JP7639738B2 - Fuel tank pressure control device - Google Patents

Description

This disclosure relates to a fuel tank pressure control device that adjusts the internal pressure of a vehicle fuel tank.

Internal pressure control devices that adjust the internal pressure of a fuel tank of a vehicle equipped with a fuel pump inside are known (see, for example, Patent Document 1). This internal pressure control device includes a vapor conduit that is provided between the fuel tank and the canister and that guides fuel vapor (evaporated fuel) generated in the fuel tank to the canister, a control valve (shutoff valve) that is provided in the vapor conduit and that controls the opening and closing of the flow path of the vapor conduit, and a surge tank that is provided in the vapor conduit between the control valve and the fuel tank and that temporarily stores the vapor generated in the fuel tank. The control valve of this internal pressure control device is basically open, but is closed when the altitude is above a predetermined altitude, the temperature of the fuel in the fuel tank is above a predetermined temperature, and the pressure in the surge tank is below a predetermined pressure. This prevents the internal pressure of the fuel tank from being reduced at high altitudes, which would cause the boiling point of the fuel to drop, and prevents a large amount of vapor from being generated in the fuel tank.

Special Publication No. 06-031576

In the fuel tank described above, it is necessary to suppress the rise in internal pressure in order to protect the fuel tank and prevent the cap from becoming stuck on the filler neck. For this reason, a control valve (shutoff valve) between the fuel tank and a surge tank or the like is opened in response to an increase in internal pressure in order to guide vapor in the fuel tank to the surge tank or the like and reduce the internal pressure. However, depending on the properties of the fuel in the fuel tank and the surrounding environment (atmospheric pressure, temperature, etc.), a large amount of vapor may be generated in the fuel tank in response to the drop in internal pressure caused by the opening of the control valve, which may cause vapor lock in the fuel supply system connected to the fuel pump that pumps fuel from the fuel tank.

Therefore, the primary objective of this disclosure is to prevent vapor lock from occurring in the fuel supply system while suppressing an increase in the internal pressure of the fuel tank.

The fuel tank pressure control device disclosed herein is a fuel tank pressure control device that adjusts the internal pressure of the fuel tank by opening and closing a shutoff valve disposed between the fuel tank and the canister of a vehicle, and opens the shutoff valve when the internal pressure of the fuel tank is equal to or greater than a valve opening threshold, and sets the valve opening threshold in consideration of the atmospheric pressure when it is determined that the vapor concentration in the fuel tank is high.

1 is a schematic configuration diagram of a vehicle including a fuel tank pressure control device according to the present disclosure. 2 is a schematic diagram showing the configuration of an evaporated fuel treatment device for the internal combustion engine of the vehicle shown in FIG. 1; 3 is a control block diagram of the evaporated fuel processing device shown in FIG. 2 . 5 is a flowchart showing an example of a routine executed to determine whether or not pressure relief is required for a fuel tank. 4 is a flowchart showing an example of a routine executed to properly operate an internal combustion engine and an evaporated fuel treatment device in a state where the vapor concentration in a fuel tank is high. 10 is a flowchart for determining whether or not the shutoff valve 30 can be opened, i.e., whether or not depressurization of the fuel tank 10 can be resumed, after the shutoff valve is closed. 5 is a time chart showing the change over time in the fuel pressure and the state of the shutoff valve in the fuel supply system when the vapor concentration in the fuel tank is high. 5 is a flowchart showing an example of a routine executed to set a target internal pressure of a fuel tank. 5 is a flowchart illustrating an example of a routine executed to suppress a sudden decrease in internal pressure while a shutoff valve is opened to release pressure from a fuel tank. 5 is a time chart showing the change over time in the fuel pressure and the state of the shutoff valve in the fuel supply system when the vapor concentration in the fuel tank is high.

Next, the form for implementing the invention of this disclosure will be described with reference to the drawings.

Figure 1 is a schematic diagram of a vehicle including a fuel tank pressure control device of the present disclosure. The vehicle 1 shown in the figure is a hybrid vehicle including an engine 2, a single-pinion planetary gear 3 as a power distribution mechanism, a gear train 4, motor generators MG1 and MG2, both of which are synchronous generator motors (three-phase AC motors), a battery (electricity storage device) 5, a power control device (hereinafter referred to as "PCU") 6 that is connected to the battery 5 and drives the motor generators MG1 and MG2, and a hybrid electronic control unit (hereinafter referred to as "HVECU") 100 that controls the entire vehicle.

The engine 2 of the vehicle 1 is an internal combustion engine that converts the reciprocating motion of the piston PS (see FIG. 2) caused by the combustion of a mixture of gasoline or the like (hydrocarbon fuel) and air in a plurality of combustion chambers (cylinders) 2c into the rotational motion of the crankshaft (output shaft) CS. That is, in the engine 2, air cleaned by the air cleaner 2a is drawn into each combustion chamber 2c through the intake pipe 2i, the throttle valve 2s, an intake valve (not shown), etc., and fuel is injected into the intake air from the port injection valve 2jp of the intake port 2p and/or the in-cylinder injection valve 2jd of each combustion chamber 2c. Furthermore, the mixture of air and fuel explodes and burns in each combustion chamber 2c due to an electric spark from an ignition plug (not shown), causing the piston PS to reciprocate and rotate the crankshaft CS. The engine 2 is controlled by an engine electronic control unit (hereinafter referred to as "engine ECU") 200. The engine ECU 200 includes a microcomputer with a CPU, ROM, RAM, input/output interface, etc. (not shown), various drive circuits, various logic ICs, etc., and performs intake air volume control, fuel injection control, ignition timing control, etc. for the engine 2.

The planetary gear 3 is a differential rotation mechanism including a sun gear 3s, a ring gear 3r, and a planetary carrier 3c that rotatably supports a plurality of pinion gears 3p. As shown in FIG. 1, the sun gear 3s is connected to the rotor of the motor generator MG1, and the planetary carrier 3c is connected to the crankshaft CS of the engine 2 via a damper mechanism DD. The ring gear 3r rotates coaxially and integrally with the counter drive gear 4a (output member) of the gear train 4. In addition to the counter drive gear 4a, the gear train 4 includes a counter driven gear 4b and a final drive gear (drive pinion gear) 4c. The final drive gear 4c meshes with the differential ring gear Dr of the differential gear DF and is connected to the left and right wheels (drive wheels) W via the differential gear DF and the drive shaft DS. As a result, the planetary gear 3, the gear train 4, and the differential gear DF form a transaxle that transmits a portion of the output torque of the engine 2, which serves as a power generation source, to the wheels W and connects the engine 2 and the motor generator MG1 to each other.

The motor generator MG1 mainly operates as a generator that converts at least a portion of the power from the engine 2 operated under load into electric power. The motor generator MG2 is connected to the left and right wheels W via a differential gear DF including a drive gear 4d, a counter driven gear 4b, a final drive gear 4c, and a differential ring gear Dr, and a drive shaft DS. The motor generator MG2 mainly operates as an electric motor that is driven by at least one of the electric power from the battery 5 and the electric power from the motor generator MG1 to generate a drive torque on the drive shaft DS.

The battery 5 is, for example, a lithium ion secondary battery or a nickel-hydrogen secondary battery. The battery 5 is managed by a battery management electronic control device (hereinafter referred to as "battery ECU") 500 including a microcomputer having a CPU (not shown). The PCU 6 includes a first inverter that drives the motor generator MG1, a second inverter that drives the motor generator MG2, a boost converter that can boost the power from the battery 5 and reduce the power from the motor generators MG1 and MG2 (all not shown). The PCU 6 is controlled by a motor electronic control device (hereinafter referred to as "MGECU") 600 including a microcomputer having a CPU (not shown). The HVECU 100 includes a microcomputer having a CPU, various drive circuits, various logic ICs, etc. The HVECU 100 exchanges information with the ECUs 200, 500, 600 and a brake electronic control device (not shown) that controls a hydraulic brake actuator (not shown) to comprehensively control the vehicle 1.

FIG. 2 is a schematic diagram showing an evaporative fuel processing device 20, which is an auxiliary device of the engine 2, and FIG. 3 is a control block diagram of the evaporative fuel processing device 20. The evaporative fuel processing device 20 is for suppressing leakage of fuel vapor (evaporative fuel) generated in a fuel tank 10 that stores fuel to be supplied to each combustion chamber 2c of the engine 2 to the outside. The fuel tank 10 has a fuel inlet pipe 11 for supplying fuel into the fuel tank 10 through a fuel filler port (not shown) of the vehicle 1, a vent line 12, a check valve 13 for regulating the backflow of fuel from the inside of the fuel tank 10 to the fuel filler port, a fuel sender gauge 14 for detecting the liquid level of the fuel in the fuel tank 10 by a float, and a tank internal pressure sensor 15 for detecting the internal pressure (tank internal pressure) Pt of the fuel tank 10. In this embodiment, the tank internal pressure sensor 15 detects the differential pressure between the pressure (absolute pressure) in the fuel tank 10 and the atmospheric pressure _Patm as the internal pressure Pt. 3, the fuel sender gauge 14 and the tank internal pressure sensor 15 each transmit a signal indicating a detection value to an engine ECU 200 which serves as a pressure control device for the fuel tank 10. In addition, the engine 2 is provided with an atmospheric pressure sensor AP which detects the atmospheric pressure _Patm , and the atmospheric pressure sensor AP transmits a signal indicating a detection value to the engine ECU 200.

A low-pressure fuel passage (fuel supply system) 16L is connected to the top of the fuel tank 10, and a fuel pump (pump module) 17 connected to the low-pressure fuel passage 16L is disposed inside the fuel tank 10. The fuel pump 17 is an electric pump driven by power from an auxiliary battery (not shown) and controlled by the engine ECU 200. Each port injection valve 2jp of the engine 2 is supplied with fuel pumped by the fuel pump 17 through the low-pressure fuel passage 16L and a low-pressure delivery pipe. Furthermore, a high-pressure fuel passage 16H branches off from the middle of the low-pressure fuel passage 16L. The high-pressure fuel passage 16H includes, in order from the branching point with the low-pressure fuel passage 16L, an electromagnetic fuel pressure control valve 18 and a mechanical pump 19, which is, for example, a piston pump driven by the engine 2. Each in-cylinder injection valve 2jd of the engine 2 is supplied with fuel pumped by the mechanical pump 19 through a check valve (not shown) and a high-pressure delivery pipe.

2, a low-pressure fuel pressure sensor LFP is provided in the low-pressure fuel passage 16L to detect a low-pressure fuel pressure (hereinafter simply referred to as "fuel pressure") _PFL , which is the pressure of fuel supplied from the fuel pump 17 to the low-pressure fuel passage 16L (each port injection valve 2jp). Furthermore, a high-pressure fuel pressure sensor (not shown) is provided in the high-pressure fuel passage 16H to detect a high-pressure fuel pressure, which is the pressure of fuel supplied from the mechanical pump 19 to each in-cylinder injection valve 2jd. The low-pressure fuel pressure sensor LFP and the high-pressure fuel pressure sensor each transmit a signal indicative of a detection value to the engine ECU 200.

As shown in FIG. 2, the vapor fuel processing device 20 includes a canister 22, a vapor passage 24 connecting the fuel tank 10 and the canister 22, a purge passage 26, an air passage 28, and a shutoff valve 30 installed in the middle of the vapor passage 24. The canister 22 has activated carbon as an adsorbent disposed therein, and adsorbs the vapor fuel in the fuel tank 10 with the adsorbent. One end (upstream end) of the vapor passage 24 is connected to the fuel tank 10 so as to communicate with the gas layer in the fuel tank 10, and the other end (downstream end) of the vapor passage 24 is connected to the canister 22 so as to communicate with the inside of the canister 22.

In addition, one end (upstream end) of the purge passage 26 is connected to the canister 22 so as to communicate with the inside of the canister 22, and the other end (downstream end) of the purge passage 26 is connected to the intake pipe 2i downstream of the throttle valve 2s of the engine 2. Furthermore, a purge valve 27 capable of blocking the purge passage 26 is installed in the middle of the purge passage 26. The purge valve 27 is an opening/closing valve controlled by the engine ECU 200 and is normally maintained in a closed state. In addition, one end of the air passage 28 is connected to the canister 22 via a key-off pump module 40 as a diagnostic component used for fault diagnosis of the evaporated fuel processing device 20. The key-off pump module 40 includes a switching valve (shutoff valve) 41 and a vacuum pump (reducing pressure pump) 45, which are opening/closing valves controlled by the engine ECU 200, and a canister internal pressure sensor 47 that detects the internal pressure Pc of the canister 22 and transmits it to the engine ECU 200. When the switching valve 41 is open, it allows communication between the inside of the canister 22 and the atmospheric passage 28, and when it is closed, it blocks communication between the two. When the switching valve 41 is closed, the vacuum pump 45 can reduce the pressure (create negative pressure) inside the canister 22. Furthermore, an air filter 29 is installed midway through the atmospheric passage 28, and the other end of the atmospheric passage 28 is open to the atmosphere.

The shutoff valve 30 is a flow rate adjustment valve controlled by the engine ECU 200. When in a closed state, it closes the vapor passage 24 to block communication between the fuel tank 10 and the canister 22, and when in an open state, it adjusts the flow rate of gas flowing through the vapor passage 24. The shutoff valve 30 includes a casing 31, a valve seat 32 formed in the casing 31, a valve body 33 arranged in the casing 31 so as to be freely movable in the axial direction, and a stepping motor 34 arranged in the casing 31 and connected to the valve body 33 via a valve guide (not shown). The stepping motor 34 is controlled by the engine ECU 200 and moves the valve body 33 back and forth in the axial direction relative to the valve seat 32. When the stepping motor 34 is operated, the valve body 33 approaches the valve seat 32, and a seal member (not shown) of the valve body 33 abuts against the valve seat 32, thereby closing the shutoff valve 30. In addition, as the stepping motor 34 operates, the valve body 33 separates from the valve seat 32, and the sealing member (not shown) of the valve body 33 separates from the valve seat 32, opening the shut-off valve 30. Furthermore, after the start switch of the vehicle 1 is turned on, the start switch is turned off, the shut-off valve 30 is opened or closed at high speed, and the shut-off valve 30 is initialized during a fault diagnosis of the evaporated fuel processing device 20, etc. This initialization rotates the stepping motor 34 so that the rotation start position of the stepping motor 34 coincides with the opening start position of the shut-off valve 30, which is learned separately.

In the above-described evaporative fuel treatment device 20, while the vehicle 1 is parked (while the engine 2 is not in operation), the shutoff valve 30 is kept closed, and the evaporative fuel in the fuel tank 10 does not flow into the canister 22. Also, while the vehicle 1 is parked, the purge passage 26 is kept in a blocked state by closing the purge valve 27, and the canister 22 is kept in communication with the air passage 28 by opening the switching valve 41. Furthermore, in the evaporative fuel treatment device 20, when the start switch (ignition switch) of the vehicle 1 is turned off and the key of the vehicle 1 is turned off (when the engine 2 is not in operation), the engine ECU 200 diagnoses the presence or absence of leaks in the vapor passage 24 and the purge passage 26.

On the other hand, after the start switch is turned on, the engine ECU 200 communicates the inside of the canister 22 with the air passage 28 and opens the purge valve 27 in response to the establishment of predetermined purge conditions including at least that the engine 2 is operating. As a result, the intake negative pressure of the engine 2 (intake pipe 2i) is supplied into the canister 22 through the purge passage 26, and air flows into the canister 22 from the air passage 28. Furthermore, when the purge valve 27 is open and the internal pressure Pt of the fuel tank 10 is equal to or higher than the valve opening threshold (tank internal pressure threshold) Pop, the engine ECU 200 opens the shutoff valve 30 to depressurize the fuel tank 10. As a result, vapor (evaporated fuel) in the fuel tank 10 flows into the canister 22 through the vapor passage 24 (shutoff valve 30). The adsorbent in the canister 22 is then purged by air flowing into the canister 22, and the vapor that has been released from the adsorbent is guided together with the air to the intake pipe 2i of the engine 2 and combusted in the combustion chamber 2c.

Figure 4 is a flow chart showing an example of a routine executed by the engine ECU 200 to determine whether or not pressure release from the fuel tank 10 is required. The routine shown in Figure 4 is repeatedly executed by the engine ECU 200 at predetermined time intervals (very short time intervals) while the engine 2 is operating after the start switch is turned on. When starting the routine in Figure 4, the engine ECU 200 acquires data necessary for determining whether or not pressure release is required, such as the internal pressure Pt (after appropriate smoothing processing) of the fuel tank 10 detected by the tank internal pressure sensor 15, a separately set valve opening threshold Pop, and separately set values of the vapor high concentration flag Fvh and the shutoff valve open flag Fop (step S100).

The valve opening threshold Pop is set based on the internal pressure Pt and the atmospheric pressure _Patm when it is determined that the vapor concentration, which is the concentration of evaporated fuel (vapor) in the gas present in the fuel tank 10, is high, and is set to a predetermined constant value Pref (for example, a value of about 2 kPa) when it is not determined that the vapor concentration in the fuel tank 10 is high. The vapor high concentration flag Fvh is set to "1" when it is determined that the vapor concentration in the fuel tank 10 is high, and is set to "0" when it is not determined that the vapor concentration in the fuel tank 10 is high. The shutoff valve opening flag Fop is set to "1" when the shutoff valve 30 should be opened, and is set to "0" when the shutoff valve 30 should be closed.

After the processing of step S100, the engine ECU 200 determines whether the acquired internal pressure Pt of the fuel tank 10 is less than the valve opening threshold Pop (step S110). If it is determined that the internal pressure Pt of the fuel tank 10 is equal to or greater than the valve opening threshold Pop (step S110: NO), the engine ECU 200 sets the above-mentioned shutoff valve open flag Fop to "1" (step S115) and temporarily terminates the routine of FIG. 4. If the shutoff valve open flag Fop is set to "1" in step S115 and the shutoff valve 30 is closed, the engine ECU 200 operates the stepping motor 34 at a low speed (e.g., 30 msec/step) that does not require the above-mentioned initialization to open the shutoff valve 30. This allows the vapor (evaporated fuel) in the fuel tank 10 to flow into the canister 22 via the vapor passage 24 (shutoff valve 30), thereby lowering the internal pressure Pt of the fuel tank 10.

On the other hand, if it is determined in step S110 that the internal pressure Pt of the fuel tank 10 is less than the valve opening threshold Pop (step S110: YES), the engine ECU 200 determines whether the above-mentioned shutoff valve open flag Fop is "1" (step S120). If it is determined that the internal pressure Pt is less than the valve opening threshold Pop and the shutoff valve open flag Fop is "0" and the shutoff valve 30 is closed (step S120: NO), the engine ECU 200 sets (maintains) the shutoff valve open flag Fop to "0" without permitting the shutoff valve 30 to open (step S170), and temporarily ends the routine of FIG. 4.

If it is determined in step S120 that the internal pressure Pt is less than the valve opening threshold Pop and the valve opening flag Fop is "1" and the valve closing valve 30 is open (step S120: YES), the engine ECU 200 determines whether the vapor high concentration flag Fvh acquired in step S100 is "0" (step S130). If it is determined that the vapor high concentration flag Fvh is "0" (the vapor concentration in the fuel tank 10 is not high) (step S130: YES), the engine ECU 200 sets the valve closing threshold Pcl to a value obtained by subtracting a constant value η _const (for example, a value around 1.0 kPa) previously determined as a hysteresis from the valve opening threshold Pop acquired in step S100 (step S140).

On the other hand, when it is determined in step S130 that the vapor high concentration flag Fvh is "1" (the vapor concentration in the fuel tank 10 is high) (step S130: NO), the engine ECU 200 derives a hysteresis η (Pt) corresponding to the internal pressure Pt of the fuel tank 10 acquired in step S100 from a hysteresis setting map (not shown) (step S150). Furthermore, in step S150, the engine ECU 200 sets a value obtained by subtracting the hysteresis η (Pt) from the valve opening threshold Pop acquired in step S100 to the valve closing threshold Pcl. The hysteresis setting map used in step S150 specifies a hysteresis adapted for each of the multiple internal pressures Pt through experiments, analysis, etc. In addition, in the hysteresis setting map of this embodiment, the hysteresis assigned to each of the multiple internal pressures Pt is set to a value less than the above-mentioned constant value η _const .

After processing step S140 or S150, the engine ECU 200 determines whether the internal pressure Pt of the fuel tank 10 acquired in step S100 is equal to or lower than the closing threshold Pcl set in step S140 or S150 (step S160). If it is determined that the internal pressure Pt of the fuel tank 10 is higher than the closing threshold Pcl (step S160: NO), the engine ECU 200 determines that the internal pressure Pt of the fuel tank 10 has not sufficiently decreased after opening the shutoff valve 30, and sets (maintains) the shutoff valve open flag Fop to "1" without allowing the shutoff valve 30 to close (step S115), and temporarily ends the routine of FIG. 4. Also, if it is determined in step S160 that the internal pressure Pt of the fuel tank 10 is equal to or lower than the valve closing threshold Pcl (step S160: YES), the engine ECU 200 determines that the internal pressure Pt of the fuel tank 10 has been sufficiently reduced by the opening of the shutoff valve 30, sets the shutoff valve open flag Fop to "0" to permit the shutoff valve 30 to be closed (step S170), and temporarily ends the routine of FIG. 4. When the shutoff valve open flag Fop is set to "0" in step S170, the engine ECU 200 operates the stepping motor 34 at a low speed (e.g., 30 msec/step) that does not require the above-mentioned initialization, for example, to close the shutoff valve 30.

As described above, the engine ECU 200, which serves as a pressure control device for the fuel tank 10, closes the shutoff valve 30 when the internal pressure Pt of the fuel tank 10 becomes equal to or lower than the closing threshold Pcl, which is lower than the opening threshold Pop, after opening the shutoff valve 30 to release pressure from the fuel tank 10 (step S110: NO, step S170). In addition, when the engine ECU 200 determines that the high vapor concentration flag Fvh is "1" (step S130: NO), it reduces the hysteresis indicating the difference between the opening threshold Pop and the closing threshold Pcl compared to when it determines that the high vapor concentration flag Fvh is "0" (steps S140, S150). As a result, even if the shutoff valve 30 is opened so that the internal pressure Pt of the fuel tank 10 changes gradually according to the reference pressure reduction amount ρref described below when the vapor concentration in the fuel tank 10 is high, it is possible to prevent the internal pressure Pt of the fuel tank 10 from decreasing suddenly from the time when the internal pressure Pt of the fuel tank 10 becomes equal to or greater than the valve opening threshold Pop until the internal pressure Pt becomes equal to or less than the valve closing threshold Pcl.

When the engine ECU 200 determines that the high vapor concentration flag Fvh is "1" (the vapor concentration in the fuel tank 10 is high) (step S130: NO), the engine ECU 200 sets a hysteresis indicating the difference between the opening threshold Pop and the closing threshold Pcl based on the internal pressure Pt of the fuel tank 10 (step S150). That is, the higher the internal pressure Pt of the fuel tank 10, the greater the amount of vapor passing through the stop valve 30 within a unit time. Therefore, by setting the difference between the opening threshold Pop and the closing threshold Pcl based on the internal pressure Pt of the fuel tank 10, it is possible to effectively suppress a sudden decrease in the internal pressure Pt of the fuel tank 10 between when the internal pressure Pt of the fuel tank 10 becomes equal to or greater than the opening threshold Pop and when the internal pressure Pt of the fuel tank 10 becomes equal to or less than the closing threshold Pcl.

Fig. 5 is a flow chart showing an example of a routine executed by the engine ECU 200 to properly operate the engine 2 and the evaporated fuel treatment device 20 in a state where the vapor concentration in the fuel tank 10 is high. The routine shown in Fig. 5 is also repeatedly executed by the engine ECU 200 at predetermined time intervals (very short time intervals) while the engine 2 is operating after the start switch is turned on. When starting the routine of Fig. 5, the engine ECU 200 acquires data necessary for determining the degree of the vapor concentration in the fuel tank 10, such as the internal pressure Pt of the fuel tank 10 detected by the tank internal pressure sensor 15, the fuel pressure _PFL detected by the low fuel pressure sensor LFP, the atmospheric pressure (current atmospheric pressure) _Patm detected by the atmospheric pressure sensor AP, the intake air temperature Ta, which is the temperature of the intake air detected by a temperature sensor (not shown) installed in the intake pipe 2i, and the estimated vapor concentration Cv, which is an estimated value of the vapor concentration in the fuel tank 10 (step S200). The estimated vapor concentration Cv is calculated separately by the engine ECU 200 based on the difference between the air-fuel ratio in each combustion chamber 2c when the purge valve 27 is open and the target air-fuel ratio, etc.

Next, the engine ECU 200 judges whether the vapor concentration in the fuel tank 10 is high based on the fuel pressure _PFL , the atmospheric pressure _Patm , the intake air temperature Ta, and the estimated vapor concentration Cv acquired in step S100 (step S210). In step S210, the engine ECU 200 judges whether the atmospheric pressure _Patm is equal to or lower than a predetermined pressure, and judges whether the intake air temperature Ta is equal to or higher than a predetermined temperature. In step S210, the engine ECU 200 also judges whether the estimated vapor concentration Cv is equal to or higher than a threshold value set based on the atmospheric pressure _Patm . Furthermore, in step S210, the engine ECU 200 judges whether the fuel pressure _PFL is sufficiently close to a target lower limit fuel pressure (target fuel pressure) Ptag, which is the lower limit of the target value of the pressure of the fuel in the low pressure fuel passage 16L, i.e., the lower limit of the fuel pressure to be supplied to the low pressure fuel passage 16L by the fuel pump 17. In this embodiment, when it is determined that the vapor concentration in the fuel tank 10 is not high, the target lower limit fuel pressure Ptag is set to, for example, any one of 300 kPa, 400 kPa, and 500 kPa depending on the operating state of the engine 2, etc.

The engine ECU 200 determines that the vapor concentration in the fuel tank 10 is high when the atmospheric pressure P _atm is equal to or lower than a predetermined pressure, the intake air temperature Ta is equal to or higher than a predetermined temperature, and the estimated vapor concentration Cv is equal to or higher than the threshold value (step S220: YES). The engine ECU 200 also determines that the vapor concentration in the fuel _{tank 10 is high when the atmospheric pressure P atm} is equal to or lower than a predetermined pressure, the intake air temperature Ta is equal to or higher than a predetermined temperature, and the fuel pressure P _FL is lower than the target lower limit fuel pressure P tag by a predetermined value or more and is not sufficiently close to the target lower limit fuel pressure P tag (step S220: YES). Furthermore, the engine ECU 200 determines that the vapor concentration in the fuel tank 10 is not high in other cases (step S220: NO). If it is determined in step S220 that the vapor concentration in the fuel tank 10 is not high (step S220: NO), the engine ECU 200 sets the high vapor concentration flag Fvh to “0”, sets the valve opening threshold Pop to the fixed value Pref, and resets the timer and a fuel pressure reduction counter C _L (step S225), after which the routine of FIG. 5 is temporarily terminated.

On the other hand, when it is determined in step S220 that the vapor concentration in the fuel tank 10 is high (step S220: YES), the engine ECU 200 turns on a timer that measures the elapsed time t since it was determined that the vapor concentration in the fuel tank 10 is high (step S230), and sets the above-mentioned high vapor concentration flag Fvh to "1" (step S240). Furthermore, the engine ECU 200 sets the valve opening threshold Pop in consideration of the atmospheric pressure P _atm acquired in step S200 (step S250). In step S250, the engine ECU 200 derives a value corresponding to the atmospheric pressure P _atm acquired in step S200 from a map (not shown), and sets the valve opening threshold Pop to the larger of the value derived from the map and the internal pressure Pt of the fuel tank 10 acquired in step S200. The map used in step S250 specifies a value that can be set as the valve opening threshold Pop adapted through experiments, analyses, etc. for each of a plurality of atmospheric pressures P _atm . The engine ECU 200 also sets the value of the valve opening threshold Pop set in step S250 as the initial target internal pressure Pint when the shutoff valve 30 is opened in a state where the vapor concentration in the fuel tank 10 is high, and stores this in the RAM or non-volatile memory (step S260). Furthermore, the engine ECU 200 stores the atmospheric pressure _Patm acquired in step S200 as the reference atmospheric pressure P0 _atm in the RAM or non-volatile memory (step S270).

Next, the engine ECU 200 increases the target lower limit fuel pressure Ptag (step S280). That is, when it is determined in step S220 that the vapor concentration in the fuel tank 10 is high, the target lower limit fuel pressure Ptag is increased from the previous value (e.g., 300, 400, or 500 kPa) to a predetermined value (e.g., a value of about 650 kPa) in step S280. This increases the discharge pressure (rotation speed) of the fuel pump 17 to increase the fuel pressure _PFL in the low-pressure fuel passage 16L, making it possible to suppress the occurrence of vapor lock in the low-pressure fuel passage 16L. Furthermore, the engine ECU 200 sets a fuel pressure drop determination threshold P _L for determining whether or not there is a risk of vapor lock occurring in the low-pressure fuel passage 16L (step S290). In step S290, engine ECU 200 sets the fuel pressure drop determination threshold P L to a value (e.g., Ptag - 200 kPa) obtained by subtracting a predetermined value α (e.g., a value around 200 kPa) from the target lower limit fuel pressure Ptag (e.g., 300, 400, or 500 kPa) before it was changed (raised) in step _S280 .

After the process of step S290, the engine ECU 200 judges whether the fuel pressure _PFL acquired in step S200 is equal to or less than the fuel pressure drop judgment threshold P _L set in step S290 (step S300). If the engine ECU 200 judges that the fuel pressure _PFL is equal to or less than the fuel pressure drop judgment threshold P _L (step S300: YES), the engine ECU 200 increments the fuel pressure drop counter C _L (step S310). Furthermore, the engine ECU 200 sets the shutoff valve open flag Fop to "0" to prohibit the shutoff valve 30 from opening (step S320), and temporarily ends the routine of FIG. 5. If the engine ECU 200 judges that the fuel pressure _PFL is greater than the fuel pressure drop judgment threshold P _L in step S300 (step S300: NO), the engine ECU 200 skips the processes of steps S310 and S320 so that the value of the shutoff valve open flag Fop is maintained at the previous value, and temporarily ends the routine of FIG. 5.

When the shutoff valve open flag Fop is set to "0" in step S320 and the shutoff valve 30 is open to release the pressure in the fuel tank 10, the engine ECU 200 operates the stepping motor 34 at a low speed (e.g., 30 msec/step) that makes the above-mentioned initialization unnecessary to close the shutoff valve 30. As a result, when it is determined that the vapor concentration in the fuel tank 10 is high based on at least the atmospheric pressure _Patm and that the fuel pressure _PFL in the low-pressure fuel passage 16L is decreasing (step S220: YES, step S300: YES), the shutoff valve 30 is forcibly closed.

That is, when the vapor concentration in the fuel tank 10 is high, if the shutoff valve 30 is opened in response to an increase in the internal pressure Pt of the fuel tank 10, a large amount of vapor may be generated in the fuel tank 10 in response to a decrease in the internal pressure Pt caused by the opening of the shutoff valve 30. Furthermore, if a large amount of vapor is generated in the fuel tank 10, the fuel pressure _PFL in the low-pressure fuel passage 16L (the discharge pressure of the fuel pump 17) decreases due to vapor entrapment by the fuel pump 17. In light of this, when the engine ECU 200, which is the control device of the engine 2, determines that the vapor concentration in the fuel tank 10 is high based on at least the atmospheric pressure P _atm and that the fuel pressure _PFL in the low-pressure fuel passage 16L is decreasing (step S220: YES, step S300: YES), it sets the shutoff valve open flag Fop to "0" to close the shutoff valve 30 (step S320).

As a result, the closing of the shutoff valve 30 suppresses a decrease in the internal pressure Pt of the fuel tank 10 and the generation of vapor, so that it is possible to effectively suppress a decrease in the fuel pressure _PFL in the low-pressure fuel passage 16L and the occurrence of vapor lock. Furthermore, when the fuel pressure _PFL in the low-pressure fuel passage 16L is not decreasing (step S220: YES, step S300: NO), the shutoff valve 30 is allowed to open, and an increase in the internal pressure Pt of the fuel tank 10 can be suppressed. As a result, in the engine 2, it is possible to effectively suppress the occurrence of vapor lock in the low-pressure fuel passage 16L while suppressing an increase in the internal pressure Pt of the fuel tank 10.

Furthermore, when the engine ECU 200 determines that the vapor concentration in the fuel tank 10 is high (step S220: YES), it sets the valve opening threshold Pop taking into consideration the atmospheric pressure _Patm (step S250). That is, when the engine ECU 200 determines that the vapor concentration in the fuel tank 10 is high, it sets the valve opening threshold Pop to the larger of a value corresponding to the atmospheric pressure _Patm obtained from a map (not shown) and the internal pressure Pt of the fuel tank 10. As a result, when the vapor concentration in the fuel tank 10 is high, the valve opening threshold Pop is appropriately set, and even if the surrounding atmospheric pressure _Patm is low, the internal pressure Pt of the fuel tank 10 is not suddenly decreased when the stop valve 30 is opened, thereby suppressing the generation of a large amount of vapor in the fuel tank 10.

Here, if the shutoff valve 30 is open and the shutoff valve open flag Fop is set to "0" in step S320 of FIG. 5, the shutoff valve 30 will be closed. In this case, it is preferable to keep the shutoff valve 30 open and continue depressurizing the fuel tank 10. Therefore, when the shutoff valve 30 is closed in response to the shutoff valve open flag Fop being set to "0" in step S320, the engine ECU 200 executes the routine of FIG. 6 at predetermined time intervals (very short time) to determine whether or not to open the shutoff valve 30, i.e., whether or not to resume depressurizing the fuel tank 10. The routine of FIG. 6 is also executed when the shutoff valve 30 is opened in response to the processing of step S615 of FIG. 4 after it is determined in step S220 of FIG. 5 that the vapor concentration in the fuel tank 10 is high.

At the start of the routine of Fig. 6, the engine ECU 200 acquires data necessary for the judgment, such as the fuel pressure _PFL detected by the low-pressure fuel sensor LFP and the above-mentioned elapsed time t (step S400). Next, the engine ECU 200 judges whether the elapsed time t acquired in step S400 exceeds a predetermined valve opening restriction time tref0 (step S410). In this embodiment, the valve opening restriction time tref0 is, for example, a value of about 200 msec. If it is determined in step S410 that the elapsed time t is equal to or less than the valve opening restriction time tref0 (step S410: NO), the engine ECU 200 temporarily ends the routine of Fig. 6 at that point in time, and executes the processing from step S400 onwards when the next execution timing arrives.

Also, when it is determined in step S410 that the elapsed time t exceeds the valve opening restriction time tref0 (step S410: YES), the engine ECU 200 determines whether the fuel pressure _PFL acquired in step S400 is equal to or higher than a predetermined valve opening permission pressure (valve opening permission threshold) P _H (step S420). The valve opening permission pressure P _H is a pressure that can prevent the occurrence of vapor lock in the low pressure fuel passage 16L, and in this embodiment, it is set to a value (e.g., a value of about 620 kPa) slightly lower than the target lower limit fuel pressure Ptag (e.g., a value of about 650 kPa) raised in step S280 of FIG. 5. When it is determined that the fuel pressure _PFL is lower than the valve opening permission pressure P _H (step S420: NO), the engine ECU 200 temporarily ends the routine of FIG. 6 at that time, and executes the processing from step S400 onwards in response to the arrival of the next execution timing.

On the other hand, when it is determined in step S420 that the fuel pressure _PFL is equal to or higher than the valve-opening permission pressure _PH (step S420: YES), the engine ECU 200 sets the shut-off valve open flag Fop to "1" to permit the shut-off valve 30 to open (step S430), and temporarily ends the routine of Fig. 6. When the shut-off valve open flag Fop is set to "1" in step S430, the engine ECU 200 operates the stepping motor 34 at a low speed (e.g., 30 msec/step) that does not require the above-mentioned initialization, to open the shut-off valve 30.

That is, in the vehicle 1, as shown in Fig. 7, the shutoff valve 30, which has been once closed, is prohibited from being opened based on the fuel pressure _PFL in the low-pressure fuel passage 16L from the time t1 when it is determined that the vapor concentration in the fuel tank 10 is high until a predetermined valve-opening restriction time tref0 has elapsed. This makes it possible to effectively prevent the shutoff valve 30 from being opened in response to a temporary rise in the fuel pressure _PFL (see part A in Fig. 7) caused by, for example, fuel pulsation generated in the mechanical pump 19 of the high-pressure fuel passage 16H after the target lower limit fuel pressure _Ptag is set high in step S280 in Fig. 5 and before the fuel pressure PFL in the low-pressure fuel passage 16L becomes sufficiently high. Furthermore, in the vehicle 1, when the fuel pressure PFL in the low pressure fuel passage 16L becomes equal to or higher than the valve opening permission pressure _PH based on the target lower limit fuel pressure Ptag raised in step S280 (step S420: YES, time _t2 in FIG. 7) after the valve opening restriction time tref0 has elapsed since it was determined that the vapor concentration in the fuel tank 10 is high, the closing valve 30 is permitted to open. This makes it possible to resume depressurization of the fuel tank 10 by opening the closing valve 30 only after the fuel pressure _PFL in the low pressure fuel passage 16L has risen sufficiently to a level at which vapor lock can be avoided after the target lower limit fuel pressure Ptag has been set high.

Now, if the processing of steps S310 and S320 in FIG. 5 is skipped and the shutoff valve 30 is closed, the shutoff valve 30 is maintained in a closed state. Also, if the processing of steps S310 and S320 is skipped and the shutoff valve 30 is open, the shutoff valve 30 is maintained in an open state. In this case, the shutoff valve 30 is controlled to open at an opening degree corresponding to, for example, the estimated vapor concentration Cv, etc., until it is determined that the vapor concentration in the fuel tank 10 is high. Then, after determining that the vapor concentration in the fuel tank 10 is high (step S220: YES, step S300: NO), the engine ECU 200 sets the target internal pressure P* of the fuel tank 10 to gradually decrease over time, and controls the shutoff valve 30 so that the internal pressure Pt becomes the target internal pressure P*. More specifically, the engine ECU 200 converts the target internal pressure P* into a flow rate and controls the stepping motor 34 so that the vapor passes through the shutoff valve 30 at that flow rate.

Figure 8 is a flowchart showing a routine that is repeatedly executed by the engine ECU 200 at predetermined time intervals (very short time intervals) to set the target internal pressure P* of the fuel tank 10 after it is determined that the vapor concentration in the fuel tank 10 is high. The routine in Figure 8 is also repeatedly executed at predetermined time intervals (very short time intervals) after it is determined in step S220 in Figure 5 that the vapor concentration in the fuel tank 10 is high and the shutoff valve 30 is opened in response to the processing of step S615 in Figure 4.

At the start of the routine of Fig. 8, the engine ECU 200 acquires data necessary for setting the target internal pressure P*, such as the atmospheric pressure (current atmospheric pressure) P _atm detected by the atmospheric pressure sensor AP, the above-mentioned reference atmospheric pressure P0 _atm , and the value of the fuel pressure reduction counter C _L (step S500). Next, the engine ECU 200 calculates the reduction amount ρ of the target internal pressure P* per execution cycle (predetermined time) of the routine of Fig. 8 (step S510). In step S510, the engine ECU 200 calculates the reduction amount ρ by subtracting the product of a similarly predetermined change amount Δρ and the value of the fuel pressure reduction counter C _L from a predetermined reference reduction amount ρref according to the following formula (1). In this embodiment, the reference reduction amount ρref is set so as to reduce the target internal pressure P* at, for example, 2 kPa/min while it is determined that the vapor concentration in the fuel tank 10 is high, and ρref = 2 kPa x execution cycle / 60 sec. The amount of change Δρ is a constant value (for example, Δρ=approximately 0.5 kPa×execution cycle/60 sec) that is adapted through experiments and analyses so as to be smaller than the reference pressure reduction amount ρref.

ρ=ρref−Δρ× _CL …(1)

Furthermore, the engine ECU 200 calculates an atmospheric pressure correction amount ΔP _atm by subtracting the atmospheric pressure (current atmospheric pressure) P _atm from the reference atmospheric pressure P0 _atm acquired in step S500 (step S520). The atmospheric pressure correction amount ΔP _atm indicates the difference between the current atmospheric pressure P _atm and the reference atmospheric pressure P0 _atm , which is the atmospheric pressure when it is determined that the vapor concentration in the fuel tank 10 is high. Then, the engine ECU 200 sets the target internal pressure P* by adding the atmospheric pressure correction amount ΔP _atm to a value obtained by subtracting the pressure reduction amount ρ from the target internal pressure (previous target internal pressure) P* set at the previous execution of the routine of FIG. 8 (step S530), and temporarily ends the routine of FIG. 8. It should be noted that immediately after the start of the routine of FIG. 8, the initial target internal pressure Pint set in step S260 of FIG. 5 becomes the previous target internal pressure in step S530.

In this manner, when the engine ECU 200, which serves as the pressure control device for the fuel tank 10, opens the shutoff valve 30 to release the pressure of the fuel tank 10 when the vapor concentration in the fuel tank 10 is high, it reduces the target internal pressure P* by the predetermined pressure reduction amount ρ and corrects it with the atmospheric pressure correction amount ΔP _atm at predetermined time intervals (steps S500-S530). This allows the internal pressure Pt of the fuel tank 10 to be gradually reduced in accordance with the surrounding atmospheric pressure P _atm , making it possible to simultaneously suppress an increase in the internal pressure of the fuel tank 10 and suppress the occurrence of vapor lock.

5, the fuel pressure reduction counter C _L is incremented every time the fuel pressure P FL in the low-pressure fuel passage 16L is reduced while the shutoff valve 30 is open in response to the vapor concentration in the fuel tank 10, as described below. Therefore, by the process of step S510 in FIG 8, the reduction amount ρ of the target internal pressure P _* is reduced in accordance with an increase in the value of the fuel pressure reduction counter C _L indicating the number of times it has been determined that the fuel pressure P _FL in the low-pressure fuel passage 16L has been reduced. As a result, the reduction amount ρ of the target internal pressure P* is reduced every time it is determined that the fuel pressure P _FL in the low-pressure fuel passage 16L has been reduced, so that the internal pressure Pt of the fuel tank 10 can be reduced gradually while suppressing the generation of vapor.

However, if the vehicle 1 is traveling at high altitudes or if the fuel tank 10 contains, for example, highly volatile winter fuel, there is a risk that a large amount of vapor will be generated in the fuel tank 10 in response to a sudden drop in the internal pressure Pt caused by the opening of the shut-off valve 30 due to changes in atmospheric pressure or fuel properties. In light of this, while the shut-off valve 30 is opened to release pressure from the fuel tank 10 when the vapor concentration in the fuel tank 10 is high, the engine ECU 200 repeatedly executes the routine of FIG. 9 at predetermined time intervals (very short time intervals) in parallel with the routine of FIG. 8 in order to suppress a sudden drop in the internal pressure Pt.

At the start of the routine of FIG. 9, the engine ECU 200 acquires data necessary for the judgment, such as the fuel pressure _PFL detected by the low-pressure fuel sensor LFP and the above-mentioned elapsed time t (step S600). Next, the engine ECU 200 judges whether the elapsed time t acquired in step S600 exceeds a predetermined first duration (predetermined time) tref1 (step S610). In this embodiment, the first duration tref1 is, for example, a value of about 200 msec. If it is judged in step S610 that the elapsed time t is equal to or less than the first duration tref1 (step S610: NO), the engine ECU 200 judges whether the fuel pressure _PFL acquired in step S600 is equal to or less than the fuel pressure drop judgment threshold value P _L (step S650). While it is judged in step S610 that the elapsed time t is equal to or less than the first duration tref1, the fuel pressure drop judgment threshold value P _L is a relatively small value set in step S290 of FIG. 5.

When the engine ECU 200 determines that the elapsed time t is longer than the first duration tref1 (step S610: YES), it determines whether the elapsed time t is equal to or shorter than the second duration tref2 that is longer than the first duration tref1 (step S620). When the engine ECU 200 determines that the elapsed time t is equal to or shorter than the second duration tref2 in step S620 (step S620: YES), it sets the fuel pressure drop determination threshold P _L based on the target lower limit fuel pressure Ptag (step S630). In step S630, the engine ECU 200 sets the fuel pressure drop determination threshold P _L to a value obtained by subtracting a predetermined value α (e.g., a value of about 200 kPa) from the target lower limit fuel pressure Ptag (e.g., a value of about 650 kPa) raised in step S280 of FIG. 5 . That is, when the elapsed time t exceeds the first duration tref1, the fuel pressure drop determination threshold value P _L is changed to a value higher than the previous value (the value set in step S290 in FIG 5) After the process of step S630, engine ECU 200 determines whether or not the fuel pressure P _FL acquired in step S600 is equal to or lower than the fuel pressure drop determination threshold value P _L set in step S630 (step S650).

Also, when it is determined in step S620 that the elapsed time t exceeds the second duration tref2 (step S620: NO), the engine ECU 200 sets the fuel pressure drop determination threshold P L to a value obtained by subtracting a predetermined value β (β<α, for example, a value of about 140 kPa) from the target lower limit fuel pressure _{Ptag (for example, a value of about 650 kPa) raised in step S280 of FIG. 5 (step S640). As a result, when the elapsed time t exceeds the second duration tref2, the fuel pressure drop determination threshold P L is} changed to a value higher than the previous value (the value set in step S630). That is, the fuel pressure drop determination threshold P _L is set to a value higher in stages as the elapsed time t becomes longer. Then, the engine ECU 200 determines whether the fuel pressure P _FL acquired in step S600 is equal to or lower than the fuel pressure drop determination threshold P _L set in step S640 (step S650).

When it is determined that the fuel pressure _PFL acquired in step S600 is greater than the fuel pressure drop determination threshold P _L set in step S290, step S630 or step S640 in Fig. 5 (step S650: NO), the engine ECU 200 temporarily ends the routine in Fig. 9 at that point in time, and executes the processes in and after step S600 when the next execution timing arrives. When it is determined that the fuel pressure _PFL acquired in step S600 is equal to or less than the fuel pressure drop determination threshold P _L set in step S290, step S630 or step S640 in Fig. 5 (step S650: YES), the engine ECU 200 increments a fuel pressure drop counter C _L (step S660), and determines whether the value of the fuel pressure drop counter C _L is equal to or greater than "2" (step S670).

When it is determined that the value of the fuel pressure reduction counter C _L is less than "2" (step S670: YES), the engine ECU 200 sets the shutoff valve open flag Fop to "0" and specifies closing at a low speed (e.g., 30 msec/step) in order to suppress a drop in the internal pressure of the fuel tank 10 by closing the shutoff valve 30 (step S680), and temporarily ends the routine of Fig. 9. When it is determined that the value of the fuel pressure reduction counter C _L is "2" or more (step S670: NO), the engine ECU 200 sets the shutoff valve open flag Fop to "0" and specifies closing at a high speed (e.g., 4 msec/step) in order to suppress a drop in the internal pressure of the fuel tank 10 by closing the shutoff valve 30 (step S690), and temporarily ends the routine of Fig. 9.

As described above, when the engine ECU 200 determines that the vapor concentration in the fuel tank 10 is high (step S220: YES), it increases the target lower limit fuel pressure Ptag in the low pressure fuel passage 16L compared to when it determines that the vapor concentration in the fuel tank 10 is not high (step S280 in FIG. 5). Furthermore, while the elapsed time t after it is determined that the vapor concentration in the fuel tank 10 is high is equal to or less than the first duration (predetermined time) tref1, the engine ECU 200 maintains the fuel pressure drop determination threshold P _L at a relatively small value based on the target lower limit fuel pressure Ptag before it was raised as described above, and when the elapsed time t exceeds the first duration tref1, it changes the fuel pressure drop determination threshold P _L to a relatively high value based on the target lower limit fuel pressure Ptag raised as described above (steps S610-S640). This makes it possible to increase the discharge pressure (rotation speed) of the fuel pump 17 and thereby increase the fuel pressure _PFL in the low-pressure fuel passage 16L, thereby effectively preventing the occurrence of vapor lock in the low-pressure fuel passage 16L. In addition, as can be seen from Fig. 10, it is possible to prevent a situation in which the fuel pressure PFL in the low-pressure fuel passage 16L is determined to be lowered even when the fuel pressure _PFL is ensured (see part B in the figure).

10, the engine ECU 200 gradually increases the fuel pressure drop determination threshold value P _L over time based on the target lower fuel pressure limit P tag while the vapor concentration in the fuel tank 10 is high (steps S610-S640). This effectively prevents erroneous determination of a drop in the fuel pressure P _FL in the low pressure fuel passage 16L.

Furthermore, when the vapor concentration in the fuel tank 10 is high, in response to the first determination that the fuel pressure _PFL in the low-pressure fuel passage 16L is decreasing (step S670: YES, time t10 in FIG. 10), the engine ECU 200 sets the shutoff valve open flag Fop to "0" and specifies a low-speed valve closing (step S680). In this case, as shown in FIG. 10, the engine ECU 200 closes the shutoff valve 30 at a low speed (e.g., 30 msec/step) that makes the above-mentioned initialization unnecessary. As a result, after the shutoff valve 30 is closed, when the fuel pressure _PFL in the low-pressure fuel passage 16L increases to the valve-opening permission pressure _PH or higher (time t20 in FIG. 10), the shutoff valve 30 can be quickly opened without executing initialization.

In this embodiment, after the shutoff valve 30 is closed, when the fuel pressure _PFL in the low-pressure fuel passage 16L increases to equal to or higher than the valve-opening permission pressure _P (time t20 in FIG. 10), the engine ECU 200 operates the stepping motor 34 at a low speed (e.g., 30 msec/step) that makes the above-mentioned initialization unnecessary to open the shutoff valve 30. In this way, by opening the shutoff valve 30 at a low speed that makes initialization unnecessary in response to the establishment of the opening condition after the shutoff valve 30 is closed, it becomes possible to quickly open the shutoff valve 30 without executing initialization in response to the subsequent drop in the fuel pressure _PFL in the low-pressure fuel passage 16L.

Also, when the vapor concentration in the fuel tank 10 is high, in response to the second determination that the fuel pressure _PFL in the low-pressure fuel passage 16L is low (step S670: NO, time t20 in FIG. 10), the engine ECU 200 sets the shutoff valve open flag Fop to "0" and specifies high-speed valve closing in order to suppress a drop in the internal pressure of the fuel tank 10 by closing the shutoff valve 30 (step S690). In this case, since it is assumed that the fuel pressure _PFL is dropping again due to the influence of the fuel properties and the atmospheric pressure _Patm after it is determined that the vapor concentration in the fuel _tank 10 is high, the engine ECU 200 closes the shutoff valve 30 at the highest speed (e.g., 4 msec/step). This makes it possible to suppress a sudden drop in the internal pressure Pt of the fuel tank 10 and suppress the occurrence of vapor lock in the low-pressure fuel passage 16L.

In the above embodiment, the shutoff valve 30 is closed when it is determined that the vapor concentration in the fuel tank 10 is high and that the fuel pressure _PFL in the low-pressure fuel passage 16L is equal to or lower than the fuel pressure drop determination threshold P _L , but the present invention is not limited to this. That is, for example, the fuel pressure drop determination threshold P _L may be set to an extremely large value, and when it is determined that the vapor concentration in the fuel tank 10 is high, the fuel pressure _PFL in the low-pressure fuel passage 16L may be regarded as being low and the shutoff valve 30 may be forcibly closed. That is, when the vapor concentration in the fuel tank 10 is high, there is a risk of vapor lock occurring, so that the shutoff valve 30 may be uniformly prohibited from opening at the point in time when it is determined that the vapor concentration is high. This makes it possible to effectively suppress the occurrence of vapor lock in the low-pressure fuel passage 16L. In addition, the invention of the present disclosure is useful for vehicle 1, which is a hybrid vehicle in which the vapor concentration in the fuel tank 10 tends to become high due to intermittent operation of engine 2, but a vehicle equipped with engine 2 to which the invention of the present disclosure is applied may have only engine 2 as a power source that outputs power for driving.

As described above, the fuel tank pressure control device disclosed herein is a fuel tank pressure control device 200 that adjusts the internal pressure (Pt) of the fuel tank (10) by opening and closing the shutoff valve (30) disposed between the fuel tank (10) and the canister (22) of the vehicle (1), and opens the shutoff valve (30) when the internal pressure (Pt) of the fuel tank (10) is equal to or greater than a valve opening threshold (Pop) (step S110: NO, step S170), and sets the valve opening threshold in consideration of the atmospheric pressure when it is determined that the vapor concentration in the fuel tank (10) is high (step S220: YES, step S250).

The fuel tank pressure control device disclosed herein opens the shutoff valve when the internal pressure of the fuel tank is equal to or greater than the valve opening threshold. Furthermore, the pressure control device sets the valve opening threshold taking into account the atmospheric pressure when it is determined that the vapor concentration in the fuel tank is high. This makes it possible to prevent a sudden decrease in the internal pressure of the fuel tank when the shutoff valve opens, thereby suppressing the generation of a large amount of vapor in the fuel tank, even when the surrounding atmospheric pressure is low. As a result, the fuel tank pressure control device disclosed herein makes it possible to effectively suppress the occurrence of vapor lock in the fuel supply system while suppressing an increase in the internal pressure of the fuel tank.

Furthermore, when it is determined that the vapor concentration in the fuel tank (10) is high (step S220: YES), the pressure control device (200) may set the valve opening threshold (Pop) to the greater of a predetermined value corresponding to the atmospheric pressure (P _atm ) and the internal pressure (Pt) of the fuel tank (10) (step S250). This makes it possible to appropriately set the valve opening threshold when the vapor concentration in the fuel tank is high.

Furthermore, the pressure control device (200) may close the shut-off valve when the internal pressure (Pt) of the fuel tank (10) becomes equal to or lower than a closing threshold (Pcl) that is less than the opening threshold (Pop) after opening the shut-off valve (30) (step S110: NO, step S170), and when it is determined that the vapor concentration in the fuel tank (10) has increased (step S130: NO), it may make the difference (η(Pt)) between the opening threshold (Pop) and the closing threshold (Pcl) smaller (steps S140, S150) compared to when it is determined that the vapor concentration in the fuel tank (10) has not increased (step S130: YES, η _const ). This makes it possible to prevent a sudden decrease in the internal pressure of the fuel tank between when it reaches or exceeds the valve-opening threshold and when it falls below the valve-closing threshold, even if the shut-off valve is opened so that the internal pressure of the fuel tank changes gradually when the vapor concentration in the fuel tank is high.

Furthermore, when it is determined that the vapor concentration in the fuel tank (10) is high (step S130: NO), the pressure control device (200) may set the difference (η(Pt)) between the valve opening threshold (Pop) and the valve closing threshold (Pcl) based on the internal pressure (Pt) of the fuel tank (10) (step S150). That is, the higher the internal pressure of the fuel tank, the greater the amount of vapor that passes through the stop valve within a unit time. Therefore, by setting the difference between the valve opening threshold and the valve closing threshold based on the internal pressure of the fuel tank, it is possible to effectively suppress a sudden decrease in the internal pressure of the fuel tank between when the internal pressure of the fuel tank becomes equal to or higher than the valve opening threshold and when the internal pressure of the fuel tank becomes equal to or lower than the valve closing threshold.

However, the invention of this disclosure is in no way limited to the above embodiment, and it goes without saying that various modifications can be made within the scope of the present disclosure. Furthermore, the above embodiment is merely one specific form of the invention described in the Summary of the Invention section, and does not limit the elements of the invention described in the Summary of the Invention section.

The invention disclosed herein can be used in the vehicle manufacturing industry, etc.

1 vehicle, 2 engine (internal combustion engine), 2a air cleaner, 2c combustion chamber, 2i intake pipe, 2jd in-cylinder injection valve, 2jp port injection valve, 2p intake port, 2s throttle valve, 3 planetary gear, 4 gear train, 5 battery, 6 power control unit (PCU), 10 fuel tank, 15 tank internal pressure sensor, 16H high-pressure fuel passage, 16L low-pressure fuel passage, 17 fuel pump, 20 evaporative fuel treatment device, 22 canister, 24 vapor passage, 26 purge passage, 27 purge valve, 28 air passage, 29 air filter, 30 shutoff valve, 31 casing, 32 valve seat, 33 valve body, 34 stepping motor, 100 hybrid electronic control unit (HVECU), 200 engine electronic control unit (

Claims (4)

A pressure control device for a fuel tank for a vehicle, the pressure control device adjusting an internal pressure of the fuel tank by opening and closing a shutoff valve disposed between the fuel tank and a canister,
A pressure control device for a fuel tank that opens the shutoff valve when the internal pressure of the fuel tank is equal to or greater than a valve opening threshold, and sets the valve opening threshold taking into account atmospheric pressure when it is determined that a vapor concentration in the fuel tank is high. 2. The fuel tank pressure control device according to claim 1,
A fuel tank pressure control device that, when it is determined that the vapor concentration in the fuel tank is high, sets the valve opening threshold to the greater of a predetermined value corresponding to atmospheric pressure and the internal pressure of the fuel tank. 3. The fuel tank pressure control device according to claim 1,
A fuel tank pressure control device that closes the shut-off valve when the internal pressure of the fuel tank falls below a closing threshold which is less than the opening threshold after the shut-off valve is opened, and that, when it is determined that the vapor concentration in the fuel tank is high, makes the difference between the opening threshold and the closing threshold smaller than when it is determined that the vapor concentration in the fuel tank is not high. 4. The fuel tank pressure control device according to claim 3,
a pressure control device for a fuel tank that sets a difference between the valve opening threshold and the valve closing threshold based on the internal pressure of the fuel tank when it is determined that the vapor concentration in the fuel tank is high;

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