WO2017204718A1

WO2017204718A1 - A wheeled motor vehicle and a method for controlling the flow of electric power of an electric system of such a vehicle

Info

Publication number: WO2017204718A1
Application number: PCT/SE2017/050494
Authority: WO
Inventors: Ninos Poli
Original assignee: Scania Cv Ab
Priority date: 2016-05-25
Filing date: 2017-05-15
Publication date: 2017-11-30
Also published as: DE112017002140T5; SE1650726A1; SE539664C2

Abstract

A wheeled motor vehicle comprises an electric motor (4) config- ured to assist a driver of the vehicle to steer the vehicle and an electric system comprising an arrangement configured to provide electric power to the electric motor and other consumers (10-13) of electric power of the vehicle. A data collector is arranged to collect data useable for calculating/estimating a maximum electric power possibly needed for accurate function of the electric motor and a control unit (8) calculates/estimates said maximum electric power and controls the arrangement to have an amount of electric power possible to deliver to the electric motor exceeding said max- imum electric power.

Description

A wheeled motor vehicle and a method for controlling the flow of electric power of an electric system of such a vehicle TECHN ICAL FI ELD OF TH E INVENTION

The present i nvention relates to a wheeled motor veh icle comprising

• an electric motor configured to assist a driver of the vehicle to steer the vehicle, and

• an electric system comprising an arrangement configured to provide electric power to said electric motor and other consumers of electric power of said veh icle ,

as well as a method for control ling the flow of electric power of an electric system of a wheeled motor vehicle accordi ng to the preamble of the independent method claim .

The invention is not restricted to a special type of wheeled motor vehicles, although the invention is particularly applicable to uti lity vehicles in the form of trucks or lorries and buses, but the invention does also cover for i nstance tractors, wheel loaders and passenger cars.

Furthermore, the wheeled motor vehicle may have a propulsion system of any conceivable type, such as on ly having an i nternal combustion engine, in which said arrangement comprises a generator for providing electric power, such an internal combustion engine in combination with an electric machine in a hybrid vehicle in which electric power for said electric motor may then be pro- vided also through a DC/DC converter of the hybrid system , or a purely electrically driven vehicle in which the arrangement may provide electric power to said electric motor th rough such a converter. Electric batteries incl uded in the electric system may of course also be used for provide electric power to the electric motor.

Said electric motor may be a part of any known type of equipment used to assist a driver of a wheeled motor vehicle to steer the vehicle, but the invention is particularly directed to such equipment in the form of an EH PS ( Electro Hydraulic Power Steeri ng) or an EPS (Electric Power Steering) arranged in a truck, wh ich is a reason for hereinafter primari ly discussi ng the invention for that particular application thereof so as to ill umi nate the invention but accordingly not in any way restrict it thereto. EH PS will hereinafter be used when referri ng to said type of equipment but does then represent all other equipment of this type.

When drivi ng such a motor veh icle the electric system thereof may for different reasons be overloaded, which may be caused by particular operating conditions of the vehicle, and electric batteries of the vehicle may at the same ti me have a rather poor charging level . Would then a driving situation occur in which the EH PS is to be used there will possibly not be enough electric power available for accurate function of the EH PS and this may then be shut down which may be really life threatening . In the case of a hybrid vehicle such an overload may occur due to an unusually high consumption of electric power by members, such as fans, water pumps, compressors etc. , used to cool components of the hybrid system , which will then jeopardize the accurate function of the EH PS when needed. BACKG ROUN D ART

US 201 0/0006360 A1 discloses a hybrid veh icle which has an EH PS for assisting the driver of the vehicle to steer the vehicle. This vehicle is provided with a system addressing a possible battery defect arising during driving of the vehicle i n a high voltage power source of the vehicle taking care of supply of electric power to the EH PS by change of operating mode upon occurrence of such a defect. However, this document does not discuss the above problems of overloading the electric system so that there will not be enough electric power for accu rate function of the EH PS.

Also, US 2004/01 48075 describes a motor vehicle. SUMMARY OF TH E INVENTION

The object of the present invention is to provide a wheeled motor vehicle as well as a method of the type defined in the i ntroduction bei ng improved i n at least some aspect with respect to such motor vehicles and methods already known .

This object is with respect to the wheeled motor vehicle obtai ned by providing such a vehicle with the features listed in the characterizing part of appended patent claim 1 .

By having a data col lector configured to, during operation of the vehicle, collect data useable for calcu lating/estimating a maximum electric power possibly needed for accurate function of said electric motor in the existi ng drivi ng situation of the vehicle , and a un it configured to calculate/estimate said maxi mum electric power based on said data received from said data collector and to control the arrangement to have an amount of electric power possible to del iver to the electric motor in the existing driving situation exceeding said maxi mum electric power there wi ll always, in every driving situation of the vehicle, be enough electric power available for the electric motor, such as of an EH PS, so that this wi ll then function accurately even i n case of a suddenly occu rri ng driving situation requiring a maximum electric power to the EH PS, such as would the vehicle have to turn sharply on a dry road at a low speed.

Accordi ng to an embodiment of the invention said control unit is configured to, based on said data received from said data collector, determi ne whether a change of the operation of said arrange- ment is to be carried out for obtaining a said amount of electric power possible to deliver to the electric motor. Thus, it is by this achieved that no action has to be taken with respect to the control of said arrangement if not really necessary for ensuring that enough electric power would be available for the electric motor i n the existing driving situation .

Accordi ng to another embodiment of the i nvention the control un it is configured to control said arrangement to reduce the electric power delivered to said other consumers wou ld said amount of electric power not be available for the electric motor . This means that the feed of electric power to consumers not critical for the proper function of the vehicle wil l then be reduced for ensuri ng that said amount of electric power is available for the electric motor and by that for the EH PS when needed. Accordi ng to another embodiment of the i nvention said control unit is configured to control said arrangement to increase the electric power available for being delivered to said electric motor and other consumers of electric power would said amount of electric power not be available for the electric motor. This constitutes another efficient and reliable option to ensu re that the EH PS has enough power to fu nction accurately irrespectively of the conditions prevailing . Accordi ng to another embodiment of the i nvention said data collector comprises a member config ured to measu re the system voltage of said electric system , and said control u nit is configu red to determi ne that there is a need to increase the amount of electric power available for said electric moto r when the system voltage measured is below a predetermi ned level for a predetermined period of time. An overload of the electric system resulting in a need to increase the amou nt of electric power available for said electric motor may reliably be determined in this way. Accordi ng to another embodiment of the i nvention said data collector comprises a member config ured to measure the consu mption of electric power by said other consu mers of electric power, and said control u nit is configured to compare a value of the consumption of electric power measured with a value of a maxim um electric power, wh ich may be provided by said arrangement in the existing driving situation , and to reduce the electric power delivered to said other consumers or increase the electric power available for being delivered to said electric motor and other consumers if the difference between these val ues is less than said amount. It is by th is ensured that there will be enoug h electric power available for an accurate function of the EH PS irrespectively of the existi ng and approaching drivi ng situation of the vehicle. Accordi ng to another embodiment of the i nvention said data collector is configured to collect said data i n the form of the condition of the surface of the road the vehicle is drivi ng on . Such data could indicate how much electric power may be needed for an accurate function of the EH PS, and the same apply for data in the form of the velocity of the veh icle, which said data collector is configured to collect according to another embodiment of the i nvention .

Accordi ng to another embodiment of the i nvention said data collector comprises a G PS (Global Positioning System) device con- fig ured to collect said data i n the form of the extension of the road the vehicle is driving on . The use of a G PS device to collect such data makes it possible to predict the amount of electric power that may be needed for accurate function of the EH PS, since this data will tel l the control unit of the vehicle if the vehicle is approaching any location where the EH PS may be needed, such a sharp turn , a roundabout etc.

Accordi ng to another embodiment of the invention said control unit is in case of receiving data from said G PS device informing about a substantially straig ht road over a distance above a predetermined length ahead of the veh icle configured to leave said arrangement as it is irrespectively of other said data collected by said data collector. Accordi ngly, the control unit will then leave said arrangement as it is even if it is calculated or esti mated that there will not be enoug h electric power for an accurate function of the EHPS would this require much power, since the GPS device informs that the EHPS will in any case not be needed at all for a certain time of travel corresponding to said predetermined length, which perhaps may be 200 m - 2 km.

According to another embodiment of the invention said control unit is configured to control said arrangement to have an amount of electric power possible to deliver to the electric motor exceeding said maximum electric power in case of receiving data from said GPS device informing that the vehicle is approaching a location, such as a turn of the road or a roundabout, where the vehicle may possibly change direction. Thus, the control unit will then ensure that there will be enough electric power available for accurate function of the EHPS when there is a real need to engage the EHPS.

According to another embodiment of the invention said data collector is configured to collect said data in the form of the state of a direction indicator of the vehicle, and said control unit is config- ured to delay a control of said arrangement until said direction indicator is actuated. This means that the control unit is prevented from unnecessarily controlling said arrangement when the vehicle is approaching a turn or a roundabout but not carrying out a turn, such as in an intersection.

According to another embodiment of the invention the motor vehicle comprises at least one electric machine for the propulsion of the vehicle with components associated therewith, such as electric batteries, an inverter, a DC/DC-converter etc., as well as members configured to cool these components, and the control unit is config ured to control said arrangement to reduce the electric power del ivered to said cool ing members would said amount of electric power not be avai lable for the electric motor. This constitutes a favourable way to ensure that enoug h electric power will be available for said electric motor, since there wi ll be no harm caused by shortly reducing the electric power fed to these cooling members, and a substantial reduction of electric power may be obtained by such a reduction .

Accordi ng to another embodiment of the i nvention said electric system comprises an arrangement with a service battery, a start battery connected in parallel with the service battery, consumers of electric energy comprising a start motor connected between op- posite poles of the service battery on a consumer side thereof opposite to the side for con nection of the service battery to the start battery and a switch arranged between one pole of the service battery and one pole of the start battery so as to enable closi ng and opening of a current path between the start battery and said consumer side of the service battery, said switch is normally open during driving of the vehicle, and the control u nit is configu red to control said arrangement to increase the electric power available for being delivered to said electric motor and other consumers of electric power by controlli ng said switch to close said current path between the start battery and the consumer side of the service battery would said amount of electric power not be available for the electric motor. The connection of said start battery to the consumer side of the service battery is an efficient measure to be taken when more electric power is needed for ensu ring an appro- priate function of the EH PS of the vehicle, si nce the start battery of such an electric system will have a high chargi ng degree even if the consumption of electric power of said consumer is that hig h that the charging degree of the service battery is low. Accordi ng to another embodi ment of the invention said electri c motor is a part of an EH PS (Electro Hydraulic Power Steering) , an EPS ( Electric Power Steering) or an EST (Electric Steered Tag axle) . The object of the present invention is with respect to the method obtained by providing a method according to the appended independent method claim . The advantages of such a method appear clearly from the above discussion of a motor vehicle accordi ng to the present invention .

The i nvention also relates to a computer program , a computer program product and an electronic control unit havi ng the features of the claims directed to a computer prog ram , a computer program product and an electronic control unit, respectively.

Other advantageous features as well as advantages of the present invention appear from the description followi ng below.

BRI EF D ESCRI PTION OF TH E DRAWINGS

With reference to the appended drawings, below fol lows a specific description of embodiments of the i nvention cited as examples.

In the drawings: Fig 1 is a si mplified view illustrating a wheeled motor veh icle of the type to wh ich the present invention relates,

Fig 2 is a schematic view of parts of a motor veh icle relevant for a first embodiment of the invention i n a drivi ng situation of the vehicle, is a view correspondi ng to Fig 2 of the vehicle i n another driving situation , are views corresponding to Figs 2 and 3 for a vehicle according to a second embodiment of the invention , is a flow chart illustrating the steps carried out in a method according to an embodi ment of the invention , and

Fig 8 is a schematic view i llustrating an electronic control unit for implementing a method according to the invention .

DETAILE D DESCRI PTION OF EMBODI M ENTS OF TH E INVENTION

Fig 1 illustrates schematical ly a wheeled motor vehicle 1 in the form of a truck with a front axle 2, which in a conventional way can be steered by connection to the vehicle's steering wheel 3. An electric motor 4 as a part of an EH PS (Electrio Hydraulic Power Steering) 5 is configured to assist a driver of the veh icle to steer the vehicle. The vehicle has an electric system 6 indicated by a box with an arrangement 7 configu red to provide electric power to the electric motor and other consumers of electric power of the vehicle. The vehicle has an electronic control unit 8 configured to control the electric system of the vehicle. Fig 2 illustrates schematically a part of the electric system of a motor vehicle according to a first embodiment of the invention in which said arrangement in the case of a hybrid vehicle has a DC/DC converter 9 configured to provide electric power to the electric motor of the EH PS 5 and other consumers 10-13 of electric power. In the case of a motor vehicle having only an internal combustion engine for the propulsion thereof the box 9 stands for a generator. The arrangement thus also includes 24V service batteries 14 of the vehicle. In case of a hybrid vehicle the consumers of electric power 10-13 may include members for cooling compo- nents associated with the electric machine of the vehicle, such as electric batteries, an inverter, the DC/DC converter etc., in the form of cooling fans 10, water pumps 11 and compressors 12. The vehicle has of course many more consumers of electric power, such as heaters, lightening, music players, etc., which are left out here for simplicity. It is shown by the dashed lines 15, 16 how the EHPS 5 and said consumers of electric power are fed by electric power through the converter/generator 9 and possibly also through the service batteries 14 when needed. The vehicle has a data collector 17 configured to, during operation of the vehicle, collect data useable for calculating/estimating a maximum electric power possibly needed for accurate function of the EHPS 5 in the existing driving situation of the vehicle. Said data collector 17 can in accordance with some embodiments comprise a member 18 configured to measure the system voltage of the electric system and provide the control unit 8 with results from these measurements. In accordance with some embodiments the data collector can also comprises a GPS device 19 configured to collect data in the form of the extension of the road the vehicle is driving on and sending these data to the control unit 8. In the case of a hybrid vehicle the total amount of electric power fed by the converter 9 to the consumers 10-13 and the EHPS is reported to the control unit 8.

The control unit 8 is configured to calculate/estimate the maximum electric power possibly needed for accurate function of the EHPS based on the data received from the data collector 17 and to control said arrangement to have an amount of electric power possible to deliver to the EHPS 5 in the existing driving situation exceeding said maximum electric power. Fig 3 illustrates how such control may be carried out in case of a calculation or estimation that the electric power that may be provided to the EHPS 5 and the consumers of electric power 10-13 is not high enough for ensuring that the EHPS 5 will get enough electric power with the existing fed of electric power to said consumers. The control unit 8 may have received information about the consumption of the electric power of said consumers 10-13 from a member 40 which is that high that there will not be sufficient electric power available for accurate function of the EHPS 5 under certain circumstances, such as a need to make a sharp turn on a dry road surface at low speed. In the case of a hybrid vehicle said consumption may for example be 6.5 kW and it is known that the maximum power that may be provided through the converter 9 is 7 kW and a maximum electric power possibly needed for an accurate function of the EHPS 5 may be 2 kW. In such a case the control unit 8 will control said consumers 10-13 in order to consume less power, e.g. reduce the r.p.m. of them or shutting all or some of them down. In case of presence of said cooling members as consumers 10-12 these may consume a lot of power and readily overload the electric system. However, the control unit may then also consider information received from the GPS device 19 and decide to leave the feeding of electric power as illustrated in Fig 2 even if a said too high consumption of electric power by the consumers 10-13 is reported would the GPS device inform about a substantially straight road over a distance above a predetermined length ahead of the vehicle, which means that said maximum electric power possibly needed for accurate function of the EHPS 5 will be low in the existing driving situation of vehicle. The control unit 8 is, however, configured to control said arrangement to have an amount of electric power possible to deliver to the EHPS 5 exceeding said maximum electric power in case of receiving data from the GPS device 19 informing that the vehicle is approaching a location, such as a turn of the road or a roundabout, where the vehicle may possibly change direction. Such information from the GPS device 19 may then cause a change of feeding of electric power as illustrated in Fig 3. This change of feeding of electric power may also be caused by a measurement result of the member 18 showing that the system voltage is below a predetermined level for a predetermined period of time.

The data collector 17 may also, such as through the GPS device 19, collect data in the form of the condition of the surface of the road the vehicle is driving on and this and also the velocity of the vehicle may be used by the control unit 8 to calculate the maximum electric power possibly needed for accurate function of the EHPS 5. Furthermore, it is possible to have the control unit 8 configured to reduce the feed of electric power to some consumers of electric power of the vehicle when the veh icle is approaching a location where the EH PS 5 is predicted to be used irrespectively of how much electric power is available for the function of the EH PS 5 as a safety measure. Heati ng of the vehicle and other not critical consumers of electric power will then for instance be automatically switched off until such a location has been passed by the vehicle. This eli minates the risk of dips of the system voltage of the electric system which may cause flickering of the head l ig hts of the vehicle which would not be acceptable and even more serious, the EH PS may be sh ut down . Furthermore, for not unnecessarily changi ng or interrupting the feed of electric power to said other consumers 1 0- 1 3 of the vehicle the control u nit 8 may be config ured to consider information from a direction indicator of the vehicle and to make a said change on ly if such information indicates that the vehicle will really make a turn when approachi ng for instance an intersection . It is also possible that the control unit may receive information from the steering wheel of the veh icle that a change of di rection is started and then control said arrangement to change the way of feeding of electric power carried out by said arrangement, such as from the situation shown i n Fig 2 to that shown in Fig 3.

Fig 4 i llustrates schematically the appearance of the electric sys- tern of a motor vehicle accordi ng to a second embodi ment of the invention having besides the service batteries 1 4 two start batteries 20 connected i n parallel with the service batteries. On ly one consumer 21 of electric energy besides the EH PS 5 is shown here, but there are of course a n umber of such consumers. This con- sumer is here considered to be a start motor connected between opposite poles 22, 23 of the service batteries on the consumer side thereof opposite to the side for con nection of the service batteries to the start batteries. A switch 24 is arranged between on e pole 22 of the service batteries and one pole of the start batteries so as to enable closing and opening of a current path between the start batteries and the consumer side of the service batteries. The switch is normal ly open as ill ustrated in Fig 4 duri ng driving of the vehicle. But the switch 24 is closed before all types of start motor starts, i .e. when the combustion engine is started by means of the start motor. This also includes start motor starts in "engine-pause"- position which takes place in stop/start-situations and electrical operation . The switch 24 is then kept closed sufficiently long for completely recharging the start batteries before opening . The control unit 8 is config ured to control said arrangement to increase the electric power avai lable for bei ng delivered to the EH PS and other consumers of electric power by controlli ng the switch 24 to close said current path between the start batteries and the consumer side of the service batteries would the amount of electric power needed for the EH PS not be available. The control unit 8 may for deciding upon how to control the switch 24 receive the same type of information as disclosed above wh ile maki ng reference to Figs 2 and 3, such as from a G PS device, a member measuring the system voltage, a member measuring the consumption of electric power by consumers, the velocity of the vehicle, the condition of the surface of the road the veh icle is driving on , actuation of a direction indicator etc. It is shown in Fig 4 that the EH PS 5 is operating and that the generator/converter 9 may provide enough electric power for accurate function of the EH PS 5. It is shown in Fig 5 that the converter/generator 9 is not able to alone provide enough electric power to the EH PS 5, so that electric power is also fed to the EH PS from the service batteries 1 4. The control unit 8 may now have received data through which it has determined that there is a need to increase the electric power avai lable to be fed to the EHPS 5 and do for that sake control the switch 24 to close, so that electric power may also be fed from the start batteries 20 to the EHPS 5, which is shown in Fig 6. Such closing of the switch 24 may also be combined with other measures such as temporarily reducing the feed of power to not critical consumers o r completely disconnect them , and the switch 24 may also be controlled to au- tomatically be closed before each turn to be carried out by the vehicle.

Fig 7 ill ustrates a flow chart of a method according to an embodiment of the present invention carried out for control ling the flow of electric power of an electric system of a wheeled motor veh icle of the type shown in Figs 1 -6. The method is started with a step S i by col lecting data useable for calculating/estimating a maximum electric power possibly needed for accurate function of an electric motor of an EH PS. Said maximum electric power is then calcu- lated/estimated i n a step S2. The question : Is more electric power than said maxi mum electric power avai lable to be delivered to the EH PS? is then asked in a step S3. If the answer to this question is "No" the method is continued through a step S₄ of controlli ng the arrangement to make enoug h electric power available for the fu nc- tion of the EH PS.

Computer program code for i mplementing a method accordi ng to the invention is with advantage incl uded in a computer program which can be read into the internal memory of a computer, e.g . the internal memory of an electronic control unit of a motor vehicle. Such a computer program is with advantage provided via a computer program product comprising a data storage medium which can be read by a computer and which has the computer program stored on it. Said data storage medium is for example an optical data storage medium in the form of a CD ROM disc, a DVD disc etc. , a magnetic data storage medi um i n the form of a hard disc, a diskette, a cassette tape etc. , or a flash memory or a memory of the ROM, PROM , EPROM or EEP ROM type. Fig . 8 illustrates very schematically an electronic control u nit 8 comprising an execution means 31 , e.g . a central processor unit (CPU), for execution of computer software. The execution means 31 commun icates with a memory 32, e.g . of the RAM type, via a data bus 33. The control unit 8 comprises also a non-transitory data storage medium 34, e.g . in the form of a flash memory or a memory of the ROM , PROM, EPROM or E EPROM type. The execution means 31 commu nicates with the data storage medium 34 via the data bus 33. A computer program comprising computer program code for i mplementing a method accordi ng to the invention , e.g . in accordance with the embodiment il lustrated in Fig . 7 is stored on the data storage medium 34.

The invention is of course in no way restricted to the embodiments described above, since many possibilities for modifications thereof are likely to be obvious to one ski lled in the art without havi ng to derivate from the scope of i nvention defined in the appended claims.

It is pointed out that it is with in the scope of the invention to have the control u nit to not carry out any calculatio n but only an estima- tion , such as in the form of, when receiving data about a turn coming , an automatic disconnection of certain consumers of electric power, such as said cooling members, heaters or the like. It is also poi nted out that the i nvention ensures that the maxi mum electric power needed for the electric motor in the existing driving situation is always made available, but this amount has not to be as high as the amount the electric motor may need under other conditions as appears from the dependent claims. The data collector configured to collect data useable for calculating/esti mating a maxi mum electric power possibly needed for accurate fu nction of the electric motor in the existing driving situation of the vehicle may be embodied in n umerous different ways of which some have been described i n the above disclosure.

Claims

A wheeled motor vehicle comprising

• an electric motor (4) configured to assist a driver of the vehicle to steer the vehicle,

• an electric system comprising an arrangement (7) configured to provide electric power to said electric motor and other consumers (10-13) of electric power of said vehicle,

• a data collector (17) configured to, during operation of the vehicle, collect data useable for calculating/estimating a maximum electric power possibly needed for accurate function of said electric motor (4) in the existing driving situation of the vehicle, and

• a unit (8) configured to calculate/estimate said maximum electric power based on said data received from said data collector and to control said arrangement (7) to have an amount of electric power possible to deliver to the electric motor (4) in the existing driving situation exceeding said maximum electric power, characterized in that said data collector comprises a GPS (Global Positioning System) device (19) configured to collect said data in the form of the extension of the road the vehicle is driving on, that said control unit (8) is in case of receiving data from said GPS device (19) informing about a substantially straight road over a distance above a predetermined length ahead of the vehicle configured to leave said arrangement as it is irrespectively of other said data collected by said data collector (17), that said control unit (8) is configured to control said arrangement (7) to have an amount of electric power possi- ble to deliver to the electric motor (4) exceeding said maximum electric power in case of receiving data from said GPS device (19) informing that the vehicle is approaching a location, such as a turn of the road or a roundabout, where the vehicle may possibly change direction, that said data collector (17) is configured to collect said data in the form of the state of a direction indicator of the vehicle, and that said control unit (8) is configured to delay a control of said arrangement (7) until said direction indicator is actuated.

A motor vehicle according to claim 1, characterized in that said control unit (8) is configured to, based on said data received from said data collector(17), determine whether a change of the operation of said arrangement (7) is to be carried out for obtaining a said amount of electric power possible to deliver to the electric motor (4).

A motor vehicle according to claim 1 or 2, characterized in that the control unit (8) is configured to control said arrangement (7) to reduce the electric power delivered to said other consumers (10-13) would said amount of electric power not be available for the electric motor.

A motor vehicle according to any of the preceding claims, characterized in that said control unit (8) is configured to control said arrangement (7) to increase the electric power available for being delivered to said electric motor (4) and other consumers (10-13) of electric power would said amount of electric power not be available for the electric motor. A motor vehicle according to any of the preceding claims, characterized in that said data collector comprises a member ( 18) configured to measure the system voltage of said electric system , and that said control unit (8) is configured to determine that there is a need to increase the amou nt of electric power available for said electric motor (4) when the system voltage measured is below a predetermined level for a predetermined period of time.

A motor vehicle according to any of precedi ng claims, characterized in that said data collector comprises a member (40) configured to measure the consumption of electric power by said other consumers ( 1 0- 1 3) of electric power, and that said control unit (8) is configured to compare a value of the consumption of electric power measured with a value of a maximum electric power, which may be provided by said arrangement i n the existing driving situation , and to reduce the electric power delivered to said other consu mers or i ncrease the electric power available for being del ivered to said electric motor (4) and other consu mers ( 1 0- 1 3) if the difference between these values is less than said amount.

A motor vehicle according to any of the preceding claims, characterized i n that said data collector ( 1 7) is configu red to col lect said data in the form of the condition of the surface of the road the vehicle is driving on .

A motor vehicle according to any of the preceding claims, characterized i n that said data collector ( 1 7) is configu red to col lect said data in the form of the velocity of the vehicle. A motor vehicle accordi ng to claim 3, characterized in that it comprises at least one electric machine for the propulsion of the vehicle with components associated therewith , such as electric batteries, an inverter, a DC/DC-converter (9) etc. , as wel l as members ( 1 0- 1 2) configu red to cool these components, and that the control unit (8) is configured to control said arrangement (7) to reduce the electric power delivered to said cooling members ( 1 0- 1 2) would said amount of electric power not be available for the electric motor.

A motor vehicle according to any of the preceding claims, characterized in that said electric system comprises an arrangement (7) with a service battery ( 1 4) , a start battery (20) con nected in paral lel with the service battery, consu mers of electric energy comprisi ng a start motor (21 ) con nected between opposite poles of the service battery on a consumer side thereof opposite to the side for connection of the service battery to the start battery and a switch (24) arranged between one pole of the service battery and one pole of the start battery so as to enable closing and opening of a current path between the start battery (20) and said consumer side of the service battery ( 1 4) , that said switch is normal ly open during driving of the vehicle, and that the control unit (8) is configured to control said arrangement (7) to increase the electric power available for being delivered to said electric motor (4) and other consumers of electric power by controlling said switch (24) to close said current path between the start battery (20) and the consumer side of the service battery ( 1 4) would said amount of electric power not be available for th e electric motor.

A motor vehicle according to any of the preceding claims, characterized in that said electric motor (4) is a part of an EH PS (5) (Electro Hydraul ic Power Steering) , an EPS (Electric Power Steering) or an EST (Electric Steered Tag axl e) .

A method for controlling the flow of electric power of an electric system of a wheeled motor vehicle, said motor vehicle ( 1 ) comprisi ng an electric motor (4) config ured to assist a driver of the vehicle to steer the veh icle and said electric syste m comprisi ng an arrangement (7) configured to provide electric power to said electric motor (4) and other consumers ( 1 0- 1 3) of electric power of said vehicle, comprising the steps of

• collecting data, during operation of the vehicle, useable for calculating/estimating a maximum electric power possibly needed for accurate function of said electric motor (4) in the existi ng driving situation of the vehicle,

• calculating/estimating said maximum electric power based on said data collected,

• controlling said arrangement to have an amou nt of electric power possible to del iver to the electric motor (4) in the existing driving situation exceeding said maximum electric power,

characterized in that said collecti ng step comprises collecting of data in the form of the extension of the road the vehicle is driving on by use of a G PS (Global Positioning System) device, that in case of collecting data through said G PS device informing about a substantially straight road over a distance above a predetermined length ahead of the vehicle said arrangement is left as it is irrespectively of other said data collected, that controlling of said arrangement to have an amount of electric power possible to deliver to the electric motor ex- ceeding said maximu m electric power is carried out i n case of having collected data throug h said G PS device informing that the vehicle is approach ing a location , such as a turn of the road or a roundabout, where the vehicle may possib le change direction , that data is also collected in the form of the state of a di recti ng indicator of the vehicle, and that a said controlling of said arrangement is delayed until said direction indicator is actuated. 3. Computer program comprising computer prog ram code for causing a computer to implement a method accordi ng to clai m

1 2 when the computer program is executed in the computer. 4. A computer program product comprisi ng a non -transitory data storage medium (34) which can be read by a computer and on which the program code of a computer prog ram according to claim 1 3 is stored. 5. An electronic control unit of a motor vehicle comprising an execution means (31 ) , a memory (32) connected to the execu- tion means and a non-transitory data storage medi um (34) which is connected to the execution means (31 ) and on which the computer program code of a computer program according to claim 1 3 is stored.