JP4352635B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine for effectively reducing NOx and particulates (particularly smoke) discharged from the internal combustion engine (particularly a diesel engine).
[0002]
[Prior art]
In order to reduce NOx discharged from the internal combustion engine, EGR is performed to return part of the exhaust gas into the intake air. If this EGR amount is too small, a sufficient NOx reduction effect cannot be obtained. If the EGR amount is too large, especially in a diesel engine, oxygen in the cylinder is insufficient and particulates (especially smoke) increase. In order to avoid this, it is necessary to increase the EGR amount to the limit of the smoke generation limit and reduce NOx without the generation of smoke.
[0003]
For this reason, the invention described in Japanese Patent Application Laid-Open No. 60-122259 discloses a technique for feedback control of EGR so that the oxygen concentration in the exhaust gas is used as an index and this becomes a predetermined value. This is intended to increase the EGR to the limit of smoke generation by setting the oxygen concentration in the exhaust gas, which has a strong correlation with particulates, particularly the amount of smoke generation, to a predetermined value or more.
[0004]
Further, an exhaust aftertreatment device such as a catalyst is generally installed for exhaust purification, but in order to make the catalyst work even when the exhaust temperature is low, in the invention described in Japanese Patent Application Laid-Open No. 5-156993, the main injection A technique for post-injecting a small amount of fuel in a later expansion stroke is disclosed. As a result, the exhaust temperature rises, and the catalyst is quickly activated by the reaction heat of HC supplied to the catalyst, and the exhaust aftertreatment device can be operated effectively.
[0005]
[Problems to be solved by the invention]
However, when the above-described conventional techniques are combined, that is, when EGR is feedback-controlled by the oxygen concentration in the exhaust gas and further post-injection is performed in order to effectively use the exhaust aftertreatment device such as a catalyst, the following problems occur. appear.
As shown in FIG. 9, when the post-injection is performed in the expansion stroke after the main injection (1) in the vicinity of TDC (top dead center), the temperature in the cylinder decreases as the piston descends.
[0006]
If the in-cylinder temperature is A or higher in the figure, the post-injected fuel burns in the cylinder, and if the in-cylinder temperature is not higher than A, the post-injected fuel before the crank angle B {2} However, the fuel that has been post-injected after the crank angle B does not burn in the cylinder. This boundary temperature A changes from moment to moment depending on engine operating conditions or in-cylinder conditions during post-injection. Accordingly, the post-injected fuel may burn in the cylinder depending on conditions or may reach the catalyst without being burned.
[0007]
On the other hand, a limit current type oxygen concentration sensor is widely used to detect the oxygen concentration in exhaust gas. In order to detect the oxygen concentration with high accuracy using this sensor, the sensor temperature is within a predetermined range (for example, 600). It is necessary to keep at a high temperature (˜700 ° C.), and the temperature is usually controlled by an electric heater provided in the sensor section. When the injected fuel reaches the sensor after not combusting in the cylinder, the fuel is combusted in the high-temperature heater, and oxygen in the vicinity of the sensor is consumed at this time. As shown in FIG. The oxygen concentration detected by the sensor deviates from the oxygen concentration detected by the sensor. As a result, there is a problem that the EGR cannot be accurately controlled and the emission is deteriorated.
[0008]
This problem is aimed at significantly reducing NOx and particulates of the diesel engine at the same time, greatly increasing the exhaust gas recirculation amount, or slowing the fuel combustion by retarding the injection timing of the main fuel, This is particularly noticeable in low emission combustion in which the temperature in the cylinder at the time of combustion is lowered below the smoke generation temperature. This is because, in this combustion, a larger amount of EGR is performed than usual, so that a larger amount of smoke is generated when the EGR amount is deviated.
[0009]
The present invention has been made on the basis of the above circumstances, and its object is to accurately calculate the oxygen concentration in the exhaust gas even when the post-injection is performed in the expansion stroke of the internal combustion engine in order to activate the exhaust gas purification means. It is an object of the present invention to provide an exhaust emission control device for an internal combustion engine that can perform an EGR control.
[0013]
[Means for Solving the Problems]
  (Claims1Invention)
  The present invention relates to an exhaust gas recirculation means for returning part of the exhaust gas of the internal combustion engine into the intake air, an exhaust gas purification means installed in the exhaust pipe of the internal combustion engine, and an exhaust pipe upstream of the exhaust gas purification means. An oxygen concentration detecting means for detecting the oxygen concentration of the exhaust gas, an exhaust gas recirculation amount adjusting means for adjusting the exhaust gas recirculation amount so that the exhaust oxygen concentration detected by the oxygen concentration detecting means becomes a preset target value, and exhaust purification Post-injection means for post-injecting a small amount of fuel in the expansion stroke of the internal combustion engine to activate the means, and estimating whether the post-injected fuel injected by the post-injection means burns in the cylinder of the internal combustion engine Or a post-injection combustion determination means for detecting.
[0014]
In the above configuration, the exhaust gas recirculation amount adjusting means corrects the exhaust oxygen concentration to be decreased when the post-injection combustion determining means determines that the post-injected fuel is not combusted in the cylinder of the internal combustion engine. The exhaust gas recirculation amount is adjusted so that the corrected target value is obtained.
As a result, even when the post-injected fuel reaches the oxygen concentration detecting means without being burned in the cylinder, it is possible to control the exhaust gas recirculation amount to an appropriate amount by correcting the decrease in the target value of the exhaust oxygen concentration. Become.
[0015]
  (Claims2Invention)
  The present invention relates to an exhaust gas recirculation means for returning part of the exhaust gas of the internal combustion engine into the intake air, an exhaust gas purification means installed in the exhaust pipe of the internal combustion engine, and an exhaust pipe upstream of the exhaust gas purification means. An oxygen concentration detecting means for detecting the oxygen concentration of the exhaust gas, an exhaust gas recirculation amount adjusting means for adjusting the exhaust gas recirculation amount so that the exhaust oxygen concentration detected by the oxygen concentration detecting means becomes a preset target value, and exhaust purification Post-injection means for post-injecting a small amount of fuel in the expansion stroke of the internal combustion engine to activate the means, and estimating whether the post-injected fuel injected by the post-injection means burns in the cylinder of the internal combustion engine Or a post-injection combustion determination means for detecting.
[0016]
In the above configuration, the exhaust gas recirculation amount adjusting means increases the output of the oxygen concentration detecting means when the post-injection combustion determining means determines that the post-injected fuel is not combusted in the cylinder of the internal combustion engine. The exhaust gas recirculation amount is adjusted using the corrected oxygen concentration.
As a result, even when the post-injected fuel reaches the oxygen concentration detection means without being burned in the cylinder, it is possible to control the exhaust gas recirculation amount to an appropriate amount by increasing the output of the oxygen concentration detection means. Become.
[0017]
  (Claims3Invention)
  Claim1Or2In the exhaust gas purification apparatus for an internal combustion engine described in 1.
  The post-injection combustion determining means includes an operating state detecting means for detecting the operating state of the internal combustion engine, and whether or not the post-injected fuel is combusted based on the output of the operating state detecting means, the timing of the post-injection, and the injection amount. Determine.
  That is, the in-cylinder temperature, the in-cylinder pressure, and the like at the time of post-injection are estimated from the operating state of the internal combustion engine (for example, the rotational speed and load), the post-injection timing, and the injection amount, and whether or not the post-injected fuel burns based on this. Determine whether. Thereby, since the presence or absence of the combustion of the post-injected fuel can be known, it is possible to appropriately control the exhaust gas recirculation amount based thereon.
[0018]
  (Claims4Invention)
  Claim1Or2In the exhaust gas purification apparatus for an internal combustion engine described in 1.
  The post-injection combustion determining means is obtained from the output of the operating state detecting means for detecting the operating state of the internal combustion engine, the exhaust temperature detecting means installed upstream of the exhaust purifying means and detecting the exhaust temperature, and the output of the operating state detecting means. Exhaust temperature comparison means for comparing the estimated exhaust temperature and the detected exhaust temperature detected by the exhaust temperature detection means, and the difference between the estimated exhaust temperature obtained by the exhaust temperature comparison means and the detected exhaust temperature is smaller than a predetermined value In addition, it is determined that the post-injected fuel is not combusted. This directly detects an increase in the exhaust gas temperature due to the combustion of the post-injected fuel in the cylinder, and it is possible to more accurately determine the presence or absence of the combustion of the post-injected fuel in the cylinder.
[0019]
  (Claims5Invention)
  Claims 1 to4In any one of the internal combustion engine exhaust gas purification apparatuses described in
  The internal combustion engine significantly increases the exhaust gas recirculation amount, or delays the fuel injection timing of the main injection for generating engine output, thereby slowing down the fuel combustion of the internal combustion engine and reducing the temperature in the cylinder during fuel combustion. Fuel temperature lowering means for lowering the smoke generation temperature or lower is provided.
[0020]
As described above, the technique of proceeding combustion of an internal combustion engine (particularly a diesel engine) at a low temperature is very useful for significant simultaneous reduction of NOx and particulates (particularly smoke). To achieve this, It is very important to control the exhaust gas recirculation of an extremely large amount (for example, 70% or more) more accurately than in the past. On the other hand, in this combustion, since the amount of HC emission increases, exhaust purification by a catalyst is essential. Therefore, by applying the present invention to such combustion, extremely clean combustion can be realized more accurately.
[0021]
  (Claims6Invention)
  Claims 1 to5In any one of the internal combustion engine exhaust gas purification apparatuses described in
  A catalyst having oxidation performance is carried on the exhaust purification means.
  Thereby, harmful components can be easily purified with an oxidation catalyst. This can be applied to either a flow-through type catalyst or a particulate filter.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 2 is an overall configuration diagram of an exhaust purification device applied to a four-cylinder diesel engine.
As shown in FIG. 2, a diesel engine 1 to which this exhaust purification device is applied is equipped with a common rail type fuel injection device, and high pressure fuel pumped from a high pressure pump (not shown) is always stored in the common rail 2 to obtain a desired Injected from the injector 3 at pressure, injection amount, and injection timing.
[0023]
The exhaust gas purification apparatus includes an exhaust gas recirculation pipe 6 connecting the exhaust pipe 4 and the intake pipe 5 of the engine 1, an EGR amount control valve 7 provided in the exhaust gas recirculation pipe 6, and EGR cooling provided in the middle of the exhaust gas recirculation pipe 6. Device 8, intake throttle valve 9 provided in intake pipe 5, trap filter 11 installed downstream of turbo 10, various sensors (described later) for detecting the operating state of engine 1, and information detected by these various sensors The electronic control unit 12 (hereinafter referred to as ECU 12) for controlling the operation of the system is configured based on the above.
[0024]
The EGR amount control valve 7 and the intake throttle valve 9 are directly driven by, for example, air pressure (negative pressure) or an electric motor, and by setting both to a predetermined opening, a predetermined amount of exhaust gas is recirculated to the intake side.
The EGR cooling device 8 cools EGR gas (exhaust gas recirculated into the intake air through the exhaust gas recirculation pipe 6) through heat exchange with the cooling water (not shown). A high laminated fin type is used. Thereby, the EGR gas is introduced into the cylinder in a state where it is cooled and contracted to a high density, not in a state where it is expanded at a high temperature. As a result, the amount of inert gas in the cylinder can be increased without significantly reducing the amount of oxygen sucked into the cylinder, so that a larger amount of EGR can be performed without increasing the smoke.
[0025]
The trap filter 11 is formed by alternately sealing a honeycomb-shaped flow path made of a porous ceramic such as cordierite or silicon carbide, and an oxidation catalyst mainly containing a noble metal such as Pt or Pd on the filter surface. Is carried.
In the trap filter 11, when exhaust gas containing particulates discharged from the engine 1 passes through the wall surface of the porous ceramic, particulate particles larger than the filter pore diameter are mainly collected on the filter surface. In addition, harmful components such as HC and CO discharged during combustion can be purified by the action of the oxidation catalyst.
[0026]
The amount (deposition amount) of the particulates collected by the trap filter 11 is detected based on the differential pressure across the filter 11, and the filter 11 is regenerated when the accumulation amount exceeds a predetermined value. The regeneration of the filter 11 is performed by post-injecting a small amount of fuel during the expansion stroke of the engine 1. At this time, the temperature of the particulates is lower than usual due to the action of the oxidation catalyst supported on the filter surface (in the absence of a catalyst, a temperature of 600 ° C. or higher is required for particulate combustion, but in the presence of a catalyst, 450 ° C. The temperature rise of the filter 11 is small.
[0027]
The ECU 12 inputs information detected by various sensors such as an engine speed sensor 13, an accelerator opening sensor 14, an injection pressure sensor 15, a differential pressure sensor 16, and an oxygen concentration sensor 17, and based on these information, each cylinder The electromagnetic valve 3a for driving the injector 3 and various actuators such as the intake throttle valve 9 and the EGR amount control valve 7 are electrically controlled, and the trap filter 11 needs to be regenerated based on the output of the differential pressure sensor 16 If it is determined that regeneration is necessary, a small amount of fuel is post-injected during the expansion stroke.
[0028]
The engine speed sensor 13 is disposed on the crankshaft (not shown) of the engine 1 and detects the engine speed.
The accelerator opening sensor 14 detects the accelerator opening from the depression amount of an accelerator pedal (not shown).
The injection pressure sensor 15 is attached to the common rail 2 and detects the fuel pressure in the common rail 2.
The differential pressure sensor 16 is installed at a position where the exhaust pressure can be detected before and after the trap filter 11 and detects the differential pressure across the trap filter 11.
[0029]
The oxygen concentration sensor 17 is attached to the exhaust pipe 4 upstream of the trap filter 11 and detects the oxygen concentration in the exhaust pipe 4.
This oxygen concentration sensor 17 is of a known limit current type that is generally widely used. For example, as shown in FIG. 3, a sensor element 17B is arranged inside a cover 17A having a vent hole 17a, and the sensor element Exhaust gas is introduced from the vent hole 17a to the outside of 17B, and the atmosphere is introduced to the inside of the sensor element 17B.
[0030]
When a voltage is applied to the sensor element 17B, a limit current corresponding to the oxygen concentration in the exhaust gas is generated. However, in order to accurately detect the oxygen concentration with the sensor element 17B, it is necessary to keep the temperature of the sensor element 17B within a predetermined range (for example, 600 to 700 ° C.). Therefore, an electric heater 17C is disposed close to the inside of the sensor element 17B, and the temperature of the sensor element 17B is controlled by the electric heater 17C.
[0031]
Next, the operation of the exhaust emission control device according to the present invention (the processing procedure of the ECU 12) will be described based on the flowchart shown in FIG.
Step 100 ... The engine speed NE, the accelerator opening, and the differential pressure across the trap filter 11 are read from the outputs of the engine speed sensor 13, the accelerator opening sensor 14, and the differential pressure sensor 16.
[0032]
Step 101 (Post-injection Necessity Determining Means of the Present Invention): It is determined whether or not to perform post-injection from the sensor output read in Step 100. This determination is performed by determining whether or not the trap filter 11 needs to be regenerated by a known method. For example, the output of the differential pressure sensor 16 is corrected by the output of an intake air amount sensor (not shown) to calculate the particulate accumulation amount on the trap filter 11, and regeneration is necessary when the calculated accumulation amount exceeds a predetermined value. It is determined that Here, when it is determined that “no post injection is necessary”, the process proceeds to Step 102, and when it is determined that “post injection is necessary”, the process proceeds to Step 106.
[0033]
Step 102 ... The target exhaust oxygen concentration is calculated from a map or the like stored in advance in the ECU 12 based on the engine speed NE and the accelerator opening read in Step 100.
Step 103... The oxygen concentration in the exhaust gas is read from the output of the oxygen concentration sensor 17.
Step104… Compare the target value of exhaust oxygen concentration (target exhaust oxygen concentration calculated in Step102) with the actually detected value (oxygen concentration read in Step103), and the difference between them is a predetermined value (for example, 0.2%) It is determined whether it is smaller. Here, when the difference between the two is equal to or greater than the predetermined value, the process proceeds to Step 105, and when the difference between the two is smaller than the predetermined value, this routine is terminated.
[0034]
Step 105 ... Adjust the EGR amount and return to Step 103 again. Here, the exhaust oxygen concentration detected by the oxygen concentration sensor 17 is fed back, and the opening degree of the EGR amount control valve 7 is controlled. Alternatively, instead of the EGR amount control valve 7, the intake throttle valve 9 may be feedback controlled.
[0035]
Step 106 ... The intake throttle valve 9 and the EGR amount control valve 7 are set to the opening determined from the engine conditions read in Step 100. That is, the opening degree of both is set by open loop control without performing feedback control based on the exhaust oxygen concentration.
Step 107 (Post-injection means of the present invention)... Post-injection is executed, and this routine is terminated. The timing and amount of post-injection are determined based on the operating conditions of the engine 1 and stored in the ECU 12 in advance.
[0036]
(Effects of the first embodiment)
When the EGR amount is controlled by feeding back the exhaust oxygen concentration (sensor output) so that the oxygen concentration in the exhaust gas becomes the target value, as shown in FIG. 4, the target value of the exhaust oxygen concentration (black point a in the figure). ) Is adjusted so that EGR is obtained. As a result, emissions such as particulates and NOx and fuel consumption are maintained at optimum values at the black dots in the figure.
[0037]
However, when the post-injected fuel does not burn in the cylinder and reaches the oxygen concentration sensor 17 without being burned, and burns in the sensor unit, oxygen in the vicinity of the sensor is consumed, so the sensor output is indicated by a broken line in the figure. Decreases as shown. In this case, the sensor output (black point b in the figure) deviates from the target value with the EGR amount of d in the figure. As a result, it is determined that the EGR amount is excessive with respect to the target value, and the EGR amount is reduced to e in the figure so that the sensor output becomes the target value (white point c in the figure).
[0038]
As a result of the above, the emission and the fuel consumption shift to the white points in the figure, respectively, and deviate greatly from the optimum values indicated by the black points.
On the other hand, in the present invention, when performing post-injection, the output of the oxygen concentration sensor 17 is not fed back to control the EGR amount, but the above-mentioned problems can be avoided by controlling the EGR amount by open loop control. . Therefore, a favorable operating state can be maintained regardless of the presence or absence of post-injection.
[0039]
In the above-described embodiment, the trap filter 11 is used as the exhaust purification unit and the post-injection is performed for the regeneration. However, the exhaust purification unit is a flow-through type oxidation catalyst or NOx catalyst. It may be supported on a catalyst having other oxidation performance. Further, the present invention is not limited to the regeneration of the trap filter 11, and is also applied when post-injection is performed to raise the exhaust gas temperature or the catalyst temperature to the catalyst activation temperature when the catalyst is inactive, such as when the engine is started.
[0040]
In addition, in order to significantly reduce NOx and particulates (especially smoke) discharged from the diesel engine 1 at the same time, a technology that combines an extremely large amount of EGR and the retardation of the injection timing is effective. In this type of combustion, A large amount of EGR needs to be accurately controlled, and feedback based on exhaust oxygen concentration is particularly useful.
[0041]
In addition, while reducing smoke, the amount of HC emissions increases, so it is necessary to purify the exhaust gas using a catalyst having oxidation performance. Therefore, in order to make it possible to purify the exhaust gas even during low-speed running with low catalyst activity, it is necessary to raise the temperature of the catalyst above the activation temperature, and post-injection is very promising as a means for that purpose. In this case, since the EGR control with higher accuracy is required in combination with the post injection, a great effect can be obtained by combining with the present embodiment.
[0042]
(Second Embodiment)
FIG. 5 is a flowchart showing a processing procedure of the ECU 12 in the second embodiment.
In the present embodiment, the overall configuration of the system is the same as that of the first embodiment, and the description thereof is omitted.
The operation of the exhaust emission control apparatus according to the present invention will be described based on the flowchart shown in FIG.
[0043]
Step 200 ... The engine speed NE, the accelerator opening, and the differential pressure across the trap filter 11 are read from the outputs of the engine speed sensor 13, the accelerator opening sensor 14, and the differential pressure sensor 16.
Step 201 (Post-injection Necessity Determining Means of the Present Invention): It is determined whether or not to perform post-injection from the sensor output read in Step 200 (refer to Step 101 of the first embodiment for a specific determination method). Here, when it is determined that “no post-injection is necessary”, the process proceeds to Step 206, and when it is determined that “post-injection is necessary”, the process proceeds to Step 202.
[0044]
Step 202 (Post-injection means of the present invention) ... Post injection is executed. The timing and amount of post-injection are determined based on the operating conditions of the engine 1 and stored in the ECU 12 in advance.
Step 203 ... Calculate the in-cylinder temperature Tc at the time of post injection. Although the in-cylinder temperature Tc with respect to the crank angle of the engine 1 changes as shown in FIG. 9, it is determined by the operating conditions of the engine 1 (for example, the rotational speed and the load). Accordingly, the in-cylinder temperature Tc at the time of post-injection (crank angle for post-injection) performed in Step 202 is calculated from the operating conditions.
[0045]
Step 204 (Post-Injection Combustion Determination Means of the Present Invention) It is determined whether or not the in-cylinder temperature Tc calculated in Step 203 is higher than the reference temperature T0. This reference temperature T0 is the lowest temperature at which the post-injected fuel burns in the cylinder under the engine conditions. The reference temperature T0 is stored in advance in the ECU 12, and is set to a constant value (for example, 1000K) or a value that varies depending on engine conditions. Here, when it is determined that Tc <T0, the process proceeds to Step 205, and when it is determined that Tc ≧ T0, the process proceeds to Step 206.
[0046]
Step 205... A correction amount for correcting the exhaust oxygen concentration to decrease is calculated. That is, when the in-cylinder temperature Tc at the time of post-injection is lower than the reference temperature T0, the post-injected fuel reaches the oxygen concentration sensor 17 without burning in the cylinder and burns at the sensor unit. Since oxygen is consumed at that time, the oxygen concentration sensor 17 cannot detect the oxygen concentration that should originally be detected (remaining as a result of combustion in the cylinder).
[0047]
In order to avoid this, when the unburned fuel reaches the oxygen concentration sensor 17, the exhaust oxygen concentration that is the target of EGR amount control is corrected to decrease by the amount of oxygen consumed by the sensor unit. Here, the correction amount is calculated. When calculating the correction amount, for example, the correction amount is changed in accordance with the difference between Tc and T0, and the smaller the difference is, the smaller the correction amount is.
[0048]
Step 206 ... The corrected target oxygen concentration is calculated by adding the correction amount calculated in Step 205 to the target oxygen concentration before correction. However, when the determination result of Step 201 is NO and when the determination result of Step 204 is NO, the target oxygen concentration before correction is set. The target oxygen concentration before correction is calculated based on the engine speed NE and the accelerator opening read in Step 200. This is stored in advance in the ECU 12 based on the operating conditions of the engine 1.
Step 207: The oxygen concentration in the exhaust gas is read from the output of the oxygen concentration sensor 17.
[0049]
Step 208 ... The target value of the exhaust oxygen concentration (the corrected target exhaust oxygen concentration calculated in Step 206) is compared with the actually detected value (the oxygen concentration read in Step 207), and the difference between the two is a predetermined value (for example, 0. 0). 2%) or less. If the difference between the two is equal to or greater than the predetermined value, the process proceeds to Step 209. If the difference between the two is smaller than the predetermined value, the present routine is terminated.
Step 209: Adjust the EGR amount and return to Step 207 again.
[0050]
In this embodiment, when it is determined that the post-injected fuel does not burn in the cylinder (when the determination result in Step 204 is NO), the output of the oxygen concentration sensor 17 is lower than the actual oxygen concentration in the exhaust gas. However, since the target value of the exhaust oxygen concentration is corrected to decrease, the EGR amount is not significantly reduced and can be controlled to an appropriate amount. Therefore, a favorable operating state can be maintained regardless of the presence or absence of post-injection.
[0051]
(Third embodiment)
FIG. 6 is a flowchart showing a processing procedure of the ECU 12 in the third embodiment.
In the present embodiment, the overall configuration of the system is the same as that of the first embodiment, and the description thereof is omitted.
The operation of the exhaust emission control apparatus according to the present invention will be described based on the flowchart shown in FIG. However, in this embodiment, a part of the operation described in the second embodiment is changed, and only the parts (Step 305 to Step 307) different from the second embodiment will be described here.
[0052]
Step 305... A correction amount for increasing the output of the oxygen concentration sensor 17 is calculated. That is, when the in-cylinder temperature Tc at the time of post-injection is lower than the reference temperature T0, the post-injected fuel reaches the oxygen concentration sensor 17 without burning in the cylinder and burns at the sensor unit. Since oxygen is consumed at that time, the oxygen concentration sensor 17 cannot detect the oxygen concentration that should originally be detected (remaining as a result of combustion in the cylinder).
[0053]
In order to avoid this, when the unburned fuel reaches the oxygen concentration sensor 17, the oxygen concentration in the exhaust gas detected by the oxygen concentration sensor 17 is increased by an amount corresponding to the amount of oxygen consumed by the sensor unit. To do. Here, the correction amount is calculated. When calculating the correction amount, for example, the correction amount is changed in accordance with the difference between Tc and T0, and the smaller the difference is, the smaller the correction amount is.
[0054]
Step 306 ... The target exhaust oxygen concentration is calculated based on the engine speed NE and the accelerator opening that are read in Step 300. This is stored in advance in the ECU 12 based on the operating conditions of the engine 1.
Step 307: The oxygen concentration in the exhaust gas is read from the output of the oxygen concentration sensor 17, and the corrected oxygen concentration is calculated according to the correction amount calculated in Step 305.
[0055]
In this embodiment, when it is determined that the post-injected fuel does not burn in the cylinder (when the determination result in Step 304 is NO), the unburned fuel is burned and oxygen is consumed in the sensor unit. Even if the output of the oxygen concentration sensor 17 decreases, the output of the oxygen concentration sensor 17 is corrected to increase, so that the EGR amount is not significantly reduced and can be controlled to an appropriate amount. Therefore, a favorable operating state can be maintained regardless of the presence or absence of post-injection.
[0056]
(Fourth embodiment)
FIG. 7 is an overall configuration diagram of an exhaust purification device applied to the four-cylinder diesel engine 1, and FIG. 8 is a flowchart showing a processing procedure of the ECU 12 in the fourth embodiment.
This embodiment differs from the system described in the first embodiment only in that a temperature sensor 18 is installed in the exhaust pipe 4 upstream of the trap filter 11, and the other system configurations are the same. The description is omitted.
[0057]
The operation of the exhaust emission control apparatus according to the present invention will be described based on the flowchart shown in FIG.
Step 400 ... From the outputs of the engine speed sensor 13, the accelerator opening sensor 14, the differential pressure sensor 16, and the temperature sensor 18, the engine speed NE, the accelerator opening, the differential pressure across the trap filter 11, and the trap filter 11 Read the temperature Ta of the inflowing exhaust gas.
[0058]
Step 401 (Post-injection Necessity Determining Means of the Present Invention): It is determined from the sensor output read in Step 400 whether or not post-injection is to be performed (see Step 101 in the first embodiment for a specific determination method). Here, when it is determined that “post injection is necessary”, the process proceeds to Step 402, and when it is determined that “no post injection is necessary”, the process proceeds to Step 406.
Step 402 (Post-injection means of the present invention)... Post injection is executed. The timing and amount of post-injection are determined based on the operating conditions of the engine 1 and stored in the ECU 12 in advance.
[0059]
Step 403 ... The exhaust gas temperature Tt is calculated based on the operating conditions of the engine 1 read in Step 400. The correlation between the operating condition of the engine 1 and the exhaust temperature is stored in the ECU 12 in advance.
Step 404 (Exhaust temperature comparison means of the present invention): It is determined whether or not the actual exhaust temperature Ta read in Step 400 is higher than the exhaust temperature Tt calculated in Step 403. If Ta ≦ Tt is determined, the process proceeds to Step 405. If Ta> Tt is determined, the process proceeds to Step 406.
[0060]
Step 405... A correction amount for correcting the exhaust oxygen concentration to decrease is calculated. That is, even if the post-injection is being performed, if Ta ≦ Tt, the post-injected fuel does not burn in the cylinder, so the post-injected fuel reaches the oxygen concentration sensor 17 and burns at the sensor unit. Since oxygen is consumed at that time, the oxygen concentration sensor 17 cannot detect the oxygen concentration that should originally be detected (remaining as a result of combustion in the cylinder).
[0061]
In order to avoid this, when the unburned fuel reaches the oxygen concentration sensor 17, the exhaust oxygen concentration that is the target of EGR amount control is corrected to decrease by the amount of oxygen consumed by the sensor unit. Here, the correction amount is calculated. When calculating the correction amount, for example, the correction amount is changed according to the difference between Ta and Tt, and the smaller the difference is, the smaller the correction amount is, so that more accurate correction is possible.
[0062]
Step 406... The corrected target oxygen concentration is calculated by adding the correction amount calculated in Step 405 to the target oxygen concentration before correction. However, when the determination result of Step 401 is NO and when the determination result of Step 404 is NO, the target oxygen concentration before correction is set. The target oxygen concentration before correction is calculated based on the engine speed NE and the accelerator opening read in Step 400. This is stored in advance in the ECU 12 based on the operating conditions of the engine 1.
Step 407 ... The oxygen concentration in the exhaust gas is read from the output of the oxygen concentration sensor 17.
[0063]
Step 408 ... The target value of the exhaust oxygen concentration (the corrected target exhaust oxygen concentration calculated in Step 406) is compared with the actually detected value (the oxygen concentration read in Step 407). 2%) or less. If the difference between the two is equal to or greater than the predetermined value, the process proceeds to Step 409. If the difference between the two is smaller than the predetermined value, the present routine is terminated.
Step 409: Adjust the EGR amount and return to Step 407 again.
[0064]
In the present embodiment, the actual exhaust temperature Ta is compared with the exhaust temperature Tt calculated based on the operating conditions of the engine 1 to determine whether or not the post-injected fuel burns in the cylinder. It is possible to more accurately determine whether the injected fuel has burned in the cylinder.
In the present embodiment, as in the second embodiment, the case where the target oxygen concentration is corrected has been described as an example. However, the output of the oxygen concentration sensor 17 may be corrected as in the third embodiment. .
[Brief description of the drawings]
FIG. 1 is a flowchart showing a processing procedure of an ECU according to a first embodiment.
FIG. 2 is an overall configuration diagram of an exhaust emission control device (first embodiment).
FIG. 3 is a schematic diagram showing the structure of an oxygen concentration sensor.
FIG. 4 is a graph showing the relationship between the EGR amount, the emission, and the fuel consumption when the EGR amount is feedback controlled with respect to the target value of the exhaust oxygen concentration.
FIG. 5 is a flowchart showing a processing procedure of an ECU according to the second embodiment.
FIG. 6 is a flowchart showing a processing procedure of an ECU according to a third embodiment.
FIG. 7 is an overall configuration diagram of an exhaust emission control device (fourth embodiment).
FIG. 8 is a flowchart showing a processing procedure of an ECU according to a fourth embodiment.
FIG. 9 is a graph showing a correlation between fuel injection and an average temperature in a cylinder.
FIG. 10 is a graph comparing actual oxygen concentration in exhaust gas and sensor output.
[Explanation of symbols]
1 Diesel engine (internal combustion engine)
6 Exhaust gas recirculation pipe (exhaust gas recirculation means)
7 EGR amount control valve (exhaust gas recirculation means)
9 Intake throttle valve (exhaust gas recirculation means)
11 Trap filter (exhaust gas purification means)
12 ECU (exhaust gas recirculation amount adjusting means)
13 Engine speed sensor (operating state detection means)
14 Accelerator opening sensor (operating state detection means)
17 Oxygen concentration sensor (oxygen concentration detection means)
18 Temperature sensor (exhaust temperature detection means)

Claims (6)

Exhaust gas recirculation means for returning a part of the exhaust gas of the internal combustion engine into the intake air;
Exhaust purification means installed in the exhaust pipe of the internal combustion engine;
An oxygen concentration detection means installed in the exhaust pipe upstream of the exhaust purification means for detecting the oxygen concentration in the exhaust;
Exhaust gas recirculation amount adjusting means for adjusting the exhaust gas recirculation amount so that the exhaust oxygen concentration detected by the oxygen concentration detection means becomes a preset target value;
Post-injection means for post-injecting a small amount of fuel in the expansion stroke of the internal combustion engine to activate the exhaust purification means;
An exhaust purification device for an internal combustion engine comprising post-injection combustion determination means for estimating or detecting whether post-injected fuel injected by the post-injection means is combusted in a cylinder of the internal combustion engine,
The exhaust gas recirculation amount adjusting means reduces and corrects the target value of the exhaust oxygen concentration when the post-injection combustion determining means determines that the post-injected fuel does not burn in the cylinder of the internal combustion engine. An exhaust gas purification apparatus for an internal combustion engine, wherein an exhaust gas recirculation amount is adjusted so that a later target value is obtained. Exhaust gas recirculation means for returning a part of the exhaust gas of the internal combustion engine into the intake air;
Exhaust purification means installed in the exhaust pipe of the internal combustion engine;
An oxygen concentration detection means installed in the exhaust pipe upstream of the exhaust purification means for detecting the oxygen concentration in the exhaust;
Exhaust gas recirculation amount adjusting means for adjusting the exhaust gas recirculation amount so that the exhaust oxygen concentration detected by the oxygen concentration detection means becomes a preset target value;
Post-injection means for post-injecting a small amount of fuel in the expansion stroke of the internal combustion engine to activate the exhaust purification means;
An exhaust purification device for an internal combustion engine comprising post-injection combustion determination means for estimating or detecting whether post-injected fuel injected by the post-injection means is combusted in a cylinder of the internal combustion engine,
The exhaust gas recirculation amount adjusting means increases the output of the oxygen concentration detecting means when the post-injection combustion determining means determines that the post-injected fuel is not combusted in the cylinder of the internal combustion engine, and corrects the correction. An exhaust gas purification apparatus for an internal combustion engine, characterized in that an exhaust gas recirculation amount is adjusted using a subsequent oxygen concentration. The exhaust emission control device for an internal combustion engine according to claim 1 or 2 ,
The post-injection combustion determination unit includes an operation state detection unit that detects an operation state of the internal combustion engine. Whether the post-injection fuel burns based on the output of the operation state detection unit, the timing of the post-injection, and the injection amount. An exhaust purification device for an internal combustion engine, characterized by determining whether or not. The exhaust emission control device for an internal combustion engine according to claim 1 or 2 ,
The post-injection combustion determining means includes an operating state detecting means for detecting an operating state of the internal combustion engine, an exhaust temperature detecting means installed upstream of the exhaust purification means for detecting an exhaust temperature, and an operating state detecting means. Exhaust temperature comparison means for comparing the estimated exhaust temperature obtained from the output with the detected exhaust temperature detected by the exhaust temperature detection means, and the difference between the estimated exhaust temperature obtained by the exhaust temperature comparison means and the detected exhaust temperature is An exhaust emission control device for an internal combustion engine, wherein when it is smaller than a predetermined value, it is determined that the post-injected fuel is not combusted. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4 ,
The internal combustion engine significantly increases the exhaust gas recirculation amount or retards the fuel injection timing of the main injection for generating engine output, thereby slowing down the fuel combustion of the internal combustion engine and An exhaust emission control device for an internal combustion engine, comprising fuel temperature lowering means for lowering the temperature to a smoke generation temperature or lower. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 5 ,
An exhaust gas purification apparatus for an internal combustion engine, wherein the exhaust gas purification means carries a catalyst having oxidation performance.

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