FR2901839A1 - EXHAUST GAS PURIFICATION SYSTEM AND EXHAUST GAS PURIFICATION METHOD - Google Patents

Abstract

Decreases in intake air volume in an engine (1) in response to changes in the environment result in an increase in the amount of PM emissions. In view of this situation, a fuel supply interval correction coefficient is calculated based on the variation of a quantity of PM emissions to adjust a reference fuel supply interval to determine a target fuel supply interval (steps ST4 and ST8). By adjusting the fuel supply interval, a fuel supply amount appropriate to the change in the amount of PM material emissions is obtained, thereby preventing clogging of the injection hole of a fuel valve. additional (25) while maintaining fuel economy.

Description

EXHAUST GAS PURIFICATION SYSTEM AND METHOD FOR PURIFYING THE EXHAUST GAS

EXHAUST GAS

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system and method for purifying exhaust gas from an internal combustion engine using a catalyst. More particularly, the invention relates to an exhaust gas purification system having an additional fuel valve that provides fuel to an exhaust pipe as well as to an exhaust purification process for exhaust gas purification. supply fuel to the exhaust duct.

  2. Description of the Related Art In general, lean-burn internal combustion engines, such as diesel engines, operate predominantly in the lean combustion mode with a high air-fuel ratio (lean mixture). Thus, such engines are generally equipped with a NO storage catalyst, in the exhaust duct to purify the exhaust gas by absorbing the nitrogen oxides (hereinafter "NOX") contained in the exhaust gas. 'exhaust. When the amount of NO, absorbed by the NO storage catalyst. saturation, a NO reduction reaction, is necessary to regenerate the NO storage capacity of the catalyst. One approach to reduce NO is to add a NO reducer (light gasoline or other fuel) upstream of the NO storage catalyst. in the exhaust duct in order to decrease the oxygen concentration in the catalytic converter and thus to use reducing agents, such as hydrocarbons and excess carbon monoxide, to promote the reduction of NOS. Exhaust gas from diesel engines contains particulate matter whose main component is carbon (hereinafter "PM"), soot, a soluble organic fraction (SOF), etc. These emissions cause air pollution. A conventional exhaust gas purification system for diesel engines, which is designed to purify such PM materials and other emissions, has a particulate filter disposed in the exhaust duct. The particulate filter traps the PM materials contained in the exhaust gas passing through the exhaust duct, thereby reducing the amount of emissions of PM materials released into the atmosphere. For example, a diesel particulate filter (DPF) or a NO particle reduction system catalyst. Diesel (DPNR) can be used as a particulate filter. Deposits of PM material accumulate on the particulate filter as the amount of PM material trapped in the filter increases, causing the particulate filter to clog up with the PM material deposits. Therefore, the pressure loss of the exhaust gas passing through the particulate filter increases and as a result, the engine exhaust back-pressure increases. This reduces the engine power output and fuel economy. To solve the problems mentioned above, a conventional technique provides fuel to the exhaust duct (upstream of the particulate filter) to increase the temperature of the exhaust gas, thus promoting the oxidation (combustion) of the deposits of PM materials on the particulate filter (catalyst regeneration process of PM materials).

  As described above, in the NO reduction process, and the PM material catalyst regeneration process, both of which are provided to maintain catalyst exhaust purification performance, fuel is supplied to the catalyst conduit. exhaust using an additional fuel valve disposed in the exhaust duct. However, because the injection hole of the additional fuel valve is exposed within the exhaust duct, certain substances in the exhaust gas, such as soot and SOF fraction, can adhere and form deposits on the valve hole. This creates a concern that the exposure of the deposits to an exhaust gas at high temperatures can alter the properties of the substances and solidify them and clog the valve hole. An exemplary approach for preventing the additional fuel valve from becoming clogged is disclosed in JP-A-2003-222 019, in which fuel is supplied at all times, except during NOX and fuel reduction. regenerating the PM material catalyst, to decrease the temperature of the distal end of the additional fuel valve. If the intake air volume in the engine is decreased, for example due to changes in the environment, such as changes in atmospheric pressure when driving from a lower altitude to a higher altitude , or during a transition from normal driving to transient driving. This results in an increase in the amount of PM emissions. As the amount of PM emissions increases, the amount of PM material that adheres to and enters the injection hole of the supplemental fuel valve increases, which contributes to the accumulation of material deposits. PM. PM material deposits can clog the injection hole of the additional fuel valve. To solve a problem such as clogging of the injection hole, the additional amount of fuel (the additional amount of fuel per unit time) can be adjusted when the amount of PM material emissions reaches the maximum of the allowable fluctuation. However, adjusting the extra amount of fuel in this way may create another concern with regard to a reduced fuel economy trend.

  SUMMARY OF THE INVENTION The invention provides an exhaust purification system that maintains fuel economy while preventing clogging of the additional fuel valve injection hole. A first aspect of the invention relates to an exhaust gas purification system comprising a catalyst disposed in an exhaust duct in an internal combustion engine and an additional fuel valve for supplying fuel to the fuel duct. exhaust. The exhaust gas purification system includes adjusting means for adjusting the amount of fuel that is supplied from the supplemental fuel valve to the exhaust duct based on the change in the amount of particulate matter emissions. from a combustion chamber in the internal combustion engine.

  A second aspect of the invention is similar to the first aspect, except that the exhaust gas purification system further comprises adjustment means which regulates the amount of fuel that is supplied from the fuel valve. additional to the exhaust duct per unit of time based on the change in the amount of particulate matter (PM) emissions from the combustion chamber in the internal combustion engine. The intake air volume to the engine decreases with changes in the environment, such as a change in atmospheric pressure due to driving from a lower altitude to a higher altitude or from a transition from normal driving to transient driving. This results in an increase in the amount of PM emissions. In view of such a situation, the amount of fuel supply per unit of time is set on the basis of the change in the amount of PM emissions (for example, the change in air volume of real admission). This provides a suitable amount of fuel supply to change the amount of PM emissions by preventing excessive fuel supply. As a result, clogging of the injection hole of the additional fuel valve is prevented, while fuel economy is maintained. In accordance with the second aspect, an approach for adjusting the amount of fuel supply per unit time, wherein a reference fuel supply interval is multiplied by a correction coefficient to determine a target fuel supply interval is provided, where the reference fuel supply interval depends on the operating condition of the internal combustion engine, and the correction coefficient depends on the change in the amount of PM emissions. More particularly, in this approach, if the actual intake air volume in the internal combustion engine is less than the reference intake air volume (if the air volume ratio (air volume d the actual intake divided by the reference intake air volume) is low), the reference fuel supply interval is multiplied by a correction factor to determine the target fuel supply interval, where the correction coefficient varies or shortens the fuel supply interval, i.e., by increasing the amount of fuel supply per unit of time. In the exhaust gas purification system having the additional fuel valve to supply fuel to the exhaust pipe, when the atmospheric temperature (exhaust temperature) at the distal end of the fuel valve additional increases by a preset reference value, the temperature of the distal end of the additional fuel valve also increases, producing PM material deposits. PM material deposits can clog the injection hole of the fuel supply valve. As a result, there appears to be a need to increase the amount of fuel supply. In view of this situation, according to a third aspect of the invention, the target fuel supply interval is determined by taking into consideration the temperature of the distal end of the fuel supply valve. The third aspect of the invention is similar to the first aspect of the invention, except that the exhaust gas purification system further comprises: adjusting means for adjusting the feed interval in fuel to supply fuel from the supplemental fuel valve to the exhaust duct based on the variation of the amount of particulate matter emissions from the combustion chamber in the internal combustion engine (variation in the amount of fuel). PM), and additional fuel valve temperature estimation means for estimating the temperature of the additional fuel valve.

  The adjusting means compares the first and second correction coefficients with each other, where the first correction coefficient modifies or shortens the fuel supply interval if the actual intake air volume in the engine is less than the reference intake air volume and the second correction coefficient modifies or shortens the fuel supply interval if the additional fuel valve temperature, as estimated by the additional fuel valve temperature, increases. The reference fuel supply interval is multiplied by the coefficient among the first and second correction coefficients that results in the shortest fuel supply interval to determine the target fuel supply interval. As described above, the correction coefficient, which results in the shortest fuel supply interval (largest fuel supply amount per unit of time) is selected to adjust the feed interval. in reference fuel, a first correction coefficient dependent on the change in the amount of PM emissions, the other temperature dependent correction coefficient of the distal end of the additional fuel valve. This allows a fuel supply interval to be set for any one of the condition changes that is most likely to cause clogging of the additional fuel valve injection hole, where Conditions are a temperature increase of the distal end of the additional fuel valve and an increase in the amount of PM material emissions due to changes in the environment or during transient driving conditions. As a result, clogging of the injection hole of the additional fuel valve can be effectively prevented. In addition, a fuel supply amount appropriate to the variation of the above specific conditions is provided. This prevents excessive fuel supply. As a result, while fuel economy is maintained and clogging of the injection hole of the additional fuel valve is prevented. Although increasing the amount of fuel supply per unit of time prevents clogging of the injection hole of the additional fuel valve, the fuel can also react with oxygen in the catalyst, which can lead to catalyst temperature to exceed a certain range of values (for example 750 C). An approach is offered to avoid this situation in which, when the temperature of a catalyst is greater than or equal to a prescribed value, the amount of fuel supply per unit time is reduced depending on the temperature of the catalyst (ie ie the variation of the temperature of the catalyst with respect to the preset value). This approach helps to avoid a problem of thermal degradation of the catalyst due to excessively high catalyst temperatures caused by the increased amount of fuel supply.

  An exemplary approach is provided to reduce the amount of fuel supply per unit of time, in which the target fuel supply interval, shorter than the reference fueling interval (for example the corrected target fuel delivery interval) is used to shorten the fueling time per interval shown in Figure 8. This approach not only provides a shorter fuel supply interval, which can prevent clogging. injection hole of the additional fuel valve, but also ensures a smaller total amount of fuel supply. Therefore, while an excessive increase in catalyst temperature is prevented, clogging of the injection hole of the additional fuel valve is also prevented. Another approach is provided to prevent an excessive increase in catalyst temperature, in which a restrictive correction or increase in the amount of fuel supply per unit of time is performed, so that the catalyst temperature, estimated on the basis of the exhaust gas temperature, does not exceed a prescribed value. Inventions in accordance with the second and third aspects may further include catalyst temperature sensing means which detects the temperature of the catalyst. If the variation of the catalyst temperature, detected by the temperature sensing means, is greater than or equal to a preset value, the adjusting means can reduce the amount of fuel supply per unit of time as a function of the variation in temperature. the temperature of the catalyst. Inventions in accordance with the second and third aspects 40 may further include a coolant temperature sensing means for detecting the temperature of the coolant in the internal combustion engine. If the change in the coolant temperature, detected by the coolant temperature sensing means, is greater than or equal to a preset value, the adjusting means reduces the amount of fuel supply per unit time. depending on the variation of the coolant temperature.

  The internal combustion engine may be a diesel engine. The internal combustion engine can be mounted on a vehicle. In addition, a fourth aspect of the invention relates to an exhaust purification process which supplies fuel to an exhaust duct in an internal combustion engine, the exhaust duct having a catalyst disposed therein. -this. The exhaust gas purification process includes adjusting the amount of fuel that is supplied from the supplemental fuel valve to the exhaust duct based on the variation in the amount of particulate matter emissions from a fuel system. combustion chamber in the internal combustion engine. According to the fourth aspect, the amount of fuel may be a quantity of fuel that is supplied from the supplemental fuel valve to the exhaust duct per unit of time. In accordance with the fourth aspect, to adjust the amount of fuel, the reference fueling interval may be multiplied by the correction coefficient which depends on the change in the amount of particulate matter emissions to determine the fueling interval. target fuel supply. According to the fourth aspect, to adjust the fuel quantity, if the actual intake air volume in the internal combustion engine is smaller than the reference intake air volume, the supply interval Reference fuel may be multiplied by a correction factor to adjust or shorten the fuel supply interval to determine the target fuel supply interval.

  According to the fourth aspect, the amount of fuel may be a fuel gap that is provided from the supplemental fuel valve to the exhaust duct. The invention according to the fourth aspect may further comprise estimating the temperature of the additional fuel valve. To adjust the amount of fuel, the first and second correction coefficients are compared to each other, where the first correction coefficient is intended to modify or shorten the fuel supply interval if the volume of air The actual intake in the internal combustion engine is less than the reference intake air volume and the second correction coefficient is intended to modify or shorten the fuel supply interval if the Additional fuel, which is estimated by the additional fuel change temperature estimation means, increases. Then, the reference fuel supply interval is multiplied by either one of the first and second correction coefficients, resulting in a shorter fuel supply interval, and the differential interval. target fuel supply is determined. The invention according to the fourth aspect may further comprise sensing the temperature of the catalyst. To adjust the amount of fuel, when the temperature of the catalyst detected by the catalyst temperature detection means is greater than or equal to a preset value, the amount of fuel supply per unit of time is reduced as a function of the temperature of the catalyst. catalyst. According to the fourth aspect, a fuel injection amount per unit of time can be reduced by shortening the supply interval while the fueling time per minute is reduced. A fifth aspect of the invention relates to exhaust gas purification comprising: a disposed in an exhaust duct in a regulator or fuel, interval

  an internal combustion engine catalyst system, an additional fuel valve for supplying fuel to the exhaust duct, and a control portion for adjusting a fuel quantity that is supplied from the supplemental fuel valve to the exhaust duct based on the variation of the amount of particulate matter emissions from a combustion chamber in the internal combustion engine. In a sixth aspect of the invention, the exhaust gas purification process may further include adjusting the fuel quantity which is supplied from the additional fuel valve to the exhaust pipe on the basis of the variation in the amount of particulate matter emissions from the combustion chamber in the internal combustion engine. In accordance with the aspects of the invention mentioned above, in view of the amount of PM emissions that can increase the amount under the conditions of driving on flat and normal ground, a: amount of fuel supply per unit time (fuel supply interval) is set based on the change in the amount of PM emissions. This allows a suitable fuel supply amount to vary the amount of PM material emissions, thus preventing clogging of the injection hole of the additional fuel valve, while maintaining fuel economy.

  BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects, features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings, in which like reference numerals are provided. are used to represent identical elements, and in which: Figure 1 is a simplified diagram showing an example of a diesel engine equipped with an exhaust gas purification system according to the invention, Figure 2 is a Synoptic diagram of the configuration of a control system comprising an electronic control unit (ECU); Fig. 3 is a flowchart showing an example of a fuel supply interval correction process executed by the unit ECU, Figure 4 is a map for calculating a reference fuel supply interval, which is used in the processing of Figure 5 is a map illustrating a fuel supply interval correction coefficient which is used in the fuel supply interval correction process of Figure 3. FIG. 6 is a map illustrating a correction coefficient X for a quantity of PM emissions, which is used in the correction process of the fuel supply interval of FIG. 3, FIG. 7 is a map illustrating a fuel supply interval correction coefficient which is used in the fuel supply interval correction process of FIG. 3; FIG. 8 illustrates a feed interval and a duration Fig. 9 is another example illustrating the fuel supply interval correction coefficient map, which varies depending on the temperature of the fuel end. distal to the additional fuel valve.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the invention will be described below with reference to the drawings. The general configuration of a diesel engine using a fuel supply device of the invention is described with reference to FIG. 1. In this embodiment, the diesel engine 1 (hereinafter referred to as "engine 1" ) can be a four-cylinder direct injection engine in the cylinders with common supply rail. The engine 1 comprises, as main components, a fuel supply system 2, combustion chambers 3, an intake system 6 and an exhaust system 7. The fuel supply system 2 comprises a fuel supply pump 21, a common supply manifold 40 22, injectors (fuel injection valves) 23, an additional fuel valve 25, an engine fuel pipe 26 and a fuel pipe 27 The fuel supply pump 21 draws fuel from the fuel tank and pressurises the fuel to supply the pressurized fuel to the common fuel rail 22 through the engine fuel pipe 26. The common feed ramp 22 functions as an accumulator to maintain the fuel pressure supplied from the fuel supply pump 21 to a prescribed level (by accumulating the high pressure fuel supplied from the fuel supply pump). fuel supply pump 21). The common feed ramp 22 distributes fuel accumulated to the injectors 23. Each injector 23 is a solenoid valve designed to open when a specified voltage is applied and spray the fuel into the associated combustion chamber 3. The feed pump 21 is designed to supply a portion of the fuel sucked from the fuel tank to the supplemental fuel valve 25 through the fuel line 27. The supplemental fuel valve 25 is a solenoid valve designed to open when a specified voltage is applied and supply fuel to the exhaust system 7 (from exhaust ports 71 to an exhaust manifold 72). An injection hole of the additional fuel valve 25 is exposed within the exhaust system 7. The intake system 6 has an intake manifold 63 connected to intake ports formed in the cylinder head. An intake pipe 64, included in the intake duct, is connected to the intake manifold 63. An air purifier 65, an air flow meter 32 and a throttle valve 62 are arranged in the duct. admission in order from the upstream side. The air flow meter 32 is adapted to output an electrical signal which indicates the volume of air flow in the intake duct through the air cleaner 65. The exhaust system 7 includes a manifold exhaust pipe 72 connected to the exhaust ports 71 formed on the cylinder head. The exhaust pipes 73 and 74, included in the exhaust duct, are connected to the exhaust manifold 72. A catalytic converter 4 is also disposed in the exhaust duct. The catalytic converter 4 comprises a storage reduction catalyst NOS 4a and a reduction catalyst DPNR 4b. The NOS storage reduction catalyst 4a is designed to absorb NOS in the presence of a high oxygen concentration in the exhaust gas when the oxygen concentration in the exhaust gas is high and to reduce the NOS in the exhaust gas. NO2 or NO as emissions in the presence of a low oxygen concentration and a large amount of reducing component (unburned component of fuel, such as hydrocarbons) in the exhaust gas when the oxygen concentration is low and excess reducer (i.e., unburned fuel, such as hydrocarbons) in the exhaust gas. NOS emissions as NO2 or NO react immediately with the hydrocarbons or CO contained in the exhaust gas, so that NO2 or NO is reduced to N2. The reduction of NO2 or NO to N2 causes hydrocarbons or CO to be oxidized to H2O or 002. In one example, the DPNR reduction catalyst 4b employs a porous ceramic structure that contains the NOS storage reduction catalyst. Particulate matter in the exhaust gas is trapped as it passes through the porous wall. When the air-fuel ratio of the exhaust gas is poor, the NOS storage reduction catalyst absorbs the NOS contained in the exhaust gas. When the fuel air ratio is rich, the stored NOS are reduced. The DPNR reduction catalyst 4b also oxidizes and burns the trapped PM materials. The exhaust gas purification system comprises the catalytic converter 4, the additional fuel valve 25 and the fuel line 27, as well as an electronic control unit (ECU) 100. The ECU 100 controls the operation of the additional fuel valve 25. The engine 1 comprises a turbocharger (compressor) 5. The turbocharger 5 comprises a turbine shaft 5a, a turbine wheel 5b and a compressor wheel 5c, the turbine wheel 5b and the turbine wheel. compressor 5c are connected to each other via the turbine shaft 5a. The compressor wheel 5c faces the inside of the intake pipe 64, while the turbine wheel 5b exposes the inside of the exhaust pipe 73. The turbocharger 5 thus configured uses an exhaust circulation (pressure d exhaust) received by the turbine wheel 5b to rotate the compressor wheel 5c to force air into the engine. In this embodiment, the turbocharger 5 is a variable nozzle turbocharger having a variable nozzle nozzle mechanism 5d on the turbine wheel 5b side. The overpressure of the engine 1 can be adjusted by controlling the degree of opening of the variable nozzle nozzle mechanism 5d. The intake system 6 has an intermediate cooling device 61 provided on the intake pipe 64. The intermediate cooling device 61 is designed to cool the intake air, the temperature of which has increased due to forced entry. The throttle valve 62 is also provided in the intake pipe 64 downstream of the intermediate cooling device 61. The throttle valve 62 is a solenoid valve whose opening varies continuously. The throttle valve 62 reduces the cross section of the intake air duct under certain conditions to control (decrease) the intake air volume.

  The engine 1 comprises an exhaust gas recirculation duct (EGR) 8 which connects the intake system 6 and the exhaust system 7. The EGR 8 recirculation duct recirculates a certain portion of the exhaust gas to the intake system 6 as required and supplies this exhaust gas back to the combustion chambers 3 to decrease the combustion temperature. This decreases the amount of NOS emissions. The EGR 8 recirculation duct comprises an EGR 81 recirculation valve and an EGR 82 recirculation cooling device which cools the exhaust gas that passes (recirculates) through the EGR 8 recirculation duct. The EGR recirculation volume to be introduced. from the exhaust system 7 in the intake system 6 (volume of exhaust gas to be recirculated) can be adjusted by controlling the degree of opening of the EGR 81 recirculation valve.

  The sensors will now be described. The engine 1 has several types of sensors installed at specific locations thereof. The sensors output signals that indicate the environmental conditions of the specific locations as well as signals indicating the operating conditions of the engine 1. For example, the air flow meter 32, upstream of the throttle valve 62 in the intake system 6 outputs a signal which indicates the detected flow rate of the intake air (intake air volume). The intake temperature sensor 33, disposed on the intake manifold 63, outputs a signal which indicates the detected temperature of the intake air. The intake pressure sensor 34, disposed on the intake manifold 63, outputs a signal which indicates the detected pressure of the intake air. An A / C (air-fuel ratio) sensor 35, downstream of the catalytic converter 4 in the exhaust system 7, outputs a detection signal which varies continuously as a function of the oxygen concentration in the gas exhaust. An exhaust gas temperature sensor 36, downstream of the catalytic converter 4 in the exhaust system 7, outputs a signal which indicates the temperature of the detected exhaust gas. A common feed ramp pressure sensor 37 outputs a signal that indicates the detected pressure of the fuel stored in the common feed ramp 22. A fuel pressure sensor 38 outputs a signal that indicates the detected pressure. fuel flowing through the fuel line 27 (fuel pressure). The ECU will now be described. As indicated in FIG. 2, the ECU 100 comprises a CPU 101, a read-only memory 102, a random access memory 103 and a backup RAM 104. The read-only memory 102 stores several control programs, maps to be used for execute these control programs and other data. The CPU 101 executes various operations in accordance with the respective control programs and maps stored in the ROM 102. The result of the operations in the CPU 101 and the data received as input from the respective sensors are temporarily stored in the memory. 103. The backup RAM 104 is a non-volatile memory for storing data stored during a power failure, for example when the motor 1 stops. The read-only memory 102, the CPU 101, the random access memory 103 and the backup RAM 104 are connected to each other via a bus 107, while connected to an input interface 105 and at an output interface 106. The input interface 105 connects to the air flow meter 32, the inlet temperature sensor 33, the inlet pressure sensor 34, the A / C ratio sensor 35, the exhaust gas temperature sensor 36, the common supply manifold pressure sensor 37 and the fuel pressure sensor 38. In addition, the input interface 105 connects to a temperature sensor of the engine. water 31, an atmospheric pressure sensor 39, a thrust sensor on the accelerator 40 and a crank position sensor 41. The water temperature sensor 31 outputs a signal which indicates the temperature of the crankshaft. coolant detected in the engine 1. Atmos pressure sensor Phérique 39 detects the atmospheric pressure which varies according to the conditions of the environment, including the altitude. The throttle trigger sensor 40 outputs a signal which indicates the detected displacement of the accelerator pedal. The crank position sensor 41 outputs a pulse when the output shaft (crankshaft) of the engine 1 rotates at a given angle. In turn, the output interface 106 connects to the injector 23, the additional fuel valve 25, the variable nozzle vane mechanism 5d, the throttle valve 62, the EGR 81 recirculation valve, and other.

  The ECU 100 executes the respective commands in the engine 1 based on the outputs from the sensors mentioned above. The ECU 100 also performs a PM catalyst regeneration control and a fuel supply interval correction process, which will be described later. Next, the PM material catalyst regeneration control will be described. The ECU unit 100 first estimates the amount of PM material deposits in the DPNR reduction catalyst 4b. An approach for estimating the amount of 2M material deposits is to use a map plotted with experimental data on the PM material adhesion value that varies depending on the operating conditions of the engine 1 (for example, the gas temperature of the engine). exhaust, the amount of fuel injection and engine speed). The adhesion values of PM materials read from the map are summarized to obtain the amount of PM material deposits. Another approach would be to estimate the amount of PM deposition based on the driving distance or the driving time of the vehicle. Yet another variant is to use a differential pressure sensor, disposed in the catalytic converter 4, to detect the differential pressure between the upstream and downstream of the reduction catalyst DPNR 4b. The amount of PM material deposits trapped by the DPNR reduction catalyst 4b is calculated based on the output of the differential pressure sensor. If the estimated amount of PM material deposition is greater than or equal to a specified reference value, the ECU 100 determines to begin the regeneration of the DPNR reduction catalyst 4b and performs the PM material catalyst regeneration control. More particularly, the ECU 100 calculates a feed quantity and a required fuel supply interval based on the engine speed output from the crank position sensor 41 with reference to the map previously plotted with the experimental results. According to the result of the calculation, the ECU 100 controls the operation of the additional fuel valve 25, through which fuel is supplied to the exhaust system 7 continuously. The fuel supply results in an increase in the temperature of the DPNR reduction catalyst 4b, which promotes the oxidation of the PM material deposits in the DPNR reduction catalyst 4b in H2O and CO2 emissions. In addition to the PM material catalyst regeneration control, the ECU 100 may perform a sulfur poisoning recovery command or a NO reduction command. The sulfur poisoning recovery control releases the sulfur from the NO 4a storage reduction catalyst and the DPNR 4b reduction catalyst. This is achieved by increasing the temperature of the catalyst by continuously supplying fuel from the additional fuel valve 25 while controlling the air-fuel ratio of the exhaust gas to the stoichiometric or richer ratio. The NOX control is provided to reduce the NOx stored in the NOx storage reduction catalyst, 4a and the DPNR reduction catalyst 4b to N2, CO2 and H2O by intermittently supplying fuel from the NOx storage reduction valve. additional fuel 25. The PM material regeneration control, the sulfur poisoning recovery control and the NOX reduction control are performed individually as appropriate. When it is necessary to execute all three commands simultaneously, these commands can be executed according to the sequence described above.

  Then, the correction treatment of the fuel supply interval will be described. As mentioned above, the intake air volume in the engine 1 mounted on the vehicle decreases according to certain changes in the environment, such as a change in atmospheric pressure or during a transition from a normal driving to transient conduct. This increases the amount of PM emissions. As the amount of PM emissions increases, the amount of PM material adhering to, and entering, the injection hole of the supplemental fuel valve 25 increases, which contributes to the accumulation of material deposits. PM. The PM material deposits may clog the injection hole of the supplemental fuel valve 25. When the temperature of the exhaust gas at the distal end of the supplemental fuel valve 25 increases from the preset reference temperature, the temperature of the distal end itself of the additional fuel valve 25 also increases, producing deposits of PM materials. The PM material deposits may clog the injection hole of the additional fuel valve 25. To solve this problem, in this embodiment, a correction coefficient of the fuel supply interval, eminttemp, which is used to correct the fuel supply interval, is calculated on the basis of the temperature of the distal end of the additional fuel valve 25. In addition, a correction coefficient of the fuel supply interval, emintpm , which is used to correct the fuel supply interval, is calculated on the basis of the change in the amount of PM emissions due to changes in the environment or during transient driving conditions. Between eminttemp and emintpm, the correction coefficient of the fuel supply interval that results in a larger amount of fuel supply per unit of temos, is selected as the target fuel supply interval. This provides the characteristic of conserving fuel economy, while preventing clogging of the injection hole of the additional fuel valve 25.

  A specific example of the fuel supply interval correction process is described below with reference to the flowchart of FIG. 3. The ECU 100 executes the fuel supply interval correction process. . A subroutine of this correction process is repeated at a predetermined time interval. In step ST1, the engine speed Ne is read from the output of the crank position sensor 41 to calculate a required fuel supply quantity Q based on engine speed Ne with reference to a map. , as shown in Fig. 4. The relationship between the engine speed Ne and the required fuel supply amount Q is obtained in advance by means of experiments, calculation, etc. Then, the map used to calculate the required fuel supply quantity Q is prepared by plotting the relationship between the engine speed Ne and the required fuel supply quantity Q and stored in the read-only memory 102 of the ECU. In step ST2, a reference fuel supply interval Tb (see FIG. 8) is calculated on the basis of the required fuel supply quantity Q and engine speed Ne with reference to the map shown in Figure 4. The map for calculating the reference fuel supply interval is also plotted with experimental and computational data on the relationship between the required fuel supply quantity Q and the of the engine Ne and the reference fuel supply interval Tb. The read-only memory 102 of the ECU 100 stores this map in advance. In step ST2, a reference exhaust gas temperature (ambient temperature of the additional fuel valve 25) is also obtained when the reference fuel supply interval Tb is calculated. In step ST3, the correction coefficient of the fuel supply interval, eminttemp, which is used to correct the fuel supply interval, is calculated on the basis of the temperature of the distal end of the fuel supply interval. the additional fuel valve 25. More particularly, on the basis of the difference between the reference exhaust gas temperature obtained in step ST2 and the current exhaust gas temperature (variation of the temperature of the exhaust gas). ATh exhaust), the correction coefficient of the fuel supply interval, eminttemp, is calculated by referring to the map shown in Figure 5. The map for calculating the feed interval correction coefficient in Figure 5 is plotted with experimental and calculation data on the relation between the variation of the exhaust gas temperature ATh and the correction coefficient of fuel supply interval, eminttemp. The read-only memory 102 of the ECU 100 stores this map in advance. The fuel supply interval correction coefficient, eminttemp, is pre-set to be smaller as the change in exhaust gas temperature ATh increases. When the fuel supply interval correction coefficient, eminttemp, which is calculated based on the temperature of the distal end of the supplemental fuel valve, is reduced, the fuel supply interval becomes smaller. short.

  It should be understood that the temperature of the exhaust gas (ambient temperature of the additional fuel valve 25) can be calculated using a specific map for calculating the exhaust gas temperature. The map can use experimental and computation data on 40 engine speed Ne, intake temperature, atmospheric pressure, etc. as parameters. The read-only memory 102 of the ECU unit 10E) can store this map in advance. Alternatively, an exhaust gas temperature sensor may be provided for detecting and outputting the temperature of the exhaust gas upstream of the turbocharger 5. In step ST4, the supply interval correction coefficient in fuel, emintpm, used to correct the fuel supply interval, is calculated on the basis of the change in the amount of PM emissions due to changes in the environment or during transient driving conditions . More particularly, firstly, an air volume ratio and a correction coefficient X (excess air ratio) for the amount of PM emissions are calculated.

  The air volume ratio will now be described. The air volume ratio, gnr, is calculated by dividing the actual intake air volume in the engine 1, which is obtained from the output of the air flow meter 32, by the volume of air reference intake under flat driving conditions (air volume ratio gnr = intake air volume divided by the reference intake air volume). Next, the calculation of the correction coefficient X. for the quantity of PM emissions will be described. On the basis of the air volume ratio gnr calculated in the above-mentioned treatment and the atmospheric pressure (detected value) obtained from the output signal of the atmospheric pressure sensor 39, the correction coefficient 2L ,, emgpmimd , for the amount of PM emissions, is calculated by referring to the map of Figure 6. The correction coefficient map X of Figure 6 is plotted with experimental and calculation data on the correction coefficient X , using the ratio of air volume gnr and atmospheric pressure as parameters. The read-only memory 102 of the ECU 100 stores this map in advance. The correction coefficient X, emgpmlmd, is increased when the air volume ratio gnr and the atmospheric pressure decrease. On the basis of the correction coefficient X, emgpmlmd, thus calculated, the fuel supply interval correction coefficient, emintpm, is calculated by referring to the map of FIG. 7. The map for calculating the coefficient the fuel supply interval correction shown in Fig. 7 is plotted with experience and calculation data on the relationship between the correction coefficient emgpmlmd, and the fuel supply interval correction coefficient, emintpm. The read-only memory 102 of the ECU 100 stores this map in advance. The fuel interval correction coefficient, emintpm, is pre-set to be smaller when the change in the amount of PM emissions (correction factor emgpmlmd) increases. When the fuel interval correction coefficient, emintpm, decreases, the fuel supply interval becomes shorter. In steps ST5 to ST7, the fuel supply interval correction coefficient, eminttemp, calculated in step ST3, is compared with the fuel interval correction coefficient, emintpm, calculated at step ST4. The smaller value of the two is selected, that is, the one that results in a larger amount of fuel per unit of time. More particularly, if the fuel supply interval correction coefficient, eminttemp, which depends on the temperature of the distal end of the supplemental fuel valve, is smaller than the supply interval correction coefficient. in fuel, emintpm, which depends on the variation of the quantity of PM emissions (if the result of the determination in step ST5 is true), the correction coefficient, eminttemp, is selected as the correction coefficient target fuel supply interval, emintad (step ST6). Conversely, if the fuel supply interval correction coefficient, emintpm, is smaller than the correction coefficient of the fuel supply interval, eminttemp (if the result of the determination in step ST5 is false), the correction coefficient, emintpm, is selected as the correction coefficient of the target fuel supply interval, emintad (step ST7). In step ST8, the correction coefficient of the target fuel supply interval, emintad, selected in step ST6 or ST7, is multiplied by the reference fuel supply interval, calculated at step ST2, to obtain a target fuel supply interval (target fuel supply interval = [reference fuel supply interval before correction] x emintad). Then, the subroutine ends. In accordance with the fuel supply interval correction processing, either one of the fuel interval correction coefficients, emintter.p or emintpm, is selected to correct the fuel interval. target fuel supply. In particular, the correction coefficient, which results in a shorter feed interval (a larger amount of fuel feed per unit of time) is selected. This allows the fuel supply interval to be appropriately corrected for any one of the condition changes that is most likely to cause clogging of the additional fuel valve injection hole 25, when the temperature of the distal end of the supplemental fuel valve 25 increases, or when the amount of PM emissions increases due to changes in the environment or during transient driving conditions. As a result, the clogging of the injection hole of the additional fuel valve 25 is effectively prevented. Also, in accordance with the fuel supply interval correction treatment, a fuel supply amount (fuel supply amount per unit of time) appropriate to the above specific condition change is provided. This maintains the fuel economy in contrast to the case where the fuel supply amount is set when the amount of PM emissions reaches the maximum of the allowable fluctuation. Although increasing the amount of fuel supply per unit of time prevents clogging of the injection hole of the additional fuel valve 25, the fuel also reacts with the oxygen in the catalyst, which can cause the catalyst temperature to exceed a certain range of values (for example 750 C). An approach to avoid such a situation is presented as follows. The temperature of the DPNR reduction catalyst 4b is estimated on the basis of the temperature of the exhaust gas detected by the exhaust gas temperature sensor 35. If the estimated catalyst temperature is greater than or equal to a prescribed temperature, the amount of fuel supply per unit of time is reduced in accordance with the estimated catalyst temperature (more particularly, the change in catalyst temperature from a preset value). As a result, an excessive increase in catalyst temperature is prevented. It should be understood that the temperature prescribed for the catalyst temperature can be empirically obtained by taking the certain range of catalyst temperature (eg 750 C) into consideration. An approach for reducing the amount of fuel supply per unit of time, the interval fueling time shown in Figure 8 can be shortened, while the target fuel supply interval remains unchanged after the fuel supply interval has been corrected. Not only does this approach provide a shorter feed interval, which prevents clogging of the additional fuel valve injection hole, but it also provides a smaller total amount of fuel supply. Thus, while an excessive increase in catalyst temperature is prevented, clogging of the injection hole of the additional fuel valve 25 is also prevented. To prevent an excessive increase in catalyst temperature, the following approach can also be taken. The temperature of the DPNR reduction catalyst 4b can be estimated on the basis of the temperature of the exhaust gas detected by the exhaust gas temperature sensor 35. Then, on the basis of the estimated current catalyst temperature, and of the target fuel supply interval, the increase in catalyst temperature, which results from the supply of fuel to the target fuel supply interval, is estimated. A correction or restrictive increase in the amount of fuel supply per unit of time is performed so that the estimated catalyst temperature does not exceed a prescribed value (a value determined on the basis of the maximum allowable catalyst temperature).

  Another embodiment of the invention is further described. In the embodiment described above, any one of the fuel interval correction coefficients, eminttemp or emintpm, is used to determine the target fuel supply interval. However, the invention is not limited to the embodiment mentioned above. Instead, the target fuel supply interval can be calculated using only the fuel interval correction coefficient, emintpm. Also, in the embodiment described above, the reference fuel supply interval Tb is multiplied by the fuel supply interval correction coefficient, eminttemp or emintpm, to correct the amount of fuel. fuel supply. Alternatively, the reference fuel supply duration per interval (see Figure 8) may be multiplied by the fuel supply interval correction coefficient, eminttemp or emintpm, to correct the feed amount. in fuel per unit of time. In order to correct the fuel feeding time per interval, the fuel supply interval correction coefficient, eminttemp, is set to be larger as the change in exhaust gas temperature ATh increases. In addition, the fuel interval correction coefficient, emintpm, is pre-set to be larger when the change in the amount of PM emissions (correction coefficient emgpmlmd) increases. In the embodiment described above, the fuel supply interval correction coefficient, eminttemp, which depends on the temperature of the distal end of the supplemental fuel valve 25, is calculated on the basis of the variation of the temperature of the exhaust gas ATh. Alternatively, the fuel supply interval correction coefficient, eminttemp, may be calculated on the basis of the engine coolant temperature 1, obtained from a signal outputted by the temperature sensor. water 31, with reference to the map of FIG.

  In the embodiment described above, a direct injection four-cylinder diesel engine is equipped with the exhaust gas purification system of the invention. However, the invention is not limited to this embodiment. Alternatively, other diesel engines, having any number of cylinders, such as a direct injection six-cylinder diesel engine, may also be equipped with the exhaust gas purification system of the invention. In addition, the invention is limited to use with direct injection diesel engines but can also be applied to other types of diesel engines. In addition, the invention can be used not only with vehicle engines but also for engines designed for other purposes.

  In the embodiment previously described, the catalytic converter 4 comprises the NOX storage reduction catalyst 4a and the DPNR reduction catalyst 4b. Alternatively, the catalytic converter 4 may comprise a DPF filter in addition to the NO220 storage reduction catalyst 4a or an oxidation catalyst. Although the invention has been described with reference to exemplary embodiments thereof, it should be understood that the invention is not limited to the embodiments or designs described. On the contrary, it is intended that the invention covers various modifications and equivalent arrangements. Furthermore, although the various elements of the embodiments are represented in various combinations and configurations, other combinations and configurations, including more elements, fewer elements, or only a single element, are also within range. of the invention.

Claims (20)

  An exhaust gas purification system comprising a catalyst (4) disposed in an exhaust duct of an internal combustion engine (1) and an additional fuel valve (2.5) which supplies fuel to the fuel duct. exhaust system, characterized by comprising: adjusting means (100) for adjusting an additional amount of fuel which is supplied by the additional fuel valve (25) based on a variation in the amount of particulate matter emitted from a combustion chamber of the internal combustion engine (1).   An exhaust gas purification system according to claim 1, wherein: the adjusting means (100) adjusts the additional amount of fuel which is supplied from the additional fuel valve (25) to the exhaust duct by unit of time. 20   An exhaust gas purification system according to claim 2, wherein: the adjusting means (100) multiplies a reference fuel supply interval by a correction coefficient which depends on the variation of the quantity of materials Particulates emitted to determine a target fuel supply interval.   4. The exhaust gas purification system of claim 3, wherein: the adjusting means (100) multiplies a reference fuel supply interval by a correction coefficient to change the feed interval. in fuel to determine the target fuel supply interval, when a real intake air volume in the internal combustion engine (1) is smaller than an intake air volume of: reference.   An exhaust gas purification system according to claim 1, wherein: the adjusting means (100) adjusts a fuel supply interval of a fuel which is supplied from the additional fuel valve (25) to exhaust duct per unit of time.   An exhaust purification system according to claim 5, further comprising: temperature estimation means of the additional fuel valve (25) for estimating a temperature of the additional fuel valve (25), wherein the adjusting means (100) compares a first correction coefficient with a second correction coefficient, the first correction coefficient is used to change the fuel supply interval when the actual intake air volume in the internal combustion engine (1) is smaller than the reference intake air volume, the second correction coefficient is used to change the fuel supply interval when the estimated temperature of the additional fuel valve (25) increases and multiplies the reference fuel supply interval by the correction coefficient among the first and second correction coefficients which gives the shortest fuel supply interval to determine the target fuel supply interval.   An exhaust purification system according to any one of claims 1 to 6, further comprising: catalyst temperature detecting means (36) for detecting a temperature of the catalyst (4), wherein the adjusting means (100) reduces the additional amount of fuel per unit of time depending on the detected catalyst temperature when the sensed catalyst temperature is greater than or equal to a preset value.   An exhaust gas purifying system according to any one of claims 1 to 6, further comprising: a catalyst temperature detecting means (36) for detecting a catalyst temperature (4), in which Adjusting means (100) reduces the additional amount of fuel per unit of time depending on the temperature of the detected catalyst when the variation of the detected catalyst temperature is greater than or equal to a pre-set value.   An exhaust purification system according to any one of claims 1 to 6, further comprising: a coolant temperature sensing means (31) for detecting a coolant temperature in the engine wherein the adjusting means (100) reduces the additional amount of fuel per unit of time depending on the temperature of the catalyst detected when the variation of the temperature of the detected coolant is greater than or equal to pre-established value.   An exhaust purification system according to any one of claims 7 to 9, wherein a fuel injection amount per unit of time is reduced by shortening the fuel supply interval, while the fueling time per interval is reduced. 25   An exhaust purification system according to any one of claims 1 to 10, wherein the internal combustion engine (1) is a diesel engine. 30   An exhaust gas purification system according to any one of claims 1 to 11, wherein the internal combustion engine (1) is mounted on a vehicle.   An exhaust gas purifying process which supplies fuel to an exhaust pipe of an internal combustion engine (1), the exhaust pipe having a catalyst (4) disposed therein, characterized by understanding: an adjustment of an additional amount of fuel that is provided by the additional fuel valve (25) based on a change in the amount of particulate matter emitted from a combustion chamber of the combustion engine internal (1).   An exhaust purification method according to claim 13, wherein the additional amount of fuel that is supplied from the additional fuel valve (25) to the exhaust duct per unit of time is adjusted to regulate the extra amount of fuel. 10   15. The exhaust gas purifying method according to claim 14, wherein a reference fuel supply interval is multiplied by a correction coefficient which depends on the change in the amount of particulate matter emitted to determine an interval. target fuel supply to adjust the additional amount of fuel.   16. The exhaust gas purifying method according to claim 15, wherein the reference fuel supply interval is multiplied by a correction coefficient which adjusts the fuel supply interval to determine the interval. target fuel supply when an actual intake air volume for the internal combustion engine (1) is smaller than a reference intake air volume to control the amount of fuel.   17. The exhaust gas purifying method according to claim 13, wherein the fuel quantity is a fuel gap which is supplied from the supplemental fuel valve (25) to the exhaust duct. 35   The exhaust gas purification method of claim 17, further comprising the step of: estimating a temperature of the additional fuel valve (25), wherein a first correction coefficient and a second correction coefficient are compared, the first correction coefficient is used to modify the fuel supply interval when the actual intake air volume in the internal combustion engine (1) is smaller than the intake air volume. reference, and the second correction coefficient is used to change the fuel supply interval when the estimated temperature of the additional fuel valve (25) increases and the reference fuel supply interval is multiplied by the correction coefficient among the first and second correction coefficients which gives the shortest fuel supply interval, whereby the interval target fuel supply is determined.   19. The exhaust gas purification method according to any one of claims 13 to 18, further comprising the step of: detecting the temperature of the catalyst, wherein the additional amount of fuel per unit time is reduced when the temperature of the detected catalyst is greater than or equal to a preset value to adjust the additional amount of fuel.   20. The exhaust gas purification method according to claim 19, wherein: a fuel injection amount per unit of time is reduced by shortening the fuel supply interval when the fueling time interval is reduced.