JP5077047B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention executes enrichment control for enriching the air-fuel ratio of the exhaust gas flowing into the catalyst to be less than the stoichiometric air-fuel ratio in order to reduce the oxygen storage amount of the catalyst, and the estimated oxygen storage amount is not more than a predetermined amount. The present invention relates to a control device for an internal combustion engine that stops the enrichment control on condition that the determination is made.

  An example of this type of internal combustion engine is disclosed in Patent Document 1. In such an internal combustion engine including the internal combustion engine described in Patent Document 1, a catalyst having an oxygen storage function is provided in the exhaust passage. In such a catalyst, oxygen is stored when reducing NOx flowing into the catalyst, and the stored oxygen is released when oxidizing unburned components such as CO flowing into the catalyst. In addition, the maximum amount of oxygen that can be stored in the catalyst (hereinafter referred to as oxygen storage amount) is the maximum oxygen storage amount, and when the oxygen storage amount of the catalyst reaches the maximum oxygen storage amount, NOx is further purified. Can not do it. Further, when no oxygen is stored in the catalyst, unburned components cannot be purified. Therefore, in order to sufficiently exhibit such a purification function of the catalyst, it is important to maintain the oxygen storage amount of the catalyst at an appropriate amount.

  On the other hand, fuel cut control for interrupting fuel injection is performed during deceleration operation of the internal combustion engine. At this time, since a large amount of oxygen flows into the catalyst in a short time, the oxygen storage amount of the catalyst increases, and in many cases, the maximum oxygen storage amount is reached. For this reason, when the fuel cut control is stopped and the fuel injection is restarted, the oxygen storage amount of the catalyst is close to the maximum oxygen storage amount for a while, so even if NOx flows into the catalyst, it is purified. The problem of not being able to do occurs.

  Thus, after the fuel cut control is stopped, the fuel injection amount of the internal combustion engine is increased, and enrichment control is executed to make the air-fuel ratio of the exhaust gas flowing into the catalyst richer than the stoichiometric air-fuel ratio. As a result, the oxygen storage amount of the catalyst can be reduced by allowing the unburned component to flow into the catalyst, and even if NOx flows into the catalyst, it can be suitably purified.

In the technique described in Patent Document 1, the oxygen storage amount of the catalyst is estimated, and the enrichment control is stopped when the estimated oxygen storage amount becomes a predetermined amount or less. In addition, the oxygen concentration on the downstream side of the exhaust of the catalyst is detected when a predetermined time has elapsed since the enrichment control is started, and the enrichment control is performed when the detected oxygen concentration is lower than the predetermined concentration. I try to stop. Thereby, even when the estimated oxygen storage amount is larger than the predetermined amount, the enrichment control can be stopped at an early stage if the actual oxygen storage amount of the catalyst is predicted to be small.
JP 2005-69187 A

  However, it may be desirable to continue the enrichment control to further reduce the oxygen storage amount of the catalyst even when the oxygen concentration on the exhaust gas downstream side of the catalyst is lower than a predetermined concentration. However, in the conventional control device for an internal combustion engine, the enrichment control is stopped when the oxygen concentration on the exhaust gas downstream side of the catalyst is lower than a predetermined concentration, so there is still room for improvement in this respect.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a control device for an internal combustion engine capable of stopping the enrichment control at a more accurate timing.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
(1) The invention according to claim 1 is an estimation means for estimating an oxygen storage amount of an exhaust purification catalyst provided in an exhaust passage, and an exhaust gas flowing into the catalyst to reduce the oxygen storage amount of the catalyst. The enrichment control for enriching the air / fuel ratio more than the stoichiometric air / fuel ratio is executed, and the enrichment control is stopped on the condition that the oxygen storage amount estimated by the estimation means is determined to be equal to or less than a predetermined amount. In a control apparatus for an internal combustion engine comprising a rich control means, a concentration cell type whose output varies depending on whether the air-fuel ratio on the exhaust downstream side of the catalyst is richer or leaner than the stoichiometric air-fuel ratio includes an oxygen sensor, the rich control means, when the oxygen sensor indicates that the air-fuel ratio is on the lean side sets a first predetermined amount as the predetermined amount, the output of the oxygen sensor is the air When the ratio indicates that it is on the rich side, a second predetermined amount larger than the first predetermined amount is set as the predetermined amount, and the second predetermined amount is such that the air-fuel ratio is richer from the lean side than the stoichiometric air-fuel ratio. The gist of the present invention is that it is set to an amount smaller than the oxygen storage amount of the catalyst estimated to change to the side .

  According to the above configuration, the predetermined amount for stopping the enrichment control is increased when the oxygen concentration on the downstream side of the exhaust of the catalyst is low compared to when the oxygen concentration is high. For this reason, when the actual oxygen storage amount is predicted to be small, the predetermined amount can be made larger than when the actual oxygen storage amount is predicted to be large. As a result, even if the oxygen concentration on the exhaust gas downstream side of the catalyst becomes lower than the predetermined concentration, the enrichment control is not stopped immediately, but the estimated oxygen storage amount depends on the oxygen concentration on the exhaust gas downstream side of the catalyst. The enrichment control is continued until the predetermined amount or less is reached. Therefore, the enrichment control can be stopped at a more accurate timing.

That is, as this, a predetermined amount for stopping the enrichment control, by appropriately setting the one of the first predetermined amount and the second predetermined amount in response to the oxygen concentration downstream of the catalyst, enrichment Control can be stopped at a more appropriate timing.

The oxygen sensor of concentrated light cell type, when the oxygen concentration of the exhaust downstream of the catalyst is higher than a predetermined concentration outputs a voltage lower than the predetermined voltage, the predetermined voltage or more when the oxygen concentration is predetermined concentration or less Is output. For this reason, the output voltage of the oxygen sensor sets the first predetermined amount as the predetermined amount when less than the predetermined voltage, setting the second predetermined amount as the predetermined amount when the output voltage of the oxygen sensor is the predetermined voltage or more You just have to do it.

(2) The invention of claim 1, such as by the invention of claim 2, wherein the enrichment control means, wherein on condition that the interrupting fuel cut control fuel injection of the internal combustion engine is stopped It can be embodied in such a manner that the enrichment control is started.

  1 to 6, an embodiment in which the control device for an internal combustion engine according to the present invention is embodied as a control device for an in-vehicle gasoline engine (hereinafter, “engine 10”) will be described. The engine 10 is a port injection type multi-cylinder internal combustion engine.

FIG. 1 shows a schematic configuration of the engine 10 and an electronic control unit 60 that controls the engine 10.
Each cylinder of the engine 10 is provided with a spark plug 12 that ignites a mixture of fuel and air in the combustion chamber 11. An intake port 22 that is opened and closed by an intake valve 21 is connected to the combustion chamber 11, and a fuel injection valve 13 that injects fuel toward the intake port 22 in the middle of the intake passage 20 connected to the intake port 22 is a cylinder. It is provided for each. A surge tank 23 is connected in the middle of the intake passage 20, and a throttle valve 25 whose opening degree is adjusted by a throttle motor 24 is provided upstream of the surge tank 23. When the opening degree of the throttle valve 25 is changed, the amount of air supplied to the combustion chamber 11 through the intake passage 20 is adjusted accordingly.

  Further, an exhaust port 32 that is opened and closed by an exhaust valve 31 is connected to the combustion chamber 11, and a catalytic converter 33 is provided in the middle of the exhaust passage 30 connected to the exhaust port 32. The catalytic converter 33 is provided with a three-way catalyst (hereinafter referred to as “catalyst 34”) as an exhaust purification catalyst. The catalyst 34 has an oxygen storage function, stores oxygen when reducing NOx flowing into the catalyst 34, and is stored in the catalyst 34 when oxidizing unburned components such as CO flowing into the catalyst 34. Release oxygen.

  The engine 10 is provided with various sensors for detecting the operating state. That is, an accelerator opening sensor 51 that detects the amount of depression of the accelerator pedal 41 (hereinafter referred to as “accelerator opening ACCP”) and an engine rotation speed sensor 52 that detects the engine rotation speed NE from the rotation of the crankshaft are provided. Further, a reference crank angle sensor 53 for detecting the rotation phase of the intake camshaft to determine the reference crank angle, and a throttle opening sensor 54 for detecting the opening of the throttle valve 25 (hereinafter referred to as “throttle opening TA”) are provided. Is provided. Further, on the upstream side of the throttle valve 25, an air flow meter 55 for detecting the amount of air taken into the combustion chamber (hereinafter referred to as “intake air amount GA”) is provided. Further, a cooling water temperature sensor 56 for detecting the temperature of the engine cooling water (hereinafter referred to as “engine cooling water temperature THW”) is provided. Further, an air-fuel ratio sensor 57 for detecting the air-fuel ratio of the exhaust gas flowing into the catalytic converter 33 is provided upstream of the catalytic converter 33 in the exhaust passage 30. An oxygen sensor 58 that detects the air-fuel ratio of the exhaust gas flowing out from the catalytic converter 33 is provided downstream of the catalytic converter 33 in the exhaust passage 30. In addition to these sensors, various sensors are provided as necessary. Detection signals of these sensors 51 to 58 are input to an electronic control unit 60 that executes various controls of the engine 10.

Here, output characteristics of the air-fuel ratio sensor 57 and the oxygen sensor 58 will be described.
FIG. 2 shows the relationship between the actual air-fuel ratio and the output voltage Vaf of the air-fuel ratio sensor 57, and FIG. 3 shows the relationship between the actual air-fuel ratio and the output voltage Vox of the oxygen sensor 58.

  As shown in FIG. 2, the air-fuel ratio sensor 57 outputs a voltage Vaf that is proportional to the actual air-fuel ratio, and the larger the air-fuel ratio, that is, the higher the air-fuel ratio is on the lean side, the larger the voltage Vaf is. Output. Note that this corresponds to the voltage when the voltage V1 is the stoichiometric air-fuel ratio.

  As shown in FIG. 3, the oxygen sensor 58 outputs a voltage Vox of about 1 V when the actual air-fuel ratio is richer than the stoichiometric air-fuel ratio, and the actual air-fuel ratio is leaner than the stoichiometric air-fuel ratio. Sometimes it outputs a voltage Vox of about 0V. Further, when the air-fuel ratio changes from the rich side to the lean side across the stoichiometric air-fuel ratio, the voltage Vox changes rapidly. Note that this corresponds to a voltage when the voltage V2 changes from the rich side to the lean side (or from the lean side to the rich side) with the theoretical air-fuel ratio interposed therebetween.

  As shown in FIG. 1, the electronic control unit 60 includes a memory for storing a program for executing various controls, a calculation map, and various data calculated when the control is executed. For example, the following controls are executed based on the engine operating state or the like ascertained from the output values of various sensors including the sensors 51 to 58. That is, the fuel injection amount Q is calculated based on the throttle control for controlling the throttle valve 25 in accordance with the accelerator opening ACCP that is requested by the driver, the engine rotational speed NE, the intake air amount GA, and the like. Fuel injection control for controlling the fuel injection valve 13 according to Q is executed. Further, the air-fuel ratio of the air-fuel mixture is estimated based on the detection result of the air-fuel ratio sensor 57, and the air-fuel ratio correction value for the fuel injection amount Q is calculated so that the air-fuel ratio thus estimated becomes the target air-fuel ratio. Air-fuel ratio feedback control for increasing / decreasing the amount Q is executed. Furthermore, various controls such as a fuel cut control for interrupting fuel injection when the vehicle is decelerated, and a rich control for making the air-fuel ratio of the exhaust gas flowing into the catalyst 34 richer than the stoichiometric air-fuel ratio after the fuel cut control is stopped. Run.

  Further, during the operation of the engine 10, the intake air amount GA and the output voltage Vaf of the air-fuel ratio sensor 57 are monitored, and the oxygen storage amount EOX is based on the intake air amount GA and the output voltage Vaf of the air-fuel ratio sensor 57. I try to estimate. Then, the enrichment control is stopped on the condition that it is determined that the estimated oxygen storage amount EOX is equal to or less than the predetermined amount EOXth.

  Here, for example, if the intake air amount GA is constant, that is, if the amount of exhaust gas flowing into the catalyst 34 is constant, when the air-fuel ratio of the exhaust gas flowing into the catalyst 34 is leaner than the stoichiometric air-fuel ratio, the exhaust gas As the air-fuel ratio of the engine becomes leaner, the increase amount of the oxygen storage amount EOX per unit period is calculated to be larger. On the other hand, when the air-fuel ratio of the exhaust gas flowing into the catalyst 34 is richer than the stoichiometric air-fuel ratio, the reduction amount of the oxygen storage amount EOX per unit period is calculated to be larger as the exhaust air-fuel ratio is richer. It has become. Further, the larger the intake air amount GA is, the larger the amount of increase (or decrease) in the oxygen storage amount EOX per unit time is calculated, assuming that the amount of exhaust gas flowing into the catalyst 34 is larger.

  By the way, the oxygen storage amount of the catalyst 34 has a maximum oxygen storage amount which is an upper limit value, and when the oxygen storage amount of the catalyst 34 reaches the maximum oxygen storage amount, NOx cannot be further purified. Further, when no oxygen is occluded in the catalyst 34, the unburned components cannot be purified. Therefore, in order to sufficiently exhibit such a purification function of the catalyst 34, it is important to maintain the oxygen storage amount of the catalyst 34 at an appropriate amount.

  On the other hand, when the vehicle is decelerated, specifically, when the engine speed NE is equal to or higher than a predetermined speed and the accelerator opening ACCP is “0”, fuel cut control is executed. At this time, since a large amount of oxygen flows into the catalyst 34 in a short time, the oxygen storage amount of the catalyst 34 increases, and in many cases, the maximum oxygen storage amount is reached. For this reason, when the fuel cut control is stopped and the fuel injection is restarted, the oxygen storage amount of the catalyst 34 is close to the maximum oxygen storage amount for a while. The problem that cannot be purified occurs.

  Therefore, in the present embodiment, after the fuel cut control is stopped, the fuel injection amount Q is increased, and the enrichment control for making the air-fuel ratio of the exhaust gas flowing into the catalyst 34 richer than the stoichiometric air-fuel ratio is executed. . As a result, the amount of oxygen stored in the catalyst 34 is reduced by allowing unburned components to flow into the catalyst 34.

During the enrichment control, the output voltage Vox of the oxygen sensor 58 is monitored, and when the output voltage Vox is lower than the predetermined voltage V2, the first predetermined amount E1 is set as the predetermined amount EOXth. When the output voltage Vox of the oxygen sensor 58 is equal to or higher than the predetermined voltage V2, a second predetermined amount E2 (E2> E1) larger than the first predetermined amount E1 is set as the predetermined amount EOXth. Here, when the output voltage Vox of the oxygen sensor 58 changes from the state lower than the predetermined voltage V2 to the predetermined voltage V2, that is, the air-fuel ratio on the downstream side of the catalyst 34 changes from the lean side to the rich side with respect to the stoichiometric air-fuel ratio. Sometimes, the second predetermined amount E2 is set so that the oxygen storage amount EOX estimated at that time is larger than the second predetermined amount E2. Incidentally, the first predetermined amount E1 is set to a value that is ¼ times the maximum oxygen storage amount EOXmax, and the second predetermined amount E2 is set to a value that is 2.5 times the first predetermined amount.
<Oxygen storage amount calculation process>
Next, the oxygen storage amount calculation process will be described in detail with reference to FIG. FIG. 4 is a flowchart showing the procedure of the oxygen storage amount calculation process. A series of processing shown in this flowchart is repeatedly executed at predetermined crank angles by the electronic control unit 60 during operation of the engine 10.

In this process, first, the output voltage Vaf of the air-fuel ratio sensor 57 at that time is read, and it is determined whether or not the output voltage Vaf is equal to or higher than a predetermined voltage V1 (step S101). That is, it is determined whether the air-fuel ratio of the exhaust gas flowing into the catalyst 34 is leaner than the stoichiometric air-fuel ratio. If the output voltage Vaf of the air-fuel ratio sensor 57 is equal to or higher than the predetermined voltage V1 (step S101: “YES”), then, the intake air amount GA at that time and the output voltage Vaf of the air-fuel ratio sensor 57 are Is read. Based on the intake air amount GA and the output voltage Vaf of the air-fuel ratio sensor 57, the amount of oxygen storage amount EOX increased from the previous control cycle to the current control cycle (hereinafter referred to as “current oxygen increase amount EOXinc”). ") Is calculated (step S102). Here, as described above, the larger the intake air amount GA and the greater the output voltage Vaf of the air-fuel ratio sensor 57, the greater the current oxygen increase amount EOXinc is calculated. When the air supplied to the combustion chamber 11 flows into the catalyst 34 as it is during the fuel cut control, the oxygen concentration coefficient (0.21) with respect to the intake air amount GA is used instead of the calculation method described above. Can be used as the current oxygen increase amount EOXinc. When the current oxygen increase amount EOXinc is calculated in this manner, the oxygen storage amount in the current control cycle (hereinafter referred to as “current oxygen storage amount EOX”) is then calculated based on the following arithmetic expression (1) (Step S1). S103). That is, a value obtained by adding the current oxygen increase amount EOXinc to the oxygen storage amount EOX in the previous control cycle is calculated as the current oxygen storage amount EOX.

EOX ← EOX + EOXinc (1)

Once the current oxygen storage amount EOX is thus calculated, it is next determined whether or not the calculated oxygen storage amount EOX is greater than or equal to the maximum oxygen storage amount EOXmax (step S104). Here, a fixed value obtained in advance by experiments or the like is used as the maximum oxygen storage amount EOXmax.

  If the oxygen storage amount EOX is greater than or equal to the maximum oxygen storage amount EOXmax in the determination process of step S104 (step S104: “YES”), the maximum oxygen storage amount EOXmax is set as the current oxygen storage amount EOX ( In step S105), this series of processes is temporarily terminated.

  On the other hand, when the calculated oxygen storage amount EOX is less than the maximum oxygen storage amount EOXmax in the determination process of step S104 (step S104: “NO”), step S105 is skipped, that is, calculated. This oxygen storage amount is set as it is as the current oxygen storage amount EOX, and this series of processes is temporarily terminated.

On the other hand, if the output voltage Vaf of the air-fuel ratio sensor 57 is less than the predetermined voltage V1 in the determination process of step S101 (step S101: “NO”), then, the intake air amount GA and the air-fuel ratio at that time The output voltage Vaf of the sensor 57 is read. Then, based on the intake air amount GA and the output voltage Vaf of the air-fuel ratio sensor 57, the amount by which the oxygen storage amount EOX has decreased from the previous control cycle to the current control cycle (hereinafter referred to as “current oxygen decrease amount EOXdec”). ]) Is calculated (step S106). Here, as described above, as the intake air amount GA is larger and the output voltage Vaf of the air-fuel ratio sensor 57 is smaller, the current oxygen reduction amount EOXdec is larger. When the current oxygen decrease amount EOXdec is calculated in this manner, the current oxygen storage amount EOX is then calculated based on the following equation (2) (step S107). That is, the current oxygen storage amount EOX is calculated by subtracting the current oxygen decrease amount EOXdec from the oxygen storage amount EOX in the previous control cycle.

EOX ← EOX-EOXdec (2)

Once the current oxygen storage amount EOX is thus calculated, it is next determined whether or not the calculated oxygen storage amount EOX is equal to or less than “0” (step S108). As a result, when the oxygen storage amount EOX is equal to or less than “0” (step S108: “YES”), “0” is set as the current oxygen storage amount EOX (step S109), and this series of processes is performed. Is temporarily terminated.

On the other hand, when the calculated oxygen storage amount EOX is larger than “0” in the determination process of step S108 (step S108: “NO”), step S109 is skipped, that is, the calculated oxygen The occlusion amount is set as it is as the current oxygen occlusion amount EOX, and this series of processes is temporarily terminated. Incidentally, when the engine 10 is shipped from the factory or when the catalyst 34 is replaced, the oxygen storage amount EOX is initialized to “0”.
<Rich processing>
Next, the enrichment control will be described with reference to FIG. FIG. 5 is a flowchart showing the processing procedure of the enrichment control. A series of processing shown in this flowchart is executed by the electronic control unit 60 on condition that the fuel cut control is stopped.

  In this process, first, the enrichment control is started as the process of step S201. Next, the output voltage Vox of the oxygen sensor 58 at that time is read, and it is determined whether or not the output voltage Vox is less than the predetermined voltage V2 (step S202). That is, it is determined whether the air-fuel ratio of the exhaust gas flowing out from the catalyst 34 is leaner than the stoichiometric air-fuel ratio. Here, when the output voltage Vox of the oxygen sensor 58 is less than the predetermined voltage V2 (step S202: “YES”), next, the predetermined amount EOXth for stopping the enrichment control is set to the first predetermined amount E1. (Step S203). On the other hand, when the output voltage Vox of the oxygen sensor 58 is not less than the predetermined voltage V2 (step S202: “NO”), the predetermined amount EOXth for stopping the enrichment control is set to be greater than the first predetermined amount E1. A large second predetermined amount E2 (E2> E1) is set (step S204).

  When the predetermined amount EOXth for stopping the enrichment control is thus set, it is next determined whether or not the oxygen storage amount EOX at that time is equal to or less than the predetermined amount EOXth (step S205). As a result, if the oxygen storage amount EOX is not less than or equal to the predetermined amount EOXth (step S205: “NO”), then the processing of the previous steps S202 to S204 is repeatedly executed.

  On the other hand, when the oxygen storage amount EOX is equal to or less than the predetermined amount EOXth in the determination process in step S205 (step S205: “YES”), the enrichment control is then stopped (step S206). A series of processing ends.

Next, with reference to FIG. 6, the operation of the control apparatus for an internal combustion engine according to the present embodiment will be described. FIG. 6 is a graph showing the transition of the estimated oxygen storage amount EOX.
When the fuel cut control is stopped and the enrichment control is started at timing t1, the oxygen storage amount EOX gradually decreases. Here, when the output voltage Vox of the oxygen sensor 58 becomes equal to or higher than the predetermined voltage V2 by the timing t3 when the oxygen storage amount EOX becomes the first predetermined amount E1, the predetermined amount EOXth for stopping the enrichment control is the first. 2 A predetermined amount E2 is set. Accordingly, the enrichment control is stopped on condition that the oxygen storage amount EOX is equal to or less than the second predetermined amount E2. That is, when the output voltage Vox of the oxygen sensor 58 becomes equal to or higher than the predetermined voltage V2 before the oxygen storage amount EOX becomes equal to or lower than the second predetermined amount E2, the timing t2 at which the oxygen storage amount EOX becomes equal to the second predetermined amount E2 thereafter. The enrichment control is stopped at. When the output voltage Vox of the oxygen sensor 58 changes from the state lower than the predetermined voltage V2 to the predetermined voltage V2, the oxygen storage amount EOX estimated at that time becomes larger than the second predetermined amount E2, so that the richness is achieved. The control is not immediately stopped, and the enrichment control is continued until the oxygen storage amount EOX becomes equal to or less than the second predetermined amount E2. Incidentally, when the output voltage Vox of the oxygen sensor 58 becomes equal to or higher than the predetermined voltage V2 from when the oxygen occlusion amount EOX becomes equal to or less than the second predetermined amount E2 until it reaches the first predetermined amount E1, the enrichment control is performed immediately thereafter. Is stopped.

  On the other hand, when the output voltage Vox of the oxygen sensor 58 does not become the predetermined voltage V2 by the timing t3 when the oxygen storage amount EOX becomes the first predetermined amount E1, the first amount is set as the predetermined amount EOXth for stopping the enrichment control. A predetermined amount E1 is set. Accordingly, the enrichment control is stopped on condition that the oxygen storage amount EOX is equal to or less than the first predetermined amount E1. Note that the electronic control device 60 of the present embodiment corresponds to the estimation unit and the enrichment control unit according to the present invention. Further, the oxygen sensor 58 of the present embodiment corresponds to oxygen concentration detection means.

According to the control apparatus for an internal combustion engine according to the present embodiment described above, the following effects can be obtained.
(1) The electronic control unit 60 of the engine 10 flows into the estimation means for estimating the oxygen storage amount of the exhaust purification catalyst 34 provided in the exhaust passage 30 and the catalyst 34 to reduce the oxygen storage amount of the catalyst 34. Is executed on the condition that the oxygen storage amount EOX estimated by the estimation means is determined to be equal to or less than the predetermined amount EOXth, and the enrichment control for enriching the air-fuel ratio of the exhaust gas to be richer than the stoichiometric air-fuel ratio is executed. And enrichment control means for stopping the control. In addition, oxygen concentration detection means for detecting the oxygen concentration on the exhaust gas downstream side of the catalyst 34 is provided, and the enrichment control means stops the enrichment control when the oxygen concentration during the enrichment control is low compared to when it is high. The predetermined amount EOXth is increased. Thus, when the oxygen concentration on the exhaust gas downstream side of the catalyst 34 is low, the predetermined amount EOXth for stopping the enrichment control is made larger than when the oxygen concentration is high, so that the actual oxygen storage amount is predicted to be small. The predetermined amount EOXth can be made larger than when it is predicted that there are sometimes many. Thus, even if the oxygen concentration on the exhaust gas downstream side of the catalyst 34 becomes lower than the predetermined concentration, the enrichment control is not immediately stopped, but the estimated oxygen storage amount EOX is equal to the oxygen concentration on the exhaust gas downstream side of the catalyst. The enrichment control is continued until a predetermined amount EOXth or less set according to the above. Therefore, the enrichment control can be stopped at a more accurate timing.

  (2) The enrichment control means sets the first predetermined amount E1 as the predetermined amount EOXth when the oxygen concentration is higher than the predetermined concentration, and the first predetermined amount E1 as the predetermined amount EOXth when the oxygen concentration is equal to or lower than the predetermined concentration. The second predetermined amount E2 that is larger than the predetermined value is set. As described above, the predetermined amount EOXth for stopping the enrichment control is appropriately set from the first predetermined amount E1 and the second predetermined amount E2 according to the oxygen concentration on the downstream side of the catalyst, thereby enriching. Control can be stopped at a more appropriate timing.

  The control device for an internal combustion engine according to the present invention is not limited to the configuration exemplified in the above embodiment, and may be implemented as, for example, the following form appropriately modified.

In the above-described embodiment, the present invention is embodied as a control device for a multi-cylinder internal combustion engine. However, it can be embodied as a control device for a single-cylinder internal combustion engine.
In the above embodiment, the present invention is embodied as a control device for a port injection type internal combustion engine, but is embodied as a control device for a direct injection type internal combustion engine that directly injects fuel into the combustion chamber 11. You can also.

  In the above embodiment, the oxygen storage amount EOX is estimated based on the intake air amount GA and the output voltage Vaf of the air-fuel ratio sensor 57 that detects the air-fuel ratio of the exhaust gas flowing into the catalyst 34. The configuration of the estimation means for estimating the quantity EOX is not limited to this. In addition, for example, instead of the intake air amount GA, a sensor that directly detects the flow rate of the exhaust gas flowing into the catalyst 34 may be provided, and the oxygen storage amount may be estimated based on the detection result of the sensor.

  In the enrichment control of the above embodiment, the air-fuel ratio of the exhaust gas flowing into the catalyst 34 is made richer than the stoichiometric air-fuel ratio by increasing the fuel injection amount Q, but the configuration of the enrichment control means is It is not limited to this. In addition, for example, the air-fuel ratio of the exhaust gas flowing into the catalyst 34 may be made richer than the stoichiometric air-fuel ratio by adding fuel or the like toward the catalyst 34 in the exhaust passage 30.

  In the above embodiment, a fixed value obtained in advance by experiments or the like is used as the maximum oxygen storage amount EOXmax. Instead, the state amount of the catalyst 34 at that time is estimated, and the state amount is determined according to the state amount. The maximum oxygen storage amount may be variably set. In this case, in view of the fact that the maximum oxygen storage amount increases as the bed temperature of the catalyst 34 increases, the bed temperature of the catalyst 34 may be detected and the maximum oxygen storage amount may be obtained based on the bed temperature. In view of the fact that the maximum oxygen storage amount decreases as the deterioration of the catalyst 34 progresses, the deterioration state of the catalyst 34 may be estimated and the maximum oxygen storage amount may be obtained based on the deterioration state. Even when the maximum oxygen storage amount is estimated in this way, it is impossible to avoid the estimated catalyst storage amount deviating from the actual oxygen storage amount. By applying the present invention, The enrichment control can be stopped at a more appropriate timing.

  In the above embodiment, the enrichment control is started on the condition that the fuel cut control is stopped. However, the enrichment control is started on the condition that the fuel cut control is stopped. It is not limited. In short, if it is necessary to reduce the oxygen storage amount of the catalyst 34, this can be executed at an arbitrary timing.

  In the above embodiment, when the output voltage Vox of the oxygen sensor 58 is less than the predetermined voltage V2, the predetermined amount EOXth for stopping the enrichment control is set to the first predetermined amount E1. The predetermined voltage here is not limited to the voltage V2 when changing from the rich side to the lean side (or from the lean side to the rich side) with the theoretical air-fuel ratio interposed therebetween. That is, instead of the predetermined voltage V2, a voltage in the vicinity of the predetermined voltage V2 can be employed.

  In the above embodiment, the oxygen concentration downstream of the catalyst 34 is detected by the concentration cell type oxygen sensor 58, but the oxygen concentration detection means according to the present invention is not limited to this. Alternatively, for example, as shown in FIG. 7, the oxygen concentration on the exhaust downstream side of the catalyst 34 may be detected by a limiting current type oxygen sensor, that is, a sensor similar to the air-fuel ratio sensor 57 of the above embodiment. In this case, as shown in FIG. 8, the predetermined amount EOXth for stopping the enrichment control may be decreased as the output voltage Vafdn of the air-fuel ratio sensor 59 on the exhaust downstream side of the catalyst 34 is increased. When the predetermined amount EOXth is set in this way, the enrichment control can be stopped at a more accurate timing.

  In the above embodiment, the predetermined amount EOXth for stopping the enrichment control is increased through the enrichment control unit when the oxygen concentration during the enrichment control is low compared to when the oxygen concentration is high. The enrichment control means according to the present invention is not limited to this. In addition, for example, the oxygen storage amount may be estimated to be smaller when the oxygen concentration during the enrichment control is low than when the oxygen concentration is high. Thereby, when the actual oxygen storage amount is predicted to be small, the oxygen storage amount can be estimated to be smaller than when the actual oxygen storage amount is predicted to be large. Therefore, for example, even if the oxygen concentration on the downstream side of the exhaust of the catalyst becomes lower than a predetermined concentration, the enrichment control is not immediately stopped, but the oxygen storage estimated according to the oxygen concentration on the downstream side of the exhaust of the catalyst. The enrichment control is continued until the amount becomes a predetermined amount or less. Therefore, the enrichment control can be stopped at a more accurate timing.

The schematic diagram which shows typically the schematic structure about the control apparatus of the internal combustion engine concerning one Embodiment of this invention. The graph which shows the output characteristic of an air fuel ratio sensor. The graph which shows the output characteristic of an oxygen sensor. The flowchart which shows the process sequence of the calculation process of the oxygen storage amount in the embodiment. The flowchart which shows the process sequence of the enrichment control in the embodiment. It is a graph for demonstrating the effect | action of the embodiment, Comprising: The graph which shows transition of the estimated oxygen storage amount. The schematic diagram which shows typically schematic structure centering on a catalyst about the modification of the control apparatus of the internal combustion engine of this invention. The graph which shows the relationship between the output voltage of the air fuel ratio sensor which detects the oxygen concentration of the exhaust-gas downstream side of a catalyst, and the predetermined amount for stopping enrichment control about the modification.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Engine, 11 ... Combustion chamber, 12 ... Spark plug, 13 ... Fuel injection valve, 20 ... Intake passage, 21 ... Intake valve, 22 ... Intake port, 23 ... Surge tank, 24 ... Throttle motor, 25 ... Throttle valve, DESCRIPTION OF SYMBOLS 30 ... Exhaust passage, 31 ... Exhaust valve, 32 ... Exhaust port, 33 ... Catalytic converter, 34 ... Catalyst, 41 ... Accelerator pedal, 51 ... Accelerator opening sensor, 52 ... Engine speed sensor, 53 ... Standard crank angle sensor, 54 ... throttle opening sensor, 55 ... air flow meter, 56 ... cooling water temperature sensor, 57, 59 ... air-fuel ratio sensor, 58 ... oxygen sensor, 60 ... electronic control device.

Claims (2)

Estimating means for estimating the oxygen storage amount of the exhaust purification catalyst provided in the exhaust passage, and a rich mechanism for making the air-fuel ratio of the exhaust gas flowing into the catalyst richer than the stoichiometric air-fuel ratio in order to reduce the oxygen storage amount of the catalyst A control device for an internal combustion engine, comprising: enrichment control means for executing enrichment control and stopping the enrichment control on condition that the oxygen storage amount estimated by the estimation means is less than or equal to a predetermined amount In
A concentration cell-type oxygen sensor whose output changes depending on whether the air-fuel ratio on the exhaust downstream side of the catalyst is richer or leaner than the stoichiometric air-fuel ratio ;
The enrichment control means sets the first predetermined amount as the predetermined amount when the oxygen sensor indicates that the air-fuel ratio is on the lean side , and the output of the oxygen sensor indicates that the air-fuel ratio is on the rich side Is set as the predetermined amount, a second predetermined amount greater than the first predetermined amount,
The internal combustion engine according to claim 1, wherein the second predetermined amount is set to an amount smaller than an oxygen storage amount of the catalyst estimated to change the air-fuel ratio from a lean side to a rich side with respect to a stoichiometric air-fuel ratio . Control device. The control apparatus for an internal combustion engine according to claim 1 ,
The control device for an internal combustion engine, wherein the enrichment control means starts the enrichment control on condition that fuel cut control for interrupting fuel injection of the internal combustion engine is stopped.

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