Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L21/00—Use of working pistons or pistons-rods as fluid-distributing valves or as valve-supporting elements, e.g. in free-piston machines
  • F01L21/04—Valves arranged in or on piston or piston-rod
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01P—COOLING OF MACHINES OR ENGINES IN GENERAL; COOLING OF INTERNAL-COMBUSTION ENGINES
  • F01P1/00—Air cooling
  • F01P1/04—Arrangements for cooling pistons
• • 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
  • F02B33/00—Engines characterised by provision of pumps for charging or scavenging
  • F02B33/02—Engines with reciprocating-piston pumps; Engines with crankcase pumps
  • F02B33/06—Engines with reciprocating-piston pumps; Engines with crankcase pumps with reciprocating-piston pumps other than simple crankcase pumps
  • F02B33/10—Engines with reciprocating-piston pumps; Engines with crankcase pumps with reciprocating-piston pumps other than simple crankcase pumps with the pumping cylinder situated between working cylinder and crankcase, or with the pumping cylinder surrounding working cylinder
  • F02B33/12—Engines with reciprocating-piston pumps; Engines with crankcase pumps with reciprocating-piston pumps other than simple crankcase pumps with the pumping cylinder situated between working cylinder and crankcase, or with the pumping cylinder surrounding working cylinder the rear face of working piston acting as pumping member and co-operating with a pumping chamber isolated from crankcase, the connecting-rod passing through the chamber and co-operating with movable isolating member
• • 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
  • F02B75/00—Other engines
  • F02B75/02—Engines characterised by their cycles, e.g. six-stroke
  • F02B2075/022—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle
  • F02B2075/025—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle two

Definitions

• the present invention relates to an improved two-stroke internal combustion engine with improved efficiency and reduced exhaust emissions.
• the invention relates to two-stroke reciprocating internal combustion engines, without limitations on power, cylinder capacity and type of fuel used, whether of the carburation or injection type, whether ignited by sparking (as in the otto cycle) or by compression (as in the diesel cycle) , whether fed by natural induction or supercharged. .
• a two-stroke engine produces more power than a four-stroke engine of the same cylinder capacity because it doubles the frequency of the working strokes performed by the piston.
• the two-stroke engine made according to the present invention is of the type with unidirectional scavenging, that is to say, one with transfer or inlet ports located at the base of the cylinder, corresponding to the bottom dead centre of the piston, and exhaust ports at the top of the cylinder, close to the cylinder head or on the cylinder head itself.
• This type of scavenging is called unidirectional scavenging.
• the burnt gases are pushed out through a controlled valve located in the cylinder head.
• the exhaust cycle may be asymmetrical because it is started by a command that opens the exhaust valve and does not depend simply on the action of the piston. It is therefore much more efficient than the exhaust cycle of traditional two-stroke engines.
• the two-stroke engine made according to the present invention also has an intake and precompression chamber that is separate from the crank mechanism, allowing the crank mechanism to be lubricated in the same way as a four-stroke engine, with recycling of lubricating oil, and thus without escape of lubricating oil through the engine exhaust.
• the engine made according to the present invention can be advantageously applied not only to vehicles of many different kinds, such as motor cars, two- or three-wheeled vehicles, mopeds, motorcycles and scooters, but also to tools and implements such as power saws, lawn mowers and so on.
• the present invention can also be advantageously used in the field of marine engines such as outboard motors.
• the main advantages of conventional two-stroke engines are that they are easier to build, lighter and have a high specific power output potential .
• catalytic converters are only partly effective in eliminating emissions and two-stroke engines equipped with catalytic converters cannot meet the requirements of the strictest anti-pollution regulations.
• a catalytic converter has a limited life on account of the large quantity of oil expelled by the engine and as a result, the converter has to be changed relatively frequently. This creates an additional problem linked to the disposal of used converters.
• direct injection into the combustion chamber this is uneconomical since it involves high-pressure injection and because the injection cycle must be performed in a very short space of time, which makes it difficult to control the quantity of mixture fed to the engine, especially in small engines at partial loads.
• the scavenging cycle is performed by air and oil, the oil being necessary for lubrication, and the problem of pollution caused by the burnt oil therefore remains.
• scavenging the combustion chamber with abundant air is disadvantageous in terms of efficiency because the pumping work required is substantially wasted.
• the combustion chamber is effectively scavenged without unnecessary loss of air to the exhaust.
• lubrication is very important for internal combustion engines, since it improves mechanical efficiency, reducing the power required to overcome the passive resistance of moving parts while maintaining their mechanical properties, and preventing or reducing wear on reciprocating engine parts.
• oil is pumped from the crankcase to the different parts to be lubricated and excess oil returns to the crankcase.
• the crankcase of the four-stroke engine can therefore be filled with an abundant supply of heavy oil.
• the present invention therefore provides an improved two- stroke engine in an attempt to overcome the above mentioned drawbacks.
• the present invention provides a two-stroke engine as specified in claim 1.
• FIG. 1 shows the guide piston of the engine illustrated in Figure 1, partly in cross section
• FIG. 3 is a top view of the guide piston of the engine illustrated in Figure 1;
• Figure 4 shows a cross section of the piston of the engine illustrated in Figure 1;
• FIG. 5 is a bottom view of the piston of the engine illustrated in Figure 1; - Figure 6 illustrates another embodiment of the engine made according to the present invention;
• the two-stroke engine is labelled 1 as a whole.
• the engine 1 comprises a base 2 closed at the bottom by a sump 3 designed to contain lubricating oil 4.
• the crankcase 2 houses a crankshaft 5 that turns about pins
• the crankshaft 5 has a crank pin 7 to which a connecting rod 8 is attached in a known manner.
• the top of the connecting rod 8 is joined to a piston pin 9 to which a guide piston 10 is also joined.
• the guide piston 10 moves up and down in a cylindrical sleeve 11 and has grooves 12 made in it to allow air and lubricant to pass freely into the section above it.
• a rod 14 which is fixed to the guide piston itself or which is made as integral part of it.
• the inside of the rod 14 comprises a hollow section 14a not only for lightness but also to allow oil to reach the piston 20.
• the hole 17 is surrounded by a collar 18 and if necessary the collar 18 can be provided with gaskets (not illustrated) fitted between it and the rod 14. There is a very small amount of clearance between the sides of the hole 17 and the rod 14. Thus, even if the collar 18 is not fitted with gaskets, a good seal is obtained during the reciprocating motion of the rod 14 in the hole 17 and collar 18.
• the collar 18 comprises an upper end 18a that is flared in the direction of the hole 17.
• the flared end 18a is designed to collect the lubricating oil that is carried up past the hole 17 and to facilitate its flowing back into the crankcase 2.
• a cylinder head 19 closes the top of the cylinder 15 within which a substantially disc shaped piston 20 runs.
• the piston 20 is connected to the rod 14 and has an upper packing ring 21a and a lower packing ring 21b to prevent leakage between piston and cylinder. There are no oil scraper rings.
• the piston 20 divides the cylinder 15 into an upper section 22, where the combustion chamber is, and a lower section 23 where there is an intake and precompression chamber, for example a crankcase/pump.
• the two sections communicate through a plurality of transfer ports 24, also referred to simply as ports 24, made in the side wall 25 at the base of the cylinder 15.
• the cylinder head 19 comprises a spark plug 26 and at least one exhaust pipe 27, equipped with a closing valve 28, which may be controlled by conventional means such as, for example, a shaft and cam 29.
• the piston 20 does not have a skirt and therefore requires much less lubricant to enable it to move up and down within the cylinder 15. To further reduce the lubricant requirement, there may be a relatively large clearance between the piston 20 and the cylinder 15 since the seal is guaranteed by the packing rings 21a and 21b which are the only parts in contact with the cylinder wall .
• the piston skirt is not necessary because the piston 20 does not have to sustain the sideways thrusts due to the crank mechanism and does not therefore have to act as a guide for the connecting rod 8 and crankshaft 5 since the thrusting actions are borne directly by the guide piston 10.
• the latter being located in the area of the crankcase 2, has an abundant supply of oil either by splash lubrication or by force feed lubrication through a pump (not illustrated) .
• the absence of sideways thrusts by the piston 20 also has another important advantage, and that is that the cylinder 15 is not subject to ovality and that means the close, sealed fit between the cylinder 15 and the piston 20 lasts much longer.
• the underside of the piston 20 comprises a plurality of radial fins 20c over which fresh air is blown during each engine cycle, and which transfer heat from the crown of the piston 20 to the lower section 23 to reduce the high temperatures reached by the crown of the piston 20.
• the lower section 23 communicates directly, through an induction manifold 30 equipped with reed valves 31, with a carburettor 32 of known type designed to supply the required mixture of air and fuel.
• the carburettor 32 is equipped with a filter 33 that communicates with the crankcase 2 area through a connecting pipe 34.
• the oil vapour in the crankcase 2 is sucked into the cylinder 15 and contributes sufficiently to the lubrication of the piston.
• the upper part of the engine also known as the "dry area” is lubricated in the same way as a four-stroke engine.
• the piston 20 can therefore be lubricated by the oil vapour sucked in from the crankcase 2 and/or by the oil film transferred by the rod 14 during its reciprocating motion through the crankcase 2.
• the lubrication of the upper part of the engine can be adapted to different requirements.
• the tolerance of fit between the piston 20 and the cylinder 15 may be very large and hence the oil requirement is much smaller than that of any other type of piston, with a significant advantage in terms of reduced emissions.
• valve 28 is an exhaust valve, it always operates at relatively high pressures and hence the lubricating oil on the valve stem does not tend to leak through the valve guide .
• the air-fuel mixture is sucked in from the carburettor 32 and passes through the valve 31 into the lower section 23.
• the piston 20 moves towards its bottom dead centre, it drives the air- fuel mixture from the lower section to the upper section 22 through the ports 24.
• the exhaust valve 28 is opened by the cam 29.
• the fresh charge of air fuel mixture displaces the gases burnt during the previous combustion cycle and drives them towards the exhaust pipe 27 but without mixing with them.
• the air fuel mixture is near the exhaust valve 28, the latter closes and prevents fuel from being lost through the exhaust.
• a timing diagram typical of the present engine shows a symmetrical transfer cycle around the bottom dead centre. Transfer is, however, very efficient because the lower section 23, acting like a pump, has a small clearance volume and is almost completely swept by the piston 20.
• the transfer ports 24 can be increased in number and they may be very narrow and hence relatively undersized, as shown in Figure 9. Also, it is also easier to increase the number of transfer ports because there is no need for an exhaust port in the wall of the cylinder 15.
• the transfer ports 24 may be arranged at a constant angle relative to the cylinder wall 25 and there are enough ports to enable the size of each single port to be reduced.
• the transfer port 24, on the side of the induction manifold 30 may be connected with the latter.
• the transfer ports may be oriented in an oblique direction (not illustrated) relative to the axis 15a of the cylinder 15.
• the exhaust cycle is asymmetrical because it is achieved by opening the exhaust valve 28 whose operation is independent of the position of the piston 20.
• the closing of the exhaust valve 28 can be sufficiently advanced to prevent the escape of the air-fuel mixture fed in through the transfer ports 24.
• the exhaust valve 28 may be tuned in such a way as to be opened to a lesser or greater degree so as to obtain engines with different operating characteristics, such as torque at low revolutions per minute or higher maximum power.
• the exhaust valve 28 may also be tuned in such a way that it opens or closes with different timing, that is to say, the exhaust valve 28 opens or closes at different times relative to the position of the piston 20 and the related crankshaft 5. This may be achieved by a device for varying the timing of the cam 29. At low revolutions per minute and high loads, the exhaust timing can be advanced by a few degrees to facilitate the expulsion of burnt gases or closed in advance to prevent the escape of fresh gases.
• FIGs 2 and 3 show the guide piston 10 of the engine illustrated in Figure 1, where the rod 14 is integral with the guide piston. There are no grooves because the guide piston 10 fulfils additional functions as explained below.
• Figures 4 and 5 show the piston 20 of the engine illustrated in Figure 1.
• the piston has no skirt and has cooling fins 20c.
• Figures 7 and 8 illustrate another embodiment of the piston shown in Figures 4 and 5.
• the transfer cycle does not have a fixed timing. Transfer occurs only when the pressure in the lower section 23 of the cylinder 15 exceeds by a defined value the pressure in the upper section 22 of the cylinder 15.
• the transfer cycle is thus automatically adjusted to the operating conditions of the engine. It follows therefore that the transfer cycle may also be asymmetrical relative to the bottom dead centre.
• the transfer cycle will therefore be a function of the pressure in the upper section 22, the pressure in the lower section 23, the force of the return springs 56 of the poppet valves 52 and the pressure loss through the holes 51.
• Figure 6 illustrates an embodiment of the engine where the lower section acts as a reciprocating compressor.
• the guide piston 10 has no grooves 12 in it and thus works like an ordinary piston moving in the sleeve 11, which is shaped like a cylinder, sucking air in through a first tube 40 and pushing air out through a second tube 41 to the engine's exhaust pipe 27.
• the first tube 40 is equipped with a filter 42.
• the air compressed by the guide piston 10 is driven into the intake of the cylinder 15 in such a manner as to supercharge the engine .
• the lower section acts as a pneumatic pump for injecting the fuel directly into the combustion chamber.
• the guide piston 10 and the related sleeve 11 may therefore perform the different functions of compressor, supercharger and pneumatic injection pump without requiring the addition of a lot of other parts and thus greatly simplifying engine design.
• the piston does not have a skirt acting as a guide for the crank mechanism allows it to be fitted in the cylinder with a larger tolerance of fit, avoiding contact between the piston and the cylinder and eliminating the risk of piston seizure.
• the piston moves within the cylinder in a straight, axial direction only, thus greatly reducing friction and, consequently, the need for their lubrication is also much less.
• Another advantage is that it has fewer parts compared to an equivalent four-stroke engine.
• a four-stroke engine delivering the same power output as the engine made according to the present invention must have twice as many cylinders and pistons and related crank mechanism.
• the two-stroke engine disclosed here requires only one exhaust valve for each cylinder, while a four stroke engine must also have an intake valve .
• the lower part of the two-stroke engine made according to the present invention may serve as compressor, a supercharger and a pneumatic injection pump with the addition of practically no other parts, thus greatly simplifying engine design.
• Yet another advantage of the present invention is the fact that the lubricating oil is recovered and re-used as in a four- stroke engine, thus increasing the reliability of the engine and reducing pollution due to burnt oil.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Lubrication Of Internal Combustion Engines (AREA)
• Cylinder Crankcases Of Internal Combustion Engines (AREA)
• Combustion Methods Of Internal-Combustion Engines (AREA)
• Supercharger (AREA)

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• 2000
  • 2000-05-17 AU AU2000251004A patent/AU2000251004A1/en not_active Abandoned
  • 2000-05-17 EP EP00935466A patent/EP1282764B1/fr not_active Expired - Lifetime
  • 2000-05-17 AT AT00935466T patent/ATE272167T1/de not_active IP Right Cessation
  • 2000-05-17 WO PCT/IT2000/000197 patent/WO2001088350A1/fr not_active Ceased
  • 2000-05-17 DE DE60012585T patent/DE60012585T2/de not_active Expired - Fee Related
  • 2000-05-17 ES ES00935466T patent/ES2223528T3/es not_active Expired - Lifetime

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