JP2010025077A - Device and method for air-fuel ratio control of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine activation of an oxygen sensor, and appropriately control an air-fuel ratio, on the basis of an output voltage of an oxygen sensor in exhaust gas. <P>SOLUTION: An air-fuel ratio control device which controls the ratio (air-fuel ratio) of a mass of air to a mass of fuel in an air-fuel mixture is provided with the oxygen sensor for detecting the concentration of oxygen contained in the exhaust gas, and a controller for controlling the air-fuel ratio on the basis of signals of the oxygen sensor. When an output value of the oxygen sensor after engine start-up becomes lower than a first set reference value over a period of a first set time period, the control device makes a first fuel-injection control on the basis of the output value of the oxygen sensor. When an output value of the oxygen sensor becomes lower than the first set reference-value over a period of a second set time period, the control device makes a second fuel-injection control on the basis of the output value of the oxygen sensor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio control apparatus and an air-fuel ratio control method for an internal combustion engine that controls an air-fuel ratio based on a measurement result of oxygen concentration in exhaust gas discharged from the internal combustion engine.

  Conventionally, as control for optimizing the mixing ratio (air-fuel ratio) of fuel and air in an internal combustion engine, the oxygen concentration in the exhaust gas discharged from the internal combustion engine is detected by an oxygen sensor, and based on the detected value, the fuel concentration Feedback control for adjusting the injection amount is performed.

  In general, an oxygen sensor used for air-fuel ratio control of such an internal combustion engine has a sensor body constituted by a zirconia element (solid electrolyte). When the zirconia element reaches a predetermined temperature (for example, 300 ° C.), an electromotive force is generated due to an oxygen concentration difference between the exhaust gas and the atmosphere, and the electromotive force is determined by the oxygen concentration ratio. That is, the output voltage of the oxygen sensor by the zirconia element shows a high voltage value when the air-fuel mixture is richer than the stoichiometric air-fuel ratio (14.7 in the case of a gasoline internal combustion engine) (rich state), and the air-fuel mixture is thinner than the stoichiometric air-fuel ratio. When in the (lean state), a low voltage value is indicated. Therefore, a rich lean determination is performed by setting a reference value near the middle of the output voltage value of the oxygen sensor, and when the rich sensor is higher than the reference set value in the rich lean determination, it is rich. Judged as lean. When the fuel injection amount is determined to be rich, the fuel injection amount is decreased. When the fuel injection amount is determined to be lean, the fuel injection amount is increased, and control is performed to bring the air-fuel ratio closer to the stoichiometric air-fuel ratio.

  However, the above-described oxygen sensor is not activated unless the sensor element is heated to a predetermined temperature or higher, and the oxygen concentration cannot be detected accurately. Usually, the oxygen sensor element is heated by high-temperature exhaust gas, and its output is stabilized when the oxygen sensor element reaches a predetermined activation temperature or higher.

  FIG. 4 shows the temperature characteristics of the oxygen sensor. FIG. 4 shows that the output voltage of the oxygen sensor is high in a low temperature (inactive) state, gradually decreases after starting, and when the sensor element temperature rises to some extent, a rich and lean voltage difference begins to occur (incomplete activation). After that, it shows that the voltage difference between rich and lean is kept constant (it is completely active). Therefore, in order to accurately perform the rich lean determination in the air-fuel ratio control of the internal combustion engine, it is necessary to first determine whether or not the oxygen sensor is sufficiently activated.

  FIG. 5 shows a first example of a conventional oxygen sensor activation determination method in air-fuel ratio control of an internal combustion engine. As shown in FIG. 5, in order to determine the activation of the oxygen sensor, first, (1) it is checked whether the output value of the oxygen sensor is equal to or lower than a preset activation determination voltage. Then, (2) it is checked whether a state where the output value of the oxygen sensor is equal to or lower than a preset activation determination voltage has elapsed for a predetermined time. When both of the above checks (1) and (2) are “YES”, it is determined that the oxygen sensor has been activated, and the routine proceeds to rich lean determination of air-fuel ratio control. .

Further, as a second example of the oxygen sensor activation determination in the conventional air-fuel ratio control, whether or not the output of the oxygen sensor is equal to or higher than a preset first activity determination value when it is determined that the fuel is being cut. Next, when it is continuously determined whether or not the output of the oxygen sensor is equal to or higher than the second activation determination value lower than the first activation determination value, the activity of the oxygen sensor is determined. There is known an oxygen sensor activation determination device for determination (see, for example, Patent Document 1).
Japanese Patent No. 2745754

  On the other hand, in recent years, in order to quickly activate the oxygen sensor, an oxygen sensor incorporating a heater for heating the sensor element is used. However, since the power supply for energizing the heater usually uses a battery or a generator, if the power supply voltage becomes low due to insufficient charging of the battery or insufficient electromotive force of the generator, the amount of heat generated by the heater is reduced. Will be reduced. In this case, the sensor element is not heated sufficiently, and its temperature rise becomes slow. Similarly, in the case of running in the rain, the temperature rise of the sensor element is delayed. If the temperature rise of the sensor element becomes slow, the drop in the output voltage of the oxygen sensor shown in FIG. 4 also slows down, and there is a risk that an erroneous determination will occur in the rich lean determination even if it is determined that the oxygen sensor is activated. is there.

  FIG. 6 is a schematic diagram for explaining erroneous determination of rich lean determination in the above-described conventional air-fuel ratio control of an internal combustion engine. As shown in FIG. 6, when the temperature of the oxygen sensor element is slow and the sensor output voltage does not decrease easily, even if it is determined that the activation is complete by the activation determination, the oxygen sensor element may actually be in an incompletely active state. There is. In such a case, although the air-fuel ratio state is lean, the output voltage of the oxygen sensor is equal to or higher than the rich lean determination voltage, so that it is erroneously determined as rich. Further, if the fuel injection amount is reduced based on this erroneous determination, an internal combustion engine operation control failure such as an internal combustion engine stop due to over leaning will be caused. Thus, the conventional activation determination and rich lean determination have a problem that the determination accuracy deteriorates when the temperature of the sensor element is slow.

  Conventionally, air-fuel ratio control that performs activation determination based on the temperature of the sensor element (element internal resistance) has been developed. According to this apparatus, accurate determination can be made quickly, but there is a problem that the cost increases.

  The present invention has been made in view of the above-described problems of the prior art. By performing the oxygen sensor activation determination and the rich lean determination in two stages, the air-fuel ratio control is accurate and excellent in stability. It is an object of the present invention to provide an air-fuel ratio control apparatus and an air-fuel ratio control method for an internal combustion engine that can perform the above.

  Therefore, in order to solve the above problems, the present invention includes an air-fuel ratio control apparatus for an internal combustion engine that controls the ratio of air mass to fuel mass (air-fuel ratio) in a fuel-air mixture. An oxygen sensor for detecting the oxygen concentration and a control device for controlling the air-fuel ratio based on a signal from the oxygen sensor, wherein the control device outputs an output value of the oxygen sensor after the start of the internal combustion engine. The first fuel injection control is performed based on the output value of the oxygen sensor when it falls below the first reference set value for a set time of 1, and then the output value of the oxygen sensor is set to the second set time. The second fuel injection control is performed based on the output value of the oxygen sensor when the value falls below the second reference set value set lower than the first reference set value over a period of time. Air-fuel ratio control device for internal combustion engine To provide.

  Here, in the first fuel injection control, the control device performs the second fuel injection control based on whether an output value of the oxygen sensor exceeds a predetermined first rich lean determination voltage. Is performed based on whether or not the output value of the oxygen sensor exceeds a predetermined second rich lean determination voltage.

In order to solve the above problems, the present invention provides an air mass and a fuel mass in a fuel-air mixture based on an output value of an oxygen sensor that outputs a signal proportional to the oxygen concentration contained in the exhaust gas. In an air-fuel ratio control method for an internal combustion engine that controls the ratio (air-fuel ratio) of
(A) a process of energizing the oxygen sensor when the internal combustion engine is started;
(B) a step of confirming that the output value of the oxygen sensor has fallen below a first reference set value over a first set time;
(C) a step of performing first fuel injection control based on an output value of the oxygen sensor;
(D) a step of confirming that the output value of the oxygen sensor has fallen below a second reference set value set lower than the first reference set value over a second set time;
(E) There is provided an air-fuel ratio control method for an internal combustion engine characterized by comprising steps of performing a second fuel injection control based on an output value of the oxygen sensor.

  Here, the first fuel injection control is performed based on whether or not the output value of the oxygen sensor exceeds a predetermined first rich lean determination voltage, and the second fuel injection control is performed by the oxygen sensor. This is performed based on whether the output value exceeds a predetermined second rich lean determination voltage.

  According to the present invention, the activation determination and the rich lean determination of the oxygen sensor are performed in two stages, respectively, so that the power supply voltage to be supplied to the heater disposed in the oxygen sensor is low voltage or in the rain Even in the case of running or the like, the accuracy of rich lean determination can be improved.

  Further, the activation determination and the rich lean determination can be performed from a state in which the output voltage of the sensor element is high as compared with the conventional oxygen sensor activation determination. Therefore, the time until the determination can be shortened.

  Furthermore, since the determination based on the output value and time of the oxygen sensor is performed instead of the activation determination based on the temperature of the sensor element, the cost can be reduced.

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

FIG. 1 is a graph (schematic diagram) for explaining activation determination and rich lean determination of the oxygen sensor 12 (FIG. 2) in the air-fuel ratio control apparatus and method of the present invention.
In the graph shown in FIG. 1, the vertical axis represents the output voltage of the oxygen sensor using a zirconia element, and the horizontal axis represents the elapsed time after starting the internal combustion engine. By the way, as described above, the oxygen sensor 12 using a zirconia element exhibits a high output value when the internal combustion engine is operated in a rich state (the oxygen concentration in the exhaust gas is low), and the internal combustion engine is operated in a lean state. When the engine is in a high state (the oxygen concentration in the exhaust gas is high), it has a characteristic that exhibits a low output value.

  As shown in FIG. 1, for a while after the internal combustion engine is started, even if the oxygen sensor 12 is not activated or activated, the internal combustion engine is started in a rich state, thereby causing exhaust gas in the exhaust gas. The oxygen sensor 12 shows a high output value. Thereafter, as the temperature of the oxygen sensor 12 gradually rises, the output voltage of the oxygen sensor 12 decreases as the rich operation at the start of the internal combustion engine is eliminated.

  Then, when a predetermined time elapses after starting the internal combustion engine (after 23 seconds in the example of FIG. 1), the output value of the oxygen sensor 12 reaches the first set time (2 to 3 seconds in the example of FIG. 1). Over the first reference set value (1000 mV in the example of FIG. 1), the first fuel injection control is performed based on the output value of the oxygen sensor 12.

  Here, the first set time is determined based on the difference between the first rich lean determination voltage and the second rich lean determination voltage. The first fuel injection control is performed based on whether or not the output value of the oxygen sensor 12 exceeds a predetermined first rich lean determination voltage.

  Thereafter, a second reference set value (see FIG. 1) in which the output value of the oxygen sensor 12 is set lower than the first reference set value over a second set time (1 to 2 seconds in the example of FIG. 1). In the first example, it is confirmed that the voltage is lower than 600 mV), and the second fuel injection control is performed based on the output value of the oxygen sensor 12. Here, the second set time is preferably longer in order to make a more accurate determination, but in order to make the determination quickly, an appropriate time is set based on the voltage characteristics of the oxygen sensor. Then, the second fuel injection control is performed based on whether or not the output value of the oxygen sensor 12 exceeds a predetermined second rich lean determination voltage.

  FIG. 2 is a block diagram showing the configuration of the air-fuel ratio control apparatus for an internal combustion engine according to the present invention. As shown in FIG. 2, the air-fuel ratio control device 10 of the present invention includes a control unit 11 and an oxygen sensor 12. The control unit 11 monitors the output value of the oxygen sensor 12, and based on this, the activation determination of the oxygen sensor 12 and the rich lean determination of the air-fuel ratio in the internal combustion engine 21 are performed. Further, fuel injection control based on the rich lean determination is performed. The oxygen sensor 12 is installed in the exhaust gas path of the internal combustion engine 21 and is disposed, for example, in the exhaust pipe 21A for exhaust gas exhaust or in the muffler (not shown) of the vehicle on which the internal combustion engine is mounted. Outputs voltage according to oxygen concentration. The oxygen sensor 12 includes a heater 12A.

  The control unit 11 converts the analog value output from the oxygen sensor 12 into an A / D converter, the above-described first reference set value, second reference set value, first set time, second The memory includes a ROM that stores a fixed value such as a set time and a control program, and a RAM that stores a variable value and the like, and a CPU that performs arithmetic processing.

  FIG. 3 is a flowchart showing a processing flow in the air-fuel ratio control method for an internal combustion engine according to the present invention.

  In the present invention, as described above, the activation determination and the rich lean determination of the oxygen sensor 12 are performed in two stages. Specifically, as shown in FIG. 3, after the internal combustion engine 21 is started, the first stage activation determination is performed. First, the internal combustion engine 21 is started and energized to the heater 12A (step S1). Next, the control unit 11 determines whether or not the current oxygen sensor output voltage value is lower than a preset first stage activation determination voltage value (step S2).

  Here, if the oxygen sensor output voltage value is lower than the first stage activation determination voltage value, it is determined whether or not the state continues for a predetermined time T1 time (for example, 3 seconds) (step S3). When it is sustained, the control unit 11 determines that the first stage activation determination is active, and proceeds to the next step.

  If it is determined to be active in the first stage activation determination, the process proceeds to the first stage rich lean determination. That is, the control unit 11 determines whether or not the current oxygen sensor output voltage value is higher than the first stage rich lean determination voltage value (step S4). If the value is high, the control device determines that the fuel is rich and performs control to reduce the fuel injection amount (step S5). On the other hand, if the value is low, the control unit 11 determines that the fuel is lean and performs control to increase the fuel injection amount (step S6).

  Next, the process proceeds to the second stage activation determination. In this second stage activation determination, the control unit 11 determines whether or not the current oxygen sensor output voltage value is lower than a preset second stage activation determination voltage value (step S7). At this time, the second stage activation determination voltage value is set to a value lower than the first stage activation determination voltage value. If the oxygen sensor output voltage value is lower than the second-stage activation determination voltage value, it is determined whether or not the state continues for a predetermined time T2 (for example, 3 seconds) (step S8). If it is sustained, the control unit 11 determines that it is active in the second stage activation determination, and proceeds to the next step.

  If it is determined to be active in the second stage activation determination, the process proceeds to the second stage rich lean determination. That is, the control unit 11 determines whether or not the current oxygen sensor output voltage value is higher than the second-stage rich lean determination voltage value (step S9). At this time, the second stage rich lean determination voltage value is set to a value lower than the first stage rich lean determination voltage value. When the oxygen sensor output voltage value is higher than the second stage rich lean determination voltage value, the control device determines that the oxygen is rich and performs control to reduce the fuel injection amount (step S10). On the other hand, if the value is low, the control unit 11 determines that the fuel is lean and performs control to increase the fuel injection amount (step S11). The two-stage activation determination and rich-lean determination are repeated while the internal combustion engine 21 is being driven, and fuel injection control based on this is performed each time.

  In the above embodiment, the processing in the case where the heater built-in type oxygen sensor is used has been described. However, even when the heaterless oxygen sensor is used, the air-fuel ratio control of the internal combustion engine can be performed in the same flow. In the case of a heaterless oxygen sensor, it is heated and activated by exhaust gas.

  Since it comprised as mentioned above, according to this invention, the power supply voltage which supplies with electricity to the heater arrange | positioned inside an oxygen sensor by performing activation determination and rich lean determination of an oxygen sensor in two steps, respectively. The rich lean determination accuracy can be improved even in the case of low voltage or traveling in the rain.

  Further, the activation determination and the rich lean determination can be performed from a state in which the output voltage of the sensor element is high as compared with the conventional oxygen sensor activation determination. Therefore, the time until the determination can be shortened.

  Furthermore, since the determination based on the output value and time of the oxygen sensor is performed instead of the activation determination based on the temperature of the sensor element, the cost can be reduced.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, Based on the meaning of this invention, various deformation | transformation are possible, These are excluded from the scope of the present invention. is not.

  The present invention relates to an air-fuel ratio control device and an air-fuel ratio control method for an internal combustion engine that controls the air-fuel ratio based on the measurement result of the oxygen concentration in the exhaust gas discharged from the internal combustion engine. Have

The graph (schematic diagram) for demonstrating activation determination of an oxygen sensor and rich lean determination in the air fuel ratio control apparatus and method of this invention is shown. 1 is a block diagram showing a configuration of an air-fuel ratio control apparatus for an internal combustion engine according to the present invention. 3 is a flowchart showing a flow of processing in an air-fuel ratio control method for an internal combustion engine according to the present invention. It is a temperature characteristic figure of the general oxygen sensor which measures the oxygen concentration in the exhaust gas of an internal-combustion engine. It is a schematic diagram which shows the outline of the activation determination of the oxygen sensor in the air-fuel ratio control of the conventional internal combustion engine. It is a schematic diagram for demonstrating the misjudgment of the rich lean judgment in the air fuel ratio control of the conventional internal combustion engine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Air fuel ratio control apparatus 11 Control part 12 Oxygen sensor 12A Heater 21 Internal combustion engine 21A Exhaust pipe

Claims (4)

In an air-fuel ratio control apparatus for an internal combustion engine that controls a ratio of air mass to fuel mass (hereinafter referred to as “air-fuel ratio”) in a mixture of fuel and air,
An oxygen sensor for detecting the oxygen concentration contained in the exhaust gas;
A control device for controlling the air-fuel ratio based on a signal of the oxygen sensor,
When the output value of the oxygen sensor falls below a first reference set value for a first set time after the internal combustion engine is started, the control device performs the first fuel operation based on the output value of the oxygen sensor. When the injection control is performed and then the output value of the oxygen sensor falls below the second reference set value set lower than the first reference set value over a second set time, the oxygen sensor An air-fuel ratio control apparatus for an internal combustion engine, wherein second fuel injection control is performed based on an output value. The controller is
The first fuel injection control is performed based on whether an output value of the oxygen sensor exceeds a predetermined first rich lean determination voltage,
The second fuel injection control is performed based on whether the output value of the oxygen sensor exceeds a predetermined second rich lean determination voltage.
The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein: Based on the output value of the oxygen sensor that outputs a signal proportional to the oxygen concentration contained in the exhaust gas, the ratio of the air mass to the fuel mass (hereinafter referred to as “air-fuel ratio”) in the fuel-air mixture is controlled. In an air-fuel ratio control method for an internal combustion engine,
(A) a process of energizing the oxygen sensor when the internal combustion engine is started;
(B) a step of confirming that the output value of the oxygen sensor has fallen below a first reference set value over a first set time;
(C) a step of performing first fuel injection control based on an output value of the oxygen sensor;
(D) a step of confirming that the output value of the oxygen sensor has fallen below a second reference set value set lower than the first reference set value over a second set time;
(E) performing a second fuel injection control based on the output value of the oxygen sensor;
An air-fuel ratio control method for an internal combustion engine comprising the steps of: The first fuel injection control is performed based on whether an output value of the oxygen sensor exceeds a predetermined first rich lean determination voltage,
The second fuel injection control is performed based on whether an output value of the oxygen sensor exceeds a predetermined second rich lean determination voltage.
The air-fuel ratio control method for an internal combustion engine according to claim 3.

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