JP2016169710A - Control device for internal combustion engine - Google Patents

Abstract

CONSTITUTION: Each of oxygen concentration sensors 52 and 54 has a zirconia element and detects the oxygen concentration of an exhaust passage 34 for air-fuel ratio control. An ECU 64 measures the resistance value of a zirconia element ZE1 thereby to detect the temperature drop quantity of the zirconia element for a fuel cut period, and adjust the rich injection quantity of a fuel on the basis of a temperature drop quantity. A rich injection is executed after the lapse of a fuel cut period, so that the oxygen having been occluded in a catalyst 50 for the fuel cut period is consumed.EFFECT: A rich injection quantity after the lapse of a fuel cut period can be highly precisely controlled.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to rich injection of fuel after the elapse of the fuel cut period so as to consume oxygen stored in an exhaust purification catalyst (hereinafter simply referred to as “catalyst”) during the fuel cut period. The present invention relates to a control device for an internal combustion engine.

  In a vehicle having a fuel cut function, fuel injection is stopped when the foot is released from the accelerator pedal on a downhill or the like, and is restarted when the accelerator pedal is depressed again. However, when the fuel injection is stopped, oxygen is occluded in the catalyst, and the reduction ability, that is, the purification ability of nitrogen oxides is reduced. Therefore, normally, rich injection is executed when fuel injection is resumed to recover the purification ability of the catalyst.

  In relation to this, in Patent Document 1, combustion of the internal combustion engine is stopped when the coast stop condition is satisfied, and fuel is injected immediately before the rotation of the internal combustion engine is stopped. The fuel injection amount is adjusted based on the amount of oxygen adsorbed on the catalyst, whereby the overoxygen state of the catalyst due to fuel cut can be appropriately eliminated.

JP 2013-189951 A

  However, Patent Document 1 does not disclose a method for detecting the amount of oxygen adsorbed on the catalyst in detail, and the rich injection amount of fuel cannot be adjusted with high accuracy.

  Therefore, a main object of the present invention is to provide a control device for an internal combustion engine that can control the rich injection amount after the fuel cut period has passed with high accuracy.

  The control apparatus for an internal combustion engine according to the present invention includes a zirconia element in a control apparatus for an internal combustion engine that performs rich injection of fuel after the elapse of the fuel cut period so as to consume oxygen stored in the catalyst during the fuel cut period. Detected by an oxygen concentration sensor that detects the oxygen concentration of the exhaust system for air-fuel ratio control, a detecting means that measures the resistance value of the zirconia element and detects the temperature drop of the zirconia element during the fuel cut period, and a detecting means Adjusting means for adjusting the fuel rich injection amount based on the temperature decrease amount is provided.

  By detecting the amount of temperature decrease of the zirconia element during the fuel cut period, the temperature of the catalyst can be accurately determined. Thus, the rich injection amount after the fuel cut period has elapsed can be controlled with high accuracy. Moreover, since it can respond with the existing device called an oxygen concentration sensor, the cost for improving a precision 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) It is an illustration figure which shows an example of the setting state of an oxygen concentration sensor when generating an electromotive force, (B) is an illustration figure which shows an example of the setting state of an oxygen concentration sensor when measuring resistance. It is a graph which shows an example of the relationship between the amount of intake air at the time of fuel cut, outside temperature, and the temperature fall amount of a catalyst. It is a graph which shows an example of the relationship between idle stop time and the temperature fall amount of a catalyst. It is a graph which shows an example of the relationship between catalyst temperature and oxygen storage amount. (A) is a waveform diagram showing a fuel cut period, (B) is a waveform diagram showing an example of a change in integrated intake air amount during the fuel cut period, and (C) is attached to the wall surface of the intake pipe. It is a wave form diagram showing an example of change of the amount of fuel increased. It is a flowchart which shows a part of operation | movement of ECU shown in FIG. It is a flowchart which shows a part of other operation | movement of ECU shown in FIG. It is a flowchart which shows a part of other operation | movement of ECU shown in FIG.

  Referring to FIGS. 1 and 2, a vehicle 10 of this embodiment includes a four-stroke engine (internal combustion engine) 12 that employs a premixed combustion system as a power source. An intake passage (intake system) 32 is connected to the combustion chamber 16 provided in the cylinder 14 through an intake valve 18, and an exhaust passage (exhaust system) 34 is connected through 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.

  The intake passage 32 is provided with a single throttle valve 36 whose opening degree is adjusted by the valve motor 40 and a fuel injection device 38 assigned to each cylinder 14 to inject fuel into the intake passage 32. A surge tank 42 for leveling the air flow rate is provided at a position downstream of the throttle valve 36 and upstream of the fuel injection device 38 (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 76 shown in FIG. 2 to start the engine 12. The electric power of the battery 78 is supplied to the starter 70 through the relay 76 in the on state, and the starter 70 performs cranking by the electric power of the battery 78. As a result, the engine 12 is started.

  In the idle state, the throttle valve 36 is adjusted by the valve motor 40 so as to indicate an opening degree at which the idle state can be maintained. The intake air amount and the fuel injection amount of the fuel injection device 38 are defined by the opening degree of the throttle valve 36. An air-fuel mixture obtained by mixing air and fuel exhibits a stoichiometric air-fuel ratio except during rich injection described later. When the accelerator pedal 44 is depressed from this state, the throttle valve 36 is opened by the valve motor 40. As a result, the intake air amount and the fuel injection amount of the fuel injection device 38 increase while maintaining the stoichiometric air-fuel ratio.

  In the premixed fuel system, the fuel injected from the fuel injection device 38 is sprayed on the wall surface of the intake passage 32. The fuel adhering to the wall surface is vaporized by the heat of the intake passage 32 and the heat of the intake air, thereby generating an air-fuel mixture.

  The air-fuel mixture is supplied to the combustion chamber 16 when the intake valve 18 is opened. The supplied air-fuel mixture is ignited by a spark plug (not shown) 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 speed of the engine 12 is measured by a rotary encoder 46 provided in the vicinity of 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 74s of the alternator 74 via the belt 72. The rotational force of the rotating shaft 74s 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 48 through the exhaust passage 34. The catalyst 50 provided in the muffler 48 oxidizes and reduces carbon monoxide, hydrocarbons and nitrogen oxides contained in the combustion gas to generate water, carbon dioxide and nitrogen. From the vehicle 10, the gas thus purified is discharged.

  An oxygen concentration sensor 52 is provided at a position upstream of the catalyst 50 in the exhaust passage 34, and an oxygen concentration sensor 54 is provided at a position downstream of the catalyst 50 in the exhaust passage 34. 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 52 and 54.

  Referring to FIGS. 3A to 3B, each of oxygen concentration sensors 52 and 54 includes zirconia element ZE1 and a heater (not shown). 3A shows the operation when the heater is on, and FIG. 3B shows the operation when the heater is off.

  In FIG. 3A, the zirconia element ZE1 is kept at a high temperature and exhibits ionic conductivity. As a result, an oxygen ion flow is generated from the atmosphere with a high oxygen concentration toward the exhaust gas with a low oxygen concentration. Since oxygen ions are negatively charged, an electromotive force is generated between both end electrodes of the zirconia element ZE1. The oxygen concentration is determined by the value of the electromotive force generated in this way.

  In FIG. 3B, a current is supplied to the low-temperature zirconia element ZE1. When the voltage value V between the both end electrodes of the zirconia element ZE1 is divided by the supply current value I, the resistance value of the zirconia element ZE1 is obtained. Since the resistance value of the zirconia element ZE1 shows temperature dependence, when the resistance value of the zirconia element ZE1 is obtained, the temperature of the zirconia element ZE1 is determined.

  Returning to FIG. 1, when the vehicle 10 starts to go down a hill or decelerates at an intersection, when the foot is released from the accelerator pedal 56, the ECU 64 considers that the fuel cut condition is satisfied and executes the fuel cut. As a result, fuel injection from the fuel injection device 38 is stopped. If the accelerator pedal 56 is depressed again before the vehicle 10 stops, the ECU 64 assumes that the fuel injection conditions are satisfied and restarts the fuel injection. The fuel injection device 38 injects fuel, which accelerates the vehicle 10.

  Further, when the vehicle 10 is stopped by depressing the brake pedal 58, the ECU 64 considers that the idle stop condition is satisfied and stops idling. When the foot is released from the brake pedal 58 in this state, the ECU 64 considers that the idle start condition is satisfied and turns on the relay 76. 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, the fuel adhering to the wall surface of the intake passage 32 is vaporized and decreases or disappears. Further, air containing no fuel component is supplied to the catalyst 50, and an amount of oxygen depending on the temperature of the catalyst 50 is occluded in the catalyst 50. The reduction ability of nitrogen oxides by the catalyst 50, that is, the purification ability, is reduced by the oxygen stored in the catalyst 50.

  Here, the amount of fuel adhering to the wall surface of the intake passage 32 and the purification ability of the catalyst 50 are recovered by executing rich injection when fuel injection is resumed. However, in order to optimize the amount of fuel to be added for rich injection, it is necessary to accurately detect the state of fuel adhering to the wall surface of the intake passage 32 and the state of oxygen storage in the catalyst 50.

  Therefore, in this embodiment, the ECU 64 is caused to execute processing according to the flowcharts of FIGS. 8 to 10 with reference to the graphs shown in FIGS.

  The graph of FIG. 4 shows the relationship between the intake air amount, the outside air temperature, and the temperature decrease amount of the catalyst 50 when the fuel is cut. The graph of FIG. 5 shows the relationship between the idle stop time and the temperature decrease amount of the catalyst 50. The graph of FIG. 6 shows the relationship between the temperature of the catalyst 50 and the amount of oxygen stored in the catalyst 50. A control program corresponding to the flowcharts shown in FIGS. 8 to 10 is stored in a nonvolatile memory 64m provided in the ECU 64.

  Referring to FIG. 8, in step S1, it is repeatedly determined whether or not the fuel cut condition is satisfied. If a determination result is updated from NO to YES, it will progress to step S3 and will perform a fuel cut. As a result, fuel injection from the fuel injection device 38 is stopped. In step S5, the intake air amount per unit time is calculated based on the opening degree of the throttle valve 36, the rotation speed of the engine 12 is calculated based on the output of the rotary encoder 46, and the intake air amount and rotation thus obtained are calculated. The current temperature of the catalyst 50 is calculated based on the number.

  In step S7, the oxygen concentration sensor 54 is set to the state shown in FIG. 3B, and the current resistance value of the zirconia element ZE1 is measured. If the heater provided in the oxygen concentration sensor 54 is on, the heater is turned off prior to step S7.

  In step S9, it is determined whether or not a fuel injection condition is satisfied. In step S11, it is determined whether or not an idle stop condition is satisfied. If the decision result in the step S11 is YES, an idle stop is executed in a step S13, and it is repeatedly discriminated whether or not an idle start condition is satisfied in a step S15.

  If the determination result in step S9 is YES or if the determination result in step S15 is YES, the process proceeds to step S17, and the amount of air sucked during the fuel cut is determined based on the rotational speed of the engine 12 and the time when the fuel cut is executed. Based on and. In step S19, the outside air temperature is measured through the temperature sensor 60.

  In step S21, the amount of air temperature calculated in step S17 and the outside air temperature measured in step S19 are applied to a function corresponding to the graph shown in FIG. calculate.

  In step S23, it is determined whether or not the engine 12 is in an idle stop state. If the determination result is NO, the process proceeds to step S29 as it is. If the determination result is YES, the following processing is executed in steps S25 and S27. Then, the process proceeds to step S29. In step S25, the idle stop time is measured based on the output of the clock circuit 62. In step S27, the measured idle stop time is applied to a function corresponding to the graph shown in FIG. 5 to calculate the amount of decrease in the temperature of the catalyst 50 caused by the idle stop.

  In step S29, the same processing as in step S7 described above is executed, and the current resistance value of the zirconia element ZE1 provided in the oxygen concentration sensor 54 is measured. In step S31, the amount of decrease in the temperature of the zirconia element ZE1 due to the fuel cut and the idling stop executed as necessary is calculated based on the resistance value measured in each of steps S7 and S29.

  In step S33, the amount of decrease calculated in step S21 and the amount of decrease calculated in step S27 and the temperature calculated in step S5 are subtracted as necessary, and the correction is made with reference to the amount of decrease calculated in step S31. The calculation is executed to calculate the current temperature of the catalyst 50. In step S35, the oxygen storage amount of the catalyst 50 is acquired by applying the temperature calculated in step S33 to a function corresponding to the graph shown in FIG. In step S37, the amount of fuel required to digest the oxygen stored in the catalyst 50 is calculated based on the oxygen storage amount acquired in step S35.

  In step S39, the intake air amount during the fuel cut period and the idle stop period is calculated based on the opening of the throttle valve 36, the outside air temperature is measured through the temperature sensor 60, and the calculated intake air amount and the measured outside air amount are measured. The amount of fuel to be attached to the wall surface of the intake passage 32 is calculated based on the temperature. Therefore, the fuel amount calculated in step S39 is increased as the vehicle speed is higher or the outside temperature is higher, and is decreased as the vehicle speed is lower or the outside temperature is lower.

  In step S41, it is determined again whether or not the engine 12 is in the idling stop state. If the determination result is NO, the process proceeds to step S45 as it is. If the determination result is YES, the idle start (relay 76 of the relay 76 is performed). On), the process proceeds to step S45. As a result of the processing in step S43, cranking is executed and idling is resumed.

  In step S45, rich injection in which the amount of fuel calculated in steps S37 and S39 is added is executed. At this time, the oxygen concentration sensors 52 and 54 are set to the state shown in FIG. 3A (the heater is turned on if necessary), and the amount of fuel for obtaining the theoretical air-fuel ratio is calculated. To the calculated fuel amount, the fuel amount guarded with a predetermined upper limit value and lower limit value is added to the total amount of the fuel amount calculated in step S37 and the fuel amount calculated in S39. From the fuel injection device 38, the amount of fuel thus obtained is injected.

  As a result, a part of the injected fuel adheres to the wall surface of the intake passage 32 and the other part of the injected fuel is supplied to the catalyst 50 as an incombustible gas. Referring to FIGS. 7A to 7C, the amount of fuel adhering to the wall surface increases as the integrated intake air amount increases during the fuel cut period. Further, the oxygen stored in the catalyst 50 is consumed by the supplied incombustible gas.

  The reason why the guard is applied at the predetermined upper limit value and the lower limit value as described above is to avoid the instability of the fuel injection amount due to the excessive increase or the excessive increase.

  When the rich injection is completed, normal injection is executed in step S47. The fuel injection device 38 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 S47 is completed, the process returns to step S1.

  As can be seen from the above description, each of the oxygen concentration sensors 52 and 54 has the zirconia element ZE1, and detects the oxygen concentration in the exhaust passage 34 for air-fuel ratio control. The ECU 64 measures the resistance value of the zirconia element ZE1 to detect the temperature decrease amount of the zirconia element ZE1 during the fuel cut period (S31), and adjusts the fuel rich injection amount based on the temperature decrease amount (S35, S37). . The rich injection is executed after the fuel cut period has elapsed (S45), whereby oxygen stored in the catalyst 50 during the fuel cut period is consumed.

  By detecting the temperature decrease amount of the zirconia element ZE1 during the fuel cut period, the temperature of the catalyst 50 can be accurately determined. Thus, the rich injection amount after the fuel cut period has elapsed can be controlled with high accuracy. Moreover, since it can respond with the existing device called an oxygen concentration sensor, the cost for improving a precision can be suppressed.

DESCRIPTION OF SYMBOLS 10 ... Vehicle 12 ... Engine 16 ... Combustion chamber 32 ... Intake passage 34 ... Exhaust passage 50 ... Catalyst 52, 54 ... Oxygen concentration sensor 60 ... Temperature sensor 62 ... Clock circuit 64 ... ECU
ZE1 ... Zirconia element

Claims (1)

In a control device for an internal combustion engine that performs rich injection of fuel after the elapse of the fuel cut period in order to consume oxygen stored in the exhaust purification catalyst during the fuel cut period,
An oxygen concentration sensor having a zirconia element and detecting the oxygen concentration of the exhaust system for air-fuel ratio control,
Detecting means for detecting a temperature drop amount of the zirconia element during the fuel cut period by measuring a resistance value of the zirconia element; and adjusting a rich injection amount of the fuel based on the temperature drop amount detected by the detecting means A control device for an internal combustion engine, comprising adjusting means for

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