SE1551565A1

SE1551565A1 - Method and system for facilitating steering of a vehicle during driving along a road

Info

Publication number: SE1551565A1
Application number: SE1551565A
Authority: SE
Inventors: Andersson Jonny; Bredberg Linus
Original assignee: Scania Cv Ab
Priority date: 2015-12-01
Filing date: 2015-12-01
Publication date: 2017-06-02
Also published as: DE112016005072B4; DE112016005072T5; SE539430C2; WO2017095301A1

Abstract

ABSTRACT The present invention relates to a method for facilitating steering of a vehicleduring driving along a road. The method comprises the steps of: determiningthe vehicle speed (212); determining the curvature of the road (214); anddetermining (220) a required yaw rate for the vehicle based upon the thusdetermined vehicle speed and curvature of the road. The method further(230)compensating the steering torque of the vehicle due to influence of curvature comprises determining a curvature compensation torque forbased upon said determined required yaw rate and a gain function relating to steering torque and yaw rate of the vehicle. The present invention also relates to a system for facilitating steering of avehicle during driving along a road. The present invention also relates to avehicle. The present invention also relates to a computer program and acomputer program product. (Pig. 6)

Description

METHOD AND SYSTEM FOR FACILITATING STEERING OF A VEHICLEDURING DRIVING ALONG A ROAD TECHNICAL FIELD The invention relates to a method for facilitating steering of a vehicle duringdriving along a road according to the preamble of claim 1. The invention alsorelates to a system for facilitating steering of a vehicle during driving along aroad. The invention also relates to a vehicle. The invention in addition relatesto a computer program and a computer program product.

BACKGROUND ART ln order to facilitate steering during driving along a road systems forcontrolling the torque are utilized. Such systems include active steeringsystems which for example are able to make the steering wheel feel stiffer athigher vehicle speed to get the steering stable when driving on a straightroad. The curvature of the road when the road is turning will however result in the driver needing to apply more force to the steering wheel.

Further, external effects such as road banking, i.e. cross sloped configurationof the road, and/or lateral wind will require additional force from the driver inorder to keep the vehicle on the road.

With automated driving using torque control, for example a lane keep assistfunction, such external effects may cause the lane keeping function to resultin repeated bouncing against the boundary of the lane within which thevehicle is intended to be kept, and thus create behaviour of the vehicle whichis uncomfortable for vehicle occupants. The external effects will then pushthe vehicle against one side of the lane. Also when driving manually, the driver needs to keep a constant torque at the steering wheel to compensatefor these effects, which can be tiresome.

US5694319, DE3625392 and FR2915447 disclose applications where thedifference between a measured value of the yaw rate and a set point aredetermined, the set point being determined by means of a mathematicalmodel based upon the angle of the steering wheel. The thus determineddifference is used for influencing automatic steering of a vehicle.

There is however a need for simplifying the way of providing a basis forinfluencing steering of a vehicle during driving along a road.

OBJECTS OF THE INVENTION An object of the present invention is to provide a method for facilitatingsteering of a vehicle during driving along a road which provides an easy andefficient way of compensating the steering of the vehicle due to the curvatureof the road.

An object of the present invention is to provide a method for facilitatingsteering of a vehicle during driving along a road which provides an easy andefficient way of compensating the steering of the vehicle due to externalforces.

Another object of the present invention is to provide a system for facilitatingsteering of a vehicle during driving along a road which provides an easy andefficient way of compensating the steering of the vehicle due to the curvatureof the road.

Another object of the present invention is to provide a system for facilitatingsteering of a vehicle during driving along a road which provides an easy andefficient way of compensating the steering of the vehicle due to externalforces.

SUMMARY OF THE INVENTION These and other objects, apparent from the following description, areachieved by a method, a system, a vehicle, a computer program and acomputer program product, as set out in the appended independent claims.Preferred embodiments of the method and the system are defined inappended dependent claims.

Specifically an object of the invention is achieved by a method for facilitatingsteering of a vehicle during driving along a road. The method comprises thesteps of: determining the vehicle speed; determining the curvature of theroad; and determining a required yaw rate for the vehicle based upon thethus determined vehicle speed and curvature of the road. The method furthercomprises determining a curvature compensation torque for compensatingthe steering torque of the vehicle due to influence of curvature based uponsaid determined required yaw rate and a gain function relating to steeringtorque and yaw rate of the vehicle.

The vehicle speed is determined continuously or intermittently during drive ofthe vehicle. The curvature of the road is determined continuously orintermittently during drive of the vehicle. The required yaw rate determined bymeans of the thus determined vehicle speed and curvature of the roadcorresponds to the yaw rate required for the vehicle to keep the vehicle in thedirection of the curvature or the road. More specifically, according to anembodiment, the required yaw rate determined by means of the thusdetermined vehicle speed and curvature of the road corresponds to the yawrate required for the vehicle to keep the vehicle in the direction of thecurvature or the road when the orientation of the vehicle essentiallycorresponds to a direction corresponding to the curvature of the road at thelocation of the vehicle.

The gain function comprises static gain. ln most drive situations comprisingnormal driving along a road, the gain function, by means of which thecurvature compensation torque is determined based upon said determinedrequired yaw rate, is a static gain which efficiently facilitates obtaining thecurvature compensation torque utilizing the fact that the change of thecurvature of the road is normally very small over a certain time/distance andmay be assumed essentially static/non-changing. This provides for a veryefficient compensation of the steering torque of the vehicle due to influenceof curvature.

The gain function may for certain situations facilitate taking certain dynamicbehaviour into account, e.g. when there are passages of quick changes ofthe curvature along the road. The gain function may also be dependent onvehicle speed, wheel angle, load on front shaft and/or other parameters thatmay affect which gain, e.g. static gain, that is applicable at a certain momentof time. Such parameters may be modelled by means of a modelling means.

Hereby an easy and efficient method for compensating the steering of thevehicle due to external forces is facilitated. For automated steering functionssuch as lane keep assist, compensation due to curvature of the road willprevent the vehicle from bouncing against the boundary of the lane withinwhich the vehicle is intended to be kept. For manual driving, the driver willhave a much increased comfort and does not have to compensate for effectsdue to curvature of the road.

According to an embodiment the method comprises the step ofcompensating the steering torque of the vehicle based upon said determined CUFVSIUFG COmpGnSaÜOn IOFQUG.

By thus compensating the steering torque of the vehicle based upon saiddetermined curvature compensation torque comfort for the operator of thevehicle will be increased which may prevent stiff shoulder, stiff neck and thelike.

According to an embodiment the method further comprises the steps of:detecting the yaw rate of the vehicle; modelling the yaw rate of the vehiclebased upon the steering torque of the vehicle; comparing the detected andmodelled yaw rate; determining the influence of external forces on the yawrate based on said comparison of detected and modelled yaw rate, saidexternal forces comprising external forces emanating from one or more of:influence of cross sloped configuration of the road; influence of lateral wind;and influence of flat tire; and, based upon the determined influence ofexternal forces on the yaw rate and said gain function determining anexternal force compensation torque for compensating the steering torque ofthe vehicle due to influence of external forces.

Hereby an easy and efficient method for compensating the steering of thevehicle due to external forces is facilitated. By thus basing the modelled yawrate upon the steering torque of the vehicle compensation of the steering ofthe vehicle without the need of information regarding the steering angle of thesteering wheel of the vehicle. For automated steering functions such as lanekeep assist, compensation of external forces will prevent the vehicle frombouncing against the boundary of the lane within which the vehicle isintended to be kept. For manual driving, the driver will have a muchincreased comfort and does not have to compensate for external effects suchas longer periods of road banking, i.e. cross sloped configuration of the road,and/or side wind.

The gain function comprises static gain. ln most drive situations comprisingnormal driving along a road, the gain function, by means of which theexternal force compensation torque is determined, is a static gain whichefficiently facilitates obtaining the external force compensation torque utilizingthe fact that the change of the external forces, e.g. road banking, is normallyvery small over a certain time/distance and may be assumed essentiallystatic/non-changing. This provides for a very efficient compensation of thesteering torque of the vehicle due to influence of external forces.

The gain function may for certain situations facilitate taking certain dynamicbehaviour into account, e.g. when there are passages of quick changes ofthe curvature along the road. The gain function may also be dependent onvehicle speed, wheel angle, load on front shaft and/or other parameters thatmay affect which gain, e.g. static gain, that is applicable at a certain momentof time. Such parameters may be modelled by means of the modelling means for modelling the yaw rate.

According to an embodiment the method comprises the step ofcompensating the steering torque of the vehicle based upon said determined CUfVaïUfe COmpenSaÜOn tOfqUe.

By thus compensating the steering torque of the vehicle based upon saiddetermined external force compensation torque comfort for the operator ofthe vehicle will be increased which may prevent stiff shoulder, stiff neck andthe like.

According to an embodiment of the method the result of said comparisonbetween the detected and modelled yaw rate is filtered so as to avoidinfluence of rapid changes. Hereby a more efficient compensation isobtained, further lmproving the comfort during driving along a road in thatrapid changes are avoided.

According to an embodiment the method further comprises the step ofdetermining a compensation torque based upon said determined curvaturecompensation torque and said determined external force compensationtorque; and compensating the steering torque based upon said determined compensation torque.

Hereby the influence of both curvature and external effects are taken intoaccount, wherein steering of the vehicle is facilitated in an efficient way. Bythus compensating the steering torque of the vehicle based upon saiddetermined compensation torque comfort for the operator of the vehicle willbe increased which may prevent stiff shoulder, stiff neck and the like.

According to an embodiment of the method the modelled yaw rate isobtained via a transfer function. By applying a transfer function an efficientway of obtaining the modelled yaw rate is facilitated. The transfer function isconfigured to transfer the steering torque to the modelled yaw rate. Thetransfer function comprises calculating what the yaw rate would be after acertain time based upon a certain steering torque, i.e. a certain torqueapplied on the steering wheel of the vehicle. The method thus comprises thestep of obtaining the modelled yaw rate from the steering torque by means ofa transfer function.

According to an embodiment of the method said gain function is obtained viasaid transfer function.

According to an embodiment of the method said gain function comprises astatic gain. The static gain provides information regarding the torque thatneeds to be maintained in order to maintain a constant yaw rate. ln mostdrive situations comprising normal driving along a road, the gain function, bymeans of which the curvature compensation torque is determined basedupon said determined required yaw rate, is a static gain which efficientlyfacilitates obtaining the compensation torque utilizing the fact that the changeof the curvature of the road and external effects are normally very small overa certain time/distance and may be assumed essentially static/non-changing,such a static gain therefor being efficient for obtaining the compensationtorque. This thus provides for a very efficient compensation of the steering torque of the vehicle due to influence of curvature and external forces.

Specifically an object of the invention is achieved by a system for facilitatingsteering of a vehicle during driving along a road, characterized by means fordetermining the vehicle speed; means for determining the curvature of theroad; means for determining a required yaw rate for the vehicle based uponthe thus determined vehicle speed and curvature of the road; means fordetermining a curvature compensation torque for compensating the steering torque of the vehicle due to influence of curvature based upon said determined required yaw rate and a gain function relating to steering torqueand yaw rate of the vehicle.

According to an embodiment the system further comprises means fordetecting the yaw rate of the vehicle; means for modelling the yaw rate of thevehicle based upon the steering torque of the vehicle; means for comparingthe detected and modelled yaw rate; means for determining the influence ofexternal forces on the yaw rate based on said comparison of detected andmodelled yaw rate, said external forces comprising external forces emanatingfrom one or more of: influence of cross sloped configuration of the road;influence of lateral wind; and influence of flat tire; and means for determiningan external force compensation torque for compensating the steering torqueof the vehicle due to influence of external forces based upon the determinedinfluence of external forces on the yaw rate and said gain function.

According to an embodiment the system comprises filtering means forfiltering the result of said comparison between the detected and modelledyaw rate so as to avoid influence of rapid changes.

According to an embodiment the system further comprises means fordetermining a compensation torque based upon said determined curvaturecompensation torque and said determined external force compensationtorque; and means for compensating the steering torque based upon said determined compensation torque.

According to an embodiment of the system the modelled yaw rate is obtainedvia a transfer function.

According to an embodiment of the system said gain function is obtained viasaid transfer function.

According to an embodiment of the system said gain function comprises astatic gain.

The system for facilitating steering of a vehicle during driving along a road isadapted to perform the methods as set out herein.

The system according to the invention has the advantages according to thecorresponding method claims.

Specifically an object of the invention is achieved by a vehicle comprising asystem according to the invention as set out herein.

Specifically an object of the invention is achieved by a computer program forfacilitating steering of a vehicle during driving along a road, said computerprogram comprising program code which, when run on an electronic controlunit or another computer connected to the electronic control unit, causes theelectronic control unit to perform methods as set out herein.

Specifically an object of the invention is achieved by a computer programproduct comprising a digital storage medium storing the computer program.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention reference is made to the following detailed description when read in conjunction with theaccompanying drawings, whereín like reference characters refer to like parts throughout the several views, and in which: Fig. 1 schematically illustrates a side view of a vehicle according to thepresent invention; Fig. 2 schematically illustrates a plan view of the vehicle in fig. 1 driving in a curve of a road; Fig. 3 schematically illustrates a rear view of the vehicle in fig. 1 beingsubjected to external forces comprising on cross sloped configuration of theroad and influence of lateral wind; Fig. 4 schematically illustrates a steering configuration of a vehicle andrelated torques according to an embodiment of the invention; Fig. 5 schematically illustrates a block diagram of a system for faciiitatingsteering of a vehicle during driving along a road according to an embodiment of the present invention; Fig. 6 schematically illustrates a block diagram of a system for providing acompensation torque for faciiitating steering of a vehicle during driving alonga road according to an embodiment of the present invention; Fig. 7 schematically illustrates a block diagram of a system for providing acompensation torque for faciiitating steering of a vehicle during driving alonga road according to an embodiment of the present invention; Fig. 8 schematically illustrates a block diagram of a method for faciiitatingsteering of a vehicle during driving along a road according to an embodimentof the present invention; and Fig. 9 schematically illustrates a computer according to an embodiment of thepresent invention.

DETAILED DESCRIPTION Hereinafter the term “link” refers to a communication link which may be aphysical connector, such as an optoelectronic communication wire, or a non-physical connector such as a wireless connection, for example a radio ormicrowave link.

Hereinafter the term “steering torque“ refers to the total input torque acting onthe steering column of the vehicle.

The “steering torque”, i.e. the total input torque acting on the steering column,comprises a driver torque and according to an embodiment, a possible 11 assistance torque being a boost of the driver torque. The steering torquefurther comprises an external torque being a demanded torque for steeringthe vehicle. Fig. 4 illustrates an example of a steering configuration and howthe steering torque relates to driver torque and external torque.

Hereinafter the term “curvature“ refers to the conventional definition ofcurvature which is 1/r, where “r” is the radius of a curve, the unit being [1/m].

Fig. 1 schematically illustrates a side view of a vehicle 1 according to thepresent invention. The exemplified vehicle 1 is a heavy vehicle in the shapeof a truck. The vehicle according to the present invention could be anysuitable vehicle such as a bus or a car. The vehicle comprises a system l, ll,lll for facilitating steering of a vehicle during driving along a road R.

Fig. 2 schematically illustrates a plan view of the vehicle in fig. 1 driving in acurve of a road R. The curvature of the road R affects the behaviour of thevehicle requiring steering compensation from the driver of the vehicle 1.

Fig. 3 schematically illustrates a rear view of the vehicle 1 in fig. 1 beingsubjected to external forces. The vehicle has wheels of which left and rightrear wheels LR, RR are shown. The external forces comprise cross slopedconfiguration of the road R on which the vehicle 1 is travelling. The crosssloped configuration of the road R is called road banking, the road R having acertain inclination oi such that water is allowed to run off the road. Theexternal forces comprise influence of lateral wind A. The external forces mayalso comprise a flat tire on a wheel of the vehicle.

With automated driving using torque control, for example a lane keep assistfunction, such external effects may cause the lane keeping function to resultin repeated bouncing against the boundary of the lane within which thevehicle is intended to be kept, and thus create behaviour of the vehicle whichis uncomfortable for vehicle occupants. The external effects will then pushthe vehicle against one side of the lane. Also when driving manually, the 12 driver needs to keep a constant torque at the steering wheel to compensatefor these effects, which can be tiresome.

The present invention provides method and system for facilitating steering ofa vehicle during driving along a road so as to compensate for such externalforces. This is achieved by detecting the yaw rate of the vehicle andmodelling the yaw rate of the vehicle and comparing the detected andmodelled yaw rate. The modelled yaw rate is based upon the steering torqueof the vehicle. The influence of external forces on the yaw rate is determinedbased on the comparison of detected and modelled yaw rate. Acompensation torque for compensating the steering torque of the vehicle isthen determined based upon the determined influence of external forces onthe yaw rate. The steering torque is compensated based upon the determined compensation torque.The present invention is described in more detail with reference to fig. 4-9.

Fig. 4 schematically illustrates a steering configuration of a vehicle andrelated torques according to an embodiment of the invention.

The vehicle comprises a steering wheel SW. The steering wheel SW isconnected to the front wheels LF, RF via a steering column SC connected toa link arrangement LA for turning the wheels LF, RF.

The driver torque DT is provided by applying torque to the steering wheelSW. The driver torque DT is determined by means of a torque sensor TS.The driver torque DT is boosted by means of a gain G so as to obtain anassistance torque AT which represents a boost of the driver torque in order toobtain a good feeling for the driver by steering the vehicle. The assistancetorque AT may vary with vehicle speed. The assistance torque AT is provideda specific feeling during steering of the vehicle such that by low speeds ahigh boost is provided to facilitate drive at low speeds and at high speed alow gain is provided in order to stiffen the steering wheel SW. 13 An external torque ET may according to an embodiment be provided which isadded to the assistance torque AT. The external torque ET would accordingto a variant have the effect that if the driver lets go of the steering wheel SWit is only the external toque ET that provides the steering. During drive incurve the external torque ET may be added in order to follow the curvature.The external torque may correspond to a compensation torque determined inaccordance with the present invention. The external torque ET may alsocomprise a torque based on a lane keep assistance function. lf a certain external torque ET is demanded, e.g. 5 Nm to the right, i.e.external torque = - 5 Nm, and the driver keeps the steering wheel totally still,and the boost correspond to a certain gain, e.g. 2, the driver will feel a torqueof 5/2=2,5 Nm in the steering wheel SW.

The steering torque ST is the total input torque to the steering column SC.The steering torque ST is boosted by means of the link arrangement LAconnected to the steering column SC. The steering torque ST is the drivertorque DT + the assistance torque AT and where applicable also + theexternal torque ET. The steering torque ST is thus determined by means ofthe torque sensor TS and the gain G and by adding the possible externaltorque ET. The external torque ET is a demanded torque and thus knownand provided from an electronic control unit.

Fig. 5 schematically illustrates a system I for facilitating steering of a vehicleduring driving along a road according to an embodiment of the presentinvenﬂon.

The system I comprises an electronic control unit 100.

The system I comprises means 112 for determining the vehicle speed. Themeans 112 for determining the vehicle speed comprises according to anembodiment the speedometer of the vehicle. The vehicle speed isdetermined continuously or intermittently during drive of the vehicle. 14 The system I comprises means 1 14 for determining the curvature of the road.The means 114 for determining the curvature of the road may comprise anysuitable means for determining the curvature of the road. The means 114 fordetermining the curvature of the road comprises according to an embodimenta global positioning system, GPS, for continuously or intermittentlydetermining the position of the vehicle and map data comprising informationabout the curvature of the road. The means 114 for determining the curvatureof the road comprises according to an embodiment detecting means such asone or more camera units for detecting road marks and/or crash barriersand/or side of the road so as to continuously or intermittently determining thecurvature of the road in connection to the position of the vehicle. The means114 for determining the curvature of the road comprises according to anembodiment detection means for detecting a vehicle in front of the vehicledriving in the same direction for determining the curvature of the road onwhich the vehicle is driving. The curvature of the road is determined continuously or intermittently during drive of the vehicle.

The system I comprises means 120 for determining a required yaw rate forthe vehicle based upon the thus determined vehicle speed and curvature ofthe road. The means 120 for determining a required yaw rate for the vehiclebased upon the thus determined vehicle speed and curvature of the roadcomprises calculation means. The means 120 for determining a required yawrate for the vehicle based upon the thus determined vehicle speed andcurvature of the road is according to an embodiment comprised in theelectronic control unit 100.

The required yaw rate determined by means of the thus determined vehiclespeed and curvature of the road corresponds to the yaw rate required for thevehicle to keep the vehicle in the direction of the curvature or the road. Morespecifically, according to an embodiment, the required yaw rate determinedby means of the thus determined vehicle speed and curvature of the roadcorresponds to the yaw rate required for the vehicle to keep the vehicle in the direction of the curvature or the road when the orientation of the vehicleessentially corresponds to a direction corresponding to the curvature of theroad at the location of the vehicle.

The system I comprises means 130 for determining a curvaturecompensation torque for compensating the steering torque of the vehicle dueto influence of curvature based upon said determined required yaw rate anda gain function relating to steering torque and yaw rate of the vehicle. Themeans 130 for determining a curvature compensation torque comprisescalculation means. The means 130 for determining a curvature compensationtorque is according to an embodiment comprised in the electronic control unit 100.

The gain function comprises static gain. The static gain is the gain providedby the system when the time goes to infinity. The static gain is used fordetermining the required steering torque in order to compensate for the errorcorresponding to the difference between the detected and modelled yaw rate.

According to an embodiment of the system the gain function and hence thestatic gain is arranged to be obtained via a transfer function of a modellingmeans. ln most drive situations comprising normal driving along a road, the gainfunction, by means of which the curvature compensation torque isdetermined based upon said determined required yaw rate, is a static gainwhich efficiently facilitates obtaining the curvature compensation torqueutilizing the fact that the change of the curvature of the road is normally verysmall over a certain time/distance and may be assumed essentially static/non-changing.

The system I comprises means 142 for determining the steering torque. Themeans 142 for determining the steering torque may comprise any suitabletorque sensor for determining the steering torque. The means 142 fordetermining the steering torque may comprise the electronic control unit. The 16 means 142 for determining the steering torque may be arranged to determinethe steering torque in accordance with the determination of the steeringtorque as described with reference to fig. 3.

The system I comprises means 144 for detecting the yaw rate of the vehicle.The means 144 for detecting the yaw rate comprises any suitable detectorunit for detecting the yaw rate. The detector unit is configured todetect/measure the rotation in the x/y-plane. The detector unit is according toan embodiment a gyro configured to sense the rotation in the x/y-plane. Thedetection by means of said detector unit is according to an embodiment performed continuously.

The system I comprises modelling means 150 for modelling the yaw rate ofthe vehicle. The modelling means 150 is arranged to model the yaw ratebased upon the steering torque of the vehicle. The modelling means 150 isarranged to provide a model wherein a certain torque gives a certain yawangle and how quickly it affects yaw rate. The modelling means 150 isaccording to an embodiment a dynamic model built up by means of mGaSUFemGHtS.

The modelling means 150 is arranged to obtain the modelled yaw rate via atransfer function. The transfer function is comprised in the modelling means150 and is configured to transfer the steering torque to a yaw rate. Thetransfer function is configured to calculate which yaw rate it would be within acertain time based on a certain steering torque as input.

The transfer function of the modelling means 150 is configured to provide arelationship between steering torque and yaw rate. The transfer function ofthe modelling means 150 is configured to provide said gain function andhence said static gain relating to the torque required for obtaining a constantyaw rate. The transfer function of the modelling means 150 is configured toprovide a moment of inertia relating to the rate of change of the yaw rate dueto turning of the steering wheel of the vehicle. 17 The system I comprises means 160 for comparing the detected and modelledyaw rate. The means 160 for comparing the detected and modelled yaw ratecomprises calculation means for calculating the difference between thedetected and modelled yaw rate. The means 160 is according to anembodiment comprised in the electronic control unit 100.

The system I comprises filtering means F for filtering the result of saidcomparison between the detected and modelled yaw rate so as to avoidinfluence of rapid changes. The comparison is thus performed during acertain time span and by filtering the result such rapid changes can beavoided.

The system I comprises means 170 for determining the influence of externalforces on the yaw rate based on said comparison of detected and modelledyaw rate. lf there is a difference in the comparison of detected and modelledyaw rate the difference is assumed to relate to external forces.

According to an embodiment of the system said external forces emanatefrom one or more of: influence of cross sloped configuration of the road; influence of lateral wind; and influence of flat tire. lf there is no difference in the comparison of detected and modelled yaw ratethere is likely no influence of external forces. This would be the case if theroad is essentially horizontal and there are no lateral wind affecting thevehicle.

The system I comprises means 180 for determining an external forcecompensation torque for compensating the steering torque of the vehiclebased upon the determined influence of external forces on the yaw rate andsaid gain function.

The gain function comprises static gain. ln most drive situations comprisingnormal driving along a road, the gain function, by means of which theexternal force compensation torque is determined, is a static gain which 18 efficiently facilitates obtaining the external force compensation torque utilizingthe fact that the change of the external forces, e.g. road banking, is normallyvery small over a certain time/distance and may be assumed essentiallystatic/non-changing.

The static gain is used for determining the required steering torque in order tocompensate for the error corresponding to the difference between thedetected and modelled yaw rate.

The system I comprises means 192 for determining a compensation torquebased upon said determined curvature compensation torque and saiddetermined external force compensation torque. The means 192 fordetermining a compensation torque comprises calculation means. Themeans 192 for determining a compensation torque is according to anembodiment comprised in the electronic control unit 100.

The system I comprises means 194 for compensating the steering torquebased upon said determined compensation torque. The means 194 forcompensating the steering torque based upon said determined compensationtorque is arranged to be added/subtracted so as to compensate for thetorque provided by the external forces such that only the vehicle relatedtorque/driver torque affects the driving of the vehicle such that the vehicle isnot affected by the external forces. Thus, the experience for the driver will bethe same as if there were no external forces, e.g. no lateral wind and nobanked road.

According to an embodiment external forces could also be detected.

According to an embodiment the external force relating to cross slopedconfiguration of the road, i.e. road banking is detected by means of detectingthe lateral acceleration. The yaw rate due to cross sloped configuration of theroad can thus be determined by calculation by dividing the thus detectedlateral acceleration with the vehicle speed and subtracting the measured yaw Fate. 19 The external force relating to lateral wind could also be detected by means of one or more detector units.

The electronic control unit 100 is operably connected to the means 112 fordetermining the vehicle speed via a link 12. The electronic control unit 100 isvia the link 12 arranged to receive a signal from said means 112 representingdata for vehicle speed.

The electronic control unit 100 is operably connected to the means 114 fordetermining the curvature of the road via a link 14. The electronic control unit100 is via the link 14 arranged to receive a signal from said means 114representing data for curvature of the road along which the vehicle istravelling.

The electronic control unit 100 is operably connected to the means 120 fordetermining a required yaw rate for the vehicle based upon the thusdetermined vehicle speed and curvature of the road via a link 20a. Theelectronic control unit 100 is via the link 20a arranged to send a signal to saidmeans 120 representing data for vehicle speed.

The electronic control unit 100 is operably connected to the means 120 fordetermining a required yaw rate for the vehicle based upon the thusdetermined vehicle speed and curvature of the road via a link 20b. Theelectronic control unit 100 is via the link 20b arranged to send a signal to saidmeans 120 representing data for curvature of the road along which thevehicle is travelling.

The electronic control unit 100 is operably connected to the means 120 fordetermining a required yaw rate for the vehicle based upon the thusdetermined vehicle speed and curvature of the road via a link 20c. Theelectronic control unit 100 is via the link 20c arranged to receive a signal fromsaid means 120 representing data for required yaw rate for the.

The electronic control unit 100 is operably connected to the means 130 fordetermining an curvature compensation torque for compensating the steeringtorque of the vehicle based upon the determined influence of curvatures onthe yaw rate and said gain function via a link 30a. The electronic control unit100 is via the link 30a arranged to send a signal to said means 130 representing data for influence of curvatures on the yaw rate.

The electronic control unit 100 is operably connected to the means 130 fordetermining an curvature compensation torque for compensating the steeringtorque of the vehicle based upon the determined influence of curvatures onthe yaw rate and said gain function via a link 30b. The electronic control unit100 is via the link 30b arranged to send a signal to said means 130representing data for static gain from the transfer function.

The electronic control unit 100 is operably connected to the means 130 fordetermining an curvature compensation torque for compensating the steeringtorque of the vehicle based upon the determined influence of curvatures onthe yaw rate and said gain function via a link 30c. The electronic control unit100 is via the link 30c arranged to receive a signal from said means 130representing data for compensation torque for compensating the steeringtorque of the vehicle.

The electronic control unit 100 is operably connected to the means 142 fordetermining the steering torque via a link 42. The electronic control unit 100is via the link 42 arranged to receive a signal from said means 142representing data for steering toque.

The electronic control unit 100 is operably connected to the means 144 fordetecting the yaw rate of the vehicle via a link 44. The electronic control unit100 is via the link 44 arranged to receive a signal from said means 144representing data for the detected yaw rate of the vehicle.

The electronic control unit 100 is operably connected to the modelling means150 for modelling the yaw rate of the vehicle via a link 50a. The electronic 21 control unit 100 is via the link 50a arranged to send a signal to said means150 representing data for the steering toque.

The electronic control unit 100 is operably connected to the modelling means150 for modelling the yaw rate of the vehicle based on the steering torque viaa link 50b. The electronic control unit 100 is via the link 50b arranged toreceive a signal from said means 150 representing data for the modelled yawrate.

The electronic control unit 100 is operably connected to the modelling means150 for modelling the yaw rate of the vehicle based on the steering torque viaa link 50c. The electronic control unit 100 is via the link 50c arranged toreceive a signal from said means 150 representing data for static gain.

The electronic control unit 100 is operably connected to the means 160 forcomparing the detected and modelled yaw rate via a link 60a. The electroniccontrol unit 100 is via the link 60a arranged to send a signal to said means160 representing data for detected yaw rate.

The electronic control unit 100 is operably connected to the means 160 forcomparing the detected and modelled yaw rate via a link 60b. The electroniccontrol unit 100 is via the link 60b arranged to send a signal to said means160 representing data for modelled yaw rate.

The electronic control unit 100 is operably connected to the means 160 forcomparing the detected and modelled yaw rate via a link 60c. The electroniccontrol unit 100 is via the link 60c arranged to receive a signal from saidmeans 160 representing data for result of comparison between detected andmodelled yaw rate, i.e. data for difference between detected and modelledyaw rate.

The electronic control unit 100 is operably connected to the filtering means Ffor filtering the result of said comparison between the detected and modelledyaw rate so as to avoid influence of rapid changes via a link Fa. The 22 electronic control unit 100 is via the link Fa arranged to send a signal to saidmeans F representing data for result of comparison between detected andmodelled yaw rate.

The electronic control unit 100 is operably connected to the filtering means Ffor filtering the result of said comparison between the detected and modelledyaw rate so as to avoid influence of rapid changes via a link Fb. Theelectronic control unit 100 is via the link Fb arranged to receive a signal fromsaid means F representing data for filtered result of comparison betweendetected and modelled yaw rate.

The electronic control unit 100 is operably connected to the means 170 fordetermining the influence of external forces on the yaw rate based on saidcomparison of detected and modelled yaw rate via a link 70a. The electroniccontrol unit 100 is via the link 70a arranged to send a signal to said means170 representing data for filtered result of comparison between detected andmodelled yaw rate.

The electronic control unit 100 is operably connected to the means 170 fordetermining the influence of external forces on the yaw rate based on saidcomparison of detected and modelled yaw rate via a link 70b. The electroniccontrol unit 100 is via the link 70b arranged to receive a signal from saidmeans 170 representing data for influence of external forces on the yaw rate.

The electronic control unit 100 is operably connected to the means 180 fordetermining an external force compensation torque for compensating thesteering torque of the vehicle based upon the determined influence ofexternal forces on the yaw rate and said gain function via a link 80a. Theelectronic control unit 100 is via the link 80a arranged to send a signal to saidmeans 180 representing data for influence of external forces on the yaw rate.

The electronic control unit 100 is operably connected to the means 180 fordetermining an external force compensation torque for compensating the steering torque of the vehicle based upon the determined influence of 23 external forces on the yaw rate and said gain function via a link 80b. Theelectronic control unit 100 is via the link 80b arranged to send a signal to saidmeans 180 representing data for static gain from the transfer function.

The electronic control unit 100 is operably connected to the means 180 fordetermining an external force compensation torque for compensating thesteering torque of the vehicle based upon the determined influence ofexternal forces on the yaw rate and said gain function via a link 80c. Theelectronic control unit 100 is via the link 80c arranged to receive a signal fromsaid means 180 representing data for compensation torque for compensatingthe steering torque of the vehicle.

The electronic control unit 100 is operably connected to the means 192 fordetermining a compensation torque based upon said determined curvaturecompensation torque and said determined external force compensationtorque via a link 92a. The electronic control unit 100 is via the link 92aarranged to send a signal to said means 192 representing data for influenceof external forces on the yaw rate.

The electronic control unit 100 is operably connected to the means 192 fordetermining a compensation torque based upon said determined curvaturecompensation torque and said determined external force compensationtorque via a link 92b. The electronic control unit 100 is via the link 92barranged to send a signal to said means 192 representing data for static gainfrom the transfer function.

The electronic control unit 100 is operably connected to the means 192 fordetermining a compensation torque based upon said determined curvaturecompensation torque and said determined external force compensationtorque via a link 92c. The electronic control unit 100 is via the link 92carranged to receive a signal from said means 192 representing data forcompensation torque for compensating the steering torque of the vehicle. 24 The electronic control unit 100 is operably connected to the means 194 forcompensating the steering torque based upon said determined compensationtorque via a link 94a. The electronic control unit 100 is via the link 94aarranged to send a signal to said means 194 representing data forcompensation torque for compensating the steering torque of the vehicle.

The electronic control unit 100 is operably connected to the means 194 forcompensating the steering torque based upon said determined compensationtorque via a link 94b. The electronic control unit 100 is via the link 94barranged to receive a signal from said means 194 representing data forcompensating the steering torque.

Fig. 6 schematically illustrates a block diagram of a system ll for providing acurvature compensation torque for facilitatlng steering of a vehicle duringdriving along a road according to an embodiment of the present invention.

The system ll could be a subsystem to the system l. The system ll maycomprise parts of the system l. The system ll could be a subsystem to thesystem lll described with reference to fig. 7.

The system ll comprises means 212 for determlnlng the vehicle speed. Themeans 212 for determining the vehicle speed comprises according to anembodiment the speedometer of the vehicle. The vehicle speed isdetermined continuously or intermittently during drive of the vehicle.

The system ll comprises means 214 for determining the curvature of theroad. The means 214 for determining the curvature of the road may compriseany suitable means for determining the curvature of the road. The means 214for determining the curvature of the road may be determined accordance withthe means 214 for determining the curvature of the road described withreference to fig. 5. The curvature of the road is determined continuously orintermittently during drive of the vehicle.

The system ll comprises means 220 for determining a required yaw rate forthe vehicle based upon the thus determined vehicle speed and curvature ofthe road. The means 220 for determining a required yaw rate for the vehiclebased upon the thus determined vehicle speed and curvature of the road comprises calculation means.

The means 220 for determining a required yaw rate is operably connected tothe means 212 for determining the vehicle speed via a link 220a. The means220 is via the link 220a arranged to receive data representing vehicle speed.

The means 220 for determining a required yaw rate is operably connected tothe means 214 for determining the curvature of the road via a link 220b. Themeans 220 is via the link 220b arranged to receive data representing curvature of the road.

The system ll comprises means 252 for providing a gain function. The means252 for providing a gain function is arranged to provide the gain functionbased on steering torque and yaw rate of the vehicle. The means 252 isarranged to receive a signal via a link 252a representing data for steeringtorque of the vehicle. The means 252 is arranged to receive a signal via alink 252b representing data for yaw rate of the vehicle, the data for yaw ratebeing data for detected yaw rate of the vehicle.

The gain function comprises or constitutes a static gain.

The means 252 comprises a parameter estimation means for estimating thestatic gain. The parameter estimation means may comprise a static gainestimated by a certain parameter based on vehicle configuration such asvehicle weight, wheel base and the like and may according to anembodlment be a fixed value.

The means 252 comprises according to an embodlment a transfer function,wherein the gain function and hence the static gain is configured to beprovided by means of the transfer function. 26 The means 252 is according to an embodiment comprised in a modellingmeans 250 comprising said transfer function. The modelling means 250 maybe configured according to the modelling means 150 described withreference to fig. 5. The modelling means 250 may be configured according tothe modelling means 350 described with reference to fig. 7.

The modelling means 250 may provide a signal via a link 250b representinga modelled yaw rate.

The system ll comprises means 230 for determining a curvaturecompensation torque for compensating the steering torque of the vehicle dueto influence of curvature based upon said determined required yaw rate and a gain function relating to steering torque and yaw rate of the vehicle.

The means 230 for determining a curvature compensation torque forcompensating the steering torque of the vehicle due to influence of curvatureis operably connected to the means 220 for determining a required yaw ratevia a link 230a. The means 230 is via the link 230a arranged to receive asignal representing data for required yaw rate.

The means 230 for determining a curvature compensation torque forcompensating the steering torque of the vehicle due to influence of curvatureis operably connected to the means 252 via a link 230b. The means 230 isvia the link 230b arranged to receive a signal representing data for gainfunction, the data for gain function according to a preferred embodimentcomprising data for static gain. The static gain is the gain provided by thesystem when the time goes to infinity. The static gain is used for determiningthe required torque in order to compensate for curvature of the road.

The means 230 for determining a curvature compensation torque is arrangedto process the data for required yaw rate and the data for gain function, e.g.data for static gain, so as to obtain the curvature compensation torque. 27 The thus obtained curvature compensation torque may via a link 230c besent to a means for compensating the steering torque. Compensation of thesteering torque is thus based upon the determined curvature compensationtorque. The determined curvature compensation torque may beadded/subtracted to the steering torque so as to compensate for the torqueprovided by the curvature. The determined curvature compensation torque may be comprised or constitute the external torque ET according to fig. 4.

Fig. 7 schematically illustrates a block diagram of a system lll for providing acompensation torque for facilitating steering of a vehicle during driving alonga road according to an embodiment of the present invention.

The system lll could be a subsystem to the system l. The system lll maycomprise parts of the system l. The system lll is arranged to providegenerally the same information as the system l.

The system lll comprises means 312 for determining the vehicle speed. Themeans 312 for determining the vehicle speed comprises according to anembodiment the speedometer of the vehicle. The vehicle speed isdetermined continuously or intermittently during drive of the vehicle.

The system lll comprises means 314 for determining the curvature of theroad. The means 314 for determining the curvature of the road may compriseany suitable means for determining the curvature of the road. The means 314for determining the curvature of the road may be determined accordance withthe means 314 for determining the curvature of the road described withreference to fig. 5. The curvature of the road is determined continuously orintermittently during drive of the vehicle.

The system lll comprises means 320 for determining a required yaw rate forthe vehicle based upon the thus determined vehicle speed and curvature ofthe road. The means 320 for determining a required yaw rate for the vehiclebased upon the thus determined vehicle speed and curvature of the road comprises calculation means. 28 The means 320 for determining a required yaw rate is operably connected tothe means 312 for determining the vehicle speed via a link 320a. The means320 is via the link 320a arranged to receive data representing vehicle speed.

The means 320 for determining a required yaw rate is operably connected tothe means 314 for determining the curvature of the road via a link 320b. Themeans 320 is via the link 320b arranged to receive data representingcurvature of the road.

The system lll comprises a transfer function G(z) configured to provide arelationship between steering torque and yaw rate. The transfer function G(z)is part of a modelling means 350. The transfer function G(z) is thuscomprised in the modelling means 350 and is configured to transfer thesteering torque to a yaw rate. The transfer function G(z) of the modellingmeans 350 is configured to provide a gain function relating to steering torqueand yaw rate of the vehicle. The gain function comprise a static gain. Thetransfer function G(z) of the modelling means 350 is configured to provide astatic gain relating to steering torque and yaw rate of the vehicle.

The system lll comprises means 330 for determining a curvaturecompensation torque for compensating the steering torque of the vehicle dueto influence of curvature based upon said determined required yaw rate and a gain function relating to steering torque and yaw rate of the vehicle.

The means 330 for determining a curvature compensation torque forcompensating the steering torque of the vehicle due to influence of curvatureis operably connected to the means 320 for determining a required yaw ratevia a link 330a. The means 330 is via the link 330a arranged to receive asignal representing data for required yaw rate.

The means 330 for determining a curvature compensation torque forcompensating the steering torque of the vehicle due to influence of curvatureis operably connected to the means 350 via a link 330b. The means 330 is via the link 330b arranged to receive a signal representing data for gain 29 function, the data for gain function according to a preferred embodimentcomprising data for static gain. The static gain is the gain provided by thesystem when the time goes to infinity. The static gain is used for determiningthe required torque in order to compensate for curvature of the road.

The means 330 for determining a curvature compensation torque is arrangedto process the data for required yaw rate and the data for gain function, e.g.data for static gain, so as to obtain the curvature compensation torque.

The modelling means 350 is arranged for modelling the yaw rate of thevehicle. The modelling means 350 is arranged to model the yaw rate basedupon the steering torque of the vehicle. The modelling means 350 isarranged to receive a signal via a link 350a representing data for steeringtorque.

The modelling means 350 is arranged to provide a model wherein a certaintorque gives a certain yaw angle and how quickly it affects yaw rate. Themodelling means 350 is according to an embodiment a dynamic model built up by means of measurements.

The transfer function G(z) is configured to calculate which yaw rate it wouldbe within a certain time based on a certain steering torque as input via thelink 350a.

The static gain provided by the transfer function G(z) of the modelling means350 is further relating to the torque required for obtaining a constant yaw rate.The transfer function G(z) of the modelling means 350 is configured toprovide a moment of inertia relating to the rate of change of the yaw rate dueto turning of the steering wheel of the vehicle.

The system lll comprises means 360 for comparing detected and modelled yaw rate.

The means 360 for comparing the detected and modelled yaw rate isarranged to receive a signal via a link 220a representing detected yaw rate.

The means 360 for comparing the detected and modelled yaw rate isarranged to receive a signal via a link 350b representing the modelled yawrate.

The means 360 for comparing the detected and modelled yaw ratecomprises calculation means for calculating the difference between thedetected and modelled yaw rate.

The system lll comprises filtering means F for filtering the result of saidcomparison between the detected and modelled yaw rate so as to avoidinfluence of rapid changes.

The filtering means F is arranged to receive a signal via a link 3600representing data for result of comparison between the detected andmodelled yaw rate.

The comparison is thus performed during a certain time span and by filteringthe result such rapid changes can be avoided.

The influence of external forces on the yaw rate is determined based on saidcomparison of detected and modelled yaw rate. lf there is a difference in thecomparison of detected and modelled yaw rate the difference is assumed torelate to external forces. The external forces emanate from one or more of:influence of cross sloped configuration of the road; influence of lateral wind;and influence of flat tire.

The system lll comprises means 380 for determining an external forcecompensation torque for compensating the steering torque of the vehiclebased upon the determined influence of external forces on the yaw rate.

The means 380 for determining an external force compensation torque isoperably connected to the modelling means 350 and hence the transferfunction G(z) via a link 350c. The means 380 for determining an externalforce compensation torque is arranged to receive a signal via the link 350crepresenting data for static gain. The static gain is the gain provided by the 31 system when the time goes to infinity. The static gain is used for determiningthe required torque in order to compensate for the error.

A static gain for obtaining said compensation torque is thus arranged to beobtained via said transfer function G(z) of the modelling means 350.

The means 380 for determining an external force compensation torque isoperably connected to the filtering means F via a link Fb. The means 380 fordetermining an external force compensation torque is arranged to receive asignal via the link Fb representing data for filtered result of comparisonbetween the detected and modelled yaw rate.

The means 380 for determining an external force compensation torque isarranged to process the data for static gain and the data for result ofcomparison between the detected and modelled yaw rate so as to obtain theexternal torque compensation torque.

The system I comprises means 392 for determining a compensation torquebased upon said determined curvature compensation torque and saiddetermined external force compensation torque. The means 392 fordetermining a compensation torque comprises calculation means.

The means 392 for determining a compensation torque is operablyconnected to the means 330 for determining a curvature compensationtorque via a link 330c. The means 392 for determining a compensationtorque is via the link 330c arranged to receive a signal representing data for CUFVaIUFG COmpênSaÜOH IOfqUe.

The means 392 for determining a compensation torque is operablyconnected to the means 380 for determining an external force compensationtorque via a link 380a. The means 392 for determining a compensationtorque is via the link 380a arranged to receive a signal representing data for external force compensation torque. 32 The means 392 for determining a compensation torque is arranged toprocess the data for curvature compensation torque and the data for externalforce compensation torque so as to obtain the compensation torque.

The thus obtained compensation torque may via a link 392a be sent to ameans for compensating the steering torque. Compensation of the steeringtorque is thus based upon the determined compensation torque. Thedetermined compensation torque may be added/subtracted to the steeringtorque so as to compensate for the torque provided by curvature/externalforces. The determined compensation torque may be comprised or constitutethe external torque ET according to fig. 4.

Fig. 8 schematically illustrates a block diagram of a method for facilitatingsteering of a vehicle during driving along a road according to an embodiment of the present invention.

According to the embodiment the method for facilitating steering of a vehicleduring driving along a road comprises a step S1. ln this step the vehiclespeed is determined.

According to the embodiment the method for facilitating steering of a vehicleduring driving along a road comprises a step S2. ln this step the curvature ofthe road is determined.

According to the embodiment method for facilitating steering of a vehicleduring driving along a road comprises a step S3. ln this step a required yawrate for the vehicle is determined based upon the thus determined vehiclespeed and curvature of the road.

According to the embodiment the method for facilitating steering of a vehicleduring driving along a road comprises a step S4. ln this step a curvaturecompensation torque for compensating the steering torque of the vehicle dueto influence of curvature is determined based upon said determined required 33 yaw rate and a gain function relating to steering torque and yaw rate of thevehicle.

The vehicle speed is determined continuousiy or intermittently during drive ofthe vehicle. The curvature of the road is determined continuousiy orintermittently during drive of the vehicle. The required yaw rate determined bymeans of the thus determined vehicle speed and curvature of the roadcorresponds to the yaw rate required for the vehicle to keep the vehicle in thedirection of the curvature or the road. l\/lore specifically, according to anembodiment, the required yaw rate determined by means of the thusdetermined vehicle speed and curvature of the road corresponds to the yawrate required for the vehicle to keep the vehicle in the direction of thecurvature or the road when the orientation of the vehicle essentiallycorresponds to a direction corresponding to the curvature of the road at thelocation of the vehicle.

The gain function comprises static gain. ln most drive situations comprisingnormal driving along a road, the gain function, by means of which thecurvature compensation torque is determined based upon said determinedrequired yaw rate, is a static gain which efficiently facilitates obtaining thecurvature compensation torque utilizing the fact that the change of thecurvature of the road is normally very small over a certain time/distance andmay be assumed essentially static/non-changing. This provides for a veryefficient compensation of the steering torque of the vehicle due to influence of curvature.

The gain function may for certain situations facilitate taking certain dynamicbehaviour into account, e.g. when there are passages of quick changes ofthe curvature along the road. The gain function may also be dependent onvehicle speed, wheel angle, load on front shaft and/or other parameters thatmay affect which gain, e.g. static gain, that is applicable at a certain momentof time. Such parameters may be modelled by means of a modelling means. 34 Hereby an easy and efficient method for compensating the steering of thevehicle due to external forces is facilitated. For automated steering functionssuch as Iane keep assist, compensation due to curvature of the road bymeans of the curvature compensation torque will prevent the vehicle frombouncing against the boundary of the Iane within which the vehicle isintended to be kept. For manual driving, the driver will have a muchincreased comfort and does not have to compensate for effects due tocurvature of the road.

According to an embodiment the method comprises the step ofcompensating the steering torque of the vehicle based upon said determined CUfVaIUfe COmpeﬂSaIlOn IOFQUG.

Hereby an easy and efficient method for compensating the steering of thevehicle due to external forces is facilitated. By thus basing the modelled yawrate upon the steering torque of the vehicle compensation of the steering of the vehicle without the need of information regarding the steering angle of thesteering wheel of the vehicle. For automated steering functions such as lanekeep assist, compensation of external forces will prevent the vehicle frombouncing against the boundary of the lane within which the vehicle isintended to be kept. For manual driving, the driver will have a muchincreased comfort and does not have to compensate for external effects suchas longer periods of road banking, i.e. cross sloped configuration of the road,and/or side wind.

By thus compensating the steering torque of the vehicle based upon saiddetermined external force compensation torque comfort for the operator of 36 the vehicle will be increased which may prevent stiff shoulder, stiff neck andthe like.

According to an embodiment of the method the result of said comparisonbetween the detected and modelled yaw rate is filtered so as to avoidinfluence of rapid changes. Hereby a more efficient compensation isobtained, further improving the comfort during driving along a road in thatrapid changes are avoided.

According to an embodiment the method further comprises the step ofdetermining a compensation torque based upon said determined curvaturecompensation torque and said determined external force compensationtorque; and compensating the steering torque based upon said determinedcompensation torque.

According to an embodiment of the method said gain function is obtained viasaid transfer function. 37 According to an embodiment of the method said gain function comprises astatic gain. The static gain provides information regarding the torque thatneeds to be maintained in order to maintain a constant yaw rate. ln mostdrive situations comprising normal driving along a road, the gain function, bymeans of which the curvature compensation torque is determined basedupon said determined required yaw rate, is a static gain which efficientlyfacilitates obtaining the compensation torque utilizing the fact that the changeof the curvature of the road and external effects are normally very small overa certain time/distance and may be assumed essentially static/non-changing,such a static gain therefor being efficient for obtaining the compensationtorque. This thus provides for a very efficient compensation of the steeringtorque of the vehicle due to influence of curvature and external forces.

With reference to figure 9, a diagram of an apparatus 500 is shown. Thecontrol unit 100 described with reference to fig. 5 may according to anembodiment comprise apparatus 500. Apparatus 500 comprises a non-volatile memory 520, a data processing device 510 and a read/write memory550. Non-volatile memory 520 has a first memory portion 530 wherein acomputer program, such as an operating system, is stored for controlling thefunction of apparatus 500. Further, apparatus 500 comprises a bus controller,a serial communication port, I/O-means, an A/D-converter, a time date entryand transmission unit, an event counter and an interrupt controller (notshown). Non-volatile memory 520 also has a second memory portion 540.

A computer program P is provided comprising routines for facilitating steeringof a vehicle during driving along a road according to an embodiment of thepresent invention. The program P comprises routines for determining thevehicle speed. The program P comprises routines for determining thecurvature of the road. The program P comprises routines for determining arequired yaw rate for the vehicle based upon the thus determined vehiclespeed and curvature of the road. The program P comprises routines fordetermining a curvature compensation torque for compensating the steering 38 torque of the vehicle due to influence of curvature based upon saiddetermined required yaw rate and a gain function relating to steering torqueand yaw rate of the vehicle. The program P comprises routines forcompensating the steering torque based upon said determined curvaturecompensation torque. The program P comprises routines for detecting theyaw rate of the vehicle. The program P comprises routines for modelling theyaw rate of the vehicle, the modelled yaw rate being based upon the steeringtorque of the vehicle. The modelled yaw rate is according to a variantobtained via a transfer function. The program P comprises routines forcomparing the detected and modelled yaw rate. The program P comprisesroutines for filtering the result of said comparison between the detected andmodelled yaw rate so as to avoid influence of rapid changes. The program Pcomprises routines for determining the influence of external forces on theyaw rate based on said comparison of detected and modelled yaw rate. Theprogram P comprises routines for determining an external forcecompensation torque for compensating the steering torque of the vehiclebased upon the determined influence of external forces on the yaw rate andsaid gain function determining. The external forces emanate from one ormore of: influence of cross sloped configuration of the road; influence oflateral wind; and influence of flat tire. The gain function is obtained via saidtransfer function. Said gain function comprises a static gain. The program Pcomprises routines for compensating the steering torque based upon saiddetermined external force compensation torque. The program P comprisesroutines for compensating the steering torque based upon said determinedexternal force compensation torque. The program P comprises routines fordetermining a compensation torque based upon said determined curvaturecompensation torque and said determined external force compensationtorque. The program P comprises routines for compensating the steeringtorque based upon said determined compensation torque. The computerprogram P may be stored in an executable manner or in a compressed condition in a separate memory 560 and/or in read/write memory 550. 39 When it is stated that data processing device 510 performs a certain functionit should be understood that data processing device 510 performs a certainpart of the program which is stored in separate memory 560, or a certain partof the program which is stored in read/write memory 550.

Data processing device 510 may communicate with a data communicationsport 599 by means of a data bus 515. Non-volatile memory 520 is adaptedfor communication with data processing device 510 via a data bus 512.Separate memory 560 is adapted for communication with data processingdevice 510 via a data bus 511. Read/write memory 550 is adapted forcommunication with data processing device 510 via a data bus 514. To thedata communications port 599 e.g. the links connected to the control units100 may be connected.

When data is received on data port 599 it is temporarily stored in secondmemory portion 540. When the received input data has been temporarilystored, data processing device 510 is set up to perform execution of code ina manner described above. The signals received on data port 599 can beused by apparatus 500 for determining the vehicle speed. The signalsreceived on data port 599 can be used by apparatus 500 for determining thecurvature of the road. The signals received on data port 599 can be used byapparatus 500 for determining a required yaw rate for the vehicle based uponthe thus determined vehicle speed and curvature of the road. The signalsreceived on data port 599 can be used by apparatus 500 for determining acurvature compensation torque for compensating the steering torque of thevehicle due to influence of curvature based upon said determined requiredyaw rate and a gain function relating to steering torque and yaw rate of thevehicle.

The signals received on data port 599 can be used by apparatus 500 forcompensating the steering torque based upon said determined curvaturecompensation torque. The signals received on data port 599 can be used byapparatus 500 for detecting the yaw rate of the vehicle. The signals received on data port 599 can be used by apparatus 500 for modelling the yaw rate ofthe vehicle, the modelled yaw rate being based upon the steering torque ofthe vehicle. The modelled yaw rate is according to a variant obtained via atransfer function. The signals received on data port 599 can be used byapparatus 500 for comparing the detected and modelled yaw rate. Thesignals received on data port 599 can be used by apparatus 500 for filteringthe result of said comparison between the detected and modelled yaw rateso as to avoid influence of rapid changes. The signals received on data port599 can be used by apparatus 500 for determining the influence of externalforces on the yaw rate based on said comparison of detected and modelledyaw rate and said gain function determining. The signals received on dataport 599 can be used by apparatus 500 for determining an external forcecompensation torque for compensating the steering torque of the vehiclebased upon the determined influence of external forces on the yaw rate. Theexternal forces emanate from one or more of: influence of cross slopedconfiguration of the road; influence of lateral wind; and influence of flat tire.The gain function is obtained via said transfer function. Said gain functioncomprises a static gain. The signals received on data port 599 can be usedby apparatus 500 for compensating the steering torque based upon saiddetermined external force compensation torque. The signals received ondata port 599 can be used by apparatus 500 for determining a compensationtorque based upon said determined curvature compensation torque and saiddetermined external force compensation torque. The signals received ondata port 599 can be used by apparatus 500 for compensating the steeringtorque based upon said determined compensation torque.

Parts of the methods described herein can be performed by apparatus 500by means of data processing device 510 running the program stored inseparate memory 560 or read/write memory 550. When apparatus 500 runsthe program, parts of the methods described herein are executed. 41 The foregoing description of the preferred embodiments of the presentinvention has been provided for the purposes of illustration and description. ltis not intended to be exhaustive or to limit the invention to the precise formsdisclosed. Obviously, many modifications and variations will be apparent topractitioners skilled in the art. The embodiments were chosen and describedin order to best explain the principles of the invention and its practicalapplications, thereby enabling others skilled in the art to understand theinvention for various embodiments and with the various modifications as aresuited to the particular use contemplated.

Claims

1. A method for facilitating steering of a vehicle (1) during driving along aroad (Fl), characterized by the steps of: - determining the vehicle speed; - determining the curvature of the road; - determining a required yaw rate for the vehicle based upon the thusdetermined vehicle speed and curvature of the road; and, - based upon said determined required yaw rate and a gain functionrelating to steering torque and yaw rate of the vehicle determining acurvature compensation torque for compensating the steering torque of thevehicle due to influence of curvature.

2. A method according to claim 1, further comprising the steps of: - detecting (S1) the yaw rate of the vehicle; - modelling (S2) the yaw rate of the vehicle based upon the steering torqueof the vehicle; - comparing (S3) the detected and modelled yaw rate; - determining (S4) the influence of external forces on the yaw rate basedon said comparison of detected and modelled yaw rate, said external forcescomprising external forces emanating from one or more of: influence of crosssloped configuration of the road; influence of lateral wind; and influence of flattire; and, - based upon the determined influence of external forces on the yaw rateand said gain function determining (S5) an external force compensationtorque for compensating the steering torque of the vehicle due to influence ofexternal forces..

3. A method according to claim 2, further comprising the step of determininga compensation torque based upon said determined curvature compensationtorque and said determined external force compensation torque; andcompensating the steering torque based upon said determined compensationtorque. 43

4. A method according to any of claims 2-4, wherein the modelled yaw rateis obtained via a transfer function (G(z)).

5. A method according to claim 5, wherein said gain function is obtained viasaid transfer function (G(z)).

6. A method according to any preceding claims, wherein said gain functioncomprises a static gain.

7. A system (|; ll; lll) for facilitating steering of a vehicle (1) during drivingalong a road (R), characterized by means (112; 212; 312) for determiningthe vehicle speed; means (114; 214; 314) for determining the curvature of theroad; means (120; 220; 320) for determining a required yaw rate for thevehicle based upon the thus determined vehicle speed and curvature of theroad; and means (130; 230; 330) for determining a curvature compensationtorque for compensating the steering torque of the vehicle due to influence ofcurvature based upon said determined required yaw rate and a gain functionrelating to steering torque and yaw rate of the vehicle.

8. A system according to claim 7, further comprising means (144) fordetecting the yaw rate of the vehicle; means (150; 350) for modelling the yawrate of the vehicle based upon the steering torque of the vehicle; means(160; 360) for comparing the detected and modelled yaw rate; means (170)for determining the influence of external forces on the yaw rate based on saidcomparison of detected and modelled yaw rate, said external forcescomprising external forces emanating from one or more of: influence of crosssloped configuration of the road, influence of lateral wind, and influence of flattire; and means (180; 380) for determining an external force compensationtorque for compensating the steering torque of the vehicle due to influence ofexternal forces based upon the determined influence of external forces onthe yaw rate and said gain function.

9. A system according to claim 8, further comprising means (192; 392) for determining a compensation torque based upon said determined curvature 44 compensation torque and said determined external force compensationtorque; and means (194) for compensating the steering torque based uponsaid determined compensation torque.

10. A system according to any of claims 2-4, wherein the modelled yaw rateis obtained via a transfer function (G(z)).

11. A system according to claim 5, wherein said gain function is obtained viasaid transfer function (G(z)).

12. A system according to any preceding claims, wherein said gain functioncomprises a static gain.

13. A vehicle (1) comprising a system (I) according to any of claims 6-10.

14. A computer program (P) for faciiitating steering of a vehicle during drivingalong a road, said computer program (P) comprising program code which,when run on an electronic control unit (100) or another computer (500)connected to the electronic control unit (100), causes the electronic controlunit to perform the steps according to claim 1-5.

15. A computer program product comprising a digital storage medium storingthe computer program according to claim 14.