JPH09166053A - Evaporative fuel control system for internal combustion engine - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide an evaporated fuel control device capable of preventing a purge flow rate from becoming excessive and maintaining a stable engine operating state when an intake system pressure sensor is determined to be abnormal. . SOLUTION: When the absolute pressure sensor 11 in the intake pipe is determined to be abnormal, the throttle valve opening θTH is a predetermined opening θ.
It is determined whether it is smaller than THFSPCS (S6, S
7) When θTH <θTHSPCS, the valve opening duty DOUTPG of the purge control valve 24 is set to 0 (S10) and the purge is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaporated fuel which temporarily stores evaporated fuel generated in a fuel tank and supplies the evaporated fuel to an intake system of an internal combustion engine at a proper time and controls the supply amount according to the engine operating condition. Regarding the control device.

[0002]

2. Description of the Related Art Evaporative fuel generated in a fuel tank is temporarily stored in a canister, and when an internal combustion engine is in a predetermined operating state, a purge passage provided in an engine intake system and having an opening downstream of a throttle valve is provided. An evaporative fuel processing apparatus configured to purge the evaporative fuel via the above is conventionally known (for example, JP-A-62-20669).

Further, when the pressure sensor for detecting the pressure in the intake system of the engine is judged to be abnormal, and when the pressure sensor is judged to be abnormal, the engine is controlled by using an alternative pressure value corresponding to the opening of the throttle valve. A control device adapted to perform the above is also conventionally known (Japanese Patent Laid-Open Publication No. 59-231147).

[0004]

However, since the alternative pressure value is set on the higher load side (safety side) than the actual value in consideration of the characteristic variation of the throttle valve opening sensor, etc., this alternative pressure value is set. When the purge flow rate of the evaporated fuel is controlled using the value, the purge flow rate becomes excessive and the air-fuel ratio becomes overrich, which may result in unstable engine operation.

The present invention has been made in view of this point, and when the intake system pressure sensor is determined to be abnormal, it is possible to prevent the purge flow rate from becoming excessively large and maintain a stable engine operating state. It is an object of the present invention to provide an evaporated fuel control device capable of achieving

[0006]

To achieve the above object, the present invention provides a canister for adsorbing vaporized fuel generated from a fuel tank, and a canister provided between the canister and an intake system of an internal combustion engine. For purging the intake system to the downstream side of the throttle valve, a purge control valve for controlling the flow rate of evaporated fuel supplied to the intake system via the purge passage, and a pressure in the intake system are detected. In a fuel vapor control apparatus for an internal combustion engine, comprising: a pressure sensor for controlling the purge control valve using a detection value of the pressure sensor; and an abnormality determining means for determining an abnormality of the pressure sensor, When the pressure sensor is determined to be abnormal and the opening of the throttle valve is smaller than the predetermined opening,
A purge stopping means for stopping the purge is provided.

According to the present invention, when it is determined that the pressure sensor in the intake system is abnormal, and the throttle valve opening is smaller than the predetermined opening, the purge of the evaporated fuel is stopped.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram of an internal combustion engine and a control system therefor according to an embodiment of the present invention. Reference numeral 1 indicates, for example, a four-cylinder internal combustion engine (hereinafter referred to as “engine”). A throttle body 3 is provided in the middle of the intake pipe 2, and a throttle valve 4 is arranged inside the throttle body 3. A throttle valve opening degree (θTH) sensor 5 is connected to the throttle valve 4 and outputs an electric signal according to the opening degree of the throttle valve 4 to supply it to an electronic control unit (hereinafter referred to as “ECU”) 6. .

A fuel injection valve 7 is provided for each cylinder between the engine 1 and the throttle valve 4 and slightly upstream of an intake valve (not shown) of the intake pipe 2, and each fuel injection valve 7 is provided with a fuel pump 8. Is connected to the fuel tank 9 and is electrically connected to the ECU 6, and the valve opening time of the fuel injection valve 7 is controlled by a signal from the ECU 6.

An intake pipe absolute pressure (PBA) sensor 11 is provided immediately downstream of the throttle valve 4 via a pipe 10. The absolute pressure signal converted into an electric signal by the absolute pressure sensor 11 is sent to the ECU 6. Supplied.

An intake air temperature (TA) sensor 12 is mounted downstream of the absolute pressure sensor 11, detects the intake air temperature TA, outputs a corresponding electric signal, and supplies it to the ECU 6. Engine water temperature (T
The W) sensor 13 is composed of a thermistor or the like, detects the engine water temperature (cooling water temperature) TW, outputs a corresponding temperature signal, and supplies it to the ECU 6.

An engine speed (NE) sensor 14 is mounted around a cam shaft or crank shaft (not shown) of the engine 1, and a signal pulse (hereinafter, referred to as "hereinafter referred to as" a pulse signal "at a predetermined crank angle position for every 180 degrees rotation of the crank shaft of the engine 1). (Referred to as “TDC signal pulse”), and this TDC signal pulse is supplied to the ECU 6.

O 2 sensor 1 as an exhaust gas concentration detector
Reference numeral 6 is attached to the exhaust pipe 15 of the engine 1, detects the oxygen concentration in the exhaust gas, outputs a signal according to the concentration, and supplies the signal to the ECU 6. At the ECU 6, the atmospheric pressure P
An atmospheric pressure sensor 33 that detects A and a voltage sensor 34 that detects a voltage VB of a battery (not shown) that supplies power to the ECU 6 and the purge control valve 24 are connected, and the detection signals thereof are supplied to the ECU 6. To be done.

The upper portion of the closed fuel tank 9 is provided with a passage 20.
It communicates with the canister 21 via a, and the canister 21 communicates with the downstream side of the throttle valve 4 of the intake pipe 2 via the purge passage 23. The canister 21 is the fuel tank 9
The adsorbent 22 that adsorbs the evaporated fuel generated inside is built in,
It has an outside air intake 21a. A two-way valve 20 composed of a positive pressure valve and a negative pressure valve is arranged in the middle of the passage 20a, and a purge control valve 24 which is a duty control type solenoid valve is arranged in the middle of the purge passage 23. . The solenoid of the purge control valve 24 is connected to the ECU 6, and the purge control valve 24 is controlled according to a signal from the ECU 6 to change the temporal ratio of the valve opening time (valve opening duty). Passage 20a, 2-way valve 20, canister 2
1, the purge passage 23 and the purge control valve 24 constitute an evaporative emission control device.

According to this evaporative fuel discharge inhibiting device, the evaporative fuel generated in the fuel tank 9 pushes the positive pressure valve of the two-way valve 20 open when it reaches a predetermined set pressure, flows into the canister 21, and becomes a canister. It is adsorbed by the adsorbent 22 in 21 and stored. The purge control valve 24 is an ECU
The evaporated fuel temporarily opened and stored in the canister 21 during the valve opening / closing operation according to the duty control signal from the control valve 6 is discharged to the outside air provided in the canister 21 due to the negative pressure in the intake pipe 2. It is sucked into the intake pipe 2 through the purge control valve 24 together with the outside air sucked from the intake port 21a, and is sent to each cylinder. Also, the fuel tank 9
Is cooled and the negative pressure in the fuel tank increases, the negative pressure valve of the two-way valve 20 opens, and the evaporated fuel temporarily stored in the canister 21 is returned to the fuel tank 9. In this way, the fuel vapor generated in the fuel tank 9 is prevented from being released to the atmosphere.

The downstream side of the throttle valve 4 of the intake pipe 2 is connected to the exhaust pipe 15 via an exhaust gas recirculation passage 30, and an exhaust gas recirculation valve (EGR) for controlling the exhaust gas recirculation amount is provided in the middle of the exhaust gas recirculation passage 30. Valve) 31 is provided.

The exhaust gas recirculation valve 31 is a solenoid valve having a solenoid, and the solenoid is connected to the ECU 6 so that the valve opening can be changed by a control signal from the ECU 6. The exhaust gas recirculation valve 31 is provided with a lift sensor 32 that detects the valve opening degree, and the detection signal is supplied to the ECU 6.

The ECU 6 determines the engine operating state based on the engine parameter signals from the above-mentioned various sensors, and the valve opening degree of the exhaust gas recirculation valve 31 set according to the intake pipe absolute pressure PBA and the engine speed NE. Command value LCMD
And exhaust gas recirculation valve 31 detected by the lift sensor 32
A control signal is supplied to the solenoid of the exhaust gas recirculation valve 31 so that the deviation from the actual valve opening value LACT of the above is zero.

The ECU 6 shapes the input signal waveforms from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, and the like, a central processing circuit (hereinafter referred to as "the central processing unit"). "CPU"),
It comprises a storage means for storing various calculation programs executed by the CPU and calculation results, an output circuit for supplying drive signals to the fuel injection valve 7, the purge control valve 24 and the exhaust gas recirculation valve 31.

The CPU determines various engine operating states such as a feedback control operating region to the stoichiometric air-fuel ratio by the O2 sensor 16 and an open loop control operating region based on the above-mentioned various engine parameter signals, and determines the engine operating state. Accordingly, the fuel injection time T of the fuel injection valve 7
OUT, the valve opening duty of the purge control valve 24 and the valve opening command value LCMD of the exhaust gas recirculation valve are calculated.

The fuel injection by the fuel injection valve 7 is performed in synchronization with the TDC signal pulse, and the fuel injection time TOUT is calculated by the following equation (1).

TOUT = TI × KO2 × KPA × KEGR × KEVAP × K1 + K2 (1) Here, TI is the basic fuel amount, specifically, the engine speed N
The TI is a basic fuel injection time determined according to E and the intake pipe absolute pressure PBA, and a TI map for determining this TI value is stored in the storage means.

KO2 is an air-fuel ratio correction coefficient, which is set according to the output value of the O2 sensor 16 during air-fuel ratio feedback control, and is set to a predetermined value according to the engine operating state during open loop control.

KPA is an atmospheric pressure correction coefficient set according to the detected atmospheric pressure PA, and KEGR is an EGR correction coefficient set according to the exhaust gas recirculation amount during execution of exhaust gas recirculation.

KEVAP is an evaporation correction coefficient for compensating for the influence of evaporative fuel due to purging, and is set to 1.0 when purging is not performed, and 0 to when purging is performed.
Set to a value between 1.0. The smaller the value of the coefficient KEVAP, the greater the effect of the purge.

K1 and K2 are other correction coefficients and correction variables calculated according to various engine parameter signals, respectively, so that various characteristics such as fuel consumption characteristics and engine acceleration characteristics can be optimized according to engine operating conditions. Is set to any value.

The CPU of the ECU 6 controls the fuel injection valve 7 and the purge control valve 24 based on the result calculated as described above.
And a signal for driving the exhaust gas recirculation valve 31 is output via an output circuit.

FIG. 2 is a flowchart of the main routine of the purge control process for calculating the valve opening duty DOUTPG of the purge control valve 24. This processing is executed by the CPU of the ECU 6 every predetermined time (for example, 80 msec).

First, in step S1, a purge permission flag FP indicating "1" indicating that the execution of purge is permitted.
It is determined whether or not GACT is "1", and when FPGAACT = 0 and purging is not permitted, the cumulative purge flow rate SQPG is set to "0" (step S5).
Proceed to step S10. Here, the cumulative purge flow rate SQP
G is a parameter calculated by integrating the flow rate after the start of purging, and is specifically calculated by the process of FIG.

When FPGAACT = 1 in step S1 and purging is permitted, it is determined whether or not the intake pipe absolute pressure sensor 11 is determined to be abnormal (step S6), and it is determined to be abnormal. If not, the process proceeds to step S8. If it is determined to be abnormal, it is determined whether or not the throttle valve opening θTH is smaller than a predetermined opening θTHSPSPCS (for example, 20 degrees) (step S7), and θTH ≧ θ
If it is THFSPCS, the process proceeds to step S8, where θ
If TH <θTHFSPCS, the process proceeds to step S10 to stop the purge.

When it is determined by the above steps S6 and S7 that the intake pipe absolute pressure sensor 11 is abnormal, the throttle valve opening θTH is the predetermined opening θTHFSPC.
When it is smaller than S, the purge is stopped, so the absolute intake pipe absolute pressure P corresponding to the throttle valve opening θTH is set.
It is possible to prevent the air-fuel ratio from becoming excessively rich by controlling the purge flow rate using the alternative value of BA, and to maintain a stable engine operating state.

In step S8, the fuel cut flag FFC indicating that the fuel cut is being executed is indicated by "1".
Is "1", and if FFC = 1 and the fuel is being cut, step S10 is performed to stop the purge.
If FFC = 0 and the fuel cut is not in progress, the process proceeds to step S9.

At step S10, the valve opening duty DO
UTPG is set to "0", then the transient correction coefficient KPGTR of the purge flow rate is set to the initial value KPGTRST (step S11), and the process proceeds to step S12.

In step S9, the DOU shown in FIG.
Execute the TPG calculation process, open the valve duty DOUTPG
Is calculated and the process proceeds to step S12.

In step S12 and the subsequent steps, the valve opening duty D
This is OUTPG limit processing, and whether or not the DOUTPG value calculated in step S9 is smaller than 0 and 100%.
It is determined whether or not it is larger (steps S12, S1
3), when DOUTPG <0, DOUTPG =
0 (step S15), and DOUTPG> 100
If this is the case, then DOUTPG = 100 (step S14), this processing ends, and 0 ≦ DOUTPG ≦ 100.
If this is the case, the present process is immediately terminated.

FIG. 3 shows DO at step S9 in FIG.
It is a flow chart of UTPG calculation processing.

In step S21, the target flow rate QPG is calculated by the processing of FIG. Next, the DOUTPG table shown in FIG. 5A is searched according to the target flow rate QPG, and the valve opening duty DOUTPG is calculated (step S2).
2). A plurality of broken lines shown in FIG. 5A indicate a differential pressure DP (= PA-PBA) between the atmospheric pressure PA and the intake pipe absolute pressure PBA.
Are respectively DP1, DP2, DP3, DP4, DP5
The smaller the differential pressure DP, the more the broken line is used. That is, DP1 <DP2 <DP
There is a relationship of 3 <DP4 <DP5. The smaller the differential pressure DP, the valve opening duty DOUTP for obtaining the same flow rate.
This is because G becomes large. The differential pressure DP is DP1 to DP
If it is not equal to 5, perform interpolation calculation and perform DOUTPG
Calculate the value. When it is determined that the intake pipe absolute pressure sensor 11 is abnormal, step S22 is executed by using an alternative value according to the throttle valve opening θTH instead of the sensor output.

In the following step S23, the battery voltage V
According to B, the DDPGVB table shown in FIG. 5B is searched and the battery voltage correction term DDPGVB is calculated. Next, the valve opening duty DOU calculated in step S22
Correction is performed by adding the battery voltage correction term DDPGVB to TPG (step S24), and this processing ends.

FIG. 4 is a flow chart of the target flow rate calculation processing in step S21 of FIG.

First, in step S31, the deviation amount DKO2PG is calculated by the following equation (2).

DKO2PG = KO2PG-O2LMTL (2) Here, KO2PG is an air-fuel ratio correction coefficient KO calculated by the following equation (3) during execution of air-fuel ratio feedback control.
O2LMTL is the lower limit value of this KO2 value. Therefore, this deviation amount DKO2P
When G is small, the KO2 value is the lower limit value O2LM.
It is close to TL, indicating that the effect of purging is large.

KO2PG = C × KO2 + (1−C) × KO2PG (3) Here, C is a constant set to a value between 0 and 1, KO
2 is the KO2 value when the proportional term is generated during the execution of the air-fuel ratio feedback control (immediately after the O2 sensor output is inverted), and KO2 on the right
PG is a previously calculated value.

In the following step S32, the deviation amount DKO2
It is determined whether PG is 0 or less. When DKO2PG ≦ 0, DKO2PG = 0 is set (step S33),
If DKO2PG> 0, immediately proceed to step S
Proceed to 34.

In step S34, the deviation amount DKO2PG
According to the above, the KPGKO2 table shown in FIG. 6A is searched, and the KO2 level correction coefficient KPGKO2 is calculated. K
In the PGKO2 table, the DKO2PG value is a predetermined value DKO.
When 2PG0 or more, KPGKO2 = 1.0, predetermined value D
In a range smaller than KO2PG0, the KPGKO2 value decreases as the DKO2PG value decreases, that is, when the influence of purging is large, the purge flow rate is reduced according to the degree of the influence.

In the following step S37, the basic target flow rate QPGBASE is calculated by the following equation (4).

QPGBASE = KQPG × TIM × KPA × KEGR × NE (4) Here, TIM, KPA, and KEGR are expressed by the above formula (1).
Is a basic fuel amount, an atmospheric pressure correction coefficient, and an EGR correction coefficient, and KQPG is a predetermined coefficient for converting the fuel amount into a target flow rate. Therefore, the basic target flow rate QPGBA
SE has a value proportional to the amount of fuel supplied to the engine per unit time.

In the following step S38, the KPGTA table shown in FIG. 6B is searched according to the intake air temperature TA to calculate the intake air temperature correction coefficient KPGTA. The KPGTA table is set so that the KPGTA value tends to decrease as the intake air temperature TA increases. Next, the cumulative purge flow rate SQ
The KSQPG table shown in FIG. 6C is searched according to the PG, and the integrated flow rate correction coefficient KSQPG is calculated (step S39). The KSQPG table shows the cumulative purge flow rate S
As the QPG increases, the KSQPG value tends to increase.

In the following step S40, the amount of change DTH (= θTH (current value) −θTH) in the throttle valve opening θTH.
(Previous value)) is smaller than a predetermined negative change amount DTHPCSM (for example, -1.0 degree), and DTH <DT
If it is HPCSM, it is determined that the engine is in the deceleration transient state, the transient correction coefficient KPGTR is set to a predetermined value KPGTRDEC (for example, 0.2) smaller than 1.0 (step S41), and the process proceeds to step S45.

When the answer to step S40 is negative (NO), that is, when DTH≥DTHPCSM, the predetermined addition term DKPGTR is added to the transient correction coefficient KPGTR to increase it (step S42), and the KPGTR value exceeds 1.0. It is determined whether or not (step S43). And KP
When GTR> 1.0, KPGTR = 1.0 is set (step S44), and when KPGTR ≦ 1.0, the process immediately proceeds to step S45.

In step S45, the above-mentioned correction coefficients are applied to the following equation (5) to obtain the basic target flow rate QPGBASE.
The overall correction coefficient KPGTOTAL of is calculated.

KPGTOTAL = KPGKO2 × KPGTA × KSQPG × KPGTR (5) Next, the overall correction coefficient KPGTOTAL is multiplied by the basic target flow rate QPGBASE to calculate the target flow rate QPG (step S46), and the calculated QPG value is predetermined. Value DS
It is determined whether it is smaller than QPG (step S4).
7). When QPG ≧ DSQPG, the cumulative purge flow rate SQPG is calculated by the following equation (6), and when QPG <DSQPG, the cumulative purge flow rate SQPG is calculated (steps S48, S49), and this processing is performed. To finish.

SQPG = SQPG (n-1) + QPG (6) SQPG = SQPG (n-1) + DSQPG (7) where (n-1) is added to indicate the previous value, The predetermined value DSQPG is a value (for example, 1 L / min) corresponding to the minimum unit (LSB) in the calculation process of the integrated purge flow rate SQPG.

As described above, according to this processing, when it is determined that the engine is in the deceleration transient state, the transient correction coefficient KPG
TR is a predetermined value KPGTR which is a small value of about 0.2
Set to DEC (steps S40, S4
Since 1), the target flow rate QPG is corrected in the decreasing direction (see time t1 in FIG. 7), the air-fuel ratio is prevented from being overriched in the deceleration transient state, and good exhaust gas characteristics can be maintained. . Further, after the time t1, the target flow rate QPG is gradually increased in steps S42 to S44, so that it is possible to prevent a rapid change in the air-fuel ratio.

[0055]

As described above in detail, according to the present invention, when it is determined that the pressure sensor in the intake system is abnormal, the purge of the evaporated fuel is performed when the throttle valve opening is smaller than the predetermined opening. Since the engine is stopped, it is possible to prevent the purge flow rate from becoming excessive and maintain a stable engine operating state when it is determined that the intake system pressure sensor is abnormal.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an internal combustion engine and a control device thereof according to an embodiment of the present invention.

FIG. 2 is a flowchart of a main routine of purge control.

FIG. 3 is a flowchart of a process of calculating a valve opening duty of a purge control valve.

FIG. 4 is a flowchart of a target flow rate calculation process.

5 is a diagram showing a table used in the processing of FIG.

FIG. 6 is a diagram showing a table used in the processing of FIG. 4;

FIG. 7 is a diagram for explaining a change in target flow rate due to the processing of FIG.

[Explanation of symbols]

 1 Internal Combustion Engine 2 Intake Pipe 4 Throttle Valve 5 Throttle Valve Opening Sensor 6 Electronic Control Unit 9 Fuel Tank 11 Intake Pipe Absolute Pressure Sensor 21 Canister 23 Purge Passage 24 Purge Control Valve

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yukito Fujimoto 1-4-1 Chuo, Wako-shi, Saitama

Claims (1)

[Claims] 1. A purge provided between a canister for adsorbing vaporized fuel generated from a fuel tank and the canister and an intake system of an internal combustion engine, for purging the vaporized fuel downstream of a throttle valve of the intake system. A passage, a purge control valve for controlling the flow rate of evaporated fuel supplied to the intake system through the purge passage, a pressure sensor for detecting the pressure in the intake system, and a detection value of the pressure sensor. An evaporative fuel control device for an internal combustion engine, comprising: a control unit that controls the purge control valve; an abnormality determination unit that determines whether the pressure sensor is abnormal; and the pressure sensor is determined to be abnormal, and the throttle valve is opened. And a purge stop means for stopping the purge when the degree of opening is smaller than a predetermined opening degree.