Method and system for managing an active scr device of an aftertreatment system ats

Abstract

The ATS comprises an SCR device and is connected to an internal combustion engine (E) so as to receive an exhaust gas flow from at least one cylinder (C) of the internal combustion engine (E) when fuel is injected into the cylinder (C) and combusted in the cylinder (C); after an engine shutdown command has been detected, NH3 storage is increased in such SCR device so that the increased NH3 storage is prepared for a subsequent cold start of the internal combustion engine (E); the NH3 storage is increased by injecting a reducing agent into the ATS and by supplying an air flow towards the SCR device; such air flow flows through the cylinder (C) after fuel injection has been switched off.

Description

[0001] Cross-references to related applications

[0002] This patent application claims priority to Italian Patent Application No. 102020000024646, filed on October 19, 2020, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates to a method for managing an active SCR (selective catalytic reduction) device, particularly in the field of heavy-duty vehicles, for managing an ATS (aftertreatment system). Background Technology

[0004] Internal combustion engines, especially diesel internal combustion engines, have an ATS (aftertreatment system) that includes an active SCR device for neutralizing NOx in the exhaust gases produced by such internal combustion engines.

[0005] When the NH3 stored in the SCR unit is used to neutralize NOx, the SCR unit is defined as "active". The NH3 is generated by the pyrolysis and subsequent hydrolysis of a liquid reducing agent, which is injected into the exhaust gas stream by means of a suitable metering feed module.

[0006] In this specification, SCR device refers to "active SCR device".

[0007] The main problem with ATS during engine cold starts is that it is difficult to pyrolyze and subsequently hydrolyze the liquid reducing agent to provide NH3 for ATS, because the heat content of the exhaust gas produced by the internal combustion engine is quite low and insufficient to heat the components that define ATS and provide energy for the latent heat of the liquid reducing agent.

[0008] Despite the low hydrolysis efficiency of the reducing agent—which leads to solid deposits in the metering module—the SCR unit will still achieve its optimal operating conditions. In fact, the NH3 storage capacity of the SCR unit decreases as its temperature increases.

[0009] Furthermore, the NH3 storage in SCR units is typically limited by a safety factor to prevent NH3 leakage during sudden acceleration. In fact, NH3 leakage is also considered part of engine emissions and should therefore be limited as much as possible.

[0010] The safety factor defines the reduction value as a function of temperature, making the limit curve essentially similar to the rated storage curve, which expresses storage capacity as a function of temperature, and spaced apart from the rated storage curve.

[0011] Emissions regulations are becoming increasingly stringent, including for cold-start conditions. As a result, a major trend among manufacturers is to implement devices called NSCs (NOx storage catalysts) or PNAs (passive NOx absorbers), which can catalyze or absorb NOx as long as the active SCR unit reaches its ignition temperature.

[0012] However, contrary to regulations, NSC and PNA devices cannot achieve high durability. Therefore, it is necessary to manage active SCR devices to cope with engine cold starts without implementing additional NOx storage devices such as NSC or PNA.

[0013] EP 3557016 teaches that when an engine shutdown command is detected and the engine is no longer in use, the NH3 storage is increased, such that the increased NH3 storage prepares for a subsequent engine cold start. Specifically, airflow is supplied to the SCR unit via an EGR duct to bypass the engine.

[0014] In this type of solution, it is necessary to find a favorable alternative to the prior art solution disclosed in EP 3557016, in particular with fewer parts and / or reduced space required for these parts, to achieve the desired increase in NH3 storage when the engine is off.

[0015] Therefore, the purpose of this invention is to meet the above-mentioned needs. Summary of the Invention

[0016] The aforementioned objective is achieved by a method for managing an active SCR device for ATS as claimed in claims 1 to 14 and by a system as claimed in claims 15 to 16.

[0017] Specifically, according to the present invention, when an engine shutdown command is detected, the engine fuel injection is shut off, and airflow is supplied toward the SCR device through at least one engine cylinder, while the reducing agent metering module injects reducing agent to increase the NH3 storage in the SCR device.

[0018] In this way, variations in the ATS layout are not strictly necessary. When the metering module is activated in the ATS, an airflow directed towards the SCR unit flows through the engine.

[0019] According to a first embodiment of the invention, this airflow is supplied by compression in the engine cylinders, particularly by the engine crankshaft driven (directly or indirectly) by an electric motor.

[0020] According to a second embodiment of the invention, the airflow is supplied by an electrically driven supercharged compressor located at the intake line that directs air to the engine cylinders. In a variant, the airflow is supplied by driving a turbine in the exhaust line to operate the turbine as a blower.

[0021] Because of this invention, the ATS and engine do not require additional channel devices and / or additional blowers / compressors to direct airflow toward the ATS circulation, while the metering module is activated and the fuel injection of the internal combustion engine is shut off.

[0022] Furthermore, the air supply and reducing agent dosage are managed by a control unit, ensuring that the invention does not result in any pollutant emissions, especially NH3, during operation after an engine shutdown command. Attached Figure Description

[0023] The invention will become fully apparent from the following detailed description, which should be read with reference to the accompanying drawings, which are given only by way of exemplary and non-limiting example, in which:

[0024] Figure 1 The layout of a preferred embodiment of the method for performing an active SCR device for managing an ATS, according to the present invention, is shown.

[0025] Figure 2 A graph showing the storage capacity curves in the publicly disclosed SCR device is presented: the rated curve (with the engine off-fire) and the limit curve used to prevent NH3 leakage during engine acceleration. Detailed Implementation

[0026] Figure 1 An internal combustion engine E is schematically shown, which includes:

[0027] At least one cylinder C, particularly four cylinders C labeled 1 to 4 respectively;

[0028] Intake line IP, which is connected to engine E in a known manner to direct air into cylinder C via corresponding intake valve IV; and

[0029] Exhaust line EP, which is connected to engine E in a known manner, so as to receive exhaust gas from cylinder C through the corresponding exhaust valve EV when fuel is injected into and burned in the cylinder.

[0030] Engine E can operate according to any cycle (such as the Diesel cycle).

[0031] The ATS is operatively connected to the exhaust line EP to treat exhaust gases before they are released into the ambient atmosphere, thereby reducing pollutants. The ATS includes an SCR device, which is known per se. Figure 1 In the specific embodiment shown, the ATS also includes a DOC (diesel oxidation catalyst) and / or a DPF (diesel particulate filter) disposed upstream of the SCR unit, but the ATS may differ from that shown.

[0032] An engine control unit (ECU) is implemented to control the operation of the engine (E), particularly controlling fuel injection in cylinder (C). Specifically, the ECU controls the operation of valves IV and EV via VVA (Variable Valve Actuation). In addition, several sensors (not shown), including temperature sensors and NH3 and / or NOx sensors, are implemented. Typically, at least one NOx sensor and / or NH3 sensor is located downstream of the SCR unit.

[0033] The ECU is programmed to further control the metering module J1 based on signals received from the NH3 and / or NOx sensors and / or based on at least one temperature signal, to inject liquid reducing agent into the ATS, at the SCR unit, and / or upstream of the SCR unit. Specifically, an algorithm running in the ECU determines the optimal amount of NH3 stored in the SCR to achieve the desired NOx conversion during engine operation. The same algorithm also limits the NH3 storage in the SCR to prevent NH3 leakage during sudden acceleration.

[0034] Figure 2 The NH3 storage capacity as a function of the SCR device is shown. Two storage curves are indicated:

[0035] Rated or maximum storage capacity when the engine is not ignited; when the engine is not ignited, the NH3 storage capacity is higher than the NH3 storage capacity during operation due to the higher partial pressure of NH3 in the exhaust stream.

[0036] Limited storage capacity, which is set by design to prevent NH3 leakage during engine acceleration (when the engine is running).

[0037] When the metering module J1 is controlled during normal operation—that is, when engine E is running—the value of the limited storage capacity curve can be considered as the target for NH3 storage in the SCR unit.

[0038] Refer again Figure 1 The intake line IP is equipped with a booster compressor SC, which is driven by an electric motor M and pressurizes the fresh air entering the cylinder C in pairs.

[0039] The intake line IP also features a valve FV positioned between the compressor SC and cylinder C. In diesel engines, this valve FV is a throttle valve, typically implemented to restrict the intake passage during cold cycles to increase pumping losses and shift the engine point for faster engine / ATS warm-up. In gasoline engines, the valve FV is a standard throttle valve, implemented to meterly deliver a mass of air into cylinder C for fuel combustion.

[0040] The exhaust pipe EP is equipped with a turbine T, which has a shaft mechanically coupled to a motor G. The motor G includes a generator electrically connected to a battery pack BAT to supply power to the battery pack BAT. The battery pack BAT is then electrically connected to a motor M to supply power to the motor. Figure 1 In the specific example shown, the motor G and the motor M are mechanically disconnected from each other, that is, they are electrically connected only through the battery pack BAT so that they can be controlled and / or operated independently of each other.

[0041] Specifically, engine E is equipped with a high-pressure EGR system to circulate a portion of the exhaust gas from exhaust line EP to intake line IP at a point downstream of compressor SC (taking into account the direction of fresh air flow). The EGR system includes pipe EGRP and metering valve EGRV along pipe EGRP. A cooler EGRC is also arranged along pipe EGRP.

[0042] Regardless of the presence of the EGR system, when the ECU detects a shutdown command (e.g., the vehicle driver moves the key to the off position), fuel injection in engine E is shut off, and the metering module J1 remains on or is enabled, preferably with a modified storage target to achieve NH3 enrichment in the SCR unit.

[0043] Specifically, during this NH3 enrichment process using the metering module J1, the NH3 storage target can be relative to the... Figure 2 The restricted storage curve visible in the lower region increases, approaching... Figure 2 The rated storage curve in the upper region.

[0044] Engine E includes a crankshaft CR, which is connected to a driveshaft via a gear transmission GT and / or a clutch CL, and the driveshaft is adapted to drive the vehicle wheels W.

[0045] The engine crankshaft CR is directly or via a transmission (not shown) connected to the electric motor MG. The electric motor is defined as an electric motor-generator or an electric motor. According to a preferred variant, the electric motor MG is integrated into the components of the clutch CL.

[0046] According to a first preferred embodiment of the invention, if necessary, the crankshaft can remain rotating even when fuel injection is shut off, thanks to the motor MG. In practice, after fuel injection is shut off in response to a shutdown command, the engine E is driven by the motor MG to use the engine cylinder C as a compressor to supply airflow toward the SCR unit and thus hydrolyze the reducing agent injected by the metering module J1, thereby increasing the NH3 storage in such an SCR unit as described above.

[0047] When the engine E is driven by the electric motor MG in this off state, the crankshaft CR must be disconnected from the wheels W. According to a preferred example, the transmission GT has gears that can be engaged by an actuator under the control of a control unit (e.g., an ECU), and in this transmission GT, a shutdown command automatically causes engagement / selection of a neutral or parking state to automatically disconnect the engine crankshaft CR from the wheels W. According to a variant, or in combination with a neutral or parking state, the clutch CL is actuated under the control of a control unit (e.g., an ECU), and a shutdown command automatically causes the clutch CL to disengage. If automatic disconnection from the wheels W is not provided, manual disconnection must be performed by the vehicle driver: in this case, only if a disconnection between the crankshaft CR and the wheels W has been detected, the electric motor MG operates to drive the engine E and supply airflow toward the SCR device.

[0048] Using this first embodiment, the compressor SC and / or turbine T can be independent, and they are preferably bypassed by the airflow generated when the engine E is used as a compressor. As an example, bypass lines (not shown) are provided at the intake line IP and / or the exhaust line EP. Specifically, airflow in the bypass lines is either prohibited or permitted by switching at least one valve (not shown). In this way, flow restrictions (i.e., undesirable pressure drops) at the compressor SC and / or turbine T can be avoided when the engine E is used as a compressor.

[0049] In this first preferred embodiment, valves IV and EV are preferably operated by VVA, i.e., by an electric drive system controlled to regulate the timing of the opening and closing of valves IV and EV. When the engine E operates as a compressor, VVA is adjusted to achieve a valve timing configuration different from that set during normal operation of the engine E. In particular, VVA is adjusted to operate the engine E as a two-stroke reciprocating machine (instead of a four-stroke reciprocating machine) to draw in air along the intake stroke and compress air along the subsequent compression stroke.

[0050] According to the second preferred embodiment, after fuel injection has been shut off, the crankshaft CR stops and therefore does not rotate, and an airflow is supplied toward the SCR unit via the operating motor M to drive the compressor SC and to use this compressor SC as a blower. In this case, at least one passage is provided through the intake valve IV and the exhaust valve EV for at least one cylinder C. For this purpose, at least one of valves IV and / or EV is controlled to open if at least one of valves IV and / or EV is actually closed when the crankshaft CR stops and, for example, the air passage is disabled before the operating motor M is used to drive the compressor SC.

[0051] As an alternative or in combination with the operation of motor M, in order to generate an airflow through cylinder C and toward the SCR unit, motor G is defined by a motor-generator (rather than solely by a generator) and operated to drive turbine T to rotate while crankshaft CR is not rotating, so that this turbine T acts as a blower to draw in airflow through engine cylinder C and intake line IP. Similarly, in this case, if no passage is actually (e.g., accidentally) provided when crankshaft CR stops rotating, such a passage will be formed through at least one engine cylinder C by opening at least one of valves IV and EV. Specifically, valves IV and EV are operated by VVA, which is adjusted to define the aforementioned passage and allow airflow to circulate from intake line IP to exhaust line EP through engine cylinder C even when engine E is completely shut off (i.e., when fuel injection is off and crankshaft CR is not rotating).

[0052] The optimal choice is to drive both the compressor SC and the turbine T simultaneously, so that the two blowers are arranged in series to achieve higher pressure. If only the compressor SC is driven or only the turbine T is driven to generate airflow toward the SCR unit, a bypass line and corresponding valve (not shown) can be provided to bypass the turbine T or compressor SC respectively, as described above for the first embodiment, to avoid pressure drop.

[0053] According to the variant, the engine E is driven by the electric motor MG as a compressor, and at the same time the compressor SC and the turbine T are driven as blowers to obtain three compression stages that supply airflow toward the SCR unit.

[0054] In any of the foregoing embodiments, preferably, the EGRP conduit remains closed. Therefore, fresh air is supplied to the SCR unit through the cylinders of engine E without affecting the EGR system.

[0055] For any of the foregoing embodiments, preferably, if valve FV is actually closed when fuel injection is off, then valve FV is controlled to be open to avoid pressure drop at such valve FV when airflow is supplied to the SCR unit via engine E. Alternatively (not shown), a bypass line with a corresponding valve is provided such that airflow supplied to the SCR unit bypasses valve FV.

[0056] For any of the foregoing embodiments, based on the ATS temperature and / or engine temperature, continuous control of NH3 enrichment is preferably performed to interrupt or prohibit the process when such temperature is below a given threshold, for example when waste heat is insufficient to provide hydrolysis.

[0057] Furthermore, during operation, the amount of NH3 stored in the SCR unit at the end of a hot run depends primarily on the average temperature of the SCR unit before and at the time of engine shutdown. When the engine must perform a "cold" cycle upon the next start-up, excessively high temperatures may not allow sufficient NH3 storage to address NOx emissions.

[0058] Therefore, according to the variant, the start of NH3 storage increase is delayed until the ATS temperature or engine temperature has fallen below another given threshold. Specifically, NH3 increase is performed if the detected temperature is within a predetermined temperature range.

[0059] Alternatively, at the exact moment fuel injection is shut off, air compression is activated, and the reducing agent metering module J1 is activated or remains activated.

[0060] In parallel with the above control, preferably, the injection of reducing agent is performed until the above storage target is reached.

[0061] Preferably, the SCR device is arranged so that it is always passed through by the exhaust gases produced by the internal combustion engine during fuel combustion. This means that, preferably, the SCR device is arranged directly along the exhaust line EP, rather than on a possible bypass line.

[0062] It should be apparent that, due to the computer program in the computer-readable medium that includes program code means for performing the claimed method, the above-described method can be advantageously implemented when such program is run on a control unit such as an ECU.

[0063] Furthermore, it should be understood that modifications may be made to the above-described methods and systems without exceeding the scope of protection defined by the appended claims.

[0064] In particular, the method and system of the present invention can be implemented in an engine that is not installed in a vehicle.

Claims

1. A method for managing an active selective catalytic reduction (ATR) device for an aftertreatment system, the ATR device being connected to an internal combustion engine (E) to receive exhaust gas from at least one cylinder (C) of the internal combustion engine (E) during fuel injection into and combustion in the cylinder (C); the method comprising the steps of: After an engine shutdown command has been detected, the NH3 storage in the selective catalytic reduction unit is increased, such that the increased NH3 storage prepares the internal combustion engine (E) for subsequent cold starts; wherein the step of increasing the NH3 storage is performed by injecting a reducing agent into the aftertreatment system and by supplying an airflow toward the selective catalytic reduction unit; wherein, after fuel injection is shut off, the airflow flows through the cylinder (C); wherein the internal combustion engine (E) includes a crankshaft (CR) coupled to an electric motor (MG) including a first electric motor; and wherein the airflow is supplied by driving the crankshaft (CR) by the first electric motor.

2. The method according to claim 1, wherein, The internal combustion engine (E) includes an intake valve (IV) and an exhaust valve (EV) operated by a variable valve to manage the inflow of air into the cylinder (C) and the outflow of gas from the cylinder (C), respectively; and wherein the variable valve actuation is adjusted before or during the activation of the first electric motor so that the internal combustion engine (E) operates as a two-stroke reciprocating machine.

3. The method according to claim 2, wherein, Upon detecting the shutdown command and before driving the crankshaft (CR), the internal combustion engine (E) automatically disconnects from the driveshaft suitable for driving the vehicle wheels.

4. The method according to claim 1, wherein, An intake line (IP) is connected to the internal combustion engine (E) to direct air to the cylinder (C), and the intake line (IP) is provided with a valve (FV); wherein the valve is controlled to open so that the airflow flows through the valve (FV).

5. The method according to claim 1, wherein, The EGR system is equipped with an EGR pipe (EGRP) to circulate exhaust gases from the exhaust line to the intake line (IP) when fuel is injected into the cylinder (C) and burned in the cylinder (C), and wherein the EGR pipe (EGRP) remains closed when the air flow is supplied.

6. The method according to claim 1, wherein, Before the shutdown command is detected, the metering module (J1) is controlled according to a limited NH3 storage target below the rated NH3 storage capacity to avoid NH3 leakage during engine acceleration, and wherein the NH3 storage in the selective catalytic reduction unit is increased to achieve a modified target that is higher than the limited NH3 storage target and lower than or equal to the rated NH3 storage capacity.

7. A method for managing an active selective catalytic reduction (ATR) device for an aftertreatment system, the ATR device being connected to an internal combustion engine (E) to receive exhaust gas from at least one cylinder (C) of the internal combustion engine (E) during fuel injection into and combustion in the cylinder (C); the method comprising the steps of: After an engine shutdown command has been detected, the NH3 storage in the selective catalytic reduction unit is increased, such that the increased NH3 storage prepares the internal combustion engine (E) for subsequent cold starts; wherein the step of increasing the NH3 storage is performed by injecting a reducing agent into the aftertreatment system and by supplying an airflow toward the selective catalytic reduction unit; wherein, after fuel injection is shut off, the airflow flows through the cylinder (C); wherein, a turbine (T) is arranged between the internal combustion engine (E) and the aftertreatment system, the turbine (T) being mechanically coupled to a motor (G) defining a motor-generator; and wherein, the airflow is supplied by the turbine (T) being driven by the motor (G).

8. The method according to claim 7, wherein, The internal combustion engine (E) includes: Crankshaft (CR); An intake valve (IV) and an exhaust valve (EV) are operated by a variable valve to manage the inflow of air into the cylinder (C) and the outflow of gas from the cylinder (C), respectively. Furthermore, the crankshaft (CR) does not rotate, and at least one of the intake valve (IV) and the exhaust valve (EV) is opened by adjusting the variable valve, and the airflow flows through a passage formed in the internal combustion engine (E).

9. A method for managing an active selective catalytic reduction (ATR) device for an aftertreatment system, the ATR device being connected to an internal combustion engine (E) to receive exhaust gas from at least one cylinder (C) of the internal combustion engine (E) during fuel injection into and combustion in the cylinder (C); the method comprising the steps of: After an engine shutdown command has been detected, the NH3 storage in the selective catalytic reduction unit is increased, such that the increased NH3 storage prepares the internal combustion engine (E) for subsequent cold starts; wherein the step of increasing the NH3 storage is performed by injecting a reducing agent into the aftertreatment system and by supplying an airflow toward the selective catalytic reduction unit; wherein, after fuel injection is shut off, the airflow flows through the cylinder (C), wherein an intake line (IP) is connected to the internal combustion engine (E) to guide air into the cylinder (C), the intake line (IP) being provided with a supercharger (SC) connected to a second electric motor; and wherein the airflow is supplied by the supercharger (SC) which is driven by the second electric motor as a blower.

10. The method according to claim 9, wherein, A turbine (T) is arranged between the internal combustion engine (E) and the aftertreatment system, the turbine (T) being mechanically connected to a motor (G) that defines a motor-generator; and wherein, while driving the supercharger (SC), the airflow is supplied through the turbine (T) which is driven by the motor (G) as a blower.

11. A system for performing a method for managing an active selective catalytic reduction apparatus for a post-treatment system; said system comprising: An internal combustion engine, the internal combustion engine including at least one cylinder (C) and a crankshaft connected to an electric motor including a first electric motor, An intake line for directing air to the cylinder (C). An exhaust line (EP) for receiving exhaust gas flow from the cylinder (C) when fuel is injected into and burned in the cylinder (C); An aftertreatment system connected to the exhaust pipe (EP) and including an active selective catalytic reduction device; A turbine, the turbine being disposed between the internal combustion engine and the aftertreatment system, the turbine being mechanically coupled to a motor defining a motor-generator; An intake line is connected to the internal combustion engine to direct air into the cylinders, and the intake line is equipped with a supercharger connected to a second electric motor. A quantitative feeding module (J1) is used to inject the reducing agent into the post-treatment system; An electronic control unit is configured to control the internal combustion engine and the metering module (J1) to increase the NH3 storage in the selective catalytic reduction device after an engine shutdown command has been detected, such that the increased NH3 storage prepares for a subsequent cold start of the internal combustion engine (E), and the electronic control unit is configured to supply airflow through the cylinder (C) after fuel injection has been shut off by controlling at least one of the first electric motor, the motor-generator, and the second electric motor.

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