Fuel system, controll arrangement and method for controlling a fuel system

Abstract

Control arrangement (100) and a method for controlling a fuel system (10) to supply fuel to a combustion engine (2) of a vehicle (1 ) at a pressure equal to or higher than a first threshold pressure. The fuel system (10) comprises one or more storage tanks (11 , 12, 13, 14) configured for storage of fuel. The fuel system (10) also comprises a first and a second intermediate tank (15, 16), each configured to receive fuel from the one or more storage tanks (11 , 12, 13, 14) for supply to the combustion engine (2). The fuel system (10) also comprises a control fluid circuit (20) adapted to supply a control fluid to each of the first intermediate tank (15) and the second intermediate tank (16) to compress fuel contained therein. The method comprises a step (a) of controlling the control fluid circuit (20) so as to supply control fluid to the first intermediate tank (15) at least until fuel contained therein reaches the first threshold pressure, and a step (b) of controlling the control fluid circuit (20) so as to supply control fluid the second intermediate tank (16) at least until fuel contained therein reaches the first threshold pressure, wherein steps (a) and (b) are performed sequentially and repeatedly.

Description

The present disclosure relates in general to a method for controlling a fuel system of a vehicle. The present disclosure also relates in general to a control arrangement configured to control a fuel system of a vehicle.BACKGROUNDThe efforts to reduce tailpipe emissions has led vehicle manufacturers to explore a variety of different technologies, such as electrification or usage of carbon-free fuels in combustion engines. Electrification of heavy-duty vehicles is however not an easy task e.g., since it requires very large battery packs to meet the power demand and acceptable driving range. These battery packs lead to increased costs, add weight to the vehicle and typically also a reduced available cargo space. An increased weight of the vehicle and reduced cargo space both affect the operating costs of the vehicle. Therefore, although electrification is generally seen as the preferred option within the industry, combustion engines may still (if run on carbon-free fuels) present a viable solution for heavy-duty vehicles, and can likely be implemented faster and more cost-efficiently than converting to electric vehicles.One example of a carbon-free fuel that may be used in combustion engines is hydrogen. Given the high cost of hydrogen and the higher efficiency of compression-ignition engines compared to the so-called Otto cycle engines, it is preferable to use compression-ignition combustion engines for hydrogen fuel applications. More specifically, high-pressure direct injection (HPDI) combustion engines are preferred. In such combustion engines, hydrogen is directly injected at a high pressure near the end or after the compression of air in the engine. Typically a hydrogen pressure in the order of about 350 bar is needed to overcome the in-cylinder pressure of about 200-300 bar.Hydrogen may be stored in pressurized form in one or more storage tanks (often at least two storage tanks) onboard the vehicle. Typically, hydrogen may be fueled to such storage tanks to a predetermined pressure, often in the order of about 700 bar (or in some cases about 1000 bar), at a fuel station. As the hydrogen stored onboard the vehicle is consumed by the combustion engine, the pressure in the storage tanks decreases and eventually reaches a pressure that is insufficient for injection into the combustion engine. As evident from the above mentioned figures, this may typically occur when only about half of the hydrogen from the storage tanks has been consumed.In order to allow using more of the hydrogen fueled to the vehicle, it would be necessary to increase the pressure of the hydrogen before injection. Preferably, it would be desirable to be able to increase pressure of hydrogen from at least about 100 bar to the injection pressure, such as about 350 bar.Including a compressor in the fuel system may allow increasing the pressure such that more of the hydrogen fueled to the vehicle may be used to propel the vehicle. However, developing a compressor capable of reliably increasing the pressure of hydrogen over a sufficiently large pressure range is not an easy task. Today, a high-pressure compressor having a reasonable size and being suitable for onboard does not appear to exist on the market.SUMMARYThe object of the present invention is to provide a solution, suitable for use onboard a vehicle, for increasing pressure of gaseous fuel to a needed or desired first threshold pressure suitable for supply to a combustion engine of the vehicle.The object is achieved by the subject-matter of the appended independent claim(s).The present disclosure relates to a method, performed by a control arrangement, for controlling a fuel system of a vehicle to supply gaseous fuel to a combustion engine of the vehicle at a pressure equal to or higher than a first threshold pressure. Said fuel system comprises one or more storage tanks configured for storage of gaseous fuel onboard the vehicle. The fuel system further comprises a first intermediate tank and a second intermediate tank, each configured to receive gaseous fuel from the one or more storage tanks for supply to the combustion engine via a common supply line of the fuel system. The fuel system also comprises a control fluid circuit adapted to supply a control fluid to each of the first intermediate tank and the second intermediate tank to compress gaseous fuel contained therein, said control fluid circuit comprising a pump and a plurality of control valves. The method comprises the following steps:(a) controlling the control fluid circuit so as to supply control fluid to the first intermediate tank at least until gaseous fuel contained in the first intermediate tank reaches the first threshold pressure, and(b) controlling the control fluid circuit so as to supply control fluid the second intermediate tank at least until gaseous fuel contained in the second intermediate tank reaches the first threshold pressure,wherein steps (a) and (b) are performed sequentially and repeatedly.The herein described method provides a simple and cost-effective solution, suitable for use onboard a vehicle, for increasing pressure of gaseous fuel to a needed or desired first threshold pressure suitable for supply to a combustion engine of the vehicle. Moreover, the herein described method has the advantage of allowing to increase the pressure of gaseous fuel, through utilization of the first and second intermediate tanks and the control fluid circuit, over a broad pressure difference between the pressure in the one or more storage tanks and the first threshold pressure. Thereby, more of the gaseous fuel fueled to the vehicle may actually be utilized by the combustion engine, which in turn increases the possible driving range for the vehicleThe herein described solution for increasing the pressure of gaseous fuel to be supplied to a combustion engine of a vehicle also has the advantage of not relying on the presence of a compressor in the fuel system. Thus, the solution also avoids the need for development of a high-pressure compressor, suitable for use onboard the vehicle (in terms of size, weight, as well as cost), and which is able to increase the pressure of gaseous fuel over a sufficiently large pressure range.According to a first alternative of the herein described method, step (a) may comprise controlling the control fluid circuit to pump control fluid from the second intermediate tank to the first intermediate tank, and step (b) may comprise controlling the control fluid circuit to pump control fluid from the first intermediate tank to the second intermediate tank. This has the advantage of requiring only a relatively low volume of control fluid in the control fluid circuit. Moreover, this provides an energy efficient solution for requiring less pump work compared to, for example, if the control fluid would be pumped to the first and second intermediate tanks, respectively, from a reservoir held at atmospheric pressure.The method according to the first alternative may further comprise a step (c) of controlling the control fluid circuit to temporarily turn off the pump while allowing a volume of control fluid contained in the first intermediate tank and the second intermediate tank, respectively, to be at least partly leveled out. In such a case, step (c) is performed after step (a) but prior to step (b), and / or after step (b) but prior to step (a). Depending on the type of pump comprised in the control fluid circuit, this may in some cases increase energy efficiency of the fuel system.According to a second alternative of the herein described method, each of steps (a) and (b) may comprise controlling the control fluid circuit to supply control fluid to the respective intermediate tank from a reservoir of the control fluid circuit, and the steps (a) and (b) are performed alternately. This has the advantage of allowing gaseous fuel to be supplied to the combustion engine continuously at a substantially constant pressure. This may be achieved since the first and second intermediate tanks need not simultaneously stop supplying gaseous fuel to the combustion engine as control fluid need not be pumped directly from one of the first and second intermediate tanks to the other one of the first and second intermediate tanks to compress the gaseous fuel contained therein.The present disclosure also relates to a control arrangement configured to control a fuel system of a vehicle to supply gaseous fuel to a combustion engine of the vehicle at a pressure equal to or higher than a first threshold pressure. Said fuel system comprises one or more storage tanks configured for storage of gaseous fuel onboard the vehicle. The fuel system further comprises a first intermediate tank and a second intermediate tank, each configured to receive gaseous fuel from the one or more storage tanks for supply to the combustion engine via a common supply line of the fuel system. The fuel system also comprises a control fluid circuit adapted to supply a control fluid to each of the first intermediate tank and the second intermediate tank to compress gaseous fuel contained therein, said control fluid circuit comprising a pump and a plurality of control valves. The control arrangement is configured to (i) control the control fluid circuit so as to supply control fluid to the first intermediate tank at least until gaseous fuel contained in the first intermediate tank reaches the first threshold pressure, and (ii) control the control fluid circuit so as to supply control fluid the second intermediate tank at least until gaseous fuel contained in the second intermediate tank reaches the first threshold pressure, wherein the control arrangement is configured to perform (i) and (ii) sequentially and repeatedly.The control arrangement provides the same advantages as described above with regard to the corresponding method for controlling a fuel system of a vehicle.According to a first alternative, the control arrangement may be configured to control the control fluid circuit to supply control fluid to the first intermediate tank through controlling the control fluid circuit to pump control fluid from the second intermediate tank, and to control the control fluid circuit to supply control fluid to the second intermediate tank through controlling the control fluid circuit to pump control fluid from the first intermediate tank.The control arrangement may further be configured to, between the supply of control fluid to the first intermediate tank and the supply of control fluid to the second intermediate tank, control the control fluid circuit to temporarily shut off the pump while allowing a volume of control fluid contained in the first intermediate tank and the second intermediate tank, respectively, to be at least partly leveled out.According to a second alternative, the control arrangement may be configured to control the control fluid circuit to alternately supply control fluid to the first intermediate tank and the second intermediate tank, respectively, from a reservoir of the control fluid circuit.The present disclosure further relates to a fuel system for a vehicle. The fuel system comprises one or more storage tanks configured for storage of gaseous fuel onboard the vehicle. The fuel system also comprises a first intermediate tank and a second intermediate tank, each configured to receive gaseous fuel from the one or more storage tanks for supply to a combustion engine of the vehicle via a common supply line of the fuel system. The fuel system also comprises a control fluid circuit adapted to supply a control fluid to each of the first intermediate tank and the second intermediate tank to compress gaseous fuel contained therein. The control fluid circuit comprises a pump and a plurality of control valves. The fuel system also comprises the control arrangement as described above.By means of the herein described fuel system, gaseous fuel may be supplied to a combustion engine of the vehicle at a pressure equal to or higher than a first pressure threshold even when the pressure of the gaseous fuel contained in the one or more storage tanks is reduced below said first pressure threshold. Thus, the fuel system allows for increasing the amount of gaseous fuel, fueled to the vehicle, that may actually be used for operating a combustion engine of the vehicle. Moreover, this is achieved without the need for a compressor. This may in turn reduce the cost of the fuel system as well as reduce the weight thereof. Moreover, since the first and second intermediate tanks may be made small, the fuel system has a form factor that allows for a more flexible arrangement thereof onboard the vehicle compared to, for example, if a compressor would be used for increasing pressure of the gaseous fuel. Furthermore, the herein described fuel system overcomes the difficulties in developing a compressor that is capable of increasing pressure of gaseous fuel over a sufficiently large pressure range while at the same time being suitable for use onboard the vehicle.The plurality of control valves may comprise a first control valve arranged upstream of the pump and in a first line connectingthe first intermediate tankwith the pump, a second control valve arranged downstream of the pump and in a second line connecting the first intermediate tank with the pump, a third control valve arranged upstream of the pump and in a third line connectingthe second intermediate tankwith the pump, and a fourth control valve arranged downstream of the pump and in a fourth line connecting the second intermediate tank with the pump. Among other things, this allows for controlling the control fluid circuit to sequentially and repeatedly increase pressure of gaseous fuel in the first and second intermediate tanks, respectively, without the need for more than one pump in the control fluid circuit (although more than one pump may be included, if desired).The fuel system may further comprise a first check valve arranged in a first fuel line downstream of the first intermediate tank and upstream of the common supply line, and a second check valve arranged in a second fuel line downstream of the second intermediate tank and upstream of the common supply line. Thereby, it may be prevented that gaseous fuel may start to flow in an undesired direction, towards the one or more storage tanks, after having been compressed in the first or second intermediate tank.The fuel system may further comprise a third intermediate tank arranged in the common supply line. This has the advantage of reducing the pulsation of high-pressure supply of gaseous fuel, resulting from the temporary stop of supply from the first and second intermediate tanks while control fluid is pumped therebetween, before the gaseous fuel reaches the combustion engine. More specifically, the third intermediate tank allows the pulsed pressure to be levelled out in view of being arranged in the common supply line.The control fluid circuit may further comprise a control fluid reservoir arranged upstream of the pump. This has the advantage of allowing control fluid to be pumped to the first and second intermediate tanks from the control fluid reservoir instead of directly between said intermediate tanks. Thereby, the supply of gaseous fuel from one of the first and second intermediate tanks need not be interrupted while control fluid is pumped into the other one of the first and second intermediate tanks. Thus, the pulsation of high-pressure supply of gaseous fuel may be overcome even without the presence of the above described third intermediate tank.Moreover, the fuel system may further comprise a bypass line configured to allow gaseous fuel from the one or more storage tanks to bypass the first intermediate tank and second intermediate tank when a pressure of gaseous fuel from the one or more storage tanks is above a second threshold pressure, said second threshold pressure being equal to or higher than the first threshold pressure. This allows for the gaseous fuel to be directly supplied to the combustion engine as long as the pressure in the one or more storage tanks is sufficiently high. This may in turn reduce the amount of gaseous fuel, fueled to the vehicle, that may come into contact with the control fluid. Thereby, the amount of possible carbon pick-up by the fuel, in case the control fluid would comprise carbon (such as in case of the control fluid comprising hydraulic oil), may be reduced.Each of the first intermediate tank and the second intermediate tank may suitably have an internal volume of equal to or less than 10 liters. This has the advantage of, among other things, allowing the first and second intermediate tanks to easily be installed onboard the vehicle. Furthermore, it reduces the volume of control fluid needed in the control fluid circuit.The present disclosure also relates to a vehicle comprising the above described control arrangement and / or the fuel system as described above. Said vehicle may further comprise a combustion engine configured to be operated on gaseous fuel, such as hydrogen. The combustion engine may suitably be a high-pressure direct injection (HPDI) combustion engine, but is not limited thereto. The vehicle may for example be a land-based heavy-duty vehicle, such as a bus or a truck, but is not limited thereto.The present disclosure also relates to a computer program comprising instructions which, when executed by the control arrangement as described above, cause the control arrangement to carry out the above described method for controlling a fuel system.Moreover, the present disclosure relates to a computer-readable medium having stored thereon the computer program described above.Fig. 1 schematically illustrates an example of a vehicle,Fig. 2 represents a flowchart schematically illustrating a first exemplifying embodiment of a method for controlling a fuel system in accordance with the present disclosure,Fig. 3 schematically illustrates a first exemplifying embodiment of a fuel system in accordance with the present disclosure,Fig. 4 schematically illustrates a second exemplifying embodiment of a fuel system in accordance with the present disclosure,Fig. 5 schematically illustrates an exemplifying embodiment of a device which may comprise, consist of, or be comprised in the herein described control arrangement.DETAILED DESCRIPTIONThe invention will be described in more detail below with reference to various exemplifying embodiments and the accompanying drawings. The invention is however not limited to the exemplifying embodiments discussed and / or shown in the drawings, but may be varied within the scope of the appended claims. Furthermore, the drawings shall not be considered drawn to scale as some features may be exaggerated in order to more clearly illustrate the invention or features thereof.The present disclosure relates to a method for controlling a fuel system of a vehicle for the purpose of supplying gaseous fuel to a combustion engine of said vehicle at a pressure equal to or higher than a first predefined threshold pressure. Said first predefined threshold pressure may for example correspond to a needed or desired pressure for injection of the gaseous fuel to the combustion engine. The gaseous fuel may for example be hydrogen, but is not limited thereto. For example, the gaseous fuel may alternatively be compressed natural gas (CNG). Moreover, the combustion engine may suitably be a high-pressure direct injection (HPDI) combustion engine. HPDI combustion engines are as such known in the art, and will therefore not be further described herein. In case the combustion engine is an HPDI combustion engine, the fuel system may be described as a high-pressure direct injection fuel system or a HPDI fuel system. The herein described method for controlling the fuel system may be performed by a control arrangement configured therefore.The fuel system, controlled in accordance with the herein described method, comprises one or more storage tanks configured for storage of gaseous fuel onboard the vehicle. The one or more storage tanks may suitably be configured to storage of pressurized gaseous fuel, such as up to pressures of at least 700 bar. The fuel system further comprises a first intermediate tank and a second intermediate tank, each configured to receive gaseous fuel from the one or more storage tanks for supply to the combustion engine via a common supply line of the fuel system. In other words, the first and second intermediate tanks may be regarded as arranged in parallel in a flow path of the gaseous fuel from the one or more storage tanks to the combustion engine. It should here be noted that one or more additional intermediate tanks, configured to receive gaseous fuel from the one or more storage tanks for supply to the combustion engine via the common supply line of the fuel system, in addition to the first and second intermediate tanks and arranged in parallel therewith along the flow path of gaseous fuel, may be comprised in the fuel system, if desired. However, this would add complexity and is typically not needed, and is therefore less desirable. The fuel system further comprises a control fluid circuit adapted to supply control fluid to each of the first intermediate tank and the second intermediate tank (and any possible additional intermediate tank arranged in parallel with the first and second intermediate tanks as described above) to thereby compress gaseous fuel contained in the respective intermediate tanks. The control fluid may suitably be hydraulic oil. Alternatively, the control fluid may for example be water. The control fluid circuit comprises a pump and a plurality of control valves. The term “control valve” is in the present disclosure considered to encompass any type of valve that may be actively controlled, suitably by a controller or the like (such as the herein described control arrangement), for the purpose of controlling flow therethrough.The herein described method for controlling a fuel system comprises a step (a) of controlling the control fluid circuit so as to supply control fluid to the first intermediate tank at least until gaseous fuel contained in the first intermediate tank reaches the first threshold pressure. The method further comprises a step (b) of controlling the control fluid circuit so as to supply control fluid the second intermediate tank at least until gaseous fuel contained in the second intermediate tank reaches the first threshold pressure. Moreover, in accordance with the present method, the steps (a) and (b) are performed sequentially and repeatedly. In other words, the steps (a) and (b) are repeatably performed one after another. After compression of the gaseous fuel in one of the first and second intermediate tanks, as a result of the supply of control fluid thereto increasing the pressure in the respective intermediate tanks, the gaseous fuel may be supplied to the combustion engine at an appropriate pressure therefore (as defined by the first threshold pressure) via the common supply line.According to a first alternative of the herein described method, step (a) may comprise controlling the control fluid circuit to pump control fluid from the second intermediate tank to the first intermediate tank, and step (b) may comprise controlling the control fluid circuit to pump control fluid from the first intermediate tank to the second intermediate tank. In other words, to sequentially and repeatedly increase the pressure of gaseous fuel contained in the first and second intermediate tanks, control fluid from a first one of the first and second intermediate tanks may be pumped into a second one of the first and second intermediate tanks and thereafter be pumped back into the first one of the first and second intermediate tanks. This is an easy and energy efficient way of increasing the pressure of the gaseous fuel through compression of the gaseous fuel sequentially in the first and second intermediate tanks, respectively.In case control fluid is pumped directly between the first and second intermediate tanks for the purpose of compressing gaseous fuel contained in said intermediate tanks, the method may optionally further comprise a step (c) of controlling the control fluid circuit to temporarily turn off the pump while allowing a volume of control fluid contained in the first intermediate tank and the second intermediate tank, respectively, to be at least partly leveled out. In such a case, step (c) is performed after step (a) but prior to step (b), and / or after step (b) but prior to step (a). This may in some cases result in a reduction of the pump work needed.According to a second alternative of the herein described method, each of the steps (a) and (b) may comprise controlling the control fluid circuit to supply control fluid to the respective intermediate tank (of the first and second intermediate tanks) from a reservoir of the control fluid circuit. In such a case, steps (a) and (b) may not only be performed sequentially and repeatedly, but also alternately. When two steps are described as performed alternately in the present disclosure, this should be interpreted as the steps being performed sequentially without any intermediate steps therebetween. In other words, the steps (a) and (b) may performed directly following each other, or a first one of the steps (a) and (b) may be commenced before the second one of steps (a) and (b) has been fully completed, and vice versa, when control fluid is pumped from a control fluid reservoir. Although steps (a) and (b) may partially overlap, they are to be regarded as being performed sequentially in view of the first threshold pressure being reached at different points in time, during the conduct of the herein described method, in the first and second intermediate tanks, respectively. Pumping the control fluid to the first and second intermediate tanks, respectively, from a reservoir has the advantage of considerably reducing a pulsed supply of gaseous fuel to the common supply line (which occurs when the control fluid is pumped directly between the first and second intermediate tanks without passing through a reservoir). This is because the control fluid may start to be pumped into one of the first and second intermediate tanks while the other one of said intermediate tanks is still supplying gaseous fuel to the common supply line. However, pumping of control fluid from a reservoir, instead of from one of the first and second intermediate tanks, requires more pump work and therefore results in a significant increase in energy losses.The performance of the herein described method for controlling a fuel system of a vehicle may be governed by programmed instructions. These programmed instructions may take the form of a computer program which, when executed by a computer, cause the computer to effect desired forms of control action. Such a computer may for example be comprised in the control arrangement as described herein. A computer is in the present disclosure considered to mean any hardware or hardware / firmware device implemented using processing circuity such as, but not limited to, a processor, Central Processing Unit (CPU), a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA), a System-on-Chip (SoC), a programmable logic unit, a microprocessor, an application-specific integrated circuit, or any other device capable of electronically performing operations in a defined manner.The above described programmed instructions, which may take the form of a computer program, may be stored on a computer-readable medium. Hence, the present disclosure also relates to a computer-readable medium storing instructions, which when executed by a computer, cause the computer to carry out the herein described method for controlling a fuel system of a vehicle. As previously mentioned, such a computer may be comprised in the herein described control arrangement. The computer-readable medium may be a non-transitory computer-readable medium, such as a tangible electronic, magnetic, optical, infrared, electromagnetic, and / or semiconductor system, apparatus, and / or device.The present disclosure further relates to a control arrangement configured to control a fuel system of a vehicle. The control arrangement may be configured to perform any one of the steps of the method for controlling a fuel system of a vehicle as described above.More specifically, the present disclosure relates to a control arrangement configured to control a fuel system of a vehicle so as to supply gaseous fuel to a combustion engine of the vehicle at a pressure equal to or higher than a first threshold pressure. Said fuel system comprises one or more storage tanks configured for storage of gaseous fuel onboard the vehicle. The fuel system also comprises a first intermediate tank and a second intermediate tank, each configured to receive gaseous fuel from the one or more storage tanks for supply to the combustion engine via a common supply line of the fuel system. Moreover, the fuel system comprises a control fluid circuit adapted to supply a control fluid to each of the first intermediate tank and the second intermediate tank to compress gaseous fuel contained therein, said control fluid circuit comprising a pump and a plurality of control valves. The control arrangement is configured to:(i) control the control fluid circuit so as to supply control fluid to the first intermediate tank at least until gaseous fuel contained in the first intermediate tank reaches the first threshold pressure, and(ii) control the control fluid circuit so as to supply control fluid the second intermediate tank at least until gaseous fuel contained in the second intermediate tank reaches the first threshold pressure, andwherein the control arrangement is configured to perform (i) and (ii) sequentially and repeatedly.The control arrangement may comprise one or more control units. In case of the control arrangement comprising a plurality of control units, each control unit may be configured to control a certain function / step or a certain function / step may be divided between more than one control units. The control arrangement may be a control arrangement of the fuel system as such. Alternatively, the control arrangement may be any other control arrangement of the vehicle but configured to communicate with the fuel system for the purpose of performing the herein described method. The control arrangement may for example be comprised in an engine management system of the vehicle.According to a first alternative, the control arrangement may be configured to control the control fluid circuit to supply control fluid to the first intermediate tank through controlling the control fluid circuit to pump control fluid from the second intermediate tank, and to control the control fluid circuit to supply control fluid to the second intermediate tank through controlling the control fluid circuit to pump control fluid from the first intermediate tank. In other words, the control arrangement may according to the first alternative be configured to control the control fluid circuit in order to sequentially and repeatedly compress gaseous fuel contained in the respective first and second intermediate tanks by pumping control fluid directly from one of said first and second intermediate tanks to the other one of said first and second intermediate tanks.In case the control arrangement being configured to pump control fluid directly from one of said first and second intermediate tanks to the other one of said first and second intermediate tanks, the control arrangement may optionally further be configured to, between the supply of control fluid to the first intermediate tank and the supply of control fluid to the second intermediate tank, control the control fluid circuit to temporarily shut off the pump while allowing a volume of control fluid contained in the first intermediate tank and the second intermediate tank, respectively, to be at least partly leveled out.According to a second alternative, the control arrangement may be configured to control the control fluid circuit to alternately supply control fluid to the first intermediate tank and the second intermediate tank, respectively, from a control fluid reservoir of the control fluid circuit to thereby sequentially and repeatedly compress gaseous fuel contained in the first and second intermediate tanks, respectively.The present disclosure also relates to a fuel system for, or in, a vehicle. The fuel system comprises one or more storage tanks configured for storage of gaseous fuel onboard the vehicle. As previously mentioned, the one or more storage tanks may suitably be configured for storage of pressurized gaseous fuel. The fuel system further comprises a first intermediate tank and a second intermediate tank, each configured to receive gaseous fuel from the one or more storage tanks for supply to a combustion engine of the vehicle via a common supply line of the fuel system. The fuel system also comprises a control fluid circuit adapted to supply a control fluid to each of the first intermediate tank and the second intermediate tank for the purpose of compressing gaseous fuel contained therein. The control fluid circuit comprises at least one pump and a plurality of control valves. The fuel system may suitably also comprise the herein described control arrangement configured to control a fuel system to supply gaseous fuel to a combustion engine at a pressure equal to or higher than a first threshold pressure.The plurality of control valves of the control fluid circuit may comprise a first, a second, a third, and a fourth control valve. Each of the plurality of control valves of the control fluid circuit may for example be a solenoid valve. The first control valve may be arranged upstream of the pump and in a first control fluid line connecting the first intermediate tank with the pump. The second control valve may be arranged downstream of the pump and in a second control fluid line connecting the first intermediate tank with the pump. The third control valve may be arranged upstream of the pump and in a third control fluid line connecting the second intermediate tank with the pump. Moreover, the fourth control valve may be arranged downstream of the pump and in a fourth control fluid line connecting the second intermediate tank with the pump.The fuel system may further comprise a plurality of check valves configured to control the flow direction of the gaseous fuel within the fuel system. For example, the fuel system may suitably comprise a first check valve, arranged in a first fuel line downstream of the first intermediate tank and upstream of the common supply line, and a second check valve, arranged in a second fuel line downstream of the second intermediate tank and upstream of the common supply line. Thereby, gaseous fuel may flow from each of the first and second intermediate tanks into the common supply line after having been compressed to a pressure which is higher that the pressure in the common supply line, which in turn should be equal to (or higher than) the first threshold pressure. The fuel system may also comprise a third check valve arranged in a third fuel line upstream of the first intermediate tank, and a fourth check valve arranged in fourth fuel line upstream of the second intermediate tank. The third and fourth check valves may each be configured to ensure that gaseous fuel may not flow in a direction towards the one or more storage tanks as a result of increased pressure in the first and second intermediate tanks, respectively, during compression of gaseous fuel contained therein. The third and fourth check valves may however each be configured to allow flow of gaseous fuel from the one or more storage tanks into the corresponding first or second intermediate tank at a comparatively low pressure, suitably a pressure below 100 bar (for example about 80 bar or about 70 bar), to allow as much of the gaseous fuel stored in the one or more storage tanks to be supplied to the combustion engine of the vehicle. Any one of the above described check valves may naturally be replaced with another type of one-way valve, if desired, such as a one-way control valve, without departing from the present disclosure.The fuel system may further comprise a third intermediate tank arranged in the common supply line. In case the control fluid is pumped directly from the first intermediate tank to the second intermediate tank, and vice versa, for the purpose of compressing gaseous fuel contained in either one of the first and second intermediate tanks, respectively, there will inherently be a pulsation of the high-pressure supply of gaseous fuel to the combustion engine. The reason therefore is that control fluid cannot be transferred between the first and second intermediate tanks without the pressure in the intermediate tank from which the control fluid is transferred decreasing such that said intermediate tank will (temporary) stop supplying gaseous fuel before the pressure of gaseous fuel contained in the intermediate tank to which the control fluid is pump may be sufficiently increased. The effect of said pulsation may be overcome by arranging an additional tank in the common supply line, i.e. the above mentioned third intermediate tank. Said third intermediate tank allows for levelling out the pulsation of gaseous fuel supplied from the first and second intermediate tanks. It should here be noted that, in contrast to the first and second intermediate tanks, the third intermediate tank is not connected to the control fluid circuit and no control fluid is therefore supplied to the third intermediate tank. Described differently, the third intermediate tank is merely part of the flow path of gaseous fuel from the one or more storage tanks to the combustion engine, and not part of the control fluid circuit.Alternatively or additionally, the control fluid circuit may further comprise a control fluid reservoir arranged upstream of the pump. This allows for control fluid to be pumped from the control fluid reservoir to each of the first and second intermediate tanks, as opposed to directly from one of the first and second intermediate tanks to the other one of the first and second intermediate tanks. Thereby, the first and second intermediate tanks may operate essentially independently of each other, since it allows for one of the first and second intermediate tanks to be supplied with control fluid while the other one of the first and second intermediate tanks is still supplying gaseous fuel to the combustion engine via the common supply line. Thereby, the fuel system has the ability to supply gaseous fuel at a substantially constant pressure to the combustion engine even if the above described third intermediate tank, arranged in the common supply line, would not be present. However, pumping control fluid from a control fluid reservoir has the drawback of a significantly increased energy consumption compared to the alternative of pumping the control fluid directly between the first and second intermediate tanks. This is due to such a control fluid reservoir typically being at substantially atmospheric pressure, which means that a considerably higher amount of pump work is needed to supply a sufficient amount of control fluid to the first and second intermediate tanks to reach the intended pressure of the gaseous fuel contained therein.In order to reduce the risk for potential carbon pick-up by the gaseous fuel, resulting from the gaseous fuel coming into contact with the control fluid, each of the first and second intermediate tanks may suitably comprise a separation member in the form of a moveable and / or flexible membrane configured to separate the control fluid from the gaseous fuel inside the respective intermediate tank. Such membranes are as such known in the art, and will therefore not be further described in the present disclosure.Additionally, or alternatively, the fuel system may comprise a bypass line configured to allow gaseous fuel from the one or more storage tanks to bypass the first intermediate tank and second intermediate tank when a pressure of gaseous fuel from the one or more storage tanks is above a second threshold pressure, said second threshold pressure being equal to or higher than the first threshold pressure. Thereby, the gaseous fuel need not pass through the first and second intermediate tanks, and thereby come in contact with the control fluid, as long as the pressure of the gaseous fuel flowing from the one or more storage tanks is so high that it need not be raised. This also contributes to a reduction of potential carbon pick-up. The bypass line may suitably comprise a fifth check valve configured to prevent flow of gaseous fuel in a direction towards the one or more storage tanks when the pressure therein is below the second threshold pressure.The first and second intermediate tanks can suitably be made relatively small, to thereby not take up so much space onboard the vehicle and reducing the amount of control fluid needed to increase the pressure of gaseous fluid contained in the respective intermediate tank. For example, each of the first and second intermediate tanks may suitably have an internal volume of equal to or less than 10 liters. Preferably, each of the first and second intermediate tanks may have an internal volume of from 3 to 8 liters.Figure 1 schematically illustrates an example of a vehicle 1, here illustrated as a truck. The vehicle comprises a combustion engine 2. The combustion engine 2 may for example be a HPDI combustion engine. The vehicle 1 further comprises at least one storage tank 11 configured for storage of gaseous fuel, on which the combustion engine 2 is to be operated, onboard the vehicle 1. Suitably, the at least one storage tank 11 may be configured to store the gaseous fuel in a pressurized state and at ambient temperatures. The gaseous fuel may for example be hydrogen, but is not limited thereto. The at least one storage tank 11 may be part of a fuel system (not shown), such as the herein described fuel system comprising a first and second intermediate tank and a control fluid circuit configured to allow compression of gaseous fuel contained in said first and second intermediate tanks.The vehicle 1 may further comprise a control arrangement 100 configured to control the fuel system, as shown in the figure. Such a control arrangement 100 may be part of the fuel system as such, or be separate from the fuel system, without departing from the present disclosure.Figure 2 represents a flow chart of one exemplifying embodiment of the herein described method for controlling a fuel system of a vehicle to supply gaseous fuel to a combustion engine of the vehicle at a pressure equal to or higher than a first threshold pressure. The method may for example be a method for controlling a fuel system of the vehicle 1 shown in Figure 1 for the purpose of supplying gaseous fuel to the combustion engine 2 thereof. In any case, the fuel system, which is controlled in accordance with the herein described method, comprises one or more storage tanks configured for storage of gaseous fuel onboard the vehicle. The fuel system further comprises a first intermediate tank and a second intermediate tank, each configured to receive gaseous fuel from the one or more storage tanks for supply to the combustion engine via a common supply line of the fuel system. The fuel system also comprises a control fluid circuit adapted to supply a control fluid to each of the first intermediate tank and the second intermediate tank to compress gaseous fuel contained therein, said control fluid circuit comprising a pump and a plurality of control valves.The method may comprise a first step S101 of determining whether the pressure of gaseous fuel stored in the one or more storage tanks of the fuel system is sufficient for allowing injection into the combustion engine at a desired pressure therefore. This may for example comprise (or consist of) determining whether the pressure of gaseous fuel in the common supply line is equal to or above the desired injection pressure. Alternatively, or additionally, this may comprise determining whether the pressure of gaseous fuel stored in the one or more storage tanks is above the first threshold pressure (or a second threshold pressure that is somewhat higher that the first threshold pressure). If the answer is yes, the method may be reverted to start.Otherwise, the method may proceed to subsequent steps.The method comprises a step S102 of controlling the controlling the control fluid circuit so as to supply control fluid to the first intermediate tank at least until gaseous fuel contained in the first intermediate tank reaches the first threshold pressure. The step S102 is in the present disclosure also denominated as a step (a). More specifically, step S102 comprises controlling the pump and the plurality of control valves of the control fluid circuit so that control fluid is supplied (i.e. pumped) into the first intermediate tank. Thereby, gaseous fuel present in the first intermediate tank will be compressed by means of the control fluid at least until it reaches the first threshold pressure. The gaseous fuel compressed in the first intermediate tank to the targeted pressure may thereby be supplied to the combustion engine of the vehicle via the common supply line.After step S102, the method comprises a step S103 of controlling the control fluid circuit so as to supply control fluid to the second intermediate tank at least until gaseous fuel contained in the second intermediate tank reaches the first threshold pressure. Step S103 is in the present disclosure also denominated as a step (b). More specifically, step S103 comprises controlling the pump and the plurality of control valves of the control fluid circuit so that control fluid is supplied (i.e. pumped) into the second intermediate tank. Thereby, gaseous fuel present in the second intermediate tank will be compressed by means of the control fluid at least until the gaseous fuel reaches the first threshold pressure. The gaseous fuel compressed in the second intermediate tank to the targeted pressure may thereby be supplied to the combustion engine of the vehicle via the common supply line.After step S103, the method is reverted back to step S102. Thus, the steps S102 and S103 are performed sequentially and repeatedly.It should here be noted that while any one of the steps S102 and S103 are performed, control fluid may be let out (either by being pumped out of, or being allowed to flow into a reservoir therefore) of the intermediate tank which is not currently supplied with control fluid. This results in a reduction of pressure in said intermediate tank, allowing it to be refilled with gaseous fuel from the one or more storage tanks. Also this may be achieved trough control of the control fluid circuit. More specifically, the control fluid may be let out of any one of the first and second intermediate tanks through control of the plurality of control valves, and optionally also the pump.The above described exemplifying embodiment of the herein described method, as illustrated in Figure 2, may be utilized for controlling any one of the exemplifying embodiment of fuel systems as will be described in the following with reference to Figures 3 and 4, respectively.Figure 3 schematically illustrates a first exemplifying embodiment of a fuel system 10 in accordance with the present disclosure. The fuel system 10 may be arranged onboard a vehicle, such as the vehicle 1 shown in Figure 1. The fuel system 10 is configured to supply gaseous fuel to a combustion engine 2 of the vehicle. The combustion engine 2 is in the figure illustrated by dashed lines in view of not being part of the fuel system 10 as such. The fuel system 10 may be controlled by a control arrangement 100 configured therefore. Said control arrangement 100 may be a part of the fuel system 10. Alternatively, the control arrangement 100 may be separate from the fuel system 10, but configured to communicate therewith for the purpose of controlling the fuel system 10. The herein described method for controlling a fuel system of a vehicle may be practiced on the fuel system 10 shown in the figure.The fuel system 10 comprises one or more storage tanks configured for storage of gaseous fuel onboard the vehicle. In the figure, the fuel system 10 is shown to comprise a first storage tank 11, a second storage tank 12, a third storage tank 13 and a fourth storage tank 14, but is not limited thereto. Each of the storage tanks 11, 12, 13, 14 is configured for storage of gaseous fuel to be supplied to the combustion engine 2. Moreover, each of the storage tanks 11, 12, 13, 14 are, as shown in the figure, fluidly connected to the combustion engine 2 via common fuel flow path 18. The common fuel flow path 18 may comprise at least a common supply line 40, a first fuel line 41, a second fuel line 42, a third fuel line 43, and a fourth fuel line 44, as will be further described below. The common flow path 18 may further comprise a fuel output line 46, as shown in the figure. Said fuel output line 46 is arranged at an upstream end of the fuel system 10 and is arranged to form a common fuel output line for the storage tanks 11, 12, 13, 14. The previously mentioned common supply line 40 is arranged at a downstream end of the fuel system 10, and is thus arranged to be connected to the combustion engine 2. The common fuel flow path 18 may further comprise a bypass line 45, in the figure illustrated as a dashed line in view of being optional.The fuel system 10 comprises a first intermediate tank 15 and a second intermediate tank 16. The first and second intermediate tanks 15, 16 are arranged in parallel as seen in the flow direction of the gaseous fuel along the common fuel flow path 18. It should however be noted that the first and second intermediate tanks 15, 16 need not be physically arranged in parallel onboard the vehicle, but may each be arranged at any position where there is an available space therefore. The fuel system 10 further comprises a control fluid circuit 20 adapted to supply a control fluid to each of the first intermediate tank 15 and the second intermediate tank 16 for the purpose of compressing gaseous fuel contained therein. Said control fluid circuit 20 will be described in more detail below.It should here be noted that each of the first and second intermediate tanks 15, 16 may suitably have a considerably smaller internal volume than an internal volume of each of the storage tanks 11, 12, 13, 14. The internal volume of each of the first and second intermediate tanks 15, 16 may advantageously be equal to or less than 10 liters.Each of the first intermediate tank 15 and the second intermediate tank 16 are configured to receive gaseous fuel from the storage tanks 11, 12, 13, 14 for supply to the combustion engine 2. Thus, each of the first and second intermediate tanks 15, 16 are fluidly connected to the storage tanks 11, 12, 13, 14 as well as to the common supply line 40. More specifically, the first intermediate tank 15 is fluidly connected to the common fluid line 40 via a first fluid line 41 . In other words, the first fluid line 41 is arranged downstream of the first intermediate tank 15, but upstream of the common supply line 40. Similarly, the second intermediate tank is fluidly connected to the common supply line 40 via a second fluid line 41. Thus, the second fluid line 42 is arranged upstream of the second intermediate tank 16, but downstream of the common supply line 40. Moreover, the first intermediate tank 15 is fluidly connected to the storage tanks 11, 12, 13, 14 via a third fuel line 43, either directly or via the fuel output line 46, when present. Similarly, the second intermediate tank 16 is fluidly connected to the storage tanks 11, 12, 13, 14 via a fourth fuel line 44, either directly or via the fuel output line 46 as shown in the figure.The common fuel flow path 18 may optionally further comprise a bypass line 45 as shown in the figure. Said bypass line 45 is configured to allow gaseous fuel from the storage tanks 11, 12, 13, 14 to bypass the first intermediate tank 15 as well as the second intermediate tank 16 when a pressure of gaseous fuel from the storage tanks 11, 12, 13, 14 is above a second threshold pressure. Such a second threshold pressure may be equal to or higher than the first threshold pressure. In other words, the bypass line 45, if present, allows gaseous fuel to flow from the storage tanks 11, 12, 13, 14 to the common supply line 40 without passing through the first and second intermediate tanks 15, 16 as long as the pressure of the gaseous fuel is sufficiently high that it need not be increased to be delivered to the combustion engine 2. It should here be noted that if the bypass line 45 is not present, the gaseous fuel may instead flow through the first and second intermediate tanks 15, 16 even when the pressure thereof need not be increased. In such a case, the control fluid circuit 20 need not be actively controlled until the pressure of the gaseous fuel from the storage tanks 11, 12, 13, 14 falls below the first threshold pressure.To control the flow direction of gaseous fuel through the fuel system 10, the common fuel flow path 18 may suitably comprise various check valves. These check valves may be configured to open at any pressure, and thus be embodied by simple one-way valves, or may be configured to open at substantially the same or at different predefined pressures. In the latter case, said predefined pressures could for example differ depending on the position or the respective check valve within the fuel system 10. As shown in the figure, the fuel system 10 may comprise a first check valve 51 arranged in the first fuel line 41. The first check valve 51 is thus arranged downstream of the first intermediate tank 15, but upstream of the common supply line 40. The first check valve 51 may be configured to open at a any pressure below or equal to the first pressure threshold and only allow flow of gaseous fuel in the direction towards the common supply line 40. Moreover, the fuel system 10 may comprise a second check valve 52 arranged in the second fuel line 42. The second check valve 52 is thus arranged downstream of the second intermediate tank 16, but upstream of the common supply line 40. The second check valve 52 functions in the same way as the first check valve 51, but with respect of the second intermediate tank 16. Like the first check valve 51, the second check valve 52 may be configured to open at a any pressure below or equal to the first pressure threshold and only allow flow of gaseous fuel in the direction towards the common supply line 40.The fuel system 10 may suitably also comprise a third check valve 53, arranged in third fuel line 43, and a fourth check valve 54, arranged in the fourth fuel line 44. Each of the third and fourth check valves 53, 54 prevents gaseous fuel to flow in a direction towards the storage tanks 11, 12. 13. 14 (for example due to the compression of gaseous fuel in the first and second intermediate tanks, respectively). The third and fourth check valves 53, 54 may suitably be configured to open so as to allow flow of gaseous fuel from the storage tanks 11, 12, 13, 14 into the first and second intermediate tanks 15, 16 at a pressure considerably lower than the first threshold pressure, preferably at a pressure of at most 100 bar. Advantageously, each of the third and fourth check valves 53, 54 may be embodied as simple one-way valves that are configured to allow flow in a single direction at any pressure, or at least any pressure equal to or higher than atmospheric pressure.As previously mentioned, the fuel system 10 may also comprise a bypass line 45 configured to allow gaseous fuel from the storage tanks 11, 12, 13, 14 to bypass the first intermediate tank 15 and second intermediate tank 16 when the pressure of the gaseous fuel from the storage tanks 11. 12. 13. 14 is above a second threshold pressure. To prevent gaseous fuel to flow from the common supply line 40 back towards the storage tanks 11, 12, 13, 14, especially when the pressure in the storage tanks are lower than in the common supply line 40, a fifth check valve 55 may suitably be arranged in said bypass line 45. Said fifth check valve 55 may also be configured to open at the second threshold pressure to allow gaseous fuel to bypass the first and second intermediate tanks 15, 16 when the pressure inside the storage tanks 11, 12, 13, 14 is sufficiently high to allow it to be directly distributed to the combustion engine 2.As previously mentioned, the fuel system 10 further comprises a control fluid circuit 20. The control fluid circuit 20 is adapted to supply a control fluid, such as hydraulic oil or water, to each of the first intermediate tank 15 and the second intermediate tank 16 for the purpose of compressing gaseous fuel contained in each of the first and second intermediate tanks 15, 16. The control fluid circuit 20 comprises a plurality of control valves, including a first control valve 21, a second control valve 22, a third control valve 23, a fourth control valve 24. The control fluid circuit also comprises at least one pump 25. The pump 25 may be an electric pump or a mechanical pump, without departing from the present disclosure.As shown in the figure, the first control valve 21 is arranged upstream of the pump 25 and in a first line 31 connecting the first intermediate tank 15 with the pump 25. The second control valve 22 is arranged downstream of the pump 25 and in a second line 32 connecting the first intermediate tank 15 with the pump 25. The third control valve 23 is arranged upstream of the pump 25 and in a third line 33 connecting the second intermediate tank 16 with the pump 25. Moreover, the a fourth control valve 24 is arranged downstream of the pump 25 and in a fourth line 34 connecting the second intermediate tank 16 with the pump 25. The pump 25 is arranged in a fifth line 35 which connects the first line 31 and the third line 33, upstream of the pump 25, with the second line 32 and the fourth line 35, downstream of the pump 25. It should here be noted that each of the above described first to fifth lines 31, 32, 33, 34, 35 are control fluid lines. Moreover, these control fluid lines are each part of the control fluid circuit 20.As previously mentioned, the herein described method for controlling a fuel system of a vehicle to supply gaseous fuel to a combustion engine of said vehicle at a pressure equal to or higher than a first pressure threshold comprises a step (a) and a step (b) which are performed sequentially and repeatedly. Said method may be practiced on the fuel system 10 shown in Figure 3, as will be described in more detail in the following.For the purpose of illustrating the herein described method, let’s imagine an initial state at which the herein described method is initiated, for example due to that the pressure of the gaseous fuel contained in the storage tanks 11, 12, 13, 14 has decreased to a pressure just below the first threshold pressure. At this stage, the pressure of the gaseous fuel contained in the first and second intermediate tanks 15, 16 is substantially equal. Likewise, the volume of control liquid contained in the first and second intermediate tanks 15, 16, respectively, is substantially the same.The method may then start with step (a), during which the control fluid circuit 20 is controlled so as to supply control fluid to the first intermediate tank 15 at least until the gaseous fuel contained therein reaches the first threshold pressure. This is performed by controlling the second control valve 22 and the third control valve 23 to an open state and controlling the first control valve 21 and the fourth control valve 24 to a closed state, as well as controlling the pump 25 to pump control fluid within the control fluid circuit 20. Thereby, control fluid will flow from the second intermediate tank 16, through the pump 25, to the first intermediate tank 15 (in other words, control fluid is supplied to the first intermediate tank 15). This causes an increase in pressure of the gaseous fuel contained in the first intermediate tank 15 as a result of being subjected to compression by the control fluid. When the pressure inside the first intermediate tank 15 increases above a pressure in the common supply line 40, the gaseous fuel from the first intermediate tank 15 will start to flow, via the first fuel line 41, to the common supply line 40. This may continue until the first intermediate tank 15 is substantially emptied of gaseous fuel and nearly filled with control fluid.At the same time, the pressure in the second intermediate tank 16 will decrease as a result of the reduced amount of control fluid contained therein. This will in turn lead to gaseous fuel from the storage tanks 11, 12, 13, 14 to be transferred into the second intermediate tank 16. This may be continued until the second intermediate tank 16 is nearly filled with gaseous fuel and nearly emptied of control liquid.The method then proceeds to step (b), which comprises controlling the control fluid circuit so as to supply control fluid to the second intermediate tank 16 at least until gaseous fuel contained in the second intermediate tank 16 reaches the first threshold pressure. This is performed by controlling the first control valve 21 and the fourth control valve 24 to an open state and controlling the second control valve 22 and the third control valve 23 to a closed state, as well as controlling the pump 25 to pump control fluid within the control fluid circuit 20.Thereby, control fluid will flow from the first intermediate tank 15, through the pump 25, to the second intermediate tank 16 (in otherwords, control fluid is supplied to the second intermediate tank 16). This causes an increase in pressure of the gaseous fuel contained in the second intermediate tank 16 as a result of being subjected to compression by the control fluid. When the pressure inside the second intermediate tank 16 increases above a pressure in the common supply line 40, the gaseous fuel from the second intermediate tank 16 will start to flow, via the second fuel line 42, to the common supply line 40. This may continue until the second intermediate tank 16 is substantially emptied of gaseous fuel and nearly filled with control fluid.At the same time, the pressure in the first intermediate tank 15 will decrease as a result of the reduced amount of control fluid contained therein. This will in turn lead to gaseous fuel from the storage tanks 11, 12, 13, 14 to be transferred into the first intermediate tank 15. This may be continued until the first intermediate tank 15 is nearly filled with gaseous fuel and nearly emptied of control liquid.After step (b), as described above, step (a) is repeated and thereafter followed by a repetition of step (b). In otherwords, steps (a) and (b) are performed sequentially (i.e. in a certain order) and repeated.From the above, it may be realized that when the above described method is practiced on the fuel system 10 as shown in Figure 3, gaseous fuel will be supplied to the common supply line 40 in a slightly pulsed manner. This is a result of neither the first intermediate tank 15, nor the second intermediate tankl 6 supplying gaseous fuel to the common supply line 40, at the point in time at which the method is switched from step (a) to step (b), or vice versa. A pulsed supply of gaseous fuel to the combustion engine 2 is generally not desirable. To address this issue, the fuel system 10 according to the first exemplifying embodiment as shown in Figure 3 further comprises a third intermediate tank 17. Said third intermediate tank 17 is arranged in the common supply line 40. The presence of such a third intermediate tank 17 allows for leveling out the pulsation so that gaseous fuel will be supplied to the combustion engine 2 at a more constant pressure.It should here be noted that, in contrast to the first and second intermediate tanks 15, 16, the third intermediate tank is not connected to the control fluid circuit. Thus, the third intermediate tanks is only intended to be supplied with gaseous fuel that is already compressed or at least has a pressure equal to or higher than the first threshold pressure.Figure 4 schematically illustrates a second exemplifying embodiment of a fuel system 10 according to the present disclosure. The second exemplifying embodiment corresponds to the fuel system 10 shown in Figure 3 except that the control fluid circuit 20 further comprises a reservoir 26 for control fluid. Furthermore, the fuel system 10 shown in Figure 4 does not comprise the third intermediate tank 17 (arranged in the common supply line 40) shown in Figure 3, although such a third intermediate tank 17 may still be included in the fuel system 10, if desired.Like for the fuel system shown in Figure 3, the herein described method for controlling a fuel system of a vehicle may be practiced on the fuel system 10 shown in Figure 4. However, in contrast to when the method is performed on the fuel system shown in Figure 3, control fluid is not pumped directly from the first intermediate tank 15 into the second intermediate tank 16, and vice versa. Instead, control fluid is pumped from the reservoir 26 into the respective intermediate tanks 15, 16 when gaseous fuel contained therein is to be compressed. Moreover, control fluid leaving each of the first and second intermediate tanks 15, 16 is collected in the reservoir 26.The second exemplifying embodiment, as shown in Figure 4, of the herein described fuel system 10 has the advantage of allowing step (a) to be initiated even before step (b) has been fully completed, and vice versa. More specifically, the first intermediate tank 15 may still be supplying gaseous fuel to the common supply line 40 when the step of controlling the control fluid circuit to supply control fluid to the second intermediate tank 16 is initiated. Similarly, the second intermediate tank 16 may still be supplying gaseous fuel to the common supply line 40 when the step of controlling the control fluid circuit to supply control fluid to the first intermediate tank 15 is initiated. It should however be noted that the first threshold pressure will in accordance with the herein described method be reached at different points in time in the first and second intermediate tanks 15, 16 even when control fluid is pumped from the reservoir 16. Therefore, steps (a) and (b) are still to be regarded as performed sequentially. They should also be regarded as performed alternately in view of lack of presence of any intermediate step between the steps (a) and (b).Figure 5 schematically illustrates an exemplifying embodiment of a device 500. The control arrangement 100, configured to control a fuel system, as described above may for example comprise the device 500, consist of the device 500, or be comprised in the device 500.The device 500 comprises a non-volatile memory 520, a data processing unit 510 and a read / write memory 550. The non-volatile memory 520 has a first memory element 530 in which a computer program, e.g. an operating system, is stored for controlling the function of the device 500. The device 500 further comprises a bus controller, a serial communication port, I / O means, an A / D converter, a time and date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory 520 has also a second memory element 540.There is provided a computer program P that comprises instructions for controlling a fuel system of a vehicle to supply gaseous fuel to a combustion engine of the vehicle at a pressure equal to or higher than a first threshold pressure. . Said fuel system comprises one or more storage tanks configured for storage of gaseous fuel onboard the vehicle. The fuel system further comprises a first intermediate tank and a second intermediate tank, each configured to receive gaseous fuel from the one or more storage tanks for supply to the combustion engine via a common supply line of the fuel system. The fuel system also comprises a control fluid circuit adapted to supply a control fluid to each of the first intermediate tank and the second intermediate tank to compress gaseous fuel contained therein, said control fluid circuit comprising a pump and a plurality of control valves. The computer program comprises instructions for performing a step (a), which comprises controlling the control fluid circuit so as to supply control fluid to the first intermediate tank at least until gaseous fuel contained in the first intermediate tank reaches the first threshold pressure. The computer program further comprises instructions for performing a step (b), which comprises controlling the control fluid circuit so as to supply control fluid the second intermediate tank at least until gaseous fuel contained in the second intermediate tank reaches the first threshold pressure. The computer program further comprises instructions for performing the above described steps (a) and (b) sequentially and repeatedly.The program P may be stored in an executable form or in a compressed form in a memory 560 and / or in a read / write memory 550.The data processing unit 510 may perform one or more functions, i.e. the data processing unit 510 may effect a certain part of the program P stored in the memory 560 or a certain part of the program P stored in the read / write memory 550.The data processing device 510 can communicate with a data port 599 via a data bus 515. The non-volatile memory 520 is intended for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is intended to communicate with the data processing unit 510 via a data bus 511. The read / write memory 550 is adapted to communicate with the data processing unit 510 via a data bus 514. The communication between the constituent components may be implemented by a communication link. A communication link may be a physical connection such as an optoelectronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link.When data are received on the data port 599, they may be stored temporarily in the second memory element 540. When input data received have been temporarily stored, the data processing unit 510 is prepared to effect code execution as described above.Parts of the methods herein described may be effected by the device 500 by means of the data processing unit 510 which runs the program stored in the memory 560 or the read / write memory 550. When the device 500 runs the program, methods herein described are executed.

Claims

1. A method, performed by a control arrangement (100), for controlling a fuel system (10) of a vehicle (1 ) to supply gaseous fuel to a combustion engine (2) of the vehicle (1 ) at a pressure equal to or higher than a first threshold pressure,the fuel system (10) comprising:one or more storage tanks (11, 12, 13, 14) configured for storage of gaseous fuel onboard the vehicle (1 ),a first intermediate tank (15) and a second intermediate tank (16), each configured to receive gaseous fuel from the one or more storage tanks (11, 12, 13, 14) for supply to the combustion engine (2) via a common supply line (40) of the fuel system (10), anda control fluid circuit (20) adapted to supply a control fluid to each of the first intermediate tank (15) and the second intermediate tank (16) to compress gaseous fuel contained therein, said control fluid circuit (20) comprising a pump (25) and a plurality of control valves (21, 22, 23, 24);the method comprising the following steps:(a) controlling (S102) the control fluid circuit (20) so as to supply control fluid to the first intermediate tank (15) at least until gaseous fuel contained in the first intermediate tank (15) reaches the first threshold pressure, and(b) controlling (S103) the control fluid circuit (20) so as to supply control fluid the second intermediate tank (16) at least until gaseous fuel contained in the second intermediate tank (16) reaches the first threshold pressure,wherein steps (a) and (b) are performed sequentially and repeatedly.

2. The method according to claim 1, whereinstep (a) comprises controlling the control fluid circuit (20) to pump (25) control fluid from the second intermediate tank (16) to the first intermediate tank (15), and step (b) comprises controlling the control fluid circuit (20) to pump (25) control fluid from the first intermediate tank (15) to the second intermediate tank (16).

3. The method according to claim 2, further comprising a step of:(c) controlling the control fluid circuit (20) to temporarily turn off the pump (25) while allowing a volume of control fluid contained in the first intermediate tank (15) and the second intermediate tank (16), respectively, to be at least partly leveled out, wherein step (c) is performed after step (a) but prior to step (b), and / or after step (b) but prior to step (a).

4. The method according to claim 1, wherein each of steps (a) and (b) comprises controlling the control fluid circuit (20) to supply control fluid to the respective intermediate tank (15, 16) from a reservoir of the control fluid circuit (20), and the steps (a) and (b) are performed alternately.

5. A control arrangement (100) configured to control a fuel system (10) of a vehicle (1 ) to supply gaseous fuel to a combustion engine (2) of the vehicle (1 ) at a pressure equal to or higher than a first threshold pressure,said fuel system (10) comprising:one or more storage tanks (11, 12, 13, 14) configured for storage of gaseous fuel onboard the vehicle (1),a first intermediate tank (15) and a second intermediate tank (16), each configured to receive gaseous fuel from the one or more storage tanks (11, 12, 13, 14) for supply to the combustion engine (2) via a common supply line (40) of the fuel system (10), anda control fluid circuit (20) adapted to supply a control fluid to each of the first intermediate tank (15) and the second intermediate tank (16) to compress gaseous fuel contained therein, said control fluid circuit (20) comprising a pump (25) and a plurality of control valves (21, 22, 23, 24);the control arrangement (100) being configured to:(i) control the control fluid circuit (20) so as to supply control fluid to the first intermediate tank (15) at least until gaseous fuel contained in the first intermediate tank (15) reaches the first threshold pressure, and(11) control the control fluid circuit (20) so as to supply control fluid the second intermediate tank (16) at least until gaseous fuel contained in the second intermediate tank (16) reaches the first threshold pressure, andwherein the control arrangement (100) is configured to perform (i) and (ii) sequentially and repeatedly.

6. The control arrangement (100) according to claim 5, wherein the control arrangement (100) is configured to control the control fluid circuit (20) to supply control fluid to the first intermediate tank (15) through controlling the control fluid circuit (20) to pump (25) control fluid from the second intermediate tank (16), and to control the control fluid circuit (20) to supply control fluid to the second intermediate tank (16) through controlling the control fluid circuit (20) to pump (25) control fluid from the first intermediate tank (15).

7. The control arrangement (100) according to claim 6, wherein the control arrangement (100) further is configured to, between the supply of control fluid to the first intermediate tank (15) and the supply of control fluid to the second intermediate tank (16), control the control fluid circuit (20) to temporarily shut off the pump (25) while allowing a volume of control fluid contained in the first intermediate tank (15) and the second intermediate tank (16), respectively, to be at least partly leveled out.

8. The control arrangement (100) according to claim 5, wherein the control arrangement (100) is configured to control the control fluid circuit (20) to alternately supply control fluid to the first intermediate tank (15) and the second intermediate tank (16), respectively, from a reservoir (26) of the control fluid circuit (20).

9. A fuel system (10) for a vehicle (1), said fuel system (10) comprising:one or more storage tanks (11, 12, 13, 14) configured for storage of gaseous fuel onboard the vehicle (1),a first intermediate tank (15) and a second intermediate tank (16), each configured to receive gaseous fuel from the one or more storage tanks (11, 12, 13, 14) for supply to a combustion engine (2) of the vehicle (1 ) via a common supply line (40) of the fuel system (10),a control fluid circuit (20) adapted to supply a control fluid to each of the first intermediate tank (15) and the second intermediate tank (16) to compress gaseous fuel contained therein, said control fluid circuit (20) comprising a pump (25) and a plurality of control valves (21, 22, 23, 24), anda control arrangement (100) according to any one of claims 5 to 8.

10. The fuel system (10) according to claim 9, wherein the plurality of control valves comprises:a first control valve (21 ) arranged upstream of the pump (25) and in a first line (31 ) connecting the first intermediate tank (15) with the pump (25),a second control valve (22) arranged downstream of the pump (25) and in a second line (32) connecting the first intermediate tank (15) with the pump (25),a third control valve (23) arranged upstream of the pump (25) and in a third line (33) connecting the second intermediate tank (16) with the pump (25), anda fourth control valve (24) arranged downstream of the pump (25) and in a fourth line (34) connecting the second intermediate tank (16) with the pump (25).

11. The fuel system (10) according to any one of claims 9 and 10, wherein the fuel system (10) further comprises:a first check valve (51 ) arranged in a first fuel line (41) downstream of the first intermediate tank (15) and upstream of the common supply line (40), anda second check valve (52) arranged in a second fuel line (42) downstream of the second intermediate tank (16) and upstream of the common supply line (40).

12. The fuel system (10) according to any one of claims 9 to 11, further comprising a third intermediate tank (17) arranged in the common supply line (40).

13. The fuel system (10) according to any one of claims 9 to 12, wherein the control fluid circuit (20) further comprises a control fluid reservoir (26) arranged upstream of the pump (25).

14. The fuel system (10) according to any one of claims 9 to 13, further comprising a bypass line (45) configured to allow gaseous fuel from the one or more storage tanks (11, 12, 13, 14) to bypass the first intermediate tank (15) and second intermediate tank (16) when a pressure of gaseous fuel from the one or more storage tanks (11, 12, 13, 14) is above a second threshold pressure, said second threshold pressure being equal to or higher than the first threshold pressure.

15. The fuel system (10) according to any one of claims 9 to 14, wherein each of the first intermediate tank (15) and the second intermediate tank (16) has an internal volume of equal to or less than 10 liters.

16. A vehicle (1) comprising a control arrangement (100) according to anyone of claims 5 to 8 and / or a fuel system (10) according to any one of claims 9 to 15.

17. A computer program comprising instructions which, when executed by a control arrangement (100) according to any one of claims 5 to 8, cause the control arrangement (100) to carry out the method according to any one of claims 1 to 4.

18. A computer-readable medium having stored thereon the computer program according to claim 17.