Engine with resonator on exhaust pipe and vehicle comprising said engine

Abstract

An internal combustion engine 9 comprises at least one piston-cylinder system 13 having an intake port and an exhaust port. An exhaust pipe 17 is connected to the exhaust port 13.5, and a catalytic converter 19 and a muffler 21 are arranged in this order along the exhaust pipe. The catalytic converter 19 is located upstream of the muffler 21 with respect to the exhaust gas flow direction along the exhaust pipe 17. The resonant system 29 is connected to the exhaust pipe 17 and includes a resonant pipe 25 and a resonant cavity 27. A resonant tube 25 fluidly couples the exhaust pipe 17 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 an exhaust gas flow direction along the exhaust pipe 17. The resonant tube 25 and the exhaust tube 17 are tangent at the connection position thereof.

Description

Technical Field

[0001] The present invention relates to improvements to internal combustion engines. In particular, the present invention relates to improvements to the exhaust system of a reciprocating internal combustion engine. Background Art

[0002] Internal combustion engines, specifically reciprocating engines, comprise a piston-cylinder system for generating mechanical power and are widely used in the automotive industry. The use of fuel to power internal combustion engines also has an impact on the environment due to the presence of unburned fuel and other impurities in the combustion gases.

[0003] In order to reduce environmental pollution, catalytic converter devices are increasingly being used on exhaust pipes (upstream of the muffler); these devices are configured to remove pollutants from the exhaust gas from the engine's combustion chamber before releasing it into the environment.

[0004] The catalytic converter, also known as the catalytic converter, specifically converts carbon monoxide (CO) into carbon dioxide (CO2) through an oxidation process and converts unburned hydrocarbons into steam and carbon dioxide. The catalytic converter also has the function of converting nitrogen oxides (NO x ) into nitrogen (N2) and oxygen.

[0005] Catalytic converters installed in exhaust pipes provide valuable assistance in reducing pollutants released into the atmosphere, but they can negatively impact engine performance because their presence in the exhaust pipe creates pressure waves in the exhaust stream that are reflected toward the engine's exhaust port. These pressure waves increase the engine's exhaust pressure and, therefore, reduce the engine's efficiency. Reduced efficiency in internal combustion engines negatively impacts fuel consumption and, ultimately, the environment.

[0006] EP1939415, EP2163739, and EP0554875 disclose internal combustion engines having a resonator connected to the exhaust pipe upstream of the catalytic converter. These prior art devices include a resonator connected to the exhaust pipe by connecting it orthogonally to the exhaust pipe. These systems do not effectively address the above-mentioned problems.

[0007] The present invention aims to alleviate the above-mentioned disadvantages of reciprocating internal combustion engines equipped with a catalytic converter. Summary of the Invention

[0008] According to one aspect, in order to fully or partially solve the problems of the prior art, an internal combustion engine is described herein, which includes at least one piston-cylinder system having an intake port and an exhaust port, wherein an exhaust pipe is connected to the exhaust port, and a catalytic converter and a muffler are arranged in sequence along the exhaust pipe. The catalytic converter is located upstream of the muffler with respect to the exhaust gas flow direction along the exhaust pipe. Characteristically, the engine includes a resonance system connected to the exhaust pipe. The resonance system includes a resonance pipe and a resonance cavity. The resonance pipe fluidically connects the exhaust pipe to the resonance cavity, and the resonance pipe is connected to the exhaust pipe upstream of the catalytic converter with respect to the exhaust gas flow direction along the exhaust pipe. In the illustrated embodiment, the resonance pipe and the resonator have different cross-sections, and the cross-section of the resonance pipe is smaller than the cross-section of the resonator.

[0009] Advantageously, the resonance pipe is approximately tangential to the exhaust pipe at a connection point between the resonance pipe and the exhaust pipe.

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

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

[0012] The present invention will now be better understood by reference to the following description and accompanying drawings, which illustrate, by way of example, non-limiting embodiments of the present invention. More particularly, in the drawings:

[0013] Figure 1 shows a side view of a vehicle equipped with an engine according to the present invention;

[0014] Figure 2 shows a schematic diagram of an engine according to the invention, complete with exhaust system;

[0015] Figure 3 and Figure 4 shows experimental diagrams related to the characteristics of the engine according to the present invention;

[0016] Figure 5 A diagram showing an improved resonant cavity; and

[0017] Figure 6 A view showing an exhaust system according to the invention in a further exemplary embodiment is shown. DETAILED DESCRIPTION

[0018] Figure 1 A commercial vehicle is schematically shown on which an engine of the described type may be mounted. The vehicle 1 may, for example, comprise a single front steered wheel 3 or two front steered wheels 3 and a pair of rear drive wheels 5.

[0019] Figure 2An engine 9 that can be installed in a vehicle 1 is schematically shown. The engine 9 includes an exhaust system, generally designated 11, and a piston-cylinder system 13. The piston-cylinder system 13 may include a single cylinder 13.1 in which a piston 13.2 is slidably accommodated. Reference numeral 13.3 denotes a connecting rod-crankshaft system that converts the reciprocating motion of the piston 13.2 within the cylinder 13.1 into the rotational motion of the output shaft. Reference numeral 13.4 denotes an intake port of the piston-cylinder system 13, and reference numeral 13.5 denotes an exhaust port of the piston-cylinder system 13. Reference numeral 13.6 denotes a combustion chamber defined within the cylinder 13.1.

[0020] Although the present description relates to an engine having a single piston-cylinder and single intake and exhaust ports, it is also possible to produce engines 9 having multiple piston-cylinder systems and / or providing more than one intake port and / or more than one exhaust port.

[0021] The exhaust system 11 includes an exhaust pipe 17 having an input end 17.1 and an output end 17.2. The input end is connected to the combustion chamber 13.6 via the exhaust port 13.5. The output end 17.2 can release the exhaust gas generated by the combustion of the fuel in the combustion chamber 13.6 into the environment.

[0022] A catalytic converter (or pre-catalytic converter) 19 is arranged along the exhaust pipe 17. An exhaust or muffler 21 is arranged downstream of the catalytic converter 19 with respect to the exhaust gas flow direction G in the exhaust pipe 17a. Further elements (not shown) for reducing pollutants contained in the exhaust gas may be arranged between the catalytic converter 19 and the muffler 21 or may be integrated into the latter.

[0023] The branch 23 merging into the resonance pipe 25 in the exhaust pipe 17 is located at a point in the exhaust pipe 17 upstream of the catalytic converter 19 , between the inlet side 19 . 1 of the catalytic converter 19 and the exhaust port 13 . 5 .

[0024] The resonance pipe 25 extends from the branch 23 to the resonance cavity 27. The resonance pipe 25 and the resonance cavity 27 together form a resonance system as a whole, which is indicated by 29.

[0025] In an advantageous embodiment, as Figure 2 As shown, the resonance pipe 25 and the exhaust pipe 17 are approximately tangent at the location where they are connected to each other (i.e., at the bifurcation 23). Approximately tangent generally means the following configuration, that is, making the total exhaust flow in the exhaust pipe 17 approximately tangent to the flow in the resonance pipe 25. For example, the center lines, that is, the axis of the exhaust pipe 17 and the axis of the resonance pipe 25, can be tangent to each other. Figure 21 , the axis or centerline of the exhaust pipe 17 is indicated by 17.1, and the axis or centerline of the resonance pipe 25 is indicated by 25.1. A straight extension of the axis 25.1 is tangent to the curve defining the axis 17.1 of the exhaust pipe at a position upstream of the bifurcation 23, the position upstream of the bifurcation 23 being relative to the exhaust gas flow direction in the exhaust pipe 17.

[0026] During operation of the internal combustion engine 9, the exhaust ports are opened and closed due to the operation of the exhaust valves (not shown) synchronized with the engine cycle, thereby generating pressure waves in the exhaust pipe 17. These pressure waves are reflected at the input end 19.1 of the catalytic converter 19 to the material contained in the catalytic converter 19, generating reflected pressure waves that are reflected in the direction of the exhaust gas flow ( Figure 2 The arrow G in the figure propagates in the opposite direction.

[0027] The reflected pressure wave causes an increase in pressure at the exhaust port 13.5, which increases the back pressure at the output that the combustion gases must overcome during the exhaust phase of the operating cycle of the engine 9. This increase in back pressure caused by the pressure wave reflected by the catalytic converter 19 has a negative impact on the output of the engine 9, because the greater the back pressure, the lower the output of the engine power.

[0028] The resonance 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 resonance system 29 is dimensioned so that, under normal use of the engine 9, i.e., within the speed range in which the engine is normally maintained to maximize the torque and / or power delivered, the resonance system 29 resonates, generating a pressure wave at the bifurcation 23 having the same frequency as the pressure wave reflected by the catalytic converter 19 and having a phase opposite to that of the reflected pressure wave.

[0029] The pressure waves reflected by the catalytic converter 19 and the pressure waves generated by the resonance of the resonance system 29 (which pass through the resonance pipe 25, which is essentially tangential 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 branch 23. This is because the pressure waves produce destructive interference.

[0030] In fact, the pressure wave generated in the resonance system 29 destroys the pressure wave reflected by the catalytic converter 19 or at least reduces its intensity.

[0031] The net result of this phenomenon is that the negative effect of the reflected pressure wave in increasing back pressure at the exhaust port 13.5 is reduced or eliminated.

[0032] Generally, the solution proposed herein is advantageous for example for reciprocating internal combustion engines having steady-state operating conditions typically between 2400 rpm and 5000 rpm, more specifically between 3600 rpm and 4200 rpm.

[0033] In some embodiments, at an exhaust gas temperature under steady-state operating conditions of the internal combustion engine, the resonant cavity 27 may have a fundamental resonant frequency between 10 Hz and 30 Hz, preferably between 14 Hz and 18 Hz, and more preferably between 16 Hz and 18 Hz. Typically, the fundamental resonant frequency may be around 16 ± 7 Hz, where the frequency variation is caused by temperature variations of the exhaust gas, which affect the fundamental resonant frequency by changing the speed of sound in the exhaust gas. The latter is practically given by the following formula

[0034]

[0035] in:

[0036] 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 the ratio of the specific heat at constant pressure to the specific heat at constant volume;

[0037] S is the cross section of the pipe 25

[0038] L is the length of the pipe 25

[0039] V is the volume of the resonant cavity.

[0040] The resonant frequency value of 16-18 Hz is associated with the idea of ​​optimizing the maximum torque and, in particular, the maximum power of the engine. Since both advantages cannot be achieved due to the fixed geometry of the resonator, it may be advantageous to choose a resonant frequency value that provides a certain positive contribution to the maximum torque and allows full use of the energy contribution of the pressure wave to increase the maximum power.

[0041] To achieve this, in the described embodiment, a resonator geometry was chosen that allows operation between 16 and 18 Hz. In fact, at an engine speed of 2300 rpm, an engine fundamental frequency of 2250 (± 50) / 60 = 37 Hz is achieved, which corresponds to a resonant frequency of the resonator of approximately 37 / 2 = 18 Hz (2 because it is a four-stroke engine and an energy contribution is obtained every 2 revolutions of the drive shaft). In practice, through numerical simulations, the dimensions of the resonator can be configured so that, through the Helmholtz relationship, the resonant frequency is equal to approximately 16 Hz. With this optimized geometry, it is possible to utilize the energy contribution of the first-order frequency (16-18 Hz) to increase the torque and to utilize multiples of this frequency to increase the maximum power. In fact, the maximum power achieved by the resonator is achieved at a speed of approximately 4300 rpm and an engine fundamental frequency of approximately 4300 / 60 = 71 Hz, i.e. a resonant frequency of approximately 71 / 2 = 36 Hz, exactly twice the first-order resonant frequency mentioned above.

[0042] Finally, a system with a relatively wide bandwidth for a class of low-speed engines (such as the APE 300 engine) is obtained, the main features of which are as follows.

[0043] As from Figure 2 As can be seen in FIG, the cross section of the resonance cavity 27 is larger than the cross section of the resonance tube 25. Generally, in particularly advantageous embodiments, the ratio of the cross section area of ​​the resonance cavity to the cross section area of ​​the resonance tube is between 35 and 55, preferably between 40 and 50, and more preferably between 43 and 48.

[0044] In some embodiments, the resonant cavity 27 has a substantially cylindrical shape with a circular cross-section having a first diameter D1 , and the resonant tube has a circular cross-section with a second diameter D2 smaller than the first diameter D1 .

[0045] The internal volume of the resonant cavity 27 can be, for example, between 2800 and 3400 cm 3 between 3000 and 3200 cm 3 In some embodiments, the length of the resonance tube is between 90 and 100 cm, preferably between 92 and 97 cm.

[0046] The distance between the connection point between the exhaust pipe 17 and the resonance pipe 25, ie the branch 23, and the exhaust port 13.5 may be between 90 and 115 mm, preferably between 100 and 105 mm.

[0047] Figure 3 and Figure 4 It is shown that the applicant has manufactured a Figure 2 The exhaust system 11 is shown as experimental test results performed on an APE 300 engine. Specifically, the APE 300 engine is a four-stroke Otto cycle engine with the following characteristics:

[0048] Number of cylinders: 1

[0049] Liquid-cooled

[0050] Number of valves per cylinder: 2

[0051] Cylinder angle: 75°

[0052] Aluminum cylinder head

[0053] Cylinder material: cast iron

[0054] Engine displacement: 306cm 3

[0055] Compression ratio: 9.5+ / -0.5:1

[0056] Bore × stroke: 72 × 75 mm.

[0057] The exhaust system configuration used for the test is as follows:

[0058] -Resonance tube length: 950mm

[0059] -Inner diameter of resonance tube D2: 19mm

[0060] - Internal volume of the resonance cavity 27: 3150 cm 3

[0061] -Axial length of the resonant cavity 27: 245 mm

[0062] -Outer diameter of resonant cavity 27: 130mm

[0063] -Thickness of the metal plate of the resonant cavity 27: 1.2 mm

[0064] - Distance from bifurcation 23 to exhaust port: 100mm

[0065] - Cross section of the resonance tube 25 and the resonance cavity 27: circular

[0066] Figure 3 The horizontal axis of the graph represents the rotational speed value (in rpm), the vertical axis on the left represents the transmitted power (in kW), and the vertical axis on the right represents the transmitted torque (in Nm). Curves W0 and C0 respectively represent the transmitted power and torque of the engine without the resonant system 11. Curves W1 and C1 respectively represent the transmitted power and torque of the engine equipped with the resonant system 11.

[0067] exist Figure 3 As can be seen in FIG, at any speed value between about 2400 rpm and about 5000 rpm, the torque C1 and the power W1 are higher than the torque and power delivered by the same engine without the resonant system.

[0068] therefore, Figure 3 The diagram shows how the resonant system described herein provides advantages in engine efficiency.

[0069] Similar advantages can be achieved in terms of reduced consumption. Figure 4 The horizontal axis of the graph represents the engine speed (rpm). The vertical axis represents the fuel consumption rate (expressed in g / kWh) on the left and the fuel consumption per hour (expressed in kg / h) on the right.

[0070] Curves Ch0 and Cs0 represent the hourly consumption and the consumption rate, respectively, of an engine without the resonance system 11. Curves Ch1 and Cs1 represent the hourly consumption and the consumption rate, respectively, of an engine equipped with the resonance system 11. When the resonance system 11 is used, both the hourly consumption and the consumption rate are reduced by approximately 4-5% over the entire useful speed range (between approximately 2400 rpm and approximately 5000 rpm).

[0071] The efficiency of the vehicle 1 in which the engine 9 is mounted can be further improved by associating a generator with the resonant system 11. This can be achieved by using a generator 31 (e.g. a linear alternator) mounted on the base 27.1 of the resonant cavity 27, as shown in FIG. Figure 5 The linear alternator 31 converts the energy transmitted by the vibrating base 27.1 of the resonant cavity 27 to the moving parts of the linear alternator 31. The generated electrical energy can be converted into direct current in a rectifier 35, which is located on an electrical line 33 connecting the linear alternator 31 and a battery 37 of the vehicle 1.

[0072] Figure 6 FIG. 2 shows another embodiment of an exhaust system according to the present invention. Figure 2 Parts identical or equivalent to those shown and described above. Figure 6 The exhaust system 11 and Figure 2 The main difference of the exhaust system 11 is that the resonance chamber 27 is integrated into a single block 20, into which the exhaust or muffler 21 is also inserted. The muffler 21 and the resonance chamber 27 are suitably separated from each other, for example by a metal plate 22, to prevent the flow in the muffler and the flow in the resonance chamber from interacting.

Claims

1. An internal combustion engine comprising: at least one piston-cylinder system having an intake port and an exhaust port, wherein an exhaust pipe is connected to the exhaust port, a catalytic converter and a muffler are arranged in sequence along the exhaust pipe, the catalytic converter being located upstream of the muffler with respect to a flow direction of exhaust gas along the exhaust pipe; a resonance system connected to the exhaust pipe, wherein the resonance system includes a resonance pipe and a resonance cavity, wherein the resonance pipe fluidically couples the exhaust pipe to the resonance cavity; wherein the resonance pipe is connected to the exhaust pipe upstream of the catalytic converter relative to a direction of exhaust gas flow along the exhaust pipe; It is characterized in that the resonance pipe is approximately tangent to the exhaust pipe at a connection position between the resonance pipe and the exhaust pipe. 2 . The internal combustion engine of claim 1 , wherein the exhaust pipe and the resonance pipe are configured such that the overall exhaust flow in the exhaust pipe is approximately tangential to the flow in the resonance pipe. 3 . The internal combustion engine according to claim 1 , wherein an axis of the exhaust pipe and an axis of the resonance pipe are tangent to each other at the connection position of the resonance pipe and the exhaust pipe.

4. An internal combustion engine according to any one of the preceding claims, wherein the dimensions of the resonance system are set so that the pressure wave generated in the resonance system is formed at the connection position between the resonance tube and the exhaust pipe to be in phase opposite to the pressure wave generated in the exhaust pipe by the catalytic converter.

5. An internal combustion engine according to any one of the preceding claims, wherein at an exhaust gas temperature under steady-state operating conditions of the internal combustion engine, the resonance cavity has a first fundamental resonance frequency between 10 Hz and 30 Hz, preferably between 14 Hz and 18 Hz, more preferably between 16 Hz and 18 Hz.

6. An internal combustion engine according to any one of the preceding claims, wherein: The cross section of the resonance cavity is larger than the cross section of the resonance tube.

7. The internal combustion engine according to claim 6, characterized in that The ratio of the cross-sectional area of ​​the resonance cavity to the cross-sectional area of ​​the resonance tube is between 35 and 55, preferably between 40 and 50, and more preferably between 43 and 48.

8. An internal combustion engine according to claim 6 or 7, wherein the resonance cavity has a substantially cylindrical shape with a circular cross-section having a first diameter, and the resonance tube has a circular cross-section with a second diameter smaller than the first diameter.

9. An internal combustion engine according to any one of the preceding claims, wherein the internal volume of the resonance cavity is between 2800 and 3400 cm 3 between 3000 and 3200 cm 3 between.

10. An internal combustion engine according to any one of the preceding claims, wherein the length of the resonance tube is between 90 and 100 cm, preferably between 92 and 97 cm.

11. The internal combustion engine according to any one of the preceding claims, wherein the connection between the exhaust pipe and the resonance pipe is located at a distance of between 90 and 115 mm, preferably between 100 and 105 mm, from the exhaust port of the cylinder.

12. An internal combustion engine according to any preceding claim, wherein maximum engine power and maximum engine torque are delivered at a speed between 2400 rpm and 5000 rpm.

13. An internal combustion engine according to any one of the preceding claims, wherein the resonant cavity is coupled to a generator driven by the vibrations of the walls of the resonant cavity and capable of converting mechanical energy transmitted to the generator into electrical energy.

14. An internal combustion engine according to any preceding claim, wherein the resonance chamber is integrated into a block containing the muffler.

15. A vehicle comprising an internal combustion engine according to one or more of the preceding claims.

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