JPH05312113A - Evaporative emission control device - Google Patents

Abstract

PURPOSE:To provide an evaporative emission control device capable of carrying out the most suitable purge control without damaging air-fuel ratio controllability. CONSTITUTION:A fuel tank 6 is communicated through to a canister 8, and in the canister 8, activated carbon 9 is stored and a purge air introduction port 15 is formed. The canister 8 is communicated through to an air intake pipe 2 by a discharge passage 10. In the middle of the discharge passage 10, a solenoid valve 11 for purge is provided. An ECU 27 duty-controls the solenoid valve 11 for purge in accordance with an intake air amount. On the purge air introduction port 15 of the canister 8, a pressure air pump 17 is provided through a pressure governing chamber 16. A pressure regulator 18 makes pressure differential between pressure of the purge air introduction port 15 and air intake pipe pressure constant by way of regulating pressure of the pressure governing chamber 16 in accordance with the air intake pipe pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel evaporative gas diffusion prevention device.

[0002]

2. Description of the Related Art In recent years, attention has been paid to the problem of air pollution caused by fuel vapor emitted from a vehicle into the atmosphere. And
The fuel evaporative gas diffusion prevention device disclosed in Japanese Patent Laid-Open No. 62-153553 or the like temporarily adsorbs the fuel evaporative gas generated in the fuel tank to the activated carbon of the canister. Furthermore, by utilizing the fact that the intake pipe pressure of the internal combustion engine is negative when the internal combustion engine is operating, the fuel evaporative gas adsorbed in the canister is connected to the purge solenoid valve together with the fresh air from the purge air inlet of the canister. It is designed to be released through the intake pipe.

[0003]

However, although the intake pipe pressure changes with the change of the operating state of the internal combustion engine, when the intake pipe pressure changes, the pressure at the purge air inlet of the canister and the intake pipe pressure change. The differential pressure of changes. for that reason,
The purge flow rate changes and the air-fuel ratio controllability deteriorates.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel evaporative gas diffusion preventive device capable of performing optimum purge control without impairing air-fuel ratio controllability.

[0005]

According to the present invention, there is provided a canister, which is in communication with a fuel tank, accommodates an adsorbent for adsorbing fuel evaporative gas in the fuel tank, and has a purge air introduction port, the canister and an internal combustion engine. A discharge passage communicating with the intake pipe, an opening / closing means provided in the discharge passage for opening and closing the passage, and a purge air introduction port of the canister, the air pressure at the purge air introduction port being equal to or higher than atmospheric pressure. And a pressure adjusting means for adjusting the pressure of the purge air introducing port of the canister according to the intake pipe pressure to make the differential pressure between the purge air introducing port pressure and the intake pipe pressure constant. A fuel evaporative gas diffusion prevention device including purge control means for controlling the opening / closing means to release the fuel evaporative gas from the canister to the intake pipe of the internal combustion engine in accordance with the operating state of the internal combustion engine. The is to its gist.

[0006]

The pressure source is used to pressurize the air at the purge air introducing port, and the pressure adjusting means adjusts the pressure at the purge air introducing port of the canister in accordance with the pressure of the intake pipe to adjust the pressure at the purge air introducing port. Keep the pressure difference with the intake pipe pressure constant. Then, the purge control means controls the opening / closing means to release the fuel vaporized gas of the canister to the intake pipe of the internal combustion engine according to the operating state of the internal combustion engine. As a result, fuel evaporative emission is performed in a state where the pressure difference between the purge air inlet of the canister and the intake pipe pressure is constant, and the intake pressure changes as the operating state of the internal combustion engine changes. Also, the amount of fuel evaporative emission is always constant.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to the drawings. An engine 1 as an internal combustion engine shown in FIG. 1 is mounted on a vehicle, and an intake pipe 2 is installed in the engine 1.
Are connected. A throttle valve 3 is provided in the intake pipe 2, and intake air according to the opening degree of the throttle valve 3 is taken into the engine 1 through an air cleaner 4. An air flow meter 5 is provided in the intake pipe 2, and the intake air amount is detected by the air flow meter 5. In addition, throttle valve 3
The pressure of the intake pipe 2 on the downstream side is detected by the pressure sensor 28.

The upper surface of the fuel tank 6 is connected to the intake pipe 2 downstream of the throttle valve 3 by a purge pipe 7. A canister 8 is arranged in the middle of the purge pipe 7, and activated carbon 9 as an adsorbent is stored in the canister 8.
Then, the fuel evaporative gas in the fuel tank 6 is adsorbed by the activated carbon 9 in the canister 8. The purge pipe 7 has a discharge passage 10 on the intake pipe 2 side of the canister 8, and a purge solenoid valve 11 as an opening / closing means is provided in the discharge passage 10.

In this purging solenoid valve 11, a valve body 12 is constantly urged by a spring (not shown) in a direction to open the seat portion 13. However, by exciting the coil 14, the valve body 12 is seated in the seat portion 13. Is designed to close.
Therefore, the release passage 10 is opened by demagnetizing the coil 14 of the purging solenoid valve 11, and the release passage 10 is closed by exciting the coil 14. Then, an electronic control unit (hereinafter referred to as ECU) 2 as a purge control means
By the duty control of the purging solenoid valve 11 by 7, the purging solenoid valve 11 has a predetermined opening degree, and the fuel evaporative gas adsorbed on the activated carbon 9 of the canister 8 is introduced into the intake pipe 2 together with the fresh air from the purge air inlet 15. Is released.

A pressure adjusting chamber 16 is connected to the purge air introducing port 15 of the canister 8. A pressure air pump 17 as a pressure source is provided in the pressure regulation chamber 16, and the pressure air pump 17 is constantly driven by the engine 1. The pressurized air pump 17 is driven to supply pressurized air into the pressure regulating chamber 16, so that the pressure in the pressure regulating chamber 16 becomes equal to or higher than the atmospheric pressure. The pressure regulator chamber 16 is adjusted by the pressure regulator 18 serving as a pressure adjusting means so as to have a constant differential pressure with respect to the pressure of the intake pipe 2.

FIG. 2 shows the structure of the pressure adjusting section. The inside of the casing 19 of the pressure regulator 18 is the diaphragm 2
It is divided by 0 into a first chamber 21 and a second chamber 22.
The first chamber 21 communicates with the inside of the pressure regulation chamber 16, and the second chamber 22 communicates with the intake pipe 2 downstream of the throttle valve 3 by a communication pipe 23 (see FIG. 1). That is, the pressure of the pressure regulation chamber 16 is introduced into the first chamber 21, and the intake pipe pressure is introduced into the second chamber 22. One end of the atmosphere communication pipe 24 is arranged in the first chamber 21 of the pressure regulator 18, and the other end of the atmosphere communication pipe 24 is open to the atmosphere. The diaphragm 20 in the casing 19 has a first spring 26.
A force that deforms is applied to the chamber 21 side. A valve body 25 is fixed to the diaphragm 20, and the valve body 25 opens and closes the opening of the atmosphere introducing pipe 24 as the diaphragm 20 is deformed.

Then, with respect to the set load of the spring 26 for urging the valve body 25 in the closing direction, the first chamber 21 and the second chamber 2
When the force that urges the valve element 25 in the opening direction due to the pressure difference from the valve 2 is small, the valve element 25 closes the atmosphere communication pipe 24.
Further, when the pressure difference between the first chamber 21 and the second chamber 22 becomes equal to or more than the set load of the spring 26, the valve body 25 operates to relieve the pressure in the first chamber 21 from the atmosphere communication pipe 24.

The pressure in the pressure adjusting chamber 16 (that is, the purge air introducing port 15 of the canister 8) is adjusted as shown in FIG.
That is, the intake pipe pressure (relative pressure to atmospheric pressure) is -40
When the pressure is 0 mmHg or less, the pressure of the purge air introduction port 15 (pressure adjusting chamber 16) becomes atmospheric pressure. Also, the intake pipe pressure is -40
When the operating load is 0 mmHg or more, the pressure in the pressure regulation chamber 16 also increases, and the pressure difference between the pressure regulation chamber 16 and the intake pipe pressure is 400
mmHg becomes constant. In other words, 400m which is critical pressure
It is set to mHg.

Next, the operation of the fuel evaporative gas diffusion preventing device thus constructed will be described. As shown in FIG. 3, the pressure regulator 18 keeps the intake pipe pressure at -400 m.
When the pressure is less than mHg, the purge air inlet 15 (pressure regulating chamber 1
The pressure of 6) becomes atmospheric pressure. Also, the intake pipe pressure is -400
When the operating load is equal to or higher than mmHg, the pressure in the pressure regulation chamber 16 also increases, and the differential pressure between the purge air introduction port 15 (pressure regulation chamber 16) and the intake pipe pressure becomes 400 mmHg constant. Thus, the pressure regulator 18 keeps the pressure difference between the inlet and outlet of the purging solenoid valve 11 at 400 mmHg (critical pressure) or more.

In such a state, the ECU 27 takes in the intake air amount Q by the air flow meter 5 and takes in the intake pipe pressure by the pressure sensor 28 as shown in the flowchart of FIG. 5 (step 51). And
The ECU 27 calculates the opening degree of the purging solenoid valve 11 using the map shown in FIG. 4, and controls the purging solenoid valve 11 with a duty ratio corresponding to the opening degree of the purging solenoid valve 11 (step 52). ). As a result, the purge gas (fuel evaporative gas + fresh air) according to the intake air amount Q is released from the canister 8 to the intake pipe 2. That is, the duty is controlled so that the optimum purge amount is obtained according to the engine operating parameter.

At this time, since the pressure difference at the inlet and outlet of the purging solenoid valve 11 is always 400 mmHg (critical pressure) or more, it is linear with respect to the opening degree of the purging solenoid valve 11 in the entire operating region of the engine 1. A good purge flow rate characteristic can be obtained. As a result, it is not necessary to adapt the drive duty of the purging solenoid valve 11 for each operating region, and it is possible to calculate the purge amount with respect to the intake air amount and perform precise control. Further, when the pressurized air pump 17 and the pressure regulator 18 were not provided, a sufficient purge flow rate could not be secured in the high load region where the differential pressure between the discharge passage 10 of the canister 8 and the purge air introduction port 15 was small. By using the compressed air pump 17 and the pressure regulator 18, a sufficient purge flow rate can be secured even in a high load region.

Then, the ECU 27 judges whether the intake pipe pressure (relative pressure with respect to the atmospheric pressure) P is -400 mmHg or less (step 53).
Is stopped, and the pressurized air pump 17 is driven when the following conditions are not satisfied (steps 54 and 55). By doing so, the life of the pressurized air pump 17 can be extended.

The opening of the purging solenoid valve 11 may be determined by engine parameters such as engine speed and throttle opening, in addition to the intake air amount. As described above, in the present embodiment, the pressurized air pump 17 (pressurizing source) is provided at the purge air introduction port 15 of the canister 8, and the pressure regulator 18 (pressure adjusting means) is used to purge the canister 8 according to the intake pipe pressure. The pressure of the inlet port 15 was adjusted so that the pressure difference between the purge air inlet port 15 and the intake pipe pressure was kept constant. As a result, the fuel evaporative emission is performed in a state where the pressure difference between the purge air introduction port 15 of the canister 8 and the intake pipe pressure is constant, and the intake pressure changes as the operating state of the engine 1 changes. However, if the opening degree of the purging solenoid valve 11 is the same, the amount of fuel evaporative emission is always constant. Therefore, optimal purge control can be performed without impairing the air-fuel ratio controllability. Also, the pressure difference at the inlet and outlet of the purging solenoid valve 11 is always 400 mmH.
Since the pressure is equal to or higher than g (critical pressure), a sufficient purge flow rate can be secured even during high load operation in which the negative pressure in the intake pipe becomes small.

The present invention is not limited to the above embodiment. For example, although the pressurized air pump 17 is used only for supplying purge air in the above embodiment, air is introduced into the exhaust system of the engine. A part of the pressure of an air pump for other purposes such as a secondary air pump for this purpose or an air mixing injector may be used.

Further, in the above embodiment, the intake pipe pressure sensor 28
When the intake pipe pressure by -400 mmHg or less, the driving of the pressurized air pump 17 was stopped.
May be always driven by the engine 1.

[0021]

As described in detail above, according to the present invention,
It has an excellent effect that the optimum purge control can be performed without impairing the air-fuel ratio controllability.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a fuel evaporative gas diffusion prevention device.

FIG. 2 is a diagram showing a pressure adjusting unit.

FIG. 3 is a diagram showing pressure regulation characteristics.

FIG. 4 is a diagram showing a map for determining the opening degree of a purging solenoid valve.

FIG. 5 is a flowchart illustrating the operation of the ECU.

[Explanation of symbols]

 2 Intake pipe 6 Fuel tank 8 Canister 9 Activated carbon as adsorbent 10 Release passage 11 Purge solenoid valve as opening / closing means 15 Purge air inlet 17 Pressurized air pump as pressurizing source 18 Pressure regulator as pressure adjusting means 27 Purge ECU as control means

Claims (3)

[Claims] 1. A canister which communicates with a fuel tank, accommodates an adsorbent for adsorbing fuel evaporative gas in the fuel tank, and has a purge air introduction port, and a discharge passage which communicates the canister with an intake pipe of an internal combustion engine. An opening / closing means provided in the discharge passage for opening and closing the passage, and a pressure source provided at the purge air introduction port of the canister for making the air pressure at the purge air introduction port equal to or higher than atmospheric pressure. A pressure adjusting means for adjusting the pressure of the purge air introducing port of the canister according to the intake pipe pressure to make the differential pressure between the pressure of the purge air introducing port and the intake pipe pressure constant; And a purge control means for controlling the opening / closing means to release the fuel vaporized gas of the canister to the intake pipe of the internal combustion engine. 2. The fuel evaporative gas diffusion prevention device according to claim 1, wherein the pressure adjusting means sets the purge air introduction port to the atmospheric pressure when the intake pipe pressure is equal to or lower than a predetermined value. 3. The pressurizing source is a pressurized air pump driven by an internal combustion engine, and the pump is stopped when the intake pipe pressure is below a predetermined value. Fuel evaporation gas diffusion prevention device.