EP1519021A2 - Vorrichtung zur Bestimmung der Alterung eines Katalysators einer Brennkraftmaschine - Google Patents

Vorrichtung zur Bestimmung der Alterung eines Katalysators einer Brennkraftmaschine Download PDF

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Publication number
EP1519021A2
EP1519021A2 EP04023104A EP04023104A EP1519021A2 EP 1519021 A2 EP1519021 A2 EP 1519021A2 EP 04023104 A EP04023104 A EP 04023104A EP 04023104 A EP04023104 A EP 04023104A EP 1519021 A2 EP1519021 A2 EP 1519021A2
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European Patent Office
Prior art keywords
fuel
catalyst
richening
exhaust
period
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Application number
EP04023104A
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English (en)
French (fr)
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EP1519021B1 (de
EP1519021A3 (de
Inventor
Masaaki c/o Toyota Jidosha K. K. Kobayasi
Naoyuki c/o Toyota Jidosha K. K. Tsuzuki
Masaaki c/o Toyota Jidosha K. K. Yamaguchi
Keiichi c/o K. K. Toyota Jidoshokki Mizuguchi
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Toyota Industries Corp
Toyota Motor Corp
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Toyota Industries Corp
Toyota Motor Corp
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Publication of EP1519021A3 publication Critical patent/EP1519021A3/de
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1401—Introducing closed-loop corrections characterised by the control or regulation method
    • F02D41/1402—Adaptive control
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
    • F02D41/0275—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a NOx trap or adsorbent
    • F02D41/028—Desulfurisation of NOx traps or adsorbent
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/1446—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being exhaust temperatures
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/1454—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio
    • F02D41/1456—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio with sensor output signal being linear or quasi-linear with the concentration of oxygen

Definitions

  • the present invention relates to an apparatus for controlling an exhaust purification apparatus provided in the exhaust system of an internal combustion engine and to an apparatus for determining deterioration of such a catalyst.
  • a typical exhaust purification catalyst is poisoned with sulfur components contained in fuel.
  • the degree of sulfur poisoning is increased, the NOx storage reduction performance of the catalyst is degraded. Therefore, when a certain amount of sulfur components is accumulated in the NOx storage reduction catalyst, a temperature increase process is executed to heat the catalyst. Also, the air-fuel ratio of exhaust gas is richened to perform a sulfur release control is executed in which sulfur components are discharged from the NOx storage reduction catalyst.
  • Japanese Laid-Open Patent Publication No. 2000-274232 discloses a technology for preventing the concentration of sulfur components in exhaust gas from being excessive by intermittently richening air-fuel ratio of exhaust gas. Specifically, an execution period, in which the air-fuel ratio is richened, and an intermission period, in which the air-fuel ratio is not richened, are alternately repeated.
  • the length of the execution period is set such that the maximum value of the catalyst bed temperature due to richening of the air-fuel is less than the temperature at which the exhaust purification catalyst starts deteriorating due to heat.
  • the temperature of a brand new exhaust purification catalyst and the temperature of an old exhaust purification catalyst are increased in different manners even if the air-fuel ratio is richened under the same conditions.
  • the maximum value of the catalyst bed temperature of a brand new exhaust purification catalyst when the air-fuel ratio is richened is higher. Therefore, if the conditions of the execution period are designed for old catalysts, the catalyst bed temperature will be excessively increased by richening the air-fuel ratio when the exhaust purification catalyst is still brand new, which can cause the catalyst to prematurely deteriorate.
  • the conditions of the execution period are designed for a brand new catalyst and the catalyst is gradually worn out, the execution period can end even if the catalyst bed temperature has not been sufficiently increased. This hinders effective emission of sulfur components and degrades the accuracy of the sulfur release control. As a result, the emission deteriorates and the period of the sulfur poisoning is extended, which degrades the fuel economy.
  • the present invention to provide a catalyst control apparatus for an internal combustion engine, which apparatus readily suppresses an excessive increase in a catalyst bed temperature and degradation of accuracy of sulfur release control.
  • the present invention also pertains to a catalyst deterioration determination apparatus used in the catalyst control apparatus to determine the degree of deterioration of an exhaust purification catalyst.
  • an apparatus for controlling an exhaust purification catalyst is provided.
  • the catalyst is located in an exhaust system of an internal combustion engine.
  • the apparatus repeats a richening period and a non-richening period.
  • the apparatus intermittently supplies fuel to exhaust gas at a section upstream of the catalyst, thereby lowering the air-fuel ratio of exhaust gas that contacts the catalyst to a value equal to or less than the stoichiometric air-fuel ratio.
  • the apparatus does not supply fuel to exhaust gas.
  • the apparatus includes deterioration degree detecting means and changing means.
  • the deterioration degree detecting means detects the degree of deterioration of the exhaust purification catalyst.
  • the changing means changes the ratio of the duration of the richening period to the duration of the non-richening period according to the deterioration degree of the exhaust purification catalyst detected by the deterioration degree detecting means.
  • the present invention also provides an apparatus for detecting a degree of deterioration of an exhaust purification catalyst located in an exhaust system of an internal combustion engine.
  • the apparatus includes fuel supply means, catalyst bed temperature detecting means, and deterioration degree determination means.
  • the fuel supply means intermittently supplies fuel to exhaust gas at a section upstream of the exhaust purification catalyst.
  • the catalyst bed temperature detecting means detects a physical quantity that represents an actual catalyst bed temperature of the exhaust purification catalyst.
  • the deterioration degree determination means that the smaller a range of fluctuation of the physical quantity, which fluctuation being caused by supply of fuel to exhaust gas and detected by the catalyst bed temperature detecting means, the greater the deterioration degree of the exhaust purification catalyst.
  • Fig. 1 is a block diagram illustrating a general configuration of a vehicle diesel engine and a control system according to a first embodiment.
  • the control system functions as a catalyst control apparatus and a catalyst deterioration determination apparatus.
  • the diesel engine 2 has cylinders.
  • the number of the cylinders is four, and the cylinders are denoted as #1, #2, #3, and #4.
  • a combustion chamber 4 of each of the cylinders #1 to #4 includes an intake port 8.
  • the combustion chambers 4 are connected to a surge tank 12 via the intake ports 8 and an intake manifold 10. Each intake port 8 is opened and closed by an intake valve 6.
  • the surge tank 12 is connected to outlets of an intercooler 14 and supercharger through an intake passage 13.
  • an compressor 16a of an exhaust turbocharger 16 functions as a supercharger.
  • An inlet of the compressor 16a is connected to an air cleaner 18.
  • An exhaust gas recirculation (hereinafter, referred to as EGR) passage 20 is connected to the surge tank 12.
  • An EGR gas supply port 20a of the EGR passage 20 opens to the surge tank 12, so that the surge tank 12 and the EGR passage 20 communicate with each other.
  • a throttle valve 22 is located in a section of the intake passage 13 between the surge tank 12 and the intercooler 14.
  • An intake flow rate sensor 24 and an intake temperature sensor 26 are located between the compressor 16a and the air cleaner 18.
  • the combustion chamber 4 of each of the cylinders #1 to #4 includes an exhaust port 30.
  • the combustion chambers 4 are connected to an inlet of an exhaust turbine 16b via the exhaust ports 30 and an exhaust manifold 32.
  • Each exhaust port 30 is opened and closed by an exhaust valve 28.
  • An outlet of the exhaust turbine 16b is connected to an exhaust passage 34. Exhaust gas is drawn into the exhaust turbine 16b at a section of the exhaust manifold 32 that is close to the fourth cylinder #4.
  • the first catalytic converter 36 supports an NOx storage reduction catalyst 36a, which functions as an exhaust purification catalyst.
  • NOx storage reduction catalyst 36a When exhaust gas is regarded as an oxidizing atmosphere (lean) during a normal operation of the diesel engine 2, the NOx storage reduction catalyst 36a occludes nitrogen oxides (NOx) in exhaust.
  • the NOx storage reduction catalyst 36a When the exhaust gas is regarded as a reducing atmosphere (stoichiometric or lower air-fuel ratio), the NOx storage reduction catalyst 36a emits occluded NOx in the form of nitrogen monoxide. The emitted nitrogen monoxide is reduced by hydrocarbon and carbon monoxide. In this manner, the first catalytic converter 36 removes NOx from exhaust gas, thereby purifying the exhaust gas.
  • the second catalytic converter 38 which is located downstream of the first catalytic converter 36, accommodates a filter 38a.
  • the filter 38a has a monolithic wall.
  • the wall has pores through which exhaust gas passes.
  • the areas of the wall defining the pores are coated with a layer containing a NOx storage reduction catalyst, which functions as an exhaust purification catalyst. That is, the NOx occlusion reduction catalyst is supported by the filter 38a. Therefore, when exhaust gas passes through the pores, NOx in the exhaust gas is removed as described above. Also, when exhaust gas passes through the pores, particulate matter in the exhaust gas is trapped by the wall of the filter 38a. The trapped particulate matter starts being oxidized by active oxygen generated when NOx is occluded under a high temperature oxidizing atmosphere.
  • the second catalytic converter 38 removes NOx and particulate matter in exhaust gas, thereby purifying the exhaust gas.
  • the second catalytic converter 38 is integrated with the first catalytic converter 36.
  • the third catalytic converter 40 which is located downstream of the first and second catalytic converters 36, 38, supports an oxidation catalyst 40a.
  • the oxidation catalyst 40a oxides hydrocarbon and carbon monoxide in exhaust gas to purify the exhaust gas.
  • a first exhaust temperature sensor 44 is located between the NOx storage reduction catalyst 36a and the filter 38a.
  • a second exhaust temperature sensor 46 and an air-fuel ratio sensor 48 are located between the filter 38a and the oxidation catalyst 40a. The second exhaust temperature sensor 46 is closer to the filter 38a, and the air-fuel ratio sensor 48 is located closer to the oxidation catalyst 40a.
  • the air-fuel ratio sensor 48 detects the air-fuel ratio of exhaust gas based on components of the exhaust gas, and outputs electric signal in linear proportion to the detected air-fuel ratio.
  • the first exhaust temperature sensor 44 detects an exhaust temperature T exin at the corresponding position.
  • the second exhaust temperature sensor 46 detects an exhaust temperature T exout at the corresponding position.
  • Pipes of a differential pressure sensor 50 are connected to a section upstream of the filter 38a and a section downstream of the filter 38a.
  • the differential pressure sensor 50 detects the pressure difference ⁇ P between the sections upstream and downstream of the filter 38a, thereby detecting the degree of clogging in the filter 38a, or the degree of accumulation of particular matter.
  • An EGR gas intake port 20b of the EGR passage 20 is provided in the exhaust manifold 32, which connects the exhaust manifold 32 to the EGR passage 20.
  • the EGR gas intake port 20b is located at a section of the exhaust manifold 32 that is close to the first cylinder #1, which section is opposite to a section of the exhaust manifold 32 at which the exhaust turbine 16b introduces exhaust gas.
  • An iron based EGR catalyst 52, an EGR cooler 54, and an EGR valve 56 are located in the EGR passage 20 in this order from the EGR gas intake port 20b to the EGR gas supply port 20a.
  • the iron based EGR catalyst 52 functions to reform EGR gas and to prevent clogging of the EGR cooler 54.
  • the EGR cooler 54 cools reformed EGR gas.
  • a fuel injection valve 58 is provided at each of the cylinders #1 to #4 to directly inject fuel into the corresponding combustion chamber 4.
  • the fuel injection valves 58 are connected to a common rail 60 with fuel supply pipes 58a.
  • the common rail 60 is supplied with fuel by a variable displacement fuel pump 62, which is electrically controlled. High pressure fuel supplied from the fuel pump 62 to the common rail 60 is distributed to the fuel injection valves 58 through the fuel supply pipes 58a.
  • a fuel pressure sensor 64 for detecting the pressure of fuel is attached to the common rail 60.
  • the fuel pump 62 supplies low-pressure fuel to a fuel adding valve 68 through a fuel supply pipe 66.
  • the fuel adding valve 68 is provided in the exhaust port 30 of the fourth cylinder #4 and injects fuel to the exhaust turbine 16b. In this manner, fuel adding valve 68 adds fuel to exhaust gas. Addition of fuel to exhaust gas by the fuel adding valve 68 is performed in a catalyst control procedure, which is described below.
  • An electronic control unit (ECU) 70 is mainly composed of a digital computer having a CPU, a ROM, and a RAM, and drive circuits for driving other devices.
  • the ECU 70 reads signals from the intake flow rate sensor 24, the intake temperature sensor 26, the first exhaust temperature sensor 44, the second exhaust temperature sensor 46, the air-fuel ratio sensor 48, the differential pressure sensor 50, an EGR opening degree sensor in the EGR valve 56, the fuel pressure sensor 64, and a throttle opening degree sensor 22a.
  • the ECU 70 reads signals from an acceleration pedal sensor 74 that detects the depression degree of an acceleration pedal 72, or an acceleration pedal depression degree ACCP, a coolant temperature sensor 76 that detects the temperature of coolant THW of the diesel engine 2, an engine speed sensor 80 that detects the number of revolutions NE of a crankshaft 78, and a cylinder distinguishing sensor 82 that distinguishes cylinders by detecting the rotation phase of the crankshaft 78 or the rotation phase of the intake cams.
  • an acceleration pedal sensor 74 that detects the depression degree of an acceleration pedal 72, or an acceleration pedal depression degree ACCP
  • a coolant temperature sensor 76 that detects the temperature of coolant THW of the diesel engine 2
  • an engine speed sensor 80 that detects the number of revolutions NE of a crankshaft 78
  • a cylinder distinguishing sensor 82 that distinguishes cylinders by detecting the rotation phase of the crankshaft 78 or the rotation phase of the intake cams.
  • the ECU 70 Based on received signals, the ECU 70 obtains the operating condition of the engine 2. Based on the obtained engine condition, the ECU 70 controls the amount and the timing of fuel injection by the fuel injection valves 58. Further, the ECU 70 controls the opening degree of the EGR valve 56, the throttle opening degree with the motor 22b, and the displacement of the fuel pump 62. Also, the ECU 70 executes filter regeneration control and sulfur release control, which will be described below.
  • the ECU 70 executes either of a normal combustion mode and a low temperature combustion mode.
  • a normal combustion mode a large amount of exhaust gas is recirculated so that the combustion temperature is slowly increased. This simultaneously reduces NOx and smoke.
  • an EGR valve opening map for the low temperature combustion mode is used.
  • the low temperature combustion mode is executed in a low load, middle-to-high rotation speed region.
  • feedback control is executed by adjusting a throttle opening degree TA based on an air-fuel ratio AF detected by the air-fuel ratio sensor 48.
  • normal EGR control including a case where no exhaust gas is recirculated
  • an EGR valve opening map for the normal combustion mode is used.
  • the ECU 70 also executes four catalyst control procedures, which include a filter regeneration mode, a sulfur release control mode, a NOx reduction mode, and a normal mode.
  • the filter regeneration mode particulate matter deposited on the filter 38a of the second catalytic converter 38 is heated, so that the particulate matter is combusted and split into carbon dioxide and water.
  • addition of fuel from the fuel adding valve 68 is repeated in an air-fuel ratio higher than the stoichiometric air-fuel ratio so that the catalyst bed temperature is increased to a high temperature which is, for example, in a range from 600°C to 700°C.
  • after injection may be performed in which fuel is injected from the fuel injection valve 58 into the combustion chambers 4 during the expansion stroke or the exhaust stroke.
  • sulfur components are emitted from the NOx storage reduction catalysts of the first and second catalytic converters 36, 38 so that the NOx occlusion capacity of the converters 36, 38, which has been lowered due to poisoning of sulfur, is restored.
  • a temperature increase process is executed, in which addition of fuel from the fuel adding valve 68 is repeated so that the catalyst bed temperature is increased to a high temperature which is, for example, 650°C.
  • an air-fuel ratio lowering process is executed in which intermittent addition of fuel from the fuel adding valve 68 is performed so that the air-fuel ratio is changed to the stoichiometric air-fuel' ratio or a value slightly lower than the stoichiometric air-fuel ratio.
  • after injection may be performed by the fuel injection valve 58.
  • NOx reduction mode NOx occluded by the NOx storage reduction catalysts of the first and second catalytic converters 36, 38 is reduced to nitrogen.
  • a by-product carbon dioxide and water are formed when NOx is reduced to nitrogen.
  • a process is executed, in which addition of fuel from the fuel adding valve 68 is repeated at a relatively long interval so that the catalyst bed temperature is increased to a not so high temperature which is, for example, in a range from 250°C to 500°C.
  • another process is executed, in which the air-fuel ratio is changed to the stoichiometric air-fuel ratio or a value lower than the stoichiometric air-fuel ratio.
  • Fig. 2 is a flowchart of this control.
  • the control is repeatedly executed by the ECU 70 at a predetermined interval. That is, the sulfur release control is a periodical interruption process routine.
  • the ECU 70 determines whether requirements for executing the sulfur release control are satisfied at step S102.
  • the execution requirements of the sulfur release control include that the amount of sulfur poisoning is no less than a predetermined amount, that the filter regeneration mode is not currently selected, and that the temperatures of the NOx storage reduction catalysts of the first and second catalytic converters 36, 38, which are estimated from the exhaust temperatures T exin , T exout , are not significantly high or low, and are in an appropriate temperature range.
  • the ECU 70 proceeds to step S104 and determines whether requirements for starting a sulfur emitting process are satisfied.
  • the starting requirement of the sulfur emitting process is that the catalyst bed temperatures of the NOx storage reduction catalysts of the first and second catalytic converters 36, 38 have reached to values near a target temperature (for example, 650°C), specifically, that an estimated catalyst bed temperature of the NOx storage reduction catalyst is no less than 600°C.
  • the estimated catalyst bed temperatures of the NOx storage reduction catalysts of the first and second catalytic converters 36, 38 may be computed based on the operating condition of the engine 2 (for example, the number of revolutions NE of the engine 2) and the amount of added fuel. Alternatively, the estimated catalyst bed temperatures may be estimated from the exhaust temperature T exin .
  • the ECU 70 proceeds to step S106 and executes temperature increase control.
  • the NOx storage reduction catalyst 36a is assumed to be brand new, and a predetermined amount fuel is intermittently added to exhaust from the fuel adding valve 68 such that the NOx storage reduction catalyst 36a is not excessively heated and the estimated catalyst bed temperature of the NOx storage reduction catalyst 36a is not less than 600°C.
  • the catalyst bed temperature of the NOx storage reduction catalyst of the second catalytic converter 38 is close to the catalyst bed temperature of the NOx storage reduction catalyst 36a of the first catalytic converter 36, the catalyst bed temperature of the NOx storage reduction catalyst of the second catalytic converter 38 fluctuates less than the catalyst bed temperature of the NOx storage reduction catalyst 36a. Therefore, the NOx storage reduction catalyst 36a of the first catalytic converter 36 is more likely to be excessively heated than the NOx storage reduction catalyst of the second catalytic converter 38 during the sulfur emitting process. Thus, the following description will focus on the NOx storage reduction catalyst 36a.
  • step S106 Even if the starting requirements of the sulfur emitting process are determined to be unsatisfied, the temperature increase control is executed at step S106, and the starting requirement of the sulfur emitting process will eventually be satisfied. Then, the ECU 70 proceeds to step S108 instead of step S106, after step S104. Then, as show in Fig. 3, the ECU 70 executes deterioration degree determination process. Subsequently, at step S110, the ECU 70 executes the sulfur emitting process.
  • the ECU 70 When the deterioration degree determination process is started, the ECU 70 first determines whether requirements for executing the deterioration degree determination process are satisfied at step S122 as shown in Fig 3.
  • the execution requirements of the deterioration degree determination process include a condition where the value of the exhaust temperature T exin detected by the first exhaust temperature sensor 44 is periodically changed in a stable manner, that is, a condition where the operating condition of the engine 2 (for example, and the load and the number of revolution E of the engine 2) are stable.
  • the ECU 70 When determining that the execution requirements of the deterioration degree determination process are not satisfied, the ECU 70 ends the deterioration degree determination process, and proceeds to the sulfur emitting process shown in Fig. 4.
  • step S123 determines whether an amplitude value A mpin has been obtained in the current sulfur release routine.
  • the ECU 70 ends the deterioration degree determination process, and proceeds to the sulfur emitting process shown in Fig. 4.
  • step S124 the ECU 70 executes a process for obtaining the maximum value T inmax of the exhaust temperature T exin detected by the first exhaust temperature sensor 44.
  • step S126 the ECU 70 executes a process for obtaining the minimum value T inmin of the exhaust temperature T exin .
  • a richening period R t during which the air-fuel ratio of exhaust is richened
  • a non-richening period L t during which the air-fuel ratio is not richened
  • the actual catalyst bed temperature of the NOx storage reduction catalyst 36a is repeatedly increased during the richening period R t and decreased during the non-richening period L t .
  • the exhaust temperature T exin detected by the first exhaust temperature sensor 44 represents the actual catalyst bed temperature of the NOx storage reduction catalyst 36a.
  • the maximum value T inmax of the exhaust temperature T exin represents the maximum value of the catalyst bed temperature during the richening period R t
  • the minimum value T inmin of the exhaust temperature T exin represents the minimum value of the catalyst bed temperature during the non-richening period L t .
  • the ECU 70 obtains the maximum value T inmax , if there is any, from the values of the exhaust temperature T exin detected by the first exhaust temperature sensor 44 during the sulfur emitting process.
  • the ECU 70 obtains the minimum value T inmin , if there is any, from the values of the exhaust temperature T exin detected by the first exhaust temperature sensor during the sulfur emitting process.
  • the ECU 70 determines whether the maximum value T inmax and the minimum value T inmin both have been obtained. When determining that the one or both of the maximum value T inmax and the minimum value T inmin have not been obtained, the ECU 70 ends the deterioration degree determination process, and proceeds to the sulfur emitting process shown in Fig. 4.
  • the maximum value T inmax appears at time t0 when the air-fuel ratio of exhaust gas is richened during the richening period R t .
  • the minimum value T inmin appears at time t1 by stopping the richening of the air-fuel ratio of exhaust gas during the non-richening period L t .
  • the ECU 70 obtains the maximum value T inmax and the minimum value T inmin at steps S124 and S126, respectively.
  • the ECU 70 determines that both of the maximum value T inmax and the minimum value T inmin have been obtained.
  • the ECU 70 proceeds to step S130 and computes the amplitude value A mpin according to a formula 1: A mpin ⁇ T inmax - T inmin Then, the ECU 70 ends the deterioration degree determination process, and proceeds to the sulfur emitting process shown in Fig. 4.
  • the computed amplitude value A mpin is stored in nonvolatile memory in the ECU 70, and is maintained when the ECU 70 is turned off.
  • the ECU 70 When the sulfur emitting process is started, the ECU 70 first determines whether the amplitude value A mpin has been obtained in the current sulfur release control at step S152 as shown in Fig 4. When determining that the amplitude value A mpin has not been obtained, the ECU 70 proceeds to step S154, and sets the duration of the richening period R t to an initial value R tint .
  • the initial value R tint is a value obtained through experiments.
  • the initial value R tint is determined such that a brand new NOx storage reduction catalyst 36a does not deteriorate due to heat even if richening with fuel added by the fuel adding valve 68 is continued for the duration of the initial value R tint .
  • a brand new NOx storage reduction catalyst 36a will deteriorate due to heat if the catalyst bed temperature exceeds a predetermined temperature (for example, the upper limit temperature shown in Fig. 6).
  • the ECU 70 computes the duration of the non-richening period L t , which should be determined for setting the catalyst bed temperature of the NOx storage reduction catalyst 36a to a target bed temperature T cat .
  • the computation is executed using a map g, based on the initial value R tint , a heat value H ex obtained by adding fuel of a predetermined amount Q add to exhaust gas from the fuel adding valve 68, the exhaust temperature T ex that contacts the NOx storage reduction catalyst 36a, an exhaust amount V ex , a heat capacity C ex of the exhaust system, and the target bed temperature T cat .
  • the predetermined value Q add is an amount of fuel that is added to exhaust from the fuel adding valve 68 when the duration of the richening period R t is set to the initial value R tint .
  • the heat value H ex is an amount of heat generated by oxidation of fuel of the predetermined value Q add when a brand new NOx storage reduction catalyst 36a is used.
  • the exhaust temperature T ex is estimated based on the engine operating condition (the load and the number of revolution NE of the engine 2).
  • the exhaust amount V ex represents the amount of exhaust that is exhaust during a period including the richening period R t and the non-richening period L t , and is computed based on an intake flow rate GA detected by the intake flow rate sensor 24 and the total time of the richening period R t and the non-richening period L t .
  • the heat capacity C ex is a value that has been obtained through experiments in advance, and a fixed value determined by the type of engine.
  • the ECU 70 determines whether the elapsed time since the richening has been started is equal to or more than a richening period R t .
  • the ECU 70 proceeds to step S162, and causes the fuel adding valve 68 to add fuel to exhaust. That is, at step S162, the ECU 70 starts or continues richening of exhaust gas.
  • the ECU 70 increments the value of the first counter. Then, the ECU 70 ends the sulfur emitting process.
  • step S166 the ECU 70 does not cause the fuel adding valve 68 to add fuel to exhaust gas. That is, the richening is stopped at step S166.
  • step S168 based on a second counter that shows elapsed time since the richening has been stopped, the ECU 70 determines whether the elapsed time since the richening has been stopped is equal to or more than a non-richening period L t .
  • the ECU 70 proceeds to step S170.
  • step S170 the ECU 70 increments the second counter, and ends the sulfur emitting process.
  • step S172 the ECU 70 clears the value of the first counter value.
  • step S174 the ECU 70 clears the value of the second counter. Then, the ECU 70 ends the sulfur emitting process.
  • the ECU 70 sets the duration of the richening period R t to the initial value R tint at step S154. Further, at step S158, the ECU 70 computes the duration of the non-richening period L t using the map g, and proceeds to step 160. In this case, since the richening has not even been started, the time elapsed after the richening period R t was started has not reached the richening period R t . Therefore, the ECU 70 proceeds to step S162 and causes the fuel adding valve 68 to add fuel to exhaust gas. In this manner, richening of exhaust gas is started again.
  • the ECU 70 does not proceed to step S154 after step S152, but to step 156 in the sulfur emitting process.
  • step S156 the ECU 70 computes the duration of the richening period R t to be set. The computation is executed using a map f shown in Fig. 5, based on the size of an amplitude value A mpin , which represents the degree of deterioration of the NOx storage reduction catalyst 36a.
  • the richening period R t is set to a short value to correspond to the catalyst bed temperature, which rapidly increases after the richening is started.
  • the richening period R t is set to a long value to correspond to the catalyst bed temperature, which slowly increases after the richening is started.
  • the duration of the non-richening period L t to be set is computed at subsequent step S158 based on the map g using the initial value R tint , the heat value H ex , the exhaust temperature T ex , the heat capacity C ex , and the target bed temperature T cat .
  • the ECU 70 performs addition of fuel at step S162. Then at step S164, the ECU 70 increments the value of the first counter.
  • step S156 the ECU 70 sets the duration of the richening period R t based on the amplitude value A mpin .
  • the ECU 70 determines that the requirements for executing the sulfur release control are not satisfied at step S102, while executing the sulfur release control shown in Fig. 2. The ECU 70 then ends the sulfur release control. Thereafter, if the execution requirements are satisfied, for example, when the sulfur poisoning amount reaches the predetermined amount, the deterioration degree determination process and the sulfur emitting process are executed. That is, the duration of the richening period R t is set to the initial value R tint at step S154, and the amplitude value A mpin is computed at steps S124 to S130. Then, based on the computed amplitude value A mpin , the duration of the richening period R t is set at step S156.
  • Fig. 6 shows changes in the air-fuel ratio of exhaust gas and the catalyst bed temperature in a case where the NOx storage reduction catalysts of the first and second catalytic converters 36, 38 are brand new.
  • the duration of the richening period R t computed based on the amplitude value A mpin is the same as the initial value R tint .
  • Fig. 7 is a graph showing changes in the air-fuel ratio of exhaust gas and the catalyst bed temperature in a case where the NOx storage reduction catalyst 36a has deteriorated to some extent.
  • the duration of the richening period R t computed based on the amplitude value A mpin is longer than the initial value R tint . Therefore, like the case where the NOx storage reduction catalyst 36a is brand new, which is shown in Fig. 6, the catalyst bed temperature of the NOx storage reduction catalyst 36a is increased to a value equal to or higher than the target temperature such that the maximum value T inmax does not exceed the upper limit temperature.
  • the first exhaust temperature sensor 44 corresponds to catalyst bed temperature detecting means that detects a physical quantity representing the actual catalyst bed temperature of the exhaust purification catalyst.
  • the ECU 70 functions as deterioration degree detecting means that detects the deterioration degree of the exhaust purification catalyst, and changing means that changes the ratio of the duration of the richening period to the duration of the non-richening period according to the deterioration degree of the exhaust purification catalyst detected by the deterioration degree detecting means.
  • the ECU 70 also functions as fuel supply means that intermittently supplies fuel to exhaust gas at a section upstream of the exhaust purification catalyst, and as deterioration degree determination means. The narrower the range of fluctuation of the physical quantity detected by the catalyst bed temperature as the fuel supply means supplies fuel to exhaust gas, the higher the deterioration degree of the exhaust purification catalyst that is determined by the deterioration degree determination means.
  • the deterioration degree determination process shown in Fig. 3 and steps S152, S154 of the sulfur emitting process shown in Fig. 4 correspond to a process executed by the deterioration degree detecting means.
  • Step S156 of the sulfur emitting process corresponds to a process executed by the changing means.
  • the sulfur emitting process corresponds to a process executed by the fuel supply means.
  • the deterioration degree determination process and step S156 of the sulfur emitting process correspond to a process executed by the deterioration degree determination means.
  • the first embodiment has the following advantages.
  • the richening period R t in which the air-fuel ratio of exhaust gas is richened
  • the non-richening period L t in which the air-fuel ratio is not richened
  • the catalyst bed temperature of the NOx storage reduction catalyst 36a is repeatedly increased and decreased.
  • the amplitude value A mpin reflects fluctuation (amplitude) of the catalyst bed temperature. The more deteriorated the NOx storage reduction catalyst 36a, the smaller the magnitude of the amplitude value A mpin , or the magnitude of fluctuation of the catalyst bed temperature. Therefore, the amplitude value A mpin indicates the degree of deterioration of the NOx storage reduction catalyst 36a.
  • the duration of the richening period R t is set relatively short.
  • the duration of the richening period R t is set relatively long. Therefore, with changes of the degree of deterioration of the NOx storage reduction catalyst 36a, an increase in the catalyst bed temperature of the NOx storage reduction catalyst 36a is prevented from being excessive or too little.
  • the amplitude value A mpin is computed in a state where the duration of the richening period R t is set to the initial value R tint . Based on the amplitude value A mpin thus computed, the degree of deterioration of the NOx storage reduction catalyst 36a is determined. In this manner, since the duration of the richening period R t has a constant value (the initial value R tint ) when the amplitude value A mpin is computed, the computed amplitude value A mpin accurately corresponds to the degree of deterioration of the NOx storage reduction catalyst 36a.
  • the amount of fuel added by the fuel adding valve 68 during the richening period R t is the minimum value. Therefore, when determining the degree of deterioration of the NOx storage reduction catalyst 36a by computing the amplitude value A mpin , the NOx storage reduction catalyst 36a is unlikely to be excessively heated.
  • the degree of deterioration of the exhaust purification catalyst is not determined based on the amplitude value A mpin , but is determined based on the rate of increase of the exhaust temperature T exin . Also, in the second embodiment, not the duration of the richening period R t , but the duration of the non-richening period L t is changed according to the degree of deterioration of the exhaust purification catalyst.
  • a deterioration degree determination process of Fig. 8 is executed instead of the deterioration degree determination process of Fig. 4, and a sulfur emitting process of Fig. 9 is executed instead of the sulfur emitting process of Fig. 4.
  • Other processes and the hardware configuration are the same as those of the first embodiment.
  • the ECU 70 When the deterioration degree determination process of Fig. 8 is started, the ECU 70 first determines whether requirements for executing the deterioration degree determination process are satisfied at step S202.
  • the requirements for executing the deterioration degree determination process are the same as those of the deterioration degree determination process of Fig. 3.
  • the ECU 70 When determining that the execution requirements of the deterioration degree determination process are not satisfied, the ECU 70 ends the deterioration degree determination process, and proceeds to the sulfur emitting process shown in Fig. 9. On the other hand, when determining that the execution requirements of the deterioration degree determination process are satisfied, the ECU 70 proceeds to step S204 and computes a detection interval t dt of the exhaust temperature T exin . The computation is performed using a map h shown in Fig. 10 based on the intake flow rate GA. The ECU 70 detects the exhaust temperature T exin at a point in time where the detection interval t dt has elapsed from when the fuel adding valve 68 added fuel to exhaust gas in the sulfur emitting process shown in Fig. 9, which will be discussed below.
  • the catalyst bed temperature of the NOx storage reduction catalyst 36a is increased, and the exhaust temperature T exin is increased, accordingly.
  • the rate of increase of the exhaust temperature T exin changes according to the degree of deterioration of the NOx storage reduction catalyst 36a and the intake flow rate GA. Specifically, the higher the deterioration degree of the NOx storage reduction catalyst 36a, the lower the rate of increase of the exhaust temperature T exin .
  • the greater the intake flow rate GA the higher the rate of increase of the exhaust temperature T exin .
  • the detection interval t dt is computed and set using the map h shown in Fig. 10 such that the rate of increase of the exhaust temperature T exin is always constant regardless of the value of the intake flow rate GA as long as the degree of deterioration of the NOx storage reduction catalyst 36a is the same.
  • the ECU 70 determines whether time elapsed from when the fuel adding valve 68 started adding fuel to exhaust gas is being currently counted.
  • the counting is started at step S212, which will be discussed below.
  • the ECU 70 proceeds to step S208 and determines whether now is the time to start addition of fuel by the fuel adding valve 68.
  • the ECU 70 determines that now is the time to start addition of fuel if the ECU 70 determined that the period from when the richening had been started did not reach the richening period R t at step S240 of the sulfur emitting process shown in Fig. 9 in the previous execution of the sulfur release control. Otherwise, the ECU 70 determines that now is not the time to start addition of fuel.
  • the ECU 70 When determining that now is not the time to start addition of fuel, the ECU 70 ends the deterioration degree determination process, and proceeds to the sulfur emitting process shown in Fig. 9. On the other hand, when determining that now is the time to start addition of fuel, the ECU 70 sets the exhaust temperature T exin detected at the moment to the initial exhaust temperature T a . Then, at subsequent step S212, the ECU 70 starts counting time elapsed from when addition of fuel from the fuel adding valve 68 was started. Thereafter, the ECU 70 ends the deterioration degree determination process, and proceeds to the sulfur emitting process shown in Fig. 9.
  • the ECU 70 In the case where counting of the time elapsed from when addition of fuel from the fuel adding valve 68 was started was started during the previous execution of the deterioration degree determination process, the ECU 70, in the subsequent execution of the deterioration degree determination process, does not proceed to step S208 after step S206, but proceeds to step S214. Then, at step S214, the ECU 70 determines whether time elapsed from when addition of fuel was started has reached the detection interval t dt . When determining that the time elapsed since addition of fuel was started has not reached the detection interval t dt , the ECU 70 ends the deterioration degree determination process, and proceeds to the sulfur emitting process shown in Fig. 9.
  • the ECU 70 at step S216 computes a temperature difference ⁇ T in between the exhaust temperature T exin detected at the moment and the initial exhaust temperature T a according to a formula 2: ⁇ T in ⁇ T exin - T a
  • the temperature difference ⁇ T in corresponds to the rate of increase of the exhaust temperature T exin in a referential exhaust flow rate state when the detection interval t dt is used as a unit.
  • the ECU 70 stops counting time elapsed from when addition of fuel was started. Thereafter, the ECU 70 ends the deterioration degree determination process, and proceeds to the sulfur emitting process shown in Fig. 9.
  • the temperature difference Tin is set to an initial value ⁇ T inint that corresponds to a brand new NOx storage reduction catalyst 36a is used.
  • the ECU 70 first execute a computation process k( ⁇ T in , ⁇ T inint , ⁇ T ine , T ex ) based on the temperature difference ⁇ T in , the initial value ⁇ T inint , a temperature difference ⁇ T ine , and the exhaust temperature T ex , thereby computing a fuel purification rate K ex .
  • the temperature difference ⁇ T ine will be discussed below.
  • a fuel purification rate K exs for a case where a non-deteriorated catalyst is used and a fuel purification rate K exe for a case where a deteriorated catalyst is used are obtained using a fuel purification map shown in Fig. 11, which is related to the fuel purification rate K exs and the fuel purification rate K exe .
  • the computed fuel purification rates K exs , K exe are prorated by the temperature differences ⁇ T in , ⁇ T ine and the initial value ⁇ T inint . As a result, the fuel purification rate K ex is obtained.
  • the fuel purification rate K ex is computed according to a formula 3: K ex ⁇ K exs - ⁇ (K exs - K exe ) ⁇ ( ⁇ T inint - ⁇ T in ) / ( ⁇ T inint - ⁇ T ine ) ⁇
  • the fuel purification rate K exs is obtained through experiments in which the temperature T ex of exhaust gas that contacts the NOx storage reduction catalyst 36a is used as a parameter. Also, the fuel purification rate K exs is a fuel purification rate by a brand new NOx storage reduction catalyst 36a, that is, a non-deteriorated NOx storage reduction catalyst 36a. The fuel purification rate K exe is also obtained through experiments in which the exhaust temperature T ex as a parameter. The fuel purification rate K exe is a fuel purification rate by an old NOx storage reduction catalyst 36a, that is, a somewhat deteriorated NOx storage reduction catalyst 36a.
  • the temperature difference ⁇ T ine is a value obtained through experiments and corresponds to the temperature difference ⁇ T in that is computed when a somewhat deteriorated NOx storage reduction catalyst 36a is used.
  • the ECU 70 sets the duration of the richening period R t to the initial value R tinit .
  • This process is the same as the process of step S154 in the sulfur emitting process shown in Fig. 4.
  • the ECU 70 computes the heat value H ex of a single addition of fuel according to a formula 4: H ex ⁇ (K ex /K exs ) ⁇ H exint
  • H ex ⁇ (K ex /K exs ) ⁇ H exint A constant H exint in the formula 4 is a heat value of a single addition of fuel when a brand new NOx storage reduction catalyst 36a is used.
  • the ECU 70 computes the non-richening period L t using the map g at step S238.
  • the map g is the same map g that is used at step S158 of the sulfur emitting process shown in Fig. 4.
  • Steps 240, S242, S244, S246, S248, S250, S252, and S254 in Fig. 9, which are executed by the ECU 70 after step S238 are each the same as steps S160, S162, S164, S166, S168, S170, S172, and S174 of the sulfur emitting process shown in Fig. 4.
  • the deterioration degree of the NOx storage reduction catalyst 36a is reflected on the temperature difference ⁇ T in .
  • the smaller the temperature difference ⁇ T in the more deteriorated the deterioration of the NOx storage reduction catalyst 36a is determined to be.
  • the temperature difference ⁇ T in which reflects the deterioration degree of the NOx storage reduction catalyst 36a, is reflected on the duration of the non-richening period L t through the fuel purification rate K ex and the heat value H ex . Therefore, the more deteriorated the NOx storage reduction catalyst 36a, the shorter the duration of the non-richening period L t is set so that the catalyst bed temperature reaches the target bed temperature.
  • Fig. 12 is a graph showing changes in the air-fuel ratio of exhaust gas in the second embodiment when the NOx storage reduction catalyst 36a is brand new.
  • Fig. 13 is a graph showing changes in the air-fuel ratio of exhaust gas and the catalyst bed temperature in the second embodiment when the NOx storage reduction catalyst 36a has deteriorated to some extent.
  • the temperature difference ⁇ T in between the catalyst bed temperature at points in time t20, t22, where the fuel adding valve 68 starts adding fuel to exhaust gas, and the catalyst bed temperature at pints in time t21, t23, where the detection period t dt has elapsed from points in time t20, t22 is relatively great.
  • the duration of the non-richening period L t is set relatively long so that the catalyst bed temperature reaches the target bed temperature.
  • the temperature difference ⁇ T in between the catalyst bed temperature at points in time t30, t32, where the fuel adding valve 68 starts adding fuel to exhaust gas, and the catalyst bed temperature at pints in time t31, t33, where the detection period t dt has elapsed from points in time t30, t32 is relatively small.
  • the duration of the non-richening period L t is set relatively short so that the catalyst bed temperature reaches the target bed temperature.
  • the deterioration degree determination process shown in Fig. 8 corresponds to a process executed by the deterioration degree detecting means.
  • Steps S232, S236, S238 of the sulfur emitting process shown in Fig. 9 correspond to a process executed by the changing means.
  • the sulfur emitting process corresponds to a process executed by the fuel supply means.
  • the deterioration degree determination process and step S232 of the sulfur emitting process correspond to a process executed by the deterioration degree determination means.
  • the second embodiment has the following advantage.
  • the richening period R t and the non-richening period L t are alternately repeated. Every time the richening period R t or the non-richening period L t is executed, the catalyst bed temperature of the NOx storage reduction catalyst 36a is repeatedly increased and decreased. The more deteriorated the NOx storage reduction catalyst 36a, the smaller the temperature difference ⁇ T in , which corresponds to the rate of increase of the catalyst bed temperature due to the start of the richening period R t , becomes. That is, the deterioration degree of the NOx storage reduction catalyst 36a is reflected on the temperature difference ⁇ T in . Therefore, the deterioration degree of the NOx storage reduction catalyst 36a is easily determined based on the temperature difference ⁇ T in .
  • the duration of the non-richening period L t is set relatively short. Accordingly, a decrease of the fuel emitting efficiency due to an insufficient increase of the catalyst bed temperature is suppressed. In this manner, even if the deterioration degree of the NOx storage reduction catalyst 36a is changed, the catalyst bed temperature is not excessively increased, and the sulfur release control is executed accurately.
  • the duration of the non-richening period L t is changed based on the amplitude value A mpin , which is computed through the deterioration degree determination process shown in Fig. 3.
  • a sulfur emitting process shown in Fig. 14 is executed instead of the sulfur emitting process shown in Fig. 4.
  • Other processes and the hardware configuration are the same as those of the first embodiment.
  • step S302 is the same as the process of step S154 in the sulfur emitting process shown in Fig. 4.
  • the ECU 70 determines whether the amplitude value A mpin has already been obtained in the current execution of the sulfur release process at step S304. When determining that the amplitude value A mpin has not been obtained, the ECU 70 proceeds to step S306, and sets the duration of the non-richening period L t to the initial value L tint .
  • the initial value L tint is set such that the average catalyst bed temperature of the NOx storage reduction catalyst 36a when the fuel adding valve 68 is adding fuel to exhaust in a case where the initial value R tint is set as the duration of the richening period R t , and the NOx storage reduction catalyst 36a is brand new becomes the target bed temperature.
  • Steps 314, S316, S318, S320, S322, S324, S326, and S328 in Fig. 14, which are executed by the ECU 70 after step S306 are each the same as steps S160, S162, S164, S166, S168, S170, S172, and S174 of the sulfur emitting process shown in Fig. 4.
  • the initial values R tint and L tint are set as the duration of the richening period R t and the duration of the non-richening period L t , respectively, and through the deterioration degree determination process shown in Fig. 3, the maximum value T inmax and the minimum value T inmin are obtained and the amplitude value A mpin is computed.
  • step S308 the ECU 70 performs a computation process m (A mpin , A mpinint , A mpe , T ex ) based on the amplitude value A mpin , an initial value A mpinint , and an amplitude value A mpe to compute the fuel purification rate K ex .
  • a fuel purification rate K exs for a case where a non-deteriorated catalyst is used and a fuel purification rate K exe for a case where a deteriorated catalyst is used are obtained using a fuel purification map shown in Fig. 11 based on the exhaust temperature T ex .
  • the computed fuel purification rates K exs , K exe are prorated by the amplitude values A mpin , A mpe and the initial value A mpinint .
  • the fuel purification rate K ex is obtained.
  • the fuel purification rate K ex is computed according to a formula 5: K ex ⁇ K exs - ⁇ (K exs - K exe ) ⁇ (A mpinint - A mpin ) / (A mpinint - A mpe ) ⁇
  • the initial value A mpinint corresponds to the amplitude value A mpin obtained when a non-deteriorated NOx storage reduction catalyst 36a is used.
  • the amplitude value A mpe corresponds to the amplitude value A mpin obtained when a deteriorated NOx storage reduction catalyst 36a is used.
  • step S310 the ECU 70 computes the heat value H ex of a single addition of fuel according to the formula 4. Further, at subsequent step S312, the ECU 70 computes the non-richening period L t using the map g.
  • the process of step S312 is the same as the process of step S158 in the sulfur emitting process shown in Fig. 4. Thereafter, the ECU 70 ends the sulfur emitting process after executing the above described steps S314 to S328.
  • the deterioration degree of the NOx storage reduction catalyst 36a is reflected on the amplitude value A mpin .
  • the smaller the amplitude value A mpin the more deteriorated the NOx storage reduction catalyst 36a is determined to be.
  • the amplitude value A mpin which reflects the deterioration degree of the NOx storage reduction catalyst 36a, is reflected on the duration of the non-richening period L t through the fuel purification rate K ex and the heat value H ex . Therefore, the more deteriorated the NOx storage reduction catalyst 36a, the shorter the duration of the non-richening period L t is set so that the catalyst bed temperature reaches the target bed temperature.
  • Fig. 15 is a graph showing changes in the air-fuel ratio of exhaust gas and the catalyst bed temperature according to the third embodiment, when the NOx storage reduction catalyst 36a has deteriorated to some extent.
  • changes in the air-fuel ratio of exhaust gas and the catalyst bed temperature when the NOx storage reduction catalyst 36a is brand new are the same as those of the first embodiment shown in Fig. 6.
  • the duration of the non-richening period L t is set shorter than the initial value L tint so that the catalyst bed temperature reaches the target bed temperature.
  • the deterioration degree determination process shown in Fig. 3 and steps S304, S306 of the sulfur emitting process shown in Fig. 14 correspond to a process executed by the deterioration degree detecting means.
  • Steps S308 to S312 of the sulfur emitting process correspond to a process executed by the changing means.
  • the sulfur emitting process corresponds to a process executed by the fuel supply means.
  • the deterioration degree determination process and step S308 of the sulfur emitting process correspond to a process executed by the deterioration degree determination means.
  • the third embodiment has the following advantage.
  • the richening period R t and the non-richening period L t are alternately repeated. Every time the richening period R t or the non-richening period L t is executed, the catalyst bed temperature of the NOx storage reduction catalyst 36a is repeatedly increased and decreased.
  • the amplitude value A mpin which represents the amplitude of the exhaust temperature T exin detected by the first exhaust temperature sensor 44, reflects fluctuation (amplitude) of the catalyst bed temperature. The more deteriorated the NOx storage reduction catalyst 36a, the smaller the magnitude of the amplitude value A mpin becomes, that is, the magnitude of fluctuation of the catalyst bed temperature becomes. Therefore, the amplitude value A mpin indicates the degree of deterioration of the NOx storage reduction catalyst 36a.
  • the duration of the non-richening period L t is set relatively long through the processes of steps S308, S310, and S312.
  • the duration of the non-richening period L t is set relatively long. In this manner, in the third embodiment, the duration of the non-richening period L t , not the duration of the richening period R t , is changed.
  • an increase in the catalyst bed temperature of the NOx storage reduction catalyst 36a is prevented from being excessive or too little with changes of the degree of deterioration of the NOx storage reduction catalyst 36a.
  • the deterioration of the NOx storage reduction catalyst 36a due to an excessive increase in the catalyst bed temperature and a decrease in the sulfur emitting efficiency due to insufficient increase in the catalyst bed temperature are prevented.
  • the amplitude value A mpin is computed in a state where the duration of the non-richening period L t is set to the initial value L tint . Based on the amplitude value A mpin thus computed, the degree of deterioration of the NOx storage reduction catalyst 36a is determined. In this manner, since the duration of the non-richening period L t has a constant value (the initial value L tint ) when the amplitude value A mpin is computed, the computed amplitude value A mpin accurately corresponds to the degree of deterioration of the NOx storage reduction catalyst 36a.
  • the duration of the richening period R t is changed based on the temperature difference ⁇ T pin , which is computed through the deterioration degree determination process shown in Fig. 8.
  • a sulfur emitting process shown in Fig. 16 is executed instead of the sulfur emitting process shown in Fig. 9.
  • Other processes are the same as those of the second embodiment, and the hardware configuration is the same as that of the first embodiment.
  • the ECU 70 When the sulfur emitting process shown in Fig. 16 is started, the ECU 70 first computes the duration of the richening period R t to be set at step S402. The computation is executed using a map p shown in Fig. 17 based on the temperature difference ⁇ T in , which reflects the degree of deterioration of the NOx storage reduction catalyst 36a. The greater the temperature difference ⁇ T in , the less deteriorated the NOx storage reduction catalyst 36a and the higher the oxidation efficiency for fuel at the NOx storage reduction catalyst 36a (the same as the fuel purification rate) . In this case, the richening period R t is set to a short value to correspond to the catalyst bed temperature, which rapidly increases after the richening is started.
  • the richening period R t is set to a long value to correspond to the catalyst bed temperature, which slowly increases after the richening is started.
  • step S404 the ECU 70 computes the non-richening period L t using the map g.
  • the process of step S404 is the same as the process of step S158 in the sulfur emitting process shown in Fig. 4.
  • Steps 406, S410, S412, S414, S416, S418, and S420 in Fig. 16, which are executed by the ECU 70 after step S404 are each the same as steps S160, S162, S164, S166, S168, S170, S172, and S174 of the sulfur emitting process shown in Fig. 4.
  • the deterioration degree of the NOx storage reduction catalyst 36a is reflected on the temperature difference ⁇ T in , and the temperature difference ⁇ T in is reflected on the duration of the richening period R t by means of the map p. Therefore, the more deteriorated the NOx storage reduction catalyst 36a, the longer the duration of the richening period R t is set.
  • Fig. 18 is a graph showing changes in the air-fuel ratio of exhaust gas and the catalyst bed temperature according to the fourth embodiment, when the NOx storage reduction catalyst 36a has deteriorated to some extent.
  • changes in the air-fuel ratio of exhaust gas and the catalyst bed temperature when the NOx storage reduction catalyst 36a is brand new are the same as those of the second embodiment shown in Fig. 12.
  • the duration of the richening period R t is set shorter than the initial value L tint as the temperature difference ⁇ T in is decreased, so that the catalyst bed temperature reaches the target bed temperature and that the NOx storage reduction catalyst 36a is not excessively heated.
  • the deterioration degree determination process shown in Fig. 8 corresponds to a process executed by the deterioration degree detecting means.
  • Steps S402, S404 of the sulfur emitting process shown in Fig. 16 correspond to a process executed by the changing means.
  • the sulfur emitting process corresponds to a process executed by the fuel supply means.
  • the deterioration degree determination process and step S402 of the sulfur emitting process correspond to a process executed by the deterioration degree determination means.
  • the fourth embodiment has the following advantage.
  • the richening period R t and the non-richening period L t are alternately repeated. Every time the richening period R t or the non-richening period L t is executed, the catalyst bed temperature of the NOx storage reduction catalyst 36a is repeatedly increased and decreased. The more deteriorated the NOx storage reduction catalyst 36a, the smaller the temperature difference ⁇ T in , which corresponds to the rate of increase of the exhaust temperature T exin due to the start of the richening period R t , becomes. That is, the deterioration degree of the NOx storage reduction catalyst 36a is reflected on the temperature difference ⁇ T in . Therefore, the deterioration degree of the NOx storage reduction catalyst 36a is easily determined based on the temperature difference ⁇ T in .
  • the duration of the richening period R t is set relatively short based on the map p of Fig 17. Accordingly, an excessive increase of the catalyst bed temperature of the NOx storage reduction catalyst 36a due to richening of the air-fuel ratio of the exhaust gas is prevented. Thereafter, when the ECU 70 determines that the NOx storage reduction catalyst 36a has deteriorated to some extent since the temperature difference ⁇ T in has been decreased, the duration of the richening period R t is set relatively long based on the map p of Fig 17. Accordingly, a decrease of the fuel emitting efficiency due to an insufficient increase of the catalyst bed temperature is suppressed. In this manner, even if the deterioration degree of the NOx storage reduction catalyst 36a is changed, the catalyst bed temperature is not excessively increased, and the sulfur release control is executed accurately.
  • the durations of the non-richening period L t and the richening period R t are not set to the initial values when computing the temperature difference ⁇ T in , but set to values that correspond to the state at the time.
  • the duration of the non-richening period L t and the richening period R t may be set to the initial values when the sulfur release control is started, and the sulfur emitting process may be executed after the durations are set to values that correspond to the temperature difference ⁇ T in after the temperature difference ⁇ T in is computed.
  • the initial exhaust temperature T a is detected immediately after richening of the air-fuel ratio of exhaust gas is started in the richening period R t .
  • the initial exhaust temperature T a may be detected when a standby period, which corresponds to the intake flow rate GA, has elapsed after the richening period R t is started.
  • the air-fuel ratio of exhaust gas is richened by causing the fuel adding valve 68 to add fuel to exhaust.
  • the air-fuel ratio of exhaust gas may be richened by other means.
  • the air-fuel ratio of exhaust gas may be richened, for example, by after injection, in.which fuel is injected into the combustion chambers from the fuel injection valve 58 during an expansion stroke or exhaust stroke.
  • the duration of one of the non-richening period L t and the richening period R t is changed according to the degree of deterioration of the exhaust purification catalyst. However, the durations of both may be changed.
  • the present invention is not limited to diesel engines, but may be applied to lean combustion gasoline engines.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)
EP20040023104 2003-09-29 2004-09-28 Vorrichtung zur Bestimmung der Alterung eines Katalysators einer Brennkraftmaschine Expired - Lifetime EP1519021B1 (de)

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JP2003337696A JP4314089B2 (ja) 2003-09-29 2003-09-29 内燃機関の触媒制御装置及び触媒劣化判定装置
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FR2927362A1 (fr) * 2008-02-07 2009-08-14 Renault Sas Procede et dispositif pour la regeneration d'un dispositif de post-traitement de gaz d'echappement
EP2415984A1 (de) * 2009-03-31 2012-02-08 Toyota Jidosha Kabushiki Kaisha Abgasreinigungssystem für einen brennkraftmotor
WO2014007749A1 (en) * 2012-07-06 2014-01-09 Scania Cv Ab Method for estimating quantity of sulphur accumulated in exhaust after treatment system
CN107208517A (zh) * 2015-01-20 2017-09-26 五十铃自动车株式会社 排气净化系统和 NOx 净化能力恢复方法
CN113272533A (zh) * 2019-01-11 2021-08-17 罗伯特·博世有限公司 用于确定废气后处理系统的老化行为的方法和装置

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US9297289B2 (en) 2011-09-06 2016-03-29 Toyota Jidosha Kabushiki Kaisha Exhaust gas purification apparatus for an internal combustion engine
JP5862438B2 (ja) * 2012-04-25 2016-02-16 トヨタ自動車株式会社 内燃機関の制御装置
KR101526768B1 (ko) * 2013-12-27 2015-06-05 현대자동차주식회사 질소산화물 정화 장치의 탈황 방법
KR101610463B1 (ko) * 2014-04-02 2016-04-07 현대자동차주식회사 내연기관 질소산화물 정화 장치의 탈황 방법
DE102023202560A1 (de) 2023-03-22 2024-09-26 Volkswagen Aktiengesellschaft Verfahren zum Betreiben eines Dieselmotors sowie Dieselmotor

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EP2415984A1 (de) * 2009-03-31 2012-02-08 Toyota Jidosha Kabushiki Kaisha Abgasreinigungssystem für einen brennkraftmotor
EP2415984A4 (de) * 2009-03-31 2014-05-14 Toyota Motor Co Ltd Abgasreinigungssystem für einen brennkraftmotor
WO2014007749A1 (en) * 2012-07-06 2014-01-09 Scania Cv Ab Method for estimating quantity of sulphur accumulated in exhaust after treatment system
CN107208517A (zh) * 2015-01-20 2017-09-26 五十铃自动车株式会社 排气净化系统和 NOx 净化能力恢复方法
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CN107208517B (zh) * 2015-01-20 2020-03-13 五十铃自动车株式会社 排气净化系统和NOx净化能力恢复方法
CN113272533A (zh) * 2019-01-11 2021-08-17 罗伯特·博世有限公司 用于确定废气后处理系统的老化行为的方法和装置

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EP1519021B1 (de) 2006-08-09
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JP4314089B2 (ja) 2009-08-12
EP1519021A3 (de) 2005-07-20
JP2005105871A (ja) 2005-04-21

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