EXHAUST GAS PURIFICATION SYSTEM AND CONTROL METHOD THEREFOR

Abstract

An exhaust gas purification system comprising an internal combustion engine (10) and an exhaust pipe (20) connected to an exhaust manifold (18) of the internal combustion engine (10), comprising: a catalyst (40) arranged on the exhaust pipe (20) on a rear side of the internal combustion engine (10), a catalyst for selective catalytic reduction on a diesel particulate filter (SDPF) (60) arranged on the exhaust pipe (20) on a rear side of the catalyst (40), a reducing agent injector (50) arranged on the exhaust pipe (20) between the catalyst (40) and the SDPF (60), the reducing agent injector (50) injecting a reducing agent, and a control device (70) which controls an amount of reducing agent injected by the reducing agent injector (50), wherein the control device (70) calculates an amount of ammonia leakage, and wherein the control device (70) reduces the amount of reducing agent injection if a temperature change in an interior of the SDPF (60) per unit time is greater than a reference value and a first NOx amount measured by a second NOx sensor (82) at a rear end of the SDPF (60) is greater than a NOx model value, and increases the amount of reducing agent injection if the first NOx amount is smaller than the NOx model value, wherein: the SDPF (60) comprises a plurality of disks (60a, 60b and 60c) in a direction of exhaust gas flow, each of the plurality of disks (60a, 60b and 60c) having a circular cell (60a_10) arranged at a center of the respective one of the plurality of disks (60a, 60b and 60c), and one or more cells (60a_1 to 60a_8) having the same cross section and arranged around the circular cell (60a_10).

Description

TECHNICAL FIELD

[0001] The present disclosure / invention relates to an exhaust gas purification system with a catalyst for selective catalytic reduction on a diesel particulate filter (SDPF) and a control method therefor. BACKGROUND

[0002] A selective catalytic reduction (SCR) catalyst is a catalyst that purifies NOx contained in exhaust gases. By adding a reducing agent such as urea, ammonia, carbon monoxide, and hydrocarbons to the exhaust gas, the SCR catalyst reduces the NOx contained in the exhaust gas through a reduction-oxidation reaction with the reducing agent.

[0003] When a lean NOx trap (LNT) and an SCR catalyst are used together, the diesel particulate filter can be coated with the SCR catalyst due to space constraints. A selective catalytic reduction catalyst on a diesel particulate filter (SDPF) absorbs particulate matter from the exhaust gas and removes the NOx contained in the exhaust gas.

[0004] Generally, a NOx sensor is installed at the front and rear ends of an SCR to measure the NOx purification efficiency of the SCR system. The difference between the values ​​measured at the front and rear ends of the SCR indicates the level / degree of NOx purification and describes the efficiency of the SCR system. However, this vehicle-mounted NOx sensor also reacts to NH3 and detects NH3 as NOx.

[0005] Sufficient NH3 is supplied to one section of the SCR system, but insufficient NH3 is supplied to the remaining sections. In a section with sufficient NH3 supply, the NH3 is absorbed and slips through once the supply exceeds the absorption capacity. If urea injection is stopped to reduce NH3 slip through in the section with sufficient NH3 supply, NOx purification is inhibited in a section with insufficient NH3 supply, thereby increasing the amount of NOx discharged from the tailpipe.

[0006] If NH3 leakage occurs in a section of the SCR, the NOx sensor at the rear end of the SCR mistakes the leaked NH3 as unpurified NOx, thereby controlling the system to increase the amount of urea supplied. In this case, NH3 leakage continuously increases, and the NOx purification efficiency measured by the NOx sensors at the front and rear ends of the SCR deteriorates. Consequently, it is impossible to control the regulation / correction of urea injection and monitor SCR efficiency. In other words, although the SCR continues to maintain good purification efficiency, the purification efficiency measured by a NOx sensor may be determined to be deteriorated. Therefore, from an OBD (On-Board Diagnostics) perspective, a normal SCR may be diagnosed as a faulty SCR.

[0007] In particular, if NH3 is detected during overrun, the detection range is limited and the detection is inaccurate under different driving / propulsion conditions. Furthermore, the contribution of NOx and NH3 to NOx purification efficiency cannot be identified.

[0008] Furthermore, it is not recognized whether the SCR system, which determines the NOx purification efficiency as low, is really malfunctioning to have a low NOx purification performance, or whether a good NOx purification performance is maintained, but a falsification of the sensor value occurs due to an NH3 slippage.

[0009] Consequently, a normal component may be diagnosed as a defective component because the degree of influence of NH3 leakage on NOx purification efficiency is not determined, and in this case, the entire SCR component must be replaced, which generates high costs.

[0010] The information provided in this background section is provided only to enhance understanding of the background of the invention and may therefore contain information that does not represent prior art known to a person skilled in the art.

[0011] DE 10 2013 203 580 A1 discloses a method for monitoring an exhaust gas aftertreatment system of an internal combustion engine having a first SCR catalyst device and optionally at least one second SCR catalyst device arranged downstream in the exhaust gas flow direction. At least one metering device for reactants for the SCR catalyst devices is provided upstream of the first SCR catalyst device. An NH3 sensor is arranged downstream of the first SCR catalyst device and, in the case of a second SCR catalyst device, upstream of the second SCR catalyst device. The signal of the NH3 sensor is monitored as a function of the temperature in the exhaust gas aftertreatment system, and a check is carried out to determine whether the measurable signal of the NH3 sensor matches an expected signal. EXPLANATION OF THE INVENTION

[0012] The present disclosure / invention is based on the object of providing an exhaust gas purification system and a control method therefor, which is capable of detecting the NH3 slip in real time by using a NOx sensor value at a rear end of the SDPF and a model value, adjusting / setting the amount of urea injection, and improving the reliability of OBD diagnosis under various driving conditions / driving conditions in which NH3 slip is generated.

[0013] An exhaust gas purification system comprising an internal combustion engine and an exhaust pipe connected to an exhaust manifold of the internal combustion engine, according to the present invention, comprises: a catalyst (e.g., a catalyst device) arranged on an exhaust pipe on a rear side (downstream side) of the internal combustion engine, a catalyst for selective catalytic reduction on a diesel particulate filter (SDPF) arranged on the exhaust pipe on a rear side of the catalyst (or the catalyst device), a reducing agent injector (e.g., a reducing agent injection device) arranged on the exhaust pipe between the catalyst and the SDPF and injecting a reducing agent, and a control device that controls an amount of reducing agent injected by the reducing agent injector, wherein the control device controls an amount (e.g., height, e.g.Degrees) of ammonia slippage is calculated and the amount of reductant injection is reduced if a temperature change inside the SDPF per unit time is greater than a reference value and a first NOx amount measured by a second NOx sensor at a rear end of the SDPF is greater than a NOx model value, and the amount (e.g., height, e.g., degrees) of reductant injection is increased if the first NOx amount is smaller than the NOx model value. The SDPF has a plurality of disks in a direction of an exhaust flow (e.g., along an exhaust flow), and each of the plurality of disks has a circular cell arranged at a center of each of the plurality of disks, and one or more cells having the same cross section (e.g., with respect to each other) and arranged around the circular cell.

[0014] For example, the control device may perform a malfunction diagnosis when a NOx purification efficiency is greater than a critical NOx purification efficiency.

[0015] The NOx purification efficiency can be calculated, for example, by a ratio obtained by dividing a value obtained by subtracting the first NOx amount from a second NOx amount measured by a first NOx sensor at a front end of the SDPF by the second NOx amount.

[0016] The exhaust gas purification system may further include a selective catalytic reduction (SCR) catalyst on the exhaust pipe at the rear end of the SDPF for reducing NOx contained in the exhaust gas by utilizing NH3 passed through from the SDPF.

[0017] The catalyst (or catalyst device) may comprise a NOx trap (LNT) catalyst.

[0018] The catalyst (or catalyst device) may comprise a diesel oxidation catalyst (DOC).

[0019] According to an exemplary embodiment of the present disclosure / invention, NH3 can be reduced during driving and the best possible NOx purification efficiency can be maintained by detecting the NH3 slippage of the SDPF and optimizing the amount of urea injection.

[0020] Furthermore, it can prevent leaked NH3 from being falsely measured as NOx by a NOx sensor, and the amount of leaked NOx and NH3 at the rear end of the SDPF can be calculated and thus predictable (expected).

[0021] Furthermore, the influence of NH3 slip on NOx purification efficiency can be determined in real time, which can improve the reliability of OBD diagnosis under different driving conditions / power conditions in which NH3 slip is generated. BRIEF DESCRIPTION OF THE CHARACTERS Fig. 1 shows a schematic view of an exhaust gas purification system according to an exemplary embodiment of the present disclosure / invention. Fig. 2 is a block diagram illustrating the relationship of input and output of a control device of the exhaust gas purification system according to an exemplary embodiment of the present disclosure / invention. Fig. 3 is a perspective view schematically illustrating an SDPF used in an exemplary embodiment of the present disclosure / invention. Fig. 4 is a side cross-sectional view schematically illustrating an SDPF used in an exemplary embodiment of the present disclosure / invention. Fig. 5 shows a front cross-sectional view illustrating an example of cells used in an exemplary embodiment of the present disclosure / invention. Fig. 6 shows a flowchart illustrating a method for adjusting / setting the amount of reductant injection in an exhaust gas purification system according to an exemplary embodiment of the present disclosure / invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] In the following, an exemplary embodiment of the present disclosure / invention will be described in detail with reference to the accompanying drawings.

[0023] The sizes and thicknesses of the structures shown in the drawings are chosen for convenience of description, so that the present disclosure / invention is not limited to these structures shown in the drawings, and the thicknesses may be exaggerated to better clarify some parts and regions.

[0024] Those parts / components that do not relate to the description of the exemplary embodiments are not shown to make the description clearer, and like reference numerals denote like elements throughout the description.

[0025] Terms such as “first” and “second” etc. are used to distinguish components with the same name, but do not specify a particular order.

[0026] Fig. 1 shows a schematic view of an exhaust gas purification system according to an exemplary embodiment of the present disclosure / invention.

[0027] An exhaust gas purification system for an internal combustion engine has, as in Fig. 1 shown on: an internal combustion engine 10, an exhaust pipe 20, an exhaust gas recirculation (EGR) device 30, a NOx trap (lean NOx trap, LNT) (e.g. LNT catalyst (e.g. just called catalyst or catalyst device)) 40, a reductant injector (e.g. reductant injection device) 50, a catalyst for selective catalytic reduction on a diesel particulate filter (SDPF) 60 and a control device 70. The control device 70 can be, for example, an electronic control unit (ECU).

[0028] The internal combustion engine 10 combusts an air-fuel mixture in which fuel and air are mixed to convert chemical energy into mechanical energy. The internal combustion engine 10 is connected to an intake manifold 16 to receive the air into a combustion chamber 12, and is connected to an exhaust manifold 18 so that the exhaust gas generated in the combustion process is collected in the exhaust manifold 18 and discharged to the outside. A (fuel) injector (e.g., a (fuel) injection device) 14 is attached to the combustion chamber 12 to inject the fuel into the combustion chamber 12.

[0029] A diesel engine is illustrated here, but a lean-burn gasoline engine can also be used. When using a gasoline engine, the mixture is introduced into the combustion chamber 12 through the intake manifold 16, and a spark plug (not shown) is installed on the combustion chamber 12 for ignition. Furthermore, when using an internal combustion engine with gasoline direct injection (GDI), the injector 14 is attached to the combustion chamber 12, just like in a diesel engine.

[0030] The exhaust pipe 20 is connected to the exhaust manifold 18, so that the exhaust gas is discharged to the exterior of the vehicle. The LNT 40, the reductant injector 50, and the SDPF 60 are attached to the exhaust pipe 20 to remove the hydrocarbons, carbon monoxide, particulate matter, and nitrogen oxides contained in the exhaust gas.

[0031] The EGR device 30 is attached to the exhaust pipe 20 to recirculate a portion of the exhaust gas discharged from the engine 10 to the engine 10 through the EGR device 30. Furthermore, the EGR device 30 is connected to the intake manifold 16 to control the combustion temperature by mixing a portion of the exhaust gas with air. This combustion temperature control is performed by controlling an amount of exhaust gas supplied to the intake manifold 16 under the control of the control device 70. Accordingly, a recirculation valve (not shown) controlled by the control device 70 may be attached to the conduit connecting the EGR device 30 and the intake manifold 16.

[0032] A first oxygen sensor 72 is mounted on the exhaust pipe 20 on the rear side (downstream side) of the EGR device 30 to detect an amount of oxygen contained in the exhaust gas passing through the EGR device 30 and transmit the detected amount of oxygen to the control device 70, thereby enabling the control device 70 to assist in performing lean / rich control of the exhaust gas. In this specification, a measured value of the first oxygen sensor 72 is referred to as the air-fuel ratio of the front end of the LNT 40.

[0033] Furthermore, a first temperature sensor 74 is attached to the exhaust pipe 20 at the rear side of the EGR device 30 to detect a temperature of the exhaust gas passing through the EGR device 30.

[0034] The LNT 40 is mounted on the exhaust pipe 20 at the rear of the EGR device 30. The LNT 40 adsorbs the nitrogen oxides (NOx) contained in the exhaust gas in a lean atmosphere, desorbs the adsorbed nitrogen oxides in a rich atmosphere, and reduces the nitrogen oxides contained and / or desorbed in the exhaust gas. Furthermore, the LNT 40 oxidizes the carbon monoxide (CO) and hydrocarbons (HC) contained in the exhaust gas.

[0035] It should be understood that hydrocarbons refer to all carbon and hydrogen compounds contained in the exhaust gas and fuel. Furthermore, the LNT 40 is explained as an example of the first catalyst, although the first catalyst can also be a diesel oxidation catalyst (DOC).

[0036] A second oxygen sensor 76, a second temperature sensor 78 and a first NOx sensor 80 are mounted on the exhaust pipe 20 rearward of the LNT 40.

[0037] The second oxygen sensor 76 measures the amount of oxygen contained in the exhaust gas introduced into the SDPF 60 and transmits a signal of the measured oxygen amount to the control device 70. Based on the detected values ​​of the first oxygen sensor 72 and the second oxygen sensor 76, the control device 70 can perform lean / rich control. In this specification, a value measured by the second oxygen sensor 76 is referred to as the air-fuel ratio of the front end of the filter.

[0038] The second temperature sensor 78 measures a temperature of the exhaust gas introduced into the SDPF 60 and transmits a signal of the measured temperature to the control device 70. A third temperature sensor 90 may be further arranged to detect the temperature of the exhaust gas exiting the SDPF 60 and transmit a signal of the detected temperature to the control device 70.

[0039] The first NOx sensor 80 measures an amount of NOx contained in the exhaust gas introduced into the SDPF 60 and transmits a signal of the measured amount to the control device 70. The amount of NOx measured by the first NOx sensor 80 can be used to determine the amount of reductant injected by the reductant injector 50.

[0040] The reductant injector 50 is mounted on the exhaust pipe 20 upstream of the SDPF 60 and is controlled by the control device 70 to inject reductant into the exhaust gas. Typically, the reductant injector 50 injects urea, and the injected urea is converted into ammonia by hydrolysis.

[0041] However, the reducing agent is not limited to urea. For convenience of description, ammonia is used as the reducing agent below, and urea is injected by the reducing agent injector 50. However, it should be understood that, within the scope of the appended claims, other reducing agents besides ammonia are also within the scope of the present disclosure / invention.

[0042] A mixer 55 may be attached to the exhaust pipe 20 rearward of the reducing agent injector 50 so that the reducing agent is evenly mixed with the exhaust gas.

[0043] The SDPF 60 is arranged on the exhaust pipe 20 rearward of the mixer 55 to collect particulate matter contained in the exhaust gas and to reduce the nitrogen oxides contained in the exhaust gas by using the reducing agent injected by the reducing agent injector 50.

[0044] The SDPF 60 can, as in Fig. 3 to Fig. 5, one or more discs 60a, 60b, and 60c along the exhaust flow (in series), and each of the discs 60a, 60b, and 60c has one or more cells, each having the same cross-section. For example, a disc 60a may include a plurality of cells 60a_1 to 60a_10.

[0045] The controller 70 recognizes the SDPF 60 as a plurality of slices 60a, 60b, and 60c for calculating the reducing agent injection amount. That is, the slices 60a, 60b, and 60c of the SDPF 60 are arranged in a row along the exhaust flow and may be physically or virtually separated. The lengths of the respective slices 60a, 60b, and 60c are equal to each other, thereby minimizing memory capacity, calculation time, and the like.

[0046] Furthermore, the control device 70 divides each slice 60a, 60b, and 60c into a plurality of cells 60a_1 to 60a_10 and recognizes them as such. The number of cells 60a_1 to 60a_10 constituting a slice can be determined by a developer by considering calculation accuracy, memory capacity, and calculation time. Furthermore, the n-th cell of each slice is arranged at the same position as the n-th cell of the other slices in the radial and circumferential directions, and the shapes thereof are also equal to each other. Furthermore, the areas of the cells are equal to each other. As shown in Fig. As shown in Figure 5, each fan-shaped cell 60a_1 to 60a_8 is equal, and a central angle thereof is equal. Circular cells 60a_10 may be arranged in the center, and the cells 60a_1 to 60a_8 with the fan-shaped pieces (intersecting the portions of the circular cells) have the same central angle and are arranged around the circular cells 60a_10. The areas of the respective cells are equal to each other, and the position and shape of the nth cell of each slice are equal, thereby minimizing memory capacity and calculation time.

[0047] In each cell 60a_1 to 60a_10, the physical / chemical characteristics, such as the nitrogen oxide concentration, the ammonia concentration, and the temperature, are the same. Furthermore, it is assumed that the exhaust gas, NOx, ammonia, and the like are not movable or migrate between the cells 60a_1 to 60a_10 of each disk 60a, 60b, and 60c.

[0048] The number of disks 60a, 60b and 60c, the shape of the disks 60a, 60b and 60c, the number of cells 60a_1 to 60a_10 and the shape of the cells are not limited to those shown here as examples and can be determined by the developer in consideration of the accuracy of the model calculation.

[0049] Furthermore, an additional SCR catalyst may be provided on the exhaust pipe 20 at the rear end of the SDPF 60, which reduces the NOx contained in the exhaust gas by using the NH3 passed through the SDPF 60. The additional SCR catalyst may further purify the NOx if the SDPF 60 does not completely purify the NOx. The additional SCR catalyst may be provided separately from the SDPF 60.

[0050] A differential pressure sensor 66 is attached to the exhaust pipe 20. The differential pressure sensor 66 measures a pressure difference between the front end and the rear end of the SDPF 60 to transmit a signal corresponding to the measured difference to the controller 70. The controller 70 can control the SDPF 60 to be regenerated if the pressure difference measured by the differential pressure sensor 66 is equal to or greater than a specified pressure.

[0051] In this case, the particulate matter collected in the SDPF 60 can be combusted by post-injection of fuel through the injector 14.

[0052] Furthermore, a second NOx sensor 82 is mounted on the exhaust pipe 20 rearward of the SDPF 60. The second NOx sensor 82 detects the amount of nitrogen oxides contained in the exhaust gas discharged from the SDPF 60 and transmits a signal corresponding to the measured amount to the control device 70. The control device 70 can observe whether the SDPF 60 is normally removing the nitrogen oxides contained in the exhaust gas based on the detected value of the second NOx sensor 82. That is, the second NOx sensor 82 can be used to evaluate the performance of the SDPF 60.

[0053] The control device 70 determines an operating condition of the internal combustion engine 10 based on the signals detected by the sensors and controls the lean / rich control and the amount of reducing agent injected by the reducing agent injector 50 based on the determined operating conditions of the internal combustion engine 10.

[0054] For example, the control device 70 controls the air-fuel ratio to a rich atmosphere to remove nitrogen oxides from the LNT 40 (referred to as "LNT regeneration" in this specification) and to remove nitrogen oxides from the SDPF 60 by injecting reductant. The lean / rich control can be performed by adjusting the amount of fuel injected by the injector 14 and an injection time (e.g., injection timing).

[0055] The control device 70 calculates the internal temperature of the SDPF 60, the amount of ammonia absorbed in the SDPF 60, and the amount of NOx contained in the exhaust gas at the rear end of the LNT 40 based on engine driving conditions and an expected (e.g., estimated) NOx purification efficiency of the SDPF 60.

[0056] For this purpose, the control device 70 stores characteristics of absorption and oxidation of ammonia according to an internal temperature of the SDPF 60, characteristics of desorption of ammonia according to an internal temperature of the SDPF 60, and characteristics of NOx leakage of the LNT 40 in a rich atmosphere.

[0057] The characteristics of ammonia absorption and oxidation according to the internal temperature of the SDPF 60, the characteristics of ammonia desorption according to the internal temperature of the SDPF 60, and the characteristics of NOx leakage of the LNT 40 in a rich atmosphere, etc., can be defined as representations through many experiments. Furthermore, the control device 70 performs the regeneration of the SDPF 60 and the desulfurization of the LNT 40.

[0058] The control device 70 may be implemented as one or more processors operated by a predetermined program, and the predetermined program may be programmed to perform each step of the method for controlling the exhaust gas purification system according to the exemplary embodiment of the present disclosure / invention.

[0059] Fig. 2 is a block diagram illustrating the relationship of input and output of a control device 70 of the exhaust gas purification system according to an exemplary embodiment of the present disclosure / invention.

[0060] As in Fig. 2, the first oxygen sensor 72, the first temperature sensor 74, the second oxygen sensor 76, the second temperature sensor 78, the first NOx sensor 80, the second NOx sensor 82, the third temperature sensor 90, the differential pressure sensor 66 and an intake amount sensor 11 may be electrically connected to the control device 70 and transmit the detected values ​​to the control device 70.

[0061] The first oxygen sensor 72 detects an amount of oxygen in the exhaust gas passing through the EGR device 30 to transmit a signal corresponding to the amount to the control device 70. The control device 70 can assist in performing lean / rich control of the exhaust gas based on the amount of oxygen contained in the exhaust gas detected by the first oxygen sensor 72. The value detected by the first oxygen sensor 72 can be represented by a lambda. The lambda represents a ratio of an actual air-fuel ratio to a theoretical air-fuel ratio. The atmosphere is lean if lambda is greater than 1, and the atmosphere is rich if lambda is less than 1.

[0062] The first temperature sensor 74 detects a temperature of the exhaust gas passing through the EGR device 30 to transmit a signal corresponding to the detected temperature to the control device 70.

[0063] The second oxygen sensor 76 measures an amount of oxygen contained in the exhaust gas discharged from the LNT 40 (and / or entering the SDPF 60, if applicable) to transmit a signal corresponding to the measured amount of oxygen to the controller 70.

[0064] The second temperature sensor 78 measures a temperature of the exhaust gas introduced into the SDPF 60 to transmit a signal corresponding to the measured temperature to the control device 70.

[0065] The first NOx sensor 80 measures an amount of NOx contained in the exhaust gas introduced into the SDPF 60 to transmit a signal corresponding to the measured amount to the control device 70.

[0066] The second NOx sensor 82 detects an amount of nitrogen oxides contained in the exhaust gas discharged from the SDPF 60 to transmit a signal corresponding to the detected amount to the control device 70.

[0067] The differential pressure sensor 66 measures a pressure difference between the front end and the rear end of the SDPF 60 to transmit a signal corresponding to the measured difference to the control device 70, and the third temperature sensor 90 measures a temperature of the exhaust gas discharged from the SDPF 60 to transmit a signal corresponding to the measured temperature to the control device 70.

[0068] The control device 70 determines an engine operating condition, a fuel injection amount, a fuel injection timing, a fuel injection pattern, a reduction in the injection amount, a regeneration timing of the SDPF 60 and a regeneration / desulfurization timing of the LNT 40 based on the transmitted values ​​and outputs signals for controlling the (fuel) injector 14 and the reductant injector 50 to the reductant injector 50 and to the injector 14.

[0069] In the exhaust gas purification system according to the exemplary embodiment of the present disclosure / invention, in addition to the Fig. 2, a plurality of sensors may be installed, but are omitted for simplicity of description.

[0070] Fig. 6 shows a flowchart illustrating a method for adjusting / setting the amount of reductant injection in an exhaust gas purification system according to an exemplary embodiment of the present disclosure / invention.

[0071] In relation to Fig. 6, the control device 70 starts to control when the internal combustion engine 10 starts.

[0072] First, the controller 70 calculates an internal temperature of the SDPF 60. The controller 70 may calculate the internal temperature of the SDPF 60 according to the driving information. The driving information may include an engine speed, a fuel injection amount, an outside temperature, or a coolant temperature.

[0073] The controller 70 calculates a temperature change (dT / dt) per unit time of the interior of the SDPF 60 and determines whether or not the temperature change (dT / dt) per unit time of the interior of the SDPF 60 is greater than a first predetermined value (S601). Here, the first predetermined value may be at least approximately 10°C.

[0074] Subsequently, if the temperature change (dT / dt) per unit time of the inside of the SDPF 60 is larger than the predetermined value, the controller 70 determines whether or not a NOx measurement value at the rear end of the SDPF 60 is larger than a NOx model value (S602).

[0075] Subsequently, if the NOx measurement value at the rear end of the SDPF 60 is larger than the NOx model value, the controller 70 calculates (S603) and reduces the amount of reducing agent injection (S604).

[0076] If the NOx measurement value at the rear end of the SDPF 60 is not greater than the NOx model value, the controller 70 determines a deficiency in purification efficiency (S605) and increases the amount of reducing agent injection (S606).

[0077] The control device 70 performs a malfunction diagnosis when a NOx purification efficiency of the SDPF 60 is greater than a critical NOx purification efficiency (η threshold ). Here, the malfunction diagnosis determines that the SDPF 60 has failed.

[0078] The NOx purification efficiency of the SDPF 60 is calculated by a / the ratio obtained by subtracting a value obtained by subtracting the NOx measurement value at the rear end of the SDPF 60 (NO xDsmeas ) from the NOx measurement value at the front end of the SDPF 60 (NO xUsmeas ), by the NOx measurement value at the front end of the SDPF 60 (NO xUsmeas). The conditions of the malfunction analysis can be expressed as an equation (1). NoxUS meas−NOxDs measNOxUs meas>ηthreshold

[0079] Furthermore, the NOx measurement value is measured at the rear end of the SDPF 60 (NO xDsmeas ) is calculated by taking the NOx model value at the rear end of the SDPF 60 (NO xDsmodel ) and a value of the product of an amount of ammonia leakage (NH 3slip ) and a proportion / ratio of the NH3 (X) detected as NOx by the second NOx sensor 82.

[0080] Consequently, equation (1) can be expressed as equation (2). NoxUS meas−(NOxDs meas+χ*NH3slip)NoxUS meas>ηthreshold

[0081] Furthermore, equation (2) can be expressed as equation (3). This time, the model NOx purification efficiency (η model ) given as a difference from the NOx model value at the rear end of the SDPF 60 (NOxDsmodel ) and the NOx measurement value at the front end of the SDPF 60 (NO xUsmeas ) divided by the NOx measurement at the front end of the SDPF 60 (NO xUsmeas ). ηmodel−χ*NH3slipNoxUS meas>ηthreshold

[0082] Furthermore, equation (3) can be expressed as equation (4). ηmodel−ηthreshold>χ*NH3slipNoxUS meas

[0083] The control device 70 calculates a limit value of the NOx purification efficiency (η limit ) by achieving a critical NOx purification efficiency (η threshold ) of the malfunction analysis and a NOx purification efficiency of a sensor offset (η offset ) must be subtracted from the model NOx abatement efficiency. This is expressed in equation (5). ηlimit=ηmodel−ηthreshold−ηoffset

[0084] This can be expressed as equation (6) by substituting equation (5) into equation (4). ηlimit>χ*NH3slipNoxUS meas−ηoffset

[0085] If equation (6) is satisfied, that is, the limit value of NOx purification efficiency (η limit ) is greater than the difference of a value consisting of the product of the amount of ammonia leakage (NH 3slip ) and a proportion / ratio of the NH3 detected as NOx by the second NOx sensor 82 (X) divided by the measured value of the first NOx sensor 80 at the front end of the SDPF, and the NOx purification efficiency of a sensor offset (η offset ), the control device 70 can perform a malfunction analysis. If equation (6) is not satisfied, the malfunction analysis stops.

[0086] According to the exemplary embodiments of the present disclosure / invention, NH3 can be reduced during driving and the best possible NOx purification efficiency can be maintained by detecting the NH3 slippage of the SDPF 60 and optimizing the amount of urea injection.

[0087] Furthermore, leaked NH3 from a second NOx sensor 82 can be prevented from being erroneously measured as NOx, and the amount of leaked NOx and NH3 at the rear end of the SDPF 60 can be calculated and thus predictable (expected).

[0088] Furthermore, the influence of NH3 slip on NOx purification efficiency can be determined in real time, which can improve the reliability of OBD diagnosis under different driving conditions / powertrain conditions in which NH3 slip is generated. LIST OF REFERENCE SYMBOLS 10 Internal combustion engine 11 Intake flow sensor 12 Combustion chamber 16 intake manifold 18 exhaust manifold 20 exhaust pipe 30 Exhaust gas recirculation device (EGR device) 40 Catalyst (NOx trap, LNT catalyst) 50 Reductant injector 55 mixers 60 Catalyst for selective catalytic reduction on a diesel particulate filter (SDPF) 60a, 60b, 60c disc 60a_1 - 60a_8 cell 60a_9 circular cell 66 Differential pressure sensor 70 Control device 72 first oxygen sensor 74 first temperature sensor 76 second oxygen sensor 78 second temperature sensor 80 first NOx sensor 82 second NOx sensor 90 third temperature sensor

Claims

[1] An exhaust gas purification system comprising an internal combustion engine (10) and an exhaust pipe (20) connected to an exhaust manifold (18) of the internal combustion engine (10), comprising: a catalyst (40) arranged on the exhaust pipe (20) on a rear side of the internal combustion engine (10), a catalyst for selective catalytic reduction on a diesel particulate filter (SDPF) (60) arranged on the exhaust pipe (20) on a rear side of the catalyst (40), a reducing agent injector (50) arranged on the exhaust pipe (20) between the catalyst (40) and the SDPF (60), the reducing agent injector (50) injecting a reducing agent, and a control device (70) which controls an amount of reducing agent injected by the reducing agent injector (50), wherein the control device (70) calculates an amount of ammonia leakage, and wherein the control device (70) reduces the amount of reducing agent injection if a temperature change in an interior of the SDPF (60) per unit time is greater than a reference value and a first NOx amount measured by a second NOx sensor (82) at a rear end of the SDPF (60) is greater than a NOx model value, and increases the amount of reducing agent injection if the first NOx amount is smaller than the NOx model value, wherein: the SDPF (60) comprises a plurality of disks (60a, 60b and 60c) in a direction of exhaust gas flow, each of the plurality of disks (60a, 60b and 60c) having a circular cell (60a_10) arranged at a center of the respective one of the plurality of disks (60a, 60b and 60c), and one or more cells (60a_1 to 60a_8) having the same cross section and arranged around the circular cell (60a_10). [2] Exhaust gas purification system according to claim 1, wherein: the control device (70) performs a malfunction analysis when a NOx purification efficiency of the SDPF (60) is greater than a critical NOx purification efficiency. [3] Exhaust gas purification system according to claim 2, wherein: the NOx purification efficiency of the SDPF (60) is calculated by a ratio obtained by dividing a value obtained by subtracting the first NOx amount from a second NOx amount measured by a first NOx sensor (80) at a front end of the SDPF (60) by the second NOx amount. [4] Exhaust gas purification system according to one of claims 1-3, further comprising: a selective catalytic reduction (SCR) catalyst on the exhaust pipe (20) at the rear end of the SDPF (60) for reducing NOx contained in the exhaust gas by utilizing NH3 pass-through from the SDPF (60). [5] The exhaust gas purification system according to any one of claims 1-4, wherein: the catalyst comprises a NOx trap (LNT) catalyst (40). [6] The exhaust gas purification system according to any one of claims 1-5, wherein: the catalyst has a diesel oxidation catalyst (DOC).

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