JP5796277B2 - Exhaust gas purification system - Google Patents

Description

  In the present invention, particulate matter (Particulate Matter; hereinafter referred to as PM) in exhaust gas of a diesel engine is collected by a diesel particulate filter (hereinafter referred to as DPF) and discharged to the outside. The present invention relates to an exhaust gas purification system that reduces the amount of PM.

  An exhaust gas purification system that collects PM discharged from a diesel engine with a filter called DPF and reduces the amount of PM discharged to the outside is known. As such an exhaust gas purification system, a system using a continuous regeneration type DPF device including a DPF and a DOC (Diesel Oxidation Catalyst) provided on the upstream side of the DPF is known.

  In the continuous regeneration type DPF device, when the exhaust gas temperature is high, PM trapped in the DPF is continuously burned and purified, and the DPF is self-regenerated, but when the exhaust gas temperature is low, the DOC Since the temperature is not lowered and activated, it becomes difficult to oxidize PM and self-regenerate DPF. As a result, PM accumulates on the DPF and the clogging of the DPF proceeds, causing a problem of increased exhaust pressure.

  Therefore, in the exhaust gas purification system, when the PM accumulation amount in the DPF exceeds a predetermined amount, the fuel is subjected to multistage delayed injection (multi-injection) or post-injection (post-injection) in the cylinder (in-cylinder). DPF regeneration is performed in which the temperature of the exhaust gas flowing into the DPF is forcibly raised to burn and remove the PM collected in the DPF.

  Multistage delayed injection (multi-injection) is performed in order to raise the temperature of the exhaust gas discharged from the engine and raise the temperature of the DOC to the catalyst activation temperature. In post-injection (post-injection), a large amount of unburned fuel is supplied into the exhaust gas, and the supplied unburned fuel is oxidized (combusted) at the DOC, so that the exhaust gas temperature at the DPF inlet is burned by PM. This is done to raise the temperature above that.

  Further, in the exhaust gas purification system, EGR (Exhaust Gas Recirculation) control is performed in which part of the exhaust gas discharged from the engine is recirculated to the intake side to reduce NOx.

  In this EGR control, an EGR pipe that connects an intake manifold and an exhaust manifold of the engine is provided, and an EGR valve that is provided in the EGR pipe is adjusted to adjust the opening degree of the EGR valve, whereby EGR that is the amount of exhaust gas recirculated to the intake side The amount (or EGR rate) is controlled. The EGR pipe is provided with an EGR cooler for cooling the exhaust gas recirculated to the intake side.

  In conventional exhaust gas purification systems, if EGR control is performed during DPF regeneration (during post-injection), exhaust gas containing a large amount of unburned fuel is recirculated to the intake side, causing engine parts (piston rings, etc.) May be damaged or the performance of the EGR cooler may be deteriorated. Therefore, the conventional exhaust gas purification system has a problem that the EGR control cannot be performed during the DPF regeneration, and the exhaust gas during the DPF regeneration deteriorates.

  Therefore, the present applicant performs the exhaust pipe injection in which fuel is directly injected into the exhaust pipe instead of the post injection (post injection), and performs the EGR control even during the DPF regeneration. An exhaust gas purification system that improves exhaust gas is being proposed. In this exhaust gas purification system, the opening degree of the EGR valve is determined based on the engine speed and the fuel injection amount.

JP 2010-106691 A Japanese Patent No. 4175281

  By the way, in the DPF regeneration, when the flow rate of the exhaust gas increases during the DPF regeneration, a large amount of fuel must be injected to raise the temperature of the exhaust gas, which causes a problem of deterioration of fuel consumption. In order to suppress such a deterioration in fuel consumption, the exhaust gas purification system controls the boost pressure of the turbocharger low in order to efficiently raise the temperature of the exhaust gas by reducing the flow rate of the exhaust gas as much as possible during DPF regeneration. Is common.

  However, in the above-described exhaust gas purification system that performs EGR control during DPF regeneration, if the accelerator pedal is depressed during DPF regeneration to accelerate the vehicle, the engine speed and fuel injection amount increase and the exhaust manifold pressure increases. However, since the pressure (boost pressure) of the intake manifold remains low, a large amount of exhaust gas is recirculated to the intake side. At this time, since the opening degree of the EGR valve is controlled regardless of the boost pressure, the EGR valve is opened despite a small amount of air taken in by the engine, and a large amount of exhaust gas is recirculated to the intake side. The amount will be excessive.

  If the EGR amount becomes excessive, the flow rate of the exhaust gas supplied to the continuous regeneration type DPF device decreases. As a result, the air-fuel ratio λ, which is the ratio of the air amount to the fuel amount, falls below 1, and unburned fuel is discharged at the DOC. It becomes impossible to oxidize. Then, the unburned fuel is discharged into the atmosphere without being treated, and there arises a problem that white smoke or black smoke is generated.

  Furthermore, if the EGR amount becomes excessive, the flow rate of exhaust gas supplied to the turbine of the turbocharger also decreases, so that the turbine rotation delays. As a result, the boost pressure is delayed, resulting in insufficient power, resulting in poor acceleration performance. Problem arises.

  Therefore, the object of the present invention is to solve the above problems, suppress the deterioration of exhaust gas during DPF regeneration, and even when the vehicle is accelerated during DPF regeneration, white smoke and black smoke are not generated, It is an object to provide an exhaust gas purification system capable of obtaining an excellent acceleration performance.

  The present invention has been developed to achieve the above object, and is provided in an exhaust pipe of an engine and collects particulate matter in exhaust gas, and an exhaust manifold and an intake manifold of the engine. And an EGR valve that adjusts the amount of exhaust gas recirculated from the exhaust manifold to the intake manifold, and controls the opening of the EGR valve based on the engine speed and the fuel injection amount. And a target boost pressure for determining a target boost pressure based on a boost pressure sensor for detecting a boost pressure from the pressure of the intake manifold, an engine speed and a fuel injection amount. The target boost pressure and the boost determined by the calculation unit and the target boost pressure calculation unit Based on a difference between the detected boost pressure sensor, which is the diesel particulate filter exhaust gas purification system and an EGR valve opening correction section for correcting the opening degree of the EGR valve at the time of reproducing.

  The EGR valve opening correction unit obtains a compensation value for the opening of the EGR valve based on the difference between the target boost pressure and the boost pressure, and the compensation value is determined based on the engine speed and the fuel injection amount. The opening degree of the EGR valve may be corrected by subtracting from the opening degree of the EGR valve.

  According to the present invention, exhaust gas that suppresses deterioration of exhaust gas during DPF regeneration and does not generate white smoke and black smoke even when the vehicle is accelerated during DPF regeneration, and can provide sufficient acceleration performance. A purification system can be provided.

1 is a system configuration diagram of an engine, an intake / exhaust system, and a fuel injection system in a vehicle to which an exhaust gas purification system of the present invention is applied. (A) is a setting example of a normal EGR map, and (b) is a diagram showing a setting example of a DPF regeneration EGR map. In this invention, it is a figure which shows the example of a setting of a target boost pressure map. In this invention, it is a figure which shows the example of a setting of the coefficient map for a correction | amendment. In this invention, it is a figure which shows the example of a setting of a compensation value map. In this invention, it is the figure which showed the opening degree of the EGR valve after correction | amendment when the coefficient for correction | amendment was set to -1 in a map format. It is a figure explaining operation | movement of the exhaust gas purification system of this invention, (a) is a target boost pressure when a vehicle is started and accelerated, and the change of boost pressure, (b) explains the change of the opening degree of an EGR valve. FIG. In this invention, it is a graph explaining the air fuel ratio at the time of acceleration, and the density | concentration (HC density | concentration) of the unburned fuel contained in the exhaust gas discharged | emitted. It is a flowchart which shows the control flow at the time of determining the opening degree of the EGR valve in the exhaust gas purification system of this invention.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a system configuration diagram of an engine, an intake / exhaust system, and a fuel injection system in a vehicle to which an exhaust gas purification system according to the present embodiment is applied.

  First, the configuration of the exhaust system will be described. An exhaust pipe 103 for exhausting the exhaust gas of the engine 101 to the atmosphere is connected to the exhaust manifold 102 of the engine 101, and the exhaust manifold 102 is connected to the uppermost stream of the exhaust pipe 103. And an intake manifold 104 are provided with an EGR pipe 105. The EGR pipe 105 is provided with an EGR cooler 106 that cools the exhaust gas, and an EGR valve 107 that adjusts an EGR amount (or EGR rate) that is the amount of exhaust gas that is recirculated from the exhaust manifold 102 to the intake manifold 104. ing.

  A turbine 109 of the high-pressure stage turbocharger 108 is provided downstream of the exhaust pipe 103, and a turbine 111 of the low-pressure stage turbocharger 110 is provided further downstream. An exhaust brake valve 112 that closes the exhaust pipe 103 is provided downstream of the turbine 111, and a continuous regeneration type DPF device 113 is provided further downstream. The continuous regeneration type DPF device 113 includes a DOC 114 that promotes oxidation of fuel injected into the exhaust pipe 103 during DPF regeneration, and a DPF 115 that collects PM. An exhaust throttle 116 is provided downstream of the continuous regeneration type DPF device 113, and the exhaust pipe 103 is opened to the atmosphere downstream of the exhaust throttle 116. The exhaust pipe 103 may be provided with an SCR (Selective Catalytic Reduction) device (not shown).

  Next, the configuration of the intake system will be described. The intake manifold 104 is connected to the intake manifold 104 for taking air into the engine 101 from the atmosphere. The uppermost stream of the intake pipe 117 is open to the atmosphere, and an air cleaner 118 for removing foreign matters such as dust is provided downstream thereof. A compressor 119 of the low-pressure stage turbocharger 110 is provided downstream of the air cleaner 118, and a compressor 120 of the high-pressure stage turbocharger 108 is provided further downstream. An intercooler 121 for cooling the intake air supercharged by the low-pressure stage turbocharger 110 and the high-pressure stage turbocharger 108 is provided downstream of the compressor 120, and an intake throttle 122 for limiting the intake air amount is further provided downstream. Is provided. An intake pipe 117 is connected to the intake manifold 104 downstream of the intake throttle 122.

  Next, the configuration of the fuel injection system will be described. The piston head 132 is configured to make a stroke in a cylinder 131 that is shown with a part of the engine 101 broken, and fuel is injected into the cylinder 131. The injector 133 is attached, and the injection port of the injector 133 is disposed above the top dead center position of the piston head 132. Although the drawing is shown in a simplified manner, the engine 101 has a plurality of cylinders 131, and each cylinder 131 is provided with an injector 133. Each injector 133 is supplied with high-pressure fuel from a common rail 134. Although not shown in detail, the injector 133 has a valve body that is driven by the electromagnetic force of the coil, and the injection port is opened according to the time width (energization time) of the pulse current that is energized to the coil.

  A high-pressure fuel pipe 136 that supplies high-pressure (common rail fuel pressure) fuel from the high-pressure pump 135 is connected to the common rail 134. Connected to the high-pressure pump 135 is an intermediate-pressure fuel pipe 138 that supplies fuel at an intermediate pressure (exhaust pipe injection fuel pressure) that is lower than the common rail fuel pressure and higher than the atmospheric pressure from the feed pump 137. The feed pump 137 takes in fuel from the atmospheric pressure fuel tank 139 through the low-pressure fuel pipe 140. The feed pump 137 is connected to a crankshaft (not shown), and is rotated in association with the engine 101 and sends out fuel with a delivery force according to the engine speed, so that the fuel of the exhaust pipe injection fuel pressure according to the engine speed. Can be supplied to the intermediate pressure fuel pipe 138.

  In the present invention, an exhaust pipe injector 141 for injecting fuel into the exhaust pipe 103 is provided downstream of the turbine 111 of the low-pressure stage turbocharger 110 and upstream of the exhaust brake valve 112. Fuel from a feed pump 137 is supplied to the exhaust pipe injector 141 via an intermediate pressure fuel pipe 138.

  A recovery fuel pipe 142 that recovers excess fuel to the fuel tank 139 is connected to each of the high-pressure pump 135, the common rail 134, and the injector 133.

  Next, sensors will be described.

  The engine 101 is provided with a water temperature sensor 151 that detects the coolant temperature, a crank angle sensor 152 that detects an index on a crankshaft (not shown) as a reference position of the crank angle, an oil level sensor 153 that detects the remaining amount of engine oil, and the like. It is done. The exhaust manifold 102 is provided with an engine exhaust temperature sensor 154. The intake manifold 104 is provided with a boost pressure sensor 155 that detects a boost pressure from the pressure of the intake manifold.

  The continuous regeneration type DPF device 113 includes a DOC inlet exhaust gas temperature sensor 156 that detects an exhaust gas temperature at the inlet of the DOC 114, a DPF inlet exhaust gas temperature sensor 157 that detects an exhaust gas temperature at the inlet of the DPF 115, and an inlet of the DPF 115. A differential pressure sensor 158 that detects a differential pressure that is a pressure difference between the exhaust gas and the outlet is provided. When PM accumulates in the DPF 115, the differential pressure increases as the accumulation amount increases, so that the DPF regeneration timing can be determined based on the differential pressure. Based on the DPF inlet exhaust gas temperature detected by the DPF inlet exhaust gas temperature sensor 157, the temperature of the DPF 115 during DPF regeneration or the like can be confirmed.

  The intermediate pressure fuel pipe 138 is provided with an exhaust pipe injection fuel pressure sensor 159 that detects an exhaust pipe injection fuel pressure that is a fuel pressure applied to the exhaust pipe injector 141. A fuel temperature sensor 160 that detects the temperature of the fuel is provided at the inlet of the high-pressure pump 135. The common rail 134 is provided with a common rail fuel pressure sensor 161 that detects a common rail fuel pressure that is a fuel pressure applied to the injector 133 of each cylinder 131. An air flow sensor (MAF sensor) 162 that detects the flow rate of the air sucked into the intake pipe 117 is provided downstream of the air cleaner 118 of the intake pipe 117.

  The high-pressure stage turbocharger 108 is provided with a high-pressure stage turbo rotational speed sensor 163 that detects the rotational speed of a shaft connecting the turbine 109 and the compressor 120.

  In addition to the illustrations and explanations, it is assumed that the engine 101, the intake / exhaust system, and the fuel injection system are provided with all conventionally known sensors.

  Next, the configuration of the control system will be described.

  The high-pressure stage turbocharger 108 is a variable nozzle turbocharger, and a nozzle actuator 164 that adjusts the opening area of the turbine 109 is provided upstream of the turbine 109. The turbo controller 165 controls the supercharging amount or the supercharging pressure by driving the nozzle actuator 164 while referring to the rotational speed of the shaft detected by the high-pressure stage turbo rotational speed sensor 163.

  Means for controlling each part of the vehicle including fuel injection to the engine 101 is incorporated as a program in an electronic control unit (ECU) 171. The ECU 171 performs control such as fuel injection control by constantly detecting engine speed, accelerator opening, load torque, air amount, and the like as engine parameters representing the engine state.

  The ECU 171 performs multi-stage delay injection (multi-injection) or exhaust pipe injection every time the travel distance of the vehicle reaches a predetermined distance or when the differential pressure detected by the differential pressure sensor 158 exceeds a predetermined value. Thus, a forced regeneration unit 172 that forcibly raises the temperature of the exhaust gas flowing into the DPF 115 and burns and removes the PM collected in the DPF 115 is mounted.

  The ECU 171 is equipped with an EGR control unit 173 that controls the opening degree of the EGR valve 107 based on the engine speed and the fuel injection amount.

  The EGR control unit 173 obtains the opening degree of the EGR valve 107 with reference to the normal EGR map 174 during normal time when DPF regeneration is not performed, and with reference to the EGR map 175 during DPF regeneration during DPF regeneration. . A setting example of the normal EGR map 174 is shown in FIG. 2A, and a setting example of the DPF regeneration EGR map 175 is shown in FIG.

  As shown in FIGS. 2A and 2B, the normal EGR map 174 and the DPF regeneration EGR map 175 are maps in which the opening of the EGR valve 107 is set for each engine speed and fuel injection amount. It is. The opening degree of the EGR valve 107 is set while performing a test in advance and confirming the output torque of the engine 101, the amount of exhausted NOx, the presence or absence of generation of white smoke, and the like. Note that “large” and “small” in FIGS. 2A and 2B indicate the degree of opening of the EGR valve 107 to be set.

  Comparing the normal EGR map 174 and the DPF regeneration EGR map 175, the normal EGR map 174 indicates that the opening of the EGR valve 107 is relatively low even in a low fuel injection amount region (that is, a low load region). On the other hand, in the DGR regeneration EGR map 175, the opening degree of the EGR valve 107 is made small (or in the region where the fuel injection amount is low (the region surrounded by the broken line A in FIG. 2B)) (or larger). The opening degree is set to 0 (fully closed). This is because, during DPF regeneration, if the EGR valve 107 is opened at a low load when the exhaust gas flow rate is low, the flow rate of the exhaust gas supplied to the continuous regeneration type DPF device 113 decreases, and the air-fuel ratio λ falls below 1 to the DOC 114. This is because the unburned fuel cannot be oxidized, and the unburned fuel supplied by the exhaust pipe injection is discharged into the atmosphere without being processed, and white smoke or the like is generated.

  In the exhaust gas purification system according to the present embodiment, a target boost pressure calculation unit 176 that calculates a target boost pressure based on the engine speed and the fuel injection amount, and a target boost pressure that is calculated by the target boost pressure calculation unit 176 And an EGR valve opening correction unit 177 that corrects the opening of the EGR valve 107 based on the difference between the boost pressure detected by the boost pressure sensor 155. The target boost pressure calculation unit 176 and the EGR valve opening correction unit 177 are mounted on the ECU 171.

  The target boost pressure calculation unit 176 is configured to obtain the target boost pressure with reference to the target boost pressure map 178 in which the target boost pressure is set for each engine speed and fuel injection amount. A setting example of the target boost pressure map 178 is shown in FIG. “Large” and “Small” in FIG. 3 indicate the size of the target boost pressure to be set. As shown in FIG. 3, the target boost pressure map 178 is a region where the target boost pressure is small, the engine speed is high, and the fuel injection amount is high in a region where the engine speed is low and the fuel injection amount is low (low rotation and low load region). The target boost pressure is set to be large in the (high rotation high load region).

  The EGR valve opening correction unit 177 obtains a compensation value for the opening of the EGR valve 107 based on the difference between the target boost pressure and the boost pressure, and uses the EGR control unit 173 to calculate the opening value of the EGR valve 107. By subtracting from the degree, the opening degree of the EGR valve 107 is corrected. The EGR valve opening degree correction unit 177 corrects the opening degree of the EGR valve 107 only during DPF regeneration.

  More specifically, the EGR valve opening correction unit 177 refers to a correction coefficient map 179 in which a correction coefficient is set for each difference between the target boost pressure and the boost pressure, obtains a correction coefficient, and performs engine rotation. The maximum value of the compensation value of the opening of the EGR valve 107 is obtained by referring to the compensation value map 180 in which the maximum value of the compensation value of the opening of the EGR valve 107 is set for each number and the fuel injection amount. A compensation value for the opening degree of the EGR valve 107 is obtained by multiplying the maximum compensation value for the opening degree 107 by a correction coefficient. The corrected opening degree of the EGR valve 107 is obtained by subtracting the obtained compensation value of the opening degree of the EGR valve 107 from the opening degree of the EGR valve 107 obtained by the EGR control unit 173. The EGR control unit 173 controls the EGR valve 107 using the corrected opening degree of the EGR valve 107.

  An example of setting the correction coefficient map 179 is shown in FIG. As shown in FIG. 4, the correction coefficient map 179 is set so that the value of the correction coefficient decreases (in terms of absolute value) as the difference between the target boost pressure and the boost pressure increases. A value of −1 to 0 is set as the value of the correction coefficient.

  An example of setting the compensation value map 180 is shown in FIG. “Large” and “Small” in FIG. 5 represent the magnitude of the maximum value of the compensation value of the opening degree of the EGR valve 107 to be set. As shown in FIG. 5, in the compensation value map 180, the maximum value of the compensation value of the opening degree of the EGR valve 107 is small in the region where the engine speed is low, and the opening degree of the EGR valve 107 is in the region where the engine speed is high. The maximum compensation value is set to be large.

  The opening degree of the EGR valve 107 after correction when the compensation value map 180 of FIG. 5 is subtracted from the EGR map 175 for DPF regeneration in FIG. 2B (when the correction coefficient is −1) in a map format. As shown in FIG. As shown in FIG. 6, in the region where the engine speed is low (the region surrounded by the broken line B in the figure), the corrected opening degree of the EGR valve 107 is small (or the opening degree is 0 (fully closed)). In the region where the rotational speed is high and the fuel injection amount is high (the region surrounded by the broken line C in the drawing), the exhaust gas flow rate is high, and there is no possibility that white smoke or the like is generated or the acceleration performance is deteriorated. Is not 0 (fully closed), but is about half the opening of the EGR valve 107 before correction.

  Next, the operation of the exhaust gas purification system according to this embodiment will be described.

  As shown in FIG. 7A, consider a case where the vehicle is started from a state where the vehicle is stopped (vehicle speed = 0) and the vehicle is gradually accelerated.

  As shown in FIGS. 7A and 7B, when the vehicle is stopped, the actual boost pressure is almost atmospheric pressure, and the difference between the target boost pressure and the boost pressure becomes large, and the EGR valve The opening of 107 is very small.

  When the vehicle is started and gradually accelerated, the engine speed and the fuel injection amount increase, and the target boost pressure gradually increases. At this time, since the opening degree of the EGR valve 107 is set small (or opening degree 0), the amount of exhaust gas recirculated to the intake side becomes small (or zero), and the turbines of the turbochargers 108 and 110 Since the amount of exhaust gas supplied to 109 and 111 increases, the boost pressure gradually increases, and the boost pressure approaches the target boost pressure. As the boost pressure approaches the target boost pressure, the difference between the target boost pressure and the boost pressure becomes smaller, so the opening degree of the EGR valve 107 gradually increases, and the difference between the target boost pressure and the actual boost pressure becomes smaller. When it becomes 0, the opening degree of the EGR valve 107 is not corrected, and the opening degree of the EGR valve 107 as set in the DGR regeneration EGR map 175 is obtained. In FIG. 7B, the opening degree of the EGR valve 107 in the related art without correction is indicated by a broken line.

  By performing such control, it becomes possible to secure the flow rate of the exhaust gas supplied to the continuous regeneration type DPF device 113 even at the time of acceleration. Therefore, as shown in FIG. Although the fuel ratio λ (thick solid line in the figure) becomes small, it does not become less than 1, and the concentration of unburned fuel (HC concentration, solid thin line in the figure) contained in the exhaust gas to be discharged is also kept low at 100 ppm or less. And the generation of white smoke and the like can be prevented.

  In contrast, in the conventional exhaust gas purification system that does not correct the opening of the EGR valve 107, the air-fuel ratio λ (dashed broken line in the figure) at the time of acceleration is less than 1, and is not included in the exhaust gas to be discharged. The concentration of fuel (HC) (thin broken line in the figure) also increases to 1000 ppm or more, and white smoke or the like is generated.

  Next, a control flow for determining the opening degree of the EGR valve 107 in the exhaust gas purification system according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 9, first, in step S1, the EGR control unit 173 determines whether the DPF regeneration is being performed. If NO is determined in step S1, in step S2, the EGR control unit 173 obtains the opening degree of the EGR valve 107 with reference to the normal EGR map 174 based on the engine speed and the fuel injection amount. Proceed to S9.

  When YES is determined in step S1, in step S3, the EGR control unit 173 obtains the opening degree of the EGR valve 107 with reference to the DPF regeneration EGR map 175 with the engine speed and the fuel injection amount, Proceed to step S4.

  In step S4, the target boost pressure calculation unit 176 obtains the target boost pressure by referring to the target boost pressure map 178 with the engine speed and the fuel injection amount. After obtaining the target boost pressure, the process proceeds to step S5.

  In step S5, the EGR valve opening degree correction unit 177 refers to the correction coefficient map 179 based on the difference between the target boost pressure obtained in step S4 and the boost pressure detected by the boost pressure sensor 155, and obtains a correction coefficient. After obtaining the correction coefficient, the process proceeds to step S6.

  In step S6, the EGR valve opening correction unit 177 refers to the compensation value map 180 with the engine speed and the fuel injection amount, and obtains the maximum value of the compensation value of the opening of the EGR valve 107. After obtaining the maximum value of the compensation value of the opening degree of the EGR valve 107, the process proceeds to step S7.

  In step S7, the EGR valve opening correction unit 177 multiplies the maximum compensation value of the opening of the EGR valve 107 obtained in step S6 by the correction coefficient obtained in step S5 to open the EGR valve 107. Find the degree compensation value. After obtaining the compensation value of the opening degree of the EGR valve 107, the process proceeds to step S8.

  In step S8, the EGR valve opening degree correcting unit 177 subtracts the compensation value for the opening degree of the EGR valve 107 obtained in step S7 from the opening degree of the EGR valve 107 obtained in step S3, thereby opening the EGR valve 107. Correct the degree. After correcting the opening degree of the EGR valve 107, the process proceeds to step S9.

  In step S9, the EGR control unit 173 controls the EGR valve 107 using the opening degree of the EGR valve 107 obtained in step S2 or the corrected opening degree of the EGR valve 107 obtained in step S8. Thereafter, the control is terminated.

  As described above, in the exhaust gas purification system according to the present embodiment, the target boost pressure calculation unit 176 that calculates the target boost pressure and the target boost pressure calculation unit 176 determine the target boost pressure based on the engine speed and the fuel injection amount. An EGR valve opening correction unit 177 that corrects the opening of the EGR valve 107 based on the difference between the target boost pressure and the boost pressure detected by the boost pressure sensor 155.

  As a result, even when EGR control is performed during DPF regeneration, an excessive amount of EGR during acceleration is suppressed, and the flow rate of exhaust gas supplied to the continuous regeneration type DPF device 113 is maintained to maintain the air-fuel ratio. Since λ can be maintained at 1 or more, it becomes possible to oxidize unburned fuel in the DOC 114 and suppress generation of white smoke and the like.

  Further, since it is possible to suppress an excessive amount of EGR, the flow rate of the exhaust gas supplied to the turbines 109 and 111 of the turbochargers 108 and 110 during acceleration can be increased so that the turbine can be smoothly turned around. Thus, it is possible to quickly increase the boost pressure during acceleration and obtain sufficient acceleration performance.

  In other words, according to the present invention, exhaust gas that suppresses the deterioration of exhaust gas during DPF regeneration and does not generate white smoke or the like even when the vehicle is accelerated during DPF regeneration can provide sufficient acceleration performance. A gas purification system can be realized.

  The present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the spirit of the present invention.

101 Engine 102 Exhaust manifold 103 Exhaust pipe 104 Intake manifold 105 EGR pipe 107 EGR valve 115 Diesel particulate filter (DPF)
141 Exhaust pipe injector
155 Boost pressure sensor 172 Forced regeneration unit 173 EGR control unit 174 Normal EGR map 175 DPF regeneration EGR map 176 Target boost pressure calculation unit 177 EGR valve opening correction unit 178 Target boost pressure map 179 Correction coefficient map 180 Compensation Value map

Claims (2)

A diesel particulate filter that is provided in the exhaust pipe of the engine and collects particulate matter in the exhaust gas;
An EGR valve that is provided in an EGR pipe that connects an exhaust manifold and an intake manifold of the engine, and that adjusts an amount of exhaust gas recirculated from the exhaust manifold to the intake manifold;
An EGR control unit for controlling the opening of the EGR valve based on the engine speed and the fuel injection amount;
In an exhaust gas purification system equipped with
A boost pressure sensor for detecting a boost pressure from the pressure of the intake manifold;
A target boost pressure calculation unit for obtaining a target boost pressure based on the engine speed and the fuel injection amount;
When the target boost pressure is higher than the boost pressure, the maximum value of the EGR valve opening compensation value obtained from the engine speed and the fuel injection amount, the target boost pressure obtained by the target boost pressure calculation unit, and the boost It based the difference between the boost pressure detected by pressure sensor, a, and a EGR valve opening degree correction section for correcting the opening degree of the EGR valve at the time of regeneration of the diesel particulate filter,
The EGR valve opening degree correction section, the difference becomes larger between the target boost pressure and the boost pressure, and wherein the corrected so that the opening of the EGR valve at the time of regeneration of the diesel particulate filter is reduced Exhaust gas purification system.   The EGR valve opening correction unit obtains a compensation value for the opening of the EGR valve based on the difference between the target boost pressure and the boost pressure, and the compensation value is determined based on the engine speed and the fuel injection amount. The exhaust gas purification system according to claim 1, wherein the opening degree of the EGR valve is corrected by subtracting from the opening degree of the EGR valve.

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