JPH05240119A - Fuel vapor controller - Google Patents

Abstract

(57) [Abstract] [Purpose] In a throttle purge type fuel vapor control device, a large flow rate purge is enabled and an air-fuel ratio overrich is prevented from occurring during idling. A solenoid valve 6 is provided in a purge passage 5 that connects a portion of an intake pipe 12 near a throttle valve 11 and a canister 3. The solenoid valve 6 closes the purge passage 5 at least when the throttle valve 11 is fully closed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel vapor control device for preventing fuel vapor generated from a fuel tank of an automobile or the like from being released to the atmosphere.

[0002]

2. Description of the Related Art In order to prevent the fuel vapor generated from a fuel tank from being released into the atmosphere and causing air pollution, the fuel vapor is adsorbed and collected by a canister filled with activated carbon or the like. Controllers are commonly used. In these devices, in order to prevent the activated carbon from being saturated by the adsorbed fuel vapor, the canister is purged by using the negative pressure of the intake pipe during engine operation, and the fuel vapor is discharged from the activated carbon to be inhaled into the engine. ing.
That is, a method is generally adopted in which a purge passage that connects the canister and the engine intake passage is provided for purging the canister, and the fuel vapor is sucked from the canister by the intake pipe negative pressure generated during engine operation.

However, if the purge passage is connected to an opening (purge port) provided in the intake passage on the downstream side of the throttle valve for purging, a negative pressure is always applied to the purge port, especially the throttle valve. The negative pressure acting on the purge port increases during idle operation when the valve is fully closed. For this reason, if a purge port is provided on the downstream side of the throttle valve, a large amount of fuel will be released from the canister during idle operation, and the air-fuel mixture supplied to the engine will become excessive in fuel, making idle rotation unstable, or in extreme cases. There may be a problem with the engine stalling.

In order to prevent this problem, a so-called throttle purge type fuel vapor control device has been devised in which the purge port is arranged in the intake pipe in the vicinity of the throttle valve. In the throttle purge system, the purge port opening position of the intake pipe is located upstream of the valve body of the throttle valve when the throttle valve is fully closed, and downstream of the valve body when the throttle valve is slightly open. Is set to.
By providing the purge port at such a position, it is possible to prevent negative pressure when the throttle valve is fully closed during idle operation or the like from acting on the purge port. Further, when the throttle valve is partially opened, a negative pressure acts on the purge port, so that the canister can be purged.

An example of the throttle purge type fuel vapor control device is disclosed in Japanese Patent Application Laid-Open No. 58-35256. The device of the publication does not only prevent a large amount of fuel from being discharged into the intake pipe due to a large negative pressure acting on the purge port when the throttle valve is fully closed by using the throttle purge system. A flow control valve that operates at the engine temperature is installed in the engine to adjust the purge flow rate of the canister according to the engine temperature. That is, when the engine temperature is high, the amount of evaporation from the fuel tank also increases. Therefore, in the device of the publication, the amount of fuel vapor released to the intake pipe is reduced by reducing the purge flow rate when the engine temperature is high. This is because if a large amount of fuel is released when the engine temperature is high, the air-fuel ratio may become excessively fueled, for example, when the throttle valve has a partial opening and the intake flow rate is small, resulting in deterioration of exhaust gas properties and exhaust purification. This is because problems such as overheating of the catalyst may occur.

[0006]

However, even if the throttle purge system is adopted and negative pressure does not act on the purge port when the throttle valve is fully closed, fuel may be released from the canister during idle operation. .. For example, when the outside air temperature is high, the vaporization amount of fuel increases and the vapor pressure also increases. Therefore, a large amount of fuel vapor may leak from the canister to the purge port even if the negative pressure does not act on the purge port.

If the fuel vapor leaks when the throttle valve is fully closed and the intake air flow rate is small, idle instability and stall due to excess fuel may occur as described above. Further, in an engine having an electronically controlled fuel control device that performs learning control of the air-fuel ratio using an exhaust air-fuel ratio sensor, learning control is erroneously performed and the engine air-fuel ratio during normal operation is controlled to the lean side. , There may be a problem that the amount of NOx emission increases.

A check ball type control valve, which is generally used in the past, is provided in the purge passage so that the control valve opens only when the differential pressure across the control valve exceeds a certain value. To some extent, this problem can be prevented by purging the canister. However, when the capacity of the fuel tank is large, the amount of fuel vapor generated is also large, so the amount of vapor adsorbed in the canister also increases. Therefore, in order to prevent the saturation of the canister, it is necessary to flow a relatively large amount of purge flow during operation, and if the above-mentioned check ball is provided in the purge passage, the purge cannot be performed sufficiently due to an increase in the line resistance. May occur.

In view of the above problems, the present invention enables a large flow rate purge of a canister without providing a resistance member such as a check ball in the purge passage, and also causes an air-fuel ratio overrich during idle operation. It is an object of the present invention to provide a throttle purge type fuel vapor control device capable of preventing the above.

[0010]

According to the present invention, a canister for adsorbing evaporated fuel from a fuel tank and a purge passage for connecting the canister and an intake passage of an engine are provided, and the fuel adsorbed in the canister is provided. In the fuel vapor control device for discharging the air into the intake passage through the purge passage, the purge passage is connected to the intake pipe at least at a position upstream of the throttle valve when the throttle valve is fully closed, and at least A fuel vapor control apparatus is provided, which is provided with valve means for closing the purge passage when the engine is idle.

[0011]

With the use of the valve means provided in the purge passage, the purge passage is closed at least when the throttle valve is fully closed so that the air-fuel ratio does not become overrich during idle operation. Further, since a check ball or the like having a large conduit resistance is not provided in the purge passage, a large flow rate of the canister can be purged under conditions other than when the throttle valve is fully closed.

[0012]

FIG. 1 shows an embodiment of the fuel vapor control device of the present invention. In the figure, 21 is an engine, 1 is an engine 2
A fuel tank 1 and 3 are canisters filled with activated carbon or the like. The canister 3 is connected to the gas phase portion of the fuel tank 1 by a communication pipe 2 such as a hose. Further, reference numeral 18 is a pressure regulating valve for allowing vapor to flow into and out of the canister 3 when a difference occurs between the pressure in the fuel tank 1 and the pressure in the canister due to temperature change or the like.

The canister 3 communicates with the atmosphere through the atmosphere opening hole 4 and also the engine 21 through the purge passage 5.
Is connected to the intake pipe 12. In the present embodiment, the purge passage 5 is not provided with a control valve such as a check ball having a large flow resistance, but is provided with an electromagnetic shutoff valve 6 having a low resistance when the valve is opened.

The purge passage 5 is connected to a purge port 8 that opens near the throttle valve 11 of the intake pipe 12, and the intake pipe 1
Communicate with 2. The throttle valve 11 has a well-known butterfly type valve body, and the purge port 8 has a throttle valve 11 when the valve body of the throttle valve 11 is fully closed.
When the throttle valve 11 is located upstream of the valve body and the throttle valve 11 is rotated to bring the throttle valve 11 into the partial opening state, the throttle valve 11 is located downstream of the valve body.

Therefore, when the throttle valve 11 is fully closed, the purge port 8 maintains a pressure substantially equal to the atmospheric pressure even if a negative pressure is generated in the intake pipe on the downstream side of the throttle valve. On the other hand, when the throttle valve 11 is in the partial opening state, the purge port 8 comes to be positioned on the downstream side of the valve body of the throttle valve 11, so that the negative pressure in the intake pipe acts on the purge port 8.

The reference numeral 9 in FIG. 1 indicates the intake pipe 1.
The air cleaners 2 and 10 are air flow meters for directly measuring the intake air amount, and include, for example, a potentiometer to generate an output signal of an analog voltage proportional to the intake air amount. The throttle valve 11 is provided with an idle switch 17 that outputs a signal indicating whether the throttle valve is fully closed. Reference numeral 15 denotes a cooling water temperature sensor provided in the cooling passage of the engine, which generates an output signal of an analog voltage according to the engine cooling water temperature.

Air flow meter 10, idle switch 1
7. The output of the cooling water temperature sensor 15 is input to the control circuit shown in FIG. In this embodiment, the control circuit 16 is R
It is configured as a known microcomputer including an OM (read only memory), a RAM (random access memory), a CPU (central processing unit), an input / output interface, etc., and as described later, the cooling water temperature and the intake air amount, the idle switch 17 Whether or not the canister 3 can be purged is determined from the output or the like, and the opening / closing operation of the solenoid valve 6 is performed through a drive circuit (not shown).

FIG. 2 is a flow chart showing the opening / closing control operation of the solenoid valve 6 of the control circuit 16 in this embodiment. This routine is executed every fixed time or every predetermined rotation angle of the engine crankshaft (for example, every 360 degrees). When the routine starts, it is determined in step 100 whether the engine cooling water temperature THW read from the cooling water temperature sensor 15 is lower than a predetermined temperature T ₀ .

The temperature T ₀ is a temperature at which the engine is judged to be warmed up, and for example, in the present embodiment, T ₀ = 50 ° C. is set. When the cooling water temperature THW is lower than T _0, in order to stop the purging of the canister 3, the routine proceeds to step 140, where the solenoid valve 6 is closed. As a result, fuel leakage from the purge port 8 is completely prevented. When the engine is not warmed up, the purging is stopped because the exhaust purification catalyst does not reach the activation temperature when the engine temperature is low, the conversion rate of HC, CO, etc. is reduced, and the air-fuel ratio control is performed. Since the O ₂ sensor is also not activated, the air-fuel ratio cannot be controlled. Therefore, if excess fuel is supplied by purging, H in the exhaust gas will be reduced.
This is because C and CO may increase significantly.

Further, when the engine temperature is low, the fuel injection amount may be increased, and if the purge is performed in this state, the air-fuel ratio may become overrich, so the purge is stopped at the low temperature. THW ≧ 100 in step 100
If it is determined to be T ₀ , step 110 and step 1
The intake air amount per engine revolution (Q /
N) is lower than a predetermined value (Q / N) ₀ (step 11)
0) and whether the throttle valve is fully closed (step 12)
0), is determined. If either of the steps 110 and 120 is negative, the solenoid valve 6 is closed in step 140, the purging of the canister 3 is stopped, and only if both steps 110 and 120 are affirmative. In step 130, the solenoid valve 6 is opened. As a result, the canister 3 is purged by the air sucked from the atmosphere opening hole 4, and the fuel vapor adsorbed on the activated carbon is discharged into the intake pipe 12 via the purge passage 5, the solenoid valve 6, the purge port 8 and the like. As described above, the purge passage 5 is not provided with a check ball or the like that generates a pipe resistance, and the pipe resistance when the solenoid valve 6 is open is small. Can be drained.

The throttle valve is fully closed (step 13
0) other than 0), whether or not the purge is possible is determined by the value of (Q / N) (step 120) because the relative position of the purge port 8 and the throttle valve 11 varies within a certain tolerance. This is because the negative pressure applied to the purge port 8 may fluctuate at a position where the valve 11 is slightly opened from the fully closed state. When the intake air amount is small, the purge is stopped and a large amount of fuel is generated due to the negative pressure fluctuation. This is to prevent inhalation.

Further, by determining whether or not purging is possible based on the amount of intake air, for example, when traveling on a long downhill road in a state where the throttle valve is slightly opened and the idle switch is turned off. Even if the intake air amount is smaller than that at the time of idling, the purge is performed and the air-fuel ratio is prevented from becoming overrich. Here, the predetermined value (Q / N) ₀ is a value smaller than (Q / N) during engine idle or deceleration operation.

In this embodiment, purging is stopped when the intake air amount (Q / N) per engine revolution is smaller than a predetermined value in step 110, but instead of (Q / N) The purge may be stopped when the air amount Q is smaller than a predetermined value, the fuel injection amount TAU is smaller than a predetermined value, or when the fuel cut is being executed.

[0024]

As described above, the present invention has the effects of enabling a large flow rate purge of the canister and reliably preventing the air-fuel ratio from becoming overrich during idling.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a fuel vapor control device of the present invention.

FIG. 2 is a flowchart showing the operation of the fuel vapor control device of the present invention.

[Explanation of symbols]

 1 ... Fuel tank 2 ... Communication pipe 3 ... Canister 4 ... Atmosphere opening hole 5 ... Purge passage 6 ... Solenoid valve 8 ... Purge port 9 ... Air cleaner 10 ... Air flow meter 11 ... Throttle valve 12 ... Intake pipe 15 ... Cooling water temperature sensor 16 Control circuit 17 Idle switch 18 Pressure regulator 21 Engine

Claims (1)

[Claims] 1. A canister for adsorbing evaporated fuel from a fuel tank, and a purge passage connecting the canister with an intake passage of an engine, wherein the fuel adsorbed in the canister is introduced into the intake passage through the purge passage. In the fuel vapor control device that discharges to the fuel vapor control device, the purge passage is connected to a position of the intake pipe that is on the upstream side of the throttle valve at least when the throttle valve is fully closed, and the purge passage is closed at least during idle operation of the engine. A fuel vapor control device comprising a valve means for controlling the fuel vapor.