NL1042988B1

NL1042988B1 - Novel two-stroke engine

Info

Publication number: NL1042988B1
Application number: NL1042988A
Authority: NL
Inventors: Tjeerd Sijtse Ijsselstein Ing
Original assignee: Cereus Tech B V
Priority date: 2018-09-11
Filing date: 2018-09-11
Publication date: 2020-05-29

Abstract

The present invention provides a method and a device which eliminate the disadvantages that characterize the prior art two-stroke engine. The crankcase is sealed fluidically and isolated from the cylinder. The crankcase is provided with a dedicated lubricating oil system. The Reed valve on the crankcase is eliminated. The engine comprises a membrane pump or other suitable type of pump that is actuated by the pressure cycles in the crankcase caused by the reciprocating movement of the piston of the engine. The suction side of the pump is connected with the outlet of the fuel supply, e.g. a carburetor, with a Reed valve in between. The discharge side of the membrane pump is connected to the inlet of a fuel injector that injects the fuel/air mixture directly into the cylinder of the two-stroke engine where, after the mixture is compressed by the upwardly moving piston it is ignited by a spark of a spark plug, which spark plug in some embodiments is integrated in the fuel injector of the engine. When equipped with a pilot valve type fuel injector the twostroke gasoline engine according to the invention will be very efficient and is likely to produce less pollution than the average prior art four-stroke engines.

Description

NOVEL TWO-STROKE ENGINE

FIELD OF THE INVENTION

The invention relates to the field of two stroke engines, especially gasoline fueled two stroke engines.

BACKGROUND OF THE INVENTION

Two-stroke engines have several advantages compared to four-stroke engines, including for example:

- two-stroke engines fire once for each revolution of the crankshaft, while fourstroke engines fire once every other revolution. This gives a two-stroke engine roughly twice the power of a four-stroke engine of the same size;

- Two-stroke engines usually do not have valves, which results in a simplified construction and a relatively low weight;

- Two-stroke engines can work in any orientation, which can be useful for, for example, an engine for a chainsaw. A standard four-stroke engine may have problems with oil flow if it is not in an upright position.

These advantages make two-stroke engines lighter, simpler and less expensive to manufacture than four-stroke engines. Two-stroke engines also have the potential to pack about twice the power into the same space because there are twice as many power strokes per revolution. The combination of a lower weight and twice the power gives two-stroke engines an attractive power-to-weight ratio compered to many fourstroke engine designs.

However, two-stroke engines also have some significant disadvantages. A short explanation of the operation of a two-stroke engine is given below in order to better understand the disadvantages. As a general difference, two-stroke engines don't have a dedicated lubrication oil system for the wear-prone components of the engine, such as for example the connection between the connecting rod and the piston and the connecting rod and the crankshaft or for lubrication between the piston rings and cylinder wall. Gasoline fueled two-stroke engines use a mixture of gasoline and lubricating oil as fuel instead of pure gasoline.

A two-stroke engine basically consists of a cylinder with a piston that can reciprocate in the cylinder between a top and a bottom position, the top position being the position in which the fuel and air mixture in the cylinder is compressed to the maximum extent by the piston. The piston is connected to a crankshaft through a connecting rod.

Contrary to four-stroke engines, two-stroke engines have an essentially gas-tight 10 crankcase, which crankcase is in open connection with the cylinder when the piston is in the vicinity of its bottom position and the inlet port for the air/fuei/oil mixture is uncovered.

As the air/fuei mixture in the cylinder above the piston is compressed, a vacuum is created in the crankcase. This vacuum opens the so-called Reed valve and sucks a fresh 15 air/fuel/oii mixture in from the carburetor. So, in conventional two-stroke engines the intake of the air/fuel/oil mixture occurs through the crankcase. A spark plug at the top of the cylinder will fire when the piston is near the top position (TDC) and the fuel and air mixture ignites. The resulting explosion drives the piston downward. As the piston moves downward, it is compressing the air/fuei mixture in the crankcase and wili push 20 it to the inlet port of the combustion chamber. However, before the piston has moved downward far enough to uncover the fuel inlet port, the exhaust port is uncovered to release exhaust gases. When the piston bottoms out it has pressurized the mixture in the crankcase, so the mixture fiows into the cylinder, displacing the remaining exhaust gases and filling the cylinder with a fresh charge of the fuei/air mixture. Usually, the 25 piston has a roof shaped top, which forces the inlet mixture toward the cylinder top.

The mixture than returns downward in a ioop shape movement forcing the exhaust gases to leave the combustion chamber.

Now the momentum in the crankshaft starts driving the piston back toward the spark plug for the compression stroke. Once the piston makes it to the end of the compression stroke, the spark plug fires again to repeat the cycle, it's called a two stroke engine because there is a compression stroke and then a combustion stroke, in a four-stroke engine, there are separate intake, compression, combustion and exhaust strokes. As will be ciear now, some of the disadvantages of two-stroke engines are:

- Two-stroke engines have a substantially shorter lifetime than four-stroke engines. The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear significantly faster;

The consumption of two-stroke oil is expensive; Two-stroke engines do not use fuel efficiently;

The majority of (gasoline) engines according to the two-stroke principle suffer from poor purging of waste gases due to the fact that the inducted mass flow is entering the cylinder through ports in the cylinder wall causing cross flows, which results in limited/poor flush induction. So, there is some dilution of the fresh fuel/oil mixture with waste gases;

- Two-stroke engines are very polluting. The pollution comes from two sources. The first source is the (partial) combustion of the lubricating oil that is added to the gasoline. The oil makes all two-stroke engines smoky to some extent, and a badly worn two-stroke engine can emit huge clouds of oily smoke. The second source relates to slippage of some of the fresh fuel/oil mixture. Each time a new charge of air/fuel/oil is loaded Into the combustion chamber, part of it leaks out, slips, through the exhaust port. The leaking hydrocarbons from the fresh fuel/oil mixture are quite harmful for the environment.

Unless the above-mentioned disadvantages of two-stroke engines can be eliminated, the end of the lifecycle of the two-stroke engine is imminent.

SUMMARY OF THE INVENTION

The present invention provides a method and a device which eliminate the disadvantages that characterize the prior art two-stroke engine. The crankcase will be isolated fluidically from the cylinder and will be provided with dedicated lubricating oil.

042988

The Reed valve on the crankcase is eliminated. A membrane pump, also known as a diaphragm pump, or another suitable type of pump that is actuated by the pressure cycles in the crankcase caused by the upward and downward movement of the piston is connected with its suction side to the fuel supply, for example from a carburetor, with a Reed valve in between. The discharge side of the membrane pump is connected to the inlet of a fuel injector that injects the fuei/air mixture originating from the carburetor directly into the cylinder of the two-stroke engine where, It Is ignited by a spark of the spark plug after the mixture is compressed by the upward moving piston. When equipped with a pilot valve type fuel injector the two-stroke gasoline engine according to the invention will be very efficient and may produce less pollution than the average prior art four-stroke engines. The two-stroke engine according to the invention also includes embodiments which comprise a turbocharger on the waste gas outlet side to recover energy from the waste gases and a compressor for compressing the inlet air before it enters the cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, 20 in which;

FIG. 1 shows a schematic vertical section of an embodiment of the improved two-stroke engine according to the present invention;

FIG. 2 shows a schematic longitudinal section of an embodiment of the fuel 25 injector of the improved two-stroke engine according to the invention;

FIG. 3(a) is a schematic partial side view of an adapter-type embodiment of the fuel injector of the improved two-stroke engine according to the invention;

FIG. 3(b) is a schematic bottom view of the adapter-type embodiment of the fuel injector of the improved two-stroke engine according to the invention shown in a side view in FIG. 3(a);

FIG. 4 shows a schematic vertical section of another embodiment of the improved two-stroke engine according to the present invention with measures for increasing the inlet-air pressure;

FIG. 5 shows a schematic vertical section of an embodiment of a slide valve for the control of the inlet air and consequently the boost pressure of the improved two-stroke engine according to the invention;

FIG, 6 shows a schematic longitudinal section of an embodiment of a breather for the membrane pump of an improved two-stroke engine according to the invention.

identical or similar parts have been designated with identical or similar reference numbers in the drawings.

DETAILED DESCRIPTION OF THE INVENTION

It is an objective of the present invention to provide a two-stroke engine, especially a two-stroke gasoline engine which can comply with the latest regulatory requirements with respect to emissions from internal combustion engines.

FIG, 1 shows a schematic vertical section of an embodiment of a one cylinder twostroke engine according to the present invention with a crankcase 1 and a cylinder 2, also referred to as combustion chamber 2, wherein, the crankcase and the cylinder of the engine according to the invention do not have a fluidic connection in any of the positions of the piston 3 that reciprocates in the cylinder. The invention envisions that the crankcase is essentially fluidically sealed, meaning that essentially no fluids are entering or leaving the crankcase during operation of the engine. In the embodiment shown in FIG. 1 the piston 3 also fulfils the function of a moving, in this case reciprocating, sealing element for the crankcase. A minute quantity of oil that forms the lubrication between the piston rings and the cylinder wall may enter the combustion chamber, in the situation shown in FIG. 1 the piston is approximately in a position halfway between top dead centre and bottom dead centre. The embodiment of the two-stroke engine according to the invention shown in FIG. 1 further shows a membrane pump 4 or diaphragm pump 4 wherein a first compartment on a first side of the pump membrane is fluidicaily connected to the crankcase of the engine. In the embodiment shown in FIG. 1 the membrane pump 4 is connected to the crankcase through a conduit 5, However, the invention aiso comprises embodiments of the twostroke engine in which the membrane pump, or another suitable type of a positive displacement pump such as for example a piunger pump, is connected fluidicaily directly to the crankcase. The pressure cycles in the crankcase due to the reciprocating movements of the piston will move the membrane of the membrane pump back and forth, thus actuating the pump. The membrane of course could also be activated by a camshaft or other drive means driven by the crankshaft. The pump action that results from the movement of the membrane will cause the pump to suck an air/fuel mixture from the carburetor (which carburetor is not shown in FIG. 1 since the carburetor as such does not comprise novel features) or another source through a conduit 6, followed by discharge of this air/fuel mixture through the discharge side of the pump through a conduit 7 to a pilot valve type fuel injector 8, hereinafter also referred to as PV type fuel injector, installed in the top of the cylinder, in this case mounted in the cylinder head 9. The air/fuel intake system comprises a Reed valve 10 between the inlet end of the conduit 6 and the outlet of the carburetor. During the compression stroke the Reed valve closes and the pump discharges and pressurizes the air/fuel mixture for it to flow through conduit 7 to the inlet of the PV type fuel injector 8.

After the explosion in the combustion chamber has taken place and the piston approaches its bottom position, the exhaust gases, also referred to as waste gases, will leave through the exhaust port 11, which port will be uncovered and, hence, will be in fluidic connection with the combustion chamber when the piston is in the vicinity of its lowest position. Contrary to the prior art two-stroke engines, the two-stroke engine according to the invention does not require an overlap between the opening of the exhaust port and the injection of a fresh air/fuel mixture. The pressurized air/fuel mixture originating from the membrane pump can be injected into the combustion chamber by the fuel injector against the pressure that builds up inside the combustion chamber during the compression stroke, after closing of the exhaust port by the piston on its way upward. So, the slippage of fresh hydrocarbons through the exhaust can be prevented. The flushing of waste gas with the fresh air/fuel mixture has become a oneway, top to bottom, flow instead of a bi-directional loop shaped flow. The embodiment of the PV type fuel injector s shown in FIG. 1 comprises an integrated spark plug. This is advantageous for at least two reasons, i.e.: it assures that the cylinder head does not require two holes, one for a fuel injector and one for a spark plug, and secondly, it ensures that the point of origin of the spark is located in the immediate vicinity of the points of entrance of the fuel air mixture into the combustion chamber. In order to incorporate the spark plug function the embodiment of the PV type fuel injector 8 shown in FIG. 1 comprises a central electrode 12, a mass electrode 13 and an insulator 14 around the central electrode.

A PV fuel injector, as was first disclosed in an earlier patent application by the applicant of the present patent application, comprises an injector with a much larger number of nozzle holes, which nozzle holes have a substantially smaller diameter than the nozzle holes of conventional needle and seat type fuel injectors. In certain embodiments the PV fuel injector comprises 40 nozzle holes with a diameter of 50 micrometers each, which nozzle holes are divided over 5 rows of 8 nozzle holes each, wherein a pilot valve, a plunger-like element, moves axially inside the fuel injector whereby the pilot valve moves to open more rows of nozzle holes as more power is demanded from the engine in which the injector is installed. So, instead of injecting more fuel through a fixed number of nozzle holes, whereby the fuel jets become more massive, which results in an unfavorable surface area to fuel volume ration and hence to less favorable combustion conditions, the pilot valve fuel injector increases the number of fuel jets while keeping the size of each fuel jet small. This results in better combustion conditions and, therefore, in better circumstances for complete combustion. There are also embodiments of the PV fuel injector with for example 100 or more nozzle holes with a diameter of approximately 40 micrometers each or even smaller.

FIG. 2 shows a schematic iongitudinal section of an embodiment of the fuel injector of the two-stroke engine according to the invention. As already mentioned and shown in less detail In FIG. 1 this embodiment comprises a pilot valve type fuel injector with an integrated spark plug. The pilot valve type fuel injector comprises a body or housing 8a 5 wherein a spring loaded pilot valve 15 can slide axially along a part of the insulator 14 of the spark plug that is integrated in the fuel injector. So, the insulator functions as a core or guide around which the pilot valve can move axially. The embodiment of the PV fuel injector shown in FIG. 2 comprises two rows of nozzle holes 16a and 16b.

In the position of the pilot valve shown in FIG. 2 the external wall of the spring loaded 10 pilot valve 15 closes the inlet side of the nozzle bores 16a and 16b inside the body 8a of the fuel injector. When the fuel pressure increases the pilot valve 15 Is moved downward against the spring force and after sufficient downward movement of the pilot valve the inlet of the first row of nozzle holes 16a will obtain a fluidic connection with the fuel chamber 17 in the fuel injector and fuel will start to be injected through 15 the nozzle holes 16a in the first row of nozzle holes. With increasing power and fuel demand from the engine the pilot valve will move further downward and the second row of nozzle holes 16b will open. The number of nozzle hole rows of the fuel injector is not restricted to only two rows as shown schematically in the embodiment in FIG. 2, but can include a larger number of nozzle hole rows if desired/required.

In the embodiment of the PV fuel injector of the improved two-stroke engine according to the invention shown schematically in FIG. 2 the PV fuel injector and spark plug are integrated into one device. However, the invention also includes embodiments of the improved two-stroke engine in which the fuel injector comprises an adapter type fitting with installation engagement means in its centre in which a 25 standard spark plug can be installed. FIG. 3(a) is a schematic partial side view of an embodiment of said adapter-type fuel injector of the improved two-stroke engine according to the invention. FIG. 3(b) is a schematic bottom view of the adapter-type embodiment of the fuel injector of the improved two-stroke engine according to the invention shown In a side view in FIG. 3(a).

In yet another embodiment the fuel injector and spark plug are two completely separated components that are installed in the cylinder heads in two individual fittings in the cylinder head.

The equations for calculation of the power, torque and mean effective pressure (M_ep) of an engine show that, in general, the engine performance parameters are proportional to the mass of air inducted per cycle. This air-inlet mass (by nature) primarily depends on the air-inlet density at a given oxygen percentage. Especially in situations in which operation of an engine at varying altitudes, i.e. situations in which the intake air density may be varying substantially, is required, boosting the density can prevent or at least minimize the occurrence of fuel-air mixtures that are too rich in fuel relative to the oxygen that is available.

Therefore, the performance of a two-stroke engine can be increased by compressing the inlet-air prior to entering the cylinder, analogous to the mode of operation of most modern prior art four-stroke engines. The present invention includes three possible means of achieving an inlet air pressure boost in a two-stroke engine. FIG. 4 shows a schematic vertical section of an embodiment of the two-stroke engine according to the present invention with measures for increasing the inlet-air pressure. All the basic components, such as for example the piston, cylinder, crankcase, etc. of the twostroke engine shown schematically in FIG. 4 that have not been provided with a reference number are substantially identical to the components of the embodiment shown in FIG. 1.

in the embodiment of the improved two-stroke engine according to the invention shown in FIG. 4, the engine comprises an exhaust gas driven turbo charger 18. By expansion of the hot exhaust gases, the turbine wheel including the shaft 18a of the turbo charger 18 rotates, enabling the recovery of energy from the waste gases. The invention envisages that the shaft 18a of the turbocharger for example is coupled to the shaft 19a of an air compression feature 19, hereinafter also referred to as the compressor 19. While in the drawing of FIG. 4 the turbo charger 18 and the compressor 19 are not positioned such that the respective shafts 18a and 19a can be coupled directly, the improved two-stroke engine according to the invention includes embodiments in which the turbo charger IS and the compressor 19 are for example integrated in one turbo machinery unit.

The inlet of the air compressor 19 is fed with air compressed by the crankcase membrane of the membrane pump 4. For accurate boost pressure control, for example, a bleeding valve 20 positioned in the conduit to the inlet of the compressor 19 may be governing the air flow in dependency of for example the throttle position or any other suitable control parameter.

As an alternative the control of the inlet-air mass flow can also be realized by waste gate controls on the expansion of hot gases towards the turbo charger turbine 18 in order to reduce turbine revolutions, as commonly used. During transient conditions, this mode of operation has a slight disadvantage compared to controls on the inlet of the compressor, since the phenomenon of turbo-lag is less noticeable in the latter. The throttling of compressor intake air significantly slows down engine revolutions during a reduction of the engine set-speed due to resistant pressure on the secondary side of the piston.

Instead of letting the turbo charger turbine 18 drive the compressor 19, the compressor may also be driven by an alternative drive, such as for example an electric motor, which may be speed governed in order to control the air mass flow effectively and accurately.

The turbo charger 18 may also drive an alternator, whereby the electric energy generated by the alternator may be used for any suitable purpose, such as for example, powering an electric motor to drive the compressor.

The maximum displacement of the membrane volume, i.e. the metered inducted mass of air per cycle, of the membrane pump 4 is designed for the supply of enough air for enabling the maximum engine performance. For accurate boost pressure controls, a bleeding valve 20 may be governing the flow and/or the pressure difference across the Inlet flow, in dependency of, for example, the throttle position or any other control parameter. The cost, additional weight, installation space, etc., of the control and drive devices discussed above may be prohibitive for simple and cheap engines, however, there are many more demanding applications for which additional power and torque requirements justify implementation of an improved two-stroke engine according to the invention.

In order to prevent possible undesired changes in pressure over time inside the 5 crankcase due to for example atmospheric or temperature effects, a limited amount of fresh air bleeding into or exhausted from the crankcase can be arranged by a breather. This ensures that each and every stroke of the piston has an equal effect on the mass of air inducted per cycle. This can be realized by bleeding air in or out at the end of each stroke as soon as the membrane of the membrane pump 4 or alternatively the 10 displacement piston of a piston pump, if used, hits its end position. The aforementioned measures do not interfere with the methods of air-fuel controls.

In case a positive displacement (piston) pump is used, the delivery of such a device can be metered by an axially adjustable entrance opening of the inlet air. For that purpose a slide valve of the type of which a vertical cross section of an embodiment is shown 15 schematically in FIG. 5 can provide for a continuous (as opposed to a discrete) flow control, for example, as a function of the throttle position of the engine or any other suitable control parameter. The position of the sliding valve is determining the actually displaced volume for each and every stroke of the piston. The more the slide valve is positioned near the end of the piston stroke, the less the supplied additional volume will be. The more the position of the sliding is valve near the lowest position of the piston, the higher the supplied additional volume, and consequently the higher the boost pressure will become.

FIG. 6 shows a schematic longitudinal section of an embodiment of a breather that can be installed on the membrane pump 4 of a two-stroke engine according to the 25 invention. The invention envisions the installation of a breather 21a on the crankcase side compartment of the pump and/or a breather 21b on the compressor side compartment of the pump as shown in FIG. 4.

While the embodiments of the two-stroke engine according to the Invention shown 30 schematically in FIG. 1 and FIG. 3 comprise only one cylinder, the two-stroke engine according to the invention may comprise any number of cylinders that is deemed useful and/or required for a desired application. Of course, the two-stroke engine according to the invention can be applied advantageously not only in vehicles of many different kinds, such as for example motorcycles, mopeds, scooters and motor cars, but also in for example lawn mowers, outboard motors, etc.. Due to the hydrocarbon fuel slippage that is inherent to conventional two-stroke engines and that is readily visible by the oily film on the water surface in the vicinity of a two-stroke outboard engine, the application of the two-stroke engine according to the invention in outboard motors will have an immediately visible beneficial effect by eliminating hydrocarbon slippage and, hence, by eliminating the formation of oily films on surface water.

The improved two-stroke engine according to the invention includes embodiments with a carburetor as well as embodiments with direct fuel injection. Reference to the outlet of the carburetor shall be construed to include a fuel supply conduit in the case of embodiments of the improved two-stroke engine that do not comprise a carburetor. Where in the description or in the claims a reference is made to a membrane pump this shall be construed to also include the possibility of the use of for example a piston pump or any other suitable positive displacement pump.

As described above, the invention may especially be embodied in the following embodiments, wherein the embodiments are merely numbered for reference reasons.

1. A two-stroke internal combustion engine with a fluidically sealed crankcase (1), at least one cylinder (2) and a reciprocating piston (3) which constitutes a movable sealing element for the crankcase , wherein, a positive displacement pump is fluldically connected to the crankcase (1) and is actuated by fluids in the sealed crankcase which fluids undergo pressure cycles as a result of the reciprocating movement of the piston (3) in the cylinder (2) of the engine.

2, The two-stroke engine according to embodiment 1, wherein, the positive displacement pump is actuated by a crankshaft driven camshaft or by other crankshaft driven drive means.

3. The two-stroke engine according to embodiment 2, wherein, the suction side of the positive displacement pump is fluidicaHy connected to the outlet of the carburetor of the engine.

4. The two-stroke engine according to any of the preceding embodiments, wherein, the engine comprises a Reed valve (10) between the outlet of the carburetor and the inlet of the suction side of the positive displacement pump.

5. The two-stroke engine according to any of the preceding embodiments, wherein, the engine comprises a fuel injector (8) for injecting fuel directly into the combustion chamber (2).

6. The two-stroke engine according to embodiment 5, wherein, the discharge side of the positive displacement pump is fluidicaHy connected to the fuel injector (8).

7. The two-stroke engine according to embodiment 5 or 6, wherein, the fuel injector comprises a pilot valve type fuel injector.

8. The two-stroke engine according to any of the embodiments 5 - 7, wherein, the fuel injector comprises an adapter-type fuel injector with internal engagement means for a spark plug.

9. The two-stroke engine according to any of the embodiments 5-8, wherein, the fuel injector comprises an integrated spark plug.

10. The two-stroke engine according to any of the preceding embodiments, wherein, the positive displacement pump comprises a membrane pump (4) or a piston pump.

11. The two-stroke engine according to any of the preceding embodiments, wherein, the engine comprises a compressor (19) for compressing the air entering the cylinder (2).

12. The two-stroke engine according to any of the preceding embodiments, wherein, the engine comprises a turbo charger (18) for the recovery of energy from the waste gases of the engine.

13. The two-stroke engine according to embodiment 11, wherein, the compressor (19) is driven by the turbo charger (18) or an electric motor.

14. The two stroke engine according according to any of the embodiments 11 -13, wherein, a bieeding valve (20) is fiuidically connected to the suction side of the compressor (19).

15. The two-stroke engine according to any of the preceding embodiments, wherein, 5 the positive displacement pump (4) comprises a breather (21a) on the crankcase side compartment of the pump and/or a breather (21b) on the compressor side compartment of the pump.

The term comprise includes also embodiments wherein the term comprises means 10 consists of. The term and/or especially relates to one or more of the items mentioned before and after and/or. For instance, a phrase item 1 and/or item 2 and similar phrases may relate to one or more of item 1 and item 2. The term comprising may in an embodiment refer to consisting of but may in another embodiment also refer to containing at least the defined species and optionally one 15 or more other species,

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. it is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb to comprise and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article a or an preceding an element does not exclude the presence of a plurality of such elements.

In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The various aspects discussed in this application can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined,, and that also more than two embodiments can be combined.

Claims

A two-stroke internal combustion engine comprising a fluid tight crankcase (1), at least one cylinder (2) and a piston (3) which moves the piston up and down in the cylinder and forms a movable sealing element for the crankcase, characterized in: that a positive displacement pump is fluidly connected to the crankcase (1) and is driven by fluids in the fluid-tight crankcase which undergo fluid pressure cycles due to the movements of the piston (3) in the cylinder (2) of the engine.

Two-stroke engine according to claim 1, characterized in that the positive displacement pump is driven by a camshaft driven by the crankshaft or by other drive means driven by the crankshaft.

Two-stroke engine according to claim 1 or 2, characterized in that the suction side of the positive displacement pump is in fluid communication with the outlet of the carburettor of the engine.

Two-stroke engine according to one or more of the preceding claims, characterized in that the engine comprises a reed valve (10) between the outlet of the carburettor and the inlet of the suction side of the positive displacement pump.

Two-stroke engine according to one or more of the preceding claims, characterized in that the engine comprises a device (8) for injecting fuel directly into the combustion chamber (2) of the engine.

Two-stroke engine according to claim 5, characterized in that the discharge side of the positive displacement pump is in fluid communication with the device (8) for injecting fuel directly into the combustion chamber.

Two-stroke engine according to claim 5 or 6, characterized in that the device (8) for injecting fuel directly into the combustion chamber of the engine comprises a slide atomizer

Two-stroke engine according to one or more of claims 5 to 7, characterized in that the device for injecting fuel directly into the combustion chamber of the engine comprises an adapter with internal spark plug engaging means.

Two-stroke engine according to one or more of claims 5 to 8, characterized in that the device for injecting fuel directly into the combustion chamber of the engine comprises an integrated spark plug.

Two-stroke engine according to one or more of claims 2 to 9, characterized in that the positive displacement pump comprises a diaphragm pump (4) or a piston pump.

Two-stroke engine according to one or more of the preceding claims, characterized in that the engine has a compressor (19) for compressing the air supply to the cylinder.

Two-stroke engine according to one or more of the preceding claims, characterized in that the engine comprises a turbocharger (18) for recovering energy from the waste gases.

Two-stroke engine according to claim 11 or 12, characterized in that the compressor (19) is arranged to be driven by the turbocharger (18) or by an electric motor.

Two-stroke engine according to one or more of claims 11-13, characterized in that a bleed valve (20) is in fluid communication with the suction side of the compressor (19).

Two-stroke engine according to one or more of the preceding claims, characterized in that the positive displacement pump (4) comprises a bleed valve (21a) on the crankcase side of the pump and / or a bleed valve (21b) on the compressor side of the pump.