Fuel tank system

Abstract

To provide a fuel tank system capable of suppressing discharge of fuel vapor during engine stop at low cost.SOLUTION: One embodiment is a fuel tank system including a fuel tank (15), a canister (34) capable of adsorbing and desorbing fuel vapor generated in the fuel tank (15), a vapor passage (31) allowing the fuel tank and the canister (34) to communicate with each other, a sealing valve (52) disposed in the vapor passage (31) for sealing the fuel tank (15), and a sealing pressure switching mechanism (92) configured to set a sealing pressure of the sealing valve (52) to a first sealing pressure when the parking brake (170) is released and to a second sealing pressure higher than the first sealing pressure when the parking brake (170) is applied. 170.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel tank system. [Background technology]

[0002] Vehicles equipped with internal combustion engines typically include a canister that captures evaporated fuel from a fuel tank by adsorption. A vapor passage connecting the fuel tank to the canister may be provided with a relief valve for controlling the internal pressure of the fuel tank. For example, Japanese Patent Laid-Open Publication No. 10-259765 discloses a fuel tank system that includes a combined valve consisting of two check valves connected in parallel in opposite directions. One check valve opens when the internal pressure of the fuel tank reaches a predetermined negative pressure, and the other check valve opens when the internal pressure reaches a predetermined positive pressure, thereby maintaining the internal pressure at an appropriate level. This publication also discloses a modified configuration in which one check valve is replaced with a solenoid valve that can be electronically controlled by an ECU. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-259765 Summary of the Invention [Problem to be solved by the invention]

[0004] Meanwhile, increasingly strict regulations on evaporative hydrocarbon emissions (evaporative emissions) are being imposed on vehicles equipped with internal combustion engines in various countries. One way to suppress fuel vapor emissions through the canister is to install a shut-off valve in the purge passage, which seals the fuel tank at a certain pressure to limit the amount of vapor adsorbed to the canister. If the shut-off valve's sealing pressure is too low, the vapor pressure in the fuel tank can easily exceed the closing pressure due to rising daytime temperatures, especially when the engine is stopped, causing the valve to open. If this happens, fuel vapor exceeding the canister's collection capacity may pass through the shut-off valve, potentially resulting in its release into the atmosphere.

[0005] When the engine is running, the canister is purged (scavenged) with outside air as needed, causing the adsorbed fuel to be desorbed and drawn into the engine's intake air. However, in plug-in hybrid electric vehicles and bi-fuel vehicles that use compressed natural gas (CNG) as their primary fuel, the engines are operated less frequently. This reduces the number of opportunities to purge the canister, while fuel is stored in the tank for longer periods, making it easier for adsorbed fuel to accumulate in the canister.

[0006] Increasing the sealing pressure of the shut-off valve requires a certain level of strength in the fuel tank and piping, which increases costs. Also, if a solenoid valve is used for the shut-off valve to control its opening while the engine is running, a pressure sensor must be installed in the fuel tank, which also increases costs.

[0007] There is a need for a fuel tank system that can reduce fuel vapor emissions while the engine is stopped at low cost. [Means for solving the problem]

[0008] One aspect of the present technology is a fuel tank system including: a fuel tank, a canister capable of adsorbing and desorbing fuel vapor generated in the fuel tank, a vapor passage connecting the fuel tank and the canister, a parking brake operated by a driver, a shutoff valve disposed in the vapor passage for closing the fuel tank, and a sealing pressure switching mechanism configured to set the sealing pressure of the shutoff valve to a first sealing pressure when the parking brake is released and to set the sealing pressure of the shutoff valve to a second sealing pressure higher than the first sealing pressure when the parking brake is applied. This allows the sealing pressure of the shutoff valve to be increased while the parking brake is applied, thereby suppressing the emission of fuel vapor while the engine is stopped.

[0009] In some embodiments, the sealing pressure switching mechanism is configured to open the isolation valve when the parking brake is released.

[0010] In some embodiments, the shut-off valve has an axially movable shaft and a diaphragm that elastically seals around the shaft, and is configured so that the sealing pressure of the shut-off valve varies depending on the axial position of the shaft. This allows the shaft to be stably supported by the diaphragm, and by mechanically operating the shut-off valve with the shaft, a complex configuration is not required.

[0011] In some embodiments, the sealing pressure switching mechanism has a switching member mechanically connected to a movable member of the parking brake, and the axial position of the shaft changes with the movement of the switching member, thereby enabling the sealing pressure of the isolation valve to be reliably switched in response to the operation of the parking brake.

[0012] In some embodiments, the switching member has a plurality of engagement portions that the shaft can engage at different positions, each engagement portion corresponding to a different sealing pressure of the sealing valve, thereby enabling the sealing pressure of the sealing valve to be reliably switched using a mechanical configuration.

[0013] In some embodiments, the switching member is slidably supported, and each of the engagement portions of the switching member is a recess or a through-hole that can engage with an end of the shaft, and the position of the shaft changes as the switching member slides. As a result, the shaft is pressed against the recess or the through-hole, and the sealing pressure of the shut-off valve is stabilized. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a configuration diagram of a variable sealed fuel tank system equipped with a sealing pressure switching mechanism according to one embodiment; [Figure 2] FIG. 1 is an external view of a valve assembly including a tank isolation valve and a pressure relief valve. [Figure 3] FIG. 1 is a cross-sectional view of a tank isolation valve with the shaft in an upward position and forced open. [Figure 4] FIG. 2 is a cross-sectional view of a tank isolation valve in a closed position. [Figure 5] 1 is a cross-sectional view of a tank isolation valve in an open position as a result of the internal pressure of the fuel tank exceeding the sealing pressure. [Figure 6] FIG. 2 is a cross-sectional view of a pressure relief valve in a closed position. [Figure 7] FIG. 2 is a cross-sectional view of a pressure relief valve in an open position as a result of excessive positive pressure in the fuel tank. [Figure 8] FIG. 2 is a cross-sectional view of a pressure relief valve in an open position as a result of excessive negative pressure in the fuel tank. [Figure 9] FIG. 10 is a top view of a slide plate slidably supported and connected to a parking brake guy cable. [Figure 10] 10 is a cross-sectional view of the slide plate taken along line XX in FIG. 9. [Figure 11] FIG. 10 is a bottom view of the slide plate of FIG. 9. [Figure 12] 10 is a cross-sectional view of the slide plate taken along line XII-XII in FIG. 9. [Figure 13] This is a cross-sectional view showing the shaft of the tank shut-off valve engaged with the through hole as a result of the parking brake being released and the slide plate sliding to the left, with the tank shut-off valve being forced open. [Figure 14] This is a cross-sectional view showing the shaft of the tank isolation valve engaged in the recess as a result of the parking brake being applied and the slide plate sliding to the right, and the tank isolation valve being in a closed state with a high sealing pressure. [Figure 15] 11 is a cross-sectional view corresponding to FIG. 10 of a slide plate having recesses of different depths as another embodiment. [Figure 16] 16 is a bottom view of the slide plate of FIG. 15, corresponding to FIG. 11. FIG. [Figure 17] 16 is a cross-sectional view showing the shaft of the tank isolation valve engaged in the deep recess when using the slide plate of FIG. 15, with the tank isolation valve in a closed position at low sealing pressure. [Figure 18]16 is a cross-sectional view showing the shaft of the tank isolation valve engaged in the shallow recess when using the slide plate of FIG. 15, with the tank isolation valve in a closed position at high sealing pressure. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0016] [Engine System] 1 shows an engine system for a vehicle such as an automobile as one embodiment. The engine system includes an engine (not shown) and a fuel tank 15 that stores fuel for the engine. The engine system also includes a control device 45 electrically connected to various actuators included in a purge valve 40 and other devices, as well as various sensors (not shown).

[0017] The engine system includes a fuel supply system 19. The fuel supply system 19 is provided with a fuel pump 20 in a fuel tank 15 that draws in fuel from the fuel tank 15, pressurizes it, and discharges it. The fuel pumped up from the fuel tank 15 by the fuel pump 20 is supplied through a fuel supply passage 24 and injected into the intake passage of the engine by an injector (not shown).

[0018] An inlet pipe 16 is connected to the fuel tank 15 for introducing fuel into the fuel tank 15 from a filler opening when refueling. A cap 17 is removably attached to the opening at the end of the inlet pipe 16, which serves as the filler opening. The cap 17 is equipped with a negative pressure relief valve 18 that relieves excessive negative pressure generated in the fuel tank. A lid (not shown) is provided on the vehicle body to cover the filler opening.

[0019] [Fuel vapor treatment system] The engine system includes an evaporated fuel processing system 12. The evaporated fuel processing system 12 is equipped with a canister 34 that collects evaporated fuel (vapor) generated in a fuel tank 15. The gas phase of the fuel tank 15 communicates with the canister 34 via a vapor passage 31, and the canister 34 communicates with the atmosphere via an atmospheric passage 42. The vapor passage 31 and the atmospheric passage 42 form a vent line. The canister 34 adsorbs fuel vapor using an adsorbent material (not shown) containing activated carbon. When the pressure inside the fuel tank 15 increases, evaporated fuel moves through the vapor passage 31 and is collected in the canister 34. A float valve 36 is provided inside the fuel tank 15 to prevent liquid fuel from flowing into the vapor passage 31 from the fuel tank 15.

[0020] A tank shut-off valve 52 is disposed in the vapor passage 31. The tank shut-off valve 52 seals (seals) the fuel tank as necessary to reduce the amount of evaporated fuel adsorbed into the canister 34. A bypass passage 90 (FIG. 3) that bypasses the tank shut-off valve 52 is provided in the vapor passage 31, and a pressure relief valve 54 that relieves excessive positive or negative pressure generated in the fuel tank 15 is disposed in this bypass passage 90. The pressure relief valve 54 has the function of both relieving positive pressure and negative pressure in the fuel tank 15.

[0021] The evaporated fuel processing system 12 includes a purge passage 32 that connects a canister 34 to the intake passage downstream of the throttle valve. A purge valve 40, which is an electromagnetic valve, is disposed in the purge passage 32. An air filter 43 is disposed in an atmospheric passage 42. The atmospheric passage 42 and the purge passage 32 form a purge line.

[0022] [Fuel vapor treatment] The vapor treatment system 12 basically operates as follows. Under normal conditions, the pressure relief valve 54 is closed. While the vehicle is moving or stopped but the parking brake is not applied, the tank shut-off valve 52 is closed at a low sealing pressure or is open. While the vehicle is moving, the control device 45 can purge the canister 34 under specified purge conditions. Specifically, by opening the purge valve 40, the engine's intake negative pressure is applied to the inside of the canister 34. As a result, air is drawn into the canister 34 from the atmosphere through the atmospheric passage 42, causing the fuel molecules adsorbed to the canister 34 to desorb. The desorbed fuel vapor is drawn into the intake passage along with the air and is ultimately burned in the engine. When the parking brake is applied, such as while the vehicle is parked or refueling, the tank shut-off valve 52 switches to a high sealing pressure via a switching mechanism 92, which will be described in detail later. This suppresses adsorption of vaporized fuel into the canister 34.

[0023] [Tank shut-off valve] 2 to 5, the tank shut-off valve 52 has a housing 60 that forms a valve chamber. The tank shut-off valve 52 is fixed to an appropriate component 167 under the vehicle body via a mounting portion 63 provided on the housing 60 by an appropriate method such as bolting.

[0024] The tank shut-off valve 52 includes a valve element 96 and a valve seat 72 formed around the inlet of the valve chamber in the housing 60. When the valve element 96 moves upward and separates from the valve seat 72, the vapor passage 31 is opened (FIGS. 3 and 5). When the valve element 96 moves downward and comes into close contact with the valve seat 72, the vapor passage 31 is closed (FIG. 4). The valve element 96 has a plate portion 115 facing the valve seat 72, and an annular sealing member 117 fixed to the plate portion 115 and made of an elastic material such as rubber or elastomer.

[0025] The tank shutoff valve 52 is equipped with a valve operating member 94 that controls the sealing pressure exerted by a valve element 96. The valve operating member 94 is supported so as to be movable in the axial direction (up and down in FIG. 3 ) relative to the housing 60. The valve operating member 94 has a shaft portion 93 that extends from the outside to the inside (valve chamber) of the housing 60, and a cylindrical guide wall portion 102 that stabilizes the opening and closing movement of the valve element 96. The guide wall portion 102 and the shaft portion 93 are connected by a connecting plate portion 103. The periphery of the shaft portion 93 is sealed by a diaphragm 95 that is stretched over the opening of the housing 60. The shaft portion 93 is elastically supported by at least the diaphragm 95.

[0026] The valve element 96 is urged in the closing direction (downward) relative to the valve operating member 94 by a valve spring 98. The valve spring 98 is a compression coil spring arranged inside a cylindrical portion 114 that extends from a plate portion 115 of the valve element 96 on the side opposite to the seal member 117, and is held between the plate portion 115 of the valve element 96 and the connecting plate portion 103 of the valve operating member 94.

[0027] The valve operating member 94 is biased in the valve opening direction (upward) relative to the housing 60 by an auxiliary spring 112. The auxiliary spring 112 is a compression coil spring disposed on the outside of the guide wall portion 102 of the valve operating member 94. The auxiliary spring 112 can be held, for example, between a protrusion 104 formed on the outer peripheral surface of the guide wall portion 102 of the valve operating member 94 and the inner wall surface of the housing 60.

[0028] The valve disc 96 is movable axially (up and down) within the valve actuation member 94. An engagement means is provided between the valve actuation member 94 and the valve disc 96, allowing the valve actuation member 94 to lift the valve disc 96. The engagement means can be composed of, for example, an engagement portion 122 formed on the outer peripheral surface of the cylindrical portion 114 of the valve disc 96, and an engagement portion 124 formed on the inner peripheral surface of the guide wall portion 102 of the valve actuation member 94.

[0029] [Tank shutoff valve operation] 3, when the valve operating member 94 is in the upper position, the valve body 96 is raised to a position away from the valve seat 72 via the engagement of the engagement portions 122, 124, and the tank shut-off valve 52 is forcibly held in the open state. Therefore, even if the internal pressure of the fuel tank 15 drops, the tank shut-off valve 52 cannot close the vapor passage 31.

[0030] When the shaft portion 93 is pressed down, the valve operating member 94 descends against the auxiliary spring 112. During this process, the valve disc 96 first comes into close contact with the valve seat 72, closing the vapor passage 31 (sealing the fuel tank 15). As a result of this, the valve disc 96 is prevented from further descending, and as shown in Figure 4, the engaging portion 124 of the valve operating member 94 leaves the engaging portion 122 of the valve disc 96, allowing only the valve operating member 94 to further descend.

[0031] When the internal pressure of the fuel tank 15 is not high, the valve element 96 is held in the valve closed position by the biasing force of the valve spring 98. When the internal pressure of the fuel tank 15 (more precisely, the pressure relative to the canister side) increases and exceeds the sealing pressure, the valve element 96 moves upward against the valve spring 98, as shown in FIG. 5, and the vapor passage 31 is opened. The biasing force of the valve spring 98 is determined by the length of the valve spring 98, and the length of the valve spring 98 depends on the position of the connecting plate portion 103 of the valve operating member 94. Therefore, the sealing pressure exerted by the valve element 96 can be adjusted by changing the axial (vertical) position of the valve operating member 94 via the shaft portion 93.

[0032] When the force pressing down on the shaft portion 93 is released, the valve operating member 94 rises due to the biasing force of the auxiliary spring 112. During this process, the engaging portion 124 of the valve operating member 94 comes into contact with the engaging portion 122 of the valve body 96. As the valve operating member 94 rises further, the valve body 96 separates from the valve seat 72, and the tank shut-off valve 52 is forced open again (Figure 3).

[0033] [Switching mechanism] The switching mechanism 92 (FIG. 1) is configured to increase the sealing pressure of the tank shut-off valve 52 when the parking brake 170 is applied compared to the sealing pressure when the parking brake 170 is released. Note that the sealing pressure may be zero when the parking brake 170 is released, which includes the state in which the tank shut-off valve 52 is open. This allows the sealing pressure of the tank shut-off valve 52 to be increased when the vehicle is parked as long as the parking brake 170 is applied, thereby suppressing the emission of fuel vapor.

[0034] The switching mechanism 92 has a switching member mechanically coupled to a movable member, such as a hand lever 172, provided on an operating device 171 of the parking brake 170. The movement of the switching member changes the axial position of the shaft portion 93 of the tank shut-off valve 52. As shown in FIGS. 13 and 14 , in one embodiment, the switching member is a sliding member, such as a slidably supported slide plate 180, and the position of the shaft portion 93 can be changed by the sliding of the slide member. The slide plate 180 is slidably supported, for example, by two guide rails 182 that hold the edges on both sides ( FIGS. 9 to 12 ). As described above, the tank shut-off valve 52 is configured so that the sealing pressure of the shut-off valve changes depending on the axial position of the valve operating member 94. Therefore, the switching mechanism 92 can switch the sealing pressure of the shut-off valve via the movement of a switching member, such as the slide plate 180. Figure 13 shows the state in which the shaft portion 93 is in an upper position and the tank shut-off valve 52 is forcibly opened (sealing pressure is zero), and Figure 14 shows the state in which the shaft portion 93 is in a lower position and the tank shut-off valve 52 is closed at a high sealing pressure (e.g., 8 kPa).

[0035] As shown in FIG. 1 , an operating device 171 including operating devices such as a hand lever 172 and a foot pedal is disposed at the driver's seat and operated by the driver, while a switching member is disposed near the tank shutoff valve 52. The parking brake 170 is configured to transmit operation from the hand lever 172 of the operating device 171 to a brake device provided on a wheel via a retractable brake cable 175. When the hand lever 172 is raised, the brake cable 175 is pulled, activating the brake device (applying the parking brake 170), and when the hand lever 172 is lowered, the brake cable 175 returns, releasing the brake device. In one embodiment, the brake cable 175 is provided with an appropriate distributor 176, which distributes the advance / retract movement of the brake cable 175 to a branch cable 177. As shown in FIGS. 9 to 12 , a cable fixing portion such as a cable lug 184 is provided at the end of the slide plate 180, to which the end of the branch cable 177 of the parking brake 170 is fixed. Therefore, when the hand lever 172 is pulled up, the slide plate 180 slides to the right as viewed in the figure, and when the hand lever 172 is lowered, the slide plate 180 slides to the left. In another embodiment (not shown), the connection between the hand lever 172 and the slide plate 180 or the shaft portion 93 may be partially electrically established via a switch, actuator, or the like.

[0036] As shown in Figures 9 to 12, a switching member such as slide plate 180 has multiple engagement portions with which shaft portion 93 can engage at different axial positions. Each engagement portion can be, for example, a recess or a through hole with which the end of shaft portion 93 can engage. Each engagement portion corresponds to a different sealing pressure of tank shut-off valve 52. In one embodiment, recess 186 corresponding to a high sealing pressure and through hole 188 corresponding to zero sealing pressure can be provided. This allows shaft portion 93 to be pressed against the edge of recess 186 or through hole 188, thereby stabilizing the sealing pressure of tank shut-off valve 52.

[0037] 13 and 14, the tip 97 of the shaft portion 93 can be rounded. Meanwhile, smooth slopes 189 can be provided on both sides between the depression 186 and the through-hole 188 of the slide plate 180. This allows the tip 97 of the shaft portion 93 to easily move between the depression 186 and the through-hole 188 while climbing over the slopes 189 when the slide plate 180 slides. In another embodiment (not shown), the tip 97 of the shaft portion 93 may not terminate, but may have some structure that can engage with an engaging portion of the slide plate 180.

[0038] As shown in Figures 15 to 18, in another embodiment, instead of through-hole 188, a second recess 190 that is deeper than first recess 186 and corresponds to a small, non-zero sealing pressure can be used. Figure 17 shows a state in which tip 97 of shaft portion 93 is fitted into deep recess 190 and tank shut-off valve 52 is closed at a low sealing pressure (e.g., 4.9 kPa), while Figure 18 shows a state in which tip 97 of shaft portion 93 is fitted into shallow recess 186 and tank shut-off valve 52 is closed at a high sealing pressure (e.g., 8 kPa). In another embodiment, through-hole 188 can be made to correspond to a small, non-zero sealing pressure without using second recess 190. Naturally, various other embodiments are possible with regard to the specific shape of the engagement portion and the specific value of the sealing pressure.

[0039] [Pressure relief valve] 3, the pressure relief valve 54 is provided in a bypass passage 90 that bypasses the tank shut-off valve 52. Therefore, a tank-side portion 80 of the bypass passage 90 is connected to a location in the vapor passage 31 upstream of the tank shut-off valve 52 (for example, the inlet passage 75 of the tank shut-off valve 52). Similarly, a canister-side portion 88 of the bypass passage 90 is connected to a location in the vapor passage 31 downstream of the tank shut-off valve 52 (for example, the outlet passage 76 of the tank shut-off valve 52).

[0040] As shown in Figures 7 to 9, the pressure relief valve 54 has a housing 61 that forms a valve chamber. In one embodiment, the tank shut-off valve 52 and the pressure relief valve 54 can be provided as a valve assembly 38 (Figure 2) in which the housings 60, 61 are integrally configured. In this case, the valve assembly 38 is attached to a component 167 under the vehicle body via a mounting portion 63 formed on the housing 60 of the tank shut-off valve 52. However, in another embodiment (not shown), the pressure relief valve 54 can also be provided as a separate unit from the tank shut-off valve 52.

[0041] The pressure relief valve 54 has a valve chamber containing a positive pressure relief valve element 134 and a negative pressure relief valve element 136, which are axially movable independently of each other. Since the positive pressure relief valve element 134 is generally disposed outside the negative pressure relief valve element 136, hereinafter the former will also be referred to as the outer valve element 134, and the latter will also be referred to as the outer valve element 136.

[0042] The outer valve element 134 for positive pressure relief has an annular plate portion 138 with a central hole 143. The housing 61 has a valve seat 82 formed of a metal annular plate member embedded around the inlet of the valve chest. The outer periphery of the annular plate portion 138 faces the valve seat 82. When the valve element 134 (together with the inner valve element 136) moves upward and away from the valve seat 82, the bypass passage 90 is opened (FIG. 7). When the valve element 134 moves downward and comes into close contact with the valve seat 82, the bypass passage 90 is closed (FIG. 6). The valve element 134 is urged in the closing direction (downward) relative to the housing 61 by a coil spring 154. The coil spring 154 is disposed, for example, inside an outer cylinder portion 140 extending from the annular plate portion 138 of the valve element 134, and is held between the annular plate portion 138 and the housing 61.

[0043] The annular plate portion 138 of the valve disc 134 has an annular seal member 163 made of an elastic material such as rubber or elastomer, fixed to its underside by adhesive or the like. The seal member 163 has an annular seal portion 165 that protrudes toward the valve seat 82. When the valve disc 134 is closed, the biasing force of the coil spring 154 causes the annular seal portion 165 to come into close contact with the valve seat 82, sealing the gap. A stopper piece 145 that restricts the descent of the valve disc 134 is formed on the underside of the annular plate portion 138, outside the seal member 163. The fully closed position of the valve disc 134 is determined by this stopper piece 145.

[0044] The inner valve element 136 for negative pressure relief has a plate portion 156 and a shaft portion 157 extending from the plate portion 156. The shaft portion 157 of the valve element 136 is inserted into a central hole 143 of the annular plate portion 138 of the outer valve element 134, and is slidably fitted into an inner cylindrical portion 139 that is supported from the inner periphery of the annular plate portion 138 via a plurality of support ribs. The inner periphery of the annular plate portion 138 of the outer valve element 134 functions as a valve seat for the inner valve element 136 and faces the plate portion 156 of the inner valve element 136. When the inner valve element 136 moves downward and the plate portion 156 moves away from the outer valve element 134, the central hole 143 (i.e., the bypass passage 90) is opened (FIG. 8). When the inner valve element 136 moves upward and the plate portion 156 comes into close contact with the outer valve element 134, the central hole 143 is closed (FIG. 9). The inner valve element 136 is urged in the closing direction (upward) relative to the outer valve element 134 by a second coil spring 161 arranged inside the aforementioned coil spring 154. The second coil spring 161 is arranged outside the inner cylinder portion 139 of the outer valve element 134 and is held, for example, between a flange-shaped spring receiving portion 159 provided around the shaft portion 157 and the annular plate portion 138 of the outer valve element 134.

[0045] The seal member 163 provided on the outer valve body 134 has a second annular seal portion 164 that protrudes toward the plate portion 156 of the inner valve body 136 inside the aforementioned annular seal portion 165. When the inner valve body 136 is closed, the biasing force of the inner coil spring 161 causes the plate portion 156 to come into close contact with this inner annular seal portion 164, sealing the gap. The inner cylinder portion 139 of the outer valve body 134 and the spring bearing portion 159 of the inner valve body 136 abut against each other to restrict the descent of the inner valve body 136 and determine the fully open position of the inner valve body 136.

[0046] [Pressure relief valve operation] There is a possibility that the tank shut-off valve 52 may fail and become unable to relieve the positive pressure in the fuel tank 15. In this case, if the internal pressure of the fuel tank 15 (more precisely, the pressure relative to the canister 34 side) increases excessively, the outer valve body 134 of the pressure relief valve 54 rises against the outer coil spring 154, causing the outer annular seal portion 165 to move away from the valve seat 82 and opening the bypass passage 90 (FIG. 7). This relieves the positive pressure in the fuel tank 15 until the outer valve body 134 closes again.

[0047] Conversely, there is also the possibility that the pressure relief valve 54 may malfunction and become unable to relieve positive pressure. In this case, if the internal pressure of the fuel tank 15 increases excessively and exceeds the sealing pressure of the tank shut-off valve 52, the valve element 96 of the tank shut-off valve 52 opens against the valve spring 98, opening the vapor passage 31 (FIG. 5). This relieves the positive pressure in the fuel tank 15 until the valve element 96 closes again. The opening pressure of the pressure relief valve 54 during positive pressure relief can be set, for example, to a value equal to or greater than the sealing pressure of the tank shut-off valve 52 when the parking brake 170 is released.

[0048] Unless the tank shut-off valve 52 is held open, it cannot relieve the negative pressure in the fuel tank 15. If the internal pressure of the fuel tank 15 drops excessively, the inner valve body 136 of the pressure relief valve 54 will descend against the inner coil spring 161, causing the plate portion 156 of the inner valve body 136 to move away from the inner annular seal portion 164, opening the bypass passage 90 (FIG. 8). This relieves the negative pressure in the fuel tank 15 until the inner valve body 136 closes again.

[0049] If the pressure relief valve 54 fails and is no longer able to relieve the negative pressure, the negative pressure in the fuel tank 15 can be alleviated by the negative pressure relief valve 18 (FIG. 1) provided in the cap 17.

[0050] As described above, even if either the tank shutoff valve 52 or the pressure relief valve 54 fails to open, the system as a whole can still relieve pressure in the fuel tank 15. On the other hand, if either of these valves fails to close, evaporated fuel moves from the fuel tank to the canister 34, increasing the amount of fuel adsorbed by the canister 34 compared to normal. However, even if the purge conditions are met and the canister 34 is purged, the vehicle can still be driven normally.

[0051] [Other embodiments] While the embodiment described above uses a single combined pressure relief valve 54 that provides both positive and negative pressure relief, an alternative embodiment (not shown) may use separate positive and negative pressure relief valves connected in parallel.

[0052] Although various embodiments have been described above, the present technology is not limited to these embodiments, and various changes, substitutions, and improvements can be made by those skilled in the art. [Explanation of symbols]

[0053] 12 Fuel vapor treatment system 15 Fuel Tank 16 Inlet pipe 17 Cap 18 Vacuum relief valve 19 Fuel supply system 20 Fuel pump 22 Fuel filter 24 Fuel supply passage 31 Vapor passage 32 Purge Passage 34 canister 36 Float valve 38 Valve Assembly 40 Purge valve 42 Atmospheric Passage 43 Air Filter 45 Control Device 52 Tank shut-off valve 54 Pressure relief valve 60 Tank shut-off valve housing 61 Pressure relief valve housing 63 Mounting part 72 Tank shut-off valve seat 75 Tank shutoff valve inlet 76 Tank shutoff valve outlet 78 Step 80 Tank side of bypass passage 82 Pressure relief valve seat 88 Canister side of bypass passage 90 Bypass Passage 92 Switching mechanism 93 Shaft section 94 Valve operating member 95 diaphragm 96 Tank shut-off valve body 97 Tip 98 valve spring 102 Guide wall 103 Connection plate 104 Overhang 112 Auxiliary spring 114 Cylindrical part 115 Board part 117 Sealing material 122 Valve body engagement portion 124 Engagement portion of valve operating member 134 Valve body for positive pressure relief (outside) 136 Negative pressure relief (inner) valve body 138 Annular plate 139 Inner cylinder 140 outer cylinder 143 Center hole 145 Stopper piece 152 Anti-slip member 154 outer coil spring 156 Board part 157 Shaft 159 Spring holder 161 Inner coil spring 163 Sealing material 164 Annular seal 165 Annular seal 167 Lower body components 170 Parking brake 171 Operating device 172 Hand Lever 175 brake cable 176 Distribution device 177 Branch Cable 180 Slide Plate 182 guide rail 184 Cable Lug 186 Depression 188 through hole 189 Smooth Slope 190 Deep depression

Claims

1. 1. A fuel tank system comprising: A fuel tank and a canister capable of adsorbing and desorbing fuel vapor generated in the fuel tank; a vapor passage communicating the fuel tank with the canister; a parking brake operated by the driver; a shutoff valve disposed in the vapor passage for closing the fuel tank; a sealing pressure switching mechanism configured to set the sealing pressure of the shut-off valve to a first sealing pressure when the parking brake is released, and to set the sealing pressure of the shut-off valve to a second sealing pressure greater than the first sealing pressure when the parking brake is applied.

2. 2. The fuel tank system of claim 1, A fuel tank system, wherein the sealing pressure switching mechanism is configured to open the isolation valve when the parking brake is released.

3. 3. The fuel tank system of claim 1 or 2, The sealing valve has an axially movable shaft and a diaphragm that elastically seals around the shaft, A fuel tank system configured such that the sealing pressure of the shutoff valve changes depending on the axial position of the shaft.

4. 4. The fuel tank system of claim 3, The sealing pressure switching mechanism has a switching member mechanically connected to a movable member of the parking brake, The fuel tank system is configured such that the axial position of the shaft changes with the movement of the switching member.

5. 5. The fuel tank system of claim 4, the switching member has a plurality of engaging portions with which the shaft can engage at different positions, A fuel tank system in which each engagement portion corresponds to a different sealing pressure of the shut-off valve.

6. 6. The fuel tank system of claim 5, The switching member is slidably supported, each of the plurality of engaging portions of the switching member is a recess or a through hole with which an end portion of the shaft can be engaged; A fuel tank system in which the position of the shaft changes as the switching member slides.

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