FOR OPERATING A VEHICLE TANK ARRANGEMENT

BACKGROUND OF THE INVENTION

FIELD OF THE DISCLOSURE

[0001] The present disclosure relates to a tank arrangement, to a vehicle comprising a tank arrangement as well as to a method for operating a vehicle tank arrangement.

DESCRIPTION OF THE RELATED ART

[0002] Various systems and techniques are known for storing fuel in vehicles. In trucks, it has become common to use a dual tank configuration in which two tanks are used to store the necessary fuel. Among other possible

configurations, it is common to store fuel in a master tank and one or more so- called "slave" tanks. Fuel for the vehicle engine can be drawn from both the master tank and the slave tank. More recently, it has become common to draw fuel for the vehicle engine directly from the master tank and indirectly, i.e. via the master tank, from the slave tanks.

[0003] A common problem associated with such indirect master-slave configurations, however, is that it is difficult to draw the full capacity of fuel from the slave tanks; a certain percentage of fuel always remains in the slave tanks. This unused capacity / remaining fuel translates into reduced range and increased weight. Moreover, such indirect master-slave configurations often require refilling to be done in a certain order, i.e. one specific tank must be filled before the other tank can be filled. [0004] Another common problem associated with such master-slave configurations is that a parking of the vehicle on a slope can result in a flow of fluid into the slave tank, thus emptying the master tank. This emptying of the master tank can cut off the flow of fuel to the engine.

[0005] Various solutions have been proposed for addressing these problems. For example, WO 2010/068149 teaches a tank arrangement in which the master tank and the slave tank are connected by a balancing pipe. A suction pipe feeds fuel to the vehicle engine and a return pipe feeds fuel from the engine to at least one of the fuel tanks. The balancing pipe is provided with a first end to supply fuel to the master tank and a second end to suck fuel out of the slave tank. A check valve is arranged upstream of the return pipe in the balancing pipe between the two tanks allowing a flow direction from the second tank to the first tank and blocking a flow in the reverse direction. However, this approach does not allow the slave tank to be sufficiently emptied.

[0006] JP 51-148120 provides a continuous supply of fuel from a slave tank to a master tank by taking advantage of the difference between the negative pressure associated with the reduction of fuel in the master tank and the atmospheric pressure acting on the surface of fuel in the slave tank in a fueling device with multiple fuel tanks. However, this technique is not without disadvantages. For example, if the flow of fuel from the slave tank to the master tank becomes blocked, the resultingly large negative pressure in the master tank will inhibit the flow of fuel from the master tank to the engine. Moreover, this technique prohibits estimation of the total amount of fuel based on measurement in a single tank since the level of fuel in the slave tank will often differ significantly from the level of fuel in the master tank. Indeed, there is a risk of destroying the master tank if the fuel flow between the master tank and the slave tank is completely blocked.

[0007] It is an object of the present disclosure to address the aforementioned shortcomings of the prior art. BRIEF SUMMARY OF THE DISCLOSURE

[0008] This object is solved by a tank arrangement according to claim 1 as well as a vehicle according to claim 13 and a method according to claim 15.

[0009] The present invention is based on the idea to provide a tank

arrangement for a vehicle, in particular a truck, which comprises an air pressure regulating system that regulates an air pressure of the first fuel tank and/or an air pressure of the second fuel tank so that the air pressure in the first fuel tank is lower than the air pressure in the second fuel tank. Due to the greater pressure in the second tank, fuel is reliably transported through the balancing pipe from the second tank to the first tank. Accordingly, fuel can be emptied from the second tank into the first tank to the fullest degree possible.

[0010] Additionally, the disclosed tank arrangement comprises at least one first fuel tank and at least one second fuel tank, which are connected by a balancing pipe. Hereinafter, the at least one first fuel tank and at least one second fuel tank will be referred to as "the first tank'V'the second tank," respectively.

Accordingly, the term "the first/second tank" is to be interpreted as meaning any one or more of the at least one first / second tanks.

[0011] In case the first/second tank comprises more than one tank for maximizing the fuel volume on a truck, each tank can be made of the same or of different material. Thereby even the master tank, from where the fuel is preferably solely supplied to the engine can consist of more than one tank, as long as air can move freely near to top of tank and fuel can move freely near to bottom of tank.

[0012] According to a preferred embodiment, the tank arrangement comprises a one way valve, such as a check valve, that is arranged in the balancing pipe between the at least two tanks for allowing a flow direction from the second tank to the first tank and blocking a flow in the reverse direction. The one way valve ensures that fuel cannot flow from the first tank back into the second tank, e.g. if the vehicle is on a slope. Nonetheless, due to the pressure difference between the first and second tanks, the fuel flowing through the balancing pipe from the second tank can overcome the flow resistance imposed by the one way valve and thus flows to the first tank.

[0013] According to a further preferred embodiment, the air pressure regulation system may comprise a first air passage that connects the first fuel tank with an ambient atmosphere and exhibits a first resistance to air passing therethrough. The air pressure regulation system may moreover comprise a second air passage that connects the second fuel tank with the ambient atmosphere and exhibits a second resistance to air passing therethrough. The first resistance of the first air passage may be larger than the second resistance of the second air passage.

[0014] Preferably, the first and/or second resistance can be determined by the cross-sectional area and/or the lengths of the first and/or second air passage. In other words, the cross-sectional area and/or the length of the first / second air passage can be chosen such that the resistance imposed by the first air passage to air passing therethrough is larger than the resistance imposed by the second air passage to air passing therethrough. In this manner, air passing through the first air passage experiences a larger pressure drop than air passing through the second air passage. Accordingly, the pressure in the second tank can be made higher than the pressure in the first tank just using simple passive devices such as accordingly dimensioned air passages, e.g. pipes or tubes.

[0015] According to a further preferred embodiment, the air pressure regulation system may comprise at least one air filter in the first and/or second air passage. The first and/or second resistance will then be at least partly defined by the resistance imposed by the air filter to air passing therethrough. The resistance of the air filter in the first air passage can be made larger than the resistance of an air filter in the second air passage. The resistance imposed by the filters can be adjusted through the thickness and/or density of a filter material used in the respective filter. Using one or more passive components such as an air filter to regulate the pressure in the first tank to a lower pressure than the pressure in the second tank is a cheap and reliable technique for transporting fuel from the second tank to the first tank.

[0016] Alternatively or additionally, the air pressure regulation system may comprise a pressurizing device, e.g. an air pump or a control valve that regulates an influx of pressurized air, for regulating the pressure in the second fuel tank to a higher air pressure than the air pressure in the first fuel tank. Such a pressurizing device could also be activated when pressure sensors within the tanks determine that passive components of the air pressure regulation system are failing to maintain the desired pressure difference, e.g. as could occur if an air filter to the second tank becomes clogged. Such a pressurizing device could likewise be of utility in transporting fuel over a long distance, e.g. from a second tank located in the aft of the vehicle, or over a significant difference in height, e.g. if the second tank must be positioned much lower than the first tank on the vehicle. The pressurized air already available on the truck could be tapped as a source of pressurized air for the pressurizing device.

[0017] According to a further preferred embodiment, the balancing pipe may comprise a first leg to supply fuel to the first tank and a second leg to suck fuel from the second tank. The ends of the first and/or second leg may extend to the gravitational bottommost portion of the first and/or second fuel tank,

respectively. Preferably, the second leg of the balancing pipe may have a clearance of not more than 4 cm, preferably not more than 2 cm, to the second tank bottom.

[0018] By providing the end of the second leg in the gravitationally bottommost portion of the second tank, nearly the full volume of the fluid in the second tank can be transported out of the second tank via the balancing pipe as gravity pulls the fuel in the second tank to the gravitationally bottommost portion of the second tank. Since the end of the second leg will remain submerged in the fuel until only a predetermined percentage (e.g. 5%, 1% or even 0.1% of a total volume) of fuel remains in the second tank, the pressure difference between the first tank and the second tank will push the fuel through the balancing pipe into the first tank. Providing the end of the first leg in the gravitationally bottom portion of the first tank can ensure that the balancing pipe remains full of fuel until the fuel level in the second tank drops below the level of the end of the second leg. As in the so-called "siphon effect," retention of fuel in the balancing pipe can help to offset the balance of hydrostatic pressure at the respective ends and thus facilitate fuel transport from the second tank to the first tank.

[0019] Additionally, the tank arrangement of a further preferred embodiment may comprise a return pipe for feeding fuel from the engine to at least one of the first and/or second tanks. The aforementioned one way valve, may be arranged upstream of the return pipe. The one way valve, may provide an automatic purging function to remove air from the balancing pipe between the first and second tank. The connection between the fuel return pipe and the balancing pipe can be configured such that fuel entering the balancing pipe from the return pipe flows toward the first tank, where a suction pipe (e.g. driven by a fuel pump coupled to the engine) may be arranged, thus maintaining the siphon effect during driving.

[0020] The tank arrangement may moreover be configured so as to ensure that all air is removed from the balancing pipe by using the return fuel velocity in the return pipe, an ejector device and the one way valve. Accordingly, when an empty tank is refilled, the tank arrangement purges itself automatically and resumes its desired operation. For example, the return pipe and the balancing pipe may be merged at an ejector device supporting fuel transport from the second tank to the first tank, wherein the return pipe is attached to a high pressure side and the balancing pipe is attached to a suction side of the ejector device. Similarly, the return pipe may join the balancing pipe in a valve unit comprising an ejector device supporting fuel transport from the second tank to the first tank, wherein the one way valve and the ejector valve are integrated in the valve unit.

[0021] According to a further preferred embodiment, the tank arrangement may comprise a suction pipe from the first tank to the engine for feeding fuel to the engine, wherein preferably, the suction pipe is the sole supply of fuel to the engine. Additionally, the tank arrangement may comprise a fuel level sensor for sensing the fuel level in the first tank. Drawing fuel solely from the first tank allows the suction system to be simplified. Similarly, it is advantageous if the fuel level needs only be measured in one tank.

[0022] It should be noted that the tank arrangement preferably has a structure that allows containment of a volume of fluid, in particular a volume of fuel and air. The first tank and the second tank can be formed as separate elements and may be formed of metal or plastic. Each of the first and second tanks may have a volume on the order of several tens, several hundreds or several thousands of liters, wherein the first tank may have a larger volume than the second tank. Each of the tanks may comprise more than one container made of the same material or of different materials, the individual containers being connected by piping.

[0023] The balancing pipe may be a pipe or tube or comprise piping or tubing, wherein the balancing pipe or any part thereof may be formed of metal and/or plastic. Moreover, the balancing pipe may form a closed passage from the end of the second leg in the second tank to the end of the first leg in the first tank and/or may be connected to other conduits that do not lead to the first tank or the second tank. A flow of fuel from the second tank into such other conduits may be inhibited by orientation of the other conduit relative to the force of gravity, by one or more passive devices, e.g. by a one-way valve or by a section of pipe having a higher flow resistance than the portion of the balancing pipe leading to the first tank, and/or by one or more active devices, e.g. by a pump that pressurizes a fluid in the other conduit to a pressure that is higher than a pressure of the fuel in the second tank.

[0024] The air pressure regulating system may comprise solely passive pressure regulating devices, solely active pressure regulating devices or a mixture of active and passive pressure regulating devices.

[0025] As discussed above, an interior volume of the first and/or second tank is in gaseous communication with an ambient atmosphere or another air reservoir via the first and/or second air passage. Thereby, the first and/or second fluid passage may constitute the sole path of gaseous communication between the interior volume of the first and/or second tank and the ambient atmosphere and/or another air reservoir excepting the aforementioned balancing pipe between the first and second tank.

[0026] As discussed above, the first air passage may comprise a first pipe that imposes a first resistance to a portion or all of the air passing through the first air passage and the second air passage may comprise a second pipe that imposes a second resistance to a portion or all of the air passing through the second air passage. The resistance imposed by the pipes can be adjusted through the length and/or cross-sectional area of the respective pipe. The first pipe may have a cross-sectional area that is less than 20%, less than 5% or even less than 1% than the smallest cross-sectional area of the second pipe. The first pipe may have a length that is longer than the length of the second pipe. Using one or more passive components such as a pipe to regulate the pressure in the first tank to a lower pressure than the pressure in the second tank is a cheap and reliable technique for transporting fuel from the second tank to the first tank.

[0027] According to a further preferred embodiment, the first air passage and/or the second air passage may comprise a relief valve that automatically vents air into the inner volume of the first/second tank if the pressure in the first/second tank falls below a predetermined pressure, e.g. on the order of 15 mbar, relative to the ambient atmosphere. In this manner, the pressure in the first/second tank can be regulated. Furthermore, an undesirably large pressure difference between the first and second tank can be avoided. As fuel is drawn out of the first/second tank, the pressure in the respective tank decreases unless fluid at a higher pressure is vented into the respective tank. This decrease in pressure makes it increasingly more difficult to draw fuel from the respective tank. Moreover, this decrease in pressure may lead to a pressure difference in the various tanks. If tanks having differing inner pressures have a fuel connection, this can lead to fuel being transported from the higher pressure tank to the lower pressure tank. If such a transport of fuel does not lead to pressure equilibrium between the tanks, e.g. because fuel is regularly drawn from the lower pressure tank and/or because a bidirectional flow of fuel is prevented by a one-way valve, this can lead to the higher pressure tank being entirely emptied before the lower pressure tank begins to significantly empty. However, an emptying of the respective tanks at differing rates can impede simple measurement of the volume of fluid contained in the storage system. In general, it is desirable to be able to ascertain the volume of fuel contained in the tank arrangement by measuring the volume of fuel in solely one of the tanks.

[0028] In a further aspect, the present disclosure teaches a vehicle comprising a tank arrangement as described elsewhere in this disclosure. The vehicle may be a truck, car, train engine or ship, for example, preferably comprising a combustion engine, wherein the tank arrangement may constitute a fuel storage system of the vehicle, e.g. a system for storing fuel to be consumed by the combustion engine of the vehicle.

[0029] According to a further preferred embodiment, the vehicle may be configured such that the combustion engine draws fuel from said second tank solely via said first tank. Moreover, the vehicle may be configured such that surplus fuel that is drawn from the first tank, yet not consumed by the combustion engine, is returned via a return pipe, e.g. as described supra, to the first and second tank or solely to the first tank. The return pipe may be in fluid connection with the balancing pipe, e.g. via a one-way valve that prevents a flow of fluid in a direction away from the first tank. A vehicle employing a tank arrangement as disclosed herein can store its fuel in two or more tanks that are physically separated from one another. This makes it possible to distribute the weight of the fuel in a more desirable manner. This also makes it possible to reduce the size of the individual fuel tanks without compromising the overall capacity of the fuel storage system, i.e. without compromising the range of the vehicle. Smaller-sized tanks can be more easily accommodated in the vehicle than large tanks.

[0030] On the other hand, the fuel stored in the second tank can be used in addition to the fuel stored in the first tank, whereby the driving range of the vehicle can be increased.

[0031] The first tank and the second tank may be mounted in the vehicle such that, in a normal operating orientation of the vehicle on level ground, the gravitationally bottommost inner volume of the first tank and the gravitationally bottommost inner volume of the second tank are roughly at the same height, or are at different heights preferably depending on which configurations of the first and second tank facilitate transport of the liquid from the second tank to the first tank.

[0032] The present disclosure also teaches a method for operating a vehicle tank arrangement as described elsewhere in this disclosure. The method comprises the step of regulating an air pressure of the first fuel tank and/or an air pressure of the second fuel tank such that the air pressure in the first fuel tank is lower than the air pressure in the second fuel tank.

[0033] As discussed supra, the pressure regulating system may be effected using solely passive pressure regulating devices, solely active pressure regulating devices or a mixture of active and passive pressure regulating devices. Due to the greater pressure in the second tank, fluid can be reliably transported through the conduit from the second tank to the first tank.

[0034] Preferably, fuel is drawn from the second tank to an engine via the balancing pipe and the first tank. Since fuel is always drawn from the first tank, it suffices if fuel is only filled into the first tank. In situations where it is not necessary to fill the full volume of the tanks to reach the desired destination, this spares the driver the hassle of having to fill fuel into various tanks.

[0035] The first and/or second tank may comprise a vent, e.g. a ball valve, that allows fluid communication between the inner volume of the first/second tank and the ambient atmosphere when the tank arrangement is an operational orientation and that prevents fluid communication between the inner volume of the first/second tank and the ambient atmosphere when the tank arrangement is upturned or unduly tilted. The vent may be provided along the first / second air passage.

[0036] Furthermore, the first and/or second tank may comprise a relief valve that automatically vents air from the inner volume of the first/second tank if the pressure in the first/second tank exceeds a predetermined pressure relative to the ambient atmosphere. Such a relief valve is useful for alleviating undue pressure that may result when fuel that was cold when filled into the tanks warms up and expands e.g. due to changes in the ambient temperature. The relief valve may be provided along the first / second air passage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The novel features of the invention, as well as the invention itself, both as to its structure and its operation will be best understood from the accompanying figures, taken in conjunction with the accompanying description. The Figures show:

Fig. 1 a schematic view of a first embodiment of a tank arrangement in accordance with the present disclosure;

Fig. 2 a schematic view of a second embodiment of a tank arrangement in accordance with the present disclosure;

Fig. 3 a schematic view of a third embodiment of a tank arrangement in accordance with the present disclosure;

Fig. 4 a schematic view of a fourth embodiment of a tank arrangement in accordance with the present disclosure;

Fig. 5 a schematic view of a fifth embodiment of a tank arrangement in accordance with the present disclosure; and

Fig. 6 a schematic view of a sixth embodiment of a tank arrangement in accordance with the present disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 shows a first embodiment of a tank arrangement 100 in accordance with the present disclosure. The tank arrangement 100 illustrated in Fig. 1 comprises a first tank 10 as a master tank and a second tank 20 as a slave tank. The first tank 10 is shown as containing fuel 11 as well as air 12. The second tank 20 is likewise shown as containing fuel 21 as well as air 22.

[0039] The tank arrangement 100 illustrated in Fig. 1 moreover comprises a balancing pipe 30. The balancing pipe 30 may comprise an optional filter 31 for filtering fuel drawn from the second tank 20 into the balancing pipe 30, and may comprise an optional one way valve, such as a check valve 32 that prevents a reflux of fluid from the balancing pipe 30 into the second tank 20. Preferably, the balancing pipe 30 has an inner diameter of 12 mm or more. [0040] The tank arrangement 100 illustrated in Fig. 1 further comprises an air pressure regulating system 40 that regulates the pressure of the air 12 in the first tank 10 to a pressure that is lower than the pressure of the air 22 in the second tank 20. As described above, the air pressure regulating system 40 can be modified to alternatively or additionally regulate the pressure of the air 22 in the second tank 20 to a pressure that is higher than the pressure of the air 12 in the first tank 10. This pressure difference between the two tanks 10, 20 facilitates transport of fuel from the second tank 20 to the first tank 10 through balancing pipe 30, even if the upper surface of the fuel 21 in the second tank 20 is lower than the upper surface of the fuel 11 in the first tank 10 by a difference in height Ah.

[0041] The air pressure regulating system 40 may be part of a ventilation system that allows an exchange of air between the interior of the respective tank 10, 20 and the ambient atmosphere. The air pressure regulating system 40 may likewise be part of a fuel sender that transports fuel from the respective tank 10, 20 to a consumer and/or that is used to gauge the level of fuel in the respective tank 10, 20.

[0042] The tank arrangement 100 further comprises a first air passage 60 that allows for fluid communication between the inner volume of the first tank 10 and the ambient atmosphere and/or an additional air reservoir. Thereby, instead of air any other suitable gas or liquid can be used. The first air passage 60 may comprise one or more sections of pipe 61 that form one or more respective portions of the first air passage 60. The sections of pipe 61 may have an inner diameter of roughly 6 mm.

[0043] As shown in Fig. 1 , the first air passage 60 comprises at least one flow- restricting element 64 that imposes a resistance to a portion or all of the air passing through the first air passage 60, e.g. such that the air flowing through the first fluid passage 60 experiences a (significant) pressure drop. For example, the flow-restricting element 64 may be a tubular section having a length of e.g. 30 cm to 100 cm and an inner diameter of less than 2 mm, e.g. an inner diameter of 1 or 1.2 mm. The tubular section may be mounted with a section of pipe 61 of larger inner diameter such that all or at least most part of the air passing through the first fluid passage 60 passes through the tubular section. The flow-restricting element 64 thus constitutes an element of the air pressure regulating system 40, i.e. contributes to the regulation of the pressure of the air in the first (or second, as the case may be) tank 10.

[0044] Instead of a flow-restricting element 64 having a fixed or predetermined diameter it is also possible to use a flow restricting element having a variable cross-sectional area. Thereby, the variable cross-sectional area can

automatically or manually be adjusted.

[0045] The tank arrangement 100 illustrated in Fig. 1 further comprises a second air passage 50 that allows for fluid communication between the inner volume of the second tank 20 and the ambient atmosphere. As mentioned above, the second air passage 50 may also be in fluid communication with an additional air or fluid reservoir, in which instead of air any other suitable fluid can be stored.

[0046] The second air passage 50 may also comprise one or more sections of pipe 51 that form one or more respective portions of the second air passage 50. The sections of pipe 51 have an inner diameter that does not cause a significant pressure drop to the air passing therethrough, e.g. an inner diameter larger than 5 mm. Due to the different inner diameter of pipe 51 and pipe 61 , the air pressure of the second tank adjusts much faster to the ambient air pressure than the air pressure of the first tank. Thereby, an air pressure difference in the first and second tank is established, which in turn allows for the second tank to be emptied to a higher degree than a second tank known from the state of the art. [0047] Additionally, the second air passage 50 may comprise an air filter 52 that filters a portion or all of the air passing through the second air passage 50 and/or a valve 53, e.g. a ball valve, which regulates the flow of air in the second fluid passage 50. The valve 53 may be configured to be in a normally open position and to close if the tank arrangement 100 is unduly tilted or upturned. The valve 53 may likewise be configured to be in a normally closed position and to open if the ambient pressure exceeds the pressure of the air 22 in the second tank 20 by a predetermined amount, or vice-versa.

[0048] As shown in Fig. , the tank arrangement 100 supplies fuel to a combustion engine 200. Specifically, the combustion engine 200 comprises a fuel suction pipe 210 that draws fuel 11 from the bottom portion of the first tank 10 and supplies the fuel 11 to the combustion engine 200. The fuel suction pipe 210 may have an inner diameter of roughly 9 mm and may comprise an optional filter 211 that filters the fuel 11 drawn from the first tank 10 into the fuel suction pipe 210.

[0049] Additionally, the combustion engine 200 comprises a return pipe 220 for returning surplus fuel from the combustion engine 200 to the first tank 10. The return pipe 220 may have a typical inner diameter of roughly 6 mm to 9 mm. In the illustrated embodiment, the return pipe 220 feeds into the balancing pipe 30 and may comprise a one way valve, such as a check valve (not shown) that prevents a flow of fluid from balancing pipe 30 into return pipe 220.

[0050] Preferably, the return pipe 220 joins the balancing pipe 30 in

operational interaction with an ejector device (not shown) in a valve unit (not shown). A flow of return fuel returning from the engine 200 to the ejector device sucks fuel from the second tank 20 into the first tank 10. The ejector device can by way of example be designed as a Venturi valve or the like.

[0051] The other Figures 2 to 5 show further preferred embodiments of a tank arrangement 100 in accordance with the present disclosure. Excepting the first air passage 60, the features of the other embodiment illustrated in Figs. 2 to 5 correspond to the first embodiment illustrated in Fig. 1 and described above.

[0052] In the embodiment illustrated in Fig. 2, the first air passage 60 comprises an air filter 62 that filters a portion or all of the air passing through the first air passage 60. In the embodiment illustrated in Fig. 2, the first air passage 60 moreover comprises an (optional) valve 63, e.g. a ball valve, that regulates the flow of air in the first air passage 60. The valve 63 may be configured to be in a normally open position and to close if the tank arrangement 100 is unduly tilted or upturned. The valve 63 may likewise be configured to be in a normally closed position and to open if the ambient pressure exceeds the pressure of the air 12 in the first tank 10 by a predetermined amount, or vice-versa. The air filter 62 and the valve 63 may or may not constitute substantial elements of the air pressure regulating system 40. In other words, the resistance imposed by the air filter 62 and the valve 63 to the air flowing through the first air passage 60 can contribute to the overall air flow resistance. However, in the embodiment shown in Fig 2, the intrinsic resistances of the air filter 62 and the valve 63 are adapted to not impose a significant additional resistance to the air flow.

Embodiments, where the air filter 62 and/or the valve 63 contribute to or constitute the air flow resistance of the air pressure regulating system 40 will be explained later on.

[0053] In the embodiment illustrated in Fig. 3, a filter 62 configured to filter a portion or all of the air passing through the first air passage 60 constitutes the air pressure regulating system 40. As described above, the resistance imposed by the filter 62 to said portion or all of the air passing through the air fluid passage 60 can be adjusted by adjusting the thickness and/or density of a filter material used in the filter 62.

[0054] Thereby, the resistance to the air flow into the first tank can be regulated to be higher than the resistance to the air flow into the second tank. Consequently, air pressure balancing in the first tank is retarded compared to the air pressure balancing in the second tank, which in turn allows for emptying the second tank to a higher degree compared to the known tank arrangements.

[0055] In the embodiment illustrated in Fig. 4, a valve 63 that regulates the flow of air in the first air passage 60 constitutes the fluid pressure regulating system 40. Valve 63 may be a pressure regulating valve configured to be in a normally closed position and to open if the ambient pressure exceeds the pressure of the air 12 in the first tank 10 by a predetermined amount. As fuel 11 is drawn from the first tank 10, the pressure within the first tank 10 will fall. Although this drop in pressure in the first tank 10 can create a pressure difference between the first tank 10 and second tank 20 that facilitates the transport of fuel 21 from the second tank 20 to the first tank 10, this uncontrolled drop in pressure in the first tank 10 can impede or even fully prevent the withdrawal of fuel 11 from the first tank 10. Accordingly, valve 63 regulates the pressure within the first tank 10, e.g. relative to the ambient atmosphere, e.g. by opening when the ambient pressure exceeds the pressure of the air 12 in the first tank 10 by a

predetermined amount. Valve 63 can be a passive device, e.g. a spring-biased relief valve, or an active device, e.g. a servo valve that opens and closes in response to an open/close signal generated in response to signals from accordingly positioned pressure sensors (not shown).

[0056] On the other hand, the valve 63 (and also the valve 53) may also be adapted to open in case the pressure in the first (second) tank exceeds the ambient air pressure and/or a predetermined pressure threshold. A too high air pressure in the tank can occur if, e.g. cold fuel is filled into the tank that warms up and/or expands due to a change of the ambient temperature.

[0057] In the embodiment illustrated in Fig. 5, all or at least two of the flow- restricting elements as discussed in the previous embodiments contribute to the total air flow resistance in the air passage 60. Accordingly, the first air passage 60 comprises a flow-restricting element 64 as taught above with reference to Figs. 1 and 2, an air filter 62 as taught above with reference to Fig. 3 and a valve 63 as taught above with reference to Fig. 4. Any or all of the air filter 62, the valve 63 and the flow-restricting element 64 may constitute significant elements of the air pressure regulating system 40, i.e. may contribute to the regulation of the pressure of the air 11 in the first tank 10.

[0058] In the embodiment illustrated in Fig. 6, the balancing pipe 30 is located between the bottom parts of tanks 10, 20 rather than above them, which is also provided with a one way valve 32. Instead of an arrangement of the balancing pipe 30 between the tanks 10, 20, the balancing pipe 30 may also be arranged below the tanks 10, 20. As in the previously described embodiments, a return pipe that allows a return flow of fuel into the first tank 10 may feed into the balancing pipe 30.

[0059] Naturally, the teachings of Figs. 1 to 6are equally applicable for regulating the air pressure in the second tank via the second air passage 50 in addition or as an alternative to the pressure regulation via the first air passage 60 taught in Figs. 1 to 6. Moreover, it is also possible to regulate the air pressure of the second tank to a higher level than the air pressure in the first tank. This can be achieved e.g. by providing pressurized air to the second tank, whereby the air pressure in the second tank is actively controlled to a higher level than the ambient air pressure and/or than the air pressure in the first tank.

[0060] In addition to the illustrated features, the tank arrangement 100 of any of Figs. 1 to 6 may comprise any of the features described supra. Moreover, any of the illustrated features may be modified as described supra.

[0061] While various embodiments of the present invention have been disclosed and described in detail herein, it will be apparent to those skilled in the art that various changes may be made to the configuration, operation and form of the invention without departing from the spirit and scope thereof. In particular, it is noted that the respective features of the invention, even those disclosed solely in combination with other features of the invention, may be combined in any configuration excepting those readily apparent to the person skilled in the art as nonsensical. Likewise, use of the singular and plural is solely for the sake of illustration and is not to be interpreted as limiting. Except where the contrary is explicitly noted, the plural may be replaced by the singular and vice-versa.

REFERENCE SIGNS:

10 first tank, master tank

11 fuel

12 air

20 second tank, slave tank

21 fuel

22 air

30 balancing pipe

31 filter

32 check valve

33 first leg

34 second leg

40 air pressure regulating system

50 second air passage

51 pipe

52 air filter

53 valve

60 first air passage

61 pipe

62 air filter

63 valve

64 flow restricting element

100 tank arrangement

200 combustion engine

210 fuel suction pipe

211 filter

220 return pipe