JP2006329086A - Evaporated-fuel treatment device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent evaporated fuel in a canister from being saturated even if a detection characteristic of an airflow meter is varied in an evaporated-fuel treatment device for controlling a purge flow rate from an intake air flow rate. <P>SOLUTION: A difference between an intake air flow rate Qa detected by the airflow meter and an intake air flow rate Qb determined by a throttle opening degree TVO and an engine revolving speed Ne is calculated. When the difference is equal to or more than a threshold value, the purge flow rate calculated from the intake air flow rate Qa is amended according to a correction value calculated from the difference. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an evaporated fuel processing apparatus that collects evaporated fuel generated in a fuel tank in a canister and purges the evaporated fuel collected in the canister into an intake passage of an engine.

Patent Document 1 discloses an air-fuel ratio control device for an engine that controls the duty ratio of the purge flow rate to the intake passage of the engine based on the intake air flow rate and the intake pipe pressure of the engine.
Japanese Patent No. 3315025

By the way, when the purge flow rate is controlled in accordance with the intake air flow rate of the engine, the detection result of the air flow meter is used. However, the detection characteristics of the air flow meter may deteriorate over time.
If there is an error in the detection result of the air flow meter due to the deterioration of the detection characteristics, the purge flow rate will become excessive or insufficient, but conventionally the purge flow rate is normally controlled in the deteriorated state before the failure diagnosis of the air flow meter. It had been.

For this reason, for example, if the detection characteristic that detects the intake air amount less than the actual deterioration occurs, the purge flow rate is excessively reduced, and the evaporated fuel amount in the canister may reach the saturation amount. The present invention has been made in view of the above problems, and even if the detection characteristics of the air flow meter are deteriorated, it is possible to avoid a large excess or deficiency in the purge flow rate. In particular, the evaporated fuel in the canister reaches a saturation amount. It is an object of the present invention to provide an evaporative fuel processing apparatus that can avoid this.

Therefore, in the first aspect of the invention, the purge flow rate of the evaporated fuel purged from the canister is controlled based on the intake air flow rate of the engine detected by the air flow meter,
A change in the detection characteristic of the air flow meter is detected, and the purge flow rate is corrected according to the change in the detection characteristic.
According to this configuration, the purge flow rate is controlled based on the intake air flow rate detected by the air flow meter, but the change in the detection characteristic of the air flow meter, that is, the detection error characteristic of the intake air amount by the air flow meter is detected, and the intake air The purge flow rate is corrected according to the flow rate detection error.

Therefore, for example, when a lower intake air flow rate than actual is detected due to deterioration of the air flow meter, the purge flow rate based on the detected value of the intake air flow rate is increased and corrected to substantially correspond to the actual intake air flow rate. The purge flow rate can be controlled.
According to the second aspect of the present invention, the change in the detection characteristics of the air flow meter is calculated based on the intake air flow rate detected by the air flow meter and the intake air flow rate calculated from the effective opening area of the intake passage to be variably controlled and the engine speed. It was set as the structure detected by comparison.

According to this configuration, the intake air flow rate predicted from the effective opening area of the intake passage that is variably controlled (for example, a value represented by the throttle opening) and the engine rotation speed, and the intake air flow rate detected by the air flow meter, The change in the detection characteristic of the air flow meter is detected on the assumption that this deviation corresponds to the detection error amount of the air flow meter.
Therefore, it is possible to quantitatively determine the change in the detection characteristics of the air flow meter, and to appropriately correct the purge amount.

According to the third aspect of the invention, the purge flow rate is corrected according to the deviation between the intake air flow rate detected by the air flow meter and the intake air flow rate calculated from the effective opening area of the intake passage to be variably controlled and the engine speed. It was set as the structure to do.
According to this configuration, the intake air flow rate predicted from the effective opening area of the intake passage that is variably controlled (for example, a value represented by the throttle opening) and the engine rotation speed, and the intake air flow rate detected by the air flow meter, Since the deviation corresponds to the detection error amount of the air flow meter, the purge flow rate is corrected in accordance with the detection error amount, so that the purge flow rate is increased or decreased by the detection error amount of the intake air flow rate.

  Therefore, even if there is a detection error in the air flow meter, the purge flow rate can be corrected to an amount commensurate with the actual intake air flow rate.

Embodiments of the present invention will be described below.
FIG. 1 is a system configuration diagram of an internal combustion engine in the embodiment.
In FIG. 1, an internal combustion engine (engine) 1 is a gasoline engine mounted on a vehicle not shown.
The intake system of the internal combustion engine 1 is provided with a throttle valve 2, which controls the intake air flow rate of the engine 1.

Further, an electromagnetic fuel injection valve 4 is provided for each cylinder in the manifold portion of the intake pipe 3 downstream of the throttle valve 2.
The fuel injection valve 4 is opened by an injection pulse signal output in synchronism with engine rotation from an engine control unit (hereinafter referred to as ECU) 20 incorporating a microcomputer, and fuel is injected. Burns in the combustion chamber of the engine 1.

Further, the internal combustion engine 1 is provided with an evaporative fuel processing device.
The evaporative fuel processing device collects evaporative fuel generated in the fuel tank 5 in the canister 7 via the evaporative fuel introduction passage 6, purges the evaporative fuel collected in the canister 7, and supplies it to the engine 1. And burn it.
The canister 7 is a container filled with an adsorbent 8 such as activated carbon.

Further, a fresh air inlet 9 is formed in the canister 7 and a purge passage 10 is led out.
The purge passage 10 is connected to an intake pipe 3 (intake passage) downstream of the throttle valve 2 via a purge control valve 11 which is a normally closed electromagnetic valve.
The purge control valve 11 is opened by a purge control signal output from the ECU 20.

When a predetermined purge permission condition is satisfied during operation of the engine 1, the purge control valve 11 is controlled to open, and as a result, the suction negative pressure of the engine 1 acts on the canister 7. The evaporated fuel adsorbed on the canister 7 is purged by the air.
Then, the purge gas containing the purged evaporated fuel is sucked into the intake pipe 3 through the purge passage 10 and then burned in the combustion chamber of the engine 1.

Detection signals from various sensors are input to the ECU 20.
The various sensors include a crank angle sensor 21 that outputs a crank angle signal in synchronization with the rotation of the engine 1, an air flow meter (AFM) 22 that measures the intake air flow rate Qa of the engine 1, and an opening TVO of the throttle valve 2. A throttle sensor 23 for detecting the air-fuel ratio, an air-fuel ratio sensor 24 for detecting the air-fuel ratio of the combustion mixture based on the oxygen concentration in the exhaust, and the like are provided.

The engine speed Ne can be calculated based on the generation period of the crank angle signal from the crank angle sensor 21 or the number of generations within a predetermined time.
The air flow meter 22 is, for example, a known hot-wire mass flow meter, and the throttle sensor 23 is a sensor that detects the rotational axis angle of the butterfly throttle valve 2 using a potentiometer.

Further, the air-fuel ratio sensor 24 may be a wide-range air-fuel ratio sensor that linearly detects the air-fuel ratio, or may be a stoichiometric sensor that detects rich / lean of the actual air-fuel ratio with respect to the theoretical air-fuel ratio.
The ECU 20 controls the opening degree of the purge control valve 11 according to the purge flow rate calculated based on the intake air flow rate Qa detected by the air flow meter 22 in order to increase the purge flow rate as the intake air flow rate increases. However, the detection characteristics of the air flow meter 22 change due to deterioration with time, for example, as shown in FIGS.

The detection characteristics after deterioration shown in FIG. 2 and FIG. 3 show that the detected value of the minimum flow rate increases and changes compared to the initial state, while the increase rate of the air flow meter output with respect to the increase change of the intake air flow rate becomes small and high Detects a lower flow rate than the actual flow rate.
Here, when the purge flow rate is determined based on the detection result of the air flow meter 22 showing the characteristics after deterioration, the purge amount is controlled to be smaller than the amount corresponding to the actual intake air flow rate in the region where the intake air flow rate is large. (See FIG. 4).

Therefore, in the present embodiment, as shown in the flowchart of FIG. 5, the purge flow rate is corrected with respect to the change in the detection characteristic of the air flow meter 22.
In the flowchart of FIG. 5, first, in step S11, the intake air flow rate Qa at that time is calculated from the detection output of the air flow meter 22.
In the next step S12, the intake air flow rate Qb is calculated from the engine speed Ne and the throttle opening TVO at that time.

The throttle opening TVO is a variable corresponding to the effective opening area of the intake passage that is variably controlled, and the intake air flow rate Qb is calculated after the throttle opening TVO is converted into the effective opening area. good.
Further, the intake air flow rate Qb is preferably corrected to a value corresponding to the mass flow rate based on the atmospheric pressure and the intake air temperature at that time.

In step S13, a deviation ΔQ between the intake air flow rate Qb and the intake air flow rate Qa is calculated as an error amount (see FIG. 6).
ΔQ = Qb−Qa
In step S14, it is determined whether or not the deviation ΔQ (error amount) is less than a threshold value SL.

When the deviation ΔQ is less than the threshold value SL, the air flow meter 22 has no significant change in detection characteristics, and the actual intake is determined by determining the purge flow rate based on the intake air flow rate Qa detected by the air flow meter 22. It is determined that the purge flow rate can be controlled substantially corresponding to the air flow rate, and the process proceeds to step S15.
In step S15, the target purge flow rate is calculated based on the intake air flow rate Qa and the conversion coefficient K stored in advance.

Target purge flow rate = intake air flow rate Qa x K
On the other hand, if it is determined in step S14 that the deviation ΔQ is greater than or equal to the threshold value SL, the process proceeds to step S16.
The state where the deviation ΔQ is equal to or greater than the threshold value SL is that the intake air flow rate Qa detected by the air flow meter 22 is less than a predetermined amount than the intake air flow rate Qb predicted from the engine speed Ne and the throttle opening TVO. This state indicates that the detected flow rate of the air flow meter 22 is smaller than the actual amount due to a change in the detection characteristics of the air flow meter 22 (see FIG. 6).

When the intake air flow rate Qa is less than the actual amount, the purge flow rate is set too low based on the intake air flow rate Qa, so that the evaporative fuel purge process cannot be sufficiently performed and the canister 7 is saturated. There is a possibility of becoming in a state.
In step S16, a purge flow correction value is calculated based on the deviation ΔQ (error amount) and the conversion coefficient K (see FIG. 7).

Correction value = ΔQ × K
In the next step S17, the target purge flow rate is calculated based on the following equation.
Target purge flow rate = Qa × K + correction value In step S18, it is determined based on the engine load, the engine speed, and the like whether or not the permission condition for executing the purge is satisfied.

If the purge execution permission condition is satisfied, the process proceeds to step S19, where a purge valve control signal corresponding to the target purge flow rate is output, and the evaporated fuel is purged from the canister 7.
According to the above control, even if the detection characteristic of the air flow meter 22 changes and an amount smaller than the actual intake air flow rate is detected, it is possible to control the purge flow rate substantially corresponding to the actual intake air flow rate. (Refer to FIG. 7) By setting the purge flow rate too low, the canister 7 can be prevented from becoming saturated.

In the above embodiment, when the deviation ΔQ is large, the purge flow rate based on the intake air flow rate Qa detected by the air flow meter 22 is corrected according to the deviation ΔQ, but when the deviation ΔQ is large, The intake air flow rate used for calculation of the flow rate can be switched from Qa to Qb.
Further, in the above embodiment, the change in the detection characteristic of the air flow meter 22 is detected by comparing the intake air flow rate Qa and the intake air flow rate Qb, but based on the intake air flow rate Qa detected by the air flow meter 22. It is possible to detect a change in the detection characteristic of the air flow meter 22 based on the air-fuel ratio as a result of controlling the fuel injection amount by the fuel injection valve 4.

For example, when the intake air flow rate Qa is smaller than the actual amount, the fuel injection amount is set too small with respect to the actual intake air amount, and the air-fuel ratio becomes lean, so that such lean tendency is detected. Thus, a change in the detection characteristic of the air flow meter 22 can be detected.
Specifically, the result of feedback control of the fuel injection amount so that the air-fuel ratio detected by the air-fuel ratio sensor 24 becomes the target air-fuel ratio is calculated for each operating region divided by engine load and engine speed. In the case of learning as the fuel ratio learning correction value (see FIG. 8), the change in the air fuel ratio learning correction value due to the engine speed when the engine load is constant is the base air fuel ratio (air fuel ratio correction) due to the difference in the intake air flow rate. The change tendency of the air-fuel ratio in a state where no is applied is schematically shown (see FIG. 9).

  The fuel injection amount increase correction request shows a lean tendency of the base air-fuel ratio, and as the air-fuel ratio learning correction value increases toward the increase correction side, the detection value by the air flow meter 22 may be less than the actual amount. If the base air-fuel ratio tends to become leaner as the intake air flow rate increases, the base air-fuel ratio matches the detection characteristic change pattern of the air flow meter 22 (see FIG. 2). It can be determined that the lean tendency is due to a change in the detection characteristics of the air flow meter 22.

Here, if a correction value is set in accordance with the air-fuel ratio learning correction value and the purge flow rate based on the intake air flow rate Qa is corrected with the correction value, the purge flow rate is increased by the detection error of the air flow meter 22 as a result. It will be corrected.
It is obvious that the air flow meter 22 is not limited to the hot-wire type, and the change in detection characteristics is not limited to the pattern as shown in FIG.

Further, when the purge flow correction value is equal to or greater than a predetermined value, it is possible to determine an abnormality in the detection characteristics of the air flow meter 22.
Further, the amount of vaporized fuel collected in the canister 7 is estimated, and the purge flow rate is limited only when it is determined that there is a possibility that the collected amount is more than a predetermined value and the canister 7 is saturated. Can be corrected.

Here, technical ideas other than the claims that can be grasped from the above embodiment will be described together with effects.
(A) In the evaporated fuel processing apparatus according to claim 2 or 3,
An evaporative fuel processing apparatus, wherein an opening of a throttle valve interposed in the intake passage is detected as an effective opening area of the intake passage that is variably controlled.

According to such a configuration, it is possible to easily obtain an estimated value of the intake air flow rate that is detected as the opening degree of the throttle valve and compared with the detection result of the air flow meter by detecting the effective opening area of the intake passage.
(B) In the evaporative fuel processing apparatus according to claim 3,
The evaporated fuel processing apparatus, wherein the purge flow rate is corrected according to the deviation when the deviation is equal to or greater than a predetermined value.

According to such a configuration, it is possible to correct the purge flow rate when the detection characteristic of the air flow meter changes so that the purge flow rate needs to be corrected, and to effectively perform the purge flow rate correction process.
(C) The evaporative fuel processing apparatus according to claim 1,
Evaporative fuel processing characterized in that a change in detection characteristics of the air flow meter is detected based on a base air-fuel ratio when a fuel injection amount to the engine is controlled based on an intake air flow rate detected by the air flow meter. apparatus.

According to this configuration, if a deviation occurs between the actual intake air flow rate and the detected value due to a change in the detection characteristics of the air flow meter, the base air-fuel ratio becomes rich or lean. A change in the detection characteristics of the air flow meter can be estimated from the tendency of the air-fuel ratio to become rich or lean.
(D) In the evaporative fuel processing apparatus according to any one of claims 1 to 3,
An evaporative fuel processing apparatus that estimates the amount of evaporative fuel collected in the canister and corrects the purge flow rate only when the amount of evaporative fuel is greater than or equal to a predetermined amount.

  According to this configuration, the purge flow rate can be corrected only when it is determined that the canister may become saturated.

The system diagram of the engine in an embodiment. The diagram which shows the change of the detection characteristic of the airflow meter in embodiment. The diagram which shows the detection error by the change of the detection characteristic of the airflow meter in embodiment. The diagram which shows the correlation of the change of the detection characteristic of the airflow meter in embodiment, and a purge flow rate. 6 is a flowchart showing correction control of a purge flow rate in the embodiment. The diagram which shows the detection of the detection error amount of the airflow meter in embodiment. The diagram which shows the correlation of the correction value in embodiment and the purge flow volume correct | amended by this correction value. The figure which shows the map of the air fuel ratio learning value in embodiment. The diagram which shows the estimation of the detection error of the airflow meter based on the air-fuel ratio learning value in embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Throttle valve, 3 ... Intake pipe, 4 ... Fuel injection valve, 5 ... Fuel tank, 6 ... Evaporative fuel introduction path, 7 ... Canister, 8 ... Adsorbent, 9 ... Fresh air introduction port, 10 ... Purge passageway, 11 ... Purge control valve, 20 ... Engine control unit, 21 ... Crank angle sensor, 22 ... Air flow meter, 23 ... Throttle sensor, 24 ... Air-fuel ratio sensor

Claims (3)

In an evaporative fuel processing apparatus for collecting evaporative fuel generated in a fuel tank in a canister and purging the evaporative fuel collected in the canister to an intake passage of an engine,
While controlling the purge flow rate of the evaporated fuel to be purged based on the intake air flow rate of the engine detected by an air flow meter,
An evaporative fuel processing apparatus that detects a change in a detection characteristic of the air flow meter and corrects the purge flow rate according to the change in the detection characteristic. Changes in the detection characteristics of the air flow meter are detected by comparing the intake air flow rate detected by the air flow meter with the intake air flow rate calculated from the effective opening area of the intake passage to be variably controlled and the engine speed. The evaporated fuel processing apparatus according to claim 1. The purge flow rate is corrected according to a deviation between the intake air flow rate detected by the air flow meter and the intake air flow rate calculated from the effective opening area of the intake passage to be variably controlled and the engine rotation speed. The evaporative fuel processing apparatus according to claim 2.

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