WO2019235992A1

WO2019235992A1 - Method and control unit for controlling a state of fuel provided to an engine

Info

Publication number: WO2019235992A1
Application number: PCT/SE2019/050497
Authority: WO
Inventors: Erik Sunnegårdh; Magnus Johansson
Original assignee: Scania Cv Ab
Priority date: 2018-06-04
Filing date: 2019-05-29
Publication date: 2019-12-12
Also published as: SE542542C2; SE1850672A1

Abstract

A method and control unit for controlling a state of fuel provided from a fuel tank to an engine are presented. The fuel tank stores fuel in gaseous and liquid state, and includes at least one gaseous fuel output conduit and at least one liquid fuel output conduit. The method includes: - determining a maximal liquid torque T_{max_liq} being providable by the engine if fuel in the liquid state is provided to the engine; - determining a requested engine torque T_req; - comparing the requested engine torque T_req with the maximal liquid torque T_{max_liq}; and - controlling, if the requested engine torque T_req is higher than the maximal liquid torque T_{max_liq}; T_req> T_{max_liq}; fuel flows through one or more of the at least one gaseous fuel output conduit and the at least one liquid fuel output conduit such that only fuel in the gaseous state is provided to the engine.

Description

METHOD AND CONTROL UNIT FOR CONTROLLING A STATE OF FUEL PROVIDED TO AN ENGINE

Field of invention

The present invention relates to a method for controlling a state of fuel provided from a fuel tank to an engine, as defined in the preamble of claim 1. The present invention also relates to a control unit arranged for controlling a state of fuel provided from a fuel tank to an engine, as defined in the preamble of claim 15. The present invention also relates to a computer program and a computer-readable medium comprising instructions for carrying out the method according to the invention .

Background of invention

The following background information is a description of the background of the present invention, which thus not

necessarily has to be a description of prior art.

Vehicles, such as for example cars, buses and trucks, are driven forward by an engine torque produced by an engine in the vehicle. This engine torque is provided to the driving wheels of the vehicle through a powertrain. The torque may be created at least partly in a combustion engine by combustion of fuel being injected into the engine, i.e. injected into the cylinders of the engine.

The fuel used for the combustion in the engine may for example include liquified natural gas (LNG) . Such liquified natural gas (LNG) is often stored in at least one pressurized fuel tank. In the tank, fuel in gaseous and liquid state is stored. The pressurized fuel tank includes a gaseous fuel output conduit in contact with the gaseous state fuel, and a liquid fuel output conduit in contact with the liquid state fuel. Thus, liquid state fuel may be provided to the engine through the liquid fuel output conduit, and gaseous state fuel may be provided to the engine through the gaseous fuel output

conduit .

The pressure P_gas of the gaseous state fuel is used as, or is at least related to, a drive pressure P_drive utilized for pushing the fuel out from the pressurized tank, i.e. utilized for driving the fuel out through the liquid or gaseous fuel output conduits. Therefore, the pressure P_gas of the gaseous state fuel has to be high enough, i.e. above a minimum gas pressure threshold P_{gas min/} in order to be able to push the fuel out from tank. However, in order to prevent the pressurized tank from exploding, the pressure P_gas of the gaseous fuel may not be allowed to increase above a maximal gas pressure threshold P_{gas max/} which for example may have a value in the region of 20 bar. A safety valve may be arranged for opening the valve when the gaseous pressure P_gas reaches the maximal gas pressure threshold P_{gas max/} thereby letting gaseous state fuel pass out to the ambient air, in order to reduce the gaseous pressure P_gas .

Generally, the gaseous state fuel has a higher octane

number/rating than the liquid state fuel has, since the lighter hydrocarbons are evaporated from the liquid state fuel when the gaseous state fuel is created. The liquid state fuel includes a mixture of various hydrocarbons providing a lower octane number/rating than the evaporated lighter hydrocarbons in the gaseous state fuel result in.

However, gaseous state fuel takes up a much greater volume than liquid state fuel due to its much lower density.

Therefore, the pressurized fuel tank should at least partly include fuel in liquid form in order to provide an acceptable reach/range for a vehicle comprising the tank and the engine. The differing octane numbers/ratings for the gaseous and liquid states of the fuel may be used such that the liquid state fuel is used under some conditions and that the gaseous state fuel is used under other conditions. For example, the gaseous state fuel may be used when a higher torque is

requested, e.g. for accelerations or for driving uphill. To achieve this, a mechanical economizer has in conventional solutions been arranged to switch between supplying liquid state fuel and gaseous state fuel to the engine. Such a mechanical economizer has e.g. been arranged as a mechanical switch, which is able to switch between connecting the gaseous fuel output conduit of the tank to the engine and connecting the liquid fuel output conduit to the engine.

SUMMARY OF INVENTION

The mechanical economizer used in conventional solutions is arranged to switch between providing liquid and gaseous state fuel to the engine at a gas pressure P_gas corresponding to a predetermined switch threshold P_{gas sw} th of the gaseous state fuel, often having a value corresponding to a gas pressure P_gas of 12 bar; P_gas = 12 bar. For example, if the gas pressure P_gas of the gaseous state fuel is increased above the switch threshold P_{gas sw th/} the economizer switches to provide only gaseous state fuel to the engine. Correspondingly, if the gas pressure P_gas of the gaseous state fuel is decreased below the switch threshold P_{gas sw th}, the economizer switches to provide only liquid state fuel to the engine.

However, due to component individual variations, different mechanical economizer individuals may switch at different gaseous pressures P_gas, although they are all designed to switch at the threshold P_{gas sw} th · Thus, different mechanical economizer individuals may provide different states

(gaseous/fluid) of the fuel to its respective engines at the same gaseous P_gas . These component individual variations results in an unreliable control of the state of fuel being provided to the engine. Therefore, the torque being providable by the engine is also uncertain, since the octane number/rate of the fuel provided to the engine is not reliably controlled.

Also, the state of the fuel being provided to the engine has an influence on the pressure P_gas of the gaseous fuel, and therefore has an influence on the drive pressure P_drive used for pushing the fuel to the engine. Generally, if gaseous state fuel is provided to the engine, the pressure P_gas of the gaseous fuel is decreased. The uncertainty of the mechanical economizer may therefore cause drive pressure P_drive problems. For example, if gaseous state fuel is provided to the engine although liquid state fuel should have been provided to the engine, the gaseous pressure P_gas, and thus the drive pressure P_drive, may be unnecessarily decreased, possibly to a point when the efficiency of the engine is affected since the fuel is not properly provided to the engine. On the other hand, if liquid state fuel is provided to the engine although gaseous state fuel should have been provided to the engine, the gaseous pressure P_gas, may be unnecessarily increased, possibly to a level at which the above-mentioned safety valve opens and lets gaseous state fuel pass out to the ambient air, whereby valuable fuel is wasted.

Thus, the uncertainty of the conventionally used mechanical economizer may cause engine control difficulties, and may also unnecessary increase the fuel consumption.

It is therefore an object to solve at least some of the above- mentioned disadvantages.

The object is achieved by the above mentioned method for controlling a state of fuel provided from a fuel tank to an engine, the fuel tank storing fuel in gaseous and liquid state, and including at least one gaseous fuel output conduit and at least one liquid fuel output conduit according to the characterizing portion of claim 1, the method including:

- determining a maximal liquid torque T_max n_q being providable by the engine if fuel in the liquid state is provided to the engine ;

- determining a requested engine torque T_req;

- comparing the requested engine torque T_req with the maximal liquid torque T_{max iiq}; and

- controlling, if the requested engine torque T_req is higher than the maximal liquid torque T_{max iiq}; T_req > T_{max iiq}; fuel flows through one or more of the at least one gaseous fuel output conduit and the at least one liquid fuel output conduit such that only the fuel in the gaseous state is provided to the engine .

Hereby, the gaseous state fuel, having a higher octane

number/rate, may be saved for usage in situations when it is really needed, i.e. in situations when a requested engine torque T_req is so high that it cannot be provided by combustion of liquid state fuel. This is a great improvement over the conventional mechanical economizer, which switches only based on the gas pressure P_gas .

Thus, by usage of the present invention, it is possible to optimize the state of the fuel and/or the ratio between gaseous and liquid states of the fuel being provided to the engine, in order to match the needs of the engine, i.e. in order to match the requested torque T_req. Hereby, the torque being providable by the engine may also be adapted to the usage of the vehicle, since fuel having an adapted octane number/rate may always be provided to the engine. The

conventional mechanical economizer, however, does not take the usage of the vehicle into consideration when performing the switching between gaseous and liquid state fuel.

Thus, the present invention facilitates a reliable and

accurate control of the controllable electronic economizer, which enables that higher torques may be provided by the engine when needed, since more gaseous state fuel (having higher octane number/rate) will be available for being

provided to the engine when needed.

Also, the fuel consumption is reduced by usage of the present invention, since the safety valve needs to be opened more seldom.

According to an embodiment of the present invention, the method further includes:

- controlling fuel flows through one or more of the at least one gaseous fuel output conduit and the at least one liquid fuel output conduit such that the fuel provided to the engine includes a majority of the fuel in the liquid state if the requested engine torque T_req is lower than or equal to the maximal liquid torque T_max_i_iq; T_req < T_max_i_iq.

Hereby, the higher octane number/rate gaseous state fuel is saved for usage in situations when it is really needed, i.e. in situations when a requested engine torque T_req is so high that it cannot be provided by combustion of liquid state fuel.

According to an embodiment of the present invention, the fuel provided to the engine includes one in the group of:

- 100% fuel in the gaseous state ;

- a mixture of the fuel in the gaseous state and in the liquid state; and

- 100% fuel in the liquid state. Hereby, an adaption of the ratios between gaseous and liquid state fuel being provided to the engine is adapted in relation to the requested torque T_req. The engine is then provided with the fuel it needs to provide the requested torque T_req, at the same time as no valuable gaseous state fuel is wasted.

Instead, the higher octane number/rate gaseous state fuel is saved for usage in situations when it is really needed.

- determining a pressure P_gas of the fuel in the gaseous state;

- comparing the pressure P_gas of the fuel in the gaseous state with a first pressure threshold Pi _th/ the first pressure threshold Pi _th being related to a pressure P_{gas min} needed for providing the fuel flows through one or more of the at least one gaseous fuel output conduit and the at least one liquid fuel output conduit; and

- controlling, if the pressure P_gas is lower than the first pressure threshold Pi _th; P_gas < Pi _th ; fuel flows through one or more of the at least one gaseous fuel output conduit and the at least one liquid fuel output conduit such that only the fuel in the liquid state is provided to the engine.

Hereby, is it secured that the gas pressure P_gas is high enough for being able to push the fuel out from the tank, and to the engine, i.e. that a high enough drive pressure P_drive is available. For example, the first pressure threshold Pi_th may, according to an embodiment, be equal to the pressure P_{gas min} needed for providing the fuel flows through one or more of the at least one gaseous fuel output conduit and the at least one liquid fuel output conduit.

According to an embodiment of the present invention, the first pressure threshold Pi _th is determined based at least on one or more in the group of:

- at least one feature of the fuel tank; and

- at least one feature of a fuel providing system arranged for providing the fuel from the tank to the engine.

Since the first pressure threshold Pi _th is adapted to the features of the fuel tank and/or of the fuel providing system of the vehicle, is it secured that the gas pressure P_gas is high enough for being able to push the fuel out from precisely the fuel tank arranged in the system/vehicle .

- determining a pressure P_gas of the fuel in the gaseous state;

- comparing the pressure P_gas of the fuel in the gaseous state with a second pressure threshold P_{2 th/} the second pressure threshold P_{2 th} being related to a maximally allowed pressure P_{gas max} for the tank; and

- controlling, if the pressure P_gas is higher than the second pressure threshold P_{2 th/} P_gas > P_{2 th/} fuel flows through one or more of the at least one gaseous fuel output conduit and the at least one liquid fuel output conduit such that only the fuel in the gaseous state is provided to the engine.

Hereby, the risk for wasting fuel due to opening of the safety valve is reduced, since the second pressure threshold P_{2 th} is determined related to a maximally allowed pressure P_{gas max} for the tank. For example, the herein described second pressure threshold P_{2 th} may, according to an embodiment, be equal to the maximally allowed pressure P_{gas max} for the tank minus a safety offset Pg_as_offset ?2_th^— Pgas_max ^— Pgas_offset where the safety offset P_{gas offset} has a value providing reliable protection against a tank explosion. Also, a pressure region Pi _th - P_{2 th} between the first pressure threshold Pi _th and the second pressure threshold P_{2 th} is defined by some embodiments of the present invention. This pressure region Pi _th - P_{2 th} does not even exist for a

conventional mechanical economizer, since the conventional mechanical economizer switches only based on the pressure. The pressure region Pi _th - P_{2 th} created by the embodiments of the present invention may be utilized for controlling the

electronic controllable economizer in relation to the

requested engine torque T_req. Hereby, a more efficient usage of the gaseous state fuel, and thereby also a more powerful engine, may be achieved.

According to an embodiment of the present invention, the second pressure threshold P_{2 th} is determined based at least on one or more in the group of:

- a required volume of the fuel in the gaseous state in the tank;

- a type of vehicle including the fuel tank and the engine;

- a usage of a vehicle including the fuel tank and the engine;

- at least one feature of the fuel tank;

- a level of fuel in the fuel tank;

- a relation between amounts of the fuel in the gaseous state and the fuel in the liquid state in the fuel tank;

- a temperature in the fuel tank;

- an ambient temperature outside the fuel tank; and

- at least one requirement related to a full tank parking time period for a vehicle including the fuel tank and the engine.

Since the second pressure threshold P_{2 th} is adapted to the features of the fuel providing system of the vehicle, the risk for having to open the safety valve is reduced, whereby also a reduction of the fuel consumption is achieved over time. According to an embodiment of the present invention, the maximal liquid torque T_max n_q is determined adaptively when the engine runs, and is based on a performance of the engine.

Hereby, the maximal liquid torque T_{max iiq} may adaptively be very accurately determined.

According to an embodiment of the present invention,

information related to the controlling of the fluid flows is stored and utilized together with the performance of the engine resulting from the controlling in/for the adaptive determination of the maximal liquid torque T_maxn_q.

Hereby, the maximal liquid torque T_{max iiq} may be accurately determined .

According to an embodiment of the present invention, a value of the maximal liquid torque T_{max iiq} is actively adjusted, and the adaptive determination of the maximal liquid torque T_max n_q is based on the active adjustment and on a performance of the engine resulting from the active adjustment of the maximal liquid torque T_max_i_iq.

Hereby, the maximal liquid torque T_{max iiq} may be accurately determined by the active adaptive determination.

According to an embodiment of the present invention, the maximal liquid torque T_{max liq} is determined by running a test engine corresponding to the engine on the fuel in the liquid state in a test cell and measuring a resulting torque Ti_{iq t}est·

Hereby, the maximal liquid torque T_{max iiq} may be easily

determined, with no addition to the complexity of the vehicle.

According to an embodiment of the present invention, the maximal liquid torque T_{max iiq} is determined by: - determining a tendency for engine knocking when the fuel in the liquid state is provided to the engine; and

- determining the maximal liquid torque T_max n_q based on the determined tendency for engine knocking.

Hereby, the maximal liquid torque T_{max iiq} may be easily and accurately determined. The maximal liquid torque T_{max iiq} may be determined in the vehicle. The value for the maximal liquid torque T_{max iiq} may be updated continuously.

The object is also achieved by the above-mentioned control unit arranged for controlling a state of fuel provided from a fuel tank to an engine, the fuel tank storing fuel in gaseous and liquid state, and including at least one gaseous fuel output conduit and at least one liquid fuel output conduit, according to the characterizing portion of claim 15. The control unit includes:

- first means arranged for determining a maximal liquid torque T_{max iiq} being providable by the engine if fuel in the liquid state is provided to the engine;

- second means arranged for determining a requested engine torque T_req;

- means arranged for comparing the requested engine torque T_req with the maximal liquid torque T_{max liq}; and

- means arranged for controlling, if the requested engine torque T_req is higher than the maximal liquid torque T_{max iiq}; T_req > T_{max iiq}; fuel flows through one or more of the at least one gaseous fuel output conduit and the at least one liquid fuel output conduit such that only the fuel in the gaseous state is provided to the engine.

The control unit has the same advantages as stated above for the method. According to an embodiment of the present invention, the means arranged for controlling the fuel flows is further arranged for :

- controlling fuel flows through one or more of the at least one gaseous fuel output conduit and the at least one liquid fuel output conduit such that the fuel provided to the engine includes a majority of the fuel in the liquid state if the requested engine torque T_req is lower than or equal to the maximal liquid torque T_max_i_iq; T_req £ T_max_i_iq.

- 100% fuel in the gaseous state ;

- a mixture of the fuel in the gaseous state and in the liquid state; and

- 100% fuel in the liquid state.

According to an embodiment of the present invention, the control unit further includes:

- means arranged for determining a pressure P_gas of the fuel in the gaseous state;

- means arranged for comparing the pressure P_gas of the fuel in the gaseous state with a first pressure threshold Pi _th_/ the first pressure threshold Pi _th being related to a pressure

P_{gas min} needed for providing the fuel flows through one or more of the at least one gaseous fuel output conduit and the at least one liquid fuel output conduit; and

- means arranged for controlling, if the pressure P_gas is lower than the first pressure threshold Pi _th; P_gas < Pi th ; fuel flows through one or more of the at least one gaseous fuel output conduit and the at least one liquid fuel output conduit such that only the fuel in the liquid state is provided to the engine . According to an embodiment of the present invention, the control unit further includes means arranged for determining the first pressure threshold Pi _th based at least on one or more in the group of:

- at least one feature of the fuel tank; and

- means arranged for comparing the pressure P_gas of the fuel in the gaseous state with a second pressure threshold P_{2 th}, the second pressure threshold P_{2 th} being related to a maximally allowed pressure P_{gas max} for the tank; and

- means arranged for controlling, if the pressure P_gas is higher than the second pressure threshold P₂ th/ P_gas > P₂ th/ fuel flows through one or more of the at least one gaseous fuel output conduit and the at least one liquid fuel output conduit such that only the fuel in the gaseous state is provided to the engine.

According to an embodiment of the present invention, the control unit further includes means for determining the second pressure threshold P_{2 th} based at least on one or more in the group of:

- a required volume of the fuel in the gaseous state in the tank;

- a type of vehicle including the fuel tank and the engine;

- a usage of a vehicle including the fuel tank and the engine;

- at least one feature of the fuel tank;

- a level of fuel in the fuel tank;

- a temperature in the fuel tank;

- an ambient temperature outside the fuel tank; and

According to an embodiment of the present invention, the control unit further includes means arranged for determining the maximal liquid torque T_max n_q when the engine runs, based on a performance of the engine.

According to an embodiment of the present invention, the control unit further includes means arranged for storing information related to the controlling of the fluid flows, and means arranged for utilizing the information together with the performance of the engine resulting from the controlling in the adaptive determination of the maximal liquid torque T_max ii_q.

According to an embodiment of the present invention, the control unit includes means arranged for actively adjusting a value of the maximal liquid torque T_max n_q, and means arranged for adaptive determining the maximal liquid torque T_{max liq} based on the active adjustment and on a performance of the engine resulting from the active adjustment of the maximal liquid torque T_max_i_iq.

According to an embodiment of the present invention, the control unit further includes means arranged for determining the maximal liquid torque T_max n_q by running a test engine corresponding to the engine on the fuel in the liquid state in a test cell and measuring a resulting torque Ti_{iq t}est·

According to an embodiment of the present invention, the control unit further includes means arranged for determining the maximal liquid torque T_{max iiq} by: - determining a tendency for engine knocking when the fuel in the liquid state is provided to the engine; and

The object is also achieved by the above-mentioned computer program and computer-readable medium.

Detailed exemplary embodiments and advantages of the method, control unit, computer program and computer-readable medium according to the invention will below be described with

reference to the appended drawings illustrating some preferred embodiments .

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described in more detail with reference to attached drawings illustrating examples of embodi ments of the invention in which:

Figure 1 is a schematic illustration of a non-limiting example of a vehicle in which the embodiments of the present invention may be implemented,

Figure 2 is a schematic illustration of a fuel providing system, in which the embodiments of the present invention may be implemented,

Figures 3a-b show a conventional economizer and valves that may be used according to some embodiments of the present invention, respectively,

Figure 4 shows a flow chart diagram for some embodiments of the present invention, Figure 5 schematically illustrates various pressures and actions made according to some embodiments of the present invention, and

Figure 6 is a schematic illustration of a control unit

according to some embodiments of the present invention.

DETAILED DESCRIPTION OF INVENTION

Figure 1 schematically shows an example vehicle 100, such as a truck, a bus, a car, or another suitable vehicle, which will be used to explain the present invention. The present

invention is, however, not limited to use in heavy goods vehicles as the one shown in figure 1, but may also be used in essentially any vehicle, such as lighter vehicles, e.g.

passenger cars.

The vehicle 100, shown schematically in figure 1, comprises an engine 101, which may comprise a combustion engine, for example an engine consuming liquified natural gas (LNG) , in order to create a torque being provided for driving the vehicle, e.g. an engine working according to the diesel cycle, or an engine working according to the Otto cycle for which an electric spark ignites a fuel and air mixture in the engine cylinders. Essentially, the engine 101 may in this document comprise any device which transforms chemical energy to mechanical energy, and uses gaseous and liquid state fuel for its combustion. The engine then provides energy in form of a torque to the powertrain. Exhaust gases produced by the engine 101 are purified by an exhaust treatment system 150. The vehicle may also comprise one or more other power sources, such as e.g. an electrical machine, as is understood by a skilled person.

The engine 101 may, for example, in a customary fashion, via an output shaft 102 of the engine 101, be connected with a gearbox 103, via a clutch 106 and an input shaft 109 connected to the gearbox 103. An output shaft 107 from the gearbox 103, also known as a propeller shaft, drives the driving wheels 110, 111 via a final gear 108, such as e.g. a customary differential, and drive shafts 104, 105 connected with the final gear 108.

A fuel providing system 120, including at least one

pressurized fuel tank 121, is arranged for providing the engine 101 with fuel. The fuel providing system 120 is

described more in detail below.

A control unit 140 is in figure 1 schematically illustrated as receiving signals and/or providing control signals from and/or to the engine 101 and/or the pressurized fuel tank 121. The control unit 140 may also receive and/or provide control signals to and/or from other devices in the vehicle 100.

According to some embodiments of the present invention, as described in this document, the control unit 140 may also comprise first determining means 141, e.g. a first

determination unit 141, second determining means 142, e.g. a second determination unit 142, comparison means 143, e.g. a comparison unit 143, and control means 144, e.g. a control unit 144. These control means/units/devices 141, 142, 143, 144 are described more in detail below, and may be divided

physically into more than the herein described control

means/systems/units 140, or may be arranged in less control systems/units than herein described.

As mentioned above, and as schematically illustrated in figure 2, the fuel used for the combustion in the engine 101 may for example include gaseous 125 and liquid 126 state fuel, such as e.g. states of a liquified natural gas (LNG) . Such gaseous and liquid state fuel is stored in a fuel tank 121, which often is a pressurized fuel tank. The fuel tank includes a gaseous fuel output conduit 122 in contact with the gaseous state fuel 125, and a liquid fuel output conduit 123 in contact with the liquid state fuel 126. Liquid state fuel 126 may therefore be provided to the engine through the liquid fuel output conduit 123, and gaseous state fuel 125 may be provided to the engine through the gaseous fuel output conduit 122. The tank 121 may include the above-mentioned safety valve 124 arranged for opening the valve 124 if the gaseous pressures P_gas reaches the maximal gas pressure threshold P_{gas max} · Hereby, the gaseous state fuel is allowed to pass out into the ambient air outside of the system/vehicle, which efficiently limits/reduces the gaseous pressure P_gas .

Conventional fuel providing systems 120 have been equipped with a mechanical economizer, schematically illustrated in figure 3a, arranged to switch between connecting either the gaseous fuel output conduit 122 or the liquid fuel output conduit 123 to the engine, e.g. via a fuel arrangement 128, such as pipe and/or a tube. The conventional mechanical economizer has the above-mentioned drawbacks/disadvantages.

The present invention, and its embodiments, may instead utilize an electronically controlled economizer 127

schematically illustrated in figure 3b. The electronically controlled economizer 127 includes at least one controllable valve 129 arranged in at least one of the gaseous fuel output conduit 122 and the liquid fuel output conduit 123. For example, one such electronically controllable valve 129 may be arranged at each one of the the gaseous fuel output conduit 122 and the liquid fuel output conduit 123. By usage of the electronically controlled economizer 127, the portions/ratios of gaseous 125 and liquid 126 state fuel to be provide to the engine, e.g. via a fuel arrangement 128, may easily be achieved. Thus, by usage of the electronically controlled economizer 127, it is not only possible to choose to provide either gaseous or liquid state fuel to the engine (as for the conventional mechanical economizer in figure 3a) . Instead, it is possible to control the controllable at least one valve 129 of the electronically controlled economizer 127 such that essentially any combination/mixture of gaseous 125 and liquid 126 state fuel is provided to the engine. Thus, essentially any ratio of gaseous 125 and liquid 126 fuel, and therefore also any variety of octane numbers/rates, may hereby be provided to the engine by the control of the at least one controllable valve 129.

Figure 4 shows a flow chart diagram for a method 400 according to an embodiment of the present invention, i.e. a method for controlling a state of fuel provided from a fuel tank 121 to an engine 101, wherein the fuel tank 121 is storing fuel in gaseous 125 and liquid 126 state. The tank 121 includes at least one gaseous fuel output conduit 122 and at least one liquid fuel output conduit 123.

The method steps of figure 4 may be performed in another order than the order illustrated in figure 4, as long as the

information needed for performing a step is available when the step is to be performed.

In a first step 410 of the method, e.g. performed by use of a below described first determination unit/means 141, a maximal liquid torque T_max n_q being providable by the engine 101 if fuel in the liquid state 125 is provided to the engine 101 is determined .

In a second step 420 of the method, performed e.g. by use of a below described second determination unit/means 142, a

requested engine torque T_req is determined. The requested engine torque is a well-known parameter commonly used in vehicle control systems, such as e.g. in an engine control system. The requested engine torque may be determined in a number of ways known by a skilled person.

In a third step 430 of the method, performed e.g. by use of a below described comparison unit/means 143, the requested engine torque T_req is compared with the maximal liquid torque T_{max liq} determined in the first step 410.

In a fourth step 440 of the method, e.g. performed by use of a below described controlling unit/means 144, if the in the second step 420 determined requested engine torque T_req is higher than the in the first step 410 determined maximal liquid torque T_{max iiq}; T_req > T_max n_q; then fuel flows through one or more of the at least one gaseous fuel output conduit 122 and the at least one liquid fuel output conduit 123 are controlled such that only the fuel in the gaseous state 125 is provided to the engine 101.

By usage of the present invention, the valuable gaseous state fuel 125, having a higher octane number/rate, may be saved for situations when it is really needed, i.e. for intelligent usage in situations when a requested engine torque T_req is so high that it cannot be provided by usage of liquid state fuel. Thus, the higher octane number gaseous state fuel 125 may be saved for usage in e.g. uphill and/or acceleration situations when the present invention is used. This is a great

improvement over the conventional mechanical economizer, which performed switching only based on the gas pressure P_gas .

Thus, the choice of the state of the fuel to be provided to the engine may, by usage of the present invention, be coupled to the usage of the vehicle, e.g. to an operational point of the vehicle and/or to a driving situation, which makes it possible to optimize the state of the fuel and/or the ratio between gaseous and liquid states of the fuel being provided to the engine. Hereby, the torque being providable by the engine may also be adapted to the usage of the vehicle.

Also, the present invention facilitates a reliable and

accurate control of the controllable electronic economizer, such that gas pressures P_gas closer to the maximal gas pressure threshold P_{gas max} may safely be utilized, which enables that higher torques may be provided by the engine, since more gaseous state fuel (having higher octane number/rate) will be available for being provided to the engine 101.

Figure 5 illustrates some pressures and actions taken under certain conditions in various pressure regions. According to an embodiment, the above mentioned fourth step 440 includes a further step 245 of controlling the fuel flows through one or more of the at least one gaseous fuel output conduit 122 and the at least one liquid fuel output conduit 123 such that the fuel provided to the engine 101 includes a majority, i.e. > 50%, of the fuel in the liquid state 126 if the requested engine torque T_req is lower than or equal to the maximal liquid torque T_max n_g; T_reg h T_max ii_g.

In the middle of figure 5, the method steps 440 and 445 are illustrated as taken within a gas pressure P_gas interval between a first pressure threshold Pi _th and a second pressure threshold P_{2 th} · The first pressure threshold Pi _th is here related to, may e.g. be corresponding/equal to the above mentioned minimum gas pressure P_{gas min} needed for pushing the fuel out from the tank 121; Pi _th = P_{gas min/} and may as a non limiting example have a value corresponding to a gas pressure P_gas of 10 bar; Pi_th = 10 bar. The second pressure threshold P_{2 th} may indicate a pressure over which an amount of the gaseous state fuel 125 in the tank 121 needs to be reduced in order to avoid that the pressure P_gas of the gaseous state fuel 125 reaches the maximally allowed pressure P_gas max for the tank, which would trigger an opening of the safety valve 124. Thus, the second pressure threshold P₂ th is related to the maximally allowed gas pressure P_gas max for the tank 121, and may as a non limiting example correspond to a gas pressure P_gas of 18 bar;

P2 th = 18 bar. The maximally allowed pressure P_gas max may as a non-limiting example correspond to a gas pressure P_gas of 20 bar; P_gas max = 20 bar. Thus, there may be a safety margin/offset P_{gas offset}; of e.g. 2 bar between the maximally allowed pressure Pgas_max and the second pressure threshold P₂_th; P_gas_offset = P_gas_max - P₂ th = 2 bar .

According to an embodiment of the present invention, when the gas pressure P_gas is within the above-mentioned pressure interval Pi _th - P₂ th, various levels of requested torque result in various fuel state mixtures, such as 100% fuel in the gaseous state, a mixture of the fuel in the gaseous state and in the liquid state, or 100% fuel in the liquid state.

A couple of non-limiting examples of fuel state ratios are given in the following. One or more of such examples ratios may, according to an embodiment of the present invention, be utilized as initial values for one or more of the embodiments of fuel state control described in this document.

According to a control algorithm, if the requested engine torque T_req is higher than the maximal liquid torque T_{max iiq}; T_req > T_{max iiq}; then 100% fuel in gaseous state 125, i.e. 0% fuel in liquid state 126, may be provided to the engine 101.

According to a control algorithm, if the requested engine torque T_req is lower than or equal to the maximal liquid torque T_max ii_q; T_req £ T_max i_iq; then 100% fuel in liquid state 126, i.e. 0% fuel in gaseous state 125, may be provided to the engine 101.

According to a control algorithm, if the requested engine torque T_req is higher than 110% of the maximal liquid torque T_max n_q; T_req > 1.1 * T_{max iiq}; then 100% fuel in gaseous state 125, i.e. 0% fuel in liquid state 126, may be provided to the engine 101.

According to a control algorithm, if the requested engine torque T_req is in an interval between 80% and 110% of the maximal liquid torque T_max i_q; 0.8*T_max i_q < T_req < 1. l*T_max i_q; then a mixture of fuel in gaseous state 125 and liquid state 126 may be provided to the engine.

According to a control algorithm, if the requested engine torque T_req is higher than 90% of the maximal liquid torque T_max n_q; T_req > 0.9*T_{max iiq}; then 100% fuel in gaseous state 125, i.e. 0% fuel in liquid state 126, may be provided to the engine 101.

According to a control algorithm, if the requested engine torque T_req is in an interval between 80% and 90% of the maximal liquid torque T_max i_aq; 0.8*T_max i_aq ^ T_req ^ 0.9*T_max i_aq; then a mixture of fuel in gaseous state 125 and liquid state 126 may be provided to the engine.

According to a control algorithm, if the requested engine torque T_req is lower than or equal to 80% of the maximal liquid torque T_{max iiq}; T_req £ 0.8*T_{max iiq}; then 100% fuel in liquid state 126 may be provided to the engine 101.

According to an embodiment of the present invention, the method 400 illustrated in figure 4 further includes a fifth step 450 of determining a pressure P_gas of the fuel in the gaseous state 125. The gas pressure P_gas may e.g. be determined by usage of one or more sensors. The one or more sensors may be arranged at/within the tank 121 and/or at/within the at least one gaseous state fuel output conduit 122.

The method 400 may also include a sixth step 460 of comparing the determined pressure P_gas of the fuel in the gaseous state 125 with the first pressure threshold Pi_th· As mentioned above, the first pressure threshold Pi _th may here indicate a pressure needed for providing the fuel flows through one or more of the at least one gaseous fuel output conduit 122 and the at least one liquid fuel output conduit 123, i.e. for providing the fuel to the engine.

The method may also include a seventh step 470 of controlling, if the determined pressure P_gas is lower than the first

pressure threshold Pi th/ P_gas < Pi th/ fuel flows through one or more of the at least one gaseous fuel output conduit 122 and the at least one liquid fuel output conduit 123 such that only fuel in liquid state 125 is provided to the engine 101. As mentioned above, the control 470 may be achieved by use of one or more flow controlling arrangements, including e.g. one or more valves mounted in and/or at one or more of the at least one gaseous fuel output conduit 122 and the at least one liquid fuel output conduit 123, i.e. by the use of the

electrically controlled economizer 127. According to an embodiment, for which Pi _th = P_{gas min/} the control step 470 is thus performed if P_gas < P_gas min· The control step 470 is

illustrated at the bottom of figure 5.

As is illustrated in figure 4, the method 400 may according to an embodiment, any time after the fifth step 450 of

determining the gas pressure P_gas, include an eighth step 480 of comparing the determined pressure P_gas of the gaseous state fuel 125 with the second pressure threshold P_{2 th} · As mentioned above, the second pressure threshold P₂ th is related to a maximally allowed pressure P_{gas max} for the tank 121, at which the safety valve 124 opens.

The method 400 may, according to an embodiment, also include a ninth step 490 of controlling, if the determined gas pressure Pgas is higher than the pressure threshold P₂ th ; Pgas > P2 th/ fuel flows through one or more of the at least one gaseous fuel output conduit 122 and the at least one liquid fuel output conduit 123 such that only gaseous state fuel 125 is provided to the engine 101. As mentioned above, the control 490 may be achieved by use of one or more flow controlling arrangements, including e.g. one or more valves mounted in and/or at one or more of the at least one gaseous fuel output conduit 122 and the at least one liquid fuel output conduit 123, i.e. by the use of the electrically controlled economizer 127. The control 490 is illustrated at the top of figure 5.

Thus, as is illustrated in figure 5, according to various embodiments of the present invention, depending on the

value/level of the gas pressure P_gas and/or depending on the requested torque, the electrically controlled economizer 127 is controlled for providing liquid state fuel 126, gaseous state fuel 125 or a mixture of gaseous and liquid state fuel to the engine. Hereby, a very exact control of the fuel being provided to the engine is achieved for a large variety of vehicle uses and/or engine operational modes. A very exact and reliable control of the engine and its provided torque may hereby be achieved. Also, the fuel consumption is reduced since the safety valve may be opened less often.

As illustrated in figure 5, according to the embodiments of the present invention, a pressure region Pi _th - P2 th between the first pressure threshold Pi _th and the second pressure threshold P_{2 th} is defined, in which the electronic controllable economizer 127 may be controlled in relation to the requested engine torque T_req. This pressure region Pi _th - P₂ th does not even exist for a conventional mechanical economizer, since the conventional mechanical economizer switches only based on the pressure .

The pressure region P_{2 t}h - P2 th created by the embodiments of the present invention may, as is mentioned above, be utilized for a more accurately control the state of fuel being provided to the engine. Hereby, a more efficient usage of the gaseous state fuel, and thereby also a more powerful engine when needed, may be achieved. Also, the more exact and reliable control of the state of fuel being provided to the engine reduces the need for opening the safety valve 124, which lowers the fuel consumption over time.

The first pressure threshold Pi _th/ which is utilized in various embodiments of the present invention, may be determined in a number of ways. According to an embodiment, the first pressure threshold Pi _th is determined based on at least one feature of the fuel tank 121, such as for example a size, a geometrical design and/or an output conduit design for the fuel tank 121. According to an embodiment, the first pressure threshold Pi _th is determined based on at least one feature of a fuel

providing system 120 arranged for providing the fuel from the tank 121 to the engine 101, wherein such system features may include geometrical forms and/or dimensions for piping between the tank 121 and the engine 101 and/or for a (common) fuel rail providing pressurized fuel to the injectors arranged for injecting fuel into the engine.

The second pressure threshold P2 _th/ which is also utilized in various embodiments of the present invention, may be determined in a number of ways. According to an embodiment, the second pressure threshold P_{2 th} may be determined based on a required volume of the gaseous state fuel 125 in the tank 121 and/or on the type and/or usage of the vehicle 100. For example, a bus or a garbage truck, i.e. vehicles often

moving/driving short distances between its stops, may have a lower/smaller value for the second pressure threshold P2 _th/ whereas e.g. long haulage trucks, i.e. vehicles driving/moving longer distances between its stops, may have a higher/greater value for the second pressure threshold P2 _th · Further,

according to an embodiment, the second pressure threshold P_{2 th} may be determined based on at least one feature of the fuel tank 121, a level of fuel in the fuel tank 121, a relation between amounts of the gaseous state 125 and liquid state 126 fuel in the fuel tank 121, a temperature in the fuel tank 121, an ambient temperature outside the fuel tank/system/vehicle, and/or at least one requirement related to a full tank parking time period for the vehicle 100 including the fuel tank 121. Generally, the gas pressure P_gas in the fuel tank 121 slowly increases over time if the vehicle is standing still with the engine off/not running. If the gaseous state fuel is not consumed, the gas pressure P_gas will after some time reach dangerous gas pressure P_gas levels, e.g. at 20 bar, wherefore the safety valve 124 is arranged to open, in order to mitigate further increase of the gas pressure P_gas in the fuel tank. In various regions, there is legislation and/or rules defined that specify a time period during which a full tanked vehicle should manage to stand still, i.e. to be parked, without having to open the safety valve 124.

As is mentioned above, the maximal liquid torque T_max n_q is used in various embodiments of the present invention. The maximal liquid torque T_{max iiq} may, according to an embodiment, be determined 410 adaptively during normal operation of the vehicle, i.e. when the engine 101 runs. The determination 410 of the maximal liquid torque T_{max iiq} is then based on a

performance of the engine 101. For example, information related to the controlling 440 of the fluid flows, i.e.

control of the electrically controlled economizer 127, is stored and is utilized, together with the determined

performance of the engine 101 resulting from the controlled flows, i.e. resulting from the control of the economizer, for the adaptive determination 410 of the maximal liquid torque T_{max iiq} · A value of the maximal liquid torque T_{max iiq} may here for example be actively adjusted, and thereafter the maximal liquid torque T_{max iiq} is adaptively determined 410 based on that made active adjustment and on a determined performance of the engine 101 resulting from the active adjustment of the maximal liquid torque T_{max iiq}. In other words, a change/adjustment of the maximal liquid torque T_{max iiq} is here first actively

effected, and thereafter the effect of this change/adjustment is analyzed. The analysis is then possibly followed by another adj ustment/change of the maximal liquid torque T_{max iiq}.

According to an embodiment, the maximal liquid torque T_{max liq} is determined 410 by first determining a tendency for engine knocking when the fuel in the liquid state is provided to the engine, e.g. based on information provided by one or more knocking sensors, which may be acoustic sensors arranged at the engine 101, and/or based on a knowledge of the octane number of the fuel provided to the engine. When the tendency for engine knocking has been determined, the maximal liquid torque T_{max iiq} may be determined based on the determined

tendency, e.g. by, if knocking is detected, adjusting the ignition, and thereby also adjusting the providable torque, until the knocking stops. The maximal liquid torque T_max n_q is then determined as the torque providable without engine knocking occurring.

Correspondingly, the maximal gaseous torque T_{max gas} is,

according to an embodiment, determined 410 by first

determining a tendency for engine knocking when the fuel in the gaseous state is provided to the engine, e.g. by usage of the above mentioned one or more knocking sensors and/or based on the octane number of the fuel provided to the engine. When the tendency for engine knocking has been determined, the gaseous torque T_{max gas} may be determined based on the determined tendency, by adjusting the ignition until the knocking stops, as mentioned above. The gaseous torque T_{max gas} is then

determined as the torque providable without engine knocking occurring .

The determination of the maximal gaseous torque T_{max gas} and/or the maximal liquid torque T_max n_q providable by the engine 101 may, according to an embodiment, be performed by running a test engine corresponding to the engine 101 in the vehicle 100 e.g. in a test cell/laboratory environment, and measuring resulting gaseous and/or liquid test torques T_gas test_/ Ti_iq test· The maximal gaseous and/or liquid torques T_{max gas}, T_{max iiq} are then determined based on the respective gaseous and/or liquid test torques T_gas-test, Ti_iq-test.

A person skilled in the art will appreciate that the

embodiments of the method for controlling a state of fuel provided from a fuel tank 121 to an engine 101, according to the present invention, may also be implemented in a computer program, which, when it is executed in a computer, instructs the computer to execute the method. The computer may be included in the herein described system and/or may be

coupled/connected to the herein described system. The computer program is usually constituted by a computer program product 603 stored on a non-transitory/non-volatile digital storage medium, in which the computer program is incorporated in the computer-readable medium of the computer program product. The computer-readable medium comprises a suitable memory, such as, for example: ROM (Read-Only Memory), PROM (Programmable Read- Only Memory) , EPROM (Erasable PROM) , Flash memory, EEPROM (Electrically Erasable PROM), a hard disk unit, etc.

Figure 6 shows in schematic representation a control

unit/system/means 600/140. The control unit/system/means

600/140 comprises a computing unit 601, which may be

constituted by essentially any suitable type of processor or microcomputer, for example a circuit for digital signal processing (Digital Signal Processor, DSP) , or a circuit having a predetermined specific function (Application Specific Integrated Circuit, ASIC) . The computing unit 601 is connected to a memory unit 602 arranged in the control unit/system/means 600/140, which memory unit provides the computing unit 601 with, for example, the stored program code and/or the stored data which the computing unit 601 requires to be able to perform computations. The computing unit 601 is also arranged to store partial or final results of computations in the memory unit 602.

In addition, the control unit/system/means 600/140 is provided with devices 611, 612, 613, 614 for receiving and transmitting input and output signals. These input and output signals may comprise waveforms, impulses, or other attributes which, by the devices 611, 613 for the reception of input signals, can be detected as information and can be converted into signals which can be processed by the computing unit 601. These signals are then made available to the computing unit 601. The devices 612, 614 for the transmission of output signals are arranged to convert signals received from the computing unit 601 in order to create output signals by, for example, modulating the signals, which can be transmitted to other parts of and/or systems within or outside the vehicle.

Each of the connections to the devices for receiving and transmitting input and output signals can be comprise one or more of a cable; a data bus, such as a CAN bus

(Controller Area Network bus), a MOST bus (Media Orientated Systems Transport bus), or some other bus configuration; or by a wireless connection. A person skilled in the art will appreciate that the above-stated computer can be constituted by the computing unit 601 and that the above- stated memory may be constituted by the memory unit 602.

Control systems in modern vehicles commonly comprise

communication bus systems including one or more

communication buses for linking a number of electronic control units (ECU's), or controllers, and various components located on the vehicle. Such a control system may comprise a large number of control units/means and the responsibility for a specific function can be divided amongst more than one control unit/means. Vehicles of the shown type thus often comprise significantly more control units/means than are shown in figures 1, 2 and 6, which is well known to the person skilled in the art within this technical field.

In the shown embodiment, the present invention is implemented in the control unit/system/means 600/140. The invention can also, however, be implemented wholly or partially in one or more other control units/systems/means already present in the vehicle, or in some control unit/system/means dedicated to the present invention. According to an aspect of the invention, a control unit 140 arranged for controlling a state of fuel provided from a fuel tank 121 to an engine 101 of a vehicle 100 is presented. As mentioned above, the fuel tank 121 stores fuel in gaseous 125 and liquid 126 state, and includes at least one gaseous fuel output conduit 122 and at least one liquid fuel output conduit 123.

The control unit 140 includes a first determination unit/means 141, arranged for determining 410 a maximal liquid torque T_{max iiq} being providable by the engine 101 if fuel in the liquid state 126 is provided to the engine 101, as described above.

The control unit 140 further includes a second determination unit/means 142, arranged for determining 420 a requested engine torque T_req, as described above.

The control unit 140 also includes a comparison unit/means

143, arranged for comparing 430 the requested engine torque T_req with the maximal liquid torque T_{max iiq}, as described above.

The control unit 140 also includes a controlling unit/means

144, arranged for controlling 440, if the requested engine torque T_req is higher than the maximal liquid torque T_{max iiq}; T_req > T_{max iiq}; fuel flows through one or more of the at least one gaseous fuel output conduit 122 and the at least one liquid fuel output conduit 123 such that only gaseous state fuel 125 is provided to the engine 101, as described above.

By activation of the above described first determination unit/means 141, the second determination unit/means 142, the comparison unit/means 143, and the controlling unit/means 144, the above described method is performed, which has the above- mentioned advantages. Here and in this document, units/means are often described as being arranged for performing steps of the method according to the invention. This also includes that the units/means are designed to and/or configured to perform these method steps.

The at least one control unit 140 is in figures 1 and 2 illustrated as including separately illustrated units/means 141, 142, 143, 144. Also, the control system/means 140 may include or be coupled to other control means/units, such as e.g. an engine control device/means, a clutch control unit, an exhaust treatment system control unit, and/or a gearbox control unit. These means/units/devices 141, 142, 143, 144,

140 may, however, be at least to some extent logically

separated but implemented in the same physical unit/device. These means/units/devices 141, 142, 143, 144, 140 may also be part of a single logic unit which is implemented in at least two different physical units/devices. These

means/units/devices 141, 142, 143, 144, 140 may also be at least to some extent logically separated and implemented in at least two different physical means/units/devices. Further, these means/units/devices 141, 142, 143, 144, 140 may be both logically and physically arranged together, i.e. be part of a single logic unit which is implemented in a single physical means/unit/device . These means/units/devices 141, 142, 143,

144, 140 may for example correspond to groups of instructions, which can be in the form of programming code, that are input into, and are utilized by at least one processor when the units/means are active and/or are utilized for performing its method step, respectively. It should be noted that the control unit/means 140 may be implemented at least partly within the vehicle 100 and/or at least partly outside of the vehicle 100, e.g. in a server, computer, processor or the like located separately from the vehicle 100. As mentioned above, the units 141, 142, 143, 144 described above correspond to the claimed means 141, 142, 143, 144 arranged for performing the embodiments of the present

invention, and the present invention as such.

The control unit 140 according to the present invention can be arranged for performing all of the above, in the claims, and in the herein described embodiments method steps. The control unit is hereby provided with the above described advantages for each respective embodiment.

A skilled person also realizes that the above described control unit may be modified according to the different embodiments of the method of the present invention. The present invention is also related to a vehicle 100, such as a truck, a bus or a car, including the herein described control unit 140.

The inventive method, and embodiments thereof, as described above, may at least in part be performed with/using/by at least one device. The inventive method, and embodiments thereof, as described above, may be performed at least in part with/using/by at least one device that is suitable and/or adapted for performing at least parts of the inventive method and/or embodiments thereof. A device that is suitable and/or adapted for performing at least parts of the inventive method and/or embodiments thereof may be one, or several, of a control unit, an electronic control unit (ECU) , an electronic circuit, a computer, a computing unit and/or a processing unit .

With reference to the above, the inventive method, and

embodiments thereof, as described above, may be referred to as an, at least in part, computerized method. The method being, at least in part, computerized meaning that it is performed at least in part with/using/by the at least one device that is suitable and/or adapted for performing at least parts of the inventive method and/or embodiments thereof.

With reference to the above, the inventive method, and

embodiments thereof, as described above, may be referred to as an, at least in part, automated method. The method being, at least in part, automated meaning that it is performed

with/using/by the at least one device that is suitable and/or adapted for performing at least parts of the inventive method and/or embodiments thereof.

The present invention is not limited to the above described embodiments. Instead, the present invention relates to, and encompasses all different embodiments being included within the scope of the independent claims.

Claims

1. A method (400) for controlling a state of fuel provided from a fuel tank (121) to an engine (101), said fuel tank (121) storing fuel in gaseous (125) and liquid (126) state, and including at least one gaseous fuel output conduit (122) and at least one liquid fuel output conduit (123);

characterized by

- determining (410) a maximal liquid torque T_max n_q being providable by said engine (101) if fuel in said liquid state (125) is provided to said engine (101);

- determining (420) a requested engine torque T_req;

- comparing (430) said requested engine torque T_req with said maximal liquid torque T_{max iiq}; and

- controlling (440), if said requested engine torque T_req is higher than said maximal liquid torque T_{max iiq}; T_req > T_{max iiq}; fuel flows through one or more of said at least one gaseous fuel output conduit (122) and said at least one liquid fuel output conduit (123) such that only said fuel in said gaseous state (125) is provided to said engine (101) .

2. The method (400) as claimed in claim 1, further including :

- controlling (445) fuel flows through one or more of said at least one gaseous fuel output conduit (122) and said at least one liquid fuel output conduit (123) such that said fuel provided to said engine (101) includes a majority of said fuel in said liquid state (126) if said requested engine torque T_req is lower than or equal to said maximal liquid torque T_{max iiq};

Treq <— T-*-max l q ·

3. The method (400) as claimed in any one of claims 1-2, wherein said fuel provided to said engine (101) includes one in the group of: - 100% fuel in said gaseous state (125);

- a mixture of said fuel in said gaseous state (125) and in said liquid state (126); and

- 100% fuel in said liquid state (126) .

4. The method (400) as claimed in any one of claims 1-3, further including:

- determining (450) a pressure P_gas of said fuel in said gaseous state (125);

- comparing (460) said pressure P_gas of said fuel in said gaseous state (125) with a first pressure threshold Pi_th/ said first pressure threshold Pi _th being related to a pressure

P_{gas min} needed for providing said fuel flows through one or more of said at least one gaseous fuel output conduit (122) and said at least one liquid fuel output conduit (123); and

- controlling (470), if said pressure P_gas is lower than said first pressure threshold Pi _th/ P_gas < Pi th ; fuel flows through one or more of said at least one gaseous fuel output conduit (122) and said at least one liquid fuel output conduit (123) such that only said fuel in said liquid state (125) is

provided to said engine (101) .

5. The method (400) as claimed in claim 4, wherein said first pressure threshold Pi _th is determined based at least on one or more in the group of:

- at least one feature of said fuel tank (121); and

- at least one feature of a fuel providing system (120) arranged for providing said fuel from said tank (121) to said engine ( 101 ) .

6. The method (400) as claimed in any one of claims 1-5, further including:

- determining (450) a pressure P_gas of said fuel in said gaseous state (125); - comparing (480) said pressure P_gas of said fuel in said gaseous state (125) with a second pressure threshold P₂ th, said second pressure threshold P₂ th being related to a maximally allowed pressure P_{gas max} for said tank (121); and

- controlling (490), if said pressure P_gas is higher than said second pressure threshold P_{2 t}h/ P_gas > P2 th/ fuel flows through one or more of said at least one gaseous fuel output conduit (122) and said at least one liquid fuel output conduit (123) such that only said fuel in said gaseous state (125) is provided to said engine (101) .

7. The method (400) as claimed in claim 6, wherein said second pressure threshold P_{2 t}h is determined based at least on one or more in the group of:

- a required volume of said fuel in said gaseous state (125) in said tank (121);

- a type of vehicle (100) including said fuel tank (121) and said engine (101);

- a usage of a vehicle (100) including said fuel tank (121) and said engine (101);

- at least one feature of said fuel tank (121);

- a level of fuel in said fuel tank (121) ;

- a relation between amounts of said fuel in said gaseous state (125) and said fuel in said liquid state (126) in said fuel tank (121) ;

- a temperature in said fuel tank (121);

- an ambient temperature outside said fuel tank (121); and

- at least one requirement related to a full tank parking time period for a vehicle (100) including said fuel tank (121) and said engine (101) .

8. The method (400) as claimed in any one of claims 1-7, wherein said maximal liquid torque T_max n_q is determined (410) adaptively when said engine (101) runs, and is based on a performance of said engine (101) .

9. The method (400) as claimed in claim 8, wherein information related to said controlling (440) of said fluid flows is stored and utilized together with said performance of said engine (101) resulting from said controlling (440) for the adaptive determination (410) of said maximal liquid torque

Tmax liq ·

10. The method (400) as claimed in claim 8, wherein a value of said maximal liquid torque T_{max iiq} is actively

adjusted, and said adaptive determination (410) of said maximal liquid torque T_{max iiq} is based on the active adjustment and on a performance of said engine (101) resulting from the active adjustment of said maximal liquid torque T_{max iiq}.

11. The method (400) as claimed in any one of claims 1-7, wherein said maximal liquid torque T_max n_q is determined (410) by running a test engine corresponding to said engine (101) on said fuel in said liquid state (126) in a test cell and measuring a resulting torque Ti_{iq t}est·

12. The method (400) as claimed in any one of claims 1-7, wherein said maximal liquid torque T_{max liq} is determined (410) by :

- determining a tendency for engine knocking when said fuel in said liquid state (126) is provided to said engine (101); and

- determining said maximal liquid torque T_max n_q based on said determined tendency for engine knocking.

13. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any one of claims 1-12.

14. A computer-readable medium comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any one of claims 1-12.

15. A control unit (140) arranged for controlling a state of fuel provided from a fuel tank (121) to an engine (101), said fuel tank (121) storing fuel in gaseous (125) and liquid (126) state, and including at least one gaseous fuel output conduit (122) and at least one liquid fuel output conduit

(123); characterized by

- first means (141) arranged for determining (410) a maximal liquid torque T_{max iiq} being providable by said engine (101) if fuel in said liquid state (126) is provided to said engine (101) ;

- second means (142) arranged for determining (420) a

requested engine torque T_req;

- means (143) arranged for comparing (430) said requested engine torque T_req with said maximal liquid torque T_{max iiq}; and

- means (144) arranged for controlling (440), if said

requested engine torque T_req is higher than said maximal liquid torque T_{max iiq}; T_req > T_{max iiq}; fuel flows through one or more of said at least one gaseous fuel output conduit (122) and said at least one liquid fuel output conduit (123) such that only said fuel in said gaseous state (125) is provided to said engine ( 101 ) .