This application relates to an evaporation system for hybrid vehicles equipped with an electric motor and an internal combustion engine working in cooperation. BACKGROUND OF THE INVENTION

There is interest in producing passenger vehicles driven by an electric motor powered by a rechargeable battery (for example, a lithium- ion battery). The operating range of the battery powered vehicle would be increased using an onboard electric generator driven, upon demand, by a gasoline engine. For relatively short driving excursions, the capacity of the battery would suffice and the gasoline engine would not be started. At the completion of such trips the battery would be recharged from an AC source. Such a vehicle is sometimes called a plug-in hybrid vehicle.

Since many local driving trips could be completed within the electrical power capacity of the battery it is anticipated that many days could pass without starting the gasoline engine, but the engine would be necessary when longer trips are taken. It is contemplated that battery-only trips (before plug-in recharging) would be limited in range and the gasoline engine-driven electric generator would be used to increase the range of the vehicle.

Despite its intermittent usage the plug-in hybrid gasoline engine will, of course, require on-board fuel storage. Gasoline stored in a vehicle fuel tank is exposed to ambient heating which increases the vapor pressure of the volatile hydrocarbon fuel. In conventional gasoline powered engines, fuel tank vapor (typically comprising lower molecular weight hydrocarbons) is vented to a canister containing high surface area carbon granules for temporary adsorption of fuel tank emissions. Later, during engine operation ambient air is drawn through the carbon granule bed to purge adsorbed fuel vapor from the surfaces of the carbon particles and carry the removed fuel into the air induction system of the vehicle engine. As stated, such plug-in hybrid vehicles operate mostly on batteries which are charged during the night by plugging into home AC outlets. A plug-in hybrid vehicle IC engine may not run for several days which results in no purging (cleaning) of the evaporative emission control canister by engine operation.

To fully respect the environment and comply with emissions standards, the canister has to be purged regularly and, to overcome the issue of hybrid vehicle powertrain several solutions have been developed.

Reddy, in application WO2009042354, proposes to utilize a microwave generator to heat up and purge the absorbed fuel vapors and drive them back through the fuel vapor vent into the fuel tank.

Devries and Peters, in application US20090007890, propose a multi-path evaporative purge system operating under four conditions in order in order to purge two canisters interconnected by several three-way valves.

Additionally, there are known pressurized metallic-tank systems that keep all vapors generated. All hydrocarbons are kept inside tank pressurized up to 400 mbar. During diurnal cycles the evaporative canister has no contact with the gas vapors.

These systems are complex and subsequently costly. The system operational conditions demands close surveillance and supervision while inter working relation of the components necessitates multiple and complicated connections. Finally, components such as steel tank, valves, sensors are costly components.

SUMMARY OF THE INVENTION

The object of the present invention is to resolve these problems by proposing an evaporative system for hybrid vehicles, and more specifically for plug-in hybrid vehicles [PHEV] that is simple and cost effective. The system proposed by the invention is:

A fuel vapor management system for a powertrain including an internal combustion engine, the system comprising a fuel tank and a fuel evaporative canister so that fuel vapors can transfer from the fuel tank to the fuel evaporative canister. Advantageously, the system further comprises a separate container to where part of the fuel vapor contained in the fuel tank can be transferred and stored in case of increasing pressure in the fuel tank due to the ambient conditions, and from where the stored fuel vapor can be returned to the fuel tank in case of decreasing pressure in the fuel tank due to the ambient conditions, so that under any ambient conditions the fuel tank is maintained substantially at a

predetermined level of pressure.

Additionally, a pump connected between the fuel tank and the container ensures the transfers of the vapor from the fuel tank to the container. The container can build-up in pressure to a maximum level that is superior to the predetermined level. A hose connected in parallel to the pump and is controlled by a first valve which enables the return of the pressurized vapor from the container to the fuel tank.

Furthermore, a second valve controls the entry of the fuel vapor in the canister in order to prevent, in case of increasing pressure in the fuel tank due to the ambient conditions, the fuel vapor coming from the fuel tank or from the container from entering the canister and saturating it.

In a first embodiment, the container is connected between the fuel tank and the canister so that the fuel vapor transferring from the fuel tank to the canister has to go through the container.

In a second embodiment, the fuel tank and the container are both directly connected to the canister so that the fuel vapor can directly be transferred from the fuel tank to the canister and from the container to the canister.

Advantageously, an electronic control unit monitors the pressure and the temperature in the fuel tank and in the container and controls the operation of the pump and the valves so that the pressure inside the fuel tank remains substantially at the predetermined level of pressure.

It is expected that the predetermined level of pressure is substantially the atmospheric pressure so the fuel tank remains at the atmospheric pressure under any ambient conditions.

The invention further comprises a method for managing fuel vapor pressure in a fuel tank, the method comprising the steps of:

- monitoring the vapor pressure in the fuel tank and, if the pressure exceeds a predetermined level,

- transferring the fuel vapor to an external container until the pressure in the fuel tank (20) falls below the predetermined level. The method further comprises the steps of:

- pressurizing the fuel vapor inside the container by activating the pump and closing the first valve and the second valve so that the pressure inside the fuel tank is maintained substantially at the predetermined level of pressure.

- returning to the fuel tank the fuel vapor pressurized in the container by deactivating the pump and only opening the first valve so the pressure inside the fuel tank is maintained substantially at the predetermined level of pressure.

In case of the first embodiment, the method further comprises the step of:

- transferring to the canister the fuel vapor present in the fuel tank under refueling conditions, by deactivating the pump and opening the first (60) and the second valve.

In case of the second embodiment, the method further comprises the step of:

- transferring to the canister the fuel vapor present in the fuel tank under refueling conditions, by deactivating the pump and only opening the second valve.

Advantageously, for all embodiments, the method comprises the step of:

- releasing to the canister the vapor pressurized in the container to the maximum level by only opening the second valve, thus providing a safety function when the engine being stopped but still dissipating heat tending to increase the pressure level in the container and the pump being stopped.

Optionally, the method comprises the step of setting the predetermined level of pressure substantially at the atmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying figures wherein: Figure 1 is a schematic representation of a first embodiment of the evaporative system where the fuel tank, the container and the canister are assembled in series.

Figure 2 is a schematic representation of a second embodiment of the evaporative system where the fuel tank, the container and the canister are assembled in parallel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 and Figure 2 represent an evaporative system 18 [EVAP] as per the present invention. The system 18 is implemented in a vehicle 10 having a powertrain 12 comprising an internal combustion engine 14 [ICE] cooperating with an electrical motor 16.

The system 18 comprises a fuel tank 20, an EVAP canister 50, at least one container 42, a pump 36, a first valve 60 and a second valve 62 and an electronic control unit [ECU] 90.

The fuel tank 20 has an inside bottom 22, where resides liquid fuel 26 and an inside top 24 where naturally concentrates vapor fuel 28. The tank is provided with a first orifice 30 and a second orifice 32. As an alternative (not represented), the fuel tank 20 may only be provided with a single orifice that serves the dual purpose of the above mentioned orifices 30 and 32.

The EVAP canister 50 is provided with a vapor inlet 52, an ambient air outlet 56 and is connected to the engine via a port 54.

The container 42 is provided with an inlet 44 and an outlet 46. As an alternative not represented, the system could, to ease the overall packaging of the system 18 in the vehicle, be provided with a plurality of containers 42.

The pump 36 is provided with a pump inlet 38 and a pump outlet 40. As a non limiting example for dimensioning the system 18, the container 42 has an internal volume of about 10% of the internal volume of the fuel tank 42.

In a first embodiment illustrated by Figure 1, the system is assembled as follow:

A first hose 70 connects the first orifice 30 of the tank 20 to the pump inlet 38. A second hose 72 connects the pump outlet 40 to the inlet 44 of the container 42.

A third hose 74 connects the container outlet 46 to the second valve 62.

A fourth hose 76 connects the second valve 62 to the vapor inlet 52 of the EVAP canister 50.

A fifth hose 78 connects the second orifice 32 of the tank 20 to the first valve 60.

A sixth hose 80 connects the second valve 72 to the first valve 60, the fourth and second hoses, 72 80, being interconnected at the first T-junction 84.

The ECU 90 monitors the pressure and the temperature in the fuel tank

20 and in the container 42 and drives accordingly the valves 60 62 and the pump 36.

In a first configuration, the ICE 14 is turned-off and accumulation of fuel vapor 28 occurs inside the fuel tank 20.

The ECU 90 closes the first valve 60 and the second valve 62, the pump

36 pumps the vapor 28 out off the fuel tank 20 and transfers it via the first hose 70 and the second hose 72 into the container 42. The container 42 builds-up in pressure while the tank 20 remains not pressurized.

In a second configuration, the ICE 14 is turned-off and the fuel vapor 28 does not accumulate inside the fuel tank 20.

The ECU 90 opens the first valve 60 and closes the second valve 62, the vapor 28 stored under pressure in the container 42 is recirculated back to the fuel tank 20 through the second hose 72, the first T-junction 84, the sixth hose 80, the fifth hose 78 and back to the tank 20 via the second orifice 32. The tank 20 remains not pressurized.

In a third configuration, the ICE 14 runs and the canister 50 is purged. All valves, 60 62, are normally closed. Depending on the conditions, the valves, 60 62, and the pump 36 regulate pressures in the tank 20 and in the container 42 as in the first or second configuration. In case of accumulation of fuel vapor 28 inside the tank 20, the first configuration applies. If vapor 28 do not accumulate in the tank 20, the second configuration applies.

In a fourth configuration, the fuel tank 20 is refuelled with fuel 26, and fuel vapor 28 accumulates in the fuel tank 20. The ECU 90 opens the valves, 60 62, to transfer fuel vapor 28 to the canister 50 over the hoses 74, 76, 78 and 80 for the first embodiment. This is independent of the ICE condition whether it is running or not.

In a second embodiment illustrated by Figure 2, the system is assembled as follow:

The container 42 has a single orifice, 44 46, serving the dual purpose of inlet and outlet.

A first hose 70 connects the first orifice 30 of the tank 20 to the pump inlet 38.

A second hose 72 connects the pump outlet 40 to the container inlet- outlet 44 46.

A third hose 80 connects the second hose 72 to the first valve 60, the second and third hoses, 72 80 being interconnected at a first T-junction 84.

A fourth hose 74 connects the first valve 60 to the second valve 62. A fifth hose 78 connects to the second orifice 32 of the tank 20 to the fourth hose 74, the fourth and fifth hoses 74 78 being interconnected at the second T-junction 86.

A sixth hose 76 connects the second valve 62 to the vapor inlet 52 of the EVAP canister 50.

The ECU 90 monitors the pressure and the temperature in the fuel tank

20 and in the container 42 and drives accordingly the valves 60 62 and the pump 36.

In a similar manner as with the first embodiment, the vapor 28 present in the tank 20 can be expelled from the tank 20 and pressurized by the pump 36 and stored in the container 42 while both valves 60 62 are closed. Then the vapor 28 can be released back to the fuel tank 20 in only opening the first valve 60 or sent to the canister 50 in opening both valves 60 62.

A difference of this second embodiment relative to the first embodiment is that to release the vapor 28 from the tank 20 only the second valve 62 has to be open and, to release the vapor 28 from the container 42 the first valve 60 has to be open.

In both embodiments, the vapor 28 stored in the container 42 are sent back to the fuel tank 20 when the pressure in the fuel tank 20 returns close to the atmospheric pressure. This typically occurs overnight when the engine is off and its temperature decreases and returns to ambient.

In the configuration when the fuel tank 20 is refuelled with fuel 26, and fuel vapor 28 accumulates in the fuel tank 20, the ECU 90 opens the valves, 60 62, to transfer fuel vapor 28 to the canister 50 over the hoses 74, 76, 78. This is independent of the ICE condition whether it is running or not.

The system as per the invention additionally provides a safety function. In the case the container's 42 maximum inner pressure is reached (e.g. 4 bars) and the engine is turned off, it may happen, for instance on a hot day after a long drive, that the engine continues to dissipate heat and the pressure in the container 42 continues to increase. Under these circumstances, the vapors 28 in the container 42 are sent to the canister 50.