Two-stroke engine with opposite pistons with improved discharge

Abstract

A two-stroke engine (1) with opposite pistons (5, 6) comprises a body (2) in which there is arranged a plurality of cylinders (3) arranged adjacent to each other and with parallel longitudinal axes, in each cylinder there being present two pistons (5, 6) movable in an opposite manner towards an area (11) of the cylinder wherein the fuel is introduced, the cylinders having intake and discharge ports (12). At all discharge ports (12) of the cylinders there is arranged a rotary valve (17) adapted to allow a discharge of combustion gases of each cylinder towards an engine exhaust pipe.

Description

[0001] TWO-STROKE ENGINE WITH OPPOSITE PISTONS WITH IMPROVED DISCHARGE

[0002] The present invention relates to a two-stroke engine with opposite pistons , according to the preamble of the main claim .

[0003] The two-stroke engine with opposite pistons have long been known and have been used on various types of vehicles , whether land, sea or air vehicles . Such engines comprise a body in which there are present various cylinders (two, three or more ) having longitudinal axes that are parallel to each other; the cylinders are arranged adjacent to each other and contain, each, two movable pistons with directions opposite to each other . Each piston is associated with its own crack shaft and the crack shafts move in a coordinated fashion through suitable connections to gearwheels and / or belts . Such crack shafts are therefore connected, usually through gears , to a drive shaft or output shaft of the engine .

[0004] The pistons of each cylinder converge, in their movement , towards a combustion area or combustion chamber of the respective cylinder where there is introduced, usually by injection, a combustion fuel . Furthermore, each cylinder has intake ports and discharge ports arranged in different areas of the cylinder .

[0005] As known, in the current technique of two-stroke engines , the discharge ports carry out their function when a piston determines the opening thereof through the movement thereof .

[0006] The two-stroke engines of the type indicated above are without the cylinder head of the engine, and this allows to avoid the use of head gaskets , and of the valves with the relevant control members . Therefore, a two-stroke engine of the type indicated above is lighter than four-stroke engines with a single piston per cylinder with an equal power, as well as more compact than the latter . Furthermore, a two- stroke engine of the type indicated above is even more efficient than a similar engine with single piston per cylinder .

[0007] Usually, such two-stroke engine with opposite pistons is also oversupplied .

[0008] However, the aforementioned engines have a possible problem resulting from the pressure loss in the combustion chambers given that the discharge ports are often without valves and it is only the piston that opens or closes them with its movement .

[0009] The pressure loss also results in a reduction of the efficiency of the engine .

[0010] US7448352 regards an engine with opposite pistons with the aim of overcoming the problem of bringing the source of ignition of the fuel, present in the combustion chamber, into such chamber . Therefore, there is provided for the presence, in each cylinder, of a cylindrical rotary sleeve which also acts as an intake and discharge valve rotating in the cylinder . Such cylindrical sleeve brings , transversely thereto and therefore to the cylinder in which it is arranged, two electrodes , the first being adapted to receive a sliding electrical power supply (brush type ) from a "finger" connected to a conductor which protrudes from the engine block . Such finger slides on a segment of said first electrode outside the cylindrical sleeve . The first electrode terminates in the cylinder and faces the other electrode which is in contact with the sleeve . The first electrode is instead insulated by the sleeve .

[0011] US2008 / 115771 relates to an engine with opposite pistons . In each cylinder there is arranged a slidable sleeve axially adapted to close the intake and the discharge of the cylinder . US2010 / 170466 relates to an engine with opposite pistons where there is provided for, even in this prior art document , a sleeve in each cylinder . The sleeve may rotate around the axis of the cylinder and controls a valve member (valve with obturator) which opens and closes , moving, the intake and discharge openings of the relative cylinder .

[0012] US2012 / 055451 describes a four-stroke engine with opposite pistons with a single cylinder . There are provided for valve modules for opening and closing the intake and discharge openings in the cylinder .

[0013] US7650860 and US5878707 describe engines (not with opposite pistons ) with a rotary valve at the head of the engine .

[0014] An object of the present invention is to provide a two- stroke engine with opposite pistons which is improved with respect to the similar prior art engines .

[0015] In particular, an object of the present invention is to provide an engine of the type mentioned above wherein, by providing a simple but effective mechanism can avoid or however reduce as much as possible a pressure loss in the combustion chamber, a loss which occurs through the discharge ports of the cylinders .

[0016] Another object of the invention is to provide an engine of the type mentioned above which has an efficiency, power and improved performance with respect to similar existing engines .

[0017] A further object of the invention is to provide an engine which, considering the same engine displacement , has lower consumptions with respect to similar two-stroke engine with opposite pistons of the prior art .

[0018] Another object of the invention is to provide an engine of the type mentioned above which, at the discharge, has lower harmful emissions with respect to engines of the prior art with the same power .

[0019] These and other objects which shall be apparent to the person skilled in the art are attained by a two-stroke engine with opposite pistons according to the attached main claim .

[0020] For a better understanding of the present invention, the following drawings are attached hereto, purely by way of non-limiting example, wherein : figure 1 is a lateral perspective view of an engine according to the invention; figure 2 is a front view of the engine of figure 1 ; figure 3 is a perspective view from the right of the engine of figure 1 with some parts omitted for the sake of greater clarity with respect to such figure ; figure 4 is a top perspective view of the engine of figure 1 ; figure 5 is a bottom and left perspective view of the engine of figure 1 with some parts omitted for the sake of greater clarity; figure 6 is a bottom and right perspective view of the engine of figure 1 , with some parts omitted for the sake of greater clarity; and figure 7 is a slightly bottom perspective view of the part indicated with A in figure 1 and with some parts removed for the sake of greater clarity .

[0021] With reference to the figures mentioned above, a two- stroke engine with opposite pistons is generally indicated with 1 . It is preferably associated with a compressor which may be of the volumetric type (as shown in the drawings and indicated with V) , centrifuge type, rotary type or turbocompressed type . The engine 1 comprises a body 2 inside which there are arranged, in the embodiment of the figures provided by way or non-limiting example of the invention, three cylinders 3 . In figures 4 , 5 and 6 there is shown only one of such cylinders . Such cylinders are arranged adjacent to each other and they have parallel longitudinal axes .

[0022] In each cylinder 3 there is present a pair of pistons 5 and 6, movable in a manner opposite to each other . The pistons 5 are associated with and driven by a corresponding crack shaft 7 by means of connecting rods 9, while the pistons 6 are associated with and driven by another crack shaft 8 by means of connecting rods 10 .

[0023] Using usual injectors , not shown in the figures , fuel is introduced into an area 11 of each cylinder 3 (which we will define as combustion area or combustion chamber) . The fuel may be any fuel known as diesel fuel or also as Bio-Fuel, hydrogen fuel or other .

[0024] Furthermore, each cylinder 3 , has intake ports (not shown) for comburent air and discharge ports 12 for e jecting combustion gases from the engine 1 . Such intake and discharge ports are usually distant from each other and arranged on each cylinder .

[0025] The crack shafts 7 and 8 are associated with corresponding gears 13 and 14 arranged on one side of the body 2 of the engine 1 and they transfer the motion thereof , in a usual manner, to a gear or gearwheel 15 that is larger than the gears 13 and 14 keyed on an output shaft or engine 16 . In figure 5 the transfer mentioned above occurs due to the cooperation of the gears 13 and 14 with other gearwheels indicated with in its entirety with 13A and 14A, respectively .

[0026] According to the invention, on one side of the engine and at all the cylinders 3 , in particular at the discharge ports of the cylinders 3 and frontally with respect thereto there is arranged a single rotary valve 17 inserted into its own guard 18 fixed to the body 2 of the engine 1 . Therefore, the guard 18 has openings 19, 20 and 21 connected to exhaust manifolds or to a common gases exhaust pipe (not shown) which at the end trans fers the combustion gases to a silencer or exhaust pipe of a vehicle ( land, air or sea vehicle ) on which the engine 1 is fitted .

[0027] None of the prior art documents mentioned in the introductory part of the present document describes and suggests the use of a single rotary valve to transfer the burnt gases from all cylinders towards a common gas discharge .

[0028] The rotary valve 17 comprises a solid body 22 having a substantially cylindrical ("shaft-like" ) shape, but on whose surface, there are three cavities 23 , 24 and 25 each adapted to be positioned, in a step of the rotation around a longitudinal axis W thereof of the rotary valve 17 , facing a corresponding discharge port of the cylinders .

[0029] Therefore, the valve is arranged externally and on one side of all cylinders 3 , at all discharge ports 12 of the cylinders and the rotation axis W thereof lies on a plane perpendicular to the mutually parallel longitudinal axes of the cylinders 3 . Given that the rotary valve is provided with the cavities 23 , 24 and 25 adapted to be positioned facing the discharge ports 12 , these ports 12 are also arranged along a single plane or axis parallel to the axis W of the single rotary valve 17 which faces said ports . This is clearly visible at least in figures 4 and 5 .

[0030] The three cavities 23 , 24 and 25 are obtained in the body 22 of the rotary valve 17 in a manner angularly staggered with respect to each other in the surface of such body . In this manner they are arranged facing the corresponding discharge ports at angularly different times of the rotation of the rotary valve around the longitudinal axis W thereof , as will be described hereinafter .

[0031] At the cavities 23 , 24 and 25 there is also present a longitudinal wall (that is parallel to the axis W) of the body 22 or, respectively, a wall 23A, 24A and 25A . Each of such walls closes on one side the corresponding cavity . When one of the cavities 23 , 24 and 25 ( for example the cavity 23 in figure 7 ) is at a respective discharge port of one of the three cylinders 3 , the longitudinal walls ( 24A and 25A in the example ) present at the other cavities (that are angularly staggered with respect to each other on corresponding sections perpendicular to the longitudinal axis W) are arranged facing the discharge ports of the other two cylinders . As described hereinafter, this allows to maintain the appropriate pressure in the cylinders that are not in the discharge step .

[0032] The body 22 of the rotary valve 17 ( similar to a shaft that is excavated on the surface where the cavities mentioned above are found) has two opposite ends 17A and 17B : on the end 17A there is arranged a bearing 30 and the assembly is arranged in a seat 31 provided for in a side wall 33 of the guard 18 which has a wall with a substantially box-like shape . In other words , such guard 18 has the side wall 33 and detached therefrom are at least three walls 34 , 35 , 36 which define longitudinal walls on three sides of the body of guard . The fourth longitudinal wall of such body may be avoided given that it is in direct contact with the body 2 of the engine and it is arranged at the discharge ports of the cylinders 3 .

[0033] The wall 35 has openings 19, 20 and 21 mentioned above . Possibly, there may also be provided for a fourth "physical" wall of the guard 18 in contact with the body 2 of the engine and provided with openings similar to those of the wall 35 mentioned above and arranged facing the latter .

[0034] The guard 18 is also arranged on the side of the body 2 of the engine 1 , on the side of all cylinders 3 with an axis (coinciding with that W of the rotary valve 17 ) orthogonal to that of the cylinders 3 ( in a plan lateral view of the engine ) . The guard 18 is arranged facing the discharge ports 12 of the cylinders 3 .

[0035] Returning to the body 22 of the rotary valve 17 , such body has the end 17B carrying a bearing (or equivalent mechanical de-coupling member 40 similar to the one 30 mentioned above ) arranged in a hole 41 of a part 42 of the body 2 supporting the gears and gearwheels 13 , 13A, 14 , 14A, 15 mentioned above . In particular, such part has a side 42A inside the body 2 , faced by the rotary valve 17 and a side 42B, outside the body 2 , at which there are present the aforementioned gears rotating on support shafts rotatably carried by such side 42B of the part 42 .

[0036] The end 17B is therefore associated with a gear 45 arranged at the side 42B of the part 42 mentioned above . Such gear meshes directly with the gear or gearwheel 15 associated with the drive shaft 16 . Therefore, the rotation of the valve 17 is in phase with the rotation of the gear 15 and therefore with the phases of the two-stroke engine 1 carried out by the pairs of opposite pistons 5 and 6.

[0037] This allows the rotary valve 17 to have its own cavities 23 , 24 and 25 still at the discharge ports of the cylinders 3 when the step for discharging burnt gases is carried out in each of them .

[0038] The timing of the rotary valve 17 may obviously also be obtained in another manner for example using a toothed belt or chain .

[0039] Therefore, when using the engine 1 , depending on the rotation speed of the drive shaft 16 there is also a corresponding rotation of the rotary valve 17 in phase with such shaft ( for example due to the cooperation between the gears 15 and 45 described above ) . Therefore, each cavity 23, 24 , 25 of such rotary valve (arranged on the side of all cylinders 3 ) is at the respective discharge port of the corresponding cylinder 3 in which the combustion gas discharge step is being carried out ; at the same time, the discharge ports of the other cylinders are closed by the longitudinal walls present at the other cavities .

[0040] For example, if the cavity 23 is arranged at the discharge port of the cylinder mentioned above, the exhaust gases can pass from the latter through such cavity and the opening 19 present in the wall 35 of the guard 18 in which there is arranged the rotary valve 17 . Such gases may therefore reach the discharge duct , which is arranged frontally to the openings 19, 20 and 21 of the guard 18 . This corresponds to what is shown in figure 7 .

[0041] Simultaneously, the longitudinal walls 24A and 25A of the body 22 of the rotary valve 17 are positioned frontally to the discharge ports of the other two cylinders of the engine avoiding a pressure loss in the latter .

[0042] As mentioned, this allows to avoid a pressure loss in the cylinders where the other phases of the two-stroke engine are carried out .

[0043] The engine conformed as described that is provided with the rotary valve 17 arranged on the same side of all cylinders 3 frontally with respect to their discharge ports 12 , is easy to provide and allows to improve the volumetric efficiency in absolute terms . The rotary valve 17 effectively and precisely allows to change the duration of the opening of the discharge ports , and this is not currently possible in the prior art solutions , wherein the two-stroke engine is the piston which adjusts the opening and the closing of the discharge ports , performing its own ascending or descending motion . Bearing in mind that the discharge ports are obtained in the cylinder in a position preset by the manufacturer, in the prior art solutions without specific valves , there is no way to close the discharge ports if not through the motion of the piston, which during the cycle leaves the corresponding discharge port which is open until the passage of the piston; therefore, given the generation of pressure loss and therefore volumetric efficiency loss in the cylinder, this results in absolute loss in efficiency, performance and an increase in consumptions .

[0044] The application of the engine 1 is particularly effective and makes the use of these engines in multiple applications interesting : aeronautical, transport , civil, military, nautical, motorsports ; for example using an engine with opposite pistons of the type described above, with respect to a conventional four-stroke engine, this allows to increase the thermal efficiency ratio from 36% ( 4-stroke engine ) to an efficiency exceeding 55% on opposite pistons with the rotary valve 17 .

[0045] Therefore, this proves a lower consumption and an increase in the performance with relative decreased in emission and consumptions .

[0046] The rotary valve is preferably made of a steel alloy .

[0047] Herein described is a preferred embodiment of the invention applied to an engine with three cylinders and six pistons . Obviously, the solution of the rotary valve 17 may also be applied to two-stroke engines with a different number of cylinders in which the opposite pistons move . All this while maintaining the characteristics of the invention which are indicated in the claims below .

Claims

CLAIMS1. Two-stroke engine with opposite pistons comprising a body (2) in which there is arranged a plurality of cylinders (3) arranged adjacent to each other and with parallel longitudinal axes, in each cylinder there being present two pistons (5, 6) movable in an opposite manner along the longitudinal axis of the corresponding cylinder (3) , the cylinders having ports (12) for the discharge of combustion gases which are delivered to at least one engine exhaust pipe, characterised in that all discharge ports (12) of the cylinders (3) arranged adjacent and parallel to each other are arranged on the same axis or plane, and in that at said discharge ports (12) there is present a single rotary valve (17) having a body (22) arranged frontally with respect to all discharge ports and rotary round a longitudinal axis (W) adjacent on a plane perpendicular to the longitudinal axes of the cylinders (3) arranged adjacent and parallel to each other, said rotary valve (17) being arranged externally on one side of all cylinders (3) and being adapted to alternately place in communication the single discharge ports (12) of the cylinders (3) with said at least one exhaust pipe, the successful communication of an discharge port (12) of a cylinder with said exhaust pipe resulting in the simultaneous closure of the discharge ports of the other cylinders .

2. Two-stroke engine according to claim 1, characterised in that the body (22) of the single rotary valve (17) has the shape of a cylindrical shaft and it has cavities (23, 24, 25) obtained in its surface adapted to be positioned at the discharge ports (12) of the relative cylinders frontally to the discharge ports there being arranged the rotary valve (17) , such cavities being obtained in said surface angularly rotated with respect to each other so hat said cavities (23,24, 25) are arranged facing towards the discharge ports (12) of the corresponding cylinders (3) at different times of the rotation of said rotary valve (17) around a longitudinal axis (W) thereof.

3. Engine according to claim 1, characterised in that said rotary valve rotates in phase with the rotation of the drive shaft .

4. Engine according to claim 3, characterised in that said rotary valve is functionally connected to the drive shaft .

5. Motor according to claim 4, characterised in that said rotary valve is associated with a gearwheel (45) which cooperates with a gearwheel (15) keyed on the drive shaft (16) .

6. Two-stroke engine according to claim 4, characterised in that said drive shaft (16) is connected through a belt or chain to said rotary valve (17) .

7. Two-stroke engine according to claim 1, characterised in that said rotary valve (17) is inserted into a guard (18) fixed to the body (2) of the engine laterally to the cylinders (3) and frontally to the discharge ports (12) of such cylinders .

8. Two-stroke engine according to claim 7, characterised in that said rotary valve (17) has a first end (17A) carrying a mechanical de-coupling member (30) and arranged in a seat (31) provided for in the guard (18) , said rotary valve (17) having a second end (17B) supported by the body (2) of the engine .

9. Two-stroke engine according to claims 5 and 8, characterised in that said second end (17B) of the rotary valve carries the gearwheel (45) cooperating with the gearwheel (15) keyed to the drive shaft (16) , between said body (2) of the engine and said second end (17B) there beingpresent a mechanical de-coupling member (40) .

10. Two-stroke engine according to claim 7, characterised in that said guard (18) is box-shaped and it has openings (19, 20, 21) adapted to allow the through-flow of the combustion gases exiting from the rotary valve (17) towards at least one exhaust manifold for the burnt gases of the engine, said openings (19, 20, 21) being adapted to allow the through-flow of the combustion gases exiting from the cylinders (3) through each of the cavities (23, 24, 25) of the rotary valve (17) when each cavity is in the position adapted to open the corresponding discharge port (12) of the corresponding cylinder.

11. Two-stroke engine according to claim 2, characterised in that to each cavity (23, 24, 25) of the body (22) of the rotary valve there corresponds a part (23A, 24A, 25A) adapted to close the discharge port (12) of the corresponding cylinder (3) when the combustion gases are not to be ejected from the latter.

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