WO2019211371A1

WO2019211371A1 - Engine with cooperating pistons based on a two-stroke cycle

Info

Publication number: WO2019211371A1
Application number: PCT/EP2019/061229
Authority: WO
Inventors: Remo Felice SALERI
Original assignee: Saleri Remo Felice
Priority date: 2018-05-04
Filing date: 2019-05-02
Publication date: 2019-11-07
Also published as: IT201800005066A1

Abstract

An internal combustion engine (1) comprises at least two motor units (1m, 2m, 3m), each of them (1m, 2m, 3m) operates according to a two-stroke cycle and includes a cylinder (2), a piston (3) slidably housed in the cylinder (2), the cylinder (2) and the piston (3) defining a combustion chamber (4) inside the cylinder (2), its own exclusive crankcase (6) connected to an end of the cylinder, and its own exclusive crankshaft housed in the crankcase (6). Suitably, the internal combustion engine (1) comprises at least one fluid passage (9) between the crankcase of a first motor unit and the combustion chamber of a second motor unit, and further comprises a load valve (10) arranged at the fluid passage (9), wherein that load valve (10) is apt to allow a supply from the crankcase of the first motor unit to the combustion chamber of the second motor unit due to an expansion movement of the piston of the first motor unit.

Description

Title:“Engine with cooperating pistons based on a two-stroke cycle”

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DESCRIPTION

Technical Field

The present invention relates to an internal combustion engine, in particular an engine comprising at least two motor units each of them operating on the basis of a two-stroke cycle, and the following description is done with reference to this field of application with the only aim of simplifying the exposition thereof.

Background Art

Internal combustion engines are to this day a means of propulsion which is difficult to replace, mostly in the transport field.

As it is well known, an internal combustion engine comprises a cylinder, inside which a piston slides, and a crankcase which houses the crankshaft, which is driven into rotation by a connecting rod-crank mechanism connected to the piston. At an end of the cylinder, called in the field“head”, a combustion chamber is defined while the crankcase is arranged at the opposite end.

In a two-stroke engine there are an intake port and an exhaust port in close proximity to the bottom dead center (BDC), for the introduction of fresh charge and the discharge of combusted gases respectively, while in a four-stroke engine those flows are regulated by valves generally located on the cylinder head.

In a two-stroke engine, the expansion phase (which corresponds to a rotation of about 180° of the crankshaft) occurs for each full rotation of the crankshaft, while in a four- stroke engine two full rotations of the crankshaft are needed to carry out a cycle. Since the expansion phase is the sole active phase (with energy transfer), it results that a two-stroke cycle has twice as many active phases with respect to the four-stroke one for the same revolutions. Thus, the nominal power of a two-stroke engine is twice that of a four- stroke one.

However, the two-stroke engine has a limited efficiency since in general a portion of the fresh charge passes directly through the transfer port (through which fresh charge is introduced from the crankcase to the cylinder) in the exhaust port without being involved in the combustion cycle. Thus, not all the introduced fuel contributes to the combustion and the unburned part increases the pollutants introduced into the environment.

In addition, it is known that a two-stroke engine has lubrication problems due to the fact that it is not possible to position in the crankcase spray nozzles which convey the oil against the cylinder walls, being that crankcase a container of the fresh charge before it is transferred inside the cylinder. For this reason, mixtures of oil and fuel are used, whose combustion generates further polluting emissions.

Both two-stroke engines and four-stroke engines generally have a low real efficiency, irrespective of the type of fuel being used (normally comprised between 0.25 and 0.5).

The two-stroke engine is also characterized by a great construction simplicity and by reduced maintenance costs, as well as by theoretically higher performances than a four-stroke engine, having in fact twice as many useful cycles and the need for a lower number of moving components with relevant frictions and leaks.

Another known defect of engines is due to the difficulty of inserting a sufficient amount of air for a correct combustion, rather than to the difficulty of inserting fuel. The fuel-comburent ratio cannot in fact diverge too much from the stoichiometric value in Otto-cycle engines, otherwise this results in a non-optimum combustion with a lower efficiency.

In order to increase engine efficiency, the boosting technique is often used, which allows an amount of air to be introduced into the cylinder, that is higher than the amount an engine would normally intake (in aspirated engines in fact that amount is always lower than the engine displacement because of load losses of the fluids) allowing the amount of fuel to be increased and accordingly the power and maximum pressure thereof to be increased.

However, the above solution is not free from drawbacks as well, since boosting leads to an energy absorption by the engine and, according to the type of boosting being used, other devices are necessary to couple machines like turbines (which are structured to correctly operate at a steady number of revolutions) to the engine which instead works in a wider range of revolutions. A further disadvantage of the boosting of the prior art is that by compressing air it heats and accordingly the density thereof decreases, actually frustrating the advantage of boosting. That is why some exchangers called intercoolers are inserted, which are charged with bringing the air back to a low temperature.

However, in the latter case too, the engine efficiency is reduced because combusted gases must be discharged at a pressure that is higher than the atmospheric one, so that they have enough force to spontaneously pass through the exhaust manifold. In addition, the engine includes the components responsible for maintaining that boosting, as well as for maintaining the optimum temperature and the lubrication, involving such a complexity as to cause a low overall efficiency.

The technical problem of the present invention is to provide an internal combustion engine having such functional and structural features as to allow the limitations and drawbacks still affecting two- stroke engines manufactured according to the prior art to be overcome, in particular a high efficiency and high performances to be achieved without increasing the construction complexity thereof.

Disclosure of Invention

The solution idea underlying the present invention is to provide an internal combustion engine which comprises a plurality of motor units, each comprising its own combustion chamber, wherein the supply of the combustion chamber of a motor unit occurs based on the movement of a piston of another motor unit. In particular, the combustion chamber of a motor unit is in fluid communication with the crankcase of the other motor unit, and the supply of that combustion chamber is regulated by the opening/closing of a suitable valve.

Based on that solution idea, the above technical problem is solved by an internal combustion engine operating according to a two stroke- cycle, comprising at least two motor units, each of those motor units including a cylinder, a piston slidably housed in the cylinder, the cylinder and the piston defining a combustion chamber inside the cylinder, its own exclusive crankcase connected to an end of the cylinder, and its own exclusive crankshaft housed in the crankcase, said internal combustion engine being characterized in that it comprises at least one fluid passage between the crankcase of a first motor unit and the combustion chamber of a second motor unit, and in that it further comprises a load valve arranged at the fluid passage, wherein the load valve is apt to allow a supply from the crankcase of the first motor unit to the combustion chamber of the second motor unit due to an expansion movement of the piston of the first motor unit.

More particularly, the invention comprises the following additional characteristics, taken individually or in combination if required.

According to an aspect of the present invention, the internal combustion engine can comprise three motor units, wherein the crankcase of a first motor unit is adjacent and in fluid communication with the combustion chamber of a second motor unit, the crankcase of the second motor unit is adjacent and in fluid communication with the combustion chamber of a third motor unit, and the crankcase of the third motor unit is adjacent and in fluid communication with the combustion chamber of the first motor unit.

According to an aspect of the present invention, each of the three motor units can be arranged on a respective side of an equilateral triangle, the crankshafts of each of those motor units being located at the vertices of that equilateral triangle and having a relative phase substantially of 120°.

According to another aspect of the present invention, the crankshaft in the crankcase can be associated with a crank having a cam profile, the load valve being in engagement with that cam profile and being configured to be driven and opened during at least one portion of the rotation of that cam profile.

According to another aspect of the present invention, the internal combustion engine can comprise an inlet valve at the crankcase for the inlet of fresh charge due to the compression movement of a piston.

Yet according to another aspect of the present invention, the crankshaft in the crankcase can be associated with a crank having a cam profile, the inlet valve being in engagement with that cam profile and being configured to be driven and opened during at least one portion of the rotation of that cam profile.

The above inlet valve can be also a reed valve.

Furthermore, the load valve can be a poppet valve.

According to another aspect of the present invention, each of the pistons can comprise a first portion having a first diameter and a second portion having a second diameter that is greater than the first diameter, the first portion facing the cylinder head, and the second portion facing the crankcase, so as to increase a pumping effect during the movement of the pistons.

According to another aspect of the present invention, the cylinder can be shaped so as to comprise a first cylinder portion having a diameter corresponding to the diameter of the first portion of the piston, and a second cylinder portion having a diameter corresponding to the diameter of the second portion of the piston, so as to define a variable volume chamber in the second cylinder portion during the piston stroke.

Yet according to another aspect of the present invention, the internal combustion engine can comprise nebulizing means apt to introduce a nebulized lubricating fluid at a surface of the piston, and a check valve configured to allow the inlet of that nebulized lubricating fluid inside the cylinder, that piston comprising a fluid path in communication with a fluid path in the crankshaft for the recirculation of the nebulized lubricating fluid.

Yet according to another aspect of the present invention, the internal combustion engine can comprise an exhaust port provided on a wall of the cylinder for the discharge of combusted gases, and a closing valve apt to hermetically close the exhaust port during the compression movement of the piston.

In addition, at least one crankshaft of a motor unit can be counter rotating with respect to the crankshafts of the other motor units.

Yet according to another aspect of the present invention, the internal combustion engine can be a spark-ignition engine or a compression- ignition engine. Finally, the at least one fluid passage can be made at the cylinder head, the crankcase of a motor unit communicating with the head of another motor unit.

The features and advantages of the engine according to the invention will become apparent from the following description of an embodiment thereof, given by way of non-limiting example with reference to the accompanying drawings.

Brief Description of Drawings

In the drawings:

Figure 1 schematically shows an internal combustion engine according to the present invention;

Figures 2A-2C schematically show successive phases of the operation of the internal combustion engine according to the present invention, wherein each phase differs from the previous one by a rotation of 120° of the crankshaft; and

Figures 3A and 3B schematically show a front view and a perspective view, respectively, of a piston of the internal combustion engine according to the present invention.

Modes for Carrying Out the Invention

With reference to the figures, and particularly to the example of figure 1 , an internal combustion engine according to the present invention is globally and schematically indicated with 1.

It is worth noting that the figures represent schematic views and are not drawn to scale, but they are instead drawn so as to emphasize the important features of the invention. Furthermore, in the figures, the different elements are schematically represented, the shape thereof being allowed to vary according to the desired application. In addition, it is worth noting that in the figures identical reference numbers refer to identical elements in shape or function. Finally, particular expedients described in relation to an embodiment shown in a figure can be used also for the other embodiments illustrated in the other figures.

The internal combustion engine 1 of the present invention comprises a plurality of motor units, each of them operates based on a two-stroke cycle. A construction example is described hereinbelow wherein the internal combustion engine 1 of the present invention is a spark-ignition engine, although it could be a compression-ignition engine, as indicated hereafter.

Specifically, each motor unit comprises a cylinder 2 and a piston 3 slidably housed in that cylinder 2. The cylinder 2 and the piston 3 define a combustion chamber 4 relating to the cylinder 2 and inside which fresh charge (fuel or an oil-fuel mixture) is supplied. The combustion chamber 4 is placed at the head of the cylinder 2.

Traditionally, a spark plug 5 arranged in close proximity to the combustion chamber 4 generates a spark which initiates the combustion of the fresh charge in that combustion chamber 4 and causes the initiation of the expansion phase (or active phase) of the piston 3 inside the cylinder 2.

Each motor unit further comprises a crankcase 6 connected to an end of the cylinder 2, in particular the end which is opposite to the head, that crankcase 6 housing a crankshaft. The rotation of the crankshaft is caused by a traditional connecting rod-crank mechanism, wherein a connecting rod 7 is connected to the piston 3 and causes the rotation of a crank 8.

As in traditional two-stroke engines, the piston 3 of each motor unit is sliding between two positions, called in the field bottom dead center (herein indicated as BDC) and top dead center (herein indicated as TDC). The movement from BDC to TDC represents the compression phase (or passive phase) of the piston, while the movement from TDC to BDC due to the trigger of the charge in the combustion chamber 4 represents the expansion phase (or active phase) of the piston.

Advantageously according to the present invention, the internal combustion engine 1 comprises at least one fluid passage 9 between the crankcase of a first motor unit and the combustion chamber of a second motor unit, which are thus put in fluid communication with each other, so that the fresh charge selectively passes from the crankcase of that first motor unit to the combustion chamber of that second motor unit.

In particular, the internal combustion engine 1 comprises a load valve 10 arranged at the fluid passage 9 so as to allow a supply from the crankcase of the first motor unit to the combustion chamber of the second motor unit due to the expansion movement of the piston of the first motor unit.

In other words, the load valve 10 is configured so as to allow fresh charge to pass from the crankcase of the first motor unit to the combustion chamber of the second motor unit during at least one portion of the expansion phase of the piston of the first motor unit.

In this way, advantageously according to the present invention, the movement of a piston of a motor unit thereby determining the operation of the cycle of another motor unit, in particular of an adjacent motor unit.

It must be noted that the present invention does not provide the presence of a common combustion chamber for several motor units, but a combustion chamber for each motor unit, which is supplied by virtue of the movement of a piston of another adjacent motor unit.

The connection between the crankcase of a motor unit and the cylinder head of a next motor unit thus causes that crankcase to operate as a storage unit for that next motor unit.

Furthermore, each motor unit comprises an inlet valve 1 1 at the crankcase 6 for the inlet of fresh charge in that crankcase 6 during the compression movement of the piston 3, i.e. during at least one portion of the passive phase (from BDC to TDC) of that piston 3.

In addition, each motor unit comprises an exhaust port 12 provided on a wall of the cylinder 2 for the discharge of combusted gases, as well as a closing valve of that port (not shown in the figures) apt to hermetically close that exhaust port 12 during the compression movement of the piston 2.

In a preferred embodiment of the present invention, the internal combustion engine 1 comprises three motor units connected to each other, a first motor unit being herein indicated as lm, a second motor unit being herein indicated as 2m and a third motor unit being herein indicated as 3m. Each motor unit preferably comprises the same mechanical components and, for simplicity, figure 1 indicates the numeral references only of the first motor unit lm, the same numeral references being obviously identifiable also for motor units 2m and 3m.

In particular, in this preferred embodiment, the crankcase of the first motor unit lm is adjacent and in fluid communication with the combustion chamber of the second motor unit 2m, the crankcase of the second motor unit 2m is adjacent and in fluid communication with the combustion chamber of the third motor unit 3m, and the crankcase of the third motor unit 3m is adjacent and in fluid communication with the combustion chamber of the first motor unit lm, as represented in figure 1.

In particular, each of the three motor units lm, 2m and 3m is arranged on a side of an equilateral triangle, the crankshafts of each of those motor units lm, 2m, 3m being located at the vertices of that equilateral triangle. Those crankshafts rotate in a synchronous way with a relative phase substantially of 120°.

Though the above-explained embodiment is considered as preferred, the present invention is not limited thereto and it also provides other configurations, for example a configuration wherein there are only two motor units. In this case, the adopted architecture is similar to that of a Boxer engine, with the difference that in the engine of the present invention the crankshaft is not arranged in the middle of the cylinders but at the ends.

In addition, configurations with more than three motor units are possible. In particular, though the configuration with three motor units already leads to a fractionization of the engine displacement, it is also possible to provide a configuration with a greater number of cylinders and thus a greater number of motor units.

It is possible to adopt complex architectures, for example to provide the presence of a series of equilateral triangles which are offset with respect each other by 60° (by way of star of David) having in common the intersection point of median lines, i.e. the point where the drive shaft is generally arranged, or it is possible to provide the presence of a series of star-arranged triangles having in common a vertex where the drive shaft is arranged (by way of radial engine) .

Suitably, in accordance with an embodiment of the present invention, the crank 8 in the crankcase 6 of each motor unit has a cam profile P, the rotation of that cam profile P causing alternately the opening and the closing of the load valve 10 and of the inlet valve 1 1.

In particular, the load valve 10 of a motor unit is in engagement with the cam profile P and it is configured to be driven and opened during at least one portion of the rotation of that cam profile P, in particular during the expansion phase of the relevant piston of that motor unit.

Similarly, the inlet valve 1 1 of a motor unit, which is as well in engagement with the cam profile P, is configured to be driven and opened during at least one portion of the rotation of that cam profile P, in particular during the compression phase of the relevant piston.

Obviously, this embodiment must not be considered as limiting the range of the present invention. For example, the inlet valve 1 1 can also be a reed valve or more generally an automatic valve. In this case, the inlet valve 1 1 operates automatically by virtue of the high difference between the vacuum which is being created in the movement of the piston from BDC to TDC and the pressure generated in the opposite phase.

Furthermore, the load valve 10 is a poppet valve, although other solutions are obviously possible. In addition, it is possible to provide a roller control which works with a sealed bearing or which slides on a bushing or other low-friction material.

The load valve 10 (and thus the fluid passage 9) is arranged in the head of the cylinder 2 in a preferably central position and it generally has a diameter that is greater than the valves normally used in known engines since it is no longer necessary to provide some space for further valves in the head of the cylinder 2. Since the load valve 10 is not in direct contact with the flue gas flow leaving the combustion chamber 4, there are no particular requirements for the selection of the materials or treatments for that valve.

Furthermore, the fluid passage 9 wherein the load valve 10 is housed has a reduced length, with a thickness-exceeding limited size. All this results in reducing possible turbulence phenomena.

The present invention will be now shown in detail in the preferred embodiment thereof wherein there are three motor units lm, 2m and 3m, each of them is arranged on a side of an equilateral triangle, wherein the crankcase of a motor unit is in contact with the cylinder head of a next motor unit. As observed above, the crankshafts of those motor units lm, 2m and 3m are located at the vertices of that equilateral triangle and have a phase of 120°.

Figures 2A-2C schematically show successive phases of the operation of the internal combustion engine 1 in the preferred embodiment with three motor units, wherein each phase differs from the previous one by a rotation of 120° of the crankshaft. In other words, in each phase, a movement of the pistons which causes a rotation of 120° of the crank associated therewith is being considered.

In particular, because of the above-explained architecture and of the phase of the crankshafts, if considering a starting point (represented in figure 2A) wherein the piston of the first motor unit lm is at TDC, then the crank associated with the piston of the second motor unit 2m is rotated by 120° with respect to that of the first motor unit lm, and in the second motor unit 2m the exhaust port 12 is open. The crank associated with the piston of the third motor unit 3m is instead rotated by 240° with respect to that of the first motor unit lm and the piston of the third motor unit 3m is thus ready to start the compression phase. Obviously, it is assumed that fresh charge was introduced into the crankcase of the first motor unit 1 m through the inlet valve 1 1 during a previous movement of the piston of the first motor unit from BDC to TDC.

In other words, in figure 2 A the internal combustion engine 1 is in a condition in which the piston of the motor unit lm is at TDC, the piston of the second motor unit 2m has concluded the expansion phase, while the piston of the third motor unit 3m is ready to start the compression phase.

At this stage, in a second phase shown in figure 2B, through the spark plug 5, or by compression-ignition, the detonation occurs in the combustion chamber of the first motor unit lm. Accordingly, the piston of the first motor unit lm carries out the expansion phase, causing the rotation of the crank associated therewith, whose cam profile is in engagement with the load valve arranged between the crankcase of that first motor unit lm is the combustion chamber of the second motor unit 2m. The rotation of the cam profile causes the opening of the load valve, which allows thereby the previously stored fresh charge to be introduced into the crankcase of the first motor unit 1 m in the combustion chamber of the motor unit 2m.

Furthermore, in this second phase, the piston of the second motor unit 2m is positioned so that the exhaust port 12 is still open at the end of the rotation of 120° of the crank. In fact, in this second phase, the piston of the second motor unit 2m has concluded the expansion phase and, after passing through BDC, it begins the compression phase, and thus the global stroke of that piston in this phase is null (i.e. it has carried out two opposite-sign movements going back to the initial position represented in figure 2A). Accordingly, in this second phase, it is possible to consider the piston of the second motor unit 2m as still with the exhaust port open (in the present description this phase of the piston is called“discharge/ stalemate phase”). The configuration of the internal combustion engine 1 in this phase allows, in the second motor unit 2m, a one-way gas flow from the combustion chamber to the exhaust port and it thus allows an optimum scavenging of combusted gases. This is due to the concurrent opening of the load valve on the cylinder head and of the exhaust port in the lower part of the cylinder (i.e. the part which is closest to the crankcase).

Still in this second phase, the piston of the third motor unit 3m carries out the compression phase and thus the rotation of the crank associated therewith causes the opening of the inlet valve for the introduction of fresh charge in the crankcase of that third motor unit 3m due to the vacuum created during the rise of the piston from BDC to TDC.

In other words, in figure 2B the internal combustion engine 1 is in a condition in which the piston of the first motor unit lm has concluded the expansion phase and it begins the discharge/ stalemate phase, the piston of the second motor unit 2m has concluded the discharge/ stalemate phase and it is ready to begin the compression phase, while the piston of the third motor unit 3m is at TDC and it is in the detonation phase. In a third phase represented in figure 2C, i.e. after a further rotation of 120°, the piston of the first motor unit lm is in the stalemate phase with the exhaust port open, while the piston of the second motor unit 2m carries out the compression phase and simultaneously the inlet valve opens in the crankcase of that second motor unit 2 m for the introduction of fresh charge therein. The piston of the third motor unit 3m is instead in the expansion phase and causes the opening of the load valve which connects the crankcase of that third motor unit 3m to the combustion chamber of the first motor unit lm. In other words, in figure 2C the internal combustion engine 1 is in a condition in which the piston of the first motor unit lm has concluded the discharge/ stalemate phase and it is ready to start the compression phase, the piston of the second motor unit 2m is at TDC and it is in the detonation phase, while the piston of the third motor unit 3m has concluded the expansion phase and it starts the discharge/ stalemate phase.

Finally, in a fourth phase (not represented in the figures), wherein as always a next movement of the pistons which causes a next rotation of 120° of the crank associated therewith is being considered, the piston of the first motor unit lm starts the compression phase, the piston of the second motor unit 2m starts the expansion phase, while the piston of the third motor unit 3m is in the stalemate phase. At the end of this phase, each crankshaft has performed a full rotation and it goes back to the initial point illustrated in figure 2A.

Accordingly, whenever a piston moves from TDC to BDC, by virtue of the movement of the crank (whose cam profile is in engagement with the corresponding load valve) fresh charge coming from the crankcase of a motor unit is introduced into the detonation chamber of a next motor unit. Vice versa, in the opposite movement from BDC to TDC, the inlet valve is controlled which allows the fresh charge coming from a supply system to be introduced into the crankcase.

In this embodiment, for each full revolution of the crankshafts, there are three detonations.

Since the crankshafts of the three motor units are offset to each other by 120°, while the piston of the first motor unit lm is at TDC (that is the starting point represented in figure 2A), the piston of the second motor unit 2m has travelled 3/4 of its stroke. In the next 120° of rotation of the crank, the stroke transmitted to the piston of the second motor unit 2m is equal to 1 /4 of the stroke in the first 60°, where it substantially reaches BDC, and it is still equal to 1 /4 of the stroke in the next 60°. In this rotation phase, where moving air volumes slow down the flow thereof to reverse then the direction thereof, inertias of gases have time to stabilize.

Furthermore, since in the stalemate phase of a piston the fresh charge which contributes to push combusted gases towards the exhaust port is injected in the relevant combustion chamber, that exhaust port has, with respect to BDC, a distance that is at least slightly greater than 1 /4 of the piston stroke, that distance being estimated along a longitudinal axis H-H of the cylinder 2.

Referring now to figures 3A and 3B, advantageously according to the present invention, each piston 3 comprises a first portion PI having a first diameter D 1 and a second portion P2 having a second diameter D2 that is greater than the first diameter D l . It must be observed that, herein, the term “diameter” always means a maximum transverse dimension.

In particular, the first portion PI is the portion of the piston 3 facing the head of the cylinder 2 (also defined as “piston crown”) while the second portion P2 is the portion of the piston 3 facing the crankcase 6, so as to increase the pumping effect during the movement of pistons. In fact, since each piston 3 has a diameter that is greater in the portion thereof facing the crankcase 6, the treated air volume for the same stroke is greater. This involves a natural boosting which improves the scavenging and allows a steady air increase at any rotation speed.

In other words, each piston 3 comprises a body 3b which extends along a longitudinal axis H-H and which includes in turn the two portions PI and P2 with the two different diameters D l and D2, the first portion PI extending along that longitudinal axis H-H more than the second portion P2.

Preferably, the free end of the first portion PI houses at least one pair of piston rings 13a and 13b, as it is customary for two-stroke engines, while the second portion P2 houses at least one piston ring 13c.

The cylinder 2 of each motor unit is shaped so as to comprise a first cylinder portion having a diameter substantially corresponding to the diameter D 1 of the first portion PI of the piston 3, and a second cylinder portion having a diameter substantially corresponding to the diameter D2 of the second portion P2 of the piston 3. In the second cylinder portion, a variable-volume chamber V is thereby defined, whose volume varies during the stroke of the piston 3.

The double-diameter configuration of the pistons 3 determines the treated air volume for the same stroke to be greater at the second portion P2, thus obtaining a natural and steady boosting which is useful to improve the scavenging phase. By increasing the comburent it is thus possible to increase the fuel as well and to have a more effective combustion.

In order to lighten the piston 3, the body 3b can be formed by two inverted poppets having different diameters, although the present invention is not limited thereto.

The variable volume chamber V can be also used to lubricate the piston 3, which is typically difficult in two-stroke engines. In particular, when the piston 3 moves from TDC to BDC, the volume of the variable volume chamber V increases creating a vacuum, and thus, if a communication is provided with the outside of the cylinder 2, an intake occurs in this chamber.

In particular, according to an embodiment of the present invention, the internal combustion engine 1 comprises nebulizing means (not illustrated in the figures) apt to introduce a nebulized lubricating fluid at a surface of the piston 3. By way of non-limiting example, nebulizing means can comprise a valve of the Venturi type, which intakes a small amount of oil together with air so as to create a nebulization of air and oil which is conveyed directly against the walls of the piston 3 at the variable volume chamber V.

In addition, in this embodiment, a check valve is provided (not shown in the figures as well) configured to allow the inlet of the nebulized lubricating fluid inside the cylinder 2 and thus to stop the movement of the lubricant fluid in the opposite direction. In fact, when the piston reverses its own motion and it moves from BDC to TDC, the pressures reverse and the lubricating fluid would be pushed in the hole which it entered the cylinder 2 through.

Advantageously according to the present invention, as schematically illustrated in figures 3A and 3B, the piston 3 comprises a fluid path in communication with a fluid path in the connecting rod / crank and in the crankshaft for the recirculation of the nebulized lubricating fluid. Those fluid paths can be channels inside the piston 3, or they can be obtained by splitting that piston 3 in an internal portion and in an external portion, forming a passage between those portions.

The presence of the fluid paths inside the piston and/or of splines (for example in the piston pin) allows the nebulized lubricating fluid to reach the most critical areas, for example at the piston rings 13a and 13b or at the piston pin, and it ensures that it can come out of the crankshaft through those splines and holes after licking all sliding parts. A filter apt to condense the nebulized lubricating fluid is arranged downstream of the lubrication circuit, allowing oil to be recovered for a new cycle and air to be released, which is introduced into an air box so as not to pollute the environment with oil residues. In this embodiment, the presence of a further check valve is also provided, which is arranged specularly to the other above-described check valve, in order to allow the pumping work.

In this embodiment, when the piston moves from BDC to TDC, the variable volume chamber V would be in communication with the open exhaust port 12 and this would prevent the nebulized lubricating fluid from being pumped. For this reason, at the exhaust port 12, a valve which allows the passage of combusted gases only during the discharge/ stalemate phase is provided, that valve then closing the exhaust port 12 in the other phases to compel the nebulized lubricating fluid to travel in the fluid path inside the piston, piston pin, connecting rod, crank, to the outlet in the crankshaft. This valve as well can be controlled by an eccentric on the crank or in any other suitable way.

In addition, the configuration of the engine of the present invention gives the possibility to rotate in a counter-rotating way at least one crankshaft of a motor unit with respect to the crankshafts of the other motor units, thereby reducing the overall gyroscopic effect.

Finally, it must be observed that the architecture described in the present invention can be indifferently adopted both for a spark-ignition engine and for a compression-ignition engine (i.e. a diesel engine), making that engine particularly versatile.

In conclusion, the present invention provides an engine with integral pistons in a two-stroke cycle which comprises a plurality of motor units, each comprising its own combustion chamber, wherein the supply of the combustion chamber of a motor unit occurs as a function of the movement of a piston of another motor unit. In particular, the combustion chamber of a motor unit is in fluid communication with the crankcase of the other motor unit and the supply of that combustion chamber is regulated by the opening/closing of a suitable valve.

Advantageously according to the present invention, the innovative arrangement of the components of the engine determines the cycle of a first motor unit to occur by virtue of the pumping effect of the piston of a second adjacent unit, whose crankcase serves as a storage unit for that first motor unit, containing the fresh charge which will be then introduced into the combustion chamber of the next unit.

The passage of fresh charge inside the combustion engine of the present invention is suitably regulated by the opening/ closing of the load valves and inlet valves, which are synchronized and timed to each other so that, in a motor unit, fresh charge is introduced into the crankcase during the compression phase of the piston, while during the expansion phase that fresh charge is transferred in the combustion chamber of the adjacent motor unit.

Those valves are advantageously controlled by the crank (which has preferably a cam profile which the valves are in engagement with) and, as a further advantage, it is possible to have more space for phase or lift transformers.

The possibility to house a single valve in the head of the cylinders allows the size thereof to be increased and accordingly the load losses linked thereto to be reduced also as a result of an intake duct having a reduced length.

In the preferred embodiment wherein there are three motor units cooperating with each other, the present invention allows in addition to have three detonations for each full revolution of the crankshaft.

In each motor unit, the hottest part (i.e. the cylinder head) is always put in communication with the coldest part of the adjacent motor unit (i.e. the crankcase) obtaining a cooling also by conduction, also by virtue of the fact that the crankcase has a size that is greater than the cylinder head and it can be highly finned. This can make a liquid cooling unnecessary, thus removing all the components necessary to that aim. In addition it must be observed that the fresh charge contributes as well to the heat exchange from inside the engine and that it is no longer necessary to compress/heat the air before introducing it in the cylinders, as it occurs in normal boostings, but an amount thereof that is greater than the engine displacement is injected when the chamber has the maximum volume, thus making air cooling systems of the intercooler type unnecessary.

Furthermore, since the discharge of combusted gases is favoured by the introduction of fresh charge, the engine of the present invention is capable of working with low compression ratios, contributing to the cooling ease.

The engine of the present invention has a high number of active phases, which provide enough power already at a low number of revolutions, and in conjunction with the above, it is capable of working at a temperature and stress conditions that are lower with respect to engines according to the prior art.

The fact of having three detonations per revolution of the crankshaft involves a considerable torque already at a low number of revolutions. Accordingly, this architecture allows to manage without the gearshift or to have a more limited one in view of the wide range of revolutions with a substantial torque.

The particular architecture adopted allows in addition to have a one way flow inside each motor unit, which also allows an improved scavenging phase, which is also given by the adoption of a suitably shaped piston with two portions having a different diameter. This piston shape allows in addition to have an air volume that is greater in the crankcase than the piston displacement, involving a greater amount of air for the boosting, as illustrated above.

Suitably, each motor unit is equipped with its own combustion chamber, contrary to the engines with opposed pistons of the prior art which provide the presence of a single common combustion chamber.

The presence of nebulizing means and fluid passages in the piston and crankshaft allows on the one hand the problem of engine lubrication to be solved, on the other hand it also involves the piston cooling. By virtue of this lubrication system, there is little oil circulating, but forced to circulate only where necessary, that engine being in fact able to work in temperature and stress conditions that are lower with respect to known engines. This expedient leads to the removal of the lubrication pump in favour of cost-effectiveness, lightness, simplification and strength.

The innovative configuration of the engine of the present invention makes it appropriate both for the Otto cycle and for the diesel cycle as well as for the Atkinson and Miller cycle, the presence and arrangement of the load and supply valves making it a particularly versatile engine. In the case of the Otto cycle it is possible to regulate the supply through a throttle valve on the load duct or through the regulation of the lift and of the duration of the opening of the inlet valve by means of phase or lift transformers on the crank cam.

The internal combustion engine of the present invention has a low number of repeated components, making it suitable for a mass production.

In addition, the possibility to have three shafts which turn in a synchronous way offers the possibility to use one of them for electrical services, one of them for auxiliary services, leaving one of them free for mechanical transmission.

Being detonation phases very close, the need for a flywheel is only limited to the regulation of peaks. The air box which normally takes on a considerable importance in aspirated engines, is no longer an essential component in the engine of the present invention, since air is pumped.

In addition, the engine of the present invention can be conveniently applied in the manufacture of drones, in fact it is enough to key three propellers on the three crankshafts and to arrange a lift control system for driving.

Furthermore, the possibility to have a small and powerful engine can result in the manufacture of a vehicle having an engine on each wheel rather than a single engine, with improvements in relation to the leaks and frictions for components such as joints and differentials which would no longer be necessary.

Finally, the engine of the present invention is capable of working also by intaking only air in crankcases rather than an air/ fuel mixture. In this case, it is convenient to replace bushings with rolling bearings. A direct or indirect injection in the fluid passage that houses the load valve is the preferred solution, although the adoption of a carburetor upstream of all crankcases would result in an almost steady flow given by the vacuum generated by three intakes per revolution. The reduced length of the fluid passages which house load valves solves the problems due to the different duct length which are typical of aspirated engines. For this reason too, the engine of the present invention can be both a spark-ignition engine and a compression-ignition engine.

It is thus evident that the illustrated engine solves the technical problem of the present invention, having a high efficiency and high performances and at the same time a simple base architecture.

Obviously, a person skilled in the art, in order to meet contingent and specific requirements, will be allowed to bring to the above-described engine several modifications and alternatives, all comprised in the scope of protection of the invention as defined by the following claims.

Claims

1. An internal combustion engine (1), comprising at least two motor units (lm, 2m, 3m), each of said motor units (lm, 2m, 3m) operating according to a two-stroke cycle and including:

a cylinder (2);

a piston (3) slidably housed in said cylinder (2), said cylinder (2) and said piston (3) defining a combustion chamber (4) inside said cylinder (2);

its own exclusive crankcase (6) connected to an end of said cylinder (2); and

its own exclusive crankshaft housed in said crankcase (6), said internal combustion engine (1) being characterized in that it comprises at least one fluid passage (9) between the crankcase of a first motor unit and the combustion chamber of a second motor unit, and in that it further comprises a load valve (10) arranged at said fluid passage (9), wherein said load valve (10) is apt to allow a supply from said crankcase of said first motor unit to said combustion chamber of said second motor unit due to an expansion movement of the piston of said first motor unit.

2. The internal combustion engine (1) according to claim 1 , characterized in that it comprises three motor units (lm, 2m, 3m), wherein the crankcase of a first motor unit (lm) is adjacent and in fluid communication with the combustion chamber of a second motor unit (2m), the crankcase of said second motor unit (2m) is adjacent and in fluid communication with the combustion chamber of a third motor unit (3m), and the crankcase of said third motor unit (3m) is adjacent and in fluid communication with the combustion chamber of said first motor unit (lm).

3. The internal combustion engine (1) according to claim 2, characterized in that each of said three motor units (lm, 2m, 3m) is arranged on a respective side of an equilateral triangle, the crankshafts of each of said motor units (lm, 2m, 3m) being located at the vertices of said equilateral triangle and having a relative phase substantially of 120°.

4. The internal combustion engine (1) according to any one of the preceding claims, characterized in that said crankshaft in said crankcase (6) is associated with a crank (8) having a cam profile (P), said load valve (10) being in engagement with said cam profile (P) and being configured to be driven and opened during at least one portion of the rotation of said cam profile (P).

5. The internal combustion engine (1) according to any one of the preceding claims, characterized in that it comprises an inlet valve (1 1) at said crankcase (6) for the inlet of fresh charge due to the compression movement of a piston.

6. The internal combustion engine (1) according to claim 5, characterized in that said crankshaft in said crankcase (6) is associated with a crank (8) having a cam profile (P), said inlet valve (1 1) being in engagement with said cam profile (P) and being configured to be driven and opened during at least one portion of the rotation of said cam profile

(P)·

7. The internal combustion engine (1) according to claim 5, characterized in that said inlet valve (1 1) is a reed valve.

8. The internal combustion engine (1) according to any one of the preceding claims, characterized in that said load valve (10) is a poppet valve.

9. The internal combustion engine ( 1) according to any one of the preceding claims, characterized in that each of said pistons (3) comprises a first portion (PI) having a first diameter (D l) and a second portion (P2) having a second diameter (D2) that is greater than said first diameter (D l), said first portion (PI) facing the head of the cylinder (2), and said second portion (P2) facing the crankcase (6), so as to increase a pumping effect during the movement of said pistons.

10. The internal combustion engine (1) according to claim 9, characterized in that said cylinder (2) is shaped so as to comprise a first cylinder portion having a diameter corresponding to the diameter (D l) of said first portion (PI) of said piston (3), and a second cylinder portion having a diameter corresponding to the diameter (D2) of said second portion (P2) of said piston (3), so as to define a variable volume chamber (V) in said second cylinder portion during the stroke of said piston (3).

1 1. The internal combustion engine ( 1 ) according to any one of the preceding claims, characterized in that it comprises nebulizing means apt to introduce a nebulized lubricating fluid at a surface of said piston (3), and a check valve configured to allow the inlet of said nebulized lubricating fluid inside the cylinder (2), said piston (3) comprising a fluid path in communication with a fluid path in the crankshaft for the recirculation of said nebulized lubricating fluid.

12. The internal combustion engine ( 1 ) according to any one of the preceding claims, characterized in that it comprises an exhaust port (12) provided on a wall of said cylinder (2) for the discharge of combusted gases, and a closing valve apt to hermetically close said exhaust port (12) during the compression movement of said piston (3).

13. The internal combustion engine (1) according to any one of the preceding claims, characterized in that at least one crankshaft of a motor unit is counter-rotating with respect to the crankshafts of the other motor units.

14. The internal combustion engine (1) according to any one of the preceding claims, characterized in that it is a spark-ignition engine or a compression-ignition engine.

15. The internal combustion engine (1) according to any one of the preceding claims, characterized in that said at least one fluid passage (9) is made at the head of said cylinder (2), the crankcase of a motor unit communicating with the head of another motor unit.