Direct injection internal combustion reciprocating engine and thermodynamic cycle according to which said engine can operate

Abstract

The invention relates to a reciprocating internal combustion engine with direct injection operating according to a modified Otto or Diesel cycle in order to re- duce the operating temperature, when maximum power is not required, with a consequent reduction in heat loss. The engine subject of the invention absorbs minimal power in the suction phase and makes it possible, when maximum power is not required, to increase the compression ratio and consequently the efficiency. The engine subject of the invention provides, for each cylinder, the use of two check valves in the suction pipe and a motorized inlet valve whose opening cycle varies according to the required power. According to a variant of the engine subject of the invention, the latter allows the replacement of the re- sidual burnt gases present in the combustion chamber of each cylinder with air and recirculated gases, pre-loading one of the two check valves mentioned above. The engine subject of the invention therefore allows the replacement of the residual burnt gases with air in order to further reduce the operating tem- peratures of the engine at the same required power, or to increase its filling, and therefore the power, at the same operating cycle.

Description

[0001] Direct injection internal combustion reciprocating engine and thermodynamic cycle according to which said engine can operate

[0002] Field of application of the invention

[0003] The present invention finds application in the sector of reciprocating internal combustion engines with direct injection. More precisely, the present invention refers to an engine of the aforementioned type operating according to a modified “Otto” or equivalently “Diesel” thermodynamic cycle.

[0004] Review of known art

[0005] Reciprocating internal combustion engines with direct injection operating according to an “Otto” or “Diesel” thermodynamic cycle are known. They comprise one or more pistons housed in respective cylinders and connected, by respective connecting rods, to a camshaft (also called “crankshaft”). Each piston performs, inside its own cylinder, a rectilinear reciprocating motion which is converted into a rotary motion of the camshaft by means of a rotary thrust crank mechanism (also known as “connecting rod-crank mechanism”). The rectilinear reciprocating motion of each piston is obtained by implementing a thermodynamic cycle comprising four phases:

[0006] • a first phase, the suction phase, during which the volume of the combustion chamber increases and atmospheric air is sucked into the combustion chamber;

[0007] • a second phase, the compression phase, during which the volume of the combustion chamber decreases, thus compressing the atmospheric air contained therein, and during which the fuel, if petrol, is introduced;

[0008] • a third phase, the ignition or injection, combustion and expansion phase, in which the following take place:

[0009] the injection and immediate ignition of the fuel, if diesel,

[0010] or

[0011] the ignition of the fuel, if petrol,

[0012] and

[0013] the consequent increase in the volume of the combustion chamber caused by the expansion of the gases present therein which in turn is caused by the pressure increase due to the combustion;• a fourth and final phase, the exhaust phase, during which the volume of the combustion chamber decreases and the exhaust gases generated there by the combustion process are expelled into the atmosphere.

[0014] Purposes of the invention

[0015] The purpose of the present invention is to provide a reciprocating internal combustion engine with internal injection which constitutes an alternative to known engines of the same type.

[0016] Another purpose of the present invention is to indicate a thermodynamic cycle according to which the aforementioned engine can operate.

[0017] Summary of the invention

[0018] The subject of the present invention is a reciprocating internal combustion engine comprising:

[0019] • a crankcase;

[0020] • one or more cylinders firmly connected to said crankcase;

[0021] • for each of said cylinders, a piston housed in said cylinder so as to be constrained by the latter to perform a translational motion with respect to said cylinder and internally thereof;

[0022] • a camshaft connected to said crankcase so that it can rotate, relative to the latter, around its own axis;

[0023] • for each of said pistons, a connecting rod extending longitudinally from a connecting rod small end to a connecting rod big end,

[0024] said connecting rod being hinged:

[0025] - at its small end, to said piston

[0026] and

[0027] - at its big end, to said camshaft

[0028] so that a rotation of said camshaft with respect to said crankcase about its axis causes a reciprocating rectilinear translational motion of said piston within and with respect to said cylinder in which said piston is housed;

[0029] • a cylinder head firmly connected to said crankcase so as to occlude each of said cylinders at an upper base thereof so that, for each of said cylinders, said engine comprises a combustion chamber delimited by said cylinder, by a portion of said cylinder head occluding said cylinder and by the crown of saidpiston housed in said cylinder,

[0030] each of said pistons being movable within and relative to said cylinder in which said piston is housed between at least:

[0031] - a bottom dead centre at which the distance between said piston and said portion of said cylinder head occluding said cylinder in which said piston is housed is maximum, and therefore at which the volume of said combustion chamber of said cylinder (i.e. , of said combustion chamber which said engine comprises for said cylinder) in which said piston is housed is maximum

[0032] and

[0033] - a top dead centre at which the distance between said piston and said portion of said cylinder head occluding said cylinder in which said piston is housed is minimum, and therefore at which the volume of said combustion chamber of said cylinder in which said piston is housed is minimum;

[0034] • a first pipe, an inlet pipe, for taking air from the atmosphere;

[0035] • for each of said cylinders, a second pipe for the admission of atmospheric air into said combustion chamber of said cylinder,

[0036] said second pipe comprising:

[0037] - an inlet at which said second pipe is connected to said first pipe;

[0038] - an outlet opposite said inlet and positioned at said portion of said cylinder head occluding said cylinder,

[0039] said second pipe being connected to said combustion chamber of said cylinder at said outlet,

[0040] so as to put said first pipe in communication with said combustion chamber of said cylinder;

[0041] • for each of said cylinders, a third pipe for the expulsion from said combustion chamber of said cylinder of any exhaust gases present in said combustion chamber of said cylinder,

[0042] said third pipe comprising:

[0043] - an inlet placed at said portion of said head occluding said cylinder, said third pipe being connected to said combustion chamber of said cylinder at said inlet;- an outlet opposite said inlet of said third pipe;

[0044] • a fourth pipe, an exhaust pipe, for the expulsion of exhaust gases into the atmosphere,

[0045] each of said third pipes is connected, at its own outlet, to said fourth pipe: - so as to put said combustion chamber, to which said third pipe is connected at its inlet, in communication with said fourth pipe

[0046] and

[0047] - for the expulsion into the atmosphere of any exhaust gases present in said combustion chamber to which said third pipe is connected at its inlet;

[0048] • for each of said second pipes, a first valve, the inlet valve, at said outlet of said second pipe,

[0049] said first valve can assume at least:

[0050] - a first, opening configuration, at which said first valve allows atmospheric air to flow through:

[0051] said second pipe

[0052] into

[0053] said combustion chamber to which said second pipe is connected at its outlet;

[0054] - a second, closing configuration, at which said first valve prevents atmospheric air from flowing through:

[0055] said second pipe

[0056] into

[0057] said combustion chamber to which said second pipe is connected at its outlet;

[0058] • for each of said third pipes, a second valve, the exhaust valve, at said inlet of said third pipe,

[0059] said second valve can assume at least:

[0060] - a first, opening configuration, at which said second valve allows any exhaust gases present in said combustion chamber to which said third pipe is connected at its inlet, to flow from:

[0061] said combustion chamber to which said third pipe is connected at its inletinto

[0062] said third pipe;

[0063] - a second, closing configuration, at which said second valve prevents any exhaust gases present in said combustion chamber to which said third pipe is connected at its inlet from flowing from:

[0064] said combustion chamber to which said third pipe is connected at its inlet

[0065] into

[0066] said third pipe;

[0067] • for each of the said cylinders:

[0068] - an injector for introducing into said combustion chamber of said cylinder, a fuel to be subjected to combustion in said combustion chamber of said cylinder, together with atmospheric air. The engine which is the subject of the invention is therefore a direct injection engine,

[0069] and, if said fuel is petrol,

[0070] - a spark plug for triggering the combustion of said fuel in said combustion chamber of said cylinder, together with atmospheric air;

[0071] • a fifth pipe, for exhaust gas recirculation, comprising an inlet and an outlet opposite said inlet of said fifth pipe,

[0072] said fifth pipe being connected:

[0073] - at its inlet, to said fourth pipe downstream of said outlets respectively of said third pipes with reference to the direction of flow of said exhaust gases from said combustion chambers towards the atmosphere

[0074] and

[0075] - at its outlet, to said first pipe upstream of said inlets respectively of said second pipes with reference to the direction of flow of the air from the atmosphere towards said combustion chambers,

[0076] so as to put said fourth pipe in communication with said first pipe;

[0077] • a third valve (also known as “EGR valve”) installed along said fifth pipe to regulate the flow rate of exhaust gases from said fourth pipe through said fifth pipe to said first pipe;

[0078] • cooling means installed along said fifth pipe for cooling exhaust gases takenfrom said fourth pipe and through said fifth pipe, admitted into said first pipe, wherein, according to the invention, said engine further comprises, for each of said cylinders:

[0079] • a fourth valve, a check valve, installed along said second pipe connected to said combustion chamber of said cylinder, and therefore downstream of said outlet of said fifth pipe with reference to the direction of flow of air from the atmosphere towards said combustion chambers,

[0080] said fourth valve allowing air from the atmosphere and said exhaust gases from said fifth pipe to reach said combustion chamber of said cylinder by flowing along said first pipe and said second pipe connected to said combustion chamber of said cylinder,

[0081] said fourth valve preventing gases coming from said combustion chamber of said cylinder from reaching both said outlet of said fifth pipe and the atmosphere flowing through said first pipe;

[0082] • a sixth pipe comprising an inlet and an outlet opposite said inlet of said sixth Pipe,

[0083] said sixth pipe being connected:

[0084] - at its inlet, to said second pipe connected to said combustion chamber of said cylinder downstream of said fourth valve of said cylinder with reference to the direction of flow of air from the atmosphere towards said combustion chamber of said cylinder,

[0085] and

[0086] - at its outlet, directly to the atmosphere or to said fourth pipe preferably downstream of said inlet of said fifth pipe with reference to the direction of flow of said exhaust gases from said combustion chambers towards the atmosphere,

[0087] so as to put said second pipe, connected to said combustion chamber of said cylinder, in communication with said fourth pipe;

[0088] • a fifth valve, a check valve, installed along said sixth pipe of said cylinder, said fifth valve allowing gases from said combustion chamber of said cylinder to reach the atmosphere or said fourth pipe flowing through said sixth pipe, said fifth valve preventing atmospheric air or exhaust gases coming from saidfourth pipe from reaching said second pipe connected to said combustion chamber of said cylinder flowing through said sixth pipe.

[0089] Other innovative features of the present invention are illustrated in the following description and referred to in the dependent claims.

[0090] According to one aspect of the invention, each of said cylinders comprises: • a support firmly connected to said crankcase so that said cylinder is firmly connected to said crankcase at said support;

[0091] • a liner housed in said support so as to be constrained by the latter to perform a translational motion with respect to said support and internally thereof, said piston housed in said cylinder being housed in said cylinder at said liner so as to be constrained, by the latter, to perform a translational motion related to said liner and internally thereof,

[0092] said liner being constrained to translate within and relative to said support in which it is housed in the same direction in which said piston housed in said liner is constrained to translate within and relative to the latter,

[0093] said combustion chamber of said cylinder being delimited by said liner possibly together with said support, by said portion of said head occluding said cylinder and by the crown of said piston housed in said liner,

[0094] a translation of said liner within and with respect to said support away from said portion of said cylinder head occluding said cylinder causing an increase in the volume of said combustion chamber,

[0095] a translation of said liner within and with respect to said support towards said portion of said cylinder head occluding said cylinder causing a decrease in the volume of said combustion chamber;

[0096] • handling means suitable for moving said liner within and with respect to said support.

[0097] According to another aspect of the invention, said engine further comprises: • a catalytic converter (also known as a “catalyst”) installed along said fourth pipe downstream of said outlets of said third pipes respectively and upstream of said inlet of said fifth pipe with reference to the direction of flow of said exhaust gases from said combustion chambers towards the atmosphere, said catalytic converter being suitable for reducing the concentration of nitro-gen oxide, carbon monoxide and unburned fuel in said exhaust gases from said third pipes and flowing through said catalytic converter;

[0098] • a sensor (also known as a “lambda probe”) installed along said fourth pipe downstream of said outlets of said third pipes and upstream of said catalytic converter with reference to the direction of flow of said exhaust gases from said combustion chambers towards the atmosphere, and suitable for detecting the concentration of oxygen in said exhaust gases coming from said third pipes.

[0099] Another object of the patent is a thermodynamic cycle according to which the aforementioned engine, the object of the invention, can operate, referring to one of said pistons (since the motion of the other pistons of the engine is constrained to that of the camshaft) in the case in which there is more than one (i.e. , if the engine includes more cylinders) and starting from a configuration in which:

[0100] • said piston is at its top dead centre;

[0101] • said first valve located at said outlet of said second pipe connected to said combustion chamber of said cylinder in which said piston is housed, is in said second configuration (i.e., it is closed);

[0102] • said second valve located at said inlet of said third pipe connected to said combustion chamber of said cylinder in which said piston is housed, is in said second configuration (i.e., it is closed),

[0103] said cycle including the following phases:

[0104] a) a first phase, the suction phase, during which:

[0105] • said piston moves from its top dead centre to its bottom dead centre and

[0106] • said first valve, located at said outlet of said second pipe connected to said combustion chamber of said cylinder in which said piston is housed, is made to assume said first configuration (i.e., it is opened),

[0107] so that:

[0108] atmospheric air is drawn into said combustion chamber of said cylinder in which said piston is housed flowing through said first pipe and said second pipe connected to said combustion chamber of said cylinder in which saidpiston is housed

[0109] and possibly (depending on the EGR valve)

[0110] • exhaust gases are drawn, from said fourth pipe, into said combustion chamber of said cylinder in which said piston is housed, flowing through said fifth pipe, said first pipe and said second pipe connected to said combustion chamber of said cylinder in which said piston is housed,

[0111] said atmospheric air and possibly said exhaust gases being mixed with each other in said combustion chamber of said cylinder in which said piston is housed,

[0112] said fifth valve of said cylinder in which said piston is housed preventing atmospheric air or said exhaust gases from being drawn into said combustion chamber of said cylinder in which said piston is housed through said sixth pipe.

[0113] The first valve is therefore not returned to the second configuration (i.e. , it is not closed) at the end of the suction phase;

[0114] b) a second phase, of initial compression, during which:

[0115] • said piston moves from its bottom dead centre to its top dead centre without reaching it

[0116] and

[0117] • said first valve placed at said outlet of said second pipe connected to said combustion chamber of said cylinder in which said piston is housed, is made to assume said second configuration (i.e., it is closed),

[0118] so that, until said first valve has assumed said second configuration, said mixture formed, during said first phase, in said combustion chamber of said cylinder in which said piston is housed, is partly expelled from said combustion chamber of said cylinder in which said piston is housed, into the atmosphere or into said fourth pipe flowing through said second pipe connected to said combustion chamber of said cylinder in which said piston is housed and said sixth pipe,

[0119] said fourth valve of said cylinder in which said piston is housed preventing said mixture formed, during said first phase, in said combustion chamber of said cylinder in which said piston is housed, and partly expelled from saidcombustion chamber of said cylinder in which said piston is housed, from reaching both said outlet of said fifth pipe and the atmosphere flowing through said first pipe;

[0120] c) a third phase, of final compression, during which:

[0121] • said piston continues to move towards its top dead centre until it reaches it and, if said fuel is petrol,

[0122] • said injector of said cylinder in which said piston is housed injects said fuel into said combustion chamber of said cylinder in which said piston is housed,

[0123] so that said mixture formed, during said first phase, in said combustion chamber of said cylinder in which said piston is housed also mixes with said fuel introduced by said injector of said cylinder in which said piston is housed, in said combustion chamber of said cylinder in which said piston is housed; d) a fourth phase, of combustion and expansion, during which:

[0124] • if said fuel is petrol, said spark plug of said combustion chamber of said cylinder in which said piston is housed triggers the combustion of said fuel or

[0125] • if said fuel is diesel, said injector of said cylinder in which said piston is housed injects said fuel into said combustion chamber of said cylinder in which said piston is housed, so as to start the combustion of said fuel, so that, due to the combustion of said fuel, said piston moves from its top dead centre to its bottom dead centre;

[0126] e) a fifth phase, the exhaust phase, during which:

[0127] • said piston moves from its bottom dead centre to its top dead centre and

[0128] • said second valve placed at said inlet of said third pipe connected to said combustion chamber of said cylinder in which said piston is housed, is made to assume said first configuration (i.e., it is opened) and subsequently back to said second configuration (i.e., it is closed),

[0129] so that exhaust gases are expelled from said combustion chamber of said cylinder in which said piston is housed, into said fourth pipe flowing through said third pipe connected to said combustion chamber of said cylinder inwhich said piston is housed,

[0130] to then return to the said first phase.

[0131] According to another aspect of the invention, for each of said cylinders said fifth valve is preloaded, i.e., it allows gases coming from said combustion chamber of said cylinder to reach the atmosphere or said fourth pipe by flowing through said sixth pipe of said cylinder only when the pressure upstream of said fifth valve of said cylinder, with reference to the direction of flow of gases from said combustion chamber of said cylinder towards the atmosphere or towards said fourth pipe, is higher than a set value.

[0132] Another object of the patent is a thermodynamic cycle according to which the aforementioned engine, the object of the invention, can operate in the case in which the said fifth valve is preloaded,

[0133] referring to one of the said pistons (since the motion of the other pistons of the engine is constrained to that of the camshaft) in the case in which there is more than one (i.e., if the engine includes more cylinders) and starting from a configuration in which:

[0134] • said piston is at its top dead centre;

[0135] • said first valve located at said outlet of said second pipe connected to said combustion chamber of said cylinder in which said piston is housed, is in said first configuration (i.e., it is open);

[0136] • said second valve located at said inlet of said third pipe connected to said combustion chamber of said cylinder in which said piston is housed, is in said second configuration (i.e., it is closed),

[0137] said cycle including the following phases:

[0138] a) a first phase, the suction phase, during which the piston moves from its top dead centre to its bottom dead centre so that:

[0139] • atmospheric air is drawn into said combustion chamber of said cylinder in which said piston is housed by flowing through said first pipe and said second pipe connected to said combustion chamber of said cylinder in which said piston is housed

[0140] and possibly (depending on the EGR valve)

[0141] • exhaust gases are drawn, from said fourth pipe, into said combustionchamber of said cylinder in which said piston is housed, flowing through said fifth pipe, said first pipe and said second pipe connected to said combustion chamber of said cylinder in which said piston is housed,

[0142] said atmospheric air and possibly said exhaust gases being mixed with each other in said combustion chamber of said cylinder in which said piston is housed,

[0143] said fifth valve of said cylinder in which said piston is housed preventing atmospheric air or said exhaust gases from being drawn into said combustion chamber of said cylinder in which said piston is housed through said sixth pipe.

[0144] The first valve is already in the first configuration (i.e., it is open) at the beginning of the suction phase and remains in the first configuration (i.e., it remains open) for the entire suction phase, i.e., it is not brought into the second configuration (i.e., it is not closed) at the end of the suction phase;

[0145] b) a second phase, of initial compression, during which:

[0146] • said piston moves from its bottom dead centre to its top dead centre without reaching it

[0147] and

[0148] • said first valve placed at said outlet of said second pipe connected to said combustion chamber of said cylinder in which said piston is housed, is made to assume said second configuration (i.e., it is closed),

[0149] so that, until said first valve has assumed said second configuration, said mixture formed, during said first phase, in said combustion chamber of said cylinder in which said piston is housed, is partly expelled from said combustion chamber of said cylinder in which said piston is housed, and:

[0150] • as long as the pressure upstream of said fifth valve of said cylinder in which said piston is housed, with reference to the direction of gas flow towards the atmosphere or towards said fourth pipe, is not greater than said set value,

[0151] retained by said fifth valve of said cylinder in which said piston is housed upstream of said fifth valve of said cylinder in which said piston is housed, with reference to the direction of gas flow towards the atmosphere or to-wards said fourth pipe,

[0152] and

[0153] • to a possible exceeding, by the pressure upstream of said fifth valve of said cylinder in which said piston is housed, with reference to the direction of flow of gas towards the atmosphere or towards said fourth pipe, of said set value,

[0154] expelled into the atmosphere or into said fourth pipe through said second pipe connected to said combustion chamber of said cylinder in which said piston is housed and said sixth pipe of said cylinder in which said piston is housed,

[0155] said fourth valve of said cylinder in which said piston is housed preventing said mixture formed, during said first phase, in said combustion chamber of said cylinder in which said piston is housed, and partly expelled from said combustion chamber of said cylinder in which said piston is housed, from reaching both said outlet of said fifth pipe and the atmosphere by flowing through said first pipe, so that, at the end of said second phase, said mixture formed, during said first phase, in said combustion chamber of said cylinder in which said piston is housed, and partly expelled from said combustion chamber of said cylinder in which said piston is housed, is at least partly housed and compressed within the volume limited by said first valve located at said outlet of said second pipe connected to said combustion chamber of said cylinder in which said piston is housed, said fourth valve and said fifth valve of said cylinder in which said piston is housed, at a pressure equal to or lower than said set value;

[0156] c) a third phase, of final compression, during which:

[0157] • said piston continues to move towards its top dead centre until it reaches it and, if said fuel is petrol,

[0158] • said injector of said cylinder in which said piston is housed injects said fuel into said combustion chamber of said cylinder in which said piston is housed,

[0159] so that said mixture formed, during said first phase, in said combustion chamber of said cylinder in which said piston is housed also mixes with saidfuel introduced by said injector of said cylinder in which said piston is housed, in said combustion chamber of said cylinder in which said piston is housed; d) a fourth phase, of combustion and expansion, during which:

[0160] • if said fuel is petrol, said spark plug triggers the combustion of said fuel or

[0161] • if said fuel is diesel, said injector of said cylinder in which said piston is housed injects said fuel into said combustion chamber of said cylinder in which said piston is housed, so as to start the combustion of said fuel, so that, due to the combustion of said fuel, said piston moves from its top dead centre to its bottom dead centre;

[0162] e) a fifth phase, the exhaust phase, during which:

[0163] • said piston moves from its bottom dead centre to its top dead centre, • said second valve placed at said inlet of said third pipe connected to said combustion chamber of said cylinder in which said piston is housed, is made to assume said first configuration (i.e., it is opened) and subsequently back to said second configuration (i.e., it is closed)

[0164] and

[0165] • said first valve located at said outlet of said second pipe connected to said combustion chamber of said cylinder in which said piston is housed, is made to assume said first configuration after said second valve is made to assume said first configuration (i.e., the first valve is opened after the second valve has been opened), and before said second valve is made to resume said second configuration (i.e., the first valve is opened before the second valve is closed)

[0166] so that:

[0167] • said mixture formed, during said first phase, in said combustion chamber of said cylinder in which said piston is housed, and partly housed within the volume limited by said first, fourth and fifth valves at a pressure equal to or lower than said set value flows, by pressure difference, into said combustion chamber of said cylinder in which said piston is housed through said second pipe connected to said combustion chamber of said cylinder in which said piston is housedand

[0168] • exhaust gases together with part of said mixture flowing into said combustion chamber of said cylinder in which said piston is housed flowing through said second pipe connected to said combustion chamber of said cylinder in which said piston is housed, are expelled from said combustion chamber of said cylinder in which said piston is housed, into said fourth pipe flowing through said third pipe connected to said combustion chamber of said cylinder in which said piston is housed,

[0169] to then return to the said first phase.

[0170] The first valve is therefore brought into the first configuration (i.e. , it is opened) before the exhaust phase ends, and maintained in the first configuration (i.e., it is kept open) for the return to the suction phase.

[0171] Brief description of the figures

[0172] Further purposes and advantages of the present invention will become clear from the following detailed description of examples of its embodiment and from the attached drawings, given purely for explanatory and non-limiting purposes, in which:

[0173] - Figure 1 shows, in straight section and schematically, a portion of a reciprocating internal combustion engine according to the present invention;

[0174] - Figure 2 shows, in straight and schematic section, the portion of the engine of figure 1 at the end of a suction phase that takes place starting from the configuration shown in figure 1 ;

[0175] - Figure 3 shows, in straight section and schematic, the portion of the engine of figure 1 during an initial compression phase that takes place starting from the configuration shown in figure 2;

[0176] - Figure 4 shows, in straight and schematic section, the portion of the engine of figure 1 at the end of the initial compression phase of figure 3;

[0177] - Figure 5 shows, in straight and schematic section, the portion of the engine of figure 1 at the end of a final compression phase that takes place starting from the configuration shown in figure 4;

[0178] - Figure 6 shows, in straight and schematic section, the portion of the engine of figure 1 at the end of a combustion and expansion phase that takes placestarting from the configuration shown in figure 5;

[0179] - Figure 7 shows, in straight and schematic section, the portion of the engine of figure 1 during an exhaust phase that takes place starting from the configuration shown in figure 6;

[0180] - Figure 8 shows, in straight and schematic section, a portion (corresponding to the portion in figure 1 ) of a first variant of the engine in figure 1 ;

[0181] - Figure 9 shows, in straight section and schematic, the engine portion of figure 8 during an initial compression phase corresponding to the initial compression phase of the engine portion of figure 1 shown in figure 3;

[0182] - Figure 10 shows, in straight and schematic section, the engine portion of figure 8 during an exhaust phase corresponding to the exhaust phase of the engine portion of figure 1 shown in figure 7;

[0183] - Figure 11 shows, in straight and schematic section, a portion (corresponding to the portion in figure 1 ) of a second variant of the engine in figure 1 in a first configuration of maximum volume of the combustion chamber;

[0184] - Figure 12 shows, in straight and schematic section, the portion of the engine of figure 11 in a second configuration of minimum volume of the combustion chamber.

[0185] Detailed description of some preferred embodiments of the invention

[0186] In the following description a figure may also be illustrated with reference to elements not expressly indicated in that figure but in other figures. The scale and proportions of the various elements depicted do not necessarily correspond to the real ones.

[0187] Figure 1 shows an engine 1 , the subject of the invention, with reciprocating internal combustion motion. The engine 1 comprises a crankcase in which one or more cylinders 2 are housed, each of which is firmly connected to the same. For simplicity, the figures show a portion of the engine 1 including a single cylinder 2. The engine 1, for each cylinder 2, comprises a piston 3 housed in said cylinder 2 so as to be constrained, by the latter, to translate with respect to the cylinder 2 internally thereof. The engine 1 also includes a camshaft, not visible in the figures, connected to the crankcase so as to be able to rotate, with respect to the latter, around its own axis. For each piston 3 (and consequently for eachcylinder 2) the engine 1 comprises a connecting rod 4 hinged to said piston 3 at its small end and to the camshaft at its big end so as to give rise to a rotary thrust crank mechanism, i.e., in such a way that a rotation of the camshaft with respect to the crankcase of the engine 1 and around its axis determines an alternative rectilinear translation of the piston 3 inside and with respect to the cylinder 2 in which the piston 3 is housed. The engine 1 also includes a cylinder head 5 firmly connected to the crankcase so as to occlude each of the cylinders 2 at the upper base thereof so that, for each cylinder 2, the engine 1 comprises a combustion chamber 6 (clearly visible in figure 2) delimited laterally by the cylinder 2, above by the portion of the cylinder head 5 occluding the cylinder 2 and below by the crown of the piston 3 housed in the cylinder 2. Each piston 3 is movable inside and with respect to the cylinder 2 in which the piston 3 is housed between at least one bottom dead centre at which the distance between the piston 3 and the portion of the cylinder head 5 occluding the cylinder 2 in which the piston 3 is housed is maximum (and therefore at which the volume of the combustion chamber 6 of the cylinder 2 in which the piston 3 is housed is maximum), and a top dead centre at which the distance between the piston 3 and the portion of the cylinder head 5 occluding the cylinder 2 in which the piston 3 is housed is minimum (and therefore at which the volume of the combustion chamber 6 of the cylinder 2 in which the piston 3 is housed is minimum). In figure 1 the piston 3, visible in said figure, is at the top dead centre.

[0188] The engine 1 comprises an inlet pipe 7 (previously identified as the “first pipe” and placed on the left in the figure) for drawing air from the atmosphere and, for each cylinder 2, a pipe 8 (previously identified as the “second pipe”) for introducing atmospheric air into the combustion chamber 6 of said cylinder 2. The pipe 8 of each cylinder 2 includes an inlet port 9 at which pipe 8 is connected to pipe 7, and an outlet port 10 opposite port 9 and placed at the portion of the cylinder head 5 occluding said cylinder 2. The pipe 8 of each cylinder 2, at its own port 10, is connected to the combustion chamber 6 of said cylinder 2. Pipe 8 of each cylinder 2 therefore puts pipe 7 in communication with the combustion chamber 6 of said cylinder 2. The engine 1, for each cylinder 2, also comprises a pipe 11 (previously identified as the “third pipe”) for the expulsion from thecombustion chamber 6 of said cylinder 2 of any exhaust gases present therein. Pipe 11 of each cylinder 2 includes an inlet port 12 located at the portion of the cylinder head 5 occluding said cylinder 2, and an outlet port 13 opposite port 12. Pipe 11 of each cylinder 2, at its own port 12, is connected to the combustion chamber 6 of said cylinder 2. The engine 1 also includes an exhaust pipe 14 (previously identified as the “fourth pipe” and located on the right in the figure) to which each pipe 11 is connected at its own port 13 so as to put the combustion chamber 6 to which pipe 11 is connected (at its own port 12) in communication with pipe 14, for the expulsion into the atmosphere of any exhaust gases present in the combustion chamber 6 to which pipe 11 is connected (at its own port 12).

[0189] The engine 1 , for each pipe 8 (and consequently for each cylinder 2), comprises a motorized inlet valve 15 (i.e., operable by using a preferably hydraulic or electric motor), previously identified as the “first valve” and positioned at port 10 of said pipe 8. The valve 15 of each pipe 8 can assume at least a first configuration, of opening, at which the valve 15 allows atmospheric air to flow through pipe 7 into the combustion chamber 6 to which pipe 8 is connected (at its own port 10), and a second configuration, of closing, at which the valve 15 prevents atmospheric air from flowing through pipe 7 into the combustion chamber 6 to which pipe 8 is connected (at its own port 10). In figure 1 the valve 15 visible in said figure is in the second configuration, i.e., it is closed.

[0190] The engine 1, for each pipe 11 (and consequently for each cylinder 2), comprises an exhaust valve 16 previously identified as the “second valve” and positioned at port 12 of said pipe 11. Valve 16 of each pipe 11 can assume at least a first configuration, of opening, at which valve 16 allows any exhaust gases present in the combustion chamber 6 to which said pipe 11 is connected (at its own port 12) to flow from said combustion chamber 6 (to which pipe 11 is connected at its own port 12) into pipe 14, and a second configuration, of closing, at which valve 16 prevents any exhaust gases present in said combustion chamber 6 (to which pipe 11 is connected at its own port 12) from flowing from said combustion chamber 6 (to which pipe 11 is connected at its own port 12) into pipe 14. In figure 1 the valve 16 visible in the said figure is in the second config-uration, that is, it is closed.

[0191] The engine 1 is a direct injection engine and, for each cylinder 2, comprises an injector 17 for introducing into the combustion chamber 6 of said cylinder 2 a fuel to be subjected to combustion (in said combustion chamber 6) together with atmospheric air. If the fuel is petrol, the engine 1 , for each cylinder 2, will comprise a spark plug 18 to trigger the combustion of the petrol in the combustion chamber 6 of said cylinder 2 together with atmospheric air.

[0192] Similar to known engines of the same type, the engine 1 also comprises an exhaust gas recirculation pipe 19 (previously identified as the “fifth pipe”) including an inlet port 20 and an outlet port 21 opposite port 20. As can be seen in figure 1, pipe 19 is connected to pipe 14 at port 20 and downstream of the ports 13 (“downstream” with reference to the direction of flow of the exhaust gases from the combustion chambers 6 towards the atmosphere), and it is connected to pipe 7 at port 21 and upstream of the ports 9 (“upstream” with reference to the direction of flow of the atmospheric air towards the combustion chambers 6). Pipe 19 therefore connects pipe 14 with pipe 7. The engine 1 also includes a valve 22 called “EGR” (previously identified as “third valve”) installed along pipe 19 to control the flow rate of exhaust gases taken from pipe 14 and through pipe 19 introduced into pipe 7. This engine 1 also includes a heat exchanger 23 (falling within the previously mentioned “cooling means”) also installed along pipe 19 in order to cool the exhaust gases taken from pipe 14 and through pipe 19 introduced into pipe 7.

[0193] The engine 1 differs from known engines of the same type in that it includes, for each cylinder 2, a check valve 24 (previously identified as a “fourth valve” and preferably of the reed type) installed along pipe 8 connected to the combustion chamber 6 of said cylinder 2, and therefore downstream of port 21 (“downstream” with reference to the direction of flow of air from the atmosphere towards the combustion chambers 6). Valve 24 allows air from the atmosphere and exhaust gases from pipe 19 to flow through pipe 8 in which it is installed towards combustion chamber 6 of cylinder 2 to which said pipe 8 is connected. Conversely, it being a “check valve”, valve 24 prevents gases from combustion chamber 6 to which pipe 8 is connected and inside which valve 24 is located,from reaching both port 21 and the atmosphere by flowing through pipe 7.

[0194] The engine 1 also comprises, for each cylinder 2, a pipe 25 (previously identified as the “sixth pipe”) including an inlet port 26 and an outlet port 27 opposite port 26. As can be seen in figure 1 , pipe 25 is connected to pipe 8 connected to the combustion chamber 6 of said cylinder 2 at port 26 downstream of valve 24 installed along said pipe 8 (“downstream” with reference to the direction of flow of the air from the atmosphere towards the combustion chamber 6), and, at port 27, directly with the atmosphere or to pipe 14 downstream of port 20 (“downstream” with reference to the direction of flow of the exhaust gases from the combustion chambers 6 towards the atmosphere). Pipe 25 of each cylinder 2 therefore links pipe 14 with pipe 8 connected to the combustion chamber 6 of said cylinder 2. A further check valve 28 (previously identified as the “fifth valve” and preferably of the reed type) is installed along each pipe 25. Valve 28 allows gases coming from the combustion chamber 6 connected, via its own pipe 8, to pipe 25 along which valve 28 is installed, to flow through pipe 25 towards the atmosphere or towards pipe14. Conversely, being a “check valve”, valve 28 prevents atmospheric air or exhaust gases coming from pipe 14 from reaching pipe 8 to which pipe 25 is connected in which valve 28 is installed, by flowing through pipe 25.

[0195] The engine 1 may also include a catalytic converter 29 installed along pipe 14 downstream of inlets 13 and upstream of inlet 20 (“downstream” and “upstream” with reference to the direction of flow of exhaust gases from combustion chambers 6 towards the atmosphere). The catalytic converter 29 is suitable for reducing the concentration of nitrogen oxide, carbon monoxide and unburned fuel in the exhaust gases coming from pipes 11 and flowing through it. If the engine 1 includes a catalytic converter 29, it also includes at least one sensor 30 known as “lambda probe” and installed downstream of inlets 13 and upstream of the catalytic converter 29 (“downstream” and “upstream” with reference to the direction of flow of exhaust gases from combustion chambers 6 towards the atmosphere). The sensor 30 is suitable for detecting the concentration of oxygen in the exhaust gases coming from pipes 11.

[0196] If the engine 1 includes a catalytic converter 29, each pipe 25 will preferably beconnected to pipe 14, at port 27, downstream of port 20, rather than downstream of ports 13 and upstream of the catalytic converter 29 (“downstream” and “upstream” with reference to the direction of flow of exhaust gases from combustion chambers 6 towards the atmosphere).

[0197] Having now completed the description of the engine 1 as a whole, a thermodynamic cycle according to which the engine 1 can operate will be illustrated below, with reference to the piston 3 shown in figure 1 and starting from a configuration, also shown in figure 1 , in which the piston 3 is at the top dead centre and valves 15 and 16 (respectively positioned at port 10 of pipe 8 connected to the combustion chamber 6 of the cylinder 2 in which said piston 3 is housed, and at port 12 of pipe 11 connected to the combustion chamber 6 of the cylinder 2 in which said piston 3 is housed) are both closed.

[0198] The aforementioned thermodynamic cycle comprises a first phase, the suction phase, during which the piston 3 moves from the top dead centre to the bottom dead centre, valve 15 (placed at port 10 of pipe 8 connected to the combustion chamber 6 of the cylinder 2 in which said piston 3 is housed) is opened (i.e., said valve 15 is made to assume the first configuration). As a result of the above, atmospheric air is drawn into combustion chamber 6 (of cylinder 2 in which piston 3 is housed) via pipe 7 and pipe 8 connected to combustion chamber 6 (of cylinder 2 in which piston 3 is housed), and possibly exhaust gases, depending on the regulation operated by valve 22, are drawn into the combustion chamber 6 (of cylinder 2 in which piston 3 is housed) via pipe 19, pipe 7 and pipe 8 connected to combustion chamber 6 (of cylinder 2 in which piston 3 is housed). The atmospheric air and possibly exhaust gases therefore mix with each other in the combustion chamber 6 (of cylinder 2 in which piston 3 is housed). During the suction phase, valve 28 (of cylinder 2 in which piston 3 is housed) prevents atmospheric air or exhaust gases from being sucked into the combustion chamber 6 (of cylinder 2 in which piston 3 is housed) by flowing through pipe 25 (of cylinder 2 in which piston 3 is housed).

[0199] Figure 2 shows the portion of the engine 1 that is being referred to in order to illustrate the thermodynamic cycle according to which the engine 1 can operate, at the end of the suction phase. As can be seen in this figure, valve 15 is notclosed at the end of the suction phase.

[0200] The suction phase is followed by a second phase, of initial compression, shown in figure 3 and during which the piston 3 moves from the bottom dead centre towards the top dead centre without however reaching it and valve 15 (placed at port 10 of pipe 8 connected to the combustion chamber 6 of the cylinder 2 in which said piston 3 is housed) is closed. The upward translation of the piston 3 causes that, as long as valve 15 is open (as shown in figure 3), the mixture formed, during the suction phase, in the combustion chamber 6 (of cylinder 2 in which piston 3 is housed) is partly expelled from said combustion chamber 6 into the atmosphere or into pipe 14 by flowing through pipe 8 connected to the combustion chamber 6 (of cylinder 2 in which piston 3 is housed) and pipe 25. During the initial compression phase, valve 24 (of cylinder 2 in which piston 3 is housed) prevents the mixture formed, during the suction phase, in the combustion chamber 6 (of cylinder 2 in which piston 3 is housed) and partly expelled from said combustion chamber 6, from reaching both port 21 and the atmosphere by flowing through pipe 7.

[0201] Figure 4 shows the portion of the engine 1 that is being referred to to illustrate the thermodynamic cycle according to which the engine 1 can operate, at the end of the initial compression phase.

[0202] The initial compression phase is followed by a third, the final compression phase during which, while valves 15 and 16 (respectively positioned at port 10 of pipe 8 connected to the combustion chamber 6 of cylinder 2 in which said piston 3 is housed, and at port 12 of pipe 11 connected to the combustion chamber 6 of cylinder 2 in which said piston 3 is housed) are both closed, piston 3 continues to move towards the top dead centre until it reaches it and if the fuel is petrol, injector 17 of cylinder 2 in which piston 3 is housed injects petrol into the combustion chamber 6 of cylinder 2 in which piston 3 is housed, so that the mixture formed, during the suction phase, in the combustion chamber 6 (of cylinder 2 in which piston 3 is housed) mixes with the fuel in the combustion chamber 6 (of cylinder 2 in which piston 3 is housed).

[0203] Figure 5 shows the portion of the engine 1 , that is being referred to, to illustrate the thermodynamic cycle according to which the engine 1 can operate, at theend of the final compression phase.

[0204] The final compression phase is followed by a fourth phase, of combustion and expansion, during which, while valves 15 and 16 (respectively positioned at port 10 of pipe 8 connected to the combustion chamber 6 of cylinder 2 in which said piston 3 is housed, and at port 12 of pipe 11 connected to the combustion chamber 6 of cylinder 2 in which said piston 3 is housed) are both closed, if the fuel is petrol, the spark plug 18 of the combustion chamber 6 (of cylinder 2 in which said piston 3 is housed) triggers the combustion of the petrol or, if the fuel is diesel, the injector 17 of cylinder 2 in which said piston 3 is housed introduces diesel into the combustion chamber 6 (of cylinder 2 in which said piston 3 is housed) so as to start the combustion of the diesel. As a result of the combustion of the fuel, piston 3 moves from the top dead centre to the bottom dead centre.

[0205] Figure 6 shows the portion of the engine 1 that is being referred to in order to illustrate the thermodynamic cycle according to which the engine 1 can operate, at the end of the combustion and expansion phase.

[0206] The combustion and expansion phase is followed by a fifth and final phase, the exhaust phase, shown in figure 7 and during which piston 3 moves from the bottom dead centre to the top dead centre and valve 16 (placed at port 12 of pipe 11 connected to the combustion chamber 6 of cylinder 2 in which said piston 3 is housed) is opened (as visible in figure 7) and subsequently closed. As a result of the above, the exhaust gases are expelled from the combustion chamber 6 (of cylinder 2 in which said piston 3 is housed) into pipe 14, flowing through pipe 11 connected to the combustion chamber 6 (of cylinder 2 in which said piston 3 is housed).

[0207] At the end of the exhaust phase, the portion of the engine 1 , that is being referred to, to illustrate the thermodynamic cycle according to which the engine 1 can operate, is in (i.e. , returns to) the configuration shown in figure 1 , so that the thermodynamic cycle described above can be restarted.

[0208] To understand the advantages associated with the use of the engine 1, it is appropriate to make the following preliminary considerations.

[0209] In general, in reciprocating internal combustion engines, the value reached bythe temperature at the end of the compression phase is proportional to the compression ratio and, as is well known, cannot exceed values that would lead to self-combustion of the fuel, if petrol. The value reached by the temperature at the end of the compression phase does not depend on the power required by the engine.

[0210] In known engines of the same type as the engine 1, the control of the rate of atmospheric air that is sucked in is obtained by throttling the inlet pipe. This means that the air sucked into the combustion chamber is, with respect to the atmosphere, at a upper pressure but at the same temperature. Throttling the inlet pipe involves an isenthalpic transformation for the sucked air. Consequently, since the temperature of the air at the beginning of the compression phase is equal to that of the ambient air, regardless of the degree of throttling of the supply, the temperature reached at the end of compression will also be the same, since the latter depends on the initial temperature and on the compression ratio of the engine.

[0211] Advantageously, in the engine 1 the inlet pipe is never throttled and the partial filling of each cylinder 2, and therefore the regulation of the power of the engine 1 , is obtained by expelling the excess air intake towards pipe 14. The intaken air at the end of the suction phase is at a pressure slightly different from the atmospheric one and a fraction of it, inversely proportional to the required power, is expelled during the initial compression phase. The actual compression (i.e., the aforementioned final compression phase) therefore begins with a mixture of air and gas recirculated at approximately atmospheric pressure. The air is at room temperature. The mixture is at a slightly higher temperature. The motorization of valve 15 of each cylinder 2 ensures that the compression stroke is variable as a function of the required power and starting from a pressure slightly different from the atmospheric one. More precisely, the angular position of the camshaft at which valve 15 of each cylinder 2 is closed at the end of the initial compression phase is adjustable, so as to vary the opening cycle of valve 15 as a function of the power required. Valve 15 of each cylinder 2 is also advantageously opened at the lift useful for minimizing pressure loss.

[0212] The presence, for each cylinder 2, of pipe 25 for the discharge of excess aspi-rated air and with it of part of the recirculated exhaust gases advantageously ensures, in any operating condition of the engine 1 (required power and rotation speed), the filling of the combustion chamber 6 of said cylinder 2 with air at approximately atmospheric temperature and pressure, and advantageously ensures the definition of the mass of combustion air necessary to obtain the required power through the expulsion of part of the aspirated air through pipe 25 of said cylinder 2 and the closing position of valve 15 with respect to that of the piston 2, and, consequently, when the maximum possible power is not required, advantageously ensures, with respect to the known Otto cycle or Diesel cycle, a lower temperature of the gases in all phases of the thermodynamic cycle and therefore a lower dispersion of heat through the walls of cylinder 2 and cylinder head 5, with a consequent increase in efficiency and a lower quantity of nitrogen oxides produced, or, alternatively, the possibility of operating with higher compression ratios, thus obtaining higher efficiency.

[0213] Introducing into pipe 14, through each pipe 25, the portion of mixture that is expelled during the initial compression phase from the combustion chambers 6 also advantageously ensures the presence of air in pipe 14 and this is useful for reducing polluting combustion components thanks to better oxidation of the combustion products, especially in the time immediately following the ignition of the engine 1 , when the catalytic converter 29 is not sufficiently hot to function properly.

[0214] In addition to what has been said, in the suction phase of the thermodynamic cycle according to which the engine 1 operates, the difference between the atmospheric pressure values and those in each cylinder 2 is minimal, independent of the power required by the engine 1 , and only due to the inevitable pressure loss in pipe 7. The same modest pressure difference will act on the two sides of each piston 2, the one facing the combustion chamber 6 and the opposite one minimising the power absorbed by the engine 1 in the suction phase. A simplified version of the engine 1 could be without the catalytic converter 29 and sensor 30, leaving only the air blown into pipe 14 to oxidise the combustion products.

[0215] Figure 8 shows a direct injection internal combustion reciprocating engine 31which is a variant of engine 1. For simplicity, a portion of engine 31 including a single cylinder 2 and corresponding to the portion of engine 1 shown in the preceding figures is shown in the figures.

[0216] Engine 31 differs from engine 1 in that each valve 28 is preloaded. Each valve 28 allows gases from the corresponding combustion chamber 6 to reach the atmosphere or pipe 14 by flowing through pipe 25 in which valve 28 is installed only when the pressure upstream of valve 28 (“upstream” with reference to the direction of flow of gases from combustion chamber 6 towards the atmosphere or towards pipe 14) is higher than a set value.

[0217] Similarly to what was done for engine 1, a thermodynamic cycle according to which engine 31 can operate will be illustrated below, with reference to piston 3 shown in figure 8 and starting from a configuration, also shown in figure 8, in which piston 3 is at top dead centre, valve 15 (placed at port 10 of pipe 8 connected to combustion chamber 6 of cylinder 2 in which said piston 3 is housed) is open and valve 16 (placed at port 12 of pipe 11 connected to combustion chamber 6 of cylinder 2 in which said piston 3 is housed) is closed.

[0218] The thermodynamic cycle according to which the engine 31 can operate comprises a first phase, the suction phase, during which the piston 3 moves from the top dead centre to the bottom dead centre. As a result of the above, atmospheric air is drawn into the combustion chamber 6 (of the cylinder 2 in which the piston 3 is housed) flowing through pipe 7 and pipe 8 connected to the combustion chamber 6 (of cylinder 2 in which piston 3 is housed), and possibly exhaust gases, depending on the regulation operated by the valve 22, are drawn into the combustion chamber 6 (of cylinder 2 in which piston 3 is housed) flowing through pipe 19, pipe 7 and pipe 8 connected to the combustion chamber 6 (of cylinder 2 in which piston 3 is housed). The atmospheric air and possibly exhaust gases therefore mix with each other in the combustion chamber 6 (of cylinder 2 in which piston 3 is housed). During the suction phase, valve 28 (of cylinder 2 in which piston 3 is housed) prevents atmospheric air or exhaust gases from being drawn into combustion chamber 6 (of cylinder 2 in which piston 3 is housed) by flowing through pipe 25 (of cylinder 2 in which piston 3 is housed). Valve 15 is already open at the start of the suction phase, and it is not closed atthe end of the same phase.

[0219] The suction phase of the thermodynamic cycle according to which the engine 31 can operate is followed by a second phase, of initial compression, shown in figure 9 and during which the piston 3 moves from the bottom dead centre towards the top dead centre without however reaching it and valve 15 (placed at port 10 of pipe 8 connected to the combustion chamber 6 of the cylinder 2 in which said piston 3 is housed) is closed. The upward translation of the piston 3 causes that, as long as the valve 15 is open (as shown in figure 9), the mixture formed, during the suction phase, in the combustion chamber 6 (of cylinder 2 in which piston 3 is housed) is partially expelled from said combustion chamber 6 and, as long as the pressure upstream of valve 28 (of cylinder 2 in which piston 3 is housed) (“upstream” with reference to the direction of flow of the gases from the combustion chambers 6 towards the atmosphere or towards pipe 14) is not higher than the above-mentioned set value, it is retained by valve 28 (of cylinder 2 in which piston 3 is housed) upstream of the same (as shown in figure 9). In the event that the pressure upstream of valve 28 (of cylinder 2 in which piston 3 is housed) (“upstream” with reference to the direction of flow of gases from combustion chambers 6 towards the atmosphere or towards pipe 14) exceeds the above-mentioned set value, the mixture formed during the suction phase in combustion chamber 6 (of cylinder 2 in which piston 3 is housed) and partly expelled from said combustion chamber 6 is dispersed into the atmosphere or piped to pipe 14 via pipe 8 connected to combustion chamber 6 (of cylinder 2 in which piston 3 is housed) and pipe 25. During the initial compression phase, valve 24 (of cylinder 2 in which piston 3 is housed) prevents the mixture formed during the suction phase in combustion chamber 6 (of cylinder 2 in which piston 3 is housed) and partly expelled from said combustion chamber 6 from reaching both port 21 and the atmosphere flowing through pipe 7 so that, at the end of the initial compression phase, the mixture formed, during the suction phase, in the combustion chamber 6 (of cylinder 2 in which piston 3 is housed) and partly expelled from said combustion chamber 6 is at least partly housed and compressed within the volume limited by valve 24 (of cylinder 2 in which piston 3 is housed), valve 28 (of cylinder 2 in which piston 3 is housed)and valve 15 (placed at port 10 of pipe 8 connected to the combustion chamber 6 of cylinder 2 in which said piston 3 is housed) at a pressure equal to or lower than the aforementioned set value (preferably at a pressure slightly higher than the atmospheric value).

[0220] The initial compression phase of the thermodynamic cycle according to which the engine 31 can operate is followed by a third phase, the final compression phase during which, while valves 15 and 16 (respectively positioned at port 10 of pipe 8 connected to the combustion chamber 6 of cylinder 2 in which said piston 3 is housed, and at port 12 of pipe 11 connected to the combustion chamber 6 of cylinder 2 in which said piston 3 is housed) are both closed, the piston 3 continues to move towards the top dead centre until it reaches it and, if the fuel is petrol, the injector 17 of the cylinder 2 in which the piston 3 is housed introduces petrol into the combustion chamber 6 of the cylinder 2 in which the piston 3 is housed so that the mixture formed, during the suction phase, in the combustion chamber 6 (of cylinder 2 in which the piston 3 is housed) mixes with the petrol in the combustion chamber 6 (of cylinder 2 in which the piston 3 is housed).

[0221] The final compression phase of the thermodynamic cycle according to which the engine 31 can operate is followed by a fourth phase, of combustion and expansion, during which, while valves 15 and 16 (respectively positioned at port 10 of pipe 8 connected to the combustion chamber 6 of the cylinder 2 in which said piston 3 is housed, and at port 12 of pipe 11 connected to the combustion chamber 6 of cylinder 2 in which said piston 3 is housed) are both closed, if the fuel is petrol, the spark plug 18 of the combustion chamber 6 (of cylinder 2 in which said piston 3 is housed) triggers the combustion of the petrol or, if the fuel is diesel, the injector 17 of the cylinder 2 in which the piston 3 is housed introduces diesel into the combustion chamber 6 (of cylinder 2 in which the piston 3 is housed) so as to start the combustion of the diesel. Due to the combustion of the fuel, piston 3 moves from top dead centre to bottom dead centre.

[0222] The combustion and expansion phase of the thermodynamic cycle according to which the engine 31 can operate is followed by a fifth and final phase, the exhaust phase, shown in figure 10 and during which the piston 3 moves from thebottom dead centre to the top dead centre, valve 16 (placed at port 12 of pipe 11 connected to the combustion chamber 6 of cylinder 2 in which said piston 3 is housed) is opened (as visible in figure 10) and subsequently closed, and valve 15 (placed at port 10 of pipe 8 connected to the combustion chamber 6 of cylinder 2 in which said piston 3 is housed) is opened (as visible in figure 10) after valve 16 is opened and before the latter is closed. As a result of the above, the mixture formed during the suction phase in combustion chamber 6 (of cylinder 2 in which piston 3 is housed) and partly housed within the volume limited by valve 24 (of cylinder 2 in which piston 3 is housed), valve 28 (of cylinder 2 in which piston 3 is housed) and valve 15 (placed at port 10 of pipe 8 connected to combustion chamber 6 of cylinder 2 in which said piston 3 is housed) at a pressure equal to or lower than the aforementioned set value flows, due to a difference in pressure, into said combustion chamber 6 through pipe 8 connected to said combustion chamber 6. During this phase, the exhaust gases, together with part of the aforementioned mixture flowing into combustion chamber 6 (of cylinder 2 in which said piston 3 is housed), are expelled from said combustion chamber 6 into pipe 14 through pipe 11 connected to said combustion chamber 6. Please note that valve 15 is not closed at the end of the exhaust phase.

[0223] The opening of valve 15 before the end of the exhaust phase advantageously determines a flushing of the combustion chamber 6, i.e. , the replacement of hot burnt gases with air and recirculated gases at low temperature. This determines a lowering of the operating temperatures of the engine 31, at the same power, and consequently would allow a further increase in the compression ratio, and consequently in the efficiency. Furthermore, the fact that a modest quantity of air flows in the exhaust pipe 14 ensures the presence in the catalytic converter 29 of oxygen necessary for its optimal operation. A simplified version of the engine 31 could be without the catalytic converter 29 and the sensor 30, entrusting only the air blown into the pipe 14 with the task of oxidizing the combustion products.

[0224] At the end of the exhaust phase, the portion of the engine 31 that is being referred to in order to illustrate the thermodynamic cycle according to which the engine 31 can operate is (i.e., returns) to the configuration shown in figure 8, sothat the thermodynamic cycle described above can be restarted.

[0225] As described above, in engine 31 the air is also used to expel the burnt gases from each combustion chamber 6, obtaining a further lowering of the temperatures in the two compression phases and a greater filling of the engine. With the same actual compression stroke and rotation speed, the greater load of combustion air corresponds to a significant increase in power, especially when the actual compression stroke is at least half of the nominal one (this is because part of the air that replaces the residual combustion gases is also expelled in the first part of the compression stroke).

[0226] Figure 11 shows a direct injection internal combustion reciprocating engine 41 which is another variant of engine 1 (or equivalently a variant of engine 31). For simplicity, a portion of engine 41 including a single cylinder 2 and corresponding to the portion of engine 1 and the portion of engine 31 shown in the preceding figures is shown in the figures.

[0227] Engine 41 differs from engine 1 in that each of the cylinders 2 comprises a support 42 firmly connected to the crankcase of engine 41 (so that said cylinder 2 is firmly connected to the crankcase at the support 42), and a liner 43 preferably tubular and housed in the support 42 so as to be constrained, by the latter, to perform a translational motion with respect to the support 42 and internally therein. Piston 3 housed in each cylinder 2 of engine 41 is housed in the liner 43 of the latter so as to be constrained, by said liner 43, to perform a translational motion relating to the liner 43 and internally therein. The liner 43 of each cylinder 2 is constrained to translate inside and with respect to the support 42 in which it is housed in the same direction in which the piston 3 housed in said liner 43 is constrained to translate inside and with respect to said liner 43. As can be seen in figure 11, the combustion chamber 6 of each cylinder 2 is delimited by the liner 43 (housed in the support 42 of said cylinder 2) possibly together with the support 42 (of said cylinder 2) in which it is housed, by the portion of the cylinder head 5 occluding said cylinder 2 from above and by the crown of the piston 3 housed in the liner 43 (housed in the support 42 of said cylinder 2). For each cylinder 2, a translation of the liner 43 (housed in the support 42 of said cylinder 2) inside and with respect to the support 42 (of said cylinder 2) inwhich it is housed, away from the portion of the head 5 occluding said cylinder 2 at the top causes an increase in the volume of the combustion chamber 6 of said cylinder 2. Similarly, for each cylinder 2, a translation of the liner 43 (housed in the support 42 of said cylinder 2) inside and with respect to the support 42 (of said cylinder 2) in which it is housed, towards the portion of the head 5 occluding said cylinder 2 at the top causes a decrease in the volume of the combustion chamber 6 of said cylinder 2. The engine 41, for each cylinder 2, also comprises a system (falling within the previously mentioned “movement means”) suitable for making the liner 43 (housed in the support 42 of said cylinder 2) translate inside and with respect to the support 42 (of said cylinder 2) in which it is housed. For each cylinder 2, the movement system of the liner 43 housed in the support 42 of said cylinder 2 preferably comprises a ring nut 44 fitted onto a portion (lower in the figure) of the liner 43 furthest from the head 5. The ring nut 44 is threaded (internally) on the liner 43. The ring nut 44 is also toothed externally and is preferably rotated around its own longitudinal axis by a worm screw 45 coupled with the ring nut 44 and in turn rotated by a small, preferably electric stepper motor. In the figure it is possible to note that the liner 43 of each cylinder 2 is preferably cooled by the engine oil which reaches the liner 43, crossing the wall of support 42 in which it is housed, through hole 46. By means of suitable passage surfaces, preferably axial or helical millings, the engine oil also ensures the lubrication of the surfaces of the ring nut 44 coupled to the liner 43 and to the engine crankcase 41. In each cylinder 2 the ring nut 44 also supports the thrust produced by the combustion on the liner 43 of said cylinder 2.

[0228] Advantageously, an adjustment of the volume of the combustion chamber 6 allows an adjustment of the compression ratio of the engine 41. A gradual variation of the compression ratio of the engine, as a function of the required power, allows the thermodynamic efficiency to be optimised in all operating conditions. Figure 11 shows the above-mentioned portion of the engine 41 with the liner 43 included in said engine portion at its lower limit stop (so that the volume of the corresponding combustion chamber 6 is maximum). Figure 12 shows the above-mentioned portion of the engine 41 with the liner 43 included in said en-gine portion at its upper limit stop (so that the volume of the corresponding combustion chamber 6 is minimum).

[0229] Please note that, although in this description, as well as in the claims, reference is made exclusively, for convenience of illustration, to petrol and diesel, the en-gine object of the invention, in its variants, could operate using other equivalent fuels such as LPG, methane and biofuels. In particular, the term “petrol” stands for any fuel that requires combustion to be triggered.

[0230] Based on the description provided for a preferred embodiment, it is obvious that some changes can be introduced by those skilled in the art without thereby de-parting from the scope of the invention as defined by the following claims.

Claims

C L A I M S1. Reciprocating internal combustion engine (1, 31, 41) comprising:• a crankcase;• one or more cylinders (2) firmly connected to said crankcase;• for each of said cylinders (2), a piston (3) housed in said cylinder (2) so as to be constrained, by the latter, to perform a translational motion with respect to said cylinder (2) and internally thereof;• a camshaft connected to said crankcase so that it can rotate, relative to the latter, around its own axis;• for each of said pistons (3), a connecting rod (4) extending longitudinally from a connecting rod small end to a connecting rod big end,said connecting rod (4) being hinged:- at its small end, to said piston (3)and- at its big end, to said camshaftso that a rotation of said camshaft with respect to said crankcase around its own axis determines a reciprocating rectilinear translational motion of said piston (3) inside and with respect to said cylinder (2) in which said piston (3) is housed;• a cylinder head (5) firmly connected to said crankcase so as to occlude each of said cylinders (2) at its upper base so that, for each of said cylinders (2), said engine (1, 31, 41) comprises a combustion chamber (6) delimited by said cylinder (2), by a portion of said cylinder head (5) occluding said cylinder (2) and by the crown of said piston (3) housed in said cylinder (2),each of said pistons (3) being movable within and with respect to said cylinder (2) in which said piston (3) is housed between at least:- a bottom dead centre at which the distance between said piston (3) and said portion of said cylinder head (5) occluding said cylinder (2) in which said piston (3) is housed is maximum, and therefore at which the volume of said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed is maximumand- a top dead centre at which the distance between said piston (3) and said portion of said cylinder head (5) occluding said cylinder (2) in which said piston (3) is housed is minimum, and therefore at which the volume of said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed is minimum;• a first pipe (7) for taking air from the atmosphere;• for each of said cylinders (2), a second pipe (8) for the introduction of atmospheric air into said combustion chamber (6) of said cylinder (2),said second pipe (8) comprising:- an inlet port (9) at which said second pipe (8) is connected to said first Pipe (7);- an outlet port (10) opposite said inlet port (9) and positioned at said portion of said head (5) occluding said cylinder (2),said second pipe (8) being connected to said combustion chamber (6) of said cylinder (2) at said outlet port (10),so as to put said first pipe (7) in communication with said combustion chamber (6) of said cylinder (2);• for each of said cylinders (2), a third pipe (2) for the expulsion from said combustion chamber (6) of said cylinder (2) of any exhaust gases present in said combustion chamber (6) of said cylinder (2),said third pipe (11 ) comprising:- an inlet port (12) placed at said portion of said head (5) occluding said cylinder (2),said third pipe (11) being connected to said combustion chamber (6) of said cylinder at said inlet port (12);- an outlet port (13) opposite said inlet port (12) of said third pipe (11);• a fourth pipe (14) for the expulsion of exhaust gases into the atmosphere, each of said third pipes (11) is connected to said fourth pipe (14) at its own outlet (13):- so as to put said combustion chamber (6) in communication with said fourth pipe (14) to which said third pipe (11) is connected at its own inlet port (12)and- for the expulsion into the atmosphere of any exhaust gases present in said combustion chamber (6) to which said third pipe (11) is connected at its inlet port (12);• for each of said second pipes (8), a first valve (15) at said outlet port (19) of said second pipe (8),said first valve (15) can assume at least:- a first configuration at which said first valve (15) allows atmospheric air to flow from:said second pipe (8)intosaid combustion chamber (6) to which said second pipe (8) is connected at its outlet port (10);- a second configuration at which said first valve (15) prevents atmospheric air from flowing from:said second pipe (8)intosaid combustion chamber (6) to which said second pipe (8) is connected at its outlet port (10);• for each of said third pipes (11), a second valve (16) at said inlet port (12) of said third pipe (11),said second valve (16) can assume at least:- a first configuration at which said second valve (16) allows any exhaust gases present in said combustion chamber (6) to which said third pipe (11) is connected at its inlet port (12), to flow from:said combustion chamber (6) to which said third pipe (11) is connected at its inlet port (12)intosaid third pipe (11);- a second configuration at which said second valve (16) prevents any exhaust gases present in said combustion chamber (6) to which said third pipe (11) is connected at its inlet port (12), from flowing from:said combustion chamber (6) to which said third pipe (11) is connected at its inlet port (12)intosaid third pipe (11);• for each of said cylinders (2):- an injector (17) for the introduction into said combustion chamber (6) of said cylinder (2), of a fuel to be subjected to combustion in said combustion chamber (6) of said cylinder (2), together with atmospheric air, and, if said fuel is petrol,- a spark plug (18) for triggering the combustion of said fuel in said combustion chamber (6) of said cylinder (2), together with atmospheric air;• a fifth pipe (19) comprising an inlet port (20) and an outlet port (21) opposite said inlet port (20) of said fifth pipe (19),said fifth pipe (19) being connected:- at its inlet port (20), to said fourth pipe (14) downstream of said outlet ports (13) respectively of said third pipes (11) with reference to the direction of flow of said exhaust gases from said combustion chambers (6) towards the atmosphereand- at its outlet port (21), to said first pipe (7) upstream of said inlet ports (9) respectively of said second pipes (8) with reference to the direction of flow of the air from the atmosphere towards said combustion chambers (6), so as to put said fourth pipe (14) in communication with said first pipe (7); • a third valve (22) installed along said fifth pipe (19) to regulate the flow rate of exhaust gases taken from said fourth pipe (14) through said fifth pipe (19), and introduced through the latter into said first pipe (7);• cooling means (23) installed along said fifth pipe (19) to cool exhaust gases taken from said fourth pipe (14) through said fifth pipe (19), and introduced through the latter into said first pipe (7),said engine (1 , 31 , 41 ) being characterised by the fact that it also comprises, for each of said cylinders (2):• a fourth valve (24), a check valve, installed along said second pipe (8) con-nected to said combustion chamber (6) of said cylinder (2), and therefore downstream of said outlet (21) of said fifth pipe (19) with reference to the direction of flow of air from the atmosphere towards said combustion chambers (6),said fourth valve (24) allowing air from the atmosphere and said exhaust gases from said fifth pipe (19) to reach said combustion chamber (6) of said cylinder (2) flowing through said first pipe (7) and through said second pipe (8) connected to said combustion chamber (6) of said cylinder (2),said fourth valve (24) preventing gases coming from said combustion chamber (6) of said cylinder (2) from reaching both said outlet (21 ) of said fifth pipe (19) and the atmosphere by flowing through said first pipe (7);• a sixth pipe (25) comprising an inlet port (26) and an outlet port (27) opposite said inlet port (26) of said sixth pipe (25),said sixth pipe (25) being connected:- at its inlet port (26), to said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) downstream of said fourth valve (24) of said cylinder (2) with reference to the direction of flow of air from the atmosphere towards said combustion chamber (6) of said cylinder (2), and- at its outlet (27), directly to the atmosphere or to said fourth pipe (14), so as to put said second pipe (8) connected to said combustion chamber (6) of said cylinder in communication with said fourth pipe (14);• a fifth valve (28), a check valve, installed along said sixth pipe (25) of said cylinder (2),said fifth valve (28) allowing gases from said combustion chamber (6) of said cylinder (2) to reach the atmosphere or said fourth pipe (14) flowing through said sixth pipe (25),said fifth valve (28) preventing atmospheric air or exhaust gases coming from said fourth pipe (14) from reaching said second pipe (8) connected to said combustion chamber (6) of said cylinder (2), flowing through said sixth pipe (25).

2. Engine (41) according to claim 1, characterised in that, for each of saidcylinders (2), said sixth pipe (25), if connected, at its own outlet (27), to said fourth pipe (14), is connected to said fourth pipe downstream of said inlet port (20) of said fifth pipe (19) with reference to the direction of flow of said exhaust gases from said combustion chambers (6) towards the atmosphere.

3. Engine (41) according to claim 1 or 2, characterised in that each of said cylinders (2) comprises:• a support (42) firmly connected to said crankcase so that said cylinder (2) is firmly connected to said crankcase at said support (42);• a liner (43) housed in said support (42) so as to be constrained, by the latter, to perform a translational motion with respect to said support (42) and internally to the same,said piston (3) housed in said cylinder (2) being housed in said cylinder (2) at said liner (43) so as to be constrained, by the latter, to perform a translational motion with respect to said liner (43) and internally thereof,said liner (43) being constrained to translate inside and with respect to said support (42) in which it is housed in the same direction in which said piston (3) housed in said liner (43) is constrained to translate inside and with respect to the latter,said combustion chamber (6) of said cylinder (2) being delimited by said liner (43) possibly together with said support (42), by said portion of said cylinder head (5) occluding said cylinder (2) and by the crown of said piston (3) housed in said liner (43),a translation of said liner (43) inside and with respect to said support (42) away from said portion of said head (5) occluding said cylinder (2) causing an increase in the volume of said combustion chamber (6),a translation of said liner (43) inside and with respect to said support (42) towards said portion of said head (5) occluding said cylinder (2) causing a decrease in the volume of said combustion chamber (6);• movement means (44, 45) suitable for moving said liner (43) inside and with respect to said support (42).

4. Engine (1, 31, 41) according to one of the preceding claims, characterised in that it further comprises:• a catalytic converter (29) installed along said fourth pipe (14) downstream of said outlets (13) respectively of said third pipes (11) and upstream of said inlet (20) of said fifth pipe (19) with reference to the direction of flow of said exhaust gases from said combustion chambers (6) towards the atmosphere, said catalytic converter (29) being suitable for reducing the concentration of nitrogen oxide, carbon monoxide and unburned fuel in said exhaust gases coming from said third pipes (11) and flowing through said catalytic converter (29);• a sensor (30) installed along said fourth pipe (14) downstream of said outlets (13) respectively of said third pipes (11) and upstream of said catalytic converter (29) with reference to the direction of flow of said exhaust gases from said combustion chambers (6) towards the atmosphere, and suitable for detecting the concentration of oxygen in said exhaust gases coming from said third pipes (11).

5. Engine (1, 31, 41) according to claim 4 when dependent on claim 1 or when dependent on claim 3 dependent on claim 1, characterised in that, for each of said cylinders (2), said sixth pipe (25), if connected, at its own outlet (27), to said fourth pipe (14), is connected to said fourth pipe downstream of said outlets (13) respectively of said third pipes (11), and upstream of said catalytic converter (29), with reference to the direction of flow of said exhaust gases from said combustion chambers (6) towards the atmosphere.

6. Thermodynamic cycle according to which an engine (1, 41) according to one of the preceding claims can operate,referring to one of said pistons (3) in case there is more than one and starting from a configuration in which:• said piston (3) is at its top dead centre;• said first valve (15) placed at said outlet port (10) of said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is in said second configuration;• said second valve (16) placed at said inlet port (12) of said third pipe (11) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is in said second configuration,said cycle including the following phases:a) a first phase, the suction phase, during which:• said piston (3) moves from its top dead centre to its bottom dead centre, • said first valve (15) placed at said outlet port (10) of said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is made to assume said first configuration, so that:• atmospheric air is sucked into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed flowing through said first pipe (7) and said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housedand possibly• exhaust gases are sucked, from said fourth pipe (14), into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, flowing through said fifth pipe (19), said first pipe (7) and said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed,said atmospheric air and possibly said exhaust gases being mixed with each other in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed,said fifth valve (28) of said cylinder (2) in which said piston (3) is housed preventing atmospheric air or said exhaust gases from being sucked into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, flowing through said sixth pipe (25);b) a second phase, of initial compression, during which:• said piston (3) moves from its bottom dead centre towards its top dead centre without reaching itand• said first valve (15) placed at said outlet port (10) of said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is made to assume said second configuration, so that, until said first valve (15) has assumed said second configuration,said mixture formed, during said first phase, in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is partly expelled from said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, into the atmosphere or into said fourth pipe (14) flowing through said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed and said sixth pipe (25),said fourth valve (24) of said cylinder (2) in which said piston (3) is housed preventing said mixture formed, during said first phase, in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, and partly expelled from said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, from reaching both said outlet port (21) of said fifth pipe (19), and the atmosphere by flowing through said first pipe (7);c) a third phase, of final compression, during which:• said piston (3) continues to move towards its top dead centre until it reaches itand, if said fuel is petrol,• said injector (17) of said cylinder (2) in which said piston (3) is housed injects said fuel into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed,so that said mixture formed, during said first phase, in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed also mixes with said fuel introduced by said injector (17) of said cylinder (2) in which said piston (3) is housed, in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed;d) a fourth phase, of combustion and expansion, during which:• if said fuel is petrol, said spark plug (18) of said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed triggers the combustion of said fuelor• if said fuel is diesel, said injector (17) of said cylinder (2) in which said piston (3) is housed injects said fuel into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, so as to start the combus-tion of said fuel,so that, due to the combustion of said fuel, said piston (3) moves from its top dead centre to its bottom dead centre;e) a fifth phase, the exhaust phase, during which:• said piston (3) moves from its bottom dead centre to its top dead centre and• said second valve (16) placed at said inlet port (12) of said third pipe (11) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is made to assume said first configuration and subsequently back to said second configuration,so that exhaust gases are expelled from said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, into said fourth pipe (14) flowing through said third pipe (11) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed,to then return to the said first phase.

7. Thermodynamic cycle according to which an engine (1, 41) according to one of claims 1 to 5 can operate,referring to one of said pistons (3) in case there is more than one and starting from a configuration in which:• said piston (3) is at its top dead centre;• said first valve (15) placed at said outlet port (10) of said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is in said first configuration;• said second valve (16) placed at said inlet port (12) of said third pipe (11) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is in said second configuration,said cycle including the following phases:a) a first phase, the suction phase, during which said piston (3) moves from its top dead centre to its bottom dead centre so that:• atmospheric air is sucked into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed flowing through said first pipe (7) and said second pipe (8) connected to said combustion chamber (6) ofsaid cylinder (2) in which said piston (3) is housedand possibly• exhaust gases are sucked, from said fourth pipe (14), into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, flowing through said fifth pipe (19), said first pipe (7) and said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed,said atmospheric air and possibly said exhaust gases being mixed with each other in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed,said fifth valve (28) of said cylinder (2) in which said piston (3) is housed preventing atmospheric air or said exhaust gases from being sucked into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, flowing through said sixth pipe (25);b) a second phase, of initial compression, during which:• said piston (3) moves from its bottom dead centre towards its top dead centre without reaching itand• said first valve (15) placed at said outlet port (10) of said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is made to assume said second configuration, so that, until said first valve (15) has assumed said second configuration, said mixture formed, during said first phase, in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is partly expelled from said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, into the atmosphere or into said fourth pipe (14) flowing through said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed and said sixth pipe (25),said fourth valve (24) of said cylinder (2) in which said piston (3) is housed preventing said mixture formed, during said first phase, in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, and partly expelled from said combustion chamber (6) of said cylinder (2) in which saidpiston (3) is housed, from reaching both said outlet port (21) of said fifth pipe (19), and the atmosphere by flowing through said first pipe (7);c) a third phase, of final compression, during which:• said piston (3) continues to move towards its top dead centre until it reaches itand, if said fuel is petrol,• said injector (17) of said cylinder (2) in which said piston (3) is housed injects said fuel into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed,so that said mixture formed, during said first phase, in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed also mixes with said fuel introduced by said injector (17) of said cylinder (2) in which said piston (3) is housed, in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed;d) a fourth phase, of combustion and expansion, during which:• if said fuel is petrol, said spark plug (18) of said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed triggers the combustion of said fuelor• if said fuel is diesel, said injector (17) of said cylinder (2) in which said piston (3) is housed injects said fuel into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, so as to start the combustion of said fuel,so that, due to the combustion of said fuel, said piston (3) moves from its top dead centre to its bottom dead centre;e) a fifth phase, the exhaust phase, during which:• said piston (3) moves from its bottom dead centre to its top dead centre, • said second valve (16) placed at said inlet port (12) of said third pipe (11) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is made to assume said first configuration and subsequently back to said second configurationand• said first valve (15) positioned at said outlet port (10) of said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is made to assume said first configuration after said second valve (16) is made to assume said first configuration, and before said second valve (16) is made to resume said second configuration, so that exhaust gases are expelled from said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, into said fourth pipe (14) flowing through said third pipe (11) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed,to then return to the said first phase.

8. Engine (31) according to one of claims 1 to 5, characterised in that for each of said cylinders (2) said fifth valve (28) allows gases coming from said combustion chamber (6) of said cylinder (2) to reach the atmosphere or said fourth pipe (14) by flowing through said sixth pipe (25) only when the pressure upstream of said fifth valve (28) of said cylinder (2), with reference to the direction of flow of gases from said combustion chamber (6) of said cylinder (2) towards the atmosphere or towards said fourth pipe (14), is higher than a set value.

9. Thermodynamic cycle according to which an engine (31) according to claim 8 can operate,referring to one of said pistons (3) in case there is more than one and starting from a configuration in which:• said piston (3) is at its top dead centre;• said first valve (15) placed at said outlet port (10) of said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is in said first configuration;• said second valve (16) placed at said inlet port (12) of said third pipe (11) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is in said second configuration,said cycle including the following phases:a) a first phase, the suction phase, during which said piston (3) moves from its top=dead centre to its bottom dead centre so that:• atmospheric air is sucked into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed flowing through said first pipe (7) and said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housedand possibly• exhaust gases are sucked, from said fourth pipe (14), into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, flowing through said fifth pipe (19), said first pipe (7) and said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed,said atmospheric air and possibly said exhaust gases being mixed with each other in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed,said fifth valve (28) of said cylinder (2) in which said piston (3) is housed preventing atmospheric air or said exhaust gases from being sucked into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, flowing through said sixth pipe (25);b) a second phase, of initial compression, during which:• said piston (3) moves from its bottom dead centre towards its top dead centre without reaching itand• said first valve (15) placed at said outlet port (10) of said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is made to assume said second configuration, so that, until said first valve (15) has assumed said second configuration, said mixture formed, during said first phase, in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is partly expelled from said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, and:• as long as the pressure upstream of said fifth valve (28) of said cylinder (2) in which said piston (3) is housed, with reference to the direction of gas flow towards the atmosphere or towards said fourth pipe (14), is not higherthan said set value,retained by said fifth valve (28) of said cylinder (2) in which said piston (3) is housed upstream of said fifth valve (28) of said cylinder (2) in which said piston (3) is housed, with reference to the direction of gas flow towards the atmosphere or towards said fourth pipe (14),and• to a possible exceeding of said set value by the pressure upstream of said fifth valve (28) of said cylinder (2) in which said piston (3) is housed, with reference to the direction of gas flow towards the atmosphere or towards said fourth pipe (14),expelled into the atmosphere or into said fourth pipe (14) through said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, and said sixth pipe (25),said fourth valve (24) of said cylinder (2) in which said piston (3) is housed, preventing said mixture formed, during said first phase, in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, and partly expelled from said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, from reaching both said outlet (21) of said fifth pipe (19), and the atmosphere by flowing through said first pipe (7), so that, at the end of said second phase, said mixture formed, during said first phase, in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, and partly expelled from said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is at least partly housed and compressed within the volume limited by said first valve (15) placed at said outlet (10) of said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, said fourth valve (24) and said fifth valve (28) of said cylinder (2) in which said piston (3) is housed, at a pressure equal to or lower than said set value;c) a third, final compression phase, during which:• said piston (3) continues to move towards its top dead centre until it reaches itand, if said fuel is petrol,• said injector (17) of said cylinder (2) in which said piston (3) is housed injects said fuel into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed,so that said mixture formed, during said first phase, in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed also mixes with said fuel introduced by said injector (17) of said cylinder (2) in which said piston (3) is housed, in said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed;d) a fourth phase, of combustion and expansion, during which:• if said fuel is petrol, said spark plug (18) triggers the combustion of said fuelor• if said fuel is diesel, said injector (17) of said cylinder (2) in which said piston (3) is housed injects said fuel into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, so as to start the combustion of said fuel,so that, due to the combustion of said fuel, said piston (3) moves from its top dead centre to its bottom dead centre;e) a fifth phase, the exhaust phase, during which:• said piston (3) moves from its bottom dead centre to its top dead centre, • said second valve (16) placed at said inlet port (12) of said third pipe (11) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is made to assume said first configuration and subsequently back to said second configurationand• said first valve (15) located at said outlet port (10) of said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, is made to assume said first configuration after said second valve (16) is made to assume said first configuration, and before said second valve (16) is made to resume said second configuration so that:said mixture formed, during said first phase, in said combustion chamber(6) of said cylinder (2) in which said piston (3) is housed, and partly housed within the volume limited by said first, fourth and fifth valves (15, 24, 28) at a pressure equal to or lower than said set value flows, by pressure difference, into said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed through said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housedand• exhaust gases together with part of said mixture flowing into said combus- tion chamber (6) of said cylinder (2) in which said piston (3) is housed flowing through said second pipe (8) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, are expelled from said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed, into said fourth pipe (14) flowing through said third pipe (11) connected to said combustion chamber (6) of said cylinder (2) in which said piston (3) is housed,then return to the said first phase.

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