Evaporative emission control system and method

Abstract

The present disclosure provides "Evaporative Emission Control Systems and Methods". A method for operating a vehicle having an internal combustion engine is provided, the method comprising: regulating pressure in a fuel tank to reduce fuel tank vent emissions by scheduling engine start events based on a rate of change of fuel tank pressure, wherein the rate of change of the fuel tank pressure is determined based on ambient temperature and tank pressure.

Description

Technical Field

[0001] This disclosure relates to a vehicle having an evaporative emission control system and a method for operating the vehicle and the system. Background Technology

[0002] Vehicles already utilize sealed fuel tanks in their fuel delivery systems to reduce evaporative emissions. However, sealed fuel tanks can accumulate excessive pressure during day and night operation. Hybrid vehicles exacerbate this problem because their engines and fuel delivery systems remain unused for longer periods than in non-hybrid vehicles. Furthermore, the trend towards hybrid electric vehicle designs aimed at reducing fuel consumption leads to additional reductions in engine operating time, further worsening the problem of fuel tank pressure buildup. In previous evaporative emission control systems, regular emissions from the vapor filter and fuel tank occurred during engine operation. However, when the engine remains unused for extended periods, the pressure in the fuel tank can reach undesirable levels. Additionally, some emission requirements necessitate that fuel vapors be captured by the carbon filter only during refueling. Evaporative emission control systems that allow carbon capture only during refueling are typically called non-integrated refueling canister-only systems (NIRCOS). Therefore, in these systems, the carbon filter cannot be loaded at other times, leading to fuel tank pressure buildup. Pressure buildup can lead to overpressure within the tank, necessitating the venting of fuel vapors into the carbon filter canister, which is undesirable in NIRCOS. In other evaporative emission control systems, fuel vapors can be directly released into the environment when the fuel tank reaches its venting limit.

[0003] US 6,557,534 discloses a hybrid vehicle with a vapor control system that purges the carbon filter canister when the fuel tank pressure or the time since the last purge cycle exceeds a threshold. The inventors have recognized several drawbacks of the vehicle disclosed in US 6,557,534. For example, US 6,557,534 does not consider the effect of ambient temperature on the tank pressure or perform any predictive calculations. Therefore, the tank pressure may unexpectedly exceed the venting pressure, leading to increased evaporative emissions. Furthermore, the vapor control system in US 6,557,534 does not isolate the carbon filter canister from the fuel tank. Therefore, the vapor control system cannot comply with certain emission standards that require the carbon filter canister to be installed only during refueling. Consequently, the engine in US 6,557,534 may not be able to meet certain emission requirements, thus limiting the number of vehicles available for sale in the market. Summary of the Invention

[0004] To overcome at least some of the aforementioned problems, the inventors have developed a method for operating a vehicle with an internal combustion engine, the method comprising: regulating the pressure in the fuel tank by scheduling engine starting events based on the rate of change of fuel tank pressure to reduce fuel tank exhaust emissions, wherein the rate of change of fuel tank pressure is determined based on ambient temperature and tank pressure. In this way, the rate of change of tank pressure can be extrapolated to predict whether the tank pressure is expected to exceed the pressure that triggers fuel tank exhaust, and in response to this prediction, mitigation measures can be taken to reduce the fuel tank pressure. Therefore, the likelihood of fuel tank degradation due to overpressure conditions can be reduced, while also reducing the vapor filter load. As a result, evaporative emissions can be reduced, thereby reducing the engine's environmental impact.

[0005] It should be understood that the above-described invention is presented in a simplified form as a selection of concepts further described in the detailed embodiments. This does not imply identification of the key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims following the detailed embodiments. Furthermore, the claimed subject matter is not limited to solutions to any of the shortcomings mentioned above or in any part of this disclosure. Attached Figure Description

[0006] Figure 1 A schematic diagram of a vehicle with an internal combustion engine is shown.

[0007] Figure 2 An example of a hybrid vehicle is shown.

[0008] Figure 3 A method for regulating the pressure in the fuel tank by scheduling engine start-up events is shown.

[0009] Figure 4 This illustrates another method for regulating the pressure in the fuel tank of a hybrid vehicle by scheduling engine start-up events.

[0010] Figure 5 A method for purging a fuel vapor filter canister during engine operation is shown.

[0011] Figure 6 A method for starting an engine is shown.

[0012] Figure 7 The diagram illustrates the control strategy used to regulate the pressure in the fuel tank. Detailed Implementation

[0013] This specification relates to a vehicle with an evaporative emissions control system and a method that predicts when an overpressure condition triggering fuel tank vapor discharge will occur, taking into account the fuel tank pressure and the effect of ambient temperature on the tank pressure. When such a prediction is made, engine start-up and fuel vapor purging events are scheduled to reliably reduce the likelihood of a fuel tank overpressure condition. In this way, unnecessary carbon filter loading is avoided. Consequently, engine evaporative emissions are reduced. Furthermore, predicting when an overpressure condition will occur allows the system to effectively schedule engine start-up and vapor purging events so that, if necessary, these events do not interfere with other operations in the vehicle. Regulating the fuel tank pressure as described above also allows for faster fuel tank depressurization times (if needed) during hot weather conditions and enables the fuel tank pressure to be maintained within a desired range. In one example, overpressure prediction can be performed using the rate of pressure change in the fuel tank, calculated using the effect of tank pressure and ambient temperature on the fuel tank pressure. Therefore, the confidence level of the prediction can be increased, thereby reducing the likelihood of incorrect predictions of fuel tank vapor discharge. Figure 1 A schematic diagram of a vehicle with an internal combustion engine is shown, the internal combustion engine having an evaporative emission control system. Figure 2 An example of a hybrid electric vehicle is shown. Figure 3 This demonstrates a method for predicting when a fuel tank overpressure condition will occur and taking preventative action. Figure 4 A more detailed method is shown for predicting whether a fuel tank overpressure condition will occur and taking preventative actions to reduce the likelihood of such an overpressure condition. Figure 5 A method for purging fuel vapor filter canisters is shown. Figure 6 A method for starting the engine when a starting threshold is reached is shown. Figure 7 The graph shows an example of a strategy used to predict when a fuel tank overpressure condition will occur and to take preventative actions to reduce the likelihood of such an overpressure condition.

[0014] Figure 1 A schematic diagram of a vehicle 100 including an internal combustion engine 102 is shown. Although Figure 1 Schematic diagrams of various engines and engine system components are provided; however, it should be understood that at least some components may have the same characteristics as... Figure 1 The components shown have different spatial locations and greater structural complexity than they actually are.

[0015] Figure 1The diagram also depicts an intake system 104 that supplies air to cylinder 106. It should be understood that a cylinder may be referred to as a combustion chamber. Piston 108 is located within cylinder 106. Piston 108 is coupled to crankshaft 110 via piston rod 112 and / or other suitable mechanical components. It should be understood that crankshaft 110 may be coupled to a transmission that supplies power to the drive wheels. Although... Figure 1 An engine 102 with one cylinder is depicted. In other examples, the engine 102 may have additional cylinders. For example, the engine 102 may include multiple cylinders that can be positioned in a group.

[0016] The intake system 104 includes an intake duct 114 and a throttle valve 116 coupled to the intake duct. The throttle valve 116 is configured to regulate the airflow supplied to the cylinder 106. For example, the throttle valve 116 may include a rotatable plate that alters the airflow through which the intake air passes. In the depicted example, the throttle valve 116 feeds air to the intake duct 118 (e.g., an intake manifold). The intake duct 118 then directs the air to the intake valve 120. The intake valve 120 opens and closes to allow the intake airflow to enter the cylinder 106 at a desired time. Furthermore, in other examples, such as in a multi-cylinder engine, additional intake airflow passages may branch from the intake duct 118 and feed intake air to other intake valves. It should be understood that the intake duct 118 and the intake valve 120 are included in the intake system 104. Furthermore, Figure 1 The engine shown includes one intake valve and one exhaust valve. However, in other examples, cylinder 106 may include two or more intake valves and / or exhaust valves.

[0017] An exhaust system 122 configured to manage exhaust from cylinder 106 is also included. Figure 1 In the depicted vehicle 100, the exhaust system 122 includes an exhaust valve 124, which is designed to open and close to allow and prevent exhaust gas from flowing from the cylinder to downstream components. For example, the exhaust valve may include a lift valve having a valve stem and a valve head positioned in the closed position and sealing against the cylinder inlet.

[0018] The exhaust system 122 also includes an emission control device 126 coupled to an exhaust duct 128 downstream of another exhaust duct 130 (e.g., an exhaust manifold). The emission control device 126 may include filters, catalysts, absorbers, combinations thereof, etc., for reducing exhaust tailpipe emissions. The engine 102 also includes an ignition system 132 (e.g., spark plugs) including an energy storage device 134 designed to provide energy to the ignition device 136. Alternatively or additionally, the engine 102 may perform compression ignition.

[0019] Figure 1Fuel delivery system 138 is also shown. Fuel delivery system 138 supplies pressurized fuel to fuel injector 140. In the example shown, fuel injector 140 is a direct fuel injector coupled to cylinder 106. Alternatively or additionally, fuel delivery system 138 may also include a port fuel injector designed to inject fuel upstream of cylinder 106 into intake system 104. For example, a port fuel injector may be an injector with a nozzle that injects fuel into the intake manifold at a desired time. Fuel delivery system 138 includes fuel tank 142 and fuel pump 144 designed to flow pressurized fuel to downstream components. For example, fuel pump 144 may be an electric pump with a piston and an inlet in the fuel tank that draws fuel into the pump and delivers pressurized fuel to downstream components. However, other suitable fuel pump configurations have been contemplated. Furthermore, fuel pump 144 is shown located within fuel tank 142. Alternatively or additionally, the fuel delivery system may include a second fuel pump (e.g., a higher-pressure fuel pump) located outside the fuel tank. Fuel line 146 provides fluid communication between fuel pump 144 and fuel injector 140. Fuel delivery system 138 may include additional components, such as a higher-pressure pump, valves (e.g., check valves), return lines, etc., to enable the fuel delivery system to inject fuel at desired pressures and time intervals.

[0020] During engine operation, cylinder 106 typically undergoes a four-stroke cycle, which includes: intake stroke, compression stroke, expansion stroke, and exhaust stroke. During the intake stroke, the exhaust valve is typically closed and the intake valve is open. Air is introduced into the combustion chamber via a corresponding intake duct, and the piston moves to the bottom of the combustion chamber to increase its volume. The position of the piston near the bottom of the combustion chamber and at the end of its stroke (e.g., when the combustion chamber is at its maximum volume) is generally referred to by those skilled in the art as bottom dead center (BDC). During the compression stroke, both the intake and exhaust valves are closed. The piston moves toward the cylinder head to compress the air in the combustion chamber. The point at the end of its stroke and closest to the cylinder head (e.g., when the combustion chamber is at its minimum volume) is generally referred to by those skilled in the art as top dead center (TDC). In a process referred to herein as injection, fuel is introduced into the combustion chamber. In a process referred to herein as ignition, the fuel injected into the combustion chamber is ignited by a spark from an ignition device, resulting in combustion. However, in other examples, compression can be used to ignite the air-fuel mixture in the combustion chamber. During the expansion stroke, the expanding gas pushes the piston back to the BDC (Burning DC). The crankshaft converts this piston movement into rotational torque on the rotating shaft. During the exhaust stroke, in conventional designs, the exhaust valve opens to release any remaining combusted air-fuel mixture into the corresponding exhaust passage, and the piston returns to the TDC (Turning DC).

[0021] Vehicle 100 also includes an evaporative emission control system 148. The evaporative emission control system 148 may be included in vehicle system 149, which in some cases also includes a fuel delivery system 138. The evaporative emission control system 148 may include a fuel tank 142 and a fuel tank isolation valve 150 coupled to a vapor line 152 extending into the fuel tank 142. Specifically, the vapor line 152 extends from a region 154 above liquid fuel 155 where fuel vapor can reside into the fuel tank 142, which stores liquid fuel 155 (e.g., gasoline, diesel, alcohol, combinations thereof). Thus, in some cases, the vapor line 152 may extend through the upper portion of the top wall 156 or side wall 157 of the fuel tank. The fuel tank isolation valve 150 is designed to open and close to allow and prevent fuel vapor from flowing through it. For example, the fuel tank isolation valve 150 may be a solenoid valve with mechanical components for flow regulation. However, other suitable types of fuel tank isolation valves have been contemplated.

[0022] The evaporative emissions control system 148 also includes a fuel vapor filter 158 designed to store fuel vapor. The fuel vapor filter 158 may include a carbon section 160 (e.g., an activated carbon section) for trapping fuel vapor. When the valve is in the open position, the fuel vapor filter 158 receives fuel vapor from the fuel tank isolation valve 150 via a vapor line 162. A pressure sensor 164 is shown coupled to the vapor line 152. Therefore, the pressure sensor 164 may be configured to monitor the pressure in the fuel tank 142. For example, the pressure sensor 164 may in one case be a pressure transducer. A buffer filter 166 may also be included in the evaporative emissions control system 148, between the fuel vapor filter 158 and the engine 102. The buffer filter can be used to reduce any large hydrocarbon or fuel vapor spikes that will enter the engine to prevent an overly rich condition. Therefore, the buffer filter can be used to suppress any fuel vapor spikes flowing between the fuel tank and the engine.

[0023] In the example shown, the filter canister purge valve 168 is located in the vapor line 170, which extends between the fuel vapor filter canister 158 and the intake system 104, and particularly the intake duct 118 at the junction 172. However, in other examples, the fuel vapor may be directed to other suitable locations within the intake system 104. At the junction 172, the vapor line 170 leads to the intake duct 118.

[0024] The evaporative emissions control system 148 may also include an evaporative leak check module (ELCM) 173. ELCM 173 includes the three components depicted in the example: a pump 174, an ELCM pressure sensor 175, and a valve 176 (e.g., a switching valve). Pump 174 may be a vacuum pump, and the pump and valve 176 may operate sequentially during a purging operation to allow upstream airflow through the fuel vapor filter canister 158 and ultimately into the intake system 104. In other examples, ELCM 173 may include only valve 176 and pump 174, or only valve 176. ELCM 173 facilitates airflow into the fuel vapor filter canister 158 to allow fuel vapor to flow through vapor line 170 and into the intake system 104. ELCM 173 is shown coupled to line 177, which is coupled to the fuel vapor filter canister 158.

[0025] Figure 1 The controller 180 in vehicle 100 is also shown. Specifically, the controller 180 is in Figure 1The computer, shown as a conventional microcomputer, includes: a microprocessor unit 181, an input / output port 182, a read-only memory 183, a random access memory 184, a keep-alive memory 185, and a conventional data bus. The controller 180 is configured to receive various signals from sensors coupled to the engine 102. These sensors may include an engine coolant temperature sensor 179, an exhaust component sensor 186, an exhaust airflow sensor 187, an intake airflow sensor 188, a manifold pressure sensor 189, an engine speed sensor 190, a fuel tank pressure sensor 191, an ambient temperature sensor 192, a pressure sensor 164, etc. Additionally, the controller 180 is also configured to receive throttle position (TP) from a throttle position sensor 193 coupled to a pedal 194 actuated by the operator 195.

[0026] Additionally, controller 180 can be configured to trigger one or more actuators and / or send commands to components. For example, controller 180 can trigger adjustments to throttle valve 116, fuel injector 140, fuel tank isolation valve 150, ELCM 173, fuel pump 144, filter purge valve 168, etc. Specifically, in one example, controller 180 can send signals to actuators in fuel tank isolation valve 150 to open and / or close valves for valve adjustment. Furthermore, controller 180 can be configured to send control signals to actuators in fuel pump 144 and fuel injector 140 to control the amount and timing of fuel injection supplied to cylinder 106. Controller 180 can also send control signals to throttle valve 116 to change engine speed. Other adjustable components receiving commands from the controller can also function in a similar manner.

[0027] Therefore, controller 180 receives signals from various sensors and, based on the received signals and instructions stored in the controller's memory (e.g., non-transitory memory), employs various actuators to adjust engine operation. Thus, it should be understood that controller 180 can send and receive signals from evaporative emission control system 148. For example, adjusting fuel tank isolation valve 150 may include a command device actuator adjusting components in the fuel tank isolation valve to trigger the opening and closing of the valve, as described above.

[0028] In yet another example, the adjustment amounts for components, devices, actuators, etc., can be empirically determined and stored in predetermined lookup tables and / or functions. For example, one table may correspond to conditions related to the position of the filter canister purge valve, while another table may correspond to conditions related to the position of the fuel tank isolation valve. Furthermore, it should be understood that the controller 180 can be configured to implement the methods, control strategies, etc., described herein.

[0029] In one example, controller 180 may include instructions stored in memory, which can be executed by a processor to monitor the pressure in the fuel tank and the ambient temperature. In one example, monitoring pressure and temperature may include receiving and interpreting signals from pressure and temperature sensors. Controller 180 may also include instructions for using the monitored fuel tank pressure and ambient temperature to determine whether the pressure in the fuel tank is expected to exceed a threshold pressure. The threshold pressure may be a venting threshold, which triggers the venting of fuel vapors from the fuel tank 142 to the evaporative emissions control system 148. In one example, a prediction related to the venting threshold may be initiated when the fuel pressure in the tank reaches a trigger pressure less than the venting threshold. The venting threshold is the threshold that triggers a fuel vapor venting event from the fuel tank to the evaporative emissions control system. Furthermore, the venting threshold may be determined based on the shape, size, material construction, etc., of the fuel tank. In one example, the venting threshold may be a pressure in the range of 27 kPa to 32 kPa. However, many suitable venting thresholds have been envisioned.

[0030] In a specific example, venting prediction may include generating a pressure profile using readings from an in-chamber pressure sensor and an ambient temperature sensor. The rate of change (e.g., slope) of the pressure profile can then be calculated. This rate of change can then be used to predict whether and / or when the in-chamber pressure reaches a venting threshold.

[0031] When the controller determines that the tank pressure is expected to reach the venting threshold within a predetermined time period, the engine start event and the fuel tank vapor purging event are scheduled by the controller together. Therefore, the engine start event and the fuel vapor purging event can then be initiated at the scheduled time. In this way, undesirable fuel vapor filter loading is avoided, which reduces evaporative emissions. For example, if the fuel tank reaches the venting limit and is vented while the fuel vapor filter is full, fuel vapor can be released into the surrounding atmosphere. Furthermore, the reliability of the fuel tank vapor purging strategy is improved compared to other systems that do not predict when the fuel tank will reach an overpressure condition and do not schedule engine start to prevent overpressure conditions. It should be understood that the fuel tank vapor purging event can be scheduled independently of the amount of fuel vapor stored in the fuel vapor filter coupled to the fuel tank. In this way, during conditions where engine operation is not required, such as when the electric motor is operating, the engine can be forced to run to facilitate fuel tank vapor purging. For example, an engine starting event can be scheduled in response to a prediction that the fuel tank will reach a bleed threshold when the electric motor is running (e.g., powering the vehicle) and that the energy storage device has stored more energy than the threshold. In another example, an engine starting event can be scheduled in response to a prediction of a bleed threshold when the electric motor is operating (e.g., powering the vehicle), an engine speed below the threshold, and the energy storage device having the desired energy stored therein. Furthermore, the engine can be shut off after the fuel tank pressure drops below a second threshold pressure. In one example, the second threshold pressure can be a pressure in the range of 7 kPa to 15 kPa. However, various threshold pressures can be used. In this way, if needed, the engine can operate sequentially with in-tank fuel vapor purging for only the duration required to reach a safe pressure level in the fuel tank. Therefore, in-tank fuel vapor purging operations can be implemented efficiently.

[0032] refer to Figure 2 The figure schematically depicts a vehicle 201 having a hybrid drive system 200. The hybrid drive system 200 includes an internal combustion engine 202. It should be understood that the hybrid drive system 200 may include... Figure 1 Of the vehicles shown in 100. Therefore, Figure 2 The vehicle 201 and engine 202 shown may include the above reference. Figure 1 At least a portion of the features, components, systems, etc. of the vehicle 100 and engine 102 described, or vice versa.

[0033] Engine 202 is coupled to transmission 204. Transmission 204 may be a manual transmission, an automatic transmission, or a combination thereof. Additionally, it may include various additional components, such as a torque converter and / or other gears such as a final drive unit. Transmission 204 is shown coupled to drive wheels 206, which in turn contact the road surface 208.

[0034] In this exemplary embodiment, the hybrid drive system 200 also includes an energy conversion device 210, which may include a motor, a generator, etc., and combinations thereof. The energy conversion device 210 is further shown coupled to an energy storage device 212, which may include a battery, a capacitor, a flywheel, a pressure vessel, etc. The energy conversion device can be operated to absorb energy from vehicle motion and / or the engine and convert the absorbed energy into an energy form suitable for storage by the energy storage device (i.e., providing generator operation). The energy conversion device can also be operated to supply output (power, work, torque, speed, etc.) to the drive wheels 206 and / or the engine 202 (i.e., providing motor operation). It should be understood that in some embodiments, the energy conversion device may include only a motor, only a generator, or both a motor and a generator, in addition to including various other components for providing appropriate energy conversion between the energy storage device and the vehicle drive wheels and / or the engine.

[0035] The depicted connections between the engine 202, energy conversion device 210, transmission 204, and drive wheels 206 indicate the transfer of mechanical energy from one component to another, while the connection between the energy conversion device and the energy storage device indicates the conversion of various forms of energy, such as electrical and mechanical. For example, torque can be transmitted from the engine 202 via the transmission 204 to drive the vehicle drive wheels 206. As described above, the energy storage device 212 can be configured to operate in generator mode and / or motor mode. In generator mode, the hybrid drive system 200 absorbs some or all of the output from the engine 202 and / or transmission 204, which reduces the amount of drive output or braking torque delivered to the drive wheels 206. For example, this operation can be employed to achieve efficiency gains through regenerative braking, improved engine efficiency, etc. Furthermore, the output received by the energy conversion device can be used to charge the energy storage device 212. In motor mode, the energy conversion device can, for example, supply mechanical output to the engine 202 and / or transmission 204 using electrical energy stored in a battery.

[0036] Hybrid drive embodiments may include a full hybrid system, wherein the vehicle may operate on the engine, only the energy conversion device (e.g., a motor), or a combination of both. Assisted or mild hybrid configurations may also be employed, where the engine is the primary torque source, and the hybrid drive system is used to selectively deliver additional torque, such as during accelerator pedal operation or other conditions. Furthermore, a starter / generator and / or intelligent alternator system may be used. (Refer to above) Figure 2 The various components described can be made from, for example Figure 1 The vehicle controller 180 shown is controlled by the vehicle controller.

[0037] As should be understood from the foregoing, the exemplary hybrid drive system 200 can have various operating modes. In a full hybrid implementation, for example, the drive system can operate using the energy conversion device 210 (e.g., an electric motor) as the sole torque source to propel the vehicle. In one example, this "electric only" operating mode can be employed during braking, low speeds, stopping at traffic lights, etc. However, in other examples, the "electric only" mode can be implemented under a wider range of operating conditions, such as at higher speeds. In another mode, the engine 202 is engaged and acts as the sole torque source to power the drive wheels 206. In yet another mode, which may be called an "auxiliary" mode, the energy conversion device 210 can supplement and cooperate with the torque provided by the engine 202. As indicated above, the energy conversion device 210 can also operate in generator mode, where torque is absorbed from the engine 202 and / or the transmission 204. Furthermore, the energy conversion device 210 can be used to increase or absorb torque during transitions between different combustion modes of the engine 202 (e.g., during transitions between spark ignition and compression ignition modes). Additionally, an external energy source 214 can provide power to the energy storage device 212. The external energy source 214 can be, for example, a charging station socket or other suitable power outlet, a solar panel, a portable energy storage device, etc.

[0038] Figure 3 A method 300 for operating a vehicle with an internal combustion engine is shown, the method reducing evaporative emissions. For example, method 300, and other methods described herein, can be found via the reference above. Figure 1 and Figure 2 The methods described herein can be implemented using other suitable vehicles, engines, systems, and components. However, in other examples, the methods 300 and / or other methods described herein can be implemented using other suitable vehicles, engines, systems, and components.

[0039] At point 302, the method includes determining operating conditions. These operating conditions may include fuel pressure within the fuel tank, ambient temperature, engine speed, engine load, manifold air pressure, throttle position, exhaust composition, exhaust temperature, engine temperature, etc. It should be understood that pressure profiles may be generated based on fuel tank pressure and ambient temperature. Furthermore, operating conditions may be determined based on signals transmitted from sensors in the engine and / or vehicle. Additionally or alternatively, in some examples, certain operating conditions may be inferred from other operating parameters.

[0040] Next, at 304, the method includes determining whether the fuel pressure inside the tank is expected to exceed a first threshold pressure based on the rate of change of the fuel tank pressure inferred from the fuel pressure inside the tank and the ambient temperature. As previously discussed, the first threshold pressure may be a venting threshold that triggers the discharge of fuel vapor from the fuel tank. The first threshold pressure may be, for example, a pressure in the range of 27 kPa to 32 kPa. However, many different pressure thresholds have been envisioned. Fuel tank pressure prediction can also be performed independently of fuel vapor filter loading. For example, different methods, such as those described herein, can be implemented when the vapor filter is overloaded. Figure 5 The method described.

[0041] If it is determined that the fuel pressure in the tank is not expected to exceed the first threshold pressure (No at 304), the method proceeds to step 305. At step 305, the method includes maintaining the current engine operating parameters. After step 305, the method returns to step 302. However, if it is determined that the fuel pressure in the tank is expected to exceed the first threshold pressure (Yes at 304), the method proceeds to 306.

[0042] At 306, the method includes: regulating fuel tank pressure to reduce fuel tank exhaust emissions. Regulating the fuel tank pressure may include steps 308-314. At 308, the method includes: scheduling an engine starting event, wherein the starting event is scheduled before a time when the fuel tank pressure is expected to exceed a first threshold pressure. Scheduling the engine starting event may include: initiating combustion in the engine cylinders via scheduling fuel injection and cylinder ignition. In this way, the engine can be operated to generate a vacuum in the intake system to facilitate vapor purging operations.

[0043] At 310, the method includes scheduling a fuel tank vapor purge event. It should be understood that the fuel tank vapor purge event can be coordinated with an engine start-up event. For example, the fuel tank vapor purge event can be scheduled at a time interval after a start-up event occurs.

[0044] At 312, the method includes initiating an engine start-up event at a planned time. Next, at 314, the method includes initiating a fuel tank vapor purging event after initiating the engine start-up event at the planned time. Initiating the fuel tank vapor purging event may include opening the fuel tank isolation valve, the filter canister purge valve, and the valves in the ELCM. Initiating the fuel tank vapor purging event may also include operating the pump in the ELCM. In this way, a vacuum can be generated in the engine's intake system, and fuel vapor from the fuel tank can then be purged to prevent overpressure conditions in the canister. Therefore, the likelihood of fuel tank degradation due to overpressure conditions is reduced, while also reducing evaporative emissions.

[0045] At 316, the method includes determining whether the fuel tank pressure is below a second threshold pressure. The second threshold pressure may correspond to a safe pressure level in the fuel tank that is lower than a first threshold pressure. For example, in one example, the second threshold pressure may be a pressure in the range of 7 kPa to 15 kPa. However, various threshold pressures have been envisioned. In this way, when the fuel tank reaches a safe pressure level where overpressured fuel tank degradation is unlikely, the purging operation can be interrupted and the engine can be shut down.

[0046] If it is determined that the fuel tank pressure is not lower than the second threshold pressure (No at 316), the method moves to 318. At 318, the method includes maintaining engine operation and fuel tank purging operation. In this way, engine and steam purging operations can be continuously performed when it is determined that the fuel tank pressure is not lower than the second threshold.

[0047] On the other hand, if it is determined that the fuel tank pressure is below the second threshold pressure (yes at 316), the method proceeds to 320. At 320, the method includes interrupting the fuel tank vapor purging operation. For example, the filter canister purge valve may be closed and / or the ELCM may be shut off. Next, at 322, the method includes shutting off the engine. It should be understood that in the case of a hybrid vehicle, the electric motor can be operated after the engine is shut off. Specifically, in one example, the electric motor may stop at step 312 when the engine is started and start at step 322 when the engine is shut off. However, in other examples, the electric motor may be operated while performing steps 302-322. Furthermore, in other examples, the electric motor may not operate during steps 302-322, such as when the hybrid vehicle is briefly stopped, such as in traffic jams, at parking lights, etc.

[0048] Go to Figure 4 The figure depicts a method 400 for operating a vehicle having an internal combustion engine and an electric motor, the method reducing evaporative emissions. At 402, the method includes determining operating conditions that may include steps 404-406. At 404, the method includes determining fuel tank pressure, and at 406, the method includes determining ambient temperature. Additionally, other operating conditions, such as engine speed, engine load, manifold air pressure, throttle position, etc., may be determined.

[0049] At 408, the method includes: determining whether the chamber pressure sensor is functioning as required. Determining whether the chamber pressure sensor is functioning as required may include: determining whether a signal is being received from the chamber pressure sensor and whether the pressure sensor signal is within the expected range.

[0050] If it is determined that the internal pressure sensor is not functioning as required (No at 408), the method ends. However, if it is determined that the internal pressure sensor is functioning as required (Yes at 408), the method proceeds to 410.

[0051] At 410, the method includes determining whether the engine is off. If the engine is not off (no at 410), the method proceeds to 412. At 412, the method includes maintaining engine operation. After 412, the method returns to 402. However, in other examples, the method may end after step 412.

[0052] On the other hand, if it is determined that the engine is off (yes at 410), the method proceeds to 414. At 414, the method includes: determining whether the fuel tank pressure is expected to exceed a first threshold pressure. The first threshold pressure may be a pressure in the range of 27 kPa to 32 kPa. The first threshold pressure may correspond to the pressure that triggers a fuel vapor venting event from the fuel tank to the evaporative emissions control system. In some examples, fuel vapor may be vented into the surrounding environment. It should be understood that a first threshold pressure may be set to trigger such venting to prevent fuel tank degradation. Furthermore, the prediction that the fuel tank pressure exceeds the first threshold pressure may be based on the above reference. Figure 3 The described techniques are used to determine, for example, the rate of pressure change and extrapolate predicted pressure based on the rate of pressure change.

[0053] If it is determined that the fuel tank pressure is not expected to exceed a first threshold pressure (No at 414), the method moves to 416, where the method includes maintaining the engine off. It should be understood that maintaining the engine off may include preventing combustion operation in the cylinders of the engine. On the other hand, if it is determined that the fuel tank pressure is expected to exceed the threshold (Yes at 414), the method moves to 418. At 418, the method includes scheduling a start-up event, and at 420, the method includes scheduling a fuel tank vapor purge event. The start-up event and the fuel tank purge event can be scheduled before the time when the fuel tank pressure is expected to exceed the first threshold. Furthermore, it should be understood that the fuel tank purge event can be scheduled after engine start-up. In this way, predictive techniques can be used to trigger fuel tank vapor purge to reduce evaporative emissions.

[0054] At 422, the method includes initiating an engine start-up event at a scheduled time. Next, at 424, the method includes initiating a fuel tank vapor purging event at a scheduled time. Initiating the fuel tank vapor purging event may include opening the fuel tank isolation valve, the filter purge valve, and the valves in the ELCM. Initiating the fuel tank vapor purging event may also include operating the pump in the ELCM. In this way, the pressure in the fuel tank can be reduced while avoiding an increase in evaporative emissions.

[0055] At 426, the method includes determining whether the fuel tank pressure is below a second threshold pressure. In one example, the second threshold pressure may be a pressure in the range of 7 kPa to 15 kPa. If the fuel tank pressure is not below the second threshold pressure (no at 426), the method proceeds to 428, where the method includes maintaining engine operation and fuel tank vapor purging operation. Alternatively, if the fuel tank pressure is below the second threshold pressure (yes at 426), the method proceeds to 430. At 430, the method includes interrupting the fuel tank vapor purging operation and initiating engine shutdown. (Refer to the above...) Figure 3 As discussed, the electric motor in the vehicle can be operated during steps 402-430. In some cases, the electric motor can be shut off at step 422 and restarted at step 430. In this way, engine operation and electric motor operation can be coordinated to improve vehicle efficiency.

[0056] Figure 5 A method 500 for purging a fuel vapor filter canister based on canister loading is shown. It should be understood that method 500 can be performed independently of... Figure 3 and Figure 4 This is achieved through a method for predicting fuel tank vapor exhaust. At point 502, the method includes: determining operating conditions. These operating conditions may include fuel vapor filter load, engine speed, engine load, manifold air pressure, throttle position, manifold airflow, etc.

[0057] At 504, the method includes determining whether the engine is running. If it is determined that the engine is not running (No at 504), the method ends. Conversely, if it is determined that the engine is running (Yes at 504), the method proceeds to 506. At 506, the method includes determining whether fuel vapor filter canister purging is desired. This determination may be based on the vapor level in the canister. If it is determined that fuel vapor filter canister purging is undesirable (No at 506), the method returns to 502. Conversely, if it is determined that fuel vapor filter canister purging is desired, the method proceeds to 508, where the method includes opening the canister purging valve. Next, at 510, the method includes opening the ELCM valve. Additionally, in one example, the ELCM pump may also be opened at step 510. Method 500, when the fuel vapor filter canister is full, enables a separate purging strategy independent of the fuel tank vapor purging operation.

[0058] Figure 6 A method 600 for starting an engine is shown. It should be understood that method 600 can be used independently of... Figure 3 and Figure 4This is achieved through a predictive fuel tank vapor exhaust method implemented in method 600. Specifically, in some examples, the engine start initiated in method 600 can override the engine start and stop control strategies in methods 300 and 400. Furthermore, it should be understood that method 600 can be implemented only when the engine is off. Additionally, method 600 can be implemented during the operation of the electric motor in the vehicle.

[0059] At 602, the method includes: determining operating conditions. These operating conditions may include fuel vapor filter load, engine speed, engine load, manifold air pressure, throttle position, manifold airflow, energy storage device charging status, duration between refueling events, and refueling event magnitude, etc.

[0060] Next, at 604, the method includes: determining whether an engine starting threshold has been reached. The engine starting threshold may include a condition where the fuel vapor filter canister load exceeds a threshold. For example, the fuel vapor filter canister load may be close to its upper limit, and therefore the engine may automatically start to facilitate a filter canister purging operation. In another example, the starting threshold may include: the fuel tank pressure exceeding a threshold pressure (such as referenced...). Figure 3 and Figure 4 The condition of the first threshold pressure discussed. In this way, overpressure conditions in the fuel tank can be mitigated. In yet another example, fuel usage time (e.g., the duration between refueling events) can be used as a starting threshold to prevent fuel degradation in the tank due to fuel stagnation. In yet another example, the amount of energy stored in an energy storage device can be used as a starting threshold. For example, if the amount of energy stored in a battery powering an electric motor drops below a threshold, the engine can be started to generate power. In yet another example, it can be determined whether a threshold number of refueling events has been reached and, in response to this determination, the engine can be started (e.g., directly).

[0061] If it is determined that the engine starting conditions have not been met (No at 604), the method returns to 602. Conversely, if it is determined that the engine starting conditions have been met (Yes at 604), the method proceeds to 606. At 606, the method includes initiating an engine start. A steam purging strategy can also be implemented when a start is initiated in response to a steam filter canister loading threshold, wherein fuel vapor flows from the steam filter canister into the intake system. For example, the filter canister purge valve can be opened and the ELCM can be operated to initiate or increase the airflow through the fuel vapor filter canister.

[0062] Now go to Figure 7 Exemplary Figure 700 graphically depicts a fuel tank vapor purging method (such as...) Figure 4 and Figure 5The method shown includes ambient temperature, fuel tank pressure, engine operating conditions, and electric motor operating conditions during the process. Furthermore, Figure 700 corresponds to the above reference. Figure 1 and Figure 2 The vehicles, engines, and components described. Figure 7 The examples are drawn to scale, even without numerical labels for each point. This allows for estimation of relative timing differences by plotting the dimensions. However, other relative timings can be used if needed. The pressure curve is indicated at 702, and the ambient temperature curve at 704. It should be understood that ambient temperature affects fuel tank pressure, and therefore the pressure curve can be adjusted based on ambient temperature. Specifically, the pressure curve prediction can be adjusted based on ambient temperature. The internal combustion condition is indicated at 706. This condition includes an "ON" condition and an "OFF" condition. The "ON" condition indicates that the engine is performing a combustion cycle, and the "OFF" condition indicates that the engine is off and not performing combustion. The control signal for the canister purge valve is indicated at 708, and the control signal for the fuel tank isolation valve is indicated at 710. The control signals for both the canister purge valve and the fuel tank isolation valve have "OPEN" and "CLOSED" values. The "open" state corresponds to a valve configuration through which fuel vapor can flow, and the "closed" state corresponds to a valve configuration that prevents fuel vapor from flowing through the valve. It should be understood that the valve may have multiple different open positions corresponding to different degrees of valve opening. An ELCM signal is indicated at 712. The ELCM signal may correspond to a control signal sent to the ELCM to open or close the ELCM. Opening the ELCM may include: opening the ELCM valve and / or operating the ELCM pump. Conversely, closing the ELCM may include: closing the ELCM valve and / or interrupting the operation of the ELCM pump. In another example, opening and closing the ELCM may include: opening only the ELCM valve or operating only the ELCM pump. The electric motor status is indicated at 714. The "on" state indicates when the electric motor is operated to power the drive wheels, and the "off" state indicates that the electric motor is not operating. As shown, the electric motor remains on during the duration of the fuel tank vapor purging method. However, other electric motor control strategies have been envisioned, such as turning off the electric motor at t2 and turning it on at t5. In another example, the electric motor output may decrease at t2 and / or t5.

[0063] When the pressure curve exceeds the trigger threshold 716, the slope 717 of the pressure curve is calculated. In the example shown, the rise and extension of the pressure curve are calculated. In other examples, the instantaneous pressure curve slope can be calculated. The slope of the pressure curve can be extrapolated to determine when the pressure in the fuel tank is expected to exceed the venting threshold 718 at time t4. As mentioned above, the venting threshold 718 may correspond to the threshold at which fuel tank vapor venting is required to avoid a decrease in fuel tank pressure.

[0064] In response to a prediction that the fuel tank pressure will reach the bleed threshold 718, an engine start-up event is scheduled at time t2 and a fuel tank vapor purging event is scheduled at time t3. The fuel tank vapor purging event includes opening the fuel tank isolation valve and the filter purge valve, and opening the ELCM to facilitate the flow of fuel vapor from the fuel tank to the intake system. In this way, overpressure conditions in the fuel tank can be predicted, and mitigation measures can be taken to avoid overpressure conditions while also preventing an increase in evaporative emissions.

[0065] At time t5, the fuel tank pressure drops below the second threshold pressure of 720. This second threshold pressure is a desired amount of fuel tank pressure lower than the bleed threshold, reducing the likelihood of an overpressure condition recurring within a short time interval. For example, the second threshold pressure could be ambient pressure. In this way, vapors from the fuel tank can be purged until the fuel tank reaches the desired pressure.

[0066] The technical effects of scheduling engine start-up events in response to a prediction that the fuel tank will reach its venting limit are to avoid uncontrolled fuel vapor canister loading, reduce evaporative emissions, provide faster canister depressurization time during hot weather conditions, maintain the fuel tank within the desired pressure range, and / or improve the fuel reliability of the fuel tank vapor venting strategy.

[0067] The invention will be further described in the following paragraphs. In one aspect, a method for operating a vehicle having an internal combustion engine is provided, the method comprising: regulating the pressure in the fuel tank by scheduling a first engine start event based on a rate of change in fuel tank pressure to reduce fuel tank exhaust emissions, wherein the rate of change in fuel tank pressure is determined based on ambient temperature and tank pressure. The method may further comprise: scheduling a fuel tank purge event after the engine start event to purge fuel vapor from the fuel tank via an evaporative emissions control system. The method may further comprise: initiating an engine shutdown event after the engine start event, when the pressure in the fuel tank drops below a second threshold pressure. The method may further comprise: operating an electric motor in the vehicle to provide power to drive wheels during the regulation of the pressure in the fuel tank. The method may further comprise: initiating a second engine start directly in response to determining that vapor storage in the fuel vapor filter canister in the emissions control system has exceeded a threshold. In yet another example, the method may further comprise: initiating a second engine start directly in response to determining that the fuel tank has reached a second threshold pressure.

[0068] In another aspect, a vehicle system is provided, the vehicle system comprising: an internal combustion engine coupled to drive wheels; a fuel delivery system supplying fuel to the internal combustion engine and including a fuel tank; and a controller including instructions stored in a memory executable by a processor, the instructions for monitoring pressure in the fuel tank and ambient temperature, determining, based on the fuel tank pressure and the ambient temperature, whether the pressure in the fuel tank is expected to exceed a first threshold pressure, wherein the first threshold pressure triggers a fuel vapor exhaust event from the fuel tank; and if it is determined that the fuel tank pressure is expected to exceed the first threshold pressure, scheduling an engine start event in the internal combustion engine.

[0069] In another aspect, a method is provided for operating a vehicle comprising an electric motor and an internal combustion engine, the method comprising: operating the electric motor when the internal combustion engine is off; monitoring pressure and ambient temperature in a fuel tank of a fuel delivery system for delivering fuel to the internal combustion engine; determining, based on the pressure in the fuel tank and the ambient temperature, whether the fuel tank is expected to exceed a first threshold pressure that triggers a fuel tank purging event in an evaporative emission control system; and determining when the pressure in the fuel tank is expected to exceed the first threshold pressure, scheduling a first engine start event in the internal combustion engine and scheduling a fuel tank purge event in the evaporative emission control system after the start event. The method may further comprise: initiating the start event at a planned time, and after initiating the first engine start event and when the fuel tank pressure drops below a second threshold pressure, shutting off the internal combustion engine while maintaining operation of the electric motor. The method may further comprise: initiating a second engine start event in response to determining that the number of refueling events in the fuel tank has exceeded a threshold.

[0070] In any aspect or combination of these aspects, the fuel tank purging event can be scheduled to occur before the predicted time when fuel tank vapor exhaust is expected to occur in the evaporative emissions control system.

[0071] In any aspect or combination of these aspects, scheduling the first engine start-up event based on the rate of change of the fuel tank pressure may include: determining, based on the rate of change of the fuel tank pressure, whether the pressure in the fuel tank is expected to exceed a first threshold pressure within a predetermined time interval.

[0072] In any aspect or combination of these aspects, the fuel tank pressure regulation can be achieved independently of the amount of fuel vapor stored in the fuel vapor filter canister coupled to the fuel tank.

[0073] In any aspect or combination of these aspects, the vehicle system may further include: an electric motor coupled to the drive wheels; and instructions stored in a memory and executable by the processor, the instructions being used to operate the electric motor to provide power to the drive wheels when the internal combustion engine is off, prior to monitoring the fuel tank pressure.

[0074] In any aspect or combination of these aspects, the vehicle system may further include: instructions stored in a memory executable by the processor, the instructions being used to: initiate the start-up event at a planned time, and, after initiating the start-up event in the internal combustion engine and when the fuel tank pressure drops below a second threshold pressure, shut down the internal combustion engine while maintaining the operation of the electric motor.

[0075] In any aspect or combination of these aspects, determining whether the fuel tank pressure is expected to exceed the first threshold pressure may include: determining when the rate of change of the fuel tank pressure indicates that the fuel tank pressure is expected to exceed the threshold within a predetermined time interval.

[0076] In any aspect or combination of these aspects, the vehicle system may further include instructions stored in memory and executable by the processor, the instructions being used to schedule a fuel tank vapor purge event in the evaporative emissions control system following the scheduled first engine start event.

[0077] In any aspect or combination of these aspects, the fuel tank vapor purging event can be scheduled independently of the amount of fuel vapor stored in the fuel vapor filter canister coupled to the fuel tank.

[0078] In any of these aspects or combinations, determining whether the fuel tank is expected to exceed the first threshold pressure can be based on the rate of change of the pressure in the fuel tank.

[0079] In any aspect or combination of these aspects, the method may further include: initiating the start-up event at a planned time, and after initiating the start-up event and when the fuel tank pressure drops below a second threshold pressure, shutting off the internal combustion engine while maintaining the operation of the electric motor.

[0080] In any aspect or combination of these aspects, the electric motor may remain operational when the internal combustion engine is turned off.

[0081] In any aspect or combination of these aspects, the fuel tank purging event can be scheduled independently of the amount of fuel vapor stored in the fuel vapor filter canister coupled to the fuel tank.

[0082] In any aspect or combination of these aspects, the vehicle system may also include instructions stored in memory and executable by the processor, the instructions being used to trigger the start of a second engine in direct response to determining that vapor storage in the fuel vapor filter canister in the emissions control system has exceeded a threshold or that the fuel tank has reached a second threshold pressure.

[0083] It should be noted that the exemplary control and estimation routines included herein can be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in non-transitory memory and can be executed by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multitasking, multithreading, etc. Thus, the various actions, operations, and / or functions shown can be executed in the order shown, can be executed in parallel, or may be omitted in some cases. Similarly, the processing order is not necessarily necessary to achieve the features and advantages of the exemplary embodiments described herein, but is provided for ease of illustration and description. One or more of the actions, operations, and / or functions shown can be repeatedly executed according to the specific strategy used. Furthermore, the actions, operations, and / or functions can be graphically represented as code to be programmed into the non-transitory memory of a computer-readable storage medium in an engine control system, wherein the actions are implemented by executing the instructions in conjunction with an electronic controller in a system including various engine hardware components.

[0084] It should be understood that the configurations and routines disclosed herein are exemplary in nature, and these specific embodiments should not be considered limiting, as many variations are possible. For example, the above-described techniques can be applied to other types of engines (V-6, I-4, I-6, V-12, opposed 4-cylinder, etc.), vehicle systems, etc. The subject matter of this disclosure includes all novel and non-obvious combinations and sub-combinations of various systems and configurations, as well as other features, functions, and / or characteristics disclosed herein.

[0085] The following claims specifically point to certain combinations and sub-combinations that are considered novel and not obvious. These claims may refer to a “one” element or a “first” element or its equivalent. Such claims should be understood to include a combination of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the claims herein or by presenting new claims in this application or related applications. Such claims, whether broader, narrower, identical, or different from the scope of the original claims, are considered to be included within the subject matter of this disclosure.

[0086] Those skilled in the art will further understand that although the invention has been described by way of example with reference to several embodiments, the invention is not limited to the disclosed embodiments, and alternative embodiments may be constructed without departing from the scope of the invention as defined in the appended claims.

[0087] According to the present invention, a method for operating a vehicle having an internal combustion engine, the method comprising: adjusting the pressure in the fuel tank by scheduling a first engine starting event based on a rate of change of fuel tank pressure to reduce fuel tank exhaust emissions, wherein the rate of change of fuel tank pressure is determined based on ambient temperature and internal tank pressure.

[0088] According to one embodiment, a further feature of the invention is that a fuel tank purge event is scheduled after the first engine start event to purge fuel vapor from the fuel tank via an evaporative emissions control system.

[0089] According to one embodiment, the fuel tank purging event is scheduled to occur before a predicted time when fuel tank vapor discharge is expected to occur in the evaporative emissions control system.

[0090] According to one embodiment, scheduling the first engine start-up event based on the rate of change of the fuel tank pressure includes: determining whether the pressure in the fuel tank is expected to exceed a first threshold pressure within a predetermined time interval based on the rate of change of the fuel tank pressure.

[0091] According to one embodiment, a further feature of the invention is that an electric motor in the vehicle is operated to provide power to the drive wheels during the regulation of the pressure in the fuel tank.

[0092] According to one embodiment, a further feature of the invention is that a second engine is started directly in response to determining that the vapor storage in the fuel vapor filter canister in the emission control system has exceeded a threshold.

[0093] According to one embodiment, a further feature of the invention is that the second engine is started directly in response to determining that the fuel tank has reached a second threshold pressure.

[0094] According to the present invention, a vehicle system is provided, the vehicle system comprising: an internal combustion engine coupled to drive wheels; a fuel delivery system supplying fuel to the internal combustion engine and including a fuel tank; and a controller including instructions stored in a memory executable by a processor, the instructions being configured to monitor pressure and ambient temperature in the fuel tank, determine, based on the fuel tank pressure and the ambient temperature, whether the pressure in the fuel tank is expected to exceed a first threshold pressure, wherein the first threshold pressure triggers a fuel vapor exhaust event from the fuel tank; and if it is determined that the fuel tank pressure is expected to exceed the first threshold pressure, schedule a first engine start event in the internal combustion engine.

[0095] According to one embodiment, a further feature of the invention is: an electric motor coupled to a drive wheel; and instructions stored in a memory executable by the processor, the instructions being used to operate the electric motor to provide power to the drive wheel when the internal combustion engine is off, prior to monitoring the fuel tank pressure.

[0096] According to one embodiment, a further feature of the invention is that: instructions stored in a memory executable by the processor are used to: initiate the start-up event at a planned time, and after initiating the start-up event in the internal combustion engine and when the fuel tank pressure drops below a second threshold pressure, shut down the internal combustion engine while maintaining the operation of the electric motor.

[0097] According to one embodiment, determining whether the fuel tank pressure is expected to exceed the first threshold pressure includes: determining when the rate of change of the fuel tank pressure indicates that the fuel tank pressure is expected to exceed the threshold within a predetermined time interval.

[0098] According to one embodiment, a further feature of the invention is that: instructions stored in a memory and executable by the processor are used to schedule a fuel tank vapor purge event in the evaporative emissions control system after the scheduled first engine start event.

[0099] According to one embodiment, the fuel tank vapor purging event is scheduled independently of the amount of fuel vapor stored in the fuel vapor filter canister coupled to the fuel tank.

[0100] According to one embodiment, a further feature of the invention is that: instructions stored in a memory and executable by the processor are used to trigger the start of a second engine in direct response to determining that the vapor storage in the fuel vapor filter canister in the emission control system has exceeded a threshold or that the fuel tank has reached a second threshold pressure.

[0101] According to one embodiment, the engine start event is scheduled independently of the amount of fuel vapor stored in the fuel vapor filter canister coupled to the fuel tank, and even if the amount of stored vapor is below a lower threshold, which is below an upper threshold, wherein when the upper threshold is reached, engine start is triggered independently of the monitored pressure.

[0102] According to the present invention, a method for operating a vehicle comprising an electric motor and an internal combustion engine includes: operating the electric motor when the internal combustion engine is off; monitoring pressure and ambient temperature in a fuel tank of a fuel delivery system for delivering fuel to the internal combustion engine; determining, based on the pressure in the fuel tank and the ambient temperature, whether the fuel tank is expected to exceed a first threshold pressure that triggers a fuel tank purging event in an evaporative emission control system; and determining when the pressure in the fuel tank is expected to exceed the first threshold pressure, scheduling a first engine start event in the internal combustion engine and scheduling a fuel tank purging event in the evaporative emission control system after the first engine start event.

[0103] According to one embodiment, determining whether the fuel tank is expected to exceed the first threshold pressure is based on the rate of change of the pressure in the fuel tank.

[0104] According to one embodiment, a further feature of the invention is that a second engine start event is initiated in response to determining that the number of refueling events in the fuel tank has exceeded a threshold.

[0105] According to one embodiment, the electric motor remains operational when the internal combustion engine is turned off.

[0106] According to one embodiment, the fuel tank purging event is scheduled independently of the amount of fuel vapor stored in the fuel vapor filter canister coupled to the fuel tank.

Claims

1. A method for operating a vehicle having an internal combustion engine, comprising: Overpressure conditions in the fuel tank are predicted by using the rate of change of pressure in the fuel tank, and the prediction of overpressure conditions includes predicting when venting will occur in the fuel tank; The pressure in the fuel tank is regulated by scheduling the first engine start-up event based on predicted overpressure conditions to reduce fuel tank exhaust emissions; The rate of change of the fuel tank pressure is determined based on ambient temperature and tank pressure; a fuel tank purge event is scheduled after the first engine start event to purge fuel vapor from the fuel tank via an evaporative emission control system, wherein the fuel tank purge event is scheduled to occur before a predicted time when fuel tank vapor exhaust is expected to occur according to the evaporative emission control system.

2. The method of claim 1, wherein scheduling the first engine starting event based on the predicted overpressure condition comprises: It is determined whether the pressure in the fuel tank is expected to exceed a first threshold pressure within a predetermined time interval based on the rate of change of the pressure in the fuel tank.

3. The method of claim 1, further comprising: The electric motor in the vehicle is operated to provide power to the drive wheels during the adjustment of the pressure in the fuel tank.

4. The method of claim 1, further comprising: The second engine is started in direct response to determining that the vapor storage in the fuel vapor filter canister in the emission control system has exceeded a threshold.

5. The method of claim 1, further comprising: The second engine is started directly in response to determining that the fuel tank has reached the second threshold pressure.

6. A vehicle system comprising: An internal combustion engine, said internal combustion engine being coupled to drive wheels; A fuel delivery system, which supplies fuel to the internal combustion engine and includes a fuel tank; and The controller includes instructions stored in memory that are executable by a processor, the instructions being used to: Monitor the pressure and ambient temperature in the fuel tank; Based on the pressure in the fuel tank and the ambient temperature, it is determined whether the pressure in the fuel tank is expected to exceed a first threshold pressure, wherein the first threshold pressure triggers a fuel vapor venting event from the fuel tank; Predict the moment when the pressure in the fuel tank reaches the first threshold pressure; and If it is determined that the pressure in the fuel tank is expected to exceed the first threshold pressure, a first engine start-up event is scheduled in the internal combustion engine before the predicted time when the pressure in the fuel tank reaches the first threshold pressure.

7. The vehicle system of claim 6, further comprising: An electric motor coupled to a drive wheel; Instructions, stored in memory and executable by the processor, are used for: Before monitoring the fuel tank pressure, the electric motor is operated to provide power to the drive wheels when the internal combustion engine is off.

8. The vehicle system of claim 7, further comprising instructions stored in memory and executable by the processor, the instructions being used for: Initiate the startup event at the planned time; and After the start-up event in the internal combustion engine is initiated and when the fuel tank pressure drops below a second threshold pressure, the internal combustion engine is shut down while maintaining the operation of the electric motor.

9. The vehicle system of claim 6, wherein determining whether the fuel tank pressure is expected to exceed the first threshold pressure comprises: Determine when the rate of change of the fuel tank pressure indicates that the fuel tank pressure is expected to exceed the threshold within a predetermined time interval.

10. The vehicle system of claim 6, further comprising instructions stored in memory and executable by the processor, the instructions being used for: Following the first engine start event scheduled, a fuel tank vapor purge event is scheduled in the evaporative emissions control system.

11. The vehicle system of claim 10, wherein the fuel tank vapor purging event is scheduled independently of the amount of fuel vapor stored in a fuel vapor filter canister coupled to the fuel tank.

12. The vehicle system of claim 10, further comprising instructions stored in memory and executable by the processor, the instructions being used for: The second engine is triggered in direct response to determining that the vapor storage in the fuel vapor filter canister in the emission control system has exceeded a threshold or that the fuel tank has reached a second threshold pressure.

13. The vehicle system of claim 6, wherein the engine start event is scheduled independently of the amount of fuel vapor stored in a fuel vapor filter canister coupled to the fuel tank, and even if the amount of stored vapor is below a lower threshold, which is below an upper threshold, wherein when the upper threshold is reached, engine start is triggered independently of the monitored pressure.

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