JP2016180342A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress surplus fuel amount for purging oxygen occluded in a catalyst.SOLUTION: A recirculation passage 56 includes an intake port 56a connected to an exhaust passage 36 and an exhaust port 56b connected to an intake passage 32 to recirculate exhaust gas. EGR valves 58a, 58b are provided in the vicinity of the intake port 56a and in the vicinity of the exhaust port 56b, respectively to control recirculation of purified gas in the recirculation passage 56. An ECU 64 closes the EGR valves 58a, 58b at start of a fuel cut period, and opens the EGR valves 58a, 58b and executes rich injection at the completion of the fuel cut period.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device for an internal combustion engine, and in particular, to consume oxygen stored in an exhaust purification catalyst (hereinafter simply referred to as “catalyst”) during a fuel cut period, The present invention relates to a control device for an internal combustion engine that supplies an exhaust purification catalyst.

  An example of this type of control device is disclosed in Patent Document 1. According to this document, when the idle stop condition is satisfied, the fuel is cut and the EGR control valve is fully opened. The intake air whose oxygen concentration is reduced by the recirculated exhaust gas is supplied to the three-way catalyst by utilizing the inertial rotation of the engine for a while after the fuel cut. As a result, it is possible to prevent the NOx purification rate by the three-way catalyst from being reduced during restart after idle stop.

Japanese Patent Laying-Open No. 2005-330886

  However, if the inertial rotation of the engine in the fuel cut state continues, the proportion of oxygen contained in the recirculated exhaust gas in the EGR pipe gradually increases. As a result, when the engine is restarted, oxygen stored in the catalyst may reach saturation. In order to purge oxygen in such a state, it is necessary to supply fuel to the catalyst, and extra fuel is required for purging.

  Therefore, a main object of the present invention is to provide a control device for an internal combustion engine that can suppress fuel for purging oxygen stored in a catalyst.

  An internal combustion engine control apparatus according to the present invention is an internal combustion engine control apparatus that supplies a fuel component to an exhaust purification catalyst after the fuel cut period has elapsed so as to purge oxygen stored in the exhaust purification catalyst during the fuel cut period. A recirculation passage which has an intake port connected to the exhaust passage and an exhaust port connected to the intake passage, and is provided in the vicinity of each of the return passage, the intake port and the exhaust port, And a valve control means for closing the valve during the fuel cut period and opening the valve after the fuel cut period.

  Exhaust gas flowing through the exhaust passage is returned to the intake passage through the return passage. However, the valve is closed during the fuel cut period, and the exhaust is confined in the recirculation passage. The exhaust gas in the recirculation passage is supplied to the catalyst through the intake passage, the internal combustion engine, and the exhaust passage after the fuel cut period has elapsed. Oxygen stored in the catalyst during the fuel cut period is purged by carbon monoxide and hydrocarbons contained in the exhaust gas thus supplied. As a result, fuel for purging oxygen stored in the catalyst can be suppressed.

  The above object, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

It is a block diagram which shows a part of principal part structure of the vehicle of this Example. It is a block diagram which shows the other part of principal part structure of the vehicle of this Example. (A) is a graph which shows an example of the change of the air fuel ratio after completion | finish of a fuel cut, (B) is a graph which shows an example of the change of the oxygen concentration in a catalyst after a fuel cut is complete | finished. It is a flowchart which shows a part of operation | movement of ECU shown in FIG.

  Referring to FIGS. 1 and 2, a vehicle 10 of this embodiment includes a 4-stroke engine (internal combustion engine) 12 as a power source. An intake passage 32 is connected to the combustion chamber 16 provided in the cylinder 14 via an intake valve 18, and an exhaust passage 36 is connected via an exhaust valve 20. 1, only a single cylinder 14 is shown, but the engine 12 has a plurality of cylinders 14, 14,. The intake passage 32 branches to each cylinder 14 at a position upstream of the intake valve 18.

  An air cleaner 34 that separates dust from the atmosphere, a single throttle valve 38 whose opening degree is adjusted by a valve motor 42, and each cylinder 14 are assigned to the intake passage 32 to inject fuel into the intake passage 32. A fuel injection device 40 is provided. A surge tank 44 for leveling the air flow rate is provided at a position downstream of the throttle valve 38 and upstream of the fuel injection device 40 (a branch position of the intake passage 32).

  When an IG on operation is performed by an ignition key (not shown), the ECU (control device) 64 turns on the relay 74 shown in FIG. 2 to start the engine 12. The power of the battery 78 is supplied to the starter 76 via the relay 74 in the on state, and the starter 76 performs cranking with the power of the battery 78. As a result, the engine 12 is started.

  In the idle state, the throttle valve 38 is adjusted by the valve motor 42 so as to indicate an opening degree at which the idle state can be maintained. The amount of intake air that has passed through the air cleaner 34 and the fuel injection amount of the fuel injection device 40 are defined by the opening of the throttle valve 38. An air-fuel mixture obtained by mixing air and fuel exhibits a stoichiometric air-fuel ratio except during rich injection described later. When an accelerator pedal (not shown) is depressed from this state, the ECU 64 drives the valve motor 42 with reference to the detection result of the accelerator position sensor 62. The throttle valve 38 is opened by a valve motor 42, whereby the intake air amount and the fuel injection amount of the fuel injection device 40 increase while maintaining the theoretical air-fuel ratio.

  The air-fuel mixture obtained by mixing the intake air and the injected fuel is supplied to the combustion chamber 16 when the intake valve 18 is opened. The supplied air-fuel mixture is ignited by the spark plug 30 immediately before the piston 22 connected to the crankshaft 26 via the connecting rod 24 reaches the top dead center. The piston 22 moves up and down by the explosion of the air-fuel mixture, whereby the crankshaft 26 rotates. A flywheel 28 is attached to the crankshaft 26, and fluctuations in the rotational speed of the crankshaft 26, that is, the rotational speed of the engine 12 are suppressed by the flywheel 28.

  The rotational force of the crankshaft 26 is transmitted to a drive shaft (not shown) via the torque converter 66 and the continuously variable transmission 68 shown in FIG. As a result, the vehicle 10 moves forward or backward. The rotational force of the crankshaft 26 is also transmitted to the rotating shaft 72 s of the alternator 72 via the belt 70. The rotational force of the rotating shaft 72s is converted into electric power, and the converted electric power is stored in the battery 78.

  Returning to FIG. 1, the air after burning the air-fuel mixture, that is, the combustion gas, is discharged from the combustion chamber 16 when the exhaust valve 20 is opened, and is supplied to the muffler 46 through the exhaust passage 36. The catalyst 48 provided in the muffler 46 oxidizes and reduces carbon monoxide, hydrocarbons, and nitrogen oxides contained in the combustion gas, thereby generating water, carbon dioxide, and nitrogen. From the vehicle 10, the gas thus purified is discharged. However, carbon monoxide, hydrocarbons, and nitrogen oxides cannot be completely oxidized / reduced, and a part of each of carbon monoxide, hydrocarbons, and nitrogen oxides is mixed in the purified gas.

  An oxygen concentration sensor 50 is provided at a position upstream of the catalyst 48 in the exhaust passage 36, and an oxygen concentration sensor 52 is provided at a position downstream of the catalyst 48 in the exhaust passage 36. The ECU 64 adjusts the fuel injection amount to an amount corresponding to the theoretical air-fuel ratio based on the detection results of the oxygen concentration sensors 50 and 52.

  The recirculation passage 56 constituting the EGR device 54 has an intake port 56 a connected to the exhaust passage 36 and an exhaust port 56 b connected to the intake passage 32, and couples the exhaust passage 36 and the intake passage 32 to each other. More specifically, the intake port 56 a is connected to the exhaust passage 36 at a position downstream of the catalyst 48, and the exhaust port 56 b is connected to the intake passage 32 at the position of the surge tank 44.

  In the reflux passage 56, two EGR valves 58a and 58b and a single EGR cooler 60 are provided. The EGR valve 58a is disposed in the vicinity of the intake port 56a, the EGR valve 58b is disposed in the vicinity of the exhaust port 56b, and the EGR cooler 60 is disposed at a position sandwiched between the EGR valves 58a and 58b.

  A part of the purified gas generated by the catalyst 48 is returned to the surge tank 44 through the return passage 56 when the EGR valves 58a and 58b are opened. The temperature of the purified gas to be refluxed is suppressed by the EGR cooler 60, thereby increasing the density of the purified gas. The pumping loss of the engine 12 is reduced by mixing high-density purified gas with intake air.

  When the vehicle 10 starts to go down a hill or decelerates at an intersection, when the foot is released from the accelerator pedal, the ECU 64 considers that the fuel cut condition is satisfied and executes the fuel cut. Thereby, the fuel injection from the fuel injection device 40 is stopped. If the accelerator pedal is depressed again before the vehicle 10 stops, the ECU 64 assumes that the fuel injection condition is satisfied and restarts the fuel injection. The fuel injection device 40 injects fuel, thereby accelerating the vehicle 10.

  Further, when the vehicle 10 stops due to depression of the brake pedal, the ECU 64 considers that the idle stop condition is satisfied and stops idling. When the foot is released from the brake pedal in this state, the ECU 64 considers that the idle start condition is satisfied and turns on the relay 74. As a result, cranking is executed and idling is resumed.

  Thus, the vehicle 10 has a fuel cut function that interrupts the injection of fuel into the engine 12 when the fuel cut condition is satisfied, and further, the idle stop that stops idling when the idle stop condition is satisfied. It has a function.

  However, when the fuel cut is executed, air containing no fuel component is supplied to the catalyst 48, and oxygen is occluded in the catalyst 48. The reduction ability of nitrogen oxides by the catalyst 48, that is, the purification ability, is reduced by the oxygen stored in the catalyst 48. Here, the purification ability of the catalyst 48 is recovered by executing rich injection when fuel injection is resumed.

  That is, when the fuel injection is resumed, if the extra fuel shown by hatching in FIG. 3A is injected, the excess fuel is supplied to the catalyst 48 as an incombustible gas, and the oxygen stored in the catalyst 48 is purged. . As a result, the oxygen concentration in the catalyst 48 decreases as shown by the solid line in FIG. Note that a broken line shown in FIG. 4B indicates a change in oxygen concentration when fuel for purging is not injected.

  However, an increase in the amount of fuel to be added for rich injection (= the amount of fuel for purging oxygen stored in the catalyst 48) causes a reduction in fuel consumption. Therefore, in this embodiment, a part of the purified gas is confined in the recirculation passage 56 during the fuel cut period, and the purified gas in the recirculation passage 56 is supplied to the catalyst 48 via the engine 12 after the fuel cut period has elapsed. ing.

  Carbon monoxide and hydrocarbons mixed in the purified gas are oxidized by oxygen stored in the catalyst 48 and converted into carbon dioxide and water. That is, part of the oxygen stored in the catalyst 48 is purged by the refluxed purified gas. Thereby, the amount of fuel to be added for purging can be suppressed.

  Specifically, the process according to the flowchart shown in FIG. The control program corresponding to this flowchart is stored in a nonvolatile memory 64m provided in the ECU 64.

  Referring to FIG. 4, in step S1, it is repeatedly determined whether or not the fuel cut condition is satisfied. When the determination result is updated from NO to YES, the EGR valves 58a and 58b are closed in step S3, and the fuel cut is executed in step S5. Strictly speaking, in step S3, the EGR valve 58b is first closed, and then the EGR valve 58a is closed. As a result, part of the purified gas from the catalyst 48 is confined in the recirculation passage 56, and the fuel injection from the fuel injection device 40 is stopped.

  In step S7, it is determined whether or not a fuel injection condition is satisfied. In step S9, it is determined whether or not an idle stop condition is satisfied. If the determination result in the step S9 is YES, an idle stop is executed in a step S11, and it is repeatedly determined whether or not an idle start condition is satisfied in a step S13. When the determination result in step S13 is updated from NO to YES, idling is resumed in step S15.

  If the process of step S15 is completed or if the determination result of step S7 is YES, the EGR valves 58a and 58b are opened in step S17, and rich injection is executed in step S19.

  The purified gas confined in the recirculation passage 56 flows into the surge tank 44 by the processing in step S17 and is supplied to the catalyst 48 via the combustion chamber 16. Further, the fuel injection device 40 injects extra fuel for purging oxygen stored in the catalyst 48. The injected extra fuel is supplied to the catalyst 48 as non-combustible gas without being burned in the combustion chamber 16. Oxygen occluded in the catalyst 48 is purged by carbon monoxide and hydrocarbons mixed in the purified gas and purged by non-combustible gas.

  When rich injection is completed, normal injection is executed in step S21. The fuel injection device 40 injects an amount of fuel that provides a stoichiometric air-fuel ratio. As a result, the engine 12 operates in a normal state. When the process of step S21 is completed, the process returns to step S1.

  As can be seen from the above description, the recirculation passage 56 has the intake port 56 a connected to the exhaust passage 36 and the exhaust port 56 b connected to the intake passage 32 to recirculate the purified gas. The EGR valves 58a and 58b are provided in the vicinity of the intake port 56a and the exhaust port 56b, respectively, in order to adjust the recirculation of the purified gas through the recirculation passage 56. The ECU 64 closes the EGR valves 58a and 58b at the start of the fuel cut period (S3), opens the EGR valves 58a and 58b at the end of the fuel cut period, and executes rich injection (S17, S19).

  Oxygen occluded in the catalyst 48 during the fuel cut period is purged by the non-combustible gas by the rich injection and purged by the purified gas confined in the reflux passage 56. Thereby, it is possible to suppress an excessive amount of fuel for purging oxygen stored in the catalyst 48.

  In this embodiment, the intake port 56 a of the reflux passage 56 is connected to the exhaust passage 36 at a position downstream of the catalyst 48. However, the intake port 56 a of the recirculation passage 56 may be connected to the exhaust passage 36 at a position upstream of the catalyst 48.

DESCRIPTION OF SYMBOLS 10 ... Vehicle 12 ... Engine 16 ... Combustion chamber 32 ... Intake passage 36 ... Exhaust passage 48 ... Catalyst 50, 52 ... Oxygen concentration sensor 64 ... ECU

Claims (1)

A control device for an internal combustion engine that supplies a fuel component to the exhaust purification catalyst after the fuel cut period has elapsed to purge oxygen stored in the exhaust purification catalyst during the fuel cut period,
A recirculation passage that has an intake port connected to the exhaust passage and an exhaust port connected to the intake passage to recirculate the exhaust;
A valve provided in the vicinity of each of the intake port and the exhaust port for adjusting the recirculation of the exhaust gas through the recirculation passage; and closing the valve during the fuel cut period and opening the valve after the fuel cut period elapses A control device comprising valve control means.

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