JPS58133439A - Air-fuel ratio controller of internal-combustion engine - Google Patents

Abstract

PURPOSE:To prevent worsening of an inversion rate of a catalyst, by normally setting an injection quantity of fuel only suitable for lean combustion and performing excess correction of a fuel supply quantity at a decrease of catalytic temperature below a prescribed value to prevent an abnormal decrease of the catalytic temperature. CONSTITUTION:An ignition pulse (a) fed to a waveform shaper circuit 141 from an ignition coil 8 is changed to a square pulse (b) and fed to a divider circuit 142 and F/V converter 143. The fed pulse (b) is converted to 1/N frequency in the circuit 142 and fed to one input terminal of an AND circuit 146. While the pulse (b) fed to the converter 143 is converted to a voltage signal in accordance with an engine speed and compared with an output of a constant voltage circuit 144 in a comparator 145. And only when output voltage of the converter 143 is lower than preset voltage, a high level signal is fed to the other input terminal of the circuit 146. Further the circuit 146 outputs a square pulse (c) to a control unit 6 only when a high level signal is output from the comparator 145.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for an internal combustion engine equipped with a fuel injection device.

In this type of internal combustion engine, for example, as shown in Figure Ia1,
A fuel injection valve 3 was installed in the intake passage 2 of the engine body 1, and the amount of fuel supplied was calculated by a control unit according to the intake air amount detected through the output signal of an air flow meter or the like provided in the intake passage 2. Then, the control signal obtained by this calculation is supplied to the fuel injection valve 3 to optimally control the fuel supply amount. In addition, the concentrations of hydrocarbons (hereinafter referred to as HC), -carbon oxides (hereinafter referred to as CO), nitrogen oxides (hereinafter referred to as NOx), and oxygen (hereinafter referred to as 03) contained in the machine mlO exhaust are It is well known that the air-fuel ratio (hereinafter referred to as A/F) K of the air-fuel mixture supplied to the combustion chamber of the engine 1 changes as shown in FIG. 2. (Technical manual published by Nissan Motor Co., Ltd. in 1975, "Type 50 electronically controlled fuel injection system", p. 83) On the other hand, in order to detoxify the exhaust from engine 1, as shown in Figure 1, A catalyst 5 may be interposed in the middle of the passage 4. The exhaust temperature and the catalyst inlet temperature or catalyst temperature, which depends on the exhaust temperature, are A as shown in Figure 3.
/F, and the conversion rate of CO, HC, etc. is I
As shown in the N4 diagram, it changes depending on the catalyst temperature. For this reason, when the engine is operated with A/F in the B area in Fig. 2, the exhaust temperature and catalyst inlet temperature are within the B' and B'' areas in Fig. 3, and the As shown in the figure, the conversion rate of CO2HC by the catalyst can be maintained well.

However, if a lean burn system is adopted in which the A/F is moved to region A in FIG. 2 in order to improve the fuel efficiency of the engine, the exhaust temperature decreases as shown in region KA' in FIG. 3. Also, at this time, even though the 0sll[ in the exhaust gas becomes ^^, the concentration of CO2He becomes small and the temperature cannot be expected to rise due to the oxidation action of the catalyst, so the temperature change of the catalyst decreases, as shown in Fig. 4. As shown in region A', the conversion rate of the catalyst decreases significantly. For this reason, lean-burn internal combustion engines have a problem in that it is difficult to sufficiently detoxify exhaust gas using a catalyst.

The present invention has been made by focusing on these conventional problems, and is designed to improve fuel efficiency by setting the amount of fuel injected to an amount commensurate with lean combustion, while reducing the catalyst temperature to below a predetermined value. When this occurs, the purpose of the present invention is to prevent deterioration of the conversion rate of the catalyst and stabilize the exhaust treatment function by correcting the increase in fuel supply fik to prevent an abnormal drop in catalyst temperature.

The present invention will be explained in detail below based on illustrated embodiments.

FIG. 5 is a block diagram showing an embodiment of the present invention.A control unit 6 that calculates the amount of fuel supplied is connected to the output terminal of an air flow meter 7 installed in the intake passage of the engine. , a voltage corresponding to the engine intake air amount is supplied to the control unit 6 as an air amount signal. In addition, the control unit 6 is supplied with voltage pulses outputted from the ignition coil i, electric power outputted from the battery 9, and engine operation information outputted from various sensors and switches 10, so as to control the control unit 6 according to the engine operation state. The control signal (fuel injection amount) output to the fuel injection valve 11 is optimally controlled. 12 is a wire from the ignition coil 8 to an input terminal A of a fuel increase circuit 140, which will be described later, and 13 is a wire from an output terminal of the fuel increase circuit 14 to the control unit 6.

As shown in FIG. 6, the fuel increase circuit 14 includes a waveform shaping circuit 141 that shapes the ignition pulse a output from the ignition coil 8 into a rectangular pulse b, and a waveform shaping circuit 141 that shapes the frequency of the rectangular pulse b output from the waveform shaping circuit 141. A frequency divider circuit 142 having an N-adic counter or the like that converts 1/H to 1/H, and a frequency that inputs nine rectangular pulses b output from the waveform shaping circuit 141 and outputs nine voltages according to the frequency of the pulses b. - a voltage converter (hereinafter referred to as an F/v converter) 143;
The output of the constant voltage circuit 144 and the output of the F/V converter 143 are supplied to a comparator 145.

Note that the comparator 145 outputs a high level signal when the output voltage of the F/v converter 143 is lower than the output voltage of the constant voltage circuit 144, and conversely outputs a low level signal when the output voltage is higher than the output voltage of the constant voltage circuit 144. Output.

By supplying the output of the frequency dividing circuit 142 and the output of the comparator 145 to the AND circuit 146, when the output of the comparator 145 is at the NO level, the frequency dividing circuit 142
The nine rectangular pulses output from the nine rectangular pulses are supplied to an arithmetic circuit 61 of the control unit 6, and the output of this arithmetic circuit 61 is supplied to an injection valve drive circuit 62 as a fuel increase signal. It is needless to mention in detail that the arithmetic circuit 61 is provided with an injection pulse signal e that responds to the injection amount determined according to each machine signal supplied to the control unit 6.

In the above configuration, from the ignition coil 8 to the waveform shaping circuit 1
The ignition pulse a supplied to 41 becomes a rectangular pulse b and is supplied to a frequency dividing circuit 142 and an F/V converter 143. The frequency dividing circuit 142 divides the supplied rectangular pulse b into 1/N
is converted into a frequency of 1 and supplied to one input terminal of the AND circuit 146.

Also, the rectangle supplied to the F/v converter 143? (The pulse b is converted into a voltage signal according to the frequency of the pulse, that is, the engine speed, and is output from the constant voltage circuit 144 (set voltage)
is compared with the ratio IIR unit 145.

Only when the output voltage of the F/V converter 143 is lower than the set voltage, the catalyst inlet temperature, which changes depending on the engine speed, is set to a predetermined value (a temperature slightly higher than the temperature at which the conversion rate suddenly decreases). ) and becomes AN only when running.
A high level signal is supplied to the other input terminal of the D circuit 146. Note that the low level signal output from the comparator 145 is grounded. Also, AN
The D circuit 146 outputs the rectangular pulse output from the frequency dividing circuit 142 to the control unit 6 from the B terminal only when a high level signal is output from the comparator 145.

Therefore, just before the engine speed decreases, the catalyst inlet temperature decreases, and the conversion rate of the catalyst decreases, the fuel injection amount is periodically increased and corrected to enrich the A/F. For this reason, a decrease in the catalyst inlet temperature is suppressed, and a deterioration of the conversion rate is prevented. Although the control of the injection amount is facilitated by periodically increasing the amount of fuel, it is also possible to continuously increase the amount of fuel.

Moreover, specifically, A shown in FIGS. 2 to 1@4.

Driving in the A' area and adjusting it to B by increasing the amount.

It is sufficient to prevent deterioration of the conversion rate by operating in the B' region.

Figure 1i7 is a diagram showing changes in catalyst inlet temperature due to changes in engine speed, and a in the diagram indicates the lowest level at which the conversion rate of the catalyst does not deteriorate. Furthermore, the broken line in Figure 7 shows the conventional example.As is clear from this figure, according to the present invention, it is possible to prevent a drop in the catalyst inlet temperature, so that the conversion rate by the catalyst can be maintained at a good level. can. In the figure, b is the average catalyst inlet temperature when the measure according to the present invention is taken.

FIG. 8 shows an embodiment in which the catalyst temperature is detected by a temperature sensor 15. That is, in the above embodiment, the catalyst inlet temperature is indirectly detected from the engine speed detected through the ignition pulse, but when the load increases even when the engine is rotating at low speeds, the catalyst inlet temperature changes. is high, A/F
Even if the catalyst is thin, the conversion rate of the catalyst may not deteriorate.

However, as in the embodiment shown in FIG.
If the catalyst temperature is directly detected, unnecessary fuel increase corrections can be avoided and fuel efficiency can be further improved. 16 is a resistor, and the temperature sensor 15 is composed of a thermistor or the like.

Furthermore, in the m1 example, since the fuel injection pulse signal is obtained based on the ignition pulse, the fuel increase timing cannot necessarily be optimized and a response delay may occur. Therefore, in such a case, as shown in FIG. 9, the output of the comparator 145 is supplied to the one-shot circuit 148, and the output of the one-shot circuit 148 and the output of the AND circuit 146 are
By outputting through the R circuit 147, a response delay in the increase correction can be eliminated, and the margin for the set temperature can be reduced.

In the embodiment shown in FIG. 10, the output of the comparator 145 is supplied to the frequency dividing circuit 142 as a reset signal. Therefore, in this case, the time determined according to the decreasing slope of the catalyst temperature can be used as a margin for the set temperature, so it is possible to increase the amount of fuel just before the conversion rate deteriorates, and similarly, as shown in FIG. As in the example, one-shot circuit 1
By adding 48 and the OR circuit 141, it is possible to start increasing the amount of fuel in a complete cycle immediately before the catalyst temperature decreases.

As explained above, according to the present invention, in addition to the control unit that calculates the fuel supply amount, there is provided a fuel increase circuit that increases and corrects the nine injection amount signals calculated by the control unit, so that the catalyst temperature is lower than a predetermined value. When the vehicle descends, the fuel increase circuit is activated to correct the A/F enrichment, so even when performing lean burn to improve fuel efficiency, deterioration of the catalyst conversion rate is prevented and the exhaust gas is reduced. Deterioration of characteristics is avoided.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a conventional example, Fig. 2 is a relation diagram between A/F and exhaust configuration, Fig. 3 is a relation diagram between A/F and catalyst inlet temperature,
Fig. 4 is a diagram of the relationship between the catalyst inlet l1tL and the conversion rate, Fig. 5 is a block diagram of the configuration of the first embodiment of the present invention, Fig. 6 is a block diagram of the fuel increase circuit, and Fig. 7 is the engine rotation. 8 to 11 are block diagrams of second to fifth embodiments of the fuel increase circuit used in the present invention. 1... Engine 3... Fuel injection valve 5... Catalyst 6... Control unit 1... Air flow meter 8... Ignition coil 14... Fuel increase circuit 15... Temperature sensor patent Applicant: Nissan Motor Co., Ltd. Agent
Patent Attorney Fujio Sasashima Figure 1 7/1 Figure 2 ' Figure 3 Figure 4 ε

Claims (2)

[Claims] (1) Control unit that calculates the amount of fuel supplied based on the intake air amount of the internal combustion engine) 1! : An internal combustion engine equipped with a means for injecting and supplying fuel to an intake system based on the output of a 1 m unit, and an exhaust after-treatment device equipped with a catalyst that detoxifies engine exhaust gas, wherein the temperature of the catalyst is controlled. and a fuel increase means for detecting through the means and increasing the fuel supply amount signal output from the control unit when the engine is operated in a region where the catalyst temperature is below a predetermined value. Air-fuel ratio control device for internal combustion engines. (2) The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the fuel increase correction by the fuel increase means is performed periodically.