EP0260283A4

EP0260283A4 - Two stroke engine with isolated crankcase.

Info

Publication number: EP0260283A4
Application number: EP19870901301
Authority: EP
Inventors: John Robert Mcrae Bennett
Original assignee: Bennett Automotive Technology Pty Ltd
Current assignee: Bennett Automotive Technology Pty Ltd
Priority date: 1986-03-07
Filing date: 1987-03-06
Publication date: 1988-11-09
Also published as: WO1987005359A1; KR880701319A; EP0260283A1; BR8706095A

Abstract

An internal combustion engine operating on a two-stroke cycle principle including a unitary piston arrangement comprising a combustion piston (4) operating in a combustion cylinder (1) and a compression or pumping piston (5) operating in a compression cylinder (2), the compression piston having a larger diameter than the combustion piston, and a connecting assembly comprising a piston rod (10), a gudgeon pin (12) fixed in the piston rod eye (11), the outer ends of the pin being rotatably accommodated in a cylindrical crosshead (15) coaxial with the piston rod and reciprocating with the pistons (4, 5) within a bore (16) in the crankcase casting (17). The assembly (10, 12, 15) connects the piston arrangement (4, 5) to the crankshaft (14) mounted in the crankcase (17) via connecting rod (13) and a dividing wall (28) is provided whereby the cylinders (1, 2) are isolated from the region surrounding the crankshaft (14) within the crankcase (17).

Description

TWO STROKE ENGINE WITH ISOLATED CRANKCASE

This invention relates to internal combustion engines and in particular to the two-stroke type piston internal combustion engine. _ς The crankcase-scavenged, two-stroke type piston engine is compact and can be made with a high power-to-weight ratio. It is commonly employed as a power unit for light vehicles and as a light industrial engine. The operating principle of this type of engine is

_1Q well-known in the art. In its simplest statement, during the upstroke of the piston, the charge is compressed ahead of it whilst a depression is created in the sealed crankcase below it inducing into the crankcase a flow of fuel-air mixture through a suitable induction system and means of m - carburetion. The flow of mixture into the crankcase is regulated by a simple valve such as a reed valve or by the uncovering of a suitably positioned port by the skirt of piston as it ascends the bore. On the downstroke of the piston following ignition of the charge, gas pressure

_2Q generated by combustion does work upon it, the underside of the piston compressing the fuel air mixture in the crankcase ahead of it.

The crankcase is connected by a suitable duct to a narrow slot or transfer port positioned in the lower

₂₅ cylinder bore and the exhaust and induction systems are connected to similar ports positioned in the lower cylinder bore, generally on the opposite side of the cylinder bore from the transfer port and above and below it respectively. The movement of the piston uncovers the various ports in

2_Q sequence to admit fuel-air mixture to the crankcase, to allow the discharge of combustion products through the exhaust system and the admission of a new charge to the cylinder from the crankcase.

The exhaust and transfer ports are located and

₃₅ aligned such that the opening of the exhaust port and the blowdown of the exhausting combustion products will slightly precede the opening of the transfer port and the entry of the next charge to the cylinder. The induction inflow to the cylinder may be directed by the shaping and alignment of the transfer port, or may impinge upon a prominence on the piston crown which deflects it sharply upward, such that minimal mixing occurs of the new charge with the exhaust end gases. As the crankcase is utilised as part of the induction system, it cannot be used as a lubricant reservoir.

Lubrication is provided by an admixture of lubricating oil with the fuel or by metering of lubricating oil with the induction airflow, which lubricant finds its way to the various moving parts. Lubrication is thus by way of a total loss system.

The crankcase-scavenged, two-stroke piston engine suffers from a number of shortcomings which have inhibited its application to a wider range of uses. These shortcomings can be classified generally into three categories: exhaust emissions and noise, engine life and • efficiency. As this type of engine is lubricated by a total-loss system, its exhaust emissions are often characterised by blue oil smoke and a strong and rather offensive odour. This type of lubrication system is not satifactory for high-power operation and engines. operated at their rated power generally have relatively short lives.

Additionally, during some phases of operation, a small part of each incoming charge is lost through the open exhaust port, resulting in an unacceptably high level of hydrocarbon exhaust emissions.

Because this type of engine operates most efficiently with a free-flowing, tuned exhaust system, noise levels tend to be higher than would be considered normal for a four-stroke engine of the same general size and power output. Also, during overrun operation, missfiring tends to occur due to lean mixtures, making a characteristic sound which is considered by some to be objectionable.

The introduction of lubricating oil into the fuel or induction airflow results in the generation of an elevated level of combustion products. The lubricating oil also creates a tendency towards fouling of the spark plug and, as a result, poor quality combustion. Both of these effects resulting from the presence of lubricating oil in the combustion chamber may lead to accelerated wear of the piston ring and cylinder bore.

Interference between the piston ring and the exhaust port in the lower cylinder wall frequently leads to piston ring failure. This is particularly so where high

10 cylinder pressures are generated to obtain higher power. Because it is necessary to accommodate three ports, one above the other in the lower cylinder bore, the effective stroke of the piston is liπ-ited. Designers sometimes mitigate this effect by extending the length of the cylinder -._ς bore and stroke of the piston and thus the length of the connecting rod. The result is an inefficient ratio of connecting rod length to stroke and a loss of torque magnification. This effect, and the loss of part of the incoming charge through the exhaust port during some phases

20 of operation, both act to reduce fuel efficiency.

Notwithstanding the fact that one firing pulse occurs for each revolution of the engine, the power output is not double that of a comparable four-stroke engine of similar swept volume.

The object of the invention is to provide a

25 two-stroke type piston engine which embodies the virtues of this type of engine, vis: compactness and high power-to-weight ratio, whilst reducing or eliminating the abovementioned shortcomings.

With this object in view there is provided by one

30 aspect of the present invention an internal combustion engine comprising co-axial combustion and compression cylinders, respective pistons arranged to reciprocate in unison in the cylinders, means connecting said pistons eccentrically with a crank shaft whereby reciprocating

35 movement of the pistons induces rotation of the crank shaft, said cylinders being physically isolated from said crank shaft whereby a combustion charge is not compressed in a region surrounding said crank shaft.

This arrangement has the particular advantage of preventing the transportation of lubricating oil droplets from the cranks case to the firing cylinder and thus the generation of hydrocarbon emissions. Additionally the arrangement enables the employment of conventional pressurized oil lubrication to the crank shaft in place of the provision of lubricating oil as an admixture to the

10 fuel.

In accordance with another aspect of the present invention there is provided an internal combustion engine comprising co-axial combustion and compression cylinders, respective pistons arranged to reciprocate in unison in the m - cylinders, a piston rod connecting said pistons to guide means supported to reciprocate in unison with said pistons, and connecting rod means connecting the guide means eccentrically to a crank shaft whereby reciprocating movment of the pistons induces rotary movement of the crank shaft. _n Conveniently the guide means includes a fixed cylindrical or part cylindrical surface co-axial with the cylinders, and a member having complementary surfaces slidably co-operating with the fixed surfaces. The piston rod and connecting rod means are each connected to said

__ member by a gudgeon pin, with at least the connecting rod means being rotatable relative to the member about an axis parallel to the crankshaft axis. The arrangement of this guide means has the effect of eliminating lateral forces on the piston members which has particular advantages in improving engine life by minimizing damage to piston rings

30 caused by their passing over the exhaust parts in the cylinder wall.

As discussed above, the combustion and compression cylinders are isolated from the area housing the crankshaft and guide means, to prevent lubricating and finding its way

35 to the cylinders in an uncontrolled way. The isolation is preferably in the form of a wall or partition between the cylinders and the crankcase through which the piston rod extends in sealed relation. Means may be provided to permit a controlled flow of oil or oil mist from the crankcase to the cylinders.

Also with the above stated object in view there is provided by another aspect of the present invention an internal combustion engine having an air induction system through which air is induced to an engine combustion chamber, means to deliver fuel into the induced air, and means to interrupt the fuel supply when the engine is running under no load, that is when the engine is operating in an overrun condition driven by external forces.

The means to interrupt the fuel supply may be adapted to stop the flow of fuel or to provide an alternative air path to the induction system that does not pass through a carburettor of other fuel metering device.

The interruption to the fuel supply during over-run operation can result in substantial fuel saving and reduced emissions.

The normal braking effect of the engine on over-run may be further increased by advancing the opening of the exhaust valve during over-run conditions and thereby obtaining a compression braking effect. Conveniently exhaust valve opening can be advanced to about the top dead centre position of the engine piston. Preferably the interruption of the fuel supply, the advancing of the opening of the exhaust valve and the provision of wide open throttle are integrated to operate in conjunction when the engine is in an over-run condition.

With the above stated object in view there is further provided an internal combustion engine preferably of the two-stroke cycle type having a combustion chamber, a compression chamber and one or more transfer passages communicating said chambers whereby a fuel-air charge is delivered to the combustion chamber from the compression chamber through the transfer passage or passages, and means to regulate the fuel-air mixture velocity through at least one transfer passage in relation to engine load and/or speed.

Variable throttling means is provided to regulate the volume of fuel-air mixture entering the engine.

In one embodiment of the present invention, an engine is provided in which two pistons are mounted coaxially, close together in a fixed positional relationship at the outer end of a piston rod, forming, in effect, one composite piston. The smaller and upper or outermost of the two pistons works in a firing cylinder. The larger and lower or innermost piston is formed as a radial extension of the circumference of the lower skirt of the smaller piston and works in a pumping cylinder.

The piston rod passes through a partition in the inner end of the pumping cylinder and terminates at its lower or innermost end in a cylindrical eye, the axis of which is normal to that of the piston rod. Passing through the eye of the piston rod is a gudgeon pin which connects it in a fixed positional relationship to an open-ended, cylindrical crosshead which reciprocates in a cylindrical bore the axis of which is coaxial with the axis of the piston rod.

Carried on the gudgeon pin are the little ends of two connecting rods, the big ends of which are carried on the crank pin of a crankshaft. The connecting rod little ends are bushed or provided with bearings in such a way as to permit their articulation about the gudgeon pin in a plane normal to the axis of rotation of the crankshaft. Connecting the lower or innermost end of the pumping cylinder to the lower or innermost part of the firing cylinder bore are a plurality of transfer ducts, each having ingress to the firing cylinder through one of a plurality of narrow slots or transfer ports.

Provision is made to wholly or partly throttle one or more of the transfer ports during part throttle operation. The lower or innermost end of the pumping cylinder communicates to the outside of the engine via an inlet duct which is opened and closed by a rotary valve disc mounted on the crankshaft centred on its plane of rotation. The entrance to the inlet duct is covered by a thick disc-like cover or throttling block in which are formed three ports, the centre, or charge port, of which is fitted with a suitable carburettor or fuel metering means and the other two braking air ports of which are fitted with ducts communicating, in common with the fuel metering means, to a suitable air cleaning means. The said throttling block may

10 be pivoted to a limited extent to bring the centre or charge port of the said cover wholly or partly into register with the mouth of the inlet duct so as to provide a full or partial flow of fuel-air mixture into the engine. A greater degree of rotation of the throttling block displaces the m _ς central charge port from register with the mouth of the inlet duct and presents to the said inlet duct one of the two braking air ports, to admit a full flow of filtered air to the inlet duct during compression braking.

The head of the firing chamber is fitted with a spark plug and an exhaust port opened and closed by a

20 suitable valve actuated by a suitable mechanism driven from the crankshaft-speed balancing shaft. The drives of the rotary valve disc and the exhaust valve actuating cam are made in such a way as to permit backlash to occur when the crankshaft is driven in a reverse sense, the degree of

25 backlash being that necessary to permit the operation of the engine in a reverse sense. The throttling block is provided with an extension arm upon which is mounted an angled cam plate which coacts with a plunger provided in the end cover of the crankshaft-speed balance shaft. Rotation in either

30 direction of the throttling block causes the angled cam plate to raise or depress the said plunger.

Movement of the plunger actuates a mechanism to advance or retard the timing of the exhaust valve according to the degree of throttling. The central or mid position of

35 the said plunger coincides with the full throttle position of the throttling plate. As the engine is throttled, the exhaust cam timing is progressively advanced to provide earlier opening and closing of the exhaust valve. Past the idling position, the throttling block can be bodily rotated to the braking position in which exhaust cam timing is advanced to open the exhaust valve at approximately top dead centre of the firing piston, and one of the braking air ports is brought fully into register with the mouth of the inlet duct. In this way, the engine becomes, in effect, an air compressor for braking purposes. The spark plug is connected to an ignition system which provides suitably-timed high-tension impulses.

The crankcase is partially filled with lubricating oil. The external surfaces of the firing cylinder are provided with suitable finning or coolant jacketing, heat being conducted away by airflow from a suitable fan or by a flow of liquid coolant circulated by a suitable punp. Vibration induced by the reciprocating engine components is counteracted, where required, by balance weights carried upon one or more shafts driven from the crankshaft. Two such engine units may be combined in a horizontally-opposed arrangement in which the crankcases become common. The counterweighted shafts may be dispensed with in this case, and the primary out of balance forces compensated for by counterweighting of the flywheel.

A particular embodiment of the invention is now described with reference to the accompanying drawings in which:

Figure 1 is a vertical cross section of the engine through a plane coincident with the cylinder diameters and normal to the plane of rotation of the crankshaft.

Figure 2 is a vertical cross section of the crankcase of the engine through a plane coincident with the axis of rotation of the crankshaft and in which the crosshead, part of one connecting rod, part of one half of the crankshaft and the rotary valve disc are also shown sectioned through the same plane.

Figure 3 is a cross-sectional view of a sliding valve and its actuating screw positioned at the base of the pumping cylinder, by means of which the openings to the transfer ducts may be progressively closed off.

Figure 4 is a cross-sectional view of the partition member between the pumping cylinder and the crankcase, showing a means of metering lubricant into the pumping cylinder.

Figure 5 is an end view of the arrangement of the exhaust camshaft drive dog at the drive end of the crankshaft-speed balance shaft.

Figure 6 is a longitudinal cross-sectional view, through a plane parallel to the axes of the firing and pumping cylinders, of the exhaust camshaft drive shaft, crankshaft-speed balance shaft and exhaust camshaft advance and retard mechanism.

Figure 7 is a plan view of the throttling block complete with its various attachments.

With reference to Figure 1, Cylinder head casting 3 has machined in it firing cylinder 1 in which firing piston 4 works and pumping cylinder 2 in which pumping piston 5 works. Firing piston 4 is fitted with single compression piston ring 6 and pumping piston 5 is fitted with single compression piston ring 7. The two said pistons are parts of a single complex piston in which pumping piston 5 is formed as a radial extension of the circumference of the lower skirt of firing piston 4. A central boss of the complex piston comprising the said firing and pumping pistons is fixed to the tapered head of piston rod 10 by bolt 9. in an alternative embodiment, the upper or outer end of piston rod 10 is provided with a threaded shank onto which the said central boss of the said complex piston is screwed. The height of the said firing and pumping pistons in their respective cylinders at top dead centre, and thus the compression ratios of those cylinders, is thus screwably adjustable, the pistons being locked into position after adjustment by bolt 9.

Piston rod 10, the axis of which is coaxial with the axis of the said firing and pumping cylinders, passes through partition member 28 at the lower or inner end of pumping cylinder 2, the entry of oil into pumping cylinder 2 being controlled by sealing means 29. Piston rod 10 terminates at its lower or inner end in a cylindrical eye 11, the axis of which is normal to that of the said piston rod. Fixed in the said piston rod eye is gudgeon pin 12, the outer ends of which are carried in open-ended, cylindrical crosshead 15. Cylindrical crosshead 15, the axis of which is coaxial with that of piston rod 10, works in bore 16 in crankcase casting 17. Carried on gudgeon pin 12 are the little ends of two connecting rods 13, which are provided with suitable bushes or bearings which permit the connecting rods to articulate about the gudgeon pin in a plane normal to the plane of rotation of the crankshaft. The big ends of connecting rods 13 are provided with suitable bearings 23 and are carried on crankpin 14 of crankshaft 19.- Crankshaft 19 is rotatably supported in bearings 20 housed in crankcase 17. Crank pin 14 is an integral part of one half of crankshaft 19 and is fixed in an interference fit to the other half of crankshaft 19 by means of dowel 21 and bolt 22. Suitable seals 33 are provided in the crankcase main bearing bores to prevent loss of lubricant from the crankcase.

Cylinder head casting 3 is fastened to crankcase casting 17 with partition member 28 sandwiched in between by means of a plurality of through bolts and nuts 18.

The lower or inner end of pumping cylinder 2 communicates with the lower or inner end of firing cylinder 1 by means of a plurality of transfer ducts 26. Each of the said transfer ducts has ingress to firing cylinder 1 through one of a plurality of transfer ports 27. Transfer ports 27 are shaped and directed so that the collective discharge through them will produce a powerful vortex within the lower or inner part of firing cylinder 1.

To relieve pressure during starting cranking, the space 34 between the head of pumping cylinder 2 and pumping piston 5 is vented to pumping cylinder 2 through one or more suitable orifices through pumping piston 5 which may be fitted with sintered metal flow restrictors. The lower or inner end of pumping cylinder 2 communicates to the exterior of the engine via inlet duct 24, the flow through which is interrupted by rotary valve disc 25 mounted directly on crankshaft 19 on its plane of rotation. In an alternative embbdiment, reverse flow back down inlet duct 24 to rotary valve disc 25 is impeded by a light reed valve situated at

10 the point of entry of inlet duct 24 into pumping chamber 2. Rotary valve disc 25 is made with a central boss 78 into which is pressed bushing 79, upon which bushing rotary valve disc 25 is free to rotate about a journal of crankshaft 19.-- Central boss 78 of rotary valve disc 25 is made with a m - radially projecting dog 81 which is positioned to engage a complementary dog 83 (depicted in broken line) projecting axially inward from rotary valve disc drive collar 80. Rotary valve disc drive collar 80 is fixed to the aforesaid journal of crankshaft 19 and, rotating with it in either direction, causes dog 83 to engage dog 81, causing rotary

20 valve disc 25 to rotate with it. The circumferential widths of dogs 83 and 81 are such that, regardless of the direction of rotation of rotary valve disc 25, the passage of its metering or valving aperture past the mouth of inlet duct 24 will always be properly timed for correct engine operation.

25 Crankshaft end cover 84 forms a mounting pad for the carburetion throttling means which rotates around bolt 82.

The cylinder head of firing cylinder 1 is fitted with an exhaust port 35 which is opened and closed, in the preferred embodiment, by barrel type exhaust valve 30.

30 Exhaust valve 30 is operated in a semi-rotary sense by lever arm 31, which is itself operated by means of a suitable cam and valve train. In alternative embodiments, exhaust port 35 is opened and closed by means of a disc valve, rotary valve or poppet valve, each operated by a suitable

35 mechanism.

The engine is equipped with a suitable means of generating high tension current pulses, suitably synchronised to crankshaft rotation and supplied by a conductor to sparking plug 32. The engine is equipped with a fly-wheel (not shown), which may be counterweighted to counteract primary out of balance forces to an extent desirable for the particular use of the engine. To counteract the resultant lateral out of balance forces, provision is made to carry in the lower crankcase 17 parallel to crankshaft 19, a weighted balance shaft driven at crankshaft speed by gear wheel 36 on crankshaft 19. Where cancellation of higher orders of vibration is required, provision is made to gear drive from the crankshaft at twice crankshaft sp3ed, a small balance weight situated at the approximate centre of gravity of the engine. For cooling purposes, gearwheel 36 and its mating gear 48 on the said weighted crankshaft-speed balance shaft depicted in Figure 6, can be made to act as a gear-type oil pump and pump lubricating oil from crankcase 17 through galleries in cylinder head casting 3. In an alternative embodiment, an eccentric formed on the said crankshaft or crankshaft-speed balance shaft drives a reciprocating pump for the same purpose. In high-power embodiments of oil-cooled versions of the engine, an external heat exchanger is provided, the effect of which may be enhanced by airblast from a fan incorporated into the flywheel or by an electrical fan. In air-cooled versions of the engine, finning is provided around the exterior of firing cylinder 1 and cooling air blast is generated by a fan incorporated into the flywheel and conveyed to the said firing chamber finning by suitable ducting.

In an embodiment permitting the compounding of a number of engines, crankcase casting 17 is provided with mounting lugs which permit it to be fixed to the periphery of a circular support frame. Carried on a shaft running in bearings at the centre of the said support frame is a bull wheel, the peripheral gear teeth of which engage those of a driving gear fitted to crankshaft 19 of each engine. Suitable provisions are made to control the power output of the engines so compounded.

With reference to Figure 3, in one embodiment, to maximise the airflow velocity through transfer ducts 26 at part throttle operation, annular throttling plate 37 is rotatably accommodated in annular slot 41 between the base of cylinder head casting 3 and partition member 28. Formed into the base of cylinder head casting 3 is housing 40 in a bore in which is accommodated adjustment worm 39.

10 Adjustment worm 39 engages teeth (not shown) on a sector of the periphery of annular throttling plate 37. Annular throttling plate 37 is provided with a plurality of openings 38, one of which is made to register exactly with the opening at the lower end of one transfer duct 26, and each m - circumferentially successive one of which is made longer in a circumferential sense. At the point of minimum movement of annular throttling plate 37, no obstruction to flow is offered to any transfer duct 26. Rotation of adjustment worm 39 causes rotation of annular throttling plate 37. The displacement in a peripheral sense of the openings 38 in

20 annular throttling plate 37 causes the occlusion of the openings of successive transfer ducts 26. In this way, the speed of flow of the fuel-air mixture in the ducts which remain unobstructed is kept high, thus reducing its residence time. In an alternative embodiment, adjusting

25 worm 39 is replaced with a toothed wheel, the axis of rotation of which is normal to the axis of pumping cylinder 2. The teeth of the said wheel coact with complementary teeth formed on a peripheral sector of annular throttling plate 37 in such a way that rotation of the said wheel

30 causes rotation of the said annular throttling plate. In a further embodiment, progressive throttling to transfer ducts 26 is achieved by the provision of two annular throttling plates 37, superimposed in annular slot 41, and contra-rotated in a peripheral sense by means of a pair of

35 the said adjustment worms or toothed wheels to move their openings 38 into or out of coincidence. In a simpler embodiment, the fully circular annular throttling plate 37 is replaced by one or more individual throttling plates which are moved in synchronisation with the engine power controls by levers or other means to close off their respective transfer ducts as power is reduced.

Lubrication of the bores of firing cylinder 1 and pumping cylinder 2 can be sufficiently provided for by lubricant which finds its way past piston rod seals 29 or past crankshaft seals 33 to the inner face of rotary valve

10 disc 25 and thence to pumping chamber 2. Lubricant finding its way to pumping chamber 2 ultimately finds its way to firing cylinder 1. Where lubrication by seal leakage is insufficient, as may be the case in higher power applications of the engine, seal leakage is increased by the m m. provision of one or more narrow, shallow grooves in the area of the piston rod or crankshaft journal swept by the seal. In an alternative embodiment, provision is made to allow a small flow of lubricant from the area of crosshead bore 16 through partition member 28 into pumping cylinder 2. With

_7n reference to Figure 4, one or more bushings 43 are provided in partition member 28, through which bushing is drilled orifice 42 which may be filled if required with a sintered metal flow-restricting material. Attached at one point of the upper or outer face of bushing 43 is metal reed 44. In

_,. operation, the depression created in pumping cylinder 2 during induction is sufficient to draw up a small amount of lubricant through orifice 42. During the compression stroke, reed 44 is forced against the upper surface of bushing 43, preventing reverse flow through orifice 42 and

_₀ displacing some of the said lubricant into pumping cylinder 2 from whence airflow carries it to firing cylinder 1.

With reference to Figure 6, balance shaft 46 is supported in bearings 47 carried in crankcase casting 17 and driven at crankshaft speed by means of gear wheel 48 meshing

__ with the said gear wheel 36 on crankshaft 19. Coaxial with balance shaft 46 is exhaust camshaft drive shaft 45, sufficient clearance being provided between the said shafts to permit them to rotate independently. As depicted in Figure 5, balance shaft 46 is provided at its driven end with a part-circular dog 49 projecting axially from its end. Rotation of balance shaft 46 in either direction causes dog 49 to engage complementary dog 50 on exhaust camshaft driveshaft 45, causing it to rotate. The circumferential width of the said dogs is such that regardless of the direction in which the crankshaft, and thus balance shaft 46, is driven, the basic timing of the exhaust valve will be

10 correctly set for engine operation. The exhaust camshaft driveshaft 45 is threaded at projecting end 65 to provide a drive for the spark ignition means which is mounted upon pad 66. Rotary motion imparted to exhaust camshaft driveshaft 45 is transmitted to bush 51 fixed to its other end. Bush 51 m - is made with helical splines on its outer face, which splines coact with mating helical splines on the inner face of sliding sleeve 52. The outer face of sliding sleeve 52 is made with helical splines in the opposite sense to those of its inner face, which splines coact with mating helical

20 splines on the inner face of exhaust camshaft 53 which is supported in bearings 55 carried in camshaft cover 63. Sliding plunger 56 enters camshaft cover 63 coaxial with exhaust camshaft driveshaft 45, its inner bore being provided with needle bearing 57 which supports an axial

25 extension of sliding sleeve 52. Inward axial force from sliding plunger 56 is transmitted to sliding sleeve 52 by thrust race 59. Inward movement of sliding sleeve 52 so generated, compresses spring 58 between the end of exhaust camshaft driveshaft 45 and the inner face of axial extension

30 of sliding sleeve 52. The coaction of the helical splines on sleeve 51, sliding sleeve 52 and camshaft 53 is such that inward axial movement of sliding sleeve 52 causes displacement of camshaft 53 in a clockwise direction and outward axial movement, under the influence of spring 58,

_₅ causes displacement of camshaft 53 in a counter clockwise direction. The pitch of the said helical splines is made such that axial forces generated by their coaction as torque is applied through exhaust camshaft driveshaft 45 to drive camshaft 53 are equal and opposed. Camshaft 53 carries upon it exhaust cam 54 which coacts with cam follower 62 sliding in pushrod tube 64. Inward axial forces imposed upon exhaust camshaft driveshaft 45 by the said exhaust cam advance and retard mechanism are carried by sleeve 51 through thrust 67 to the end of balance shaft 46. Axial movement of sliding plunger -56, for the purpose of adjusting exhaust cam advance, is obtained by sliding of angled cam

10 plate 70 through slot 61 in the said sliding plunger as cam plate 70 sweeps in a plane normal to the axis of exhaust camshaft driveshaft 45.

With reference to Figure 7, carburettor throttling block 68 is mounted upon pad 84 and is free to rotate about m - bolt 82, these last two features being depicted in Figure 2. Attached to throttling block 68 is actuating lever 69 and exhaust cam advance and retard cam plate 70. Passing through throttling block 68 and arranged close together on an arc close to the periphery of it are charge port 71 with

~_n a braking air port 72 on either side of it. Mounted in register with charge port 71 is carburettor or fuel mixer 73 and mounted in register with the two braking air ports 72 are ducts 74. Carburettor 73 and ducts 74 are all connected to plenum 75 to which is mounted air cleaning means 77 on

₂₅ short mounting duct 76. With throttling block 68 mounted upon its pad, exhaust cam advance and retard cam plate 70 passes through angled slot 61 in sliding plunger 56 as depicted in Figure 6.

In operation, rotation of crankshaft 19 causes

__ upward displacement of connecting rods 13, crosshead 15, piston rod 10 and thus pumping piston 5 and firing piston 4. The depression created in pumping chamber 2 beneath pumping piston 5 causes atmospheric pressure to force a flow of air through the aircleaning means 77 and 76, through carburettor

__ 73 where a fuel-air mixture is created, through charge port 71 in throttling block 68, through the metering or valving aperture in rotary valve disc 25 which is timed to be ^" coincident with the mouth of inlet duct 24, and through the said inlet duct to pumping chamber 2. Further rotation of crankshaft 19 causes a downward movement of both pistons, pumping piston 5 compressing the induced charge in the pumping chamber and displacing it into transfer ducts 26 where it is retained by the skirt of firing piston 4 covering transfer ports 27 and into inlet duct 24 where it is retained by disc valves 25, the metering or valving aperture of which is no longer coincident with the mouth of

10 the said inlet duct. As both pistons approach bottom dead centre, the valve mechanism opens exhaust valve 30, further downward movement of firing pistion 4 uncovering transfer ports 27, admitting a new charge to firing cylinder 1. Subsequent upward movement of the two pistons compresses the m - charge in firing cylinder 1 whilst simultaneously inducing a new charge in the aforesaid manner into pumping cylinder 2, ignition occurring as firing piston 4 approaches top dead centre. Combustion-generated gas pressure propels firing piston 4 downward, the force being transmitted to crankshaft 19 via piston rod 10 and connecting rods 13. Downward

20 movement of pumping piston 5 compresses the induced charge in the pumping cylinder in the manner aforesaid. As firing piston 4 approaches bottom dead centre, exhaust valve 30 opens, blowing down the gaseous products of combustion. Further downward movement of the firing piston uncovers

25 transfer ports 27, admitting a new charge from pumping cylinder 2. The arrangement of the transfer ports is such that the flow of fuel-air mixture discharged from them is directed downwards towards the crown of firing piston 4 and more or less tangential to a circle within firing cylinder 1

30 concentric with its bore, and the radius of which is approximately half that of the said firing cylinder. Swirl produced by offset of the transfer ports in the manner aforesaid acts to positively locate the new charge within the cylinder and segregate it from the combustion end gases.

35 The cycle is then continuously repeated, power being varied by controlling the flow of fuel-air mixture into inlet duct 24 by means of rotation of throttling block 68. Where annular throttle plate 37 is provided, as depicted in Figure 3, its movement is synchronised with that of the said throttling block, transfer ducts 26 being progressively obstructed as power is reduced. The throttling of the said transfer ducts serves to maintain a high airspeed and thus a low residence time for the flow of fuel-air mixture through the unobstructed transfer ducts.

Prior to starting the engine, the throttle or power

10 control is selected to forward or reverse. To facilitate this selection, separate forward and reverse power controls may be provided, a single power control may be provided in conjunction with a forward/reverse selector, or separate forward and reverse quadrants may be provided for a single m - power control. With further reference to Figure 7, with a forward/idle selection made, throttling block 68 is rotated counter-clockwise so that its charge port 71 just begins to register with the mouth of inlet duct 24, allowing a small flow of fuel-air mixture. At the same time, exhaust cam

₅ advance and retard cam plate has substantially raised sliding plunger 56 as depicted in Figure 6, advancing the exhaust cam to the idle operation position. After engine start, progressive movement of the power control to increase power transmits a force to actuating lever 69 causing _ym. throttling block 68 to rotate clockwise, bringing its charge port 71 further into register with the mouth of inlet duct 24, and permitting a greater flow of fuel-air mixture into the engine and thus the generation of more power. Rotation of throttling block 68 causes exhaust cam advance and retard

30 camplate 70 to partially depress sliding plunger 56, thus retarding the exhaust cam. With the power control selected to the full power position, sliding plunger 56 is in a mid position. During deceleration, from its idle position the power control may be moved bodily further counter-clockwise, to a braking selection. In this position, braking air port

35 72 is moved into full register with the mouth of inlet port 24, admitting a full flow of filtered air to the engine. At the same time, sliding plunger 56 is fully raised by the action of exhaust cam advance and retard cam plate 70 to cause exhaust valve operation to be fully advanced to top dead centre of the firing piston. In this way, the engine may be made to operate, in effect, as an air compressor for braking purposes. With the power control selected to reverse operation, seal friction and the like during starting cranking of the engine causes exhaust camshaft driveshaft 45 as depicted in Figure 6 and rotary valve disc

10 25 as depicted in Figure 2 to reposition themselves for reverse operation by the rotary transposition of dogs 49 and 50 and dogs 81 and 83 representively. In a reverse/idling selection, throttling block 68 is rotated clockwise and is rotated counter-clockwise to increase power. Reverse m m. braking is selected by rotating throttling block 68 fully clockwise. In this position, the action of exhaust cam advance and retard cam plate 70 fully depresses sliding plunger 56 to fully advance exhaust valve operation to top dead centre of the firing piston for reverse braking. At

20 the same time, reverse braking air port 72 is brought fully into register with the mouth of inlet duct 24. Selection of the power control to idle and thence to an increased power selection progressively raises sliding plunger 56 until full reverse power is obtained with the said sliding plunger in its mid position.

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Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. An internal combustion engine comprising co-axial combustion and compression cylinders, respective pistons arranged to reciprocate in unison in the cylinders, means connecting said pistons eccentrically with a crank shaft whereby, reciprocating movement of the pistons induces rotation of the crank shaft, said cylinders being physically isolated from said crank shaft whereby a combustion charge is not compressed in a region surrounding said crank shaft.

2. An internal combustion engine according to claim 1 wherein said means connecting the pistons to said crank shaft comprises a piston rod means connecting said pistons to guide means supported to reciprocate in unison with said pistons and connecting rod means connecting the guide means eccentrically to the crank shaft.

3. An internal combustion engine according to claim 2 wherein the guide means comprises a fixed member having a cylindrical or part cylindrical surface co-axial with the combustion and compression cylinders, and a sliding member having complementary surfaces slidably engaging with the cylindrical surface of the fixed member.

4. An internal combustion engine according to any one of claims 1 to 3 wherein said pistons are formed as a unitary member comprising a combustion piston having a first diameter and a compression piston having a second diameter longer than said first diameter, the compression piston being formed as a radial extension of a skirt region of said combustion piston. 5. An internal combustion engine according to claim 3 wherein wall means is provided between the cylinders and the region surrounding said crank shaft, said piston rod means passing through said wall means and seal means provided between said wall means and the piston rod means to operationally seal the cylinders from the said region surrounding the crank shaft.

6. An internal combustion engine according to claim 2 wherein said pistons are adjustable along said piston rod means to thereby vary compression of a charge received in said cylinders.

7. An internal combustion engine according to claim 3 wherein said piston rod means is supported on a gudgeon pin carried by said sliding member, said connecting rod means being formed by a pair of elements, one end of each of said connecting rod elements being pivotally supported on either side of the piston rod means on said gudgeon pin, the other end of each of said connectng rod elements being pivotally mounted on a crank pin of said crank shaft.

8. An internal combustion engine according to claim 4 including a plurality of charge transfer passages leading from an end of the compression cylinder adjacent the crank shaft to said combustion cylinder at a position adjacent said compression cylinder, said charge transfer passages being spaced peripherally around said cylinders.

9. An internal combustion engine according to claim 8 wherein said charge transfer passages include entry means to said combustion cylinder configured to create vortex flow conditions within said combustion cylinder. 10. An internal combustion engine according to claim 8 further including throttle valve means associated with one or more of said charge transfer passages to throttle flow therethrough and thereby increase the velocity of flow therethrough.

11. An internal combustion engine according to claim 1 further including induction means for inducing a combustible charge into said compression cylinder, said induction means including valve means which is closed during a compression stroke of the compression piston.

12. An internal combustion engine according to claim 11 wherein said valve means includes a rotary valve member mounted on said crank shaft adapted to open or close an induction passage in timed relation and in response to rotation of said crank shaft and movement of said compression piston.

13. An internal combustion engine according to claim 12 further including control means co-operating between said crank shaft and said rotary valve member to ensure correct operation of said rotary valve member regardless of the direction of rotation of the crank shaft.

14. An internal combustion engine according to claim 1 including an air induction system through which air is induced for eventual delivery to the combustion cylinder, means to deliver fuel into the air induced, and means to interrupt the fuel supply when the engine is operating in an overrun condition driven by external forces. 15. An internal combustion engine according to claim 14 further including means for advancing opening of exhaust valve means controlling flow through an exhaust passage from said combustion cylinder, said advancing of the opening of the exhaust valve means being actuated directly in response to positioning of an engine throttle control.

16. An internal combustion engine according to claim 1 further including means operable between the crank shaft and an exhaust valve operating mechanism to ensure correct operation of the exhaust valve operating mechanism regardless of the direction of rotation of the crank shaft.

17. An internal combustion engine comprising co-axial combustion and compression cylinders, respective pistons arranged to reciprocate in unison in the cylinders, a piston rod connecting said pistons to guide means supported to reciprocate in unison with said pistons, and connecting rod means connecting the guide means eccentrically to a crank shaft whereby reciprocating movement of the pistons induces rotation of the crank shaft.

18. An internal combustion engine arrangement comprising a plurality of internal combustion engines according to any one of claims 1 to 7 wherein the crank shaft of each internal combustion engine is adapted to drive, through coupling means, a single output shaft.

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