SE542604C2 - A method for controlling an electrical steering system and an electrical steering system - Google Patents

Abstract

Methods and systems for controlling an electrical steering system are described. The electrical steering system can be a power steering system or a steer-by-wire system. The electrical steering system provides an assisting steering torque boost in response to a boost curve, where the boost curve defines a relationship between at least one input parameter and the current assisting steering torque boost provided by the electrical steering system. The electrical steering system has at least two boost curves, and the electrical steering system switches from use of a first boost curve of the at least two boost curves to use of a second boost curve of the at least two boost curves in response to one or more pre-defined condition(s). Hereby a driver can for example more easily conduct an emergency situation maneuver and feel a better support from the steering system of the vehicle because the assistance from the second boost curve can be higher than the assistance from the first boost curve.

Description

lO Å TÄETHOD FOR CGNTRÜLLENG AN ELECTRECALSTEERiNG SYSTEM AND AN ELECTRECÅL STEERENG SYSTEM Technical field The invention relates to a system, a method and a computer program for steeringof a vehicle. ln particular the invention relates to a system, a method and acomputer program for steering of a vehicle provided with electrical steering, suchas power steering or steer-by-wire steering.

Background Today different types of electrical steering systems have become more and morecommon in vehicles such as cars, trucks, buses and other motorized vehicles. Theelectrical steering systems can for example be a power steering system thatoperates as the sole servo device or a power steering system supplemented by ahydraulic servo steering system. Combinations of power steering systems andhydraulic steering servo systems are typically more common in heavier vehiclessuch as trucks and buses. ln addition so-called steer-by-wire systems are nowbeing introduced in some vehicles. ln a steer-by-wire system there is no directmechanical linkages between the steering wheel and the wheels. The control ofthe direction of the wheels is instead established through electric motor(s) whichare actuated by electronic control units that senses the steering wheel input fromthe driver.

When using a power steering system or a steer-by-wire system, the applied powerfrom the electrical steering system is typically controlled by one or moreparameters. The parameters can for example be the steering torque applied by thedriver, the steering angle, and the vehicle velocity. The additional torque providedby the electrical steering system to assist the driver is then set in relation to thecurrent value of the parameters. Known electrical steering systems for assisting adriver are for example set out in US patent No. 6,134,490 and US patentapplication No. 2009/0259367.

The assisting torque provided by the electrical steering system typically follows acurve that amplifies the torque provided by the driver. The amplifying curve can be lO termed a boost curve. The boost curve sets out a relationship between the driverapplied input torque and/or other parameter values and the assisting torque thatan electrical motor of the electrical steering system generates. The boost curvemay in a very simple system take the form of a straight line that is proportional tothe driver applied input torque. ln a conventional implementation application, theboost curve has several features which provide for an improved driver feel. lt is forexample desired to provide for a low gain of the curve for small input torques. Withlow gain, the electrical assisting torque is small. This ensures that the steeringsystem is not unnecessarily sensitive to very small adjustments in input torquewhen travelling in a straight line. Another desirable feature of a boost curve is thatthe gradient of the curve is high at high levels of input torque for example duringmaneuvers at low-speed such as parking maneuvers. lf the gradient of the boostcurve is high, the boost curve can be said to have a high gain. Also it is typicallydesired that there is a smooth transition between low gain of the boost curve forlow input torques and high gain of the boost curve. A sudden step changes in theboost curve would be felt by the driver and could generate an unwanted steeringfeel, see also US patent No. 6, 282,472. ln sum, the boost curve is typicallyinverse proportional to the torque on the wheel felt by the driver so that theassistance of the electrical steering system is higher the higher torque that isapplied by the driver. The boost curve will typically follow a continuous curve thatfollows the applied torque and possibly some other parameter(s) such as thespeed of the vehicle. ln Fig. 1 an exemplary boost curve is depicted. The boost curve in Fig.1 showsthat the higher the torque applied by the driver, regardless of the direction of thetorque applied by the driver, the more assisting torque from the electrical steeringsystem is received. A negative value of the torque applied by the drivercorresponds to a torque in the direction opposite to when the torque applied is apositive value. Also the assisting torque is shown as the absolute value of theassisting torque. ln other words, the assisting torque is always acting in the samedirection as the torque applied by the driver when following the boost curve in Fig.1. ln particular the assisting torque can be non-linear as shown by the boost curvein Fig. 1. lt is also possible that the assisting torque is determined by more than lO parameter. For example both the driver applied torque and the vehicle speed can be used to determine the assisting torque as set out in the boost curve.

There is a constant desire to improve the steering in motorized vehicles. This alsoapplies to motorized vehicles provided with an electrical steering system such as apower steering system or a steer-by-wire system. Hence, there is a need for animproved electrical steering system for motorized vehicles. At the same time it isadvantageous if the electrical steering system behaves in a predictable manner that the driver feels is safe and comfortable.

Summary lt is an object of the invention to provide an improved steering of a vehicle.

This object and or other objects can, at least partly, be obtained by the electricalsteering system, the method and the computer program product as set out in the appended claims.

The inventor has realized that in some situations there is a need for a highincrease in assisting torque from the electrical steering system. For exampleduring an evasive maneuver it can be advantageous to suddenly provide asignificantly increased assisting torque. At the same time the assisting torqueshould preferably not be applied in a stepwise manner which could be interpretedby the driver as a lost in control of the vehicle in that the steering of the vehicle isfelt to be unpredictable. ln sum it would be desired to be able to apply asignificantly higher torque in some situations. At the same time it would also beadvantageous to maintain a feel of the driver that the additional torque is not applied in a single step.

By utilizing at least two different boost curves, wherein one of the boost curves atthe time determines the applied assisting torque and by switching between thedifferent boost curves based on a pre-determined threshold value of one or moreparameters, a fast transition to a state where a high assisting torque is applied canbe achieved. By using at least two different boost curves that one at the timedetermines the current assisting torque given to the driver, the electrical steering lO system can be made to switch from one, first, boost curve giving a relatively lowadditional torque to another, second, boost curve giving a higher torque with thesame input parameter value(s) in response to some pre-determined eventoccurring. By using, at least, two different boost curves the electrical steeringsystem is able to switch to a boost curve giving a higher assisting torque if aparticular condition is determined to exist. For example if it is, based on someinput parameter(s), determined that the driver is conducting an evasive maneuver,the electrical steering system can switch to another boost curve providing moreassisting torque at the same set of input parameter value(s). ln order for the drivernot to feel a step change in applied additional torque from the electrical steeringsystem, the transition from one boost curve to another boost curve can take placeduring a short transition period. During the short transition period the electricalsteering system can advantageously be configured to interpolate between theassisting torque associated with the first boost curve and the assisting torqueassociated with the second boost curve at the current set of input parameter value(s). ln accordance with one embodiment a method for controlling an electrical steeringsystem is provided. The electrical steering system can be a power steering systemor a steer-by-wire system. The electrical steering system provides an assistingsteering torque boost in response to a boost curve, where the boost curve definesa relationship between at least one input parameter and the current assistingsteering torque boost provided by the electrical steering system. The electricalsteering system has at least two boost curves, and the electrical steering systemswitches from use of a first boost curve of the at least two boost curves to use of asecond boost curve of the at least two boost curves in response to one or morepre-defined condition(s). Hereby a driver can more easily conduct an emergencysituation maneuver and feel a better support from the steering system of thevehicle because the assistance from the second boost curve can be higher than the assistance from the first boost curve.

Ihe pre-defined condition is one or morethreshold value(s)-.-fiT-he»-thiresheäei--vai-ueçsši-ean--be--a--vaiue based on one or more of lO the following parameters: steering torquefvehieiesfpw, steering angle, steeringangle derivative, steering torque derivative, ESP sensor value, ABS sensor value,and TCS sensor value. ln accordance with one embodiment the switch from a first boost curve to asecond boost curve takes place during a transition period and during saidtransition period, the assisting steering torque is a steering torque given by aninterpolation of the first and second boost curve values. Hereby it is avoided that the driver feels a step change in the applied assisting torque. ln accordance with one embodiment the electrical steering system upon detectionthat the at least one or more pre-defined condition(s) is satisfied switches to thesecond boost curve in less than 50 ms. ln accordance with one embodiment the electrical steering system switches backfrom the second boost curve to the first boost curve in response to one or morepre-defined condition(s).

The disclosure also extends to a system for aiding a driver in a vehicle providedwith an electrical steering system adapted to follow the above methods and to avehicle provided with such an electrical steering system. Also disclosed areinstructions for a software program that can be used for implementing the method.The software program instructions can be in the form of a computer programproduct or a computer program. The hardware used to execute the software cancomprise one or many processors that can be arranged to execute software storedin a readable storage media. The processor(s) can be implemented by a singlededicated processor, by a single shared processor, or by a plurality of individualprocessors, some of which may be shared or distributed. Moreover, a processoror may include, without limitation, digital signal processor (DSP) hardware, ASIChardware, read only memory (ROM), random access memory (RAM), and/or otherstorage media. lO Brief description of the drawinqs The invention will now be described by way of non-Iimiting examples, and withreference to the accompanying drawings, in which: - Fig. 1 is a view of an exemplary conventional boost curve, - Fig. 2 is a general view of a vehicle provided with an electrical steering system,- Fig. 3 depicts a power steering system,- Fig. 4 depicts the use of two boost curves,- Fig. 5 illustrates switching between two boost curves,- Fig. 6 is a detail of Fig. 5, - Fig. 7 is a view illustrating some hardware components in an electricalsteering system, - Fig. 8 is a flowchart illustrating some steps performed in an electricalsteering system, and - Fig. 9 is a view of a controller device for controlling the assisting torque inan electrical steering system.

Detailed Description ln the following, a detailed description of the invention will be given. ln the figures,like reference numerals designate identical or corresponding elements throughoutthe several figures. lt will be appreciated that these figures are for illustration onlyand are not in any way restricting the scope of the invention. The descriptionbelow refers to an electrical steering system for a vehicle. A vehicle can typicallybe any motorized road vehicle such as a car, a lorry, a bus or a truck. Theelectrical steering system can also be implemented in any other vehicle. Also it ispossible to combine features from different described embodiments to meetspecific implementation needs. lO ln Fig. 2 a vehicle 100 represented as a truck is shown. The vehicle 100 isprovided with a steering mechanism 102. The steering mechanism 102 cantypically be a steering wheel as shown in Fig. 2, but could also be anothermechanism such as a stick. The steering mechanism 102 is operatively connectedto an electrical steering system 104. The electrical steering system 104 cantypically be a power steering system or a steer-by-wire system or any similarsystem where some or all of the steering power to the vehicle 100 is provided by the electrical steering system 104. ln Fig. 3 an exemplary steering system comprising an electrical steering system104 is depicted. ln the example of Fig. 3 the electrical steering system is a powersteering system, but the teachings herein are equally applicable to a steer-by-wiresystem. The steering system comprises a steering mechanism 102. ln Fig. 3, thesteering mechanism 102 is a steering wheel. By controlling and rotating thesteering wheel the driver can control the direction of the vehicle in accordance withthe intention of the driver via a steering column 106. The intentions of the drivercan be facilitated by the electrical steering system 104. Typically, the electricalsteering system 104 comprises a controller 108 and a motor 110. The controller108 can be a micro-computer adapted to control the motor 110 to provide anassisting steering torque in response to one or many input parameters. Typically,the input parameter(s) is/are one or more of a steering torque applied by thedriver, a vehicle speed and a steering angle. Other input parameters could also beused. ln some embodiments a power steering system can be supplemented by ahydraulic servo steering system 112. ln such an embodiment an assisting torque isadded by the electrical steering system, but the vehicle also relies on a hydraulicservo to provide additional torque. By adding the electrical steering system it ispossible to provide different steering feels for the driver at different driving conditions.

As set out above, the assisting steering torque provided by the electrical steeringsystem can follow a boost curve. The boost curve represents a relationshipbetween one or more input parameter(s) and the current assisting steering torqueboost provided by the electrical steering system. ln accordance with some lO embodiments the electrical steering system has at least two boost curves and isadapted to switch from one boost curve to another when a certain condition isdetected. For example, in an emergency situation when a driver is required tomake fast direction changes, a normal boost curve may provide too little steeringtorque boost and the driver may feel that the vehicle is heavy to maneuver. Bydetecting the emergency situation and switching to another boost curve providinga higher steering torque boost, the driver can more easily conduct the emergencysituation maneuver and feel a better support from the steering system of thevehicle. Other situations when a high torque can be required are for exampleduring parking or similar actions. Such other situations can also be detected. ln Fig. 4 a view of two boost curves is shown. One boost curve labeled “normalboost curve” 401 and another boost curve labeled “emergency boost curve” 403are shown. As indicated by their names the normal boost curve 401 is the boostcurve applied by the electrical steering system during normal driving conditions. lnFig. 4 the boost curves are shown as the assisting boost provided for differentinput values of driver applied torque. lt is of course possible the assisting steeringtorque can depend on other or additional input parameters than the steeringtorque applied by the driver. Such other input parameters can be, withoutlimitation, steering torquefvehéele-epeed, steering angle, steering angle derivative,steering torque derivative. The boost curves in Fig.4 show that the higher thetorque applied by the driver, regardless of the direction of the torque applied by thedriver, the more assisting torque from the electrical steering system is received. Anegative value of the torque applied by the driver corresponds to a torque in thedirection opposite to when the torque applied is a positive value. Also the assistingtorque is shown as the absolute value of the assisting torque. ln other words, theassisting torque is always acting in the same direction as the torque applied by thedriver when following the boost curves in Fig. 4. ln particular the assisting torquecan be non-linear as shown by the boost curves in Fig. 4. ln general the differentboost curves used can be any boost curve that provides a good steering feel forthe driver. ln some embodiments the boost curves are continuous curves. ln some embodiments the boost curves used do not have any steps that can be felt by the lO driver or the boost curves do not have any steps that are felt to a degree which isuncomfortable for the driver. lf it is determined by the electrical steering system that an additional steeringtorque boost is desired, the electrical steering system can switch to using theboost curve 403. The driver will then receive more assisting steering torque. Theamount of additional steering torque received will typically depend on where on theboost curve the vehicle is currently operated, i.e. the current set of input parametervalue(s). For example, as is seen in Fig. 4, a switch to the “emergency boostcurve” 403 will provide for more assisting torque. Further in the example of Fig. 4the additional assisting torque is higher, the higher value of applied driver torque. ln Fig. 5 switching between two boost curves is illustrated in an exemplary drivingscenario. Fig. 5 depicts the torque generated as a function of time. The torque isthe combined torque generated by the driver and the electrical steering system,here a power steering system. ln Fig. 5 the steering wheel torque generated by thedriver and the assisting steering wheel torque generated by the power steeringsystem are shown separately. Further, in the example of Fig. 5, the driver firstdrives during normal driving conditions and the assistance from the power steeringsystem follows a first boost curve. The first boost curve can be the normal boostcurve 401 of Fig. 4. Then, at some time designated T1, the electrical steeringsystem in response to a detected condition triggers a change from using thenormal boost curve 401 to using another, second, boost curve. The second boostcurve can be the emergency boost curve 403 in Fig. 4. For example the electricalsteering system can detect a rapid movement in the steering wheel by, forexample, detecting a high value in the derivative of the steering wheel torque. lnthis example, when a threshold value, such as a value of the derivative of thesteering wheel torque is exceeded, the electrical steering system switches to theuse the emergency boost curve at a time T2. ln Fig. 6 a detail 'A' from Fig. 5 is shown. The time from when the need for anotherboost curve is detected until the another boost curve is applied should be short. ln a typical implementation the time from T1 to T2 is less than 50 ms, for example in the range 10 - 50 ms or even less than that. lf the switch time is made short thedriver will not feel the switch from one boost curve to another or the change willnot be felt to a degree which is uncomfortable. ln accordance with someembodiments the switch from one boost curve to another can take place during atransition period during which the electrical steering system interpolates betweenthe two boost curves during a short time period. Hereby the change will besmoothened even further. The time during which the interpolation takes place canbe less than 50 ms. ln Fig. 6 the interpolation can take place during the periodfrom T1 to T2. ln other words the transition can take place from when the conditiontriggering a switch to another boost curve until the another boost curve is reached.The transition period can typically be about or less than 50 ms. ln Fig. 5 a time T3 is also shown. The time T3 is when the need for an increasedassisting steering torque no longer exists as determined by the electrical steeringsystem. For example the emergency boost curve 403 is no longer needed. When itis determined that there is no longer a need for the increased assisting steeringtorque the electrical steering system can switch back to the normal boost curve401. The switch back can be determined based on any suitable condition. Forexample, it is possible to use the same input parameters as when switching to theemergency boost curve, but with potentially other threshold values. ln anotherembodiment the condition for switching back is a timer that times out when thetriggering condition has not existed for some pre-determined period of time. lt ispossible to switch back during a transition period using for example a low-passfilter whereby the switch back is smoothened so that the driver will not notice theswitch back. The time during which the electrical steering system switches backfrom the emergency boost curve to the normal boost curve can typically be longerthan the time during which the emergency boost curve is switched to. For examplethe time during which the emergency boost curve is switched to the normal boostcurve can be less than 200 ms. ln Fig. 7 various hardware components of the electrical steering system 104 aredepicted. The electrical steering system 104 comprises a micro-computer 108adapted to execute computer program instructions. The micro-computer 108 can lO 11 be adapted to receive different input parameters. Examples of parameters that canbe fed to the micro-computer can be one or more of the following parameters:vehicle speed, steering angle, steering torque, ESP (Electronic StabilityProgramme) parameters, ABS (Anti-lock breaking system) parameters TCS(Traction Control System) parameters. ln order to receive such parameters themicro-computer 108 can be operatively connected to one or more of a vehiclespeed sensor 714, a steering angle sensor 716, a steering torque sensor 718, anESP system 720, an ABS system 722 and a TCS system 724. Other parameterscan also be used by the electrical steering system such as yaw-rate sensor values and input values from individual wheels speed sensors.

The micro-computer 108 comprises functional modules adapted to perform varioustasks in conjunction with controlling the assisting steering torque of the electricalmotor 110. Such functional modules can comprise a differentiation module 702 forgenerating the derivative of one or more sensor values. For example thedifferentiation module 702 can determine the derivative of the steering torqueand/or the steering angle from received sensor values of the steering angle sensorand the steering torque sensor. The micro-computer can further comprise anemergency detection module 704 for determining when an emergency situation ispresent. The module 704 can also be adapted to detect other conditions that cantrigger a change in boost curve to be applied. The emergency detection modulecan for example be programmed to detect an emergency situation when a steeringangle derivative or a steering torque derivative exceeds a threshold value. ln otherexemplary embodiments the emergency detection module is programmed to useother parameters to determine the existence of an emergency situation. Theemergency detection module can then be programmed to compare any receivedor derived parameter with a threshold value or even to compare combination ofparameter values with threshold values to determine the existence of anemergency situation. The micro-computer 108 further comprises functionalmodules for storing different boost curves. ln Fig. 7 the different boost curves arerepresented by the normal boost curve module 706 and the emergency boostcurve module 708. lt is envisaged that there can be more than two different boostcurves in the system 104 that the micro-computer 108 can use when controlling lO 12 assisting torque applied by the motor 110. Further, the micro-computer 108 cancomprise an interpolation module 710. The interpolation module is adapted toderive values for the assisting torque to be provided by the motor 110 duringtransition from one boost curve to another boost curve. ln other words, as set outabove, it can be undesired to provide a step change in the assisting torqueprovided in accordance with a first boost curve when switching to the assistingtorque provided in accordance with a second boost curve. lnstead during atransition period the interpolation module 710 generates an assisting torque valueto be used that is an interpolation of the first and second boost curves. Theinterpolation can be any suitable interpolation that at the beginning of the transitionperiod sets the assisting torque. The micro-computer 108 can also comprise afault detection module 712. The fault detection module 712 can provide diagnosisof the system to prevent undesired events. For example, if both a torque sensorand a steering angle sensor are provided, the values should be correlated fromthese two sensors. lf the output values from the two sensors do not correlate, the fault detection module can prevent the triggering of the use of another boost curve. ln another example, the fault detection module can prevent using an emergencyboost curve for a too long time such that when a pre-determined time has lapsed,the fault detection module forces a return to a normal boost curve. ln Fig. 8 a flow chart illustrating some steps that can be performed in an electricalsteering system when controlling the (assisting) steering torque in a vehicle. Theprocedural steps illustrated in Fig. 8 can be seen as pseudo-code instructions for acomputer program that can be executed in a micro- processor of an electricalsteering system 104 of a vehicle. The steps are typically performed using a computer program stored in a memory accessible by a processor unit.

First, in a step 802, the electrical steering system is in an initial state and applyinga normal boost curve. Then, at some time, the electrical steering systemdetermines that another boost curve is to be applied in a step 804 by detecting aboost curve switch condition. The determination in step 804 can be based on oneor more parameters values. For example the electrical steering system can takeinto account one or more of the following input parameters: steering torque, lO 13 steering angle, steering angle derivative, steering torque derivative,ESP sensor value, ABS sensor value, and TCS sensor value. The parameters caneither be fed directly to the electrical steering system or in some cases derivedwithin the electrical steering system. ln accordance with one embodiment whenone of the input parameters exceeds a threshold value the electrical steeringsystem determines that the boost curve is to be changed. ln accordance withsome embodiments the electrical steering system forms a threshold value based on a combination of more than one input parameters.

Next, in a step 806, the electrical steering system selects which other boost curveto use if there are more than one boost curve to switch to. ln other words, therecan be many boost curves, more than two boost curves, and the electrical steeringsystem can select which boost curve to switch to based on, for example, whichinput parameter threshold value that has been exceeded. Then in a step 810, anew boost curve is applied. The transition to the new boost curve can inaccordance with some embodiments take place during a transition period duringwhich the electrical steering system interpolates between the old boost curve and the new boost curve. The interpolation can take place in a step 808.

When it is determined that the new boost curve is not to be applied any more theprocedure in Fig. 8 can return to the initial state with the old boost curve in step812. When returning to the initial state the electrical steering system can apply alow-pass filter in a step 814 in order to make the return transition smooth. ln analternative embodiment the procedure applies another boost curve than the boostcurve applied in step 802 when leaving the new boost curve in step 812. Thedetermination of when to leave the new boost curve in step 812 can be based onone or more pre-defined conditions such as the steering wheel torque being belowa threshold-value. The determination of when to leave the new boost curve canalso be made based on a timer that times out when the first one or moreconditions are not satisfied for a pre-determined period of time. When the timertimes out after, for example a few seconds, the old boost curve or another boost curve is applied. Leaving the new boost curve can also be determined by a fault lO 14 detection module. For example when a timer times out the system is forced to return to a normal boost curve.

Further, Fig. 9 is a view of a micro-computer 108 for processing signals in anelectrical steering system and to control a motor 110 of the electrical steeringsystem 104. The micro-computer 108 can comprise computer program modules min a memory 902 of a respective computer program comprising executableprogram code which, when run by a processor 904 causes the processor unit toperform the actions as described herein. The processor 904 may comprise asingle Central Processing Unit (CPU), or could comprise two or more processingunits. For example, the processor 904 may include general purposemicroprocessors; instruction set processors and/or related chips sets and/orspecial purpose microprocessors such as Application Specific Integrated Circuits (ASlCs). The processor 904 may also comprise a storage for caching purposes.

The memory 902 thus comprises a computer readable medium on which acomputer program is stored e.g. in the form of computer program modules For example, the memory 902 can be a flash memory, a Random-Access Memory(RAM), a Read-Only Memory (ROM) or an Electrically Erasable ProgrammableROM (EEPROM), and the program modules m could in alternative embodimentsbe distributed on different computer program products in the form of memorieswithin the micro-computer. The micro-computer 108 can further comprise acommunication interface 906. The communication interface 906 may be arrangedto receive different input parameters such as set out above. ln one embodimentthe communication interface 906 can comprise a chip set adopted forcommunication via a CAN bus (Controller Area Network) or communicationadopted to ISO 11898.

Using the systems, the methods, and computer programs as set out herein it ispossible to achieve an improved steering of a vehicle. This is achieved in that thesteering system is enabled to select different boost curves for different drivingconditions. Also, transition between different boost curves can be made in amanner that is felt safe and predictable by a driver of the vehicle.

Claims (15)

1. A method for controlling an electrical steering system (104) of a vehicle (100),wherein the electrical steering system provides an assisting steering torque boostin response to a boost curve, said boost curve defining a relationship between atleast one input parameter and the current assisting steering torque boost providedby the electrical steering system, characterized in that the electrical steeringsystem has at least two boost curves (401 ; 403), and wherein the electricalsteering system switches (810) from use of a first boost curve of said at least twoboost curves to use of a second boost curve of said at least two boost curves inresponse to one or more first pre-defined condition(s) and wherein the first pre-defined condition is one or more threshold value(s), and wherein the thresholdvalue(s) is a value based on one or more of the following parameters: steeringtorque, vei-wieše--speed-,- steering angle, steering angle derivative, steering torquederivative, ESP sensor value, ABS sensor value, and TCS sensor value.

2. The method according to claim 1, wherein the switch from a first boost curve toa second boost curve takes place during a transition period and that during saidtransition period, the assisting steering torque is a steering torque given by aninterpolation (808) of the first and second boost curve values.

3. The method according to any of claims 1 - 2, wherein the electrical steeringsystem upon detection that said at least one or more first pre-defined condition(s)is satisfied switches to the second boost curve in less than 50 ms.

4. The method according to any of claims 1 - 3, further comprising switching back(812) to the first boost curve in response to one or more second pre-defined condition(s).

5. The method according to any of claims 1 - 4, wherein said electrical steering system is a power steering system. lO 16

6. The method according to claim 5, wherein, the power steering system issupplemented by a hydraulic servo system (112) adapted to provide additionalservo steering torque.

7. An electrical steering system (104) for providing an assisting steering torqueboost in response to a boost curve in a vehicle (100), said boost curve defining arelationship between at least one input parameter and the current assistingsteering torque boost provided by the electrical steering system, characterized inthat the electrical steering system has at least two boost curves (401 ; 403), andwherein the electrical steering system is adapted to switch from use of a first boostcurve of said at least two boost curves to use of a second boost curve of said atleast two boost curves in response to one or more first pre-defined condition(s)and wherein the first pre-defined condition is one or more threshold value(s), andwherein the threshold value(s) is a value based on one or more of the followingparameters: steering torque, vehicle-sweet; steering angle, steering anglederivative, steering torque derivative, ESP sensor value, ABS sensor value, andTCS sensor value.

8. The electrical steering system according to claim 7, wherein the electricalsteering system is adapted to switch from a first boost curve to a second boostcurve during a transition period wherein the electrical steering system is adaptedto during said transition period apply an assisting steering torque that is given byan interpolation of the first and second boost curve values.

9. The electrical steering system according to any of claims 7 - 8, wherein theelectrical steering system is adapted to upon detection that said at least one ormore first pre-defined condition(s) is satisfied switch to the second boost curve inless than 50 ms.

10. The electrical steering system according to any of claims 7 - 9, wherein theelectrical steering system is adapted to switching back to the first boost curve inresponse to one or more second pre-defined condition(s). lO 17

11. The electrical steering system according to any of claims 7 - 10, wherein said electrical steering system is a power steering system.

12. A motorized vehicle (100) comprising an electrical steering system according to any of claims 7 -11.

13. The motorized vehicle according to claim 12, wherein the electrical steeringsystem is supplemented by a hydraulic servo system (112) adapted to provide additional servo steering torque.

14. A computer program product comprising a non-transitory computer readablemedium storing computer instructions for generating a value of an assistingsteering torque for an electrical steering system, wherein the electrical steeringsystem provides an assisting steering torque boost in response to a boost curve,said boost curve defining a relationship between at least one input parameter andthe current assisting steering torque boost provided by the electrical steeringsystem and where the electrical steering system has at least two boost curves that can be followed, the computer instructions comprising: instructions (810) for switching from use of a first boost curve to use of a secondboost curve in response to one or more first pre-defined condition(s) wherein thefirst pre-defined condition is one or more threshold value(s), and wherein thethreshold value(s) is a value based on one or more of the following parameters:steering torque, vehicle speed, steering angle, steering angle derivative, steering torque derivative, ESP sensor value, ABS sensor value, and TCS sensor value.

15. A computer program comprising instructions for generating a value of anassisting steering torque for an electrical steering system, wherein the electricalsteering system provides an assisting steering torque boost in response to a boostcurve, said boost curve defining a relationship between at least one inputparameter and the current assisting steering torque boost provided by the lO 18 electrical steering system and where the electrical steering system has at least twoboost curves that can be followed, the computer program instructions comprisingsoftware code causing a processor executing the instructions to: - switch (810) from use of a first boost curve to use of a second boost curve inresponse to one or more first pre-defined condition(s) wherein the first pre-definedcondition is one or more threshold value(s), and wherein the threshold value(s) isa value based on one or more of the following parameters: steering torque, vehiclespeed, steering angle, steering angle derivative, steering torque derivative, ESP sensor value, ABS sensor value, and TCS sensor value.