JPH0530978B2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention relates to an air-fuel ratio learning control device for an electronically controlled fuel injection internal combustion engine, and in particular, to prevent air-fuel ratio learning from progressing in the wrong direction due to deterioration of an O ₂ sensor, etc. In order to prevent this, the present invention relates to a device that performs appropriate learning control while monitoring the state of the signal of an O ₂ sensor.

<Background technology> In an electronically controlled fuel injection type internal combustion engine, the injection amount
Ti is determined by the following formula.

Ti=Tp×COEF×α+Ts Here, Tp is the basic injection amount, Tp=K×Q/N
It is. K is a constant, Q is the intake air flow rate, and N is the engine speed. COEF is various correction coefficients. α is an air-fuel ratio feedback correction coefficient for air-fuel ratio feedback control (λ control) to be described later. Ts is a voltage correction amount, which is used to correct changes in the injection flow rate of the fuel injector due to changes in battery voltage.

Regarding λ control, an O ₂ sensor is installed in the exhaust system to detect the actual air-fuel ratio, and the slice level determines whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio, and fuel is injected to achieve the stoichiometric air-fuel ratio. For this purpose, the above-mentioned air-fuel ratio feedback correction coefficient α is determined, and by varying this α, the stoichiometric air-fuel ratio is maintained.

Here, the value of the air-fuel ratio feedback correction coefficient α is changed by proportional-integral (PI) control to ensure stable control.

In other words, the output voltage of the O ₂ sensor is compared with the slice level voltage, and if it is higher or lower than the slice level, the air-fuel ratio is rich (lean) without suddenly enriching or thinning the air-fuel ratio. ), the air-fuel ratio is controlled to be leaner (richer) by first lowering (raising) it by P, and then gradually lowering (raising) it by I.

However, in the region where λ control is not performed, α=
1 and set various correction coefficients COEF to obtain the desired air-fuel ratio.

By the way, if the base air-fuel ratio when α = 1 in the λ control region could be set to the stoichiometric air-fuel ratio (λ = 1), feedback control would not be necessary. valves, pressure regulators,
control unit) variations and changes over time,
Feedback control is performed because the base air-fuel ratio deviates from λ=1 due to factors such as non-linearity of the pulse width-flow rate characteristic of the fuel injection valve and changes in operating conditions and environment.

However, if the base air-fuel ratio deviates from λ=1, it takes time to stabilize the step in the base air-fuel ratio to λ=1 through feedback control when the operating range changes significantly. For this purpose, the proportionality and integral constants (P/I) are increased, which causes overshoot and undershoot, resulting in poor controllability. In other words, if the base air-fuel ratio deviates from λ=1, the air-fuel ratio will be controlled within a range that deviates considerably from the stoichiometric air-fuel ratio.

As a result, the three-way catalyst is operated at a point where its conversion efficiency is poor, and not only does the cost increase due to the increase in the amount of precious metal in the catalyst, but the conversion efficiency further deteriorates as the catalyst deteriorates, forcing the catalyst to be replaced. There was a problem.

Therefore, in Japanese Patent Application No. 58-76221, the present applicant set the base air-fuel ratio to λ = 1 by learning, thereby eliminating the deviation from λ = 1 caused by the step in the base air-fuel ratio during transient times, and We have proposed a base air-fuel ratio learning control device that makes it possible to reduce the P/I ratio, improve controllability, and thereby reduce the cost of catalysts.

That is, a map of learning correction coefficients αo corresponding to engine operating conditions such as engine speed and load is provided in the RAM, and when calculating the injection amount Ti, the basic injection amount Tp is corrected by αo as shown in the following equation.

Ti=Tp×COEF×α×αo+Ts Then, the learning of αo proceeds in the following steps.

In a steady state, the engine operating conditions and α are detected.

αo that has been learned and stored up to now in accordance with the engine operating conditions is searched.

A new value αo is set by weighted average from the α and αo and stored.

By the way, in such an air-fuel ratio learning control device, since the learning method is a weighted average method, complete learning cannot be performed.
If the O ₂ sensor deteriorates, there is a risk that not only the sensor will not learn properly, but also that the learning will progress in an abnormal direction, and improvements in this respect were needed.

<Purpose of the Invention> In view of the above-mentioned actual situation, the present invention improves the learning method to achieve extremely good air-fuel ratio learning control, and also to prevent errors in air-fuel ratio learning due to deterioration of the O ₂ sensor, etc. The purpose is to prevent this from progressing and improve the safety of learning control.

<Structure of the Invention> For this reason, the present invention, as shown in FIG.
an air-fuel ratio feedback correction coefficient setting means that compares the actual air-fuel ratio detected based on the signal from the _O2 sensor with the stoichiometric air-fuel ratio and sets an air-fuel ratio feedback correction coefficient by proportional-integral control; A learning correction coefficient search means for searching a learning correction coefficient stored in RAM corresponding to engine operating conditions such as load; A learning correction coefficient updating means that adds a new learning correction coefficient and updates the learning correction coefficient data for the same engine operating condition in the RAM, and multiplies the basic injection amount by the air-fuel ratio feedback correction coefficient and the learning correction coefficient. In addition to providing an injection amount calculating means for calculating the injection amount by calculating the injection amount, and a driving pulse signal output means for outputting a driving pulse signal corresponding to the calculated injection amount to the fuel injection valve, the inversion period of the signal of the O ₂ sensor is provided. an O ₂ sensor signal reversal period measuring means for measuring the normal reversal period of the O ₂ sensor signal from the engine rotation speed; and a normal range setting means for determining the range of the normal reversal period of the O 2 sensor signal from the engine rotation speed; update stop means for determining whether or not the learning correction coefficient is within a predetermined range determined by , and stopping the function of the learning correction coefficient update means when it is outside the range.

That is, when setting the learning correction coefficient, a new learning correction coefficient αo is set by adding a predetermined proportion of the deviation amount Δα of the air-fuel ratio feedback correction coefficient α from the reference value to the learning correction coefficient αo (see the following formula). ) is a method for updating learning correction coefficient data for the same engine operating conditions in RAM to ensure proper learning.

αo ← αo + Δα/M (M is a constant) In addition, focusing on the fact that the rich/lean reversal period of the O ₂ sensor signal is within a predetermined range depending on the engine speed under normal conditions, the reversal period When the value falls outside the above range, it is determined that the O ₂ sensor has deteriorated, and the learning correction coefficient is not updated.

<Example> Examples will be described below.

Figure 2 shows the hardware configuration.

1 is CPU, 2 is P-ROM, 3 is for learning control
CMOS-RAM, 4 is an address decoder.
Note that a backup power supply circuit is used for the RAM 3 in order to retain the memory contents even after the key switch is turned off.

The hot wire air flow meter 5 is used as an analog input signal to the CPU 1 for controlling the fuel injection amount.
intake air flow rate signal from the throttle sensor 6, throttle opening signal from the throttle sensor 6, water temperature signal from the water temperature sensor 7, exhaust oxygen concentration signal from the _O2 sensor 8,
There is a battery voltage from the battery 9, which is adapted to be input via an analog input interface 10 and an A/D converter 11. 1
2 is an A/D conversion timing controller.

Digital input signals include ON/OFF signals from an idle switch 13, a start switch 14, and a neutral switch 15, and these are inputted via a digital input interface 16.

In addition, for example, from the crank angle sensor 17
Reference signals for every 180 degrees and position signals for every 1 degree are inputted via the one-shot multi-circuit 18. In addition, the vehicle speed sensor 19
The vehicle speed signal is inputted via the waveform shaping circuit 20.

An output signal from the CPU 1 (a drive pulse signal to the fuel injection valve) is sent to the fuel injection valve 22 via a current control circuit 21.

Here, the CPU 1 performs input/output operations, arithmetic processing, etc. according to a program (stored in the ROM 2) based on the flowchart (fuel injection amount calculation routine) shown in FIG. 3, and controls the fuel injection amount.

Next, the flowchart shown in FIG. 3 will be explained.

The intake air flow rate Q obtained from the signal from the air flow meter 5 at S1 and the crank angle sensor 17
The basic injection amount Tp (=K×Q/N) is calculated from the engine speed N obtained from the signal from the engine.

Set various correction coefficients COEF in S2.

In S3, the output voltage of the O ₂ sensor 8 and the slice level voltage are compared and the air-fuel ratio feedback correction coefficient α is set by proportional-integral control.

In S4, a voltage correction amount Ts is set based on the battery voltage from the battery 9.

Engine speed N and basic injection amount (load) at S5
Search for the corresponding learning correction coefficient αo from Tp.
Note that the map of the learning correction coefficient αo for the rotational speed N and the basic injection amount Tp is stored in the rewritable RAM 3, and all αo=1 at the time when learning has not started.

S6 to S9 are provided to monitor the state of the signal of the O ₂ sensor 8. In S6, the rich/lean reversal period T of the output voltage of the O ₂ sensor 8 (see Figure 4) is measured, and in S7 Then calculate the frequency = 1/T. Then, in S8, a predetermined normal frequency range (min to max) is searched from the engine speed N. and,
In S9 the frequency is within that range (min~max)
Determine whether it is within the range. Here, if it is within the range, the process proceeds to the next step S10, but if it is outside the range, it is determined that the O ₂ sensor 8 has deteriorated, etc., and the process proceeds to S16.

That is, the frequency of the signal from the O ₂ sensor 8 changes in proportion to the engine speed N, but is determined within a certain range if the engine speed N is constant.
If the frequency of the signal from the actual O ₂ sensor 8 becomes high and goes out of range, it is considered to be due to the influence of noise, etc., and if it becomes low and goes out of range, it is thought to be due to deterioration due to aging or a drop in temperature. It will be done. Therefore, in these cases, the learning correction coefficient αo is not updated in S14 and S15.

S10 to S13 are provided to detect a steady state, and S10 determines a change in vehicle speed based on the signal from the vehicle speed sensor 19, and S11 determines the gear position based on the signal from the neutral switch 15. Then, in S12, a change in the throttle opening degree is determined based on the signal from the throttle sensor 6, and in S13, it is determined whether a predetermined time has elapsed, and if it is within the predetermined time, the process returns to S10. In this way, if the change in vehicle speed is less than a predetermined value within a predetermined time, the gear is engaged, and the change in throttle opening is less than a predetermined value, it is determined that the vehicle is in a steady state, and steps S14 and S15 are performed. The learning correction coefficient αo is updated. In addition, if the change in vehicle speed exceeds a predetermined value at any point within a predetermined time, if the vehicle speed becomes neutral, or if the change in throttle opening exceeds a predetermined value, it is determined that the state is in a transient state, The learning correction coefficient αo is not updated in S14 and S15.

When the O ₂ sensor signal is determined to be normal and in a steady state, the learning correction coefficient αo is updated as follows.

Calculation is performed according to the following formula from the learning correction coefficient αo retrieved from the engine speed N and basic injection amount Tp in S14 and the current air-fuel ratio feedback correction coefficient α, and the value is set as the new learning correction coefficient αo. do.

αo←αo+Δα/M Note that Δα indicates the deviation amount of α from the standard value, and Δα
=α− _α1 , and the reference value _α1 is generally 1.0.
Moreover, M is a constant.

In S15, a new learning correction coefficient αo is written to the corresponding engine speed N and basic injection amount Tp in RAM3. That is, the data in RAM3 is updated.

In S16, the injection amount Ti is calculated according to the following formula.

Ti = Tp × COEF × α × αo + Ts Here, if the signal of O ₂ sensor 8 is normal and in a steady state, the updated value is used as αo, and if the signal of O ₂ sensor 8 is abnormal or in a transient state is used as is.

The injection amount Ti is calculated above, and a drive pulse signal corresponding to the injection amount Ti is given to the fuel injection valve 22 at a predetermined timing via the current control circuit 21.

<Effects of the Invention> As explained above, according to the present invention, by improving the learning method, the learning becomes appropriate.
As a result, the base air-fuel ratio can be set to λ = 1, and the λ generated from the step in the base air-fuel ratio during transient
By eliminating the deviation from =1, it is possible to achieve extremely good learning control of the air-fuel ratio. Also,
The rich/lean reversal period of the O ₂ sensor signal is measured, and the degree of deterioration of the O ₂ sensor is determined based on this, and the learning correction coefficient is not updated when deterioration occurs. , learning will not progress in the wrong direction, improving the safety of learning control. In addition, when determining the degree of deterioration of the O ₂ sensor, by making the range for determining the reversal period of the rich/lean signal of the O ₂ sensor dependent on the engine speed, it is possible to determine the degree of deterioration in all operating ranges. Detailed judgments can be made and judgments can be made with high precision.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the configuration of the present invention, Figure 2 is a block diagram showing the configuration of the present invention.
The figure is a hardware configuration diagram showing an embodiment of the present invention, FIG. 3 is a flowchart of the same, and FIG. 4 is a
FIG. 3 is a characteristic diagram of the output voltage of an O ₂ sensor. 1...CPU, 3...CMOS for learning control
RAM, 5...Air flow meter, 8... _O2 sensor, 17...Crank angle sensor, 22...Fuel injection valve.

Claims (1)

[Claims] 1 Basic injection amount calculation means that calculates the basic injection amount from the intake air flow rate and engine speed, and the actual air-fuel ratio and stoichiometric air-fuel ratio detected based on the signal from the O ₂ sensor installed in the exhaust system. An air-fuel ratio feedback correction coefficient setting means that compares and sets an air-fuel ratio feedback correction coefficient by proportional-integral control, and searches for a learning correction coefficient stored in RAM corresponding to engine operating conditions such as engine speed and load. a learning correction coefficient search means for searching for a learning correction coefficient; and a learning correction coefficient for adding a predetermined percentage of the deviation amount from the reference value of the air-fuel ratio feedback correction coefficient to the learning correction coefficient to set a new learning correction coefficient; learning correction coefficient updating means for updating the data of; injection amount calculation means for calculating the injection amount by multiplying the basic injection amount by the air-fuel ratio feedback correction coefficient and the learning correction coefficient; A drive pulse signal output means that outputs a drive pulse signal to the fuel injection valve, an O ₂ sensor signal reversal period measuring means that measures the reversal period of the O ₂ sensor signal, and an O 2 sensor signal reversal period measuring means that measures the O ₂ sensor signal from the engine rotation speed when it is normal. a normal range setting means for determining the range of the reversal period; and a normal range setting means for determining whether the measured reversal period is within a predetermined range determined by the engine speed at that time, and determining the learning correction coefficient when it is outside the range. 1. An air-fuel ratio learning control device for an electronically controlled fuel injection type internal combustion engine, comprising update stopping means for stopping the function of the updating means.