JP2009156052A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure the stability of an air-fuel ratio feedback control system at the time of low engine water temperature in an engine (internal combustion engine) performing the air-fuel ratio feedback control based on an output signal of an A/F sensor disposed in an exhaust passage. <P>SOLUTION: The air-fuel ratio feedback control gain (proportional gain and integration gain) is set variably according to the cooling water temperature THW of an engine sensed by a water temperature sensor (steps ST203, ST204). By setting an appropriate air-fuel ratio feedback control gain corresponding to responsiveness decline of the A/F sensor output at the time of low engine water temperature (temperature lower than the engine warming-up temperature), stability of the control system is ensured by restraining hunting of the exhaust air-fuel ratio. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine that performs air-fuel ratio feedback control based on an output signal of an exhaust gas sensor disposed in an exhaust passage.

  In an internal combustion engine (hereinafter also referred to as an engine) mounted on a vehicle, an exhaust purification catalyst is disposed in an exhaust passage. A typical three-way catalyst is an exhaust purification catalyst.

  The three-way catalyst oxidizes unburned components (hydrocarbon: HC, carbon monoxide: CO) in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the catalyst is substantially the stoichiometric air-fuel ratio, and at the same time nitrogen oxides The exhaust gas is purified by the function of reducing (NOx). Specifically, the three-way catalyst has an oxygen storage function for storing (storing) oxygen. When the air-fuel ratio of the inflowing exhaust gas is rich, the unburned HC is stored in the stored oxygen. Oxidizes unburned components such as CO (releases oxygen). On the other hand, when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is lean, oxygen obtained by reducing oxygen and NOx in the exhaust gas is occluded inside. In this way, the three-way catalyst can effectively purify unburned HC, CO, and NOx in the exhaust gas discharged from the combustion chamber of the engine.

  The purification characteristic of such a three-way catalyst depends on the air-fuel ratio (A / F) indicating the combustion state of the engine, and the three-way catalyst functions most effectively when the air-fuel ratio is in the vicinity of the stoichiometric air-fuel ratio. This is because if the air-fuel ratio is lean and the amount of oxygen in the exhaust gas is large, the oxidation action becomes active but the reduction action becomes inactive. On the other hand, if the air-fuel ratio is rich and the amount of oxygen in the exhaust gas is small On the contrary, the reduction action becomes active, but the oxidation action becomes inactive, so that all of the above three harmful components of HC, CO and NOx cannot be purified well.

  From such a point, in an engine mounted on a vehicle, an A / F sensor (a sensor having a linear characteristic with respect to an air-fuel ratio) is disposed in an exhaust passage, and based on an output value of the A / F sensor. The air-fuel ratio feedback control is performed so that the air-fuel ratio (actual air-fuel ratio) matches the stoichiometric air-fuel ratio.

  For the air-fuel ratio feedback control, for example, PI (proportional / integral) control is used. In PI control, the proportional term and integral term are calculated based on the deviation between the output value (actual air-fuel ratio) of the A / F sensor and the target air-fuel ratio, and the calculated proportional term and integral term are summed up to perform feedback correction. The amount is calculated.

  Specifically, the feedback correction amount is calculated based on the arithmetic expression [feedback correction amount = deviation × GnP + deviation time integral value × GnI] and reflected in the fuel injection amount. In this arithmetic expression, GnP is a proportional gain, and GnI is an integral gain.

  In addition, there exists a technique of the following patent documents 2 and 3 as a technique regarding the responsiveness of an exhaust gas sensor in the air-fuel ratio control of an internal combustion engine.

In the technique described in Patent Document 2, when the element temperature of the oxygen sensor is low immediately after the engine is started, the rich / lean determination threshold value is corrected to suppress deterioration in air-fuel ratio controllability even in a low temperature state. Yes. Further, in the technique described in Patent Document 3, when the responsiveness of the sensor output decreases due to the aging of the oxygen sensor, the delay due to aging (sensor response deterioration) is reduced by performing gain correction of the air-fuel ratio feedback control. Absorbed by control gain.
JP 2006-220085 A Japanese Utility Model Publication No. 6-1747 JP 2000-27688 A

  By the way, the air-fuel ratio feedback control is started on the condition that the engine coolant temperature has reached the air-fuel ratio feedback control start temperature, but the period from the air-fuel ratio feedback control start temperature until the engine warm-up temperature is reached. When the temperature is low, the response of the A / F sensor deteriorates and the air-fuel ratio feedback control becomes unstable.

  For example, as shown in FIG. 7 (a), if the coolant temperature is equal to or higher than the warm-up temperature (after warm-up), the change in fuel injection amount (increase or decrease: see FIG. 6 (a)), exhaust gas air-fuel ratio Since the responsiveness of the A / F sensor output with respect to the disturbance affecting the air is good, the air-fuel ratio of the exhaust gas converges to the theoretical air-fuel ratio (for example, A / F = 14.5) at an early stage.

  On the other hand, when the coolant temperature is lower than the warm-up temperature (for example, a temperature close to the air-fuel ratio feedback control start temperature), as shown in FIG. 7B, the change in fuel injection amount (increase or decrease): Since the response of the A / F sensor output to a disturbance that affects the exhaust gas air-fuel ratio becomes worse, the air-fuel ratio feedback control system becomes unstable at the same gain as the warm-up temperature or higher. The air-fuel ratio of the exhaust gas greatly fluctuates (hunting) with respect to the stoichiometric air-fuel ratio. When this happens, exhaust emissions worsen. In addition, drivability deteriorates because the output torque of the engine fluctuates.

  The present invention has been made in view of such circumstances, and in an internal combustion engine that performs air-fuel ratio feedback control based on an output signal of an exhaust gas sensor (A / F sensor) disposed in an exhaust passage, the engine is at a low water temperature. An object of the present invention is to realize air-fuel ratio control capable of ensuring the stability of the air-fuel ratio feedback control system.

-Solving principle-
The solution principle of the present invention taken to achieve the above object is that, in an internal combustion engine that performs air-fuel ratio feedback control, the air-fuel ratio varies depending on the responsiveness of the exhaust gas sensor (A / F sensor) that changes depending on the cooling water temperature. The feedback control gain is variably set. By such gain setting, it is possible to ensure the stability of the control system at the time of engine low water temperature.

-Solution-
Specifically, the present invention relates to an exhaust gas sensor disposed in an exhaust passage of an internal combustion engine, and when an air-fuel ratio feedback control execution condition is satisfied, the air-fuel ratio of the exhaust gas is set to a target air-fuel ratio based on the output of the exhaust gas sensor. And an air-fuel ratio control device for an internal combustion engine provided with an air-fuel ratio feedback control means for controlling the fuel injection amount so as to match the above. In such an air-fuel ratio control apparatus, a water temperature sensor that detects the cooling water temperature of the internal combustion engine, and a gain that variably sets the gain of the air-fuel ratio feedback control according to the cooling water temperature detected by the water temperature sensor And setting means.

  More specifically, the air-fuel ratio feedback control means executes air-fuel ratio feedback control by proportional and integral operations based on the output of the exhaust gas sensor, and the gain setting means responds to the cooling water temperature detected by the water temperature sensor. The proportional gain and integral gain of the air-fuel ratio feedback control are set. More specifically, when the cooling water temperature detected by the water temperature sensor is low, the proportional gain is set on the larger side and the integral gain is set on the smaller side compared to the case where the cooling water temperature is high.

  According to the present invention, the gain (proportional gain and integral gain) of the air-fuel ratio feedback control (PI control) is variably set according to the cooling water temperature of the internal combustion engine. An appropriate air-fuel ratio feedback control gain can be set in accordance with a decrease in responsiveness of the / F sensor output. As a result, even when the cooling water temperature is low (water temperature lower than the engine warm-up temperature), hunting of the exhaust air / fuel ratio as shown in FIG. 7B can be suppressed, and the convergence of the air / fuel ratio feedback control can be suppressed. And the stability of the control system can be ensured. As a result, it is possible to improve the exhaust mission and the drivability.

  In the present invention, as a specific configuration of the gain setting means, an air-fuel ratio feedback control gain is set with the operating state of the internal combustion engine including the cooling water temperature (specifically, the engine speed, the engine load factor, and the cooling water temperature) as parameters. A configuration having a gain calculation map for calculating (proportional gain and integral gain), and setting the air-fuel ratio feedback control gain with reference to the gain calculation map based on the cooling water temperature detected by the water temperature sensor Can be mentioned.

  In the present invention, a failure detection means for detecting a failure of the water temperature sensor is provided, and when the water temperature sensor is broken, the gain of the air-fuel ratio feedback control is set to the failure dedicated gain. In this case, for example, a gain (proportional gain and integral gain) adapted based on the coolant temperature after engine warm-up is used as a gain exclusively for failure (during failure). If such a fail safe is employed, normal air-fuel ratio feedback control can be executed even when the water temperature sensor fails, and the stability of the control system after warm-up can be ensured. it can.

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

  First, an engine (internal combustion engine) to which the present invention is applied will be described.

-Engine-
FIG. 1 is a diagram showing a schematic configuration showing an example of an engine 1 to which the present invention is applied. FIG. 1 shows only the configuration of one cylinder of the engine 1.

  The engine 1 in this example is, for example, a four-cylinder gasoline engine, and includes a piston 1b that forms a combustion chamber 1a and a crankshaft 15 that is an output shaft. The piston 1b is connected to the crankshaft 15 via the connecting rod 16, and the reciprocating motion of the piston 1b is converted into rotation of the crankshaft 15 by the connecting rod 16.

  A signal rotor 17 having a plurality of protrusions (teeth) 17 a on the outer peripheral surface is attached to the crankshaft 15. A crank position sensor (engine speed sensor) 24 is disposed near the side of the signal rotor 17. The crank position sensor 24 is, for example, an electromagnetic pickup, and generates a pulsed signal (output pulse) corresponding to the protrusion 17a of the signal rotor 17 when the crankshaft 15 rotates. Further, a water temperature sensor 21 that detects the temperature of the cooling water for the engine 1 (cooling water temperature THW) is disposed in the cylinder block 1 c of the engine 1.

  A spark plug 3 is disposed in the combustion chamber 1 a of the engine 1. The ignition timing of the spark plug 3 is adjusted by the igniter 4. The igniter 4 is controlled by an ECU (Electronic Control Unit) 100.

  An intake passage 11 and an exhaust passage 12 are connected to the combustion chamber 1 a of the engine 1. An intake valve 13 is provided between the intake passage 11 and the combustion chamber 1a. By opening and closing the intake valve 13, the intake passage 11 and the combustion chamber 1a are communicated or blocked. Further, an exhaust valve 14 is provided between the exhaust passage 12 and the combustion chamber 1a. By opening and closing the exhaust valve 14, the exhaust passage 12 and the combustion chamber 1a are communicated or blocked. The opening / closing drive of the intake valve 13 and the exhaust valve 14 is performed by each rotation of the intake camshaft and the exhaust camshaft to which the rotation of the crankshaft 15 is transmitted.

  In the intake passage 11, an air cleaner 7, a hot-wire air flow meter 22 that detects the intake air amount, an intake air temperature sensor 23 (built in the air flow meter 22), and an electronically controlled throttle that adjusts the intake air amount of the engine 1. A valve 5 is arranged. The throttle valve 5 is driven by a throttle motor 6. The opening degree of the throttle valve 5 is detected by a throttle opening degree sensor 25.

  The throttle opening of the throttle valve 5 is driven and controlled by the ECU 100. Specifically, the throttle valve 5 is opened so that an optimum intake air amount (target intake air amount) corresponding to the engine 1 operating state such as the engine speed and the accelerator pedal depression amount (accelerator opening) is obtained. Control the degree. More specifically, the actual throttle opening of the throttle valve 5 is detected using the throttle opening sensor 25, and the actual throttle opening coincides with the throttle opening (target throttle opening) at which the target intake air amount can be obtained. Thus, the throttle motor 6 of the throttle valve 5 is feedback controlled.

  A three-way catalyst 8 is disposed in the exhaust passage 12 of the engine 1. The three-way catalyst 8 has an oxygen storage capacity, adsorbs excess oxygen when the air-fuel ratio of the exhaust gas is lean, and releases deficient oxygen when the air-fuel ratio of the exhaust gas is rich. Thus, carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) contained in the exhaust gas discharged from the combustion chamber 1a are purified.

  An A / F sensor 27 is disposed in the exhaust passage 12 upstream of the three-way catalyst 8. The A / F sensor 27 is a sensor that exhibits linear characteristics with respect to the air-fuel ratio of the exhaust gas discharged from the combustion chamber 1a.

  A fuel injection injector 2 is disposed in the intake passage 11. Fuel of a predetermined pressure is supplied from the fuel tank to the injector 2 by a fuel pump, and the fuel is injected into the intake passage 11. This injected fuel is mixed with intake air to form an air-fuel mixture and introduced into the combustion chamber 1a of the engine 1. The air-fuel mixture (fuel + air) introduced into the combustion chamber 1a is ignited by the spark plug 3 and burns and explodes. The piston 1b reciprocates due to combustion / explosion of the air-fuel mixture in the combustion chamber 1a, and the crankshaft 15 rotates.

  The operating state of the engine 1 is controlled by the ECU 100. For example, the fuel injection amount from the injector 2 to the intake passage 11 (fuel injection time that is the valve opening time of the injector 2) is controlled by the ECU 100 by air-fuel ratio feedback control described later.

-ECU-
As shown in FIG. 2, the ECU 100 includes a CPU 101, a ROM 102, a RAM 103, a backup RAM 104, and the like.

  The ROM 102 stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU 101 executes various arithmetic processes based on various control programs and maps stored in the ROM 102. The RAM 103 is a memory that temporarily stores calculation results of the CPU 101, data input from each sensor, and the like. The backup RAM 104 is a nonvolatile memory that stores data to be saved when the engine 1 is stopped, for example. Memory.

  The CPU 101, ROM 102, RAM 103, and backup RAM 104 are connected to each other via a bus 107 and are connected to an input interface 105 and an output interface 106.

  The input interface 105 includes a water temperature sensor 21, an air flow meter 22, an intake air temperature sensor 23, a crank position sensor 24, a throttle opening sensor 25, an accelerator opening sensor 26 that outputs a detection signal corresponding to the depression amount of the accelerator pedal, and A / F sensors 27 and the like are connected, and the output signals of the sensors, that is, the coolant temperature THW, the intake air amount, the intake air temperature, the engine speed NE, the throttle opening, the accelerator opening, and the air-fuel ratio signal Is input to the ECU 100. On the other hand, the output interface 106 is connected to the injector 2, the igniter 4 of the spark plug 3, the throttle motor 6 of the throttle valve 5, and the like.

  An air-fuel ratio control device is realized by the injector 2, the air flow meter 22, the A / F sensor 27, the ECU 100, and the like.

  The ECU 100 executes various controls of the engine 1 including the following air-fuel ratio feedback control based on the detection signals of the various sensors described above.

-Air-fuel ratio feedback control-
First, the purification characteristics of the three-way catalyst 8 depend on the air-fuel ratio (A / F) indicating the combustion state of the engine 1, and the three-way catalyst 8 functions most effectively when the air-fuel ratio is close to the theoretical air-fuel ratio. In addition, harmful three components of HC, CO, and NOx in the exhaust gas can be purified well. In order to maintain the purification performance of the three-way catalyst 8, air-fuel ratio feedback control is executed in this example.

  The air-fuel ratio feedback control in this example uses PI (proportional / integral) control. Specifically, the feedback correction amount is calculated based on the following equation (1) and reflected in the fuel injection amount (the fuel injection time that is the valve opening time of the injector 2), so that the air-fuel ratio of the exhaust gas is the target. Feedback control is performed to match the air-fuel ratio (theoretical air-fuel ratio).

Feedback correction amount = deviation × GnP + deviation time integral value × GnI (1)
Here, deviation = [target air / fuel ratio−actual air / fuel ratio (output value of A / F sensor 27)], GnP: proportional gain, and GnI: integral gain.

  In the feedback correction amount calculation formula (1), the proportional term (deviation × GnP) is a component that affects the responsiveness, and the integral term (deviation time integral value × GnI) is a component that affects the steady-state deviation. It is.

  In this example, as described later, the proportional gain GnP and the integral gain GnI are variably set according to the coolant temperature THW of the engine 1. However, when the water temperature sensor 21 has failed (failed), the proportional gain and integral gain dedicated for failing are set.

-Air-fuel ratio feedback gain setting process-
By the way, in the air-fuel ratio feedback control, as described above, the cooling water temperature THW of the engine 1 is started on the condition that it has reached the air-fuel ratio feedback control start temperature. The responsiveness of the A / F sensor 27 is deteriorated until the warm-up temperature is reached (low temperature). For example, when the coolant temperature THW is lower than the engine warm-up temperature (for example, a temperature close to the air-fuel ratio feedback control start temperature), a change in fuel injection amount (increase / decrease), a disturbance that affects the exhaust gas air-fuel ratio Since the responsiveness of the A / F sensor 27 with respect to the above becomes worse, the control system becomes unstable, and the exhaust air-fuel ratio greatly fluctuates (hunts) with respect to the stoichiometric air-fuel ratio as shown in FIG. In such a situation, exhaust emission deteriorates and drivability deteriorates.

  In consideration of such points, in this example, the air-fuel ratio feedback control gain (proportional gain GnP and integral gain GnI) is variably set according to the responsiveness of the A / F sensor 27 that varies depending on the coolant temperature THW. Thus, it is characterized in that the stability of the air-fuel ratio feedback control system is ensured.

  A specific example of the air-fuel ratio feedback gain setting process will be described with reference to the flowchart shown in FIG. The control routine shown in FIG. 3 is repeatedly executed at predetermined intervals in the ECU 100.

  Prior to the description of the air-fuel ratio feedback gain setting process, a map used in this example will be described with reference to FIGS.

  The map shown in FIG. 4 is a three-dimensional map used for calculating the proportional gain GnP of the above-described feedback correction amount arithmetic expression (1) using the engine speed NE, the load factor KL of the engine 1 and the coolant temperature THW as parameters. In this example, a plurality of (four in this example) two-dimensional maps Pmap1, Pmap2, Pmap3, and Pmap4 are used. This proportional gain calculation map is stored in the ROM 102 of the ECU 100.

  Each of the two-dimensional maps Pmap1 to Pmap4 constituting the proportional gain calculation map has a plurality of types (four types) of cooling water temperatures (for example, THW1, THW2) set in advance using the engine speed NE and the load factor KL as parameters, respectively. , THW3, THW4, THW1 <THW2 <HTHW3 <THW4, THW4: Cooling water temperature after engine warm-up), the proportional gain GnP that makes the stability (convergence) of the air-fuel ratio feedback control system good is This is a map of values obtained by experiments and the like in consideration of the relationship. In these two-dimensional maps Pmap1 to Pmap4, if the engine speed NE and the load factor KL are the same, the proportional gain GnP is set to be larger as the coolant temperature THW is lower.

  Note that the load factor KL is the ratio of the intake air amount in the current operating state to the maximum intake air amount to the engine 1, for example, the intake air amount obtained from the output signal of the air flow meter 22 and the crank position sensor 24. It is calculated based on the engine speed NE obtained from the output signal.

  The map shown in FIG. 5 is a three-dimensional map used to calculate the integral gain GnI of the feedback correction amount calculation formula (1) using the engine speed NE, the load factor KL of the engine 1 and the coolant temperature THW as parameters. In this example, a plurality of (four in this example) two-dimensional maps Imap1, Imap2, Imap3, and Imap4 are used. This integral gain calculation map is also stored in the ROM 102 of the ECU 100.

  Each of the two-dimensional maps Imap1 to Imap4 constituting the integral gain calculation map uses the engine speed NE and the load factor KL as parameters, and sets a plurality of (four types) of cooling water temperatures (proportional gain GnP). Experiments were conducted in consideration of the relationship with the above-mentioned proportional gain GnP, with respect to the integral gain GnI at which the stability (convergence) of the air-fuel ratio feedback control system is good at the same water temperature (THW1, THW2, THW3, THW4) as in the case of conformity. This is a map of the values obtained by the above. In these two-dimensional maps Imap1 to Imap4, if the engine speed NE and the load factor KL are the same, the integral gain GnI is set to be smaller as the cooling water temperature THW is lower.

  Then, by reading the proportional gain GnP and the integral gain GnI using the gain calculation maps shown in FIGS. 4 and 5, the coolant temperature THW is low (the temperature after the engine warm-up is lower than the warm-up temperature of the engine 1). Water temperature), an air-fuel ratio feedback control gain (proportional gain GnP, integral gain GnI) can be set in accordance with a decrease in response of the A / F sensor 27 at the low water temperature. Stability can be ensured.

  In this example, a map Pmap4 suitable for the cooling water temperature after engine warm-up among a plurality of two-dimensional maps Pmap1 to Pmap4 constituting the proportional gain calculation map (three-dimensional map) will be described later. Used as a dedicated map for failure of the water temperature sensor 21. Similarly, with respect to the integral gain, a map Imap4 adapted to the cooling water temperature after engine warm-up is selected from the plurality of two-dimensional maps Imap1 to Imap4 constituting the integral gain calculation map (three-dimensional map). It is used as a dedicated map when the sensor 21 fails.

  Next, the control routine shown in FIG. 3 will be described for each step.

  In step ST201, it is determined whether or not an air-fuel ratio feedback control execution condition is satisfied. If the determination result is affirmative, the process proceeds to step ST202.

  Specifically, for example, the cooling water temperature THW detected by the water temperature sensor 21 is equal to or higher than the air-fuel ratio feedback control start water temperature, and the element temperature of the A / F sensor 27 is equal to or higher than a predetermined activation temperature. If the above conditions are satisfied, it is determined that the air-fuel ratio feedback control execution condition is satisfied, and the process proceeds to step ST202. If the determination result in step ST201 is negative, the process returns. The element temperature of the A / F sensor 27 is detected by using, for example, the fact that there is a correlation between the element impedance (AC impedance) of the sensor element and the element temperature, and the detected element impedance. The device temperature is indirectly detected based on the above.

  In step ST202, it is determined whether or not the water temperature sensor 21 that detects the coolant temperature of the engine 1 is normal. If the determination result is affirmative, the process proceeds to step ST203. When the determination result of step ST202 is negative (when the water temperature sensor 21 fails), the process proceeds to step ST205.

  For the failure of the water temperature sensor 21, for example, detection of disconnection between two terminals of the sensor, detection of short circuit between the two terminals of the sensor, or stack detection in which the sensor output does not change, and any one of these disconnection / short circuit or stack is performed. When one is detected, it is determined that the water temperature sensor has failed.

  In step ST203, the coolant temperature THW of the engine 1 is calculated based on the output signal of the water temperature sensor 21.

  In step ST204, the map shown in FIGS. 4 and 5 is used by using the engine speed NE and the load factor KL read from the output signals of the crank position sensor 24 and the air flow meter 22, and the coolant temperature THW calculated in step ST203. With reference, the proportional gain GnP and the integral gain GnI are read.

  The ECU 100 then uses the proportional gain GnP and the integral gain GnI read in step STST204 to calculate the feedback correction amount by the above equation (1): [feedback correction amount = deviation × GnP + deviation time integral value × GnI]. It is calculated and reflected in the fuel injection amount (fuel injection time which is the valve opening time of the injector 2).

  When the cooling water temperature THW calculated in step ST203 is different from the cooling water temperature adapted to the two-dimensional maps Pmap1 to Pmap4 in FIG. 4 and the two-dimensional maps Imap1 to Imap4 in FIG. 5, the cooling water temperature THW is higher than the calculated cooling water temperature THW. Fuel is obtained by calculating a proportional gain GnP and an integral gain GnI by using a two-dimensional map on the lower side and a two-dimensional map on the lower side and performing an interpolation operation based on the two adjacent two-dimensional maps to obtain a feedback correction amount. This is reflected in the injection amount (fuel injection time).

  On the other hand, when the determination result of step ST202 is negative, that is, when the water temperature sensor 21 is failing, based on the engine speed NE and the load factor KL using the above-described dedicated map at the time of failure (Pmap4, Imap4). The proportional gain GnP and the integral gain GnI are read (step ST5), and the proportional gain GnP and the integral gain GnI are used to calculate the above equation (1): [feedback correction amount = deviation × GnP + deviation time integral value × GnI]. The feedback correction amount is calculated and reflected in the fuel injection amount (fuel injection time).

  As described above, according to this example, the proportional gain GnP and the integral gain GnI of the air-fuel ratio feedback control (PI control) are made variable according to the cooling water temperature THW of the engine 1, and when the cooling water temperature THW is low, Since the proportional gain GnP for PI control is set to a large value and the integral gain GnI is set to a small value in response to a decrease in responsiveness of the A / F sensor 27 at a low water temperature, an appropriate air-fuel ratio feedback can be obtained even at a low water temperature. It becomes possible to set the control gain. As a result, even when the coolant temperature THW is low (water temperature lower than the warm-up temperature of the engine 1), the exhaust air-fuel ratio hunting as shown in FIG. Convergence is improved and stability of the control system can be ensured. As a result, it is possible to improve the exhaust mission and the drivability.

  Further, in this example, when the water temperature sensor 21 fails, the proportional gain GnP and the integral gain GnI of the air-fuel ratio feedback control are set with reference to the dedicated map at the time of failure (map adapted with the cooling water temperature after warming up). Therefore, even when the water temperature sensor 21 fails, normal air-fuel ratio feedback control can be executed, and the stability of the control system after engine warm-up can be ensured.

-Other embodiments-
In the above example, the example in which the present invention is applied to the air-fuel ratio control of the engine in which the three-way catalyst is arranged in the exhaust passage is shown. However, the present invention is not limited to this, and the air-fuel ratio in the exhaust gas is theoretically limited. Applicable to air-fuel ratio control of engines where other types of catalysts that have the function of converting various harmful components in exhaust gas into harmless components with high conversion efficiency under conditions near the air-fuel ratio are arranged in the exhaust passage It is.

  In the above example, the present invention is applied to the air-fuel ratio control of a four-cylinder gasoline engine. However, the present invention is not limited to this, and for example, any other number of cylinders such as a cylinder six-cylinder gasoline engine can be used. It can also be applied to air-fuel ratio control of multi-cylinder gasoline engines.

  The present invention can also be applied to air-fuel ratio control of a V-type multi-cylinder gasoline engine or a vertical multi-cylinder gasoline engine. Furthermore, the present invention is not limited to a port injection type gasoline engine, but can also be applied to air-fuel ratio control of an in-cylinder direct injection type gasoline engine.

In the present invention, in addition to the A / F sensor 27 disposed in the exhaust passage 12 on the upstream side of the three-way catalyst 8, an empty engine is provided in which the O ₂ sensor is disposed in the exhaust passage 12 on the downstream side of the three-way catalyst 8. It is also applicable to fuel ratio control.

It is a schematic structure figure showing an example of an engine to which the present invention is applied. It is a block diagram which shows the structure of control systems, such as ECU. It is a flowchart which shows the control routine of the air fuel ratio feedback gain setting process which ECU performs. It is a figure which shows an example of the map for proportional gain calculation. It is a figure which shows an example of the map for integral gain calculation. It is a figure which shows the change of the responsiveness of the A / F sensor output with respect to fuel injection amount change. It is a Bode diagram showing frequency response characteristics of air-fuel ratio feedback control.

Explanation of symbols

1 Engine 2 Injector 8 Three-way catalyst 11 Intake passage 12 Exhaust passage 21 Water temperature sensor 22 Air flow meter 24 Crank position sensor (engine speed sensor)
27 A / F sensor (exhaust gas sensor)
100 ECU

Claims (5)

When the exhaust gas sensor disposed in the exhaust passage of the internal combustion engine and the air-fuel ratio feedback control execution condition are satisfied, the fuel injection amount is set so that the air-fuel ratio of the exhaust gas matches the target air-fuel ratio based on the output of the exhaust gas sensor An air-fuel ratio control apparatus for an internal combustion engine comprising an air-fuel ratio feedback control means for controlling
A water temperature sensor for detecting a cooling water temperature of the internal combustion engine, and gain setting means for variably setting the gain of the air-fuel ratio feedback control according to the cooling water temperature detected by the water temperature sensor. An air-fuel ratio control device for an internal combustion engine. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1,
The air-fuel ratio feedback control means executes air-fuel ratio feedback control by proportional and integral operations based on the output of the exhaust gas sensor, and the gain setting means performs the air-fuel ratio feedback control according to the cooling water temperature detected by the water temperature sensor. An air-fuel ratio control apparatus for an internal combustion engine, characterized in that a proportional gain and an integral gain for fuel ratio feedback control are set. The air-fuel ratio control apparatus for an internal combustion engine according to claim 2,
The gain setting means sets the proportional gain to a larger side and sets the integral gain to a smaller side when the cooling water temperature detected by the water temperature sensor is lower than when the cooling water temperature is high. An air-fuel ratio control device for an internal combustion engine. The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 3,
The gain setting means sets a gain calculation map for calculating an air-fuel ratio feedback control gain using the operating state of the internal combustion engine including the cooling water temperature as a parameter, and is based on the cooling water temperature detected by the water temperature sensor. An air-fuel ratio control apparatus for an internal combustion engine, wherein an air-fuel ratio feedback control gain is set with reference to the gain calculation map. The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 4,
An air-fuel ratio control apparatus for an internal combustion engine, comprising: failure detection means for detecting a failure of the water temperature sensor, wherein the air-fuel ratio feedback control gain is set to a failure dedicated gain when the water temperature sensor is malfunctioning.

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