Method and system for detecting a leak in a fuel system

Abstract

It is proposed a method for detecting a leak in a fuel system of a combustion engine comprising a fuel tank. The method is such that it comprises the steps of: obtaining a first set of data comprising at least a pressure data measured in the fuel system at a first time; adding energy to fluids contained in the fuel system, said energy being produced or wasted by means already present on board the vehicle for other purposes; obtaining a second set of data comprising at least a pressure data measured in the fuel system at a second time; determining the presence/absence of a leak in said fuel system by calculating a predetermined function on the basis of said first and second sets of data.

Claims

1. A method for detecting a leak in a fuel system of a combustion engine of a hybrid vehicle, the fuel system comprising a fuel tank and a fuel pump, the fuel system providing fuel to the engine for combustion of the fuel by the engine, the method comprising: obtaining a first set of data comprising at least a pressure data measured in the fuel system at a first time; then powering the fuel pump so as to heat fuel in the fuel tank, thereby adding energy to the fuel; then obtaining a second set of data comprising at least a pressure data measured in the fuel system at a second time; then determining a presence/absence of a leak in said fuel system by calculating a predetermined function based on said first and second sets of data.

2. The method according to claim 1, wherein said first set of data further comprises a temperature data measured in the fuel system at the first time, and said second set of data further comprises a temperature data measured in the fuel system at the second time.

3. The method according to claim 1, wherein said predetermined function is further calculated based on information relative to the fuel flowing out of the fuel system during a time interval between the first and second times.

4. The method according to claim 1, wherein the combustion engine is on board of a hybrid vehicle comprising an electrical engine.

5. The method according to claim 4, which is performed when the combustion engine is not running but when the electrical engine is running.

6. The method according to claim 4, wherein the hybrid vehicle is a plug-in hybrid vehicle.

7. The method according to claim 1, wherein adding energy to the fuel comprises: closing fuel injection valves at the combustion engine.

8. The method according to claim 7, wherein the fuel system comprises a recirculation path of the fuel configured to maximize movement of the fuel and/or mixing of the fuel with air and vapor.

9. The method according to claim 1, wherein pressure is directly induced in the fuel system by pumping air into the fuel tank using a coolant driven air pump.

10. The method according to claim 1, wherein a fuel level input is used to establish a heat capacity of the fuel present in the fuel tank.

11. A fuel system comprising a fuel tank, a temperature sensor, a pressure sensor, a processor and a mechanism to conduct the adding of the energy to fluids contained in the fuel system, said energy being produced or wasted by another mechanism already present on board the vehicle for other purposes; said temperature sensor and said pressure sensor being arranged to measure conditions inside said fuel tank and operatively connected to said processor; wherein said processor is configured to carry out the method of claim 1.

12. A non-transitory computer readable medium having stored thereon a computer program for use in a fuel system comprising a fuel tank, a temperature sensor, a pressure sensor, a processor and a mechanism to conduct the adding of energy to fluids contained in the fuel system, said energy being produced or wasted by another mechanism already present on board the vehicle for other purposes; said temperature sensor and said pressure sensor being arranged to measure conditions inside said fuel tank and operatively connected to said processor, wherein said processor is configured to carry out, when executed, the method according to claim 1.

Description

(1) These and other aspects and advantages of the invention will be further clarified with respect to the accompanying figures, in which:

(2) FIG. 1 illustrates a fuel tank system according to one embodiment of the invention;

(3) FIG. 2 illustrates a fuel tank system according to another embodiment of the invention;

(4) FIG. 3 illustrates a fuel tank system according to another embodiment of the invention;

(5) FIG. 4 represents a flow chart of a method according to an embodiment of the present invention; and

(6) FIG. 5 illustrates a fuel tank system according to another embodiment of the invention.

(7) FIG. 6 illustrates a fuel tank system according to still another embodiment of the invention.

(8) In a particular embodiment of the invention, the integrity (absence of leak) of the fuel system can be determined by comparing a first pair of measurements (p.sub.1, T.sub.1) with a second pair of measurements (p.sub.2, T.sub.2), the second pair being taken after controlled introduction of an amount of heat and/or pressure to the fuel tank. The present invention is further based on the insight that this determination can be made without using the engine or a dedicated device generating heat and/or pressure but instead, by using such heat/pressure source available on the vehicle, preferably a (plug-in) hybrid vehicle.

(9) The determination of the integrity of the fuel system can be made by calculating a function of the four measured variables (p.sub.1, T.sub.1, p.sub.2, T.sub.2), and comparing this function to a predetermined value.

(10) In an exemplary way, the predetermined value may be a ratio of two pressure-temperature ratios, determined before and after the addition of energy to the fuel system, respectively. If the value of this ratio of ratios is outside a predetermined range, the existence of a fuel leak may be declared.

(11) The ratio analysis is based on the premise that, for a closed system, the pressure (p)/absolute temperature (T) ratio is constant:

(12) $\frac{p_1}{T_1}=\frac{p_2}{T_2}$

(13) The above equation, known as Gay-Lussac's law is a special case of the ideal gas law, which states that
pV=nRT

(14) in which the volume (V) of the gas system and the quantity (n) of gas particles also appear.

(15) For a system with constant volume, a set of measurements in which

(16) $\frac{p_1}{T_1}>\frac{p_2}{T_2}$

(17) is indicative of a decrease in the quantity of gas in the system (n.sub.1>n.sub.2), which could signify the presence of a leak.

(18) There is typically an amount of liquid fuel inside the fuel system, as well as a gaseous phase consisting of a mixture of fuel vapor and air. The measurements and calculations cited above may be applied to the gaseous phase. However, the pressure of the gaseous phase will be influenced by the vapor pressure of the fuel in the tank, which is in turn influenced by the temperature of the system. As a result, it can become necessary to incorporate additional data elements (i.e. factors) to the basic function of ratios. For example, these data elements can include the influence of a fuel's intrinsic vapor pressure, and the base temperature at which the test begins, to further define this vapor pressure level.

(19) In the event that there is no internal pressure in the tank at the beginning of the test, the system must rely on the fact that a temperature rise will result in a pressure rise based on the change in temperature and the factors stated above. Based on this, it is possible to determine to some degree of accuracy the leak in the system, since we have a theoretical P2 and an actual P2.

(20) The FIGS. 1, 2, 3, 5 and 6 show a fuel system 1 that is in fluid communication with a charcoal canister 2 via fluid line 4. The charcoal canister 2 has another fluid line 5 connected to the intake manifold 3 of the internal combustion engine. A valve 6 is disposed in the fluid line 5 to allow for selective communication between the charcoal canister 2 and the intake manifold 3. There is an additional communication between the charcoal canister 2 and the atmosphere. This communication can be selectively controlled via a valve 8 to create completely sealed system. An additional valve 7 is placed on the intake manifold 3 commonly known as the throttle valve, to control the amount of intake air. The fuel system further comprises a pressure sensor 9 adapted for measuring the pressure inside the fuel tank 1.

(21) An additional valve (not pictured) could be disposed in the fluid line 4 for isolating the tank 1 from the canister 2 to avoid unwanted loading of the vapor storage canister 2. In this case the valve (not pictured) would ideally be open during the test, in order to test the complete system.

(22) FIGS. 1, 2, 3 and 6 show a battery cooling system as present in a plug-in hybrid vehicle. The cooling system comprises a battery 10 which is cooled via a cooling fluid flowing through a first heat exchanger 11 for taking up heat at the side of the battery 10. The cooling fluid furthermore flows through a second heat exchanger 12 for being cooled down. The cooling fluid is pumped via a pump 13 from the first heat exchanger 11 to the second heat exchanger 12 and back, thereby flowing in a closed loop.

(23) The fuel tank of FIGS. 1, 2, 3, 5 and 6 further comprises a temperature sensor 19. Although the figures show only one temperature sensor 19 and only one pressure sensor 9, several of these sensors can be placed at strategic locations in the fuel tank to get a more detailed measurement of temperatures and pressures present in the fuel tank. As explained above, in a closed fuel tank, leaks can be detected via pressure and temperature information before and after a temperature change.

(24) In one embodiment of the invention, as shown in FIG. 1, battery heat is used to heat the fuel in the fuel tank. To this end, a third heat exchanger 14 is provided inside the fuel tank. A three-way valve 17 is provided in the cooling liquid circuit, whereby the three-way valve can direct the cooling liquid to the second heat exchanger 12 without passing through the third heat exchanger 14 (normal operation) and whereby the three-way valve can direct the cooling liquid to the third heat exchanger 14, so that heat is transferred to the fuel in the tank 1. In this manner, so-called waste energy, heat from the batteries, is used as energy input in the leak detection process, thereby making this process energy efficient. No extra energy has to be produced, because pump 13 runs anyway to cool the batteries.

(25) To further enhance the accuracy of the leak detection system, a fuel level input 18 could be used in a preferred embodiment, to establish the heat capacity of the fuel present in the fuel tank. Since there is a different thermal mass that needs to be heated in a full tank as compared to a substantially empty tank, the temperature rise inside the tank could potentially be different depending on the fuel level when adding energy to the tank.

(26) FIG. 2 shows an embodiment similar to the embodiment of FIG. 1 that could be used in the case that the fuel tank (1) needs to resist to internal pressure (which is generally the case with hybrid vehicles). In this embodiment, the regular heat exchanger 14 is replaced by a reinforcing heat exchanger 20 disposed in the tank 1 and which is in the shape of a structural member or truss system. The vertices of the heat exchanger 20 are attached to the inner surface of the tank 1 via an interface piece 21 which is either welded or rivet snapped to the interior of the tank.

(27) FIG. 3 shows yet another embodiment similar to the embodiment of FIGS. 1 and 2, whereby battery heat is used to heat the fuel inside the fuel tank. However battery heat is not directly transferred to the fuel or fuel tank via the cooling liquid, but is transferred via air flowing over the second heat exchanger 12 when cooling down the cooling liquid at the second heat exchanger 12. The air flowing over the second heat exchanger 12 is guided in a channel comprising an air directing valve 26. The valve 26 is provided either to direct the air away from the fuel tank 1, or to direct the air to flow over and directly adjacent the fuel tank 1 so that the energy (heat) captured by the air in the second heat exchanger 12 is partially transferred to the fuel tank 1 thereby heating the fuel tank 1 and the fuel. An advantage of this embodiment is that the cooling liquid does not enter the fuel tank 1 so that there is no risk of fluid exchange/contamination between the two systems.

(28) A flow chart explaining the method according to the invention is shown in FIG. 4. The flowchart shows, in a first step, the measurement of a first temperature and a first pressure. After the first step, energy is added to the fuel system as second step. As explained in relation with the FIGS. 1, 2, 3, 5 and 6, several techniques can be applied to add energy to the fuel system. In a third step, a second temperature and a second pressure are measured. Finally the first temperature and pressure measurement and the second temperature and pressure measurement are used as factors in a predetermined formula for calculating a leak factor indicative of the chance of presence of a leak.

(29) Signaling the presence of a leak can then, the case being, be conducted in any suitable manner known to the skilled person, for example by lighting up an indicator at the dashboard of the vehicle.

(30) FIG. 5 shows an alternative embodiment of the present invention, whereby the energy added to the fuel system does not originate from the batteries. In this embodiment, a fuel pump 22 is disposed in the fuel system 1 to deliver liquid fuel to the intake 3. To regulate the pressure that is delivered to the intake 3 a pressure regulator or bypass valve 23 is disposed in the system. In this embodiment, a control strategy would be implemented to close the fuel injectors on the engine intake 3 and send power to the fuel pump 22 causing it to heat up. The heat from the fuel pump 22 would in turn heat up the fuel at a specified rate linked to the physical properties of the pump. Since the fuel injectors are closed, fuel would be recirculated back into the fuel tank 1 causing for additional pressure generation due to the effect of turbulence in the fluid. Based on the pressure rise due to the addition of heat and turbulence, it can be determined if the fuel system has a leak or not.

(31) FIG. 6 depicts another embodiment of the invention in which pressure is directly induced in the fuel system 1 by pumping air into the system via means of a coolant driven air pump 25. In this embodiment, a pump 13 is used to flow coolant through a heat exchanger 11 in the vehicles battery 10 to cool it, as in the embodiments of FIGS. 1 to 3. After exiting the battery 10, the fluid flows through the disclosed air pump 25 (which is like an impeller powered by the flow of coolant) and then through a heat exchanger 12 that is used to further cool the fluid before being cycled back through the battery 10. In normal operation, a diverter valve 27 diverts the air flow from the pump 25 to the atmosphere, resulting in minimal loading on the pump 25. When a leak check is commanded by the vehicle, the diverter valve 27 directs the flow of air from the canister 2 into the tank 1 and seals the port to the atmosphere. As a result, the pressure in the tank increases at a known rate, allowing the vehicle to determine if there is a leak in the system. If there is a leak, naturally the pressure rise will be lower than that of a sealed system. The pressure sensor (9) can be used to measure this.

(32) Although the invention has been disclosed by means of a limited number of concrete embodiments, this was done to illustrate the invention, and not to limit its scope. The skilled person shall understand that features described in connection with specific embodiments may be combined with features from other embodiments to achieve the corresponding effects and advantages.