LU101983B1

LU101983B1 - Vehicle fuel system with vapour pressure control

Info

Publication number: LU101983B1
Application number: LU101983A
Authority: LU
Inventors: Paul Reuther; David Hill
Original assignee: Plastic Omnium Advanced Innovation & Res
Priority date: 2020-08-10
Filing date: 2020-08-10
Publication date: 2022-02-10

Abstract

The invention relates to a method for controlling the fuel vapour pressure in a vehicle fuel system (1) on board of a vehicle and to the vehicle fuel system implementing said method. The method comprising the step of: a. Switching the vehicle to a key off mode; b. Providing a fluid communication between a fuel tank (10) and a canister (11); c. Sealing the canister (11) and the fuel tank (10) from the external atmosphere (18), d. .Measuring the pressure, Pt, in the fuel tank (10) ; e. Wherein, when the pressure, Pt, measured at step C is equal or greater than a first threshold, closing the fluid communication between the canister (11) and the fuel tank (10) and providing a fluid communication between the canister (11) and the external atmosphere (18).

Description

Vehicle fuel system with vapour pressure control Technical field of the invention The present invention relates to the field of vehicle fuel systems and to the method for controlling the fuel vapour pressure in a vehicle fuel system on board of a vehicle, preferably a hybrid vehicle.

Background of the invention Vehicle fuel systems on board of a vehicle may be used to store and provide fuel to engines. For example, an automotive vehicle including an internal combustion engine may be provided with a fuel system including vehicle fuel tank that stores liquid fuels such as gasoline, diesel, methanol, ethanol, and/or other fuels. Liquid fuels in a vehicle fuel tank may evaporate into volatile fuel vapour in the vehicle fuel tank. Vehicle fuel systems are generally provided with a vapour outlet for venting fuel vapour from the fuel system to the atmosphere. The emission of fuel vapour to the atmosphere contributes to vehicle emissions.

To control and reduce the emission of volatile fuel vapour, vehicle fuel systems are typically provided with a canister, which traps the fuel vapour on a material generally based on active carbon. Moreover, leak detection method have been implemented to detect the presence of possible leak in the vehicle fuel system on board of a vehicle.

For example, the document US42663462 discloses a leak detection method of a vehicle fuel system on board of a vehicle, said vehicle fuel system comprising a canister. Unfortunately, the method disclosed may induce a canister deterioration during the performing of said method.

The document US 2013/0074583 A1 discloses a leak detection method of a vehicle fuel system, said vehicle fuel system comprising a canister. The vehicle fuel system and the method disclosed require the use of a specific vacuum source, which renders the vehicle fuel system complex, expensive and prone to failure by the inherent nature of complex components used.

There is thus a need to improve the existing vehicle fuel systems and the methods for controlling the fuel vapour pressure in a vehicle fuel system on board of a vehicle, more particularly during a leak detection method.

Summary of the invention It is an object of the present invention to provide a method for controlling the fuel vapour pressure in a vehicle fuel system on board of a vehicle, which preserves said vehicle fuel system.

It is another object of the present invention to provide a robust vehicle fuel system comprising a canister, said vehicle fuel system being configured to perform methods for controlling the fuel vapour pressure.

The above objectives are accomplished by a method and a vehicle fuel system according to the present invention.

According to a first embodiment of the invention, the method for controlling the fuel vapour pressure in a vehicle fuel system on board of a vehicle, preferably on board of a hybrid vehicle, the method comprising the following steps of: a. Switching the vehicle to a key off mode; b. Providing a fluid communication between a fuel tank and a canister, c. Sealing the canister and the fuel tank from the external atmosphere, d. Measuring a pressure value, Pt, in the fuel tank (10); e. when the pressure, Pt, measured at step c. is equal or greater than a first pressure threshold, closing the fluid communication between the canister and the fuel tank and providing a fluid communication between the canister and the external atmosphere.

Advantageously, the method for controlling the fuel vapour pressure in a vehicle fuel system on board of a vehicle according to the invention permits to avoid a deterioration of the canister, preferably a carbon canister, of the vehicle fuel system. The method allows for an optimized canister design that does not need to be engineered to withstand excessive internal pressure in the case of uncontrolled key — off mode. The method permits also a simple leak check configuration of the complete evaporative emissions system on a vehicle, which in response to positive pressure inside the fuel tank that would indicate the vehicle fuel system is sealed, reverting the vehicle fuel system to a key off mode in which the canister, preferably the carbon canister, is not subjected to undue pressure, possibly for weeks on end if the vehicle is not driven, while still being able to seal the fuel tank from atmospheric pressure to avoid fuel vapour migration to the canister, preferably to the carbon canister, while the vehicle is parked.

Preferably, the step b. of providing a fluid communication between a fuel tank and a canister, preferably a carbon canister, and the step c. of sealing the canister, preferably a carbon canister, and the fuel tank from the external atmosphere are performed simultaneously. Preferably, during step e. the closing of the fluid communication between the canister, preferably the carbon canister, and the fuel tank and the providing of a fluid communication between the canister, preferably the carbon canister, and the external atmosphere are performed simultaneously.

Preferably, the measurement of the pressure, Pt, in the fuel tank, is performed in the vapour dome of the fuel tank.

Preferably, the first pressure threshold is around 100 mbars, more preferably equal to 100 mbars, relative to the atmospheric pressure. By setting a first threshold around 100 mbars, it is possible to make this measurement within the first hour after the vehicle was switched to a key off mode the vehicle, and truly limit the pressure inside the canister, preferably the carbon canister, to relatively short periods of time relative to its total useful life.

According to a preferred embodiment, the method for controlling the fuel vapour pressure in a vehicle fuel system on board of a vehicle, preferably on board of a hybrid vehicle, according to the invention is such that the pressure, Py, in the fuel tank is measured at several different time intervals, t.

By the expression “several different time intervals, t.”, we intend to mean that the pressure measurements are performed at different time, the time length of each measurement may vary, preferably the measurement are performed on a punctual mode, the time length of the time intervals may vary, preferably the time length of the time intervals is constant.

It is advantageous to measure the pressure value, Pt, in the fuel tank at several time intervals after that the vehicle was switched to a key off mode, preferably the measurement of the pressure, Py, is performed every hour for at least 5 hours. This is due to the fact that there is the likelihood that the pressure inside the tank will increase or decrease substantially during this time period.

If only a single measurement is performed, it is possible that the pressure could increase to the first pressure threshold after the single measurement of the pressure value in the fuel tank during the dormant phase, the phase during which the vehicle is on key off mode, and still subject the canister, preferably the carbon canister, to undue pressure for an uncontrolled amount of time.

Taking several measurements of pressure value increases the likelihood that the system can react to critical pressure in the fuel tank.

Preferably a 5 to 6 hour period can be optimal as it minimizes the unmeasured time after vehicle is switched to the key off mode, however stays below a threshold of 6 hours as defined in the on board diagnostics regulations defining the minimum soak time required to necessitate a leak detection event.

According to a particular embodiment of the previous one, the method for controlling the fuel vapour pressure in a vehicle fuel system on board of a vehicle, preferably on board of a hybrid vehicle, according to the invention is such that said method comprises an additional step e1., wherein the values of the pressure, Pi, measured in step c. at several different time intervals, t, are compared against each other, If none of the differences between the pressure values, Pı, measured are greater or equal to a second pressure threshold, concluding that there is a leak in the vehicle fuel system and providing fluid communication between the fuel tank and the external atmosphere via the canister, preferably the carbon canister.

The inventors have found that if the pressure differences between the pressure values, Pi, measured remains under a second pressure threshold during the time intervals, t, defined, then it can be ascertained that there is a leak in the fuel system.

It can be advantageous for the environment to open the fuel tank vapor dome to the atmosphere via the canister to sequester hydrocarbon vapors.

As fuel vapor flow out of the tank to accommodate for thermal expansion of the gas will take the path of least resistance, opening the venting system will channel the majority of the fuel vapours through the canister, thus greatly reducing the amount of hydrocarbons that exit through the leak in the vehicle fuel system and directly to the atmosphere.

In other words, if the vehicle fuel system is open to the atmosphere via the canister, there will be no pressure drop across the leak orifice to create flow to the external air, limiting any vapor escape solely to diffusion.

According to another particular embodiment, the method for controlling the fuel vapour pressure in a vehicle fuel system on board of a vehicle, 5 preferably on board of a hybrid vehicle, according to the invention is such that said method comprises an additional step e2., wherein the pressure values, Pt, measured in step c. at several different time intervals, t, are compared against each other, If the differences between the pressure, Pi, measured are greater or equal to the second pressure threshold, closing the fluid communication between the canister and the fuel tank and providing a fluid communication between the canister and the external atmosphere.

In the event that the pressure inside the fuel tank does not meet the first pressure threshold relative to atmospheric pressure, yet the pressure values, Pt, measured at several different time intervals, t, show differences above the second pressure threshold, it is also possible to ascertain that there is no leak in the vehicle fuel system and as such seal the fuel tank from the canister, preferably the carbon canister, but allow the canister, preferably the carbon canister, normalize to atmospheric pressure.

According to a particular embodiment, the method for controlling the fuel vapour pressure in a vehicle fuel system on board of a vehicle, preferably on board of a hybrid vehicle, according to the invention is such that a measurement of a temperature, Ti, is performed in step c.

Measuring the temperature, Ti preferably at the defined pressure measurement time intervals, provides the advantage of linking pressure changes above or below the thresholds. The main advantage of this exists when the pressure is below the second threshold value between all the measured points compared. If there is sufficient temperature change the ideal gas law allows confirmation that there is a leak in the system. If there is not sufficient temperature change then it can not be confirmed that there is a leak in the fuel system, in which case there is no good reason to change the state of the sealing of the venting system. Furthermore it has the advantage over systems of prior art which would then rely on several days of drive events to statistically ascertain | that the temperature changed enough to warrant a pressure change inside the system if it was leak free. Thus the detection methodology can reliably detect a leak within roughly 1-2 days instead of 5 or more.

According to a particular embodiment, the method for controlling the fuel vapour pressure in a vehicle fuel system on board of a vehicle, preferably on board of a hybrid vehicle, according to the invention is such that the temperatures, Ti, are measured in the vapour dome of the fuel tank.

It is advantageous to measure this temperature in the fuel vapor dome as it gives the most accurate measurement of the temperature change linked to the pressure change inside the tank. In prior art systems ambient temperature has been used, however there is a weak correlation between this temperature and the temperature inside the vapor dome of the tank especially with respect to different vehicle architectures where the fuel tank is located adjacent to different thermal masses. The result was vehicle by vehicle calibration of the proper threshold temperatures which is costly and time consuming, and will likely still result in similar uncertainties as are describes with the lack of a temperature measurement.

It is a second object of the present invention to provide a robust vehicle fuel system comprising a canister, said vehicle fuel system being configured to perform methods for controlling the fuel vapour pressure in vehicle fuel system.

According to a first embodiment of a vehicle fuel system on board of a “vehicle according to the invention, said vehicle fuel system comprises: e a fuel tank; e a canister; e a means for controlling the fluid communication between the fuel tank and the canister and between the canister and the external atmosphere, wherein said means comprises at least a bi-phase valve; e a pressure sensor provided to measure the pressure in the fuel system, said pressure sensor being located in the vapour dome of the fuel tank; : e a temperature sensor,

e an electronic control unit (ECU) controlling the means for controlling the fluid communication between the fuel tank and the canister and between the canister and the external atmosphere, said electronic controlling unit (ECU) provided to performed the steps of the method according to the invention.

By having bi-phase valves to control the pressure between the fuel tank and the canister, preferably the carbon canister, and the canister, preferably the carbon canister, and the atmosphere, it is possible to achieve different states of tank sealing or opening without requiring constant power to the components of the vehicle fuel system. This is advantageous over the prior art which generally uses normally open or normally closed solenoid valves to achieve at least one of these positions. Such designs are prohibitive if it is necessary to achieve one of the non-normal or powered stated during the vehicle off period as typically such valves draw 200 to 1000 mA of power where an acceptable level is in the range of 200 microamperes in a vehicle off state to avoid long term battery drain. By having 2 bi-phase valves it is possible to have several venting architectures, which can be advantageous over having only 1 valve in such a configuration. For example it become impossible to achieve a state where both valves are open in an unpowered state after a leak is detected, but also to be able to have one or both valves closed in the event that the system is still in evaluation mode as described in the first embodiment of the method according to the invention or after it has achieved one of the thresholds as disclosed in embodiments of the method according to the invention.

By the expression “bi-phase-valve”, we intend to mean a valve such that the maintaining of the valve in an open or closed position does not require energy, in contrary to a solenoid valve for example.

According to a particular embodiment of a vehicle fuel system on board of a vehicle, preferably a hybrid vehicle, according to the invention, said vehicle fuel system is such that the means for controlling the fluid communication between the fuel tank and the canister and between the canister and the external atmosphere consists of bi-phase valves.

It is advantageous to control the fluid communication between the fuel tank and carbon canister and atmosphere using bi-phase valves an example such a system of valves is described in US Patent 9,616,744 wherein a stepper motor is used to drive 2 valves, allowing for more than 2 venting configurations, as would be the case with 2 normally biased solenoid valves.

According to a particular embodiment of a vehicle fuel system on board of a vehicle, preferably a hybrid vehicle, according to the invention, said vehicle fuel system is such that the canister is an active carbon canister.

It is advantageous to have an active carbon canister in a fuel system in order to capture the vapors that are displaced from the fuel tank during the refueling of a vehicle. This carbon canister has the advantage of being able to store relatively large amounts of vapors within the porous carbons structure at ambient temperature, yet allows the vapor to be removed from the structure with sufficient flow across the carbon surface.

According to a particular embodiment of a vehicle fuel system on board of a vehicle, preferably a hybrid vehicle, according to the invention, said vehicle fuel system is such that the temperature sensor is located in the vapour dome | of the fuel tank.

It is advantageous to have a temperature sensor mounted in the vapor dome of the fuel system to measure the temperature of the fuel vapor as it gives a direct correlation to the thermal expansion of the vapor driving the pressure increase in a sealed fuel tank. It is possible to measure the fuel temperature or the ambient temperature, but each of these induce an additional transfer function prone to calibration and reduction in resolution and accuracy of the measurement of the temperature in the fuel tank vapor dome.

By the expression “a vehicle fuel system on board of a vehicle, preferably a hybrid vehicle", we intend to mean that the vehicle fuel system according to the invention is configured to be installed on board of a conventional vehicle or hybrid vehicle, preferably on board of a hybrid vehicle.

The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

Brief description of the drawings Fig. 1 is a vertical cross-section of a vehicle fuel system according to the invention performing a step of the method for controlling the fuel vapour pressure according to the invention Fig. 2 is a vertical cross-section of a vehicle fuel system according to the invention performing a step of the method for controlling the fuel vapour pressure according to the invention Fig. 3 is a vertical cross-section of a vehicle fuel system according to the invention performing the a step of the method for controlling the fuel vapour pressure according to the invention Description of illustrative embodiments The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preciude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to

10 - LU101983 devices consisting only of components À and B. it means that with respect to the present invention, the only relevant components of the device are A and B. Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or. “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments. In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Figure 1 illustrates a vehicle fuel system (1) according to the invention said, vehicle fuel system (1) comprises a fuel tank (10), a canister (11), a means for controlling the fluid communication (12) between the fuel tank (10) and the canister (11) and between the canister (11) and the external atmosphere (18), wherein said means (12) comprises at least a bi-phase valve (120), a pressure sensor (13) provided to measure the pressure in the vehicle fuel system (1), said pressure sensor (13) being located in the vapour dome (100) of the fuel tank (10), a temperature sensor (14) and an electronic control unit (ECU) controlling the means for controlling the fluid communication (12) between the fuel tank (10) and the canister (11) and between the canister (11) and the external atmosphere, said electronic controlling unit (ECU) provided to performed the steps of the method according to the invention. In this figure, the fuel tank (10) is fluidly connected to the canister (2) by means of vent lines (14,15) and the means for controlling the fluid communication (12). The fuel tank (10) and the canister (11) are sealed by the means for controlling the fluid communication (12) constituted by bi-phase valves (12) and an engine purge valve (17). A pressure sensor (13) and a temperature sensor (16) are disposed in the vapour dome (100) of the fuel tank (1) in order to measure the pressure and temperature of the vehicle fuel system (1). In this configuration, it is possible to determine the leak tightness of the vehicle fuel system by comparing the pressure, Pt, and temperature, Ti, measurements at different time intervals, t, but also to determine that the vehicle fuel system is leak tight purely by observing a minimum internal tank pressure relative to the ambient pressure outside the fuel tank (10). The challenge however is that in this situation the canister (11) is subjected to pressure that could either exceed the designed limits of the canister or allow vapour from the fuel tank (10) to escape to the external atmosphere in the event that the canister (11) is impacted and broken Figure 2 shows a step of the method for controlling the fuel vapour pressure in a vehicle fuel system (1) on board of a vehicle according to the invention.

During this step, the fuel tank (10) is isolated from a canister (11) by and the means for controlling the fluid communication (12). The fuel tank (10) is sealed from the atmosphere (18) and the canister (2) is fluidly connected to the atmosphere (18) by the means for controlling the fluid communication (12) In this configuration the fuel tank (1) is sealed to limit hydrocarbons from accruing in the canister (11), and avoids pressurization of the canister (11) that could pose a risk in which the canister (11) is subjected to pressure that could either exceed the designed limits of the component or allow vapor from the fuel tank (10) to escape in the event that the canister is impacted and broken.

A leak check of the vehicle fuel system (1) including the canister (11) is not possible in this condition.

Figure 3 shows a step of the method for controlling the fuel vapour pressure in a vehicle fuel system (1) on board of a vehicle according to the invention.

During this step, the fuel tank (10) is fluidly connected to a canister (11) by means of vent lines (14, 15) and the means for controlling the fluid communication (12). The canister (11) is fluidly connected to the atmosphere (18) by the means for controlling the fluid communication (12). In this configuration, the fuel tank (10) is allowed to vent hydrocarbons to the canister (11) where the hydrocarbons are adsorbed, and clean air exits the canister (11) via the means for controlling the fluid communication (12) to the external atmosphere.

This position avoids positive pressure inside the fuel tank (10) or the canister (11) relative to the external atmosphere (18) by pushing hydrocarbons directly to the external atmosphere (18 by pressure balancing the vehicle fuel system (1) through the active carbon canister (11)

Claims

1. Method for controlling the fuel vapour pressure in a vehicle fuel system (1) on board of a vehicle, the method comprising the following steps of: a. Switching the vehicle to a key off mode; b. Providing a fluid communication between a fuel tank (10) and a canister (11); c. Sealing the canister (11) and the fuel tank (10) from the external atmosphere (18), d. Measuring the pressure, Pt, in the fuel tank (10); e. Wherein, when the pressure, Pt, measured at step C is equal or greater than a first pressure threshold, closing the fluid communication between the canister (11) and the fuel tank (10) and providing a fluid communication between the canister (11) and the external atmosphere (18);

2. Method for controlling the fuel vapour pressure in a vehicle fuel system (1) on board of a vehicle according to claim 1, wherein the pressure, Pt, in the fuel tank (10) is measured at several different time intervals.

3. Method for controlling the fuel vapour pressure in a vehicle fuel system (1) on board of a vehicle according to claim 2, wherein said method comprises an additional step e1., wherein the values of the pressure, Pi, measured in step c. at several different time intervals, t, are compared against each other, If none of the differences between the pressure values, Pt, measured are greater or equal to a second pressure threshold, concluding that there is a leak in the vehicle fuel system (1) and providing fluid communication between the fuel tank (10) and the external atmosphere (18) via the canister (11).

4. Method for controlling the fuel vapour pressure in a vehicle fuel system (1) on board of a vehicle according to claim 2, wherein said method comprises an additional step e2., wherein the values of the pressure, Pi, measured in : step c. at several different time intervals, t, are compared against each other, If the differences between the pressure values, Pi, measured are greater or equal to the second pressure threshold, closing the fluid communication between the canister (11) and the fuel tank (10) and providing a fluid communication between the canister (11) and the external atmosphere (18).

5. Method for controlling the fuel vapor pressure in a vehicle fuel system (1) on board of a vehicle according to any one of the preceding claims, wherein a measurement of a temperature, Ti, is performed in step c.

6. Method for controlling the fuel vapor pressure in a vehicle fuel system on board of a vehicle according to claim 5 and any one of the claims 3 to 4, wherein the temperatures, Tt, are measured in the vapour dome of the fuel tank.

7. A vehicle fuel system (1) on board of a vehicle comprising: e a fuel tank (10); e a canister (11); * a means for controlling the fluid communication (12) between | the fuel tank (10) and the canister (11) and between the canister (11) and the external atmosphere (18), wherein said means comprises at least a bi-phase valve (120); e a pressure sensor (13) provided to measure the pressure in the vehicle fuel system (1), said pressure sensor (13) being located in the vapour dome (100) of the fuel tank (10); + a temperature sensor (16); e an electronic control unit (ECU) controlling the means for controlling the fluid communication (12) between the fuel tank (10) and the canister (11) and between the canister (11) and the external atmosphere (18), said electronic controlling unit (ECU) provided to performed the steps of the method according to any one of the claims 1 to 6.

8. Vehicle fuel system (1) on board of a vehicle according to claim 7, wherein the means for controlling the fluid communication (12) between the fuel tank (10) and the canister (11) and between the canister (11) and the external atmosphere (18) consists of bi-phase valves (120).

9. Vehicle fuel system (1) on board of a vehicle according to any one of claims 7 to 8, wherein the canister (11) is an active carbon canister.

10. Vehicle fuel system on board of a vehicle according to any one of claims 7 to 8, wherein the temperature sensor (16) is located in the vapour dome (100) of the fuel tank (10).