JPH0329982B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio control device for a carburetor mainly applied to automobile engines and the like.

[Prior Art] Three-way catalysts are widely used in modern automobiles as one of exhaust gas purification means. However,
Such a three-way catalyst cannot efficiently purify all of the _NOx , HC, and CO contained in the exhaust gas unless the air-fuel ratio of the air-fuel mixture is maintained at a value near the stoichiometric air-fuel ratio (14.5).

Therefore, a flow control valve (so-called air bleed control valve) is installed in the air bleed passage of the carburetor, and this flow control valve is controlled by feedback based on the output of the O ₂ sensor that detects the oxygen concentration in the exhaust gas. Accordingly, an air-fuel ratio control device (so-called feedback cab system) has been developed and used to maintain the air-fuel ratio of the air-fuel mixture supplied to the engine near the stoichiometric air-fuel ratio.

[Problems to be Solved by the Invention] However, simply using this method is likely to cause problems when the temperature of the carburetor increases due to idling or the like. That is, if the engine is left in an idling state in a high-temperature atmosphere, the temperature of the carburetor may become abnormally high and vapor may be generated in the gasoline in the float chamber, fuel passage, etc. As a result, there is a problem in that stable combustion in the engine is impaired, idle rotation becomes unstable, and engine stall is likely to occur.

As a result of various experiments to solve this problem, the inventor of the present invention found that when the idle rotation becomes unstable, the output of the O ₂ sensor changes greatly in a hunting state. The rough idle state can be detected, and when the idle speed becomes unstable, the feedback control that controls the air-fuel ratio to near the stoichiometric air-fuel ratio is stopped, and the flow control valve It has been discovered that the rotation of the engine can be stabilized by fixing it at a holding position set to the richer side than the average opening degree during feedback control.

The present invention was made based on the above circumstances and investigation results, and can easily detect and deal with rough idling conditions, and can reliably and effectively prevent engine stalling when left idling. It is an object of the present invention to provide an air-fuel ratio control device for a carburetor that can solve the above problems.

[Means for solving the problems] In order to achieve such objects, the present invention has the following features:
A flow control valve 8 that opens and closes the air bleed passages 6 and 7 of the vaporizer 1, and an O ₂ that detects the oxygen concentration in the exhaust gas.
a feedback control means A that opens and closes the flow rate control valve 8 based on the signal from the O ₂ sensor 14 to control the air-fuel ratio of the air-fuel mixture supplied to _the engine to a set value; Rough idle detection means B detects that the idle rotation of the engine has become unstable based on the signal of
When the rough idle detection means B detects that the idle rotation has become unstable, the control by the feedback control means A is eliminated and the opening degree of the flow rate control valve 8 is adjusted to the average step position during feedback control. Warm-up correction coefficient (BFWL) that changes according to the coolant temperature in the learned value (LAMDA)
The invention is characterized in that it is equipped with a rough idle control means C that holds the engine at a rich side holding position multiplied by .

[Operation] According to such a configuration, the flow rate control valve 8 is normally placed under the control of the feedback control means A, and the air-fuel ratio is controlled to be constant based on the feedback signal from the O ₂ sensor 14.

On the other hand, in this state, if vapor is generated in the carburetor 1 due to reasons such as being left in a high-temperature atmosphere and the engine rotation becomes unstable, the output of the O ₂ sensor 14 will rise and fall rapidly, resulting in a so-called hunting state. Become. When the rough idle detection means B detects this, the rough idle control means C releases the flow rate control valve 8 from the control of the feedback control means A and fixes it at the rich side holding position (HLDOL). . The rich side holding position (HLDOL) is obtained by multiplying the learned value of the average step position during feedback control by the warm-up correction coefficient (BFWL), which changes depending on the cooling water temperature, and changes depending on the operating condition. Change. Therefore, as long as the warm-up correction coefficient (BFWL) is appropriately set, it is possible to perform the necessary and minimum air-fuel ratio rich control even if rough idling occurs in any driving condition. Therefore, compared to the case where the flow rate control valve 8 is fixed at a constant rich side holding position during rough idle, fuel efficiency and emission can be maintained in a better state.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 2 to 6.

In the figure, 1 indicates a carburetor for an automobile engine, 2 is a mixing chamber of this carburetor 1, and 3 is a mixing chamber of this carburetor 1.
4 is a main jet, 4 is a throttle valve, 5 is a float chamber, and 6 and 7 are air bleed passages.
The air bleed passages 6 and 7 can be opened and closed by a flow control valve 8.

The flow rate control valve 8 includes a valve seat 11 and a needle valve 12 in a valve box 9 with an inlet 8a open to the atmosphere and an outlet 8b connected to the air bleed passages 6 and 7. The needle valve 12 is moved forward and backward toward the valve seat 11 by a stepper motor 13 to control the amount of outside air flowing into the air bleed passages 6 and 7. In this embodiment, the needle valve 12 is set to move from the fully closed position to the fully open position by operating the stepper motor 13 from 0 steps to 100 steps.

Further, 14 is an O ₂ sensor provided in an exhaust pipe 15 located upstream of the three-way catalytic converter. This O ₂ sensor 14 outputs a low level voltage when the air-fuel ratio of the air-fuel mixture is leaner than the conversion point that exists near the stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas is high; When the air-fuel ratio of the air-fuel mixture is richer than the conversion point and the oxygen concentration in the exhaust gas is low, a Hi level voltage is output.

Further, 21 is a microcomputer system for controlling the flow rate control valve 8, which includes feedback control means A and rough idle detection means B.
It also plays a role as a rough idle control means C.

This microcomputer system 21 includes a central processing unit 22, a memory 23, and interfaces 24 and 25. Then, at least the above-mentioned
Signal a from _O2 sensor 14, signal b from idle switch 26, signal c from water temperature sensor 27
A signal d from the vehicle speed sensor 28 is input, and a feedback control signal e is sent from the output side interface 25 to the flow control valve 8.
Alternatively, a rough idle control signal f is output. The idle switch 26 is a switch that is turned on when the throttle valve 4 has returned to the closed position. The water temperature sensor 27 is for detecting the engine cooling water temperature, and includes a thermistor (not shown) that converts the cooling water temperature into an analog electrical signal, and an A/D converter that converts the output of this thermistor into a digital electrical signal. It is equipped with a container (not shown). Further, the vehicle speed sensor 28 is for detecting the traveling speed of the vehicle, and uses, for example, a sensor for speed display.

Then, the microcomputer system 2
1 has a built-in program as schematically shown in FIG.

That is, first, in step 51, the O ₂ sensor 1 is
4, a signal b from the idle switch 26, a signal c from the water temperature sensor 27, a signal d from the vehicle speed sensor 28, and the like are input. Next, in step 52, it is determined whether conditions for performing feedback control during idling are satisfied. In other words, roughly speaking, the engine cooling temperature is
The condition is that the temperature is 60℃ or higher, and the vehicle speed is 10
If the conditions that the idle switch is in the ON state at a speed of less than Km are satisfied, it is assumed that the idle feedback condition is satisfied and the process proceeds to step 53. In step 53, it is determined whether or not the output of the O ₂ sensor 14 exceeds the upper set value 0.6V. If it exceeds, the process proceeds to step 54; if it does not, the process proceeds to step 5.
Proceed to step 5. At step 54, the upper increment counter CHIGH is cleared and the process proceeds to step 56. In step 56, it is determined whether the count value of the lower increment counter CLOW is less than 1 second, and if it is less than 1 second, the process proceeds to step 57.
If it is longer than seconds, the process advances to step 71. In step 57, it is determined whether or not the flag FCNTH is set to 1. If 1 is set, the process proceeds directly to step 81, but if 1 is not set, the flag FCNTH is set to 1 in step 58. 1 and flag in step 59.
Clear FCNTL and proceed to step 80. At step 80, the counter CNT is incremented by 1 and the process proceeds to step 81. On the other hand, when proceeding from step 53 to step 55, the output of the O ₂ sensor 14 is set to the lower set value of 0.3V.
It is determined whether or not the current value is below the current value, and if it is, the process moves to step 61, and if it is not, the process directly proceeds to step 81. In step 61, the lower increment counter CLOW is cleared, and the process proceeds to step 62. In step 62, it is determined whether the count value of the upper increment counter CHIGH is less than 1 second. If it is less than 1 second, the process proceeds to step 63, and if it is more than 1 second, the counter CNT is cleared in step 71. At the same time, in step 72, flags FCNTH,
After clearing each FCNTL, proceed to step 81. When the process proceeds to step 63, it is determined whether or not the flag FCNTL is set to 1. If 1 is set, the process directly proceeds to step 81; however, if 1 is not set, the process proceeds directly to step 81. sets the flag FCNTL to 1 in step 64, and sets the flag to 1 in step 65.
Clear FCNTH and proceed to steps 80 and 81. In step 81, it is determined whether the count number of the counter CNT has reached 10 or more, and if it is 10 or more, a flag is set in step 82.
Set YHLD and proceed to step 83, and if it is less than 10, proceed directly to step 83. In step 83, it is determined whether or not the flag YHLD is set. If it is set (1), the process proceeds to step 84; if it is not set, the process proceeds to step 85. Step 84
Now, move the flow control valve 8 to the rich side holding position HLDOL.
to hold. This rich side holding position HLDOL is
A warm-up correction coefficient BFWL of 1 or less is added to the learned value LAMDA of the average step position during feedback control.
The coefficient BFWL is the sixth
As shown in the figure, it is set to change depending on the engine cooling water temperature. On the other hand, in step 85, normal idle feedback control is executed. That is, this idle feedback control determines whether the signal of the O ₂ sensor 14 is a Low level signal (lean detection signal) or a Hi level signal (rich detection signal), and ), the flow control valve 8
is operated in the closing direction at a predetermined speed, and when the signal from the O ₂ sensor 14 is a Hi level (rich detection signal) signal, the flow rate control valve 8 is operated in the opening direction at a predetermined speed. Note that the step 52
If it is determined in step 91 that the idle feedback control condition is not satisfied, the flag YHLD is cleared in step 91, and the flag YHLD is cleared in step 92.
Clear the counter CNT and return to step 51.

With such a configuration, in an idling operating state where the engine rotation is relatively stable, the control shown in FIG.
→ 55 → 81 → 83 → 85, and as shown in Figure 4, normal feedback control is executed and the air-fuel ratio of the mixture supplied to the engine is controlled to be close to the stoichiometric air-fuel ratio. . If the engine is left in a high-temperature atmosphere during idling operation under such feedback control, and vapor is generated in the fuel passage of the carburetor 1, resulting in unstable engine rotation, As shown in FIG. 5, the output of the O ₂ sensor 14 rises and falls rapidly at short time intervals. And it takes
When hunting of the O ₂ sensor output is repeated 10 times or more, the feedback control is stopped, and the flow rate control valve 8 is moved to the rich side holding position HLDOL and fixed. That is, the above
The output of the O ₂ sensor 14 rises and falls beyond the upper set value 0.6V and the lower set value 0.3V, and moreover, from the point at which the output falls below the upper set value 0.6V, it drops to the minimum value and further decreases. The elapsed time until the lower set value exceeds 0.3V and rises to the maximum value, and then the upper set value
The elapsed time until it falls below 0.6V is 1 for each
If it is less than 1 second, the counter CNT will count up by 1, and the count amount will be 10
If this is the case, rough idle control is executed in step 84. Specifically, when the output of the O ₂ sensor 14 exceeds the upper set value 0.6V, the control shown in FIG.
6 and then lower increment counter
If one second has not elapsed since CLOW started timing, step 57 → 58 → 59 → 80
Then, the counter CNT is incremented by 1. After that, while the output of the O ₂ sensor 14 exceeds the upper limit set value 0.6V, the flag FCNTH is set to 1, so the third
The control shown in the figure is in steps 51→52→53→54.
→56 →57 →81, and the upper increment counter CHIGH continues to be cleared. During this time, the lower increment counter CLOW continues to count up as time passes, but if this is less than 1 second, this route is repeatedly executed. Then, when the output of the O ₂ sensor 14 falls below the upper set value 0.6V, from that point on, the third
Since the control shown in the figure progresses from 51 → 52 → 53 → 55 → 81, the upper increment counter
Timing starts when CHIGH is no longer cleared. Then, when the output of the O ₂ sensor 14 further decreases and falls below the lower limit setting value of 0.3V, at that point, the control shown in FIG.
2→53→55→61→62, and if the count value of the upper increment counter CHIGH is less than 1 second, further steps 63→6
The counter CNT is incremented by 1 in the order of 4→65→80. And then the O ₂
While the output of the sensor 14 is below the lower limit set value 0.3V, the flag FCNTL is set to 1, so the control shown in FIG.
→53→55→61→62→63→81, and the lower increment counter CLOW continues to be cleared. During this time, the upper increment counter CHIGH continues to count up as time passes, but if this is less than 1 second, this route is repeatedly executed. And the _O2
When the output of sensor 14 exceeds the lower set value 0.3V,
From that point on, the control shown in FIG. 3 changes from 51→52→
Since the count progresses from 53 to 55 to 81, the lower increment counter CLOW is no longer cleared and time measurement starts. Then, when the output of the O ₂ sensor 14 exceeds the upper limit setting value of 0.6V, the control shown in FIG. 3 is resumed from step 53 to step 5.
You will proceed to step 4 and repeat the above operations. Therefore, during such hunting, the output of the O ₂ sensor 14 reaches the upper set value of 0.6V.
The counter CNT increases by 1 each time it goes below or exceeds the lower set value 0.3V.
When the value of the counter CNT becomes 10 or more, a flag YHLD is set at step 82, and the flow control valve 8 is held at the rich side holding position HLDOL at step 84. In addition,
When the idling state is canceled due to the start of the vehicle, etc., the control proceeds from step 52 to steps 91 and 92 and the flag THLD and counter CNT are cleared, so that the flow rate control valve 8 is held on the rich side. The fixed state of the position is released.

Therefore, according to this device, during rough idle, the feedback control is stopped and the flow rate control valve 8 is held at the rich side holding position HLDOL, so that a rich air-fuel mixture is supplied to the engine. The rough idle state can be quickly corrected and the rotation of the engine can be stabilized. Moreover, since the rough idle state can be detected only by the output of the O ₂ sensor 14, the configuration is simple and implementation is easy.

In addition, in the above example, the output of the O ₂ sensor is
We have explained the case where it is determined that hunting has occurred for the first time when the vehicle goes up and down 10 times or more in a short period of time, and controls for rough idle are performed, but of course the number of times is not limited to 10. . However, if the number of times is too small, there is a risk of malfunction due to temporary fluctuations in engine rotation, so it is desirable to set the number of times to the level of the above example.

[Effects of the Invention] Since the present invention has the above-described configuration, it is possible to easily detect and deal with rough idle conditions, and reliably and effectively eliminate the occurrence of engine stalls when left idling. Accordingly, it is possible to provide an air-fuel ratio control device for a carburetor that can control the air-fuel ratio of a carburetor. In particular, in the present invention, when a rough idle condition is detected, the position of the flow control valve is not set to a fixed position, but to a warm-up correction coefficient that changes according to the cooling water temperature to a learned value of the average step position during feedback control. I try to hold it at the position obtained by multiplying it. Therefore, by controlling the air-fuel ratio to the minimum necessary rich side even during rough idle,
Engine stall can be prevented,
Very good results can be obtained in terms of fuel economy and exhaust gas purification.

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram for clearly explaining the present invention. 2 to 6 show an embodiment of the present invention, FIG. 2 is a system explanatory diagram, FIG. 3 is a flowchart showing a control procedure, FIGS. 4 and 5 are action explanatory diagrams, FIG. 6 is an explanatory diagram showing control setting conditions. A... Feedback control means, B... Rough idle detection means, C... Rough idle control means, 1... Carburizer, 8... Flow rate control valve, 14...
O ₂ sensor, 21...microcomputer system.

Claims (1)

[Claims] 1. A flow control valve that opens and closes the air bleed passage of the carburetor, an O ₂ sensor that detects the oxygen concentration in the exhaust gas, and a mixture that opens and closes the flow control valve based on the signal from this O ₂ sensor to supply the mixture to the engine. a feedback control means for controlling the air-fuel ratio of the engine to a set value; a rough idle detection means for detecting that the idle rotation of the engine has become unstable based on a signal from the O ₂ sensor; and the rough idle detection means. When it is detected that the idle rotation has become unstable, the control by the feedback control means is eliminated and the opening degree of the flow rate control valve is adjusted to the learned value of the average step position during feedback control according to the cooling water temperature. 1. An air-fuel ratio control device for a carburetor, comprising: rough idle control means for holding the rich side holding position multiplied by a varying warm-up correction coefficient.