JPS60156952A - Air-fuel ratio controller - Google Patents

Abstract

PURPOSE:To improve the running property of an engine, by delaying or advancing the ignition timing with regard to an optimal ignition timing corresponding to an aimed air-fuel ratio, depending on the increasing or decreasing control of the air-fuel ratio of the engine, to reduce the torque fluctuation thereof. CONSTITUTION:A comparison circuit 25 receives the output of an oxygen sensor 11 through an amplifier 23 and a reference voltage Vo from a reference power source 24 to judge whether the current ratio of fuel to air is higher or lower than an aimed value. The comparison circuit 25 sends out a signal R/L to an integration circuit 26, which calculates a compensation coefficient alpha for compensating the current air-fuel ratio to be equal to the aimed value, and sends out the compensation coefficient to a compensation circuit 27, which calculates a final injection quantity Tt so that a corresponding injection signal St is sent out to an injector 5 by a drive circuit 28 to inject the quantity Tt of fuel. The compensation coefficient alpha is also applied to an ignition timing control means 29 so that a comparison circuit 35 acts to increase the angle of ignition timing delay when the compensation coefficient alpha indicates a fuel increasing timing.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an air-fuel ratio control device for an engine, and more particularly to an air-fuel ratio feedback control device using an oxygen sensor.

(Prior art) Recently, in order to accurately control the air-fuel ratio of the engine intake air-fuel mixture to a target value, an oxygen sensor has been installed in the exhaust system to control the air-fuel ratio in the exhaust gas, which has a correlation with the air-fuel ratio. The fuel supply amount is controlled by feed puncture. Furthermore, from the viewpoint of energy conservation, attempts have recently been made to perform feedpatch control of the air-fuel ratio so as to cause the engine to burn a lean mixture to improve fuel efficiency.

As a conventional air-fuel ratio control device of this type, the one shown in FIG. 1 is known, for example (``Account's 1953 Exhaust Gas Countermeasures'' Journal of the Society of Automotive Engineers, February 1977 issue). In FIG. 1, reference numeral 1 denotes an in-line four-cylinder engine. Intake air is supplied from an air flow meter 2 to each cylinder through an intake pipe 3, and fuel is introduced through a fuel pipe 4 and is injected into each cylinder by a fuel injector 5. Sprayed near the boat. Further, each cylinder is provided with an ignition plug 6, and a secondary ignition signal (high voltage) S'l) 2 is supplied to the ignition plug 6 from an ignition coil 8 at a predetermined ignition timing via a distributor 7. be done. Then, the injected fuel is ignited and exploded by the ignition secondary signal Sp2, becomes exhaust gas, and is introduced into the catalytic converter 10 through the exhaust pipe 9.
0x) is purified by a three-way catalyst and discharged. The intake air flow rate Qa is detected by an air flow meter 2, and the rotation speed N of the engine 1 is detected by a distributor 7 having a built-in crank angle sensor. On the other hand, an oxygen sensor 11 is provided in the exhaust pipe 9, and the oxygen sensor 11 collectively detects the oxygen concentration of exhaust gas discharged from each cylinder. Each signal from the air flow meter 2, distributor 7 and oxygen sensor 11 is inputted to a control unit 12, and the control unit 7+-12
controls the injection amount of the fuel injector 5 based on these signals to perform footbank control of the air-fuel ratio.

That is, the control unit 2 is composed of a supply amount calculation circuit 13 and an air-fuel ratio correction circuit 14,
The supply amount calculation circuit 13 calculates the basic injection amount Tp based on the intake air amount Qa and the rotation speed N, and also performs various increase corrections (for example, increase correction based on the cooling water temperature) on this basic injection amount WTp as the corrected injection amount Ts. Air-fuel ratio correction circuit 1
Output to 4. The air-fuel ratio correction circuit 14 sets a target air-fuel ratio according to operating conditions, and also adjusts the output S of the oxygen sensor 9.
A correction coefficient α for correcting the current air-fuel ratio to the target air-fuel ratio is calculated based on O. Then, the corrected injection amount Ts is multiplied by this correction coefficient α to calculate the final injection amount −rt corresponding to the target air-fuel ratio which is the control J11 target, and the injection signal St is output to the injector 5. In this case, the corrected injection Jjl T s is increased or decreased at a constant rate by the correction coefficient α, and is controlled so that the amount of fuel always corresponds to the target air-fuel ratio. The injector 5 injects fuel by the final injection MTt based on the injection signal 3t.

On the other hand, the ignition timing is optimally controlled according to the rotational speed and engine load by a centrifugal advance mechanism or a vacuum advance mechanism built into the distributor 7.

However, with such conventional air-fuel ratio control devices, the average oxygen concentration of exhaust gas discharged from all cylinders is detected, and based on this detection result, the fuel injection amount of the golden cylinder is increased or increased by a predetermined amount. While it was collectively controlled at the weight reduction correction timing, the ignition timing was not controlled at all regardless of changes in the air-fuel ratio, so the air-fuel ratio of all cylinders was controlled at the same timing, causing torque fluctuations in the engine. However, there is a problem in that such torque fluctuations cannot be reduced by controlling the ignition timing.

In other words, the cylinder manufacturing control for controlling the air-fuel ratio to the target air-fuel ratio is, in other words, the increase/decrease control of the fuel injection amount. This is done by increasing or decreasing the injection amount. on the other hand,
The engine shaft torque (net torque effectively extracted from the output shaft (crankshaft) of the engine) is approximately proportional to the fuel injection amount, and as the fuel injection amount increases or decreases, the torque also increases or decreases. Therefore, due to the relationship between the two, for example, the torque increases at the timing of the increase correction, and the torque decreases at the timing of the increase correction. the result,
Torque fluctuations occur due to thin air-fuel ratio control.

Further, such torque fluctuations occur significantly when the target air-fuel ratio is set to an air-fuel ratio leaner than the stoichiometric air-fuel ratio (hereinafter referred to as a lean air-fuel ratio). In other words, as shown in Fig. 2, which shows the relationship between shaft torque T and air-fuel ratio A/F (hereinafter referred to as T-A/F characteristic), engine shaft torque has a gradual peak near the stoichiometric air-fuel ratio, and then changes around the stoichiometric air-fuel ratio. tends to decline rapidly. Specifically, the shaft torque is maximum at A/F=12.5. This is because near this air-fuel ratio, ignition is easiest and the combustion speed is also high. Therefore, for example, when the target air-fuel ratio is the stoichiometric air-fuel ratio, the torque fluctuation is 8T for the S thin fluctuation ΔA/F of the air-fuel ratio.
, will be a small value. On the other hand, when the target air-fuel ratio is a lean air-fuel ratio, the variation is ΔT2 (8T2>Δ1゛) for the same a thin variation ΔA/F.

) becomes a large value. Furthermore, since the period of such torque fluctuations matches the speed of air-fuel ratio feedback control (tube manufacturing control) (usually about 0.5 to 311z),
For example, when the vehicle is running, longitudinal vibration (surge) of the vehicle occurs, and when idling, the rotational speed fluctuates, causing problems such as unstable idling.

By the way, as is well known, the combustion state of the air-fuel mixture, which is closely related to the shaft torque, is greatly influenced by the ignition timing as well as the air-fuel ratio, intake air amount, compression pressure, etc. Therefore, although the details will be described later, if the ignition timing is appropriately controlled in conjunction with cylinder manufacturing control of the air-fuel ratio, torque fluctuations can be reduced. However, such effective ignition timing control is not performed at all, and torque fluctuations cannot be reduced. In other words, conventional ignition timing control does not contribute at all to torque fluctuations associated with cylinder manufacturing fluctuations in air-fuel ratio.

(Purpose of the Invention) Therefore, the present invention retards the ignition timing in accordance with cylinder manufacturing control of the air-fuel ratio, starting from the optimum ignition timing corresponding to the target air-fuel ratio, thereby constantly changing the combustion state of the air-fuel mixture with torque fluctuations. The objective is to control the torque to a minimum, thereby reducing torque fluctuations and improving engine drivability.

(Structure of the Invention) The air-fuel ratio control device according to the present invention includes an oxygen sensor that detects the oxygen concentration in the exhaust gas of the engine, a supply amount calculation means that calculates the amount of fuel supplied based on the operating state of the engine, and an oxygen sensor that detects the oxygen concentration in the exhaust gas of the engine. (Based on this correction coefficient)
and an ignition timing control means for controlling the ignition timing of the engine according to the value of the correction coefficient. This is to control the combustion state of the air-fuel mixture so that the torque fluctuation is always minimized regardless of the cylinder manufacturing fluctuation.

(Example) Hereinafter, the present invention will be explained based on the drawings.

3 to 6 are diagrams showing an embodiment of the present invention.

First, the configuration will be explained. This example is applied to an in-line four-cylinder engine like the conventional example, and its schematic configuration is the first one.
Since it is the same as that shown in the figure, the explanation will be omitted, and a block configuration diagram of the main part is shown in FIG.

Further, in FIG. 3, blocks having the same configuration as the conventional one are simply given the same reference numerals and their explanations will be omitted.

In FIG. 3, 21 is a supply amount calculation circuit (supply amount calculation means), and the supply amount calculation circuit 21 is connected to the air flow meter 2.
Based on the output Qa of the engine and the output N of the crank angle sensor (distributor) 7, the basic injection amount Tp (Tp=to-Qa/N) is determined.

K: constant) is calculated and output to the air-fuel ratio control means 22. The air-fuel ratio control means 22 includes a Banfa amplifier 23 and a reference power source 24.
, a comparison circuit 5, an integration circuit 26, a correction circuit 27, and a drive circuit 28. The comparison circuit 25 is inputted with the output gas SO of the oxygen sensor 11 via the amplifier and the reference power supply. A reference voltage VO from 24 is input. This reference voltage Vo is set to a value corresponding to the target air-fuel ratio. Therefore, the comparison circuit 25 determines whether the current air-fuel ratio is richer or leaner than the target air-fuel ratio, and outputs a rich/lean signal R/L to the integrating circuit U. The integral circuit 26 calculates a correction coefficient α for correcting the current air-fuel ratio to the target air-fuel ratio by (integral) control based on the rich/lean signal R/L, and the correction circuit 2
Output to 7. This correction coefficient α is calculated according to the degree of deviation of the current air-fuel ratio from the target air-fuel ratio, and the slope of the correction ratio (the slope of integral control) is constant. The correction circuit 27 includes
Roughly, the basic injection amount 1゛p from the supply amount calculation circuit 21 is input, and the correction circuit 27 calculates the basic injection amount ゛p at a predetermined ratio (i.e., the slope of the integral control) based on the correction coefficient α. The final injection amount Tt corresponding to the target air-fuel ratio is calculated by increasing or decreasing the amount and outputs it to the drive circuit side. On the second day of the drive circuit, the injection signal St corresponding to the final injection amount]
is output to the injector 5. And injector 5
is attached to the intake pipe 3 near the intake bow I,
It is driven by the injection signal 3t and injects a final injection amount of 1゛t of fuel.

The output of the integration circuit 26, that is, the correction coefficient α, is input to the ignition timing control means 29, and the correction coefficient α is input to the ignition timing control means 29.
9 is composed of a waveform shaping circuit 30, a retard control circuit 31, and an amplifier circuit 32.

A primary ignition signal Spt from a pink-up coil 33 is input to the waveform shaping circuit 30, and this pickup coil 33 is built into the distributor tough.
The cylinder engine outputs a pulse signal (primary ignition signal) Sp+ once every 20°. Although not shown, the relative position (position with respect to the piston of the cylinder) of the pickup coil 33 is varied by a centrifugal advance mechanism or a vacuum advance mechanism incorporated in the distributor. Therefore, the pickup coil 33 corresponds to the engine rotation speed N and the engine load (Tp).
Timing to output a pulse signal according to (ignition timing)
Shift (e.g. move forward). The waveform shaping circuit 30 shapes the pulsed primary ignition signal S1) into a rectangular waveform and outputs it to the retard control circuit 31 as a shaped signal Ss.

The retard control circuit 31 includes an integrating circuit 34 and a comparing circuit 35, and controls the ignition timing according to the value of the correction coefficient α. That is, the integrating circuit 34 receives the shaped signal S
s is integrated by a predetermined integral constant and outputted to the comparison circuit 35 as an integral signal Si. The comparator circuit 35 is further inputted with the correction coefficient α, and the comparator circuit 35 receives the integral signal Si.
and the value of the correction coefficient α, and when Si>α [■1]
Thus, when Si<α, a retard signal Sd which becomes (L) is output. Therefore, this retard signal Sd is the ignition primary signal S
l't is corrected according to the value of the correction coefficient α,
When the correction coefficient α is at the increase correction timing, ignition 1
The angle at which the ignition timing is delayed compared to the next signal Spl (hereinafter referred to as
The retard amount τ) gradually increases, and when it is time for the reduction correction, the retard amount τ gradually decreases. The retard signal Sd is then amplified by the amplifier circuit 32 and then supplied to the power transistor 36. The power transistor 36 operates as a 0N10FF in synchronization with the fall/rise of the retard signal Sd, controls the primary current of the ignition coil 8 intermittently, and supplies a high voltage ignition 2 to the secondary side of the ignition coil 8.
The next signal Sp2 is induced and supplied to the spark plug 6 via the distributor 7.

The secondary ignition signal Sp2 is supplied in synchronization with the rise of the retard signal Sd, and the crank angle difference between the secondary ignition signal Sp2 and the primary ignition signal Sp□ becomes the retard amount τ ( (See Figure 6 below).

Next, the action will be explained.

Generally, as shown in the T-A/F characteristics, the engine shaft torque peaks near the stoichiometric air-fuel ratio and decreases before and after that, so the air-fuel ratio of all cylinders is controlled at once at a predetermined feed-hack cycle. As a result, torque fluctuations occur.

Incidentally, the axis I-lux has a close relationship with the combustion state of the air-fuel mixture, and is influenced not only by the air-fuel ratio but also by, for example, the ignition timing. That is, FIG. 4 is a diagram showing the relationship between ignition timing and air-fuel ratio under the condition of equal intake air amount, and the solid line T in the figure represents the equiaxed torque curve, and the broken line H represents the equal HC emission curve. ing. Therefore, for example, when the target air-fuel ratio is set to the stoichiometric air-fuel ratio indicated by point A in the figure, if the air-fuel ratio in the force direction of arrow ΔA is shifted during cylinder manufacturing control, torque fluctuations will occur. On the other hand, if the ignition timing is controlled in the direction of the arrow Δ' in synchronization with the rich opening control at this time, the shaft torque will change to the equiaxed torque curve T
As a result, torque fluctuations can be reduced. This principle is the same even when the target air-fuel ratio is set to a predetermined lean air-fuel ratio (point B in the figure), and the arrows ΔB and ΔB' are controlled in the same way as the arrows ΔA and Δ' above. Each direction is indicated.

Therefore, in this embodiment, focusing on this principle, the air-fuel ratio is set to the richer side than the target air-fuel ratio at the optimum ignition timing (hereinafter referred to as the center ignition timing) corresponding to the target air-fuel ratio, which is the center of control of the air-fuel ratio. When the ignition timing is controlled, the ignition timing is retarded, and when the ignition timing is controlled to the lean side, the ignition timing is advanced to improve the air-fuel ratio. This reduces torque fluctuations associated with 1ilJ control.

In other words, the 5th FI! As shown in Ja-c, the retardation amount τ0 of the center ignition timing (hereinafter referred to as the center retardation amount. Also, when expressed as a correction coefficient α, this is the retardation of the optimum ignition timing corresponding to the average value α of the correction coefficient α). α
〉α, the ignition timing is delayed by 11 rich retard angles expressed by the relationship τB〉τ0 according to the value of α, and when α is less than α, the ignition timing is delayed according to the value of α and expressed by the relationship 〈τ0. The ignition timing is delayed by the lean retard amount τ5 (
This means that the ignition timing is advanced from the center ignition timing).

Next, control using the above retard amount will be explained with reference to the timing chart shown in FIG.

First, as shown in Figure G a, the current air-fuel ratio changes at timing t1.
When the rich side changes from the lean side to the lean side, the rich/lean signal R/L changes as shown in the figure, and the correction coefficient α changes according to this rich/lean signal R/L.
Correct the air-fuel ratio to the rich side with the slope shown in . On the other hand, the primary ignition signal Sp is appropriately advanced in accordance with the engine speed and engine load, as shown in Figure 6d, and this primary ignition signal Sp is waveform-shaped and A rectangular shaped signal Ss as shown in FIG. The retard control circuit 31 integrates this shaped signal Ss and compares the integral value (integral signal) Si (see FIG. 6C) with a correction coefficient α to generate a retard signal as shown in FIG. 6g. Output Sd. At this time, the rising edge of the retard signal Sd is the correction coefficient α
It gradually becomes delayed as the number increases. In addition, as shown in FIG. 6j, the retardation amount τ is the center retardation amount in a period t where 1<12, with the timing t2 at which the correction coefficient α crosses the average value α corresponding to the target air-fuel ratio as a boundary. The lean retardation amount τL is smaller (advanced) than τ0, τLl, τ, λ---1. On the other hand, in the period t where 1>12, the center retardation amount τ91 is larger (delayed) than the center retardation amount τ0. , τR2−
The rich retard amount τR has a value of -'-. Then, the power transistor 36 is controlled to 0N10FF by this retard signal Sd as shown in the sixth figure, and the ignition secondary signal 31)2 shown in the figure i is supplied to the spark plug 6. Therefore, the ignition timing is advanced during the period (t2 to 1.) in which the air-fuel ratio is controlled to be leaner than the target air-fuel ratio, and delayed in the period (1, to t2) in which the air-fuel ratio is controlled to be richer (see FIG. 6C). As a result, the combustion state of the air-fuel mixture is always controlled to minimize torque fluctuations based on the principle shown in FIG. 4, regardless of cylinder manufacturing fluctuations in the air-fuel ratio, and engine torque fluctuations can be reduced.

Therefore, it is possible to prevent the vehicle from swinging back and forth, and to stabilize idling. In addition, if the ignition timing is controlled as described above, H
As is clear from the C emissions curve H, it is possible to reduce the HC emissions when controlling the air-fuel ratio toward the richer direction, and to suppress the rise in exhaust gas temperature.

It is also possible to reduce the amount of X emissions.

Furthermore, the above-mentioned effect becomes particularly noticeable when the target air-fuel ratio is set to a lean air-fuel ratio.

Note that the retard amount τ can be changed to an arbitrary value by changing the integral constant of the integrating circuit 34. For example, if it is set appropriately depending on the operating conditions and engine model, torque fluctuations can be further reduced. can be reduced.

(Effect) According to the present invention, the air-fuel ratio iJ! The ignition timing can be controlled according to the lean control, and the combustion state of the air-fuel mixture can be controlled so that the 1-lux fluctuation is always minimized. the result,
It is possible to reduce torque fluctuations and improve engine drivability.

[Brief explanation of the drawing]

Fig. 1.2 is a diagram showing a conventional air-fuel ratio control device, Fig. 1 is a schematic diagram thereof, Fig. 2 is a diagram showing its T-A/F characteristics, and Figs. 3 to 6 are diagrams showing the present invention. FIG. 3 is a block diagram of the embodiment; FIG. 4 is a diagram showing the relationships between ignition timing, air-fuel ratio, shaft torque, and HC emissions; FIGS. Timing charts for explaining the ignition timing control, and FIGS. 6A to 6J are timing charts for explaining the retard amount control. 11----Oxygen sensor, 21--Supply amount calculation means, 22--Air-fuel ratio control means, 29--Ignition timing control means. Patent Applicant Nissan Motor Co., Ltd. Representative Patent Attorney Agagun Part

Claims (1)

[Claims] an air-fuel ratio control means that calculates a correction coefficient for correcting the air-fuel ratio to a target air-fuel ratio, increases or decreases the fuel supply amount based on the correction coefficient, and performs feedback control of the air-fuel ratio;
An air-fuel ratio control device comprising: ignition timing control means for controlling ignition timing of an engine according to the value of the correction coefficient. (21) When the air-fuel ratio is controlled to the leaner side than the target air-fuel ratio by the correction coefficient with the optimal ignition timing corresponding to the target air-fuel ratio as a boundary, the ignition timing control means delays the ignition timing and controls the ignition timing to the lean side. 2. The air-fuel ratio control device according to claim 1, wherein the air-fuel ratio control device advances the ignition timing when the engine is running.