Method for an internal combustion engine with a fuel vapor recovery system

Abstract

A method for an internal combustion engine having a fuel vapor recovery system, comprising: Providing (204) a first venting amount to the fuel vapor canister (22) during a diurnal condition; and Providing (220) a second venting amount to the fuel vapor canister (22) during a purge condition, the second amount being greater than the first amount, further comprising: providing (234) a third canister vent amount during a monitoring condition, the third amount being less than the first amount.

Description

[0001] Vehicles may be equipped with evaporative emission control systems to reduce the release of fuel vapors into the atmosphere. For example, vaporized hydrocarbons (HC) from a fuel tank may be stored in a fuel vapor canister packed with an adsorbent that adsorbs and stores the vapors. When the internal combustion engine is operating at a later time, the evaporative emission control system allows the vapors to be injected into the engine intake manifold for use as fuel. Furthermore, these evaporative emission control systems can be monitored during certain conditions to detect degradation of system components, such as leaks.

[0002] As state of the art, reference is made to US 2012 / 0 145 133 A1 and DE 101 46 841 A1.

[0003] The present inventors have recognized that canister purge issues are occurring in a growing number of vehicle applications, such as start / stop and hybrid applications, due to lower available engine vacuums. Solutions are known that utilize a two-way (open / closed) canister vent valve and an open vent system, with the vent valve in a normally open position during diurnal conditions, such as during refueling and other engine-off conditions. The present inventors have recognized that method approaches that utilize a normally open canister vent valve, in which the vent valve is placed in a fully open position, may result in reduced vapor storage capacity during diurnal conditions and may require a greater amount of vacuum to effectively purge the canister.Furthermore, in some examples, these approaches rely on a fuel tank isolation valve to effectively monitor and flush the system, which can increase costs.

[0004] A solution to these problems is specified in the independent claims. To solve these problems, one approach provides a method for an internal combustion engine with a fuel vapor recovery system. The method includes providing a first venting amount to a fuel vapor canister during a diurnal condition and providing a second venting amount to the fuel vapor canister during a purge condition, the second amount being greater than the first amount.

[0005] In this way, vapor formation in a fuel vapor recovery system can be reduced and the vapor storage capacity of the canister can be used more effectively by limiting the fresh air supply to the canister during diurnal operations. By limiting the fresh air path at the canister vent during diurnal operations and allowing the build-up of positive pressure in the evaporative system, vapor formation can be reduced and an increased pressure quantity can be present during purge and monitoring conditions without resorting to costly valve systems. By limiting the canister vent, vapor can also be forced over the canister bed at a lower velocity, which allows for a longer residence time in the canister and ensures that the canister bed material in the filter bed captures more vapor before reaching the atmosphere.

[0006] It should be noted that the above summary is intended to introduce, in a simplified form, a selection of concepts that are further described in the following detailed description. It is not intended to identify central or essential features of the claimed subject matter, the scope of which is determined solely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited solely to implementations for solving the disadvantages noted above or in any other part of this disclosure. Fig. Figure 1 is a schematic diagram of an internal combustion engine and an associated emission control system. Fig. 2 shows an exemplary method for operating an internal combustion engine with a fuel vapor recovery system according to the disclosure. Fig. 3 shows exemplary diagrams of operating states of a vent valve and purge valve during various conditions according to the disclosure.

[0007] The following description relates to systems and methods for operating an internal combustion engine having a fuel vapor recovery system such as that described in Fig. 1. The fuel vapor recovery system may include a fuel vapor canister and a three-position canister vent valve that can be adjusted to provide different amounts of vent to the fuel vapor canister during different conditions, as shown in the Fig. 2 and Fig. 3 shown.

[0008] Fig. 1 is a schematic representation of a vehicle system 6. In some examples, vehicle system 6 may be a hybrid vehicle system. Vehicle system 6 includes an internal combustion engine system 8 coupled to an emissions control system 23 and a fuel system 18. Internal combustion engine system 8 may include an engine 10 having a plurality of cylinders 30. Engine 10 includes an engine intake 23 and an engine exhaust 25. Engine intake 23 includes a throttle valve 62 fluidly connected to engine intake manifold 44 via an intake passage 42. Engine exhaust 25 includes an exhaust manifold 48 leading to an exhaust passage 35 that directs exhaust gas to the atmosphere. Engine exhaust 25 may include one or more emissions control devices 70, which may be mounted in a closely coupled position within the exhaust.One or more emission control devices may include a three-way catalyst, a lean NOx trap, a diesel particulate filter, an oxidation catalyst, etc. It will be appreciated that other components such as a variety of valves and sensors may be included in the engine.

[0009] Fuel system 18 may include a fuel tank 20 coupled to a fuel pumping system 21. Fuel pumping system 21 may include one or more pumps for pressurizing fuel delivered to the injectors of engine 10, such as the illustrated example injectors 66. Although only a single injector 66 is illustrated, additional injectors are provided for each cylinder. As can be seen, fuel system 18 may be a returnless fuel system, a return fuel system, or various other types of fuel systems. Vapors generated within fuel system 18 may be routed via vapor recovery line 31 to a fuel vapor canister 22 before being purged to engine intake 23. Vapor recovery line 31 may optionally include a fuel tank isolation valve.Among other functions, the fuel tank isolation valve may allow the fuel vapor canister to be maintained at a low pressure or vacuum without increasing the rate of fuel evaporation from the tank (which would otherwise occur when the fuel tank pressure is lowered). A fuel tank pressure transducer (FTPT) 120, or fuel tank pressure sensor, may be provided between the fuel tank 20 and the canister 22 to provide a determination of fuel tank pressure and for engine-off leak detection. The fuel tank pressure transducer may alternatively be located in vapor recovery line 31, purge line 28, vent line 27, or canister 22 without compromising its ability to detect leaks when the engine is off.

[0010] Fuel vapor canister 22 may be filled with a suitable adsorbent and configured to temporarily retain fuel vapors (including vaporized hydrocarbons) during fuel tank refill operations, "run-down" (i.e., vaporized fuel during vehicle operation), and other diurnal conditions. The adsorbent used, in one example, is activated carbon. Canister 22 may further include a vent line 27 that can vent gases from canister 22 to atmosphere when it stores or retains fuel vapors from fuel system 18. Vent line 27 may also allow fresh air to be drawn into canister 22 when stored fuel vapors from fuel system 18 are purged to engine intake 23 via purge line 28 and purge valve 112.Although the present example illustrates vent line 27 in conjunction with unheated fresh air, various modifications may be used. The flow of air and vapors between fuel vapor canister 22 and the atmosphere may be regulated by actuating a canister vent valve 108.

[0011] Canister vent valve 108 may be a three-way or three-position valve. Valve 108 may be adjustable, for example, between a de-energized or unenergized state, a first energized state, and a second energized state. For example, vent valve 108 may be controlled by actuating one or more solenoids (not shown) to control a state of the valve. The de-energized state may be a valve position of the valve in which no electrical current is applied to the valve, such that the valve is normally in the de-energized state until current is applied to the valve to adjust it to the first or second energized state. For example, the de-energized state of vent valve 108 may provide a first amount of venting to canister 22.This de-energized state of the vent valve may limit the amount of venting provided to the container by a first amount and may correspond to a valve position that is throttled, limited, or partially closed.

[0012] The first energized state may provide a second vent amount to the reservoir, wherein the second vent amount is greater than the first vent amount provided to the reservoir when the valve is in the de-energized state. For example, in response to certain conditions, a first amount of current may be applied to the vent valve to place the vent valve in the first energized state. In some examples, the first energized state may be a fully open valve position such that a vent limiting amount provided to the reservoir in the first energized state is less than the vent limiting amount provided to the reservoir when the valve is in the de-energized state. The first energized, or fully open, state may be used during purge conditions, as further described below with respect to Fig. 2 described in more detail.

[0013] The second energized state may provide a third amount of venting to the container, wherein the third amount of venting is less than the first amount of venting provided to the container when the valve is in the de-energized state. For example, in response to certain conditions, a second amount of current that is different from the first amount of current used in the first energized state may be applied to the vent valve to place the vent valve in the second energized state. In some examples, the second energized state may be a fully closed valve position such that substantially no venting is provided to the container. This second energized, or fully closed, state may be monitored during monitoring conditions, e.g.during a leak test, to completely isolate the fuel vapor system from the atmosphere, as described below with regard to . Fig. 2 described in more detail.

[0014] To reduce vapor formation and more effectively utilize the vapor storage capacity, the fresh air vent valve 108 can be limited to a valve position corresponding to the de-energized state during diurnal operations, such as refueling. In this state, the valve can be partially open, so that a valve opening amount in this de-energized position is smaller than a valve opening amount in the first energized state. By limiting or restricting the fresh air path at the canister vent during diurnal operations, a positive pressure can build up in the fuel evaporation system, leading to a reduction in vapor formation.By limiting the vessel vent in the de-energized state, steam can also be forced across the vessel bed at a lower velocity, allowing a longer residence time in the vessel, ensuring that the vessel bed material in the filter bed captures more steam before reaching atmosphere. Because the purge system can be isolated from the vessel vent valve, the limited vent valve position in the de-energized state can allow pressure to build up in the system, reducing steam buildup rates. As pressure increases, the steam would slowly migrate towards the vent valve and atmosphere, but due to the longer sweep time of the vessel bed, steam can be more effectively stored in the filter bed before reaching atmosphere.

[0015] During purge monitoring conditions, the vent valve can be forced closed by setting the valve to the second energized state, and pressure and temperature changes can be monitored to check the isolated system for leaks or other causes of performance degradation. During purge conditions, the vent valve can be forced open by setting the valve to the first energized state, allowing air from the atmosphere to be drawn into the canister to purge fuel from the canister and deliver the purged fuel to an engine intake.

[0016] Such a process approach can reduce costs associated with a non-integrated refueling canister-only system (NIRCOS) by using existing fuel evaporative emission control systems, such as conventional plastic fuel tanks instead of metal ones, and standard valves instead of costly fuel tank isolation valves (FTIVs). Furthermore, the canister vent valve position can be adjusted in the de-energized state to allow the maximum pressure to build up that can be handled by the existing system, rather than increasing the thickness of the fuel tank or other components in the system.

[0017] Vehicle system 6 may also include control system 14. Control system 14 is illustrated as receiving information from a plurality of sensors 16 (various examples of which are described herein) and sending control signals to a plurality of actuators 81 (various examples of which are described herein). Sensors 16 may include, as one example, exhaust gas sensor 126, which is coupled upstream of the emissions control device, temperature sensor 128, and pressure sensor 129. Other sensors, such as pressure, temperature, air / fuel ratio, and composition sensors, may be coupled at various locations in vehicle system 6, as discussed in more detail herein. As another example, actuators may include fuel injector 66, valve 112, and throttle body 62. Control system 14 may include a controller 12.The controller may receive input data from various sensors, process that input data, and trigger the actuators in response to the processed input data based on a programmed instruction or code instruction sequence according to one or more routines. An example control routine is described below with reference to . Fig. 2 described.

[0018] Fig. 2 shows an exemplary method 200 for operating an internal combustion engine with a fuel vapor recovery system by adjusting the state of a three-position canister vent valve, such as valve 108 described above. In particular, the canister vent valve may be selectively adjusted to provide a first amount of venting to the fuel vapor canister during a diurnal condition, a second amount of venting to the fuel vapor canister in excess of the first amount during a purge condition, and a third amount of venting to the fuel vapor canister during a monitor condition, the third amount being less than the first amount.

[0019] At 202, method 200 includes determining whether diurnal conditions exist. Diurnal conditions may be engine or vehicle operating conditions where temperature changes cause accelerated evaporation of fuel from the fuel tank. For example, diurnal conditions may involve a refueling operation or other engine-off conditions where ambient temperatures increase. For example, a diurnal condition may occur while the engine is not running. Determining a diurnal condition may be based on various sensors in the vehicle system, such as pressure and temperature sensors, used to determine an amount of fuel evaporation from the fuel tank. For example, if a fuel evaporation amount exceeding a threshold is detected, diurnal conditions may exist.If diurnal conditions exist at 202, method 200 continues to 204.

[0020] At 204, method 200 includes providing a first venting amount to the fuel vapor canister. For example, vent valve 108 may be adjusted to limit a fuel vapor canister venting amount by a first amount. As noted above, vent valve 108 may include three different positions corresponding to a de-energized state, a first energized state, and a second energized state. When no power is applied to vent valve 108, the valve may be in the de-energized or de-energized state such that the valve is partially closed and limits the supply of fresh air to the canister. Thus, at 206, method 200 may include adjusting the vent valve to a de-energized state or maintaining the vent valve in the de-energized state.In some examples, this may involve removing or interrupting a power or actuation source applied to the valve so that the valve returns to its de-energized, limited state.

[0021] At 208, method 200 includes closing a purge valve or maintaining the purge valve closed. For example, purge valve 112 may be a normally closed valve and may be closed or maintained closed during diurnal operations. As described further below, in some examples, purge valve 112 may remain closed until a purge operation is initiated.

[0022] If diurnal conditions are not present at 202, method 200 proceeds to 210 to determine if purge conditions are present. Purge conditions may be confirmed based on various engine and vehicle operating parameters, including: an amount of hydrocarbons stored in canister 22 exceeding a threshold, an emission control device 70 temperature exceeding a threshold, a temperature of canister 22, fuel temperature, number of engine starts since the last purge operation (such as the number of starts exceeding a threshold), an amount of time elapsed since the last purge operation, fuel properties, and various others. As another example, a purge could occur for on-board diagnostic (OBD) hardware check or altitude adjustment of engine operation. If purge conditions are present at 210, method 200 proceeds to 212.

[0023] At 212, method 200 includes initiating a purge operation. Initiating a fuel vapor purge operation may include sending a request to open the vent valve coupled to the fuel vapor canister and maintaining the vent valve open at a desired value throughout the duration of the fuel vapor purge operation. For example, a controller may open (e.g., by energizing a canister vent solenoid) the canister vent valve 108 to a fixed open position corresponding to the first energized state and maintain the vent valve open in the fixed position throughout the fuel vapor purge operation without adjustments to the vent valve position. By maintaining the vent valve open in a fixed position during a fuel vapor purge operation, fresh air may be drawn through vent line 27 to purge fuel vapor stored in the fuel vapor canister.

[0024] However, in other examples, as described further below, the vent valve may first be adjusted to the de-energized state so that the canister vent is restricted immediately after purge is initiated. For example, by providing increased flow restriction upon purge initiation, the purge valve 112 in purge line 28 may be opened more quickly, and then, as described further below, after the purge valve 112 is fully open, the vent valve may be adjusted to the first energized state to fully open the canister vent 108.

[0025] In some examples, initiating a purge operation may also include calculating a purge vacuum for a desired purge rate. For example, air pressure and air temperature in line 28 or intake manifold 44 may be determined so that component adjustment may be performed to achieve a desired purge rate. For example, controller 12 may adjust purge valve 112 to achieve the desired purge flow rate.

[0026] At 214, method 200 may include providing the first vent amount to the fuel vapor canister after initiating the purge operation. At 216, method 200 may include, for example, adjusting the vent valve to the de-energized state such that the vent valve limits the flow of air drawn from the atmosphere through the canister when the purge valve is adjusted from a closed position to an open position.

[0027] At 218, method 200 includes opening the purge valve or maintaining the purge valve open. For example, while the vent valve 108 is limiting the air drawn through canister 22, the purge valve may be adjusted at a rate based on the limiting amount provided by the vent valve 108. The vent valve may remain in the limited position until the purge valve 112 is fully open or in its final purge position, where the final position may be based on a desired purge rate.

[0028] At 220, method 200 includes providing a second vent amount to the fuel vapor canister after the purge valve is adjusted to its final position. At 222, method 200 may, for example, include adjusting the vent valve to a first energized state. Here, the second vent amount is greater than the first vent amount provided to the canister by the vent in the de-energized state. The increased second vent amount may correspond to the first energized state of the vent valve 108 and may be a fully open valve position. The vent valve may be adjusted from the de-energized state to the fully open position after a duration following the purge valve opening. The duration may, for example, be based on the time it takes for the purge valve to adjust to its final open position.

[0029] At 224, method 200 includes determining whether the canister is purged. This may include, for example, determining whether an amount of fuel vapor purged from the canister falls below a threshold level. The amount of fuel vapor may be a fuel concentration in the purge stream (fuel fraction), a fuel mass flow rate, etc. For example, if the amount of fuel vapor purged in the canister is less than the threshold level or an amount of fuel stored in the canister falls below a threshold, the purging process may be terminated. If the canister is not purged at 224, method 200 includes maintaining the purge valve open and providing the second vent amount to continue the canister purge.

[0030] If the canister is purged at 224, or if purging is complete, method 200 continues to 226. At 226, method 200 includes closing the purge valve and, at 228, providing the first vent amount to the fuel vapor canister. At 230, the method includes, for example, adjusting the vent valve to the de-energized state. Additionally, during a transition between purge and non-purge conditions, fuel injection to the engine may be adjusted. Adjusting may include, for example, adjusting fuel injection in response to purge flow during purge conditions, and adjusting fuel injection in response to air flow during non-purge conditions.

[0031] If purge conditions are not present at 210, method 200 proceeds to 232 to determine if monitoring conditions are present. For example, monitoring conditions may include leak check conditions and may be based on an engine off condition or an engine on condition. Leak checks may be scheduled to occur periodically in response to engine shutdowns, for example. During monitoring conditions, the evaporative emission control system may be sealed off from the atmosphere and monitored for leaks or other causes of performance degradation. If monitoring conditions are present at 232, method 200 proceeds to 234.

[0032] At 234, method 200 includes providing a third vent amount to the evaporative canister. For example, during a monitoring condition, a third vent amount may be provided to the canister, wherein the third vent amount is less than the first vent amount provided by the vent valve in the de-energized state. Thus, at 236, method 200 includes adjusting the vent valve to a second energized state to adjust the vent valve to an energized closed position to seal the canister from the atmosphere such that no canister venting occurs during monitoring. At 238, method 200 further includes opening the purge valve or maintaining the purge valve open.

[0033] At 240, method 200 includes monitoring pressure changes in the evaporative emission control system to determine if a leak is present or if other causes of performance degradation in the system are present. At 242, method 200 includes determining if monitoring has been completed. If monitoring has not been completed at 242, method 200 continues monitoring pressure changes at 240. However, if monitoring has been completed at 242, method 200 continues to 244. At 244, method 200 includes providing a first amount of vent to the canister. At 246, method 200 may include adjusting the vent valve to the de-energized state such that the vent valve is again partially open in a limited position.

[0034] Fig. Figure 3 shows exemplary diagrams of operating states of a vent valve and purge valve during diurnal, purge, and monitoring conditions. In particular, Fig. 3 at 302, a graph indicating a state of canister vent valve 108 under diurnal, monitoring, and purge conditions. At 302, the state labeled "0" corresponds to the de-energized valve state in which the valve is partially open, the state labeled "1" corresponds to the first energized valve state in which the valve is fully open, and the state labeled "2" corresponds to the second energized valve state in which the valve is fully closed. At 304, Fig. 3 is a graph showing the position of purge valve 112, either open or closed, under diurnal, monitoring and purge conditions.

[0035] Before time t1, a diurnal condition exists and the purge valve is closed and the vent valve is in the de-energized state, providing a limited amount of venting to the fuel vapor canister. The diurnal condition can be, for example, a refueling operation where the engine is not running. At t1, a monitoring condition begins; for example, a leak test can be initiated while the engine is off. Thus, at t1, the vent valve is moved to the second energized state to fully close the vent valve and terminate the venting provided to the canister. Here, the purge valve remains closed and the system is monitored during the monitoring condition from time t1 to time t2 to detect leaks in the system.

[0036] At time t2, the monitoring condition ends and a second diurnal condition begins. For example, the engine may remain off at time t2 and ambient temperatures may be rising. Thus, at time t2, power is removed from the vent valve, causing the vent valve to be de-energized to provide limited venting of the fuel vapor canister until time t3, when a purge event is initiated. For example, at time t3, the engine may be running and an amount of fuel vapor stored in the canister may exceed a threshold, causing a purge event to be initiated. Thus, the purge valve may be commanded to open at time t3, and the vent valve may remain de-energized for a duration from time t3 to time t4 while the purge valve opens.At time t4, the vent valve can be adjusted to the first energized state, placing it in a fully open vent position to allow the fuel vapor canister to be purged. At time t5, the purging process ends and a third diurnal condition begins. Thus, at time t5, power is removed from the vent, returning the valve to its de-energized state and closing the purge valve again.

Claims

[1] A method for an internal combustion engine with a fuel vapor recovery system, comprising: Providing (204) a first venting amount to the fuel vapor canister (22) during a diurnal condition; and Providing (220) a second venting amount to the fuel vapor canister (22) during a purge condition, the second amount being greater than the first amount, further comprising: providing (234) a third canister vent amount during a monitoring condition, the third amount being less than the first amount. [2] A method for an internal combustion engine with a fuel vapor recovery system, comprising: Providing (204) a first venting amount to the fuel vapor canister (22) during a diurnal condition; and Providing (220) a second venting amount to the fuel vapor canister (22) during a purge condition, the second amount being greater than the first amount, further comprising: in response to a purge operation, adjusting a canister vent valve (108) to provide (214) the first venting amount to the fuel vapor canister (22) and then opening (218) a purge valve (112) and adjusting the canister vent valve (108) to provide (220) the second venting amount to the fuel vapor canister (22) after a period of time following the opening (218) of the purge valve (112). [3] A method for an internal combustion engine with a fuel vapor recovery system, comprising: Providing (204) a first venting amount to the fuel vapor canister (22) during a diurnal condition; and Providing (220) a second venting amount to the fuel vapor canister (22) during a purge condition, the second amount being greater than the first amount, wherein providing (204) the first venting amount at the fuel vapor container (22) includes adjusting (216) a venting valve (108) to a non-energized state, and wherein providing (220) the second venting amount at the fuel vapor container (22) includes adjusting (222) the venting valve (108) to a first energized state, further comprising: adjusting (238) the vent valve (108) to an energized closed position during a monitoring condition. [4] The method of claim 1, wherein the monitoring condition is a leakage check operation and wherein the third venting amount is substantially no venting. [5] The method of any one of claims 1, 3 and 4, further comprising: opening (218) a purge valve (112) while providing (214) the second venting amount to the fuel vapor canister (22) during the purge condition. [6] The method of any one of claims 1 to 5, further comprising: closing or maintaining closed (208) a purge valve (112) while providing (204) the first venting amount to the fuel vapor canister (22) during the diurnal condition. [7] Method according to one of claims 1 to 6, wherein the daily periodic condition is a refueling operation.

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