JPH02259253A - Air-fuel ratio control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve exhaust purifying performance by introducing secondary air to a catalytic converter at the time of idle operation or the like, in case of controlling air-fuel ratio in accordance with an output of each oxygen concentration sensor provided in the up and downstream of the catalytic converter in an exhaust system. CONSTITUTION:An exhaust passage 3 arranges a catalytic converter (ternary catalyst) 9 providing in its upstream side part an upstream O2 sensor 17 detecting concentration of oxygen in exhaust gas while in the downstream side part similarly a downstream O2 sensor 18 detecting the concentration of oxygen in the exhaust gas. Each O2 sensor 17, 18 is used providing the characteristic suddenly changing output voltage in the vicinity of theoretical air-fuel ratio. While a secondary air introducing passage 20 is connected between the catalytic converter 9 and the upstream O2 sensor 17. At the time of idle operation and low load operation, secondary air is introduced from the secondary air introducing passage 20 to the catalytic converter 9 while an air-fuel ratio control is performed by an ECU so that an output value of the upstream O2 sensor 17 becomes a preset value.

Description

Detailed Description of the Invention <Public Expenses for Industrial Use> The present invention relates to an air-fuel ratio control method for controlling the air-fuel ratio of an air-fuel mixture based on an output signal of an oxygen concentration sensor provided in an exhaust system of an internal combustion engine.

<Conventional technology> The ratio of air and fuel in the mixture sent to the internal combustion engine, that is, the air-fuel ratio (A/F), is changed according to the driving conditions of the vehicle to keep harmful components in exhaust gas low and improve engine performance. Control is being carried out to increase the thermal efficiency of This control uses an oxygen sensor (02 sensor) that detects the oxygen concentration in exhaust gas and an air-fuel ratio control device that controls the air-fuel ratio of the air-fuel mixture, and the air-fuel ratio of the air-fuel mixture is adjusted based on the output of the 02 sensor. This method performs feedback control of the air-fuel ratio control device so that the air-fuel ratio is close to the stoichiometric air-fuel ratio.

In the method described above, an 02 sensor is provided upstream of a catalytic converter installed in the exhaust system of an internal combustion engine, and based on the electromotive force (output) of the 02 sensor when detecting oxygen concentration, the air-fuel ratio is determined to be higher than the stoichiometric air-fuel ratio. It is determined whether the air-fuel ratio is when the fuel is rich (rich state) or when the fuel is thinner than the stoichiometric air-fuel ratio (lean state), and the result is fed back to the air-fuel ratio control device.

Furthermore, in recent years, a dual 0□ sensor system in which a No. 202 sensor is also provided on the downstream side of the catalytic converter has come into use.

This was done by focusing on the fact that there is little unreacted oxygen (0°) in the exhaust gas after passing through the catalytic converter, and sensor No. 202 was used to provide accurate feedback. It is something. In other words, the control set value of the 02 sensor for the mixture in which the output value of the 202 sensor is the set voltage is calculated, and the air-fuel ratio of the mixture is controlled based on the control set value (dual feedback control).
. This dual feedback control is performed over the entire operating range regardless of engine speed and load.

By using dual feedback control, even if unburned components affect the output of the 02 sensor, it can be finely adjusted (corrected) by the 202 sensor, allowing accurate air-fuel ratio control. become.

<Problems to be Solved by the Invention> Since the dual 02 sensor system described above performs feedback control over the entire operating range, the amount of 02 stored in the three-way catalyst of the catalytic converter is always maintained at the ffi amount. ing. In this case, if the A/F of the air-fuel mixture is adjusted to be slightly richer during acceleration, the 202nd sensor immediately after acceleration will output a richer state, and the air-fuel ratio control device will output a richer state. It will be judged. For this reason, the system controls the air-fuel mixture to be in a lean state, and lean spikes occur when transitioning from acceleration to steady or deceleration operation. As a result, the mixture A
Depending on the /F adjustment, there is a possibility that the emission level in a driving pattern in which acceleration and deceleration are repeated may deteriorate.

The present invention has been made in view of the above situation, and an object of the present invention is to provide an air-fuel ratio control method for an internal combustion engine that can obtain a good emission level even in a driving pattern in which acceleration and deceleration are repeated.

<Means for Solving the Problems> In order to achieve the above object, the air-fuel ratio control method for an internal combustion engine of the present invention provides a catalytic converter that accommodates a three-way catalyst in the exhaust system of the internal combustion engine. A first oxygen concentration sensor that outputs an output according to the concentration is provided upstream of the catalytic converter, and a second oxygen concentration sensor that outputs an output according to the oxygen concentration in the exhaust gas is provided downstream of the catalytic converter. In the air-fuel ratio control device, the air-fuel ratio control device includes a control means for controlling the air-fuel ratio of the internal combustion engine based on the output value of the oxygen concentration sensor and the second oxygen concentration sensor, and the air-fuel ratio control device includes: A secondary air introduction passage is provided, and during normal operation, the output value of the second oxygen concentration sensor is calculated as the set value for the air-fuel mixture, and the control set value of the first oxygen concentration sensor is calculated based on the control set value. The air-fuel ratio control device controls the air-fuel ratio so that the output value of the first oxygen concentration sensor becomes the set value without calculating the control set value during idle operation and low-load operation. The catalytic converter is characterized in that the air-fuel ratio is controlled by the catalytic converter, and secondary air is introduced into the catalytic converter from the secondary air introduction passage.

Embodiment Fig. 1 shows a schematic configuration of an internal combustion engine implementing an air-fuel ratio control method according to an embodiment of the present invention, and Fig. 2 shows a schematic configuration of an internal combustion engine implementing an air-fuel ratio control method according to an embodiment of the present invention. A flowchart is shown.

The configuration of an internal combustion engine implementing the present invention will be explained based on FIG.

The engine E has an intake passage 2 and an exhaust passage 3 that communicate with the combustion chamber 1. The intake passage 2 and the combustion chamber 1 are communicated with each other by an intake valve 4, and the exhaust passage 3 and the combustion chamber 1 are connected to each other. The communication is controlled by the exhaust valve 5.

In addition, an air cleaner 6 is installed in the intake passage 2 in order from the upstream side.
, throttle valve 7 and electromagnetic fuel injection valve (electromagnetic valve) 8
The exhaust passage 3 is provided with a catalytic converter (three-way catalyst) 9 and a muffler (not shown) for purifying exhaust gas in order from the upstream side thereof. Note that the electromagnetic valves 8 are provided in the intake manifold portion in correspondence with the number of cylinders (multi-point fuel injection system).

The throttle fp7 is connected to the accelerator pedal via a wire cable, so that the degree of opening changes depending on the amount of depression of the accelerator pedal. The throttle valve 7 is also driven to open and close by an idle speed control motor (ISC motor) 10, so that the opening degree of the throttle valve 7 can be changed without pressing the accelerator pedal during idling. It is also possible to do so.

With such a configuration, the air taken in through the air cleaner 6 according to the opening degree of the throttle valve 7 is mixed with the fuel from the solenoid valve 8 in the intake manifold part to an appropriate air-fuel ratio, and ignited in the combustion chamber 1. By igniting the plug at an appropriate timing, the mixture is combusted and generates engine torque, and then is discharged into the exhaust passage 3 as exhaust gas, and the catalytic converter 9 converts Co, HC, and N in the exhaust gas.
After purifying the three harmful components of Ox, the sound is muffled by a muffler and released into the atmosphere.

Furthermore, in order to control this engine E, various sensors are provided. First, on the intake passage 2 side, an air flow sensor 11 that detects the intake air amount from Karman vortex information, an intake air temperature sensor 12 that detects the intake air temperature, and an atmospheric pressure sensor 1 that detects the atmospheric pressure are installed in the air cleaner installation part.
3 is provided, and the throttle valve is installed in the part where the throttle valve is installed.
A potentiometer type throttle sensor 14 for detecting the opening of the throttle valve 7, an idle switch 15 for detecting the idling state, and a motor positive sensor 16 for detecting the position of the ISC motor 10 are provided.

Further, on the exhaust passage 3 side, an upstream 02 sensor 17 as a first oxygen concentration sensor for detecting the oxygen concentration (0° concentration) in the exhaust gas is provided at the upstream side of the catalytic converter 9. A downstream 02 sensor 18 as a second oxygen concentration sensor for detecting 02a degrees in exhaust gas is provided at the downstream side of the exhaust gas. Upstream 02 sensor 1
7 and the downstream 02 sensor 18 both apply the principle of a solid electrolyte oxygen concentration battery, and their output voltage has the characteristic of rapidly changing near the stoichiometric air-fuel ratio, and the output is in a leaner state than the stoichiometric air-fuel ratio. The voltage is low, and the output voltage in the rich state is higher than the stoichiometric air-fuel ratio. Note that the downstream O2 sensor 18 may be provided inside the catalytic converter 9.

Other sensors include a water temperature sensor 19 that detects the engine cooling water temperature and a vehicle speed sensor that detects the vehicle speed, as well as a crank angle sensor that detects the crank angle and a TDC that detects the top dead center of the first cylinder (reference cylinder). A sensor is provided. The detected values of these sensors are input to an electronic control unit ECU as a control means.

Further, a secondary air introduction passage 20 is provided between the upstream 02 sensor 17 and the catalytic converter 9 in the exhaust path Ri3.

The air-fuel ratio control method in the internal combustion engine configured as described above will be specifically explained.

During normal operation, the output of the downstream 02 sensor 18 is the set voltage (
Setting f118 (e.g. 0.3 to 0.6 V) Set the control constant (control setting value) of A/F (stoichiometric air-fuel ratio) feedback control based on the upstream 02 sensor 17 so that je matches.
The electronic control unit ECU calculates the rich/lean determination voltage, post-determination delay time, skip amount, and integral gain, and performs air-fuel ratio control using the calculated values as control constants. During idling operation and low load operation, the calculation of control constants is stopped and A/F feedback control by the upstream O sensor 17 is performed), and secondary air is introduced from the secondary air introduction passage 920 to supply oxygen to the catalytic converter 9. Accumulate too much □. By storing excess oxygen 02 in the catalytic converter 9 during idle operation and low load operation, the catalytic converter 9 can absorb rich components discharged during acceleration following idle operation and low load operation. For this reason, the catalytic converter 9
Downstream 02 sensor 18 that brings the downstream air-fuel ratio into a rich state
The output is not on the rich side. Therefore, control to lean state is not performed during acceleration, and the air-fuel ratio does not become lean state during transition from acceleration to steady state or deceleration. As a result, a good emission level can be obtained even in a driving pattern where acceleration and deceleration are repeated.

In addition, in the method described above, the electronic control unit ECU
Although the control constant for A/F feedback control by the ° sensor 17 is calculated, a second A/F feedback correction coefficient may be calculated instead of the control constant.

Next, the control situation of the above-mentioned air-fuel ratio control method will be explained based on the flowchart shown in FIG.

The operating state is detected and it is determined whether warming up is complete or not. If warm-up has not been completed, the fuel injection amount in that state is calculated, and if warm-up has been completed, it is determined whether the engine is in idle operation or low-load operation.

If not in idle or low load operation, downstream 02
The output of the sensor 18 is sampled, a control constant is calculated based on the output value, and the friJ control constant is stored.

After storing the control constants, the output of the upstream 02 sensor 17 is sampled, the A/F feedback coefficient is calculated using the control constants, and the fuel injection amount is calculated based on this.

If the result of the determination is idling or low load operation, the latest stored I! Read Irm constants. flli II vs
After reading the constants, introduce secondary air from the secondary air inlet 20, sample the output of the upstream 02 sensor 17, calculate the A/F feedback coefficient using the control constants, and calculate the fuel injection amount. Do the following.

The air-fuel ratio control method is implemented based on the above control flow.

<Effects of the Invention> The air-fuel ratio control method for an internal combustion engine of the present invention stores excess oxygen in the catalytic converter during idling and low-load operation, so that excess oxygen is not discharged during acceleration following idling and low-load operation. The catalytic converter can absorb the rich components. As a result, a rich state output will not be generated in the second oxygen sensor, no rich spike will occur, control to lean state will not be performed during acceleration, and lean spikes will not occur when transitioning from acceleration to steady or deceleration operation. Does not occur. Therefore, the rich spike during acceleration,
Also, it is possible to prevent a drop spike following a rich spike, and a good emission level can be obtained even in a driving pattern where acceleration and deceleration are repeated.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an internal combustion ays that implements an air-fuel ratio control method according to an embodiment of the present invention, and FIG. 2 is a flowchart of the air-fuel ratio control method according to an embodiment of the present invention. In the drawing, E is the engine, 1 is the combustion chamber, 2 is the intake passage, 3 is the exhaust passage, 8 is the electromagnetic fuel injection valve (electromagnetic valve), 9 is the catalytic converter, 17 is the upstream 0□ sensor, 18 is the downstream 02 Sensor 20 is a secondary air introduction passage. Patent applicant Mitsubishi Motors Corporation Agent

Claims (1)

[Claims] A catalytic converter that accommodates a three-way catalyst is provided in the exhaust system of the internal combustion engine, and a first oxygen concentration sensor that outputs an output according to the oxygen concentration in the exhaust gas is provided on the upstream side of the catalytic converter. A second oxygen concentration sensor is provided on the downstream side of the catalytic converter, and a control means for controlling the air-fuel ratio of the internal combustion engine based on the output values of the first oxygen concentration sensor and the second oxygen concentration sensor. In the air-fuel ratio control device, a secondary air introduction passage is provided between the catalytic converter and the first oxygen concentration sensor, and the output value of the second oxygen concentration sensor is a set value during normal operation. A control set value of the first oxygen concentration sensor is calculated, and the air-fuel ratio control device performs air-fuel ratio control based on the control set value, and the control set value is not calculated during idle operation and low load operation. The air-fuel ratio is controlled by the air-fuel ratio control device so that the output value of the first oxygen concentration sensor becomes a set value, and secondary air is introduced into the catalytic converter from the secondary air introduction passage. Air-fuel ratio control method for internal combustion engines.