SE544147C2

SE544147C2 - A method and a control arrangement for determining a conversion coefficent of a hydaulic system

Info

Publication number: SE544147C2
Application number: SE1951405A
Authority: SE
Inventors: Niclas Lindström; Vaheed Nezhadali
Original assignee: Scania Cv Ab
Priority date: 2019-12-06
Filing date: 2019-12-06
Publication date: 2022-01-11
Also published as: SE1951405A1; DE102020130538A1

Abstract

A method for determining a conversion coefficient (K) of a hydraulic system (132) including a pressurized part (142), wherein the method comprises: deactivating (201 ; 301) a fluid flow source device (140); when the fluid flow source device (140) is inactive, determining (202; 303), by a sensor (148), one or more pressure drops (Δp, Δp1, Δp2, Δp3, Δp4, Δp5, Δp6) associated with a fluid flow through a pressurized fluid conduit (144a, 144b) of the pressurized part (142) and a fluid flow restriction device (146); when the fluid flow source device (140) is inactive, determining (203; 304) a restriction return fluid flow (qreturn); determining (204; 305) the conversion coefficient (K) based on the determined restriction return fluid flow (qreturn) and the determined pressure drop (Δp, Δp1, Δp2, Δp3, Δp4, Δp5, Δp6); and using (205; 306) the conversion coefficient (K). A computer program and a computer-readable medium are also disclosed. Further, a control arrangement (150, 400) for determining the conversion coefficient (K) and a hydraulic system (132) including the control arrangement (150, 400) are disclosed. A vehicle (100) comprising the hydraulic system is disclosed.

Description

A METHOD AND A CONTROL ARRANGEMENT FOR DETERMINING ACONVERSION COEFFICENT OF A HYDAULIC SYSTEM Technical field Aspects of the present invention relate to a method for determining a Conversioncoefficient of a hydraulic system. Aspects of the present invention also relate to acomputer program comprising instructions which, when the program is executed by acomputer, cause the computer to carry out a method of the above-mentioned sort, orrelate to a computer-readable medium comprising instructions which, when theinstructions are executed by a computer, cause the computer to carry out a method ofthe above-mentioned sort. Further, aspects of the present invention relate to a controlarrangement for determining a conversion coefficient of a hydraulic system. Aspectsof the present invention also relate to a hydraulic system including a controlarrangement of the above-mentioned sort. Further, aspects of the present inventionrelate to a vehicle comprising a hydraulic system of the above-mentioned sort.

Background The properties or features of hydraulic lines, for example hoses and/or pipes, and/orof other parts of a hydraulic system having a pressurized part may for example bedependent on the temperature and pressure of the fluid in the pressurized part of thehydraulic system. Thus, when characterizing a hydraulic system having hydraulic lines,the temperature and/or the pressure of the fluid in the pressurized part should be considered.

Summary The inventors of the present invention have found that changes in temperature and/orpressure of the fluid in the pressurized part of the hydraulic system make it difficult tocharacterize the hydraulic system and/or determine a conversion coefficient of thehydraulic system, and the determination of the conversion coefficient may not be accurate enough.

An object of the invention is to provide a solution which mitigates or solves thedrawbacks and problems of conventional solutions.

The above and further objects are solved by the subject matter of the independentclaims. Further advantageous embodiments of the invention can be found in the dependent claims.

According to a first aspect of the invention, the above mentioned and other objects areachieved with a method for determining a conversion coefficient (K) of a hydraulicsystem. The hydraulic system comprises one or more f|uid tanks for storing a f|uid, one or more f|uid flow source devices hydraulically connected to the f|uid tank,wherein the f|uid flow source device is configured to provide a source f|uid flow (qsource)of the f|uid to a pressurized part of the hydraulic system, one or more pressurized f|uid conduits which is/are part of the pressurized partof the hydraulic system, one or more sensors for determining one or more pressures (p) of the f|uid inthe pressurized part of the hydraulic system, and one or more f|uid flow restriction devices hydraulically connected to the f|uidflow source device and the f|uid tank, wherein the f|uid flow restriction device isconfigured to provide a restriction return f|uid flow (qfeiufn) to the f|uid tank. The methodcomprises: 0 Deactivating the f|uid flow source device such that substantially no source f|uidflow (qsoufce) is provided from the f|uid flow source device to the pressurized partof the hydraulic system; 0 When the f|uid flow source device is inactive, determining, by usage of thesensor, one or more pressure drops (Ap, Api, Apa) associated with the f|uid flowthrough the pressurized f|uid conduit and the f|uid flow restriction device; 0 When the f|uid flow source device is inactive, determining the restriction returnf|uid flow (qreiurn); 0 Determining the conversion coefficient (K) of the hydraulic system based on thedetermined restriction return f|uid flow (qreiurn) and on the determined pressuredrop (Ap, Api, Aps); and 0 Using the conversion coefficient (K).

An advantage of the method according to the first aspect is that a useful and improvedconversion coefficient Kis attained in an efficient manner. By means of embodimentsof the method according to the first aspect, the conversion coefficient K may beexpressed as a function of the pressure p of the f|uid in the pressurized part of thehydraulic system. ln other words, conversion coefficients K which are pressure-dependent may be provided. Thus, a value of the conversion coefficient K can beassociated with a specific pressure in the pressurized part of the hydraulic system, forexample with the aid of a look-up table (LUT). By using the improved conversioncoefficient Kin view of the current pressure, the hydraulic system, more specificallythe pressurized part of the hydraulic system, can be more accurately characterized. Byusing the improved conversion coefficient K, the pressure of the f|uid in the pressurizedpart of the hydraulic system can be efficiently controlled or regulated, for example bycontrolling or regulating the f|uid flow source device by means of the improvedconversion coefficient K The method according to the first aspect can also enable theadaptation of the conversion coefficient Kindependent of the length of the pressurizedf|uid conduit, the material of the pressurized f|uid conduit and at any temperature. Byusing the improved conversion coefficient K, the hydraulic system can be monitored and/or diagnosed in an efficient manner.

According to an advantageous embodiment of the method according to the first aspect,the determined conversion coefficient (K) is a pressure drop (Ap) to f|uid flowconversion coefficient (K), which depends on a volume of the pressurized part of thehydraulic system. By means of this embodiment, the hydraulic system, morespecifically the pressurized part of the hydraulic system, can be more accuratelycharacterized.

According to a further advantageous embodiment of the method according to the firstaspect, the system stiffness of the pressurized part of the hydraulic system varies overtime and is dependent on at least one of the group of:A temperature (T) of the f|uid in the pressurized part of the hydraulic system;A pressure (p) of the f|uid in the pressurized part of the hydraulic system;A pressurized volume of the pressurized part of the hydraulic system; and At least one feature of the pressurized fluid conduit.

According to another advantageous embodiment of the method according to the firstaspect, the conversion coefficient (K) is determined by dividing the determinedpressure drop (Ap) by the determined restriction return fluid flow (qfeium). By means ofthis embodiment, the hydraulic system, more specifically the pressurized part of thehydraulic system, can be characterized in an efficient manner.

According to yet another advantageous embodiment of the method according to thefirst aspect, the method comprises: 0 When the fluid flow source device is inactive, determining the restriction return fluid flow (qfeiurn) based on a predetermined model or equation.

By means of this embodiment, the hydraulic system, more specifically the pressurizedpart of the hydraulic system, can be characterized in an efficient manner and thusefficiently monitored and controlled or regulated.

According to still another advantageous embodiment of the method according to thefirst aspect, the restriction return fluid flow (qreiurn) is determined based at least on thepressure (p) of the fluid in the pressurized part of the hydraulic system, the pressure(plank) of the fluid in the fluid tank and a predetermined constant (Gren/m). By means ofthis embodiment, the hydraulic system, more specifically the pressurized part of thehydraulic system, can be characterized in an efficient manner and thus efficientlymonitored and/or controlled or regulated.

According to an advantageous embodiment of the method according to the first aspect,the restriction return fluid flow (qreiurn) is determined based on the following model or equation: where Cfefum is a predetermined constant, p is the density of the fluid, psensof is thedetermined pressure (p) of the fluid in the pressurized part of the hydraulic system andpfank is the pressure of the fluid in the fluid tank. By means of this embodiment, a furtherimproved conversion coefficient Kis attained in an efficient manner. By means of thisembodiment, the hydraulic system, more specifically the pressurized part of thehydraulic system, can be characterized in an efficient manner and thus efficientlymonitored and/or controlled or regulated.

According to a further advantageous embodiment of the method according to the firstaspect, when the fluid flow source device is inactive, a pressure (p) of the fluid in thepressurized part of the hydraulic system is reduced from a first pressure value (p1) toa second pressure value (pa) during a first time period (At1) from a first point in time (t1)to a second point in time (t2), wherein the pressure drop (Ap1) corresponds to thechange of the pressure (p) of the fluid in the pressurized part of the hydraulic systemfrom the first pressure value (p1) to the second pressure value (pa), and wherein thefirst time period (Ati) has a length such that the pressure drop (Ap1) is approximatedas being linear. By means of this embodiment, a further improved conversioncoefficient K is attained in an efficient manner. By means of this embodiment, thehydraulic system, more specifically the pressurized part of the hydraulic system, canbe characterized in an efficient manner and thus efficiently monitored and/or controlled or regulated.

According to another advantageous embodiment of the method according to the firstaspect, the first time period (At1) has a length such that the restriction return fluid flow(qreiurn) during the first time period (At1) is approximated as the average restrictionreturn fluid flow based on the restriction return fluid flow (qrelurn) at the first point in time(t1) and the restriction return fluid flow (qreiurn) at the second point in time (t2). By meansof this embodiment, a further improved conversion coefficient K is attained in anefficient manner. By means of this embodiment, the hydraulic system, more specificallythe pressurized part of the hydraulic system, can be characterized in an efficientmanner and thus efficiently monitored and/or controlled or regulated.

According to yet another advantageous embodiment of the method according to thefirst aspect, when the fluid flow source device is inactive, a pressure (p) of the fluid inthe pressurized part of the hydraulic system is reduced from a third pressure value (ps)to a fourth pressure value (p4) during a second time period (Ats) from a third point intime (ts) to a fourth point in time (t4), wherein the pressure drop (Aps) corresponds tothe change of the pressure (p) of the fluid in the pressurized part of the hydraulicsystem from the third pressure value (ps) to the fourth pressure value (p4), and whereinthe second time period (Ats) has a length such that the pressure drop (Aps) isapproximated as being linear. By means of this embodiment, a further improvedconversion coefficient K is attained in an efficient manner. By means of thisembodiment, the hydraulic system, more specifically the pressurized part of thehydraulic system, can be characterized in an efficient manner and thus efficientlymonitored and/or controlled or regulated.

According to still another advantageous embodiment of the method according to thefirst aspect, the second time period (Ats) has a length such that the restriction returnfluid flow (qreiurn) during the second time period (Ats) is approximated as the averagerestriction return fluid flow based on the restriction return fluid flow (qfeiurn) at the thirdpoint in time (ts) and the restriction return fluid flow (qreiufn) at the fourth point in time(t4). By means of this embodiment, a further improved conversion coefficient K isattained in an efficient manner. By means of this embodiment, the hydraulic system,more specifically the pressurized part of the hydraulic system, can be characterized inan efficient manner and thus efficiently monitored and/or controlled or regulated.

The above-mentioned time periods (Ati, Ats) and points in time (t1, ta, ts, t4) areadvantageously part of the same test or the same test sequence. Thus, the above-mentioned pressure drops (Ap1(t), Aps(t)) and the determinations made at the above-mentioned points in time (t1, ta, ts, t4) may be part of the same test or the same test sequence.

According to an advantageous embodiment of the method according to the first aspect,a value of the conversion coefficient (K) is determined for each time period (Ati, Ats),whereby the conversion coefficient (K) is expressible as a function of the pressure (p) of the fluid in the pressurized part of the hydraulic system, wherein each value of theconversion coefficient (K) is included in a look-up table together with its associatedpressure value. By means of this embodiment and by using the look-up table, thepressure p of the fluid in the pressurized part of the hydraulic system can be efficientlymonitored and/or controlled or regulated. Further, by means of this embodiment andby using the look-up table, an improved fluid injector device diagnosis can be attained.

According to a further advantageous embodiment of the method according to the firstaspect, the method is triggered by at least one of the group of: An engine startup of a combustion engine associated with the hydraulicsystem; An engine shutdown of a combustion engine associated with the hydraulicsystem; An end of a predetermined time period; and An adaption of the conversion coefficient (K) without requests competing withthe method.

According to another advantageous embodiment of the method according to the firstaspect, the hydraulic system comprises one or more fluid injector devices included inthe pressurized part of the hydraulic system and hydraulically connected to the fluidflow source device by at least one of the one or more pressurized fluid conduits andhydraulically connected to the fluid flow restriction device, wherein the fluid injectordevice is configured to provide an injection fluid flow (qinjecior) out from the pressurizedpart of the hydraulic system upon activation, wherein the method comprises:0 Deactivating the fluid injector device such that substantially no injection fluidflow (dam-em) out from the pressurized part of the hydraulic system is provided;0 When the fluid flow source device and the fluid injector device are inactive,determining, by usage of the sensor, one or more pressure drops (Ap, Api, Apa)associated with the fluid flow through the pressurized fluid conduit, through thefluid injector device and through the fluid flow restriction device; and0 When the fluid flow source device and the fluid injector device are inactive, determining the restriction return fluid flow (qreium).

By means of this embodiment, a further improved Conversion coefficient Kis attainedin an efficient manner, which is useful for hydraulic systems having a f|uid injectordevice. By using the improved conversion coefficient K, a f|uid dosing accuracy or af|uid injection accuracy can be maintained, monitored and/or improved in an efficientmanner, for example by contro||ing or regulating the f|uid injector device by means ofthe further improved conversion coefficient K. Further, by means of this embodiment,a f|uid injector device can be efficiently diagnosed by means of the improvedconversion coefficient K. As mentioned above, the method according to the first aspectcan also enable the adaptation of the conversion coefficient K independent of thelength of the pressurized f|uid conduit, the material of the pressurized f|uid conduit andat any temperature. As a result of this, the robustness of the f|uid dosing accuracydiagnostics or f|uid injection accuracy diagnostics is increased and removes diagnostic dependency on the hydraulic system and environment variables.

According to a further advantageous embodiment of the method according to the firstaspect, the f|uid is one of the group of:0 An additive, for example urea, used in an exhaust gas after-treatment systemof the vehicle, wherein the f|uid injector device is an additive injector;0 A fuel, wherein the f|uid injector device is a fuel injector configured to inject fuelinto a combustion engine of the vehicle; and0 An oil, wherein the f|uid injector device is an oil injector configured to inject oilinto one or more components of the vehicle.By means of this embodiment, an efficient exhaust gas after-treatment can beperformed, an efficient fuel injection can be attained and/or an efficient oil injection can be provided.

According to still another advantageous embodiment of the method according to thefirst aspect, the method comprises: 0 Activating the f|uid injector device; and 0 lnjecting fluid in the form of the injection fluid flow (qinjecior) into an exhaust gasafter-treatment system for treating the exhaust gas from a combustion engineof a vehicle.

By means of this embodiment, the fluid injector device can be efficiently monitoredand/or diagnosed and a faulty fluid injector device with under-dosing problems can beidenüﬁed.

According to yet another advantageous embodiment of the method according to thefirst aspect, the using of the conversion coefficient (K) comprises: 0 Determining, when the fluid flow source device is inactive, the injection fluid flow(qanjecior) based on the determined conversion coefficient (K), the determinedpressure drop (Ap, Api, Apa) and the determined restriction return fluid flow(qfewfn) By means of this embodiment, the fluid injector device can be efficiently monitoredand/or diagnosed and a faulty fluid injector device with under-dosing problems can be identified in an efficient manner.

According to an advantageous embodiment of the method according to the first aspect,the using of the conversion coefficient (K) comprises: 0 Determining the injection fluid flow (qinjecior) based on the determined conversioncoefficient (K), the determined pressure drop (Ap, Api, Apa), a modelled valueof the source fluid flow (qsource) and the determined restriction return fluid flow(qfewfn) By means of this embodiment, the fluid injector device can be efficiently monitoredand/or diagnosed and a faulty fluid injector device with under-dosing problems can be identified in an efficient manner.

According to a further advantageous embodiment of the method according to the firstaspect, the using of the conversion coefficient (K) comprises at least one of:0 Determining a diagnosis of the fluid injector device;0 Determining at least one blockage of the fluid in the pressurized part of thehydraulic system; and 0 Calibrating at least one parameter associated with a regulation of the fluidinjector device.

By means of this embodiment, a faulty injector device can be efficiently identified, a biockage of the fluid can be efficiently identified and/or a calibration of a parameter associated with the regulation or control of the fluid injector device can be efficiently performed.

According to another advantageous embodiment of the method according to the firstaspect, the sensor comprises a pressure sensor for measuring the pressure (p) of thefluid in the pressurized part of the hydraulic system, wherein the step of determiningthe pressure drop (Ap, Api, Apa) involves the usage of the pressure sensor.

According to a second aspect of the invention, the above mentioned and other objectsare achieved with a computer program comprising instructions which, when theprogram is executed by a computer, cause the computer to carry out the methodaccording to any one of the embodiments disclosed above or below. The advantagesof the computer program according to the second aspect correspond to the above- orbelow-mentioned advantages of the method according to the first aspect and its embodiments.

According to a third aspect of the invention, the above mentioned and other objectsare achieved with a computer-readable medium comprising instructions which, whenthe instructions are executed by a computer, cause the computer to carry out themethod according to any one of embodiments disclosed above or below. Theadvantages of the computer-readable medium according to the third aspectcorrespond to the above- or below-mentioned advantages of the method according tothe first aspect and its embodiments.

According to an aspect of the present invention, the above-mentioned computerprogram and computer-readable medium are configured to implement the method and its embodiments described herein.

According to a fourth aspect of the invention, the above mentioned and other objectsare achieved with a control arrangement for determining a conversion coefficient (K)of a hydraulic system, wherein the hydraulic system comprises one or more fluid tanks for storing a fluid, one or more fluid flow source devices hydraulically connected to the fluid tank,wherein the fluid flow source device is configured to provide a source fluid flow (qsource)of the fluid to a pressurized part of the hydraulic system, one or more pressurized fluid conduits which is/are part of the pressurized partof the hydraulic system, one or more sensors for determining one or more pressures (p) of the fluid inthe pressurized part of the hydraulic system, and one or more fluid flow restriction devices hydraulically connected to the fluidflow source device and the fluid tank, wherein the fluid flow restriction device isconfigured to provide a restriction return fluid flow (qfeiufn) to the fluid tank, wherein thecontrol arrangement is configured to: deactivate the fluid flow source device such that substantially no source fluidflow (qsource) is provided from the fluid flow source device to the pressurized part of thehydraulic system, when the fluid flow source device is inactive, determine, by usage of thesensor, one or more pressure drops (Ap, Api, Apa) associated with the fluid flowthrough the pressurized fluid conduit and the fluid flow restriction device, when the fluid flow source device is inactive, determine the restriction returnfluid flow (qreiurn), determine the conversion coefficient (K) of the hydraulic system based on thedetermined restriction return fluid flow (qreiufn) and on the determined pressure drop(Ap, Api, Apa), and use the conversion coefficient (K).The advantages of the control arrangement according to the fourth aspect correspondto the above- or below-mentioned advantages of the method according to the first aspect and its embodiments.

According to a fifth aspect of the invention, the above mentioned and other objects areachieved with a hydraulic system comprising 12 one or more fluid tanks for storing a fluid, one or more fluid flow source devices hydraulically connected to the fluid tank,the fluid flow source device being configured to provide a source fluid flow (qsource) ofthe fluid to a pressurized part of the hydraulic system, one or more pressurized fluid conduits which is/are part of the pressurized partof the hydraulic system, one or more sensors for determining one or more pressures (p) of the fluid inthe pressurized part of the hydraulic system, one or more fluid flow restriction devices hydraulically connected to the fluidflow source device and the fluid tank, the fluid flow restriction device being configuredto provide a restriction return fluid flow (qreiufn) to the fluid tank, and the control arrangement according to any one of the embodiments disclosedbelow or above. The advantages of the hydraulic system according to the fifth aspectcorrespond to the above- or below-mentioned advantages of the method according tothe first aspect and its embodiments.

According to an advantageous embodiment of the hydraulic system according to thefifth aspect, the fluid flow restriction device is hydraulically connected to one or more fluid injector devices by at least one of the one or more pressurized fluid conduits. lt will be appreciated that all the embodiments described for the method aspects of theinvention are applicable also to at least one of the control arrangement aspects andthe hydraulic system aspects of the invention. Thus, all embodiments described for themethod aspects of the invention may be performed by the control arrangement, whichmay also be a control device, i.e. a device, or by the hydraulic system. As mentionedabove, the control arrangement and its embodiments and the hydraulic system and itsembodiments have advantages corresponding to the advantages mentioned above forthe method and its embodiments.

According to a sixth aspect of the invention, the above mentioned and other objectsare achieved with a vehicle comprising the hydraulic system according to any one ofthe above- or below-mentioned embodiments. The vehicle may comprise a combustion 13 engine and an exhaust gas after-treatment system for treating the exhaust gas fromthe combustion engine.

According to an advantageous embodiment of the vehicle according to the sixthaspect, the fluid is one of the group of: An additive, for example urea, used in an exhaust gas after-treatment systemof the vehicle, wherein the fluid injector device is an additive injector; A fuel, wherein the fluid injector device is a fuel injector configured to inject fuelinto a combustion engine of the vehicle; and An oil, wherein the fluid injector device is an oil injector configured to inject oilinto one or more components of the vehicle.By means of this embodiment, an efficient exhaust gas after-treatment can beperformed, an efficient fuel injection can be attained and/or an efficient oil injection canbe provided.

Brief Description of the DrawingsEmbodiments of the invention will now be illustrated, for exemplary purposes, in moredetail by way of embodiments and with reference to the enclosed drawings, where similar references are used for similar parts, in which: Figure 1 is a schematic view illustrating a vehicle according to the sixth aspect ofthe invention, in which embodiments of the present invention may beimplemented, and a hydraulic system according to the fifth aspect of theinvenﬁon; Figure 2 is a flow chart illustrating aspects of a first embodiment of the methodaccording to the first aspect of the invention; Figure 3 is a flow chart illustrating further aspects of a second embodiment of themethod according to the first aspect of the invention; Figure 4 is a schematic diagram illustrating aspects of the embodiments of themethod according to the first aspect of the invention; Figure 5 is a schematic view illustrating an embodiment of the hydraulic system according to the fifth aspect of the invention in more detail; and 14 Figure 6 is a schematic view illustrating an embodiment of the control arrangementaccording to the fourth aspect of the invention, in which a methodaccording to any one of the herein described embodiments may beimplemented.

Detailed Description With reference to figure 1 , a vehicle 100 is schematically shown. The vehicle comprisesa powertrain 102 which comprises a combustion engine 104, for example an internalcombustion engine or another combustion engine, which in a conventional manner, viaa first output shaft 106 and usually via a flywheel, is connected to a gearbox 108 via aclutch 110. However, instead of a powertrain comprising a combustion engine, or inaddition thereto, the vehicle may include one or more electrical machines and may thus for example be an electric vehicle or a so-called hybrid vehicle.

The combustion engine 104 is controlled by the engine”s control system via a controldevice 112. Likewise, the clutch 110 and the gearbox 108 may be controlled by theengine”s control system, with the help of one or more control devices (not shown). Thecontrol device 112 and/or another control device may thus be configured to control thecombustion engine 104, the clutch 110, the gearbox 108, and/or any otherunits/devices/entities of the vehicle 100. However, in figure 1, only theunits/devices/entities of the vehicle 100 useful for understanding the embodiments of the present invention are illustrated.

Naturally, the powertrain 102 of the vehicle 100 may be of a different type, such as atype with a conventional automatic gearbox, a type with a hybrid driveline etc. Asmentioned above, the powertrain 102 may include one or more electrical machines,implementing a so-called hybrid drive. The vehicle 100 comprises four wheels 114,116, 118, 120. The electrical machine may be arranged essentially anywhere, as longas torque is provided to one or more of the wheels 114, 116, 118, 120, for exampleadjacent to one or more of the wheels 114, 116, 118, 120, as is understood by a skilled person. lO The vehicle 100 may comprise a propeller shaft 122 from the gearbox 108 which drivestwo of the wheels 114, 116 via a central gear 124, for example a conventionaldifferential, and two drive shafts 126, 128 of the vehicle 100, the two drive shafts 126,128 being connected to the central gear 124. The vehicle 100 may comprise a fueltank 129, and the combustion engine 104 may be provided with fuel from the fuel tank129 coupled to the combustion engine 104.

The vehicle 100 may comprise an exhaust gas after-treatment system 130, which alsomay be called an exhaust gas purification system, for treatment/purification of theexhaust gas/emissions resulting from the combustion in the combustion chamber ofthe combustion engine 104. The exhaust gas after-treatment system 130 may becontrolled by an exhaust gas after-treatment control device 172, which maycommunicate with the control device 112. ln general, the combustion engine 104 comprises cylinders.

Further, the vehicle comprises a hydraulic system 132. ln the embodiment shown infigures 1 and 5, the hydraulic system 132 comprises one or more fluid injector devices134, 136, more specifically a first fluid injector device 134 and a second fluid injectordevice 136. However, instead of two fluid injector devices 134, 136, the hydraulicsystem 132 may comprise only one fluid injector device 134, 136 or more than two fluidinjector devices 134, 136. Further, in alternative embodiments, both of the first andsecond fluid injector devices 134, 136 may be excluded from the hydraulic system 132.ln alternative embodiments, the first and second fluid injector devices 134, 136 maybe replaced by a fuel injector for injecting fuel into the combustion engine 104 of thevehicle 100 or an oil injector configured to inject oil into one or more components of the vehicle 100 or any other suitable injector.

The shown hydraulic system 132 is configured to inject fluid in the form of an additive,for example urea, into the exhaust gas after-treatment system 130 of the vehicle 100to be used in the exhaust gas after-treatment system 130 for treating the exhaust gasfrom the combustion engine 104. The additive is injected into the exhaust gas after-treatment system 130 of the vehicle 100 by means of the fluid injector devices 134,136. ln alternative embodiments, the fluid is a fuel, wherein the fluid injector device is 16 a fuel injector configured to inject fuel into the combustion engine 104 of the vehicle100. ln other alternative embodiments, the fluid is an oil, wherein the fluid injectordevice is an oil injector configured to inject oil into one or more components of thevehicle 100. How and why urea is used is explained in more detail in connection withfigure 5. Although each of the first and second fluid injector devices 134, 136 of theembodiment shown in figures 1 and 5 is an additive injector 134, 136, the hydraulicsystem could be any other hydraulic system according to alternative embodiments,both in a vehicle or elsewhere, for example without the fluid injector devices, where itis relevant or important to thoroughly characterize the hydraulic system, especially a pressurized part of the hydraulic system.

With reference to figures 1 and 5, the hydraulic system 132 includes one or more fluidtanks 138 (or containers or vessels) for storing a fluid, for example an additive, such as urea. ln the embodiment shown in figures 1 and 5, one fluid tank 138 is provided.

With reference to figures 1 and 5, the hydraulic system 132 includes one or more fluidflow source devices 140 hydraulically connected to the fluid tank 138. “Hydraulicallyconnected” or “hydraulically connecting” in the context of the present disclosure meansthat there is a hydraulic connection between the two entities, for example between thefluid flow source device 140 and the fluid tank 138, or in alternative words, that the twoentities, for example the fluid flow source device 140 and the fluid tank 138, are inhydraulic or fluid communication with one another. Thus, a fluid can move between thetwo entities, for example between the fluid flow source device 140 and the fluid tank138. Two entities which are hydraulically connected can be directly or indirectlyhydraulically connected, i.e. there may be additional elements in the fluid or flow pathbetween the two entities. ln the embodiment shown in figures 1 and 5, one fluid flowsource device 140 is provided. The fluid flow source device 140 may be a pump orpump device having a structure known to the skilled person. The fluid flow sourcedevice 140 is configured to provide a source fluid flow qsource of the fluid to a pressurizedpart 142 of the hydraulic system 132. The unit of the source fluid flow qsource may bekg/s. The pressurized part 142 of the hydraulic system 132 is explained in more detail hereinbelow. 17 With reference to figures 1 and 5, the hydraulic system 132 includes one or morepressurized fluid conduits 144a,144b being part of the pressurized part 142 of thehydraulic system 132. The pressurized fluid conduit 144a, 144b, which also may becalled fluid line or hydraulic line, may be a pipe, a tube or a flexible hose orcombinations thereof. Thus, the pressurized fluid conduit 144a, 144b may be rigidand/or flexible/elastic.

With reference to figures 1 and 5, the hydraulic system 132 includes one or more fluidflow restriction devices 146 hydraulically connected to the fluid flow source device 140and the fluid tank 138. ln the embodiment shown in figures 1 and 5, one fluid flowrestriction device 146 is provided. The fluid flow restriction device 146 is configured toprovide a restriction return fluid flow qreiurn to the fluid tank 138. The unit of therestriction return fluid flow qfeiurn may also be kg/s. The fluid flow restriction device 146may comprise an orifice, a slot, an aperture or an opening or a more complex devicefor providing a restriction return fluid flow qfeiurn to the fluid tank 138. The fluid flowrestriction device 146 may be hydraulically connected to one or more fluid injectordevices 134, 136 by at least one 144a of the one or more pressurized fluid conduits144a, 144b. Alternatively, the fluid flow restriction device may located in one of the firstand second fluid injector devices 134, 136, more specifically in the second fluid injectordevice 136 which is downstream of the first fluid injector device 134.

With reference to figures 1 and 5, the pressurized part 142 of the hydraulic system 132extends from the fluid flow source device 140 to the fluid flow restriction device 146.Thus, the pressurized part 142 of the hydraulic system 132 includes the first fluidinjector device 134, the second fluid injector device 136 and the pressurized fluidconduit 144a, 144b or conduits 144a, 144b. ln general, the entire fluid flow sourcedevice 140 is not included in the pressurized part 142 of the hydraulic system 132.However, according to some aspects, a part of the fluid flow source device 140 maybe part of the pressurized part 142 of the hydraulic system 132 when the fluid flow source device 140 is active, for example when the fluid flow source device 140 ispumping. lO 18 The system stiffness of the pressurized part 142 of the hydraulic system 132 variesover time and is dependent on at least one of the group of: a temperature Tof the fluidin the pressurized part 142 of the hydraulic system 132; a pressure p of the fluid in thepressurized part 142 of the hydraulic system 132; a pressurized volume of thepressurized part 142 of the hydraulic system 132; at least one feature of thepressurized fluid conduit 144a, 144b.

As mentioned above, each of the first fluid injector device 134 and the second fluidinjector device 136 is included in the pressurized part 142 of the hydraulic system 132.ln the shown embodiment, each of the first and second fluid injector devices 134, 136is hydraulically connected to the fluid flow source device 140 by at least one 144b ofthe one or more pressurized fluid conduits 144a, 144b. Each of the first and secondfluid injector devices 134, 136 is hydraulically connected to the fluid flow restrictiondevice 146, for example via one 144a of the one or more pressurized fluid conduits144a, 144b. Each of the first and second fluid injector devices 134, 136 is configuredto provide an injection fluid flow qinjecior out from the pressurized part 142 of thehydraulic system 132 upon activation. Alternatively, the first fluid injector device 134and the second fluid injector device 136 may together provide an injection fluid flowqanjecior out from the pressurized part 142 of the hydraulic system 132 upon activation.The unit of the fluid flow injection fluid flow qinjecior may be kg/s.

With reference to figure 1, in the shown embodiment, in view of the direction of theexhaust gas flow through the exhaust gas after-treatment system 130, the first fluidinjector device 134 is located downstream of the second fluid injector device 136.However, in alternative embodiments, the first fluid injector device 134 may instead belocated upstream of the second fluid injector device 136. Thus, the first and secondfluid injector devices 134, 136 may change locations in exhaust gas after-treatmentsystem 130 with one another.

With reference to figures 1 and 5, the hydraulic system 132 includes one or moresensors 148 for determining one or more pressures p of the fluid in the pressurizedpart 142 of the hydraulic system 132. The sensor 148 may determine the pressure p based on various parameters and may be a so-called virtual pressure sensor. 19 However, according to an advantageous embodiment, the sensor 148 comprises apressure sensor 148 for measuring the pressure p of the fluid in the pressurized part142 of the hydraulic system 132. The pressure sensor 148 may for example measurethe pressure in the pressurized part 142 of the hydraulic system 132 close to the fluidflow restriction device 146. Thus, the pressure sensor 148 may be located in thepressurized part 142 of the hydraulic system 132 close to the fluid flow restrictiondevice 146 and measure the pressure close to the fluid flow restriction device 146.With reference to figure 1, as an alternative or addition thereto, a second sensor 149for determining and/or measuring the pressure p of the fluid in the pressurized part 142of the hydraulic system 132 may be provided. The second sensor 149 may be a secondpressure sensor located in the pressurized part 142 of the hydraulic system 132 at asecond location different from the location of the pressure sensor 148 and thus measure the pressure at said second location.

Further, with reference to figures 1, 5 and 6, the hydraulic system 132 includes acontrol arrangement 150, 400 for determining a conversion coefficient Kof a hydraulicsystem 132. Aspects of the control arrangement 150, 400 are disclosed in more detail hereinbelow in connection with figures 5 and 6.

With reference to figure 2, aspects of a first embodiment of the method for determininga conversion coefficient Kof a hydraulic system 132 according to the first aspect areillustrated. When the hydraulic system 132 does not include any fluid injector device134, 136, the method may include the following steps: 0 Deactivating 201 the fluid flow source device 140 such that substantially nosource fluid flow qsource is provided from the fluid flow source device 140 to thepressurized part 142 of the hydraulic system 132; 0 When the fluid flow source device 140 is inactive, determining 202, by usage ofthe sensor 148, one or more pressure drops Ap, Api, Apa, or pressurereductions, associated with the fluid flow through the pressurized fluid conduit144a, 144b and through the fluid flow restriction device 146; When the fluid flow source device 140 is inactive, determining 203 the restrictionreturn fluid flow qfeiurn provided by the fluid flow restriction devices 146 to thefluid tank 138; Determining 204 the conversion coefficient Kof the hydraulic system 132 basedon the determined restriction return fluid flow qfeiurn and on the determinedpressure drop Ap, Ap1, Apa; and Using 205 the conversion coefficient K.

The step of determining 202 the pressure drop Ap, Ap1, Ape, may involve the usage of a pressure sensor 148. “Substantially no source fluid flow qsource” in the context of the present disclosure means that there is no relevant fluid flow leaving the fluid flow source device 140 and entering the pressurized part 142 of the hydraulic system 132.

However, an irrelevant amount of fluid may leave the fluid flow source device 140 and enter the pressurized part 142 of the hydraulic system 132.

With reference to figure 3, aspects of a second embodiment of the method for determining a conversion coefficient Kof a hydraulic system 132 according to the first aspect are illustrated. When the hydraulic system 132 include one or more fluid injector devices 134, 136, the method may include the following steps: Deactivating 301 the fluid flow source device 140 such that substantially nosource fluid flow qsource is provided from the fluid flow source device 140 to thepressurized part 142 of the hydraulic system 132; Deactivating 302 the fluid injector device 134, 136 such that substantially noinjection fluid flow qinjecior out from the pressurized part 142 of the hydraulicsystem 132 is provided; When the fluid flow source device 140 and the fluid injector device 134, 136 areinactive, determining 303, by usage of the sensor 148, one or more pressuredrops Ap, Ap1, Ape, associated with the fluid flow through the pressurized fluidconduit 144a, 144b, through the fluid injector device 134, 136 and through thefluid flow restriction device 146; 21 0 When the fluid flow source device 140 and the fluid injector device 134, 136 areinactive, determining 304 the restriction return fluid flow qfeiurn provided by thefluid flow restriction devices 146 to the fluid tank 138; 0 Determining 305 the conversion coefficient Kof the hydraulic system 132 basedon the determined restriction return fluid flow qfeiurn and on the determinedpressure drop Ap, Ap1, Apa; 0 Using 306 the conversion coefficient K; 0 Activating 307 the fluid injector device 134, 136; 0 lnjecting fluid 308 in the form of the injection fluid flow qinjecior into the exhaustgas after-treatment system 130 for treating the exhaust gas from thecombustion engine 104 of the vehicle 100; and 0 l\/lonitoring 309 the injection performance of the fluid injector device 134, 136,whereby a diagnosis of the fluid injector device 134, 136 can be determined.

With reference to Figure 3, the step of tuning 310 pressure control/regulationparameters can be performed instead of performing steps 307, 308 and 309, forexample in order to calibrate pressure-related regulation or control parameters. Thestep of determining 303 the pressure drop Ap, Ap1, Apa may involve the usage of apressure sensor 148. “Substantially no injection fluid flow qinjecior” in the context of thepresent disclosure means that there is no relevant fluid flow leaving the pressurizedpart 142 of the hydraulic system 132 via the fluid injector device 134, 136. However,an irrelevant amount of fluid may be discharged from the fluid injector device 134, 136and thus leave the the pressurized part 142 of the hydraulic system 132. The using ofthe conversion coefficient Kmay comprise the step of determining 309, when the fluidflow source device 140 is inactive, the injection fluid flow qinjecior based on thedetermined conversion coefficient K, the determined pressure drop Ap, Ap1, Apa andthe determined restriction return fluid flow qreiufn. ln an alternative embodiment, theusing of the conversion coefficient Kmay comprise the step of determining the injectionfluid flow qinjecior based on the determined conversion coefficient K, the determinedpressure drop Ap, Ap1, Apa, a modelled value of the source fluid flow qsource and the determined restriction return fluid flow qreiurn. 22 ln the shown embodiments, the determined Conversion coefficient Kis a pressure dropAp to fluid flow conversion coefficient K, which depends on a volume of the pressurizedpart 142 of the hydraulic system 132. The coefficient Kmay also be called a dischargecoefficient or stiffness coefficient which is dependent on the structure of the hydraulicsystem 132, for example the properties/features of the fluid flow restriction device 146,such as the size of the orifice of the fluid flow restriction device 146.

When the fluid flow source device 140 is inactive, the step of determining 203, 304 therestriction return fluid flow qfeinrn may be based on a predetermined model or equation.ln an alternative embodiment, the return fluid flow qfeinrn may instead be measured bymeans of a fluid flow sensor. When the restriction return fluid flow qfeinrn is determinedbased on a predetermined model or equation, the restriction return fluid flow (qrennn)may be determined based at least on the pressure p of the fluid in the pressurized part142 of the hydraulic system 132, the pressure plank of the fluid in the fluid tank 138 anda predetermined constant Cfefnfn. The predetermined constant Crennn may be based onknowledge of the restriction return fluid flow of the fluid flow restriction device 146 at aspecific pressure. As an alternative or in addition thereto, the predetermined constantCrennn may be based on the structure of the fluid flow restriction device 146, for examplethe size of the orifice of the fluid flow restriction device 146. More specifically, therestriction return fluid flow qfeinrn may be determined based on the following model or equation: qTEÉUTTI : TEÜLLTTI (PSETISOT _ ptaïlk) where Cfennn is the above-mentioned predetermined constant, p is the density of thefluid, psensnf is the determined pressure p of the fluid in the pressurized part 142 of thehydraulic system 132 and plank is the pressure of the fluid in the fluid tank 138. Thepressure plank may be determined by a sensor, for example measured by a pressuresensor, or may be given as a specific predetermined value for the fluid tank 138 used. ln general, according to aspects of the present invention, the conversion coefficient Kis determined by dividing the determined pressure drop Ap by the determined 23 restriction return fluid flow qreiurn, wherein the restriction return fluid flow qreiurn may bedetermined by means of the above-mentioned model or equation [1]. This is disclosed in more detail hereinafter. lf the hydraulic system 132 includes only one fluid injector device 134 (with referenceto figure 1, the second fluid injector device 136 may be inactive or absent), duringnormal operation, the hydraulic system 132 can be expressed by following equation ormodel: ddi; I Külsource _ qinjector _ qreturn) [2] The term dp/dt is the pressure change and corresponds to Ap(t). The fluid flow sourcedevice 140 provides the source fluid flow qsource to the pressurized part 142 of thehydraulic system 132, the fluid injector device 134 provides the injection fluid flowqmjecior out from the pressurized part 142 of the hydraulic system 132, and the fluid flowrestriction device 146 provides the restriction return fluid flow qfeiurn to the fluid tank 138out from the out from the pressurized part 142 of the hydraulic system 132. lf thesecond fluid injector device 136 is present, there would be a second injection fluid flowqanjecior in equation [2]. ln equation [2], the source fluid flow qsource is positive because itis fed to the pressurized part 142 of the hydraulic system 132, while the other two fluidflows, namely the injection fluid flow qinjecior and the restriction return fluid flow qreiurn,are negative because they are leaving or discharged from the pressurized part 142 ofthe hydraulic system 132. ln other words, the source fluid flow qsource is the input of thepressurized part 142 and the injection fluid flow qinjecior and the restriction return fluidflow qfeiurn are the output of the pressurized part 142 of the hydraulic system 132. lf the fluid flow source device 140 and the fluid injector device 134, or fluid injectordevices 134, 136, are deactivated and thus inactive, the source fluid flow qsource andthe injection fluid flow qinjecior are zero, and the equation [2] can be formulated as follows: 24 The equation [3] can also be expressed as: K = - Ap(t)/qrewrn_ The restriction return fluidflow qfeiurn may be given by the above-mentioned equation [1], or, as mentioned above,may instead be measured by means of a fluid flow sensor.

With reference to figure 4, a diagram is shown which illustrates a test procedure forestimating or determining the conversion coefficient K. The diagram shows thepressure p of the fluid in the pressurized part 142 of the hydraulic system 132 atdifferent points in time. A value of the conversion coefficient Kmay be determined foreach time period Ati (between p1 and pa), Atz (between p2 and ps), Ate, (between ps andp4), At4 (between p4 and ps), Ats (between ps and pe) and Ate (between pe and pv) of ap|ura|ity of time periods Ati, Atz Ats, At4, Ats, Ate. With reference to figure 4, in theshown embodiment, a value of the conversion coefficient Kis determined for each timeperiod Ati, Atz Ats, At4, Ats, Ate of six time periods Ati, Atz Ats, At4, Ats, Ate in total.

First, at a point in time illustrated by the dotted vertical line in the diagram of figure 4,the fluid flow source device 140 and the fluid injector device 134, 136 (if included) aredeactivated, whereupon the pressure p of the fluid in the pressurized part 142 of thehydraulic system 132 is reduced or drops while the restriction return fluid flow qreiurnpasses the fluid flow restriction device 146. ln the embodiment shown in the diagramof figure 4, the pressure drops around 3400 hPa (from 7800 hPa to 4400 hPa) betweent1 = 54.4 seconds and tv = 56.7 seconds. Thus, when the fluid flow source device 140and the fluid injector device 134, 136 are inactive, the pressure p of the fluid in thepressurized part 142 of the hydraulic system 132 is reduced from a first pressure valuep1 to a second pressure value p2 during a first time period Ati from a first point in timet1 to a second point in time t2. The pressure drop Api corresponds to the change of thepressure p of the fluid in the pressurized part 142 of the hydraulic system 132 from thefirst pressure value p1 to the second pressure value p2. The first time period Ati has alength such that the pressure drop Api is approximated as being linear. Further, thefirst time period Ati has a length such that the restriction return fluid flow qreiurn duringthe first time period Ati is approximated as the average restriction return fluid flowbased on the restriction return fluid flow qreiurn at the first point in time t1 and therestriction return fluid flow qreiurn at the second point in time t2. The average restriction return fluid flow, or the mean of the restriction return fluid flow, during the first timeperiod At1 can thus be expressed as (qreiurnjn qreiurn_i2)/2_ This results in the following general equation: pt+At _ pt I _K (qreturnj + qreturn_t+At) At 2 where pi corresponds to p1 and pum corresponds to p2 for the above-mentioned specificcase for At1. Consequently, based on equation [4], the conversion coefficient Kcan be expressed by the general equation: = _ 2(Pt+At- Pr) Aﬂqreturnj+qreturn_t+AT) l\/lore specifically, with reference to the method illustrated in figure 4, a first pressure p1of the fluid in the pressurized part 142 is determined, for example measured by thepressure sensor 148, at a first point in time t1. The first point in time t1 may be 54.4seconds and the first pressure p1 may be 7800 hPa when viewing the embodiment inFigure 4. A second pressure p2 of the fluid in the pressurized part 142 is determined ata second point in time t2, for example measured by the pressure sensor 148. Thesecond point in time t2 may be 54.7 seconds and the second pressure p2 may be 7050hPa when viewing the embodiment in Figure 4. For each point in time t1, ta, therestriction return fluid flow qfeiurn is determined by means of the above-mentionedequation [1], or, as mentioned above, may instead be measured by means of a fluidflow sensor. Based on the equation [5], in this specific case for At1, the conversion coefficient K can be expressed as: I _ 2(p2_p1) (152 _ tlxqreturnjl +qreturn_t2) The conversion coefficient Kin equation [6] is thus related to the first time period At1(t2-t1), the pressure drop Ap1(t) = p2-p1 and each of the pressures p1 and p2. lO 26 A corresponding procedure can be repeated for the second time period Ats from thesecond point in time ts to a third point in time ts, i.e. a third pressure ps of the f|uid in thepressurized part 142 is determined at a third point in time ts, for example measured bythe pressure sensor 148_ The second pressure ps at the second point in time ts isreused. For the third point in time ts, the restriction return f|uid flow qrsiurn is determinedby means of the above-mentioned equation [1], or, as mentioned above, may insteadbe measured by means of a f|uid flow sensor. The value of the restriction return f|uidflow qrsiurn for ts, which already has been determined, is reused. Based on the equation[5], in this specific case for Ats, the conversion coefficient K can be expressed as: = _ 2 (P3 _p2) (153- tzxqreturnjz +qreturn_t3) The conversion coefficient Kin equation [7] is thus related to the second time periodAts (ts-ts), the pressure drop Ap2(t) = ps-ps and each of the pressures ps and ps.

The conversion coefficient Kcan be determined for the subsequent pressure drops infigure 4 in a corresponding manner, namely for the pressure drops Aps = p4-ps, Ap4 =ps-p4, Aps = pe-ps and Apa = p7-pe and the time periOdS A13 (t4-ts), A14 (t5-t4), Ats (te-ts)and Ats(t1-ts). Based on the conversion coefficients K (K1, K2, Ks, K4, Ks, Ks) for all thetime periods Ati, Atz, Ats, At4, Ats, Ats and the pressure drops Api, Apa, Aps, Ap4, Aps,Aps, the conversion coefficient Kis expressible as a function of the pressure p of thef|uid in the pressurized part 142 of the hydraulic system 132. Each value of theconversion coefficient K(p) may be included in a look-up table, LUT, together with itsassociated pressure value or values. For example, in the LUT, the conversioncoefficient K1 for Ati can be associated with the pressure p1; the conversion coefficientK2 for Ats can be associated with the pressure ps; the conversion coefficient Ks for Atscan be associated with the pressure ps, the conversion coefficient K4 for At4 can beassociated with the pressure p4; the conversion coefficient Ks for Ats can be associatedwith the pressure ps, and the conversion coefficient Ks for Ats can be associated withthe pressure ps. This is advantageous, since the stiffness of the pressurized part 142of the hydraulic system 132 may vary in dependence of the current pressure of the f|uid in the pressurized part 142 of the hydraulic system 132. The look-up table, LUT, 27 may, inter alia, be used when performing a fluid injector device diagnosis, or whenregulating the pressure p of the fluid in the pressurized part 142 of the hydraulic system132. ln view of the above, the following is also valid: when the fluid flow source device 140and the fluid injector device 134, 136, if included in the hydraulic system 132, areinactive, a pressure p of the fluid in the pressurized part 142 of the hydraulic system132 is reduced from a third pressure value pe, to a fourth pressure value p4 during athird time period Ate, from a third point in time te, to a fourth point in time t4. The pressuredrop Ape, corresponds to the change of the pressure p of the fluid in the pressurizedpart 142 of the hydraulic system 132 from the third pressure value pe, to the fourthpressure value p4. The third time period Ate, has a length such that the pressure dropApe, is approximated as being linear. Further, the third time period Ate, has a length suchthat the restriction return fluid flow qreiurn during the third time period Ate, is approximatedas the average restriction return fluid flow based on the restriction return fluid flow qreiurnat the third point in time te, and the restriction return fluid flow qreiurn at the fourth pointin time t4. These aspects are in a corresponding way valid for the time periods At4 (ts-t4), Ats (te-ts) and Ate(t1-te) and the pressure drops Ap4(t) (ps-p4), Aps(t) (pe-ps) and Ape(t)(pv-pe) in figure 4. lt is understood that more Kvalues (or fewer) can be determined formore pressure drops and time periods, and these Kvalues may be added to the look-up table. ln the shown embodiments, the above-mentioned time periods At1,At2, Ate, At4,Ats, Ateand points in time t1, te, te,, t4, ts, te, tv are part of the same test or the same testsequence. Thus, in the shown embodiments, the above-mentioned pressure dropsAp1(t), Ap2(t), Ape,(t), Ap4(t), Aps(t), Ape(t) and the determinations and measurementsmade at the above-mentioned points in time t1, te, te,, t4, ts, te, tv are part of the sametest or the same test sequence.

The method may be triggered by at least one of the group of: an engine startup of acombustion engine 104 associated with the hydraulic system 132; an engine shutdownof a combustion engine 104 associated with the hydraulic system 132; an end of a 28 predetermined time period; an adaption of the Conversion coefficient K withoutrequests competing with the method.

The using of the Conversion coefficient Kmay comprise at least one of: determining adiagnosis of the fluid injector device 134, 136; determining at least one biockage of thefluid in the pressurized part 142 of the hydraulic system 132; calibrating at least one parameter associated with a regulation of the fluid injector device 134, 136.

Further, by means of both the pressure sensor 148, which may be located in thepressurized part 142 of the hydraulic system 132 at a first location and thus measurethe pressure at the first location, and the second pressure sensor 149 (see figure 1)located in the pressurized part 142 at a second location different from the first locationand thus measuring the pressure at the second location, conversion coefficient Kvalues for two different locations, i.e. the first and second locations, in the pressurizedpart 142 may be determined during the same test or the same test sequence. Hereby,two different look-up tables, LUT, may be formed, wherein the first LUT includes Kvales and their associated pressure values for the first location and the second LUTincludes Kvales and their associated pressure values for the second location. The twolook-up tables may then, for example, be applied to the first location and second location, respectively.

Unless disclosed otherwise, it should be noted that the method steps illustrated infigures 2 and 3 and described herein do not necessarily have to be executed in theorder illustrated in figure 2 or figure 3. The steps may essentially be executed in any suitable order.

With reference to figure 5, an embodiment of the hydraulic system 132 according tothe fifth aspect is schematically illustrated in more detail. ln figure 5, the hydraulicsystem 132 is configured for a fluid in the form of an additive, such as urea, and isapplied to an exhaust gas after-treatment system 130 for which each of the fluid injectordevices 134, 136 of the hydraulic system 132 is an additive/urea injector.

Figure 5 schematically shows the exhaust gas after-treatment system 130 of figure 1 29 in more detail. The exhaust gas after-treatment system 130 is connected via anexhaust pipe 152 to the combustion engine 104. Exhaust gas generated at combustionin the combustion engine 104 and the exhaust stream 154 (indicated with arrows) areled to the second fluid injector device 136 of the hydraulic system 132. The secondfluid injector device 136 is configured to provide an injection fluid flow qinjecior, whichmay comprise a first additive, for example urea or AdBlue, into the exhaust stream 154.AdBlue is basically urea mixed with water. A first reduction catalyst device 156 isprovided downstream of the second fluid injector device 136. The first reductioncatalyst device 156 is arranged to reduce nitrogen oxides NOx in the exhaust stream154 through the use of the first additive added to the exhaust stream 154 by the secondfluid injector device 136. ln more detail, the first reduction catalyst device 156 uses anadditive, for example ammonia NHs, or a substance from which ammonia may begenerated/formed/released, for the reduction of nitrogen oxides NO, in the exhauststream 154.

The exhaust gas after-treatment system 130 includes a particulate filter 158, which atleast partly comprises a catalytically oxidising coating, downstream of the firstreduction catalyst device 156. The particulate filter 158 is thus arranged both to catchand to oxidise soot particles, and to oxidise one or several of nitrogen oxides NO andincompletely oxidised carbon compounds in the exhaust stream 154.

Downstream of the particulate filter 158, the first fluid injector device 134 of thehydraulic system 132 is provided. The first fluid injector device 134 is configured toprovide an injection fluid flow qinjecior, which may include a second additive, to theexhaust stream 154. The second additive may comprise ammonia NHs, or asubstance, for example AdBlue, from which ammonia may begenerated/formed/released_ ln the shown embodiment, the second additive consists of the same additive as the above-mentioned first additive.

The shown exhaust gas after-treatment system 130 also comprises a second reductioncatalyst device 160, which is arranged downstream of the first fluid injector device 134.The second reduction catalyst device 160 is arranged to reduce nitrogen, oxides NOxin the exhaust gas stream 154 through use of the second additive and, if the first lO additive remains in the exhaust gas stream 154 when this reaches the secondreduction Catalyst device 160, also through use of the first additive. A diesel oxidationcatalyst (DOC) 170 may be provided between the first reduction catalyst device 156and the particulate filter 158. The DOC 170 has several functions and is normally usedprimarily to oxidise, during the exhaust treatment, remaining hydrocarbons CXHV (alsoreferred to as HC) and carbon monoxide CO in the exhaust gas stream 154 into carbondioxide C02 and water H20.

The exhaust gas after-treatment system 130 may also be equipped with one or severalsensors, such as one or several NOx-sensors 162, 164, 166 and/or one or severaltemperature sensors 168, 164, which are configured to determine NOx-concentrationsand temperatures, respectively, in the exhaust gas after-treatment system 130. The162, 164, 166, 168 sensors may be connected to an exhaust gas after-treatmentcontrol device 172. The exhaust gas after-treatment control device 172 may beconnected to and communicate with the control arrangement 150 and the controldevice 112.

With reference to figure 5, in the shown embodiment, in view of the direction of theexhaust gas flow 154 through the exhaust gas after-treatment system 130, the firstfluid injector device 134 is located downstream of the second fluid injector device 136.However, in alternative embodiments, the first fluid injector device 134 may instead belocated upstream of the second fluid injector device 136. Thus, the first and secondfluid injector devices 134, 136 may change locations in the exhaust gas after-treatmentsystem 130 with one another.

As mentioned above and with reference to figures 1, 5 and 6, a control arrangement150 for determining a conversion coefficient Kof a hydraulic system according to thefourth aspect is provided. The control arrangement 150 is configured to: deactivate 201 the fluid flow source device 140 such that substantially nosource fluid flow qsource is provided from the fluid flow source device 140, for examplea pump, to the pressurized part 142 of the hydraulic system 132, when the fluid flow source device 140 is inactive, determine 202, by usage ofthe sensor 148, one or more pressure drops Ap, Ap1, Apa, Apa, Ap4, Aps, Ape associated lO 31 with the fluid flow through the pressurized fluid conduit 140 and the fluid flow restrictiondevice 146, when the fluid flow source device 140 is inactive, determine 203 the restrictionreturn fluid flow qreiurn, determine 204 the conversion coefficient Kof the hydraulic system 132 basedon the determined restriction return fluid flow qfeiurn and on the determined pressuredrops Ap, Ap1, Ap2, Apa, Ap4, Aps, Ape, and use 205 the conversion coefficient K.

According to an embodiment of the control arrangement 150 according to the fourthaspect, the control arrangement 150 is configured to: deactivate 301 the fluid flow source device 140 such that substantially nosource fluid flow qsource is provided from the fluid flow source device 140, deactivate 302 the fluid injector device 134, 136 such that substantially noinjection fluid flow orm-em out from the pressurized part 142 of the hydraulic system 132is provided, when the fluid flow source device 140 and the fluid injector device 134, 136are inactive, determine 303, by usage of the sensor 148, one or more pressure dropsAp, Ap1, Apa, Apa, Ap4, Aps, Ape associated with the fluid flow through the pressurizedfluid conduit 144a, 144b, through the fluid injector device 134, 136 and through thefluid flow restriction device 146, when the fluid flow source device 140 and the fluid injector device 134, 136are inactive, determine 304 the restriction return fluid flow qfeiurn provided by the fluidflow restriction devices 146 to the fluid tank 138, determining 305 the conversion coefficient K of the hydraulic system 132based on the determined restriction return fluid flow qreiurn and on the determinedpressure drops Ap, Ap1, Apa, Apa, Ap4, Aps, Ape, and use 306 the conversion coefficient K.

With reference to figure 5, the shown control arrangement 150 may include a firstdeactivation and activation unit 180 for deactivating and activating the fluid flow sourcedevice 140 to perform the deactivation step 201, 301. The first deactivation andactivation unit 180 is directly or indirectly connected to the fluid flow source device 140 32 and configured to directly or indirectly communicate with the fluid flow source device140. The shown control arrangement 150 may include a second deactivation andactivation unit 182 for deactivating and activating each fluid injector device 134, 136 toperform the deactivation step 302 and the activation step 307. The second deactivationand activation unit 182 is directly or indirectly connected to the first and second fluidinjector devices 134, 136 and configured to directly or indirectly communicate with thefirst and second fluid injector devices 134, 136. The shown control arrangement 150may include a first determining unit 184 for determining, by use of the pressure sensor148, the pressure drops Ap, Ap1, Apa, Apa, Ap4, Aps, Ape to perform the determinationstep 202, 303. The first determining unit 184 is directly or indirectly connected to thesensor 148 and configured to directly or indirectly communicate with the sensor 148.The shown control arrangement 150 may include a second determining unit 186 fordetermining the restriction return fluid flow qreiurn to perform the determination step 203,304. The shown control arrangement 150 may include a third determining unit 188 fordetermining the conversion coefficient Kof the hydraulic system 132 to perform thedetermination step 204, 305. The control arrangement 150 may be connected to and communicate with the control device 112.

Figure 6 shows in schematic representation a control arrangement400/150, which maycorrespond to or may include one or more of the above-mentioned units 180, 182, 184,186, 188 of the control unit 150. The control arrangement 400/150, which may be orinclude a control unit 400, may comprise a computing unit 401, which can beconstituted by essentially any suitable type of processor or microcomputer, for examplea circuit for digital signal processing (Digital Signal Processor, DSP), or a circuit havinga predetermined specific function (Application Specific lntegrated Circuit, ASIC). Thecomputing unit 401 is connected to a memory unit 402 arranged in the controlarrangement 400/150. The memory unit 402 provides the computing unit 401 with, forexample, the stored program code and/or the stored data which the computing unit401 requires to be able to perform computations. The computing unit 401 is also arranged to store partial or final results of computations in the memory unit 402. ln addition, the control arrangement 400/150 is provided with devices 411, 412, 413,414 for receiving and transmitting input and output signals. These input and output 33 signals can contain waveforms, impulses, or other attributes which, by means of thedevices 41 1 , 413 for the reception of input signals, can be detected as information andcan be converted into signals which can be processed by the computing unit 401.These signals are then made available to the computing unit 401. The devices 412,414 for the transmission of output signals are arranged to convert signals receivedfrom the computing unit 401 in order to create output signals by, for example,modulating the signals, which can be transmitted to other parts of and/or systems inthe vehicle 100.

Each of the connections to the devices for receiving and transmitting input and outputsignals can be constituted by one or more of a cable; a data bus, such as a CAN bus(Controller Area Network bus), a l\/IOST bus (l\/ledia Orientated Systems Transport bus), or some other bus configuration; or by a wireless connection.

Control systems in modern vehicles commonly comprise communication bus systemsconsisting of one or more communication buses for linking a plurality of electroniccontrol units (ECU's), or controllers, and various components located on the vehicle.Such a control system can comprise a large number of control units or controlarrangements and the responsibility for a specific function can be divided amongstmore than one control unit or control arrangement. Vehicles of the shown type thusoften comprise significantly more control units or control arrangements than are shownin figures 5 and 6, which is well known to the person skilled in the art within thistechnical field. Alternatively or in addition thereto, the embodiments of the presentinvention may be implemented wholly or partially in one or more other control units already present in the vehicle.

Here and in this document, units are often described as being provided for performingsteps of the method according to embodiments of the invention. This also includes thatthe units are designed to and/or configured to perform these method steps.

The units 180, 182, 184, 186, 188 of the control arrangement 150 are in figure 5illustrated as separate units. These units 180, 182, 184, 186, 188 may, however, belogically separated but physically implemented in the same unit, or can be both logically 34 and physically arranged together. These units 180, 182, 184, 186, 188 may forexample correspond to groups of instructions, which can be in the form of programmingcode, that are input into, and are utilized by a processor/computing unit 401 when theunits are active and/or are utilized for performing its method step.

The control arrangement 150, 400, e.g. a device or a control device, according toembodiments of the present invention may be arranged for performing all of the methodsteps mentioned above, in the claims, and in connection with the herein describedembodiments. The control arrangement 150, 400 is associated with the above described advantages for each respective embodiment.

According to the second aspect of the invention, a computer program 403 (see figure6) is provided, comprising instructions which, when the program is executed by acomputer, cause the computer to carry out the method according to one or more of theembodiments disclosed above.

According to the third aspect of the invention, a computer-readable medium isprovided, comprising instructions which, when the instructions are executed by acomputer, cause the computer to carry out the method according to one or more of theembodiments disclosed above.

The person skilled in the art will appreciate that a the herein described embodimentsof the method according to the first aspect may be implemented in a computerprogram, which, when it is executed in a computer, instructs the computer to executethe method. The computer program is usually constituted by a computer programproduct 403 stored on a non-transitory/non-volatile digital storage medium, in whichthe computer program is incorporated in the computer-readable medium of thecomputer program product. The computer-readable medium comprises a suitablememory, such as, for example: ROIVI (Read-Only l\/lemory), PROIVI (ProgrammableRead-Only l\/lemory), EPROIVI (Erasable PRONI), Flash memory, EEPROIVI(Electrically Erasable PRONI), a hard disk unit, etc. ln the above, the method, the computer program 403, the computer-readable medium,the control arrangement 150, 400 and the hydraulic system 132 have been disclosedin connection with a vehicle 100. However, it should be understood that the method,the computer program 403, the computer-readable medium, the control arrangement150, 400 and the hydraulic system 132 can be used for other applications instead of avehicle 100, or for other applications within a vehicle 100, with or without any fluidinjector device 134, 136.

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

Claims

1. A method for determining a Conversion coefficient (K) of a hydraulic system(132), the hydraulic system (132) comprisingone or more fluid tanks (138) for storing a fluid,one or more fluid flow source devices (140) hydraulically connected to the fluidtank (138), the fluid flow source device (140) being configured to provide a source fluidflow (qsoufce) of the fluid to a pressurized part (142) of the hydraulic system (132),one or more pressurized fluid conduits (144a, 144b) being part of thepressurized part (142) of the hydraulic system (132),one or more sensors (148) for determining one or more pressures (p) of thefluid in the pressurized part (142) of the hydraulic system (132), andone or more fluid flow restriction devices (146) hydraulically connected to thefluid flow source device (140) and the fluid tank (138), the fluid flow restriction device(146) being configured to provide a restriction return fluid flow (qfeiurn) to the fluid tank(138), wherein the method comprises:0 Deactivating (201 ; 301) the fluid flow source device (140) such that substantiallyno source fluid flow (qsource) is provided from the fluid flow source device (140)to the pressurized part (142) of the hydraulic system (132);0 When the fluid flow source device (140) is inactive, determining (202; 303), byusage of the sensor (148), one or more pressure drops (Ap, Ap1, Ap2, Apa, Ap4,Aps, Ape) associated with the fluid flow through the pressurized fluid conduit(144a, 144b) and the fluid flow restriction device (146);0 When the fluid flow source device (140) is inactive, determining (203; 304) therestriction return fluid flow (qreiurn);0 Determining (204; 305) the conversion coefficient (K) of the hydraulic system(132) based on the determined restriction return fluid flow (qreiurn) and on thedetermined pressure drop (Ap, Ap1, Apa, Apa, Ap4, Aps, Ape); and 0 Using (205; 306) the conversion coefficient (K).

2. A method according to claim 1, wherein the determined Conversion coefficient(K) is a pressure drop (Ap) to f|uid flow conversion coefficient (K), which depends on avolume of the pressurized part (142) of the hydraulic system (132).

3. A method according to claim 1 or 2, wherein the conversion coefficient (K) isdetermined by dividing the determined pressure drop (Ap) by the determined restriction fetUlTl HOW (qreturn).

4. A method according to any one of the preceding claims, wherein the methodcomprises:0 When the f|uid flow source device (140) is inactive, determining the restriction return f|uid flow (qreiurn) based on a predetermined model or equation.

5. A method according to any one of the preceding claims, wherein when the f|uidflow source device (140) is inactive, a pressure (p) of the f|uid in the pressurized part(142) of the hydraulic system (132) is reduced from a first pressure value (p1) to asecond pressure value (p2) during a first time period (Ati) from a first point in time (t1)to a second point in time (t2), wherein the pressure drop (Api) corresponds to thechange of the pressure (p) of the f|uid in the pressurized part (142) of the hydraulicsystem (132) from the first pressure value (p1) to the second pressure value (pa), andwherein the first time period (Ati) has a length such that the pressure drop (Api) is approximated as being linear.

6. A method according to claim 5, wherein the first time period (Ati) has a lengthsuch that the restriction return f|uid flow (qfeiurn) during the first time period (Ati) isapproximated as the average restriction return f|uid flow based on the restriction returnf|uid flow (qreiurn) at the first point in time (ti) and the restriction return f|uid flow (qreiurn) at the second point in time (t2).

7. A method according to claim 5 or 6, wherein when the f|uid flow source device(140) is inactive, a pressure (p) of the f|uid in the pressurized part (142) of the hydraulicsystem (132) is reduced from a third pressure value (ps) to a fourth pressure value (p4) during a second time period (Ats) from a third point in time (ts) to a fourth point in time (t4), wherein the pressure drop (Apa) corresponds to the change of the pressure (p) ofthe fluid in the pressurized part (142) of the hydraulic system (132) from the thirdpressure value (pa) to the fourth pressure value (p4), and wherein the second timeperiod (Ata) has a length such that the pressure drop (Apa) is approximated as being linear.

8. A method according to c|aim 7, wherein a value of the conversion coefficient(K) is determined for each time period (At1, Ata), whereby the conversion coefficient(K) is expressible as a function of the pressure (p) of the fluid in the pressurized part(142) of the hydraulic system (132), and wherein each value of the conversion coefficient (K) is included in a look-up table together with its associated pressure value.

9. A method according to any one of the preceding claims, wherein the hydraulicsystem (132) comprises one or more fluid injector devices (134, 136) included in thepressurized part (142) of the hydraulic system (132) and hydraulically connected to thefluid flow source device (140) by at least one of the one or more pressurized fluidconduits (144b) and hydraulically connected to the fluid flow restriction device (146),the fluid injector device (134, 136) being configured to provide an injection fluid flow(dam-actor) out from the pressurized part (142) of the hydraulic system (132) uponactivation, wherein the method comprises: 0 Deactivating (302) the fluid injector device (134, 136) such that substantially noinjection fluid flow (dam-actor) out from the pressurized part (142) of the hydraulicsystem (132) is provided; 0 When the fluid flow source device (140) and the fluid injector device (134, 136)are inactive, determining (303), by usage of the sensor (148), one or morepressure drops (Ap, Ap1, Apa, Apa, Ap4, Apa, Apa) associated with the fluid flowthrough the pressurized fluid conduit (144a, 144b), the fluid injector device (134,136) and the fluid flow restriction device (146); and 0 When the fluid flow source device (140) and the fluid injector device (134, 136)are inactive, determining (304) the restriction return fluid flow (qraiurn).

10. A method according to any one of the preceding claims, wherein the f|uid isone of the group of:0 An additive, for example urea, used in an exhaust gas after-treatment systemof the vehicle, wherein the f|uid injector device is an additive injector;0 A fuel, wherein the f|uid injector device is a fuel injector configured to inject fuelinto a combustion engine of the vehicle; and0 An oil, wherein the f|uid injector device is an oil injector configured to inject oil into one or more components of the vehicle.

11. A computer program (403) comprising instructions which, when the programis executed by a computer, cause the computer to carry out the method according toany one of the preceding claims.

12. A computer-readable medium comprising instructions which, when theinstructions are executed by a computer, cause the computer to carry out the methodaccording to any one of the claims 1 to 10.

13. A control arrangement (150, 400) for determining a conversion coefficient (K)of a hydraulic system (132), the hydraulic system (132) comprising one or more f|uid tanks (138) for storing a f|uid, one or more f|uid flow source devices (140) hydraulically connected to the f|uidtank (138), the f|uid flow source device (140) being configured to provide a source f|uidflow (qsoufce) of the f|uid to a pressurized part (142) of the hydraulic system (132), one or more pressurized f|uid conduits (144a, 144b) being part of thepressurized part (142) of the hydraulic system (132), one or more sensors (148) for determining one or more pressures (p) of thef|uid in the pressurized part (142) of the hydraulic system (132), and one or more f|uid flow restriction devices (146) hydraulically connected to thef|uid flow source device (140) and the f|uid tank (138), the f|uid flow restriction device(146) being configured to provide a restriction return f|uid flow (qfeiurn) to the f|uid tank(138), wherein the control arrangement (150) is configured to: deactivate (201 ; 301) the fluid flow source device (140) such that substantiallyno source fluid flow (qsource) is provided from the fluid flow source device (140) to thepressurized part (142) of the hydraulic system (132), when the fluid flow source device (140) is inactive, determine (202; 303), byusage of the sensor (148), one or more pressure drops (Ap, Ap1, Ap2, Apa, Ap4, Aps,Ape) associated with the fluid flow through the pressurized fluid conduit (144a, 144b)and the fluid flow restriction device (146), when the fluid flow source device (140) is inactive, determine (203; 304) therestriction return fluid flow (qreiurn), determine (204; 305) the conversion coefficient (K) of the hydraulic system(132) based on the determined restriction return fluid flow (qreiurn) and on thedetermined pressure drop (Ap, Ap1, Apa, Apa, Ap4, Aps, Ape), and use (205; 306) the conversion coefficient (K).

14. A hydraulic system (132) comprising one or more fluid tanks (138) for storing a fluid, one or more fluid flow source devices (140) hydraulically connected to the fluidtank (138), the fluid flow source device (140) being configured to provide a source fluidflow (qsoufce) of the fluid to a pressurized part (142) of the hydraulic system (132), one or more pressurized fluid conduits (144a, 144b) being part of thepressurized part (142) of the hydraulic system (132), one or more sensors (148) for determining one or more pressures (p) of thefluid in the pressurized part (142) of the hydraulic system (132), one or more fluid flow restriction devices (146) hydraulically connected to thefluid flow source device (140) and the fluid tank (138), the fluid flow restriction device(146) being configured to provide a restriction return fluid flow (qfeiurn) to the fluid tank(138), and the control arrangement (150) as claimed in claim 13.

15. A vehicle (100) comprising the hydraulic system (132) as claimed in claim 14.