JP4115162B2 - Exhaust gas purification control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to an exhaust gas purification control device for an internal combustion engine, and more particularly, activates a catalyst provided in the exhaust passage of the internal combustion engine at an early stage by introducing secondary air and correcting an increase in fuel supply amount during cold start. The present invention relates to an exhaust gas purification control device for an internal combustion engine that reduces emissions.
[0002]
[Prior art]
Conventionally, a catalyst is provided in the middle of an exhaust passage of an internal combustion engine, and the exhaust gas is purified by the catalyst. However, at the time of cold start, there is a problem that the purification rate is low until the catalyst is in a so-called inactive state where the catalyst is cooled and the catalyst is warmed and activated. In response to such problems, various apparatuses and methods have been proposed for the purpose of actively warming the catalyst and activating it early to reduce exhaust emissions during cold start.
[0003]
(First Conventional Example) As a general prior art at the time of filing of the present application, for example, after starting the engine, the ignition timing is retarded to raise the exhaust temperature, and then the secondary air is introduced in the vicinity of the exhaust valve Thus, CO and HC in the exhaust gas are reduced by reburning in the exhaust passage, and at the same time, warming up of the catalyst is promoted.
[0004]
(Second Conventional Example) Japanese Patent Laid-Open No. 60-88870 discloses that the temperature of exhaust gas discharged from the engine is positively increased by increasing the idle speed and retarding the ignition timing after starting the engine. It is disclosed that the catalyst is warmed up to promote warm-up to achieve early activation.
[0005]
(Third Conventional Example) In Japanese Patent Laid-Open No. 9-119310, after the engine is started, after the catalyst inlet gas temperature reaches the catalyst activation start temperature, the fuel supply amount is increased and the secondary air is supplied to the catalyst. It is disclosed that the catalyst is introduced upstream to promote the oxidation reaction in the catalyst, and the catalyst is rapidly warmed up for early activation.
[0006]
(Fourth Conventional Example) Japanese Patent Application Laid-Open No. 9-103647 discloses that after starting the engine, secondary air is introduced to the upstream side of the catalyst, and the catalyst inlet gas temperature reaches the catalyst activation start temperature. It is disclosed that fuel supply amount increase correction is performed using an increase correction value calculated based on the degree of deterioration to promote the oxidation reaction in the catalyst and to activate the catalyst at an early stage.
[0007]
[Problems to be solved by the invention]
However, when the ignition timing described in the first conventional example and the second conventional example is retarded, the retarding of the ignition timing leads to instability of combustion in the combustion chamber, so it must be continued for a long time. It is difficult. Further, as described in the first conventional example, when secondary air is introduced near the exhaust valve and recombusted, exhaust emission cannot be reduced by 100%. It is necessary to reduce the fuel increase immediately after starting, but if it is reduced, the catalyst temperature rise effect due to re-combustion also decreases. Therefore, the techniques described in the first conventional example and the second conventional example have a problem that only a temporary effect immediately after starting can be obtained.
[0008]
In the case of the third conventional example, since the secondary air and fuel increase start after the catalyst rises to the activation start temperature, the exhaust emission cannot be purified until the activation start temperature is reached. In particular, when the distance between the engine and the catalyst is large, such as in an automobile engine, there is a problem that the time until the catalyst temperature reaches the activation start temperature becomes long and the purification rate of exhaust emission becomes low. is there.
[0009]
In the case of the fourth conventional example, a fuel increase correction value for increasing the fuel supply amount is set in accordance with the degree of deterioration of the catalyst based on the rise in temperature at which the catalyst is activated in accordance with the degree of deterioration of the catalyst. The catalyst activation start temperature is always adjusted to a constant temperature. Therefore, for a new catalyst that has not deteriorated, the amount of fuel is not increased, only the introduction of secondary air is performed, and the catalyst performance of the new catalyst is intentionally reduced, resulting in deterioration. Used according to the catalyst. For this reason, the catalyst performance of a new catalyst cannot be fully utilized, and there exists a problem that efficiency is bad.
[0010]
Further, in the case of the third conventional example and the fourth conventional example, control is performed to start increasing the amount of fuel at the same time as the catalyst temperature reaches the activation start temperature, but immediately after the catalyst temperature reaches the catalyst activation start temperature. Since the catalyst has just started its activity, the oxidation function of the catalyst is still low. If the amount of fuel supply is increased at once with such an oxidation function being low, a large amount of CO and HC may be temporarily discharged. On the other hand, the rate at which the temperature of the catalyst rises in proportion to the amount of fuel increase, so it is necessary to reflect the amount of fuel increase little by little. Must be set.
[0011]
The present invention has been made in view of the above points, and an object of the present invention is to provide an exhaust gas purification control device for an internal combustion engine that actively activates a catalyst during cold start to reduce exhaust emissions. There is.
[0012]
[Means for Solving the Problems]
An exhaust gas purification control apparatus for an internal combustion engine according to claim 1 that solves the above-described problem, a cold start state determination means that determines whether or not the operation state of the internal combustion engine is a cold start state, and an internal combustion engine Secondary air introduction start means for starting the introduction of secondary air upstream of the catalyst provided in the middle of the exhaust passage of the internal combustion engine based on the determination that the operating state of the engine is a cold start state; Fuel increase correction means for starting the increase correction of the fuel supply amount by raising the temperature to the catalyst activation start temperature at which activation starts, and exhaust by raising the catalyst temperature to the catalyst complete activation temperature at which the catalyst temperature is fully activated An early activation stop means for stopping the introduction of secondary air into the passage and the increase correction of the fuel supply amount, and the fuel increase correction means gradually increases the fuel supply amount in accordance with an increase in the temperature of the catalyst. Increase compensation And wherein the Ukoto.
[0013]
[Means for Solving the Problems]
An exhaust gas purification control apparatus for an internal combustion engine according to claim 1 that solves the above-described problem, a cold start state determination means that determines whether or not the operation state of the internal combustion engine is a cold start state, and an internal combustion engine Secondary air introduction start means for starting introduction of secondary air upstream of the catalyst provided in the exhaust passage of the internal combustion engine based on the determination that the operation state of the engine is a cold start state;After the secondary air introduction start means starts introducing secondary airThe temperature of the catalystRising of the catalystCatalyst activation start temperature to start activationUntil the catalyst temperature reaches the catalyst activation start temperature.The fuel increase correction means for starting the increase correction of the fuel supply amount, and the introduction of the secondary air into the exhaust passage and the fuel supply amount of the catalyst by the temperature of the catalyst rising to the catalyst complete activation temperature at which the activation is completely started Early activation stop means for stopping the increase correction, and the fuel increase correction means performs a gradual increase correction for gradually increasing the fuel supply amount in accordance with an increase in the temperature of the catalyst.
[0014]
According to a second aspect of the present invention, in the exhaust gas purification control apparatus for an internal combustion engine according to the first aspect, the fuel increase correction means corrects the increase in the fuel supply amount when the catalyst temperature falls below the catalyst activation start temperature. The method is characterized in that when the catalyst temperature is again equal to or higher than the catalyst activation start temperature, the gradual increase correction for gradually increasing the fuel supply amount is resumed.
[0015]
According to the present invention, during the correction of the gradual increase, the catalyst temperature is lower than the catalyst activation start temperature, for example, due to excessive cooling of the catalyst due to the introduction of secondary air. In this case, the fuel supply amount increase correction is stopped. Thereby, when the catalyst temperature falls below the catalyst activation start temperature and the oxidation function of the catalyst stops, it is possible to prevent the exhaust emission from deteriorating due to an excessive fuel supply amount. In addition, when the catalyst temperature again becomes equal to or higher than the catalyst activation start temperature, the gradual increase correction of the fuel supply amount is resumed, so that the gradual increase correction according to the temperature increase rate of the catalyst can be performed.
[0016]
According to a third aspect of the present invention, in the exhaust gas purification control apparatus for an internal combustion engine according to the first or second aspect, the early activation stop means determines whether or not the vehicle is in a running state. When detecting the running state, control is performed to stop the introduction of secondary air into the exhaust passage and the increase correction of the fuel supply amount.
[0017]
According to the present invention, since the traveling state detection means detects the traveling state of the automobile, the introduction of the secondary air into the exhaust passage and the increase correction of the fuel supply amount are stopped. It can be prevented that the air-fuel ratio balance is lost due to the change and the purification rate of the exhaust emission is lowered.According to a fourth aspect of the present invention, in the exhaust gas purification control apparatus for an internal combustion engine according to any one of the first to third aspects, the upstream side and the downstream side of the catalyst at a predetermined timing. ₂ Catalyst deterioration rate calculating means for calculating the catalyst deterioration rate of the catalyst based on the concentration; catalyst activation start temperature calculating means for calculating the catalyst activation start temperature based on the catalyst deterioration rate calculated by the catalyst deterioration rate calculating means; And a catalyst complete activation temperature calculating means for calculating the catalyst complete activation temperature based on the catalyst deterioration rate calculated by the rate calculation means. According to a fifth aspect of the present invention, in the exhaust gas purification control apparatus for an internal combustion engine according to the fourth aspect, the catalyst activation start temperature and the catalyst complete activation temperature become higher as the catalyst deterioration rate increases. It is characterized by being set. A sixth aspect of the present invention is the exhaust gas purification control apparatus for an internal combustion engine according to the fourth or fifth aspect, wherein the fuel increase correction value required for raising the temperature of the catalyst from the catalyst activation start temperature to the catalyst complete activation temperature. The fuel increase correction request value calculating means for calculating the fuel increase correction request value based on the catalyst deterioration rate is provided. The fuel increase correction means provides a fuel increase correction request for increasing the fuel supply amount. A gradual increase correction is performed by gradually increasing the fuel increase correction request value calculated by the value calculation means. According to a seventh aspect of the present invention, in the exhaust gas purification control apparatus for an internal combustion engine according to the sixth aspect, the fuel increase correction request value is set so as to perform more increase correction as the catalyst deterioration rate increases. It is characterized by.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 5 is an explanatory diagram of the overall configuration of an internal combustion engine to which the present invention is applied. The internal combustion engine in the present embodiment is an automobile engine, for example, a horizontally opposed engine.
[0019]
An intake manifold 3 is connected to the cylinder head 2 of the engine 1 so as to communicate with each intake port 2 a formed in the cylinder head 2. A throttle chamber 5 is communicated with the intake manifold 3 via an air chamber 4, and an air cleaner 7 is attached to the upstream side via an intake pipe 6. An intake air amount sensor 8 that detects an intake air amount to the engine 1 is attached immediately downstream of the air cleaner 7. The throttle chamber 5 is provided with a throttle valve 5a that is linked to an accelerator pedal (not shown). A throttle opening sensor 9 that outputs a voltage corresponding to the throttle opening is connected to the throttle valve 5a. An ISC valve 10a for adjusting the amount of intake air during idling is attached to the ISC passage 10 that bypasses the throttle valve 5a. On the upstream side of each intake port 2a of each cylinder of the intake manifold 3, an injector 11 is attached toward the intake port 2a.
[0020]
In addition, a spark plug 12 is attached to the cylinder head 2 for each cylinder. These spark plugs 12 are connected to an igniter 36 (see FIG. 6) via an ignition coil. The injector 11 is communicated with a fuel tank 16 through a fuel pipe 15. A fuel pump 17 is attached to the fuel tank 16, and the fuel is pumped to the injector 11 by the fuel pump 17.
[0021]
An exhaust manifold 21 is connected to the cylinder head 2 so as to communicate with each exhaust port 2 b formed in the cylinder head 2. In the collective portion of the exhaust manifold 21, a front O as a first air-fuel ratio sensor for detecting the oxygen concentration in the exhaust gas is provided.₂Sensor (FO₂Sensor) 22 is attached, and a catalyst 23 is interposed downstream thereof. Similarly, on the downstream side of the catalyst 23, there is a rear O as a second air-fuel ratio sensor for detecting the oxygen concentration in the exhaust gas.₂Sensor (RO₂Sensor) 24 is attached. An exhaust temperature sensor 25 for detecting the temperature of the exhaust gas flowing into the catalyst is attached in the vicinity of the upstream entrance of the catalyst 23.
[0022]
One end of a secondary air introduction passage 26 communicating with the air cleaner 7 of the intake pipe 6 is connected to the vicinity of the exhaust valve in the exhaust port 2 b of the cylinder head 2. The secondary air control valve 26a is interposed in the. A reed valve 26b is attached between the secondary air control valve 26a of the secondary air introduction passage 26 and the exhaust port 2b. When the secondary air control valve 26a is opened, the reed valve 26b is opened by the negative pressure in the exhaust port 2b, and the atmosphere (secondary air) is introduced into the exhaust port 2b through the air cleaner 7. When the secondary air control valve 26a is closed, the communication in the secondary air introduction passage 26 is blocked and the introduction of the secondary air is stopped.
[0023]
A knock sensor 28 is attached to the cylinder block 1a of the engine 1 and a cooling water temperature sensor 29 for detecting the cooling water temperature in the cooling water passage of the cylinder block 1a is attached. A crank angle sensor 30 for detecting the rotational angle position of the crankshaft 1b and the engine rotational speed Ne is attached. Reference numeral 31 denotes a cam angle sensor that detects the rotational angle position of the cam shaft 2 c provided in the cylinder head 2. Reference numeral 33 denotes an intake pipe pressure sensor that detects an intake pipe pressure downstream of the throttle valve. In addition, the description of the members shown in the figure that are not directly related to the function of the present invention is omitted.
[0024]
The engine 1 having the above configuration is controlled by an electronic control unit (ECU) 32 shown in FIG. The ECU 32 is a well-known central processing unit including a CPU, a ROM storing a control program, a RAM storing various data, a backup RAM storing various learning data, an input / output circuit, a bus line connecting them, and the like. It is mainly composed of computer systems. Further, as shown in FIG. 6, on the input side of the input / output circuit, there are a throttle opening sensor 9, an intake air amount sensor 8, an intake pipe pressure sensor 33, a cooling water temperature sensor 29, an exhaust temperature sensor 25, an FO.₂Sensor 22, RO₂A sensor 24 is connected, and a cam angle sensor 31, a crank angle sensor 30, and a knock sensor 28 are further connected. Further, a vehicle speed sensor 34 for detecting the vehicle traveling speed and a select lever position sensor 35 for detecting the select position of the A / T (automatic transmission) select lever are connected. On the other hand, an igniter 36 is connected to the output side of the input / output circuit, and an ISC valve 10a, an injector 11, and a secondary air control valve 26a are connected.
[0025]
The ECU 32 performs various arithmetic processes based on detection signals from the sensors, and outputs control signals to various actuators such as the injector 11 and the ISC valve 10a based on the calculation results to control the operating state of the engine 1. . For example, the air-fuel ratio feedback control, which is one of the engine controls, is a basic method for determining the basic fuel supply amount from the intake air amount Q of the engine detected by the intake air amount sensor 8 and the engine speed Ne detected by the crank angle sensor 30. The fuel injection pulse width Tp (= K × Q / Ne; K is a constant) is calculated, and the basic fuel injection pulse width Tp is calculated as FO.₂Air-fuel ratio correction is performed using an air-fuel ratio feedback correction coefficient LAMBDA set based on the output of the sensor 22 and various increase correction coefficients COEF set based on detection signals from the coolant temperature sensor 29, the throttle opening sensor 9, and the like. Is done by. Further, as is well known, the basic fuel injection pulse width Tp is learned and corrected, and further, the voltage is corrected to obtain the fuel injection pulse width Ti that determines the final fuel supply amount. A signal corresponding to the fuel injection pulse width Ti obtained here is output to the injector 11 and a considerable amount of fuel is injected from the injector 11.
[0026]
Further, the ECU 32 performs exhaust gas purification control that improves the exhaust gas purification rate at the time of cold start as one of engine operation controls. Here, when the engine 1 is cold-started, the introduction of secondary air and the increase correction of the fuel supply amount are performed, the catalyst 23 is activated early, and the exhaust emission is reduced.
[0027]
The exhaust gas purification control of the engine 1 by the ECU 32 will be described according to the flowchart of FIG. FIG. 1 is a flowchart for explaining an exhaust gas purification control process of the engine 1, and FIG. 2 is a time chart for explaining a control state at the time of exhaust gas purification control.
[0028]
First, in step S101, the engine speed Ne, the cooling water temperature Tw, the intake air amount Q, and the like are detected by each sensor, and the engine operating state is detected based on these. At the same time, the catalyst deterioration rate X, which is one of the learning data stored in the backup RAM of the ECU 32, is read, and the catalyst activation start, which is the temperature at which the catalyst 23 starts to be activated based on the catalyst deterioration rate X, is read. The catalyst complete activation temperature Tp which is the temperature at which the catalyst 23 is completely activated and the fuel increase correction value for correcting the increase in the fuel supply amount, and the catalyst 23 is fully activated from the catalyst activation start temperature Ts. A fuel increase correction request value Fc0, which is a fuel increase correction value necessary for raising the temperature to the temperature Tp, is calculated and temporarily stored in the RAM of the ECU 32, respectively.
[0029]
The catalyst deterioration rate X is obtained when the engine 1 is in steady operation during normal driving.₂Sensor 22 and RO₂O upstream and downstream of the catalyst 23 detected by the sensor 24₂It is calculated by comparing the densities, stored in the backup RAM as learning data, and updated at a predetermined timing.
[0030]
FIG. 3 is a graph showing the relationship between the catalyst activation temperature and the fuel increase correction request value and the catalyst deterioration rate X. The catalyst activation start temperature Ts and the catalyst complete activation temperature Tp are set so as to become higher as the catalyst deterioration rate X increases, that is, as the degree of deterioration of the catalyst 23 increases, and the fuel increase correction request value Fc0 is also set to perform more increase correction as the catalyst deterioration rate X increases.
[0031]
Since the actual catalyst activation start temperature Ts and the catalyst complete activation temperature Tp increase and change as the deterioration of the catalyst 23 progresses, the catalyst activation start temperature Ts and the catalyst complete activation temperature Tp are estimated according to the deterioration state of the catalyst 23. Then, based on the estimated catalyst activation start temperature Ts and the catalyst complete activation temperature Tp, the introduction of secondary air and the increase correction of the fuel supply amount are performed.
[0032]
Next, in step S102, it is determined whether or not the operating state of the engine 1 is a cold start state. Here, when the engine speed Ne is 500 rpm or less (Ne ≦ 500 rpm) and the cooling water temperature at the start is Tw of 0 ° or more (Tw ≧ 0 °) (YES), the engine is in the cold start state. If it is determined that there is, the process proceeds to step S103. If at least one of the conditions is not satisfied (NO), it is determined that the engine is not in the cold start state, and this flow is exited (return). The determination process in step S102 corresponds to the cold start state determination means of claim 1.
[0033]
In step S103, the secondary air introduction start engine speed Nair capable of starting the introduction of secondary air is calculated based on the cooling water temperature Tw at the time of starting. Then, the process proceeds to step S104 in order to determine whether or not the engine speed Ne has exceeded the speed at which the introduction of secondary air can be started. FIG. 4 is a graph showing the relationship between the secondary air introduction start engine speed Nair and the coolant temperature Tw. As shown in FIG. 4, the secondary air introduction start engine speed Nair is set so that the secondary air introduction start engine speed Nair that introduces secondary air decreases as the cooling water temperature Tw rises. Yes.
[0034]
In step S104, it is determined whether or not the current engine speed Ne has reached the secondary air introduction start engine speed Nair calculated in S103 (Ne ≧ Nair), and the secondary air introduction start engine speed Nair or less. If it is determined that the engine speed is low (NO), the process returns to the process of step S103 again, and the secondary engine speed Ne is increased until the engine speed Ne is higher than the secondary air introduction start engine speed Nair. There is no introduction. On the other hand, if it is determined in step S104 that the engine speed Ne has reached the secondary air introduction start engine speed Nair (YES), the process proceeds to step S105, and the valve opening control of the secondary air control valve 26a is performed. Thus, introduction of secondary air is started. The determination process in step S104 corresponds to the secondary air introduction start means of claim 1.
[0035]
When the introduction of secondary air is started in step S105, the process proceeds to step S106, and first, a fuel increase correction value Fc for increasing the fuel supply amount is corrected._nIs initially set to zero (Fc_n= 0), this fuel increase correction value Fc_n(= 0) is reflected in the fuel supply amount. Therefore, after the start of secondary air introduction, the fuel increase correction value Fc_nThe fuel increase correction value Fc gradually from the state without the fuel increase correction due to_nAnd the fuel increase correction value Fc_nThus, the fuel supply amount is gradually increased and corrected by correcting the fuel supply amount.
[0036]
Next, the process proceeds to step S107, where the current exhaust gas temperature (representing the catalyst temperature) Te based on the detection signal of the exhaust temperature sensor 25 is equal to or higher than the catalyst activation start temperature Ts obtained based on the catalyst deterioration rate X in step S101. It is determined whether or not there is. Here, when the exhaust gas temperature Te is lower than the catalyst activation start temperature Ts (NO), the process returns to step S106, and only the secondary air is introduced until the temperature becomes equal to or higher than the catalyst activation start temperature Ts. It waits without performing the increase correction of the fuel supply amount. If it is determined that the exhaust gas temperature Te is equal to or higher than the catalyst activation start temperature Ts (YES), the process proceeds to step S108 and subsequent steps in order to correct the fuel supply amount.
[0037]
In step S108 to step S110, a process for performing a gradual increase correction for gradually increasing the fuel supply amount is performed. First, in step S108, the fuel increase correction value Fc for increasing the fuel supply amount is corrected._nIs gradually updated. Fuel increase correction value Fc_nIs obtained by the following equation (1).
[0038]
Fc_n= Fc_(N-1)+ Fd ……… ▲ 1 ▼
According to equation (1), the fuel increase correction value Fc_nIs the previously obtained fuel increase correction value Fc_(N-1)Is obtained by adding a predetermined fuel correction value increase amount Fd. In the present embodiment, the fuel correction value increase amount Fd is the previously determined fuel increase correction value Fc._(N-1)Is set to a value that increases 2%.
[0039]
In step S108, the fuel increase correction value Fc_nIs obtained, the routine proceeds to step S109, where the fuel increase correction value Fc_nIs reflected in the fuel supply amount. Therefore, when the fuel is injected from the injector 11 at a predetermined timing, the fuel increase correction value Fc_nFuel increased by the amount is injected.
[0040]
Next, the process proceeds to step S110, and the fuel increase correction value Fc obtained in step S108._nHas reached the fuel increase correction request value Fc0 obtained based on the catalyst deterioration rate X in step S101 (Fc_nIt is determined whether ≧ Fc0) or not.
[0041]
Here, the fuel increase correction value Fc_nIs determined to be less than the fuel increase correction request value Fc0 (NO in step S110), the process returns to the determination in step S107, and whether or not the current exhaust gas temperature Te is higher than the catalyst activation start temperature Ts. Determine again. If it is determined that the temperature is higher than the catalyst activation start temperature Ts (YES in step S107), the fuel increase correction value Fc is determined in step S108._nIs further updated by the fuel correction value increase amount Fd, and the fuel increase correction value Fc is updated in step S109._nIs reflected in the fuel supply amount. Therefore, the fuel increase correction value Fc_nIs gradually increased until the fuel increase correction request value Fc0 is reached, and as a result, a gradual increase correction for gradually increasing the fuel supply amount is performed.
[0042]
On the other hand, in step S110, the fuel increase correction value Fc_nIs determined to be less than the fuel increase correction request value Fc0 (NO), the process returns to the determination in step S107 again. If it is determined in step S107 that the exhaust gas temperature (catalyst temperature) Te is lower than the catalyst activation start temperature Ts (NO), the process returns to step S106, and the fuel supply amount increase correction is stopped. In such a state, the fuel increase correction value Fc_nIs initially set to zero, and this fuel increase correction value Fc_nIs reflected in the fuel supply amount, so that the fuel increase correction value Fc substantially_nThe fuel supply amount increase correction due to is canceled.
[0043]
When the exhaust gas temperature (catalyst temperature) Te becomes equal to or higher than the catalyst activation start temperature Ts again (YES in step S107), the process proceeds to step S108 and subsequent steps to gradually increase the fuel supply amount. Correction is resumed. Accordingly, it is possible to perform a gradual increase correction according to the temperature increase rate of the catalyst 23.
[0044]
Thereby, for example, when the catalyst 23 is excessively cooled by the introduction of the secondary air and the catalyst temperature becomes lower than the catalyst activation start temperature Ts, the correction of gradually increasing the fuel supply amount may be temporarily stopped. it can. Therefore, even though the oxidation function of the catalyst is stopped, it is possible to prevent the exhaust emission from deteriorating because the fuel increase correction is continued and the fuel increase becomes excessive.
[0045]
As shown in the graph of FIG. 2, in the conventional case, at the same time as the exhaust gas temperature Te reaches the catalyst activation start temperature Ts, the fuel increase correction value Fc0 is reflected in the fuel supply amount and the fuel supply amount is increased at once. Therefore, there is a risk that the HC emission amount temporarily increases suddenly (broken line in FIG. 4E). However, according to the processing according to the present invention, since the fuel supply amount is gradually increased in accordance with the increase in the catalyst temperature, the incremental increase correction is performed, so that the ability of the oxidation function of the catalyst 23 to be improved as the catalyst temperature increases. Accordingly, the amount of fuel can be increased appropriately. Therefore, for example, immediately after the start of the increase correction, it is possible to prevent the fuel from being increased at a stroke regardless of the temperature state of the catalyst 23, and to prevent a large amount of CO and HC from being discharged temporarily.
[0046]
And the fuel increase correction value Fc_nIs a fuel increase correction request value Fc0 or more (Fc_nIf it is determined that ≧ Fc0) (YES in step S110), the loop processing of step S107 to step S110 is exited, and the process proceeds to step S111. The processing in step S107 to step S110 corresponds to the fuel increase correction means of claim 1.
[0047]
In steps S111 to S114, it is determined whether or not the catalyst temperature has increased to the catalyst complete activation temperature Tp. First, in step S111, whether or not the exhaust gas temperature (catalyst temperature) Te is equal to or higher than the catalyst complete activation temperature Tp determined based on the catalyst deterioration rate X in step S101 based on the detection signal of the exhaust temperature sensor 25. Is judged. If the exhaust gas temperature Te is equal to or higher than the catalyst complete activation temperature Tp (YES in step S111), the down timer process in steps S113 and S114 is performed to determine whether or not the temperature state is maintained for a predetermined time or more. Migrate to
[0048]
In step S113, the accumulated time determination value TMp_(N-1)The value obtained by decrementing 1 from 1 is a new cumulative time judgment value TMp._nIs set as (TMp_n= TMp_(N-1)-1). In step S114, the cumulative time determination value TMp obtained in step S113._nIs subtracted to 0 (TMp_n= 0), and it is determined whether or not the exhaust gas temperature (catalyst temperature) Te has been maintained at a temperature equal to or higher than the catalyst complete activation temperature Tp for a predetermined time.
[0049]
And the cumulative time judgment value TMp_nIs determined to be 0 (YES in step S114), it is determined that the catalyst temperature has been warmed to the catalyst complete activation temperature Tp, and the introduction of secondary air and the fuel supply amount increase correction are to be stopped. The process proceeds to step S115 and subsequent steps. In the present embodiment, the accumulated time determination value TMp_nIs set to 50, and the control routine is set to 100 ms. Therefore, if the exhaust gas temperature Te is maintained at a temperature state equal to or higher than the catalyst complete activation temperature Tp for 5 seconds or more, it is determined that the catalyst temperature has been warmed to the catalyst complete activation temperature Tp.
[0050]
In step S115, the fuel increase correction value Fc_nIs set to 0 (Fc_n= 0), and in step S116, the fuel increase correction value Fc_nIs reflected in the fuel supply amount, and control is performed to close the secondary air control valve 26a and stop the introduction of secondary air. Thereby, the introduction of the secondary air and the increase correction of the fuel supply amount are stopped, and this flow is finished (return). The processing of step S115 and step S116 corresponds to the early activation stop means of claim 1.
[0051]
On the other hand, if it is determined in step S111 that the exhaust gas temperature (catalyst temperature) Te has not risen to the catalyst complete activation temperature Tp (NO), or the determination in step S114 is the cumulative time determination value TMp._nIf NO is determined to be 0 (NO), the process proceeds to step S112.
[0052]
In step S112, it is determined whether or not the automobile having the engine 1 is in a traveling state. Here, when the vehicle speed sensor 34 detects a vehicle speed equal to or higher than a predetermined speed, or when the select lever position sensor 35 outputs a D (travel) range as the position position of the select lever, the vehicle is in a travel state. It is judged.
[0053]
If it is determined in step S112 that the vehicle is in the traveling state (YES), the process proceeds to step S115 and subsequent steps, and control for immediately stopping the fuel supply amount increase correction and the introduction of secondary air is performed. As a result, it is possible to prevent the exhaust emission from deteriorating due to the air-fuel ratio balance being lost due to a change in the operating state of the internal combustion engine due to traveling.
[0054]
If it is determined in step S112 that the vehicle is not in a running state (NO), the process proceeds to step S111 again to determine whether the current exhaust gas temperature Te is equal to or higher than the catalyst complete activation temperature Tp. Is done. When it is determined that the exhaust gas temperature Te is equal to or higher than the catalyst complete activation temperature Tp (YES), the process proceeds to step S113 and the accumulated time determination value TMp._nIs decremented, and in step S114, the accumulated time judgment value TMp_nIt is determined again whether or not becomes zero. Thus, the accumulated time judgment value TMp_nUntil the value becomes 0, it is possible to determine whether or not the exhaust gas temperature Te has been maintained at a temperature equal to or higher than the catalyst complete activation temperature Tp for a predetermined time by repeatedly performing the processing of step S111 to step S114.
[0055]
In step S114, the cumulative time determination value TMp_nIs determined to be 0 (YES), the process proceeds to step S115 and the subsequent steps to stop the introduction of the secondary air and the increase correction of the fuel supply amount. End the exhaust gas purification control (return).
[0056]
Thus, according to the embodiment of the present invention, the exhaust gas temperature Te is maintained at a temperature equal to or higher than the catalyst complete activation temperature Tp for a predetermined time, whereby the catalyst temperature is warmed to the catalyst complete activation temperature Tp. Therefore, the catalyst 23 can be reliably activated.
[0057]
Further, after the catalyst 23 is completely activated, by correcting the increase in the fuel supply amount and stopping the introduction of the secondary air, the catalyst 23 is abnormally heated by unnecessary secondary air, or the fuel supply amount is unnecessary. By increasing the amount, it is possible to prevent the exhaust emission from deteriorating and the fuel consumption from deteriorating.
[0058]
The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the present embodiment, the fuel correction value increase amount Fd for increasing the fuel increase correction value is set to a constant value, but may be a variable value that changes according to the temperature state of the catalyst 23, for example.
[0059]
【The invention's effect】
According to the first aspect of the present invention, at the cold start, the introduction of the secondary air is started first, and when the catalyst temperature rises and reaches the catalyst activation start temperature, the fuel supply amount is increased. Since the gradually increasing correction for gradually increasing the amount is started at the same time, the amount of fuel can be appropriately increased according to the ability of the oxidation function of the catalyst to be improved as the catalyst temperature increases. Therefore, it is possible to prevent a large amount of CO and HC from being temporarily discharged due to a sudden increase in fuel regardless of the temperature state of the catalyst after the start of the increase correction.
[0060]
According to the second aspect of the present invention, when the catalyst temperature becomes lower than the catalyst activation start temperature during the gradual increase correction, the fuel supply amount increase correction is stopped. When the temperature falls below the catalyst activation start temperature and the oxidation function of the catalyst stops, it is possible to prevent the exhaust emission from deteriorating due to an excessive fuel supply amount. In addition, since the fuel supply amount gradually increases again when the catalyst temperature becomes equal to or higher than the catalyst activation start temperature, the fuel supply amount is gradually increased according to the temperature increase rate of the catalyst. It can be performed.
[0061]
According to the invention of claim 3, since the traveling state detecting means detects the traveling state of the automobile, the introduction of the secondary air into the exhaust passage and the increase correction of the fuel supply amount are stopped. It is possible to prevent the exhaust emission from deteriorating due to the change in the operating state and the deterioration of the exhaust emission.
[Brief description of the drawings]
FIG. 1 is a flowchart illustrating an engine exhaust gas purification control process.
FIG. 2 is a time chart for explaining a control state during exhaust gas purification control.
FIG. 3 is a graph showing a relationship between a catalyst activation temperature and a fuel increase correction request value and a catalyst deterioration rate.
FIG. 4 is a graph showing the relationship between secondary air introduction start engine speed and cooling water temperature.
FIG. 5 is an explanatory diagram of the overall configuration of an internal combustion engine according to the present invention.
FIG. 6 is a configuration diagram of a control circuit.
[Explanation of symbols]
1 engine (internal combustion engine)
22 FO₂Sensor
23 Catalyst
24 RO₂Sensor
25 Exhaust temperature sensor
26a Secondary air control valve
29 Cooling water temperature sensor
Nair Secondary air introduction start engine speed
Ts Catalyst activation start temperature
Tp catalyst complete activation temperature
Fc0 Fuel increase correction request value
Fc_n  Fuel increase correction value
Fd Fuel correction value increase
TMp_n  Cumulative time judgment value

Claims (7)

Cold start state determining means for determining whether the operating state of the internal combustion engine is a cold start state;
Secondary air introduction starting means for starting the introduction of secondary air upstream of the catalyst provided in the middle of the exhaust passage of the internal combustion engine based on the determination that the operating state of the internal combustion engine is a cold start state;
The fuel supply amount increase correction is performed until the temperature of the catalyst rises and reaches the catalyst activation start temperature at which the activation of the catalyst starts after the secondary air introduction start means starts introducing the secondary air. Fuel increase correction means for starting an increase correction of the fuel supply amount when the temperature of the catalyst reaches the catalyst activation start temperature without performing,
Early activation stop means for stopping the introduction of secondary air into the exhaust passage and the increase correction of the fuel supply amount when the temperature of the catalyst rises to the catalyst complete activation temperature at which activation starts completely. Prepared,
The exhaust gas purification control apparatus for an internal combustion engine, wherein the fuel increase correction means performs a gradual increase correction for gradually increasing the fuel supply amount as the temperature of the catalyst increases. The fuel increase correction means includes
When the catalyst temperature falls below the catalyst activation start temperature, stop the fuel supply amount increase correction,
2. The exhaust gas purification of an internal combustion engine according to claim 1, wherein when the catalyst temperature becomes equal to or higher than the catalyst activation start temperature again, the gradually increasing correction for gradually increasing the fuel supply amount is resumed. Control device. The early activation stopping means includes
When the traveling state detecting means for determining whether or not the vehicle is in a traveling state detects the traveling state, control is performed to stop the introduction of secondary air into the exhaust passage and the increase correction of the fuel supply amount. The exhaust gas purification control apparatus for an internal combustion engine according to claim 1 or 2. O at the upstream side and downstream side of the catalyst at a predetermined timing ₂ Catalyst deterioration rate calculating means for calculating the catalyst deterioration rate of the catalyst based on the concentration;
Catalyst activation start temperature calculating means for calculating the catalyst activation start temperature based on the catalyst deterioration rate calculated by the catalyst deterioration rate calculating means;
Catalyst complete activation temperature calculating means for calculating the catalyst complete activation temperature based on the catalyst deterioration rate calculated by the catalyst deterioration rate calculating means;
The exhaust gas purification control device for an internal combustion engine according to any one of claims 1 to 3, wherein The exhaust gas purification control of an internal combustion engine according to claim 4, wherein the catalyst activation start temperature and the catalyst complete activation temperature are set to become higher as the catalyst deterioration rate increases. apparatus. Fuel increase correction request value calculation means for calculating a fuel increase correction request value, which is a fuel increase correction value necessary for raising the temperature of the catalyst from the catalyst activation start temperature to the catalyst complete activation temperature, based on the catalyst deterioration rate. Have
The fuel increase correction means gradually increases a fuel increase correction value for increasing the fuel supply amount until the fuel increase correction request value calculated by the fuel increase correction request value calculation means is reached, thereby performing the gradual increase correction. The exhaust gas purification control apparatus for an internal combustion engine according to claim 4 or 5, wherein the control is performed. The exhaust gas purification control apparatus for an internal combustion engine according to claim 6, wherein the fuel increase correction request value is set so as to perform more increase correction as the catalyst deterioration rate increases.

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