JPH09264168A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To purify exhaust gas with a simple structure by regulating the pressure within a float chamber according to the output of an oxygen sensor mounted on the exhaust side to perform air-fuel ratio control. SOLUTION: An oxygen sensor 13 is mounted on an exhaust pipe 11, and when the output of the oxygen sensor 13 is changed to a value showing the rich side and lean side, a solenoid valve 19 is opened and closed according to this change. Namely, when it shows the rich side, the solenoid valve 19 is OFF and an atmospheric pressure inlet passage 29 is opened. Thus, when the atmospheric pressure inlet passage 29 is closed, the pressure of a float chamber 23 is reduced, and when the atmospheric pressure inlet passage 29 is opened, the pressure of the float chamber 23 is raised. When the pressure of the float chamber 23 is high, much fuel is supplied to a venturi part 7 to make air-fuel ratio rich, and when the pressure of the float chamber 23 is low, the fuel quantity to be supplied to the venturi part 7 is reduced to make air-fuel ratio lean.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine, particularly an internal combustion engine using a carburetor as a fuel supply system, such as a general-purpose engine used for small vessels, small generators, lawn mowers and the like. It is a thing.

[0002]

2. Description of the Related Art Conventionally, for example, a lawn mower uses a small-sized and inexpensive general-purpose engine. Generally, a general-purpose engine discharges exhaust gas whose temperature and flow velocity do not change significantly, and usually does not have a complicated electronic control device.

This type of general-purpose engine has a simpler structure than that of, for example, an automobile engine, and some of them do not have a battery. However, since they are easy to handle, they are the driving source for various devices. Is often used as.
Also, in a general-purpose engine, as a method of supplying fuel,
Usually, a system using a carburetor that supplies fuel by utilizing a differential pressure from the float chamber to the intake manifold side is adopted.

On the other hand, regarding automobile engines, the standards for exhaust gas are set strictly, so that an oxygen sensor or the like for detecting the oxygen concentration in the exhaust gas is used, and C in the exhaust gas is used.
Although control for reducing O, HC, etc. is performed, such control is not currently performed for a general-purpose engine used in a lawn mower or the like.

[0005]

However, in recent years,
From the viewpoint of maintaining a good environment, not only automobile engines but also other general-purpose engines are required to take measures against exhaust gas in order to purify the exhaust gas and reduce CO and HC. There is. In particular, this type of general-purpose engine has a limited operating environment and operating conditions compared to automobile engines, and since many of them are generally small and low-priced, exhaust gas countermeasures are as simple as possible and low cost. What can be realized in is desired.

The present invention has been made to solve the above problems, and an object thereof is to provide an air-fuel ratio control device for an internal combustion engine, which can purify exhaust gas with a simple structure. To do.

[0007]

In order to achieve the above object, the invention of claim 1 is a carburetor type air-fuel ratio control apparatus for an internal combustion engine which supplies fuel in a float chamber to an intake side of the internal combustion engine. An air-fuel ratio control device for an internal combustion engine is characterized in that the air-fuel ratio is controlled by adjusting the pressure in the float chamber according to the output of an oxygen sensor mounted on the side.

According to a second aspect of the present invention, as a means for adjusting the pressure in the float chamber, an electromagnetic valve for controlling the opening and closing of a path for introducing pressure into the float chamber according to the output of the oxygen sensor is used. The gist of the air-fuel ratio control device for an internal combustion engine according to claim 1 is as follows.

According to a third aspect of the present invention, the passage includes a negative pressure introducing passage for introducing the negative pressure on the intake side into the float chamber, and / or
Alternatively, the air-fuel ratio control device for an internal combustion engine according to claim 2 is characterized in that it is an atmospheric pressure introducing path for introducing atmospheric pressure into the float chamber.

According to a fourth aspect of the present invention, the solenoid valve switches between a negative pressure introducing passage for introducing the negative pressure on the intake side into the float chamber and an atmospheric pressure introducing passage for introducing atmospheric pressure into the float chamber. The gist of the air-fuel ratio control device for an internal combustion engine according to claim 3 is.

According to a fifth aspect of the present invention, the air-fuel ratio is set by
The gist of the air-fuel ratio control device for an internal combustion engine according to any one of claims 2 to 4 is that the control is performed according to the degree of throttling of the path. A sixth aspect of the present invention provides the air-fuel ratio control device for an internal combustion engine according to the fifth aspect, wherein the degree of the throttle is set by setting the diameter of the throttle nozzle.

[0012]

In the first aspect of the invention, the air-fuel ratio is controlled by adjusting the pressure in the float chamber according to the output of the oxygen sensor mounted on the exhaust side.
The air-fuel ratio can be preferably controlled with a simple structure.

That is, when the pressure in the float chamber is high, the pressure difference between the pressure in the float chamber and the negative pressure in the intake manifold, for example, is large, so more fuel is supplied than when the pressure difference is small. On the contrary, when the pressure in the float chamber is low, the pressure difference between the pressure in the float chamber and the negative pressure in the intake manifold is small, so that the fuel supply amount is small.

Further, in the present invention, since the carburetor system is used, the internal combustion engine can be started and warmed up without any trouble even when the necessary power is not supplied from the power source at the time of starting and the air-fuel ratio control device does not operate. . According to the second aspect of the invention, as the means for adjusting the pressure in the float chamber, a solenoid valve for controlling the opening / closing of the path for introducing the pressure into the float chamber according to the output of the oxygen sensor can be adopted.

That is, the solenoid valve is turned on / off (opened / closed) in accordance with the lean or rich signal of the oxygen sensor, for example.
The pressure in the float chamber can be adjusted to a desired value by controlling or by controlling the duty. According to the third aspect of the invention, the solenoid valve is provided in the negative pressure introducing passage for introducing the negative pressure on the intake side into the float chamber and / or the atmospheric pressure introducing passage for introducing the atmospheric pressure into the float chamber, whereby the pressure inside the float chamber is increased. Can be adjusted.

For example, when the solenoid valve is provided in the atmospheric pressure introducing passage, the degree of atmospheric pressure introduction can be adjusted, while when the solenoid valve is provided in the negative pressure introducing passage, the negative pressure introduction degree is adjusted. As a result, it is possible to adjust the pressure in the float chamber. It should be noted that when the solenoid valve is provided in the atmospheric pressure introducing passage, the solenoid valve is easier to mount due to the structure of the carburetor.

According to the fourth aspect of the present invention, the solenoid valve is used to switch between the negative pressure introducing passage for introducing the negative pressure on the intake side into the float chamber and the atmospheric pressure introducing passage for introducing the atmospheric pressure into the float chamber. The pressure of can be adjusted.
According to the fifth aspect of the present invention, the target air-fuel ratio level can be set by determining the degree of throttling of the paths such as the negative pressure introduction path and the atmospheric pressure introduction path.

For example, when the solenoid valve is fully opened, the pressure in the float chamber is determined by the amount of air flowing into or out of the float chamber. This amount of air is naturally the route through which air is supplied. It will be determined by the condition (diameter of the diaphragm) such as the diameter of. That is, since the pressure in the float chamber is determined by the degree of throttling by the negative pressure introduction path and the atmospheric pressure introduction path, the degree of fuel supply is also determined,
As a result, the target air-fuel ratio also depends on the degree of the throttle.

Specifically, as shown in FIG. 1, when the pressure in the float chamber changes and the degree of throttling of the negative pressure introduction path is large (the path is narrow), (as indicated by the alternate long and short dash line) ) The gradient at the time of pressure decrease becomes gentle, the period in which much fuel is supplied becomes longer, and as a result, the air-fuel ratio moves to the rich side. Conversely, when the degree of restriction of the negative pressure introduction path is small (the path is wide), the slope of the pressure decrease (as indicated by the chain double-dashed line) becomes steep, and the period in which much fuel is supplied is short. As a result, the air-fuel ratio moves to the lean side. On the other hand, when the degree of throttling of the atmospheric pressure introduction path is large (the path is narrow), the slope at the time of increasing the pressure becomes gentle (as indicated by the alternate long and short dash line), and the period for which fuel is supplied is reduced As a result, the air-fuel ratio moves to the lean side.
Conversely, when the degree of throttling of the atmospheric pressure introduction path is small (wide path), the slope at the time of pressure rise becomes steep (as shown by the chain double-dashed line), and the fuel supply is short and the supply period is short. As a result, the air-fuel ratio moves to the rich side.

According to the sixth aspect of the invention, means for setting the diameter of the aperture nozzle can be employed as means for setting the degree of aperture.

[0021]

Embodiments of the air-fuel ratio control system for an internal combustion engine according to the present invention will be described. a) First, the configuration of an air-fuel ratio control device (hereinafter simply referred to as an air-fuel ratio control device) of a carburetor type general-purpose engine used in, for example, a lawn mower according to this embodiment will be described.

FIG. 2 shows the schematic construction of the air-fuel ratio control system of this embodiment. In this embodiment, the carburetor 9 consisting of the fuel supply section 5 and the venturi section 7 is attached to the intake pipe 3 of the general-purpose engine 1. In addition, the oxygen sensor 13 is attached to the exhaust pipe 11. In this device, the signal from the oxygen sensor 13 is converted into the sensor signal processing circuit 15
And the solenoid valve drive circuit 17 based on the processing result.
A drive signal is output from the solenoid valve, the solenoid valve 19 of the fuel supply unit 5 is driven based on the drive signal, the fuel supply amount is adjusted, and the air-fuel ratio is controlled.

Each configuration will be described in detail below. The oxygen sensor 13 uses, as a detection element, an oxygen concentration battery in which platinum electrodes are provided on both surfaces of a zirconia solid electrolyte substrate, and the electromotive force of the oxygen concentration battery changes suddenly due to stoichiometry.

The fuel supply unit 5 is a fuel tank (not shown).
Float chamber 23 that stores the fuel supplied from the tank by adjusting the float 21 up and down, a nozzle 25 that communicates the bottom of the float chamber 23 and the venturi portion 7 to supply the fuel into the intake pipe 3, and a float chamber. 23 and the upper portion of the float chamber 23 (where air is present), the throttle valve 27 and the nozzle. 25, and a negative pressure introducing passage 31 that communicates with the position between 25.

The atmospheric pressure introducing path 29 and the negative pressure introducing path 31 are paths for introducing the atmospheric pressure and the negative pressure, respectively.
The atmospheric pressure introducing passage 29 and the negative pressure introducing passage 31 are provided with diaphragms 29a and 31a each having a predetermined opening diameter. In addition, the atmospheric pressure introduction path 29 has two openings for opening and closing the path.
The solenoid valve 19 for controlling the position is arranged.

B) Next, the operation of the air-fuel ratio control system of this embodiment will be described. As shown in FIG. 4, when the output of the oxygen sensor 13 changes to a value indicating a rich side and a lean side across a reference value (for example, 0.6 V), the solenoid valve 19 is controlled to open and close according to the change.

Specifically, when the sensor output indicates rich, the solenoid valve 19 is turned on to close the atmospheric pressure introducing passage 29, and conversely, when the sensor output indicates lean, the solenoid valve 19 is turned off.
Then, the atmospheric pressure introducing passage 29 is opened. As a result, for example, when the atmospheric pressure introducing passage 29 is closed, the degree of introduction of the negative pressure is increased, so that the pressure in the float chamber 23 gradually decreases, and conversely, when the atmospheric pressure introducing passage 31 is opened, the atmospheric pressure is introduced. Therefore, the pressure in the float chamber 23 gradually increases.

Here, the state in which the pressure in the float chamber 23 is high is a state in which the pressure in the float chamber 23 and the pressure difference between the venturi portion 7 become large and a large amount of fuel is supplied to the venturi portion 7. The air-fuel ratio of the fuel-air mixture becomes rich, so that the output of the oxygen sensor 13 also shows rich. On the contrary, when the pressure in the float chamber 23 is low, the differential pressure becomes small and the amount of fuel supplied to the venturi portion 7 becomes small, so that the air-fuel ratio of the fuel mixture becomes lean, and thereby, The output of the oxygen sensor 13 also shows lean.

The speed at which the pressure in the float chamber 23 moves up and down (inclination in the graph of FIG. 4) is determined by the throttles 29a, 31a.
Is determined by the size of the apertures 29a, 31
The target average air-fuel ratio (target air-fuel ratio) is set by a. In this embodiment, in order to stabilize the engine output and prevent the exhaust temperature from rising, the target air-fuel ratio is on the slightly rich side (for example, air-fuel ratio; A / F = 13 to 14).
Is set to

For example, if the degree of the throttle 31a of the negative pressure introducing passage 31 is reduced (the path is widened), the negative pressure is easily introduced, so that the pressure in the float chamber 23 is as shown by the one-dot chain line in FIG. , Compared to the case of a solid line where the degree of aperture is large, it decreases rapidly. As a result, the period of the output indicating the richness of the oxygen sensor 13 is shortened, so that the average air-fuel ratio (although it is richer than stoichiometric) changes slightly leaner than when the degree of throttling is large. When the degree of the throttle 31a is increased, on the contrary, the average air-fuel ratio is in the rich direction. Further, in the case of the throttle 29a of the atmospheric pressure introducing passage 29, it works in the opposite manner to the throttle 31a of the negative pressure introducing passage 31.

In this way, the target air-fuel ratio can be controlled by controlling the opening / closing of the solenoid valve 19 according to the output of the oxygen sensor 13 while the target air-fuel ratio is set in advance by the throttles 29a and 31a. That is, the air-fuel ratio is determined by the output state of the oxygen sensor 13, that is, the period indicating rich and the period indicating lean, so that the throttle 29 as described above.
The target air-fuel ratio can be controlled by setting the degrees of a and 31a.

Further, in this embodiment, the start and stop timings of the air-fuel ratio control device are set as follows.・ Start of air-fuel ratio control At low temperature (at start), from the viewpoint of engine output emphasis,
The air-fuel ratio control by the solenoid valve 19 is not executed until the detection element 13a of the oxygen sensor 13 reaches a certain temperature. That is, at the time of starting, a large amount of fuel is supplied in a state in which the solenoid valve 19 is turned off and the atmospheric pressure introducing passage 31 is fully opened so that the initial fixed value becomes richer than the target air-fuel ratio.
Therefore, the air-fuel ratio in this case is determined by the diaphragms 29a and 31a.

Specifically, since the internal resistance of zirconia has temperature dependence, it is as shown in FIG. 3 (power supply 13a, resistance 1
3b and the detection element 13c made of titania), the sensor output is low at low temperature and decreases as the temperature becomes higher, as shown in FIG. 5. For example, when the sensor output is 1 V or less, The air-fuel ratio control is started on the assumption that the warm-up state has been reached after a predetermined time has passed from the start.

Stop of air-fuel ratio control When the load (throttle opening) is near 100%, the general-purpose engine 1 is driven at a high load and the temperature of the general-purpose engine 1 is high. To
The air-fuel ratio is not substantially controlled by the solenoid valve 19, and the air-fuel ratio is set to the initial rich side.

Particularly, in this embodiment, the opening 31b of the negative pressure introducing passage 31 on the side of the intake pipe 3 serves as the opening a of the throttle valve 7 and the nozzle 25 (set at the narrowest position of the venturi portion 7). Is provided near the throttle valve 7.
Therefore, the negative pressure introduced from the negative pressure introduction path 31 approaches the atmospheric pressure as the throttle valve 7 opens.
Therefore, a little before the load reaches 100%, the solenoid valve 1
The control of the float chamber pressure by 9 can be substantially defeated.

Thus, in this embodiment, the oxygen sensor 1
Since the electromagnetic valve 19 for controlling the opening / closing of the atmospheric pressure introducing passage 29 according to the output of No. 3 is provided, the average air-fuel ratio of the general-purpose engine 1 is preferably controlled to the target air-fuel ratio with a simple configuration to purify the exhaust gas. can do. Further, since the atmospheric pressure introducing path 29 and the negative pressure introducing path 31 are provided with the throttles 29a and 31a, the target air-fuel ratio is set and the air-fuel ratio control is not performed by the diameters of the throttles 29a and 31a. The initial air-fuel ratio can be set.

Furthermore, at the time of start-up, the air-fuel ratio control by the solenoid valve 19 is not performed, and a slightly larger amount of fuel is supplied, so engine stalling can be prevented. Moreover, when the load is near 100%, the air-fuel ratio control is not substantially performed and the engine is operated on the rich side, so that overheating of the general-purpose engine 1 can be prevented.

It is needless to say that the present invention is not limited to the above-mentioned embodiments and can be carried out in various modes without departing from the gist of the present invention. (1) For example, as in the above-described embodiment, the solenoid valve may not be provided in the atmospheric pressure introducing passage, but the solenoid valve may be provided in the negative pressure introducing passage. In this case, the opening / closing control of the solenoid valve is performed in the opposite manner to the case where the solenoid valve is arranged in the negative pressure introducing passage, that is, the opening and closing are reversed.

(2) Further, both the negative pressure solenoid valve and the atmospheric pressure introducing passage may be provided with a solenoid valve. In this case, the configuration becomes complicated, but there is an advantage that more precise control can be performed. (3) Further, the throttles may be provided in either one of the negative pressure introducing passage and the atmospheric pressure introducing passage, or may be eliminated. This is because the diameter of the path and the like exerts the function of the diaphragm as it is without disposing a special diaphragm.

(4) It is not necessary to provide both the negative pressure introducing passage and the atmospheric pressure introducing passage as the passage, and only the atmospheric pressure introducing passage may be used. (5) Instead of the solenoid valve that controls the opening and closing of the atmospheric pressure introducing passage, for example, as shown in FIG. 6, a solenoid valve that switches the path between the float chamber and the atmospheric pressure side or the negative pressure side may be provided. Even in this case, since the pressure introduced into the float chamber can be changed, the same effect as that of the above embodiment can be obtained.

(6) In the above embodiment, the solenoid valve is controlled to open or closed according to the lean or rich signal of the oxygen sensor, but duty ratio control during the valve opening period may be performed, for example.

[0042]

As described above in detail, according to the present invention, the pressure in the float chamber is controlled by controlling the opening / closing of the path by using, for example, an electromagnetic valve in accordance with the output of the oxygen sensor attached to the exhaust side. Since the air-fuel ratio is controlled and adjusted, exhaust gas from a general-purpose engine or the like can be purified with a simple structure.

[Brief description of drawings]

FIG. 1 is a graph showing the pressure in a float chamber that changes due to the action of a throttle.

FIG. 2 is an explanatory diagram showing a configuration of an air-fuel ratio control device according to an embodiment.

FIG. 3 is a circuit diagram showing a configuration of an oxygen sensor.

FIG. 4 is a graph showing the operation of the air-fuel ratio control system of the embodiment.

FIG. 5 is a graph showing the relationship between sensor output and element temperature.

FIG. 6 is an explanatory diagram showing another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... General-purpose engine 3 ... Intake pipe 5 ... Fuel supply part 7 ... Venturi part 9 ... Carburetor 11 ... Exhaust pipe 13 ... Oxygen sensor 19 ... Electromagnetic valve 23 ... Float chamber 25 ... Nozzle 27 ... Throttle valve 29 ... Atmospheric pressure introduction path 29a , 31a ... Restrictor 31 ... Negative pressure introduction path

Claims (6)

[Claims] 1. In a carburetor type air-fuel ratio control apparatus for an internal combustion engine, which supplies fuel in a float chamber to an intake side of the internal combustion engine, a pressure in the float chamber according to an output of an oxygen sensor mounted on an exhaust side. An air-fuel ratio control device for an internal combustion engine, wherein the air-fuel ratio is controlled by adjusting the. 2. A solenoid valve for controlling the opening and closing of a path for introducing pressure into the float chamber according to the output of the oxygen sensor is used as the means for adjusting the pressure inside the float chamber. 1. The air-fuel ratio control device for an internal combustion engine according to 1. 3. The negative pressure introducing passage for introducing the negative pressure on the intake side into the float chamber and / or the atmospheric pressure introducing passage for introducing atmospheric pressure into the float chamber. The air-fuel ratio control device for an internal combustion engine according to claim 2. 4. The solenoid valve switches between a negative pressure introducing passage for introducing the negative pressure on the intake side into the float chamber and an atmospheric pressure introducing passage for introducing atmospheric pressure into the float chamber. An air-fuel ratio control device for an internal combustion engine according to claim 3. 5. The air-fuel ratio control device for an internal combustion engine according to claim 2, wherein the air-fuel ratio is set according to the degree of throttle of the path. 6. The air-fuel ratio control device for an internal combustion engine according to claim 5, wherein the degree of the throttle is set by setting the diameter of the throttle nozzle.