An internal combustion engine with a resonator combined with the intake pipe

Abstract

The internal combustion engine (9), comprises a cylinder-piston system (13) with an intake port (13.4), into which an intake valve (13.8) is inserted, and an exhaust port (13.5) into which an exhaust valve (13.9) is inserted. The engine further comprises an intake pipe (37) fluidly coupled with the intake port (13.4), and a throttle valve (39) positioned along the intake pipe (37). A first resonator (43) is connected to the intake pipe (37). The first resonator (43) comprises a resonant cavity (46) having a resonant volume thereof placed in direct fluid coupling only with a resonant duct (47) and, by means of the resonant duct (47), with the intake pipe in a position between the throttle valve (39) and the intake valve (13.8).

Description

AN INTERNAL COMBUSTION ENGINE WITH A RESONATOR COMBINED WITH THE INTAKE PIPEDESCRIPTIONTECHNICAL FIELD

[0001] The present invention relates to improvements in internal combustion engines. In particular, the present invention relates to improvements to the intake pipes of reciprocating internal combustion engines to improve the performance thereof.BACKGROUND ART

[0002] Internal combustion engines, especially reciprocating internal combustion engines, comprising cylinder-piston systems for the generation of mechanical power, are widely used in the automotive industry. The use of fuels to power internal combustion engines has a significant environmental impact.

[0003] There is therefore ongoing research aimed at increasing the efficiency and performance of internal combustion engines without increasing harmful emissions.

[0004] It is known to introduce temporary air storage volumes along the intake pipes of an engine with the main purpose of tuning the intake pipes. An example of this is disclosed in US2003106516.

[0005] It is also known to partially restrict the air flow in an intake pipe and, by means of smaller ducts, inject air at high velocity near the intake valve to create vorticity. An example of this is disclosed in US6092503.

[0006] It is also known to position resonators in the exhaust pipes of engines, as described in US2012260626, or to arrange sound traps along the intake pipes of engines, to reduce the emitted noise, as disclosed in US5283398.SUMMARY

[0007] According to an aspect, an internal combustion engine is disclosed herein comprising at least one cylinder-piston system having an intake port into which an intake valve is inserted, and an exhaust port, into which an exhaust valve is inserted.The engine further comprises an intake pipe fluidly coupled with the intake port, and a throttle valve positioned along the intake pipe. To improve the efficiency of the engine, a first resonator connected to the intake pipe is provided. The first resonator comprises a resonant cavity having a resonant volume thereof fluidly coupled with the intake pipe in a position between the throttle valve and the intake valve. The resonator therefore comprises a closed volume, called the resonant volume, communicating with the intake pipe by means of a resonant duct. As will become clear from what is described in detail below, the resonator thus configured allows obtaining an improvement in the engine efficiency.

[0008] In some embodiments, the engine may also comprise a second resonator connected to an exhaust pipe. The combination of the two resonators may result in increased engine efficiency.

[0009] In embodiments, one or more of said resonators are Helmholtz resonators.

[0010] Further advantageous features and embodiments of the internal combustion engine are described below and defined in the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention will be better understood by following the description and the attached drawings, which illustrate illustrative and non-limiting embodiments of the invention. More in particular, the drawings show in:Fig. 1 a vehicle on which an internal combustion engine is installed;Fig. 2 a diagram of the engine of the vehicle in Fig. 1 complete with an intake pipe and an exhaust system with the relative resonant systems associated therewith;Fig. 3 and 4 a diagram illustrating the effect of the resonator associated with the engine intake;Fig. 5 to 10 a series of diagrams illustrating the advantageous effects of using one or two resonant systems in combination with the internal combustion engine; and Fig. I l a diagram of an embodiment in which the intake resonant system and the air filter form an integrated unit.DETAILED DESCRIPTION

[0012] Fig. 1 schematically shows a commercial vehicle on which an engine of thetype described may be installed. The vehicle 1 may comprise a single steered front wheel 3 or two steered front wheels 3, and a pair of rear drive wheels 5, for example. The number 9 schematically shows an engine, equipped with an intake system, generically indicated with 10, and an exhaust system generically indicated with 11.

[0013] The present solution is suitable for engines with one or more intake valves, one or more exhaust valves, and one or more cylinders. In the following, for the sake of simplicity, a single-cylinder engine with an intake channel and a related intake valve and an exhaust channel and a related exhaust valve is illustrated by way of non-limiting example. However, this configuration must be considered exemplary and not limiting.

[0014] Fig. 2 illustrates the engine 9 with the respective intake system 10 and the respective exhaust system 11 in greater detail. The number 13 indicates a cylinderpiston system, which may comprise a single cylinder 13.1 in which a piston 13.2 is slidably housed. The number 13.3 indicates a connecting rod-crank system that converts the reciprocating motion of the piston 13.2 in the cylinder 13.1 into a rotary motion of the output shaft, of which 13.7 indicates the rotation axis. The number 13.4 indicates an intake port and 13.5 indicates an exhaust port of the cylinder-piston system 13. The number 13.6 indicates the combustion chamber defined inside the cylinder 13.1. The intake port 13.4 is selectively closed and opened by means of an intake valve 13.8 and the exhaust port 13.5 is selectively opened and closed by means of an exhaust valve 13.9.

[0015] Although in the present description reference is made to an engine with a single cylinder-piston system 9, and single intake and exhaust ports, the possibility of making the engine 9 with a plurality of cylinder-piston systems and / or of providing more than one intake port and / or more than one exhaust port is not excluded.

[0016] The intake system 10 comprises (see Figs. 1 and 2) an inlet grille 31 and an air filter 35, fluidly coupled with the inlet grille 31 through a duct 33. The path of the air entering the engine 9 comprises, in addition to the inlet grille 31, the duct 33 and the air filter 35, an intake pipe 37, having an inlet 37.1 fluidly coupled with the air filter 35 and an outlet coupled with the intake port 13.4. The number 37A indicates the axis of the intake pipe 37.

[0017] A throttle valve 39 is placed along the intake pipe 37, which partially closesthe intake pipe 37 and which is connected to the accelerator pedal (not shown) with which the driver interacts with the engine 9 to increase the delivered power.

[0018] In the illustrated embodiment, the fuel is supplied to the engine 9 through an inj ector 41 , placed upstream of the intake port 13.4, between this and the throttle valve, preferably adjacent to the intake port 37.2 made in the cylinder head 13.1 of the cylinder-piston system 13.

[0019] The engine 9 comprises a first resonator 43, combined with the intake pipe 37 and fluidly coupling therewith. In the illustrated embodiment, the first resonator 43 comprises a resonant chamber or cavity 46 in turn comprising a resonant volume fluidly coupled solely with a resonant duct 47. In other words, the resonant chamber or cavity 46 is a closed chamber, the only opening of which is represented by the connection formed by the resonant duct 47. The number 47A indicates the axis of the resonant duct 47. The intake pipe 37 is joined to the resonant cavity 46 by means of the resonant duct 47. The resonant cavity 46 may be connected to the resonant duct 47 by means of an elastic fitting 49.

[0020] The resonant duct 47 is connected to the intake pipe 37 in a position 51, in the vicinity of the intake port 13.4. In practice, the reference number 51 indicates a branch or bifurcation from which the resonant duct 47 branches off from the intake pipe 37. The two ducts 47, 37 form, at the branch 51, an acute angle a, i.e. an angle less than 90°, preferably less than 45°.

[0021] The end portion of the resonant duct 47, starting from the cylinder head 13.1, may be straight.

[0022] Advantageously, at the connection point 51 between the resonant duct 47 and the intake pipe 37, said two ducts are tangent to each other. This generally means a configuration such that the total flow of gases in the intake pipe 37 is approximately tangent to the flow in the resonant duct 47. For example, the central axis or median line 37A of the intake pipe 37 and the central axis or median line 47A of the resonant duct 47 are tangent in a point downstream of the connection (point 51) between the two ducts, with respect to the supply direction of the air taken in by the engine 9. More precisely, the straight extension of the axis or median line 47A is tangent to the curve defining the axis or median line 17.1 of the intake pipe 37 in a point upstream of thebifurcation 51 with respect to the direction of air flow in the intake pipe 37.

[0023] Advantageously, the resonant duct 47 is positioned, with respect to the intake pipe 37, the intake port 13.4 and the intake valve 13.8, such that the intake valve 13.8 is visible from inside the end portion of the resonant duct 47. Thereby, pressure waves generated by closing the intake valve 13.8 reach the resonant volume of the resonant cavity 46 by means of the resonant duct 47 with minimal losses.

[0024] The connection point between the intake pipe 37 and the resonant duct 47 may be located at a distance of between 40 and 80 mm, preferably around 60 mm from the intake port 13.8.

[0025] Preferably, the resonant duct 47, and more precisely the inlet thereof connected to the intake pipe 37, is positioned upstream of the injector, with respect to the direction of air flow. Advantageously, the inlet of the resonant duct 47 is located close to the injector 41, i.e. in a position closer to the injector than to the throttle valve 39. Preferably, the inlet of the resonant duct 47 is located next to the injector 41, for example from about 20 to about 5 mm therefrom, in particular about 10 mm therefrom. This positioning promotes a timely interaction of the air wave generated by the resonator 43 with the fuel sprayed by the injector 41 and an optimal mixing of air and fuel before entering the combustion chamber.

[0026] Thereby, the pressure wave coming from the resonant cavity 46, and which advances along the resonant duct 47 towards the intake port 13.4, hits the fuel charge emitted from the injector in a concordant direction, thus facilitating the injection and mixing of the air-fuel introduced into the cylinder. This aspect optimizes the subsequent injection, reducing unbumed fuel and simultaneously generating a certain degree of over-powering, as will be described later with reference to the diagrams in Figs. 9 and 10. In practice, at certain engine speeds, the pressure waves generated by the resonator 43 in response to the pressure waves exiting from the combustion chamber 13.6, create a turbulence that facilitates mixing of the fuel and air together, before they enter the combustion chamber 13.6.

[0027] Advantageously, as visible in the diagram of Fig. 2, the resonant cavity 46 has a larger cross section than the cross section of the resonant duct 47. For example, the ratio of the cross-sectional area between the resonant cavity 46 and the cross-sectional area of the resonant duct 47 may be between 5 and 20, preferably between 8 and 15, more preferably between 10 and 12.

[0028] In general, the resonant cavity 46 may have a substantially cylindrical shape with a circular or prismatic section, and the resonant duct 47 may have a circular section with a cross section smaller than the cross section of the resonant cavity 46.

[0029] The resonant cavity 46 together with the resonant duct 47 form a Helmholtz resonator, as illustrated in Figs. 2, 4 and 11.

[0030] In some embodiments, the resonant cavity 46 has an internal volume between 500 cm3and 3500 cm3, preferably between 900 cm3and 2000 cm3, more preferably between 1000 cm3and 1500 cm3. For example, the resonant volume of the resonant cavity may be approximately five times greater than the displacement of the engine, or more precisely of the cylinder-piston system, to which the resonant cavity 46 is connected.

[0031] The resonant duct 47 may have a length between 20 cm and 100 cm, preferably between 30 cm and 40 cm. The resonant duct 47 may have an internal circular section with a diameter for example between 8 mm and 20 mm, preferably between 10 mm and 15 mm.

[0032] In some embodiments, the engine may be configured so as to deliver maximum power and maximum torque at a rotational speed between 2400 rpm and 5000 rpm.

[0033] The first resonator 43 may have a fundamental resonance frequency between 10 Hz and 30 Hz, preferably between 14 Hz and 18 Hz, more preferably between 16 Hz and 18 Hz at the temperature of the air taken into the engine.

[0034] The fundamental resonance frequency is defined byin which: c is the speed of sound in the fluid medium contained in the resonator, said speed cbeing a function of the temperature and of the ratio between specific heat at constant pressure and specific heat at constant volume;S is the section of the resonant duct 47L is the length of the resonant duct 47 andV is the volume of the resonant cavity 46.

[0035] The internal combustion engine of any one of the preceding claims, wherein the maximum engine power and the maximum engine torque are delivered at a rotation speed between 2400 rpm and 5000 rpm.

[0036] The function of the first resonant system is as follows. When the engine 9 operates at low rpm with the throttle valve 39 partially closed, the opening and closing movements of the intake valve 13.8 generate shock waves that propagate from the intake port 13.4 towards the resonant duct 47 and the resonant cavity 46. More specifically, each time the intake valve 13.8 closes, a shock wave is generated which propagates towards and into the resonator 43.

[0037] The first resonator 43 has been sized to work with the engine under partial load conditions. The partial load condition is characterised by small openings of the throttle valve 39, i.e. with the throttle valve partially closed, and by an engine revolution range of 2600 - 3800 rpm. This partial load condition is typical for use in urban environments with high traffic density. For small openings, the resonator 43 allows a carbureted air / fuel mixture to oscillate, because it is located between the throttle valve and the engine head. This facilitates the launch of the mixture into the intake pipe at the moment of opening of the intake valve 13.8, giving the mixture high speed. The higher speed of the mixture allows for the generation of greater vorticity than would be possible without a resonator.

[0038] This circumstance allows for a high flame speed in the combustion chamber, which improves combustion efficiency. As a result, for the same power, hourly fuel consumption is reduced with respect to an engine with conventional architecture.

[0039] By appropriately sizing the resonator, it is also possible to exploit a certain degree of over-powering, ensuring that the sign of the wave (i.e. the advancement direction of the wave front) is positive, i.e. oriented towards the intake port, when the intake valve opens. This happens in particular when the opening frequency of theintake valve 13.8 is substantially the same frequency with which the resonant volume 46 vibrates.

[0040] When the throttle valve is fully open, the resonator continues to work and is tuned, for this application, in the maximum power zone, i.e. between 4000 and 4500 rpm. In this case the engine is able to deliver a higher maximum power with respect to the same engine without a resonator. In summary, the resonator 43 is used by the engine to optimize fuel consumption under partial load conditions and to maximize power output when the throttle valve is fully open (e.g. when overtaking, when downshifting, and when revving up and simultaneously opening the throttle valve).

[0041] Finally, resonator 43 allows the vehicle to be more responsive during rapid throttle opening thanks to a reserve of air / fuel mixture, present in the resonator cavity.

[0042] These shock waves generate a resonant movement of the air and the fuel injected therein, in the volume of the intake pipe 37 between the branch 51 and the intake valve 13.8. The oscillating motion generated in the gas mass entering and exiting the resonator 43 improves the mixing of air and fuel. Furthermore, when the intake valve 13.8 is opened in the subsequent intake step, a better filling of the combustion chamber, and thus a sort of over-powering, is achieved. In the known solutions, a mass of air is transferred to increase or reduce the air supply to the combustion chamber and consequently vary the engine torque. In the present invention, however, there is no transfer of air mass, but a simple oscillation thereof in and out of the resonator 43 at predetermined oscillation frequencies of the resonator 43 itself.

[0043] The pressure wave of the air exiting the resonator 43 is in the same direction as the air flow flowing in the intake pipe 37 towards the intake port 13.4. The pressure wave generated by the resonator 43 thus energizes the air flow in the intake pipe 37, increasing the linear momentum thereof shortly before the intake valve 13.8 closes. This has the further effect of increasing the flow speed during the closing step of the intake valve 13.8, increasing the turbulence across the intake valve 13.8 and therefore the combustion efficiency. This results in lower fuel consumption.

[0044] The effect of these phenomena allows for improved engine operation by reducing average consumption, increasing power output and reducing the generation of unburned fuel.

[0045] The advantages obtainable with the first resonator 43 associated with the intake of the engine 9 will be described in greater detail later with reference to some numerical data obtained in tests carried out on an engine produced by the applicant.

[0046] In the embodiment illustrated in Fig. 2, the engine 9 comprises a second resonator combined with the exhaust system 11. Although, as demonstrated further on, an engine equipped with both the first resonator and the second resonator has particular advantages in terms of increased performance and limitation of emissions, the present invention also relates to an engine (and related vehicle) which comprises only the first resonator 43, associated with the intake of the engine 9, since even in the absence of the second resonant system, substantial advantages are obtained in terms of performance and reduced emissions.

[0047] In the illustrated embodiment, the exhaust system 11 comprises an exhaust pipe 17, with an inlet end 17.1 and an outlet end 17.2. The inlet end is connected to the combustion chamber 13.6 through the exhaust port(s) 13.5. The outlet end 17.2 is adapted to release into the environment the exhaust gases generated by the combustion of the fuel in the combustion chamber 13.6.

[0048] A catalytic converter (or pre-catalytic converter) 19 is arranged along the exhaust pipe 17. Downstream of the catalytic converter 19, with respect to the flow direction G of the exhaust gases in the exhaust pipe 17, a muffler or silencer 21 is arranged. Between the catalytic converter 19 and the silencer 21, or integrated into the latter, further elements (not shown) may be arranged to reduce the pollutants contained in the exhaust gases.

[0049] In a point in the exhaust pipe 17 placed upstream of the catalytic converter 19, between an inlet side 19.1 of the catalytic converter 19 and the exhaust port 13.5, there is a branch 23, or bifurcation, in which a resonant duct 25 of the exhaust is inserted into the exhaust pipe 17.

[0050] The resonant duct 25 of the exhaust extends from the branch 23 to a resonant cavity 27 of the exhaust. The resonant duct 25 of the exhaust and the resonant cavity 27 of the exhaust cumulatively form an exhaust resonator, herein also referred to as second resonator, overall indicated with 29.

[0051] In advantageous embodiments, as shown in Fig. 2, the resonant duct 25 of the exhaust and the exhaust pipe 17 form, in the area of the branch 23, an acute angle P, i.e. an angle less than 90° and preferably less than 45°.

[0052] In embodiments, in the area of the branch 23, the resonant duct 25 of the exhaust is approximately tangent to the exhaust pipe 17 in the mutual connection point, i.e. at the bifurcation 23. Approximately tangent in general means a configuration such that the overall flow of exhaust gases in the exhaust pipe 17 is approximately tangent to the flow in the resonant duct 25 of the exhaust. For example, the median lines, i.e. the axes of the exhaust pipe 17 and the resonant duct 25 of the exhaust may be tangent to each other. In Fig. 2 the axis or median line of the exhaust pipe 17 is indicated with 17.1 and the axis or median line of the resonant duct 25 of the exhaust is indicated with 25.1. The straight extension of the axis 25.1 is tangent to the curve defining the axis 17.1 of the exhaust pipe 17 in a point upstream of the bifurcation 23 with respect to the flow direction of the exhaust gas in the exhaust pipe 17.

[0053] During operation of the internal combustion engine 9, the opening and closing of the exhaust port due to the operation of the exhaust valve 13.9 in synchrony with the execution of the engine cycles causes pressure waves in the exhaust pipe 17. These pressure waves are reflected on the material contained in the catalytic converter 19 at the inlet end 19.1 of the latter, generating reflected pressure waves that propagate in the opposite direction with respect to the flow direction of the exhaust gas (arrow G in Fig. 2).

[0054] The reflected pressure waves cause an increase in the pressure at the exhaust port 13.5, which increases the back pressure at the outlet, which the combustion gases must overcome in the exhaust phase of the engine 9 operating cycle. This increase in back pressure due to the pressure waves reflected by the catalytic converter 19 negatively affects the efficiency of the engine 9, as the higher the back pressure, the lower the power output of the engine.

[0055] The second resonator 29 is configured to reduce or eliminate this negative effect due to the presence of the catalytic converter 19 in the exhaust pipe 17. To this end, the resonator 29 is sized so that, under normal operating conditions of the engine 9, i.e. in the rpm range at which the engine is usually maintained to maximize thetorque and / or power delivered, the resonator 29 resonates, generating pressure waves at the bifurcation 23 having the same frequency as the pressure waves reflected by the catalytic converter 19 and out of phase with respect to the reflected pressure waves.

[0056] The pressure waves reflected by the catalytic converter 19 and the pressure waves generated by resonance of the resonator 29, which pass through the resonant duct 25 substantially tangent to the exhaust pipe 17, tend to cancel each other out in the section of the exhaust pipe 17 between the exhaust port 13.5 and the bifurcation 23. This is because the pressure waves give rise to a destructive interference phenomenon.

[0057] In practice, the pressure waves generated in the second resonator 29 destroy the pressure waves reflected by the catalytic converter 19, or at least reduce the intensity thereof.

[0058] The end result of this phenomenon is a reduction or elimination of the negative effect of the reflected pressure waves in terms of increased back pressure at the exhaust port 13.5.

[0059] Typically, the use of the second resonator 29 is advantageous for reciprocating internal combustion engines which have for example an operating speed typically between 2400 rpm and 5000 rpm, and more specifically between 3600 rpm and 4200 rpm.

[0060] In some embodiments, the resonant cavity 27 of the exhaust may have a fundamental resonant frequency between 10 Hz and 30 Hz, preferably between 14 Hz and 18 Hz, even more preferably between 16 Hz and 18 Hz, at the temperature of the exhaust gases in steady state operating conditions of the internal combustion engine. Typically the fundamental resonance frequency may be around 16 + 7 Hz, where the variation in frequency is attributable to the variation in temperature of the exhaust gas which, by modifying the speed of sound in the exhaust gas, affects the fundamental resonance frequency, as defined above.

[0061] The chosen resonance frequency value of 16 - 18 Hz is linked to the idea of optimising the engine in maximum torque and in particular in maximum power. Since both advantages cannot be achieved with a fixed resonator geometry, it may beadvantageous to choose a resonance frequency adapted to provide a certain positive contribution to the maximum torque and which allows the energy contribution of the pressure waves to be used to best enhance the maximum power.

[0062] To do this, in the described embodiment, a resonator geometry was chosen that allows working between 16 and 18 Hz. In fact, at 2300 rpm of the engine, a fundamental frequency of the engine is obtained of 2250 (±50) / 60=37 Hz which corresponds approximately to a resonance frequency of the resonator of 37 / 2 =18 Hz (2 because it is a 4-stroke engine and the energy contribution occurs every 2 revolutions of the drive shaft).

[0063] As can be seen in Fig. 2, the resonant cavity 27 of the exhaust has a cross section greater than the cross section of the resonant duct 25. Typically, in particularly advantageous embodiments, the ratio of the cross-sectional area between the resonant cavity and the cross-sectional area of the resonant duct is between 35 and 55, preferably between 40 and 50, more preferably between 43 and 48.

[0064] In some embodiments, the resonant cavity 27 of the exhaust has a substantially cylindrical shape with a circular section, with a first diameter DI, and the resonant duct has a circular section with a second diameter D2, smaller than the first diameter DI.

[0065] The resonant cavity 27 may have, for example, an internal volume between 2800 and 3400 cm3, preferably between 3000 and 3200 cm3. In some embodiments the resonant duct has a length between 90 and 100 cm, preferably between 92 and 97 cm.

[0066] The connection point between the exhaust pipe 17 and the resonant duct 25 of the exhaust, i.e. the bifurcation 23, may be located at a distance of between 90 and 115 mm, preferably between 100 and 105 mm from the exhaust port 13.5.

[0067] Figures 5 to 10 show the results of experimental tests carried out on an APE 300 engine produced by the applicant, equipped with a first resonator 43 associated with the intake and possibly equipped with a second resonator 29 on the exhaust 11, made as described above.

[0068] In particular, the APE 300 engine used for the tests illustrated herein is a four-stroke Otto cycle engine with the following features:- number of cylinders: 1- liquid cooling- number of valves per cylinder: 2- cylinder inclination: 75°- aluminium cylinder head- cylinder material: cast iron- displacement: 306 cm3- compression ratio 9.5+ / -0.5: 1- bore x stroke: 72 x 75 mm.

[0069] The exhaust system 11 used for the tests was configured as follows:- resonant duct length: 950 mm- internal diameter D2 of the resonant duct: 19 mm- internal volume of the resonant cavity 27: 3150 cm3- axial length of the resonant cavity 27: 245 mm- external diameter of the resonant cavity 27: 130 mm- thickness of the resonant cavity 27 sheet: 1.2 mm- distance of the bifurcation 23 from the exhaust port: 100 mm- section of the resonant duct 25 and the resonant cavity 27: circular

[0070] The first resonator 43 on the intake system 43 used for the test was configured as follows:- internal volume of the resonant cavity 46: 1200 cc- resonant duct 47 length: 300 mm- internal diameter of the resonant duct 47: 12 mm- minimum diameter of the intake port 13.8: 12 mm

[0071] In the diagram in Fig. 5 the values of the rotation speed in rpm of the engine 9 are shown on the X axis, and on the Y axis on the left the power delivered in kW and on the right the torque delivered in Nm. The curves W0 and CO represent the power and torque delivered by the engine without both resonant systems 43 and 29, respectively. The curves W1 and Cl represent the power and torque delivered by the engine equipped with only the first resonator 43 associated with the intake system 10, respectively. The curves W2 and C2 represent the power and torque delivered by the engine equipped with only the second resonator 29 associated with the exhaust system 11,respectively.

[0072] Fig. 5 shows that at any rpm value between approximately 2400 rpm and approximately 5000 rpm both the torque C2 and the power W2 are higher than the torque and power delivered by the same engine without the resonator. Similar advantages may be seen when observing the curves Cl and Wl, although the advantages are perceptible starting from higher values of the engine 9 rpm.

[0073] The diagram in Fig. 5 therefore shows how the resonators described herein provide advantages in terms of engine efficiency.

[0074] Similar advantages may be seen in terms of reduced consumption. The diagram in Fig. 6 shows the rotation speed (rpm) of the engine on the X axis. The specific fuel consumption expressed in g / kWh is shown on the left Y axis. The hourly fuel consumption in kg / h is shown on the right side.

[0075] The curve ChO and the curve CsO represent, respectively, the hourly consumption and the specific consumption of the engine without the resonators 43 and 29. The curves Chi and Csl represent, respectively, the hourly consumption and the specific consumption of the engine equipped with the first resonator 43, while the curves Ch2 and Cs2 represent, respectively, the hourly consumption and the specific consumption of the engine equipped with the second resonant system 29.

[0076] Both the hourly consumption and the specific consumption are approximately reduced in the case of using the resonator 29 and also in the case of using the resonator 43. Advantages are achieved in particular in the useful rotation speed range between approximately 2400 rpm and approximately 5000 rpm.

[0077] Figs. 7 and 8 show diagrams indicating the same quantities as Figs. 5 and 6, but with a comparison between the operation of the engine 9 in the absence of resonant systems (curves CO, ChO and CsO) and with the presence of both resonant systems 43 and 29.

[0078] Figs. 9 and 10 illustrate diagrams of volume and pressure as a function of the rotation angle of the drive shaft under different conditions of partial closure of the throttle valve 39. Fig. 9 refers to a situation detected with the engine rotating at 3000 rpm and with the throttle valve 39 open by 10%. Fig. 10 refers to a situation with thesame rpm and the throttle valve open by 20%.

[0079] The angular position of the drive shaft is shown on the x axis. The curve XI represents the volume of the combustion chamber 13.6 and is obviously the same in the two diagrams. The curve X2 represents the opening and closing movement of the intake valve 13.8, which is also the same in the two diagrams. The curve X3 represents the pressure trend in the intake pipe 37 at the area where the injector 41 is positioned, in the presence of the first resonator 43. The curve X4 represents the pressure trend in the intake pipe, at the area where injector 41 is positioned, in the absence of a resonator. The curve X5 shows the pressure trend in the combustion chamber in the presence of the resonator 43. Lastly, the curve X6 shows the pressure trend in the combustion chamber in the absence of the resonator 43.

[0080] The curves in Figs. 9 and 10 clearly show that the presence of the resonator 43 leads to an increase in pressure in the intake pipe during the opening phase of the intake valve and a consequent higher pressure in the combustion chamber, which corresponds to a greater degree of filling of the combustion chamber and therefore a better use of the fuel in the case in which the resonator 43 combined with the intake system 10 is present.

[0081] The diagrams in Figs. 3 and 4 schematically represent a vortex V generated by the presence of the resonator 43, a vortex which promotes the mixing of air and fuel and therefore improves the homogeneity of the air-fuel mixture in the combustion chamber. This results in improved combustion and a reduction in unburned fuel, as well as an over-powering effect.

[0082] The effects summarised above result in the best engine operating conditions, with a reduction in fuel consumption for the same power delivered.

[0083] The positive effects of the presence of the resonator 43 decrease as the degree of opening of the throttle valve increases.

[0084] Fig. 11 shows an improved embodiment, in which the first resonator 43 is combined with the air filter 35. In this embodiment, the air filter 35 is housed inside the resonator 46, which has an inlet 33 connected to the grille 31. The inlet 33 does not interfere with the operation of the resonator. The housing of the air filter 35 insidethe volume of the resonant cavity 46 of the first resonator 43 is advantageous because it entails a cooling of the air filter box and a more compact configuration of the intake system.

[0085] In a particular embodiment (not shown) of the present invention, it is envis- aged to inject small quantities of demineralized water from a tank installed on the vehicle 1 into the resonator 43. Since the pressure inside the volume of the resonant cavity 46 is lower than the atmospheric pressure, and since this volume is heated by the nearby engine, the demineralized water evaporates and the sound waves exiting from the resonator 43 move, in addition to the air, small quantities of water vapour which, entering the combustion chamber, prevent the formation of oxides. Thereby the quantity of NOx produced as a result of the high temperatures in the combustion chamber is drastically reduced.

Claims

Claims1. An internal combustion engine (9), comprising: at least one cylinder-piston system (13) comprising: an intake port (13.4) into which an intake valve (13.8) is positioned; and an exhaust port (13.5) into which an exhaust valve (13.9) is positioned; an intake pipe (37) fluidly coupled with the intake port (13.4); and a throttle valve (39) positioned along the intake pipe (37); characterisedcomprising a first resonator (43) connected to the intake pipe (37); wherein the first resonator (43) comprises a resonant cavity (46) having a resonant volume placed in direct fluid coupling only with a resonant duct (47) and, by means of the resonant duct (47), with the intake pipe (37), in a position between the throttle valve (39) and the intake valve (13.8).

2. The internal combustion engine (9) of claim 1, wherein the resonant duct comprises an end portion connected to the intake pipe (37); wherein preferably the end portion of the resonant duct (47) is straight.

3. The internal combustion engine (9) of claim 1 or 2, comprising a fuel injector (41) positioned between a connection point of the resonant duct (47) to the intake pipe (37) and the intake port (13.4).

4. The internal combustion engine (9) of claim 3, wherein the connection point of the resonant duct (47) to the intake pipe (37) is placed close to the fuel injector (41), preferably at approximately 10 mm, so that a pressure wave coming from the resonant duct (47) hits a fuel charge delivered from the fuel injector (41) pushing it towards the intake port (13.4).

5. The internal combustion engine (9) of any one of claims 2 to 4, wherein the end portion of the resonant duct (47) is approximately tangent to the intake pipe (37) at the connection point between the resonant duct and the intake pipe.

6. The internal combustion engine (9) of one of claims 2 to 5, wherein the resonant duct (47) is positioned, with respect to the intake pipe (37), the intake port (13.4) and the intake valve (13.8), such that the intake valve (13.8) is visible from inside the end portion of the resonant duct (47).

7. The internal combustion engine (9) of any one of claims 2 to 6, wherein the resonant cavity (46) has a cross section greater than the cross section of the resonant duct (47), preferably the ratio between the cross-sectional area of the resonant cavity (46) and the cross-sectional area of the resonant duct (47) is between 5 and 20.

8. The internal combustion engine (9) of any one of claims 2 to 7, wherein the resonant cavity (46) has a substantially cylindrical shape with a circular or prismatic section, with a first cross section, and the resonant duct (47) has a circular section with a second cross section, smaller than the first cross section.

9. The internal combustion engine (9) of any one of the preceding claims, wherein the intake pipe (37) and the intake port (13.4) have a substantially constant cross section between the connection point of the resonant duct (47) and the intake valve (13.8).

10. The internal combustion engine (9) of any one of the preceding claims, wherein the intake pipe (37) is fluidly coupled with an air filter (35); wherein preferably the air filter (35) is housed inside the resonant cavity (46) of the first resonator (43).

11. The internal combustion engine (9) of any one of the preceding claims, comprising a second resonator (29) connected to an exhaust pipe (17); wherein preferably the second resonator (29) comprises a resonant duct of the exhaust (25) and a resonant cavity of the exhaust (27); wherein preferably the resonant duct of the exhaust (25) places the exhaust pipe (17) fluidly coupled with the resonant cavity of the exhaust (27); wherein preferably the resonant duct of the exhaust (25) is connected to the exhaust pipe (17) upstream of a catalytic converter (19), placed in the exhaust pipe (17), with respect to the direction of flow of the exhaust gases along the exhaust pipe (17).

12. The internal combustion engine (9) of claim 11, wherein the resonant duct of the exhaust (25) is approximately tangent to the exhaust pipe (17) in connection point between the resonant duct of the exhaust (25) and the exhaust pipe (17).

13. The internal combustion engine (9) of claim 11 or 12, wherein the exhaust pipe (17) and the resonant duct of the exhaust (25) are configured such that the total flow of exhaust gases in the exhaust pipe (17) is approximately tangent to theflow in the resonant duct of the exhaust (25).

14. The internal combustion engine (9) of any one of claims 11 to 13, comprising one or more of the following features: the axis of the exhaust pipe (17) and the axis of the resonant duct of the exhaust (25) are tangent to each other in the connection point between the resonant duct of the exhaust (25) and the exhaust pipe (17); the second resonator (29) is sized so that pressure waves form in the connection point between the resonant duct of the exhaust (25) and the exhaust pipe (27), generated in the second resonant system (29), out of phase with respect to the pressure waves generated in the exhaust pipe (17) by the catalytic converter (19); the resonant cavity of the exhaust (27) has a fundamental resonant frequency between 10 Hz and 30 Hz, preferably between 14 Hz and 18 Hz, even more preferably between 16Hz and 18 Hz at the temperature of the exhaust gases in steady state operating conditions of the internal combustion engine; the resonant cavity of the exhaust (27) has a cross section greater than the cross section of the resonant duct of the exhaust (25); the resonant cavity of the exhaust (27) has an internal volume between 2800 and 3400 cm3, preferably between 3000 and 3200 cm3.

15. The internal combustion engine (9) of any one of the preceding claims, wherein the resonator (43) is a Helmholtz resonator.

16. A vehicle (1) comprising an internal combustion engine (9) as claimed in any one of the preceding claims.

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