US20130255080A1 - Free Piston Engine Generator - Google Patents
Free Piston Engine Generator Download PDFInfo
- Publication number
- US20130255080A1 US20130255080A1 US13/992,995 US201113992995A US2013255080A1 US 20130255080 A1 US20130255080 A1 US 20130255080A1 US 201113992995 A US201113992995 A US 201113992995A US 2013255080 A1 US2013255080 A1 US 2013255080A1
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- United States
- Prior art keywords
- cylinder
- piston
- engine
- intake
- chamber
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21K—MAKING FORGED OR PRESSED METAL PRODUCTS, e.g. HORSE-SHOES, RIVETS, BOLTS OR WHEELS
- B21K3/00—Making engine or like machine parts not covered by sub-groups of B21K1/00; Making propellers or the like
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C23/00—Extruding metal; Impact extrusion
- B21C23/02—Making uncoated products
- B21C23/04—Making uncoated products by direct extrusion
- B21C23/14—Making other products
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
- F02B63/00—Adaptations of engines for driving pumps, hand-held tools or electric generators; Portable combinations of engines with engine-driven devices
- F02B63/04—Adaptations of engines for driving pumps, hand-held tools or electric generators; Portable combinations of engines with engine-driven devices for electric generators
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
- F02B71/00—Free-piston engines; Engines without rotary main shaft
- F02B71/04—Adaptations of such engines for special use; Combinations of such engines with apparatus driven thereby
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K7/00—Arrangements for handling mechanical energy structurally associated with dynamo-electric machines, e.g. structural association with mechanical driving motors or auxiliary dynamo-electric machines
- H02K7/18—Structural association of electric generators with mechanical driving motors, e.g. with turbines
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K7/00—Arrangements for handling mechanical energy structurally associated with dynamo-electric machines, e.g. structural association with mechanical driving motors or auxiliary dynamo-electric machines
- H02K7/18—Structural association of electric generators with mechanical driving motors, e.g. with turbines
- H02K7/1869—Linear generators; sectional generators
- H02K7/1876—Linear generators; sectional generators with reciprocating, linearly oscillating or vibrating parts
- H02K7/1884—Linear generators; sectional generators with reciprocating, linearly oscillating or vibrating parts structurally associated with free piston engines
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49229—Prime mover or fluid pump making
- Y10T29/49231—I.C. [internal combustion] engine making
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- General Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Output Control And Ontrol Of Special Type Engine (AREA)
- Valve Device For Special Equipments (AREA)
- Combustion Methods Of Internal-Combustion Engines (AREA)
- Cylinder Crankcases Of Internal Combustion Engines (AREA)
- Manufacture Of Motors, Generators (AREA)
Abstract
A free-piston engine generator comprising an engine cylinder, a piston configured to move within the cylinder, a cylinder housing having a bore for receiving the engine cylinder and a plurality of magnetisable elements arranged within the cylinder housing to be adjacent the cylinder along at least a portion of its length.
Description
- The present invention relates to a free piston engine generator and a method of manufacturing an engine generator. In particular, the present invention relates to a free piston engine generator which has a construction arranged to optimise the efficiency of the generator and to provide good control of piston position and piston motion by the generator.
- Electrical power can be generated using a linear generator coupled to a free piston engine, wherein the linear movement of the reciprocating piston through one or more electrical coils generates magnetic flux change, as disclosed in U.S. Pat. No. 7,318,506, for example. As the piston moves within the cylinder past the coils it interacts with a switched magnetic flux within the stator elements to generate electrical power that can be used for useful work or stored for later use.
- However, the efficiency of such an electrical power generation system is highly dependent on the thickness of the cylinder wall and the proximity of the power generation electrical elements to the piston reciprocating within the engine cylinder.
- According to the present invention there is provided a free-piston engine generator comprising an engine cylinder, a piston configured to move within the cylinder, a cylinder housing having a bore for receiving the engine cylinder and a plurality of magnetisable elements arranged within the cylinder housing to be adjacent the cylinder along at least a portion of its length.
- In the present invention, the particular arrangement of the cylinder housing which allows the plurality of magnetisable elements to be positioned adjacent the cylinder optimises the efficiency of the free piston engine generator and provides good control of the piston position and piston motion by the generator.
- Preferably, the cylinder housing has one or more recesses that permit the plurality of magnetisable elements to be positioned adjacent the cylinder. Preferably, the magnetisable elements are positioned in direct physical contact with the cylinder. Preferably, one or more of the magnetisable elements acts as a stator in the generator.
- Preferably, the cylinder is secured within the cylinder housing by an adhesive which provides thermal insulation between the cylinder and cylinder housing.
- Preferably, the cylinder housing comprises a plurality of elements that are assembled coaxially onto the cylinder.
- Preferably, the cylinder housing includes cooling means for cooling the cylinder.
- Preferably, the cylinder has a wall thickness that is less than 5% of the cylinder's internal diameter, wherein the wall thickness is typically less than about 2 mm.
- Preferably, the piston comprises alternating laminated magnetisable core elements and non-magnetising spacer elements. Preferably, the intake means are located at a central position along the cylinder, which simplifies the engine arrangement and makes this arrangement more compact by allowing a common intake means to supply fluid into each combustion chamber.
- Furthermore, by positioning the intake means at a position removed from the exhaust valve, scavenging of burned gases can be greatly improved by the unidirectional scavenging flow provided within each combustion chamber, which in turns results in improved efficiency, reduced unburned fuel hydrocarbons and lower costs.
- Preferably, the intake means comprises both an air intake means and a fuel injection means, so that fuel injection into a combustion chamber may occur during the admission of intake charge air. The intake means may also comprise a plurality of air intake means and at least one fuel injection means. Providing the air intake means and fuel injection means together in the intake means allows both these features to share a common sliding port valve, each being recessed within the void behind this sliding port valve. This results in a simpler and hence cheaper construction.
- Preferably, the air intake means comprises a sliding port valve and a secondary valve such as a solenoid poppet valve, barrel valve or other valve means arranged in series with the sliding port valve. The secondary valve can allow air into the chamber at any time when the sliding port valve is uncovered by the piston, which allows good control of the expansion ratio in response to a combustion event, independently of the position of the piston within the limits defined by the opening and closing positions of the sliding port valve.
- Preferably, the fuel injection means comprises two injectors arranged one on each side of the air intake secondary valve to allow fuel to be injected directly into the respective chamber independently of whether the intake secondary valve is open or closed. The injectors are, ideally, piezo-injectors, which allow for precise, low cost electronic actuation and control of the fuel injection.
- Preferably, the fuel injection means is configured to inject fuel immediately prior to the closing of the slide valve to ensure that fuel injected cannot be carried to and out of the exhaust port by scavenging air intake charge before the exhaust valve is closed, reducing hydrocarbon emissions.
- Preferably, ignition means are provided in each chamber to initiate combustion of the compressed air-fuel mixture. Use of spark ignition fuels and their related operating cycles inherently generate less particulate emissions than compression ignition fuels and cycles.
- Preferably, an exhaust means is provided in each combustion chamber to allow for burnt gases to be exhausted from the chamber following combustion.
- Preferably, the exhaust means is a solenoid poppet valve provided in each combustion chamber, with the valves being coaxial with the cylinder such that the limiting area in the exhaust flow may approach 40% of the cylinder bore section area, reducing exhaust gas back-pressure during exhaust and scavenging.
- Preferably, the cylinder has a length at least ten times greater than its diameter, which provides reduced variability of compression ratio in each cycle, resulting from a low rate of change of compression ratio with piston displacement error at top dead centre.
- Preferably, the piston is configured to be elongate and the engine cylinder has a bore dimensioned such that a compression ratio of between 10:1 and 16:1 can be achieved. This is higher than can be achieved in a conventional spark ignition engine due to detonation (knocking). Preferably, the engine is a ‘flex-fuel’ engine operating on any mixture of gasoline, anhydrous ethanol and hydrous ethanol. The compression ratio may be optimised by the engine management system according to the particular ethanol/gasoline/water blend that is used.
- Also, an expansion ratio greater than twice the compression ratio is obtained. A long expansion stroke allows more of the combustion energy to be transferred into the piston, and in addition allows more time for control (i.e. to react to measured piston speed variability).
- Preferably, the intake means is positioned a suitable distance from the exhaust valve to ensure that a compression ratio of between 10:1 and 16:1 can be achieved.
- According to the present invention there is also provided a method of manufacturing an engine generator, comprising providing a cylinder configured to accommodate at least one piston that is free to reciprocate within the cylinder, securing the cylinder within a cylinder housing that has a bore arranged to receive and provide structural support for the cylinder and arranging a plurality of magnetisable elements adjacent the cylinder such that, when the piston moves within the cylinder, it induces magnetic flux as it passes the plurality of magnetisable elements.
- Preferably, one or more recesses in the cylinder housing are provided for receiving the plurality of magnetisable elements.
- Preferably, one or more sections of the cylinder housing along the length of the cylinder are removed to expose one or more sections of the cylinder wall and the plurality of magnetisable elements are arranged within the recesses such that they are in direct physical contact with the cylinder wall.
- According to the present invention there is also provided a method of manufacturing an engine, comprising providing a cylinder configured to accommodate at least one piston that is free to reciprocate within the cylinder, extruding a cylinder housing that is arranged to retain and provide structural support for the cylinder, and securing the cylinder within the cylinder housing such that the cylinder wall is reinforced by the structure of the cylinder housing.
- Preferably, the plurality of magnetisable elements are arranged to provide load-bearing support to the cylinder. Preferably, the magnetisable elements are arranged to provide a force against the cylinder wall, for example they may be biased against the cylinder wall, or may be pre-loaded such that they apply a force against the cylinder wall when positioned adjacent it.
- Preferably, the cylinder is secured within the cylinder housing an adhesive material on the outside of the cylinder, wherein the adhesive material provides thermal insulation between the cylinder and cylinder housing.
- Preferably, the cylinder housing is provided with cooling means for cooling the cylinder.
- Preferably, the interior wall of the cylinder is coated with a friction-reducing material to reduce friction between the interior wall and a piston passing along it.
- Preferably, the thickness of the cylinder wall is less than 5% of the cylinder's internal diameter, wherein the thickness of the cylinder wall is typically less than about 2 mm.
- According to the present invention there is also provided a vehicle having a free piston engine generator, as described above.
- The construction of the engine generator of the present invention provides a number of important advantages over the typical free piston engine generator construction, in which two cylinder heads are affixed to two cylinders, with a separate electrical machine assembly located axially between the cylinders.
- The cylinder housing is, preferably, formed by extrusion of a ductile material, such as aluminium alloy. Advantageously, the elongated construction permits the use of extrusion manufacturing technology to form the cylinder housing, rather than casting or extensive CNC machining technology used for conventional engines. Extrusion offers a faster manufacturing cycle time and higher tolerances before machining operations than casting, reducing finished part cost. Similarly, the cylinder may be formed from extrusion or other mature, low cost tube-forming manufacturing technologies. This construction therefore reduces the overall cost of the engine's cylinder assembly.
- Furthermore, the contiguous form of the cylinder housing, which remains unbroken across the mid-section of the engine, ensures that both combustion chambers are coaxially aligned with high precision and provides a continuous bearing surface for the piston to travel across. This permits the piston to move over and past a centrally disposed intake, as described herein, whilst minimising the amount of wear to the inner surface of the cylinder during the operating life of the engine generator.
- Although the cylinder housing is, preferably, a single extruded element, it could, alternatively, be formed by the coaxial assembly of a stack of dissimilar extruded elements onto a common cylinder. For example, two extrusions may be placed either side of an intake means, wherein the extrusions are assembled coaxially onto the cylinder.
- Ideally, the wall of the cylinder housing extrusion should be sufficiently thick and/or strong that it is load-bearing to allow a much thinner cylinder wall to provide wear and sealing surfaces than would otherwise be required. The cylinder housing, ideally, has sections of material removed along the length of the cylinder to form one or more recesses that, ideally, expose the wall of the cylinder housed within. The recesses are formed through the cylinder housing, preferably extending from the outer surface inwards, such that the recesses open outwards. A plurality of magnetisable elements can be positioned in close proximity to the cylinder by arranging them in the one or more recesses, each magnetisable element preferably fixed directly to the wall of the cylinder, which separates them from the moving magnetic circuit elements of the piston.
- The cylinder wall thickness dimension is an important determinant of the efficiency of the electrical machine, and should be as small as possible for high efficiency. By providing adequate load bearing strength using the cylinder housing and magnetisable stator elements, the cylinder wall is not required to bear cylinder fluid pressures and may be made considerably thinner subject to manufacturing, assembly and wear constraints.
- The inner and outer surfaces of the cylinder provide substrates for wear and thermal coatings respectively. A thermal coating can be applied to the cylinder outer surface in the form of an adhesive material to provide a secure, insulating and load bearing bond between the cylinder and cylinder housing. Furthermore, the arrangement of securing a cylinder within the cylinder housing provides the advantage that the mating surfaces of the respective components do not need to be finished to any particular standard, other than to allow the cylinder to be fitted within the cylinder housing.
- A free piston engine generator according to the present invention has a number of applications. For example, it may be integrated in a series-hybrid electric vehicle power train incorporating a transient electrical power store and one or more drive motors suitable for use as an automotive power source in small passenger vehicles, wherein electrical power generated by the free piston engine is accumulated in an electrical energy storage device on board the vehicle to be delivered to the vehicle drive motors on demand.
- As a power source for a small passenger vehicle, the present invention preferably runs on a two-stroke engine cycle with spark ignition, with four cylinders being arranged in a planar configuration such that the engine might be transverse mounted beneath the front or rear seats of the vehicle, offering significantly more design flexibility to the layout of the passenger and storage spaces compared to a conventional internal combustion engine.
- Each cylinder includes a free piston whose movement induces electrical power in a linear generator arranged around each cylinder, and whose movement is controllable by various means including the timing of valve and ignition events, and by modulation of the power drawn from or supplied to the piston on each stroke. The movement of pistons is synchronised such that the engine is fully balanced, wherein the piston, ideally, comprises alternating magnetisable elements and non-magnetising spacer elements.
- Furthermore, each cylinder is charged by means of an intake mechanism that introduces fluid into the cylinder at a position distal from each end of the cylinder. The intake mechanism includes a poppet valve and sliding port valve in series such that the timing of the intake flow events may be controlled independently of the piston positions relative to the cylinders. Exhaust gas leaves the cylinders from exhaust valve mechanisms located at the end of each cylinder.
- The geometry of the cylinder and disposition of the intake and exhaust mechanisms are such that the exhaust scavenging is completed with limited mixing between intake fluid and exhaust fluid. The combustion chamber geometry offers a low surface area-to-volume ratio, and low conductivity materials are used in the piston crown and cylinder head, so that minimal heat is rejected from the engine. The cylinder and piston geometry provides an expansion ratio which is at least two times the compression ratio.
- The arrangement, and number, of cylinders used is, however, dependent on the application and the engine operating cycle can also be varied for different applications, for example: spark ignition internal combustion; homogeneous charge compression ignition internal combustion; and heterogeneous charge compression ignition. Some of the features of the present invention may also be embodied with an external combustion cycle. Examples of external combustion cycle embodiments include use of the present invention as a gas expander for fluid from a gas turbine exhaust, an organic rankine cycle or a Stirling cycle. In a Stirling engine, heat from an external combustion source is supplied to the chamber containing compressed working fluid at top dead centre. After expansion, the exhaust gases are expelled to a closed cooling chamber before being readmitted to the chamber through the intake means in a closed circuit.
- The fuel in various alternative embodiments may be hydrous ethanol, anhydrous ethanol-gasoline blends, or gasoline. The invention may also be embodied as using diesel, bio-diesel, methane (CNG, LNG or biogas) or other gaseous or liquid fuels. In an external combustion embodiment a wide range of combustible fuels may be used.
- Accordingly, in conjunction with an energy storage system to provide peak transient power output requirements, the present invention provides a low-cost, high efficiency power supply for small passenger vehicle automotive applications, and many other applications where low cost and high efficiency are key design considerations, for example as a static power generator for distributed power generation.
- An example of the present invention will now be described, with reference to the accompanying figures, in which:
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FIG. 1 shows a longitudinal section through a cylinder having a piston according to an example of the present invention; -
FIG. 2 is a longitudinal section through the piston, showing the construction from planar elements; -
FIG. 3 is a perpendicular section through the piston, showing the concentric arrangement of the shaft and planar elements; -
FIG. 4 is a sectional view of the cylinder ofFIG. 3 illustrating the magnetic flux in switched stator elements caused by movement of the piston according tot the present invention; -
FIG. 5 a is a perpendicular section through a cylinder showing the linear generator stator and the magnetic circuit formed by a permeable element in the first piston; -
FIG. 5 b is a perpendicular section of an alternative linear generator stator arrangement for two adjacent cylinders wherein the linear generator stator and the magnetic circuit are formed by a permeable element in the first piston; -
FIG. 6 is a partial sectional view of the cylinder illustrating its construction; -
FIG. 7 is a more detailed longitudinal section of the intake poppet valve, intake port valve and fuel injector arrangement during the intake charge displacement scavenging phase; -
FIG. 8 is a more detailed longitudinal section of the exhaust means including the exhaust poppet valve and actuator during the exhaust phase; -
FIG. 9 is a time-displacement plot showing the changing piston position within a cylinder during a complete engine cycle, and the timing of engine cycle events during this period; -
FIG. 9 a is a table showing different compression ratio control means that may be employed to control the compression ratio in a typical engine cycle; -
FIG. 9 b is a flow chart corresponding to the table inFIG. 9 a; -
FIG. 10 is a pressure-volume plot showing a typical cylinder pressure plot during a complete engine cycle; -
FIG. 11 is a schematic longitudinal section through a cylinder at top dead centre, at the end of the compression phase and around the time of spark ignition and initiation of the combustion event in the first chamber; -
FIG. 12 is a schematic longitudinal section through a cylinder mid way through the expansion phase of the first chamber; -
FIG. 13 is a schematic longitudinal section through a cylinder at the end of the expansion phase, but before the intake poppet valve has opened; -
FIG. 14 is a schematic longitudinal section through a cylinder following the opening of the intake poppet valve to chargechamber 1, allowing intake charge fluid pressure to equalise the lower cylinder pressure in the first chamber; -
FIG. 15 is a schematic longitudinal section through a cylinder following the opening of the exhaust poppet valve, and whilst the intake poppet valve remains open, scavenging the first chamber; -
FIG. 16 is a schematic longitudinal section through a cylinder during fuel injection into the first chamber after the intake poppet valve has closed; -
FIG. 17 is a schematic longitudinal section through a cylinder during lubricant injection onto the piston outer surface; -
FIG. 18 is a schematic longitudinal section through a cylinder whilst the exhaust poppet valve is open, and after the intake poppet valve and sliding port valve have closed such that continuing expulsion of exhaust gases from the first chamber is achieved by piston displacement; -
FIG. 19 is a schematic longitudinal section through a cylinder mid way through the compression phase in the first chamber; -
FIGS. 20A and 20B shows a section of a cylinder housing of an engine generator according to the present invention both with (A) and without (B) the electrical machine attached; -
FIG. 20C shows a perpendicular section of a cylinder housing of an engine generator through plane X-X indicated onFIG. 20A ; -
FIG. 21 is a schematic perpendicular section of a four cylinder engine construction through the intake means including the electrical charge compressor; -
FIG. 22 is a schematic perpendicular section of a four cylinder engine construction through the electrical generator means; and -
FIG. 23 is a schematic perpendicular section of a four cylinder engine construction through the exhaust means. -
FIG. 1 shows an example of an engine according to the present invention, comprising a hollowlinear cylinder 1. Apiston 2 is provided within thecylinder 1, thepiston 2 having a constant diameter that is configured to be slightly smaller than the inside diameter of thecylinder 1, but only to the extent that thepiston 2 is free to move along the length of thecylinder 1. Thepiston 2 is otherwise constrained in coaxial alignment with thecylinder 1, thereby effectively partitioning thecylinder 1 into afirst combustion chamber 3 and asecond combustion chamber 4, each chamber having a variable volume depending on the position of thepiston 2 within thecylinder 1. No part of thepiston 2 extends outside thecylinder 1. Using thefirst chamber 3 as an example, each of thechambers variable height 3 a and afixed diameter 3 b. - The
cylinder 1 is, preferably, rotationally symmetric about its axis and is symmetrical about a central plane perpendicular to its axis. Although other geometric shapes could potentially be used to perform the invention, for example having square or rectangular section pistons, the arrangement having circular section pistons is preferred. Thecylinder 1 has a series of apertures 1 a, 1 b provided along its length and distal from the ends, preferably in a central location. Through motion of thepiston 2, the apertures 1 a, 1 b form a sliding port intake valve 6 a, which is arranged to operate in conjunction with an air intake 6 b provided around at least a portion of thecylinder 1, as is described in detail below. - The
cylinder 1 preferably has a length at least ten times greater than its diameter to provide reduced variability of compression ratio in each cycle, as a result of a low rate of change of compression ratio with piston displacement error at top dead centre. -
FIG. 2 shows apiston 2 having anouter surface 2 a and comprising acentral shaft 2 c onto which are mounted a series of cylindrical elements. These cylindrical elements may include apiston crown 2 d at each end of thecentral shaft 2 c, eachpiston crown 2 d preferably constructed from a temperature resistant and insulating material such as ceramic. The pistoncrown end surface 2 b is, preferably, slightly concave, reducing the surface area-to-volume ratios of the first andsecond chambers - The
piston crown 2 d includes oil control features 2 e to control the degree of lubrication wetting of thecylinder 1 during operation of the engine. These features comprise a groove and an oil control ring as are commonly employed in conventional internal combustion engines. - Laminated
core elements 2 f are also mounted on thepiston shaft 2 c. Eachcore element 2 f is constructed from laminations of a magnetically permeable material, such as iron ferrite, to reduce eddy current losses during operation of the engine. - Spacer elements 2 g are also mounted on the
piston shaft 2 c. Each spacer element 2 g ideally has low magnetic permeability and is preferably constructed from a lightweight material such as aluminium alloy and has avoid 2 h formed within it to further reduce its weight and hence reduce mechanical forces exerted on the engine utilising it. The spacer elements 2 g are included to fix the relative position of each of thecore elements 2 f and also act to limit the loss of “blow-by” gases flowing out of eachchamber piston 2 assembly to a minimum. - Bearing elements 2 i are also mounted on the
piston shaft 2 c, located at approximately 25% and 75% of the length of thepiston 2 to reduce the risk of thermally-induced distortion of the axis of thepiston 2 causing it to lock in thecylinder 1 or otherwise damage thecylinder 1. Each bearing element 2 i features a weight-reduction void 2 j and has a diameter very slightly larger than thecore elements 2 f and the spacer elements 2 g. The bearing elements 2 i also have a profiledouter surface 2 k for bearing the weight of thepiston 2, and any other side loads present, whilst keeping frictional losses and wear to a minimum. The bearing element 2 i are preferably constructed from a hard, wear resistant material such as ceramic or carbon and the profiledouter surface 2 k may be coated in a low friction material. Alternatively, bearing elements may incorporate roller bearing features as are commonly used in sliding applications. - Similar to the piston crown, or perhaps instead of, the bearing element 2 i may also include oil control features to control the degree of lubrication wetting of the
cylinder 1 during operation of the engine. These features comprise a groove and an oil control ring as are commonly employed in conventional internal combustion engines. - The total length of the piston is, preferably, five times its diameter and is at least sufficient to completely close the sliding port valve such that at no time does the sliding port valve allow
combustion chambers -
FIG. 3 is a sectional view of thepiston 2, showing thepiston shaft 2 c passing through acore element 2 f. The piston shaft ends 2 l are mechanically deformed or otherwise fixed to the piston crowns 2 d such that theelements 2 f, 2 g, 2 i that are mounted to thepiston shaft 2 c are securely retained under the action of tension maintained in thepiston shaft 2 c. - The alternating arrangement of
core elements 2 f and spacers 2 g positions thecore laminations 2 f at the correct pitch for efficient operation as, for example, part of a linear switched reluctance generator machine comprising the movingpiston 2 and a linear generator means, for example a plurality of coils spaced along the length of the cylinder within which the piston reciprocates. -
FIG. 4 shows an example of linear generator means 9 provided around the outside of thecylinder 1, along at least a portion of its length, for facilitating the transfer of energy between thepiston 2 and electrical output means 9 e. The linear generator means 9 includes a number ofcoils 9 a and a number ofstators 9 c, in the form of magnetisable elements, alternating along the length of the linear generator means 9. - The linear generator means 9 may be of a number of different electrical machine types, for example a linear switched reluctance generator. In the arrangement shown, coils 9 a are switched by switching
device 9 b so as to induce magnetic fields within themagnetisable stators 9 c and thepiston core laminations 2 e. Themagnetisable stators 9 c may be laminated or constructed from a soft magnetic composite (SMC) material, for example. In each approach the stators are constructed from electrically conducting and magnetisable elements separated by non-conducting material which reduces heat losses from magnetically induced eddy currents. - The transverse magnetic flux created in the
magnetisable stators 9 c andpiston core laminations 2 f under the action of the switched coils 9 a is also indicated inFIG. 4 . The linear generator means 9 functions as a linear switched reluctance device, or as a linear switched flux device. Power is generated at the electrical output means 9 e as the flux circuits, established in themagnetisable stators 9 c and induced in thepiston core laminations 2 f, are cut by the motion of thepiston 2. This permits a highly efficient electrical generation means without the use of permanent magnets, which may demagnetise under the high temperature conditions within an internal combustion engine, and which might otherwise add significant cost to the engine due the use of costly rare earth metals. - Additionally, a
control module 9 d may be employed, comprising several different control means, as described below. The different control means are provided to achieve the desired rate of transfer of energy between thepiston 2 and electrical output means 9 e in order to deliver the maximum electrical output whilst satisfying the desired motion characteristics of thepiston 2, including compression rate and ratio, expansion rate and ratio, and piston dwell time at top dead centre of eachchamber - A valve control means may be used to control the
intake valve 6 c and theexhaust valve 7 b. By controlling the closure of theexhaust valve 7 b, the valve control means is able to control the start of the compression phase. In a similar way, the valve control means can also be used to control exhaust gas recirculation (EGR), intake charge and compression ratio. - A compression ratio control means that is appropriate to the type of electrical machine may also be employed. For example, in the case of a switched reluctance machine, compression ratio control is partially achieved by varying the phase, frequency and current applied to the switched coils 9 a. This changes the rate at which induced transverse flux is cut by the motion of the
piston 2, and therefore changes the force that is applied to thepiston 2. Accordingly, thecoils 9 a may be used to control the kinetic energy of thepiston 2, both at the point ofexhaust valve 7 b closure and during the subsequent deceleration of thepiston 2. - A spark ignition timing control means may then be employed to respond to any residual cycle-to-cycle variability in the compression ratio to ensure that the adverse impact of this residual variability on engine emissions and efficiency are minimised, as follows. Generally, the expected compression ratio at the end of each compression phase is the target compression ratio plus an error that is related to system variability, such as the combustion event that occurred in the
opposite combustion chamber piston 2 to optimize the combustion event for the expected compression ratio at the end of each compression phase. - The target compression ratio will normally be a constant depending on the
fuel 5 a that is used. However, a compression ratio error may be derived from a +/−20% variation of thecombustion chamber height 3 a. Hence if the target compression ratio is 12:1, the actual compression ratio may be in the range 10:1 to 15:1. Advancement or retardation of the spark ignition event by the spark ignition timing control means will therefore reduce the adverse emissions and efficiency impact of this error. - Additionally, a fuel injection control means may be employed to control the timing of the injection of
fuel 5 a so that it is injected into acombustion chamber - Furthermore, a temperature control means may be provided, including one or more temperature sensors positioned in proximity to the
coils 9 a, electronic devices and other elements sensitive to high temperatures, to control the flow of cooling air in the system via thecompressor 6 e in response to detected temperature changes. The temperature control means may be in communication with the valve control means to limit engine power output when sustained elevated temperature readings are detected to avoid engine damage. - Further sensors that may be employed by the
control module 9 d preferably include an exhaust gas (Lambda) sensor and an air flow sensor to determine the amount offuel 5 a to be injected into a chamber according to the quantity of air added, for a given fuel type. Accordingly, a fuel sensor may also be employed to determine the type of fuel being used. -
FIG. 5 a shows a perpendicular section through one of themagnetisable stator elements 9 c, showing the arrangement ofcoils 9 a andstators 9 c relative to each other. An alternative embodiment is shown inFIG. 5 b, in which asingle stator 9 c andcoil 9 a are used to induce magnetic flux in twoadjacent pistons 2. This configuration has a cost advantage compared to that shown inFIG. 5 a due to the reduced number ofcoils 9 a required. -
FIG. 6 is a sectional view of thecylinder 1, which is preferably constructed from a material of low magnetic permeability, such as an aluminium alloy. Theinner surface 1 c of thecylinder 1 has a coating 1 e of a hard, wear-resistant material such as nickel silicon-carbide, reaction bonded silicon nitride, chrome plating, or other metallic, ceramic or other chemical coating. On the outer surface 1 d, an insulator coating 1 f such as zirconium oxide or other sufficiently thermally insulating ceramic is applied. It will be apparent to a skilled person that the whole cylinder has an identical construction to this sectional view of the part of the cylinder close to thecylinder end 1 g. -
FIG. 7 shows the intake means 6 provided around thecylinder 1, the intake means 6 comprising apertures 6 a, which are a corresponding size and align with the apertures 1 a, 1 b provided in thecylinder 1, and an air intake 6 b. The apertures 6 a in the intake means 6 are connected by achannel 6 h in which anintake poppet valve 6 c is seated. Thechannel 6 h is of minimal volume, either having a short length, small cross sectional area or a combination of both, to minimise uncontrolled expansion losses within thechannel 6 h during the expansion phase. - The
intake poppet valve 6 c seals thechannel 6 h from anintake manifold 6 f provided adjacent to thecylinder 1 as part of the air intake 6 b. Theintake poppet valve 6 c is operated by apoppet valve actuator 6 d, which may be an electrically operated solenoid means or other suitable electrical or mechanical means. - When the sliding port intake valve 6 a and the
intake poppet valve 6 c are both open with respect to one of the first orsecond chambers intake manifold 6 f is in fluid communication with that chamber via thechannel 6 h. The intake means 6 is preferably provided with arecess 6 g arranged to receive theintake poppet valve 6 c when fully open to ensure that fluid can flow freely through thechannel 6 h. - The air intake 6 b also includes an
intake charge compressor 6 e which may be operated electrically, mechanically, or under the action of pressure waves originating from the air intake 6 b. Theintake charge compressor 6 e can also be operated under the action of pressure waves originating from an exhaust means 7 provided at each end of thecylinder 1, as described below, or by a conventional exhaust turbocharger device. Theintake charge compressor 6 e may be a positive displacement device, centrifugal device, axial flow device, pressure wave device, or any suitable compression device. Theintake charge compressor 6 e elevates pressure in theintake manifold 6 f such that when the air intake 6 b is opened, the pressure in theintake manifold 6 f is greater than the pressure in thechamber intake manifold 6 f, thereby permitting a flow of intake charge fluid. - Fuel injection means 5 are also provided within the intake means 6, such as a solenoid injector or piezo-
injector 5. Although a centrally positionedsingle fuel injector 5 may be adequate, there is preferably afuel injector 5 provided either side of theintake poppet valve 6 c and arranged proximate to the extremities of the sliding port valves 6 a. Thefuel injectors 5 are preferably recessed in the intake means 6 such that thepiston 2 may pass over and past the sliding port intake valves 6 a and air intake 6 b without obstruction. Thefuel injectors 5 are configured to inject fuel into therespective chambers - Lubrication means 10 are also provided preferably recessed within the intake means 6 and arranged such that the
piston 2 may pass over and past the intake means 6 without obstruction, whereby the piston may be lubricated. -
FIG. 8 shows the exhaust means 7 provided at each end of thecylinder 1. The exhaust means 7 comprises acylinder head 7 a removably attached, by screw means or similar, to the end of thecylinder 1. Within eachcylinder head 7 a is located anexhaust poppet valve 7 b, coaxially aligned with the axis of thecylinder 1. Theexhaust poppet valve 7 b is operated by an exhaustpoppet valve actuator 7 c, which may be an electrically operated solenoid means or other electrical or mechanical means. Accordingly, when theintake poppet valve 6 c and theexhaust poppet valve 7 b within the first orsecond chamber - The exhaust means 7 also includes an
exhaust manifold channel 7 d provided within the cylinder head, into which exhaust gases may flow, under the action of a pressure differential between the adjacent first orsecond chamber exhaust manifold channel 7 d when theexhaust poppet valve 7 b is open. The flow of the exhaust gases can be better seen in the arrangement of cylinders illustrated inFIG. 20 , which shows the direction of the exhaust gas flow to be substantially perpendicular to the axis of thecylinder 1. - Ignition means 8, such as a spark plug, are also provided at each end of the
cylinder 1, the ignition means 8 being located within thecylinder head 7 a and, preferably, recessed such that there is no obstruction of thepiston 2 during the normal operating cycle of the engine. - The, preferably, coaxial arrangement of the
exhaust poppet valve 7 b with the axis of thecylinder 1 allows theexhaust poppet valve 7 b diameter to be much larger relative to the diameter of thechambers - Each
cylinder head 7 a is constructed from a hard-wearing and good insulating material, such as ceramic, to minimise heat rejection and avoid the need for separate valve seat components. -
FIG. 9 shows a time-displacement plot of an engine according to the present invention, illustrating the movement of thepiston 2 over the course of a complete engine cycle. Although the operation of the engine is described here with reference to thefirst chamber 3, a skilled person will recognise that the operation and sequence of events of thesecond chamber 4 is exactly the same as thefirst chamber 3, but 180 degrees out of phase—that is to say, top dead centre for thefirst chamber 3 occurs at the same time as bottom dead centre for thesecond chamber 4. -
FIG. 9 a is a table showing a number of different compression ratio control means that may be employed to control the compression ratio in response to changes in signals received from a number of different variables which can affect the compression ratio during an engine cycle.FIG. 9 b is a flow chart corresponding toFIG. 9 a. The compression ratio control means may comprise part of thecontrol module 9 d, discussed earlier. - Both the table and flow chart illustrate the main variables which can affect the compression ratio at the different stages (A to F) of an engine cycle, such as the one illustrated in
FIG. 9 . These variables include: power demand from user, the fuel type being used, the compression ratio and knock status from the previous engine cycle, piston position, and the kinetic energy of a piston. The table and flow chart illustrate the different processes that take place to control the compression ratio and how the different variables affect these throughout an engine cycle and also the subsequent effect of each process, which can have an effect on more than one of the control processes throughout the engine cycle. It can be seen that in the last step of the sequence, once the expected compression ratio has been determined, optimum ignition timing is achieved by the spark ignition timing control means adjusting the timing of the spark event. - The events A to F, highlighted throughout the engine cycle, correspond to the events A to F illustrated in
FIG. 10 , which shows a typical pressure-volume plot for acombustion chamber FIGS. 9 to 10 are referred to in the following discussion ofFIGS. 11 to 19 . - Considering now a complete engine cycle, at the start of the engine cycle, the
first chamber 3 contains a compressed mixture composed primarily of pre-mixed fuel and air, with a minority proportion of residual exhaust gases retained from the previous cycle. It is well known that the presence of a controlled quantity of exhaust gases is advantageous for the efficient operation of the engine, since this can reduce or eliminate the need for intake charge throttling as a means of engine power modulation, which is a significant source of losses in conventional spark ignition engines. In addition, formation of nitrous oxide pollutant gases are reduced since peak combustion temperatures and pressures are lower than in an engine without exhaust gas retention. This is a consequence of the exhaust gas fraction not contributing to the combustion reaction, and due to the high heat capacity of carbon dioxide and water in the retained gases. -
FIG. 11 shows the position of the piston relative to thecylinder 1, defining the geometry of thefirst chamber 3 at top dead centre (A). This is also around the point of initiation of the combustion phase AB. The distance between the top of thepiston 2 b and the end of thefirst chamber 3 is at least half the diameter of thefirst chamber 3, giving a lower surface area to volume ratio compared to combustion chambers in conventional internal combustion engines, and reducing the heat losses from thefirst chamber 3 during combustion. The ignition means 8 are recessed within thecylinder head 7 a so that in the event that thepiston 2 approaches top dead centre in an uncontrolled manner there is no possibility of contact between the ignition means 8 and thepiston crown 2 d. Instead, compression will continue until the motion of thepiston 2 is arrested by the continuing build up of pressure due to approximately adiabatic compression in thefirst chamber 3. With reference toFIG. 10 , the combustion expansion phase AB is initiated by an ignition event (A). -
FIG. 12 shows the position of thepiston 2 relative the linear generator means 9 mid-way through the expansion phase (AB and BC). Thefirst chamber 3 expands as thepiston 2 moves under the action of the pressure differential between thefirst chamber 3 and thesecond chamber 4. The pressure in thesecond chamber 4 at this point is approximately equivalent to the pressure in theintake manifold 6 f. The expansion of thefirst chamber 3 is opposed by the action of the linear generator means 9, which may be modulated in order to achieve a desired expansion rate, to meet the engine performance, efficiency and emissions objectives. -
FIG. 13 shows the position of thepiston 2 at bottom dead centre relative to thefirst chamber 3. At the end of the expansion phase (C), the motion of thepiston 2 is arrested under the action of the linear generator means 9 and the pressure differential between thefirst chamber 3 and thesecond chamber 4. The pressure in thesecond chamber 4 at this point is approximately equal to the high pressure in thefirst chamber 3 at its top dead centre position (A). Preferably, the expansion ratio is at least two times the compression ratio, wherein the compression ratio is in the range of 10:1 to 16:1. This gives an improved thermal efficiency compared to conventional internal combustion engines wherein the expansion ratio is similar to the compression ratio. -
FIG. 14 shows the arrangement of thepiston 2 and intake means 6 and the initial flow of intake gas at the time of bottom dead centre during the intake equalisation phase (CD). This arrangement can also be seen inFIG. 7 . At this point, the sliding port intake valve 6 a is open due to thepiston 2 sliding through and past the apertures 1 a, 1 b provided along theinner wall 1 c of thecylinder 1. The pressure in thefirst chamber 3 is lower than the pressure in theintake manifold 6 f due to the over-expansion reducing fluid pressure in thefirst chamber 3 and due to theintake compressor 6 e elevating the pressure in theintake manifold 6 e. Around this time, theintake poppet valve 6 c is opened by intakepoppet valve actuator 6 d allowing intake charge to enter thefirst chamber 3 withincylinder 1 whose pressure approaches equalisation with the pressure at theintake manifold 6 f. A short time after theintake poppet valve 6 c opens, theexhaust poppet valve 7 b is also opened allowing exhaust gases to exit thefirst chamber 3 under the action of the pressure differential between thefirst chamber 3 and theexhaust manifold channel 7 d, which remains close to ambient atmospheric pressure. -
FIG. 15 shows the position of thepiston 2 during the intake charge displacement scavenging phase (DE). Exhaust gas scavenging is achieved by the continuing displacement of exhaust gas in thefirst chamber 3 into theexhaust manifold channel 7 d with fresh intake charge introduced at the piston end of thefirst chamber 3. Once the intended quantity of intake charge has been admitted to thefirst chamber 3, theintake poppet valve 6 c is closed and the expulsion of exhaust gas continues by the movement of thepiston 2, as shown inFIG. 17 , explained below. -
FIG. 16 shows the arrangement of thepiston 2 and intake means 6 at the point of fuel injection (E).Fuel 5 a is introduced directly onto the approachingpiston crown 2 d which has the effects of rapidly vaporising fuel, cooling thepiston crown 2 d and minimising the losses and emissions of unburned fuel as a wet film on theinner wall 1 c of thecylinder 1, which might otherwise vaporise in thesecond chamber 4 during the expansion phase. -
FIG. 17 shows the position of thepiston 2 during lubrication (E), whereby a small quantity of lubricant is periodically introduced by the lubrication means 10 directly to the pistonouter surface 2 a as it passes the intake sliding port valve 6 a. This arrangement minimises hydrocarbon emissions associated with lubricant wetting of the cylinder inner wall, and may also reduce the extent of dissolution of fuel in the cylinder inner wall oil film. Oil control ring features 2 e are included in thepiston crown 2 d and/or bearing elements 2 i to further reduce the extent of lubricant wall wetting in the first andsecond chambers -
FIG. 18 shows the position of thepiston 2 during the piston displacement scavenging phase EF. Theintake poppet valve 6 c is closed and the expulsion of exhaust gas continues by the movement of thepiston 2. Thepiston 2 at this time is moving towards the exhaust means 7 and reducing the volume of thefirst chamber 3 due to the combustion event in thesecond chamber 4. - As a result of the relatively larger diameter of the exhaust poppet valve, as discussed above, the limiting area in the exhaust flow past the valve stem may approach 40% of the cylinder bore section area, resulting in low exhaust back pressure losses during both the intake charge displacement scavenging phase (DE) and piston displacement scavenging phase (EF).
-
FIG. 19 shows a longitudinal section of the position of thepiston 2 relative to thecylinder 1 mid-way through the compression phase (FA). When a sufficient exhaust gas expulsion has been achieved, such that the proportion of exhaust gas in the fluid in thefirst chamber 3 is close to the intended level, theexhaust poppet valve 7 b is closed and the compression phase (FA) begins. Compression continues at a varying rate as thepiston 2 a ccelerates and decelerates under the action of the pressure differential between thefirst chamber 3 and thesecond chamber 4. The pressure in thesecond chamber 4 is at this point falling during the expansion phases (AB and BC) and by the action of the linear generator means 9. The linear generator force may be modulated in order to achieve the desired compression rate to meet the engine performance, efficiency and emissions objectives. The compression rate in thefirst chamber 3 is substantially equal to and opposite the expansion rate inchamber 4. -
FIGS. 20A and 20B , in particular, show how thecylinder 1 is, preferably, located coaxially within acylinder housing 11, which provides structural support to thecylinder 1 and can also be arranged to provide cooling means. Thecylinder housing 11 may be slightly shorter than thecylinder 1 and thecylinder heads 7 a may be attached, by screw fixings or any other suitable means, to thecylinder housing 11 to maintain compression between eachcylinder head 7 a and the surface of each cylinder end 1 d.FIG. 20C shows section of thecylinder housing 11 having anelectrical machine 9 e attached - The
cylinder housing 11 is, preferably, formed by extrusion of a ductile material, such as aluminium alloy, and arranged to provide structural support and cooling means 12 whilst allowing the electricalpower generating components 9 a-9 e to be integrated in close and accurately defined proximity to the movingpiston 1 within thecylinder 1. - The wall of the
cylinder housing 11 extrusion is, ideally, sufficiently thick and/or strong that it is load-bearing to allow a muchthinner cylinder 1 wall that provides wear and sealing surfaces than would otherwise be required. As mentioned above, the generator of the present invention comprises a plurality ofmagnetic coils 9 a arranged in thecylinder housing 11, a plurality of stators, in the form ofmagnetisable elements 9 c and thepiston 2, which acts as the translator in this instance. - The
cylinder housing 11, preferably, has sections of material removed along the length of thecylinder 1 to form one ormore recesses 15 that, ideally, extend through thecylinder housing 11 to expose the wall of thecylinder 1 housed within. A plurality of the, ideally, load-bearing,magnetisable elements 9 c can be positioned in close proximity to thecylinder 1 by arranging them in the one ormore recesses 15, eachmagnetisable element 9 c preferably being fixed directly to the wall of thecylinder 1, which separates them from the movingmagnetic circuit elements 2 f of thepiston 2. - In the example shown, only one
magnetisable element 9 c is provided to a recess. However, it should be noted that two or moremagnetisable elements 9 c recesses may be positioned within asingle recess 15 if desired, depending on desired performance characteristics, and that not allrecesses 15 have to contain the same number ofmagnetisable elements 9 c, if any. The inner and outer surfaces of thecylinder 1 provide substrates for wear and thermal coatings respectively. A thermal coating can be applied to the outer surface of thecylinder 2 in the form of an adhesive material, for example, to provide a secure, insulating and load bearing bond between thecylinder 1 andcylinder housing 11. -
FIG. 21 shows an exemplary engine arrangement comprising four free-piston engines configured to operate in cycles that are synchronised to create a fully balanced engine. In this configuration, the overall length of the engine generating 50 kw with a thermal efficiency of around 50% is approximately 1400 mm. Thecylinder housing 11 can be attached, by screw fixings or any other suitable means, to astructural housing 13 which provides the basis for mechanical attachment of the engine to a vehicle or other device drawing electrical power from the electrical output means 9 e such as is shown inFIG. 22 . Anenclosure 14 provides a physical enclosure for the engine, manifolds and control systems. Interfaces are provided across theenclosure 14 for intake and exhaust flows, admission of fuel and lubricant, rejection of heat, output of electrical power and input of electrical power for start-up and control. -
FIG. 23 shows an end view of an arrangement in which acylinder head 7 a houses four engines, whereby exhaust gases exit an engine'scombustion chamber exhaust poppet valve 7 b and flow substantially perpendicular to the axes of thecylinders 1. - Advantageously, with the present invention, the narrow bore geometry of the
first chamber 3, and the relative positions of the intake means 6 and exhaust means 7, which are located at opposite ends of thefirst chamber 3, permits a highly efficient and effective scavenging process with little mixing between the intake charge and the exhaust gases. This scheme offers several advantages compared to scavenging in conventional two stroke engines or in free piston two stroke engines. - Firstly, the expulsion of exhaust gases can be accurately controlled by the timing of the exhaust valve closure, providing variable internal exhaust gas recirculation as a means of engine power control without the need for a throttling device and the associated engine pumping losses.
- Secondly, the limited mixing between the retained exhaust gas and the intake charge may improve the completeness of combustion since the combustion flame front within the fresh charge is not interrupted by pockets of non-combustible exhaust gas mixed with the combustible fuel/air mixture.
- Thirdly, the introduction of
fuel 5 a by the fuel injector means 5 shortly before the closure of the sliding intake port valve 6 a, and also the introduction of lubricant by the lubrication means 10 around this time, is unlikely to result in fuel or lubricant entrainment in the exhaust gases and cause tailpipe hydrocarbon emissions. - Furthermore, the geometry of the
chambers piston 2 b and the end of thechambers chamber chamber first chamber 3 at top dead centre due to combustion variations in thesecond chamber 4, control system tolerances or other sources of variability, are considerably reduced. Engine operating cycle stability and control are considerably improved by this feature. - By arresting the motion of the
piston 2 at top dead centre (A), a desired compression ratio may be achieved. A target compression ratio may be in the range 10:1 to 16:1, and higher compression ratios will in general enable higher thermal efficiencies to be achieved. Different compression ratio targets may be set for different fuels, to take advantage of the octane number characteristics of the particular fuel or blend of fuels in use. Any combination of feedback signals from a knock-sensor, from piston motion, from exhaust gas composition, and from other engine operating characteristics may be used as input to thecontrol module 9 d in order to achieve the desired compression rate and ratio. - An additional benefit of this embodiment compared to other internal combustion engines is that noise levels are reduced due to the over-expansion cycle and which results in a low pressure differential across the exhaust valve immediately prior to opening. As a result, the shock waves propagating through the exhaust system and causing exhaust noise in a conventional internal combustion engine or free piston engine are substantially avoided.
- If the present invention was incorporated into a low cost passenger vehicle having a series hybrid drive train configuration, the cost to the vehicle user as a means for automotive electrical power generation are reduced compared to existing internal combustion engine designs. This reduction in cost is a result of a number of factors, including the low cost of fuel per unit of electrical power generated due to high thermal efficiency. Other factors include the low cost of component manufacture due to the relatively small number of high tolerance dimensions required and hence the low cost of component assembly. Also, the cost of maintenance is low due to the small number of separate components and moving parts required.
- Furthermore, the avoidance of complex auxiliary systems and the elimination of complex force transmission pathways including highly stresses hydrodynamic plain bearings characteristic of conventional internal combustion engines and the low cost of materials for the engine, due to the reduced part count and the small number of components having functional design constraints that require the use of high cost materials such as permanent magnets or specialised alloys of aluminium or steel are all factors that help to keep the cost down.
- The thermal efficiency is also improved compared to existing internal combustion engine designs. In addition to the factors already discussed, the improved efficiency is also a result of good heat exchange, transferring a proportion of the exhaust, engine and electrical generator heat losses into the intake charge, reduced frictional losses due to the elimination of cylinder wall loads during conversion of cylinder pressure load to crankshaft torque and the elimination of throttling losses due to engine power modulation being achieved by variable intake charge flow duration at full intake boost pressure and variable internal exhaust gas recirculation, and not by throttling intake air flow as is done in a conventional spark ignition engine.
- In addition, tailpipe emissions (including NOx, hydrocarbon and particulate emissions) are reduced compared to other known free piston engine designs. This reduction in tailpipe emissions is a result of a number of factors, including: improved control of compression ratio in each cycle due to the elongated electrical generator geometry, which results in a high electrical control authority over piston movement during the compression stroke and therefore a lower piston displacement error at top dead centre; and variable retained exhaust gas composition of compressed charge to reduce peak combustion temperatures and pressures which determine NOx formation.
Claims (10)
1.-30. (canceled)
31. A method of manufacturing an engine, comprising providing a cylinder configured to accommodate at least one piston that is free to reciprocate within the cylinder, extruding a cylinder housing that is arranged to retain and provide structural support for the cylinder, and securing the cylinder within the cylinder housing such that the cylinder wall is reinforced by the structure of the cylinder housing.
32. The method of claim 31 , further comprising arranging the one or more magnetisable elements to provide load-bearing support to the cylinder.
33. The method of claim 31 , further comprising securing the cylinder within the cylinder housing an adhesive material on the outside of the cylinder, wherein the adhesive material provides thermal insulation between the cylinder and cylinder housing.
34. The method of claim 31 , further comprising providing the cylinder housing with cooling means for cooling the cylinder.
35. The method of claim 31 , further comprising coating the interior wall of the cylinder with friction-reducing material between the interior wall and a piston passing along it.
36. The method of claim 31 , further comprising reducing the thickness of the cylinder wall to a thickness that is less than 5% of the cylinder's internal diameter.
37. The method of claim 36 , further comprising limiting the thickness of the cylinder wall to less than about 2 mm.
38. The method of claim 31 , further comprising constructing the piston using alternating magnetisable elements and non-magnetisable spacer elements.
39. The method of claim 31 , further comprising providing one or more recesses in the cylinder housing that permit a plurality of magnetisable elements to be positioned adjacent the cylinder.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GBGB1021406.2A GB201021406D0 (en) | 2010-12-17 | 2010-12-17 | Free piston engine generator |
GB1021406.2 | 2010-12-17 | ||
PCT/GB2011/051154 WO2012080709A1 (en) | 2010-12-17 | 2011-06-21 | Free piston engine generator |
Publications (1)
Publication Number | Publication Date |
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US20130255080A1 true US20130255080A1 (en) | 2013-10-03 |
Family
ID=43567358
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US13/992,995 Abandoned US20130255080A1 (en) | 2010-12-17 | 2011-06-21 | Free Piston Engine Generator |
Country Status (8)
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US (1) | US20130255080A1 (en) |
EP (1) | EP2542768A1 (en) |
KR (1) | KR20130129245A (en) |
CN (1) | CN103261626B (en) |
BR (1) | BR112013015180B1 (en) |
GB (2) | GB201021406D0 (en) |
WO (1) | WO2012080709A1 (en) |
ZA (1) | ZA201303751B (en) |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2494217B (en) * | 2012-01-19 | 2014-10-08 | Libertine Fpe Ltd | A linear electrical machine with a piston and axially segmented cylinder |
CN103498733B (en) * | 2013-09-29 | 2016-04-06 | 北京理工大学 | A kind of motion control method of free-piston internal combustion engine generator |
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GB2476495A (en) * | 2009-12-24 | 2011-06-29 | Libertine Fpe Ltd | Free piston engine |
GB2476496A (en) * | 2009-12-24 | 2011-06-29 | Libertine Fpe Ltd | Piston for an engine generator, eg a free piston engine |
-
2010
- 2010-12-17 GB GBGB1021406.2A patent/GB201021406D0/en not_active Ceased
-
2011
- 2011-06-21 BR BR112013015180-3A patent/BR112013015180B1/en active IP Right Grant
- 2011-06-21 EP EP11743855A patent/EP2542768A1/en not_active Withdrawn
- 2011-06-21 WO PCT/GB2011/051154 patent/WO2012080709A1/en active Application Filing
- 2011-06-21 GB GB1110442.9A patent/GB2482375B/en active Active
- 2011-06-21 KR KR1020137018614A patent/KR20130129245A/en not_active Application Discontinuation
- 2011-06-21 US US13/992,995 patent/US20130255080A1/en not_active Abandoned
- 2011-06-21 CN CN201180060677.9A patent/CN103261626B/en active Active
-
2013
- 2013-05-23 ZA ZA2013/03751A patent/ZA201303751B/en unknown
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US4669791A (en) * | 1984-09-06 | 1987-06-02 | Integrated Circuit Systems, Ltd. | Connector apparatus |
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Also Published As
Publication number | Publication date |
---|---|
GB2482375A (en) | 2012-02-01 |
KR20130129245A (en) | 2013-11-27 |
BR112013015180B1 (en) | 2021-02-09 |
GB201110442D0 (en) | 2011-08-03 |
BR112013015180A2 (en) | 2020-06-09 |
ZA201303751B (en) | 2019-01-30 |
GB2482375B (en) | 2012-07-18 |
CN103261626A (en) | 2013-08-21 |
GB201021406D0 (en) | 2011-01-26 |
CN103261626B (en) | 2016-01-20 |
WO2012080709A1 (en) | 2012-06-21 |
EP2542768A1 (en) | 2013-01-09 |
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