JP2592349B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

The present invention relates to an apparatus for controlling an air-fuel ratio of an internal combustion engine,
In particular, the present invention relates to an apparatus for learning a feedback correction coefficient of an air-fuel ratio.

<Conventional Technology> As a conventional air-fuel ratio control device for an internal combustion engine, for example, there is one disclosed in Japanese Patent Application Laid-Open No. 60-240840.

To explain the outline of this, the intake air flow rate Q of the engine
And detects the rotational speed N corresponding to the quantity of air sucked into the cylinder basic fuel supply quantity _{T P (= K · Q /} N; K is a constant) is calculated, and the engine temperature the basic fuel supply quantity T _P The feedback correction is performed by the signal from the air-fuel ratio sensor (oxygen sensor) that detects the air-fuel ratio of the air-fuel mixture by detecting the oxygen concentration in the exhaust gas, and the correction is finally performed by the battery voltage. to set the supply amount T _I.

Then, by outputting a driving pulse signal having a pulse width corresponding to the thus set fuel supply quantity T _I at a predetermined timing, so that injects supply a predetermined amount of fuel to the engine.

By the way, the air-fuel ratio feedback correction based on the signal from the air-fuel ratio sensor is performed so as to control the air-fuel ratio near the target air-fuel ratio (the stoichiometric air-fuel ratio).

This is because the conversion efficiency (purification efficiency) of a three-way catalyst that is interposed in the exhaust system and oxidizes CO and HC (hydrocarbon) in the exhaust gas and reduces and purifies NOx is the exhaust state during stoichiometric air-fuel ratio combustion. This is because it is set to function effectively.

The air-fuel ratio sensor generating an electromotive force (output voltage) has a characteristic that suddenly changes at the stoichiometric air-fuel ratio near the output voltage V ₀
And a reference voltage (slice level) SL corresponding to the stoichiometric air-fuel ratio to determine whether the air-fuel ratio of the air-fuel mixture is rich or lean with respect to the stoichiometric air-fuel ratio. Then, for example, when the air-fuel ratio is lean (rich), after increasing (reducing) the large proportional constant P in the first feedback correction coefficient α to be multiplied to the basic fuel supply quantity T _P, by a predetermined integral constant I gradually The output voltage V ₀ is compared with a reference voltage (slice level) SL corresponding to the stoichiometric air-fuel ratio to determine whether the air-fuel ratio of the air-fuel mixture is rich or lean with respect to the stoichiometric air-fuel ratio. Then, for example, when the air-fuel ratio is lean (rich), the feedback correction coefficient to be multiplied to the basic fuel supply quantity T _P alpha
The after initial increase large compared constant P in (decrease) the stoichiometric air-fuel ratio by gradually increasing (decreasing) the gradually increasing the fuel supply amount T _I (reduced) correction by a predetermined integral constant I Control near the fuel ratio.

Further, in such an air-fuel ratio control device, the deviation of the air-fuel ratio from the target value in the non-feedback control region or the deviation from the stoichiometric air-fuel ratio during the transient operation in which the operation region during feedback control moves. To control
At the time of air-fuel ratio feedback control, it has been generalized to perform learning control by setting a learning correction value Kl so that the average value of the air-fuel ratio feedback correction coefficient α approaches a reference value under a predetermined steady-state operating condition (Japanese Patent Publication No. Sho 63). -36408).

<Problem to be Solved by the Invention> This learning control is performed, and in a predetermined operation region,
In order to improve the stability, the output of the air-fuel ratio sensor is monitored until the output is inverted a predetermined number of times, and the average value of the feedback correction coefficient α during this time is calculated. Is fixed to an average value, and the learning correction value Kl is also fixed to a value calculated based on the average value of the feedback correction coefficient α.

However, as described above, in the system provided with the method of fixing the feedback correction coefficient α and the learning correction value Kl after a predetermined period, when the engine is shipped or the battery is removed,
It takes time to learn the air-fuel ratio deviation from the state in which the learning correction value Kl is set to the initial value, which deteriorates drivability and exhaust emission characteristics during this time.

The present invention has been made in view of such a conventional problem. In a state where learning is not progressing, the fixing of the feedback correction coefficient and the learning correction value is delayed, so that the internal combustion engine which solves the above-described problem has an idle state. It is an object to provide a fuel ratio control device.

<Means for Solving the Problems> Therefore, as shown in FIG. 1, the present invention provides an air-fuel ratio detecting means for detecting an air-fuel ratio in response to a concentration ratio of a gas component in exhaust gas; Air-fuel ratio feedback control means for controlling the air-fuel ratio to be closer to the target air-fuel ratio using a feedback correction coefficient set in accordance with the output of the controller, and a learning correction for storing a learning correction value of the feedback correction coefficient for each operation region. Value storage means, and a new learning correction value is set based on the learning correction value and the feedback correction coefficient retrieved from the learning correction value storage means so that the average value of the feedback correction coefficient converges to a predetermined value. Learning correction value updating means for updating the learning correction value of the corresponding operation area of the learning correction value storage means with the learning correction value; An air-fuel ratio control device for an internal combustion engine, comprising: a feedback control unit and a learning correction value updating unit, and a clamp unit for fixing the feedback correction coefficient and the learning correction value. Learning progress degree determination means for determining the progress degree of learning update; learning wherein the learning progress degree determination means determines an initial predetermined period in which the air-fuel ratio feedback control means and the learning correction value update means are operated in the clamp means. Operating period setting means set according to the degree of progress of the update.

<Operation> When the progress of the learning update determined by the learning progress determining means is equal to or less than a predetermined value, in a predetermined operation region, the initial operation of operating the air-fuel ratio feedback control means and the learning correction value updating means in the clamp means. In order to set the predetermined period of time according to the progress of the learning update determined by the learning progress determining means, in the initial state where the progress of the learning update is low, the predetermined period is set to be long and the learning is advanced. As the degree increases, the predetermined period is set shorter, so that stable drivability can be obtained from an earlier stage.

<Example> An example of the present invention will be described below with reference to the drawings.

2, an air flow meter for detecting an intake air flow rate Q is provided in an intake passage 12 of an engine 11.
A throttle valve 14 for controlling the intake air flow rate Q in conjunction with the accelerator pedal 13 and an accelerator pedal is provided, and an electromagnetic fuel injection valve 15 is provided for each cylinder in a downstream manifold portion.

The fuel injection valve 15 is driven to open by an injection pulse signal from a control unit 16 containing a microcomputer, and injects fuel supplied from a fuel pump (not shown) under pressure and controlled to a predetermined pressure by a pressure regulator. Further, a water temperature sensor 17 for detecting a cooling water temperature Tw in a cooling jacket of the engine 11 is provided, and an exhaust passage 18 detects an air-fuel ratio of an air-fuel mixture supplied to the engine by detecting an oxygen concentration in the exhaust gas. Air-fuel ratio sensor
19 is provided, further downstream in the exhaust CO, HC oxidation and NO _x
-Way Catalyst as an Exhaust Purification Catalyst for Reduction and Washing
20 are provided.

Further, a distributor (not shown) has a built-in crank angle sensor 21 which counts a crank unit angle signal output from the crank angle sensor 21 in synchronization with the engine rotation for a certain period of time, or a crank reference angle signal. Is measured and the engine speed N is detected.

Next, the air-fuel ratio control routine by the control unit 16 will be described with reference to the flowcharts of FIGS. FIG. 3 shows a fuel injection amount setting routine, which is performed at predetermined intervals (for example, 10 ms).

In step (denoted by S in the figure) 1, the amount of intake air per unit rotation is determined based on the intake air flow rate Q detected by the air flow meter 13 and the engine speed N calculated based on a signal from the crank angle sensor 21. the basic fuel injection quantity T _P corresponding to operation by the following equation.

T _P = K × Q / N (K is a constant) In step 2, various correction coefficients COEF are set based on the cooling water temperature Tw detected by the water temperature sensor 17.

In step 3, a feedback correction coefficient α set based on a signal from the air-fuel ratio sensor 19 by a later-described feedback correction coefficient setting routine is read, and a learning correction value of the air-fuel ratio feedback correction coefficient α described later is set.
RAM based Kl on the engine speed N and the basic fuel injection quantity T _P
Search and read from the operation area corresponding to. Here, the RAM that stores the learning correction value Kl constitutes a learning correction value storage unit.

In step 4, a voltage correction amount T _S is set based on the battery voltage value. This is for correcting a change in the injection flow rate of the fuel injection valve 15 due to the battery voltage fluctuation.

In step 5, a final fuel injection amount T _I is calculated according to the following equation.

In _{T I = T P × COEF ×} α × Kl + T S Step 6, is set in the output register the computed fuel injection valve T _I.

Consequently, when a fuel injection timing of a predetermined engine rotation synchronization, fuel injection is performed a drive pulse signal having a pulse width of the calculated fuel injection amount T _I is given to the fuel injection valve 15.

Next, an air-fuel ratio feedback correction coefficient setting routine will be described with reference to FIG. This routine is executed in synchronization with the engine rotation.

In step 11, it is determined whether the feedback control and the learning control of the air-fuel ratio have been started, and if not started, this routine ends.

If it has started, the process proceeds to step 12, and it is determined whether or not a predetermined operating condition under which the control described below is performed.
If the predetermined operating conditions are not satisfied, step
Proceeding to 22, the air-fuel ratio feedback correction coefficient α is set. Here, the feedback correction coefficient α is determined by comparing the output voltage V ₀ of the air-fuel ratio sensor 19 with a reference voltage (slice level) SL corresponding to the stoichiometric air-fuel ratio, as described in the description of the related art. Is lean (rich) with respect to the stoichiometric air-fuel ratio
In the case of (1), the large proportional constant P is first increased (decreased) and then gradually increased (decreased) by a predetermined integral constant I.

Next, at step 23, the learning correction value Kl is updated and set. The learning correction value Kl is a predetermined ratio of the deviation Δα of the currently set feedback correction coefficient α (or the average value of the latest inversion value and the previous inversion value) from the reference value α ₀ (= 1). The value of the learning correction value Kl of the current operation region is updated by adding the value to the learning correction value Kl of the current operation region.

If the predetermined operating condition is satisfied in step 12, the process proceeds to step 14, in which the value of a reversal measurement counter NSLCNT that measures the number of reversals of the output value of the air-fuel ratio sensor 19 is reset to 0, and then the process proceeds to step 15 and subsequent steps.

In step 15, the air-fuel ratio feedback correction coefficient α is set in the same manner as in step 22, and in step 16,
The learning correction value Kl is updated in the same manner as in step 23.

In step 17, it is determined whether or not the output of the air-fuel ratio sensor 19 has been inverted. And when it is reversed, step 18
Proceed to, after incrementing the inverted measurement counter NSLCNT, upon non-inversion proceeds directly to step 19, the value of the inverted measurement counter NSLCNT determines whether reaches a predetermined value NSLCNT _1.

Here, the predetermined value NSLCNT _1, as shown in FIG. 6, is variably set according to the value of the learning update counter CLRN. Specifically, the value of NSLCNT ₁ when the value of the CLRN is small, that is large enough at low progress of learning update, progress is set to be smaller as it increases.

Then, in the determination of step 19, the inversion measurement counter NSLC
Until the value of NT reaches a predetermined value NSLCNT _1, the program proceeds to step 20 when it reaches the NSLCNT ₁ returns to step 15, a predetermined value IDL values of inversion measurement counter NSLCNT the average value of the feedback correction coefficient α in the measurement And the feedback correction coefficient α is fixed at the value obtained by adding the learning correction value Kl to the value updated in step 16. In step 20 and step 22, the feedback correction coefficient α
A function of setting, by a routine described in the third diagram for setting a fuel injection quantity T _I by using the feedback correction coefficient α is an air-fuel ratio feedback control means is configured,
Similarly, the learning correction value updating means is constituted by the function of setting the learning correction value Kl in step 20 and step 23, and the learning means is clamped by the function of clamping the average value of the feedback correction coefficient α and the learning correction value Kl in step 20. Is configured.

Next, at step 21, it is determined again whether or not the predetermined operating condition is satisfied as in step 12, and when it is satisfied, the fixed state at step 20 is continued. To end.

Here, the learning update counter CLRN constitutes the function of the learning progress degree judging means, and the ROM storing the NLCNT ₁ shown in FIG.
Constitute the operation period setting means.

In this manner, in order to improve stability under predetermined operating conditions, the average value of the feedback correction coefficient α for a predetermined number of times and a learning correction value based on the average value are clamped. When learning is not progressing, for example, when learning is started from a state where the learning correction value is initialized when removed, a predetermined period for performing feedback control and learning after entering the predetermined operating condition is set to be delayed. Thereby, the progress of learning can be promoted, and the reliability of the learning correction value can be increased, so that drivability and exhaust emission characteristics can be ensured.

Further, when the degree of learning is large and the reliability of the learning correction value is high, the predetermined period is shortened, and the average value of the feedback correction coefficient and the learning correction value are clamped early, so that the learning is stabilized in a short time. Driving can be started.

FIG. 5 shows a learning rotation counting routine. This routine is triggered and executed when the learning correction value Kl is updated in steps 23 and 20 in FIG.

In step 31, it is determined whether or not the learning correction value stored in the RAM has been initialized before shipment or by removing the battery.

If it has been initialized, the process proceeds to step 32 to reset the value of the learning update counter CLRN to 0, and if it has not been initialized, the process directly proceeds to step 33, where the learning correction value Kl
It is determined whether or not has been updated. If it has been updated, the routine proceeds to step 34, where the learning update counter CLRN is incremented. If it has not been updated, this routine is terminated.

<Effects of the Invention> As described above, according to the present invention, when the progress of the learning update such that the learning correction value is initialized is low,
By adopting a configuration in which a predetermined period for performing the feedback control and the learning control until the feedback correction coefficient and the learning correction value under the predetermined operating condition are clamped is prolonged, the progress of learning is promoted, and the reliability of the learning correction value is increased. Therefore, drivability and exhaust emission characteristics can be ensured.

Further, when the degree of learning is large and the reliability of the learning correction value is high, the predetermined period is shortened, and the average value of the feedback correction coefficient and the learning correction value are clamped early, so that the learning is stabilized in a short time. Driving can be started.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, and FIG.
FIG. 3 is a flowchart showing a fuel injection amount setting routine, FIG. 4 is a flowchart showing an air-fuel ratio control routine, FIG. 5 is a flowchart showing a learning number counting routine, FIG. FIG. 4 is a diagram showing characteristics of values used in the embodiment. 11 ... engine, 15 ... fuel injection valve, 16 ... control unit, 18 ... exhaust passage, 19 ... air-fuel ratio sensor

Claims (1)

(57) [Claims] An air-fuel ratio detecting means for detecting an air-fuel ratio in response to a concentration ratio of a gas component in exhaust gas, and a target air-fuel ratio using a feedback correction coefficient set according to an output of the air-fuel ratio detecting means. Air-fuel ratio feedback control means for controlling to approach the air-fuel ratio, learning correction value storage means for storing a learning correction value of the feedback correction coefficient for each operation region, and a learning correction value retrieved from the learning correction value storage means. Based on the feedback correction coefficient and the feedback correction coefficient, a new learning correction value is set so that the average value of the feedback correction coefficient converges to a predetermined value. Operating the learning correction value updating means for updating the correction value; and operating the air-fuel ratio feedback control means and the learning correction value updating means only for a predetermined period in a predetermined operation region. An air-fuel ratio control device for an internal combustion engine, comprising: a feedback correction coefficient and a clamp means for fixing a learning correction value. The learning progress determination means for determining the progress of learning update by the learning correction value updating means. An operation period in which an initial predetermined period for operating the air-fuel ratio feedback control unit and the learning correction value updating unit in the clamping unit is set according to the learning update progress determined by the learning progress determination unit. An air-fuel ratio control device for an internal combustion engine, comprising: a setting unit.