JP2009002172A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine that can certainly suppress CO or HC in exhaust gas exiting from an exhaust-gas purification catalyst during catalyst warm-up even when a capturing amount of the catalyst is suppressed, and can achieve both an exhaust-gas purification performance and a reduction of cost. <P>SOLUTION: The exhaust emission control device for the internal combustion engine includes an EGR means for re-circulating a part of exhaust gas from the engine to an intake manifold side through an EGR passage, and an exhaust-gas purification catalyst for purifying an exhaust component discharged into an exhaust passage. The exhaust emission control device also includes a catalyst floor temperature sensor for detecting a catalyst floor temperature of the exhaust-gas purification catalyst. An ECU 50 includes functions as a basic EGR amount calculating means for calculating a basic EGR amount based on an operating condition of the engine, and an amount-reduction compensating means for executing an amount-reduction compensation of the basic EGR amount within a range of catalyst temperature up to its reach of a predetermined exhaust-gas purification temperature Tca in accordance with a rise of the purification performance during the catalyst warm-up and temperature-increase based on the detected temperature Tc by the catalyst floor temperature sensor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification control device for an internal combustion engine, and more particularly to an exhaust gas purification control device for an internal combustion engine that limits the EGR amount when the exhaust purification catalyst warms up.

  It is generally known that exhaust gas recirculation (EGR), that is, exhaust gas recirculation, is effective in reducing NOx, which is a harmful component in exhaust gas. Since misfire due to EGR is likely to occur when cold, the amount of EGR is reduced. It is known.

  For example, in a diesel engine, the content of particulate matter such as soot and SOF (Soluble Organic Fraction) in exhaust gas, that is, particulate matter (hereinafter simply referred to as PM), is higher than that of a gasoline engine. In many cases, if the combustion of the engine is improved so as to reduce this PM, NOx (nitrogen oxide) in the exhaust gas increases, so EGR is often employed to reduce the NOx. However, if a large amount of EGR is performed, the ignition of the fuel is delayed in the combustion chamber, the oxygen becomes insufficient due to a decrease in the combustion temperature and an increase in the combustion ratio in the latter stage of the expansion stroke, and in addition to PM, carbon monoxide (CO) and unburned hydrocarbon There is a possibility that harmful exhaust components such as system compounds (HC) may increase.

  As a conventional type of exhaust gas purification device for an internal combustion engine of this type, for example, when the excess air ratio is lowered to increase the temperature of exhaust gas required by the exhaust gas purification device when starting the engine, the EGR (exhaust gas recirculation) rate is suitably controlled. Therefore, the basic EGR rate (map value) is obtained from the basic EGR rate (fresh air intake amount / intake amount (including exhaust gas recirculation amount)) map based on the engine speed and the fuel injection amount, and the engine cooling water temperature is calculated. Accordingly, it is known that the target EGR rate is calculated by obtaining a water temperature correction coefficient from a preset water temperature correction table and multiplying the basic EGR rate by the water temperature correction coefficient obtained in the water temperature correction table. (For example, refer to Patent Document 1).

Further, by dividing the fuel injection into pilot injection before compression top dead center and main injection after compression top dead center, the temperature and pressure in the combustion chamber is increased by pilot injection and the main injection timing is delayed, There is known one that increases exhaust energy, effectively warms up the exhaust purification catalyst to the activation temperature, and suppresses the HC concentration in the exhaust gas (see, for example, Patent Documents 2 and 3).
Japanese Unexamined Patent Publication No. 2003-41983 (see paragraph 0062) JP 2004-245133 A JP 2003-65121 A

  However, in the conventional exhaust gas purification control device for an internal combustion engine as described above, the basic EGR amount that becomes the base value of the EGR amount is determined based on the engine speed and the fuel injection amount, and the engine cooling water temperature and the outside air temperature are determined. Therefore, even if the catalyst bed temperature does not reach the activation temperature at which the exhaust gas can be purified (hereinafter also referred to as the purification temperature), if the engine cooling water temperature rises to a predetermined temperature, the EGR amount increases. Therefore, the EGR amount reduction (including the cut) is not performed during the temperature rise of the catalyst. Therefore, if the amount of the exhaust purification catalyst (for example, the amount of the precious metal supported on the catalyst) is suppressed, the exhaust gas that has passed through the exhaust purification catalyst is likely to contain harmful components such as CO and HC, and the amount of the exhaust purification catalyst that is expensive. Could not be suppressed. That is, conventionally, it has been impossible to achieve both the exhaust purification performance of the exhaust purification device and the cost reduction.

  In particular, the difference between the rise in engine coolant temperature and the rise in catalyst bed temperature due to catalyst warm-up at the time of start varies greatly depending on the temperature of the exhaust purification catalyst at start-up. It was impossible to correct the EGR amount sufficiently reflecting the temperature characteristics of the rise (activation) of the exhaust gas purification performance of the purification catalyst. Therefore, if the EGR amount reduction (including cut) is not performed in the operating range where the deviation is large, the EGR rate increases at a stage where the CO purification rate (HC purification rate) of the exhaust purification catalyst is low. Unless a sufficient amount of catalyst is secured, CO and HC emissions will increase.

  In view of this, the present invention accurately executes the reduction correction of the EGR amount in accordance with the rising characteristic of the exhaust purification performance during the temperature rise of the exhaust purification catalyst, so that the catalyst is warming up even if the amount of the exhaust purification catalyst carried is suppressed. An object of the present invention is to provide an exhaust gas purification control device for an internal combustion engine that can achieve both the exhaust gas purification performance and cost reduction of the exhaust gas purification device by reliably suppressing CO and HC in the exhaust gas exiting the catalyst. .

  In order to achieve the above object, the internal combustion engine exhaust gas purification control apparatus according to the present invention includes (1) EGR means for recirculating a part of the exhaust gas of the internal combustion engine to the intake manifold side through the EGR passage, and the exhaust passage of the internal combustion engine. In an exhaust gas purification control device for an internal combustion engine having an exhaust gas purification catalyst for purifying exhaust gas components exhausted, based on catalyst bed temperature detection means for detecting the catalyst bed temperature of the exhaust gas purification catalyst, and the operating state of the internal combustion engine The basic EGR amount calculating means for calculating the basic EGR amount for recirculating the exhaust gas to the intake manifold side, and the purification performance during warming up of the exhaust purification catalyst based on the detected temperature of the catalyst bed temperature detecting means A reduction correction means for executing a reduction correction for the basic EGR amount within a temperature range until the exhaust purification catalyst reaches a predetermined exhaust purification temperature in response to the rise of the exhaust purification catalyst. Characterized in that was.

  With this configuration, the catalyst bed temperature at the start-up is detected by the catalyst bed temperature detecting means, and within the temperature range until the exhaust purification catalyst reaches a predetermined exhaust purification temperature, the rising performance of the purification performance at the time of warming up is achieved. Accordingly, a reduction correction for the basic EGR amount is executed. Therefore, even if the amount of the exhaust purification catalyst supported is suppressed, CO and HC in the exhaust gas exiting the catalyst during the catalyst warm-up can be reliably suppressed, and both the exhaust purification performance and the cost reduction of the exhaust purification device can be achieved. Become. The detection of the catalyst bed temperature here includes not only direct detection by a sensor or the like but also indirect detection, for example, detection by estimating the catalyst bed temperature based on the exhaust gas temperature.

  In the exhaust gas purification control device for an internal combustion engine according to (1), (2) the temperature reduction of the exhaust gas purification catalyst is within a temperature range until the exhaust gas reduction catalyst reaches a predetermined exhaust gas purification temperature. A reduction correction coefficient that changes so as to decrease the reduction correction amount of the EGR amount in accordance with is calculated and detected by the catalyst bed temperature detection means within a temperature range until the exhaust purification catalyst reaches a predetermined exhaust purification temperature. It is preferable to calculate the reduction correction amount based on the reduction correction coefficient corresponding to the temperature and the basic EGR amount.

  With this configuration, while using the existing map information for calculating the basic EGR amount according to the characteristics of the internal combustion engine, the reduction correction coefficient corresponding to the catalyst bed temperature detected at the start by the catalyst bed temperature detecting means is further used. The exhaust gas purification catalyst can be finely corrected for reduction of the basic EGR amount within the temperature range until the exhaust gas purification catalyst reaches a predetermined exhaust gas purification temperature, according to the rise characteristic of the purification performance at the time of warming up. Even if the supported amount is suppressed, CO and HC in the exhaust gas exiting the catalyst during the warm-up of the catalyst are more reliably suppressed.

  In the exhaust gas purification control apparatus for an internal combustion engine of (2), (3) the reduction correction unit is configured to reduce the reduction by multiplying the basic EGR amount by the reduction correction coefficient corresponding to the temperature detected by the catalyst bed temperature detection unit. It is preferable to calculate the amount and correct the amount of decrease from the basic EGR amount by the amount of decrease correction.

  In this case, the reduction correction coefficient can be easily set based on the temperature characteristic of the purification performance of the exhaust purification catalyst.

  In the exhaust gas purification control apparatus for an internal combustion engine according to (2) or (3), preferably, (4) the reduction correction coefficient is maximized in a catalyst bed temperature range where the exhaust gas purification rate of the exhaust gas purification catalyst is minimum. At the same time, within a temperature range until the exhaust purification catalyst reaches a predetermined exhaust purification temperature, the exhaust purification catalyst decreases at a reduction rate that is inversely proportional to the increase rate of the exhaust purification rate according to the warming-up temperature of the catalyst bed temperature detecting means. Is.

  In this case, not only can the weight reduction correction coefficient be easily set based on the temperature characteristics of the purification performance of the exhaust purification catalyst, but also more reliably suppress CO and HC in the exhaust gas exiting the catalyst during catalyst warm-up. Is done.

  According to the present invention, the catalyst bed temperature at the time of start-up is detected by the catalyst bed temperature detection means, and the purification performance at the catalyst warm-up temperature rise is within the temperature range until the exhaust purification catalyst reaches the predetermined exhaust purification temperature. Since the reduction correction for the basic EGR amount is executed according to the start-up characteristics, even if the amount of the exhaust purification catalyst supported is suppressed, the CO and HC in the exhaust gas exiting the catalyst during the catalyst warm-up are surely suppressed. Therefore, it is possible to provide an exhaust gas purification control device for an internal combustion engine that can achieve both the exhaust gas purification performance and cost reduction of the exhaust gas purification device.

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

FIG. 1 is a diagram showing an exhaust gas purification control apparatus for an internal combustion engine according to an embodiment of the present invention, and shows an example in which the present invention is applied to a multi-cylinder diesel engine.
First, the configuration will be described.

  As shown in FIG. 1, an engine 10 that is an internal combustion engine for a vehicle has a plurality of cylinders 11. The engine 10 supplies fuel to combustion chambers (not shown in detail) in each cylinder 11. Common rail type fuel injection device 12 for injecting, intake device 13 for sucking air into the combustion chamber, exhaust device 14 for exhausting exhaust gas from the combustion chamber, and intake device using exhaust energy in exhaust device 14 A turbocharger 15 that compresses the air in 13 and supercharges the air in the combustion chamber, and an exhaust gas recirculation device 16 that recirculates and recirculates a part of the exhaust gas to the intake side are provided.

  The fuel injection device 12 includes a supply pump 21 that pumps fuel from a fuel tank (not shown), pressurizes the fuel to a high fuel pressure (fuel pressure), and discharges the fuel, a common rail 22 into which fuel from the supply pump 21 is introduced, and the common rail And a fuel injection valve 23 that injects fuel supplied through the cylinder 22 at a timing and opening degree (duty ratio) corresponding to an injection command signal from an electronic control unit (hereinafter referred to as ECU) 50 described later. Has been.

  The supply pump 21 is driven using, for example, the rotational power of the engine 10, and the common rail 22 distributes and supplies the high-pressure fuel supplied from the supply pump 21 to the plurality of fuel injection valves 23 while keeping it even. The fuel injection valve 23 is constituted by a known needle valve that is electromagnetically driven, and the injection command is controlled by controlling the ratio of the valve opening time during the predetermined time in accordance with a pulse-like injection command signal for every predetermined time. Fuel (for example, light oil) of a fuel injection amount corresponding to the signal can be injected and supplied into the combustion chamber.

  In the present embodiment, fuel injection in one combustion cycle in the engine 10 includes pilot injection executed before a piston (not shown) reaches the compression top dead center, and after the time when the piston passes the compression top dead center ( Main injection executed after compression top dead center) and post-injection intended to be supplied into the exhaust aftertreatment device 44 as unburned hydrocarbon (HC) together with exhaust gas rather than in-cylinder combustion. The operation is divided into a plurality of injections. The fuel injection device 12 further includes a fuel addition nozzle 24 that injects a part of the fuel pumped up by the supply pump 21 into the exhaust device 14, and the fuel addition nozzle 24 applies fuel at a fuel pressure equal to or higher than a predetermined pressure. When opened, the fuel can be injected into the exhaust manifold 41 of the exhaust device 14.

  The intake device 13 includes an intake manifold 31, an intake pipe 32 upstream of the intake manifold 31, an air cleaner 33 that cleans intake air using a filter on the upstream side of the intake pipe 32, and excess air on the downstream side of the turbocharger 15. An intercooler 34 that cools the intake air whose temperature has been raised by the supply, an air flow meter 35 that detects an intake air amount that is an intake flow rate of fresh air, a throttle valve 36 that adjusts the intake air amount into the engine 10, and an intake air An intake air temperature sensor 37 that detects the current intake air temperature in the manifold 31 on the cylinder side from the EGR valve 62 (described later) is mounted.

  The exhaust device 14 includes an exhaust manifold 41, an exhaust pipe 42 on the downstream side thereof, an A / F sensor 43 that is a wide area air-fuel ratio sensor located on the downstream side of the turbocharger 15, and the A / F sensor 43. An exhaust aftertreatment device 44 having an exhaust purification catalyst (not shown in detail) attached to the exhaust pipe 42 on the downstream side and purifying exhaust components exhausted into the exhaust passage of the engine 10; It includes a catalyst bed temperature sensor 45 (catalyst bed temperature detection means) for detecting the catalyst bed temperature of the exhaust purification catalyst.

Although not shown in detail, the exhaust aftertreatment device 44 includes a known exhaust purification catalyst that purifies a predetermined exhaust component exhausted into the exhaust pipe 42 (exhaust passage) of the engine 10. An oxidation catalyst in which a noble metal such as platinum (Pt) is supported on a ceramic core having a structure is housed in a cylindrical case. The exhaust aftertreatment device 44 oxidizes (HC + O ₂ ) hydrocarbon (HC) in the exhaust gas to change it into carbon dioxide (CO ₂ ) and water (H ₂ O), and at the same time, carbon monoxide in the exhaust gas. (CO) is oxidized to (CO + _{O 2)} can be changed into carbon dioxide (CO _2). The exhaust aftertreatment device 44 may include a known DPF (diesel particulate filter) that removes soot (soot) components in the exhaust gas after the oxidation catalyst.

  FIG. 2 is a temperature characteristic diagram of the exhaust purification performance showing the relationship between the exhaust purification performance of the oxidation catalyst in the exhaust aftertreatment device 44 and the catalyst bed temperature.

As shown in the figure, the exhaust aftertreatment device 44 has a catalyst bed temperature exceeding a predetermined exhaust purification temperature Tca (or an average exhaust gas temperature at a predetermined time corresponding to a change in the catalyst bed temperature is a predetermined value). Most of the hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas change to carbon dioxide (CO ₂ ) and water (H ₂ O) when activated It can be made to. Further, during the temperature increase until the exhaust purification temperature Tca is reached, the oxidation catalyst of the exhaust aftertreatment device 44 is not activated until it reaches the vicinity of the exhaust purification temperature Tca, and the CO purification rate (or HC) near the exhaust purification temperature Tca. (Purification rate) has a temperature characteristic that increases rapidly. Therefore, the exhaust aftertreatment device 44 is warmed up to a temperature slightly exceeding the exhaust purification temperature Tca, and then converts most of the hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas to carbon dioxide (CO ₂ ). And water (H ₂ O).

  The post-injection in the fuel injection device 12 and the added fuel injection from the fuel addition nozzle 24 increase the exhaust temperature or the oxidation catalyst (or further DPF in the subsequent stage) with respect to such characteristics of the exhaust aftertreatment device 44. It is designed to be executed in order to enhance the action.

  As shown in FIG. 1, the turbocharger 15 has an intake air compressor 15a and an exhaust turbine 15b that are integrally connected to each other in the rotational direction, and rotates the intake air compressor 15a by rotating the exhaust turbine 15b with exhaust energy. Therefore, positive pressure air can be sucked into the engine 10.

  The exhaust gas recirculation device 16 is an EGR means for recirculating a part of the exhaust gas of the engine 10 to the intake manifold 31 side. The exhaust gas recirculation device 16 has an exhaust gas recirculation passage that bypasses the combustion chamber in the engine 10 and connects the exhaust passage in the exhaust manifold 41 and the intake passage in the intake manifold 31, that is, an EGR passage 61. The EGR passage 61 is provided with an EGR valve 62 for adjusting the exhaust gas recirculation amount, and an exhaust cooler for cooling the exhaust gas recirculated through the EGR passage 61, that is, an EGR cooler 63. The EGR passage 61 is a passage that recirculates a part of the exhaust gas from the exhaust passage side to the intake passage side of the engine 10, and the EGR cooler 63 uses a part of the EGR passage 61 as a cooling passage, and has an inlet 63a and an outlet 63b. Have. The EGR valve 62 can be switched between an open state in which the EGR passage 61 is connected to the intake passage and a closed state in which the connection is restricted, for example, shut off.

  The exhaust gas recirculation device 16 further includes a bypass passage 64 capable of bypassing the EGR cooler 63 and supplying the exhaust gas recirculated from the exhaust passage side to the intake passage side to the EGR valve 62, and an inlet 63a of the EGR cooler 63. An EGR cooler bypass valve 65 disposed at a branch portion from the EGR passage 61 to the bypass passage 64 located in the vicinity of the EGR passage, and an EGR oxidation catalyst unit 66 for oxidizing unburned fuel in the exhaust gas are provided. . Here, the EGR cooler bypass valve 65 is a bypass opening / closing valve that can be switched between a valve opening state in which the bypass passage 64 is opened and a valve closing state in which the bypass passage 64 is closed.

  The EGR valve 62 is configured to open and close by, for example, a valve body 62a (see FIG. 1) being moved forward and backward in the vertical direction in FIG. Further, the EGR cooler bypass valve 65 opens the bypass passage 64 by opening the valve and closes the inlet side of the EGR cooler 63, and closes the bypass passage 64 by opening the valve and opens the inlet side of the EGR cooler 63. It is like that. The EGR cooler bypass valve 65 rotates a plate-like valve body (not shown) to open the valve indicated by a dotted line in FIG. 1 and from the position toward the bypass passage 64 in the clockwise direction in FIG. The valve is switched to the rotated valve closing position.

  On the other hand, the energization control of the supply pump 21, the fuel injection amount control by the fuel injection valve 23, the opening control of the throttle valve 36, the opening control of the EGR valve 62 and the EGR cooler bypass valve 65, and the like are electronically controlled by the ECU 50. The ECU 50 is configured to execute a predetermined control program every predetermined time.

  As shown in FIG. 1, the ECU 50 includes a CPU (Central Processing Unit) 51, a ROM (Read Only Memory) 52, a RAM (Random Access Memory) 53, an EEPROM 54 (Electronically Erasable and Programmable Read Only Memory), and an A / D converter. And an input interface circuit 56 including a buffer and the like, and an output interface circuit 57 including a drive circuit and the like.

  An input interface circuit 56 of the ECU 50 includes an air flow meter 35, an intake air temperature sensor 37, an A / F sensor 43, a catalyst bed temperature sensor 45, an accelerator opening sensor 71 for detecting depression of an accelerator pedal (not shown), and a throttle valve 36. A throttle opening sensor 72 for detecting the opening degree, a crank angle sensor 73 (rotation speed sensor) for outputting a signal corresponding to the engine speed from the crank rotation in a predetermined angle unit, a traveling speed or a wheel of a vehicle on which the engine 10 is mounted A vehicle speed sensor 74 for detecting the rotational speed, an intake pipe pressure sensor 75 for detecting the intake pressure (supercharging pressure) of the engine 10, and the like are connected, and these sensor groups 35, 37, 43, 45 and 71 to 75 are connected. Information is taken into the ECU 50.

  Connected to the output interface circuit 57 of the ECU 50 are a supply pump 21, a plurality of fuel injection valves 23, a fuel addition nozzle 24, an EGR valve 62, and an EGR cooler bypass valve 65 via respective drive circuits (not shown).

  The ROM 52 of the ECU 50 checks the acceleration request from the accelerator opening sensor 71 taken into the input interface circuit 56, and takes in the engine speed and the like from the crank angle sensor 73 at predetermined time intervals into the combustion chamber of the engine 10. A calculation processing program for calculating the fuel injection amount and injection timing, the target air amount to be sucked into each cylinder of the engine 10, and the like are stored. Here, the arithmetic processing program serving as the target injection timing calculation means executes fuel injection in one combustion cycle in the engine 10 with an injection amount smaller than the main injection amount before the piston reaches compression top dead center (TDC). The operation is divided into a plurality of injections including pilot injection and main injection executed after the piston has passed through the compression top dead center, and the operation state obtained from the target injection timing map according to the operation state of the engine 10 The optimal pilot injection timing and the target injection timing of the main injection can be calculated.

  Further, in the ROM 52, an exhaust post-processing is performed based on a basic EGR amount calculation program for calculating a basic EGR amount for recirculating exhaust from the exhaust manifold 41 side to the intake manifold 31 side, and a detected temperature Tc of the catalyst bed temperature sensor 45. In accordance with the rise characteristic of the purification performance during the warming-up temperature of the exhaust purification catalyst in the device 44, the reduction correction for the basic EGR amount is performed within the temperature range until the exhaust purification catalyst reaches the predetermined exhaust purification temperature Tca. Each of the weight loss correction programs to be executed is stored. The ECU 50 executes these programs in the ROM 52 while transferring data to and from the RAM 53 by the CPU 51 and taking in information from the input interface circuit 56, whereby the basic EGR amount calculating means and the reduction correction are executed. Functions as a means.

  The ECU 50 is the basic EGR amount calculation means, for example, for the entire operating range specified by the engine speed and the fuel injection amount (corresponding to the load), and is optimal in exhaust purification performance without misfire or pre-ignition. Map data acquired in advance by an operation test as an EGR amount with the highest purification rate and the lowest exhaust emission is stored and stored in the ROM 52 as a basic EGR amount map, which will be described later. A basic EGR amount calculation program in the ROM 52 for calculating an optimum EGR amount from the basic EGR amount map based on the number and the detected value of the fuel injection amount, and a working memory in the RAM 53 are included.

  The ECU 50 as the weight reduction correction means determines whether or not the exhaust purification catalyst in the exhaust aftertreatment device 44 has reached a predetermined exhaust purification temperature Tca based on the detected temperature Tc of the catalyst bed temperature sensor 45, and the exhaust purification. Within the temperature range until the catalyst reaches a predetermined exhaust purification temperature Tca, the basic EGR amount calculated by the function of the basic EGR amount calculating means is corrected to decrease.

  Further, this reduction correction means stores in advance in ROM 52 a reduction correction coefficient h (see FIG. 3) that changes so as to reduce (reduce) the reduction correction amount of the EGR amount in accordance with the temperature rise of the exhaust purification catalyst. It is calculated by the reduction correction coefficient map or the reduction correction coefficient calculation formula, and corresponds to the detected temperature Tc of the catalyst bed temperature sensor 45 within the temperature range until the exhaust purification catalyst reaches a predetermined exhaust purification temperature Tca. The amount of reduction correction is calculated based on the amount of reduction correction coefficient and the basic EGR amount.

  Here, the reduction correction coefficient h has the minimum exhaust purification rate (the CO purification rate or the HC purification rate shown in FIG. 2) of the exhaust purification catalyst in the exhaust aftertreatment device 44, as in the reduction correction coefficient map shown in FIG. In the temperature range until the exhaust purification catalyst reaches a predetermined exhaust purification temperature Tca, it is inversely proportional to the rate of increase in the exhaust purification rate according to the warming-up temperature of the exhaust purification catalyst. It decreases at a decreasing rate.

  3 and 4 are diagrams for explaining the functions of the basic EGR amount calculation means and the reduction correction means of the ECU 50. FIG. 3 shows the operating state of the engine 10 and the catalyst bed temperature of the exhaust aftertreatment device 44. FIG. 4 is a block diagram illustrating a process for calculating the final EGR amount based on the operating state of the engine 10 and the calculated EGR correction amount.

  As shown in both figures, the ECU 50 calculates the EGR correction amount obtained by multiplying the basic EGR correction amount Eb by the reduction correction coefficient h corresponding to the detected temperature Tc of the catalyst bed temperature sensor 45 by the function as the reduction correction means. The final EGR amount is calculated by subtracting from the basic EGR amount by the EGR correction amount, that is, by reducing the amount (see FIG. 4).

  Here, in the basic EGR amount map shown in FIG. 4, the vertical axis indicates the fuel injection amount q and the horizontal axis indicates the engine speed Ne obtained by the crank angle sensor 73 (rotational speed sensor). The basic EGR amount is acquired by a preliminary operation test and map data is created, and the fuel injection amount q is a preliminary test based on the accelerator opening detected by the accelerator opening sensor 71 and the engine speed Ne. The required torque is calculated from the map data acquired by the above method and set as the fuel injection amount corresponding to the required torque. Further, the basic EGR correction amount map shown in FIG. 3 may be substantially the same as the basic EGR amount map for obtaining the basic EGR amount obtained based on the engine speed and the fuel injection amount as the operating state of the engine 10. You may have EGR amount data after correcting the basic EGR amount based on other parameters (for example, cooling water temperature) in advance. Further, the basic EGR correction amount map may obtain a reduction correction coefficient in which the basic EGR amount is 1. However, in this case, the subtraction process shown in FIG. 4 is performed by multiplication (final EGR amount = basic EGR amount × It is replaced with the weight loss correction coefficient.

  The ROM 52 also stores an EGR valve opening degree control program that determines the target opening degree of the EGR valve 62 according to the calculated final EGR amount and controls the opening degree of the EGR valve 62 to the target value.

  Further, in the ROM 52, the pilot injection amount by the fuel injection device 12, the pilot interval (the period from the pilot injection completion timing to the main injection start timing), the main injection timing, the injection pressure, according to the temperature detected by the catalyst bed temperature sensor 45. A correction program, a map, and a working memory for supplementarily correcting any one of the post injection amount and the post injection timing in the direction of decreasing CO and HC are stored, and the ECU 50 corrects the EGR amount described above. In addition, the auxiliary correction is executed on the basis of the map data obtained in the previous experiment. The direction for correcting any one of the pilot injection amount, the pilot interval, the main injection timing, the injection pressure, the post injection amount, and the post injection timing is a correction direction for reducing CO and HC. The direction and the amount of correction are prepared in advance as map data and stored in the ROM 52 so that the parameter increases or decreases accordingly.

  Next, the operation will be described.

  When the engine 10 is operated, a plurality of programs stored in the ROM 52 in the ECU 50 are respectively executed at a predetermined cycle or timing.

  FIG. 5 is a graph showing how the EGR sensitivity of the NOx component and CO (or HC) component in the exhaust gas of the engine 10, that is, how the exhaust component concentration changes with respect to the change in the EGR amount.

  When the engine 10 is in operation, as shown in FIG. 5, in contrast to the change in the EGR amount (corresponding to the EGR rate), in the operation state where the EGR amount is small, the exhaust concentration of the NOx component in the exhaust gas increases while the CO In an operating state with a large EGR amount, the exhaust concentration of NOx components in the exhaust gas is lowered, while the exhaust concentration of CO and HC is increased.

  Therefore, in the present embodiment, first, at a stage where the exhaust purification catalyst in the exhaust aftertreatment device 44 does not reach the predetermined exhaust purification temperature Tca and is not in an active state and the exhaust purification rate is low, for example, pilot injection The EGR amount is decreased by correcting the decrease in the EGR amount while suppressing NOx by correcting any of the amount, the pilot interval, the main injection timing, the injection pressure, the post injection amount, and the post injection timing.

  Next, when the catalyst bed temperature of the exhaust purification catalyst in the exhaust aftertreatment device 44 approaches the predetermined exhaust purification temperature Tca and the exhaust purification rate is increasing, the EGR amount is exhausted in the exhaust aftertreatment device 44. Based on the temperature characteristic of the purification catalyst, the amount of correction for reducing the EGR amount is changed in accordance with the temperature detected by the catalyst bed temperature sensor 45 so that the amount of decrease in correction is based on the catalyst bed temperature.

  Next, at a stage where the catalyst bed temperature of the exhaust purification catalyst in the exhaust aftertreatment device 44 exceeds the predetermined exhaust purification temperature Tca and the exhaust purification rate has sufficiently increased, the EGR amount is not increased, but the EGR amount is increased. NOx is reduced.

  Specifically, a basic EGR amount that is a base value for calculating the EGR amount by the exhaust gas recirculation device 16 is calculated based on the engine speed of the engine 10 and the fuel injection amount. In the temperature range until the exhaust gas purification catalyst in the exhaust aftertreatment device 44 reaches a predetermined exhaust gas purification temperature Tca, and the rising performance of the purification performance when the exhaust gas purification catalyst warms up In accordance with (see FIG. 2), a reduction correction for the basic EGR amount is executed.

  That is, as shown in FIG. 3, an EGR correction amount is calculated by multiplying the basic EGR correction amount Eb by a reduction correction coefficient h corresponding to the detected temperature Tc of the catalyst bed temperature sensor 45, and as shown in FIG. A final EGR amount is calculated by executing a subtraction process for subtracting the amount of correction from the basic EGR amount.

  Therefore, even if the supported amount of the exhaust purification catalyst in the exhaust aftertreatment device 44 is suppressed to the required amount after activation, CO and HC in the exhaust gas exiting the catalyst during catalyst warm-up are reliably suppressed, The exhaust purification performance of the exhaust aftertreatment device 44 and the cost reduction can be achieved at the same time.

  In the present embodiment, the reduction correction coefficient h corresponding to the catalyst bed temperature detected at the start by the catalyst bed temperature sensor 45 while utilizing the existing map information for calculating the basic EGR amount according to the characteristics of the engine 10. Is further used to perform a reduction correction according to the rising characteristics of the exhaust purification performance at the time of warm-up within the temperature range until the exhaust purification catalyst in the exhaust aftertreatment device 44 reaches a predetermined exhaust purification temperature Tca. As a result, it is possible to reliably suppress CO and HC in the exhaust gas exiting the catalyst during catalyst warm-up while suppressing the amount of the exhaust purification catalyst carried in the exhaust aftertreatment device 44.

  Moreover, since the reduction correction coefficient h for the reduction correction can be easily set to the optimal reduction correction coefficient based on the temperature characteristics of the purification performance of the exhaust purification catalyst in the exhaust aftertreatment device 44, the catalyst CO and HC in the exhaust gas exiting the catalyst during warm-up are more reliably suppressed.

  Thus, according to the exhaust purification control apparatus of the present embodiment, the catalyst bed temperature at the start is detected by the catalyst bed temperature sensor 45, and the exhaust purification catalyst in the exhaust aftertreatment device 44 reaches the predetermined exhaust purification temperature Tca. In the temperature range until the temperature reaches, the reduction correction for the basic EGR amount is executed in accordance with the rising characteristic of the purification performance when the catalyst warms up, and the exhaust purification catalyst is carried in the exhaust aftertreatment device 44. Even if the amount is suppressed, CO and HC in the exhaust gas exiting the catalyst during catalyst warm-up can be reliably suppressed, and both the exhaust purification performance and cost reduction of the exhaust purification device can be achieved.

  In the above-described embodiment, the catalyst bed temperature is directly detected by the catalyst bed temperature sensor 45. However, the catalyst bed temperature is estimated and indirectly detected based on the integrated value or average value of the exhaust temperature. You can also. In the present embodiment, the internal combustion engine is a diesel engine, but other internal combustion engines may be used.

  As described above, the present invention detects the catalyst bed temperature at the time of start-up by the catalyst bed temperature detecting means, and within the temperature range until the exhaust purification catalyst reaches the predetermined exhaust purification temperature, Since the reduction correction for the basic EGR amount is executed in accordance with the start-up characteristics of the purification performance, the CO and HC in the exhaust gas exiting the catalyst during catalyst warm-up can be reduced even if the amount of the exhaust purification catalyst supported is suppressed. An exhaust purification control device for an internal combustion engine that can be reliably suppressed and can achieve both an exhaust purification performance and a cost reduction can be provided, and an exhaust purification control device for an internal combustion engine, In particular, the present invention is useful for all exhaust gas purification control devices for internal combustion engines that limit the EGR amount when the exhaust gas purification catalyst warms up.

1 is a diagram showing an exhaust gas purification control device for an internal combustion engine according to an embodiment of the present invention, showing an example in which the present invention is applied to a multi-cylinder diesel engine. It is a temperature characteristic diagram of the exhaust purification performance showing the relationship between the exhaust purification performance of the exhaust purification catalyst and the catalyst bed temperature in one embodiment. It is a block diagram explaining the process which calculates the EGR correction amount based on the operating state of the engine and the catalyst bed temperature of the exhaust purification catalyst in one embodiment. It is a block diagram explaining the process which calculates the last EGR amount based on the driving | running state of the engine and the calculated EGR correction amount in one Embodiment. It is a graph which shows how the EGR sensitivity of the NOx component and CO component in the exhaust gas of the engine of one embodiment, that is, the exhaust component concentration changes with respect to the change of the EGR amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 11 Cylinder 12 Fuel-injection apparatus 13 Intake apparatus 14 Exhaust apparatus 15 Turbo supercharger 15a Intake air compressor 15b Exhaust turbine 16 Exhaust gas recirculation apparatus (EGR means)
DESCRIPTION OF SYMBOLS 21 Supply pump 22 Common rail 23 Fuel injection valve 24 Fuel addition nozzle 31 Intake manifold 32 Intake pipe 33 Air cleaner 34 Intercooler 35 Air flow meter 36 Throttle valve 37 Intake temperature sensor 41 Exhaust manifold 42 Exhaust pipe 43 A / F sensor (Wide area air-fuel ratio sensor) )
44 Exhaust aftertreatment device 45 Catalyst bed temperature sensor (catalyst bed temperature detection means)
50 ECU (electronic control unit, basic EGR amount calculation means, reduction correction means)
51 CPU
52 ROM
53 RAM
54 EEPROM
56 Input interface circuit 57 Output interface circuit 61 EGR passage 62 EGR valve 63 EGR cooler 64 Bypass passage 65 EGR cooler bypass valve 66 EGR oxidation catalyst unit 71 Accelerator opening sensor 72 Throttle opening sensor 73 Crank angle sensor 74 Vehicle speed sensor 75 Intake pipe Pressure sensor

Claims (4)

An exhaust gas purification control apparatus for an internal combustion engine, comprising: EGR means for recirculating a part of the exhaust gas of the internal combustion engine to the intake manifold side through the EGR passage; and an exhaust purification catalyst for purifying an exhaust component exhausted into the exhaust passage of the internal combustion engine. In
Catalyst bed temperature detecting means for detecting the catalyst bed temperature of the exhaust purification catalyst;
Basic EGR amount calculating means for calculating a basic EGR amount for recirculating exhaust gas to the intake manifold side based on an operating state of the internal combustion engine;
Based on the detected temperature of the catalyst bed temperature detecting means, the exhaust purification catalyst within the temperature range until the exhaust purification catalyst reaches a predetermined exhaust purification temperature according to the rise of the purification performance during warming-up of the exhaust purification catalyst. An exhaust purification control apparatus for an internal combustion engine, comprising: a reduction correction means for executing a reduction correction for the basic EGR amount.   The reduction correction that the reduction correction means changes so as to decrease the reduction correction amount of the EGR amount in accordance with the temperature rise of the exhaust purification catalyst within the temperature range until the exhaust purification catalyst reaches a predetermined exhaust purification temperature. A coefficient is calculated, and based on the reduction correction coefficient corresponding to the detected temperature of the catalyst bed temperature detecting means and the basic EGR amount within a temperature range until the exhaust purification catalyst reaches a predetermined exhaust purification temperature. 2. The exhaust gas purification control apparatus for an internal combustion engine according to claim 1, wherein a reduction correction amount is calculated.   The reduction correction means calculates a reduction correction amount obtained by multiplying the basic EGR amount by the reduction correction coefficient corresponding to the detected temperature of the catalyst bed temperature detection means, and reduces the correction from the basic EGR amount by the reduction correction amount. The exhaust gas purification control apparatus for an internal combustion engine according to claim 2.   The reduction correction coefficient is maximized in a catalyst bed temperature region where the exhaust purification rate of the exhaust purification catalyst is minimum, and the catalyst bed is within a temperature range until the exhaust purification catalyst reaches a predetermined exhaust purification temperature. 4. The exhaust gas purification control apparatus for an internal combustion engine according to claim 2, wherein the exhaust gas purification control apparatus decreases at a rate that is inversely proportional to an increase rate of the exhaust gas purification rate according to a warm-up temperature rise of the temperature detecting means.

Images