JPS62206252A - Air-fuel ratio feedback controlling device for carburetor engine - Google Patents

Abstract

PURPOSE:To maintain the optimum air-fuel ratio at the time of idling by controlling the mixture ratio regulating actuator of a carburetor when idling based on a pulse signal which is outputted from an air-fuel ratio sensor provided on an exhaust system into which a secondary air is introduced. CONSTITUTION:A secondary air introducing pipe 28 which is controlled in its opening and closing by means of a secondary air introducing valve 30 having a reed valve 30A, is connected to an exhaust manifold 20. At the time of idling, a negative pressure from a throttle port 12A is introduced into the secondary air introducing valve 30 and opens the valve 30. An air-fuel ratio sensor 22 is provided on the lower course of the secondary air introducing pipe 28 and, based on a pulse signal generated at the time of idling, an electronic control unit 42 controls the bleed control valve 44 of a carburetor.

Description

[Detailed description of the invention] [Industrial application field]

The present invention provides air-fuel ratio feedback 1l for carburetor engines.
113 control device, particularly suitable for use in adjusting the air-fuel ratio at idle to a desired air-fuel ratio in an automobile carburetor engine equipped with a system for supplying secondary air to the exhaust system. The air-fuel ratio of the exhaust system is detected by an air-fuel ratio sensor, and the mixture ratio of the carburetor is adjusted according to the detected air-fuel ratio.
4′! The present invention relates to an improvement in an air-fuel ratio feedback control device for a carburetor engine that performs feedback control of the air-fuel ratio of an air-fuel mixture by controlling an II actuator.

[Conventional technology]

In a carburetor engine that has an air-fuel ratio (A/F) feedback control device using an air-fuel ratio sensor (hereinafter referred to as 02 sensor), for example, when the engine is idling, the input of the feedback signal is stopped and the exhaust gas is controlled. A method of supplying secondary air to the system may be used. With this secondary air supply system, the basic air-fuel ratio (carb base A/F) set in the carburetor can be set richer than the stoichiometric air-fuel ratio, so smooth idling operation can be maintained. It has the excellent advantage that sufficient exhaust gas purification performance can be obtained even with low catalyst quality by supplying air. By the way, the secondary air supply system employing the above-mentioned secondary air supply method uses a secondary air supply system having a secondary air introduction valve 30 as shown in FIG. A nine-person device (air suction system) is used. When using the secondary air introduction device in this way, the characteristics of the secondary air introduction ffi (ASri) with respect to the idle speed are as follows:
For example, as shown in FIG. 4, peaks and valleys occur at a certain idle speed. At this time, if the idle speed of the engine is stable, the amount of secondary air introduced can be stabilized at its peak value (7. There are cases where the idle speed fluctuates and the engine is operated in the valley shown in Figure 4. In this case, consider the variations shown in Figure 5 caused by manufacturing tolerances of the carburetor, etc. As a result, the air-fuel ratio of the exhaust gas may drop to nearly 14.6, reducing the purification performance of the catalytic converter into which the exhaust gas is introduced, and making H2S more likely to occur. This is because the air-fuel ratio pulsates, as shown in FIG. 6(A), for example, so there is always a momentary period of 11 in which the air-fuel ratio changes to the rich side. When pulsating, the output signal of the 02 Senna becomes a pulse signal, for example as shown in FIG.
4.6>, this is because the signal is no longer output from the 02 sensor when the actual air-fuel ratio of the exhaust gas becomes lean. In this way, when the output signal of the 02 sensor becomes pulse-like,
Since it is difficult to control the carburetor to follow it, feedback control of the air-fuel ratio is usually not performed during idling, and the air-fuel ratio of the exhaust gas is controlled by the secondary air introduction device.
It was in order.

[Problems to be Solved by the Invention] However, in general, the air-fuel ratio at idle is 1!, considering exhaust gas and idle stability! [! The best value is a range slightly richer than the stoichiometric fuel ratio (for example, 13°5-14), and the air-fuel ratio is
In addition to variations due to ffi tolerances, it is also affected by the properties of the fuel used and the ambient temperature, and considering that it generally changes in the rich direction, it is necessary to always keep the air-fuel ratio at idle at the best value with the secondary air introduction device. Having an accent had the problem of being extremely difficult. (Object of the Invention) The present invention has been made in view of the above-mentioned conventional problems, and provides a carburetor engine capable of finely feedback controlling the air-fuel ratio even during idling operation. An object of the present invention is to provide an air-fuel ratio feedback control device. By controlling the mixture ratio adjustment actuator of the carburetor according to the air-fuel ratio,
In support of air-fuel ratio feedback control of a carburetor engine in which the air-fuel ratio of the air-fuel mixture is feedback-controlled, means for detecting a pulse signal output from an air-fuel ratio sensor in accordance with pulsations in the air-fuel ratio of the exhaust system during idling operation; The above object has been achieved by comprising means for processing a detection pulse signal and controlling the mixture ratio W4 adjustment actuator during idle operation based on the processed signal. [Operation] For example, as shown in FIG. 6 above, during idling, the output signal of the air-fuel ratio sensor, for example, the o2 sensor ().
The leaner the air-fuel ratio is, the narrower the pulse width becomes.
It is difficult to perform feedback control following the output signal of the air-fuel ratio sensor. Also, as can be understood from the figure, the average air-fuel ratio (symbol A in the figure) is FI! The closer the air-fuel ratio is to 14.6), the wider the pulse width of the output signal of the air-fuel ratio sensor becomes. Therefore, the inventor focused on the pulse width of this output (t-port) and found that it is possible to roughly determine the average value of the air-fuel ratio at idle based on the pulse signal of the air-fuel ratio sensor output. This invention has been made based on the above findings, and has the following effects.In the present invention, the pulse signal output from the air-fuel ratio sensor in accordance with the change in the air-fuel ratio of the exhaust system is processed, The actuator for the mixture ratio WA'M! is controlled based on the FI! signal. Therefore, the air-fuel ratio of the exhaust gas can be precisely feedback-controlled even during idling, so the average air-fuel ratio during idling can be controlled with good stability. Things can be controlled.

【Example】

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an air-fuel ratio feedback control system for a carburetor engine according to the present invention will be described in detail with reference to the drawings. The carburetor engine to which this embodiment is applied is constructed as shown in FIG. That is, this carburetor engine 10 is equipped with a two-barrel carburetor 12. This carburetor 12 is equipped with a primary throttle valve 14 that rotates in conjunction with an accelerator pedal (not shown). The opening degree of the primary throttle valve 14 is detected by a throttle switch 16. Although not shown in FIG. 2, the carburetor 512 mainly includes a low-speed system t8 that supplies fuel during low-speed rotation, a main system that supplies fuel during normal times, and a system in which the primary throttle valve 14 is opened at a predetermined time. A secondary system may be provided that includes a secondary throttle valve that is opened in conjunction with the secondary throttle valve when the load is high. An intake manifold 18 is connected downstream of the carburetor 12 . A negative pressure switch 19 is connected to the intake manifold 18, which operates in response to intake pipe negative pressure. The air-fuel mixture formed in the carburetor 12 and taken into the main body of the engine 10 via the intake manifold 18 is combusted in a combustion chamber (not shown) and becomes D1 gas. An exhaust manifold 20 is provided to collect this exhaust gas. On the downstream side of the collecting part of the exhaust manifold 20, there is 1! of residual oxygen in the exhaust gas! LY2 elemental temperature sensor (hereinafter referred to as 02 sensor) for detecting the air-fuel ratio of the exhaust system from
22 are provided. An IA trachea 24 is connected to the downstream side of the exhaust manifold 20, and a three-way catalytic converter 26, for example, is connected to the downstream side of the exhaust f:I24. A secondary air introduction valve (hereinafter referred to as ASV) 30 is connected to the exhaust manifold 20 via a secondary air introduction pipe 28. This ASV30 has a reed valve of 30A.
For example, secondary air introduced from an air cleaner (not shown) through a secondary air pipe 32 is introduced into the exhaust manifold 20 using exhaust pulsation. The diaphragm chamber 30B of the ASV 30 is connected to a throttle port 12A formed immediately below the fully open position of the primary throttle valve 14 of the carburetor 12 via a negative pressure delay valve (hereinafter referred to as VTV) 34. The VTV 34 includes a throttle 34A and a return valve 34B, and has the function of delaying the negative pressure transmitted from the throttle port 12A to the diaphragm chamber 30B side of the ASV 30. This VTV 34 is used mainly during deceleration or idling when the primary throttle valve 14 is fully open and negative pressure is generated in the throttle port 12A.
It has the function of delaying the transmission of negative pressure to the diaphragm chamber 30B of the ASV 30 and allowing secondary air to pass through the ASV 30. The output negative pressure of the VTV 34 is also transmitted to the diaphragm chamber 36A of the throttle positioner 36. This throttle positioner 36 mainly has the function of reducing the closing speed of the primary throttle valve 14 during deceleration to prevent afterfire. A rotational speed signal from a rotational speed sensor 39 disposed on the destroyer 38, an output of one of the negative pressure switches, an output of the throttle switch 16, an output of the 02 sensor 22, and a water temperature switch disposed on the main body of the engine 10. 40
The output and the like are input to an electronic control unit (hereinafter referred to as ECU) 42, where various processes are performed to form, for example, a feedback control l signal. This ECU4
For example, the bleed control valve (hereinafter referred to as EBCV) is controlled by the feedback control signal obtained in step 2.
44 is driven, and by changing the air bleed to the carburetor 12, the air-fuel ratio is feedback-controlled. For example, when the ECU 42 uses an analog circuit,
It is constructed as shown in detail in FIG. That is, the output signal of the 02 sensor 22 passes through the input buffer amplifier 142A, and is converted by the comparator 42B into 1 for the rich signal R and 0 for the lean signal. The conversion signal is sent to the OR circuit 42
8 and is input to the feedback circuit 42G. The feedback circuit 42G creates a feedback control signal that follows the input signal, and the created division signal is input to the output circuit 42E via a gate circuit 420 that is turned on during feedback lit control. The output circuit 42E drives the EBCV 44 by turning on and off the output transistor 42F, for example.
Feedback 11 control is performed.゛During the feedback control in which the gate circuit 42D is turned on, the product switch 40. Negative pressure switch 1
9, and the output of high rotation detection comparator 42L are all 1.
Then, it is assumed that the feedback condition has been established, and at this time, the gate circuit 42D is turned on by the output signal from the AND circuit 420, and feedback control is performed. Note that the signal input to the high rotation detection comparator 421 is the engine rotation speed Ne obtained by inputting the output of the rotation speed sensor 39 into a frequency-voltage conversion (hereinafter referred to as F-V conversion) circuit 42J and converting it into a voltage signal. The high rotation detection comparator 42 outputs 1 when the engine rotation @No is smaller than the setting 1iT]N2. Further, a low rotation detection comparator 42K that outputs 1 when the engine rotation speed Ne is larger than a set value N1 is connected to the F-V conversion circuit 42J. By the way, at idle, the signal output from the 02 sensor 22 is a narrow pulse-like signal (rich pulse signal) as shown in FIG. 6, so the feedback circuit 42C follows that signal. It is a turnaround to perform feedback control. Therefore, an AND circuit 42U inputs the output signal of the throttle switch 16 and the output signal of the low rotation detection comparator 42 to the inverting input terminal, respectively, and a monostable circuit 42T is configured to operate only when idling by the output of the BAND circuit 42U. is connected between the comparator 42B and the OR circuit 423. This monostable circuit 42T is connected to the pulse 4fj PI detected during idle as described above.
By converting the signal into a signal with a desired pulse width and inputting it to the feedback circuit 42G via the OR circuit 428,
This allows feedback control to be performed in the same way as normal even when the vehicle is idling. In this 19th case, the air-fuel ratio can be controlled to a desired idle air-fuel ratio by appropriately selecting the monostable pulse width of the monostable circuit 42T. Note that 42V in FIG. 1 is the feedback memory value that is set by opening the gate circuit 42W when the throttle switch 16 is off, that is, when the throttle switch 16 is idling, in order to prevent the memory value in the feedback circuit 42 from being destroyed during idling and deceleration. It is a memory circuit that stores . Next, regarding the second embodiment in which a microcomputer is used for the ECLI 42 and feedback control is performed by a routine stored in its software, the third embodiment will be described.
The explanation will be given according to the flowchart shown in the figure. First, in step 100, six signals of the water temperature switch 40, one negative pressure switch, and the throttle switch 16 are read, and in step 110, it is determined from the read signals whether the engine is @I11 or not. If the determination result is negative, the process proceeds to a cold processing routine (not shown) to warm up the engine. On the other hand, if the determination result is positive, the process proceeds to step 120, and it is determined from the read output 1B red of the throttle switch 16 whether or not the engine is in an idle state. If the determination result is negative and the tapping is not in the idle state, the routine proceeds to a routine for performing feedback control processing in order to perform normal feedback processing. On the other hand, if the determination result is positive, the process proceeds to step 130, where the output signal of the 02 sensor 22 is read, and in step 140, it is determined from the read signal whether or not the air-fuel ratio is rich. When the determination result is positive, that is, the air-fuel ratio is on the rich side, the width T of the output pulse (rich pulse) of the 02 sensor 22
Calculate. Next, in step 160, a current for driving the EBCV 44 is determined in proportion to the calculated pulse width T, and the EBCV 44 is controlled by this driving current,
This routine is performed again from step 100. On the other hand, if the determination result in the previous step 140 is negative, the process proceeds to step 170, maintains the drive current of the EBCV 44 determined last time, controls the EBCV 44, and ends this routine. In the embodiment described above, the rich pulse of the O2 sensor 22, which is generated due to the pulsation of the air-fuel ratio (A/F) when secondary air is supplied to the exhaust system, is used to accurately determine the average air-fuel ratio at idle. Can be well controlled. In the above embodiment, feedback control was performed using the analog circuit shown in FIG. 1 or the flowchart shown in FIG. It is obvious that the present invention is not limited to this embodiment and can be applied to feedback control using other analog circuits and flowcharts. Further, in the above embodiment, the EBCV4/I was used as the actuator for adjusting the mixture ratio of the carburetor, but the scope of application of the present invention is not limited to this, and other actuators for adjusting the mixture ratio may be used. Obviously, it is equally applicable to carburetor engines.

【Effect of the invention】

As described above, according to the present invention, it is possible to perform feedback control of the air-fuel ratio of exhaust gas during idling operation using a pulse signal output from an air-fuel ratio sensor. Therefore, the air-fuel ratio can be set to the desired air-fuel ratio even in the valley characteristic where little secondary air is introduced as shown in FIG. 4 above.
Since the average air-fuel ratio during idling can be stabilized, the generation of 11c, Co, and H2S in exhaust gas can be reduced. Furthermore, since the control point of the air-fuel ratio can be controlled to be slightly richer than 14.6, engine idle stability is improved. Furthermore, since the air-fuel ratio can be controlled to the lean side without supplying a large amount of secondary air, for example, the secondary air 3? It is possible to reduce costs by reducing the capacity and size of P immigration pipes and ASVs. In addition, even if there are variations in accuracy of the carburetor, for example, the upper and lower limits at which the idle air-fuel ratio can be controlled can be set widely, making it possible to loosen the accuracy control of the carburetor, which improves productivity. have an effect.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the main components of an electronic control unit used in an embodiment of the air-fuel ratio feedback control device for a carburetor engine according to the present invention, and FIG. 3 is a sectional view including a partial block diagram, and FIG. 3 is a flowchart showing a routine programmed in the electronic control unit to explain the operation of another embodiment of the present invention. The four causes are polygraphs showing an example of secondary air introduction m with respect to the idle speed, Figure 5 is a polygraph showing an example of variations in the air-fuel ratio at idle due to manufacturing variations in carburetors, and Figure 6 is a polygraph showing an example of secondary air introduction m with respect to the idle rotation speed. FIG. 4 is a diagram showing an example of the relationship between the instantaneous value of the air-fuel ratio at the valley of the air supply system and the output signal of 02 centigrade. 10...engine, 12...carburizer, 16...throttle switch, 19...9 pressure switch, 22...oxygen 111! I(02) sensor, 40...
Water temperature switch, 42...Electronic control unit (ECU), 42B...
Comparator, 42G...Feedback circuit, 42J...Frequency-voltage (F-V)! J9! circuit, 4
2K...Low rotation detection comparator, /12Q142U
...AND circuit, 428...OR circuit, 42T...monostable circuit.

Claims (1)

[Claims] (1) The air-fuel ratio of the exhaust system into which secondary air is introduced is detected by an air-fuel ratio sensor, and the mixture ratio adjustment actuator of the carburetor is controlled according to the detected air-fuel ratio. An air-fuel ratio feedback control device for a carburetor engine that performs feedback control of a fuel ratio, comprising means for detecting a pulse signal output from an air-fuel ratio sensor in response to pulsations in the air-fuel ratio of the exhaust system during idling operation; and a detection pulse signal. An air-fuel ratio feedback control device for a carburetor engine, comprising: means for processing the mixture ratio adjusting actuator during idle operation based on the processed signal.