Engine with resonator on the exhaust pipe and vehicle comprising said engine

Abstract

The internal combustion engine 9 comprises at least one piston¬ cylinder system 13 with a suction port and an exhaust port. An exhaust pipe 17, along which a catalytic converter 19 and a silencer 21 are arranged in sequence, is connected to the exhaust port 13.5. The catalytic converter 19 is placed upstream of the silencer 21 with respect to the direction of exhaust gas flow along the exhaust pipe 17. A resonant system 29 is connected to the exhaust pipe 17, and comprises a resonant tube 25 and a resonant cavity 27. The resonant tube 25 places the exhaust pipe 17 in fluid connection with the resonant cavity 27, and the resonant tube 25 is connected to the exhaust pipe 17 upstream of the catalytic converter 19 with respect to the direction of exhaust gas flow along the exhaust pipe 17. The resonant tube 25 is tangent to the exhaust pipe 17 at their connection point 23.

Description

ENGINE WITH RESONATOR ON THE EXHAUST PIPE AND VEHICLECOMPRISING SAID ENGINEDESCRIPTIONTECHNICAL FIELD

[0001] The present invention relates to improvements to internal combustion engines. In particular, the present invention relates to improvements to exhaust systems of reciprocating internal combustion engines.BACKGROUND ART

[0002] Internal combustion engines, in particular reciprocating internal combustion engines, comprising piston-cylinder systems for mechanical power generation, are widely used in the automotive sector. The use of fuel to supply internal combustion engines has an environmental impact also due to the presence of unburnt fuel and other impurities in the combustion gas.

[0003] In order to reduce environmental pollution, catalytic converter devices are increasingly used on the exhaust pipe, upstream of the silencer; these devices are configured to remove pollutants from the exhaust gases coming from the combustion chamber or chambers of the engine, before releasing the exhaust gases into the environment.

[0004] Catalytic converters, also call cat converters, in particular convert carbon monoxide (CO) into carbon dioxide (CO2) and convert unburnt hydrocarbons into steam and carbon dioxide, through oxidization processes. Catalytic converters also have the function of converting nitrogen oxides (NOx) into nitrogen (N2) and oxygen, through a reduction reaction.

[0005] Catalytic converters fitted in the exhaust pipe provide valuable assistance in reducing pollutants released into the atmosphere, but have a negative impact in terms of engine performance, as their presence in the exhaust pipe generates pressure waves in the exhaust gas flow, which are reflected toward the exhaust port or ports of the engine. These pressure waves increase the exhaust pressure of the engine and therefore reduce the efficiency thereof. Reduced efficiency of the internal combustion enginenegatively affects fuel consumption and hence, ultimately, environmental impact.

[0006] Internal combustion engines with resonators connected to the exhaust pipe, upstream of the catalytic converter are disclosed in EP1939415, EP2163739 and EP0554875. These prior art devices comprise a resonator connected to the exhaust pipe through a connection orthogonal to the exhaust pipe. These systems do not solve the problem indicated above in an efficient manner.

[0007] The invention intends to reduce the abovementioned drawbacks of reciprocating internal combustion engines equipped with catalytic converter.SUMMARY

[0008] According to an aspect, to completely or partly solve the problems of the prior art, described herein is an internal combustion engine, comprising at least one pistoncylinder system with a suction port and an exhaust port, wherein an exhaust pipe, along which a catalytic converter and a silencer are arranged in sequence, is connected to the exhaust port. The catalytic converter is placed upstream of the silencer with respect to the direction of exhaust gas flow along the exhaust pipe. Characteristically, the engine comprises a resonant system connected to the exhaust pipe. The resonant system comprises a resonant tube and a resonant cavity. The resonant tube places the exhaust pipe in fluid connection with the resonant cavity and the resonant tube is connected to the exhaust pipe upstream of the catalytic converter with respect to the direction of exhaust gas flow along the exhaust pipe. In illustrated embodiments, the resonant tube and the resonant cavity have different cross sections, the resonant tube having a cross section smaller than the cross section of the resonant cavity.

[0009] Advantageously, the resonant tube is approximately tangent to the exhaust pipe in the connection point between resonant tube and exhaust pipe.

[0010] Further advantageous features and embodiments of the engine according to the invention are described below and defined in the appended dependent clams.

[0011] The invention also relates to a motor vehicle comprising an engine as defined above.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention will now be better understood by following the description and the accompanying drawings, which illustrate by way of example a non-limiting embodiment of the invention. More in particular, in the drawing:Fig.1 shows a side view of a vehicle equipped with an engine according to the invention;Fig.2 shows a schematic view of the engine according to the invention, complete with exhaust system;Figs. 3 and 4 show experimental diagrams relating to the features of the engine according to the invention;Fig.5 shows a diagram of an improved resonant cavity; andFig.6 shows a diagram of an exhaust system according to the invention in a further embodiment.DETAILED DESCRIPTION

[0013] Fig. l schematically shows a commercial vehicle on which an engine of the type described can be installed. The vehicle 1 can, for example, comprise a single front steered wheel 3 or two front steered wheels 3, and a pair of rear drive wheels 5.

[0014] Fig.2 schematically illustrates an engine 9 that can be installed in the vehicle 1. The engine 9 comprises an exhaust system indicated as a whole with 11 and a pistoncylinder system 13, which can comprise a single cylinder 13.1 in which a piston 13.2 is slidingly housed. Reference number 13.3 indicates a connecting rod-crankshaft system that converts the reciprocating motion of the piston 13.2 in the cylinder 13.1 into a rotary motion of the output shaft. Reference number 13.4 indicates a suction port and reference number 13.5 indicates an exhaust port of the piston-cylinder system 13. The reference number 13.6 indicates the combustion chamber defined within the cylinder 13.1.

[0015] Although the present description refers to an engine with a single pistoncylinder and single suction and exhaust ports, it would also be possible to produce the engine 9 with a plurality of piston-cylinder systems and / or to provide more than one suction port and / or more than one exhaust port.

[0016] The exhaust system 11 comprises an exhaust pipe 17, with an input end 17.1 and an output end 17.2. The input end is connected to the combustion chamber 13.6 through the exhaust port or ports 13.5. The output end 17.2 is capable of releasing the exhaust gases, generated by the combustion of fuel in the combustion chamber 13.6, into the environment.

[0017] A catalytic converter (or pre-catalytic converter) 19 is arranged along the exhaust pipe 17. An exhaust or silencer 21 is arranged downstream of the catalytic converter 19, with respect to the direction of exhaust gas flow G in the exhaust pipe 17a. Further elements for reducing the pollutants contained in the exhaust gases (not shown) can be arranged between the catalytic converter 19 and the silencer 21, or can be integrated into the latter.

[0018] A branch 23, into which a resonant tube 25 merges in the exhaust pipe 17, is placed in a point of the exhaust pipe 17 upstream of the catalytic converter 19, between an input side 19.1 of the catalytic converter 19 and the exhaust port 13.5.

[0019] The resonant tube 25 extends from the branch 23 to a resonant cavity 27. The resonant tube 25 and the resonant cavity 27 together form a resonant system indicated as a whole with 29.

[0020] In advantageous embodiments, as represented in Fig.2, the resonant tube 25 is approximately tangent to the exhaust pipe 17 in the mutual connection point, i.e., at the fork 23. Approximately tangent is meant in general as a configuration such that the total flow of exhaust gas in the exhaust pipe 17 is approximately tangent to the flow in the resonant tube 25. For example, the median lines, i.e., the axes of the exhaust pipe 17 and of the resonant tube 25 can 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 tube 25 is indicated with 25.1. The rectilinear extension of the axis 25.1 is tangent to the curve defining the axis 17.1 of the exhaust pipe in a point upstream of the fork 23 with respect to the direction of flow of the exhaust gas in the exhaust pipe 17.

[0021] During operation of the internal combustion engine 9, opening and closing of the exhaust port due to operation of the exhaust valve (not shown) synchronized with the engine cycles causes pressure waves in the exhaust pipe 17. These pressure wavesreflect on the material contained in the catalytic converter 19 at the input end 19.1 of the latter, generating reflected pressure waves that propagate in a direction opposite to the direction of exhaust gas flow (arrow G in Fig.2).

[0022] The reflected pressure waves cause a pressure increase at the exhaust port 13.5, which increases the back pressure at the output, which the combustion gases must overcome in the exhaust phase of the operating cycle of the engine 9. This back pressure increase caused by the pressure waves reflected by the catalytic converter 19 negatively affects the output of the engine 9, as the greater the back pressure, the lower the output in terms of engine power.

[0023] The resonant system 29 is configured to reduce or eliminate this negative effect caused by the presence of the catalytic converter 19 in the exhaust pipe 17. To this end, the resonant system 29 is sized such that, in normal conditions of use of the engine 9, i.e., in the range of rpm at which the engine is normally maintained to maximize the torque and / or the power delivered, the resonant system 29 resounds generating pressure waves at the fork 23 having the same frequency as the pressure waves reflected by the catalytic converter 19 and in counterphase with respect to the reflected pressure waves.

[0024] The pressure waves reflected by the catalytic converter 19 and the pressure waves generated through resonance of the resonant system 29, which pass through the resonant tube 25 substantially tangent to the exhaust pipe 17, tend to cancel each other out in the section of exhaust pipe 17 between the exhaust port 13.5 and the fork 23. This is because the pressure waves give rise to a phenomenon of destructive interference.

[0025] In practice, the pressure waves that are generated in the resonant system 29 destroy, or at least reduce the intensity of, the pressure waves reflected by the catalytic converter 19.

[0026] The final result of this phenomenon is a reduction or an elimination of the negative effect of the reflected pressure waves in terms of increase of back pressure at the exhaust port 13.5.

[0027] Typically, the solution proposed herein is advantageous for reciprocatinginternal combustion engines that have, for example, a steady-state operating condition typically between 2400 rpm and 5000 rpm, and more in particular between 3600 rpm and 4200 rpm.

[0028] In some embodiments, the resonant cavity 27 can have a fundamental resonance 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 exhaust gas temperature under steady-state operating conditions of the internal combustion engine. Typically, the fundamental resonance frequency can be around 16 + 7 Hz, where the frequency variation is due to the temperature variation of the exhaust gas which, by changing the speed of sound in the exhaust gas, affects the fundamental resonance frequency. The latter is, in fact, given by the formulawherein: c is the speed of sound in the fluid medium contained in the resonant system, said speed c being a function of the temperature and of the ratio of the specific heat at constant pressure to the specific heat at constant volume;S is the cross section of the tube 25L is the length of the tube 25V is the volume of the resonant cavity.

[0029] The value of 16 - 18 Hz of the resonance frequency is linked to the idea of optimizing the maximum torque and in particular the maximum power of the engine. As with a fixed geometry of the resonator it is not possible to obtain the two advantages, it may be advantageous to choose a resonance frequency value capable of providing a certain positive contribution to the maximum torque and which allows the best use of the energy contribution of the pressure waves to enhance the maximum power.

[0030] To do this, in the described embodiment a geometry of the resonator that allows operation between 16 and 18 Hz has been chosen. In fact, at 2300 rpm of the engine a fundamental frequency of the engine of 2250 (±50) / 60=37 Hz is obtained,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 is obtained every 2 revolutions of the drive shaft). In practice, through a numerical simulator, the size of the resonator can be configured such that, through the Helmholtz relation, the resonance frequency is equal to approximately 16 Hz. With this optimized geometry it is possible to exploit the energy contribution of the first order frequency (16 - 18 Hz) to obtain an increase in torque and a multiple of this frequency to enhance the maximum power. In fact, the maximum power with the resonator is achieved at approximately 4300 rpm and the fundamental frequency of the engine is approximately 4300 / 60=71 Hz, i.e., a resonance frequency of approximately 71 / 2=36 Hz which is exactly twice the first order resonance frequency mentioned above.

[0031] Ultimately, a system was obtained which has a relatively wide bandwidth for a low speed engine category such as an APE 300 engine, the main features of which are indicated below.

[0032] As can be seen in Fig. 2, the resonant cavity 27 has a cross section which is greater than the cross section of the resonant tube 25. Typically, in particularly advantageous embodiments, the ratio of the cross-sectional area of the resonant cavity to the cross-sectional area of the resonant tube is between 35 and 55, preferably between 40 and 50, more preferably between 43 and 48.

[0033] In some embodiments, the resonant cavity 27 has a substantially cylindrical shape with a circular cross section, with a first diameter DI, and the resonant tube has a circular cross section with a second diameter D2, smaller than the first diameter DI .

[0034] The resonant cavity 27 can, for example, have an internal volume between 2800 and 3400 cm3, preferably between 3000 and 3200 cm3. In some embodiments, the resonant tube has a length between 90 and 100 cm, preferably between 92 and 97 cm.

[0035] The connection point between the exhaust pipe 17 and the resonant tube 25, i.e., the fork 23, can be at a distance between 90 and 115 mm, preferably between 100 and 105 mm, from the exhaust port 13.5.

[0036] Figs. 3 and 4 show the results of experimental tests performed on an APE 300engine manufactured by the Applicant, equipped with an exhaust system 11 as shown in Fig. 2. In particular, the APE 300 engine is a 4-stroke Otto cycle engine with the following features: number of cylinders: 1 liquid cooled number of valves per cylinder: 2 cylinder angle: 75° aluminium cylinder head cylinder material: cast iron engine displacement: 306 cm3compression ratio 9.5+ / -0.5: 1 bore x stroke: 72 x 75 mm.

[0037] The exhaust system used for the test was configured as follows:- length of the resonant tube: 950 mm- inner diameter D2 of the resonant tube: 19 mm- inner volume of the resonant cavity 27: 3150 cm3- axial length of the resonant cavity 27: 245 mm- outer diameter of the resonant cavity 27: 130 mm- thickness of the sheet metal of the resonant cavity 27: 1.2 mm- distance of the fork 23 from the exhaust port: 100 mm- cross section of the resonant tube 25 and of the resonant cavity 27: circular

[0038] The diagram of Fig.3 indicates on the abscissa the values of the rotational speed in rpm and on the ordinate on the left the power delivered in kW and on the right the torque delivered in Nm. The curves W0 and CO respectively represent the power and the torque delivered by the engine without the resonant system 11. The curve W 1 and Cl respectively represent the power and the torque delivered by the engine equipped with the resonant system 11.

[0039] In Fig. 3 it can be seen that at any value of rpm between approximately 2400 rpm and approximately 5000 rpm both the torque Cl and the power W1 are higher than the torque and the power delivered by the same engine without the resonant system.

[0040] Therefore, the diagram of Fig.3 shows how the resonant system described herein provides advantages in terms of engine efficiency.

[0041] Similar advantages can be obtained in terms of reduction of consumption. The diagram of Fig.4 indicates on the abscissa the rotational speed (rpm) of the engine. On the ordinate the specific fuel consumption expressed in g / kWh is indicated on the left, while the hourly fuel consumption in kg / h is indicated on the right.

[0042] The curve ChO and the curve CsO respectively indicate the hourly consumption and the specific consumption of the engine without the resonant system 11. The curves Chi and Csl respectively indicate the hourly consumption and the specific consumption of the engine provided with the resonant system 11. Both the hourly consumption and the specific consumption are reduced by approximately 4-5% in the case of use of the resonant system 11 in all the useful rotational speed range, between approximately 2400 rpm and approximately 5000 rpm.

[0043] The efficiency of the vehicle 1 on which the engine 9 is installed can be further improved by associating an electrical generator with the resonant system 11. This can be implemented using an electrical generator 31, for example a linear alternator, installed on a base 27.1 of the resonant cavity 27, as shown schematically in Fig.5. The linear alternator 31 converts the energy transmitted by the vibrating base 27.1 of the resonant cavity 27 to the moving component of the linear alternator 31. The electrical energy generated can be converted into direct current in a rectifier 35 placed on an electrical line 33 connecting the linear alternator 31 to a battery 37 of the vehicle 1.

[0044] Fig. 6 shows a further embodiment of the exhaust system according to the invention. The same numbers indicate parts which are identical or equivalent to those shown in Fig. 2 and described above. The exhaust system 11 of Fig.6 differs from the exhaust system 11 of Fig. 2 mainly in that the resonant cavity 27 is integrated into a single block 20 into which the exhaust or silencer 21 is also inserted. The silencer 21 and the resonant cavity 27 are appropriately separated from each other, for example by a metal sheet 22, to prevent the flows in the silencer and in the resonant cavity from interacting with each other.

Claims

Claims1. An internal combustion engine, comprising: at least one piston-cylinder system with a suction port and an exhaust port, wherein an exhaust pipe, along which a catalytic converter and a silencer are arranged in sequence, is connected to the exhaust port, the catalytic converter being placed upstream of the silencer with respect to the direction of exhaust gas flow along the exhaust pipe; a resonant system connected to the exhaust pipe, wherein the resonant system comprises a resonant tube and a resonant cavity, wherein the resonant tube fluidly couples the exhaust pipe with the resonant cavity; wherein the resonant tube is connected to the exhaust pipe upstream of the catalytic converter with respect to the direction of exhaust gas flow along the exhaust pipe; characterized in that the resonant tube is approximately tangent to the exhaust pipe at the connection point between the resonant tube and the exhaust pipe.

2. The internal combustion engine of claim 1, wherein the exhaust pipe and the resonant tube are configured so that the overall flow of exhaust gas in the exhaust pipe is approximately tangent to the flow in the resonant tube.

3. The internal combustion engine of claim 1 or 2, wherein the axis of the exhaust pipe and the axis of the resonant tube are tangent to each other at the connection point between the resonant tube and the exhaust pipe.

4. The internal combustion engine of any one of the preceding claims, wherein the resonant system is sized such that pressure waves, generated in the resonant system, are formed at the connection point between the resonant tube and the exhaust pipe in counterphase with respect to pressure waves generated in the exhaust pipe by the catalytic converter.

5. The internal combustion engine of any one of the preceding claims, wherein the resonant cavity has a first 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 exhaust gas temperature under steady-state operating conditions of the internal combustion engine.

6. The internal combustion engine of any one of the preceding claims, wherein: the resonant cavity has a cross section greater than the cross section of the resonant tube.

7. The internal combustion engine of claim 6, wherein the ratio of the cross-sectional area of the resonant cavity to the cross-sectional area of the resonant tube is between 35 and 55, preferably between 40 and 50, more preferably between 43 and 48.

8. The internal combustion engine of claim 6 or 7, wherein the resonant cavity has a substantially cylindrical shape with a circular cross section, with a first diameter, and the resonant tube has a circular cross section with a second diameter, smaller than the first diameter.

9. The internal combustion engine of any one of the preceding claims, wherein the resonant cavity has an internal volume between 2800 and 3400 cm3, preferably between 3000 and 3200 cm3.

10. The internal combustion engine of any one of the preceding claims, wherein the resonant tube has a length between 90 and 100 cm, preferably between 92 and 97 cm.

11. The internal combustion engine of any one of the preceding claims, wherein the connection point between the exhaust pipe and the resonant tube is between 90 and 115 mm, preferably between 100 and 105 mm from the exhaust port of the cylinder.

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

13. The internal combustion engine of any one of the preceding claims, wherein the resonant cavity is coupled with an electric generator driven by the vibration of a wall of the resonant cavity and capable of converting the mechanical energy transmitted to the electric generator into electrical energy.

14. The internal combustion engine of any one of the preceding claims,wherein the resonant cavity is integrated into a block containing the silencer.

15. A vehicle comprising an internal combustion engine as claimed in one or more of the preceding claims.

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