JPS58119956A - Fuel vapor emission preventing device in internal-combustion engine - Google Patents

Abstract

PURPOSE:To prevent the supply of excessive rich mixture experienced upon engine restarting for avoiding deterioration of discharge emission, difficulty in restarting, etc., by adjusting purge air in association with the outputs of alcohol concentration and fuel temperature sensors. CONSTITUTION:A solenoid valve 21 is energized so that a shut-off valve 24 is lifted up overcoming a spring 25 when the alcohol concentration in fuel is higher than a predetermined value and as well the temperature of fuel is higher than a predetermined value, and therefore, a second purge air orifice 19 is opened. Further, purge air is mainly led to the second purge orifice 19, and therefore, a mixture from the first purge air orifice 9' is thinned by purge air from the second purge air orifice 19, thereby the thickening of mixture fed to an internal- combustion engine 16 is restriced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel vapor evaporation prevention device for an internal combustion engine, and more particularly to a canister purge control κ.

As a conventional fuel vapor evaporation prevention device, for example, Fig. 1K
As shown, fuel vapor generated in a fuel tank 1 is led to a canister 4 via a 7-well vent line 2 and a check valve 3, and is then transferred to an adsorbent 6 such as activated carbon filled in the canister 4 via filters 5 and 7. Some are designed to temporarily store fuel vapor. Reference numeral 8 denotes a purge air introduction part which opens the bottom of the canister 4 to the atmosphere through the filter 7.

Further, an orifice 9 for controlling the amount of purge air is provided in the upper space of the canister 4, which is separated from the adsorbent 6 via the filter 5, and this orifice 9 is opened and closed by a purge control valve 10 to control the canister 4 during engine operation. It is possible to purge. 11 is a spring that biases the diaphragm valve 12 of the purge control valve 10 to close; 13 is a vacuum signal line that communicates the negative pressure chamber of the purge control valve 10 with the vaporizer throttle valve; 11 is an air cleaner, and 18 is an air cleaner element.

An example of such a conventional structure is NAP8-
Z1978 Technical Manual P-17VsfJ. There is a disclosure in the figure.

In the above configuration, when the engine 1 is started, negative pressure is generated in the carburetor throttle valve section, and this negative pressure passes through the vacuum signal line 13 to the negative pressure chamber of the purge valve 10. be guided. Further, since the negative pressure becomes stronger as the rotational speed of the engine 16 increases, when the rotational speed of the engine 16 exceeds a predetermined value, the diaphragm valve 12 is pulled up against the spring 11 and opened. Then, the orifice 9 is opened, so the negative pressure in the intake pipe 15 is guided to the canister 4, and the purge air flows from the purge air introduction part 8 through the filter T into the canister 4 in an amount determined by the orifice S.
Fuel vapor adhering to the surface of the adsorbent 6 is purged.

This purge air mixes with the fuel vapor released from the adsorbent 6, flows into the intake pipe 15 through the purge line 14, and is sent into the combustion chamber of the engine 16.

However, in such conventional fuel vapor evaporation prevention devices, when a highly volatile fuel such as alcohol-mixed gasoline, which is gasoline mixed with alcohol such as methanol or ethanol, is used, a so-called azeotropic phenomenon occurs. This increases the volatility of the lubricant. In particular, if the engine is operated under high load and then stopped and then restarted within a few minutes, the engine ambient temperature will have reached 40 to 60 degrees, so the fuel vapor filling the canister will start the engine. A large amount flows into the intake pipe during or after startup. As a result, the air-to-air ratio of the engine intake air-fuel mixture is reduced, which sharpens exhaust emissions (increases CO).
In addition, in extreme cases, the air-fuel mixture becomes too rich, making it difficult to restart the engine or deteriorating the stability of the engine.

The present invention has been made in view of the above K@, and detects the presence or absence of alcohol in the fuel and the alcohol concentration using an alcohol intensity sensor, and detects the presence or absence of alcohol in the fuel and the alcohol concentration when the alcohol concentration is equal to or higher than a predetermined value and the fuel temperature is a predetermined value. In such cases, increase the amount of purge air to suppress the enrichment of the mixture ratio of fuel and air purged into the intake system, thereby preventing the supply of an excess a mixture that is seen at restart. The purpose of this is to avoid deterioration of exhaust emissions and difficulty in restarting the engine.

The present invention will be explained in detail below based on the embodiment shown in FIG. 2K. In the figure, portions K having the same functions as those of the conventional example shown in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. K, the carburetor 4 is provided with a first purge air orifice V that is controlled to open when the negative pressure in the vaporizer throttle valve reaches a predetermined level or higher, as in the conventional case. Separately, a barge air orifice 7 chair 19 is provided, and the barge line 14 is communicated with the upper space K of the canister 4 via these two orifices v and 19.

On the other hand, an alcohol concentration sensor 20 for detecting the alcohol concentration in the fuel is provided at a location where liquid fuel is always present, such as the fuel tank 1, a fuel filter (not shown), or a fuel line, etc., and the output of this alcohol concentration sensor 20 is A "1-on-off valve 24 is attached via the shaft 23 to the tip of the solenoid valve 21 that operates based on the
The purge air orifice lit is opened and closed. Incidentally, the output signal of the alcohol concentration sensor 20 is transmitted through a capacitance-frequency conversion circuit 22a and a frequency-voltage converter 2.
2b and inverting amplifier 22c cape 1 configured processing circuit 22
The alcohol concentration is supplied to the solenoid valve 21 via the fuel temperature sensor 28, and the solenoid valve 21 is activated only when the alcohol concentration detected through the alcohol concentration window 20 is above a predetermined value and the fuel temperature is above the predetermined value. The communication is activated to open the purge air orifice 1s @2. 25
26 is an air introduction pipe for introducing the second purge air OLIICE 1IK purge air, and 21 is a pore provided in the wall of the air introduction pipe 26.

In the above configuration, for example, in the case of Arsul mixed gasoline in which alcohol is mixed with gasoline at a volume ratio of about 15, the volatility of the fuel increases due to the so-called azeotropic phenomenon, compared to the case of pure gasoline. Approximately twice as much fuel vapor is generated under the same conditions. In addition, most of the fuel vapor generated in this way is stored in the canister 4 and discharged into the intake system through the purge line 14 when the engine 16 is operated, but it is temporarily stored in the adsorbent 6 of the canister 4. Since there is a large amount of stored fuel vapor, the mixture ratio of purge air and fuel discharged into the intake system via the purge line 14 will be approximately twice as rich as when using pure gasoline if the amount of purge air is constant. There is no need to elaborate on what happened.

Therefore, when a lean mixture is discharged into the intake system as described above, the air-fuel ratio of the mixture supplied to engine 1 becomes excessively rich, leading to an increase in CO emissions, and in extreme cases, The stability of the engine may drop significantly and it may become impossible to operate (unable to start).

However, according to the present invention, when the alcohol concentration in the fuel is above a predetermined value and the fuel temperature is above a predetermined value, the solenoid valve 21 is energized and the spring 25 is
Since the on-off valve 24 is pulled up against K, the second purge air orifice 1s is opened. In addition, since purge air is mainly guided to the second purge air orifice 1s, the air-fuel mixture flowing out from the first purge air orifice V is diluted by the purge air flowing out from the second purge air orifice 1, which is different from the conventional method. This prevents the rich air-fuel mixture from flowing into the intake system, suppressing the concentration of the air-fuel mixture supplied to the engine 16.

In the embodiment, the purge air introduction section 8 and the second purge air orifice 1s are communicated through the air introduction pipe 26, and a small hole 27 is provided in the air introduction pipe 26 to allow part of the fuel vapor to flow through the air introduction pipe 26. Although purging is possible, only the purge air may be guided to the second nozzle air orifice 1l.

Also, when the amount of fuel vapor generated is small, such as when the alcohol concentration is below a predetermined value or when the fuel temperature is below a predetermined value, the second barge air orifice 19 is closed, so the same procedure as in the conventional case is performed. -ji will be carried out.

Incidentally, there is a type of alcohol concentration sensor 20 that utilizes the difference in dielectric constant between gasoline and alcohol. A capacitance-frequency conversion circuit is connected to the circuit, and as shown in the example, by applying a voltage of a predetermined frequency to generate CB, the difference in capacitance is extracted as a frequency change, and then this is converted into a voltage. If you extract it as a value, you can achieve the desired purpose.

As explained above, according to the present invention, since the amount of barge air is increased when the alcohol concentration in the fuel and the fuel temperature are each above a predetermined value, there is sufficient flow when fuel vapor is generated frequently. The amount of air can be obtained, and enrichment of the engine mixture can be suppressed. Therefore, over-enrichment of the engine intake air-fuel mixture due to canister nozzle is eliminated, and CO emissions can be reduced, and at the same time, the stability of the engine can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional example, and FIG. 2 is a block diagram of an embodiment of the present invention. 1...Fuel tank 2...Fuel vent line 3
... Check valve 4 ... Canister 6 ... Adsorbent ... Purge air introduction section V ... First purge air orifice 10 ... Nocturnal control valve 14
...Hersiline 1S...Intake pipe 16...Engine 1
s...Second nozzle air orifice 20...Alcohol concentration sensor 1...Solenoid valve 24...Opening/closing valve 28...Fuel temperature sensor -292-

Claims (1)

[Scope of Claims] (1) In an internal combustion engine equipped with a carburetor that is filled with an adsorbent to temporarily store fuel vapor generated in a fuel tank and that causes the stored fuel vapor to be sucked into the engine together with purge air. It is equipped with an alcohol concentration sensor that detects the alcohol concentration, a fuel temperature sensor that detects the temperature of the fuel, and a purge control valve that controls the amount of purge air in the canister. A fuel vapor evaporation prevention device for an internal combustion engine configured to adjust the amount of purge air by adjusting the amount of purge air. and a second barge air orifice that increases abdominal opening when the alcohol freshness and fuel temperature detected through a concentration sensor and a fuel temperature sensor are above a predetermined value. The fuel vapor evaporation prevention device for an internal combustion engine according to item 1.