JPS5825543A - Air-to-fuel ratio control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To enhance the accuracy of air-to-fuel ratio control and the purifying performance of exhaust gas over a wide range of the load on the engine etc. by setting a map for the constant of feedback control made by an air-to-fuel ratio sensor according to the characteristics of the sensor and by reading this map for making the optimum feedback control. CONSTITUTION:Output from the air-to-fuel ratio sensor to sense the oxygen density is related to the air-to-fuel ratio feedback correction factor f(A/F) through treatment including an integral process, to provide such feedback constants as reversing delay times TDL, TDR, skip widths RSL, RSR, integral constants KIL, KIR, etc. The ratio of the amount of taken-in-air a (16) to the revolving speed of engine N (22) shall be mapped with respect to the speed N with at least one of the abovementioned constants, for example time TDL, being matched previously with the characteristics of the air-to-fuel ratio sensor 36, and be put in memory in the ROM66 of the control circuit 50. Accordingly, the basic injection time for the fuel can be corrected by determining the abovementioned factor f(A/F) through read-out of the time TDL on accordance with the condition of loading a/N of the engine to be followed by output processing of the sensor 36. Thus the injector 44 and idling speed control valve 48 are feedback controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control method for an internal combustion engine, and particularly to a method for controlling an air-fuel ratio of an internal combustion engine, and in particular, a method for controlling a catalyst inflow gas, which is suitable for use in an automobile internal combustion engine in which exhaust gas purification measures are taken using a three-way catalyst. using an air-fuel ratio sensor that detects the secondary air-fuel ratio of
Feedback control of the air-fuel ratio control actuator is performed using a feedback control signal obtained by performing processing including integration on the output of the air-fuel ratio sensor, so that the air-fuel ratio of the air-fuel mixture or the catalyst inflow gas becomes a desired air-fuel ratio. This invention relates to improvements in an engine air-fuel ratio control method.

In recent years, it has become necessary to perform precise air-fuel ratio control in internal combustion engines, especially automotive internal combustion engines that require strict exhaust gas purification measures. It includes a scatter concentration sensor for sensing the secondary air-fuel ratio of the inflowing gas, and an air-fuel ratio control actuator for controlling the air-fuel ratio of the air-fuel mixture or the catalyst inflowing gas, and includes an integral for the output of the oxygen concentration sensor. Feedback control is performed on the air-fuel ratio control actuator using a feedback control signal obtained by performing the processing to make the residual oxygen concentration in the catalyst inflow gas equal to the residual oxygen concentration when a mixture at the stoichiometric air-fuel ratio is combusted. This has been put into practical use.

Such air-fuel ratio control has the characteristic that good exhaust gas purification performance can be obtained regardless of changes in engine operating conditions.

However, conventionally, any one of the feedback control constants, such as the reversal delay time, skip width, and integral constant, used when performing processing including integration on the output of the oxygen concentration sensor, is set to the engine rotational speed. Note that the characteristics of the oxygen concentration sensor, which changes depending on the engine speed and engine load, may not match the value of the feedback control constant 1. When the engine is in a high load range, the center value of the air-fuel ratio deviates, reducing exhaust gas purification performance and causing a large amount of harmful components to be emitted.

The present invention was made in order to eliminate the above-mentioned conventional drawbacks, and it is possible to select the value of the optimum table feedback control constant according to the characteristics of the air-fuel ratio sensor that change depending on the engine rotation speed and engine load. An object of the present invention is to provide an air-fuel ratio control method for an internal combustion engine that can improve air-fuel ratio control accuracy and improve exhaust gas purification performance.

The present invention uses an air-fuel ratio sensor that senses the secondary air-fuel ratio of the catalyst inflow gas and an air-fuel ratio control actuator that controls the air-fuel ratio of the air-fuel mixture or the catalyst inflow gas, and integrates the output of the air-fuel ratio sensor. In the air-fuel ratio control method for an internal combustion engine, the air-fuel ratio control actuator is feedback-controlled by a feedback control signal obtained by performing processing including A small number of feedback control constants (both one type) used when performing processing including integration on the output of the fuel ratio sensor are mapped in advance according to the characteristics of the air-fuel ratio sensor, and engine speed and engine load are mapped in advance. The above object is achieved by processing the output of the air-fuel ratio sensor according to the value read from the map.

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

An electronically controlled engine equipped with an embodiment of an electronically controlled fuel injection device employing the air-fuel ratio control method for an internal combustion engine according to the present invention is shown in FIGS. an air flow meter 16 disposed downstream 11 of the air cleaner 14 of 12 for detecting the intake air amount of the engine; and an intake temperature sensor disposed within the air flow meter 16 for detecting the intake air temperature. 18 and
A crank angle sensor 22 is built into the distributor 20, which has a shaft 20a that rotates in accordance with the engine rotation, and generates a pulse signal in accordance with the engine rotation. A cooling water temperature sensor 26, a throttle position sensor 30 for detecting the opening degree and the rate of change in the opening degree of an intake throttle valve 28, which is disposed in the intake passage 12 and is opened and closed in conjunction with the accelerator pedal, and A catalytic converter 34Vc filled with a catalyst, for example, a three-way catalyst, is disposed on the downstream side of the exhaust manifold 32 into which exhaust gas formed by combustion flows. An oxygen concentration sensor 36 for sensing the secondary air-fuel ratio, a vehicle speed sensor 4° for detecting the running speed of the vehicle, that is, the vehicle speed from the rotational speed of the output shaft of the transmission 38, and an intake manifold 42 of the engine 10. an injector 44 for injecting fuel into the intake passage 12;
An idle rotation speed control valve 48 consisting of a pulse motor, an electromagnetic actuated valve, etc. is disposed in a surge tank 46 in the middle of the engine and is used to control the flow rate of air that bypasses the intake throttle valve 28 during idle. The basic fuel injection time is calculated according to the air amount and the engine speed, and the calculated basic fuel injection time is obtained by performing processing including integration on the output of the oxygen concentration sensor 36. The digital electronic control circuit 50 performs air-fuel ratio feedback correction based on a feedback control signal generated by the engine, and outputs a fuel injection signal to the injector 44. In FIG. 1, 52a is a spark plug, and in FIGS. 1 and 2, 54 is a battery.

As shown in detail in FIG. 2, the digital electronic control circuit 50 includes an air 70-meter 16, an intake air temperature sensor 18. An analog-to-digital converter 60 having a multiplexer function for converting analog signals output from the cooling water temperature sensor 26, oxygen concentration sensor 36, and battery 54 into digital signals, and outputs from the crank angle sensor 22 and throttle position sensor 30. inputs the digital signal, and converts the calculation result into a signal suitable for outputting the injector 44 and idle rotation speed control valve 481C.
Input/output interface circuit 62 with buffer function
, a central processing circuit 64 equipped with a crystal oscillator 64m, a read-only memory 66, a random access memory,
It consists of a sled 68 and a random access memory 70 for power backup.

The operation will be explained below. First, the digital electronic control circuit 50
Based on Fi, the intake air IQ output from the air flow meter 16, and the engine rotational speed N calculated from the output from the crank angle sensor 22, the basic fuel injection time TP is calculated using the following equation.

Tp=ni-' ・・・・・・・・・・・・(1)
Here is the butterfly coefficient.

Furthermore, the effective synchronous injection time τ1 is calculated by correcting the basic injection time Tp according to the signals from each sensor using the following equation.

τ1=Tp −/(A/F') ・f(WL) ・
f (THA)X (1 + f (ASE) + f (AFW) + f (OTP) )
...(2) Here, f(A/F) is the air-fuel ratio feedback correction coefficient, f(WL
) is the warm-up increase correction coefficient, f (THA ) is the intake air temperature correction coefficient, f (ASE) 1; 1 after-start increase correction coefficient, / (A
EW)t;j acceleration increase correction coefficient during warm-up, /(OTP) is overheat (output) increase coefficient, f(R8)Fi reduction coefficient.

The synchronous injection time τS is calculated by adding the invalid injection time rv corresponding to the response delay time of the injector 44 when the battery voltage drops to the effective synchronous injection time τ1 obtained in this way, as shown in the following equation. do.

tB*τ1+τV ・……−・・−・(3) A fuel injection signal corresponding to this synchronous injection time τS is output from the injector 44FC, and the injector 44 is opened for the synchronous injection time τS in synchronization with the engine rotation. , fuel is injected into the intake manifold 42 of the engine.

The air-fuel ratio feedback correction in this embodiment is performed as follows. That is, first, processing including integration is performed on the output of the oxygen concentration sensor 36 as shown in FIG.
Inversion delay time TDx, , TDR, skilough width R8L used when obtaining (A/F').

R2H, integral constant KII, KIR (subscript T- indicates that when the output of the oxygen concentration sensor changes from lean to rich,
At least one type of feedback control constant 1 such as the subscript R1i (which also corresponds to the case where the change from rich to lean), etc. For example, the reversal delay time TD when changing from lean to rich
X, according to the characteristics of the oxygen concentration sensor 36 in advance, and the engine speed dust and suction (in the case of a vehicle with a manual transmission)
, or Fi as shown in Table 2 (for vehicles with automatic transmissions) and stored in the digital electronic control circuit 50's only memory 66Vc.

Table 1 Table 2 T Ds < T D4 , Nt'<Nt', (
! L), t < (-Q-), z, TD+'<NN T Dr'< T Ds'< T D4'< T
DI'.

Also, the reversal delay time TD when changing from rich to lean
R is, for example, engine rotational speed N, engine, skip width R8L, R2Htit, switching between idle state and off-idle state, and integral constant KII, .
KIR is set to change in proportion to engine rotational speed NK.

Using the feedback control constants mapped in this way, in actual air-fuel ratio feedback control, the reversal delay time TDX,' is determined according to the ratio of the engine rotation speed N, the engine rotation speed, and the intake air amount to the operating conditions. By reading and processing the output of the oxygen concentration sensor 36 using the read value, the air-fuel ratio feedback correction coefficient f (A/F ) as shown in FIG. (2) Correct the basic fuel injection time Tp using 2.

Specifically, first, according to the map shown in Table 1 or Table 2 above, each data TDL (IX) (where IX is an index from 0 to 8
).

Table 3 Next, from the engine speed N and intake air tQ, according to the index calculation routine as shown in FIG.
Calculate index IX. Furthermore, according to the determined index IX, necessary data is read out from the mapped data as shown in Table 3 above and used for calculation.

In the above embodiment, only the reversal delay time TDL when changing from lean to rich is mapped, but other feedback control constants may also be mapped or divided. Of course, it is also possible to create a map using a map with a different direction.

In the embodiments described above, the present invention was applied to an electronically controlled engine in which the fuel injection time was controlled by a digitalized electronically controlled fuel injection device, but the scope of application of the present invention is not limited to this. , for example, by controlling the air-fuel ratio control actuator to control the effective area of a fuel passage or an air bleed passage for forming an air-fuel mixture, or by controlling the flow t of secondary air mixed into the exhaust gas. Therefore, by using a control solenoid valve that controls the air-fuel ratio of the air-fuel mixture or the gas flowing into the catalyst, it can be similarly applied to general internal combustion engines that are not equipped with an electronically controlled fuel injection device.

As described above, according to the present invention, it is possible to select the optimum value of the feedback control constant in accordance with the characteristics of the air-fuel ratio sensor that change depending on the engine speed and engine load. Therefore, without sacrificing any area,
Air-fuel ratio control accuracy can be improved in all areas,
It has an excellent effect of improving exhaust gas purification performance.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view, including a partial block diagram, showing the configuration of an electronically controlled engine in which an embodiment of an electronically controlled fuel injection device employing the air-fuel ratio control method for an internal combustion engine according to the present invention is installed. , FIG. 2 is a block diagram showing the specific configuration of the digital electronic control circuit in the embodiment, and FIG. 3 shows an example of the relationship between the oxygen concentration sensor output and the air-fuel ratio feedback correction coefficient in the embodiment. The diagram shown in FIG. 4 is a flowchart showing a routine for calculating an index used in reading out mapped feedback control constants, also in the embodiment described above. 10...Engine, 16...Air flow meter, 2
0... Distributor, 22... Crank angle sensor, 28... Intake throttle valve, 34... Catalytic converter, 36... Oxygen concentration sensor, 44-... Injector, 50... Digital electronic control circuit. Agent Takaya Ron (and 1 other person)

Claims (1)

[Claims] (1) Using an air-fuel ratio sensor that senses the secondary air-fuel ratio of the catalyst inflow gas and an air-fuel ratio control actuator that controls the air-fuel ratio of the air-fuel mixture or the catalyst inflow gas, an integral is calculated for the output of the air-fuel ratio sensor. In the air-fuel ratio control method for an internal combustion engine, the air-fuel ratio control actuator is feedback-controlled by a feedback control signal obtained by performing a process that includes the step of controlling the air-fuel ratio of the air-fuel mixture or the catalyst inflow gas to a desired air-fuel ratio. At least one kind of feedback control constant used when performing processing including integration on the output of the sensor is set in advance,
Create a map according to the characteristics of the air-fuel ratio sensor,
An air-fuel ratio control method for an internal combustion engine, characterized in that the output of the air-fuel ratio sensor is processed using a t value read from the map in accordance with engine rotational speed and engine load.