JP3765646B2 - Evaporative fuel emission prevention device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for preventing evaporative fuel emission of an internal combustion engine, and in particular, prevents the evaporative fuel from being discharged from the fuel tank to the outside air by controlling the internal pressure of the fuel tank to be negative when the internal combustion engine is operated and stopped. The present invention relates to an evaporative emission preventing device for an internal combustion engine.
[0002]
[Prior art]
In order to prevent the evaporated fuel in the fuel tank mounted on the vehicle from being released into the outside air, the fuel tank is connected to the intake pipe of the internal combustion engine via the canister, and the evaporated fuel in the fuel tank is connected to the internal combustion engine. A technique is known in which processing is performed by a canister when the engine is stopped, and combustion is performed by the internal combustion engine when the internal combustion engine is operated.
[0003]
Further, as an improvement of the above technique, the internal pressure of the fuel tank is reduced to a negative pressure when the internal combustion engine is operated, and the internal pressure of the fuel tank is maintained at a negative pressure not only during the operation of the internal combustion engine but also after the internal combustion engine is stopped. For this reason, there has already been proposed an evaporative fuel emission preventing device for an internal combustion engine which prevents the evaporative fuel in the fuel tank from being released into the outside air even when the filler cap is opened (for example, Japanese Patent Application No. 9-9 39740).
[0004]
In this apparatus, a temperature sensor for detecting the temperature of the fuel in the fuel tank and a tank internal pressure sensor for detecting the internal pressure of the fuel tank are provided, and the fuel tank is predicted according to the temperature of the fuel in the fuel tank. A target pressure value that is excessively negative in consideration of an increase in internal pressure is determined. Then, by utilizing the negative pressure in the intake pipe during operation of the internal combustion engine, so that the internal pressure of the fuel tank becomes the target pressure value, the detection value of the tank pressure sensor feedback quality Tsu system valve opening To control. Thereby, normally, the internal pressure of the fuel tank can be maintained at the target pressure value.
[0005]
[Problems to be solved by the invention]
However, in the above prior art, the negative pressure to the target pressure value of the fuel tank is performed during traveling of the vehicle in order to use the negative pressure in the intake pipe when the internal combustion engine is operated, and the negative pressure of the fuel tank is reduced. When the control valve is opened to perform the control, the evaporated fuel in the fuel tank is sucked into the intake pipe, the air-fuel ratio of the air-fuel mixture in the intake pipe changes suddenly, a shock occurs, and the drivability deteriorates. There is a problem that the characteristics deteriorate.
[0006]
The present invention has been made to solve the above-described problems of the prior art, and its object is to perform the air-fuel ratio of the air-fuel mixture in the intake pipe when the negative pressure in the fuel tank is reduced by the negative pressure in the intake pipe. It is an object of the present invention to provide an evaporative fuel emission preventing device for an internal combustion engine that can prevent the deterioration of drivability and exhaust emission characteristics due to abrupt changes.
[0007]
[Means for solving problems]
In order to achieve the above-described object, an evaporated fuel discharge prevention device for an internal combustion engine according to claim 1 is provided in the middle of the evaporated fuel passage, an evaporated fuel passage connecting a fuel tank and an intake system of the internal combustion engine. A control valve that opens and closes the evaporated fuel passage, and a control that controls the opening of the control valve so that the internal pressure of the fuel tank becomes negative when the internal combustion engine is operated and stopped other than when idling An evaporative fuel emission preventing device for an internal combustion engine, comprising: an operating state detecting means for detecting an operating state of the internal combustion engine, wherein the control means determines the opening of the control valve in accordance with the operating state of the internal combustion engine. It is characterized by setting.
[0008]
With this configuration, the opening of the control valve is set in accordance with the operating state of the internal combustion engine, so that the internal pressure of the fuel tank becomes negative when the control means is operating and stopped including when the internal combustion engine is not idling. When controlling the opening degree of the control valve, the opening degree of the control valve is set according to the operating state of the internal combustion engine. As a result, the evaporated fuel in the fuel tank is suddenly drawn into the intake system and shock is applied. As a result, it is possible to prevent the operability from deteriorating and to prevent the exhaust emission characteristics from deteriorating due to a sudden change in the air-fuel ratio of the air-fuel mixture in the intake system.
[0009]
The evaporative fuel emission preventing apparatus for an internal combustion engine according to claim 2 is the evaporative fuel emission preventing apparatus for the internal combustion engine according to claim 1, wherein the operating state detecting means detects a rotation speed of the internal combustion engine. A sensor and a pressure sensor for detecting the pressure in the intake system, wherein the control means sets the degree of opening of the control valve as the rotational speed of the internal combustion engine increases or as the pressure in the intake system increases. It is characterized by a large setting.
[0010]
With this configuration, the control means sets the opening degree of the control valve to be larger as the rotational speed of the internal combustion engine is larger or as the pressure in the intake system is higher, so that the evaporated fuel in the fuel tank is in the intake system. A sudden inhalation can be reliably prevented.
[0011]
The evaporative fuel emission preventing apparatus for an internal combustion engine according to claim 3 is the evaporative fuel emission preventing apparatus for the internal combustion engine according to claim 1 or 2, wherein the control means starts to reduce the internal pressure of the fuel tank. In this case, the opening degree of the control valve is gradually increased until the set opening degree is reached.
[0012]
With this configuration, since the opening degree of the control valve is gradually increased, it is possible to more reliably prevent the evaporated fuel in the fuel tank from being rapidly sucked into the intake system.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0014]
FIG. 1 is an overall configuration diagram showing the configuration of a fuel vapor release prevention device for an internal combustion engine according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an internal combustion engine (hereinafter simply referred to as “engine”) having, for example, four cylinders, and a throttle valve 3 is arranged in the middle of an intake pipe 2 of the engine 1. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3, and an electric signal corresponding to the opening of the throttle valve 3 is output to an electronic control unit (hereinafter referred to as “ECU”) 5. Supply.
[0015]
A fuel injection valve 6 is provided for each cylinder in the middle of the intake pipe 2 and slightly upstream of an intake valve (not shown) between the engine 1 and the throttle valve 3. Each fuel injection valve 6 is connected to a fuel tank 9 via a fuel supply pipe 7, and a fuel pump 8 is provided in the middle of the fuel supply pipe 7. The fuel tank 9 has an oil supply port 10 for refueling, and a filler cap 11 is attached to the fuel supply port 10.
[0016]
The fuel injection valve 6 is electrically connected to the ECU 5, and the valve opening time of the fuel injection is controlled by a signal from the ECU 5.
[0017]
An intake pipe absolute pressure (PBA) sensor 13 for detecting an intake pipe absolute pressure PBA as a pressure sensor for detecting the pressure in the intake system and an intake air temperature as an outside air temperature are provided downstream of the throttle valve 3 in the intake pipe 2. An intake air temperature (TA) sensor 14 for detecting TA is attached. The fuel tank 9 includes a tank internal pressure (Pt) sensor 15 that detects a tank internal pressure (absolute pressure) Pt (mmHg) of the fuel tank 9 and a fuel temperature (Tg) that detects a temperature Tg of the fuel in the fuel tank 9. ) Sensor 16 is provided.
[0018]
A rotational speed (NE) sensor 17 for detecting the engine rotational speed is mounted around a cam shaft or a crankshaft (not shown) of the engine 1. The NE sensor 17 outputs a pulse (TDC signal pulse) at a predetermined crank angle position every 180 ° rotation of the crankshaft of the engine 1. Detection signals of the sensors 13 to 17 are supplied to the ECU 5.
[0019]
Next, the evaporative fuel release inhibiting system 31 composed of the fuel tank 9, the evaporative fuel passage 20 and the like will be described.
[0020]
The fuel tank 9 is connected to the downstream side of the throttle valve 3 of the intake pipe 2 via the evaporated fuel passage 20. The evaporated fuel passage 20 is opened and closed in the middle of the evaporated fuel passage 20 to control the internal pressure of the fuel tank 9. A control valve 30 is provided. The control valve 30 is a duty control type electromagnetic valve configured to control the flow rate of the evaporated fuel generated in the fuel tank 9 by changing the duty ratio of the control signal, and the operation of the control valve 30 is as follows. It is controlled by the ECU 5. The control valve 30 may be a linear control type electromagnetic valve whose opening degree can be changed linearly. When the control valve 30 is a duty control type, the duty ratio corresponds to the “opening degree of the control valve” in the claims.
[0021]
The ECU 5 shapes input signal waveforms from various sensors, corrects the voltage level to a predetermined level, and converts an analog signal value into a digital signal value, a central processing circuit (hereinafter referred to as “CPU”). A storage means for storing a calculation program executed by the CPU, a calculation result, and the like, an output circuit for supplying a drive signal to the fuel injection valve 6 and the control valve 30, and the like.
[0022]
The CPU of the ECU 5 controls the amount of fuel supplied to the engine 1 according to the output signals of various sensors such as the θTH sensor 4 and the PBA sensor 13. Since the fuel amount control is not the subject of the present invention, the description thereof is omitted.
[0023]
The CPU of the ECU 5 determines the duty ratio of the control valve 30 based on the processing of FIG. 2 according to the output signals of the PBA sensor 13 and the NE sensor 17 described above. FIG. 2 shows a program for performing control processing for preventing evaporative fuel release in the evaporative fuel release preventing apparatus according to the embodiment of the present invention. The processing in FIG. 2 is executed every predetermined time (for example, 10 msec).
[0024]
First, in step S1, it is determined whether or not the engine 1 is in operation by detecting cranking of the engine 1, and in step S2, it is determined whether or not the engine 1 is in a fuel cut. When the engine 1 is stopped or the fuel is being cut in each determination of steps S1 and S2, the CPU of the ECU 5 holds the negative pressure in the fuel tank 9 controlled to a target pressure value Po described later. Therefore, the control valve 30 is closed (step S3), then the count value N is set to 0 (step S4), and this process is terminated.
[0025]
If it is determined in steps S1 and S2 that the engine 1 is not operating and the fuel is not cut, the fuel temperature Tg in the fuel tank 9 detected by the Tg sensor 16 is taken in (step S5), and then the Pt sensor. The internal pressure Pt of the fuel tank 9 detected by 15 is taken in (step S6). Further, the intake pipe absolute pressure PBA detected by the PBA sensor 13 is taken in (step S7), and the engine speed NE detected by the NE sensor 17 is taken in (step S8).
[0026]
Further, a target pressure value (absolute pressure) Po (mmHg) in the fuel tank 9 is calculated by a predetermined setting method (for example, Japanese Patent Application No. 9-39740) (step S9). This target pressure value Po is an excessively negative pressure value that anticipates the tank pressure increase in the fuel tank 9 so that the negative pressure in the fuel tank 9 can be maintained even after the engine 1 is stopped. is there. As a factor of the increase in the internal pressure of the fuel tank 9 that can be predicted, the component that evaporates at a temperature lower than the fuel temperature among the components contained in the fuel evaporates due to the amount of heat stored in the fuel tank 9 at that temperature. In addition, due to a rise in the temperature of the fuel in the fuel tank 9 due to a rise in the outside air temperature, a part of the fuel evaporates as described above.
[0027]
Next, it is determined whether or not the tank internal pressure Pt of the fuel tank 9 is larger than the target pressure value Po (step S10). When Pt ≦ Po, it is necessary to further reduce the tank internal pressure Pt of the fuel tank 9 to a negative pressure. Since there is not, step S3 and S4 are performed and this processing is ended.
[0028]
When Pt> Po in step S10, the process proceeds to step S11 to determine whether or not the intake pipe absolute pressure PBA is smaller than the tank internal pressure Pt. If PBA ≧ Pt, the tank internal pressure Pt is set by the intake pipe absolute pressure PBA. Further, it is determined that the pressure cannot be reduced, and steps S3 and S4 are executed, and this process is terminated.
[0029]
When PBA <Pt in step S11, the target duty ratio DRO (%) of the control valve 30 set as shown in FIG. 3 according to the engine speed NE and the intake pipe absolute pressure PBA is searched (step S12). . In FIG. 3, the target duty ratio DRO (%) of the control valve 30 is set to increase as at least one of the engine speed NE and the intake pipe absolute pressure PBA increases. The target duty ratio DRO takes such a value that the tank internal pressure Pt in the fuel tank 9 is equal to or less than the target pressure value (absolute pressure) P o (mmHg).
[0030]
In subsequent step S13, the count value N is incremented by 1, and then in step S14, it is determined whether or not the count value N has reached a predetermined value N1 (for example, 100). Since the predetermined value N1 is not initially set, steps S15 to S17 are skipped. When N = N1 in step S14, the process proceeds to step S15, and a predetermined value Δd (for example, 5%) is added to the duty ratio DR of the control valve 30.
[0031]
Next, in step S16, the control valve 30 is opened based on the duty ratio DR calculated in step S15 (step S16), and the count value N is set to 0 (step S17).
[0032]
Further, it is determined whether or not the duty ratio DR of the control valve 30 is larger than the target duty ratio DRO searched in step S12 (step S18). If it is larger, the duty ratio DR of the control valve 30 becomes the target duty ratio DRO. As a result, steps S3 and S4 are executed, and this process is terminated. On the other hand, when DR <DRO in step S18, the above steps S13 to S17 are repeatedly executed.
[0033]
According to the processing of FIG. 2, the duty ratio DR of the control valve 30 is gradually increased by a predetermined value Δd at predetermined time intervals until reaching the target duty DRO searched in step S12, and the fuel tank 9 is placed in the intake pipe 2. It is possible to reliably prevent the fuel vapor 9 from being aspirated suddenly and to avoid a shock at the start of the negative pressure of the fuel tank 9. FIG. 4 shows changes in the opening degree of the control valve 30 at this time.
[0034]
In the present embodiment, the function as the control means in the claims is provided as software in the ECU 5 as shown in the flowchart of FIG.
[0035]
With the above configuration, during the operation of the engine 1, the negative pressure in the intake pipe 2 is applied to the fuel tank 9 by controlling the duty ratio DR of the control valve 30 to the target duty ratio DRO. Is maintained at the predetermined target pressure value Po. As a result, the inside of the fuel tank 9 is maintained at a negative pressure not only during the operation of the engine 1 but also after the engine is stopped, and even if the filler cap 11 is opened for refueling, the evaporated fuel in the fuel tank 9 is prevented from being released to the outside air. be able to. Further, the duty ratio DR of the control valve 30 is gradually increased by a predetermined value Δd at predetermined time intervals until the target duty ratio DRO searched in step S12 is reached, and the evaporated fuel in the fuel tank 9 is placed in the intake pipe 2. It is possible to prevent a sudden shock due to a sudden intake and a deterioration in drivability, and a deterioration in exhaust emission characteristics due to a sudden change in the air-fuel ratio of the air-fuel mixture in the intake pipe 2.
[0036]
【The invention's effect】
As described above in detail, according to the evaporated fuel release prevention device for the internal combustion engine according to claim 1, the opening degree of the control valve is set according to the operating state of the internal combustion engine, so that the control means is the internal combustion engine. When the opening degree of the control valve is controlled so that the internal pressure of the fuel tank becomes negative during operation including when the engine is not idling and when it is stopped, the opening degree of the control valve depends on the operating state of the internal combustion engine. As a result, the evaporative fuel in the fuel tank is aspirated suddenly into the intake system and a shock occurs, preventing the deterioration of operability and the air-fuel ratio of the air-fuel mixture in the intake system changes abruptly. Thus, the exhaust emission characteristics can be prevented from deteriorating.
[0037]
According to the evaporated fuel release prevention device for an internal combustion engine according to claim 2, the control means sets the opening of the control valve to be larger as the rotational speed of the internal combustion engine is larger or the pressure in the intake system is higher. Therefore, it is possible to reliably prevent the evaporated fuel in the fuel tank from being rapidly sucked into the intake system.
[0038]
According to the evaporated fuel release preventing device for an internal combustion engine according to claim 3, since the opening degree of the control valve is gradually increased, it is more reliable that the evaporated fuel in the fuel tank is rapidly sucked into the intake system. Can be prevented.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing a configuration of an evaporative fuel emission preventing apparatus for an internal combustion engine according to an embodiment of the present invention. FIG. 2 is an evaporative fuel emission in the evaporative fuel emission preventing apparatus according to an embodiment of the present invention. It is a flowchart of the program which performs control processing of prevention.
FIG. 3 is an engine speed-intake pipe absolute pressure graph for explaining a method of setting a target duty ratio DRO of the control valve 30;
FIG. 4 is a time-control valve duty ratio graph showing a change in the opening degree of the control valve 30;
[Explanation of symbols]
1 Internal combustion engine 2 Intake pipe 3 Throttle 5 ECU (control means)
9 Fuel tank 10 Refueling port 11 Filler cap 13 Intake pipe absolute pressure sensor (pressure sensor)
15 Tank internal pressure sensor 16 Fuel temperature sensor 17 Rotational speed sensor 20 Evaporated fuel passage 30 Control valve 31 Evaporated fuel release suppression system

Claims (3)

A fuel vapor passage which connects the intake system of the fuel tank and the internal combustion engine, provided in the middle of the evaporation fuel passage, and a control valve for opening and closing the evaporation fuel passage, during operation contain other than idling of the internal combustion engine and An operating state for detecting an operating state of the internal combustion engine in an evaporative fuel discharge prevention device for an internal combustion engine, comprising: a control means for controlling the opening of the control valve so that the internal pressure of the fuel tank becomes a negative pressure when stopped An evaporative fuel emission prevention device for an internal combustion engine, comprising: a detection means, wherein the control means sets an opening of the control valve in accordance with an operating state of the internal combustion engine.   The operating state detection means includes a rotation speed sensor that detects the rotation speed of the internal combustion engine, and a pressure sensor that detects a pressure in the intake system, and the control means determines an opening degree of the control valve. 2. The evaporative fuel discharge device for an internal combustion engine according to claim 1, wherein the larger the number of revolutions of the engine or the higher the pressure in the intake system, the larger the setting.   3. The control unit according to claim 1, wherein the control unit gradually increases the opening degree of the control valve until the set opening degree is reached when starting to reduce the internal pressure of the fuel tank. 4. An evaporative fuel discharge device for an internal combustion engine.

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