JP2008297948A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device equipped with a particulate filter (DPF) for collecting PM contained in exhaust gas and properly performing regeneration control for burning and removing the PM deposited in the DPF. <P>SOLUTION: The filter regeneration control is started on the condition that a PM deposition amount in the DPF reaches a predetermined value (steps ST2, ST5), when an element impedance of an air-fuel ration sensor becomes smaller that a predetermined value Z2 (value corresponding to a burnable temperature of the PM) after starting of the regeneration control, termination time of the regeneration control is calculated and termination timing of the regeneration control is determined (steps SR6 to ST8). By thus determining the regeneration control termination timing based on the element impedance correlative to element temperature of the air-fuel ratio sensor, the entire PM deposited in the DPF can be surely burnt and the regeneration control can be terminated at proper timing. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device that purifies exhaust gas from an internal combustion engine, and more particularly to an exhaust gas purification device that includes a filter that collects particulate matter contained in the exhaust gas.

  Exhaust gas discharged when an internal combustion engine (hereinafter also referred to as an engine) such as a gasoline engine or a diesel engine mounted on a vehicle or the like contains a substance that is not preferably discharged into the atmosphere as it is. Yes. In particular, in the exhaust gas of diesel engines, particulate matter containing carbon as a main component (hereinafter sometimes referred to as PM (Particulate Matter)), SOOT (soot), SOF (Soluble Organic Fraction), etc. Is included, causing air pollution.

  As a device for purifying PM in exhaust gas, a particulate filter is placed in the exhaust passage of a diesel engine, and PM contained in the exhaust gas flowing through the exhaust passage is collected, thereby reducing the amount of emissions released into the atmosphere. Exhaust gas purification devices that reduce the amount are known.

  As the particulate filter, for example, a DPF (Diesel Particulate Filter) or a DPNR (Diesel Particulate-NOx Reduction system) catalyst is used.

  When PM is collected using a particulate filter (hereinafter sometimes simply referred to as “filter”), if the amount of collected PM increases and the filter is clogged, the exhaust gas that passes through the filter is collected. The pressure loss of the engine increases, and the engine exhaust back pressure accompanying this increases the engine output and fuel consumption. As a method for solving this problem, control (filter regeneration control) is performed in which PM accumulated on the filter is burned and removed by adding fuel to the exhaust passage (upstream of the filter) to raise the exhaust temperature. .

  In addition, as another method for increasing the exhaust temperature in the regeneration control of the filter, a method of increasing the exhaust temperature by retarding the fuel injection timing, or the air / fuel ratio (A / F) by reducing the intake air amount of the engine. There is a method to raise the exhaust temperature by lowering.

  In such filter regeneration control, the PM accumulation amount on the filter is estimated, and when the PM accumulation amount reaches a predetermined reference value (limit accumulation amount), it is determined that it is time to regenerate the filter and fuel is added. Playback control is being implemented.

  Specifically, for example, a pressure sensor that detects a differential pressure between the upstream pressure and downstream pressure of the filter (a differential pressure before and after the filter) is provided, and an output value (differential pressure detection value) of the pressure sensor is a predetermined value. The filter regeneration control is started when the value reaches (a value corresponding to the limit accumulation amount), and the filter regeneration control is terminated when the output value of the pressure sensor becomes a predetermined value (regeneration control end determination value) or less. (For example, refer to Patent Document 1).

  Further, an exhaust temperature sensor for detecting the temperature of the exhaust gas flowing through the exhaust passage is provided, and the PM regeneration amount is estimated based on the exhaust temperature detected by the exhaust temperature sensor to perform filter regeneration control (for example, , See Patent Document 2).

  On the other hand, in an engine mounted on a vehicle, an oxygen concentration in exhaust gas is detected by an air-fuel ratio sensor arranged in an exhaust passage, and the exhaust air-fuel ratio becomes an appropriate target air-fuel ratio based on the detected oxygen concentration. The air-fuel ratio feedback control is executed.

  In an air-fuel ratio sensor used for air-fuel ratio feedback control or the like, it is necessary to keep the sensor element in an active state in order to maintain detection accuracy. For this reason, a heater (for example, an electric heater) for heating the sensor element is provided, and energization of the heater is controlled so that the element temperature becomes a predetermined activation temperature.

In order to perform such heater energization control, it is necessary to detect the temperature of the sensor element, but in general, the element temperature is not directly detected, but the element impedance (AC impedance) of the sensor element and the element temperature are not detected. Using the fact that there is a correlation between them, the element impedance is detected, and the element temperature is indirectly detected based on the detected element impedance.
JP 2004-036454 A JP 2006-291828 A JP 2003-097333 A JP 2001-355503 A

  By the way, when a pressure sensor is used for filter regeneration control, the pressure sensor cannot grasp that the entire filter has been regenerated.

  First, the PM accumulated on the filter may not be uniformly burned and removed throughout the filter, and the PM may be partially removed. When the PM deposited on the filter is partially removed and a part of the filter is blown through, the differential pressure before and after the filter decreases. When the differential pressure before and after the filter decreases in this way, the output value of the pressure sensor becomes equal to or less than a predetermined value (regeneration control end determination value), and regeneration (PM combustion) of the entire filter is not completed. Regardless, the filter regeneration control ends. Furthermore, when PM accumulates in the part where the filter is blown out and the part is clogged, the regeneration control of the filter is started again, so that the regeneration control is repeated in a short period of time. There is.

  In the conventional filter regeneration control described above, a sensor for obtaining information necessary for regeneration control, such as a pressure sensor and an exhaust temperature sensor, is necessary.

  The present invention has been made in view of such circumstances, and in an exhaust emission control device provided with a filter that collects particulate matter contained in exhaust gas from an internal combustion engine, PM deposited on the filter is burned. It is an object of the present invention to provide a technique capable of appropriately executing the regeneration control to be removed.

  The present invention provides a filter that is disposed in an exhaust passage of an internal combustion engine and collects particulate matter in exhaust gas, an air-fuel ratio sensor that is disposed in the exhaust passage, and a particulate matter deposited on the filter. A regeneration control means for performing regeneration control for combustion / removal, and detecting an element impedance of the air-fuel ratio sensor in the exhaust purification device that starts the regeneration control when a predetermined condition is satisfied, Based on this, the end timing of the reproduction control is determined.

  As a specific configuration of the present invention, after the filter regeneration control is started, when the element impedance of the air-fuel ratio sensor becomes smaller than a predetermined value, the regeneration control end time is calculated to determine the regeneration control end timing. The structure of doing can be mentioned.

  Next, the operation of the present invention will be described.

  First, in the present invention, filter regeneration control is started when a predetermined condition is satisfied. Specifically, the amount of particulate matter deposited on the filter is estimated, and filter regeneration control is started on the condition that the amount of particulate matter deposited has reached a predetermined value (limit deposition amount). As the filter regeneration control, for example, a method of burning and removing particulate matter by adding fuel to the exhaust passage upstream of the filter and raising the exhaust temperature is adopted.

  When starting the regeneration control of the filter, if the element temperature of the air-fuel ratio sensor is high (activation temperature) due to heater heating, the heater heating is stopped and the element temperature of the air-fuel ratio sensor is changed to the particulate matter. After the temperature is lowered to a temperature lower than the combustible temperature (for example, a temperature at which element impedance can be detected), the exhaust temperature is increased by adding fuel or the like.

  Next, the end timing of the filter regeneration control is determined based on the element impedance of the air-fuel ratio sensor. Specifically, the element impedance correlated with the element temperature of the air-fuel ratio sensor is detected, and when the element impedance becomes smaller than a predetermined value (a value corresponding to the combustible temperature of the particulate matter), the regeneration is performed. The control end time is calculated to determine the end timing of the regeneration control. The regeneration control end time is a time during which the particulate matter deposited on the filter can sufficiently burn, and is calculated based on, for example, the integrated intake air amount of the internal combustion engine and the element temperature of the air-fuel ratio sensor. Then, when the regeneration control stop time calculated in this way has elapsed, the filter regeneration control is terminated.

  As described above, according to the present invention, the element impedance that is correlated with the element temperature (exhaust temperature) of the air-fuel ratio sensor is detected, and the regeneration control end time is calculated based on the element impedance, and the filter regeneration control is performed. Since the end timing is determined, the regeneration control end time that allows the entire particulate matter deposited on the filter to be reliably burned is experienced through experiments and calculations in advance using the element impedance of the air-fuel ratio sensor as a parameter. Therefore, regeneration control can be properly terminated at a timing when the entire particulate matter deposited on the filter is sufficiently combusted. As a result, there is no occurrence of a problem that the regeneration control ends even though the regeneration of the entire filter is not completed, and the regeneration control of the filter can be appropriately executed.

  In addition, in the present invention, since the air-fuel ratio sensor for controlling the internal combustion engine is used and the regeneration control of the filter is performed based on the element impedance of the air-fuel ratio sensor, the regeneration control of the pressure sensor, the exhaust temperature sensor, etc. There is no need to mount a sensor for obtaining necessary information.

  In the present invention, the heater heating of the sensor element of the air-fuel ratio sensor is stopped before the filter regeneration control is started, and when the element impedance of the air-fuel ratio sensor rises above a predetermined value after the heater heating is stopped. Start playback control.

  In this manner, when the heater heating is stopped and the element temperature of the air-fuel ratio sensor is once lowered, the filter regeneration control is started, so that even if the exhaust temperature rises due to the regeneration control, the sensor element of the air-fuel ratio sensor Excessive heating can be prevented, and the sensor element can be protected.

  In the present invention, when filter regeneration control is executed by adding fuel to the exhaust passage, the element impedance of the air-fuel ratio sensor during regeneration control is a predetermined value (element impedance corresponding to a temperature suitable for combustion of particulate matter). The amount of fuel added is controlled so that When such control is performed, it becomes possible to maintain the element impedance (element temperature) of the air-fuel ratio sensor, that is, the filter bed temperature, at a temperature suitable for particulate matter combustion during regeneration control. It can be carried out efficiently and stably.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

-Engine-
A schematic configuration of a diesel engine to which the present invention is applied will be described with reference to FIG.

  A diesel engine 1 (hereinafter referred to as “engine 1”) in this example is, for example, a common rail in-cylinder direct injection four-cylinder engine, and includes a fuel supply system 2, a combustion chamber 3, an intake passage 6, an exhaust passage 7, and the like. Is configured as the main part.

  The fuel supply system 2 includes a supply pump 21, a common rail 22, an injector (fuel injection valve) 23, a shutoff valve 24, a fuel addition valve 25, a fuel pressure control valve 26, a fuel metering valve 27, an engine fuel passage 28, and an added fuel. A passage 29 and the like are provided.

  The supply pump 21 pumps fuel from the fuel tank, makes the pumped fuel high pressure, and then supplies the pumped fuel to the common rail 22 via the engine fuel passage 28. The common rail 22 has a function as a pressure accumulation chamber that holds (accumulates) the high-pressure fuel supplied from the supply pump 21 at a predetermined pressure, and distributes the accumulated fuel to the injectors 23. The injector 23 is an electromagnetically driven on-off valve that opens when a predetermined voltage is applied and injects fuel into the combustion chamber 3.

  Further, the supply pump 21 supplies a part of the fuel pumped from the fuel tank to the fuel addition valve 25 through the addition fuel passage 29. The fuel addition valve 25 is an electromagnetically driven on-off valve that opens when a predetermined voltage is applied and adds fuel from the exhaust port 71 of the exhaust passage 7 to the exhaust manifold 72. The shutoff valve 24 shuts off the fuel supply by shutting off the added fuel passage 29 in an emergency.

  The intake passage 6 includes an intake manifold 63 connected to an intake port formed in the cylinder head, and an intake pipe 64 connected to the intake manifold 63. An air cleaner 65, an air flow meter 32, a throttle valve 62, an intake air temperature sensor 33, and an intake air pressure sensor 34 are disposed in the intake passage 6 in order from the upstream side.

  The exhaust passage 7 includes an exhaust manifold 72 connected to an exhaust port 71 formed in the cylinder head, and an exhaust pipe 73 connected to the exhaust manifold 72. The exhaust pipe 73 is provided with a DPF 4 that collects PM in the exhaust gas.

  As shown in FIGS. 2A and 2B, the DPF 4 is formed of a cylindrical ceramic structure 40 made of a porous material (for example, cordierite). The inside of the ceramic structure 40 has a honeycomb structure partitioned in a lattice shape by cell partition walls 41 (see FIG. 2A), and a plurality of gas inflow side cells 42 and gas outflow side cells 43 are provided. (See FIG. 2B). The gas inflow side cell 42 is a gas flow path whose end on the exhaust gas downstream side is closed, and the gas outflow side cell 43 is a gas flow path whose end on the exhaust gas upstream side is closed. The gas inflow side cell 42 and the gas outflow side cell 43 are adjacent to each other via a cell partition wall (filter partition wall) 41 that becomes a filter during gas flow.

  In the DPF 4 having the above structure, the exhaust gas flowing into the gas inflow side cell 42 from the upstream side opening 42a passes through the cell partition wall 41 and is adjacent to the gas outflow side as shown by the arrow in FIG. It flows into the cell 43 and is discharged from the downstream opening 43a. Thus, when the exhaust gas passes through the cell partition wall 41, PM contained in the exhaust gas is collected by the cell partition wall 41, and PM discharge can be suppressed.

  The DPF 4, the fuel addition valve 25, the added fuel passage 29, an air-fuel ratio sensor 101 described later, and an ECU (Electronic Control Unit) 200 that performs open / close control of the fuel addition valve 25 and the like constitute an exhaust purification device. Yes.

  The engine 1 is provided with a turbocharger (supercharger) 5. The turbocharger 5 includes a turbine wheel 52 and a compressor impeller 53 that are connected via a turbine shaft 51.

  The compressor impeller 53 is disposed facing the intake pipe 64, and the turbine wheel 52 is disposed facing the exhaust pipe 73. Such a turbocharger 5 supercharges intake air by rotating the compressor impeller 53 using the exhaust flow (exhaust pressure) received by the turbine wheel 52. The turbocharger 5 in this example is a variable nozzle type turbocharger, and a variable nozzle vane mechanism 54 is provided on the turbine wheel 52 side. By adjusting the opening degree of the variable nozzle vane mechanism 54, the engine 1 is overcharged. The supply pressure can be adjusted.

  An intake pipe 64 of the intake passage 6 is provided with an intercooler 61 for forcibly cooling intake air whose temperature has been raised by supercharging in the turbocharger 5. A throttle valve 62 is provided on the downstream side of the intercooler 61. The throttle valve 62 is an electronically controlled on-off valve whose opening degree can be adjusted in a stepless manner, and the flow area of the intake air is reduced under a predetermined condition, and the supply amount of the intake air is adjusted ( It has a function to reduce).

  Further, the engine 1 is provided with an EGR passage (exhaust gas recirculation passage) 8 that connects the intake passage 6 and the exhaust passage 7. The EGR passage 8 is configured to reduce the combustion temperature by recirculating a part of the exhaust gas to the intake passage 6 as appropriate and supplying the exhaust gas again to the combustion chamber 3, thereby reducing the amount of NOx generated. The EGR passage 8 is provided with an EGR valve 81 and an EGR cooler 82 for cooling the exhaust gas passing (refluxing) through the EGR passage 8, and by adjusting the opening degree of the EGR valve 81. The EGR amount (exhaust gas recirculation amount) introduced from the exhaust passage 7 into the intake passage 6 can be adjusted.

-Sensors-
Various sensors are attached to each part of the engine 1, and signals related to the environmental conditions of each part and the operating state of the engine 1 are output.

  For example, the air flow meter 32 is disposed upstream of the throttle valve 62 in the intake passage 6 and outputs a detection signal corresponding to the intake air amount. The intake air temperature sensor 33 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the intake air temperature. The intake pressure sensor 34 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the intake air pressure. The rail pressure sensor 35 outputs a detection signal corresponding to the fuel pressure stored in the common rail 22.

  The air-fuel ratio sensor 101 is disposed in the exhaust pipe 73 (downstream of the DPF 4) of the exhaust passage 7 and outputs a detection signal corresponding to the exhaust air-fuel ratio. The structure of the air-fuel ratio sensor 101 will be described.

-Air-fuel ratio sensor-
The air-fuel ratio sensor 101 is a stacked air-fuel ratio sensor and includes a sensor element 110, a breathable inner cover 116, an outer cover 117, and the like, as shown in FIG. The air-fuel ratio sensor 101 incorporates a heater 102 for heating the sensor element 110.

  The sensor element 110 includes a plate-shaped solid electrolyte layer (for example, partially stabilized zirconia) 111, an atmosphere side electrode (for example, a platinum electrode) 112 formed on one surface of the solid electrolyte layer 111, and the other of the solid electrolyte layer 111. The exhaust-side electrode (for example, platinum electrode) 113 and the diffusion resistance layer (for example, porous ceramic) 114 formed on the surface of the substrate.

  The atmosphere side electrode 112 of the sensor element 110 is disposed in the atmosphere duct 115. The atmosphere duct 115 is open to the atmosphere, and the atmosphere flowing into the atmosphere duct 115 contacts the atmosphere side electrode 112.

  The surface of the exhaust side electrode 113 is covered with the diffusion resistance layer 114, and a part of the exhaust gas flowing through the exhaust pipe 73 on the downstream side of the DPF 4 is diffused by the diffusion resistance layer 114 to the exhaust side electrode 113. Contact. The exhaust gas passes through the small hole 117a of the outer cover 117 and the small hole 116a of the inner cover 116 and reaches the sensor element 110 (exhaust side electrode 113).

  The heater 102 is composed of a linear heating element that generates heat when energized from a vehicle-mounted battery power supply VB (see FIG. 5), and heats the entire sensor element 110 by the heat generated by the heating element.

  In the air-fuel ratio sensor 101 having the above structure, a detection voltage VR (= [VAF +] − [VAF−]), which will be described later, is applied between the atmosphere side electrode 112 and the exhaust side electrode 113. A current corresponding to the oxygen concentration in the exhaust gas flows through the fuel ratio sensor 101.

-ECU / Air-fuel ratio sensor control circuit-
As shown in FIG. 4, the ECU 200 includes a CPU 201, a ROM 202, a RAM 203, a backup RAM 204, and the like.

  The ROM 202 stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU 201 executes various arithmetic processes based on various control programs and maps stored in the ROM 202. The RAM 203 is a memory that temporarily stores calculation results of the CPU 201, data input from each sensor, and the backup RAM 204 is a nonvolatile memory that stores data to be saved when the engine 1 is stopped, for example. Memory.

  The ECU 200 includes a water temperature sensor 31 that outputs a signal corresponding to the cooling water temperature of the engine 1, an air flow meter 32, an intake air temperature sensor 33, an intake air pressure sensor 34, an air-fuel ratio sensor 101, a rail pressure sensor 35, and a depression amount to the accelerator pedal. An accelerator opening sensor 36 that outputs a detection signal according to the engine speed, a crank position sensor 37 that detects the rotation speed (engine rotation speed) of the crankshaft that is the output shaft of the engine 1, and the like are connected.

  The ECU 200 is connected to an injector 23, a shutoff valve 24, a fuel addition valve 25, a variable nozzle vane mechanism 54, a throttle valve 62, an EGR valve 81, a heater 102 of the air-fuel ratio sensor 101, and the like.

  Next, the configuration of the control circuit 210 that controls the air-fuel ratio sensor 101 will be described with reference to FIG. The control circuit 210 is incorporated in the ECU 200.

  The control circuit 210 of the air-fuel ratio sensor 101 in this example includes operational amplifiers OP1 to OP4, shunt resistors R1, resistors R2 to R7, a reference voltage generation circuit 211, a pulse application circuit 212, a transistor 213 for controlling the heater 102, and the like. I have.

  The reference voltage generation circuit 211 includes three resistors R11, R12, and R13 connected in series between the power supply VC and the ground, and a voltage VAF + (for example, 3.3 V) between the resistors R11 and R12. Is generated, and a voltage VFA− (for example, 2.9 V) is generated between the resistors R12 and R13.

  The voltage VAF + generated between the resistor R11 and the resistor R12 is applied to the plus side terminal of the operational amplifier OP1 through the operational amplifier OP3 and the pulse application circuit 212. Further, the voltage VAF− generated between the resistors R12 and R13 is directly applied to the plus side terminal of the operational amplifier OP2.

  The output terminal of the operational amplifier OP1 is connected to the positive side input terminal (terminal on the atmosphere side electrode 112 side) 101a of the air-fuel ratio sensor 101 via the shunt resistor R1, and the negative terminal of the operational amplifier P1 via the resistors R1 and R2. Connected to the side terminal.

  The output terminal of the operational amplifier OP2 is connected to the negative side input terminal (terminal on the exhaust side electrode 113 side) 101b of the air-fuel ratio sensor 101 via resistors R3 and R5, and the operational amplifier OP2 via the resistors R3 and R4. Connected to the negative terminal.

  The voltage VAF + is applied from the operational amplifier OP1 to the positive input terminal 101a of the air-fuel ratio sensor 101. Further, the voltage VAF− is applied from the operational amplifier OP2 to the negative input terminal 101b of the air-fuel ratio sensor 101. As a result, a difference voltage (for example, 0.4 V) between the voltage VAF + and the voltage VAF− is generated between the input terminals 101a and 101b of the air-fuel ratio sensor 101 (between the atmosphere side electrode 112 and the exhaust side electrode 113). It is applied as a detection voltage VR for detecting the oxygen concentration therein.

  A pulse application circuit 212 is provided between the output terminal of the operational amplifier OP3 and the positive terminal of the operational amplifier OP1. The pulse application circuit 212 applies a voltage applied to the plus side terminal of the operational amplifier OP1, that is, a voltage VAF + applied to the plus side input terminal 101a (atmosphere side electrode 112) of the air-fuel ratio sensor 101 to a predetermined change width ΔVAF (for example, ΔVAF). = 0.2V), and is changed at a predetermined cycle between the plus side and the minus side.

  One end of the heater 102 is connected to the battery power source VB. A transistor 213 is connected to the other end of the heater 102. The base of the transistor 213 is connected to the CPU 201, and energization of the heater 102 is controlled by turning on / off the transistor 213 in accordance with a heater control signal from the CPU 201.

  In the circuit configuration described above, the same current as the current (sensor current Is) flowing through the air-fuel ratio sensor 101 flows through the shunt resistor R1 connected between the operational amplifier OP1 and the air-fuel ratio sensor 101. The both-end potential difference (V1-V2) is a value proportional to the sensor current Is. Therefore, the sensor current Is of the air-fuel ratio sensor 101 can be detected by calculating the potential difference (V1−V2) across the shunt resistor R1.

  Therefore, in this example, the voltage V1 on the air-fuel ratio sensor 101 side of the shunt resistor R1 is guided to the plus terminal of the operational amplifier OP4 via the resistor R6, and the voltage V2 on the opposite side of the shunt resistor R1 from the air-fuel ratio sensor 101 side is obtained. It is led to the negative terminal of the operational amplifier OP4 via a resistor R7, and the voltage difference (V1-V2) is calculated and amplified.

  The output signal V3 of the operational amplifier OP4 is digitally converted by an analog-digital converter (ADC) 214 for detecting a sensor current and then input to the CPU 201. The CPU 201 calculates the sensor current Is from the output signal V3 (signal after digital conversion) of the operational amplifier OP4, and calculates the air-fuel ratio of the exhaust gas based on the sensor current Is.

  Further, the voltage V1 and the voltage V2 at both ends of the shunt resistor R1 are input to the CPU 201 through analog / digital converters (ADC) 215 and 216 for impedance detection, respectively. In the CPU 201, the element impedance (AC impedance) of the air-fuel ratio sensor 101 is based on the input voltage V1, V2 and the change width ΔVAF of the voltage VAF + applied to the plus-side input terminal (atmosphere-side electrode 112) of the air-fuel ratio sensor 101. Is detected.

  The element impedance is based on the voltage change ΔV (ΔVAF) of the voltage applied to the sensor element 110 and the current change ΔI (current change amount obtained from the potential difference (V1−V2) across the shunt resistor R1) caused by the voltage change ΔV. Thus, it can be obtained from an arithmetic expression [element impedance = ΔV / ΔI].

  Here, since there is a correlation between the element temperature of the air-fuel ratio sensor 101 and the element impedance, the element temperature of the air-fuel ratio sensor 101 is estimated based on the element impedance detected by the above processing using this relationship. can do.

  ECU 200 obtains the temperature of sensor element 110 based on the element impedance of air-fuel ratio sensor 101 detected in the above processing, and the actual element temperature is a target value (the activation temperature of the sensor element (for example, 750 ° C.)). Thus, the duty ratio of the heater control signal to the transistor 213 is calculated so as to control the energization of the heater 102.

  Further, the ECU 200 executes various controls of the engine 1 based on the outputs of the various sensors described above. Further, the ECU 200 executes the following filter regeneration control.

-Filter regeneration control-
First, in the filter regeneration control of this example, the regeneration control of the DPF 4 is started on the condition that the amount of PM deposited on the DPF 4 has reached a predetermined value, and the regeneration control end timing is based on the element impedance of the air-fuel ratio sensor 101. It is characterized in that it is determined.

  A specific example of the filter regeneration control will be described with reference to FIGS. The control routine for filter regeneration control shown in FIG. 6 is repeatedly executed at predetermined time intervals in the ECU 200. Even during the execution of the control routine shown in FIG. 6, the element impedance of the air-fuel ratio sensor 101 is sequentially detected by the above-described processing.

  In step ST1, the amount of PM deposited on the DPF 4 is estimated. As a method for estimating the PM accumulation amount, for example, the PM adhesion amount corresponding to the operating state of the engine 1 (for example, the fuel injection amount, the engine speed, etc.) is obtained in advance through experiments or the like and mapped. A method is adopted in which the required PM adhesion amount is integrated to obtain the PM deposition amount.

  In step ST2, when the PM estimation amount estimated in step ST1 becomes larger than a predetermined value (limit accumulation amount), it is determined that it is the regeneration timing of the DPF 4, and the process proceeds to step ST3. If the determination result of step ST2 is negative, this routine is temporarily exited.

  In step ST3, the heater 102 of the air-fuel ratio sensor 101 is turned off. The processing in step ST3 is performed for the purpose of protecting the air-fuel ratio sensor 101.

  Specifically, if the regeneration control of the DPF 4 is executed when the element temperature of the air-fuel ratio sensor 101 is high (active temperature), the sensor element 110 may be excessively heated, and this is avoided. Therefore, before the regeneration control of the DPF 4 is started, the heater 102 of the air-fuel ratio sensor 101 is turned off and the element temperature of the air-fuel ratio sensor 101 is once lowered.

  In this way, the heater 102 is turned off and the element temperature of the air-fuel ratio sensor 101 is once reduced, so that the air-fuel ratio sensor can be used even if the exhaust temperature rises due to regeneration control of the DPF 4 (fuel addition to the exhaust passage 7). The sensor element 110 of 101 can be prevented from being heated to a high temperature, and the sensor element 110 can be protected.

  Note that when the element temperature of the air-fuel ratio sensor 101 decreases due to the heater 102 being turned off, the element impedance of the air-fuel ratio sensor 101 increases (see FIG. 7).

  Next, in step ST4, it is determined whether or not the element impedance has risen above a predetermined value Z1. When the determination result is affirmative (element impedance> Z1), regeneration control of the DPF 4 is started (step ST5).

The regeneration control of the DPF 4 is performed by a process of intermittently repeating fuel addition to the exhaust passage 7 (the exhaust manifold 72 on the upstream side of the DPF 4) by controlling the opening and closing of the fuel addition valve 25. The amount of fuel added during regeneration control is controlled so that the element impedance of the air-fuel ratio sensor 101 matches a predetermined value Z3 (element impedance corresponding to a temperature suitable for PM combustion) (see FIG. 7). By such fuel addition, the exhaust temperature (the bed temperature of the DPF 4) rises, and the PM deposited on the DPF 4 is oxidized and discharged as H ₂ O or CO ₂ . Further, when the exhaust gas temperature rises due to fuel addition, the temperature of the air-fuel ratio sensor 101 rises accordingly, and the element impedance decreases (see FIG. 7).

  The predetermined value Z1 used for the determination process in step ST4 is set to a value close to the element impedance detection limit value of the air-fuel ratio sensor 101 (a value corresponding to the lower limit value of the element temperature at which the element impedance can be detected). To do.

  After starting the regeneration control of the DPF 4 described above, it is determined whether or not the element impedance of the air-fuel ratio sensor 101 has decreased below a predetermined value Z2 (step ST6), and the element impedance is less than the predetermined value Z2 (element impedance <Z2). At this point, it is determined that the element temperature of the air-fuel ratio sensor 101, that is, the exhaust temperature has reached a temperature at which PM combustion is possible, and the process proceeds to step ST7. The predetermined value Z2 used for the determination process in step ST6 is set in consideration of the relationship between the element temperature (PM combustion possible temperature) of the air-fuel ratio sensor 101 and the element impedance.

  In step ST7, the regeneration control end time Te of the DPF 4 is calculated. Specifically, the integrated intake air amount (integrated amount from the start of regeneration control) is calculated based on the output signal of the air flow meter 32, the element temperature of the air-fuel ratio sensor 101 is estimated from the element impedance, and the integrated intake air is calculated. Based on the air amount and the element temperature, the regeneration control end time Te is calculated with reference to a previously created map. As shown in FIG. 7, the regeneration control end time Te is the time from when the element impedance becomes less than a predetermined value Z2 (element impedance <Z2) to the end of the regeneration control.

  Note that the map for obtaining the regeneration control end time Te has experienced through experiments and calculations, etc., the time required for the PM accumulated in the DPF 4 to sufficiently burn using the integrated intake air amount and the element temperature (element impedance) as parameters. The obtained values are mapped and stored in the ROM 202 of the ECU 200.

  In step ST8, it is determined whether or not the regeneration control end time Te calculated in step ST7 has elapsed since the element impedance of the air-fuel ratio sensor 101 is less than the predetermined value Z2, and the determination result is affirmative. At this point, the regeneration control of the DPF 4 is terminated (step ST9).

  As described above, according to the regeneration control of this example, the regeneration control end time Te is calculated based on the element impedance correlated with the element temperature (exhaust temperature) of the air-fuel ratio sensor 101, and the regeneration control end of the DPF 4 is completed. Since the timing is determined, the regeneration control can be appropriately terminated at a timing when the entire particulate matter deposited on the filter is sufficiently combusted. As a result, the regeneration control of the DPF 4 ends although the problem when the pressure sensor (differential pressure sensor) is used for the regeneration control, that is, the regeneration (PM combustion) of the entire DPF 4 is not completed. Therefore, the regeneration control of the DPF 4 can be appropriately executed.

  In addition, since the air-fuel ratio sensor 101 for controlling the engine 1 is used and the regeneration control of the filter is executed based on the element impedance of the air-fuel ratio sensor 101, it is necessary for the regeneration control of the pressure sensor, the exhaust temperature sensor, etc. It is no longer necessary to mount a sensor for obtaining accurate information.

  Further, in this example, when the regeneration control of the DPF 4 is performed, the amount of fuel added is controlled so that the element impedance of the air-fuel ratio sensor 101 matches a predetermined value Z3 (element impedance corresponding to a temperature suitable for PM combustion). Therefore, during regeneration control, the element impedance (element temperature) of the air-fuel ratio sensor 101, that is, the bed temperature of the DPF 4 can be maintained at a temperature suitable for PM combustion, and combustion of PM accumulated in the DPF 4 can be efficiently performed. It can be carried out well and stably.

-Other embodiments-
In the above example, PM is burned and removed from the DPF by adding fuel to the exhaust passage to raise the exhaust temperature, but other methods may be employed. For example, by delaying the fuel injection timing (ignition delay control) and increasing the exhaust temperature, or by reducing the air intake ratio of the engine and increasing the exhaust temperature, You may make it perform combustion and removal of PM.

  In the above example, an example in which the present invention is applied to an exhaust emission control device for an engine equipped with a stacked air-fuel ratio sensor has been shown. However, the present invention is not limited to this, and a cup-type air-fuel ratio sensor is installed. The present invention can also be applied to an engine exhaust gas purification device.

  In the above example, the example in which the present invention is applied to the exhaust gas purification apparatus provided with the DPF has been shown. However, the present invention is not limited to this, and the present invention is applied to an exhaust gas purification apparatus provided with another particulate filter such as DPNR. Is also applicable.

  In the above example, the exhaust purification apparatus of the present invention is applied to an in-cylinder direct injection 4-cylinder diesel engine. However, the present invention is not limited to this, and other examples such as an in-cylinder direct injection 6-cylinder diesel engine, etc. It can also be applied to diesel engines with any number of cylinders. Moreover, the exhaust emission control device of the present invention can be applied to other types of diesel engines without being limited to in-cylinder direct injection diesel engines.

  Furthermore, the exhaust emission control device of the present invention can also be applied to a lean combustion gasoline engine in which the operating range in which the engine operation is performed by using a high air-fuel ratio (lean atmosphere) mixture for combustion occupies most of the entire operating range. It is.

It is a schematic structure figure showing an example of a diesel engine to which the present invention is applied. It is a figure which writes together and shows the front view (A) and center longitudinal cross-sectional view (B) of DPF. It is sectional drawing which shows the structure of an air fuel ratio sensor. It is a block diagram which shows the structure of control systems, such as ECU. It is a circuit diagram which shows the structure of the control circuit of an air fuel ratio sensor. It is a flowchart which shows an example of the reproduction | regeneration control of a filter. It is a time chart which shows the change of the element impedance at the time of regeneration control of a filter.

Explanation of symbols

1 engine (internal combustion engine)
2 Fuel Supply System 21 Supply Pump 23 Injector 24 Shutoff Valve 25 Fuel Addition Valve 29 Addition Fuel Passage 4 DPF (Particulate Filter)
7 exhaust passage 71 exhaust port 72 exhaust manifold 73 exhaust pipe 101 air-fuel ratio sensor 110 sensor element 102 heater (for air-fuel ratio sensor heating)
200 ECU

Claims (4)

A filter that is disposed in an exhaust passage of the internal combustion engine and collects particulate matter in the exhaust gas, an air-fuel ratio sensor that is disposed in the exhaust passage, and burns and removes the particulate matter deposited on the filter. An exhaust emission control device that performs regeneration control, and starts the regeneration control when a predetermined condition is satisfied,
An exhaust emission control device for detecting an element impedance of the air-fuel ratio sensor and determining an end timing of the regeneration control based on the element impedance. The exhaust emission control device according to claim 1,
An exhaust gas purification characterized by calculating a regeneration control end time and determining a regeneration control end time when an element impedance of the air-fuel ratio sensor becomes smaller than a predetermined value after the regeneration control is started. apparatus. The exhaust emission control device according to claim 1 or 2,
Before starting the regeneration control, the heater heating of the sensor element of the air-fuel ratio sensor is stopped. After the heater heating is stopped, the regeneration control is performed when the element impedance of the air-fuel ratio sensor becomes larger than a predetermined value. An exhaust emission control device characterized by starting. The exhaust emission control device according to any one of claims 1 to 3,
An exhaust emission control device that performs the regeneration control by adding fuel to the exhaust passage and controls the fuel addition amount so that the element impedance of the air-fuel ratio sensor during the regeneration control becomes a predetermined value.

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