Method and system for controlling oxygen purification of a three-way catalyst

Abstract

A method for controlling oxygen purification of a three-way catalyst (TWC) (60), the method comprising: Setting (S250), by a control device (70), an air-fuel ratio (AFR) upstream of the TWC (60) to a target AFR when the oxygen purge of the TWC is performed after a fuel cut, Maintaining (S260), by the control device (70), the target AFR until the oxygen purification is completed, Monitoring (S280), by the control device (70), when a vehicle accelerates after completion of the oxygen purification, and Maintaining, by the control device (70), the target AFR for a predetermined delay time after determining that the vehicle is accelerating.

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] The present invention relates to a method and system for controlling oxygen purge of a three-way catalyst (TWC). More particularly, the present invention relates to a method and system for controlling oxygen purge of a three-way catalyst that can minimize nitrogen oxide (NOx) slippage from the TWC during oxygen purge of the TWC. Description of the technology used

[0002] A vehicle is equipped with a catalytic converter to reduce emissions (EM) contained in the exhaust gas. Exhaust gas flowing from an internal combustion engine through an exhaust manifold is forced into a catalyst attached to an exhaust pipe and purified therein. The exhaust noise is then reduced as it passes through a muffler, and the exhaust gas is then released into the air through a tailpipe. The catalyst purifies the EM contained in the exhaust gas. A particulate filter is also installed in the exhaust pipe to capture particulate matter (PM) in the exhaust gas.

[0003] A three-way catalyst (TWC) is a type of catalyst that reacts with hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx), which are harmful components of the exhaust gas, to remove these components. TWCs are primarily installed in gasoline vehicles and utilize Pt / Rh, Pd / Rh, or Pt / Pd / Rh systems.

[0004] The internal combustion engine equipped with the TWC performs fuel cut-off to improve fuel economy under specific driving conditions. In this case, an oxygen storage material in the TWC stores oxygen (O 2 ). Since the NOx purification efficiency is poor when the oxygen storage material contains a large amount of O 2 stores, an oxygen purification is carried out to remove the O stored in the TWC 2 Oxygen purification is accomplished by controlling the air-fuel ratio (AFR) of the exhaust gas upstream of the TWC to be rich.

[0005] The AFR of the exhaust gas is rich during oxygen purification, while the AFR in the TWC is rich due to the O 2is lean when fuel cutoff is performed. Therefore, the TWC cannot reduce NOx but instead exhausts it. The concentration of NOx escaping from the TWC is closely related to controlling the AFR upstream of the TWC during oxygen purge.

[0006] Fig. 1 is a graph showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to a conventional, exemplary control strategy for increasing vehicle speed after decreasing. The graphs in Fig. 1 shows an example vehicle speed during vehicle acceleration after fuel cutoff, an example AFR control upstream of the TWC performed for the example vehicle speed, and an example concentration change of NOx escaping from the TWC during the example AFR control. It can be seen that the vehicle speed during vehicle acceleration after fuel cutoff, the AFR control upstream of the TWC performed for the vehicle speed, and the concentration change of NOx escaping from the TWC during AFR control are not always according to the Fig. 1 shown diagrams may vary.

[0007] With reference to Fig. 1, the control device continuously detects a driving condition of the vehicle, such as vehicle speed, engine speed, the opening of an accelerator pedal position sensor, an intake amount, etc., and determines whether a fuel cut-off condition is met. The control device is configured to determine that the fuel cut-off condition is met and executes the fuel cut-off at a determined time (t fco ). Since the fuel is not injected during fuel cut-off, the AFR (here referred to as "Lambda (λ)") upstream of the TWC is rapidly increased (i.e., the AFR upstream of the TWC quickly becomes a lean AFR) and the vehicle speed is gradually reduced.

[0008] After the fuel cut-off, the control device carries out the oxygen purification at a time (t fci ) to check the O stored in the TWC2 by resuming the fuel supply that was stopped.

[0009] During early oxygen purge, lambda is rapidly reduced to a target AFR (i.e., the AFR upstream of the TWC becomes a rich AFR). Since the AFR within the TWC is lean, NOx initially begins to escape from the TWC at this time. Here, the concentration of NOx escaping from the TWC during early oxygen purge is referred to as the first slip concentration X1.

[0010] The control device then gradually increases the lambda and continues with the oxygen purification.

[0011] If it is determined that the vehicle initially accelerates all at once (t pc), the control device stops oxygen purification and resets the lambda to a stoichiometric AFR (λ=1). At this moment, NOx begins to escape from the TWC secondarily. Here, the concentration of NOx escaping from the TWC after vehicle acceleration is referred to as the second slip concentration X2.

[0012] The control device then controls the lambda according to the driving condition (typically the lambda is feedback controlled as stoichiometric AFR).

[0013] When the vehicle undergoes secondary acceleration after the initial acceleration (i.e., a change in vehicle acceleration), NOx escapes from the TWC for the third time. Here, the concentration of NOx escaping from the TWC after the vehicle's secondary acceleration is referred to as the third slip concentration X3.

[0014] However, it was found that the first, second and third slip concentrations X1, X2 and X3 are related to the AFR control upstream of the TWC in the oxygen purification.

[0015] The information in this Background of the Present Invention section is provided merely to facilitate understanding of the general background of the present invention and is not intended as an acknowledgment or any form of suggestion that this information constitutes prior art already known to a person skilled in the art.

[0016] For example, from DE 10 2018 127 177 A1 a method for controlling oxygen purification of a three-way catalyst (TWC) is known, the method comprising adjusting, by a control device, an air-fuel ratio (AFR) upstream of the TWC to a target AFR when the oxygen purification of the TWC is carried out.

[0017] Furthermore, DE 10 2004 009 615 A1 discloses a method for determining the current oxygen loading of a TWC. BRIEF EXPLANATION

[0018] The present invention is directed to providing a method and system for controlling oxygen purge of a three-way catalyst (TWC) having the advantages of reducing the concentration of nitrogen oxide (NOx) escaping from the TWC during oxygen purge by optimally controlling the air-fuel ratio upstream of the TWC.

[0019] For this purpose, the invention provides a method for controlling oxygen purification of a three-way catalyst (TWC) with the features according to claims 1 and 7, respectively, and a system for controlling oxygen purification of a TWC with the features according to claim 12. Further embodiments of the method and the system are described in the associated dependent claims.

[0020] According to the present invention, an air-fuel ratio upstream of a three-way catalyst is quickly adjusted to a target AFR value, and the target AFR value is then maintained until oxygen purification is completed. Therefore, the first, second, and third slip concentrations can be reduced.

[0021] Since the target AFR is maintained for a predetermined delay time after the oxygen purification is completed, the third slip concentration can be further reduced.

[0022] Since the target AFR is maintained for a standby period even after the oxygen purge is completed and it is determined whether a vehicle is accelerating after the standby period is completed, the secondary and tertiary slip concentrations can be further reduced.

[0023] The methods and apparatus of the present invention have other advantages which will be apparent from or more particularly explained in the accompanying drawings, which are incorporated herein, and the following detailed description, which together serve to explain certain principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to a conventional exemplary control strategy for an increasing vehicle speed after a reduction, Fig. 2 is a schematic diagram of a system for controlling oxygen purification of a TWC according to an exemplary embodiment of the present invention, Fig. 3 is a diagram showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to a first exemplary control strategy for a repeatedly changing vehicle speed, Fig. 4 is a graph showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to a second exemplary control strategy for a repeatedly changing vehicle speed, Fig. 5 is a graph showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to a third exemplary control strategy for a repeatedly changing vehicle speed, Fig. 6 is a graph showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to a fourth exemplary control strategy for a repeatedly changing vehicle speed, Fig. 7 is a graph showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to a fifth exemplary control strategy for a repeatedly changing vehicle speed, Fig. 8 is a diagram showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to a sixth exemplary control strategy for a repeatedly changing vehicle speed, Fig. 9 is a diagram showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to the seventh and eighth exemplary control strategies for a repeatedly changing vehicle speed, Fig. 10 is a block diagram of a system for controlling oxygen purification of a TWC according to an exemplary embodiment of the present invention, Fig. 11 is a flowchart of a method for controlling oxygen purification of a TWC according to an exemplary embodiment of the present invention, and Fig. 12 is a graph showing examples of NOx concentration escaping from a TWC when conventional AFR control and AFR control according to exemplary embodiments of the present invention are performed for the same vehicle speed change.

[0024] It should be understood that the accompanying drawings are not necessarily to scale and present a somewhat simplified representation of various features illustrating the basic principles of the present invention. The specific design features of the present invention contained herein, including, for example, specific dimensions, orientations, locations, and shapes, will be determined in part by the particular intended application and usage environment.

[0025] In the figures, reference numerals refer to the same or equivalent parts of the present invention in the different figures of the drawing. DETAILED DESCRIPTION

[0026] It is to be understood that the terms “vehicle” or “vehicle-...” or any similar term used herein includes motor vehicles in general, such as passenger vehicles, including so-called sport utility vehicles (SUVs), buses, trucks, numerous commercial vehicles, as well as e.g. watercraft, including a variety of boats and ships, as well as e.g. aircraft and the like, and further also hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels produced from resources other than petroleum). A so-called hybrid vehicle, as referred to herein, is a vehicle that has two or more power sources, e.g. vehicles that are powered by both gasoline and electricity.

[0027] Furthermore, it will be understood that one or more of the methods or aspects listed below may be performed by at least one control device. The term "control device" may refer to a hardware device that includes a memory and a processor. The memory is configured to store program instructions, and the processor is specifically programmed to execute the program instructions to perform one or more operations described further below. Furthermore, it will be understood that the methods listed below may be performed by a system that includes the control device, as described in detail below.

[0028] Furthermore, the control device of the present invention may be implemented as a non-transitory, computer-readable medium containing executable program instructions executed by a processor or the like. Examples of computer-readable media include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards, and optical data storage devices. The computer-readable medium may also be distributed over a computer network so that the program instructions are stored and executed in a distributed manner, for example, through a telematics server or a controller area network (CAN).

[0029] The term “stoichiometric AFR” or other similar term as used herein refers to a weight ratio for a fuel and an oxygen (O 2 ) that must be oxidized to achieve complete combustion and means λ = 1.

[0030] The term “lean AFR” or other similar term as used herein refers to a condition where the actual fuel quantity is less than the fuel quantity required at stoichiometric AFR and means λ > 1.

[0031] The term “rich AFR” or other similar term as used herein refers to a condition where the actual fuel quantity is greater than the fuel quantity required at stoichiometric AFR and means λ < 1.

[0032] In the following, various exemplary embodiments of the present invention are described in detail with reference to the accompanying drawings.

[0033] Fig. 2 is a schematic diagram of a system for controlling oxygen purge of a TWC according to an exemplary embodiment of the present invention.

[0034] As in Fig. 2, a system for controlling oxygen purification of a three-way catalyst (TWC) according to an exemplary embodiment of the present invention includes an internal combustion engine 10, an exhaust pipe 40, the three-way catalyst 60, and a control device 70.

[0035] The internal combustion engine 10 combusts an air-fuel mixture to convert chemical energy into mechanical energy. The internal combustion engine 10 includes a combustion chamber 12, an intake valve 14, a spark plug 15, an exhaust valve 16, an injector 18, an intake manifold 20, and an exhaust manifold 22.

[0036] The combustion chamber 12 is connected to the intake manifold 20 and receives air or a mixture of air and fuel. An intake port is formed on the combustion chamber 12 and is provided with the intake valve 14. The intake valve 14 is actuated by rotation of a camshaft connected to a crankshaft to open or close the intake port. When the intake valve 14 opens the intake port, the air or the air-fuel mixture in the intake manifold 20 flows into the combustion chamber 12 through the intake port. When the intake valve 14 closes the intake port, however, the air or the air-fuel mixture in the intake manifold 20 does not flow into the combustion chamber 12. Furthermore, the combustion chamber 12 is connected to the exhaust manifold 22, so that the exhaust gas produced during the combustion process is collected in the exhaust manifold 22 and flows out into the exhaust pipe 40.An exhaust port is formed at the combustion chamber 12 and is provided with the exhaust valve 16. The exhaust valve 16 is also actuated by the rotation of the camshaft connected to the crankshaft to open or close the exhaust port. When the exhaust valve 16 opens the exhaust port, the exhaust gas in the combustion chamber 12 flows through the exhaust port to the exhaust manifold 22. When the exhaust valve 16 closes the exhaust port, the exhaust gas in the combustion chamber 12 does not flow to the exhaust manifold 22.

[0037] Depending on the type of internal combustion engine, the combustion chamber 12 may be provided with the injector 18 to inject fuel into the combustion chamber 12 (for example, in the case of a gasoline direct injection engine). Furthermore, depending on the type of internal combustion engine, the spark plug 15 may be provided at an upper portion of the combustion chamber 12 to ignite the air-fuel mixture in the combustion chamber 12 (for example, in a gasoline engine).

[0038] The exhaust pipe 40 is connected to the exhaust manifold 22 to discharge the exhaust gases to the outside. Various catalysts are mounted on the exhaust pipe 40 to remove the emissions (EM) contained in the exhaust gas. For simplicity, the TWC 60 is exemplified as being mounted on the exhaust pipe 40, but it should be understood that the catalyst mounted on the exhaust pipe 40 is not limited to the TWC 60.

[0039] The TWC 60 is mounted on the exhaust pipe 40 through which the exhaust gas discharged from the internal combustion engine 10 flows. The pollutants contained in the exhaust gas, including CO, HC, and NOx, are converted into harmless components through an oxidation reaction in the TWC 60. Since the TWC 60 is well known to those skilled in the art, a detailed description will be omitted.

[0040] The exhaust pipe 40 is provided with a plurality of sensors 42, 44 and 46 for detecting a combustion condition and a function of the TWC 60.

[0041] The temperature sensor 42 is mounted on the exhaust pipe 40 upstream of the TWC 60, detects a temperature of the exhaust gas upstream of the TWC 60, and transmits a corresponding signal to the control device 70.

[0042] The first oxygen sensor 44 is mounted on the exhaust pipe 40 upstream of the TWC 60, detects the O 2concentration in the exhaust gas upstream of the TWC 60 and transmits a corresponding signal to the control device 70. An air-fuel ratio (hereinafter referred to as "λ") of the exhaust gas described here refers to an air-fuel ratio (AFR) upstream of the TWC 60 and may be a value detected by the first oxygen sensor 44. In addition, AFR control described here refers to controlling the AFR of the exhaust gas as a target AFR according to a driving condition.

[0043] The second oxygen sensor 46 is mounted on the exhaust pipe 40 downstream of the TWC 60, detects the O 2 concentration in the exhaust gas downstream of the TWC 60 and transmits a corresponding signal to the control device 70. A value detected by the second oxygen sensor 46 can be used to determine whether an oxygen storage capacity (OSC) of the TWC 60 is completely consumed, that is, whether oxygen purification is complete.

[0044] In addition to the sensors 42, 44, and 46 described herein, a system for controlling the internal combustion engine may also include various sensors. For example, an additional temperature sensor may be mounted on the exhaust pipe 40 downstream of the TWC 60 to detect the temperature of the exhaust gas downstream of the TWC 60. In addition, as shown in Fig. 10, the system for controlling oxygen purification of a three-way catalyst may further include a vehicle speed sensor 48, an engine speed sensor 50, and an air flow sensor 52. Furthermore, the system for controlling oxygen purification of the TWC may also include a NOx sensor, an HC sensor, or a CO sensor mounted on the exhaust pipe 40, and the concentration of EM contained in the exhaust gas may be detected through these sensors.

[0045] The control device 70 is electrically connected to the sensors 42, 44, 46, 48, 50, and 52 to receive signals corresponding to the values ​​detected by the sensors 42, 44, 46, 48, 50, and 52. Based on the signals, it determines the combustion state, the AFR of the exhaust gas, whether the TWC 60 is operating normally, whether the oxygen purification is complete, and / or the driving state of the vehicle. The control device 70 controls at least an ignition timing of the spark plug 15, the AFR of the exhaust gas, and a fuel injection amount and / or a fuel injection timing of the injector 18 based on the determination results.The control device 70 may be implemented with one or more processors executed by a predetermined program, and the predetermined program may be programmed to execute each step of a method for controlling oxygen purification of a three-way catalyst according to an exemplary embodiment of the present invention.

[0046] With reference to Fig. 3 to Fig. 9, a NOx concentration escaping from the TWC 60 when the AFR ratio upstream of the TWC 60 (i.e., the AFR of the exhaust gas) is controlled according to various control strategies when oxygen purification is performed after fuel cutoff will be described below. For better understanding and ease of description, repeatedly changing vehicle speeds are represented as a running state of the vehicle. Here, the repeatedly changing vehicle speed includes a region where the vehicle speed decreases and a region where the vehicle speed increases. The region where the vehicle speed decreases and the region where the vehicle speed increases are alternately repeated.

[0047] Fig. 3 is a diagram showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to a first exemplary control strategy for a repeatedly changing vehicle speed, Fig. 4 is a graph showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to a second exemplary control strategy for a repeatedly changing vehicle speed, Fig. 5 is a graph showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to a third exemplary control strategy for a repeatedly changing vehicle speed, Fig. 6 is a graph showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to a fourth exemplary control strategy for a repeatedly changing vehicle speed, Fig. 7 is a graph showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to a fifth exemplary control strategy for a repeatedly changing vehicle speed, Fig. 8 is a graph showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to a sixth exemplary control strategy for a repeatedly changing vehicle speed, and Fig. 9 is a graph showing examples of the NOx concentration escaping from a TWC when an AFR upstream of the TWC is controlled according to seventh and eighth example control strategies for a repeatedly changing vehicle speed.

[0048] In Fig. 3 to Fig. 8, a bold solid line represents the AFR (λ) upstream of the TWC 60, a thin solid line represents the vehicle speed, a bold dotted line represents the target AFR (λtar), and a dash-dotted line represents the concentration of NOx escaping from the TWC 60.

[0049] In Fig. 9, an upper solid line represents the AFR upstream of the TWC 60 according to the seventh control strategy, an upper dash-dot line represents the AFR upstream of the TWC 60 according to the eighth control strategy, an upper dash-double-dot line represents the AFR downstream of the TWC 60 according to the seventh control strategy, and an upper dotted line represents the AFR upstream of the TWC 60 according to the eighth control strategy, a lower solid line represents the vehicle speed, a lower dash-dot line represents the concentration of NOx escaping from the TWC 60 when the AFR is controlled according to the seventh control strategy, and a lower dotted line represents the concentration of NOx escaping from the TWC 60 when the AFR is controlled according to the eighth control strategy.

[0050] The Fig. 3 to Fig. The vehicle speed shown in Figure 9 is designed so that the Fig. The vehicle speed change shown in Figure 1 is repeated. This allows NOx to escape from the TWC 60 three times within a given period. This means that the first to third slip concentrations X1, X2, and X3 can occur.

[0051] Fig. 3 and Fig. 4 are diagrams comparing the first, second, and third slip concentrations X1, X2, and X3 according to the AFR control pattern of the exhaust gas when the oxygen purification of the TWC 60 is performed. The target AFR (λ tar ) of the first control strategy is the same as the (λ tar ) of the second control strategy, and the oxygen purification time of the first control strategy is the same as that of the second control strategy.

[0052] According to the first AFR tax pattern in Fig. 3, when oxygen purification starts after fuel cut-off is performed due to a reduction in vehicle speed, the AFR upstream of the TWC 60 is quickly adjusted to the target AFR (λ tar ). The AFR upstream of the TWC 60 is then gradually increased until the vehicle speed increases again. When the vehicle speed increases, the AFR upstream of the TWC 60 is returned to the stoichiometric AFR value (λ=1).

[0053] According to the second AFR tax pattern in Fig. 4, when oxygen purification starts after fuel cut-off is performed due to a reduction in vehicle speed, the AFR upstream of the TWC 60 is quickly adjusted to a predetermined rich AFR value (λ > λ tar ) and then gradually adjusted to the target AFR value (λ tar ). The AFR upstream of the TWC 60 is then used as the target AFR (λtar ) until the vehicle speed is increased again. When the vehicle speed is increased, the AFR upstream of the TWC 60 is quickly returned to the stoichiometric AFR value (λ=1).

[0054] Here, "rapidly adjusting, increasing, reducing, or restoring to a specific AFR" when a specific condition is met means adjusting a fuel injection amount so that the AFR is the specific AFR when the specific condition is met. For example, "rapidly adjusting to a target AFR" when a specific condition is met means quickly injecting the amount of fuel that causes an AFR upstream of a TWC 60 to become the target AFR based on a current intake amount when the specific condition is met.

[0055] Here, "gradually adjusting, increasing, decreasing, or restoring a specific AFR" when a specific condition is met means that a fuel injection amount is adjusted so that the AFR becomes the specific AFR within a predetermined time interval when the specific condition is met. For example, "gradually adjusting to a target AFR" when a specific condition is met means that an AFR is gradually increased or reduced to the target AFR from the time the specific condition is met until the predetermined time interval has passed. Currently, the fuel amount is gradually increased or decreased during the predetermined time interval.

[0056] With reference to Fig. 3 and Fig. 4, the first slip concentration X1 and the third slip concentration X3 are relatively low and the second slip concentration X2 is relatively high when the AFR control upstream of the TWC 60 is performed according to the first control strategy, while the second slip concentration X2 is relatively low and the first slip concentration X1 and the third slip concentration X3 are relatively high when the AFR control upstream of the TWC 60 is performed according to the second control strategy. It can be seen that the first slip concentration X1 and the third slip concentration X3 are reduced when the AFR upstream of the TWC 60 is quickly adjusted to the target AFR (λ tar ) is set, while the second slip concentration X2 is reduced when a period during which the AFR upstream of the TWC 60 is set as the target AFR (λ tar) is maintained. That is, it can be seen that the AFR control pattern affects all of the first, second, and third slip concentrations X1, X2, and X3.

[0057] Fig. 5 and Fig. 6 are diagrams comparing the first, second, and third slip concentrations X1, X2, and X3 according to the target EGR when the oxygen purification of the TWC 60 is performed. The AFR control pattern of the third control strategy is the same as or similar to that of the fourth control strategy, and the oxygen purification duration of the third control strategy is the same as that of the fourth control strategy. The target AFR (λ tar ) of the third control strategy is about 0.84 and the target AFR (λ tar ) of the fourth tax strategy is approximately 0.78.

[0058] According to the AFR control pattern of the third control strategy and the fourth control strategy, when the oxygen purification starts after the fuel cut is performed due to a reduction in vehicle speed, the AFR upstream of the TWC 60 is quickly adjusted to a predetermined rich AFR value (λ > λ tar ) and then gradually adjusted to the target AFR value (λ tar ). The AFR upstream of the TWC 60 is then used as the target AFR (λ tar ) until the vehicle speed is increased again. When the vehicle speed is increased, the AFR upstream of the TWC 60 is quickly returned to the stoichiometric AFR value (λ=1).

[0059] With reference to Fig. 5 and Fig. 6, the first slip concentration X1 is reduced, while the second slip concentration X2 and the third slip concentration X3 have only a slight difference when the AFR upstream of the TWC 60 is controlled according to the fourth control strategy, compared to controlling the AFR upstream of the TWC 60 according to the third control strategy. It can be seen that the target AFR (λ tar ) affects the first slip concentration X1, but hardly affects the second slip concentration X2 and the third slip concentration X3. In addition, the first slip concentration X1 decreases when the target AFR (λ tar ) becomes lower (i.e. the target AFR becomes richer).

[0060] Fig. 7 and Fig. 8 are graphs comparing the first, second, and third slip concentrations X1, X2, and X3 as a function of the oxygen purge duration during which the oxygen purge of the TWC 60 is performed. The AFR control pattern of the fifth control strategy is the same as or similar to that of the sixth control strategy, and the target AFR of the fifth control strategy is the same as that of the sixth control strategy. However, the oxygen purge duration t1 of the fifth control strategy is shorter than t2 of the sixth control strategy.

[0061] According to the AFR control pattern of the fifth and sixth control strategies, when oxygen purification starts after fuel cut-off due to a reduction in vehicle speed, the AFR upstream of the TWC 60 is quickly adjusted to a predetermined rich AFR value (λ > λ tar ) and then gradually adjusted to the target AFR value (λ tar). The AFR upstream of the TWC 60 is then used as the target AFR (λ tar ) until the vehicle speed is increased again. When the vehicle speed is increased, the AFR upstream of the TWC 60 is quickly returned to the stoichiometric AFR value (λ=1).

[0062] With reference to Fig. 7 and Fig. 8 shows that the first slip concentration X1 and the second slip concentration X2 differ only slightly, while the third slip concentration X3 is greatly reduced when the AFR upstream of the TWC 60 is controlled according to the sixth control strategy, compared to when the AFR upstream of the TWC 60 is controlled according to the fifth control strategy. This shows that the oxygen purge duration affects the third slip concentration X3, but hardly affects the first slip concentration X1 and the second slip concentration X2. Furthermore, the longer the oxygen purge duration, the lower the third slip concentration X3.

[0063] Fig. 9 is a graph comparing the first, second, and third slip concentrations X1, X2, and X3 according to a target AFR maintenance period (a period for which the target AFR is maintained) when the oxygen purification of the TWC 60 is performed. The AFR control pattern of the seventh control strategy is the same as or similar to that of the eighth control strategy, and the target AFR of the seventh control strategy is the same as that of the eighth control strategy. However, the target AFR is maintained before the vehicle accelerates according to the seventh control strategy, while the target AFR is maintained after the vehicle accelerates according to the eighth control strategy.

[0064] According to the AFR control pattern of the seventh and eighth control strategies, when oxygen purification starts after fuel cutoff due to a reduction in vehicle speed, the AFR upstream of the TWC 60 is quickly adjusted to a predetermined rich AFR value (λ > λ tar) and then gradually adjusted to the target AFR value (λ tar ). The AFR upstream of the TWC 60 is then used as the target AFR (λ tar ) until the oxygen purification is completed.

[0065] According to the AFR control pattern of the seventh control strategy, when oxygen purification is completed, the AFR upstream of the TWC 60 is quickly restored to stoichiometric AFR (λ=1). Currently, the vehicle is accelerating, and the AFR downstream of the TWC 60 temporarily becomes rich AFR.

[0066] According to the AFR control pattern of the eighth control strategy, the AFR upstream of the TWC 60 is set as the target AFR (λ tar ) even after oxygen purification is complete and will continue to be used as the target AFR (λ tar ) as the vehicle accelerates and a predetermined deceleration time has elapsed. After this time, the AFR upstream of the TWC 60 is quickly returned to stoichiometric AFR (λ=1).

[0067] Here, a point in time at which oxygen purification is completed means a point in time at which the oxygen storage capacity (OSC) of the TWC 60 is completely consumed, that is, a point in time at which the AFR downstream of the TWC 60 becomes stoichiometric AFR. Here, the AFR downstream of the TWC 60 becomes stoichiometric AFR, the AFR downstream of the TWC 60 is within 97%-100% of the stoichiometric AFR, and is lean AFR or stoichiometric AFR. The AFR downstream of the TWC 60 can be detected by the second oxygen sensor 46.

[0068] With reference to Fig. 9 that there is only a slight difference between the first slip concentration X1 and the second slip concentration X2, while the third slip concentration X3 is greatly reduced when the AFR upstream of the TWC 60 is controlled according to the eighth control strategy, compared to controlling the AFR upstream of the TWC 60 according to the seventh control strategy. Consequently, it is necessary to set the AFR upstream of the TWC 60 as the target AFR (λ tar ) from the time of acceleration of the vehicle until the end of the predetermined deceleration time in order to reduce the third slip concentration X3.

[0069] In summary, it is necessary to determine the target AFR (λ tar ) richer, the AFR upstream of the TWC quickly reaches the target AFR (λ tar ) in the early oxygen purge, increasing the duration during which the AFR upstream of the TWC 60 is used as the target AFR (λ tar) and increase the oxygen purification time to reduce the first, second, and third slip concentrations X1, X2, and X3. In addition, it is also necessary to set the AFR upstream of the TWC 60 as the target AFR (λ tar ) from the acceleration of the vehicle until the end of the predetermined deceleration time.

[0070] The inputs and outputs of the control device 70 in the system for controlling oxygen purification of a three-way catalyst according to an exemplary embodiment of the present invention will be described below with reference to Fig. 10 described in detail.

[0071] Fig. 10 is a block diagram of a system for controlling oxygen purge of a TWC according to an exemplary embodiment of the present invention.

[0072] Fig. Figure 10 shows a simple example of the inputs and outputs of the control device 70 for implementing the system for controlling oxygen purification of a three-way catalyst according to an exemplary embodiment of the present invention. It is clear that the inputs and outputs of the control device 70 according to an exemplary embodiment of the present invention are not limited to the Fig. 10 illustrated exemplary embodiment.

[0073] As in Fig. 10, the control device 70 is electrically connected to the temperature sensor 42, the first and second oxygen sensors 44 and 46, the vehicle speed sensor 48, the engine speed sensor 50, and the air flow sensor 52, and receives the signals corresponding to the values ​​sensed by the sensors 42, 44, 46, 48, 50, and 52.

[0074] The temperature sensor 42 detects the temperature of the exhaust gas upstream of the TWC 60 and transmits the corresponding signal to the control device 70. The control device 70 can predict a substrate temperature of the TWC 60 based on the signal.

[0075] The first oxygen sensor 44 detects the concentration of O contained in the exhaust gas. 2 upstream of the TWC 60 and transmits the corresponding signal to the control device 70. The second oxygen sensor 46 detects the concentration of O contained in the exhaust gas 2 downstream of the TWC 60 and transmits the corresponding signal to the control device 70. The control device 70 can determine whether the TWC 60 is operating normally based on the signals from the first and second oxygen sensors 44 and 46 and performs AFR control of the internal combustion engine 10.

[0076] The vehicle speed sensor 48 detects the vehicle speed and transmits the corresponding signal to the control device 70. The control device 70 can determine whether the vehicle is accelerating or decelerating based on the vehicle speed detected by the vehicle speed sensor 48.

[0077] The engine speed sensor 50 detects the speed of the internal combustion engine 10 and transmits the corresponding signal to the control device 70. The control device 70 can further determine whether the vehicle is accelerating or decelerating based on the speed of the internal combustion engine 10 detected by the engine speed sensor 50.

[0078] The air flow sensor 52 is attached to an intake pipe or intake line to detect the amount of air flowing into the intake system (ie, the intake amount) and transmit the corresponding signal to the control device 70.

[0079] The control device 70 determines the combustion state, the AFR of the exhaust gas, whether the TWC 60 is operating normally, whether oxygen purification is complete, and / or the driving state of the vehicle based on the values ​​detected by the sensors 42, 44, 46, 48, 50, and 52. The control device 70 can control at least one of the following parameters based on the determination: the ignition timing of the spark plug 15, the AFR of the exhaust gas, and the fuel injection amount and fuel injection timing of the injector 18.

[0080] The controller 70 may determine the amount of fuel that forms a desired AFR of the exhaust gas based on the current intake amount and control the AFR upstream of the TWC 60 by controlling the injector 18 to inject the determined amount of fuel.

[0081] A method for controlling oxygen purification of a three-way catalyst according to an exemplary embodiment of the present invention will be described below with reference to Fig. 11 described in detail.

[0082] Fig. 11 is a flowchart of a method for controlling oxygen purge of a TWC according to an exemplary embodiment of the present invention.

[0083] As in Fig. As shown in Figure 11, when the engine is started in step S200, the vehicle is driven according to the driver's manipulation in step S210. That is, the control device 70 determines a current operating state based on the signals transmitted from a plurality of sensors 42, 44, 46, 48, 50, and 52 and controls the operation of the engine according to the current operating state.

[0084] While the vehicle is being driven, the control device 70 determines whether a fuel cut condition is met in step S220. For example, if a driver releases the accelerator pedal on a downhill road, the fuel cut condition may be met. Since the fuel cut condition is well known to those skilled in the art, further description will be omitted.

[0085] If the fuel cutoff condition is not satisfied in step S220, the control device 70 returns to step S210 to control the operation of the engine 10. Therefore, the vehicle is driven by the driver's manipulation before the engine is turned off.

[0086] If the fuel cutoff condition is met in step S220, the control device 70 performs the fuel cutoff in step S230. This stops the supply of fuel to the combustion chamber 12, and the vehicle travels by inertia.

[0087] During the fuel cutoff, the control device 70 determines whether a fuel cutoff stop condition is met in step S240. The fuel cutoff stop condition may be met, for example, when the driver accelerates the vehicle by depressing the accelerator pedal again or the engine speed is reduced below a predetermined speed. Since the fuel cutoff stop condition is well known to those skilled in the art, further description will be omitted.

[0088] If the fuel cut-off stop condition is not satisfied in step S240, the control device 70 returns to step S230 to cut off the supply of fuel to the combustion chamber 12.

[0089] When the fuel cut-off stop condition is met in step S240, the control device 70 resumes supply of the cut-off fuel. Therefore, the removal of the O stored in an oxygen storage of the TWC 60 begins. 2 due to the fuel shutoff. This means that oxygen purging is initiated and carried out.

[0090] Oxygen purification begins by quickly adjusting the AFR upstream of the TWC 60 to the target AFR in step S250. Therefore, the first and second slip concentrations X1 and X2 can be reduced.

[0091] For example, when a fuel cut-off stop signal is input, the controller 70 determines the amount of fuel that causes the AFR upstream of the TWC 60 to become the target AFR based on the current intake amount detected by the air flow sensor 52. The controller 70 controls the injector 18 to inject the determined amount of fuel. Therefore, the AFR upstream of the TWC 60 is quickly adjusted to the target AFR. The target AFR may be, for example, a value below 0.85 (based on lambda), but is not limited to this.

[0092] After the AFR upstream of the TWC 60 is quickly adjusted to the target AFR, the controller 70 maintains the AFR upstream of the TWC 60 as the target AFR in step S260. Thereafter, the controller 70 determines whether the oxygen purification is completed in step S270. As described above, the controller 70 determines whether the oxygen purification is completed by determining whether the AFR downstream of the TWC 60 becomes stoichiometric AFR based on the value detected by the second oxygen sensor 46.

[0093] If the oxygen purification is not completed in step S270, the controller 70 returns to step S260 to continuously maintain the AFR upstream of the TWC 60 as the target AFR.

[0094] When the oxygen purification is completed in step S270, the control device 70 determines whether the vehicle is accelerating in step S280. The control device 70 may determine whether the vehicle is accelerating at the current time if a standby time has elapsed after the oxygen purification is completed. Furthermore, the control device 70 may continuously maintain the AFR as the target AFR upstream of the TWC 60 until the standby time has elapsed after the oxygen purification is completed. The second and third slip concentrations X2 and X3 may be reduced by maintaining the target AFR until the standby time has elapsed after the oxygen purification is completed. The standby time may be a value within 0.5 to 1 second, but is not limited to this.

[0095] If the vehicle is not accelerating in step S280, the controller 70 returns to step S210. Therefore, the AFR upstream of the TWC 60 is quickly adjusted to the stoichiometric AFR and then controlled based on the vehicle's driving condition.

[0096] When the vehicle accelerates in step S280, the controller 70 quickly adjusts the AFR upstream of the TWC 60 to the stoichiometric AFR in step S290 after a delay time (td) has passed. Furthermore, the AFR upstream of the TWC 60 is maintained as the target AFR during the predetermined delay time (td). Therefore, the third slip concentration X3 can be reduced. The predetermined delay time (td) can be a value within 1 second to 3 seconds, but is not limited thereto.

[0097] Fig. 12 is a graph showing examples of NOx concentration escaping from a TWC when conventional AFR control and AFR control according to exemplary embodiments of the present invention are performed for the same vehicle speed change.

[0098] A left diagram in Fig. 12 shows the AFR value upstream of the TWC 60 and the NOx concentration escaped from the TWC 60 according to the conventional AFR control at the same speed change of the vehicle, and a right diagram in Fig. 12 shows the AFR value upstream of the TWC 60 and the NOx concentration that escaped from the TWC 60 according to the AFR control of the present invention at the same speed change of the vehicle. In addition, in the left diagram of Fig. 12, a solid line represents the first AFR control pattern and the concentration of NOx leaked from the TWC when the AFR is controlled according to the first AFR control pattern, and a dotted line represents the second AFR control pattern and the concentration of NOx leaked from the TWC when the AFR is controlled according to the second AFR control pattern.

[0099] With reference to Fig. 12, when the AFR upstream of the TWC 60 is quickly adjusted to the target AFR in the early oxygen purge, the first slip concentration X1 can be reduced. Furthermore, the second slip concentration X2 can be reduced by the controller maintaining the target AFR until the end of the oxygen purge. Furthermore, the third slip concentration X3 can be reduced by continuing to maintain the target AFR during the predetermined delay time (td) after the vehicle acceleration.

[0100] According to the exemplary embodiment of the present invention, when the fuel cutoff condition is satisfied after the fuel cutoff, the AFR upstream of the TWC 60 is quickly adjusted to the target AFR, the target AFR is maintained until the predetermined delay time (td) has passed after the vehicle accelerates, and then the AFR upstream of the TWC 60 is quickly adjusted to the stoichiometric AFR. Therefore, all of the first, second, and third slip concentrations X1, X2, and X3 can be reduced.

[0101] For ease of explanation and to accurately define the appended claims, the terms "upper...", "lower...", "inner...", "outer...", "top", "bottom", "upward", "downward", "front...", "backward...", "front", "backward", "inside", "outside", "inside", "outside", "inward / inward", "outside / outward", "forward / forward" and "backward / rearward" are used to describe features of the exemplary embodiments with reference to positions of those features shown in the drawings.

Claims

[1] A method for controlling oxygen purification of a three-way catalyst (TWC) (60), the method comprising: Setting (S250), by a control device (70), an air-fuel ratio (AFR) upstream of the TWC (60) to a target AFR when the oxygen purge of the TWC is performed after a fuel cut, Maintaining (S260), by the control device (70), the target AFR until the oxygen purification is completed, Monitoring (S280), by the control device (70), when a vehicle accelerates after completion of the oxygen purification, and Maintaining, by the control device (70), the target AFR for a predetermined delay time after determining that the vehicle is accelerating. [2] The method of claim 1, wherein the oxygen purification is terminated when the AFR downstream of the TWC (60) reaches a stoichiometric AFR. [3] The method of claim 1, further comprising adjusting (S290) the AFR upstream of the TWC (60) to the stoichiometric AFR after the target AFR has been maintained for the predetermined delay time. [4] The method according to claim 1 or 3, wherein the predetermined delay time is within a range of 1 second to 3 seconds. [5] The method of claim 3 or 4, further comprising adjusting the AFR upstream of the TWC (60) to the stoichiometric AFR when the vehicle is not accelerating after completion of the oxygen purge. [6] The method according to any one of claims 1 and 3 to 5, wherein the target AFR is maintained for a standby time after completion of the oxygen purification and when the vehicle accelerates is determined after the standby time has elapsed. [7] A method for controlling oxygen purification of a three-way catalyst (TWC), the method comprising: Setting (S250), by a control device (70), an air-fuel ratio (AFR) upstream of the TWC (60) to a target AFR when the oxygen purge of the TWC is performed after a fuel cut, Maintaining (S260), by the control device (70), the target AFR until the oxygen purification is completed, Determining (S280), by the control device (70), when the vehicle accelerates, and Setting (S290), by the controller (70), the AFR upstream of the TWC (60) to a stoichiometric AFR when it is determined that the vehicle is accelerating after the target AFR is maintained for a predetermined delay time. [8] The method of claim 7, wherein the oxygen purification is terminated when the AFR downstream of the TWC (60) reaches the stoichiometric AFR. [9] The method according to claim 7 or 8, wherein the predetermined delay time is within a range of 1 second to 3 seconds. [10] The method of any one of claims 7 to 9, further comprising adjusting the AFR upstream of the TWC (60) to the stoichiometric AFR by the controller (70) when the vehicle is not accelerating after completion of the oxygen purge. [11] The method according to any one of claims 7 to 10, wherein the target AFR is maintained for a standby time after the oxygen purge is completed and when the vehicle accelerates is determined after the standby time has elapsed. [12] A system for controlling oxygen purification of a three-way catalyst (TWC) (60), the system comprising: an internal combustion engine (10) arranged to generate power by combusting an air-fuel mixture and expelling an exhaust gas through an exhaust pipe (40), an injector (18) arranged to supply the fuel to the internal combustion engine, a control device (70) connected to the injector and configured to adjust an air-fuel ratio (AFR) upstream of the TWC (60), wherein the TWC (60) is mounted on the exhaust pipe (40) downstream of the internal combustion engine and is arranged to clean the emissions contained in the exhaust gas, wherein the control device (70) is configured to adjust the AFR upstream of the TWC (60) by determining a fuel quantity to be supplied to the internal combustion engine based on a current intake quantity and by controlling the injector (18) to inject the determined fuel quantity, and wherein the control device (70) is configured to set the AFR upstream of the TWC (60) to a target AFR and maintain the target AFR until the oxygen purge is completed when the oxygen purge is performed while the oxygen in the TWC is purified after a fuel cut-off during which the fuel injection is stopped, and wherein the control device (70) is configured to determine when the vehicle accelerates after the oxygen purification is completed and, when the vehicle accelerates, to maintain the target AFR for a predetermined delay time. [13] The system of claim 12, wherein the oxygen purification is completed when the AFR downstream of the TWC (60) reaches a stoichiometric AFR. [14] The system of claim 12, wherein the predetermined delay time is in a range of 1 second to 3 seconds. [15] The system of claim 12 or 14, wherein the control device (70) is arranged to adjust the AFR upstream of the TWC (60) to the stoichiometric AFR when the predetermined delay time has elapsed after completion of the oxygen purge. [16] The system according to any one of claims 12, 14 and 15, wherein the control device (70) is arranged to adjust the AFR upstream of the TWC (60) to the stoichiometric AFR when the vehicle is not accelerating after completion of the oxygen purge. [17] The system according to any one of claims 12 and 14 to 16, wherein the controller (70) is arranged to maintain the target AFR for a standby time after completion of the oxygen purification and to determine when the vehicle accelerates after the standby time has elapsed.

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