JPH01271649A - Device for controlling air-fuel ratio of engine - Google Patents

Abstract

PURPOSE:To improve fuel consumption without sucrificing a traveling property in an engine having a carburetor by carrying out lean-burn control after carrying out control through a theoretic air-fuel ratio in a shifting zone to the lean- burn control. CONSTITUTION:An output signal from an O2 sensor 6 is taken in by a feedback control value setting means 27 to set a feedback control value lambda0. On the other hand, signals from a water temperature sensor 9 and a crank angle sensor 8 are taken in by a lean-burn judging means 28. When the lean-burn judging means 28 judges to be in a lean-burn control condition, a lean burn control value setting means 30 receives the judged signal after a certain time, to make a value in which a correction value alpha is added to a feedback control value theta0 a lean-burn control value lambda1. A certain time after the lean-burn judgment, the lean-burn control value lambda1 is used for a control signal lambda by a switchover means 29.

Description

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

The present invention relates to an air-fuel ratio control device for an automobile engine.

[Conventional technology]

This type of air-fuel ratio control includes a method of feedback controlling the intake air amount of the carburetor based on the value detected by the 02 sensor;
A method of feedback controlling a fuel injection system is known. In conventional air-fuel ratio control systems, lean burn control is used only in low load areas based on the engine speed and intake air volume, but in this case, there is a risk of lean burn even during gentle acceleration, which could worsen driving performance. There is. There are also systems that interrupt lean burn control and perform feedback control due to changes in operating conditions to learn air-fuel ratio deviations, but there is a risk of surges occurring. Therefore, there are systems that execute lean burn control during steady running, such as the air-fuel ratio control system disclosed in Japanese Patent Laid-Open No. 60-13936 or Japanese Patent Laid-Open No. 59-10765.

[Problem to be solved by the invention]

However, the above prior art relates to an injection method, and in the case of a carburetor, lean burn is estimated from a feedback control value based on the output of the 02 sensor during constant speed driving without using a lean burn sensor, and feedback control is performed. If the value is simply held at a predetermined value,
Variations in performance due to manufacturing errors in the carburetor or operating conditions can cause the air-fuel ratio to become unstable, and especially when driving at high altitudes, there is a risk of problems such as engine stoppage due to excessive lean. In addition, there are systems that detect the air-fuel ratio during lean burn control using a lean burn sensor, such as the one published in Japanese Patent Application Laid-open No. 2615/1, and perform feedback control on this, but the lean burn sensor is expensive. It is. The present invention has been made based on the above-mentioned circumstances, and when shifting to lean burn control based on the detection signal from the existing 02 sensor in operational control of an engine having a carburetor, after performing control at the stoichiometric air-fuel ratio in the transition region. The purpose of the present invention is to provide an air-fuel ratio control device for an engine that can improve fuel efficiency without sacrificing drivability by performing lean burn control, and can also correct variations in performance of carburetors, etc.

[Means to solve the problem]

Therefore, in the present invention, the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio by changing the control value of the actuator that varies the mixing state of fuel and air in the carburetor based on the output signal of the 02 sensor. a feedback control value setting means for setting a feedback control value based on the output signal of the sensor; a lean burn determination means for determining constant speed driving based on the rate of change in engine speed and determining lean burn control; and the lean burn determination means for determining lean burn control. Lean burn control value setting means for setting a control value in lean burn from the control value taken in from the feedback control value setting means after performing feedback control a predetermined number of times when lean burn is determined by the lean burn control means; A switching means is provided for switching and outputting a control value from the feedback control value setting means and a control value from the lean burn control value setting means in response to a signal from the burn determination means.

[For production]

Therefore, when performing feedback control of the air-fuel ratio of the carburetor, lean burn control can be performed only when the engine speed is constant, and fuel efficiency can be improved without sacrificing drivability. In addition, since the basic information for lean burn control judgment is obtained only by the engine speed sensor, there is no need to prepare expensive special sensors such as lean burn sensors.Furthermore, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio after a certain speed. Since the control value for inburn control is determined based on the control value during feedback control, it is not affected by variations in carburetor performance.

【Example】

Embodiments of the present invention will be specifically described below with reference to the drawings. Referring to FIG. 1, a carburetor and its air-fuel ratio control system will be explained. Reference numeral 1 denotes a carburetor main body, which has a venturi 3 upstream of a primary air-fuel mixture road 2 and a throttle valve 4 downstream. The main fuel passage 6 from the bottom of the float chamber 5 is connected to a main air bleed 8 with a main jet 7.
A main nozzle 9 communicates with the venturi 3 from this main air bleed 8. Main fuel passage 6
There is a slow jet 12 equipped with a slow air bleed 11 in the slow fuel passage 1o that branches off from the middle of the throttle valve, and furthermore, the slow fuel passage 10 has a bypass port 13 immediately upstream of the throttle valve fully open position and an idle boat 1 downstream thereof.
4, and sucks out fuel while mixing air in the main and slow systems. As an air-fuel ratio control system, a float chamber 5 and a main fuel passage 6
A fuel passage 15 is provided in a bypass manner between the main air bleed 81PI and the main air bleed 81PI, and a control jet 16 is installed in the middle of this fuel passage 15. In addition, the slow fuel passage 10
An air passage 17 communicates with the downstream side of the slow jet 12, and a control air bleed 1 is connected in the middle of this air passage 17.
8 will be installed. And the valve body 16a of the control jet 16
and the valve body 18a of the control air bleed 18 are connected to the common rod 1.
9, and the control jet 16 and control air bleed 18 are controlled by turning on and off the solenoid 20 as an actuator.
One side is closed and the other side is opened. Here, for example, when the solenoid 20 is turned off, the rod 19 is moved upward by the spring force, the control air bleed 18 is closed, and the control jet 16 is opened, thereby reducing air and increasing fuel to make it rich. On the other hand, when the solenoid 20 is turned on, the air is increased and the fuel is decreased to make the engine lean, thereby setting the air-fuel ratio on the lean side where the on-duty ratio of the solenoid 20 is large. On the other hand, a three-way catalyst 22 is installed in the exhaust system of the engine body 21, and a signal from the 02 sensor 23 is sent to the control unit 24.
Enter. In addition, signals such as engine speed from the crank angle sensor 25 and water temperature from the water temperature sensor 26 are input to the control unit 24.
The duty signal is input to the solenoid 20. Figure 2 shows the control unit 2 for air-fuel ratio control.
FIG. 4 is a block diagram structurally showing the functions of No. 4; Here, the output signal of the 02 sensor 23 is taken into the feedback control value setting means 27, where a feedback control value λ0 (for example, duty ratio) is set by calculation. On the other hand, signals from the water temperature sensor 26 and the crank angle sensor 25 are taken into the lean burn determining means 28. Here, it is determined whether the water temperature is at least a predetermined value (warm-up has been completed), and it is also determined whether the engine speed is within a predetermined speed. When this same condition is satisfied, the engine speed at that time does not change by more than a predetermined value (the vehicle is in a constant speed running state), and it is determined that the lean burn control is in a condition. The output signal from the feedback control value setting means 27 is supplied to the switching means 29 and also to the lean burn control value setting means 30. The lean burn control value setting means 30 receives a determination signal after a predetermined period of time when the lean burn determination means 28 determines that the lean burn control condition is met. Based on this determination signal, the output signal from the feedback control value setting means 27 at that time, that is, the feedback control value λ0, is stored, and then the value obtained by adding the correction value α to the stored feedback control value λ0 is used for lean burn. The control value λ1 (for example, duty ratio) is set as the control value λ1 (eg, duty ratio). The switching means 29 uses the lean burn control value λ1 determined by the lean burn control value setting means 30 as the control signal λ after a predetermined period of time when the lean burn determination means 28 makes a lean burn determination. If lean burn is not determined, the feedback control value λ0 from the feedback control value setting means 27 is used as the control signal λ to drive the actuator 13 via the drive circuit 31. In this way, lean burn control can be achieved only in a predetermined rotational range and in a steady running state, so fuel efficiency can be improved without sacrificing running performance. Furthermore, even if there is variation in the performance of the carburetor 1, the lean burn control value setting means 30 calculates the lean burn control value based on the feedback control value, so that the lean burn control value is substantially corrected. It does not affect fuel ratio control, nor does it require expensive lean burn sensors. In order to realize such air-fuel ratio control, the control unit 24 performs arithmetic processing according to chart 70 as shown in FIG. Tw >
If the 0 condition determined by Tw 1 is satisfied, step 51
03, enter the engine speed N, and proceed to step 5.
Comparison with set rotation speed N1 and N2 at 104, N2>
Based on N>N1, it is determined whether or not the rotation speed is within a predetermined rotation speed range. If it is in the predetermined rotation speed region, step 5105
, and determines whether the timer is in the reset state (lean burn determination starting point). The timer is TIME=O
If so, the process moves to step 8106 to start a timer, and in step 5107 the engine speed N is stored as a comparison value NO. If the timer has already started, it is not TIME=O, so the process moves to step 8108 and compares whether TIME≧t (t is a predetermined time). If the predetermined time has not elapsed, the maximum value NH of N is determined in step 8118, and the process proceeds to step 8116.
Feedback control is continued based on the output of the second sensor 23, and a flag is further set to 1 in step 5117. If the predetermined time has elapsed, the timer is reset in the next step 5109, and in step 5110, the maximum engine rotation speed N14 for that period and the previously stored comparison value N are calculated.
o (ΔN=lNH−Nol) and compares it with a preset value ΔN1 in the next step 5111. Here, ΔN1 is set to a value that takes into account an error in engine rotational speed in a steady running state. And ΔN ΔN1
If it is determined in step 5112 that the vehicle is in a constant speed running state, it is determined in step 5112 whether flag F is 1 or not. Since the flag F is set to F=1 when feedback control is performed based on the output of the 02 sensor, F=1 at the start of lean burn control, so the process moves to step 5113. Here, the feedback control value λ0 based on the output of the 02 sensor is stored as the lean burn control value λ1 as the first lean burn control value. And step 511
4, the flag F is set to F=O. If this is the second or subsequent program execution after the lean burn control determination, then (
If lean burn control is already in progress), since F=O, the determination in step 5112 results in step 5115.
Here, the lean burn control value λ1 is λ0+
It is calculated as α (α is a predetermined correction value for the lean burn side). The water temperature Tw is TV≦Tw1, or the engine speed N is N≧N2, N≦N1, and furthermore, ΔN≧Δ
If it is N1, it is out of lean burn control, so the process moves to steps 3102, 5104, 3111 to 5116, and the drive circuit 31 is driven based on the feedback control value λ0 based on the output of the 02 sensor. In step 5117, the flag F is set to F=1.

【Effect of the invention】

As described in detail above, the present invention detects the appropriate timing for lean burn control from detection signals from existing sensors in the operation control of an engine having a carburetor, and performs lean burn control without sacrificing running performance. It is possible to improve fuel efficiency without having to do this, correct for variations in performance of the carburetor, etc., and have the effect of not affecting control.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, FIG. 2 is a block diagram of air-fuel ratio control by a control unit,
FIG. 3 is a flowchart of the air-fuel ratio control. 1... Carburetor body, 20... Solenoid, 23...
・02 sensor, 24...control unit, 27
. . . Feedback control value setting means, 28 . . . Lean burn judgment means, 29 . . . Switching means, 30 . . . Lean burn control value setting means.

Claims (1)

[Claims] Based on the output signal of the O_2 sensor, the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio by changing the control value of the actuator that varies the mixing state of fuel and air in the carburetor based on the output signal of the O_2 sensor. A feedback control value setting means for setting a feedback control value, a lean burn determination means for determining constant speed driving based on a rate of change in engine speed and determining lean burn control, and a lean burn determination by the lean burn determination means. After performing feedback control a predetermined number of times,
Lean burn control value setting means sets a control value in lean burn from the control value taken in from the feedback control value setting means, and the control value from the feedback control value setting means and lean 1. An air-fuel ratio control device for an engine, comprising switching means for switching and outputting a control value from a burn control value setting means.