JPS59147844A - Air-fuel ratio control device - Google Patents

Abstract

PURPOSE:To obtain an optimum air-fuel ratio at all times in a system to control fuel supply volume by a feed-back based on an output of an O2 sensor by changing a standard voltage at the time of the above feed-back control based on an output of a suction air volume sensor. CONSTITUTION:An output signal Vs of an O2 sensor provided at an exhaust air system is inputted in a plus terminal of a comparator 3 via a buffer amplifier 2, while in a minus terminal, a standard voltage Ve from a standard voltage operation circuit 11 is inputted and based on the compared results of both signals Vs and Ve, the fuel supply volume to the engine is controlled via a control unit 4. The standard voltage operation circuit 11 inputs the output signal Va of the suction air volume sensor 16 into a primary lagging circuit 14 via a buffer amplifier 12 and the primary lagging signal Vav to have a fixed time delay of time is inputted in a subtraction circuit 15 via a buffer amplifier 13. Here, it is made to output the standard voltage Ve which is arrived by subtracting K(constant)XVav from the basic standard voltage Veo.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field The present invention relates to an air-fuel ratio control device that performs feed-hack control on the amount of fuel supplied to an engine based on the output of an oxygen sensor that detects the oxygen concentration in exhaust gas of the engine.

[2] Prior art As a conventional air-fuel ratio control device, for example, "NAPS, three-way catalyst system, 1978 technical manual" (August 1978)
The one described on pages 11 to 1G (published by Nissan Motor Co., Ltd.) is known, and can be shown as shown in FIG. In Figure 1, numeral 1 is an oxygen sensor that detects the oxygen concentration in the engine's exhaust gas.The electromotive force changes suddenly at the stoichiometric air-fuel ratio, and the electromotive force is high when the mixture is rich and low when the mixture is lean. It has the following characteristics. The output signal V of this oxygen sensor 1
s is input to the plus terminal of the comparator 3 via the buffer amplifier 2, and a predetermined reference voltage Ve is input to the minus terminal of the comparator 3. This reference voltage Ve is set to an intermediate voltage of output voltage fluctuations of the oxygen sensor 1. Therefore, when Vs>Ve, that is, when the air-fuel mixture is richer than the stoichiometric air-fuel ratio, the comparator 3 outputs an H signal (high level signal) to the control unit 4, and Vs<Ve.
e, that is, when the air-fuel mixture is thinner than the stoichiometric air-fuel ratio -, an L signal (low level 49%) is output to the control unit 4. The control unit 4 increases or decreases the amount of fuel supplied to the engine based on the signal from the comparator 3, and the rate of this increase or decrease correction is constant. Therefore, this air-fuel ratio control device has buffer amplifier 2, ratio! A feed bank control circuit 5 composed of a 3dit 3 and a control unit 4 increases or decreases the amount of fuel supplied to the engine at a fixed rate based on the output of the oxygen sensor 1, thereby adjusting the air-fuel mixture to the stoichiometric air-fuel ratio. Nearby control.

However, in such conventional air-fuel ratio control devices, the amount of fuel supplied to the engine is increased or decreased at a fixed rate based on the output of the oxygen sensor, so the response time of the oxygen sensor is If the (50% response time of the oxygen sensor output) is different between the rise and fall, there is a problem in which the control center of the air-fuel ratio for feedbank control deviates from the stoichiometric air-fuel ratio. As shown in Figure 2, the relationship with temperature is that while the rise response time Tr becomes slightly longer as the temperature of the oxygen sensor decreases, the fall response time Tf becomes significantly longer as the temperature decreases. Become. Therefore, the falling response time Tf becomes longer than the rising response time Tr due to a decrease in temperature, and the difference between the falling response time Tf and the rising response time Tr increases as the temperature decreases. the result,
For example, if the air-fuel ratio changes as shown in FIG. 3A, the output of the oxygen sensor changes as shown in FIG. 3S at high temperatures, and this output voltage becomes the reference voltage V.

Since it is determined whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio at the point where the air-fuel ratio intersects with , the air-fuel ratio at high temperature is determined as shown in FIG. 3d. Here, the rise response time Tr of the oxygen sensor at high temperature is
, and the falling response time Tf are almost equal, and the air-fuel ratio judgment at high temperatures faithfully represents the actual air-fuel ratio change, although there is a delay in the response time (Tr#Tf). On the other hand, at low temperatures, the rise response time Tr2 of the oxygen sensor does not change much, but the fall response time Tr2 becomes longer, and the output of the oxygen sensor changes as shown in FIG. 3C. Therefore, the air-fuel ratio at low temperatures is determined as shown in FIG. 3e, and the time during which it is determined that the air-fuel ratio is richer than the stoichiometric air-fuel ratio is longer than the time when the air-fuel ratio is actually richer. Then, if the amount is increased or decreased at a fixed rate based on these air-fuel ratio judgments, the stoichiometric air-fuel ratio becomes the main control point for the air-fuel ratio at high temperatures.
At low temperatures, for example, it is determined that the air-fuel ratio is rich based on the output of the oxygen sensor as shown in FIG. Therefore, this results in an increase in fuel consumption and a decrease in engine output, and particularly in vehicles using a three-way catalyst, a problem arises in that the conversion rate of the three-way catalyst deteriorates.

[3] Purpose of the Invention Therefore, the present invention provides a reference voltage for determining whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio by comparing the output voltage of the oxygen sensor with the intake air amount, which is related to the temperature of the oxygen sensor. The purpose is to set the control center of the air-fuel ratio to the stoichiometric air-fuel ratio by changing the air-fuel ratio based on the air-fuel ratio.

[4] Configuration of the Invention The air-fuel ratio control device of the present invention includes an oxygen sensor that detects the oxygen concentration in the exhaust gas of an engine and outputs a voltage signal, and a system that compares the output voltage of the oxygen sensor with a predetermined reference voltage and controls the engine. An air-fuel ratio control device comprising: a feedback control circuit for increasing or decreasing the amount of fuel supplied; an intake air amount sensor that detects the intake air amount of the engine; By changing the reference voltage based on , the control center of the air-fuel ratio is set to the stoichiometric air-fuel ratio.

[5] Examples The present invention will be described in detail below with reference to the drawings.

5 to '7 are diagrams showing one embodiment of the present invention, and in explaining this embodiment, the same components as those of the conventional example shown in FIG. 1 are given the same reference numerals.

First, to explain the configuration, in FIG.
The reference voltage Ve from the reference voltage calculation circuit 11 is input to the minus terminal of the comparator 3.

The reference voltage calculation circuit 11 includes buffer amplifiers 12, 13,
- It is composed of a next delay circuit 14 and a subtraction circuit 15, and the reference voltage calculation circuit 11 receives an intake air amount signal Va from an intake air amount sensor (for example, an air flow meter) 16 that detects the intake air amount of the engine. . This intake air amount signal Va is input to the first-order lag circuit 14 via the buffer amplifier 12, and the second-order lag circuit 14 is connected to a resistor R1 and a capacitor C.
1. Therefore, −th lag circuit 1
4 outputs the first-order delayed signal Vav of the intake air amount signal Va to the subtraction circuit 15 via the buffer amplifier 13.

The subtraction circuit 15 includes an operational amplifier OP1, resistors R2, R6, and R
4, R9 and a reference voltage generator L,
The reference voltage generator L V , generates a predetermined basic reference voltage Veo
is outputting. Therefore, the subtraction circuit 15 outputs a reference voltage Ve obtained by subtracting KXVav (K is a constant) from the basic reference voltage Veo, that is, Ve=Veo−KVav, to the negative terminal of the comparator 3, and this reference voltage Ve is 6th
As shown in the figure, from the basic reference voltage Veo to the intake air amount Vav
decreases at a constant rate as .

Then, when the output voltage Vs of the oxygen sensor 1 is higher than the reference voltage Ve, that is, when Vs>Ve, the comparator 3 outputs an H signal to the control unit 4, and ■S<V
When e, an L signal is output to the control unit 4.

The control unit 4 calculates the basic fuel supply amount based on the engine rotational speed signal and the intake air amount signal, and then multiplies the basic fuel supply amount by various correction coefficients to determine the final fuel supply amount.

The correction coefficients include a water temperature increase correction coefficient, a start-up and post-start increase correction coefficient, and among these, there is a correction coefficient α determined based on the output signal from the oxygen sensor 1. The control unit 1-4 determines whether to perform an increase correction or a decrease correction based on the signal from the comparator 3, that is, the signal from the oxygen sensor 1, and determines the value of the correction coefficient α.

The buffer amplifier 2, comparator 3, reference voltage calculation circuit 11, and control unit 4 constitute a feed bank control circuit I7.

Next, the action will be explained.

Generally, the amount of heat generated by combustion is related to the amount of intake air.
Particularly in engines where the air-fuel ratio is kept constant through feedbank control, once the amount of intake air is determined, the amount of heat generated is determined and the exhaust temperature is determined. Therefore, the exhaust gas temperature can be determined by detecting the intake air amount, and the exhaust gas temperature can be determined easily and inexpensively without directly measuring the high temperature exhaust gas temperature. However, there is a time delay between the time when the flow rate of the intake air is detected and the time it undergoes combustion and becomes the exhaust gas, and while the instantaneous value of the intake air amount fluctuates greatly depending on the opening and closing of the throttle valve, the exhaust temperature changes only slowly. be. therefore,
The instantaneous value of the intake air amount does not indicate the exhaust gas temperature at that time, but its second-order delayed signal is approximately the same as the exhaust temperature at that time. As a result, the first-order lag signal Vav of the intake air amount signal Va output by the -order lag circuit 14 indicates the exhaust temperature, that is, the temperature of the oxygen sensor 1. Therefore, the subtraction circuit 15 changes and outputs the reference voltage Ve based on the temperature of the oxygen sensor 1, and the reference voltage Ve is expressed by the formula (Ve=Ve).

-KVav), it decreases as the temperature increases. That is, in response to a change in the air-fuel ratio as shown in FIG. 7a, the output signal Vs of the oxygen sensor 1 has a rise response time Tr and a fall response time T' at high temperatures, as shown in FIG. f is equal, and at low temperature, Fig. 7C
As shown in the figure, the falling response time TfO is longer than the rising response time Tr. Then, the reference voltage Ve at high temperature
is an intermediate value of the output fluctuations of the oxygen sensor 1, so the output signal of the oxygen sensor 1 is equal to the reference voltage V from the actual air-fuel ratio change.
The time it takes to cross e, that is, the apparent rise and fall response times Tro, TfO, and the rise and fall response times Tr-Tr are equal, as shown in Figure 7, but at low temperatures, As shown in FIG. 7C, since the reference voltage Ve increases, the apparent response time Tro,
Tfo and response times Tr and Tf are different. However, the apparent rise response time Tro and the apparent fall response time Tfo are equal. That is, the apparent rising response time 〒"0 and the apparent falling response time T f o
are almost equal to each other as shown in FIG. 8 with respect to the temperature change of the oxygen sensor 1. Therefore, even at low temperatures, the air-fuel ratio can be determined accurately, even though there is a delay in the apparent response time Tro, Tfo, and the actual air-fuel ratio change can be accurately determined.
The judgment will not deviate to the lean side or the rich side.

As a result, the control center of the air-fuel ratio can always be set to the stoichiometric air-fuel ratio, making it possible to save fuel consumption and improve engine output. Particularly in vehicles using a three-way catalyst, the conversion rate of the three-way catalyst can be improved.

[6] Effects According to the present invention, the reference voltage for determining whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio by comparing with the output voltage of the oxygen sensor is set based on the intake air amount that clearly indicates the temperature of the oxygen sensor. Since it can be changed, the control center of the air-fuel ratio can always be set to the stoichiometric air-fuel ratio easily and inexpensively. Therefore, fuel consumption can be saved and engine output can be improved, and in particular, in a vehicle using a three-way catalyst, the conversion rate of the three-way catalyst can be improved.

[Brief explanation of the drawing]

1 to 4 are diagrams showing a conventional air-fuel ratio control device, with FIG. 1 being a schematic configuration diagram thereof, FIG. 2 being a graph showing the relationship between the temperature and response time of the oxygen sensor, and FIGS. Fig. 4 is an explanatory diagram of its operation, Figs. 5 to 7 are diagrams showing the air-fuel ratio control device of the present invention, Fig. 5 is its configuration diagram, and Fig. 6 shows the relationship between its reference voltage and intake air amount. 7 is an explanatory diagram of its operation, and FIG. 8 is a graph showing the relationship between the temperature of the oxygen sensor and the apparent response time. l ---Oxygen sensor, 16---Intake air amount sensor, 17--Feed bank control circuit. Patent Applicant Nissan Motor Co., Ltd. Representative Patent Attorney Agagun Part

Claims (1)

[Claims] An oxygen sensor that detects the oxygen concentration in the engine exhaust gas and outputs a voltage signal, and a feedback control circuit that compares the output voltage of the oxygen sensor with a predetermined reference voltage and corrects the amount of fuel supplied to the engine to increase or decrease. An air-fuel ratio control device comprising: an intake air amount sensor for detecting an intake air amount of the engine; and the feedback control circuit changes the reference voltage based on the output of the intake air amount sensor. Air-fuel ratio control device.