JP2005330886A - Engine idle stop control unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the NOx conversion from dropping by a ternary catalyst when restarting after an idle stop. <P>SOLUTION: When idle stop conditions are established, fuel is cut and an EGR control valve is fully opened, thus reducing oxygen concentration in intake air by reflux exhaust gas. The intake air in which the oxygen concentration has dropped is supplied to the ternary catalyst by utilizing the tentative inertia rotation of an engine after the fuel cut, and the catalyst prevents oxygen from becoming excessive. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

    The present invention relates to an engine idle stop control device.

The engine idle stop control device automatically stops the engine when the vehicle is temporarily stopped, such as waiting for traffic lights or traffic jams, for the purpose of preventing air pollution caused by exhaust gas and improving fuel efficiency. This is a system that automatically restarts the engine (see Patent Document 1). Further, a catalyst converter having a built-in three-way catalyst having a function of purifying NOx in the exhaust gas is provided in the exhaust passage of the engine, and this three-way catalyst contains an OSC (Oxygen Storage Capacity) material. It is normal.
Japanese Examined Patent Publication No. 3-47421

    The engine continues to rotate for a while even if the fuel supply is cut. The same applies to a vehicle equipped with the idle stop control device in which fuel cut is performed to temporarily stop the engine when a predetermined idle operation state is reached. For this reason, the intake air after the fuel cut is not used for combustion in the engine combustion chamber, but passes through the combustion chamber and flows into the catalytic converter of the exhaust passage, and the OSC material of the three-way catalyst has saturated oxygen storage amount. It becomes a state or a state close to saturation.

    Therefore, when the engine is restarted in such a state and the exhaust gas flows into the catalytic converter, the three-way catalyst has an excess of oxygen and forms a highly oxidizing atmosphere as described above. It will be disadvantageous. In other words, HC and CO in the exhaust gas are rapidly oxidized by the three-way catalyst, and the reducing agent (partially oxidized HC and CO) necessary for NOx reduction becomes insufficient, and the NOx purification efficiency temporarily decreases. To do. Thus, in a vehicle equipped with an idle stop control device, engine stop and restart are frequently repeated. Therefore, even if the NOx purification rate is temporarily reduced, countermeasures are taken. It is desirable.

    As a countermeasure, it can be considered that the air-fuel ratio is temporarily made rich at the time of restart, and unburned fuel is supplied to the catalytic converter. However, it goes against fuel efficiency improvement, which is one of the purposes of the idle stop control device.

    Therefore, an object of the present invention is to solve the problem of temporary reduction in the NOx purification rate at the time of restart without causing deterioration of fuel consumption in a vehicle including the idle stop control device.

    According to the present invention, the oxygen concentration of the intake air flowing into the engine combustion chamber is lowered when the engine enters a predetermined idle operation state in which the engine is stopped.

That is, the invention according to claim 1 includes a catalytic converter including a catalyst having a function of purifying NOx in exhaust gas,
A fuel injection valve for supplying fuel to the engine;
In an engine idle stop control device comprising engine stop means for shutting off the fuel supply by the fuel injection valve and stopping the engine when a predetermined idle operation state is detected,
An oxygen concentration control means is provided for reducing the oxygen concentration of the intake air sucked into the combustion chamber when the predetermined idle operation state is detected.

    Therefore, when the predetermined idle operation state is detected, the oxygen concentration of the intake air is reduced, so that even if the engine continues to rotate for a while after the fuel supply is cut off, the intake air having a high oxygen concentration is prevented from flowing into the catalytic converter. Is done. That is, it is possible to prevent the catalyst from forming a highly oxidizing atmosphere. Therefore, the NOx purification rate is prevented from temporarily decreasing when the engine is restarted, and fuel is not additionally supplied, so that deterioration of fuel consumption can be avoided.

Preferably, in a case provided with exhaust gas recirculation control means for controlling the amount of exhaust gas recirculated to the intake system of the engine according to the operating state of the engine,
The exhaust gas recirculation control means functions as the oxygen concentration control means.

    Therefore, since the exhaust gas recirculation control means is used for reducing the oxygen concentration of the intake air when the predetermined idle operation state is detected, it is not necessary to separately provide a dedicated oxygen concentration control means, which is advantageous for cost reduction.

    Preferably, the exhaust gas recirculation control means suppresses recirculation of the exhaust gas when in an idle operation state other than the predetermined idle operation state, and cancels the suppression when the exhaust gas recirculation control unit is in the predetermined idle operation state. It is to reduce the oxygen concentration in the intake air.

    Accordingly, when the suppression of exhaust gas recirculation is canceled during the predetermined idle operation state, the recirculation amount of the exhaust gas to the intake system is increased, and the oxygen concentration of the intake air can be reliably reduced.

    Preferably, the predetermined idle operation state is a state in which at least two of the condition that the accelerator opening of the engine is zero and the shift range is a non-traveling range and the condition that the vehicle speed is zero are satisfied.

    This reliably reflects the driver's intention to temporarily stop the vehicle when the engine is idling.

    As described above, according to the present invention, when the predetermined idle operation state is detected, the predetermined idle operation state is detected in the engine idle stop control device that shuts off the fuel supply and stops the engine. Since it is provided with an oxygen concentration control means for reducing the oxygen concentration of the intake air taken into the combustion chamber when the operation is performed, intake air with a high oxygen concentration flows into the catalytic converter at the time of idling stop without causing deterioration of fuel consumption. This can be prevented, and is advantageous in reducing air pollution by suppressing deterioration of NOx purification of the catalyst.

    Further, according to the exhaust gas recirculation control means for controlling the exhaust gas recirculation amount according to the operating state of the engine as the oxygen concentration control means, it is not necessary to separately provide a dedicated oxygen concentration control means. It becomes advantageous for reduction.

    Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

    In the engine idling stop control apparatus shown in FIG. 1, reference numeral 1 denotes a multi-cylinder gasoline engine body of a vehicle (only one cylinder is shown in FIG. 1), and a piston 3 is loaded in the cylinder 2. A combustion chamber is formed above it. An intake port 5 and an exhaust port 6 are formed in the combustion chamber and are opened and closed by an intake valve 7 and an exhaust valve 8, respectively.

    The cylinder head is provided with a spark plug 11 so that the tip spark portion faces the combustion chamber. A fuel injection valve 12 supplies fuel to the engine body. In this example, fuel is injected into a manifold or intake port and supplied to the combustion chamber.

    An intake passage 13 is connected to the intake port 5, and an air cleaner 14, an air flow sensor 15, an intake temperature sensor 16, a throttle valve 17, and a throttle opening are sequentially connected to the intake passage 13 from the upstream side to the downstream side. A degree sensor 18 and a surge tank 19 are provided, and an idle adjustment passage 13a that bypasses the throttle valve 17 is provided.

    An exhaust passage 20 is connected to the exhaust port 6, and a catalytic converter 22 incorporating a three-way catalyst 21 containing an OSC material is provided in the middle of the exhaust port 6. The intake passage 13 and the exhaust passage 20 are connected by an EGR (exhaust gas recirculation) passage 23 that recirculates a part of the exhaust gas to the intake system, and the opening degree of the EGR passage 23 can be adjusted by an EGR control valve 24. . The EGR passage 23 is provided with a cooler 25 for cooling the recirculated exhaust gas.

Further, the engine body 1 is provided with an engine water temperature sensor 26 and an engine rotation sensor 27, and the exhaust gas oxygen concentration for feedback control of the air-fuel ratio of the engine is provided in a portion upstream of the catalytic converter 22 in the exhaust passage 20. An O ₂ sensor 28 for detecting the above is provided.

The air flow sensor 15, the intake air temperature sensor 16, the throttle opening sensor 18, the engine water temperature sensor 26, the engine rotation sensor (crank angle sensor) 27 and the O ₂ sensor 28, and a switch (P brake SW for detecting the operation of the parking brake) 29) A shift position sensor 30, an accelerator opening sensor 31, and a vehicle speed sensor 32 for detecting a shift range of the transmission are connected to an ECU (engine control unit) 35, and the ECU 35 controls the fuel injection valve 12 and the EGR control valve 24. Give a signal to control.

    Next, fuel injection control and exhaust gas recirculation control by the ECU 35 will be described.

    First, the ECU 35 includes fuel injection control means and exhaust gas recirculation control means. The fuel injection control by the fuel injection valve 12 is based on the engine speed and the engine load (accelerator opening), and sets the injection amount and the injection timing with reference to a map that is preset and electronically stored. And is further corrected based on the engine water temperature, the intake air temperature, and the like. Furthermore, fuel injection is stopped when a predetermined idle operation state described later is detected.

    Further, the exhaust gas recirculation control by the EGR control valve 24 is performed based on the engine speed and the engine load (accelerator opening), referring to a map that is set in advance and stored electronically, and determines the EGR control valve opening. This is done by setting. Specifically, as shown in FIG. 2, the EGR control valve opening is controlled to increase as the engine speed increases and the engine load increases. The exhaust gas recirculation is suppressed so that the gas recirculation amount becomes zero (EGR control valve fully closed), and the suppression is released in order to reduce the oxygen concentration of the intake air in a predetermined idle operation state described later.

    That is, the exhaust gas recirculation control means is configured to function as an oxygen concentration control means for reducing the oxygen concentration of the intake air when a predetermined idle operation state is reached. The EGR passage 23 and the EGR control valve 24 constitute intake air concentration adjusting means for adjusting the intake air concentration.

    Hereinafter, engine stop control by the ECU 35 will be described.

    First, the predetermined idle operation state is a state in which an idle stop execution condition is satisfied, specifically, a condition that the accelerator opening is zero, and a condition that the shift range is a non-traveling range (parking range or neutral range). The state where all of the condition that the vehicle speed is zero and the condition that the parking brake is operating (ON state) are satisfied. Therefore, the parking brake switch 29, the shift position sensor 30, the accelerator opening sensor 31, and the vehicle speed sensor 32 constitute detection means for detecting a predetermined idle operation state. It should be noted that when the three conditions of zero accelerator opening, shift to non-traveling range and zero vehicle speed are satisfied, or one of the conditions of zero accelerator opening, shifting to non-driving range, zero vehicle speed, and parking brake on It may be determined that a predetermined idle operation state has been established when the condition is satisfied.

    The exhaust gas recirculation control means suppresses the exhaust gas recirculation by setting the opening of the EGR control valve 24 to zero in a normal idle operation state, but cancels the suppression when the predetermined idle operation state is detected, and performs EGR. The opening degree of the control valve 24 is fully opened, and the EGR control valve 24 is fully closed when rotation of the crankshaft of the engine is stopped. In this case, the engine rotation sensor 27 constitutes means for detecting engine stop. On the other hand, the fuel injection control means stops the fuel injection by the fuel injection valve 12 when the predetermined idle operation state is detected.

    FIG. 3 shows the control flow for idling stop. In step S1 after the start, a detection signal such as the engine speed is read, and in the subsequent step S2, it is determined whether or not the idling stop execution condition is satisfied based on the detection signal. To do. If the execution condition is not satisfied, the process returns. If the execution condition is satisfied, the process proceeds to step S3, the EGR control valve 24 is fully opened, and fuel injection by the fuel injection valve 12 is stopped in the subsequent step S4. .

    In a subsequent step S5, it is determined whether or not the engine has been stopped based on a signal from the engine rotation sensor. If the engine stop is not determined, control of fully opening the EGR control valve 24 and stopping fuel injection is continued. When it is determined that the engine has been stopped, the routine proceeds to step S6 where the EGR control valve 24 is fully closed and the routine returns.

    FIG. 4 shows a time chart of the idle stop control. When the vehicle is temporarily stopped from the running state, when the engine enters the idle operation state, fuel injection necessary for the idle operation is performed (fuel ON state), while the EGR control valve. 24 is fully closed. When the idle stop execution condition is satisfied in this state, fuel injection is stopped (fuel OFF), and the EGR control valve 24 is fully opened. Even after the fuel injection is stopped, the EGR control valve 24 is kept fully open during inertial rotation of the engine, and the EGR control valve is fully closed after the rotation of the engine is completely stopped.

    Therefore, during the inertial rotation of the engine after the fuel injection is stopped, the exhaust gas is recirculated to the intake system through the EGR passage 23, so that the oxygen concentration of the intake air decreases. Then, the intake air with the reduced oxygen concentration passes through the combustion chamber of the engine and flows into the three-way catalyst 21 of the catalytic converter 22, and the oxygen storage of the OSC material of the three-way catalyst 21 becomes excessive, that is, Thus, the inside of the catalytic converter 22 is prevented from becoming an excessively oxidizing atmosphere.

    Therefore, when the engine is restarted, HC and CO in the exhaust gas flowing into the catalytic converter 22 do not rapidly oxidize but effectively act as a reducing agent for NOx in the exhaust gas, and the NOx purification rate is temporarily reduced. It is suppressed that it falls. In addition, the engine stop control only returns the exhaust gas to the intake system when the engine stop execution condition is satisfied, and does not add fuel. The recirculation of the exhaust gas suppresses the engine body 1 from being cooled, which is advantageous for restarting the engine when the outside air temperature is low.

    In the engine stop control, as shown in the time chart of FIG. 4, the full open command of the EGR control valve 24 and the fuel cut (fuel injection stop) are executed simultaneously, but irregular combustion is not caused by the recirculated exhaust gas. Within the range, the fuel cut timing may be delayed with respect to the fully open command of the EGR control valve 24. Thereby, the intake air whose exhaust gas is recirculated and the oxygen concentration is reduced can be sufficiently supplied to the three-way catalyst, which is advantageous in preventing the inside of the catalytic converter 22 from becoming an excessively oxidizing atmosphere. .

    In the above embodiment, in-manifold injection or port injection is adopted as the fuel injection method of the fuel injection valve, but in-cylinder direct injection may be adopted.

1 is an overall configuration diagram of an engine stop control device according to the present invention. FIG. It is a graph which shows roughly the relationship between an engine speed and an engine load, and the opening degree of an EGR control valve. It is a flowchart of the engine stop control which concerns on this invention. It is a time chart figure of the control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine main body 4 Combustion chamber 12 Fuel injection valve 13 Intake passage 19 Exhaust passage 21 Three-way catalyst 22 Catalytic converter 23 EGR passage 24 EGR control valve

Claims (4)

A catalytic converter containing a catalyst having a function of purifying NOx in exhaust gas;
A fuel injection valve for supplying fuel to the engine;
In an engine idle stop control device comprising engine stop means for shutting off the fuel supply by the fuel injection valve and stopping the engine when a predetermined idle operation state is detected,
An engine idle stop control device comprising oxygen concentration control means for reducing the oxygen concentration of intake air taken into the combustion chamber when the predetermined idle operation state is detected. In claim 1,
Exhaust recirculation control means for controlling the amount of exhaust gas recirculated to the intake system of the engine according to the operating state of the engine,
An engine idle stop control device, wherein the exhaust gas recirculation control means functions as the oxygen concentration control means. In claim 2,
The exhaust gas recirculation control means suppresses the recirculation of the exhaust gas in an idle operation state other than the predetermined idle operation state, and cancels the suppression in the predetermined idle operation state to release the oxygen concentration of the intake air. An engine idle stop control device characterized by reducing the engine. In any one of Claim 1 thru | or 3,
The predetermined idle operation state is a state in which at least two of the condition that the accelerator opening of the engine is zero and the shift range is a non-traveling range and the condition that the vehicle speed is zero are satisfied. Engine idle stop control device.

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