JP2596999B2 - Air-fuel ratio control device for vaporizer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for a carburetor mainly applied to an automobile.

[Prior Art] A three-way catalyst widely used as one of exhaust gas purifying means is contained in exhaust gas unless the air-fuel ratio of an air-fuel mixture is maintained at a value near a stoichiometric air-fuel ratio. CO, HC, NO
All of _x cannot be purified efficiently. Therefore, in an engine having a carburetor, a flow control valve that opens and closes an air bleed passage, an oxygen sensor that detects the oxygen concentration in exhaust gas, and the flow control valve based on a signal from the oxygen sensor are provided. Usually, an air-fuel ratio control device including a feedback control means for opening and closing is provided. The air-fuel ratio of the air-fuel mixture supplied to the engine is adjusted by adjusting the opening of the flow control valve based on the signal from the oxygen sensor and adjusting the amount of air supplied through the air bleed passage. The value is kept near the fuel ratio.

However, if the control speeds of the flow control valves are the same at the time of idling and the time of non-idling, it becomes difficult to perform control suitable for each engine condition. Therefore, as a prior art of the present invention, as shown in, for example, JP-A-58-30445, the control is different from that at the time of opening the throttle valve for opening and closing the flow control valve at a high speed at the time of idling. There is something. That is, in such a device, as shown schematically in FIG. 7, when it is detected by an idle switch or the like that the accelerator is depressed and the throttle valve is opened, the flow control valve is operated at a high speed. Normal feedback control for controlling the air-fuel ratio to be constant by opening and closing is performed. And
When it is detected that the accelerator is released and the throttle valve is at the idle position (idle switch-open), the flow control valve is gradually returned to the control position at the time of idling, and thereafter the flow control valve is moved at a low speed. Few of them perform idle feedback control for opening and closing to control the air-fuel ratio to be constant.

Also, when the engine is in a low-speed / high-load state, such as when climbing a hill, the air bleed passage is temporarily closed by holding the flow control valve fixed to the “closed” side, during which the rich air-fuel mixture is discharged. Some products are supplied to

[Problem to be Solved by the Invention] However, such a configuration tends to cause the following inconvenience. That is, when the accelerator is depressed from the idling state at the time of starting or the like, a large amount of fuel is supplied at a time by the acceleration pump or the main jet, but the supply of air from the air bleed passage tends to be delayed. Becomes rich. After that, the flow control valve is controlled to open to follow, and when the accelerator is returned with the air-fuel mixture approaching the stoichiometric air-fuel ratio, the air-fuel ratio is temporarily set because the flow control valve is open. May become lean, causing the engine speed to drop excessively or cause engine stall.

Further, when the flow control valve is fixedly held at the "closed" side when climbing a hill or the like, the clutch is "disengaged" and the accelerator is returned after climbing the hill. The air-fuel mixture becomes over-rich, and the rough idle is likely to occur, in combination with the fact that the negative pressure rapidly changes to the vacuum side and the fuel in the intake pipe is sucked out.

An object of the present invention is to solve the above problems.

[Means for Solving the Problems] To achieve the above object, the present invention, as shown in FIG. 1, uses an air-fuel ratio control device for a carburetor and an air bleed passage (7) for a carburetor (1). A flow control valve (8) for adjusting the air-fuel ratio of the air-fuel mixture supplied to the engine by opening and closing the engine, an oxygen sensor (15) for detecting the oxygen concentration in the exhaust gas, An idle feedback control means (20) for opening and closing the flow control valve (8) at a low speed to adjust the air-fuel ratio to be constant when the throttle valve (4) is in the idle position based on the signal; 4) When the control returns to the idle position and is in a control state other than the fuel cut at the time of deceleration, the control immediately when the throttle valve is opened is changed to the idle feedback control by the idle feedback control means (20). Characterized in that the made by including an idle control start position a mean value of the control position and for controlling the switching means (21) of said flow control valve (8) with immediately start switch to click control.

[Operation] With this configuration, when the throttle valve (4) is in the open position, predetermined control is performed according to the engine condition. For example, when certain conditions are satisfied, such as when the engine speed after the completion of warm-up is within a predetermined range, the flow control valve (8) is set to a high speed based on a signal from the oxygen sensor (15). , And normal feedback control for adjusting the air-fuel ratio of the air-fuel mixture to a constant value is performed. Alternatively, when climbing a hill or the like where high output is required, control is performed such that the flow control valve (8) is fixedly held at the “closed” side and the air-fuel ratio feedback control is temporarily stopped.

On the other hand, when the throttle valve (4) returns to the idle position and is in a control state other than the fuel cut at the time of deceleration, the control switching means (21) immediately changes the control at the time of opening the throttle valve to the idle feedback control means (20). ), The control immediately starts after switching to the idle feedback control, and the average value of the idle control position of the flow control valve (8) becomes the control start position. At the time of idling, the flow control valve (8) is opened and closed at a low speed based on a signal from the oxygen sensor (15), and idle feedback control is performed to adjust the air-fuel ratio of the air-fuel mixture to a constant value. Become.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 2 to 4.

In the drawing, reference numeral 1 denotes a carburetor mounted on an intake manifold of an engine, 2 denotes a mixing chamber, 3 denotes a main jet, 4 denotes a throttle valve, 5 denotes a float chamber, and 6 denotes an air bleed.
A flow control valve ABCV8 is provided in the air bleed passage 7, which is a starting end of the air bleed 6, and the flow control valve A
The inlet 8a of the BCV 8 is open to the atmosphere. Flow control valve ABCV
8 moves the pointed valve element 9 forward and backward with respect to the valve seat 10 and changes the opening area of the air passage formed between the valve element 9 and the valve seat 10 to reduce the amount of air flow. The valve 9 is attached to the tip of an operating rod 12 of a stepper motor 11. Then, the stepper motor 11 is controlled by an electronic control unit 13 to be described later, and the valve element 9 corresponds to the stoichiometric air-fuel ratio when the air-fuel ratio feedback control is performed from the fully closed position (0 step) to the fully open position (100 steps). The advancing / retreating operation is performed based on the intermediate position (50 steps) thus set.

On the other hand, an oxygen sensor 15 is disposed upstream of the catalytic converter 14 provided in the exhaust system. This oxygen sensor 15
Generates a low voltage when the air-fuel ratio of the mixture is leaner than the conversion point existing near the stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas is high, and the air-fuel ratio of the mixture When the oxygen concentration in the exhaust gas is low on the rich side of the point, a high voltage can be generated.

The electronic control unit 13 includes a microcomputer unit including a central processing unit 16, a memory 17, an input interface 18, and an output interface 19, and serves as the idle feedback control unit 20 and the control switching unit 21. A function of performing normal feedback control for adjusting the air-fuel ratio of the air-fuel mixture to a constant value by moving the flow control valve ABCV8 at high speed before and after the intermediate position when the throttle valve 4 is opened. It also has. Then, at least a signal a from the oxygen sensor 15 is input to the input interface 18.
And a signal b from the idle switch 22 and the like, and a feedback control signal c is output from the output interface 19 to the flow control valve ABCV8. The idle switch 22 is an ON / OFF switch that is “closed” when the throttle valve 4 is in the open position and “open” when it is in the idle position.

Further, the electronic control unit 13 has a built-in program as schematically shown in FIG. First, assuming that the warm-up has been completed, in step 51, the idle switch 22 is controlled based on the signal b from the idle switch 22.
Is "open" or "closed". If it is "closed", it is determined that the throttle valve 4 is in the open state, and the process proceeds to step 52. If it is "open", it is determined that the throttle valve 4 is at the idle position and the process proceeds to step 53. In step 52, the normal feedback control F / B is performed on the assumption that predetermined conditions for performing the air-fuel ratio feedback control, such as that the engine speed is within a predetermined range and the fuel power is not being increased, are satisfied. Do.

On the other hand, in step 53, idle feedback control
Perform F / B and proceed to step 54. In step 54, the idle control position of the flow control valve ABCV8 during the idle feedback control is learned. For example, an average value of the sum of the control position on the high opening side and the control position on the low opening side of the flow control valve ABCV8 is calculated, and the calculated value is stored in a predetermined address. The value is updated constantly. The above control is repeatedly executed after the engine is started.

According to such a configuration, when the throttle valve 4 is in the open state and other special control is not preferentially performed, for example, when the fuel power is not being increased, the fourth control is performed.
Normal feedback control as shown schematically in the figure
F / B is performed, and the flow control valve ABCV8 is opened and closed at a high speed to adjust the air-fuel ratio (steps 51 to 52). That is,
When the output voltage of the oxygen sensor 15 is leaner than the conversion point and the oxygen concentration in the exhaust gas is high, the flow control valve AB
The opening of the CV8 is narrowed by a predetermined value in a skip shape, and then rapidly reduced by a predetermined value. For this reason, the amount of oxygen mixed into the air-fuel mixture via the air bleed passage 7 is rapidly reduced, and the air-fuel ratio of the air-fuel mixture rapidly changes to near the stoichiometric air-fuel ratio. Further, when the output voltage of the oxygen sensor 15 is on the rich side of the conversion point and the oxygen concentration in the exhaust gas is low, the opening of the flow control valve ABCV8 is increased in a skip shape by a fixed value, and thereafter, the predetermined It increases rapidly by value. For this reason, the amount of oxygen mixed into the air-fuel mixture via the air bleed passage 7 increases rapidly, and the air-fuel ratio of the air-fuel mixture rapidly changes to near the stoichiometric air-fuel ratio. Then, by repeatedly performing such control, the air-fuel ratio when the throttle valve 4 is opened converges to near the stoichiometric air-fuel ratio and is maintained.

On the other hand, when the throttle valve 4 returns to the idle position and other special control is not performed with priority, for example, when deceleration fuel cut is not performed, the flow control valve AB
The control position of CV8 is immediately returned from the control position during normal feedback control to the control position during idle feedback control. Then, as schematically shown in FIG.
The idle feedback control F / B in which the average value at the time of the previous idle feedback control is the control start position HLDFCX is performed, and the flow control valve ABCV8 is opened and closed at a low speed (steps 51 → 53 → 54). That is, when the output voltage of the oxygen sensor 15 is leaner than the conversion point and the oxygen concentration in the exhaust gas is high, the opening of the flow control valve ABCV8 is gradually reduced. Therefore, the amount of oxygen mixed into the air-fuel mixture via the air bleed passage 7 is gradually reduced, and the air-fuel ratio of the air-fuel mixture changes near the stoichiometric air-fuel ratio. On the other hand, when the output voltage of the oxygen sensor 15 is on the rich side from the conversion point and the oxygen concentration in the exhaust gas is low, the opening of the flow control valve ABCV8 is gradually increased. For this reason, the amount of oxygen mixed into the air-fuel mixture via the air bleed passage 7 gradually increases, and the air-fuel ratio of the air-fuel mixture changes near the stoichiometric air-fuel ratio. By repeatedly performing such control, the air-fuel ratio at the time of idling converges to near the stoichiometric air-fuel ratio and is maintained.

Therefore, with this configuration, when the throttle valve 4 returns from the open position to the idle position and the amount of intake air is minimized, the control position of the flow control valve ABCV8 rapidly increases to the center of the idle control position. Since it is returned, the fuel supply amount and the intake air amount match. Therefore, when the accelerator is returned immediately after starting and stopped, as in the conventional case, the flow control valve AB
Since the CV8 is not held on the open side for a while, the air-fuel ratio becomes lean, and such a problem that the engine stall is less likely to occur.

Note that, in the above-described embodiment, the case where the normal feedback control of the air-fuel ratio is switched to the idle feedback control has been described. However, the present invention is not limited to the above-described embodiment, and includes the following examples.

For example, when the flow control valve is fixedly held at "closed" at low speed and high load such as when climbing a hill, the flow rate control valve can be suitably used for switching to idle feedback control. When such control is performed, a program as schematically shown in FIGS. 5 and 6 may be set in the electronic control unit 13. The same reference numerals are used for the portions corresponding to FIG. 3, and the description is omitted. In step 51 in FIG. 5, the idle switch
It is determined whether the idle switch 22 is “open” or “closed” based on the signal “b” from the idle switch 22. If it is "closed", it is determined that the throttle valve 4 is in the open state, and the process proceeds to step 52. If it is "open", it is determined that the throttle valve 4 is at the idle position and the process proceeds to step 53. Steps
At 52, as schematically illustrated in FIG. 6, the flow control valve ABCV
8 is fixed to 0 step.

According to such a configuration, when the throttle valve 4 is in the open state and the engine is in the low-speed / high-load state, the flow control valve ABCV8 is fixedly held at “closed” and the air bleed passage is closed. Since 7 is closed, a rich air-fuel mixture is supplied to the engine. When the throttle valve 4 is returned to the idle position after climbing in such a situation, the air-fuel mixture becomes over-rich in the related art, resulting in rough idle. According to this embodiment, As soon as the throttle valve 4 is returned to the idle position, the flow control valve ABCV8 is also returned to the idle position, so that an appropriate amount of air is supplied through the air bleed passage 7. For this reason, the over-rich state of the air-fuel mixture immediately after the switching of the control can be effectively mitigated, and rough idle hardly occurs.

[Effects of the Invention] According to the present invention having the above configuration, it is possible to prevent the air-fuel ratio from temporarily becoming lean or over-rich immediately after switching from the air-fuel ratio control to the idle feedback control when the throttle valve is opened. Since the suppression can be effectively suppressed, it is possible to provide a highly reliable air-fuel ratio control device for a carburetor, which can effectively eliminate the problem that engine stall occurs immediately after switching.

[Brief description of the drawings]

FIG. 1 is a structural explanatory view for clarifying the present invention, FIGS. 2 to 4 show one embodiment of the present invention, FIG. 2 is a structural diagram schematically showing the entire apparatus, and FIG. FIG. 4 is a flowchart showing a control procedure, and FIG. 4 is a timing chart showing a control mode. FIG. 5 is a flowchart corresponding to FIG. 3 showing another embodiment of the present invention, and FIG. 6 is a timing chart showing a control mode in the embodiment. FIG. 7 is a timing chart showing a conventional example. DESCRIPTION OF SYMBOLS 1 ... Vaporizer 4 ... Throttle valve 7 ... Air bleed passage 8 ... Flow control valve 13 ... Electronic control device 14 ... Catalytic converter 15 ... Oxygen sensor 20 ... Idle feedback control means 21 ... Control switching means

Claims (1)

(57) [Claims] 1. A flow control valve for controlling an air-fuel ratio of an air-fuel mixture supplied to an engine by opening and closing an air bleed passage of a carburetor, an oxygen sensor for detecting an oxygen concentration in exhaust gas, and the oxygen sensor. An idle feedback control means for opening and closing the flow control valve at a low speed to adjust the air-fuel ratio to be constant when the throttle valve is in the idle position based on a signal from the throttle valve, and returning the throttle valve to the idle position and decelerating the throttle valve. When the control state is other than the hour fuel cut, the control is immediately switched from the control at the time of opening the throttle valve to the idle feedback control by the idle feedback control means and immediately started, and the average value of the idle control position of the flow control valve is controlled. Carburetor characterized by comprising control switching means for setting the position Air-fuel ratio control system.