Technical field
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The present invention relates to exhaust systems for vehicular traction engines, particularly two-stroke spark-ignition engines for motorcycles as well as for similar vehicles, such as mopeds, motor tricycles and quadricycles, ATVs, and the like.
Present status of the art
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As is well known, the maximum amount of pollutants that can be released into the atmosphere from a vehicular traction engine is subject to increasingly stringent standards and regulations. Therefore, exhaust gas expulsion systems have been developed within which the exhaust gases produced by combustion interact with one or more catalysts. Of particular importance in these systems is the rapidity with which the catalysts heat up and reach activation temperature, above which they are reactive and have good conversion efficiency.
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Vehicle type-approval cycles involve a cold start, so the first moments of operation drastically affect the final result. For this reason, in recent years manufacturers have begun to adopt arrangements to accelerate catalyst heating, for example, by using electrical heating elements and/or bringing the catalysts closer and closer to the engine to make more effective use of the thermal energy made available by the exhaust gases.
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Bringing the catalysts closer to the exhaust port accelerates the deterioration of the catalyst masses and, in general, adversely affects thermal efficiency because high back pressures are formed between the exhaust port and the catalyst causing excessive amounts of combustion gases to enter the combustion chamber; in addition, abnormal combustion and self-ignition phenomena occur which increase exhaust pollutants.
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Hence, particularly for two-stroke spark-ignition engines, the problem of efficiently reducing the pollutants released into the atmosphere at the time of engine ignition, while avoiding the negative consequences mentioned above, is particularly relevant.
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The reactions occurring in catalysts are oxidation-reduction reactions, so it is important that the air/fuel ratio be as close as possible to that which optimizes the efficiency of the catalysts, this is usually done by optimizing the titer of the mixture that feeds the engine, supplying the catalysts with a gas mixture to be processed with the right air/pollutant titer so as to maximize their conversion efficiency, and finally by arranging the exhaust gas treatment devices in a position suitably distant from the engine exhaust port.
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In order to increase the efficiency of motorcycle catalytic converters, as shown in
WO2019087039 , it is generally known to introduce an amount of air into the exhaust duct to increase the oxygen content of the exhaust gases prior to entering the catalytic converter. The increased oxygen content improves the catalysis of monoxide and unburned hydrocarbons.
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In order to improve, in exhaust systems, the air/fuel ratio, configurations are known in which combustion air is introduced not only through the vacuum generated in the exhaust system during engine operation, but also by means of an electrically driven pump (2) that pushes air into a three-way valve (3) driven by a solenoid controlled by the engine's ECU (1) whose function is to regulate the air flow rate in the two branches downstream of the valve. With this configuration, it is possible to manage both the carburetion of the mixture entering the engine and the air flow rate that the catalytic converters must process. Excess air, which is not routed to the engine, escapes to the atmosphere from the third port of the three-way valve. In the case of fuel being fed through a carburetor, the pump makes it possible to overcome the limitation constituted by having to use only the air drawn in by the vacuum generated during engine operation, with the consequent limits imposed by the velocity of the air passing through the engine; this, for example, prevents maneuvers such as forced leaning during rapid deceleration phases, as well as rapid enrichment during abrupt acceleration phases.
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In general, known type exhaust ducts provide that downstream of the engine exhaust port there is an absorber (6), positioned at a suitable distance from the exhaust port, followed by an electric heater (7) integrated with a first catalyst (9), followed by the main catalyst (10), therefore it is normal for there to be one or more catalysts.
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The terms upstream and downstream refer to the normal direction of flow of gases in the exhaust expulsion duct.
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The main function of the absorber is to retain unburned hydrocarbons at the moment of ignition, when the catalysts have not yet reached the minimum activation temperature. Its presence upstream of the heater is necessary because, although the latter significantly accelerates the activation of the catalysts, in the first seconds after starting they are unable to treat the large quantity of unburned hydrocarbons produced by a two-stroke spark ignition engine. Advantageously, the absorber selectively retains pollutants, and in particular unburned hydrocarbons, until it reaches its characteristic temperature, which depends on the impregnation of the absorber itself. At temperatures higher than the characteristic temperature, the absorber stops retaining pollutants and begins to release those retained.
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In the known art, automatic air injection systems are used that exploit the depression generated in the exhaust systems. The major limitation of these systems, however, is that they only work well in very limited engine operating intervals, which means they do not allow for the management of the titer of gas sent to the catalysts in a continuous and timely manner. These systems use components called AIS (Air Intake System), i.e. valves that open outwards by exploiting the depression that cyclically forms in the exhaust duct following the passage of the exhaust gases. Usually, inside these AIS valves there is a very thin sheet of harmonic steel, or other elastic material, which opens in certain conditions of depression in the duct to allow external air to be sucked into the duct. These components obviously only work after the engine has started and only if the right pressure conditions occur, which is why they have a very limited operating interval.
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Some solutions are known that are aimed exclusively at improving the reduction of polluting compounds emitted by the vehicle; for example, patent application
US5634331A shows a device for purifying the exhaust gases of an internal combustion engine, equipped with an absorber arranged in the exhaust duct of the engine, a catalytic converter placed downstream of the absorber and a heater to electrically heat the catalytic converter. A secondary air supply device, the operation of which is controlled by the engine's electronic control unit, introduces fresh air into the exhaust duct in an intermediate position between the absorber and the catalytic converter.
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A similar solution is illustrated in patent
EP3642460B1 which shows a secondary air line, with a second secondary valve that regulates the flow of fresh air to the engine exhaust duct and a first secondary valve that introduces fresh air into the exhaust gases exiting the engine exhaust valve, immediately downstream of the cylinder head, in order to facilitate the exothermic conversion of unburned compounds.
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None of the currently known devices allows ambient air to be taken by means of a single pump and directed partly towards the engine inlet, at the mixing organ between air and fuel to be used as a comburent, and partly into the exhaust duct of the exhaust gases, precisely downstream of an absorber and upstream of a heater which precedes the catalytic converter, to reduce the concentration of pollutants emitted by the vehicle.
Objects and summary of the invention
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In the field of two-stroke spark-ignition engines, there is therefore a need for a device capable of reducing the emission of pollutants in the first moments of operation, immediately after starting the engine.
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A further purpose of the present invention is to extend the life of the catalysts in the exhaust duct.
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Another aim achieved by the invention is the stabilization and optimization of combustion, significantly reducing exhaust back pressures.
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Not the last aim of this invention is to improve the thermal efficiency of the engine.
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This and other purposes, are achieved by means of a device including at least one pump (2) for insufflating comburent air, taking it from the atmosphere and transferring it into the engine, at the one or more mixing organs that regulate the supply of the mixture of fuel and comburent to the engine itself, i.e., directly into the combustion chamber in the case of electronic ignition engines or through at least one carburetor, injecting air into the atomization circuit, by means of a three-way valve (3) controlled by the vehicle's electronic control unit (1); the latter increases or decreases the amount of air according to requirements.
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When the three-way valve (3) closes the duct that transfers air to the engine (4), the air is diverted to the third way of the valve and from there is delivered to the exhaust duct, precisely downstream of the absorber (6) and upstream of the heater (7) that comes before the first catalyst (9). Downstream of the first catalyst (9) is the main catalyst (10). The heater (7) is controlled from the control unit (1) by means of a special pilot system (8) that turns it off when the operating temperature is reached; in the simplest embodiments, control can be time-dependent, but more refined embodiments are possible in which heater shutdown is controlled by temperature probes and/or sensors that assess the state of charge of the vehicle battery and interrupt power to the heater if there is a risk of depleting the battery charge.
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When the vehicle is started, the control unit (1) manages the parameters of the engine (4), air pump (2), heater (7), and begins to modulate the adjustment of the three-way valve (3).
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With the configuration described above, at the time the vehicle is started, when the air/fuel mixture is adjusted to be rich, thus with little air, the excess air leaving the pump (2) and discarded by the three-way valve (3) is diverted to the heater (7) in an active way, because it is pushed by the pump, and not in a passive way, as is the case with the traditional system that takes advantage of the pulsating vacuum that is cyclically created in the exhaust duct by the passage of exhaust gases.
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Thanks to the action of the heater (7), the temperature at which the catalysis of the pollutants that have not been stopped by the absorber begins is quickly reached in the first catalyst (9) and the oxidation-reduction reaction occurs at its best, thanks to the flow of air received from the three-way valve. The heat produced by this reaction also activates the main catalyst (10). Finally, the exhaust gases, treated and converted, pass through the silencer (11) located at the end of the exhaust duct, at the end opposite to the one connected to the engine, and exit into the environment. Once the start-up transient is over and the operating temperatures are reached, the catalysis process proceeds autonomously as long as the engine is running.
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A particularly complete embodiment involves the use of a probe (12) connected with the control unit (1) to control the catalyst temperature (9).
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It is also possible to complete the device by inserting, between the engine exhaust port and the absorber (6), an oxygen probe (5) connected to the control unit (1), for possible feedback on the three-way valve.
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At steady state, the control unit (1) controls the three-way valve (3) in such a way that a portion of the air leaving the pump (2) is directed to the engine such that an air/fuel ratio preferably between 14,8 and 15,1 is obtained.
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Constructive solutions are also possible in which the air from the three-way valve delivered into the exhaust duct is not inserted downstream of the absorber and upstream of the heater, but is inserted downstream of the first catalyst and upstream of the main catalyst, or even in both positions, if appropriate by equipping the system with suitable check valves. The inlet of air upstream of the main catalyst allows the oxygen content within the main catalyst to be increased and thus improve the catalysis of the exhausts already pre-catalyzed in the first catalyst.
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Additional solutions are also possible in which the exhaust duct includes additional catalysts and/or air inlet points.
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A filter may be mounted upstream of the three-way valve to prevent any impurities in the air from reaching the engine or catalysts.
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It should be noted that in the present patent text, for the sake of clarity, it has been deemed preferable to refer to the heater (7), the first catalyst (9) and the main catalyst (10) as separate elements, however, it is possible for two or more of them to be integrated to form a single element without falling outside the same inventive concept.
Brief description of the drawings
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- Figure 1 shows a schematic view of a first embodiment of the device suitable for being applied to an engine equipped with a carburetor; the first outlet duct (31) of the three-way valve (3) is connected to the atomizer circuit (14) of the carburetor (13), the latter draws in air from the environment and introduces a mixture of air and fuel into the engine (4).
- Figure 2 shows a schematic view of a second embodiment of the device suitable for being applied to an injection engine; the first outlet duct (31) of the three-way valve (3) injects air into the combustion chamber of said engine (4), at a fuel injector.
- Figure 3 shows a schematic view of the embodiment of the device suitable for being applied to an injection engine comprising at least a first fuel injector located immediately downstream of the throttle body (17) and at least a second fuel injector located at the combustion chamber of said engine.
Detailed description of an embodiment of the invention
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The following description of one or more embodiments of the invention refers to the accompanying drawings and should not be considered limiting of the invention, the scope of which is defined in the appended claims. The same numerical references in the drawings indicate the same or similar elements. The drawings are not necessarily represented to scale.
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In the embodiment shown in Figure 1, the device is applied to an engine equipped with a carburetor (13) and comprises an air pump (2) which is turned on when the engine is started and is pneumatically connected to a three-way valve (3) comprising a solenoid controlled in frequency by an electronic control unit (1), the two outlet ducts (31, 32) of the three-way valve are respectively pneumatically connected to the carburetor (13) and to the exhaust gas exhaust duct, in particular, the first outlet duct (31) of said three-way valve (3) is connected to the atomizer circuit (14) of the carburetor (13). This configuration allows very advantageously both to manage the combustion mixture titer and to optimize the vaporization of the combustion mixture itself. In the case of engines equipped with more than one carburetor, the first outlet duct (31) of said three-way valve (3) is divided into as many secondary branches as there are carburetors, each branch being connected to a respective carburetor.
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The present invention can also be applied, mutatis mutandis, in the case of engines without a carburetor and equipped with electronic fuel injection. Figure 2 shows an embodiment of the device applied to an electronically injected engine in which said first outlet duct (31) of said three-way valve (3) is connected to the combustion chamber of the engine and injects air at an injector (16) that feeds fuel directly into the combustion chamber, in this way the vaporization and homogenization of the combustion mixture is optimized. In the case of multi-cylinder engines, in which a fuel injector is provided for each cylinder, the first outlet duct (31) of said three-way valve (3) is divided into as many secondary branches as there are such injectors, each branch being connected to the engine combustion chamber at a respective fuel injector.
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Figure 3 shows a implementation solution in which the same device is applied to an electronically fuel-injected engine equipped with a first injector (16) that feeds fuel directly into the combustion chamber and a second injector (18) that feeds fuel into the fuel feed system downstream of the throttle body (17); in the configuration described here, said first outlet duct (31) of the three-way valve (3) is connected to the combustion chamber and feeds air at said first injector that injects fuel directly into the combustion chamber.
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When the engine is started (4), the control unit actuates the solenoid in such a way that a portion of the air discharged from the pump (2) is directed to the carburetor, while the remaining air is delivered to the exhaust duct. Preferably, the actuation of the solenoid is such as to obtain a so-called rich fuel-air mixture, i.e., particularly rich in fuel.
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The exhaust gas expulsion duct begins downstream of the engine exhaust port and includes, progressively, an absorber (6), a heater (7), a first catalyst (9), a main catalyst (10), and the final silencer (11) through which the gases are expelled into the atmosphere.
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The second outlet duct (32) that exits from the three-way valve delivers air into the exhaust gas expulsion duct by feeding it downstream of the absorber (6) and upstream of the heater (7).
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The absorber works in a "cold state", retaining mainly unburned hydrocarbons; the heater (7) is turned on at the same time as the vehicle is started and serves to facilitate catalysis in the first catalyst (9), heating it until the oxidation-reduction reactions taking place there, which are exothermic, have raised its temperature sufficiently. Then the gases exiting the first catalyst (9) pass into the main catalyst (10) and finally are expelled into the atmosphere by passing through the silencer (11) located at the tail end of the expulsion duct. Often the heater (7) and the first catalyst (9) are integrated forming a single component.
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The heater (7) is turned on by means of a piloting system (8), which also provides for its shutdown at steady state, when operating temperatures have been reached; shutdown can be controlled by a timer or by a temperature probe. In more complete versions, the pilot system is also functionally connected with a detector of the vehicle battery charge, so that it will not activate if there is insufficient power in the battery.
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In the embodiment shown in the figures there is also an oxygen probe (5), placed between the engine exhaust port and the absorber (6), said probe is functionally in contact with the control unit, the latter can act on the distribution of the air exiting the three-way valve according to what the probe detects.
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Particularly complete systems also include a sensor (12) that detects the temperature of the catalysts and is functionally connected with the control unit (1) to manage the delivery of electricity to the heater. By adjusting the amount of air delivered to the gas expulsion duct, the temperature of the catalysts can be changed.
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Preferably, the catalysts are of the trivalent type.
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According to a particularly complete embodiment of the device, the second outlet duct (32) of the three-way valve (3) includes a one-way check valve (15) that minimizes the potentially harmful effect of the back pressure on the exhaust side.