WO2017003365A1

WO2017003365A1 - Method and system for diagnosing a fuel system

Info

Publication number: WO2017003365A1
Application number: PCT/SE2016/050667
Authority: WO
Inventors: Ola Stenlåås; Susanna JACOBSSON; Carlos JORQUES MORENO; Andre ELLNEFJÄRD
Original assignee: Scania Cv Ab
Priority date: 2015-07-01
Filing date: 2016-06-30
Publication date: 2017-01-05
Also published as: SE541175C2; DE112016002306T5; SE1550927A1

Abstract

The present invention pertains to a method for diagnosis of a fuel system in a vehicle (100), wherein said vehicle (100) comprises a combustion engine (101) and at least one fuel tank (215A, 215B; 209) for receiving fuel, wherein said fuel system comprises a first, fuel pump (212A; 210A) for us in. the transfer of fuel between said first fuel tank (215A, 215B; 209) and said combustion engine (101), and a second fuel pump (212B; 210B) arranged to operate in parallel with said first fuel pump (212A; 210A) in the transfer of fuel between said, first fuel tank (215A, 215B; 209) and said combustion, engine (101). The method comprises: - determining, with the use of a representation of a. power consumption for said first (212A; 210A) and second (212B; 210B) fuel pump, respectively, the presence of a first fuel flow error in said fuel system.

Description

METHOD AMD SYSTEM FOR DIAGNOSING A FUEL SYSTEM Field of the invention

The present invention relates to a ruet.hod for diagnosis of a. fuel system according to the preamble of claim 1. The invention also relates to a system and a vehicle, as well as a computer program and a computer program product, which implement the method according to the invention.

Background of the invention

The present invention relates to fuel systems in vehicles , and in particular to heavy goods vehicles such as trucks, buses and machines. These types of vehicles are often relatively heavy, and also travel long distances. In summary, this entails a requirement that the vehicles be equipped with relatively large fuel tanks. For example, such vehicles may be equipped with a fuel tank holding in the range of 500 - 1000 litres, where such volume may also be divided over two fuel tanks arranged in the vehicle .

The fuel tanks thus consist of relatively large volumes, which entails, when the fuel level drops, that any remaining fuel is moved around in the fuel tank as a result of the vehicle's movements. Fuel transfer from the fuel tank to the vehicle's combustion engine is usually carried out with the use of a fitting, submerged in the fuel tank, with an inlet through which the fuel is sucked up with the help of a pump. In order for fuel to be sucked up with said pump, however, the inlet of the fitting must be surrounded by fuel, and not by air.

In relation to fuel systems in vehicles, a fuel pump is often used, arranged in connection with the combustion engine to dra up fuel, the fuel pump being mechanically connected to the combustion engine and operated by the driving shaft of the combustion engine. This solution entails that the fuel pump must be able to pump a relatively large amount of fuel already at low rotational speeds, i.e. lower rotational speeds than the idling speed of the combustion engine, in order to be able to pump a sufficient amount of fuel to the combustion engine when the start engine is working, in order for the combustion engine to be able to start at all. This in turn means the fuel pump will be over-dimensioned during progress, with consequential losses associated therewith.

Furthermore, a fuel pump operated by the combustion engine's output shaft may, if it begins to draw up air, e.g. because of a low fuel level, begins to cavitate, and as a consequence the pump may not begin to draw up fuel again without first being- stopped, which thus also means that the vehicle must be stopped before the fuel supply may be resumed.

The above disadvantages may be reduced with the use of a fuel pump that is electrically operated, i.e. a fuel pump operated with an electric motor, which means that the speed of the fuel pump may be controlled independently of the speed of the output shaft of the combustion engine. Furthermore, in such systems the safety is enhanced with the use of fuel pumps operating in parallel .

Summary of the invention

One objective of the present invention is to provide a method to diagnose a fuel system in a vehicle. This objective is achieved with a method according to claim 1.

The present invention relates to a method for diagnosis of a fuel system in a vehicle, wherein said vehicle comprises a combustion engine and at least one fuel tank for receiving fuel, wherein said fuel system comprises a first fuel pump for use in the transfer of fuel between said first, fuel tank and said combustion engine, and a second fuel pump arranged to operate in parallel with said first fuel pump in connection with transfer of fuel between said first, fuel tank and. said combustion engine. The method comprises:

- determining, with the use of a representation of a. power consumption for said first and second fuel pump, respectively, the presence of a first fuel flow error in said fuel system.

Use of electrically operated fuel pumps may mitigate problems that may arise in connection with the use of fuel pumps operated by the output shaft of the combustion engine.

Furthermore, dependability is a very important parameter, in particular in relation to heavy goods vehicles, and obviously a functioning- fuel supply is also a very important parameter for dependability. For this reason, according to the present, invention a system is used, where two electrically operated fuel pumps operating in parallel are used to transfer fuel from the vehicle's fuel tank to said, combustion engine, for example to a fuel supply system arranged in said, combustion engine, such as e.g. a fuel injection system, e.g. a Common Rail system.

The fuel pumps may be arranged for individual control, e.g. by way of individual control of the respective associated electric motors. Through the use of fuel pumps operating in parallel, e.g. a redundancy is obtained, which facilitates that fuel may be transferred even when one of t e fuel pumps is

ma1functioning .

In relation to fuel systems in general, dependability is very important, and therefore it is also desirable to be able to identify an incorrect function in the fuel system at as early a stage as possible, and the present invention relates to a method for diagnosis of a system with fuel pumps operating in parallel. Furthermore, if an error arises, it is desirable to be able to identify t e cause of the error without extensive troubleshooting. For example, components in a fuel system may be difficult to access, e.g. because components such as fuel pumps may be arranged inside a fuel tank. The present invention relates, in particular, to a method facilitating identification of the presence of, and/or cause of errors in the fuel flow. According to the invention, this is achieved with the use of information relating to the operation of the fuel pumps, and in particular to the power consumption of the fuel pumps .

According to one embodiment, information from a pressure sensor arranged upstream of the fuel pumps is also used. Through the use of fuel pumps operating in parallel it is possible, through a representation of the power consumption for each respective fuel pump and, according to one embodiment, a signal from said pressure element, to carry out diagnoses and detect errors, which would otherwise be difficult to locate without replacing the pump, wherein a good indication of the occurrence of errors in the fuel system upstream of said fuel pumps may be obtained.

For example, when a single fuel pump is used, it may be

difficult to determine whether an error is due to the fuel pump as such, or whether the error is located at a different place in the system, with the consequence that the fuel pump in such a system may need to be replaced at the diagnosis in order for an existing error to be isolated. According to the present invention, troubleshooting is facilitated as the error may be identified without any need for a pump replacement .

According to the present invention, the diagnosis is carried out through the use of a representation of the fuel pumps'^' power, wherein several types of malfunction may be identified. According to one embodiment, said power consumption is used to determine whether the fuel flow upstream of the fuel pumps is blocked and/or whether there is a leakage. With the use of a pressure signal from pressure elements arranged upstream, of the fuel pumps, added accuracy in the isolation of the error may be obtained .

The invention is applicable in different types of fuel systems, and. according to one embodiment a transfer tank, also called a. "catch-tank" or "tech-tank", but referred to herein as a transfer tank, arranged between the combustion engine and said first at least one main tank, is used, wherein the method comprises supply of fuel to said transfer tank from said first main tank, before a transfer to said fuel supply system from said transfer tank takes place, and wherein said transfer tank preferably consists of a smaller tank, compared with said first fuel tank. The volume of the transfer tank may e.g. be a volume within the interval 1-10%, or 1-5%, of the total volume of said at least one main tank.

The transfer tank is thus substantially smaller than the main tank, which means that it is also less sensitive to the

movements of the fuel in the tank, resulting from movement and road gradients. When the transfer tank is full, it therefore functions as a buffer on occasions when fuel may not be drawn out of the main tank, e.g. because of a low fuel level combined with an incline, so that fuel may be transferred to the fuel supply system from the transfer tank even when fuel in said first main tank is not available, and so that the transfer tank may be refilled when conditions so allow and the main tank's fuel is available again. Such a solution thus allows that an even larger proportion of the main tank's fuel may be used before a refill is required. According to one embodiment, said first and second fuel pump, respectively, is used for transfer of fuel to said transfer tank from, said at. least one main tank on the fuel's path toward said corabustion engine. According to another embodiment, said first and second fuel pump,

respectively, is used, for transfer of fuel from said transfer tank to said combustion engine. According to one embodiment, a. first pair of fuel pumps operating in parallel is used to transfer fuel to said transfer tank from said at least one main tank, and a second pair of fuel pumps operating in parallel is used for transfer of fuel from, said transfer tank to said fuel supply system, where the present invention is applicable to both these pairs, and where diagnosis may be carried out simultaneously or at separate times for the respective pairs.

Further characteristics of the present invention and advantages thereof will be described in the detailed description of example embodiments set out below and in the enclosed drawings.

Fig. 1A schematically shows a vehicle, in which the present invention may advantageously be used.

Fig. IB shows a control device in a vehicle control system.

Fig. 2 schematically shows a fuel system, in which the

present invention may be applied.

Fig. 3 schematica11y shows an example method according to

one embodiment of the present invention.

Fig. 1A schemat ical ly shows a powertrain in a vehicle 100, according to an embodiment of the present invention . The vehicle 100 shown schematically in Fig. 1A comprises a

powertrain with an internal combustion engine 101, which in a customary manner, via an output shaft on the internal

combustion engine 101, usually via a flywheel 102, is connected to a gearbox 103 via a clutch 106. The combustion engine 101 is controlled by the control system of the vehicle 100 via an engine control device 115. Likewise, in the present example, the clutch 106 and the gearbox are controlled by a control device 116. Further, an output shaft 107 from the gearbox 103 drives the driving wheels 113, 114 via a final gear 108, e.g. a customary differential, and the drive shafts 104, 105 connected to said final gear 108, Fig. 1A thus shows a powertrain of a specific type, but the invention is applicable at all types of

powertrains, and also at all types of vehicles, as long as these are operated by a combustion engine.

The displayed vehicle also comprises a fuel system, where Fig. 1A shows two main fuel tanks 215A, 215B from which fuel is supplied to the combustion engine via supply to a fuel supply system arranged at the combustion engine 101, in the present example an injection system 204, via a transfer tank 209. The fuel system's functio s are controlled by a control device 230. Additional details in the exemplified fuel system are displayed in Fig, 2, and described below.

According to the above, the present invention relates to diagnosis of a fuel system. The method according to the

invention may be arranged to be carried out by some applicable control device in. the vehicle's control system., and may e.g. be arranged to be carried out. by the control device 230 or

alternatively by another applicable control device in the vehicle, such as e.g. the engine control device 115. The control device may thus consist of any suitable control device in the vehicle's control system. The invention may also be implemented, in a control device ded.ica.ted to the present.

invention .

Generally, such control systems consist of a. communications bus system, consisting of one or several communication buses to connect a number of electronic control devices (ECUs), or controllers, and different components arranged in the vehicle

100. Such a. control system may thus comprise a. large number of control devices, and the responsibility for a specific function may be distributed among more than one control device. For the sake of simplicity, in Fig, 1A only a very limited number of control devices are displayed.

The function of the control device 230 (or the control

device (s) at which the present invention is implemented) according to the present invention, may, e.g. depend on signals from different sensors, such as e.g. signals from pressure sensors 228, 229 as set out below. Furthermore, the function according to the invention may depend on signals from the fuel pump(s) that ensure transfer of fuel from a fuel tank to the injection system as set out below, where the signals may comprise information relating- to e.g. rotational speed, torque emitted, fuel flow, and/or power consumption. The control may also depend on signals from one or several other control devices .

Furthermore, the control is often carried out by programmed instructions. These programmed instructions typically consist of a computer program, which, when executed in a control device, causes the control device to carry out the desired control action, such as a method step according to the present invention .

The computer program is usually a part of a computer program product, where the computer program product comprises an applicable storage medium 121 (see Fig. IB) , with the computer program stored on said storage medium 121. The computer program may be stored in a non-volatile way on said storage medium. Said digital storage medium 121 may e.g. consist of any from the following group : ROM (Read-Only Memory) , PROM (Programmable Read-Only Memory) , EPROM (Erasable PROM) , Flash, EEPROM

(Electrically Erasable PROM) , a hard disk unit, etc. , and may be set up in or in combination with the control device, where the computer program is executed by the control device. By q changing the cotriputer program ' s inst.ructions, the vehicle's behaviour may thus be adjusted in a specific situation.

An example control device (control device 230) is shown

schematically in Fig, IB, and the control device in turn may comprise a calculation unit 120, which may consist of e.g. a suitable type of processor or microcomputer, e.g. a circuit for digital signal processing- (Digital Signal Processor, DSP) , or a circuit with a predetermined specific function (Application Specific Integrated Circuit, ASIC) . The calculation unit 120 is connected to a memory unit 121, which provides the calculation unit 120 with e.g. the stored program code and/or the stored data that the calculation unit 120 needs in order to be able to carry out calculations, e.g. to determine whether an. error code should be activated. The calculation unit 120 is also set up to store interim or final results of calculations in the memory unit 121.

Further, the control device is equipped with devices 122, 123, 124, 125 for receiving and sending of input and output signals. These input and output signals may contain waveforms, pulses or other attributes which, by the devices 122, 125 for the receipt of input signals, may be detected as information for processing by the calculation unit 120. The devices 123, 124 for sending output signals are arranged to convert the calculation result from the calculation unit 120 into output signals for transfer to other parts of the vehicle's cont ol system and/or the component (s) for which the signals are intended. Each one of the connections to the devices for receiving and sending of input and output signals may consist of one or several of the following: a cable; a data bus, such, as a CAN (Controller Area Network) bus, a MOST (Media Oriented Systems Transport) bus, or any other bus configuration; or of a wireless connection. A first example embodiment for diagnosis of the fuel system is displayed in Fig. 3. The method is exemplified in connection with the fuel system displayed in Fig. 2 , which is described i further detail below, but is applicable also to other types of fuel systems where fuel pumps operating in parallel are used. The present invention is thus applicable in all types of fuel systems, i.e. also in fuel systems without a transfer tank.

In relation to the method 300 in Fig. 3, this begins at step 301, where it is determined, whether the fuel system should be diagnosed. When a diagnosis of the fuel system must be carried out, the method continues to step) 302. According to one embodiment, diagnosis of the fuel system may be arranged to be carried out. continuously according to the present i vention, a soon as a fuel pump must be activated or is activated.

According to one embodiment, the transition from step 301 to step 302 may be arranged to occur e.g. when a signal from a pressure sensor, such as from one of the pressure sensors 228, 229 below^", indicates an abnormally high and/or low pressure, and/or when one or several parameters in relation to the control of the fuel pumps, such, parameters related to speed, or power consumption, indicate that, the system may be

malfunctioning. According to one embodiment, the diagnosis according to the invention may be arranged to be carried out e.g. at applicable intervals. The transition from step 301 to 302 may also be arranged to be controlled by a. detection of th occurrence of noise of a certain type in a pressure sensor signal. For example, the pressure signal may be filtered, wherein e.g. the occurrence of noise signals, e.g. exceeding a certain amplitude in some applicable frequency band, may be used as a criterion for t e transitio to step 302 si ce the occurrence of an error may be suspected in this case. The choice of frequency for analysis may e.g. be arranged to be dependent on the prevailing pump speed and/or relevant flow, where the choice of frequency band may e.g. be empirically determined. This analysis of the pressure signal may thus be arranged to be carried out continuously or at applicable intervals, wherein the diagnosis of the fuel system may be carried out. when the analysis of the pressure signal indicates that an error may occur. The inventors of the present invention have also realised that frequency analysis may be applied generally in systems of the type displayed in Fig. 2 , and such frequency analysis is exemplified in the parallel Swedish patent application SE1550926-8, "FORFAR MDE OCH SYSTEM FOR DXAGMOSTXSERXNG V ETT BRANSLESYSTEM XX" ''METHOD AMD SYSTEM FOR DIAGNOSING A FUEL SYSTEM II), with the same filing date and inventor as the present application. This application is described in more detail below, Furthermore, the method may, in cases where more than one pair of parallel fuel pumps is used, as in the example shown in Fig. 2, where the fuel system, relates to the respective pairs, be arranged for individual diagnosis. The method displayed may thus be used individually, simultaneously or sequentially, for the pairs of fuel pumps arranged in. parallel, described, below.

Fig. 2 shows the fuel system in Fig. 1A in more detail. In the system illustrated in Fig. 2, two main tanks 215A, 215B are used, each of which, holds a. relatively large amount of fuel, such as e.g. a fuel amount in the interval 300-1000 litres. By using- several tanks, it is possible to obtain a greater total fuel capacity than what might otherwise be possible while using only a single tank, as there may be a shortage of large, connected spaces in vehicles and as it may thus be difficult to find a possible location for a single tank of the desired size. The two main tanks 215A, 215B are connected with each other via a passage 216 i the lower par of the tanks 215A, 215B, so that, fuel may flow from one of the tanks to the other. Likewise, the tanks are connected with each other at. the upper edge via a deaeration filter 214.

Fuel is drawn from the main tank 215A, to which the fuel in the main tank 215B also flows, via a fuel armature 213. The inlet 213A of the fuel armature 213 is preferably arranged deep in the tank, i.e. near the bottom of the tank, in order to ensure that as a great a volume as possible may be drawn. A certain distance from the bottom of the tank may be advantageous, e.g. in order to avoid that gravel, deb is and other objects that may have entered the tank be drawn up. The fuel level in the tank may be determined with the use of a level sensor 217. The fuel is sucked up by at least one of a pair of fuel pumps 212A, 212B arranged in parallel, and the fuel drawn up by the fuel pumps 212A, 212B is pumped, in the present example, via a pre- filter 211 for separation of water in a customary manner, to an intermediate tank 209, a transfer tank, as set out above, which is substantially smaller than the main tanks 215A, 215B. The size of the transfer tank 209 may e.g. be in the range of 15-50 litres, or e.g. have a size which, in relation to the total volume of the main tanks, constitutes a volume in the range of 1-10%, or 1-5%, of the total volume of the main tanks.

Furthermore, the geometry of the transfer tank is preferably such that it has a height which exceeds, or preferably

substantially exceeds, the width and the depth, respectively. The transfer tank is thus preferably relatively high and relatively narrow, in order to reduce negative impact of slushing to the extent possible.

The pumps 212A, 212B for transfer of fuel from the main tanks 215A, 215BB to the transfer tank. 209 may advanta.geou.sly be arranged inside the transfer tank 209, which is indicated with dashed lines in Fig. 2. Obviously, this is not necessarily the case, and. obviously, Fig, 2 is an entirely logical diagram, of t e fuel system, where no proportionate comparisons may be made between various component parts of the fuel system. For

example, all fuel pumps displayed may be of the same type.

Neither may any conclusions be drawn regarding the physical placement of the respective component parts, other than it.

being indicated explicitly in the figure that the fuel pumps in the example displayed may be arranged in the transfer tank. According to another embodiment of the present invention, this is not the case, however. The fuel pumps 212A, 212B, as well as the fuel pumps 210A, 21GB described below, are electrically operated fuel pumps, where a respective electric motor 222A, 222B, 221A, 221B is used to operate the respective fuel pumps as set out below, A fuel pump with an associated electric motor may in practice consist of an integrated part.

The fuel pumps 21 OA, 21 OB, which are arranged for parallel operation, in a manner corresponding to the pumps 212A, 21233, are used to transfer fuel from the transfer tank 209 to the combustion engine's 101 injection system. These electrically operated fuel pumps 21 OA, 210B may also be arranged in the transfer tank 209, as well as the fuel filter 211. In the system, displayed, two pairs of fuel pumps 210A-B, 212A-B for transfer of fuel from the main tank to the injection system are thus displayed. By arranging the fuel pumps 21 OA, 210B, 212A, 2123, and electric motors associated therewith, in the transfer tank 209, the fuel in the transfer tank may be used, to cool components, while, in the reverse, the fuel may be heated with excess heat from electric motors/fuel pumps. The respective fuel pumps, as well as the fuel filter 211 may alternatively be arranged in another applicable place, such as e.g. in one of the main tanks or entirely outside the fuel tanks .

The fuel is moved, in the present example, from the transfer- tank 209, via. a conduit 218 and a. second fuel filter 207, to an injection system, where a high pressure pump (or another mechanical pressure increasing device such as e.g. a unit injector) 204 pressurises the fuel to a very high pressure for supply to a common rail 201, in order to supply it to the combustion engine's combustion chamber via the respective injectors 202.

The injection system displayed in Fig. 2 thus consists of a so- called Common Rail System, which thus entails that all- injectors (and thus combustion chambers) are supplied by the common rail 201. The pressure in the fuel conduit 201 may be controlled with the use of a valve 203. The function of the fuel filters is not described herein, since such function constitutes prior art.

Excess fuel from the high pressure pump 204 may be returned to the transfer tank 209 (according to the present example) , or alternatively to the main tanks 215A, 215B (indicated with a. dashed line 225) via a conduit 219, 224. Likewise, excess fuel from injectors 202 and/or from the fuel conduits 201 may be returned in a corresponding manner from an overflow conduit 220, 224. The returned fuel may also consist, of a lubricant for, respectively, the high pressure pump 204 and the injectors 202, etc. The returned fuel is usually heated, so that such excess heat may be used to heat the fuel by way of returning the fuel to the applicable fuel tank, as described above.

Further, Fig. 2 shows pressure sensors 228 and 229 designed to determine the pressure of the fuel flow upstream of the

respective parrs of parallel fuel pumps.

The solution displayed has the advantage that, with the use of the substantially smaller transfer tank described above, which is therefore also substantially less sensitive to slushing fuel and the incline of the vehicle, jointly with the use of

electrically operated, fuel pumps, various advantages may be achie eci , such as e.g. impro ed range , s i.nce a. 1arger

withdrawal from the main tanks is permitted before refilling is required. Furthermore, the use of electrically operated pumps entails advantages with respect to e.g. energy consumption, compared with a fuel pump operated with an output shaft of the combustion engine.

In the case that, at step 301, it is determined that the fuel system must be diagnosed with respect to the fuel transfer from the main tank 215A, 215B to the transfer tank 209, then at step 302 it is determined whether the pressure indicated by the pressure sensor 228 exceeds a pressure threshold p_Kml . Where this is the case, a flag, or a variable _hjvh is activated.

When the pressure indicated by the pressure sensor 228 does not exceed the pressure threshold p_liml the flag ¾ ,,_;¾¾ί3 left inactive, and the method continues to step 303.

At step 303 it is determined whether the fuel pumps' 212A, 212B power consumption exceeds some applicable power consumption. This may be determined by using some applicable representation of the fuel pumps'^' power consumption. The determination at step 303 is carried out for each fuel pump 212A, 212B separately, and. when the power consumption for at least one of the fuel pumps 212A, 2I2B exceeds a threshold value, the method

continues to step 304.

A representation of the fuel pumps ' power consumption may be determined in some applicable manner, e.g. by determining the electricity consumption of the electric engines 222A, 222B, considered to be the fuel pumps' electricity consumption and referred to below as i_2l2A and i_{2A B} . Alternatively, e.g. the fuel pumps' speed jointly with an indication of a torque emitted by the respective pumps may be used to determine a representation of the power consumption. According to the present example, the fuel pumps' (electric engines') power consumption is used as a representation of the power consumption, and at step 303 it is determined whether the electricity consumption exceeds any applicable current i_xs[ .

This determination is carried out for each fuel pump 212A, 212B separately, and when the electricity consumption for at least one of the fuel pumps 212A, 212B exceeds the threshold value i,_inil , the method continues to step 304 while simultaneously corresponding flags i_{2J2A Mgh}and/ori_{2l2B Mgk} are activated in

applicable cases. In cases where the electricity consumption does not exceed the threshold value i_lim, for any of the fuel pumps the method may be arranged to revert to step 301, since i this case it is deemed, unlikely that there is a block of the flow, e.g. due to an incorrect indication from the pressure sensor 228. Alternatively, the power consumption may be

building up, and the power thresholds may be reached at a later time, wherein, if so, one or both the conditions at step 303 may be fulfilled.

At step 304 a diagnosis is carried out, based on the result of the determinations conducted at steps 302-303. In case any of ½i2.4 Mgh ' iiB high and p_hghl have been activated, the method

continues to step 305. When all of these flags have been activated, this indicates that the fuel flow upstream of both the fuel pumps 212A, 212B is blocked, wherein an error code a indicating this may be activated and the driver may be

notified. The method may then end..

Once it has been established that there is an error in the fuel system, another method may also be arranged to be activated, where the diagnosis is carried out e.g. some applicable number of times, i order to determine whether the er or is tempo ary or permanent. If it is determined during this method that the 1 problem is temporary, the fuel supply may be arranged to resume. Furthermore, in the diagnosis the maximum pressure to which the pressure in the fuel system is permitted to rise may consist of some applicable pressure, falling below a pressure at which there is a risk of components in the fuel system breaking ,

Furthermore, when the error relates to the transmission of fuel from the main tank to the transfer tank, the driver may be notif ed that only the amount of fuel remaining in t.he t.ra.nsfer tank may be used to move the vehicle to a garage.

If at step 304 it is determined that the flags L_y,_{A Uoh} , i,_{i2B hi h} have been activated, but that this is not the case in relation to ρ_κφ) , the method continues to step 306. When i_{2]2A Mh} , i_{2l2B hih} have been activated, but not p_{u i} , this indicates that the fuel flow upstream of both the fuel pumps 212A, 21233 but downstream, of the pressure sensor 238 is blocked, alternatively leaking, wherein an error code b indicating this may be activated in order to facilitate service measures. Likewise, the driver may be notified of the occurrence of errors in the fuel system.

If it is determined at step 304 that only one of the flags i,_{l2A hiek} , i_{2V2B U h} has been activated, while simultaneously the flag p_highl has not been activated, the method continues to step

307 and. step 308, respectively. In these cases, it may be determined that the fuel flow from one of the fuel pumps ( the one for which the flag was not activated) functions correctly, while the flow is blocked upstream of the second fuel pump, but before the flow from the two pumps are joined. Thus, the error may in this case be isolated to one specific fuel pump.

Corresponding error codes c and d respectively may be activated at respective occurrence of errors. Furthermore, according to one embodiment of the invention, the signal from the pressure sensor may be used in such a manner that if the pressure falls below some applicable pressure, which may consist of a pressure which is abnormally low for the fuel system, the blockage may be deemed to have occu red downstream of the pressure sensor. A low pressure may also indicate the occurrence of a leakage upstream of the fuel pumps, which may also be detected e.g. by comparing the fuel pumps' power consumption with the pump speed, where an

abnormally high speed, for one or both the pumps in relation to the prevailing power consumption, i.e. a lower power

consumption in relation to the speed than expected, may be used as an indication of the occurrence of a leak. The occurrence of a leak, may also be arranged to be determined by way of a step response test, which may e.g. determine whether the pressure is rising to the extent desired in response to a speed change in the fuel pumps. If the pressure does not rise to the extent desired, this may be used, as an indication of the occurrence of a leak. Such step response tests are also described in said parallel application.

Overall, the invention entails that a good indication of the malfunction may be obtained with the invention. By determining the power consumption for the respective pumps in a pair of pumps operating in parallel, errors may be identified, which would otherwise not be possible to identify. At the use of one single fuel pump it may be very difficult to determine whether the fuel pump malfunctions, or whether the fuel flow is blocked or exposed to leakage for some other reason. Thanks to the use of the present invention, good localisation of an error that has occurred may be achieved, where the error may be identified already during the journey, and facilitating troubleshooting at a subsequent garage visit. Furthermore, in the embodiment displayed., a pressure sensor 228 has been used in the diagnosis. This pressure sensor may be randomly placed in the fuel circuit upstream of the fuel pumps, and thus does not necessarily need to be placed downstream of the pre-fliter 211 and the main fuel filter 207. The pressure sensor 228 (as well as the pressure sensor 229) may, however, be arranged to be randomly placed upstream of the respective pairs of fuel pumps . Furthermore, more than one pressure sensor may be arranged between the fuel pumps 212A, 21233 and the transfer tank 209, and between the fuel pumps 210A, 210B and the injection system 204, respectively, wherein signals from several pressure sensors may be used at the diagnosis, with further possibilities of identifying errors .

According to one embodiment of the invention, the diagnosis is carried out by using only a representation of the fuel pumps ' power consumption, where thus only the power consumption is used to identif errors in the fuel transmission. In this case, basically the same diagnosis as the one above may be carried out, but whereat less accuracy with respect to the localisation of the error may be obtained due to the lack of a pressure sensor signal .

In Fig. 3, an example embodiment according to the invention is exemplified for the fuel pumps 212A, 21233 for transmission of fuel from the main tanks 215A, 215B to the transfer tank 209. The method displayed is equally applicable with respect to diagnosis of the part of the fuel system relating to the fuel pumps 221A, 221B, where the pressure sensor 229 may be used in a manner corresponding to the use of the pressure sensor 228. Here as well, the error may be indicated to the driver of the vehicle, and in case of blockage of the fuel flow in this part of the system, the vehicle is at risk of coming to a standstill substantially immediately . Furthermore, according to the above, the present, invention may be applied jointly with a diagnostic method described in the parallel Swedish patent application number 1550926-8, entitled "FGRFARANDE OCH SYSTEM FOR DIAGNOSTISERING AV ETT

BRANSLESYSTEM II" (METHOD AND SYSTEM FOR DIAGNOSING FUEL

SYSTEM II} , with the same filing date as the present

application, and the same inventor. Said parallel application describes a method for diagnosis of a fuel system of the type displayed in this application, where the signal from the pressure sensor element is filtered, and wherein the filtered signal is used to detect, in particular, leakages in the fuel system. Thus, both the methods according to the present

application and the methods according to said application may be used, at diagnosis of fuel systems .

As mentioned above, the present invention is not limited to fuel systems with a transfer tank, but the invention is applicable in all types of fuel systems where electrically operated fuel pumps operating in parallel may be arranged.

Further, more than two, for example three fuel pumps may be arranged to operate in parallel, wherein a. representation of power consumption for the respective fuel pump may be used at the diagnosis.

Other embodiments of the method and the system according to the invention are available in the claims enclosed hereto. It should also be noted that the system may be modified according to various embodiments of the method according to the invention (and vice versa) and that the present invention is in no way limited to the above embodiments of the method according to the invention, but relates to and comprises all embodiments within the scope of the enclosed independent claims.

Claims

Method for diagnosis of a fuel system in a vehicle (100), wherein said vehicle (100) comprises a combustion engine (101) and at least one fuel tank (215A, 215B; 209) for receipt of fuel, wherein said fuel system comprises a first fuel pump (212A; 210A) for use when transferring fuel between said first main tank (215.A, 215B; 209) and said combustion engine (101), and a second fuel pump

(212B; 210B) arranged to operate in parallel with said first fuel pump (212A; 210A) when transferring fuel between said first fuel tank (215A, 215B; 209) and said combustion engine (101) characterised in that the method comprises :

- determining, with the use of a representation of a power consumption for said first (212A; 210A) and second (212B; 210B) fuel pump, respectively, the presence of a first fuel flow error in said fuel system.

Method according to claim 1, further comprising:

- determining, with the use of a representation of a power consumption for said first (212A; 21 OA.) and second (212B; 210B) fuel pump, respectively, the presence of a first fuel flow error in said fuel system upstream of said first (212A; 210A) and/or second fuel pump (212B; 21GB) ,

Method according to claim. 2, wherein said fuel flow error consists of a blockage of the fuel flow upstream of said first (212A; 210A) and/or second (212B; 210B) fuel pump.

Method according to claim. 2, wherein said fuel flow error consists of a leakage in the fuel flow upstream of said first (212A; 210A) and/or second (212B; 210B) fuel pump.

Method according to any of claims 2-4, further

comprising :

- determining, with the use of said representations of power consumption for said first (212A; 210A) and second (212B; 210B) fuel pump, respectively, whether the fuel flow is blocked upstream or downstream of a point at which the flows from the respective fuel pumps loin,

6. Method according to any of the claims 1-5, further

comprising, at said determination of the occurrence of a first fuel flow error in said fuel system:

- determining said occurrence based also on a signal from, a pressure sensor element (228, 229) arranged upstream of a first (212A; 210A) and second (212B; 210B) fuel pump, respectively, in said fuel system.

7. Method, according to claim 6, also comprising, when a first fuel flow error is considered to be present in said fuel system:

- generating- a. signal indicating an error upstream of said, pressure sensor element, if one of said pressure sensor elements exceeds a first pressure, and/or

- generating a signal indicating an error downstream of said pressure sensor element if one of said pressure se sor elements falls below a first, pressure.

8. Method according to claim 6 or 7, further comprising:

- carrying- out said determination of said occurrence of a first fuel flow error in said fuel system when a filtered pressure signal from said pressure sensor element. (228, 229) indicates the occurrence of noise signals in a first frequency band, such as a speed and/or flow dependent frequency band.

9. Method according to any of the previous claims, further comprising :

- determining said representat ion of a power consumption for said first (212A; 210A) and second (212B; 210B) fuel pump, respectively, at least partly based on an electricity consumption for said first (212A; 210A) and second (212B 210B) fuel pump, respectively.

Method according to any of the previous claims, further comprising :

- carrying out several consecutive determinations of whether a first fuel flow error in said fuel system is deemed to be present, and

- generating a signal representing the presence of an error in said fuel system only if said several consecutive determinations indicate the presence of said first fuel flow error.

Method, according to any of t e previous claims, wherein said vehicle (100) also comprises a transfer tank (209) arranged between a fuel supply system (204) and said at least one first nk (215A) , wherei the method comprises supplying fuel to said transfer tank (209) from said first main tank (215A) and then further on, from said transfer tank to said combustion engine (101), wherein said transfer tank (209) is a smaller tank than said first main tank. (209A) , and wherein said first and second fuel pumps are used to transfer fuel from said first main tank (215A) to said transfer tank (209) or to transfer fuel further from said transfer tank to said fuel, supply system (204) .

Method according to claim 11, wherein the method also comprises, when the presence of a blockage of, and/or leak from, the fuel flow to said transfer tank has been

determined., to notify the driver of said vehicle that only the fuel amount in said transfer tank is available for consumption ,

Method, according to claim 11 or 12, wherein a. first, pair of pumps arranged for parallel operation is used to transfer fuel from said at least one fi st ma.in tank.

(209A) to said transfer tank, and wherein a second pair of pumps arranged for parallel operation is used to transfer fuel from said transfer tank to said fuel supply system. (204), wherein each pair of fuel pumps is controlled according to any of claims 1-10, , Method, according- to any of the previous claims, wherein said, at least one fuel tank consists of a main tank or a transfer tank, arranged between said combustion engine and said main tank, , Computer program comprising a program code which, when

said p ogram code is executed in a computer, achieves that said computer carries out the method according to any of claims 1-14, , Computer program product comprising a computer-readable medium and a computer program according to claim 15, said computer program being comprised in said computer-readable medi m. , System for diagnosis of a fuel system in a vehicle (100), wherein said vehicle (100) comprises a combustion engine (101) and at least one fuel tank (215A, 215B; 209) for receipt, of fuel, wherein said fuel system comprises a first fuel pump (2I2A; 210A) for use when transferring fuel between said first main tank (215A, 215B; 209) and said combustion engine (101), and a second fuel pump

(212B; 210B) arranged to operate in parallel with said. f irst fue 1 pump (212 A ; 210A) when t ransferring fue1 between said first fuel tank (215A, 215B; 209) and said combustion engine (101) characterised in that the system comprises elements to:

- dete mine, with the use of a representation of a power consumption for said first (212A; 210A) and second (212B; 210B) fuel pump, respectively, the presence of a first fuel flow error in said fuel system.

Vehicle (100), characterised in that it comprises a system accord.ing to c1a im 1 ^'7.