provide one or more piston motion and/or position input signals to the electronic control system. 565810 - 18- 16. A cogeneration system according to claim 15 wherein the engine comprises an encoder arranged to provide a piston motion and/or position input signal or signals to the electronic control system. 17. A cogeneration system according to any one of claims 1 to 16 wherein the generator comprises a stator comprising multiple windings and the control system is arranged to control piston motion by controlling energising power to the stator windings. 18. A cogeneration system according to claim 17 including one or more sensors arranged to sense piston motion and/or position and provide one or more piston motion and/or position input signals to the electronic control system and the electronic control system is arranged to generate drive signals to power electronic switches driving multiple individual stator windings to control piston motion. 19. A cogeneration system according to claim 17 wherein including one or more sensors arranged to sense piston motion and/or position and provide one or more piston motion and/or position input signals to the electronic control system and the electronic control system is arranged to control commutation between multiple stator poles to control piston motion. 20. A cogeneration system according to claim 17 wherein the control system is arranged to drive individual stator windings to control piston motion by controlling a flux profile of the stator windings. 21. A cogeneration system according to any one of claims 1 to 20 wherein the rotors are mounted for oscillating rotational movement about separate spaced axes. 22. A cogeneration system according to any one of claims 1 to 20 wherein the rotors ate mounted for oscillating rotational movement about a common axis. 23. A cogeneration system according to any one of claims 1 to 22 wherein each rotor has a substantially circular periphery about it's axis of motion. 565810 - 19- 24. A cogeneration system according to any one of claims 1 to 22 wherein each rotor comprises a major part having a curved periphery on one side of the axis of morion of the rotor and a minor part on the other side of the axis of motion of the rotor. 25. A cogeneration system according to any one of claims 1 to 24 wherein the rotors are of substantially equal mass and have a combined mass distribution that substantially balances the reciprocating mass of the piston(s). 26. A cogeneration system according to any one of claims 1 to 25 wherein the mass of the rotors and piston(s) lies in substantially the same plane. 28. A cogeneration system according to any one of claims 1 to 26 wherein a connecting member connects to one rotor on one side of the axis or axes of movement of the rotors, and a connecting member connects to the other rotor on the other side thereof. 29. A cogeneration system according to any one of claims 1 to 26 wherein the rotors have gears formed on a peripheral part of each rotor, which engage a rack on either side of a connecting member to the piston. 30. A cogeneration system according to any one of claims 1 to 26 wherein a peripheral part of each rotor friction engages with a connecting member to the piston. 31. A cogeneration system according to any one of claims 1 to 30 wherein the rotors are coupled to a connecting member to the piston by flexible connecting elements. 32. A cogeneration system according to any one of claims 1 to 31 including a biasing arrangement to bias the rotors to a neutral position in which the piston is intermediate of its stroke length in the cylinder. 33. A cogeneration system according to any one of claims 1 to 31 wherein the piston(s) is or are of a heat engine. 34. A cogeneration system according to any one of claims 1 to 31 wherein the piston(s) is or are of a Stirling engine. 56580-' - 35. A cogeneration system according to any one of claims 1 to 31 wherein the piston(s) is or are of an internal combustion engine. 36. A cogeneration system according to any one of claims 1 to 33 wherein the piston(s) is or are of a Rankine cycle machine. 37. A cogeneration system according to any one of claims 1 to 36 wherein one or more of the rotors comprises a permanent magnet or an electromagnet and the cogeneration system comprises a stator or stators associated with the rotor or rotors so that movement of the rotor(s) generate (s) an emf in the stator(s). 38. A cogeneration system according to any one of claims 1 to 36 wherein a stator or stators comprises a permanent or electromagnet and the rotor or rotors comprise a winding or windings so that movement of the rotor(s) generate(s) an emf in the rotor winding(s). 39. A cogeneration system according to any one of claims 1 to 36 wherein one rotor comprises a permanent or electromagnet and another rotor comprises a winding so that relative movement between the rotors generates an emf in the winding or windings, 40. A cogeneration system according to any one of claims 1 to 39 wherein one or more of the rotors comprises a permanent or an electromagnet and a voltage can be applied to a stator or stators to drive oscillating movement of the rotor(s) and movement of the piston(s). 41. A cogeneration system according to any one of claims 1 to 36 wherein the generator is a linear generator. 42. A cogeneration system according to claim 41 wherein the piston(s) drive one or more elements of the linear generator to move reciprocally through or within a wound stator. 43. A cogeneration system according to any one of claims 1 to 42 comprising a spring or springs between a piston and another part of the machine which is compressed or deflected during one part of piston motion to store energy and is released during another part of piston motion to release energy to thereby reduce the power consumption r balancing rotors. 565810 -21- 44. A cogeneration system according to any one of claims 1 to 42 comprising a spring or springs between balancing rotors of the machine which is compressed or deflected during one part of rotor motion to store energy and is released during another part of rotor morion to release energy to thereby reduce the power consumption for movement of the rotors. 45. A cogeneration system according to any one of claims 1 to 44 wherein the electronic control system is arranged to supply electric power to the generator to cause the generator to act as an electric motor during part of piston motion. 46. A cogeneration system according to any one of claims 1 to 45 which is a micro-combined heat and power (microCHP) unit. 46. A cogeneration system according to claim 46 which is wall mountable. DATED THIS DAY OF febfO©^ ZOO^\ AJ R PER AGENTS FOR THE APPLICANT