JP2008151025A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an NOx discharge amount in restarting an engine from an automatic stop state even when the engine is automatically stopped immediately after fuel cut recovery in deceleration, in a system having a function to automatically stop an engine during vehicular stop. <P>SOLUTION: A deceleration state and a brake operation state are monitored during fuel cut in deceleration, and whether automatic stop is executed or not is predicted immediately after fuel cut recovery in deceleration from behaviors thereof. As a result, when it is predicted that automatic stop will not be executed immediately after fuel cut recovery in deceleration, a correction amount of a fuel increase amount in the fuel cut recovery in deceleration is set to a correction amount (normal amount) required for reducing an O<SB>2</SB>storage amount of a catalyst increased in the fuel cut in deceleration to a level capable of ensuring an NOx elimination rate. When it is predicted that automatic stop will be executed immediately after cut recovery in deceleration, the correction amount of the fuel increase amount in fuel cut recovery in deceleration is increased relative to the correction amount (normal amount) in the case where it is predicted that the automatic stop will not be executed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an internal combustion engine control apparatus having a function of automatically stopping an internal combustion engine (engine) while the vehicle is stopped.

  In recent years, vehicles equipped with an automatic engine stop device (so-called idling stop device) are increasing for the purpose of reducing fuel consumption and exhaust emission. For example, when the driver automatically stops the engine when the driver stops the vehicle, and then the driver performs an operation (such as a brake release operation) to start the vehicle. The engine is automatically started.

In general, if a predetermined fuel cut condition during deceleration (for example, the throttle is fully closed and the engine rotational speed is equal to or higher than the fuel cut return rotational speed during deceleration) is satisfied during vehicle deceleration, the fuel cut during deceleration is executed to reduce fuel consumption. After that, when the engine rotational speed becomes equal to or lower than the fuel cut return rotational speed during deceleration, the fuel injection is resumed from the fuel cut during deceleration and fuel injection is restarted. In this case, during the fuel cut at deceleration, the intake air passes through the engine cylinder as it is and flows into the catalyst installed in the exhaust passage, so that excess oxygen (O ₂ ) is supplied to the catalyst, The O ₂ storage amount (oxygen storage amount) of the catalyst increases. Thus, when the O ₂ storage amount of the catalyst increases, the purification rate of NOx (lean component) in the exhaust gas decreases and the NOx emission amount increases.

As a countermeasure against this, as shown in Patent Document 1 (Japanese Patent Laid-Open No. 2003-172176), the fuel injection amount is temporarily corrected to be increased at the time of deceleration fuel cut recovery to reduce the O ₂ storage amount of the catalyst. There is something.
JP 2003-172176 A (first page)

In a vehicle equipped with an engine automatic stop device, the automatic stop condition may be satisfied immediately after the deceleration fuel cut is restored, and the engine may be automatically stopped by executing the fuel cut at the stop. In such a case, even if the fuel injection amount is increased by the same amount as before when the fuel cut during deceleration is corrected to reduce the O ₂ storage amount of the catalyst, it flows from the tail pipe of the exhaust pipe during the subsequent automatic stop. Because the catalyst is exposed to the outside air (atmosphere) and the amount of O ₂ storage increases, the amount of O ₂ storage of the catalyst when restarting from the automatic stop state increases, and the NOx purification rate during restart decreases. As a result, the amount of NOx emissions increases.

The present invention has been made in view of such circumstances, and therefore the object of the present invention is to reduce the O ₂ storage amount of the catalyst when restarting from the automatic stop state even when the automatic stop is performed immediately after the fuel cut at the time of deceleration. Therefore, it is possible to provide a control device for an internal combustion engine that can reduce the NOx emission amount at the time of restart.

In order to achieve the above object, the invention according to claim 1 is directed to an automatic stop control means for executing a fuel cut at stop and stopping the internal combustion engine when a predetermined automatic stop condition is satisfied during operation of the internal combustion engine. During deceleration of the internal combustion engine, the deceleration fuel cut means for executing the fuel cut during deceleration during the period when the fuel cut condition during deceleration is satisfied, and the fuel injection amount is temporarily corrected to increase when the fuel cut during deceleration is restored. In a control device for an internal combustion engine having a fuel increase correction means for reducing an O ₂ storage amount of a catalyst for purifying exhaust gas, a fuel cut return at deceleration based on a deceleration state and a brake operating state during fuel cut at deceleration Automatic stop prediction means for predicting whether or not to stop automatically immediately after the fuel increase correction means is predicted to automatically stop immediately after the fuel cut during deceleration by the automatic stop prediction means. It is obtained so as to increase than would be predicted not to automatically stop the fuel increase correction amount at the time when the fuel cut return decelerated while.

In short, if you monitor the deceleration state and brake operation state during fuel cut at deceleration, you can predict whether or not to automatically stop immediately after return from fuel cut at deceleration from their behavior, so automatic stop immediately after return from fuel cut at deceleration Then, when predicted, the fuel increase correction amount at the time of deceleration fuel cut return is increased more than when it is predicted not to automatically stop. In this way, if it is predicted that the automatic stop will occur immediately after the fuel cut at the time of deceleration is restored, the O ₂ storage amount of the catalyst immediately after the fuel cut at the time of deceleration is at a level that can secure a purification rate of HC, CO, etc. (rich components). However, since it automatically stops immediately after the fuel cut during deceleration, the purification rate of HC, CO, etc. in the exhaust gas hardly decreases, and the catalyst is not because O ₂ storage amount increases, the O ₂ storage amount of the catalyst for restarting the automatic stop state can be recovered to a level that ensures NOx purification rate, reducing the NOx emissions at the restart Can do.

In this case, when it is predicted by the automatic stop prediction means that the automatic stop will not be stopped immediately after the deceleration fuel cut return, the fuel increase correction amount at the time of the deceleration fuel cut return is increased during the deceleration fuel cut. The O ₂ storage amount of the catalyst thus obtained may be set to an amount necessary for reducing the NOx purification rate to a level that can ensure the NOx purification rate (hereinafter referred to as “normal amount”). In this way, when the automatic stop is not performed immediately after the fuel cut at the time of deceleration is recovered, the O ₂ storage amount of the catalyst can be reduced to a level at which the NOx purification rate can be secured by the fuel increase correction at the time of the fuel cut recovery at the time of deceleration. In addition, it is possible to prevent a reduction in the NOx purification rate after returning from the fuel cut during deceleration.

  Further, as in claim 3, when it is difficult to predict whether or not to automatically stop immediately after the deceleration fuel cut return by the automatic stop prediction means, the fuel increase correction amount at the time of deceleration fuel cut return is the normal amount or It is better to set a larger amount. In this way, even when it is difficult to predict whether or not to automatically stop immediately after returning to the fuel cut during deceleration, it is possible to secure a normal amount or a fuel increase correction amount that is higher than the normal amount, and a NOx purification rate that is higher than the conventional amount. Can be secured.

Hereinafter, an embodiment embodying the best mode for carrying out the present invention will be described.
First, a schematic configuration of the entire engine control system will be described with reference to FIG.
An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 which is an internal combustion engine, and an air flow meter 14 for detecting the intake air amount is provided downstream of the air cleaner 13. A throttle valve 15 and a throttle opening sensor 16 for detecting the throttle opening are provided on the downstream side of the air flow meter 14. The intake pipe 12 is provided with a bypass passage 25 that bypasses the throttle valve 15, and an idle speed control valve (ISC valve) 26 is provided in the bypass passage 25.

  Further, a surge tank 17 is provided on the downstream side of the throttle valve 15, and an intake pipe pressure sensor 18 for detecting the intake pipe pressure is provided in the surge tank 17. The surge tank 17 is provided with an intake manifold 19 for introducing air into each cylinder of the engine 11, and a fuel injection valve 20 for injecting fuel is attached in the vicinity of the intake port of the intake manifold 19 of each cylinder. Yes. A spark plug 21 is attached to the cylinder head of each cylinder. A cooling water temperature sensor 27 that detects the cooling water temperature and a crank angle sensor 28 that detects the engine rotation speed are attached to the cylinder block of the engine 11.

  On the other hand, a catalyst 23 such as a three-way catalyst for reducing CO, HC, NOx and the like in the exhaust gas, a NOx occlusion reduction type catalyst, and the like is provided in the middle of the exhaust pipe 22 of the engine 11. On the downstream side, exhaust gas sensors 24 and 25 (oxygen sensor, air-fuel ratio sensor, etc.) for detecting any one of gas component concentration such as oxygen concentration of exhaust gas, air-fuel ratio, and rich / lean are provided. Needless to say, the present invention can be applied to a configuration in which the exhaust gas sensor 25 is not provided on the downstream side of the catalyst 23.

  The various sensor outputs described above are input to an engine control device (hereinafter referred to as “engine ECU”) 29. The engine ECU 29 is mainly composed of a microcomputer, and executes various control programs stored in a built-in ROM (storage medium) to thereby determine the fuel injection amount of the fuel injection valve 20 according to the engine operating state. The ignition timing of the spark plug 21 is controlled. The engine ECU 29 feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the engine 11 based on the outputs of the exhaust gas sensors 24 and 25 during engine operation.

  An automatic stop control device (hereinafter referred to as “eco-run ECU”) 30 communicates with the engine ECU 29 as automatic stop control means for controlling automatic engine stop / restart for the purpose of reducing fuel consumption and exhaust emissions. It is provided so that it can. The eco-run ECU 30 is mainly composed of a microcomputer, and when a predetermined automatic stop condition (for example, the brake switch is turned on at idle after warm-up and the vehicle speed is equal to or lower than a predetermined value) is established during engine operation. Then, an automatic stop request (fuel cut request) is output to the engine ECU 29. When the engine ECU 29 receives an automatic stop request from the eco-run ECU 30, the engine ECU 29 immediately executes a fuel cut at stop to stop the fuel injection of the fuel injection valve 20 and automatically stop the engine 11. After that, the eco-run ECU 30 detects that an operation (for example, a brake release operation, an accelerator stepping operation, a shift operation to the D range, etc.) for starting the vehicle by the driver is detected, and the restart condition is satisfied. 11 is started, the fuel injection of the fuel injection valve 20 is restarted, and the engine 11 is restarted.

Further, the engine ECU 29 performs deceleration fuel during a period during which a predetermined deceleration fuel cut condition (for example, the throttle is fully closed and the engine rotational speed is equal to or higher than the deceleration fuel cut return rotational speed) is satisfied. Fuel increase correction means that functions as a fuel cut means during deceleration for executing the cut, and that temporarily increases the fuel injection amount when returning from the fuel cut during deceleration to reduce the O ₂ storage amount (oxygen storage amount) of the catalyst 23. Function as.

By the way, there is a case where the automatic stop condition is satisfied immediately after the deceleration fuel cut is recovered and the engine 11 is automatically stopped by executing the fuel cut at the stop. In such a case, even if the fuel injection amount is corrected to be increased by the same amount as before when the fuel cut at deceleration is corrected to reduce the O ₂ storage amount of the catalyst 23, the tail pipe of the exhaust pipe 22 during the subsequent automatic stop. Since the catalyst 23 is exposed to the outside air (atmosphere) flowing in from the catalyst and the O ₂ storage amount increases, the O ₂ storage amount of the catalyst 23 when restarting from the automatic stop state increases, and NOx at the time of restarting The purification rate decreases and the amount of NOx emissions increases.

As a countermeasure, in this embodiment, the engine ECU 29 monitors the deceleration state (engine speed reduction rate, vehicle speed reduction rate, etc.) and brake operation status (brake switch ON / OFF, etc.) during fuel cut during deceleration. From these behaviors, it functions as an automatic stop prediction means that predicts whether or not to automatically stop immediately after returning from fuel cut during deceleration. The fuel increase correction amount at the time of return is set to a correction amount (normal amount) necessary to reduce the O ₂ storage amount of the catalyst 23 increased during the fuel cut at the time of deceleration to a level that can secure the NOx purification rate.

On the other hand, if it is predicted that the automatic stop will occur immediately after the fuel cut at the time of deceleration, the fuel increase correction amount at the time of the fuel cut return at the time of deceleration is increased from the correction amount (normal amount) when it is predicted that the fuel cut will not be stopped automatically. Set to the increase correction amount during automatic stop. At this time, the increase correction amount at the time of automatic stop is set to a value obtained by estimating the amount of fuel required to consume the increased amount of O ₂ storage during the automatic stop and increasing the amount of fuel by an amount greater than the normal amount. Just do it.

  Also, if it is difficult to predict whether or not to automatically stop immediately after the fuel cut during deceleration, whether or not the fuel increase correction amount at the time of deceleration fuel cut return is an intermediate value between the normal amount and the automatic stop increase correction amount. Set to. Alternatively, the fuel increase correction amount at the time of deceleration fuel cut recovery may be set to a normal amount, or to an automatic stop increase correction amount. In short, if it is set to a normal amount or a larger amount than that, good. In the following description, the fuel increase correction amount when it is difficult to predict automatic stop is referred to as “an increase correction amount when prediction is difficult”.

  The fuel increase correction at the time of deceleration fuel cut return described above is executed by the engine ECU 29 according to the fuel increase correction routine at the time of deceleration fuel cut return of FIG. When this routine is started, first, at step 101, it is determined whether or not the ignition switch is ON (ON), and if the ignition switch is OFF (OFF), it waits until it is turned ON.

  Thereafter, when the ignition switch is turned on, the routine proceeds to step 102, where it is determined whether or not the fuel cut condition during deceleration is satisfied by whether or not the following three conditions (1) to (3) are all satisfied: To do.

(1) The engine 11 is after warming up
(2) Throttle fully closed (accelerator fully closed)
(3) The engine speed must be equal to or higher than the fuel cut return speed at deceleration. If there is a condition that does not satisfy any of these three conditions (1) to (3), the fuel cut condition at deceleration is The fuel cut at deceleration is not executed.

  On the other hand, if all of the above three conditions (1) to (3) are satisfied, it is determined that the deceleration fuel cut condition is satisfied, and the routine proceeds to step 103 where the deceleration fuel cut flag is turned on. To perform fuel cut during deceleration.

  Thereafter, in step 104 and step 105, it is predicted whether or not to automatically stop immediately after the deceleration fuel cut return based on the deceleration state and the brake operation state during the deceleration fuel cut as follows. First, in step 104, it is determined whether or not the brake switch is ON (brake is being operated). If the brake switch is OFF, it is difficult to predict whether or not to automatically stop immediately after the fuel cut during deceleration. Therefore, the process proceeds to step 111, where the fuel increase correction amount at the time of deceleration fuel cut recovery is set to the difficult to predict increase correction amount. This difficult-to-predict increase correction amount is set to one of (a) normal amount, (b) automatic stop increase correction amount, and (c) an intermediate value between the normal amount and automatic stop increase correction amount.

  On the other hand, if it is determined in step 104 that the brake switch is ON (braking), the process proceeds to step 105, where deceleration is performed depending on whether or not both of the following two conditions (i) and (ii) are satisfied. It is determined whether or not an automatic stop is predicted immediately after the recovery from the fuel cut.

(i) The rate of decrease in engine speed is more rapid than the predetermined value K1
Engine speed reduction rate <predetermined value K1
(Or | engine speed reduction rate |> | predetermined value K1 |)
(ii) The rate of decrease in vehicle speed is more rapid than the predetermined value K2.
Vehicle speed reduction rate <predetermined value K2
(Or | car speed reduction rate |> | predetermined value K2 |)
Instead of the above condition (ii), the vehicle speed may be less than the predetermined value K3.

  If “Yes” is determined in step 105, that is, if both the engine speed and the vehicle speed are rapidly decreased during the fuel cut during deceleration (or if the vehicle speed is less than the predetermined value K 3), step 108. The process proceeds to step 109, and it is predicted that the automatic stop is performed immediately after the fuel cut at the time of deceleration, and the process proceeds to step 109, where the fuel increase correction amount at the time of the fuel cut return at the deceleration is set to the increase correction amount at the automatic stop. The increase correction amount at the time of automatic stop is set to an increase correction amount that is larger than the normal amount.

On the other hand, if “No” is determined in Step 105, the process proceeds to Step 106, where the fuel increase correction amount at the time of deceleration fuel cut return is set, and the O ₂ storage amount of the catalyst 23 increased during the fuel cut at deceleration is set to NOx. The correction amount (normal amount) necessary to reduce the purification rate to a level that can ensure it is set.

  An example of fuel increase correction at the time of deceleration fuel cut recovery of the present embodiment described above will be described with reference to the time chart of FIG. In FIG. 3, the case where the automatic stop is performed immediately after the fuel cut during deceleration is indicated by a solid line, and the case where the automatic stop is not performed is indicated by a dashed line.

  In the example of FIG. 3, the deceleration fuel cut condition is satisfied until the time t2, the deceleration fuel cut flag is set to ON, and the deceleration fuel cut is executed. Then, at time t1 during the fuel cut during deceleration, the brake pedal is depressed and the brake switch is turned on.

  During this fuel cut during deceleration, automatic stop immediately after return from fuel cut during deceleration based on the deceleration state (engine speed reduction rate and vehicle speed reduction rate, etc.) and brake operation state (ON / OFF of brake switch, etc.) The fuel increase correction amount at the time of deceleration fuel cut return is set at the time of deceleration fuel cut return (time t2) according to the prediction result. For example, when it is predicted that the automatic stop is performed immediately after the fuel cut at the time of deceleration is recovered, the fuel increase correction amount at the time of the fuel cut at the time of deceleration is increased more than the correction amount (the normal amount) when it is predicted that the automatic stop is not performed ( Set to the increase correction amount during automatic stop).

  In the example shown by the solid line in FIG. 3, the automatic stop condition is satisfied immediately after the deceleration fuel cut return (time t3), the stop fuel cut flag is turned on, the stop fuel cut is executed, and the engine 11 is automatically stopped. . Thereafter, at the time t4 when the driver detects an operation to start the vehicle (for example, a brake release operation, an accelerator stepping operation, a shift operation to the D range, etc.), the restart condition is satisfied and the fuel cut flag at the time of stop Is turned off, cranking of the engine 11 is started, and immediately after that (time t5), the fuel injection of the fuel injection valve 20 is restarted and the engine 11 is restarted.

According to the present embodiment described above, the deceleration state and the brake operation state are monitored during the fuel cut during deceleration, and whether or not to automatically stop immediately after returning from the fuel cut during deceleration is predicted from those behaviors. When it is predicted that the automatic stop will occur immediately after returning from the fuel cut, the fuel increase correction amount at the time of deceleration fuel cut return is increased compared to the case where it is predicted that the fuel cut will not be stopped automatically. If it is predicted to stop automatically, there is a possibility that the O ₂ storage amount of the catalyst 23 immediately after the fuel cut at the time of deceleration is less than a level at which the purification rate of HC, CO, etc. (rich component) can be secured. Since the automatic stop immediately after the fuel cut is restored, the purification rate of HC, CO, etc. in the exhaust gas hardly decreases, and the O ₂ storage amount of the catalyst 23 during the automatic stop Therefore, the O ₂ storage amount of the catalyst 23 when restarting from the automatic stop state can be recovered to a level that can secure the NOx purification rate, and the NOx emission amount at the time of restart can be reduced.

In addition, when it is predicted that the automatic stop is not performed immediately after the fuel cut at the time of deceleration is returned, the O ₂ storage amount of the catalyst 23 increased during the fuel cut at the time of the fuel cut at the time of deceleration is calculated as the NOx purification rate. Is set to the amount necessary to reduce the fuel to a level where it can be ensured (normal amount). the O ₂ storage amount of 23 can be reduced to a level that ensures NOx purification ratio, it is possible to prevent a decrease in NOx purifying ratio after the fuel cut recovery deceleration.

  Also, if it is difficult to predict whether or not to automatically stop immediately after returning to fuel cut at deceleration, the fuel increase correction amount at the time of fuel cut recovery at deceleration is set to the normal amount or more. Even when it is difficult to predict whether or not to automatically stop immediately after returning from the fuel cut during deceleration, it is possible to ensure a normal amount or more fuel increase correction amount, and to ensure a higher NOx purification rate than conventional. it can.

1 is a schematic configuration diagram of an entire engine control system showing an embodiment of the present invention. It is a flowchart which shows the flow of the fuel increase correction routine at the time of deceleration fuel cut return. It is a time chart explaining an example of fuel increase correction at the time of deceleration fuel cut return.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 15 ... Throttle valve, 20 ... Fuel injection valve, 21 ... Spark plug, 22 ... Exhaust pipe, 23 ... Catalyst, 24, 25 ... Exhaust gas sensor, 29 ... Engine ECU ( Fuel cut means during deceleration, fuel increase correction means, automatic stop prediction means), 30 ... eco-run ECU (automatic stop control means)

Claims (3)

An automatic stop control means for stopping the internal combustion engine by executing a fuel cut during stop when a predetermined automatic stop condition is satisfied during operation of the internal combustion engine, and a fuel cut condition during deceleration during the operation of the internal combustion engine. Fuel reduction means for executing fuel cut during deceleration during a period during which fuel is decelerated, and fuel increase for reducing the O ₂ storage amount of the catalyst for purifying exhaust gas by temporarily increasing the fuel injection amount when returning from the fuel cut during deceleration In a control device for an internal combustion engine comprising correction means,
Automatic stop prediction means for predicting whether or not to automatically stop immediately after the fuel cut during deceleration based on the deceleration state and the brake operating state during the fuel cut during deceleration;
The fuel increase correction means is more likely to not automatically stop the fuel increase correction amount at the time of deceleration fuel cut return when the automatic stop prediction means is predicted to automatically stop immediately after the deceleration fuel cut return. A control device for an internal combustion engine, characterized in that it is increased. The fuel increase correction means increases the fuel increase correction amount at the time of deceleration fuel cut return during the fuel cut at deceleration when the automatic stop prediction means predicts that the fuel stop will not automatically stop immediately after the fuel cut return at deceleration. _2. The control device for an internal combustion engine according to claim 1, wherein the O ₂ storage amount of the catalyst is set to an amount (hereinafter referred to as “normal amount”) required to reduce the NOx purification rate to a level that can ensure a NOx purification rate. .   The fuel increase correction means determines the fuel increase correction amount at the time of deceleration fuel cut return when the automatic stop prediction means cannot predict whether or not to automatically stop immediately after the deceleration fuel cut return. 3. The control device for an internal combustion engine according to claim 2, wherein the control amount is set to a larger amount.

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