Fuel vapor recovery apparatus

[0001] This application claims priority to Japanese patent application serial number 2015-044479, filed Mar. 6, 2015, the contents of which are incorporated herein by reference in their entirety for all purposes.

[0002] Not applicable.

[0003] This disclosure relates to a fuel vapor recovery apparatus including an adsorbent canister capable of capturing fuel vapor, a vapor passage introducing the fuel vapor produced in a fuel tank to the adsorbent canister, an atmospheric air passage fluidly communicating the adsorbent canister with the atmosphere, and a purge passage introducing the fuel vapor captured in the adsorbent canister to an intake pipe of an internal combustion engine.

[0004] Japanese Laid-Open Patent Publication No. 2007-177728 discloses a conventional fuel vapor recovery apparatus. Referring to FIG. 6, such conventional fuel vapor recovery apparatus 100 has an adsorbent canister 102 capable of trapping fuel vapor, a vapor passage 104 introducing the fuel vapor produced in a fuel tank 103 to the adsorbent canister 102, an atmospheric air passage 105 fluidly communicating the adsorbent canister 102 with the atmosphere, and a purge passage 107 introducing the fuel vapor captured in the adsorbent canister 102 to an intake pipe 120 of an internal combustion engine (not shown). The purge passage 107 is provided with a purge pump 110 for generating gas flow from the adsorbent canister 102 through the purge passage 107 to the intake pipe 120 of the engine. The purge passage 107 is further provided with a flow control valve 112 downstream of the purge pump 110. According to the above-described configuration, when the purge pump 110 is started under a condition where the engine is running, the atmospheric air can be drawn into the adsorbent canister 102 through the atmospheric air passage 105 in order to forcibly purge the fuel vapor captured in the adsorbent canister 102 and introduce the fuel vapor into the intake pipe 120 of the engine. During this operation, the flow control valve 112 can regulate a flow rate of the gas flowing through the purge passage 107 toward the intake pipe 120 of the engine.

[0005] The fuel vapor recovery apparatus 100 is configured such that when the purge pump 110 provided along the purge passage 107 is driven, the fuel vapor adsorbed in the adsorbent canister 102 is forcibly purged by the air. Thus, there is a possibility that inner pressure of the purge passage 107 upstream of the flow control valve 112 becomes higher than the atmospheric pressure. When the engine is stopped under a condition where the inner pressure of the purge passage 107 is higher than the atmospheric pressure, the inner pressure of the adsorbent canister 102 fluidly communicating with the purge passage 107 might become higher than the atmospheric pressure after the purge pump 110 is stopped. Accordingly, there is a possibility that the fuel vapor adsorbed in the adsorbent canister 102 might flow into the atmosphere through the atmospheric air passage 105. Therefore, there has been a need for an improved fuel vapor recovery apparatus.

[0006] In one aspect of this disclosure, a fuel vapor recovery apparatus includes an adsorbent canister capable of capturing fuel vapor, a vapor passage connecting the adsorbent canister to a fuel tank, an atmospheric air passage communicating the adsorbent canister with the atmosphere, a purge passage coupling the adsorbent canister to an intake pipe of an internal combustion engine, a purge pump configured to generate a gas flow from the adsorbent canister to the intake pipe through the purge passage, a flow control valve provided at the purge passage downstream of the purge pump in a direction of the gas flow and configured to regulate the gas flow through the purge passage, and a decompressor configured to decrease pressure upstream of the flow control valve in the direction of the gas flow when the pressure upstream of the flow control valve in the direction of the gas flow is higher than the atmospheric pressure.

[0007] According to this aspect of the present disclosure, when the pressure upstream of the flow control valve in the gas flow is higher than the atmospheric pressure under a condition where the gas flow from the adsorbent canister to the intake pipe of the engine through the purge passage is generated, the decompressor decreases the pressure upstream of the flow control valve. Thus, while the engine is running, the pressure upstream of the flow control valve, that is, the pressure in the purge passage, the adsorbent canister and the fuel tank is kept equal to or lower than the atmospheric pressure. Accordingly, when the engine and the purge pump are stopped, the pressure upstream of the flow control valve does not become higher than the atmosphere. Therefore, the diffusion of the fuel vapor from the adsorbent canister to the atmosphere through the atmospheric air passage can be prevented or reduced.

[0014] Each of the additional features and teachings disclosed above and below may be utilized separately or in conjunction with other features and teachings to provide improved fuel vapor recovery apparatuses. Representative examples, which utilize many of these additional features and teachings both separately and in conjunction with one another, will now be described in detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skilled in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Only the claims define the scope of the claimed invention. Therefore, combinations of features and steps disclosed in the following detailed description may not be necessary in the broadest sense, and are instead taught merely to particularly describe representative examples. Moreover, various features of the representative examples and the dependent claims may be combined in ways that are not specifically enumerated in order to provide additional useful embodiments of the present teachings.

[0015] A fuel vapor recovery apparatus 20 according to a first embodiment will be described based on FIGS. 1 and 2. Referring to FIG. 1, the fuel vapor recovery apparatus 20 is combined with an engine system 10 for a vehicle and is configured to prevent fuel vapor produced in a fuel tank 15 of the vehicle from leaking into the outside.

[0016] As shown in FIGS. 1 and 2, the fuel vapor recovery apparatus 20 includes an adsorbent canister 22, a vapor passage 24, a purge passage 26 and an atmospheric air passage 28. Each of the vapor passage 24, the purge passage 26 and the atmospheric air passage 28 is coupled to the adsorbent canister 22. The adsorbent canister 22 is filled with an adsorbent (not shown), such as an activated carbon, for adsorbing fuel vapor produced in the fuel tank 15. The vapor passage 24 is configured to introduce the fuel vapor from the fuel tank 15 to the adsorbent canister 22. One end (upstream end) of the vapor passage 24 is fluidly communicated with an air layer in the fuel tank 15, and the other end (downstream end) of the vapor passage 24 is fluidly communicated with the inside of the adsorbent canister 22. The atmospheric air passage 28 is configured to communicate the adsorbent canister 22 with the atmosphere. A base end of the atmospheric air passage 28 is coupled to the adsorbent canister 22, and the other end of the atmospheric air passage 28 is open to the atmosphere at a position near a fill opening 15h of the fuel tank 15. An air filter 28a is provided in the middle of the atmospheric air passage 28.

[0017] The purge passage 26 is configured to introduce the fuel vapor from the adsorbent canister 22 to an intake pipe 16 of an internal combustion engine 14 (referred to as “engine”, hereinafter). The purge passage 26 has one end (upstream end) fluidly communicating the inside of the adsorbent canister 22 and the other end (downstream end) fluidly communicating the intake pipe 16 downstream of a throttle valve 17. The purge passage 26 has a purge pump 26p, a pressure sensor 26s and a flow control valve 26v in order from the upstream end to the downstream end. The purge pump 26p is operated based on signals output from an engine control unit (ECU) 19 and is configured to produce a gas flow from the adsorbent canister 22 through the purge passage 26 to the intake pipe 16 of the engine 14 while the engine 14 is running. The pressure sensor 26s is configured to measure the inner pressure of the purge passage 26 upstream of the flow control valve 26v and to output pressure detection signals to the ECU 19. The flow control valve 26v is configured to regulate the flow rate of the gas flowing through the purge passage 26 while the purge pump 26p is driven. The flow control valve 26 is operated based on signals output from the ECU 19.

[0018] When the engine 14 of the vehicle is stopped, the flow control valve 26v is closed in order to block fluid communication through the purge passage 26, and the purge pump 26p is stopped. Thus, the fuel vapor vaporized in the fuel tank 15 is introduced into the adsorbent canister 22 through the vapor passage 24 and is adsorbed on the adsorbent filled in the adsorbent canister 22. Then, after starting engine 14, when predetermined purge conditions are satisfied, the ECU 19 performs an operation for purging the fuel vapor adsorbed on the adsorbent in the adsorbent canister 22.

[0019] During this operation, the purge pump 26p is driven and the flow control valve 26v is opened. Thus, negative pressure generated at an inlet side (upstream side) of the purge pump 26p is applied to the adsorbent canister 22, so that inner pressure of the adsorbent canister 22 becomes negative. Accordingly, the air flows into the adsorbent canister 22 through the atmospheric air passage 28. Further, gases flow from the fuel tank 15 into the adsorbent canister 22, so that the fuel tank 15 is depressurized. A mixture of the air and the gases, flowing into the adsorbent canister 22, purges the fuel vapor adsorbed on the adsorbent and is introduced into the purge pump 26p through the purge passage 26 together with the fuel vapor. Then, the mixture containing the fuel vapor is pressurized by the purge pump 26p and is supplied to the intake pipe 16 of the engine 14 via the flow control valve 26v and the downstream end of the purge passage 26. That is, the fuel vapor removed from the adsorbent filled in the adsorbent canister 22 is introduced into the intake pipe 16 of the engine 14 together with the air and is burned in the engine 14. During this operation, the ECU 19 controls the opening amount of the flow control valve 26v in order to regulate the air-fuel ratio of an air-fuel mixture supplied to the engine 14.

[0020] When the purge pump 26p is driven, the mixture containing the fuel vapor is pressurized by the purge pump 26p and is supplied to the intake pipe 16 of the engine 14 via the flow control valve 26v and the purge passage 26. During this operation, because the intake pipe 14 of the engine 16 is fluidly communicated with the purge passage 26, inner pressure of the purge passage 26 downstream of the flow control valve 26v is constantly negative due to the negative pressure in the intake pipe 16. Whereas, although the negative pressure in the intake pipe 16 of the engine 14 is applied to the purge passage 26 upstream of the flow control valve 26v via the flow control valve 26v, the inner pressure of the purge passage 26 upstream of the flow control valve 26v might be higher than the atmospheric pressure due to discharge pressure (positive pressure) of the purge pump 26p. When the engine 14 and the purge pump 26p are stopped under a condition where the pressure P in the purge passage 26 upstream of the flow control valve 26v is positive (i.e., P>0 kPa in gauge pressure), the inner pressure of the adsorbent canister 22 fluidly communicating the purge passage 26 might become positive. Thus, there is a possibility that the fuel vapor trapped in the adsorbent canister 22 may diffuse to the outside atmosphere through the atmospheric air passage 28. The ECU 19 is configured to perform a decompression control for preventing such diffusion of the fuel vapor. The ECU 19 includes a memory for storing control programs and a processor for executing the control program, so that the decompression control is operated based on the control programs stored in the memory of the ECU 19.

[0021] That is, the ECU 19 monitors the pressure in the purge passage 26 upstream of the flow control valve 26v (and downstream of the purge pump 26p) by using the pressure sensor 26s. When the pressure in the purge passage 26 becomes positive, the ECU 19 performs the decompression control in order to decrease the pressure in the purge passage 26 upstream of the flow control valve 26v. The decompression control includes decreasing the rotation number N of the purge pump 26p (e.g., rotation number N may be the revolutions of the purge pump 26p impeller per some unit time), increasing the valve opening amount of the flow control valve 26v, and decreasing the pressure in the intake pipe 16 of the engine 14.

[0022] To decrease the rotation number N of the purge pump 26p, the ECU 19 may decrease voltage applied to a driving motor of the purge pump 26p. Thus, the rotation number of the driving motor is decreased, so that the rotation number N of the purge pump 26p is also decreased. When the rotation number N of the purge pump 26p decreases, the discharge pressure of the purge pump 26p decreases such that the pressure in the purge passage 26 upstream of the flow control valve 26v decreases. Further, when the ECU 19 increases the valve opening amount of the flow control valve 26v, pressure loss at the flow control valve 26v decreases. Accordingly, influence of the negative pressure in the intake pipe 16 of the engine 14 on the pressure in the purge passage 26 upstream of the flow control valve 26v becomes greater, so that differential pressure between the pressure in the intake pipe 16 and the pressure in the purge passage 26 upstream of the flow control valve 26v decreases. Consequently, the pressure in the purge passage 26 upstream of the flow control valve 26v decreases.

[0023] To decrease the pressure in the intake pipe 16 of the engine 14, the ECU 19 may perform a control operation for decreasing the circulating volume of exhaust gas or changing the circulation timing of the exhaust gas in an exhaust gas recirculation system (EGR), or for increasing the rotation number of the engine 14 (e.g., the rotation number of engine 14 may be the number of revolutions of an output shaft of engine 14 per some unit time), etc. Because the intake pipe 16 of the engine 14 is in fluid communication with the purge passage 26, when the pressure in the intake pipe 16 of the engine 14 is lowered, the pressure in the purge passage 26 is also decreased. Accordingly, when the decompression control is carried out by decreasing the pressure in the intake pipe 16, the pressure in the purge passage 26 upstream of the flow control valve 26v decreases.

[0024] The decompression control can be performed by carrying out any one of decreasing the rotation number N of the purge pump 26p, increasing the valve opening amount of the flow control valve 26v and decreasing the pressure in the intake pipe 16 of the engine 14, or by simultaneously or sequentially carrying out at least two of them. Because of the decompression control, the pressure in the purge passage 26 upstream of the flow control valve 26v can be efficiently decreased while the purge pump 26 is running. That is, the ECU 19 corresponds to a decompressor of this disclosure.

[0025] According to the fuel vapor recovery apparatus 20, under a condition where gas flows from the adsorbent canister 22 to the intake pipe 16 of the engine 14 through the purge passage 26, when the pressure upstream of the flow control valve 26v becomes higher than the atmospheric pressure, the ECU 19 performs the decompression control in order to decrease the pressure upstream of the flow control valve 26v. Thus, while the engine 14 is running, it is able to prevent the pressure upstream of the flow control valve 26v, i.e., the pressure in the fuel tank 15, the adsorbent canister 22 and the purge passage 26 upstream of the flow control valve 26v, from remaining at a higher pressure than the atmospheric pressure. Accordingly, after the engine 14 and the purge pump 26p are stopped, the inner pressure of the purge passage 26, the adsorbent canister 22 and others does not become higher than the atmospheric pressure. Therefore, the diffusion of the fuel vapor from the adsorbent canister 22 to the atmosphere through the atmospheric air passage 28 can be prevented or reduced. Further, because the pressure sensor 26s is provided for measuring the pressure in the purge passage 26 upstream of the flow control valve 26v, the pressure upstream of the flow control valve 26v can be accurately detected.

[0026] In the first embodiment, the pressure sensor 26s is provided along the purge passage 26 upstream of the flow control valve 26v such that based on the pressure signals output from the pressure sensor 26s, the ECU 19 performs the decompression control by decreasing the rotation number N of the purge pump 26p, increasing the valve opening amount of the flow control valve 26v and/or decreasing the pressure in the intake pipe 16 of the engine 14. Whereas, the ECU 19 can be modified to carry out the decompression control based on a map that is prepared based on a relationship between the pressure in the purge passage 26 upstream of the flow control valve 26v, the rotation number N of the purge pump 26p, the negative pressure (kPa) in the intake pipe 16 of the engine 14 and the valve opening amount (%) of the flow control valve 26v in order to prevent the pressure upstream of the flow control valve 26v from becoming positive.

[0027] In a second embodiment, the ECU 19 may store a first map shown in FIG. 3 and perform the decompression control based on the first map. The first map of FIG. 3 shows the calculated pressure P in the purge passage 26 upstream of the flow control valve 26v, which is estimated based on the rotation number N of the purge pump 26p and the valve opening amount (%) of the flow control valve 26v under a condition where the pressure in the intake pipe 16 of the engine 14 is kept at −5 kPa. According to the first map, when the valve opening amount of the flow control valve 26v is 22% and the rotation number of the purge pump 26p is N1, the pressure P in the purge passage 26 is P1 (P1>0 kPa, i.e., positive pressure), so that the decompression control is required. In this state, by increasing the valve opening amount of the flow control valve 26v to 80% while keeping the rotation number of the purge pump 26p at N1, the pressure P in the purge passage 26 is presumed to decrease to P2 (P2<0 kPa, i.e., negative pressure). Alternatively, by decreasing the rotation number of the purge pump 26p to N2 (N2<N1) while keeping the valve opening amount of the flow control valve 26v at 22%, the pressure P in the purge passage 26 is presumed to decrease to P3 (P3<0 kPa, i.e., negative pressure).

[0028] Further, the ECU 19 may store a second map shown in FIG. 4 and perform the decompression control based on the second map. The second map of FIG. 4 shows the calculated pressure P in the purge passage 26, which is estimated based on the pressure PK in the intake pipe 16 of the engine 14 and the valve opening amount (%) of the flow control valve 26v under a condition where the rotation number N of the purge pump 26p is maintained constant. According to the second map, when the valve opening amount of the flow control valve 26v is 88% and the pressure PK in the intake pipe 16 is 0 kPa, the pressure P in the purge passage 26 is P4 (P4>0 kPa, i.e., positive pressure), so that the decompression control is required. In this state, by decreasing the pressure PK in the intake pipe 16 of the engine 14 to −5 kPa while keeping the valve opening amount of the flow control valve 26v at 88%, the pressure P in the purge passage 26 is presumed to decrease to P6 (P6<0 kPa, i.e., negative pressure). Further, under the condition where the pressure PK in the intake pipe 16 of the engine 14 is −5 kPa, when the valve opening amount of the flow control valve 26v is decreased to 40%, the pressure in the purge passage 26 is presumed to be P5 (P6<P5<0 kPa) and thus can be kept in negative. According to the second embodiment, the pressure P in the purge passage 26 upstream of the flow control valve 26v can be estimated depending on the maps shown in FIGS. 3 and 4, so that the pressure sensor 26s can be omitted in order to cut production cost of the fuel vapor recovery apparatus 20.

[0029] Further, the above-described embodiments can be modified variously. For example, in a third embodiment as shown in FIG. 5, the pressure sensor 26s may be provided at the fuel tank 15 located at a position upstream of the purge passage 26 and the adsorbent canister 22 for detecting inner pressure of the fuel tank 15. And, the purge pump 26p may be located along the atmospheric air passage 28 upstream of the adsorbent canister 22. In addition, the vapor passage 24 and the purge passage 26 may be directly coupled to each other as shown by each dashed line in FIGS. 2 and 5.