Device and control method for fuel vapor treatment device

Abstract

A fuel vapor treatment device comprises: a purge passage (16) that communicates a canister (3) and an intake passage (17) of an internal combustion engine (1); a fuel vapor passage (23) that communicates the canister (3) and a sealed fuel tank (2); a shut-off valve (26); a bypass valve (24); and a pair of purge control valves (28A, 28B). When purging the canister (3), the shut-off valve (26) is closed, the bypass valve (24) is opened, and the two purge control valves (28A, 28B) are duty-controlled. When releasing pressure in the fuel tank (2), the shut-off valve (26) is opened, the bypass valve (24) is closed, and only one of the purge control valves (28B) is duty-controlled.

Description

Control method and device for evaporative fuel treatment device

[0001] The present invention relates to an evaporated fuel treatment device that uses a canister to treat evaporated fuel generated in a fuel tank, and more particularly to purge control in an evaporated fuel treatment device for a so-called sealed type fuel tank.

[0002] A widely used fuel vapor treatment system is a system in which fuel vapor generated in a vehicle's fuel tank is temporarily adsorbed in a canister using an adsorbent such as activated carbon to prevent it from leaking to the outside, and then, while the internal combustion engine is running, fresh air is introduced to purge the fuel components from the canister and introduce them into the intake system of the internal combustion engine.In recent years, a type of fuel vapor treatment system has been widely adopted in which a shutoff valve is provided in a fuel vapor passage connecting the fuel tank and the canister, and this shutoff valve is basically kept closed except when refueling, thereby keeping the fuel tank sealed.

[0003] In an evaporative fuel treatment device for a sealed fuel tank equipped with a shut-off valve as described above, the pressure inside the fuel tank may become high while the shut-off valve is closed, and in such cases it is necessary to release the pressure inside the fuel tank.

[0004] Patent Document 1 discloses a configuration in which two purge control valves are provided in parallel in a purge passage leading from a canister to an intake passage of an internal combustion engine, thereby ensuring a large purge gas flow rate when purging the canister.

[0005] However, Patent Document 1 does not disclose how to use multiple purge control valves when releasing pressure in the fuel tank.

[0006] Japanese Patent Application Laid-Open No. 2008-215287

[0007] This invention is a control method for an evaporated fuel treatment device comprising: a purge passage connecting a canister and an intake passage of an internal combustion engine; an evaporated fuel passage connected to an intermediate portion of the purge passage connecting the canister and a fuel tank; a shut-off valve opening and closing the evaporated fuel passage; a bypass valve opening and closing the purge passage on the canister side of the connection between the purge passage and the evaporated fuel passage; and a plurality of purge control valves arranged in parallel with each other in the purge passage, wherein when purging the canister, the shut-off valve is closed, the bypass valve is opened, and duty control is performed on all the purge control valves; and when releasing the pressure in the fuel tank, the shut-off valve is opened, the bypass valve is closed, duty control is performed on one purge control valve, and the other purge control valves are closed.

[0008] By this control, when purging the canister, purge gas with a relatively low concentration of fuel components can be introduced into the intake passage of the internal combustion engine at a relatively large flow rate via the multiple purge control valves.On the other hand, when the fuel tank becomes high pressure and pressure relief is required, a relatively small amount of fuel vapor with a high concentration of fuel components in the fuel tank is metered into the intake passage via a single purge control valve.

[0009] The fuel vapor treatment device according to the present invention is configured to treat a fuel vapor in a fuel tank in a fuel tank that is purged from a canister.

[0010] 1 is an explanatory diagram showing the configuration of an embodiment of an evaporated fuel treatment device according to the present invention. A vehicle (not shown) is equipped with an internal combustion engine 1 and a sealed fuel tank 2. The vehicle is also equipped with an evaporated fuel treatment device using a canister 3 to treat evaporated fuel generated in the fuel tank 2 during refueling. The fuel tank 2 has a fuel filler pipe 5 with a filler cap 4 detachably attached to a filler opening at its tip. A fuel pump unit 7 that supplies fuel to a fuel injection system (not shown) of the internal combustion engine 1 is housed inside the fuel tank 2. The filler opening is covered with an electrically locked fuel lid (not shown) to prevent the filler cap 4 from being opened.

[0011] The canister 3 has a synthetic resin case that forms a U-shaped flow path, and the inside of the U-shaped flow path is filled with an adsorbent such as activated carbon. At one end of the U-shaped flow path in the flow direction, there is provided a charge / purge port 14 that serves as an inlet for evaporated fuel and an outlet for purge gas containing fuel components, and at the other end in the flow direction, there is provided a drain port 15 that takes in outside air during purging and opens the inside of the canister 3 during charging.

[0012] The drain port 15 is provided with a drain cut valve 13 that opens and closes the drain port 15. The drain cut valve 13 has the function of closing the system during leak diagnosis and is configured as a normally open solenoid valve that opens when not energized. If a pressure pump (not shown) is provided for leak diagnosis, the drain cut valve 13 is configured to switch between a flow path open to the outside air and a flow path that communicates with the pressure pump.

[0013] The charge / purge port 14 is connected via a purge passage 16 to an intake system of the internal combustion engine 1, for example, to an intake passage 17 upstream of a collector section 18. The internal combustion engine 1 of one embodiment is a supercharged engine equipped with a turbocharger, and a turbocharger compressor 20 is located upstream of a throttle valve 19, and a negative pressure generating valve 21 for generating negative pressure is disposed upstream of this compressor 20. The tip of the purge passage 16 is connected between the compressor 20 and the negative pressure generating valve 21.

[0014] The tip of an evaporated fuel passage 23 is connected to the middle portion of the purge passage 16. The charge / purge port 14 of the canister 3 is connected to the upper space of the fuel tank 2 via this evaporated fuel passage 23. In other words, a portion of the purge passage 16 near the charge / purge port 14 (the section from the connection with the evaporated fuel passage 23 to the charge / purge port 14) essentially functions as both the purge passage 16 and the evaporated fuel passage 23. A bypass valve 24 for opening and closing the charge / purge port 14 is provided in this section that serves both the purge passage 16 and the evaporated fuel passage 23. This bypass valve 24 is a normally open solenoid valve that is open when not energized.

[0015] The end of the evaporated fuel passage 23 on the fuel tank 2 side is connected to the upper space of the fuel tank 2 via an FLV valve 25 that prevents liquid fuel from overflowing into the evaporated fuel passage 23 when the fuel liquid level is at a high position.

[0016] A shutoff valve 26 for opening and closing the evaporated fuel passage 23 is provided midway through the evaporated fuel passage 23. In principle, the shutoff valve 26 is configured as a normally closed solenoid valve that is closed when not energized, to shut off communication between the canister 3 and the fuel tank 2 and seal the fuel tank 2 except when refueling. In one embodiment, the shutoff valve 26 is equipped with a mechanical relief valve 27 for releasing pressure in the fuel tank 2 in the unlikely event that the shutoff valve 26 malfunctions.

[0017] The purge passage 16 is provided with a pair of purge control valves 28, each consisting of a duty-controllable solenoid valve, for controlling the flow rate of purge gas. Specifically, a portion of the purge passage 16 branches into a pair of parallel purge passages 16a, 16b, and a first purge control valve 28A and a second purge control valve 28B are disposed therein, respectively. That is, the two purge control valves 28A, 28B are disposed in parallel with each other. Hereinafter, when there is no need to distinguish between the two, they will be collectively referred to as the purge control valve 28. In one embodiment, the first purge control valve 28A and the second purge control valve 28B are normally-closed solenoid valves of essentially the same type and with the same capacity. However, the first purge control valve 28A and the second purge control valve 28B may be solenoid valves with different capacities.

[0018] The two purge control valves 28 are duty-controlled by a controller 30 for the evaporated fuel treatment system via a PCM circuit 31. The controller 30 is connected to an engine controller via a CAN communication network (not shown), receives information about the operating state of the internal combustion engine 1 from the engine controller, and outputs information about the operation of the evaporated fuel treatment system to the engine controller. The controller 30 controls the entire evaporated fuel treatment system, including, as part of its functions, purge control via the purge control valve 28 and pressure release control of the fuel tank 2. The controller 30 also includes a tank pressure sensor 32 that detects the pressure in the fuel tank 2 and a canister pressure sensor 33 that detects the pressure in the canister 3 as pressure sensors for detecting pressure within the system. The canister pressure sensor 33 is used during leak diagnosis.

[0019] In the evaporated fuel treatment device configured as described above, basically, only evaporated fuel generated during refueling is adsorbed in the canister 3, and the canister 3 does not adsorb evaporated fuel at times other than when refueling. In other words, the evaporated fuel treatment device of this embodiment is suitable for hybrid vehicles that are capable of so-called EV running with the internal combustion engine 1 stopped, and in this type of vehicle, there are fewer opportunities to purge the canister 3, so adsorption of evaporated fuel by the canister 3 is limited to when refueling.

[0020] Next, the operation of the above-described fuel vapor treatment device will be described.

[0021] When the vehicle is stopped (when the internal combustion engine 1 is stopped), the electromagnetic valves are basically not energized, the isolation valve 26 is closed, the bypass valve 24 is open, the purge control valve 28 is closed, and the drain cut valve 13 is open. Therefore, the fuel tank 2 is kept sealed.

[0022] During refueling, the shutoff valve 26 is open, the bypass valve 24 is open, the purge control valve 28 is closed, and the drain cut valve 13 is open. Therefore, fuel vapor generated as the fuel tank 2 is refueled is introduced into the canister 3 via the evaporated fuel passage 23. The fuel components are adsorbed by the adsorbent in the canister 3 and are not released to the outside.

[0023] The fuel components adsorbed in the canister 3 during refueling are introduced into the intake passage 17 of the internal combustion engine 1 for treatment the next time the internal combustion engine 1 is operated and enters an operating state in which introduction of purge gas is permitted. FIG. 2 is an explanatory diagram showing the operation (gas flow) during purging of the canister 3. When purging the canister 3, the block valve 26 is closed, the bypass valve 24 is open, and the drain cut valve 13 is open. Both the first purge control valve 28A and the second purge control valve 28B are duty-controlled (PWM-controlled) by drive pulse signals of a predetermined cycle. More specifically, the first purge control valve 28A and the second purge control valve 28B are driven with a 180° phase difference between their ON periods so that the ON periods of the drive pulse signals are complementary to each other.

[0024] As described above, the tip of the purge passage 16 is connected between the compressor 20 and the negative pressure generating valve 21 of the intake passage 17, and the negative pressure generated by the negative pressure generating valve 21 acts on the tip of the purge passage 16. On the other hand, the drain port 15 of the canister 3 is open to the atmosphere. Therefore, the pressure difference between the two causes air to be introduced into the canister 3 from the drain port 15. This air flow causes fuel components adsorbed by the adsorbent in the canister 3 to desorb, and the fuel components become purge gas and flow into the intake passage 17. By treating the purge gas using the pair of purge control valves 28A, 28B in this way, a large amount of purge gas can be introduced into the internal combustion engine 1, making it possible to efficiently treat the purge gas within the relatively short operating period of the internal combustion engine 1.

[0025] Meanwhile, during vehicle operation, for example, when the outside air temperature is high, the pressure in the sealed fuel tank 2 may increase. When the pressure detected by the tank pressure sensor 32 exceeds a threshold, a process to release the pressure in the fuel tank 2 is executed, assuming that the internal combustion engine 1 is operating. FIG. 3 is an explanatory diagram showing the operation (gas flow) during this pressure release. When releasing the pressure in the fuel tank 2, the check valve 26 opens and the bypass valve 24 closes. Then, either the first purge control valve 28A or the second purge control valve 28B, for example, the second purge control valve 28B, is duty-controlled. The other first purge control valve 28A is maintained in a closed state. Due to the pressure difference between the pressure in the fuel tank 2 and the negative pressure in the intake passage 17, fuel vapor flows from the fuel tank 2 to the intake passage 17, thereby releasing the pressure in the fuel tank 2. At this time, only the second purge control valve 28B is duty-controlled, so the flow rate of gas introduced into the intake passage 17 is accurately metered to a relatively small amount.

[0026] Unlike the purge gas from the canister 3, the gas flowing out of the fuel tank 2 when the pressure in the fuel tank 2 is released is almost entirely fuel vapor. Therefore, in order to suppress fluctuations in the air-fuel ratio, the flow rate of the gas must be limited to a small amount compared to the flow rate of the purge gas from the canister 3. Furthermore, while air is introduced from the drain port 15 when the canister 3 is purged, no air is introduced when the pressure in the fuel tank 2 is released. For example, in one embodiment, the gas flow rate when the pressure in the fuel tank 2 is released is set to about 1 / 10 of the gas flow rate when the canister 3 is purged. By controlling the flow of fuel vapor, which should be kept small, with a single purge control valve 28 in this way, the air-fuel ratio accuracy of the internal combustion engine 1 is improved.

[0027] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment and various modifications are possible. For example, the number of purge control valves 28 is not limited to two, and three or more may be provided. Furthermore, the present invention is not limited to hybrid vehicles or internal combustion engines with superchargers, but can be widely applied to vehicles equipped with an internal combustion engine and a fuel tank.

Claims

1. A control method for an evaporated fuel treatment device comprising: a purge passage connecting a canister and an intake passage of an internal combustion engine; an evaporated fuel passage connected to an intermediate portion of the purge passage connecting the canister and a fuel tank; a shut-off valve for opening and closing the evaporated fuel passage; a bypass valve for opening and closing the purge passage on the canister side of the connection between the purge passage and the evaporated fuel passage; and a plurality of purge control valves arranged in parallel with each other in the purge passage, wherein, when purging the canister, the shut-off valve is closed, the bypass valve is opened, and duty control is performed on all of the purge control valves; and, when releasing pressure in the fuel tank, the shut-off valve is opened, the bypass valve is closed, duty control is performed on one purge control valve, and the other purge control valves are closed.

2. The method for controlling an evaporated fuel treatment device according to claim 1, wherein the fuel tank is a sealed fuel tank.

3. The method for controlling an evaporated fuel treatment device according to claim 1, wherein the plurality of purge control valves comprises two purge control valves.

4. The method for controlling an evaporated fuel treatment device according to claim 1, wherein air is introduced into the canister through a drain port during purging of the canister.

5. The method for controlling an evaporated fuel treatment device according to claim 1, wherein a negative pressure generating valve is provided upstream of the throttle valve in the intake passage, and the purge passage is connected between the throttle valve and the negative pressure generating valve.

6. A control device for an evaporated fuel treatment device comprising: a purge passage communicating a canister with an intake passage of an internal combustion engine; an evaporated fuel passage connected to an intermediate portion of the purge passage communicating the canister with a fuel tank; a shut-off valve opening and closing the evaporated fuel passage; a bypass valve opening and closing the purge passage on the canister side of the connection between the purge passage and the evaporated fuel passage; a plurality of purge control valves arranged in parallel with each other in the purge passage; and a controller, wherein the controller closes the shut-off valve and opens the bypass valve and performs duty control of all the purge control valves when purging the canister, and opens the shut-off valve and closes the bypass valve, and performs duty control of one purge control valve and closes the other purge control valves when releasing pressure in the fuel tank.

Images