JPS6255447A - Air-fuel ratio feedback control device for carburetor engine - Google Patents

Abstract

PURPOSE:To enhance the follow-up capability at the time of a high load by making the lean side integration constant of the integration circuit of an air-fuel ratio feedback control device at the time of high load larger than that at the time of partial load until the first lean signal is detected. CONSTITUTION:In an engine equipped with a carburetor, the output signal of an O2 sensor 22 is entered into a comparator 42B via a preamplifier 42A, and further the output signal of the comparator is entered into an integration circuit 42C. In parallel with the resistance R1 of the lean side integration circuit in the integration circuit 42C, a series circuit of a resistance R2 and a gate switch G1 is connected. And, when a high load is detected by a negative pressure switch 19, the gate switch G1 is opened to increase the lean side integration constant Kl. Thus, the follow-up delay at the time of a high load can be economically eliminated.

Description

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

The present invention relates to an air-fuel ratio feedback control device for a carburetor engine, and in particular, an air-fuel ratio feedback control device for detecting the air-fuel ratio of the engine, which is suitable for use in a carburetor engine equipped with an output increasing FFI mechanism such as a power valve or a secondary valve. a fuel ratio sensor; a control circuit that performs at least integral processing on an output signal of the air-fuel ratio sensor to form an air-fuel ratio feedback control I signal;
The present invention relates to an improvement in an air-fuel ratio feedback control device for a carburetor engine, which includes an actuator that controls the air-fuel ratio based on the control signal, and an output increase ffi 131 structure.

[Conventional technology]

an air-fuel ratio sensor that detects the air-fuel ratio of the engine; a control circuit that performs at least integral processing on the output signal of the air-fuel ratio sensor to form an air-fuel ratio feedback control signal; and an actuator that controls the air-fuel ratio based on the control signal. An air-fuel ratio feedback control device for a carburetor engine is known. In the feedback control circuit of such a feedback control device, the output signal of the air-fuel ratio sensor is processed using a skip ff1Rs, a lean integral constant KA, and a rich integral constant 1(r) as shown in FIG. As a result, a feedback control signal V' is formed. Here, each of the constants is set to an appropriate value in consideration of the controllability of the air-fuel ratio, that is, the purification rate and drivability.

[Problems to be Solved by the Invention] However, in reality, there are restrictions to suppress surging at light loads, so output increasing mechanisms such as power valves and secondary valves are used during high loads. As shown by the broken line A in Figure 6, the base air-fuel ratio (A/F) becomes rich, the feedback m becomes insufficient, and the control air-fuel ratio transiently shifts to the rich side, as shown by the solid line B in Figure 6. It was inevitable that the situation would fluctuate. Therefore, HC, Co
This has caused problems such as the emission of harmful components such as, and deterioration of fuel efficiency. In FIG. 6, vAC indicates the air-fuel ratio when dilution is performed by introducing secondary air during feedback stop, such as during deceleration or idling. On the other hand, when the output increment mechanism such as the power valve or secondary valve becomes inactive, it becomes overcompensated immediately after returning to light load operation, causing the control air-fuel ratio to fluctuate toward the lean side. . Therefore, in this case, there have been problems in that the harmful component Nox is released, and the lean engine also reduces drivability and causes breath surging. In order to solve these problems, the idea is to introduce a microcomputer, divide the engine operating state into a data map, and program the optimal constants (R3, KA, Kr) for each data area. It will be done. However, if a microcomputer is used, the system needs to be upgraded and the cost will increase significantly, so unless the microcomputer is used for multiple purposes such as an electronically controlled fuel injection engine for comprehensive control of the engine, the cost will be particularly high. This is not really a solution for a carburetor engine that cannot be applied much. Furthermore, as something similar to the present invention, Japanese Patent Application Laid-Open No. 52-110
332 detects acceleration or deceleration and causes the integral circuit of the feedback control circuit to charge or discharge a certain amount of charge in the direction in which the air-fuel ratio is expected to change during a certain period of time, thereby skipping ff1R3. It is proposed to change. If this method is used, a certain amount of correction can be added to the feedback control signal Vf at high loads.
A certain degree of effectiveness can be expected by configuring a circuit that subtracts (discharges) when the load returns from a high load to a light load. However, this method has a problem in that it is difficult to adapt to various driving modes because the correction width is fixed. In order to solve such problems,
Although it is conceivable to perform the correction width in multiple passes, it is obvious that the circuit configuration becomes more complex and the cost increases. OBJECT OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and economically solves the follow-up delay at high loads in the simple feedback control circuit used in the conventional carburetor engine. Therefore, an object of the present invention is to provide an air-fuel ratio feedback control device for a carburetor engine that can improve exhaust purification efficiency and fuel efficiency without impairing drivability.

[Means to solve the problem]

The present invention provides an air-fuel ratio sensor that detects an air-fuel ratio of an engine, a control circuit that performs at least integral processing on an output signal of the air-fuel ratio sensor to form an air-fuel ratio feedback control signal, and In the air-fuel ratio feedback control device for a carburetor engine, the air-fuel ratio feedback control device includes an actuator for controlling the engine, and an output increase mechanism, and a means for detecting that the engine load is high; The above-mentioned object is achieved by including means for making the lean-side integral constant for feedback control larger than at partial load. Further, in an embodiment of the present invention, the high load detection means is a negative pressure switch that is activated by detecting intake pipe negative pressure. Further, in another embodiment of the present invention, the high load detection means includes:
The operation of the output increasing mechanism is detected. Further, in another embodiment of the present invention, at the time of the high load, the lean side integral constant is changed and the feedback control signal up to that point is stored, and when the partial load returns, the control is restarted from the stored value. It was designed to do so.

[Effect]

The present invention includes an air-fuel ratio sensor that detects the air-fuel ratio of the engine, a control circuit that performs at least integral processing on the output signal of the air-fuel ratio sensor to form an air-fuel ratio feedback control signal, and During air-fuel ratio feedback control of a carburetor engine equipped with an actuator that controls the fuel ratio and an output increase mechanism, the first lean signal is generated during high load when the output increase mechanism makes the base air-fuel ratio richer than at partial load. The lean-side integral constant for feedback control is set to be larger than that at partial load until . Therefore, the time required to reach the target air-fuel ratio is shortened, feedback controllability is improved, and the follow-up delay at high angle loads in the simple feedback control circuit used in conventional carburetor engines can be solved in a timely manner. This makes it possible to improve exhaust purification efficiency and fuel efficiency without impairing drivability. Furthermore, when the high load detection means is a negative pressure switch that is operated by detecting the intake pipe negative pressure, the high load detection means can be constructed at low cost. Further, if the high load detection means is configured to detect the operation of the output increasing FFI mechanism, a separate switch or sensor is not required. In addition, when the lean-side integral constant is changed during the high load, the previous wave pack control signal is memorized, and when the partial load returns, the control is restarted from the memorized value. , it is possible to quickly return to the original feedback control state and prevent over lean. [Example] Referring to the drawings, an example of the air-fuel ratio feedback control system for a carburetor engine according to the present invention will be described in detail in (2) below. The overall configuration of the carburetor engine to which this embodiment is applied is as follows.
As shown in the figure, this carburetor engine has a carburetor 12 (1) δ. The carburetor 12 is equipped with an output increaser ff1tJ structure (not shown) such as a throttle valve 14 that rotates in motion with an accelerator pedal (not shown), a power valve, and a secondary valve. The opening degree of the throttle valve 14 is determined by the throttle switch 1.
6 has been detected. An intake manifold 18 is connected downstream of the carburetor 12 . One negative pressure switch 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 sucked into the engine body 10 via the intake manifold 18 is combusted in a combustion chamber (not shown I8) and becomes exhaust 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 a residual amount of residual R in the exhaust gas. An oxygen concentration sensor (hereinafter referred to as 02 sensor) 22 is provided to detect the air-fuel ratio from time to time. An exhaust pipe 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 pipe 24. A secondary air introduction valve 30 is connected to the exhaust manifold 20 via a secondary air introduction pipe 28. This secondary air introduction valve 30 is equipped with a reed valve 30A, and the secondary air introduced from, for example, an air cleaner (I!5 in the figure) through the secondary air introduction pipe 32 utilizes the pulsation of exhaust gas. and is introduced into the exhaust manifold 20. The diaphragm chamber 30B of the secondary air introduction valve 30 is connected to the throttle valve 14 of the carburetor 12 via the negative pressure delay valve 34.
It is connected to an idle boat 12A formed directly below the fully open position. The negative pressure delay valve 34 includes a throttle 34A and a check valve 34B, and is connected to the secondary air introduction valve 30 from the idle boat 12A.
It has the effect of delaying the negative pressure transmitted to the diaphragm chamber 30B side. This negative pressure delay valve 34 applies negative pressure to the diaphragm chamber 30B of the secondary air introduction valve 30 mainly during deceleration or idling when the throttle valve 14 is fully closed and negative pressure is generated in the idle boat 12A. It has the effect of allowing the secondary air to pass through the secondary air introduction valve 30 by transmitting the information with a delay. The output negative pressure of the negative pressure delay valve 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 throttle valve 14 during deceleration to prevent afterfire. The primary ignition voltage from the destroyer 38, the output of the negative pressure switch 19, the output of the throttle switch 16, the output of the O2 sensor 22, the output of the water temperature switch 40 disposed in the engine body 10, etc. are controlled by an electronic control unit. (hereinafter referred to as ECU) 42, where various processes are performed to form, for example, a feedback control signal Vf. For example, the bleed control valve 44 is driven by the feedback control signal Vf determined by this ECtJ42, and the air-fuel ratio is feedback-controlled by changing the air bleed (2) to the carburetor 12. The ECU 42 is configured as shown in detail in FIG. That is, the output signal of the 02 sensor 22 passes through a preamplifier 42A and is converted into a rich signal "1" and a lean signal 110" by a comparator 42B. In response to this, the integral circuit 42G skips ff1Rs, and lean side integral constant fiK! , a rich-side integral constant Kr is set. In addition, in FIG. 1, only the integral circuit with the lean side integral constant is shown. When the intake pipe negative pressure in the intake manifold 18 becomes lower than a predetermined value (when the load becomes high), the negative pressure switch 19 is turned off, the switching circuit 42D is also turned off, and the output of the OR circuit 42E becomes 1''. Then, the gate switch G1 is turned on and the resistor R2 is connected to the integrating circuit 42C. Therefore, the integrating chamber RKA of the integrating circuit 42C is as follows (
1) It becomes a large value shown by the formula. K℃-1/ ((R1//R2) C) ... (1
) Here, R+ and C are a resistor and a capacitor, respectively, built into the integrating circuit 42G. Conversely, when the intake pipe negative pressure becomes higher than a predetermined value (partial load), the gate switch G1 is turned off, the resistor R2 is disconnected, and the integral constant of the integrating circuit 42G becomes as follows. This is a small value shown in equation (2). KJ=1/R+C...(2) In this way, λ can be switched to the lean integration constant depending on the load, and the set value of one negative pressure switch can be used to control the operation of the power valve and secondary valve of the carburetor 12. If they are selected to be interlocked, feedback control can be performed using an appropriate integral constant depending on the operating state. When the load is high, at the same time as changing the integral constant KJ2, open the gate switch G2 to stop the memory circuit 42F.
L, , holds the value of the feedback control signal V[ at that time. This occurs immediately after transitioning from high load to partial load.
By turning on the gate switch G3 and transferring the stored value '5Jrm to the integrating circuit 42C, the original feedback state can be quickly returned to prevent over lean. Also, as a feature of this circuit, when the negative pressure switch 19 is off and the output of the comparator 42B is a lean signal, that is, when the feedback control slightly exceeds the target air-fuel ratio, for example 14.6, the lean side integral constant I am trying to return the temperature to its original value. This is because the NAND circuit 42G generates '1' under the above conditions, and the delay circuit 42H
This is achieved by holding a suitable time at , and then opening the gate switch G1 via the OR circuit 42E. This prevents the control air-fuel ratio from running out of control toward the lean side. In this way, when the feedback control according to the present invention is implemented, as shown in FIGS. 3 and 4, the followability during high loads and the controllability when returning to partial load are significantly improved. Note that the NO circuit 42J of the ECU 42 outputs a signal that becomes 1'' when the water temperature switch 40 outputs a predetermined temperature or higher, a signal that becomes 1'' when the throttle switch 16 output exceeds the idle opening, and an ignition 1 signal that outputs the distributor 38. The next voltage is set to a voltage proportional to the engine speed by a frequency-voltage converter circuit (hereinafter referred to as F/V converter circuit) 42K, and a signal that becomes 1'' below a predetermined engine speed by a comparator 42L is used to set the feedback stop condition. In other words, when the logic Fl!fa of the conditions that the engine cooling water temperature is above a predetermined temperature, the throttle opening is above the idle opening, and the engine speed is below a predetermined speed is established, the gate switch G4 is is turned on, and output circuit 4
A control signal is output to the bleed control valve 44 via 2M, and feedback control is executed. On the other hand, for example, during idle when the amount of NOx generated is low, the Goo 1 switch G4 is turned off, feedback control is stopped, and the air-fuel ratio is set to a predetermined value on the richer side than the stoichiometric air-fuel ratio to ensure idle stability. control is performed. In addition, not only when the load is high but also when the feedback control is stopped, the gate switch G is activated by the output of the OR circuit 42N.
2 and G3 are turned on and off, the control signal Vf immediately before the stop of the feedbank control is stored, and when the feedback is restarted, the control is started from the stored value Vfm. In this embodiment, the high angle load detection means is a negative pressure switch f that is activated by detecting the intake pipe negative pressure in the intake manifold 18.
19, the high load detection means is very simple and inexpensive. Note that the configuration of the high load detection means is not limited to this, and it is also possible to detect the operation of a power valve, a secondary valve, etc., for example. In this case, a separate switch or sensor is not required. Furthermore, in this embodiment, in addition to changing the lean-side integral constant KA during high load, the previous feedback control signal Vf is stored, and when returning to partial load, the
IP! Since the control is restarted from the value Vfm, the original feedback control state can be quickly returned for one summer.
It is possible to prevent over lean. Note that when overleaning when returning to the original feedback control state is not a problem, it is also possible to omit storing the feedback control signal. In the above embodiment, the air-fuel ratio control actuator is the bleed control valve 44, but the type of air-fuel ratio control actuator is not limited thereto. Furthermore, in the embodiments described above, the present invention was applied to a carburetor engine in which the secondary air introduction valve 30 was used.
It is clear that the scope of the invention is not limited thereto and is equally applicable to other carburetor engines that do not include a secondary air intake valve. [Effect of R Light] As explained above, according to the present invention, it is possible to shorten the time required to reach the target air-fuel ratio at high load by reducing the time required to reach the target air-fuel ratio by 6. Tracking delays during high loads in the circuit can be solved economically. Therefore, the exhaust purification efficiency can be improved without impairing drivability, and the fuel efficiency can also be improved, which is a significant effect.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an electronic control unit used in an embodiment of an air-fuel ratio feedback control device for a carburetor engine in which the present invention is adopted, and FIG. 2 is a block diagram showing the configuration of an electronic control unit in which the present invention is adopted. FIG. 3 is a block diagram showing the overall configuration of the carburetor engine, and FIG. 4 is a diagram showing an example of the relationship among the negative pressure switch, air-fuel ratio, feedback control signal, and output of the 02 ton sensor in the above embodiment. is an enlarged diagram of the part ■ in Fig. 3, Fig. 5 is a diagram showing feedback control constants used in a conventional air-fuel ratio feedback control device, and Fig. 6 is a diagram showing the air-fuel ratio and feedback in the conventional example. It is a tj diagram showing an example of the relationship between control signals and vehicle speed. 10... Engine body, 12... Carburetor, 19... Negative pressure switch, 22... Oxygen concentration (02) sensor, 42...Electronic control unit (E(jJ), 42C...
・Integrator circuit, 42'F...Memory circuit, G1・
...Gate switch, 44...Bleed control valve, Kβ...Lean side integral constant, Vf...Feedback control signal, ■fm...Feedback control signal memory value.

Claims (4)

[Claims] (1) An air-fuel ratio sensor that detects the air-fuel ratio of the engine; a control circuit that performs at least integral processing on the output signal of the air-fuel ratio sensor to form an air-fuel ratio feedback control signal; In an air-fuel ratio feedback control device for a carburetor engine, which includes an actuator to control and an output increase mechanism, means for detecting that the engine load is high, and when the engine load is high, an initial lean signal is detected. An air-fuel ratio feedback control device for a carburetor engine, comprising: means for making a lean-side integral constant for feedback control larger than at partial load. (2) The air-fuel ratio feedback control device for a carburetor engine according to claim 1, wherein the high load detection means is a negative pressure switch activated by detecting intake pipe negative pressure. (3) The air-fuel ratio feedback control device for a carburetor engine according to claim 1, wherein the high load detection means is configured to detect the operation of the output increase mechanism. (4) When the load is high, the lean integral constant is changed and the previous feedback control signal is memorized, and when the partial load returns, control is resumed from the memorized value. An air-fuel ratio feedback control device for a carburetor engine according to claim 1.