JP2018031354A - Exhaust emission control device for engine system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To oxidize and eliminate unburnt components passing through a catalyst after warming up the catalyst, in a relatively easy configuration.SOLUTION: An exhaust emission control device provided in an engine system including an engine 1, an intake passage 2, an exhaust passage 3, and a supercharger 5 includes a front catalyst 10 and a rear catalyst 11 for purifying exhaust gas to be exhausted from the engine 1 into the exhaust passage 3, and fresh air introduction means for introducing fresh air into the exhaust passage 3 behind the rear catalyst 11 to oxidize and eliminate unburnt components passing through the rear catalyst 11 after warming up both catalysts 10, 11. The fresh air introduction means is configured using an EGR passage 22 and an EGR valve 24. Its configuration is such that, when an intake pressure is lower than an exhaust pressure, EGR gas flows via the EGR passage 22 and the EGR valve 24 from the exhaust passage 3 to the intake passage 2, and, when the intake pressure (a supercharging pressure) is higher than the exhaust pressure, the fresh air is introduced via the EGR passage 22 and the EGR valve 24 from the intake passage 2 to the exhaust passage 3 behind the rear catalyst 11.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust purification device that is provided in an engine system including an engine and includes a catalyst that purifies exhaust exhausted from the engine, and more specifically, is configured to oxidize and purify unburned components that have passed through the catalyst. The present invention relates to an exhaust purification device for an engine system.

  Conventionally, as this type of technology, for example, an exhaust purification device described in Patent Document 1 below is known. This device is configured to purify HC components and CO components (unburned components) by supplying active oxygen components into the exhaust discharged from the engine. Specifically, this apparatus includes a three-way catalyst provided in the exhaust passage, an upstream active oxygen component supplying means for supplying an active oxygen component to the exhaust passage upstream of the three-way catalyst, and an exhaust passage downstream of the three-way catalyst. HC adsorbent provided on the downstream side, downstream active oxygen component supply means for supplying an active oxygen component to an exhaust passage upstream of the HC adsorbent and downstream of the three-way catalyst, upstream active oxygen component supply means, and downstream Active oxygen component supply control means for controlling the side active oxygen component supply means. According to this configuration, when the engine is cold-started, the active oxygen component is supplied to the upstream side of the three-way catalyst by the upstream-side active oxygen component supply means, so that the unburned components in the exhaust gas are oxidized by the three-way catalyst. Purify. Further, unreacted unburned components that have not been purified and have passed through the three-way catalyst are adsorbed on the HC adsorbent. Then, by supplying an active oxygen component from the downstream active oxygen component supply means to the HC adsorbent, the adsorbed unburned component is oxidized and purified. This suppresses the discharge of unburned components to the outside when the engine is cold started. In the above configuration, ozone is used as the active oxygen component, and an air supply pump and an ozone generator are used as the upstream active oxygen component supply means and the downstream active oxygen component supply means.

JP 2008-150980 A

  However, although the exhaust purification device described in Patent Document 1 can oxidize and purify unburned components in the exhaust when the engine is cold-started, an air supply pump, an ozone generator, and an HC adsorbent must be provided as the devices. In other words, the apparatus becomes large and complicated, which causes a problem in terms of vehicle mounting.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an engine system capable of oxidizing and purifying unburned components that have passed through the catalyst after the catalyst has been warmed up with a relatively simple configuration. An object is to provide an exhaust emission control device.

  In order to achieve the above object, an exhaust purification device for an engine system according to claim 1 comprises an intake passage for introducing intake air into the engine and an exhaust passage for deriving exhaust gas from the engine. A catalyst provided in the engine system for purifying exhaust gas exhausted from the engine to the exhaust passage, and after the catalyst warms up, in order to oxidize and purify unburned components that have passed through the catalyst, The purpose is to provide a fresh air introduction means for introducing fresh air.

  According to the configuration of the above invention, the exhaust gas discharged from the engine to the exhaust passage is purified by the catalyst. Here, after the catalyst is warmed up, fresh air is introduced into the exhaust passage behind the catalyst by the fresh air introducing means, so that the high-temperature unburned components that have passed through the catalyst without being purified by the catalyst are introduced. Reacts with fresh air.

  To achieve the above object, according to a second aspect of the present invention, in the first aspect of the present invention, the engine system includes a supercharger for supercharging intake air in the intake passage during engine operation, and an engine. An exhaust gas recirculation passage for allowing a part of the exhaust gas discharged from the exhaust gas to flow into the intake air passage as an exhaust gas recirculation gas and returning it to the engine, and an exhaust gas recirculation valve for adjusting the flow rate of the exhaust gas recirculation gas flowing through the exhaust gas recirculation passage The exhaust gas recirculation passage includes an exhaust gas recirculation inlet for introducing the exhaust gas recirculation gas from the exhaust passage, and an exhaust gas recirculation outlet for leading the exhaust gas recirculation gas to the intake passage. It is connected to the rear exhaust passage, the exhaust gas recirculation outlet is connected to the intake air passage downstream from the supercharger, and the intake pressure in the air intake passage near the exhaust gas recirculation outlet is applied to the exhaust passage near the exhaust gas recirculation inlet. The exhaust gas recirculation gas is configured to flow from the exhaust passage to the intake passage through the exhaust gas recirculation valve when the exhaust pressure becomes lower than the exhaust pressure, and the fresh air introduction means is configured using the exhaust gas recirculation passage and the exhaust gas recirculation valve. It is intended that fresh air is introduced from the intake passage to the exhaust passage behind the catalyst through the exhaust recirculation passage and the exhaust recirculation valve when the intake pressure becomes higher than the exhaust pressure.

  According to the configuration of the above invention, in addition to the operation of the invention according to claim 1, when the intake pressure in the intake passage near the exhaust recirculation outlet becomes lower than the exhaust pressure in the exhaust passage near the exhaust recirculation inlet, When the recirculation valve is opened, exhaust recirculation gas flows from the exhaust passage to the intake passage through the exhaust recirculation passage and the exhaust recirculation valve. On the other hand, since the exhaust gas recirculation passage and the exhaust gas recirculation valve are used as fresh air introduction means, when the intake pressure becomes higher than the exhaust pressure, the exhaust gas recirculation valve is opened so that the exhaust gas behind the catalyst is exhausted from the intake passage. Fresh air is introduced into the passage through the exhaust recirculation passage and the exhaust recirculation valve. Therefore, it is not necessary to provide a dedicated configuration for introducing fresh air into the exhaust passage behind the catalyst.

  In order to achieve the above object, the invention according to claim 3 further comprises control means for controlling the exhaust gas recirculation valve in the invention according to claim 2, wherein the control means has an intake pressure higher than the exhaust pressure. When the air pressure is low, the exhaust gas recirculation gas is caused to flow into the intake passage so that the exhaust gas recirculation valve is controlled to open according to the operating state of the engine, and when the intake pressure is higher than the exhaust pressure, fresh air is introduced into the exhaust passage behind the catalyst. The purpose is to maintain and control the exhaust recirculation valve in the open state when the intake pressure switches from a state lower than the exhaust pressure to a high state. And

  According to the configuration of the above invention, in addition to the operation of the invention according to claim 2, when the intake pressure is lower than the exhaust pressure, the exhaust gas recirculation is caused to flow into the intake passage according to the operating state of the engine. The valve is controlled to open. On the other hand, when the intake pressure is higher than the exhaust pressure, the exhaust gas recirculation valve is controlled to open in order to introduce fresh air into the exhaust passage behind the catalyst. Further, when the intake pressure is switched from a state lower than the exhaust pressure to a higher state, the exhaust recirculation valve in the valve open state is controlled to remain open. Therefore, when switching from the state in which the exhaust gas recirculation gas flows into the intake passage to the state in which fresh air is introduced into the exhaust passage, the exhaust recirculation valve is not closed once, so that the region where the exhaust recirculation gas flows into the intake passage reaches its upper limit. Can be expanded.

  In order to achieve the above object, the invention described in claim 4 further comprises control means for controlling the exhaust gas recirculation valve in the invention described in claim 2, wherein the control means is configured such that the intake pressure is higher than the exhaust pressure. In order to flow the exhaust gas recirculation gas into the intake passage when it is low, the exhaust gas recirculation valve is controlled to open according to the operating state of the engine, and when the intake air pressure is higher than the exhaust pressure, the exhaust gas discharged from the engine The purpose is to control the opening of the exhaust gas recirculation valve in order to introduce fresh air into the exhaust passage behind the catalyst when the amount of unburned components increases.

  According to the configuration of the above invention, in addition to the operation of the invention according to claim 2, when the intake pressure is lower than the exhaust pressure, the exhaust gas recirculation is caused to flow into the intake passage according to the operating state of the engine. The valve is controlled to open. On the other hand, when the intake pressure is higher than the exhaust pressure and the amount of unburned components in the exhaust discharged from the engine increases, the exhaust recirculation valve is used to introduce fresh air into the exhaust passage behind the catalyst. The valve opening is controlled. Therefore, when the unburned components passing through the catalyst increase, the high-temperature unburned components react with the introduced fresh air and are oxidized and purified.

  In order to achieve the above object, the invention according to claim 5 is the invention according to claim 3 or 4, wherein the intake pressure detection means for detecting the intake pressure in the intake passage near the exhaust gas recirculation outlet, The intake air amount detecting means for detecting the intake air amount in the intake passage upstream from the exhaust gas recirculation outlet, and the intake air amount calculating means for calculating the intake air amount of the engine sucked into the engine are further provided. The exhaust pressure is calculated based on the detected intake amount, and the rear of the catalyst is determined based on the calculated exhaust pressure, the detected intake pressure, and the opening degree of the exhaust gas recirculation valve that is controlled to open by the control means. The purpose is to calculate the engine intake air amount by calculating the fresh air introduction amount introduced into the exhaust passage and subtracting the calculated fresh air introduction amount from the detected intake air amount.

  According to the configuration of the above invention, in addition to the operation of the invention according to claim 3 or 4, when fresh air is introduced from the intake passage to the exhaust passage behind the catalyst, the amount of intake air from the engine is increased accordingly. It becomes smaller than the intake air amount detected by the amount detecting means. Here, the amount of fresh air introduced into the exhaust passage is calculated based on the calculated exhaust pressure, the detected intake pressure, and the opening of the exhaust gas recirculation valve, and the fresh air is calculated from the detected intake amount. The engine intake air amount is calculated by subtracting the introduction amount. Therefore, even when fresh air is introduced into the exhaust passage behind the catalyst from the intake passage, an engine intake amount that can be used for various controls of the engine can be obtained. Further, it is not necessary to provide a dedicated detection means for detecting the exhaust pressure in order to obtain the engine intake air amount.

  According to the first aspect of the present invention, the unburned components that have passed through the catalyst after the catalyst is warmed up can be oxidized and purified with a relatively simple configuration, and the exhaust emission can be improved.

  According to the invention described in claim 2, in addition to the effect of the invention described in claim 1, in order to introduce fresh air into the exhaust passage behind the catalyst, it is necessary to provide a dedicated configuration and a dedicated space separately. In addition, the cost increase of the engine system can be suppressed.

  According to the invention described in claim 3, in addition to the effect of the invention described in claim 2, effects such as fuel consumption reduction and NOx reduction by the exhaust gas recirculation gas can be maximized.

  According to the invention described in claim 4, in addition to the effect of the invention described in claim 2, unburned components increased in the exhaust gas can be effectively oxidized and purified, and deterioration of exhaust emission can be suppressed. it can.

  According to the invention described in claim 5, in addition to the effects of the invention described in claim 3 or 4, even when fresh air is introduced from the intake passage into the exhaust passage behind the catalyst during engine operation, Various engine controls can be appropriately executed based on the engine intake air amount supplied to the engine.

1 is a schematic configuration diagram illustrating a gasoline engine system according to a first embodiment. FIG. 3 is a side cross-sectional view schematically illustrating a rear catalyst in an exhaust passage according to the first embodiment. The AA sectional view taken on the line of FIG. 2 which shows the outline of a post catalyst according to the first embodiment. The flowchart which concerns on 1st Embodiment and shows the content of the fresh air introduction control. The exhaust pressure map referred in order to obtain | require the exhaust pressure proportional to intake air amount concerning 1st Embodiment. The graph which concerns on 1st Embodiment and shows the image of the determination area | region. The flowchart which concerns on 1st Embodiment and shows the content of the fresh air introduction restriction | limiting control. The graph which shows the relationship of the various parameters by 1st Embodiment by the fresh air introduction control and the fresh air introduction control. The flowchart which concerns on 2nd Embodiment and shows the content of exhaust gas purification control. The fresh air introduction amount map referred to in order to obtain the fresh air introduction amount according to the fresh air introduction differential pressure and the target EGR opening according to the second embodiment. The flowchart which shows the content of the fresh air introduction control concerning 3rd Embodiment. The engine load determination value map referred to in order to obtain | require the engine load determination value according to 3rd Embodiment according to an engine speed. An atmospheric pressure correction value map referred to in order to obtain an atmospheric pressure correction value proportional to the atmospheric pressure according to the third embodiment. The schematic block diagram which concerns on 4th Embodiment and shows a gasoline engine system. The flowchart which concerns on 4th Embodiment and shows the content of the fresh air introduction restriction | limiting control. The fresh air introduction permission intake amount map referred to in order to obtain the fresh air introduction permission intake amount according to the vapor concentration according to the fourth embodiment. The flowchart which shows the content of purge flow volume restriction | limiting control concerning 5th Embodiment. The maximum purge flow rate map referred to in order to obtain the maximum purge flow rate according to the intake air amount and the vapor concentration according to the fifth embodiment. A schematic structure figure showing a gasoline engine system concerning a 6th embodiment. The schematic block diagram which shows a gasoline engine system concerning 7th Embodiment. The schematic block diagram which shows a gasoline engine system in connection with 8th Embodiment. The schematic block diagram which shows a gasoline engine system concerning 9th Embodiment. A sectional side elevation showing an outline of a back catalyst in an exhaust passage concerning a 10th embodiment. Sectional drawing which concerns on 11th Embodiment and shows an EGR valve. Sectional drawing which concerns on 12th Embodiment and shows an EGR valve. A sectional side elevation showing an outline of a new air introduction device and a back catalyst in an exhaust passage concerning a 13th embodiment.

<First Embodiment>
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of an engine system exhaust gas purification apparatus according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 shows a schematic configuration diagram of a gasoline engine system of this embodiment. A gasoline engine system mounted on an automobile includes a reciprocating engine 1. The engine 1 is provided with an intake passage 2 for introducing intake air into each cylinder and an exhaust passage 3 for deriving exhaust gas from each cylinder. A supercharger 5 is provided in the intake passage 2 and the exhaust passage 3. In the intake passage 2, an air cleaner 4, a compressor 5 a of the supercharger 5, an intercooler 6, a throttle device 7 and an intake manifold 8 are provided in this order from the upstream side. The throttle device 7 is configured to adjust the intake air amount Ga in the intake passage 2 by opening and closing a butterfly throttle valve 7a. Intake manifold 8 includes a surge tank 8 a and a plurality of branch passages 8 b that branch from surge tank 8 a to each cylinder of engine 1. In the exhaust passage 3, an exhaust manifold 9, a turbine 5 b of the supercharger 5, and a front catalyst 10 and a rear catalyst 11 arranged in series are provided in this order from the upstream side. The pre-catalyst 10 and the post-catalyst 11 are for purifying exhaust gas, and are composed of a three-way catalyst. The rear catalyst 11 is located on the most downstream side as a member related to exhaust purification, and no member related to exhaust purification is provided in the exhaust passage 3 downstream of the rear catalyst 11. The engine 1 has a well-known configuration, generates power by burning a mixture of fuel and air, and discharges exhaust gas after combustion. That is, the engine 1 includes a fuel supply device (not shown) for supplying fuel and an ignition device (not shown) for igniting a mixture of fuel and intake air. The fuel supply device includes a fuel tank, a fuel pump, an injector, and the like, and the ignition device includes an ignition plug, an ignition coil, and the like. The turbocharger 5 supercharges (increases) the intake air in the intake passage 2 by rotating the turbine 5b according to the flow of exhaust during operation of the engine 1 and rotating the compressor 5a in conjunction therewith. It has become.

  The gasoline engine system includes an exhaust gas recirculation device (EGR device) 21. This device 21 includes an exhaust gas recirculation passage (EGR passage) 22 for flowing a part of exhaust discharged from the engine 1 to the exhaust passage 3 as exhaust gas recirculation gas (EGR gas) to the intake passage 2 and recirculating to each cylinder. The exhaust gas recirculation cooler (EGR cooler) 23 provided in the EGR passage 22 for cooling the EGR gas, and the exhaust gas recirculation valve provided in the EGR passage 22 downstream of the EGR cooler 23 for adjusting the flow rate of the EGR gas. (EGR valve) 24. The EGR passage 22 includes an EGR inlet 22a and a plurality of EGR outlets 22b for EGR gas. An EGR distribution pipe 25 having a plurality of EGR outlets 22 b is provided on the downstream side of the EGR passage 22. The EGR distribution pipe 25 is provided in the branch passage 8 b of the intake manifold 8. In this embodiment, the EGR inlet 22 a is connected to the exhaust passage 3 downstream from the rear catalyst 11. The plurality of EGR outlets 22b of the EGR distribution pipe 25 are connected to the respective branch passages 8b. The plurality of EGR outlets 22b are connected to the respective branch passages 8b in order to introduce the EGR gas evenly into the respective cylinders through the respective branch passages 8b.

  In this embodiment, the EGR valve 24 is configured by an electrically operated valve having a variable opening. The EGR valve 24 desirably has characteristics of a large flow rate, high response, and high resolution. Therefore, in this embodiment, as a structure of the EGR valve 24, for example, a “double eccentric valve” described in Japanese Patent No. 5759646 can be adopted as a basic configuration. This double eccentric valve is configured for large flow control. Here, detailed description of the EGR valve 24 is omitted.

  Next, an example of the electrical configuration of the gasoline engine system will be described. In FIG. 1, various sensors 51 to 56 provided in the engine system constitute an operation state detection unit for detecting the operation state of the engine 1. A water temperature sensor 51 provided in the engine 1 detects the temperature (cooling water temperature) THW of the cooling water flowing inside the engine 1 and outputs an electrical signal corresponding to the detected value. A rotational speed sensor 52 provided in the engine 1 detects a rotational speed (engine rotational speed) NE of the crankshaft and outputs an electrical signal corresponding to the detected value. An air flow meter 53 provided in the air cleaner 4 detects the intake air amount Ga flowing through the air cleaner 4 and outputs an electrical signal corresponding to the detected value. The air flow meter 53 corresponds to an example of the intake air amount detection means of the present invention. The intake pressure sensor 54 provided in the surge tank 8a detects the intake pressure PM in the intake passage 2 downstream from the throttle device 7 and outputs an electrical signal corresponding to the detected value. The intake pressure sensor 54 corresponds to an example of the intake pressure detection means of the present invention. A throttle sensor 55 provided in the throttle device 7 detects an opening degree (throttle opening degree) TA of the throttle valve 7a and outputs an electric signal corresponding to the detected value. The oxygen sensor 56 provided in the exhaust passage 3 between the turbine 5b and the pre-catalyst 10 detects the oxygen concentration Ox in the exhaust and outputs an electrical signal corresponding to the detected value. In addition, the automobile of this embodiment is provided with an atmospheric pressure sensor 57 for detecting the atmospheric pressure PA. The atmospheric pressure sensor 57 outputs an electrical signal corresponding to the detected value of the atmospheric pressure PA.

  The gasoline engine system further includes an electronic control unit (ECU) 60 that controls the system. Various sensors 51 to 57 are connected to the ECU 60. In addition to the EGR valve 24, an ECU (not shown) and an ignition coil (not shown) are connected to the ECU 60. The ECU 60 corresponds to an example of a control unit of the present invention. As is well known, the ECU 60 includes a central processing unit (CPU), various memories, an external input circuit, an external output circuit, and the like. The memory stores predetermined control programs related to various controls. The CPU executes fuel injection control, ignition timing control, EGR control, exhaust purification control, and the like based on a predetermined control program based on detection signals from various sensors 51 to 57 input via the input circuit. ing.

  In this embodiment, the ECU 60 controls the EGR valve 24 according to the operating state of the engine 1 in the EGR control. Specifically, the ECU 60 controls the EGR valve 24 to be fully closed when the engine 1 is stopped, idling, decelerating, and accelerating, and during other operations, the target EGR is controlled according to the operating state. The opening degree Tegr is obtained, and the EGR valve 24 is controlled to the target EGR opening degree Tegr. At this time, when the EGR valve 24 is opened, a part of the exhaust gas discharged from the engine 1 to the exhaust passage 3 and passing through the front catalyst 10 and the rear catalyst 11 is used as EGR gas, the EGR passage 22 and the EGR valve 24. And, it flows into the intake passage 2 (intake manifold 8) via the EGR distribution pipe 25 and the like, and is returned to each cylinder of the engine 1.

  Next, the configuration of the exhaust emission control device will be described. In general, in the fuel injection control of the engine, the fuel injection amount is corrected to increase (fuel increase) in order to prevent combustion failure in a high load operation region and to prevent catalyst overheating in a high intake air amount region. . In the engine system provided with the supercharger 5 as in this embodiment, the exhaust temperature is high, so the operating range in which the fuel increase is performed is widened, and the increase ratio of the fuel increase is relatively high. As a contradiction, unburned components such as HC and CO that cannot be purified by the front catalyst 10 and the rear catalyst 11 tend to increase. Therefore, in this embodiment, the exhaust gas is purified by the two catalysts 10 and 11, and after the two catalysts 10 and 11 are warmed up, the unburned gas that has not passed through the rear catalyst 11 without being purified by the two catalysts 10 and 11. The components are oxidized and purified (burned and purified).

  The exhaust purification device of this embodiment is configured using an EGR device 21 in addition to the front catalyst 10 and the rear catalyst 11. In this embodiment, the EGR passage 22 that is originally used for flowing EGR gas from the exhaust passage 3 to the intake passage 2 is a new one for introducing a part of the intake air from the intake passage 2 to the exhaust passage 3 as fresh air. Functions as an air passage. The EGR valve 24 functions as a fresh air regulating valve that regulates the flow of fresh air in the opposite direction to the flow of EGR gas, in addition to the original function of regulating the flow of EGR gas. That is, the EGR passage 22 and the EGR valve 24 correspond to an example of the fresh air introducing means of the present invention.

  FIG. 2 is a schematic side sectional view of the rear catalyst 11 in the exhaust passage 3. FIG. 3 shows an outline of the post-catalyst 11 by a cross-sectional view taken along line AA in FIG. As shown in FIGS. 2 and 3, the rear catalyst 11 has an outer diameter larger than the outer diameter of the exhaust passage 3, and on the upstream side (immediately before), an upstream cone portion that converges toward the exhaust passage 3. 11a is provided, and on the downstream side (rear side), a downstream cone portion 11b that converges toward the exhaust passage 3 is provided. 2 and 3, when the top side of the rear catalyst 11 is the top side and the bottom side is the ground side, the EGR inlet 22a is connected to the downstream cone portion 11b at a position closer to the top side of the rear catalyst 11. As shown in FIG. 2, the EGR inlet 22a is disposed at a position relatively close to the rear catalyst 11, that is, a position at which the exhaust gas flow velocity is relatively slow. As a result, the contact time between the fresh air introduced from the EGR inlet 22a into the downstream cone portion 11b and the exhaust gas flowing out from the rear catalyst 11 is increased. Moreover, as shown in FIG. 3, the EGR passage 22 in the vicinity of the EGR inlet 22a is connected to the downstream cone portion 11b so as to be substantially circumscribed or inscribed on the outer periphery of the downstream cone portion 11b. Thus, fresh air introduced from the EGR inlet 22a to the downstream cone portion 11b flows along the inner periphery of the cone portion 11b and turns.

  Here, the fresh air introduction control executed by the ECU 60 to introduce fresh air to the rear of the rear catalyst 11, that is, the downstream cone portion 11b, of the exhaust purification control will be described. FIG. 4 is a flowchart showing the contents of the fresh air introduction control.

  When the processing shifts to this routine, in step 100, the ECU 60 determines the engine speed NE, the intake air amount Ga, the engine load KL, the coolant temperature THW, the intake pressure PM, and the throttle opening based on the detection values of the various sensors 51-56. The degree TA is taken in, and the target EGR opening degree Tegr obtained by the separate EGR control is taken in. Here, the ECU 60 can determine the engine load KL from the relationship between the engine speed NE and the throttle opening degree TA.

  Next, at step 110, the ECU 60 obtains the exhaust pressure PMex in the exhaust passage 3 downstream from the rear catalyst 11 based on the intake air amount Ga. For example, the ECU 60 can obtain the exhaust pressure PMex proportional to the intake air amount Ga by referring to the exhaust pressure map shown in FIG.

  Next, in step 120, the ECU 60 determines whether or not the intake pressure PM is lower than the exhaust pressure PMex. Here, FIG. 6 shows an image of the determination area in a graph. In this graph, the vertical axis indicates the intake pressure PM, and the plurality of straight lines that descend to the right indicate isobars of the exhaust pressure PMex. The vertical axis is divided into a positive pressure and a negative pressure around the atmospheric pressure PA. The exhaust pressure PMex increases toward the right side. As shown in FIG. 6, the fresh air region and the EGR region are divided by a determination line LD indicated by a broken line. If the determination result in step 120 is affirmative, the ECU 60 proceeds to step 130. If the determination result is negative, the ECU 60 proceeds to step 140.

  In step 130, the ECU 60 determines that the region is the EGR region, permits EGR control, and then returns the process to step 100.

  On the other hand, in step 140, the ECU 60 determines that the region is a fresh air region, and opens the EGR valve 24 in order to introduce fresh air into the exhaust passage 3 behind the rear catalyst 11. Here, the ECU 60 can adjust the opening degree of the EGR valve 24 as needed. Thereafter, the ECU 60 returns the process to step 100.

  In the above-described fresh air introduction control, the intake pressure PM and the intake air amount Ga among the various parameters detected by the various sensors 51 to 56 can be used to determine the fresh air region. Here, in order to detect the exhaust pressure PMex, a dedicated pressure sensor may be provided in the exhaust passage 3. However, since the arrangement environment is very severe, the reliability and mountability of the pressure sensor become a problem. Therefore, in this embodiment, the exhaust pressure PMex is obtained based on the intake air amount Ga having a correlation with the exhaust pressure PMex.

  Next, the restrictions on the introduction of fresh air after the introduction of fresh air will be described. FIG. 7 is a flowchart showing the contents of the fresh air introduction restriction control.

  When the process proceeds to this routine, in step 200, the ECU 60 determines whether or not there is a fresh air region determination. That is, it is determined whether or not a fresh air region has been determined by the fresh air introduction control shown in FIG. If this determination result is affirmative, the ECU 60 proceeds to step 210, and if this determination result is negative, the ECU 60 returns the process to step 200.

  After step 200, in step 210, the ECU 60 takes in the detected intake pressure PM.

  Next, in step 220, the ECU 60 determines whether or not the intake pressure PM is lower than a predetermined high supercharging pressure PTH. Here, the high supercharging pressure PTH means a supercharging pressure that serves as a reference for stopping the introduction of fresh air behind the rear catalyst 11. This is because if the fresh air is introduced into the exhaust passage 3 up to the high supercharging pressure range, the supercharging efficiency in the compressor 5a is lowered, and the output of the engine 1 may be reduced. Therefore, in step 220, it is determined whether or not the supercharging pressure (intake pressure PM) has reached an upper limit at which fresh air introduction can be permitted. If the determination result in step 220 is affirmative, the ECU 60 proceeds to step 230. If the determination result is negative, the ECU 60 proceeds to step 240.

  In step 230, the ECU 60 permits introduction of fresh air. That is, the ECU 60 maintains and controls the EGR valve 24 in the valve open state while the valve is in the open state. Thereafter, the ECU 60 returns the process to step 200.

  On the other hand, in step 240, the ECU 60 prohibits fresh air introduction. That is, the ECU 60 fully closes the EGR valve 24 in the valve open state. At this time, the ECU 60 can, for example, close the EGR valve 24 at a predetermined constant speed, or change the valve closing speed of the EGR valve 24 on the way. Thereafter, the ECU 60 returns the process to step 200.

  Here, FIG. 8 is a graph showing the relationship between various parameters by the above-described fresh air introduction control and fresh air introduction restriction control. This graph shows the relationship of (a) EGR valve opening, (b) EGR gas flow rate, and (c) fresh air introduction amount with respect to engine load KL. In this graph, the opening of the EGR valve 24 is permitted in the range of the load k1 to the load k7 as indicated by the arrow R1. The conventional opening of the EGR valve is permitted in the range of the load k1 to the load k2 indicated by the arrow R2 and the altitude correction range indicated by the broken line arrow R3. The supercharging region of the engine 1 is implemented in the range of the load k4 to the load k8 as indicated by the arrow R4. As indicated by an arrow R5, a high load region is indicated between the load k7 and the load k8. As indicated by arrows R6 and R7, the boundary at which the supercharging pressure (intake pressure PM) becomes larger than the exhaust pressure PMex is the load k5.

  As shown in FIG. 8A, the EGR valve opening changes as the engine load KL increases. That is, the EGR valve 24 is fully closed in a light load region lower than the load k1, increases between the load k1 and the load k5 until it is fully opened, and maintains the full open, and gradually increases between the loads k5 and k7. Opening decreases. Conventionally, as indicated by a broken line in FIG. 8A, the EGR valve is closed from fully open to fully closed between the load k3 and the load k4. On the other hand, in this embodiment, the EGR valve 24 is fully opened even between the load k3 and the load k5. Here, the reason why the EGR valve 24 is kept open even when the engine load KL reaches the value of the supercharging region that should be closed is to allow the fresh air to flow back through the EGR passage 22. With this, it is possible to give a range corresponding to a change in environmental conditions (such as atmospheric pressure) in the determination of the fresh air region. In addition, this makes it possible to execute EGR to the maximum extent until the fresh air region. Further, the determination of the fresh air region is deviated by the difference in the engine load KL and the engine rotation speed NE. For this reason, if the EGR valve 24 is opened within the EGR region and the EGR valve 24 is closed outside the EGR region, the judgment criterion for the fresh air region must be switched depending on the engine load KL and the engine rotational speed NE. I will have to. Moreover, when the individual difference of the EGR valve 24 is considered, the range (high load side) in which the EGR valve 24 is opened becomes narrow. Therefore, in this embodiment, as shown in FIG. 8A, the EGR valve 24 is not closed even when the engine load KL becomes a value in the supercharging region (load k3 to load k5).

  As shown in FIGS. 8B and 8C, the EGR gas flow rate and the fresh air introduction amount vary depending on the relationship between the opening and closing of the EGR valve 24 and the supercharging region. That is, in the light load region lower than the load k1, the EGR gas flow rate becomes zero, and the EGR gas flow rate increases or decreases between the load k1 and the load k5. Conventionally, as indicated by a broken line in FIG. 8B, the EGR gas flow rate has decreased toward zero between the load k3 and the load k4. On the other hand, in this embodiment, the EGR gas flow rate can be obtained even between the load k3 and the load k5. On the other hand, as shown in FIG. 8C, the fresh air introduction amount increases or decreases between the load k5 and the load k7. The reason why the introduction of fresh air is cut off in the high load range of the load k7 or more is to secure the intake air amount required by the engine 1 in the high load range.

  According to the exhaust purification device for an engine system in this embodiment described above, the exhaust discharged from the engine 1 to the exhaust passage 3 is purified by the front catalyst 10 and the rear catalyst 11. Here, after the front catalyst 10 and the rear catalyst 11 are warmed up, fresh air is introduced into the exhaust passage 3 behind the rear catalyst 11 from the intake passage 2 via the EGR passage 22 and the EGR valve 24. High-temperature unburned components that have passed through the rear catalyst 11 without being purified by the front catalyst 10 and the rear catalyst 11 undergo an oxidation reaction with the introduced fresh air. That is, high-temperature unburned components react with fresh air and burn. Here, in order to purify unburned components that have passed through the post-catalyst 11, unlike the conventional example, an air supply pump, an ozone generator, and an HC adsorbent are not provided, and the EGR passage 22 and the fresh air introduction means are provided. An EGR device 21 including an EGR valve 24 is used. For this reason, after the front catalyst 10 and the rear catalyst 11 are warmed up, the unburned components that have passed through the rear catalyst 11 can be oxidized and purified with a relatively simple configuration. As a result, the exhaust emission of the engine 1 can be improved.

  According to the configuration of this embodiment, due to the arrangement of the EGR inlet 22a with respect to the downstream cone portion 11b of the rear catalyst 11, the contact time between the fresh air introduced into the downstream cone portion 11b and the exhaust gas flowing out from the rear catalyst 11 is long. And fresh air flows along the inner periphery of the downstream cone portion 11b and turns. For this reason, mixing of a high temperature unburned component and fresh air can be accelerated | stimulated. As a result, unburned components can be effectively oxidized and purified. In the rear catalyst 11, the EGR inlet 22a is connected to the downstream cone portion 11b at a position closer to the top side. For this reason, even if condensed water is generated in the rear catalyst 11, it is possible to prevent the condensed water from entering the EGR inlet 22a.

  According to the EGR device 21 of this embodiment, the intake pressure PM in the intake passage 2 (intake manifold 8) near the EGR outlet 22b is the exhaust pressure PMex in the exhaust passage 3 (downstream cone portion 11b) in the vicinity of the EGR inlet 22a. When it becomes lower, the EGR valve 24 is opened, so that EGR gas flows from the exhaust passage 3 to the intake passage 2 through the EGR passage 22 and the EGR valve 24. On the other hand, since the EGR passage 22 and the EGR valve 24 are used as fresh air introduction means, when the intake pressure (supercharging pressure) PM becomes higher than the exhaust pressure PMex, the EGR valve 24 is opened, thereby Fresh air is introduced from the passage 2 into the exhaust passage 3 behind the rear catalyst 11 via the EGR passage 22 and the EGR valve 24. Therefore, it is not necessary to provide a dedicated configuration for introducing fresh air into the exhaust passage 3 behind the rear catalyst 11. For this reason, in order to introduce fresh air into the exhaust passage 3 behind the rear catalyst 11, it is not necessary to separately provide a dedicated configuration or a dedicated space, and the cost of the engine system can be suppressed.

  According to the configuration of this embodiment, when the intake pressure PM is lower than the exhaust pressure PMex, the EGR valve 24 is controlled to open according to the operating state of the engine 1 by the ECU 60 in order to flow EGR gas into the intake passage 2. Is done. On the other hand, when the intake pressure PM is higher than the exhaust pressure PMex, the EGR valve 24 is controlled to open by the ECU 60 in order to introduce fresh air into the exhaust passage 3 behind the rear catalyst 11. When the intake pressure PM is switched from a state lower than the exhaust pressure PMex to a higher state, the EGR valve 24 in the valve open state is maintained and controlled by the ECU 60 while being in the valve open state. Therefore, when switching from the state in which the EGR gas flows into the intake passage 2 to the state in which the fresh air is introduced into the exhaust passage 3, the EGR valve 24 is not closed once, so the EGR region in which the EGR gas flows into the intake passage 2 It can be expanded to the upper limit. In this embodiment, as shown in FIG. 8, since the EGR valve 24 is set to open to the supercharging region, the EGR enabling condition (intake pressure PM <exhaust pressure) due to environmental changes (atmospheric pressure, etc.) Even if PMex) changes, it is automatically switched to introduction of fresh air without determining a fresh air region. For this reason, effects such as fuel consumption reduction and NOx reduction by EGR gas can be exhibited to the maximum extent.

  According to the configuration of this embodiment, when the intake pressure PM is lower than the exhaust pressure PMex, the EGR valve 24 is controlled to open according to the operating state of the engine 1 by the ECU 60 in order to flow EGR gas into the intake passage 2. Is done. On the other hand, when the intake pressure PM is higher than the exhaust pressure PMex and unburned components in the exhaust discharged from the engine 1 increase, fresh air is introduced into the exhaust passage 3 behind the rear catalyst 11. Further, the EGR valve 24 is controlled to be opened by the ECU 60. For example, when the engine 1 is operating at a high load, the fuel injection amount supplied to the engine 1 by the fuel injection control is increased and corrected in order to prevent overheating of the front catalyst 10 and the rear catalyst 11 and to suppress knocking of the engine 1. Unburned components in the exhaust may increase. Also in this case, the EGR valve 24 is controlled to open and fresh air is introduced into the exhaust passage 3 behind the rear catalyst 11. Therefore, even when the amount of unburned components passing through the post-catalyst 11 increases, the high temperature unburned components react with the introduced fresh air and are oxidized and purified. For this reason, the unburned components increased in the exhaust can be effectively oxidized and purified, and deterioration of exhaust emission can be suppressed.

  In this embodiment, as shown in FIG. 8, the introduction of fresh air into the exhaust passage 3 is stopped in the high supercharging region of the engine 1, that is, the high load region. For this reason, in the high load region, it is possible to suppress a decrease in supercharging efficiency by the supercharger 5 and to prevent a decrease in the output of the engine 1.

Second Embodiment
Next, a second embodiment of the engine system exhaust gas purification apparatus according to the present invention will be described in detail with reference to the drawings.

  In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. Hereinafter, different points will be mainly described.

  As described above, in this exhaust purification device, in the fresh air region, a part of the intake air flowing through the intake passage 2 is introduced as fresh air into the exhaust passage 3 behind the rear catalyst 11. For this reason, the intake air smaller than the intake air amount Ga detected by the air flow meter 53 is supplied to the engine 1. As a result, if the detected intake air amount Ga is used as it is in fuel injection control, the air-fuel ratio of the engine 1 shifts to rich, and exhaust emission and fuel consumption may be deteriorated. Therefore, in this embodiment, the intake air amount Ga used for various engine controls such as fuel injection control is corrected. In this embodiment, the ECU 60 corresponds to an example of the intake air amount calculation means of the present invention.

  FIG. 9 is a flowchart showing the contents of the exhaust purification control. In FIG. 9, the contents of steps 100 to 140 are the same as those in the flowchart of FIG. When the processing shifts to this routine, the ECU 60 executes the processing of step 100 to step 130, and then sets the intake air amount Ga detected by the air flow meter 53 as the final intake air amount GA in step 150. The ECU 60 stores the final intake air amount GA in the memory, and then returns the process to step 100.

  On the other hand, in step 160 after shifting from step 140, the ECU 60 obtains the fresh air introduction differential pressure ΔPM by subtracting the exhaust pressure PMex from the intake pressure PM.

  Next, at step 170, the ECU 60 determines a fresh air introduction amount Gaex based on the fresh air introduction differential pressure ΔPM and the target EGR opening degree Tegr. The ECU 60 can obtain the fresh air introduction amount Gaex according to the fresh air introduction differential pressure ΔPM and the target EGR opening degree Tegr, for example, by referring to the fresh air introduction amount map shown in FIG.

  Next, in step 180, the ECU 60 obtains an engine supply intake air amount Gaeng supplied to the engine 1 by subtracting the fresh air introduction amount Gaex from the intake air amount Ga detected by the air flow meter 53.

  In step 190, the ECU 60 sets the engine supply intake air amount Gaeng as the final intake air amount GA. The ECU 60 stores the final intake air amount GA in the memory, and then returns the process to step 100.

  According to the exhaust purification device for an engine system of this embodiment described above, when fresh air is introduced from the intake passage 2 into the exhaust passage 3 behind the rear catalyst 11, the engine actually taken into the engine 1 correspondingly. The intake air amount becomes smaller than the intake air amount Ga detected by the air flow meter 53. Here, fresh air introduced into the exhaust passage 3 based on the exhaust pressure PMex calculated by the ECU 60, the intake pressure PM detected by the intake pressure sensor 54, and the target EGR opening degree Tegr calculated by the ECU 60. The introduction amount Gaex is calculated. Further, the final intake air amount GA which is the engine intake air amount is calculated by subtracting the fresh air introduction amount Gaex from the detected intake air amount Ga. Therefore, even when fresh air is introduced from the intake passage 2 into the exhaust passage 3 behind the rear catalyst 11, a final intake amount GA that can be used for various controls of the engine 1 is obtained. Further, in order to obtain the final intake air amount GA, it is not necessary to provide a dedicated detection means for detecting the exhaust pressure PMex. For this reason, even when fresh air is introduced from the intake passage 2 into the exhaust passage 3 behind the rear catalyst 11 during operation of the engine 1, various engines are used based on the final intake amount GA that is actually supplied to the engine 1. Control can be executed properly. For example, erroneous control of the engine 1 that miscalculates the air-fuel ratio to the rich side can be avoided. As a result, the exhaust emission of the engine 1 and the deterioration of fuel consumption can be prevented.

<Third Embodiment>
Next, a third embodiment of the engine system exhaust gas purification apparatus according to the present invention will be described in detail with reference to the drawings.

  This embodiment is different from the above embodiments in terms of the contents of fresh air introduction control. FIG. 11 is a flowchart showing the contents of the fresh air introduction control of this embodiment.

  When the process proceeds to this routine, in step 300, the ECU 60 determines the engine speed NE, the intake air amount Ga, the engine load KL, the coolant temperature THW, the intake pressure PM, and the throttle opening based on the detection values of the various sensors 51-56. The degree TA is taken in, and the target EGR opening degree Tegr obtained by separate EGR control is taken in.

  Next, at step 310, the ECU 60 takes in the atmospheric pressure PA based on the detection value of the atmospheric pressure sensor 57.

  Next, at step 320, the ECU 60 obtains an engine load determination value Kakl based on the engine speed NE. As an example, the ECU 60 can obtain the engine load determination value Kakl corresponding to the engine speed NE by referring to the engine load determination value map shown in FIG. As shown by a broken line (thick broken line, broken line) in FIG. 12, the engine load determination value Kakl serving as the boundary between the fresh air region and the EGR region varies depending on the difference between the flat ground and the highland, that is, the difference in the atmospheric pressure PA.

  Next, at step 330, the ECU 60 determines an atmospheric pressure correction value Kpakl of the engine load KL based on the atmospheric pressure PA. As an example, the ECU 60 can obtain the atmospheric pressure correction value Kpakl proportional to the atmospheric pressure PA by referring to the atmospheric pressure correction value map shown in FIG.

  Next, in step 340, the ECU 60 determines whether or not the engine load KL is smaller than the result obtained by subtracting and correcting the atmospheric pressure correction value Kpakl from the engine load determination value Kakl. The atmospheric pressure correction value Kpakl is subtracted and corrected from the engine load determination value Kakl as shown by a broken line (thick broken line, broken line) in FIG. It is because it changes according to. If the determination result is affirmative, the ECU 60 proceeds to step 350. If the determination result is negative, the ECU 60 proceeds to step 360.

  In step 350, the ECU 60 determines that the region is the EGR region, permits EGR control, and then returns the process to step 300.

  On the other hand, in step 360, the ECU 60 determines that it is in the fresh air region, and opens the EGR valve 24 in order to introduce fresh air to the rear of the rear catalyst 11. Here, the ECU 60 can appropriately control the opening degree of the EGR valve 24 as necessary. Thereafter, the ECU 60 returns the process to step 300.

  According to the exhaust gas purification apparatus of the engine system in this embodiment described above, the engine speed of various parameters detected by various sensors 51 to 56 in order to determine the fresh air region in the fresh air introduction control. In addition to NE and engine load KL, atmospheric pressure PA detected by atmospheric pressure sensor 57 is used. For this reason, the determination of the fresh air region can be corrected according to the atmospheric pressure PA that changes depending on the altitude, and the determination accuracy can be improved. Further, the atmospheric pressure PA detected by the atmospheric pressure sensor 57 can be used for general purposes in control other than the fresh air introduction control.

<Fourth embodiment>
Next, a fourth embodiment of the engine system exhaust gas purification apparatus according to the present invention will be described in detail with reference to the drawings.

  FIG. 14 shows a schematic configuration diagram of the gasoline engine system of this embodiment. In this embodiment, the gasoline engine system includes the evaporated fuel processing device (including the canister 32) 30 for processing the evaporated fuel (vapor) generated in the fuel tank 31. Different. In this embodiment, the ECU 60 corresponds to an example of a control unit and a purge control unit of the present invention.

  As shown in FIG. 14, the evaporated fuel processing device 30 collects and processes the vapor generated in the fuel tank 31 without releasing it into the atmosphere. The apparatus 30 includes a canister 32 that temporarily collects vapor generated in the fuel tank 31 through a vapor passage 33. The canister 32 contains an adsorbent (not shown) that adsorbs vapor. The upstream purge passage 34 extending from the canister 32 is connected to the first downstream purge passage 35 connected to the intake passage 2 downstream of the throttle device 7 and the intake passage 2 between the air cleaner 4 and the compressor 5a. 2 branches to the downstream purge passage 36. A purge pump 37 and a purge control valve 38 are provided in the upstream purge passage 34. The purge pump 37 sucks vapor from the canister 32 and discharges it to the upstream purge passage 34. The purge control valve 38 adjusts the vapor flow rate in the upstream purge passage 34. A first check valve 39 is provided in the first downstream purge passage 35. A second check valve 40 is provided in the second downstream purge passage 36. In this embodiment, the upstream purge passage 34, the first downstream purge passage 35, the second downstream purge passage 36, the purge pump 37, and the purge control valve 38 correspond to an example of the purge means of the present invention.

  According to the fuel vapor processing apparatus 30 described above, when the engine 1 is operated, the intake negative pressure generated in the intake passage 2 downstream from the throttle valve 7a acts on the canister 32 through the first downstream purge passage 35 and the like. The air containing the vapor collected in the canister 32 is purged to the intake passage 2 downstream from the throttle valve 7a through the upstream purge passage 34 and the first downstream purge passage 35. The air containing the purged vapor is taken into the engine 1 for combustion and processed. A purge control valve 38 provided in the upstream purge passage 34 is controlled by the ECU 60 in order to adjust the vapor purge flow rate in the upstream purge passage 34. A fuel passage 41 extending from the fuel tank 31 pumps fuel to an injector (not shown) provided in the engine 1 by the action of a fuel pump 42 provided in the fuel tank 31. The atmospheric port 43 provided in the canister 32 introduces atmospheric air into the canister 32 when vapor or the like is purged from the canister 32 through the upstream purge passage 34. In this embodiment, the ECU 60 controls the purge pump 37 and the purge control valve 38 in order to execute the evaporated fuel processing control. In this embodiment, the ECU 60 corresponds to an example of the purge control means of the present invention.

  FIG. 15 is a flowchart showing the contents of the fresh air introduction restriction control of this embodiment. When the process proceeds to this routine, in step 400, the ECU 60 determines whether or not there is a fresh air region determination. For example, it is determined whether or not a fresh air region has been determined in the fresh air introduction control shown in FIG. If this determination result is affirmative, the ECU 60 proceeds to step 410, and if this determination result is negative, the ECU 60 returns the process to step 400.

  In step 410, the ECU 60 takes in the intake air amount Ga based on the detection value of the air flow meter 53.

  Next, at step 420, the ECU 60 takes in the vapor concentration Fgpg determined by the separate evaporated fuel processing control. The vapor concentration Fgpg corresponds to the vapor concentration calculated per unit target purge rate based on, for example, a feedback correction coefficient shift (air-fuel ratio shift) in air-fuel ratio control that occurs when the vapor is purged.

  Next, at step 430, the ECU 60 obtains an intake air amount (new air introduction permission intake amount) Kgapg at the time of new air introduction permission based on the vapor concentration Fgpg. The ECU 60 can obtain the fresh air introduction permission intake air amount Kgapg corresponding to the vapor concentration Fgpg, for example, by referring to the fresh air introduction permission intake air amount map shown in FIG. In this map, the fresh air introduction permission intake air amount Kgapg is set to increase in a curve as the vapor concentration Fgpg increases.

  Next, in step 440, the ECU 60 determines whether or not the intake air amount Ga is greater than the fresh air introduction permission intake air amount Kgapg. If this determination result is affirmative, the ECU 60 proceeds to step 450, and if this determination result is negative, the ECU 60 proceeds to step 460.

  In step 450, the ECU 60 permits introduction of fresh air. That is, the ECU 60 maintains the opened EGR valve 24 in the opened state. Thereafter, the ECU 60 returns the process to step 400.

  On the other hand, in step 460, the ECU 60 prohibits fresh air introduction. That is, the ECU 60 fully closes the opened EGR valve 24. Thereafter, the ECU 60 returns the process to step 400.

  According to the exhaust purification device for an engine system in this embodiment described above, in addition to the actions and effects of the above-described embodiments, the following actions and effects are obtained. That is, when fresh air is introduced into the exhaust passage 3 behind the rear catalyst 11, the purge control valve 38 is controlled by the ECU 60 in order to purge the vapor. Therefore, in addition to the normal exhaust gas discharged from the engine 1 to the exhaust passage 3, a part of the vapor is discharged from the engine 1 to the exhaust passage 3 as unburned components and cannot be completely purified by the front catalyst 10 and the rear catalyst 11 Even after passing through the catalyst 11, the high-temperature unburned components react with the introduced fresh air and are oxidized and purified. For this reason, in addition to preventing the exhaust emission and fuel consumption of the engine 1 from deteriorating, it is also possible to prevent the deterioration of the evaporation emitted to the atmosphere.

  According to the configuration of this embodiment, fresh air is positively introduced behind the rear catalyst 11 even in the supercharging region to oxidize and purify unburned components and improve exhaust emission. However, when supercharging is performed in the low rotation region (low intake air amount region) of the engine 1, high-concentration vapor may be purged into the intake passage 2, and the air-fuel ratio of the intake air may become richer than the stoichiometric air. Therefore, in this embodiment, when the air-fuel ratio of the intake air becomes richer than the stoichiometric due to the purge of the vapor, in order to prohibit the introduction of fresh air into the exhaust passage 3 behind the rear catalyst 11, the ECU 60 The EGR valve 24 is controlled to close.

<Fifth Embodiment>
Next, a fifth embodiment of the engine system exhaust gas purification apparatus according to the present invention will be described in detail with reference to the drawings.

  In this embodiment, when fresh air is introduced into the exhaust passage 3 behind the rear catalyst 11, the purge flow rate is limited according to the vapor concentration as the vapor is purged from the canister 32 to the intake passage 2. This is different from the fourth embodiment. FIG. 17 is a flowchart showing the contents of the purge flow rate restriction control of this embodiment.

  When the processing shifts to this routine, in step 500, the ECU 60 determines the engine speed NE, the intake air amount Ga, the engine load KL, the coolant temperature THW, the intake pressure PM, and the throttle opening based on the detection values of the various sensors 51-56. The degree TA is taken in, and the target EGR opening degree Tegr obtained by separate EGR control is taken in. Further, the ECU 60 takes in the vapor concentration Fgpg determined by the separate evaporated fuel processing control.

  Next, in step 510, the ECU 60 determines a target purge flow rate Tevp. For example, the ECU 60 can obtain the target purge flow rate Tevp based on the intake air amount Ga.

  Next, in step 520, the ECU 60 determines whether or not there is a fresh air region determination. The ECU 60 proceeds to step 530 if the determination result is affirmative, and proceeds to step 560 if the determination result is negative.

  In step 530, the ECU 60 obtains a maximum purge flow rate Kpgmax based on the vapor concentration Fgpg and the intake air amount Ga. For example, the ECU 60 can obtain the maximum purge flow rate Kpgmax corresponding to the intake air amount Ga and the vapor concentration Fgpg by referring to the maximum purge flow rate map shown in FIG. In this map, the maximum purge flow rate Kpgmax is set to be proportional to the intake air amount Ga and to increase as the vapor concentration Fgpg decreases.

  Next, in step 540, the ECU 60 determines whether or not the target purge flow rate Tevp is less than the maximum purge flow rate Kpgmax. The ECU 60 proceeds to step 550 when the determination result is negative, and proceeds to step 560 when the determination result is affirmative.

  In step 550, since the target purge flow rate Tevp exceeds the maximum purge flow rate Kpgmax, the ECU 60 sets the maximum purge flow rate Kpgmax as the target purge flow rate Tevp, and the process proceeds to step 560.

  In step 560 after the transition from step 520, step 540 or step 550, the ECU 60 sets the target purge flow rate Tevp as the final target purge flow rate TEVP.

  Then, in step 570 after the transition from step 560, the ECU 60 controls the purge control valve 38 to the final target purge flow rate TEVP, and then returns the process to step 500. Thereby, the purge flow rate purged into the intake passage 2 is adjusted. Here, when the target purge flow rate Tevp is set to the maximum purge flow rate Kpgmax, the purge flow rate is limited to the maximum purge flow rate Kpgmax.

  According to the exhaust purification device for an engine system in this embodiment described above, when the air-fuel ratio of the intake air becomes richer than the stoichiometry due to vapor purge, the maximum purge flow rate at which the vapor purge flow rate is a predetermined upper limit value The purge control valve 38 is controlled by the ECU 60 so as to be limited to Kpgmax.

<Sixth Embodiment>
Next, a sixth embodiment of the engine system exhaust gas purification apparatus according to the present invention will be described in detail with reference to the drawings.

  In this embodiment, the configuration is different from those of the above embodiments in terms of the connection position of the EGR passage 22 with respect to the rear catalyst 11. FIG. 19 schematically shows the gasoline engine system of this embodiment. As shown in FIG. 19, in this embodiment, when the operation of the engine 1 is in the supercharging region, the EGR of the EGR passage 22 is assumed on the assumption that the temperature of the exhaust gas flowing out from the rear catalyst 11 becomes relatively high. The inlet 22 a is connected to the exhaust passage 3 at a position behind the rear catalyst 11 and away from the rear catalyst 11.

  Therefore, according to the configuration of this embodiment, even when the temperature of the exhaust gas flowing out from the rear catalyst 11 in the supercharging region is relatively high, the position at which fresh air is introduced from the EGR inlet 22a to the exhaust passage 3 Therefore, the temperature of the post-catalyst 11 does not increase excessively due to the oxidation reaction with fresh air. For this reason, the post-catalyst 11 can be kept at an allowable temperature.

<Seventh embodiment>
Next, a seventh embodiment of the engine system exhaust gas purification apparatus according to the present invention will be described in detail with reference to the drawings.

  This embodiment differs from the sixth embodiment in terms of the position of the rear catalyst 11 in the exhaust passage 3 and the connection position of the EGR passage 22. FIG. 20 schematically shows the gasoline engine system of this embodiment. As shown in FIG. 20, in this embodiment, the front catalyst 10 is disposed near the engine 1, and the rear catalyst 11 is disposed away from the engine 1. And even when the operation of the engine 1 is in the supercharging region, the EGR inlet 22a of the EGR passage 22 is located behind the rear catalyst 11 assuming that the temperature of the exhaust gas flowing out from the rear catalyst 11 is relatively low. Then, it is connected to the exhaust passage 3 at a position close to the rear catalyst 11.

  Therefore, according to the configuration of this embodiment, even when the temperature of the exhaust gas flowing out from the rear catalyst 11 in the supercharging region is relatively low, the position at which fresh air is introduced from the EGR inlet 22a to the exhaust passage 3 is the rear catalyst. Therefore, fresh air tends to flow into the rear catalyst 11. The fresh air flows into the rear catalyst 11 because pulsation is generated in the exhaust in the exhaust passage 3. When fresh air flows into the rear catalyst 11, unburned components are reduced by the oxidation reaction. Since the oxidation reaction at the catalyst occurs at a relatively low temperature, even if the temperature of the exhaust gas flowing out from the rear catalyst 11 is relatively low, unburned components can be reduced by the oxidation reaction by introducing fresh air. Further, since the temperature of the post-catalyst 11 is relatively low, the post-catalyst 11 can be kept at an allowable temperature even if the temperature of the post-catalyst 11 is increased due to the oxidation reaction.

<Eighth Embodiment>
Next, an eighth embodiment of the exhaust purification device for an engine system according to the present invention will be described in detail with reference to the drawings.

  This embodiment is different from the above embodiments in terms of the configuration relating to the EGR inlet of the EGR passage 22. FIG. 21 schematically shows the gasoline engine system of this embodiment. As shown in FIG. 21, in this embodiment, the upstream side of the EGR passage 22 branches into a first upstream EGR passage 22A and a second upstream EGR passage 22B, and a three-way valve 29 is provided at the branch portion. The first upstream EGR passage 22A includes an EGR inlet 22a, and the second upstream EGR passage 22B includes another EGR inlet 22c. The EGR inlet 22 a is connected to the exhaust passage 3 at a position behind the rear catalyst 11 and close to the rear catalyst 11. Another EGR inlet 22 c is connected to the exhaust passage 3 at a position near the front catalyst 10 in front of the front catalyst 10. The three-way valve 29 is an electromagnetic valve, and is controlled to be switched by the ECU 60 in order to selectively communicate the downstream side of the EGR passage 22 with the first upstream EGR passage 22A or the second upstream EGR passage 22B. It has become. In this embodiment, the ECU 60 switches the three-way valve 29 to connect the downstream EGR passage 22 to the first upstream EGR passage 22A when the supercharging pressure in the supercharging region becomes relatively high. On the other hand, the ECU 60 switches the three-way valve 29 to connect the downstream EGR passage 22 to the second upstream EGR passage 22B except when the supercharging pressure is relatively high.

  Therefore, according to the configuration of this embodiment, when the supercharging pressure becomes relatively high, fresh air can be introduced behind the rear catalyst 11, and the same effect as that of the first embodiment can be obtained. be able to. In cases other than the case where the supercharging pressure becomes relatively high, the EGR gas is taken into the second upstream EGR passage 22B from the EGR inlet 22c, and the EGR gas flows smoothly into the downstream EGR passage 22. be able to.

<Ninth Embodiment>
Next, a ninth embodiment of the engine system exhaust gas purification apparatus according to the present invention will be described in detail with reference to the drawings.

  In this embodiment, the configurations of the EGR device 21 and the fresh air introducing means are different from those of the above embodiments. FIG. 22 schematically shows the gasoline engine system of this embodiment. As shown in FIG. 22, this embodiment includes an LPL type EGR device 21. That is, the EGR passage 22 provided with the EGR cooler 23 and the EGR valve 24 has its EGR inlet 22 a connected to the exhaust passage 3 between the front catalyst 10 and the rear catalyst 11, and the EGR outlet 22 b from the air cleaner 4. It is connected to the intake passage 2 downstream and upstream from the compressor 5a. The fresh air introduction means for introducing fresh air into the exhaust passage 3 behind the rear catalyst 11 includes a fresh air introduction passage 46 and a flow control valve 47. The fresh air introduction passage 46 includes a fresh air inlet 46 a for taking in fresh air from the intake passage 2 and a fresh air outlet 46 b for deriving fresh air to the exhaust passage 3. The fresh air inlet 46a is connected to the intake passage 2 immediately after the compressor 5a, and the fresh air outlet 46b is connected to the exhaust passage 3 behind the rear catalyst 11. Since the fresh air inlet 46a is arranged immediately after the compressor 5a, relatively hot fresh air is introduced to the rear of the rear catalyst 11 via the fresh air introduction passage 46 and the flow rate control valve 47. The flow rate control valve 47 is composed of an electromagnetic valve and is controlled to be opened and closed by the ECU 60 in order to control the flow of fresh air in the fresh air introduction passage 46. Since the EGR device 21 of this embodiment is an LPL type, fresh air cannot be introduced into the exhaust passage 3 through the EGR passage 22 during supercharging when the supercharger 5 operates. Therefore, a dedicated fresh air introduction passage 46 that can introduce fresh air into the exhaust passage 3 even during supercharging is provided, and the fresh air flowing through the passage 46 is adjusted by the flow control valve 47.

  Therefore, according to the configuration of this embodiment, fresh air can be introduced into the exhaust passage 3 behind the rear catalyst 11 even in the gasoline engine system including the LPL type EGR device 21. For this reason, after the front catalyst 10 and the rear catalyst 11 are warmed up, the unburned components that have passed through the rear catalyst 11 can be oxidized and purified with a relatively simple configuration. As a result, the exhaust emission of the engine 1 can be improved.

<Tenth Embodiment>
Next, a tenth embodiment embodying the exhaust purification system for an engine system according to the present invention will be described in detail with reference to the drawings.

  This embodiment is different from the above embodiments in terms of how the EGR passage 22 is connected to the rear catalyst 11. FIG. 23 is a side sectional view schematically showing the rear catalyst 11 in the exhaust passage 3. As shown in FIG. 23, in this embodiment, fresh air introduced from the EGR inlet 22a of the EGR passage 22 into the exhaust passage 3 (downstream conical portion 11b) behind the rear catalyst 11 flows out of the rear catalyst 11. The EGR inlet 22 a is disposed toward the end face of the rear catalyst 11.

  Therefore, according to the configuration of this embodiment, the fresh air introduced from the EGR inlet 22a into the exhaust passage 3 (downstream cone portion 11b) easily collides with the high-temperature unburned components that have passed through the rear catalyst 11. For this reason, mixing of a high temperature unburned component and fresh air can be accelerated | stimulated. As a result, unburned components can be effectively oxidized and purified.

<Eleventh embodiment>
Next, an eleventh embodiment that embodies an exhaust purification system for an engine system according to the present invention will be described in detail with reference to the drawings.

  In this embodiment, the configuration is different from the above-described embodiments in terms of the configuration of the EGR valve used in the EGR device 21. FIG. 24 is a sectional view showing the EGR valve 26 of this embodiment. As shown in FIG. 24, the EGR valve 26 is a poppet type, and includes a valve seat 62 provided in the housing 61, a valve body 63 provided so as to be seatable on the valve seat 62, and a valve seat 62. A valve shaft 64 for opening and closing the body 63, an actuator 65 for reciprocating the valve shaft 64 (stroke motion), and a valve closing that urges the valve body 63 in a direction to seat (close) the valve seat 62 And a spring 66.

  In each of the above embodiments, when the intake pressure PM becomes lower than the exhaust pressure PMex, the EGR valve 24 is controlled to open in order to flow the EGR gas into the intake passage 2, and the intake pressure PM (supercharging pressure) is set to the exhaust pressure PMex. When higher, the EGR valve 24 is controlled to be opened in order to introduce fresh air into the exhaust passage 3 (downstream conical portion 11b) behind the rear catalyst 11. On the other hand, in this embodiment, when the intake pressure PM (supercharging pressure) becomes higher than the exhaust pressure PMex, the EGR valve 26 is controlled to close in the same manner as the normal EGR control. Instead, the EGR valve 26 is mechanically opened at a predetermined condition by adjusting the urging force of the valve closing spring 66 that urges the valve body 63 of the EGR valve 26 in the valve closing direction. Here, “mechanically opening the valve” means that the differential pressure between the intake pressure (supercharging pressure) PM and the exhaust pressure PMex and the mechanical backlash of the valve body 63 are not controlled without opening the EGR valve 26. This means that the valve is opened by forming a gap between the valve body 63 and the valve seat 62.

  Therefore, according to the configuration of this embodiment, as in the above embodiments, when the intake pressure PM (supercharging pressure) becomes higher than the exhaust pressure PMex, and after the front catalyst 10 and the rear catalyst 11 are warmed up, Since fresh air is introduced into the exhaust passage 3 (downstream conical portion 11b) behind the rear catalyst 11 from the intake passage 2 via the EGR passage 22 and the EGR valve 24, high-temperature unburned gas that has passed through the rear catalyst 11 Ingredients react with fresh air. For this reason, the unburned components that have passed through the rear catalyst 11 after the warm-up of the front catalyst 10 and the rear catalyst 11 can be oxidized and purified with a relatively simple configuration. As a result, the exhaust emission of the engine 1 can be improved.

<Twelfth embodiment>
Next, a twelfth embodiment that embodies an exhaust purification system for an engine system according to the present invention will be described in detail with reference to the drawings.

  This embodiment differs from the seventh embodiment in the configuration of the EGR valve. FIG. 25 is a sectional view showing the EGR valve 28 of this embodiment. As shown in FIG. 25, the EGR valve 28 is a butterfly type, and a valve seat 72 provided in the housing 71, a valve body 73 provided so as to be seatable on the valve seat 72, and the valve seat 72 are valved In order to press the valve body 73 against the valve seat 72 in the fully closed state, a rotation shaft 74 that rotates the valve body 73 to open and close the body 73, a drive mechanism 75 that rotates the rotation shaft 74, and And a biasing device 77 including a spring 76 that biases the rotating shaft 74 in the diametrical direction thereof.

  In this embodiment, as in the seventh embodiment, when the intake pressure PM (supercharging pressure) is higher than the exhaust pressure PMex, the EGR valve 28 is controlled to be closed in the same manner as in the normal EGR control. . Instead, in the fully closed state, the EGR valve 28 is mechanically opened at a predetermined condition by adjusting the urging force of the spring 76 that urges the rotating shaft 74 in the diameter direction.

  Therefore, even with the configuration of this embodiment, the same operations and effects as those of the seventh embodiment can be obtained.

<13th Embodiment>
Next, a thirteenth embodiment that embodies an exhaust purification system for an engine system according to the present invention will be described in detail with reference to the drawings.

  This embodiment is different from the above embodiments in terms of the configuration of the fresh air introducing means. FIG. 26 is a side sectional view schematically showing the fresh air introduction device 81 and the rear catalyst 11 in the exhaust passage 3. In this embodiment, in order to introduce fresh air into the exhaust passage 3 behind the rear catalyst 11, a fresh air introduction device 81 is provided instead of using the EGR passage 22 and the EGR valve 24. The device 81 includes a fresh air passage 82 connected to the exhaust passage 3 (downstream conical portion 11 b), a check valve 83, an air pump 84, and an air cleaner 85 provided in series in the passage 82. According to this device 81, when the air pump 84 operates, the outside air purified by the air cleaner 85 is introduced as fresh air into the fresh air passage 82, and the exhaust passage behind the rear catalyst 11 via the check valve 83. 3 is introduced. The arrangement of the fresh air outlet 82a in the fresh air passage 82 is the same as that of the EGR inlet 22a in the first embodiment. The check valve 83 regulates the backflow of exhaust from the exhaust passage 3. In this embodiment, the fresh air introduction device 81 corresponds to an example of the fresh air introduction means of the present invention.

  Therefore, according to the configuration of this embodiment, fresh air is introduced into the exhaust passage 3 behind the rear catalyst 11 by operating the air pump 84 when the engine 1 is in operation and after the rear catalyst 11 is warmed up. It reacts with the high-temperature unburned components that have passed through the post-catalyst 11. For this reason, the unburned components that have passed through the rear catalyst 11 after the warm-up of the front catalyst 10 and the rear catalyst 11 can be oxidized and purified with a relatively simple configuration. As a result, the exhaust emission of the engine 1 can be improved.

  Note that the present invention is not limited to the above-described embodiments, and a part of the configuration can be changed as appropriate without departing from the spirit of the invention.

  (1) In each of the above embodiments, the present invention is embodied in a configuration in which the front catalyst 10 and the rear catalyst 11 are provided in series in the exhaust passage 3 and then fresh air is introduced into the exhaust passage 3 behind the catalyst 11. On the other hand, the present invention is embodied in a configuration in which three or more catalysts are provided in series in the exhaust passage, and fresh air is introduced into the exhaust passage behind the catalyst located on the most downstream side. For example, a catalyst may be provided and fresh air may be introduced into the exhaust passage behind the catalyst.

  (2) In each of the above embodiments, the present invention is embodied in a configuration in which the front catalyst 10 and the rear catalyst 11 are provided in series in the exhaust passage 3 and then fresh air is introduced into the exhaust passage 3 behind the catalyst 11. It can also be configured such that fresh air is introduced into both the exhaust passage behind the front catalyst and the exhaust passage behind the rear catalyst.

  (3) In each of the above embodiments, the present invention is embodied in a gasoline engine system, but may be embodied in a diesel engine system.

  The fourth embodiment includes the following inventions (first to third inventions) in relation to the inventions according to claims 3 to 5 of the present application. Appendices.

<First Supplementary Invention>
The engine system includes:
A fuel tank for storing fuel supplied to the engine;
A canister for collecting evaporated fuel generated in the fuel tank;
Purge means for purging the vaporized fuel collected in the canister to the intake passage;
A purge control means for controlling the purge means;
6. The purge control unit according to claim 3, wherein the purge control unit controls the purge unit to purge the evaporated fuel when the fresh air is introduced into the exhaust passage behind the catalyst. An exhaust purification device for an engine system according to any one of the above.

  According to the configuration of the first supplementary invention, in addition to the operation of the invention according to any one of claims 3 to 5, the purge of the evaporated fuel is performed when fresh air is introduced into the exhaust passage behind the catalyst. The purge means is controlled. Therefore, in addition to the normal exhaust discharged from the engine to the exhaust passage, a part of the evaporated fuel is discharged from the engine to the exhaust passage as an unburned component. Unburned components react with the fresh air introduced.

  According to the configuration of the first supplementary invention, in addition to the effect of the invention according to any one of claims 3 to 5, purging can be promoted while preventing deterioration of the exhaust emission of the engine.

<Second Supplementary Invention>
The control means is for prohibiting introduction of the fresh air into the exhaust passage behind the catalyst when the air-fuel ratio of the intake air becomes richer than stoichiometric due to the purge of the evaporated fuel with respect to the intake passage. The exhaust purification device for an engine system according to the first supplementary invention, wherein the exhaust gas recirculation valve is controlled to be closed.

  According to the configuration of the second supplementary invention, in addition to the action of the first supplementary invention, when the air-fuel ratio of the intake air becomes richer than the stoichiometry due to the purge of the evaporated fuel, a new exhaust passage to the exhaust passage behind the catalyst is performed. In order to prohibit the introduction of air, the exhaust gas recirculation valve is controlled to close. Accordingly, it is possible to prevent fresh air containing a fuel component that does not undergo oxidation reaction from being introduced into the exhaust passage behind the catalyst.

  According to the invention described in the second supplementary invention, in addition to the effect of the first supplementary invention, it is possible to effectively prevent the deterioration of the exhaust emission of the engine.

<Third additional invention>
The purge control unit controls the purge unit to limit the purge flow rate of the evaporated fuel to a predetermined upper limit value when the air-fuel ratio of the intake air becomes richer than the stoichiometric due to the purge of the evaporated fuel. An exhaust purification device for an engine system according to the first or second supplementary invention, wherein

  According to the configuration of the third supplementary invention, in addition to the action of the first supplementary invention or the second supplementary invention, when the air-fuel ratio of the intake air becomes richer than the stoichiometric due to the purge of the evaporated fuel, the evaporated fuel The purge means is controlled so that the purge flow rate is limited to a predetermined upper limit value. Therefore, the unburned component due to the evaporated fuel is suppressed to a certain upper limit value.

  According to the configuration of the third supplementary invention, in addition to the effects of the first supplementary invention or the second supplementary invention, it is possible to prevent deterioration of exhaust emission due to excessive purging of the evaporated fuel.

  The present invention can be used for gasoline engine systems and diesel engine systems.

1 Engine 2 Intake passage 3 Exhaust passage 5 Supercharger 10 Pre-catalyst 11 Rear catalyst 22 EGR passage (exhaust gas recirculation passage, fresh air introduction means)
22a EGR inlet (exhaust gas recirculation inlet)
22b EGR outlet (exhaust gas recirculation outlet)
24 EGR valve (exhaust gas recirculation valve, fresh air introduction means)
26 EGR valve (exhaust gas recirculation valve, fresh air introduction means)
28 EGR valve (exhaust gas recirculation valve, fresh air introduction means)
31 Fuel tank 32 Canister 34 Upstream purge passage (purge means)
35 First downstream purge passage (purge means)
36 Second downstream side purge passage (purge means)
37 Purge pump (purge means)
38 Purge control valve (purge means)
53 Air flow meter (intake air amount detection means)
54 Intake pressure sensor (Intake pressure detection means)
60 ECU (control means, intake air amount calculation means, purge control means)
81 Fresh air introduction device (fresh air introduction means)
82 Fresh air passage (fresh air introduction means)
84 Air pump (new air introduction means)

Claims (5)

Provided in an engine system having an intake passage for introducing intake air into the engine and an exhaust passage for deriving exhaust from the engine;
A catalyst for purifying exhaust discharged from the engine to the exhaust passage;
In order to oxidize and purify unburned components that have passed through the catalyst after the catalyst has been warmed up, it is provided with fresh air introduction means for introducing fresh air into the exhaust passage behind the catalyst. An exhaust purification device for an engine system. The engine system includes:
A supercharger for supercharging the intake air in the intake passage during operation of the engine;
An exhaust gas recirculation passage for allowing a part of the exhaust gas discharged from the engine to flow into the intake air passage as an exhaust gas recirculation gas to be recirculated to the engine;
An exhaust recirculation valve for adjusting a flow rate of the exhaust recirculation gas flowing through the exhaust recirculation passage;
The exhaust gas recirculation passage includes an exhaust gas recirculation inlet for introducing the exhaust gas recirculation gas from the exhaust passage, and an exhaust gas recirculation outlet for deriving the exhaust gas recirculation gas to the intake passage. Connected to the exhaust passage behind the catalyst, the exhaust recirculation outlet is connected to the intake passage downstream of the supercharger, and the intake pressure in the intake passage near the exhaust recirculation outlet is near the exhaust recirculation inlet The exhaust gas recirculation gas flows through the exhaust gas recirculation valve from the exhaust gas passage to the intake air passage when lower than the exhaust pressure in the exhaust gas passage.
The fresh air introducing means is configured by using the exhaust gas recirculation passage and the exhaust gas recirculation valve, and the exhaust gas from the intake passage to the exhaust passage behind the catalyst when the intake pressure becomes higher than the exhaust pressure. The exhaust purification device for an engine system according to claim 1, wherein the fresh air is introduced through a recirculation passage and the exhaust recirculation valve. A control means for controlling the exhaust gas recirculation valve;
The control means controls the opening of the exhaust gas recirculation valve in accordance with an operating state of the engine so that the exhaust gas recirculation gas flows into the intake passage when the intake air pressure is lower than the exhaust gas pressure. When the pressure is higher than the exhaust pressure, the exhaust recirculation valve is controlled to open to introduce the fresh air into the exhaust passage behind the catalyst, and the intake pressure is higher than the exhaust pressure. 3. The exhaust purification device for an engine system according to claim 2, wherein the exhaust gas recirculation valve in the valve open state is maintained and controlled in the valve open state when switching to. A control means for controlling the exhaust gas recirculation valve;
The control means controls the opening of the exhaust gas recirculation valve in accordance with an operating state of the engine so that the exhaust gas recirculation gas flows into the intake passage when the intake air pressure is lower than the exhaust gas pressure. In order to introduce the fresh air into the exhaust passage behind the catalyst when the pressure is higher than the exhaust pressure and the unburned components in the exhaust discharged from the engine increase. The exhaust purification device for an engine system according to claim 2, wherein the exhaust recirculation valve is controlled to open. An intake pressure detecting means for detecting an intake pressure in the intake passage near the exhaust gas recirculation outlet;
An intake air amount detecting means for detecting an intake air amount in the intake passage upstream of the exhaust gas recirculation outlet;
An intake air amount calculating means for calculating an engine intake air amount sucked into the engine, wherein the intake air amount calculating means calculates the exhaust pressure based on the detected intake air amount, and calculates the exhaust pressure. The amount of fresh air introduced into the exhaust passage behind the catalyst is calculated based on the exhaust pressure, the detected intake pressure, and the opening degree of the exhaust gas recirculation valve controlled to open by the control means. 5. The exhaust purification device for an engine system according to claim 3, wherein the engine intake air amount is calculated by subtracting the fresh air introduction amount calculated from the detected intake air amount.

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