Fuel vapor processing device

Abstract

Fuel vapor processing device (20), comprising: a container (22) with an adsorbent for adsorbing fuel vapor generated in a fuel tank (15); a steam line (24) connecting the container (22) and the fuel tank (15); as well as a shut-off valve (40) arranged in the steam line (24), wherein the shut-off valve (40) is closed when a stroke amount is less than a predetermined amount, and the shut-off valve (40) is open when the stroke amount is greater than or equal to the predetermined amount, wherein the shut-off valve (40) has a stepper motor (50) designed to adjust the stroke amount, characterized by the fact that the fuel vapor processing device (20) comprises an ECU (19) which is configured • to determine (S101) whether an initialization request is present to initialize the shut-off valve (40) in order to rotate the shut-off valve (40) in the valve closing direction to a predetermined initial position, and, • when an initialization request to initialize the shut-off valve (40) is present (S101: YES), to determine (S102) whether the fuel tank pressure (15) is within a specified pressure range close to ambient pressure, wherein the ECU (19) is further configured to, if the fuel tank pressure (15) is within the specified pressure range close to ambient pressure (S102: YES), set a second step count (S2) that is greater than a first step count (S1) that the stepper motor (50) is turned in the valve closing direction when the tank pressure is outside the specified pressure range (S102: NO).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] Embodiments of the present invention relate to a fuel vapor processing device configured to process fuel vapor generated in a fuel tank. 2. Description of the state of the art

[0002] For this type of device, for example, a device has been proposed that includes a canister containing an adsorbent for adsorbing fuel vapor generated in a fuel tank; and a shutoff valve with a stepper motor arranged in a vapor line connecting the canister and the fuel tank (see JP 2015-218659 A). Japanese patent application JP 2015-218659 A discloses that, when the stepper motor is detected to be out of sync, an initialization is performed to move the shutoff valve to a predetermined initial position at an initialization time determined in advance as the best time that does not adversely affect the operation of an engine. WO 2016 / 035655 A1 also discloses a vaporized fuel processing device in which vaporized fuel in a fuel tank is adsorbed by a canister.the adsorbed evaporated fuel is sucked into an engine, a shut-off valve that controls communication between the fuel tank and the container is provided in a path connecting the fuel tank and the container, and a float valve for preventing fuel from flowing out of the fuel tank into the path is provided, wherein the evaporated fuel processing device includes: a refueling switch that is operated to instruct a start of refueling of a fuel tank and to output a refueling start signal; an internal pressure sensor that detects a pressure in a space inside the fuel tank as an internal pressure; and a shut-off valve control means that, when the refueling start signal is output from the refueling switch and when the internal pressure of the fuel tank detected by the internal pressure sensor is higher than a predetermined pressure,causes the shut-off valve to open within a range in which the float valve does not operate, and increases the valve opening speed of the shut-off valve in accordance with a reduction in the internal pressure of the fuel tank from a valve opening start time.

[0003] The rotation amount (or rotation angle) of the stepper motor is controlled in a unit of step. When initializing the check valve, the stepper motor is usually rotated by a predetermined number of steps (i.e., a predetermined number of steps) in a valve-closing direction from a position where the stepper motor's step count is "0" (i.e., the initial position).

[0004] Such control is effective for reliably initializing the check valve when the position where the stepping motor's step number is "0" deviates from an actual initial position. However, if the predetermined step number is a fixed value, the above-described control may accelerate the wear of the check valve if the position where the stepping motor's step number is "0" does not deviate from the actual initial position. SUMMARY

[0005] Based on the problems described above, it is therefore an object of embodiments of the present invention to propose a fuel vapor processing device which is designed to both enable appropriate initialization of the shut-off valve and prevent wear or deterioration of the shut-off valve.

[0006] The above object of the embodiments of the present invention can be achieved with a fuel vapor processing device comprising: a canister having an adsorbent for adsorbing fuel vapor generated in a fuel tank; a vapor line connecting the canister and the fuel tank;and a shut-off valve arranged in the vapor line, wherein the shut-off valve is closed when a lift amount is less than a predetermined amount, and the shut-off valve is open when the lift amount is greater than or equal to the predetermined amount, wherein the shut-off valve has a stepper motor configured to adjust the lift amount, and the fuel vapor processing device comprises an initialization device configured to, when an initialization request is present to rotate the shut-off valve in the valve closing direction toward a predetermined initial position and a tank pressure of the fuel tank is in a predetermined pressure range close to the ambient pressure, increase a step number with which the stepper motor is rotated in the valve closing direction compared to when the tank pressure is outside the predetermined pressure range.

[0007] When the shut-off valve is closed, the tank pressure of the fuel tank is higher or lower than the ambient pressure to a certain extent. Otherwise, the pressure in the tank is maintained at atmospheric pressure except in certain cases, such as for fault diagnosis. Thus, when the shut-off valve is not closed due to step-out, the tank and fuel tank communicate via the vapor line, and the tank pressure of the fuel pressure thus becomes the ambient pressure. In other words, when the tank pressure of the fuel tank is close to the atmospheric pressure, the shut-off valve is probably not closed. Conversely, when the tank pressure is higher or lower than the ambient pressure to a certain extent, the shut-off valve is most likely closed.

[0008] The inventors paid attention to this point and configured the fuel vapor processing device as described above. In other words, the fuel vapor processing device is designed to enable the initialization device to increase the number of steps by which the stepping motor is rotated in the valve closing direction compared to when the tank pressure is outside the predetermined range (i.e., when the shutoff valve is most likely closed), since the shutoff valve is most likely not closed when the tank pressure of the fuel tank is within the predetermined pressure range.

[0009] Thus, the shutoff valve can be appropriately initialized because the stepper motor makes a relatively large number of steps in the valve closing direction during shutoff valve initialization when the tank pressure is within the specified pressure range. On the other hand, deterioration of the shutoff valve can be prevented because the stepper motor makes a relatively small number of steps in the valve closing direction during shutoff valve initialization when the fuel tank pressure is outside the pressure range.

[0010] The “specified pressure range” may be defined as a range that can be regarded as the ambient pressure, for example, in view of the measurement accuracy of a pressure sensor capable of measuring the tank pressure, measurement errors caused by the mounting position of the pressure sensor in the fuel tank, or the like.

[0011] The nature, applicability and further features of this invention will become more apparent from the following detailed description, which refers to preferred embodiments of the invention, taking into account the figures briefly described below. SHORT DESCRIPTION OF THE DRAWING Fig. 1 is a view showing the overall structure of a fuel vapor processing apparatus according to an embodiment; Fig. 2 is a longitudinal sectional view showing a state of the check valve according to the embodiment; Fig. 3 is a flowchart showing an initialization process of the shut-off valve according to the embodiment; and Fig. 4A and Fig. 4B are conceptual diagrams showing a concept of a temporal change in the number of steps of a stepping motor in an initialization process according to the embodiment. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0012] Hereinafter, a fuel vapor processing apparatus according to an embodiment of the present invention will be described with reference to Fig. 1 to 4 described. (Overall structure)

[0013] A configuration of the fuel vapor processing apparatus according to the embodiment of the present invention will be described below with reference to Fig. 1 explained. Fig. 1 shows the overall structure of the fuel vapor processing device according to the embodiment.

[0014] In Fig. 1, a fuel vapor processing device 20 is arranged in an engine system 10 of a vehicle, not shown, and is designed to prevent fuel vapor generated in a fuel tank 15 of the vehicle from escaping.

[0015] The fuel vapor processing device 20 has a canister 22, a vapor line 24, a purge line 26, and an ambient air or fresh air line 28. The canister 22 is filled with activated carbon as an adsorbent. The canister 22 is configured to adsorb the vaporized fuel in the fuel tank 15 using the adsorbent. The vapor line 24 is connected at one end to a gas layer portion in the fuel tank 15 and at the other end to the canister. The vapor line 24 has a shutoff valve 40 configured to switch between connecting and shutting off the vapor line 24. The purge line 26 is connected at one end to the canister 22 and at the other end to a throttle valve 17 in an intake line 26 of an engine 14. The flushing line 26 has a flushing valve 26v which is designed to switch between connecting and shutting off the flushing line 26.

[0016] The container 22 is connected to the ambient air line 28, one end of which opens to the environment. The ambient air line 28 has an air filter 28a. The ambient air line 28 further has a switching valve 28v configured to switch between connecting and shutting off the ambient air line 28. The switching valve 28v is arranged closer to the container 22 than the air filter 28a. The switching valve 28v comprises, for example, a normally open solenoid valve that is open when the solenoid is not energized. The ambient air line 28 also has a pump 28p configured to forcibly supply ambient or fresh air to the container 22. The pump 28p is arranged in parallel with the switching valve 28v.The pump 28p may be any type of pump as long as it can pressurize the interior of a system including the canister 22 and the fuel tank 15, but is preferably configured such that it does not generate gas flow in an OFF state.

[0017] The shutoff valve 40, the purge valve 26v, the switching valve 28v, and the pump 28p are controlled based on signals from an electronic control unit (ECU) 19. In other words, in this embodiment, part of the functions of the ECU 9 are used for various electronic controls of the vehicle as part of the fuel vapor processing device 20.

[0018] The fuel vapor processing device 20 includes a tank pressure sensor 15s disposed in the fuel tank 15; and an evaporative system pressure sensor (hereinafter referred to as "system pressure sensor") 26s disposed in the purge line 26 closer to the canister 22 than the purge valve 26, as pressure sensors configured to detect the pressure in the system. The tank pressure sensor 25s is configured to detect the pressure of a region on the fuel tank 15 side, among two regions into which the system is divided by the shut-off valve 40. The system pressure sensor 26s is configured to detect the pressure of a region including the canister 22 (or more precisely, a region into which the system is divided by the purge valve 26v, the switching valve 28v, and the shut-off valve 40) (hereinafter referred to as "system pressure"), among two regions into which the system is divided by the shut-off valve 40.The ECU 19 is designed to receive signals from the tank pressure sensor 15s and the system pressure sensor 26s. (Overview of the operation of the fuel vapor processing device)

[0019] An overview of the operation of the fuel vapor processing device 20 configured as above will be described below. The ECU 19 is configured to appropriately open the purge valve when a predetermined purge condition is met during vehicle travel. At this time, the switching valve 28v is opened, and the ambient air thus flows in via the ambient air passage 28 due to a negative intake pressure of the engine 14. The fuel vapor purged from the adsorbent of the canister 22 by the ambient air is introduced into an intake passage 17 of the engine 14 via the purge valve 26v. The ECU 19 is further configured to open the shutoff valve 40 and execute pressure relief control of the fuel tank 15 when the pressure of the fuel tank 15 detected by the tank pressure sensor 15s is higher than a predetermined pressure.Various existing aspects can be used for the control regarding the purging of vaporized fuel or fuel vapor adsorbed by the adsorbent of the canister 22 and the pressure relief control of the fuel tank 15. Therefore, an explanation of the details of these controls will be omitted. (Structure of the check valve)

[0020] A structure of the check valve 40 is described with reference to Fig. 2 described. Fig. 2 is a longitudinal sectional view showing a state of the check valve according to the embodiment.

[0021] The shutoff valve 40 is a flow control valve configured to close the steam line 24 in a valve-closed state and to control a flow of a gas flowing in the steam line 24 in a valve-opened state. Fig. 2, the check valve 40 is formed with a valve housing 42, a stepper motor 50, a valve guide 60, and a valve body 70. The valve housing 42 has a valve chamber 44, an inlet line 45, and an outlet line 46. The valve chamber 44, the inlet line 45, and the outlet line 46 form a fluid line.

[0022] The stepper motor 50 is mounted on an upper part of the valve housing 42. The stepper motor 50 has a motor body 52 and an output shaft 54 ​​protruding from a lower surface of the motor body 52 and configured to rotate in a forward and reverse direction. The output shaft 54 ​​is concentrically disposed in the valve chamber 44 of the valve housing 42, and an external thread 54n is formed on an outer peripheral surface of the output shaft 54.

[0023] The valve guide 60 has a cylindrical wall 62 and a top wall 64 configured to close an upper end opening of the cylindrical wall 62 and formed in the shape of a cylindrical lid. A cylindrical shaft 66 is concentrically formed in a central portion of the top wall 64. An internal thread 66w is formed on an inner peripheral surface of the cylindrical shaft 66. The valve guide 66 is arranged to be movable in the axial direction (or vertical direction), while rotation about the axial direction relative to the valve housing 42 is stopped by an unillustrated detent or rotation stopper.

[0024] The external thread 54n of the output shaft 54 ​​of the stepper motor 50 is screwed into the internal thread 66w of the cylindrical shaft 66 of the valve guide 60. This allows the valve guide 60 to move up and down in the axial direction based on the forward or reverse rotation of the output shaft 54 ​​of the stepper motor. An auxiliary spring 68 is arranged around the valve guide 60 and is designed to bias the valve guide 60 upward.

[0025] The valve body 70 has a cylindrical wall 72 and a bottom wall 74 configured to close a lower end opening of the cylindrical wall 72 and formed in the shape of a cylindrical bottom. A sealing element 76 made of, for example, a disc-shaped, rubber-elastic material is arranged on a lower surface of the bottom wall 74. The valve body 70 is concentrically arranged in the valve guide 60. The sealing element 76 of the valve body 70 is arranged to abut against an upper surface of a valve seat of the valve housing 42 (near an end on the side of the valve chamber 44 in the inlet line 45).

[0026] On an outer peripheral surface of the cylindrical wall 72 of the valve body 70, a plurality of coupling projections 72t are formed circumferentially. The coupling projections 72t of the valve body 70 are fitted into vertical groove-like coupling recesses 62m formed on an inner peripheral surface of the cylindrical wall 62 of the valve guide 60, so that they are rotatable relative to each other in the vertical direction to a predetermined extent. The valve guide 60 and the valve body 72 are configured to move integrally upward (i.e., in a valve-opening direction), while bottom walls 62b of the coupling recesses 62m of the valve guide 60 abut against the coupling projections 72t of the valve body 70 from below.A valve spring 77 is concentrically arranged between the upper wall 64 of the valve guide 60 and the lower wall 74 of the valve body 70, which is designed to always press the valve body 70 downwards with respect to the valve guide 60 (ie in a valve closing direction). (How the shut-off valve works)

[0027] The operation of the check valve 40 configured as above will be explained below. The check valve 40 is configured to rotate the stepper motor 50 in the valve opening direction or valve closing direction at a predetermined number of steps (i.e., a predetermined number of steps) based on the signals from the ECU 19. Due to the screw function of the external thread 54n of the output shaft of the stepper motor 50 and the internal thread 66w of the cylindrical shaft 66 of the valve guide 60, the valve guide 60 can thus move in the vertical direction by a predetermined amount of lift.

[0028] In an initial state of the check valve 40, the valve guide 60 is held at a lower limit position, and a lower end surface of the cylindrical wall 62 abuts against the upper end surface of the valve seat of the valve housing 42. In this state, the coupling projections 72t of the valve body 70 are located above the bottom walls 62b of the coupling recesses 62m of the valve guide 60 (see Fig. 2), and the sealing element 76 of the valve body 70 is pressed against the upper surface of the valve seat of the valve housing 42 by the spring force of the valve spring 77. A position of the check valve 40 in the initial state (specifically, a position of the valve guide 60) is an example of the "initial position" according to embodiments of the present invention.

[0029] When the stepping motor 50 is rotated in the valve-opening direction from the initial state of the check valve 40, the valve guide 60 moves upward due to the screw function of the external thread 54n and the internal thread 66w, and the bottom surfaces 62b of the coupling recesses 62m of the valve guide 60 abut against the coupling projections 72t of the valve body 70 from below. When the stepping motor 50 is then further rotated in the valve-opening direction and the valve guide 60 moves further upward, the valve body 70 moves upward with the valve guide 60, and the sealing element 76 of the valve body 70 detaches from the valve seat of the valve housing 42. This opens the check valve 40. (Initialization process of the shut-off valve)

[0030] Next, an initialization process of the shut-off valve 40 according to the embodiment will be described with reference to Fig. 3 and Fig. 4 described.

[0031] In Fig. 3, the ECU 19 as part of the fuel vapor processing device 20 determines whether there is a request to initialize the shutoff valve 40 (step S101). Initialization of the shutoff valve 40 is requested, for example, when the ignition is turned off; the ignition is turned on; on-board diagnostics (OBD) of the fuel vapor processing device 20 is started, and the like. The "ECU 19" of the embodiment is an example of the "initialization device" according to the embodiments of the present invention.

[0032] If the determination in step S101 determines that there is no request to initialize the shutoff valve 40 (step S101: NO), the process is terminated. Then, the ECU 19 executes the process in step S101 again after a predetermined period of time has elapsed.

[0033] On the other hand, if the determination of step S101 determines that there is a request to initialize the shutoff valve 40 (step S101: YES), the ECU 19 determines whether the pressure of the fuel tank 15 detected by the tank pressure sensor 15s is the atmospheric pressure (step S102). Specifically, the ECU 19 determines whether the tank pressure is within a predetermined pressure range near the atmospheric pressure (i.e., greater than or equal to a predetermined value -A and less than or equal to the predetermined value A).

[0034] The "preset value A" is set to a value that is higher than the ambient pressure due to the measurement accuracy of the tank pressure sensor 15s, measurement errors caused by the mounting position of the tank pressure sensor 15s in the fuel tank 15, or the like. The "preset value -A" is set to a value that is lower than the ambient pressure due to the measurement accuracy of the tank pressure sensor 15s, measurement errors caused by the mounting position of the tank pressure sensor 15s in the fuel tank 15, or the like.

[0035] When it is determined in the determination of step S102 that the tank pressure is not equal to the atmospheric pressure, that is, when it is determined that the tank pressure is outside the predetermined pressure range (step S102: NO), the ECU 19 sets a target step number of the stepping motor 50 to a predetermined number S1, and initializes the shutoff valve 40 (step S104).

[0036] The "specific number S1" is less than "0." In other words, when initializing the shutoff valve 40, the ECU 19 can rotate the stepping motor 50 in the valve-closing direction from a position where the stepping motor's step number is "0" to a number of steps indicated by the specific number S1 (or a specific number S2 described later). Rotating the stepping motor 50 in the valve-closing direction from the position where the stepping motor's step number is "0" is referred to as "pushing" in the embodiment.

[0037] The initialization of the check valve 40 when the target step number of the stepping motor 50 is set to the specific number S1 is described with reference to Fig. 4A. Fig. 4A shows that the specific number S1 is “-8”, but is not limited to this.

[0038] It is assumed that the tank pressure in the determination from step S102 at a time t1 of Fig. 4A is not the ambient pressure. As a result, the ECU 19 can energize and open the switching valve 28v, can set the target step number to "-8" (ie, the specified number S1), and can begin the initialization of the shut-off valve 40.

[0039] As in Fig. 4A, the ECU 19 may rotate the stepping motor 50 in the valve-closing direction step by step. The step number is "0" at time t2. Even after this, the ECU 19 may rotate the stepping motor 50 in the valve-closing direction. When the step number reaches "-8," the ECU 19 may stop the rotation of the stepping motor 50 (at time t3) and change the step number to "0." In other words, the ECU 19 is configured to redefine the position of the check valve 40 corresponding to the step number "-8" (more precisely, the position of the valve guide 60) as the step number "0" before time t3. The ECU 19 may then rotate the stepping motor 50 a predetermined number of steps (or four steps here) in the valve-opening direction, open the switching valve 28v (at time t4), and complete the initialization of the check valve 40.

[0040] The valve guide 60 is easily separated from the valve seat of the valve body 42 by rotating the stepping motor 50 in the valve closing direction by the predetermined number of steps from “0”. Thus, it is possible to prevent excessive force from acting between the valve guide 60 and the valve seat due to a change in environmental conditions such as temperature.

[0041] Back to Fig. 3, when it is determined in the determination of step S102 that the tank pressure is equal to the atmospheric pressure, that is, when it is determined that the tank pressure is within the predetermined pressure range (step S102: YES), the ECU 19 sets the target step number of the stepping motor 50 to a predetermined number S2 which has a larger absolute value than the predetermined number S1, and initializes the shutoff valve 40 (step S103).

[0042] The initialization of the check valve 40 when the target step number of the stepping motor 50 is set to the specific number S2 is described with reference to Fig. 4B. Fig. 4B shows that the specific number S2 is “-248”, but is not limited to this.

[0043] It is assumed that the tank pressure in the determination from step S102 at a time t5 of Fig. 4B is the ambient pressure. As a result, the ECU 19 can energize and open the switching valve 28v, can set the target step number to "-248" (ie, the specified number S2), and can begin the initialization of the shutoff valve 40.

[0044] As in Fig.As shown in Fig. 4B, the ECU 19 may rotate the stepping motor 50 in a valve-closing direction in steps. When the step count reaches "-248," the ECU 19 may stop the rotation of the stepping motor 50 (at time t7) and change the step count to "0." The ECU 19 may then rotate the stepping motor 50 a predetermined number of steps (or four steps here) in the valve-opening direction, open the switching valve 28v (at time t8), and complete the initialization of the shutoff valve 40. (Technical effect)

[0045] It is possible that an actual position of the check valve 40 (i.e., an actual position of the valve guide 60) is offset from a position corresponding to the step number of the stepping motor 50 (i.e., protrudes). For this reason, pushing is performed when the check valve 40 is initialized. However, if pushing is performed uniformly, that is, if the step number at which the stepping motor 50 is rotated in the valve closing direction starting from the step number "0" is set to a fixed value, pushing will accelerate the wear or deterioration of the check valve 40 because there is no out-of-sync. On the other hand, if the step number associated with pushing is set relatively small to avoid deterioration of the check valve 40, if out-of-sync occurs, the out-of-sync may not be corrected due to insufficient pushing.

[0046] Incidentally, the switching valve 28v is basically open, and when the purge valve 26v is closed, the pressure on a side of the fuel vapor processing device 20 that is closer to the canister 22 than to the shutoff valve 40 is the atmospheric pressure. Thus, if the shutoff valve 40 is inadvertently opened, the tank pressure of the fuel tank 15 (the pressure in the fuel tank) is also the atmospheric pressure. Therefore, if it is determined in step S102 (in other words, before the initialization of the shutoff valve 40) that the tank pressure of the fuel tank 15 is the atmospheric pressure, the position of the shutoff valve 40 is most likely offset toward the valve opening side rather than corresponding to the position corresponding to the step number of the stepping motor 50 (i.e., protruding), and thus open.

[0047] On the other hand, when the shutoff valve 40 is closed, the tank pressure of the fuel tank is obviously higher or lower than the ambient pressure. Therefore, if it is determined in step S102 (in other words, before the initialization of the shutoff valve 40) that the tank pressure of the fuel tank 15 is not the ambient pressure, the shutoff valve 40 is most likely closed.

[0048] If it is determined in step S102 that the tank pressure of the fuel tank 15 is the ambient pressure, i.e., the shutoff valve 40 is most likely open due to being out of sync, the target step number is set to the predetermined number S2, which relatively increases the step number of the pushing. The absolute value of the predetermined number S2 is preferably greater than a step number corresponding to a fully open position of the shutoff valve 40. With such a configuration, the shutoff valve 40 can be reliably initialized.

[0049] On the other hand, if it is determined in step S102 that the tank pressure of the fuel tank 15 is not the atmospheric pressure, that is, the shutoff valve is most likely closed, the target step number is set to the predetermined number S1, which relatively reduces the step number of the bumping. Thus, deterioration of the shutoff valve 40 due to bumping can be prevented.

[0050] Thus, with the fuel vapor processing device 20, it is possible to both enable appropriate initialization of the shut-off valve 40 and prevent wear or deterioration of the shut-off valve 40.

Claims

[1] Fuel vapor processing device (20), comprising: a container (22) with an adsorbent for adsorbing fuel vapor generated in a fuel tank (15); a vapor line (24) connecting the container (22) and the fuel tank (15); and a check valve (40) arranged in the steam line (24), wherein the check valve (40) is closed when a stroke amount is less than a predetermined amount, and the check valve (40) is open when the stroke amount is greater than or equal to the predetermined amount, wherein the check valve (40) has a stepper motor (50) designed to adjust the stroke amount, characterized by , that the fuel vapor processing device (20) comprises an ECU (19) which is designed • to determine (S101) whether there is an initialization request to initialize the shut-off valve (40) in order to rotate the shut-off valve (40) in the valve closing direction towards a predetermined initial position, and, • if there is an initialization request to initialize the shut-off valve (40) (S101: YES), to determine (S102) whether a tank pressure of the fuel tank (15) is in a predetermined pressure range close to the ambient pressure, wherein the ECU (19) is further configured to, when the tank pressure of the fuel tank (15) is in the predetermined pressure range close to the ambient pressure (S102: YES), set a step number with which the stepping motor (50) is rotated in the valve closing direction to a second step number (S2) which is greater than a first step number (S1) with which the stepping motor (50) is rotated in the valve closing direction when the tank pressure is outside the predetermined pressure range (S102: NO).

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