GB2288637A - Two-stroke engine piston containing a valve - Google Patents

Abstract

Valving edges 18 formed on the connecting rod 6 control a piston port 29 connecting a chamber in the piston 9 having transfer ports (15, Fig. 12) with pressurised air from an inlet port 30 or the crankcase (Fig. 5). The exhaust port 3 may be controlled by a variable timing rotary valve (42, Fig. 25) acting as a balancing shaft in conjunction with a contra-rotating balance shaft (40). The engine may be supercharged. <IMAGE>

Description

IMPROVEMENTS IN TMO-STROKE ENGINES Pa TECHNICAL FIELD Two-stroke engines are now in wide use in three out of four almost distinct categories of usage, with the fourth category due to expand noticeably in the next few years. The categories (each with its own specialised version of the engine) are : (i) A "traditional" very simple low cost version - used in Lawn mowers; handheld tools; cycle motors etc.

(ii) An "improved" version with "tuned" ports, disk/reed valves - for higher power outboard motors; motor cycles; micro-light aircraft, etc.

(iii) Diesel engines, often requiring one or more "poppet" valves, a low pressure air supply; a high pressure Injector, and a strongly made heavy constructlon - for generators; emergency pumps; marine use, etc.

(iv) A "sophisticated" two stroke using ancillaries (Supercharger; Turbo charger; Electronic engine management; fuel injectors etc.) developed for "four-stroke" transport use - but with the elimination of: poppet valves and their drive mechanism, also the separate cylinder head requirement.

As announced to-date all the two-stroke versions not using poppet valves or their equivalent mechanism suffer In various amounts from wastage of input air and/or fuel, plus exhaust contamination of input since the piston control of gas flow is not sufficiently effective over a wide range of speeds d: loads. Stepped pistons of high reciprocating mass can also benefit from a gudgeon-free; 'gate-valve' design.

Economy with fuel and pollution from exhaust (including "noise pollution") is now becoming more important. Traditional designs are often used for short duration activities so the need for economy of fuel tended to be subjugated to cost /simplicity requirements. Future legislation is likely to restrict their use.

The innovative ideas in this application have been crystalised into two distinct embodiment types: the simpler version suitable for adoption into categories (i) and (ii) above, and the sophisticated embodiment for (iii)end(iv)- giving sequential exhaust > overlap > recharge normally without crankcase compression, mainly controlled by three moving parts; Piston, Connecting-rod and Crankshaft.

The new piston design such as in the P.C.T. application GB 91/00493 published in the U.K. as patent GB2261492B(August, 1994) can be modified to improve "breathing efficiency" of two-strokes as described in this application.

BACKGROUND ART Categories (i) and (ii). Although a range of variations have been tried for inlet; transfer, exhaust and lubrication methods - the most widely used are similar to the basic version shown in the symbolic drawings on sheet 1, so that versions with a "flat-top" piston can be envisaged as using angled transfer ports which direct the Incoming charge to the cylinder such that it is angled to the top of the cylinder rather than the exhaust port. When this is arranged so that the "route-length" of the various passageslports cause gas resonance then the latest "loop scavenge" and "tuned" engines, are relatable to these diagrams, needing no further description here since this innovation Is relevant to both.

Lubrication either by adding oil to the fuel or by "total loss" to the bearings Is not especislly relevant In these first two categories of this application and Is therefore omitted. Similarly the engines not requiring use of the crenkcase for suctionlcompression recharge of the cylinder are covered in the following: Categories (oil) and (iv). Diesel two-strokes are often provided with an "external" low pressure air supply fed by poppet valve to the cylinder starting near the end of the (port controlled) exhaust sector and continuing to sn optimum fill position. With inlet and exhaust at opposite ends of the cylinder scavenging of exhaust fumes Is excellent. High compression improves thermal efficiency. A dry sump with pressure feed of bearing oil Is standard practice.

Its main disadvantages concern: high weight; costleomplication of injector - of poppet valves; of multiple piston rings and the fuel oil's burnllniection rate which severely restricts engine r.p.m. With less perfect scavenging and the ring plus injection restrictions, the proposed innovation eliminates the poppet valve and cam mechanism from such engines. Some modern fuel systems can raise rpm.

Recent innovations In volatile fuel engines have Included: the Allen Adiabatic lean burn combustion with approximately 17:1 C.R. (ij +30%) needing controlled water injection to stabilise combustion; Dr. D. Merritt high efficiency segregated internal Catalytic Combustion (allowing high r.p.m. and minimal pollution) and the Miller high-boost supercharged variation on the Otto cycle (this present innovation will permit Its equivalent on the two-stroke cycle). Various combined air/fuel injection systems are currently being developed. (e.g. "Orbital") Modern materials and manufacturing methods are being applied to stepped piston designs over 60 years old, with considerable success despite high piston mass. See: Car Design de Technology October 1992,p.28 > 30. Different separation configurations, GB A 223 8830, and GB A 224 6394. Prior Art: USA 5,205,245 & GB 901 2349.

FUTURE DEVELOPMENT Market requirements for a range of multi-cylinder engines: powerful, reliable and smooth running; with the ability to accept turbo-charging, may produce combined technology co-operation. Evolvement of safe handling of hydrogen with controlled cylinder head "injection" into the developed 'combustion separation' is a strong contender for a future pollution free reliable engine.

GENERAL DESCRIPTION For many years designers have sought to produce an engine with the mechanical simplicity of the two-stroke - but with the 2'Breathing Manners" of the four-stroke: here is described the first system to meet these sequential control requirements.

The manufacture of a piston in two halves allows a more complex shape to be cast than is practical with theconventlonal design. Restricting the rotation of the crankshaft to one direction allows use of the connecting-rod to piston relationship to be developed as a 'gate' valve which in its simplest form allows the traditional two-stroke to transfer crankcase air/mixture to the cylinder after the exhaust port has closed. The second embodiment is the more sophisticated development (shown in Figs. 8 to Fig. 29 inclusive ) which keeps the pressurised input out of communication with the crankcase interior thus allowing conventional low cost automobile plain bearings to be used throughout the engine. Thus the conventional sump with lubricating oil out of contact with the rotating crank but pumped under pressure to shell bearings is appropriate. Elimination of the high pressure contact line on cams required for poppet valves removes a major source of break-up of the "long-molecular chains" used for "viscosity extension" in most lubricating oils.

The drawings shown are based on a petrol/gasoline (or similar fuel) engine with a choice of fuel injection positions (eg. intake - transfer passage(s) - cylinder head )the final shape/sizes of the ports will be to the choice of the design/production /combustion engineers and to suit the intended application. Several of the above Merritt systems are developed for a range of fuels with minimal pollution.

Variations can be made at the design stage in the height of the various ports, a restriction on width of any one opening is made by the length of unsupported piston ring(s) exposed to the gap. The cross-sectional area of transfer ports may be made uniformly constant with a streamlined fairing at the cylinder wall.

This may be substituted with a venturi; where fuel injection is into the passage.

For simplicity the transfer ports are shown as open-sided slots. Similarly, many of the sectioned piston elevations omit obstructing portions to eliminate excessive dotted lines and to clarify gas flow routes. Where sections are shown for comparison purposes, the various juxtaposition portions may not be in strictly the same plane of section. Minimum Gas path X-section > 12% piston area.

The largest angle of connecting-rod swing is minimised by having a high pivot axis at (or even above) the piston crown, and the amount of tip clearance required by the gate shutter depends not only on crank / rod /cylinder proportions, but also on the offset in the pivot-line from the cylinder longitudinal axis.

Some timing overlap is desirable between the end of the exhaust and the start of the cylinder recharge, in order to facilitate a smooth exchangelsubstitution of gasses above the piston. Transfer "ends" with air only - thus the "crevice" above & around the piston rings will not contain fuel likely to produce unburnt hydrocarbons.

The start and duration of the fuel Injection will normally be set by the electronic engine management system to eliminate fuel loss via the exhaust port, with transfer ports arranged to give an initial rotary motion to the techerge gas entering the cylinder - a swirl increased prior to ignition by conservation of angular momentum into the smaller diameter combustion chamber, also with "squish"induced turbulence from the 'V' internal edges. All intended to promote thorough combustion. This is ensured by Merritt's high C. R. controlled mixing system.

Some considerable variation is available at the design stage to alter the portions of each crankshaft revolution serving any selected function of the two stroke cycle and the amount of overlap between adjacent functions; but once decided and assembled variation is restricted to:- ignition timing, injection duration, fuel selection! "mixture-strength" and charging pressure - except when some additional movable control/restriction(s) are introduced into the gas flow.

Fig. 24 introduces two views of a rotating constriction in the exhaust port, in this instance illustrated with a gear drive from the crankshaft providing contra-rotation at crank speed with variable positioning of the rotor (Advance - Retard). Starting at Fig. 25 is a group of drawings depicting exhaust rotors which at twice crankshaft r.p.m. are combined with matching balance shafts to provide substantial cancellation of secondary engine vibration. Constriction is provided without contact of the exhaust passage (total sealing Is not required) leakage would be less than 25% of unrestricted flow, and normally 5% > %.

To this end the rotor may have a tapered (conical) configuration; allowing close none-contacting adjustment via use of end packing washers, or similar.

The 'hot path' rotor would normally be of Titanium; steel coated/plated with Ti; or "engineering ceramic". For the 900 'V' cylinder configuration, Fig. 27, two balance shafts may be combined. Fig.28 indicates a chain or a low cost 'internal tooth' belt; allowing over 220 advance and retard of the exhaust constrictors with under 2% variation of secondary balance force - advance normally controlled by the electronic engine management unit. Such devices allow better control of: gas flow; pollution; power output, & particularly in the "twice r.p.m." case, exhaust noise.

Using the above (pre and post construction) variables a wide range of user requirements can be satisfied. The two sets of drawings - with and without- exhaust rotor, are to illustrate operations Involved; not maximum performance etc.

The non-rotor example in the accompanying drawings used the following Crankshaft - degrees of rotation.

Power stroke 115 Exhaust sector 128 (Exhaust only 50) Cylinder recharge 95 (Recharge only 17) Overlap - 78 Compression sector 100 Total (one revolution) 3600 The exhaust rotor (at approx. mid position) examples used sectors as follows : Power stroke 127 Exhaust sector 73 to 87 approx.

Cylinder recharge 103 Overlap - 40 to 54 approx. (Exhaust alone 33: pure rech. 48+62) Compression sector 98 (Vol. power=130% of compression.) For compression ignition use, selection of high strength/temperature materials; additional piston rings with a change in combustion chamber size and shape, with an injector substituted for the spark plug(s), is indicated. For high r.p.m. with multi-fuels and minimum pollution the Segregating, Internal Catalytic Combustion system is required. (All performance estimations are subject to test verification.) The various ancillary devices are not shown since a wide choice is available depending on intended use. E g. a 3-lobe Bern; a Lysholm (or equivalent) medium pressure Supercharger followed by an efficient intercooler then needs a "late" closing transfer-port with a low effective compression ratio and a much greater expansion to create a two-stroke version of the Miller four-stroke cycle (High torque; reduced temperature exhaust.) Alternatively, (even simultaneously) , a modest pressure, 0e79bar (11 6 psi) and effective 9+ to 1 compression ratio using a low inertia turbo charger with multi-row cooled bearings, can offer a quiet exhaust with low specific fuel consumption. A 'vane' or similar low cost electric pump would be required for starting purposes. A stepped piston is a viable basic choice.

Comparisons are made between the intake area (as a percentage of cylinder area) in a modern "touring" two valves per cylinder (4-stroke)and the Inletport/ transfer passage area to cylinder area of this design. After allowance for length of opening; double the number of openings(in two revolutions): only a low inlet boost pressure of 0.2 bar (3 psi) at low r.p.m. rising with speed to probably 0.9 bar (13.2 psi) - to compensate for the turbulent intake route & gate valve on the twostroke - is(with inter-cooling) required for four-stoke equivalent specific output. REFERENCE TO THE DRAWINGS Sheet 1 is diagrammatic with Figs.1 to 4 depicting a "traditional" two-stroke cycle of operations.

Fig. 5 indicates the new "long" connecting rod pivoting near the piston crown or top. Sheet 2 illustrates in Fig.6 the 4 section of a typical category (i)tc(ii) piston; with below, a "little-end," and a pictorial view of the latter on the left.

Fig.7 (left) a general view from above the piston, and (right) a schematic diagram of the lower part of the cylinder.

Categories (iii) and (iv). Fig. 8 is a graphical outline of the inlet comparison between four-stroke and two-stroke engines described above. Fig. 9 is a section through a typical cylinder showing port arrangement. Fig. 10 is a sectioned piston suitable to the cylinder above. On the left is the corresponding connecting-rod top and little end. Fig.1 1 is a pseudo section through the cylinder and the lower part of its piston to present a comparison of ports and flow passages.

Fig. 12 is a pictorial representation of the piston's two matching halves and below is depicted the little end nested against a part cylindrical ceramic bearing pad. (The conic-frustum style bearings described in G B 2261492 B may be used with variable pressure piston rings - but are not shown here for brevity).

Fig. 13 is one piston half with two arrows to illustrate the two pathways (duplicated in the other half) conducting cooled pressurised air from the inlet port to the transfer ports when the piston/rod (once /rev.) are in the appropriate position. Figures 14 to 21 inclusive illustrate progressive stages of the new controlled two-stroke cycle. Fig. 22 shows a compact 900 "V" alternative (for least-vibration engines) to the in-line 3 cylinder engine. Fig. 23 is the alternative version of the piston with input flow 'down' through the gate valve - and with transfer ports moved further from 30, operation is as Figs.14 to 21. Reduction of 'overlap loss' is indicated by use of an exhaust rotary valve in Fig. 24,-but adding complexity, in exchange for improved gas flow control and efficiency for a wider range of speeds and loads. The A.~ R. indicates one possible point where the engine management unit can control/vary the relative position of the exhaust restrictor while rotating. The three centre lines through the gear wheel pivots & meshing points indicate a Stephenson's link motion which allows the advance and retard to move in a straight line over a limited range. The rotor is dynamically balanced and not contacting its casing.

Figs. 25 dc 26 are comparable with the cycle Figs. 14 to 21 but adding two contra-rotating, unbalanced opposing shafts running at twice crackshaft r.p.m.

arranged such that their mutual resultant un-balance force largely cancels the secondary out of balance vibration due to the piston & part of its connecting rod.

In a typlcal'in-lind engine this force is approximately of the primary balance forces.

One of the shafts includes the non-contacting exhaust restrictor which need not necessarily have its centre of areator mass coinciding with the second harmonic cancelling centre of mass. The small arrow '39' shows the instantaneous direction of action of each balance shaft at the crank position drawn. The sequence of action is from Ignition to just after the start of Exhaust in Fig. 25 and in Fig. 26 from Pre-Transfer where the gate valve is about to open through to a short Compression stroke with a cooled charge which allows the next working stroke to be (as drawn) - 130% greater volume.

Fig. 27 shows the alternative version of the 900 unit shown in Fig. 22, with three balance shafts (since the non-exhaust shaft '40' can contain the equivalent balance weights for both the exhaust rotor balance shafts). Two pressure oil deliverytubes are shown, '34' and the alternative unconventional big end shown in greater detail in Fig. 30. The 900 unit' may include a compressor + one two-stroke.

Fig. 28 shows an arrangement via chain (such as duplex muti-plate) or by an internal-tooth flexible belt either of which is being driven by a combination wheel. The combination wheel, which may carry "temperature shrunk" toothed gear rings to mesh, for example,with helical teeth on the crankshaft vibration damper and the combination balance shaft gear wheelis also shown enlarged.

A H R indicates how the engine management unit may advance or retard both exhaust rotors equally and simultaneously, while the spring symbol indicates how slack belt/chain motion may be controlled. (No."Teeth" for illustration only).

Fig 29, top right is a pictorial view of a typical two-stroke cylinder barrel casting with; cooling, transfer, gas inlet, exhaust and combined cylinder head. Two arrows indicate the location for the exhaust restrictor 42. The bottom drawings are the side elevation and a view on the section 'A A' of a rotor which may not require weights 48, except in the dynamically balanced case of a restrictor running at crankshaft r.p.m.

Fig. 30 (top) An "exploded" pictorial view of component parts of an unconventional dual big-end bearing which takes advantage of substantially uni-directional loading on two-stroke connecting rods. Lower drawing is a side elevation showing the secondary rod 61 in mid position relative to 62. Lower left, is an enlarged pictorial view of the sloping interlock required on the 'free' ends of an alternative pair of thick 1800 shells which surround the crank bearing, further reducing the number of comonents required.

The design gives a large bearing area within less overall width than traditional dual bigends and eliminates any "rocking-couple" forces, while using fewer parts. Often the wide crank bearing necessitates having removable web-weights to allow grinding access.

Such weights are normally located by a step groove for centripetal acceleration loads.

Fig. 31 illustrates how a simplified low reciprocating mass version of the Merritt segregated compression/combustion system of GB A 2 246 394 may be adopted. L.H.is shown near the end of exhaust/start of recharge: centre, sprayed fuel 56 is clear of the hot "tower" interior; right - combustion with injector protected by labyrinth seal 52.

DRAWING DETAIL-. gLL ENBODINENTS In all the figures the following annotation applies : 1/ shows a reed valve closed. 2/ reed valve open. 3/ an exhaust port.

4/ "long" transfer port. 5/ "short" transfer port. 6/ High pivot con-rod.

7/"Traditional" exhaust period. 8/ Widened + delayed transfer or inlet period.

9/Asymmetric "half" piston. 10/ Ceramic Insert. 11/ Slot for top ring.

12/ Oil control ring slot. 13/ Location of pressure pad. 14/ Ceramic bearing.

15/ Transfer exit port. 16/ Shield for transfer port. 17/ Oil "Total Loss" type.

18/ Port opening control edge. 19/ "Low-friction" coating. 20/Little end.

21/ Hinge case. 22/Shield for exhaust port. 23! min. angle '18' clears '24'.

24/ Opening edge of slot -- defining start of transfer period.

25/ Locus of piston surface when fitted with conic bearings at '20' (shown at '10'posy.) 26/ Transfer openings in the cylinder wall. 27/ Exhaust port in cylinder wall.

28/ Schematic view of part of cylinder showing notch to align with '10'.

29/ Flow passage in piston -- inlet port to gate valve (part shown in most Figs.) 30/ Port for (cooled) compressed air (from intercooler).

31/Integral Head and Cylinder. 32/ Turbulent combustion chamber.

33/Automotive type lubrication system. 34/ Oil supply passage/route.

35/"Dry-sump" oil return route to filter/cooler/storage/pump.

36/one possible position for fuel injection (of several options).

37/ Sealing lip at one end of '6' slot. 381100% balance factor for one cylinder.

39/ Instantaneous direction of action for resultant force in balance shaft.

40/ Balance shaft (2 x crank r.p.m.) 41/ Contra-balance shaft (2 x crank r.p.m.) 42/ Exhaust restrictor. 43/ Appropriate spark-plug or glow-plug for starting only.

44/ Core hole. 45/ Hole for spark plug. 46/ Clearance adjustment taper.

47/ Balance adjustment hole (Alternative "internal" balanced restrictor/rotor).

48/ External balance weights (especially for dynamically balanced crank r.p.m.) 49/ Special shape cast surface (interference bonds to adjacent cast surface).

50/ Passage for coolant. 51/ Injector; partially protected by seal 52 from combustion.

52/ Labyrinth seal above jet orifices. 53/ Merritt segregating unit (part of piston top) 54/ Exhaust flow; about to be rapidly curtailed by rotor at 2 x crankshaft r.p.m.

55/ 'White arrows' - indicating air flow from inlet port via gate valve & transfer ports.

56/ Fuel sprayed above hot "tower" interior; vaporising, but with insufficient "burn"air.

57/ Air only compression. 58/ Annular transfer space: vapour+some air to air at 59.

59/ "Inside" of combustion chamber - may be coated with catalytic material.

60/ Space for limited compression for air trapped below injector.

61/ Secondary connecting rod (Al.alloy) 62/ Primary connecting rod.

63/ Steel backed shell bearing. 64/ One of two shells (light reverse loads) 65/ Chrome outer face, thick 1800 shell. 66/'Free end'interlock. 67/ Conven. face.

68/ Steel/nodular iron big end cap. 69/ Locking tabs. 70/ Maximum swing of 61.

Categories (i) and (ii).

Fig. 7 illustrates the angled "noise-reduction" slots for "rotary" (and small power) two-strokes where silencer space is very limited, also shown is typical port arrangements for a twin transfer "flat-top" piston. The ports '26' are angled to cause a "loop-scavenge" flow on both sides of the exhaust port.

The sloping "notch" in burn resistant insert '10' is arranged to align with the corresponding small notch in the cylinder wall (at the top "corner" of the exhaust port) only when the piston is descending. On the up stroke the slot in '10' moves off the edge of the port, minimising extra gas loss into the exhaust.

The small gradual uncovering simulates the four-stroke's exhaust valve opening subjectively diminishing the high frequency impact of the comparatively quick exposure of high exhaust pressure on a traditional two-stroke engine.

Both these port control benefits may be used less effectively on a little end using cylindrical style bearings i.e. without the'rotational' motion shown at '25'.

Categories (iii) and (iv).

Fig. 8 L.H. side shows inlet valve opening on a typical modern (2 valves per cylinder) engine; up to 17 > 18 % of the piston ares. The valve acceleration being limited by spring load v. cam pressure and wear rates.

The R.H. outline of the two-stroke "inlet period" determined by a short portion of piston movement. The area limit is approximately 13 % of piston area, but attained and curtailed more quickly. The area shown is approximately 44-46% of the 4-stoke case, but in two revolutions is equivalent to some 91% of the four-stroke's intake capacity but suffers the disadvantage of a more convoluted flow path. However a small to moderate input boost pressure should compensate for the restrictions and additional drag from turbulence, for power equivalence.

PRESSURE CHARGED TWO-STROKE CYCLE Fig. 14 shows the piston descending, leaving the position of maximum torque; with crankshaft driven in a clockwise direction by the combustion pressures generated in the previous cycle. The connecting rod is st the position of maximum swing. The inlet port 30 has communication via passages 29 to the feed (lower) side of the gate-valve, but the control edges 18 are overlapping the opening edges 24 thus the pressure flow is stopped. The transfer and exhaust ports are closed by the piston walls and combined/reinforced with the piston rings.

Fig.15. Already fairly hot medium pressure gas from combustion has expanded into the now uncovered passages 5, into the piston (above the still closed gate): expanded and cooled appreciably. Air retained here from the previous cycle is further compressed from the inrush. The exhaust port is closed, but about to open.

The open inlet port still has access to the underside only of the closed gate.

Fig. 16. Here the exhaust port is partly open by the slowing piston. The gate valve is closing the inlet supply off from the transfer ports. The high pressure gas is beginning to flow at increasing rate into the exhaust system via cylinder ports 27 into manifold 3, simultaneously dropping the pressure above the piston. Compressed air and gas inside the piston and transfer passages 5 are now beginning to exceed the pressure above the piston and starting to flow upward; joining the flow toward the exhaust port.

DB will further compress the trapped air which will absorb heat from the enclosing piston.

This 'compression' may well compensate the pressure drop due to leakage, dc help cool the piston. This heated air will be discharged with the exhaust gasses as described for Figs. 16 & 17. The exhaust is closed & will remain so for over one third of a crankshaft revolution giving the "power" stroke. This concludes the description of operation.

Other related patent applications describe a piston & ring "unit" which reduces contact force (and thus wear) in the vicinity of the ports; & separately a low cost method for assembling complex multi-cylinder blocks in a modular style with minimum machining.

The selection of materials will depend on the specific output/ efficiency for a given application. An aluminium alloy cylinder block with chrome (or nickel/silicon carbide coated) bores allows small clearances with an aluminium alloy piston skirt. A Titanium (or MMC of AL/Li 8090 +17% ceramic particulates) would be suitable for the crown and "ring-lands" of a piston with a hot running central "tower," as shown for the segregated compression low pollution/multi fuel Fig.31 version. Helical rings eliminate "gap" loss.

C O N C L USIO NS Category (i) and (ii). Although this piston (unlike the four-stroke) is not normally a straight substitution for a traditional piston + connecting rod unit; for engine manufacturers prepared to modify their engines, most of the benefits previously available only from dual pistons on "V" connecting rods ("split singles") are now obtainable with a single piston unit with the vibration and friction reductions of lower reciprocating mass. Noticeable improvement can be expected in torque at low to medium R.P.M. with general improved economy and possible reduced exhaust noise levels.

Categories (iii) and (iv). This design marks a significant improvement in the gas flow control of two-stroke engines. Equally the segregated compression and steady volume combustion system provides an ultra low pollution;fuel tolerant optionwith either spark or catalytic ignition. Both these systems when combined with good primary and secondary mechanical balance can provide an exceptionally smooth, quiet and thermally efficient engine. Using modular assembly techniques allows a diversity of layouts and power outputs even from one bore & stroke size. Modern materials will allow long life combined with low weight and reliability. Future development of safe hydrogen transportation will allow the economical, low toxic exhaust, Merritt system with its low CO2 emission from conventional fuel: to become virtually pollution free.

Clearly, the combination of several patents provides a multi-option engine design.

The compromise of only 3 instead of 4 balance shafts on the "V" engines is made by reducing the balance weights below the 4-shaft optimum value-so that high frequency torsional vibration is barely detectable. A second option is to use one exhaust shaft dynamically balanced; with the close coupled set balancing piston+rod vibration, or again, any experimentally verified smooth running combination of these two cases.

Claims (14)

CLAIMS I claim:

1. A two stroke internal combustion engine comprising a cylinder with a piston slidably sealed in the cylinder, the cylinder including at least one transfer port and at least one exhaust port, with the said transfer port being connecled into intermittent communication witl7 the inlet manifold via a moving gate valve within the piston, the said valve operated and controlled by the relative arc motion occurring between the said piston and its constra ining connecting rod.

2. A two stroke internal combustion engine according to claim 1 in which two or more transfer ports are positioned within the said cylinder on each side of an inlet port which is so positioned that the air flow from the inlet manifold through the said port is constrained to flow through the said gate valve within the piston and out of the piston into the transfer ports at only one portion of the crankshaft rotation.

3. A two stroke internal combustion engine according to claim 2 in which the inlet port is positioned to feed air flow into the sealed crankcase below the said piston such that the said gate valve controls and restricts air flow from the vicinity of the connecting rod to the transfer ports communicating with the piston.

4. A two stroke internal combustion engine according to claim 3 in which the flow of air through the said gate valve occurs at only one portion of the crankshaft rotation.

5. A two stroke engine according to claim 1 in which the said inlet manifold is supplied with cooled pressurised air sourced from a supercharger or from an exhaust turbo-charger or from both of these operating in conjunc tion with each other either sequentially or simultaneously.

6. A two stroke engine according to claim 1 in which the said gate valve is supplied with pressurised air from the larger diameter of a stepped piston.

7. A two stoke engine according to claim 6 in which the compressed air originating from the stepped piston is augmented by compressed air from an exhaust turbo-charger.

8. A two stroke engine according to claim 1 which contains at least two cylinders with a least one cylinder and its respective piston with said gate valve is used as a compressor for the air supply to the other cylinder(s).

9. A two stroke engine according to any of the above claims which has a rotating non-contacting restrictor placed in or near the said cylinder exhaust port to reduce exhaust flow to augment the working fluid control obtained by the said gate valve.

10. A two stoke internal combustion engine according to claim 9 in which the said rotating constrictor is dynamically balanced and rotates at crankshaft revolutions per minute.

11. A two stroke internal combustion engine according to claim 10 in which the rotating constrictor is out of balance but matched with a counter rotating balance shaft, both the said rotating shafts revolving at twice crankshaft revolutions per minute, arranged to reduce secondary engine vibration and torque induced vibration.

12. A two stroke internal combustion engine according to any of the previous claims which contains a contoured slot in the edge of the piston top positioned to align with a corresponding slot in the top edge of the exhaust port such as to mute the audible high transient shock wave at the start of the high pressure discharge of exhaust gas.

13. A two stroke internal combustion engine according to any of the previous claims which contains conic-frusto section bearing surfaces within the said piston arranged to give the piston a small rotational motion about the cylinder axis derived from the angular swing of the connecting rod in relation to the piston.

14. A two stroke internal combustion engine substantially as described in the associated text and drawings.