• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The invention relates to a method for steering assistance of a vehicle (1), the vehicle (1) comprising a steering assist system (4) adapted to control the steering wheel torque required to be applied by the driver (T) to achieve a certain steering angle (M^), wherein the steering wheel (6) in a normal mode has a neutral position (P) in which the steered wheels (8) are directed in parallel with the longitudinal extension of the vehicle (1), wherein the steering assist system (4) is adapted to apply a return torque acting clockwise (+T) and a return torque acting counter-clockwise (-T) on the steering wheel (6), striving to turn the steering wheel (6) back to the neutral position (P). The method comprising the steps of predicting (s101) the curvature of the road on which the vehicle (1) is travelling; and controlling (s102) the required steering wheel torque (T) based on the predicted road curvature. The invention also relates to a steering assist system (4), a vehicle (1) comprising such a system (4), a computer program (P) and a computer program product.(Fig. 1)
    公开号:SE1650513A1
    申请号:SE1650513
    申请日:2016-04-18
    公开日:2017-10-19
    发明作者:Sidén Peter；BERGKVIST Johannes
    申请人:Scania Cv Ab；
    IPC主号:
    专利说明:

    A method for steering assistance and a steering assist system TECHNICAL FIELD The present invention relates to a method for steering assistance of a vehicle,a steering assist system, a vehicle comprising such a system, a computerprogram and a computer program product according to the appended claims.
    BACKG ROUND vehicles eentrnehly corrrerise steering assist systerns assistiitg the driver suchthat the tergue applied te a steering wheel is arneliiied and transrnitted te thesteered tft/heels through the steering wheel column. This irvay, large and heavyvehicles can he maneeuvred hy the driver' with less efleri. Seine steeringassist systems are ceniigured such that an active return tergue tries te turn thesteering wheel hack te a neutral pesltien in which the steered wheels aredirected straight ahead. This triray, ii the driver turns the steering wheel andthen let it go, the steering wheel will auterrtalically ge hack le the neutralposition. The return terdue is the terque the driver feels when turning thesteering wheel and therehy determines the steering wheel tcrdue required tehe applied hy the driver te turn the steering wheel te a desired steering angle.Serrle steering assist systems use electric meters and can therehy tfary thesteering assistance depencling en driving conditions, wherehy the requiredsteering wheel tcrdue to he applied hy the driver varies depenoling en drivingcenditieii. ll too little steering wheel torgue is required te achieve the desired steeringangle, the steering wheel may he perceived as unstable *which rnay heuneeirilortahle ler the driver. ll tee much steering yvheel terdue is required lt isdillicult ler the driver te turn the steering wheel and thus te steer the vehicle.Since the driver typicaliy turns the steering wheel less (smaller steering angle)during high speeds and more (larger steering angle) during low seeecls, some steering assist systems are contigured to varv the required steeriitg wheeiterdue depending en the vehieie speed. During high vehicie sneeds therequired steering vvheei torque that the driver has to appiy is tyeicaiiy iarger.This way, when driving ter exarheie en a highway, the steering becomes :herestaieie. Liitewise, steerirtg assist systems tehd to deerease the requiredsteering vvheei torque and thus provide mere assistance when the vehieiespeed is iew. "the steering assistance ntay aise vary based en factorsindioating that the vehicie is corneriittg er driving on a curvy road. USWWSQQA dissieses a steering assist system integrating a magnitude of the iateraieoceieratidn during a period ot time and adaptiveiy rnodiiies the steerihgassistance resoohsive to the vehicie operation. This way, the steeringassistance is increased when repeated turning rnarteetivres are deteoted andthe driver can steer the vehieie vvitit iess eitert. in serhe situatiehs, a sudden change ih required steering wheei terciue may hedisadvantageotrs. Fer exampie, it a vehieie is suddeniy ieraited tvhiie drivingthrough a eurve, such that the vehicie speed abruptiy deereases heidw theiirnit tor deereesing the steering eiiert, the driver might perceive the increasedassistance as it the vehicie is siipping on the road surface. Eiïtêiddsëšß Atdiseieses an adaptive steering assist system »where the steering assistance isdeterrhined according to two inees. ii it is decided that the vehieie is not in ahigh attention-reduiring state, a man is seiected based en vehicie speed and iiit decided that the vehieie is in a high attehtien-reduirirtg state the same manas previousiy seieeted is seiected again. This means that it a vehicie is tirstrunning with itigh speed en a straight road with a first steering assistance andthen ahruptiy hrakes through a curve, the steering assistance wiii he the sameas during the high speed driving even though the vehieie speed is iow. Thisway, the erehiem »with sudden and inconvenient increase et steeringassistance is aveided.
    SUMMARY OF THE INVENTION Despite known solutions in the field, there is still a need to develop a methodfor steering assistance of a vehicle and a steering assist system, whichincrease the safety and the driver comfort.
    An object of the present invention is to achieve an advantageous method forsteering assistance, which increases the safety and the driver comfort.
    Another object of the invention is to achieve an advantageous steering assistsystem, which increases the safety and the driver comfort.
    The herein mentioned objects are achieved by a method for steeringassistance, a steering assist system, a vehicle, a computer program and acomputer program product according to the independent claims.
    According to an aspect of the present invention a method for steeringassistance of a vehicle is provided. The vehicle comprises a steering assistsystem adapted to control the steering wheel torque required to be applied bya driver to achieve a certain steering angle, wherein the steering wheel in anormal mode has a neutral position in which the steered wheels of the vehicleare parallel with the longitudinal extension of the vehicle, wherein the steeringassist system is adapted to apply a return torque acting clockwise and a returntorque acting counter-clockwise on the steering wheel, striving to turn thesteering wheel back to the neutral position. The method comprises the stepsof: - predicting the curvature of the road on which the vehicle is travelling; and - controlling the required steering wheel torque based on the predicted roadcurvature.
    Steerirtg assist systems are used te assist the driver and thus te reduce thedriver effort when steering a vehicle. Many systems are cenflgured to centret the steering assistance hased on current driving conditions such as vehiotespeed. it is known that steering assistance is needed the most at iovir vehictesheeds tor exarnhie vviteh driving on curvy roads, parking iots or sirniiar. it isaise known that it is desired te have a stiit/'stahie steering vvheei when drivingwith high speed en tor exantpie a high way. With a steering assist systemahhiying an active return torogue striving to turn the steering vvheei hack to theneutrai position (zero position) the driver vviii peroeive the return tdrque as aresistance to turn the steerirtg wheei. The steering wheei toroue required to heaoptied hy the driver, and thus the driver ettert, therehy dehends on the returnitoroue. Other factors such as vvind, iaterat inctination (banking) oi the road etc.wiii aiso atiect the driver etiert when steering a vehicie. it is desired to minšrrrizethe driver eitort without rnaking the steering wheei urtstahie. By oredioting thecurvature ot the road on which a vehioie is traveiiing, the steering assistsystern cart oorttroi the steering wheel tordue required to he aphiied hy thedriver based on the nredictiert and therehy make sure that the driver ettort isrhinirrtized when needed. Aise, cehtrary tc known soiutiorrs, hy certtreiiirtg therequired steering wheei torogue hased on a oredicted curvattrre, the steeringassist systern is prepared to controi the required steering tvheei torcrue pre-entotiveiy or just in tirrte te when it is needed. in known soiutiorts the steerirtgassistance is controiied based on current driving conditions and there is thusaitvays a certain time tag heiore the adeduate steering assistance is given. Byoontroiiing the required steerirtg wheei tordue, and thus the steeringassistance, hased on a predicted curvature, such time tag is avoided. With themethod according to the invehtion, the driver gets the assistance when hedesiresifneeds it, tvhich increases the driver corntort. Aiso, sirice the steeringassistance is oontroiied based oh a predictien ot the read ourvature ahruhtcitanges ot steerihg assistance white driving through a curve, is avoided.Safety is therehy increased.
    The steering assist system oreterahiy oorriprises art eieotrio servornechanisrriwith an eiectrio motor. The active return torque is suitahiy appiied hy theeieetrio servonteohanisrri directiy to the steering wheei ooiurrth. The steering assistance and thus the required steering iivheei torque can thereby becontroiied in a iiexibie way.
    The torque appiied to the steering vvheei by the driver is herein caiied steeringwheei torque. The torque reqiiired to be appiied by the driver to achieve acertain steering angle is thus caiied required steering wheei torque.
    The neutral position of the steering wheel may also be called a centre positionor zero position and is the position of the steering wheel where no appliedreturn torque is actlng on the steering wheel. ln the normal mode, the neutralposition of the steering wheel is such that the steered wheels of the vehicle are directed straight ahead, in parallel with the longitudinal extension of the vehicle.
    The steering angle is zero degrees when the steering wheel is in the neutralposition in the normal mode. The steering angle is defined as the angle of thesteering wheel in relation to the neutral position of the steering wheel in thenormal mode. Steering angles achieved by turning the steering wheel to theright may be defined as positive steering angles and steering angles achievedby turning the steering wheel to the left may be defined as negative steeringangles. lt could however be the other way around depending on the steeringsystem.
    The clockwise respective the counter-clockwise return torque applied by thesteering assist system is acting in the opposite direction to the steering wheeltorque applied by the driver. Thus, if the driver is turning the steering wheel tothe right, the return torque acting counter-clockwise is striving to turn thesteering wheel back to the neutral position and if the driver is turning thesteering wheel to the left, the return torque acting clockwise is striving to turnthe steering wheel back to the neutral position. The return torque actingclockwise may be defined as a positive torque and the return torque actingcounter-clockwise may be defined as a negative torque, but it can also be theother way around depending on the steering system. The absolute value of thereturn torque acting clockwise and the return torque acting counter-clockwise is the same in the normal mode. The return torque is suitably controlled as afunction of the steering angle. The return torque is suitably controlled toincrease with the steering angle up to a certain steering angle, after which thereturn torque stays the same. The return torque thus suitably increasesgradually up to a predetermined maximum value. The predeterminedmaximum value of the return torque is suitably chosen such that the steeringwheel feels stable while allowing the driver to turn the steering wheel withouttoo big effort. ln the normal mode, the maximum value for the return torqueacting clockwise is suitably the same as the maximum value of the returntorque acting counter-clockwise.
    According to an aspect of the invention the curvature of the road is predictedby means of road data/map information relating to the current trajectory of thevehicle. The steering assist system suitably comprises road data/mapinformation received by means of a navigation unit, for example a GPS. Thesteering assist system is suitably adapted to retrieve road data/mapinformation from various sources according to conventional methods, forexample from camera/sensor means arranged on the vehicle, from systems onother vehicles, or from external servers/systems. The road data enables thesteering assist system to predict the curvature of the road ahead, such that the steering assistance can be planned thereafter.
    According to an aspect of the invention, when a curve is predicted, therequired steering wheel torque that the driver has to apply is decreased in thedirection of the curve. The required steering wheel torque is suitablydecreased in the direction of the curve just before entering the curve. Therequired steering wheel torque is suitably decreased in relation to the steeringwheel torque required in the normal mode. That is, if a curve to the right ispredicted the steering assist system makes sure that the required steeringwheel torque for turning the steering wheel to the right is decreased. The drivereffort is thereby decreased and the driver comfort is increased. By decreasingthe required steering wheel torque just before entering the curve, the driver immediately gets the assistance he needs. Also, by decreasing the requiredsteering wheel torque only in the direction of the curve, the steering wheelremains stable.
    According to an aspect of the invention the required steering wheel torque isdecreased by decreasing the return torque acting opposite to the curvedirection. lf the predicted curve turns to the right, the driver is expected to turnthe steering wheel to the right to a certain steering angle. Thus, by decreasingthe return torque acting counter-clockwise, the steering wheel torque that thedriver needs to apply to achieve said steering angle is decreased. The drivercomfort is thereby increased. Suitably, the maximum value of the return torqueacting opposite to the curve direction is decreased. Alternatively or additionallythe return torque acting opposite to the curve direction is decreased bymodifying the growth rate up to the maximum value, such that maximum valueis reached at a larger steering angle. By decreasing the return torque actingopposite to the curve direction it becomes smaller than the return torque actingin the curve direction. lt is thus easier to turn the steering wheel in the curvedirection than opposite to the curve direction. lf the driver turns the steeringwheel in the curve direction and subsequently lets it go, the decreased returntorque may not be able to turn the steering wheel back to the neutral positionsince the other return torque acting in the curve direction is larger. This way,the vehicle may turn slightly in the direction of the curve even when the driverdoesn't apply a steering wheel torque.
    According to an aspect of the invention the required steering wheel torque thatthe driver has to apply is decreased by displacing the neutral position of thesteering wheel by an offset angle. The neutral position is suitably displaced inthe curve direction. As discussed earlier the default neutral position of thesteering wheel is in the normal mode a centred position where the steeredwheels are parallel with the longitudinal extension of the vehicle. This meansthat if the driver turns the steering wheel either to the right or the left, and thenlet go of the steering wheel, the return torque will turn the steering wheel back to the neutral position, the steered wheels will become parallel with theIongitudinal extension of the vehicle and the vehicle will thus travel straightahead. By displacing the neutral position with an offset angle, the neutralposition will no longer mean that the steered wheels are parallel with theextension of the vehicle. lf, for example, a curve to the right is predicted, theneutral position of the steering wheel is displaced to the right in relation to theneutral position in the normal mode (zero degree angle). This way, the returntorques will strive to turn the steering wheel to the offset neutral position inwhich the steered wheels are directed to the right. Thus, if the driver lets go ofthe steering wheel the vehicle will still turn slightly to the right instead of goingstraight ahead. The neutral position is preferably displaced by an offset anglesmaller than the steering angle required to follow the curve. The purpose of theinvention is not to automatically steer the vehicle but to assist the driver. Bydisplacing the neutral position with an offset angle smaller than the requiredsteering angle, the driver only has to turn the steering wheel corresponding tothe difference between the required steering angle and the offset angle. Thisway, the steering wheel torque required to be applied by the driver isdecreased.
    The extent of the decrease of the required steering wheel torque preferablydepends on the curvature of the curve. The required steering wheel torque issuitably decreased more the sharper the bend of the curve. When the steeringassist system predicts a curve it retrieves information about the curve such ascurvature, length etc. Based on this the required steering wheel torque isdecreased to a value considered to be safe and comfortable for the driver. Theextent of the decrease of the required steering wheel torque may also dependon external factors such as wind, the road inclination etc. ln the case wherethe required steering wheel torque is decreased by decreasing the returntorque acting opposite to the curve direction, the maximum value of said returntorque is suitably decreased to a predetermined value depending on thecurvature of the curve. ln the case where the required steering wheel torque isdecreased by displacing the neutral position of the steering wheel, a steering angle required to follow the curve is calculated. The neutral position of thesteering wheel is preferably displaced with an offset angle between 25-75 % ofthe required steering angle. For example, if the required steering angle iscalculated to 4 degrees the offset angle is set between 1-3 degrees. Suitably,a predetermined maximum offset angle is set. The maximum offset angle issuitably set such that the driver perceives it as driving on a straight road with asafe bank angle. The offset angle is suitably controlled such that it never exceeds the predetermined maximum offset angle.
    According to an aspect of the invention the required steering wheel torque thatthe driver has to apply is decreased by applying an assist torque in thedirection of the curve. The assist torque is suitably applied by the steeringassist system directly to the steering wheel column. By applying an assisttorque in the curve direction, the required steering wheel torque that the driverneeds to apply in the direction of the curve will be decreased with the amountof the assist torque and the required steering wheel torque that the driver needto apply opposite to the curve direction will be increased with the amount of theassist torque. lt will thus require more effort to turn the steering wheel in thedirection opposite to the curve, and it will require less effort to turn the steeringwheel in the curve direction. Also, due to the assist torque the return torqueacting against the curve direction will not be able to turn the steering wheel tothe neutral position once the steering wheel has been turned in the direction ofthe curve. Thus, should the driver let go of the steering wheel, the vehicle willturn slightly in the direction of the curve.
    The decrease of the required steering wheel torque is preferably performedgradually. Suitably, the decrease is initiated just before entering the predictedcurve and intensifies with the bend of the curve. This way, sudden and abruptdecreases of required driver effort is avoided and the driver will not be shockedwhen it becomes easier to turn the steering wheel. ln a similar way, when thevehicle is leaving the curve the required steering wheel torque is gradually increased back to the normal mode. This way, a smooth and comfortablesteering assistance is achieved.
    The various methods of decreasing the required steering wheel torque mentioned herein may be combined.
    According to an aspect of the invention the method further comprises the stepto increase the return torque acting in direction of the curve. This way, it willrequire more effort to turn the steering wheel in the direction opposite to thecurve and the driver will thereby be stopped from turning the steering wheel inthe wrong direction.
    When an essentially straight road is predicted, the normal mode is suitablymaintained and the required steering wheel torque is unchanged. As describedearlier, if the vehicle is leaving a curve and a straight road is predicted afterthat, the required steering wheel torque is gradually increased up to the valuein the normal mode. When an essentially straight road is predicted it is thusensured that the neutral position of the steering wheel is not offset and that thereturn torque is the same in both directions. Alternatively, if a straight road ispredicted the required steering wheel torque is increased in both directions byincreasing the return torque on both sides. This way, the effort to turn thesteering wheel is increased and the steering wheel is stable in the neutral position.
    According to an aspect of the invention a steering assist system associatedwith a vehicle is provided. The steering assist system is adapted to control thesteering wheel torque required to be applied by a driver to achieve a certainsteering angle, wherein the steering wheel in a normal mode has a neutralposition in which the steered wheels of the vehicle are directed in parallel withthe longitudinal extension of the vehicle, wherein the steering assist system isadapted to apply a return torque acting clockwise and a return torque actingcounter-clockwise on the steering wheel, striving to turn the steering wheel 11 back to the neutral position. The steering assist system comprises a controlunit adapted to predict the curvature of the road on which the vehicle istravelling and to control the required steering wheel torque based on thepredicted road curvature.
    The steering assist system is suitably connected to the steering wheel, thesteering wheel column and the steered wheels of the vehicle. The steeringassist system may be mechanically and/or electrically connected to thesteering wheel, the steering wheel column and the steered wheels. ln the normal mode the neutral position of the steering wheel is such that thesteered wheels of the vehicle are directed straight ahead, in parallel with thelongitudinal extension of the vehicle. Also, in the normal mode the value of theclockwise and counter-clockwise return torques applied by the steering assistsystem are the same.
    The control unit is preferably adapted to predict the curvature of the road bymeans of road data/map information relating to the current trajectory of thevehicle. The control unit suitably comprises road data/map informationreceived from a navigation unit, for example a GPS. The control unit is suitablyadapted to retrieve road data/map information from various sources accordingto conventional methods, for example from camera/sensor means arranged onthe vehicle, from systems on other vehicles, or from external servers/systems.With the road data the control unit can predict the curvature of the road aheadand the required steering wheel torque can be controlled thereafter.
    When a curve is predicted the control unit is preferably adapted to decreasethe required steering wheel torque in the direction of the curve. The control unitis suitably adapted to decrease the required steering wheel torque just beforethe vehicle enters the curve. By controlling the required steering wheel torquebased oh a predšction of the road curvature the control uhit is prepared tocontrol the required steering wheel torque pre-emptively or just ih time to tvhen 12 it is needed, without time lag. By decreasing the required steering wheeltorque just before the tfehicie is entering the curve the driver assistance isprovided when needed.
    The control unit is preferably adapted to decrease the required steering wheeltorque by decreasing the return torque acting opposite to the curve direction.Suitably, the control unit is adapted to decrease the maximum value of the FGÉUFH tOfqUe.
    The control unit is preferably adapted to decrease the required steering wheeltorque by displacing the neutral position of the steering wheel by an offsetangle. The control unit is suitably adapted to displace the neutral position inthe curve direction. The control unit is adapted to displace the neutral positionin relation to the neutral position in the normal mode. Thus, by displacing theneutral position with an offset angle, the neutral position will no longer meanthat the steered wheels are parallel with the extension of the vehicle. Thecontrol unit is preferably adapted to displace the neutral position by an offsetangle smaller than the steering angle required to follow the curve.
    The control unit is preferably adapted to determine the extent of the decreaseof the required steering wheel torque depending on the curvature of the curve.Suitably, the control unit is adapted to decrease the required steering wheeltorque more the sharper the bend of the curve is. When the control unit haspredicted a curve it retrieves information about the curve such as curvature,length etc. Based on this the control unit is adapted to decrease the requiredsteering wheel torque to a value considered to be safe and comfortable for thedriver. ln the case where the required steering wheel torque is decreased bydecreasing the return torque, the control unit is suitably adapted to decreasethe maximum value of the return torque to a predetermined value dependingon the curvature of the curve. ln the case where the required steering wheeltorque is decreased by displacing the neutral position of the steering wheel,the control unit is adapted to predict a steering angle required to follow the 13 curve. The control unit is further suitably adapted to displace the neutralposition of the steering wheel with an offset angle between 25-75 % of therequired steering angle. Suitably, the control unit comprises a predeterminedmaximum offset angle corresponding to a safe bank angle of the road. Thecontrol unit is preferably adapted to control the offset angle such that it neverexceeds the predetermined maximum offset angle.
    The control unit is preferably adapted to decrease the required steering wheeltorque by applying an assist torque in the direction of the curve. The effect ofthis is that it will require more effort to turn the steering wheel in the directionopposite to the curve and it will require less effort to turn the steering wheel inthe curve direction.
    The control unit is suitably adapted to combine the various methods ofdecreasing the required steering wheel torque mentioned herein.
    The control unit is preferably adapted to decrease the required steering wheeltorque gradually. Suitably, the control unit is adapted to initiate the decreasejust before entering the predicted curve and to intensify the decrease with thebend of the curve. This way, sudden and abrupt steering assistance is avoidedand the safety is thereby increased. ln a similar way, when the vehicle isleaving the curve the control unit is adapted to gradually increase the requiredsteering wheel torque back to the normal mode. This way, a smooth andcomfortable steering assistance is achieved.
    The control unit may be adapted to increase the return torque acting indirection of the curve. This way, the driver effort to turn the steering wheel inthe direction opposite to the curve is increased. The driver will therebyperceive it even easier to turn the steering wheel in the curve direction and thesteering wheel is perceived as stable. 14 Further objects, advantages and novel features of the present invention willbecome apparent to one skilled in the art from the following details, and alsoby putting the invention into practice. Whereas the invention is describedbelow, it should be noted that it is not restricted to the specific detailsdescribed. Specialists having access to the teachings herein will recognisefurther applications, modifications and incorporations within other fields, whichare within the scope of the invention.
    BRIEF DESCRIPTION OF THE DRAWINGS For fuller understanding of the present invention and further objects and advantages of it, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which: Figure 1 schematically illustrates a vehicle according to an embodiment of the invention; Figure 2a-c schematically illustrates the function of a normal state of a steeringassist system according to an embodiment of the invention; Figure 3a-c schematically illustrates the function of a steering assist systemaccording to an embodiment of the invention; Figure 4a-c schematically illustrates the function of a steering assist systemaccording to an embodiment of the invention; Figure 5a-c schematically illustrates the function of a steering assist systemaccording to an embodiment of the invention; Figure 6a-c schematically illustrates the function of a steering assist systemaccording to an embodiment of the invention; Figure 7a-c schematically illustrates the function of a steering assist systemaccording to an embodiment of the invention; Figure 8 schematically illustrates a flow chart for a method for steeringassistance of a vehicle according to an embodiment of theinvenüon;and Figure 9 schematically illustrates a control unit or computer according to an embodiment of the invention.
    DETAILED DESCRIPTION OF THE DRAWINGS Figure 'i scnernaticeiiy shows a side view ot e. irehisie i according to enembedirneni of the invfertiion. The vehicle t inciucies a combustion engine 2, asteering assist system 4 adapted to centret the steering vviteei torque requiredto be appiied by a driver TD to achieve e certain steering angie W et thesteering wneei 6. The steering assist systern 4 is thus ssnrtected to thesteering tvneei 6 and to the sieered wneeis 8 of the vehieie t. The steeringassist system 4 suitably comprises a control unit 5 and an electricservomechanism with an electric motor (not shown) connected to the controlunit 5. The steering assist system 4 is further adapted to predict the curvatureof the road on which the vehicle 1 is travelling and to control the requiredsteering wheel torque TD based on this prediction. The vehicle 1 may be aheavy vehicle, e.g. a truck or a bus. The vehicle 1 may alternatively be apassenger car. The vehicle may be a hybrid vehicle comprising an electricmachine (not shown) in addition to the combustion engine 2. ln the coming figures various embodiments of the steering assistanceachieved with the steering assist system 4 will be described. Each embodimentwill be described in relation to a figure of the vehicle 1 in a predicted curve 10(Fig. 2a, 3a, 4a, 5a, 6a and 7a), a figure of the torques acting on the steeringwheel 6 (Fig. 2b, 3b, 4b, 5b, 6b and 7b) and a figure showing an example of 16 the torque acting on the steering wheel 6 as a function of the steering angle LP(Fig. 2c, 3c, 4c, 5c, 6c and 7c). The torque shown in figures 2c-7c is thus theeffect of the torque applied by the steering assist system. lt is to be understoodthat the torque acting on the steering wheel 6 is meant to include torque actingon the steering wheel column. ln the examples described in Figures 2a-c to7a-c the curve 10 is turning to the right. lt is to be understood that the principleof the steering assist system is the same irrespective of the curve direction. lnfigures 2c-7c the steering angles to the left are illustrated as negative steeringangles and steering angles to the right are illustrated as positive steeringangles. Likewise, the torque acting on the steering wheel 6 to the right (in thecurve direction) is illustrated as positive toque and torque acting on thesteering wheel 6 to the left (opposite the curve direction) is illustrated asnegative torque. The graph shown in figures 2c-7c thus corresponds to therequired steering wheel torque that the driver needs to apply TD to achieve theexemplified steering angles. This example shows the relationship betweentorque and steering angle as a linear function. lt is to be understood that this isonly an example and the relationship between torque and steering angle couldbe implemented in various ways.
    Figure 2a-c schenfiaticatly shows the function of a steering assist system 4 in anormal mode according to an embodiment of the invention. The normal modeis specifically suitable when the steering assist system 4 predicts a straightroad. However, in this example the steering assist system 4 has predicted acurve 10. The steering assist system 4 is suitably arranged in a vehicleaccording to Figure 1.
    The steering assist system 4 is configured such that the steering wheel 6 ofthe vehicle 1 in the normal mode has a neutral position P in which the steeredwheels 8 are parallel with the longitudinal extension of the vehicle 1. Thesteering wheel 6 and the neutral position P are illustrated in Figure 2b. Thesteering assist system 4 is further configured to apply a return torque actingclockwise +TR and a return torque acting counter-clockwise -TR on the 17 steering wheel 6, striving to turn the steering wheel 6 back to the neutralposition P. The respective return torque +TR, -TR is illustrated with an arrow inFigure 2b. This means that if the driver turns the steering wheel 6 in this modeand subsequently lets it go, the return torques +TR, -TR will turn the steeringwheel 6 back to the neutral position P, the steered wheels 8 will be directed inparallel with the longitudinal direction of the vehicle 1 and the vehicle 1 willthus drive straight ahead. This is illustrated by the solid line in Figure 2a. Thedashed line in Figure 2a illustrates the desired trajectory through the curve. lnorder to follow the desired trajectory in Figure 2a a certain steering angle W isrequired. The steering angle W is generally defined as the angle in relation tothe neutral position P of the steering wheel 6 in the normal mode. ln theneutral position P in the normal mode, the steering angle W is zero. Therequired steering angle ß to follow the desired trajectory is illustrated in Figure2b. To achieve the required steering angle ß the driver has to apply a certainsteering wheel torque TD to the steering wheel 6. The steering wheel torquerequired to be applied by the driver TD is illustrated as an arrow in the curvedirection in Figure 2b.
    The torque acting on the steering wheel 6 is disclosed as a function of thesteering angle W in Figure 2c. ln order to turn the steering wheel 6 the drivermust apply a corresponding steering wheel torque in the opposite direction.The steering wheel torque required to be applied by the driver TD is therebyequal in size to the torque illustrated in the graph but directed in the oppositedirection. Other factors such as wind and inclination of the road may also affectthe required steering wheel torque TD but such factors are omitted here for thesake of clarity. ln this embodiment the torque acting on the steering wheel 6consists of the return torques +TR, -TR. The return torque acting clockwise +TRis defined as a positive torque and the torque acting counter-clockwise -TR isdefined as a negative torque. As illustrated in Figure 2c each return torque +TR,-TD is controlled to increase with the steering angle W up to a certain steeringangle, after which the return torque +TD, -TR remains constant. The respective return torque +TR, -TR thus increase gradually up to a predetermined maximum 18 value +TDmaX, -Tgmaß The predetermined maximum value of the return torque+TDmaX, -TRmaX is suitably chosen such that the steering wheel 6 feels stablewhile allowing the driver to turn the steering wheel 6 without too big effort. lnthe normal mode, the maximum value of the return torque acting clockwise+TRmaX is the same as the maximum value of the return torque acting counter-clockwise -TRmaw ln the following example the maximum value of the returntorques +TDmaX, -TRmaX may be 3 Nm.
    To achieve the steering angle A the steering wheel 6 must be turned to the leftand steering angle A is thus a negative steering angle. The return torqueacting on the steering wheel 6 is thus the return torque acting clockwise +TR,which is a positive torque. The torque acting on the steering wheel 6 atsteering angle A is the predetermined maximum return torque in the clockwisedirection +TRmaX. The torque is thus illustrated as a positive torque of +3 Nm.The steering wheel torque required to be applied by the driver TD to achievesteering angle A is thus 3 Nm to the left.
    Steering angle B is zero degrees and is thus the neutral position P of thesteering wheel 6. ln this position no torque is acting on the steering wheel 6.The steering wheel torque required by the driver TD to achieve steering angleB is thus 0 Nm.
    With steering angle C the steering wheel 6 is turned slightly to the right and thereturn torque acting counter-clockwise -TD is acting on the steering wheel 6.The torque acting on the steering wheel 6 is thus illustrated as a negativetorque and in this example steering angle C corresponds to -1 Nm. Thesteering wheel torque required by the driver TD to achieve steering angle C isthus 1 Nm to the right.
    At steering angle ß, which is required to follow the curve 10, the return torqueacting counter-clockwise -TD is acting on the steering wheel 6. The torqueacting on the steering wheel 6 is thus disclosed as a negative torque and 19 corresponds to the maximum value of the return torque -TDmaw Thus, in thisexample the required steering angle ß corresponds to -3 Nm. The steeringwheel torque required by the driver TD to achieve steering angle ß is thus 3 Nmto the right.
    Steering angle D corresponds to steering angle A but the steering wheel 6 isturned to the right and steering angle D is thus positive and the return torqueacting counter-clockwise -TR is acting on the steering wheel 6. The torqueacting on the steering wheel 6 is the maximum value of the return torqueacting counter-clockwise -TDmaX. Thus, in this example steering angle Dcorresponds to -3 Nm. The steering wheel torque required by the driver TD toachieve steering angle D is thus 3 Nm to the right.
    The steering angle HJ after which the return torque +TD, -TD remains constantmay be between 4-8 degrees.
    Figure 3a-c schematicaily shows the function of a steering assist system 4according to an embodiment of the invention. The steering assist system 4suitably corresponds to the steering assist system 4 disclosed in Figure 1-2. lnthis embodiment the steering assist system 4 has predicted a curve 10 and therequired steering wheel torque TD is decreased in direction of the curve 10 bydecreasing the return torque -TR acting opposite to the curve direction. Sincethe predicted curve 10 turns to the right, the driver must turn the steeringwheel 6 to the right to the required steering angle ß in order to follow the curve.Thus, by decreasing the return torque acting counter-clockwise -TD, thesteering wheel torque that the driver needs to apply TD to achieve said steeringangle ß is decreased. The driver comfort is thereby increased.
    The decrease of the return torque acting counter-clockwise -TD is illustrated inFigure 3c where the maximum value of the return torque in the counter-clockwise direction -TDmaX is decreased. The maximum value of the return torque acting counter-clockwise -TDmaX is now -2 Nm instead of -3 Nm as described in Figure 2. The return torque acting counter-clockwise -TD isthereby smaller than the return torque acting clockwise +TD. This means that ifthe driver turns the steering wheel 6 to the right and subsequently lets it go,the counter-clockwise return torque -TD may not be able to turn the steeringwheel 6 back to the neutral position P since the other return torque +TR islarger. This way, the vehicle 1 will turn slightly in the direction of the curve 10even when the driver doesn't apply a steering wheel torque TD. This isillustrated by the solid line in Figure 3a.
    The torque acting on the steering wheel 6 and thus the steering wheel torquerequired by the driver TD with the steering assistance according to thisembodiment will be described in relation to Figure 3c. ln this embodiment thetorque acting on the steering wheel 6 consists of the return torques +TR, -TD The torque acting on the steering wheel 6 at steering angles A, B and C arethe same as in Figure 2c. The steering wheel torque required by the driver TDto achieve steering angle A is thus 3 Nm to the left. Steering angle B is zerodegrees and no torque is acting on the steering wheel 6 whereby the steeringwheel torque required by the driver TD is O Nm. With steering angle C thesteering wheel 6 is turned slightly to the right and the steering wheel torquerequired by the driver TD to achieve steering angle C is thus 1 Nm to the right.
    At the steering angle ß required to follow the curve 10 the return torque actingcounter-clockwise -TR is acting on the steering wheel 6. The torque acting onthe steering wheel is thus disclosed as a negative torque and corresponds tothe decreased maximum value of the return torque in the counter-clockwisedirection -TDmew Thus, in this example the required steering angle ßcorresponds to -2 Nm. The steering wheel torque required by the driver TD toachieve steering angle ß is thus 2 Nm to the right. Similarly, at steering angleD the torque acting on the steering wheel 6 is the decreased maximum valueof the return torque, -TRmaX. Thus, in this example steering angle D 21 corresponds to -2 Nm and the steering wheel torque required by the driver TDis 2 Nm to the right. lt is thus obvious that with a steering assistance according to this embodimentthe driver effort is decreased compared to the normal mode.
    Figure 4a-c sclwernatically shows the function of a steering assist system 4according to an embodiment of the invention. The steering assist system 4suitably corresponds to the steering assist system 4 disclosed in Figure 1-3. lnthis embodiment the steering assist system 4 has predicted a curve 10 and therequired steering wheel torque TD is decreased in direction of the curve 10 bydisplacing the neutral position P of the steering wheel 6 by an offset angle O.The neutral position P is displaced in the curve direction and is thus displacedto the right of the neutral position in the normal mode. This way, the returntorques +TR, -TR will strive to turn the steering wheel 6 to the offset neutralposition P in which the steered wheels 8 are directed to the right. Thus, if thedriver lets go of the steering wheel 6 the vehicle 1 will still turn slightly to theright instead of going straight ahead. This is illustrated by the solid line inFigure 4a. ln this example, the neutral position P has been displaced by an offset angle Owhich is between 25-75 °/> of the required steering angle ß. This way, thedriver only has to turn the steering wheel 6 corresponding to the differencebetween the required steering angle ß and the offset angle O in order toachieve the required steering angle ß. Displacing the neutral position P by theoffset angle O corresponds to moving the graph of the steering wheel torqueapplied by the steering assist system TSW in Figure 2c to the right. The effect ofthis displacement will be described in relation to the steering angles previouslymentioned in Figures 2c and 3c. ln this embodiment the torque acting on thesteering wheel 6 consists of the return torques +TR, -TR. 22 At the steering angle A, the torque acting on the steering wheel 6 is thepredetermined maximum return torque acting clockwise +TDmaX. The torqueacting on the steering wheel 6 is thus a positive torque +3 Nm. The steeringwheel torque required to be applied by the driver TD to achieve steering angleA is thus 3 Nm to the left.
    Steering angle B is zero degrees but no longer represents the neutral positionP of the steering wheel 6. Thus, the return torque acting in the clockwisedirection +TR is acting on the steering wheel 6 in order to turn the steeringwheel 6 to the offset neutral position P. The torque acting on the steeringwheel 6 in steering angle B is now +1 Nm. The steering wheel torque requiredby the driver TD to achieve steering angle B is thus 1 Nm to the left.
    Steering angle C is the offset angle O and thus represents the offset neutralposition P of the steering wheel 6. No torque is acting on the steering wheel 6in this position and the steering wheel torque required by the driver TD toachieve steering angle C is thus 0 Nm.
    At the steering angle ß required to follow the curve 10 the return torque actingcounter-clockwise -TR is acting on the steering wheel 6. However, due to thedisplacement of the neutral position P the return torque -TD in this position issmaller than in the normal mode. The torque acting on the steering wheel 6 isin this example approximately -1,75 Nm. The steering wheel torque requiredby the driver TD to achieve steering angle ß is thus approximately 1,75 Nm tothe right.
    At steering angle D the torque acting on the steering wheel 6 is the maximumvalue of the return torque acting counter clockwise -TDmaX, -3 Nm. The steeringwheel torque required by the driver TD is thereby 3 Nm.
    Figure 5a-c schematicaily shows the function of a steering assist system 4according to an embodiment of the invention. The steering assist system 4 23 suitably corresponds to the steering assist system 4 disclosed in Figure 1-4. lnthis embodiment the steering assist system 4 has predicted a curve 10 and therequired steering wheel torque TD is decreased in direction of the curve 10 byapplying an assist torque TA in the direction of the curve 10. By applying anassist torque TA in the curve direction, the torque acting in the direction of thecurve will be increased with the amount of the assist torque TA and the driverthus has to apply a higher torque to turn the steering wheel opposite to thecurve direction. Also, by applying the assist torque TA in the curve directionless effort is required by the driver to turn the steering wheel 6 in the curvedirection. The addition of an assist torque TA corresponds to moving the graphin Figure 2c upwards. The effect of adding the assist torque TA is that thetorque acting on the steering wheel 6 opposite to the curve direction is smallerthan in the normal mode. lt is thereby easier to turn the steering wheel 6 in thecurve direction. The effect of this steering assistance will be described inrelation to various steering angles in Figure 5c.
    At the steering angle A, the torque acting on the steering wheel 6 is thepredetermined maximum return torque acting clockwise +TAmaX plus the assisttorque TA. ln this example the assist torque may be +1 Nm. The torque actingon the steering wheel 6 is thus +4 Nm. The steering wheel torque required bythe driver TD to achieve steering angle A is thus 4 Nm to the left.
    Steering angle B is zero degrees and is the neutral position P of the steeringwheel 6. However, due to the assist torque TA acting in the clockwise directionsteering angle B is no longer the effective neutral position. Adding the assisttorque TA will thus have the same effect as displacing the neutral position P.Thus, the torque acting on the steering wheel 6 in steering angle B is now +1Nm. The steering wheel torque required by the driver TD to achieve steeringangle B is thus 1 Nm to the left.
    Steering angle C is now the effective neutral position P of the steering wheel 6in that no torque is acting on the steering wheel 6 in this position. The steering 24 wheel torque required by the driver TD to achieve steering angle C is thus 0Nm.
    At the steering angle ß required to follow the curve 10 the torque acting on thesteering wheel 6 is approximately -1,75 Nm. The steering wheel torquerequired by the driver TD to achieve steering angle ß is thus approximately 1,75 Nm to the right.
    At steering angle D the torque acting on the steering wheel 6 is -2 Nm. Thesteering wheel torque required by the driver TD is thereby 2 Nm.
    Figure 6a-c schematicaily shows the function of a steering assist system 4according to an embodiment of the invention. The steering assist system 4suitably corresponds to the steering assist system 4 disclosed in Figure 1-5. lnthis embodiment the steering assist system 4 has predicted a curve 10 and therequired steering wheel torque TD is decreased in direction of the curve 10 bydisplacing the neutral position P of the steering wheel 6 by an offset angle Oand by decreasing the return torque -TR acting opposite to the curve direction.The return torque -TR is decreased by decreasing the maximum value of thereturn torque acting counter-clockwise -TRmaX. This embodiment is thus acombination of the embodiments described in Figures 3a-c and 4a-c. Theeffect of the steering assistance according to this embodiment is described in Figure 6c.
    At the steering angle A, the torque acting on the steering wheel 6 is thepredetermined maximum return torque acting clockwise +TRmaX, +3 Nm. Thesteering wheel torque required by the driver TD to achieve steering angle A isthus 3 Nm to the left.
    Steering angle B is zero degrees but is no longer the neutral position P of thesteering wheel 6 since the neutral position P has been displaced. Thus, thetorque acting on the steering wheel 6 in steering angle B is the return torque acting clockwise +TR with the value +1 Nm. The steering wheel torque requiredby the driver TD to achieve steering angle B is thus 1 Nm to the left.
    Steering angle C is the offset neutral position P of the steering wheel 6 whereno torque is acting on the steering wheel 6. The steering wheel torque requiredby the driver TD to achieve steering angle C is thus 0 Nm.
    At the steering angle ß required to follow the curve 10 the return torque actingcounter-clockwise -TR is acting on the steering wheel 6. Since the return torqueacting counter-clockwise -TD was decreased the torque acting on the steeringwheel 6 is approximately -1,75 Nm. The steering wheel torque required by thedriver TD to achieve steering angle ß is thus approximately 1,75 Nm to theright.
    At steering angle D the return torque acting counter-clockwise -TR is acting onthe steering wheel 6. Since the return torque -TR was decreased the torqueacting on the steering wheel 6 is the decreased maximum value of the returntorque -TRmaM -2 Nm. The steering wheel torque required by the driver TD isthereby 2 Nm.
    Figure 7a-c sctternaticaily shows the function of a steering assist system 4according to an embodiment of the invention. The steering assist system 4suitably corresponds to the steering assist system 4 disclosed in Figure 1-6. lnthis embodiment the steering assist system 4 has predicted a curve 10 and therequired steering wheel torque TD is decreased in direction of the curve 10 bydecreasing the return torque -TR acting opposite to the curve direction. ln theembodiment described in Figures 3a-c the maximum value of the return torqueacting opposite to the curve direction -TRmaX was decreased, which made iteasier to turn the steering wheel 6 in the curve direction. ln this embodimentthe maximum value of the return torque acting opposite to the curve direction -TRmaX is likewise decreased but the increase of the return torque -TR as afunction of the steering angle W is also modified. The return torque acting 26 counter-clockwise -TR is suitably controlled such that it has a lower increaserate. That is, the maximum value of the return torque acting counter-clockwise-TRmaX is reached at a larger steering angle W than in the normal mode.Suitably, the return torque acting clockwise +TR is controlled such that it has ahigher increase rate. This way, the driver will meet a higher resistance atsmaller steering angles W when turning the steering wheel 6 in the directionopposite to the curve direction.
    The decrease of the return torque acting counter-clockwise -TR is illustrated inFigure 7c where the maximum value of the return torque in the counter-clockwise direction -TDmaX is decreased. The maximum value of the returntorque acting counter-clockwise -TRmaX is now -2 Nm instead of -3 Nm asdescribed in Figure 2. The torque acting on the steering wheel 6 at steeringangle C and ß is smaller than in the embodiment described in Figures 3a-c.The steering wheel torque required by the driver TD to achieve steering angleA is 3 Nm to the left. Steering angle B is zero degrees and no torque is actingon the steering wheel 6 whereby the steering wheel torque required by thedriver TD is O Nm. At steering angle C the steering wheel torque required bythe driver TD is 0,5 Nm to the right due to the modified increase rate. Also dueto the modified increase rate the steering wheel torque required by the driverTD to achieve the steering angle ß is 1,25 Nm to the right. The torque acting onthe steering wheel 6 at steering angle D is the decreased maximum value ofthe return torque acting counter-clockwise -Tpimaw Thus, the steering wheeltorque required by the driver TD is 2 Nm.
    Figure 8 schematically illustrates a flow chart for a method for steeringassistance of a vehicle 1 according to an embodiment of the invention. Thevehicle 1 comprises a steering assist system 4 adapted to control the steeringwheel torque required to be applied by a driver TD to achieve a certain steeringangle W, wherein the steering wheel 6 in a normal mode has a neutral positionP in which the steered wheels 8 of the vehicle 1 are parallel with thelongitudinal extension of the vehicle 1, wherein the steering assist system 4 is 27 adapted to apply a return torque acting clockwise +TR and a return torqueacting counter-clockwise -TR, each striving to turn the steering wheel 6 back tothe neutral position P. The method comprises the steps of predicting s101 thecurvature of the road on which the vehicle 1 is travelling; and controlling s102the required steering wheel torque TD based on the predicted road curvature.
    The return torque acting clockwise +TR is preferably defined as a positivetorque and the return torque acting counter-clockwise -TR is preferably definedas a negative torque. The absolute value of the return torque acting clockwise+TR and the return torque acting counter-clockwise -TR is the same in thenormal mode. The respective return torque +TR, -TR is suitably controlled toincrease with the steering angle LP up to a certain steering angle, after whichthe return torque +TR, -TD stays the same. The respective return torque +TR, -TD thus suitably increases gradually up to a predetermined maximum value+TRmaX, -TRmaX. The predetermined maximum value of the return torque +TRmaX,-TDmaX is suitably chosen such that the steering wheel 6 feels stable whileallowing the driver to turn the steering wheel 6 without too big effort.
    The step to predict s101 the curvature of the road on which the vehicle 1 istravelling is suitably performed by means of road data/map information relatingto the current trajectory of the vehicle 1. The steering assist system 4 suitablycomprises road data/map information received by means of a navigation unit,for example a GPS. The steering assist system 4 is suitably adapted to retrieveroad data/map information from various sources according to conventionalmethods, for example from camera/sensor means arranged on the vehicle 1,from systems on other vehicles, or from external servers/systems. The roaddata enables the steering assist system 4 to predict the curvature of the roadahead, such that the steering assistance can be planned thereafter.
    The step to control s102 the required steering wheel torque TD based on thepredicted road curvature may comprise to decrease the required steeringwheel torque TD in the direction of a curve 10 when a curve 10 is predicted. 28 The required steering wheel torque TD is suitably decreased just beforeentering the curve 10. By decreasing the required steering wheel torque TDonly in the direction of the predicted curve 10, the resistance in the oppositedirection is still the same and the driver will perceive it as being much easier toturn the steering wheel 6 in the direction of the curve 10. The required steeringwheel torque TD is suitably decreased in relation to the steering wheel torquerequired in the normal mode. That is, if a curve to the right is predicted thesteering assist system 4 makes sure that the required steering wheel torque TDfor turning the steering wheel 6 to the right is decreased. The driver effort isthereby decreased and the driver comfort is increased. By decreasing therequired steering wheel torque TD just before entering the curve, the driverimmediately gets the assistance he needs.
    The step to control s102 the required steering wheel torque TD based on thepredicted road curvature may comprise to decrease the required steeringwheel torque TD by decreasing the return torque +TD, -TD acting opposite tothe curve direction. lf the predicted curve 10 turns to the right, the driver isexpected to turn the steering wheel to the right to a certain steering angle W.Thus, by decreasing the return torque acting counter-clockwise -TR, thesteering wheel torque that the driver needs to apply TD to achieve said steeringangle W is decreased. The driver comfort is thereby increased. The returntorque +TR, -TD acting opposite to the curve direction is suitably decreased bydecreasing the maximum value of the return torque +TRmaX, -TRmaX.Alternatively, the return torque +TR, -TD acting opposite to the curve direction isdecreased by modifying the increase of the return torque +TR, -TD in relation tothe steering angle W, such that the return torque +TR, -TR acting opposite tothe curve direction has a lower increase rate. The return torque acting oppositeto the curve direction thereby becomes smaller than the return torque acting inthe curve direction. lt is thus easier to turn the steering wheel 6 in the curve direction than opposite to the curve direction. 29 The step to control s102 the required steering wheel torque TD based on thepredicted road curvature may comprise to decrease the required steeringwheel torque TD by displacing the neutral position P of the steering wheel 6 byan offset angle O. The neutral position P is suitably displaced in the curvedirection. The default neutral position of the steering wheel 6 is in the normalmode a centred position (with steering angle zero degrees) where the steeredwheels 8 are parallel with the longitudinal extension of the vehicle 1. Bydisplacing the neutral position P with an offset angle O, the neutral position Pwill no longer mean that the steered wheels 8 are parallel with the longitudinalextension of the vehicle 1. lf, for example, a curve to the right is predicted, theneutral position P of the steering wheel 6 is displaced to the right in relation tothe zero degree angle. This way, the return torques +TR, -TR will strive to turnthe steering wheel 6 to the offset neutral position in which the steered wheels 8are directed to the right. Thus, if the driver lets go of the steering wheel 6 thevehicle will still turn slightly to the right instead of going straight ahead. Theneutral position is preferably displaced by an offset angle O smaller than asteering angle ß required to follow the curve 10. By displacing the neutralposition P with an offset angle O smaller than the required steering angle ß,the driver only has to turn the steering wheel 6 corresponding to the differencebetween the required steering angle ß and the offset angle O. This way, thereturn torque acting in direction opposite to the curve will be smaller than in thenormal mode for the required steering angle ß. The steering wheel torquerequired to be applied by the driver TD is thereby decreased.
    The required steering wheel torque TD is preferably decreased based on thecurvature of the curve 10. The required steering wheel torque TD is suitablydecreased more the sharper the bend of the curve 10. When the steeringassist system 4 predicts a curve 10 it retrieves information about the curve 10such as curvature, length etc. Based on this the required steering wheel torque TD is decreased to a value considered to be safe and comfortable for the driver. ln the case where the required steering wheel torque TD is decreased bydecreasing the return torque +TR, -TR acting opposite to the curve direction, the maximum value of the return torque +TDmaX, -TDmaX is suitably decreased toa predetermined value depending on the curvature of the curve. ln the casewhere the required steering wheel torque TD is decreased by displacing theneutral position P of the steering wheel 6, a steering angle ß required to followthe curve is predicted. The neutral position P of the steering wheel 6 ispreferably displaced with an offset angle O between 25-75 °/> of the requiredsteering angle ß. For example, if the required steering angle ß is determined to4 degrees the offset angle O is set between 1-3 degrees. Suitably, apredetermined maximum offset angle is set, corresponding to a safe bankangle of the road. The offset angle O is suitably controlled such that it neverexceeds the predetermined maximum offset angle.
    The decrease of the required steering wheel torque TD is preferably performedgradually. Suitably, the decrease is initiated just before entering the predictedcurve 10 and intensifies with the bend of the curve 10. This way, sudden andabrupt decreases of required driver effort is avoided and the driver will not beshocked when it becomes easier to turn the steering wheel 6. ln a similar way,when the vehicle 1 is leaving the curve 10 the required steering wheel torqueTD is gradually increased back to the normal mode. This way, a smooth andcomfortable steering assistance is achieved.
    The step to control s102 the required steering wheel torque TD based on thepredicted road curvature may comprise to decrease the required steeringwheel torque TD in the curve direction by applying an assist torque TA in thedirection of the curve. By applying an assist torque TA in the curve direction,the resultant torque acting on the steering wheel 6 in the direction of the curve10 will be increased with the amount of the assist torque TA and the resultanttorque acting on the steering wheel 6 opposite to the curve direction will bedecreased with the amount of the assist torque TA. The effect of this is that itwill require more effort to turn the steering wheel 6 in the direction opposite tothe curve 10, and it will require less effort to turn the steering wheel 6 in the curve direction. 31 The various methods of decreasing the required steering wheel torque TD maybe combined.
    The method may further comprise the step to increase the return torque +TR, -TD acting in direction of the curve. This way, it will require more effort to turnthe steering wheel 6 in the direction opposite to the curve and the steeringwheel 6 is still considered to be stable.
    The step to control s102 the required steering wheel torque TD based on thepredicted road curvature may comprise to maintain the normal mode when it ispredicted that the road will be essentially straight. The required steering wheeltorque TD is thereby unchanged. lf the vehicle 1 is leaving a curve 10 and astraight road is predicted after that, the required steering wheel torque TD issuitably gradually increased up to the value in the normal mode. lt is thusensured that the neutral position P of the steering wheel 6 is not offset and thatthe return torque +TR, -TD is the same in both directions. Alternatively, if astraight road is predicted the required steering wheel torque TD may beincreased in both directions by increasing the return torque +TD, -TR on bothsides in relation to the normal mode. This way, the effort to turn the steeringwheel is increased and the steering wheel 6 is stable in the neutral position P.
    Figure 9 schematically illustrates a device 500. The control unit 5 describedwith reference to Figure 1 may in a version comprise the device 500. The term“link” refers hereln to a communication link which may be a physicalconnection such as an optoelectronic communication line, or a non-physicalconnection such as a wireless connection, e.g. a radio link or microwave link.The device 500 comprises a non-volatile memory 520, a data processing unit510 and a read/write memory 550. The non-volatile memory 520 has a firstmemory element 530 in which a computer program, e.g. an operating system,is stored for controlling the function of the device 500. The device 500 furthercomprises a bus controller, a serial communication port, I/O means, an A/D 32 converter, a time and date input and transfer unit, an event counter and aninterruption controller (not depicted). The non-volatile memory 520 has also asecond memory element 540.
    There is provided a computer program P which comprises routines for amethod for steering assistance of a vehicle 1 according to the invention. Thecomputer program P comprises routines for predicting the curvature of a roadon which the vehicle is travelling. The computer program P comprises routinesfor contro|ing the required steering wheel torque TD based on the predictedroad curvature. The computer program P comprises routines for decreasingthe required steering wheel torque TD in the curve direction by decreasing thereturn torque +TD, -TR acting opposite the curve direction. The computerprogram P comprises routines for decreasing the required steering wheeltorque TD in the curve direction by displacing the neutral position P of thesteering wheel 6 with an offset angle O. The computer program P comprisesroutines for decreasing the required steering wheel torque TD in the curvedirection by applying an assist torque TA in the curve direction. The computerprogram P comprises routines for increasing the return torque +TR, -TR actingin the curve direction. The program P may be stored in an executable form orin a compressed form in a memory 560 and/or in a read/write memory 550.
    Where the data processing unit 510 is described as performing a certainfunction, it means that the data processing unit 510 effects a certain part of theprogram stored in the memory 560 or a certain part of the program stored inthe read/write memory 550.
    The data processing device 510 can communicate with a data port 599 via adata bus 515. The non-volatile memory 520 is intended for communication withthe data processing unit 510 via a data bus 512. The separate memory 560 isintended to communicate with the data processing unit 510 via a data bus 511.The read/write memory 550 is adapted to communicating with the dataprocessing unit 510 via a data bus 514. 33 When data are received on the data port 599, they are stored temporarily inthe second memory element 540. When input data received have beentemporarily stored, the data processing unit 510 is prepared to effect codeexecution as described above.
    Parts of the methods herein described may be effected by the device 500 bymeans of the data processing unit 510 which runs the program stored in thememory 560 or the read/write memory 550. When the device 500 runs theprogram, methods herein described are executed.
    The foregoing description of the preferred embodiments of the presentinvention is provided for illustrative and descriptive purposes. It is not intendedto be exhaustive or to restrict the invention to the variants described. Manymodifications and variations will obviously be apparent to one skilled in the art.The embodiments have been chosen and described in order best to explainthe principles of the invention and its practical applications and hence make itpossible for speciaiists to understand the invention for various embodiments and with the various modifications appropriate to the intended use.
    权利要求:
    Claims (18)
    [1] 1. A method for steering assistance of a vehicle (1), the vehicle (1) comprisinga steering assist system (4) adapted to control the steering wheel torquerequired to be applied by the driver (TD) to achieve a certain steering angle (LP),wherein the steering wheel (6) in a normal mode has a neutral position (P) inwhich the steered wheels (8) are directed in parallel with the longitudinalextension of the vehicle (1), wherein the steering assist system (4) is adaptedto apply a return torque acting clockwise (+TR) and a return torque actingcounter-clockwise (-TR) on the steering wheel (6), striving to turn the steeringwheel (6) back to the neutral position (P), the method comprising the steps of: - predicting (s101) the curvature of the road on which the vehicle (1) istravelling; and - controlling (s102) the required steering wheel torque (TD) based on thepredicted road curvature.
    [2] 2. The method according to claim 1, wherein the curvature of the road ispredicted (s101) by means of road data/map information relating to the currenttrajectory of the vehicle (1 ).
    [3] 3. The method according to claim 1 or 2, wherein, when a curve (10) ispredicted, the required steering wheel torque (TD) is decreased in the directionof the curve (10).
    [4] 4. The method according to claim 3, wherein the required steering wheeltorque (TD) is decreased by decreasing the return torque (+TR, -TD) acting onthe steering wheel (6) opposite to the curve direction.
    [5] 5. The method according to any of claims 3-4, wherein the required steeringwheel torque (TD) is decreased by displacing the neutral position (P) of thesteering wheel (6) by an offset angle (O).
    [6] 6. The method according to any of claims 3-5, wherein the required steeringwheel torque (TD) is decreased by applying an assist torque (TA) in thedirection of the curve (10).
    [7] 7. The method according to any of claims 3-6, wherein the decrease of therequired steering wheel torque (TD) is performed gradually.
    [8] 8. The method according to any of claims 3-7, wherein the method furthercomprises the step to increase the return torque (+TD, -TR) acting in directionof the curve.
    [9] 9. A steering assist system (4) associated with a vehicle (1), adapted to controlthe steering wheel torque required to be applied by a driver (TD) to achieve acertain steering angle (W), the steering wheel (6) having a neutral position (P)in which the steered wheels (8) of the vehicle (1) are directed in parallel withthe longitudinal extension of the vehicle (1 ), wherein the steering assist system(4) is adapted to apply a return torque acting clockwise (+TR) and a returntorque acting counter-clockwise (-TR) on the steering wheel (6), striving to turnthe steering wheel (6) back to the neutral position (P), characterized in that itcomprises a control unit (5) adapted to predict the curvature of the road onwhich the vehicle (1) is travelling and to control the required steering wheeltorque (TD) based on the predicted road curvature.
    [10] 10. The system according to claim 9, wherein the control unit (5) is adapted topredict the curvature of the road by means of road data/map informationrelating to the current trajectory of the vehicle (1 ).
    [11] 11. The system according to any of claims 9-10, wherein the control unit (5) isadapted to, when a curve (10) is predicted, decrease the required steeringwheel torque (TD) in the direction of the curve (10). 36
    [12] 12. The system according to any of claims 9-11, wherein the control unit (5) isadapted to decrease the required steering wheel torque (TD) by decreasing thereturn torque (+TR, -TR) acting on the steering wheel (6) opposite to the curvedirection.
    [13] 13. The system according to any of claims 9-12, wherein the control unit (5) isadapted to decrease the required steering wheel torque (TD) by displacing theneutral position (P) of the steering wheel (6) by an offset angle (O).
    [14] 14. The system according to any of claims 9-13, wherein the control unit (5) isadapted to decrease the required steering wheel torque (TD) by applying anassist torque (TA) in the direction of the curve.
    [15] 15. The system according to any of claims 9-14, wherein the control unit (5) isadapted to increase the return torque (+TR, -TR) acting in direction of the curve.
    [16] 16. A vehicle, characterized in that it comprises a system (4) according toany of claims 9-15.
    [17] 17. A computer program (P), wherein said computer program comprisesprogram code for causing an electronic control unit (5; 500) or a computer(500) connected to the electronic control unit (5; 500) to perform the stepsaccording to any of the claims 1-8.
    [18] 18. A computer program product comprising a program code stored on acomputer-readable medium for performing the method steps according to anyof claims 1-8, when said computer program is run on an electronic control unit(5; 500) or a computer (500) connected to the electronic control unit (5; 500).
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    同族专利:
    公开号 | 公开日
    SE541114C2|2019-04-09|
    DE102017003280A1|2017-10-19|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US5717590A|1995-09-15|1998-02-10|General Motors Corporation|Adaptive variable assist steering control|
    DE602008004435D1|2008-04-02|2011-02-24|Gm Global Tech Operations Inc|Adaptive steering control for a motor vehicle|
    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    SE1650513A|SE541114C2|2016-04-18|2016-04-18|A method for steering assistance and a steering assist system|SE1650513A| SE541114C2|2016-04-18|2016-04-18|A method for steering assistance and a steering assist system|
    DE102017003280.7A| DE102017003280A1|2016-04-18|2017-04-04|Steering support method and steering assistance system|
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