JP2016113950A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine suitable for improving a purification rate of exhaust gas during a high load operation.SOLUTION: An exhaust emission control device for an internal combustion engine includes: the engine 1 operated by using an air fuel mixture at an air fuel ratio deviated from a stoichiometric ratio by increasing fuel amount during a high load operation; and a manifold catalyst 3 and an underfloor catalyst 4 installed on the upstream and downstream sides of an exhaust passage 2 of the engine 1 to purify exhaust gas. The exhaust emission control device for the internal combustion engine further includes: an exhaust gas cooling device 5 disposed between the manifold catalyst 3 and the underfloor catalyst 4 to cool exhaust gas passing through the exhaust passage 2 so as to inhibit the temperature of the exhaust gas from being raised and exceeding a preset set temperature; and a secondary air supply device 6 serving as an air fuel ratio correction section for injecting secondary air between the exhaust gas cooling device 5 and the underfloor catalyst 4 to set the air fuel ratio of the exhaust gas flowing in to the underfloor catalyst 4 to a stoichiometric ratio during the high load operation of the engine 1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine.

  2. Description of the Related Art An exhaust gas purification device that purifies exhaust gas of an internal combustion engine during high load operation where the temperature of the exhaust gas becomes high has been proposed (see Patent Document 1). In this exhaust purification device, a secondary air supply device is disposed downstream of the catalyst, and the amount of fuel is increased and enriched to protect exhaust components such as the catalyst from high-temperature exhaust gas during high-load operation. Exhaust gas is supplied to the catalyst, and a rich component that cannot be purified by the catalyst is purified by oxidizing it with oxygen in the secondary air downstream of the catalyst.

JP 2007-138882 A

  However, in the above conventional example, in order to prevent overheating of the catalyst, the enrichment component must be reduced only by the oxidation reaction while ensuring the exhaust gas temperature downstream of the catalyst, so that the exhaust gas purification rate is improved. There was a limit.

  Accordingly, the present invention has been made in view of the above problems, and an object thereof is to provide an exhaust gas purification device for an internal combustion engine suitable for improving the exhaust gas purification rate during high-load operation.

  An internal combustion engine exhaust gas purifying apparatus according to the present invention includes an internal combustion engine that is operated with an air-fuel ratio mixture that increases or decreases fuel during high load operation and deviates from stoichiometry, and upstream and downstream of an exhaust passage of the internal combustion engine. An upstream catalyst and a downstream catalyst that are disposed on the side and purify the exhaust gas. And the exhaust gas cooling device which is arrange | positioned between an upstream catalyst and a downstream catalyst, cools the exhaust gas which passes an exhaust passage, and suppresses that the temperature rises exceeding the preset preset temperature. And an air-fuel ratio in which the air-fuel ratio of the exhaust gas that flows into the downstream catalyst by injecting secondary air or secondary fuel between the exhaust gas cooling device and the downstream catalyst during high-load operation of the internal combustion engine is stoichiometric And a correction unit.

  Therefore, in the present invention, the high-temperature exhaust gas discharged from the internal combustion engine during high load operation is cooled by the exhaust gas cooling device, so that the temperature is prevented from rising beyond a preset temperature. For this reason, even if the air-fuel ratio exhaust gas discharged from the internal combustion engine is stoichiometrically exhausted by the air-fuel ratio correction unit and supplied to the downstream catalyst, the exhaust gas can be purified without deteriorating the downstream catalyst. The exhaust gas purification rate can be improved.

1 is a schematic configuration diagram of an exhaust gas purifying device for an internal combustion engine showing a first embodiment of the present invention. It is a purification characteristic diagram with respect to the exhaust gas air-fuel ratio of the underfloor catalyst. It is a purification characteristic figure with respect to the exhaust gas temperature of an underfloor catalyst. It is a control diagram of a flow path switching valve in exhaust heat recovery control. It is a flowchart of secondary air supply control. It is a time chart by secondary air supply control. It is a detailed time chart between predetermined time by secondary air supply control. It is a schematic block diagram of the exhaust-gas purification apparatus of the internal combustion engine which shows 2nd Embodiment of this invention. It is a flowchart of secondary fuel supply control. It is a time chart by secondary fuel supply control. It is a detailed time chart between predetermined time by secondary fuel supply control.

  Hereinafter, an exhaust gas purifying device for an internal combustion engine of the present invention will be described based on each embodiment.

(First embodiment)
FIG. 1 is a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine according to a first embodiment to which the present invention is applied.

In FIG. 1, the exhaust gas purifying apparatus for an internal combustion engine converts harmful substances (HC, CO, NOx) in the exhaust of the engine 1 into harmless substances (H ₂ O, CO ₂ ) and reduces them into the outside air. In order to discharge, a manifold catalyst 3 and an underfloor catalyst 4 are arranged in this order in the exhaust passage 2. Further, the exhaust gas purifying device for the internal combustion engine includes an exhaust gas cooling device 5 and a secondary air supply device 6 for reducing the temperature of the exhaust gas between the manifold catalyst 3 and the underfloor catalyst 4.

  The manifold catalyst 3 contains a known three-way catalyst having a function of purifying hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) contained in the exhaust gas. The manifold catalyst 3 has a smaller capacity than the underfloor catalyst 4 and has a small amount of exhaust gas purification, but is a catalyst that can be activated quickly when high-temperature exhaust gas flows. The manifold catalyst 3 can adsorb HC when the catalyst temperature is low, and can oxidize the adsorbed HC into carbon dioxide and water while desorbing the adsorbed HC as the catalyst temperature increases. An inlet air-fuel ratio sensor 41 is provided at the inlet of the manifold catalyst 3.

  The underfloor catalyst 4 has a large capacity and a large exhaust gas purification capacity. The underfloor catalyst 4 incorporates a known three-way catalyst having a function of purifying HC, CO and NOx contained in the exhaust gas when the catalyst temperature becomes higher than the activation temperature. As is well known, when the air-fuel ratio of the supplied exhaust gas is stoichiometric (14.7), the three-way catalyst has a maximum purification rate of unburned HC, CO, and NOx, and is on the rich side. In such a case, the purification rate of unburned HC and CO is reduced, and when it is on the lean side, the purification rate of nitrogen oxides NOx is reduced (see FIG. 2). The three-way catalyst exhibits a purification action when the temperature of the exhaust gas supplied is, for example, in the temperature range of 400 to 950 [° C.] (see FIG. 3). When exhaust gas having a temperature exceeding this temperature range is supplied to the three-way catalyst, purification of the three-way catalyst is hindered and catalyst deterioration occurs. Therefore, the exhaust gas to be supplied needs to have a temperature within the above temperature range. An exhaust temperature sensor 42 is provided at the inlet of the underfloor catalyst 4. An O2 sensor 43 is provided at the outlet of the underfloor catalyst 4.

  The exhaust gas cooling device 5 includes a bypass passage 11 that branches the exhaust passage 2 downstream of the manifold catalyst 3 and joins again at the inlet of the underfloor catalyst 4. A flow path switching valve 12 that adjusts the amount of exhaust gas flowing through the exhaust passage 2 and the bypass passage 11 by adjusting the opening area of the exhaust passage 2 is disposed at a branch portion between the exhaust passage 2 and the bypass passage 11. Yes.

  When the inlet of the bypass passage 11 is closed and the exhaust passage 2 is fully opened, the flow path switching valve 12 causes the entire amount of exhaust gas to flow through the exhaust passage 2, and the exhaust passage 2 is closed and the inlet of the bypass passage 11 is fully opened. The total amount of exhaust gas is caused to flow through the bypass passage 11. Further, the flow path switching valve 12 sets the exhaust passage 2 to an intermediate opening between the fully open state and the fully closed state, whereby the amount of exhaust gas flowing through the exhaust passage 2 and the bypass passage 11 according to the opening ratio of the exhaust passage 2. The amount of exhaust gas flowing through can be continuously adjusted. The open / close position of the flow path switching valve 12 is controlled by the exhaust heat recovery control unit 10.

  The bypass passage 11 is provided with an exhaust heat recovery unit 13 that recovers exhaust heat of exhaust gas and lowers the temperature of exhaust gas passing therethrough. The exhaust heat recovery unit 13 circulates the cooling water of the engine 1, for example, the cooling water of the radiator 15 through a pump (not shown), and exchanges heat between the exhaust gas passing through the exhaust heat recovery unit 13 and the circulating cooling water. Thus, the temperature of the exhaust gas passing therethrough is lowered. The exhaust heat recovery control unit 10 includes a coolant temperature signal from the water temperature sensor 44, a temperature signal from the exhaust temperature sensor 42 provided at the inlet of the underfloor catalyst 4, and an operation of the engine 1 from the engine control unit 7 (ECU). A status signal is input. The amount of cooling water introduced into the exhaust heat recovery unit 13 is adjusted by a flow rate control valve 14 controlled by the exhaust heat recovery control unit 10.

  The exhaust heat recovery control unit 10 receives an exhaust temperature sensor 42 and a water temperature sensor 44 provided at the inlet of the underfloor catalyst 4 when the operation state of the engine 1 from the engine control unit 7 (ECU) is increasing the high load fuel. Based on the temperature signal, the opening / closing position of the flow path switching valve 12 and the opening degree of the flow control valve 14 are controlled.

  That is, the range of the exhaust gas temperature at which the underfloor catalyst 4 effectively exhibits the purifying action is, for example, in the range of 400 to 950 [° C.], and if this temperature range is exceeded, the exhaust purification by the underfloor catalyst 4 is hindered. This leads to catalyst deterioration. Therefore, the exhaust heat recovery control unit 10 sets a temperature rise suppression value lower than the upper limit temperature of the purifiable temperature range of the underfloor catalyst 4 and the exhaust gas temperature rises beyond the set temperature rise suppression value. Then, the flow path switching valve 12 and the flow rate control valve 14 are controlled to lower the exhaust gas temperature below the temperature rise suppression value.

  FIG. 4 shows the difference between the exhaust gas temperature and the temperature rise suppression value as the vertical axis, the diversion rate of the flow path switching valve 12 with the fully open state of the bypass passage 11 being 1 and the fully closed state being 0, and the horizontal axis. 3 is a control diagram of a flow path switching valve 12. FIG. In addition, the point A on the vertical axis in the figure is the exhaust gas temperature when the flow rate of the flow path switching valve 12 is zero, and the exhaust gas temperature and the temperature rise suppression value are lowered downward from the point A as a starting point. Assign the difference (target drop temperature). And the B1-B3 line drawn to the lower right is a control diagram of the flow-path switching valve 12 as the diversion rate of the flow-path switching valve 12 increases from A point. The plurality of control diagrams B1 to B3 are described because the amount of heat exchange between the exhaust gas and the cooling water increases or decreases according to the flow rate of cooling water introduced into the exhaust heat recovery unit 13 and the cooling water temperature. As the water temperature decreases and the flow rate increases, the descending slope of the control diagram increases as B1 → B2 → B3.

  The exhaust heat recovery control unit 10 obtains a point C based on the difference from the point A, for example, the inlet temperature of the underfloor catalyst 4 based on the control diagram. Next, when the characteristic line set by the temperature and flow rate of the cooling water circulating through the exhaust heat recovery device 13 is B2, it is determined that the diversion rate of the flow path switching valve 12 is the D point. And the flow-path switching valve 12 is operated with the actuator which is not shown in figure, and it adjusts to the opening degree so that it may become the diversion rate D.

  As a result, the exhaust gas that has passed through the manifold catalyst 3 is diverted into the exhaust passage 2 and the bypass passage 11 based on the diversion ratio set by the opening degree of the flow path switching valve 12. The exhaust gas passing through the bypass passage 11 is cooled by heat exchange with the cooling water when passing through the exhaust heat recovery device 13, and the temperature of the exhaust gas decreases. Therefore, when the exhaust gas in the exhaust passage 2 and the bypass passage 11 merges at the inlet of the underfloor catalyst 4, the exhaust gas that has passed through the exhaust passage 2 and the exhaust gas that has been cooled through the bypass passage 11 are mixed. The exhaust gas whose temperature has dropped below the temperature rise suppression value is supplied to the underfloor catalyst 4. As the temperature decrease amount of the exhaust gas flowing into the underfloor catalyst 4, for example, a decrease of about 100 to 150 [° C.] is possible. Therefore, even if the exhaust gas in the stoichiometric state is purified, the underfloor catalyst 4 is deteriorated due to overheating. Exceeding the limit temperature that causes

  As described above, when the exhaust gas cooling device 5 needs to cool the exhaust gas, the exhaust gas is introduced into the bypass passage 11 by the flow path switching valve 12 by a necessary amount, and the exhaust heat recovery unit 13 Can be cooled. For this reason, when cooling is required, cooling can be started immediately if the bypass passage 11 is opened by the flow path switching valve 12. Moreover, since the amount of exhaust gas to be cooled can be adjusted according to the opening degree of the flow path switching valve 12, the cooling capacity can be adjusted immediately. In addition, the exhaust heat recovery unit 13 is not installed in the exhaust passage 2 where exhaust gas always flows, but is installed in the bypass passage 11 through which the exhaust gas is selectively flowed by the operation of the flow path switching valve 12. Even if the heat recovery unit 13 is operated in a constantly cooled state, the exhaust gas is not supercooled.

  The secondary air supply device 6 injects secondary air into the exhaust gas and changes the air-fuel ratio of the exhaust gas from the rich state to the stoichiometric state. The secondary air supply device 6 includes a tank 21 that stores secondary air, a pump 22 that supplies secondary air to the tank 21, a secondary air nozzle 23 that supplies secondary air to the inlet of the underfloor catalyst 4, and a secondary air A secondary air control unit 20 that controls the air pump 22 and the secondary air nozzle 23. The secondary air control unit 20 drives the secondary air pump 22 based on a signal from the pressure sensor 24 provided in the tank 21 so that the secondary air tank 21 is always filled with secondary air of a predetermined pressure. To do.

  The secondary air control unit 20 receives an engine intake air amount measurement value (AFM) from the air flow meter, a manifold catalyst when the operating state of the engine 1 from the engine control unit 7 (ECU) is high and fuel is increasing. The secondary air supply to the inlet of the underfloor catalyst 4 is controlled via the secondary air nozzle 23 based on the upstream catalyst inlet air-fuel ratio from the three inlet air-fuel ratio sensors 41 and the output value of the O2 sensor 43.

  FIG. 5 is a flowchart of secondary air supply control executed by the secondary air control unit 20 when the amount of fuel is increasing at a high load. FIG. 6 is a time chart based on secondary air supply control including the operation of the exhaust gas cooling device 5, and FIG. 7 is based on secondary air supply control expressing the range from time t2 to time t3 in FIG. 6 in more detail. It is a time chart. Below, the operation | movement of secondary air supply control including the operation | movement in the exhaust-gas cooling device 5 is demonstrated based on FIGS.

  FIG. 6 shows that the vehicle starts acceleration at time t1, shifts to steady travel at time t3, shifts to deceleration travel with fuel cut at time t5, and stops at time t6 (B) to (H). ) Shows changes in each part. In FIG. 6, (B) is the exhaust heat recovery control, (C) is the inlet temperature of the underfloor catalyst 4, (D) is the inlet air-fuel ratio of the manifold catalyst 3, and (E) is included in the outlet exhaust gas of the manifold catalyst 3. (F) shows the operating state of the secondary air supply device 6, (G) shows the inlet air-fuel ratio of the underfloor catalyst 4, and (H) shows the unpurified component discharged from the underfloor catalyst 4.

  In FIG. 6, first, when the vehicle shifts to acceleration traveling at time t1, the engine load increases and the exhaust gas temperature rises (FIG. 6C). In FIG. 6C, the exhaust gas temperature flowing into the manifold catalyst 3 indicated by the two-dot chain line rises, and the exhaust gas temperature flowing into the underfloor catalyst 4 indicated by the solid line also rises following it. When the engine control unit 7 determines that the operation state is the high load operation state and starts fuel increase at time t2, the air-fuel ratio of the exhaust gas supplied to the manifold catalyst 3 changes from the stoichiometric state to the rich side ( (See FIG. 6D and FIG. 7B). For this reason, the exhaust gas that has passed through the manifold catalyst 3 contains unpurified components HC and CO (FIG. 6E).

  In this embodiment, when the high load operation is continued and the exhaust gas temperature flowing into the underfloor catalyst 4 exceeds the set temperature rise suppression value, the exhaust heat recovery control is started at time t2, and the flow path switching valve 12 is turned on. The bypass passage 11 is opened and a part of the exhaust gas corresponding to the temperature of the exhaust gas is diverted to the bypass passage 11. As a result, the exhaust gas cooled by passing through the exhaust heat recovery unit 13 and the exhaust gas passing through the exhaust passage 2 are mixed and cooled at the inlet of the underfloor catalyst 4 (hatched region in FIG. 6C). Gas is supplied to the underfloor catalyst 4. For this reason, even if the underfloor catalyst 4 continues to purify the exhaust gas during high load operation, the temperature rise is suppressed, and catalyst deterioration due to overheating can be suppressed.

  On the other hand, the secondary air control unit 20 of the secondary air supply device 6 increases the fuel injection amount at a high load to increase the fuel injection amount to enrich the air-fuel ratio and operate the engine 1 in step S1 of FIG. It is determined whether or not. As shown in FIG. 7B, at time t2, when the amount of fuel is increasing due to high load operation, the secondary air control unit 20 executes the process of step S2, and the internal pressure of the secondary air tank 21 reaches the predetermined value. If the condition is satisfied, the process of step S3 is executed. If the determinations in step S1 and step S2 are NO, the current process ends.

In step S3, the amount of secondary air to be injected is calculated. That is, during the high load fuel increase, the rich component concentration of the exhaust gas flowing into the underfloor catalyst 4 exceeds the purification capacity (oxidation treatment capacity) of the underfloor catalyst 4, so that the air-fuel ratio at the inlet of the underfloor catalyst 4 of the exhaust gas is stoichiometric. In order to do this, it is necessary to add secondary air. The amount of air injection required to stoichiometrically exhaust the exhaust gas having a rich inlet air-fuel ratio of the underfloor catalyst 4 includes an engine intake air amount measurement value (AFM) from the air flow meter and an upstream from the inlet air-fuel ratio sensor 41. Based on the catalyst inlet air-fuel ratio,
Secondary air amount = (14.7−A / F sensor value) × engine intake air amount measurement value (AFM)
And calculate. And the secondary air nozzle 23 is controlled so that it may become the calculated air injection quantity, and secondary air is supplied to the inlet_port | entrance of the underfloor catalyst 4 (FIG.6 (F), FIG.7 (C), time t21). This air injection amount control is executed by feedforward control (F / F control) based on the measured intake air amount (AFM) and the upstream catalyst inlet air-fuel ratio.

  In the present embodiment, the temperature of the underfloor catalyst 4 can be suppressed from exceeding a preset temperature, and the exhaust gas stoichiometricized by the secondary air supply device 6 can be supplied to the underfloor catalyst 4. Exhaust gas can be purified without causing catalyst deterioration due to excessive temperature rise.

  Next, in step S4, the secondary air control unit 20 of the secondary air supply device 6 determines whether or not the output of the O2 sensor 43 at the outlet of the underfloor catalyst 4 has swung from the rich state to the lean state during the air injection amount control. judge. When the lean state is not achieved, the secondary air injection is continued, and when the lean state is swung, the supply of the secondary air is temporarily stopped.

  The exhaust gas mixed with the secondary air is supplied to the underfloor catalyst 4 from time t21, and as shown in FIG. 7F, the oxygen storage amount of the catalyst is temporarily reduced by the purification of the rich exhaust gas. To do. Thereafter, the storage amount gradually increases to compensate for the amount consumed by the exhaust gas purification by mixing the secondary air, and the oxygen storage amount becomes the FULL state at time t22. For this reason, as shown in FIG. 7 (E), the exhaust gas component discharged from the underfloor catalyst 4 suddenly changes from the rich state to the lean state. Due to this change, the secondary air supply device 6 stops the secondary air injection in the feedforward control (F / F control), assuming that the determination of the change in the measured value of the O2 sensor 43 in step S4 is satisfied.

  At this time t22, the oxygen storage amount of the underfloor catalyst 4 is in the FULL state, and therefore, a little nitrogen oxide NOx component is discharged as an unpurified component in the exhaust gas discharged from the underfloor catalyst 4 (FIG. 7 ( G)).

  In step S5, the secondary air control unit 20 of the secondary air supply device 6 supplies secondary air with the reduced injection amount, and decreases until the output swings to the rich side by feedback control of the O2 sensor 43. Secondary air is supplied by the injected amount. As a result, the oxygen storage amount in the underfloor catalyst 4 is gradually reduced to an appropriate value due to the balance between the amount of supply by the reduced secondary air and the amount consumed by the purifying action of the exhaust gas. The output value of the O2 sensor 43 is returned to the rich side again (time t3).

  The secondary air control unit 20 of the secondary air supply device 6 determines that the measured value of the O2 sensor 43 has returned to the rich state in step S6, proceeds to step S7, and stops the supply of secondary air. End the process. The secondary air control unit 20 of the secondary air supply device 6 executes the processing of step S1 to step S7 every predetermined time while the operation state during the high load fuel increase is continued.

  The exhaust gas component supplied to the underfloor catalyst 4 from the time t2 to the time t3 by the processing of the step S1 to the step S7 of the secondary air supply device 6 is changed from the rich state of the broken line to the solid stoichiometric state of FIG. It is said. Therefore, it can be sufficiently purified by the underfloor catalyst 4 to prevent the unpurified components HC and CO from being discharged as emissions as shown by the broken line in FIG. 6 (H).

  When the vehicle shifts to steady running at time t3, the engine control unit 7 changes from the high load running state to the steady running state, and therefore stops the fuel increase. Further, since the exhaust gas temperature from the engine 1 gradually decreases, the exhaust gas temperature at the inlet of the underfloor catalyst 4 also gradually decreases. For this reason, when the exhaust gas temperature input to the exhaust heat recovery control unit 10 falls below the temperature rise suppression value at time t4, the exhaust heat recovery control unit 10 closes the bypass passage 11 with the flow path switching valve 12, The entire amount of exhaust gas flows into the underfloor catalyst 4 via the exhaust passage 2.

  In the present embodiment, the following effects can be achieved.

  (A) The exhaust gas purifying device for an internal combustion engine according to the present embodiment includes an engine 1 that is operated with an air-fuel ratio mixture that has increased the amount of fuel during high-load operation and is out of stoichiometry, and an upstream side of the exhaust passage 2 of the engine 1. And a manifold catalyst 3 and an underfloor catalyst 4 that are disposed on the side and the downstream side to purify exhaust gas. And it is arrange | positioned between the manifold catalyst 3 and the underfloor catalyst 4, and exhaust gas cooling which cools the exhaust gas which passes the exhaust passage 2, and suppresses that the temperature exceeds a preset preset temperature is suppressed. Air-fuel ratio correction in which secondary air is injected between the exhaust gas cooling device 5 and the underfloor catalyst 4 and the air-fuel ratio of the exhaust gas flowing into the underfloor catalyst 4 is stoichiometric during high load operation of the device 5 and the engine 1 And a secondary air supply device 6 as a unit.

  That is, in this embodiment, the high-temperature exhaust gas discharged from the engine 1 during high load operation is cooled by the exhaust gas cooling device 5, and the temperature is prevented from rising beyond a preset temperature. For this reason, even if the exhaust gas of the air-fuel ratio which has been exhausted from the engine 1 is stoichiometrically supplied by the secondary air and supplied to the underfloor catalyst 4, the underfloor catalyst 4 can be purified without deteriorating. The exhaust gas purification rate can be improved.

  (A) The exhaust passage 2 includes a bypass passage 11 that opens at an inlet and an outlet at a downstream portion of the manifold catalyst 3 and an upstream portion of the underfloor catalyst 4 and bypasses the exhaust passage 2. A device 5 is installed. The exhaust gas cooling device 5 restricts the flow rate of the exhaust gas flowing through the exhaust passage 2 and the flow rate of the exhaust gas flowing through the bypass passage 11 when the temperature of the exhaust gas passing through the exhaust passage 2 reaches a preset set temperature. The flow path switching valve 12 is provided as a bypass flow rate control unit that controls the flow rate of the exhaust gas flowing in the bypass passage 11 so as to increase the flow rate.

  That is, when the exhaust gas needs to be cooled, the exhaust gas can be cooled by the exhaust gas cooling device 5 by introducing the exhaust gas into the bypass passage 11 by a required amount by the flow path switching valve 12. For this reason, when cooling is required, cooling can be started immediately if the bypass passage 11 is opened by the flow path switching valve 12. Moreover, since the amount of exhaust gas to be cooled can be adjusted according to the opening degree of the flow path switching valve 12, the cooling capacity can be adjusted immediately.

  (C) The exhaust gas cooling device 5 is configured by an exhaust heat recovery unit 13 that circulates cooling water of the engine 1 and recovers exhaust heat of exhaust. For this reason, the cooling water of the engine 1 can be effectively used for cooling the exhaust gas.

  (D) The secondary air supply device 6 as an air-fuel ratio correction unit is based on the amount of air supplied to the engine 1 during high load operation and the deviation between the air-fuel ratio of exhaust gas discharged from the engine 1 and stoichiometry. It is calibrated to inject the calculated amount of secondary air by feedforward control. For this reason, the air-fuel ratio of the exhaust gas can be corrected without a control delay by feedforward control.

(Second Embodiment)
FIGS. 8-11 shows 2nd Embodiment of the exhaust gas purification apparatus of the internal combustion engine to which this invention is applied. That is, FIG. 8 is a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine, and FIG. 9 is a flowchart of secondary fuel supply control that is executed when the secondary fuel control unit is operating in a lean state at a high load. It is. FIG. 10 is a time chart based on the secondary fuel supply control including the operation of the exhaust gas cooling device 5, and FIG. 11 is a time chart based on the secondary fuel supply control showing the portion from time t13 to time t14 in more detail. . In the present embodiment, in the high-load operation state, a configuration for the case where the lean state is achieved by reducing the amount of fuel without being stoichiometric due to prevention of knocking or the like is added to the first embodiment. The same devices as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted or simplified. The description of the secondary air supply device 6 is omitted.

  In FIG. 8, in the exhaust gas purifying apparatus for the internal combustion engine of the present embodiment, in response to the fuel being reduced to a lean state in the high load operation state, between the manifold catalyst 3 and the underfloor catalyst 4, An exhaust gas cooling device 5 for reducing the temperature of the exhaust gas and a secondary fuel supply device 8 are provided. The exhaust gas cooling device 5 is configured in the same manner as in the first embodiment, and the exhaust air-fuel ratio is made lean by reducing the fuel injection amount from the stoichiometric state when the engine 1 is in a high load operation state from the engine control unit 7 (ECU). It is configured to operate when in a high load lean operation state.

  The secondary fuel supply device 8 injects secondary fuel into the exhaust gas and changes the air-fuel ratio of the exhaust gas from the lean state to the stoichiometric state. The secondary fuel supply device 8 controls a secondary fuel nozzle 32, a secondary fuel nozzle 32 that supplies secondary fuel, for example, a tank 31 that stores gasoline, a secondary fuel nozzle 32 that supplies secondary fuel to the inlet of the underfloor catalyst 4, and a secondary fuel nozzle 32. And a next fuel control unit 30.

  When the operating state of the engine 1 is in a high load lean operation from the engine control unit 7 (ECU), the secondary fuel control unit 30 determines the engine intake air amount measurement value (AFM) from the air flow meter, the manifold catalyst 3 Based on the upstream catalyst inlet air-fuel ratio from the inlet air-fuel ratio sensor 41 and the output of the O2 sensor 43, the secondary fuel supply to the inlet of the underfloor catalyst 4 is controlled via the secondary fuel nozzle 32.

  Next, the operation of the secondary fuel supply control, including the operation in the exhaust gas cooling device 5, will be described based on FIGS.

  FIG. 10 shows (B) to (H) at each time when the vehicle starts acceleration at time t11, shifts to steady travel at time t14, shifts to deceleration travel with fuel cut at time t16, and stops at time t17. ) Shows changes in each part. That is, (B) is exhaust heat recovery control, (C) is the inlet temperature of the underfloor catalyst 4, (D) is the inlet air-fuel ratio of the manifold catalyst 3, and (E) is unpurified contained in the outlet exhaust gas of the manifold catalyst 3. (F) shows the operating state of the secondary fuel supply device 8, (G) shows the inlet air-fuel ratio of the underfloor catalyst 4, and (H) shows the unpurified component discharged from the underfloor catalyst 4.

  In FIG. 10, first, at time t11, when the vehicle shifts to acceleration traveling, the engine load increases and the exhaust gas temperature rises (FIG. 10C). In FIG. 10C, the exhaust gas temperature flowing into the manifold catalyst 3 indicated by the two-dot chain line rises, and the exhaust gas temperature flowing into the underfloor catalyst 4 indicated by the solid line also rises following it. When the engine control unit 7 determines that the operation state is a high load operation state and starts fuel reduction at time t13, the air-fuel ratio of the exhaust gas supplied to the manifold catalyst 3 changes from the stoichiometric state to the lean side. (See FIG. 10D and FIG. 11B). For this reason, the exhaust gas that has passed through the manifold catalyst 3 contains unpurified component NOx (FIG. 10E).

  When the high load operation is continued and the exhaust gas temperature flowing into the underfloor catalyst 4 exceeds the set temperature rise suppression value, the exhaust heat recovery control is started (FIG. 10B), and the flow path switching valve 12 is started. Is activated, the bypass passage 11 is opened, and a part of the exhaust gas corresponding to the temperature of the exhaust gas is diverted to the bypass passage 11. Then, the exhaust gas cooled after passing through the exhaust heat recovery unit 13 and the exhaust gas passing through the exhaust passage 2 were mixed and cooled at the inlet of the underfloor catalyst 4 (hatched region in FIG. 10C). Is supplied to the underfloor catalyst 4. For this reason, the temperature increase of the underfloor catalyst 4 is suppressed, and deterioration due to overheating is suppressed.

  On the other hand, the secondary fuel control unit 30 of the secondary fuel supply device 8 performs the high load fuel reduction in step S11 of FIG. 9 in which the engine 1 reduces the fuel injection amount when the load is high and the exhaust air-fuel ratio becomes lean. It is determined whether or not. As shown in FIG. 11B, at time t13, when the engine 1 is in an operating state in which the fuel is reduced in the high load operation, the secondary fuel control unit 30 executes the process of step S12, and the secondary fuel If the fuel amount in the tank 31 satisfies the predetermined value, the process of step S13 is executed. If the determinations at step S11 and step S12 are NO, the current process ends.

In step S13, the secondary fuel control unit 30 calculates the amount of secondary fuel to be injected. That is, during the reduction of the high load fuel, the lean component concentration of the exhaust gas flowing into the underfloor catalyst 4 exceeds the purification capacity (oxidation capacity) of the underfloor catalyst 4, so that the air-fuel ratio of the exhaust gas at the inlet of the underfloor catalyst 4 is stoichiometric. In order to do so, it is necessary to add secondary fuel. The fuel injection amount required to make the under-floor catalyst 4 inlet air-fuel ratio stoichiometric is the engine intake air amount measured value (AFM) from the air flow meter and the upstream catalyst inlet from the inlet air-fuel ratio sensor 41 of the manifold catalyst 3. Based on the air / fuel ratio,
Secondary fuel amount = (A / F sensor value−14.7) × engine intake air amount measurement value (AFM)
And calculate. And the secondary fuel control part 30 controls the secondary fuel nozzle 32 so that it may become the computed fuel injection quantity, and supplies a secondary fuel to the inlet_port | entrance of the underfloor catalyst 4 (FIG.11 (C), time t31). . This fuel injection amount control is executed by feedforward control (F / F control) based on the measured intake air amount (AFM) and the upstream catalyst inlet air-fuel ratio.

  Next, in step S14, the secondary fuel control unit 30 of the secondary fuel supply device 8 moves to the rich side after the output value of the O2 sensor 43 at the outlet of the underfloor catalyst 4 changes to the lean state during the fuel injection amount control. It is determined whether or not the fuel has swung. When the fuel cannot swing to the rich side, the secondary fuel injection is continued. When the fuel has swung to the rich side, the supply of the secondary fuel is temporarily stopped.

  The exhaust gas mixed with the secondary fuel is supplied to the underfloor catalyst 4 from time t31. As shown in FIG. 11F, the oxygen storage amount of the underfloor catalyst 4 is reduced by lean exhaust gas purification. It rises temporarily. After that, it is consumed by exhaust gas purification due to the mixing of the secondary fuel and gradually decreased, and the oxygen storage amount becomes the EMPTY state at time t32. For this reason, as shown in FIG. 11 (E), the exhaust gas component discharged from the underfloor catalyst 4 suddenly changes from the lean state to the rich state. Due to this change, the secondary fuel control unit 30 of the secondary fuel supply device 8 assumes that the measurement value change determination of the O2 sensor 43 in step S14 is satisfied, and the secondary fuel of the feedforward control (F / F control). Stop spraying.

  At time t32, since the oxygen storage amount of the underfloor catalyst 4 is in the EMPTY state, some HC and CO components are discharged as unpurified components in the exhaust gas discharged from the underfloor catalyst 4 (FIG. 11 (G )reference).

  Next, the process proceeds to step S15, where the secondary fuel is supplied by the reduced injection amount, and the secondary fuel is supplied by the reduced injection amount until the output fluctuates to the rich side by the feedback control of the O2 sensor 43. As a result, the oxygen storage amount in the underfloor catalyst 4 is gradually increased to an appropriate value due to the balance between the reduced secondary fuel supply amount and the amount consumed by the purifying action of the exhaust gas. The output value of the sensor 43 is returned to the rich side again (time t14).

  The secondary fuel control unit 30 of the secondary fuel supply device 8 determines that the measured value of the O2 sensor 43 has returned to the rich state in step S16, and proceeds to step S17 to stop the supply of secondary fuel. End the process. The secondary fuel control unit 30 of the secondary fuel supply device 8 executes the processing of step S11 to step S17 every predetermined time while the operating state of the engine 1 is continuing the heavy load fuel reduction.

  The exhaust gas component supplied to the underfloor catalyst 4 is changed from the lean state of the broken line in FIG. 10G to the solid stoichiometric state by the processing of step S11 to step S17 of the secondary fuel supply device 8. 4 can be sufficiently purified, and the unpurified component NOx can be prevented from being discharged as emission as shown by the broken line in FIG.

  When the vehicle shifts to steady running at time t14, the engine control unit 7 changes from the high load running state to the steady running state, and therefore stops the fuel reduction. Further, since the exhaust gas temperature from the engine 1 gradually decreases, the exhaust gas temperature at the inlet of the underfloor catalyst 4 also gradually decreases. For this reason, when the exhaust gas temperature input to the exhaust heat recovery control unit 10 falls below the temperature rise suppression value at time t15, the bypass passage 11 is closed by the flow path switching valve 12, and the entire amount of exhaust gas is exhausted to the exhaust passage 2. To flow into the underfloor catalyst 4.

  In the present embodiment, in addition to the effects (A) and (C) in the first embodiment, the following effects can be achieved.

  (E) The exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment includes an engine 1 that is operated with an air-fuel ratio mixture that is out of stoichiometry by reducing fuel during high load operation, and upstream of the exhaust passage 2 of the engine 1. And a manifold catalyst 3 and an underfloor catalyst 4 that are disposed on the side and the downstream side to purify exhaust gas. And it is arrange | positioned between the manifold catalyst 3 and the underfloor catalyst 4, and exhaust gas cooling which cools the exhaust gas which passes the exhaust passage 2, and suppresses that the temperature exceeds a preset preset temperature is suppressed. Air-fuel ratio correction in which secondary fuel is injected between the exhaust gas cooling device 5 and the underfloor catalyst 4 and the air-fuel ratio of the exhaust gas flowing into the underfloor catalyst 4 is stoichiometric during high load operation of the device 5 and the engine 1 And a secondary fuel supply device 8 as a unit.

  That is, the high-temperature exhaust gas discharged from the engine 1 during high-load operation is cooled by the exhaust gas cooling device 5 and the temperature is prevented from rising beyond a preset temperature. For this reason, even if the exhaust gas of the air-fuel ratio that has been removed from the engine 1 is stoichiometrically supplied by the secondary fuel and supplied to the underfloor catalyst 4, the underfloor catalyst 4 can be purified without being deteriorated. The exhaust gas purification rate can be improved.

  (F) The air-fuel ratio correction unit calculates the amount of secondary fuel calculated by the amount of air supplied to the engine 1 during high-load operation and the deviation between the air-fuel ratio of exhaust gas exhausted from the engine 1 and stoichiometry. It has the process of injecting by feedforward control. For this reason, the air-fuel ratio of the exhaust gas can be corrected without a control delay by feedforward control.

1 engine (internal combustion engine)
2 Exhaust passage 3 Manifold catalyst (upstream catalyst)
4 Underfloor catalyst (downstream catalyst)
5 Exhaust gas cooling device 6 Secondary air supply device (air-fuel ratio correction means)
7 Engine control unit 7
8 Secondary fuel supply device (Air-fuel ratio correction means)
10 Waste heat recovery control unit 11 Bypass passage 12 Flow path switching valve (Bypass flow control unit)
13 Waste heat recovery device 14 Flow control valve

Claims (6)

An internal combustion engine that is operated with an air-fuel ratio mixture that is out of stoichiometry by increasing or decreasing fuel during high-load operation;
An upstream catalyst and a downstream catalyst installed on the upstream side and downstream side of the exhaust passage of the internal combustion engine to purify exhaust gas;
An exhaust gas cooling device disposed between the upstream catalyst and the downstream catalyst for cooling the exhaust gas passing through the exhaust passage and suppressing the temperature from rising beyond a preset temperature. ,
An air-fuel ratio in which the air-fuel ratio of the exhaust gas injected into the downstream catalyst by injecting secondary air or secondary fuel between the exhaust gas cooling device and the downstream catalyst during high load operation of the internal combustion engine is stoichiometric And an exhaust gas purifying device for an internal combustion engine. The internal combustion engine is operated with a rich air-fuel ratio mixture that increases the amount of fuel during high-load operation and deviates from stoichiometry,
2. The internal combustion engine according to claim 1, wherein the air-fuel ratio correction means uses the air-fuel ratio of exhaust gas that injects secondary air and flows into the downstream catalyst during high-load operation of the internal combustion engine as a stoichiometry. Exhaust gas purification equipment. The internal combustion engine is operated with a lean air-fuel ratio mixture in which fuel is reduced and off stoichiometry during high load operation,
2. The internal combustion engine according to claim 1, wherein the air-fuel ratio correction unit uses the air-fuel ratio of exhaust gas that injects secondary fuel and flows into the downstream catalyst during high-load operation of the internal combustion engine as a stoichiometry. Exhaust gas purification equipment. The exhaust passage includes a bypass passage that opens at an inlet and an outlet at a downstream portion of the upstream catalyst and an upstream portion of the downstream catalyst to bypass the exhaust passage,
The exhaust gas cooling device is installed in the bypass passage, and restricts the flow rate of the exhaust gas flowing through the exhaust passage when the temperature of the exhaust gas passing through the exhaust passage reaches a preset temperature. The exhaust of the internal combustion engine according to any one of claims 1 to 3, further comprising bypass flow rate control means for controlling a flow rate of the exhaust gas flowing through the bypass passage so as to increase a flow rate of the exhaust gas flowing through the exhaust gas. Gas purification device.   5. The exhaust gas cooling device according to claim 1, wherein the exhaust gas cooling device includes an exhaust heat recovery unit that recovers exhaust heat of exhaust gas by circulating cooling water of an internal combustion engine. An exhaust gas purification device for an internal combustion engine as described.   The air-fuel ratio correction means is a secondary air or secondary air whose amount is calculated by the amount of air supplied to the internal combustion engine during high load operation and the deviation between the air-fuel ratio of exhaust gas discharged from the internal combustion engine and stoichiometry. The exhaust gas purifying device for an internal combustion engine according to any one of claims 1 to 5, further comprising a process of injecting fuel by feedforward control.

Images